Synergy of adsorption and visible-light photocatalytic degradation of methylene blue by a bifunctional Z-scheme heterojunction of WO3/g-C3N4

Abstract A novel bifunctional Z-scheme heterojunction possessing high adsorption and photocatalytic activity, WO3/g-C3N4 with well-defined morphology has been successfully synthesized by in-situ liquid phase process and characterized by various analytical techniques. The degradation experiments demonstrate that the Z-scheme photocatalyst shows a synergistic effect between adsorption and photocatalysis for the removal of methylene blue (MB) under visible-light irradiation, with the optimum adsorption and photocatalytic activity both found at 30 wt% WO3/g-C3N4. Under illumination, the photodegradation performance of 30 wt% WO3/g-C3N4 is improved to 2.5 and 2.7 times that of pure g-C3N4 and pure WO3, respectively. The possible mechanism for the photocatalytic activity enhancement could be attributed to the formation of a Z-scheme heterojunction system based on the active species trapping experiments. Furthermore, the investigations of adsorption kinetics and isotherm show that the adsorption process can be well described by pseudo-second-order kinetic model, and the adsorption capacity of 30 wt% WO3/g-C3N4 is enhanced to 4 times that of pure WO3, with a maximum of 97.00 mg g−1 determined by Langmuir isotherm. As evidenced by N2 physisorption, zeta potential and time-resolved photoluminescence measurements, the significant enhancement of the integrated adsorption and photocatalytic degradation efficiency is mainly due to the synergistic advantages of large surface area, negative zeta potential and facilitated charge separation of the composite.