Liquid-Phase Synthesis And Characterization Of Copper-Based Nanomaterials

The design and synthesis of nanometerials is hot research fields for nanoscience, and is also the base of the application and future development of nanotechnology. Although there are many methods reported for preparing nanomaterials, it is still difficult to obtain materials with controllable morphologies and sizes. Therefore, it is an important task in the field of material that how to develop new methods to design and synthesis of nanomaterials and realize the control of nanoparticles size, distribution, morphology and surface modification.This paper is focused on the controlled synthesis of copper-based inorganic nanoparticles, such as Cu, Cu2O and copper-based core-shell nanostructures. Growth mechanism and primary characterizations of nanoparticles are conducted. The advantages of liquid chemical synthesis technology in controlling the materials microstructures, morphologies and size are used. The detailed information of the dissertation is listed as follows.1. Selective synthesis of copper nanowires and nanroplates via a hydrothermal processCu nanowires and nanoplates have been selectively synthesized by controlling the release rate and the concentration of the free Cu+ via a surfactant-assisted hydrothermal process. The experiments show that when CTAC was used as surfactant, the release rate of the free Cu+ and the reduction process were controlled by CuCl, and Cu nanowires were obtained. When CTAB was used as surfactant, while other conditions were kept constant, When CTAB was used as surfactant, CuBr formed via the combination of Cu+ ions and Br- ions from CTAB. The free Cu+ concentration in the solution was decreased duo to the less solubility of CuBr than CuCl in the aqueous solution, and the formation of Cu atoms becomes slower, under such a condition may favor the growth of Cu plate-like structures.2 Hydrothermal synthesis of Cu2O microcrystals with various morphologiesA hydrothermal process has been developed to prepare Cu2O particles by reducing the Cu(II)-citrate complex with NaH2PO2. It has been known that the reducing power and reaction rate of NaH2PO2 change with varying of pH in aqueous solution, so reduction kinetically of system could be controlled by adjusting pH. As a face-centered cubic structure, the formation of Cu2O cubic might result from the{111} facets of Cu2O were eliminated because of their higher growth rate and the{100} facets remained because they have the lower growth rate. So the cubes of CU2O enclosed with six{100} facets were obtained. The results of chemical kinetic tests indicate that under acidic condition NaH2PO2 in inactivated state and the reduction rate becomes slow. The formation of Cu2O eight-pod particles can attribute to the fact that the reduction rate becomes slower as the pH is increased and the growth of six {100} facets are incomplete.3 Synthesis of Cu2O hollow nanocubes under solvothermal conditionWe synthesized Cu2O hollow nanocubes through a simple hydrothermal method without templates and surfactant. It is believed that both oriented attachment and Ostwald ripening should be the main formation mechanisms for the hollow nanocubes through TEM images at different time. In the first stage, initial nanoparticles are assumed in order to reduce their high surface energy. As the reaction proceeds, the concentration of the nanoparticles is decreased and the factor of oriented attachment is dominant in the reaction system. The loose structure is formed due to the oriented attachment process finishes so fast. In the later stage, crystallites located in the outermost surface of aggregates are larger and would grow at the expense of smaller ones inside, so the solid evacuation occurred, and hollow nanocubes were obtained. The experiment results indicate that the reaction time, temperature and the amount of water in the reaction system have some effect on the final morphology of Cu2O hollow nanocubes.4. Synthesis of Cu2O-Au core-shell nanospheres and Ag-Cu core-shell nanoparticles through solution method.(a) Cu2O-Au core-shell nanospheres were successfully prepared on a large scale through simple solution methods at room temperature in a very short time. Cu2O-Au nanospheres with core-shell structure were prepared by coating Au shell over Cu2O core. Cu2O cores were first prepared via the reaction between Cu(NO3)2 and N2H4.Then addition and subsequent reduction of HAuCl4 with excess N2H4 resulted in the formation of Au nanoparticles, which deposited on the Cu2O surface to form core-shell structure. At the same time, the evolution of the gap between core and shell could be attributed to the gradual consumption of the outmost surface of Cu2O core by H+ from HAuCl4. (b) A simple method has been developed for the synthesis of Ag-Cu core-shell nanoparticles, based on the use of DMF as both reductant and solvent, in the presence of PVP. At the early reaction stage, Ag+ ions are reduced first forming the core of the core-shell structure. The Ag core is acting as the nucleic center for the growth of the Cu2O layer. With the further reaction, Cu2+ ions are reduced subsequently and the shell of Cu2O nanoparticles are formed surrounding the Ag core. With a longer process time, the void space between core and shell could be observed, we presume that the formation of the void space between core and shell could attribute to the Ostwald ripening mechanism, accompanying with the reductive conversion of Cu2O to Cu. At the same time, Cu2O nanoparticles were transformed to Cu nanoparticles gradually, and Ag-Cu core-shell nanoparticles were obtained.