Hydroxyl Radical Based Photocatalytic Degradation of Halogenated Organic Contaminants and Paraffin on Silica Gel

Photochemical materials are of scientific and practical importance in the field of photocatalysis. In this study, the photochemistry of several organic contaminants, including decabromodiphenyl ether (BDE-209), halogenated phenols (C6X5OH, X = F, Cl, Br) and paraffin, on silica gel (SG) surface was investigated under simulated solar irradiation conditions. Photolysis of these compounds at the solid/air interface proceeds with different rates yielding various hydroxylation products, and hydroxyl radical was determined as the major reactive species. According to density functional theory (DFT) calculations, the reaction of physically adsorbed water with reactive silanone sites (>Si═O) on silica was indispensable for the generation of •OH radical, where the required energy matches well with the irradiation energy of visible light. Then, the BDE-209 was selected as a representative compound to evaluate the photocatalytic performance of SG under different conditions. The SG material showed good stability in the photodegradation process, and was able to effectively eliminate BDE-209 under natural sunlight. These findings provide new insights into the potential application of SG as a solid surface photocatalyst for contaminants removal.