Olive pomace-derived graphene quantum dots decorated with iron oxide nanoparticles for efficient malathion removal from environmental water: Theoretical and experimental studies

Abstract

With increasing water pollution, research has focused on developing green, cost-effective, and sustainable materials for efficient water treatment. In this study, graphene quantum dots (GQDs) derived from olive pomace were synthesized via a simple hydrothermal method and decorated with iron oxide nanoparticles (Fe₃O₄) to form GQDs@Fe₃O₄ nanocomposites for malathion removal from environmental water. The physicochemical properties of these nanocomposites were characterized using SEM, FTIR, XRD, UV–Vis spectroscopy, and nitrogen adsorption-desorption techniques. The adsorption efficiency of the synthesized adsorbent was evaluated by measuring its adsorption capacity and removal efficiency, considering various parameters such as initial pH, initial concentration, temperature, adsorbent dosage, contact time, and salt concentration. Adsorption behavior was analyzed using kinetic and isothermal models, revealing that the Freundlich isotherm (R² = 0.9996) and the pseudo-first-order kinetic model (R² = 0.9998) provided the best fit for the malathion adsorption process. Under optimal conditions (5 mg L⁻¹ malathion, 30 mg adsorbent, 210 min), a maximum removal efficiency of 87.19 ± 4.47 % was achieved at 298.15 K, increasing to 97.24 ± 2.19 % at 323.15 K. When applied to real water samples from river and dam sources, the nanocomposites maintained a removal efficiency of 73–67 %, demonstrating their practical applicability. FTIR analysis confirmed the presence of malathion on the adsorbent surface post-adsorption, providing insights into the adsorption mechanism, which was further investigated through theoretical calculations. These findings highlight the high adsorption capacity, rapid removal efficiency, and reusability of GQDs@Fe₃O₄ nanocomposites, demonstrating their potential as an environmentally sustainable and cost-effective solution for pesticide removal from aquatic environments.