Copper-Loaded Chitosan Hydrogel for Efficient Removal of Organophosphate Pesticides from the Water Matrix: Preparation, Characterization, and Mechanistic Insights

Pesticides, along with their well-recognized beneficial effects on crop productivity, are also known for their various harmful effects on human health. As a consequence of their extensive use, increasing concentrations of pesticides have been detected in the aquatic environment. To mitigate the health consequences related to environmental pesticide exposure, their removal from the water matrix becomes important. The removal of organophosphate pesticides (OPs) from water requires adsorbents that combine rapid kinetics, selectivity, and sustainable synthesis. In this study, a Cu-incorporated chitosan (Cu–CS) hydrogel was developed by using a simple aqueous route and evaluated for the adsorption of multiple OPs. A batch adsorption experiment with varying temperatures, pH, adsorbent dose, contact time, and adsorbate concentration was used to achieve efficient adsorption conditions for all the analytes. The hydrogel exhibited fast adsorption kinetics, reaching near-equilibrium within 5 min, and showed competitive adsorption capacities in the range of 17–24 mg g–1 for most OPs. Adsorption behavior followed a pseudo-second-order kinetic model, along with the Langmuir isotherm, confirming chemisorption as the preferred mechanism for removal of OPs, along with additional support by physisorption as suggested by in-line R2 values of the Freundlich isotherm model. The incorporation of Cu introduced coordination-driven selectivity among OPs, while the anomalously low adsorption of quinalphos was attributed to steric hindrance and limited accessibility of coordination sites. Unlike conventional chitosan-based and carbonaceous adsorbents that typically require longer contact times, Cu–CS hydrogel offers a favorable balance between adsorption capacity, kinetics, and biobased process simplicity. The significant removal efficiency (≥88%), except quinalphos, of the hydrogel in the groundwater sample demonstrates the potential of Cu-functionalized chitosan hydrogel as practical and rapid adsorbents for OPs remediation.