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

Abstract

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 (Qst). Even so, the CO2 uptake of sample was without drop after five cycles, and the sample could be regenerated under a mild condition.