A New Approach to Enhancing the CO2 Capture Performance of Defective UiO-66 via Post-Synthetic Defect Exchange

Abstract

Zirconium-based metal-organic frameworks (Zr-MOFs) are a subclass of MOFs known for their remarkable stability, especially in the presence of water. This makes them extremely attractive for practical applications, including CO<sub>2</sub> capture from industrial emission sources; however, the CO<sub>2</sub> adsorption capacity of Zr-MOFs is moderate compared to that of the best performing MOFs reported to date. Functionalization of Zr-MOFs with amino groups has been demonstrated to increase their affinity for CO<sub>2</sub>. In this work, we assessed the potential of post-synthetic defect exchange (PSDE) as an alternative approach to introduce amino functionalities at missing-cluster defective sites in formic acid modulated UiO-66. Both pyridine-containing (picolinic acid and nicotinic acid) and aniline-containing (3-aminobenzoic acid and anthranilic acid) monocarboxylates were integrated within defective UiO-66 with this method. Non-defective UiO-66 modified with linkers bearing the same amino groups (2,5-pyridinedicarboxylic acid and 2-aminoterephthalic acid) were prepared by classical post-synthetic ligand exchange (PSE), in order to compare the effect of introducing functionalities at defective sites versus installing them on the backbone. PSDE reduces the porosity of defective UiO-66, but improves both the CO<sub>2</sub> uptake and the CO<sub>2</sub>/N<sub>2</sub> selectivity, whereas PSE has no effect on the porosity of non-defective UiO-66, improving the CO<sub>2</sub> uptake but leaving selectivity unchanged. Modification of defective UiO-66 with benzoic acid reveals that pore size reduction is the main factor responsible for the observed uptake improvement, whereas the presence of nitrogen atoms in the pores seems to be beneficial for increasing selectivity. <br>

Eco-Friendly Fabrication of a Highly Selective Amide-Based Polymer for CO2 Capture

“…20,21 Similar results where precursors containing amino group improved the interaction between CO 2 molecules and the pore wall contributed to the improved selectivity have been reported elsewhere. 8,[33][34][38][39][40] The selectivity of HCP-MAAM-2 was found to be 53 at 273 K and dropped to 38 at 298 K. The corresponding purity of CO 2 stream at the two temperatures was 91% and 88% respectively. As the temperature decreases, adsorption capacity increases, while selectivity increases, which is a common adsorption behaviour.…”

Emerging porous materials for carbon dioxide adsorptive capture: progress and challenges

“…44 We note that both ultramicroporosity and amine groups lead to the formation of efficient sandwich-like CO 2 binding sites, boosting CO 2 capacity. Unlike the above linker-functionalization strategy, A. Koutsianos et al 45 used a post-synthetic defect exchange technique to introduce nitrogen moieties, revealing that defective nitrogen sites have great potential in boosting CO 2 capacity with a 25-50% improvement. Similarly, another study used a mixed-linker strategy to create amino-defective UiO-66(Zr).…”