Soft Chemical Synthesis And Characterization On Micro/nanostructured Magnesium Hydroxide And Zinc Oxide

The ability to control and manipulate the physical and chemical properties of materials as we desired is one of the challenging issues in chemistry and materials science.The size- and shape-dependent physical properties of inorganic nanoparticles provide tunable materials with broad potential applications,and the fabrication of structurally complex nanoparticles further enhances their functionality.This dissertation aims at searching for effective solution routes to synthesize complex micro/nanostructured magnesium hydroxide and zinc oxide,control the morphology of the products by adjusting the reaction conditions.Elelctrodeposition has evolved recently to a simple and effective liquid phase method for fabrication of homogenous thin layers of insoluble materials,such as metal,ceramics,metal sulfide and metal hydroxide.Electrodeposition usually operates at room temperature and the quantity of deposition is determined by Faraday law,which is very suitable for preparing thin films.Thickness and structure of films can be precisely controlled by electrochemical parameters on conductive substrate of complex shapes,such as deposition potential,current density and solution composition.Moreover,electrodeposition is an economical deposition method due to simple process and inexpensive equipment.The chemical-liquid-deposition process,an analogue to the widely used chemical-vapor-deposition technique,has been well developed for production of insoluble solid films or materials through continuous supply,transport,and chemical reaction of film constituent in a liquid phase.Its basic requirement is heterogeneous chemical reaction on the substrate surface.This method has several merits:(a) appropriate deposition rates can be easily obtained;(b)operation can be achieved at low temperature at ambient conditions;(c)relatively uniform films can be formed on substrates of complex shapes and different size;(d)composition and crystallite of films can be precisely controlled by deposition conditions.Magnesium hydroxide is widely used as halogen-free flame retardant filler in composites materials,catalysis,and additive in refractory and paint,precursor for ceramics.Pure magnesium hydroxide,hexagonal or amorphous platelet crystal,is an inorganic weak alkali product.Due to its relatively strong buffer capacity,high activity and adsorption ability,safe disposal and treatment,magnesium hydroxide is considered to green and safe neutralization agent,environment friendly fire-retardant and the third alkaline while being noncorrosive,nontoxic and nonpoisonous.Znic oxide,an important direct n-type semiconductor with a band gap of 3.37 eV and a large exciton binding energy of 60 meV,and a high efficiency of exciton recombination at room temperature,has excellent optical,chemical,and electrical properties while being nontoxic,inexpensive,and chemically stable.ZnO has attracted considerable attention recently for various potential applications in optoelectronics,paints,cosmetics,catalysis and gas sensor.The main work of this thesis is systematically study on novel soft synthesis and characterization of micro/nanostructured magnesium hydroxide and zinc oxide.The details are given as follows:1.Lamellar-like and 3D flower-like Mg(OH)₂ were synthesized in formamide and glycine aqueous solution at near room temperature and room temperature through simple molecule assisted chemical-liquid-deposition process.Effects of reactant concentration,time and temperature on micro/nanostructured magnesium hydroxide were systematically investigated.The possible formation mechanism of these special micro/nanostructures was also discussed.The convenient,self-seeding growth of Mg(OH)₂ nanostructure not only has an attractive economical,but also avoids the incorporation of exotic metals and metals oxides as catalysts or seed particles, respectively.The exclusion of exotic metal catalysts and counterions(from Mg salt involved in other wet-chemical approaches)is very crucial for fabricating reliable and exquisite materials without unintentional properties.2.Uniform magnesium hydroxide thin film was obtained from directly electrolysis of magnesium nitrate aqueous solution at room temperature.The film with net-like was built up of nanowall.The as-synthesized magnesium hydroxide with highly textural lamellar mesostructure analogue to zeolite and layered double hydroxide was confirmed by XRD,TG/DSC,FT-IR techniques.Secondly,effects of sodium acetate and water-soluble ionic liquid additives on electrodeposited magnesium hydroxide microstructure were studied,then the influence of synthesis parameters on the morphological characteristics and size of magnesium hydroxide thin films deposited from nitrate bath was investigated,such as concentration of additive,duration and applied potential.A possible interaction mechanism responsible for morphologies evolution of thin films was preliminarily elucidated.3.A novel route was developed to prepare the polycrystalline ZnO thin films with(002)orientation enhancement by air annealing of zinc metallic films electrodeposited from nonaqueous solution without using any catalyst and template. Effects of annealing temperature,applied potential,annealing duration,different zinc salt precursor on thin films were systematically conducted.4.Urchin-like built up of nanorod/tube and spindle-like ZnO were synthesized in formamide and potassium bromate aqueous solution at near room temperature through simple chemical-liquid-deposition process.Effects of reactant concentration on zinc oxide micro/nanostructures and photofluorescence was carried out.The possible formation mechanisms of these unique micro/nanostructures were also presented.Secondly,effects of trisodium citrate additive on chemical-liquid-deposition zinc oxide nano/microstructure were executed.Finally,the influence of different substrate on the nature of zinc oxide grown from zinc nitrate and hexamethylenetetramine system through chemical-bath-deposition process was investigated.Novel micro/nanostructured zinc oxide can be directly obtained by simply adjusting reaction parameters at ambient conditions.In this thesis,unique micro/nanostructured magnesium hydroxide and zinc oxide were fabricated through simple chemical-liquid-deposition and cathodic electrodeposition.These methods have advantage over convenient,easy to operation. Moreover,the as-synthesized films were uniform thickness,good adhesion and well tailoring of shape and size compared with other methods.