Efficient photocatalytic oxidation of gaseous toluene in a bubbling reactor of water.

Conventional gas-solid photocatalytic oxidation (SPCO) of VOCs has drawbacks such as accumulation of intermediates and catalytic deactivation. In this study, gas-liquid photocatalytic oxidation (LPCO) was exploited to improve the catalytic activity and stability by continuously bubbling VOCs into water. Toluene and commercial TiO2 (P25) were chosen as the representative VOC pollutant and photocatalyst, respectively. Toluene removal efficiency in LPCO was about 6 times of that in conventional SPCO, and no intermediates were detected in the exhaust of LPCO probably due to its high degradation and mineralization rates. However, plentiful intermediates were identified by GC-MS and ITMS both in the gas outlet and on the surface of catalyst in SPCO, which may lead to photocatalytic deactivation. Moreover, LPCO exhibited superior catalytic activity towards typical soluble VOCs such as formaldehyde compared to SPCO. The soluble intermediates formed from toluene degradation can be easily removed by sustaining UV irradiation to avoid water pollution and the water after purification can be reused in LPCO. This study provides a novel gas-liquid photocatalytic oxidation to replace conventional gas-solid photocatalytic oxidation for the sake of better catalytic activity and fewer by-products.