Facile synthesis, characterization and photocatalytic performance of Au-Ag alloy nanoparticles dispersed on graphitic carbon nitride under visible light irradiations

The well-dispersed nanoparticles of Au-Ag alloys on graphitic carbon nitride (g-C₃N₄), with varying ratios of Au, were synthesized by a facile route. The diffuse reflectance spectroscopy (DRS) verified the upsurge in the intensity of characteristic surface plasmonic resonance (SPR) absorption bands with the increasing Au contents. The photoluminescence (PL) spectroscopy estimated the role of surface dispersed Au-Ag alloy NPs on the luminescence properties of g-C₃N₄ and the suppression the probable recombination of photo-generated excitons. The structural characterization by XRD and morphological assessment by SEM revealed the uniform dispersion of Au-Ag alloy nanoparticles on the surface of g-C₃N₄ whereas XPS analysis endorsed the presence of Au and Ag in metallic form. The HRTEM analysis confirmed the homogeneous distribution of Au and Ag contents in the alloys. The photocatalytic activity of the Au-Ag/g-C₃N₄ was evaluated in the exposure of natural sunlight and artificial visible light for the degradation of dye substrate and compared with that of g-C₃N₄, Ag/g-C₃N₄ and Au/g-C₃N₄. The Au-Ag alloy modified g-C₃N₄ photocatalysts exhibited significantly higher activity for the decolorization of Rhodamine B in the visible light as compared to pure, Ag and Au loaded g-C₃N₄ that signified the contributing role of SPR in the degradation process. The individual role of SPR in the photocatalytic process was also verified by using monochromatic (532 nm) visible laser light. The mineralization ability of the synthesized alloy catalysts was estimated by TOC removal efficiency. The kinetics of the degradation/mineralization processes under various experimental conditions was also evaluated.