Two-Step Visible Light Photocatalytic Dye Degradation Phenomena in Ag₂O-Impregnated ZnO Nanorods via Growth of Metallic Ag and Formation of ZnO/Ag⁰/Ag₂O Heterojunction Structures

Visible light photocatalytic activity follows the single-slope pseudo-first-order reaction kinetics in pristine ZnO nanorods, while for pure Ag 2 O, a two-slope paradigm is pursued with a higher slope at a later period. For the Ag 2 O-impregnated ZnO heterostructured nanorod photocatalyst, the two-step photocatalysis phenomena proceed with dye degradation rate constants emerging higher than those of individual ZnO and Ag 2 O, at both time zones. Improved performance of ZnO/Ag 2 O heterostructures arises initially from the reduced e – /h + recombination rate by the synergistic effect between ZnO and Ag 2 O. At a later phase, metallic Ag is produced, which traps the valence electrons of Ag 2 O nanoparticles and advances the e – /h + separation across the ZnO/Ag 0 /Ag 2 O heterojunction structures, rendering them promptly accessible for dye degradation. At an increased Ag 2 O loading, the photodegradation rate constants boost up in both time zones, and the corresponding crossover time ( t C ) between the two phases steadily diminishes, leading toward a unique photocatalytic phenomenon that prevails with a superior rate constant. The optimized ZAO 25 heterostructure photocatalyst demonstrates ∼96.24% photodegradation of methylene blue (MB) dye within 30 min of visible light exposure, and its degradation rate constant is ∼0.24848 min –1, which is ∼26.75 times superior than that of pristine ZnO samples. The metal-induced biphasic photocatalysis phenomena have never been reported earlier.