Synthesis And Properties Of Metal Oxides And Mwtallic Copper Nanocrystals

Nanomaterials, often referred the research forward filed of material science, havepotential applications in many fields due to their special physicochemical properties.When the size of material reaches nanometer scale, the physical and chemicalproperties differ greatly from their corresponding bulk materials. Metal oxides andtransition metal nanomaterials have attracted considerable attention for their potentialapplications in gas sensing, lithium ion batteries, solar cells, catalysis,surface-enhanced Raman scattering and biological sensing. As we all known, theproperty of nanomaterials is not only related to their sizes, but also closely related totheir surface structure, exposed crystal facets and dimension. Therefore, one cancontrol any one of these parameters to fine tune the properties of these nanomaterials.To fulfill the widely applications of these excellent nanomaterials, much effort hasbeen paid to regulate the size, morphology and surface structure of nanomaterials withsimple, economic, efficient and environmentally friendly preparation routes. In thisthesis, our research mainly focuses on the solvothermal synthsis of metal oxides andtransition metal nanomaterials. Moreover, the properties of the as-preparednanomaterials were discussed.So far, there are many technical methods to produce metal oxide nanocrystals(NCs), such as calcination, decomposition, dehydration, ion-exchange reaction, and soon. Among these numerous routes, the thermal decomposition is one of the mostpromising techniques for making highly crystalline and size-controlled metal oxideNCs. However, this method commonly adopts some complex metal precursorsincluding metal carboxylates, metal acetylacetonates, etc. To overcome this problem, we have developed a facile one-pot strategy for the preparation of metal oxidesnanocrystals. This strategy adopted common, inexpensive and air-stable bulk metaloxides as raw materials with oleic acid and oleylamine as ligands. In the reactionprocess, bulk metal oxides gradually dissolve and form metal-oleic acid complexes.When the temperature exceeds a critical value, homogeneous nucleation occurs toform metal oxides nanocryatals. By this method, we successfully synthesizednanosized metal oxides (CdO, ZnO, PbO, SnO and Ga2O3) from their bulkcounterparts. The size, shape and structure of the synthesized metal oxides were easilymanipulated by changing the reaction parameters, such as time, temperature andconcentration of reactant. For lead oxide, both the orthorhombic and the tetragonalPbO were successfully synthesized by varying the reaction temperature. By changingthe reaction environment， both pure SnO and SnO2nanocrystals were successfullyprepared.In recent years, copper, as a typical transition metal, have been studied extensivelydue to its good performance. However, controllable synthesis and catalytic propertiesof copper system are rarely reported. In this thesis, we report a reproducible and facileapproach to synthesize faceted copper nanocrystals (Cu NCs) using an inexpensivecopper oxide as precursor with oleic acid as ligand and oleylamine as reducing agent.By high temperature organic inject synthetic route,9.5nm copper cubes,18.0nm and21.5nm copper polyhedron were successfully prepared by controlling the reactiontime. The reduction of p-nitrophenol to p-aminophenol is chosen as a model reactionto evaluate the catalytic activity of the Cu NCs. The results proved that the catalyticreaction follows pseudo first order kinetics. The catalytic reaction was studied atdifferent temperatures of20,25,30,35, and40℃. Their corresponding activationenergy, entropy of activation, pre-exponential factors, and turnover frequency werecalculated by the Arrhenius equation. It could be observed that9.5nm Cu cubesexhibited the highest catalytic activity, and18.0nm Cu polyhedrons showed betterperformance than21.5nm Cu polyhedrons. The mechanism for the enhancement ofcatalytic activities of Cu cubes involved three aspects, including a highersurface-to-volume ratio, the higher surface energy of {100} facet and the lower redox potential. In addition, we studied the recyclability and stability of9.5nm coppercubes. The conversion percent remained almost unchanged whereas the activity of thecatalysts reduced to84%with the fifth usage. Even after20days storage, the catalyticperformance of9.5nm copper cube only show a slight decrease in activity. Therefore,this facile route provided a useful platform for the fabrication of Cu catalysts whichhave the potential to replace noble metals (e.g., gold, silver, platinum, etc.) for certaincatalytic applications.On the basis of the the above work, we explore and improve the experimentalmethod to obtain a green, more simple method to synthesize copper nanocrystals. Inrecent years, more and more scientists turn their attention to the "green chemistry".Many countries in the world have regard "green chemistry" as one of the maindirections of chemical progress in the new century. One of the main features of greenchemistry is to use non-toxic, harmless materials. In this paper, we have chosen theedible olive oil as a solvent and ligand with copper oxide as the starting material forsynthesis of copper nanocrystals. In this reaction, different morphologies and sizes ofthe copper nanocrystals can be obtained by changing the reaction conditions. In thepresence of sodium borohydride, the obtained copper nanocubes exhibit high catalyticactivity in the degradation of dyes and the CO oxidation. Moreover, the coppernanocubes exhibit excellent surface enhanced Raman scattering (SERS) performance.