ZnO/Ag2O/g-C3N4 composite heterostructures with Ag0-induced superior visible light photocatalytic activity via unique bi-phasic dye-degradation phenomena

Abstract

ZnO-nanostructures, having low in-vivo toxicity and bio-degradability, need appropriate architectures, aiding maximal photon absorption and minimal charge recombination, for endorsing efficient photocatalysis. Accordingly, ZnO-nanorods are impregnated with Ag2O-nanoparticles and embedded on g-C3N4-nanosheets (ZAO/GCN), the photocatalytic performance of which is primarily attributable to augmented optical absorption via narrow band gap, fast propagation of photo-electrons with reduced recombination, inducted by the synergistic interactions between ZnO/Ag2O/g-C3N4, and the improved specific surface area and pore-volume of g-C3N4 sheets providing efficient adsorption of the dye-molecules. Subsequently, metallic Ag0 formation helps scavenge the valence electrons of Ag2O nanoparticles, thus encouraging e–/h+ detachment and faster dye-degradation. Eventually, photo dye-degradation starts by forming g-C3N4/ZnO/Ag2O double-junction and accelerates by g-C3N4/ZnO/Ag0/Ag2O triple-junction via inducting the unique bi-phasic two-slope photocatalysis phenomena. During photocatalysis, h+ acts as the predominant reactive species, O2•–, e–, and OH• being substantially less relevant. On increasing g-C3N4 loading, dye-degradation improves with corresponding faster crossover time (tC) via the enhanced contribution of trapped conduction band electrons (etr−) of g-C3N4 generating surplus Ag0. The optimized ZAO/GCN1.0 photocatalyst demonstrates the visible-light MB dye-degradation efficiency of ∼94.5% with a rate-constant (∼0.0933 min−1) ∼10 times superior to ZnO, which, including the robust design and recyclability, could pave the way for advanced water disinfection.