Mechanism And Applications Of Noncovalent Functionalization Of Carbon Nanotubes Using Aromatic Organics

Since their discovery, carbon nanotubes (CNTs) have attracted great scientific attention, owning to their unique structural, mechanical and electronic properties. CNTs are expected to have potential applications in many fields, such as nanocomposite materials, reinforced structures, nanoelectronic devices and field emission displays etc. Because of the intrinsic inert surface properties, unmodified CNTs exhibit low reactivity and solubility in most solvent systems, making the dispersion, modification, and assembly difficult. Controlling the surface functionality and thus surface properties of CNTs is therefore critical for many fundamental researches and potential applications. Sidewall functionalization is one of the most important ways to make functionalized nanotubes. The most obvious advantage of using noncovalent binding is that it maintains the sp graphene structures and thus preserving the unique electronic characteristics of CNTs. The noncovalent modification with aromatic molecules is a very simple operation and the interaction is strong enough to help CNTs compatible with the chemical and biological environments. This thesis focuses on the nonconvalent modification of CNT sidewalls using different polycyclic aromatic molecules. A series of molecule/CNT adducts was fabricated and the factors affecting the molecule/CNT interactions were investigated. Using different aromatic molecules, separation of metallic and semiconducting single-wall carbon nanotubes (SWCNTs) were successfully achieved. Further investigations on the applications of these novel molecule/CNT adducts in photovoltaic energy conversion were carried out. The main contents of this theisi are listed blow.1. A systematic study on the noncovalent interaction between single walled carbon nanotubes (SWCNTs or SWNTs) and a series of aromatic molecules has been conducted. The main purpose of this work is to understand how the molecular structure affects their adsorptions on the SWCNTs. Two factors have been found to play the key roles, which are molecular morphology and charge. It was found that the adsorption quantity of aromatic molecules was strongly dependent on the molecular morphology, which follows the general rule as polynuclear > pseudo planar molecules > planar azo > non-planar. Meanwhile, when the molecular morphology is similar, the adsorption is dependent on the molecular charge. The above finding reveals thatπ-πstacking between the aromatic molecules and the SWCNT side wall is the main driving force for the adsorption, while electrostatic interaction also plays an important role. Fluorescence quenching was observed on most of the molecules, but different quenching mechanisms may exist for different molecules. This work provides a general guideline for choosing aromatic molecules for non-covalent modification of SWCNTs, and insights to the interactions between SWCNTs and the aromatic molecules.2. Surfactant free dispersion of SWCNTs in aqueous solutions were achieved by using an aromatic molecule Xylenol Orange (XO). Dispersion of SWCNTs in aqueous solutions is an important issue for many applications. Conventional methods for dispersing SWCNTs relys on using different surfactants, which causes foaming problem and introduces insulate surface coating to SWCNTs. We have found that an aromatic molecule XO exhibited excellent ability to disperse SWCNTs and gave stable suspensions with higher concentration than conventional surfactants. The XO dispersed SWCNTs are sensitive to pH values of the solution and therefore can be used as adjust the degree of aggregation of the SWCNTs. This work provides new hybrid SWCNTs for potential applications in the fields of sensing, and composite materials.3. Separation of metallic and semiconducting single-walled carbon nanotubes (SWCNTs) are of great importance for SWCNT-based nano-electronics. We propose a tandem extraction strategy for efficient separation of different types of SWCNTs. This strategy is based on a chiral angle discriminated adsorption of soluble condensed benzenoid aromatic molecules on SWCNTs, which induce different dispersibility of SWCNTs in various organic solvents. The proposed tandem extraction strategy involves two extraction steps, in which the first step extracts metallic SWCNTs with large chiral angles and the subsequent step enriches large chiral angle semiconducting SWCNTs. This separation strategy is tested on a series of condensed benzenoid aromatic molecules. Both experimental and theoretical results show that the separation efficiency is strongly dependent on the molecular morphology, i.e. higher aspect ratio gives better separation results. The separation efficiency is also dependent on the SWCNT diameter and the solvent properties. This tandem extraction strategy may also be applied to other available noncovalent separation reagents to improve their separation efficiency.4. Novel SWCNTs/perylene heterojunction were constructed byπ-πstacking interactions and their light-induced charge transfer properties were studied. In this work, we synthesized N,N'-di-(n-butyl)-3,4,9,10-perylenetetracarboxylic diimide (PTB) to make perylene derivatives soluble in many solvents. The fluorescence quenching of PTB solution was observed when SWCNT is present, indicating possible photo-induced charge transfer took palce in the nanohybrids. The SWNTs/PTB bulk hybrids were drop-casted onto ITO electrode for photoelectrochemistry measurements. From photocurrent measurements under different bias give stable and high photocurrent response which is promising for novel photovoltaic devices.