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University of Macau / Faculty of Science and Technology. / Department of Civil and Environmental Engineering

M.Ing. / A number of distinctly different local and international media specifications are currently being used in South Africa. Along with some opposing requirements, these specifications all specify different testing procedures to be used in the evaluation of filter media. Furthermore the already confusing situation is being complicated by a lack of knowledge as to the general properties of South African filter media ...

<p>This study has shown that OH˙ radicals can be generated in an Fe/O2 cell from the electrode products via Fenton&rsquo / s reaction and used for water disinfection. The cell system in which the experiments were carried out was open and undivided and contained two electrodes with iron (Fe) as the anode and oxygen (O2) gas diffusion electrode. Typically, 100 ml of Na2SO4.10H2O (0.5M) solution was used as a background electrolyte. OH˙ radicals were produced in-situ in an acidic solution aqueous by oxidation of iron (II), formed by dissolving of the anode, with hydrogen peroxide (H2O2). The H2O2 was electrogenerated by reduction of oxygen using porous reticulated vitreous carbon (RVC) as a catalyst.</p>

<p>A comparative study of electrolysers using different anodic materials for the electrolysis of brine (sodium chloride) for the production of sodium hypochlorite as a source of available chlorine for disinfection of rural water supplies has been undertaken. The electrolyser design used was tubular in form, having two chambers i.e. anode inside and cathode outside, separated by a tubular inorganic ceramic membrane. The anode was made of titanium rod coated with a thin layer of platinum and a further coat of metal oxide. The cathode was made of stainless steel wire. An assessment of these electrolysers was undertaken by studying the effects of some variable parameters i.e.current, voltage and sodium chloride concentration. The cobalt electrolyser has been shown to be superior as compared to the ruthenium dioxide and manganese dioxide electrolysers in terms of hypochlorite generation. Analysis of hydroxyl radicals was undertaken since there were claims that these are produced during brine electrolysis. Hydroxyl radical analysis was not successful, since sodium hypochlorite and hypochlorous acid interfere using the analytical method described in this study.</p>

在過去的幾十年中，人們越來越關心由致病微生物引起的水傳播疾病的爆發。作為一種綠色技術，太陽能光催化在不引起二次污染的殺滅各種致病微生物方面引起了廣泛關注。但是，目前最廣泛應用的TiO₂光催化劑僅在紫外光激發範圍內有效，而紫外光僅占太陽光譜的4%。因為太陽光譜中有45%是可見光，所以新型可見光催化劑的開發是現今光催化技術亟待解決的問題。另一方面，目前對於光催化殺菌機理的研究報導非常稀少而且主要集中于紫外-TiO₂光催化系統中，而對於可見光催化系統中的殺菌機理研究還鮮有報導。 / 本研究介紹三種新型可見光催化劑的殺菌性能。它們是B,Ni共摻TiO₂微米球（BNT），BiVO₄納米管（BV-NT）和CdIn₂S₄微米球（CIS）。其中一種是修飾的TiO₂催化劑，另兩種是新型的非TiO₂基催化劑。採用加入各種湮滅劑結合一種分離裝置的研究方法系統研究了三種催化劑的可見光殺菌機理。首先，研究發現當用BNT作為光催化劑的時候，可見光催化降解染料和殺菌之間存在巨大的差異。對於光催化降解染料，光催化反應主要發生在催化劑的表面，是由表面活性物質如h⁺, ・OHs和・O₂⁻參與，而細菌可以被擴散物種如・OH[subscript b]和H₂O₂，以不直接接觸催化劑表面的方式被殺死。可擴散的H₂O₂在這種殺菌過程中起了最重要的作用，而它可以在催化劑價帶以・OH[subscript b]溶液體相耦合和・OH[subscript s]催化劑表面耦合兩種方式產生。 / 其次，在用BV-NT作為光催化劑可見光殺滅大腸桿菌的過程中，光生空穴（h⁺）以及由空穴產生的氧化物種，如・OH[subscript s], H₂O₂和・HO₂/・O₂⁻，是主要的活性物種。但是這個殺菌過程只有很少量的H₂O₂可以擴散到溶液中，導致有效殺菌需要細菌和光催化表面直接接觸。研究還發現，細菌本身可以捕獲光生電子（e⁻）來降低空穴-電子複合率，這個作用在無氧氣參與的殺菌過程中尤為明顯。透射電鏡顯示，細菌的破壞是由細胞壁開始從外到內的被破壞。研究認為，表面羥基・OH[subscript s]比溶液體相羥基・OH[subscript b]更加重要，並且很難從BV-NT表面擴散進容易中。 / 最後，研究還發現CIS也具有不接觸細菌而有效可見光催化殺滅大腸桿菌的能力，這也歸結為可擴散H₂O₂，而不是・OH的作用。H₂O₂可以通過・O₂⁻從催化劑導帶和價帶同時產生。本研究提供了幾種具有應用前景的高效可見光催化殺菌催化劑，並對其光催化機理提出了新的思路，指出可見光催化殺菌機理與使用的光催化劑是密切相關的。更重要的是，本研究建立了一種簡便易行的研究方法，可用於對其他各種可見光催化殺菌系統進行深入的機理研究。 / During the last few decades, there has been an increasing public concern related to the outbreak of waterborne diseases caused by pathogenic microorganisms. As a green technology, solar photocatalysis has attracted much attention for the disinfection of various microorganisms without secondary pollution. However, the most commonly used TiO₂ photocatalyst is only active under UV irradiation which accounts for only 4% of the solar spectrum. Therefore, new types of photocatalysts that can be excited by visible light (VL) are highly needed, as 45% of the solar spectrum is covered by VL. In addition, existing reports on the mechanisms of photocatalytic bacterial disinfection are rather limited and mostly based on TiO₂-UV irradiated systems, thus the mechanisms in visible-light-driven (VLD) photocatalystic disinfection systems are far from fully understandable. / In this study, three different kinds of VLD photocatalysts were discovered for the photocatalytic bacterial disinfection. They were B-Ni-codoped TiO₂ microsphere (BNT), bismuth vanadate nanotube (BV-NT), and cadmium indium sulfide (CIS). One was modified TiO₂-based photocatalyst, and the other two were new types of non-TiO₂ based photocatalyst. The mechanisms of VLD photocatalytic disinfection were investigated by multiple scavenging studies combined with a partition system. Firstly, significant differences between VLD photocatalytic dye decolorization and bacterial disinfection were found in the case of BNT as the photocatalyst. For photocatalytic dye decolorization, the reaction mainly occurred on the photocatalyst surface with the aid of surface-bounded reactive species (h⁺, ・OH[subscript s] and ・O₂⁻), while bacterial cell could be inactivated by diffusing reactive oxidative species such as ・OH[subscript b] and H₂O₂ without the direct contact with the photocatalyst. The diffusing H₂O₂ played the most important role in the photocatalytic disinfection, which could be produced both by the coupling of ・OH[subscript b] in bulk solution and ・OH[subscript s] on the surface of photocatalyst at the valence band. / Secondly, when using BV-NT as the photocatalyst for Escherichia coli K-12 inactivation, the photogenerated h⁺ and reactive oxidative species derived from h⁺, such as ・OH[subscript s], H₂O₂ and ・HO₂/・O₂⁻, were the major reactive species. However, the inactivation requires close contact between the BV-NT and bacterial cells, as only a limited amount of H₂O₂ can diffuse into the solution to cause the inactivation. The bacterial cells can trap e⁻ in order to minimize e⁻-h⁺ recombination, especially under anaerobic condition. Transmission electron microscopic study indicated the destruction process of bacterial cell began from the cell wall to other cellular components. The ・OH[subscript s] was postulated to be more important than ・OH[subscript b] and was not supposed to be released very easily from BV-NT surface. / Finally, it was found that E. coli cells could be effectively inactivated without the direct contact with CIS, which was attributed to the function of diffusing H₂O₂ rather than ・OH. H₂O₂ was produced from both conduction and valance bands with the involvement of ・O₂⁻, which were detected by ESR spin-trap with DMPO trapping technology. While this study provided promising candidates of efficient VLD photocatalysts for water disinfection as well as deep insights into the disinfection mechanisms, it was notable that the photocatalytic disinfection mechanisms were quite dependent on the selected photocatalysts. Nevertheless, the research methodology established in this study was proved to be facile and versatile for the in-depth investigation of mechanisms in different VLD photocatalyst systems. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Wanjun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 140-170). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Acknowledgements --- p.i / Abstract --- p.vi / List of Figures --- p.xvi / List of Plates --- p.xxiii / List of Tables --- p.xxiv / List of Equations --- p.xxv / Abbreviations --- p.xxvii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Water disinfection --- p.1 / Chapter 1.2 --- Traditional water disinfection methods --- p.2 / Chapter 1.2.1 --- Chlorination --- p.2 / Chapter 1.2.2 --- Ozonation --- p.3 / Chapter 1.2.3 --- UV irradiation --- p.4 / Chapter 1.3 --- Advanced oxidation process --- p.5 / Chapter 1.4 --- Photocatalysis --- p.6 / Chapter 1.4.1 --- Fundamental mechanism for TiO₂ photocatalysis --- p.7 / Chapter 1.4.2 --- Photocatalytic water disinfection --- p.12 / Chapter 1.5 --- Visible-light-driven photocatalysts for water disinfection --- p.16 / Chapter 1.5.1 --- Modified TiO₂ photocatalysts --- p.16 / Chapter 1.5.1.1 --- Surface modication of TiO₂ by noble metals --- p.16 / Chapter 1.5.1.2 --- Ion doped TiO₂ --- p.18 / Chapter 1.5.1.3 --- Dye-sensitized TiO₂ --- p.19 / Chapter 1.5.1.4 --- Composite TiO₂ --- p.20 / Chapter 1.5.2 --- Non-TiO₂ based photocatalysts --- p.22 / Chapter 1.5.2.1 --- Metal oxides --- p.22 / Chapter 1.5.2.2 --- Metal sulfides --- p.24 / Chapter 1.5.2.3 --- Bismuth metallates --- p.25 / Chapter 1.6 --- Photocatalystic disinfection mechanisms --- p.27 / Chapter 2 --- Objectives --- p.30 / Chapter 3 --- Comparative Study of Visible-light-driven Photocatalytic Mechanisms of Dye Decolorization and Bacterial Disinfection by B-Ni-codoped TiO₂ Microspheres --- p.32 / Chapter 3.1 --- Introduction --- p.32 / Chapter 3.2 --- Experimental --- p.35 / Chapter 3.2.1 --- Materials --- p.35 / Chapter 3.2.2 --- Characterizations --- p.36 / Chapter 3.2.3 --- Photocatalytic decolorization of RhB --- p.36 / Chapter 3.2.4 --- Photocatalytic disinfection of E. coli K-12 --- p.37 / Chapter 3.2.5 --- Partition system --- p.40 / Chapter 3.2.6 --- Scavenging study --- p.41 / Chapter 3.2.7 --- Analysis of ・OH and ・O₂⁻ --- p.42 / Chapter 3.2.8 --- Analysis of H₂O₂ --- p.43 / Chapter 3.3 --- Results and Discussion --- p.44 / Chapter 3.3.1 --- XRD and SEM images --- p.44 / Chapter 3.3.2 --- Photocatalytic decolorization of RhB --- p.46 / Chapter 3.3.2.1 --- Role of reactive species --- p.46 / Chapter 3.3.2.2 --- Partition system for dye decolorization --- p.49 / Chapter 3.3.3 --- Photocatalytic bacterial disinfection --- p.51 / Chapter 3.3.3.1 --- Role of reactive species --- p.51 / Chapter 3.3.3.2 --- Partition system for bacterial disinfection --- p.54 / Chapter 3.3.3.3 --- pH effects --- p.58 / Chapter 3.3.3.4 --- Role of H₂O₂ --- p.60 / Chapter 3.3.4 --- Role of ・O₂⁻ in RhB decolorization and bacterial disinfection --- p.67 / Chapter 3.4 --- Conclusions --- p.75 / Chapter 4. --- Visible-light-driven Photocatalytic Inactivation of E. coli K-12 by Bismuth Vanadate Nanotubes: Bactericidal Performance and Mechanism --- p.76 / Chapter 4.1 --- Introduction --- p.76 / Chapter 4.2 --- Experimental --- p.78 / Chapter 4.2.1 --- Materials --- p.78 / Chapter 4.2.2 --- Photocatalytic bacterial inactivation --- p.80 / Chapter 4.2.3 --- Bacterial regrowth ability test --- p.82 / Chapter 4.2.4 --- Analysis of reactive species --- p.82 / Chapter 4.2.5 --- Preparation procedure for bacterial TEM study --- p.83 / Chapter 4.2.6 --- Analysis of bacterial catalase activity --- p.84 / Chapter 4.2.7 --- Analysis of potassium ion leakage --- p.84 / Chapter 4.3 --- Results and Discussion --- p.85 / Chapter 4.3.1 --- Photocatalytic bacterial inactivation --- p.85 / Chapter 4.3.2 --- Mechanism of photocatalytic inactivation --- p.87 / Chapter 4.3.2.1 --- Role of primary reactive species --- p.87 / Chapter 4.3.2.2 --- Role of direct contact effect --- p.96 / Chapter 4.3.3 --- Destruction model of bacterial cells --- p.98 / Chapter 4.3.4 --- Analysis of radical production --- p.104 / Chapter 4.4 --- Conclusions --- p.109 / Chapter 5 --- CdIn₂S₄ Microsphere as an Efficient Visible-light-driven Photocatalyst for Bacterial Inactivation: Synthesis, Characterizations and Photocatalytic Inactivation Mechanisms --- p.111 / Chapter 5.1 --- Introduction --- p.111 / Chapter 5.2 --- Experimental --- p.113 / Chapter 5.2.1 --- Synthesis --- p.113 / Chapter 5.2.2 --- Characterizations --- p.114 / Chapter 5.2.3 --- Photocatalytic bacterial inactivation --- p.116 / Chapter 5.3 --- Results and Discussion --- p.117 / Chapter 5.3.1 --- Characterizations of Photocatalyst --- p.117 / Chapter 5.3.2 --- Photocatalytic bacterial inactivation and mechanism --- p.121 / Chapter 5.3.3 --- Destruction process of bacterial cell --- p.128 / Chapter 5.3.4 --- Analysis of radical generation --- p.131 / Chapter 5.4 --- Conclusions --- p.133 / Chapter 6 --- General Conclusions --- p.135 / Chapter 7 --- References --- p.140

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