In situ analysis of the adsorption behaviors of CO2 on the surface of MIL-91(Al)

Abstract

To prevent global warming caused by the burning of fossil fuels, the formation of metal organic framework materials (i.e., MOFs) is a promising approach for efficient and scalable CO₂ adsorption from air. In this study, a novel stable layered bis-phosphonate MOF, i.e., MIL-91(Al), has been synthesized for adsorption of CO₂ under ambient conditions. XRD, N₂ adsorption–desorption isotherms, FTIR and HRTEM were employed to characterize the synthesized MIL-91(Al). The results show that MIL-91(Al) demonstrates an excellent adsorption performance for CO₂ (i.e., the maximum adsorption can reach up to 2.4 mmol g⁻¹) and a relatively high selectivity for CO₂vs. other gases (e.g., N₂ or CH₄). Moreover, the adsorption behavior of CO₂ onto the surface of MIL-91(Al) has also been investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The DRIFTS results show that CO₂ can be adsorbed by both the free polar groups (N⋯H–OP) and the Al–OH–Al bond. The special adsorption behavior is caused by the layered structure of MIL-91(Al) which leads to the exposure of Al on the surface.