Tricomponent brookite/anatase TiO2/g-C3N4 heterojunction in mesoporous hollow microspheres for enhanced visible-light photocatalysis

The three major polymorphs of TiO2, anatase, rutile, and brookite, are widely utilised to form heterojunction semiconductors for superior photocatalytic performance due to their unique optical properties and tunable morphologies. Mesoporous brookite/anatase TiO2/g-C3N4 hollow microspheres were prepared from pre-made, amorphous TiO2 microspheres via a facile nanocoating procedure and showed mixed phases of brookite (48%), anatase (44%), and rutile (8%). The mesoporous hollow microspheres exhibited a unique shell morphology of packed TiO2/g-C3N4 nanosheets, porosity with pore volume of 0.20 cm3 g−1 and surface area of 37.1 m2 g−1. Compared with mesoporous g-C3N4, the composite hollow microspheres coated with 10 wt% g-C3N4 were 5-fold more active in degrading phenol under visible light irradiation. In contrast with mesoporous pristine anatase or rutile TiO2/g-C3N4 composites, the photocatalytic activity was improved for the multiphase TiO2/g-C3N4 material due to the more negative conduction band, which benefitted electron transfer. A mechanism for the enhanced photocatalytic behaviour was proposed for the mesoporous brookite/anatase/rutile TiO2/g-C3N4 hollow microspheres, showing that the multicomponent heterojunction could enhance the photocatalytic properties in the visible range.