A step forward towards optimized iron–nickel bimetal oxide core–shell nanoparticles and their magnetic properties

Abstract

The core–shell nanoparticles of Fe3O4 and NiO are synthesized under different reaction conditions and are characterized by UV–vis and fluorescence spectroscopy, DLS, SEM, EDX, XRD, VSM, and FTIR spectroscopy. These techniques evaluated optimal synthetic conditions for desired size, morphology, stability, and crystallinity of these core–shell nanoparticles. Increasing the concentration of salt for shell material (Fe3O4 or NiO) in core–shell NPs resulted in better coating and increase in hydrodynamic size from 227 nm to 531 nm for (Fe3O4)NiO, and 244 nm to 544 nm for (NiO)Fe3O4, whereas lower concentration and higher temperature (80 °C) for (Fe3O4)NiO and lower temperature (25 °C) for (NiO)Fe3O4, higher pH 13 and 11 for (Fe3O4)NiO and (NiO)Fe3O4 respectively, and fast (quick) addition of reactants produces homogenous small sized nanoparticles. Stability is generally attained at higher concentration, higher temperature (80 °C), higher pH (13 and 11 for (Fe3O4)NiO and (NiO)Fe3O4 respectively), and slow addition (10 min) of reactants. Fluorescence enhancement is observed for (Fe3O4)NiO core–shell NPs at high concentration, temperature, pH and slow addition of reactants, representing proper coating of NiO. For (NiO)Fe3O4 NPs, fluorescence quenching is observed at higher concentration, lower temperature, higher pH, and slow addition of reactants representing proper coating of Fe3O4. XRD depicted pure cubic crystalline nature of these core–shell nanoparticles without any impurity. The identified optimized conditions are useful for obtaining nanoparticles with desired properties for various applications including sensing and catalysis etc. Magnetic properties of pure and core–shell nanoparticles show ferrimagnetic behavior for Fe3O4 NPs and weak ferromagnetic or superparamagnetic behavior NiO NPs.