Supramolecule self-assembly approach to direct Z-scheme TiO2/g-C3N4 heterojunctions for efficient photocatalytic degradation of emerging phenolic pollutants

Abstract

To improve the visible-light photocatalytic oxidation activity of anatase TiO2 or graphitic carbon nitride (g-C3N4) towards organic pollutants, the present work develops a supramolecule self-assembly approach combined with thermal polycondensation to construct direct Z-scheme-dictated TiO2/g-C3N4 heterojunctions. This in-situ route not only leads to the TiO2/g-C3N4 with porous sheet-like nanostructures but also establishes hydrogen-bonded intimate interfacial contact between TiO2 and g-C3N4. The TiO2/g-C3N4 heterojunctions demonstrate significantly enhanced visible-light photocatalytic activity in the degradation of emerging phenolic pollutants, acetaminophen and methylparaben, as compared with TiO2, P25 TiO2 and g-C3N4; additionally, TiO2-to-g-C3N4 molar ratio in the heterojunctions influences the activity remarkably. This enhanced photocatalytic oxidation performance is mainly ascribed to the direct Z-scheme-dictated charge carrier transfer mechanism, driven by well-matched energy band structures of TiO2 and g-C3N4 as well as the intimate interfacial contact between TiO2 and g-C3N4. Accordingly, the spatial separation of the photogenerated charge carriers is boosted; simultaneously, strong redox ability of electrons on conduction band of g-C3N4 and holes on valence band of TiO2 is retained. Therefore, abundant reactive oxygen species like •O2− anion radicals and •OH radicals are generated. These reactive oxygen species together with holes are responsible for the elevated photocatalytic oxidation performance of TiO2/g-C3N4 heterojunctions.