Large-area metal–organic framework (MOF) single crystal membrane materials hold great appeal in gas separation field due to their outstanding separation selectivity and permeability. Nevertheless, it is currently difficult to prepare MOF single crystals large enough for gas separation tests owing to the limited manufacturing processes. In this work, we fabricate a self-supporting MOF single crystal (Co-btec SC) membrane with 0.3 × 0.1 cm 2 dimension via a facile supersaturation synthesis strategy. Benefiting from the one-dimensional (1D) transmission pathway and three-dimensional (3D) connection network, the obtained Co-btec SC has ultra-high permeability of 47,647 Barrer. Besides, the H 2 O molecules firmly filled in the pore channels greatly improve the affinity and solubility for CO 2 , and thus Co-btec SC yields CO 2 preferential permeation in CO 2 /H 2 mixture with superior CO 2 /H 2 selectivity of 18.79. In addition, the Co-btec SC shows dramatic high-temperature and high-humidity separation stabilities. To demonstrate the versatility of this strategy, we also successfully fabricated hydrogen-bonded organic framework single crystals (HOF SCs) with the size of about 0.4 cm. This supersaturation strategy opens a new way to fabricate the large-area MOF single crystal membranes.
Hydrogen/carbon dioxide (H 2 /CO 2 ) separation for sustainable energy is in desperate need of reliable membranes at high temperatures. Molecular sieve membranes take their nanopores to differentiate sizes between H 2 and CO 2 but have compromised at a marked loss of selectivity at high temperatures owing to diffusion activation of CO 2 . We used molecule gatekeepers that were locked in the cavities of the metal-organic framework membrane to meet this challenge. Ab initio calculations and in situ characterizations demonstrate that the molecule gatekeepers make a notable move at high temperatures to dynamically reshape the sieving apertures as being extremely tight for CO 2 and restitute with cool conditions. The H 2 /CO 2 selectivity was improved by an order of magnitude at 513 kelvin (K) relative to that at the ambient temperature.
Surface grafting modification was proposed to improve the surface polarity of polyacrylonitrile hollow fiber-supported polydimethylsiloxane (PDMS) membrane. The initiator 3-aminopropyltriethoxysilane containing one amine group was integrated into PDMS, and polyvinyl pyrrolidone (PVP) with strong polarity was connected to the surface by reacting with amine groups. Surface grafting modification was proven on X-ray photoelectron spectroscopy. The sharp decrease (from ∼98° to ∼28°) in water contact angle of the PDMS membrane indicated the significant improvement in surface polarity after the modification. The surface roughness of the PDMS membrane increased with the modification, and the PDMS surface immersed for 40 s was almost covered with PVP. The membrane immersed in PVP solution for 10 s improved CO 2 /H 2 , CO 2 /CH 4 , and CO 2 /N 2 selectivities . While CO 2 permeance slightly decreased from ∼2500 GPU to ∼2440 GPU. For the separation of CO 2 /CH 4 and CO 2 /N 2 mixed gases , all CO 2 /CH 4 and CO 2 /N 2 selectivities were improved after the modification. For the separation of CO 2 /H 2 mixed gas, CO 2 /H 2 selectivity was improved when the immersion time was below 30 s.
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