Engineering hollow covalent organic framework particle through self‐templated crystallization

Abstract Nano/microparticles with hollow structures have many applications in various fields. However, engineering hollow covalent organic framework (COF) particles in a simple and efficient manner remains a significant challenge. In this study, we propose a self‐template crystallization method to prepare imine‐based COF microparticles with tailored shell thickness and high crystallinity. This method involves the post‐transformation of amorphous microparticles in a highly reversible reaction system containing monofunctional competitors. The amorphous precursors with high‐Gibbs free energy decompose and reconstruct to form highly crystalline COFs in situ on the particle surface. This process allows for the preparation of various Schiff‐base COF particles with good crystallinity and tailored hollow structures, with diameters ranging from 120 to 680 nm and shell thicknesses of 27–96 nm. These COF particles have well‐defined micropore sizes centered between 1.0 and 4.0 nm and a high‐specific surface area of up to 543 m 2 g −1 . The resulted COF particles could be used to support ethylene oligomerization catalysts for improving their activity and selectivity, that is, the mass fraction of α‐olefins above C 10 increased from almost zero to 52.7% after COF supporting. Our method thus provides an efficient way to precisely tailor the microstructure and morphology of COF materials for advanced applications.