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.     

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.     

Ti~(3+)自掺杂的纳米TiO_2的制备及其可见光催化性能

以TiH2为Ti源,H2O2为氧化剂,首先通过表面氧化得到不同状态的前驱体凝胶,然后采用后续水热处理制备Ti3+自掺杂的纳米Ti O2.考察了前驱体凝胶状态及水热处理时间对材料结构和性能的影响.利用X射线衍射、透射电子显微镜、X射线光电子能谱、电子顺磁共振波谱和紫外-可见漫反射光谱手段对样品进行表征.以次甲基蓝溶液为模拟废水评价样品的可见光催化降解性能.结果表明,与纯Ti O2相比,Ti3+的自掺杂使材料在可见光区有明显的吸收,并具有良好的可见光催化降解性能和循环使用性能.当采用黄色凝胶为前驱体时,在160°C下水热处理24 h所得样品在可见光下光催化降解次甲基蓝的反应速率常数(0.0439 min-1)是纯Ti O2的18.3倍.     

可见光下Fe3+掺杂对K2La2Ti3O10分解水制氢性能的影响

采用溶胶-凝胶法制备了Fe3+掺杂的Fe-K2La2Ti3O10光催化剂, 并通过X射线衍射(XRD)、紫外-可见漫反射(DRS)、X射线光电子能谱(XPS)等技术对其进行了表征和分析, 考察了不同掺杂量对K2La2Ti3O10的性质及光催化分解水制氢活性的影响. 结果表明, Fe-K2La2Ti3O10在400-650 nm范围内显示强吸收, 光谱响应扩展到可见光区(λ>400 nm), 掺杂Fe3+后, K2La2Ti3O10的可见光区的光催化制氢活性显著提高, 掺杂量为nFe/nTi=0.04时活性最佳, 当催化剂用量为0.1 g, 反应液为CH3OH(30 mL)+H2O(90 mL)时, 产氢量达到1.92 μmol·h-1, 为未掺杂时的4倍.     

Development of new photocatalytic water splitting into H2 and O2 using two different semiconductor photocatalysts and a shuttle redox mediator IO3-/I-

A new type of photocatalytic reaction that splits water into H2 and O2 was designed using a two-step photoexcitation system composed of an iodate/iodide (IO3-/I-) shuttle redox mediator and two different photocatalysts, one for H2 evolution and the other for O2 evolution. Photocatalytic oxidation of water to O2 and reduction of IO3- to I- selectively proceeded with good efficiencies over TiO2-rutile and Pt-WO3 photocatalysts under UV and visible light irradiations, respectively. The O2 evolution selectively proceeded even in the presence of a considerable amount of I- in the solutions, although the oxidation of water is thermodynamically less favorable than oxidation of I-. Both the adsorption property of IO3- anions and the oxidation property of the photocatalysts are doubtless responsible for the selective oxidation of water. On the other hand, photocatalytic reduction of water to H2 and oxidation of I- to IO3- proceeded over Pt-TiO2-anatase and Pt-SrTiO3:Cr/Ta (codoped with Cr and Ta) photocatalysts under UV and visible light, respectively. The combination of two different photocatalysts results in a stoichiometric evolution of H2 and O2 via the redox cycle of IO3- and I-. The photocatalytic water splitting under visible light irradiation (lambda > 420 nm) was demonstrated by using the Pt-SrTiO3:Cr/Ta, Pt-WO3, and IO3-/I- shuttle redox mediator.     

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 SrTiO₃ (ABO₃‐type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er³⁺ 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 BO₆ octahedra promoted energy transfer from the high‐energy excited states of Er³⁺ with B‐site occupancy to the host SrTiO₃ and thus enhanced the band‐to‐band transition of the host SrTiO₃. Consequently, the erbium‐doped SrTiO₃ species with B‐site occupancy showed higher photocatalytic activity than those with A‐site occupancy for visible‐light‐driven H₂ or O₂ 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 H₂ and O₂ evolution and that the site occupancy of doped elements in ABO₃‐type perovskite oxides greatly determines the photocatalytic activity.     

Photocatalytic hydrogen production from water over M-doped La2Ti2O7 (M = Cr, Fe) under visible light irradiation (lambda > 420 nm)

In the search for efficient photocatalysts working under visible light, we have investigated the effect of cation substitution on a layered perovskite, La2Ti2O7. Among various metal dopants, only Cr and Fe induced intense absorption of visible light (lambda > 400 nm), and only these catalysts produced H2 photocatalytically from water in the presence of methanol under visible light irradiation (lambda > 420 nm). The polymerized complex method was found to be more efficient for fabrication of the present catalysts producing a more homogeneous structure than the solid-state reaction. The characterization by XRD, UV-vis DRS, XPS, and XANES revealed that doped Cr and Fe were present in the Cr3+ and Fe3+ states substituting for Ti sites in the La2Ti2O7 lattice. The theoretical calculation indicated that the most significant feature in the electronic band structure of the metal-doped La2Ti2O7 was the formation of a partially filled 3d band in the band gap of La2Ti2O7, while the contribution of these dopants on the valence band was negligible. Excitation of electrons from this localized interband to the conduction band of La2Ti2O7 was responsible for visible light absorption and the H2 evolution from water under visible light.     

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.     

C-N-S-TiO2光催化剂的制备、表征及其性能

以钛酸四丁酯为钛源、功能生物小分子胱氨酸为掺杂剂,采用溶胶-凝胶法同步合成了C-N-S-TiO2光催化剂,利用XRD、XPS、FT-IR和DRS等测试技术对样品的结构及物化性能进行了表征。XRD和DRS分析表明,共掺杂抑制了TiO2晶粒的生长,提高了晶相转变温度,且C-N-S-TiO2样品的吸收带边明显"红移",光吸收范围一直延长至800 nm左右。XPS分析结果显示,C-N-S-TiO2样品表面产生了杂质能级,C、S元素分别取代部分晶格Ti4+以CO23-和S6+形式存在;而N峰呈宽化状态,以O—Ti—N和Ti—O—N键存在,且样品表面羟基含量明显增加。以罗丹明B染料为模型污染物,考察了该催化剂的可见光催化活性。结果表明,与P25 TiO2比较,C-N-S-TiO2光催化剂活性得到改进,C-N-S-TiO2光催化剂在470～800 nm波长下辐射120 min后对罗丹明B的降解率可高达83%。     

Cr2O3/C@TiO2核壳型复合材料的设计合成及其光催化产氢性能

随着社会经济的快速发展,能源危机和环境污染问题成为世界各国关注的焦点.通过光催化剂将太阳能用于污染物降解、分解水产氢、CO2还原及有机物合成等领域,是解决上述问题的理想途径.过渡金属氧化物TiO2因其稳定性高、催化活性好、制备简单等优点,被认为是最理想的光催化材料.然而,TiO2带隙较宽、光响应范围窄、光量子效率低等缺点限制了其实际应用.将碳或Cr2O3与TiO2结合形成复合结构已被证明可以有效提升其光催化性能.另一方面,金属离子的掺杂可以有效提高氧化钛的可见光响应.本文利用具有高比表面积的金属有机骨架材料MIL-101(Cr)纳米材料作为模板、镉源和碳源,首先在MIL-101(Cr)表面可控生长TiO2纳米颗粒,获得MIL-101(Cr)@TiO2复合结构;然后在氮气保护下碳化形成Cr2O3/C@TiO2核壳型复合材料.碳化后,制备的复合材料具有模板的八面体形貌和高比表面积,MIL-101(Cr)中的Cr元素一部分会形成Cr2O3,一部分会掺杂到TiO2中,使得TiO2的吸收边红移.此外,Cr2O3/C@TiO2中的C有利于光的吸收和载流子的分离.这种独特的纳米结构赋予Cr2O3/C@TiO2复合材料优异的光催化性能.在300 W氙灯照射下,该复合材料光解水产氢的速率为446μmol h?1 g?1,约为纯TiO2的4倍.在可见光照射下,Cr2O3/C@TiO2分解水产氢的速率为25.5μmol h?1 g?1.将获得的粉体催化剂制备成光电极发现,Cr2O3/C@TiO2在全幅光照射下的光电流密度在0.4 V(vs.Ag/AgCl)下达到2.3 mA/cm2,约为纯TiO2的3.5倍.Cr2O3/C@TiO2光催化产氢活性的提高一方面是由于Cr掺杂到TiO2中使得其具有可见光响应,另一方面MIL-101碳化获得的Cr2O3/C有效促进了光生载流子的分离.     

Cr2O3/C@TiO2核壳型复合材料的设计合成及其光催化产氢性能

随着社会经济的快速发展,能源危机和环境污染问题成为世界各国关注的焦点.通过光催化剂将太阳能用于污染物降解、分解水产氢、CO2还原及有机物合成等领域,是解决上述问题的理想途径.过渡金属氧化物TiO2因其稳定性高、催化活性好、制备简单等优点,被认为是最理想的光催化材料.然而,TiO2带隙较宽、光响应范围窄、光量子效率低等缺点限制了其实际应用.将碳或Cr2O3与TiO2结合形成复合结构已被证明可以有效提升其光催化性能.另一方面,金属离子的掺杂可以有效提高氧化钛的可见光响应.本文利用具有高比表面积的金属有机骨架材料MIL-101(Cr)纳米材料作为模板、镉源和碳源,首先在MIL-101(Cr)表面可控生长TiO2纳米颗粒,获得MIL-101(Cr)@TiO2复合结构;然后在氮气保护下碳化形成Cr2O3/C@TiO2核壳型复合材料.碳化后,制备的复合材料具有模板的八面体形貌和高比表面积,MIL-101(Cr)中的Cr元素一部分会形成Cr2O3,一部分会掺杂到TiO2中,使得TiO2的吸收边红移.此外,Cr2O3/C@TiO2中的C有利于光的吸收和载流子的分离.这种独特的纳米结构赋予Cr2O3/C@TiO2复合材料优异的光催化性能.在300 W氙灯照射下,该复合材料光解水产氢的速率为446μmol h?1 g?1,约为纯TiO2的4倍.在可见光照射下,Cr2O3/C@TiO2分解水产氢的速率为25.5μmol h?1 g?1.将获得的粉体催化剂制备成光电极发现,Cr2O3/C@TiO2在全幅光照射下的光电流密度在0.4 V(vs.Ag/AgCl)下达到2.3 mA/cm2,约为纯TiO2的3.5倍.Cr2O3/C@TiO2光催化产氢活性的提高一方面是由于Cr掺杂到TiO2中使得其具有可见光响应,另一方面MIL-101碳化获得的Cr2O3/C有效促进了光生载流子的分离.     

Photocatalysts of Cr Doped TiO2 Film Prepared by Micro Arc Oxidation

A series of Cr doped TiO2 films were prepared by micro arc oxidation (MAO) using an electrolyte of Na3PO4+K2Cr2O7. X-ray diffraction and scanning electron microscopy revealed that the films mainly consisted of anatase phase with a porous surface morphology. The films have an excellent photocatalytic effect for degradation of methylene blue and decomposition of water under visible light illumination. This arises from the formation of Cr3+/Cr4+ and oxygen vacancy energy levels owing to Cr doping. The former reduces the electron-hole recombination chance, while the latter generates a new gap between the conduction band (CB) and valence band (VB) of TiO2, which lowers the photo energy of the excited electron in the VB to the oxygen vacancy states. The mechanisms for film synthesis during the MAO process are also presented.     

Mechanism of photocatalytic activities in Cr-doped SrTiO3 under visible-light irradiation: an insight from hybrid density-functional calculations

We used hybrid density-functional calculations to clarify the effect of substituting chromium for titanium (Cr(Ti)) on photocatalytic activities of Cr-doped SrTiO(3). A singly negative Cr(Ti)?, which is relevant to a lower oxidation state of Cr, is advantageous for the visible light absorption without forming electron trapping centers, while other charge states are inactive for the photocatalytic reaction. Stabilizing the desirable charge state (Cr(Ti)?) is feasible by shifting the Fermi level towards the conduction band. Our theory sheds light on the photocatalytic properties of metal-doped semiconductors.     

Hydrothermal synthesis of Na(0.5)La(0.5)TiO3-LaCrO3 solid-solution single-crystal nanocubes for visible-light-driven photocatalytic H2 evolution

Cubic perovskite structure photocatalysts of Na(0.5)La(0.5)TiO(3) and (Na(0.5)La(0.5)TiO(3))(1.00)(LaCrO(3))(0.08) solid solution that consisted of well-defined single-crystal nanocubes were successfully prepared by means of facile and surfactant-free hydrothermal reactions for the first time. The results from different instrumental characterizations and theoretical calculations consistently confirmed the formation of nanocubic single-crystal solid solution of (Na(0.5)La(0.5)TiO(3))(1.00)(LaCrO(3))(0.08), and clearly revealed the modification of its physicochemical properties compared with those of Na(0.5)La(0.5)TiO(3). In particular, the effective narrowing of the bandgap (from 3.19 to 2.25 eV) by Cr(3+) in the solid solution made it possible to utilize visible light. The solid-solution configuration maintained the charge balance to preserve the valence of Cr(3+) rather than Cr(6+), and accommodated Cr(3+) with high content to form new energy bands instead of localized impurity levels. The hydrothermal preparation strategy ensured the formation of single crystals with high purity, few defects, and regulated morphology; it also guaranteed the valences of Ti(4+) and Cr(3+) in the solid solution. Consequently, the recombination of photogenerated carriers could be effectively suppressed to benefit photocatalytic H(2) evolution. (Na(0.5)La(0.5)TiO(3))(1.00)(LaCrO(3))(0.08) nanocubic single-crystal solid solution showed stable photocatalytic activity, and thus was proved to be a promising candidate for visible-light-driven photocatalytic H(2) evolution.     

原位合成稳定的Ti3+自修饰介孔TiO2光催化剂在环境净化中的应用

半导体光催化剂TiO2因具有绿色环保无污染、化学稳定性好及可实现稳定产氢等优点而广泛应用于光解水、废水处理和空气净化等领域.然而,锐钛矿相TiO2禁带宽度约为3.2 eV,仅对紫外光响应.而在太阳光中,44%左右为可见光,紫外光仅占不到4%.为了提高TiO2对太阳光的利用率和在可见光照射下的光催化活性,近年来人们采用掺杂金属/非金属离子以及与可见光催化剂复合等方法对TiO2进行改性.但是这些离子掺杂的方法会不可避免地在TiO2晶格中形成结构缺陷,这些结构缺陷作为光生电子和空穴的复合中心不利于电子和空穴分离.最近研究表明,通过Ti3+自掺杂可以很好提高TiO2可见光催化活性,但是目前制备Ti3+掺杂TiO2的方法较复杂,形成的Ti3+掺杂易在表面积聚而被进一步氧化,影响其光催化稳定性,不利于实际应用.因此,开发具有良好电子-空穴分离效率的可见光催化剂引起了广泛的研究兴趣.本文通过原位自掺杂Ti3+来提高TiO2可见光光催化活性.以TiCl3为钛源, H2O为溶剂, F127为软模板,采用溶剂挥发诱导自组装的方法制备了蠕虫状Ti3+自掺杂的介孔TiO2.采用X射线衍射(XRD)、N2物理吸附、紫外-可见漫反射(UV-vis)、透射电子显微镜和电子顺磁共振(EPR)对所制备样品结构、结晶度和形貌等进行了表征分析.通过控制表面活性剂用量和焙烧温度优化了Ti3+自掺杂介孔TiO2的光催化活性.结果表明,在模拟太阳光照射下,所制样品对气相光催化氧化NO和水相降解有机染料亚甲基蓝表现出优异的催化性能和稳定性. Ti3+自掺杂介孔TiO2有效扩展了催化剂的光吸收范围,提高了光生电子空穴的迁移效率.其优异的光催化活性和稳定性主要归因于掺杂在TiO2骨架中的Ti3+和所合成催化剂多孔性之间的协同效果.固体UV-vis结果表明,所合成的TiO2具有很好的可见光响应,主要归因于在TiO2材料合成过程中,部分Ti3+未被完全氧化, Ti3+掺入可以有效降低TiO2的禁带宽度.通过计算可知合成的TiO2禁带宽度为2.7 eV.通过低温EPR测试进一步证明了Ti3+的存在,而且Ti3+主要掺杂在TiO2体相中. N2物理吸附结果表明,随焙烧温度不断提高,所得产物的比表面积先增加后减少,当焙烧温度在500 oC时,比表面积最大,但至550 oC时,比表面积、孔径和孔体积增大,表明催化剂的孔结构被破坏.表面活性剂F127的用量对样品比表面积和孔径大小也有影响,当其用量为0.54 g时,所得产物的比表面积最大.我们将所合成的TiO2应用于污染气体NO的氧化,考察了焙烧温度和表面活性剂用量对光催化剂性能的影响.结果表明,当表面活性剂用量为0.54 g,焙烧温度为500oC时,所制催化剂在模拟太阳光和可见光照射下都表现出最好的NO去除转化率.将使用过的催化剂离心洗涤后进行连续反应3.5 h,依然保持很高的NO去除转化率.催化剂高活性及稳定性的主要原因是Ti3+的掺杂将TiO2光响应范围拓展到可见光区域,且Ti3+掺杂和介孔结构之间的协同作用有利于促进光生电子和空穴的分离.当催化剂在低于500 oC焙烧时,所得催化剂结晶度较低,不利于光生电子-空穴的分离,而高温焙烧则会导致催化剂介孔结构遭到破坏,不利于NO气体吸附和产物脱附.表面活性剂对催化剂活性影响较小,在可见光照射下催化剂均表现出很好的光催化活性.此外,该Ti3+自掺杂介孔TiO2在液相条件下对有机染料亚甲基蓝也表现出很好的去除效果,可见光照射2 h,亚甲基蓝去除率接近100%.     

Adsorption and reaction of CO and CO2 on oxidized and reduced SrTiO3(100) surfaces

The adsorption and reaction of CO and CO(2) on oxidized and reduced SrTiO(3)(100) surfaces have been studied with temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). XPS results indicate that the oxidized SrTiO(3)(100) surfaces are nearly defect-free with predominantly Ti(4+) ions whereas the sputter-reduced surfaces contain substantial amounts of defects. Both CO and CO(2) are found to adsorb weakly on the oxidized SrTiO(3)(100) surfaces. On sputter-reduced surfaces, enhanced reactivity of CO and CO(2) is observed due to the presence of oxygen vacancy sites, which are responsible for dissociative adsorption of these molecules. Our studies indicate that the CO and CO(2) molecules exhibit relatively weaker interactions with SrTiO(3)(100) compared to those with TiO(2)(110) and TiO(2)(100) surfaces. This is most likely an influence of the Sr cations on the electronic structure of the Ti cations in the mixed oxide of SrTiO(3).     

Photocatalytic activity of SrTiO3 codoped with nitrogen and lanthanum under visible light illumination

Yellow SrTiO3 powders codoped with nitrogen and lanthanum (STO:N,La) were studied as visible light photocatalysts. The crystal phase of STO:N,La exhibited a pure perovskite phase, and O and Sr sites atoms were substitutionally doped with N and La atoms, respectively. The first principle calculation of STO:N,La indicated that the edge of the N(2p) band is situated above the valence band, which consisted of O(2p) orbitals, and the La orbitals did not exist in the band gap of SrTiO3. STO:N,La exhibited a higher oxidation activity of gaseous 2-propanol under vis illumination than SrTiO3 doped only with nitrogen (STO:N). The high activity of STO:N,La was due to the decrease in the oxygen vacancies, which acted as electron-hole recombination centers, because codoping with La3+ and N3- ions maintained the charge balance. The optimum doping density of N and La for visible light activity was 0.5%, and STO:N,La(0.5%) had an activity under UV illumination similar to pure SrTiO3.     

Fe_3O_4/SrTiO_3复合光催化剂降解甲基橙

用共沉淀法制备了SrTiO3光催化剂及Fe3O4/SrTiO3复合光催化剂.通过紫外-可见漫反射光谱、XRD、SEM-EDX对其进行表征,以甲基橙为探针分子考察其光催化性能.结果表明,适量Fe3O4的掺入可明显提高Sr-TiO3光催化剂对可见光的吸收,从而增强其光催化性能;在光降解甲基橙的反应中,掺杂10%Fe3O4的SrTiO3光催化剂其催化活性是纯SrTiO3光催化剂的两倍.     

Photocatalytic oxidation of propylene with molecular oxygen over highly dispersed titanium, vanadium, and chromium oxides on silica

Photocatalytic oxidation of propylene with molecular oxygen at room temperature was investigated over various silica-supported metal oxides with low loading. The photocatalytic active site is assumed to be the isolated tetrahedrally coordinated metal oxides in the ligand-to-metal charge-transferred state, such as (Mdelta- -OLdelta+). Photocatalytic epoxidation of propylene into propylene oxide was promoted over silica-supported V and Ti oxides at steady state. Over silica-supported Cr oxide, the propylene oxide formation rate was remarkably decreased with the time course in the reaction. The oxidation state and the coordination environment of the supported Ti, V, and Cr oxide species were determined by diffuse reflectance UV-vis spectroscopy (DRS) and electron spin resonance (ESR). During the photocatalytic oxidation, the oxidation state of the Ti4+ species was not varied. On the other hand, the V5+ species was partially reduced to V4+ and the Cr6+ species was successively reduced to Cr5+ and Cr3+. An isotopic tracer study of the C3H6-18O2 reaction suggests the difference of the active oxygen species between TiO2/SiO2 and V2O5/SiO2. The active oxygen species on TiO2/SiO2 is derived from molecular oxygen. On the other hand, the photogenerated products on V2O5/SiO2 incorporate the lattice oxygen of the surface metal oxide species. It is suggested that the kinds of terminal ligand (hydroxyl or oxo) of the tetrahedrally coordinated metal oxides on silica decide the active oxygen species in the photocatalytic oxidation. A photoinduced hole center on the monohydroxyl (SiO)3Ti-OH species activates molecular oxygen that reacts with propylene. In the case of the monooxo (SiO)3V=O and dioxo (SiO)2Cr=O2 species, the photoactivated lattice oxygen (OL-) directly reacts with propylene.     

制备方法对SrTiO_3可见光光催化活性的影响

采用分步沉积法、溶胶-凝胶法和共沉淀法分别制备了SrTi-F,SrTi-S和SrTi-C三种SrTiO3复合氧化物,XRD,UV-V is,BET,SEM,TEM和EDX对样品进行了表征,并考察了SrTiO3降解亚甲基蓝的可见光光催化活性。结果表明,SrTi-S和SrTi-C样品表现为纯钙钛矿晶相,SrTi-F样品除钙钛矿晶相外还掺杂有少量的Sr2TiO4杂晶相。光催化活性测试表明,SrTi-F表现出最高的活性,其一级反应速率常数是商用P25样品的4.6倍。杂晶相Sr2TiO4的存在有利于SrTiO3复合氧化物光生电子和空穴的传导,可提高催化剂光催化活性。