Application Of Vinyl Covalent Organic Framework Materials In The Capture Of Radioactive Iodine And The Organic Solvent Nanofiltration Membrane Separation

Covalent Organic Frameworks（COFs）are porous crystalline materials prepared from covalently linked molecular organic building blocks.COFs can integrate organic functional small molecular units into a clear topological structure to form a network crystalline polymer with open pores,which provides a new platform for the design of periodically ordered organic porous materials.In recent years,COFs materials have shown great potential in post-modification synthesis,such as adsorption separation,energy storage,catalysis,optoelectronic devices and membrane separation.In this paper,vinyl functionalized covalent organic framework material（COF-V）was selected as the research object,and the capture performance of COF-V for radioactive iodine nuclides in aqueous solution was explored.At the same time,COF-V membrane prepared by liquid-liquid interfacial polymerization was also studied for organic solvent nanofiltration membrane separation process.The main research work of this paper was as follows:（1）In this work,2,5-divinylterephthalaldehyde and 1,3,5-tris（4-aminophenyl）benzene monomer were used to successfully synthesize covalent organic framework materials（COF-V）with hcb topology.In this chapter,spherical and filamentous COF-V with uniform morphology were prepared by adjusting the type of reaction solvent and acetic acid content.COF-V material had large specific surface area,high porosity and low density.The adsorption performance of spherical COF-V powder for Na¹³¹I in aqueous solution was explored.The adsorption capacity of COF-V for Na¹³¹I in aqueous solution was as high as 437.8 mg g^-1,and the removal rate of Na¹³¹I was more than 90%in water from 181.3 MBq（4.9 mCi）to 1017.5 MBq（27.5 mCi）.Through NaI adsorption experiments and DFT theoretical simulation studies,it was found that the COF-V material mainly achieved effective capture of iodine ions in aqueous solution by forming aπ-conjugated system C-H...I^-with a weak hydrogen bond mechanism.In addition,cationic covalent organic frameworks were prepared by introducing allyl trimethyl ammonium chloride quaternary ammonium salt polymer small molecules into COF-V materials through free radical polymerization.It was also used in NaI adsorption in aqueous solution;the results showed that the adsorption capacity of NaI in water was 503 mg g^-1.（2）It was very ideal to achieve precise selective separation in organic solvents with high permeability,but it has not yet been achieved because it requires strict control of the selectivity of nanofiltration membranes.In this work,a vinyl-containing covalent organic framework membrane was prepared by liquid-liquid interfacial polymerization.Self-supporting COF-V membranes with different thicknesses were successfully prepared by adjusting the type of organic phase solvent,catalyst type and monomer concentration.The pore size was fine-tuned at the nanoscale by thiol-ene‘click chemistry’Specifically,sodium 3-mercaptopropanesulfonate was grafted onto the surface and inner pores of the COF-V membrane.Fourier transform infrared spectroscopy.X-ray photoelectron spectroscopy and surface charge confirmed the successful preparation of post-modification.Nitrogen adsorption proved that the pore size was significantly reduced.In the COF-V membrane,the methanol pure solvent permeability reaches 132 L m^-2h^-1bar^-1,and the molecular weight cutoff（MWCO）was 700 g mol^-1.After post-modification,the maximum pore size decreased from 2.6 nm to1.5 nm,and MWCO decreased from 700 to 440 g mol^-1.In addition,this work clearly demonstrated that the COF-V-SO₃Na membrane has excellent practicability in purifying active pharmaceutical ingredients from organic liquids,and has a good rejection rate for tetracycline and vitamin B₁₂;in order to explore more application potential,this work expands the extraction of stevioside enrichment solutes and recovery solvents.The results show that the COF-V-SO₃Na membrane has a 100%rejection rate for stevioside.This work reveals the great potential of unique 2D COFs post-modified covalent organic framework membranes in the industrial application of producing outstanding OSN membranes.