<p>Usled visoke fotokatalitičke efikasnosti u procesima preči&scaron;ćavanja voda i vazduha, titan(IV)-oksid (TiO₂) se u poslednje vreme sve vi&scaron;e ispituje u oblasti za&scaron;titi životne okoline. Međutim usled visokih zahteva koje fotokatalizatori u ovoj oblasti treba da zadovolje, kao &scaron;to su aktivnost, selektivnost, netoksičnost, ekonomičnost i stabilnost, potreba za razvojem fotokatalizatora sa povoljnijim karakteristikama se sve vi&scaron;e nameće kao prioritet za buduća istraživanja. Inovativni pristup ove doktorske disertacije je usmeren upravo ka razvoju novih kompleksnih sistema na bazi oksida titana i slojevitih hidroksida, osvrćući se na postavljenu polaznu hipotezu o mogućem sinergetskom efektu komponenata u dostizanju visoke fotokatalitičke efikasnosti, kao i u pobolj&scaron;anju njihovih op&scaron;tih katalitičkih performansi. ZnAl i NiAl slojeviti hidroksidi su izabrani kao nosači aktivne komponente (TiO₂). Modifikacija postojećih metoda sinteze je izvr&scaron;ena kako bi se pospe&scaron;ila interakcija aktivne komponente i nosača. Komparativna istraživanja novonastalih materijala pripremljenih primenom četiri nove metode sinteze pokazala su da se izborom metodologije sinteze i prirode interakcije između aktivne faze TiO₂ i aktivnog nosača mogu pobolj&scaron;ati fotokatalitičke performanse kompozitnih materijala u odnosu na referentne vrednosti dobijene za ZnAl slojevite hidrokside. Iako je udeo TiO₂ veoma mali u novonastalim kompleksnim sistemima, fotokatalitička efikasnost razgradnje model polutanta je zadovoljavajuća, usled pobolj&scaron;ane dostupnosti aktivnih centara i usled limitiranja aglomeracije TiO₂. Potvrđeno je da metoda i uslovi sinteze bitno utiču na strukturu, teksturu i povr&scaron;inske karakteristike formiranih kompozita, uz rezultujuće značajne razlike i u fotokatalitičkim svojstvima sintetisanih materijala. Komparativna ispitivanja fotokatalitičke efikasnosti uz primenu odabranih test reakcija (razgradnje metilenskog plavog, rodamina B i metil oranža) pokazala su da uzorci sintetisani metodom impregnacije u baznoj sredini pokazuju najbolje fotokatalitičke performanse u &scaron;irem spektru zračenja, &scaron;to je pripisano formiranju faza ZnO i ZnTiO₄ u ovim uslovima, detektovanih XRD, FTIR i XPS analizama. Takođe, mikrobiolo&scaron;ke analize na antimikrobno dejstvo su pokazale da, iako TiO₂ ne pokazuje inhibitoran efekat, uzorci sintetisani impregnacijom u baznoj sredini imaju i najizraženiji inhibitorni efekat na rast gram-pozitivnih i gram-negativnih bakterija, &scaron;to dodatno ukazuje na doprinos sinergetskog efekta slojevitih oksida i aktivne faze me&scaron;ovitih oksida u formiranju aktivnih centara visoke fotokatalitičke aktivnosti. Uzorci dobijeni primenom metoda koprecipitacije pokazuju nižu, ali zadovoljavajuću fotokatalitičku aktivnost, dok uzorci sintetisani metodom impregnacije u neutralnoj sredini pokazuju najnižu fotokatalitičku aktivnost i mali inhibitorni efekat.<br />Istraživanja u ovoj doktorskoj disertaciji dala su doprinos novim saznanjima o karakteristikama kompozitnih materijala tipa TiO₂/ZnAl slojeviti hidroksidi bitnim za obezbeđenje fotokatalitičke aktivnosti materijala ovog tipa u &scaron;irem spektru zračenja (UV/VIS), kao i ukupnih performansi koje omogućuju njihovu primenu u različitim ekolo&scaron;kim procesima (preči&scaron;ćavanje vode i vazduha od organskih, neorganskih i biolo&scaron;kih polutanata).</p> / <p>Recently, titanium-dioxide (TiO₂) has been extensively researched in the field of environmental protection due to its high photocatalytic efficiency in processes for water and air purification. Considering the high demands that are constantly set for photocatalysts in this field of research, such as activity, selectivity, stability, cost-effective and non-toxic, the need to develop photocatalysts with better characteristics is becoming increasingly evident as a priority for future research. The novel approach of this Ph.D. thesis is oriented towards the development of new complex systems on the basis of titanium-dioxide and layered double hydroxides, taking into account the hypothesis about their possible synergetic effect achieving high photocatalytic efficiency and obtaining better overall catalytic performances. ZnAl and NiAl layered double hydroxides have been chosen as the catalyst support of the active component (TiO₂). In order to initiate the interaction between the active component and support, current synthesis methods have been modified. The novel materials were synthesized using four new different synthesis methods. Comparative investigation showed that the synthesis method, as well as the nature of the interaction between the active phase and the support can improve the overall photocatalytic performances of the composite materials when compared to the referent values obtained from ZnAl layered double hydroxides. Although the TiO₂ amount is low in the novel complex systems, photocatalytic efficiency for the degradation of model pollutants is satisfactory due to improved accessibility to the active centres, as well as due to limitation of TiO₂ agglomeration. It was confirmed that the synthesis method and conditions considerably affect the structural, textural and surface characteristics of the formed composites, resulting in significant differences in photocatalytic characteristics of the synthesized materials. Comparative research of photocatalytic efficiency in the chosen test reactions (methylene blue, rhodamine B, and methyl orange degradation) showed that the samples synthesized by the wet impregnation method in alkaline solution exhibited the best photocatalytic performance in the wide range of radiation that attributed to the formation of ZnO phase and ZnTiO₄ detected by XRD, FTIR and XPS analysis. Also, the research on the antimicrobial activity showed that, although TiO₂ has no inhibitory effect, the samples synthesized by the wet impregnation method in alkaline solution have the highest inhibitory effect on the&nbsp;growth of gram-positive and gram-negative bacteria, confirming the contribution of the synergic effect to the formation of active centres with high photocatalytic activity. The samples obtained by the coprecipitation method had lower, but satisfactory photocatalytic activity, while samples synthesized by the wet impregnation method in water solution showed the lowest photocatalytic activity, as well as low inhibitory effect on the bacteria growth. The research in this Ph.D. thesis contributed to the knowledge on the characteristics of novel composite materials TiO₂/ZnAl layered hydroxides that are of essential importance concerning their photocatalytic activity in the wide range of radiation (UV / VIS), as well as their overall performance that enable their use in a variety of ecological processes, such purification of water and air pollution from organic, inorganic and biological pollutants.</p>

Recently developed mathematical tools for the modelling of contact problems on thin film structures are adapted to allow the investigation of arbitrarily mixed purely isotropic and transversally isotropic laminate structures. The new tool is applied to model a variety of load problems resulting in the failure of windsurfing boards consisting of a relatively thin laminate shell and a soft polymer foam core. It is shown that local impact and distributed bending loads due to “bad landing” after high jumps or contact with parts of the sailing gear (the so called rig) especially the front part of the boom are leading to the most critical stress distributions resulting in failure. So most of the investigated boards were damaged because the rider (windsurfer) landed flat and thus produced a sudden impact force under his feet (impact defect). Other overloading occurred due to overturning of so called loop movements or the landing of the board exactly on respectively between two waves and this way producing high bending moments. Some of those typical loads are analysed in detail and the stresses occurring in the complex structure of the windsurfing boards are evaluated.

Le but de cette thèse est l’obtention de matériaux multiferroïques par l’insertion de molécules organiques dans une matrice magnétique d’hydroxide simple lamellaire. Durant cette thèse a été démontré la faisabilité de la fonctionnalisation d’hydroxides simples lamellaires de cuivre et de cobalt par des molécules possédant des fonctions d’accroche acide phosphonique. Le développement des techniques de pré-fonctionnalisation a permis de fonctionnaliser ces hydroxides simple lamellaire par une variété importantes de molécules (fluorènes, benzènes, thiophènes et complexes de métaux de transition) afin d’apporter une propriété additionnelle au magnétisme de l’hydroxyde. Les premières mesures ont permis de mettre en évidence un couplage entre temperature d’ordre magnétique et anomalie diélectrique. La complexité de la mesure des propriétés diélectriques avec ces échantillons (sur poudre pastillées à froid) ont mis en lumière la nécessité d’obtenir des tailles de cristallites plus importantes. Des efforts sur la taille des cristallites ont donc été effectués et ont permis d’obtenir des monocristaux d’hydroxy- dodecylsulfate de cuivre. / The main goal of this thesis is to obtain multiferroic materials via the intercalation of organic molecules in a magnetic inorganic matrix made of layered simple hydroxide. The possibility to use phosphonic acid as grafting moiety for the functionalization of layered simple hydroxides has been demonstrated during this thesis. Pre-functionalization techniques has allowed the functionalization of layered simple hydroxides of copper and cobalt with a wide variety of molecules (fluorenes, benzenes, thiophenes or transition- metal complexes) to bring an additional property to the magnetic properties of the layered hydroxide. The first measurements revealed a coupling between magnetic ordering temperature and dielectric anomaly. The dielectric properties measurements proved to be difficult with the samples (on cold-pressed pellets) and shown the usefulness of developing new methods to improve the cristallite size. To that end, new syntheses procedures led to the obtention of mono crystals of copper-hydroxidodecylsulfonate allowing to get additional structural informations.

Sustainability issues have been a popular and important topic on the world’s agenda the recent years, which has caused businesses to follow the policies of operating more sustainable. One of the latest introduced guidelines is the Global Goals imposed by the United Nations to be met by 2030. In light of these goals, awareness regarding sustainability issues among consumers and other stakeholders has increased, leading to that change is inevitable for businesses to start operating sustainably. The concept of sustainable business model innovation therefore becomes relevant. There is a lot of research regarding sustainable business model innovation. However, the research is heavily focusing on theoretical aspects of it, and less is given to the practical creation and implementation of sustainable business models. Further, less focus is given to start-up companies specifically. Due to the identified research gap, this study aims to answer the research question: “How can start-ups successfully create and implement sustainable business models to become an established actor on its specific market?” The purpose of this study is to create an understanding and contribute with extended knowledge of how sustainability is practiced in start-ups. More specifically, how sustainable business models are created and implemented in start-ups. A qualitative abductive approach was used to fulfill this purpose. Additionally, six semi-structured interviews were conducted with founders of start-ups and business coaches from Swedish incubators, which were structured based on the themes from the Lean Start-up Framework (LSF). This framework, along with the Triple Layered Business Model Canvas (TLBMC) showed to be of importance after the theoretical review. The key findings retrieved displayed that the LSF is suitable to describe the sustainable start-up process as well. Yet, the TLBMC needs to be integrated to fulfill the purpose of sustainability. Further, the benefit versus impact is shown to be of great importance whereas the framework’s components were modified in that sense as well in those cases needed. This study theoretically contributes to extended knowledge and additional components of the Lean Start-up framework that are advocated to be crucial to create a sustainable business model. These additional components are further of value for the existing field of research. Practically, by the extended and modified framework, it offers valuable insight for entrepreneurs with a business idea where the purpose is to offer a sustainable value proposition. Lastly, this study contributes to a social level by providing guidelines on the implementation of sustainability in the business model, leading to the encouragement to operate sustainably and towards a better environment and society.

The intercalation of surfactant anions, namely sodium dodecyl sulphate, sodium benzene sulphonate and lauric acid, into commercial layered double hydroxides (LDH-CO3) with approximate composition [Mg0.654AI0.346 (OH)2](CO3)0.173.0.5H2O] was explored. LDH-CO3 is commercially available in bulk form owing to its large scale applications as a PVC stabiliser and acid scavenger in polyolefins. It is therefore of interest to investigate intercalation methods using LDH-CO3 as starting material. The intercalation method used was compared with the pre existing procedures, for instance the co-precipitation, ion exchange and regeneration methods. Due to the tenacity with which the carbonate ion is held in LDH-CO3, direct ion exchange is an intricate matter. Hence, in the regeneration method the carbonate ion is removed by thermal treatment and the LDH-surfactant is obtained by reaction of the LDH and surfactant in an aqueous medium. Nevertheless, the resulting products are impure and poorly crystallised, and only partial intercalation is achieved. The underlying principle of the current method is protonation of the carbonate anion to a monovalent anion that is easily exchanged with surfactant anions. Improved results were obtained when water-soluble organic acids were used, the most suitable being lower aliphatic carboxylic acids, e.g. acetic, butyric and hexanoic acid. In contrast, higher linear aliphatic carboxylic acids are preferentially intercalated to the anionic surfactants. In both cases the carboxylic acids are assumed to assist intercalation by facilitating the elimination of the carbonate ions present in the anionic clay galleries. X-ray diffraction analysis, thermal analysis and infrared spectroscopy confirmed the monolayer intercalation of LDH-dodecyl sulphate and LDH-dodecylbenzene sulphonate. In contrast, LDH-laurate featured a bilayer structure. / Dissertation (MSc)--University of Pretoria, 2009. / Chemistry / unrestricted

The interconnection of components of industrial automation and control systems (IACS) and enterprise systems involved in processes ranging from generation and transmission to billing within electric utilities poses challenges regarding cyber security as well as division of organisational responsibility. One means of organising these components and systems is to use a zone model in which they are segmented, offering layered defences as well as a logical grouping. One such zone model is the zone model under review, which was presented by Zerbst et al. in a CIRED paper from 2009. This master thesis reviews that zone model and compares it to other industry standard zone models which have been found to be able to be categorised into either functional based models or layered defence models. The outcome is a rough definition of what kind of content fits in the various zones of the reviewed model, as well as a normalised zone model to be used for comparison. A suggested method for dividing system components into zones is based on the 4R-method considering the response time, resolution, reliability and reparability of the system component, although its accuracy has not been empirically tested.

Hierarchical arrangement of biological composites such as nacre and bone containing high filler (ceramic) content results in high strength and toughness of the natural material. In this study we mimic the design of layered bone microstructure and fabricate an optimal multifunctional bio-nanocomposite having strength, toughness and corrosion resistance. Poly (butylene adipate-co-terephthalate) (PBAT), a biodegradable polymer was used as a substrate material with the reinforcement of LDH (Layered double hydroxide) as a nanofiller in different concentrations to achieve enhancement in mechanical properties as well as processing related thermostability. Corrosion resistance was increased by mimicking a layered structured which incorporated a tortuous diffusion path.

The new nickel/layered silicate nanocomposites were electrodeposited from different pHs to study the influence on the metal ions/layered silicate plating solution and on the properties of the deposited films. Nickel/layered silicate nanocomposites were fabricated from citrate bath atacidic pHs (1.6−3.0), from Watts’ type solution (pH ~4-5), and from citrate bath at basic pH (~9). Additionally, the new nickel/molybdenum/layered silicate nanocomposites were electrodeposited from citrate bath at pH 9.5. The silicate, montmorillonite (MMT), was exfoliated by stirring in aqueous solution over 24 hours. The plating solutions were analyzed for zeta potential, particle size, viscosity, and conductivity to investigate the effects of the composition at various pHs. The preferred crystalline orientation and the crystalline size of nickel, nickel/layered silicate, nickel/molybdenum, and nickel/molybdenum/layered silicate films were examined by X-ray diffraction. The microstructure of the coatings and the surface roughness was investigated by scanning electron microscopy and atomic force microscopy. Nickel/molybdenum/layered silicate nanocomposites containing low content of layered silicate (1.0 g/L) had increase 32 % hardness and 22 % Young’s modulus values over the pure nickel/molybdenum alloy films. The potentiodynamic polarization and electrochemical impedance measurements showed that the nickel/molybdenum/layered silicate nanocomposite layers have higher corrosion resistance in 3.5% NaCl compared to the pure alloy films. The corrosion current density of the nickel/molybdenum/layered silicate nanocomposite composed of 0.5 g/L MMT is 0.63 µA·cm-2 as compare to a nickel/molybdenum alloy which is 2.00 µA·cm-2.

Le but de ce travail de thèse est d’étudier et de rationaliser, à l’aide de mécanismes réactionnels, le comportement sous irradiation de différents matériaux argileux. Les systèmes d’intérêt ont d’abord été le talc synthétique, qui est le prototype d’un matériau non gonflant. Sous irradiation par des électrons accélérés, la production de dihydrogène dans ce système, uniquement due aux groupes hydroxyle de surface, est du même ordre de grandeur que celle obtenue dans l’eau liquide. Ce rendement est divisé par 30 dans le cas du talc naturel de Luzenac, mettant ainsi en évidence l’importance des impuretés comme capteurs des précurseurs du dihydrogène. Des smectites synthétiques, qui sont des matériaux gonflants, ont ensuite été étudiées.Les résultats mettent en évidence la radiolyse de l’eau confinée dans l’espace interfoliaire, qui conduit à des rendements de production de H2 pouvant être deux à trois fois supérieurs à ceux mesurés dans l’eau. Ils sont similaires pour la saponite et la montmorillonite, montrant que la localisation de la charge foliaire ne joue qu’un rôle mineur. Enfin, l’étude des hydroxydes doubles lamellaires ou argiles anioniques, prouve que, dans ce cas, c’est la nature de l’anion dans l’espace interlamellaire qui pilote la réactivité. En parallèle à ces mesures, des expériences de spectroscopie paramagnétique de l’électron ont permis de proposer des mécanismes réactionnels. Enfin, tous les résultats obtenus sont d’intérêt dans le contexte du stockage des déchets radioactifs. / The aim of this PhD thesis is to study and understand, by proposing reaction mechanisms, the behavior under irradiation of various clay materials. The systems of interest were first synthetic talc, which is the prototype of a non-swelling material. Under irradiation by accelerated electrons, the production of dihydrogen in this system, due solely to surface hydroxyl groups, is of the same order of magnitude as the one obtained in liquid water. This yield is divided by 30 in the case of natural talc from Luzenac, thus highlighting the importance of the impurities as scavengers of the precursors of dihydrogen. Synthetic smectites, which are swelling materials, were then studied.The results evidence the radiolysis of water confined in the interlayer space, leading to H2 yields which may be two to three times higher than those measured in water. Moreover, they are similar for montmorillonite and saponite, evidencing that the charge location plays only a minor role. Finally, the study of double layered hydroxides or anionic clays shows that, in this case, the nature of the anion in the interlamellar space controls the reactivity. Parallel to these measurements, electron paramagnetic spectroscopy experiments have enabled proposing reaction mechanisms. Finally, all these results are of interest in the context of the disposal of radioactive waste.

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