The effect of group IIIA metal ion dopants on the photocatalytic activities of nanocrystalline Sr0.25H1.5Ta2O6·H2O

A series of group IIIA metal ion electron acceptors doped into Sr(0.25)H(1.5)Ta(2)O(6)·H(2)O (HST) samples have been prepared by an impregnation and calcination method for the first time. The samples are characterized by XRD, TEM, DRS and XPS. The variations in the electronic structure and photoelectric response after metal ion doping are investigated by theoretical calculations and photocurrent experiments, respectively. Results show that the metal ions can be efficiently incorporated into the HST crystal structure, which is reflected in the lattice contraction. Meanwhile, the photoabsorption edges of the metal-doped HST samples are red shifted to a longer wavelength. Taking into account the ionic radii and electronegativities of the dopants, as well as the XRD and XPS results, it is concluded that Ta(5+) ions may be partially substituted by the Al(3+) and Ga(3+) ions in the framework, while In(3+) ions are the favourable substitutes for Sr(2+) sites in the cavity. The first-principles DFT calculations confirm that the variation of the band structure is sensitive to the type of group IIIA metal ion. Introducing the dopant only at the Ta site induces an obvious variation in the band structure and the band gap becomes narrow. Meanwhile, an 'extra step' appeared in the band gap, which can trap photogenerated electrons from the valance band (VB) and could enhance the charge mobility and the photocurrent. For the photocatalytic degradation of methyl orange in an aqueous solution and in benzene in the gas phase, the doped samples show superior photocatalytic activities compared with both undoped samples and TiO(2). The enhanced photocatalytic activities can be well explained by their electronic structure, photoabsorption performance, photoelectric response, and the concentration of the active species. Due to the fact that Ga ion doping can create an acceptor impurity level and change the electronic band, efficiently narrowing the band gap, the Ga-doped sample shows the highest photocatalytic activity.     

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.     

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.     

Ce-doped ZnO (Ce(x)Zn(1-x)O) becomes an efficient visible-light-sensitive photocatalyst by co-catalyst (Cu2+) grafting

We have fabricated an efficient visible-light-sensitive Cu(2+)-grafted Ce-doped ZnO photocatalyst (Cu(2+)-Ce(x)Zn(1-x)O) by adopting a metal ion doping and co-catalyst modification. Impurity states were formed below the conduction band (CB) edge in Ce(x)Zn(1-x)O, and these impurity states induce the visible-light absorption. Ce(x)Zn(1-x)O without a Cu(2+)-co-catalyst showed negligible visible-light activity due to the low reduction power of electrons in impurity levels. Surprisingly, Cu(2+)-modification over Ce(x)Zn(1-x)O drastically increased its visible-light activity. Excited electrons in impurity states can transfer to the Cu(2+)-ions on the surface and form Cu(2+)/Cu(+) redox couples, which cause the efficient oxygen reduction through a multi-electron reduction process. One of the striking features of the present study is that the metal doped semiconductors which were inactive due to their impurity states become efficient visible-light photocatalysts upon co-catalyst modification. The successful strategy used here for designing a highly active visible-light photocatalyst would provide numerous opportunities to develop an efficient metal-ion based visible-light photocatalyst.     

Ag/TiO2光催化氧化还原反应脱除水体中无机氮

采用光催化还原法制备了高活性的载银二氧化钛光催化剂,并用XRF、TEM、XRD及XPS、UV-Vis方法对催化剂进行了表征.考察了负载Ag的含量、催化剂制备时间、搅拌气体的种类以及Fe²⁺的添加等条件对该催化剂光催化水体脱氮活性的影响.结果表明:载银量1.0%时去除效果最佳;制备催化剂时光照时间不充分会使催化剂失去还原效力;氮气保护下催化剂反应活性更高;Fe²⁺的加入利于光催化反应;2 h光催化含氨氮和亚硝基氮的水样,总脱氮率达到了63.9%.     

Synthesis of porous zinc gallate prisms composed of highly oriented nanoparticles by an in situ conversion reaction

Porous ZnGa(2)O(4) prisms assembled by highly oriented nanoparticles have been fabricated by an in situ chemical conversion approach. We report, for the first time, that a solid α-Ga(2)O(3) precursor can be directly converted into ZnGa(2)O(4) rather than through the intermediate GaOOH. Based on a detailed study of the evolution of ZnGa(2)O(4) prisms, a growth mechanism is proposed for the in situ conversion reaction. During this conversion process, the precursor morphology can be highly retained, which is attributed to the similar atomic arrangements of the Ga and O atoms and excellent matching of the lattice spacing between the α-Ga(2)O(3) and ZnGa(2)O(4) prisms. The direct reaction between the precursor α-Ga(2)O(3) and Zn(2+) ions is more efficient than that between the byproduct GaOOH and Zn(2+) ions. Moreover, the photoluminescent color of the ZnGa(2)O(4) phosphor can be tuned by doping with Mn(2+) ions. Efficient energy transfer (ET) from the host lattice to the Mn(2+) centers is observed, whereas ET from the defects to the Mn(2+) ions is prohibited. The fabricated ZnGa(2)O(4) products have potential in the field of display applications.     

Heterometal alkoxides as precursors for the preparation of porous Fe- and Mn-TiO2 photocatalysts with high efficiencies

Transition-metal-doped titanium glycolates (M-TG, with M=Fe, Mn), which are the first non-stoichiometric heterometal alkoxides, have been synthesised through a solvothermal doping approach. X-ray diffraction, UV/Vis diffuse reflectance and ESR spectroscopy revealed that the dopant ion (Fe(3+) or Mn(2+)) is substituted for Ti(4+) in the TG lattice. Fe(3+) prolongs the crystallisation time of Fe-TG, whereas Mn(2+) has a smaller effect on the crystallisation time in comparison with Fe(3+). The as-synthesised M-TG materials were used directly as single-source precursors for the preparation of metal-doped titania (M-TiO(2)) through a simple thermal treatment process. The as-prepared M-TiO(2) materials maintain the rod-like morphology of the precursors and possess a mesoporous structure with high crystallinity. It has been proved that the dopant ions are incorporated into the TiO(2) lattice at the Ti(4+) positions. The photocatalytic activities of the M-TiO(2) materials obtained were evaluated by testing the degradation of phenol under UV irradiation. From the photocatalytic results, it was concluded that high crystallinity, a large surface area and appropriate transition-metal-doping are all beneficial to the enhancement of the photocatalytic performance of the doped TiO(2) material. In addition, it was noted that in comparison with Mn-TiO(2), Fe-TiO(2) shows higher photocatalytic activity due to the better inhibition effect of Fe(3+) on recombination of photogenerated electron-hole pairs. In contrast to the conventional nanosized TiO(2) photocatalyst, the micrometre-sized M-TiO(2) particles we obtained can be easily separated and recovered after the photocatalytic reactions.     

Cobalt Ion-Doped TiO(2) Photocatalyst Response to Visible Light

Photocatalytic activity under visible light irradiation was generated by doping a small amount of Co(2+) ions into TiO(2) particles. Nanometer-sized particles with the composition xCoO-(100-x) TiO(2) (xCo/TiO(2); 0300 nm) light irradiation but also induced the visible light (lambda>400 nm) response. The highest photocatalytic activities were obtained at x=0.03 for both irradiations. Copyright 2000 Academic Press.     

Zn-TiO2/AC复合催化剂的制备及其光催化活性

以硝酸锌、钛酸四丁酯和活性炭为原料,采用真空吸附法制备了不同组成的Zn TiO₂/AC.通过X射线衍射(XRD)和透射电镜(TEM)对催化剂进行了表征.选择较难降解的Cl₃CCOOH作为探针分子考察了其光催化活性.结果表明,掺锌能提高TiO₂/AC的催化活性,当Zn的摩尔分数为0.5%(相对TiO₂)、处理温度为400℃,溶液的pH值为6时,Zn TiO₂/AC催化剂具有很好的光催化活性.     

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.     

Characterizations of lanthanum trivalent ions/TiO2 nanopowders catalysis prepared by plasma spray

Lanthanum trivalent ions (La(3+)) doped titanium dioxide (TiO(2)) nanopowders in the range of 20-60 nm were prepared successfully by plasma spray in the self-developed plasma spray equipment. The photocatalytic activity of samples at different doping concentrations in photocatalytic degradation of methyl orange was discussed. The nanopowders prepared were characterized by transmission electron microscopy, X-ray diffraction, ultraviolet-visible spectra, photoluminescence (PL) and X-ray photoelectron spectroscopy. The results show that La(3+) doping increased the photocatalytic activity of TiO(2) greatly, the optimal doping concentration was 0.5 at%. The La(3+) doping decreases the particle size and the distribution of particle sizes becomes more uniform. The doped powders were the mixture of anatase and rutile phase. The contents of anatase phase decreased firstly and then increased with an increase in the contents of La(3+). The intrinsic absorption band of La(3+) doped TiO(2) nanopowders appears red shift from that of pure TiO(2) nanopowders. The intensity of PL spectra increases and then decreases with increasing the content of La(3+). The PL spectral intensity reaches its peak when the ratio of La(3+)/TiO(2) is 0.2 at%. There are O, Ti, C and La elements in the prepared La(3+) doped TiO(2) nanopowders, La element still exists in trivalent and Ti element always exists in tetravalent.     

锌掺杂对SrTiO_3光催化性能的影响

制备了锌掺杂的SrTiO3光催化剂,测试了掺杂样品在400 W高压汞灯照射下,分解纯水制氢的活性。考察了锌的掺杂量及样品的焙烧温度对其光催化活性的影响,并对掺锌与未掺杂样品进行了XRD、UV-vis、XPS及SEM表征分析。结果表明,Zn掺入可显著提高SrTiO3的光催化活性,适宜的锌掺杂摩尔分数为1%左右,相应的掺杂量下,适宜的焙烧温度为950℃左右,上述条件制得掺锌SrTiO3的产氢速率较未掺杂样品提高了120%左右。表征结果显示,掺摩尔分数1%的锌未改变SrTiO3的晶体结构及结晶完整性,但样品表面发生了锌的富集,而且在一定的掺杂范围内,锌掺杂使SrTiO3催化剂的粒度有所增大。推测掺入的Zn与存在于SrTiO3表面的富钛相反应生成Zn2TiO4,使SrTiO3表面的缺陷浓度降低,光催化活性提高。     

磁载WO3－TiO2／SiO2／Fe3O4复合光催化剂的制备及其光催化活性

 用溶胶－凝胶法在表面包覆了SiO2的磁基体Fe3O4上负载TiO2,从而得到了易于磁性固液分离的磁载WO3－TiO2／SiO2／Fe3O4复合光催化剂,并通过IR,XRD,SEM和XPS等测试手段对催化剂进行了表征．研究了磁载WO3－TiO2／SiO2／Fe3O4复合光催化剂对亚甲基蓝溶液脱色的性能,并考察了WO3掺杂量对样品催化活性的影响．结果表明,n（WO3）／n（TiO2）＝0．001时,磁载WO3－TiO2／SiO2／Fe3O4复合光催化剂的催化活性最高,循环使用3次时脱色率仍保持在98％．     

Overall water splitting on (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution photocatalyst: relationship between physical properties and photocatalytic activity

The physical and photocatalytic properties of a novel solid solution between GaN and ZnO, (Ga(1-x)Zn(x))(N(1-x)O(x)), are investigated. Nitridation of a mixture of Ga(2)O(3) and ZnO at 1123 K for 5-30 h under NH(3) flow results in the formation of a (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution with x = 0.05-0.22. With increasing nitridation time, the zinc and oxygen concentrations decrease due to reduction of ZnO and volatilization of zinc, and the crystallinity and band gap energy of the product increase. The highest activity for overall water splitting is obtained for (Ga(1-x)Zn(x))(N(1-x)O(x)) with x = 0.12 after nitridation for 15 h. The crystallinity of the catalyst is also found to increase with increasing the ratio of ZnO to Ga(2)O(3) in the starting material, resulting in an increase in activity.     

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.     

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.     

Photocatalytic activity enhancement in doped titanium dioxide by crystal defects

Visible light sensitive Fe(3+) and Ce(4+) co-doped nano TiO(2) photocatalyst has been prepared by a modified aqueous sol-gel method and the activity has been measured in terms of degradation of MB dye. Both dopants shifted the absorption profile of TiO(2) to the visible region and improved activity. Fe(3+) ions trapped the charge carriers due to the stable electronic configuration and improved their separation. Ce(4+) ions, which were mainly located at the grain boundaries, cause dislocations by bending the valence and conduction bands of TiO(2) and prevent the recombination of photoexcited electrons and holes. The co-doped TiO(2) compositions exhibited higher photocatalytic activity than that of pure titania and commercially available Degussa P25 under visible light by utilising the individual and synergistic contributions of Fe(3+) and Ce(4+) dopants, respectively.     

Characterization of ruthenium oxide nanocluster as a cocatalyst with (Ga(1-x)Zn(x))(N(1-x)Ox) for photocatalytic overall water splitting

The formation and structural characteristics of Ru species applied as a cocatalyst on (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) are examined by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. RuO(2) is an effective cocatalyst that enhances the activity of (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) for overall water splitting under visible-light irradiation. The highest photocatalytic activity is obtained for a sample loaded with 5.0 wt % RuO(2) from an Ru(3)(CO)(12) precursor followed by calcination at 623 K. Calcination is shown to cause the decomposition of initial Ru(3)(CO)(12) on the (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) surface (373 K) to form Ru(IV) species (423 K). Amorphous RuO(2) nanoclusters are then formed by an agglomeration of finer particles (523 K), and the nanoclusters finally crystallize (623 K) to provide the highest catalytic activity. The enhancement of catalytic activity by Ru loading from Ru(3)(CO)(12) is thus shown to be dependent on the formation of crystalline RuO(2) nanoparticles with optimal size and coverage.     

二氧化钛与针铁矿复合光催化材料的制备与光催化性能

以四氯化钛为钛源,针铁矿(α-FeOOH)为载体,采用水解沉淀法制备了金红石相二氧化钛(Ti₂O)与α-FeOOH的复合光催化材料,并采用X射线衍射、扫描电子显微镜、透射电子显微镜、X射线能量散射谱和X射线光电子能谱对样品进行了表征.结果表明,低温下,金红石相Ti₂O包覆于α-FeOOH表面,并形成复合结构;较高温下,铁离子进入金红石相Ti₂O晶格,并形成铁掺杂金红石相Ti₂O纳米管;中温下,样品兼有复合和掺杂两者特征.在室温下以甲基橙为降解对象,采用钨灯+氘灯(波长200~800nm)为光源,对样品的光催化活性进行了测试.结果表明,样品对甲基橙的光催化降解效果良好;与纯α-FeOOH和金红石相Ti₂O相比,不同结构样品的光催化活性均有所提高,其中,复合兼掺杂型样品的光催化活性最高.由此可见,与α-FeOOH复合和铁掺杂是提高Ti₂O光催化活性的有效途径.