Water-repellent membrane advances desalination

Researchers have developed a polymeric membrane that can desalinate seawater and brines at ambient temperature and pressure.

The research, carried out by an international research team led by scientists at King Abdullah University of Science and Technology (KAUST), was published in the journal Nature Communications.

“Water scarcity is severe in Saudi Arabia and is reaching unprecedented levels in countries once thought to be safe from such pressures,” said Noreddine Ghaffour, who led the research. “We urgently need to produce freshwater from seawater and brines at any scale, efficiently and cost-effectively, while conserving energy.”

Conventional membrane-based technologies such as reverse osmosis are most cost-effective at very large scales and depend on sophisticated energy-recovery systems. Even under these conditions, treating highly concentrated brines remains difficult because of the extreme pressures required.

Membrane distillation provides an alternative approach, but it typically relies on elevated temperatures to vaporise water before it passes through a membrane and condenses as freshwater.

The membrane developed by Ghaffour’s team consists of an ultrathin polymeric film supported by a porous substrate and is designed for membrane distillation at low temperatures. The film contains sub-nanometre-sized pores and has a highly water-repellent — or superhydrophobic — surface, allowing the process to operate under ambient pressure.

In the system, warm saline water at approximately 25ºC flows along one side of the membrane, while cooler water at 20ºC flows along the other. This small temperature difference creates a natural driving force that pulls only water vapour across the membrane, where it condenses as pure water, leaving salt and other contaminants behind.

“What distinguishes our membrane is its ultra-thin separating layer, only a fraction of a micrometre thick, combined with a highly water-repellent surface,” said project team member Mohamed Obaid Awad. “This superhydrophobicity is crucial because it prevents liquid seawater from entering and flooding the membrane pores.”

At the nanoscale, the membrane remains ‘air-filled’, ensuring that only water vapour can pass through. Water does not need to boil to evaporate; even at room temperature some water molecules naturally escape into the vapour phase. Here, the extremely small pores enhance this effect by increasing local vapour pressure, facilitating evaporation.

The membrane also demonstrates high rejection of salt and acts as a total barrier to boron and other contaminations, preventing dissolved ions from entering the vapour pathway and improving performance in realistic desalination conditions.

“Salt ions and other dissolved species cannot evaporate under these conditions and are therefore excluded,” said Sofiane Soukane, a member of the research team. “Also, the membrane material is resistant to chlorine-based oxidants, which improves durability and long-term stability.”

Moving beyond the laboratory, the team is currently testing the technology in a pilot plant at KAUST.

“Lessons from the pilot study will guide how we scale up membrane production,” Ghaffour said. “We have several industrial partners keen to get involved.”

Image caption: The ultra-thin separating membrane developed by the KAUST team has extremely small pores and is highly hydrophobic, which increases the local vapour pressure and allows only water vapour to pass through. ©2026 KAUST