ZnO-Nanorod/Ag<sub>2</sub>O-Nanoparticle/rGO-Nanosheet Heterostructures as Photocatalysts for Enhanced Degradation of Harmful Aqueous Phase Contaminants under Extended Visible Light Exposure
Payel Sahu, Debajyoti Das
Abstract
This study concentrates on the fabrication of nanocomposites based on zinc oxide (ZnO) reinforced with reduced graphene oxide (rGO) nanosheets and silver oxide (Ag 2 O) nanoparticles with varying rGO contents utilizing conventional hydrothermal (for ZnO nanorod synthesis), modified Hummers’ method (for GO synthesis), and coprecipitation method and studies on the impacts of the subsequent composites’ structural, morphological, and chemical characteristics on their photocatalytic activities. In addition to increasing surface area and carrier concentration, the optimal defects in ZnO/Ag 2 O/rGO also provide an alternate transport pathway, for e – /h + pairs’ separation and prolonging carrier recombination, which are the desirable properties for efficient photocatalytic applications. The improved photocatalytic efficiency of ZnO/Ag 2 O/rGO heterostructures with varying rGO content has been attributed to the relatively narrow band gap and the enhanced separation efficiency of e – /h + pairs, which follows a double-sloped photocatalytic kinetics with a higher slope at a later phase and the respective crossover times ( t C ) between the two phases reduce steadily. The pure ZnO photocatalyst exhibits single-sloped pseudo-first-order kinetics under extended visible light exposure. The formation of the Ag 2 O/Ag 0 /ZnO/rGO heterojunction through the production of metallic Ag (Ag 0 ), which scavenges the valence e – of Ag 2 O nanoparticles and accelerates the e – /h + separation, might be responsible for the increased catalytic activity in higher time zones. The most effective dye degradation [methyl orange (MO)] percentage was attained with ZAGO 0.5 . The optimized ZAGO 0.5 heterostructure photocatalyst demonstrates ∼99.68% photodegradation of MO dye with a rate constant of ∼0.26 min –1 within 35 min of extended visible light exposure, which is ∼32 times higher than that of the pristine ZnO photocatalyst. The as-prepared ZAGO heterostructure photocatalyst demonstrates their effectiveness as multifunctional nanomaterials for removing harmful aqueous phase contaminants and offers ample opportunities for developing enhanced water treatment systems.