Mechanisms toward visible-light degradation of fluoroquinolone in water using chitosan enhanced Cu-Cu2O photocatalysts

The widespread use of antibiotics and their negative impact on the environment make a key challenge in wastewater treatments. In this study, Cu-Cu₂O-chitosan (Cu-Cu₂O-CTs) photocatalysts are synthesized via a simple wet chemical method for the photocatalytic degradation of antibiotics. The experimental results show the degradation efficiency of enrofloxacin (ENR) reaches 99.99 % under optimal conditions, and the catalyst retains over 70 % removal efficiency after four consecutive cycles. The enhanced photocatalytic performance of Cu-Cu₂O-CTs is primarily attributed to the incorporation of chitosan, which effectively reduces electron-hole recombination, and improves light utilization efficiency. Mechanistic analysis reveals that O₂⁻ is the dominant reactive oxygen species (ROS), targeting specific active sites on the ENR molecule and ultimately leading to mineralization. Density Functional Theory (DFT) computations of the Fukui function are used to identify the two nitrogen atoms in the piperazine ring as the primary reactive sites that trigger the degradation pathway. Additionally, three distinct degradation pathways of ENR are proposed by integrating LC-MS analysis, and the toxicity of intermediates is effectively predicted. This study presents a simple and practical approach for designing Cu₂O-based photocatalysts and provides in-depth insights into the degradation mechanisms of ENR, highlighting the potential of Cu-Cu₂O-CTs for wastewater treatment.