Core-shell superparamagnetic monodisperse nanospheres based on amino-functionalized CoFeO@SiO for removal of heavy metals from aqueous solutions

To remove heavy metals from aqueous solutions, amino-functionalized superparamagnetic CoFeO@SiO (CoFeO@SiO-NH) core-shell nanospheres were designed and constructed. In particular, well-defined CoFeO nanoparticles (NPs) were synthesized by reverse co-precipitation. The shell of the CoFeO NPs was composed of amorphous silica (SiO), which had a thickness of ∼35 nm. Monodisperse CoFeO@SiO nanospheres grafted with more amino groups had a greater adsorption capacity and higher removal efficiency for heavy metal ions (Cd(ii): 199.9 mg g, 99.96%; Cu(ii): 177.8 mg g, 88.05%; Pb(ii): 181.6 mg g, 90.79%). The effects of the pH, initial concentrations, reaction temperature and time on the adsorption of heavy metal ions by CoFeO@SiO-NH were analyzed systematically. The adsorption process on the nanospheres was well described by the Langmuir model. The adsorption kinetics can be best fitted by the pseudo-second-order kinetics model. Analysis of a thermodynamic study of Cu(ii) showed that the process of adsorption is spontaneous and endothermic in nature. Owing to the superparamagnetic properties with a high saturation magnetization value (32.92 emu g) of CoFeO@SiO-NH, the metal-loaded nanospheres can be quickly removed from an aqueous solution (30 s) by magnetic separation. Moreover, the nanospheres exhibited good reusability for up to five cycles. The results confirm that the monodisperse amino-functionalized CoFeO@SiO magnetic nanospheres could be a potential adsorbent for the effective and regenerable removal of heavy metals from aqueous solutions.