Interfacial defect engineering and photocatalysis properties of hBN/MX2 (M = Mo,W, and X = S,Se heterostructures

Van der Waals (VDW) heterostructures have attracted significant research interest due to their tunable interfacial properties and potential applications in many areas such as electronics, optoelectronic, and heterocatalysis. In this work, the influences of interfacial defects on the electronic structures and photocatalytic properties of hBN/MX₂ (M = Mo, W, and X=S, Se) are studied using density functional theory calculations. The results reveal that the band alignment of hBN/MX₂ can be adjusted by introducing vacancies and atomic doping. The type-I band alignment of the host structure is maintained in the heterostructure with n-type doping in the hBN sublayer. Interestingly, the band alignment changed into the type-II heterostructrue due to V_B defect and p-type doping is introduced into the hBN sublayer. This can conduce to the separation of photo-generated electron-hole pairs at the interfaces, which is highly desired for heterostructure photocatalysis. In addition, two Z-type heterostructures including hBN(Be_B)/MoS₂, hBN(Be_B)/MoSe₂, and hBN(V_N)/MoSe₂ are achieved, showing the decreasing of band gap and ideal redox potential for water splitting. Our results reveal the possibility of engineering the interfacial and photocatalysis properties of hBN/MX₂ heterostructures via interfacial defects.     

数码相机在液体黏度测量中的应用

采用数码相机拍摄数字影像并输入计算机,通过Flash MX软件工具对物理现象进行动态的实验研究,实现了液体黏度的测定.     

On Injective and Cofibrant Equivariant Minimal Models

Let X be a G-connected nilpotent simplicial set, where G is a finite Hamiltonian group. We construct a cofibrant equivariant minimal model of X with the strong homotopy type of the injective minimal model of X defined by Triantafillou.     

Characterization of wax as a potential diffraction intensity standard for macromolecular crystallography beamlines

A number of commercially available waxes in the form of thin disc samples have been investigated as possible diffraction intensity standards for macromolecular crystallography synchrotron beamlines. Synchrotron X‐ray powder diffraction measurements show that beeswax offers the best performance of these waxes owing to its polycrystallinity. Crystallographic lattice parameters and diffraction intensities were examined between 281 and 309 K, and show stable and predictable thermal behaviour. Using an X‐ray beam of known incident flux at λ = 1 Å, the diffraction power of two strong Bragg reflections for beeswax were quantified as a function of sample thickness and normalized to 10¹⁰ photons s^?1. To demonstrate its feasibility as a diffraction intensity standard, test measurements were then performed on a new third‐generation macromolecular crystallography synchrotron beamline.     

Theoretical study of intra- and inter-chain magnetic interactions in [Ni(chxn)2Br]Br2

The intra- and the inter-chain magnetic interactions in [Ni(chxn)₂Br]Br₂, which is one of the typical one-dimensional (1-D) MX complexes are examined by using an unrestricted hybrid DFT (UB3LYP) method. Calculated effective exchange integral (J) value along the 1-D chain is 2J_Intra = −4016 K and is close to an experimental result (−3600 K). On the other hand, a very weak anti-ferromagnetic inter-chain interaction through Br⁻ ions is observed. The value is estimated to be 2J_Inter = −2 to −6 K. In addition to the J values, transfer integral (t), on-site Coulomb repulsion (U) and charge transfer energy (E^CT) values along the 1-D chain are also estimated to be 0.46, 2.46 and 0.6 eV, respectively.     

A Plausible Mechanism for the Mutagenic Activity (Salmonella typhimurium TA100) of MX Compounds: A Formation of CG-CG+-CG Radical Cation by One-electron Reduction

Abstract

Combining our previous QSAR work with recent high-level quantum mechanical calculations, a plausible mechanism for the mutagenic activity of halogenated furanones (so called MX compounds) in Salmonella typhimurium TA100 tester strain is proposed. The mechanism involves one-electron reduction as a key step and it seems reasonable to suggest that the mutagenicity of these direct-acting compounds may be a purely thermodynamic phenomenon, rather than the result of site-specific binding or adduct formation. Overall, the proposed model is consistent with the most experimental findings.     

基于MX_4结构的配位化合物析氢反应催化性能

具有MX4结构的(M=Fe,Co,Ni,Cu等,X=N,S,Se等)小分子配位化合物及配位聚合物(MX4催化剂),由于其新颖的结构和优异的电催化析氢性能受到研究人员越来越多的关注。本文综述了MX4催化剂的研究进展,其中MX4催化剂活性受金属中心、配位原子、配体的结构以及材料的形貌、尺寸等因素的影响。理论计算有助于分析催化剂中这些因素对催化剂活性的影响,也有助于通过理论模拟,设计更合理的催化剂分子结构。     

Elucidating 2D Charge-Density-Wave Atomic Structure in an MX–Chain by the 3D-ΔPair Distribution Function Method**

Many solids, particularly low-dimensional systems, exhibit charge density waves (CDWs). In one dimension, charge density waves are well understood, but in two dimensions, their structure and their origin are difficult to reveal. Herein, the 2D charge-density-wave atomic structure and stabilization mechanism in the bromide-bridged Pd compound [Pd(cptn)₂Br]Br₂ (cptn=1R,2R-diaminocyclopentane) is investigated by means of single-crystal X-ray diffraction employing the 3D-Δpair distribution function (3D-ΔPDF) method. Analysis of the diffuse scattering using 3D-ΔPDF shows that a 2D-CDW is stabilized by a hydrogen-bonding network between Br⁻ counteranion and the amine (NH₂) group of the cptn in-plane ligand, and that 3D ordering is prevented due to a weak plane to plane correlation. We extract the effective displacements of the atoms describing the atomic structure quantitatively and discuss the stabilization mechanism of the 2D-CDW. Our study provides a method to identify and measure the key interaction responsible for the dimensionality and stability of the CDW that can help further progress of rational design.     

Matrix effects in the gas chromatographic-mass spectrometric determination of brominated analogues of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone

Brominated analogues (BMXs) of the strong drinking water mutagen MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) were found to be subject to strong matrix induced chromatographic response enhancement effects. We evaluated different ways to reduce errors in quantification including comparison of gas chromatographic inlet systems, improved clean up of sample extracts, and preparation of calibration standards in the sample matrix. The best quantitative accuracy and long term performance were achieved when the calibration standards were prepared in sample matrix, samples were cleaned up with C18-resin in conjunction with solid phase extraction (SPE) with Oasis HLB cartridges, and gas chromatography with PTV splitless injection was used. This method enables the determination of MX and BMXs from 500 ml water sample with quantitation limits of 1 ng/l or less.