Sol-gel auto-combustion technique was used to synthesize spinel ferrite nanoparticles of Mn0.2Co0.8Fe2O4 (MCF). Using the modified Stöber method, these magnetic nanoparticles were encapsulated with silica to form the core/shell Mn0.2Co0.8Fe2O4/SiO2 (MCFS). The phase composition, morphology, particle size, and saturation magnetization of the encapsulated nanoparticles were studied using X-ray diffraction (XRD), high resolution-transition electron microscopy (HR-TEM), and vibrating sample magnetometer (VSM). HR-TEM images indicated that particle size of the nanoparticles ranged from 15 to 40 nm, and VSM measurements showed that Ms of uncoated and coated samples were 65.668 emu/g and 61.950 emu/g and the Hc values were 2,151.9 Oe and 2,422.0 Oe, respectively. The effects of metal concentration, solution pH, contact time, and adsorbent dose of the synthesized nanoparticles on lead (Pb2+) ions removal from an aqueous solution were investigated. Based on Langmuir isotherm model, the results for peak adsorption capacity of the adsorbent under optimal conditions was 250.5 mg/g and 247 mg/g for MCF and MCFS, respectively. We concluded that Pb2+ adsorption occurred via a chemisorption mechanism based on the analysis of adsorption kinetics. The adsorbents displayed consistent adsorption efficiencies following three cycles of regeneration, indicating that these magnetic nanoparticles are promising candidates for wastewater purification.

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