Photocatalytic Degradation Of Aqueous Phenol By Supported Heteropoly Compounds

Polyoxometalates(POMs), a class of moleculariy defined inorganic metal-oxide clusters, posses intriguing structures and diverse properties and exhibit a unique combination of physical and chemical properties. They have been widely used as acid and oxidation catalysts in homogeneous and heterogeneous systems . Meanwhile , POMs are also effective photocatalysts, and their photoactivities originate from their unique structure. Therefore, they attract increasing attention worldwide. However, the catalytic activities of the POMs are greatly limited due to their very low specific surface areas(e.g., H3PW12O40 9m2/g and H4SiW12O40 10m2/g), so polar molecules can only react on the surface of the POMs. And they are easy to lose and it is difficult to separate them from the reaction systems. Therefore, many attempts have been made to enhance the catalytic activity of the POMs. Preparation of solid POMs by incorporating the POMs into porous materials effectively, it will be of fundamental and practical significance.Inthispaper, Polyoxornetalates were immobilized into a silica matrix by means of a sol-gel technique. The ptotocatarytic degradation and oxidation of aqueous phenol solution had been studied under low-pressure mercury lamp. It showed that phenol was remarkably photolized under the condition of the experiment. Solid acid catalysts with macrospores and large surface areas are insoluble and easily separable. Meanwhile, the study on the relation between Ihe photo-degradation and some factors had been undertaken.At the same time, Complex film were synthesized by incorporating H3PW12O40 and/or H4SiW12O40 into polyvinyl alcohol matrix via chemical self-assembled rnelhod. The complex film with high specific surface areas are insoluble and readily separable. Trace aqueous phenol were degraded and mineralized into CO2 and H2O by irradiating a complex film in the near UV area.In this paper, the concentration of phenol was determined by a spedrophotorneter, the TOC value (mineralization of phenol)was determined by TOC analyzer. The results indicated:Poryoxometalates immobilizing into a silica matrix by means of a sol-gel technique have excellent photo catalytic activity , which could degradate phenol in aqueous solution effectively.Complex film which was synthesized by incorporating H3PW12O40 and/or H3PW12O40 into polyvinyl alcohol matrix via chemical self-assembled method is simpler and lower-priced. And it is excellent photo catalytic, which could degradate phenol in aqueous sohricai effectively too.The phenol degradation rate have relationship with the volume of catalysts, the weight ratio of catalysts.By using each synthesized composite, an aqueous phenol was easily photodegradated and mineralizedStudies on the reaction indicate that photo generation of OH radicals originating from neutralization of OH groups on the catalyst surface with positive photo holes is responsible for the oxidation of the organic substrates in aqueous solution.Separation and recovery of the solid catalysts is easy.Therefore, the catalysts exhibits the potential for practical applications.