Synthesis of Highly Selective Magnetic Mesoporous Adsorbent

Abstract

Magnetic MCM-41 of large surface area (ca. 800 m2 g−1) and high magnetization (ca. 8.3 emu g−1) was prepared at a reasonable iron oxide nanoparticles loading of 10 wt % by a two-step synthesis process. The 8 nm iron oxide nanoparticles (i.e., 30 m2 g−1) were embedded in the MCM-41 with no observable effects on the particle morphology and pore symmetry, but a slight change (i.e., <20%) in the textural properties and surface chemistry was detected. Aminopropyls (2.7 mmol g−1) were grafted on the mesopore channels followed by the adsorption of 1.2 mmol g−1 Fe3+ to prepare selective adsorbents for arsenic(V) and chromium(VI) oxyanions. Detailed analyses indicated that the surface modifications of the magnetic and nonmagnetic MCM-41 by aminopropyls and Fe3+ yield similar site chemistry and accessibility. The Fe3+-magMCM-41 and Fe3+-MCM-41 displayed comparable adsorption capacity and selectivity. Both adsorbed only As(V) and Cr(VI) oxyanions (i.e., 1.0 and 2.0 mmol g−1, respectively), and none of the Cu(II). The magnetic adsorbent was easily dispersed in aqueous solution and can be removed by a magnet (1550 G) at a rate of 1 cm min−1 compared to 0.004 cm min−1 by gravity.