The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	Controlled reduction of graphene oxide and graphene oxide-carbon nanotube hybrids and their applications
Author:	Azizighannad, Samar
View Online:	njit-etd2021-092 (xiv, 130 pages ~ 12.6 MB pdf)
Department:	Department of Physics
Degree:	Doctor of Philosophy
Program:	Materials Science and Engineering
Document Type:	Dissertation
Advisory Committee:	Mitra, S. (Committee chair) Ravindra, N. M. (Committee member) Farinas, Edgardo Tabion (Committee member) Zhou, Tao (Committee member) Ahn, Ken Keunhyuk (Committee member)
Date:	2021-05
Keywords:	Carbon nanotubes Graphene oxide Hybrids Reduced graphene oxide
Availability:	Unrestricted
Abstract:	Graphene and graphene derivatives are widely used in diverse research and industrial applications. Graphene production on a large scale is carried out by exfoliating graphite oxide and producing graphene oxide (GO), which comprises of graphene sheets with different oxygen-containing functional groups such as hydroxyl, carboxyl, and carbonyl. GO is reduced to reduced graphene oxide (rGO), which has properties that are closer to graphene. Properties of GO and rGO depend upon the oxygen content, and the effect of reducing oxygen content on the aqueous behavior of rGOs is not well understood. In an effort to understand how properties of rGO change as GO is reduced, a stepwise reduction of the same GO to rGO containing different levels of oxygen was carried out, and their corresponding chemical and colloidal properties are reported. Starting with GO containing 49 percent oxygen, rGOs containing 31, 19, and 9 percent oxygen were synthesized. The aqueous behavior in terms of solubility and dispersibility is presented. In the second part, the controlled synthesis of reduced graphene oxide-carbon nanotube (rGO-CNT) hybrids and their aqueous behavior is reported. The CNTs are suspended in an aqueous dispersion of GO, and the GO-CNT hybrids are reduced in-situ in a controlled fashion using nascent hydrogen. Several hybrids with oxygen content ranging from 26 to 2% were synthesized. The properties of the hybrids with a low degree of reduction were closer to GO, while those with a high degree of reduction were closer to CNTs. Solubility, dispersibility, hydrophobicity, critical coagulation concentration (CCC value), and zeta potential of the hybrids are studied and compared. Finally, as a major application of some of the above-mentioned materials is the development of polyacrylamide (PAM) gel polymer electrolytes (PGE) with doped nano carbons. Carboxylated CNTs referred to as (fCNTs), GO, and the hybrid of fCNT/GO embedded in the PGE were fabricated as supercapacitors (SC). Thermal stability of the pristine PGE increased with the addition of carbon nanomaterials which led to lower capacitance degradation and longer cycle life of the SCs. The fCNT/GO-PGE showed the best thermal stability, which was 50% higher than PGE. Viscoelastic properties of PGEs were improved with the incorporation of GO and fCNT/GO into the PGE structure. Oxygen-containing groups in GO and fCNT/GO formed hydrogen bonds with polymer chains and improved the elasticity of PGE. Yet, fCNT-PGE showed a slightly lower viscous strain modulus due to its ununiform distribution in the polymer matrix and the defects that were formed within. Furthermore, ion diffusion between GO layers improved in carbon-based composites, which was enhance in fCNT/GO-PGE because fCNTs decreased the aggregation of GO sheets and enhanced the ion channels, thus increasing the ionic conductivity from 41 to 132 mS cm-1. Finally, MnO2-based supercapacitors containing PGE, fCNT-PGE, GO-PGE, and fCNT/GO-PGE electrolytes were fabricated, and their performances were examined. This research demonstrated the effectiveness of carbon nanomaterials as dopants in polymer gel electrolytes for property enhancements.