Abstract:
In this work, we synthesized three nanofluids based on tin dioxide-coated gold
nanocomposites (Au@SnO2) using a two-step method. First, we synthesized gold (Au)
nanomaterials, then encapsulated them with tin dioxide (SnO2) through spontaneous
hydrothermal encapsulation. Finally, we dispersed them into an ethylene glycol base fluid.
The materials were analysed using various physicochemical techniques, such as Powder X-
Ray diffraction (XRD), Transmission and Scanning electron microscopy (TEM and SEM),
and Ultraviolet-Visible spectroscopy (UV-Vis). The diffraction patterns of the materials
showed that the composite structures consisted of an FCC Au core and a mesoporous SnO2
shell.
TEM and SEM micrographs showed that the Au@SnO2 nanocomposites had
spherical, rod-like, and prism-like shapes. To assess the structural stability of these different
types of Au@SnO2 nanocomposites, their TEM micrographs were collected and analysed
over a three-month period. The results showed that the Au@SnO2 nanocomposites had better
structural stability than their counterparts that were not coated with SnO2 and were exposed
to the same conditions.
During an additional evaluation of the materials' structural stability, their ultraviolet-
visible absorption spectra were analysed over a three-month period. The results indicated
that by encapsulating the Au nanostructures with SnO2 with an appropriate coating thickness
size in the range from 50 nm to 150 nm, both the structural stability and optical properties
of the materials can be significantly improved. The study was based on the observation of
localized surface plasmonic resonance absorption peaks at a wavelength of 550 nm, which
showed an increase in intensity and a narrower bandwidth upon the encapsulation of the gold
nanostructures with SnO2. In contrast, the pure uncoated Au nanostructures showed low
intensity and broad absorption peaks at the same wavelength. Furthermore, for the last two
months of the study, a red shift to a higher wavelength of 600 nm was observed for the high
intensity absorption peaks of the coated nanostructures, while the uncoated ones did not
show any such shift.
Thermal conductivity of the Au-based nanofluids, both coated and uncoated with tin
dioxide, was measured using the transient hot-wire method. The results showed that the
thermal conductivity of the nanofluids made up of SnO2-coated gold nanostructures
increased by more than 10%. Additionally, the thermal conductivity of the SnO2-coated Au
2
nanofluids was observed to rise with an increase in the thickness of the SnO2 layer
encapsulating the Au nanostructures. These findings suggest that the Au-based nanofluids
coated with SnO2 have potential applications in thermal energy management and electronic
cooling systems.
