Mechanochemical synthesis of a robust cobalt-based metal-organic framework for adsorption separation methane from nitrogen

Efficient capture dilute methane (CH4) from nitrogen (N-2) is of significant importance in both environment and economical aspects. However, CH4/N-2 separation is still a great challenge in gas separation field limited by their close physical properties. Herein, we developed the mechanochemical synthesis of a cobalt-based pillar-layer metal-organic framework, Co(AIP)(BPY)(0.5), for adsorption separation of CH4/N-2 mixture. This synthetic method allowed Co(AIP)(BPY)(0.5) accessible rapidly and sustainably at the gram scale. By varying the grinding time, a series of mechanochemically synthesized Co(AIP)(BPY)(0.5) products were obtained and CO2 adsorption measurements confirmed that Co(AIP)(BPY)(0.5)-25 obtained by grinding for 25 min had the highest porosity. Then CH4/N-2 adsorption and separation of the resulting Co(AIP)(BPY)(0.5)-25 was studied. CH4 and N-2 uptakes of Co (AIP)(BPY)(0.5)-25 were 1.03 and 0.26 mmol/g at 298 K and 5 bar, showing preferential adsorption of CH4 over N-2 and the CH4/N-2 selectivity with 7.3. Meanwhile, the excellent potential separation ability of CH4/N-2 mixtures with different concentrations on Co(AIP)(BPY)(0.5)-25 was confirmed by simulated breakthrough experiments. Molecular simulations revealed that spheroidal CH4 molecules were located in the center of the pores while most of linear N-2 molecules were only distributed near the walls of the pores due to the difference in geometrical structures. This work provides an example of rapid mechanochemical synthesis of Co(AIP)(BPY)(0.5) within short time for separating CH4/N-2 mixture.