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Effects of doping of metal cations on morphology, activity, andvisible light response of photocatalysts参杂金属阳离子对光催化剂的形态，活性，对光的回应的影响Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japanb Core Research Evolutional Science and Technology, Japan Science and Technology Agency (CREST/JST), Japan应用化学系，理学院，东京大学的科学，1-3神乐坂，新宿区，东京162-8601，日本B核心科学与技术演进的研究，日本科学技术振兴机构（顶/日本时间），日本Received 23 March 2007; accepted 23 July 2007Available online 28 July 20072007年3月23日收到，2007年7月23日接受，2007年7月28日在网上提供摘要 Effects of doping of metal cations into wide band gap semiconductor photocatalysts on morphology, visible light response, and photocatalyticperformance were studied.金属离子对宽带隙半导体光催化剂的形态，可见光感特性和光催化性能的影响的研究Doping of lanthanide and alkaline earth ions improved activity of a NaTaO3 photocatalyst for water splitting.镧系元素和碱土金属离子掺杂提高了NaTaO3光催化剂对水的分解的活性Lanthanum was the most effective dopant. The NaTaO3:La with a NiO cocatalyst gave 56% of a quantum yield at 270 nm.镧掺杂剂是最有效的。NaTaO3与一氧化镍助催化剂在270纳米提高了56的量子产率This remarkable photocatalytic activity was brought by formations of nano-crystalline particle and surface nano-step structure by the doping这显著的光催化活性是由纳米晶体颗粒表面纳米结构的一步编队所带来的On the other hand, metal cation doping into ZnS, TiO2, and SrTiO3 gave visible light responses for H2 or O2 evolution from aqueous solutions containing of sacrificial reagents.另一方面，硫化锌，二氧化钛和钛酸锶的金属阳离子的参杂对包含献祭试剂的水溶液分解成氢气和氧气的响应The visible light responses were due to the electronic transition from donor levels formed with dopants to conduction bands of the host photocatalysts可见光响应的原因是电子跃迁从参杂过的施主能级到光催化剂传导带Codoping was effective to compensate charge unbalance brought by doping of transition metal cations, resulting in the improvement of visible light response for photocatalytic reactions.共掺杂对补偿不平衡的过渡金属离子，掺杂是有效的，引起光催化反应的可见光响应改善Among the transition metal-doped photocatalysts, SrTiO3 doped with Rh (SrTiO3:Rh) was the novel metal oxide photocatalyst that produced H2 under visible light irradiation.在过渡金属掺杂的光催化剂，参杂了铑（钛酸锶：铑）的钛酸锶是一种新型金属氧化物型的光催化剂，可以在可见光照射的情况下产生氢气The SrTiO3:Rh photocatalyst was employed with O2 evolution photocatalysts such as BiVO4 and WO3 for construction of Z-scheme systems that were active for water splitting into H2 and O2 under visible light irradiation.钛酸锶：铑光催化剂发展为用于氧气的制备，例如BiVO4和WO3用于Z型计划体制建设，水在可见光照射下分解成氢气和氧气的催化剂2007 Elsevier B.V. All rights reserved.2007年爱思唯尔B.诉保留所有权利1. IntroductionPhoton energy conversion reactions using semiconductorelectrodes 17 and powdered photocatalysts 825have been extensively studied since the HondaFujishimaeffect 26 was reported. Efficient water splitting into H2and O2 using a powdered photocatalyst is attractivebecause it can be a clean and simple process for H2 productionusing a natural energy. Water splitting utilizing solarlight, that is called solar hydrogen production, is thefinal target in the present research field.1 简介光子能量转换用半导体反应电极1-7和粉状催化剂8-25已被广泛研究，因为本田藤岛效应26的报道。水使用粉末光催化剂高效分解成氢气和O2是有吸引力的因为它可以是一个H2的清洁生产，工艺简单,使用自然能源。利用太阳能分解水光，这被称为 太阳能产氢，是在目前的研究领域最终的目标。* Corresponding author. Address: Department of Applied Chemistry,Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka,Shinjuku-ku, Tokyo 162-8601, Japan. Tel.: +81 35228 8267; fax: +8135261 4631.E-mail address: a-kudors.kagu.tus.ac.jp (A. Kudo).*通讯作者。地址：应用化学系，理学院，东京理科1-3神乐坂大学新宿区，东京162-8601，日本。电话：。+81 35228 8267传真：+8135261 4631。E - mail地址：a-kudors.kagu.tus.ac.jp（答：工藤）。Many metal oxide photocatalysts have been reported for water splitting so far. The present authors have found many niobate and tantalate photocatalysts 19,20,25.Some metal oxide photocatalysts such as NaTaO3 show high activities for water splitting although they work only under UV irradiation because of their wide band gaps. Domen and coworkers have reported water splitting using metal (oxy)nitride photocatalysts that are nonoxide materials 21,23,24. Water splitting under visible light irradiation has been achieved by some photocatalyst systems 16,18,21,24. However, the efficiencies are not satisfying. Development of new photocatalyst materials is still animportant topic.至今有分解水方面有许多报道金属氧化物光触媒。本文作者发现有很多钽铌酸和光触媒19,20,25。有些人，如NaTaO3光表现出较高的对水的分裂活动尽管它们在紫外光照射下工作，不仅是因为他们的宽带隙金属氧化物催化剂。 Domen和同事报告了光催化剂分解水制氢是利用氮化物非氧化物材料21,23,24金属（氧）。在可见光照射下水分也被一些分裂光触媒系统实现16,18,21,24。但是，效率并不令人满意。新型光触媒材料开发仍是一个重要的课题。Photocatalytic activities are affected by particle size,crystallinity, surface properties, etc. These factors are controlled by changes in a preparation method, loading of acocatalyst, and introducing a foreign element. Doping of a foreign element into a photocatalyst is one of the strategies that can affect the morphology (particle size and surface structure) of photocatalyst particles. On the other hand, doping of transition metal cations into photocatalysts with wide band gaps such as TiO2 and SrTiO3 hasbeen studied for a long time in the research field of photoelectrochemistry and photocatalysis in order to modify electronic structure and develop materials with visible light responses 2734. However, doping is regarded as an unsuitable method because photocatalytic efficiencies drastically decrease in many cases, even if visible light absorption bands are obtained. Recently, anion doping of nitrogen, sulfur, and carbon has been extensively investigated 3538.光催化活性受颗粒大小，结晶度，表面特性等影响，这些都是由制备方法引起变化的因素，装载助催化剂，并引入外来因素。使用光催化剂是其中一种策略，可以影响催化剂粒子的形貌（颗粒大小和表面结构）之一。另一方面，过渡金属离子掺杂宽禁带的光催化剂，如二氧化钛和钛酸锶在被研究的光电化学和光催化研究领域有很长一段时间，以便修改电子结构和发展与可见光响应材料27-34。然而，掺杂被认为是一种不适合的方法，因为光催化效率大大降低，在许多情况下，甚至可以吸收可见光波段获得。最近，阴离子掺杂氮，硫，碳被广泛的研究35-38。The present review paper introduces the improvement of the activity of a NaTaO3 photocatalyst by doping lanthanum and alkaline earth metals. Development of visible light-driven photocatalysts by doping of metal ions into ZnS, TiO2, and SrTiO3 of wide band gap semiconductor photocatalysts is also reported. In the present paper, dopingmeans the substitution of dopants for metal cations of the host materials at crystal lattice points. The amounts of dopants are quite large (0.14%).本次审查介绍掺杂镧和碱土金属的一NaTaO3光催化活性的提高。可见光光驱动发展的催化剂，金属离子进入硫化锌，二氧化钛和宽禁带半导体光催化剂钛酸锶掺杂也有报道。在本文件中，掺杂指掺杂在主体材料为金属离子在晶格点替代。对掺杂的数额是相当大（0.1-4）。2. Highly efficient water splitting using NiO-loaded NaTaO3 photocatalysts doped with lanthanum and alkaline earth metal ions 39,402。高效分解水用镧和碱土金属离子掺杂氧化镍负载NaTaO3光催化剂39,40NaTaO3 loaded with a NiO cocatalyst is a highly active photocatalyst for water splitting 41. In general, photocatalytic activities are increased when the particle size becomes small and highly crystalline 4244. Therefore, the authors tried to reduce the particle size of the NaTaO3 photocatalyst by doping. Fig. 1 shows SEM photographs of nondoped and La-doped NaTaO3. The particle size of Ladoped NaTaO3 was 0.10.7 lm while that of nondoped NaTaO3 was 23 lm. The particle sizes of NaTaO3 also became small by doping of Ca, Sr, and Ba. The surface of nondoped NaTaO3 was smooth whereas La-doped NaTaO3 particles had surface nanostructure with steps of315 nm. It was also observed for Ca-, Sr-, and Ba-doped NaTaO3. Thus, the doping of La, Ca, Sr, and Ba affected the morphology of the NaTaO3 particle. This effect wasdue to the difference in ionic radii between dopants and Na cation 45. Ionic radii of La3 , Ca2 , Sr2 , and Ba2 are 1.50, 1.48, 1.58, and 1.75 A in 12-coordination, respectively. Those values are similar to an ionic radius of Na (1.53A ). On the other hand, in six-coordination, ionic radii of La3 , Ca2 , Sr2 , and Ba2 are 1.17, 1.14, 1.32, and 1.49A , respectively. Those values are smaller than the ionic radius of Ta5 (0.78A ). Therefore, Na in NaTaO3, an A site in perovskite structure, is replaced with those dopants. Crystalline and fine particles, and surface nanostep structure were formed by suppression of crystal growth due to distortion of local structure. These effects were not observed for Mg-doping一氧化镍是一种助催化剂NaTaO3与一氧化镍光分解水的41高活性催化剂。一般情况下，光催化活动增加时，粒径变小，高度结晶42-44。因此，笔者试图减少兴奋剂方面的NaTaO3光催化剂粒子的大小。图。 1显示nondoped和La掺杂NaTaO3光扫描电镜照片。该Ladoped NaTaO3光粒径为0.1-0.7流明的nondoped NaTaO3光而为2-3流明。 NaTaO3光粒子的大小也变小了钙，锶，钡和掺杂。对nondoped NaTaO3光表面光滑而掺镧NaTaO3光颗粒的表面纳米结构的步骤3-15纳米。另据观察钙，锶，钡和掺杂NaTaO3光。因此，镧，钙，锶，钡和影响了NaTaO3光粒子形貌掺杂。这种效应是由于在与钠离子之间掺杂离子半径差异45。镧离子半径，钙，锶，钡和是1.50，1.48，1.58，1.75和12 -协调，分别。这些价值观是相似的安娜（1.53A）离子半径。另一方面，在六协调，镧，钙，锶，钡离子半径和1.17，1.14，1.32和1.49A，分别。这些值均高于Ta5（0.78A）的离子半径较小。因此，在NaTaO3光钠，钙钛矿结构中A位，被替换的掺杂剂。晶和细颗粒物和表面nanostep结构，形成了由晶体生长的抑制由于局部结构的扭曲。这些影响并没有观察到镁兴奋剂。Table 1 shows photocatalytic activities for water splitting on La-, Ca-, Sr-, and Ba-doped NaTaO3. The activity of NaTaO3 was increased by La-, Ca-, Sr-, and Ba-dopingand was drastically improved by NiO-loading. The NiO cocatalyst works as a H2 evolution site. La-doped NaTaO3 with the NiO cocatalyst showed the highest activity. The apparent quantum yield of this photocatalyst was 56% at 270 nm. Vigorous evolution of bubbles of H2 and O2 was observed using a 200-W XeHg lamp.表1显示了水对镧，钙，锶，钡和掺杂NaTaO3光催化分裂活动。 NaTaO3光活性的增加腊，钙，锶，钡和兴奋剂并大幅提高了NiO的加载。而NiO助剂工程作为产氢的网站。镧掺杂的NiO助剂NaTaO3光具有最高的活性。这种光催化剂的表观量子效率为56，至270纳米。氢气和氧气的蓬勃发展，观察气泡用200瓦氙汞灯Table 2 shows H2 or O2 evolution from aqueous solutions containing of sacrificial reagents on La-, Ca-, Sr-, and Ba-doped NaTaO3 photocatalysts. The photocatalyticactivities of the H2 and O2 evolution were increased 1.21.3 and 34 times by doping, respectively. This result suggests that the doping mainly affects the formation of O2 evolution sites表2显示了氢气或氧气从上镧，钙，锶，钡和掺杂NaTaO3光催化剂牺牲试剂含水溶液的演变。光催化氢气和氧气的演化活动分别增加了兴奋剂1.2-1.3和3-4倍。这一结果表明，掺杂主要影响析氧地盘平整工程。TEM and SEM observation revealed that PbO2 was oxidatively photodeposited on grooves of the surface nanostep structure by the reaction of Pb2+ with photogeneratedholes. This result indicates that the grooves work as oxidation sites for photocatalytic reactions. On the other hand, EXAFS analyses of nickel indicate that the NiO cocatalystwas loaded on the surface like a cluster. The nickel oxide species were detected on the edge and flat surface by TEMEDS, except for grooves, as shown in Fig. 2. Theedges and grooves on the surface nanostep structure work as reduction and oxidation sites for photocatalytic reactions, respectively. The separation of the reduction sitefrom the oxidation site is important to achieve water splitting of an uphill reaction to suppress a backward reaction to form H2O from H2 and O2. The surface nanostep structure contributes to the formation of the separated reaction sites.TEM和SEM观察发现，氧化photodeposited二氧化铅是对受铅反应槽+表面nanostep结构与光生孔。这一结果表明，作为光催化反应槽氧化用地。另一方面，镍的EXAFS分析表明，氧化镍助剂像装上了一个群集的表面。氧化镍物种的边缘检测和透射电镜- EDS的平面上，除槽，如图所示。 2。该沟槽边缘和表面上nanostep为减少和光催化氧化反应结构的工作地点分别。该网站的分离减少从氧化网站重要的是要实现水资源的上坡反应的分裂抑制落后反应，形成水的氢气和氧气。表面nanostep结构有助于分离反应位点的形成。Thus, the photocatalytic activity for water splitting of NaTaO3 was significantly improved by La-, Ca-, Sr-, and Ba-doping. It is due to the formation of highly crystalline fine particles and surface nanostep structure in which a H2 evolution site is separated from an O2 evolution site因此，镧，钙，锶，钡和催化剂对水的NaTaO3光催化分解活性显着提高了。这是由于高结晶细颗粒和表面结构，其中一nanostep H2的进化是从一个网点的网点分离析氧的形成。3. Visible light response of doping photocatalysts3。可见光响应光催化剂的掺杂3.1. Design of visible light driven photocatalysts by doping of metal ions 193.1。可见光的金属离子掺杂光催化剂驱动设计19The band structure, in which the bottom of a conduction band level is more negative than a redox potential of H+/H2 (0 V vs. NHE) and the top of a valence band is more positive than a redox potential of O2/H2O (1.23 V vs. NHE), is required for water splitting into H2 and O2 by semiconductor photocatalysts. Valence band levels ofmetal oxide photocatalysts with d0 or d10 configuration are too positive (ca. 3 V vs. NHE) compared with the redox potential of O2/H2O. Therefore, the band gaps of photocatalysts for water splitting are inevitably wider than 3 eV. These photocatalysts respond to only UV. Making new valence bands or electron donor levels above thevalence band consisting of O2p orbitals (band engineering) is indispensable to develop visible light-responsive photocatalysts. If a dopant forms an electron donor level in the band gap of a host semiconductor photocatalyst, the photocatalystmay show visible light response as shown in Fig. 3. This idea is also applied to metal sulfide photocatalysts such as ZnS with UV response. Visible-active photocatalystsobtained by doping are presented in the following.该能带结构，其中一个是导带底水平比氧化还原电位负的H + /氢气（向0 V对比NHE的）和一价带顶比一个更积极的O2/H2O氧化还原电位（1.23 V对NHE），是需要水为H2和O2分裂的半导体光催化剂。价带水平D10的配置与d0或金属氧化物催化剂是太积极（约3伏对NHE的），而对O2/H2O氧化还原电位。因此，光催化剂分解水的带隙宽度大于3 eV的必然。这些只紫外线光催化剂反应。使上述新价带或电子施主能级价带O2p轨道（带工程）组成的发展是必不可少的可见光响应光催化剂。如果掺杂形式在一台主机带隙的半导体光催化剂的电子供体的水平，光触媒可能会出现明显的光响应，如图所示。 3。这种思想也适用于金属硫化物光催化剂反应，如与紫外线硫化锌。可见光活性光催化剂掺杂，得到的列于下。3.2. Visible light response of ZnS photocatalysts doped with metal ions 46483.2。可见与金属离子掺杂的ZnS光催化剂的光响应46-48Metal ion doping into oxide photocatalysts has beenextensively studied, but not for sulfide photocatalysts. A ZnS photocatalyst with a wide band gap (3.6 eV) has a highconduction band. It shows high activity for H2 evolution without any assistance of cocatalysts such as Pt in the presence of a sacrificial reagent 42. The authors have tried to dope metal cations into the ZnS photocatalyst to make it visible light responsive. Fig. 4 shows diffuse reflectance spectra of Cu-, Ni-, and Pb-doped ZnS. Visible light absorption band tails were obtained in addition to the band gap absorption band of the ZnS host. These metal cationdoped ZnS photocatalysts showed activities for H2 evolution from aqueous solutions containing of S2 and/or SO2 3 of electron donors as shown in Table 3. Loading of cocatalysts such as Pt was not necessary for the H2 evolution, indicating that the high conduction band of the ZnS host was maintained after the doping of metal cations.金属氧化物催化剂离子掺杂进了beenextensively研究，但没有硫化物光催化剂。一个有宽禁带的ZnS光催化剂（3.6 eV）的具有高 导带。这表明高，如没有任何铂在一个牺牲试剂的存在42 cocatalysts援助产氢活性。笔者尝试进入到涂料的ZnS光催化剂金属离子，使其可见光响应。图。 4显示弥漫性铜，镍，铅掺杂的ZnS的反射光谱。可见光吸收带尾，获得除带隙的ZnS基质吸收带。这些金属的ZnS光催化剂cationdoped显示，产氢活性的研究S2和/或电子供体，如表3所示，3个含有二氧化硫的水溶液。如装载的cocatalysts铂没有必要的，而H2演变，表明了硫化锌举办高导带后的金属离子掺杂维持。Thus, it was found that metal cation doping was effective for visible light response of metal sulfide photocatalysts因此，人们发现，金属离子掺杂的金属硫化物对可见光光催化剂的光反应有效。3.3. Photocatalytic activities of transition metal-dopedSrTiO3:Rh 493.3。光催化活性过渡金属SrTiO3：铑49Although SrTiO3 with 3.2-eV band gap can not absorb visible light, SrTiO3 powders doped with Rh, Ir, Ru, and Mn possess absorption bands in a visible light region as shown in Fig. 5. These doping photocatalysts showed activities for H2 or O2 evolution from aqueous solutions with sacrificial reagents as shown in Table 3. Rh-doped SrTiO3showed the highest activity among oxide photocatalysts for H2 evolution. Fig. 6 shows an action spectrum the SrTiO3:Rh photocatalyst, and diffuse reflectance spectra before and after the H2 evolution reaction. The color was changed from dark purple to yellow during the photocatalytic reaction. At the same time, the intensities of an absorption bands around 580 and 1000 nm decreased while that around 450 nm increased. These changes in the spectrum and color were observed during an induction period of the photocatalytic H2 evolution. These results indicate that doped Rh species with high oxidation numbers was reduced to Rh3+ by photogenerated electrons at the beginningstage of the photocatalytic reaction. The onset of the action spectrum agreed with that of diffuse reflectance spectrum after the photocatalytic reaction, indicating that the photocatalytic H2 evolution proceeds with excitation from an electron donor level consisting of Rh3+ to the conduction band of the SrTiO3 host. This SrTiO3:Rh photocatalyst plays an important role on a Z-scheme photocatalyst system for water splitting under visible light irradiation as mentioned in Section 4.虽然与3.2 - eV的带隙不能吸收可见光，钛酸锶粉体铑，铱，钌掺杂和Mn具备可见光区的吸收带，如图所示钛酸锶。 5。这些掺杂光催化剂显示，氢气或氧气与演化的活动，如表3所示牺牲试剂水溶液。铑钛酸锶掺杂表明，H2的进化的氧化物光催化剂活性最高。图。 6显示了一个行动谱钛酸锶：铑催化剂，和漫反射光谱之前和之后的产氢反应。颜色呈暗紫色改为黄色，在光催化反应。与此同时，约580和1000 nm处的吸收峰强度的下降而增加约450纳米。在频谱和颜色，观察这些变化过程中的光催化产氢诱导期。这些结果表明，掺铑高氧化数种减少到Rh3 +的光生电子在一开始光催化反应阶段。该行动开始就此与光谱漫反射光谱光催化反应后，表明激发的光催化产氢与从电子供体水平的收益组成的Rh3 +对钛酸锶主机的导带。这钛酸锶：铑催化剂起着可见光照射下，如第4条所述的一种分解水的Z -计划催化剂体系的重要作用。3.4. Effect of codoping on photocatalytic activities of TiO2 and SrTiO3 doped with transition metals 50533.4。对二氧化钛光催化活性，并与过渡金属掺杂钛酸锶共掺杂效应50-53The successful example of the SrTiO3:Rh photocatalyst in which visible light response was obtained by transition metal doping was introduced above. However, in most cases, transition metal doping results in a drastic decrease in photocatalytic activities because the dopants work as recombination sites between photogenerated electrons and holes. In contrast to this common sense, the authors developed a TiO2:Rh/Sb photocatalyst with visible light response 50. The special feature of this photocatalyst is codoping Sb with Rh. Fig. 7 shows dependence of photocatalytic O2 evolution from an aqueous silver nitrate solution on TiO2:Rh/ Sb upon the ratio of doped Sb to Rh. When only Rh was doped into TiO2 no activity was obtained. TiO2:Rh without codoping of Sb contained Rh4+ because Rh was doped at a Ti4+ site. The Rh4+ species predominantly works as a recombination site. As the ratio of codoped Sb increased,the formation of Rh4+ was suppressed. Codoping with Sb5+ produces Rh3+ forming an electron donor level, due to keeping of the charge balance. The same dependencywas observed for a TiO2:Cr/Sb photocatalyst 51. Fig. 8 shows the dependency of photocatalytic O2 evolution on TiO2:Rh(1.3%)/Sb(2.6%) upon cutoff wavelength of theincident light and a diffuse reflectance spectrum. The