Comparative studies on spinal ferrite $$\hbox {MFe}₂\hbox {O}₄$$ MFe 2 O 4 (M = Mg/Co) nanoparticles as potential adsorbents for Pb(II) ions

Ferrite nanoparticles (NPs) with composition $$\hbox {MFe}₂\hbox {O}₄$$ (M = Mg/Co) were synthesized by a facile combustion method. NPs were characterized employing various physico-chemical techniques. X-ray diffraction patterns confirmed the phase purity, transmission electron micrographs indicated that NPs are spherical and average diameter of maximum fraction of NPs was in the range of 20–30 nm. Magnetic studies revealed that the saturation magnetization values for $$\hbox {MgFe}₂\hbox {O}₄$$ and $$\hbox {CoFe}₂\hbox {O}₄$$ NPs were 13.17 and 41.12 emu $$\hbox {g}^-1$$ , respectively. The Brunauer–Emmett–Teller surface area of $$\hbox {CoFe}₂\hbox {O}₄$$ and $$\hbox {MgFe}₂\hbox {O}₄$$ NPs was 22.98 and 34.39 $$\hbox {m}²$$ $$\hbox {g}^-1$$ , respectively. Synthesized ferrite NPs and activated charcoal were comparatively analysed as adsorbents for removal of Pb(II) ions. The factors influencing uptake behaviour of Pb(II) ions viz. adsorbent dose, pH, concentration, temperature and contact time were quantified. The adsorption data showed good correlation with Langmuir and Freundlich models as compared to Dubinin–Radushkevich model. The maximum adsorption capacity displayed a two-fold increase for NPs as compared to activated charcoal. The easy magnetic separation of ferrite NPs from the solution and their regeneration with 0.1 N NaOH for reuse without any loss make them potential adsorbents. The trend in ascending order for the elimination of Pb(II) ions from the solution was activated charcoal $$<\hbox {CoFe}₂\hbox {O}₄$$ $$\hbox {NPs}< \hbox {MgFe}₂\hbox {O}₄$$ NPs. The observed differences in the adsorption potential of NPs are explained on the basis of structural and magnetic properties and the surface area of NPs.