Date of Award

1-1-2012

Document Type

Campus Access Dissertation

Department

Civil and Environmental Engineering

First Advisor

Navid B Saleh

Abstract

The goal of this study is to systematically investigate the effects of variation in electronic structure on aggregation of chiral single-walled carbon nanotubes (SWNTs) and their transport in landfill conditions. This study involves four key tasks: functionalization of chirally separated SWNTs, aggregation kinetics of covalently and non-covalently functionalized SWNTs, aggregate structure determination, and transport behavior in conditions relevant to landfills. SWNTs with (6,5) SG65 and (7,6) SG76 chiralities are analyzed with near infra-red (NIR). Covalent functionalization was performed with acid etching where non-covalent modification was done with commonly used surfactants. Uniform dispersion of such SWNTs are used in aggregation transport studies. Results indicate that SG76 has higher aggregation propensity compared to SG65due to higher van der Waal's interaction energy between tubes. Such behavior also resulted in tighter aggregate packing for SG76. Presence of surfactants dominatedaggregation behavior over chirality; where,aggregation largely depended on surfactant structure. Sodium dodecyl benzene sunfonate (SDBS) served as the most effective stabilizer followed by sodium deoxycholate (SDOCO) and sodium dodecyl sulfate (SDS). Molecular modeling was performed with chiral specific SWNTs and surfactants to better understand their interaction behavior which provided insight through interaction energy and conformational differences. The deposition behavior of

SWNTs studied with saturated 1-D columns using plastics, paper, glass, and food surrogates as collector media, used both young (acetic acid) and old (humic acid) leachates. Results show that relative humic acid concentrations play a key role in SWNT deposition; i.e., higher the humic acid concentration, higher is the elution. The media-specific study identified paper as the dominant collector media to retain SWNTs, followed by metal, plastics, and glass.

The dissertation highlights the fact that electronic structure of SWNTs can play a dominant role in fate and transport and thus require careful consideration in environmental health and safety studies of these tubular helicoids. In addition, the studies report role of surfactant type in SWNT fate and transport. Results indicate that SWNTs can be mobile in landfill conditions, depending on chemistry and collector media. Further studies are required to better understand role of chirality on SWNT fate in complex natural environment.

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