Removal of Cr(III, VI) by quaternary ammonium and quaternary phosphonium ionic liquids functionalized silica materials

Abstract

Abstract A series of silica-based organic–inorganic hybrid materials were prepared by the sol–gel process for Cr(III) and Cr(VI) adsorption. These silica materials generally had high surface areas, good physical–chemical stability and high thermal stability. Trialkylmethylammonium bis 2,4,4-trimethylpentylphosphinate ([A336][C272]) and trihexyl(tetradecyl)phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL 104) were explored as porogens to prepare porous silica and as extractants to extract chromium ions. Cyphos IL 104 and [A336][C272] functionalized silica sorbents (SG-2, SG-5) can be effectively used for the removal of Cr(III) and Cr(VI) from aqueous solutions by adjusting pH values, whereas trialkylmethylammonium chloride (Aliquat 336) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) functionalized silica sorbents (SG-3, SG-4) can only be used for the removal of the single chromium species, Cr(VI) or Cr(III). The maximum adsorption amounts of Cr(III) and Cr(VI) were 2.14 and 19.31 mg g−1 for SG-2 and 2.32 and 15.29 mg g−1 for SG-5. Langmuir and Freundlich isotherm models were used to evaluate the adsorption of Cr(III) and Cr(VI) on sol–gel sorbents. The adsorption kinetics of Cr(III) and Cr(VI) on SG-2 and SG-5 could be well described by pseudo-second-order kinetic model. In terms of Cr(III) and Cr(VI) uptake capacities and kinetics, SG-2 and SG-5 appeared to be more suitable for Cr(III) and Cr(VI) removal than SG-3 and SG-4.