【作者】 李纲；

【导师】 张其春；

【作者基本信息】 成都理工大学 ， 矿物材料学， 2007， 硕士

【摘要】 光催化氧化技术是一种新型的废水处理技术，具有处理效率高、工艺设备简单、操作条件易控制、无选择性地降解有机污染物等突出优点，已在废水处理领域显示出巨大的应用潜力。有关CeO₂作为三效催化剂、化学机械抛光（CMP）材料、氧气传感器、固体氧化物燃料电池（SOFC）、紫外吸收材料等的研究较多。在光催化应用方面，CeO₂均被作为一种助剂掺杂到其它氧化物中来增强本体氧化物的光催化活性，鲜见对以CeO₂为基质的光催化剂的研究。因此，本论文以制具具有高降解能力的铈基光催化剂为目标，探讨用实验室常规方法制备二氧化铈基光催化剂的可能性，为其工业化应用提供理论依据。主要研究内容和获得的认识如下：（1）以铈盐为原料，分别采用四种常规湿化学方法，即高分子网络凝胶法、直接沉淀法、两步沉淀法、溶胶聚沉法制备出纳米CeO₂。以亚甲基兰溶液为降解模型，考察了纯纳米CeO₂的紫外光催化性能。实验结果表明，采用实验室常规方法制备的纯CeO₂纳米粉体的光催化性能极其微弱。（2）为了改善CeO₂纳米粉体的光催化性能，分别以两步沉淀法、溶胶聚沉法制备出的CeO₂为起始，采用浸渍一沉淀法在其表面复合微量Ag，经过低温焙烧，得到Ag／CeO₂复合物并考察了其紫外光光催化性能。光催化结果表明，与纯CeO₂纳米粉体相比，Ag／CeO₂-1（溶胶聚沉法所得粉体复合Ag所得）的紫外光催化性能显著改善，表现出良好的紫外光催化性能；而Ag／CeO₂-2（两步沉淀法所得粉体复合Ag所得）的紫外光催化性能未见明显提高。催化效果的差异体现了溶胶聚沉法制备出的CeO₂性质的特殊性。（3）对高降解能力铈基光催化剂Ag／CeO₂-1的制备工艺和光催化降解条件进行了优化研究。优化的制备工艺为：用0.1mol／L AgNO₃浸渍CeO₂后，加入2％Na₂CO₃溶液与之反应，将所得沉淀依次水洗、醇洗，350℃焙烧2h。优化的粉体投加量为2g／L；初始pH值对催化剂的降解性能有明显的影响，强酸或强碱性条件有利于亚甲基兰溶液的降解；前30min亚甲基兰溶液的紫外光催化降解速率方程为ln（C₀／C）=—0.0222+0.02056t，表观降解速率常数为0.02056 min^-1，显示出一级动力学特征。（4）初步研究了Ag／CeO₂-1催化剂在阳光下的降解性能。阳光下，Ag／CeO₂-1催化剂对可见光具有良好的光响应性，表明其是一种广谱的光催化剂。（5）针对回流胶溶法制备溶胶耗时的缺点，改进了纳米CeO₂水溶胶的制备工艺，即利用铈（Ⅳ）与非铈稀土的氢氧化物的溶解pH值的差异，选择性地溶解非铈稀土氢氧化物，快速制备出含有La³⁺的纳米CeO₂水溶胶。该改进方法不仅使制备溶胶的流程大为简化，获得的溶胶稳定性高，而且最终获得的目标产物的光催化能力与回流胶溶法所得溶胶衍生产物的催化能力相近。本论文的研究的价值在于，首次采用实验室常规方法制备出了具有高降解能力的、对紫外光和可见光均具有良好光响应的广谱铈基催化剂。该研究拓宽了光催化剂的开发思路，也为新型催化剂的开发提供了理论基础，这对于充分利用我国得天独厚的铈稀土资源必将产生深远的影响。更多还原

【Abstract】 Photocatalytic oxidation technology has a great potential for the removal of organic pollutants from wastewater by virtue of its high treatment efficiency, simple processing equipment, easy operation conditions and decomposing organic pollutants non-selectively.Many researches have been focused on the performances of cerium oxide as a excellent material in the fields of three-way catalysts, chemical-mechanical polishing （CMP）, oxygen gas sensor, solid oxide fuel cells （SOFC）, UV absorbent and so on. It is well known that the photocatalytic activity of MO_x photocatalysts can be reinforced by doping limited cerium. However, study on photocatalytic activity of pure CeO₂ has rarely been reported.In the present work, the probability of preparing photocatalyst of ceria matrix with high activity will be studied.The main research contents and conclusions are as followed:（1）Nanometer ceria was prepared by four different methods （polyacrylamide method; direct precipitation method; two-stage precipitation method and sol-aggregation method） using cerium salts as starting materials. The tests on photocatalytic degrading of methylene blue （MB） using as-prepared pure CeO₂ were investigated. The photocatalytic activity of pure CeO₂ was very weak according to the experimental results.（2） Ag/CeO₂ composite powders were obtained by loading little Ag on the surface of pure CeO₂ through immersion-precipitation method. Then photocatalytic experiments were carried out under ultra-violet light. Ag/CeO₂-1 sample （derived from sol-aggregation） showed an excellent photocatalytic performance compared to non-modified ceria powders. In contrast, there was no obvious enhancement in the photocatalytic activity for Ag/CeO₂-2（derived from two-stage precipitation）. The significant different photocatalytic performance for degrading MB between the two samples indicated the specialty of CeO₂ powders from sol-aggregation method.（3） In order to obtain Ag/CeO₂ photocatalyst with good photocatalytic behavior, the preparation treatments were optimized. In addition, the suitable conditions for degrading organic pollutants were systematically studied. The optimum preparation conditions for the catalyst were as followed: nanometer CeO₂ powders from sol-aggregation method were immersed with 0.1 mol/L AgNO₃, then 2% Na₂CO₃ was added to react. Subsequently, the precipitation was washed with distilled water and absolute alcohol, successively. Finally, the intermediate was calcinated at 350℃for 2h. Effects of dosage of powders and reaction pH on degradation ratio were determined, respectively. The results indicated that the photocatalytic activity reached the maximum, when the amount of catalyst was 2.0 g/L, the initial pH value was distributed in the range of strong acidity or alkalinity. The rate of photodegradation in aqueous solution was followed first-order kinetics before the first 30 minutes. It can be stated as the equation: In （C₀/C）=-0.0222+0.02056t.（4） The photocatalytic activity under solar light was studied also. The photocatalyst of Ag/CeO₂ exhibited a good visible-light response, namely, had a broad-spectrum activity for degrading organic pollutants.（5） An improved method for preparing CeO₂ sol was proposed. Namely, CeO₂ sol accompanied with La³⁺ could be obtained rapidly based on the different pH values when hydroxide mixture composed of cerium （Ⅳ） and other non-cerium rare earth were solubilised by nitric acid. It overcame the time-consuming disadvantages compared with the original method. Not only was the process treatment via the new improved method shortened dramatically, but the mixed sol was very stable. What’s the most important was the property of the objected-product wasn’t impaired.The value of this paper was that the photocatalyst of ceria matrix with good activity was firstly obtained by laboratory conventional method. The present work will enlarge the research idea and offer a theoretical basis for developing new photocatalyst, which has far reaching influence on benefiting a unique advantage of cerium resources in our country.更多还原