The photocatalyst based on a composite WO.sub.3--SiC/TiO.sub.2 semiconductor and subjected to radiation whose wavelength is at least partly less than 400 nm gives1 photocatalytic oxidation of volatile organic compounds and leads to their total mineralisation into CO.sub.2 and H.sub.2O.The process for the photocatalytic purification of industrial, agricultural or domestic gaseous effluent may be conducted at room pressure and temperature. Its conversion rate is high and stable.