Freshwater production from oily seawater has long presented a difficult engineering problem: the same membranes designed to purify water can quickly become clogged by oil. A research team from Pusan National University in South Korea and collaborating institutions in Singapore has now developed a multifunctional membrane that tackles both challenges at once. The asymmetric hydrogel membrane removes oil from contaminated seawater while using sunlight to drive desalination, achieving more than 99.99% oil rejection and producing freshwater at a rate of 1.29 kilograms per square meter per hour.
The advance addresses a growing global concern. Population growth, industrial expansion, and climate change are intensifying freshwater shortages across regions including Africa, the Middle East, and Southeast Asia. Solar-driven desalination is attractive because it uses sunlight rather than fossil fuels or large amounts of grid electricity. In these systems, solar energy heats water at a specialized surface, causing it to evaporate while salts and other nonvolatile contaminants remain behind. The vapor can then be condensed into freshwater. Yet oily coastal water, refinery wastewater, and industrial discharge can severely undermine the process.
Oil droplets are especially damaging because they adhere to membrane surfaces and block the pathways through which water must move. This phenomenon, known as fouling, reduces water production and can alter the membrane’s wetting behavior, making it harder to control evaporation. Many laboratory studies of solar desalination have relied on clean saltwater, which does not reflect the complex conditions found near harbors, offshore operations, industrial zones, and oil-contaminated shorelines. The new study takes a different approach by designing oil separation and solar evaporation into one coordinated membrane structure.
The membrane uses a Janus architecture, a term borrowed from the two-faced Roman god and used in materials science to describe a structure with two chemically and physically distinct sides. Its hydrophilic side consists of a hydrogel made from chitosan and polyvinyl alcohol. Because this surface strongly interacts with water, it allows water to pass while resisting the attachment and penetration of oil droplets. Chitosan, a biopolymer derived from chitin, also contributes abundant polar functional groups that support water transport and help create a hydrated protective layer at the membrane interface.
The opposite side is hydrophobic and engineered to absorb sunlight efficiently. It contains copper oxide nanoparticles enclosed in a carbon shell, known as CuO@NC, and incorporated into a nanofiber layer. Copper oxide can absorb solar radiation, while the carbon coating improves light harvesting and photothermal conversion. When sunlight strikes this surface, the absorbed energy is transformed into heat. That heat concentrates near the water–air interface, where it accelerates evaporation without requiring the entire volume of seawater to be heated.
Separating these functions between two surfaces is central to the membrane’s performance. The hydrophilic hydrogel side acts as an oil-rejection barrier, while the hydrophobic photothermal side supplies the heat needed for evaporation. In a conventional single-layer design, attempts to improve solar absorption can interfere with water transport or increase the risk of fouling. The Janus configuration reduces this conflict by assigning contaminant separation and energy conversion to different layers while maintaining contact between them.
In experiments, the membrane rejected more than 99.99% of oil from contaminated seawater. Its performance remained stable when the researchers tested different oil droplet sizes and reused the material repeatedly. During solar desalination, the membrane reached an evaporation rate of 1.29 kilograms of water per square meter per hour, nearly three times the rate reported for a conventional single-layer membrane used for comparison. The result suggests that protection from oil fouling does not necessarily require sacrificing the high evaporation rates needed for practical solar water treatment.
“By harnessing renewable solar energy and integrating contaminant separation with freshwater production in a single membrane platform, our technology has the potential to reduce energy consumption, operational complexity, and secondary waste generation,” says Professor Sanghyun Jeong of Pusan National University, who led the research. The integrated design could eliminate the need for a separate oil-removal stage before desalination, potentially simplifying treatment systems in locations where infrastructure, electricity, and maintenance resources are limited.
The researchers describe the membrane as an example of a broader strategy for designing multifunctional water-treatment materials. Instead of arranging several independent treatment units in sequence, engineers could build membranes in which each layer performs a specialized task while supporting the others. Such systems may eventually be adapted for polluted coastal waters, industrial wastewater, and concentrated brines generated during desalination. Before commercial deployment, however, longer-term testing will be needed to evaluate durability, cleaning requirements, performance under changing weather conditions, and behavior in waters containing mixtures of oil, salts, organic compounds, and suspended particles. The study nevertheless offers a striking demonstration of how a “double-faced” membrane could turn sunlight and contaminated seawater into a more practical source of freshwater.
Subject of Research: Experimental development of a multifunctional membrane for integrated oil–water separation and solar-driven seawater desalination.
Article Title: Dual-functional asymmetric CuO@NC-based Janus hydrogel membrane for integrated oil–water separation and solar-driven desalination for sustainable use
Web References: https://doi.org/10.1016/j.desal.2026.120395
References: Desalination, DOI: 10.1016/j.desal.2026.120395
Image Credits: Cannot be reused without permission.
Keywords
Solar desalination, oily seawater, Janus membrane, hydrogel membrane, oil–water separation, photothermal materials, copper oxide nanoparticles, freshwater production, membrane fouling, water treatment, desalination technology, sustainable engineering
