| Mankind’s increasing demand for energy has led to the fast expansion of nuclear industry.As an important raw material of the nuclear industry,the main source uranium is ore U3O8.However,the uranium on land could only be used to supply nuclear energy for 80～120 years.Therefore,the continuous supply of uranium is of great significance to ensure the safe development of nuclear energy.The uranium in seawater is thousands of times that on land and can sustain nuclear power generation for thousands of years.On the other hand,the operation of the nuclear industry produces a large amount of uranium-containing radioactive wastewater.In addition,nuclear accident and other uses of uranium also risks the release of radioactive uranyl into the environment.The half-life of uranium is between millions of years and billions of years and is the most common radioactive contaminant because of its toxicity and radioactivity,the World Health Organization(WHO)sets a maximum uranium concentration of 30 μg/L in drinking water.Therefore,it is very necessary to prepare new materials and develop new technologies for separating uranium from seawater and radioactive wastewater.At present,the separation of uranium has received widespread attention,but there are still difficulties in the efficient separation of uranium.However,low adsorption rate due to the low concentration of uranium in seawater and radioactive wastewater;poor selectivity because of high salinity and co-existing ions in the medium,and the biofouling on the surface of the material will lead to a decrease in adsorption capacity.These factors remain the great challenges for the efficient separation of uranyl ions.This thesis intends to focus on the challenges of seawater uranium extraction and uranium separation from radioactive wastewater,a series of uranyl ion adsorbents based on functional polymers were designed and prepared according to the environmental characteristics of seawater and radioactive wastewater.Based on functional polymer adsorbents,a series of polymer functional materials are designed and synthesized according to the different requirements and characteristics of the adsorption environment.The physical structure,chemical composition and adsorption properties of the prepared adsorbents were systematically investigated,and the structure-activity relationship of the materials was discussed.According to the results,the material structure was optimized and the adsorption mechanism was studied.The specific studies of this paper are as below:(1)Oxime and guanidine functionalized polypropylene nonwoven fabric for uranium recovery from seawater with antibiofouling activity and high selectivityRadiation-grafting,ring-opening and oximation reaction were used to obtain the oxime and guanidine functionalized polypropylene nonwoven fabric.The successful synthesis of materials was verified by FT-IR,XPS,FE-SEM,EDX,and water contact angles.The adsorption equilibrium could be reached in 4 h,and the maximum adsorption capacity was calculated to be about 120.5 mg/g by using Langmuir isotherm model with the C0 of 10～100 ppm.In natural seawater,the functionalized adsorbent showed highly selective for uranium(Ⅵ).Thanks to the existence of guanidine group,the antibacterial assay exhibited that the prepared functionalized PP nonwoven fabric has excellent antibacterial properties to both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus.The adsorption mechanism may be attributed to the interaction of multiple functional groups with uranium according to the XPS analysis.(2)Positively charged conjugated microporous polymers with antibiofouling activity for ultrafast and highly selective uranium extraction from seawaterThe conjugated microporous polymer was decorated with carboxyl and oxime groups by click reaction after the Sonogashira-Hagihara reaction of 1,3,5-triethynylbenzene and 1,3-dibromo-5,5-dimethylhydantoin.Solid-state 13C NMR,FT-IR,XPS,TEM and FE-SEM were utilized to verify the successful preparation of the polymer.The batch sorption experiments showed the adsorption equilibrium can be reached within 5 min at pH 8 and 298.15K,the maximum adsorption capacity reached 197.6 mg/g by using Langmuir isotherm model with the C0 of 10～100 ppm.Furthermore,the adsorption test in real seawater also showed the ultrafast and high selectivity adsorption because of the synergistic effects of porous structure,positive charge and ligands.In addition,the polymer loaded filter membrane shows outstanding antibiofouling activity against S.aureus and E.coli and excellent adsorption performance in uranium added real seawater.XPS spectra study suggested that except for oxime and carboxyl ligands,hydantoin in polymer skeleton can also interact with uranium(Ⅵ).(3)Thermal-responsive ion-imprinted magnetic microspheres for selective separation and controllable release of uranium from highly saline radioactive effluentsThe thermal-responsive ion-imprinted microspheres was prepared by radical polymerization of N-isopropylacrylamide and vinyl phosphoric acid on the surface of Fe3O4 with N,N’-methylenebisacrylamide as crosslinker and uranium as template ion.Compared with the non-imprinted adsorbent,UIMM showed better adsorption performance because of the specific recognition sites.Moreover,the adsorption equilibrium could be achieved within 10 min with the maximum adsorption capacities of 122.7 mg/g and 231.5 mg/g at 298.15 K and 305.15 K,respectively.What’s more,above the LCST of PNIPAM,highly efficient desorption can be realized,which avoids the secondary contamination associated with the use of large amounts of eluents.In addition,the magnetic properties of the adsorbents enable the material to be separated quickly in an external magnetic field,which greatly improves the practical performance.XPS spectra reveal that most of U(Ⅵ)was complexed by phosphonic acid and N-isopropylacrylamide on the surface of the adsorbent while a part of uranium(Ⅵ)was reduced to U(Ⅳ)by Fe2+of Fe3O4.(4)COFs functional electrodes for simultaneous remove of UO22+and ReO4with fast adsorption kinetics and high adsorption capacities by electric adsorptionCarboxyl functionalized covalent organic frameworks(COF-1)and cationic COF(COF-2)were loaded onto the surface of cathode and anode,respectively.The electric field will drive UO22+and ReO4-(the non-radioactive surrogate of TcO4-)to move to the electrodes,which will be absorbed by the functional electrodes,thereby achieve the simultaneous removal of radioactive cations and anions from low-level liquid wastes.The powerful electric driving force in the process of electric adsorption can make ion migration to the inside electrode materials quickly,therefore the active sites in the adsorption materials can be make full utilize.The maximum adsorption capacities were 411.5 mg U/g COF-1 and 984.4 mg Re/g COF-2 by the electric adsorption method,which was 2.5 times and 2.1 times respectively compared with physical-chemical adsorption,and the adsorption equilibrium time from 2 h to shorten to less than 30 min.In addition,1 mol/L HNO3 can be used as the eluent to achieve efficient elution,and remains a high adsorption efficiency after 5 cycles of adsorption and desorption,which can greatly improve the practical performance.XPS study found that a large number of target ions were bound to the adsorbents,and covalent bonds were formed between U(Ⅵ)and the carboxyl group on COF-1,and Re(Ⅶ)was bound to cationic COF-2 through ion exchange.This work reports a new strategy for the simultaneous recovery of uranium and technetium from low-level liquid wastes,which can be extended to the simultaneous efficient removal of other radioactive ions from wastewater,thus achieving deep purification of wastewater. |
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