Absorption characteristics and solar thermal conversion of Fe3O4@Au core/shell nanoparticles for a direct-absorption solar collector

The distribution of magnetic nanomaterials in fluids can be controlled through an external field, which makes them promising candidates for regulating the heat exchange in direct absorption solar collectors (DASCs). However, the weak absorption of Fe3O4 in the visible range limits their capacity to harvest solar energy. Owing to the unique localized surface plasmon resonance effect, Au nanoparticles (NPs) exhibit strong absorption from the visible range to the near-infrared range. In this paper, the effect of morphological parameters and external factors on the optical properties and photothermal conversion of Fe3O4@Au core/shell NPs is studied experimentally and theoretically. The results show that Fe3O4@Au core/shell NPs with radius of the Fe3O4 core of 30 nm, Au shell thickness of 9 nm, volume fractions of 10−6, and penetration depth of 1 cm exhibit an optimal solar thermal conversion in DASCs. In addition, Fe3O4@Au core/shell NPs with a radius of Fe3O4 core of 20–30 nm were prepared using the coprecipitation method. The temperature of the Fe3O4@Au nanofluids increases from room temperature to 42 °C, demonstrating their excellent photothermal conversion performance. This work provides a guidance for utilizing the solar energy and controlling the photothermal distribution of nanofluids using Fe3O4@Au core/shell NPs.