It takes a long time to desalinate water using a traditional solar still. But University of Houston engineer Hadi Ghasemi is using ordinary graphite to speed up the process.
"We took graphite and put it into the microwave for seven seconds," Ghasemi says. The gases in the mineral cause the outer layer to expand and pop. "It's exactly like a popcorn!"
The result is a thin, porous material that looks like a black sponge. It floats on the surface of water, like a sponge. But instead of soaking up liquid, the pores soak up the sun, Ghasemi and his colleagues reported in the journal Nature Communications back in July.
The graphite has holes in it with just the right shape to concentrate solar energy and create tiny hot spots in the graphite. Water creeps into the holes through capillary action (just as water moves up the stem of a plant to its leaves). The droplets then heat up quickly and evaporate.