Document Type

Dissertation

Date of Award

5-31-2016

Degree Name

Doctor of Philosophy in Chemistry - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Tamara M. Gund

Third Advisor

Edgardo Tabion Farinas

Fourth Advisor

Yong Ick Kim

Fifth Advisor

Pradyot Patnaik

Abstract

Carbon nanotubes (CNTs) are known to have unique mechanical, thermal and electrical properties which make them attractive for a wide range of applications ranging from batteries to sensors. CNTs are rolled up graphene sheets where the single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) are classified according to the number of concentric rings. In this dissertation, the focus is on several different aspects of MWCNTs. These include purification, functionalization and colloidal behavior.

MWCNTs are insoluble in solvents and therefore some degree of functionalization is required prior to their real-world applications. Oxidation debris is generated during carboxylation which is usually the first step in their functionalization. Our group has previously developed microwave induced functionalization of MWCNTs which is a fast process that provides high degree of functionalization. One of the objectives of this research is to study the oxidation debris generated during microwave functionalization.

Oxidation debris affects the dimension of MWCNTs and their surface properties which influence dispersion and stability in chemical and biological environment. Removal of this debris is needed to obtain high purity functionalized MWCNTs. Dilute base-washing is usually used to remove oxidation debris by converting the acidic groups in the debris into their conjugate salts so that they are dissolved and removed. Conventional washing takes a long time and consumes a lot of chemicals. Therefore, another objective of this research is to study the feasibility of microwave induced base washing as a rapid method for removing oxidation debris.

The degree of functionalization of MWCNTs is an important factor that has not been addressed to date. The effects of the degree of functionalization on physical and chemical properties as well as bioactivity and toxicity are yet to be studied in any detail. The degree of functionalization is altered by varying the treatment time in microwave induced functionalization. Chemical, physical, electrochemical and colloidal behavior of the carboxylated MWCNTs is studied. Variations in chemical, physical, colloidal and electrochemical properties are presented in this dissertation.

Another important aspect of MWCNTs is that they are usually mixtures of different sizes and represent significant variability within the group. The size of MWCNTs affects the physical and chemical properties, biological behaviors and dispersibility. For example, applications in electronics, biological, and optical devices benefit from shorter nanotubes (less than 500 nm), while others like field emission displays require relatively longer tubes (500-2000 nm) due to their more uniform emission. The size dependent behavior of CNTs is also not well understood. Of particular interest to this research is the aqueous dispersibility and colloidal behavior of functionalized MWCNT. In this research, the colloidal behavior of MWNCTs that are functionalized to the same degree but have different length is studied.

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