Abstract
Direct absorption solar collectors, which use optical nanofluids to volumetrically absorb and convert sunlight into heat, have emerged as promising devices to harvest solar-thermal energy for many heat-related applications. Nanofluids, however, generally suffer from aggregation issues and the widely investigated water-based fluids only enable solar-thermal harvesting at relatively low temperatures. Herein, we report a facile way to prepare stably dispersed reduced graphene oxide-ethylene glycol (rGO-EG) fluids for solar-thermal energy harvesting at medium temperatures. Without the use of complex surface modification process, the homogeneous dispersion of rGO-EG fluids was achieved by utilizing the favorable interaction between the oxygen-containing groups on the rGO surfaces and EG molecules. The rGO-EG fluids were prepared by reducing the GO-EG fluids that are uniformly dispersed with ethanol-wetted GO through a single step of heating. The prepared rGO-EG fluids have suitable thermophysical properties for direct solar-thermal energy harvesting, such as broadband absorption of sunlight, high specific heat capacity and low viscosity. The rGO-EG fluids have shown stable uniform dispersion up to 120 °C and have demonstrated consistent solar-thermal energy harvesting performance during repeated solar radiation at ∼110 °C.