2020, 33(1): 1-7.
doi: 10.1063/1674-0068/cjcp1910173
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2020, 33(1): 13-22.
doi: 10.1063/1674-0068/cjcp1910191
Experimental vibrational spectra of heavy light XH stretching vibrations of simple molecules have been analyzed using the local mode model. In addition, the bond dipole approach, which assumes that the transition dipole moment (TDM) of the XH stretching mode is aligned along the XH bond, has helped analyze experimental spectra. We performed theoretical calculations of the XH stretching vibrations of HOD, HND\begin{document}$^-$\end{document} \begin{document}$^-$\end{document} \begin{document}$^-$\end{document} \begin{document}$^-$\end{document}
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Solid oxide fuel cells (SOFCs) are regarded to be a key clean energy system to convert chemical energy (e.g. H2 and O2) into electrical energy with high efficiency, low carbon footprint and fuel flexibility. The electrolyte, typically doped zirconia, is the “state of the heart” of the fuel cell technologies, determining the performance and the operating temperature of the overall cells. Yttria stabilized zirconia (YSZ) have been widely used in SOFC due to its excellent oxide ion conductivity at high temperature. The composition and temperature dependence of the conductivity has been hotly studied in experiment and, more recently, by theoretical simulations. The characterization of the atomic structure for the mixed oxide system at different compositions is the key for elucidating the conductivity behavior, which, however, is of great challenge to both experiment and theory. This review presents recent theoretical progress on the structure and conductivity of YSZ electrolyte. We compare different theoretical methods and their results, outlining the merits and deficiencies of the methods. We highlight the recent results achieved by using stochastic surface walking global optimization with global neural network potential (SSW-NN) method, which appear to agree with available experimental data. The advent of machine-learning atomic simulation provides an affordable, efficient and accurate way to understand the complex material phenomena as encountered in solid electrolyte. The future research directions for design better electrolytes are also discussed.
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The pharmaceutically active compound atenolol, a kind of β-blockers, may result in adverse effects both for human health and ecosystems if it is excreted to the surface waters resources. To effectively remove atenolol in the environment, photodegradation, both direct and indirect, driven by sunlight is likely to play an important role. Among indirect photodegradation, singlet oxygen (1O2), as a pivotal reactive species, is likely to determine the fates of atenolol. Nevertheless, the kinetic information on the reaction of atenolol with singlet oxygen has not well been investigated and the reaction rate constant is still ambiguous. Herein, the reaction rate constant of atenolol with singlet oxygen is investigated directly through observing the decay of the 1O2 phosphorescence at 1270 nm. It is determined that the reaction rate constant between atenolol and 1O2 is 7.0×105 M-1 s-1 in D2O, 8.0×106 M-1 s-1 in ACN and 8.4×105 M-1 s-1 in EtOH, respectively. Furthermore, the solvent effects on the title reaction was also investigated. It is revealed that the solvents with strong polarity and weak hydrogen donating ability are suitable to achieve high rate constant values. These kinetics information on the reaction of atenolol with singlet oxygen may provide fundamental knowledge to the indirect photodegradation of β-blockers.
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In order to reduce the impact of CdS photogenerated electron-hole recombination on its photocatalytic performance, a narrow band gap semiconductor MoS2 and organic macromolecular cucurbit[n]urils(Q[n]) were used to modify CdS. Q[n]/CdS-MoS2 (n=6, 7, 8) composite photocatalysts were synthesized by hydrothermal method. Infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) and photoluminescence spectrum (PL) were used to characterize the structure, morphology and optical properties of the products, and the catalytic degradation of the solutions of methylene blue, rhodamine B and crystal violet by Q[n]/CdS-MoS2 composite catalyst was investigated. The results showed that the Q[n] played a regulatory role on the growth and crystallization of CdS-MoS2 particles, Q[n]/CdS-MoS2 (n=6, 7, 8) formed flower clusters with petal-like leaves, the flower clusters of petal-like leaves increased the surface area and active sites of the catalyst, the Q[n]/CdS-MoS2 barrier width decreased, the electron-hole pair separation efficiency was improved in the Q[6]/Cds-MoS2. Q[n] makes the electron-hole pair to obtain better separation and migration. The Q[6]/CdS-MoS2 and Q[7]/CdS-MoS2 have good photocatalytic activity for methylene blue, and the catalytic process is based on hydroxyl radical principle.
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The laser-induced fluorescence excitation spectra of UF have been recorded in the range of 17000−19000 cm-1 using two-dimensional spectroscopy. High resolution dispersed fluorescence spectra and fluorescence decay curves time-resolved fluorescence spectroscopy were also recorded. Three rotationally resolved bands have been intensively analyzed, and all bands were found to be derived from the ground state X(1)4.5 with a rotational constant of 0.23421 cm-1. The low-lying electronic states have been observed near 435 and 651 cm-1 in the dispersed fluorescence spectra, which were assigned as Ωʹ = 3.5, and 2.5, respectively. The vibrational constants for the X(1)4.5 and X(1)3.5 states have been calculated. The branching ratios of the dispersed fluorescence spectra for the [18.62]3.5, [17.72]4.5, and [17.65]4.5 states were reported. Radiative lifetimes of 332(9), 825(49), and 433(15) ns for the [18.62]3.5, [17.72]4.5, and [17.65]4.5 states were obtained by fitting the fluorescence decay curves time-resolved fluorescence spectroscopy, respectively. Transition dipole moments were performed using the branching ratios and the radiative lifetimes.
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The lattice parameters, bulk modulus, first derivative of the bulk modulus, electronic band structures, phonon dispersion curves and phonon density of states calculations for Li2AlGa and Li2AlIn Heusler alloys are performed and comparised in this study using Density Functional Theory within the Generalized Gradient Approximation. Computed lattice parameters display a good aggrement with the literature. Obtained electronic band structures of both Heusler alloys showed that they are in semi-metallic structure. Phonon dispersion curves and the phonon density of states graphs are also obtained in order to study the lattice dynamics of these Heusler alloys. It is noticed that Li2AlGa and Li2AlIn Heusler alloys are dynamically stable in the ground state. Except for the lattice parameters any other obtained results could not been compared with the literature since these calculations are performed fort he first time in the literature. Eventually, these calculations gathered from this study will provide an important contribute to the researchers.
Dimension-controllable supramolecular organic frameworks (SOFs) with aggregation-enhanced fluorescence are hierarchically fabricated through the host-guest interactions of CB[8] and coumarin-modified tetraphenylethylene derivatives (TPEC). The three-dimensional (3D) layered SOFs could be constructed from the gradual stacking of two-dimensional (2D) mono-layered structures via simply regulating the self-assembly conditions including the culturing time and concentration. Upon light irradiation under the wavelength of 350 nm, the photodimerization of coumarin moieties occurred, which resulted in the transformation of the resultant TPECn/CB[8]4n 2D SOFs into robust covalently-connected 2D polymers with molecular thickness. Interestingly, the supramolecular system of TPECn/CB[8]4n exhibited intriguing multicolor fluorescence emission from yellow to blue from 0 to 24 hours at 365 nm irradiation, possessing potential applicability for cell imaging and photochromic fluorescence ink.
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A slow and clean fluorine atom beam source is one of the essential components for the low-collision energy scattering experiment involving fluorine atom. In this paper, we describe a simple yet effective photolysis fluorine atom beam source based on ultraviolet laser photolysis, the performance of which was demonstrated by high-resolution time-of-flight spectra from the reactive scattering of F+HD→HF+D. This beam source paves the way for studies of low energy collisions with fluorine atoms.
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The interaction of reactants with catalysts has always been an important subject for catalytic reactions. As a promising catalyst with versatile applications, titania has been intensively studied for decades. In this paper we have investigated the role of bridge bonded oxygen vacancy (O<sub>v</sub>) in methyl groups and CO adsorption on rutile TiO<sub>2</sub>(110) (R-TiO<sub>2</sub>(110)) with the temperature programmed desorption (TPD) technique. The results show a clear different tendency of the desorption of methyl groups adsorbed on bridge bonded oxygen (O<sub>b</sub>), and CO molecules on the five coordinate Ti<sup>4+</sup> sites (Ti<sub>5c</sub>) as the O<sub>v</sub> concentration changes, suggesting that the surface defects may have crucial influence on the absorption of species on different sites of R-TiO<sub>2</sub>(110).
Owing to their unique structural, electronic, and physico-chemical properties, molybdenum clusters are expected to play an important role in future nanotechnologies. However, their ground states are still under debate. In this study, the crystal structure analysis by particle swarm optimization (CALYPSO) approach is used for the global minima search, which is followed by first-principles calculations, to detect an obvious dimerization tendency in Mo<sub>n</sub> (n = 2-18) clusters when the 4<i>s</i> and 4<i>p</i> semicore states (SCS) are not regarded as the valence states. Further, the clusters with even number of atoms are usually magic clusters with high stability. However, after including the 4<i>s</i> and 4<i>p</i> electrons as valence electrons, the dimerization tendency exhibits a drastic reduction because the average hybridization indices H<sub>sp</sub>, H<sub>sd</sub>, and H<sub>pd</sub> are reduced significantly. Overall, this work reports new ground states of Mo<sub>n</sub> (n = 11, 14, 15) clusters and proves that SCS are essential for Mo<sub>n</sub> clusters.
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Rational designs of electrocatalytic active sites and architectures are of great importance to develop cost-efficient non-noble metal electrocatalysts towards efficient oxygen reduction reaction (ORR) for high-performance energy conversion and storage devices. In this paper, active amorphous Fe-based nanoclusters (Fe NC) are elaborately embedded at the inner surface of balloon-like N-doped hollow carbon (Fe NC/C<sub>h</sub> sphere) as an efficient ORR electrocatalyst with an ultrathin wall of about 10 nm. When evaluated for electrochemical performance, Fe NC/C<sub>h</sub> sphere exhibits decent ORR activity with a diffusion-limited current density of ~5.0 mA cm<sup>-2</sup> and a half-wave potential of ~0.81 V in alkaline solution, which is comparable with commercial Pt/C and superior to Fe nanoparticles (NP) supported on carbon sheet (Fe NP/C sheet) counterpart. The electrochemical analyses combined with electronic structure characterizations reveal that robust Fe-N interactions in amorphous Fe nanoclusters are helpful for the adsorption of surface oxygen-relative species, and the strong support effect of N-doped hollow carbon is benefit for accelerating the interfacial electron transfer, which jointly contributes to improved ORR kinetics for Fe NC/C<sub>h</sub> sphere.
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In order to search for high energy density materials, various 4, 8-dihydrodifurazano[3,4-b,e]pyrazine based energetic materials were designed. Density functional theory was employed to investigate the relationships between the structures and properties. The calculated results indicated that the properties of these designed compounds were influenced by the energetic groups and heterocyclic substituents. The –N3 energetic group was found to be the most effective substituent to improve the heats of formation of the designed compounds while the tetrazole ring/–C(NO2)3 group contribute much to the values of detonation properties. The analysis of bond orders and bond dissociation energies showed that the addition of –NHNH2, –NHNO2, –CH(NO2)3 and –C(NO2)3 groups will decrease the bond dissociation energies remarkably. Compounds A8, B8, C8, D8, E8, and F8 were finally screened as the potential candidates for high energy density materials since these compounds possess excellent detonation properties and acceptable thermal stabilities. Additionally, the electronic structures of the screened compounds were calculated.
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Alkyl dinitrites have attracted attention as an important type of nitrosating agent and a pollution source in atmosphere. The reactivity and chemistry of alkyl dinitrites induced by the two ONO functional groups are relatively unknown. In this work, decomposition of 1,3-cyclohexane dinitrite and 1,4-cyclohexane dinitrite are studied by electron impact ionization mass spectroscopy (EI-MS). Apart from NO<sup>+</sup> (m/z 30), fragment ions m/z 43 and 71 are most abundant for the 1,3-isomer. On the other hand, fragments m/z 29, 57, 85 and 97 stand out in the EI-MS spectrum of 1,4-isomer. Possible dissociation mechanisms of the two dinitrites are investigated by theoretical calculations. The results reveal that the ring-opening of 1,3-cyclohexane dinitrite mainly starts from the intermediate ion (M-NO)<sup>+</sup> by cleavage of two αC-βC bonds. For 1,4-cyclohexane dinitrite, in addition to the decomposition via intermediate (M-NO)<sup>+</sup>, cleavage of βC-βC bonds can occur directly from the parent cation M<sup>+</sup>. The results will help to understand the structural related chemistry of alkyl dinitrites in atmosphere and in NO transfer process.
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After binding to human serum albumin (HSA), bilirubin could undergo photo-isomerization and photo-induced cyclization process. The latter process would result the formation of a product named lumirubin. These photo induced behaviors are the fundamental of clinical therapy for neonatal jaundice. Previous studies have reported that the addition of long chain fatty acids is beneficial to the generation of lumirubin, yet no kinetic study have revealed the mechanism behind. In this study, how palmitic acid affects the photochemical reaction process of bilirubin in HSA is studied by using femtosecond transient absorption and fluorescence up-conversion techniques. With the addition of palmitic acid, the excited population of bilirubin prefers to return to its hot ground state (S0) through a 4 picosecond decay channel rather than the intrinsic ultrafast decay pathways (<1 picosecond). This effect prompts the Z-Z to E-Z isomerization at the S0 state and then further increase the production yield of lumirubin. This is the first time to characterization the promoting effect of long chain fatty acid in the process of phototherapy with femtosecond time resolution spectroscopy and the results can provide useful information to benefit the relevant clinical study.
The photochemical reaction of potassium ferrocyanide (K4Fe(CN)6}) exhibits excitation wavelength dependence and non-Kasha rule behavior. In this study, the excited-state dynamics of K4Fe(CN)6 were studied by transient absorption spectroscopy. Excited state electron detachment (ESED) and phtoaquation reactions were clarified by comparing the results of 260 , 320 , 340 , and 350 nm excitations. ESED is the path to generate a hydrated electron (eaq-). ESED energy barrier varies with the excited state, and it occurrs even at the first singlet excited state (1T1g). The 1T1g state shows ~0.2 ps lifetime and converts into triplet [Fe(CN)6]4- by intersystem crossing. Subsequently, 3[Fe(CN)5]3- appears after one CN- ligand is ejected. In sequence, H2O attacks [Fe(CN)5]3- to generate [Fe(CN)5H2O]3- with a time constant of approximately 20 ps. The 1T1g state and eaq- exhibit strong reducing power. The addition of UMP to the K4Fe(CN)6 solution decreased the yield of eaq- and reduced the lifetimes of the eaq- and 1T1g state. The obtained reaction rate constant of 1T1g state and UMP was 1.7×1014 M-1 s-1, and the eaq- attachment to UMP was ~8×109 M-1 s-1. Our results indicate that the reductive damage of K4Fe(CN)6 solution to nucleic acids under ultraviolet irradiation cannot be neglected.
In the pioneering work by R. A. Marcus, the solvation effect on electron transfer (ET) processes was investigated, giving rise to the celebrated nonadiabatic ET rate formula. In this work, on the basis of the thermodynamic solvation potentials analysis, we reexamine Marcus’ formula with respect to the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Interestingly, the obtained RRKM analogue, which recovers the original Marcus’ rate that is in a linear solvation scenario, is also applicable to the nonlinear solvation scenarios, where the multiple curve-crossing of solvation potentials exists. Parallelly, we revisit the corresponding Fermi’s golden rule results, with some critical comments against the RRKM analogue proposed in this work. For illustration, we consider the quadratic solvation scenarios, on the basis of physically well-supported descriptors.
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Abstract The structure and stability of the compounds MRg+ and MRgF (Rg= Ar, Kr and Xe; M= Co, Rh and Ir ) were investigated using the B3LYP, MP2, MP4(SDQ) and CCSD(T) methods. We reported the geometry, vibrational frequencies and thermodynamics properties of these compounds. A series of theoretical methods on the basis of wavefunction analysis, including NBO, AIM, ELF and energy decomposition analysis, were performed to explore bonding nature of the M-Rg and Rg-F bonds. These bonds are mainly noncovalent, the metal weakly interacts with Rg in MRg+, but their interaction is much stronger in MRgF. The neutral molecule MRgF can be well described by the Lewis structure [MRg]+F-.
Rhodium-catalyzed cycloaddition reaction was calculated by density functional theory (DFT) M06-2X method to directly synthesize benzoxepine and coumarin derivatives. In this paper, we conducted a computational study of two competitive mechanisms in which the carbon atom of acetylene or carbon monoxide attacked and inserted from two different directions of the six-membered ring reactant to clarify the principle characteristics of this transformation. The calculation result reveal (1) the insertion process of alkyne or carbon monoxide is the key step of the reaction; (2) For the (5 + 2) cycloaddition reaction of acetylene, higher energy is required to break the Rh-O bond of the reactant, and the reaction tends to complete the insertion from the side of the Rh-C bond; (3) For the (5 + 1) cycloaddition of carbon monoxide, both reaction paths have lower activation free energy, and the two will generate a competition mechanism.
Laser flash photolysis was used to investigate the photoinduced reactions of excited triplet of bioquinone molecule duroquinone (DQ) with tryptophan (Trp) and tyrosine (Tyr) in Acetonitrile-Water (MeCN-H2O) and Ethylene Glycol-Water (EG-H2O) solutions. The reaction mechanisms were analyzed and the reaction rate constants were measured based on Stern-Volmer equation. The H-atom transfer reaction from Trp (Tyr) to 3DQ* is dominant after the formation of 3DQ* during the laser photolysis. For DQ and Trp in MeCN-H2O and EG-H2O solutions, 3DQ* captures H-atom from Trp to generate duroquinone neutral radical DQH•, carbon-centered tryptophan neutral radical Trp•/NH and nitrogen-centered tryptophan neutral radical Trp/N•. For DQ and Tyr in MeCN-H2O and EG-H2O solutions, 3DQ* captures H-atom from Tyr to generate duroquinone neutral radical DQH• and tyrosine neutral radical Tyr/O•. The H-atom transfer reaction rate constants of 3DQ* with Trp (Tyr) are on the level of 109 L•mol-1•s-1, nearly controlled by diffusion. The reaction rate constants of 3DQ* with Trp (Tyr) in MeCN/H2O solution is larger than that in EG/H2O solution, which agree with Stokes–Einstein relationship qualitatively
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Consistency between density functional theory calculations and X-ray photoelectron spectroscopy measurements confirms our predications on the undercoordination-induced local bond relaxation and core level shift of alkali metal, which determine the surface, size and thermal properties of materials. Zone-resolved photoelectron spectroscopy analysis method and bond order-length-strength theory can be utilized to quantify the physical parameters regarding bonding identities and electronic property of metal surfaces, which allows for the study of the core-electron binding-energy shifts in alkali metals. By employing these methods and first principle calculation in this work, we can obtain the information of bond and atomic cohesive energy of under-coordinated atoms at the alkali metal surface. In addition, the effect of size and temperature towards the binding-energy in the surface region can be seen from the view point of Hamiltonian perturbation by atomic relaxation with atomic bonding.
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Methyl 2-furoate (FAME2) is a renewable biofuel with the development of the new synthesis method of dimethyl furan-2,5-dicarboxylate. The potential energy surfaces (PES) of H-abstractions and OH-additions between FAME2 and hydroxyl radical (OH) were studied at the CCSD(T)/CBS//M062X/cc-pVTZ level. The following isomerization and decomposition reactions were also determined for the main radicals produced. The results show that the H-abstraction on the branch methyl group is the dominant channel and that the OH-addition reactions on the furan ring has a significant pressure dependency. The current rate coefficients provide important kinetic data for the further improving of the combustion mechanism of FAME2, which bring a trusty reference for further research on practical fuels.
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A protein may exist as an ensemble of different conformations in solution, which cannot be represented by a single static structure. Molecular dynamics (MD) simulation has become a useful tool for sampling protein conformations in solution, but force fields and water models are important issues. This work presents a case study of the bacteriophage T4 lysozyme (T4L). We have found that MD simulations using a classic AMBER99SB force field and TIP4P water model cannot well describe hinge-bending domain motion of the wild-type T4L at the timescale of one micorsecond. Other combinations, such as a residue-specific force field called RSFF2+ and a dispersion-corrected water model TIP4P-D, are able to sample reasonable solution conformations of T4L, which are in good agreement with experimental data. This primary study may provide candidates of force fields and water models for further investigating conformational transition of T4L.
蛋白质在溶液中可能以不同构象的集合形式存在，不能用单一的静态结构来表示。分子动力学模拟已成为对蛋白质溶液构象进行采样的有用工具，但力场和水模型的准确性是一个关键问题。这项工作介绍了对噬菌体T4溶菌酶（T4L）的个例研究。我们发现，使用经典的力场和水模型，如AMBER99SB/TIP4P，1微秒时间尺度的分子动力学模拟不能很好地描述野生型T4L的结构域开合运动。但是其它力场和水模型组合，如残基特异性力场RSFF2+和离散校正的水模型TIP4P-D，能够对T4L溶液构象进行较为合理的采样，且与实验数据有良好的一致性。我们的初步研究可为进一步通过长时间分子动力学模拟及自由能计算研究T4L的构象转变机制提供力场和水模型的选择。
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Photocatalytic water splitting to generate hydrogen gas is an ideal solution for environmental pollution and unsustainable energy issues. In the past few decades, many efforts have been made to increase the efficiency of hydrogen production. One of the most important ways is to achieve light absorption in the visible range to improve the conversion efficiency of solar energy into chemical energy, but it still presents great challenges. We here predicted a novel organic film, which can be obtained by polymerizing HTAP molecules, as an ideal material for photocatalytic water splitting. Basing on first-principles calculations and Born-Oppenheimer quantum molecular dynamic simulations, the metal-free two-dimensional nanomaterial has proven to be structurally stable and with a direct band gap of 2.12 eV, which satisfies the requirement of light absorption in the visible range. More importantly, the conduction bands and valence bands completely engulf the redox potentials of water, making the such film a promising photocatalyst for water splitting. This construction method through the topological periodicity of organic molecules provides a design scheme for the photocatalyst for water splitting.
Huge tunneling magnetoresistance in a magnetic tunnel junction with Heusler alloy Co2MnSi electrodes
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Magnetic tunnel junction with a large tunneling magnetoresistance has attracted great attention due to its importance in the spintronics applications. By performing extensive density functional theory calculations combined with the nonequilibrium Green's function method, we examine the spin-dependent transport properties of a magnetic tunnel junction, in which a non-polar SrTiO3 barrier layer is sandwiched between two Heusler alloy Co2MnSi electrodes. Theoretical results clearly reveal that the near perfect spin-filtering effect appears in the parallel magnetization configuration (PC). The transmission coefficient in the PC at the Fermi level is several orders of magnitude larger than that of in the antiparallel magnetization configuration, resulting in a huge tunneling magnetoresistance (i.e. >10^6), which originates from the coherent spin-polarized tunneling, due to the half-metallic nature of Co2MnSi electrode and the significant spin-polarization of the interfacial Ti 3d orbital.
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Binding and release of ligands are critical for biological functions of many proteins, and thus it is important to determine these highly dynamic processes. Although there are experimental techniques to determine structure of a protein-ligand complex, it only provides a static picture of the system. With the rapid increase of computing power and improved algorithms, molecule dynamics (MD) simulations have diverse of superiority in probing the binding and release process. However, it remains a great challenge to overcome the time and length scales when the system becomes large. This article presents an enhanced sampling tool for ligand binding and release, which is based on iterative multiple independent MD simulations guided by contacts formed between the ligand and the protein. From the simulation results on adenylate kinase (AdK), we observe the process of ligand binding and release while the conventional MD simulations at the same time scale cannot.
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Ruthenium (Ru) serves as a promising catalyst for ammonia synthesis via the Haber-Bosch process, identification of the structure sensitivity to improve the activity of Ru is important but not fully explored yet. We present a calculation and micro-kinetic rate calculation on nitrogen activation, a crucial step in ammonia synthesis, over a variety of hexagonal close-packed (hcp) and face-center cubic (fcc) Ru facets. Hcp {21-30} facet exhibits the highest activity toward N<sub>2</sub> dissociation in hcp Ru, followed by the monatomic step sites. The other hcp Ru facets have N<sub>2</sub> dissociation rates at least three orders lower. Fcc {211} facet shows the best performance for N<sub>2</sub> activation in fcc Ru, followed by {311}, which indicates stepped surfaces make great contributions to the overall reactivity. Although hcp Ru {21-30} facet and monatomic step sites have lower or comparable activation barriers compared with fcc Ru {211} facet, fcc Ru is proposed to be more active than hcp Ru for N<sub>2</sub> conversion due to the exposure of the more favorable active sites over step surfaces in fcc Ru. Our work provides new insights into the crystal structure sensitivity of N<sub>2</sub> activation for mechanistic understanding and rational design of ammonia synthesis over Ru catalysts.
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The potential energy landscape of the neutral Ni<sub>2</sub>(CO)<sub>5</sub> complex was re-examined. A new <i>C</i><sub>2V</sub> structure with double bridging carbonyls is found to compete with the previously proposed triply carbonyl-bridged <i>D</i><sub>3h</sub> isomer for the global minimum of Ni<sub>2</sub>(CO)<sub>5</sub>. Despite that the tri-bridged isomer possesses the more favored (18, 18) configuration as described in the textbook, where both metal centers satisfy the 18-electron rule, the neutral Ni<sub>2</sub>(CO)<sub>5</sub> complex prefers the di-bridged geometry with (18, 16) configuration. The isomerization energy decomposition analysis reveals that the structural preference is a consequence of the maximization of electrostatic and orbital interactions.
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The kinetics for hydrogen (H) adsorption on Ir(111) electrode has been studied in both HClO4 and H2SO4 solutions by impedance spectroscopy. In HClO4, the adsorption rate constant for H adsorption on Ir(111) increases from 1.74×10-8 to 3.47×10-7mol.cm-2.s-1 with the decrease of the applied potential from 0.2 to 0.1 V (vs. RHE), which is ca. one to two orders of magnitude slower than that on Pt(111) under otherwise identical condition. This is explained by the stronger binding of water to Ir(111), which needs a higher barrier to reorient during the under potential deposition of H from hydronium within the hydrogen bonded water network. In H2SO4, the adsorption potential is ca. 200 mV negatively shifted, accompanied by a decrease of adsorption rate by up to one order of magnitude, which is explained by the hindrance of the strongly adsorbed sulfate/bisulfate on Ir(111). Our results demonstrate that under electrochemical environment, H adsorption is strongly affected by the accompanying displacement and reorientation of water molecules that initially stay close to the electrode surface.
In order to study the effect of different modification methods on polysilsesquioxane(POSS) modified cellulose, molecular dynamics methods was used to establish a pure cellulose model and a series of modified models modified by POSS in different ways. And their thermodynamic properties were calculated. The results showed that the performance of modified cellulose models was better than that of unmodified model, and the modified effect was the best when two cellulose chains were grafted onto POSS by chemical bond (M2 model). Compared with pure cellulose model, the cohesive energy density and solubility parameters of M2 model are increased by 9%, and the values of tensile modulus, bulk modulus, shear modulus and Cauchy pressure increased 38.6%, 29.5%, 41.1% and 29.5%, respectively. In addition, the free volume fraction and mean square displacement of each model were calculated and analyzed in this paper. Compared with pure cellulose model, the molecular chain entanglement of cellulose was increased due to the existence of the chemical bonds in the M2 model, which made the cellulose molecular chains occupied more free volume, so that the system had a smaller free volume fraction, inhibited the chain movement of cellulose chains, and thus improved the thermal stability of cellulose.
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The interaction between Amyloid β (Aβ) peptide and acetylcholine receptor is the key for our understanding of how Aβ fragments block the ion channels within the synapses and thus induce Alzheimer's disease. Here, molecular docking and molecular dynamics (MD) simulations were performed for the structural dynamics of the docking complex consists of Aβ and α7-nAChR (α7 nicotinic acetylcholine receptor), and the inter-molecular interactions between ligand and receptor were revealed. The results show that Aβ25-35 bound to α7-nAChR through hydrogen bonds and complementary shape, and the Aβ25-35 fragments would easily assemble in the ion channel of α7-nAChR, then block the ion transfer process and induce neuronal apoptosis. The simulated amide-I band of Aβ25-35 in the complex is located at 1650.5 cm-1, indicating the backbone of Aβ25-35 tends to present random coil conformation, which is consistent with the result obtained from cluster analysis. Currently existed drugs were used as templates for virtual screening, eight new drugs were designed and semi-flexible docking was performed for their performance. The results show that, the interactions between new drugs and α7-nAChR are strong enough to inhibit the aggregation of Aβ25-35 fragments in the ion channel, and also be of great potential in the treatment of Alzheimer's disease.
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The hierarchical stochastic Schrödinger equations (HSSE) are a kind of numerically exact wavefunction-based approaches suitable for the quantum dynamics simulations in a relatively large system coupled to a bosonic bath. Starting from the influence-functional description of open quantum systems, this review outlines the general theoretical framework of HSSEs and their concrete forms in different situations. The applicability and efficiency of HSSEs are exemplified by the simulations of ultrafast excitation energy transfer processes in large-scale systems.
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The binding energy spectrum (BES) and electron momentum profiles (EMPs) of the inner orbitals of methyl iodide have been measured using an electron momentum spectrometer at the impact energy of 1200 eV plus binding energy. Two peaks in the BES, arising from the spin-orbit (SO) splitting, are observed and the corresponding EMPs are obtained. Relativistic density functional calculations are performed to elucidate the experimental EMPs of two SO splitting components, showing agreement with each other except for the intensity in low momentum region. The measured high intensity in the low momentum region can be further explained by the distorted wave calculation.
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Stars with masses between 1 and 8 solar masses (M⊙) lose large amounts of material in the form of gas and dust in the late stages of stellar evolution, during their Asymptotic Giant Branch phase. Such stars supply up to 35% of the dust in the interstellar medium and thus contribute to the material out of which our solar system formed. In addition, the circumstellar envelopes of these stars are sites of complex, organic chemistry with over 80 molecules detected in them. We show that internal ultraviolet photons, either emitted by the star itself or from a close-in, orbiting companion, can significantly alter the chemistry that occurs in the envelopes particularly if the envelope is clumpy in nature. At least for the cases explored here, we find that the presence of a stellar companion, such as a white dwarf star, the high flux of UV photons destroys H2O in the inner regions of carbon-rich AGB stars to levels below those observed and produces species such as C+ deep in the envelope in contrast to the expectations of traditional descriptions of circumstellar chemistry.
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Assembling of a few particles into a cluster commonly occurs in many systems. However, it is still challenging to precisely control particle assembling, due to the various amorphous structures induced by thermal fluctuations during cluster formation. Although these structures may have very different degrees of aggregation, a quantitative method is lacking to describe them, and how these structures evolve remains unclear. Therefore a significant step towards precise control of particle self-assembly is to describe and analyze various aggregation structures during cluster formation quantitatively. In this work, we are motivated to propose a method to directly count and quantitatively compare different aggregated structures. We also present several case studies to evaluate how the aggregated structures during cluster formation are affected by external controlling factors, e.g., different interaction ranges, interaction strengths, or anisotropy of attraction. We also discuss some findings, which may promote further precise control of particle assembling.
Two-photon fluorescence dyes have shown promising applications in biomedical imaging. However, the substitution site effect on geometric structures and photophysical properties of fluorescence dyes is rarely illustrated in detail. In this work, a series of new lipid droplets detection dyes are designed and studied, molecular optical properties and non-radiative transitions are analyzed. The intramolecular weak interaction and electron-hole analysis reveal its inner mechanisms. All dyes are proved to possess excellent photophysical properties with high fluorescence quantum efficiency and large stokes shift as well as remarkable TPA cross section. Our work reasonably elucidates the experimental measurements and the effects of substitution site on two-photon absorption and excited states properties of Lipid droplets detection NAPBr dyes are highlighted, which could provide a theoretical perspective for designing efficient organic dyes for lipid droplets detection in biology and medicine fields.
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We predict two novel group 14 element alloys Si2Ge and SiGe2 in P6222 phase in this work through first-principles calculations. The structures, stability, elastic anisotropy, electronic and thermodynamic properties of these two proposed alloys are investigated systematically. The proposed P6222-Si2Ge and -SiGe2 have a hexagonal symmetry structure, and the phonon dispersion spectra and elastic constants indicate that these two alloys are dynamically and mechanically stable at ambient pressure. The elastic anisotropy properties of P6222-Si2Ge and -SiGe2 are examined elaborately by illustrating the surface constructions of Young’s modulus, the contour surfaces of shear modulus, and the directional dependences of Poisson’s ratio, as well as discussing and comparing the differences with their corresponding group 14 element allotropes P6222-Si3 and -Ge3. Moreover, the Debye temperature and sound velocities are analyzed to study the thermodynamic properties of the proposed P6222-Si2Ge and -SiGe2.
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The vacuum ultraviolet (VUV) photodissociation of OCS via the F 31Π Rydberg states was investigated in the range of 134–140 nm, by means of the time-sliced velocity map ion imaging technique. The images of S (1D2) products from the CO (X1Σ+) + S (1D2) dissociation channel were acquired at five photolysis wavelengths, corresponding to a series of symmetric stretching vibrational excitations in OCS (F 31Π, v1=0-4). The total translational energy distributions, vibrational populations and angular distributions of CO (X1Σ+, v) coproducts were derived. The analysis of experimental results suggests that the excited OCS molecules dissociate to CO (X1Σ+) and S (1D2) products via non-adiabatic couplings between the upper F 31Π states and the lower-lying states both in the C∞v and Cs symmetry. Furthermore, strong wavelength dependent behavior has been observed: the greatly distinct vibrational populations and angular distributions of CO (X1Σ+, v) products from the lower (v1=0-2) and higher (v1=3,4) vibrational states of the excited OCS (F 31Π, v1) demonstrate that very different mechanisms are involved in the dissociation processes. This study provides evidence for the possible contribution of vibronic coupling and the crucial role of vibronic coupling on the VUV photodissociation dynamics.
The ring-polymer molecular dynamics (RPMD) was used to calculate the thermal rate coefficients and kinetic isotope effects of the heavy-light-heavy abstract reaction Cl + XCl → XCl + Cl (X=H, D, Mu). For the Cl + HCl reaction, the excellent agreement between the RPMD and experimental values provides a strong proof for the accuracy of the RPMD theory. And the RPMD results also consistent with results from other theoretical methods including improved-canonical-variational-theory and quantum dynamics. The most novel finding is there is a double peak in Cl + MuCl reaction near the transition state, leaving a free energy well. It comes from the mode softening of the reaction system at the peak of the potential energy surface. Such an explicit free energy well suggests strongly there is an observable resonance. And for the Cl + DCl reaction, the RPMD rate coefficient again gives very accurate results comparing with experimental values. The only exception is at the temperature of 312.5 K, at this temperature, results from RPMD and all other theoretical methods are close to each other but slightly lower than the experimental value, which indicates experimental or potential energy surface deficiency.
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The ring-polymer molecular dynamics (RPMD) was used to calculate the thermal rate coefficients of the multi-channel roaming reaction H + MgH → Mg + H2. Two reaction channels, tight and roaming, are explicitly considered. This is a pioneering attempt of exerting RPMD method to multi-channel reactions. With the help of a newly developed optimization-interpolation protocol for preparing the initial structures and adaptive protocol for choosing the force constants, we have successfully obtained the thermal rate coefficients. The results are consistent with those from other theoretical methods, such as variational transition state theory (VTST) and quantum dynamics (QD). Especially, RPMD results exhibit negative temperature dependence, which is similar to results from VTST but different from ones from ground state QD calculations.
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Four organic small-molecule hole transport materials (D41, D42, D43 and D44) of tetraarylpyrrolo[3,2-b]pyrroles were prepared. They can be used without doping in the manufacture of the inverted planar perovskite solar cells. Tetraarylpyrrolo[3,2-b]pyrroles are accessible for one-pot synthesis. D42, D43 and D44 possess acceptor-π-donor-π-acceptor structure, on where the aryl bearing substitutes of cyan, fluorine and trifluoromethyl, respectively. Instead, the aryl moiety of D41 is in presence of methyl with a donor-π-donor-π-donor structure. The different substitutes significantly affected their molecular surface charge distribution and thin-film morphology, attributing to the electron-rich properties of fused pyrrole ring. The size of perovskite crystalline growth particles is affected by different molecular structures, and the electron-withdrawing cyan group of D42 is most conducive to the formation of large perovskite grains. The D42 fabricated devices with power conversion efficiency 17.3% and retained 55% of the initial PCE after 22 days in dark condition. The pyrrolo[3,2-b]pyrrole are efficient electron-donating moiety for hole transporting materials to form good substrate in producing perovskite thin film.
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Herein we present a facile approach for the preparation of a novel hierarchically porous carbon, in which seaweeds serve as carbon source and KOH as activator. The fabricated KOH-activated seaweed carbon (K-SC) displays strong affinity towards tetracycline (TC) with maximum uptake quantity of 853.3 mg g–1, significantly higher than other TC adsorbents. The superior adsorption capacity ascribes to large specific surface area (2614 m2 g−1) and hierarchically porous structure of K-SC, along with strong π–π interactions between TC and K-SC. In addition, the as-prepared K-SC exhibits fast adsorption kinetics, capable of removing 99% of TC in 30 min. Meanwhile, the exhausted K-SC can be regenerated for four cycling adsorption without an obvious degradation in capacities. More importantly, pH and ionic strengths barely affect the adsorption performance of K-SC, implying electrostatic interactions hardly play any role in TC adsorption process. Furthermore, the K-SC packed fixed-bed column (0.1 g of adsorbents) can continually treat 2780 mL solution spiked with 5.0 mg g–1 TC before reaching the breakthrough point. All in all, the fabricated K-SC equips with high adsorption capacity, fast adsorption rate, glorious anti-interference capability and good reusability, which make it holding great feasibilities for treating TC contamination in real applications.
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Three kinds of thermochromic materials (DC8, DC12, DC16) were synthesized by linking the rigid 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (bpeb) with different lengths of alkyl chains. They exhibit remarkable fluorescent color changes under the irradiation of 365 nm light with elevating temperature, which is supposed to be caused by the transition between the crystal state and the amorphous state. Interestingly, the DC16 solid also has a photochromic character. It should be noticed that the phase transition temperatures of three materials measured by differential scanning calorimetry are higher than those of the fluorescence color changes during the heating process. Thus, the allochroic effect is attributed to the synergistic effect of both heating and photo-inducement (365 nm). Ethanol can turn the heated powder into the initial crystal again which indicates that their thermochromic behavior is reversible and makes the fluorescence recover. This study is of significance for understanding the structure-property relation and guides thermochromic molecular design.
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The issues of low crystallinity and slow crystallization rate of poly (lactic acid) have been widely addressed. In this work, we find that doping PLA with Zn(Ⅱ) ions can speed up the process of crystallization of PLA. Three kinds of Zn(Ⅱ) salts (ZnCl2, ZnSt and ZnOAc) were tested in comparison with some other ions such as Mg(Ⅱ) and Ca(Ⅱ). The increased crystallinity and crystallization rate of PLA doping with Zn(Ⅱ) are reflected in FT-IR and variable temperature Raman spectroscopy. The crystallinity is further confirmed or measured with differential scanning calorimetry and X-ray diffraction. The crystallinity of the PLA/ZnSt-0.4% material can reach 22.46% and the crystallinity of the PLA/ZnOAc-0.4% material can reach 24.83%, as measured with DSC.
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Theoretical study was carried out with OX2 (X = Halogen) molecules and calculation results showed that delocalized π36 bonds exists in their electronic structures and O atoms adopt the sp2 type of hybridization, which violated the VSEPR theory’s prediction of sp3 type. Delocalization stabilization energy (DSE) was proposed to measure delocalized π36 bond’s contribution to energy decrease and proved that it brings extra-stability to the molecule. According to our analyses, these phenomena can be summarized as a kind of coordinating effect.
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The boom in ultra-thin electronic devices and the growing need for humanization greatly facilitated the development of wearable flexible micro-devices. But the technology to deposit electrode material on flexible substrate is still in its infancy. Herein, the flexible symmetric micro-supercapacitors made of carbon nanotubes (CNTs) on commercial printing paper as electrode materials were fabricated by combining tetrahedral preparator auxiliary coating method and laser-cutting interdigital configuration technique on a large scale. The electrochemical performance of obtained micro-supercapacitors can be controlled and tuned by simple choosing the different model of tetrahedral preparatory to obtain CNTs film of different thickness. As expected, the micro-supercapacitor based on CNTs film can deliver an areal capacitance of up to 4.56 mF cm-2 at current of 0.02 mA. Even if, micro-supercapacitor undergo continuous 10000 cycles, the performance of device can still remain nearly 100%. The as-demonstrated tetrahedral preparator auxiliary coating method and laser-cutting interdigital configuration technique provide new perspective for preparing microelectronics in an economical way. The paper electrode appended by CNTs achieves steerable areal capacitance, showing broad application prospect in fabricating asymmetric micro-supercapacitor with flexible planar configurations in the future.
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Smart functional microgels hold great potential in a variety of applications, especially in drug transportation. However, current drug carriers based on physiological internal stimuli cannot efficiently orientate to designated locations. Therefore, it is necessary to introduce the self-propelled particles to the drug release of the microgels. In order to study self-propulsion of microgels induced by light, it is also a challenge to prepare micron-sized microgels so that they can be observed directly under optical microscopes. This paper presents a method to prepare phototactic microgels with photoresponsive properties. The microgel particles is observed by confocal laser scanning microscopy (CLSM). The photoresponsive properties of microgels are fully investigated by various instruments. Light can also regulate the state of the microgel solution, making it switch between turbidity and clarity. The phototaxis of particles irradiated by UV light was studied, which may be used for microgels enrichment and drug transportation and release.
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In this study, the application of bovine serum albumin (BSA) to glucose- sensitive materials was proposed for the first time. Au-CuO bimetallic nanoclusters (Au-CuO/BSA) were prepared using BSA as a template, the new sensing material (Au-CuO/BSA/MWCNTs) was synthesized by mixing with multi-walled carbon nanotubes (MWCNT) and applied to non-enzymatic electrochemical sensors to detect glucose stably and effectively under neutral conditions. The scanning electron microscopy was used to investigate the morphology of the synthesized nanocomposite. The electrochemical properties of the sensor were studied by cyclic voltammetry. Glucose detection experiments showed that Au-CuO/BSA/MWCNTs/Au electrode had good glucose detection ability, stability, accuracy, repeatability, and high selectivity in neutral environment. Unlike existing glucose-sensitive materials, due to the use of BSA, the composite material is firmly fixed to the electrode surface without a Nafion solution, which reduces the current blocking effect on the modified electrode. The composite materials can be effectively preserved for extremely long periods, higher than 80% activity was maintained at room temperature in a closed environment for 3 to 4 months, due to the special effects of BSA. In addition, the feasibility of using BSA in glucose-sensitive materials was confirmed.
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Our experimental progresses on the reaction dynamics of dissociative electron attachment (DEA) to carbon dioxide (CO2) are summarized in this review. First, we introduce some fundamentals about the DEA dynamics and provide an epitome about the DEAs to CO2. Second, our development on the experimental techniques is described, in particular, on the high-resolution velocity map imaging apparatus in which we put a lot of efforts during the past two years. Third, our findings about the DEA dynamics of CO2 are surveyed and briefly compared with the others’ work. At last, we give a perspective about the applications of the DEA studies and highlight the inspirations in the production of molecular oxygen on Mars and the catalytic transformations of CO2.
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Si (111) electrode has been widely used in electrochemical and photoelectrochemical studies. The potential dependent measurements of the second harmonic generation (SHG) were performed to study Si (111) electrolyte interface. At different azimuthal angles of the Si (111) and under different polarization combinations, the curve of the intensity of SHG with extern potential have different form of line or parabola. A quantitative analysis showed that this differences of the potential-dependence can be explained by the isotropic and anisotropic contribution of the Si (111) electrode. The change in isotropic and anisotropic contribution of the Si (111) electrode may be attributed to the increase in doping concentration of Si (111) electrodes.
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Reactions of gas-phase species with small molecules are being actively studied to understand the elementary steps and mechanistic details of related condensed-phase processes. Activation of the very inert N≡N triple bond of dinitrogen molecule by isolated gas-phase species has attracted considerable interest in the past few decades. Apart from molecular adsorption and dissociative adsorption, interesting processes such as C–N coupling and degenerate ligand exchange were discovered. The present review article focuses on the recent progress on adsorption, activation, and functionalization of N2 by gas-phase species (particularly metal cluster ions) using mass spectrometry, infrared photo-dissociation spectroscopy, anion photoelectron spectroscopy, and quantum chemical calculations including density functional theory and high-level ab-initio calculations. Recent advances including characterization of adsorption products, dependence of clusters' reactivity on their sizes and structures, and mechanisms of N≡N weakening and splitting have been emphasized and prospects have been discussed.
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Defect-mediated processes in two-dimensional transition metal dichalcogenides have a significant influence on their carrier dynamics and transport properties, however, the detailed mechanisms remain poorly understood. Here, we present a comprehensive ultrafast study on defect-mediated carrier dynamics in ion exchange prepared few-layer MoS<sub>2</sub> by femtosecond time-resolved Vis-NIR-MIR spectroscopy. The broadband photobleaching feature observed in the near-infrared transient spectrum discloses that the mid-gap defect states are widely distributed in few-layer MoS<sub>2</sub> nanosheets. The processes of fast trapping of carriers by defect states and the following nonradiative recombination of trapped carriers are clearly revealed, demonstrating the mid-gap defect states play a significant role in the photoinduced carrier dynamics. The positive to negative crossover of the signal observed in the mid-infrared transient spectrum further uncovers some occupied shallow defect states distributed at less than 0.24 eV below the conduction band minimum. These defect states can act as effective carrier trap centers to assist the nonradiative recombination of photo-induced carriers in few-layer MoS<sub>2</sub> on the picosecond time scale.
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Silicon bulk etching is an important part of micro-electro-mechanical system (MEMS) technology. In this work, a novel etching method is proposed based on the vapor from TMAH solution heated up to boiling point. The monocrystalline silicon wafer is positioned over the solution surface and can be anisotropically etched by the produced vapor. This etching method does not rely on the expensive vacuum equipment used in dry etching. Meanwhile, it presents several advantages like low roughness, high etching rate and high uniformity compared with the conventional wet etching methods. The etching rate and roughness can reach 2.13 μm/min and 1.02 nm, respectively. To our knowledge, this rate is the highest record for the wet etching based on TMAH. Furthermore, the diaphragm structure and Al-based pattern on the non-etched side of wafer can maintain intact without any damage during the back-cavity fabrication. Finally, an etching mechanism has been proposed to illustrate the observed experimental phenomenon. It is suggested that there is a water thin film on the etched surface during the solution evaporation. It is in this water layer that the ionization and etching reaction of TMAH proceed, facilitating the desorption of hydrogen bubble and the enhancement of molecular exchange rate.
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Methyl vinyl ketone oxide (MVCI), an unsaturated four-carbon Criegee intermediate produced from the ozonolysis of isoprene has been recognized to play a key role in determining the tropospheric OH concentration. It exists in four configurations (anti_anti, anti_syn, syn_anti and syn_syn) due to two different substituents of saturated methyl and unsaturated vinyl groups. In this study, we have carried out the electronic structure calculation at the multi-configurational CASSCF and multi-state MS-CASPT2 levels, as well as the trajectory surface-hopping (TSH) nonadiabatic dynamics simulation at the CASSCF level to reveal the different fates of syn/anti configurations in photochemical process. Our results show that the dominant channel for the S1-state decay is a ring closure, isomerization to dioxirane, during which, the syn(C-O) configurations with an intramolecular hydrogen bond show slower nonadiabatic photoisomerization. More importantly, it has been found for the first time in photochemistry of Criegee intermediate that the cooperation of two heavy groups (methyl and vinyl) leads to an evident pyramidalization of C3 atom in MVCI, which then results in two structurally-independent minimal-energy crossing points (CIs) towards the syn(C-O) and anti(C-O) sides, respectively. The preference of surface hopping for a certain CI is responsible for the different dynamics of each configuration.
Residues of tetracycline antibiotics (TCs) in environments may be harmful to human. Due to their high polarities, it is extremely challenging to efficiently enrich TCs with low concentrations in natural waters for analysis. In this work, a magnetic metal-organic framework (MOF) Fe3O4@[Cu3(btc)2] was synthesized and applied as a dispersive micro-solid phase extraction (DMSPE) adsorbent for TCs enrichment. Effects of DMSPE conditions including extraction time, solution pH, and elution solvent on the extraction efficiencies of TCs were investigated. Results show that TCs could be enriched efficiently by Fe3O4@[Cu3(btc)2], and electrostatic interaction between TCs and Fe3O4@[Cu3(btc)2] dominated this process. Combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS), four TCs residues (oxytetracycline, tetracycline, chlortetracycline, and doxycycline) in natural waters were determined. The detection limits (LOD, S/N=3) of the four antibiotics were 0.01-0.02 μg/L, and the limits of quantitation (LOQ, S/N=10) were 0.04-0.07 μg/L. The recoveries obtained from river water and aquaculture water spiked with three TCs concentration levels ranged from 70.3-96.5% with relative standard deviations of 3.8-12.8%. Results indicate that the magnetic MOFs based DMSPE is simple, rapid and high-loading for antibiotics enrichment from water, which further expand the practical application of MOFs in sample pretreatment for environmental pollutant analysis.
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The photodissociation dynamics of AlO at 193 nm is studied using time-sliced ion velocity mapping. Two dissociation channels are found through the speed and angular distributions of aluminum ions: one is one photon dissociation of the neutral AlO to generate Al(2Pu) + O(3Pg), and the other is two-photon ionization and then dissociation of AlO+ to generate Al+(1Sg) + O(3Pg). Each dissociation channel includes the contribution of AlO in the vibrational states v = 0-2. The anisotropy parameter of the neutral dissociation channel is more dependent on the vibration state of AlO than the ion dissociation channel.
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Au@Au@Ag double shell nanoparticles were fabricated and characterized using TEM, STEM-Mapping and UV-Vis methods. Using crystal violet (CV) as Raman probe, the SERS activity of the as-prepared Au@Au@Ag nanoparticles was studied by comparing to Au, Au@Ag and Au@Au core-shell nanoparticles prepared by the same methods. Moreover, it can be found that the SERS activity was enhanced obviously by introducing of NaCl. The concentrations of NaCl played a key role in SERS detection. With appropriate concentration of NaCl, the limit of detection as low as 10?10 M CV can be achieved. The possible enhanced mechanism was also discussed. Furthermore, with simple sample pretreatment, the detection limit of 5 μg/g Rhodamine B (RhB) in chili powders can be achieved. The results highlight the potential utility of Au@Au@Ag for detection of illegal food additives with low concentrations.
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We report a study on photo-ionization of benzene and aniline with incidental subsequent dissociation by the customized reflection time-of-flight mass spectrometer utilizing a deep ultraviolet (DUV) 177.3 nm laser. Highly efficient ionization of benzene is observed with a weak C4H3+ fragment formed by undergoing disproportional C−C bond dissociation. In comparison, a major C5H6+• fragment and a minor C6H6+• radical are produced in the DUV ionization of aniline pertaining to the removal of CNH* and NH* radicals, respectively. First-principles calculation is employed to reveal the photo-dissociation pathways of these two molecules having a structural difference of just an amino group. It is demonstrated that hydrogen atom transfer (HAT) plays an important role in the cleavage of C−C or C−N bonds in benzene and aniline ions. This study helps understand the underlying mechanisms of chemical bond fracture of benzene ring and related aromatic molecules.
Recent experiments report the rotation of FA (FA= HC[NH2]2+) cations significantly influence the excited-state lifetime of FAPbI3. However, the underlying mechanism remains unclear. Using ab initio nonadiabatic (NA) molecular dynamics combined with time-domain density functional simulations, we have demonstrated that eeorientation of partial FA cations significantly inhibits nonradiative electron-hole recombination with respect to the pristine FAPbI3 due to the decreased NA coupling by localizing electron and hole in different positions and the suppressed atomic motions. Slow nuclear motions simultaneously increase the decoherence time but which is overcomed by the reduced NA coupling, extending electron-hole recombination time scales to several nanoseconds and being about 3.9 times longer than that in pristine FAPbI3, which occurs within sub-nanosecond and agrees with experiment. Our study established the mechanism for the experimentally reported prolonged excited-state lifetime, providing rational strategy for design of high performance of perovskite solar cells and optoelectronic devices.
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Langevin Dynamics (LD) simulations were conducted to study the collapse of grafted partially charged 4-arm star chains onto the oppositely charged grafting electrode in the presence of trivalent salt coions. Simulation results revealed that the average charge fraction of the grafted star chains and the salt concentration play critical roles in the competitive adsorption of charged monomers and trivalent salt coions onto the oppositely charged electrode. For grafted star chains with relatively high charge fraction, charged monomers are the dominant species collapsing on the oppositely charged electrode with the emergence of charge reversal on the grafting electrode. At a low charge fraction such that the total amount of charges on a grafted star molecule is comparable to that of a trivalent salt coion, trivalent salt coions absorb more strongly onto the electrode than grafted stars even at very low salt concentration. It was found that at relatively low charge fraction of star chains, the addition of trivalent salt coions does not lead to charge overcompensation of the surface charges on the grafting electrode. The stretching of star brushes under an electric field in the presence of trivalent salt coions was also briefly investigated.
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The solvent dependence on the photophysical and photochemical behaviors of thioxanthen-9-one (TX) has been investigated by the nanosecond laser flash photolysis. In the transient absorption spectra of TX in CH3CN, the band at 627 nm is attributed to the triplet TX (3TX*). The self-quenching rate constant ksq of 3TX* is reduced in the protic solvents. This may be due to the fact that the exciplex being formed by hydrogen bonding effect probably could influence the process of collisional quenching of 3TX*. In the presence of DPA, reduction of 3TX* occurs via a typical two-step mechanism of the electron/proton transfer. The bands at ~420 nm, ~683 nm and ~780 nm in CH3CN are respectively assigned to TXH? radical, TX?? anion radical and DPA?+ cation radical. No obvious medium effect is observed for the electron transfer between 3TX* and DPA, which indicates the 3nπ* and 3ππ* states of TX should have the approximate ability to attract electron. However, a solvent dependence is found in the dynamic decay of TX?? anion radical. In the strongly acid aqueous acetonitrile (pH=3.0), a dynamic equilibrium between protonated and unprotonated TX is observed. Once photolysis, 3TXH+* is produced, which contributes to the new band at 520 nm.
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Sum frequency generation vibrational spectroscopy (SFG-VS) is a powerful technique for determining molecular structures at both buried interface and air surface. Distinguishing the contribution of SFG signals from buried interface and air surface is crucial to the applications in devices such as microelectronics and bio-tips. Here we demonstrate that the SFG spectra from buried interface and air surface can be differentiated by controlling the film thickness and employment of surface-plasmon enhancement. Using substrate-supported PMMA films as a model, we have visualized the variations in the contribution of SFG signals from buried interface and air surface. By monitoring carbonyl and C-H stretching groups, we found that SFG signals are dominated by the moieties (-CH2, -CH3, -OCH3 and C=O) segregated at the PMMA/air surface for the thin films while they are mainly contributed by the groups (-OCH3 and C=O) at the substrate/PMMA buried interface for the thick films. At the buried interface, the tilt angle of C=O decreases from 65° to 43° as the film preparation concentration increases; in contrast, the angles at the air surface fall in the range between 38° and 21°. Surface plasmon generated by gold nanorod can largely enhance SFG signals, particularly the signals from the buried interface.
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Inspired by the branching corrected surface hopping (BCSH) method [J. Xu and L. Wang, J. Chem. Phys. 150, 164101 (2019)], we present two new decoherence time formulas for trajectory surface hopping. Both the proposed linear and exponential formulas characterize the decoherence time as functions of the energy difference between adiabatic states and correctly capture the decoherence effect due to wave packet reflection as predicted by BCSH. The relevant parameters are trained in a series of 200 diverse models with different initial nuclear momenta and the exact quantum solutions are utilized as references. As demonstrated in the three standard Tully models, the two new approaches exhibit significantly higher reliability than the widely used counterpart algorithm while holding the appealing efficiency, thus promising for nonadiabatic dynamics simulations of general systems.
Diffusion of tracer particles in active bath has attracted extensive attention in recent years. So far, most studies have considered isotropic spherical tracer particles, while the diffusion of anisotropic particles has rarely been involved. Here we investigate the diffusion dynamics of a rigid rod tracer in a bath of active particles by using Langevin dynamics simulations in a two-dimensional space. Particular attention is paid to how the translation(rotation) diffusion coefficient DT (DR) change with the length of rod L and active strength Fa. In all cases, we find that rod exhibits superdiffusion behavior in a short time scale and returns to normal diffusion in the long time limit. Both DT and DR increase with Fa, but interestingly, a nonmonotonic dependence of DT (DR) with the rod length has been observed. We have also studied to the translation-rotation coupling of rod, and interestingly, we find a negative translation-rotation coupling indicating that rod diffuses more slowly in parallel direction compared to that in the perpendicular direction, a counterintuitive phenomenon that would not exist in an equilibrium counterpart system. Moreover, this anomalous (diffusion) behavior is reentrant with the increase of Fa, suggesting two competitive roles played by the active feature of bath particles.
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G-C3N4 coupled with high specific area TiO2 (HSA-TiO2) composite was prepared by a simple solvothermal method, which was easy to operate with low energy consumption. Degradation of methyl orange test results showed that HSA-TiO2 effectively improved the photocatalytic activity effectively. PEC test results indicated that the separation of photo-generated carriers and the charge carrier migration speed of TiO2 were improved after combination with g-C3N4. G-C3N4/ HSA-TiO2 showed strong photocatalytic ability. The degree of degradation of methyl orange by 6%-g-C3N4/ HSA-TiO2 could reach up to 92.44%. Furthermore, it revealed good cycle performance. The photocatalytic mechanism of g-C3N4/ HSA-TiO2 was proposed.
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A fundamental study on C?C coupling that is the crucial step in the Fischer-Tropsch synthesis (FTS) process to obtain multi-carbon products is of great importance to tailor catalysts and then guide a more promising pathway. It has been demonstrated that the coupling of CO with the metal carbide can represent the early stage in the FTS process, while the related mechanism is elusive. Herein, the reactions of the CuC3H– and CuC3– cluster anions with CO have been studied by using mass spectrometry and theoretical calculations. The experimental results showed that the coupling of CO with the C3H– moiety of CuC3H– can generate the exclusive ion product COC3H–. The reactivity and selectivity of this reaction are greatly higher than that on the reaction of CuC3– with CO, and this H-assisted C?C coupling process was rationalized by theoretical calculations.
Photo-induced proton coupled electron transfer (PCET) is essential in the biological, photosynthesis, catalysis and solar energy conversion processes. Recently, p-nitrophenylphenol (HO-Bp-NO<sub>2</sub>) has been used as a model compound to study the photo-induced PCET mechanism using ultrafast spectroscopy. In transient absorption spectra both singlet and triplet exhibited PCET behavior. When we focused on the PCET in the triplet state, a new sharp band attracted us. This band had not been observed for p-nitrobiphenyl which is without hydroxyl substitution. To assign the new band, acidic solutions were used as an additional proton donor. Based on results in strong (~10<sup>-1</sup> M) and weak (~10<sup>-4</sup> M) acidic solutions, the new band is identified as the open shell singlet O-Bp-NO<sub>2</sub>H, which is generated through protonation of nitro O in <sup>3</sup>HO-Bp-NO<sub>2</sub> followed by deprotonation of hydroxyl. Kinetics analysis indicates the formation of radical •O-Bp-NO<sub>2</sub> competes with O-Bp-NO<sub>2</sub>H in the way of concerted electron-proton transfer and/or proton followed electron transfers and is responsible for the low yield of O-Bp-NO<sub>2</sub>H. The results in the present work will make it clear that how the <sup>3</sup>HO-Bp-NO<sub>2</sub> deactivates in aprotic polar solvents and provide a solid benchmark for the deeply studying the PCET mechanism in triplets of analogous aromatic nitro compound.
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Stimuli-responsive polymer gels have recently attracted great attention due to their heat/solvent resistance, dimensional stability, and unique sensitivity to external stimuli. In this work, we synthesized thiol-functionalized TPE and constructed polymer gels through thiol-ene click reaction. The synthetic process of the polymer gels could be monitored by fluorescence emission of TPE moieties based on AIE mechanism. In addition, due to the dual redox- and acidresponsiveness of the polymer gels, in the presence of DTT and TFA, fluorescence quenching of the polymer gels can be observed. This stimuli-responsive characteristics endows the polymer gels with potential applications in fluorescent sensing and imaging, cancer diagnosis and selfhealing materials.
A Multi-Domain High-Resolution Platform for Integrated Spectroscopy and Microscopy Characterizations
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In recent decades, materials science has experienced rapid development and posed increasingly high requirements for the characterizations of structures, properties, and performances. Herein, we report on our recent establishment of a multi-domain (energy, space, time) high-resolution platform for integrated spectroscopy and microscopy characterizations, offering an unprecedented way to analyze materials in terms of spectral (energy) and spatial mapping as well as temporal evolution. We present several proof-of-principle results collected on this platform, including in-situ Raman imaging (high-resolution Raman, polarization Raman, low-wavenumber Raman), time-resolved photoluminescence imaging, and photoelectrical performance imaging. It can be envisioned that our newly established platform would be very powerful and effective in the multi-domain high-resolution characterizations of various materials of photoelectrochemical importance in the near future.
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Hydrogels show versatile properties and are of great interest in the fields of bioelectronics and tissue engineering. Understanding the dynamics of the water molecules trapped in the three-dimensional polymeric networks of the hydrogels is crucial for us to elucidate their mechanical and swelling properties at the molecular level. In this report, the poly(DMAEMA-co-AA) hydrogels were synthesized and characterized by the macroscopic swelling measurements under different pH conditions. Furthermore, the microscopic structural dynamics of pH stimulus responsive hydrogels were studied using FTIR and ultrafast IR spectroscopies from the viewpoint of the SCN-anionic solute as the local vibrational reporter. Ultrafast IR spectroscopic measurements showed the time constants of the vibrational population decay of SCN- were increased from 14±1 ps to 20±1 ps when the pH of the hydrogels is varied from 2.0 to 12.0. Rotational anisotropy measurements further revealed that the rotation of SCN- anionic probe was restricted by the three-dimensional network formed in the hydrogels and the rotation of SCN- anionic probe can’t decay to zero especially at the pH of 7.0. These results presented in this study are expected to provide molecular level understanding of the microscopic structure of the cross-linked polymeric network in the pH stimulus-responsive hydrogels.
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Among various photocatalytic materials, Z-scheme photocatalysts have drawn tremendous research interest due to the high photocatalytic performance in solar water splitting. Here, we perform extensive hybrid density functional theory calculations to explore electronic structures, interfacial charge transfer, electrostatic potential profile, optical absorption properties, and photocatalytic properties of a proposed two-dimensional small-lattice-mismatched GaTe/Bi2Se3 heterostructure. Theoretical results clearly reveal that the examined heterostructure with a small direct band gap can effectively harvest the broad spectrum of the incoming sunlight. Due to the relative strong interfacial built-in electric field in the heterostructure and the small band gap between the valence band maximum of GaTe monolayer and the conduction band minimum of Bi2Se3 nanosheet with slight band edge bending, the photogenerated carriers transfer via Z-scheme pathway, which results in the photogenerated electrons and holes effectively separating into the GaTe monolayer and the Bi2Se3 nanosheet for the hydrogen and oxygen evolution reactions, respectively. Our results imply that the artificial 2D GaTe/Bi2Se3 is a promising Z-scheme photocatalyst for overall solar water splitting.
The IRMPD spectrum of the protonated heterodimer of ProPheH+, in the range of 2700-3700 cm-1, has been obtained with a Fourier-transform ion cyclotron mass spectrometer combined with an IR OPO laser. The experimental spectrum shows one peak at 3560 cm?1 corresponding to the free carboxyl O-H stretching vibration, and two broad peaks centered at 2935 and 3195 cm?1. Theoretical calculations were performed on the level of M062X/6-311++G(d,p). Results show that the most stable isomer is characterized by a charge-solvated structure in which the proton is bound to the unit of Pro. Its predicted spectrum is in good agreement with the experimental one, although the coexistence of salt-bridged structures cannot be entirely excluded.
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A Mn3O4 coating is approved to modify the surface of LiNi0.5Mn1.5O4 particles by a simple wet grinding method for the first time, which realize an great improvement in electronic conductivity from 1.53?10-7 S cm-1 to 3.15?10-5 S cm-1 after 2.6% Mn3O4 coating. The electrochemical test resualts demonstrate that the Mn3O4 coating dramatically enhances both the rate performance and cycling capability (at 55 °C) of LiNi0.5Mn1.5O4. Among the samples, 2.6% Mn3O4-coated LiNi0.5Mn1.5O4 not only exhibits excellent rate capability (a large capacity of 108 mAh g-1 at 10 C rate) but also keep 78% capacity retention at 55 °C and 1 C rate after 100 cycles.
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Formaldehyde and hydrogen peroxide are two important realistic molecules in atmospheric chemistry. We implement path integral Liouville dynamics (PILD) to calculate the dipole-derivative autocorrelation function for obtaining the infrared (IR) spectrum. In comparison to exact vibrational frequencies, PILD faithfully capture most nuclear quantum effects in vibrational dynamics as temperature changes and as the isotopic substitution occurs.
Two non-ionic hydro-fluorocarbon hybrid surfactants with and without hydroxyl groups were synthesized and compared. They exhibited good thermal stability and superior surface activity. It was observed that the hydroxyl group had a profound effect on modifying the surface tension of their solutions and the morphology of the formed micelles. This effect may be attributed to the rearranging of the alkane group from above the air/aqueous surface to below it and the disrupting of the interfacial water structure induced by the hydroxyl groups. This work provides a strategy to weaken the immiscibility between hydrocarbon and fluorocarbon chains by modifying their orientational structure at the interface, thus is helpful for the design of surfactants with varied interfacial properties.
Empirical potential structure refinement (EPSR) is a neutron scattering data analysis algorithm and a software package. It was developed by the British spallation neutron source (ISIS) Disordered Materials Group in 1980s, and aims to construct the most-probable atomic structures of disordered materials in the field of chemical physics. It has been extensively used during the past decades, and has generated reliable results. However, it implements a shared-memory architecture with Open Multi-Processing (OpenMP). With the extensive construction of supercomputer clusters and the widespread use of graphics processing unit (GPU) acceleration technology, it is now possible to rebuild the EPSR with these techniques in the effort to improve its calculation speed. In this study, an open source framework NeuDATool is proposed. It is programmed in the object-oriented language C++, can be paralleled across nodes within a computer cluster, and supports GPU acceleration. The performance of NeuDATool has been tested with water and amorphous silica neutron scattering data. The test shows that the software can reconstruct the correct microstructure of the samples, and the calculation speed with GPU acceleration can increase by more than 400 times, compared with CPU serial algorithm at a simulation box that consists about 100 thousand atoms. NeuDATool provides another choice to implement simulation in the (neutron) diffraction community, especially for experts who are familiar with C++ programming and want to define specific algorithms for their analysis.
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In this paper, the effect of channel length and width on the large and small-signal parameters of the Graphene Field Effect Transistor (GFET) have been explored using an analytical approach. In the case of faster saturation as well as extremely high transit frequency GFET shows outstanding performance. From the transfer curve, it is observed that there is a positive shift of Dirac point from the voltage of 0.15 V to 0.35 V because of reducing channel length from 440 nm to 20 nm and this curve depicts that graphene shows ambipolar behavior. Besides, it is found that because of widening channel the drain current increases and the maximum current is found approximately 2.4 mA and 6 mA for channel width 2μm and 5μm respectively. Furthermore, an approximate symmetrical capacitance-voltage (C–V) characteristic of GFET is obtained and found that capacitance reduces when the channel length decreases but the capacitance can be increased by raising the channel width. In addition, a high transconductance of 6.4 mS at channel length 20 nm and 4.45 mS at channel width 5 μm along with a high transit frequency of 3.95 THz has been found that demands high-speed radio frequency (RF) applications.
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The natural attapulgite (NAPT) was disaggregated by high-pressure homogenization technology combined with extrusion process to prepare the APT with disaggregated rod crystal bundles (DAPT) and larger specific surface area 133.7 m2?g-1. NAPT and DAPT were incorporated into the silicone rubber to obtain the composite NAPT-SR and DAPT-SR by mechanical blending method. After thermal oxidative ageing at 300 oC for 0.5 h, the 5% weight loss temperature of the rubber composites increased greatly from 385 oC of the neat silicone rubber to 396-399 oC with addition of NAPT and DAPT. NAPT and DAPT enhanced the interaction between the silica nanoparticles and rubber matrix thus inhibited the nanoparticle agglomeration. The conservation rate of the side methyl group in NAPT-SR and DAPT-SR was greatly improved after ageing. Therefore, the thermal oxidative degradation and ageing performance of the silicone rubber composites was significantly reinforced. Moreover, DAPT could greatly restrain the growth of nanoparticles after ageing, therefore, show the better retention of tensile strength (40.6%), elongation at break (34.9%) and tear strength (30.1%) compared with the corresponding mechanical properties of the neat silicone rubber (10.6%, 7.4% and 5.0%) after ageing.
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Two thin-film 2D organic–inorganic hybrid perovskites, i.e., 2-phenylethylammonium lead iodide (PEPI) and 4-phenyl-1-butylammonium lead iodide (PBPI) were synthesized and investigated by steady-state absorption, temperature-dependent photoluminescence, and temperature-dependent ultrafast transient absorption spectroscopy. PBPI has a longer organic chain (via introducing extra ethyl groups) than PEPI, thus its inorganic skeleton can be distorted bringing on structural disorder. The comparative analyses of spectral profiles and temporal dynamics revealed that the greater structural disorder in PBPI results in more defect states serving as trap states to promote exciton dynamics. In addition, the fine-structuring of excitonic resonances was unveiled by temperature-dependent ultrafast spectroscopy, suggesting its correlation with inorganic skeleton rather than organic chain. Moreover, the photoexcited coherent phonons were observed in both PEPI and PBPI, pointing to a subtle impact of structural disorder on the low-frequency Raman-active vibrations of inorganic skeleton. This work provides valuable insights into the optical properties, excitonic behaviors and dynamics, as well as coherent phonon effects in 2D hybrid perovskites.
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To address the limitations of the separate fluoride removal or detection in the existing materials, herein, amino-decorated metal organic frameworks NH2-MIL-53(Al) have been succinctly fabricated by a sol-hydrothermal method for simultaneous removal and determination of fluoride. As a consequence, the proposed NH2-MIL-53(Al) features high uptake capacity (202.5 mg g?1) as well as fast adsorption rate, being capable of treating 5 ppm of fluoride solution to below the permitted threshold in drinking water within 15 min. Specifically, the specific binding between fluoride and NH2-MIL-53(Al) results in the release of fluorescent ligand NH2-BDC, conducive to the determination of fluoride via a concentration-dependent fluorescence enhancement effect. As expected, the resulting NH2-MIL-53(Al) sensor exhibits selective and sensitive detection (with the detection limit of 0.31 μM) toward fluoride accompanied combined with a wide response interval (0.5?100 μM). More importantly, the developed sensor can be utilized for fluoride detection in practical water systems with satisfying recoveries from 89.6% to 116.1%, confirming its feasibility in monitoring the practical fluoride-contaminated waters.
In this study, we have developed a high-sensitivity, near-infrared photodetector (NIRPD)
based on PdSe2/GaAs heterojunction, which was made by transferring a multilayered PdSe2
film onto a planar GaAs. The as-fabricated PdSe2/GaAs heterojunction device exhibited
obvious photovoltaic behavior to 808 nm illumination, indicating that the NIRPD can be
used as a self-driven device without external power supply. Further device analysis showed
that the hybrid heterojunction exhibited a high on/off ratio ratio of 1.16×105 measured at
808 nm under zero bias voltage. The responsivity and specific detectivity of photodetector
were estimated to be 171.34 mA/W and 2.36×1011 Jones, respectively. Moreover, the device showed excellent stability and reliable repeatability. After 2 months, the photoelectric
characteristics of the NIRPD hardly degrade in air, attributable to the good stability of the
PdSe2. Finally, the PdSe2/GaAs-based heterojunction device can also function as a NIR
light sensor.
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Over the last few years, machine learning is gradually becoming an essential approach for the investigation of heterogeneous catalysis. As one of the important catalysts, binary alloys have attracted extensive attention for the screening of bifunctional catalysts. Here we present a holistic framework for machine learning approach to rapidly predict adsorption energies on the surfaces of metals and binary alloys. We evaluate different machine-learning methods to understand their applicability to the problem and combine a tree-ensemble method with a compressed-sensing method to construct decision trees for about 60,000 adsorption data. Compared to linear scaling relations, our approach enables to make more accurate predictions lowering predictive root-mean-square error by a factor of two and more general to predict adsorption energies of various adsorbates on thousands of binary alloys surfaces, thus paving the way for the discovery of novel bimetallic catalysts.
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The simple homodinuclear M-M single bonds for Group II and XII elements are difficult to obtain as a result of the fulfilled s2 electronic configurations, consequently, a dicationic prototype is often utilized to design the M+-M+ single bond. Existing studies generally use sterically bulky organic ligands L- to synthesize the compounds in an L--M+-M+-L- manner. However, here we report the design of Mg-Mg and Zn-Zn single bonds in two ligandless clusters, Mg2B7- and Zn2B7-, using density functional theory methods. The global minima of both of the clusters are in the form of M22+(B73-), where the M-M single bonds are positioned above a quasi-planar hexagonal B7 moiety. Chemical bonding analyses further confirm the existence of Mg-Mg and Zn-Zn single bonds in these clusters, which are driven by the unusually stable B73- moiety that is both σ and π aromatic. Vertical detachment energies of Mg2B7- and Zn2B7- are calculated to be 2.79 eV and 2.94 eV, respectively, for the future comparisons with experimental data.
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We carried out first-principles calculations to investigate the electronic properties of the monolayer blue phosphorene (BlueP) decorated by the group-IVB transition-metal adatoms (Cr, Mo and W), and found that the Cr-decorated BlueP is a magnetic half metal, while the Mo- andW-decorated BlueP are semiconductors with band gaps smaller than 0.2 eV. Compressive biaxial strains make the band gaps close and reopen and band inversions occur during this process, which induces topological transitions in the Mo-decorated BlueP (with strain of ??5:75%) and W-decorated BlueP (with strain of ??4:25%) from normal insulators to topological insulators (TIs). The TI gap is 94 meV for the Mo-decorated BlueP and 218 meV for the W-decorated BlueP. Such large TI gaps demonstrate the possibility to engineer topological phases in the monolayer BlueP with transition-metal adatoms at high temperature.
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We constructed two types of copper-doped metal–organic framework (MOF), i.e., Cu@UiO-66-NH2 and Cu-UiO-66-NH2. In the former, Cu2+ ions are impregnated in the pore space of the amine-functionalized, Zr-based UiO-66-NH2; while in the latter, Cu2+ ions are incorporated to form a bimetal-center MOF with Zr4+ being partially replaced by Cu2+ in the Zr–O oxo-clusters. Ultrafast spectroscopy revealed that the photoinduced relaxation kinetics associated with the ligand-to-cluster charge-transfer state are promoted for both Cu-doped MOFs relative to undoped one, but in a sequence of Cu-UiO-66-NH2 > Cu@UiO-66-NH2 > UiO-66-NH2. Such a sequence turned to be in line with the trend observed in the visible-light photocatalytic hydrogen evolution activity tests on the three MOFs. These findings highlighted the subtle effect of copper-doping location in this Zr-based MOF system, further suggesting that rational engineering of the specific metal-doping location in alike MOF systems to promote the photoinduced charge separation and hence suppress the detrimental charge recombination therein is beneficial for achieving improved performances in MOF-based photocatalysis.
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In this work, p-type Co3O4 decorated n-type ZnO (Co3O4/ZnO) nanocomposite was designed with the assistance of bacterial cellulose template. Phase composition, morphology and element distribution were investigated by XRD, SEM, HRTEM, EDS mapping and XPS. Volatile organic compounds (VOCs) sensing measurements indicated a noticeable improvement of response and decrease of working temperature for Co3O4/ZnO sensor, in comparison with pure ZnO, i.e., the response towards 100 ppm acetone was 63.7 (at a low working temperature of 180 °C), which was 26 times higher than pure ZnO (response of 2.3, at 240 °C). Excellent VOCs response characteristics could be ascribed to increased surface oxygen vacancy concentration (revealed by defect characterizations), catalytic activity of Co3O4 and the special p-n heterojunction structure, and bacterial cellulose provides a facile template for designing diverse functional heterojunctions for VOCs detection and other applications.
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The special mass shift coefficient, ΔKSMS, and field parameter factor, Ful of four multiples, 3〖s 〗^4 P→3〖p 〗^4 P^°, 3〖s 〗^4 P→3〖p 〗^4 D^°, 3〖s 〗^2 D→5〖p 〗^2 D^°, and 3〖s 〗^2 P→3〖p 〗^2 P^°, of 14N and 15N were studied using the multi-configuration Dirac–Hartree–Fock method and the relativistic configuration interaction approach. The normal mass shift, special mass shift, field shift, and isotope shift of N I were derived from the theoretical calculated ΔKSMS, ΔKSMS and Ful, and compared with the reported experimental measurements and theoretical results.
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The structures and electronic properties of the gaseous M2Pt20/? clusters (M represents the alkaline earth metal) are investigated using the density functional theory (B3LYP and PBE0) and wave function theory (SCS-MP2, CCSD and CCSD (T)). The results show that the D2h isomers with the planar structures are more stable than the C2V isomers with smaller dihedral angles and shorter Pt-Pt bond lengths. In this work we show that the mutual competition of M(s, p)-Pt(5d) interaction and Pt-Pt covalent bonding contributes to the different stabilizations of the two kinds of isomers. The M(s, p)-Pt(5d) interaction favors the planar isomers with D2h symmetry, while the Pt-Pt covalent bonding leads to the C2V isomers with bending structures. Two different crossing points are determined in the potential energy curves of Be2Pt2 with the singlet and triplet states. But there is just one crossing point in potential energy curves of Ra2Pt2 and Ca2Pt2? because of flatter potential energy curves of Ra2Pt2 with the triplet state or Ca2Pt2? with quartet state. The results reveal a unique example of dihedral angle-bending isomers with the smallest number of atoms and may help the understanding of the bonding properties of other potential angle-bending isomers.
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From the organization of animal ocks to the emergence of swarming behav- iors in bacterial suspension, populations of motile organisms at all scales display coherent collective motion. Recent studies showed the anisotropic interaction between the active particles plays a key role on the phase behaviors. Here we investigate the collective behaviors of active Janus particles that experience an anisotropic interaction that is opposite to the active force by using Langevin dynamics simulations in two dimensional space. Interestingly, the system shows emergence of collective swarming states upon increasing the total area fraction of particles, which is not observed for systems without anisotropic interaction or activity. The threshold value of area fraction c decreases with particle ac- tivity or interaction strength. We have also performed basic kinetic analysis to reproduce the essential features of the simulation results. Our results demon- strate that anisotropic interactions at the individual level are sucient to set homogeneous active populations into stable directed motion.
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Photocatalytic degradation of organic pollutants has become a hot research topic because of its low energy consumption and environmental-friendly characteristics. Bismuth oxide (Bi2O3) nanocrystals with a bandgap ranging between 2.0-2.8 eV has attracted increasing attention due to high activity of photodegradation of organic pollutants by utilizing visible light. Though several methods have been developed to prepare Bi2O3-based semiconductor materials over recent years, it is still difficult to prepare highly active Bi2O3 catalysts in large-scale with a simple method. Therefore, developing simple and feasible methods for the preparation of Bi2O3 nanocrystals in large-scale is important for the potential applications in industrial wastewater treatment. In this work, we successfully prepared porous Bi2O3 in large scale via etching commercial BiSn powders, followed by thermal treatment with air. The acquired porous Bi2O3 exhibited excellent activity and stability in photocatalytic degradation of methylene blue (MB). Further investigation of the mechanism witnessed that the suitable band structure of porous Bi2O3 allowed the generation of reactive oxygen species, such as O2-? and ?OH, which effectively degraded MB.
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The structure-property relationship of DAE-derivative (C5F-4Py) molecular isomers which involve ring-closed status and ring-open status is investigated by employing non-equilibrium Green’s function formalism combined with density functional theory. Molecular junctions are formed by the isomers connecting to Au (111) electrodes through the flanked pyridine groups. The difference of electronic structures caused by different geometry structures for the two isomers, especially the alternative single bond and double bond in ring-closed molecule, contributes the remarkable different low-bias conductance values. The LUMO orbitals of isomers are mainly channels to transport electron. In addition, the more electrons transferred to ring-closed molecular junction in equilibrium condition drop down the LUMO orbitals closer to the Fermi energy which may be to contribute larger conductance value at Fermi level. Our findings are help to understand the mechanism of the low-bias conducting mechanism of and are conductive to design of high performance molecular switching based on DAE or DAE-derivatives molecules.
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Multinanoparticles interacting with the phospholipid membranes in solution were studied by dissipative particle dynamics simulation. The nanoparticles selected have spherical or cylindrical shapes, and they have various initial velocities in the dynamical processes. Several translocation modes are defined according to their characteristics in the dynamical processes, in which the phase diagrams are constructed based on the interaction strengths between the particles and membranes and the initial velocities of particles. Furthermore, several parameters, such as the system energy and radius of gyration, are investigated in the dynamical processes for the various translocation modes. Results elucidate the effects of multiparticles interacting with the membranes in the biological processes.
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Surface passivation is one valuable approach to tune the properties of nanomaterials. The piezo- electric properties of hexagonal [001] ZnO nanowires with four kinds of surface passivations were investigated using the rst-principles calculations. It is found that in the 50% H(O), 50% Cl(Zn); 50% H(O), 50% F(Zn) passivations, the volume and surface e ects both enhance the piezoelectric coecient. This di ers from the unpassivated cases where the surface e ect was the sole source of piezoelectric enhancement. In the 100% H; 100% Cl passivations, the piezoelectric enhancement is not possible since the surface e ect is screened by surface charge with weak polarization. The study reveals that the competition between the volume e ect and surface e ect in uences the iden- ti cation of the diameter-dependence phenomenon of piezoelectric coecients for ZnO nanowires in experiments. Moreover, the results suggest that one e ective means of improving piezoelectricity of ZnO nanowires is shrinking axial lattice or increasing surface polarization through passivation.
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A distributed feedback (DFB) laser with a wavelength of 2.8 m was used to measure the species produced by water vapor glow discharge. Only the absorption spectra of OH radicals and transient H2O molecules were observed using concentration modulation (CM) spectroscopy. The intensities and orientations of the absorption peaks change with the demodulation phase, but the direction of one absorption peak of H2O is always opposite to the other peaks. The different spectral orientations of OH and H2O reflect the increase or decrease of the number of particles in the energy levels. If more transient species can be detected in the discharge process, the dynamics of excitation, ionization and decomposition of H2O can be better studied. This study shows that the demodulation phase relationship of CM spectrum can be used to study the population change of molecular energy levels.
A new kind of phenyl-functionalized magnetic fibrous mesoporous silica (Fe3O4@SiO2@KCC-1-phenyl) was prepared by copolymerization as an efficient adsorbent for the magnetic extraction of phthalate esters from environmental water samples. The obtained Fe3O4@SiO2@KCC-1-phenyl showed monodisperse fibrous spherical morphology, fairly strong magnetic response (29 emu g–1), and an abundant π-electron system, which allowed rapid isolation of the Fe3O4@SiO2@KCC-1-phenyl from solutions upon applying an appropriate magnetic field. Several variables that affect the extraction efficiency of the analytes, including the type of the elution solvent, amount of adsorbent, extraction time and reusability, were investigated and optimized. Under optimum conditions, the Fe3O4@SiO2@KCC-1-phenyl was used for the extraction of four phthalate esters from environmental water samples followed by high-performance liquid chromatographic analysis. Validation experiments indicated that the developed method presented good linearity (0.1–20 ng mL-1), low limit of detection (7.5-29 μg L–1, S/N=3). The proposed method was applied to the determination of phthalate esters in different real water samples, with relative recoveries of 93-103.4% and RSDs of 0.8–8.3 %.
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Developing low-cost and high-efficient noble-metal-free cocatalysts has been a challenge to achieve economic hydrogen production. In this work, molybdenum oxides (MoO3-x) were in-situ loaded on polymer carbon nitride (PCN) via a simple one-pot impregnation-calcination approach. Different from post-impregnation method, intimate coupling interface between high-dispersed ultra-small MoO3-x nanocrystal and PCN was successfully formed during the in-situ growth process. The MoO3-x-PCN-x photocatalyst without noble platinum (Pt) finally exhibited enhanced photocatalytic hydrogen performance under visible light irradiation (λ>420 nm), with the highest hydrogen evolution rate of 15.6 μmol/h, which was more than 3 times that of bulk PCN. Detailed structure-performance revealed that such improvement in visible-light hydrogen production activity originated from the intimate interfacial interaction between high-dispersed ultra-small MoO3-x nanocrystal and polymer carbon nitride as well as efficient charge carriers transfer brought by Schottky junction formed.
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Highly luminescent bulk two-dimensional covalent organic frameworks (COFs) attract much attention recently. Origin of their luminescence and their large Stokes shift is an open question. After first-principles calculations on two kinds of COFs using the GW method and Bethe-Salpeter equation, we find that monolayer COF has a direct band gap, while bulk COF is an indirect band-gap material. The calculated optical gap and optical absorption spectrum for the direct excitons of bulk COF agree with the experiment. However, calculated energy of the indirect exciton, in which the photoelectron and the hole locate at the conduction band minimum and the valence band maximum of bulk COF respectively, is too low compared to the fluorescence spectrum in experiment. This may exclude the possible assistance of phonons in the luminescence of bulk COF. Luminescence of bulk COF might result from exciton recombination at the defects sites. The indirect band-gap character of bulk COF originates from its AA-stacked conformation. If the conformation is changed to the AB-stacked one, the band gap of COF becomes direct which may enhance the luminescence.
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The geometric structures and vibration frequencies of para-chlorofluorobenzene (p-ClFPh) in the first excited state of neutral and ground state of cationic were investigated by resonance-enhanced multiphoton ionization (REMPI) and slow electron velocity-map imaging (SEVI). The infrared spectrum of S0 state and absorption spectrum for S1 ← S0 transition in p-ClFPh were also recorded. Based on the one-color resonant two-photon ionization (1C-R2PI) spectrum and two-color resonant two-photon ionization (2C-R2PI) spectrum, we measured the adiabatic excitation energy of p-ClFPh as 36302 ± 4 cm-1. In the 2C-R2PI SEVI spectra, the accurate adiabatic ionization potential (AIP) of p-ClFPh was extrapolated to be 72937 ± 8 cm?1 via a series of progressive measurements near threshold ionization region. In addition, Franck-Condon simulations were performed to help us confidently ascertain the main vibration modes in the S1 and D0 states. The wavenumber changes of vibration modes during the transition of S1 ← S0 and D0 ← S1 were discussed. Furthermore, the mixing of vibration modes both between S0 & S1 and S1 & D0 has been analyzed.
The geometric and electronic structures of several possible adsorption configurations of the pyrazine (C4H4N2) molecule covalently attached to Si(100) surface, which is of vital importance in fabricating functional nanodevices, have been investigated using X-ray spectroscopies. The Carbon K-shell (1s) X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy of predicted adsorbed structures have been simulated by density functional theory (DFT) with cluster model calculations. Both XPS and NEXAFS spectra demonstrate the structural dependence on different adsorption configurations. In contrast to the XPS spectra, it is found that the NEXAFS spectra exhibiting conspicuous dependence on the structures of all the studied pyrazine/Si(100) systems can be well utilized for structural identification, which has been discussed in detail in this article. In addition, according to the classification of carbon atoms, the spectral components of carbon atoms in different chemical environments have been investigated in the NEXAFS spectra as well.
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Cancer is one of the most serious issues in human life. Blocking Programmed cell death protein 1 (PD-1) and programmed death ligand-1 (PD-L1) pathway is one of the great innovation on last few years, but a few numbers of inhibitors can be able to block it. (2-methyl-3-biphenylyl) methanol (MBPM) derivative is one of them. Here, the quantitative structure-activity relationship (QSAR) established twenty (2-methyl-3-biphenylyl) methanol (MBPM) derivatives as the programmed death ligand-1 (PD-L1) inhibitors. Density functional theory (DFT) at the B3LPY/6-31+G (d, p) level was employed to study the chemical structure and properties of the chosen compounds. Highest occupied molecular orbital energy EHOMO, lowest unoccupied molecular orbital energy ELUMO, total energy ET, dipole moment DM, absolute hardness η, absolute electronegativity χ, softness S, electrophilicity ω, energy gap ΔE, etc, properties were observed and determine. Principal component analysis (PCA), multiple linear regression (MLR) and multiple non-linear regression (MNLR) analysis were carried out to establish the QSAR. The proposed quantitative models and interpreted outcomes of the compounds were based on statistical analysis. Statistical results of MLR and MNLR exhibited the coefficient was 0.661 and 0.758, respectively. Leave-one-out cross-validation (LOO-CV), r2m metric, r2m test and “Golbraikh & Tropsha’s criteria” analyses were applied for the validation of MLR and MNLR, which indicate two models are statistically significant and well stable with data variation in the external validation towards PD-L1. The obtained values specified that the two different modelings can predict the bioactivity and may be helpful and supporting for evaluation of the biological activity of PD-L1 inhibitor.
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Zinc oxide is recently being used as magnetic semiconductor with introduction of magnetic elements in it. In this work, we report phase pure synthesis of Mg and Ni co-substituted ZnO to explore its structure, optical, magnetic and photo-catalytic properties. X-ray diffraction analysis reveal the formation of hexagonal wurtzite type structure having P63mc space group without any impurity phase. UV-Vis spectrophotometry demonstrate the variation in band gap with addition of Mg and Ni content in ZnO matrix. Magnetic measurements exhibit a clear boosted magnetization in Ni and Mg co-doped compositions with its stable value of band gap corroborating the structural stability and magnetic tuning for its advanced applications in modern day spintronic devices. Photo-catalytic measurements were performed using methyl green degradation demonstrate an enhanced trend of activity in Mg and Ni co-doped compositions.
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ATP-binding cassette (ABC) exporters transport many substrates out of cellular membranes via alternating between inward-facing (IF) and outward-facing (OF) conformations. Despite extensive research efforts over the past decades, understanding of the molecular mechanism remains elusive. As these large-scale conformational movements are global and collective, we have previously performed extensive coarse-grained molecular dynamics (CG-MD) simulations of the potential of mean force (PMF) along the conformational transition pathway [Z. Wang et. al JPCB, 119, 1295?1301 (2015)]. However, the occluded (OC) conformational state, in which both the internal and external gate are closed, was not determined in the calculated free energy profile. In this paper, we extend the above methods to the calculation of the free energy profile along the reaction coordinate, d1- d2, which are the COM distances between the two sides of the internal (d1) and the external gate (d2). The PMF is thus obtained to identify the transition pathway, along which several OF-, IF- and OC- state structures are predicted in good agreement with structural experiments. Our CG-MD free-energy simulations demonstrate that the internal gate is closed before the external gate is open during the IF to OF transition and vice versa during the IF to OF transition. Our results capture the unidirectional feature of substrate translocation via the exporter, which is functionally important in biology. This finding is different from the results, in which both the internal and external gates are open reported in an X-ray experiment [Ward A. et al, PNAS, 104, 19005?19010 (2007)]. Our study sheds light on the molecular mechanism of the state transitions in the ABC exporter.
Accepted Manuscript
, Available online
Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants. Kinetic current density (jk) at certain overpotential calculated by K-L equation is commonly used as the metrics to evaluate the activity of electrocatalysts. However, it is frequently found that the jl is not correctly identified in the literatures. Instead of jK, the measured current density normalized by diffusion limiting current density (j/jL) has also been frequently under circumstance where its validity is not justified. By taking ORR/HER/HOR as examples, we demonstrate that identify the actualjL for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce jk. Our analysis reveals that j/jL is a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same. In addition, if one wants to use j/jL to compare the intrinsic activity, the concentration overpotential should be eliminated.
Crayfish Shell Waste As a Safe Biosorbent for The Removal of Cu2+ and Pb2+ from Synthetic Wastewater
Accepted Manuscript
, Available online
Crayfish shell is an abundant natural waste meanwhile a potential biosorbent for pollutants if the release of heavy metals can be ignored. In this study, the safety of crayfish shell as a biosorbent was first accessed by the release experiments involving primary heavy metal ions, such as Cu2+, Zn2+, and Cr3+, in aqueous solution under environmental conditions. Although the release concentrations of heavy metals were dependent on pH, ionic strength, and humic acid, the concentrations were still lower than the national standard. The removal of Cu2+ and Pb2+ by crayfish shell in synthetic wastewater was investigated. The results indicated that crayfish shell is an excellent biosorbent for the removal of Cu2+ and Pb2+, and the removal process involved biosorption, precipitation, and complexation. Particularly, the precipitation step is calcium species-, pH- and temperature-dependent. The maximum removal capacity of Pb2+ and Cu2+ reached 676.20 and 119.98 mg g-1, respectively. The related precipitation and complex products include Cu2CO3(OH)2, Ca2CuO3, CuCO3, Pb2CO3(OH)2, CaPb3O4, and PbCO3. This study evaluated a recyclable pathway of crayfish shell waste and provides a new explanation for the biosorption of heavy metals by crayfish shell.
Accepted Manuscript
, Available online
This work reports the systematic study of surface phenomenon and self-aggregation behavior of cationic surfactant cetyltrymethyl ammonium bromide (CTAB) with ammonium nitrate (NH4NO3) salt. Surface and thermodynamic properties of cationic surfactant CTAB with ammonium nitrate salt were investigated at different temperatures through different techniques like conductometry and surface tensiometery. The surface tension measurement was carried out to find out the critical micelle concentration (CMC), free energy of adsorption (?Gads), free energy of micellization (?Gm), minimum area per molecule (A) and surface excess concentration (Г). The study reveals that the process of micellization is spontaneous and exothermic in nature. Conductance measurement enabled us to determine CMC, degree of ionization (α), degree of counter ion binding (β). Upon addition of NH4NO3 to the surfactant solutions increase the values of α and β, although it lowers the values of CMC showing that the process of micellization is more favorable and spontaneous. The study is very helpful to develop better understanding about interaction between electrolyte and surfactant.
Accepted Manuscript
, Available online
The influence of various water soluble ions on the hydration of calcined flue gas desulphurization gypsum was investigated. The presence of K+ can significantly increase the solubility of gypsum through the precipitation of K2SO4. All cations were found to accelerate the hydration of basanite, where Ca2+ shows the weakest acceleration effect. The final crystal size is not largely influenced by different salts, except for Na+, where the giant crystal with length of >130μm is observed. Current study clarifies the influence of different ions on the hydration of basanite, which could provide sufficient guide for the pre-treatment of original flue gas desulphurization gypsum before actual application.
Accepted Manuscript
, Available online
Based on density functional theory (DFT), a new silicon allotrope (C2-Si) is proposed in this work. The mechanical stability and dynamic stability of C2-Si are examined based on the elastic constants and phonon spectrum. According to the BH/GH values, C2-Si has ductility under ambient pressure; compared with Si64, Si96, I4/mmm and h-Si6, C2-Si is less brittle. Within the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional, C2-Si is an indirect narrow band gap semiconductor, and the band gap of C2-Si is only 0.716 eV, which is approximately two-thirds that of c-Si. The ratios of the maximum and minimum values of the Young's modulus, shear modulus and Poisson's ratio in their 3D spatial distributions for C2-Si are determined to characterize the anisotropy. In addition, the anisotropy in different crystal planes is also investigated via 2D representations of the Young’s modulus, shear modulus and Poisson’s ratio. In addition, among more than ten silicon allotropes, C2-Si has the strongest absorption ability for visible light.
2021, 34(1): 1-14.
doi: 10.1063/1674-0068/cjcp2102027
In this review, we present a brief overview on the recent advances in Ångström-resolved tip-enhanced Raman spectromicroscopy. We first introduce the theoretical understanding of the confinement of light at the atomistic scale, and explain how the Raman scattering from a single molecule happens under the "illumination" of such an atomically confined light. Then we describe the latest developments on Ångström-resolved tip-enhanced Raman spectromicroscopy, particularly on a new methodology called "scanning Raman picoscopy" for visually constructing the chemical structure of a single molecule in real space. Finally, we give a perspective of this technique in various applications where identifying the chemical structures of materials at the chemical bond level is required.
2021, 34(1): 15-29.
doi: 10.1063/1674-0068/cjcp2012208
Recent progress in ultrafast lasers, ultrafast X-rays and ultrafast electron beams has made it possible to watch the motion of atoms in real time through pump-probe technique. In this review, we focus on how the molecular dynamics can be studied with ultrafast electron diffraction where the dynamics is initiated by a pumping laser and then probed by pulsed electron beams. This technique allows one to track the molecular dynamics with femtosecond time resolution and Ångström spatial resolution. We present the basic physics and latest development of this technique. Representative applications of ultrafast electron diffraction in studies of laser-induced molecular dynamics are also discussed. This table-top technique is complementary to X-ray free-electron laser and we expect it to have a strong impact in studies of chemical dynamics.
2021, 34(1): 30-42.
doi: 10.1063/1674-0068/cjcp2012222
Two-dimensional electronic spectroscopy (2DES) is a powerful method to probe the coherent electron dynamics in complicated systems. Stabilizing the phase difference of the incident ultrashort pulses is the most challenging part for experimental demonstration of 2DES. Here, we present a tutorial review on the 2DES protocols based on active phase managements which are originally developed for quantum optics experiments. We introduce the 2DES techniques in box and pump-probe geometries with phase stabilization realized by interferometry, and outline the fully collinear 2DES approach with the frequency tagging by acoustic optical modulators and frequency combs. The combination of active phase managements, ultrashort pulses and other spectroscopic methods may open new opportunities to tackle essential challenges related to excited states.
2021, 34(1): 43-50.
doi: 10.1063/1674-0068/cjcp2101002
Many physical, chemical, and biological processes happen in liquid-vapor interface and are profoundly influenced with the local microstructures. In contrast to the liquid bulk, molecular orientation is the remarkable one of asymmetric structural features of the interface. Here we report an experimental method, namely, electron-impact time-delayed mass spectrometry and give a brief review about our recent progresses. This brand-new method not only enables us to have more insights into the interfacial structures, as done with small-angle X-ray and neutron scatterings and vibrational sum frequency generation spectroscopy, but also provides opportunity to explore the electron-driven chemical reactions therein.
2021, 34(1): 51-60.
doi: 10.1063/1674-0068/cjcp2101018
Spectroscopic characterization of clusters is crucial to understanding the structures and reaction mechanisms at the microscopic level, but it has been proven to be a grand challenge for neutral clusters because the absence of a charge makes it difficult for the size selection and detection. Infrared (IR) spectroscopy based on threshold photoionization using a tunable vacuum ultraviolet free electron laser (VUV-FEL) has recently been developed in the lab. The IR-VUV depletion and IR+VUV enhancement spectroscopic techniques open new avenues for size-selected IR spectroscopies of a large variety of neutral clusters without confinement (i.e., an ultraviolet chromophore, a messenger tag, or a host matrix). The spectroscopic principles have been demonstrated by investigations of some neutral water clusters and some metal carbonyls. Here, the spectroscopic principles and their applications for neutral clusters are reviewed.
2021, 34(1): 61-70.
doi: 10.1063/1674-0068/cjcp2102026
One of the themes of modern molecular reaction dynamics is to characterize elementary chemical reactions from "quantum state to quantum state", and the study of molecular reaction dynamics in excited states can help test the validity of modern chemical theories and provide methods to control chemical reactions. The subject of this review is to describe the recent experimental techniques used to study the reaction dynamics of metal atoms in the gas phase. Through these techniques, information such as the internal energy distribution and angular distribution of the nascent products or the three-dimensional stereodynamic reactivity can be obtained. In addition, by preparing metal atoms with specific excited electronic states or orbital arrangements, information about the reactivity of the electronic states enriches the relevant understanding of the electron transfer mechanism in metal reaction dynamics.
In this study, we report the design and simulation of an electrostatic ion lens system consisting of 22 round metal plates. The opening of the extractor plate is covered with metal mesh, which is for shielding the interaction region of the lens system from the high DC voltages applied to all other plates than the repeller and extractor plates. The Simion simulation shows that both velocity-mapping and time focusing can be achieved simultaneously when appropriate voltages are applied to each of the plates. This makes the ion lens system be able to focus large ionic volumes in all three dimensions, which is an essential requirement for crossed ion-molecule scattering studies. A three-dimensional ion velocity measurement system with multi-hit and potential multi-mass capability is built, which consists of a microchannel plate (MCP), a P47 phosphor screen, a CMOS camera, a fast photomultiplier tube (PMT), and a high-speed digitizer. The two velocity components perpendicular to the flight axis are measured by the CMOS camera, and the time-of-flight, from which the velocity component along the flight axis can be deduced, is measured by the PMT. A Labview program is written to combine the two measurements for building the full three-dimensional ion velocity in real time on a frame-by-frame basis. The multi-hit capability comes from the fact that multiple ions from the camera and PMT in the same frame can be correlated with each other based on their various intensities. We demonstrate this by using the photodissociation of CH3I at 304 nm.
2021, 34(1): 81-86.
doi: 10.1063/1674-0068/cjcp2007119
The recently constructed cryogenic cylindrical ion trap velocity map imaging spectrometer (CIT-VMI) has been upgraded for coincidence imaging of both ionic and neutral photofragments from photodissociation of ionic species. The prepared ions are cooled down in a home-made cryogenic cylindrical ion trap and then extracted for photodissociation experiments. With the newly designed electric fields for extraction and acceleration, the ion beam can be accelerated to more than 4500 eV, which is necessary for velocity imaging of the neutral photofragments by using the position-sensitive imaging detector. The setup has been tested by the 355 nm photodissociation dynamics of the argon dimer cation (Ar$_2$ $^+$ ). From the recorded experimental images of both neutral Ar and ionic Ar$^+$ fragments, we interpret velocity resolutions of $\Delta v/v$ $\approx$ 4.6% for neutral fragments, and $\Delta v/v$ $\approx$ 1.5% for ionic fragments, respectively.
2021, 34(1): 87-94.
doi: 10.1063/1674-0068/cjcp2007114
By using scanning tunneling microscope induced luminescence (STML) technique, we investigate systematically the bias-polarity dependent electroluminescence behavior of a single platinum phthalocyanine (PtPc) molecule and the electron excitation mechanisms behind. The molecule is found to emit light at both bias polarities but with different emission energies. At negative excitation bias, only the fluorescence at 637 nm is observed, which originates from the LUMO→HOMO transition of the neutral PtPc molecule and exhibits stepwise-like increase in emission intensities over three different excitation-voltage regions. Strong fluorescence in region (Ⅰ) is excited by the carrier injection mechanism with holes injected into the HOMO state first; moderate fluorescence in region (Ⅱ) is excited by the inelastic electron scattering mechanism; and weak fluorescence in region (Ⅲ) is associated with an up-conversion process and excited by a combined carrier injection and inelastic electron scattering mechanism involving a spin-triplet relay state. At positive excitation bias, more-than-one emission peaks are observed and the excitation and emission mechanisms become complicated. The sharp molecule-specific emission peak at ~911 nm is attributed to the anionic emission of PtPc$^-$ originated from the LUMO+1→LUMO transition, whose excitation is dominated by a carrier injection mechanism with electrons first injected into the LUMO+1 or higher-lying empty orbitals.
2021, 34(1): 95-101.
doi: 10.1063/1674-0068/cjcp2010183
We study the photodissociation dynamics of CS$_2$ in the ultraviolet region using the time-sliced velocity map ion imaging technique. The S($^3$ P$_J$ )+CS($X^1\Sigma^+$ ) product channels were observed and identified at four wavelengths of 201.36, 203.10, 204.85 and 206.61 nm. In the measured images of S($^3$ P$_{J=2, 1, 0}$ ), the vibrational states of the CS($X^1\Sigma^+$ ) co-products were partially resolved and the vibrational state distributions were determined. Moreover, the product total kinetic energy releases and the anisotropic parameters were derived. The relatively small anisotropic parameter values indicate that the S($^3$ P$_{J=2, 1, 0}$ )+CS($X^1\Sigma^+$ ) channels are very likely formed via the indirect predissociation process of CS$_2$ . The study of the S($^3$ P$_{J=2, 1, 0}$ )+CS($X^1\Sigma^+$ ) channels, which come from the spin-orbit coupling dissociation process of CS$_2$ , shows that nonadiabatic process plays a role in the ultraviolet photodissociation of CS$_2$ .
2021, 34(1): 102-111.
doi: 10.1063/1674-0068/cjcp2004043
To obtain insight into the catalytic reaction mechanism of biodiesels over ZSM-5 zeolites, the pyrolysis and catalytic pyrolysis of methyl butanoate, a biodiesel surrogate, with H-type ZSM-5 (HZSM-5) were performed in a flow reactor under atmospheric pressure. The pyrolysis products were identified and quantified using gas chromatography-mass spectrometry (GC-MS). Kinetic modelling and experimental results revealed that H-atom abstraction in the gas phase was the primary pathway for methyl butanoate decomposition during pyrolysis, but dissociating to ketene and methanol over HZSM-5 was the primary pathway for methyl butanoate consumption during catalytic pyrolysis. The initial decomposition temperature of methyl butanoate was reduced by approximately 300 K over HZSM-5 compared to that for the uncatalyzed reaction. In addition, the apparent activation energies of methyl butanoate under catalytic pyrolysis and homogeneous pyrolysis conditions were obtained using the Arrhenius equation. The significantly reduced apparent activation energy confirmed the catalytic performance of HZSM-5 for methyl butanoate pyrolysis. The activation temperature may also affect some catalytic properties of HZSM-5. Overall, this study can be used to guide subsequent catalytic combustion for practical biodiesel fuels.
2021, 34(1): 112-124.
doi: 10.1063/1674-0068/cjcp2009163
The interaction energy of two molecules system plays a critical role in analyzing the interacting effect in molecular dynamic simulation. Since the limitation of quantum mechanics calculating resources, the interaction energy based on quantum mechanics can not be merged into molecular dynamic simulation for a long time scale. A deep learning framework, deep tensor neural network, is applied to predict the interaction energy of three organic related systems within the quantum mechanics level of accuracy. The geometric structure and atomic types of molecular conformation, as the data descriptors, are applied as the network inputs to predict the interaction energy in the system. The neural network is trained with the hierarchically generated conformations data set. The complex tensor hidden layers are simplified and trained in the optimization process. The predicted results of different molecular systems indicate that deep tensor neural network is capable to predict the interaction energy with 1 kcal/mol of the mean absolute error in a relatively short time. The prediction highly improves the efficiency of interaction energy calculation. The whole proposed framework provides new insights to introducing deep learning technology into the interaction energy calculation.
