Enhanced selective CO2 adsorption on polyamine/MIL-101(Cr) composites

The global climate change induced by greenhouse gases has stimulated active research for developing efficient strategies to mitigate CO2 emission. In the present study, we prepared a series of polyamine/ metal-organic framework (MOF) composites as highly selective CO2 adsorbents from a CO2/N-2 mixture, which is relevant to CO2 capture in flue gas. We show that loading polyethyleneimine (PEI) into MIL101( Cr) frameworks can significantly enhance the selective CO2 adsorption capacity at low pressure and ambient temperature. Further, the comparative study reveals that both the particle size of the MOF and the molecular-weight of PEI play an important role in the CO2 capture ability. Regarding the particle size, smaller MIL-101(Cr) particles can facilitate the loading of PEI into the inner pores and result in lower surface area/pore volume. Thus, the resulting PEI/MIL-101(Cr) composites possess lower CO2 adsorption capacity, but are compensated by higher selectivity of CO2 over N-2. On the other hand, lower molecular-weight linear PEI could readily diffuse into the inner pores and effectively block the N-2 adsorption. As a result, the as-prepared A-PEI-300 sample in this work exhibits an excellent CO2 uptake of 3.6 mmol g(-1) and ultrahigh CO2/N-2 selectivity at 0.15 bar and 25 degrees C. In contrast, the higher molecular-weight branched PEI is advantageous at elevated temperature, since the composites can retain high CO2 adsorption capacity owing to the large amount of primary amine groups. Overall, polyamine/MOF composites are shown to be good candidate adsorbents for CO2 capture from flue gas. To achieve the optimal CO2 capture ability, comprehensive optimization of the polyamine and MOF structures should be performed.