Adilson J. A. de Oliveira

Metalloporphyrins immobilized in Fe3O4@SiO2 mesoporous submicrospheres: Reusable biomimetic catalysts for hydrocarbon oxidation

We successfully immobilized metalloporphyrins (MeP) in mesoporous silica coating magnetite spheres. In this sense, we prepared two different classes of core@shell supports, which comprise aligned (Fe3O4-AM-MeP, MeP=FeP or MnP) and non-aligned (Fe3O4-NM-MeP, MeP=FeP or MnP) mesoporous magnetic structures. X-ray diffractometry and energy dispersive X-ray spectroscopy confirmed the mesoporous nature of the silica shell of the materials. Magnetization measurements, scanning and transmission electron microscopies (SEM/TEM), electrophoretic mobility (ζ-potential), and infrared spectroscopy (FTIR) also confirm the composition and structure of the materials. The catalysts maintained their catalytic activity during nine reaction cycles toward hydrocarbon oxidation processes without detectable catalyst leaching. The catalysis results revealed a biomimetic pattern of cytochrome P450-type enzymes, thus confirming that the prepared materials are can effectively mimic the activity of such groups.

Study of Thermal Degradation of PLGA, PLGA Nanospheres and PLGA/Maghemite Superparamagnetic Nanospheres

Poly(glycolide-co-lactide) (PLGA) nanospheres containing magnetic materials have been extensively studied because of its biomedical applications. Therefore, it is very important to know thermal properties of these materials in addition to other physical properties. Thermal degradation activation energy (Eα) of PLGA nanospheres with maghemite entrapment (PLGA-Mag), PLGA nanospheres (hollow spheres) (PLGA-H) obtained by an emulsion method and unprocessed PLGA (PLGA-R) were calculated by isoconversional Vyazovkin method based on data of TG analysis in order to evaluate modifications in thermal behavior caused by nanospheres obtainment process or by maghemite entrapment. Both hydrodynamic diameter in the range of 200-250 nm and polydispersity index lower than 0.3 are considered satisfactory. Thermal degradation of PLGA-R begins at higher temperatures than those of PLGA-H and PLGA-Mag, but processed samples presented increase in thermal stability, which was greater before processing by emulsion and in the presence of the magnetic materials. PLGA-Mag presents superparamagnetic behavior at room temperature.

Superparamagnetic maghemite loaded poly (ε- caprolactone) nanocapsules : characterization and synthesis optimization

Iron oxide nanoparticles (ION) have been studied for essential applications, like detection of biological constituents (virus, bacterials, cell, nucleic acids, protein, enzyme, etc.), magnetic bioseparation and clinic therapy and diagnosis (such as MRI magnetic fluid and hyperthermia). In this work, γ-Fe2O3 has been synthetized by a adapted sol-gel method and entraped in poly e-caprolactone (PCL) nanocapsules. The superparamagnetic nanocapsules have been formulated by double emulsion evaporation method. Some variables affecting the polydispersity index, zeta potential surface and size of nanocapsules were studied aiming optimize the formulation process of maghemite-loaded PCL nanocapsules. The following parameters were selected: sonication time, PCL concentration in organic phase, PVA concentration in external aqueous phase and maghemite/PCL weight ratio. Under these experimental conditions, the resulting nanocapsules displayed a mean size of about 346 nm and a maghemite content of about 7.5 µg/mg of nanocapsules and superparamagnetic behaviour at room temperature.

Observation of superficial antiferromagnetism in Co3O4 polycrystals

We report on a systematic study about the magnetic properties of Co3O4 polycrystals with large size distribution (100–1200 nm) and the crystallite size of 68(4) nm on average. An antiferromagnetic transition at T N = 32 K, extensively reported in the literature for Co3O4, was observed. Furthermore, another transition at T t = 14 K, which is suppressed for H ≥ 35 kOe, was also identified. An increase in the magnetic susceptibility, as well as irreversibility between zero field cooled and field cooled data below T t were observed. The non-detection of a coercive field below T t, and the fact that T t and T N are independent from the driven frequencies in ac magnetic measurements as a function of temperature, confirm that both peaks are associated to antiferromagnetic transitions.

Room Temperature Ferroic Responses in PZT/Ba-ferrite Based Ceramic Composites

The ferroic properties (ferroelectric and magnetic) of a PZT/Ba-ferrite (PZT–BaM) based ceramic composite, obtained from the conventional solid state reaction method, have been investigated. Results, obtained at room temperature, revealed intensified characteristics of both ferroelectric and magnetic responses, which make these composites a topic of studies and exploring applications in magneto-electric related devices.

Induced ferromagnetism in mechanically milled nanocrystalline In2O3 powder

In this work, we have investigated structural, optical and magnetic properties of In2O3 powder samples prepared by mechanical milling process at different milling times. These samples have evidenced a ferromagnetism order at room temperature. The optical and magnetic properties were explained by the increase of quantum confinement, defects and strain effects after mechanical milling. Introduction Undoped semiconductor oxides are well known as diamagnetic materials. However, recent studies have revealed that oxides nanostructures such as nanowires and nanoparticles can exhibit ferromagnetic order. The ferromagnetism is usually associated to the increase of defects such as oxygen vacancies, quantum confinement and etc. However, further studies are necessary in order to understand the nature of magnetic properties in undoped oxides. In this work, we have investigated structural, optical and magnetic properties of In2O3 nanoparticles (NP) prepared by mechanical milling at different milling times. We have measured X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman Spectroscopy, Photoluminescence (PL) and magnetic properties of In2O3 nanoparticles. Methods and Results Commercial undoped In2O3 powder (purity: 99.9%) has been milled under air in a planetary ball mill for different milling times. Zirconia grinding medium has been used in order to avoid any contamination with magnetic impurities. The samples were investigated using different experimental techniques such as XRD, SEM, Raman and Photoluminescence. XRD measurements were performed using a Rigaku powder diffractometer and the morphology of samples was investigated by a Field Emission Gun Scanning Electron Microscopy (FEG-SEM). The Raman and PL measurements were performed in a 0.5m Andor spectrometer coupled with a Si CCD. The magnetic characterization was performed using SQUID VSM magnetometer. The XRD data have evidenced the bcc-phase, reduction of crystallite size and changes of microstrain for all In2O3 nanoparticles. Figure 1 shows typical magnetic results obtained for the sample after 48h milling time. It was observed that after mechanical milling process the samples present ferromagnetic order. Figure 2 shows typical optical results for the same sample. The PL spectra have showed a visible band related to oxygen vacancy transition. It was observed that this band presents a blue shift with increasing milling times. The Raman spectra showed several peaks related to the cubic phase of In2O3 nanoparticles. It was also observed that for higher milling times such as 96h, additional Raman peaks were revealed due to the change of cubic crystal phase to hexagonal phase. DOI: 10.17648/bwsp-2017-70026 18th Brazilian Workshop on Semiconductor Physics (BWSP 2017) 18th Brazilian Workshop on Semiconductor Physics (BWSP 2017) -60 -40 -20 0 20 40 60 -8 -6 -4 -2 0 2 4 6 8 -0,04 0,00 0,04 -0,010 -0,005 0,000 0,005 0,010 (b) 300 K 0 h M a g n e ti z a ti o n ( 1 0 -2 e m u /g )

O uso de vídeos curtos para ensinar tópicos de semicondutores

The daily use of electronic devices, which are mostly based on semiconductor diodes and transistors, has become very common. The understanding of some concepts related to semiconductor materials is very important to achieve a better comprehension of these devices. Although this statement appears in the official documents and in national Brazilian curricular parameters (PCN), in practice there is a small number of proposals in this direction. Thus, the purpose of this article was to describe the use of a sequence with four short videos to teach introductory concepts of semiconductors at high-school level. These videos were shown to two classes of third grade of high school, with a total of 72 students. After each video, we gave the students a questionnaire with 16 Likert items, in order to measure the students’ attitudes regarding some concepts discussed in the videos. Analyzing the questionnaire results, we saw the effectiveness of the proposal, mainly with respect to the students motivation to study this subject. The majority of concepts were well assimilated, and the few difficulties were in agreement with literature. This suggests that the use of short videos is a strategy that can be more used, mainly due its versatility and very limited need of technical resources.