RESUMO Recentes avanços tecnológicos na síntese e projeto de nanopartículas magnéticas (NPMs) vêm abrindo vários caminhos para o uso destes materiais em aplicações médicas e farmacêuticas, como biosensores, carreadores de fármacos, destruição de células tumorais e separação magnética de células e proteínas. Com vista nisso, foi proposto obter o híbrido de NiFe2O4@SiO2 a partir da modificação da superfície da ferrita de níquel com 3-aminopropiltrietoxissilano, objetivando avaliar a sua formação a partir de suas propriedades estruturais, magnéticas e morfológicas, a fim de estudar a sua capacidade de imobilizar a glicose oxidase (GOx). As amostras foram analisadas por DRX, FTIR, MEV, BET/BJH, medidas magnéticas e testadas na reação de imobilização da GOx. Os resultados revelaram a formação monofásica do espinélio NiFe2O4 com tamanho de cristalito de 35 e 32 nm para as amostras antes e após a modificação da superfície; presença de bandas de absorção características do espinélio e do grupo silanol do agente silano, confirmando formação do híbrido. A modificação de superfície melhorou a área superficial e o comportamento magnético das NPMs. O estudo demonstrou que a presença do agente silano não contribuiu para a imobilização da GOx.

ABSTRACT Recent technological advances in the synthesis and design of magnetic nanoparticles (MNPs) have opened up a slew of ways for the use of these materials in medical and pharmaceutical applications, such as biosensors, drug carriers, destruction of tumor cells, and magnetic separation of cells and proteins. In view of this, we propose to obtain the hybrid NiFe2O4@SiO2 from the surface modification of the nickel ferrite with 3-aminopropyltriethoxysilane, aiming to evaluate its formation by its structural, morphological and magnetic properties, in order to test it for its performance in the immobilization of the glucose oxidase (GOx). The samples were analyzed through XRD, FTIR, SEM, BET/BJH, magnetic measurements and tested in the GOx immobilization. The results showed the single phase formation of the spinel NiFe2O4 with crystallite size of 35 and 32 nm for the samples before and after surface modification and the presence of characteristic absorption bands for the spinel and the silanol group of the silane agent, confirming the formation of the hybrid. The surface modification improved the surface area and the magnetic behavior of the NPMs. The presence of the silane agent does not contribute for the GOx immobilization.

RESUMO As nanoferritas mistas de Ni0,5Zn0,5Fe2O4 e Ni0,2Cu0,3Zn0,5Fe2O4 foram sintetizadas por reação de combustão usando ureia como combustível e um reator cônico como fonte de aquecimento para produção em bateladas de 10 g, e então, testadas como nanocatalisadores heterogêneos nas reações de transesterificação e esterificação metílica e etílica do óleo de soja para produção de biodiesel. Durante as sínteses foram registrados o tempo e a temperatura das reações, bem como observadas a liberação de gases e a cor das chamas emitidas. As amostras foram caracterizadas por DRX, EDX, FTIR, MEV/EDS, BET e cromatografia gasosa. Os testes reacionais foram executados para 10 g do óleo em duração de 1 h, razão molar 1:12 óleo:álcool, 2 % (m/m) de catalisador e conduzidas a 180 ºC. Os difratogramas de DRX e os espectros de FTIR revelaram presença da fase espinélio inverso tipo B(AB)2O4. A morfologia apresentou a formação de aglomerados de aspecto frágil e elevada área de superfície. As análises cromatográficas produziram excelentes resultados nas reações de esterificação para ambas amostras nas condições testadas, com destaque especial para Ni0,5Zn0,5Fe2O4, cujas conversões foram de 91,4 % em ésteres metílicos e de 77,8 % em ésteres etílicos, enquanto que a amostra Ni0,2Cu0,3Zn0,5Fe2O4 apresentou conversões de 75,1 e 65,1 %, respectivamente. As conversões na transesterificação metílica e etílica foram de 14 e 2 % para Ni0,5Zn0,5Fe2O4 e de 11 e 3 % para Ni0,2Cu0,3Zn0,5Fe2O4.

ABSTRACT The mixed nanoferrites of Ni0.5Zn0.5Fe2O4 and Ni0.2Cu0.3Zn0.5Fe2O4 were synthesized by combustion reaction using urea as fuel and a conical reactor as heating source in batches of 10 g, and then tested as heterogeneous nanocatalysts in the transesterification and esterification reaction of soya bean oil using the methyl and ethyl routes to biodiesel production. During the synthesis the time and temperature of the reactions were measured, and the evolved gases and the color of the emitted flames were observed. The samples were characterized by XRD, EDX, FTIR, SEM/EDS, BET and gas chromatography. The reaction tests were carried out with 10 g of oil for 1 h, oil:alcohol molar ratio of 1:12, 2 % (w/w) of catalyst, and conducted at 180 °C. The XRD patterns and the FTIR spectra revealed the presence of the inverse spinel phase type B(AB)2O4. The morphology showed the formation of agglomerates with fragile morphology and high surface area. The chromatographic analysis produced excellent results in the esterification reactions for both samples in the tested conditions, with special emphasis on Ni0.5Zn0.5Fe2O4, whose conversions were of 91.4 % in methyl esters and of 77.8 % in ethyl esters, while the Ni0.2Cu0.3Zn0.5Fe2O4 sample showed conversion of 75.1 and 65.1 %, respectively. The conversions in the methyl and ethyl transesterification were of 14 and 2 % of the Ni0.5Zn0.5Fe2O4 sample, and of 11 and 3 % for the Ni0.2Cu0.3Zn0.5Fe2O4 sample.

The purpose of this work is to evaluate the performance of Ni0.5Zn0.5Fe2O4 ferrite doped with 0.1 and 0.4 mol of Cu as a catalyst for the transesterification of soybean oil to biodiesel, using methanol. The samples were characterized by X-ray diffraction, nitrogen adsorption and scanning electron microscopy. The reaction was performed for 2 hours at a temperature of 160 °C, using 10 g of soybean oil, a molar ratio of oil: alcohol of 1:20, and 4% (w/w) of catalyst. The product of the reaction was characterized by gas chromatography, which confirmed conversion to methyl esters. The diffraction patterns showed the presence only of Ni0.5Zn0.5Fe2O4 ferrite phase with a crystallite size of 29 nm. The samples doped with 0.1 and 0.4 mol of Cu showed a surface area and particle size of 22.17 m²g- 1 and 50.47 nm; and 23.49 m²g- 1 and 47.64 nm, respectively. The morphology of both samples consisted of brittle block-shaped agglomerates with a wide particle size distribution. A comparative analysis of the two catalysts indicated that the catalyst doped with 0.4 mol of Cu showed the better performance, with a conversion rate of 50.25%, while the catalyst doped with 0.1 mol of Cu showed 42.71% conversion.