A study of modified Fe3O4 nanoparticles for the synthesis of ionic ferrofluids

XRD and XPS analyses revealed that a Fe(NO3)3·9H2O layer formed outside γ-Fe2O3 particles when Fe3O4 nanoparticles were treated with ferric nitrate. The particle density differed for untreated and treated particles and was not uniform for the latter. The specific saturation magnetization of both treated and untreated particles was used to estimate the thickness of the Fe(NO3)3·9H2O layer and the average density of the treated particles. The density of the treated particles was used to calculate the density of ferrofluids of different particle volume fractions. These values are in agreement with measured results. Therefore, the particle volume fraction can be designed to synthesize acid ionic ferrofluids based on Fe3O4 nanoparticles using Massart's method.