Postgraduate student Shaobo Han from Linköping University (Sweden) has designed a new filter for the purification of dirty or just salt water, which does not require energy to operate. It uses the heat of the sun's rays and in a passive mode constantly evaporates the liquid, separating it in the process into pure vapor and impurities. The principle is old, but in this filter it is implemented using an unusual material - thermal airgel.
Khan took cellulose as a basis, as a widespread and extremely cheap material. It was turned into an airgel and coated on one side with organic polymer PEDOT: PSS. It is known for being extremely efficient at absorbing solar radiation, especially in the infrared, thermal spectrum. As a result, the coating heats up quickly.
For better buoyancy, the airgel was placed on a porous base material through which water can seep. It rises through the pores and reaches the airgel, where it heats up and evaporates. The process is far from instantaneous, but it runs 4-5 times faster than the natural evaporation of water under the influence of the Sun. The resulting steam settles on a special plate, then the condensate flows down the chute into a collection container.
Such a filter can work indefinitely as long as the sun is shining, which makes it dependent only on the weather. True, the airgel itself must be periodically cleaned of accumulated impurities. But with regular cleaning, its lifespan is virtually unlimited, and this technology will help passively purify huge volumes of contaminated water.