Macroscopic Hexagonal Co3O4 Tubes Derived from Controllable Two-Dimensional Metal-Organic Layer Single Crystals: Formation Mechanism and Catalytic Activity

Macroscopic Co3O4 hexagonal tubes were successfully synthesized using hollow two-dimensional (2D) MOL (metal–organic layer) single crystals as sacrificial templates. The hollow 2D MOL single crystals were prepared under hydrothermal conditions with acetonitrile (MeCN) as an interference agent. The formation of hollow-structured 2D MOL single crystals was tracked by time-dependent experiments, and two simultaneous paths—namely, the crystal-to-crystal transformation in solution and the dissolution + migration (toward the external surface) of inner crystallites—were identified as playing a key role in the formation of the unique hollow structure. The calculated change in Gibbs free energy (ΔG = −1.18 eV) indicated that the crystal-to-crystal transformation was spontaneous at 393 K. Further addition of MeCN as an interference agent eventually leads to the formation of macroscopic hexagonal tubes. Among all of the as-synthesized Co3O4, Co-MeCN-O with a hexagonal tube morphology exhibited the best catalytic per...