Preparation Of Novel Functionalized COFs And Its Application In Pollutant Adsorption Detection And Electrocatalysis

At present,the earth’s environmental problems are becoming increasingly prominent,and the deterioration of the environment will further affect human life and health.Under the double mountain thought of"clear water and green mountains are gold and silver mountains"and the double carbon goal of"carbon peak and carbon neutral",on the one hand,we need to improve ecology and control pollution,on the other hand,we need to develop new clean energy and reduce carbon dioxide emissions.Covalent organic frameworks（COFs）are crystalline materials with high specific surface areas that can be designed with different regular structures according to functional requirements.After specific modification,COFs can selectively adsorb pollutants in the environment with high capacity.At the same time,COFs with fluorescence effect can also specifically detect pollutants.Loading different metal active sites on the surface of the pore can catalyze different reactions specifically,including electrocatalytic hydrogen evolution and oxygen evolution.Therefore,COFs can be effectively used as adsorption materials for environmental remediation and catalytic materials for energy development.In this paper,the imine bond is converted into quinoline unit via the Povarov reaction,and several special fluorescent COFs are prepared by introducing different functional groups,and their adsorption sensing applications for fluorinated pesticides and radioactive iodine are studied.At the same time,through the coordination of COFs and metal ions to synthesize different metal COFs composite materials,as electrocatalyst for electrolytic water hydrogen and oxygen evolution have good activities respectively.The main contents of this paper are as follows:In chapter 2,bitrifluoromethylbenzene acetylene is used as the active functional group,which is introduced into the skeleton of COFs to obtain COF-（CF₃）₂.COF-（CF₃）₂ shows remarkable stability in strong acid（12 M HCl）and strong base（14 M Na OH）.Its weight and crystallinity hardly changed before and after soaking.COF-（CF₃）₂ has extremely high specific surface area(S_BET=1533 m² g^-1)and abundant trifluoromethyl functional groups,which can rapidly and selectively adsorb fluorinated pesticides.Trifluoromethyl can interact through fluoro-fluorine interactions as well as hydrophobicity and fluorine-containing contaminants.In addition,surprisingly,the highly conjugated COF-（CF₃）₂ is able to fluoresce blue under UV excitation at 365 nm due to the cyclic addition of the highly polarized imine bond to quinoline units.Fluorescence can be selectively quenched by fluorinated pesticides,and this unique property can be used to detect trifluralin by fluorescence quenching.In chapter 3,we designed and synthesized the super-stable adsorbent COF-PA by grafting acetylene group to TPB-DMTP-COF,which can quickly adsorb iodine under the promotion of chemical reaction.The K_80%value of COF-PA is about 1.3 g h^-1,which is the COF material with the fastest adsorption rate in two-dimensional COFs.Even at low concentration,when the mass ratio of adsorbent to iodine is 1:1,the adsorption efficiency reaches 90%.In addition,the adsorption capacity of COF-PA to iodine in solution reached 820 mg g^-1.In terms of chemical stability,when COF-PA was soaked in different organic solvents,HCl（12 M）and Na OH（14 M）for a week,the crystallinity did not decrease significantly and the crystal structure was not damaged.Moreover,COF-PA showed bright yellow fluorescence under UV excitation at 365 nm.Fluorescence can be selectively quenched by iodine to detect iodine specifically.In chapter 4,COF-Pyr was synthesized by the Povalov reaction between 5-acetylene pyrimidine and TPB-DMTP-COF.The pyrimidine group is fixed in the channel as a metal ligand and the crystallinity and porosity remain unchanged during the conversion process.Subsequently,Ni@COF-Pyr and Co@COF-Pyr with COF-Pyr were obtained by coordination with nickel chloride（II）and cobalt acetate（II）,respectively.By comparing their electrocatalytic OER data,we find that Co@COF-Pyr has a good electrocatalytic performance.The overpotential of Co@COF-Pyr(450 m V,10 m A cm^-1)was lower than that of other COFs electrocatalysts.Surprisingly,the conversion frequency（TOF）value at 370 m V is as high as 0.1 s^-1,which is better than most catalysts.In Chapter 5,we prepared an efficient sp² carbon conjugated COFs catalyst Ru@COF-1 for hydrogen evolution with triazine nuclear complexation of Ru ions.The electrical conductivity of Ru@COF-1 was significantly improved under acidic conditions.At the same time,ruthenium ions as active catalytic sites can react with hydrogen ions more easily.This synergistic effect enables Ru@COF-1 to have an overpotential of about 200 m V at a current density of 10 m A cm^-2,which is lower than other COFs-based electrocatalysts reported.In addition,sp² carbon conjugated COFs have high stability under strong acidic conditions,and Ru@COF-1 electrocatalytic performance remains excellent after 1000 cycles of cyclic voltammetry（CV）scanning,which effectively makes up for the deficiency of imine COFs.Based on the density functional theory（DFT）calculation results,we found that the Ru-N₂Cl₂ group in Ru@COF-1 is the main reason for the outstanding performance of HER.This work not only proves the potential application of sp² carbon conjugated COFs in electrocatalysis,but also provides a new idea for designing stable electrocatalysts in acidic electrolytes.