Asfaltenos são constituídos de hidrocarbonetos policíclicos aromáticos que fazem parte de uma das classes de compostos químicos mais poluentes e carcinogênicos. São bem conhecidos por formarem inscrutações que obstruem tubulações, podendo até levar ao fechamento do poço. Estes podem constituir até 20% do petróleo, que ainda remanesce o principal recurso de energia usado em nosso planeta. Atualmente são convertidos em asfalto e coque durante o processo de refino, através de destilação destrutiva, exigindo altas temperaturas e emitindo compostos de enxofre na atmosfera. No entanto, sua conversão em matérias-primas mais valiosas e produtos menos poluentes, por exemplo, por craqueamento fotocatalítico ou oxidativo poderia ser uma opção mais limpa e econômica. A nanotecnologia vem sendo incorporada nas pesquisas com petróleo pelas contribuições positivas que acrescenta tanto do ponto de vista econômico como ambiental, assim como através do melhoramento e recuperação de óleos pesados. Os nanomateriais em geral possuem a vantagem de ter maior grau de dispersão e propriedades diferenciadas em relação ao bulk. Neste trabalho estudaram-se as interações entre os asfaltenos e diferentes nanomateriais com propriedades magnéticas, ópticas e eletrônicas extraordinárias, como as nanopartículas de óxido de ferro (Nmag), os híbridos de nanopartículas de ouro com óxido de grafeno reduzido (RGO@AuNP) e os nanobastões de ouro (AuNRs) respectivamente. As interações entre asfaltenos e Nmags com diferentes ligantes passivantes (C8H20O4Si e C6H17NO3Si) foram feitas através da construção de isotermas e experimentos de adsorção,revelando os tipos de ligação que ocorrem entre esses materiais, cobertura e a capacidade adsortiva. O recobrimento da nanopartícula e a concentração de asfalteno influenciam na adsorção, sendo a interação mais forte com as Nmags livres, indicando coordenação do ferro nos substituintes dos anéis aromáticos do asfalteno, tendo cobertura por monocamada. As Nmags funcionalizadas interagem por forças intermoleculares com os asfaltenos, apresentando cobertura por multicamadas. Em altas concentrações de asfalteno em tolueno, a adsorção foi mais efetiva para as Nmags funcionalizadas, pois a coordenação com o ferro é dificultada devido a formação de micela reversa, prevalecendo as interações hidrofóbicas. Houve uma drástica redução na temperatura de craqueamento dos asfaltenos na presença das Nmags, em mais de 100ºC, demonstrando seu potencial na catálise oxidativa de asfaltenos. As interações dos materiais RGO@AuNP e AuNR em filmes com asfalteno foram investigadas por microscopia hiperespectral de campo escuro. Como resultado observou-se o deslocamento e o alargamento da banda de espalhamento no espectro eletrônico, indicando a ocorrência de transferência de carga entre as espécies. A partir disso, realizaram-se fotocatálises com o RGO@AuNP à temperatura ambiente sob luz visível, utilizando o 9-antraldeído como composto modelo para o asfalteno. A reação levou à formação de endoperóxidos cíclicos, que sofreram clivagens com 90% de rendimento. Por ultimo, realizou-se um estudo mecanístico utilizando um sensor fluorogênico de espécies reativas de oxigênio (ROS) para avaliar a atividade fotocatalítica do RGO@AuNP. Mostrou-se que ocorrem transferências de elétrons fotoinduzidas da AuNP para o RGO em uma escala de tempo de ~11 fs, com eficiência quântica de ~35% e que radicais superóxidos (O2•-) podem ser gerados pelos efeitos sinérgicos da fotoexcitação do híbrido. / Asphaltenes are composed by polycyclic aromatic hydrocarbons that belong to one of the most polluting and carcinogenic chemical classes. They are well known for forming hard scales that obstruct pipelines and may even lead to the well shut down. They can constitute up to 20% of petroleum, which still remains the main source of energy used in our planet. At the present time, asphaltenes are converted into asphalt and coke by destructive distillation, in spite of the high cost and polluting technology involved, which employs high temperatures and releases sulfur compounds into the atmosphere. However, their conversion into more valuable raw materials, for instance, by photocatalytic or oxidative cracking using suitable catalysts, would be a better, more economic option. In recent years, nanotechnology has been incorporated into oil research, opening new economic and environmental perspectives, including the improvement and recovery of heavy oils. In general, nanomaterials have the advantage of being better dispersed and exhibiting differentiated properties in relation to the bulk. In this study the interactions between asphaltenes and different nanomaterials exhibiting remarkable magnetic, optical, and electronic properties, such as iron oxide nanoparticles (Nmag), hybrids of gold nanoparticles with reduced graphene oxide (RGO@AuNP) and the gold nanorods (AuNRs) respectively were investigated. The interactions between asphaltenes and Nmags with different surface-passivating ligands (C8H20O4Si and C6H17NO3Si) were made by performing isotherms curves and adsorption tests, revealing the types of binding between these materials, their coverage and the adsorptive capacity. The nanoparticle coating and the asphaltene concentration influence the adsorption. Theinteraction was stronger using the free Nmag, indicating coordination of the iron with the aromatic rings of the asphaltene, having a monolayer cover. Functionalized Nmags interact by intermolecular forces with asphaltenes, having a multilayer coverage. At high concentrations of asphaltene in toluene, the adsorption was more effective for the functionalized Nmags, since the coordination with the iron was hampered due to the formation of reverse micelle, prevailing the hydrophobic interactions. There was a drastic reduction in the asphaltene cracking temperature in the presence of Nmags, bigger than 100ºC, showing its potential on the oxidative catalysis of asphaltenes. The interactions of RGO@AuNP and AuNR materials with asphaltene films were investigated by dark field hyperspectral microscopy. As a result there was a shift and a broadening of the band in the electronic spectrum, indicating the occurrence of charge transfer between the species. From this, photocatalysis were performed with the RGO@AuNP, at room temperature, under visible light, using 9-antraldehyde (9-ATA) as a model compound for asphaltene. The reaction leads to the formation of cyclic endoperoxides that undergo further reactions, resulting in their cleavage, with 90% yield for the 9-ATA degradation. Finally, a mechanistic study was carried out using a fluorogenic sensor of reactive oxygen species to evaluate the photocatalytic activity of RGO@AuNP. It was showed that photoinduced electron transfer from AuNP to RGO can occur in ~11 fs time scale, with a quantum yield of ~35%, and superoxide radicals anions (O2•-) can be generated by synergistic effects after the hybrid photoexcitation.

"In the past decade nanomaterials have attracted the interest of scientists and engineers all over the world due to their unique properties. Through their devoted experimental efforts, limited advances have been made on the synthesis of nanomaterials, the integration of nanomaterials into the structures of larger scales, and the property study of nanomaterials to explore possible applications. Despite the huge amount of money, resources, and effort invested in nanomaterials, several challenges still remain as obstacles on the way towards the successful large scale use of nanomaterials to benefit human life and society. For example, the need for low-cost, robust, and highly productive manufacturing methods and the demand for efficient integration of nanomaterials with materials and devices of larger length scales are still left unmet. The objective of this work was to utilize cost-efficient nanofabrication methods such as template-assisted fabrication, electrodeposition, and chemical vapor deposition to fabricate nanomaterials, integrate nanomaterials with larger structures to form a hierarchical composite, and explore the application of unique nanostructured electrode in lithium-ion batteries. Thus the thesis consists of three main parts: (1) fabrication of one-dimensional inorganic nanomaterials such as metal nanowires, metal nanorods, and carbon nanotubes with good control over shape and dimension; (2) synthesis of hierarchical carbon nanofibers on carbon microfibers and/or glass microfibers; and (3) development of nanostructured anodes to improve high-rate capability of lithium-ion batteries by adapting nanorod arrays as miniature current collectors. "

Orientador: Antonio Riul Júnior / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T19:37:47Z (GMT). No. of bitstreams: 1 Jimenez_MawinJavierMartinez_D.pdf: 7578838 bytes, checksum: def5bc65d8270856f55d63211e1e0f09 (MD5) Previous issue date: 2017 / Resumo: Para alcançar alto desempenho em dispositivos e aplicações faz-se necessário uma melhor compreensão do comportamento de materiais a base de grafeno em nanoescala para otimização de design e fabricação. A síntese química é uma excelente rota alternativa para produzir compósitos em nanoestruturas bem definidas de tamanhos semelhantes, garantindo propriedades elétricas reprodutíveis para aplicações confiáveis. O grafeno, na forma de pontos quânticos (QDs, do inglês quantum dots) em dimensão zero e nanofolhas (NPLs, do inglês graphene nanoplateletes) bidimensionais (2D), são materiais emergentes com funcionalidades únicas promissoras para novas aplicações. Neste trabalho apresentamos um estudo detalhado dos mecanismos de transporte em nanoestruturas formadas pela técnica de automontagem por adsorção física (LbL, do inglês Layer-by-Layer) na forma de multicamadas, com controle de espessura em nível molecular. Os filmes LbL foram formados por óxido de grafeno reduzido (rGO) funcionalizado com diferentes polieletrólitos tanto na forma de QDs quanto nanofolhas. As caracterizações elétricas indicaram corrente limitada pela carga espacial em algumas amostras, e em outras arquiteturas moleculares, mecanismo de condução via Poole-Frenkel seguindo a lei de Mott dominada por saltos variáveis. A flexibilidade da técnica LbL aliada à dimensão dos materiais utilizados foram favoravelmente exploradas como um ajuste fino para controle da mobilidade de portadores dentro das nanoestruturas formadas. Foi observado em alguns casos uma condução planar no interior da camada contendo rGOs na estrutura LbL com mobilidade eletrônica efetiva de ~ 35 cm² V^-1 s^-1. Em outros casos um mecanismo de condução 3D (interplanar ao longo de toda nanoestrutura LbL) com mobilidade eletrônica de ~ 151 cm² V^-1 s^-1. Medidas em função da temperatura indicaram alta probabilidade de saltos randômicos entre ilhas condutoras de rGO distribuídas ao longo da camada contendo os pontos quânticos, que contribui para um maior tempo de trânsito dos portadores e, consequentemente, mobilidades menores. O oposto ocorre para as nanofolhas de rGO, que requerem maiores energias de ativação devido ao tamanho e presença de defeitos, resultando em caminhos condutores maiores e com maiores mobilidades / Abstract: To achieve high-performance in devices and applications it is important a better comprehension of the behavior at nanoscale of graphene-based materials to promote a rational design and fabrication. The chemical synthesis is an excellent alternative route to optimize graphene-based composites in well-defined nanostructures of similar sizes, ensuring reproducible electrical properties for reliable applications. Graphene as quantum dots (QDs) and nanoplatelets (NPLs) presents emerging zero- and two-dimensional (2D) materials with promising unique functionalities to novel applications. We present here a detailed study of the charge transport mechanisms in multilayered nanostructures formed by physical adsorption through the layer-by-layer (LbL) technique, with molecular level thickness control. The LbL films were formed by reduced graphene oxides (rGO) functionalized with different polyelectrolytes and processed either as QDs or nanoplatelets. The electrical characterizations indicated a space-charge-limited current (SCLC) in some samples, while in other molecular architectures it was found a Poole-Frenkel conduction mechanism dominated by a Mott-variable range hoping model. The LbL assembly together with the dimensionalty of the materials could be favorably used as a fine tuning to control the charge carrier mobility inside the formed nanostructures. The flexibility of the LbL technique together with the dimensionality of the materials were favorably explored as a fine tuning of the charge carrier mobility inside the nanostructures. It was observed in some cases a 2D intra-planar conduction within the rGO layer in the LbL films, with an effective charge carrier mobility of ~ 35 cm² V-1 s-1, and in other cases a 3D conduction mechanism (interplanar along with the LbL nanostructure) with electronic mobility of ~ 151 cm² V-1 s-1. Temperature measurements indicated a higher probability of random jumps between rGO conducting "islands" distributed along with the plane layer having quantum dots, which contributes for a longer transit time of the carriers and, consequently, lower mobility values. The opposite occurred for the rGO nanoplatelets that required higher activation energy due to size and presence of defects, resulting in larger conductive pathways and higher mobilities / Doutorado / Física / Doutor em Ciências / 1247719 / CAPES / FAPESP

Luz e oxigênio induzem reações de degradação (foto-oxidação) que modificam as propriedades físicas e químicas da matéria, efeitos nocivos da radiação ultravioleta (UV) podem causar descoloração de corantes e pigmentos, amarelamento de plásticos, perda de brilho e da propriedade mecânica (cracking) de materiais, queimaduras, câncer de pele, entre outros problemas relacionados à luz UV. A fim de reduzir os efeitos nocivos da radiação UV e alcançar uma adequada conservação das propriedades dos materiais surgem os absorvedores ou filtros UV. Uma vez que materiais nanométricos a base de cério apresentam atividade fotocatalítica menor e elevada absorção na região do UV tornam-se filtros solares com aplicabilidade em diversas áreas quando comparados aos óxidos utilizados atualmente com função de filtros solares (ZnO e TiO2). Fosfatos de cério (III) (CePO4) foram preparados por Pechini (modificado), síntese hidrotermal e microemulsão reversa; as amostras foram submetidas a tratamento térmico em distintas temperaturas com o intuito de averiguar a estrutura do CePO4 e influência desta na capacidade da absorção UV. Sistemas de óxidos metálicos contendo cério também foram estudados, sendo sintetizados por sol-gel não-alcoóxido e aplicados na forma de pó e filme fino sobre substrato de vidro. A preocupação com a morfologia e o tamanho dos materiais motivou a escolha pelas metodologias de síntese empregadas. Neste trabalho foram exploradas e elucidadas as propriedades dos materiais a base de cério em absorver luz UV, devido às transições 4f-5d dos íons Ce3+ e/ou às transições entre banda de condução e banda de valência. As amostras foram analisadas por espectroscopia de absorção no UV-Vis e na região do infravermelho (FTIR), difração de raios X (XRD), difração de elétrons, susceptibilidade magnética (MS), microscopia eletrônica de varredura (SEM), microscopia eletrônica de transmissão (TEM), espectroscopia de reflectância difusa (DRS), atividade fotocatalítica (AF) e ressonância paramagnética de elétrons (EPR). As excelentes propriedades morfológicas, ópticas e fotocatalíticas indicam a possível aplicação dos materiais à base de cério, foco de investigação do presente trabalho, como filtros solares em proteção cosmetológica (cremes, shampoos, sprays etc) ou de materiais (tintas, vernizes, vidros e outros). / Light and oxygen induce degradation reactions (photo-oxidation) that modify the physical and chemical properties of the matter. The damaging UV radiation is responsible for the discoloration of dyes and pigments, weathering, yellowing of plastics, loss of gloss and mechanical properties (cracking), sunburnt skin and other problems associated to UV light. UV absorbers or UV filters have been used in order to reduce these damaging effects and achieve an adequate conservation of the properties of the materials. In front of this problem, cerium based nanomaterials are promising inorganic UV absorbers for the substitution of zinc and titanium oxide, once it presents high UV absorptivity, a lower refraction index than TiO2 and ZnO, and a higher chemical inertia (and thus a lower photocatalytic activity). Nanostructured cerium phosphates (CePO4) were prepared by Pechini, hydrothermal and reverse microemulsion synthesis, and some parameters (calcinations temperature and reactants rate) employed in each synthesis were investigated. Cerium metal oxide systems synthesized by sol-gel (non-alcooxide) and applied as powder and thin films materials were investigated too. The methodology of the synthesis were chosen aiming ideal morphology and particles size. In this work we explored and elucidated the properties of UV absorber cerium based nanomaterials , due to 4f-5d transitions of Ce3+ ions, charge transference of Ce4+ and, a little portion is due to the contribution of valence and conduction band. The samples were characterized by UV-Vis absorption spectroscopy , Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electron diffraction, magnetic susceptibility (MS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), photocatalytic activity (PA) and electron paramagnetic resonance (EPR). The excellent morphological, optical and photocatalytic properties indicate the possible application of cerium based materials in solar protection for cosmetics (creams, shampoos, sprays etc.) or materials (paints, varnishes, glass and others).

Les matériaux nanostructurés multifonctionnels à base de terre rare (R) et métal de transition (T) présentent un intérêt croissant dans la recherche scientifique. Le développement de cet axe est basé sur la maitrise de la structure fondamentale et le comportement de la matière à l’échelle nanométrique. Dans ce travail, nous nous sommes intéressés aux alliages Pr5Co19, leurs dérivés carburés et hydrurés. Ce système cristallise dans la structure rhomboédrique de type Ce5Co19 de groupe d’espace R-3m. Le composé Pr5Co19 présente une transition magnétique de l’état ferromagnétique à l’état paramagnétique à 690 K. Une anisotropie uniaxiale avec un champ coercitif de l’ordre de 1.5 T ont été enregistrés à la température ambiante.Par ailleurs, Nous avons observé que l’insertion d’un élément léger tel que le carbone ou l’hydrogène est un moyen efficace permettant d’augmenter la température de Curie par rapport au composé parent. Les nanomatériaux, de formule générale Pr5Co19Hx, présentent des cycles d’absorption et désorption réversibles, avec une capacité d’absorption de l’hydrogène égale à 12H/f.u, soit 0.5 hydrogène par maille (H/M) au total.Parallèlement, nous nous sommes intéressés à l’étude de l’effet magnétocalorique des intermétalliques de type Pr-Co. Le composé Pr5Co19 présente un effet magnétocalorique géant de l’ordre de 5.2 J/kg.K pour un faible champ appliqué.Les nanomatériaux intermétalliques de type Pr5Co19 peuvent être ainsi considérés comme des composés multifonctionnels. Grâce à leurs propriétés structurales, magnétiques et magnétocaloriques, ils s’avèrent être de bons candidats dans le domaine des aimants permanents, mais aussi pour la réfrigération magnétique à haute température et pour le stockage de l’hydrogène, vu le besoin croissant en énergie alternative moins polluante / Multifunctional nanomaterials based on rare-earth (R) and transition metal (T) present a major interest in scientific research. We are interrested in the Pr5Co19 alloy. This system crystallizes in the rhombohedral Ce5Co19-type structure with space group R-3m. The Curie temperature Tc is about 690 K. We determined the value of the magnetization at saturation MS = 83 Am2 / kg using the approach law to saturation. A uniaxial anisotropy with a coercive field equal to 1.5 T at room temperature were obtained.Moreover, we have observed that the insertion of a light element such as carbon or hydrogen, allows to increase the Curie temperature of the system. The Pr5Co19Hx hydrides present a reversible cycle of absorption/desorption, with a hydrogen absorption capacity equal to 12H / f.u, or 0.5H / M in total.We are also interested in the study of the magnetocaloric effect of the intermetallics Pr-Co type. We have shown that Pr5Co19 compound has a giant magnetocaloric effect, of about 5.2 J / kg.K at low field.The intermetallic nanomaterials Pr5Co19 could be used as a multifunctional compound. These results indicate that it is an attractive alloy due to its structural, magnetic and magnetocaloric properties. It could be good candidates for permanent magnets, but also for magnetic refrigeration at high temperature and for hydrogen storage

Nanoparticles are increasingly incorporated into consumer products because of their unique, size-dependent properties. Although these properties are commercially appealing, data are lacking regarding the fate and reactivity of nanoparticles once incorporated into materials. This information gap prevents accurate assessment of hazards that these materials potentially present to consumers and the environment. To address this concern, new research is needed to investigate the reactivity and transformations of nanoparticles. This dissertation describes the use of an electron transparent characterization platform to observe nanoparticle transformations. Nanoparticles were tethered to the surface of an analysis platform, exposed to a variety of conditions, and evaluated for reactivity and response. The characterization of silver nanoparticles revealed the generation of new daughter nanoparticles on surfaces in ambient humid conditions. Our observations showed that the transport of material is highly dependent on relative humidity and that pH equilibria drives the deposition of new particles and degradation. We discovered, by applying these findings to macro-silver objects, that bulk silver generates new nanoparticles on surfaces. This illuminated the possibility of other, yet undiscovered, naturally occurring nanoparticles. In the second model system, 1.5 nm gold nanoparticles were tethered by a robust metal oxide bond from the terminal group of the stabilizing ligand. This strategy facilitated precise control over thiol ligand removal using a dilute ozone oxidation. Tracking particle oxidation over time allowed us to gain unprecedented control over core exposure, size maintenance, and surface tethering. This platform was also utilized as a proof-of-concept for direct observation of transformations in complex media. Ligand and core transformations were monitored in a variety of biologically relevant conditions using tethered nanoparticles. Morphological and chemical transformations were characterized and correlated to results from solution monitoring. The use of a platform based approach to evaluating the reactivity of nanoparticles in the environment holds promise for evaluations of nanoparticles and their transformation products. The demonstration of monitoring reactivity in systems equilibria, carefully controlled transformations, or complex media shows the versatility of this strategy. Only through the use of this analysis platform was the direct observation of nanoparticle transformations possible. This dissertation includes previously published, unpublished, and co-authored materials. / 10000-01-01

Hunting for improved energy storage devices based on rechargeable Li-ion batteries and other advanced rechargeable batteries is one of the hottest topics in today's society. Both Li- ion batteries and Li-O2 batteries have been studied within the thesis. The research work of this thesis contains two different parts. Part 1. The controlled synthesis of the extreme small sized nanoparticles and their application for Li-ion batteries; Part 2. The study of the O2 reduction mechanism in Li-O2 batteries with aprotic electrolytes. In the first part, two different types of extremely small-sized TiO2 nanoparticles with at lease on dimension less than 3 nm was synthesised via solvothermal/hydrothermal reaction, i.e., anatase nanosheets and TiO2(B). These nanoparticles were obtained without any contamination of long chain organic surfactants. A series of systematic characterisation methods were employed to analyse the size, phase purity, and surface condition. These extremely small-sized nanoparticles exhibit improved capacity, rate performance as anode materials for Li-ion batteries. The shapes of load curves of charge and discharge are significantly modified due to the reduced size of TiO2 nanoparticles. In chapter 3, we will see the variation of the capacity and the load curve shape of the anatase nanosheets according to their thickness and surface conditions. The origin of the excessive capacity is analysed based on the electrochemical data. It has been identified that both pseudocapacitive (interfacial) Li+ storage and the excessive Li+ -storage from the bulk contribute to the increased capacity. In chapter 4, the shape and size of the sub-3 nm TiO2(B) nanoparticles are studied, a method based the PXRD data is established. These nanoparticles demonstrate a reversible capacity of 221 mAh/g at a rate of 600 mA/g and remain 135 mAh/g at 18000 mA/g without significant capacity fading during cycling. In the last part, a systematic study of O2 reduction mechanism for aprotic Li-O2 batteries based on the combination of a series of electrochemical and spectroscopic data is presented. The novel mechanism unifies two previous models for the growth of Li2O2 during discharge, i.e., Li2O2 particle formation in the solution phase and Li2O2 film formation on the electrode surface. The new mechanism provides fundamental conceptions for the improvement of Li2O2 batteries and shed light on the future research of Li2O2 batteries.

The production of large area, high quality two-dimensional (2D) materials using chemical vapour deposition (CVD) has been an important and difficult topic in contemporary materials science research, after the discovery of the diverse and extraordinary properties exhibited by these materials. This thesis mainly focuses on the CVD synthesis of two 2D materials; bilayer graphene and monolayer tungsten disulphide (WS2). Various factors influencing the growth of each material were studied in order to understand how they affect the quality, uniformity, and size of the 2D films produced. Following this, these materials were combined to fabricate 2D vertical heterostructures, which were then spectroscopically examined and characterised. By conducting ambient pressure CVD growth with a flat support, it was found that high uniform bilayer graphene could be grown on the centimetre scale. The flat support provides for the consistent delivery of precursor to the copper catalyst for graphene growth. These results provide important insights not only into the upscaling of CVD methods for growing large area, high quality graphene and but also in how to transfer the product onto flexible substrates for potential applications as a transparent conducting electrode. Monolayer WS2 is of interest for use in optoelectronic devices due to its direct bandgap and high photoluminescence (PL) intensity. This thesis shows how the controlled addition of hydrogen into the CVD growth of WS2 can lead to separately distributed domains or centimetre scale continuous monolayer films at ambient pressure without the need for seed molecules, specially prepared substrates or low pressure vacuum systems. This CVD reaction is simple and efficient, ideal for mass-production of large area monolayer WS2. Subsequent studies showed that hexagonal domains of monolayer WS2 can have discrete segmentation in their PL emission intensity, forming symmetric patterns with alternating bright and dark regions. Analysis of the PL spectra shows differences in the exciton to trion ratio, indicating variations in the exciton recombination dynamics. These results provide important insights into the spatially varying properties of these CVD-grown TMDs materials, which may be important for their effective implementation in fast photo sensors and optical switches. Finally, by introducing a novel non-aqueous transfer method, it was possible to create vertical stacks of mixed 2D layers containing a strained monolayer of WS2, boron nitride, and graphene. Stronger interactions between WS2 on graphene was found when swapping water for IPA, likely resulting from reduced contamination between the layers associated with aqueous impurities. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, a result which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with large area coverage and controllable thickness on the atomic level.

2,4,6-trichlorophenol (TCP) is a pervasive carcinogenic water contaminant found in a wide variety of water and waste systems and is a pertinent model compound of broader aromatic organics, specifically organo-halide pesticides. These compounds are persistent in the environment and show resilience to regular water and waste treatment protocols thus warranting the development and implementation of novel treatment materials for improved contaminant removal. Zero-valent iron (ZVI) has demonstrated the ability to remove or degrade a wide variety of inorganic and organic water contaminants, including chlorophenols, and has been widely applied for in-situ groundwater remediation where contamination is often localised in a low-oxygen environment. ZVI's broader applications in water treatment have remained mainly limited due to corrosion, particle dispersion, and confinement issues in deployment. This work, therefore, explored the development, functionality, and potential application of new modified nZVI materials (nZVI-Osorb) and assessed their potential to improve iron's intrinsic functionality while also gauging the material's viability for TCP remediation in water and waste systems. Materials produced in this thesis were prepared utilising three different embedment procedures (1-pot, multiple additions, oxygen-free). All embedment methods resulted in tightly bound composites featuring high surface areas (340.2-449.1 sq. m/g) with net iron composition ranging from 10% to 29.78% by mass. Electron imaging microscopy verified even dispersion of iron throughout the substrate. Composite materials did not exhibit a delayed rate of atmospheric corrosion over nZVI controls evincing an 18% nZVI0 loss per day until reaching a stabilised concentration (7%) after 48 hrs. nZVI-Osorb composites did produce more favourable iron oxide species which remain conducive to electron transfer from core Fe0 atom. After 50 days, a majority of nZVI in nZVI-Osorb had oxidised to maghemite (30%) and magnetite (26%) compared to control nZVI producing 19% and 12% respectively. Unreactive hematite accounted for 47% of the control and just 36% of the composite. While 1-pot embedment allowed the most substantial control over final iron composition, the oxygen-free method allowed the most reliable preservation of initial nZVI0 concentrations through restricted oxidation. Materials generated through oxygen-free embedment were utilised in the following water treatment trials with TCP. Parameters related to sorption and degradation mechanisms of TCP by nZVI-Osorb were tested in aerobic conditions, e.g. surface and potable water. nZVI-Osorb materials demonstrated high extraction capacity for TCP from aqueous solutions (Qe=1286.4 ± 13.5 mg TCP/g Osorb, Qe=1253 ± 106.7 mg TCP/g nZVI-Osorb, pH 5.1, 120mg/L TCP) and followed pseudo second order kinetics. In the broader class of chlorophenols, sorptive affinity mirrored partitioning values with highly substituted chlorophenols displaying the highest sorption capacities. Degradation of TCP by nZVI-Osorb or nZVI controls was not observed due to corrosive hindrance and inadequate reductive capacity, suggesting that materials may not be suitable for highly aerated surface and potable water treatment systems. Environmental conditions pertinent to sorption and degradation mechanisms were evaluated to improve understanding and robustness of functionality in low-oxygen applications, such as wastewater and anaerobic digesters, where nZVI-Osorb treatment is anticipated to be advantageous to TCP sorption and methane production. pH was found to influence sorption dramatically. Acidic solutions below 5 found sorption > 90%. This capacity was reduced to < 30% when pH was raised above TCP pKa value (6.23) to 7 and above. Further trials found a positive effect on TCP sorption (+7.55%) linked to net pH reduction (5.1 to 3.3) with the addition of secondary acids (volatile fatty acids: acetic, propionic, butyric, 3x 100mg/L) commonly found in anaerobic digester systems. Salinity did not affect TCP sorption. The removal of dissolved and atmospheric oxygen increased total sorption (40ppm-+1.94%, 100ppm- +7.93%, 200ppm- +0.89%, 400mg/L- +14.59%) through reduced iron corrosion and the production of favorable iron oxides, but did not facilitate contaminant degradation. Biodegradation mechanisms for TCP have broadly been established, and new research has supported the improved cometabolic degradation of recalcitrant contaminants like TCP and PCP in nZVI-dosed anaerobic digesters. Model anaerobic digester systems (3.9 g/L nZVI-Osorb, 25mg/L TCP, 240 mg/L acetic, 120mg/L propionic, 120mg/L butyric acid) containing bioreactor sludge (62.5%) were observed through standard water quality diagnostics (pH, ORP, COD, head pressure) for 14 days and suggested that nZVI-Osorb did not inhibit cellular processes. Increased electron activity from iron corrosion and hydrogen gas production, increased overall pH and decreased total ORP in these AD systems. TCP degradation by-products (DCP, CP) were detected in dilute concentrations (< 0.01 mg/L) with poor recovery by LC-MS/MS. Results suggest that nZVIOsorb may be well-suited additive for AD systems. This study contributes to knowledge of the properties, functionality, and treatment mechanisms of metal-sorbent composites with a model chlorinated aromatic water contaminant in aerobic and anaerobic environments. The work identifies favourable environmental and process conditions to apply these materials in larger scale applications, particularly, anaerobic digestion and provides support for the continued refinement and improvement of nZVI based remediation systems.

Orientador: Edison Bittencourt / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2019-01-18T11:50:46Z (GMT). No. of bitstreams: 1 Camargo_Marcelode_M.pdf: 25344897 bytes, checksum: 8146c1fb634f94d4bb4152d5bcc07e66 (MD5) Previous issue date: 2010 / Resumo: Este estudo trata-se de um novo método de obtenção de fibras de nanocelulose a partir de algodão "Never Dried Cotton" NDC, (algodão nunca seco). O algodão classificado como NDC, apesar de possuir a mesma cristalinidade do algodão normal e muito mais poroso e, portanto, muito mais suscetível a eventuais tratamentos químicos. Esta maior porosidade deve-se ao fato de que o NDC, no seu estado natural, ainda não passou pelo processo de colapso do lumen devido a evaporação da seiva presente no seu interior. Com este colapso da estrutura, as inúmeras pontes de hidrogênio formadas entre as hidroxilas da celulose estabelecem-se em um arranjo molecular diferente do NDC, e neste novo arranjo os poros fecham-se irreversivelmente, num processo que na área de celulose chama-se "hornification", que diminui a acessibilidade da celulose. Neste trabalho aplicamos uma hidrolise enzimática seguida da sonicação com ultrasom de 400 e 1000 W de potencia, submetendo as amostras a 20, 30, 40, e 50 minutos de tratamento com ultrasom. As analises de microscopia eletrônica revelaram fibras com comprimento médio de aproximadamente 30 Fm e de ate 232 nm de diâmetro para a sonicação com ultrassom de 1000 W durante 50 minutos no algodão Never Dried. Na viscose com a mesma potencia e tempo de tratamento foram obtidas nano fibras de ate 197 nm. Para o ultrassom de 400 W obtivemos fibras com 800 nm de diâmetro apos 50 minutos de tratamento. Contudo somente com a microscopia de Transmissão eletrônica e que pudemos identificar a presença de nano fibras com ate 40 nm de diâmetro já com apenas 20 minutos de tratamento e utilizando o ultrassom de menor potencia de 400 W. As analises de medição de tamanho de partícula por laser demonstraram que as amostras obtidas com ultrassom de 1000 W são mais homogêneas em relação as suas dimensões. / Abstract: This study is about a new method of obtainning Cellulose nano fibers from cotton "Never Dried Cotton" NDC. The cotton classified as NDC, despite has the same cristalinity of the normal cotton it is much more porous and, therefore, much more susceptible to eventual chemical treatments. This higher porosity is because the NDC, in natural state, is not in process of collapse of the lumen due to evaporation of the sap in the interior of fiber. With the collapse of the structure makes the innumerable hydrogen links formed between cellulose hydroxyls to agroup themselves molecular arrangement different from NDC, and in this new arrangement the pores close on a irreversible way, in a process that in the cellulose field is called of "hornification", wich reduces the accessibility of the cellulose. In this work we apply an enzymatic hydrolysis followed the sonication with 400 and 1000 W power ultrasound, submitting the samples the 20, 30, 40, and 50 minutes of treatment with ultrasound. The analyses of electronic microscopy disclosed fibers with average length of approximately 30 Pm and up to 232 nm of diameter for the sonication with 1000 W ultrasound during 50 minutes in the Never Dried Cotton. Nano fibers of up to 197 nm were obtained from viscose, with the same power and time of treatment. Utilizing ultrasound of 400 W fibers with 800 nm of diameters were obtained after 50 minutes of treatment. However only with Transmission electronic Microscopy it was possible to identify the presence of nano fibers with up to 50 nm of diameter with only 20 minutes of treatment and using an ultrasound of 400 W power. The analyses of measurement of particle size with laser had disclosed that the samples gotten with ultrasound of 1000 W are more homogeneous compared to its dimensions. / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química