Fig. 7. Adsorption isotherms for adsorption of CO2 in mmen–M2(dobpdc) for M = Mg, Co, Fe, Mn, Ni, and Zn using the lattice-model with interaction energies based on those computed with the M06-L functional. (top) The adsorption isotherm based on the chain model is compared with the experimental isotherm as well as with the pair-model for mmen–Mg2(dobpdc). The step in the adsorption isotherm cannot be explained from the pair-model but can be with the chain model. (bottom) Metal dependence in the chain model. The order of the step in the adsorption isotherm corresponds to the order found experimentally from McDonald et al. 11 Nickel shows a Langmuir like adsorption isotherm, while Co initially shows Langmuir like behavior, before the ordering becomes important enough. The step for Co is found at approximately the same pressure as for Zn; this is in agreement with the chain energy found for Zn and Co at the DFT level of theory that is approximately the same value. However, Co has a higher energy for forming pairs and this will be more important initially.
