Date of Award

May 2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Junhong Chen

Committee Members

Tien-Chien Jen, Woo Jin Chang, Benjamin C. Church, Marija Gajdardziska-Josifovska

Keywords

Carbon Nanotubes, Gas Sensors, Graphene, Hybrids, Nanomaterials, Nanoparticles

Abstract

Tin dioxide (SnO2) is a well–known gas sensing material, but it becomes sensitive only at elevated temperatures (e.g., above 200 °C). Nanoparticles (NPs) combined with nanocarbons, such as carbon nanotubes (CNTs) and graphene, form a new class of hybrid nanomaterials that can exhibit fascinating gas sensing performance due to tunable electron transfer between NPs and nanocarbons induced by gas adsorption. Indeed, sensors made of SnO2 NPs&ndascoated CNTs have shown outstanding room–temperature sensing performance to various gases, including those that are undetectable by either SnO2 or CNTs alone.

The objectives of this dissertation study are to synthesize various NP–nanocarbon hybrid materials and to fabricate and characterize sensing platforms based on the resulting hybrid nanomaterials. Two simple and efficient methods have been used for the hybrid synthesis. One is a simple NP synthesis and assembly system for NP–nanocarbon hybrid nanomaterials production through combining a mini–arc plasma reactor with electrostatic force–directed assembly. The other is a simple wet–chemical method for direct fabrication of doped SnO2 NP–decorated reduced graphene oxide (RGO) sheets. In particular, CNT/Ag NP and RGO/Ag NP hybrids have been produced for fast, sensitive, and selective detection of NH3. Furthermore, a ternary hybrid of Ag NPs and SnO2 NPs–decorated CNTs has been demonstrated and showed better sensing performance than CNT/SnO2 NP hybrids likely due to the enhanced gas adsorption and electron transfer. Additionally, hybrid sensors of In–doped SnO2 NPs on RGO are shown to exhibit high selectivity to NO2 sensing. Finally, the sensing mechanism for the NP–nanocarbon system has been extensively discussed.

Based on this study, we conclude that the sensing performance (including sensitivity, selectivity, and response time) can be fine–tuned by coating nanocarbons with carefully–selected NPs (pure or doped). An attempt has been made to compare the sensing performance of hybrids based on various types of nanocarbons (e.g., multiwalled CNTs, semiconducting single–walled CNTs, RGO). Nanocarbons with superior semiconducting properties as building blocks of hybrid nanomaterials are shown to exhibit better gas sensing performance. This study provides a scientific foundation to engineer practical room–temperature gas sensors with enhanced performance.

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