Preparation And Adsorption, Photocatalysis And Corrosion Of LDHs Materials Structure

Hydrotalcite-like compounds, a layered double hydroxides with regulable structure and composition, have been widely applied in adsorption, photocatalysis and corrosion resistance areas because of its elemental exchengeable features of main layer and interlayer space. The representative LDHs structures such as MgAl,NiTi,and NiFe have versatile properties due to the component and structural diversification of component. The structure and composition of layered double hydroxides (LDHs) with adjustable features not only can modulate the main layer of elementary composition,but also can ion exchange in the interlayer space of LDHs. It has been applied in adsorption,photocatalysis and corrosion resistance. The representative of MgAl,NiTi,NiFe-LDHs could create an infinite space for the control performance, due to the feature of component and diversity of morphology.In this paper,the MgAl-LDHs nanosheets and microsheets have been parepared and the adsorption preperties of as-prepared LDHs to methyl orange and Cr(Ⅵ) anions and Ni(Ⅱ) cations have been tested. Then,the NiO/TiO2 hollow microspheres have been synthesized. The influences of experimental conditation on the morphology of product have been investagated and the formation mechanism of microspheres have been proposed. The photoelectrocatalysis performance of NiO/TiO2 hollow microspheres has been tested. Finally, the molybdate intercalated NiFe-LDHs film has been prepared, the growth process and the anti-corrosion performance has been investigated. The main results of this dissertation are as follows:In this paper, we have prepared the MgAl-LDHs nanosheets and microsheets. The methyl orange and Cr(Ⅵ) anions and Ni(Ⅱ) cations adsorption on the samples. The adsorption mechanisms of MgAl-LDHs nanosheets have been discussed. Then,NiO/TiO2 hollow microspheres have been synthesized. The influence factors of formed microspheres and the formation mechanism of microspheres have been investigated. Also, the photoelectrocatalysis of NiO/TiO2 hollow microspheres has been measured. Finally, the growth process of the molybdate intercalated NiFe-LDHs film has been researched. This route has a potential to be a "smart" film capable of responding to stimuli from the environment. The main results of this dissertation are as follows:(1) Hexagonal MgAl layered double hydroxides (MgAl-LDHs) materials comprised of nanosheets and microsheets with different precipitants were synthesized via a facile hydrothermal route. Structural characterization revealed that MgAl-LDHs nanosheets and microsheets are 100 nm and 2 pm in width, respectively. Furthermore,MgAl-LDHs nanosheets have a higher specific surface area (65.94 m2·g-1) than that of microsheets (15.75m2·g-1). The methyl orange and Cr(Ⅵ) anions and Ni(Ⅱ) cations adsorption on the as-synthesized MgAl-LDHs nanosheets and microsheets were systematically assessed by measuring the residual concentration during the adsorption process. The MgAl-LDHs nanosheets showed better adsorption performance than the MgAl-LDHs microsheets for methyl orange and Cr(Ⅵ) anions and Ni(Ⅱ) cations. The adsorption performance versus time for the adsorption of methyl orange by MgAl-LDHs nanosheets has excellent adsorption quantity (229.82 mg·L-1) with high adsorption rate. The adsorption kinetics and adsorption isotherms of Cr(VI) anion and Ni(Ⅱ) cation of MgAl-LDHs nanosheets can be described by the pseudo-second order kinetic and Langmuir isotherm with saturated adsorption of 63.8 and 92.3 mg·g-1,respectively. The adsorption mechanisms of MgAl-LDHs nanosheets including precipitation, surface complexation, isomorphic substitution and ion exchange in the interlayer space of MgAl-LDHs nanosheets are discussed in detail. Finally, based on the quick and efficient removal of heavy metal ions by MgAl-LDHs nanosheets, a filtering-type water purification device was constructed.(2) We also present a rational design for the controllable synthesis of NiO/TiO2 hollow microspheres (NTHMs) with Ti plate via a one-pot template-free synthesis strategy. Specifically, to enhance the formation of hollow microspheres, part of the titanium source is provided by the Ti plate. The hollow spherical NiO/TiO2 particles possess unique microstructural characteristics, namely, a higher specific surface area(～65.82 m2·g-1), a larger mesoporous structure (～7.79 nm), and hierarchical nanoarchitectures connected with mesopores within the shell (monodispersed size of～1 μm and shell thickness of ～80 nm). In addition,as a cocatalyst for improved catalytic activity, the incorporated NiO nanoparticles with exposed high surface energy{110} facets displayed an outstanding performance. It has been proven that this facile nanostructure possesses remarkably high photoelectrochemical and photocatalytic activities. The main mechanism for enhancement of photocatalytic activity is attributed to the construction of p-n junctions with an inner electric field between TiO2 and NiO, which can dramatically enhance the separation efficiency of the photogenerated electron-hole pairs. This strategy could be applied to fabricate mixed metal oxide hollow microspheres toward the photoelectrochemical catalysis.(3) NiFe-LDHs films were prepared in-situ growth on 316L stainless steel via one-step hydrothermal route using Ni(CH3COOH)2, Fe(NO3)3,(NH4)6Mo7O24·4H2O and urea as raw materials. The results showed that NiFe-LDHs films had the better corrosion resistance, when hydrothermal reaction reached 12 h. Meanwhile, the parameters of Rt,corrosion potential,corrosion current density and corrosion rate were 2830 KΩ·cm2, -115.0 mV, 290.0 nA·cm-2 and 88.21×10-3 mpy.