Schematic of the overall reaction, for the photocatalytic mineralisation of an organic pollutant on the surface of a titania photocatalyst film. (1) Ultra-band gap light generates electron-hole pairs. (2) Photogenerated holes migrate to the surface which then react with surface hydroxyl groups to generate hydroxyl radicals. (3) Organic pollutants are oxidised to their mineral form via the hydroxyl radicals. (4) Photogenerated electrons can react with adsorbed oxygen to generate superoxide and subsequent other reactive species which can also oxidise organic pollutants.