What holds the surface area of several football fields in the mass equivalent of a paper clip? The answer to this question has many names and performs duties ranging from catalysis to gas storage: the metal organic framework, or MOF, called Cu-BTC and also known as HKUST-1 or Basolite.
For MOFs, lots of surface area means lots of opportunity for chemical reactions. Researchers have found this reactivity can be enhanced in the model material, Basolite C300, by controlling its surrounding atmosphere and temperature, thereby changing the number of electrons on its copper atoms, manipulating the concentrations of Cu2+ and Cu+ present.
Both Cu2+ and Cu+ were known to exist in Cu-BTC, although Cu+ was thought to be present only because of sample impurities.
Using infrared spectroscopy tools at EMSL, researchers measured the ratio of Cu2+:Cu+ in Cu-BTC exposed to various conditions and showed that Cu+ can be present in high concentrationsindependent of impurities. Reduction, or the generation of the largest number of Cu+ sites, was most successful via treating Cu-BTC under vacuum at 473 K.
Re-oxidation to Cu2+ sites was most successful in an NO2 atmosphere at 473 K. Importantly, the structure of Cu-BTC was found to be very stable, not degrading after repeated reduction/oxidation cycles. The team made another novel discovery, showing for the first time in an MOF that chemical species, such as nitrites and methoxides, can form at the open Cu2+ and Cu+ sites.
The teams approach can be expanded to analyze similar materials, and their new knowledge about Cu-BTC will open doors to refine existing applications as well as create new applications for these novel materials.
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More information: J Szanyi, et al. 2012. Well-studied CuBTC still serves surprises: evidence for facile Cu2+/Cu+ interchange. Physical Chemistry Chemical Physics 14:43834390. DOI: 10.1039/c2cp23708c