Microporous polyoxometalates POMs/SiO2:: Synthesis and photocatalytic degradation of aqueous organocholorine pesticides

Microporous Keggin-type polyoxometalate materials were synthesized by incorporating H3PW12O40 and/or H4SiW12O40 into a silica matrix via a sol-gel technique. The silica-impregnated polyoxometalates (POMs/SiO2) thus obtained are insoluble and readily separable porous materials with uniform micropores and high specific surface areas. Trace aqueous organocholorine pesticides, hexachlorocyclohexane (HCH) and pentachloroenitrobenzene (PCNB), were totally degraded and. mineralized into CO2 and HCl by irradiating a POMs/SiO2 slurry in the near-UV area. The disappearance of the organocholorine compounds follows Langmuir-Hinshelwood first-order kinetics. Studies on the reaction mechanism indicate that photogeneration of OH. radicals originating from neutralization of OH- groups on the catalyst surface with positive photoholes is responsible for the oxidation of the organic substrates in aqueous solution.