Enhancement of gas–solid photocatalytic activity of nanocrystalline TiO2 by SiO2 opal photonic crystal

Abstract

A series of nc-TiO2/SiO2 opal composite photocatalytic membranes were fabricated through coating a nanocrystal TiO2 (nc-TiO2) layer onto a SiO2 opal photonic crystal layer and used as catalysts for photodegradation of gaseous acetaldehyde under 380 nm monochromatic light and white light irradiation. The photonic band gap (PBG) of the SiO2 photonic crystal was designed at the vicinity of the electronic band gap of TiO2 and tuned by the size of SiO2 microspheres constructing the SiO2 opals. It was found that the nc-TiO2/SiO2 opal composite membrane, with the PBG of the SiO2 photonic crystal overlapping with the absorption edge of TiO2, exhibited the highest photocatalytic activity, which was 1.5 times that of a control photocatalytic membrane—the membrane of nc-TiO2 coated on a disordered porous SiO2 film. The farther the photonic PBG is away from the absorption edge of TiO2, the lower the photocatalytic activity of the composite membranes; when the nc-TiO2/SiO2 opal composite membrane catalyst with PBG was completely outside of the absorption edge of TiO2, the photocatalytic enhancement was not found. The photocatalytic enhancement is attributed to the enhanced light harvest of TiO2 resulting from the absorption of reflected light at PBG of photonic crystal and attributed to the light localization of photonic crystal inside the nc-TiO2.