Enhancement of the photocatalytic activity of g-C3N4 via treatment in dilute NaOH aqueous solution

A simple, effective and environmental-friendly method was adopted for enhancing the photocatalytic activity of g-C3N4 (which was synthesized by thermal condensation of melamine) in the reduction of aqueous Cr6+ under visible-light irradiation. The enhancement was achieved via treatment of g-C3N4 in 0.2 mol/L NaOH aqueous solution at 80 °C for 6 h. The photocatalytic experiments demonstrated that the treated g-C3N4 exhibited much higher photocatalytic activity than pristine g-C3N4 in the reduction of aqueous Cr6+ under visible-light (λ>420 nm) irradiation (for example, the reduced ratios of Cr6+ in the presence of the treated g-C3N4 and pristine g-C3N4 were 100% and 29.4%, respectively, when irradiated for 120 min). Based on the characterization results of the structures and other physiochemical properties of the treated g-C3N4 and pristine g-C3N4 by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption isotherms, photocurrent measurement and electrochemical impedance spectroscopy, the possible reasons responsible for the enhanced photocatalytic activity of the treated g-C3N4 were proposed.