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

Abstract

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.