Functional Regulation Of Transition Metal Nanomaterials And Their Sorption Properties And Mechanism For Uranium

Recently decades,to remedy or accommodate global energy shortages,it is imperative to develop nuclear energy.However,uranium and its decay products might be inevitably released into the surrounding environment in the process of nuclear raw material mining and nuclear waste treatment.These radionuclides can be enriched in animals,plants and human body through the food chain,and cause serious harm to human body and the environment.Therefore,it is of great significance to develop and synthesize new adsorbent materials to remove radionuclides in water.Transition metal oxide nanomaterials play an important role in the treatment of environmental pollutants due to their unique photoelectric characteristics,ideal specific surface area,excellent surface chemical properties,superior chemical and thermal stability.Therefore,in this paper,a variety of transition metal oxide nanomaterials with different size,morphology and composition are designed to achieve the nanometer structure regulation from single-component to ternary metal oxides.Then the macroscopic kinetics and thermodynamic sorption behavior of uranyl ions are studied.The structure-activity relationship between the physical and chemical properties of these metal oxides and uranyl ions are analyzed with microscopic spectroscopy,providing theoretical basis for the future application of metal oxide nanomaterials in the remediation of uranium-containing wastewater.The main achievements are as follows:(1)Due to the high reactivity of defects on the surface of metal oxides,TiO2x,which contains a large number of oxygen defects,is introduced with the method of metal reduction.Spectral analysis proves that TiO2-x consists of anatase phase and rutile phase.The oxygen vacancy in TiO2-x shows high sorption capacity for U(Ⅵ).The results show that the sorption of U(Ⅵ)and humic acid(HA)on TiO2-x fits the pseudo-second-order rate equation,and the saturated sorption capacity of U(Ⅵ)and HA on TiO2-x is 65 mg·g-1 and 142 mg·g-1,respectively.In the ternary system of U(Ⅵ)-HA-TiO2-x,the presence of HA could enhance the sorption volume of TiO2-x on U(Ⅵ)in the full pH range(2-11),and U(Ⅵ)could also enhance the sorption rate and capacity of TiO2-x on HA.This is mainly attributed to the formation of U(Ⅵ)-HA-TiO2-x ternary complex.Both U(Ⅵ)and organic matter could be effectively removed by the oxygen-deficient TiO2-x in water.(2)In view of the limited sorption capacity of single-component metal oxides,we synthesize SiO2@Fe3O4@MnOx with SiO2 as the hard template,then carry out alkali etching on it,and finally obtain magnetic binary metal complexes with hollow hierarchical structure(Fe3O4@MnOx).On the one hand,Fe3O4@MnOx is magnetic,easy to separate,and overcome the shortcomings of TiO2-x,such as small particle size,easy to lose in water treatment;On the other hand,the hollow hierarchical structure could also effectively improve the specific surface area,increase the active sites,and.further improve the sorption capacity.The results show that the maximum sorption capacity of Fe3O4@MnOx for U(Ⅵ)and Eu(Ⅲ)is 107 mg·g-1 and 138 mg·g-1,respectively.The saturated sorption capacity of Fe3O4@MnOx for U(Ⅵ)is about 1.6 times that of the defective TiO2-x,which is also superior than most other traditional adsorbents.Combined with spectroscopic analysis,U(Ⅵ)is mainly attached to the MnⅢ-O-H site in the binary system,while Eu(Ⅲ)has strong affinity with the MnⅣ-O-H site.At the same time,the presence of HA promotes the formation of HAUO2+ and(HA)2Eu+complex in the ternary system,showing a faster sorption kinetics and enhanced sorption capacity.This study is of great significance for the removal of radionuclides from water by magnetic binary metal oxides.(3)LDHs possess superior characterizations,such as unique layered structure,high dispersibility and excellent anion exchange performance,which could be used to combine with metal oxides to form compounds.On the basis of the hard template method in the previous chapter,multicomponent metal oxides with hollow spherical structure are synthesized.The specific surface area of NiSiO is 59.09 m2·g-1.With the construction of hierarchical structure,the specific surface area of NiSiO@MgAl LDH and NiSiO@NiAl LDH correspondingly increases to 136.99 m2·g-1 and 169.20 m2·g-1,respectively,which is beneficial to faster transportion and fixation of target ions.The results of batch experiments show that the saturated sorption capacity of NiSiO@MgAl and NiSiO@NiAl on U(Ⅵ)is significantly higher than that of NiSiO,and NiSiO@NiAl exhibits the highest saturated sorption capacity of U(VI)(～136.94 mg·g-1).XPS spectroscopic analysis shows that the coordination ability of surface functional groups to U(Ⅵ)of the three materials follows Ni-OH(NiAl LDH)>Al-OH>Mg-OH>Ni-OH(NiSiO)is consistent with the Qmax results of batch experiment,which has important guiding significance for the design and construction of the nanomaterial.(4)In order to simplify the preparation process of multicomponent metal oxides,ternary metal oxides(MgFeAl LDH and NiFeAl LDH)are prepared by onestep hydrothermal method.The results show that the saturated sorption capacity is up to 167.61 mg·g-1.The sorption of U(Ⅵ)on MgFeAl LDH is fast and efficient,the reason for which might be that metal-oxygen sites(Mg-OH)exposed on the surface of MgFeAl LDH and the carbonate anions between the layers play a decisive role in the capture of target ions.The high sorption capacity and good recycling of ternary metal oxides indicate that the material is a potential excellent adsorbent for the removal of U(VI)from water.In conclusion,the surface properties of metal oxide nanomaterials are important factors which could affect their sorption properties.In this paper,based on the strategy of size,morphology and composition regulation,the hierarchical structure materials from single-component metal oxide to ternary metal oxide are constructed.Through batch experiments and spectral analysis,sorption behavior and mechanism of radionuclides on metal oxide nanomaterials are studied.These results have certain guiding significance for the design,research and development of high-performance multicomponent metal oxide system and the application of sorption performance in nuclear wastewater treatment.