Copper benzene-1,3,5-tricarboxylate (HKUST-1) – graphene oxide pellets for methane adsorption

Copper benzene-1,3,5-tricarboxylate (HKUST-1) is one of the materials holding the greatest potential for clean energy gases among microporous storage materials. Although this material is commercially available as a powder with particle size 10–20 μm, for easier handling adsorbents are preferentially employed as pellets or monoliths. Even under binder free conditions there could be a high price to pay for compacting: loss in crystallinity and in porosity. To determine the protection potential of graphene oxide (GO) a HKUST-1@GO composite was studied. The material of 16% GO was obtained in a single step solvothermal synthesis. The pristine HKUST-1 as well as HKUST1@GO formed consistent, integrated pellets when compressed at 25 and 50 bar without any binder. PowderXRD and N2 adsorption were used to monitor the changes in crystallinity and pore structure. It was found that GO has a protective effect against the 25 or 50 bar applied pressure, as 75% of the pore volume and the apparent surface area is saved in HKUST1@GO (vs. 43% and 47%, respectively, in HKUST-1) after compression. Presumably, the flexible GO sheets with high mechanical stability act as compressible spacers between the crystals thus preventing their amorphisation. Comparison of the adsorption properties of the HKUST-1 and HKUST-1@GO powders and pellets revealed that the performed compression deteriorated the structure of the MOF and thus reduced the CH4 uptake. Further studies are needed to optimize the compression pressure for a more reasonable loss in the gas uptake capacity.