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Desenvolvimento de catalisadores preparados pelo método sol-gel para a oxidação de metanol / Development of catalysts prepared by the sol-gel method for methanol oxidationKatlin Ivon Barrios Eguiluz 10 July 2008 (has links)
Este trabalho descreve o desenvolvimento e caracterização de novos materiais catalíticos para a oxidação de metanol em aplicações em células a combustível de metanol direto. Os materiais foram preparados utilizando o método sol-gel pela incorporação de diversas quantidades de metais, tais como: Ru, Ir, Ce, Mo e Pb sobre amostras de pó de Pt/C da E-Tek (10% Pt). Na maioria dos casos, o compósito resultante estava formado pelos referidos óxidos metálicos como observado nas medidas de caracterização física. Os sistemas estudados incluíram as seguintes misturas binárias: (Pt0,50-(RuO2)0,50/C, Pt0,50-(IrOx)0,50/C, Pt0,50-(CeO,sub>2)0,50/C, (PtOx)0,50-(PbOx)0,50/C, Pt0,50-(Môo3)0,50/C) e as misturas ternárias: (Pt0,25(RuO2-IrOx)0,75/C, Pt0,50 (RuO2-IrOx)0,50/C, Pt0,75(RuO2-IrOx)0,25/C, Pt0,25(RuO2-CeO2)0,75/C, Pt0,50 (RuO2-CeO2)0,50/C, Pt0,75(RuO2-CeO2)0,25/C, (PtOx)0,25(RuO2- PbOx)0,75/C, (PtOx)0,50 (RuO2-PbOx)0,50/C, (PtOx)0,75(RuO2-PbOx)0,25/C, Pt0,25(RuO2- Môo3)0,75/C, Pt0,50(RuO2-MoO3)0,50/C e Pt0,75(RuO2-MoO3)0,25/C). Medidas de difratometria de raios-X, mostraram que todos os metais incorporados às amostras de Pt/C sintetizam-se como óxidos (RuO2, IrO2, Ir2O3, CeO2, Pb3O4 e MoO3), enquanto que a platina manteve-se como Pt metálica com exceção nos compósitos contendo chumbo, nos quais na sua composição final mostraram Pt, assim como, PtO e PtO2. Os compósitos preparados pelo método sol-gel foram de tamanho nanométrico (2,8- 3,5 nm) como observado por microscopia eletrônica de transmissão assim como por difração de raios-X, enquanto que, medidas de energia dispersiva de raios-X mostraram que os compostos apresentam composições próximas aos valores usados na preparação experimental. A oxidação de metanol foi estudada em todos os compósitos por voltametria cíclica seguida pelas curvas de polarização em estado quase-estacionário com os correspondentes diagramas de Tafel e finalmente pelos testes cronoamperométricos com análise por cromatografia dos principais produtos na solução. x Os valores do coeficiente angular obtidos nos diagramas de Tafel (b) são um indicativo que a etapa determinante da velocidade da reação (rds) de eletro-oxidação de metanol sobre os catalisadores contendo Ir é a quebra de uma das ligações C-H na molécula de CH3OH com a transferência do primeiro elétron (b = 120 mV dec-1). Entretanto, para os outros catalisadores estudados os valores de (b estão em torno de 90 mV dec-1, indicando que a rds nesses casos pode ser à remoção oxidativa do COads pelos intermediários adsorvidos provenientes da oxidação da molécula de água (R-OH.). Por outro lado, análises cromatográficos dos produtos formados em solução durante os testes cronoamperométricos mostraram que o compósito Pt0,25(RuO2-IrOx)0,75/C apresentou o melhor desempenho catalítico para oxidação de metanol. Isto devido a que, sobre este catalisador, não foi observado acúmulo de formaldeído em quanto que o ácido fórmico remanescente foi menor do que o observado sobre os outros catalisadores estudados, usando cargas elétricas equivalentes. Isto é um forte indicativo de que a oxidação de metanol em este material é eficiente, oxidando também moléculas de formaldeído e ácido fórmico até CO2 sem a formação de intermediários solúveis na solução. Portanto, este estudo mostra claramente que os melhores catalisadores para a oxidação de metanol são: Pt0,25(RuO2-IrOx)0,75/C, Pt0,50(RuO2-IrOx)0,50/C e Pt0,75(RuO2-IrOx)0,25/C, confirmando que a combinação de Pt, Ru e Ir é promissora para esta aplicação. / The preparation and the physical and electrochemical characterization of several binary and tertnary new composite catalytic materials for the direct oxidation of methanol in fuel cell systems are described here. The materials were prepared using the sol-gel method for the incorporation of variable amounts of metals such as Ru, Ir, Ce, Mo and Pb onto commercial samples of Pt/C powder from E-Tek (10% Pt). In most cases, the resulting composite was formed by the corresponding metal oxides as indicated by the subsequent physical characterization measurements. The systems studied included the following binary mixtures: Pt0,50-(RuO2)0,50/C, Pt0,50-(IrOx)0,50/C, Pt0,50-(CeO,sub>2)0,50/C, (PtOx)0,50-(PbOx)0,50/C, Pt0,50-(Môo3)0,50/C and the ternary ones: Pt0,25(RuO2-IrOx)0,75/C, Pt0,50 (RuO2-IrOx)0,50/C, Pt0,75(RuO2-IrOx)0,25/C, Pt0,25(RuO2-CeO2)0,75/C, Pt0,50 (RuO2-CeO2)0,50/C, Pt0,75(RuO2-CeO2)0,25/C, (PtOx)0,25(RuO2- PbOx)0,75/C, (PtOx)0,50 (RuO2-PbOx)0,50/C, (PtOx)0,75(RuO2-PbOx)0,25/C, Pt0,25(RuO2- Môo3)0,75/C, Pt0,50(RuO2-MoO3)0,50/C and Pt0,75(RuO2-MoO3)0,25/C X-ray diffraction measurements revealed that all metals incorporated to the Pt/C samples appeared as oxides (e.g. RuO2, IrO2, Ir2O3, CeO2, Pb3O4 e MoO3) while platinum remained metallic except for the composites containing lead where the final composition showed metallic Pt as well as PtO and PtO2. The sol-gel prepared composites were nanometric in size (2.8 - 3.5 nm) as shown by electronic transmission microscopy as well as by X-ray diffraction while energy dispersive Xray measurements indicated that the composites have compositions values very close to those of the experimental preparation. Methanol oxidation was studied on all composites by cyclic voltammetry followed by quasi steady-state polarization curves with the corresponding Tafel plots and, finally, by chronoamperometric tests with analyses of the main products in solution by chromatography. xii The measured values of the Tafel coefficient (b) are an indicative that the ratedetermining- step (rds) for methanol oxidation on catalysts containing Ir is the rupture of one of the C-H bonds in the CH3OH molecule with the transference of one electron (CH3OH = ~120 mV dec-1). For the other composites studied the b values are around 90 mV dec-1 indicating that the rds in those cases could be the oxidative removal of COads by the adsorbed intermediates of the water molecule oxidation (R-OH.). On the other hand, the chromatographic analyses of the products formed in solution during the chronoamperometric tests seem to point out that the Pt0,25(RuO2-IrOx)0,75/C composite is the one with the best catalytic performance for methanol oxidation. This is because for that material an accumulation of formaldehyde was not observed while the remnant formic acid was lower than for the other tested composites using equivalent electric charges. This is a strong indicative that the oxidation of methanol on that material efficiently also oxidizes the formaldehyde and the formic acid molecules to CO2 not leaving soluble intermediates in solution. Therefore, the present studies clearly show that the best catalysts for methanol oxidation are: Pt0,25(RuO2-IrOx)0,75/C, Pt0,50(RuO2-IrOx)0,50/C e Pt0,75(RuO2-IrOx)0,25/C, thus confirming that a proper combination of Pt, Ru and Ir is very promising for such application.
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Syntéza pěnové biokeramiky pro potenciálně lékařské aplikace / Synthesis of foamed bioceramics for potential medical applicationsDoboš, Petr January 2012 (has links)
Cílem práce byla příprava porézních vzorků HAP pro potenciálně medicínské aplikace. HAP byl připraven metodou sol-gel a precipitační. Vzorky HAP byly podrobeny analýze FTIR, XRD, SEM. Takto připravený HAP byl napěněn pomocí houbové metody s jasně definovanými póry a pomocí polymerního a skleněného expanzelu s různou distribucí a velikostí pórů. U výsledných napěněných vzorků byla vyhodnocena mikrostruktura a povrchová analýza pomocí SEM, zjištěna porozita pomocí Hg porozimetru a sledována bioaktivita in vitro v SBF. Byly zjištěny jasně definované makro, mezo a mikro póry při různé distribuci. U houbové metody pomocí sol-gel došlo k vytvoření jasně definovaných a pravidelných pórů s monodisperzní porozitou. Dominantní velikost póru byla stanovena v rozmezí 1–5 µm. Celková porozita byla stanovena na 63,5 % s celkovým povrchem 3,048 1 m/g. Precipitační metodou s polymerním expanzelem došlo k polydisperznímu rozložení pórů s třemi hlavními fázemi v rozmezí: 50–100 µm, 5–10 µm a 0,5–1 µm. Celková porozita byla stanovena na 67,6 % s celkovým povrchem 19,090 3 m/g. Bioaktivita výsledných napěněných vzorků in vitro byla sledována po dobu 7 dnů v připraveném SBF. Při napěnění sol-gel houbovou metodou nevznikla výsledná bioaktivní vrstva. U precipitační metody napěněné pomocí polymerního expanzelu vznikla nepravidelná bioaktivní vrstva. Výsledky byly naměřeny pomocí SEM analýzy.
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Catalytic Performance and Characterization of Zn-doped Cryptomelane-type Manganese Dioxide For Ethanol OxidationJiang, Lulu 14 November 2012 (has links)
No description available.
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Key Factors Influencing the Structure and Electrochemical Performances of LiFePO4 via sol-gel SynthesisGuan, Chuang 20 April 2012 (has links)
No description available.
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Defects and Ferromagnetism in Transition Metal Doped Zinc OxideThapa, Sunil 18 July 2016 (has links)
No description available.
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Application of Functionalized Organosilicas in Adsorption of NitratesAmoako, Stephen 01 August 2024 (has links) (PDF)
This study addresses the critical environmental issue of elevated nitrate levels in water bodies, primarily due to excessive use of nitrogenous fertilizers and improper waste disposal. It focuses on reducing nitrate concentrations in polluted water to permissible levels through the effectiveness of hybrid materials in nitrate adsorption. We synthesized nine amino-functionalized adsorbents using grafting and sol-gel techniques. Batch adsorption tests confirmed the high nitrate adsorption capacities of these adsorbents, with sol-gel materials showing the highest efficiency due to their abundant amino group contents. Among these, the surfactant-free, sol-gel adsorbent was the most effective, combining ease of synthesis with cost-efficiency. Our study of temperature dependence revealed optimal nitrate removal at ambient conditions and decreased capacity at higher temperatures. These adsorbents remained highly efficient over five adsorption/regeneration cycles. This research significantly advances efficient nitrate removal methods, presenting a promising approach for environmental remediation.
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Synthesis of Ce3+ substituted Ni-Co ferrites for high frequency and memory storage devices by sol-gel routeSheikh, F.A., Noor ul Huda Khan Asghar, H.M., Khalid, M., Gilani, Z.A., Ali, S.M., Khan, N., Shar, Muhammad A., Alhazaa, A. 28 December 2023 (has links)
Yes / Cerium (Ce3+) substituted Ni-Co ferrites with composition Ni0.3Co0.7CexFe2−xO4 (x = 0.0–0.20, with step size
0.05) were synthesized by sol-gel method. Face-centered cubic (FCC) spinel structure was revealed by X-ray
analysis. The crystalline size was calculated ranging between 17.1 and 18.8 nm, lattice constant showed a
decreasing trend with increase of Ce3+ contents, furthermore, X-ray density was calculated between 5.30
and 5.69 g/cm3. The two characteristic spinel ferrites absorption bands were seen around 550 (cm−1) and
415 (cm−1) in Fourier transform infra-red (FTIR) spectroscopy. The microstructural and elemental studies
were carried out by field emission transmission electron microscopy (FE-TEM) and energy dispersive X-ray
(EDX) respectively, the average particle size was calculated around 21.83 nm. Magnetic studies were per-
formed by vibrating sample magnetometer (VSM), which showed that saturation magnetization Ms and
remanence Mr decreased with substitution up to x = 0.10 due to small magnetic moment of Ce3+ than Fe3+.
The coercivity Hc increased with substitution up to 908.93 Oe at x = 0.05, then it decreased following the
trend of anisotropy constant. The dielectric studies exhibited decrease in dielectric parameters with fre-
quency due to decreasing polarization in material. The dielectric loss was significantly decreased in material
at high frequency. The Cole-Cole interpretation exhibited conduction mechanism being caused by grain
boundary density. These attributes of Ce3+ substituted Ni-Co ferrites suggest their possible use in memory
storage, switching and high frequency devices like antenna and satellite systems. / The authors would like to acknowledge the Researcher's Supporting Project Number (RSP-2021/269) King Saud University, Riyadh, Saudi Arabia, for their support in this work. / The full-text of this article will be released for public view at the end of the publisher embargo on 28 Dec 2023.
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Estudo do efeito de compostos de selênio em vidros soda-cal-sílica. / Study of the effect of selenium compounds in soda-lime-silica glasses.Cavalcante, Renata Andrade Kobayashi 21 June 2013 (has links)
O selênio é utilizado como elemento colorante ou descolorante na indústria vidreira. Sua característica altamente volátil durante a fusão do vidro, com perdas de até 80%, tem sido uma questão discutida já há muito tempo. Assim, alternativas têm sido buscadas na tentativa de aumentar o rendimento do selênio. Utilizar o princípio da microencapsulação do selênio através da obtenção de vidros pelo método sol-gel apresenta-se como uma possibilidade para novos estudos. O método sol-gel permite obter vidros de alta pureza utilizando recursos mais simples que em uma fusão convencional. Este trabalho apresenta um estudo do rendimento do selênio em duas composições de vidros sodo-cálcicos. Para tanto, foram utilizadas diferentes fontes de selênio (Se0, ZnSeO3, Na2SeO3). Uma proposta desta pesquisa foi obter uma nova fonte de selênio através da síntese de um material rico em sílica pelo método sol-gel, o qual contenha selênio em sua formulação. Este material é utilizado como uma alternativa de inserção de selênio visando o aumento de seu rendimento durante a fusão, considerando-se o princípio da microencapsulação. As amostras vítreas contendo selênio apresentaram coloração rosa. Os resultados de análise química mostram que a incorporação de selênio foi maior para as amostras com maior concentração de álcalis. Uma das amostras contendo um dos materiais sintetizados pelo método sol-gel apresentou a menor perda de selênio (34%) dentre todas, indicando que o método proposto foi eficiente para a redução da volatilização deste elemento. Os ensaios de absorção óptica apresentam três bandas de absorção: 380 nm (Fe3+), 500 nm (Se0 / Se2-) e 720 nm (Fe2+). As amostras obtidas por sol-gel são amorfas, adquiriram uma forte coloração avermelhada com o tempo e os resultados obtidos nos ensaios de caracterização indicaram uma potencial aplicação deste material como sensor de umidade. / Selenium is used as a colorant and discolorant element in the glass industry. Its highly volatile characteristic during the glass melting, which causes losses around 80%, has been discussed for a long time. Meanwhile, alternatives have been searched to increase the yield of selenium. Microencapsulation of the selenium by sol-gel processing may be considered for new studies. This work presents an investigation, in laboratory scale, of the selenium yield in two model soda-lime glass compositions. Different sources of selenium (Se0, ZnSeO3, Na2SeO3) were used, which were incorporated into a silica rich material, containing the selenium source, by sol-gel method. The glass samples were obtained by melting the raw-materials at 1350°C in high alumina crucibles, and showed different grades of pink coloration. Chemical analysis results showed that the incorporation of selenium was higher in the glass containing higher concentration of alkaline elements. In terms of selenium source, the best yield (lowest loss of selenium) was 34 wt%, obtained with SG3 (synthesized material by sol-gel method) as the selenium source. The optical absorption curves presented three main absorption bands: 380 nm (Fe3+), 500 nm (Se0/Se2-) and 720 nm (Fe2+). The samples obtained by sol-gel were amorphous, acquired a strong reddish coloration with time, and indicated potential characteristics for application as a humidity sensor.
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Obtenção de material mesoporoso Nb2O5/SiO2, pelo métodp sol-gel, aplicado como adsorvente para remoção do corante violeta cristalUmpierres, Cibele Santanna January 2017 (has links)
O material SiO2/Nb2O5 (SiNb) foi preparado pelo método sol-gel e empregado como adsorvente para remoção do corante Violeta Cristal. O material foi caracterizado utilizando isotermas de adsorção/dessorção de nitrogênio, espectroscopia FTIR, pHpzc, e SEM-EDS. A análise isotérmica de N2 revelou a presença de micro e mesoporos na amostra de SiNb com área superficial específica de 747 m2g−1. No processo de adsorção do corante foram avaliados parâmetros como pH, temperatura, tempo de contato, e concentração do corante no processo. O valor de pH inicial da solução do corante que levou a uma máxima adsorção foi 7. A cinética de adsorção e equilíbrio para a adsorção do corante foram representadas por ordem-geral e Liu, respectivamente. A capacidade máxima de adsorção do corante com o adsorvente SiNb, na temperatura de 303K, foi de 116mg g-1. Dois efluentes de corantes foram simulados e usados para verificar a aplicabilidade do material SiNb para tratamento de efluentes, sendo que o adsorvente se mostrou muito eficiente na descoloração desses efluentes. / In this dissertation, SiO2/Nb2O5 (SiNb) material was prepared using sol–gel method and employed as adsorbent for removal of crystal violet dye (CV). The material was characterized using nitrogen adsorption–desorption isotherms, FTIR spectroscopy, pHpzc, and SEM-EDS. The analysis of N2 isotherms revealed the presence of micro- and mesopores in the SiNb sample with specific surface area 747 m2 g−1. For the dye adsorption process, variations of parameters such as of pH, temperature, contact time, and concentration of dye of the process were evaluated. The optimum initial pH of the CV dye solution was 7.0. The adsorption kinetic and equilibrium data for CV adsorption were suitably represented by the general-order and Liu models, respectively. The maximum adsorption capacity of the CV dye by SiNb was achieved at 303 K, which attained 116 mg g−1at this temperaure. Dye effluents were simulated and used to check the applicability of the SiNb material for treatment of effluents – the material showed very good efficiency for decolorization of dye effluents.
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Synthesis and characterization of novel black pigments / Naujų juodųjų pigmentų sintezė ir tyrimasGatelytė, Aurelija 02 April 2012 (has links)
For this doctoral dissertation there were synthesized and observed the black pigments which are important in both – in art and industry. It was the first time when using the sol-gel method in our laboratory were synthesized YFeO3, Y3Fe5O12, CoFe2O4, NiFe2O4, ZnFe2O4 nanocompounds, which latter were fitted for the black pigmentation of the ceramic glazes. / Buvo sudaryti modeliniai juodieji pigmentai iš C suodžių ir K2CO3, Ca3(PO4)2, CaCO3 bei Mg3(PO4)2.Vandeniniu zolių-gelių metodu buvo susintetinti įvairūs metalų vienfaziai nanoferatai YFeO3, Y3Fe5O12, CoFe2O4, NiFe2O4, ZnFe2O4, kurie pirmą kartą panaudoti juodaisiais keraminiais pigmentais.
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