An overview on the use of graphene-based membranes for membrane distillation

Recently, a thermally-driven membrane process known as membrane distillation (MD) has emerged as an alternative to the high-pressure membrane process for contaminants removal from water. The driving force for MD is a vapor pressure gradient produced by a temperature differential across a hydrophobic porous membrane, which results in the transfer of water vapor from hot to cold side. However, the feasibility of MD for industry adoption is hampered by several issues such as temperature polarisation effects, low permeate flux, membrane wetting, and fouling. The membrane properties are known to have a significant role in controlling the final performances of MD. This review first looks into the feature of ideal MD membrane properties. Then, the use of graphene-based materials for the development of high performances MD membrane is discussed. Besides enhancing the water permeability and selectivity of MD, the incorporation of graphene offers additional properties such as anti-fouling, antibacterial, and photodegradation. The future direction of using graphene-based photothermal material in MD for heat generation under solar irradiation is also reviewed. It is found that the localised heating at membrane surfaces by photothermal material can minimise temperature polarisation effects and subsequently enhance the driving force for effective vapour transport. Thus, a more energy-efficient MD system can be developed.