Porous materials such as zeolites, metal organic frameworks, and nanocarbons are known for their ability to selectively interact with and separate chemical species having similar sizes and functional groups. But the ability to separate charged molecules of various sizes, especially when dissolved in water, has remained a challenge. A team led by Cafer T. Yavuz of Korea Advanced Institute of Science & Technology (KAIST) has now reported a microporous network fluoropolymer that can selectively separate cationic dyes and other charged molecules from mixtures of water-soluble organics (Nat. Commun. 2016, DOI: 10.1038/ncomms13377). The researchers first prepared an inexpensive new covalent organic polymer, dubbed COP-99, by treating commercially available tetrafluorohydroquinone with potassium carbonate (shown). They found that the material pulls modestly sized charged molecules such as the dye methylene blue out of water, but it isn’t capable of sequestering larger dye molecules such as rhodamine B or uncharged molecules such as bisphenol A. The key to the material’s selectivity is its restrictive pore size and the exposed fluorine atoms, Yavuz notes, which both create hydrophobic pores and provide strong electronegative forces attractive only to charged organics. The KAIST team envisions a range of applications, including water treatment to remove artificial dyes, pesticides, and prescription drugs.