Oxygen-Selective Adsorption Property of Ultramicroporous MOF Cu(Qc)2 for Air Separation

In this work, the O2/N2 adsorption behavior of ultramicroporous MOF Cu(Qc)2, with preferential adsorption of O2 over N2, was investigated for the first time. Cu(Qc)2 was prepared using a room-temperature synthesis strategy and then characterized. High-pressure isotherms of O2 and N2 were measured at different temperatures. The molecular simulation was used to reveal the adsorption mechanism of O2 and N2 on the copper sites of Cu(Qc)2. Inverse gas chromatography (IGC) experiments were applied to measure surface free energy for O2 and N2 adsorption for evaluation of the affinity between adsorbates O2/N2 and Cu(Qc)2. Results showed that the adsorbed amounts of O2 on Cu(Qc)2 increased significantly with pressure rising, reaching as high as 4.48 mmol/g at 259 K and 50 bar, while that of N2 increased slowly to 0.98 mmol/g. The uptake ratio of O2/N2 on Cu(Qc)2 reached 4.62 at 298 K and 50 bar. The IAST-predicted O2/N2 (21:78 v/v) selectivity of Cu(Qc)2 reached 7 at 259 K and 50 bar. The ultramicroporous MOF Cu(Qc)2 is the potential for separation of O2/N2 from the air.