Design and construction of diverse dual co-catalysts decorated Z-scheme g-C3N4/WO3(002) photocatalyst for converting nitrate and sulfite

Abstract Photocatalysis technology is an effective way for converting nitrate (NO3−) and sulfite (SO32−) in wastewater to pollution-free nitrogen (N2) and exploitable ammonium sulfate ((NH4)2SO4). In this study, three novel photocatalysts, Z-scheme (Cu,Cu)/g–C3N4–(Cu,Cu)-WO3(002), Z-scheme (Cu,Ag)/g–C3N4–(Cu,Ag)-WO3(002) and Z-scheme (Cu,Ru)/g–C3N4–(Cu,Ru)-WO3(002), were prepared by photo-assisted electrostatic self-assembly method. The prepared photocatalysts are synthetically characterized by XRD, SEM, TEM, EDX, XPS, DRS, PL, TPR and EIS. The effects of different co-catalyst combinations on the activity and selectivity of the photocatalysts are evaluated. Also, the impacts of simulated solar light irradiation time, NO3− initial concentration and cycle times on the conversions of NO3− and SO32− are studied. The results display that the Z-scheme (Cu,Ag)/g–C3N4–(Cu,Ag)-WO3(002) photocatalyst can selectively convert NO3− to N2, while the Z-scheme (Cu,Ru)/g–C3N4–(Cu,Ru)-WO3(002) photocatalyst can selectively convert NO3− to NH4+. Nevertheless, the Z-scheme (Cu,Cu)/g–C3N4–(Cu,Cu)-WO3(002) photocatalyst has hardly selectivity for conversion of NO3−. These three photocatalysts all exhibit relatively strong capabilities for converting SO32− to sulfate (SO42−) due to the existence of the highly active (002) plane of WO3. Finally, the possible mechanisms on the photocatalytic conversions of NO3− and SO32− caused by Z-scheme (Cu,M)/g–C3N4–(Cu,M)-WO3(002) (M = Cu, Ag and Ru) photocatalysts are proposed.