Synthesis Of Benzodiimidazole-Based Porous Organic Polymers And Their Application In Iodine Adsorption

The capture and safe storage of radioactive iodine(¹²⁹I or ¹³¹I)are of a compelling significance in the production of nuclear energy and stockpiling garbage.Porous organic polymers（POPs）are considered as one of the most popular iodine capture and storage materials because of their large specific surface area,low density,good stability and easy modification.Previous studies have demonstrated that the introduction ofπ-conjugated systems and atoms containing lone pair electrons（such as N and S）into POPs networks can improve the iodine adsorption capacity of POPs.Therefore,we synthesized two novel monomers containing a largerπ-conjugated system and more N atoms and formed polymer networks by copolymerization,and studied the iodine adsorption properties of the resulting POPs.The main contents are as follows:（1）4’,4’’’-（1,5-dibutyl-4,8-bis（4-formylphenyl）-1,5-dihydrobenzo[1,2-d:4,5-d’]diimidazole-2,6-diyl）bis（[1,1’-biphenyl]-4-carbaldehyde）（TDI）and 4’,4’’’-（1,7-dibutyl-4,8-bis（4-formylphenyl）-1,7-dihydrobenzo[1,2-d:4,5-d’]diimidazole-2,6-diyl）bis（[1,1’-biphenyl]-4-carbaldehyde）（CDI）monomers were synthesized from1,2-dichlorobenzene.（2）Two kinds of thiazolothiazole-linked porous organic polymers TDI-DTO and CDI-DTO were synthesized by the reaction of dithiooxamide with TDI and CDI,respectively.The N₂isothermal adsorption-desorption measurement results show that the specific surface areas of TDI-DTO and CDI-DTO are 68.7 m²g^-1and 50.4 m²g^-1,respectively,and the pore volumes are 0.206 cm³g^-1and 0.129 cm³g^-1,respectively.Due to theπ-conjugated structure and thiazolothiazole and benzimidazole groups,TDI-DTO and CDI-DTO have good iodine adsorption properties.The saturated adsorption capacities of gaseous iodine for TDI-DTO and CDI-DTO are 3.07 g g^-1and 2.29 g g^-1,respectively,and the saturated adsorption capacities of iodine in solution are 1594 mg g^-1and 1363 mg g^-1,respectively.The kinetic model and thermodynamic model were used to fit the adsorption of iodine in solution.It was found that the adsorption of iodine in cyclohexane by the polymers was more consistent with the quasi-first-order kinetic model and Langmuir isothermal adsorption model.In addition,the chemical state of iodine adsorbed in TDI-DTO was studied by Raman spectroscopy,and the results showed that iodine adsorbed in TDI-DTO mainly existed in I₃^-and I₅^-forms.（3）Two kinds of imine-linked porous organic polymers TDI-PDA and TDI-BZ were synthesized by the reaction of monomer TDI with p-phenylenediamine and benzidine,respectively.The specific surface area and pore volume of the two polymers were 113.3 m²g^-1/0.528 cm³g^-1and 87 m²g^-1/0.454 cm³g^-1,respectively.Then,the adsorption capacity of TDI-PDA and TDI-BZ for gaseous iodine and solution iodine were studied,the gaseous iodine adsorption capacity was up to 5.29 g g^-1and 4.57 g g^-1,while that of solution iodine was up to 2343 mg g^-1and 2039 mg g^-1,respectively,in which the solution iodine adsorption followed the quasi-first-order kinetic model and Freundlich isothermal adsorption model.In addition,the results of Raman spectra confirmed that a charge transfer complex was formed between TDI-PDA and iodine,and the adsorbed iodine existed in the form of I₃^-and I₅^-.