Cu-BTC proves redox capable, opens new doors for catalysis and gas storage

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 concentrations—independent 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 team’s 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.