Application of magnesium ferrite nanomaterials for adsorptive removal of arsenic from water: Effects of Mg and Fe ratio

Abstract

Magnesium ferrites (MgFe2O4) drew much attention in water treatment because of higher stability, magnetic properties, availability and higher safety. MgFe2O4 having different Fe and Mg ratios were synthesized through a simple one-step solvothermal method and applied for the removal of toxic arsenic oxyanions from water. Three different magnesium ferrites, MF0.1, MF0.2 and MF0.33, were synthesized using molar Mg and Fe ratio of 10:90, 20:80 and 33:67, respectively. The Mg and Fe ratio affected the physical and magnetic properties, surface area, crystallite size, pore diameter and magnetism, of magnesium ferrites, which were evidenced by the XRD, SEMEDS, BET and VSM. Increasing Mg content reduced the pore size, pore volume and saturation magnetization but increased surface area and pHPZC. It was estimated that defective iron oxide, gamma-Fe2O3 maghemite, had been formed with the magnesium ferrites, when the ratios of Mg and Fe were non-stoichiometric. The difference in characteristics of magnesium ferrites synthesized with three ratios of Mg and Fe affected arsenic adsorption capacity and the stability of adsorbed arsenic. Arsenic adsorption data followed Freundlich isotherm model and maximum As(III) and As(V) adsorption capacities were found to be 51.48, 100.53, 103.94 mg/g and 26.06, 43.44, 45.52 mg/g by MF0.1, MF0.2 and MF0.33, respectively. Fast adsorption of arsenic was confirmed by kinetic data which followed the Pseudo-2nd-order kinetic model. The MF0.33 having stoichiometric ratio of Mg and Fe showed higher adsorption capacity and stability for arsenic than the other two at neutral pH.