| With the continuous consumption of fossil energy,to develop new energy is essential for human society.Nuclear fission energy using uranium as main fuel possesses high energy density without greenhouse gas emissions,which has developed rapidly,and may be a substitute to traditional fossil fuels.However,a large number of radioactive wastes generated by the nuclear power industry poses a serious threat to the environment and human health.Among them,uranium with strong chemical toxicity and radioactivity is the most common pollutant in various radioactive wastes.Besides,separation and recovery of uranium from wastewater not only can solve environmental safety issues,but also is an important guarantee for the sustainable development of the nuclear industry.Compared with nuclear fission,nuclear fusion possesses greater energy density,and does not produce greenhouse gases and spent fuel.Once a controllable nuclear fusion power generation is realized,it will power humans for thousands of years.Compared with other nuclear fusion,deuterium-tritium fusion is the mildest reaction and the most promising one to achieve controlled application.However,leakage of tritium with strong penetration and diffusion capabilities into the environment may cause an explosion and be a radiation damage for human body.In addition,due to extreme scarce of tritium in nature,recycling of tritium is of great significance.Therefore,a stable and efficient tritium removal system is an important guarantee for achieving controlled nuclear fusion.In short,effective prevention and treatment of radionuclide pollution is vital for the sustainable development of the nuclear fission and realization of controllable nuclear fusion.The porous organic framework is a kind of cross-linked polymer frameworks with micropores or mesoporous structures and formed by stacking molecules of the specific structure.Due to large specific surface area,adjustable porosity,stable physical and chemical properties,and rich reaction sites,porous organic frameworks possessed good application prospects in the field of environmental radiochemistry.To address the challenges of radioactive waste pollution and uranium resources in the nuclear fission industry,as well as the safety issues of the tritium process in controllable nuclear fusion,functional porous organic frameworks were developed for the separation and enrichment of key radionuclides(uranium and tritium).Specific studies of this paper are as follows:(1)Petroleum pitch-based porous aromatic frameworks with phosphonate ligand for efficient separation and enrichment of uranium from radioactive effluentsThe rapid development of the nuclear industry produces a large amount of radioactive waste liquid containing uranium,which is not only the main fuel of nuclear power plants,but also an important strategic resource of the country.However,the adsorbent faces severe tests,such as strong acidity,high radioactivity and compositional complexity of radioactive waste liquids.In response to these challenges,asphalt,a by-product of the petroleum industry,was used as a raw material to prepare a pitch-based porous aromatic framework with phosphonate ligand(PPAF)by a one-step Friedel-Crafts alkylation reaction in this study.The porous structure of PPAF could be used as an "ion sieve" for selective separation of uranyl ions,and the diethyl phosphonate ligands on PPAF could chelate U(VI)under acidic conditions as well as improve the dispersion of the adsorbent in water,which successfully solved the problems of selectivity,and hydrogen ion competition in high acidity environments,and then achieved efficient enrichment of uranium from highly acidic radioactive wastewater.Moreover,the large number of rigid benzene rings in the asphalt could effectively improve the radiation resistance and mechanical properties of the material,and enhance the service life of the material.PPAF could reach adsorption equilibrium in 40 minutes with an adsorption capacity up to 147 mg U/g at pH 1.0.PPAF had a good selectivity against various competing ions and an excellent radiation resistance in acidic solutions.In addition,PPAF could maintain 100%adsorption efficiency and complete structure after 5 adsorption-desorption cycles.In this work,asphalt,a waste of petroleum industry,was rationally reused for the efficient separation and recovery of uranium from radioactive wastewater.The three-dimensional channel of constructed by benzene ring improved the selectivity and stability of PPAF,which was expected to be practically applied to the treatment of radioactive wastewater in the future.(2)Honeycomb catalyst modified conjugated microporous polymers for separation and purification of hydrogen isotopes.With the continuous development of controlled deuterium-tritium fusion technology,it is expected to usher in a new era of nuclear fusion power generation However,the nuclear fusion industry will produce low-concentration exhaust gas containing tritium while supplying energy,which will cause serious security risks once failure to separate and purify in time.In this study,the honeycomb catalyst modified by a conjugated microporous polymer was proposed for hydrogen isotope separation and purification.Firstly,the CMPs skeleton was in-situ grafted on the surface of the honeycomb cordierite ceramics through a series of chemical reactions for a hydrophobic carrier,on which platinum was loaded to obtain a hydrophobic honeycomb catalyst(CAT).Due to the radioactivity and scarce resources of tritium,the catalytic performance was studied with hydrogen gas and deuterium gas.CAT had efficient catalytic activity at room temperature,and the hydrogen conversion was above 99%at 20000 h-1 space velocity under dry condition,whereas for commercial catalyst PII,the hydrogen conversion was only 59.8%at the same condition.In addition,due to the hydrophobicity of the substrate,CAT still maintained outstanding catalytic activity in the presence of water vapor.The isotope effect on catalyst activity was also explored,and CAT had high catalytic capacity for deuterium.Besides,the catalytic activity and chemical structure of CAT were almost unchanged after 200 kGy of ?-ray irradiation.In this work,the conjugated microporous polymers modified substrate improved the hydrophobicity of the catalyst and the distribution of platinum nanoparticles,leading to efficient separation and purification of hydrogen isotopes(3)Honeycomb catalyst modified covalent triazine skeletons for separation and purification of hydrogen isotopes.The noble metal catalyst for detritiation can deeply purify the tritium in the exhaust gas.However,the activation and long-term operation of the catalyst would cause the noble metal agglomeration and a large number of active sites being embedded,leading to low catalytic activity and stability.In this work,honeycomb cordierite was modified with covalent triazine skeletons(CTFs),and then loaded with noble metals to prepare nitrogen-rich hydrophobic catalysts.The porous and nitrogen-rich structure can improve the uniform distribution of precious metal platinum,which would inhibit the agglomeration of noble metal.Firstly,a hydrophobic and nitrogen-rich carrier was synthesized by in-situ grafting CTFs on the surface of honeycomb cordierite ceramics.After loading platinum,a honeycomb hydrophobic catalyst(HC)was obtained.The synthesis is simple and the reaction conditions are mild.For safety reasons,hydrogen gas and deuterium gas were used as the reaction gas.HC showed outstanding catalytic activity at room temperature,and the conversion rate of hydrogen was above 99%at 30000 h-1 space velocity under dry condition.Besides,the catalytic performances of HC were better than that of CAT owing to azine ring of CTFs.In this chapter,covalent triazine skeletons as the substrate inhibited the agglomeration of noble metal on the catalyst,thereby making the catalyst realize the efficient separation and enrichment of hydrogen isotopes. |
PDF Full Text Request