Since materials properties are determined by the interactions between the constituent atoms, an accurate description of the inter-atomic interactions is crucial to characterize and control material properties. Particularly, a quantitative understanding of the formation and nature of defects and impurities becomes increasingly important in the era of nanotechnology, as the imperfections largely influence many properties of nanoscale materials. Indeed, due to its technological importance and scientific interest, there have been significant efforts to better understand their behavior in semiconductors and oxides, and their interfaces, yet many fundamental aspects are still ambiguous due largely to the difficulty of direct characterization. Hence, our study has focused on developing a better understanding of atomic-scale defects and impurities using first principles quantum mechanical calculations. In addition, based on the improved understanding, we have attempted to address some engineering problems encountered in the current technology. The first part of this thesis focuses on mechanisms underlying the transient enhanced diffusion of arsenic (As) during post-implantation annealing by examining the interaction of As with vacancies in silicon. In the second part, we address some fundamental features related to plasma-assisted nitridation of silicon dioxide; this study shows that oxygen vacancy related defects play an important role in (experimentally observed) peculiar nitridation at the Si/SiO2 interface during post O2 annealing. In the third part, we examine the interaction between vacancies and dopants in sp2–bonded carbon such as graphene and nanotube, specifically the formation and dynamics of boron-vacancy complexes and their influence on the electrical properties of host materials. In the fourth part, we study the interfacial interaction between amorphous silica (a-SiO2) and graphene in the presence of surface defects in a-SiO2; this study shows possible modifications in the electronic structure of graphene upon the surface defect assisted chemical binding onto the a-SiO2 surface. In the last part, we examine the structural and electronic properties of bismuth vanadate (BiVO4) which is a promising photocatalyst for water splitting to produce hydrogen; this study successfully explains the underlying mechanism of the interesting photocatalytic performance of BiVO4 that has been experimentally found to strongly depend on structural phase and doping. / text

<p>Diss. (sammanfattning) Umeå : Umeå universitet, 1996, härtill 4 uppsatser</p> / digitalisering@umu

The layered transition metal oxide composition series of Li1+xV1-xO2 was synthesized using the solid state synthesis technique. X-ray diffraction was used to determine the dependence of structure on composition and clearly indicated a structural anomaly at x = 0 caused by the unusual magnetic ordering on the triangular lattice of the V3+ layer. To prevent magnetic frustration V3+ cations undergo orbital ordering and subsequent periodic displacent to form “trimers”. The periodicity of this phenomena results in a superlattice structure that can be observed as a faint peak in XRD spectra. The relationship between composition, superlattice peak intensity and lattice parameters was clearly documented for the first time. Li/Li1+xV1-xO2 cells were made and tested. Recent literature has shown that the transformation to 1T Li2VO2 upon lithiation is dependant on a nonzero x (ideally x = 0.07 for maximum capacity) to make a small number of tetrahedrally coordinated Li sites accessible. These sites then act as a trigger for shearing into the 1T phase. The cells described within this work intercalated significant amounts of lithium at a higher potential than the to 1T transition, possibly signifying occupation of a large number of the tetrahedral sites. LiVO2 is known to undergo delithiation even in ambient conditons and this can lead to cationic disorder. Cationic disorder is an inhibitor of anion sheet shearing and this suggests that sample handling could be a cause of the observed electrochemical behaviour. The effects of air and water exposure were investigated.

University, Diss., 2002--Dortmund.

Universiẗat, Diss., 2003--Köln.

Os altos índice de sucesso dos implantes dentais e sua indicação crescente apresentam como limitação a contaminação bacteriana com a consequente doença peri-implantar. Os métodos de tratamento ainda não se apresentam claros e seguros, portanto, meios de prevenção que impeçam a formação de biofilme e inibam o crescimento bacteriano devem ser desenvolvidos e aplicados para impedir a falha dos implantes. O objetivo deste estudo foi avaliar a efetividade de um novo antimicrobiano nanoparticulado - o vanadato de prata (AgNO3) em diferentes concentrações (2,5%; 5% e 10%), aplicado sob a forma de filme superficial sobre diferentes substratos sugeridos para dispositivos da Implantodontia. Foram selecionados os materiais poliacetal, teflon e resina acrílica e os veículos glaze e esmalte para a aplicação do nanocomposto. Análises das propriedades físicas rugosidade superficial e dureza Rockwell superficial, assim como imagens obtidas por meio da Microscopia Eletrônica de Varredura (MEV), foram utilizadas para avaliar a resistência e alterações estruturais dos grupos e portanto, a viabilidade de aplicação clínica. A análise pelo método microbiológico do halo de inibição mostrou que as bactérias P. aeruginosa, E. coli, S mutans, E. faecalis e S. aureus tiveram inibição de crescimento; enquanto nas bactérias anaeróbias P. gingivalis e P. intermedia e na levedura C. albicans não foi demonstrada a atividade antibacteriana de AgNO3. O tipo de substrato utilizado e de veículo para a aplicação de AgNO3 não influenciaram nos resultados, com exceção do S. aureus que obteve maior diâmetro do halo de inibição quando aplicado com o glaze em comparação ao esmalte (p<0,05). A proporção do nanocomposto mostrou influência nos resultados, sendo que 10% se mostrou a mais eficaz em todas as bactérias, e de modo geral sem diferença estatística com a proporção de 5% (p<0,05). Apesar de proporções menores algumas vezes não mostrarem atividade antimicrobiana, estas provocaram menor alteração nas propriedades físicas dos materiais, sendo a proporção do AgNO3 proporcional ao aumento da rugosidade e dureza superficial. Os substratos e tipo de filme não influenciaram nos resultados da rugosidade superficial após a aplicação do tratamento superficial (p>0,05), entretanto a aplicação de 10% do nanocomposto causou a alteração superficial mais significativa (7,02 ± 2,99 Ra) (p<0,05). Na dureza superficial não foi encontrada alteração significativa com o aumento da concentração do AgNO3 no poliacetal e na resina acrílica (p>0,05), no entanto no teflon, 10% de AgNO3 não alterou significativamente os valores de resistência. Apesar dos filmes não influenciarem nos resultados, o substrato poliacetal demonstrou maior dureza com diferença estatística com os demais substratos (83,0 ±10,2 HR15Yadaptado) (p<0,05). As imagens obtidas no MEV comprovaram mudanças estruturais superficiais com a presença de mais picos e vales, em comparação a superfícies sem o tratamento antimicrobiano. Como conclusão, apesar de 10% ser a concentração do AgNO3 que atingiu um maior número de espécies, essa concentração deve ser ponderada sobre o seu uso, e avaliada em estudos futuros sobre a sua viabilidade de uso clínico em função das alterações nas propriedades físicas. / The high success rate of dental implants and their growing indications show the limitation of bacterial contamination with consequent peri-implant disease. The treatment methods have not yet clear and secure, thus means for preventing the deposition of biofilm and inhibit bacterial growth must be developed and implemented to prevent failure of implants. The aim of this study was to evaluate the effectiveness of a new nanoparticulate antimicrobial - vanadate silver (AgNO3) in different concentrations (2.5%, 5% and 10%), applied as a surface film on different substrates suggested for devices of Implantology. The materials polyacetal teflon and acrylic resin and vehicles enamel / glaze were selected for the application of nanocomposite. Analyzes of the physical properties surperficial roughness and superficial hardness Rockwell, as well as images obtained by scanning electron microscopy (SEM) were used to assess the strength and structural changes of the groups and therefore the feasibility of clinical application. A microbiological method for the analysis of inhibition zone shows growth inhibition on the bacterias P. aeruginosa, E. coli, S. mutans, E. faecalis and S. aureus; while the anaerobic bacteria P. gingivalis and P. intermedia and the yeast C. albicans has not been demonstrated antibacterial activity of AgNO3. The type of substrate used and the vehicle for the application of AgNO3 did not influence the results, with the exception of S. aureus with highest diameter of inhibition zone when applied with glaze compared to enamel (p<0.05). The proportion of the nanocomposite showed influence on the results, 10% proved the most effective in all bacteria, and generally no statistical difference in the proportion of 5% (p<0.05). Although smaller proportions sometimes do not show antimicrobial activity, these caused minor change in the physical properties of materials. The ratio of AgNO3 was proportional to the increase of roughness and hardness. The substrates and film type did not influence the results of the surface roughness after applying the surface treatment (p>0.05), however the application of 10% of the nanocomposite caused surface alteration more significant (7.02 ± 2.99 Ra) (p<0.05). In hardness was not found to significantly change with concentration of AgNO3 in the acrylic resin and the polyacetal (p> 0.05). However in teflon, 10% AgNO3 did not significantly alter the resistance values. Although the films do not influence the results, polyacetal substrate showed higher hardness with statistical difference with the other substrates (83.0 ± 10.2 HR15Yadaptado) (p <0.05). The SEM images proved superficial structural changes with the presence of more peaks and valleys compared to surfaces without antimicrobial treatment. In conclusion, despite 10% being the concentration of AgNO3 that reached the highest number of species, this concentration should be thought on its use, and evaluated in future studies on the feasibility of clinical use in accordance with changes in physical properties.

Orientador: Oswaldo Luiz Alves / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-20T15:38:00Z (GMT). No. of bitstreams: 1 Holtz_RaphaelDias_D.pdf: 5088635 bytes, checksum: d278014c22731df6df2370e7da3785ba (MD5) Previous issue date: 2012 / Resumo: Neste trabalho foram desenvolvidas nanoestruturas de vanadatos de prata, de cério e de bismuto e investigadas as suas propriedades antibacterianas. Tais nanoestruturas foram sintetizadas a partir de reações de precipitação entre o vanadato de amônio e os nitratos ou cloretos dos metais correspondentes, sendo posteriormente realizados tratamentos hidrotérmicos em autoclaves providas de agitadores mecânicos e medidores de pressão e de temperatura do meio reacional. Os materiais foram caracterizados por diversas técnicas de caracterização físico-química e morfológica, sendo sua atividade antibacteriana avaliada frente às cepas de bactérias Gram-Positivas e Gram-Negativas de interesse, incluindo cepas de Staphylococcus aureus resistente à meticilina e Enterococcus resistente à vancomicina. Foi observado que o vanadato de prata apresentou uma elevada atividade antibacteriana contra diversas cepas bacterianas. O elevado potencial antibacteriano do vanadato de prata despertou o interesse em avaliar a sua utilização como aditivo antibacteriano em uma tinta comercial à base de água. Os resultados de sua adição foram promissores uma vez que foram observados halos de inibição do crescimento bacteriano. Esses resultados levantaram questionamentos importantes acerca do seu comportamento frente à microorganismos aquáticos, uma vez que existe a possibilidade de, no futuro, este material ser utilizado comercialmente como aditivo antibacteriano para tintas e revestimentos. Foram realizados experimentos de toxicidade aguda frente ao microcrustáceo Daphnia similis, sendo que os valores de CE50 foram próximos aos valores apresentados para os compostos de prata / Abstract; In this work we report the development and characterization of silver-, cerium- and bismuth vanadate nanostructures as well as their antibacterial activity. These nanostructures were synthesized from simple precipitation reaction between ammonium vanadate and nitrates/chlorides of the corresponding metals. The obtained precipitates were treated by hydrothermal process in autoclaves with pressure and temperature gauges and under mechanical stirring. These nanomaterials were characterized by several physico-chemical techniques and morphological characterization, and their antibacterial activities were evaluated against several strains of Gram-positive and Gram-Negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). We observed that nanostructured silver vanadate presented a high antibacterial activity against a broad spectrum of bacteria. These results stimulated the evaluation of silver vanadate nanostructures as a potential antibacterial additive to commercial water-based paint. It was observed a zone of bacterial growth inhibition against MRSA. The possible use of this material as an additive to water-based paints lead us to investigate the toxicity of this material against aquatic microorganisms, once this material can be commercial used in future as antibacterial additive to paints and coatings. Acute toxicity assays against Daphnia similis showed that EC50 value was close to that observed in silver-based compounds / Doutorado / Quimica Inorganica / Doutor em Ciências

La photoelectrocatalyse de l'eau par rayonnement solaire est une solution communément proposée pour la production propre d'hydrogène. En termes de rendement solaire-à-hydrogène, un tandem dual photosystème est accepté comme la configuration plus efficace concernant les cellules photoelectrocatalytique pour la dissociation de l'eau. Ce travail s'intéresse au trioxyde de tungstène (WO3) et au bismuth vanadate (BiVO4) sous la forme de photoanodes type n en couches minces pour la complétion d'oxydation de l'eau dans la demi-réaction pour la dissociation complète de l'eau dans une cellule tandem dual photosystème photoelectrocatalytique. Ces couches minces sont fabriquées par des méthodes robustes, économiques, et extensibles de sol-gel dip coating, et caractérisées par différentes techniques pour vérifier leurs caractéristiques physiques et leur performance photoelectrochimique. WO3 et BiVO4 sont optimises par nanostructuration, modification des couches interfaciales, et addition des co-catalyseurs de surface pour améliorer les performances et la stabilité, respectivement dans des conditions acides et neutres. Ces matériaux sont couples avec une photocathode de type p en oxyde de cuivre (II) pour compléter la réaction de dissociation de l'eau. La cellule photoelectrocatalytique ainsi construite est inspirée par la littérature concernant les systèmes innovateurs de tandem dual photosystèmes. Ce travail aboutit à l'une des seules cellules de dissociation de l'eau par photoelectrocatalyse à base des oxydes de métaux, fabriquée via des techniques faciles et économiques. L'efficacité de la production solaire-à-hydrogène est de 0.01%, et applied-bias-to-photon efficacité de 0.06%. / Solar water splitting by photoelectrocatalysis is a proposed long term solution for the production of renewable hydrogen. A wired dual photosystem photoelectrocatalytic cell is thermodynamically considered to possess the highest attainable solar-to-hydrogen efficiency. To realize a photoelectrocatalytic water splitting cell for practical application, facile fabrication methods and abundant low cost materials are essential. This research investigates tungsten trioxide (WO3) and bismuth vanadate (BiVO4) as thin film n-photoanodes to complete the oxygen evolution half reaction for water splitting application in a tandem dual photosystem photoeletrocatalyic water splitting cell. These thin films are fabricated by low cost, robust, scalable, sol-gel dip coating methods and characterized by several techniques to verify the physical characteristics and photochemical performance. WO3 and BiVO4 are optimized by nanostructuration, interfacial surface modification, and addition of surface co-catalysts to increase performance and stability in acidic and neutral conditions, respectively. These materials are coupled with a copper (II) oxide p-photocathode to drive the hydrogen evolution reaction in a photoelectrocatalyic cell to complete the water splitting reaction. The photoelectrocatalytic cell constructed is inspired by previous literature reports encompassing an innovative tandem dual photosystem approach. As a result, this research reports one of the only entirely metal oxide based photoelectrocatalytic water splitting cells, fabricated by inexpensive, unexcessive techniques, resulting in a solar-to-hydrogen efficiency of 0.01% and an applied bias to photon efficiency of 0.06%.

This thesis studies the development of a new method for photochemical overall water splitting using a small organic shuttle. In Section 2, BiVO4, was studied to determine the CO2 reduction mechanism and how catalytic activity decays. BiVO4 catalysts were capable of producing a maximum of 200 μmol of methanol per gram of catalyst from CO2 in basic media, and later decomposed by BiVO4. The decay of BiVO4¬ was studied by x-ray diffraction and scanning electron microscopy, demonstrating reversible decomposition of BiVO4. BiVO4 is etched, leeching vanadium into solution, while nanoparticles of bismuth oxide are deposited on the surface of BiVO4. In Section 3, ferrocyanide salts, an aqueous, cheap, and abundant photocatalyst was used for the first time to dehydrogenate aqueous formaldehyde selectively into formate and hydrogen. The catalyst is capable of record turnovers and turnover frequencies for formaldehyde dehydrogenation catalysts. A preliminary mechanism was proposed from experimental and computational data.

The effects of various catalyst synthesis parameters on the photocatalytic degradation kinetics of aqueous methyl orange dye are presented. The four factors investigated were: i) InVO4 concentration, ii) nickel concentration, iii) InVO4 calcination temperature, and iv) ballmilling time. Three levels were used for each factor. Due to the large number of possible experiments in a full factorial experiment, an orthogonal-array experimental design was used. UV-vis spectrophotometry was used to measure the dye concentration. The results show that nickel concentration was a significant parameter, with 90% confidence. The relative ranking of importance of the parameters was nickel concentration > InVO4 concentration > InVO4 calcination temperature > milling time. The results of the orthogonal array testing were used to make samples of theoretically slowest and fastest catalysts. Curiously, the predicted-slowest catalyst was the fastest overall, though both samples were faster than the previous set. The only difference between the slowest and fastest catalysts was the milling time, with the longer-milled catalyst being more reactive. From this result, we hypothesize that there is an interaction effect between nickel concentration and milling time. The slowest and fastest catalysts were characterized using energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), x-ray powder diffractometry (XRD), BET surface area analysis, and diffuse-reflectance spectroscopy (DRS). The characterization results show that the fastest catalyst had a lower band gap than the slowest one, as well as a slightly greater pore volume and average pore diameter. The results indicate that fast kinetics are achieved with low amounts of nickel and a long ball milling time. Under the levels tested, InVO4 concentration and the calcination temperature of the InVO4 precursor were not significant.