published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

A dissertation submitted to the Faculty of Science, University of the Witwatersrand in partial fulfilment of the requirement for the degree Master of Science (M.Sc.) in Chemistry. Johannesburg, 31 October 2017. / Nanotechnology has been instrumental in finding strategies of combating some of the world’s grand challenges. Water scarcity and the growing industrialization have made it an imperative to find ways of cleaning water. Photocatalysis is a promising method for water purification personified by the use of solar energy as well as nanomaterials with tailored properties. Colloidal synthesis has made it possible to synthesize new materials with tailored properties, in particular the single-source precursor method has been found to be a useful method in synthesizing nanomaterials with high purity. In the synthesis of metal chalcogenides, the single-source precursor method has an advantage of the precursor having the desired metal-chalcogenide bond hence eliminating the possible formation of side products particularly metal oxides. Herein, acylthiourea (ATU) and thiourea (TU) zinc complexes were used as precursors for the synthesis of ZnS nanoparticles. Bis(N,N-diethyl-N’-benzoylthiourea)Zn(II) [Zn(ATU)2] and bis(diaminomethylthio)Zn(II) chloride [Zn(TU)2Cl2] complexes were synthesized using a conventional method and characterized with elemental analysis, 1H NMR , 2D NMR, COSY, FTIR, mass spectrometry and X-Ray crystallography. The resultant precursors, Zn(ATU)2 and Zn(TU)2Cl2 complexes were then thermolyzed to yield ZnS nanocrystals and characterized fully. Reaction parameters that included the synthetic time, temperature, concentration and capping agents were optimized for each single-source precursor in an attempt to control the nanoparticles yielded hence their properties. Time and temperature studies generally demonstrated the most pronounced effect and with an increase, they showed increasing particle sizes through the Ostwald ripening effect. Also visible from the TEM was that the temperature had an effect on the morphology of the nanoparticles. Increasing the precursor concentration resulted in the agglomeration of nanoparticles, while using different capping agents yielded similar nanoparticles with different degrees of agglomeration. Evident from the results the ATU precursor behaved similar to the TU precursor and generally the particles obtained from the two precursors regardless of the reaction condition were very small. Preliminary investigations into the use of the synthesized nanoparticles obtained from the two precursors revealed potential in photocatalytic degradation of Rhodamine B (RhB) dye in water. While smaller particles were obtained from the synthesized nanoparticles, the degradation efficiencies were lower than the commercial ZnO and TiO2. This is due to the presence of the long-chained capping agents on the synthesized particles blocking the interaction of the core ZnS and the light. / LG2018

published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy

由於潔淨用水日漸短缺，科學家著力研究各種水淨化方法，其中以光催化技術作水淨化處理為可行的方法之一。光催化是以半導體光催化劑在光照射下所產生的活性物種（reactive oxidative species）進行消毒，其中的失活原理、各活性物種的作用和活性物種對細菌的攻擊方位，雖然已有廣範的研究，但當中仍有不清之處，比如說過氧化氫(H₂O₂)在光催化失活的作用便是其中之一，在光催化系統中所產生的H₂O₂濃度一般較低，因此其對細菌失活的效能仍然存有爭議。 / 本研究設計一種新的反應器去研究H₂O₂在連續供應模式中的失活動力學。在 8 mM 的H₂O₂下，10⁵的大腸桿菌(Escherichia coli)在8小時內完全失活。而在 2 mM 的H₂O₂ 下，並無出現顯著失活，由於該濃度遠遠高於一般光催化系統所產生的濃度（<50 μM），因此可以推斷，即使一般光催化系統所產生的H₂O₂是連續供應，也不會使細菌失活。然而在光照的情況下，其失活動力學大為不同，在強光照射(200 mW cm⁻²)下，H₂O₂的失活效率顯著增強，證明光照和過氧化氫之間存有協同效應。這現象亦出現於光預處理過(light pretreated)的大腸桿菌，進一步證實了光照改變細菌的生理機能，從而使其易於被H₂O₂失活。 / 其後我們使用RNA測序(RNA sequencing)去檢測的大腸桿菌的基因表達水平在光照下的變化，以便研究光照和H₂O₂之間的協同作用的機理。大多數涉及抵抗氧化的基因，包括過氧化氫酶(catalase, CAT)和超氧化物歧化酶(superoxide dismutase,SOD)的表達、DNA修復及細菌內的鐵含調控等等，其mRNA 水平沒有顯著的增加或減少，只有dps、fes和sodB有明顯的變化。此外，還有幾種調控細胞內的銅合量（cutA和cueR）和細胞膜組成（ompA、ompC、resx和gnsB）的基因在光照下產生顯著變化。 經RNA測序後，我們選定了10個目標基因，並選擇相對的大腸桿菌變異體(mutants)，對比他們和母體(E. coli BW25113)經過光預處理後被H₂O₂的失活效能。雖然這次研究並未找到相關基因，但研究結果表示，光照和H₂O₂的協同效應，應該是光照增加細胞膜的通透性和提高細菌內Fenton劑含量，使細菌內的羥基自由基(·OH)的濃度增加，因此加強對細菌DNA的損傷。 / 最後，我們亦比較了AgBr/Ag/Bi₂WO₆在不同的光源的照射下的對大腸桿菌的光催化失活效率。雖然發光二極管(light emitting diode)和熒光管都常用於室內照明，但AgBr/Ag/Bi₂WO₆的細菌失活效率在兩者的光照下表現出顯著的差異，而不同的發射波長下的細菌失活效率和AgBr/Ag/Bi₂WO₆光學吸收表現出良好的相關性。此外，相對其他顏色的發光二極管，綠色發光二極管照射下在犧牲劑研究(scavenger study)的結果大為不同，進一步表明了光照的發射波長(emissionwavelength)對光催化失活機制的影響。 / 本研究揭示了H₂O₂和光照在光催化失活中的重要性，並演示了H₂O₂和光照射之間的協同作用，也闡明了光照的屬性如何影響光催化下各活性物種的產生。本研究不僅提供了一個新的角度去探討的光照、H₂O₂和細菌的生理狀態在光催化失活中的重要性，也提供了新的方向和方法去研究光催化失活機制的。 / Due to the increasing concern for the need of clean drinking water, different methods for water purification have been developed. Photocatalysis, which makes use of semiconductor photocatalyst for the generation of reactive charged and oxidative species (ROSs) under light irradiation, is one of the most promising methods for water disinfection. The mechanisms of the photocatalytic inactivation have been extensively investigated. Different factors, including the roles of ROSs and the ROSs target site(s) of bacterial cell, were elaborated by different studies. However, there are still controversial issues on the role of H₂O₂ in photocatalytic inactivation. The effectiveness of the low concentration of H₂O₂ in the bacterial inactivation process is still under question. / This study designs a new reactor to study the kinetic of H₂O₂ inactivation in continuous supply mode. Complete inactivation of 5-log Escherichia coli within 8 h is achieved when 8 mM of H₂O₂ is applied. No significant inactivation was observed when 2 mM H₂O₂ is applied, this concentration of H₂O₂ is much higher than that detected in common photocatalytic system (< 50 μM). The results show that H₂O₂ produced by common photocatalytic system is not harmful to bacterial cell, even they are produced continuously. However, when light irradiation of 200 mW cm⁻² , using Xenon lamp as lighting source, was applied to the system, the inactivation efficiency of H₂O₂ was significantly enhanced, which demonstrate the synergistic effect between the light irradiation and H₂O₂. The enhancement of inactivation by H₂O₂ can also be observed with light pretreated E. coli K-12, further confirms that light irradiation alter the physiology of the bacterial cell which increases their sensitivity to H₂O₂. / In order to find out the mechanism(s) of the synergism between the light irradiation and H₂O₂, RNA sequencing (RNA-Seq) was used to reveal the change of gene expression level of the E. coli under light irradiation. The mRNA level of most of the genes involve in catalase (CAT) and superoxide dismutase (SOD) expression, DNA repairing and intracellular iron regulation did not have significant increase or decrease. Only dps, fes and sodB showed significantly changes. Moreover, some genes that related to regulation of intracellular copper (cutA and cueR) and membrane composition (ompA, ompC, resX and gnsB) also showed significantly changes under light irradiation. After the RNA-Seq, ten genes were chosen as the possible target genes that related to the mechanism(s). Then the inactivation of E. coli BW25113 (parental strain) and the isogenic deleted mutants by H₂O₂ with light pretreatment were conducted and compared. Although the gene(s) that directly involved in the mechanisms of the synergy between H₂O₂ and light irradiation are not identified in the study, the results show that genes that are important to bacterial defense of oxidative damages, such those responsible for CAT and SOD expression and DNA repairing, are not involved in the mechanism(s). Increase of cell permeability and intracellular Fenton’s reagent content should be the main causes for the enhancement of H₂O₂ under light irradiation. / Finally, the inactivation efficiency of E. coli K-12 using AgBr/Ag/Bi₂WO₆ under different lighting sources is compared. The results show that inactivation efficiency under different emission wavelength are highly correlated with the optical absorption of the AgBr/Ag/Bi₂WO₆. Photocatalytic inactivation under two indoor lighting sources, LED lamps and Fluorescence tubes, also showed significant difference. The result of scavenger study under green LED lamps is completely different from those under other colour of LED lamps, indicates that emission wavelength also has great influence in photocatalytic inactivation mechanisms. / This study reveals the roles of H₂O₂ and light irradiation in photocatalytic inactivation and demonstrates the synergism between the H₂O₂ and light irradiation. The influence of the properties of light irradiation, including the light intensity and major emission wavelength, on the ROSs production by photocatalyst is also reported as well. This study not only provides a new perspective to the importance of light irradiation, H₂O₂ and the physiology of bacteria in photocatalytic inactivation, but a new approach in the investigation of photocatalytic inactivation mechanisms as well. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Ng Tsz Wai. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 111-131). / Abstracts also in Chinese.

by Fong Wai-lan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 138-152). / Text in English; abstracts in English and Chinese. / by Fong Wai-lan. / Acknowledgements --- p.i / Abstracts --- p.ii / Contents --- p.vi / List of figures --- p.xii / List of Plates --- p.xviii / List of tables --- p.xix / Abbreviations --- p.xxi / Chemical equations --- p.xxiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Pentachlorophenol --- p.1 / Chapter 1.1.1 --- Characteristics of pentachlorophenol --- p.1 / Chapter 1.1.2 --- Use of pentachlorophenol --- p.4 / Chapter 1.1.3 --- Annual consumption and regulations for the use of pentachlorophenol --- p.4 / Chapter 1.1.4 --- Pentachlorophenol in the environment --- p.4 / Chapter 1.1.5 --- Toxicity of pentachlorophenol --- p.5 / Chapter I. --- Mechanism --- p.5 / Chapter II. --- Toxicity towards plant and animals --- p.7 / Chapter III. --- Toxicity towards human --- p.7 / Chapter 1.2 --- Treatments of pollutant --- p.9 / Chapter 1.2.1 --- Physical treatment --- p.9 / Chapter 1.2.2 --- Chemical treatment --- p.9 / Chapter 1.2.3 --- Biological treatment --- p.12 / Chapter 1.2.4 --- Advanced Oxidation Processes (AOPs) --- p.14 / Chapter Chapter 2 --- Objectives --- p.28 / Chapter 3 --- Materials and methods --- p.29 / Chapter 3.1 --- Chemical reagents --- p.29 / Chapter 3.2 --- Photocatalytic reactor --- p.29 / Chapter 3.3 --- Determination of pentachlorophenol concentration --- p.31 / Chapter 3.4 --- Optimization of reaction conditions for UV-PCO --- p.34 / Chapter 3.4.1 --- Batch system --- p.34 / Chapter 3.4.1.1 --- Effect of initial hydrogen peroxide concentration --- p.34 / Chapter 3.4.1.2 --- "Effect of initial titanium dioxide concentration, light intensity and initial pH" --- p.34 / Chapter 3.4.1.3 --- Effect of initial pentachlorophenol concentration and irradiation time & determination of total organic carbon (TOC) removal during UV-PCO --- p.36 / Chapter 3.4.2 --- Continuous system --- p.36 / Chapter 3.5 --- Optimization of reaction conditions for VL-PCO --- p.38 / Chapter 3.5.1 --- "Effect of VL source, initial hydrogen peroxide, titanium dioxide concentration，light intensity, pH and reaction volume" --- p.38 / Chapter 3.5.2 --- Effect of initial pentachlorophenol concentration and irradiation time & determination of total organic carbon (TOC) removal during VL-PCO --- p.39 / Chapter 3.6 --- Optimization of reaction conditions for S-PCO --- p.39 / Chapter 3.6.1 --- "Effect of initial hydrogen peroxide, titanium dioxide concentration，light intensity and pH" --- p.39 / Chapter 3.6.2 --- Effect of irradiation time & determination of total organic carbon (TOC) removal during S-PCO --- p.41 / Chapter 3.7 --- Modification of photocatalytic oxidation --- p.41 / Chapter 3.7.1 --- Buffering system --- p.41 / Chapter 3.7.2 --- Immobilized titanium dioxide system --- p.41 / Chapter 3.7.2.1 --- Preparation of titanium dioxide coated spiral column --- p.41 / Chapter 3.7.2.2 --- Effect of flow rate for the UV-PCO (continuos- buffering/immobilized titanium dioxide) system --- p.43 / Chapter 3.8 --- Estimation of pentachlorophenol degradation pathway by photocatalytic oxidation --- p.43 / Chapter 3.9 --- Evaluation for the toxicity change of pentachlorophenol during the degradation process --- p.43 / Chapter 3.9.1 --- Microtox® test --- p.43 / Chapter 3.9.2 --- Amphipod survival test --- p.45 / Chapter Chapter 4 --- Results --- p.47 / Chapter 4.1 --- Determination of pentachlorophenol concentration --- p.47 / Chapter 4.2 --- Optimization of reaction conditions for UV-PCO --- p.47 / Chapter 4.2.1 --- Batch system --- p.47 / Chapter 4.2.1.1 --- Effect of initial hydrogen peroxide concentration --- p.47 / Chapter 4.2.1.2 --- Effect of initial titanium dioxide concentration --- p.54 / Chapter 4.2.1.3 --- Effect of light intensity --- p.54 / Chapter 4.2.1.4 --- Effect of initial pH --- p.54 / Chapter 4.2.1.5 --- Effect of initial pentachlorophenol concentration and irradiation time & determination of total organic carbon (TOC) removal during UV-PCO --- p.61 / Chapter 4.2.2 --- Continuous system --- p.61 / Chapter 4.3 --- Optimization of reaction conditions for VL-PCO --- p.69 / Chapter 4.3.1 --- Effect of VL source --- p.69 / Chapter 4.3.2 --- Effect of initial hydrogen peroxide concentration --- p.69 / Chapter 4.3.3 --- Effect of initial titanium dioxide concentration --- p.69 / Chapter 4.3.4 --- Effect of light intensity --- p.76 / Chapter 4.3.5 --- Effect of initial pH --- p.76 / Chapter 4.3.6 --- Effect of reaction volume --- p.76 / Chapter 4.3.7 --- Effect of initial pentachlorophenol concentration and irradiation time & determination of total organic carbon (TOC) removal during VL-PCO --- p.83 / Chapter 4.4 --- Optimization of reaction conditions for S-PCO --- p.83 / Chapter 4.4.1 --- Effect of initial hydrogen peroxide concentration --- p.83 / Chapter 4.4.2 --- Effect of initial titanium dioxide concentration --- p.90 / Chapter 4.4.3 --- Effect of initial pH --- p.90 / Chapter 4.4.4 --- Effect of irradiation time & determination of total organic carbon (TOC) removal during S-PCO --- p.90 / Chapter 4.5 --- Modification of photocatalytic oxidation --- p.96 / Chapter 4.5.1 --- Buffering system --- p.96 / Chapter 4.5.2 --- Immobilized titanium dioxide system --- p.104 / Chapter 4.6 --- Estimation of pentachlorophenol degradation pathway by photocatalytic oxidation --- p.104 / Chapter 4.7 --- Evaluation of the toxicity change of pentachlorophenol during photocatalytic oxidation --- p.104 / Chapter 4.7.1 --- Microtox® test --- p.104 / Chapter 4.7.2 --- Amphipod survival test --- p.112 / Chapter Chapter 5 --- Discussion --- p.116 / Chapter 5.1 --- Determination of pentachlorophenol concentration --- p.116 / Chapter 5.2 --- Optimization of reaction conditions for UV-PCO --- p.116 / Chapter 5.2.1 --- Batch system --- p.116 / Chapter 5.2.1.1 --- Effect of initial hydrogen peroxide concentration --- p.116 / Chapter 5.2.1.2 --- Effect of initial titanium dioxide concentration --- p.117 / Chapter 5.2.1.3 --- Effect of light intensity --- p.119 / Chapter 5.2.1.4 --- Effect of initial pH --- p.119 / Chapter 5.2.1.5 --- Effect of initial pentachlorophenol concentration and irradiation time & determination of total organic carbon (TOC) removal during UV-PCO --- p.120 / Chapter 5.2.2 --- Continuous system --- p.120 / Chapter 5.3 --- Optimization of reaction conditions for VL-PCO --- p.121 / Chapter 5.3.1 --- Effect of visible light (VL) source --- p.121 / Chapter 5.3.2 --- Effect of initial hydrogen peroxide concentration --- p.121 / Chapter 5.3.3 --- Effect of initial titanium dioxide concentration --- p.122 / Chapter 5.3.4 --- Effect of light intensity --- p.123 / Chapter 5.3.5 --- Effect of initial pH --- p.124 / Chapter 5.3.6 --- Effect of reaction volume --- p.124 / Chapter 5.3.7 --- Effect of initial pentachlorophenol concentration and irradiation time & determination of total organic carbon (TOC) removal during VL-PCO --- p.124 / Chapter 5.4 --- Optimization of reaction conditions for S-PCO --- p.125 / Chapter 5.4.1 --- Effect of initial hydrogen peroxide concentration --- p.125 / Chapter 5.4.2 --- Effect of initial titanium dioxide concentration --- p.126 / Chapter 5.4.3 --- Effect of initial pH --- p.127 / Chapter 5.4.4 --- Effect of irradiation time & determination of total organic carbon (TOC) removal during S-PCO --- p.127 / Chapter 5.5 --- Modification of photocatalytic oxidation --- p.128 / Chapter 5.5.1 --- Buffering system --- p.128 / Chapter 5.5.2 --- Effect of flow rate on removal efficiency for the UV-PCO (continuos-buffering/immobilized titanium dioxide) system --- p.129 / Chapter 5.6 --- Estimation of pentachlorophenol degradation pathway by photocatalytic oxidation --- p.130 / Chapter 5.7 --- Evaluation for the toxicity change of pentachlorophenol during photocatalytic oxidation --- p.132 / Chapter 5.7.1 --- Microtox® test --- p.132 / Chapter 5.7.2 --- Amphipod survival test --- p.133 / Chapter Chapter 6 --- Conclusions --- p.135 / Chapter Chapter 7 --- References --- p.138 / Appendix i --- p.153 / Appendix ii --- p.154 / Appendix iii --- p.154

by Wong Kin-hang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 99-127). / Text in English; abstracts in English and Chinese. / by Wong Kin-hang. / Acknowledgements --- p.i / Abstracts --- p.ii / Contents --- p.vi / List of Figures --- p.ix / List of Tables --- p.x / Abbreviations --- p.xi / Chemical Equations --- p.xii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Poly chlorinated biphenyls --- p.1 / Chapter 1.1.1 --- Characteristics of polychlorinated biphenyls (PCBs) --- p.1 / Chapter 1.1.2 --- Use of polychlorinated biphenyls --- p.3 / Chapter 1.1.3 --- World-wide production of polychlorinated biphenyls --- p.7 / Chapter 1.1.4 --- Polychlorinated biphenyls in the environment --- p.8 / Chapter 1.1.5 --- Toxicity of polychlorinated biphenyls --- p.12 / Chapter I. --- Mechanism --- p.12 / Chapter II. --- Toxicity towards plant and animals --- p.13 / Chapter III. --- Toxicity towards human --- p.14 / Chapter IV. --- Enzymatic induction by PCBs --- p.14 / Chapter V. --- Carcinogenicity of PCBs --- p.18 / Chapter 1.2 --- Treatments of pollutant --- p.19 / Chapter 1.2.1 --- Physical treatment --- p.19 / Chapter 1.2.2 --- Chemical treatment --- p.20 / Chapter 1.2.3 --- Biological treatment --- p.22 / Chapter 1.2.4 --- Photocatalytic oxidation (PCO) --- p.25 / Chapter Chapter 2 --- Objectives --- p.35 / Chapter Chapter 3 --- Materials and methods --- p.36 / Chapter 3.1 --- Chemical reagents --- p.36 / Chapter 3.2 --- Photocatalytic oxidation reactor --- p.36 / Chapter 3.3 --- Separation and determination of eight PCB congeners --- p.39 / Chapter 3.4 --- Determination of tetra-CB concentration --- p.40 / Chapter 3.5 --- Determination of PCO intermediates and products --- p.41 / Chapter 3.6 --- Optimisation of reaction conditions for UV-PCO in batch system --- p.44 / Chapter 3.6.1 --- Control experiments and effect of initial titanium dioxide concentration --- p.44 / Chapter 3.6.2 --- Effect of initial hydrogen dioxide concentration and UV intensity --- p.44 / Chapter 3.6.3 --- Effect of initial titanium dioxide concentration and initial pH --- p.45 / Chapter 3.7 --- Estimation of tetra-CB degradation pathway by photocatalytic oxidation --- p.45 / Chapter 3.8 --- Evaluation for the toxicity of hydrogen peroxide and toxicity change of tetra-CB during PCO by Microtox® test --- p.45 / Chapter 3.9 --- Determination of H202 concentration after PCO --- p.47 / Chapter Chapter 4 --- Results --- p.50 / Chapter 4.1 --- Separation and determination of eight PCB congeners --- p.50 / Chapter 4.2 --- Photocatalytic oxidation of mono-CB --- p.50 / Chapter 4.3 --- Determination of tetra-CB --- p.55 / Chapter 4.4 --- Optimisation of reaction conditions for UV-PCO in batch system --- p.56 / Chapter 4.4.1 --- Control experiments and effects of initial titanium dioxide concentration --- p.56 / Chapter 4.4.2 --- Effect of initial hydrogen peroxide concentration and UV intensity --- p.56 / Chapter 4.4.3 --- Effect of initial titanium dioxide concentration and initial pH --- p.60 / Chapter 4.5 --- Estimation of tetra-CB degradation pathway by photocatalytic oxidation --- p.71 / Chapter 4.6 --- Evaluation for the toxicity of hydrogen peroxide and toxicity change of tetra-CB by Microtox® test --- p.72 / Chapter 4.7 --- Determination of H202 concentration after PCO --- p.72 / Chapter Chapter 5 --- Discussion --- p.89 / Chapter 5.1 --- Separation and determination of eight PCB congeners --- p.89 / Chapter 5.2 --- Photocatalytic oxidation of mono-CB --- p.89 / Chapter 5.3 --- Determination of tetra-CB --- p.90 / Chapter 5.4 --- Optimisation of reaction conditions for UV-PCO in batch system --- p.90 / Chapter 5.4.1 --- Control experiments and effects of initial titanium dioxide concentration --- p.91 / Chapter 5.4.2 --- Effect of initial hydrogen peroxide concentration and UV intensity --- p.91 / Chapter 5.4.3 --- Effect of initial titanium dioxide concentration and initial pH --- p.93 / Chapter 5.5 --- Estimation of tetra-CB degradation pathway by photocatalytic oxidation --- p.95 / Chapter 5.6 --- Evaluation for the toxicity of hydrogen peroxide and toxicity change of tetra-CB by Microtox® test --- p.96 / Chapter 5.7 --- Determination of H202 concentration after PCO --- p.97 / Chapter Chapter 6 --- Conclusions --- p.98 / Chapter Chapter 7 --- References --- p.99

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

No description available.

Metal-Ethylenediaminetetraacetic acid (EDTA) complexes are found in a variety of industrial process. The stability of the formed complexes makes these compounds often inert to conventional wastewater treatment systems. In this work, the photocatalytic oxidation of NiEDTA was investigated as a means of breaking up the chelated nickel. The studied variables included the light intensity rate, the catalyst (TiO2), oxygen and NiEDTA concentrations. Photocatalytic experiments showed that increasing the catalyst concentration (0.5-3.0 g/L) decreases the light penetration inside the reactor resulting in a decrease in the reaction rate. The effect of oxygen and NiEDTA concentration was shown to exhibit Langmuir-Hinshelwood type kinetics. Total organic carbon (TOC) did not show any significant mineralization of NiEDTA for all investigated conditions. As a result, the by-products of the reaction were measured and found to include ED3A (ethylenediaminetriacetic acid), N-N'-EDDA (ethylenediamindiaacetic acid), IDA (iminodiacetic acid), oxalic acid, oxamic acid, glyoxylic acid, formaldehyde, ammonia, nitrate and nitrite. ED3A was found to be the major by-product of the reaction and nitrogen added from NiEDTA was found to be released as ammonia nitrogen. Oxygen consumption experiments were demonstrated as an effective way to monitor the rate of the reaction through measurement of the electron oxygen utilization rate. Nickel precipitation experiments showed that some of the by-products of NiEDTA degradation formed complexes with nickel. Finally, a light distribution model was generated using a CFD software (Fluent 6.1.22). For the catalyst concentration range of 0.5 to 3.0 g/L, this model showed that all of the light energy supplied by a centered UV lamp is absorbed within a one centimeter distance. Using the local volumetric rate of energy absorption (LVREA) calculated from the model the rate of the reaction was expressed in terms of quantum yield. For experiments carried out with air the quantum yield showed that the degradation rate was limited from an insufficient oxygen supply for electron scavenging. Increasing the oxygen concentration to 0.60 mmole O2/L increased the quantum yield for the highest light intensity rate; however the quantum yield never reached an optimum value thus indicating that other limiting conditions exist.

Advanced oxidation processes are capable of removing organic compounds that cannot be removed by conventional water treatment methods. Among the oxidation processes, photo-catalysis using titanium dioxide (TiO2) is a promising method but suffers from rapid electron-hole recombination rates and only absorbs UV light which is a small percentage (5 percent) of the total solar radiation. Therefore there is a need to reduce the recombination rates and also extend the absorption of the photo-catalyst into the visible region which constitutes 55 percent of the total solar radiation. The major aims of this study were to prepare plasmon metal decorated and doped TiO2 photo-catalysts immobilized on quartz substrates and test their photo-catalytic and antimicrobial activities. The effect of film thickness (loading) and use of different shapes of plasmon metal nanostructures was investigated. TiO2 thin films were prepared by a sputter coating technique while plasmon metal (Au & Ag)/carbon co-doped TiO2 by a simple sol gel process and plasmon metal films were prepared by the thermal evaporation technique. Different plasmon metal nanostructures (nanorods, dendrites, nanowires and spherical nanoparticles) were prepared using a wet chemical technique using sodium borohydride as the reducing agent. Nanocomposites of co-doped TiO2 photo-catalyst and plasmon elements of different proportions were also prepared. The prepared photo-catalysts were coated onto etched and MPTMS (3-Mercaptopropyl trimethoxysliane) treated quartz glass substrate which is a stable support favouring easy recovery. The prepared materials were characterized by XRD, HRTEM, TEM, HRSEM, FT-IR, SEM, PIXE and TGA while the doped TiO2 was characterized by XPS, BET, CHNS and Raman Spectroscopy. The effect of pH of solution, presence of other contaminants and salts in solution, initial concentration of the model pollutant and type of the plasmonic elements on the photocatalytic activity of TiO2 towards 4-(4-sulfophenylazo)-N,N-dimethyl aniline (methyl orange) were also investigated. The selected TiO2 photo-catalyst films were tested for antimicrobial properties. The effect of different types of plasmon elements on the antimicrobial activity of TiO2 against E. coli ATCC 3695 was evaluated under both sunlight and weak UV light. Under UV light, Ag showed the highest enhancement in photo-catalytic activity of TiO2 than Au and Cu. The photo-catalytic activity of TiO2 increased with an increase in Ag content to an optimum loading and then started to decrease with a further increase in loading. For Cu and Au, photo-activity activity increased with an increase in plasmon metal content. Under sunlight, Cu showed the highest enhancement of TiO2 photocatalytic compared to Ag and Au. The change in order of deposition showed that Au films enhanced the photo-activity better when they were deposited underneath rather than on top of TiO2 on quartz supports but Ag films performed better in enhancing photo-activity when they were deposited on top of TiO2. The use of bimetallic layers and three layer systems of different plasmon elements enhanced photo-catalytic activity better than the use of a monometallic layer. The presence of other organic contaminants and salts in solutions was found to reduce the photo-degradation of methyl orange due to preferential adsorption of other contaminants. When the pH was increased, the photocatalytic activity of TiO2 towards methyl orange was reduced. In antimicrobial studies, it was found that the plasmon elements greatly improved the antibacterial action of TiO2 against Escherichia coli ATCC 3695 in water and the best antibacterial action was observed with silver/carbon co-doped TiO2 photo-catalyst under sunlight The doped samples consisted of polydisperse nanoparticles which were found to be beneficial for photo-catalytic activity enhancement under sunlight.