Growth of Two-Dimensional Metal–Organic Framework Nanosheet Crystals on Graphite Substrates by Thermal Equilibrium Treatment in Acetic Acid Vapor

Large two-dimensional (2D) nanosheets of crystalline coordination frameworks were prepared on highly oriented pyrolytic graphite (HOPG) by re-crystallization induced by thermal equilibrium treatment in acetic acid vapor. The nanosheets comprised 5,10,15,20-tetrakis(4-carboxyphenyl)-porphyrin (H₂TCPP) cross-linked by copper ions. We found that an acetic acid vapor environment dramatically decreased the activation energy and accelerated the recombination of coordination bonds between metal ions and carboxylate ligands in the H₂TCPP-Cu frameworks. Ultimately, two-dimensional horizontal crystal growth was induced to form monomolecular sheets as the most thermodynamically stable crystal structure on a well-defined surface.