Silver/Silver(II) oxide (Ag/AgO) loaded graphitic carbon nitride microspheres: An effective visible light active photocatalyst for degradation of acidic dyes and bacterial inactivation

Solar light induced photocatalytic oxidative degradation of organic pollutants and bacterial inactivation is an attractive strategy for water purification. Current work is on the use of silver/silver (II) oxide (Ag/AgO) grown insitu on the surface of graphitic carbon nitride (g-C3N4) as photocatalyst for the effective utilization of solar radiation, as this system can have extended visible light absorption due to the surface plasmon resonance (SPR) phenomenon of metallic silver. Ag/AgO loaded g-C3N4 microspheres (Ag/AgO/g-CNMS) were prepared by a facile thermal heating method. The structural and morphological analysis confirmed the existence of metallic Ag and AgO in mixed phase on the surface of carbon nitride. This composite exhibits significant visible light absorption and a reduction in the bandgap compared to g-C3N4 due to the SPR exhibited by the metallic silver and lower bandgap of AgO. Photoelectrochemical studies suggest lower charge transfer resistance and better capacitive behaviour for the composite compared to g-C3N4. The composite catalyst shows improved photocatalytic performance for the degradation of acid violet-7 dye (AV-7). Besides, it is found to possess significant bactericidal property for the destruction of Escherichia coli(E. coli) bacteria. This is the first report on the enhanced photocatalytic activity of a silver-g-C3N4 system comprising of silver (II) oxide. The present system containing silver (II) oxide shows significantly improved photocatalytic activity and stability compared to the Ag/Ag2O/g-C3N4 with silver (I) oxide reported earlier. The improved performance of the composite is attributed to the increased optical absorption properties and better separation of photogenerated charge carriers. The reactive oxidative species responsible for the degradation reaction is identified and a plausible degradation pathway for the AV-7 dye is presented. Furthermore, this catalyst is found to be stable and does not show any decrease in the photocatalytic activity even after several repeated cycles.