Phase transformations in nanocrystalline TiO2 milled in different milling atmospheres

The structural evolution of nanocrystalline TiO₂ milled in different milling atmospheres was studied by X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy. Rietveld refinements of the XRD data showed that high-energy ball milling induced the transformations from anatase to srilankite and rutile at room temperature and ambient pressure. The milling atmospheres with different oxygen partial pressures had an influence on the transformation kinetics of anatase. When the nanocrystalline TiO₂ powders were, respectively, milled in oxygen, air and nitrogen atmospheres, the transformation rates of anatases in turn increased with a decrease in oxygen partial pressure of the milling atmosphere, due to the reducing concentration of oxygen vacancies in the milled TiO₂ lattice.     

Preparation of a highly active nanocrystalline TiO2 photocatalyst from titanium oxo cluster precursor

Nanocrystalline TiO₂ (sample S1) was prepared from a titanium oxo cluster (Ti₇O₄(OEt)₂₀) precursor via a sol-gel route. This photocatalyst showed a higher photocatalytic activity than the TiO₂ (sample S2) obtained from titanium tetraisopropoxide. The samples were characterized by thermal analysis (TGA/DSC), X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, N₂ adsorption (BET surface area), infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy. The characterization results show that both samples are anatase nanocrystals with particle sizes of about 12 nm, but the more photocatalytically active sample S1 has more surface hydroxyl groups and larger surface area and pore volume than sample S2.     

A one-step solvothermal route for the synthesis of nanocrystalline anatase TiO2 doped with lanthanide ions

A one-step solvothermal synthesis is proposed for the preparation of nanocrystalline single-phase TiO₂ in the anatase form doped with lanthanide ions Eu³⁺, Er³⁺ and Sm³⁺. The structural properties of these products have been investigated by using X-ray powder diffraction, electron microscopy and Raman spectroscopy. Furthermore, the laser-excited luminescence spectra of the samples have been measured and analyzed. Following this route, the doping process turns out to be highly favorite and the resulting materials show an efficient luminescence in the visible region.     

两步电泳沉积制备TiO2光阳极用于高效染料敏化太阳能电池

采用不同沉积电压制备TiO₂光阳极,研究电压对薄膜沉积速率、厚度和形貌的影响。通过台阶仪、光学照片、扫描电子显微镜（SEM）、电化学交流阻抗谱、开路电压衰减曲线对光阳极和电池进行系统表征,并测试了染料敏化太阳能电池器件的电流密度-电压（J-V）曲线,计算其光电转换效率。结果表明,提高沉积电压时,光阳极薄膜的沉积速率加快,膜厚也增加,但是电压过高时,薄膜会有裂缝和覆盖不全的问题,这会对电池的效率造成负面影响。综合考虑低沉积电压条件下薄膜均匀无裂缝和高沉积电压条件下沉积速率快的优点,采用先30 V电压、后60 V电压的电泳沉积方式来制备光阳极,结果呈现协同效果,既降低了制备时间又得到高质量的薄膜,在无其他修饰的情况下,电池的光电转换效率可以达到7.29%。     

两步电泳沉积制备TiO2光阳极用于高效染料敏化太阳能电池

采用不同沉积电压制备TiO₂光阳极,研究电压对薄膜沉积速率、厚度和形貌的影响。通过台阶仪、光学照片、扫描电子显微镜(SEM)、电化学交流阻抗谱、开路电压衰减曲线对光阳极和电池进行系统表征,并测试了染料敏化太阳能电池器件的电流密度-电压(J-V)曲线,计算其光电转换效率。结果表明,提高沉积电压时,光阳极薄膜的沉积速率加快,膜厚也增加,但是电压过高时,薄膜会有裂缝和覆盖不全的问题,这会对电池的效率造成负面影响。综合考虑低沉积电压条件下薄膜均匀无裂缝和高沉积电压条件下沉积速率快的优点,采用先30 V电压、后60 V电压的电泳沉积方式来制备光阳极,结果呈现协同效果,既降低了制备时间又得到高质量的薄膜,在无其他修饰的情况下,电池的光电转换效率可以达到7.29%。     

二氧化钛多孔纳米片在染料敏化太阳电池中的应用

运用连续吸附反应法和化学腐蚀-沉积法,用ZnO/FTO(氟掺杂氧化锡)多孔纳米片为模板,制备了TiO2/FTO多孔纳米片。研究了吸附次数对形貌、光散射性能和染料敏化太阳电池性能的影响。最佳吸附次数为30,由此得到的太阳能电池的效率、短路电流密度Jsc、开路电压Voc和填充因子FF分别为:5.57%、9.26 mA·cm-2、0.835 V和72.04%。这个效率略高于P25(5.32%),但远高于ZnO(2.41%)。     

二氧化钛多孔纳米片在染料敏化太阳电池中的应用

运用连续吸附反应法和化学腐蚀-沉积法,用ZnO/FTO（氟掺杂氧化锡）多孔纳米片为模板,制备了TiO₂/FTO多孔纳米片。研究了吸附次数对形貌、光散射性能和染料敏化太阳电池性能的影响。最佳吸附次数为30,由此得到的太阳能电池的效率、短路电流密度J_sc、开路电压V_oc和填充因子FF分别为：5.57%、9.26mA·cm^-2、0.835V和72.04%。这个效率略高于P₂₅（5.32%）,但远高于ZnO（2.41%）。     

TiO2薄膜优化对染料敏化太阳电池性能的影响

纳米TiO2多孔薄膜微结构对染料敏化太阳电池(DSC)光伏性能有很大的影响。本文采用不同实验和测试方法研究和分析了溶胶-凝胶法制备纳米TiO2颗粒时的热处理温度、TiO2多孔薄膜厚度、纳米TiO2大颗粒光散射、TiCl4溶液处理和电沉积致密TiO2层对纳米多孔薄膜电极和染料敏化太阳电池光伏性能的影响,得到了最佳的优化条件,为纳米TiO2薄膜材料的批量化制作打下了良好基础。     

Effect of TiO2 crystallite size on the dispersion of Co on nanocrystalline TiO2

Nanocrystalline TiO₂ powders with average crystallite sizes of 9–15 nm were synthesized by the solvothermal method and employed as supports for Co catalysts. The value of H₂ chemisorption/specific surface area of Co/TiO₂ increased significantly with increasing TiO₂ crystallite size. It was suggested that the higher amount of Ti³⁺ surface defects on the larger crystalline TiO₂ resulted in a stronger interaction between Co and TiO₂, hence, higher dispersion of Co was obtained.     

“Unusual Ln substitutional defects”: The local chemical environment of Pr and Nd in nanocrystalline TiO2 by Ln-K edge EXAFS

The local chemical environment of the trivalent lanthanide cations in anatase TiO₂ nanopowders doped with 1 mol% of Pr or Nd, prepared via a sol-gel technique, has been studied by means of EXAFS at the Pr and Nd-K edge. Titanium dioxide can be considered an “unusual” host for doping with Ln³⁺ ions due to the large mismatch of both charge and ionic radii between the dopant and the host constituent cations. However, it can be demonstrated that the lanthanide ions enter the anatase structure as substitutional defects with respect to Ti, but that the amount of disorder around the substitutional defects is very large. For both Pr³⁺ and Nd³⁺ ions, the Ln-O and Ln-Ti distances have been found to increase by about 0.45 Å, with respect to what is found for the Ti-O and Ti-Ti distances in pure anatase. Valence-bond calculations have been used to validate the Ln-O distances obtained by the EXAFS fitting. Finally, no evidences for oxygen vacancies clustering around the substitutional defects have been found. Luminescence spectroscopy has shown that the lanthanide ions do not segregate in oxide or pyrochlore impurities phases.     

A novel architecture of poly(tetrafluoroethylene)-framed TiO2 electrodes for dye-sensitized solar cells

A novel architecture of polytetrafluoroethylene (PTFE)-framed TiO₂ electrodes is developed for dye-sensitized solar cells. The PTFE-framed TiO₂ electrodes with various thicknesses have been successfully fabricated, ranging from 20 to 160 μm. The optimal energy conversion efficiency of 9.04% is achieved with a film thickness of 60 μm. The PTFE-framed structure not only provides tunable film thickness but a reliable and cost-effective way for the mass production of photo-electrodes.     

Visible-light responsive dye-modified TiO2 photocatalyst

A series of dye-modified TiO₂ photocatalysts were synthesized using dye Chrysoidine G (CG), tolylene-2,4-diisocyanate (TDI), and commercial TiO₂ (Degussa P25) as starting materials. TDI was used as a bridging molecule whose two -NCO groups reacted with Ti-OH of TiO₂ and -NH₂ groups of CG, respectively. As a result, special organic complexes were formed on the TiO₂ surface via stable π-conjugated chemical bonds between TiO₂ and dye molecules, confirmed by FT-IR, XPS, and UV-vis spectra. Due to the existence of π-conjugated surface organic complexes, the as-synthesized photocatalysts showed a great improvement in visible absorption (400-550 nm). Methylene blue, as a photodegradation target, was used to evaluate the photocatalytic performance, and the dye-modified TiO₂ exhibited much better activity under the visible light irradiation than bare TiO₂.     

TiO2纳米线的制备及其光电性能研究

利用在钛箔表面沉积一层TiO₂纳米粒子作为晶种，与NaOH反应，制备了一维物质TiO₂纳米线。并用XRD、SEM、TEM、HRTEM及EDS等分析手段对TiO₂纳米线的成分、形貌、结构进行表征。结果表明，采用该方法制得的TiO₂纳米线直径在20～50 nm左右、长度可达几微米。反应温度能显著影响所得纳米线的形貌。研究了TiO₂纳米线的光电化学性能。随反应温度的升高TiO₂纳米线光电转换效率增大。     

TiO2 nanoparticles incorporated with CuInS2 clusters: preparation and photocatalytic activity for degradation of 4-nitrophenol

TiO₂ nanoparticles incorporated with CuInS₂ clusters were prepared in a solvothermal process and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersion X-ray analysis (EDX). Compared with pure TiO₂ nanoparticles, the TiO₂ nanoparticles incorporated with CuInS₂ clusters display higher photocatalytic activity with 99.9% of degradation ratio of 4-nitrophenol after 2 h irradiation. In order to investigate the effect of the CuInS₂ clusters on the photocatalytic activity of TiO₂ nanoparticles, diffuse reflectance UV–Vis spectra (DRS), photoluminescence (PL) spectra, and photocurrent action spectra were measured. The results indicate that the enhanced photocatalytic activity is probably due to the interface between TiO₂ and CuInS₂ as a trap of the photogenerated electrons to decrease the recombination of electrons and holes.     

The release of TiO2 and SiO2 nanoparticles from nanocomposites

There is a growing interest in the development of nanocomposites consisting of organic polymers and TiO₂ or amorphous SiO₂ nanoparticles. These nanoparticles may be released from nanocomposites. There is evidence that amorphous SiO₂ and TiO₂ nanoparticles can be hazardous. Thus, in the design of nanocomposites with such nanoparticles, hazard reduction extending to the full nanocomposite life cycle would seem a matter to consider. Options for hazard reduction include: changes of nanoparticle surface, structure or composition, better fixation of nanoparticles in nanocomposites, including persistent suppression of oxidative damage to polymers by nanoparticles, and design changes leading to the release of relatively large particles.     

静电自组装制备纳米TiO2/SiO2光催化材料

采用静电自组装方法制备了纳米TiO2/SiO2光催化材料。采用巯丙基三甲氧基硅烷偶联剂对SiO2进行干法改性,采用双氧水/冰醋酸将偶联剂巯基基团氧化为磺酸基基团。在正负电荷的吸引下,带负电荷的SiO2与带正电荷的钛聚合阳离子自发地组装在一起,经一定温度热处理得到纳米TiO2/SiO2光催化材料。采用XRD、FTIR、PL、UV-Vis DRS、SEM和ICP等对材料进行了分析和表征。采用甲基橙溶液评价材料的光催化性能。结果表明:SiO2促使锐钛矿的形成,抑制锐钛矿向金红石的转变,减小TiO2的晶粒尺寸,使得TiO2光吸收波长发生蓝移。TiO2与SiO2通过Si-O-Ti键发生结合。采用静电自组装方法制备的材料中TiO2的含量高于传统方法,导致材料的光催化性能有所提高。     

Bi2O3 /TiO2复合纳米颗粒的可见光光催化性能

采用溶胶与水热相结合的方法合成了具有可见光光催化活性的复合纳米颗粒Bi2O3/TiO2,并对其进行了X射线衍射、透射电镜、X射线光电子能谱、紫外-可见漫反射谱、红外光谱、低温N2吸附脱附及电子顺磁共振分析。结果表明,复合少量的氧化铋可显著抑制TiO2由锐钛矿到金红石的相转移过程,并将光吸收范围扩展到可见光区。可见光照射下(λ>420 nm),利用电子顺磁共振技术检测到明显的羟基自由基(.OH)信号。铋的最佳掺杂量为Bi/Ti质量比2.0%,适量铋的掺入能显著改善锐钛矿TiO2的结晶度,抑制光生电子-空穴对的复合,提高光催化量子效率。通过可见光照射下,4-氯酚的降解实验测试Bi2O3/TiO2复合纳米颗粒的可见光光催化活性。同时,利用气-质联用仪对4-氯酚降解过程的中间产物进行了测定,并提出可见光照射下的Bi2O3光敏化机理。     

TiO2 nanorods branched on fast-synthesized large clearance TiO2 nanotube arrays for dye-sensitized solar cells

A large clearance TiO₂ nanotube arrays (LTAs) has been synthesized by a not more than 12 h anodization duration and based on this a branched TiO₂ nanotube arrays (BLTs) has been achieved through TiO₂ nanorods branch-like grown on the LTAs. Some key factors and probable mechanisms of the fabrication processes on two novel nanoarchitectures are discussed. Exhilaratingly, it is found that the obtained LTAs has demonstrated large pore diameter and void spaces (pore diameter ∼350 nm; void spaces ∼160 nm; and tube length ∼3.5 μm), and the synthesized hierarchical BLTs, compared with conventional TiO₂ nanotube arrays, has shown a much stronger dye absorption performance and an approximately double of the solar cell efficiency (in our case from 1.62% to 3.18% under simulated AM 1.5 conditions).     

双介孔结构的纳米TiO2/I2复合材料的制备及其可见光催化性能

以钛酸丁酯为前驱体, 碘溶胶为碘源, 在室温下采用水解沉淀法制备了单质碘和纳米TiO₂复合的双介孔结构光催化剂(M-I₂-TiO₂). 采用X射线衍射(XRD)、透射电子显微镜(TEM)、比表面分析(BET)、紫外-可见(UV-Vis)漫反射光谱和傅里叶变换-红外光谱(FT-IR)对M-I₂-TiO₂进行了表征. 以次甲基蓝(MB)溶液为模拟废水, 对M-I₂-TiO₂的光催化性能进行了评价, 研究了不同热处理温度对光催化活性的影响. 结果表明, M-I₂-TiO₂在可见光区有显著的吸收, 300 ℃热处理得到的样品比表面积高达227.6 m²/g, 600 ℃热处理所得样品的比表面积仍高达111.8 m²/g, 而400 ℃热处理所得样品具有最好的光催化降解性能. 双介孔结构纳米TiO₂/I₂复合材料的光催化降解性能显著高于相同方法制备的纯TiO₂和Degussa P-25商业产品. 催化剂经6次重复使用其光催化活性基本保持不变.     

Catalytic oxidation of no to NO2 over Cr/TiO2 and Cu/TiO2 under oxidizing atmosphere

The catalytic activity of Cr/TiO₂ and Cu/TiO₂ for the oxidation of NO under an oxidizing atmosphere has been examined. Both catalysts had excellent ability for the oxidation of NO to NO₂ in the temperature range of 350–400°C.