Thermodynamic analysis of the breathing of amino-functionalized MIL-53(Al) upon CO2 adsorption

Carbon dioxide gas adsorption in amino-functionalized MIL-53(Al) at various temperatures has been analysed in combination with temperature programmed XRD. Similarly to the regular MIL-53(Al) material, the so-called breathing phenomenon was shown to take place in the amino-MIL-53 upon adsorption of different molecules, i.e. the transition between a large-pore (lp) and a narrow-pore (np) structure. Using the osmotic thermodynamic model analysis, the temperature–loading phase diagram was derived. The overall diagram is similar to that for the regular MIL-53(Al), but a spectacular difference is the much larger stability domain of the np structure, which can be accounted for by the increased affinity for CO2 due to the presence of the amino groups in the pore space.