纳米二氧化钛粉体的多晶型制备及形成机理

本文分别以四氯化钛、硫酸钛和钛酸丁酯为前驱物,研究了水热条件下二氧化钛微晶粉体的结晶晶型、晶粒形貌和晶粒度.采用XRD和TEM等分析手段分别对产物的晶相和晶粒形貌进行表征.实验结果表明:对于200℃水热反应,以四氯化钛为前驱物,通过加入氢氧化钠调节反应介质酸碱度,当溶液pH值小于1时,有利于形成金红石型粉体;当溶液pH值大于3并小于7时,有利于形成锐钛矿型粉体;当溶液ph值大于7时,有利于形成板钛矿型粉体.以硫酸钛为前驱物,通过控制胶体制备工艺及反应温度,制备得到锐钛矿型和板钛矿型粉体.金红石型粉体呈长条柱状,锐钛矿呈菱形或双锥状,板钛矿呈板块状.经过较为系统的实验研究,获得了金红石、锐钛矿、板钛矿三种晶相的粉体,并可通过控制前驱物的种类及酸碱度和水热反应条件随意地制备出以上三种晶相中的单晶相粉体.从结晶学出发,解释了二氧化钛纳米粉体的结晶形貌,并从晶体生长过程及生长机理的角度讨论了二氧化钛同质变体的形成机理.     

水热温度对二氧化钛结构及光催化活性的影响

以四氯化钛、环氧丙烷和乙醇为原料,采用水热法在不同温度下分别合成了金红石相纳米二氧化钛及板钛矿相与金红石相混晶结构的纳米二氧化钛,并利用X射线衍射(XRD)、透射电镜(TEM)和N2吸附-脱附对其进行了表征。以甲基橙为探针研究了不同水热温度对二氧化钛光催化活性的影响。     

低温制备锐钛矿型TiO2溶胶的性能研究

采用溶胶-凝胶法,以水为溶剂,在低于70℃下直接合成纳米锐钛矿型TiO2溶胶,研究了反应温度、pH值对溶胶晶型、晶粒大小和稳定性的影响.以不同光照下对亚甲基蓝的降解,评价了溶胶的光催化活性.结果表明:较低pH值下溶胶中的TiO2出现了金红石相与锐钛矿相组成的混晶相,而pH值相对较高时则得到纯锐钛矿相TiO2;在紫外光、日光灯和太阳光下,与P25对亚甲基蓝的降解相比,同等条件下所制备的TiO2溶胶显示出更好的光催化活性;混晶相TiO2溶胶的光催化性优于纯锐钛矿相TiO2溶胶.     

板钛矿相对TiO2纳米晶相转变的影响研究

本文以Ti(O BU) 4为前驱体 ,采用溶胶 凝胶工艺制备了TiO2 纳米晶。通过X 射线衍射 (XRD)分析证明了所制备的锐钛矿相TiO2 纳米晶中含有一些板钛矿相 ,发现在较低的热处理温度下 ,TiO2 纳米晶就发生了相转变 ,并且板钛矿 金红石相转变的过程比锐钛矿 金红石相转变过程快 ;同时锐钛矿相的晶胞常数c的变化似乎部分归因于有板钛矿相的存在。差热 热重同步分析 (DTA TGA)表明 ,在 36 0～ 5 0 0°C之间 ,可以观察到板钛矿 锐钛矿相转变的存在。最后对TiO2 纳米晶中含有的板钛矿相对锐钛矿 金红石相转变的作用机制进行了简要的分析。     

混晶结构纳米TiO2粉的光催化活性

以钛酸四丁酯为钛源制备混晶结构纳米TiO2粉,研究了纳米TiO2的光催化活性与颗粒晶相结构之间的关系．结果表明,当金红石相的质量分数少于18．53％,光催化活性随着金红石相的增多而降低;当金红石相的质量分数为18．53％-28．2％时,随着金红石相的增多,光催化活性逐渐增强,在28．2％附近具有最高的光催化活性,与纯锐钛矿结构纳米TiO2粉的光催化活性相当;金红石相含量继续增加,则光催化活性逐渐降低．适量金红石相的存在有利于锐钛矿相中的电荷分离,使光催化活性提高．     

二氧化钛催化剂晶型调控技术的研究进展

综述二氧化钛由锐钛矿向金红石晶型转变调控技术的最新成果,分析温度、氧化物和以及离子掺杂对实现晶型转变的影响规律,重点研究氧化物和离子掺杂对晶型转变的影响。结果显示:复合金属氧化物熔点低于TiO2熔点时,可促进锐钛矿型TiO2向金红石型转变;而金属氧化物熔点高于TiO2熔点时,可阻碍晶型转变;掺杂离子的离子半径、化合价、离子大小对二氧化钛晶型转变及催化性能有明显的影响,当掺杂金属离子半径大于或小于Ti4+半径,使得锐钛矿型TiO2更稳定;当掺杂离子的半径与Ti4+半径相近时,有利于锐钛矿型向金红石型转变,而体积较小的低价阴离子有利于金红石型二氧化钛的的生成,体积较大的高价阴离子则有利于锐钛矿型二氧化钛的的生成;阴阳离子共掺杂可以有效地调控二氧化钛晶型转变,并且能够提高TiO2的光催化活性。探讨二氧化钛多晶之间的协同作用,并基于二氧化钛掺杂改性的计算模拟,指出今后的发展方向。     

纳米金红石型TiO2的低温制备

分别在中性，碱性和酸性环境下对钛酸四丁酯溶液进行水解以制备纳米二氧化钛。在中性和碱性环境下水解产物是非晶态的，当温度低于700℃煅烧只能得到脱钛矿型二氧化钛。在酸性环境下，通过调整酸和水的加入量将溶液在低温下（40－50℃）水解合成了从纯锐钛矿相到不同比例锐钛矿－金红石混晶相，再到纯金红石相的纳米二氧化钛，乙醇的加入促进凝胶的形成以及锐钛相向金红石相的转化。     

不同介质中水热合成纳米TiO2粉体及其光催化性能研究

以钛酸四丁酯为原料,采用水热法分别以蒸馏水、有机小分子化合物(正丁醇、丙二酸和乙二胺水溶液)和无机酸(HNO3、H2SO4和HCl)为介质合成了TiO2纳米粉体.通过XRD和TEM对所得TiO2粉体进行了表征,研究不同介质对所得TiO2粉体的晶相组成、颗粒尺寸及形貌的影响.结果表明:以蒸馏水为介质时所得锐钛矿TiO2的颗粒尺寸分布不均匀;有机化合物抑制锐钛矿型TiO2各向异性生长趋势的能力为:正丁醇＞丙二酸＞乙二胺;相同实验条件下,HCl、H2SO4及HNO3体系中分别获得金红石、锐钛矿及锐钛矿和金红石混晶TiO2.光催化降解甲基橙的研究表明,锐钛矿和金红石混晶TiO2的光催化活性要高于纯锐钛矿结构;纯金红石型TiO2的光催化活性最差.     

板钛矿基TiO2纳米晶的结构相变和热稳定性

研究含一定量锐钛矿和金红石的板钛矿基ＴｉＯ２纳米晶的热稳定性。发现其ＤＴＡ曲线上出现两个吸热峰。ＸＲＤ相似,晶粒度和相含量分析表明,出现于３０－１６０℃温区的Ａ峰对应于脱附过程;出现了７８０－８４５℃温区的Ｂ峰对应于样品结构从板钛矿经锐钛矿向着金红石的急剧一级相变;在Ｂ峰出现前,样品中存在板钛矿向锐钛矿的缓慢转变过程;相就促进了纳米晶粒的生长。     

介孔TiO2载银纳米复合材料的制备及性能研究

运用醇热法制备介孔二氧化钛(m-TiO_2),并借助光还原法制备m-TiO_2载银(m-TiO_2/Ag)复合材料,通过透射电镜和X射线衍射等手段对复合材料的形貌和组成进行表征,并以亚甲基蓝(MB)的脱色降解来表征不同Ag含量样品的光催化性能,通过生长曲线、最小抑菌浓度和抑菌环对其抗菌性能进行表征。结果表明:用醇热法制备的m-TiO_2是以锐钛矿为主含有少量板钛矿的混晶,金属Ag颗粒沉积在m-TiO_2表面;纳米银负载可显著提高mTiO_2的可见光光催化性能;亚甲基蓝的光催化降解反应遵循一级反应动力学模型;m-TiO_2/Ag复合材料的抗菌性能随着载银量的增加而逐渐提高。     

Solvothermal-induced phase transition and visible photocatalytic activity of nitrogen-doped titania

Nitrogen-doped titania nanoparticles consisting of pure anatase, pure rutile and bicrystallites (anatase+rutile and anatase+brookite) have been prepared in TiCl(3)-HMT (hexamethylene tetramine)-alcohol solution under solvothermal process. The effect of the solvent type and amount of HMT as pH adjuster on the phase composition of titania and its visible photocatalytic activity for degradation to MO (methyl orange) was investigated. It is found that anatase gradually transferred to rutile with increase of carbon chain using methanol, ethanol, 1-propanol and 1-butanol as solvent. The pure anatase formed at the pH value of 1-2, while bicrystalline titania (anatase+rutile and anatase+brookite) at that of 7-10 in the presence of methanol. The bicrystalline (anatase+brookite) titania have the best visible photocatalytic activity among all the samples. The -(NO) and -(NH) dopants with an N (1s) binding energy of 400 eV may have positive effects on the visible light photocatalytic activity.     

不同介质中水热合成纳米TiO2粉体及其光催化性能研究

以钛酸四丁酯为原料, 采用水热法分别以蒸馏水、有机小分子化合物(正丁醇、丙二酸和乙二胺水溶液)和无机酸(HNO₃、H₂SO₄和HCl)为介质合成了TiO₂纳米粉体. 通过XRD和TEM对所得TiO₂粉体进行了表征, 研究不同介质对所得TiO₂粉体的晶相组成、颗粒尺寸及形貌的影响. 结果表明: 以蒸馏水为介质时所得锐钛矿TiO₂的颗粒尺寸分布不均匀; 有机化合物抑制锐钛矿型TiO₂各向异性生长趋势的能力为: 正丁醇>丙二酸>乙二胺; 相同实验条件下, HCl、H₂SO₄及HNO₃体系中分别获得金红石、锐钛矿及锐钛矿和金红石混晶TiO₂. 光催化降解甲基橙的研究表明, 锐钛矿和金红石混晶TiO₂的光催化活性要高于纯锐钛矿结构; 纯金红石型TiO2的光催化活性最差.     

Solvothermal synthesis of visible light responsive nitrogen-doped titania nanocrystals

Nitrogen ion-doped titania nanoparticles were obtained by the homogeneous precipitation in hexamethylenetetramine-titanium trichloride mixed solution followed by heat treatment in the solution at desired temperatures. After that the sample powders obtained were calcined in air at desired temperatures. Various phases of titania such as anatase, rutile and brookite were obtained depending on the reaction condition. Crystallite size, specific surface area and color also greatly changed as 5-50 nm, 20--200 m²·g^-1 and light gray-yellow, respectively, depending on the solvent, pH, etc. The products after calcination around 400°C were yellow indicating doping with nitrogen ion. Photocatalytic activity for the oxidative decomposition of NO in air atmosphere was also evaluated by using a continuous flow system with 1 ppm NO gas, where the high pressure mercury arcs filtered using various filters were irradiated. All colored titania nanoparticles showed photocatalytic activity under visible light irradiation for the oxidative decomposition of nitrogen monoxide in air. Especially, the nanoparticles of anatase type nitrogen-doped titania obtained by the homogeneous precipitation using hexamethylenetetramine-methanol aqueous solution around 200°C showed excellent photocatalytic activity under visible light irradiation.     

TiO2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,并值增加,Ti^3＋含量较高,光催化活性增加。     

Photocatalytic decomposition of methylene blue on nanocrystalline titania prepared by different methods

Nanocrystalline particles of pure anatase titania were prepared by two different methods. One is the sol-gel method at ambient temperature using ultrasonication (TiO₂-SG-US) and conventional stirring method (TiO₂-SG-S) and the other by surfactant assisted hydrothermal synthesis (TiO₂-HT). More uniform distribution/dispersion of the nanoparticles (SEM), marginally higher surface area, better thermal stability and phase purity are some of the advantages of preparation of nanocrystalline titania by sol gel ultrasonication method and hydrothermal synthesis method. The behavior of anatase titania in photocatalytic decomposition of methylene blue in aqueous medium was studied as a function of the method of preparation and the crystallite size. The nanoparticles prepared by ultrasonication method were more effective than both, the sample prepared by conventional stirring method and commercial Degussa P-25. The higher photocatalytic activity of TiO₂-SG-US is attributed to the more uniform size of the particles as compared to TiO₂-SG-S samples. Both TEM and XRD data on TiO₂-HT samples reveal a uniform and nanocrystalline TiO₂ particles, which showed photocatalytic activity in both UV and visible region although brookite phase was also present.     

Hydrothermal conversion of Mg2TiO4 into brookite-type TiO2 under mild conditions

A simple and mild synthetic route via a hydrothermal treatment of Mg₂TiO₄ has been developed to prepare brookite-type TiO₂. The hydrothermal conversion of Mg₂TiO₄ to brookite proceeded in 1 M HCl solution even at 100 °C. The converted brookite grains were composed of the angular particles covered on the textured surface, leaving the original morphology of Mg₂TiO₄ grains. Compared with the commercially available TiO₂ catalysts (rutile, anatase, and P25), the brookite obtained in this study showed a good photocatalytic activity toward the oxidation of benzyl alcohol to benzaldehyde under a simulated sunlight irradiation.     

Microstructures and Photocatalytic Properties of S Doped Nanocrystalline TiO2 Films

The nanocrystalline S doped titanium dioxide films were successfully prepared by the improved sol-gel process. Here TiO(C₄H₉O)₄ and CS(NH₂)₂ were used as precursors of titania and sulfur, respectively. The as-prepared specimens were characterized using x-ray diffraction (XRD), x-ray energy dispersive spectroscopy (EDS), high-resolution field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) surface area, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of organic dyes in aqueous solution. The results of XRD, FE-SEM, and BET analyses indicated that the TiO₂ films were composed of nanoparticles. S doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO₂ film, S doped TiO₂ film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the modified films is responsible for improving the photocatalytic activity.     

Influence of calcination parameters on the TiO2 photocatalytic properties

Nanocrystalline titanium dioxide (TiO₂) powders with different crystal phase composition were obtained by controlled hydrolysis and post-thermal treatments. The physicochemical properties of the powders were investigated by XRD, TEM/EDS, N₂ physic adsorption and DRS. The results obtained show that the particle size and crystalline structure are parameters strongly dependent on the calcination conditions, mainly temperature and heating rate. The influence of the TiO₂ phase composition on its photocatalytic activity, concerning the methylene blue photodegradation was studied. It was found that higher TiO₂ photocatalytic activity is related with the co-existence of the three TiO₂ polymorphs: anatase, brookite and rutile.     

Photocatalytic degradation of dyes and organic contaminants in water using nanocrystalline anatase and rutile TiO2

Nanocrystalline TiO₂ was synthesized by controlled hydrolysis of titanium tetraisopropoxide. The anatase phase was converted to rutile phase by thermal treatment at 1023 K for 11 h. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier-transform infrared absorption spectrophotometry (FT-IR) and N₂ adsorption (BET) at 77 K. This study compare the photocatalytic activity of the anatase and rutile phases of nanocrystalline TiO₂ for the degradation of acetophenone, nitrobenzene, methylene blue and malachite green present in aqueous solutions. The initial rate of degradation was calculated to compare the photocatalytic activity of anatase and rutile nanocrystalline TiO₂ for the degradation of different substances under ultraviolet light irradiation. The higher photocatalytic activity was obtained in anatase phase TiO₂ for the degradation of all substances as compared with rutile phase. It is concluded that the higher photocatalytic activity in anatase TiO₂ is due to parameters like band-gap, number of hydroxyl groups, surface area and porosity of the catalyst.     

SiO2/TiO2催化剂的制备及其光催化性能

利用钛酸四丁酯、正硅酸乙酯、乙酸和水为原料, 通过溶剂热方法制备得到SiO₂/TiO₂催化剂. 产物经XRD、Raman、TEM、BET、FT-IR和XPS表征, 结果表明: 所制备的SiO₂/TiO₂催化剂为比表面积大、结晶度高的锐钛矿TiO₂, SiO₂与TiO₂之间通过Si-O-Ti键结合. 另外, 以亚甲基蓝降解为探针反应, 考察了SiO₂/TiO₂催化剂在紫外光照射下的光催化性能. 结果表明: SiO₂/TiO₂催化剂具有比纯TiO₂更优越的光催化性能, 65min可以将亚甲基蓝(MB)彻底降解.