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Artigo submetido em abril de 2013 e aceito em outubro de 2013 RESUMOAs peneiras moleculares MCM-41 têm atraído grande interesse devido as suas propriedades de alta área específica, volume e diâmetro de poros controláveis. Estes materiais são aplicados em diversos ramos da indústria química como adsorventes, suportes catalíticos e catalisadores heterogêneos em vários processos. , com dimensões e volume de poros dentro das especificações de materiais mesoporosos, sendo estas prorpriedades semelhantes ao MCM-41 sintetizado com a sílica gel comercial, comprovando que a cinza da casca do arroz pode ser utilizada como fonte alternativa de sílica na síntese de peneiras moleculares do tipo MCM-41. PALAVRAS-CHAVE:MCM-41, síntese hidrotérmica, sílica, cinza da casca do arroz SYNTHESIS OF MCM-41 MOLECULAR SIEVE DERIVED FROM RICE HUSK ASH ABSTRACTMCM-41 molecular sieves attracted great interest due their properties, as high specific surface area, controllable diameter and pore volume. These materials have been applied as adsorbents, catalyst supports, and heterogeneous catalysts in various branches of the chemical industry. In this work, MCM-41 was synthesized from rice husk ash, natural and chemically treated, as alternative sources of silica, called CCA-MCM-41 and CCAL-MCM-41, respectively, with the aim of reusing this residue and produce a lower cost mesoporous material. The materials were synthesized by the hydrothermal method from a gel composition: CTAMBr 1,0 mol L -1 ; SiO 2 4,0 mol L -1 ; Na 2 O 1,0 mol L -1 ; H 2 O 200 mol L -1 ; and characterized by XRF, XRD, FT-IR and specific surface area determination by the BET method. The materials showed high specific surface area (905 m 2 g -1 ), with dimensions and pore volume within the specifications of mesoporous materials, which are proprieties similar to MCM-41 synthesized with commercial silica gel, proving that rice husk ash can be used as an alternative source of silica for the synthesis of MCM-41 molecular sieves.

ResumoEsse trabalho teve como objetivo sintetizar óxidos com a estrutura tipo perovskita de composição LaFeO 3 , LaFe 0,8 Al 0,2 O 3 e LaFe 0,8 Cr 0,2 O 3 pelo método sol-gel proteico, visando sua aplicação como pigmento cerâmico. Os pós resultantes do processo de síntese foram calcinados a 600 e 800 °C e em seguida caracterizados por difração de raios X com refinamento Rietveld, microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), espectroscopia na região do UV-visível e colorimetria CIE-L*a*b*. De acordo com os difratogramas de raios X, todos os pós calcinados foram monofásicos com estrutura tipo perovskita ortorrômbica. As imagens de MEV e MET revelaram que os pós foram porosos e nanométricos. As ferritas de lantânio sem dopagem apresentaram cores em tons pastel, sendo mais claros nos pós dopados com alumínio. Já a ferrita dopada com cromo apresentou coloração marrom claro. As colorações foram mais intensas com o aumento da temperatura de calcinação. Palavras-chave: pigmento, gelatina, perovskita, ferrita. Abstract

Molecular sieves MCM-41 were synthesized from rice husk ash (RHA) as alternative sources of silica, called RHA MCM-41. The material was synthesized by a hydrothermal method from a gel with the molar composition 1.00 CTMABr:4.00 SiO 2 :1.00 Na 2 O:200.00 H 2 O at 100 °C for 120 h with pH correction. The cetyltrimethylammonium bromide (CTMABr) was used as a structure template. The material was characterized by X-ray powder diffraction, FTIR, TG/DTG, and surface area determination by the BET method. The kinetics models proposed by Ozawa, Flynn-Wall, and Vyazovkin were used to determine the apparent activation energy for CTMA ? species decomposition from the pores of MCM-41 material. The results were compared with those obtained from the MCM-41 synthesized with silica gel. The synthesized material had specific surface area, size, and pore volume as specified by mesoporous materials developed from conventional sources of silica.

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Thermogravimetric data using the non-isothermal kinetic models of Flynn and Wall and ''Model-free Kinetics'' were used to determine the activation energy to study the decomposition kinetics of the ligand groups with system's metallic ions that takes part in the synthesis of PrMO 3 (M = Ni or Co). This activation energy was determined for the stage of highest decomposition of the organic matter to establish parameters in synthesis condition optimization and application of the proposed material.

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