Crystalline Covalent Triazine Frameworks:Morphology Control And Applications

A series of polymers with triazine ring as the connected units,synthesized by the highly dynamic polycondensation reaction,are named as covalent triazine frameworks（CTFs）.CTFs have many advantages such as high porosity,high surface area,high nitrogen content,and high physicochemical stability.These unique properties make CTFs potentially useful in many application fields,such as gas adsorption and separation,energy conversion and storage,heterogeneous catalysis and photocatalysis.As we all know,controlling the nanoscale morphology of materials is an important research target in material science due to the merits originated from quantum effects in a variety of applications.However,most of the studies on CTFs are focused on the synthesis,structural design,and different applications in various fields,whereas very little attention is paid to morphological study and most of the reported CTFs show irregular morphologies,probably due to the difficulty in the control of the morphology via the conventional synthetic methods.Therefore,it is of great significance to develop a mild synthetic strategy for production of CTFs with special morphology,which further enrich the morphological diversity of CTFs,and lay a foundation for exploring the impact of morphology control on the performance.In this paper,based on the"top-down"strategic idea,a new method of preparing crystalline CTFs with ultrathin sheet-like morphology by the glycerol intercalation exfoliation of blocky CTF-HC1 with lamellar structure is proposed;on the other hand,based on the"bottom-up"strategic idea,another method of preparing crystalline CTFs with fibrous morphology by mild polycondensation of aldamidine is also proposed.In addition,the practical application of CTFs with special morphology in energy conversion and storage,photocatalysis was further explored.The main contents of the paper are as follows:1)ChapterⅠ:crystalline CTFs with ultrathin sheet-like morphology was prepared by glycerol intercalation exfoliation of blocky CTF-HC1 with lamellar structure.The three vibration states of glycerol molecules at 25°C,90°C and 300°C is a key role in the process of CTF-HCl exfoliation.As the temperature increases,the vibration energy increases.When the temperature reaches 300°C,the vibration energy becomes enough large to make the glycerol occupy the CTF layer spacing at the vibrational state of the maximum cross section,resulting in the exfoliation behavior of CTF-HC1.The exfoliated E-CTF-HC1 has many advantages,such as large-size（micron-grade）,high specific surface area(717.1 m² g^-1),high crystallinity.Through the electrochemical application testing,it was found that the specific capacitance of the exfoliated E-CTF-HC1 electrode is about 3.3 times higher than that of bulk CTF-HC1 electrode due to its higher ionic conductivity.2)ChapterⅡ:synthesis of crystalline CTFs with fibrous morphology by polycondensation of aldamidine in a mixed solvent of triazine-based monomer.By adjusting the ratio of mixed solvents to control the solubility of monomers,the progress of polymerization reaction was controlled,so as to allow sufficient time to realize the crystal nucleus formation,crystal growth and subsequent self-assembly process,which facilitates the crystal grains to form fibrous MS-F-CTF-1 through theπ-πstacking interaction among the vertically stacked layers.The MS-F-CTF-1 exhibits uniform fibrous morphology with the diameter of less than 100 nm and the length of several microns,as observed from SEM and TEM imaging.This fibrous MS-F-CTF-1 has better ability of charge transfer and photoelectron-hole pair separation,which is more conducive to photocatalytic applications.It was found that the photocatalytic hydrogen production rate of MS-F-CTF-1(9589μmol h^-1g^-1)was better than that of traditional blocky CTF-HUST-HC1.