A novel amino-functionalized magnetic silica cryogel to rapidly capture and eliminate Cr(VI): Its efficient performance and synergetic mechanism

Abstract

Although silica (SiO2) cryogel possesses high surface area and physicochemical stability, the poor performance, high production cost, and difficult separation limit its capability to efficiently remove Cr(VI) from water. To address this issue, commercial water glass was chosen as the silica source, and Fe3O4 was used as the core to synthesize the magnetic SiO2 cryogel, which was then anchored with 3-(2-Aminoethylamino)propyltrimethoxysilane (APTMS) to prepare a novel cryogel named Fe3O4 @SiO2-APTMS. Successful amino functionalization was evidenced by the characterization of techniques such as SEM, TEM, FTIR, XRD, VSM, and BET. The adsorption performance of Fe3O4 @SiO2-APTMS was evaluated systematically under different conditions concerning the initial solution pH, adsorbent dosage, temperature, and coexisting anions and cations. Adsorption kinetics, isotherms, and thermodynamics revealed that the pseudo-second-order kinetic, Langmuir models preferably fitted the adsorption data, suggesting a single-layer, chemical sorption, and exothermic adsorption process occurred. The Fe3O4 @SiO2-APTMS exhibited a fast adsorption rate to Cr(VI) ions that it reached the equilibrium within 10 min when the initial Cr(VI) concentration was less than 200 mg/L, and the theoretical maximum capacity was estimated as high as 240.96 mg/g at 298 K and pH 2.0, which are superior than the majority magnetic adsorbents. Moreover, the amino-modified magnetic cryogel could be rapidly separated by the external magnetic field and maintain effective Cr(VI) removal efficiency even after 4 cycles. It was further expounded that the outstanding Cr(VI) removal performance could be attributable to electrostatic attraction coupled with reduction and chelation. The study could provide a promising alternative material for the Cr(VI)-polluted water purification and highlight the potential application of related magnetic cryogel material. The findings also implied the amino-decorated material could participate in the redox of Cr(VI) at nearly one-half of the total amount for the detoxification.