Modified metal-organic framework by a novel coordinatively unsaturated amine grafting mechanism for direct air capture of CO2

This study aimed to improve the carbon dioxide (CO2) capture and kinetics performance for direct air capture (DAC) while demonstrating the amine grafting reaction principles and its constraints using N-(2-aminoethyl) ethanolamine (AEEA) to functionalize coordinatively unsaturated metal sites in MIL-100(Fe), UiO-66(Zr), and MIL-100(Cr). Grafting experiments indicated that the grafting process is the reaction between metal sites and secondary amines of AEEA, while MOFs with high surface area and low acidity can effectively promote amine grafting without destroying the active site. Moreover, the adsorbed CO2 amounts of MF-Cr-AEEA at 400 ppm were 1.91 mmol/g of-25 degrees C and 2.42 mmol/g of 0 degrees C, and the structural decomposition temperature exceeded 400 degrees C, demonstrating excellent thermal and cold stability. As a result of the better crystal and surface structure, the internal heat and mass transfer processes were accelerated, resulting in low semi-adsorption times below 21 min. Moreover, CO2 capture cycles were established at 25 degrees C for adsorption and 80 degrees C for desorption. The results show that the adsorption capacity of MF-Cr-AEEA remained 1.86 mmol/g after seven cycles, demonstrating low renewable energy consumption and high stability.

Automated summary

This study aimed to improve CO2 capture and kinetics performance for DAC by using AEEA to functionalize metal sites in MOFs. The grafting experiments indicated that high surface area and low acidity of MOFs effectively promoted amine grafting. The MF-Cr-AEEA demonstrated excellent thermal and cold stability, and low semi-adsorption times below 21 min.