Preparation Of Aerogels Based On Porous Boron Nitride Micro/Nanofibers For The Iodine Adsorption

Nuclear energy occupies an important position in the field of energy development.However,there is an important risk in the use of nuclear energy,radioactive pollution caused by the leakage of nuclear fission products.Among the nuclear fission products,radioactive iodine has received special attention because of its extremely high volatility,which can accumulate in human’s thyroid gland and cause significant harm to human body.The effective capture and storage of iodine is of great significance for preventing the leakage of radioactive iodine and improving the safety of the nuclear industry.This paper studies the construction of aerogels based on porous BN micro/nano fibers and metallic copper/silver modified porous BN fibers,and studies their iodine adsorption and storage properties.1.BN aerogel with ultra-light density was synthesized by using boric acid and melamine as raw materials,through ultrasonic-assisted,freeze-drying and in-situ conversion.Studies have shown that the synthesized BN aerogel is composed of a large number of porous BN microfibers with a high aspect ratio,which are mounted and wound with each other.It possesses open cell structure,high specific surface area（561.92 m²/g）,large pore volume（0.45 cm³/g）and abundant surface functional groups.The adsorption performance of BN aerogel on iodine vapor and iodine that dissolved in organic solvent was studied.The results showed that the adsorption capacity of iodine vapor by BN aerogel reached～212 wt%,and the adsorption capacity of iodine in iodine/n-hexane solution with a concentration of 50 mg/L reached at 61.33 mg/g,showing an excellent iodine adsorption capacity.The isothermal adsorption curve of BN aerogel for iodine in solution follows the Freundich model,and the adsorption kinetics follows the pseudo-second-order kinetic model.2.The effect of ethanol on the elution of iodine adsorbed in BN aerogel was studied.It was found that after multiple elution treatments,about 60%of the iodine in the aerogel was removed,but about 40%of it was still kept in aerogel.The high-temperature heat treatment was used to regenerate the aerogel adsorbed iodine.It was found that heated at 900°C in N₂atmosphere can achieve a good regeneration of BN aerogel,and almost all iodine will be released.The regenerated aerogel still possesses a good adsorption effect on iodine.Thermogravimetric analysis was used to study the adsorption/desorption performance of iodine in BN aerogel.From the calculation result of Kissinger’s equation,it can be seen that the adsorption of iodine by BN aerogel is determined by the"host-guest interaction"between aerogel and iodine and the"guest-guest interaction"between iodine and iodine,the iodine adsorbed in the BN aerogel possess a higher apparent activation energy and the volatilization is suppressed.3.Copper/silver nanoparticles modified BN aerogels were successfully prepared by introducing copper or silver ions during the synthesis of BN aerogels.Compared with BN aerogels,the diameters of BN fibers in both new aerogels are significantly reduced,the compressive strength and compression resilience of aerogels are significantly improved.The specific surface areas of copper and silver-containing BN aerogels increased to 718.12 m²/g and 689.98 m²/g,respectively.Studies on the iodine adsorption performance of copper and silver-containing BN aerogels have shown that the adsorption capacity of metal-modified BN aerogels for vapor iodine has been greatly increased,and the iodine adsorption capacity of silver-containing aerogels has reached 22.3 times its own mass.Higher than other solid-phase iodine adsorbents currently known.Thermogravimetric analysis and calculation of apparent activation energy show that the presence of copper and silver can enhance the"host-guest interaction"between aerogel and iodine,which is beneficial to the adsorption of iodine by aerogel.