Functionalized aerogel with branched perfluoroalkyl groups applications in membrane distillation to enhance water reuse

The grand challenge of the water-food-energy nexus is to augment water supplies beyond what is obtainable from the hydrological cycle. To this end, membrane distillation (MD) has been broadly explored for wastewater treatment and water reuse (Camacho, 2013), such as treatment of coloured wastewater, oil-water separation, manufactured water, as well as the recovery of valuable components from wastewater, seawater or brine. Compared with other membrane-based treatment methods, MD exhibits high rejection of non-volatile compounds (theoretically 100% rejection under no wetting condition); requires mild operating temperatures (40 to 80 °C); is insensitive to feed concentration as it is a vapor driven process and operate at atmospheric pressure; and possesses the potential to be energy-efficient if integrated with waste heat and renewable energy technologies. However, MD commercialization is still in its embryonic stage due to membrane wetting issues. Herein, we develop a membrane aerogel with branched perfluoroalkyl groups as an ideal membrane possessing robust anti-wetting properties which will enable us to expand the application of MD for wastewater treatment for water recovery. Many studies have reported that the surface of a membrane can be modified with costly long-chain fluoroalkylsilane (up to C8) to improve its hydrophobicity which can help prevent wetting in MD (Brassard, Sarkar, &Perron, 2012). However, long-chain fluoroalkyl will degrade to perfluorooctanoic acid (PFOA) which is bioaccumulative and carcinogenic to humans (Vierke, Staude, Biegel-Engler, Drost, &Schulte, 2012). As an alternative, our study improved the hydrophobicity using branched perfluorobutyl groups to modify the surface by electrospraying aerogel onto commercial PVDF membranes (Lee, An, He, Woo, &Shon, 2016). Contact angle results showed that with higher fluorine content of the modified aerogels, the modified PVDF membrane demonstrated a water contact angle of 139.7. An MD test was then conducted to demonstrate the feasibility of this membrane in MD applications such as water recovery and reuse.