Enhanced removal of chromate from aqueous solution by sequential adsorption–reduction on mesoporous iron–iron oxide nanocomposites

The adsorption behavior of mesoporous iron nanocomposites was investigated with respect to chromate [Cr(VI)] removal from aqueous solutions to consider its application for purifying chromate-contaminated wastewaters. These nanocomposites were prepared by borohydride reduction in aqueous solutions containing varying concentrations of acetone as co-solvent. Using batch methods, enhanced adsorption of Cr(VI) on the nanocomposite surface was achieved at neutral pH conditions, which subsequently resulted in Cr(VI) reduction to Cr(III). The Langmuir model was found to excellently describe the adsorption process, offering a maximum adsorptive capacity of 34.1 mg/g for composites prepared with 50 % acetone concentration. The Cr(VI) removal efficiency of these iron nanocomposites is strongly dependent on the acetone concentration, as evident from their (1) increased surface area (141.1 m2/g) compared to conventional iron nanoparticles (33.2 m2/g), and (2) highly porous and acicular structure, which efficiently traps Cr(VI) through adsorption. X-ray photoelectron spectroscopy analysis of Cr(III) on the nanocomposite surface confirmed that Cr(VI) removal from solution was achieved by sequential adsorption–reduction.