Adsorption/desorption behavior of acid orange 10 on magnetic silica modified with amine groups

Two silica samples were prepared through precipitation of silica in the presence and absence of magnetite particles (Fe3O4). The products were immobilized with 3-aminopropyltriethoxysilane and characterized by means of FT-IR and X-ray. Surface area (BET), pore volume and pore diameter were also measured. The adsorption behavior of both silicas towards C.I. acid orange 10 in aqueous solutions was studied at different experimental conditions including contact time, pH and initial concentrations. The monoamine modified magnetic silica (MAMMS) displayed higher and faster adsorption relative to magnetite free one (MAMPS). The maximum adsorption capacity of the dye on MAMPS and MAMMS are 48.98 and 61.33 mg g−1, respectively. Adsorption of the dye on both MAMMS and MAMPS fitted to Langmuir adsorption model and followed the pseudo-second order kinetics. The values of Gibbs free energy of adsorption (ΔG0) were found to be −26.52 and −28.49 kJ/mol at 298 K for MAMPS and MAMMS, respectively. These negative values indicated the spontaneity of the adsorption of the dye on both silica samples. Regeneration of the dye-loaded silica was carried out using aqueous solution of pH 10. Desorption ratio of 98% was obtained over three adsorption/desorption cycles.