Hydrogel uses sunlight to harvest fresh water from the sea
In many arid coastal regions, a great quantity of valuable fresh water is lost into the atmosphere every day, as it evaporates from the surface of the ocean. This situation prompted scientists to create a new hydrogel that's highly effective at capturing moisture from the sea air, and then releasing it as fresh water.
Developed by a team at the National University of Singapore, the zinc-based material is claimed to be over eight times more absorbent than existing drying agents such as silica gel and calcium chloride – it can absorb more than four times its dry weight in water. Additionally, unlike the case with traditional drying agents, no electricity is required to get that water back out of it, plus the gel can be reused over 1,000 times.
In field tests, floating devices containing the hydrogel were placed on the surface of the ocean, at a beach. As water vapor subsequently evaporated out of the salt water, tiny airborne droplets of that vapor were collected by the gel. Once the material was saturated, it was placed in a closed glass box that was left sitting in the hot sunlight.
Upon thus being heated to between 45 and 50 ºC (113 and 122 ºF), the gel released its stored fresh water in the form of vapor. That vapor condensed on the walls of the box, and was collected in liquid form. By contrast, materials like silica gel must be heated to considerably higher temperatures, typically requiring a manmade power source.
The researchers are now looking at ways of boosting the hydrogel's absorption capacity even further, and of optimizing the water-harvesting process. In its current form, if used repeatedly throughout the day, the gel can produce over 10 liters (2.6 US gal) of fresh water per kilogram of material daily.
"Our invention also has potential to be scaled up considerably to function as a floating water-capturing farm," says Asst. Prof. Tan Swee Ching, lead scientist on the study. "This approach could benefit rural communities where access to clean water remains a challenge. By creatively applying novel solutions, we hope to contribute towards mitigating the global water crisis."
The research is described in a paper that was recently published in the journal Advanced Materials. In a previous study, the same hydrogel was also shown to be effective at lowering relative humidity within rooms.