(716c) Sub-200-Nm Thick Carbon Molecular Sieve Membranes and Modulation of Pore-Size-Distribution By Room Temperature Oxygen Functionalization

Carbon molecular sieves (CMS), hosting slit-like nanopores formed by a disordered packing of aromatic carbon strands driven by the volume exclusion effects, have emerged as a highly promising membrane material.^1–3 CMS can be synthesized with a tunable pore-size-distribution, yielding a high molecular selectivity with a sub-angstrom resolution in molecular differentiation. However, the permeance of the CMS membranes remains low due to the micron-thick selective layer, typically afforded in such films. It is challenging to reduce the thickness below 1 μm without incorporating pinhole defects which compromises the molecular selectivity. To the best of our knowledge, CMS films with thickness below 300 nm, yielding attractive gas separation performance have not been reported. Moreover, currently, there is no room temperature pore modification route to tune the molecular selectivity from the CMS membranes.

In this presentation, I will discuss two membrane fabrication routes, namely transfer and masking techniques,⁴ leading to 100 – 200 nm CMS film by preventing 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 (of the order of 15 sec) and highly-tunable post-synthetic modification method based on room temperature ozone treatment will be discussed. Gas selectivity could be improved by several folds by shrinking the CMS micropores by a fraction of an angstrom. 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

(1) Rungta, M.; Wenz, G. B.; Zhang, C.; Xu, L.; Qiu, W.; Adams, J. S.; Koros, W. J. Carbon Molecular Sieve Structure Development and Membrane Performance Relationships. Carbon N. Y. 2017, 115, 237–248.

(2) Adams, J. S.; Itta, A. K.; Zhang, C.; Wenz, G. B.; Sanyal, O.; Koros, W. J. New Insights into Structural Evolution in Carbon Molecular Sieve Membranes during Pyrolysis. Carbon N. Y. 2019, 141, 238–246.

(3) Koh, D.-Y.; McCool, B. A.; Harry W., D.; Ryan P., L. Reverse Osmosis Molecular Differentiation of Organic Liquids Using Carbon Molecular Sieve Membranes. Science. 2016, 353.

(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. Submitted, under review.