Stability of Metal-Organic Framework-Supported Amines under Exposure to Ozone Generated from Air.

Amine compounds supported on porous materials such as metal-organic frameworks (MOFs) have shown promising performance for direct air capture (DAC) due to their enhanced affinity for CO2. Although features such as adsorption capacity and selectivity are paramount in these composites, their long-term stability has a major impact on the operating cost of DAC systems. In this work, changes in carbon capture performance, crystallinity, porosity and chemical environment of the constituting atoms of MOF-amine composites are explored after exposure to ozone and NOx impurities generated from corona discharge applied to air. From the obtained results, the stabilities of Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) grafted with ethylenediamine (en), N-methylethylenediamine (men), and N,N-dimethylethylenediamine (dmen), as well as MIL-101-(Cr) MOF impregnated with polyethylenimine (PEI), are compared. A negative effect in the overall CO2 adsorption capacity is observed for all MOF composites after exposure, as well as a decrease in the adsorption step pressure of CO2 for Mg2(dobpdc) amine-grafted composites, as shown via dynamic gravimetric adsorption experiments. Spectroscopic analyses indicate that oxidation of amine groups through the formation of nitro functional groups occurs as well as a decrease in the electron-donation interaction between the supported amines and the metal nodes of the MOFs.