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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Study of TiO2 Electrochromic Films Prepared by Liquid Phase Deposition

Wang, Hung-Chi 28 July 2004 (has links)
TiO2 is a fascinating material proving its usefulness in a wide range of applications. In catalytic and electrochemical applications, it has been utilized as a stable semiconductor electrode for the conversion of solar energy into chemical or electrical energy. Especially, the cleavage of water over TiO2 using light energy is well known. The degradation of organic pollutants present in waste water, using irradiated dispersions of TiO2, is a fast growing field in basic and applied research. One can also mention that the use of TiO2 in pigments sun lotions and toothpastes and its biocompatibility. The EC phenomena of TiO2 had been reported first by Inoue et al., who produced the films by hydrolysis of titanium tetraoxide. The film show cathodic coloration and turned dark blue. The LPD-TiO2 film deposited at 40 ¢J with (NH4)2TiF6 for 0.1 M and 0.2 M for boric acid. The films were transparent in visible range and can be colored in a solution 1M LiClO4 + propylene carbonate. The deposition rate can be controlled perfectly about 43 nm/h. The 270-nm thickness LPD-TiO2 film gives the best transmittance difference at 550 nm.
2

Preparation and Characterization of TiO2-Based Nano Particles and Tests for Their Activities in Meth¬ylene Blue Photodegradation

Duan, Aoshu January 2014 (has links)
A two-step hydrothermal method was applied to synthesis Vanadium Sulfide (IV) coupled with commercial P25 on TiO2 nanoparticle (VS4-on-P25). Materials were characterized by scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-Vis), diffuse reflectance UV-Vis spectroscopy and Raman spectroscopy. Photocatalytic activity of this new material was determined by photo-degradation of Methylene blue (MB) under UV irradiation. Experiments show that the VS4-on-P25 exhibits a higher photocatalytic activity than commercial P25 by providing more active site for dye adsorption, and reducing the recombination of charge carriers. Furthermore, the VS4-on-P25 extends its light-absorption spectrum into visible-light range due to its narrower band gap. The highest photocatalytic activity was found with a VS4 loading of 6 wt.%, which outperforms pure P25 by a factor of 2.29 in MB degradation rate.
3

Structuration 1D et 2D de matériaux diélectriques par ablation laser nanoseconde : application aux couches minces et monocristaux de LiNbO3 et aux couches de TiO2 / 1D and 2D structuration of dielectric materils by nanosecond laser ablation : application to LiNbO3 thin films and monocrystals and TiO2 thin films

Meriche, Faïza 06 May 2008 (has links)
La structuration des matériaux à l échelle micro et nano métrique constitue un domaine de recherche et développement très prometteur dont le succès permettra de réaliser le saut technologique tant attendu dans le domaine de la photonique. Du point de vue du matériau, l utilisation des diélectriques de type LiNbO3 ou encore TiO2 qui possèdent des propriétés spécifiques qui différent de ceux des semi-conducteurs est de nature à élargir les performances des composants photoniques à mettre au point. De plus, l utilisation de ces matériaux sous forme de couches minces permet de s affranchir des contraintes et des limitations imposées par le cristal massif. Dans le cadre de ce travail, nous nous intéressons à la réalisation de -structures 1D et 2D par ablation laser nanoseconde dans des couches minces et monocristaux de niobate de lithium ainsi que des couches minces de TiO2. Les couches minces de LiNbO3 ont été déposées par pulvérisation cathodique rf magnétron sur saphir tandis que les couches de TiO2 ont été réalisées par voie sol-gel sur des substrats de verre. Les ablations ont été réalisées avec un laser nanoseconde de type KrF excimer (ATLEX 300 SI Model). L irradiation des échantillons a été effectuée avec un masque de 10 m de diamètre, les fréquences appliquées varient de 10 à 100 Hz et les fluences varient de 0.3 à 2.3 J/cm2. Les structures ablatées ont été observées et analysées à l aide de la microscopie optique fonctionnant en mode Nomarski et de la microscopie -Raman. Nous avons notamment étudié l influence des paramètres d ablation (nombre de pulses, fluence et fréquence de répétition) sur les caractéristiques des structures ablatées. A titre d exemple, des réseaux de 55 trous ont été réalisés avec un nombre de pulse constant (5pulses). et différentes valeurs de fluences (0.88 à 2.093J/cm2). D après les résultats obtenus, nous avons constaté que la forme des trous ainsi que leur profondeur dépendent fortement de la fluence utilisée. Les meilleurs résultats sont obtenus pour les fluences élevées. Pour l étude de l effet du nombre des pulses sur l ablation des couches, nous avons procédé à la réalisation des réseaux de 55 trous avec une fluence constante 1.467J/cm2 et une variation du nombre de pulses de 5 à 15. Le taux moyen d ablation décroît avec l accroissement du nombre de pulses. A noter que préalablement à ces études, nous avons étudié les propriétés optiques de nos couches minces en utilisant la spectroscopie des lignes noires. Les résultats ont montré que les couches sont monomodes et possèdent des pertes optiques de l ordre de 1 dB.cm-1. L objectif final de ce travail est d optimiser le processus expérimental d ablation afin d obtenir des structures sub-micrométriques pour des applications dans le domaine des télécommunications optiques. / Micro and nano structuring of materials constitutes a field of very promising research and development whose success will make it possible to carry out very important progress of photonic technology. From the material point of view, the use of dielectrics such as LiNbO3 or TiO2, which have specific properties different from those of the semiconductors, is likely to widen the performances of the photonic components to be developed. Moreover, the utilization of these materials in the form of thin layers makes it possible to release from limitations imposed by the bulk materials. In this work, we were interested in the realization of -structures 1D and 2D by using nanosecond laser ablation of lithium niobate thin layers and monocrystals as well as thin layers of TiO2. LiNbO3 thin films were deposited by RF magnetron sputtering technique on sapphire while TiO2 layers were carried out by using sol-gel method on glass substrates. Ablations were performed with a nanosecond KrF excimer laser (ATLEX 300 IF Model). The ablation of samples was carried out with a mask of 10 m of diameter. The frequencies applied vary from 10 to 100 Hz and the fluences from 0.3 to 2.3 J/cm2. Structures were observed using optical microscopy functioning in Nomarski mode and analyzed using -Raman spectroscopy. We particularly studied the influence of the ablation parameters (number of pulsate, fluence and repetition rate) on the structure features. For example, 5x5 holes gratings were carried out with a constant number of pulse (5pulses) and various values of fluences (0.88 with 2.093J/cm2). Our results showed that the shape of holes and their depth strongly depend on the fluence used. The best results were obtained for high fluences. For the study of the effect of the number of pulse on the ablation process, we realized a 5x5 holes grating with a constant fluence 1.467J/cm2 and a variation of pulse number from 5 to 15. The average rate of ablation decreases with the increase of the pulse number. Note that, before these studies, we studied the optical properties of our thin films by using m-lines spectroscopy. Results showed that our films are monomodes and have optical losses of about 1 dB.cm-1. The final objective of this work is to optimize the experimental ablation process in order to obtain sub-micrometric structures for applications in the field the photonic
4

Analyse phosphoprotéomique pour la recherche de biomarqueurs : développements et applications / Phosphoproteomics in cancer biomarkers discovery : chromatographic development and applications

Negroni, Luc 13 December 2013 (has links)
L’analyse protéomique est une méthode de choix pour la recherche de biomarqueurs. Sans à priori, elle permet d’établir un catalogue de protéines qui sont exprimées dans une cellule, un tissu ou un organisme entier. Cette approche a été mise en œuvre pour une analyse protéomique de cellules coliques cancéreuses et une analyse phosphoprotéomique de biopsies hépatiques.L’étude de cellules coliques cancéreuses transformées par le gène cytosine désaminase et traitées par la prodrogue 5-fluorocytosine a été réalisée par électrophorèse bidimensionnelle des extraits protéiques. L’analyse d’image a permis la quantification de 353 protéines et isoformes dont 14 sont surexprimées et 4 sous exprimées lors d’un traitement par la prodrogue. Parmi les protéines dont l’expression est affectée par le traitement, l’HSP90 présente un niveau d’expression constant mais est identifiée sous deux formes qui diffèrent par leur pI. L’analyse par spectrométrie de masse à identifier une phosphorylation de ser 254 qui pourrait contribuer à la régression tumorale.Après avoir développé une méthode HPLC-TiO2 pour la purification de phosphopeptides, une analyse protéomique de 24 biopsies humaines provenant de carcinomes hépatocellulaires sur foie non fibreux (nf-CHC) et de tissus sains a été réalisée avec la technologie iTRAQ. Les peptides surexprimés dans les tumeurs correspondent à des protéines de choc thermiques, des protéines liées à l’ADN/ARN (histones, protéines du splicéosome), des protéines de la phase 1 de la détoxification (carboxyestérase, époxide hydrolase), les protéines du cytosquelette (actinine, tubuline), des protéines ou enzymes anti-oxydantes (superoxide dismutase, thiorédoxine). Les peptides sous-exprimés correspondent à des protéines du cycle de l’urée, de la détoxification (alcool déhydrogénase) du métabolisme des sucres, des lipides et des acides aminés. Dans la fraction TiO2, 19 phosphopeptides sont significativement surexprimés et 15 phosphopeptides sont significativement sous exprimés, mettant en en évidence une surreprésentation du motif –(S/T)P- parmi les phosphopeptides surexprimés dans les tumeurs. Une activation des proline directed kinases ou une inhibition des phosphatases correspondantes est donc probablement un événement caractéristique des nf-CHC. Ces peptides/protéines dérégulées sont autant de biomarqueurs potentiels pour le carcinome hépatocellulaire. / Proteomic is a method of choice for biomarker research, without a priori, it establishes a directory of proteins that are expressed in a cell, tissue or an entire organism. This approach has been implemented for proteomic analysis of colon cancer cells and phosphoproteomic analysis of liver biopsies.The study of colon cancer cells transformed by the cytosine deaminase and treated with the prodrug 5-fluorocytosine was performed by two-dimensional electrophoresis. Image analysis allowed the quantification of 353 proteins, 14 isoforms are overexpressed and 4 under expressed during treatment with the prodrug. Among the proteins whose expression is affected by the treatment, HSP90 has a constant level of expression, but is identified in two isoforms that differ in their pI. Mass spectrometry identified phosphorylation of ser 254 which could contribute to tumour regression.After developed an HPLC- TiO2 method for the purification of phosphopeptides, a proteomic analysis of 24 biopsies from human hepatocellular carcinoma on non-fibrous liver (nfCHC) and normal tissue was performed with the iTRAQ technology. Peptides overexpressed in tumours correspond to HSPs, DNA / RNA binding proteins (histones, spliceosome), proteins form Phase 1 detoxification (carboxyesterase, epoxide hydrolase), the cytoskeletal proteins (actinin, tubulin), antioxidant proteins or enzymes (superoxide dismutase, thioredoxin). The under-expressed peptides belong to proteins of the urea cycle, the detoxification (alcohol dehydrogenase) metabolism of sugars, lipids and amino acids. In the TiO2 fraction, 19 phosphopeptides are significantly overexpressed and 15 phosphopeptides were significantly under-expressed. This phosphoproteome has demonstrated an overrepresentation of the (S/T)P pattern among overexpressed phosphopeptides, indicating activation of proline-directed kinases in nfCHC or inhibition of the corresponding phosphatases. These deregulated peptides/proteins are as potential biomarkers for hepatocellular carcinoma.
5

Science de surface et propriétés chimiques d'hétérostructures NiO/TiO2 monocristallin / Surface science and chemical studies of NiO/single crystal TiO2 heterostructure photocatalysts

Kashiwaya, Shun 27 November 2018 (has links)
Les photocatalyseurs à base de TiO2 ont été l’objet d’une grande attention comme une méthode durable de purification de l’air ou de l’eau, et de production d’hydrogène par décomposition de l’eau. Une stratégie avantageuse consiste à développer des héterostructures par couplage avec un autre oxyde métallique former une jonction de type Schottky ou avec un autre oxyde métallique pour créer une jonction p-n à l’interface de manière à prévenir les recombinaisons via une séparation de charge « vectorielle » à ces jonctions. De plus, les facettes cristallines jouent un rôle crucial dans le piégeage des porteurs de charge et, donc,dans les réactions rédox photoactivées. Ainsi, le dépôt sélectif de métal ou d’oxyde métallique sur des facettes spécifiques de nanocristaux de TiO2 devrait augmenter l’activité photocatalytique par l’amélioration de la séparation des charges. Dans ce travail, nous avons combiné l’emploi du cocatalyseur de type p NiO pour former des jonctions p-n avec son dépôt sélectif sur des nanocristaux de TiO2 anatase exposant des facettes bien définies. Par ailleurs, des expériences modèles de physique de surface ont été menées pour étudier les propriétés électroniques de ces hétérojonctions. / TiO2 photocatalysts have attracted attention as a sustainable method for water/air purification and hydrogen production by water splitting. An advantageous strategy is the development of heterostructures by coupling metal oxides to create a p-n junction at their interface in order to prevent there combination by vectorial charge carrier separation at these energy junctions. In addition, crystal facets play a decisive role in the trapping of charge carriers and thus photocatalytic redox reactions. Thus, selective deposition of metal or metal oxides onto specific facets would enhance the photocatalytic activity by improving charge separation. In this work, we have combined the usage of p-type NiO co-catalyst to form p-n junction with its selective deposition onto the specific facet of oriented TiO2nanocrystal photocatalysts. Furthermore, the physical model experiments have been performed to investigate the electronic properties of these heterojunctions.
6

Atividade fotocatalitica de TiO2 em matrizes de siloxano / Photocatalytic activity of TiO2 in siloxane matrices

Pacheco e Silva, Viviane 04 August 2009 (has links)
Orientadores: Inez Valeria Pagotto Yoshida, Wilson de Figueiredo Jardim / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-13T12:54:30Z (GMT). No. of bitstreams: 1 PachecoeSilva_Viviane_D.pdf: 3480980 bytes, checksum: 4c99b3d79e0972f6849d577fd58e285e (MD5) Previous issue date: 2009 / Resumo: Este trabalho relata a imobilização do TiO2 em matrizes de siloxano, como alternativa ao emprego do TiO2-pó em suspensão, para a fotodegradação de espécies orgânicas em solução aquosa, sob radiação UV-Vis ou radiação solar, tendo o ácido salicílico (AS) como modelo de poluente. Incorporou-se o TiO2-pó em uma matriz elastomérica de silicona com grau de reticulação relativamente baixo, obtida a partir de goma de poli(dimetilsiloxano) de alta massa molar, obtendo-se compósitos elastoméricos na forma de monólitos. O TiO2-pó também foi incorporado em uma matriz de silicona altamente reticulada, na presença de um agente porogênico, obtendo-se um compósito monolítico rígido e poroso, com características de ¿ceramer¿. Sintetizou-se ainda o TiO2 in situ na forma anatásio, por síntese hidrotérmica, empregando-se como matriz os compósitos contendo TiO2-pó, e placas porosas de vidro. Comparando-se a eficiência dos compósitos elastoméricos com diferentes composições, frente à fotodegradação do AS, sugeriu-se que apenas os sítios de TiO2 mais próximos da superfície iluminada tiveram acesso à radiação UVVis. Apesar das amostras com matriz elastomérica terem apresentado os maiores valores de sorção de AS, o material que apresentou a maior eficiência fotocatalítica sob radiação UV-Vis, superando inclusive o desempenho do TiO2-pó, foi o compósito poroso contendo também o TiO2 gerado in situ, provavelmente devido a sua maior área superficial. Os experimentos conduzidos com esse compósito sob radiação solar evidenciaram uma diminuição na porcentagem de fotodegradação do AS, provavelmente pela menor intensidade da radiação solar, em relação à lâmpada UVVis, associada ao efeito da atenuação da radiação no monólito. Observou-se um pequeno aumento na atividade fotocatalítica do TiO2 com o aumento no tamanho dos cristalitos de anatásio sintetizados in situ, após o tratamento térmico das placas porosas de vidro a 600°C. Os resultados apresentados neste estudo sugerem grande potencialidade na imobilização do TiO2 em matrizes de silicona, tanto pela incorporação do TiO2-pó, quanto pela síntese in situ da fase anatásio / Abstract: This study reports the immobilization of TiO2 in siloxane matrices, as an alternative to the use of TiO2-powder in suspension, for the photodegradation of organic species in aqueous solution, under UV-Vis radiation or solar radiation, having the salicylic acid (SA) as model pollutant. TiO2-powder was incorporated in an elastomeric silicone matrix with a relatively low crosslinking degree, obtained from a poly(dimethylsiloxane) gum with high molecular weight, giving rise to monolithic elastomeric composites. TiO2-powder was also incorporated in a silicone matrix with a high crosslinking degree, in the presence of a pore forming agent, resulting in a hard and porous monolithic composite, with ¿ceramer¿ characteristics. TiO2 in the anatase form was obtained in situ, by hydrothermal synthesis, on the previously prepared composites containing TiO2-powder, and also on glass porous plates. Comparing the efficiency of the elastomeric composites with different compositions, in relation to the SA photodegradation, the results suggested that only the TiO2 sites near the illuminated surface were accessed by the UV-Vis radiation. Although the samples with the elastomeric matrix presented the highest SA adsorption values, the porous composite containing the in situ obtained-TiO2 presented the highest photocatalytic efficiency, with better performance than the TiO2-powder, probably due to the high surface area of this material. When this porous composite was tested under solar radiation, the lower intensity of this radiation, in relation to the UV-Vis lamp, associated to the radiation attenuation effect in the monolith, promoted a decrease in the percentage of SA photodegradation. An increase in the size of the in situ obtained-anatase crystallites, promoted by the thermal treatment of the glass porous plates at 600°C, resulted in an increase in the photocatalytic activity of the TiO2. The results presented in this study suggest a great potential in the immobilization of TiO2 in silicone matrices, either by the incorporation of TiO2-powder, as by the in situ synthesis of the anatase form / Doutorado / Quimica Inorganica / Doutor em Ciências
7

Synthesis and Investigation of Novel Nanomaterials for Improved Photocatalysis

Chen, Xiaobo 01 June 2005 (has links)
No description available.
8

Intensification de la dégradation de polluants organiques par photocatalyse dans des émulsions de Pickering / Intensification of organic pollutants degradation by photocatalysis in Pickering emulsions

Fessi, Nidhal 22 December 2018 (has links)
Ce travail de thèse examine une nouvelle méthode prometteuse pour la dépollution efficace des eaux contaminées par des polluants organiques insolubles de type toluène, 1-méthylnaphtalène, nitrobenzène,…. Cette méthode d’oxydation avancée repose sur la photocatalyse hétérogène dans des émulsions de Pickering. Dans ce type d’émulsions, les tensioactifs stabilisants des gouttelettes huileuses sont remplacés par des nanoparticules solides à propriétés photocatalytiques élevées. Par ailleurs, ces nanoparticules solides doivent remplir les conditions de mouillabilité partielle dans les deux phases aqueuse et huileuse grâce à un équilibre hydrophile-hydrophobe à leur surface. Pour cette raison, le dioxyde de titane (TiO2) anatase a été préparé par la méthode sol-gel puis modifié par fluoration pour obtenir le catalyseur TiO2-F. L’objectif est de formuler des émulsions de Pickering de type huile dans l’eau (H/E) à partir de polluants organiques de faible solubilité dans l’eau. Les catalyseurs synthétisés ont été caractérisés par XRD, BET, SEM, DRS, XPS, et TG-TD-MS. Il a été montré que la fluoration apporte des changements importants dans les propriétés optiques du TiO2 et a amélioré l’équilibre hydrophile/hydrophobe à sa surface de façon significative. Par ailleurs, les résultats obtenus indiquent que des émulsions de Pickering stables peuvent être formulées en utilisant des particules de TiO2 ou TiO2-F de taille nanométrique. Le type et la stabilité des émulsions dépendent de la mouillabilité des nanoparticules stabilisantes évaluées par des mesures d'angle de contact. La mouillabilité des nanoparticules a été trouvée fortement dépendante du type d’huile en raison des contributions de la polarité et des interactions spécifiques avec les polluants. L'étude des émulsions de Pickering par conductivité électrique, microscopie optique et diffusion de la lumière a montré qu'une stabilité élevée a été obtenue dans des conditions de mouillage partiel : angle de contact dans l'eau compris entre 70 et 110°. L’évolution de la taille des gouttelettes d'huiles avec le rapport de masse huile/photocatalyseur a confirmé une forte adsorption des nanoparticules de catalyseur sur les gouttelettes d'huiles. Finalement, les émulsions jugées stables ont été photodégradées sous rayonnement UV. La cinétique de photodégradation des polluants organiques mesurée par HPLC a montré que la dégradation a été intensifiée en utilisant les émulsions de Pickering par rapport aux systèmes non émulsionnés. Ces résultats ont prouvé que l’utilisation des émulsions de Pickering stabilisées par des nanoparticules de dioxyde de titane constituait un moyen efficace et innovateur pour intensifier la dégradation photocatalytique des polluants organiques / This thesis examines a promising new method for the effective depollution of water contaminated by insoluble organic pollutants such as toluene, 1-methylnaphthalene, nitrobenzene, etc. This advanced oxidation method is based on heterogeneous photocatalysis in Pickering emulsions. In this type of emulsion, the stabilizing surfactants of the oily droplets are replaced by solid nanoparticles having high photocatalytic properties. Moreover, these solid nanoparticles must fulfill the conditions of partial wettability in both aqueous and oily phases thanks to a hydrophilic-hydrophobic balance on their surface. For this reason, the titanium dioxide (TiO2) anatase was prepared by the sol-gel method and then modified by fluorination to obtain the TiO2-F catalyst. The objective is to formulate Pickering oil-in-water (O/W) emulsions from organic pollutants of low water solubility. The synthesized catalysts were characterized by XRD, BET, SEM, DRS, XPS, and TG-TD-MS. It has been shown that fluorination brings about important changes in the optical properties of TiO2 (change in band gap) and improves the hydrophilic / hydrophobic balance at its surface significantly. Moreover, the obtained results indicate that stable Pickering emulsions can be formulated using TiO2 or TiO2-F nanoparticles. The type and stability of the emulsions depend on the wettability of the stabilizing nanoparticles evaluated by contact angle measurements. The wettability of the nanoparticles has been found to be highly dependent on the type of oil due to the contributions of polarity and specific interactions with pollutants. The study of Pickering emulsions by electrical conductivity, optical microscopy and light scattering showed that high stability was obtained under partial wetting conditions: contact angle in water between 70 and 110°. The change in the size of the oil droplets with the oil/photocatalyst mass ratio confirmed a strong adsorption of the catalyst nanoparticles on the oil droplets. Finally, the judged stable emulsions were photodegraded under UV radiation. The photodegradation kinetics of organic pollutants measured by HPLC showed that degradation was intensified using Pickering emulsions compared to non-emulsified systems. These results have shown that the use of Pickering emulsions stabilized by titanium dioxide nanoparticles is an effective and innovative way to intensify the photocatalytic degradation of organic pollutants
9

The functionalisation and defects of titania : a photoemission study

Jackman, Mark January 2016 (has links)
This thesis consists of photoemission studies of the rutile and anatase polymorphs of TiO2. It is split into two sections. In the first part, studies of the functionalisation of the rutile TiO2 (110) and the anatase TiO2 (101) surfaces with small organic molecules are presented. In the second part, studies of defects at the anatase TiO2 (101) surface are presented. Four organic molecules are investigated, p-aminobenzoic acid (pABA) and 3-fluoroaniline (3-FA) on anatase TiO2 (101), and dopamine and malonic acid (MA) on rutile TiO2 (110). The four adsorbates studied all have potential as dyes for dye-sensitised solar cells (DSSCS), and dopamine and pABA have the potential to be used as linkers for light sensitisers for photocatalytic applications such as DSSCs. Near-edge X-ray fine structure (NEXAFS) spectroscopy was used to determine the orientation of the molecules on the surface, and X-ray photoemission (XPS) spectroscopy was used to determine the chemical environment of the molecule on the surface. On the anatase TiO2 (101) surface, for pABA, the plane of the ring sits upright, normal to the surface, bonding through the carboxylic acid group after deprotonation. 3-FA also bonds upright, normal to the surface. It bonds through the amine group to the surface. It is unclear whether the molecule bonds dissociatively (the amine group deprotonating). On the rutile TiO2 (110) surface, dopamine is found to sit just off normal at ~ 78 º. It bonds through the catechol moiety after dissociation of the hydrogens. Both of the MA carboxylic acid protons dissociate and both moieties bond to the surface. MA is unstable under irradiation from insertion device beamlines. The defects in the anatase TiO2 (101) surface layers are investigated by XPS. Defects in the form of oxygen vacancies are observed in the band gap region of the photoelectron spectrum at around 1 eV binding energy (BE). Understanding the nature of these defects, intrinsic dopants in n-type TiO2 is imperative for photocatalytic applications. The effect of water adsorption on the stoichiometric and Ar cluster-ion-source-sputtered anatase TiO2 (101) surface is investigated at near-ambient pressures (NAP) and high vacuum. High vacuum studies show the anatase surface oxygen vacancies migrate to the subsurface region over time, as has been postulated with scanning tunnelling microscopy and density functional theory analysis. NAP-XPS is a developing technology allowing the analysis of surfaces and interfaces in "real-life" conditions. Results show water adsorbs in a similar fashion on both surfaces and reaches a saturation point between 0.6 and 1.8 mbar at room temperature, meaning there is little difference in reactivity between the stoichiometric and reduced surfaces. Oxygen vacancies are created at the TiO2 surface by insertion-device synchrotron radiation beamlines and the creation of these defects is monitored in situ with XPS. The bandgap state is made up of three components, relating to oxygen vacancies at 1.0 eV BE and two related components at 0.2 and 1.7 eV BE that are due to a surface 2D electron gas, created by electron doping via Nb impurities and synchrotron radiation-induced oxygen vacancies.
10

TiO2-based photocatalytic coatings for improving indoor air quality

Giampiccolo, Andrea January 2017 (has links)
The photocatalytic properties of titanium dioxide have been widely studied since the discovery in 1972 of water photolysis by TiO2 electrodes. Rutile and anatase are the most studied of the different TiO2 polymorphs due to their chemo-physical properties. When irradiated with ultraviolet light, TiO2 is able to absorb photons, creating on the surface an electron and a positive “hole”. This electron-hole pair then reacts with water and oxygen, generating chemical radicals. These are very unstable and reactive species which can neutralise pollutants. In the introduction pollutants and their influence in the air quality are described as well as the state of art of TiO2, photochemistry; semiconductor doping, chemo-physical principles, and TiO2 coatings. Various protocols to test photoactivity of both powders and coatings are discussed studying both gas phase and liquid phase reactions looking at UV and visible light irradiation. The sol-gel synthesis of pure and tungsten- and cobalt-doped TiO2, as well as graphene/TiO2 hybrids, was explored modifying the conditions and parameters to optimise the photocatalytic activation of TiO2 in the visible light range. A comprehensive study of manufactured and commercially available TiO2 powders and coatings was performed to identify the differences between photocatalytic properties, using electron microscopy, Raman and UV-vis diffusive spectroscopy and X-ray diffraction. An important question that was answered in this thesis is whether the physical properties of nanoparticles or their electronic properties are critical for their photocatalytic behaviour. Results for doped powders of different particle size and surface area showed how the positioning of their electronic band gap with the wavelength of the visible light source was fundamental for an effective photocatalytic process for the application wantedIn the application of TiO2 for the built environment, lime and MDF were considered as substrates for coatings. Lime-based coatings were prepared mixing commercial K7000 TiO2 with the plaster and photoactivity of the coatings was evaluated looking at formaldehyde degradation. MDF based coating were produced using both produced sol-gel pure, doped TiO2 and tested by observing degradation of Ink Intelligent inks under both UV and visible light confirming the photoactivity. Throughout this work sol-gel was employed for the production of pure and doped TiO2 nanoparticles with the anatase crystalline phase. Photocatalytic tests on the synthesised particles under UV light shows comparable performances with commercial particles. Synthesised particles and coatings shows promising performances, higher than commercially available particles when irradiated with visible light confirming a possible application in indoor environment.

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