Le développement de photocatalyseurs en couches minces supportées constitue un intérêt majeur autorisant une séparation efficace des produits de réaction, en dépit d’une réduction de leur surface spécifique par rapport à des nanopoudres du même matériau. La synthèse de revêtements de TiO2 par pulvérisation cathodique magnétron en condition réactive fait l’objet de recherches intensives. Cette technique permet de contrôler, à travers les paramètres d’élaboration, la structure et les propriétés physicochimiques et photocatalytiques des revêtements.Afin de s’affranchir de la contamination du catalyseur par le sodium du verre lors de traitements en température ou lors de recuits de couches déposées à l’ambiante, une barrière de diffusion en SiNx est intercalée et son épaisseur est fixée pour la suite de l’étude. Différentes couches de TiO2 ont été élaborées à haute pression dans un réacteur doté d’un système de contrôle en boucle fermée basé sur la spectroscopie d’émission optique. L’effet de la cristallisation in situ à différentes températures sur les différentes propriétés des revêtements TiO2 a été étudié et les propriétés de ces derniers ont été comparées à celles des échantillons synthétisés sur des substrats froids et recuits ex situ aux mêmes températures.Enfin, des premiers travaux portant sur l’influence de l’introduction de l’argent en différentes teneurs sur l’efficacité photocatalytique sous lumière visible des couches de TiO2 cristallisées in situ et ex situ sont présentés. / The development of supported photocatalysts thin films is of major interest allowing an efficient separation of the reaction products, in spite of their specific area reduction compared to nanometric scale powders. The synthesis of TiO2 coatings by reactive magnetron sputtering is the subject of intensive researches. This technique allows, trough the control of the deposition parameters, to manage the structure and the physicochemical and photocatalytic properties of the coatings. In order to hinder the sodium contamination of the catalyst from the glass substrate, either during in situ or ex situ heating of the coating, a SiNx diffusion barrier is intercalated with a fixed thickness. Different layers of TiO2 were prepared at high pressure in a reactor equipped with a closed-loop control system based on optical emission spectroscopy. The influence of the in situ crystallization at different temperatures on the properties of the TiO2 coatings was studied. These properties were compared with those of samples synthesized ex situ and at the same temperatures. Finally, first studies on the influence of silver enrichment at different contents on photocatalytic activity under visible light of TiO2 layers crystallized in situ and ex situ, are presented.

Photocatalysis is an advanced oxidation process, which has shown to possess an enhanced capability to remove a wide range of contaminants. It involves the use of a semiconductor photocatalyst and a photon source. Photocatalysis has several advantages such as mild reaction conditions like ambient temperature and pressure, good control over the reaction and faster reaction kinetics. Semiconductor photocatalysts such as TiO2, ZnO, Fe2O3, CdS, ZnS, etc. absorbs light of energy greater than or equal to its band gap and the electron in the valence band gets excited to conduction band leaving behind the hole in valence band. These charge carrier pair results in the formation of various reactive oxygen species such as hydroxyl and superoxide radicals which results in the degradation of chemical contaminants and inactivation of microorganisms. TiO2 is the most widely used catalyst in photocatalytic studies because of its high photocatalytic activity, non-toxicity and wide availability. Anatase phase TiO2 has been reported to possess higher photocatalytic activity than the rutile phase. Although there are several methods to synthesize TiO2, solution combustion synthesis is a single step process to produce pure anatase phase TiO2. The catalyst produced by this method has been shown to be superior to the commercially available Degussa P-25 catalyst for the degradation of various chemical contaminants. The present investigation focuses on the use of combustion synthesized catalyst for the inactivation of microorganisms. The photocatalytic activity was compared with commercial Degussa P-25 catalyst. The various aspects of photocatalytic inactivation reactions studied in this dissertation are: i) photocatalytic inactivation of microorganisms in presence of UV light, ii) effect of various parameters on the inactivation, iii) photocatalytic inactivation in presence of visible light, iv) use of immobilized catalyst for the photocatalytic inactivation, v) understanding of mechanism and kinetics of inactivation. Combustion synthesized TiO2 (CS-TiO2), combustion synthesized 1% Ag substituted TiO2 (Ag/TiO2 (Sub)) and 1% Ag impregnated CS-TiO2 (Ag/TiO2 (Imp)) were used as photocatalysts. The catalysts were characterized by powder XRD, TEM, BET surface area, UV-Vis spectroscopy, TGA and photoluminescence spectroscopy. The photocatalytic inactivation experiments were carried out using E. coli (K-12 MG 1655), a bacterial strain and P. pastoris (X-33), a yeast strain, as model microorganisms. The results demonstrate higher photocatalytic activity of all the combustion synthesized catalysts than commercial Degussa P-25 catalyst. The optimum catalyst concentration was 0.25 g/L and the maximum inactivation was observed in the presence of Ag/TiO2 (Imp) catalyst. Rapid and complete inactivation of the microorganisms was observed at lower initial cell concentrations. A reduced photocatalytic inactivation was observed in presence of various anions (HCO3¯ , SO4 2¯ , Cl¯ and NO3¯ ) and cations (Na, K, Caand Mg). Even a small addition of H2O2 was observed to improve the photocatalytic inactivation. At higher dosage of H2O2, a 2 min exposure was sufficient to result in a complete inactivation. Changing the initial pH of the solution was observed to have no significant effect on the photocatalytic inactivation. All the combustion synthesized catalysts showed higher activity as compared to those obtained with commercial Degussa P-25 TiO2 in presence of visible light. The higher photocatalytic activity of combustion synthesized TiO2 can be attributed to the lesser crystallite size, higher surface area, large amount of hydroxyl groups and decreased band-gap energy of the catalyst. The present study demonstrates the potential use of catalyst immobilized thin films for the photocatalytic inactivation of E. coli in the presence of UV light. The CS-TiO2 catalyst was immobilized on glass substrate by LbL deposition technique. The performance of immobilized CS-TiO2 was compared to commercial Degussa Aeroxide TiO2 P-25 (Aeroxide) catalyst. The effect of various operating parameters like catalyst loading, surface area and number of bilayers on inactivation has been investigated. It was observed that increasing the number of bilayers and the concentration did not influence the inactivation but increased surface area led to an increase in inactivation. It was observed that the catalyst immobilized on glass slides can be used for repeated experimental cycles with the same efficiency. It was observed that the inactivation process can be studied in continuous mode by using catalyst immobilized on glass beads. The work also focused attention towards understanding the microorganism inactivation mechanism and kinetic aspects. Various microscopy techniques such as optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the inactivation mechanism. From the images obtained, it was suggested that the inactivation is caused due to rupture of cell wall. The mechanism was also examined by carrying out degradation experiments on cell component such as protein and media component such as dextrose. UV alone was observed to degrade protein and the presence of catalyst showed no additional effect. On the other hand, dextrose does not respond to photocatalytic degradation even at a lower concentration. The photocatalytic degradation of Orange G dye was reduced by addition of dextrose sugar or protein which shows a possibility of competitive degradation. The kinetics of inactivation was studied by various models available in literature such as the power-law model, Chick-Watson model, modified Hom model, GInaFIT tool and a Langmuir-Hinshelwood type model. It was observed that power-law based kinetic model showed good agreement with the experimental data. A mechanistic Langmuir-Hinshelwood type model was also observed to model the inactivation reactions with certain assumptions.

Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Aromatic organic contaminants are difficult to biodegrade, and thus effective green technologies are required to remove these pollutants from the ecosystem. Tetracycline antibiotic, an organic water pollutant, can be degraded by heterogeneous photocatalysis using an appropriate catalyst, with capability in converting the visible light energy into active species. The thesis focused on silver nanoparticles anchored on silver bromide (Ag/AgBr) as a plasmonic catalyst dispersed on activated carbon (ACK), were used as a photocatalyst (AABR-ACK) in tetracycline removal. The aim is to develop a catalyst that is active in low intensity visible light, whilst the addition of activated carbon will increase the light absorption and separate the charge pairs, after the photocatalyst has been excited by the visible light. The activated carbons were derived from pinecone pyrolyzed in a microwave. The pinecone mass to potassium hydroxide impregnation ratio and microwave pyrolysis time influenced the activated carbon properties. An impregnation ratio of 2.24 and microwave pyrolysis time of 16 minutes at constant microwave power of 400 W yielded the activated carbon with the best-developed porous structure and electrochemical properties. This activated carbon was used during the optimisation of the Ag/AgBr activated carbon (AABR-ACK) catalysts preparation using a thermal polyol precipitation method and response surface methodology. The most active catalyst was the AABR-ACK 11 obtained by a preparation temperature of 140 ºC, time (17.50 minutes), mass of surfactant and activated carbon (0.26 g and 0.03 g) respectively. This catalyst had an ordered nanospheres morphology, reduced electron-hole recombination rate, better electrochemical properties and exhibited enhanced activity on the tetracycline antibiotic removal in comparison to other Ag/AgBr activated carbon catalysts. A percentage degradation of 92% was obtained in 180 minutes were obtained with the AABR-ACK 11 catalyst. The photocatalyst prepared using the best activated carbon derived from pinecone developed in this study was compared to photocatalysts prepared using commercial activated carbon and biochar. The Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon degraded the tetracycline to 92%, which is significantly higher than the percentage degradations (80% and 74%) for the catalyst prepared using commercial activated carbon and biochar catalysts respectively. The higher activity of the Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon was due to the conductive attributes of the catalyst support for accelerated transfer of photo-induced electrons. The Ag/AgBr activated carbon catalysts using pinecone- derived activated carbon also exhibited better performance on tetracycline removal when compared to photocatalysts reported in literature. Two catalyst preparation methods, thermal polyol and deposition precipitation, were compared. The thermal polyol method yielded a more active catalyst for the degradation of the tetracycline in comparison to the deposition precipitation method. The degradation reaction conditions such as pH, light intensity and degradation temperature influenced the rate of the reaction. The highest rate of degradation was obtained at a pH of seven, white light and 40 ºC temperature. The intermediate products formed because of hydroxylation, deamination, demethylation and dehydration during the photocatalytic degradation of tetracycline antibiotics were identified using liquid chromatography mass spectrometer. Quenching experiments with hydroxyl, hole, and superoxide anion species showed that the most important radical responsible for the tetracycline degradation was the superoxide anion radical.