Incorporation of Alkylamine into Metal-Organic Frameworks through a Brønsted Acid-Base Reaction for CO2 Capture.

The escalating atmospheric CO2 concentration is one of the most urgent environmental concerns of our age. To effectively capture CO2 , various materials have been studied. Among them, alkylamine-modified metal-organic frameworks (MOFs) are considered to be promising candidates. In most cases, alkylamine molecules are integrated into MOFs through the coordination bonds formed between open metal sites (OMSs) and amine groups. Thus, the alkylamine density, as well as the corresponding CO2 uptake in MOFs, are severely restricted by the density of OMSs. To overcome this limit, other approaches to incorporating alkylamine into MOFs are highly desired. We have developed a new method based on Brønsted acid-base reaction to tether alkylamines into Cr-MIL-101-SO3 H for CO2 capture. A systematic optimization of the amine tethering process was also conducted to maximize the CO2 uptake of the modified MOF. Under the optimal amine tethering condition, the obtained tris(2-aminoethyl)amine-functionalized Cr-MIL-101-SO3 H (Cr-MIL-101-SO3 H-TAEA) has a cyclic CO2 uptake of 2.28 mmol g-1 at 150 mbar and 40 °C, and 1.12 mmol g-1 at 0.4 mbar and 20 °C. The low-cost starting materials and simple synthetic procedure for the preparation of Cr-MIL-101-SO3 H-TAEA suggest that it has the potential for large-scale production and practical applications.