Synthesis Of Hydrazone Bonded Covalent Organic Frameworks And Its Application In Fluorescent Detection And Adsorption Of Heavy Metal Ions

Covalent organic frameworks（COFs）are new porous organic crystal materials connected by C,H,O,N,S,B and other light elements through strong covalent bonds,which has very unique and excellent performance,such as:low density,high porosity,large surface area,good thermal stability,and good chemical stability.At present,it has been widely used in energy storage,catalysis,adsorption and separation of gas,sensing,chromatographic separation and so on.Heavy metal polluted wastewater（containing heavy metal ions such as lead,copper,mercury,nickel and cadmium）produced in the process of industrial production is a serious environmental pollutant.With the rapid development of industrialization,a large number of heavy metal polluted wastewater has been produced in the process of electroplating,chemical industry,electronics,mineral smelting and other industrial production.Heavy metals in wastewater generally cannot be broken down completely,and they can be absorbed and enriched by living organisms.The higher the trophic level in the food chain,the more likely it is to accumulate and cause disease.Heavy metal ion pollution poses a serious threat to human beings and has serious toxicological effects on human body,such as inhibiting enzyme activities in human body and damaging human nervous tissue,kidney and other organs.Covalent organic frameworks are a new type of porous crystalline material.It has uniform and ordered structure,easily modified side chain and pore size,high designability,good fluorescence quantum yield and excellent chemical stability,so it has great potential in fluorescence sensing.At the same time,its porous structure and large specific surface area enable it to fully expose the active site.Make it an excellent adsorption material.Based on the above advantages,this paper applied covalent organic frameworks to the detection and adsorption of heavy metal ions,and carried out the following innovative research:（1）COFs connected by hydrazone bonds have a largeπconjugated system,and the interlayer hydrogen bond interaction limits the intramolecular rotation and reduces the non-radiation loss,making it an excellent signal sensor.Hydrazone bond connected TFPB-DHz Ds was simply synthesized by room temperature method.TFPB-DHz Ds has good crystallinization,large surface area,excellent fluorescence and uniform distribution of chelating sites.The evenly distributed thioether function in the pore wall makes it a highly sensitive copper ion fluorescence detector.The detection limit is 48n M.At the same time,TFPB-DHz Ds has a large specific surface area,uniform and dense pore structure,and has good chemical stability,acid and alkali resistance,so it is also an efficient copper ion adsorption material.The adsorption capacity of Cu²⁺at room temperature can reach 203 mg g^-1.（2）A 2D hydrazone bonded COF TFPB-DHz DAll-SH was designed for the first time for the detection and adsorption of mercury ions.Based on the structure of TFPB-DHz DAll,we modified the selective chelating agent 2,5-dimerto-1,3,4-thiadiazole（DMTD）to TFPB-DHz DAll to obtain TFPB-DHz DAll-SH by clicking reaction.XPS,EDS,infrared spectra and other characterization methods proved that the modification was successful.Subsequently,TFPB-DHz DAll-SH was applied to the detection and adsorption of mercury ion.The results show that TFPB-DHz DAll-SH is a kind of mercury ion sensor with high sensitivity and selectivity.At the same time,TFPB-DHz DAll-SH,as a kind of mercury-ion adsorbent,also showed excellent adsorption performance,with the adsorption capacity up to 952 mg g^-1.The adsorption efficiency can reach 99.83%within 5 min,and excellent adsorption effect is also obtained when it is applied to actual water samples.（3）A hydrazone bonded COF TFPB-DHz DAll-SH-1 was designed for the detection and adsorption of lead ions.The COF was obtained by post-modification of TFPB-DHz DAll synthesized at room temperature with 1,2-ethanedithiol.TFPB-DHz DAll-SH-1 retains the crystallinity and fluorescence properties of the original material,while introducing a large number of lead ion recognition sites.TFPB-DHz DAll-SH-1 is an efficient fluorescent sensor with specific fluorescence response to lead ions.At the same time,the adsorption capacity of Pb ions can reach 166 mg g^-1through electrostatic interaction and coordination.