The United Nations predicts that two-thirds of the world’s population will face freshwater shortages by 2025. Even today, some Middle Eastern and North African cities get most of their potable water through desalination of seawater. Commercial plants remove the salt by pumping water through semipermeable polymer membranes, a process that consumes vast amounts of energy. The easily clogged membranes require frequent cleaning that releases chemicals into the environment.

One potentially stronger, thinner, and more water-permeable membrane alternative is a single layer of graphene etched with nanopores. But nanoporous graphene tends to lose mechanical strength when scaled up above the microscale, and etching it with a dense grid of pores reduces the membrane’s structural integrity. Now Xiangfeng Duan (UCLA), Quan Yuan (Wuhan University in China), and colleagues have designed a centimeter-sized graphene membrane that effectively filters ions from seawater.

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