The Study On Preparation And Photoelectrochenlical Properties Of Cuprous Oxide Micro-and Nano-Particles

It is well known that semiconductor materials have been used extensively in many fields, such as aerospace industry and electronics industry. As a metal-oxide p-type semiconductor with a band gap of about2.0eV, cuprous oxide (Cu2O) has attracted much research interest because of its potential applications in solar energy conversion, catalysis and gas sensors. In this paper, different morphologies of Cu2O were prepared by electrodeposition and wet chemical method, and the formation mechanisms of Cu2O particles were proposed on the basis of the experimental results. Furthermore, the heterostructures of Cu2O-TiO2and Cu2O-ZnO were fabricated using the Cu2O as photosensitive agent. The optical absorption and photocurrent of these heterostructures were also measured for extending the application of Cu2O in photoelectrical field. In order to optimize the structure of these heterostrucutures, the influence of microstructure on photoelectrical properties was discussed. The content and innovation of this thesis are listed as follows:(1) Different morphologies of Cu2O particles were prepared by galvanostatic electrodeposition in sole Cu(Ac)2electrolyte. Octahedral and dendrite-like Cu2O particles were controllably prepared by changing the electrolyte status. The octahedral Cu2O particles were fabricated in static electrolyte, and the dendrite-like Cu2O particles were fabricated in stirred electrolyte. By characterizing the microstructure of dendrite-like Cu2O particles, it was found that the growth directions of dendritic branches are all along the <110> directions. Therefore, the formation mechanism of Cu2O dendrite crystals prepared in stirred electrolyte was proposed on the basis of the experimental results. Firstly, the Cu atoms precipitated from the electrolyte and grew along close-packed directions (<110> directions) to form of Cu lattice. Then, oxygen atoms diffused into Cu lattice to form Cu2O lattice. Finally, the dendrite-like Cu2O was formed with dendritic branches growing along<110> directions. So, the dendrite-like Cu2O crystals formed under a kinetic growth regime. In addition, the conduction types of Cu2O particles were different for the octahedral and dendrite-like Cu2O particles. The octahedral Cu2O particles exhibited the p-type semiconducting behavior, and the dendrite-like CU2O particles presented n-type semiconducting characteristic. This conclusion will help design more effective Cu2O p-n homojunctions for solar energy conversion.(2) Smooth and uniform nanocrystal Cu2O thin films were prepared by potentiostatic deposition method. In our experimental system, the addition of thiourea in Cu (Ac)2electrolyte enhanced the quality of Cu2O thin film. This is because that thiourea had two effects on formation of Cu2O thin film:1) thiourea worked as the heterogeneous nucleation sites for increasing the nuclei density in Cu2O electrodeposition;2) thiourea worked as capping agent for inhibiting growth of Cu2O nuclei. The parameters of electrodeposition were optimized by a series of parallel experiments, and the best quality Cu2O thin films were prepared under the potential of-0.1V (vs.SCE) in0.5mM thiourea electrolyte. Through the optical absorption and photocurrent properties measurement, the results show that the Cu2O thin film presented obvious absorption around550nm, and exhibited some visible light responses and photocurrent value under visible light illumination. However, the photocurrent obviously decayed as prolonging the illumination time.(3) The Cu2O nanoparticles were quickly prepared in solution of NaOH, N2H4·H2O and copper salt at ambient temperature by wet chemical method. NaOH agent played an important role in controlling the morphology of Cu2O in this reaction system. The spheric Cu2O particles aggregated by Cu2O nanoparticles were fabricated without NaOH. The Cu2O nanoparticles became dispersive with increasing NaOH. However, the morphology of Cu2O developed into octahedron aggregated by Cu2O nanoparticles as continuously increasing NaOH. The N2H4·H2O had a little effect on the morphology of Cu2O in the reaction systems, N2H4·H2O changed the size of Cu2O nanoparticles and degree of aggregation. With increasing N2H4·H2O, the size of Cu2O decreased and the degree of aggregation increased. In addition, the solvent had a large effect on the morphology of Cu2O in the reaction system. By controlling the proportion of water and ethanol, the morphology of Cu2O changed from sphere to octahedron. The results show that the morphology of Cu2O experienced the evolution from spheric nanogranule aggregate, through octahedral nanogranule aggregate to smooth octahedron transformation process with increasing ethanol content. The formation mechanism can be explained by combined action of Ostwald ripen (OR) and Oriented attach (OA).(4) The Cu2O-TiO2heterostructures were prepared by combining anodic oxidation and galvanostatic pulse electrodeposition. The status of electrolyte and current density had large effects on the morphology of Cu2O particles in electrodeposition. Under the condition of same current density, the octahedral CU2O particles were formed in static electrolyte, and the branched Cu2O particles were formed in stirred electrolyte. Cu2O-TiO2heterostructure exhibited obvious optical absorption and visible light responses under visible light illumination. The optical absorption and photocurrent value increased with increasing current density in static electrolyte. However, the optical absorption and photocurrent value first increased and then decreased with increasing current density in stirred electrolyte, which was relevant with morphology and crystallinity of branched and octahedral Cu2O crystals. In addition, coaxial TNTs@Cu2O heterostructures were prepared by combining anodic oxidation and potentiostatic electrodeposition. The ribs of TNTs arrays and addition of thiourea played important roles in formation of coaxial TNTs@Cu2O heterostructures. The coaxial TNTs@Cu2O heterostructure exhibited obvious optical absorption and visible light responses under visible light illumination. The photocurrent value was sharply improved compared with that of simple heterostructure. Especially, the shortcut current value of coaxial TNTs@Cu2O heterostructure was several times that of simple heterostructure.(5) The Cu2O-ZnO heterostructures were prepared by combining galvanostatic pulse and potentiostatic electrodeposition. Two different morphologies of ZnO were appeared in electrodeposition of ZnO. One was flake-like, and the other was pyramidal. Further, through adjusting the concentration of electrolyte, current density and depositon time, the formation mechanism of different morphologies of ZnO was proposed. The optical absorption and photocurrent measurement of Cu2O-ZnO heterostructure shows that the heterostructures had obvious optical absorption in visible light range, and exhibited obvious visible light responses and photocurrent value under visible light illumination. However, the reproducibility and lifetime of the heterostructure were poor in phtotochemical measurements.