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The effects of physical factors on the adsorption of synthetic organic compounds by activated carbons and activated carbon fibers.

机译：物理因素对活性炭和活性炭纤维吸附合成有机化合物的影响。

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摘要

Activated carbons (ACs) and activated carbon fibers (ACFs) have been extensively used for the removal of synthetic organic compounds (SOCs) that have been found to be toxic, carcinogenic, mutagenic or teratogenic. Adsorption of these compounds on ACs and ACFs are controlled by both physical factors and chemical interactions, which depend on the characteristics of the adsorbent (surface area, pore size distribution (PSD), and surface chemistry), the nature of the adsorbate (molecular weight and size, functional groups, polarity, solubility), and the condition of the background solution (pH, temperature, presence of competitive solutes, ionic strength). Since there are several mechanisms that can affect the adsorption, it is important to understand the role of these individual factors responsible for the adsorption of a given combination of adsorbate and adsorbent under certain background conditions. The main objective of this study was to conduct a systematic experimental investigation to understand the effects of physical factors on the adsorption of SOCs by different porous carbonaceous adsorbents. Three ACFs, with different activation levels, and three granular activated carbons (GACs) produced from two different base materials were obtained, characterized and used in the experiments. The single solute adsorption isotherms of the selected carbons were performed for benzene (BNZ), biphenyl (BP), phenanthrene (PHE) and 2-hydroxybiphenyl (2HB).;First, the role of carbon structure on the adsorption was examined and the accessible pore size regions for BNZ, BP and PHE were determined. It was found that adsorption of the selected SOCs was higher for ACFs than those of GACs due to the higher microporosity (more than 75%) and higher specific surface areas of ACFs. Both PSD and pore volume in pores less than 1 nm were important for the adsorption of BNZ, whereas accessible pore size regions for BP and PHE were determined to be approximately 1--2 nm. While adsorption of BNZ was found to be correlated with both surface areas and pore volumes, adsorption of BP and PHE was only related to the surface areas of carbons. These relationships showed that there was no restriction for BNZ molecules to access the pores of the carbons, whereas size exclusion effects were observed for BP and PHE adsorption.;Second, the effects of the molecular structure, dimension and configuration of the selected SOCs were investigated. The adsorption uptake increased with decreasing molecular dimension of each compound, and the uptake was in the order of BNZ > BP > PHE for the six heat-treated carbons. The nonplanar BP had an advantage over the planar PHE, since it was more flexible, and thus, able to access deeper regions of the pores than the rigid PHE. It was observed that BP had higher adsorption capacities as expressed on mass-basis than those of 2HB at the same concentration levels. This was attributed to the different solubilities of these SOCs since they were very similar in molecular size and configuration. On the other hand, after their concentrations were normalized with solubility, at the same reduced concentration levels, the adsorption capacities of 2HB were higher than those of BP due to the pi-pi electron-donor-acceptor interactions that resulted from the hydroxyl group in the 2HB.;Finally, to examine the role of surface oxidation, BP and 2HB adsorption isotherms on the heat-treated and oxidized ACFs were performed. The nitrogen adsorption data demonstrated that heat treatment increased the microporous surface areas by 2 to 13% compared to the oxidation of the ACF samples. Comparing the oxidized to the heat-treated ACFs, oxidized ACFs had higher oxygen and nitrogen contents and water vapor uptakes, which confirmed that they were more hydrophilic, than the heat-treated ACFs. Adsorption isotherm results demonstrated that the heat-treated ACFs had higher adsorption capacities than the oxidized ACFs, demonstrating that surface polarity had an important role in the adsorption of aromatic compounds.
机译：活性炭（ACs）和活性炭纤维（ACFs）已广泛用于去除已发现有毒，致癌，致突变或致畸的合成有机化合物（SOC）。这些化合物在AC和ACF上的吸附受物理因素和化学相互作用的控制，这取决于吸附剂的特性（表面积，孔径分布（PSD）和表面化学性质），被吸附物的性质（分子量）和大小，官能团，极性，溶解度）以及背景溶液的条件（pH，温度，竞争性溶质的存在，离子强度）。由于存在几种可能影响吸附的机制，因此重要的是要了解这些个别因素在特定背景条件下负责吸附给定的吸附物和吸附剂组合的作用。这项研究的主要目的是进行系统的实验研究，以了解物理因素对不同多孔碳质吸附剂对SOCs吸附的影响。获得了三种具有不同活化水平的ACF，以及由两种不同的基础材料生产的三种颗粒状活性炭（GAC），进行了表征并用于实验。对苯（BNZ），联苯（BP），菲（PHE）和2-羟基联苯（2HB）进行了选定碳的单溶质吸附等温线。;首先，研究了碳结构在吸附中的作用并易于获得确定了BNZ，BP和PHE的孔径大小区域。发现由于ACF的更高的微孔率（大于75％）和更高的比表面积，ACF的所选SOC的吸附高于GAC。 PSD和小于1 nm的孔中的孔体积对于BNZ的吸附都很重要，而BP和PHE的可及孔径区域确定为大约1--2 nm。虽然发现BNZ的吸附与表面积和孔体积有关，但BP和PHE的吸附仅与碳的表面积有关。这些关系表明，BNZ分子没有限制进入碳的孔，而对BP和PHE吸附则观察到尺寸排阻效应;其次，研究了所选SOC的分子结构，尺寸和构型的影响。 。吸附量随每种化合物的分子尺寸的减小而增加，六个热处理碳的吸附量依次为BNZ> BP> PHE。非平面的BP比平面的PHE有一个优势，因为它比弹性PHE更柔韧，因此能够进入更深的孔区域。观察到，在相同浓度水平下，BP的吸附能力（按质量计算）比2HB更高。这归因于这些SOC的不同溶解度，因为它们的分子大小和构型非常相似。另一方面，用溶解度对它们的浓度进行归一化后，在相同的降低浓度水平下，由于羟基中的pi-pi电子-供体-受体相互作用，2HB的吸附能力高于BP。最后，为了研究表面氧化的作用，在热处理和氧化的ACF上进行了BP和2HB吸附等温线。氮吸附数据表明，与ACF样品的氧化相比，热处理使微孔表面积增加了2％至13％。将氧化的ACF与热处理的ACF进行比较，氧化的ACF具有更高的氧和氮含量以及水蒸气吸收，这证实它们比热处理的ACF更亲水。吸附等温线结果表明，经热处理的ACF比氧化的ACF具有更高的吸附容量，表明表面极性在芳族化合物的吸附中具有重要作用。

著录项

  • 作者

    Kose, Hatice Selcen.;

  • 作者单位

    Clemson University.;

  • 授予单位 Clemson University.;
  • 学科 Engineering Environmental.
  • 学位 M.S.
  • 年度 2010
  • 页码 113 p.
  • 总页数 113
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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