Template synthesis of imine-based covalent organic framework core-shell structure and hollow sphere: a case of COFTTA-DHTA

Controllably synthesizing well-dispersed covalent organic frameworks (COFs) with uniform both morphology and size is still a challenge. Herein, we report the template-directed synthesis of COF_TTA-DHTA-based core-shell hybrids under solvothermal conditions by using amino-functionalized SiO₂ microspheres as templates coupled with stepwise addition of initial monomer molecules. The modified amino groups on the surfaces of SiO₂ templates play an important role in the formation of well-defined NH₂-f-SiO₂@COF_TTA-DHTA core-shell hybrids. COF_TTA-DHTA hollow spheres can be obtained by etching SiO₂ cores of NH₂-f-SiO₂@COF_TTA-DHTA. Both the NH₂-f-SiO₂@COF_TTA-DHTA and COF_TTA-DHTA hollow spheres possess the well-defined morphology, high crystallinity and porosity, excellent dispersion property and high chemical stability. The template synthesis method demonstrated in this work provides a general method for the shape-controlled synthesis of COF-based materials, which is important for the further applications in the fields such as energy storage, drug delivery and catalysis.