Preparation And Investigation Of Layered Double Hydroxides Hollow Structure

As a bi-metalic layered structure hydroxide, layered double hydroxides (LDHs) featured the variability of their compositions and intercalated guests, the ordered arrangement between host-guest and guest-guest, template memory effect. LDHs are one kind of important anion layered functional materials, which was warmly welcomed by catalysis, biomaterials, photochromic materials, photoelectric conversion and so on. Usually, LDHs and its derivatives have a hexagonal structure, such as bended hexagon, single hexagon, flower-like structure composed of hexagonal sheets and many assemblys origin from hexagonal plates. Few researches on hollow layered double hydroxide structure were reported. The hollow nano-materials own many characters including large surface area, low density, good penetrability, lower coefficient of thermal expansion and refractive index, more exposed active sites. Thus, the fabrication of hollow LDHs with novel structures benefits both the expansion of LDHs’family, and the development of LDHs’properties. We focused on not only the fabrication of various morphologies of hollow LDHs and their calcinations, named layered double oxide (LDO), but also the effect of their morphologies to catalysis and sterilization, which may be helpful for their future applications.Main research work and achievements:1. The former methods of synthesizing LDHs mostly base on anisotropic growth in metal ionic solutions, the products often become sheet-like structure due to priority growth perpendicular to c axis. We take advantage of one-dimensional metal hydroxide as precursor and mix-solvothermal method to form Mg/Al-CO3nanorings. The results could be explained by Kirkendall Effect. By manipulating the ratio of solvents and reaction rate, we obtained Mg/Al-CO3nanorings with high yield as the ratio of organic solvent to water was4:1(v/v). The nanorings are700-800nm in outer diameter and250nm in inner diameter. We systematically investigated the effect of reaction factors (temperature, time, metal species, precipitants and solvents) on forming LDH nanorings. Characterizations including XRD、SEM、TEM、FTIR、BET and in-situ EDXRD revealed the formation mechanism. The releasing and diffuse rate of metal ions plays an important role in forming LDH nanorings. When changing the reaction parameters, other morphology of LDHs such as nanosheets and nanoflowers could also be formed. We evaluated the catalyzed effect of LDHs with various morphologies on Knoevenagel reaction of diethyl malonate and benzaldehyde. Compared with nanosheets and flower-like LDHs, nanorings got higher catalytic activity, which may due to the higher surface area, proper structural channel and more exposed active sites.2. Inorganic hollow metal oxide spheres have many applications in gas sensor, magnetic materials and catalyst fields. However, the adsorption ability on carbon template of metal ions varies much and there exists the competitive adsorption between metal ions, which make the formation of hollow spheres with controllable metal-to-metal ratio harder. Based on the description above, we took advantage of the LDHs with the controllable component and metal-to-metal ratio as precursors, carbon spheres as templates, the negatively charged carbon spheres and positively charged LDHs precipitated by electrostatic force drive to prepare the controllable multi-metal oxide (LDO) hollow spheres. Because of the variability of LDHs, final metal oxide spheres after calcination can inherit the metal-to-metal ratio well with the LDH precursor, revealed by ICP and EDS measurements. By adjusting carbon spheres with different size, we can tune the size of hollow sphere ranging from250nm to1000nm inferred from TEM and SEM. When changing the metal ion species, variety of hollow metal oxide spheres could be formed, for instance, MgzAl-LDO, Mg3Al-LDO, Mg4Al-LDO, Ni2Al-LDO, Mg3Fe-LDO, ZnNiAl-LDO. So, the hollow multi-metalic oxide spheres could be tuned size, metal components and metal-to-metal ratio by this method, which provide abundant materials for their application. We evaluated the sterilization effect of LDO with various morphologies. Compared with nanosheets, hollow LDO sphere has better sterilization effect to staphylococcus aureus and colibacillus due to their higher surface area.