CO2 adsorption mechanisms on MOFs: a case study of open metal sites, ultra-microporosity and flexible framework

Abstract

The hazardous emission of CO₂ in the atmosphere is a concerning topic when addressing climate change issues. The mitigation of this greenhouse gas has attracted great attention in the realm of a sustainable economy, especially regarding the design of novel CO₂ capture technologies. Metal–organic frameworks (MOFs), a class of hybrid porous materials, stand out as efficient carbon capture and sequestration (CCS) materials, which have a CO₂ capacity of similar range or superior to the standard employed adsorbents, such as zeolite 13X and activated carbon. Taking into account the promising future of MOFs as CO₂ adsorbents, it is therefore of utter importance to understand the CO₂ adsorption mechanisms in these porous materials, which can contribute to further improvement of their performance. In this review, we explore the CO₂ adsorption mechanisms of diverse MOFs, namely MOF-74-Mg, HKUST-1, SIFSIX-3-M (M = Fe, Co, Ni, Cu, Zn), and ZIF-8. These materials show interesting features as open metal sites, ultra-microporosity, and flexible framework, which are present in the majority of MOFs used for this application. Studies regarding their preferential adsorption sites, water stability, CO₂–MOF complex configuration, CO₂ adsorption dynamics, bonding angle, decomposition mechanism, and swing effects were addressed in this contribution.