(278d) Interfacial Hard Templating of Hierarchically Structured, Ultrathin Carbon Molecular Sieve Membranes

Inorganic membrane materials such as carbon molecular sieves (CMS) show promise in transforming gas and liquid separations, however, they struggle from the well-known trade-off between molecular selectivity and permeability^1,2. This motivates efforts to reduce defect-free membrane thickness while simultaneously tailoring membrane texture and function. In this talk, we present a versatile silica colloidal crystal based nanocasting approach^3,4 that yields ultra-thin (15-300 nm) microporous polyimide-derived CMS self-supported on three-dimensionally ordered mesoporous (3DOm) carbon layers. We show how the large area associated with the template-replica interface in our 3DOm carbon films offers a previously unexploited handle for simultaneously tailoring microstructure of the replica phase. Specifically, we elucidate how temperature-tunable silanol surface chemistry of the template can be used to tailor the graphitic character (e.g., graphitic content relative to turbostratic carbon) of CMS replicas under mild carbonization conditions (600-900 ^oC) and in the absence of specific metal catalysts. The interfacial origin of this effect is confirmed through studies showing a sensitivity of graphitic character to film thickness. Studies also show enhancement of graphitic character in thin carbon films as compared with untemplated carbon molecular sieves, with maximum sensitivity near the beginning of the carbonization process (around 600 ^oC). We hypothesize that the interface-mediated tunability of the replica graphitic character derives from adsorption-induced orientation of pyromellitic dianhydride-co-4,4’-oxydianiline (PAA) precursors once the surface silanol density is reduced to the point of approximate registry (e.g., hydrogen-bonding) with PAA molecular dimensions. Taken together, this templating approach offers a strategy for multi-scale control over film structure. Using permeation of small gases (e.g., CO₂, N₂, O₂, H₂), we will demonstrate how the template interface-mediated structural control and reduction of film thickness can be exploited for high-flux, high selectivity separations.

References

[1] H. Foley, Micropor.Mater., 4 (1995), 95.

[2] L. Robeson, J. Memb. Sci., 62 (1991), 2.

[3] Z. Tian, M. A. Snyder, Langmuir, 30 (2014), 12411.

[4] M. Sharma, M. A. Snyder, in preparation.

[5] M. Inagaki, New Carbons, Elsevier, (2014).