PhD (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / This research has investigated the effects of conjugation on the visible light absorption capacity of polyene modified TiO2 nanoparticles as well as the efficiency of these nanoparticles for the mineralisation of acetaminophen (APAP), a non-antibiotic and chloramphenicol (CAP), an antibiotic pharmaceutical compound (PC) which are commonly used worldwide. The efficiency of polyene modified TiO2 (CPE-TiO2) compared with bare TiO2 was further assessed for the mineralisation of the selected PCs under visible light. To achieve this aim, the synthesised nanoparticles were appropriately characterised and tested for the photocatalytic degradation of acetaminophen (APAP) and chloramphenicol (CAP), under visible light. Furthermore, the mechanism and the kinetics of photocatalytic degradation of the PCs were investigated by using high-performance liquid chromatography (HPLC) to monitor the photodegradation intermediates, e.g. Hydroquinone, p-nitrophenol and oxamic acid. The DRS UV-vis spectra result of the CPE-TiO2 indicated that it has a lower band-gap than bare TiO2 nanoparticles and demonstrated a better absorption ability in the wavelength range of 400-800 nm. This result was further confirmed by other optical analyses, such as electrochemical impedance spectrometry (EIS) and photoluminescence (PL). The analysis indicated a less recombination rate of electron/hole pairs in CPE-TiO2 compared to TiO2. Notably, CPE-TiO2 nanocomposite exhibited higher photocatalytic properties for both pollutants, compared to bare TiO2 under visible light. Importantly, photocatalytic degradation experiments demonstrated that the CPE modified nanoparticles were significantly more efficient for PCs degradation (94.21 % for APAP and 80.47% for CAP) compared to bare TiO2 (27.12% for APAP and 36.12% for CAP). The role of CPE-TiO2 photocatalysis in degrading APAP and CAP was examined by varying experimental parameters such as PC concentrations, catalyst loading and solution pH. All the parameters were observed to influence the degradation of the PCs to some extent, albeit, at optimum conditions, most of these PCs were degraded within 210 minutes of visible light irradiation. A significant relationship between the ionic state (+ve or -ve based on the pH) of the solution and CPE-TiO2 photocatalytic process was observed. For the mineralisation, CPE-TiO2 photocatalysis led to higher oxidation rates compared to direct photolysis and bare TiO2 photocatalysis. The results confirm that the co-existence of multiple bonds in poly-conjugated carbon chains with a reduced band-gap in CPE-TiO2 composite were able to enhance charge separation and migration as well as improve the photocatalytic efficiency. This study has clearly demonstrated that polyene modified TiO2 nanoparticles can be applied to degrade PCs in aqueous solution and offers an attractive option for small-scale pharmaceutical wastewater treatment. However, the complex nature of real effluents with co-existing pollutants and higher levels of organic and inorganic matter may call for possible coupling of a biological process as pre- or post-treatment to improve their biodegradability.

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

Předkládaná diplomová práce se zabývá extrakcí nanočástic oxidu titaničitého z produktů osobní péče, konkrétně opalovacích krémů a následnou charakterizací těchto částic. Počet komerčně dostupných produktů s obsahem nanočástic TiO2 se neustále zvyšuje a to se sebou přináší potřebu vyhodnotit potenciální osud a nepřímou expozici TiO2 nanošástic o různých velikostí a tvarů a zkoumat jejich celý životní cyklus. Bylo zkoumáno použití ultrafiltrace a ultracentrifugace jako extrakční metody. Dvě metody pro extrakci TiO2 nanočástic byly vyvinuty a aplikovány na vzorky opalovacích krémů. Extrahované částice mohou být použity pro ekotoxikologické studie, případně experimenty v mesokosmu. Velikost částic byla stanovena pomocí metody dynamického rozptylu světla a transmisní elektronové mikroskopie.