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

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/N-2 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.

Automated summary

The study introduces a new generation of anion-pillared metal-organic frameworks (MOFs) that can be used for capturing CO2 from flue gas. The optimized design of TIFSIX-Cu-TPA shows high CO2 capacity, excellent CO2/N-2 selectivity, high thermal and chemical stability, and moderate adsorption heat for easy regeneration. Breakthrough experiments under various process conditions demonstrate the practical separation performance of the synthesized MOFs, achieving highly selective separation and sustained outstanding performance even under high humidity and multiple process cycles. In situ CO2 dosed single crystal structure and theoretical calculations reveal the molecular mechanism of CO2 adsorption in MOFs, highlighting the presence of two separate binding sites for CO2 in small and large cages, contributing to the high performance of the newly designed MOFs.