Probing bimodal sub-nanopores in carbon for ideal fast sieving separation of propylene/propane

Rigid molecular sieve is highly desirable in industrial gas separation, but persistently challenged by sluggish adsorption within inherent rigidity-confined narrow sieving pores. Herein, we report a rigid carbon-based molecular sieve featuring ink-bottle bimodal sub-nanopores for the ideal fast sieving separation of propylene/propane mixture. The tailor-made narrow pore entrance, centered at 5.0 Å, affords precise sieving capacity for propylene over propane with a high selectivity exceeding 200. Concurrently, the larger cavity located at 6.4 Å allows the exceptional fast adsorption kinetics of propylene. The measured diffusion coefficient of propylene (4.2 × 10–3 s⁻¹) is one to two orders of magnitude higher than state-of-the-art rigid molecular sieves and comparable to the non-steric diffusion observed in mesoporous zeolite. High-purity C₃H₆ production (>99.2%) is achieved in breakthrough experiments through a single adsorption–desorption cycle. This study paves an avenue to unlock rigid molecular sieves toward advanced separation of challenging gas analogues.