Design And Synthesis Of Functional Covalent Organic Framework Materials And Their Adsorption And Catalytic Properties

Covalent Organic Frameworks(COFs)are a class of highly crystalline organic polymers with the feature of ordered structural arrangements and high porosity,and are crystalline framework polymers consisting of organic monomers connected by covalent bonds in a periodical manner.COFs not only possess high crystallinity,intrinsic porosity and stability derived from the covalent bonds,but also have structural tunability and functional modifiability due to their basic organic attribute,and they have shown great potential in a wide range of applications such as adsorption and separation of substances,heterogeneous catalysis and sensing.Therefore,COFs have rapidly developed into a new class of attractive porous materials.In this thesis,an overview of the background,synthesis methods,bonding types and applications of COFs is summarized.Subsequently,three types of COFs are constructed through the design and rational selection of organic structural units,and their applications in iodine adsorption,photocatalytic oxidation and immobilization of silver nanoparticle for catalytic conversion of carbon dioxide are investigated.The details are shown below:(1)The amide-bonded triple-symmetrical aldehyde-containing ligand(named TFBT)was designed and synthesised,and two COFs,named TFBT-1 and TFBT-2,were constructed by hydrothermal syntheses of the syntheized TFBT with two triple-amine organic ligands,TAPA and TAPB,through Schiff-base condensation reactions.The structural analysis shows that both COFs,TFBT-1 and TFBT-2,are two-dimensional lamellar frameworks,which then stack to COF crystalline materials in AA-packing model and give the generation of one-dimensional channels.The adsorption studies showed that both COFs exhibited effective iodine adsorption properties under either iodine solution or iodine vapour conditions.Fourier transform infrared spectrometer(FT-IR),X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy measurements of both COFs before and after adsorption indicate that the adsorption of iodine should be attributed to the presence of a large number of exposed nitrogen adsorption sites in the pore channels of the materials.The present study shows that efficient iodine adsorption materials can be obtained by introducing nitrogen-rich sites such as amide-bonded and in situ formed Schiff bases into the framework of COFs materials.(2)Selection of photo-responsive organic units is a powerful method in constructing Photo-sensitive COFs.Porphyrin and triphenylamine are both commonly used photosensitive organic compounds,therefore,we selected them and synthesized a crystalline COF,named TFPA-TAP-COF,by solvothermal synthesis.The structural and optoelectronic properties of the synthesized TFPA-TAP-COF were tested by Fourier transform infrared spectrometer,Solid-state NMR,X-ray powder diffraction;Specific surface area analysis,Thermogravimetric analysis and UV diffuse reflectance spectroscopy,Transient photocurrent and so on.Finally,the photocatalytic properties were further investigated.It is shown that the COF can catalyse both superoxide anion radicals and singlet oxygen under aerobic light conditions,and can photocatalyse both thioether oxidation and benzylamine coupling reactions.This study shows that introduction of photo-responsive organic units into COF,efficient heterogeneous photocatalysts can be constructed.(3)Since Ag nanoparticles are effective reagents for the catalytic conversion of carbon dioxide,but they tend to aggregate into larger particles in solution,leading to deactivation in the catalytic reactions.Therefore,we selected a nitrogen-rich COF,Aza-COF,to immobilize the Ag nanoparticles by using its effective coordination with Ag ions and finally fabricated the Ag/Aza-COF composites.The prepared Ag/Aza-COF showed high catalytic efficiency for the reactions of propargyl alcohol and its derivatives as well as propargylamine with carbon dioxide at room temperature.Furthermore,Ag/Aza-COF has good stability and reusability and has great potential for practical applications in catalysis.TEM,FT-IR spectroscopy,X-ray photoelectron spectroscopy and Raman spectroscopy studies showed that the high catalytic activity should be attributed to the synergistic effect of the nitrogen-rich sites and small Ag nanoparticles.These experiments show that COFs are a group of effective porous materials for metal nanocatalyst carriers.