Preparation And Characterization Study Of Layered Double Hydroxides Via Coprecipitation Method Using T-Type Microchannel Reactor

Layered double hydroxides (LDHs) are a class of anionic clays, composed of positively charged brucite-like layers of mixed metal hydroxides with charge-balancing anions and water molecules intercalated in the gallery. Because of the flexibility in composition and the exchange ability of interlayer anions, LDHs possess a wide range of properities.These materials have various applications, such as catalyst, absorbents, flame retardant, pharmaceutics etc. In view of the high application value of LDHs, its preparation methods have garnered much attention. A lot of synthetic methods were reported, such as coprecipitation, ion-exchange, sol-gel method, separate nucleation and aging step method and so on. These methods can get a good crystallinity of LDHs samples, but the particle size and its distribution is not easy to control. Because the particle size and its distribution has an important effect on application performance, so how to get size controllable LDHs is still one of the research focuses in chemistry. Recently, because the LDHs nanosheet could be used as functional materials units, the preparation of LDHs nanosheet (or single sheet)has attracted big attention. The preparation methods include stripping method and microemulsion method, etc., but these methods or by using toxic organic solvent (such as formamide), or because of preparation of nano surface load organic matter (surfactant), the actual application is restricted, so how to get the clean surface (no load organic) nano LDHs through a simple and macroscopic preparation method is a challenging research topic. Micro reactor is also called "microstructure reactor" or "microchannel reactor" from mixed mode, according to the external power source can be divided into active microchannel reactor and passive microchannel reactor. As one of the most simple passive microchannel reactor, T-type microchannel reactor could mix two response logistics body fastly and uniformly. Compared with the macro reactor, micro reactor has completely different geometric characteristics such as micro scale, larger specific surface area, the smaller size and unique flow behavior. In the micro reactor, the micro channel can be reduced to a few microns in diameter.when the mixed fluid in a microchannel, molecular diffusion path is greatly shortened,it could be mixed uniformly in a very short tim by the mixing effect. T-type microchannel reactor has been widely used in the preparation of inorganic nano particle. With the characteristics of confinement effect and rapid sufficient reaction reaction between the mixing, the effective control of the product particle size and its distribution can be realized.The main contents of this thesis are as follows:(1) A T-type microchannel reactor was used to prepare Mg-Al layered double hydroxides (LDHs) via the coprecipitation method, and the effects of flow rate of reactant solutions, concentration of mixed salt solution and temperature on the particle size and the particle size distribution of the obtained LDH samples were examined. The results showed that the morphology and crystal structure of the LDH samples obtained using the T-type microchannel reactor were similar to those of the materials synthesized by the conventional coprecipitation method. However, the T-type microchannel reactor route could afford small particle size and very narrow distribution of particle size for the materials. The flow rate, concentration of mixed salt solution and temperature has an important influence on the particle size and the particle size distribution of the obtained LDH samples. With the increases of the flow rate and temperature, the particle size and the particle size distribution of the obtained LDH samples decreased, while with the increase of the concentration of mixed salt solution, those increased. A major advantage of the T-type microchannel reactor route is that the particle size and the particle size distribution of the as-obtained samples can be simply and effectively controlled by the flow rates of the reactant solutions. (2) Mg-Al LDHs nanosheet with clean surface was prepared by T-type microchannel reactor coprecipitation method and traditional coprecipitation method.The aggregation stability of nanosheet in Water dispersion system was studed.The result show that the single layer nanosheet could form nanoparticles through self assembly; The self assembling process would be more quickly with the higher solid content of nanosheet dispersion and higher temperature. The Mg-Al LDHs nanosheet could stabilized for over30days,so it can satisfy the general application requirements. The research provide a new way for the macro preparation of clean surface LDHs nanosheets and laid the foundation for more extensive application of LDHs nanosheets.(3) Zn2Al LDHs nanosheet with clean surface was prepared by T-type microchannel reactor coprecipitation method.The nanosheet was used as assemble primitive to prepare HCPT/Zn2Al LDHs nanocomposite with anticancer drug molecule10-hydroxyl camptothecin. The drug release behavior was investigated. The results showed that the LDHs nanosheet prepared by T-type microchannel reactor coprecipitation method have important application prospect in the field of self-assembly; HCPT/Zn2Al-LDHs nanocomposite with good sustained release effect, its release kinetics process conforms to the pseudo-second order kinetics equation, the spread of drugs within the particles is the rate control steps.