Core-satellite CeO2-Cu2O heterojunction photocatalysis monitored by SERS: Accurate kinetics and degradation pathway elucidation for acetamiprid.

The deep remediation of neonicotinoid pesticide residues in water is hindered by insufficient catalytic activity and the lack of rapid, high-sensitivity methods for monitoring degradation. In this study, a core-satellite structured CeO2-Cu2O heterojunction was prepared via a green aqueous method. Its surface is rich in oxygen vacancies and Ce3+/Ce4+, Cu+/Cu2+ dual redox couples, which synergistically activate persulfate to generate reactive oxygen species such as sulfate radicals (SO4•-). Using methylene blue (MB) as a model pollutant, reaction parameters were optimized. Under these optimized conditions, a quantitative detection method based on surface-enhanced Raman spectroscopy (SERS) was established for acetamiprid (AAP), and the resulting calibration curve was then used to monitor its degradation. Under the optimal conditions, AAP concentration of 22.27 mg/L, catalyst dosage of 0.67 g/L, 0.27 g/L persulfate and pH 11, the degradation efficiency reached 89.25% within 50 min. The pseudo-first-order rate constant determined by SERS (0.044 min-1) was substantially higher than that obtained by conventional UV-Vis spectroscopy (0.014 min-1), since SERS avoids spectral interference from intermediates. LCMS-IT-TOF identified eight degradation intermediates, based on which three major degradation pathways, namely hydroxylation, oxidation, and dealkylation, were proposed. This work constructed an efficient CeO2-Cu2O/persulfate (PS) photocatalytic system. Combined with SERS detection, it provides new experimental evidence and a technical reference for elucidating photocatalytic degradation mechanisms and remediating pesticide residues.