Controllable synthesis of mesoporous magnetite/activated carbon composites as efficient adsorbents for hexavalent chromium removal

Abstract

Mesoporous magnetite (Fe3O4) nanoparticles were synthesized via a simple process of Fe2+ and Fe3+ co-precipitating with OH− from different sources of chemical bases (NH4OH and NaOH) under ambient air. Two routes of an impregnation process were performed using deionized water or ethanol solvent with equal weight ratios of the synthesized Fe3O4 and activated carbon (AC). To reveal microstructures, surface characteristics, crystal structures, chemical functionalities and magnetization properties of the synthesized Fe3O4, AC and Fe3O4/AC composites, all of the synthesized powders were characterized using various techniques. As a model of heavy metals contaminated in wastewater effluent, hexavalent chromium (Cr(VI)) aqueous solutions were prepared in ranges of 30–50 mg/l for the adsorption experiment. Pure phase of Fe3O4 nanoparticles was formed in the synthesized route using NaOH based on characterized results. Goethite phase (α-FeOOH) mixed with the Fe3O4 phase was found in the synthesized route using NH4OH. AC and Fe3O4/AC composites showed higher efficiencies for Cr(VI) reduction in the solutions compared with the synthesized Fe3O4. Magnetic properties of the synthesized Fe3O4 and Fe3O4/AC composites could assist in separating the used absorbents out from the solutions. Adsorption mechanisms were finally discussed in terms of microstructural investigations and chemical analysis on composite surfaces.