Continuous H 2 /CO 2 separation via permselective membranes is highly sought after as pure H 2 plays a key role in H 2 economy. Aqueous nematic suspensions obtained by 1D dissolution of affordable sodium fluorohectorite allow for simple membrane fabrication by spray coating. The monolayer nanosheets have a uniform thickness of 1 nm and appreciable aspect ratio, thus self-assemble into defect-free membranes when applied onto porous mixed cellulose ester substrates. The perfectly textured restacking of individual nanosheets yields monodomain Bragg stacks with uniform interlayer space. By cation exchange with guanidinium cations, a uniform interlayer height tailored to 2.9 Å was obtained while micropores are formed between the loosely packed interlayer cations. As the interlayer height matches the kinetic diameter of H 2 and is significantly smaller compared to other relevant gas species, e. g. CO 2 , CH 4 , CO or N 2 , perfectly selective H 2 sieving may be obtained. In a Wicke-Kallenbach cell, a near-perfect separation of H 2 and CO 2 (4:1 ratio) at ambient conditions was obtained. The tortuous path created by the impermeable, large aspect ratio nanosheets reduces the permeance to disappointing 3 GPU (gas permeation units; 1 GPU = 10 −6 cm 3 cm −2 s −1 cmHg −1 ). While the separation mechanism playing on tortuous path has not been fully explored in this preliminary study, the permeance may be improved substantially in future studies by optimizing the roughness of the substrate, the aspect ratio of the nanosheets and the thickness of the membrane. • clay-based permselective membrane for efficient H 2 purification. • tailoring the interlayer height to 2.9 Å for size-sieving based H 2 /CO 2 separation. • membrane fabrication by simple spray-coating process and subsequent cation exchange. • aqueous fabrication based on silicate monolayer nanosheets for perfect ordering. • self-assembly into defect-free 1D crystalline monodomain Bragg stacks.
Federer et al. (Tue,) studied this question.