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题名: 层状材料/银/卤化银可见光催化剂的研制及降解水中有机污染物机理
作者: 吉欢欢1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 胡春
关键词: 层状材料,卤化银,可见光催化,有机物降解,光稳定性 ; layered material, silver halides, visible-light photocatalysis, organic pollutants degradation, photostability
其他题名: Development of Visible-Light Photocatalysts Based on Layered Materials/Ag/AgX (X=Br, I) and the Mechanism of Organic Pollutants Degradation
学位专业: 环境科学
中文摘要: 光催化太阳能转化是解决当前人类社会面临的环境污染和能源危机问题的 重要手段。然而,光吸收范围窄、量子效率低或催化稳定性差等因素限制了众多 光催化体系的实际应用。卤化银材料具有良好的感光性,在光催化研究中表现出 了卓越的反应活性。但是这类材料容易发生光腐蚀,并向反应体系中释放 Ag+, 造成二次污染。近几年,二维层状结构材料由于多方面的良好性能获得了研究者 的关注。本论文研制了系列层状光催化材料,并用来修饰卤化银光催化剂。制备 的复合材料在可见光甚至近红外光照射下都具有良好的催化降解有机污染物活 性,卤化银复合光催化剂显示了很好的催化稳定性,反应过程中未检测到卤化银 的分解和 Ag+的释放。提出了一种基于光生载流子转移和补偿的光催化反应机理, 为光催化技术的实际应用提供了思路。具体的研究内容如下: 1.层状 g-C3N4剥离制备 CN/Ag/AgBr:采用超声剥离法由体相 g-C3N4获得了在 水中高分散的 CN纳米片,并成功地在 CN纳米片上生长 AgBr颗粒制备了 CN/Ag/AgBr光催化剂。CN修饰的 Ag/AgBr具有较小的颗粒直径,更大的比表 面积和光电流密度等特点;研究结果表明制备条件(加料顺序,合成温度,溶剂 等)对催化剂活性有较大影响。CN/Ag/AgBr催化剂在可见光照射下对有机染料 甲基橙(MO)、2-氯酚显示了很好的光催化降解能力。 2.能带可调控的 BiO(OH)xI1-x固溶体制备:基于[Bi2O22+]层间阴离子的可替代性, 采用共沉淀法制备了系列 BiO(OH)xI1-x固溶体材料。发现随着 OH‒逐渐取代 I‒, 制备的催化剂具有从 400到 800 nm范围内可调节的光吸收范围,其带隙结构亦 随着材料组成的变化而变化,并在材料中引入了具有良好吸光性和活性的氧空位。 实验表明制备的固溶体材料具有很好的光催化降解 2-氯酚的能力,并保持了优良 的光反应稳定性。 3.化学键联的 BiO(OH)xI1-x-AgI异质结催化剂:通过共沉淀法将 BiO(OH)xI1-x固 溶体与 AgI颗粒复合制备半导体 p-n结光催化剂。由于 I的同离子效应,在 BiO(OH)xI1-x和 AgI的界面上形成了 Bi-I-Ag化学键。紧密的界面接触和化学键 的存在促进了光生载流子的传递,并且在异质结的 Z型价带结构中,AgI光激发 产生的导带电子迅速转移到 BiO(OH)xI1-x固溶体上,从而抑制了晶格 Ag+的还原, 提高了 AgI稳定性。光生空穴则转移到 AgI导带上,抑制了载流子的复合。在 光催化降解氯酚类有机污染物反应中,异质结材料没有发现 AgI的光腐蚀,反应 活性提高 9倍。 4.氧空位增强的 BiO(OH)0.06Br0.94/Ag/AgBr表面等离子基元光催化:在 BiO(OH)xBr1-x/AgBr材料中经光还原生成了 Ag等离子基元,制备的“三明治” 结构 BiO(OH)xBr1-x/Ag/AgBr等离子基元光催化剂具有 2000 nm以上的光吸收, 在可见光和近红外光照射下均具有光催化活性。在光催化降解有机污染物的反应 中没有检测到 Ag表面等离子激发产生的电子转移到 AgBr半导体导带,同时 BiO(OH)xBr1-x中的 氧空位又向 Ag纳米颗粒补偿电子,由此形成循环,抑制了催化反应中从 Ag+释放,对 2-CP和 MO可以在数分钟内完全降解。研究表明 Ag0到Ag的氧化反应,在提高光吸收范围和量子效率的同时,增强了催化剂的稳定性, 为 Ag+表面等离子基元光催化材料的实际应用提供了思路。
英文摘要: Photocatalysis is a promising technology to address the issues of the energy crisis and environmental pollution that have gained considerable interdisciplinary attention. A number of photocatalytic systems have been developed. But most of these photocatalytic materials are troubled by: (1) insufficient solar energy harvest, (2) low efficient photon utilizing and (3) poor catalytic stability. Silver halides (AgX, X=Cl, Br, I), well-known photosensitive materials, have been intensively studied in the fields of photocatalytic hydrogen evolution and photodegradation of organic pollutants due to their prominent photoactivity. However, they are unavoidably decomposed under visible-light irradiation. Recently, materials possessing a laminated structure have aroused much attention due to their excellent physico-chemical properties. In this dissertation, a series of layered materials were developed and used to modify AgX photocatalysts. The prepared heterojunction photocatalysts shown enhanced activity for organic pollutants degradation under visible even near-infrared light irradiation. AgX photo-decomposition was completely inhibited, and no release of Ag + was observed in the photoreaction. The photocatalysis mechanisms were carefully study. The main contents of this thesis are as follows: 1. CN/Ag/AgBr photocatalyst prepared from layered g-C3N4 exfoliation: High dispersing CN nanosheets in water solution were obtained by a simple ultrasonic exfoliation mothed from bulk g-C3N4. CN/Ag/AgBr was successfully synthesized by growed AgBr on the CN sheets. The CN/Ag/AgBr photocatalyst possessed smaller particle size, larger BET surface,greater photo-current intensity than Ag/AgBr,and shown enhanced pollutants photodegradation activity. Research results proved that preparation conditions much affected the property of CN/Ag/AgBr. 2. Developing BiO(OH)xI1-x solid solution with tunable band-gap structure: In consideration of the alternative inorganic ions between [Bi2O2]2+ layers, A proportion of I in BiOI were exchanged with OH to generate BiO(OH)xI1-x solid solution. Experimental results demonstrate that the light harvest and energy band were adjustable with the change of BiO(OH)xI1-x composition. Oxygen vacancies (OVs) were found in the solid solution contributed the excellent photocatalytic performance. 3. Chemical-Bond Conjugated BiO(OH)xI1-x-AgI Heterojunction: A layered BiO(OH)xI1-x solid solution was grown in situ on the surface of AgI particles by a one-pot co-crystallization method to prapare a p-n heterojunction photocatalyst. It was verified the Ag-I-Bi cross-linking bonds formed in the interface of BiO(OH)xI1-x and-AgI due to the common species of I ions. The strong interfacial interaction between BiO(OH)xI1-x and AgI by the Ag-I-Bi bond junction accelerated interfacial charge transfer and separation. BiO(OH)xI1-x-AgI exhibited high efficiency and stability for photodegradation of phenolic compounds with visible light irradiation. No significant AgI decomposition or release of Ag+ was observed in the photoreaction, and the photoactivity of AgI was enhanced almost 9-fold. 4. Oxygen Vacancy Enhanced Photostability and Activity of Plasmon-Ag Composites: BiO(OH)0.06Br0.94 solid solution with abundant oxygen vacancies was supported on Ag/AgBr using precipitation and deposition–precipitation methods. The photocatalyst showed high and stable photocatalytic activity for the degradation of chlorophenols and azodyes in water under visible to NIR light irradiation without any release of Ag . The plasmon-induced electrons from Ag NPs transfered to the CB of AgBr, while the electrons trapped on the oxygen vacancies of BiO(OH)0.06Br0.94 transfered to Ag NPs recombining with the plasmon-induced holes, inhibiting the release of Ag+。
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38636
Appears in Collections:环境水质学国家重点实验室_学位论文

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