New insights into UTSA-16

Among the metal organic framework materials proposed for CO₂ separation, UTSA-16 possesses the highest CO₂ volumetric density explained on the basis of favourable interactions between CO₂ and structural water molecules in the material, as revealed by neutron diffraction. In this study, UTSA-16 was synthesised and extensively characterised by XRD, TEM combined with EDX analysis and DR-UV-Vis, Raman and FTIR spectroscopies, as well as by TGA measurements. The synthesised material shows XRD patterns, surface area, CO₂ capacity and isosteric heat coincident to the ones reported for UTSA-16 in the original papers but a higher thermal stability and a complete removal of water upon activation under mild conditions (363 K). On the basis of EDX and IR measurements, the formula of UTSA-16 used in the present study is proposed to be K₂Co₃(cit)₂. Infrared spectroscopy clearly shows that UTSA-16 described in this work reversibly interacts with water vapor, CO and CO₂. The interaction is attributed to K⁺ species, which are present as counterions in the pores. At 1 bar and 298 K a fraction of K⁺ sites adsorbs 2 CO₂ molecules.