偕胺肟基纳米材料的合成及其对铀的吸附性能研究

发布时间：2018-08-18 09:17

【摘要】：铀是重要的核燃料资源,同时也是放射性废液中主要的污染元素之一。无论是从能源安全还是从环境保护的角度,对水体中的铀进行有效分离富集都有着很重要的现实意义。在铀的众多分离富集方法中,吸附法因具有成本低廉、工艺简单及适用范围广等优点而被广泛采用。高效吸附剂的开发无疑是吸附法在实际应用中的关键。复合材料由于可根据不同用途选择相应基体与功能基团进行复合,已成为近年来对溶液中的铀进行分离富集的研究热点。在众多功能基团中,偕胺肟官能团由于对铀的特殊络合能力,被广泛用于修饰多种多样的基体材料。基体材料方面,近年来人们的注意力逐渐转向新兴的纳米材料。本论文利用偕胺肟官能团对这些年研究得较多的常见纳米材料进行功能化,合成了如下几种复合材料,考察了所合成材料对铀的吸附性能,并对吸附机理进行了分析： 1,偕胺肟修饰磁性石墨烯合成了偕胺肟修饰磁性石墨烯(AOMGO)复合材料,并应用于水溶液中铀的吸附。吸附铀之后的材料可以在外加磁场下很方便地实现与液相分离。吸附动力学实验表明吸附过程可以在2h内达到吸附平衡。考察了pH值、离子强度、共存离子对铀吸附的影响。结果表明,铀在AOMGO材料表面的吸附受pH值影响显著,而与离子强度关系不大。吸附等温线符合Langmuir模型,在pH=5.0±0.1,T=298K时,理论最大吸附量达到1.197mmol/g。根据不同温度下的吸附等温线可计算出吸附过程的热力学参数,结果表明铀在AOMGO材料表面的吸附是自发的吸热过程。快速高效的吸附表现表明所合成的AOMGO复合材料在废水中铀的去除以及海水中铀的提取方面有着很好的应用前景。 2,偕胺肟修饰二氧化硅包覆的四氧化三铁合成了偕胺肟修饰二氧化硅包覆的四氧化三铁微球(Fe3O4@SiO2-AO)复合材料并进行了详细表征。合成的Fe3O4@SiO2-AO材料被用于吸附溶液中的铀,得益于材料中偕胺肟官能团对铀的络合能力,该材料的吸附容量相比于裸的二氧化硅包覆四氧化三铁微球(Fe3O4@SiO2)得到了很大提高。考察了接触时间、pH值、离子强度、干扰离子、铀起始浓度、温度对铀在Fe3O4@SiO2-AO材料上吸附的影响。pH值对吸附过程影响强烈而离子强度则几乎没有影响,表明吸附过程主要是内层络合。吸附等温线与Langmuir模型相吻合,在pH=5.0±0.1,T=298K时,理论最大吸附量达到0.441mmol/g。负载铀之后的材料可以通过外磁场加以分离,并可通过1mol/L的盐酸处理使吸附剂再生,实现循环利用。 3,偕胺肟功能化的磁性介孔二氧化硅在二氧化硅包覆的四氧化三铁微球表面,利用十六烷基三甲基溴化铵做结构导向剂,通过正硅酸乙酯与2-氰乙基三乙氧基硅烷的共缩聚反应包覆介孔二氧化硅层,经盐酸羟胺还原后得到偕胺肟功能化的磁性介孔二氧化硅(MMS-AO)。该材料呈现三明治结构,内核为四氧化三铁,中间层为致密的二氧化硅,最外层为偕胺肟功能化的介孔二氧化硅。得益于介孔结构和偕胺肟功能化,在pH=5.0±0.1,T=298K时,MMS-AO材料对铀的最大吸附量达1.165mmol/G,优于迄今为止见诸报道的诸多含磁性粒子材料。相比于未经偕胺肟功能化的材料,MMS-AO材料对铀的吸附选择性得到了很大改善。由于二氧化硅层对四氧化三铁内核的保护,吸附铀之后的MMS-AO材料可经1mol/L的盐酸处理得以再生。结果表明MMS-AO材料不仅比表面积大,能够实现磁分离,而且磁性核在酸性环境中有很好的稳定性。该材料在实际水体中铀的分离富集方面有非常好的应用前景。 4,偕胺肟功能化的SBA-15型介孔二氧化硅利用Pluronic P123作为结构导向剂,通过正硅酸乙酯与2-氰乙基三乙氧基硅烷共缩聚,改变其中2-氰乙基三乙氧基硅烷的摩尔比,合成了一系列SBA-15型介孔材料,并用于溶液中铀的吸附。通过吸附等温线和吸附动力学的研究分析了有机官能团引入量对吸附性能的影响。结果表明,有机功能化对吸附容量与吸附速率的影响都是双方面的。刚开始增加有机官能团含量会提高吸附性能直至达到最大值,继续增加有机官能团含量则会引起吸附性能下降。最优值对应于材料介孔有序性与有机官能团密度之间的平衡。通过材料吸附前后的X-射线光电子能谱与红外光谱分析了吸附机理,结果表明吸附主要归功于铀与偕胺肟官能团之间的络合作用。综合以上几方面的内容,本文对比了不同材料对铀吸附行为的特点,优化了材料合成条件,分析了吸附机理。本文研究内容能够为功能化介孔材料在铀污染治理和铀的选择性富集等实际应用方面提供实验依据和理论基础。
[Abstract]:Uranium is an important nuclear fuel resource and one of the major contaminating elements in radioactive waste liquid. It is of great practical significance to separate and enrich uranium in water from the point of view of energy security and environmental protection. The development of highly efficient adsorbents is undoubtedly the key to the practical application of adsorption methods. Composite materials have become a research hotspot for the separation and enrichment of uranium in solution in recent years because of their ability to choose the appropriate matrix and functional groups for different purposes. Aminoxime functional groups have been widely used to modify a variety of matrix materials due to their special complexation ability to uranium. In recent years, attention has been gradually turned to new nano-materials. In this paper, amidoxime functional groups have been used to functionalize common nano-materials which have been studied extensively in recent years. The adsorption properties of the synthesized materials on uranium were investigated, and the adsorption mechanism was analyzed.
1, modified magnetic graphene with amine.
The amidoxime modified magnetic graphene (AOMGO) composite was synthesized and applied to the adsorption of uranium in aqueous solution. The material adsorbed uranium can be easily separated from liquid phase in an external magnetic field. The adsorption kinetics experiment shows that the adsorption process can reach adsorption equilibrium within 2 hours. The adsorption of uranium by pH, ionic strength and coexisting ions was investigated. The results show that the adsorption of uranium on the surface of AOMGO material is significantly affected by pH value, but not by ionic strength. The adsorption isotherm is in accordance with Langmuir model. The theoretical maximum adsorption capacity reaches 1.197mmol/g at pH=5.0+0.1 and T=298K. The thermodynamic parameters of the adsorption process can be calculated according to the adsorption isotherm at different temperatures. The results show that the adsorption of uranium on the surface of AOMGO is a spontaneous endothermic process. The rapid and efficient adsorption performance shows that the AOMGO composite has a good application prospect in the removal of uranium from wastewater and the extraction of uranium from seawater.
2, silicon oxide coated iron oxide coated with amine.
Fe_3O_4@SiO_2-AO composite coated with amidoxime modified silica was synthesized and characterized in detail. The synthesized Fe_3O_4@SiO_2-AO material was used to adsorb uranium in solution, which was attributed to the complexation ability of Amidoxime functional groups to uranium, and its adsorption capacity was comparable to that of naked silica coated with tetroxide. The effect of contact time, pH value, ionic strength, interfering ions, initial uranium concentration and temperature on the adsorption of uranium on Fe3O4 @SiO2-AO was investigated. The effect of pH value on the adsorption process was strong, but the ionic strength was almost unchanged. The Langmuir model is consistent with each other. At pH=5.0 +0.1 and T=298K, the theoretical maximum adsorption capacity of uranium can reach 0.441mmol/g.
3, functionalized mesoporous silica with amine functionalized
Mesoporous silica was coated with hexadecyltrimethylammonium bromide (CTAB) on the surface of silica-coated ferric oxide microspheres by the co-condensation of tetraethyl orthosilicate with 2-cyanoethyltriethoxysilane. The magnetic mesoporous silica (MMS-AO) functionalized by amidoxime was prepared by the reduction of hydroxylamine hydrochloride. The core is ferric oxide, the middle layer is dense silica, and the outer layer is amidoxime functionalized mesoporous silica. Benefiting from the mesoporous structure and amidoxime functionalization, the maximum adsorption capacity of MMS-AO material for uranium is 1.165mmol/G at pH=5.0+0.1 and T=298K, which is superior to that of many reported magnetic-containing materials so far. The selectivity of MMS-AO material for uranium adsorption has been greatly improved compared with the material without amidoxime functionalization. Due to the protection of iron oxide core by silica layer, the MMS-AO material adsorbed uranium can be regenerated by 1 mol/L hydrochloric acid treatment. This material has a very good application prospect in the separation and enrichment of uranium in actual water.
4, SBA-15 type mesoporous silica functionalized with amine.
A series of SBA-15 mesoporous materials were synthesized by copolycondensation of tetraethyl orthosilicate with 2-Cyanoethyl triethoxysilane using Pluronic P123 as structure-directing agent and changing the molar ratio of 2-Cyanoethyl triethoxysilane. The adsorption isotherms and adsorption kinetics of uranium in solution were studied. The results show that the effects of organic functionalization on adsorption capacity and adsorption rate are both two-sided. Increasing the content of organic functional groups at the beginning will improve the adsorption performance until the maximum value is reached, while increasing the content of organic functional groups will decrease the adsorption performance. The adsorption mechanism was analyzed by X-ray photoelectron spectroscopy and infrared spectroscopy before and after adsorption. The results showed that the adsorption was mainly attributed to the complexation between uranium and amidoxime functional groups.
In this paper, the characteristics of uranium adsorption behavior of different materials are compared, the synthetic conditions of materials are optimized, and the adsorption mechanism is analyzed.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ136.2;TB383.1

【参考文献】