Synergetic enhancement of CO2 direct air capture with monoethanolamine-impregnated MIL-101(Cr) MOFs

Abstract

To mitigate the greenhouse effect caused by the increase of CO2 concentration in the atmosphere, research attention has shifted towards CO2 Direct Air Capture (DAC) techniques. Despite that metal organic frameworks (MOFs) functionalized with various amines are promising to serve as suitable CO2 DAC adsorbent, there is few, if any, reports utilizing monoethanolamine (MEA), the most commonly employed in amine scrubbing technologies, as adsorption active sites. Herein, we have successfully impregnated MEA into MIL-101(Cr), resulting in a notably high CO2 adsorption capacity up to 1.20 mmol/g and an impressive amine utilization efficiency of 23% under low CO2 partial pressure (400 ppm). This improved capture efficiency can be attributed to the presence of hydroxyl groups, which alter the reaction dynamics between CO2 and amine groups. DAC simulation studies predominantly utilize synthetic air to replicate the DAC performance of adsorbents, yet precisely emulating air with artificially mixed gases remains an insurmountable challenge. To overcome this, we designed a system capable of testing DAC performance and employed MEA-impregnated MIL-101(Cr) for DAC testing. The adsorbent achieved pseudo-equilibrium DAC capacities of 2.15 and 1.50 mmol/g under humid and dry conditions, respectively, signifying an enhancement in DAC performance under humid condition. Our study offers novel perspectives for DAC adsorbent research, encompassing both material and equipment considerations.