Precise tuning of pore size distribution in amorphous carbon molecular sieves at the sub-angstrom scale via a synergic mechanism of pore-making and shrinking for separating similar gases

Abstract

Developing highly efficient adsorption technology as an alternative to the currently energy-intensive cryogenic distillation for the separation of alkenes from alkanes is highly desirable in the petrochemical industry. However, this endeavor faces significant challenges due to the similar physicochemical properties and nearly identical molecular sizes of these compounds. Herein, we present a novel mechanism to control the pore size distribution (PSD) in amorphous carbon materials for fabricating a new generation of granular carbon molecular sieves. Rice grains are selected as the carbon source, and the rice-derived carbon molecular sieves (RCMS-x) are successfully prepared through a synergistic mechanism of pore-making and pore-shrinking forces induced by thermal radiation. The resulting samples are characterized using combined techniques to reveal the microdomain structure evolution in RCMS-x under thermal radiation. The sample RCMS-800 exhibits selective adsorption of C₃H₆ while nearly repelling C₃H₈, demonstrating a molecular cognition accuracy of 0.44 Å. Its uptake ratio of C₃H₆ to C₃H₈ reaches a record high of 145.4 at 298 K and 100 kPa, which is comparable to the separation performance of advanced metal–organic frameworks (MOFs). A new structural model for the PSD of amorphous carbon materials is established to clearly elucidate how amorphous RCMS-x precisely sieves C₃H₆ from C₃H₈ with 0.44 Å resolution. The underlying principle for efficiently tuning the PSD in amorphous RCMS-x through the synergistic action mechanism is logically illustrated. The exceptional selectivity, stability, and low cost make RCMS-800 highly promising for practical applications.