【作者】 周波；

【导师】 苏文辉； 刘志国；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2009， 博士

【摘要】 半导体光催化技术,通过在室温下以光为驱动力活化催化剂,利用氧化-还原反应来分解有机物、还原金属离子,在分解水制备氢气、除臭、防腐、杀菌、污水处理等多方面获得应用。但是目前研究比较成熟的催化剂二氧化钛（TiO₂）由于其禁带宽度较大,仅能利用不到5%的太阳能源。高效的可见光催化剂的研究制备已成为环境污染控制和可持续发展能源开发利用的重大课题。对于窄禁带p型半导体氧化亚铜（Cu₂O,Eg=2.0 eV）,能够直接吸收和利用可见光,对太阳光具有较强的吸收效率,被认为是继TiO₂之后,最有应用潜力的半导体光催化剂之一。基于单相半导体较高的量子复合效率不利于光催化反应的进行,本文以金属Cu作为添加剂对Cu₂O进行修饰,研究了Cu₂O/Cu复合材料的制备、光催化降解偶氮染料和苯酚,并对其催化机制进行了探讨。本文的工作分为以下三个方面:1.采用溶剂热方法以硝酸铜为原料,氮,氮-二甲基甲酰胺（DMF）和乙醇作为溶剂,通过改变反应条件,制备出了具有不同自组装结构的Cu₂O/Cu复合材料,例如,三维纳米花状结构、空心纳米球、纳米正八面体和微米空心立方体等。分析了前驱体浓度、反应步骤、反应时间、反应温度、溶剂成分比例等因素对产物形貌、相组成的影响。结果表明,以DMF为溶剂,通过两步反应（150,180℃）,低浓度时形成Cu₂O/Cu纳米花状结构,高浓度形成刺球状聚集体;溶剂中加入乙醇（DMF:乙醇=1:2）,提高反应温度（180,200℃）,降低反应时间,形成八面体形貌Cu₂O/Cu纳米材料,前驱体浓度增加导致粒子变大;如果溶剂中再加入少量水,则得到微米级空心立方体,浓度增大时空心结构消失;若使用DMF:乙醇=1:1的溶剂,采用高温（200℃）一步反应,并快速降温,形貌为空心的纳米球状,高浓度时变为实心球。随着反应时间的延长,复合材料中Cu的含量增加。2.以常见的难降解的酸性染料普施安红、甲基橙、亚甲基蓝、罗丹明B和酚类有机物苯酚作为目标降解物,利用Cu₂O/Cu催化剂进行光催化降解处理。考察了各种因素,包括形貌、Cu含量、溶液pH值、染料初始浓度、催化剂初始浓度、过氧化氢的添加、循环次数等对Cu₂O/Cu复合催化剂催化活性的影响。并运用L-H反应动力学模型研究了苯酚的光催化降解过程,求解出降解动力学参数。结果表明,Cu₂O/Cu复合催化剂的催化活性明显高于单相Cu₂O;纳米花状、空心球状和正八面体状结构Cu₂O/Cu复合催化剂要比立方体状催化剂的催化活性高出20%;过高的催化剂浓度和染料浓度都不利于催化反应的进行;溶液pH值对催化剂的活性影响很大;Cu₂O/Cu复合催化剂对罗丹明B的吸附和降解最差;过氧化氢对催化过程的降解速度和催化剂的活性都有促进的作用;经多次循环使用,催化剂对普施安红、苯酚的降解率仍然可以达到80%以上;针对失活部分,采用超声清洗和溶剂热还原技术,可以使催化剂的活性得到有效的恢复。3.对Cu₂O/Cu复合催化剂的催化机制做了初步探讨。在Cu₂O/Cu复合材料中,存在着大量由Cu₂O和Cu组成的异质结,光生载流子在异质结界面的分离,促进了催化剂的量子效率,提高了催化活性。溶剂热技术合成的Cu₂O/Cu复合材料,是由Cu₂O原位还原制得的,Cu和Cu₂O纳米粒子间的紧密接触促进了电荷的输运过程,有效的提高了催化活性。本文不采用任何模板和添加剂,利用溶剂热方法一次性合成不同形貌,不同Cu₂O/Cu比例的复合纳米材料,方法简单可行,制备成本低。合成的催化剂对有机染料和苯酚的降解具有很高的催化活性,且可以回收利用,有望在污水处理等方面获得应用。更多还原

【Abstract】 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.更多还原