【作者】 秦好丽；

【导师】 古国榜； 柳松；

【作者基本信息】 华南理工大学 ， 环境工程， 2006， 博士

【摘要】 清洁能源―――太阳能的利用,环境污染的控制与治理是人类21世纪面临和亟待解决的重大课题,因此研究开发廉价、环境友好、高性能的可直接利用太阳能的光催化材料具有巨大的社会和经济效益。本文有目的的选择原料丰富、低毒甚至无毒、结构简单的尿素为有机氮源、碳酸铵、氨水为无机氮源,常温常压,采用条件温和的Sol-Gel方法制备了具有可见光活性的纳米N/TiO₂粉末。系统的研究了不同氮源、不同掺杂方式的氮掺杂二氧化钛的制备、表征以及不同光源下的光催化性能;采用兰格缪尔-欣谢尔伍德动力学方程中的积分动力学模型分析了染料甲基橙、无色巯基苯并噻唑降解过程中吸附平衡常数Ka、光降解速率常数kr对表观速率常数kap的影响;分析了降解终产物、降解过程中的pH变化以及降解体系中pH对降解的影响;并将N/TiO₂负载于γ-Al₂O₃空心球表面,应用于流化床反应器,对有机物的降解做了初步研究。运用XRD、TEM、BET、UV-Vis DRS、TG-DSC、XPS等测试手段,研究了不同氮源所制备N/TiO₂的性质,研究表明:①350-500℃煅烧温度下制备的N/TiO₂均为锐钛矿相,随煅烧温度的升高,晶型渐趋完整,600℃以上为金红石相;晶粒因氮的掺杂而增大,且随N/Ti配比的增大而增大;②396eV处β-N1s峰的存在证明氮掺杂进入TiO₂晶格中形成N-Ti-O键,且在O2p能带之上产生一个独立存在的N2p窄带,该窄带引起N/TiO₂在可见光区的光吸收,产生可见光活性;该窄带的存在没有引起N/TiO₂光吸收边带发生红移现象;黄色N/TiO₂粉末的可见光吸收强度随N/Ti配比的增大而增大,随煅烧温度的升高及煅烧时间的延长而降低,且存在颜色越深,可见光吸收强度越大的关系;③由于尿素、碳酸铵为易分解物质,氨水为易挥发物质,加上部分氮元素在煅烧过程中氧化成NOx逸出,这些因素导致N/TiO₂为多孔材料,具有比TiO₂更多的孔道、孔型。尿素、碳酸铵、氨水为氮源所制备N/TiO₂的比表面积分别为139.31、132.76和116.32m²/g,这与纯TiO₂相比,比表面积的增大约一倍,为有机物的吸附提供有利条件;④氮的掺杂引起TiO₂晶格中的氧空缺,进而引起Ti³⁺的产生;随N/Ti配比的增加,Ti³⁺、表面羟基所占百分比含量增大。分别以卤钨灯、高压汞灯为激发光源,甲基橙、巯基苯并噻唑为分子探针,对比研究了不同制备条件所获得N/TiO₂的光催化性能,研究发现:①在滤除紫外光的卤钨灯（可见光）照射下,N/TiO₂对于甲基橙、巯基苯并噻唑的可见光催化性能均高于TiO₂;受Ti³⁺、表面羟基等因素的影响,对于不同的氮源（尿素、碳酸铵、氨水）,均存在一个最佳N/Ti配比浓度（分别为20mol%、20mol%、4mol%）,对应最佳的可见光催化活性;随煅烧温度的升高、煅烧时间的延长,N/TiO₂的可见光活性逐渐降低,600℃以上没有可见光活性;②在高压汞灯（紫外光）照射下,N/TiO₂对有机物的降解速率远高于可见光下的降解速率,以及N/TiO₂的紫外光活性低于TiO₂的现象,均源于独立存在的N2p所引发的不同光激发机理;③非均匀掺杂制备的催化剂的紫外光活性高于N/TiO₂,可见光活性正好相反。根据吸附等温线计算得到吸附平衡常数Ka,由于Ka值很大,KaC不可忽略,所以运用兰格缪尔-欣谢尔伍德动力学方程中的积分动力学模型分别对甲基橙、巯基苯并噻唑在可见光下的降解动力学进行了系统的研究,研究发现:不同氮源所制备的N/TiO₂均提高了有机物的吸附,巯基苯并噻唑的吸附量大于甲基橙;对于甲基橙降解体系,光降解速率常数对表观速率常数增大的作用较显著,对于巯基苯并噻唑体系,吸附作用的改善对表观速率常数的贡献更大,造成该差异的原因与有机物的分子结构、功能团等因素有关;不同氮源所制备的N/TiO₂催化剂与TiO₂相比,在甲基橙降解中,表观速率常数最大提高13.79倍,对巯基苯并噻唑的降解最大提高8.10倍。将N/TiO₂负载于γ-Al₂O₃空心球表面制得固定化光催化剂,应用于自制模拟流化床反应器中,在卤钨灯照射下,显示出一定的光活性;考察了浸涂方式、有氧、无氧状态以及外加H₂O₂对降解的影响,研究表明多层交叉浸涂、有氧状态及外加H₂O₂均提高了光催化活性。分别采用分光光度法、UV-Vis扫描、TOC、CODcr以及离子色谱对降解过程进行了分析。有机酸小分子的生成致使降解过程中pH略有下降。另外,改变巯基苯并噻唑体系的pH发现:碱性或酸性条件均不利于降解。更多还原

【Abstract】 The utilization of solar energy, a clear energy, control and treatment of environmental pollution are important problem that should be faced and resolved in 21th century. So the research and development on cheap photocatalysts with high performance, which can utilize solar energy directly and environmental friendly, have enormous social and economic benefit.Nano N/TiO₂ powders with visible-light activity were prepared by Sol-Gel method under mild condition, with nitrogen source from urea, salvolatile and ammonia, respectively, which are all low toxic or nontoxic, abundant materials with simple structure. A systematic study of the preparation with different nitrogen source and different doping mode, characterization and photocatalytic activity under different kinds of light were presented. The influence of photoreaction kinetic constants kr and adsorption equilibrium constants Ka on the apparent reaction kinetic constants kap was analysed with the integral mode of the Langmuir-Hinshelwood kinetics in the photodegradation process of dye methyl orange and achromaticity 2-mercaptobenzothiazole. The end products, pH alteration of photodegradation process and the influence of pH on system were investigated. The application of N/TiO₂, loading on the surface of hollow sphere ofγ-Al₂O₃, to the fluid-bed reactor was investigated preliminarily.The crystal structure, particle size, surface area, and optical absorption properties of N/TiO₂ with different nitrogen source had been investigated by means of XRD, TEM, BET, UV-Vis DRS, TG-DSC and XPS. The results were showed as follows:①The crystal structure of N/TiO₂ calcined at 350-500℃were all anatase, which was maturity with increase of calcination temperature, and changed into rutile at 600℃. The crystal size increased with doping, and augment with increase of N/Ti proportioning.②Nitrogen doped into TiO₂ lattice to form N-Ti-O, which was proved byβ-N1s at 396eV by XPS. There was independent narrowband N_2p lied upper side of O_2p, which induced no red-shift with N/TiO₂. The optical adsorption intensity of yellow N/TiO₂ enhanced with increase of N/Ti proportioning, and weakened with increase of calcination temperature and calcination time. The darker the color was, the stronger the optical adsorption was in visible light region.③Due to decomposition of urea and salvolatile, volatilization of ammonia, and the oxidation of nitrogen into NOx, N/TiO₂ formed multiporous structure. The specific area of N/TiO₂ prepared with nitrogen source from urea, salvolatile, and ammonia were 139.31, 132.76, 116.32m²/g, respectively, which were about two times as that of TiO₂, and supplied advantage condition for adsorption of organic substance on N/TiO₂.④The doping of nitrogen induced the formation of oxygen-vacancy and then induced Ti³⁺, the percent of Ti³⁺ and surface hydroxyl group increased with increase of N/Ti proportioning.Photocatalytic degradation of methyl orange and 2-mercaptobenzothiazole in N/TiO₂ suspension with different nitrogen source irradiated by tungsten halide lamp and high-pressure mercury lamp was comparatively investigated. The results showed as follows:①N/TiO₂ exhibited higher visible-light activity than TiO₂ in the degradation of methyl orange and 2-mercaptobenzothiazole under the irradiation of tungsten halide lamp filtered part of UV light. Due to effect of Ti3+ and surface hydroxyl group, there was an optimal doping of N/Ti proportioning exhibiting highest visible-light activity with 20mol%, 20mol% and 4mol% for urea, salvolatile and ammonia, respectively. The visible-light activity of N/TiO₂ weakened with increase of calcination temperature and calcination time, and N/TiO₂ calcined higher than 600℃showed no visible-light activity.②Due to the presence of independent narrowband N2p, N/TiO₂ would exhibit much higher activity for degradation of organic substance under the irradiation of high-pressure mercury lamp than the irradiation of tungsten halide lamp, and it showed worse UV-light activity than TiO₂.③Compared to N/TiO₂, N/TiO₂ with non-uniform doping showed higher UV-light activity and poor visible-light activity.According to the adsorption equilibrium constants Ka, the systematic study of kinetics should be adopted with integral mode of the Langmuir-Hinshelwood kinetics in the photodegradation process of methyl orange and 2-mercaptobenzothiazole. As a result, adsorption amount of organic substance on N/TiO₂ enlarged by nitrogen doping, and adsorption amount of 2-mercaptobenzothiazole was more than that of methyl orange. The effect of photoreaction was higher than that of adsorption in the system of methyl orange, and the reverse results in the system of 2-mercapbenzothiazole. The difference was related to molecular structure and function group of organic substance. Compared to TiO₂, kap of N/TiO₂ improved obviously, corresponding to about 13.79 times in the system of methyl orange, and 8.10 times in system of 2-mercaptobenzothiazole.The application of N/TiO₂ loading on the surface of hollow sphere ofγ-Al₂O₃ to the fluid-bed reactor was investigated preliminarily under irradiation of tungsten halide lamp, which exhibited some activity. Such factors as dip-coating mode, existence of oxygen or without oxygen, presence of H2O2 were all investigated. The results showed that multi-dip-coating mode, existence of oxygen and H2O2 would improve the photoactivity.The photocatalytic degradation process and products were investigated by means of UV-Vis adsorption spectra, TOC, CODcr, ion chromatography. Due to the formation of small molecule organic acid during the degradation process, the value of pH decreased appreciably.In addition, the condition of basic or acid would generate infaust effect in the system of 2-mercapbenzothiazole.更多还原