Water boosted CO2/C2H2 separation in L-arginine functionalized metal—organic framework
Hejin Zhu, Wenjuan Xue, Hongliang Huang, Lvyun Chen, Haoyu Liu, Chongli Zhong
Abstract
The separation of CO 2 /C 2 H 2 mixture by CO 2 -selective sorbents is an energy-efficient C 2 H 2 purification technique, but is strategically challenging due to their similar molecular size and physicochemical properties. Meanwhile, water is inevitable in CO 2 /C 2 H 2 mixture and it is usually a significant barrier because of its competitive adsorption with CO 2 . To address this challenge, herein, we report the first example of metal—organic framework (MOF) that exhibits water-boosted CO 2 adsorption and CO 2 /C 2 H 2 separation by anchoring L-arginine (ARG) on the Zr 6 cluster of MOF-808. The CO 2 affinity and capacity in the resulting MOF-808-ARG are markedly facilitated by the presence of water, while the C 2 H 2 adsorption is significantly suppressed. Specifically, CO 2 adsorption capacities in adsorption isotherm and breakthrough measurement are increased to 143% and 184%, respectively. In addition, the wet MOF-808-ARG exhibits the record CO 2 /C 2 H 2 selectivity of 1,180 under zero coverage. Breakthrough experiments reveal that CO 2 /C 2 H 2 mixture can be completely separated and the result of mass spectrometry indicates that the C 2 H 2 purity in the outlet is up to 99.9%. In situ infrared (IR) results and density functional theory (DFT) calculations reveal the water-promoted CO 2 adsorption mechanism that the formation of bicarbonate products in the presence of water is thermodynamically and kinetically more favorable than that without water. Moreover, MOF-808-ARG also possesses excellent water stability and excellent regeneration of CO 2 adsorption. This work provides a new paradigm by transforming the negative effects of water into positive ones for CO 2 /C 2 H 2 separation.