【作者】 于丽梅；

【导师】 邱介山； 赵纪军； 郝策；

【作者基本信息】 大连理工大学 ， 化学工艺， 2013， 博士

【摘要】 近二十年来,富勒烯、碳纳米管(CNTs)、石墨烯等低维碳纳米结构材料的研究一直是物理、化学、材料学等多学科交叉的热点之一。如何调控这些纳米材料的结构和性能,建立低维碳纳米材料的功能化技术方法并促进其实际应用,是人们关注的重要研究内容。通过研究并揭示低维碳纳米结构表面的化学反应构效关系,有助于建立低维碳纳米材料的功能化技术策略,亦有助于不同尺度的功能化材料的设计和合成。本文采用第一性原理方法,模拟研究了两类不同性质的单壁碳纳米管(金属和半导体型)的化学反应构效关系,着重考察了管壁完美和管壁有缺陷的碳管之差异；研究了芳香小分子与石墨烯的π-π堆叠作用。椅式和齿式单壁碳纳米管(SWNTs)是螺旋角取极值的两类典型碳管,有必要对其管壁反应的构效关系进行研究。本文用密度泛函方法,研究了碳管长度、管径相似但性质不同的金属型椅式SWNT(6,6)管和半导体型齿式SWNT(10,0)管的管壁共价功能化反应特性。鉴于双官能团化对碳纳米管性质的特殊影响,基于碳纳米管与M2型小分子(M=F、OH、NH2、H、CH3、COOH)的反应体系,对碳管的管壁反应特性进行了系统的定量化研究。以化学反应能作为判据,发现管壁反应性与SWNTs的类型无关。官能团加成到完美管壁的不同共价功能化位点时,不同位点的化学反应能的变化趋势一致,当两个官能团彼此处于六元环邻位和对位时,其化学反应活性大于两个官能团处于间位的情况。碳管的缺陷位是易于化学功能化的位置。本文用密度泛函理论(DFT),模拟研究了两种SWNTs上存在的Stone-Wales (SW)缺陷和空位缺陷的管壁反应性。通过旋转完美管的CC键,构筑出方向性不同的A型和C型两种SW缺陷管。C型SW缺陷SWNT(6,6)管和A型SW缺陷SWNT(10,0)管的管壁反应活性明显高于完美管。SW缺陷提高了SWNT(10,0)的管壁反应活性,目其幅度高于SWNT(6,6)管。A型SW缺陷SWNT(6,6)管比较特殊,其功能化反应能与完美管相比变化很小；该缺陷管连接五元环的CC键与管轴平行,无曲率差异目.键长异常的短,因此,双官能团同时连接于这两个碳原子上的几率很小,进攻官能团的原子尺寸稍大就会造成该位置无法成键,换言之,在CC键强制加合官能团会导致碳管基本结构的破坏。对于三悬挂或五元环单悬挂空位缺陷的氟化反应,当双官能团之一位于悬挂键碳原子时,反应活性有较大增加。与SW缺陷管的氟化反应能相比,三悬挂键(3DB)空位缺陷管的氟化反应能增加超过60kcal/mol,而五元环单悬挂(5-1DB)缺陷管的氟化反应能增加了40kcal/mol左右。在SWNTs上相同位点进行双官能团功能化时,反应能与官能团的类型有关,总的反应活性趋势是：F>OH>H≈NH2>CH3>COOH。一般而言,氟和羟基的共价功能化反应能为负值,氢和氨基反应能在0Kcal/mol附近,而甲基和羧基的功能化反应能为正值。燃料油中的含硫化合物会给环境、设备和催化剂带来毒害,其高效脱除方法的研究备受关注,基于碳基吸附剂的深度吸附脱硫可能是有效的途经之一。在本课题组实验研究基础上,本文用密度泛函方法,模拟研究了石墨烯与芳香小分子(噻吩、苯、苯并噻吩、二苯并噻吩和吡啶)间水平和垂直方向的非共价相互作用,发现杂环小分子水平方向作用时,吸附剂与吸附质之间以π-π堆叠方式形成稳定的吸附。芳香小分子从石墨烯上获得电荷,分子的极性和共轭π-π体系的尺寸会影响石墨烯和芳香分子间π-π堆叠作用的强度。基于Hunter-Sanders模型,研究了π-6吸引和π-π排斥作用对π-π堆叠作用的相对贡献。通过体系的吸附能和差分电子密度分析发现π-σ吸引能对π-π堆叠作用的贡献更大。更多还原

【Abstract】 In the past two decades, the low-dimensional carbon nanostructures such as fullerene, carbon nanotubes and graphene have attracted much attention in a number of fields including physics, chemistry and material science. Neverthless, how to control and tune the structure and properties of these concerned carbon nanomaterials with a low dimension remains a challenge. The functionalization of the nano-sized carbon materials is one of the possible approaches to this goal. With this in mind, it is necessary to study the relation between structure and reactivity of the low-dimensional carbon nanostructures, which will help to develop the techniques to functionalize the nano-carbons, and may shed a new light on the design and fabrication of functional materials with the nano-carbons as basic building units. In the thesis, we have examined the relations between the structure and functions of two typical SWNTs with and without defects on the side walls, and the π-π stacking interaction of several aromatic heterocyclic molecules and graphene.The armchair SWNTs with a maximal chiral angle and the zigzag SWNTs with a minimal chiral angle are two representative structures, of which the structure-property relationship needs to be addressed. We studied the side wall reactions on the metallic armchair SWNT (6,6) and the semiconducting zigzag SWNT (10,0) with the same tube length and diameter. A reaction system was constructed, in which a small molecule M2(M=F, OH, NH2, H, CH3, COOH) reacts with the side wall of SWNTs, and the reactions were evaluated in terms of the reaction energy. For the pristine SWNTs, the calculated energies of the side wall reactions are independent on the types of SWNTs, i.e. the side wall reactivity is similar for all types of SWNTs. The functional group adjacent to different sites on the SWNTs, the variation trend of the energies vs. different sites is also the same for the armchair and zigzag SWNTs. For the two groups on the ortho or para sites, their chemical reaction activity is higher than on meta sites.It is known that the defects on the side walls of SWNTs would function as the centers for chemical etching of the tubes. Using the first-principles method, we systematically examined the defect side wall reactivity of the Stone-Wales (SW) defect or vacancy defect on the SWNTs. The results show that the reactivity of the C type SW defect SWNT (6,6) and the A type SW defect SWNT (10,0) is higher than the defect-free pristine SWNTs. The chemical energies of the zigzag tubes due to the SW defect are larger than the armchair one. For the A type SW defect SWNT (6,6) with a short CC bond linking the two pentagon ring that are parallel to the axis of SWNT, no local curvature effect is observed, and the two functional groups have little chance to synchronously react with the two carbon atoms. In other words, if two functional groups react synchronously on the carbon atoms connecting two pentagon rings, the structure of SWNTs will be destroyed. For the fluorination of3DB or5-1DB vacancy defect SWNTs. it is only when a group is on the dangling bond carbon atom that a large increase of the reaction energy will be observed, while in the case of the SW defect SWNTs, it is over60kcal/mol by3DB defect SWNTs, and it is ca.40kcal/mol in the case of5-1DB defect SWNTs.For the six functional reactions of various SWNTs, the trend is also the same:F> OH> H≈NH2> CH3> COOH. The functional reaction of F or OH groups on the side walls of SWNTs is exothermic, while the H, NH2, CH3, COOH functionalization of SWNTs is endothermic.By the first-principles simulation, we performed DFT calculations at the GGA and LDA level on the noncovalent parallel and vertical interaction of graphene by aromatic heterocyclic molecules (thiophene, benzene, benzothiophene, dibenzothiophene, and pyridine). The most stable π-π stacking adsorption configurations prefer the "stack" site. The heterocyclic molecules are charge acceptors for graphene.The polarity and the size of π-conjugation can alter the magnitude of interactions between small aromatic molecules and graphene. According to the Hunter-Sanders model, we have made efforts to evaluate the relative contributions of the π-σ attraction and the π-π repulsion. It is found that the π-σ attraction energy accounts for the most of the energy in terms of the adsorption energy and the differential electron density of the complex systems.更多还原