Microwave-assisted hydrothermal nanoarchitectonics of polyethyleneimine-coated iron oxide nanoparticles

The aim of this work is to show how the magnetic properties of polyethyleneimine (PEI)-coated and naked magnetite (Fe 3 O 4 ) nanoparticles are improved when the alternative in situ PEI microwave-assisted hydrothermal synthesis method is employed in contrast to the results obtained for nanoparticles synthesized from the same precursors by a conventional co-precipitation method. As far as we know, this is the first report on “in situ” PEI-coated Fe 3 O 4 nanoparticles obtained by microwave-assisted hydrothermal synthesis. For this purpose, uncoated and PEI-coated Fe 3 O 4 nanoparticles were synthesized by the co-precipitation method (CCPM) using ammoniac as precipitating agent after heating at 80 °C and by a microwave-assisted hydrothermal method (MWAM) using urea at 140 °C during 30 min. The obtained powders so were characterized by X-ray diffraction, scanning and transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, Mössbauer spectroscopy and DC magnetization studies. It was seen that the magnetic properties of the nanoparticles strongly depend on the synthesis route and that they also vary if particles are coated by the nonmagnetic polymer (PEI). The morphology, size, surface and anisotropy effects play an important role in the magnetic behavior. In situ PEI-coated nanoparticles obtained by MWAM, with larger average size and better crystallinity, exhibited a higher coercive field and saturation magnetization values than PEI-coated nanoparticles synthesized by CCPM; the latter revealed a quasi-complete superparamagnetic behavior at room temperature. The synthesis by MWAM is a faster, simple and low-cost way to obtain in situ PEI-coated Fe 3 O 4 nanoparticles with reasonable saturation magnetization, coercivity and suitable average particle size values to be tested for biomedical applications.