The invention could help solve the problem of providing clean water off the grid or where low-cost, non-powered water purification is needed.


The filter uses sunlight to drive water purification and 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. At the heart of the device is a gel that changes depending on temperature: at room temperature, it acts as a sponge, soaking up water but when heated to 91 °F, the gel pushes the water out of its pores. The 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. The final external layer is a filtering layer of alginate, which blocks pathogens and other materials from entering the gel. The gel can purify water contaminated with petroleum and other oils, heavy metals such as lead, small molecules, and pathogens such as yeast. The gel maintains its ability to filter water for at least ten cycles of soaking and discharge with no detectable reduction in performance.


Princeton University, Princeton, New Jersey


The device filters water much more quickly than existing methods of passive solar-powered water purification that use sunlight to evaporate water. Passive filtration via gravity, as with typical household countertop filters, requires regular replacement of filters as needed.


The team is exploring ways to make the technology widely available.

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