Comparative Investigation on Photoreactivity and Mechanism of Biogenic and Chemosythetic Ag/C3N4 Composites under Visible Light Irradiation

A Ag/C3N4 nanocomposite with optimum Ag content is an efficient and green photocatalyst for pollutant degradation under visible light irradiation. In this study, we synthesized Ag NPs using NaBH4 and the squeezed out liquid (SOL) of plant biomass. The Ag NPs thus obtained have been loaded to C3N4 to form Ag/C3N4 nanocomposites that show superior photocatalytic performance toward Rhodamine B (RhB) under visible light irradiation. The photocatalytic activity of both biogenic and chemogenic Ag/C3N4 nanocomposites with different Ag contents is compared. Results show that the biogenically synthesized Ag/C3N4 exhibits better photocatalytic performance than the chemosynthetic composite. Of all the different nanocomposites prepared in this study, Ag48/C3N4 (0.048% of Ag content) exhibits excellent photoreactivity, with a reaction rate constant (k) 7-fold higher that the chemosynthetic Ag/C3N4. The observed improvement in the photoreactivity is mainly attributed to the high dispersion of Ag NPs on C3N4, facilitated by the organic compounds in SOLs. Besides, these organic compounds also enhance the photoreactivity of the catalyst by providing adsorption sited for RhB molecules and by shifting the Fermi level to more negative potential.