多种晶体结构碳纳米颗粒的制备和光学性质研究

发布时间：2018-04-24 13:58

本文选题：碳纳米颗粒 + 金刚石　；参考：《东南大学》2017年博士论文

【摘要】：碳纳米颗粒由于具有独特的物理和化学性质,因而在光电子器件、生物传感器和生物标记等领域具有良好的应用前景。碳的电子构型为1s22s22p2,碳原子具有多样化的电子轨道特性(sp、sp2、sp3),可以形成多种结构的同素异形体。碳纳米颗粒也存在不同的晶体结构。碳纳米颗粒具有良好的荧光性能,但对其发光机制仍存在争议。由于发光机制决定材料的发光性质,进而决定材料的应用范围,所以研究碳纳米颗粒的发光机制非常有必要。本论文中主要采用化学合成方法制备不同晶体结构的碳纳米颗粒,主要包括石墨结构、金刚石结构和C8结构,并对不同结构碳纳米颗粒的发光机制以及金刚石与C8间的相转换进行研究。以乙酸纤维素为碳源制得大小为1-9 nm的碳纳米颗粒,并利用光致发光谱和光致发光激发光谱对其在水溶液中的发光性质进行研究。实验结果表明,碳纳米颗粒的发射光谱除依赖激发波长外,还和溶液中的颗粒浓度有很大的关系,随浓度降低,发光峰位蓝移,移动量超过100 nm,并且发光强度随浓度降低而逐渐增强。这一变化规律不依赖于溶液的酸碱性。我们构建模型利用光再吸收机制解释了这一现象。以葡萄糖为原料制得金刚石纳米颗粒。这种颗粒表面有大量含氧基团。该纳米颗粒展现出多峰光发射,分别位于390、433、470、527和614 nm,几乎覆盖整个可见光波段。它的荧光量子产率为2.5-5%。另外以柠檬酸铵为原料制备出表面有含氮官能团的金刚石纳米颗粒。它含有位于433和447 nm的两个峰位的发光,并且荧光量子产率高达50.4%。利用表面结构和荧光分析,并结合密度泛函理论计算,发现在金刚石纳米颗粒表面存在多种与氧相关的表面缺陷,它们形成各自的缺陷能级,产生了观测到的位于不同可见光波段的荧光峰。与纯氧官能团相比,含氮官能团的最高占据分子轨道和最低不占据分子轨道重叠较多,因而导致产生较大的辐射跃迁几率和较高的量子产率。研究结果表明这些氧缺陷发光普遍存在于各种含碳纳米材料(石墨、金刚石、C8、碳化硅和氮化碳等)中。以乙二胺四乙酸为碳源在碱性条件下合成出具有Cs结构的碳纳米颗粒,颗粒尺寸分布较为集中,结晶良好,具有各种不同的形貌。在类似反应条件下在酸性溶液中制得金刚石结构碳纳米颗粒。发现这两种结构间可发生可逆相转换,即在水热条件下,向Cs纳米颗粒溶液中加入过量酸,可得到金刚石纳米颗粒;而向金刚石纳米颗粒溶液中加入过量碱,则可得到C8纳米颗粒。我们利用基于表面结构的模型解释了这种相转换现象,发现纳米颗粒表面不同的化学结构有利于不同稳定相的存在。该研究结果有助于理解碳同素异形体间的相转换过程。
[Abstract]:Because of its unique physical and chemical properties, carbon nanoparticles have a promising future in the fields of optoelectronic devices, biosensors and biomarkers. The electron configuration of carbon is 1s22s22p2.The carbon atom has a variety of electron orbital characteristics and spsp2sp3s, which can form a variety of structural isomorphism. Carbon nanoparticles also have different crystal structures. Carbon nanoparticles have good fluorescence properties, but the luminescence mechanism is still controversial. Because the luminescence mechanism determines the luminescence properties of the materials and then determines the application scope of the materials, it is very necessary to study the luminescence mechanism of carbon nanoparticles. In this thesis, carbon nanoparticles with different crystal structures were prepared by chemical synthesis, including graphite structure, diamond structure and C8 structure. The luminescence mechanism of carbon nanoparticles with different structures and the phase transition between diamond and C _ 8 were studied. Carbon nanoparticles with the size of 1-9 nm were prepared from cellulose acetate as carbon source and their luminescence properties in aqueous solution were studied by photoluminescence spectroscopy and photoluminescence excitation spectroscopy. The experimental results show that the emission spectra of carbon nanoparticles not only depend on the excitation wavelength, but also have a great relationship with the concentration of the particles in the solution. With the decrease of the concentration, the blue shift of the luminescence peak is observed. The moving amount is more than 100 nm, and the luminous intensity increases with the decrease of concentration. This rule of change does not depend on the acidity and alkalinity of the solution. We build a model to explain this phenomenon by using the light reabsorption mechanism. Diamond nanoparticles were prepared from glucose. There are a lot of oxygen groups on the surface of this particle. The nanoparticles exhibit multi-peak light emission, located at 390433470527 nm and 614 nm, respectively, covering almost the entire visible light band. Its fluorescence quantum yield is 2.5-5. In addition, diamond nanoparticles with nitrogen-containing functional groups were prepared from ammonium citrate. It contains two peaks at 433 and 447 nm, and the fluorescence quantum yield is as high as 50.4. By means of surface structure and fluorescence analysis and density functional theory calculation, it is found that there are many surface defects related to oxygen on the surface of diamond nanoparticles, which form their respective defect levels. The observed fluorescence peaks at different visible wavelengths are generated. Compared with pure oxygen functional groups, the highest occupied molecular orbitals and the lowest non-occupied molecular orbitals of nitrogen-containing functional groups overlap more, resulting in higher radiation transition probability and higher quantum yield. The results show that these oxygen defects are widely found in various carbon containing nanomaterials (graphite, diamond C8, silicon carbide and carbon nitride, etc.). Carbon nanoparticles with Cs structure were synthesized with ethylenediamine tetraacetic acid as carbon source under alkaline conditions. Diamond structure carbon nanoparticles were prepared in acid solution under similar reaction conditions. It is found that reversible phase transition can take place between these two structures, that is, diamond nanoparticles can be obtained by adding excess acid to Cs nanoparticles solution under hydrothermal conditions, and excessive alkali is added to diamond nanoparticles solution. C8 nanoparticles can be obtained. We use the surface structure model to explain the phase transition phenomenon and find that different chemical structures on the surface of nanoparticles are beneficial to the existence of different stable phases. The results help to understand the phase transition process between carbon isomers.
【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O613.71;TB383.1

【相似文献】