【作者】 李娜；

【导师】 张伟德；

【作者基本信息】 华南理工大学 ， 物理化学， 2012， 硕士

【摘要】 层状双金属氢氧化物（Layered Double Hydroxides, LDHs）是一种阴离子型层状功能材料，包括水滑石（Hydrotalcite, HT）和类水滑石化合物（Hydrotalcite-LikeCompounds, HTLCs）。因其具有独特的超分子结构和带电性、层间阴离子种类和数量的可交换性、晶粒尺寸的可调控性，使其在很多重要领域如医药，催化，吸附，生物，环境保护等具有广泛的应用。但由于自然界中的水滑石含量有限，以及自然界中的水滑石大都是镁铝水滑石，其层间阴离子主要为CO32-，限制了其在某些方面的应用。因此充分利用水滑石特殊的结构，采用人工的方法制备水滑石材料是研究这类材料的重点，具有理论意义和实用价值。本文基于水滑石主体层板的化学组成的可调变性，引入和Mg2+半径相似的Zn2+使其在一定程度上同晶取代Mg2+，通过共沉淀法成功制备出具有微球结构的三元水滑石材料ZnMgAl-LDHs。鉴于LDHs普遍具有比较大的比表面积和结构的复原性，对所制备的材料进行了吸附性能的测试。在此工作的基础上，为了克服传统光催化半导体材料存在的缺陷，利用“边缘效应”和“晶格匹配”性，制备了具有异质结构的氧化锌/水滑石复合材料。并对模拟有机污染物进行光催化降解实验，结果表明纳米水滑石对氧化锌光催化活性有明显的增强作用。具体研究工作和结论如下：（1）用水做溶剂，以尿素作为pH调节剂和沉淀剂，在较低温度下采用共沉淀的方法以锌部分替换层板上的镁离子，合成了均匀的由纳米片组成的、具有3D结构的ZnMgAl-LDHs微球。并利用水滑石的“记忆效应”对其进行了复原实验。分别通过XRD、TG、AAS、SEM、TEM和BET等手段对所制备材料的组成、结构、形貌和比表面积等性质进行表征和检测，探讨了LDHs3D微球的形成机理以及Zn的含量、溶剂和pH等因素对其形成的影响。结果表明，锌的加入对3D LDHs微球结构的形成起重要作用。以难降解的有机污染物甲基橙（MO）为模拟污染物，在pH为3时，3D LDHs微球对其表现出很强的吸附性能。对LDHs吸附甲基橙的过程分别进行了一级、二级动力学和Langmuir、Freundich模型的模拟。发现其吸附过程较符合二级动力学方程和Langmuir模型。另外，进行更重要的是，所合成的材料可以很容易地回收和重复使用，因此其具有良好的实际应用价值。（2）在共沉淀法制备的LDHs3D微球结构的基础上，采用与其它半导体形成异质结的方式进行复合改性，以提高半导体材料的光催化活性。以乙二醇和水作为混合溶剂，采用加热回流的方法使ZnO纳米颗粒在低温条件下均匀地覆盖在LDHs3D微球的片上，制备得到异质结型复合光催化剂ZnO/LDHs。同时，分别考察了溶剂、反应pH对复合材料的影响。选用有机染料苯酚作为模拟污染物，在紫外光照射下，考察了复合光催化剂降解亚甲基蓝的催化活性。研究发现，与单一的LDHs、ZnO相比，拥有最佳复合比的ZnO、LDHs的光催化活性显著提高。实验结果表明，异质结型的复合光催化剂对苯酚的催化降解存在最佳的复合比。当超过一定的复合比时其可见光催化活性反而下降。研究工作表明，复合氧化物的覆盖率对催化剂的光催化活性有十分重要的影响，半导体材料和LDHs进行复合，可以弥补某些半导体材料本身吸附性能弱的缺陷，从而提高其光催化性能。同时复合后，可以防止半导体纳米颗粒的团聚现象，使其发挥更好的光催化性能。本论文的研究工作为其它具有光催化活性的半导体材料和水滑石材料复合成异质结型复合光催化剂的制备提供了新的启示和设计思路。同时，本研究工作制备出光催化剂对有机污染物的降解具有更高的光催化活性以及可回收性，因此在污水净化等领域具有更好的实际应用价值。更多还原

【Abstract】 Layered Double Hydroxides (LDHs) are an important class of lamellar functionalmaterials, which consist of Hydrotalcite (HT) and Hydrotalcite-Like Compounds (HTLCs).They have a wide range of applications in many important industry fields, such as medicine,catalysis, adsorption, biology and environmental protection and so on, because of theirsuper-molecule structure, the anion-exchange ability and the controllable size. However, thenaturally occurring example of this class of materials is the mineral hydrotalcite,Mg6Al2(OH)16CO3·4H2O, containing carbonate ions in between the layers and the amount isvery limited. The above drawbacks of natural LDHs impose restrictions on the use of someaspects. Developing artificial methods to design novel LDHs is the key to make full use ofthem, which not only has important academic significance but also has practical value. Inthis dissertation, with the characteristics of exchangeable cations in the layers, weintroduced Zn2+into LDHs since its size matches with that of Mg2+. So, Mg2+can bepartially substituted by Zn2+in the process of coprecipitation, and the ternary threedimensional (3D) ZnMgAl-LDHs microspheres were prepared. In consideration of the largesurface area of the3D LDHs microspheres, the adsorption properties of the preparedsamples were characterized. Meanwhile, with the “edge effect”, the lattice matches betweenZnO and ZnMgAl-LDHs, the heterostructures consist of uniform ZnO nanoparticles orderlystanding at the edges of two-dimensional (2D) surfaces of ZnMgAl-LDHs nanoplatelets.Their application for degradation of organic dyes was also studied. The main points of thisdissertation are summarized as follows:Firstly,3D ZnMgAl-LDHs microspheres consisting of nanoplates were synthesized atlow temperature using urea as a precipitator. This preparation method does not use anyorganic solvent as reaction media. The as-prepared LDHs were characterized by XRD, TG,AAS, SEM, TEM and BET. The possible formation mechanism for the architectures wasdiscussed. It is proposed that the introduction of Zn2+played a key role in the formation ofthe microsphere structure. The adsorption properties of the as-prepared sample wereevaluated by adsorbing methyl orange. The3D LDHs microspheres show high adsorptioncapacity. The optimum pH value for the adsorption of MO onto LDHs is3.0. The adsorption process can be well described by the pseudo-second-order kinetic model and the adsorptionisotherm matches Langmuir model well. In addition, the LDHs microspheres can berecovered and used repeatedly.Secondly, modification of LDHs microspheres by ZnO nanoparticles withheterostructure was successfully conducted using glycol-water mixed solvents as reactionmedia and NH3·H2O as a pH adjustor. The effect of solvent and the pH value on theheterostructures were studied. The photocatalytic activity of the as-prepared composites wasevaluated by degradation of phenol in water under ultraviolet light irradiation. TheZnO/LDHs show enhanced photocatalytic activity when the molar ratio of the two differentcomponents were optimized, which can be attributed to the large surface area of LDHs andthe better dispersity of ZnO nanoparticles. With increasing the ZnO content continuously,the photocatalytic activity of the ZnO/LDHs composite photocatalyst decreases reverselybecause the aggregation of ZnO nanoparticles is prejudicial to separation of thephotoinduced carriers efficiently.The investigation indicates that degree of oxide coverage over other materials plays animportant role on photocatalytic performance of the catalysts. The coupling ofsemiconductors with LDHs can overcome its weakness effectively, and enhance itsphotocatalytic activity. The results reported in this study provide insight to construct othercomplex metal oxides with LDHs to form composite photocatalysts. The as-preparedphotocatalysts exhibit excellent photocatalytic activity for the degradation of the organicdyes. Therefore, it is promising to degrade organic pollutants in the field of wastepurification.更多还原