PKU-21: A Novel Layered Germanate Built from Ge₇ and Ge₁₀ Clusters for CO₂ Separation

The attractive properties of layered inorganic materials, which make them suitable for numerous applications in chemical industries and life sciences, originated from their crystalline framework structures. Here, we report a new layered germanate PKU-21, which was prepared by the hydrothermal synthesis method using 2-propanolamine (MIPA) as the structure-directing agent. The structure of PKU-21 was determined from synchrotron single-crystal X-ray diffraction and synchrotron powder X-ray diffraction data. It reveals a complicated framework structure containing 18 unique Ge atoms in the asymmetric unit. PKU-21 is the first layered germanate built from both Ge₇ and Ge₁₀ clusters, following the 3-dimensional germanate PKU-17. The preparation and structure of PKU-21 are discussed in comparison with PKU-17, which provides new insight into the formation mechanism of germanates. Gas sorption experiments indicate that the layered PKU-21 sample exhibits a better CO₂ sorption selectivity over N₂ and CH₄ at 298 K than at 273 K, making it a promising candidate for CO₂ separation.