MECHANOCHEMICAL SYNTHESIS OF TASK-SPECIFIC CONJUGATED POROUS NETWORKS TOWARDS ENHANCED ENERGY STORAGE

Conjugated scaffolds with high electronic conductivity, high surface area, etc. are promising materials for diverse technological applications, especially in the electrochemical field. However, the current synthesis methods are still limited to the traditional solution-based method or the ionothermal method, which always require an inert atmosphere shield, large amounts of organic solvents, noble catalysts, long reaction time up to days, and high temperatures, etc. Therefore, there is a common goal of developing conjugated scaffolds through facile, green, straightforward pathways. Mechanochemistry, which is an efficient, sustainable, solvent-free methodology, could provide a unique reaction environment to synthesize this kind of functionalized materials, resulting in materials that exhibit different properties from those produced by traditional methods. However, the current conjugated scaffolds derived from mechanochemistry are limited to the oxidative polymerization from the electron-rich building blocks. Herein, we extended the building blocks to the electron-deficient monomers (aromatic halides, aromatic nitriles) with various catalysts (magnesium, aluminum, zinc, calcium carbide) and achieved different conjugated porous scaffolds such as the poly(phthalocyanine), nitrogen-doped graphyne scaffolds for the enhanced energy storage including supercapacitor and alkali-ion batteries.

Additionally, the mechanochemistry-driven method is not only suitable for the direct synthesis of conjugated scaffolds from small molecules but also capable of being used for the post-treatment of conjugated scaffolds for their desirable properties. For instance, the trimerization reaction of terephthalonitrile to form covalent triazine frameworks (CTF) catalyzed by triflic acid could be achieved at low temperature (250 °C) for a short time, without the undesirable carbonization reaction. However, the CTF obtained by this method tends to form the staggered stacking with low surface area due to the residual triflic acid, which is hard to remove. Mechanochemistry treatment with the alkaline molten salt composed of lithium hydroxide and potassium hydroxide at ambient temperature was proposed in this dissertation to achieve the phase transformation from the staggered stacking to eclipsed stacking with high surface area. Overall, our approach on the scenario of conjugated scaffold construction can not only expand the boundaries of conventional conjugated scaffold synthesis, but also provide new opportunities to their scalable application.