ZnO And MoSexOy Modified TiO2 Nanotubes For Photoelectrochemical And Sensing Applications

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dc.contributor.authorNg, Siow Woon
dc.date.accessioned2021-03-04T02:18:01Z
dc.date.available2021-03-04T02:18:01Z
dc.date.issued2018-09
dc.description.abstractOne-dimensional (1D) anodic self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over a decade. The major drawbacks are their rather wide band gap energies (3.0–3.2 eV) with high photoactivity only in the ultraviolet (UV) spectral region (l 390 nm, 5% of the solar spectrum), relatively low conductivity and high carrier recombination rate. Furthermore, as a high aspect ratio (HAR) nanostructure, the deposition of a uniform secondary coating within the TiO2 nanotube layers remains a challenge. To overcome these critical issues, present work is intended (i) to synthesize anodic 1D TiO2 nanotube layers as an independent semiconductor and for the incorporation of secondary materials; (ii) to produce homogeneous and conformal ZnO and MoSexOy coatings by atomic layer deposition (ALD) within TiO2 nanotube layers; (iii) to form heterostructure in order to enhance charge transport efficiency, increase light absorption and extend the functional range to the visible spectral region; and (iv) to evaluate UV photodetection responses, ethanol sensing responses at low temperatures, photocurrent generation and photocatalytic degradation of methylene blue (MB). The synthesis of the TiO2 nanotube layers was carried out by a conventional electrochemical anodization of Ti sheet in fluorinated organic electrolytes. A low bias, visible-blind, UV photodetector was constructed in a sandwich structure comprising of ITO/electrolyte/TiO2 nanotubes/Ti for the first time to investigate the photodetection in UV-A, B and C spectral regions. The highest sensitivity was credited to 5 mm TiO2 nanotube layer, with sensitivity 850, responsivity 740 mA/W and short rise and decay time less than 1.5 s. Synergistic effects arising from the deposited materials and TiO2 core layer strongly influenced the photoelectrochemical (PEC) properties and substantially enhanced the photocurrent conversion efficiencies. The ZnO (19 nm) coated nanotube layers presented 80–95% incident photon-to-electron conversion efficiencies (IPCE) between 305–375 nm with the aid of 2 V bias. This value is among the highest values reported for ZnO/TiO2 combination. The MoSexOy (2 nm) coated layers demonstrated up to 40-fold higher photocurrent than the blank nanotube layers at 470 nm. As an environmental application, the MoSexOy coatings have shown to be an effective photocatalyst for MB degradation with significantly accelerated photocatalytic degradation rates at 2.259 10􀀀2 min􀀀1. It is also for the first time, MoSexOy is synthesized by ALD and deposited within HAR nanostructure. Finally, the ZnO coatings yielded an improved ethanol sensing response up to 11-fold compared to the blank nanotube layers in operating temperatures of 100– 200 C with high stability, durability, and reproducibility. Overall, the current work demonstrated that anodic self-organized TiO2 nanotube layer is functional as a sensing layer for UV and ethanol detection; and a photocatalyst in PEC and photodegradation activities.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/11727
dc.language.isoenen_US
dc.publisherUniversiti Sains Malaysiaen_US
dc.subjectNanotechnologyen_US
dc.subjectPhotocatalysisen_US
dc.titleZnO And MoSexOy Modified TiO2 Nanotubes For Photoelectrochemical And Sensing Applicationsen_US
dc.typeThesisen_US
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