Atomic Heat Contributions for Carbon Dioxide Adsorption in IRMOF-1

A grand canonical Monte Carlo simulation has been carried out to investigate CO2 adsorption in the isoreticular metal-organic framework-1 [IRMOF-1, Zn4O(1,4-benzenedicarboxylate)(3)] in the temperature range 170-310 K. We report adsorption isotherms, total isosteric heats, and the separate heat contributions resulting from fluid-fluid (FF) and fluid-IRMOF-1 (FS) interactions. For the first time, the contributions to isosteric heat from individual pore types and atom types in IRMOF-1 have been explored. The FS heat and local density distributions for both pore types confirmed that they adsorbed simultaneously in the Henry's Law region. The heat contributions from each atom location in the adsorbent in the Henry's Law region were found to be temperature dependent. The strongest adsorption site is at the corners of the larger pore size of 1.5 nm rather than in the smaller pore of 1.2 nm. We found that the O atom of carboxylate and the C atom of the phenylene C-H make the largest contribution to the isosteric heat at temperatures of <180 K and >180 K, respectively, whereas the smallest contribution is always from the O atom of the Zn4O cluster. At all temperatures, the strongest adsorbate- IRMOF-1 interaction is between CO2 and the C atom of the phenylene C-H bond at higher loadings. The total isosteric heat in the wider pore is always higher than that in the smaller at all loadings. This work opens up new opportunities to determine the heat contributions from individual pore types and atom types in other MOFs and will lead to improved design of adsorbent materials.