Industrial water pollution caused by persistent organic contaminants remains a major environmental concern, necessitating the development of efficient and advanced photocatalytic materials. In this study, we present a novel photocatalytic system based on ultrathin ZnO coatings deposited on microstructured γ-Fe2O3 films by atomic layer deposition (ALD). The microstructured γ-Fe2O3 films were prepared by the drop-casting of γ-Fe2O3–SiO2 core-shell structures with controlled shape, size and silica shell thickness. Our results demonstrate that the ALD growth rate of ZnO films is strongly influenced by the concentration of surface hydroxyl (–OH) groups on the microstructured γ-Fe2O3 films. Detailed structural and surface characterization were performed using SEM, TEM, AFM, XPS and GIXRD. Under UV irradiation, the ZnO/γ-Fe2O3 heterostructures exhibited up to threefold higher methylene blue degradation rates compared to ZnO films on flat silicon. This enhancement arises from two distinct factors observed in different samples: increased surface roughness and microstructured morphology led to larger catalytic surface area in case of samples with the intermediate silica layer; and the formation of a type I heterojunction between ZnO and γ-Fe2O3 – enabled by the direct contact between the two metal oxides for samples without an intermediate silica layer – promoted efficient separation of photogenerated charge carriers. These results demonstrate how both surface architecture and band alignment engineering can independently contribute to improved photocatalytic performance.
