Water boosted CO2/C2H2 separation in L-arginine functionalized metal—organic framework

The separation of CO2/C2H2 mixture by CO2-selective sorbents is an energy-efficient C2H2 purification technique, but is strategically challenging due to their similar molecular size and physicochemical properties. Meanwhile, water is inevitable in CO2/C2H2 mixture and it is usually a significant barrier because of its competitive adsorption with CO2. To address this challenge, herein, we report the first example of metal—organic framework (MOF) that exhibits water-boosted CO2 adsorption and CO2/C2H2 separation by anchoring L-arginine (ARG) on the Zr6 cluster of MOF-808. The CO2 affinity and capacity in the resulting MOF-808-ARG are markedly facilitated by the presence of water, while the C2H2 adsorption is significantly suppressed. Specifically, CO2 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 CO2/C2H2 selectivity of 1,180 under zero coverage. Breakthrough experiments reveal that CO2/C2H2 mixture can be completely separated and the result of mass spectrometry indicates that the C2H2 purity in the outlet is up to 99.9%. In situ infrared (IR) results and density functional theory (DFT) calculations reveal the water-promoted CO2 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 CO2 adsorption. This work provides a new paradigm by transforming the negative effects of water into positive ones for CO2/C2H2 separation.