【作者】 林香凤；

【导师】 周瑞敏；

【作者基本信息】 上海大学 ， 环境工程， 2010， 博士

【摘要】 Cu₂O是一种p型半导体,其禁带宽度仅为2.17eV,能被太阳光中的可见光激发,因此能充分利用清洁能源太阳能。Cu₂O的优点是无毒、相对价廉、化学稳定性较好。近年来已有一些关于Cu₂O可见光降解染料和持久性有机污染物的报道。然而存在的问题是氧化亚铜被光激发产生的光生空穴电子对易复合,导致光量子效率不高。而沉积导体如贵金属在Cu₂O表面或者Cu₂O和其它半导体复合能解决这些问题。目前,制备各种形貌的纳米Cu₂O的方法很多,但是电子束辐照方法制备Cu₂O及其复合物的报道却很少。本论文采用电子束辐照技术合成了Cu₂O及其Ag、TiO₂、SnO₂、SiO₂等复合物,研究了制备条件对催化剂形貌的影响。运用X射线粉末衍射（XRD）、X射线光电子能谱（XPS）、透射电镜（TEM）、扫描电镜（SEM）、红外（IR）、紫外-可见（UV-vis）等方法对所制备的光催化剂进行组成、结构和形貌的分析,同时考察了这些光催化剂在偶氮染料的可见光降解方面的应用。探讨了溶解氧和羟基自由基的活化机理。具体的研究工作集中在以下几个方面:1.以硫酸铜为原料,以聚乙二醇（PEG）和聚乙烯醇（PVA）为分散剂,异丙醇为自由基清除剂,在不加任何还原剂的条件下,电子束辐照含二价铜离子的水溶液体系制备出不同形貌的Cu₂O纳米粒子。（1）溶液体系的pH值对产物的类型影响很大,酸性条件下得到了纳米铜与氧化亚铜,弱碱性条件下得到了纳米氧化亚铜。由于用来调节pH值的氨水对产物Cu₂O有溶蚀作用,故适宜的pH在8-9之间。分散剂PEG的浓度对产物形貌有较大的影响,浓度为0.08g/L时,得到了圆球形及立方体的Cu₂O纳米粒子,浓度增大到0.2g/L时得到立方体的纳米Cu₂O。该体系所得产物纳米Cu₂O对偶氮染料甲基橙有较好的可见光降解能力,一些因素如制备体系的pH值和PEG浓度均影响降解效果,在pH8.0和PEG浓度为0.2g/L制备条件下得到的产物光催化活性最高,可见光照射70min,甲基橙的降解率达90.8%。（2）以PVA为分散剂得到了正八面体Cu₂O纳米颗粒。在这个体系中,溶液pH值也对产物形貌有影响,pH增高,过量的氨水存在溶蚀纳米Cu₂O,使产物从正八面体逐渐转变为不规格的颗粒。辐照吸收剂量也影响形貌,吸收剂量从70kGy增大到280kGy,颗粒从不规则形貌逐渐变为正八面体。纳米Cu₂O的生长机理遵循Ostwald熟化定律。对甲基橙的可见光降解表明在吸收剂量为280kGy,pH8.0制备得到的正八面体纳米Cu₂O光催化活性最好,在可见光下照射70min,甲基橙的降解率可达97.6%。2.电子束辐照含二价铜离子的酸性溶液得到纳米Cu后再水解也得到了氧化亚铜,通入空气和升高温度均能加速Cu₂O的生成。对甲基橙的可见光降解表明其活性比商品Cu₂O的高,可见光照射70min,水解得到的Cu₂O光催化体系中甲基橙的降解率为50.7%,而商品Cu₂O体系中甲基橙的降解率仅为20.8%。3.电子束辐照一步法成功合成了Ag/Cu₂O纳米复合物,Ag的引入能抑制纳米Cu₂O晶体的生长,使其分散更均匀。X射线光电子能谱分析表明复合物中Cu₂O表面易被氧化成CuO。复合物对甲基橙的可见光降解实验表明其光催化活性高于单一成分的Cu₂O,适量的Ag存在有利于提高复合物的光催化活性,原料中AgNO3与CuSO4.5H2O的摩尔比例为15%所制成的Ag/Cu₂O纳米复合物的光催化活性最高,可见光照射30min,甲基橙的降解率可达97%。过量的Ag反而使复合物的催化活性降低。4.以PVA为分散剂,通过电子束辐照含Cu2+溶液和金属氧化物的混合物,使生成的Cu₂O分别沉积在TiO₂、SnO₂、Fe2O3这三种n型半导体上,制备了p-n型复合半导体。TEM的观测表明适量TiO₂、SnO₂的引入使复合物分散更均匀。制备的复合物在可见光下对偶氮染料金橙Ⅱ的降解表明,Cu₂O（90%）/TiO₂、Cu₂O（90%） /Fe2O3催化活性比单纯的Cu₂O高,说明这两种复合物能使光生空穴电子对有效分离从而提高光催化活性。而Cu₂O（90%）/SnO₂的催化活性与Cu₂O一样高。5.通过电子束辐照含Cu2+和SiO₂的混合液,将纳米Cu₂O沉积在绝缘体SiO₂上,制备了Cu₂O/SiO₂复合物,并以金橙Ⅱ为探针测试了复合物的光催化活性,结果表明Cu₂O与SiO₂比例为5: 5、7: 3和9: 1（w: w）时催化活性较高。表明以适量的SiO₂为载体,并不损失有效光照,使催化剂的活性仍然能够保持。这种情况下添加SiO₂作为载体,可以降低光催化剂的成本。6.溶解氧的增加促进了染料的降解,而自由基清除剂异丙醇和叔丁醇则使Cu₂O和其复合物的光催化活性降低,表明光催化是通过自由基氧化进行。更多还原

【Abstract】 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 orangeⅡby 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 orangeⅡis 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.更多还原