Submitted by MARCIA ROVADOSCHI (marciar@unifra.br) on 2018-08-16T18:59:45Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_JoseFranciscoZavagliaMarques.pdf: 2049396 bytes, checksum: 211f0a7be1dce3b826d2fc80c01e126e (MD5) / Made available in DSpace on 2018-08-16T18:59:45Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_JoseFranciscoZavagliaMarques.pdf: 2049396 bytes, checksum: 211f0a7be1dce3b826d2fc80c01e126e (MD5) Previous issue date: 2014-03-27 / The photocatalytic and photoelectrochemical degradation of Rhodamine 6G dye was studied using TiO2 , TiO2 doped with N , TiO2 thin films prepared by thermal decomposition of polymeric precursors and titanates prepared by hydrothermal synthesis method. The materials synthesized by thermal decomposition of polymeric precursor method were heat-treated at 450 ° C and in the hydrothermal synthesis TiO2 in anatase phase in 40 g / L NaOH at 20 bar was thermally treated at 200 ° C. The obtained compounds were characterized by X- ray diffraction, nitrogen adsorption using the BET method and the morphology was observed by using atomic force microscopy and scanning electron microscopy. The results demonstrate that the obtaining nanostructures are titanium dioxide in the pure anatase phase and titanates, with specific areas ranging from 45 to 63 m2/g for TiO2 and 120 to 510 m2/g for titanates. Adsorption tests were performed to determine the equilibrium parameters and with the photocatalytic tests the kinetic parameters were determined. The adsorption capacity was correlated with the specific area and TiO2 in the anatase phase exhibits the higher efficiency for dye degradation and in removal of total organic carbon. The galvanostatic method with the TiO2 electrode illuminated with UV radiation shows higher degradation rate and higher removal of total organic carbon. / Neste trabalho foi estudada a degradação fotocatalítica e fotoeletroquímica do corante rodamina 6G utilizando TiO2, TiO2 dopado com N, filmes finos de TiO2 preparados pelo método da decomposição térmica de precursores poliméricos e titanatos preparados por síntese hidrotermal. Os materiais sintetizados pelo método da decomposição térmica de precursores poliméricos foram tratados termicamente a 450 °C e na síntese hidrotermal o TiO2 anatase foi tratado em meio de NaOH 40 g/L a 20 bar e 200 °C. Os compostos obtidos foram caracterizados por difração de raios-X, adsorção de nitrogênio pelo método BET e a morfologia foi observada por microscopia de força atômica e microscopia eletrônica de varredura. Os resultados comprovam a obtenção de nanoestruturas de dióxido de titânio na fase anatase pura e titanatos, com áreas específicas variando entre 45 a 63 m2/g para o TiO2 e 120 a 510 m2/g para os titanatos. Foram realizados testes de adsorção com a determinação dos parâmetros de equilíbrio e testes fotocatalíticos com a determinação dos parâmetros cinéticos. A capacidade de adsorção esta correlacionada com a área específica e TiO2 na fase anatase puro apresentou maior eficiência na degradação do corante e na remoção do carbono orgânico total. O processo galvanostático com o eletrodo de TiO2 iluminado com radiação UV mostrou maior velocidade de degradação do corante e maior remoção do carbono orgânico total.

Color filters enable photosensors to obtain spectral composition of incoming radiation, be it to mimic human vision or to separate analytical signals. Efforts to increase the resolution of these photosensors lead to decrease in size of individual picture elements – pixels, which places increasing demands on the color filter technology. Conventional color filters operating on the principle of absorption of light in organic pigments are frequently used, but they are no longer meeting growing requirements of increasing sensor resolution. Here, metasurfaces comes to an aid, utilizing nanostructures to separate colors and thus creating structural coloration. There are many approaches to separate colors using metasurfaces, but each carries certain disadvantages with their principle of operation. In this thesis, we present a novel approach to separate colors which utilizes manipulation of radiation polarization. The presented color filter is first modeled and optimizes through numerical simulations and then manufactured using nanofabrication methods. Finally, the optical response of nanostructures is verified by several optical spectroscopy methods.

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / To replace the conventional wastewater treatment technology, photocatalysis has the best potential due to its utilization of visible light to photodegrade organic and inorganic contaminants. However, agglomeration of nanoparticles leads to serious decrease in photocatalytic performance when applied in slurry form, due to hindrance effect. TiO2 semiconductor photocatalyst mediated advanced oxidation process is referred to as one of the most efficient technologies to degrade organic pollutants in water. However, TiO2 semiconductor for water purification hinders large scale applicability due to poor activity under visible light and the recombination of photogenerated electron and hole pairs. The modification of TiO2 semiconductor photocatalyst with carbon dots (CDs) is of high importance due to low toxicity, aqueous stability, enhanced surface area, economic feasibility, good biocompatibility and chemical inertness of CDs. Herein, strategies are highlighted to improve the activity of TiO2 semiconductor photocatalyst by coupling it with CDs and Fe2O3. In this study, we study the morphological influence of TiO2 nanostructures on photocatalytic degradation of tetracycline hydrochloride present in industrial wastewater. TiO2 nanostructures, nanotubes, nanospheres and nanofibers were Synthesized using the hydrothermal technique. TiO2 nanotubes, nanofibers and nanospheres were prepared by the hydrothermal treatment of TiO2 nanoparticles with different NaOH concentrations (5, 10 and 12 N) at 120 and 140 ˚C; afterwards, HCl was added until it reached pH 2. Both the crystalline phase and coordination of the TiO2 nanotubes, nanofibers and nanospheres were composed principally. Likewise, the surface area, pore volume and pore size of the TiO2 nanotubes, nanofibers and nanospheres changed with the NaOH rinsing treatment. The photocatalytic activity for tetracycline degradation were strongly enhanced by the nanofibers and nanotubes in the basic and acid media, respectively, showing a relationship between their structure and the medium. TiO2 nanostructures and the composite material were characterized by scanning electron microscope\SEM), X-Ray Diffraction (XRD), transmission electron microscope (TEM) and Fourier transform infrared (FTIR). BET surface area analysis was carried out using nitrogen adsorption desorption curves. The results show that TiO2 morphology had great influence on photocatalytic degradation of tetracycline hydrochloride due to difference in specific surface area and pore volume of nanostructures. The photocatalytic degradation experiments were carried out for three hours under visible-LED light. TiO2 nanofibers show better degradation performance than nanotubes and nanospheres due to presence of large surface area for reaction, higher porosity with dispersion of active sites at different length scales of pores and presence of oxygen vacancies. Agricultural biomass pine bark serves as a carbon source and was doped into TiO2-nanofibers (TNF) to fabricate the composite material (CD-TNF). CD-TNF composite nanofibers were prepared via a facile hydrothermal method. This study revealed that the photocatalytic efficiency of tetracycline (TC) under visible light irradiation of the composite nanofiber is higher than that of pure TiO2-nanofiber. The anchored CDs can both enhance the light absorption and suppress photogenerated electron hole recombination which results in the enhancement of catalytic and antibacterial properties. The CDs can better capture and transfer photogenerated electrons through the Ti-O-C and Fe-O-C bonds. Moreover, CDs can improve the utilization of photogenerated electrons and the electrons in CDs are captured by O2 to produce O2•- radicals and the role of O2•- radicals in the photocatalytic process is significantly improved. A new efficient photocatalyst consisting of TiO2/CD/Fe2O3 composite material was Synthesized by the hydrothermal treatment and applied in the photodegradation of 5 mg/L tetracycline hydrochloride (TC) under visible-LED light. The CDs/TiO2/Fe2O3 composite showed enhanced photocatalytic performance for tetracycline photodegradation when compared with TiO2/CDs and pure TiO2 under the visible light irradiation. The mechanism of the improved photocatalytic activity over CDs/TiO2/Fe2O3 was also investigated. The influence of the interface formation between Fe2O3 and TiO2/CDs affects severely the charges separation efficiency and enhances the electron transfer to keep on the existence of Fe3+/Fe2+ moieties that take significant role in the reaction mechanism.

Dye-sensitized solar cells (DSC) have attracted considerable scientific and industrial interest during the past decade as an economically feasible alternative to conventional photovoltaic devices. DSCs have the potential to be as efficient as silicon solar cells, but at a fraction of the cost of silicon solar cells. The unique advantage of DSC compared to conventional solar cells is that the light absorption, electron transport and hole transport are handled by different components which reduces the chance of recombination. In the present work, to facilitate DSC with good energy conversion efficiency, its performance have been evaluated as a function of titania layer morphology, redox couple concentration and the catalytic layer on the counter electrode. The results that are obtained in the present investigations have been organized as follows Chapter 1 gives a brief exposure to DSC technology. Special emphasize has been on the structure and individual components of the DSC. Chapter 2 describes various experimental techniques that are employed to fabricate and characterize DSCs under study. Chapter 3 presents a systematic study of the characteristics of DSC made of three different types of electrodes namely: TiO2 nanotubes (TNT) which have excellent electron transport properties, TiO2 microspheres (TMS) which possess high surface area and light scattering ability and TiO2 nano particles (TNP) possessing high surface area. The electronic, morphological, optical and surface properties of individual electrodes are studied. The highest efficiency of 8.03% is obtained for DSCs prepared with TMS electrodes. A higher value of effective diffusion coefficient (Deff) and diffusion length (Ln) of electrons as obtained by electrochemical impedance spectroscopy (EIS) analysis confirms a high charge collection efficiency in microsphere based cell. Chapter 4 gives a detailed study of DSCs fabricated with a tri-layer photo anode with TNTs as light scattering layer. The tri-layer structure has given an enhanced efficiency of 7.15% which is 16% higher than TNP based cell and 40% higher than TNT based cells. Chapter 5 deals with the investigations on the effect of concentration of redox couple on the photovoltaic properties of DSC for different ratios of [I2] to [LiI] (1:2, 1:5 and 1:10) with five viii concentrations of I2 namely 0.01 M, 0.03 M, 0.05 M, 0.08 M and 0.1M in acetonitrile. It is found that the open circuit potential (Voc) decreases with increase in the ratio of redox couple whereas short circuit current density (Jsc) and fill factor (FF) increase. The reason for the decline in Voc is the higher recombination between electrons in the conduction band of TiO2 and the I3- ions present in the electrolyte, induced by the absorptive Li+ ions. In addition using EIS it is found that the τ improves with the increase in [LiI] at a particular [I2], whereas at a fixed [I2]/ [LiI] ratio the increase in [I2] is found to reduce the τ and Deff due to the enhanced recombination. Chapter 6 describes the application of carbon based counter electrode (CE) materials for DSCs. Two counter electrode materials have been investigated namely (1) Multiwalled carbon nanotubes (MWCNT) synthesized by pyrolysis method and (2) Platinum decorated multiwalled carbon nanotubes (Pt/MWCNT) prepared by chemical reduction of platinum precursors. Using Pt/MWCNT composite electrode the DSC achieved an energy conversion efficiency of 6.5 %. From the analysis on symmetric cells, it is found that electro catalytic activity of Pt/MWCNT CE is similar to that of platinum CE, though the platinum loading is very less for the former. This is attributed to the effective utilization of catalyst owing to high surface area arising from the increased surface roughness. Chapter 7 discusses the application of titanium foil in place of glass substrate for the photo anode. The titanium foil offers fabrication of flexible DSC. The performance of DSC with TMS layers and aligned titania nanotube arrays (TNA) prepared by anodization method is studied. Compared to TMS based cell, TNA has given a better efficiency at a lower thickness. Chapter 8 presents the scheme used to seal DSCs and its stability analysis. We have employed the usual hot melt sealing for edge whereas hole sealing is carried out with tooth pick and a UV curable adhesive. The degradation in efficiency is found to be 20% for low efficiency cells whereas, for high efficiency cells it is found to be 45% after 45 days. The leakage of highly volatile acetonitrile through the edge and hole is found to be responsible for the reduction in the performance of the device. Hence a high temperature sealing method is proposed to fabricate stable cells. Chapter 9 gives summary and conclusions of the present work