Advanced CuO/CeO2/ZnO Ternary Nano-Photocatalysts: Efficient Utilisation of Photo-Excited Carriers under Sunlight

Abstract

Free photo-excited holes and electrons are known to promote photocatalytic processes through their intrinsically strong oxidative/reduced characteristics. However, the majority of surface carriers are highly dependent on the carrier motion along the direction of the built-in electric field created by surface states, i.e., the dangling bonds. This leads to inefficient surface photocatalytic reactions solely driven by photo-excited electrons or holes. In this chapter, we introduce a multi-component nano-particle (NP) photocatalyst platform integrating the different photo-response behaviours of n and p-type materials, exhibiting an enhanced photo-activity under a broad wavelength range, the designed band alignment is also crucial for achieving highly efficient photo-excited charge separation. The ternary CuO/CeO₂/ZnO composite nano-photocatalysts were synthesised by a straightforward two-step sol-gel method. The photo responses to both UV and visible light, as well as the visible light utilisation rates of ZnO, were synergistically intensified by co-coupling with CeO₂ and CuO. The roles of CuO and CeO₂ in photocatalytic reactions under UV and visible light were systematically explored. Specifically, under UV light, the photogenic holes (h+) of ZnO, and CeO₂, along with the produced hydroxyl radicals (·OH), were identified as the primary active species. Conversely, under visible light, superoxide radicals (·O₂-) generated by the reactions between oxygen molecules and the photo-generated electrons (e-) of CuO moving towards the catalyst surface were also found to be crucial for promoting dye decomposition. Consequently, these composites demonstrate a significantly enhanced photocatalytic degradation performance for various organic pollutants under UV and visible light excitation. The improved photo-responses, the well-matched band structures facilitating charge transfer, and the highly efficient utilisation of the photo-excited carriers in the ternary nano-heterostructure are suggested to be the key factors for the remarkable enhancement of photocatalytic performance. This chapter provides a promising design avenue for unlocking the full potential of ZnO-based photocatalysts, advancing efficient photocatalytic processes.