Two-Step Visible Light Photocatalytic Dye Degradation Phenomenain Ag2O-Impregnated ZnO Nanorods via Growth of Metallic Ag andFormation of ZnO/Ag0/Ag2O Heterojunction Structures

Visible light photocatalytic activity follows thesingle-slope pseudo-first-order reaction kinetics in pristine ZnOnanorods, while for pure Ag2O, a two-slope paradigm is pursuedwith a higher slope at a later period. For the Ag2O-impregnatedZnO heterostructured nanorod photocatalyst, the two-step photo-catalysis phenomena proceed with dye degradation rate constantsemerging higher than those of individual ZnO and Ag2O, at bothtime zones. Improved performance of ZnO/Ag2O heterostructuresarises initially from the reduced e-/h+recombination rate by thesynergistic effect between ZnO and Ag2O. At a later phase, metallicAg is produced, which traps the valence electrons of Ag2O nanoparticles and advances the e-/h+separation across the ZnO/Ag0/Ag2O heterojunction structures, rendering them promptly accessible for dye degradation. At an increased Ag2O loading, thephotodegradation rate constants boost up in both time zones, and the corresponding crossover time (tC) between the two phasessteadily diminishes, leading toward a unique photocatalytic phenomenon that prevails with a superior rate constant. The optimizedZAO25heterostructure photocatalyst demonstrates similar to 96.24% photodegradation of methylene blue (MB) dye within 30 min of visiblelight exposure, and its degradation rate constant is similar to 0.24848 min-1, which is similar to 26.75 times superior than that of pristine ZnOsamples. The metal-induced biphasic photocatalysis phenomena have never been reported earlier.