Fabrication of a novel Z-scheme g-C3N4/Bi4O7 heterojunction photocatalyst with enhanced visible light-driven activity toward organic pollutants.

In this work, highly efficient g-C3N4/Bi4O7 heterojunction photocatalysts have been successfully fabricated by a facile method. Compared with the bare photocatalysts, the obtained g-C3N4/Bi4O7 hybrid photocatalysts exhibited efficient degradation activity toward methylene blue (MB), phenol, rhodamine B (RhB), and bisphenol A (BPA) under visible light irradiation. The influences of different g-C3N4 contents on the photocatalytic efficiency of the hybrid photocatalysts have been investigated. The results revealed that the g-C3N4/Bi4O7 with g-C3N4 mass ratio of 30% exhibited the best photocatalytic activity. The activity enhancement should be ascribed to the improved visible light adsorption as well as the effective Z-scheme charge transfer according to the energy band theory. The UV-vis diffuse reflectance spectra (DRS) shows that the absorption edge of g-C3N4 move towards longer wavelength with the increment of Bi4O7 component. The strong connection between g-C3N4 and Bi4O7 was investigated using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Subsequently, the effective Z-scheme charge transfer has also been verified by using transient photocurrent measurements and electrochemical impedance spectroscopy. Controlled experiments proved that active species of O2- and h+ were produced in the degradation system, which played the major role in the degradation of MB. A possible Z-scheme degradation mechanism over g-C3N4/Bi4O7 hybrid photocatalysts was proposed.