Amine-functionalized MIL-101 sorbents modified with alkali metal cations for enhanced CO2 capture and electroreduction conversion

Mitigating the rise of atmospheric carbon dioxide (CO 2 ) levels presents one of humanity’s significant challenges. Metal-organic frameworks (MOFs) have emerged as promising materials for CO 2 capture, owing to their unique chemical structure and operability. Many researchers have demonstrated that amination treatment can further enhance CO 2 adsorption performance. However, the relatively low capture efficiency and limited cycling stability of these materials continue to impede their development. Alkali metal cations exhibit high CO 2 adsorption capacities and can be incorporated into the MOF structure to significantly enhance CO 2 capture capacity and cycling stability. Therefore, we synthesized novel alkali metal ion-doped M−NH 2 −MIL−101 (M = Li, Na, K) adsorbents using a post-modification method, successfully anchoring alkali metal cations to carboxylate group sites within the MOFs framework. The integration of microscopy, spectroscopy, and density functional theory (DFT) calculations has confirmed that the introduction of alkali-metal cations enhances the adsorption between MOFs and CO 2 , thereby providing stronger adsorption sites. Experimental studies have demonstrated that doping with 0.1 M K + (denoted as 0.1 K-NH 2 -MIL-101) exhibits a higher CO 2 adsorption capacity (8.2mmol g −1 ) at 298 K, approximately 3.2 times greater than that of NH 2 -MIL-101. Furthermore, it maintains an adsorption capacity of 7.4mmol g −1 after the sixth adsorption–desorption test, indicating excellent cyclic stability. Additionally, 0.1 K-NH 2 -MIL-101 was employed for in situ capture and electrocatalytic CO 2 reduction. By integrating 0.1 K-NH 2 -MIL-101 with a Bi-based catalyst to enhance the local CO 2 concentration, the Faraday efficiency for the formic acid product was effectively increased from 67 % to 85 %.