The large-scale anthropogenic carbon dioxide (CO₂) emission has aroused world-wild concerns nowadays. One of the key steps in carbon mitigation is CO₂ capture from stationary CO₂ emission sources such as power plants. Metal-organic frameworks (MOFs) are coordination polymers consisting of metal ions or clusters as nodes and organic ligands as spacers. The study of CO₂ capture using MOFs as adsorbents is booming because of their ultra-high surface area, uniform yet tunable pore size, and versatile chemical compositions. However, several issues still exist preventing their large scale applications, such as selectivity, stability, and material cost. In the first part of this talk, I will introduce our group’s work in circumventing the above problems through rational ligand design and crystal engineering based on UiO-66-type MOFs, with the emphases on 1) mitigating moisture interference, 2) increasing CO₂ selectivity, 3) strengthening materials stability, and 4) reducing material cost. The synthesized MOFs have undergone various tests for their eligibility in CO₂ capture, such as stability, gas sorption, and breakthrough tests. We have identified several promising MOF candidates with the CO₂ capture performance equivalent or even better than the industrial benchmark material zeolite 13X. These materials will be integrated into the next-level process and system research.

Besides adsorption-based gas separation, membrane-based gas separation has also been greatly developed in recent years. In order to combine the merits of both polymeric and inorganic membranes, mixed matrix membranes (MMMs) were invented by dispersing porous fillers into continuous polymeric matrices hoping to increase the permeability and selectivity of the resultant membranes while preserving the properties of good mechanical strength and processability of the polymeric matrices. In the second part of this talk, I will introduce our work in preparing MMMs containing lamellar MOFs or covalent organic frameworks (COFs) fillers with high-aspect-ratio, which exhibit good gas separation performance because of the increased tortuosity of gas permeation paths imposed by lamellar fillers. Lastly, I will discuss the direct fabrication of ultrathin membranes composed of 2D graphene oxide (GO) nanosheets. Because of their ultra-small thickness and precisely tunable pore size and functionality, these novel membranes may demonstrate unprecedented gas separation performance with wide applications in clean energy and environmental sustainability.