Selective removal of chromium from different aqueous systems using magnetic MCM-41 nanosorbents

Chromium (VI) oxyanions were removed selectively from various aqueous systems using magnetic MCM-41 nanosorbents of large surface area (>550 m2 g−1) and high magnetization (≥8.0 emu g−1). 10 nm magnetic iron oxide nanoparticles were embedded within 250 ± 50 nm MCM-41 to obtain a highly dispersible magnetic material, magMCM-41 that can be easily removed by a magnetic field. A highly selective nanosorbent was obtained by grafting aminopropyls and adsorbing Fe3+ on the pores of the magMCM-41. Chromium oxyanions were selectively removed over the pH range of 2–7 with high adsorption capacity of ca. 1.9 mmol g−1 (ca. 100 mg g−1) and Kd > 25,000 mL g−1 for single and binary component adsorptions from distilled, tap, mountain stream and river waters. The presence of calcium in the tap and natural waters as well as humic compounds in mountain stream and river waters resulted in a slightly lower chromium adsorption, but did not affect its superb selectivity (ca. 97%). The adsorption and separation of the chromium oxyanions were adequately described by Freundlich and LeVan–Vermeulen equations.

• Magnetic nanosorbents of excellent chromium adsorption selectivity (Kd > 25,000 mL g−1).
• Separates better than 90% chromium in aqueous systems with capacity of ca. 1.3 ± 0.2 mmol g−1.
• High magnetization (8.30 emu g−1), excellent dispersibility and recoverability from water.
• Stable in tap and natural waters even in presence of minerals and humic compounds.