Isotherm and kinetic investigations on the adsorption of organophosphorus pesticides on graphene oxide based silica coated magnetic nanoparticles functionalized with 2-phenylethylamine

The study describes the preparation of graphene oxide based silica coated magnetic nanoparticles (Fe₃O₄@SiO₂@GO) functionalized with 2-phenylethylamine (PEA) as an adsorbent for selected organophosphorus pesticides (OPPs) namely chlorpyrifos, parathion, and malathion from aqueous solution. The synthesised (Fe₃O₄@SiO₂@GO-PEA) adsorbent was characterised using Fourier transform-infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), Zeta potential, Nitrogen adsorption/desorption at 77 K, and a Vibrating Sample Magnetometer (VSM). The maximum adsorption was found at 15 min, with 15 mg adsorbent dosage using 1 μg/mL concentration. There was no significant difference in the pH condition used highlighting the potential to use the material on a variety of samples. Using non-linear methods, the sorption isotherm data were fitted to Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Sips, and Redlich and Peterson models. All three pesticides were best fit with the Sips model. Pseudo-first and pseudo-second order kinetics models were fitted to the experimental data using non-linear methods, and pseudo-second-order kinetics gave the best fit to the data for all three pesticides. The absorbent was tested for its reusability, and there was little loss in the recovery of OPPs after 10 cycles. Finally, the adsorbent was tested using real world samples from the Vaal River and Dam (South Africa), and showed greater than 86.9% recovery. The results obtained showed that the synthesised Fe₃O₄@SiO₂@GO-PEA is an efficient adsorbent for recovery and analysis of pesticides.