A new invention that uses sunlight to drive water purification could help solve the problem of providing clean water off the grid.
The device resembles a large sponge that soaks up water but leaves contaminants – like lead, oil and pathogens – behind. To collect the purified water from the sponge, one simply places it in sunlight. The researchers described the device in a paper published this week in the journal先进的材料.
The inspiration for the device came from the pufferfish, a species that takes in water to swell its body when threatened, and then releases water when danger passes, said the device’s co-inventor罗德尼普里斯特利，Pomeroy和Betty Perry Smith化学和生物工程教授，普林斯顿的创新副院长。
“Sunlight is free,” Xu said, “and the materials to make this device are low-cost and non-toxic, so this is a cost-effective and environmentally friendly way to generate pure water.”
The authors noted that the technology delivers the highest passive solar water- purification rate of any competing technology.
One way to use the gel would be to place it in a water source in the evening and the next day place it in the sunlight to generate the day’s drinking water, Xu said.
To demonstrate the device in real-world conditions, Xu took the device to Lake Carnegie on the Princeton University campus.
Xu placed the gel into the cool water (25 degree Celsius, or 77 degrees Fahrenheit) of the lake, which contains microorganisms that make it unsafe to drink, and let it soak up the lake water for an hour.
At the end of the hour, Xu lifted the gel out of the water and set it on top of a container. As the sun warmed the gel, pure water trickled into the container over the next hour.
The device filters water much more quickly than existing methods of passive solar-powered water purification methods, the researchers said. Most other solar-powered approaches use sunlight to evaporate water, which takes much longer than absorption and release by the new gel.
在新设备的核心，是一种根据温度变化的凝胶。在室温下，凝胶可以充当海绵，浸泡水。当加热至33摄氏度（91华氏度）时，凝胶对面 - 它将水从其毛孔推出。
The gel consists of a honeycomb-like structure that is highly porous. Closer inspection reveals that the honeycomb consists of long chains of repeating molecules, known as poly(N-isopropylacrylamide), that are cross-linked to form a mesh. Within the mesh, some regions contain molecules that like to have water nearby, or are hydrophilic, while other regions are hydrophobic or water-repelling.
At room temperature, the chains are long and flexible, and water can easily flow via capillary action into the material to reach the water-loving regions. But when the sun warms the material, the hydrophobic chains clump together and force the water out of the gel.
This gel sits inside two other layers that stop contaminants from reaching the inner gel. The middle layer is a dark-colored material called polydopamine that transforms sunlight into heat and also keeps out heavy metals and organic molecules. With PDA in place, the sun’s light can heat up the inner material even if the actual outdoor temperature is not very warm.
The final external layer is a filtering layer of alginate, which blocks pathogens and other materials from entering the gel.
Sujit Datta，化学和生物工程助理教授，以及Craig Arnold，苏珊国防部机械和航天工程教授和普林斯顿科技科技研究所主任，合作了该技术的发展。
The study was supported by the Princeton University Presidential Postdoctoral Fellowship Program, the National Science Foundation Materials Research Science and Engineering Center Program through the Princeton Center for Complex Materials (DMR-1420541 and 2011750), the Princeton Catalysis Initiative, and the Princeton University Eric and Wendy Schmidt Transformative Technology Fund.
The study, A bioinspired elastic hydrogel for solar-driven clean water purification, by Xiaohui Xu, Sehmus Ozden, Navid Bizmark, Craig B. Arnold, Sujit S. Datta and Rodney D. Priestley, was published in the journal先进的材料。DOI adma.202007833R2