Application of bifunctional magnetic adsorbent to adsorb metal cations and anionic dyes in aqueous solution

A magnetic adsorbent, amine-functionalized silica magnetite (NH2/SiO2/Fe3O4), has been synthesized to behave as an anionic or cationic adsorbent by adjusting the pH value of the aqueous solution to make amino groups protonic or neutral. NH2/SiO2/Fe3O4 were used to adsorb copper ions (metal cation) and Reactive Black 5 (RB5, anionic dye) in an aqueous solution in a batch system, and the maximum adsorption were found to occur at pH 5.5 and 3.0, respectively. The adsorption equilibrium data were all fitted the Langmuir isotherm equation reasonably well, with a maximum adsorption capacity of 10.41 mg g−1 for copper ions and of 217 mg g−1 for RB5. A pseudo-second-order model also could best describe the adsorption kinetics, and the derived activation energy for copper ions and RB5 were 26.92 kJ mol−1 and 12.06 kJ mol−1, respectively. The optimum conditions to desorb cationic and anionic adsorbates from NH2/SiO2/Fe3O4 were provided by a solution with 0.1 M HNO3 for copper ions and with 0.05 M NaOH for RB5.