Co3O4 nanoparticles by chemical combustion: Effect of fuel to oxidizer ratio on structure, microstructure and EPR

In this work we describe and discuss the synthesis, (micro)structure (XRD, SEM) and EPR of Co3O4 (normal spinel structure with a = 0.808 nm) nanoparticles synthesized by urea-based combustion method using cobalt nitrate precursor. Fuel-to-oxidizer ratio (ΨΨ) is used as a control parameter to investigate how lattice parameter, particle size and EPR susceptibility vary with Ψ=0.25–2Ψ=0.25–2 in steps of 0.25. The average crystalline size of Co3O4 was estimated from the X-ray diffraction peaks of powders using Scherrer’s formula and Williamson–Hall equation. The average crystalline size varies from 7(±0.1) nm to 18(±0.28) nm. The surface areas were measured using BET method and size of the particles thus deduced agree with XRD based values. The FT–IR confirms formation of Co3O4. We also calculated average micro strain of the Co3O4 nanoparticles with varying ΨΨ. The SEM micrographs give evidence for increased porosity upon increasing ΨΨ. EPR spectra has yielded the paramagnetic susceptibility of the Co3O4 nanoparticles. Band gap of Co3O4 nanoparticles was determined by UV-visible absorption edge.