Investigations On Functional Design,Synthesis And Adsorption Properties Of Covalent Organic Frameworks

Covalent organic frameworks(COFs)are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures.With predictable structural compositions and controllable functionalities,their structures and properties can be controlled to achieve targeted materials.The rational design,efficient synthesis and integrated applications of functional COFs have become one topic field of the organic materials chemistry.A key challenge in the design of functional COFs is how to keep the crystallinity unchanged when introducing functional sites to promote the selectivity and adsorption capacity in the environmental chemistry.In this thesis,five COFs with different pore structures and functional groups were synthesized based on the multi-component reaction,monomer functionalization,and reaction condition control strategies.The adsorptive properties of these COF materials are evaluated using environmental pollutants,including heavy metal ions,persistent organic pollutants,and pharmaceutical and personal care products.The relationship between the structures of COF materials and their adsorption efficiency was studied with theoretical and experimental methods,which is beneficial to the design of the specific functional COFs.This thesis consists of the following five sections.1.The COF materials and its design strategies are introduced.Recent progress of functional COFs,involving their synthesis based on the monomer functionalization,linker transformation,and multi-component reaction,and applications for adsorption are briefly reviewed.2.In view of the multiple coordination of S and-CO₂H functions for the adsorption of heavy metal ions,a carboxy-functionalized COF-S-CO₂H was designed and synthesized from vinyl COF via thiol-ene click chemistry.The structure of COF-S-CO₂H was fully characterized by FT-IR,solid ¹³C NMR,XPS,SEM,PXRD,elemental analysis,and N₂ adsorption/desorption experiments.It was found that COF-S-CO₂H has excellent adsorption capacity for Pb²⁺(123.8mg/g)and Hg²⁺(99.1 mg/g)in water.The adsorption isotherms are Langmuir model and the kinetic adsorption fits the pseudo-second order model.In the multi-ion system,COF-S-CO₂H exhibits high selectivity for Pb²⁺and Hg²⁺.For real water samples,the removal efficiencies of Pb²⁺and Hg²⁺by COF-S-CO₂H are above 99%,showing its potentiality of practical application.3.For suitably packing the solid phase extraction(SPE)column,an amino-functionalized COF-S-NH₂ was designed and synthesized form the vinyl COF with an average particle size of8-15?m via thiol-ene click reaction.The structure of COF-S-NH₂was also fully characterized.Compared with commercial absorbents such as C18,phenyl-silica,silica and SAX,COF-S-NH₂shows higher extraction efficiency for phenoxyacetic acid pesticides.Based on the optimized SPE conditions of COF-S-NH₂,a method was successfully developed for the enrichment and determination of six phenoxyacetic acid pesticides in environmental water samples combined with HPLC technique.This method features wide linearity(0.2–100 ng/m L,R²?0.9991),low limits of detection(?0.06 ng/mL),low limits of quantification(?0.20 ng/mL),and excellent precision(RSDs?8.7%).The rate of recovery ranges from 89.6%to 102.4%with RSDs?7.1%.Our method can be applied to check 2,4-dichlorophenoxyacetic acid,4-chlorophenoxyacetic acid,2-(2,4-dichlorophenoxy)propanoic acid,and dicamba in drinking water according to the EU Drinking Water Quality Directive(98/83/EC).4.Two carboxy-functionalized quinoline-linked QCA-COFs were designed and constructed via the Doebner multi-component reaction.The structures of QCA-COFs were fully identified by FT-IR,solid ¹³C NMR,PXRD,SEM,elemental analysis,and N₂ adsorption/desorption methods.The major cis-orientation of carboxy functions is speculated by PXRD and total energy analysis.The stabilization of H-bonding may result in the formation of COFs with cis-functional arms.Four typical water-soluble organic pollutants,involving rhodamine B,gentamicin,methylene blue and 2,4-dichlorophenoxyacetic acid,are utilized to evaluate the adsorptive property of QCA-COFs.Compared with the adsorbents reported,four water-soluble organic contaminants at ultra-low concentrations(20–200 ng/m L)can be effectively purged from water within 15 min.The applicability of QCA-COFs to remove four environmental pollutants from real water samples is also validated.Above 95%removal efficiencies indicate that QCA-COFs have an anti-interference ability and can be used in the water purification.5.The microwave-assisted synthesis was used to facilitate the nucleophilic substitution of2,3,5,6-tetrafluoro-4-pyridinecarbonitrile with 2,3,6,7,10,11-hexahydroxy triphenylene for the preparation of the dioxin-linked TH-COF.TH-COF owns extraordinarily large surface area of1254 m²/g and is used as the coating for the solid-phase micro-extraction(SPME)of perfluorinated alkyl substances(PFASs).The adsorptive mechanism is evaluated using FT-IR,which reveals that the pyridine N atoms of TH-COF play a key role in the adsorption process by forming hydrogen bonds with PFASs.The SPME conditions were optimized in details.Under the optimized conditions,the TH-COF-SPME-UPLC-MS/MS method shows good linearity(0.01–1000 ng/L)with R²?0.9945.The method provides low limits of detection(?0.0045 ng/L),low limits of quantification(?0.015 ng/L),and excellent precision(3.3%–7.9%).The relative recoveries from spiked real water samples are 89.5%–105%with RSD?6.7%.The results demonstrate the applicability and reliability of the TH-COF-UPLC-MS/MS method for quantifying PFASs at trace levels in real water samples.In this thesis,five functional COFs have been successfully developed by the click reaction,multi-component reaction,and microwave synthesis.They can be used for the efficient removal of heavy metal ions,dyes,antibiotics and pesticides from water.Furthermore,an accurate sample pretreatment method based on the TH-COF SPME coating was established for the determination of PFASs.Our work is of great significance for the development of functional COF materials and expanding their applications in the environmental science.