Date of Degree

2-2015

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Daniel L. Akins

Subject Categories

Chemistry | Mechanics of Materials | Nanoscience and Nanotechnology

Keywords

Chemiresistor, Electronic Nose, Nano-device, Sensors, SWNTs

Abstract

Specifically, the project involves the development of a diversified array of nanostructured gas-sensors comprised of selectively, novel surface-functionalized carbon nanotubes (for analyte selectivity by virtue of functionality). Harnessing carbon nanotubes with various electron withdrawing and donating groups help in determining their affinity toward certain prognostic gaseous markers thus increasing specificity of such created sensors. We have devised synthetic routes that have led to the facile production of covalently polyfunctionalized nanotubes in high yield. Seven carbon nanotube analogues were systematically considered and then chemically synthesized, from pristine single-walled nanotubes (SWNT's), for use as the main component of sensory units that was used for this study. The basic chemical structure of these functionalized nanotubes; namely: poly(p-phenol)-co-SWNT [1], poly(p-nitrobenzene)-co-SWNT [2], poly(p-fluorobenzene)-co-SWNT [3], poly(p-aniline)-co-SWNT [4], polybromide-SWNT [5] , poly(p-thiophenol-co-SWNT [6] and poly(p-benzonitrile-co-SWNT [7]. The ability to manufacture total organic sensors was demonstrated using carbon nanotube based architectures.

These derivatized-nanotube-based materials are designed to serve as chemoreceptors that can facilitate the development of highly selective and sensitive chemical and biological sensor arrays through an "electronic nose" approach which mimics the mammalian olfactory system. Functionalized SWNTs (f-SWNTs) were dispersed in dimethyl formamide (DMF) and mCresol and spun-applied to the interdigitated regions of micro-lithographically fabricated, pre-cleaned interdigitated microsensor electrodes (IME 1025-M-Pt and Au). Measured changes in the electrical conductivities of an array of gas sensors upon exposure to selected vapors and inert explosive materials were monitored. These changes are transduced into electrical signals, which are preprocessed and conditioned before identification by a pattern recognition system. Preliminary chemisensory was conducted on four signature vapor components of RDX explosive. Sensor data from these individual detection methods was assessed by their own individual merits, after which they were amalgamate and reclassified to present each vapor as a unique data point on a 2-dimensional map and with a minimum loss of information. Extensive characterizations on the properties of these materials were carried out using various spectroscopic and electrical techniques to assess the usefulness of functionalized single-walled carbon nanotubes. It was found that the conductivity of two functionalized materials (poly(p-aniline)-co-SWNT [4] and polybromide-SWNT [5] ) were more conductive than the pristine SWNT.

The development of consistent and successful functionalization techniques that allows for the construction of CNTs-based species of great usefulness, reversibility and selectivity for the use as sensing element, can be a challenge. We have demonstrated a proof-of-concept by exploring and using the functionalized carbon nanotubes for use as gas sensors, through the utilization of a stochastic fingerprinting methodology. However, further studies into electronic and electrochemical detection methods will provide more unique systems for R&D on the applicability of these materials to future technology.

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