NO\begin{document}$_3$\end{document} and N\begin{document}$_2$\end{document}O\begin{document}$_5$\end{document} are important participants in nocturnal atmospheric chemical processes, and their concentrations are of great significance in the study of the mechanism of nocturnal atmospheric chemical reactions. A two-channel diode laser based cavity ring-down spectroscopy (CRDS) instrument was developed to monitor the concentrations of NO\begin{document}$_3$\end{document} and N\begin{document}$_2$\end{document}O\begin{document}$_5$\end{document} in the atmosphere. The effective absorption length ratio and the total loss coefficient of the instrument were calibrated using laboratory standard samples. The effective absorption cross section of NO\begin{document}$_3$\end{document} at 662 nm was derived. A detection sensitivity of 1.1 pptv NO\begin{document}$_3$\end{document} in air was obtained at a time resolution of 1 s. N\begin{document}$_2$\end{document}O\begin{document}$_5$\end{document} was converted to NO\begin{document}$_3$\end{document} and detected online in the second CRDS channel. The instrument was used to monitor the concentrations of NO\begin{document}$_3$\end{document} and N\begin{document}$_2$\end{document}O\begin{document}$_5$\end{document} in the atmosphere of winter in Hefei in real time. By comparing the concentration changes of pollutants such as nitrogen oxides, ozone, PM\begin{document}$_{2.5}$\end{document} in a rapid air cleaning process, the factors affecting the concentrations of NO\begin{document}$_3$\end{document} and N\begin{document}$_2$\end{document}O\begin{document}$_5$\end{document} in the atmosphere were discussed.
CH\begin{document}$_3$\end{document} internal rotation is one of the typical large amplitude motions in polyatomic molecules, the spectral analysis and theoretical calculations of which, were developed by Li-Hong Xu and Jon Hougen. We observed a Doppler-free high-resolution and high-precision spectrum of 9-methylanthracene (9MA) by using the collimated supersonic jet and optical frequency comb techniques. The potential energy curve of CH\begin{document}$_3$\end{document} internal rotation is expressed by a six-fold symmetric sinusoidal function. It was previously shown that the barrier height (\begin{document}$V_6$\end{document}) of 9MA-\begin{document}$d_{12}$\end{document} was considerably smaller than that of 9MA-\begin{document}$h_{12}$\end{document} [M. Baba, et al., J. Phys. Chem. A 113 , 2366 (2009)]. We performed ab initio theoretical calculations of the multi-component molecular orbital method. The barrier reduction by deuterium substitution was partly attributed to the difference between the wave functions of H and D atomic nuclei.
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}, HCD, HSD, HPD\begin{document}$^-$\end{document}, and HSiD using local mode model and multi-dimensional normal modes. We found that consistent with previous notions, a localized 1D picture to treat the XH stretching vibration is valid even for analyzing the TDM tilt angle. In addition, while the TDM of the OH stretching fundamental transition tilted away from the OH bond in the direction away from the OD bond, that for the XH stretching fundamental of HSD, HND\begin{document}$^-$\end{document}, HPD\begin{document}$^-$\end{document}, HCD, and HSiD tilted away from the OH bond but toward the OD bond. This shows that bond dipole approximation may not be a good approximation for the present systems and that the heavy atom X can affect the transition dipole moment direction. The variation of the dipole moment was analyzed using the atoms-in-molecule method.
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.
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.
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.
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.
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.

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.

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
To obtain insight into the catalytic reaction mechanism of biodiesels over ZSM-5 zeolites, the pyrolysis and catalytic pyrolysis of methyl butanoate (MB), a biodiesel surrogate, with H-type ZSM-5 (HZSM-5) was 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 revealed that H-atom abstraction in the gas phase was the primary pathway for MB decomposition during pyrolysis, but dissociating to ketene and methanol over HZSM-5 was the primary pathway for MB consumption during catalytic pyrolysis. The initial decomposition temperature of MB was reduced by approximately 300 K over HZSM-5 compared to that for the uncatalyzed reaction. In addition, the apparent activation energies of MB 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 MB 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.
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.
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.
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.
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.
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.
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.
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.
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.
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 %.
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.
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.
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.
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.
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.
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.
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.
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.
Theoretical study was carried out with OX2 (X = Halogen) molecules and calculation results showed that delocalized π<sub>3</sub><sup>6</sup> 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 π<sub>3</sub><sup>6</sup> 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.
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.
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.
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.
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 increases in emission intensities over three different excitation regions. Strong fluorescence in region (I) is excited by the carrier injection (CI) mechanism with holes injected into the HOMO state first; moderate fluorescence in region (II) is excited by the inelastic electron scattering (IES) mechanism; and weak fluorescence in region (III) is associated with an up-conversion process and excited by a combined CI and IES 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<sup>−</sup> originated from the LUMO+1→LUMO transition, whose excitation is dominated by a CI mechanism with electrons first injected into the LUMO+1 or higher-lying empty orbitals.
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.
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.
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.
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.
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.
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.
Phototactic Photoresponsive PNIPAM Microgels
Hewen Liu
Accepted Manuscript
[Abstract](4) [PDF 0KB](1)
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.
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.
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.
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.
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.
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.
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.
2020, 33(3): i-iv.  
[Abstract](38) [PDF 5363KB](17)
Chinese abstract
Chinese Abstracts
2020, 33(3): v-vi.  
[Abstract](45) [PDF 503KB](8)
Microbial electrolysis cells (MECs) present an attractive route for energy-saving hydrogen (H2) production along with treatment of various wastewaters, which can convert organic matter into H2 with the assistance of microbial electrocatalysis. However, the development of such renewable technologies for H2 production still faces considerable challenges regarding how to enhance the H2 production rate and to lower the energy and the system cost. In this review, we will focus on the recent research progress of MEC for H2 production. First, we present a brief introduction of MEC technology and the operating mechanism for H2 production. Then, the electrode materials including some typical electrocatalysts for hydrogen production are summarized and discussed. We also highlight how various substrates used in MEC affect the associated performance of hydrogen generation. Finally we presents several key scientific challenges and our perspectives on how to enhance the electrochemical performance.
Metallophilic interaction is a unique type of weak intermolecular interaction, where the electronic configuration of two metal atoms is closed shell. Despite its significance in multidisciplinary fields, the nature of metallophilic interaction is still not well understood. In this work, we investigated the electronic structures and bonding characteristic of bimetallic Au$ _{2} $@Cu$ _{6} $ nanocluster through density functional theory method, which was reported in experiments recently [Angew. Chem. Int. Ed. 55 , 3611 (2016)]. In general thinking, interaction between two moieties of (CuSH)$ _{6} $ ring and (Au$ _{2} $PH$ _{3} $)$ _{2} $ in the Au$ _{2} $@Cu$ _{6} $ nanocluster can be viewed as a d$ ^{10} $-$ \sigma $ closed-shell interaction. However, chemical bonding analysis shows that there is a ten center-two electron (10c-2e) multicenter bonding between two moieties. Further comparative studies on other bimetallic nanocluster M$ _{2} $@Cu$ _{6} $ (M = Ag, Cu, Zn, Cd, Hg) also revealed that multicenter bonding is the origin of electronic stability of the complexes besides the d$ ^{10} $-$ \sigma $ closed-shell interaction. This will provide valuable insights into the understanding of closed-shell interactions.
The dielectric properties between in-particle/water interface and bulk solution are significantly different, which are ignored in the theories of surface potential estimation. The analytical expressions of surface potential considering the dielectric saturation were derived in mixed electrolytes based on the nonlinear Poisson-Boltzmann equation. The surface potentials calculated from the approximate analytical and exact numerical solutions agreed with each other for a wide range of surface charge densities and ion concentrations. The effects of dielectric saturation became important for surface charge densities larger than 0.30 C/m$ ^2 $. The analytical models of surface potential in different mixed electrolytes were valid based on original Poisson-Boltzmann equation for surface charge densities smaller than 0.30 C/m$ ^2 $. The analytical model of surface potential considering the dielectric saturation for low surface charge density can return to the result of classical Poisson-Boltzmann theory. The obtained surface potential in this study can correctly predict the adsorption selectivity between monovalent and bivalent counterions.
A superamphiphobic (SAP) surface was fabricated by electrodepositing Cu-Ni micro-nano particles on aluminum substrate and modifying via 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane. Scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy were employed to investigate the morphology and chemical composition. The results showed that the SAP surface had three-dimensional micro-nano structures and exhibited a maximum water contact angle of 160.0$ ^{\circ} $, oil contact angle of 151.6$ ^{\circ} $, a minimum water slide angle of 0$ ^{\circ} $ and oil slide angle of 9$ ^{\circ} $. The mechanical strength and chemical stability of the SAP surface were tested further. The experimental results showed that the SAP surface presented excellent resistance to wear, prominent acid-resistance and alkali-resistance, self-cleaning and anti-fouling properties.
In view of the high activity of Pt single atoms in the low-temperature oxidation of CO, we investigate the adsorption behavior of Pt single atoms on reduced rutile TiO$ _2 $(110) surface and their interaction with CO and O$ _2 $ molecules using scanning tunneling microscopy and density function theory calculations. Pt single atoms were prepared on the TiO$ _2 $(110) surface at 80 K, showing their preferred adsorption sites at the oxygen vacancies. We characterized the adsorption configurations of CO and O$ _2 $ molecules separately to the TiO$ _2 $-supported Pt single atom samples at 80 K. It is found that the Pt single atoms tend to capture one CO to form Pt-CO complexes, with the CO molecule bonding to the fivefold coordinated Ti (Ti$ _{5 \rm{c}} $) atom at the next nearest neighbor site. After annealing the sample from 80 K to 100 K, CO molecules may diffuse, forming another type of complexes, Pt-(CO)$ _2 $. For O$ _2 $ adsorption, each Pt single atom may also capture one O$ _2 $ molecule, forming Pt-O$ _2 $ complexes with O$ _2 $ molecule bonding to either the nearest or the next nearest neighboring Ti$ _{5 \rm{c}} $ sites. Our study provides the single-molecule-level knowledge of the interaction of CO and O$ _2 $ with Pt single atoms, which represent the important initial states of the reaction between CO and O$ _2 $.
Polydiacetylene (PDA) is one kind of the conjugated polymer with layered structure, which can serve as a host to accommodate the guest components through intercalation. In these intercalated PDAs, some of them were reported to have a nearly perfect organized structure and perform completely reversible thermochromism. Till now, these reported intercalated PDAs were made by only introducing a single component for intercalation. Here, we chose 10, 12-pentacosadiynoic acid (PCDA) as the monomer, of which the carboxyl-terminal groups can interact with either Tb$ ^{3+} $ ions or melamines (MAs). When the feeding molar ratio of PCDA, MA, and Tb$ ^{3+} $ ion was 3:267:1, only Tb$ ^{3+} $ ions were intercalated though excess MAs existed. Such Tb$ ^{3+} $-intercalated poly-PCDA exhibited completely reversible thermochromism, where almost all the carboxyl groups interacted with Tb$ ^{3+} $ ions to form the nearly perfect structure. When the feeding molar ratio of PCDA, MA, and Tb$ ^{3+} $ ion was 3:267:0.6, both Tb$ ^{3+} $ ions and MAs were intercalated. There existed some defects in the imperfect MA-intercalated domains and at the domain boundaries. The MA/Tb$ ^{3+} $-intercalated poly-PCDA exhibits partially reversible thermochromism, where the backbones near the defects are hard to return the initial conformation, while the rest, those at nearly perfect organized domains, are still able to restore the initial conformation.
In recent years, flexible pressure sensors have attracted much attention owing to their potential applications in motion detection and wearable electronics. As a result, important innovations have been reported in both conductive materials and the underlying substrates, which are the two crucial components of a pressure sensor. 1D materials like nanowires are being widely used as the conductive materials in flexible pressure sensors, but such sensors usually exhibit low performances mainly due to the lack of strong interfacial interactions between the substrates and 1D materials. In this paper, we report the use of graphene/graphene scrolls hybrid multilayers films as the conductive material and a micro-structured polydimethylsiloxane substrate using Epipremnum aureum leaf as the template to fabricate highly sensitive pressure sensors. The 2D structure of graphene allows to strongly anchor the scrolls to ensure the improved adhesion between the highly conductive hybrid films and the patterned substrate. We attribute the increased sensitivity (3.5 kPa$ ^{-1} $), fast response time ($ < $50 ms), and the good reproducibility during 1000 loading-unloading cycles of the pressure sensor to the synergistic effect between the 1D scrolls and 2D graphene films. Test results demonstrate that these sensors are promising for electronic skins and motion detection applications.
One simple and environmental friendly synthesis strategy for preparing low-cost magnetic Fe$ _3 $C@C materials has been facilely developed using a modified sol-gel approach, wherein natural magnetite acted as the iron source. A chelating polycarboxylic acid such as citric acid (CA) was employed as the carbon source, and it dissolved Fe very effectively, Fe$ _3 $O$ _4 $ and natural magnetite to composite an iron-citrate complex with the assistance of ammonium hydroxide. The core-shell structure of the as-prepared nanocomposites was formed directly by high-temperature pyrolysis. The Fe$ _3 $C@C materials exhibited superparamagnetic properties (38.09 emu/mg), suggesting potential applications in biomedicine, environment, absorption, catalysis, etc.
Smart nanoparticles that respond to pathophysiological parameters, such as pH, GSH, and H$ _2 $O$ _2 $, have been developed with the huge and urgent demand for the high-efficient drug delivery systems (DDS) for cancer therapy. Herein, cubic poly(ethylene glycol) (PEG)-modified mesoporous amorphous iron oxide (AFe) nanoparticles (AFe-PEG) have been successfully prepared as pH-stimulated drug carriers, which can combine doxorubicin (DOX) with a high loading capacity of 948 mg/g, forming a novel multifunctional AFe-PEG/DOX nanoparticulate DDS. In an acidic microenvironment, the AFe-PEG/DOX nanoparticles will not only release DOX efficiently, but also release Fe ions to catalyze the transformation of H$ _2 $O$ _2 $ to $ \cdot $OH, acting as fenton reagents. In vitro experimental results proved that the AFe-PEG/DOX nanoparticles can achieve combination of chemotherapeutic (CTT) and chemodynamic therapeutic (CDT) effects on Hela tumor cells. Furthermore, the intrinsic magnetism of AFe-PEG/DOX makes its cellular internalization efficiency be improved under an external magnetic field. Therefore, this work develops a new and promising magnetically targeted delivery and dual CTT/CDT therapeutic nano-medicine platform based on amorphous iron oxide.