RESUMO Neste trabalho foi sintetizado TiO2 pelo método Pechini em diferentes proporções de ácido cítrico/cátions metálicos visando avaliar a influência das fases anatásio e rutilo na estrutura, morfologia e gap óptico de energia. Dessa forma, as amostras foram caracterizadas por DRX, FTIR, distribuição e tamanho de aglomerados, densidade por picnometria de hélio, TGA e determinação de banda gap a partir da refletância difusa. Os resultados mostram a formação das fases anatásio e rutilo em todas as proporções de ácido cítrico/cátions metálicos avaliadas. Morfologicamente as amostras apresentaram tamanho de aglomerados entre 15,89 a 19,34 µm com densidade em torno de 3,7 g/cm3. Com relação às propriedades ópticas avaliadas observou-se que o aumento da proporção da fase rutilo em relação à fase anatásio não alterou significativamente sua banda gap, obtendo-se valores entre 2,97 a 3,00 eV.

ABSTRACT In this work, TiO2 was synthesized by the Pechini method in different proportions of citric acid/metal cations to evaluate the influence of the anatase and rutile phases on the structure, morphology and optical energy gap. Thus, the samples were characterized by XRD, FTIR, distribution and size of clusters, density by helium picnometry, TGA and determination of gap band from the diffuse reflectance. The results show the formation of the anatase and rutile phases in all proportions of citric acid/metal cations evaluated. Morphologically the samples had agglomerate size between 15,89 and 19,34 μm with density around 3.7 g/cm3. Regarding the optical properties evaluated, it was observed that the increase in the ratio of the rutile phase to the anatase phase did not significantly alter its band gap, obtaining values between 2,97 and 3,00 eV.

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.

In this work we evaluate the use of silane agent 3-aminopropyltrimethoxysilane and biopolymer chitosan to functionalize ferrites Ni0.5Zn0.5Fe2O4 using the solvent evaporation method aiming at obtaining hybrid material Ni0.5Zn0.5Fe2O4@SiO2/chitosan for use as a biosensor. The nanoparticles before and after the functionalization showed the major phase Ni0.5Zn0.5Fe2O4. The FTIR spectra showed absorption bands characteristic of CO, axial deformation of CN and SiO band from the silane agent which proved functionalization. The functionalization of ferrite Ni0.5Zn0.5Fe2O4 with chitosan caused a 36.36% reduction in saturation magnetization as compared with ferrite synthesized, however it maintained the ferrimagnetic characteristic indicating to be a promising material for the use in biotechnological applications as for example in magnetic biosensors.

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.

This work evaluated the catalytic activity of TiO2 synthesized by the Pechini method. with varying molar ratios of 2:1, 3:1 and 4:1 of citric acid/metallic cations, in the photocatalytic degradation of methyl red dye in aqueous solution. The samples were characterized by X-ray diffraction, phase quantification by Rietveld structure refinement, and textural analysis by nitrogen adsorption, and their photocatalytic performance was bench- tested. The results indicated that the 3:1 and 4:1 samples contained two phases, with 84.4 and 89% of anatase phase and 15.6 and 11% of rutile phase, respectively. The 2:1 sample contained only anatase phase. The total discoloration of methyl red dye in 24 hours confirmed the high photocatalytic efficiency of the 2:1 sample, which was ascribed to the formation of monophasic anatase.

The constant heating rate method employed in sintering studies offers several advantages over the isothermal method, particularly the fact that all the parameters that describe the sintering phenomena can be obtained from a single sample. The purpose of this work is to determine the parameters of sintering kinetics of nanosized Ni-Zn ferrite powders synthesized by combustion reaction. The nonisothermal sintering method was studied using a constant heating rate (CHR). The Ni-Zn ferrite powders, with average particle size varying from 18 nm to 29 nm, were uniaxially pressed and sintered in an horizontal dilatometer at a constant heating rate of 5.0 °C/min from 600 °C up to complete densification, which was reached at 1200 °C. The compacts were characterized by scanning electron microscopy (SEM). Experimental results revealed three different sintering stages, which were identified through the Bannister Theory. The shrinkage and the shrinkage rate analyzed showed a viscous contribution in the initial sintering stage, which was attributed to the mechanism of structural nanoparticle rearrangement.