CO2 capture and storage technologies have been adopted to eliminate anthropogenic CO2 emission. Compared with other methods, adsorptive separation technology using excellent adsorbents has attracted extensive attention for its operational flexibility and energy-efficient characteristics. Herein, we present a copper-based metal–organic framework, MOF-11, exhibiting highly efficient CO2/N2 (15:85, v/v) separation performance. There are two kinds of channels with different pore chemistries in the framework, in which dense Cu open metal sites (OMS) were found in channel I, while channel II had a narrower pore window size and was mainly decorated with −CH2 moieties from the organic ligands. At 298 K, the CO2 uptake value of MOF-11 was 4.63 mmol/g at 100 kPa and 2.92 mmol/g at 15 kPa, respectively, which was superior to many other reported MOF adsorbents. Molecular simulation indicated that CO2 dominantly occupied channel I due to the strong electrostatic interactions with the dense Cu OMS in channel I. In comparison, more N2 molecules were adsorbed into channel II through multiple weak van der Waals interactions with −CH2 moieties. Such a pore system gives MOF-11 high CO2/N2 selectivity (ca. 116 at 298 K). Moreover, the dynamic separation of CO2/N2 mixture gases on MOF-11 was further investigated by cyclic breakthrough experiments.
The separation of organic-organic azeotropic mixtures is important in the petrochemical, agrochemical, and pharmaceutical industries, which is energy-intensive by using the current distillation technology. Pervaporation process is energy-efficient for azeotropic separation, while lacks of high-performing membrane materials. In this work, to realize efficient separation of dimethyl carbonate/methanol azeotropic mixtures, a benchmarked membrane, polydimethylsiloxane (PDMS), was incorporated by zeolites with tunable pore chemistry. Specifically, MFI-type zeolite was grafted by alkyl chains with different carbon numbers (C 1 , C 4 , C 8 ), thereby providing tunable transport channels for organic molecules. Based on systematic characterizations (e.g., sorption and LF-NMR) and permeation test, we found that the organophilic alkyl chain can trap organic molecules into the zeolitic pores while may also hinder the organic diffusion through the zeolite due to the steric hindrance effect. The PDMS mixed-matrix membrane (MMM) with optimized C 1 -grafted MFI loading as high as 50 wt% exhibited separation factor of 3.6, and permeation flux of 11.5 kg m −2 h −1 for 30 wt% DMC-methanol azeotropic mixture at 40 °C. With slightly higher separation factor, the flux of PDMS MMM is 1.5-fold higher than that of the pure PDMS membrane. This work highlights the critical role of filler pore chemistry on the solution-diffusion transport and thus performance enhancement of MMM.
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