Enhanced light-to-heat conversion process for water purification using graphene-based nanofluids

Water purification meets the needs of medical, pharmaceutical, chemical, agricultural and industrial applications for clean and potable water. Various water treatment technologies are available and direct solar distillation methods allow to produce purified water combining renewable energy (e.g. solar energy) with solid surfaces and interfaces between materials and water. The aim of this work is to increase water evaporation yield of direct solar distillation systems using graphene based-nanofluids. Stable nanofluids are needed for this purpose and the strong hydrophobic character of graphene, that avoids its long time dispersion stability in water, makes necessary the use of additives to get stable suspensions. Results show an enhancement in suspension stability of graphene nanofluids up to 50 times using additives and the evaporation rate of the stable nanofluids was 70% higher compared to pure water. This enhancement in evaporation rate is due to a light-to-heat conversion process where the solar energy absorbed by graphene is transferred to water as thermal energy, thanks to the very high thermal conductivity of graphene at room temperature. The graphene nanopowder was characterized by Raman spectroscopy and XPS. The dispersion stability of graphene nanofluids was studied in presence/absence of several additives by means spectrophotometry, while their evaporation rate was evaluated by gravimetric measurements under UV-Visible irradiation generated by a solar simulator.