CO2 affinity for photo-switching MOF based CO2 capture

https://doi.org/10.1016/j.mtsust.2022.100149

“Ladewig’s group observed that CO₂ had a lower affinity toward Azo-UiO-66 in UV irradiation conditions, which caused the instantaneous release of CO₂ once it was exposed to UV light [73]. Under the UV irradiation of Azo-UiO-66, the adsorption heat (Q_ads) of CO₂ was around 31 kJ/mol^–, which was lower than at the pristine condition. The Q_ads of pristine sample was around 35 kJ/mol^–. Because the Q_ads value represents the CO₂ affinity toward MOF frameworks, it was illustrated that Azo-UiO-66 exhibited lower interaction with CO₂ molecules in cis isomer. A similar trend was also found in Azo- DMOF-1 [74]. The Q_ads value of Azo-DMOF-1 was found to be around 18 kJ/mol^– upon UV irradiation, which was 30% lower than the non-irradiated sample. Thus, UV irradiation resulted in a lower affinity between the MOF framework and CO₂ molecules and then triggered the CO₂ release. In addition, the Q_ads value toward CO₂ in Azo- DMOF-1 was higher than in DMOF-1, which proved that the introduction of AB groups to ligands contributed to the higher interaction toward CO₂ molecules. These results might be attributed to the Lewis acid and base interactions between AB groups and CO₂ molecules, which help improve the CO₂ affinity of Azo- DMOF-1.”