Highly Enhanced Photoreductive Degradation of Polybromodiphenyl Ethers with g-C ₃N ₄/TiO ₂ under Visible Light Irradiation

Abstract

A series of high activity photocatalysts g-C ₃N ₄-TiO ₂ were synthesized by simple one-pot thermal transformation method and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller (BET) surface area, and ultraviolet–visible diffuse reflectance spectroscopy (UV-Vis-DRS). The g-C ₃N ₄-TiO ₂ samples show highly improved photoreductive capability for the degradation of polybromodiphenyl ethers compared with g-C ₃N ₄ under visible light irradiation. Among all the hybrids, 0.02-C ₃N ₄-TiO ₂ with 2 wt % g-C ₃N ₄ loaded shows the highest reaction rate, which is 15 times as high as that in bare g-C ₃N ₄. The well _-matched band gaps in heterojunction g-C ₃N ₄-TiO ₂ not only strengthen the absorption intensity, but also show more effective charge carrier separation, which results in the highly enhanced photoreductive performance under visible light irradiation. The trapping experiments show that holetrapping agents largely affect the reaction rate. The rate of electron accumulation in the conductive band is the rate-determining step in the degradation reaction. A possible photoreductive mechanism has been proposed.