Adsorption of Ni(II) ions on colloidal hybrid organic–inorganic silica composites

Two new silica-based composites were prepared as adsorbents for the capture of Ni(II) ions. The first strategy consists in coating chitosan on colloidal fumed silica after acidic treatment yielding the composite SiO2 + CS. The second route involves in a first step surface condensation of triethoxysilylbutyronitrile, followed by acidic hydrolysis of the surface-bound nitrile groups affording silica particles covered by carboxylic group. In a third step, chitosan has been grafted on the surface-bound C(O)OH groups yielding the composite SiO2(CO2H) + CS. The novel hybrid materials were characterized by IR spectroscopy, scanning electron and AFM microscopy, and zeta potential measurements. Batch experiments were conducted to study the sorption performance of these composites for Ni(II) removal from aqueous NiCl2 solution at different pH. Both Langmuir, Freundlich, and Temkin isotherm models provide good fits with the experimental data. It was shown that these low-cost materials present a promising capacity to adsorb Ni(II) ions. At pH 7, the maximum adsorption capacity qmaxof Ni(II) on the adsorbent, is found to be 182 mg g−1 for SiO2 + CS, and 210 mg g−1 for SiO2(CO2H) + CS.