2020 Vol. 33, No. 4

2020, 33(4): v-vi.
目 录
2020, 33(4): i-iv.
Two-dimensional Fourier transform (2D FT) spectroscopy is an important technology that developed in recent decades and has many advantages over other ultrafast spectroscopy methods. Although 2D FT spectroscopy provides great opportunities for studying various complex systems, the experimental implementation and theoretical description of 2D FT spectroscopy measurement still face many challenges, which limits their wide application. Recently, the 2D FT spectroscopy reaches maturity due to many new developments which greatly reduces the technical barrier in the experimental implementation of the 2D FT spectrometer. There have been several different approaches developed for the optical design of the 2D FT spectrometer, each with its own advantages and limitations. Thus, a procedure to help an experimentalist to build a 2D FT spectroscopy experimental apparatus is needed. This tutorial review is intending to provide an accessible introduction for a beginner to build a 2D FT spectrometer.
We constructed two types of copper-doped metal-organic framework (MOF), i.e., Cu@UiO-66-NH$ _2 $ and Cu-UiO-66-NH$ _2 $. In the former, Cu$ ^{2+} $ ions are impregnated in the pore space of the amine-functionalized, Zr-based UiO-66-NH$ _2 $; while in the latter, Cu$ ^{2+} $ ions are incorporated to form a bimetal-center MOF, with Zr$ ^{4+} $ being partially replaced by Cu$ ^{2+} $ in the Zr$ - $O oxo-clusters. Ultrafast spectroscopy revealed that the photoinduced relaxation kinetics associated with the ligand-to-cluster charge-transfer state is promoted for both Cu-doped MOFs relative to undoped one, but in a sequence of Cu-UiO-66-NH$ _2 $$ > $Cu@UiO-66-NH$ _2 $$ > $UiO-66-NH$ _2 $. 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.
The geometric structures and vibration frequencies of $ para $-chlorofluorobenzene ($ p $-ClFPh) in the first excited state of neutral and ground state of cation were investigated by resonance-enhanced multiphoton ionization and slow electron velocity-map imaging. The infrared spectrum of S$ _0 $ state and absorption spectrum for S$ _1 $$ \leftarrow $S$ _0 $ transition in $ p $-ClFPh were also recorded. Based on the one-color resonant two-photon ionization spectrum and two-color resonant two-photon ionization spectrum, we obtained the adiabatic excited-state energy of $ p $-ClFPh as 36302$ \pm $4 cm$ ^{-1} $. In the two-color resonant two-photon ionization slow electron velocity-map imagin spectra, the accurate adiabatic ionization potential of $ p $-ClFPh was extrapolated as 72937$ \pm $8 cm$ ^{-1} $ via threshold ionization measurement. In addition, Franck-Condon simulation was performed to help us confidently ascertain the main vibrational modes in the S$ _1 $ and D$ _0 $ states. Furthermore, the mixing of vibrational modes between S$ _0 $$ \rightarrow $S$ _1 $ and S$ _1 $$ \rightarrow $D$ _0 $ has been analyzed.
A distributed feedback laser with a wavelength of 2.8 $ μ $m was used to measure the species produced by water vapor glow discharge. Only the absorption spectra of OH radicals and transient H$ _2 $O 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 H$ _2 $O is always opposite to the other peaks. The different spectral orientations of OH and H$ _2 $O reflect the increase or the 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 H$ _2 $O 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.
The geometric and electronic structures of several possible adsorption configurations of the pyrazine ({C$ _{4} $}{H$ _{4} $}{N$ _{2} $}) molecule covalently attached to Si(100) surface, which is of vital importance in fabricating functional nano-devices, 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 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. 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.
Among various photocatalytic materials, Z-scheme photocatalysts have drawn tremendous research interest due to 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 (2D) small-lattice-mismatched GaTe/Bi$ _2 $Se$ _3 $ 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 Bi$ _2 $Se$ _3 $ nanosheet with slight band edge bending, these photogenerated carriers transfer via Z-scheme pathway, which results in the photogenerated electrons and holes effectively separating into the GaTe monolayer and the Bi$ _2 $Se$ _3 $ nanosheet for the hydrogen and oxygen evolution reactions, respectively. Our results imply that the artificial 2D GaTe/Bi$ _2 $Se$ _3 $ is a promising Z-scheme photocatalyst for overall solar water splitting.
Surface passivation is one valuable approach to tune the properties of nanomaterials. The piezoelectric properties of hexagonal [001] ZnO nanowires with four kinds of surface passivations were investigated using the first-principles calculations. It is found that in the 50% H(O) and 50% Cl(Zn), 50% H(O) and 50% F(Zn) passivations, the volume and surface effects both enhance the piezoelectric coefficient. This differs from the unpassivated cases where the surface effect was the sole source of piezoelectric enhancement. In the 100% H, 100% Cl passivations, the piezoelectric enhancement is not possible since the surface effect is screened by surface charge with weak polarization. The study reveals that the competition between the volume effect and surface effect influences the identification of the diameter-dependence phenomenon of piezoelectric coefficients for ZnO nanowires in experiments. Moreover, the results suggest that one effective means of improving piezoelectricity of ZnO nanowires is shrinking axial lattice or increasing surface polarization through passivation.
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- and W-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.
The structures and electronic properties of the gaseous M$ _2 $Pt$ _2 $$ ^{0/-} $ clusters (M represents the alkaline earth metal) were investigated using the density functional theory (B3LYP and PBE0) and wave function theory (SCS-MP2, CCSD and CCSD (T)). The results indicate that the D$ _{2{h}} $ isomers with the planar structures are more stable than the C$ _{2v} $ isomers with smaller dihedral angles and shorter Pt-Pt bond lengths. 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 D$ _{2h} $ symmetry, while the Pt-Pt covalent bonding leads to the C$ _{2v} $ isomers with bending structures. Two different crossing points are determined in the potential energy curves of Be$ _2 $Pt$ _2 $ with the singlet and triplet states. But there is just one crossing point in potential energy curves of Ra$ _2 $Pt$ _2 $ and Ca$ _2 $Pt$ _2 $$ ^- $ because of flatter potential energy curves of Ra$ _2 $Pt$ _2 $ with the triplet state or Ca$ _2 $Pt$ _2 $$ ^- $ 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.
Cancer is one of the most serious issues in human life. Blocking programmed cell death protein 1 and programmed death ligand-1 (PD-L1) pathway is one of the great innovations in the last few years, a few numbers of inhibitors can be able to block it. (2-Methyl-3-biphenylyl) methanol derivative is one of them. Here, the quantitative structure-activity relationship (QSAR) established twenty (2-methyl-3-biphenylyl) methanol derivatives as the programmed death ligand-1 inhibitors. Density functional theory 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 $E_{\rm{HOMO}}$, lowest unoccupied molecular orbital energy $E_{\rm{LUMO}}$, total energy $E_{\rm{T}}$, dipole moment DM, absolute hardness $\eta$, absolute electronegativity $\chi$, softness $S$, electrophilicity $\omega$, energy gap $\Delta E$, etc., were observed and determined. 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 $R^2$ was 0.661 and 0.758, respectively. Leave-one-out cross-validation, $r^2_{\rm{m}}$ metric, $r^2_{\rm{m}}$ 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 results showed that the MNLR model predicts the bioactivity more accurately than MLR, and it may be helpful and supporting for evaluation of the biological activity of PD-L1 inhibitors.
Multinanoparticles interacting with the phospholipid membranes in solution were studied by dissipative particle dynamics simulation. The selected nanoparticles 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.
In this work, p-type Co$_3$O$_4$ decorated n-type ZnO (Co$_3$O$_4$/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 Co$_3$O$_4$/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 ℃), which was 26 times higher than pure ZnO (response of 2.3 at 240 ℃). Excellent VOCs response characteristics could be ascribed to increased surface oxygen vacancy concentration (revealed by defect characterizations), catalytic activity of Co$_3$O$_4$ 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.
In this work the surface of LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ (LMN) particles is modified by Mn$_{3}$O$_{4}$ coating through a simple wet grinding method, the electronic conductivity is significantly improved from 1.53$\times$10$^{-7}$ S/cm to 3.15$\times$10$^{-5}$ S/cm after 2.6 wt% Mn$_{3}$O$_{4}$ coating. The electrochemical test results indicate that Mn$_{3}$O$_{4}$ coating dramatically enhances both rate performance and cycling capability (at 55 ℃) of LNM. Among the samples, 2.6 wt% Mn$_{3}$O$_{4}$-coated LNM not only exhibits excellent rate capability (a large capacity of 108 mAh/g at 10 C rate) but also shows 78% capacity retention at 55 ℃ and 1 C rate after 100 cycles.
Developing low-cost and high-efficient noble-metal-free cocatalysts has been a challenge to achieve economic hydrogen production. In this work, molybdenum oxides (MoO$_{3-x}$) 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 MoO$_{3-x}$ nanocrystal and PCN was successfully formed during the in situ growth process. The MoO$_{3-x}$-PCN-$X$ ($X$=1, 2, 3, 4) photocatalyst without noble platinum (Pt) finally exhibited enhanced photocatalytic hydrogen performance under visible light irradiation ($\lambda$$>$420 nm), with the highest hydrogen evolution rate of 15.6 μmol/h, which was more than 3 times that of bulk PCN. Detailed structure-performance revealed that such improvement in visible-light hydrogen production activity originated from the intimate interfacial interaction between high-dispersed ultra-small MoO$_{3-x}$ nanocrystal and polymer carbon nitride as well as efficient charge carriers transfer brought by Schottky junction formed.
Photocatalytic degradation of organic pollutants has become a hot research topic because of its low energy consumption and environmental-friendly characteristics. Bismuth oxide (Bi$ _2 $O$ _3 $) nanocrystals with a bandgap ranging from 2.0 eV to 2.8 eV have attracted increasing attention due to high activity of photodegradation of organic pollutants by utilizing visible light. Though several methods have been developed to prepare Bi$ _2 $O$ _3 $-based semiconductor materials over recent years, it is still difficult to prepare highly active Bi$ _2 $O$ _3 $ catalysts in large scale with a simple method. Therefore, developing simple and feasible methods for the preparation of Bi$ _2 $O$ _3 $ nanocrystals in large scale is important for the potential applications in industrial wastewater treatment. In this work, we successfully prepared porous Bi$ _2 $O$ _3 $ in large scale via etching commercial BiSn powders, followed by thermal treatment with air. The acquired porous Bi$ _2 $O$ _3 $ exhibited excellent activity and stability in photocatalytic degradation of methylene blue. Further investigation of the mechanism witnessed that the suitable band structure of porous Bi$ _2 $O$ _3 $ allowed the generation of reactive oxygen species, such as O$ _2 $$ ^{-\cdot} $ and $ \cdot $OH, which effectively degraded MB.