| The development of nuclear power has been widely considered to sustainably solve the global energy shortage problem,accompanied by a large amount of radioactive waste gas.Among them,radioactive iodine is one of the main gaseous pollutants.In addition,various iodine isotopes(124I,125I,131I,etc.)are commonly used in nuclear medicine.The frequent production and application of iodine radiopharmaceuticals increase the risk of their leakage into the environment.Due to the volatility and radioactivity of iodine isotopes,its leakage may cause widespread pollution and environmental hazards.Therefore,the efficient adsorption of radioiodine isotopes is of great significance to the sustainable development of nuclear industry and nuclear medicine.Solid adsorption has been widely used for the removal and enrichment of radioactive iodine due to its simple operation and device design,low maintenance and operating costs.The performance of the adsorbent is crucial for efficient adsorption of iodine,Organic amine impregnated activated carbon and metal doped adsorbents have been widely used for radioactive waste gas treatment in the spent fuel reprocessing process.In recent years,porous aromatic polymers have also been developed for volatile iodine adsorption due to their controllable chemistry and pore structure.However,there are some bottlenecks in these materials,such as low adsorption capacity or rate,low stability and poor selectivity.In addition,the spontaneous release of adsorbed iodine is also an issue for most adsorption materials.To address the above challenges,a swellable conjugated micropore polymer(SCMP)was designed to achieve rapid capture of iodine at high temperatures and caging of adsorbed iodine at low temperatures through the expansion and contraction of the restricted pore in SCMP.In addition,nitrogen-rich silica foam(PKs)was prepared by simultaneous copolymerization and hydrolysis of PEI and KH560.PEI has a high density of amino groups,which provides a large number of iodine adsorption sites for iodine capture to realize the high-capacity adsorption and deep purification of iodine vapor.The specific research as follows:(1)Thermal-responsive conjugated micropore polymers for capture and caging of volatile iodineThe capture of radioiodine is crucial for nuclear security and environmental protection due to its volatility and superior environmental fluidity.Herein,we propose a strategy of "temperature-dependent gate" based on swellable conjugated microporous polymer(SCMP)to significantly improve the capture of volatile iodine.SCMP is constructed via the Buchwald-Hartwig coupling reaction of building monomers containing amines.It possesses a hierarchical pore structure with restricted pores,which can be "opened" and "closed" by changing the temperature.By virtue of the thermal-responsive pore structure,it reaches adsorption equilibrium for iodine in 2 h with a capacity of 4.3 g g-1 at 90℃ and retains 92.8%adsorbed iodine at room temperature.SCMP also exhibits a high adsorption capacity up to 3.5 g g-1 for dissolved iodine,as well as good radiation resistance and high selectivity for iodine against moisture,VOCs and HNO3 vapor.The adsorption mechanism of SCMP was investigated through XRD,ESR,FI-IR,and Raman,and the results showed that iodine vapor was chemically adsorbed by SCMP in the form of polyiodide ions.This work developed a new strategy for effective iodine capture,which can be extended to the separation and caging of resources or volatile pollutants in other fields.(2)Nitrogen-rich silica foam for efficient iodine captureThe development of iodine adsorption materials with simple preparation,high stability and good adsorption performance is of great importance for the purification of radioactive waste gases containing iodine in nuclear fuel reprocessing and hospital.In this work,we designed a nitrogen-rich silica foam for efficient adsorption of radioiodine isotopes.PEI and KH560 were copolymerized through the rapid reaction between the amino group of PEI and the epoxy group on KH560 to form a Si-N cross-linking network.At the same time,PEI acted as an alkali catalyst to accelerate the hydrolysis and condensation of KH560.The N content in the optimized sample PK-2 was determined by EDX to be as high as 26.2 wt%.PK-2 reached adsorption equilibrium within 5 hours at 75℃,with an adsorption capacity of 5.8 g g-1.In a dynamic experiment for the removal of low concentration iodine vapor in a simulated environment,41.2 L of iodine-containing gas with an iodine concentration of 284 mg m-3 could be completely purified by 100 mg of adsorbent at a flow rate of 150 mL min-1,indicating that PK-2 has good purification effect on iodine-containing gas.Additionally,PK-2 exhibited high adsorption capacities of up to 4.7 g g-1 and 4.9 g g-1 for dissolved iodine in water and hexane,respectively.The adsorption capacity of 4.9 g g-1 in hexane is the highest to date.PK-2 exhibit excellent selectivity towards iodine vapor in the presence of VOCs,water vapor,nitric acid vapor,and 84 disinfectant vapor.This work has developed a silica foam with simple preparation,high adsorption capacity and removal depth for volatile iodine.The foam has the potential to be used for the treatment of radioactive iodine waste gas in the nuclear industry and for air purification of iodine-containing isotopes in hospital nuclear medicine departments. |
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