Non-Noble Metal-Based Cu/CeO2 Nanofilm as a Versatile SERS-Photocatalyst Platform for Monitoring Nitrobenzene Coupling and Uric Acid Detection

Abstract

A Cu/CeO2 nanofilm-based substrate is strategically designed by exploiting the complementary functionalities of the constituents, prepared by a scalable, sequential sputtering technique. Copper nanoparticles, cost-effective and earth-abundant non-noble metals with plasmonic properties, are prone to rapid oxidation and degradation of their plasmonic nature, which is mitigated through the incorporation of a protective CeO2 layer. The CeO2 coating not only acts as an oxygen buffer but also enhances charge transfer and introduces oxygen vacancies, leading to significant Raman signal amplification as well as contributing to photocatalytic properties. The Cu/CeO2 films (20 nm) consisting of 3.2 nm Cu nanoparticles and 4.7 nm CeO2 nanoparticles show excellent SERS performance with high sensitivity (LOD─6.17 nM), spatial uniformity (∼5% RSD), enhancement factor of 1.2 × 108, and remarkable stability over a period of 7 weeks for 4-mercaptobenzoic acid as a model analyte. The substrate is successfully employed for uric acid detection─a key biomarker─at nanomolar concentrations, highlighting its biomedical sensing potential. Utilizing the strong SERS activity and photocatalytic property, the Cu/CeO2 film is demonstrated as a SERS-photocatalyst platform for monitoring the photocatalytic coupling of nitrobenzene, revealing the formation of azobenzene via an azoxybenzene intermediate, corroborated by UV–vis and FTIR spectroscopy. Overall, the Cu/CeO2 nanofilm serves as a bifunctional platform, demonstrating high-performance SERS-based sensing and catalytic monitoring, along with enhanced photocatalytic activity, thus offering promising applications in both biomedical diagnostics and catalytic mechanistic studies.