Magister Scientiae - MSc (Chemistry) / The increasing cost of fossil fuel energy production and its implication in environmental pollution and climate change created high demand for alternative and renewable sources of energy. This has led to great interest in research in the field of photovoltaic or solar cells Due to the abundance of sunlight, the technology is sustainable, non-polluting and can be implemented at places where power demand is needed, for example in rural areas. Solar cell devices that have been commercialized are currently based on silicon technology, involving the use of monocrystalline, polycrystalline and amorphous silicon. Although they produce highly efficient solar cells, the cost of Si solar cells is too high. Second generation solar cell materials such as cadmium telluride and third generation materials such as perovskites and organic polymers have been receiving much attention recently. However, they lack the efficiency of Si solar cells. This research proposes the development of high energy conservation photovoltaic cells from novel low-cost organosilicon polymers. The aim was to develop novel highly branched organosilane polymers such as poly(3-hexythiophene), polydi(thien-2-yl)dimethylsilane, poly(3-hexyl- [2,2'] bithiophenyl-5-yl)-dimethyl-thiophen-2yl-silane) as electron donors along with zinc oxide nanorod as the electron acceptor which were able to bring the efficiency of the resultant photovoltaic cell close to that of current Si solar cell. / 2021-08-31

Magister Scientiae - MSc / The main hypothesis in this study is the development of a nanocomposite mediated amperometric biosensor for detection of hydrogen peroxide. The aim is to combine the electrochemical properties of both polyaniline and ferrocenium hexafluorophosphate into highly conductive nano composites capable of exhibiting electrochemistry in non acidic media; shuttling electrons between HRP and GCE for biosensor applications. / South Africa

Philosophiae Doctor - PhD / Polyamic acid-polypyrrole (PAA/PPy) composite films were prepared and characterised for the use as conducting platforms in the design of biosensor systems. The thin films were synthesised by electrochemical method from a solution containing controlled molar ratio of chemically synthesised polyamic acid (PAA) and pyrrole monomer. Homogenous films were obtained incorporating PAA into electropolymerised polypyrrole (PPy) thin film. The concentration of PAA (1.37 × 10-6 M) was kept fixed throughout the composite ratio analysis, whilst the concentration of PPy was varied from 1.9 × 10-3 M to 9.9 × 10-3 M. The PAA/PPy thin films were electrodeposited at a glassy carbon electrode (GCE) and characterised using Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy, Atomic Force microscopy (AFM), Scanning electron microscopy (SEM) and electrochemical (CV, SWV) techniques. The composition that best represented the homogenous incorporation of PAA into PPy matrix was observed at a PAA/PPy ratio of 1: 4.13 × 10-3. This composite was observed to have two sets of coupled peaks with formal potential 99 mV and 567 mV respectively. The De determined from cyclic voltammetry using the anodic peak currents were found to be twice as high (5.82 × 10-4 cm2/s) as the De calculated using the cathodic peak currents (2.60 × 10-4 cm2/s), indicating that the composite favours anodic electron mobility. Surface morphology and spectroscopy data support the formation of a homogenous polymer blend at the synthesis ratio represented by composite 3. For the construction of a biosensor the spectroscopic and electrochemical properties of the enzyme, luciferase and the analytes i.e naphthalene and fluoranthene were evaluated. Fluorescence spectroscopy studies were carried out to characterize the enzyme’s bioluminescence response in PBS at pH 7. Luciferase showed an absorption peak at 340 nm. The bioluminescence properties of the enzyme with the analytes were explored by fluorescence spectroscopy. The emmision peak at 340 nm gradually decreased as the concentration of each analyte was increased respectively.

Philosophiae Doctor - PhD / The thesis presents a simple, sensitive, low cost and a novel graphenated polyaniline doped tungsten trioxide nanocomposite, as an electrochemical sensor for the detection and quantitative and determination of PAHs, which are ubiquitous, toxic, as well as dangerous organic pollutant compounds in the environment. The selected PAHs (anthracene, phenanthrene and pyrene) in wastewater were given priority as a result of their threat to human nature and that of the environment. In order for a healthy, non-polluted and well sustainable environment, there is need for an instrument that is capable of detecting and quantifying these organic pollutants onsite and also for constant monitoring. The nanocomposites were developed by chemical and electrochemical methods of preparations, exploiting the intrinsic properties of polyaniline, graphene and tungsten trioxide semiconducting materials. Chemically, graphene-polyaniline (GR-PANI) nanocomposite was synthesised by in situ polymerisation method, then casted on a surface of glassy carbon electrode to form GR-PANI modified electrode. The properties of the prepared electrode were investigated through morphological and spectroscopic techniques, which confirmed the formation of the composite. The electroactivity of the prepared modified electrode revealed great improvement in cyclic and square wave voltammetric response on anthracene. A dynamic range of 2.0 × 10-5 to 1.0 × 10-3 M and detection limit of 4.39 x 10-7 M was established.

>Magister Scientiae - MSc / Current water treatment technologies do not remove many endocrine disruptor compounds (EDCs) such as 17α-ethynylestradiol (EE2) in its entirety, and the amount of these pollutants that continues to enter the aquatic environment through wastewater effluents is still capable of causing harmful health effects. Therefore the development of simpler and more sensitive biosensor system for detection of EE2 must be developed which have high responsiveness, low cost and easy handling. Therefore the aim of this study was to work towards the development of rapid test system of polyaniline-laccase on gold enzyme nanobiosensor (PANI-PSSA/Lac/Glu) for water estrogens. Preliminary studies were first done on the materials used in this study: estrogens, laccase, gold nanoparticles (AuNPs), and electropolymerized PANI-PSSA. Laccase was shown to be active towards EE2 and the enzyme could be stored for over three months. EE2 solution also could be used for over three months. Buffer used in this study was found to be suitable. Phosphoric acid (H3PO4) was a suitable electrolyte than hydrochloric acid (HCl) to be used for the electropolymerization of aniline and was used because it has same ions as the McIlvaine buffer (McIlB) which the post-deposition CVs indicated the formation of electrochemically very stable film. AuNPs were successfully synthesized and its size was identified to be less than 22 nm. McIlB used for testing electrochemical properties of AuNP. CVs of GC/PANI-PSSA and GC/PANIPSSA/ Au showed no difference before and after exposure to aq. EE2 solution, an indication of being re-usable and could also serve as stable immobilising platform in laccase biosensor. When interrogating with electrochemical impedance spectroscopy (EIS), the charge transfer resistance (Rct) of both GC/PANI-PSSA and GC/PANI-PSSA/Lac/Glu showed an average increase by about 2.4% and 21% before and after exposure of EE2, respectively. This shows that the GC/PANI-PSSA/Lac/Glu was a functional EE2 biosensor and showing a positive step towards achieving a re-usable biosensor for EE2 as a model water estrogen. Future work Page | vi will focus on exploring different ways of improving the biosensor’s surface regeneration and its sensitivity to EE2.

Philosophiae Doctor - PhD / To meet a fast-growing market demand for next generation portable electronic devices with higher performance and increased device functionalities, efficient electrical energy devices with substantially higher energy, power densities and faster recharge times such as supercapacitors are needed. The overall aim of this thesis was to synthesize nanostructured sulphonated polyaniline and transition metal single, binary and ternary mixed oxide doped nanocomposites with electro-conductive properties. These nanocomposites were anchored on activated graphitic carbon and used in design of asymmetric supercapacitors. Tantalum(IV)oxide, tantalum(IV)oxide-nickel(II)oxide, tantalum(II)oxide-manganese(III)oxide, tantalum(II)oxide-nickel(II)oxide-manganese(II,III)oxide nanoparticles were synthesised using modified sol-gel methods. These were then dispersed, individually, in acidic media through sonication and incorporated in-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped with poly(4-styrene sulphonic acid). These novel polymeric nanocomposites were characterised with FTIR, UV-visible, TEM, SEM, EDS, XRD to ascertain successful polymerization, doping, morphology and entrapment of the metal oxide nanoparticles. SECM approach curves and interrogation of CV revealed that these nanocomposites are conductive and electro-active. The cells showed good supercapacitor characteristics with high specific capacitances of 170.5 Fg⁻¹ in TaO₂- PANi-PSSA, 166.1 Fg⁻¹ in TaO₂-NiO-PANi-PSSA, 248.4 Fg-1 in TaO-Mn₂O₃-PANi- PSSA and 119.6 Fg⁻¹ in TaO-NiO-Mn₃O₄-PANi-PSSA. Their corresponding energy densities were calculated as 245.5 Whg⁻¹, 179.4 Whg⁻¹, 357.7 Whg⁻¹ and 172.3 Whg⁻¹ respectively. They also gave respective power densities of 0.50 Whg⁻¹, 0.61 Whg⁻¹, 0.57 Whg⁻¹ and 0.65 Whg⁻¹ and showed good coulombic efficiencies ranging between 77.97% and 83.19%. These materials are found to have a long cycle life and therefore good electrode materials for constructing supercapacitor cells. / National Research Foundation (NRF)

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-01-20Bitstream added on 2014-06-13T18:53:39Z : No. of bitstreams: 1 soares_la_me_ilha.pdf: 1532013 bytes, checksum: 0f4004d265a97a7015b084d2b64eb7b7 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho apresenta a preparação de um silsesquioxano nanoestruturado, o cloropropilsilsesquioxano (S) que foi organofuncionalizado com os seguintes agentes modificadores: 4-amino-3-hidrazinico-5-mercapto-1,2,4-triazol (Purpald®) e o 4-amino-5-4(piridil)-4H-1,2,4-triazol-3-tiol (APTT), os materiais obtidos dessa funcionalização foram descritos como SP e SA, respectivamente. Os materiais SP e SA foram caracterizados por diversas técnicas espectroscópicas: Espectroscopia na região do infravermelho (FT-IR), Ressonância magnética nuclear 29Si e 13C no estado sólido (RMN), Difração de Raios- X (DRX), Espectroscopia de Energia Dispersiva de Raios X (EDX), Termogravimetria e Análise Térmica Diferencial (TG – DTA). Após a devida caracterização, realizaram-se estudos de adsorção de íons metálicos (Cu2+, Cd2+ e Ni2+) nos sítios ativos do SA, porém, curiosamente não se observou a mesma capacidade de sorção pelo SP. Diferentes meios foram estudados no processo de adsorção dos íons metálicos supracitados: aquoso, etanólico 99% e etanólico 42%, determinando-se o tempo de equilíbrio de adsorção, que para ambos os meios e metais esse tempo máximo foi em média 35 min. Determinado o tempo de equilíbrio de adsorção dos íons metálicos em cada sistema, determinou-se a capacidade específica de sorção (Nfmax) através de isotermas de adsorção. Para o Cu2+, os valores de Nf foram: meio aquoso (3,09 × 10-4 mol g-1), etanólico 42% (1,03 × 10-4 mol g-1) e etanólico 99% (1,86 × 10-4 mol g-1), com concentrações de íons Cu2+ variando de 1,74 a 29,64 mol L-1. Os valores encontrados para o Ni2+ foram: em meio aquoso (2,11 × 10-4 mol g-1), etanólico 42% (0,97 × 10-4 mol g-1) e etanólico 99% (1,05 × 10-4 mol g-1), com concentrações de íons Ni2+ variando de 2,25 a 33,18 mol L-1. Para os íons cádmio não foram... / This work presents the preparation of a nanostructured silsesquioxane, the cloropropilsilsesquioxano (S) that was organofunctionalised with the following modifying agents: 4-amino-3-hydrazino 5 - mercapto 1,2,4 triazole (Purpald ®) and 4- amino-5-4 (pyridyl)-4H-1,2,4-triazole-3-thiol (APTT), the materials obtained of the functionalization were described as SP and SA, respectively. The materials SA and SP were characterized by various spectroscopic techniques such as spectroscopy in the region of infrared (FTIR), nuclear magnetic resonance 29Si and 13C solid-state (NMR), X-ray diffraction (XRD), Energy Dispersive Spectroscopy Rays (EDS), Thermogravimetry and Differential Thermal Analysis (TG - DTA). After proper characterization, were carried studies on adsorption of metallic ions such as Cu2+, Ni2+ and Cd2+ in the active sites of SA, but curiously did not observe the same sorption capacity of the SP. Different methods were studied in the adsorption of metal ions above: aqueous, 99% ethanolic and 42% ethanolic, determining the adsorption equilibrium time, which for both means and metals the maximum time averaged 35 min. After determining the adsorption equilibrium time of metal ions in each system, we determined the specific sorption capacity (Nfmax) through adsorption isotherms. For Cu2+, the values of Nf were: aqueous solution (3.09 × 10-4 mol g-1), 42% ethanolic (1.03 × 10-4 mol g-1) and 99% ethanolic (1.86 × 10-4 mol g-1), with Cu2 + ion concentrations ranging from 1.74 to 29.64 mol L-1. The values obtained for the Ni2+ were: aqueous solution (2.11 × 10-4 mol g-1), 42% ethanolic (0.97 × 10-4 mol g-1) and 99% ethanolic (1.05 × 10-4 mol g-1), with Ni2 + ion concentrations ranging from 2.25 to 33.18 mol L-1. For the cadmium ions were not observed saturation of adsorption sites in the concentration range studied, not getting the maximum... (Summary complete electronic access click below)

Submitted by TAMIRES ROCHA SOUZA (tami.rs.farm@gmail.com) on 2018-05-02T19:18:53Z No. of bitstreams: 1 DEFESA - VERSÃO FINAL.pdf: 3139508 bytes, checksum: fd4ffb1d470a0125ed405e09475c39eb (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-05-02T20:06:54Z (GMT) No. of bitstreams: 1 souza_tr_me_ilha.pdf: 3139508 bytes, checksum: fd4ffb1d470a0125ed405e09475c39eb (MD5) / Made available in DSpace on 2018-05-02T20:06:54Z (GMT). No. of bitstreams: 1 souza_tr_me_ilha.pdf: 3139508 bytes, checksum: fd4ffb1d470a0125ed405e09475c39eb (MD5) Previous issue date: 2018-03-09 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho descreve a preparação de partículas formadas a partir de Pentacianonitrosilferrato (III) de sódio e Cloreto de cádmio. As partículas foram preparadas em quatro proporções empregando os solventes Água/Formamida (100:0; 80:20; 40:60; 0:100) com o objetivo de investigar a sua influência na morfologia, topologia e nas propriedades eletrocatalíticas das partículas. Os materiais foram caracterizados por técnicas espectroscópicas e eletroquímica tais como: Espectroscopia na região do infravermelho (FTIR), Espectroscopia Raman, Reflectância difusa (UV-visível), Difração de raios-X (DRX), Microscopia eletrônica de varredura (MEV), Espectrometria de energia dispersiva de raios-X (EDS), Microscopia eletrônica de transmissão (MET) e voltametria cíclica (VC). Após as caracterizações foram realizados estudos sobre as propriedades eletroquímicas dos materiais utilizando um eletrodo de pasta de grafite. Dos quatro sistemas estudados, apenas dois foram sensíveis à concentrações de isoniazida, a saber o CdNP-3 e CdNP-4. Ambos os sistemas apresentaram duas regiões lineares de sinal em função da concentração com limites de detecção de 6,80×10-5 mol L-1 e 7,07×10-4 mol L-1, e 2,18×10-4 mol L-1 e 1,16×10-3 mol L-1 para os sistemas CdNP-3 e CdNP-4, respectivamente. Para o sistema CdNP-3 observou-se uma sensibilidade amperométrica de 23,96 mA mol L-1 e 10, 83 mA mol L-1, já para CdNP-4 observou-se uma sensibilidade amperométrica de 17,80 mA mol L-1 e 5,79 mA mol L-1 para cada região linear. / The present work describes the preparation of particles formed from Sodium Pentacyanonitrosylferrate (III) and Cadmium Chloride. The particles were prepared in four ratios using solvents Water / Formamide (100:0, 80:20, 40:60, 0:100) to investigate the influence on particle morphology, topology and electrocatalytic properties. The materials were characterized by spectroscopic and electrochemical techniques such as: Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Diffuse reflectance (UV-Visible), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) and Cyclic voltammetry (CV). After the characterization studies, the electrochemical properties of materials were performed using a graphite paste electrode. Of the four systems studied, only two tests with concentrations of isoniazid, CdNP-3 and CdNP-4. Both systems presented two linear concentrations with detection limits of 6.80 × 10-5 mol L-1 and 7.07 × 10-4 mol L-1 and 2.18 × 10-4 mol L-1 and 1.16 × 10-3 mol L-1 for the CdNP-3 and CdNP-4 systems, respectively. For the CdNP-3 system, an amperometric sensitivity of 23.96 mA mol L-1 and 10.83 mA mol L-1 was observed, whereas for CdNP-4 an amperometric sensitivity of 17.80 mA mol L-1 and 5.79 mA mol L-1 for each linear region.

Philosophiae Doctor - PhD / In this work we primarily set out to investigate the technique of Aqueous Chemical Growth as a means of producing WO3 thin films that find applications in gas sensing and electrochromism. For the first time we demonstrated in this work, the heterogenous nucleation and growth of WO3 thin films on plain glass substrates and F-doped SnO2-glass substrates. This was achieved without the use of surfactants and template directing methods, using as a precursor solution Peroxotungstic Acid generated from the action of 30% H2O2 on pure W powder. The substrates used needed no surface-modification. On the plain glass substrates (soda lime silicates) a variety of micronanostructures could be observed prime of which were nanoplatelets that acted as a basic building block for the self-assembly of more hierarchical 3-d microspheres and thin films. On FTO a wide variety of micro-/nanostructures were observed dominant amongst which were urchin-like microspheres. The dominant crystallographic structure observed (through X-ray diffraction analysis, SAED, HRTEM) for the WO3 thin films on both substrate types post-annealing at 500 ˚C for a period of 1 - 2 h, was hexagonal-WO3. Next was monoclinic WO3. On rarer occasions the formation of triclinic and cubic WO3 was observed. The thin films produced showed a fairly high degree of porosity and had thicknesses in the range of 900 nm - 3.5 μm. I-V characterisation measurements using a 4-point collinear probe Keithley source alongside photoluminescence was used to establish the insulating nature of some of the films as well as their sub-stoichiometric nature. X-ray Photoelectron Spectroscopy was used to confirm the substoichiometric nature of some of the films.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-10-17T13:06:24Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Giselle BANCA.pdf: 2438394 bytes, checksum: 8b3d0cc9d7991a7ac011cdf4cdccabaf (MD5) / Made available in DSpace on 2016-10-17T13:06:24Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Giselle BANCA.pdf: 2438394 bytes, checksum: 8b3d0cc9d7991a7ac011cdf4cdccabaf (MD5) Previous issue date: 2016-02-29 / FACEPE / A esquistossomose é um sério problema de saúde pública, é uma doença negligenciada e intimamente relacionada com baixos índices de desenvolvimento social. Neste trabalho, foi realizada uma detecção eletroquímica de DNA Schistosoma mansoni com base em uma monocamada auto-montada de ácido mercaptobenzóico (MBA) imobilizando nanoestruturas compostas por nanopartículas de ouro (AuNPs) e nanopartículas de magnetita (Fe3O4_NPs). Espectroscopia de impedância eletroquímica (EIS) e voltametria cíclica (CV) foram utilizadas para monitorar o evento de bioreconhecimento do sistema de MBA-Fe3O4_NPs-AuNPs-DNAsonda revela uma resposta eletroquímica eficaz indicando a modificação da superfície. O biosistema proposto foi capaz de reconhecer sequências de nucleótidos específica de S. mansoni presente em amostras de soro e líquido cefalorraquidiano (LCR) em diferentes concentrações de DNA do genoma. O resultado do bioreconhecimento gerou um aumento na resistência de transferência de elétrons e uma diminuição dos picos de corrente em concentrações de DNA durante as medições eletroquímicas. A plataforma desenvolvida mostrou um limite de detecção do DNA de 0,781 e 0,685 pg.μL- 1 para soro e LCR respectivamente. Portanto, o biossensor obtido pode ser considerado como um instrumento útil para a detecção especifica de S. mansoni em baixas concentrações em vários fluidos biológicos. / Schistosomiasis is a neglected disease closely related to the low levels of social development and a serious public health problem. In this work, we performed an electrochemical detection of Schistosoma mansoni DNA with a self-assembled monolayer of mercaptobenzoic acid (MBA) immobilizing nanostructures composed by gold nanoparticles (AuNPs) and magnetite nanoparticles (Fe3O4_NPs). Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) were used to monitor the biorecognition event. MBA-Fe3O4_NPs-AuNPs-DNAprobe system reveals an effective electrochemical response indicating the surface modification. The proposed biosystem was capable to recognize specific nucleotide sequence of S. mansoni present in cerebrospinal fluid (CFS) serum samples at different genome DNA concentrations. The biorecognition results in an increase in the electron transfer resistance and a decrease of the current peaks at higher DNA concentrations during electrochemical measurements. The developed platform showed a DNA detection limit of 0.781 and 0.685 pg.μL- 1 for serum and CFS, respectively. Therefore, the obtained biosensor can be considered as a useful tool for specific detection of S. mansoni at low concentrations in various biological fluids.