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 4f5/2 and Au 4f7/2 ≈ 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.