Preparation Of Doped Porous Carbon For The Adsorption Of Iodine

The environmental problems and energy crisis caused by excessive use of traditional fossil fuels have attracted worldwide attention.In order to meet energy requirements,the use of nuclear energy has increased significantly.Radionuclides such as radioactive iodine are one of the inevitable products in the use of nuclear energy.Radioactive iodine must be effectively removed to prevent the harm of radioactive iodine to humans and the environment.The solid adsorption method is considered to be the best method for removing radioactive iodine because of its high removal rate,simple operation and low cost.At present,different kinds of solid adsorbents such as zeolites,metal-organic frameworks,and porous organic polymers have been reported for iodine adsorption.Porous carbon is favored because of its excellent thermal and chemical stability,high surface area,high pore volume and adjustable pore size.It has more advantages than other solid adsorbents.In this paper,a porous carbon with excellent performance was developed,which was modified by doping nano-copper particles,and the adsorption performance of iodine was investigated to reveal the iodine adsorption mechanism.Finally,the formed porous carbon was prepared from the porous carbon with the best adsorption performance.The details are as follows:(1)A series of porous carbons(NBCs)were prepared by KOH activation using benzimidazole with high nitrogen content as carbon precursor.The specific surface area,pore volume and pore structure of porous carbon were regulated by changing KOH ratio and activation temperature.The physicochemical properties of the samples were tested by SEM,BET and other characterization methods,and the adsorption properties of the samples to iodine were studied.Based on the experimental data,molecular simulation and adsorption model results,the effects of pore size and surface chemical properties on iodine adsorption performance were analyzed,and the adsorption mechanism was revealed.Iodine vapor adsorption mainly depends on the content of micropores and narrow mesopores,while nitrogen and oxygen doping have limited effects on gaseous iodine adsorption.Narrow mesopores determine the amount of iodine adsorbed by the sample in water solution.Nitrogen and oxygen groups can improve the polarity of the carbon surface,thereby improving the interaction between the carbon surface and water molecules,and effectively preventing the accumulation of iodine in the pores.Micropores determine the amount of iodine adsorbed by the adsorbent in cyclohexane solution.(2)In order to improve the iodine adsorption performance of NBCs,copper nanoparticles were doped into NBC800-2.A series of Cu/NBCs composites were synthesized by changing the amount of copper.The results showed that copper is mainly doped in porous carbon in the form of elemental.The specific surface area and pore volume of Cu/NBCs increased first and then decreased with the increase of the doping amount of the nano-copper particles.The doping of nano-copper particles increased the electrostatic force of the adsorbent on iodine,especially in cyclohexane and aqueous solution,which increased the saturated adsorption capacity of the adsorbent from 767 and 2735 mg/g to 1490 and 2878 mg/L,respectively.In addition,compared with NBC800-2,Cu/NBCs also has excellent regeneration,and after three cycles,it still maintains more than 90%of the adsorption capacity.(3)In order to meet the requirements of transportation and practical use,a series of cylindrical porous carbons with different binder ratios were prepared by using Cu/NBC0.2 as raw material and phenolic resin as binder.The optimum binder ratio was obtained by compressive strength and iodine adsorption performance test:8wt%.The maximum compressive strength of the formed porous carbon was 12.5 MPa,and the iodine adsorption amounts of iodine vapor,iodine/cyclohexane solution and iodine solution were 4765,418 and 2069 mg/g,respectively.