Synthesis Of Triphenylimidazole-based Porous Organic Polymers And Their Application In Iodine Adsorption

Porous organic polymers(POPs)are a type of polymeric materials with micro-and meso-porous structure that are formed by the covalent linkage of organic building blocks with functionalities greater than two.Owing to their large surface areas,low skeleton densities,high physicochemical stabilities,and tunable molecular structures,POPs have broad application prospects in the fields of gas separation and storage,heterogeneous catalysis,and energy storage and conversion.In recent years,POPs applied to the adsorption of radioactive iodine(RAI)has attracted wide attention due to that RAI treatment in nuclear waste is a major environmental problem.Highly efficient RAI capture is of great significance to human health and environmental protection.Many studies have proved that the introduction of?-conjugated structure,N=N/-NH₂/-OH groups,and N,S,O etc.heteroatom into the POPs can greatly improve their affinity for iodine,which therefore significantly enhances the iodine uptake.Based on this,two types of triphenylimidazole-containing POPs have been synthesized in this thesis,and their iodine adsorption performance was investigated in detail.The main research contents of this thesis are as follows:(1)Synthesis of triphenylimidazole-based POPs via Yamamoto coupling reaction and their application in iodine adsorption.Two types of novel triphenylimidazole-containing porous organic polymers,namely PTI-Et and PTI-Bu,were synthesized via Yamamoto coupling reaction by using 2,4,5-tris(4-bromophenyl)-1-ethyl-H-imidazole(TI-Et)and 2,4,5-tris(4-bromophenyl)-1-butyl-1H-imidazole(TI-Bu)as the building blocks.The results of N₂isothermal adsorption-desorption measurements show that the specific surface areas and total pore volumes of PTI-Et and PTI-Bu are 833 m²g^-1/0.76 cm³g^-1and 469 m²g^-1/0.36 cm³g^-1,respectively.Owing to their relatively high specific surface areas together with the abundant?-conjugated structure and imidazole moieties,the vapor iodine adsorption capacities of PTI-Et and PTI-Bu were estimated to be 3.92 g g^-1and 3.63 g g^-1,respectively,whereas the solution iodine adsorption capacities reached 1372 mg g^-1and 1015 mg g^-1,respectively.The solution iodine adsorption is more consistent with the pseudo-second order kinetic and Freundlich isotherm models for polymers.In addition,Raman analysis showed that the charge transfer complex was formed between PTI-Et and iodine,and the adsorbed iodine mainly existed in the form of polyiodide anions(I₃^-and I₅^-).(2)Synthesis of azo-linked triphenylimidazole-based POPs via diazo coupling reaction and their application in iodine adsorption.Two triphenylimidazole-derived amino-containing building blocks,4,4',4''-(1H-imidazole-2,4,5-triyl)trianiline(TIA)and 4,4',4'',4'''-(1,4-phenylenebis(1H-imidazole-2,4,5-triyl))tetraaniline(DTIA)were synthesized by benzoin condensation,Debus imidazole formation,and deprotection reactions by using p-acetaminobenzaldehyde as the starting material.And then three azo-linked,triphenylimidazole-containing porous organic polymers,namely TIA-HQ,TIA-PG and DTIA-HQ,were prepared by separate diazo coupling of TIA and DTIA with phloroglucinol(PG)and/or hydroquinone(HQ).The specific surface areas and total pore volumes of the three polymers are in the range of 83-493 m²g^-1and0.22-1.24 cm³g^-1,respectively.Owing to their relatively low specific surface areas,the adsorption capacity of vapor iodine are in the range of 1.89-2.13 g g^-1,while the adsorption capacity of solution iodine are in the range of 979-1031 mg g^-1for these polymers.Among which iodine adsorption in solution is more in accordance with the pseudo second order kinetic and Freundlich isotherm models.