Defective UiO-66-NH2 monoliths for optimizing CO2 capture performance

Abstract

Zirconium-based metal–organic frameworks (Zr-MOFs) have been considered promising sorbents for guest adsorption owing to their high porosity, structural and chemical versatility, and exceptional stability. Nevertheless, issues with the powder and the modest CO2 adsorption remain as major challenges for their use in industrial processes. Herein, a series of defective monolithic UiO-66-NH2 xerogels (G66-NH2-X) are prepared via adjusting the modulator concentration, featuring tunable porous structure, simple and scalable preparation process and high space–time yield. With a change in the modulator concentration, the missing linker deficiency varies from 0.57 to 1.80 per secondary building unit. The porosity and CO2 uptake capacity of the adsorbents are strongly affected by the defect concentration. At 25 ℃ and 1 bar, the defective G66-NH2-12 exhibits optimal CO2 adsorption capacity of ∼ 2.50 mmol/g and CO2/N2 ideal adsorbed solution theory selectivity of ∼ 33, exceeding those of many other CO2 benchmark adsorbents. Moreover, the G66-NH2-X adsorbents can be easily regenerated with obtained lower isosteric heat of adsorption (Qst) and show excellent sustainability of up to ∼ 99% even after five adsorption–desorption cycles. This provides a solid foundation for the development of defective granular G66-NH2-X adsorbents as future CO2 adsorption and separation media.