Morphology of Composite Fe@Au Submicron Particles, Produced with Ultrasonic Spray Pyrolysis and Potential for Synthesis of Fe@Au Core–Shell Particles

Abstract

Iron core–gold shell (Fe@Au) nanoparticles are prominent for their magnetic and optical properties, which are especially beneficial for biomedical uses. Some experiments were carried out to produce Fe@Au particles with a one-step synthesis method, Ultrasonic Spray Pyrolysis (USP), which is able to produce the particles in a continuous process. The Fe@Au particles were produced with USP from a precursor solution with dissolved Iron (III) chloride and Gold (III) chloride, with Fe/Au concentration ratios ranging from 0.1 to 4. The resulting products are larger Fe oxide particles (mostly maghemite Fe2O3), with mean sizes of about 260–390 nm, decorated with Au nanoparticles (AuNPs) with mean sizes of around 24–67 nm. The Fe oxide core particles are mostly spherical in all of the experiments, while the AuNPs become increasingly irregular and more heavily agglomerated with lower Fe/Au concentration ratios in the precursor solution. The resulting particle morphology from these experiments is caused by surface chemistry and particle to solvent interactions during particle formation inside the USP system.

Advances in Ultrasonic Spray Pyrolysis Processing of Noble Metal Nanoparticles—Review

“…Adding ferromagnetism as an additional property to these nanoparticles enhances their applicability and use cases in medical treatment [78,79], for Magnetic Resonance Imaging [80], cancer treatment [81], drug delivery systems, as well as for catalysis, sensors, and so on [82][83][84][85]. Some initial experiments for determining the capability of producing such particles with USP were conducted, in order to investigate the formation mechanisms of these particles [86,87].…”

“…When using a low concentration of iron in the precursor solution, the resulting particles have a greater number of larger AuNPs, which are more heavily agglomerated. As the ratio increases in favour of Fe, the AuNPs retain greater numbers, but become smaller and more uniform in shape [87].…”

“…Some cases of Fe/Au core-shell synthesis report growth of Au on the Fe core, or growth of Fe on an Au shell, depending on the solvent type in which the growth took place, whether it was organic, water or otherwise [88][89][90]. The selection of solvent for the precursor preparation for USP synthesis may also be revised for continuous Au shell production [87]. The observations from these experiments show that merely increasing Au content as compared to Fe content in the droplets does not produce more intrinsically uniform Au coatings, as was assumed previously.…”

“…This results in the described Au/Fe 2 O 3 particle morphologies observed in the investigation. The finding proposes that a continuous layer of Au on top of Fe oxide particles would not be possible to achieve with USP, without modifying the adhesive forces between the Fe oxide particles and Au [87].…”

“…Comparison of the Au/Fe 2 O 3 nanoparticles' structures, synthesised with a precursor concentration ratio ranging from Fe/Au = 0.1 to Fe/Au = 4, adapted from[87]. The white particles represent AuNPs, the grey particles are Fe 2 O 3.…”