Striking CO2 capture and CO2/N2 separation by Mn/Al bimetallic MIL-53

In this study, manganese (Mn) was coordinated on the Al-based MIL-53 to produce a series of MIL-53(Al)-MnN (N = 0, 1, 2, 3). These samples were synthesised by the hydrothermal approach, using varying molar Mn content. The actual Mn content in the activated MIL-53(Al)-Mn samples were found to be very low but exerting significant properties to the resultant bimetallic MOF. All samples possessed similar structure to MIL-53(Al) while the BET surface area was obviously boosted in samples of MIL-53(Al)-Mn1 and 2. The activated MIL-53(Al)-Mn samples were tested for CO2 adsorption at various pressures. The CO2 adsorption capacity at STP was increased with the Mn content. Our results showed that the CO2 adsorption capacities surpassed the MIL-53(Al) sample in previous studies. Besides, the N2 adsorption test was performed and the N2 adsorption capacity was deteriorated in MIL-53(Al)-Mn3 with the highest content of Mn2+. The isotherm adsorption results of pure CO2 and N2 adsorption at 273 K were well correlated with the Sips isotherm model. The selectivity of CO2/N2 was calculated through the ideal adsorption solution theory, which is significantly promoted in MIL-53(Al)-Mn 3 and 2 at 1 atm and 273 K. The higher selectivity was achieved in MIL-53(Al)-Mn 3 and 2. These MOFs could provide promising adsorbents for CO2 storage and CO2/N2 separation.