(660d) Ultrathin Gas-Sieving Carbon Molecular Sieve Membranes with Modulated Pore-Size Distribution By Room-Temperature Functionalization

Carbon molecular sieves (CMS) can be synthesized with a narrow pore size distribution, yielding attractive sieving performances with a sub-angstrom resolution in molecular differentiation.^1–3 However, the permeance of the CMS membranes remains low due to the micron-thick selective layer. It is challenging to reduce the thickness below 1 μm without incorporating pinhole defects which compromises the molecular selectivity. Moreover, currently, there is no room temperature pore modification route to tune the molecular selectivity from the CMS membranes. Most of the functionalization methods have been only demonstrated at a high temperature (>500 ºC), increasing the sophistication of membrane fabrication.

Herein, 100 – 200 nm CMS films were fabricated in facile transfer and masking techniques,⁴ which prevented the infiltration of the CMS precursor in the pores of the membrane support. The 100-nm-thick CMS film yielded attractive gas-sieving performances with H₂ permeance reaching up to 3060 gas permeation units (GPU) with corresponding H₂/CH₄ selectivity of 18 at 150 ^oC. Furthermore, a rapid and highly-tunable post-synthetic modification method based on room temperature ozone treatment was developed. The room-temperature oxygen functionalization could shrink the CMS micropores by a fraction of an angstrom, improving H₂/CH₄ and H₂/CO₂ selectivities by several-fold. The optimized membranes yielded H₂ permeance of 507 GPU and H₂/CH₄ selectivity of 50.7. Other membrane yielded H₂ permeance of 453 GPU and H₂/CH₄ selectivity of 106.

References

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(4) Huang, S.; Villalobos, L.F.; Babu, D. J.; He, G.; Li, M.; Züttel. A.; Agrawal, K. V. Ultrathin Carbon Molecular Sieve Films and Room-temperature Oxygen Functionalization for Gas-sieving. ACS Appl. Mater. Interfaces 2019, 11, 16729-16736.