Synthesis of S-doped Sb_2O_3 Visible Light-driven Photocatalyst and Its Facets-dependent Performance for the Degradation of Methyl Orange

S-doped Sb_2O_3 nanocrystals were synthesized using SbCl3 and thioacetamide(TAA) as starting materials by a hydrothermal method and the effects of TAA dosage on the composition and properties of resultant nanocrystals were determined.Their photocatalytic performance was evaluated using the degradation of methyl orange(MO) as a model reaction.The results suggest that TAA dosage can affect the preferential growth direction of Sb_2O_3,and further influences its photocatalytic activity.S doping can extend the optical absorption edge of Sb_2O_3 to the visible light religion,and thus endows its ability to photocatalyze the degradation of MO under visible light illumination.Based on these results,the correlations between the photocatalytic activity of S-doped Sb_2O_3 and the ratio between exposed facets,specific surface area and crystallographic defects were discussed.     

二维复合光催化剂的合成及其性能研究

摘要：通过超声辅助溶剂热法制备一种新型的二维类复合光催化剂BiOCl/MOF-5。运用XRD、SEM、BET、TEM、PL 等手段对催化剂的特殊结构和性能进行表征。在该光催化剂体系中,选取MOF-5为载体,通过与光催化剂BiOCl复合来合成一种新型的二维复合光催化剂。 结果表明,制备的催化剂均呈现出较为明显的二维形貌,且相对与单一BiOCl (3.15 mg2?g-1 )来说,该复合催化剂 (110.16 mg2?g-1 ) 的比表面积得到了明显的提高。由于催化剂的光催化性能与其比表面积和孔隙体积密切相关。复合催化剂相对较大的比表面积和适当的能带隙,有利于为反应物提供更多的活性位点和有效的传输路径,而且得益于MOF-5独特的形貌和结构,光催化剂聚集和比表面积小的问题也得到了解决。因此,该复合材料在降解有机物方面呈现出优异的光催化活性,且与纯BiOCl相比,催化剂的光催化活性得到了明显的提高。     

Understanding the synergistic effects,optical and electronic properties of ternary Fe/C/S‐doped TiO2 anatase within the DFT + U approach

Although TiO₂ is an efficient photocatalyst, its large band gap limits its photocatalytic activity only to the ultraviolet region. An experimentally synthesized ternary Fe/C/S‐doped TiO₂ anatase showed improved visible light photocatalytic activity. However, a theoretical study of the underlying mechanism of the enhanced photocatalytic activity and the interaction of ternary Fe/C/S‐doped TiO₂ has not yet been investigated. In this study, the defect formation energy, electronic structure and optical property of TiO₂ doped with Fe, C, and S are investigated in detail using the density functional theory + U method. The calculated band gap (3.21 eV) of TiO₂ anatase agree well with the experimental band gap (3.20 eV). The defect formation energy shows that the co‐ and ternary‐doped systems are thermodynamically favorable under oxygen‐rich condition. Compared to the undoped TiO₂, the absorption edge of the mono‐, co‐, and ternary‐doped TiO₂ is significantly enhanced in the visible light region. We have shown that ternary doping with C, S, and Fe induces a clean band structure without any impurity states. Moreover, the ternary Fe/C/S‐doped TiO₂ exhibit an enhanced photocatalytic activity, a smaller band gap and negative formation energy compared to the mono‐ and co‐doped systems. Moreover, the band edges of Fe/C/S‐doped TiO₂ align well with the redox potentials of water, which shows that the ternary Fe/C/S‐doped TiO₂ is promising photocatalysts to split water into hydrogen and oxygen. These findings rationalize the available experimental results and can assist the design of TiO₂‐based photocatalyst materials.     

Solvothermal synthesis and photocatalytic activity of S-doped TiO<Subscript>2</Subscript> and TiS<Subscript>2</Subscript> powders

The photocatalytic activity of S-doped TiO₂ powder depends on the S content. To synthesize S-doped TiO₂ powders with high S content, solvothermal processes were used in this work. The S-doped TiO₂ powder contains 2.0 M% sulfur and has an absorption edge of 460 nm (2.7 eV). The pure TiS₂ powder also synthesized by a solvothermal process has an absorption edge of 595 nm (2.08 eV) and broad absorption above 595 nm. The photocatalysis experiments indicate that the degradation of methyl orange is associated with the light adsorption edge. The photocatalytic activity is much larger for the pure TiS₂ powder than for partially S-doped TiO₂ powder.     

Composition dependence of the photocatalytic activities of BiOCl(1-x)Br(x) solid solutions under visible light

We prepared BiOCl(1-x)Br(x) (x=0-1) solid solutions and characterized their structures, morphologies, and photocatalytic properties by X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, Raman spectroscopy, photocurrent and photocatalytic activity measurements and also by density functional theory calculations for BiOCl, BiOBr, BiOCl(0.5)Br(0.5). Under visible-light irradiation BiOCl(1-x)Br(x) exhibits a stronger photocatalytic activity than do BiOCl and BiOBr, with the activity reaching the maximum at x=0.5 and decreasing gradually as x is increased toward 1 or decreased toward 0. This trend is closely mimicked by the photogenerated current of BiOCl(1-x)Br(x) , indicating that the enhanced photocatalytic activity of BiOCl(1-x)Br(x) with respect to those of BiOCl and BiOBr originates from the trapping of photogenerated carriers. Our electronic structure calculations for BiOCl(0.5)Br(0.5) with the anion (O(2-), Cl(-), Br(-)) and cation (Bi(3+)) vacancies suggest that the trapping of photogenerated carriers is caused most likely by Bi(3+) cation vacancies, which generate hole states above the conduction band maximum.     

Size control synthesis of sulfur doped titanium dioxide （anatase） nanoparticles, its optical property and its photo catalytic reactivity for CO2 ＋ H2O conversion and phenol degradation

Sulfur doped anatase TiO2 nanoparticles (3 nm−12 nm) were synthesized by the reaction of titanium tetrachloride, water and sulfuric acid with addition of 3M NaOH at room temperature. The electro-optical and photocatalytic properties of the synthesized sulfur doped TiO2 nanoparticles were studied along with Degussa commercial TiO2 particles (24 nm). The results show that band gap of TiO2 particles decreases from 3.31 to 3.25 eV and for that of commercial TiO2 to 3.2 eV when the particle sizes increased from 3 nm to 12 nm with increase in sulfur doping. The results of the photocatalytic activity under UV and sun radiation show maximum phenol conversion at the particle size of 4 nm at 4.80% S-doping. Similar results are obtained using UV energy for both phenol conversion and conversion of CO2+H2O in which formation of methanol, ethanol and proponal is observed. Production of methanol is also achieved on samples with a particle size of 8 and 12 nm and sulfur doping of 4.80% and 5.26%. For TiO2 particle of 4 nm without S doping, the production of methanol, ethanol and proponal was lower as compared to the S-doped particles. This is attributed to the combined electronic effect and band gap change, S dopant, specific surface area and the light source used.     

MOF-808/BiOCl复合材料的制备及其光催化性能

将高稳定性的MOF-808与BiOCl结合,采用简便的水热法制备出新型MOF-808/BiOCl复合异质结材料。以环丙沙星(CIP)为污染物,探究复合材料MOF-808/BiOCl对CIP的光催化性能。发现含有10% MOF-808的复合材料(MOF-808/BiOCl-10%)表现出最佳的光催化活性。在紫外光照射20 min内,MOF-808/BiOCl-10%对CIP的光催化降解效率高达94.7%。通过X射线粉末衍射、扫描电镜、红外光谱、荧光光谱、紫外可见漫反射光谱、光电流、电化学阻抗等表征技术来考察材料的物相组成、形貌以及光电化学性质。紫外可见漫反射光谱的结果表明,MOF-808/BiOCl-10%材料光吸收范围得到提高。同时进行了自由基捕获实验。基于以上实验数据,提出了MOF-808/BiOCl复合材料可能的光催化机理。     

A Facile Controllable Synthesis, Growth Mechanism, and Photocatalytic Properties of Nanoscale BiOCl

Nanoscale tetragonal BiOCl samples have been synthesized using Bi[SC12H25]3 and CHCl3 as bismuth and chlorine sources by solvothermal reactions. The structure, morphology, and formation process have been investigated by SEM, TEM, HRTEM, XRD, and EDX analyses. The layered crystal structure feature of BiOCl may induce the growth of nano plates, which can subsequently aggregate into 3D spherical or flower-like microstructures under the presence of ethanol. The reaction temperature and the identity of secondary solvent influence the morphology. The yield of BiOCl depends on the completeness of the reaction and the degree of a competition reduction of BiOCl to Bi by ethanol. The as-synthesized 3D quasi-spherical BiOCl sample has an optical band gap of 3.15 eV, and shows much better photocatalytic performance on the degradation of methyl orange than that of commercial P25.     

氯氧化铋催化剂的电子结构调控及其光催化性能研究

以不同Bi/Cl摩尔比例为原料设计合成了一系列BiOCl半导体催化材料。扫描电子显微镜、XRD衍射峰拟合等分析结果显示,Bi/Cl比例的改变对BiOCl的形貌、表面结构、微观电子结构均具有一定的调控作用。以Bi/Cl = 1 : 1为原料合成的BiOCl光催化剂具有最窄的带隙值（Eg=3.18 eV）,使得其具有较强的的光响应能力。光催化去除罗丹明B（RhB）结果表明,随着Bi/Cl摩尔比例的减小,BiOCl的催化性能呈现先增强后减弱的趋势。Bi/Cl = 1 : 1样品具有最优的催化活性,源于其较优异的光吸收性能以及特殊的表面特性。光催化机理研究表明,光催化去除RhB的过程中,起作用的活性物质主要为光生电子、空穴以及半导体表面产生的超氧自由基。     

DFT description on electronic structure and optical absorption properties of anionic S-doped anatase TiO2

Plane-wave-based pseudopotential density functional theory (DFT) calculations are used to characterize the doping effect of S substituting for O in anatase TiO(2). Through band structure calculation, a direct band gap is predicted in TiO(2)(-)(x)S(x). Electronic structure analysis shows that the doping S could substantially lower the band gap of TiO(2) by the presence of an impurity state of S 3p on the upper edge of the valence band. Excitations from the impurity state of S 3p to the conduction band may be responsible for the red shift of the absorption edge observed in the S-doped TiO(2). The band gap lowering and red shift of the absorption edge are found to increase as the sulfur concentration increases.     

Oxygen Vacancy‐Mediated Photocatalysis of BiOCl: Reactivity,Selectivity, and Perspectives

Semiconductor photocatalysis is a trustworthy approach to harvest clean solar light for energy conversions, while state‐of‐the‐art catalytic efficiencies are unsatisfactory because of the finite light response and/or recombination of robust charge carriers. Along with the development of modern material characterization techniques and electronic‐structure computations, oxygen vacancies (OVs) on the surface of real photocatalysts, even in infinitesimal concentration, are found to play a more decisive role in determining the kinetics, energetics, and mechanisms of photocatalytic reactions. This Review endeavors to clarify the inherent functionality of OVs in photocatalysis at the surface molecular level using 2D BiOCl as the platform. Structure sensitivity of OVs on reactivity and selectivity of photocatalytic reactions is intensely discussed via confining OVs onto prototypical BiOCl surfaces of different structures. The critical understanding of OVs chemistry can help consolidate and advance the fundamental theories of photocatalysis, and also offer new perspectives and guidelines for the rational design of catalysts with satisfactory performance.     

Effective band gap reduction of titanium oxide semiconductors by codoping from first‐principles calculations

Doping is an efficient approach to narrow the band gap of TiO₂ and enhance its photocatalytic activity. Here, we perform generalized gradient approximation (GGA)+U calculations to narrow the band gap of TiO₂ by codoping of X (F, N) with transition metals (TM = Fe, Co) to extend the absorption edge to longer visible‐light wavelengths. Our results show that all the codoped systems can narrow the band gap significantly, in particular, (F+Fe)‐codoped system could serve as remarkably better photocatalysts with both narrowing of the band gap and relatively smaller formation energies than those of (F+Co) and (N+TM)‐codoped systems. Our results provide useful guidance for codoped TiO₂ efficient for photocatalytic activity. © 2013 Wiley Periodicals, Inc.     

BiOCl/蒙脱土复合光催化剂的制备及其光催化活性

为优化BiOCl光催化剂的结构,改善其对有机污染物的吸附性能,进而提高光催化反应活性,采用超声辅助化学沉淀法制备了BiOCl/蒙脱土(MMT)复合光催化剂,并考察了MMT质量分数(w(MMT))对复合光催化剂结构及光催化反应活性的影响。 X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、傅里叶红外光谱(FTIR)和紫外-可见漫反射光谱(DRS)等的表征结果表明,所得催化剂呈微球状结构,禁带宽度为3.24 eV。 随着w(MMT)的增加,催化剂的微球状结构逐渐被破坏,但带隙能未发生明显变化。 以8-羟基喹啉为目标物考察了复合催化剂的吸附及光催化反应活性。 结果表明,随着w(MMT)增加,催化剂对8-羟基喹啉的吸附和光催化氧化活性逐渐增加,这可归因于与MMT的复合增大了比表面积并降低了光生载流子复合效率。 当w(MMT)为15%时,催化剂的吸附及光催化性能达到最佳,光照50 min后,8-羟基喹啉的降解率达到85.6%,矿化率达到51.0%。 光生空穴和超氧自由基负离子为主要的氧化活性物种。 复合催化剂还可高效降解邻苯二酚和对氨基苯甲酸。 同时,复合光催化剂表现出较强的化学稳定性,表明其具有较强的实际应用价值,可用于处理含有机酚类污染物的工业废水。     

Investigation of band offsets of interface BiOCl:Bi2WO6: a first-principles study

Density functional theory calculations are performed to study the band offsets at the interface of two photocatalytic materials BiOCl:Bi(2)WO(6). It is found that the W-O bonded interface shows the most stability. An intrinsic interface fails to enhance the charge-carrier separation due to the improper band alignment between these two materials. Sulfur (S) is proposed to replace the bulk oxygen (O) site and thus tune the band edges of BiOCl to enhance the photocatalytic performance of the heterojunction. Furthermore, the presence of S provides an extra charge to generate a clean interface with minimal gap states that also benefits carrier migration across the heterojunction.     

共模板法一步合成绣球状BiOCl/Br固溶体光催化剂

以乙二醇/十二烷基三甲基溴化铵(EG/DTAB)为共模板剂,一步制得BiOCl/Br的固溶体光催化剂,利用X射线衍射仪、扫描电子显微镜、能谱仪、N2吸附-脱附仪和紫外-可见漫反射光谱仪进行了表征.结果表明,与采用溶剂热法制得的BiOCl分级微球相比,采用EG/DTAB共模板法制得的BiOCl/Br固溶体具有更明显的分层结构,呈绣球状.同时,DTAB的Br-插入到BiOCl的晶格中,形成固溶体,减小了禁带宽度.绣球状BiOCl/Br固溶体具有比商用P25、二维BiOCl纳米片和三维BiOCl分级微球更优异的可见光间接敏化降解染料性能,当nDTAB/nKCl=0.75时,制得的BiOCl/Br固溶体8 min内在可见光下对罗丹明B(Rh B)的降解率达到97.2%;1 h后在可见光下对甲基橙(MO)的降解率达到83.6%.     

盐酸溶液处理钒酸铋增强可见光催化活性及其机理

采用盐酸水溶液处理BiVO₄ 的方法获得增强的光催化活性. 在0.1 mol·L^-1 酸溶液中浸渍反应6 h,BiVO₄ 的可见光催化降解苯酚的活性提高了3.5 倍. 采用X 射线衍射(XRD), 扫描电镜(TEM)和漫反射光谱(DRS)等表征手段研究处理后样品的晶相组成和表面形貌, 结合不同酸和氯化物处理的对照实验, 结果表明,在H⁺和Cl^-的协同作用下, BiVO₄表面部分溶出并以BiOCl 沉积, 形成了表面具有凹陷沟壑的BiVO₄颗粒与片状结构BiOCl 的复合物. 采用悬浮液光电压法测定BiOCl 平带电位, 通过BiVO₄和BiOCl 的能带分析及其混合颗粒的光催化活性测试, 确证二者间不存在颗粒间电子转移效应. 增强的光催化活性主要归因于BiVO₄表面形成了有助于光生电荷迁移的凹凸不平结构. 这种表面处理方法有望成为一种增强半导体化合物光催化活性的有效途径.     

S掺杂S-TiO_2/SiO_2可见光响应光催化剂的制备及性能

以四氯化钛为钛源,硫脲为硫源,采用液相水解-沉淀法制备了S掺杂的TiO2/SiO2(S-TiO2/SiO2)催化剂,并以苯酚为模型物,考察了催化剂在可见光区、紫外光区和太阳光下的光催化活性,以及催化剂的使用寿命和分离性能.采用X射线光电子能谱、傅里叶变换红外光谱、紫外-可见漫反射光谱、X射线衍射、透射电镜及N2吸附-脱附等技术对催化剂进行了表征.结果表明,S以+6价形式进入TiO2体相并置换晶格中的Ti4+,适量S掺杂的S-TiO2/SiO2在紫外光区、可见光区和太阳光下均表现出较高的光催化活性.SiO2与TiO2界面间有Ti-O-Si键形成,结合牢固.S掺杂在TiO2表面生成Ti-O-S键,形成新的能级结构,使光催化剂在450～550nm产生吸收,诱发TiO2可见光催化活性;同时提高了TiO2表面羟基数量.SiO2的加入可减小TiO2颗粒的平均尺寸,增大催化剂的比表面积,改善催化剂的分离性能,提高催化剂的使用寿命.     

WO3/BiOCl, a novel heterojunction as visible light photocatalyst

A bismuth oxychloride (BiOCl) nanostructure is prepared by a new low temperature route using sodium dodecyl sulfate as template and urea as hydrolytic agent. A novel heterojunction is developed between BiOCl and tungsten oxide (WO(3)) to make it an efficient visible light photocatalyst. The catalysts were characterized by X-ray diffraction analysis, Raman spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and N(2) sorption isotherms. The WO(3)/BiOCl heterojunction system extends the absorption edge to the visible region efficiently. BiOCl works as a main photocatalyst while WO(3) acts as the photosensitizer absorbing visible light in the WO(3)/BiOCl composite. The individual BiOCl and WO(3) show very low photocatalytic efficiency under visible light irradiation but their heterojunction provides unexpectedly high efficiency in decomposing rhodamine B as compared to Degussa P25, pure BiOCl, and WO(3).     

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.     

Black BiOCl with disorder surface structure prepared by Fe reduction and the enhanced photocatalytic activity

Black bismuth oxychloride (BiOCl) with disordered surface structure has been prepared by a facile Fe reduction method and successfully used as a visible-light photocatalyst. XRD and FESEM results showed that black BiOCl has pure BiOCl phase with plate-like structure. The as-prepared black sample exhibited a broad absorption covered the whole visible light region. The high-resolution TEM images revealed the disordered surface structure, which could be the reason for the black color of BiOCl. The disordered surface was not only responsible for the visible-light absorption but also played a vital role in improving the separation of photo-induced electrons and holes. Methyl orange (MO) photocatalytic degradation experiments showed that the black sample exhibited higher photocatalytic activity than the pristine BiOCl under visible light irradiation. A possible formation mechanism of black BiOCl under Fe reduction was also proposed in our research work.