Synthesis of magnetic nanodiamond-cobalt oxide (ND-Co3O4) nanocomposite material; preparation of nanofluids and estimation of thermal properties such as thermal conductivity and viscosity has been explained experimentally in this paper. The nanocomposite material has been synthesized by using in-situ growth technique and chemical coprecipitation between cobalt chloride and sodium borohydrate. The various techniques such as XRD, TEM, XPS and VSM have been used to confirm the ND and Co3O4 phase of synthesized nanocomposite. The hybrid nanofluids have been prepared by dispersing synthesized ND-Co3O4 nanocomposite in water, ethylene glycol/water mixtures. The thermal properties such as thermal conductivity and viscosity have been measured experimentally at different weight concentrations and temperatures. The results reveal that the thermal conductivity enhancements are about 16%, 9%, 14%, 11% and 10% for water, EG, 20:80%, 40:60%, and 60:40% EG/W based nanofluids at 0.15wt% concentrations and at 60°C respectively. Similarly the viscosity enhancements are about 1.45-times, 1.46-times, 1.15-times, 1.19-times, and 1.51-times for water, EG, 20:80%, 40:60%, and 60:40% EG/W based nanofluids at 0.15wt% concentrations and at 60°C respectively. Based on the experimental data new correlations for thermal conductivity and viscosity have been developed

This study presents a novel method for the development of TiO₂/reduced graphene oxide (rGO) nanocomposites for photocatalytic degradation of dyes in an aqueous solution. The synergistic integration of rGO and TiO₂, through the formation of Ti–O–C bonds, offers an interesting opportunity to design photocatalyst nanocomposite materials with the maximum absorption shift to the visible region of the spectra, where photodegradation can be activated not only with UV but also with the visible part of natural solar irradiation. TiO₂@rGO nanocomposites with different content of rGO have been self-assembled by the hydrothermal method followed by calcination treatment. The morphological and structural analysis of the synthesized photocatalysts was performed by FTIR, XRD, XPS, UV-Vis DRS, SEM/EDX, and Raman spectroscopy. The effectiveness of the synthesized nanocomposites as photocatalysts was examined through the photodegradation of methylene blue (MB) and rhodamine B (RhB) dye under artificial solar-like radiation. The influence of rGO concentration (5 and 15 wt.%) on TiO₂ performance for photodegradation of the different dyes was monitored by UV-Vis spectroscopy. The obtained results showed that the synthesized TiO₂@rGO nanocomposites significantly increased the decomposition of RhB and MB compared to the synthesized TiO₂ photocatalyst. Furthermore, TiO₂@rGO nanocomposite with high contents of rGO (15 wt.%) presented an improved performance in photodegradation of MB (98.1%) and RhB (99.8%) after 120 min of exposition to solar-like radiation. These results could be mainly attributed to the decrease of the bandgap of synthesized TiO₂@rGO nanocomposites with the increased contents of rGO. Energy gap (E_g) values of nanocomposites are 2.71 eV and 3.03 eV, when pure TiO₂ particles have 3.15 eV. These results show the potential of graphene-based TiO₂ nanocomposite to be explored as a highly efficient solar light-driven photocatalyst for water purification.