Calorimetric study of the CO2 gate sorption of elastic layer-structured metal–organic frameworks (ELM-11 and ELM-12)

Elastic layer-structured metal–organic frameworks (ELMs) have flexible structures. ELM-11 shows the gate phenomenon on CO2 sorption–desorption, and ELM-12 shows the double-step sorption of N2 at 77 K, but the CO2 sorption of ELM-12 has not been investigated in detail. Calorimetric measurements of the heats of sorption and desorption enable analysis of the sorption mechanism and behavior. The heats of sorption, desorption, and the gate phenomenon for ELM-11 and -12 were obtained calorimetrically and compared with those obtained using the van 't Hoff and Clausius–Clapeyron equations. The sorption heat was greater than that of CO2 liquefaction, despite the destabilization of the ELM resulting from interlayer expansion. Further, the heat was similar to that evaluated using van 't Hoff plots. The rapid uptake and fast rate of CO2 sorption resulting from the gate phenomenon yielded an energetically favorable process and more effective heat exchange than those of existing adsorbents, which show modest adsorption rates. Therefore, ELM-11 has applications in heat management for gas sorption. Unlike ELM-11, ELM-12 did not show gated CO2 sorption below 760 Torr but, instead, the open micropores were filled. In addition, the heat of adsorption was higher than that of the sublimation of CO2.