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Metal-decorated carbon nanotubes for gas sensing applications
This thesis reports on the investigation of metal-decorated carbon nanotubes-based sensor arrays with enhanced sensitivity and selectivity toward toxic gases. Ab initio first-principles methods were used to expedite the process of identifying the right materials with the highest potential compared t...
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| Format: | Thesis |
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AUC Knowledge Fountain
2020
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| Summary: | This thesis reports on the investigation of metal-decorated carbon nanotubes-based sensor arrays with enhanced sensitivity and selectivity toward toxic gases. Ab initio first-principles methods were used to expedite the process of identifying the right materials with the highest potential compared to in-lab trial and error as well as to provide a deeper understanding of the gas adsorption mechanism. The mechanism of NO2 adsorption on Cu-, Pt- and Ti-doped single-walled carbon nanotubes (SWCNTs) was investigated. Modelling the isolated NO2 molecule indicated the formation of a band gap between the 3π* HOMO and 5σ* LUMO levels, which were found to be the electronic states primarily involved in the bonding process. Metal doping decreased the system stability and altered the SWCNT structure. NO2 exposure caused the transfer of electrons to the gas molecules, thereby enhancing the p-type conductivity of the M-SWCNT structure. The highest charge transfer to the NO2 molecule was observed for Ti-SWCNTs (0.456 eV), while the lowest was found for Cu-SWCNTs (0.351 eV). Ti-SWCNTs exhibited the highest stability and sensitivity as a potential NO2 gas sensing material out of the 3 investigated metal dopants. The DFT predictions were verified with the experimental results. The experimental results of these Ti-, Pt-, and Cu-decorated CNTs when exposed to NO2 were found to have the same order as predicted by DFT calculations. The sensors were the fabricated using a Kapton base with a printed gold circuit and silver electrodes to decrease current losses between contacts. The synthesized material was tested upon exposure to four toxic gases; NO2, H2S, NH3 and CO. Although CO showed the weakest resistance change among the other gases, its highest resistance change was found for exposed to Ag and pristine CNTs. Cu-decorated CNTs showed the highest response to H2S out of the tested metal decorated sensors. NH3 showed a good response to Ru-decorated CNTs. The different responses generated by each of the metal dopants under the exposure of each gas generated a unique response pattern that can be used as an identifier. |
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