New-Generation Anion-Pillared Metal–Organic Frameworks with Customized Cages for Highly Efficient CO₂ Capture

Abstract

The rational design of porous materials for CO2 capture under realistic process conditions is highly desirable. However, trade-offs exist among a nanopore's capacity, selectivity, adsorption heat, and stability. In this study, a new generation of anion-pillared metal-organic frameworks (MOFs) are reported with customizable cages for benchmark CO2 capture from flue gas. The optimally designed TIFSIX-Cu-TPA exhibits a high CO2 capacity, excellent CO2/N2 selectivity, high thermal stability, and chemical stability in acid solution and acidic atmosphere, as well as modest adsorption heat for facile regeneration. Additionally, the practical separation performance of the synthesized MOFs is demonstrated by breakthrough experiments under various process conditions. A highly selective separation is achieved at 298–348 K with the impressive CO2 capacity of 2.1–1.4 mmol g−1. Importantly, the outstanding performance is sustained under high humidity and over ten repeat process cycles. The molecular mechanism of MOF's CO2 adsorption is further investigated in situ by CO2 dosed single crystal structure and theoretical calculations, highlighting two separate binding sites for CO2 in small and large cages featured with high CO2 selectivity and loading, respectively. The simultaneous adsorption of CO2 inside these two types of interconnected cages accounts for the high performance of these newly designed anionic pillar-caged MOFs.