Fine‐Tuning Sub‐Ångström Pores in Carbon Molecular Sieve Membranes via UV‐Crosslinking Induced Super‐Network Polyimide Precursors for Ultra‐Selective H ₂ Purification

ABSTRACT Achieving precise customization and structural regulation of sub‐Ångström pores of Carbon molecular sieve membranes (CMSMs) remains challenging. In this study, CMSMs with ultra‐high H 2 /CH 4 separation performance were developed by a UV induced super‐crosslinking network polyimide precursor, which was formed by click reaction through an imide intermediate that contains C≡CH and the SH as functional end groups. The as‐formed polyimide contains C═C─S in each repeat unit of the polyimide which can be crosslinked using UV light via the [2+2] reaction and form molecular “stitches” with a super‐crosslinking network. The cross‐linking node density can be easily adjusted by the UV irradiation time (0–30 min). During pyrolysis, the dimensions of the connecting interior pore necks for sub‐Ångström pores can be fine‐tuned (4.0±0.3 Å), promoting the formation of a higher concentrated (4%–8%) sub‐4 Å pores. The optimized CMS‐30 membrane demonstrates outstanding gas separation performance, with H 2 permeability of 2930 Barrer and remarkable selectivity for H 2 /CH 4 (4651), surpassing the Robeson upper bounds and outperforming most reported CMSMs. This photo‐induced super‐crosslinking network precursor method provides a versatile strategy for high‐performance CMSM by sub‐nanometer precision engineering of CMSMs.