Hierarchical Microtubular Covalent Organic Frameworks Achieved by COF-to-COF Transformation

Pore environment and aggregated structure play a vital role in determining the properties of porous materials, especially regarding the mass transfer. Reticular chemistry imparts covalent organic frameworks (COFs) with well-aligned micro/mesopores, yet constructing hierarchical architectures remains a great challenge. Herein, we reported a COF-to-COF transformation methodology to prepare microtubular COFs. In this process, the C-3-symmetric guanidine units decomposed into C-2-symmetric hydrazine units, leading to the crystal transformation of COFs. Moreover, the aggregated structure and conversion degree varied with the reaction time, where the hollow tubular aggregates composed of mixed COF crystals could be obtained. Such hierarchical architecture leads to enhanced mass transfer properties, as proved by the adsorption measurement and chemical catalytic reactions. This self-template strategy was successfully applied to another four COFs with different building units.

Automated summary

The pore environment and aggregated structure of porous materials are crucial for their properties, especially mass transfer. In this study, a COF-to-COF transformation method was used to prepare microtubular COFs. This transformation was achieved by decomposing C-3-symmetric guanidine units into C-2-symmetric hydrazine units, resulting in crystal transformation of COFs. The hierarchical structure obtained with varying reaction times led to enhanced mass transfer properties, as demonstrated by adsorption measurement and chemical catalytic reactions. This self-template strategy was also successfully applied to four other COFs with different building units.