Thermal Diffusivity Study of Organic Dyes with TiO₂ Nanoparticles by Photothermal Techniques

A photothermal study by means of thermal lens (TL) was used to monitor the detoxification of organic wastewater through bleaching of rhodamine 6G (R6G) with titanium dioxide nanoparticles (TiO₂-NPs) and in the presence of ultraviolet radiation. Thermal diffusivity change of the nanofluid with irradiation time was investigated by fitting TL experimental data to a theoretical model. Thermal diffusivity decreases as irradiation time increases. The obtained diffusivity values were 25.0 ± 0.6 × 10^–4 cm²·s⁻¹, 24.2 ± 0.5 × 10^–4 cm²·s⁻¹, 23.4 ± 0.6 × 10^–4 cm²·s⁻¹, 22.4 ± 0.6 × 10^–4 cm²·s⁻¹, 21.1 ± 0.3 × 10^–4 cm²·s⁻¹, and 19.7 ± 0.2 × 10^–4 cm²·s⁻¹, for irradiation times of 0, 15, 30, 45, 60, and 75 min, respectively. In this work, main characterization of thermal properties was carried out by thermal lens (TL) for thermal diffusivity measurement. Other techniques such as X-ray diffraction (XRD), Raman Spectroscopy, UV–Vis spectroscopy, and transmission electron microscopy (TEM) were used for complementary characterization. These studies are of great interest in catalytic sewage water pollutants’ bleaching applications.