Synthesis And Properties Of Covalent Organic Frameworks Based On Salphen Units

Covalent organic frameworks（COFs）are a new class of crystalline porous materials.They have shown broad application prospects in gas storage and separation,catalysis,optoelectronic devices,batteries and supercapacitors due to their tunable chemical composition,excellent porosity,diverse topological structure and inherent chemical stability.Based on the Salphen（N,N′-disalicylidene-o-phenylenediamine）unit,a series of functional COFs materials were designed and synthesized by the dynamic covalent aldimine condensation strategy,and their electrocatalytic properties were studied.The main contents are as follows:1.Synthesis and electrocatalytic hydrogen evolution properties of 2D Salphen based COF with double triangular pores:The 2D Salphen-based COF（Salphen-COF-1）with double triangular pores was constructed by the reaction of HATP·6HCl and 2,3-DHTA.The Fourier transform infrared（FT-IR）spectra and ¹³C CP-MAS solid-state NMR characterization preliminarily proved the formation of the C=N double bond in the product,powder X-ray diffraction combined with theoretical simulation data analysis further demonstrated that Salphen-COF-1 is a framework structure with double triangular pores（0.54 nm and 1.15 nm in diameter,respectively）and two-dimensional AA stacking.Scanning electron microscopy and transmission electron microscopy analysis showed that Salphen-COF-1 exhibited rod-like morphology.The metallated Pt₅₀-Salphen-COF-1 generated by post-modification exhibited excellent electrocatalytic hydrogen evolution activity with an overpotential of 26 m V at a current density of 10 m A cm^-2.Its excellent electrochemical performance was mainly attributed to the coordination effect between the Salphen unit-based covalent organic framework and Pt and the high density of catalytically active centers.2.Synthesis and electrocatalytic oxygen evolution properties of 2D Salphen-based COF with quadrilateral and hexagonal pores:A series of 2D Salphen-based heteroporous covalent organic frameworks（Salphen-COF-2,Ni-Salphen-COF-2,Ni Fe-Salphen-COF-2）with quadrilateral and hexagonal pores were generated in situ by the reaction of HATP·6HCl and DMDB.The analysis of powder X-ray diffraction and theoretical simulation data proved that Salphen-COF-2 is a frame structure with heteropore（0.7 nm and 1.3 nm,respectively）and two-dimensional AA stacking.Scanning electron microscopy and transmission electron microscopy analysis showed that Salphen-COF-2 exhibited uniform nanosphere morphology.The metallized Ni Fe-Salphen-COF-2 exhibited excellent electrocatalytic oxygen evolution activity with an overpotential of 266 m V at a current density of 10 m A cm^-2.Its excellent electrochemical performance was mainly attributed to its conjugated planar structure and high density of redox active centers.3.Synthesis and electrocatalytic properties of 3D Salphen-based COF with acs topology:Through the[6+2]aldehyde-amine condensation strategy,HATT·6HCl,a tri-prism monomer with D_3h symmetry,reacts with naphthalenaldehyde to generated Salphen-based covalent organic framework Salphen-COF-3 with acs topology in situ.Powder X-ray diffraction combined with theoretical simulation data analysis proved that Salphen-COF-3 is a three-dimensional porous material based on acs topology（pore size distribution is 1.1-2.1 nm）.SEM and TEM analysis showed that Salphen-COF-3 exhibits uniform nanorods morphology.The metallized Fe-Salphen-COF-3 exhibited good electrocatalytic oxygen evolution activity with an overpotential of 300 m V at a current density of 10 m A cm^-2;the metallized Pt-Salphen-COF-3 exhibited excellent electrocatalytic hydrogen evolution activity with a low overpotential of 76 m V at a current density of 10 m A cm^-2.Compared with the previous two chapters,the decrease of its performance may be attributed to the decrease of the density of catalytic active centers.