The magnetic CoFe2O4@SiO2–NH2 particles with core-shell structure are designed and synthesized. They have high adsorption capacity (170.829 mg g−1), high removal efficiency (96.93%) for heavy metals, and can be recycled easily.

To remove heavy metals from aqueous solutions, amino-functionalized superparamagnetic CoFe 2 O 4 @SiO 2 (CoFe 2 O 4 @SiO 2 -NH 2 ) core-shell nanospheres were designed and constructed. In particular, well-defined CoFe 2 O 4 nanoparticles (NPs) were synthesized by reverse co-precipitation. The shell of the CoFe 2 O 4 NPs was composed of amorphous silica (SiO 2 ), which had a thickness of $35 nm. Monodisperse CoFe 2 O 4 @SiO 2 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 À1 , 99.96%; Cu(II): 177.8 mg g À1 , 88.05%; Pb(II): 181.6 mg g À1 , 90.79%). The effects of the pH, initial concentrations, reaction temperature and time on the adsorption of heavy metal ions by CoFe 2 O 4 @SiO 2 -NH 2 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 À1 ) of CoFe 2 O 4 @SiO 2 -NH 2 , 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 CoFe 2 O 4 @SiO 2 magnetic nanospheres could be a potential adsorbent for the effective and regenerable removal of heavy metals from aqueous solutions. Fig. 1 Schematic illustration of the synthetic procedure of CoFe 2 O 4 @SiO 2 -NH 2 core-shell nanospheres (a-d, j and k) and the adsorption and regeneration process of heavy metals (d-i and l).6912 | RSC Adv., 2017, 7, 6911-6921 This journal isFig. 2 SEM and TEM images of (a and d) CFO NPs, (b and e) CFO@SiO 2 , and (c, f and g) CFO@SiO 2 -NH 2 nanospheres. (h and i) HRTEM images of CFO@SiO 2 -NH 2 nanospheres. (Inset of (i)) fast Fourier transform (FFT) pattern. 6914 | RSC Adv., 2017, 7, 6911-6921 This journal is

In this work, a novel magnetic porous adsorbent was prepared via a sol–gel method for the removal of Ce(iv) from aqueous solution.