Iodine Adsorption And H₂O₂ Electrosynthesis By Porphyrinic Covalent Organic Polymers And Their Derived Carbon Materials

Nuclear energy is a kind of clean and efficient energy,but a large amount of radioactive iodine will be produced in the process of use,which will bring serious harm to the environment and ecosystem.It is of great significance to search for efficient adsorbing materials for radioactive iodine.Recently,organic porous polymers have been found to be effective adsorption of radioactive iodine in the gas phase,but their adsorption performance for iodine in the liquid phase is poor,the adsorption capacity is low,the adsorption rate is slow,and the practical application is limited.In addition,the anthraquinone process for industrial production of hydrogen peroxide has problems of high energy consumption,high risk and high pollution.The search for green and low energy consumption production of hydrogen peroxide products has been widely concerned.Among them,electrocatalytic reduction of O₂in aqueous solution at room temperature to produce hydrogen peroxide is a popular production technology.The technology is mainly limited by the lack of efficient and stable electrocatalytic materials.In recent years,the low cost,high activity and good stability of carbon-based catalysts show good performance in electrocatalytic synthesis of H₂O₂,but the catalyst efficiency,stability and selectivity still need to be improved.In this paper,a series of porphyrin covalent porous organic polymers were prepared by using porphyrin's unique highly conjugated structure and functional groups containing rich hetero-elements as construction units to develop efficient liquid phase iodine adsorption materials.The polymer was further pyrolyzed and modified to prepare effective catalytic materials with H₂O₂properties.The specific research contents are as follows:(1)Using 2-thiophene formaldehyde,p-benzaldehyde,pyridine-benzaldehyde,homophentriformaldehyde and furan-benzaldehyde as monomers,the schiff base reaction with pyrrole was carried out,and five new porphyrin-type covalent organic polymer nanospheres were rapidly prepared by one-pot method.The abundance of electron-rich nitrogen,sulfur and oxygen atoms as well as N-H groups in porphyrin polymers can efficiently interact with iodine and CO₂through charge transfer contact.The adsorption capacity of iodine in cyclohexane solution and CO₂in exhaust gas is79 mg g^-1and 760 mg g^-1,respectively,within 3 h.(2)Functional groups with rich-SO₃H and-COOH on the surface of S,N,O and other non-metallic elements were prepared by means of pyrolysis and sulfonation of five kinds of synthesized porphyrin polymers.It is proved that the selectivity of electrocatalytic synthesis of H₂O₂can be greatly improved by sulfonation.Under alkaline conditions,the selectivity of H₂O₂can reach 90%,and the number of transferred electrons is close to the theoretical value of H₂O₂generation.This sulfonation strategy is universal and can significantly improve the selectivity of electrocatalytic synthesis of H₂O₂from various carbon materials.(3)Using p-nitrobenzaldehyde and pyrrole as monomers,a polymer containing double porphyrin structure was prepared.The polymer was rich in pores,and the-NO₂,-NH₂and pyridine N atoms contained in the structure could interact with iodine.The adsorption capacity of iodine in the liquid phase was up to 720 mg g^-1within 3 h.The derived porous carbon material obtained from pyrolysis at 800?has abundant doping sites of N element,which effectively improves the selectivity of H₂O₂produced by two-electron electroreduction of O₂.Without any modification,the selectivity can reach 76%,and the performance is almost unchanged after undergoing10 000 cycles of polarization curve test,with good electrocatalytic stability.