Mechanistic, kinetic and toxicological insights into imidacloprid degradation using a biogenic catalyst: A DFT-based approach

In this study, the removal of imidacloprid (IMD), a persistent neonicotinoid pesticide, was accomplished by Catalytic Wet Peroxide Oxidation (CWPO) process using a biogenic carbonaceous catalyst derived from urban sewage sludge (BSAC). This catalyst was synthesized through chemical and physical activation, yielding a porous material with a high surface area and heterogeneous surface chemistry properties. Its performance was evaluated under varying operational conditions, including different initial concentrations, temperatures, and water matrices. CWPO technology using BSAC material enabled the efficient degradation of IMD, achieving up to 93 % removal under optimal operation conditions (50 °C and a H₂O₂/IMD ratio of 4.6 μg H₂O₂·μg IMD −1 ), and maintained catalytic activity over multiple reuse cycles. The kinetic experimental data fitted well to a dual-site Langmuir–Hinshelwood rate expression, finding an activation energy of 16.01 kJ·mol −1 . Moreover, Density Functional Theory (DFT) calculations provided insights into the degradation mechanism, highlighting successive hydroxylation and oxidation reactions; and the estimated theoretical reactivity indices and Fukui functions supported the proposed reaction pathways. Finally, in silico toxicity assessments revealed that the main degradation products were less toxic than the parent compound, suggesting reduced environmental risk. The study demonstrated the feasibility of using waste-derived catalysts for pesticide removal, combining experimental validation, theoretical modeling, as well as toxicity evaluation to support their application in sustainable water treatment technologies. • Biogenic catalyst from sewage sludge applied for CWPO of imidacloprid. • BSAC achieved up to 93 % removal and showed good reusability. • Hyperbolic model fitted kinetics well, with activation energy of 16.01 kJ·mol −1 . • DFT calculations revealed hydroxylation and oxidation as key degradation steps. • Toxicity of degradation products was lower than that of the parent compound.