Synthesis of magnetic Fe3O4@SiO2-(-NH2/-COOH) nanoparticles and their application for the removal of heavy metals from wastewater

In this work, Fe3O4@SiO2-(-NH2/-COOH) nanoparticles were synthesized for the removal of Cd2+, Pb2+ and Zn2+ ions from wastewater. The results of characterization showed that Fe3O4@SiO2-(-NH2/-COOH) was superparamagnetic with a core–shell structure. The surface of Fe3O4 was successfully coated with silica and modified with amino groups and carboxyl groups through the use of a silane coupling agent, polyacrylamide and polyacrylic acid. The dispersion of the particles was improved, and the surface area of the Fe3O4@SiO2-(-NH2/-COOH) nanoparticles was 67.8 m2/g. The capacity of Fe3O4@SiO2-(-NH2/-COOH) to adsorb the three heavy metals was in the order Pb2+ > Cd2+ > Zn2+, and the optimal adsorption conditions were an adsorption dose of 0.8 g/L, a temperature of 30°C and concentrations of Pb2+, Cd2+ and Zn2+ below 120, 80 and 20 mg/L, respectively. The maximum adsorption capacities for Pb2+, Cd2+ and Zn2+ were 166.67, 84.03 and 80.43 mg/g. The adsorption kinetics followed a pseudo-second-order model and Langmuir isotherm model adequately depicted the isotherm adsorption process. Thermodynamic analysis showed that the adsorption of the three metal ions was an endothermic process and that increasing the temperature was conducive to this adsorption.