Photocatalytic activity and intercalation of layered perovskite-like tantalates ANdTa2O7 (A = H,Li, Na,K, Rb,Cs)

Layered perovskite-like oxides ANdTa₂O₇ (A = H, Li, Na, K, Rb, Cs) were synthesized and characterized by means of diffuse reflection spectroscopy, thermogravimetry, and simultaneous thermal and X-ray phase analysis. Comparative analysis of the photocatalytic activity of ANdTa₂O₇ in the UV-induced hydrogen evolution from an aqueous isopropanol solution was performed. NaNdTa₂O₇ and HNdTa₂O₇ are able to intercalate water to the interlayer space. The compositions and thermal stability ranges of intercalates were determined. No explicit correlation between the photocatalytic activity of layered oxides and their ability to intercalate water to the interlayer space was found.     

Photocatalytic activity of R3MO7 and R2Ti2O7 (R=Y, Gd, La; M=Nb, Ta) for water splitting into H2 and O2

The photocatalytic activities of R3MO7 and R2Ti2O7 (R=Y, Gd, La; M=Nb, Ta) strongly depended on the crystal structure. Overall, photocatalytic water splitting into H2 and O2 proceeded over La3TaO7 and La3NbO7, which have an orthorhombic weberite structure, Y2Ti2O7 and Gd2Ti2O7, which have a cubic pyrochlore structure, and La2Ti2O7, which has a monoclinic perovskite structure. All of these materials are composed of a network of corner-shared octahedral units of metal cations (TaO6, NbO6, or TiO6); materials without such a network were inactive. The octahedral network certainly increased the mobility of electrons and holes, thereby enhancing photocatalytic activity.     

La掺杂钛酸钙光催化剂在可见光下分解水制氢的影响因素

以柠檬酸为络合剂, 采用溶胶-凝胶法制备了钙钛矿型光催化剂Ca_0.99La_0.01TiO₃, 利用X射线衍射仪(XRD)、 扫描电子显微镜(SEM)、 紫外-可见漫反射光谱仪(UV-Vis DRS)等对光催化剂材料进行了表征, 并考察了N掺杂对光催化剂催化效果的影响, 探究了可见光条件下, Ca_0.99La_0.01TiO_3-xN_x在不同Pt负载量及不同种类牺牲剂中光催化分解水的产氢量, 并进行相关荧光猝灭分析. 结果表明, 在可见光条件下, Pt负载量为1%且掺杂N的钙钛矿光催化剂在Na₂SO₃/Na₂S作为牺牲剂时, 光催化分解水的产氢量最高.     

Na5(In4S)(InS4)3.6H2O, a zeolite-like structure with unusual SIn4 tetrahedra

A hydrated sodium indium sulfide, Na5(In4S)(InS4)3.6H2O, has been prepared by hydrothermal synthesis. This material contains a tetrahedral sulfur site coordinated to four trivalent indium ions, an unusual bonding pattern not previously observed in open framework chalcogenides. The structure is related to the perovskite (CaTiO3) type with simultaneous substitutions of Ti by SIn4, O by InS4, and Ca2+ by [Na5(H2O)6]5+. It is a wide-gap semiconductor and shows photocatalytic activity under UV light for hydrogen generation from aqueous solution without use of any cocatalyst.     

Characterization of Rh-Cr mixed-oxide nanoparticles dispersed on (Ga(1-x)Zn(x))(N(1-x)Ox) as a cocatalyst for visible-light-driven overall water splitting

The structure of Rh-Cr mixed-oxide (Rh(2)(-)(y)Cr(y)O(3)) nanoparticles dispersed on (Ga(1)(-)(x)Zn(x))(N(1)(-)(x)O(x)) is characterized by electron microscopy and X-ray spectroscopy. The Rh(2)(-)(y)Cr(y)O(3) nanoparticle is an efficient cocatalyst for photocatalytic overall water splitting on the (Ga(1)(-)(x)Zn(x))(N(1)(-)(x)O(x)) solid solution and is loaded onto the catalyst by impregnation from an aqueous solution containing Na(3)RhCl(6).2H(2)O and Cr(NO(3))(3).9H(2)O followed by calcination in air. Impregnation of the (Ga(1)(-)(x)Zn(x))(N(1)(-)(x)O(x)) with 1 wt % Rh and 1.5 wt % Cr followed by calcination at 623 K for 1 h provides the highest photocatalytic activity. Structural analyses reveal that the activity of this photocatalyst is strongly dependent on the generation of trivalent Rh-Cr mixed-oxide nanoparticles with optimal composition and distribution.     

LaCoO3 acting as an efficient and robust catalyst for photocatalytic water oxidation with persulfate

Cobalt-containing metal oxides [perovskites (LaCoO(3), NdCoO(3), YCoO(3), La(0.7)Sr(0.3)CoO(3)), spinel (Co(3)O(4)) and wolframite (CoWO(4))] have been examined as catalysts for photocatalytic water oxidation with Na(2)S(2)O(8) and [Ru(bpy)(3)](2+) as an electron acceptor and a photosensitizer, respectively. Catalysts with the perovskite structure exhibited higher catalytic activity as compared with the catalysts with the spinel and wolframite structures. LaCoO(3), which stabilizes Co(III) species in the perovskite structure, exhibited the highest catalytic activity in the photocatalytic water oxidation compared with CoWO(4), Co(3)O(4) and La(0.7)Sr(0.3)CoO(3) which contain Co(II) or Co(IV) species in the matrices. The high catalytic reactivity of LaCoO(3) possessing perovskite structure was maintained in NdCoO(3) and YCoO(3) which exclusively contain Co(III) species. Thus, the catalytic activity of Co ions can be controlled by the additional metal ions, which leads to development of highly reactive and robust catalysts for the photocatalytic water oxidation.     

Vibrational analysis of Ag3(PO2NH)3, Na3(PO2NH)3 x H2O, Na3(PO2NH)3 x 4H2O,

FT IR and FT Raman spectra of Ag3(PO2NH), (Compound 1), Na3(PO2NH)3 x H2O (Compound II), Na3(PO2NH)3 x 4H2O (Compound III), [C(NH2)3]3(PO2NH)3 x H2O (Compound IV) and (NH4)4(PO2NH)4 x 4H2O (Compound V) are recorded and analyzed on the basis of the anions, cations and water molecules present in each of them. The PO2NH- anion ring in compound I is distorted due to the influence of Ag+ cation. Wide variation in the hydrogen bond lengths in compound III is indicated by the splitting of the v2 and v3 modes of vibration of water molecules. The NH4 ion in compound V occupies lower site symmetry and exhibits hindered rotation in the lattice. The correlations between the symmetric and asymmetric stretching vibrations of P-N-P bridge and the P-N-P bond angle have also been discussed.     

Photophysical and photocatalytic properties of SrTiO3 doped with Cr cations on different sites

Usually, SrTiO3 monodoped with Cr cations at the Ti4+ site hardly shows visible light photocatalytic activity. Revealing the origin of this issue is important for us to find an alternative approach to make SrTiO3 active under visible light irradiation. In this paper, two Cr-doped SrTiO3-(Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3-were synthesized by a conventional solid-state reaction method, and their photophysical and photocatalytic properties were studied comparatively. It was found that both (Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3 showed considerable absorption to visible light. However, their photocatalytic activities for H2 evolution from aqueous methanol solution under visible light irradiation were significantly different: the H2 evolution rate over (Sr0.95Cr0.05)TiO3 (approximately 21 micromol/h) was more than 100 times that over Sr(Ti0.95Cr0.05)O3 (approximately 0.2 micromol/h). X-ray photoelectron spectroscopy analysis results revealed that the Cr cations doped at the Sr2+ site were all trivalent state (Cr3+), while those doped at the Ti4+ site were mixed valent states (Cr3+ and Cr6+). The different photocatalytic activities of H2 evolution are supposed to closely relate to the different valent states of Cr doped at different sites (Sr2+ or Ti4+) in SrTiO3. Possible electronic structures of (Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3 were proposed in relation to their photophysical and photocatalytic properties.     

Synthesis and photocatalytic properties of a new heteropolyoxoniobate compound: K10[Nb2O2(H2O)2][SiNb12O40)·12H2O

The synthesis and photocatalytic properties of a heteropolyoxoniobate, K(10)[Nb(2)O(2)(H(2)O)(2)][SiNb(12)O(40)]·12H(2)O (1), are reported, revealing an important role of Zr(4+) additives in the crystallization. Compound 1 exhibits overall photocatalytic water splitting activity, and its photocatalytic activity is significantly higher than that of Na(10)[Nb(2)O(2)][SiNb(12)O(40)]·xH(2)O (2). Fluorescence lifetime measurements suggest that the enhanced photocatalytic activity of 1 likely results from a larger yield of longer-lived charge trapping states in 1 due to the coordination of one water molecule to the bridging Nb(5+), leading to highly unsymmetrical seven-coordinated Nb(5+) sites.     

Relationship between cation arrangement and photocatalytic activity for Sr-Al-Nb-O double perovskite

The relationship between the photocatalytic activity and the arrangement of metal cations was investigated with Sr-Al-Nb-O double perovskite (SAN) synthesized at 1400 °C for various calcination times using a solid state reaction. Transmission electron microscopic observation revealed that SAN particles had a domain structure of completely B-site ordered (Sr(2)AlNbO(6)) and disordered (SrAl(0.5)Nb(0.5)O(3)) phases. The ordered phase fraction was determined using a newly proposed mixed-phase model for the Rietveld refinement and a method using the relative intensity of the superlattice line of powder X-ray diffraction. It turned out that the mass fraction of the ordered phase in SAN calcined at 1400 °C could be controlled by the calcination time as 33% (10 h), 37% (20 h), 44% (30 h), and 48% (50 h). Photocatalytic activities of SAN for the evolution of H(2) and O(2) respectively from aqueous solutions of methanol and AgF decreased with increasing the calcination time, that is, with increasing the fraction of the ordered phase. These results suggested that the photocatalytic activity of ordered Sr(2)AlNbO(6) should be lower than that of disordered SrAl(0.5)Nb(0.5)O(3). This is practically the first report to reveal the photocatalytic activity of SAN as well as the effect of cation ordering in oxides on the photocatalytic activity.     

Highly efficient water splitting into H2 and O2 over lanthanum-doped NaTaO3 photocatalysts with high crystallinity and surface nanostructure

NiO-loaded NaTaO(3) doped with lanthanum showed a high photocatalytic activity for water splitting into H(2) and O(2) in a stoichiometric amount under UV irradiation. The photocatalytic activity of NiO-loaded NaTaO(3) doped with lanthanum was 9 times higher than that of nondoped NiO-loaded NaTaO(3). The maximum apparent quantum yield of the NiO/NaTaO(3):La photocatalyst was 56% at 270 nm. The factors affecting the highly efficient photocatalytic water splitting were examined by using various characterization techniques. Electron microscope observations revealed that the particle sizes of NaTaO(3):La crystals (0.1-0.7 microm) were smaller than that of the nondoped NaTaO(3) crystal (2-3 microm) and that the ordered surface nanostructure with many characteristic steps was created by the lanthanum doping. The small particle size with a high crystallinity was advantageous to an increase in the probability of the reaction of photogenerated electrons and holes with water molecules toward the recombination. Transmission electron microscope observations and extended X-ray absorption fine structure analyses indicated that NiO cocatalysts were loaded on the edge of the nanostep structure of NaTaO(3):La photocatalysts as ultrafine particles. The H(2) evolution proceeded on the ultrafine NiO particles loaded on the edge while the O(2) evolution occurred at the groove of the nanostep structure. Thus, the reaction sites for H(2) evolution were separated from those of O(2) evolution over the ordered nanostep structure. The small particle size and the ordered surface nanostep structure of the NiO/NaTaO(3):La photocatalyst powder contributed to the highly efficient water splitting into H(2) and O(2).     

基于镧和铬共掺杂钛酸锶产氢光催化剂构建Z机制全分解水体系（英文）

光催化剂的晶体结构、电子结构、表面结构等都会对自身性质产生决定性的作用,因此认识和理解光催化材料自身结构和光催化性能之间的内在联系有助于设计合成更高效的光催化剂以及光催化复合体系.本文通过聚合络合法和溶胶凝胶水热法分别制备了镧和铬共掺杂的光催化剂,标记为和在碘化钠或甲醇作为牺牲试剂的产氢反应中,担载Pt的样品显示了光催化活性,而担载Pt的样品活性很低,甚至无活性.我们将这两种材料分别作为产氢光催化剂与三氧化钨耦合构建Z机制全分解水体系.研究发现,只有体系观察到了氢气和氧气的产生.在第一个10 h的循环反应中,产生的摩尔比为3.7,明显高于水分解为2的化学计量比.这是因为在反应起始时加入的是Na I,质子还原产氢反应占据了主导.随着氢气的不断产生,部分I-被氧化成了IO_3-,而IO_3-的存在就可以驱动氧气的产生,由于溶液中氧化还原电的共存就可以持续驱动氢气和氧气的同时生成.为了测试体系的稳定性,我们将前面产生的气体完全抽空后又进行第二次10 h的循环反应,总共进行三次循环反应.在第一次循环过程中氢气、氧气生成速率分别为9.1和2.4mmol h~(–1),第二次循环其速率分别为9.9和3.7mmol h~(–1),第三次循环速率分别达到10.4和4.9mmol h~(–1).此外,通过三次循环后摩尔比为2.1,接近水分解的化学计量比.结合紫外可见漫反射光谱和Mott-Schottky曲线可以确定两种样品的能带位置.从能带位置示意图可知,两种样品都具有足够负的导带电势还原质子产氢以及足够正的价带电势氧化水产氧.需要指出的是样品的导带电势比样品的导带电势更负,这意味着前者的导带电势更有利于还原质子产氢.霍尔效应测试的结果表明,两种样品均显示出n型半导体的特征,此外样品显示出比样品更快的载流子迁移率以及更高的载流子浓度.因此,两种样品不同的导带位置以及不同的载流子迁移率和载流子浓度很可能是造成两者光催化性能具有显著差异的主要原因.     

Revealing the A‐Site Effect of Lead‐Free A3Sb2Br9 Perovskite in Photocatalytic C(sp3)−H Bond Activation

The lead‐free halide perovskite A₃Sb₂Br₉ is utilized as a photocatalyst for the first time for C(sp³)?H bond activation. A₃Sb₂Br₉ nanoparticles (A₃Sb₂Br₉ NPs) with different ratios of Cs and CH₃NH₃ (MA) show different photocatalytic activities for toluene oxidation and the photocatalytic performance is enhanced when increasing the amount of Cs. The octahedron distortion caused by A‐site cations can change the electronic properties of X‐site ions and further affect the electron transfer from toluene molecules to Br sites. After the regulation of A‐site cations, the photocatalytic activity is higher with A₃Sb₂Br₉ NPs than that with classic photocatalysts (TiO₂, WO₃, and CdS). The main active species involved in photocatalytic oxidation of toluene are photogenerated holes (h⁺) and superoxide anions (^.O₂^?). The octahedron distortion by A‐site cations affecting photocatalytic activity remains unique and is also a step forward for understanding more about halide‐perovskite‐based photocatalysis. The relationship between octahedron distortion and photocatalysis can also guide the design of new photocatalytic systems involving other halide perovskites.     

Efficient overall water splitting under visible-light irradiation on (Ga(1-x)Zn(x))(N(1-x)O(x)) dispersed with Rh-Cr mixed-oxide nanoparticles: Effect of reaction conditions on photocatalytic activity

The photocatalytic activity of (Ga(1-x)Zn(x))(N(1-x)O(x)) loaded with Rh-Cr mixed-oxide (Rh(2-y)Cr(y)O3) nanoparticles for overall water splitting under visible-light irradiation (lambda > 400 nm) is investigated with respect to reaction pH and gas pressure. The photocatalytic performance of the catalyst is found to be strongly dependent on the pH of the reactant solution but largely independent of gas pressure. The present photocatalyst exhibits stable and high photocatalytic activity in an aqueous solution of pH 4.5 for 72 h. The photocatalytic performance is much lower at pH 3.0 and pH 6.2, attributable to corrosion of the cocatalyst and hydrolysis of the catalyst. The dispersion of Rh(2-y)Cr(y)O3 as a cocatalyst on the (Ga(1-x)Zn(x))(N(1-x)O(x)) surface promotes hydrogen evolution, which is considered to be the rate-determining step for overall water splitting on this catalyst.     

Site-selected doping of upconversion luminescent Er3+ into SrTiO3 for visible-light-driven photocatalytic H2 or O2 evolution

A series of upconversion luminescent erbium-doped SrTiO(3) (ABO(3)-type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er(3+) ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high-energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO(6) octahedra promoted energy transfer from the high-energy excited states of Er(3+) with B-site occupancy to the host SrTiO(3) and thus enhanced the band-to-band transition of the host SrTiO(3). Consequently, the erbium-doped SrTiO(3) species with B-site occupancy showed higher photocatalytic activity than those with A-site occupancy for visible-light-driven H(2) or O(2) evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low-energy photons and maintaining redox ability for photocatalytic H(2) and O(2) evolution and that the site occupancy of doped elements in ABO(3)-type perovskite oxides greatly determines the photocatalytic activity.     

Thermogravimetry study of ion exchange and hydration in layered oxide materials

The behavior in aqueous solutions of the two types of layered perovskite-like structures, NaLnTiO₄ titanates (Ln?=?Nd, La) belonging to the family of Ruddlesden?CPopper phases and ANdTa₂O₇ tantalates (A?=?Na, Cs, H) belonging to the family of Dion?CJacobson phases, has been studied by means of thermogravimetric analysis and powder X-ray diffraction. In the case of NaLnTiO₄ compounds, the substitution of protons for sodium cations and the water intercalation into the interlayer space of the crystal structure were observed and proton-containing layered oxides with general formula H _x Na_1?x LnTiO₄·yH₂O (0.63?<?x?<?1, 0?<?y?<?0.74) have been obtained. Investigation on the hydration in layered tantalates ANdTa₂O₇ (A?=?H, Na, Cs) showed that NaNdTa₂O₇ and HNdTa₂O₇ form compounds intercalated by water molecules. Two steps of water intercalation were observed for NaNdTa₂O₇ and HNdTa₂O₇. Stable hydrated compounds HNdTa₂O₇·0.84H₂O, NaNdTa₂O₇·0.60H₂O, and NaNdTa₂O₇·1.35H₂O were synthesized.     

Ni-CH_3CH_2NH_2/H_(1.78)Sr_(0.78)Bi_(0.22)Nb_2O_7复合层状钙钛矿的合成及光催化分解水产氢性能(英文)

自从分解水产氢被首次报道以来,许多光催化剂被开发出来并用于光催化分解水产氢.然而,由于光生电子和空穴的复合率普遍较高,大部分的光催化剂分解水产氢效率都很低.因此,开发新型高效的光催化材料至关重要.具有(Bi_2O_2)~(2+)(A_(m-1)M_mO_(3m+1))~(2-)通式的Aurivillius相层状钙钛矿材料因具有独特的层状结构、元素可调性以及优异的电荷传输和分离能力而广泛应用于光催化分解水和去除有机污染物.此外,当该类层状钙钛矿被剥离成超薄纳米片时,其光催化性能进一步提高.为了进一步提高层状钙钛矿的载流子分离能力,将客体(如贵金属,半导体等)通过化学反应的途径插入到层状钙钛矿的层间区域,从而合成出复合层状钙钛矿被广泛发展和应用.然而,引入的客体主要是贵金属和半导体,这类客体的高成本和不均匀分布制约了其进一步的应用.由于廉价、无毒和稳定等优点,镍基材料如Ni,NiO,Ni_2O_3,NiS,NiS_2,Ni(OH)2和Ni(OH)x等被广泛用作增强电极材料的光电性能和催化剂的光催化分解水产氢性能的助催化剂.本文采用简单的原位化学反应法制备出镍基配合物Ni-CH_3CH_2NH_2(Ni-EA)插层的Ni-CH_3CH_2NH_2/H_(1.78)Sr_(0.78)Bi_(0.22)Nb_2O_7(Ni-EA/HSNNs)复合层状钙钛矿;然后采用X-射线衍射(XRD)、傅立叶变换红外光谱(FTIR)、X-射线光电子能谱(XPS)、紫外-可见漫反射光谱等手段对Ni-EA/HSNNs光催化剂进行了系统的研究.XRD结果表明,引入Ni~(2+)后,HSNNs层间距减小并且平行于钙钛矿层的晶面结晶度增强,证明HSNNs沿垂直于钙钛矿层的方向出现了层层组装.FTIR和XPS结果表明,引入的Ni~(2+)与HSNNs层间和表面的乙胺分子之间存在较强的相互作用,结合高分辨透射电镜图可知,Ni的存在形态可能为配合物Ni-EA.由此可见,当向HSNNs中引入Ni~(2+)时,Ni~(2+)和HSNNs层间和表面的乙胺分子反应生成带正电的配合物Ni-EA,由于Ni-EA与HSNNs的钙钛矿层带有异种电荷,两者之间存在较强的静电相互作用力,从而引起钙钛矿纳米片HSNNs的层层组装,最后形成Ni-EA/HSNNs复合层状钙钛矿.光催化分解水产氢性能测试结果表明,当引入0.5 wt%Ni时,复合层状钙钛矿表现出最优的光催化性能.与HSNNs(241.58μmol/h)相比,0.5%Ni-EA/HSNNs的光催化分解水产氢速率(372.67μmol/h)提高了0.54倍,表现出与0.5%Pt/HSNNs可比拟的光催化活性,可见,非贵金属Ni具有替代贵金属Pt的能力.进一步的研究表明,镍基配合物Ni-EA显著增强了催化剂的光生载流子的传输和分离能力,从而提高了其光催化分解水产氢性能.该文为光催化分解水产氢提供了一种简便的合成非贵金属配合物助催化剂的方法.     

Mapping the Compositions of Zinc Tantalate for Optimum Photocatalytic Performance in Degradation of Organic Pollutants

This work aims at mapping the compositions of zinc tantalate for optimum photocatalytic performance in degradation of organic pollutants. Three zinc tantalates, low-temperature form ZnTa2O6 (LT-ZnTa2O6), high-temperature form ZnTa2O6 (HT-ZnTa2O6), and Zn3Ta2O8 were prepared by solid state method. Photocatalytic activities of these zinc tantalates were tested for the degradation of methyl orange under UV irradiation and compared with Sr2Ta2O7, an efficient catalyst previously reported. It is found that the photocatalytic activity of these tantalates follows such a sequence: LT-ZnTa2O6 > Sr2Ta2O7 > HT-ZnTa2O6 > Zn3Ta2O8, in which LT-ZnTa2O6 shows an optimum activity at least twice higher than Sr2Ta2O7. This photocatalytic performance was revealed to primarily originate from the formation of ·OH radicals as indicated by photo- luminescence measurements. The synergistic effects of chemical compositions, crystal structure, and band structure on photocatalytic performances were discussed.     

两步水热法合成Sn_2Nb_2O_7纳米晶及其高效可见光分解水制氢性能（英文）

铌基半导体光催化材料因其具有独特的晶体结构和能带结构在光催化分解水制氢领域受到科研工作者的高度关注.然而,大多数铌基半导体光催化剂仅能够在紫外光驱动下实现光催化分解水制氢,具有可见光响应的铌基半导体光催化剂不仅数量少而且活性较低,因此发展新型纳米铌基半导体光催化剂并实现其高效可见光催化分解水产氢具有重要的学术和实用意义.具有烧绿石构型的Sn_2Nb_2O_7材料由于具有较窄的禁带宽度(2.4 e V)和合适的导带和价带电势在可见光催化分解水制氢方面引起了科研人员广泛的兴趣.然而,目前报道的利用高温固相法制备的块体Sn_2Nb_2O_7材料由于颗粒尺寸较大和比表面积较小而导致光催化活性较差.因此,发展一种简便高效的制备方法实现纳米Sn_2Nb_2O_7材料的可控制备进而提高其可见光催化活性仍具有一定的挑战性.我们发展了一种简便的两步水热合成方法实现了Sn_2Nb_2O_7纳米晶的可控制备.扫描电镜和透射电镜测试结果表明,通过两步水热法得到的Sn_2Nb_2O_7纳米颗粒具有较好分散度,其平均颗粒尺寸为20 nm.X射线衍射测试结果也进一步证明,通过两步水热法可以实现Sn_2Nb_2O_7纳米晶的可控制备.比表面积测试结果表明,Sn_2Nb_2O_7纳米晶的比表面积约为52.2 m~2/g,远远大于固相法制备的块体Sn_2Nb_2O_7材料(2.3 m~2/g).大量研究表明,大的比表面积有利于半导体催化材料催化活性的提升.通过考查所制备的Sn_2Nb_2O_7纳米晶的可见光分解水制氢能力,对其催化性能进行了评价.研究结果表明,以乳酸为空穴消耗剂,负载0.3wt.%Pt纳米颗粒作为助催化剂的Sn_2Nb_2O_7纳米晶表现出优异的可见光催化分解水产氢性能,其产氢速率是块体Sn_2Nb_2O_7材料的5.5倍.Sn_2Nb_2O_7纳米晶可见光催化分解水产氢性能提高的主要原因是其具有高分散度的纳米颗粒、较大的比表面积和更正的价带电势.首先,颗粒尺寸的纳米化能够显著减小光生电子和空穴的迁移距离,实现光生载流子快速迁移到催化剂表面进而参与催化反应;其次,大的比表面积能够提供更多的催化活性位点,进而有利于催化活性的提高;最后,X射线光电子能谱测试表明,Sn_2Nb_2O_7纳米晶具有更正的价带电势,研究表明,价带电势越正,其光生空穴氧化能力越强.在光催化分解水制氢过程中,具有较强氧化能力的光生空穴通过与空穴牺牲剂乳酸快速反应而被消耗掉,抑制了光生电子与空穴的复合,进而导致其具有较高的光催化产氢活性.     

Comparative study of vibrational spectra of Rb4LiH3(SO4)4, K4LiH3(SO4)4, K4LiH3(SeO4)4, Na5H3(SeO4)4.2H2O and Na2SeO4.H2SeO3.H2O crystals. Polarized infrared and Raman studies

Vibrational spectra of M4LiH3(XO4)4 family, where M=K, Rb, X=S, Se together with Na5H3(SeO4)4.2H2O and Na2SeO4.H2SeO3.H2O crystals were compared. Similarities and differences are described. The spectroscopic manifestation of the presence of hydrogen bonds is discussed. Position of the bands corresponding to bending type of vibrations (in-plane and out-of plane) of hydrogen bonds is analyzed in the function of temperature. Small dynamic splitting of the bands due to weak interactions between ions is noticed.