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.

中文翻译：

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原位分析MIL-91（Al）表面上 CO ₂的吸附行为

为了防止由化石燃料燃烧引起的全球变暖，金属有机骨架材料（即MOF）的形成是一种有效且可扩展的从空气中吸收CO ₂的有前途的方法。在这项研究中，合成了一种新型的稳定层状双膦酸酯MOF，即MIL-91（Al），用于在环境条件下吸附CO ₂。XRD，N ₂吸附-解吸等温线，FTIR和HRTEM表征了合成的MIL-91（Al）。结果表明，MIL-91（Al）具有出色的CO ₂吸附性能（即最大吸附量可达2.4 mmol g ^-1）和对CO ₂相对于其他气体（例如N ₂或CH ₄）的相对较高的选择性。此外，还使用原位漫反射红外傅里叶变换光谱法（原位DRIFTS）研究了CO ₂在MIL-91（Al）表面上的吸附行为。DRIFTS结果表明，自由极性基团（N⋯H-OP）和Al-OH-Al键均可吸附CO ₂。特殊的吸附行为是由MIL-91（Al）的层状结构引起的，该结构导致Al暴露在表面上。