Engineering Ag⁰/Ag⁺ Interfaces via Hydrogen Reduction in ZnO-based Photocatalysts for High-efficiency Solar Phenol Degradation

Abstract This work reports the synthesis and photocatalytic evaluation of an Ag/ZnO nanocomposite for efficient degradation of phenol under solar irradiation. The photocatalyst was prepared by impregnating ZnO with AgNO₃, followed by reduction in pure hydrogen gas at 450 °C. This process resulted in the simultaneous formation of metallic silver (Ag⁰) and silver oxide (Ag₂O), incorporating both Ag⁰ and Ag¹⁺ species on the ZnO surface. X-ray photoelectron spectroscopy (XPS) confirmed the coexistence of Ag⁰ and Ag₂O at the Ag–ZnO interface, indicating that strong metal–support interactions and Fermi level alignment facilitated partial oxidation of Ag⁰ into Ag⁺, even under reducing conditions. The photocatalytic activity of the composite was significantly enhanced compared to pure ZnO, achieving ~ 98% phenol degradation within 3 h of solar exposure. This improvement is attributed to the synergistic effects of Ag⁰ and Ag₂O: Ag⁰ induces localized surface plasmon resonance (LSPR), while Ag₂O acts as an electron mediator, suppressing charge recombination and extending light absorption into the visible region. These findings highlight the critical role of controlled silver oxidation states, tailored via hydrogen treatment, in designing efficient photocatalysts for solar-driven environmental remediation. Graphical Abstract