Regulating C2H2/CO2 adsorption selectivity by electronic-state manipulation of iron in metal-organic frameworks
Cheng‐Xia Chen, Tony Pham, Kui Tan, Rajamani Krishna, Pui Ching Lan, Longfei Wang, Songbo Chen, Abdullah M. Al‐Enizi, Ayman Nafady, Katherine A. Forrest, Haiping Wang, Sicheng Wang, Chuan Shan, Lei Zhang, Cheng‐Yong Su, Shengqian Ma
Abstract
The separation of C2H2 from C2H2/CO2 mixture is of great importance, yet highly challenging in the petrochemical industry due to their similar physicochemical properties. While open-metal sites (OMSs) in metal-organic frameworks (MOFs) are known to possess high affinity toward C2H2, its selective adsorption performance regulated by the electronic state of the same OMSs remains unexplored. Here, we report a metal electronic-state manipulation approach to construct a pair of isostructural Fe-MOFs, namely LIFM-26(Fe[II]/Fe[III]) and LIFM-27(Fe[III]) with different Fe[II] or Fe[III] oxidation states on the Fe centers, which display mixed-valent Fe[II]/Fe[III] centers in the former and sole Fe[III] centers in the latter. Remarkably, LIFM-26(Fe[II]/Fe[III]) shows significantly enhanced C2H2 uptake capacity than LIFM-27(Fe[III]), attested by adsorption isotherms and IAST calculations, as well as simulated and experimental breakthrough experiments. Furthermore, in situ infrared (IR) and molecular calculations unveil that the presence of Fe[II] in LIFM-26(Fe[II]/Fe[III]) results in stronger Fe[II]–C2H2 interactions than Fe[III]–C2H2, which plays a key role in the C2H2/CO2 separation.