Physical–Chemical Properties of Magnetite Nanoparticles Doped with Ag(I) and Au(III) Cations

Abstract

The nanosized magnetite particles doped with argentum and aurum cations were obtained on the steel surface contacting with water solutions of AgNO3 and HAuCl4 in the open-air system. The as-prepared samples were characterized using the method of X-ray diffraction, different thermal analytical measurements (TG/DTG, DTA), X-ray fluorescence spectroscopy (XRFS), Fourier transform infrared spectroscopy (FTIR), chemical–analytical investigations, magnetometry, transmission (TEM), and scanning electron microscopy (SEM). As a rule, the formation of magnetite particles is accompanied by the appearance of second lepidocrocite phase. Whereas the inclusion of the noble metals cations into the magnetite crystal lattice is typical for the surface structures, the reduction of silver or gold clusters on the iron oxide surface is native to the core and shell-type nanoparticles formed in sol’s composition. Depending on the initial noble metal concentrations their wt% in the magnetite structure varies in the range from 0.2 to 1.8 for argentum and from 0.02 to 0.9 for aurum. All samples have superparamagnetic properties so they do not show remanence magnetization and coercitivity. The saturated magnetization of magnetite doped with Ag+ and Au3+ lies in the range 30–49 A · m2 · kg−1, but the presence of significant iron oxyhydroxide part in the phase composition of the samples causes to decrease such parameter to 1.3–14 A · m2 · kg−1.