High dispersion of polyethyleneimine within mesoporous UiO-66s through pore size engineering for selective CO₂ capture

As a result of the low partial pressure of CO₂ in most industrial waste gases, capturing CO₂ especially at low pressure was a priority. A facile method was utilized to build mesoporous UiO-66s with adjustable pore sizes via crystal defect engineering. The mesopores were generated through the removal of instable Cu clusters and lauric acid after reaction. The pore sizes could be controlled via adjusting the molar ratios of Cu²⁺ to Zr⁴⁺. Moreover, these meso-type UiO-66 MOFs reserved the stability after washing by HCl solution, which was more suitable for modification in harsh environment and CO₂ capture from flue gases or biogases. The most suitable dispersion of appended polyethyleneimine (PEI) inside pores was then achieved via the controllable pore sizes for CO₂ capture. The active –NH₂ from incorporated PEI could interact with CO₂ to enhance the uptake at low pressure and improve adsorption selectivities of CO₂ over N₂ and CH₄. The high dispersion of PEI also allowed guest molecules to interact with more active sites, which enhanced the affinity between CO₂ and frameworks. The strong interaction between 50PEI@meso-UiO-66-0.2Cu and CO₂ was confirmed by higher isosteric heats of adsorption (Q_st). Even so, the CO₂ uptake of sample was without drop after five cycles, and the sample could be regenerated under a mild condition.