Preparation And Properties Of Metal Nanocrystals With Surface Plasmon Resonance Properties

The optical,magnetic,and electrical properties of nanomaterials have been often affected by The oxidation of nanomaterials including the formation of a surface oxide,the partial or complete oxidation of the nanomaterials.For example,Superparamagnetic iron nanoparticle fluids lose their magnetic properties due to their oxidation.The localized surface plasmon resonance?LSPR?effect is readily observed in the visible spectrum for nanoparticles of coinage metals?i.e.,gold,silver,and copper?.Among the noble metals,the syntheses and applications?i.e.,biological applications,and environmental technology?of gold and silver nanoparticles have been widely developed to date for their LSPR behavior and the relative chemical stability.The reactivity and fast oxidation of Cu nanocrystals in air has often restricted detailed study of the Cu plasmons since their optical properties will fluctuate observably as a function of time.Cu nanomaterials prepared from earth-abundant and inexpensive materials have generated considerable interest due to their potential as viable alternatives to the rare and expensive noble-metal.The chemical and physical properties of Cu nanoparticles are modified using different synthetic methods,conditions or by means of postsynthetic chemical treatments has been mainly responsible for the rapid growth of attention on Cu nanomaterials and their applications in catalysis.Based on the copper nanoparticles,the Cu@Cu₂O nanoparticles,the Cu@Cu₂O/ZnO heterojunction structure and the Cu@Ni₁₂P₅ core-shell structure were prepared using the colloid chemistry synthesis method.A series of characterization methods were used to study the crystal structure,optical properties,morphology and particle size of the synthesized nanomaterials.The main study is divided into the following two parts:1.Under anhydrous and oxygen-free conditions,copper acetate,oleic acid,and trioctylamine were used as raw materials to prepare Cu nanocrystals by a colloidal chemical synthesis method.the Cu@Cu₂O nanocrystals exhibited a sphere-like core-shell shape with an average diameter of ca.14.4 nm.Their poor stability,the reactivity and fast oxidation of Cu nanocrystals in air has often restricted detailed study of the Cu plasmons.To improve the stability of single Cu nanomaterials for their potential LSPR applications,Cu@Ni₁₂P₅ was synthesized using nickel acetylacetonate?II?,oleylamine,and octadecene as raw materials.The results showed that the Cu nanocrystals exhibited LSPR absorbance locating at 600 nm.And the plasmonic Cu NCs was unstable and bothered by its serious surface oxidation in air.The Cu nanocrystals were unstable and easily oxidized.Ni₁₂P₅ as a coating layer,was remarkably chemically and thermally stable.However,the core-shell structure of Cu@Ni₁₂P₅ nanocrystals(i.e.,spherical Cu nanoparticles as core and Ni₁₂P₅ as shell)had the higher stability,which can prevent Cu nanoparticles contacting with air and inhibit the oxidation of Cu nanocrystals.2.Using colloidal chemistry synthesis method,copper acetate was used as precursor to prepare Cu@Cu₂O nanoparticles with smaller size under anhydrous and oxygen-free conditions.The synthesized Cu@Cu₂O nanoparticles were dispersed in n-hexane,and the nanocrystals of Cu@Cu₂O/ZnO were successfully synthesized by epitaxial growth,that is,the ZnO nanocrystals were selectively grown along the?1 1 1?crystal plane of the Cu nanocrystals.The results of XRD and UV-vis absorption spectra indicated that the morphology of the Cu@Cu₂O/ZnO nanocrystallites is lollipop-shaped,with relatively uniform size,regular morphology,and good dispersibility.Moreover,compared to the unstable,easily oxidized Cu@Cu₂O nanocrystals,the Cu@Cu₂O/ZnO nanocomposites showed excellent stability.The Cu@Cu₂O nanoparticles were partially coated with ZnO to form a Cu@Cu₂O/ZnO heterojunction so that the Cu@Cu₂O/ZnO nanocomposite was shown to be stable over more than one year.The H₂ evolution rate of the synthesized Cu@Cu₂O nanocrystals and ZnO nanorods was 5?mol g^-1 h^-1 and 278?mol g^-1 h^-1.However,Cu@Cu₂O/ZnO nanocrystals have higher photocatalytic performance,and the rate was 1472.2?mol g^-1 h^-1,which is 5 times higher than that of pure ZnO.The remarkable enhancement in photocatalytic activity in our present work was probably the results from the unique design of Cu@Cu₂O/ZnO heterojunction,which would allow the efficient electronic transfer through the Cu?Cu₂O?ZnO pathway.Furthermore,Cu@Cu₂O/ZnO nanocomposites can retard the recombination probability of electron and hole pairs and thus improve its photoactivity.