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As a result of increasing demand of power in the modern society, energy storage/consumption is playing a more important role on future economics. Therefore energy storage systems which are more environmentally friendly, low-cost and high-performance have attracted much attention. Among electrochemical systems, supercapacitors are considered as a prominent candidate for the modern energy storage systems due to the high power density, high charge/discharge rate, and long lifetimes. Nevertheless, the performance of supercapacitors is limited by the significant disadvantage of low energy density. Metal oxides with high pseudocapacitance such as MnO2 are used as the electrode materials for supercapacitors to resolve the lack of energy density in supercapacitors. The specific capacitance is notably enhanced by the metal oxides because of the reversible redox reactions. Previous studies confirmed that only a thin layer of MnO2 is involved in the redox process and is electrochemically active, which makes surface area a critical factor of energy storage. To increase surface area of MnO2, ZnO nanostructure is introduced in the electrode material as a template for electrodeposition of MnO2. In the first part of the research, we synthesize a nanomaterial which combines 0-1-2 dimensional properties of different nanostructures and significantly increases the energy capacity of MnO2. iv In the second part of the research, we demonstrate an in situ synthesis of a hybrid device that combines two materials to investigate the individual characteristic of two nanomaterials. In this study, a ZnO nanorod interface on Au nanoparticle arrays is fabricated, and results in the photo-modulation of the array characteristics. We find the use of nanoparticle arrays as electrochemical systems by electrodepositing ZnO on Au nanoparticle arrays. The method expands their potential use in sensors, multifunctional materials, single electron transistors and nanoscale energy systems. Characteristic behavior of Au nanoparticle arrays including Coulomb blockade at room temperature, single electron charging effects and a power law dependence in current-voltage were observed, and Schottky behavior and photocurrent generation due to the ZnO nanorods were also proved. From the modulation of the threshold voltage of the Au array due to the electron-hole pairs generated by photo excitation in the ZnO rods, it can be seen that the system also has coupling between the Au nanoparticles and ZnO rods other than the individual characteristics. Au nanoparticles can be used as electrochemical systems with both structural and spatial confinement of the synthesized material. The possibility of using Au nanoparticle chains as electroactive sites significantly expands their potential use in sensors, multifunctional materials, single electron transistors and nanoscale energy systems.

Made available in DSpace on 2018-08-01T21:58:48Z (GMT). No. of bitstreams: 1 tese_10764_Dissertação final 26_06_17_Renan.pdf: 2290715 bytes, checksum: 01081df9fabe571c47da4d0246edb5f8 (MD5) Previous issue date: 2017-03-28 / No presente estudo, foram sintetizadas ferritas sem dopagem (Fe2O3/Fe3O4) e ferritas dopadas com manganês (MnFe2O4(R)) a partir de reagentes comerciais, bem como (MnFe2O4(B)) a partir de manganês recuperado de pilhas de Zn-MnO2 exauridas. O cátodo de pilhas Zn-MnO2 utilizado é constituído principalmente por MnO2 e Mn3O4, de acordo com análises de difratometria de raios-X (DRX). Análise por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES) detecta a presença de zinco advindo do ânodo das pilhas. O manganês do cátodo foi lixiviado com ácido nítrico 0.5 molL-1 e utilizado como dopante na síntese de ferritas MnFe2O4(B). Os materiais sintetizados apresentaram características de MnFe2O4, de acordo com a difratometria de raios-X (DRX). As ferritas foram caracterizadas por microscopia eletrônica de varredura (MEV) e microscopia eletrônica de transmissão (MET). Nas micrografias verificou-se que os materiais apresentaram partículas e aglomerados em escala nanométrica com geometria variada e irregular. Pela análise de espectrometria de energia dispersiva de raios-X (EDS) acoplada ao MEV pôde-se observar a composição das partículas da ferritas sintetizadas. Obteve os picos de Fe e O na amostra de Fe2O3/Fe3O4 e de Fe, Mn e O nas mostras de MnFe2O4(R) e MnFe2O4(B). A composição química das ferritas foi determinada por dicromatometria para ferro e espectrometria de absorção atômica de chama (F AAS) para manganês, sendo de 66,6 % de Fe para a Fe2O3/Fe3O4, 56,6 % de Fe e 11,5 % de Mn para MnFe2O4(R) e 61,5 % de Fe e 4,5 % de Mn para MnFe2O4(B). As ferritas foram avaliadas cataliticamente na descoloração do corante azul de metileno através do processo foto Fenton heterogêneo, obtendo-se 15,6 %, 98 % e 92 % de descoloração do corante usando Fe2O3/Fe3O4, MnFe2O4(R) e MnFe2O4(B) respectivamente, em 120 minutos de reação.

This study examines the use of MnO2 and KMnO4 as strong oxidants to remove specific recalcitrant organic compounds and COD from wastewater. These compounds are deemed as potential and more cost-effective treatment in encountering the challenge to remove Pharmaceuticals and Personal Care Products (PPCPs) and Endocrine Disrupter Compounds (EDCs) in wastewater to meet water reuse standard. The literature reviews concluded that both MnO2 and KMnO4 were able to remove recalcitrant organic compounds, such as 17α-ethynylestradiol (EE2), Bisphenol A (BPA), triclosan, and dye wastewater. Simple bench scale experiments were performed to investigate COD removal by utilizing MnO2 and KMnO4 to oxidize sewage water and supernatant in a continuously stirred tank reactor at the wastewaters’ natural pH (about pH 8). The results indicated that MnO2 was effective in removing COD of wastewater and not affected by the high content of suspended solids. The effectiveness of KMnO4 in removing COD of wastewater was masked by its ability to break down and solubilize particulate organic compounds. MnO2 application could not be mixed with the presence of other metal ions (or flocculants) as their presence may inhibit the efficiency of MnO2 oxidation. On the other hand, KMnO4 oxidation efficiency was not affected and even was enhanced by the presence of magnesium and calcium ions as flocculants.

Yes / This study was focused on developing a new catalyst using metal oxide (10 %Mn) over Nano- activated Carbon (Nano-AC) particles and designing a new reactor (digital basket reactor, DBR) for the sulfur removal from kerosene oil via oxidative desulfurization (ODS). The new homemade Nano-catalyst was prepared by utilizing impregnation process and was characterized by SEM, EDX, BET, and FTIR techniques. The performance of ODS process under moderate operating conditions was significantly enhanced by the application of the new catalyst and the new reactor. The results showed that 94 % of the sulfur could be achieved at oxidation temperature of 80 ºC, oxidation time of 35 min and agitation rate of 750 rpm. The reactivity of catalyst was examined after four consecutive ODS cycles under the optimal experimental parameters and the used catalyst showed excellent stability based on oxidation efficiency. The spent catalyst was treated by methanol, ethanol and iso-octane solvents for regenerated it, and the result proved that iso-octane carried out the maximum regeneration performance. An optimization method depending on minimizing the sum of the squared error among the experimental and model predicted data of ODS technology was employed to evaluate the optimal kinetic model parameters of the reaction system. The ODS process model was able to predict the results obtained experimentally for a wide range of conditions very well by absolute average errors<5 %.

Cette thèse a pour but de développer des matériaux de cathode pour le Mg-Ion. Après avoir sélectionné l’électrolyte et les conditions de caractérisations électrochimiques, deux familles de matériau d’insertion ont été étudiées : les phases de Chevrel et les dioxydes de manganèse.Les phases de Chevrel Mo6S8 et Mo6Se8 ont été l’objet d’une étude de compréhension couplant électrochimie et analyse XPS ex situ. Les deux phases ont ainsi été caractérisées par voltampérométrie, GITT et PITT donnant des coefficients de diffusion de l’ordre de 10-11 à 10-14 cm2.s-1. Des mécanismes d’oxydoréduction non conventionnels ont été observés par analyse XPS indiquant un transfert de charge au niveau de l’anion en plus de la réduction des métaux de transition. La comparaison des deux matériaux Mo6S8 et Mo6Se8 indique que le soufre participe d’avantage au transfert de charge que le sélénium.Dans le second volet une étude comparative est menée sur deux structures prometteuses du MnO2, la hollandite et la birnessite. Il a été mis en évidence qu’une hydratation de l’électrolyte est nécessaire pour permettre l’insertion des ions Mg2+ dans les différentes structures de MnO2. Des analyses par RMN 1H et XPS ont ainsi révélé un phénomène de co-insertion des cations Mg2+ et des molécules d’eau. Cependant la cyclabilité de ces composés reste limitée et des capacités irréversibles de 50 à 80% sont mesurées. Ces travaux de compréhension sont cependant un premier pas pour la conception de nouveaux matériaux d’insertion réversibles pour les accumulateurs Mg-Ion. / This PhD thesis aims to develop Mg-Ion cathode materials. Once the electrolyte selected and the electrochemical characterization system established, two insertion materials families were studied: Chevrel phases and manganese dioxides.The Chevrel phases Mo6S8 and Mo6Se8 have been the subject of a coupled electrochemistry / XPS ex situ understanding study. The two phases were characterized by voltammetry, GITT and PITT showing diffusion coefficients ranging from 10-11 to 10-14 cm2.s-1. Unconventional redox mechanisms were observed by XPS studies indicating a charge transfer inside the anions in addition to the reduction of the transition metals. The comparison of the two materials Mo6S8 and Mo6Se8 indicates the sulfur is more involved in the charge transfer than the selenium.In the second part, two MnO2 promising structures have been selected and studied: hollandite and birnessite. We evidenced that electrolyte hydratation is needed to allow the insertion inside the different MnO2 structures. RMN 1H and XPS analyses revealed a co-insertion phenomenon involving Mg2+ cations and H2O molecules. However, these compounds exhibit a poor cyclability and irreversible capacities of 50% to 80%. This understanding work is a first step towards the design of new reversible insertion materials for Mg-Ion batteries.

Submitted by Geandra Rodrigues (geandrar@gmail.com) on 2018-09-20T12:04:51Z No. of bitstreams: 1 flaviacamposmarques.pdf: 5444687 bytes, checksum: ee4ddf83c1895a69c8df07fd21fede21 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-10-01T19:24:51Z (GMT) No. of bitstreams: 1 flaviacamposmarques.pdf: 5444687 bytes, checksum: ee4ddf83c1895a69c8df07fd21fede21 (MD5) / Made available in DSpace on 2018-10-01T19:24:51Z (GMT). No. of bitstreams: 1 flaviacamposmarques.pdf: 5444687 bytes, checksum: ee4ddf83c1895a69c8df07fd21fede21 (MD5) Previous issue date: 2018-07-26 / O presente trabalho abrange as sínteses e caracterizações nanobastões de ouro (AuNB) e nanopartículas esféricas de ouro e prata (AuNE e AgNE) recobertos por uma camada ultrafina de óxido de manganês, silício ou titânio. Utilizaram-se para caracterização das camadas dielétricas as técnicas UV-VIS, espectroscopia de absorção no infravermelho, difração raio X (XRD), voltametria cíclica (CV) e microscopia eletrônica de transmissão (TEM). As nanoestruturas plasmônicas (NP) utilizadas como substratos nas aplicações espectroscópicas são instável na presença de muitos analitos, o que pode levar à agregação e posteriormente à precipitação do material, inviabilizando a caracterização do adsorbato. O recobrimento das NP por camadas dielétricas aumenta fortemente a sua estabilidade estrutural, conservando suas propriedades plasmônicas. Nesse intuito, o escopo desse trabalho visou recobrir os AuNB por MnO2, SiO2 ou TiO2 e AuNE ou AgNE por TiO2 e verificar a sua aplicabilidade nas técnicas espectroscópicas de superfície. Por meio do deslocamento da banda de ressonância de plasmon de superfície localizado foi possível acompanhar a formação e o aumento da espessura da camada dielétrica adsorvida na interface do metal quando comparados às NP sem recobrimento, que são resultados das mudanças no índice de refração local às NP. A técnica de XRD foi utilizada para confirmar a formação dos materiais híbridos; por essa técnica foram observados halo não-cristalinos atribuídos aos óxidos e picos de difração característicos de nanoestruturas metálicas de Au. Além disso, foi possível caracterizar as NP de Au e Ag com os óxidos por meio da análise por TEM, em que foram observados recobrimentos uniformes das camadas de MnO2, SiO2 ou TiO2 envolvendo o núcleo metálico com espessuras inferiores a 6 nm. O uso da técnica de CV permitiu verificar que as cascas de óxidos não apresentaram orifícios. Os materiais híbridos otimizados foram utilizados como substratos espalhamento Raman intensificado por superfície (SERS) e fluorescência intensificada por superfície (SEF) para análise de adsorção da molécula IR-820. As medidas SERS utilizando as radiações incidentes 633 e 1064 nm mostraram um aumento significativo nas intensidades relativas de alguns modos vibracionais comparado ao espectro Raman da molécula livre, através dos quais foram realizadas as atribuições dos modos vibracionais. Já as medidas SEF obtidas com a radiação incidente 785 nm, observou-se um aumento da intensidade SEF para espessuras maiores de óxido, atribuídas ao aumento da distância entre adsorbato e a superfície condutora do metal. Além disso, foi estudada por SERS a adsorção de ácido 3-mercaptopropiônico (HMP) e ácido 4-mercaptobenzoico (HMB) nessas NP recobertas, e através dos resultados foram atribuídos os modos vibracionais mais significativos. Através dessas atribuições foi possível verificar o sitio de adsorção e a orientação das moléculas HMP e HMB. Os resultados obtidos confirmaram a formação da camada de óxido envolvendo o núcleo metálico. Além disso, as aplicações dos efeitos SERS e SEF mostraram-se bastante promissoras para os substratos sintetizados. / The present work covers the syntheses and characterizations of gold nanorods (AuNR) and gold and silver spherical nanoparticles (AuSN and AgSN) coated with ultrathin layers of manganese, silicon or titanium oxide. Dielectric layers were characterized by UV-Vis, infrared absorption spectroscopy, X ray diffraction (XRD), cyclic voltammetry (CV) and transmission electron microscopy (TEM) techniques. Plasmonic nanostructures (PN) which are used as substrates in spectroscopic applications are unstable in the presence of many analytes, thus leading to aggregation and subsequent precipitation. This instability makes the characterization of the adsorbate much more challenging. Coating PN with dielectric layers strongly increases its structural stability, while retaining their plasmonic properties. To this end, the scope of this work was to cover AuNR by ultrathin layers of MnO2, SiO2 or TiO2 and AuNS or AgNS by TiO2 and verify its applicability in surface spectroscopic techniques. By means of displacement of the localized surface plasmon resonance band, it was possible to follow the formation and increase of the thickness of the dielectric layer adsorbed at the interface of the metal when compared to PN without coating, which are results of the changes in the local refractive index to PN. The XRD technique was used to confirm the formation of the hybrid materials. It was observed non-crystalline haloes attributed to the oxides and diffraction peaks characteristic of Au metallic nanostructures. Moreover, it was possible to characterize the Ag and Au PN with oxides by means of analysis by TEM, wherein was possible to confirm the presence of uniform layer coatings of MnO2, SiO2 or TiO2 surrounding the metallic core with a thickness below 6 nm. The use of the CV technique allowed verifying that the oxide shells did not have pinholes. The optimized hybrid materials were used as surface enhanced Raman scattering (SERS) and surface enhanced fluorescence (SEF) substrates for adsorption analysis of the IR-820 molecule. The SERS measurements using incident radiations at 633 and 1064 nm showed a significant increase in the relative intensities of some vibrational modes compared to the Raman spectrum of the free molecule, through which the assignments of the vibrational modes were performed. The SEF measurements obtained with the incident radiation 785 nm showed an increase in the SEF intensity for higher oxide thicknesses, which was attributed to the increase in the distance between adsorbate and the conductive surface of the metal. Moreover, adsorption of the 3-mercaptopropionic acid (MPA) and 4-mercaptobenzoic acid (MBA) molecules in these NP coated was studied using SERS. It was possible to identify and assign the most significant vibrational modes and confirm the adsorption site of MPA and MBA molecules. The results confirmed the successful formation of the oxide layers surrounding the metallic cores. Finally, the applications of the SERS and SEF effect have shown to be very promising for the synthesized substrates.

L'objectif de ce travail était d'une part d'étudier la dégradation du phénol en milieu aqueux par un plasma GlidArc d'air humide et d'autre part d'étudier la conversion de l'acétaldéhyde dans des gaz atmosphériques par un plasma DBD généré par une haute tension impulsionnelle. Les résultats de l'étude paramétrique de la dégradation du phénol ont montré une augmentation de l'efficacité en fonction de la concentration initiale et du débit d'air humide. L'augmentation du gap entre les électrodes à occasionné celle de la concentration des ions nitrates. La majeur parie des nombreux produits de réactions est constituée d'acides carboxyliques mais aussi d'hydroquinone, de para-nitrophénol et de para-nitrosophénol. Cette identification a permis de dresser un schéma réactionnel de la dégradation du phénol. La conversion de l'acétaldéhyde a été effectuée dans des conditions de température allant de l'ambiante jusqu'à 300°C et dans deux types de mélanges: CH3CHO/N2 et CH3CHO/N2/O2 (jusqu'à 10% O2). Les résultats ont montré que le coût énergétique baisse en présence d'oxygène dans le mélange et également lorsque la température augmente. Les principaux sous-produits identifiés dans CH3CHO/N2 sont CO, H2, CH4, HCN, C2H6, CH3CN tandis que dans les mélanges oxygénés, CO2 et CO, CH2O, CH3OH sont les sous-produits les plus importants. L'étude cinétique menée à la suite de cette analyse grâce à un modèle 0D simplifié a permis de mettre en évidence le rôle primordial de la dissociation par quenching des états métastables d'azote et de l'oxydation notamment par O et OH dans la conversion de l'acétaldéhyde. La modélisation a aussi permis de comprendre les processus de formation des sous-produits majoritaires. Des catalyseurs à base de MnO2 ont été placés en aval de la zone de décharge pour décomposer l'ozone qui se forme abondamment dans les mélanges oxygénés surtout à basse température. L'oxygène atomique produit lors de cette décomposition oxyde l'acétaldéhyde résiduel et ses sous-produits. Le coût énergétique a ainsi été diminué et les concentrations des sous-produits comme CH2O et CH3OH ont été réduites. / This work aimed to study the degradation of aqueous phenol by humid air GlidArc plasma and to study the removal of acetaldehyde in atmospheric gas by pulsed DBD plasma. The parametric study of phenol degradation showed an increase in efficiency as a function of the initial concentration and humid air flow. The increase of the inter-electrodes gap has increased nitrate ions concentration. The numerous reaction products formed consist mostly of carboxylic acids. Other byproducts identified are hydroquinone, para-nitrophenol and para-nitrosophenol. By-products identification enabled drawing a reaction scheme of phenol degradation. The acetaldehyde removal has been achieved in temperature conditions ranging from ambient to 300°C and in two types of mixtures: CH3CHO/N2 and CH3CHO/N2/O2 (up to 10 % O2). The results showed that the energy cost decreases in the presence of oxygen in the mixture as well as when the temperature increases. In CH3CHO/N2, the main by-products are CO, H2, CH4, HCN, C2H6, CH3CN whereas in oxygenated mixtures, CO2 and CO, CH2O, CH3OH are the most important by-products. The kinetic study following this analysis, by using a simplified 0D model has highlighted the key role of the quenching of nitrogen metastables states and that of the oxidation of acetaldehyde, caused in particular by O and OH. The modeling also helped understanding the formation processes of major by-products. A MnO2 based catalyst was placed downstream of plasma zone in order to decompose ozone that is abundantly formed in oxygenated mixtures especially at low temperature. The atomic oxygen produced during this decomposition is used to oxidize the residual acetaldehyde and its by-products. The energy cost was thus decreased and the concentrations of certain by-products such as CH2O and CH3OH have been reduced as well.

Cette thèse a pour objectif d'améliorer les performances électrochimiques des dispositifs asymétriques C/MnO2 en formulant des oxydes de manganèse présentant des nano- ou mésostructures. Deux méthodes d’élaboration sont explorées. Le matériau mésoporeux est obtenu par réaction entre un agent structurant souple CTAP et divers alcènes A. L’impact des solutions colloïdales CTAP-A sur la texture et la microstructure de MnO2 a été étudié en proposant un modèle qui corrèle la dimension des agrégats avec le diamètre des pores de MnO2. Les performances du dispositif asymétrique sont aussi optimisées. Bien que l’emploi d’un agent structurant dur AAO n’ait pas permis d’élaborer directement un matériau d’électrode MnO2 performant, une microélectrode de MnO2 élaboré sur des nano-piliers de nickel électrodéposé sur AAO montre des propriétés électrochimiques concurrentes avec celles des microélectrodes actuelles. La bonne réponse en puissance élevée du dispositif asymétrique est due à l’excellente connexion entre les piliers et le matériau actif. Ce mémoire offre une meilleure compréhension sur la formation de MnO2 et présente des microélectrodes prometteuses pour les microsupercondensateurs. / The aim of this thesis is to improve the electrochemical performance of C/MnO2 asymmetric devices by elaborating manganese oxides exhibiting nano- or mesostructures. Two preparation methods are proposed. A mesoporous material is obtained through the reaction of soft template CTAP with various A alkenes. The effect of CTAP-A colloidal solution on MnO2 texture and microstructure has been studied by establishing the relationship between aggregates dimension and pore diameter. Asymmetric devices performances can be optimized this way. Attempts to employ AAO as hard template for developing a performant MnO2 electrode were unsuccessful. Nevertheless, a MnO2 microelectrode containing the oxide on nickel nanowires electrodeposited on AAO provided excellent electrochemical performances, comparable with current microsupercapacitor electrodes. Asymmetric device energy retention with increasing power is good due to the excellent MnO2/nickel nanowires connection. This thesis offers insights on the MnO2 formation and proposes promising microelectrodes for microsupercapacitors.

This study investigated the application of advanced oxidative processes for the homogeneous and heterogeneous degradation of a tanning effluent. The catalytic activity of a solid oxide containing manganese was evaluated in the heterogeneous systems. The experiments were performed in a photocatalytic batch reactor in laboratory scale. The solid used was the commercial product Birm®, consisting mainly of crystalline silica, silicate, aluminum and manganese dioxide. The adsorption results using Birm® in synthetic sewage adjusted to the models of Langmuir and Freundlich and established that the adsorption capacity of the Birm ® is low. The synthetic and real tannery effluents were assessed by the degradation kinetics of photochemical homogeneous (H2O2/UV) processes and heterogeneous (UV/H2O2/Birm®) at different pH, concentration of H2O2 and catalyst. The degradation kinetics of the ES followed in law and kinetics order of pseudofirst showing that the Birm® presented no catalytic activity in appreciable color degradation of the synthetic effluent. But when the solid was evaluated for the degradation of the real tannery effluent, it proved to be active, with kinetics of degradation occurring more efficiently than the homogeneous system (H2O2/UV) one. In both effluents there was a catalytic decomposition of hydrogen peroxide. However, the decomposition in ES resulted in inactive products for the catalytic oxidation or free radicals, which possibly were disabled in difusional ways and didn t react with the effluent. The increasing of the concentration of nitrate and sulfate also demonstrated a good the treatment of tanning effluent. / Este estudo investigou a aplicação de processos oxidativos avançados, homogêneos e heterogêneos, na degradação de efluentes líquidos industriais de couro sintético e real. O efluente sintético é uma solução aquosa do corante de couros Acid Orange G. O efluente real é oriundo da indústria de processamento de couro, coletado após o decantador secundário do tratamento por lodos ativados. Os experimentos foram realizados em reator fotocatalítico descontínuo em escala de laboratório. O sólido utilizado como catalisador heterogêneo é um composto comercial denominado Birm®, constituído principalmente de sílica cristalina, silicato de alumínio e dióxido de manganês. A adsorção do efluente sintético sobre o Birm® ajustou-se aos modelos de Langmuir e de Freundlich e, o sólido apresentou baixa capacidade adsortiva. As cinéticas de degradação dos efluentes pelos processos fotoquímicos homogêneo (H2O2/UV) e heterogêneo (UV/H2O2/Birm®) foram avaliadas em diferentes valores de pH, concentração de H2O2 e de catalisador. Os resultados estabeleceram o modelo cinético de pseudoprimeira ordem para a degradação do efluente sintético. O Birm® apresentou atividade catalítica apenas para o efluente de curtume, apesar de a decomposição catalítica do peróxido de hidrogênio ter ocorrido em ambos efluentes. Supõe-se que essa atividade foi potencializada pela diversidade de compostos orgânicos presentes no efluente de curtume. A degradação deste efluente também foi comprovada pelo aumento das concentrações de sulfato e nitrato.