Optimization and mechanistic evaluation of chlorpyrifos removal from aqueous solutions using Co₃O₄-g-C₃N₄...

The persistence and toxicity of pesticides such as chlorpyrifos (CPF) pose a serious threat to aquatic ecosystems due to their widespread agricultural use and resistance to natural degradation. This study reports the synthesis of a novel Co₃O₄-g-C₃N₄ nanocomposite via a simple hydrothermal method and its application as an efficient adsorbent for CPF removal from aqueous solutions. Comprehensive characterization using FE-SEM, EDS, XRD, FTIR, and BET analyses confirmed the uniform dispersion of hexagonal Co₃O₄ nanosheets on the g-C₃N₄ matrix, yielding a macroporous structure with a specific surface area of 15.95 m² g^-1 and an average pore diameter of 54.35 nm. The adsorption process was optimized using response surface methodology (RSM) combined with Box-Behnken design (BBD), considering adsorbent dosage, solution pH, contact time, and initial CPF concentration as key factors. The quadratic model exhibited excellent predictability (R² = 0.995). Optimal conditions were identified as adsorbent dose of 1.47 mg (in 5 mL solution, equivalent to 0.294 g L^-1), pH 3.51, contact time of 20.08 min, and initial CPF concentration of 19.53 mg L^-1, achieving a maximum predicted removal efficiency of 96.84%. Equilibrium studies best fitted the Freundlich isotherm model (R² = 0.9797), while kinetic data best fitted the pseudo-second-order model (R² = 0.998), indicating chemisorption dominance. Mechanistic insights suggest synergistic effects including surface complexation involving Co²⁺/Co³⁺ sites and CPF's phosphoryl groups, hydrogen bonding, and π-π interactions, with minimal contribution from electrostatic attraction due to the nonionic nature of CPF. Compared to other adsorbents, this nanocomposite provides high removal efficiency at an ultralow dosage and short contact time, underscoring its cost-effectiveness, stability, and sustainability for practical pesticide remediation in water treatment.