【作者】 王小波；

【导师】 朱丽华；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2015， 博士

【摘要】 石墨烯是碳原子以sp2杂化域呈蜂巢晶格排列构成的二维平面碳材料。石墨烯的层状结构和大的比表面积使其在吸附去除污染物时表现出高的吸附容量和快的吸附速率。石墨烯还可以通过π-π作用选择地吸附芳环类化合物。但石墨烯的水分散性较差,易团聚,影响自身的吸附能力。另一方面,环境激素是一类难以处理的污染物,特别是低浓度条件下,目前许多污水处理厂并没有行之有效的方法处理这类污染物,急需开发更有效的新方法。因此,本学位论文重点研究石墨烯的改性及其吸附性能。首先,采用改良Hummers法制备氧化石墨烯(GO),以水合肼作为还原剂,制备还原型GO (RGO),通过控制还原反应条件调控GO的还原程度。扫描电镜观察以及X-光电子能谱、拉曼和红外光谱分析表明,还原反应导致GO表面大部分的含氧基团消失。吸附实验结果表明：随着GO还原程度增加,其吸附能力逐渐增大。当水合肼与GO的质量比为1：1时,所得的RGO (RGO-1)对苯酚(PE)、4-甲酚(4-MP)和4-氯酚(4-CP)的吸附容量最大,分别为0.483、0.829和0.909mmol g-1。热力学研究结果表明该过程是自发、放热和熵值减小的物理吸附。以萘作为探针分子进行了核磁共振谱分析,结果表明,π-π作用是RGO与酚之间主要的作用力。还发现,酚的化学结构也会影响吸附,苯环上引入供电子或吸电子取代基都可以提高其在RGO上的吸附容量。然后,以RGO作为吸附剂,研究了低浓度双酚类环境激素双酚F (BPF)、双酚A (BPA)和双酚AF (BPAF)在RGO上的吸附行为,并与高浓度水平条件下的吸附行为进行了比较,发现在所考察的整个平衡浓度范围内(0.002-70mgL-1)的吸附等温线可以分成两个阶段：低浓度区域的吸附等温线符合Freundlich模型,而高浓度区域符合Langmuir模型。这归因于吸附过程诱导石墨烯形貌的转变,从而出现不同的表面吸附位点。热力学参数△G0、△H0和△S0表明该过程是一个自发、放热和熵减的物理吸附。这些参数的绝对值随着浓度的增加而减小,表明石墨烯对低浓度双酚的吸附结合力更强。利用透射电镜、原子力显微镜、X-射线衍射和Raman光谱监测石墨烯吸附前后结构和形貌的变化,发现双酚吸附量的增加导致石墨烯表面皱褶形成的凹槽区减少以及平面区增多。这一形貌的转变是等温线出现两个阶段的主要原因。最后,以氨水为氮源,在180℃下通过水热反应制备了氮修饰的RGO (N-RGO),系统地研究了双酚类环境激素(BPF和BPA)在N-RGO体系中的吸附与降解行为。结果表明：氮的引入不仅提高了RGO的吸附能力,而且赋予了石墨烯良好的催化能力,可有效地活化过硫酸盐(PS)。BPF和BPA在N-RGO上的吸附容量和降解速率常数分别约为未掺氮的RGO的1.75倍和700倍。在优化条件下(pH6.6、PS浓度0.6mmol L-1、N-RGO浓度120mg L-1),0.385mmolL-1的BPA在17min内几乎被完全去除。自由基捕获实验表明表面束缚的SO4·-是主要的活性物种。通过考察PE、4-MP、4-CP、2,4-二氯苯酚(2,4-DCP)、BPF和BPA各自单独体系和混合体系的吸附降解情况,结果表明吸附容量与降解速率常数之间具有良好的线性关系,吸附与降解过程具有协同效应。基于上述研究结果,提出了一种以N-RGO作为一种双功能材料通过吸附和催化氧化协同去除双酚类环境激素的新方法,该方法的最大优势在于利用原位催化氧化降解的协同效应,构建一种吸附-降解-再吸附-再降解的循环体系,为低浓度环境激素的去除提供了新策略。更多还原

【Abstract】 Graphene is a two-dimensional structure with honeycomb lattice plane composed of carbon atoms with sp2hybrid orbital. Due to its layer structure and large specific surface area, graphene owns high adsorption capacity and fast adsorption rate towdards the removal of contaminants in water. Graphene also selectively adsorbs aromatic compounds through strong π-π interaction. These properties make graphene be a promising alternative for removing aromatic pollutants. Environmental endocrines are hard to be removed, especially at low concentration levels. The treatment of low-level environmental endocrines is inefficient in most of the water treatment factories at present time. It is necessary to develop an efficient method for removing ultralow-level environmental endocrines from water. However, pure graphene is difficult to disperse in water and tends to aggregate, leading to a decreasing in its adsorption ability. Therefore, the dissertation focuses on the modification of graphene to improve its adsorption ability for removing contaminants.At first, graphene oxide (GO) was prepared with a modified Hummers method and then reduced to reduced graphene oxide (RGO) by using hydrazinehydrate. The reduction degree of GO was changed by controlling the synthetic conditions. The characterizing with scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy showed that the reduction removed most of the oxygen-containing functional groups on the surface of GO. The adsorption experiment showed that the adsorption ability of RGO were generally increased with increasing the reduction degree of GO. RGO-1prepared at the mass ratio of hydrazinehydrate and GO1:1was the best. Under the optimal conditions, the adsorption capacities towards phenol (PE),4-methylphenol (4-MP) and4-chlorophenol (4-CP) were0.483,0.829and0.909mmol g-1on RGO-1, respectively. The adsorption thermodynamics study indicated that the adsorption of PE,4-MP, and4-CP on GO and RGO was a spontaneous, exothermic and entropy-decreasing process. By using naphthalene as a probe, nuclear magnetic resonance spectrum suggested that π-π interaction can be considered as a major contribution factor to the promoted adsorption ability of RGO. The chemical structure of phenolic compounds also affected their adsorption on RGO, and the adsorption of phenolics on RGO was enhanced by introducing one or more electron-donating and withdrawing functional groups on the benzene ring.Secondly, the adsorption of bisphenol F (BPF), bisphenol A (BPA) and bisphenol AF (BPAF) at low levels was investigated on graphene in comparison with that at higher concentration levels. It was found that over the tested wide equilibrium concentration range from0.002mg L-1to70mg L-1, the adsorption isotherms of the bisphenols could be divided into two regions:at the lower concentration region, the adsorption isotherms followed the Freundlich model; at the higher concentration region, the adsorption isotherms obeyed the Langmuir model. This was attributed to the adsorption-induced changes in the morphology of graphene, which created different adsorption sites on the surface of graphene. The obtained values of thermodynamic parameters AG0, AH0and AS0indicated that the adsorption was a spontaneous, exothermic and entropy-decreasing process. The absolute values of these parameters tended to be increased with increasing the concentration of the bisphenols, suggesting stronger affinity of the binding sites on graphene for the adsorption of the bisphenols. As confirmed by transmission electron microscopy, atomic force microscopic, x-ray powder diffraction and Raman spectrum monitoring, it was found that surface grooved regions formed by wrinkles were decreased and flat regions were increased with increasing the bisphenol concentration for the adsorption. The highly wrinkled surface state and the lowly-wrinkled (or flat) surface state of graphene accounted for the observed two-stage adsorption isotherms.Final, nitrogen modified RGO (N-RGO) was prepared by hydrothermal treatment of GO with ammonia at180℃. The adsorption and degradation of bisphenolic xenoestrogens (BPF and BPA) in the system of N-RGO were investigated. It was found that the nitrogen modification enhanced not only its adsorption ability, but also its activation ability toward persulfate (PS). The adsorption capacity and apparent degradation rate constant of BPF and BPA on N-RGO were about1.75times and700times that on N-free RGO, respectively. The use of N-RGO (120mg L-1) and persulfate (0.6mmol L-1) almost completely removed the added bisphenols (0.385mmol L-1) at pH6.6within17min. Quenching radical species experiments indicated that the surface-bound SO4played a dominant role. The adsorption and degradation kinetics of PE,4-MP,4-CP,2,4-dichlorophenol (2,4-DCP), BPF and BPA in their individual single-pollutant solutions and mixture solution were studied. It was found that the apparent degradation rate constant of each of the phenolics was linearly increased with adsorption capacity. This may reflect the synergistic effect between adsorption and catalytic degradation. Based on the above study, we developed a new method for removing bisphenolic xenoestrogens by using N-RGO as a bifunctional material. The advantage of that was the synergistic effect between adsorption and catalysis. Such a cycling system of adsorption-degradation-adsorption-degradation provides a new strategy for removing endocrine disrupting compounds at low levels.更多还原