Real-Time Imaging and Quantitative Evolution for Pyrolysis of Carbon Dots-Encapsulated Metal-Organic Frameworks at the Nanoscale by In Situ Environmental Transmission Electron Microscopy.

The pyrolysis of metal-organic frameworks (MOF) has been widely used approach to generate hierarchical structures with the corresponding metal, metal carbide, or metal oxide nanoparticles embedded in a porous carbon matrix with a high specific surface area for industrial catalysis, energy storage and transfer, etc. MOF-derived heterogeneous catalysts can be constructed by the encapsulation of carbon dots (CDs) with plenty of hydroxyl and amine groups to enhance the performance of the final product. Controlled formation of metallic carbon structures at the nanoscale, especially matter cycling and transformation on the nanoscale interface, is important for the production of industrial catalysts as well as the research of materials science and engineering progress. However, the mass transfer at the nanoscale during the processing of MOF pyrolysis remains less understood due to the lack of direct observation. Herein, by using in situ environmental transmission electron microscopy, real-time imaging and quantitative evolution of porous carbon decorated with metal species by the pyrolysis of CDs-encapsulated zeolitic imidazolate framework-67 are achieved. The migration of Co, the flow of aggregates, and the growth of carbon nanotubes observed in the nanoscale pyrolysis laboratory working at 600 °C with an air atmosphere are present. Experimental studies based on reduction and oxidation reaction models reveal that the synergistic effect between doped graphite nitrogen and confined Co nanoparticles is beneficial for boosting catalytic performance.