过渡金属掺杂二氧化钛光催化性能的研究

采用浸渍法制备了过渡金属掺杂的光催化剂MOx/TiO2(M=Cr、Mn、Fe、Co、Ni、Cu).以乙酸的光催化氧化降解反应为探针,研究了催化剂的光催化性能.研究结果表明,经过渡金属掺杂改性的二氧化钛,光催化性能都有所提高.掺杂量有一个最佳值,在最佳掺杂量时,催化剂光催化性能的提高程度与对应金属氧化物的生成焓有很好的一致性,还发现光催化性能与过渡金属离子稳定氧化态的电子亲和势与离子半径的比值间呈现火山型关系曲线.     

Hydrogen Spillover Enhanced Hydroxyl Formation and Catalytic Activity Toward CO Oxidation at the Metal/Oxide Interface

H₂‐promoted catalytic activity of oxide‐supported metal catalysts in low‐temperature CO oxidation is of great interest but its origin remains unknown. Employing an FeO(111)/Pt(111) inverse model catalyst, we herewith report direct experimental evidence for the spillover of H(a) adatoms on the Pt surface formed by H₂ dissociation to the Pt?FeO interface to form hydroxyl groups that facilely oxidize CO(a) on the neighboring Pt surface to produce CO₂. Hydroxyl groups and coadsorbed water play a crucial role in the occurrence of hydrogen spillover. These results unambiguously identify the occurrence of hydrogen spillover from the metal surface to the noble metal/metal oxide interface and the resultant enhanced catalytic activity of the metal/oxide interface in low‐temperature CO oxidation, which provides a molecular‐level understanding of both H₂‐promoted catalytic activity of metal/oxide ensembles in low‐temperature CO oxidation and hydrogen spillover.     

Structural, Electronic, and Optical Properties of Noble Metal Clusters from First Principles

We examine low-energy isomeric forms, static polarizabilities, and optical absorption spectra of Ag _n , n = 2–8, and Au _n , n = 2–3, clusters using first principles computations within the static and time-dependent versions of the density functional theory. The noticeable decrease in the static polarizabilities of Ag₇ and Ag₈ compared to the values characteristic of Ag _n , n = 2–6, is correlated with the transition from two-dimensional to three-dimensional structures at n = 7. The optical spectra computed within the time-dependent local density approximation for the most stable structures are in good agreement with the available experimental data and the results of earlier theoretical studies. Optical spectra of higher-energy isomers typically present features that are not observed in the experimental spectra. The d electrons affect the spectra of noble metal clusters by quenching the oscillator strengths through screening of the s electrons and by getting directly involved in the excitations. Due to the larger s–d hybridization in Au compared to Ag, these effects are more pronounced in Au _n clusters.     

碱金属原子吸附PPV及其衍生物体系的结构和非线性光学性质的理论研究

采用密度泛函理论(DFT)方法系统研究了碱金属Li原子吸附亚苯基-1,2-亚乙烯基(Phenylenevinylene)聚合物(PPV)及其衍生物(具有给受体基团修饰的)体系的结构和非线性光学性质.Li原子能稳定地吸附在PPV及其衍生物的表面,吸附能高达62.3~78.2 kJ/mol.当碱金属Li原子吸附在[PPV]n(n=2~4)表面时,锂盐效应导致了Li原子和[PPV]n之间发生了明显的电荷转移过程,使体系的一阶超极化率β0从249~756 a.u.明显增加到1.16×104~1.37×105a.u..当碱金属Li原子吸附在只有给体(—NH2)或只有受体(—CN)基团修饰的PPV衍生物{[NH2-(PPV)n]/[(PPV)n-CN]}时,体系的一阶超极化率值进一步提升,分别高达1.61×105a.u.(n=4)和2.85×105a.u.(n=4).这主要源于锂盐效应和Donor-π-Acceptor之间的协同作用导致跃迁能进一步降低所致.在Li原子吸附的具有给受体基团同时修饰的PPV衍生物(Li@[NH2-(PPV)n-CN])体系中,这种协同作用得到进一步加强,显著改善了体系的一阶超极化率(高达3.56×105a.u.,n=4).     

Optical Spectra of Oligofurans: A Theoretical Approach to the Transition Energies,Reorganization Energies,and the Vibronic Activity

There is experimental evidence of high vibronic activity that accompanies the allowed transition between the ground state and the lowest electronic singlet excited state of oligofurans that contain two, three, and four furan rings. The absorption and emission spectra of the three lowest oligofurans measured at liquid nitrogen temperature show distinct fine structures that are reproduced using the projection-based model of vibronic coupling (with Dushinsky rotation included) parameterized utilizing either Density Functional Theory (DFT, with several different exchange-correlation functionals) or ab initio (CC2) quantum chemistry calculations. Using as a reference the experimental data concerning the electronic absorption and fluorescence for the eight lowest oligofurans, we first analyzed the performance of the exchange-correlation functionals for the electronic transition energies and the reorganization energies. Subsequently, we used the best functionals alongside with the CC2 method to explore how the reorganization energies are distributed among the totally symmetric vibrations, identify the normal modes that dominate in the fine structures present in the absorption and emission bands, and trace their evolution with the increasing number of rings in the oligofuran series. Confrontation of the simulated spectra with the experiment allows for the verification of the performance of the selected DFT functionals and the CC2 method.     

Computational approach on architecture and tailoring of organic metal complexes derived from streptomycin and Zn,Cd and Pb: antimicrobial effectiveness

Streptomycin has been used to derive organic metal complexes (OMCs) after metallation with ZnCl₂, CdCl₂ and PbCl₂ and characterized by elemental analysis, electronic and vibrational spectroscopy, ¹H and ¹³C NMR, mass spectroscopy (time‐of‐flight MS), magnetic measurement, thermal decomposition analysis (TGA, DTA), molecular modeling and X‐ray powder diffraction. OMCs are monomeric. Crystal system, lattice parameters, unit cell, particle size and volume of crystalline OMCs have been determined using X‐ray powder diffraction pattern analysis. The geometries of complexes were optimized on the basis of molecular modeling. Kinetic parameters were computed from thermal analysis, confirming first‐order kinetics. Molecular models have been optimized by MM2 calculations. Architecture and tailoring of the rationally designed and synthesized supramolecular models having covalent bonded oxygen or other molecular contacts extended through Huckel Charge Distribution in highest occupied molecular orbit (HOMO). Antimicrobial effectiveness of OMCs has been reported. Copyright © 2011 John Wiley & Sons, Ltd.