One-Pot Synthesis of W-TiO₂/SiO₂ catalysts for the photodegradation of p -nitrophenol

Double modifications of TiO₂ by doping with WO₃ and by dispersing on a SiO₂ support were made by the one-pot sol-gel method. Doping with W shifts the TiO₂ band gap energy from 3.2 eV to around 3.06 eV. The surface area of the supported W-TiO₂/SiO₂ material was significantly increased, by approximately 3 times, in comparison to the bare TiO₂. The photocatalytic activities of the catalysts were evaluated in the degradation reaction of p-nitrophenol in aqueous solution and basic medium. After 240 min of photodegradation, more than approximately 99% p-nitrophenol could be mineralized with the most active W-TiO₂/SiO₂ catalyst. Under UV irradiation, p-nitrophenol was initially photodegraded into hydroquinone and benzosemiquinone intermediates, which were further degraded into smaller fragments such as organic carboxylic acids and finally completely mineralized. A proposed photoreaction mechanism was presented based on the key roles of the surface hydroxyl species and superoxide radicals such as O₂ ^- and ^⋅OH, together with W⁶⁺/W⁵⁺ couples and e^-/h⁺ pairs in the catalysts in the p-nitrophenol photodegradation. The one-pot sol-gel synthesis method was proven to be effective to obtain W-TiO₂/SiO₂ catalyst with large surface area and high photocatalytic activity, and it can be also used for the preparation of other heterogeneous catalysts.