The increase in atmospheric carbon dioxide concentration linked to climate change has created a need for new sorbents capable of separating CO₂ from exhaust gases. Recently, an easily produced metal–organic framework, CALF-20, was shown to withstand over 450,000 adsorption/desorption cycles in steam and wet acid gases. Further development and industrial application of such materials require an understanding of the observed processes. Herein, we demonstrate that conditioning as-synthesized CALF-20 single crystal transforms it into a different phase, γ-CALF-20. The transformation resulted in significant structural changes, including the binding of water molecules to Zn(II), accompanied by a reduction of 9% in the unit cell volume. Our experimental findings were supported by the energy-volume dependence of CALF-20 in the presence and absence of water molecules calculated from density functional theory. We have also monitored the sorption process of the dominant greenhouse gas, CO₂, on the initial phase of CALF-20 at atomic resolution using in situ single-crystal X-ray diffraction under specific pressure. The new understanding of CALF-20 chemistry from these studies should facilitate development of novel sorbents for gas adsorption technologies.

中文翻译：

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揭示 CALF-20 中温度诱导的结构相变和 CO2 结合位点


与气候变化相关的大气二氧化碳浓度增加，产生了对能够从废气中分离_CO2 的新型吸附剂的需求。最近，一种易于生产的金属有机框架 CALF-20 被证明在蒸汽和湿酸性气体中可承受超过 450,000 次的吸附/解吸循环。此类材料的进一步开发和工业应用需要了解观察到的过程。在此，我们证明条件合成的 CALF-20 单晶将其转化为不同的相 γ-CALF-20。这种转变导致了显著的结构变化，包括水分子与 Zn（II） 的结合，伴随着晶胞体积的减少 9%。我们的实验结果得到了 CALF-20 在存在和不存在水分子时的能量-体积依赖性的支持，该依赖性由密度泛函理论计算得出。我们还在特定压力下使用原位单晶 X 射线衍射以原子分辨率监测了主要温室气体 CO₂ 在 CALF-20 初始阶段的吸附过程。从这些研究中对 CALF-20 化学的新理解应该有助于开发用于气体吸附技术的新型吸附剂。