Thermal and Optical Characteristics of TiO2@SiO2, Fe3O4@SiO2, and ZnO@SiO2 Core–Shell Nanoparticles and Their Water-Based Nanofluids

Abstract This study investigates the thermophysical and optical properties of core–shell nanoparticles composed of SiO 2 -coated TiO 2 , Fe 3 O 4 , and ZnO, along with their water-based nanofluids at a 2 % mass concentration. The nanoparticles were synthesized, characterized, and analyzed using various techniques. The results indicate total mass losses of 11.0 %, 9.5 %, and 26.5 % for TiO 2 @SiO 2 , Fe 3 O 4 @SiO 2 , and ZnO@SiO 2 , respectively. Among these, the nanofluid containing ZnO@SiO 2 nanoparticles displayed superior stability and demonstrated the most significant increase in thermal conductivity at 2.51 %. Furthermore, it was observed that all nanofluids exhibited lower specific heat capacity compared to the base fluid. Notably, the TiO 2 @SiO 2 -based nanofluid experienced the most substantial decrease at 3.5 %. Additionally, the viscosity values of the nanofluids exceeded those of the nanofluids with single particles. The core–shell nanoparticles exhibited extensive light absorption across a broad spectrum, with calculated optical band gap energies of 2.88 eV, 3.65 eV, and 3.25 eV for Fe 3 O 4 @SiO 2 , TiO 2 @SiO 2 , and ZnO@SiO 2 , respectively. These findings highlight the effectiveness of utilizing nanofluids containing core–shell-structured nanoparticles for efficient heat transfer.