Controlled fabrication of TiO2 rutile nanorod/anatase nanoparticle composite photoanodes for dye-sensitized solar cell application

We present a straightforward procedure to prepare composite photoanodes which consisted of TiO2 rutile nanorods/anatase nanoparticles synthesized under hydrothermal conditions, with the ratio of rutile to anatase controlled simply by adjusting the volume of nitric acid. The as-prepared TiO2 composites exhibited high specific surface area, light-scattering effect, and good crystallinity. The dye-sensitized solar cells (DSCs) using the TiO2 composites showed higher short-circuit photocurrent and overall conversion efficiency than the DSC from pure-anatase nanoparticles. The highest conversion efficiency was achieved from the DSC based on TiO2 nanocomposites with 24 wt% rutile nanorods, which was attributed to improved light harvesting caused by the enhancement of specific surface area and scattering effect from rutile nanorods.     

Fiber-like TiO2 nanomaterials with different crystallinity phases fabricated via a green pathway

Fiber-like TiO(2) nanomaterials were designed and created, for the first time, by in situ synthesis of TiO(2) nanoparticles in regenerated cellulose fibers in the wet state, followed by calcination at 400-800 °C to remove the cellulose matrix. The cellulose fibers were prepared in an NaOH/urea aqueous system with cooling via an industrial machine. The structure and properties of the fiber-like TiO(2) nanomaterials were characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and photocatalytic degradation tests. The results revealed that the mean diameter of the fiber-like TiO(2) nanomaterials, which consisted of TiO(2) nanoparticles with a mean size from 21 to 37 nm, was 7-8 μm. The TiO(2) nanomaterials exhibited different crystallinity phases from anatase to rutile, depending on the calcinating temperature. With a decrease in the calcinating temperature from 800 to 400 °C, the surface area of the TiO(2) nanomaterials increased. The photocatalytic activity for the degradation of methyl orange of the anatase T-400 fibers calcined at 400 °C was the highest, compared with that at 600 and 800 °C. This work provided a simple and "green" pathway for the preparation of inorganic nanomaterials with different crystal structures by using porous regenerated cellulose matrix.     

Effect of cobalt doping on the phase transformation of TiO2 nanoparticles

Co-doped TiO2 nanoparticles containing 0.0085, 0.017, 0.0255, 0.034, and 0.085 mol % Co(III) ion dopant were synthesized via sol-gel and dip-coating techniques. The effects of metal ion doping on the transformation of anatase to the rutile phase have been investigated. Several analytical tools, such as X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray analysis (EDAX) were used to investigate the nanoparticle structure, size distribution, and composition. Results obtained revealed that the rutile to anatase concentration ratio increases with increase of the cobalt dopant concentration and annealing temperature. The typical composition of Co-doped TiO2 was Ti(1-x)Co(x)O2, where x values ranged from 0.0085 to 0.085. The activation energy for the phase transformation from anatase to rutile was measured to be 229, 222, 211, and 195 kJ/mole for 0.0085, 0.017, 0.0255, and 0.034 mol % Co in TiO2, respectively.     

Transparent, anatase-free TiO2 nanoparticle dispersions

Preparation of optically transparent dispersions of TiO2 nanoparticles which are free of the anatase polymorph is a challenging process which has been difficult to control to date. Here, we report and discuss the reproducible formation of such dispersions by hydrolysis of TiCl4. Clouding times of the dispersions and the finally resulting crystal modification of TiO2 was found to depend on a number of synthesis parameters, such as the temperature profile during the reaction, the ratio between the starting substances and the rate of TiCl4 addition. A low pH value and moderate reaction temperatures were required to yield rutile particles, which were established to be formed by transformation of initially amorphous particles just prior to clouding occurred. The latter phenomenon was found to be caused by agglomeration, and not by growth of primary nanosized particles.     

Synthesis and photocatalytic performance of titanium dioxide nanofibers and the fabrication of flexible composite films from nanofibers

Titanium dioxide nanofibers were synthesized and applied in flexible composite films that are easy to handle and recycle after use. The nanofibers were obtained in a multi-step procedure. First, sodium titanate nanofibers were prepared from TiO2 nanoparticles through the alkali hydrothermal method. In the next step, sodium hydrogen titanate nanofibers were made by washing the sodium titanate nanofibers in HCl solution. Finally, the sodium hydrogen titanate nanofibers were transformed to TiO2 anatase nanofibers by calcination in air. The photocatalytic activity of TiO2 anatase nanofibers were evaluated and compared to a TiO2 nanoparticle catalyst by decomposing methyl orange dye in aqueous solutions. The achieved reaction rate constant of TiO2 anatase nanofibers was comparable to that of Degussa P25. Paper-like flexible composite films were prepared by co-filtrating aqueous dispersions of TiO2 catalyst materials and cellulose. The composite films made from the nanofibers exhibit better mechanical integrity than those of the nanoparticle-cellulose composites.     

TiO2纳米微粒的溶胶-凝胶法制备及XRD分析

本文采用溶胶 凝胶法制备二氧化钛纳米微粒。用XRD分析了二氧化钛胶体经不同温度热处理后的晶粒粒径。分析表明温度在 4 73K时TiO2 微粒呈锐钛矿结构 ,粒径约为 5 5nm。在 6 73K以上TiO2 粒径迅速增大 ,微粒出现锐钛相与金红石相混晶结构。 973K时TiO2 微粒完全转化为金红石相。用晶界结构弛豫的观点解释粒径随热处理温度变化关系     

纳米TiO2和紫外线吸收剂对丙烯酸酯涂层抗光氧化性能的影响

讨论了锐钛矿型和金红石型纳米TiO2以及2．4-二羟基二苯甲酮和2-(2-二羟基-5-苯甲基)苯并三唑等有机紫外线吸收剂的光活性．并借助失重分析和SEM分析探讨它们对丙烯酸复合涂层抗光氧化性能的影响。UV分析表明：2，4-二羟基二苯甲酮、2-(2-二羟基-5-苯甲基)苯并三唑等有机紫外线吸收剂对400nm以下的紫外线有强烈的吸收作用；金红石和锐钛矿型纳米TiO2对紫外线也有较强烈的吸收和散射作用，紫外光透过率低。且有机紫外线吸收剂随着辐射时间的延长会分解失效，而纳米TiO2较稳定。失重分析和SEM分析结果显示：锐钛矿型纳米TiO2具有光催化性，加速丙烯酸酯聚合物的光降解，而金红石型纳米TiO2则是一种有效的遮光剂。同时添加金红石型纳米TiO2和有机紫外线吸收剂能更有效提高丙烯酸酯复合涂层的抗光氧化性能。     

Organic-inorganic hybrid materials based on polyaniline/TiO(2) nanocomposites for ascorbic acid fuel cell systems

Polyaniline was grafted onto a mixture of rutile and anatase TiO(2) nanoparticles by in situ chemical oxidative polymerization. These nanocomposites were characterized by carbon, hydrogen and nitrogen (CHN) analysis, x-ray diffraction (XRD), Fourier transform infrared (FTIR), ultraviolet-visible (UV-vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. FTIR and UV-vis confirm the formation of polyaniline on TiO(2) nanoparticles. The TEM shows that the composites consist of PANI and TiO(2) nanoparticles. Compared to the neat polyaniline, PANI/TiO(2) composites show a higher capacitance and also a higher activity per mass of polyaniline. Since the PANI/TiO(2) composites are stable during the electrooxidation of ascorbic acid, they can be used as an alternative catalyst for direct ascorbic acid fuel cells.     

Improved photocatalytic activity of anisotropic rutile/anatase TiO2 nanoparticles synthesized by the Ti-peroxo complex method

Anisotropic rutile/anatase TiO2 nanoparticles (AB-TiO2) were synthesized by the Ti-peroxo complex method. Their photocatalytic activity in the degradation of Rhodamine B (RhB) was evaluated and compared to that of commercial TiO2 P25 and TiO2 obtained through the benzyl alcohol route (OB-TiO2). The samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR in DRIFT mode), Field-Emission Scanning Electronic Microscopy (FEG-SEM), N2 physisorption and UV-visible spectroscopy. Photodegradation of RhB was carried out under visible light and the results revealed a remarkable photocatalytic activity of the AB-TiO2 in terms of surface area. The excellent performance of the AB-TiO2 was explained in light of the synergistic effect of the coexistence of anatase/rutile phases, anisotropy and irreversible adsorption of organic species during sol-gel synthesis. UV-visible measurements also indicated that N-deethylation and photobleaching mechanisms occur to different extents, depending on the surface composition of the photocatalyst.     

Surface water and the origin of the positive excess specific heat for 7 nm rutile and anatase nanoparticles

Specific heats (15-350 K) have been measured on 7 nm TiO2 anatase and rutile nanoparticles containing significant amounts of surface-adsorbed water. By successively reducing the water content without changing particle size, we observed two types of water behavior. The specific heat of bare 7 nm particles was estimated using the water specific heats. Contrary to previous literature reports, the bare small particle specific heats are the same as those of the bulk, within experimental error.     

Fe-F/TiO_2复合微球的制备与光降解部分水解聚丙烯酰胺机制

以Span-80为调控剂,钛酸四丁酯(TBOT)为钛源,采用低温水解-回流法制备了Fe-F共掺杂TiO_2介孔复合微球(Fe-F/TiO_2)。通过XRD、SEM、FTIR、TG-DTA、BJH和UV-vis DRS测试方法对样品进行了结构性能表征;以部分水解聚丙烯酰胺(HPAM)为目标降解物,研究了Fe-F/TiO_2复合催化剂的光催化性能。结果表明,制得的Fe-F/TiO_2是由直径为10~15nm的纳米粒子堆砌而成的锐钛矿型介孔微球,其中Fe3+可以有效促进锐钛矿而抑制金红石相的生成,使其具有较高的热稳定性;比表面积、孔容积及平均孔径分别是145.11 m2/g、0.26cm3/g和6.23nm。在光降解HPAM的过程中,Fe3+和F-的协同效应可以提升材料的光催化性能,使FeF/TiO_2具有最高的催化活性。在紫外光及可见光条件下,0.1g的Fe-F/TiO_2降解100mL浓度为500mg/L的HPAM溶液120min,其COD去除率分别为81%和74%。     

Phase-junction Ag/TiO2 nanocomposite as photocathode for H2 generation

Developing anatase/rutile phase-junction in TiO2 to construct Z-scheme system is quite effective to improve its photoelectrochemical activity.In this work,the anatase/rutile phase-junction Ag/TiO2 nanocomposites are developed as photocathodes for hydrogen production.The optimized Ag/TiO2 nanocomposite achieves a high current density of 1.28 mA cm-2,an incident photon-to-current con-version efficiency(IPCE)of 10.8％,an applied bias photon-to-current efficiency(ABPE)of 0.32 at 390 nm and a charge carriers'lifetime up to 2000s.Such enhancement on photoelectrochemical activity can be attributed to:(i)the generated Z-scheme system in the anatase/rutile phase-junction Ag/TiO2 photocath-ode enhances the separation,diffusion and transformation of electron/hole pairs inside the structure,(ii)Ag nanodots modification in the anatase/rutile phases leading to the tuned band gap with enhanced light absorption and(iii)the formed Schottky barrier after Ag nanodots surface modification provides enough electron traps to avoid the recombination of photogenerated electrons and holes.Our results here sug-gest that developing phase-junction nanocomposite as photocathode will provide a new vision for their enhanced photoelectrochemical generation of hydrogen.     

Enhanced activity of bismuth-compounded TiO(2) nanoparticles for photocatalytically degrading rhodamine B solution

TiO(2) nanoparticles compounded with different amounts of bismuth were prepared by a sol-gel method, and the effects of compounding bismuth on the phase transformation, photoinduced charge separation and photocatalytic activity for degrading rhodamine B solution were mainly investigated, along with enhancement mechanism of photocatalytic activity of TiO(2) nanoparticles by compounding bismuth species. It can be confirmed that, by means of X-ray diffraction (XRD), surface photovoltage spectroscopy (SPS) and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), compounding bismuth can extend the optical response, and effectively inhibit the phase transformation process from anatase to rutile, consequently greatly improving the anatase crystallinity so as to promote the photoinduced charge separation. These factors are responsible for the increase in the photocatalytic activity of TiO(2) compounded with an appropriate amount of bismuth species.     

Formation of TiO2 nanoparticles by reactive-layer-assisted deposition and characterization by XPS and STM

Stoichiometric TiO2 nanoparticles (1-5 nm) were prepared by reactive-layer-assisted deposition (RLAD), in which Ti was initially deposited on a multilayer of H2O (or NO2) on a Au(111) substrate at approximately 90 K. The composition and atom-resolved structure of the nanoparticles were studied by XPS and STM. The approximately 5 nm TiO2 particles had either a rutile or anatase phase with various crystal facets. STS of the nanoparticles suggests size-dependent electronic structure. These well-defined nanoparticles can be used in molecular-level studies of the reactions and mechanisms of photocatalytic processes on TiO2 nanoparticle surfaces.     

Effect of Nb and Sc doping on the phase transformation of sol-gel processed TiO2 nanoparticles

Nb and Sc doped TiO2 nanoparticles were synthesized via sol-gel technique. Dopant concentration of each element was varied from 0.5 to 1.5 atomic%. The effect of metal ion doping and calcination temperatures on anatase to rutile phase transformation has been investigated. Samples were analyzed by various analytical methods such as X-ray diffraction (XRD), Transmission Electron Microscope (TEM), X-ray Photoelectron Spectroscopy (XPS) and Energy Dispersive X-ray Spectroscopy (EDS). XRD analyses showed that Nb and Sc doped samples calcined at 300 degrees C and 350 degrees C, respectively, were crystalline and had an anatase structure. Results showed that anatase was stable up to 700 degrees C annealing temperature for samples doped with 0.5 atomic% Nb. There was a sharp transition from anatase to rutile phase above 700 degrees C and complete rutile structure was obtained at 750 degrees C. However, the transformation from anatase to rutile was not so sharp in samples doped with 1.0 atomic% and 1.5 atomic% Nb. Results indicated that higher concentration of Nb helps to stabilize the anatase phase. For samples doped with 0.5 atomic% Sc, anatase phase is stable up to 650 degrees C. Transformation from anatase to rutile starts at temperature above 650 degrees C and 100% rutile phase was obtained at 800 degrees C while for samples doped with 1.0 atomic% and 1.5 atomic% Sc, the complete transformation from anatase to rutile takes place at an even higher temperature. Results indicate that increasing the calcination time from 0.5 to 2.0 hours at 500 degrees C does not affect the stability of anatase phase. However, TEM and XRD data showed that the increase in the annealing time leads to an increase in particles size. The rutile to anatase concentration ratio increased with temperature above the phase transformation temperature. The activation energy for the phase transformation from anatase to rutile for doped and undoped samples was also measured. There was a general rise in the activation energy with increasing dopant concentration.     

铝硅酸盐中间体对TiO2纳米粒子团聚及相转变的抑制

以粉煤灰为原料, 通过与NaOH煅烧、水解合成铝硅酸盐中间体(ASI), 向sol-gel法制备的TiO₂溶胶中加入ASI, 经处理得到钛铝硅酸盐复合材料(TiO₂/ASI). X射线衍射分析(XRD)和紫外-可见漫反射光谱(DRS)研究ASI对sol-gel方法制备TiO₂纳米晶形成过程和相转变的影响. 研究结果表明: 铝硅酸盐中间体不但能抑制TiO₂纳米粒子的团聚, 而且能够有效地抑制TiO₂由锐钛矿型向金红石型的相转变, 由此所制备TiO₂与ASI的钛铝硅酸盐复合材料(TiO₂/ASI)对溶液中亚甲基蓝的吸附性能高于单一的TiO₂或铝硅酸盐中间体.     

二氧化钛纳米晶的光催化活性研究

以苯酚的光催化降解为模型反应,研究了锐钛矿相和金红石相二氧化钛纳米晶（７￣４０ｎｍ）的光催化活性。与市售的氧化钛相比,两种晶相的纳米氧化钛均有很高的光催化活性,锐钛矿相氧化钛对苯酚的深度矿化有更高的选择性。ＴｉＯ２吸附的水及羟基会降低氧化钛的光催化活性。由于粒径减小使氧化钛的吸收带边界蓝移,粒径小的氧化钛有更高的催化活性,粒径〈１５ｎｍ时,显示出量子尺寸效应。     

Laser-assisted production of spherical TiO2 nanoparticles in water

TiO(2) nanoparticles with controllable average diameter have been obtained by laser ablation in water. A monomode ytterbium doped fiber laser (YDFL) was used to ablate a metallic titanium target placed in deionized water. The resulting colloidal solutions were subjected to laser radiation to study the resizing effect. The crystalline phases, morphology and optical properties of the obtained nanoparticles were characterized by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), x-ray energy dispersive spectroscopy (EDS) and UV-vis absorption spectroscopy. The colloidal suspensions produced consisting of titanium dioxide crystalline nanoparticles show almost perfect spherical shape with diameters ranging from 3 to 40 nm. The nanoparticles are polycrystalline and exhibit anatase as well as rutile phases.     

The fabrication of CNTs/TiO(2) photoanodes for sensitive determination of organic compounds

Titanium dioxide (TiO(2)) and carbon nanotubes (CNTs) are the two most popular functional materials in recent years. In this study, CNTs/TiO(2) composite and TiO(2) photoanodes were fabricated by a dip-coating technique, followed by subsequent calcination. The resultant photoanodes were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and UV-visible spectroscopy (UV-vis). The results suggest that the carbon nanotubes were successfully incorporated with the TiO(2) nanoparticulates without damage and that the resultant TiO(2) nanoparticles consisted of anatase and rutile. The CNTs/TiO(2) photoanodes were capable of oxidizing various types of organic compounds (e.g.?glucose, potassium hydrogen phthalate, and phenol) in aqueous solutions in a photoelectrochemical bulk cell. In comparison with the pure TiO(2) photoanode, the sensitivity of the photoanode for the detection of organic compounds has been improved by 64%, while the background current was reduced by 80% due to the introduction of the CNTs. These advantages can be ascribed to the improved adsorptivity to organic compounds, increased absorption of UV light and enhanced electron transport at the CNTs/TiO(2) photoanode due to the introduction of the CNTs.     

TiO_2纳米粒子的结构、表面特性及其光催化活性研究

采用金属醇盐水解法制备了ＴiＯ２纳米粒子,并用ＸＲＤ、ＳＰＳ、ＸＰＳ和ＥＳＲ等测试手段对ＴiＯ２粒子进行结构、性能测试．随焙烧温度的增加,ＴiＯ２粒子长大,晶型由锐钛矿向金红石型转变．以庚烷的气相光催化氧化为试验反应,考察不同温度处理的醇洗、水洗ＴiＯ２粒子的光催化活性．结果表明,醇洗粒子较水洗粒子显示出高的光催化活性,并且低温处理的粒子其光伏响应带边蓝移明显;阈值增加,Ｔｉ３＋含量较高,光催化活性增加．