Mechanisms of CO2 capture using photo-switching MOF – interaction between CO2 molecules and pore surface

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

“Hill et al. [31] firstly proposed that the increase of light-induced MOF surface energy triggered the CO₂ release. Under the UV light irradiation, the intermolecular interactions between the pore surface of Zn(AzDC)(4,4′-BPE)_0.5 and CO₂ molecules declined, which contributed to the decrease of CO₂ adsorption capacity [31]. The same reason was also reported to explain the photoswitching behavior in PCN-250 [83]. when the UV light switched on/off, the FTIR peak intensity at 527 nm underwent changes, corresponding to the reversible bending modes of ABTC ligands in PCN-250. Such suppressed localized bending of ABTCs resulted in the activation of pore surface and the surface energy increasing of PCN-250. Consequently, the interactions between CO₂ molecules and pore surface weakened so that the spontaneous CO₂ desorption was triggered. Once the light switched off or thermal heating of the sample was off, the suppressed bending of ligands relaxed so that the CO₂ capacity recovered back to its original state. Luo et al. [69] also found a similar bending movement in ECUT-15 under UV. Therefore, light can trigger a structural oscillation instead of trans to cis isomerization that was suppressed in this way. The same bending movement of C–C–N was also observed in an azo-MOF reported by Zhao’s group [48]. The light irradiation leaded to the increase of surface energy and weakened the interaction between CO₂ molecules and azo-MOFs, which then contributed to the release of CO₂.”