Fish Gill-Inspired Aerogel Tackles Long-Standing Issue In Solar Desalination

As freshwater scarcity becomes more prevalent, solar evaporation is drawing attention as a promising solution. This process involves using sunlight to heat the surface of salty or contaminated water, causing it to turn into vapor that can then be collected as clean water as it condenses. Unlike conventional desalination plants, which typically rely on pumps and large amounts of electricity, solar evaporators need little more than sunlight and a material that can absorb it and heat up efficiently. This simplicity makes the approach appealing for regions where freshwater is scarce and infrastructure is limited.

However, the same process that separates freshwater from salt creates a major problem for the evaporator. As water leaves as vapor, dissolved salt remains behind and becomes increasingly concentrated at the evaporation surface. During prolonged operation, the salt can crystallize and form deposits that block water transport and reduce the surface’s ability to absorb sunlight and convert it into heat. These problems become particularly severe when treating highly concentrated brines, as salt accumulation eventually causes the evaporator to lose its ability to produce water stably and efficiently.

To address this long-standing obstacle, a research team led by Associate Professor Jian Shi of the Faculty of Textile Science and Technology at Shinshu University, Japan, has designed a novel nature-inspired material. Their work, made available online on July 13, 2026, and will be published in Volume 18, Issue 1 of the journal Nano-Micro Letters on December 1, 2026, describes a biomass-derived aerogel, a lightweight, highly porous material that resists salt buildup even in extremely salty water. The study included co-authors Nuo Liu and Chunhong Zhu of Shinshu University and Haifeng Zhang of Nantong University.

The team took inspiration from marine fish, as Dr. Shi explains: “Marine fish live in seawater, yet their gills can continuously regulate ions and water while maintaining efficient transport under highly saline conditions. We were particularly fascinated by the fact that nature does not simply block salt; instead, it actively regulates the movement of ions and water through a sophisticated, hydrated interface.”

Building on this idea, the researchers created a porous aerogel from carboxymethyl chitosan and sodium alginate, which are two biomass-derived polymers. They also added carbon black produced from bamboo as the photothermal component that converts sunlight into heat. The polymers contain charged groups that can repel certain salt ions through what’s known as Donnan-type repulsion. Additionally, their hydrophilic groups help maintain a thin layer of water across the material's surface at all times, which helps flush away any accumulated salt along the interface.

An evaporator built using this material produced water at a rate of 2.88 kg m^-2 h^-1 under normal sunlight, outperforming some of the best evaporators reported to date. When tested in extremely salty water at a concentration nearly six times that of seawater, the evaporator ran continuously for 24 hours and through repeated day–night cycles over a week without any visible salt buildup or loss of performance.

Because the proposed evaporator is made of inexpensive biodegradable materials, the researchers see it as a practical option for ensuring sustainable and decentralized access to freshwater. “Our evaporator technology is made entirely from biomass-derived materials, offering a potentially low-cost, scalable, and environmentally friendly approach to solar-driven desalination,” notes Dr. Shi.

Looking ahead, the team believes the same design principle could extend beyond desalination to other water treatment technologies that struggle with salt buildup or fouling. “Our work shows how mimicking the sophisticated ion-regulation and water-transport functions found in nature can provide a new strategy for designing sustainable materials for water purification under challenging high-salinity conditions,” concludes Dr. Shi. “For us, this research represents more than the development of a new desalination material. It reflects our broader interest in learning from nature to solve practical engineering problems.”