Juliana Martins de Souza e Silva

Catalytic activity and stability of a chromium containing silicate in liquid phase cyclohexane oxidation

A chromium containing silicate has been prepared by an acid-catalyzed sol–gel process. The material was characterized by FTIR, UV–VIS and EPR spectroscopy as well as TPR, XRD and XRF analyses. The silicate is an efficient catalyst for the oxidation of cyclohexane with tert-butyl hydroperoxide. Leaching studies showed that catalysis is at least in part due to traces of Cr leached into the homogeneous phase. Weakly bound Cr species can be removed by soxhlet extraction, yielding a catalyst which is remarkably leaching resistant. The catalyst can be used at least four times without detectable loss of metal.

Alumina-Catalyzed Epoxidation with Hydrogen Peroxide: Recycling Experiments and Activity of Sol-Gel Alumina

Commercial alumina looses some activity after the first epoxidation reaction of (S)-limonene with hydrogen peroxide, but maintains a good activity and a very high selectivity in the subsequent three reactions. After this its activity is strongly reduced, probably due to structural modifications. Aluminas obtained by sol-gel methods are normally less active than the commercial alumina. However, the use of monomeric aluminum sec-butoxide and of oxalic acid to form stable alumina mesophases allows a very active alumina to be obtained, which catalyses the epoxidation of the less reactive cyclohexene with hydrogen peroxide in 98% yield. Close to 50% of the active oxygen is used up in the formation of molecular oxygen.

Three-dimensional non-destructive soft-tissue visualization with X-ray staining micro-tomography.

Low inherent contrast in soft tissues has been limiting the use of X-ray absorption micro-computed tomography (micro-CT) to access high-resolution structural information of animal organs. The staining agents used in micro-CT to improve the contrast fail in providing high-quality images of whole organs of animals due to diffusion problems of the staining agent into the sample. We demonstrate a staining protocol that incorporates a biochemical conditioning step prior to exposure to the staining agent that succeeds in overcoming the diffusion problems, thus quickly providing high-quality micro-CT images of whole organs of mammals. Besides of yielding non-distorted three-dimensional information at the same spatial resolution accessible in histological sections, micro-CT images of whole organs stained by our method enable easy screening of slices along any direction of the volume thus demonstrating new possibilities of structural analysis in biomedical science.

Copper Containing Silicates as Catalysts for Liquid Phase Cyclohexane Oxidation

Silicatos contendo cobre foram preparados pelo processo sol-gel catalisado por acido. Os materiais foram caracterizados por difracao e fluorescencia de raios X, espectroscopia EPR, analise elementar, fisissorcao de N2, termogravimetria, calorimetria diferencial de varredura, reducao a temperatura programada, espectroscopia FTIR e UV/VIS. Os silicatos mostram-se catalisadores eficientes para a oxidacao do cicloexano com hidroperoxido de tert-butila como oxidante e obtiveram-se cicloexanona e cicloexanol como produtos principais da reacao. O metal mostrou-se fracamente ligado a matriz de silica e foi observada lixiviacao do metal para a fase liquida. A lixiviacao foi quantificada por fluorescencia de raios X. Testes de lixiviacao mostraram que a atividade catalitica e devida as especies de cobre suportadas. O cobre lixiviado nao mostrou nenhuma atividade catalitica em fase homogenea.

Synthesis and structural characterization of nanometric ceria highly dispersed in SBA-15 with oxygen exchange capacity

Nanometric ceria-decorated SBA-15 was prepared using a route involving the impregnation of SBA-15 pores by a solution of cerium(III) 2-ethylhexanoate, followed by its thermal decomposition. According to XRF analysis, the number of successive impregnation–decomposition cycles (IDC) allows control of the CeO2/SiO2 ratio in the final material, and also the tailoring of the nanoparticle size of the fluorite CeO2nanoparticles supported in the SBA-15, as confirmed by XRD, Raman and UV-Vis spectroscopies. The mean pore size of the SBA-15 decreases with successive IDC, as observed by N2 adsorption–desorption, suggesting that CeO2 nanoparticles are located inside the SBA-15 mesopores, as confirmed by TEM and HRTEM analyses. The degree of oxygen storage capacity (OSC) was measured by the number of hydrogen uptake from the temperature programmed reduction (H2-TPR). It was found that the value of hydrogen uptake of SBA-15 submitted to one IDC corresponds to 3344 μmol of O2 per gram of CeO2, whereas those of SBA-15 submitted to five and ten IDC were 1324 and 2769 μmol of O2 per gram of CeO2, respectively.

Size controlled synthesis of highly dispersed anatase/rutile nanoparticles with photocatalytic activity toward salicylic acid degradation

TiO2 nanocrystals supported in SBA-15 pores were prepared by a simple route of successive cycles of impregnation of SBA-15 with titanium(IV) di-(n-propoxy)-di-(2-ethylhexanoate) followed by thermal treatment. Anatase and rutile phases were identified by XRD in the materials obtained after cycles 1, 3, 5, 7 and 10. Raman scattering combined with XRD and TEM shows that titania is in a nanometric regime. Increases in the size of the titania nanocrystals, as well as increases in the TiO2 content in the final material (XRF), occur after successive cycles. SAXS and N2 sorption indicate that the nanocrystals are formed inside the SBA-15 mesopores, which remain unblocked even after 10 cycles. UV-Vis (DRS) spectroscopy indicates important changes in electronic properties. The ability of SBA-15-supported titania nanocrystals to photodegrade salicylic acid was tested. There is a clear relation between the TiO2 nanoparticle size and the photocatalytic activity. Among all samples tested, the best result was obtained for the materials with the highest band-gaps and with the smallest sized titania.

Viral Inhibition Mechanism Mediated by Surface-Modified Silica Nanoparticles

Vaccines and therapies are not available for several diseases caused by viruses, thus viral infections result in morbidity and mortality of millions of people every year. Nanoparticles are considered to be potentially effective in inhibiting viral infections. However, critical issues related to their use include their toxicity and their mechanisms of antiviral action, which are not yet completely elucidated. To tackle these problems, we synthesized silica nanoparticles with distinct surface properties and evaluated their biocompatibility and antiviral efficacy. We show that nanoparticles exhibited no significant toxicity to mammalian cells, while declines up to 50% in the viral transduction ability of two distinct recombinant viruses were observed. We designed experiments to address the mechanism of antiviral action of our nanoparticles and found that their hydrophobic/hydrophilic characters play a crucial role. Our results reveal that the use of functionalized silica particles is a promising approach for controlling viral infection and offer promising strategies for viral control.

Incorporation of nanocrystals with different dimensionalities in hybrid TiO2/P3HT solar cells

Abstract. We investigate the effect of TiO2 nanoparticles–nanospheres and nanorods–inserted in the poly(3-hexylthiophene) (P3HT) matrix of TiO2/P3HT inverted hybrid solar cells. X-ray diffraction, high-resolution transmission electron microscopy, small-angle x-ray scattering, photoluminescence, and photoelectrochemical experiments were employed to investigate the structure, morphology, and photoactivity of TiO2 nanoparticles modified with 2-thiopheneacetic acid, mixed or not with P3HT. Both TiO2 nanospheres and TiO2 nanorods presented a good dispersion in the polymer matrix. The incorporation of TiO2 nanospheres and nanorods has improved the photocurrent generation, and devices with efficiency values up to 1.35% were obtained. Our results reveal that the nanoscale morphology enables an enhanced interfacial area for exciton dissociation. In particular, the nanospheres contribute with their high specific area, and the nanorods contribute with their high aspect ratio.

Selective Synthesis of Silver Nanoparticles onto Potassium Hexaniobate: Structural Organisation with Bactericidal Properties

Silver-based nanocomposites are known to act as biocides against a series of microorganisms and are largely studied as an alternative to substitute conventional antibiotics that show decreasing efficacy. In this work, an eco-friendly method to synthesize silver nanoparticles assembled on the surface of hexaniobate crystals is reported. By means of ion exchange, K(+) ions of layered potassium hexaniobate were partially substituted by Ag(+) ions and the resulting material was exposed to UV light. The irradiation allowed the reduction of silver ions with consequent formation of silver nanoparticles located only on the hexaniobate surface, whereas Ag(+) ions located in the interlayer space remained in the ionic form. Increasing UV-light exposure times allowed controlling of the silver nanoparticle size. The antibacterial effects of the pristine potassium hexaniobate and of silver-containing hexaniobate samples were tested against Escherichia coli (E. coli). The antibacterial efficacy was determined to be related to the presence of silver in hexaniobate. An increasing activity against E. coli was observed with the decrease in silver nanoparticles size, suggesting that silver nanoparticles of distinct sizes interact differently with bacterial cell walls.

Optical properties of polydisperse submicrometer aggregates of sulfur-containing zinc oxide consisting of spherical nanocrystallites

Spherical microparticles formed by agglomerated spherical nanocrystals of sulfur-containing ZnO were prepared by homogeneous precipitation of ZnS followed by thermal treatment under an air atmosphere. The samples were characterized by thermogravimetry (TG), X-ray diffraction (XRD) and Raman, UV-Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopies. The particle morphologies were observed by transmission and scanning electron microscopies (TEM and SEM), showing that spherical microparticles of sulfur-containing ZnO are formed by aggregates of 25 nm spherical nanocrystallites. XRD and TEM results show the presence of ZnO and ZnS phases for short time thermal treatments and only the ZnO wurtzite phase for longer thermal treatments. The presence of Zn–S bonds in sulfur-containing zinc oxide decreases the ZnO band gap energy as verified by DRS, probably due to a valence band offset.