Patent Picks: MOFs

Carbon Dioxide Captured From Gas Mixtures

Capturing carbon dioxide from industrial emissions would reduce the amount of the greenhouse gas released into the atmosphere. Thanks to their low cost, aqueous amine solutions are currently the most viable adsorbents for capturing CO₂. But they are not without drawbacks: Regenerating them requires considerable heat, resulting in evaporative loss, and they must be used in concert with corrosion inhibitors. Alternatives based on zeolites and amine-modified silicas absorb CO₂ through the formation of carbamate or bicarbonate species. But their low selectivity for CO₂ over other components in flue gas has significantly limited their use. MOFs might provide a solution, according to work from researchers at the University of California, Berkeley and the University of Sydney (WO 2013059527). Chemist Jeffrey R. Long and coworkers started with MOFs possessing coordinatively unsaturated metal centers along the pore surfaces (Ca, Fe, Mn, Cu, Co, Ni, Cr, or Cd coordinated to 1,3,5-benzenetristetrazolate or 1,3,5-benzenetristriazolate). They filled the pores of the MOFs with di- or trifunctional ligands where one functional group is a basic nitrogen group that binds CO₂ and another functional group is strongly bonded to the metal. Such MOFs are cost-effective and can selectively remove even small amounts of CO₂ from a number of gas mixtures, the researchers report. Compared with traditional amine scrubbers, these MOFs eliminate the need for aqueous solvents and cost less to regenerate.

Separator Boosts Battery Performance

Using metallic lithium as an anode material gives rise to rechargeable batteries with higher energy capacities. But repeatedly charging and discharging such batteries leads to the growth of lithium-based dendrites that pierce the flexible polymeric separator used to separate anode from cathode. As a result, batteries with lithium metal anodes haven’t reached their commercial potential. Nitash P. Balsara and coworkers from UC Berkeley recently described a rigid, MOF-based battery separator that might change that (U.S. 20140045074). They make the separator, which serves as a solid lithium electrolyte, by adding lithium salts to Mg₂(dobdc) (dobdc = 1,4-dioxido-2,5-benzenedicarboxylate), a common MOF, followed by soaking in a mixture of ethylene carbonate and diethyl carbonate. The researchers claim that the presence of coordinatively unsaturated Mg²⁺ cation sites in the MOFs facilitates the uptake of a lithium alkoxide, leading to higher ionic conductivity: The alkoxide anions preferentially bind the Mg²⁺ ions, allowing the Li⁺ cations to freely move along the MOFs’ one-dimensional channels.