Fenton and Photo-Fenton Degradation of Chlorpyrifos Using α-Mn₂O₃ Heterogeneous Catalysis

Chlorpyrifos, a widely used organophosphate pesticide, poses significant environmental risks due to its persistence and the formation of toxic transformation products. Despite extensive research on iron-based Fenton systems, the application of manganese oxides, particularly α-Mn₂O₃, in chlorpyrifos degradation remains insufficiently explored. In this study, we investigated the catalytic performance of α-Mn₂O₃ in Fenton and visible-light-driven photo-Fenton processes for the degradation of chlorpyrifos in aqueous systems. Chlorpyrifos oxon was identified as a transient intermediate, detected at trace levels, supporting an oxidative degradation pathway. Kinetic analysis revealed pseudo-first-order behavior, with comparable rate constants for Fenton reactions at different catalyst loadings (0.0033 min^-1 for 5 mg and 0.0028 ± 0.0006 min^-1 for 10 mg), indicating that the process is not limited by catalyst concentration under the investigated conditions. In contrast, the photo-Fenton system exhibited a higher rate constant (0.0042 min^-1) and significantly improved degradation efficiency, highlighting the role of visible-light activation. The highest removal rates of chlorpyrifos were 86.24% for Fenton experiments and 96.05% for the photo-Fenton experiment, respectively. The enhanced performance is attributed to the photocatalytic properties of α-Mn₂O₃, including its narrow bandgap and the facilitation of Mn³⁺/Mn²⁺ redox cycling, which promotes reactive oxygen species generation. These findings demonstrate that α-Mn₂O₃ is a promising non-iron catalyst for advanced oxidation processes and provide new insights into manganese-mediated Fenton-like mechanisms for the removal of organophosphate contaminants.