【作者】 徐远国；

【导师】 李华明；

【作者基本信息】 江苏大学 ， 环境工程， 2013， 博士

【摘要】 随着社会发展,能源短缺与环境污染已经成为人们关注的焦点问题。光催化技术,作为一种绿色高级氧化技术,在环境污染治理领域和能源转化方面有着广泛的应用前景。光催化技术能够将低密度的太阳能转化成高密度易存储的氢能,从而解决能源短缺问题；能够把有毒有害的有机、无机环境污染物降解或矿化成低毒、无毒的物质,减少环境污染；还可以利用太阳能光催化还原C02为低碳烷烃,一方面降低温室气体CO2的量,另一方面转化的产物还能作为燃料,变废为宝,解决能源危机。因此光催化技术有着巨大的发展潜力。然而,以Ti02为代表的传统光催化剂,由于其带隙宽而只能利用太阳光中的紫外光,大大限制了其应用范围。本论文旨在研究新型非Ti02系列光催化材料的控制合成和表面调控,以及其在环境污染物治理方面的应用。并采用XRD、XPS、SEM-EDS、TEM、DRS、PL、EIS等测试手段对合成催化剂的结构、形貌、光电性能及光催化性能进行研究,对结构与性能之间的构效关系进行深入的探讨。本文的具体研究内容如下：1.首先合成Ag纳米线,然后通过[Bmim]FeCl4离子液体氧化刻蚀Ag纳米线的方法,合成等离子体型核壳结构Ag@AgCl光催化剂。通过XRD、XPS、SEM-EDS、DRS等方法对催化剂进行表征分析,研究该材料的氧化刻蚀过程。Ag@AgCl表现出贵金属特有的表面等离子体共振吸收现象,其吸收的强度与Ag@AgCl形貌以及Ag、AgCl的比例密切相关。DRS结果表明,随着刻蚀时间的延长,光催化剂等离子体共振吸收也随之增强。实验以甲基橙染料为目标污染物,在可见光照射下考察其光催化活性,结果表明催化剂的降解能力随着等离子体共振吸收的增强而提高。其中刻蚀时间为20h的样品活性最高,40min即可降解95%的甲基橙污染物。此外该光催化剂还能有效降解高毒性的4-氯酚。构效关系研究表明,催化剂的高活性来源于Ag单质的等离子体共振吸收与AgCl之间的协同作用。2.通过水热法合成新型光催化材料Ag/AgCl/ZnO。运用XRD、 TG-DSC、SEM、TEM、DRS和XPS等手段对催化剂进行一系列表征。以甲基橙作为降解的目标污染物,在紫外光照射下考察催化剂的光催化活性。结果显示复合催化剂的光催化活性明显高于单体ZnO。进一步研究发现,Ag/AgCl与半导体光催化剂ZnO能够有效耦合,催化剂在经过多次重复性实验后,原先的Ag/AgCl/ZnO结构逐渐转变成Ag/ZnO。尽管催化剂的组成和结构发生转变,但是其活性并没有明显降低。根据光催化剂的表征结果和活性数据分析了催化剂光催化降解甲基橙可能的反应机理。3.通过一步法制备新型光催化剂CNT/Ag/AgBr,旨在利用碳纳米管(CNT)的优良导电性进一步提高等离子体型光催化剂Ag/AgBr的光催化活性。通过SEM-EDS、XPS、IR、PL等测试手段对CNT/Ag/AgBr催化剂的结构、形貌和光学性质进行了表征。在可见光照射下,与单体Ag/AgBr才相比,CNT/Ag/AgBr样品降解甲基橙染料活性更高,而且CNT的负载量对催化剂的活性有显著影响。当CNT含量为1.4at%时,复合催化剂光催化活性最高。实验结果表明,低含量的CNT有利于光生电子的转移,从而有益于复合催化剂活性的提高。通过液质联用(LC/MS)和总有机碳(TOC)对污染物的降解过程进行分析,并确定了甲基橙染料可能的降解途径。根据实验结果讨论了该催化剂可见光光催化降解机理。4.采用水热法合成了新型等离子体型光催化剂Ag/AgBr/g-C3N4,实现Ag/AgBr在g-C3N4材料表面的有效分散,进而提高复合光催化材料的性能。通过XRD、TEM、DRS、PL、IR等表征手段分析Ag/AgBr/g-C3N4催化剂的结构、形貌和光学性质。分析结果表明,Ag/AgBr和g-C3N4之间存在耦合作用,形成的异质结结构有利于光生电子和空穴的分离,从而促进Ag/AgBr/g-C3N4复合催化剂可见光降解罗丹明B活性的提升。此外,高分散的Ag/AgBr嵌入到g-C3N4的表面也能够提高复合催化剂的催化活性。结果表明,17.8at%Ag/AgBr/g-C3N4复合催化剂光催化降解能力最高,其降解速率常数是单体g-C3N4的18.3倍。进一步讨论了光催化活性和结构之间的关系。5.运用水热法合成了CNT/white g-C3N4复合光催化剂。研究发现,CNT和white g-C3N4通过静电吸引自组装结合在一起,形成CNT/-white g-C3N4。通过TEM, XRD, IR, DRS, XPS和PL等手段对合成催化剂的结构、形貌和光学性质进行表征。以亚甲基蓝染料为目标污染物评价催化剂的光催化活性。结果表明不同催化剂的光催化活性顺序为：CNT/white g-C3N4>g-C3N4>white g-C3N4。与white g-C3N4、g-C3N4相比CNT/white g-C3N4复合催化剂在1.5h时的光催化降解性能分别提升66.5%和34.5%。CNT/white g-C3N4催化剂降解速率约为white g-C3N4的8.1倍。PL分析结果表明,CNT/white g-C3N4与whiteg-C3N4相比具有更低的电子空穴复合率,因此复合材料具有较高的光催化性能。结合表征和活性实验结果,深入分析CNT/white g-C3N4光催化性能提升的内在原因。更多还原

【Abstract】 With the development of the society, energy shortage and environmental pollution have become the hot issues of human concerns. The photocatalytic technology is a green oxidation technology. It has been widely applied in the field of environmental pollution protection and energy conversion. The photocatalyst can convert the low-density solar energy into the easily stored high-density hydrogen, and solve the problem of shortage of energy. It can also reduct the CO2into low-carbon alkane, which can reduce the amount of the greenhouse gas carbon dioxide and turn it into fuel to solve the energy crisis at the same time. Besides, it can degrade toxic and harmful organic pollutants into non-toxic substances. So, photocatalytic technology has great potential for development. However, the wide band gap of the traditional photocatalyst TiO2is large, so it can only use ultraviolet light in sunlight, thus it’s scope of application are greatly limited. This paper is emphasized on the controlled synthesis of the photocatalytic materials as well as its application in environmental purification. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), TEM, UV-vis diffuse reflectance spectroscopy (DRS), photolumin-escence (PL), Electrochemical Impedance Spectroscopy (EIS) were used to test the catalyst structure, morphology, optical performance and photocatalytic properties, and the relationship between the structure and activities were also studied.The main content and conclusions are summarized below:1. In this work, Ag nanowire was firstly synthesized, and then it was etched into core-shell Ag@AgCl by [Bmim]FeCl4ionic liquid. The photocatalyst was characterized by XRD, XPS, SEM-EDS, DRS and other methods. The core-shell Ag@AgCl structure forming process was also proposed. Ag@AgCl exhibited the surface plasmon resonance absorption, which is peculiar to the noble metal. The resonance absorption is closely related with Ag@AgCl morphology and proportions. The DRS result showed that the plasmon resonance absorption increased with the etching time prolonged. The methyl orange was used as the target pollutant to test the photoactivity of the photocatalyst under visible light irradiation. The experiment result showed that the degradation ability of the catalyst with enhanced plasmon resonance absorption enhancement. Among those samples, the Ag@AgCl etched for20h showed the highest photocatalytic ability, which was able to degrade95%methyl orange in40min. In addition, the catalyst could also degrade the highly toxic4-chlorophenol. The relationship between the structure of the photocatalyst and the photocatalytic activities was disscussed, and the result indicated that the high photoactivity of the Ag@AgCl is attributed to the synergetic effect between surface plamon resonance absorption effect of Ag and AgCl.2. A new composite photocatalyst Ag/AgCl/ZnO was fabricated by a two-step synthesis method under the hydrothermal condition. The sample was characterized by XRD, TG-DSC, SEM, TEM, DRS and XPS. Methyl orange (MO) was used as a representative dye pollutant to evaluate the photocatalytic activity of Ag/AgCl/ZnO under ultraviolet light irradiation. The photocatalytic activity of Ag/AgCl/ZnO catalyst was higher than that of the pure ZnO catalyst. Further study found that Ag/AgCl and ZnO were able to form a heterojunction structure and the Ag/AgCl/ZnO structure changed to Ag/ZnO gradually after several repeated experiments. However, the photocatalytic ability of the sample was not reduced. Finally, a possible photocatalytic mechanism was proposed.3. Carbon nanotubes (CNT)-loaded Ag/AgBr was prepared by a facile, one-step hydrothermal method. The purpose of the study was to further enhance the photocatalytic activity of plasma photocatalyst Ag/AgBr by taking advantage of the excellent conductivity of CNT. The structure, morphology and optical properties of the samples were characterized by SEM-EDS、XPS、IR、PL. The CNT/Ag/AgBr composite exhibited much higher photocatalytic activity than the pure Ag/AgBr in degrading Methyl orange (MO) dye pollutant under visible light irradiation. The loading amount of CNT has a significant influence on the photoactivity of the CNT/Ag/AgBr composite. When the CNT loading amount was1.4at%, the hybrid material showed the highest photocatalytic ability. The result showed that a small amount CNT was beneficial to the photo-generate electron transfer, and the photoactivity of the CNT/Ag/AgBr could be enhanced. The degradation process of the dye solution was tested by liquid chromatography mass spectrometry (LC/MS) and total organic carbon (TOC). Based on the results, the possible degradation path of the MO dye was proposed. In addition, a possible visible light photocatalytic degradation mechanism was also discussed.4. A new plasmonic photocatalyst of Ag/AgBr/g-C3N4was prepared by a hydrothermal method. It is expected to enhance the dispersity of the Ag/AgBr on the surface of the g-C3N4, which can further enhance the photoactivity of the hybrid. XRD, TEM, DRS, PL emission spectra and IR spectra were employed to confirm the structure, morphology and optical property of the as-prepared Ag/AgBr/g-C3N4composite. XPS analysis indicated the interaction between Ag/AgBr and g-C3N4. They formed the heterojunction structure, which was facile to the separation of the electron-hole, and hence enhanced the photocatalytic activity of Ag/AgBr/g-C3N4in degrading Rhodamine B under visible light irradiation. Besides, the highly dispersion of Ag/AgBr anchored on the surface of g-C3N4was also assumed to responsible for the enhanced activity and good recycling ability. The17.8at%Ag/AgBr/g-C3N4 showed the highest photoactivity, the degradation rate constant of17.8at%Ag/AgBr/g-C3N4was as high as18.3times to that of the pure g-C3N4. The relationship between the photocatalytic activity and the structure of Ag/AgBr/g-C3N4hybrid materials was discussed.5. The white g-C3N4and CNT combined together and formed the CNT/white g-C3N4composite due to electrostatically-driven self-assem-bly by the hydrothermal method. The structure, morphology and optical properties of the white g-C3N4and CNT/white g-C3N4composite photocatalyst were characterized by TEM, XRD, IR, DRS, XPS and PL The photoactivity of the catalysts was evaluated by degrading methylene blue (MB) dye solution. The results showed that the photoactivity for the degradation of MB solution was in the following order:CNT/white g-C3N4composite> g-C3N4> the white g-C3N4. The photoactivity of the CNT/white g-C3N4composite was66.5%and34.5%higher than that of the white g-C3N4sample and that of the g-C3N4at1.5h, respectively. The degradation rate of the CNT/white g-C3N4photocatalyst was almost8.1times as high as that of the white g-C3N4. The PL result showed that the CNT/white g-C3N4have much lower electron-hole recombination rate, which leads to the enhanced photoactivity. The reason to the photoactivity of the CNT/white g-C3N4was much higher than that of g-C3N4and the white g-C3N4was discussed based on characterize and the photocatalytic experiment.更多还原