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Morphology Controlled Synthesis of ZnM(M=O、Se) and Their Properties Study

Author: ZhaoYanHua
Tutor: JingXiaoYan
School: Harbin Engineering University
Course: Applied Chemistry
Keywords: ZnO ZnSe Semiconductor gas sensor catalyticin AP thermaldecomposition
CLC: O614.241
Type: Master's thesis
Year: 2013
Downloads: 13
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Abstract


Both of ZnO and ZnSe are direct band gap Group II-VI semiconductor materials.Zinc oxide （ZnO） as an n-type semiconductor with a direct wide bandgap （3.37eV）and large excitation binding energy （60meV）, has attracted extensive researchattention for various applications.Zinc selenide （ZnSe） as an important group II-VIsemiconductor with a bulk band gap of2.69eV （460nm） at room temperature,possesses superior photovoltaic and optical properties and great potentialapplications.In order to prepare these two zinc compouds, liquid-phase chemicalsynthesis method is the most widely used in laboratory and industrial in great many ofdifferent materials preparation methods for its low cost of synthesis, the productdispersion is good, easy to control the crystal size and morphology, etc. has beenwidely studied. Our investigations are carried out as follows:Cone-shaped ZnO products assembled by microrods were successfullysynthesized staying at130℃for12h through hydrothermal method employingzincacetate as zinc source, hydrazine hydrate as alkali source and oleylamine assurfactant.The size of products is about1μm.The influence of processing parameterssuch as concentration of zinc salt, dosage of hydrazine hydrate and differentpreparation methods were investigated.When the humidity in the air of44%and theroom temperature of33℃, the concentrations of the test ethanol gas are10×10-6,100×10-6,200×10-6,300×10-6and500×10-6under this condition, respectively. Theresponse increases on increasing gas concentration in the range of10ppm,10×10-6,100×10-6,200×10-6,300×10-6and500×10-6.When the operate voltage of5V, thesensitivities of hydrothermal synthesizedproducts are1.5,2.7,3.3,3.5and3.9,respectively; when the operate voltage of4V the sensitivities of hydrothermalsynthesized products are2.4,6.7,8.1,11.2and15.2,respectively, which are higherthan the microwave method synthesized products and precipitation preparedproducts.Response and recovery times are also important parameters of in a gassensor, which were defined here as the time to reach90%of the final equilibriumvalue. All of the response and recovery time of the sensor is less than25s.Under thesame conditions,the sensitivity of the ethanol gas is higher than that of acetone gas,which subsequently demonstrated the ags sensor have sensitive and selective detection of C2H5OH.Highly crystalline octahedron-shaped ZnO particles have been successfullysynthesized by precipitation method through Zn（CH3COO）2-n-hexane water-oilsystem employing oleylamine as the surfactant at50℃. With increasing the reactiontemperature from50℃to80℃, the octahedron-shaped ZnO particles turned toflower-like products were prepared in the presence of oleylamine. In the absence ofoleylamine, the products are irregular shapes with the length size of2to4μm.Themorphology and size of the products are critically affected by the presence or absenceof oleylamine and the reaction temperature. Adding2weight%octahedron-shapedZnO to ammonium perchlorate decreased the temperature of thermal decompositionfrom447℃to305℃when the heating rate of10K/min.ZnSe microspheres were syntheised via solvothermal method employing glycerolas solvent,sodium hydroxide as alkali source, and adding double-distilled watercoordinated with glycerol.The experiment investigated the effects of the volume ratioof glycerol and water, the concentration of NaOH and reaction time on themorphology of the products. The formation of the ZnSe microspheres is due toOstwald ripening process. ZnSe microspheres showed catalyticactivity in the thermaldecomposition of ammoniumperchlorate.The hierarchical structure flower-like ZnSe and ZnSe hollow spheres weresynthesized through a simple solvothermal method employing Zn（CH3COO）2·2H2Oand Se in double-distilled water as source material, hydrazine hydrate as the alkalisource, ethylenediamine as the reducing agent and Polyvinyl Pyrrolidone （PVP） asthe surfactant. The results demonstrated that volume ratio of ethylenediamine tohydrazine is a key to control the morphorlogy of products. The cubic zinc blendestructure ZnSe hollow microspheres obtained at V（en）/V（N2H4H2O） of2:3. AsV（en）/V（N2H4H2O） increased to4:1, the products are flower-like precursorsZnSe（en）0.5. Hierarchical ZnSe crystals were obtained after calcined at500℃undera Ar atmosphere. The influence of processing parameters such as the volume ratio ofethylenediamine（en） to hydrazine hydrate（N2H4H2O）, reaction time, morphology and phase constitution of ZnSe were investigated.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Metal elements and their compounds > Section II group metal element and its compounds > The zinc Vice family (Ⅱ B group metal elements ) > Zinc Zn
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