Nanocarbon anchored on magnetic iron oxide -silica core shell nanocomposite for extraction of organophosphate pesticides from natural water

Abstract

Iron oxide nanoparticles coated with silica, were used as an anchor for graphene oxide or carbon nanotubes. The two different types of nanocomposites were characterised using various analytical techniques namely Fourier transform-infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), Zeta potential, thermogravimetric analysis, scanning, energy-dispersive X-ray spectroscopy (EDS), Nitrogen adsorption/desorption and Vibrating Sample Magnetometer (VSM). The graphene oxide based nanocomposite (Fe3O4@SiO2@GO) was functionalized with 2-phenylethylamine (Fe3O4@SiO2@GO-PEA) and then thoroughly investigated as a material for magnetic solid phase extraction (MSPE) of five selected OPPs namely azinphos methyl, dimethoate, chlorpyrifos, parathion and malathion. The optimum conditions affecting the extraction recovery were found to be 10 minutes, 20 mg of adsorbent dosage and acetone being the best desorption solvent. The linear responses were obtained in the concentration range of 0.05–0.1043 μg/mL with the correlation coefficients (R2) between 0.9943 and 0.9977. The limits of detection were in the range of 0.01-0.08 μg/mL and limit of quantification were between 0.04-0.27 μg/mL. The method provided a good repeatability with relative standard deviations (RSD) of ˂ 12%. Environmental water samples were used to assess the field applicability of the adsorbent. The recoveries obtained were in the range of 83.8-97.7% (RSD=4.7-9.9%) for Vaal River water samples and 81.1-102.1% (RSD=4.2-12%) for Vaal Dam water samples Comprehensive kinetic and thermodynamics investigations using the Fe3O4@SiO2@GO-PEA were conducted using chlorpyrifos, parathion, and malathion in water solutions. The optimum conditions for adsorption was found to be 15 minutes, 15 mg adsorbent dosage using 1 μg/mL concentration, and no significant difference on the pH condition used. The maximum adsorption of chlorpyrifos, malathion, and parathion mixture on Fe3O4@SiO2@GO-PEA at optimum condition was found to be 32.6 mg/g. Adsorption isotherm of Chlorpyrifos...