Preparation And Characterization Of Broad-spectrum Ceria Matrix Photocatalyst With High Photocatalytic Activity

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 (â…£) 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.