Aminosilane-functionalized Ti-based metal–organic framework for efficient and selective CO2 adsorption

Abstract

Carbon dioxide capture and storage (CCS) is considered as a promising strategy for reducing CO2 emissions. However, the further development of CO2 adsorption materials with high selectivity and high adsorption capacity is the top priority of this technology. In this study, we used the μ-OH sites of the MIL-125 metal–organic framework (MOF) to modify it with aminosilane to synthesize a new MOF adsorbent (SAP-MIL-125) with improved CO2 adsorption capacity at room temperature. Although there are no open metal sites on the MIL-125 surface, it is possible to load aminosilanes onto it. Under the same adsorption conditions, the CO2 adsorption by SAP-MIL-125 was significantly improved compared to that of the original MIL-125. Adsorption isotherm and kinetics models were used to clarify that the adsorption mechanism of CO2 on SAP-MIL-125 was non-homogeneous layer chemisorption. SAP-MIL-125 has excellent selectivity toward CO2 (compared to N2) and good stability over five adsorption–desorption cycles. The adsorption of CO2 by SAP-MIL-125 is a spontaneous exothermic process. An in-depth investigation of the adsorption mechanism suggests that the acid–base interactions of carbamates is the mechanism of CO2 adsorption. Density functional theory and frontier molecular orbital calculations showed that the main adsorption sites for the modified adsorbent were nitrogen-containing groups on the surface of aminosilanes, with the primary amines having the highest affinity for CO2. In conclusion, a novel material modification method for MOFs is provided, which was used to fabricate a CO2 adsorbent with great potential for development.