【作者】 刘桂芳；

【导师】 马军；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2008， 博士

【摘要】 近年来,内分泌干扰物污染问题已引起人们的广泛关注,特别是在饮用水中也检测到了内分泌干扰物质的存在,采用活性炭吸附技术去除水中有机污染物已被认为是一种最为有效和广泛的处理方法,因此,建立活性炭表面物化性质与其对特定污染物吸附能力之间的关系,为实际应用提供理论依据势在必行。本文选择两种活性炭W20(木质炭)和F20(煤质炭),通过改性处理获得具有不同表面物化性质的活性炭,选用双酚A(BPA)为内分泌干扰物的代表污染物,围绕目标物吸附能力与活性炭表面性质关系这一关键问题,详细地研究了BPA在活性炭表面的吸附行为和机理,同时选出两种活性炭探讨了影响BPA吸附的环境因素,最终考察了被选择活性炭对松花江原水和砂滤水中酚类内分泌干扰物的吸附情况。改性处理改变了活性炭的物理结构和表面化学性质,其中HNO3氧化降低了活性炭的比表面积,增加了羧基与酚羟基官能团含量,降低了等电点值;高温H2与N2还原处理对活性炭结构的改变很大程度上受炭材质与改性温度影响,并且改性处理后降低了表面酸性含氧官能团含量,增加了活性炭的等电点值;HCl和NaOH改性处理对活性炭的比表面积改变很小,但前者降低了活性炭的等电点值,而后者恰恰相反。此外,各种改性过程对活性炭上的灰份含量改变趋势各不相同。BPA在吸附过程中主要由液膜传质和孔内扩散两个过程控制,吸附行为假二级动力学吸附。进一步研究结果表明,BPA在活性炭上的吸附(HNO3氧化改性为Freundlich吸附)为Langmuir吸附,但吸附质分子并未将整个活性炭表面完全覆盖。其中高温N2处理活性炭W20N具有最高的BPA饱和吸附能力,qm达到了526.32mg/g,而HNO3氧化活性炭W20A表现出了最差的吸附能力,最大吸附量仅为175.44mg/g。BPA在活性炭上的吸附是自发和放热的物理吸附过程,并且以平伏形式吸附于炭表面;溶液pH值通过控制吸附质与吸附剂表面所带的电荷明显地影响活性炭对BPA的吸附能力,在pH=11时,强化的静电斥力导致W20与W20N表现出了最差的BPA吸附能力;溶液的离子强度也通过占据活性位、产生电荷屏蔽和盐析效应影响着目标物在活性炭上的吸附;此外,单宁酸的存在能够通过直接竞争吸附位、改变活性炭表面化学性质(如:等电点)和降低活性炭可利用的孔体积,而减少活性炭对BPA的吸附能力。机理分析结果表明,BPA在活性炭表面的吸附主要遵循π-π色散作用理论。在炭表面由于氢键作用形成的水分子簇会明显抑制活性炭的吸附能力,因此,降低活性炭表面酸性含氧官能团的含量(特别是羧酸基团),能够提高活性炭吸附BPA的能力。另外,使活性炭在吸附体系中处于自身静电荷密度为零状态,将会对BPA表现出最好的吸附能力。最后,在实际水体中酚类内分泌干扰物在活性炭上的吸附能力随着logKow的增大而增大(雌激素酮除外),其中改性炭表现出了更好的处理效果,而水中存在的天然有机物和其它有机物由于竞争吸附和孔阻塞降低了活性炭的吸附能力。因此,在实际水处理过程中,选用具有较多中孔结构的活性炭,能够提高处理过程效率,特别是通过一定的改性处理方法获得孔结构与表面化学性质有利于去除水中有机污染物的活性炭十分重要。更多还原

【Abstract】 The problem of water environment of endocrine disrupting chemicals has attractted people’s attention in recent years. Especially, some endocrine disrupting chemicals have been detected in drinking water. The adsorption of organic contaminants by activated carbons is the most effective and widely used methods to purify water. Therefore, it is imperative to establish the correlation between the surface physical and chemical properties of activated carbons and the adsorption capacity for the given contaminants, which may provide the scientific basis for the application of activated carbon.Two activated carbons, W20 (wood-based) and F20 (coal-based), were selected in this study. The activated carbons with different surface physical and chemical properties were obtained by modification. Bisphenol A was selected as the representative of endocrine disrupting chemicals in this study. A key objective was to study the relationship between the adsorption capacities of target pollutants and surface chemical characteristics of activated carbons. Therefore, the behaviors and mechanism of bisphenol A on various activated carbons were studied in detail and the factors affecting the adsorption of bisphenol A were simutaniously discussed. At last, two types of activated carbons with higher adsorption capacity were used to adsorbe phenolic endocrine disrupting chemicals spiked in Songhua River water and sand filtered water.The textural and chemical characteristics of the activated carbons were changed by modification. Nitric acid oxidation decreased the specific surface areas of the original activated carbons. But it increased the content of carboxyl and hydroxy functional groups. As a result, the zero point charges of adsorbents were decreased. In addition, the transformation of the structure of activated carbons, treated by thermic reduction under an atmosphere of H2 or N2, was influenced by the materials of carbon and the temperature of modification to a large extent. This process decreased the contents of surface acid oxygen-containing groups, which increased the zero point charge of adsorbents. However, the change of specific surface areas was small when activated carbons were modified by hydrochloric acid and sodium hydroxide. Where the former reduced the zero point charge of carbons and the latter was contrary to it. It is worth nothing that the changes of ash content were different for specific modification.The uptake of bisphenol A was mainly controlled by external mass transfer through the boundary film of liquid and intra-particular mass transfer. The behavior of adsorption was found to obey a pseudo-second order kinetic model. Further results indicated that the adsorption of bisphenol A on activated carbons was well described by the monolayer Langmiur model (except for carbon samples of nitric acid oxidation). However, the coverage of adsorbates on the surface of activated carbon was incomplete. In addition, the adsorption capacity of W20N, a thermal treatment sample under an atmosphere of N2, was the highest and its saturated adsorption capacity (qm) reached 526.32mg/g, while the nitric acid oxidation sample W20A represented the worst adsorption capacity and corresponding qm was only 175.44mg/g.The adsorption of bisphenol A on activated carbons was spontaneous and exothermic process which is due to physisorption reaction. The molecules of adsorbed bisphenol A were parallel to the surface of activated carbon. The adsorption capacities of bisphenol A on activated carbons were affected by the solution pH which determines the charge of both the carbon and the adsorbate. The initial sample W20 and its modified sample W20N indicated the worst capacities at pH =11, which attributed to the enhanced electrostatic repulsion. In addition, the ionic strength of solution can occupy the surface active sites, produce the screening effect and cause the salting-out effect, which influnced the adsorption of target pollutants on activated carbons.The analyzing results of mechanism indicated that the adsorption of bisphenol A on carbons mainly followedπ-πdispersion interaction. The water clusters, formed by the hydrogen bond between the carbon surface and water molecules, markedly restrained the adsorption capacity of activated carbons. It was favorable to improve the adsorption of bisphenol A by decreasing the content of surface acid oxygen-containing groups (especially for carboxylic groups). Moreover, the surface with zero charge density was the most favorable for the adsorption of bisphenol A in adsorptive system.At last, the adsorption capacities of selected phenolic endocrine disrupting chemicals on activated carbons increased with the increase logKow from the actual water (except for estrone). And the modified carbon represented a better efficiency for all tested water quality parameters. While the adsorption capacities of activated carbons were decreased by the natural organic matters and other organics. Therefore, the activated carbon with more mesopores could increase the purification efficiency. Especially, the activated carbon obtained by a certain modification, with the pore structure and surface chemistry favored the adsorption of organic compounds, were indispensable.更多还原