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[Ru-POM] Photo-electrocatalysis

Zhu, Jie (2011) [Ru-POM] Photo-electrocatalysis. PhD thesis, Dublin City University.

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Abstract

In the past years, photo-sensitation of polyoxometalate anions with Ruthenium polypyridyl cations has received intensive investigation as the excellent photoluminescence properties and stability of Ruthenium polypyridyl complexes in multiple redox states can be coupled to the POM in order to extend the absorbance crosssection of the resulting complex into the visible region. In this thesis, remediation of organic solvent, such as benzyl alcohol and toluene, and a number of key processes that influence the overall output from photocatalytic thin films were optimized. These steps included; (1) the extent to which the catalyst and sensitizer interact electronically, (2) the film structure since this can influence the substrate access to the catalytic centres and (3) their rate of regeneration. Thin layers of an electrostatically associated adduct formed between the polyoxomolybdate, and the ruthenium polypyridyl complex or metallopolymers have been deposited onto electrodes using alternate immersion layer-by-layer assembly. Photocatalytic properties of the ruthenium polypyridyl:polyoxometalate adduct (Ru:POM) in electrolyte-free media was firstly studied. Although slow electron transfer process occurs for Ru:POM in electrolyte-free acetonitrile, the overall photocurrent was optimized at 59±0.02 μA through a number of key steps, i.e., electrolyte, potential, etc. This photocurrent is substantially lower than those found for ruthenium dye sensitized TiO2. However, it is important to note that Grıtzel type cells use iodine as the sacrificial donor and are not usually capable of photocurrent generation with donors such as benzyl alcohol or toluene that are challenging to oxidize. In common with Ru:POM films, Raman spectroscopy reveals that the Ru-PVP:POM films exhibit an additional vibrational mode at 900 cm-1 that is not present in either of the components suggesting significant electronic communication between the ruthenium centres and the polyoxomolybdate. Despite the similarity of their redox and photonic properties, this optical transition is absent in the Ru-Co-P:POM layers. Significantly, the Ru-PVP:POM films generate a higher photocurrent (38±1 nA cm-2) than the Ru-Co-P:POM films (8.9±0.8 nA cm-2) or [S2Mo18O62]4- films (9.7±1.1 nA cm-2). These results suggest that the catalytic efficiency is strongly influenced by subtle differences in the physical structure of th metallopolymer, e.g., bulkiness of peripheral ligands, even when their redox and photophysical properties are indistinguishable. The overall photocurrent for Ru-PVP:POM was optimized further. For example, increasing the thickness of the film yielded average photocurrents for the [Ru-PVP:POM] films following two, three, five and seven layers of 46±0.8, 70±0.3, 60±1.1 and 48±1.7 nA, respectively. Combining these optimization steps the experiment involved three dip coating cycles to create the Ru-PVP:POM film in the presence of benzyl alcohol (100% V/V) in 0.1 M TBATBF4 held at a potential of +0.8 V. The optimized system produced more photocurrent (183.6±17.6 nA) than those found in the previous Ru-PVP:POM study. Finally, photo-electrocatalysis using thin films of polyoxomolybdates sensitised with ruthenium metallopolymers/gold nanoparticles using visible irradiation was described. Significantly, the efficiency of the photocatalysis depends markedly on the structure of the [RuPVP-AuNP:POM] even when photonic properties are very similar. Specifically, electrostatic thin films of [RuPVP-AuNP:POM] prepared by drop cast and dip coated methods have been achieved. Strikingly, despite their similar photonic properties, an additional optical transition at approximately 927 cm-1 is observed in the Raman spectra of pre-assembled drop cast [RuPVP-AuNP:POM] films, which was not seen in dip coated [RuPVP-AuNP:POM] films. Importantly, this electronic communication enhances the photocatalytic oxidation of benzyl alcohol by a factor of more than four. While there is clear evidence for photosensitisation in the drop cast not present for the dip coated systems, the magnitude of the photocurrent, i.e., 82.2±6.6 nAcm-2 for pre-assembled drop cast [RuPVP-AuNP:POM] at a ruthenium to Au nanoparticle mole ratio of 48:1, is twice as large as those found in [Ru-PVP:POM] films with corresponding conditions.

Item Type:Thesis (PhD)
Date of Award:November 2011
Refereed:No
Supervisor(s):Forster, Robert J. and Keyes, Tia E.
Subjects:Physical Sciences > Thin films
Physical Sciences > Photochemistry
Physical Sciences > Analytical chemistry
Physical Sciences > Electrochemistry
Physical Sciences > Nanotechnology
Physical Sciences > Chemistry
Physical Sciences > Photonics
DCU Faculties and Centres:DCU Faculties and Schools > Faculty of Science and Health > School of Chemical Sciences
Research Initiatives and Centres > National Biophotonics and Imaging Platform Ireland (NBIPI)
Research Initiatives and Centres > National Centre for Sensor Research (NCSR)
Use License:This item is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 License. View License
Funders:Science Foundation Ireland, PRTLI 4
ID Code:16607
Deposited On:30 Nov 2011 15:34 by Robert Forster. Last Modified 20 Sep 2013 04:02

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