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低浓度有机废气负载型纳米TiO_2光催化处理技术
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摘要
随着工业化进程的加快和发展所造成的环境恶化,特别是大气污染,已成为亟待解决的城市环保问题之一。由于工业源排放的有毒废气存在浓度低且扩散面积广的特点,采用传统的废气净化方法不仅昂贵而且难以应用。纳米TiO2作为一种半导体光催化材料具有无毒,催化效率高、性能稳定等突出特点,可以用于光催化净化空气,它已成为目前光催化研究领域中最活跃的方向之一。本文采用溶胶-凝胶法制备了纳米TiO2溶胶,研究了三种不同载体负载及其固定化方法,选用甲苯为目标污染物,通过自制的一套气体发生和光催化反应装置,利用气相色谱对甲苯去除效率进行测定,评价其光催化活性。最后对活性炭负载光催化剂失活的再生方法进行了研究。
     首先是在以往实验成果的基础上对TiO2溶胶制备工艺参数做了进一步研究,实验表明控制钛酸丁酯︰无水乙醇︰去离子水︰冰醋酸体积比为5︰40︰2︰5,调整溶胶pH值为4,能得到稳定的溶胶体系。溶胶形成凝胶,陈化时间约为22小时。另外在溶胶中掺杂摩尔分数1%的过渡金属钴有助于进一步减小TiO2晶粒尺寸,从而提高其光催化活性。
     分别选用铝片、不锈钢网以及竹活性炭作载体完成TiO2的负载,通过X射线衍射、FSEM扫描电镜等方法对催化剂微观结构进行表征。利用自制的光催化反应装置,以甲苯为目标污染物,对甲苯去除效率进行测定,其中以活性炭为载体,甲苯最高达到80%的光催化降解效率。去除效果为活性炭>不锈钢网>铝片。同时研究了反应初始浓度、气体流速对光催化降解甲苯效率的影响。实验研究结果表明:甲苯的去除量随负荷增加而上升,但上升趋势逐渐变缓,流量和浓度变化逐渐导致去除量变化;随负荷的进一步增加,甲苯的光催化去除量反而下降。
     最后研究了活性炭负载光催化剂失活的再生方法。利用傅立叶变换红外光谱分析了催化剂失活的原因,实验发现通过在紫外光照下通入洁净空气、微波辐照、高温处理等方法可以完全或部分恢复催化剂的活性,实现再生。但从工艺成本、时间考虑,认为微波辐照是实现催化剂再生的比较理想的方法。
The deterioration of environment, especially the atmosphere pollution, resulting from the increasing and developing of industrialization, has become one of the city's environment problems, which is an absolutely urgent problem. Nano- TiO2 is the very novel green catalyst with its renewal ability and storability of energy and friendliness of environment. Now its relevant study becomes the focus of the field of photocatalysis, especially in exhaust gas treatment. In this paper, nano-TiO2 sol was prepared by sol-gel method and different carriers and supported method were investigated. Selected toluene as the target pollutant, through a set of DIY gas occurrence and photocatalysis reaction device, mensurated its take-off efficiency by the gas chromatography to appraises its photochemical catalysis activeness. Finally has researched the deactivated charcoal-loaded photocatalyst’s regeneration method.
     Firstly, on the basis of the former research, we further studied the technical parameters of TiO2 sol preparation, it is found that to control the volume of Tetrabutyl Titanate、Anhydrous Alcohol、Water and Glacial Acetic Acid by the proportion of 5︰40︰2︰5, pH value is 4, stable sol system can be obtained. Sol forms a gel after laying for about 22 hours. Moreover, dopes the mole score of 1% transition metal Co2+in the sol can help further reduced the grain size of TiO2 crystal, thus enhancing its photochemical catalysis activeness.
     Aluminum sheet, stainless steel net and bamboo-made actived carbon are respectively selected as the TiO2 loaded carriers (the carriers which loads TiO2), and measured their performance by X-ray diffraction and FSEM techniques. Taking toluene as the target pollutant, using the photocatalysis reaction device, its take-off efficiency is mensurated, and the influence of the reactant initial concentration and the gas flow rate to toluene degradation efficiency are studied. The results showed that when taken the activated carbon is used as the carrier, the degradative efficiency of toluene can reach to 80%. The removal effect using the activated carbon is higher than the stainless steel, and that using aluminum sheet is the lowest. The take-off amounts of toluene is increased with the load increasing, but the uptrend gradually goes slow, the current capacity and the concentration change gradually lead to different removal; with the load further increasing, the take-off amounts of toluene come down.
     Finally, the regeneration method of the deactivated charcoal-loaded photocatalyst has been investigated. The reason why catalyst became deactivated has been analyzed by FT-IR technique. We found that the catalyst’s activeness can be completely or partially restored with the method of passing clean air into the reactor under ultraviolet illumination, microwave irradiation and high-temperature treatment, realizing regeneration. However, from the point of running cost and time, the microwave irradiation is one of the most ideal method to realize catalysis’s regeneration.
引文
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