Selectivity and efficient Pb and Cd ions removal by magnetic MFe2O4 (M=Co, Ni, Cu and Zn) nanoparticles

Spinel ferrite MFe2O4, (M = Co, Ni, Cu and Zn) nanoparticles (NPs) were prepared by microwave combustion method using metal nitrates as precursors, in addition to urea as fuel. Rietveld analysis of X-ray diffraction patterns indicates the formation of single phase for NiFe2O4 and ZnFe2O4, while (alpha-Fe2O3 and CuO) phases precipitate for CoFe2O4 and CuFe2O4, respectively. After annealing 800 degrees C for 16 h, single cubic CuFe2O4 phase is obtained. SEM images show spherical/undefined shaped particles at the nanoscale with broad particle size distribution and high level of agglomeration. Magnetisation-field (M-H) curves reveal ferromagnetic behaviour for CoFe2O4, NiFe2O4 and CuFe2O4, and superparamagnetic behaviour for ZnFe2O4. Interestingly, after annealing CuFe2O4 shows a superparamagnetic behaviour due phase tetragonal-cubic phase transformation. Saturation magnetization, remanence and coercivity slightly change after annealing, except for CuFe2O4, due to phase transformation from tetragonal to cubic; Ms decreases abruptly from 25.97 to 1.685 emu/g. The as-obtained spinel ferrite nanopowders are tested for two toxic metal ions removal from aqueous solutions; Cadmium (Cd2+) and lead (Pb2+) with different concentration (5, 10, 20 and 30 mg) and pH (2, 12). The maximum adsorption capacities are found at the lowest concentration (5 mg) and at alkaline medium (pH 12). The asprepared magnetic nanoparticles demonstrate enhanced efficiency for both Cd2+ and Pb2+, with maximum adsorption capacity of 69.4 and 47.1 mg/g, respectively. Interestingly, the nature of metal M has a direct influence on selectivity, CoFe2O4 toward Cd2+ while ZnFe2O4 toward Pb2+.