•OH radicals determined photocatalytic degradation mechanisms of gaseous styrene in TiO2 system under 254 nm versus 185 nm irradiation: Combined experimental and theoretical studies

The photocatalytic transformation mechanisms of styrene, were compared in TiO2 system under ultraviolet (UV) and vacuum ultraviolet (VUV) irradiations. TiO2/VUV displayed higher photocatalytic degradation and mineralization efficiencies (100% and 51% within 8 min) than TiO2/UV (86% and 21% within 60 min), and the increased efficiencies were contributed from enhanced production of (OH)-O-center dot through VUV photolysis of H2O and O-2. The addition reactions of these enhanced (OH)-O-center dot converted styrene to benzaldehyde and other small molecular carbonyl compounds in TiO2/VUV gas system. Due to absence of atmospheric (OH)-O-center dot in TiO2/UV system, styrene underwent cycloisomerisation to form a bicyclic byproduct, benzocyclobutene, which further transformed to benzocyclobutenone, benzocyclobutenol, phthalan, phthalide and phthalic anhydride on photocatalyst TiO2. Meanwhile, both systems shared same pathways from styrene to monoaromatic alcohols, ketones, aldehydes on TiO2 through (OH)-O-center dot addition. Our results provide a deep insight into (OH)-O-center dot-determined photocatalytic transformation mechanism of AHs and their final fate in atmospheric environment.