Mechanistic insight into structural and adsorptive properties of core shell reversal nanocomposites of rice husk silica and magnesium ferrite

Abstract

In this work, the adsorptive efficiency of core shell nanocomposites (NCs) of MgFe2O4 and SiO2 was comparatively studied for the removal of Pb(II) ions from aqueous solutions. Mesoporous SiO2 nanoparticles (NPs) were obtained from rice husk as source and MgFe2O4 NPs were synthesized via sol-gel method. MgFe2O4@SiO2 NC was synthesized using surfactant assisted sonication method and core shell reversal of the NC was achieved via direct precipitation method that lead to formation of SiO2@MgFe2O4 NC. The NCs were characterized employing FTIR, XRD, BET, TEM, VSM and SEM EDS analytical tools. SiO2@MgFe2O4 NC displayed higher BET surface area (459.1 m2g−1) than MgFe2O4@SiO2 (102.2 m2g−1) NC. The saturation magnetization (Ms) was 6.60 and 4.94 emug−1 for MgFe2O4@SiO2 and SiO2@MgFe2O4 respectively revealing their magnetic nature and the variation in the magnetic properties with the core-shell reversal. Adsorption process followed pseudo-second order kinetics. Thermodynamic studies confirmed the endothermic and spontaneous nature of the adsorption process. Langmuir and Freundlich isotherm models fitted more significantly than Temkin and D-R models. Values of qmax were in the range 26.67–48.08 mgg−1 and confirmed the trend of adsorption affinity i.e. MgFe2O4> SiO2@MgFe2O4> MgFe2O4@SiO2>SiO2. Adsorptive efficiency of SiO2@MgFe2O4 NC and MgFe2O4 NPs was comparable but the NC had advantage of protected magnetic core. The results signified the importance of core-shell reversal in altering the adsorptive properties of MgFe2O4-SiO2 NCs.