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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.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/22545 |
| Date | 08 September 2016 |
| Creators | Sena, Michael Segundo |
| Contributors | 13681389420, http://lattes.cnpq.br/1030834608582624, Santos, Andarair Gomes dos, 02813010421, http://lattes.cnpq.br/3470634368296605, Santos, Francisco Klebson Gomes dos, 00779263405, http://lattes.cnpq.br/0273000754120553, Moriyama, Andr? Luis Lopes, Souza, Carlson Pereira de |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM ENGENHARIA QU?MICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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