Insights into the nitridation of zero-valent iron nanoparticles for the facile synthesis of iron nitride nanoparticles

Abstract

The process of nitridation of zero-valent iron nanoparticles (ZVINPs) is investigated by employing two different synthesis strategies such as solvothermal method and gas diffusion using N₂ and NH₃. It is observed that the phase formation of different iron nitrides mainly depends on the reaction chemistry of the nitridation source and temperature. Accordingly, N₂ gas diffusion and solvothermal methods yield iron oxide phases, whereas NH₃ gas diffusion yields pure iron nitride phase with particle sizes in the nanoscale. X-ray diffraction studies complemented by Rietveld refinement confirm the formation of ε-Fe₃N and γ′-Fe₄N nanoparticles. Field emission scanning electron microscopy images revealed spherical nanoparticles with average particle sizes of 35 and 50 nm for ZVINPs and iron nitride NPs, respectively. From the magnetization studies carried out using a superconducting quantum interference device magnetometer it is found that the field-dependent hysteresis curves indicated the ferromagnetic properties of ZVINPs, ε-Fe₃N and γ′-Fe₄N NPs with coercive fields of 160, 65 and 45 Oe, respectively. Similarly, the temperature-dependent magnetization profiles revealed that the observed ferromagnetic properties of iron nitride phases can be attributed to the redistribution of electronic spin states due to both nitrogen populations and the confinement in the crystallites.