Difference of photodegradation characteristics between single and mixed VOC pollutants under simulated sunlight irradiation

In realistic Volatile organic compounds (VOC)-containing polluted air, VOCs often do not exist alone, but different VOCs coexist. The interaction between different VOCs affects their photodegradation. However, few studies have focused on the photodegradation of mixed VOCs. Herein, rGO-TiO2 photocatalysts were synthesized by a modified refluxing-solvothermal method, and applied to photocatalytic degradation of single VOC (p-xylene and ethylene) and VOC mixture (containing benzene, toluene, p-xylene). It was found that rGO-TiO2 possessed higher photocatalytic degradation activity for single VOC and VOC mixture than pure TiO2. The increased single VOC adsorption capacity, more efficient light harvesting ability, and enhanced separation efficiency of electron-hole were responsible for improved degradation performance of rGO-TiO2. In addition, superoxide radicals played a more important role than hydroxyl radicals for removing both p-xylene and ethylene. Interestingly, commercial TiO2 (P25) underwent decreased efficiency (80.0% to 63.8%) in photodegrading from single p-xylene to p-xylene in VOC mixture, while it was remained unchanged (93.5%-93.0%) for T0.2G (0.2% mass ratio of reduced graphene oxide to TiO2). This could be mainly attributed to sufficient adsorption sites provided by rGO sheets to mitigate competitive adsorption. Simultaneously, its photocatalytic activity showed no obvious decrease after five photodegradation cycles of mixed VOCs. These results suggested great potential of efficient photodegradation of VOC mixture by rGO-TiO2.