In situ transmission electron microscopy to monitor phase transitions in metal-organic frameworks

A copper pyromellitic acid template is used to prepare the Cu@C compound by calcination under nitrogen and further synthesize the CuO@C compound by aerobic calcination. Transmission electron microscope observation shows that both Cu nanoparticles and CuO nanoparticles can be uniformly coated in nanoporous carbon, indicating that the experimental method is feasible. Using the precursor HKUST-1 and the in situ heating reaction technology of a high-resolution transmission electron microscope to observe the Cu@C nanocomposites at different temperatures, the relationship between product and temperature was discussed. When heated to 350 °C, copper atoms begin to aggregate to form nanoparticles. With the increasing temperature, the particle size of nanoparticles increases from 30 to 60–70 nm. This change provides a reliable basis for preparing nanomaterials by carbonizing metal-organic frameworks as precursors or templates. In addition, the mechanism and influencing factors of porous carbon prepared with metal-organic frameworks as a precursor are discussed. Precise temperature control is a key step in the preparation of carbon-based metal nanoparticle composites with controllable sizes.