A gravity-driven process that can separate oil and water mixtures with 99.9% efficiency is described in Nature Communications this week. Specially designed reconfigurable membranes are shown to separate a variety of oil-water mixtures using only gravity, making it an energy efficient, cost-effective approach. The method could find use in the clean up of oil spills, wastewater treatment, fuel purification and the separation of commercially relevant emulsions.

Traditional membrane-based oil-water separation technologies are energy-intensive and can be limited by fouling (which slows down the process) or the inability of a single membrane to separate all types of oil-water mixtures. The membranes designed by Anish Tuteja and colleagues overcome these issues by having reconfigurable surface chemistry and using capillary forces to completely separate a range of oil-water mixtures, including emulsions. They demonstrate continuous separation of emulsions for over 100 hours without a decrease in flow.

Recent events, such as the Deepwater Horizon oil-spill in the Gulf of Mexico, have highlighted the difficulty of effective oil-water separation. The authors anticipate that their process could be used to in clean up operations, among other applications.