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Photocatalytic degradation of parabens in aqueous solutions with modified tungsten oxide nanoparticles

- Ngigi, Eric Mwangi

  • Authors: Ngigi, Eric Mwangi
  • Date: 2018
  • Subjects: Water - Purification - Photocatalysis , Photocatalysis , Environmental chemistry , Nanoparticles
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/295325 , uj:32157
  • Description: Abstract: Continuous release of pollutants into water systems has been of great concern to the scientific community because it has adverse effects on living organisms and the ecosystem. Among the most common pollutants that are released into the water systems are pharmaceutical and personal care products (PPCPs). The pollutants are introduced to environmental matrices through hospitals, industrial and domestic wastes. The class associated with personal care products are known as parabens which are endocrine disrupting compounds that have been in use for close to a century. Their release to the wastewater is in minute concentrations but known to interfere with endocrine systems. Scientists have been able to come up with ways of actually degrading these micropollutants using various methods that include among others, ultraviolet, sonochemical and semiconductors. Among the mentioned methods, semiconductors have been commonly used for degradation of these pollutants. Among the most commonly used semiconductor is Titania (TiO2) nanomaterial with the advantage of being available and non-toxic to the environment with its limitation in absorbing UV light as opposed to visible light. This study reported the use of modified tungsten trioxide nanomaterials for the degradation of selected parabens. This was achieved by modifying tungsten trioxide using metal, semiconductor and non-metal doping. The morphological features of the as-synthesized nanomaterials were studied using the following analytical instruments XRD, SEM/EDS, UV-Vis, TGA, HRTEM, FTIR, and Raman. Further, the as-synthesized nanomaterials were employed in use of environmental and biomedical applications on the basis of their physiochemical features. Mostly the application was based on the degradation of selected parabens in synthetic and real wastewater samples and biomedical applications focusing on the toxicity of tungsten trioxide. Thus, the semiconductor for use, in both environmental and biomedical applications. The following are highlights of results obtained in Chapters 4-7... , Ph.D. (Chemistry)
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First–principles studies on the development of semiconductor–based photocatalyst materials for applications in photocatalytic water splitting and degradation of pollutants

- Opoku, Francis

Photodegradation of dye effluent whilst monitoring the fate and behaviour of TiO2 in a simulated photocatalytic treatment plant

- Mahlalela, Lwazi Charles

  • Authors: Mahlalela, Lwazi Charles
  • Date: 2017
  • Subjects: Photocatalysis , Water - Purification - Photocatalysis , Titanium dioxide , Nanocomposites (Materials) , Dyes and dyeing - Environmental aspects
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/235955 , uj:24140
  • Description: M.Sc. (Chemistry) , Abstract: Titania (TiO2) has been seen as one of the best semiconductor photocatalysts capable to photodegrade organic pollutants from water. This presents a method that textile industries can use to remove organic dyes from their effluents before release. The photocatalytic activity of TiO2 nanoparticles was conducted to also examine the influence of electron acceptors on the removal of dyes from water. The interaction between TiO2 nanoparticles and industrial dyes is inevitable because of the possible application of TiO2 in the removal of dyes in textile effluents. Therefore, the possible application of TiO2 in the removal of dyes compels understanding the stability of TiO2 as influenced by industrial dyes and different abiotic factors. This is important for risk assessment purposes. The stability of TiO2 nanoparticles in the presence of disperse dye-stuff was conducted as influenced by pH, ionic strength and type of electrolyte. These parameters also influenced the physicochemical properties of the nanoparticles. Understanding fate and behaviour of engineered nanomaterials (ENMs) in wastewater treatment plants (WWTPs) is important for the environmental risk assessment of ENMs. This is due to the appearance of ENMs in WWTPs that results from the wide spread application in consumer products and industrial applications. TiO2 has been reported as one of them. Thus, before environmental risk assessment can be conducted, studies at the points at which ENMs appear in high concentrations is important and WWTPs is one of them. Due to the in availability of nanoparticle test protocols, the Organisations of Economic Co-operation and Development (OECD) guidelines for testing of chemicals (303A) have been used by several researchers to study fate and behaviour of nanoparticles of interest. Therefore, the fate and behaviour of TiO2 nanoparticles was conducted following the OECD 303A. The findings of this study are summarised as follows:..
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Rare earth doped Titania/Carbon nanomaterials composite photocatalysts for water treatment

- Mamba, Gcina

  • Authors: Mamba, Gcina
  • Date: 2015-11-12
  • Subjects: Water - Purification - Photocatalysis , Nanostructured materials , Photocatalysis , Titanium dioxide
  • Type: Thesis
  • Identifier: uj:14557 , http://hdl.handle.net/10210/15090
  • Description: PhD. (Chemistry) , Pre-synthesised gadolinium oxide decorated multiwalled carbon nanotubes (MWCNT-Gd) were coupled with titania to form nanocomposite photocatalysts (MWCNT-Gd/TiO2) using a sol-gel method. Rare earth metal ions (Eu, Nd and Gd), nitrogen and sulphur tridoped titania were decorated on MWCNT-Gd to yield composite photocatalysts (MWCNT-Gd/Eu/Nd/Gd/N,S-TiO2) by a similar method, using thiourea as nitrogen and sulphur source. Different carbon nanomaterials were incorporated into tridoped titania to form various composite photocatalysts (MWCNT/Gd,N,S-TiO2, MWCNT/Nd,N,S-TiO2, SWCNT (single walled carbon nanotube)/Nd,N,S-TiO2 and rGO (reduced graphene oxide)/Nd,N,S-TiO2) via the sol-gel method. Likewise, gadolinium doped graphitic carbon nitride (g-C3N4-Gd3+) was obtained by heating a mixture of gadolinium nitrate hexahydrate and cyanoguanidine and subsequently hybridised with MWCNT/TiO2 using the sol-gel method to yield composite photocatalysts with varying g-C3N4-Gd3+ loadings. All the prepared photocatalysts were characterised by microscopic tools (FE/FIB-SEM-EDX, TEM), crystallographic technique (XRD), spectroscopic tools (UV-Vis, Raman and FT-IR) and nitrogen sorption technique (BET).
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Efficiency of modified WO3 nanoparticles on the photoreduction of metal ions in water

- Thwala, Mpendulo Mphumelelo

  • Authors: Thwala, Mpendulo Mphumelelo
  • Date: 2018
  • Subjects: Water - Purification - Photocatalysis , Photocatalysis , Doped semiconductors , Nanocomposites (Materials)
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/279265 , uj:29988
  • Description: M.Sc. (Chemistry) , Abstract: With an increased need for clean water in South Africa, there is a need to find more techniques for water purification. The improved standards required by the World Health Organization (WHO) has led to a quest of technological advancements in finding more effective and cost friendly techniques for water purification. The use of nanoparticles (semiconductor metal oxides) has emerged as a promising approach to purify water, removing pollutants from water to low concentrations that meet the WHO standards. Tungsten trioxide (WO3) is considered as one of the best semiconductor photocatalyst capable of photodegradading organic compounds. Pristine WO3 is, however not capable of photoreducing inorganic substances in water. Therefore, this work presents a modified WO3 to improve the photocatalytic activity in the photoreduction of Cr(VI) and Cu(II) in wastewater. The modification was carried out through doping with magnesium and yttrium metals respectively. Although these aforementioned dopant metals come costly, the synthesis routes and efficiency of the doped WO3 in the reduction of Cr(VI) and Cu(II) is worthwhile. The hydrothermal method was used to synthesize WO3, Mg doped WO3 and Y doped WO3 nanoparticles. In order to understand the structure of the synthesized nanoparticles, the nanoparticles were characterized using X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), Filed emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, zeta potential, Brunauer–Emmett– Teller (BET) surface area, UV-visible spectroscopy (UV-vis), X-Ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The as-synthesized materials were confirmed to be composed of crystalline monoclinic polymorphs as shown by the XRD, FTIR and Raman spectroscopy. The average crystallite size was found to be around 32 nm with an average particle strain of 0.002498. The particle sizes were found to be of 141 nm in average as confirmed by TEM. The difference in d spacing were observed for the doped nanoparticles...
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Photocatalytic performance of nitrogen-platinum group metal co-doped Tio2 supported on carbon nanotubes for visible-light degradation of organic pollutants in water

- Kuvarega, Alex Tawanda

  • Authors: Kuvarega, Alex Tawanda
  • Date: 2013-07-24
  • Subjects: Water purification , Water purification - Organic compounds removal , Organic water pollutants , Titanium dioxide , Photocatalysis , Nanotubes , Carbon
  • Type: Thesis
  • Identifier: uj:7665 , http://hdl.handle.net/10210/8533
  • Description: D.Phil. (Chemistry) , Elimination of toxic organic compounds from wastewater is currently one of the most important subjects in water-pollution control. Among the many organic pollutants are dyes and emerging pollutants such as natural organic matter (NOM). Dyes such as Eosin Yellow (EY), an anionic xanthene fluorescent dye, can originate from many sources such as textile industrial processes, paper pulp industries and agricultural processes. Most dyes are problematic because they are resistant to conventional chemical or biological water-treatment methods and therefore persist in the environment. NOM consists of a highly variable mixture of products found in water and soils. NOM is formed as a result of the decomposition of plant and animal material and is a precursor to the formation of disinfection by-products (DBP) during water disinfection. These organic compounds cause undesirable colour, taste and odour in water. NOM affects the capacity of other treatment processes to effectively remove organic micro-pollutants or inorganic species that may be present in the water. Its removal also uses up chemicals and energy and so it is expensive to treat. Titanium dioxide (TiO2) has emerged as one of the most fascinating materials in the modern era due to its semiconducting and catalytic properties. TiO2 is a large band-gap semiconductor that exists mainly in the anatase (band gap 3.2 eV) and rutile (band gap 3.0 eV) phases. Its response to UV light has led to increased interest in its application in the photocatalysis research field. It has been investigated extensively for its super hydrophilicity and use in environmental remediation and solar fuel production. In spite of extensive efforts to apply TiO2 for environmental remediation, photocatalytic activity in the visible region has remained quite low hence the ultimate goal of this research was to fabricate highly photoactive catalysts composed of non-metal, platinum-group metal (PGM) co-doped TiO2 and carbon nanotubes (CNTs) and to apply them for water purification using solar radiation...
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Molybdenum sulfide nanostructures : synthesis and their catalytic applications

- Madima, Ntakadzeni

  • Authors: Madima, Ntakadzeni
  • Date: 2017
  • Subjects: Water - Purification - Photocatalysis , Nanostructured materials , Polymeric composites , Photocatalysis , Molybdenum compounds
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/235780 , uj:24119
  • Description: M.Sc. (Nanoscience) , Abstract: Environmental pollution (i.e. water pollution) has been an issue of great concern across the globe. Water scarcity is reported to be a huge challenge throughout the world. The South Africa water capacity will decrease dramatically in the next 10 years due to various pollutants. Dye molecules such as Methyl Blue (MB) and Rhodamine B (RhB) and heavy metals such as Chromium (Cr(VI)) are reported to be the major cause of water pollution, which results in the scarcity of clean water for human use. These pollutants are present as harmful entities in the environment due to their carcinogenic and mutagenic nature. So, the sustainability of clean water is in greater demand for all forms of life relies upon its availability. Thus the aim of this study was to synthesize molybdenum sulfide nanostructures and its nanocomposite and evaluate their photocatalytic properties towards water treatment. Molybdenum sulfide nanostructures were synthesized via hydrothermal methods using different capping agents namely Polyethylene Glycol (PEG-400) and Ethylenediaminetetraacetic acid (EDTA) and the samples were named PEG-MoS2 and EDTA-MoS2 respectively. The nanocomposite was synthesized from EDTA-MoS2 and manganese chloride. As synthesized nanostructures and nanocomposite were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning electron microscope (SEM) equipped with Energy dispersive X-ray spectroscopy (EDS), Transmission Electron Microscope (TEM), and UV-Vis Spectroscopy. Rhodamine B and Methyl Blue were chosen as a model dyes for evaluation of photocatalytic degradation performance. Using PEG-MoS2, the degradation efficiency of 97.30% was achieved for RhB in 75 min and 98.05% for Methyl Blue was achieved in 90 min. EDTA-MoS2 also shows greater potential in the removal of both RhB and MB in aqueous solution; hence 85.46% and 99.78% removals of RhB and MB dyes respectively were achieved in 90 min. PEG-MoS2 nanostructure was also tested for the photocatalytic reduction of Cr(VI) and shows the reduction efficiency of 91.05% in 75 min. The nanocomposite was tested for the photocatalytic degradation of RhB, and results show the degradation efficiency of 98.78% in 75 min. All photocatalytic studies were done under visible light irradiation (Xenon lamp was used throughout).
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Biopolymer based nanocomposites for water treatment

- Anku, William Wilson

  • Authors: Anku, William Wilson
  • Date: 2017
  • Subjects: Photocatalysis , Biopolymers - Analysis , Water - Purification - Photocatalysis , Dyes and dyeing - Environmental aspects
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/261579 , uj:27583
  • Description: Ph.D. (Chemistry) , Abstract: The devastating effects of toxic organic pollutants on human health and the environment have necessitated the need to devise holistic techniques for their effective removal from polluted water. Among these pollutants are toxic organic dyes, which are resistant to biodegradation and therefore persist in the environment for a long period of time. These dyes are also resistant to chemical, physical and other conventional methods of water treatment. Although semiconductor photocatalysis is deemed as a holistic method for the judicious eradication of dye pollutants from water, the technology is hindered by some inherent problems including the fact that most of the photocatalysts are active under ultraviolet light (UV) instead of visible light due to their wide band gap. In addition, these photocatalysts have a fast recombination rate of the photogenerated holes and electrons, which are responsible for the photocatalytic degradation process. This research work was therefore designed to modify some selected metal oxide photocatalysts including TiO2, ZrO2, ZnO, Cu2O and ZnS with transition metals, non–metals and multiwalled carbon nanotubes (MWCNTs). It was envisaged that the modified catalysts would possess superior properties over their bare counterparts, overcome their limitation, and possess excellent photocatalytic properties for the effective removal of organic pollutants from water. Three different methods of synthesis were employed in this work. These include homogeneous co–precipitation, sol–gel, and in situ copolymerisation. All the catalysts synthesised in this work were characterised using X–ray powder diffraction (XRD),..
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Doped nanotitanium dioxide for photocatalytic applications

- Dlamini, Langelihle Nsikayezwe

Metal-decorated carbon nanostructures for photocatalytic reduction of CO2

- Leudjo Taka, Anny

Tin oxide nanomaterials : synthesis and their potential in photocatalysis

- Malindisa, Ramokone Christina

  • Authors: Malindisa, Ramokone Christina
  • Date: 2018
  • Subjects: Photocatalysis , Nanostructured materials
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/279594 , uj:30028
  • Description: M.Sc. (Nanoscience) , Abstract: The lack of easy access to clean water is an issue of great concern worldwide due to the fact that clean water is essential for life. Most water bodies are now contaminated with toxic organic pollutants, particularly textile dyes, as a result of the continuous discharge of industrial and agricultural wastewater into them. The presence of these contaminants in the water bodies pose serious threat to human health and aquatic life. The need for the appropriate technology for the removal of these pollutants from water has therefore become a subject of great interest in the scientific community. Semiconductors have been widely used as the photocatalytic degradation of organic dyes in wastewater. However, this process encounters certain challenges. These challenges include the fast recombination rate of the photogenerated electron-hole pairs and the inability of the photocatalysts to function under visible light due to their wide band energy gaps. Steps to synthesize semiconductors that are able to utilize visible light and reduce the recombination rate of the electrons and holes are under consideration. In this study, we strive to synthesize semiconductors for the photocatalytic degradation of dyes and further improve their photocatalytic performance by doping them with metals and non-metals to form nanomaterials with different morphologies by use of surfactants. Hydrothermal method of synthesis was adopted in the fabrication of the nanomaterials in this research work. All the synthesized catalysts were characterized by using X–ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis) spectroscopy, and energy dispersive spectroscopy (EDS). These techniques helped to obtain information on the nanomaterial’s structure, formation, morphology, size and elemental analysis. Firstly, a comparison study on the effect of surfactant on the photocatalytic degradation performance of SnO nanoparticle was performed on the methyl orange dye under visible light illumination with interesting results. These samples were also observed to be present in the tetragonal romarchite phase of SnO. The band gaps of the surfactant modified SnO samples were wider and their visible light activities poorer compared to the pure SnO...
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Preparation of doped nanotitanium dioxide (TIO2) immobilized on polyethersulphone (PES) nanofiberes for photocatalytic degradation of water pollutants

- Chabalala, Mandla Brian

  • Authors: Chabalala, Mandla Brian
  • Date: 2016
  • Subjects: Water - Purification - Photocatalysis , Photocatalysis , Nanofiltration , Titanium dioxide
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/84406 , uj:19216
  • Description: Abstract: As the world’s population continue to grow annually, the demand of drinking water also increases. Countries that are facing water scarcity are currently facing high demand rates of clean water. One of the major contributors to water scarcity is water pollution; this is often caused by the release of wastewater by various sectors which include factories, industries and laboratories, among others. Such wastewater contains toxic materials which end up in drinking water sources and these materials are suspected of being endocrine-disruptive-chemicals (EDCs). The increase in concentrations of contaminants (particularly dyes) in water show that conventional wastewater treatments methods are not efficient enough, hence advanced technologies such as Advanced Oxidation Processes (AOPs) should be implemented to treat persistent contaminants in water. AOPs are characterized by the production of highly reactive hydroxyl (HO•) and superoxide (O2-•) anion radicals, which are suitable for a rapid, continuous and indiscriminative reaction with organic compounds inducing almost complete degradation. Such AOPs include the Fenton’s process which uses peroxide-iron (II) (H2O2/Fe2+) as the Fenton reagent and Photocatalysis which makes use of semiconductors such as titanium dioxide (TiO2). AOPs are classified as clean technology for the treatment of wastewater and can degrade micro pollutants with reaction rate of up to 109 Lmol-1s-1 yielding CO2, H2O and inorganic ions as the final products Pristine and doped TiO2 photocatalysts were prepared using a modified sol-gel method in both acidic and basic medium. The loading of N was varied from 1 to 5 %. Polyethersulphone (PES) nanofibers were electrospun from a PES polymer solution that was prepared by dissolving PES in N,N-Dimethylfomamide (DMF) at room temperature overnight. The polymer solutions of concentration 18 to 29 % PES/DMF (m/m %) were obtained. The resulting solutions were electrospun at the following conditions: 20 - 25 cm tip to collector distance, 12 kV working voltage and 0.5 ml flow rate. The electrospinning of PES/Photocatalyst (PES/PC) nanofiber was performed under the optimized conditions of PES nanofibers. The photocatalysts loading was varied between 1.5, 2 and 2.5 % while PES was , M.Sc. (Chemistry)
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Nitrogen/palladium-codoped TiO² for efficient visible light photocatalytic dye degradation

- Kuvarega, Alex T., Krause, Rui W. M., Mamba, Bhekie B.

Fate and behavior of Bi₂O₃-BiVO₄ in wastewater treatment plant under an aerobic system

- Majotena, Dineo Nnana

Nanostructured TIO₂ based materials for the photocatalytic degradation of emerging organic pollutants from aqueous solution

- Sambaza, Shepherd Sundayi

  • Authors: Sambaza, Shepherd Sundayi
  • Date: 2019
  • Subjects: Nanostructured materials , Titanium dioxide , Photocatalysis , Sewage - Purification
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/401572 , uj:33568
  • Description: Abstract : Water is regarded as the most vital of natural resources for the sustainability of life, yet freshwater systems are directly threatened by pollution. Among the many pollutants are organic emerging pollutants such as synthetic chemicals and pharmaceuticals. Bisphenol A (BPA) and ibuprofen are examples of such a synthetic organic compounds. Current wastewater treatment technologies such as membrane technology, chemical treatment and biodegradation are not always efficient in removing toxic emerging organic pollutants. This is because they were not specifically designed to remove these contaminants. Photocatalysis on the other hand, has shown great potential to remove toxic emerging pollutants from the environment. Over the years, TiO2 catalyst has been used widely for water remediation applications. Surface modification of TiO2 is necessary to extend its use in the visible region of the solar spectrum and to reduce the inherent fast recombination rate of charges. Polyaniline (PANI)-wrapped TiO2 nanorods (PANI-TiO2), obtained through the oxidative polymerization of aniline at the surface of hydrothermally pre-synthesized TiO2 nanorods, were evaluated as photocatalysts for the degradation of BPA. Fourier-transform infrared spectroscopy (FTIR) analysis revealed the successful incorporation of PANI into TiO2 by the appearance of peaks at 1577 cm-1 and 1502 cm-1 that are due to the C=C and C=N stretch of the benzoid and quinoid. Brunauer- Emmett-Teller (BET) analysis revealed the presence of mesoporous material in PANI-TiO2. Transmission electron microscopy (TEM) analysis showed that TiO2 nanorods with different diameters were synthesized. The TEM analysis showed that a thin layer of PANI wrapped the TiO2 nanorods. X-ray diffraction (XRD) and Raman spectroscopy revealed that anatase phase TiO2 was synthesized with typical Raman vii vibration peaks at 637 cm-1, 514 cm-1, 396 cm-1, and 195 cm-1. X-ray Photon Spectroscopy (XPS) survey scan of the PANI-TiO2 nanocomposite revealed the presence of C, O, Ti, and N. Photocatalytic activity evaluation under UV radiation through the effect of key parameters, including, pH, contact time, dosage and initial concentration of BPA was carried out in batch studies. Within 80 min, 99.7% of 5 ppm BPA was attained using 0.2 g/L PANI-TiO2 photocatalyst at pH 10. PANI-TiO2 showed a better performance than as-synthesized TiO2 with a rate constant of 4.46 x 10-2 min-1 compared to 2.18 x 10-2 min-1. Nitrate ions increased the rate of degradation of BPA whilst humic acid consistently inhibited the degradation of BPA. LC-MS analysis identified degradation products with m/z 213.1, 135.1 and 93.1. The PANI-TiO2 nanocomposite was reused up to five cycles with a removal of at least 80% in the fifth cycle. PANI capped WO3@TiO2 nanocomposite prepared through a three–stage synthetic route was evaluated for the degradation of ibuprofen under visible light. XRD analysis confirmed the anatase phase of TiO2 and monoclinic and orthorhombic WO3 crystalline structures were formed. The XRD analysis confirmed that the phases were not affected by wrapping in PANI.TEM analysis confirmed that TiO2 nanorods were synthesized with different diameters. TEM analysis showed that a WO3@TiO2 heterojunction was formed. A PANI layer was wrapping the heterojunction was observed. Photoluminescence analysis revealed that pairing TiO2 and WO3 resulted in improved charge separation. The charge separation was further improved by wrapping the heterojunction in a PANI matrix. DRS calculations showed that pairing TiO2 with WO3 extended the band edge to about 420 nm thus facilitating the use of the nanocomposite in the visible region of the solar spectrum. XPS analysis revealed viii the presence of W, C, O, Ti, N, and their corresponding photo electron peaks were found to be W4f, W4d, C1s, O 1s, N1s, and Ti 2p. The degradation of ibuprofen was influenced by pH with maximum degradation observed at pH 9. The degradation conformed to the Langmuir-Hinshelwood kinetic model. The rate constant, K for the degradation of ibuprofen by WO3@TiO2 and PANI/WO3@TiO2 was 2.59 x 10-2 and 3.5 x 10-2 respectively that were significantly higher than that of pristine TiO2, which was 1.92 x10-2... , Ph.D. (Chemistry)
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Photocatalysis and energy cost analysis of Vanadia Titania thin films synthesis

- Akbarzadeh, Rokhsareh, Ibrahim, Qusay, Jen, Tien-Chien

Photodegradation of pesticides in water using metal doped multi-component heterojunction photocatalyst

- Molopo, Kgoetlana Charlie

  • Authors: Molopo, Kgoetlana Charlie
  • Date: 2019
  • Subjects: Photocatalysis , Water - Purification - Photocatalysis , Pesticides
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/401075 , uj:33502
  • Description: Abstract : For many years now, South Africa has been facing water crisis. Availability of clean water is lacking, and human population increases every year. Available water is contaminated with variety of pollutants such as microbials, organic and inorganic pollutants. This is because of increased industrial and agricultural practices to satisfy the growing population demand. Organic pollutants are prominent due to high agricultural production whereby pesticides and fertilizers are applied to optimize product output. Pesticides are of huge concern due to their persistence and toxic behaviour in the environment. They are found in rivers and ground water streams after application in the field via run-off or seep into ground. Chlorpyrifos is an organophosphate pesticide widely used to control pest. Chlorpyrifos has been detected at high levels in water in Western Cape of South Africa. Department of Agriculture in South Africa banned its use as an ingredient in domestic products and pesticides in 2010 but it is still detected in the environment. Chlorpyrifos is an endocrine disrupting chemical, nerve agent and causes dizziness. This pollutant can enter human body by ingestion, dermal adsorption or inhalation. The WHO limit of chlorpyrifos in water is 30 μg/L. Several methods have been used to remove chlorpyrifos and other pollutants in water such as biological treatment and advanced oxidation processes. Advanced oxidation processes are regarded as safe and efficient pollutant removal, removing a variety of pollutants in water. This is due to utilization of highly reactive species such as hydroxyl and superoxide radicals, known for their rapid and indiscriminative behaviour towards organic compounds resulting in a complete mineralization. Photocatalysis which is a semiconductor-based method emerged as a promising organic pollutant removal method. Tungsten trioxide (WO3) has been extensively studied for degradation of heavy metals and organic pollutants. But suffer from photogenerated charge vi recombination. To curb that, doping has been used with metal/non-metal dopant and by formation of heterojunction with another semiconductor catalyst to name a few. In this study, WO3 was successfully synthesized using a hydrothermal treatment method. It was further modified with Mn2+ ion and SnS2 to improve its photocatalytic activity towards chlorpyrifos degradation by formation of Mn-WO3/SnS2. Mn- WO3/SnS2 was formed with rectangular shapes confirmed through HRTEM and FESEM. A mixture of monoclinic and hexagonal phases was identified using XRD, Raman and SAED indexing. The optical and electrochemical properties of Mn-WO3/SnS2 were studied using EIS, PL and UV-Vis-DRS. Low emission intensity corresponding to less charge recombination, smaller semi-circle diameter corresponding to less charge transfer impedance and high visible light absorbance wavelength (582 nm) were observed in comparison to those of WO3 (466 nm), Mn-WO3 (472 nm), SnS2 (512 nm) and WO3/SnS2 (572 nm). Mn-WO3/SnS2 displayed good stability and increased surface area (77 m2/g) compared to WO3 (6 m2/g). The materials were mesoporous as determined by BET analysis with pore volumes in the range of 0.02 to 0.07. Except SnS2 which displayed porous adsorbent properties. The Mn-doped composite (Mn-WO3/SnS2) nanoparticles displayed high efficiency for the degradation of chlorpyrifos in synthetic water samples within 60 minutes. UHPLC-MS-MS was used to evaluate the concentration of chlorpyrifos and deduce the degradation pathway. Mn-WO3/SnS2 degraded up to 95% chlorpyrifos removal compared to 50, 65, 75, and 85% using WO3, Mn-WO3, SnS2 and WO3/SnS2 respectively. After optimization of conditions such as pH, initial chlorpyrifos concentration and initial photocatalyst loading, 100% chlorpyrifos removal was achieved at pH 7, 1 g of nanoparticles and 1000 ppb of chlorpyrifos concentration. The complete degradation of chlorpyrifos and its major degradation by-product TCP was achieved. vii TCP was completely degraded to innocuous materials. Kinetic studies were deduced to a second order reaction at 209x10-3 M-1s-1. , M.Sc. (Chemistry)
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Photocatalytic reduction of selenium oxyanions in water using a semiconductor-like metal-organic framework coupled with black phosphorus

- Machabaphala, Kamogelo Martha

  • Authors: Machabaphala, Kamogelo Martha
  • Date: 2020
  • Subjects: Photocatalysis , Water - Purification - Selenium removal , Phosphorus , Reduction (Chemistry)
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/458477 , uj:40724
  • Description: Abstract: The water crisis has been an issue in South Africa and the whole world. The increase in population limits the supply of freshwater leading to a lack of clean water. Most of the available water is contaminated with various pollutants such as organics, inorganics, and microbial. Inorganic pollutants, in particular, are of interest because they are toxic and non-biodegradable. Anions and metals are inorganic pollutants of main environmental concern. Specifically, in this work, the presence of the two toxic selenium oxidation states, i.e. Se(IV) and Se(VI) in water is the main concern. Amongst the methods investigated for the removal of these anions from wastewater advanced oxidative processes (AOPs), specifically photocatalysis is the most attractive technique. In this work, the challenge is designing a visible light active, efficient, and reusable photocatalyst for the reduction of toxic Se(IV) and Se(VI). Metal-organic frameworks (MOFs) have attracted worldwide attention in photocatalysis application due to their outstanding properties, more specifically UiO- 66 because of its stability. However, UiO-66 suffers from low separation efficiency of photogenerated charge carriers and can only absorb UV light. UiO-66-based heterostructure have become a solution to enhance photocatalytic properties of UiO-66. In this study a series of FL-BP/UiO-66 heterostructures with various contents of UiO-66 were prepared by sonication method. Using X-ray diffraction (XRD) and selected area electron diffraction (SAED), the synthesized UiO-66 was found to be amorphous whereas Few Layers of Black Phosphorus (FL-BP) was crystalline. The XRD patterns of the heterostructures had characteristic peaks of both starting materials indicating that the heterostructures were formed. Laser Raman spectroscopy and Fourier transform-infrared (FTIR) spectroscopy revealed functional groups typical of both UiO-66 and FL-BP whereas the elements attributable to these materials were observed from X-ray photoelectron spectroscopy (XPS) and electron dispersive spectroscopy (EDS). Transmission electron microscopy (TEM), scanning electron microscopy (SEM) showed that the heterostructure composed of both UiO-66 and BP, with the nanocubes of UiO-66 embedded on the nanosheet of BP. A redshift in the position of absorption peaks of the heterostructures relative to that of UiO-66 was observed indicating that the v intended consequence of compositing UiO-66 with FL-BP was achieved. On the other hand, photoluminescence (PL) and electrochemical (EIS) studies showed that the heterostructures had lower electron-hole recombination rates compared to virgin UiO-66 and FL-BP. The Mott-Schottky plots confirmed p-n type heterojunction. Formation of the heterostructure promoted the separation of photogenerated charge carriers and enhanced visible light absorption. The conditions (solution pH, the mass of photocatalyst, pollutant initial concentration, and reductant concentration) in which the activities of the heterostructures towards the photoreduction of Se(IV) and Se(VI) were assessed were optimized using virgin UiO-66. Using these conditions, it was found that the heterostructures had higher photocatalytic activities compared to pristine UiO-66, FL-BP, and bulk BP. Heterostructure FL/U(40) showed the highest photocatalytic activity of all the materials tested. The reduction of Se(IV) and Se(VI) followed the first-order reaction. Also, FL/U(40) was shown to perform consistently high over 5 photocatalytic cycles with a total loss in activity of less than 10 %. The increased photocatalytic activity exhibited by the composites was attributed to a combination of phenomena that occurred upon the excitation of the heterostructures. These include the ability of the materials to absorb visible light and the cross-flow of the electrons and holes at the interfaces of the two materials. , M.Sc. (Chemistry)
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Photodegradation of a selected antiretroviral drug from South Africa's effluent with a heterostructure of few layer black phosphorus-niobium oxide nanoparticles (FL-BP/Nb2O5)

- Bhembe, Yoliswa Anittah

  • Authors: Bhembe, Yoliswa Anittah
  • Date: 2020
  • Subjects: Photocatalysis , Water - Purification - Photocatalysis
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/458412 , uj:40716
  • Description: Abstract: Over the years, viral infections such as influenza, herpes, and hepatitis have widely spread, with the human immunodeficiency virus (HIV) becoming even rifer. Antiretroviral (ARVs) drugs have been formulated to suppress virus activity in the body and prevent the transmission of these viruses effectively. However, the invention has come at a price as the drugs and their excreted metabolism/breakdown products generates have since generated pharmaceutical waste. With their continuous production and consumption, the pharmaceutical waste has found its passage to the central water systems, contributing to the depletion of the quality of water. The principal culprits that perpetuate the occurrence of these pollutants in various water bodies are the wastewater treatment plants (WWTPs). South Africa, facing non-ending droughts, has its hydrologic cycle unrefreshed, compelling the nation to resort to the use of recycled water. However, the removal and breaking down of these contaminants of emerging concern has thus far been a challenge and blocking access to clean and safer drinking water. A few to none effective technologies have been developed to degrade ARVs in water specifically. There is a need, therefore, to develop effective techniques to remove these pollutants, and thus purify water. Heterogeneous photocatalysis, with the use of nanomaterials, has emerged as one of the promising technologies that can be incorporated in the WWTPs to increase their efficiency. Thus, this work presents the use of a novel nanocomposite of niobium (V) oxide nanoflowers intercalated into the walls of few-layer black phosphorus (FL-BP@Nb2O5) for the photodegradation of nevirapine. Nevirapine is an ARV drug that is frequently detected from the central water bodies... , M.Sc. (Chemistry)
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