Enhancing gas selectivity in thin-film composite carbon molecular sieve membranes by platinum sputtering

Abstract

We present a novel approach to significantly boost gas-pair selectivity of thin-film composite (TFC) carbon molecular sieve (CMS) membranes by sputtering platinum on the surface of the CMS precursor polymer prior to pyrolysis. A polyimide of intrinsic microporosity (PIM-PI), 6FDA-HTB, was selected as the CMS precursor which had previously been shown to transform into an excellent CMS membrane material at moderate pyrolysis temperatures (550–600 °C). Deposition of Pt at high ion currents combined with subsequent pyrolysis at 550 °C leads to the development of an ultrathin (10–20 nm thick) Pt/CMS intermix layer consisting of a CMS matrix with a large volume fraction of embedded, fused Pt nanoparticles. The Pt phase seems to stabilize the micropores of the intermixed CMS phase as well as limit the undesired impact of defects leading to a dramatic enhancement of gas-pair selectivity of the modified TFC CMS membranes (e.g. H₂/CH₄ > 1100, CO₂/CH₄ ∼100, O₂/N₂ ∼ 11) which represent improvements of 3300, 370, and 100 % in comparison to the non-Pt-sputtered CMS control membranes. This novel, simple and effective procedure may be extendable to other types of CMS polymer precursors, membrane supports, alternative sputtering metals and the deposition parameters can be easily tuned to balance the membrane permeance against the desired selectivity.