可见光响应光催化剂BiYWO6的制备、表征及其完全分解水的研究

制备了一种可见光响应的光催化剂BiYWO6, 该体系是Bi2WO6-Y2WO6的伪二元固溶体, 其禁带宽度为2.71 eV. 其负载了助催化剂后, 可在紫外光和可见光下完全分解水生成氢气和氧气, 其中负载RuO2助催化剂的BiYWO6具有最好的光催化活性. 通过对光催化反应前后的BiYWO6和助催化剂的表面各元素的化学状态的研究证实了RuO2/BiYWO6体系的稳定性. 比较分析了BiYWO6的能带结构, 认为可见光完全分解水的性能可归因于Y和Bi在固溶体BiYWO6中形成了合适的能带结构.     

Photocatalytic Activities for Water Splitting of RuO_2-loaded MGa_2O_4（M=Zn,Ni） with d~（10） Configuration

MGa2O4(M=Zn,Ni) rods with similar crystallinity and BET surface area were prepared via a facile template-engaged reaction.The photocatalytic activities for water splitting of RuO2-loaded MGa2O4(M=Zn,Ni) were investigated under high-pressure Hg lamp.RuO2-loaded ZnGa2O4 catalyst exhibited much higher photocatalytic activity than RuO2-loaded NiGa2O4.Factors affecting the photocatalytic activities of RuO2-loaded MGa2O4(M=Zn,Ni) were discussed.It was suggested that the electronic structure of oxide semiconductor was a predominant factor of the photocatalytic behavior for RuO2-loaded MGa2O4(M=Zn,Ni).     

热分解制备的RuO2-IrO2电极研究

本文应用XPS和电化学技术研究热分解制备RuO2-IrO2电极的电化学性能和表面性质的关系, 以探讨制备寿命长, 价格低的阳极的可能途径。     

可见光响应光催化剂K4Ce2Ta10O30、K4Ce2Nb10O30及其固溶体的电子结构

基于密度泛函理论(DFT), 采用平面波赝势(PWP)以及广义梯度近似(GGA)方法, 对可见光响应的光催化剂K4Ce2Ta10O30、K4Ce2Nb10O30及其固溶体进行电子结构的第一性原理计算. 结果表明, 光催化剂K4Ce2Ta10O30和K4Ce2Nb10O30的导带分别主要由Ta 5d和Nb 4d组成, 处于高能级的电子未占据态的Ce 4f与其有很明显的重迭, 但由于其高度局域特性,不能很好地参与光生电子在导带中的传导, 从而对光催化活性的贡献很小;而其价带则由O 2p与Ta 5d (Nb 4d)的杂化轨道组成, 同时电子占据态的Ce 4f对价带也有一定的贡献, 各个电子轨道对能带结构的贡献决定了该系列可见光响应光催化剂的物理化学和光催化特性. 固溶体系列中随着Nb含量的增加, 其吸收光谱依次红移, 带隙变窄, 导带底变低, 光生电子的还原能力降低. 在固溶体K4Ce2Ta10-xNbxO30(x=2, 5, 8)中, 由于Ce 4f轨道对价带顶的贡献相对较小, 固溶体的价带顶低于K4Ce2Ta10O30、K4Ce2Nb10O30的价带顶, 光生空穴的氧化能力相对较强. 该系列光催化剂的电子结构分析结果与光催化水分解的活性实验结果有很好的一致性.     

Photophysical properties and photocatalytic activities of bismuth molybdates under visible light irradiation

Aurivillius structure Bi(2)MoO(6) (BG: 2.70 eV) that is a low-temperature phase showed an intense absorption band in the visible light region and photocatalytic activity for O(2) evolution from an aqueous silver nitrate solution under visible light irradiation, among various bismuth molybdates (Bi(2)MoO(6), Bi(2)Mo(2)O(9), and Bi(2)Mo(3)O(12)) synthesized by solid-state and reflux reactions. Bi(2)Mo(3)O(12) (BG: 2.88 eV) also showed photocatalytic activity for O(2) evolution under full-arc irradiation of a Xe lamp (lambda > 300 nm). The photocatalytic activity of the Aurivillius structure Bi(2)MoO(6) prepared by the reflux method was dependent on the annealing temperature after the preparation. The crystallinity was the important factor for the activity. Calculation by the density functional method indicated that the conduction band of Aurivillius structure Bi(2)MoO(6) was made up of Mo 4d orbitals. It turned out that the visible-light absorption of this photocatalyst was due to the transition from the valence band consisting of O 2p orbitals to the conduction band. The corner-sharing structure of the MoO(6) octahedra contributed to the visible light response and the photocatalytic performance because excitation energy and/or photogenerated electron and hole pairs began to migrate easily in the Aurivillius structure.     

光催化剂Bi1-xGdxVO4的制备和表征及其光催化分解水

通过高温固相法合成了不同组分的光催化剂Bi1-xGdxVO4(x=0, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1.0), 并用X射线衍射(XRD)、紫外-可见漫反射光谱(DRS)、比表面积分析(BET)、扫描电子显微镜(SEM)对催化剂Bi1-xGdxVO4进行了表征和分析. XRD结果表明, 在Bi1-xGdxVO4中存在两种结构, 当0.3≤x≤1.0时, Bi1-xGdxVO4为四方晶系硅酸锆型结构; 当x=0时, 为单斜晶系白钨矿结构BiVO4; 当0相似文献   

Photocatalytic property and electronic structure of triple-layered perovskite tantalates, MCa2Ta3O10 (M = Cs, Na, H, and C6H13NH3)

The Dion-Jacobson series of triple-layered perovskite tantalates (MCa2Ta3O10, M = Cs, Na, H, and C6H13NH3) were synthesized to evaluate their photocatalytic activity for overall water splitting to evolve H2/O2 under UV irradiation. The photocatalytic activity was susceptible to the hydration of interlayer space. The hydrous Na phase exhibited much higher activity (H2: 308 micromol.h(-1)) compared to the anhydrous Cs phase (24 micromol.h(-1)) and the hydrous H phase (22 micromol.h(-1)) in the presence of 0.5 wt % Ni impregnated. H2O/D2O isotopic experiment suggested that the hydrated interlayer plays as an active site for water splitting, where the high mobility of water molecule in the interlayer should correlate with the total photocatalytic activity. The FLAPW electronic structure calculation demonstrated that the terminating oxygen site, O4, which faces to the interlayer space, contributes largely to the top of the valence band. Judging from comparison with the double-layered tantalates, MLaTa2O7, in our previous study, the contribution of terminating oxygen site to the band structure is supposed to depend on the number of perovskite layers.     

TiO2/Cu2O Core/Ultrathin Shell Nanorods as Efficient and Stable Photocatalysts for Water Reduction

P‐type Cu₂O has been long considered as an attractive photocatalyst for photocatalytic water reduction, but few successful examples has been reported. Here, we report the synthesis of TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods by a redox reaction between Cu²⁺ and in‐situ generated Ti³⁺ when Cu²⁺‐exchanged H‐titanate nanotubes are calcined in air. Owing to the strong TiO₂‐Cu₂O interfacial interaction, TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods are highly active and stable in photocatalytic water reduction. The TiO₂ core and Cu₂O ultrathin film shell respectively act as the photosensitizer and cocatalyst, and both the photoexcited electrons in the conduction band and the holes in the valence band of TiO₂ respectively transfer to the conduction band and valence band of the Cu₂O ultrathin film shell. Our results unambiguously show that Cu₂O itself can act as the highly active and stable cocatalyst for photocatalytic water reduction.     

Proton and electron conductivity in hydrous ruthenium oxides evaluated by electrochemical impedance spectroscopy: the origin of large capacitance

Electrochemical impedance spectroscopy was conducted on a series of hydrous ruthenium oxides, RuO(2).xH(2)O, (x = 0.5, 0.3, 0) and a layered ruthenic acid hydrate (H(0.2)RuO(2.1).nH(2)O) in order to evaluate their protonic and electronic conduction. The capacitor response frequency was observed at lower frequency for RuO(2).xH(2)O with higher water content, which was suggested to be due to electrolyte exhaustion within the film and/or utilization of hydrated interparticle micropores that have high ionic resistance. Analysis of the impedance data indicated that the charge-transfer resistance through the film is not significantly affected by the water content in RuO(2).xH(2)O, and the capacitor frequency response is dominated by the protonic conduction. The capacitor response frequency of layered H(0.2)RuO(2.1).nH(2)O was comparable to RuO(2).0.5H(2)O. The high specific capacitance at low frequency for layered H(0.2)RuO(2.1).nH(2)O is attributed to the utilization of the expandable hydrous interlayer, which accounts for the ionic conduction. The present results demonstrate the importance of hydrous regions (either interparticle or interlayer) to allow appreciable protonic conduction for high energy and high power electrochemical capacitors.     

Correlation between the band positions of (SrTiO3)1-x.(LaTiO2N)x solid solutions and photocatalytic properties under visible light irradiation

N-doped SrTiO3 and (SrTiO3)1-x.(LaTiO2N)x samples were prepared by the thermal ammonolysis method. The photocatalytic activities of the samples were investigated in a water suspension system. Aqueous methanol solution (50 mL CH3OH + 220 mL H2O) for H2 evolution and aqueous silver nitrate solution (270 mL, 0.01 mol L(-1)) for O2 evolution were used as sacrificial reagents. The oxynitrides showed photocatalytic activities under visible light irradiation. The maximum rates of photocatalytic hydrogen and oxygen evolution under visible light irradiation (lambda > 420 nm) were 10 and 8 micromol h(-1), respectively. The samples were characterized by X-ray diffractometry, UV-Vis spectrophotometry, Fourier transform infrared spectrometry, and laser Raman spectroscopy. The unit cell edge length of (SrTiO3)1-x.(LaTiO2N)x increased linearly and their band gaps reduced from 3.18 to 2.04 eV with increasing x from 0 to 0.30. Moreover, the calculation results of (SrTiO3)0.75.(LaTiO2N)0.25 by density functional theory suggested that the band gap narrowing of the solid solutions came from the hybridization of N2p and O2p orbital. The band positions of the solid solutions were further investigated by Mott-Schottky and the onset potential method. The results suggested that the conduction band of the solid solution was lowered, which led to decrement of the hydrogen evolution rate.     

Electronic structure and photocatalytic characterization of a novel photocatalyst AgAlO2

A novel photocatalyst, AgAlO2, was prepared by cation exchange reaction and characterized by powder X-ray diffraction. The result showed AgAlO2 crystallizes in the layered orthorhombic structure with space group was Pna2(1). The energy band and electronic structures of AgAlO2 were calculated based on the crystal structure. It was found that AgAlO2 is an indirect band gap semiconductor. The valence band top mainly consists of O-2p orbitals and Ag-4d orbitals and the conduction band bottom is mainly constructed of Ag-5s5p orbitals. The band gap of AgAlO2 was estimated to be about 2.8(1) eV with UV-vis diffuse reflectance spectrometry. The photocatalytic activity of AgAlO2 was characterized by photocatalytically decomposing the dye alizarin red (AR) under visible light irradiation, and AR could be decomposed about 70% under 2 h of visible light irradiation.     

The infrared fundamental intensities and polar tensor of allene.

The polar tensor of allene was calculated from the infrared fundamental band intensities of C3H4 and C3D4. The ambiguities in the signs of the dipole moment derivatives with respect to their normal coordinates were resolved by comparison of tensor elements with ab initio calculations at the B3LYP, MP2(FC) and CCD(FC) levels with a 6/311 + + G(3d,3p) basis set. The results are similar to those previously obtained by Koga and co-workers except for the choice of an average of two sign combinations for the E symmetry elements. The values of the mean dipole moment derivatives for the sp and sp2 carbon atoms obtained in this work, 0.032 and -0.133 e, respectively, are in good agreement with the CCD(FC)/6-311 + + G(3d,3p), 0.061 and -0.128 e, and MP2(FC)/6-311 + + G(3d,3p), 0.072 and -0.153 e, theoretical results. The mean dipole moment derivatives are shown to be consistent with potential models relating 1s electron ionization energies and atomic charges.     

Photocatalyst of lamellar aggregates of RuOx-loaded perovskite nanosheets for overall water splitting

Overall photocatalytic splitting of water was achieved using a restacked aggregate of exfoliated nanosheets of Ca(2)Nb(3)O(10), which was synthesized by flocculating a colloidal suspension of the nanosheets with alkali-metal ions and a trace amount of ruthenium red, a trinuclear complex of ([(NH(3))(5)Ru-O-Ru(NH(3))(4)-O-Ru(NH(3))(5)]Cl(6). The as-restacked material showed the evolution of H(2) gas from water immediately after UV irradiation, while O(2) evolution was observed only after some induction time, which may be understood by the possible oxidation of ruthenium red to RuO(x) in the initial stage. The restacked aggregate, which was heated at 773 K to convert the ruthenium complex to the oxide, underwent the stoichiometric splitting of water upon initiation of UV illumination, verifying the hypothesis. Total decomposition of water could not be attained with the bulk layered host of KCa(2)Nb(3)O(10) as well as its RuO(x)-loaded forms obtained via a conventional impregnation procedure. This clearly demonstrates the effectiveness of the present exfoliation-restacking route for loading RuO(x) to improve and enhance the photocatalytic activities of layered semiconducting materials. A homogeneous distribution of RuO(x)was suggested by XPS depth-profile analysis on the materials obtained through the exfoliation-restacking process.     

Molecular design of organic dyes with diketopyrrolopyrrole for dye‐sensitized solar cell: A theoretical approach

Three designed metal‐free dyes based on 3‐(10‐butyl‐8‐(methylthio)‐10H‐phenothiazin‐3‐yl)‐2‐cyanoacrylic acid (V5) are investigated by density functional theory (DFT) and time‐dependent DFT to improve the efficiency of V5‐based solar cell devices. We have studied the geometrical structures, excitations, electronic structures, and conduction band shift caused by dye adsorption. The results indicate that the designed dyes have several merits compared with V5 including: (i) smaller energy band gaps and the LUMO closer to conduction band of TiO₂; (ii) wider absorption spectra and higher oscillator strength; (iii) larger dipole moment that lead to higher V_oc value. Our work suggests that the modification of π‐bridge with diketopyrrolopyrrole unit is very effective for designing novel metal‐free dyes with improved performance for dye‐sensitized solar cells (DSSCs). These findings are expected to provide a bright way to design new efficient metal‐free organic DSSCs. © 2014 Wiley Periodicals, Inc.     

Simultaneous Tuning Band Gaps of Cu2O and TiO2 to Form S-Scheme Hetero-Photocatalyst

Photocatalytic Z or S scheme merits higher redox potentials and faster charge separation. However, heterostructure photocatalysts with band gaps of bulk materials often have a type I band structure leading to poor photocatalytic activity. In view of this, we report simultaneous tuning of band gaps of Cu₂O and TiO₂, where quantum dot Cu₂O nanoparticles were formed on doped TiO₂ with Ti³⁺. The reduced size of Cu₂O made its conduction band more negative, whereas the introduction of Ti³⁺ made the absorption edge red shift to the visible light region. The as-formed heterostructure enabled an S-Scheme mechanism with remarkable activity and stability for visible light photodegradation of 4-chlorophenol (4-CP). The as-obtained photocatalysts’ activity demonstrated ca. 510-fold increase as compared to individual ones and a mechanical blend. The as-obtained photocatalysts maintained over 80 % for 5 cycles and 2 months exposure to O₂ did not decrease the degradation rate. ESR characterization and scavenger experiments proved the S-Scheme mechanism.     

Effect of doped zinc species on the photocatalytic activity of gallium oxide for hydrogen production

Zn-doped Ga(2)O(3) samples were prepared by a homogeneous precipitation (HP) method, and the local structures of Zn ions and their photocatalytic activities for hydrogen production were examined. In the sample with low doping amount, the Zn(2+) ions substituted for the Ga(3+) ions in the Ga(2)O(3) photocatalyst and enhanced the photocatalytic activity, since they would improve the migration of the photoexcited electrons in the conduction band of the Ga(2)O(3) photocatalyst. In the sample with high doping amount, the Zn ions formed a composite ZnGa(2)O(4) phase in the bulk of the Ga(2)O(3) photocatalyst to decrease the photocatalytic activity in the present reaction.     

重费米子化合物LiV2 O4电子结构的第一性原理研究

用第一性原理的FP-LMTO能带计算方法研究了重费米子化合物LiV2O4的电子结构.结果表明:费米面附近的导带是由V原子的3d电子形成的宽度为2.5eV的窄能带,是3d态在立方晶体场中具有t2g对称性的子带;它与O的2p轨道构成的能带有近1.9eV的能隙.计算得出的费米能处电子态密度和线性电子比热系数分别是11.1 states/eV f.u.和26.7 mJ/molK2.费米面处的能带色散具有电子型和空穴型两种,呈现出一种复杂的费米面结构.LSDA以及LDA+GGA计算表明, LiV2O4有一个磁矩为每个钒原子1.13μB,总能比LDA基态低约148 meV/f.u.的铁磁性基态.由目前的能带结构计算的结果无法确定这一类Kondo体系的局域磁矩的来源,表明这一化合物中的重费米子行为可能有别于在含有4f和5f稀土的重费米子合金中观察到的局域磁矩与传导电子的交换作用机制,其中存在量子相变的可能.     

Photocatalytic H2 evolution under visible-light irradiation over band-structure-controlled (CuIn)xZn2(1-x)S2 solid solutions

(CuIn)(x)Zn2(1-x)S2 solid solutions between a ZnS photocatalyst with a wide band gap and CuInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions containing sacrificial reagents SO(3)(2-) and S(2-) under visible-light irradiation (lambda >/= 420 nm). Pt (0.5 wt %)-loaded (CuIn)(0.09)Zn(1.82)S(2) with a 2.3-eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 12.5%. H(2) evolved at a rate of 1.5 L h(-1) m(-2) under irradiation with a solar simulator (AM 1.5). Diffuse reflection and photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side, as the ratio of CuInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the composition as well as the photophysical properties. DFT calculations suggested that the visible-light response should be derived from the contribution of Cu 3d and S 3p orbitals to the valence band and that of In 5s5p and Zn 4s4p orbitals to the conduction band, respectively. The contribution of these orbitals to the energy bands affected the photophysical and photocatalytic properties.     

Photocatalytic splitting of water under visible-light irradiation over the NiOx-loaded Sm2InTaO7 with 4f-d-d configuration

A new visible-light-response photocatalyst Sm₂InTaO₇ with 4f-d¹⁰-d⁰ configuration crystallized in a cubic system with the space group Fd3m was synthesized by a solid-state reaction method. NiOx-loaded Sm₂InTaO₇ showed high photocatalytic activities for H₂ evolution from pure water under visible light irradiation (λ>400 nm). Changes in the photocatalytic activity with the calcination temperature of Sm₂InTaO₇ and the amount of NiOx loaded indicated that the combination of highly crystallized Sm₂InTaO₇ and a high dispersion of NiOx particles led to high photocatalytic activity. The high photocatalytic performance of NiOx-loaded Sm₂InTaO₇ supported the existing view that the photocatalytic activity correlated with the lattice distortion. Density functional theory calculation indicated that strong dispersion from the hybridized In 5s 5p orbitals at the bottom of the conduction band was responsible for the high activity of photocatalyst Sm₂InTaO₇.