Study On The Electron Beam Irradiation Synthesis, Photocatalytic Performance Of Micro/nano- Cu₂O Nanoparticles And Their Composites

Cu₂O is a p-type semiconductor with a band gap of 2.17 eV, it can be activated by the visible light, thus, the clean energy solar energy can be effectively utilized. Cu₂O has cheap, relatively non toxic properties, and good chemical stability. In recent years, there have been some reports on the photodegradation of dyes and persistent organic pollutants by Cu₂O under visible light. There is a limitation that the carriers excitated by light cannot be transferred efficiently and are easy to recombine, to solve this problem, Cu₂O composite with other semiconductors or conductive materials such as noble metals may be a good way. Nano-Cu₂O with various morphologies has been prepared by many methods, but the reports on the electron beam irradiation synthesis of Cu₂O nanoparticles and their composites are rare.In this dissertation, the Cu₂O nanoparticles and their nanocomposites with Ag, TiO₂, SnO₂, Fe2O3 and SiO₂ were synthesized by electron beam irradiation, and the effects of preparation conditions on the morphologies were studied. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), UV-vis spectrophotometer and FT-IR spectrophotometer were used to analyze the compositions, structures and morphologies of the products. The applications of these photocatalysts on the visible light degradation of the azo dye were also studied. The activation mechanisms of dissolved oxygen and hydroxyl radical during the photodegradation of dyes were also investigated. This dissertation contains the following major parts:1. With poly (ethylene glycol) (PEG) and Polyvinyl alcohol (PVA) as templates and CuSO4 as raw materials, without further reducing reagent, with the addition of isopropanol as a scavenger of oxidative radicals such as·OH produced during water-radiolysis, nano-Cu₂O with various morphologies have been prepared by electron beam irradiation.(1)The pH value of the solution has a great influence on the types of products, the mixtures of nano-Cu and Cu₂O are obtained at acidic conditions, pure Cu₂O nanoparticles are obtained at alkaline conditions. The appropriate pH value of the solution is in the range of 8 to 9, because the ammonia which used to adjust the pH can dissolve the Cu₂O. The concentration of PEG also has a great influence on the shape of Cu₂O, a mixture of spheres and cubes can be obtained at 0.08g/L PEG, cubes are obtained at 0.2g/L PEG. The as-prepared Cu₂O nanostructures show activity toward photodegradation of MO. Influences of some parameters such as Cu₂O nanoparticles prepared at different pH values and PEG concentration are also investigated. Cu₂O nanoparticles prepared from pH 8.0 and 0.2g/L PEG show the highest photodegradation efficiencies, the degradation percentage of MO reaches to 90.8% after 70min irradiation of visible light.(2) Octahedral nano-Cu₂O can be synthesized with PVA as template. The pH values and adsorbed doses influence the shape of products. With the increase of pH, the excess ammonia will dissolve the octahedral Cu₂O into irregular particles. The obtained Cu₂O varies from irregular to octahedron by increasing the adsorbed dose from 70kGy to 280kGy. The process of crystal growth follows Ostwald ripening. Octahedral Cu₂O nanoparticles prepared from pH 8.0 and adsorbed dose of 280kGy show the highest catalytic activity on the degradation of MO under visible light, the degradation percentage of MO reaches to 90.8% after 70min irradiation.2. The nano-Cu can be obtained by the irradiation of acid solution containing Cu2+, then Cu is oxidized to Cu₂O by hydrolysis. The bubbling of air and higher temperature can accelerate the formation of Cu₂O. The photodegradation of MO on the as-prepared Cu₂O shows that it exhibits higher catalytic activity than that of commercial Cu₂O under visible light, the degradation percentage of MO reaches to 50.7% on the as-prepared Cu₂O, while it reaches to 20.8% on the commercial Cu₂O.3. The Ag/Cu₂O nanocomposites are successfully synthesized by one-step electron beam irradiation, the introduction of Ag has an inhibition effect on the growth of cuprous oxide crystallite. The XPS analysis shows that the surface of Cu₂O is easy to be oxidized to CuO. The Ag/Cu₂O nanocomposites exhibit higher catalytic activity than that of pure Cu₂O by the photodegradation of MO under visible light, and appropriate amount of Ag on the surface of the nanocomposites enhance the catalytic activity, Ag/Cu₂O nanocomposites obtained from 15%molAgNO3/CuSO4.5H2O show the best catalytic activity, the degradation percentage of MO reaches to 97% after 30min irradiation. But the excess Ag hinders the activity.4. Using PVA as template, the p-n semiconductors Cu₂O/TiO₂, Cu₂O/SnO₂ and Cu₂O/Fe2O3 can be synthesized by the irradiation of the mixtures containing TiO₂, SnO₂, Fe2O3 and Cu2+. The TEM observations demonstrate that the composites distribute more evenly with the addition of appropriate amount of TiO₂ and SnO₂. The photodegradation of orangeâ…¡by the as-prepared composites show that Cu₂O(90%)/TiO₂ and Cu₂O(90%)/Fe2O3 exhibit higher catalytic activity than that of pure Cu₂O, indicating that the photogenerated electron and hole can be effectively separated to improve the photocatalytic activity. While the Cu₂O(90%)/SnO₂ show as high photocatalytic activity as Cu₂O.5. The Cu₂O/SiO₂ composite is obtained by the irradiation of the mixtures containing SiO₂ and Cu2+, using PVA as template. The orangeâ…¡is used as the model pollutant to measure the photocatalytic activity of the Cu₂O/SiO₂ composite, the results show that the composites exhibit high catalytic activity when the ratio of Cu₂O and SiO₂ are 5: 5, 7: 3 and 9: 1 (w: w),respectively. This indicates that SiO₂ does not lose the effective light and lower the activity of photocatalyst when appropriate amount of SiO₂ acts as supports. Therefore, the addition of SiO₂ can reduce the cost of photocatalyst.6. The increase of dissolved oxygen enhances the degradation of the dye, the addition of free radical scavengers tertbutyl alcohol and isopropanol reduce the photocatalytic activity of Cu₂O nanoparticles and their composite.