MOF Membranes Stand Up To Water

The impressive capacity of various metal-organic framework (MOF) compounds to adsorb gases—especially toxic gases such as ammonia—has raised interest in these porous solids for use as gas-mask filtration materials. Filter materials are typically used as powders held in a canister fitted to the front of gas masks. But gas-mask designers aim to do away with the obtrusive canister, favoring instead a streamlined design in which the mask and filter are integrated into a low-profile unit. That design calls for making easily processable MOF membranes, which has been challenging. A team led by Jared B. DeCoste of the Edgewood Chemical Biological Center at Aberdeen Proving Ground and Seth M. Cohen of the University of California, San Diego, reports success in making robust poly(vinylidene difluoride)-HKUST-1 membranes (Chem. Sci. 2016, DOI: 10.1039/c5sc04368a). HKUST-1 is a copper-based MOF, in which paddle-wheel Cu dimers are linked by benzene-1,3,5-tricarboxylate units. High levels of humidity decompose powdered forms of HKUST-1, lowering gas-uptake capacity. In contrast, HKUST-1-polymer membranes retained their mechanical stability and theoretical ammonia capacities even after a monthlong exposure to 90% relative humidity.