Effect of Layer Sequence in Ce–Ni Bilayer Films on Catalytic Ozonation of Methylparaben

Advanced oxidation processes (AOPs), particularly catalytic ozonation, offer effective strategies for the degradation of contaminants of emerging concern (CEC). This study evaluates the role of layer sequence in Ce-Ni bilayer thin films synthesized via ultrasonic spray pyrolysis (USP) in the catalytic ozonation of methylparaben (MePB), a widely used antimicrobial preservative and representative CEC. Using water as the only solvent and benign precursors, the films were directly deposited on glass substrates. While ozonation alone led to full MePB degradation, it achieved limited mineralization. The inclusion of Ce-Ni bilayer catalysts significantly enhanced total organic carbon (TOC) removal. Notably, the Ce-Ni (L-L) configuration outperformed Ni-Ce (L-L), achieving 58.5% mineralization vs 38.6%, respectively, after 120 min. Radical scavenger experiments confirmed the generation of multiple reactive oxygen species (^•OH, ¹O₂, ^•O₂ ^-), with catalytic activity linked to surface oxygen vacancies and Ce³⁺ concentration as determined by XPS analysis. The Ce-Ni (L-L) thin film exhibited excellent stability over five reuse cycles and maintained activity in tap water, highlighting its practical robustness. Toxicity assays using <i>Lactuca sativa</i> confirmed the nontoxic nature of treated effluent. These results denote Ce-Ni thin films as a reusable, scalable, and sustainable platform for water decontamination applications.