Design And Synthesis Of Novel Functional 2D Covalent Organic Frameworks And Their Applications In Marine Resources And Environment

Covalent organic frameworks（COFs）,one of the porous materials,are crystalline frameworks constructed by diverse organic monomers with light elements（C,N,O,H）linked through covalent bonds.By virtue of its large specific surface area,ordered porous structure,flexible modification and functionalization,tunable porosity and tailored functionalities,COFs offer unlimited opportunities and possibilities for a wide variety of applications.Considering the practical requirement of marine environment remediation and marine resource utilization,several functional COFs and corresponding composite materials are elaborately designed and synthesized according to the Schiff base reaction and post-synthetic modification（PSM）strategy,and their applications in selective adsorption,lithium-sulfur battery and electrocatalytic oxygen evolution reaction are respectively investigated.The main contents are as follows.（1）Uranium,which is abundant in the ocean but exists in the form of uranyl tricarbonate([UO2（CO3）3]^4-)with an extremely low concentration of 3.3 ppb,is a significant element of nuclear energy.It is of immediate significance to the research into uranium extraction by the exploration of adsorbents for environment and resource sustainability.Herein,the new ionic COFs named COF-DG is designed and synthesized via Schiff base reaction between organic monomers diaminoguanidine hydrochloride and 1,3,5-triformylphloroglucinol.COF-DG possesses an uptake capacity of 65.6 mg g^-1 toward the[UO2（CO3）3]^4-,attributed to the chemical interaction and anion exchange between[UO2（CO3）3]^4-and the cationic COF-DG with Cl^-,as well as the electrostatic attraction.Besides,COF-DG exhibits a higher affinity and selectivity toward[UO2（CO3）3]^4-in the presence of the competing anions.（2）A suitable porous adsorbent with prominent adsorption performance and better selectivity for the target containments such as non-steroidal anti-inflammatory drugs（NSAIDs）is highly desired in wastewater treatment.Herein,two COFs（COF-NO2 and COF-NH2）with different functional groups are designed and prepared by Povarov reaction to enhance selective adsorption ability toward the Ketoprofen（KTP）molecule via functional group tuning.For KTP,due to the amino group which can interact with not only carboxylic acid but also the carbonyl group,COF-NH2 exhibits twice adsorption capacity as high as the other two counterparts Ibuprofen（IBP）and Naproxen（NPX）.However,there is no selectivity for those three NSAIDs when COF-NO2 is used as adsorbents.（3）The development of functional COFs with specific properties is an emerging research field.Herein,the functionalized COF-SQ-Ph is synthesized through the Povarov reaction between the triazine-based COFs（COF-SQ）and phenylacetylene in the flask.COF-SQ-Ph with an extendedπ-conjugated structure and enhanced structural stability is used as the sulfur loading recipient for lithium-sulfur（Li-S）batterie.Sulfur-impregnated COF-SQ-Ph marked as COF-SQ-Ph-S displays better cycling stability with a specific capacity of 618m A h g^-1 after 150 cycles due to the lithiophilic interaction between lithium polysulfides（Li PSs）and nitrogen atoms from quinoline and triazine moieties.（4）Functional triazine-based COFs with boric acid units,COF-Tr-BA,are designed and synthesized via cycloaddition of COF-Tr with（4-ethynylphenyl）boronic acid.Owing to the chemical interaction between boric acid units and adjacent dihydroxyl groups,COF-Tr-BA is used as the adsorbent for the selective adsorption of genistein isomer 4’6,7-trihydroxyisoflavone,showing an excellent selectivity and great adsorption performance with 5.4 times adsorption capacity(67.5 mg g^-1)as high as 4’5,7-trihydroxyisoflavone(12.5mg g^-1).Meanwhile,COF-Tr-BA as the sulfur host for Li-S battery also exhibits a better electrochemical property,giving an initial discharge capacity up to 1349 m A h g^-1 and a substantial capacity of 627 m A h g^-1after 200 cycles.It is attributed to the sulfiphilic interaction between the introduced boric acid groups and PSs,as well as the lithiophilic interaction between N atoms from quinoline and triazine moieties on the backbone of COF-Tr-BA and Li⁺,thus alleviating the dissolution and reducing the shuttle effect of Li PSs.（5）The search for functionalized COFs materials is significant on account of their great promise for frontline applications in various fields.Herein,a novel and convenient tactic is developed to design and fabricate the tetrazole-functionalized COFs materials with abundant nitrogen atoms,facilitating the incorporation of COFs with metal ions.In particular,aβ-ketoenamine-linked COFs named COF-TpDb is selected as the precursor to introduce the tetrazole moieties to coordinate with Co²⁺and Pd²⁺,giving two metal-coordinated COFs complexes COF-TpDb-TZ-Co and COF-TpDb-TZ-Pd.The resultant COF-TpDb-TZ-Co displays a higher oxygen evolution reaction activity with a lower overpotential of 390 m V at the current density of 10 m A cm^-2,which is much enhanced compared to COF-TpDb-TZ.In conclusion,different functional COFs materials are designed and fabricated to be applied in the fields of marine resources and the environment.It is not only promoting the development of functional COFs with more sophisticated structures and versatile properties but also facilitates the application of COFs as multifunctional materials in diverse fields.