A covalent organic framework onion structure

Achieving hierarchical nanomaterials from a bottom-up approach remains challenging. Here, we report closed-cage, onion nanostructure of covalent organic framework (COF) obtained through low-temperature solvothermal synthesis. Atomic resolution transmission electron microscopy revealed the atomic arrangement in this COF onion, which rich nitrogen was uniformly embedded periodic porous graphitic framework. The structure displayed features at 0.33 nm interlayer spacing with Van der Waals interactions predominated between layers. layers exhibited significant heterogeneity layer stacking by adopting combination different modes. Defects were also found, such as five- or seven-member rings deviating perfect hexagonal lattice. These geometrical defects resulted curving 2D layers, may have promoted formation nanostructures layer-by-layer attachment. We constructed corresponding model that predicts properties. This novel bandgap value 2.56 eV, resembling other carbon-based nanomaterials, suggesting potential applications sensors, photocatalysts, and nanoelectronics.