Covalent Organic Frameworks And Its Composites For Removal Of Organic Pollutants From Wastewater

In recent years,water pollution has been regarded as the main threat of global environmental pollution,and water recycling has become a crucial issue.Detoxification of wastewater by adsorption or photocatalytic degradation to achieve pure and drinkable water has been identified as harmless to the environment,energy saving and cost-effective.In this case,porous materials have made great progress in detecting pollutants in wastewater and treating wastewater,such as metal-organic frameworks（MOFs）and covalent organic frameworks（COFs）.Because of its low density,high specific surface area,easily controlled and adjustable pore size and strong stability,COFs is expected to become a universal porous material for purifying the environment.Therefore,TP-TAPPA-COF,Fe₃O₄@TP-TAPPA-COF,Fe₃O₄@NH₂-MOF-5@TP-TAPPA-COF composites were designed and synthesized in this study,which were used to remove organic pollutants in wastewater.the synthesis and removal conditions were optimized in detail,and the removal mechanism was studied.Chapter Ⅰ:Three-dimensional covalent organic framework materials were synthesized based on Schiff base reaction,which were used to adsorb and remove o-nitrophenol from water.In this study,N,N,N,N-tetra（p-aminophenyl）p-phenylenediamine（TAPPA）was used as amino ligand and trioxyphloroglucinol（TP）as aldehyde ligand,and a new covalent organic framework material（TP-TAPPA-COF）was synthesized by solvothermal method in the mixed solvent of mesitylene/1,4 dioxane/acetic acid.The prepared COF was characterized by SEM,Zeta potential,IR,N₂adsorption and TG.And the COF was used as an adsorbent to study the adsorption of o-nitrophenol in aqueous solution.The effects of adsorbent dosage,p H and other conditions on the adsorption of o-nitrophenol were studied,which showed excellent adsorption capacity(the adsorption capacity reached 460 mg_·g^-1).Adsorption kinetics accords with pseudo-first-order kinetic model,and adsorption isotherm follows Langmuir isotherm equation.In addition,COF showed good reusability,and the removal efficiency decreased by 11%after five consecutive cycles.Chapter Ⅱ:In order to solve the problem that COFs are difficult to be separated from aqueous solution because of its light texture,magnetic covalent organic framework composites（Fe₃O₄@TP-TAPPA-COF）were prepared by coating amino functionalized magnetic microspheres on the surface of COFs.The synthesized materials were characterized by TEM,XRD,N₂adsorption,IR and Zeta potential.The Fe₃O₄@TP-TAPPA-COF was used as adsorbent for the adsorption of 2,6-dichlorophenol in water.The effects of adsorbent dosage and p H on the adsorption of 2,6-dichlorophenol were studied.The results show that Fe₃O₄@TP-TAPPA-COF has excellent adsorption effect on 2,6-dichlorophenol,which can be well fitted by pseudo-first-order kinetics.Adsorption of 2,6-dichlorophenol by Fe₃O₄@TP-TAPPA-COF can proceed spontaneously and is an exothermic reaction.The Fe₃O₄@TP-TAPPA-COF adsorbent has good reusability,and the recovery rate is as high as85%Chapter Ⅲ:The Fe₃O₄@NH₂-MOF-5@TP-TAPPA-COF heterogeneous catalyst with high catalytic performance was prepared by covalently linking NH₂-Fe₃O₄,NH₂-MOF-5 and TP-TAPPA-COF.The materials were characterized by PL,DRS and so on.The prepared Fe₃O₄@NH₂-MOF-5@TP-TAPPA-COF catalyst was used to evaluate the photocatalytic performance of methylene blue dye（MB）in water.The effects of p H and MB concentration on the photocatalytic degradation of MB by NH₂-MOF-5,Fe₃O₄@TP-TAPPA-COF and Fe₃O₄@NH₂-MOF-5@TP-TAPPA-COF were optimized.The experimental results show that Fe₃O4@NH₂-MOF-5@TP-TAPPA-COF catalyst has good photocatalytic performance for MB,and the removal rate can reach 90%.At p H=10,the photocatalytic degradation efficiency is the best.The functional order of Fe₃O₄@NH₂-MOF-5@TP-TAPPA-COF for photocatalytic degradation of MB is e->·OH>h⁺>·O₂^-.