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Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets. / Daniel Raymond Jones

Swansea University Author: Daniel Raymond Jones

Abstract

In this work, zinc oxide nanosheets are synthesised through thermal decomposition of a layered basic zinc acetate precursor and implemented in sensors to investigate the reactions of carbon monoxide, hydrogen and methane. The mean size of nanoparticles within the nanosheets is shown to increase with...

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Published: 2015
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42243
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first_indexed 2018-08-02T18:54:14Z
last_indexed 2018-08-03T10:09:38Z
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spelling 2018-08-02T16:24:28.5421834 v2 42243 2018-08-02 Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets. 7f3a1d866625502ae897ad1672096818 NULL Daniel Raymond Jones Daniel Raymond Jones true true 2018-08-02 In this work, zinc oxide nanosheets are synthesised through thermal decomposition of a layered basic zinc acetate precursor and implemented in sensors to investigate the reactions of carbon monoxide, hydrogen and methane. The mean size of nanoparticles within the nanosheets is shown to increase with annealing temperature, and sintering occurs after heating at temperatures of 700&deg;C or higher. X-ray photoelectron and photoluminescence spectroscopy techniques demonstrate that the concentrations of both lattice oxygen species and oxygen-containing surface groups may be enhanced by increasing the annealing temperature. By using an Eley-Rideal-based physical model, the responses of the nanosheets to carbon monoxide are quantitatively related to the reaction parameters of the system. The response characteristics suggest that the carbon monoxide oxidation has activation energy 54 +/- 9 kJ mol-1 while oxygen ionosorption has an energy barrier of 72 +/- 9 kJ mol-1. The sensor recoveries are consistent with corresponding values of 42 +/- 7 kJ mol-1 and 63 +/- 10 kJ mol?&sup1; for carbon monoxide oxidation and oxygen ionosorption, respectively. In the absence of O- or CO2- surface ions, the energy difference between the Fermi level and the conduction band minimum at the surface is estimated as 590 +/- 90 meV at temperatures close to 400&deg;C. The hydrogen responses of non-functionalised sensors are found to converge at 440&deg;C, despite differing at lower temperatures. This observation is incompatible with the developed model, but it is shown that the phenomenon may be rationalised by considering that the hydrogen concentration close to the sensor surface is decreased due to the rapidity of hydrogen oxidation. Gold nanoparticles significantly enhance the hydrogen response, with gold-decorated nanosheets remaining sensitive to hydrogen below 150&deg;C. Poor sensor recovery is attributed to the formation of long-lived hydroxyl groups formed during hydrogen spillover from the gold surface. E-Thesis Materials science.;Nanotechnology. 31 12 2015 2015-12-31 COLLEGE NANME Engineering COLLEGE CODE Swansea University Doctoral Ph.D 2018-08-02T16:24:28.5421834 2018-08-02T16:24:28.5421834 Faculty of Science and Engineering School of Engineering and Applied Sciences - Uncategorised Daniel Raymond Jones NULL 1 0042243-02082018162439.pdf 10797951.pdf 2018-08-02T16:24:39.2600000 Output 15791069 application/pdf E-Thesis true 2018-08-02T16:24:39.2600000 false
title Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets.
spellingShingle Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets.
Daniel Raymond Jones
title_short Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets.
title_full Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets.
title_fullStr Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets.
title_full_unstemmed Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets.
title_sort Characterisation of the surface reactions and gas sensing properties of zinc oxide nanosheets.
author_id_str_mv 7f3a1d866625502ae897ad1672096818
author_id_fullname_str_mv 7f3a1d866625502ae897ad1672096818_***_Daniel Raymond Jones
author Daniel Raymond Jones
author2 Daniel Raymond Jones
format E-Thesis
publishDate 2015
institution Swansea University
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Uncategorised{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Uncategorised
document_store_str 1
active_str 0
description In this work, zinc oxide nanosheets are synthesised through thermal decomposition of a layered basic zinc acetate precursor and implemented in sensors to investigate the reactions of carbon monoxide, hydrogen and methane. The mean size of nanoparticles within the nanosheets is shown to increase with annealing temperature, and sintering occurs after heating at temperatures of 700&deg;C or higher. X-ray photoelectron and photoluminescence spectroscopy techniques demonstrate that the concentrations of both lattice oxygen species and oxygen-containing surface groups may be enhanced by increasing the annealing temperature. By using an Eley-Rideal-based physical model, the responses of the nanosheets to carbon monoxide are quantitatively related to the reaction parameters of the system. The response characteristics suggest that the carbon monoxide oxidation has activation energy 54 +/- 9 kJ mol-1 while oxygen ionosorption has an energy barrier of 72 +/- 9 kJ mol-1. The sensor recoveries are consistent with corresponding values of 42 +/- 7 kJ mol-1 and 63 +/- 10 kJ mol?&sup1; for carbon monoxide oxidation and oxygen ionosorption, respectively. In the absence of O- or CO2- surface ions, the energy difference between the Fermi level and the conduction band minimum at the surface is estimated as 590 +/- 90 meV at temperatures close to 400&deg;C. The hydrogen responses of non-functionalised sensors are found to converge at 440&deg;C, despite differing at lower temperatures. This observation is incompatible with the developed model, but it is shown that the phenomenon may be rationalised by considering that the hydrogen concentration close to the sensor surface is decreased due to the rapidity of hydrogen oxidation. Gold nanoparticles significantly enhance the hydrogen response, with gold-decorated nanosheets remaining sensitive to hydrogen below 150&deg;C. Poor sensor recovery is attributed to the formation of long-lived hydroxyl groups formed during hydrogen spillover from the gold surface.
published_date 2015-12-31T03:52:35Z
_version_ 1763752600266604544
score 10.999161

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