层状双金属氢氧化物（layer double hydroxides，LDHs）是一类阴离子型的层状化合物，因其独特的物理化学性质备受关注，如丰富的插层化学性质，可剥离为带正电的二维晶体，记忆效应等，该类材料同时具备了插层客体和LDHs主体的许多优点，使其在磁学、光学、电化学、药物传输、催化和吸附等方面展现出非常广阔的应用前景。本论文在回顾了层状双金属氢氧化物在制备和应用方面的研究进展的基础上，主要致力于探索新的LDHs的制备方法。以MgAl-LDHs为研究对象，深入研究其反应过程，以及不同反应条件的影响，通过X射线粉末衍射（XRD）、傅里叶变换红外光谱（FT-IR）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、离子电感耦合原子发射光谱仪（ICP）、CHN元素分析等手段对产物的组成、结构和形貌进行了表征。本工作对于明晰LDHs的形成机理，指导其可控合成和进一步应用都具有重要的意义，具有重要的理论价值和潜在的实际应用意义。论文所取得的成果如下： (1) 提出了一种合成MgAl-LDHs的新方法，我们首次采用NH3-NH4+缓冲溶液体系，以商业化的Al(OH)3为原料，与Mg2+、OHˉ和NO3ˉ在一定温度下反应，经拓扑转化制备了Mg/Al = 2.40的MgAl-LDHs。采用该方法得到的LDHs晶体具有良好的结晶度，并且保持了前驱体Al(OH)3的形貌，晶体尺寸从原来的约1 μm增大到约1.5 μm，根据晶胞参数和Mg/Al比计算得到层板面积的增大率为149%，对应边长的增大率为58%，计算结果和粒径分布测定结果十分吻合。此外，整个反应过程没有在溶液中检测到Al3+的存在，证明Al(OH)3层板没有溶解，表明LDHs的形成过程中，Mg2+、OHˉ与Al(OH)3发生了遵循如下方程式的拓扑（topotactic）反应， Al(OH)3 + yMg2+ + (2y-1)OHˉ = [MgyAl(OH)2(y+1)]+ 这个过程是赝晶转化过程，验证了我们早先提出的转化模型，即基于Al(OH)3层板的“取代-填充”反应机理：Mg2+部分取代层板中的Al3+，破坏Al(OH)3层板中Al?O?Al的连接，Al3+在固相中移动并填入Mg2+所形成的空位中，形成MgAl-LDHs层板。 (2) 深入研究了缓冲溶液体系以及pH控制对于该反应的必要性，比较了缓冲溶液体系和非缓冲体系中制备的LDHs晶体在结构和形貌上的差异。实验结果表明，pH较低（pH = 8或8.5）时，由于OHˉ的浓度很低，反应速率很慢，产物为LDHs和前驱物Al(OH)3的混合相；高pH值可以提高反应速率，但过高的pH（10或11）会造成Al(OH)3溶解，经过计算Al(OH)3碱性条件下溶解的pH约为9.84。因此pH = 9的缓冲溶液是最优选择，一方面不会使Al(OH)3溶解，另一方面可以保证较高的反应速率。此外，还研究了Mg2+浓度和反应温度对转化过程的影响，发现Mg2+向Al(OH)3层板的插入过程是一个动力学过程，Mg2+浓度是影响反应速率和产物中Mg/Al比的关键因素，较高的Mg2+浓度会提高反应速率，当Mg2+浓度从0.15 mol/L增大到0.30 mol/L时，产物中的Mg/Al比从2.40增大到3.05，但我们还无法得到Mg/Al = 2的LDHs，根据目前的实验结果，没有证据表明Mg/Al = 2，3和4的LDHs是热力学稳定的相。此外，Mg2+和Al(OH)3反应转化为LDHs的过程会优先于Mg(OH)2沉淀，尽管溶液中Mg2+浓度已经达到了Mg(OH)2沉淀的所需浓度。温度同样是影响反应速率的重要因素，温度低于140℃时，产物中有未反应的Al(OH)3，温度升高会促进反应的进行，但当反应温度高于180℃时，Al(OH)3容易脱水形成AlOOH，且AlOOH不能进一步转化为LDHs。 (3) 将上述拓扑反应的方法推广至CoAl-和NiAl-LDHs的合成。由于Co元素很容易被氧化生成Co3O4，在CoAl-LDHs的制备过程中需要加入适量的还原剂（如水合肼）。经拓扑转化制备的CoAl-和NiAl-LDHs，均保持了前驱体Al(OH)3的形貌，横向尺寸增大到2μm左右。 (4) 比较了Al(OH)3前驱物对Li+、Clˉ 的吸胀（imbibition）反应产物LiAl-LDHs与本拓扑反应产物的区别。LiAl-LDHs的晶粒尺寸横向尺寸和前驱体Al(OH)3完全一致，均为1 μm左右。验证了LiAl-LDHs的吸胀反应机理：Li+填入Al(OH)3层板中六个AlO6八面体所形成的空位中，因而不会改变其横向尺寸。

Layered double hydroxides (LDHs) have been receiving much concern for their chemical and physical properties, such as abundant intercalation chemistry, delaminate positive-charged 2D crystals, the “memory effect” that the calcined LDHs products of layered double oxides can restore the original lamellar structure, etc. This material possesses many advantages of interlayer guest species and host layers, showing a very broad application prospect in magnetics, optics, electrochemistry, drug delivery, catalysis and adsorption. This thesis firstly reviewed the research progress of preparation and application of layered double hydroxides, and then mainly focused on exploring new methods to synthesize LDHs, studying the reaction process and the influence of different reaction conditions in depth. The composition, structure and morphology were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), inductive coupled plasma atomic-emission spectroscopy (ICP), CHN Elemental analyses and so on. This work is of great significance for clarifying the formation mechanism of LDHs, guiding their controllable synthesis and further application, and has a high theoretical and practical value. The specific research contents are as follows: (1) We propose an alternative to the synthesis of MgAl-layered double hydroxides (LDH) with Mg/Al = 2.40 via controlling the topotactic reaction of Mg2+, OHˉ and NO3ˉ with Al(OH)3 in an aqueous NH3-NH4+ buffer solution (e.g pH = 9). The formed MgAl-LDHs crystals have high crystallinity and the hexagonal prism of the LDHs crystals inherits the primary morphology of Al(OH)3 with a size increase from 1.0 to 1.5 μm. According to the lattice parameters and the chemical compositions, the increase of the area from Al(OH)3 to the LDHs layer of could be calculated to ~149%, corresponding to a length increase of ~58%, which is consistent with the experimental results. Al3+ was not detected in the supernatant solution, indicating that the formation process of the MgAl-LDHs is a topotactic reaction of the precursor with the other ions. the alteration is not a simply substitution of Mg2+ for Al3+, but a process of Mg2+ substitution for Al3+ to destroy the Al?O?Al contacts and Al3+-filling in vacancy. (2) We compared the structural and morphological differences of MgAl-LDHs crystals prepared with and without buffer systems and studied the necessity of buffer solution and pH control. The lower concentration of OHˉ (or lower pH) is, the slower would be the reaction rate. Samples prepared at pH = 8 and 8.5 have high peaks of the precursor in the XRD pattern. Inversely, under higher pH, e.g. pH = 10 or 11, Al(OH)3 is dissolved before the alteration process to LDHs. The estimated pH value of Al (OH)3 dissolving is 9.84. Therefore pH must be controlled to a high value to give a high reaction rate but not too high in order to avoid the dissolution of Al(OH)3, the buffer of pH = 9 is probably the optimized value of pH in the current work. Moreover, the effect of Mg2+ concentration and reaction temperature on the alteration process was also investigated. The inserted amout of Mg2+ or Mg/Al in LDHs is an issue of kinetics, and depends on the concentrations of the reactants. The higher c(Mg2+) is, the faster the reaction rate, when the Mg2+ concentration increased from 0.15 mol/L to 0.30 mol/L, the Mg/Al of the products increased from 2.40 to 3.05, however, we could not obtained LDHs with Mg/Al = 2 in current reaction conditions, all the results of the present work have not given us any information about that LDHs with Mg/Al ratio of 2, 3, or 4 are a thermodynamically stable phase. The experimental results also reveal that the alteration reaction from Mg2+ and Al(OH)3 to MgAl-LDHs precedes the precipitation of Mg(OH)2 even though sufficient Mg2+ is introduced into the system. Temperature is another important factor affecting the rate of reaction, Lower temperature decreases the alteration reaction rate, shown by the peaks of gibbsite are still observed lower than 140?C, higher temperature increases the alteration reaction rate, but AlOOH will be formed when temperature higher than 180?C due to the decomposition of Al(OH)3 and can not convert to LDHs. (3) This method can be applied to the preparation of NiAl- and CoAl-LDHs via controlling the topotactic reaction of Al(OH)3 with corresponding metal ions, and all the products inherit the primary morphology of Al(OH)3 with a larger horizontal size of 2 μm. It is necessary to add some reducing agent, e.g. hydrazine hydrate, during the preparation of CoAl-LDHs because Co is easily to be oxidized to Co3O4. (4) Compared the differences between the LiAl-LDHs obtained by imbibition reaction of precursor Al(OH)3 with Li+, Clˉ and the MgAl-, NiAl-, CoAl-LDHs prepared by topotactic reaction. The horizontal size of LiAl-LDHs is about 1 μm, which is exactly the same as that of precursor Al(OH)3, certifying the “imbibition” mechanism: Li+ fills in the vacancies of Al(OH)3 laminate formed by the six AlO6 octahedra and does not change its lateral dimension.