Study of the thermal diffusivity of nanofluids containing SiO₂ decorated with Au nanoparticles by thermal lens spectroscopy

In this work, silicon dioxide (SiO₂) spheres and gold nanoparticles (Au) were prepared. The SiO₂ was used as a platform to deposit the gold nanoparticles. The SiO₂ structures were synthesized employing the Stöber method. Monodisperse spherical particles with mean size of 293 nm were observed by transmission electron microscopy (TEM). The gold nanoparticles were attached to the dielectric platform trough in situ reduction. The UV–Vis spectrum of SiO₂–Au showed an absorption band in the visible region associated with the presence of the gold nanoparticles. The TEM micrographs confirmed decorated SiO₂ spheres with the metallic nanoparticles of 5 nm in size. Nanofluid concentrations of 0.1–0.6 mg/ml of SiO₂ decorated with Au nanoparticles dispersed in water were prepared. The functional groups of SiO₂-functionalized spheres were followed by FTIR. The formation of gold nanoparticles was evidenced by UV–Vis spectroscopy. The crystalline structure of SiO₂ spheres and SiO₂ decorated with Au nanoparticles was determined by XRD. The thermal diffusivity as a function of concentration using the mode-mismatched thermal lens (TL) spectroscopy was studied. The results of TL spectroscopy showed an increase in the thermal diffusivity with an increase of SiO₂ decorated with Au nanoparticle concentration in the nanofluid.