Kinetics and Mechanisms of ZnO to ZIF‐8 Transformations in Supercritical CO<sub>2</sub> Revealed by In Situ X‐ray Diffraction
Michael A. Sinnwell, Quin R. S. Miller, Lili Liu, Jinhui Tao, Mark Bowden, Libor Kovařík, Dushyant Barpaga, Yi Han, Radha Kishan Motkuri, Maria L. Sushko, Herbert T. Schaef, Praveen K. Thallapally
Abstract
Abstract ZIF‐8 was synthesized in supercritical carbon dioxide (scCO 2 ). In situ powder X‐ray diffraction, ex situ microscopy, and simulations provide an encompassing view of the formation of ZIF‐8 and intermediary ZnO@ZIF‐8 composites in this nontraditional solvent. Time‐resolved imaging exposed divergent physicochemical reaction pathways from previous studies of the growth of anisotropic ZIF‐8 core@shell structures in traditional solvents. Synthetically relevant physiochemical properties of scCO 2 were integrated into classical nucleation theory, relating interfacial forces, calculated through DFTB+ based molecular dynamics (MD), with 3D nucleation outcomes. The kinetics of crystallization were examined and displayed a characteristic signature of time‐ and temperature‐dependent mechanisms over the extent of the reaction. Lastly, it is shown that subtle factors, such as the extent of reaction and the size/shape of sacrificial templates can tailor ZIF‐8 composition and size, eliciting control over hierarchical porosity in a nonconventional green solvent.