影响TiO2从锐钛型转变为金红石型的相变因素的研究

考察了V2O5、MoO3、醋酸及钾盐对TiO2由锐钛型向金红石型转变的影响，在相同条件下，V2O5对转化的促进作用优于MoO3，并且转化率随V2O5用量的增加而增大，适当使用醋酸和钾盐，也可促进TiO2由锐钛型到金红石型的相变过程。     

低温水热合成棒状金红石型纳米TiO2及光催化活性研究

低温条件下以TiCl3溶液为钛源,硝酸盐为氧化剂一步制备了高催化活性的棒状金红石型纳米TiO2.以亚甲基蓝的光催化降解为探针反应, 评价了其光催化活性.运用XRD、TEM、UV-Vis表征技术考察了金红石型纳米TiO2的晶体结构、微晶尺寸, 并对氧化合成机制作了探讨.结果表明, NO 3在水热合成过程中是关键的氧化剂;制备的纳米TiO2为棒状结构,粒径约15 nm,棒长约60 nm;光催化降解反应6 h后亚甲基蓝降解率可达53.66%,其性能远远优越于P-25(41.32%).     

纳米TiO2光催化降解有机废水及改性研究进展

纳米TiO2是近年来半导体材料用于环保领域中研究最多、最具发展前景的高新技术材料之一.作者介绍了纳米TiO2的光催化机理,并对纳米TiO2在降解有机废水等方面的应用进行了评述,还综述了近年来对纳米TiO2改性方面的研究,包括沉积贵金属、金属离子掺杂、非金属掺杂和半导体复合等技术.     

二氧化钛晶型转变研究进展

综述了二氧化钛由锐钛型向金红石型转化过程中的影响因素及转化机理,并对该转化过程涉及的一些问题进行初步探讨。     

纳米TiO2粉末的液相法制备及光学吸收特性的研究

采用水解-均相沉淀法,在常温下即可制得纯锐钛型纳米TiO2粉末,对所制得的粉末进行了TEM、XRD、EDS、XPS和UV-VIS分析。结果表明:采用水解-均相沉淀法,通过添加NH4C l和H2SO4可在室温下制得粒径为32nm的纯锐钛型纳米TiO2粉末,并且粉末粒径均匀,尺寸分布较窄;纳米TiO2粉末对波长200~360 nm范围内的紫外线有较好的吸收作用,且吸收较均匀。     

纳米TiO2光催化氧化机理及研究进展

本文探讨了TiO2光催化氧化机理及影响催化反应的因素，综述了在降解有机染料、净化空气和杀菌方面的研究进展。     

纳米TiO2薄膜光催化活性的研究进展

介绍了TiO2 膜的光催化作用机理 ,概述了影响TiO2 薄膜光催化活性的因素 ,以及贵金属沉积、金属离子沉积、复合半导体及光敏化等改性手段对TiO2 膜光催化活性的因素 ,并提出了该领域的发展方向。     

纳米微晶纤维素诱导制备方形纳米二氧化钛及其光催化性能

利用纳米微晶纤维素(CNC)作为形貌诱导剂,以TiC14为原料,在90℃下反应,时间为4.5 h,制备了出方形纳米二氧化钛。其形貌规整,尺寸分布窄,都在200 nm左右,且相结构为锐钛型单晶。对方形二氧化钛的形成机理作了简要探讨,提出“方框”机理。产物对甲基橙有优良的光催化降解性能。     

TiO2体系对酸性红B的催化超声降解过程的影响

采用处理过的市售的锐钛型和金红石型纳米TiO2作为声催化剂,低功率的超声波作为激发源,研究了纳米TiO2对酸性红B催化超声降解过程的影响.结果表明:锐钛矿纳米TiO2和金红石型纳米TiO2对酸性红B有着不同的超声降解过程.锐钛型纳米TiO2以空穴氧化为主,使酸性红B脱色和降解过程同时进行,而金红石型纳米TiO2则以自由基氧化为主,是先脱色后降解.锐钛型纳米TiO2降解效果明显优于金红石型纳米TiO2.单纯超声照射下酸性红B没有明显的脱色和降解过程发生.因此,锐钛型纳米TiO2催化超声降解有机污染物的方法具有很好的应用前景.     

纳米TiO2光催化降解污染物研究

以10W直管紫外杀菌灯为光源，以泡沫镍基纳米TiO2为催化剂，研究了低沸点有机小分子污染物的光催化降解。以丙酮为光催化降解对象，结果表明，丙酮的降解符合Langmuir-Hinshelwood准一级动力学方程，并研究了相关因素对丙酮的光催化降解的影响。并对实验现象加以解释。实验还对类似于丙酮的低沸点有机污染物，设计了一种新颖的光催化反应器。     

Photocatalytic Nb2O5-doped TiO2 nanoparticles for glazed ceramic tiles

TiO₂ nanoparticles are currently used as coating for self-cleaning building products. In order to achieve high self-cleaning efficiency for outdoor applications, it is important that titania is present as anatase phase. Moreover, it is desirable that the particle sizes are in nano-range, so that a large enough surface area is available for enhanced catalytic performance. In this work, TiO₂ nanoparticles doped with 0–5 mol% Nb₂O₅ were synthesized by co-precipitation. Nb₂O₅ postponed the anatase to rutile transformation of TiO₂ by about 200 °C, such that after calcination at 700 °C, no rutile was detected for 5 mol% Nb₂O₅-doped TiO₂, while undoped TiO₂ presented 90 wt% of the rutile phase. A systematic decreasing on crystallite size and increasing on specific surface area of TiO₂ were observed with higher concentration of Nb₂O₅ dopant. Photocatalytic activity of anatase polymorph was measured by the decomposition rate of methylene blue under ultraviolet and daylight illumination and compared to commercial standard catalyst (P25). The results showed enhanced catalysis under UV and visible light for Nb₂O₅-doped TiO₂ as compared to pure TiO₂. In addition, 5 mol% Nb₂O₅-doped TiO₂ presented higher photocatalytic activity than P25 under visible light. The enhanced performance was attributed to surface chemistry change associated with a slight shift in the band gap.     

HIPed TiO2 dense pellets with improved photocatalytic performance

The effects of heating method and temperature on physical, structural and photocatalytic behaviors of TiO₂ pellets prepared by conventional heating and hot isostatic pressing have been evaluated. The pellets of submicron TiO₂ powders were heated to 600, 650, 700, 750 and 1000 °C using both processing methods in order to compare anatase to rutile phase transformation and densification behaviors. Bulk densities and porosities were calculated using the Archimedes method. XRD analysis were performed to calculate anatase/rutile ratios. Microstructures were characterized using SEM. Photocatalytic experiments have been performed under full spectrum irradiation. Degraded methylene blue samples were periodically monitored through UV–vis spectrophotometer to determine degradation kinetics. Anatase to rutile transformation is slightly faster and densification is better for lower temperatures for conventional heating, however HIPing gives better densification above 750 °C as it also retards rutile transformation. Mixed phase structures and HIPed samples showed the best photocatalytic performance which makes this method advantageous.     

Immobilization of hydrothermally produced TiO2 with different phase composition for photocatalytic degradation of phenol

Hydrothermally produced TiO₂ powders with different phase composition (anatase, rutile and mixed phase) were immobilized on glass fibers and tested in the phenol mineralization process. Both H₂O₂ and O₂ were used as oxygen donors, and their performances were compared with those of the same TiO₂ samples as slurries.The catalytic properties of the immobilized different crystalline phases, rutile and anatase, show the same trend as the slurry samples: pure rutile displays the highest catalytic efficiency in the presence of H₂O₂, while samples containing anatase improve the photodegradation efficacy with O₂. It was suggested that the stability of the photogenerated electron–hole couple allows high activity of rutile in the presence of H₂O₂, while the relevant oxygen chemisorption on anatase causes high catalytic activity in the presence of O₂. A four parameters kinetics model shows that both reaction steps, the phenol degradation and the mineralization of the intermediates, are photoactivated by TiO₂.Photoactivity of the coated glass fibers is generally lower than that of slurries, even if their efficiencies are almost comparable when the oxidation is performed by H₂O₂, while much lower when the oxygen donor is O₂. As a matter of fact, the morphology of immobilized catalysts shows the presence of chestnut burr aggregates of large rutile crystalline rods on the glass fiber, which are much less compact than the aggregates of small anatase particles. This preserves rutile surface area from the coarsening effects; thus, when rutile is the more active species, as in the presence of H₂O₂, the photocatalytic activity is less affected by immobilization.     

The kinetics of photocatalytic degradation of trichloroethylene in gas phase over TiO2 supported on glass bead

In this investigation, a packed bed filled with coated titanium dioxide glass beads to study the kinetics of photocatalytic degradation of trichloroethylene under irradiation of 365 nm UV light. In the range of 100–500 ml/min of flowrate, the reaction rate for 6 μM TCE increased with an increasing flowrate upto 300 ml/min, while was not affected by the flowrate at the values higher than 300 ml/min. For moisture in the range of 9.4–1222.2 μM, the reaction rate of TCE was decreased with an increasing humidity. The adsorbed water on the catalyst surface could compete with the adsorption of TCE on the sites. The reaction rate of 6 μM TCE increased as the light intensity increased, and was proportional to the 0.61 order of the light intensity. Among the three L–H bimolecular form models, the experimental data had the best fit for one of models:

     

Opposite effect of gas phase H2O2 on photocatalytic oxidation of acetone and benzene vapors

The effect of additions of gas phase H₂O₂ was measured for gas phase photocatalytic oxidation of organic vapors. Photocatalytic oxidation of benzene vapor over TiO₂ in a flow reactor resulted in a quick catalyst deactivation. Additions of gas phase H₂O₂ into the reactor feed provided enhanced and sustained oxidation of benzene vapor. The increase of inlet H₂O₂ vapor concentration from 0 to about 1000 ppm led to the one order of magnitude growth of benzene vapor complete oxidation rate. The highest rate of 1.1 nmol/s was observed at C₆H₆ concentration 124 ppm and H₂O₂ concentration 1000 ppm. In the case of acetone vapor photocatalytic oxidation, the rate of complete oxidation in the flow reactor decreased with an increase of gas phase H₂O₂ inlet concentration. TiO₂ Degussa P25 provided higher oxidation rate in the presence of H₂O₂ than pure anatase TiO₂.     

Photoanodic oxidation of small organic molecules at nanostructured TiO2 anatase and rutile film electrodes

A number of applications of titanium dioxide including air and water cleaning rely on photocatalytic activity of its anatase form while others making use of UV-shielding and reflectivity properties employ rather the rutile form. Here we compare photoelectrochemical activity of TiO₂ films formed from nanocrystalline anatase and rutile particles of similar sizes and shapes. Particularly high incident photon-to-current conversion efficiencies observed for the oxidation of organic molecules at the anatase films contrast with the poor activity of the nanostructured rutile films.     

Doped and undoped anatase-based plates obtained from paper templates for photocatalytic oxidation of NOX

Titanium dioxide is frequently used for the photocatalytic degradation of organic and inorganic pollutants present in the air, such as NOx. In this work, biomorphic anatase-based plates were manufactured using paper as an innovative template for fixation of TiO₂. Ceramics with microstructure similar to paper were produced by infiltration of titanium isopropoxide (TTiP) and dopants, followed by hydrolysis in NH₄OH, air drying, and calcination at temperatures up to 1000 °C. After heat treatment, the samples were characterized by XRD, TG/DTA, BET, EPR, and SEM. Anatase was obtained as the major phase at 800 °C and remained present up to 1000 °C. In tests of photocatalytic efficiency of produced plates for degradation of NO_x gases, the best performance was obtained with a biomorphic anatase-based plate prepared using TTiP doped with 5% Zr⁴⁺, corresponding to 100% degradation of NO_x in 35 min.     

Conversion of benzoic acid during TiO2-mediated photocatalytic degradation in water

The photocatalytic degradation of benzoic acid in water over Degussa P-25 TiO₂ suspensions was studied. UVA irradiation at 365 nm was supplied by a medium pressure mercury lamp providing 25 mW cm⁻² light intensity. Experiments were conducted at benzoic acid initial concentrations between 25 and 150 mg L⁻¹, catalyst loadings between 0.2 and 1 g L⁻¹ and initial solution pH values between 2 and 10.6. Conversion increased with increasing catalyst loading up to about 0.6 g L⁻¹ and it was favored at alkaline or neutral conditions but impeded at extremely acidic conditions. Increasing initial substrate concentration led to decreased benzoic acid conversion, which was found to follow a Langmuir–Hinshelwood kinetic expression. High performance liquid chromatography (HPLC) was employed to follow benzoic acid concentration profiles as well as to identify reaction by-products, while chemical oxygen demand (COD) and total organic carbon (TOC) analyses were carried out to assess the extent of mineralization. Benzoic acid hydroxylation by-products, namely 2-, 3- and 4-hydroxybenzoic acids as well as phenol were identified as reaction intermediates, although these contributed only a small fraction of the residual organic content. Although benzoic acid at 50 mg L⁻¹ was not ecotoxic to marine photobacteria Vibrio fischeri, its photodegraded solution exhibited substantial toxicity, which, however, proved not to be due to the identified intermediates.     

纳米TiO_2光催化机理及其毒理学研究进展

主要介绍了关于半导体纳米TiO2光催化反应机制、杀菌机理及其毒理学的国内外研究进展,最后提出了其在今后发展过程中需要解决的一些问题。     

Plasma dynamic synthesis of highly defective fine titanium dioxide with tunable phase composition

Titanium dioxide is currently one of the most known promising photocatalysts. However, its use in the visible light range is limited due to its high energy gap. In this work, to solve the mentioned problem, it is proposed to obtain highly defect structures of titanium dioxide by means of a high-energy plasma dynamic synthesis method. It possible to synthesize TiO₂ Titanium dioxide powders with a tunable ratio of rutile and anatase modifications, as well as a particle size distribution were synthesized, by optimizing the synthesis conditions, including the process energy and parameters of the gaseous medium. The formation of shock-wave structures in the pulsed synthesis process results in obtaining fine particles of rutile and anatase with a highly defective crystal structure. The final product was revealed to have an extended working absorption spectrum region and a reduced band gap (2.74 eV). A possibility of photocatalytic applications for the synthesized TiO₂ powder was demonstrated in measurements of photocurrent density with time (j-t) under intermittent visible light irradiation.