Access Type

Open Access Dissertation

Date of Award

January 2020

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemical Engineering and Materials Science

First Advisor

Guangzhao Mao

Abstract

The dissertation focused on controllable seed-mediated nucleaton of charge transfer complex, namely tetrathiafulvalene bromide ((TTF)Br) and Krogmann’s salts (KCP), and their applications in sensing. On gold nanoparticle (AuNP) decorated highly oriented pyrolytic graphite (HOPG) substrate, the presence of AuNP promotes the formation of charge transfer salt nanowires. The size of these nanowires, both (TTF)Br and KCP, were found to be confined by the size of AuNPs, shown by SEM and AFM characterization. On micro-disk electrodes, charge transfer salt nanowires were found to own a linear time dependency, by both SEM and in-situ optical microscopy. The micro-disk electrodes promoted higher crystallization rate and a higher length to width ratio, comparing with nucleation of charge transfer salts on plate electrodes. Micro-disk electrodes of different size allow growth of different number of nanowires, where lower limit number on one micro-disk electrode was found 3-4. A higher uniformity of the nanowire deposition was achieved on the micro-disk electrode. By varying the deposition potentials, the compositions and crystal structures of (TTF)Br nanowires will vary accordingly. In summary, higher deposition potential promote higher deposition rate but lower Br to TTF ratio. The deposition mechanism was proposed as a competition between formation of mix-valence phase (TTF)Br, which is sensitive to deposition potential, and a solid-solid phase transition prosses in solution, which is independent from the deposition potential. Sensors were prepared by electrocrystallization at various conditions. The performance of the sensors was tested by exposing the sensors to different gases and recording impedance change at the same time. (TTF)Br nanowire sensors show >1 ppm detection limit towards ammonia gas and fast response at room temperature. KCP sensors were found to be a good humidity sensor, with > 1% relative humidity detection limit and high reproducibility. Selectivity were found to be related with the polarity. Sensing mechanisms were proposed to be related to surface adsorption and crystal structure change or surface protonation.

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