| 题名 | 新型可见光催化剂及污染物光催化降解机制的研究 |
| 作者 | 胡学香 |
| 学位类别 | 博士 |
| 答辩日期 | 2007 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 胡春 |
| 关键词 | 可见光催化机制 Visible-light-driven photocatalytic mechanism 病原菌 Pathogenic bacteria 有机污染物 Organic pollutants 多元金属氧化物 Multi-metal oxides 界面电子转换 Interfacial charge transfer |
| 其他题名 | Novel Visible-induced Photocatalysts and the Mechanism of Photocatalytic Degradation of Pollutants |
| 中文摘要 | 多相光催化以杀菌和无机化大多数有机污染物双重能力成为环境净化领域的新的生长点。但是由于存在光催化剂的催化效率低、不能有效利用太阳能中的可见光等缺点，目前光催化技术仍然不能得到广泛的应用。因此本论文的主要研究目标是开发新型高效的可见光催化剂，并研究其去除气相、水中有机污染物及病原菌的性能和光催化机制。作为高效可见光催化剂需具备两个特点：一是较强的可见光吸收；二是光致电子空穴的快速分离与高效的界面电子转换。本论文从以上两个方面出发，合成了在可见光区有强吸收的多元金属氧化物，并通过对其表面形貌的控制及表面能差势垒的构建，来加强电子与空穴的分离及界面的电子转换以获得新型高效的可见光多相光催化剂，同时研究其对病原菌、有机污染物的光催化降解活性，并探讨了可见光催化剂的光催化去除有机物、杀菌机制。研究内容和结果如下： 1. 新型高效可见光催化剂的研制 (1) NiO/SrBi2O4新型可见光催化剂 采用共沉淀法制备了在可见光区有吸收的SrBi2O4材料，并通过浸渍法合成了NiO/SrBi2O4可见光催化剂。通过扫描电子显微镜 (SEM)、X射线光电子能谱 (XPS)、电子自旋共振 (ESR)等表征手段，证明SrBi2O4表面负载了NiO以后，能够形成短路的微型光电化学原电池，加强了电子与空穴的分离，使其可见光催化效率提高了十几倍，对乙醛、病原菌等污染物的降解和无机矿化都显示了很高的可见光光催化效率。 (2) Ag3VO4可见光催化剂 通过沉淀法与水热法合成了在可见光区(400-600 nm)具有强而宽吸收的Ag3VO4化合物，并通过X射线衍射 (XRD)、SEM、紫外-可见漫反射吸收光谱 (UV-vis DRS)等手段进行了表征，建立了催化活性与催化剂材料表面形貌及晶体结构的关系，并对制备工艺进行了优化。实验结果表明钒过量、160℃水热处理48 h合成的Ag3VO4具有最高的光催化活性。进一步对Ag3VO4进行NiO负载后其光催化活性得到了十几倍的提高，且经过5次循环使用后，催化剂的活性没有明显的下降。 (3) BiVO4光催化剂 通过表面活性剂p123辅助水热法合成了BiVO4可见光催化剂。研究了pH值对其形貌及光催化活性的影响，表明pH值是控制粒子形貌和光催化活性的主要因素。在BiVO4 表面负载p-型半导体CuS后，CuS与BiVO4之间形成了p-n结，加快了电子空穴的分离，提高了偶氮染料及不同有机污染物的光催化去除效率。 2. 可见光催化降解有机污染物的机制 (1) 以NiO/SrBi2O4为催化剂，在l > 420 nm的可见光下研究了乙醛的光催化降解历程。通过傅立叶变换红外光谱 (FTIR)及对反应产物CO2的测定发现乙醛被光催化氧化为乙酸、CO2和H2O，中间产物乙酸积聚在NiO/SrBi2O4催化剂的表面使其中毒失活。而PdO负载后，加快了乙醛的降解，CO2的生成率从24%提高到80%，表明PdO的引入，通过光热催化协同作用，增加了乙醛向CO2转化的选择性，抑制了中间产物在催化剂表面的吸附，延长了催化剂的寿命。 (2) 以NiO/Ag3VO4为光催化剂，研究了可见光下 (l > 420 nm)三种偶氮染料的光催化降解历程，发现这些染料快速脱色，但总有机碳的去除却近似为零。中间产物的分析表明NiO/Ag3VO4可以选择性光催化降解偶氮染料。进一步ESR检测及不同条件下物种俘获对活性影响的实验结果证明超氧自由基是反应中的主要活性物种，并且是造成偶氮染料选择性氧化的根本原因。 (3) 以CuS/BiVO4为催化剂，研究了其对不同有机污染物 (酸性橙II，苯胺，苯酚，邻苯二甲酸二甲酯)的可见光催化降解。再一次证实了超氧自由基对偶氮染料的高度选择性氧化作用。 3. NiO/SrBi2O4可见光去除水中病原菌机制 在可见光照下 (l > 420 nm)研究了NiO/SrBi2O4光催化杀灭水中病原菌机制。结果表明NiO/SrBi2O4能在可见光下高效杀灭水中的大肠杆菌和金黄色葡萄球菌，对这两种细菌去除均能达到7 log。ESR和H2O2测试证明超氧自由基、羟基自由基和过氧化氢是主要的活性氧物种。TEM观察和钾离子浓度测定证实了NiO/SrBi2O4的可见光杀菌机制是：光催化产生的活性氧物种，逐步氧化分解细菌的细胞膜、细胞壁导致细菌死亡。反应溶液pH值影响实验表明，催化剂与细菌之间的表面静电力的相互作用对杀菌活性有重要影响。 |
| 英文摘要 | Heterogeneous photocatalysis has received much attention for mineralization organic compounds and killing harmful microorganisms. The main drawbacks of low quantum yields and the lack of visible light utilization, however, hinder its practical application. The main aims of this dissertation are to develop novel visible light photocatalysts and increase the photocatalytic efficiency, then study the mechanism of visible phototcatalytic degradation of organic pollutants and bacteria. The development of better visible light photocatalysts depends on visible light photoresponse, fast separation of electron-hole and highly effective interfacial charge transfer. Therefore, in this dissertation, several multi-metal oxides with intense absorbance in visible light region were synthesized, and the separation of electron-hole and interfacial charge transfer was accelerated by the formation of potential barrier and the control of surface morphologies to obtain highly efficient photocatalysts. The performance of these photocatalysts for removal of pathogenic bacteria and organic contaminants was investigated, then the visible light photocatalytic mechanisms are proposed. The main research contents and results are shown as following. 1. Preparation of novel visible-light photocatalyst (1) NiO/SrBi2O4 novel visible-light photocatalyst A monoclinic structure SrBi2O4 with strength absorbance in visible light region was prepared by coprecipitation method. Furthermore, NiO/SrBi2O4 photocatalyst was synthesis by impregnation method. Based on the results of SEM, XPS and ESR measurements，the formation of a short-circuited microphotoelectrochemical cell between the interface of NiO and SrBi2O4, enhances the separation of photogenerated electrons and holes, resulting in the significant increase in the visible-light photocatalytic activity. NiO/SrBi2O4 exhibited high activity for the degradation and mineralization of acetaldehyde and bacteria. (2) Ag3VO4 visible-light photocatalyst Monoclinic structure Ag3VO4 with strong absorbance in visible light region (400-600 nm) was prepared by precipitation and hydrothermal methods. Based on XRD, SEM, UV-vis DRS measurements, the relationship between photocatalytic properties and the surface morphologies, crystalline structure was founded. Ag3VO4 prepared in the excess vanadium at 160°C for 48 h by hydrothermal reaction exhibited highest visible-light-driven activity. Furthermore, the activity of the Ag3VO4 was significantly increased when a NiO was loaded. The activity of NiO/Ag3VO4 was maintained effectively after successive cyclic experiments under visible irradiation. (3) Synthesis of BiVO4 photocatalyst BiVO4 was prepared by a hydrothermal process in the presence of p123 surfactant. The effects of pH value on surface morphologies, structure and photoactivity of BiVO4 were investigated. The results indicated that pH value determined the morphologies of particle and photocatalytic activity of BiVO4. The decolorazation of acid organge II was increased when CuS loaded on the surface of BiVO4. CuS, a p-type semiconductor, can easily form p-n heterojunction to enhance the separation of electron and hole, then increase the photocatalytic efficiency of BiVO4. 2. The mechanism of visible light photocatalytic degradation of organic contaminants (1) The photocatalytic degradation of acetaldehyde by NiO/SrBi2O4 was investigated under visible light irradiation (l > 420 nm). By the analysis of FTIR and the measurement of CO2, acetaldehyde was degraded to acetic acid, CO2 and H2O. It indicated that the absorption of acetic acid on the surface of catalyst led to the deactivation of NiO/SrBi2O4. The loading of PdO increased the formation of CO2 from 24% to 80%. The synergism of PdO thermalcatalysis and NiO/SrBi2O4 photocatalysis enhanced the acetaldehyde removal and CO2 production, avoided the accumulation of intermediates and lengthened dramatically the lifetime of catalyst. (2) The photocatalytic degradation of azodyes was investigated systematically in aqueous NiO/Ag3VO4 dispersion under visible light irradiation (l > 420 nm). It indicated that dyes could be decolorized quickly without any decrease of total organic carbon. The analysis of intermediates indicated azodyes were selectively oxidized into aromatic and aliphatic acids. Electron spin resonance and the radical scavenger technologies studies suggested that the anionic superoxide radical O2-· was the predominant active species in the photocatalytic reaction, and responsible for the selective oxidation of azodyes. (3) The photocatalytic degradation of organic compounds (acid orange II, aniline, phenol, dimethyl phthalate) by CuS/BiVO4 was investigated under visible light irradiation (l > 420 nm). It also proved the high selectivity of O2-· in the photooxidation of the azodyes. 3. NiO/SrBi2O4 for destruction of pathogenic bacterial The photocatalytic inactivation mechanism of pathogenic bacteria in water was investigated systematically with NiO/SrBi2O4 under visible light (l > 420 nm) irradiation. The catalyst was found to be highly effective for the killing of Escherichia coli and Staphylococcus aureus. ESR and H2O2 measurements proved that ·OH, O2-·, H2O2 were the main active radicals. The decomposition process of the cell wall and the cell membrane was directly observed by TEM and further confirmed by the determination of potassium ion. A possible cell damage mechanism by visible-light-driven NiO/SrBi2O4 is proposed. The decomposition of cell wall and cell membrane by active radicals resulted in the bacteria death. The bacteria inactivation under different physical chemical conditions indicated that the electrostatic force interaction of bacteria-NiO/SrBi2O4 is crucial for high bactericidal efficiency. |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/34949]  |
| 专题 | 生态环境研究中心_环境水质学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 胡学香. 新型可见光催化剂及污染物光催化降解机制的研究[D]. 北京. 中国科学院研究生院. 2007. |
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