Rational design direct Z-scheme BiOBr/g-C3N4 heterojunction with enhanced visible photocatalytic activity for organic pollutants elimination

A rapid recombination of photo-generated electrons and holes, as well as a narrow visible light adsorption range are two intrinsic defects in graphitic carbon nitride (g-C3N4)-based photocatalysts. Inspired by natural photosynthesis, an artificially synthesized Z-scheme photocatalyst can efficaciously restrain the recombination of photogenerated electron-hole pairs and enhance the photoabsorption ability. Hence, to figure out the above problems, BiOBr/g-C3N4 composite photocatalysts with different mass ratios of BiOBr were successfully synthesized via a facile template-assisted hydrothermal method which enabled the BiOBr microspheres to in situ grow on the surface of g-C3N4 flakes. Furthermore, to explore the origin of the enhanced photocatalytic activity of BiOBr/g-C3N4 composites, the microstructure, photoabsorption ability and electrochemical property of BiOBr/g-C3N4 composites were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS) and photocurrent (PC) response measurements. As a result, the introduction of BiOBr on g-C3N4 to constitute a direct Z-scheme heterojunction system can effectively broaden the light absorption range and promote the separation of photo-generated electron-hole pairs. Hence, compared with pure g-C3N4 and BiOBr, the resultant BiOBr/g-C3N4 composites exhibit the remarkable activity of photodegradated rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) under visible light irradiation. Simultaneously, the optimal BiOBr content of the BiOBr/g-C3N4 composites was obtained. The BiOBr/g-C3N4 composites exhibit an excellent photostability and reusability after four recycling runs for degradation RhB. Moreover, the active-group-trapping experiment confirmed that OH, O-2(-) and h(+) were the primary active groups in the degradation process. Based on the above research results, a rational direct Z-scheme heterojunction system is contrastively analyzed and proposed to account for the photocatalytic degradation process of BiOBr/g-C3N4 composites.