Abnormal adsorption properties of the MOF CALF-20 as revealed by water and methanol vapor sorption

Abstract

MOF CALF-20 has been employed in industry due to its hydrophobic properties, which are conducive to CO₂ capture. Nevertheless, additional characteristics of this porous material are worthy of investigation, including its mechanical properties and flexibility. When CALF-20 is subjected to water vapor, it exhibits a slight contraction, which may be attributed to its hydrophobic nature. Conversely, when CALF-20 adsorbs methanol, it exhibits a 30 % increase in volume. Furthermore, our findings indicate that the interactions between MOFs and water or methanol are dependent on the crystalline phase. The aforementioned interactions exhibit a range of values between −37.8 and −54 kJ mol⁻¹ in the case of water, whereas they consistently approach −53 kJ mol⁻¹ in the case of ethanol, irrespective of the crystalline phase. This has significant implications for methanol adsorption in water-saturated CALF-20. Our findings suggest that the water confined in the pores can be pushed out by the methanol flow, whereas this phenomenon does not occur in the case of water adsorption in CALF-20 that has already been filled with methanol. These findings pave the way to improvements in Sorption-Enhanced Reaction Process technology for pure methanol production from carbon dioxide, where selective sorbents are required for shifting the methanol production equilibrium.