Poly(methacrylic acid) surface modified magnetite nanoparticles for dispersive solid-phase adsorption of chlorpyrifos pesticide from aqueous solutions

Abstract

Population growth and the increasing need for agricultural and food products, enhance usage of pesticides, which are special water pollutants. In this study, we synthesized poly(methacrylic acid) modified magnetite nanoparticles (Fe3 O4 @PMA MNPs) to remove chlorpyrifos organophosphate pesticide from aqueous samples. The structure of synthesized MNPs was characterized by vibrat-ing sample magnetometer, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and dynamic light scattering. Effective operational parameters such as pH, adsorbent mass, contact time and ionic strength were evaluated at four levels by Taguchi fractional factorial design method (OA16). Under the optimum conditions (pH = 5, adsorbent content = 2 g·L–1, ionic strength = 0.005 mol·L–1 and 30 min contact time), the removal efficiency of 89.8% was obtained. The kinetic studies at two concentrations of 5 and 25 mg·L–1 showed that chlorpy-rifos removal followed the pseudo-second-order kinetic model (R2 = 0.99, qeq = 11.31 mg·g–1) con-firming diffusion plays a key role in determining the rate of adsorption process. The adsorption equilibrium data were investigated by linear and non-linear forms of four isotherm models, and the results showed good accordance with the Dubinin–Radushkevich isotherm model (R2 = 0.99). From the thermodynamic studies, ΔH°, ΔS°, ΔG°, and Ea of adsorption process were obtained as 9.665 kJ·mol–1, 40.25 J·mol–1·K–1, –2.326 kJ·mol–1 and 8.677 kJ·mol–1, respectively. The results revealed that the adsorption process was endothermic (ΔH° > 0) and spontaneous (ΔG° < 0). The obtained values of ΔH°, ΔG° and Ea confirmed the physisorption nature of interaction. The calculated Ea and sticking probability (S*) showed the endothermic adsorption process and high probability of sticking to the surface, respectively. This study showed that Fe3 O4 @PMA MNPs are suitable adsor-bents for removing chlorpyrifos pesticide from aqueous solutions.