Made available in DSpace on 2014-12-17T15:01:26Z (GMT). No. of bitstreams: 1 AndreLLM_DISSERT.pdf: 1863413 bytes, checksum: 1d92759b3bdf5371d233d97ad885e7af (MD5) Previous issue date: 2011-07-21 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The main goal of this work was to produce nanosized ceramic materials of the family of the tungstates (tungstates of cerium and strontium), and test them for their catalytic activity in processes involving the transformation of methane (CH4). The methodology used for the synthesis of the ceramic powders involved the complexation combining EDTA-citrate. The materials characterization was performed using simple and differential thermogravimetry, x-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy (EDS). The microstructure analysis was performed using the refinement by the Rietveld method, and the crystallite size and distribution of the materials was elucidate by the Scherrer and Williamson-Hall methods. The conditions of the synthesis process for the three envisaged materials (SrWO4, SrWO4 using tungsten oxide concentrate as raw material, and Ce2(WO4)3) were adjusted to obtain a single phase crystalline material. The catalytic tests were carried out in the presence of methane and synthetic air, which is composed of 21% O2 and 79% N2. The analysis of the conversion of the reaction was done with the aid of an fourier transform infrared device (FTIR). The analysis showed that, structurally, the SrWO4 produced using raw materials of high and poor purity (99% and 92%, respectively) are similar. The ideal parameters of calcination, in the tested range, are temperature of 1000 ?C and time of calcination 5 hours. For the Ce2(WO4)3, the ideal calcination time and are temperature 15 hours and 1000?C, respectively. The Williamson-Hall method provided two different distributions for the crystallite size of each material, whose values ranged between the nanometer and micrometer scales. According to method of Scherrer, all materials produced were composed of nanometric crystallites. The analyses of transmission electron microscopy confirmed the results obtained from the Williamson- Hall method for the crystallite size. The EDS showed an atomic composition for the metals in the SrWO4 that was different of the theoretical composition. With respect to the catalytic tests, all materials were found to be catalytically active, but the reaction process should be further studied and optimized. / O objetivo principal deste trabalho foi produzir materiais cer?micos nanom?tricos da fam?lia dos tungstatos (tungstatos de c?rio e de estr?ncio), e test?-los quanto ?s suas atividades catal?ticas em processos envolvendo a transforma??o do g?s metano (CH4). A metodologia empregada para a s?ntese dos p?s cer?micos envolveu o m?todo de complexa??o combinando EDTA-Citrato. A caracteriza??o dos materiais foi feita atrav?s das t?cnicas de termogravimetria simples e diferencial, difra??o de raios-x, microscopia eletr?nica de transmiss?o, e espectroscopia de energia dispersiva (EDS). A an?lise da microestrutura foi realizada atrav?s do refinamento utilizando o m?todo de Rietveld, e para a estima??o do tamanho de gr?o e de sua distribui??o foram utilizados os m?todos de Scherrer e Williamson-Hall. As condi??es de obten??o dos tr?s materiais desenvolvidos (SrWO4, SrWO4 utilizando concentrado de ?xido de tungst?nio como mat?ria-prima, e Ce2(WO4)3) foram ajustadas para a obten??o de um material cristalino monof?sico. Os testes catal?ticos explorat?rios foram realizados na presen?a dos gases metano e ar sint?tico, composto por 21% de O2 e 79% N2. A an?lise da convers?o foi feita com o aux?lio de um equipamento de infravermelho ? transformada de Fourier. As an?lises mostraram que, estruturalmente, os materiais SrWO4 produzidos com mat?riaprima de elevada pureza (99% de pureza) e oriunda do concentrado de ?xido de tungst?nio (92% de pureza) s?o semelhantes. Seus par?metros ideais de produ??o, dentro do que foi testado, s?o temperatura de calcina??o de 1000?C e tempo de perman?ncia de 5 horas na isoterma. Para o Ce2(WO4)3, as condi??es ideais dentro do que foi testado s?o temperatura de calcina??o de 1000?C e tempo de perman?ncia na isoterma de 15 horas. O m?todo de Williamson-Hall forneceu duas distribui??es diferentes para o tamanho de cristalito de cada material, cujos valores oscilaram entre as escalas nanom?tricas e microm?tricas. Com o m?todo de Scherrer, todos os materiais produzidos possu?ram tamanho de cristalito nanom?trico. As an?lises de microscopia eletr?nica de transmiss?o confirmaram o resultado obtido com o m?todo de Williamson- Hall para o tamanho de cristalito. A EDS indicou a presen?a de diverg?ncias entre a composi??o at?mica met?lica te?rica e experimental do SrWO4. Com rela??o aos testes catal?ticos explorat?rios, os materiais se mostraram ativos por?m o processo reacional ainda precisa ser melhor estudado e otimizado.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-02-02T12:10:54Z No. of bitstreams: 1 MaiteMedeirosDeSantanaESilva_DISSERT.pdf: 2765135 bytes, checksum: 2308e88f6d7f78d3c63e10b06eee531d (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-02-07T16:43:25Z (GMT) No. of bitstreams: 1 MaiteMedeirosDeSantanaESilva_DISSERT.pdf: 2765135 bytes, checksum: 2308e88f6d7f78d3c63e10b06eee531d (MD5) / Made available in DSpace on 2017-02-07T16:43:25Z (GMT). No. of bitstreams: 1 MaiteMedeirosDeSantanaESilva_DISSERT.pdf: 2765135 bytes, checksum: 2308e88f6d7f78d3c63e10b06eee531d (MD5) Previous issue date: 2016-08-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Este trabalho descreve o planejamento experimental 2? com triplicata no ponto central para produ??o do molibdato de estr?ncio (SrMoO4) atrav?s do m?todo de complexa??o combinado EDTA/Citrato onde investigou-se a influ?ncia do pH (6, 7,5 e 9), tempo de calcina??o (3, 4 e 5h) e taxa de aquecimento (5, 7 e 10?C.min-1) em alguns de seus par?metros qu?micos e f?sicos. Com base na curva de termogravim?trica os p?s de SrMoO4 foram calcinados a 650?C.Os materiais sintetizados foram caracterizados por TG/DSC, DRX, EDX, MEV e ERD. Os par?metros de rede da estrutura cristalina foram obtidos com base no m?todo de refinamento Rietveld. Todos os padr?es de DRX foram indexados segundo a ficha JCPDS 01-085-0586, com estrutura tetragonal e grupo espacial I41/a e o par?metro residual do refinamento da estrutura variou entre 1,035 a 1,292, n?o sendo identificadas fases secund?rias e impurezas. Constatou-se a exist?ncia de diferen?as entre as intensidades relativas m?dias dos picos de difra??o de raios-x. Atrav?s de ferramentas estat?sticas, concluiu-se que a taxa de aquecimento foi a vari?vel independente que demonstrou maior influ?ncia nessa diferen?a. As analises de EDX mostraram a presen?a de desvios entre a composi??o te?rica e experimental para os elementos estr?ncio e molibd?nio; o desvio percentual variou de 0,027 a 3,67% em fun??o das condi??es de s?ntese. De acordo com as micrografias obtidas por MEV, os p?s sintetizados s?o compostos de aglomerados de part?culas, com morfologia esf?ricas irregulares e bipiramidais. De acordo com a an?lise do planejamento experimental, tendo como vari?vel dependente a energia de bandgap, os menores valores obtidos (4,18 e 4,17 eV para pH 6 e 9, respectivamente) foram as amostras calcinadas por 3h com taxa de aquecimento igual a 10?C.min-1 em compara??o aos materiais calcinados nas demais condi??es de s?nteses e os modelos estat?sticos gerados se mostraram capazes de descrever os fen?menos observados. Testes explorat?rios na fotodegrada??o da solu??o sint?tica do corante azul de metileno utilizando o material com Egap de 4,17 eV indicam que o p? testado apresenta influ?ncia na diminui??o da concentra??o do corante para os testes realizados em pH 2 e 5 obtendo aproximadamente 95% e 24% de convers?o respectivamente, e para os teste em pH 9 observou-se que a fot?lise direta ? mais efetiva na redu??o da concentra??o do corante alcan?ando em torno 67% de convers?o, por?m o processo reacional necessita ser mais estudado para melhor compreens?o dos resultados. / This work describes the 2? experimental design with center point in triplicate for the production of strontium molybdate (SrMoO4) through complexation combined Citrate/EDTA method where investigated the influence of pH (6, 7,5 and 9), time calcination (3, 4 and 5 h) and heating rate (5, 7 and 10?C min-1) in some of its chemical and physical parameters. Based on thermogravimetric curve of SrMoO4 powders were calcined at 650?C. The synthesized materials were characterized by TG/DSC, XRD, EDX, SEM and ERD. The lattice parameters of the crystal structure were obtained from the Rietveld refinement method. All the XRD patterns were indexed according to JCPDS 01-085-0586 record with tetragonal structure and space group I41/a and the residual parameter structure refinement ranged from 1.035 to 1.292, secondary phases and impurities not being identified. It was found that there are differences between the average relative intensities of the diffraction peaks of X-rays. Using statistical tools, it was found that the rate of heating was the independent variable showed the greatest influence on this difference. The EDX analysis showed the presence of deviations between the theoretical and experimental composition for strontium and molybdenum components; the percentage deviation ranged from 0.027 to 3.67% depending on the conditions of synthesis. According to the SEM micrographs, the synthesized powders are composed of agglomerates of particles with irregular and spherical morphology bipiramidal. According to the analysis of the experimental design, with the dependent variable bandgap energy, the lowest values (4.18 and 4.17 eV to pH 6 and 9, respectively) were the samples calcined for 3 hours at the same heating rate 10 C min-1 compared to the calcined material in other conditions of synthesis and the statistical models generated have been shown to describe the observed phenomena. Exploratory testing photodegradation of the synthetic solution of methylene blue dye using the material bandgap of 4.17 eV indicate that the tested powder has influence on the reduction of dye concentration for tests carried out in pH 2 and 5 getting approximately 95% and 24 % conversion respectively, and the test at pH 9 it was noted that direct photolysis is more effective in reducing the dye concentration reached around 67% conversion, but the reaction process needs more study to better understand the results.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-03-20T20:20:20Z No. of bitstreams: 1 MichaelSegundoSena_DISSERT.pdf: 3968212 bytes, checksum: a95eb22daa7a11e3816b3d91a585c55a (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-04-04T18:21:55Z (GMT) No. of bitstreams: 1 MichaelSegundoSena_DISSERT.pdf: 3968212 bytes, checksum: a95eb22daa7a11e3816b3d91a585c55a (MD5) / Made available in DSpace on 2017-04-04T18:21:55Z (GMT). No. of bitstreams: 1 MichaelSegundoSena_DISSERT.pdf: 3968212 bytes, checksum: a95eb22daa7a11e3816b3d91a585c55a (MD5) Previous issue date: 2016-09-08 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Neste trabalho, foram sitetizados materiais cer?micos nanom?tricos da fam?lia das scheelitas, o molibdato de c?rio, atrav?s do m?todo de complexa??o combinada EDTA-Citrato. Realizou-se um planejamento experimental fatorial 2? com tr?s repeti??es no ponto central para avaliar a influ?ncia dos par?metros de s?ntese, pH (5, 7,5 e 10), taxa de aquecimento (5, 7 e 10 ?C.min-1) e tempo de calcina??o (3, 4 e 5 h), na forma??o da fase, no tamanho m?dio de cristalito e no band gap do material. Os p?s foram caracterizados atrav?s das an?lises TG/DSC, DRX, EDX, MEV e DRS-UV/Vis. Atrav?s da curva da an?lise TG/DSC, observou-se a decomposi??o dos org?nicos at? a temperatura de 600 ?C, temperatura a qual foi utilizada na calcina??o dos precursores. Os difratogramas dos p?s obtidos foram indexados com a ficha cristalogr?fica JCPDS (Joint Committee on Powder Diffraction Standards) com c?digo de referencia 01-070-1382 de estrutura monocl?nica do tipo Scheelita e grupo espacial C2/c. N?o foram identificadas fases secund?rias. Os difratogramas foram refinados pelo m?todo Rietveld, onde foram obtidos os par?metros de rede e volume de c?lula unit?ria. As an?lises de EDX (% at?mica) mostram que h? desvios m?ximos de 15 e 10% entre as porcentagens at?micas te?ricas e experimentais de Ce e Mo, respectivamente. Atrav?s das imagens de MEV, observou-se que os p?s s?o formados por aglomerados de part?culas de tamanhos e formato heterog?neos, formando um material poroso. O estudo do tamanho de cristalito foi feito baseado na interpreta??o dos dados dos difratogramas. Utilizou-se os m?todos de Halder-Wagner-Langford (HWL) e de Scherrer, revelando tamanho m?dio de cristalitos variando entre 11,67 e 32,75 nm. As propriedades ?pticas das nanopart?culas foram avaliadas por meio da an?lise de DRS-UV/Vis atrav?s da qual foram medidos os band gap ?pticos que variaram entre 2,33 e 2,43 eV, caracter?stico de materiais semicondutores com potencial para aplica??es fotocatal?ticas utilizando a luz vis?vel como fonte de radia??o. O m?todo de s?ntese utilizado mostrou-se eficiente para produ??o de um material cristalino, monof?sico e de tamanho nanom?trico. Observou-se que a s?ntese realizada com pH 5, taxa de aquecimento de 5?C.min-1 e tempo de calcina??o de 3h se mostrou mais adequada para produ??o do material com as caracter?sticas desejadas de tamanho de cristalito e band gap. Os testes de fotocat?lise indicaram que o material sintetizado possui alto potencial de adsor??o do corante em pH 2, alcan?ando uma remo??o de quase 95% do corante em 30 minutos de contato, sem irradia??o de luz. O estudo do efeito da concentra??o de catalisador indicou que a diminui??o da concentra??o de molibdato de c?rio para 0,125 g.L-1 aumentou o potencial de remo??o de corante para 99% em 3 horas de rea??o. Observou-se ainda atrav?s dos testes fotocatal?ticos que a diminui??o da concentra??o do corante ocorreu pela adsor??o do azul de metileno na superf?cie do material sem degrada??o da mat?ria org?nica, dentro das condi??es experimentais adotadas. Os resultados de cin?tica de adsor??o indicaram que a adsor??o do azul de metileno nas part?culas de molibdato de c?rio pode ser descrita pelo modelo de pseudo-segunda ordem para as condi??es estudados no trabalho. / In this work, nanosized ceramic materials of scheelite family were synthesized, the cerium molybdate, through the combined complexing method EDTA-Citrate. It was conduced a 2? factorial design with three central points to evaluate the influence of synthesis parameters pH (5, 7.5 and 10), heating rate (5, 7 and 10 ? C min-1) and calcination time (3, 4, and 5 hr), on phase formation, the crystallite size and the band gap of the material. The powders were characterized by TG/DSC, XRD, EDX, SEM and DRS-UV/Vis analysis. Through TG/DSC curve, it was observed the decomposition of organics until 600 ?C, which this temperature was used in the calcination of the precursors. The XRD powders patterns were indexed to the crystallographic card JCPDS (Joint Committee on Powder Diffraction Standards) n? 01-070-1382 of Scheelite type with monoclinic structure and space group C2/c. No secondary phases were identified. The XRD patterns were refined by Rietveld method, where the lattice parameters and unit cell volume were obtained. The EDX analysis (atomic %) show that there is maximum deviation of 15 and 10% on the theoretical and experimental atomic percentages of Ce and Mo, respectively. Through the SEM images, it was observed that the powders are formed by particles agglomerations of heterogeneous format and size, forming a porous material. The crystallite size study was done based on the interpretation of data from the XRD patterns. It was used the Halder-Wagner-Langford (HWL) and Scherrer methods, revealing average size of crystallites ranging between 11.67 and 32.75 nm. The optical properties of the nanoparticles were evaluated using the DRS-UV/Vis analysis whereby the optical band gap were measured ranging from 2.33 to 2.43 eV, classifying the material as a semiconductor with potential for photocatalytic applications using visible light as the radiation source. The synthesis method used was efficient for the production of a crystalline, nanosized and single phase material. It was observed that the synthesis performed at pH 5, heating rate of 5 ?C min-1, and calcination time of 3hr were more suitable for the production of materials with the desired characteristics of crystallite size and band gap. Photocatalysis tests indicated that the synthesized material has a high potential for dye adsorption at pH 2, achieving a removal of nearly 95% of the dye in 30 minutes of contact, without light irradiation. The study of the effect of catalyst concentration indicated that the decrease of concentration of cerium molybdate to 0,125 g.L-1 increased dye removal potential to 99% in 3 hours of reaction. It was also observed through the photocatalytic tests that the decrease in concentration of the dye occurred by methylene blue adsorption on the material surface without degradation of organic matter, within the experimental conditions. The adsorption kinetics results indicated that the adsorption of Methylene Blue on cerium molybdate particles can be described by the pseudo second-order model for the conditions studied in this work.

Made available in DSpace on 2014-12-17T15:01:34Z (GMT). No. of bitstreams: 1 IndiraAFM_DISSERT_Parcial.pdf: 1021016 bytes, checksum: 339ff82fc9edc8d5f827859010abd0dc (MD5) Previous issue date: 2013-12-17 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this work it was synthesized and characterized the cobalt ferrite (CoFe2O4) by two methods: complexation combining EDTA/Citrate and hydrothermal investigating the influence of the synthesis conditions on phase formation and on the crystallite size. The powders were mainly characterized by x-ray diffraction. In specific cases, it was also used scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray fluorescence (XRF) and isotherms of adsorption and desorption of nitrogen (BET method). The study of the crystallite size was based on the interpretation of x-ray diffractograms obtained and estimated by the method of Halder-Wagner-Scherrer and Langford. An experimental design was made in order to assist in quantifying the influence of synthesis conditions on the response variables. The synthesis parameters evaluated in this study were: pH of the reaction medium (8, 9 and 10), the calcination temperature (combined complexation method EDTA/Citrate 600?C, 800?C and 1000?C), synthesis temperature (hydrothermal method 120?C, 140?C and 160?C), calcination time (combined complexation method EDTA/Citrate - 2, 4 and 6 hours) and time of synthesis (hydrothermal method 6, 15 and 24 hours). By the hydrothermal method was possible to produce mesoporous powders with high purity, with an average crystallite size up to 7 nm, with a surface area of 113.44 m?/g in the form of pellets with irregular morphology. By using the method of combined complexation EDTA/Citrate, mesoporous powders were produced with greater purity, crystallite size up to 22nm and 27.95 m?/g of surface area in the form of pellets with a regular morphology of plaques. In the experimental design was found that the hydrothermal method to all the studied parameters (pH, temperature and time) have significant effect on the crystallite size, while to the combined complexation method EDTA/Citrate, only temperature and time were significant / Neste trabalho foi sintetizada e caracterizada a ferrita de cobalto (CoFe2O4) atrav?s dos m?todos complexa??o combinada EDTA/Citrato e hidrot?rmico, investigando a influ?ncia das condi??es de s?ntese na forma??o da fase e no tamanho m?dio de cristalito. Os p?s foram caracterizados principalmente por difra??o de raios-x. Em casos espec?ficos, tamb?m foi utilizado microscopia eletr?nica de varredura (MEV), espectroscopia de energia dispersiva (EDS), fluoresc?ncia de raios-x (FRX) e isotermas de adsor??o e dessor??o de nitrog?nio (M?todo BET). O estudo do tamanho de cristalito foi baseado na interpreta??o dos difratogramas de raios-x obtidos e estimado atrav?s do m?todo de Halder-Wagner-Langford (HWL) e de Scherrer. Um planejamento experimental foi realizado com a finalidade de auxiliar na quantifica??o da influ?ncia das condi??es de s?ntese nas vari?veis-resposta. Os par?metros de s?ntese avaliados neste trabalho foram: pH do meio reacional (8, 9 e 10), temperatura de calcina??o (m?todo de complexa??o combinando EDTA/Citrato 600?C, 800?C e 1000?C), temperatura de s?ntese (m?todo hidrot?rmico 120?C, 140?C e 160?C), tempo de calcina??o (m?todo de complexa??o combinando EDTA/Citrato 2, 4 e 6 hrs) e tempo de s?ntese (m?todo hidrot?rmico 6, 15 e 24 hrs). Pelo m?todo hidrot?rmico foi poss?vel produzir p?s mesoporosos com elevado grau de pureza, com tamanho m?dio de cristalito de at? 7nm, com ?rea superficial de 113,44m?/g e na forma de aglomerados com morfologia irregular. Ao se utilizar o m?todo de complexa??o combinando EDTA/Citrato foram produzidos p?s mesoporosos com maior pureza, cristalitos com at? 22nm de tamanho, 27,95m?/g de ?rea superficial e na forma de aglomerados com morfologia regular de placas. No planejamento experimental foi constatado que no caso do m?todo hidrot?rmico todos os par?metros estudados (pH, Temperatura e tempo) apresentam efeito significativo no tamanho de cristalito, enquanto que, para o m?todo de complexa??o combinando EDTA/Citrato, apenas a temperatura e o tempo foram significativos / 2020-01-01