Highlighting the Anti-Synergy between Adsorption and Diffusion in Cation-Exchanged Faujasite Zeolites

Steering diffusion selectivity of chemical isomers within aligned nanochannels of metal-organic framework thin film

The movement of molecules (i.e. diffusion) within angstrom-scale pores of porous materials such as metal-organic frameworks (MOFs) and zeolites is influenced by multiple complex factors that can be challenging to assess and manipulate. Nevertheless, understanding and controlling this diffusion phenomenon is crucial for advancing energy-economic membrane-based chemical separation technologies, as well as for heterogeneous catalysis and sensing applications. Through precise assessment of the factors influencing diffusion within a porous metal-organic framework (MOF) thin film, we have developed a chemical strategy to manipulate and reverse chemical isomer diffusion selectivity. In the process of cognizing the molecular diffusion within oriented, angstrom-scale channels of MOF thin film, we have unveiled a dynamic chemical interaction between the adsorbate (chemical isomers) and the MOF using a combination of kinetic mass uptake experiments and molecular simulation. Leveraging the dynamic chemical interactions, we have reversed the haloalkane (positional) isomer diffusion selectivity, forging a chemical pathway to elevate the overall efficacy of membrane-based chemical separation and selective catalytic reactions.

Insights into the thermodynamic-kinetic synergistic separation of propyne/propylene in anion pillared cage MOFs with entropy-enthalpy balanced adsorption sites

Propyne/propylene (C3H4/C3H6) separation is an important industrial process yet challenged by the trade-off of selectivity and capacity due to the molecular similarity. Herein, record C3H4/C3H6 separation performance is achieved by fine tuning the pore structure in anion pillared MOFs. SIFSIX-Cu-TPA (ZNU-2-Si) displays a benchmark C3H4 capacity (106/188 cm3 g-1 at 0.01/1 bar and 298 K), excellent C3H4/C3H6 IAST selectivity (14.6-19.3) and kinetic selectivity, and record high C3H4/C3H6 (10/90) separation potential (36.2 mol kg-1). The practical C3H4/C3H6 separation performance is fully demonstrated by breakthroughs under various conditions. 37.8 and 52.9 mol kg-1 of polymer grade C3H6 can be produced from 10/90 and 1/99 C3H4/C3H6 mixtures. 4.7 mol kg-1 of >99% purity C3H4 can be recovered by a stepped desorption process. Based on the in situ single crystal analysis and DFT calculation, an unprecedented entropy-enthalpy balanced adsorption pathway is discovered. MD simulation further confirmed the thermodynamic-kinetic synergistic separation of C3H4/C3H6 in ZNU-2-Si.