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题名: 碳点参与的液相化学发光行为研究
作者: 狄帆
学位类别: 硕士
答辩日期: 2013
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 赵利霞
关键词: 碳点 ; Carbon Nanodots ; 化学发光 ; Chemiluminescence ; 液相 ; liquid
其他题名: Surprisingly-Chemiluminescence Behavior Study of Carbon Nanodots in Alkaline Solution
中文摘要:       碳点作为碳纳米材料家族的新成员,因其良好的分散性、生物相容性、较高稳定性及环境友好性引起研究人员的浓厚兴趣,其光学机理和应用研究一直是人们关注的重点。目前对于碳点光学性质的研究主要包括入射光诱导下碳点的紫外可见吸收光谱(Ultraviolet Absorption Spectrometry)、光致发光光(Photoluminescence)、通过电子注射产生的电化学发光(Electrochemiluminescence),也有部分报道是通过化学反应来研究碳点产生的化学发光行为。但是到目前为止,碳点的光学行为及其机理尚未有统一解释。因此碳点的发光机理研究仍然是一个重点和难点。 化学发光(Chemiluminescence, CL)是指在发生氧化还原反应的同时产生的发光现象,对于研究相关物理化学过程的动力学和光发射特性具有重要的理论和应用价值。化学发光反应的产生必须具备以下条件:化学发光反应可以产生能量;产生的能量可以将反应产物或中间物激发到激发态即必须存在电子激发态形成的通道;激发态物质的能量必须以直接或间接光辐射的形式释放。而碳点具有表面缺陷和特殊能级结构以及量子尺寸效应,这些可以成为诱导化学发光反应,产生光发射现象的基础。另外,因碳点还具有其他特性,如催化活性、化学反应特性和表面吸附特性等。基于碳点的这些效应和特性,我们推测碳点可以参与诱导液相化学发光反应。基于此,本文旨在对碳点的液相化学发光行为进行研究,探索可能的反应机理并尝试将其应用于环境分析。主要内容包含以下两个方面: 1、我们采用方便、快捷、绿色的微波水热法合成了碳点。在研究过程中,我们很惊讶地发现,在没有任何发光试剂和发光体系存在时,向碳点溶液中注射强碱溶液,如氢氧化钠或氢氧化钾,会产生一个快速的发光信号。在一定范围内,化学发光强度和荧光强度依赖于强碱溶液的浓度。通过对紫外可见光谱、荧光光谱、化学发光光谱、红外吸收光谱、X射线光电子能谱和电子顺磁共振波谱数据的分析,我们发现,体系中的发光物质为碳点,碳点的化学发光归因于其表面存在的能量陷阱。其可能的发光机理为:在强碱的作用下,碳点表面经历了一个化学还原的过程,热激发产生的空穴可以与化学还原反应过程中注射的电子放射性复合而产生化学发光。同时,我们也考察了用热解乙二胺四乙酸盐的方法合成的碳点,当向其中加入不同浓度的氢氧化钠时,也有类似的发光现象。对此特性的揭示将有助于我们了解这一新奇材料的独特光学性质。 2、碱性条件下氧化剂诱导的化学发光行为研究。我们发现在碱性条件下,铁氰化钾、过氧化氢、高锰酸钾等氧化剂,可以直接氧化碳点产生强烈的化学发光信号。这是一个快速的发光过程,在0.4秒内就可达到发光强度的最大值。我们使用光致发光光谱、化学发光光谱对发光物种进行验证,结果表明本体系中的发光物种仍为碳点。电子顺磁共振波谱显示碳点表面有单个占据轨道,在适当的条件下可以被氧化。由经铁氰化钾氧化处理后碳点的X射线光电子能谱分析,我们发现了706 eV 和718.9 eV 处铁单质的能谱峰。说明体系中发生了氧化还原反应,碳点被氧化,氧化剂向碳点表面注射了空穴被还原为铁单质沉积于碳点表面。基于以上研究,氧化剂直接氧化碳点产生化学发光过程可能的反应机理为:氧化剂向碳点表面注射的空穴与碳点表面的单电子发生放射性的复合而发光。碱性条件促进了发光信号的增强,原因可能是碳点在碱性条件下表面的羟基增多,而羟基是强的给电子集团,它有利于电子-空穴复合而产生更强的发光信号。 碳点这些化学发光性质的研究给我们研究碳点的光学特性开辟了一个新的途径,也为这一材料的广泛应用打下了良好的基础。
英文摘要:
      As a rising star of the nanocarbon family, carbon nanodots have attracted increasing attention due to their excellent luminescent properties such as good dispersibility, stability biocompatibility, and environmental friendliness have been widely used in many areas of fundamental and technical importance. To date, intense researches focus on the exploration of new synthesis routes, luminescence properties and mechanism of carbon dots. However, Knowledge into the origins of their optical properties is a matter of current debate and requires greater clarication. Therefore, research still focuses on the intrinsic luminescence mechanism and its further application. Chemiluminescence (CL) is the light emission through a chemical reaction, which is important to investigate the reaction dynamics and light emission properties. The CL reaction must meet the following requirements: a chemical reaction can produce energy; an electronically excited intermediate or product is obtained during the reaction, means formation an electronic excited state channel; Excited states energy release in the form of direct or indirect light emission. In addition, carbon nanodots have surface defects, special energy level structure and quantum size effect, these can be the basis to induced a chemiluminescence reaction and create the light emission. Carbon nanodots also have other properties, such as catalytic activity, surface adsorption properties, etc. Based on these effects and characteristics of carbon nanodots, we speculated that carbon can induct liquid chemiluminescence reaction. The dissertation aims to investigate the CL properties of carbon nanodots in alkaline solution, explore the possible CL mechanism and expand their analysis application. The main contents and obtained results are as follows: 1. Carbon dots were synthesized via a facile, green and economic microwave hydrothermal route. We found a surprising CL behavior of fluorescent carbon dots in the presence of a strong alkaline solution, such as NaOH or KOH. In this work, carbon dots were first demonstrated the ability of CL only in the presence of a strong alkaline solution and the possible CL emission mechanism was discussed .We observed that CL was generated when only a strongly alkaline solution was injected into the carbon dots, without the presence of any CL reagent, CL system or oxidants. The CL intensity was dependent on the concentration of the base and carbon dots in a certain range. A possible CL mechanism was studied by UV-Vis, fluorescence, CL, FTIR, XPS and EPR spectroscopy. We verified the chemiluminescent characteristics of the carbon dots and the CL could be attributed to the various surface energy traps that existed on the carbon dots. Radiative recombination of the injected electrons by “chemical reduction” of carbon dots with thermally excited generated holes was proposed. To validate the universal chemiluminescent nature of the carbon dots in the presence of a strong alkaline solution, carbon dots were prepared by pyrolysis of ethylenediaminetetraacetic acid (EDTA) salts, and similar CL behavior was accompanied with the addition of different concentrations of NaOH. The discovery may facilitate full understanding the properties of the fascinating materials. 2. The CL of Carbon dots induced by directly chemical oxidation in alkaline medium was discussed. It was found that oxidants, especially potassium ferricyanide, hydrogen peroxide and potassium permanganate, could directly oxidize carbon dots to produce strong CL emission in alkaline aqueous conditions. The CL reactions were very quick and the CL intensity reached a maximum in 0.4 s. The possible CL mechanism was proposed based on the photoluminescence spectra, CL emission spectra, X-ray photoelectron spectroscopy (XPS). The CL of the system could also be attributed to carbon dots. Meanwhile, the existent of singly occupied orbital in carbon dots was proved by electron paramagnetic resonance spectra, and holes could be injected into the carbon dots by oxidants. Moreover the XPS results after the addition of K3Fe(CN)6 demonstrated that the existence of the redox process. The peaks at 706 eV and 718.9 eV are attributed to Fe(0), which indicated that K3Fe(CN)6 can oxidize carbon dots, K3Fe(CN)6 correspondingly were reduced to Fe. Base on the above study, the possible CL mechanism of the carbon dots induced directly by chemical oxidation could be explained as the emission of light by recombination of injected holes and electrons on the surface of the carbon dots. The alkaline condition is vital to the CL emission, injected NaOH can induce the increasing of electron donating group O-H on the surface of carbon dots, which facilitated the radiative recombination of surface-trapped electrons and holes, then enhanced the CL emission. The CL properties of carbon nanodots will provide a new approach to study the optical properties of the new luminescent materials and lay a good foundation for their potential uses in many fields.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/35187
Appears in Collections:环境化学与生态毒理学国家重点实验室_学位论文

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Recommended Citation:
狄帆. 碳点参与的液相化学发光行为研究[D]. 北京. 中国科学院研究生院. 2013.
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