Synthesis and characterization of magnetic FeO@CaSiO composites and evaluation of their adsorption characteristics for heavy metal ions.

A two-component material (FeO@CaSiO) with an FeO magnetite core and layered porous CaSiO shell from calcium nitrate and sodium silicate was synthesized by precipitation. The structure, morphology, magnetic properties, and composition of the FeO@CaSiO composite were characterized in detail, and its adsorption performance, adsorption kinetics, and recyclability for Cu, Ni, and Cr adsorption were studied. The FeO@CaSiO composite has a 2D core-layer architecture with a cotton-like morphology, specific surface area of 41.56 m/g, pore size of 16 nm, and pore volume of 0.25 cm/g. The measured magnetization saturation values of the magnetic composite were 57.1 emu/g. Data of the adsorption of Cu, Ni, and Cr by FeO@CaSiO fitted the Redlich-Peterson and pseudo-second-order models well, and all adsorption processes reached equilibrium within 150 min. The maximum adsorption capacities of FeO@CaSiO toward Cu, Ni, and Cr were 427.10, 391.59, and 371.39 mg/g at an initial concentration of 225 mg/L and a temperature of 293 K according to the fitted curve with the Redlich-Peterson model, respectively. All adsorption were spontaneous endothermic processes featuring an entropy increase, including physisorption, chemisorption, and ion exchange; among these process, chemisorption was the primary mechanism. FeO@CaSiO exhibited excellent adsorption, regeneration, and magnetic separation performance, thereby demonstrating its potential applicability to removing heavy metal ions.