Mesoporous TiO₂/g-C₃N₄ Microspheres with Enhanced Visible-Light Photocatalytic Activity

Abstract

Designing a heterojunction semiconductor is an efficient strategy to extend the light response of a photocatalyst to the visible range and thus improve photocatalytic activity. Starting with mesoporous anatase TiO2 microspheres, mesoporous TiO2/g-C3N4 microspheres were prepared via a facile nanocoating procedure, with the porous TiO2 as the active supporting scaffold and g-C3N4 (3 wt %) as the visible light sensitizer. Heterojunctions formed at the TiO2/g-C3N4 interfaces separated photogenerated charges. The TiO2 surface (64.4 m2 g–1) was mostly covered by a photoactive g-C3N4 layer, while the interconnected porous network featured a large pore volume (0.30 cm3 g–1) for mass diffusion. The g-C3N4 precursor, cyanamide, a nitrogen-rich molecule, also acted as a nitrogen source to form TiO2–xNx. Substitution of N in the TiO2 lattice triggered a visible light response due to an additional N level above the TiO2 valence band that resulted in band gap narrowing to 1.5 eV. Compared with mesoporous g-C3N4, the composite microspheres were 8.5 times more active in degrading phenol under visible light irradiation. A mechanism was proposed for the TiO2/g-C3N4 heterojunction incorporated within the mesoporous structure that enhanced the photocatalytic properties.