Ethylene glycol-based solar-thermal fluids dispersed with reduced graphene oxide.

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.