Characteristic analysis of three-ecofriendly reduced graphene oxides (rGOs) and their application in water–ethanol-based fluids with different volume ratios

In this paper, three-ecofriendly reduced graphene oxides (rGOs) were obtained by using three green reducing agents (beer, wine and cocoa) to reduce the graphene oxide (GO), and were labeled as B-rGO, W-rGO and C-rGO. Meanwhile, rGO nanofluids with different water–ethanol volume ratios (25 : 75, 50 : 50, 75 : 25) were prepared based on three-ecofriendly rGOs. The structure properties of the three-ecofriendly rGOs were investigated by XRD, FR-IT, Raman spectroscopy and XPS analysis. Meanwhile, the thermophysical properties of rGO nanofluids were analyzed. Experimental results indicated that the stability and thermophysical properties of rGO nanofluids were slightly different, indicating that the properties of the nanofluids are dependent on the type of base fluids and nanoparticles. When the water–ethanol volume ratio was maintained at 25 : 75, the stability experiment results showed that W-rGO nanofluids presented excellent stability, which indirectly confirmed their excellent thermal conductivity. Furthermore, the contact angle experiment indicated that the contact angles of rGO nanofluids decreased with the increase of temperature. In a word, these three rGOs and their nanofluids exhibited preferable properties that make them promising in the field of heat transfer.