news of the week NOVEMBER 16, 2015 EDITED BY MITCH ANDRÉ GARCIA & MANNY I. FOX MORONE
HOLEY LIQUID, BATMAN!
with permanent porosity has actually been around for decades, but “the practicalities of designing such a system take skill and perseverance. This work delivers real liquids that show that property, which is a great achievement.” The researchers initially achieved liquid porosity by dissolving a hollow organic core structure coated with crown-ether surface groups in a crown-ether solvent. To optimize gas absorption capacity, the team packed the fluid with as many cage molecules as possible—one for every 12 solvent molecules. When exposed to methane, the liquid absorbs eight times as much gas as the solvent alone. But the crown ethers were hard to synthesize and the liquid thick and slow-flowing. So collaborators Andrew I. Cooper and Rebecca L. Greenaway at the University of Liverpool developed another porous liquid by coating a hollow organic cage with a mixture of diamines and dissolving it in the solvent hexachloro-
MATERIALS SCIENCE: Liquid with
permanent pores could one day help with gas separations
OW IS A NEW TYPE of liquid like the London Underground? In both, one must mind the gaps. Stuart James of Queen’s University Belfast and coworkers have devised a liquid with permanent porosity (Nature 2015, DOI: 10.1038/ nature16072). Such holey fluids could be useful in gas separation, process chemistry, and other applications, if they can be made economically. Their persistent porosity comes from hollow organic cage molecules coated with solvent-soluble surface groups. The cage openings are too small to be clogged by the surface groups or by large solvent propene. The resulting porous liquid flows ten molecules in the surrounding solvent. times as readily as the crown-ether-based mateLiquids contain spaces between their molrial. The researchers synthesize the coated cages in a ecules, but they are tiny. Bubbles can be blown into single step, and the solvent is available commercially. liquids, but they will quickly float to the surface and In earlier work, Shannon M. Mahurin and Sheng dissipate—air bubbles in glass being a rare exception. Dai at Oak Ridge National Laboratory and coworkers On the other hand, solids such as zeolites and metal- created hollow colloidal silica nanoparticles with a fluorganic frameworks have permanent pores. They can idlike polymer surface coating (Angew. Chem. Int. Ed. be used to separate molecules by size and 2015, DOI: 10.1002/anie.201409420), but can host added catalysts to drive chemical the new porous liquids are easier to moreactions. But unlike liquids, these materials “The liquids lecularly modify. Dai comments that “the can’t flow through channels or be smoothed will open up liquids will open up new frontiers in how onto surfaces. think about porosity.” new frontiers weThe James got the idea for holey liquids a surface area and gas uptake of the decade ago, when a colleague, Queen’s Uni- in how we new materials are too modest for them to versity chemical engineer David W. Rooney, think about compete with porous solids immediately, porosity.” wondered whether mixtures of porous says cage compound specialist Michael —SHENG DAI solids and liquids might be pumped through Mastalerz of Germnay’s Heidelberg Unipipes and used in continuous processes versity in a Nature commentary. “They more easily than is generally possible with porous solshould instead be seen as a prototype of a new class of ids alone. material [that] will undoubtedly find technological apPorous solids expert Russell Morris of the University plications” if these properties can be improved.—STU of St. Andrews comments that the concept of liquids BORMAN NAT UR E
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NOVEMBER 16, 2015
To generate a holey liquid (bottle), researchers dissolved a porous core structure (space-filling) with crown-ether decorations (ball and stick) in a crown-ether solvent. C = gray, O = red, N = blue, H = white.
