Effect of gold salt on electro-synthesized magnetic nanoparticles

Magnetite nanoparticles were synthesized by electrocrystallization of iron sheet using a chronoamperometric technique. The effect of HAuCl4.3H2O on structure and magnetization of iron oxide nanoparticles was investigated. Based on X-ray diffraction (XRD) patterns, all samples have cubic spinel structure of magnetite with space group. Obviously, at gold concentration higher than 0.0005 M, some extra peaks appear in the XRD pattern of the samples. In two samples synthesized with 0.001 M and 0.0015 M of gold salt, three peaks observed at 2θ below 35o correspond to formation of Au2O3 in the samples. According to these results, it is possible to form both gold and gold oxide nanoparticles in the solution by increasing the amount of gold salt in the cell. The morphology, particle size, and nanostructure of the nanoparticles were analyzed using a scanning electron microscope (SEM). Base on SEM images the mean particle size increases to about 60 nm when the concentration goes up to 0.0005 M and at higher concentration both mean particle size and distribution decreases. According to vibrating sample magnetometer (VSM) curves, clearly the highest magnetization value of about 60 Am2kg-1 is related to the sample prepared at 0.0005 M which is related to the formation of larger particles (~ 57 nm) with lower paramagnetic phase. For the sample synthesized in the cell with 0.001 M of gold salt, although the mean particle size goes up to about 50 nm and the paramagnetic second phase reduces to 13.4%, the magnetization reduces to 36 Am^2kg^-1.