TiB_2/均相硼掺杂TiO_2核/壳结构提升光催化氧化水产氧活性（英文）

光催化可实现污染物降解、分解水制氢和CO_2还原等多种氧化还原反应,因而受到了广泛关注.光催化材料中光生电荷的数目与氧化还原能力直接影响光催化反应效率,在许多光催化反应中,光生空穴氧化反应被认为速控步骤.以光催化分解水为例,质子的还原是单电子过程,水氧化产生氧气则涉及四个电子.空穴的高能量不仅可赋予其高的氧化能力,还能提高其迁出表面的能力,因此具有重要研究价值.我们组的前期工作表明,以TiB_2作为前驱体,采用水热合成和焙烧两步法可制备出间隙硼掺杂的金红石相或锐钛矿相TiO_2,间隙硼掺杂可显著降低价带顶,提升光催化氧化水产氧性能.然而,在已有的结果中,间隙硼掺杂浓度在TiO_2中均呈现从内向外逐渐增加的梯度分布,这意味着硼掺杂浓度有限,且表层更低的价带顶不利于体相光生空穴向表面迁移,因此亟需实现TiO_2中均相的间隙硼掺杂.本文以湿化的氩气为水解环境,将水解过程限域在TiB_2的表面以减少硼原子流失;同时提高水解温度,使残留的硼原子形成间隙掺杂,避免其在二次焙烧时扩散,从而在TiB_2核的表面所形成的TiO_2壳层中实现均相间隙硼掺杂,显著提高了光催化氧化水产氧活性.多种表征结果表明,直径约为6–10μm的TiB_2核表面形成了厚约400 nm的TiO_2壳层,在TiO_2/TiB_2中TiO_2壳层重量比约为30%,TiO_2壳层中锐钛矿相TiO_2占比为65 wt%,金红石相TiO_2占比为35 wt%.TiO_2壳层中间隙硼为均相分布,硼掺杂显著降低了价带顶位置,提高了光生空穴的氧化能力,从而使得TiB_2/TiO_2展现出比未掺杂的金红石、锐钛矿相及两者混合相的TiO_2均具有更高的光催化氧化水产氧的能力.     

金红石/锐钛矿混晶结构的TiO2薄膜光催化活性

采用磁控溅射法制备出一组金红石/锐钛矿混晶结构的纳米TiO2薄膜催化剂,并通过光催化降解苯酚实验考察该薄膜的催化性能.光催化实验证明,随着催化剂中金红石含量减少,催化剂的光催化活性逐渐提高.X射线衍射(XRD)、X射线光电子能谱(XPS)、表面光电压谱(SPS)和原子力显微镜(AFM)结果表明,催化剂为金红石和锐钛矿混晶结构,并随着金红石含量减少,催化剂的表面羟基(OH)和桥氧(-O-)的含量逐渐增加,而且费米能级逐渐提高.表面羟基和桥氧是有利于光催化的"活性物种";费米能级的提高使TiO2/H2O界面处TiO2的表面带弯增大,导致了价带光生空穴参加光催化反应的几率增大,有效地促进了光生载流子的分离;这些因素是催化剂光催化活性逐渐提高的主要原因.     

金红石/锐钛矿混晶结构的TiO2薄膜光催化活性

采用磁控溅射法制备出一组金红石/锐钛矿混晶结构的纳米TiO2薄膜催化剂,并通过光催化降解苯酚实验考察该薄膜的催化性能. 光催化实验证明, 随着催化剂中金红石含量减少, 催化剂的光催化活性逐渐提高. X射线衍射(XRD)、X射线光电子能谱(XPS)、表面光电压谱(SPS)和原子力显微镜(AFM)结果表明, 催化剂为金红石和锐钛矿混晶结构, 并随着金红石含量减少, 催化剂的表面羟基(OH)和桥氧(—O—)的含量逐渐增加, 而且费米能级逐渐提高. 表面羟基和桥氧是有利于光催化的“活性物种”; 费米能级的提高使TiO2/H2O 面处TiO2的表面带弯增大, 导致了价带光生空穴参加光催化反应的几率增大, 有效地促进了光生载流子的分离; 这些因素是催化剂光催化活性逐渐提高的主要原因.     

光电流法研究TiO2薄膜表面吸附氧对光催化活性的影响

采用溶胶-凝胶法制备了锐钛矿型和金红石型TiO2薄膜, 利用光电流和XPS技术研究了薄膜表面吸附氧对不同晶型TiO2光催化活性的影响. 并通过降解纯的环己烷溶液的实验来评估不同晶型TiO2的光催化活性. 结果表明, 在相同条件下, 锐钛矿型TiO2比金红石型具有明显的光催化活性. 这是由于锐钛矿型TiO2比金红石型TiO2具有较强的吸附氧的能力, 同时其光生电子与空穴的复合率相对较小所致.     

碳和钇共掺杂对混相TiO2光催化性能的影响

TiO2因其毒性低、稳定性高、制备成本低廉而获得广泛应用,特别是作为光催化剂在降解环境污染物方面受到了广泛关注;然而,纯TiO2较大的光生载流子复合率和较宽的带隙限制了其应用.元素掺杂作为一种拓宽光催化剂光吸收能力的方法广泛应用于各种光催化剂的修饰改性,而两种具有光催化性能的TiO2相共存则能有效抑制光生载流子的复合,因此采取合适的方法有效利用这两种TiO2改性的方法制备得到更具实际应用潜质的光催化剂具有一定的可行性.本文通过简单的溶胶-凝胶过程向锐钛矿相与金红石相组成的混相TiO2中共掺杂碳和钇得到了一种活性较高的可见光响应光催化剂.采用粉末X射线衍射、拉曼光谱、X射线光电子能谱和透射电镜等表征手段研究了碳和钇掺杂对TiO2结构的影响,发现碳掺杂有利于金红石相的形成且材料具有更大的晶粒尺寸,钇掺杂则有利于锐钛矿相的形成且能细化材料的晶粒尺寸,提高材料的比表面积,导致材料更好的光催化活性.材料在30 W荧光灯光照条件下的光催化降解亚甲基蓝(MB)性能的研究显示,C-Y-TiO2样品具有比单掺杂和未掺杂样品更高的光催化活性,其顺序为C-Y-TiO2>Y-TiO2>C-TiO2>TiO2≈P25.此外,降解反应动力学研究表明C-Y-TiO2样品光降解MB的速率是未掺杂样品在相同条件下降解速率的3.5倍.不同钇掺杂含量样品的结构和光催化降解MB的研究结果表明,钇掺杂显著促进了锐钛矿相TiO2的形成.这说明钇可能仅掺杂进入锐钛矿相,因此合适的钇掺杂量才能有效形成最优化的光催化性能的混相TiO2.不同热处理温度下获得的样品的光降解MB特性也表明,一定的热处理温度有利于合适的锐钛矿相和金红石相的组成,从而有利于相间的协同效应.紫外-可见光谱和荧光光谱表征分析表明,碳和钇的掺杂都拓展了其吸收光谱到可见光区域,且抑制了光生电子和空穴对的复合,进而提高了材料的光催化活性.碳和钇共掺杂的混相TiO2具有较高可见光光催化活性的主要原因有两个方面:一是元素掺杂减小了TiO2的带隙使得材料具有可见光响应;二是金属和非金属元素在锐钛矿相与金红石相TiO2中不同的掺杂特性形成的协同效应,抑制了光生电子和空穴的复合.     

Eu2O3修饰对纳米TiO2热稳定性及光催化活性的影响

通过浸渍过程实现了Eu2O3对溶胶水热法合成的锐钛矿相TiO2纳米粒子的表面修饰改性.重点研究了表面修饰对纳米锐钛矿相热稳定性及光催化活性的影响.结果表明,Eu2O3表面修饰抑制了锐钛矿相向金红石相的转变,相变温度由550℃左右升高到700℃左右,提高了纳米锐钛矿相TiO2的热稳定性,这与Eu2O3修饰在表面而阻碍了锐钛矿纳米粒子的直接接触有关.与未修饰的TiO2相比,经过700℃高温热处理的Eu2O3修饰的TiO2样品表现出了较高的光催化活性,这与其结晶度提高而有利于光生电荷分离有关.     

具有高光催化活性的黑色TiO2（B）/锐钛矿双晶TiO2-x纳米纤维

高效TiO2基光催化材料的开发一直是催化领域的研究热点,主要的策略是如何有效地分离光生载流子.制备多晶相的TiO2材料可引入异质/相结结构使电子与空穴朝不同方向移动,从而避免电子与空穴复合;另外,在TiO2中掺杂其他金属或非金属也可以有效地降低电子与空穴的复合率,掺杂的元素作为电子捕获阱俘获光生电子,以实现电子空穴的有效分离.近些年,作为一种全新的掺杂剂,氧空穴可以有效改善TiO2的光催化活性,所制TiO2具有可见光的全光谱吸收能力,因此该类TiO2呈现出黑色.通过上述方法均可以制备出高活性TiO2基光催化材料,如果能够将这些方法耦合一起,则可能制备出活性更高的光催化剂.因此,本文将异相结结构和空穴掺杂耦合起来,用多孔钛酸盐衍生物在H2中高温焙烧制得一种全新的黑色TiO2(B)/锐钛矿双晶TiO2–x纳米纤维.不同于其他TiO2基光催化材料,该样品仅由Ti和O元素组成,通过Ti和O元素的组合,形成了双晶结构和空穴掺杂两种特殊的结构,借助场发射(FESEM)、拉曼光谱(Raman)、氮气物理吸脱附、X射线光电子能谱(XPS)、热重(TG)、紫外可见漫反射光谱(UV-Vis)和荧光光谱(PL)等表征分析了样品的结构及其光催化性能间构效关系. FESEM结果显示,黑色TiO2(B)/锐钛矿双晶TiO2–x为长1–5mm、宽0.2mm的纤维结构, Raman结果表明,锐钛矿相在特征波段(140 cm–1左右)和TiO2(B)的特征波段(220–260 cm–1)均发生蓝移,说明该两相中均存在氧空穴;该样表面未检测到Ti3+,因此氧空穴可能分散在TiO2(B)和锐钛矿相的体相中.根据黑色TiO2(B)/锐钛矿双晶TiO2–x和白色TiO2(B)/锐钛矿双晶TiO2的失重差,估算出前者的O/Ti原子比为1.97.光催化降解甲基橙实验结果显示,黑色TiO2(B)/锐钛矿双晶TiO2–x的光催化活性是白色双晶TiO2的4.2倍,锐钛矿TiO2的10.5倍,且连续反应10次后未出现失活现象,显示出了良好的光催化稳定性.前期,我们已经证明了白色TiO2(B)/锐钛矿双晶TiO2由于具有TiO2(B)和锐钛矿的异相结结构,致使其电子空穴有效地分离,从而表现出优异的光催化活性;本文的PL结果显示,由于氧空穴的引入,异相结与氧空穴两者共同作用,进一步促进了黑色TiO2(B)/锐钛矿双晶TiO2–x电子与空穴的有效分离,因此黑色TiO2(B)/锐钛矿双晶TiO2–x表现出高的光催化活性.由于其特殊的结构,黑色TiO2(B)/锐钛矿双晶TiO2–x纳米纤维将在环境与能源领域表现出良好的应用前景.     

尿素为氮源N-TiO2的制备、表征及光催化性能

以钛酸丁酯为前驱体,以尿素为氮源,采用溶胶-凝胶法制备了不同N含量的TiO2光催化剂(N-TiO2).通过X-射线衍射(XRD)、紫外-可见吸收光谱(UV-Vis)、分子荧光光谱(PL)、X-射线光电子能谱(XPS)等检测手段对其结构和物理性能进行了表征.结果表明,N的掺杂能抑制锐钛矿相TiO2向金红石相的转化,能将TiO2的吸收边波长拓宽到可见光区域,能加速光生电子-空穴对的分离,提高光催化活性.在以可见光为光源进行重铬酸钾的光催化还原和苯酚的光催化氧化反应中,9%N-TiO2-500表现出了最强的光催化活性,且在光催化活性的稳定性实验中,表现出良好的光催化活性的稳定性,能多次重复使用.     

硼铈共掺杂纳米TiO2光催化降解三氯杀螨醇和菊酯类农药

采用溶胶-凝胶法在钛酸丁酯水解过程引入硼酸、硝酸铈,制备具有光催化活性的硼铈共掺杂纳米二氧化钛（TiO2）,经XRD、TEM、FT-IR、UV-Vis-DRS表征晶体结构,在日光灯照射下,光催化降解三氯杀螨醇、高氟氯氰菊酯、氟戊菊酯农药。结果表明：硼铈共掺杂的TiO2只有锐钛矿型,而纯的或掺铈的TiO2有含有锐钛矿型、金红石相和少量板钛矿型,UV-Vis-DRS测定结果表明硼铈共掺杂的TiO2禁带宽度变小,硼铈共掺杂的TiO2在可见光区吸光度高于掺杂铈和不掺杂的TiO2,在420nm~850nm有强的吸收;在同样光照下对三氯杀螨醇、高氟氯氰菊酯、氟戊菊酯的降解试验证明硼铈共掺杂纳米TiO2的光催化活性高于不掺杂或只掺杂铈的TiO2。     

稀土金属掺杂对锐钛矿型TiO2光催化活性影响的理论和实验研究

从理论和实验两方面探讨稀土金属掺杂对锐钛矿型TiO2光催化活性的影响.理论上采用基于密度泛函理论(DFT)的第一性原理,对稀土掺杂TiO2前后的几何结构、能带结构、态密度及电子结构进行了系统的研究.结果表明,Y,La,Gd,Lu,Ce,Eu,Yb和Tb掺杂有助于TiO2光催化活性的提高;而对于Pr,Nd,Pm,Sm,Dy,Ho,Er和Tm掺杂,由于在价带顶和导带底之间形成了较多的可能成为光生电子和空穴的复合中心的杂质能级,故此类稀土的掺杂浓度需要控制在较小的范围内.另一方面,采用溶胶-凝胶法制备了9种稀土金属(RE=Y,Ce,Pr,Sm,Gd,Dy,Ho,Er,Yb)掺杂的TiO2粉体,运用X射线衍射(XRD)和紫外-可见光谱法(UV-Vis)分别表征其晶体结构和光学吸收性质.结果表明,掺杂前后的TiO2均为锐钛矿相,且Ho,Pr,Ce,Sm,Y,Yb和Gd掺杂使TiO2在可见光区的吸收有不同程度的提高.理论预测与实验结果基本一致,且理论研究结果与周期表中稀土元素外层电子轨道排布规律一致,从而揭示了稀土元素掺杂的本质规律,指明了适量的稀土掺杂有利于TiO2光催化活性的提高.     

Mechanistic studies of the photocatalytic oxidation of trichloroethylene with visible-light-driven N-doped TiO2 photocatalysts

Visible-light-driven TiO2 photocatalysts doped with nitrogen have been prepared as powders and thin films in a cylindrical tubular furnace under a stream of ammonia gas. The photocatalysts thus obtained were found to have a band-gap energy of 2.95 eV. Electron spin resonance (ESR) under irradiation with visible light (lambda > or = 430 nm) afforded the increase in intensity in the visible-light region. The concentration of trapped holes was about fourfold higher than that of trapped electrons. Nitrogen-doped TiO2 has been used to investigate mechanistically the photocatalytic oxidation of trichloroethylene (TCE) under irradiation with visible light (lambda > or = 420 nm). Cl and O radicals, which contribute significantly to the generation of dichloroacetyl chloride (DCAC) in the photocatalytic oxidation of TCE under UV irradiation, were found to be deactivated under irradiation with visible light. As the main by-product, only phosgene was detected in the photocatalytic oxidation of TCE under irradiation with visible light. Thus, the reaction mechanism of TCE photooxidation under irradiation with visible light clearly differs markedly from that under UV irradiation. Based on the results of the present study, we propose a new reaction mechanism and adsorbed species for the photocatalytic oxidation of TCE under irradiation with visible light. The energy band for TiO2 by doping with nitrogen may involve an isolated band above the valence band.     

Electronic basis of visible region activity in high area Sn-doped rutile TiO2 photocatalysts

The influence of Sn doping on the anatase-to-rutile phase transition has been investigated in high area powders prepared by a sol-gel route involving alkoxide precursors. Sn doping facilitates conversion of anatase to rutile at lower temperatures than observed for undoped material. At the same time Sn-doping inhibits sintering as gauged by line widths in X-ray diffraction and gas-adsorption surface area measurements. These observations are linked to the finding of pronounced segregation of Sn to the surface of rutile TiO(2) observed in X-ray photoemission spectra. Sn-doped TiO(2) is found to exhibit enhanced visible region photocatalytic activity as compared with undoped material in dye degradation experiments. This is attributed to narrowing of the bulk bandgap at low doping levels coupled with the introduction of surface states associated with segregated Sn ions in the divalent state. The Sn(II) surface states lie above the top of the main valence band and can therefore act as trapping sites for holes produced under photoexcitation.     

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.     

Effects of molybdenum substitution on the photocatalytic behavior of BiVO4

Transition metal doping has always suffered from the disadvantage of reduction of photocatalytic activity because the dopant ions can form a discrete level in the forbidden band of the photocatalyst resulting in low mobility of electrons and holes in the dopant level and thus lowered activity. However, in this study the photocatalytic activity of an efficient visible-light sensitive photocatalyst, BiVO4, for water oxidation or organic compound degradation was found to be remarkably enhanced by molybdenum doping. The role of molybdenum doping in enhancing the photocatalytic activity of BiVO4 was investigated and discussed based on the changes of the surface acidity of the photocatalyst.     

Surface treatment of silicon carbide using TiO2(IV) photocatalyst

Silicon carbide (SiC) and diamond were decomposed to CO(2)(g) by the photocatalysis with TiO(2) at room temperature, although the decomposition rate of diamond was very slow. According to the XPS spectra of Si2p on the SiC surface, SiO(2) was simultaneously formed on the surface by the TiO(2) photocatalysis. The thickness of the SiO(2) formed on the SiC surface during the photocatalytic oxidation for 1 h was estimated to be about 40 A from the depth profile of the XPS spectra using Ar etching. The SiC surface was oxidized by the TiO(2) photocatalysis even under the condition without a direct contact with the TiO(2). This indicates that the photocatalytic oxidation of the SiC occurs due to active oxygen species photogenerated on the TiO(2) surface, but not by hole produced in the valence band of the TiO(2). Moreover, a remote surface treatment system using the quartz beads coated with TiO(2) was developed for the SiC surface oxidation. Consequently, the TiO(2) photocatalysis will be very useful for the surface treatment of SiC such as photopatterning without defects and damage to the substrate because the photocatalytic reaction is carried out under mild conditions.     

An N,N'-dialkyl-4,4'-bipyridinium-modified titanium-dioxide photocatalyst for water remediation - observation and application of supramolecular effects in photocatalytic degradation of p-donor organic compounds

The photocatalytic activity of TiO2 (Degussa P-25) modified with a 4,4'-bipyridinium monolayer (V2+-TiO2) has been compared with that of conventional TiO2-P-25 by investigating the efficiency of degradation of a series of four organic model compounds with increasing pi-donor capacity (2,4-xylidine, 2,4-dimethylphenol, hydroquinone, and dimethylhydroquinone). As far as the mechanism of the first oxidation reaction is concerned, evidence for the formation of supramolecular donor-acceptor complexes with the bipyridinium units at the semiconductor surface was obtained by comparison of the Langmuir-adsorption characteristics and the efficiencies of photodegradation of the different substrates. Furthermore, the main intermediates of the photocatalytic degradation of 2,4-xylidine were identified, and the presence of 2,4-dimethylphenol indicates that the main pathway of substrate oxidation proceeds via electron transfer from the adsorbed organic substrate to the "holes" within the valence band of the photoexcited semiconductors V2+-TiO2 and TiO2. The efficiencies of photocatalytic degradation by both V2+-TiO2 and TiO2 were limited by the trapping efficiency of the conduction band electrons by molecular oxygen.     

氟离子掺杂和吸附对二氧化钛光催化活性的影响

已有文献报道,在二氧化钛的体相和表面分别掺杂和吸附氟离子,都能加快水中有机化合物的光催化降解.前者归结于表面形成的三价钛离子促进光生载流子分离,后者归结于双电层中的氟离子促进羟基自由基脱附.但是,有关它们之间的活性差异未见有文献报道.本文采用水热法,以钛酸丁酯和氟化铵为原料,合成出具有不同氟离子掺杂量的光催化剂.通过苯酚降解反应,研究氟化钠和硝酸银外部加入对这些催化剂光催化性能的影响.结果表明:无论是处于二氧化钛的体相,还是处于二氧化钛的双电层外层和内层,这些氟离子都能促进苯酚的光催化降解.但是,它们的相对活性依次降低.此外,在催化剂的水悬浮液中,同时加入硝酸银和氟化钠,能进一步加快苯酚的光催化降解,且该反应的速率远远大于单独加入氟化钠或硝酸银时的速率总和.这说明将导带电子的还原过程和价带空穴的氧化过程耦合起来,是提高二氧化钛光催化量子效率的有效途径.     

The role of crystal phase in determining photocatalytic activity of nitrogen doped TiO2

Two series of nitrogen doped TiO(2) samples with different ratios of anatase to rutile phases were prepared by milling the mixture of P25 TiO(2) and C(6)H(12)N(4) in air and gaseous NH(3) atmosphere, respectively. Compared to air, NH(3) atmosphere plays an important role in delaying the crystallite transformation from anatase to rutile in the mechanochemical reaction of TiO(2) and C(6)H(12)N(4). In contrast to the previously reported results for pure TiO(2), it is found that nitrogen doped TiO(2) with higher content of rutile phase demonstrates higher photocatalytic activity in photodegrading pollutant Rhodamine B under both UV light and visible light irradiation (lambda>420 nm), and the amount of the surface-adsorbed water and hydroxyl groups on nitrogen doped TiO(2) have little correlations with their crystallite phases (anatase or rutile) and photocatalytic activity. The more abundant surface states characterized by photoluminescence spectroscopy together with the lowered valence band maximum of rutile TiO(2) by nitrogen doping are considered as the key factors for the higher activity of nitrogen doped TiO(2) with higher content of rutile phase.     

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.