Document Type

Dissertation

Date of Award

5-31-2012

Degree Name

Doctor of Philosophy in Environmental Science - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Carol A. Venanzi

Third Advisor

Edgardo Tabion Farinas

Fourth Advisor

Haidong Huang

Fifth Advisor

Pradyot Patnaik

Abstract

As the applications of carbon nanotubes (CNTs) proliferate, mass production and widespread use of these nanocarbons will continue to rise. While raw, unrefined, and hydrophobic carbon nanotubes tend to settle out of aqueous media/environments, water dispersible, functionalized CNTs (F-CNTs) will contaminate water resources and will also be highly bioavailable on exposure. Therefore, there is a need to develop an understanding of the fate of F-CNTs in aqueous media.

The colloidal behavior of aqueous dispersions of F-CNTs formed via carboxylation and polymer wrapping with polyvinyl pyrrolidone (PVP) is investigated. The presence of polymer on the nanotube surface provides steric stabilization, and the aggregation behavior of the colloidal system is quite different from its covalently functionalized analog. Based on hydrophobicity index (HI), particle size distribution, zeta potential as well as the aggregation kinetics studies using time-resolved dynamic light scattering, the PVP wrapped CNT is less prone to agglomeration, It is however, less stable in the long term, which is attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface.

CNTs represent a diverse group of nanotubes that vary in size, shape and chirality. Since size alters many of the properties of CNTs, it may also affect their fate and transport and is an important parameter when CNTs are in consideration as pollutants. Size dependent colloidal behavior of aqueous dispersions of carboxylated multiwall carbon nanotubes (c-MWCNTs) is presented. While the aspect ratio does not show any definite correlation, the HI, zeta potential and aggregation kinetics show dependence on the length of the c-MWCNTs. The shorter c-MWCNTs show significantly lower HI values, smaller particle aggregates, higher absolute zeta potential values and higher critical coagulation concentrations (ccc) in the presence of electrolytes. The diameter of the short c-MWCNTs does not appear to influence their aggregation behavior. The longer c-MWCNTs however, show a dependence on diameter where stability decreases with increasing CNT diameter.

The potential for contaminant specific functionalization of CNTs for water purification is explored. The adsorptive removal of arsenic from water using multiwall carbon nanotube-metal oxide hybrids (MWCNT-ZrO2 and Fe-MWCNT) is presented. The synthesis of the sorbent was facilitated by the high degree of nanotube functi onal ization using a microwave assisted process, and controlled assemblies of iron oxide and zi rconi a are possible where the MWCNT serve as an effective support for the oxides. Metal oxide loadings of up to 11% per carbon atom are achieved and the hybrids are effective in arsenic removal to below drinking water standard levels of 10 μg L-1. Equilibrium and kinetic modeling indicate a pseudo-second order sorption process fitting both the Langmuir and Freundlich isotherms. Regeneration data show that both sorbent materials can be used for effective arsenic removal in a cycl able fashion.

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