【作者】 张荣；

【导师】 张法智；

【作者基本信息】 北京化工大学 ， 化学， 2015， 硕士

【摘要】 多级结构无机功能材料能够更好利用其结构单元的性质,提高其应用性能。水滑石(LDH)是一种层状双金属氢氧化物材料,其应用范围十分广泛,主要包括吸附、催化、离子交换、阻燃剂、药物缓释等。目前多级结构水滑石的构筑方法主要采用软硬模板法,存在着模板去除过程易破坏自身结构、污染环境、操作繁琐等问题。因而创制新型的操作简单且绿色环保的多级结构水滑石组装方法具有较为重要的研究意义。论文尝试采用干胶转化法(dry gel conversion),在不借助外加软硬模板物质的情况下制备了多级结构LDH组装体。表征研究了多级结构LDH的形貌、结构及织构特性,探讨了多级结构LDH的组装过程机制,并考察了几个影响多级结构LDH形成的因素,最后将其用作水处理吸附剂材料,研究了其对重金属离子Cr(Ⅵ)和有机染料亚甲基蓝MB的吸附性能。取得的主要研究结果如下：(1)首先采用冷冻干燥技术制备了块状的无定形氢氧化铝胶体(AAH),然后将此铝前体和无水硫酸镁混合均匀后悬置于不锈钢反应釜聚四氟乙烯内衬容器的中间,以与容器底部的氨水溶液相分离,在一定的反应温度下制备了具有多级结构的硫酸根离子插层的MgAl-LDH组装体。表征研究了多级结构LDH的形貌、结构及织构特性。发现,LDH晶片取向排列组装成单层的二维水滑石组装体,其取向性为LDH粒子的ab晶面为其组装体的表面法线方向,此单层二维LDH组装体再经层层堆叠构成三维多级结构LDH自支撑体颗粒。与传统沉淀法制备的LDH粉体样品相比,该三维多级结构LDH颗粒具有100-200 nm范围内的大孔和3.9 nm的介孔孔道结构,比表面积和孔容明显增大。(2)论文对多级结构LDH的形成过程及合成影响因素进行了研究。在反应温度和压力下产生的水蒸气和氨气吸附凝聚于AAH前体的表面形成一薄层水膜,在此水膜内,AAH前体和硫酸镁发生水解,继而生成LDH晶核。推测Al前体和镁盐的不断溶解和分解给LDH晶核的生长提供了“养分”,而水膜的“限域”作用降低了LDH晶核的自由活动程度,使其不能像在水溶液合成体系中那样自由扩散,由此使得LDH晶片相互连接形成网状结构。继续晶化生长则形成多级结构LDH组装体。研究发现,AAH前体为多级结构LDH颗粒的组装提供了“自牺牲”模板。水量、碱种类及碱量等因素主要影响晶化反应体系的pH值,从而影响最终产物的晶相、组成及形貌。(3)论文将多级结构LDH粒子用作水处理吸附剂材料,研究了其对重金属离子Cr(Ⅵ)和有机染料亚甲基蓝MB的吸附性能。与传统沉淀法制备的LDH粉体样品相比,多级结构LDH对Cr(Ⅵ)和MB均显示出较高的吸附性能。更多还原

【Abstract】 Functional materials with hierarchical architecture can make better use of its properties of structural unit, improving their application performance and application scope. Layered double hydroxides have attracted increasing interest due to their potential industrial applications. In order to take full advantage of LDH material properties in the applications, a special attention has been drawn to the preparation of hierarchical architectures of LDHs. For the preparation of LDH hierarchical architectures, templating syntheses are presently the most widely used methods. However, the template method suffers from problems of materials compatibility, process complexity, not environmental friendly. Developing of template-free approach under mild conditions is highly desired and still remains a challenge.(1) A new type of hierarchically porous MgAl-layered double hydroxide (LDH) architecture, with well defined meso-/macroporous structure, was fabricated by dry gel conversion (DGC) method without the need of a surfactant and organic solvent. Predefined amorphous aluminum hydroxide (AAH) gel and anhydrous magnesium sulfate were used as Mg and Al precursor material, respectively, and aqueous ammonia as precipitating agent. This self-assembled hierarchical LDH material exhibits a bi-modal porous structure having a macroporous network with macropore sizes of 10-200 nm and a well defined mesoporous structure of pore size around 3.9 nm in the macroporous framework. LDH crystallites are orientally aligned with a multilayer manner to form the architecture structure.(2) We have studied the formation process and influencing factors of hierarchically porous MgAl-layered double hydroxide (LDH) architecture. The results suggest the preformed AAH gel as raw material is necessary for induce the construction of LDH architecture with the employed synthesis conditions. The provided a template consumpted by self-transformation. Dry gel conversion method limits the hydrotalcite nuclear proliferation that limits the growth direction of hydrotalcite, get layered double hydroxides bent perpendicular to the preformed AAH surface and interconnecte to form large holes. Water and alkali are also important to affect the pH and Nucleation in a weak hydrothermal environment. Through investigation and sample characterization, we deduced the formation process of hierarchically porous MgAl-layered double hydroxide (LDH) architecture:first form a film of water and ammonia in front of the Al surface or internal, and salt is dissolved into the Mg2+, Al3+, ammonia hydrolysis provides OH", then nucleation and crystal growth of LDHs. that resembles a weak thermal environment.(3) As an example of potential applications, the as-synthesized LDH hierarchically meso/macroporous architecture was used as adsorbent for Cr(VI) and MB Removal. LDH architecture exhibits faster elimination and higher adsorption capacity due to the large specific area and abundant pore structure in the meso/macroporous hierarchical architecture, which may benefit the diffusion and provide more adsorption sites for Cr(VI) and MB.更多还原