Water-stable Adenine-based MOFs with Polar Pores for Selective CO2 Capture

Abstract

Here, we report two novel water-stable amine-functionalized MOFs, namely IISERP-MOF26 ([NH2(CH3)(2)][Cu2O(Ad)(BDC)] center dot (H2O)(2)(DMA), 1) and IISERP-MOF27 ([NH2(CH3)(2)](1/2)[Zn4O(Ad)(3)(BDC)(2)] center dot (H2O)(2)(DMF)(1/2), 2), which show selective CO2 capture capabilities. They are made by combining inexpensive and readily available terephthalic acid and N-rich adenine with Cu and Zn, respectively. They possess 1D channels decorated by the free amine group from the adenine and the polarizing oxygen atoms from the terephthalate units. Even more, there are dimethyl ammonium (DMA(+)) cations in the pore rendering an electrostatic environment within the channels. The activated Cu- and Zn-MOFs physisorb about 2.7 and 2.2 mmol g(-1) of CO2, respectively, with high CO2/N-2 and moderate CO2/CH4 selectivity. The calculated heat of adsorption (HOA=21-23 kJ mol(-1)) for the CO2 in both MOFs suggest optimal physical interactions which corroborate well with their facile on-off cycling of CO2. Notably, both MOFs retain their crystallinity and porosity even after soaking in water for 24 hours as well as upon exposure to steam over 24 hours. The exceptional thermal and chemical stability, favorable CO2 uptakes and selectivity and low HOA make these MOFs promising sorbents for selective CO2 capture applications. However, the MOF's low heat of adsorption despite having a highly CO2-loving groups lined walls is quite intriguing.