Magnetically recoverable Ni@carbon nanocomposites: Solid-state synthesis and the application as excellent adsorbents for heavy metal ions

Various magnetic nanocomposites with carbon-coated nickel structure (Ni@Cs) for selective adsorption of Pb2+ and Cu2+ have been prepared by a simple solid-state method, in which citric acid and nickel nitrate were selected as carbon resource and magnetic substance, respectively. Ni@C-1:5/1:10/1:20 were obtained with various mass ratios (nickel nitrate/citric acid) under the experimental conditions. FESEM and TEM results reveal that the nanocomposite particles exhibit relatively homogeneous distribution in shape/size, possessing mostly carbon-coated structure. Based on the analysis of N2 adsorption–desorption isotherm, the surface areas and pore volumes of the nanocomposites (Ni@C-1:5/1:10/1:20) are (183, 220, 149) m2 g−1 and (0.29, 0.22, 0.08) cm3 g−1, respectively. The saturation magnetization values for the Ni@Cs are as high as (11.82, 5.20 and 3.84) emu g−1 obtained by the VSM. Following, the application of the Ni@Cs for the removal of heavy metal ions (Pb2+ and Cu2+) from wastewater as potential and effective adsorbents was investigated. The results reveal the adsorbents possess more accessible active sites and good dispersibility in water, exhibiting excellent performance for selectivity of Pb2+ than that of Cu2+. The results of adsorption behavior are followed the pseudo-second-order kinetics and Freundlich model between the adsorbents and the heavy metal ions. Furthermore, the adsorbents can be recovered easily with an external magnetic field, having a higher remove efficiency after several times.