Assembly of graphene on Ag3PO4/AgI for effective degradation of carbamazepine under Visible-light irradiation: Mechanism and degradation pathways

A highly efficient visible-light-driven photocatalyst Ag3PO4/AgI-Graphene (Ag3PO4/AgI-G) was synthesized through a chemical coprecipitation procedure. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were performed to study the physicochemical structural of the photocatalysts. The photocatalytic activity of the samples was examined by the carbamazepine (CBZ) degradation under artificial visible light and natural sunlight irradiation. Experimental results indicated that the introduction of low mass content of graphene enhanced the photocatalytic performance of Ag3PO4/AgI, and the photocatalytic degradation efficiency of CBZ over Ag3PO4/AgI-3% G (mass ratio of graphene: Ag3PO4/AgI = 3:100) reached 93.06% within 21 min, which was much higher than that over pure Ag3PO4 (26.92%) and Ag3PO4/AgI (74.38%). UV-vis diffuse reflectance spectra, photoluminescence (PL) spectra, transient photocurrent responses and electrochemical impedance spectra (EIS) of the samples were conducted to verify the high photocatalytic performance of the Ag3PO4/AgI-3% G. In addition, possible photocatalytic degradation pathways of CBZ were proposed based on the analysis of transformation products during the reaction. The reactive species trapping experiments and Electron spin resonance (ESR) analysis demonstrated that h(+) and center dot O-2(-) were the main active oxidant species responsible for CBZ photodegradation. The photocatalytic degradation mechanism of CBZ over Ag3PO4/AgI-3% G under visible light irradiation was schematically proposed. This study not only provides a new technique for the synthesis of Ag3PO4-based photocatalysts with high photocatalytic activity, but also demonstrates that the Ag3PO4/AgI-3% G composite could be a promising photocatalyst for the treatment of waters containing CBZ.