碳量子点的蓝光发射增强与机理研究

发布时间：2018-08-12 09:31

【摘要】：碳量子点(或称碳点)是尺寸在10 nm以下的结晶或非晶态荧光碳纳米材料,可通过自下而上(如小分子缩合)和自上而下(如石墨烯裁剪)两种方法获得,其中具有石墨烯晶格结构的碳量子点又称为石墨烯量子点。近年来,碳量子点因其优良的性质,如荧光稳定性好、毒性低以及生物相容性好等,引起了物理、化学、生物等领域科学研究者的广泛关注。虽然目前关于碳量子点的研究已经取得较大进展,但是仍面临许多有待解决的问题,高荧光量子产率碳量子点的设计合成及其机理研究正是当前人们关注的焦点之一。本论文以柠檬酸缩合法、碳纤维酸氧化和氧化石墨烯裁剪法得到的碳量子点为研究对象,从增强辐射跃迁过程和抑制非辐射跃迁过程两个方面入手,研究高量子产率蓝光碳量子点的制备方法,揭示碳量子点中类分子局域态和缺陷对于碳量子点荧光增强的作用。具体研究内容和结果如下:利用柠檬酸和乙二胺及其衍生物为原料通过水热法制备氮掺杂碳量子点,发现碳量子点的量子产率和光学带隙均与氮含量有关。通过优化反应条件,制备得到量子产率为(97.4±4.2)%的碳量子点CDs-DETA。论文全面考察了浓度、溶剂种类、pH及离子强度对CDs-DETA光学性质的影响。通过半制备液相色谱仪对CDs-DETA进行分离提纯,结合荧光光谱和时间发光光谱证实吡啶酮类小分子(AEOIP)是碳量子点高亮度荧光的唯一来源。实验结果表明,AEOIP分子、柠檬酸(CA)分子以及二乙烯三胺(DETA)分子之间能够依靠正负电荷的吸引作用形成室温下具有良好流动性的离子液体,并能够在浓度较浓时形成特定形貌的聚集体。同时,发光碳量子点流体表现为牛顿流体的特征,其粘度随温度升高呈现下降趋势。此外,利用CDs-DETA对Fe3+具有选择性荧光淬灭的特性,探讨了CDs-DETA在检测Fe3+领域的应用。采用酸氧化切割树脂基碳纤维的方法制备得到尺寸为3-5 nm且发射绿色荧光的石墨烯量子点GQDs,采用NaBH4为还原剂制备得到发射蓝色荧光的石墨烯量子点rGQDs。利用透射电子显微镜、原子力显微镜、傅里叶变换红外光谱、拉曼光谱以及X射线光电子能谱对GQDs和rGQDs的结构和形貌进行表征。结果表明,GQDs和rGQDs呈现出两种不同的光学性质。GQDs的较弱绿色荧光发射是酸氧化过程中引入的无序含氧基团缺陷辐射跃迁的结果。随着还原程度增加,石墨烯量子点的量子产率从2.6%提高至10.1%,同时,蓝色荧光的特征峰位置快速蓝移且半高宽(FWHM)变窄。据此推测,在还原过程中,石墨酚拓扑缺陷逐渐形成并发生辐射跃迁,从而导致了rGQDs的蓝色荧光发射。除此之外,石墨酚拓扑缺陷诱发的蓝色荧光寿命较长、pH敏感性低且具有激发波长依赖性。以石墨粉为原料通过酸氧化法制备石墨烯量子点,在100℃水热条件下,用氨水处理石墨烯量子点制备得到氨基修饰石墨烯量子点(N-GQDs)。原子力显微镜研究发现氨水能够进一步切割氧化石墨烯片,形成石墨烯量子点或者多孔氧化石墨烯片。傅里叶变换红外光谱证明NH3可以有效地进攻环氧基碳和羧基碳,形成-CH(OH)-CH(NH2)-和-C(=O)NH2基团。氨基修饰后,由于N-GQDs中载流子辐射复合速率得到提高且非辐射复合速率有所降低,N-GQDs的荧光量子产率从0.3%提高至9.6%。时间分辨发光光谱则表明,与含氧基团相比,含氮基团相关的局域电子激发态具有更长的荧光寿命。
[Abstract]:Carbon quantum dots (CQDs) are crystalline or amorphous fluorescent carbon nanomaterials with sizes below 10 nm. They can be obtained by bottom-up (such as small molecule condensation) and top-down (such as graphene tailoring). Among them, CQDs with graphene lattice structure are also known as graphene quantum dots. The properties of carbon quantum dots, such as good fluorescence stability, low toxicity and good biocompatibility, have attracted much attention from researchers in the fields of physics, chemistry and biology. In this paper, the preparation methods of blue-light carbon quantum dots (QDs) with high quantum yields are studied from two aspects: enhancement of radiation transition process and inhibition of non-radiation transition process. The specific research contents and results are as follows: Nitrogen-doped carbon quantum dots were prepared by hydrothermal method using citric acid and ethylenediamine and their derivatives as raw materials. It was found that the quantum yield and optical band gap of carbon quantum dots were related to nitrogen content. The effects of concentration, solvent type, pH and ionic strength on the optical properties of CDs-DETA were investigated. The CDs-DETA was separated and purified by semi-preparative liquid chromatography, and the pyridinone small molecules (AEOIP) were confirmed by fluorescence spectroscopy and time luminescence spectroscopy. The experimental results show that AEOIP, CA and DETA molecules can form ionic liquids with good fluidity at room temperature by positive and negative charge attraction, and can form clusters with specific morphology at high concentration. Carbon quantum dot fluids are characterized by Newtonian fluids, and their viscosity decreases with increasing temperature. In addition, the selective fluorescence quenching of Fe3+ by CDs-DETA is used to investigate the application of CDs-DETA in the detection of Fe3+ and the size of 3-5 nm is obtained by acid oxidation cutting resin-based carbon fibers. Graphene quantum dots (GQDs) emitting blue fluorescence were prepared by using NaBH4 as reductant. The structures and morphologies of GQDs and rGQDs were characterized by transmission electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The weak green emission of GQDs is the result of the irradiation transition of disordered oxygen-containing group defects introduced during acid oxidation. With the increase of reduction degree, the quantum yield of graphene quantum dots increases from 2.6% to 10.1%. At the same time, the characteristic peak position of blue fluorescence shifts rapidly and the half-width (FWHM) narrows. In addition, the blue fluorescence induced by graphophenol topological defect has longer lifetime, lower pH sensitivity and wavelength dependence. Graphene quantum dots were prepared by acid oxidation of graphite powder. Amino-modified graphene quantum dots (N-GQDs) were prepared by treating graphene quantum dots with ammonia at 100 C. Atomic force microscopy (AFM) showed that ammonia could further cut graphene oxide sheets to form graphene quantum dots or porous graphene oxide sheets. The fluorescence quantum yields of N-GQDs increased from 0.3% to 9.6% due to the increase of the carrier recombination rate and the decrease of the non-radiation recombination rate in N-GQDs. The time-resolved luminescence spectra showed that the quantum yields of N-GQDs increased from 0.3% to 9.6%. The localized electron excited state has longer fluorescence lifetime.
【学位授予单位】：河南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O657.3

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