石墨烯纳米片层的结构调控及其对有机污染物的吸附性能和作用机理

发布时间：2018-09-06 19:05

【摘要】：石墨烯是由sp~2杂化碳原子构成的疏水性二维纳米片层,具有优异的平面结构和物理化学性能,在电子、能源、生物医药、环境等领域显示出巨大应用前景,有望在将来作为一种超级材料应用在环境污染控制领域。本论文介绍了石墨烯基纳米材料的微观结构及其分类调控方法,并着重评述了石墨烯及其改性材料在水体有机污染去除中应用的研究进展。针对有机污染物在石墨烯界面上的作用位点不明确,石墨烯纳米片层的结构调控及其对有机污染物的吸附机理和构-效关系缺乏研究等问题,本论文以石墨烯为基础材料,通过调控石墨烯的含氧官能团、尺寸、表面褶皱孔隙等结构,改性制备了一系列石墨烯基纳米材料,利用SEM、TEM、FTIR、Raman光谱、XPS、XRD、元素分析、Zeta电位和BET-N2等手段表征材料的微观形貌、表面性质以及结构特征;较为系统地研究了石墨烯和氧化石墨烯对多环芳烃分子萘、菲、芘的吸附行为,结合吸附前后的结构表征,阐述其作用位点及构-效关系;并以重金属离子Cd~(2+)为探针物质,研究了萘和1-萘酚与Cd~(2+)在不同石墨烯界面上的协同吸附行为和机理;系统研究了石墨烯纳米材料的表面褶皱、孔隙和尺寸对有机污染物的吸附行为的影响,探讨了有机污染物在不同石墨烯纳米界面上的作用机理,并初步建立了石墨烯表面结构与污染物吸附性能之间的构-效关系。研究结果为新型石墨烯环境功能材料的设计和开发以及石墨烯环境行为的预测评估提供技术支持和理论依据。论文的主要创新性结论如下:(1)发现石墨烯和氧化石墨烯在吸附有机分子后形貌会发生特异性变化,提出了石墨烯纳米材料对PAHs分子的吸附机制。研究石墨烯和氧化石墨烯对三种不同尺寸的多环芳烃分子萘、菲、芘的吸附行为,发现:吸附系数Kd随平衡浓度的升高先增加后减小;经KHw标化排除疏水作用干扰后,小尺寸分子萘在石墨烯上的吸附亲和力更高。这说明石墨烯的作用位点在吸附过程中发生变化,对大尺寸的有机分子具有筛分作用(sieving effect)。吸附前后的SEM和TEM图证明石墨烯材料在吸附过程中构型会发生改变,由此提出石墨烯的凹槽、氧化石墨烯的边缘属于高能吸附位点,对不同大小的有机分子具有尺寸筛分作用。(2)揭示了有机、无机污染物在不同极性石墨烯界面上的吸附和复合吸附行为及作用机制。研究发现萘和1-萘酚在石墨烯界面上的吸附能力均为CRGARGGO,且1-萘酚的吸附能力强于萘。这是由于1-萘酚上的-OH与石墨烯表面的电子缺陷位点能够形成较强的n-πEDA作用,随着pH升高,1-萘酚发生解离使供电子能力增强,在1-萘酚pKa附近取得吸附最大值。GO表面的极性较强,对Cd~(2+)的吸附能力远高于CRG和ARG。Cd~(2+)共存显著抑制了 ARG对萘的吸附,而明显提高CRG和GO对萘的吸附。这是由于GO和CRG表面极性较强,吸附在表面的Cd~(2+)可以通过阳离子π键作用连接萘分子,增加其吸附位点。而ARG表面极性极弱,吸附在ARG孔隙边缘的Cd~(2+)可能对萘分子具有空间位阻作用。(3)证实了形貌结构对石墨烯表面性质和作用位点具有重要影响,阐明了石墨烯表面褶皱孔隙与有机污染物吸附速率/吸附容量之间的构-效关系,并且发现石墨烯的片层尺寸与表面缺陷、含氧官能团和比表面积密切相关。KOH活化能够显著增加石墨烯表面的褶皱和微孔结构,同时提高石墨烯界面对污染物分子的吸附容量和选择性。HOCs分子在石墨烯界面上的吸附容量与微孔体积成线性正相关,而吸附速率与微孔体积成线性负相关。HOCs分子的尺寸越大,吸附速率降低,说明石墨烯表面褶皱和微孔位点对有机分子具有尺寸筛分作用。发现随GO片层尺寸增大,表面羟基增多,同时缺陷程度提高。片层尺寸越大,还原后的团聚越严重,但是缺陷程度却越低,这说明石墨烯和氧化石墨烯的尺寸对于其表面性质和结构具有重要影响。
[Abstract]:Graphene is a hydrophobic two-dimensional nanosheet composed of sp~2 hybrid carbon atoms. Graphene has excellent planar structure and physical and chemical properties. Graphene has great application prospects in the fields of electronics, energy, biomedicine, environment and so on. It is expected to be used as a super material in the field of environmental pollution control in the future. Microstructure and classification of rice materials were reviewed. The application of graphene and its modified materials in the removal of organic pollutants in water was reviewed. The site of action of organic pollutants on the graphene interface was unclear, the structure regulation of graphene nanosheets and their adsorption mechanism and structure-effect on organic pollutants were discussed. In this paper, a series of graphene-based nano-materials were prepared by modifying graphene based on graphene by adjusting the oxygen-containing functional groups, sizes and surface folding pores. The micro-morphology of the materials was characterized by SEM, TEM, FTIR, Raman spectroscopy, XPS, XRD, elemental analysis, Zeta potential and BET-N2. The adsorption behavior of graphene and graphene oxide on polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, phenanthrene and pyrene was systematically studied, and the site of action and the structure-activity relationship were described by the structural characterization before and after adsorption. The synergistic adsorption behavior and mechanism of graphene nanomaterials were studied systematically, and the effects of surface folding, pore size and pore size on the adsorption behavior of organic pollutants were studied. The results provide technical support and theoretical basis for the design and development of novel graphene environmental functional materials and the prediction and evaluation of graphene environmental behavior. Adsorption mechanism of nano-materials on PAHs molecules was studied. The adsorption behaviors of three different sizes of PAHs molecules naphthalene, phenanthrene and pyrene on graphene and graphene oxide were studied. It was found that the adsorption coefficient Kd increased first and then decreased with the increase of equilibrium concentration, and the adsorption affinity of small size molecule naphthalene on graphene was eliminated by KHw standardization. The SEM and TEM diagrams before and after adsorption show that the configuration of graphene material will change during the adsorption process. Thus, the groove of graphene and the edge of graphene oxide belong to the high energy adsorption site are proposed. (2) The adsorption and composite adsorption behavior and mechanism of organic and inorganic pollutants on different polar graphene interfaces were revealed. It was found that the adsorption capacity of naphthalene and 1-naphthol on graphene interface were both CRGARGGO, and the adsorption capacity of 1-naphthol was stronger than that of naphthalene. With the increase of pH, the dissociation of 1-naphthol enhances the electron-supplying ability and achieves the maximum adsorption near 1-naphthol pKa. The polarity of GO surface is stronger than that of CRG and ARG. Cd~ (2+) coexistence significantly inhibits the adsorption of ARG to naphthalene. Adsorption of CRG and GO to naphthalene was enhanced obviously because of the strong polarity of GO and CRG. The adsorbed Cd ~ (2+) on the surface could connect naphthalene molecule through cation-pion bond and increase its adsorption sites. However, the polarity of ARG surface was very weak, and the adsorbed Cd ~ (2+) on the edge of ARG pore might have steric hindrance to naphthalene molecule. The morphology and structure of graphene have an important effect on the surface properties and site of action. The structure-activity relationship between the surface fold porosity and the adsorption rate/adsorption capacity of organic pollutants is clarified. It is found that the lamellar size of graphene is closely related to surface defects, oxygen-containing functional groups and specific surface area. The adsorption capacity of HOCs on the graphene interface is linearly positively correlated with the micropore volume, while the adsorption rate is linearly negatively correlated with the micropore volume. It was found that with the increase of GO lamellar size, the surface hydroxyl groups increased, and the degree of defects increased. The larger the lamellar size, the more serious the agglomeration after reduction, but the lower the degree of defects, which indicated that the size of graphene and graphene oxide had a significant effect on the surface properties and structure. Important influence.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1;X505

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