Influence of colloidal graphene oxide on photocatalytic activity of nanocrystalline TiO2 in gas-phase ethanol and benzene oxidation

Abstract

Impregnation of the nanocrystalline TiO2 Degussa/Evonik P25 by colloidal graphene oxide produced by the Hummers method (H-GO) results in a 4-fold acceleration of photocatalytic gas-phase oxidation of ethanol and benzene vapors by air oxygen as a result of enhanced separation of the photogenerated charge carriers between TiO2 and H-GO. Preliminary photochemical reduction of H-GO decreases drastically its activity in ethanol photooxidation but does not affect appreciably photocatalytic oxidation of benzene. More deeply oxidized colloidal GO produced by the Brodie method (B-GO) almost does not affect the photocatalytic properties of titania in benzene photooxidation. It is concluded that the catalytic properties of GO in the photooxidation of ethanol and benzene depend on a balance between the capabilities of the GO sheets (i) to accept photoelectrons from titania nanocrystals and (ii) to bound to the TiO2 surface. The former factor depends on the aromaticity of GO particles and increases from B-GO to H-GO to photoreduced H-GO, while the latter factor depends on the density of the functional groups on GO sheets and increases in the opposite direction.