The degradation of 4-chlorophenol with near-UV light by silica-immobilized polyoxometalate (POM-in-SiO{sub}2) catalysts has been studied. The silica-immobilized Na{sub}6W{sub}7O{sub}(24) (SW7), H{sub}4W{sub}(10)O{sub}(32) (SW10), H{sub}3PW{sub}(12)O{sub}(40) (SPW12), and H{sub}6P{sub}2W{sub}(18)O{sub}(62) (SP2W18) were prepared by means of the sol-gel hydrothermal technique through the hydrolysis of tetraethoxysilane in aqueous solution of the corresponding polyoxometalate, respectively. The degradation of 4-chlorophenol was monitored by measuring Cl{sup}- and CO{sub}2 concentrations and analyzing reaction intermediates by GC/MS analysis. During irradiation, 4-chlorophenol first dechlorinated to form hydroquinone and p-benzoquinone, and then these intermediates further mineralized to form CO{sub}2 and H{sub}2O. The degree to which 4-chlorophenol was mineralized by photocatalytic oxidation was investigated. Results indicate less than 15 for SW7 but nearly complete mineralization for SW10 after 60 mm of photoirradiation. The present studies suggest that POM-in-SiO{sub}2 catalysts may be a novel type of photocatalyts for the purification of the environmentally chlorophenol-contaminated water.
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