Facile synthesis of maghemite nanoparticle from waste green vitriol as adsorbent for adsorption of arsenite

Environmental pollution and resource waste caused by waste green vitriol from TiO2 industry have become an increasingly serious problem. To this end, magnetite nanoparticles were fabricated by the reduction of green vitriol with pyrite under nitrogen at 550 °C, and then oxidized to maghemite nanoparticles under air at 350 °C. Meanwhile, arsenite adsorption performances on maghemite nanoparticles were investigated. The properties of the as-formed samples were analyzed by X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) spectrum, transmission electron microscopy (TEM), nitrogen adsorption- desorption isotherms and X-ray photoelectron spectroscopy (XPS). The analytic results show that the as-formed samples having the average diameter of ~35 nm exhibit pure phase maghemite with cubic structure, and the BET surface area of as-formed samples is 14.63 m2·g−1. The adsorption results indicate that the isotherm and kinetics for As(III) adsorption on maghemite nanoparticles obey Langmuir isotherm and pseudo-second-order kinetic respectively, and As(III) adsorption is co-controlled via film diffusion and intraparticle diffusion. Adsorption capacity of As(III) obtained from Langmuir isotherm is 14.4 mg/g at 55 °C. Thermodynamic parameters show that As(III) adsorption onto maghemite nanoparticles is regarded as spontaneous endothermic process.