Date of Award

8-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Earth Science

Advisor

Karanfil, Tanju

Committee Member

Lee , Cindy

Committee Member

Freedman , David

Abstract

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 π-π 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.

Share

COinS