Controlled Synthesis And Photocatalytic Performance Of Cu₂O/Cu Nanocomposites

Smiconductor-based photocatalysts, activated by illumination at room temperature, are used for degradation of organic pollutants by redox reaction. They have been applied for decomposition of water into O₂ and H₂, deodorization, antisepsis, sterilization and polluted water processing as well. However, TiO₂-based photocatalysts can only be activated by ultraviolet (UV) light because of their broad band gap, hence only less than 5% solar energy can be utilized. Recently, the exploration of novel, highly efficient photocatalysts under visible light (VL) has become one of the most important research areas for environmental pollution control and renewable energy sources. As p-type semiconductor with small band gap (Eg = 2.0 eV), cuprous oxide (Cu₂O) has been considered as the most promising photocatalysts besides TiO₂, for it can be easily activated by VL, hence can sufficiently utilize solar energy. Due to the easy recombination of photoelectrons and holes, pure semiconductor exhibits very low quantum efficiency. Therefore, Cu₂O/Cu nanocomposites (NCs)were synthesized. The photocatalytic properties on decomposition of organic materials, and the mechanism of catalytic reaction were studied.The main contents of this dissertation are as the following:1. Cu₂O/Cu NCs with different self-assembly nano-architecture, e.g., 3D nanoflowers, hollow spheres, octahedra and hollow microcubes, were prepared using hydrothermal technique with Cu(NO3)2·3H2O as a precursor, and N,N-dimethylformamide (DMF)/ethanol (Et) as solvents, under different experimental conditions. The effect of the concentration of precursor, reaction time, temperature, and volumn ratio of solvent on have strong on the microstructure and phase composition of Cu₂O/Cu NCs were analyzed. The flowerlike structure was formed by a two-step reaction (150,180°C) with DMF as solvent. At higher precursor concentration, bur-like assembly was obtained. Cu₂O/Cu octahedra were formed by introducing Et into DMF (1:2), increasing reaction temperature (180,200°C), and decreasing reaction time. The size of particles increases with higher precursor concentration. If little amount of water was added further, hollow cubes were formed, and hollow structure disappears at higher precursor concentration. By using DMF/Et (1:1) as solvent, one-step reaction at 200°C, at high rate of decreasing temperature, hollow spheres were obtained, while solid spheres were formed at higher concentration of precursor. The content of Cu in composites increases with longer reaction time. 2. The photocatalytic performance of Cu₂O/Cu NCs was evaluated by the degradation of Procion Red MX-5B (PR), methyl orange (MO), methylene blue (MB), Rhodamine B (RB) and phenol. The influence of morphology, concentration of Cu, pH value, original concentration of organic materials, concentration of catalyst, addition of H₂O₂ and recycling use on the photocatalytic activity of NCs was investigated. L-H model was adopted to analyze the degradation of phenol and dynamic parameters were obtained. Experimental results indicate that Cu₂O/Cu NCs exhibit much higher photocatalytic activity than pure Cu₂O; the photodegradation rate of NCs with flower, hollow sphere and octahedron structure are 20% higher than that with microcube structure. Very high initial concentration of catalysts and organic materials can reduce the reaction rate. The pH value of reaction solution show strong influence on the photocatalytic activity. Introduction of H2O₂ enhances the performance. The degradation rate on PR and phenol remains over 80% after cycles of use. By washing under ultrasonic vibration or hydrothermal reduction routes, the photocatalysts can be recovered.3. The photocatalytic mechanism of Cu₂O/Cu NCs catalysts is analyzed. The catalysts were synthesized by partially reducing Cu₂O. It was found that many heterostructures exist in Cu₂O/Cu NCs. The dense packing of Cu₂O and Cu particles enhances charge transportation, which separates the photogenerated electron-hole pairs happens at the interfaces of heterostructures, improves the quantum efficiency, and increases the catalytic activity effectively.Cu₂O/Cu NCs were synthesized using a facile, low-cost, template-free hydrothermal route without any additive. The morphology, mass ratio of Cu/Cu₂O can be easily controlled. The catalysts show very high performance on the degradation of organic dyes and phenol. Moreover, they can be recycled for further use, making them promising catalysts on the processing of polluted water.