Thermal conductivity and photothermal characteristic of core-shell Fe3O4@C nanofluids in different particle size

Instability is a key issue that limits the application of magnetic nanofluids. In this study, Fe3O4@C nanoparticles were obtained using a carbon layer coated with a ferromagnetic material, which improved the instability of the magnetic nanofluid while obtaining higher thermal conductivity and showed excellent photothermal conversion performance in photothermal conversion experiments. Firstly, we prepared Fe3O4@C nanoparticles via the solvothermal method. We then compared different sizes of Fe3O4@C nanoparticles in terms of structure, composition, heat transfer characteristics and photothermal efficiency. The results indicate that contrary to the conventional belief that smaller nanoparticles have higher thermal conductivity, the 90.30 nm Fe3O4@C nanofluids has better thermal conductivity than 58.17 nm due to its larger proportion of carbon shells. In the photothermal conversion experiment for DASCs, the 58.17 nm group performed best, with the temperature of the 0.2 wt% sample reaching 45.80 °C and a photothermal efficiency of 60.32%.