Adsorption,Separation And Detection Of Radioactive Noble Gases Including Kr,Xe And Rn

On the one hand,the separation of the noble gas xenon/krypton(Xe/Kr)is of significant importance for industrial development and the sustainability of nuclear power.Currently,cryogenic distillation is the only commercially established method for the separation of Xe/Kr,but it suffers from high energy consumption and low efficiency.Adsorptive separation is a relatively low energy consumption method due to its mild operating conditions.It is usually used to selectively separate gas mixtures by exploiting the difference in adsorption capacity of porous solid materials for different gas components and is now widely used for Xe/Kr separation.On the other hand,the removal of the radioactive noble gas radon(Rn)is not only of great importance for human health,but also crucial for the smooth running of some cutting-edge physical experiments.Forced ventilation and physical barriers are two of the more common and efficient methods available for Rn removal,but in some specific workplaces these methods can be very limited and expensive to implement.At this moment active capture of Rn using porous materials is an excellent alternative.Therefore,the selection of porous materials is a fundamental and critical step in the physisorption method,both for the separation of Xe/Kr and for the capture of radioactive Rn.In addition,the detection and monitoring of radioactive noble gases is essential as they pose a serious threat to human health due to the high-energy radiation produced along with their decay.However,these radioactive noble gases are colorless and odorless.Hence,using the response of scintillator materials to high-energy radiation to meet the detection of radioactive noble gases is a simple and feasible method.During the last two decades,metal-organic frameworks(MOFs)and covalent organic frameworks(COFs)featuring highly designable structures and functions,have been highly sought after by worldwide materials scientists and have shown unparalleled advantages in the field of gas adsorption and separation,sensing and so on.The aim of this thesis is to construct proper porous framework materials(mainly MOFs and COFs)for efficient Xe/Kr separation and deep Rn capture,and to investigate their intrinsic adsorption and separation mechanisms with the aid of some advanced experimental characterization or density flooding theory(DFT)calculations,in order to provide a reference for the subsequent design of inert gas adsorption and separation materials with better performance.At the same time,some preliminary exploratory work on MOFs scintillators will provide a solid foundation for the subsequent search for ideal radioactive inert gas detection materials with both inert gas adsorption and high-energy radioluminescence properties.The main research contents are as follows:In Chapter 2,we synthesized three COFs with the same connection node,named AFTG-COF,TpPa-COF and TpBD-COF,where AFTG-COF and TpPa-COF are in the AA stacking configuration and TpBD-COF is in the AB stacking configuration.The three COFs have distinctly different pore structures and therefore show significant differences in the adsorption and separation performance of Xe and Kr.Based on the Xe and Kr adsorption isotherms of the three COFs,we calculated their Henry coefficients Xe/Kr selectivity and the Xe/Kr selectivity predicted by IAST theory,thus establishing the relationship between pore structure and Xe/Kr separation performance in COFs materials,which laid a solid foundation for the subsequent design and synthesis of COFs materials with better Xe/Kr separation performance.In Chapter 3,we successfully synthesized a unique case of MOFs with locally positively charged one-dimensional channels(termed LPC-MOF)and explored their performance on Xe/Kr separation.The results of single-component Xe and Kr sorption isotherms and column breakthrough experiments demonstrate the excellent Xe/Kr separation performance of LPC-MOF and the potential for radioactive waste gas treatment in nuclear power plants.In addition,the results of DFT theoretical calculations not only illustrate the underlying mechanism for the excellent Xe/Kr separation performance of LPC-MOF from a structural level,but also quantitatively give a specific value for the enhancement of the Xe/Kr separation performance by the positive charge in the adsorption site for the first time,showing that the introduction of a positive charge can amplify the difference in affinity force between the framework and Xe and Kr by a factor of six.The experimental and computational work carried out in this chapter clearly demonstrates that the introduction of positive charges at the adsorption sites in the structure of MOFs has a significant contribution to the enhancement of the Xe/Kr separation performance,paving a new path for the subsequent exploration of MOFs materials in gas adsorption and separation.In Chapter 4,we selected ZIFs materials with excellent stability performance as the structural database,and initially screened out the optimal thermodynamic performance of the Rn-capture material ZIF-7 through theoretical calculations.Subsequently,kinetic calculations point out that ligand substitution is a good solution to the high kinetic energy barrier faced by ZIF-7 during the process of Rn absorption and give the theoretically optimal substitution ratio.Experimentally,we successfully synthesized ZIF-7-Im,the modified ZIF-7 material with the closest theoretical optimal substitution ratio.Single-component gas sorption measurements have shown that ZIF7-Im has significantly different gas adsorption behavior from ZIF-7,in agreement with the predictions of the theoretical calculations.The results of Rn breakthrough experiments show that the original ZIF-7 had essentially no Rn adsorption performance,while ZIF-7-Im showed superior Rn adsorption performance compared to commercial coconut activated carbon materials,with an increase in both Rn adsorption coefficient and adsorption capacity,especially in Rn removal depth by up to two orders of magnitude compared to activated carbon.This work innovatively combines theoretical simulations with practical experiments to successfully solves the tradeoff problem arising from thermodynamic-kinetic balance in inert gas capture with ultralow partial pressure,paving the way to design better Rn adsorbents.In Chapter 5,we initially synthesized two isostructural lanthanide-based MOFs with X-ray emission luminescence(XEL)properties,termed compounds 1 and 2.The results show that humidity stability and irradiation stability of the XEL of compounds 1 and 2 have significant advantages over commercial inorganic scintillators CsI:Tl.In addition,we have achieved the linear tunability of X-ray luminescence colors in lanthanide-based MOFs scintillators by means of lanthanide ions doping for the first time.This work demonstrates the great advantages of MOFs materials in the field of high-energy radioluminescence detection and provides a basis for the subsequent search for ideal radioactive gas detection materials with both radioactive noble gas adsorption properties and high-energy radioluminescence properties in MOFs materials.