Optimization of Magnetic Behaviors of Au-NP-Decorated MWCNTs and Reduced Graphene Oxide for Biomedical Applications

Optimization of electronic/magnetic behaviors of chemically decorated diamagnetic noble-metal gold nanoparticles (Au-NPs ≈5 at. %) on multiwalled carbon nanotubes (MWCNTs) and reduced graphene oxide (r-GO) is studied for future uses of optoelectronic/magnetic and biomedical applications. The changes between Au 4f_5/2 and Au 4f_7/2 ≈ 3.7 eV in X-ray photoelectron spectroscopy and 1.1 (±0.3) eV shifts in the C K-edge in X-ray absorption near edge structure spectroscopy confirm that the reduced form of Au⁰ was present in the Au-NP-decorated nanocomposites. The potential difference (ΔV) is built due to charge creations at the interface of r-GO/MWCNTs and Au-NPs and shifts in the Fermi level (ΔE_F) due to electronic transfer effects, and as a result, the work functions are reduced from 3.2 eV (MWCNTs) to 3.0 eV (MWCNTs:Au-NPs) and 3.1 (r-GO) to 2.8 eV (r-GO:Au-NPS), respectively. Negligible remanence/coercivity in MWCNTs/r-GO (/Au-NPs) with blocking temperature ≈300 K in MWCNTs:Au-NPs accounted for the existence of diamagnetic Au-NPs in these nanocomposites, which implies a superparamagnetic nature. These results furnish the evidence about the optimization of magnetic behaviors of r-GO/MWCNTs (/Au-NPs) that may possibly be altered as a novel contrast agent for clinical magnetic resonance imaging, drug delivery, and hyperthermia applications.