Pore Environmental Modification by Alkoxy Groups in Pore-Space-Partitioned Metal-Organic Frameworks to Achieve Gas Uptake-Selectivity Balance.

Abstract

Due to the trade-off barrier between high storage capacity and high selectivity, the controllable and systematic design of metal-organic frameworks (MOFs) aiming at performance optimization is still challenging. Herein, considering the effectiveness of alkoxy group functionalization and a pore-space partition strategy, a series of rigid Mg-pacs-MOFs (SNNU-10-n, n = 1-6) with flexible side chains are built for the first time, realizing systematic pore environmental modification. The steric hindrance effects, electron-donating ability, and the flexibility of alkoxy groups are considered as key factors, which lead to a regular change of gas adsorption capacity and selectivity. Notably, methoxy-modified SNNU-10-1 with moderately high storage capacities of C2H2 (139.4 cm3 g-1), C2H4 (100.4 cm3 g-1), CO2 (105.0 cm3 g-1), and high selectivity values for equimolar C2H2/CH4 (431.8), C2H4/CH4 (164.2), and CO2/CH4 (16.1) mixture separation at 273 K and 100 kPa achieves an ideal gas uptake-selectivity balance. Breakthrough experiments verified that it could effectively separate the above-mentioned mixtures under ambient conditions, and GCMC simulation provides a deep understanding of methoxy group functionalization. Undoubtedly, this work not only realizes controllable regulation of gas adsorption behavior but also proves the validity of improving selectivity by alkoxy groups in those platforms with high gas-uptake potential to overcome the trade-off barrier.