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

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