Functionalization of Metal-Organic Frameworks for Enhanced Stability Under Humid Carbon Dioxide Capture Conditions

The anthropogenic rise in atmospheric CO₂ occurring in the past half century has led to intense research in the area of carbon capture.  Solid sorbents hold significant advantages over other scrubbing technologies due to their increased structural integrity, high carbon dioxide selectivity, and decreased energy costs.  Metal-Organic Frameworks (MOFs)—nanoporous crystals composed of metal nodes joined by organic linkers—possess the high surface area and large pore volume needed for viable carbon adsorption.  Furthermore, the functionalization of organic ligands allows for improved capture ability and other unique properties.  However, the performance of MOFs may be heavily diminished by several environmental factors common in carbon capture applications.  The high temperatures and humidity found during post-combustion flue gas filtration, for example, have been found to drastically alter the crystalline structure of the Mg/DOBDC MOF thereby reducing its capture capacity.  Countermeasures for this sort of degradation must be explored before MOFs are ready for practical use.  Here it is shown that the functionalization of Mg/DOBDC with ethylenediamine prevents the loss of stable crystal structure, likely by decreasing the hydrophilicity of the framework.  The amine functionalized MOF retained its carbon capacity after exposure to flue-like conditions, as shown with x-ray diffraction, BET and thermogravimetric analysis.