An all-solid-state Z-scheme mechanism in the enhanced photocatalytic performance of NiO–Au–ZnO triple-layer thin films

Abstract

Although thin-film photocatalysts offer practical advantages such as high recoverability and minimal secondary pollution, their performance is often hampered by their low surface area compared to their nanoparticle-based counterparts. This study demonstrates the fabrication of a triple-layer NiO–Au–ZnO heterostructure with significantly enhanced photocatalytic activity. The heterostructure, composed of solution-processed NiO and ZnO layers with a controlled sputtered Au interlayer, exhibits a well-defined layered architecture comprising NiO nanoparticles, a dense Au film, and ZnO nanorods. The continuity of this Au interlayer, achieved through optimized sputtering, was identified as the critical factor governing performance. The optimized NiO–Au–ZnO film demonstrates superior photocatalytic activity, achieving 98% degradation of methylene blue after 180 minutes alongside excellent reusability over multiple cycles. Comprehensive characterization using UV-vis, PL, XPS, and scavenger tests indicates that the enhancement is driven by an all-solid-state Z-scheme mechanism. Facilitated by the continuous Au interlayer, this mechanism promotes efficient charge carrier separation while preserving the strong redox potentials of the individual semiconductors. Notably, a discontinuous Au interlayer led to an unexpected decrease in photocatalytic performance, an effect that was attributed to a proposed antagonistic interaction between coexisting Z-scheme and type II p–n heterojunction pathways. This work underscores the critical importance of interface engineering and precise nanostructural control in thin-film systems for the rational design of advanced photocatalytic materials.