A Tio2 Photoelectrocatalytic System for Wastewater Detoxification and Disinfection

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Zhao, Huijun

Zhang, Shanqing

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Fu, Jiamo

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2010
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Abstract

This work systematically investigate the nanoparticulate TiO2 photocatalysis and photoelectrocatalysis based methods for decomposition, detoxification and disinfection of a series of biological contaminants ranged from small biological compounds such as amino acids and nucleotide bases, to large biological compounds including protein, lipid and DNA, to living microorganisms such as bacteria and virus. The small biological compounds (e.g., amino acids and nucleotide bases) are the basic building blocks of the large biological compounds (e.g., proteins and DNA), and the large biological compounds are the building blocks of the living microorganisms (e.g., bacteria and viruses). Due to the complicity involved, in order to understand the full spectrum of the decomposition, detoxification and disinfection mechanisms of living microorganisms, a bottom-up strategy was employed in this study. The photocatalytic and photoelectrocatalytic degradation of small biological compounds were firstly investigated to gain the necessary information for a better understanding of degradation mechanisms of large biological compounds. The photocatalytic and photoelectrocatalytic degradation of large biological compounds were then investigated to gain the necessary information for a better understanding of decomposition/disinfection mechanisms of living microorganisms. This was followed by the investigation of photocatalytic and photoelectrocatalytic decomposition/detoxification/disinfection of living microorganisms. Chapter 1 of the thesis provides comprehensive literature reviews of the present status of research developments relevant to this work and the justification for the research topic. Nanoparticulate TiO2 photoanode is a key element of the proposed research. Chapter 2 describes the fabrication and characterisation of the nanoparticulate TiO2 photoanode. The nanoparticulate TiO2 photoanode was successfully fabricated using a sol-gel method. The photoelectrocatalytic properties of the resultant TiO2 photoanodes were systematically evaluated using water, as well as organic model compounds in both bulk and thin-layer photoelectrochemical cells. The results indicated that the resultant photoanodes possess high photocatalytic activity. The measured net charge under the exhaustive conditions in a thin-layer photoelectrochemical cell is essentially the same as the theoretically required charge, demonstrating a superior oxidation power and 100% electron collection efficiency. Photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of small biological compounds such as amino acids and nucleotide bases were carried out in Chapters 3 and 4. These small biological compounds were found to be photocatalytically and photoelectrocatalytically degradable. The degradation efficiency of PEC method was found to be higher than that of PC method for all compounds investigated. The organic nitrogens in the original compounds can be oxidised to either NH3/NH4 + or NO3- or both, depending the chemical structures of the original compounds and the degradation methods used. Both experimental results and the theoretically calculated frontier electron densities values of (2FEDHOMO)2 and (FEDHOMO)2+(FEDLUMO)2 demonstrated that the reaction mechanisms/pathways of PEC processes differed remarkably from that of PC processes. As a part of the proposed “bottom-up” strategy, PC and PEC degradation of large biological compounds such as bovine serum albumin (BSA), lecithin and bacteria genomic DNA were performed in Chapter 5. A new method for estimating the theoretical charge required to mineralise these large biological compounds with unknown chemical formula was firstly developed and experimentally validated. The degradation efficiency of PEC method was found to be higher than that of PC method for all large biological compounds investigated. In Chapter 6, a bactericidal technique (PEC-Br) utilising in situ photoelectrocatalytically generated photohole (h+), Br2•- and active oxygen species (AOS) for instant inactivation and rapid decomposition of Gram-negative bacteria such as E. coli was proposed and experimentally validated. The method is capable of inactivating 99.90% and 100% of 9×106 CFU/mL E. coli within 0.40 s and 1.57 s, respectively. To achieve the same inactivation effect, the PEC-Br method is 358 and 199 times faster than that of the PEC method, and 2250 and 764 times faster than that of the PC method. The Chapter 7 demonstrated the bactericidal technique developed in Chapter 6 can also be applied as a virucidal technique for rapid inactivation of viruses such as replication-deficient recombinant adenovirus (RDRADS). The PEC-Br method is capable of deactivating 99.77% and 100% of RDRADS within 14.32 s and 31.65 s, respectively. The final chapter of the thesis (Chapter 8) summarises the outcomes of this study and future work.

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Thesis (PhD Doctorate)

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Doctor of Philosophy (PhD)

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Griffith School of Environment

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The author owns the copyright in this thesis, unless stated otherwise.

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Subject

photoelectrocatalytic

wastewater

detoxification

disinfection

decomposition

contaminants

bacteria

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