Evaldo Toniolo Kubaski

Effect of Pressure-Assisted Heat Treatment on Photoluminescence Emission of α-Bi2O3 Needles

Materials with high photoluminescence (PL) intensity can potentially be used in optical and electronic devices. Although the PL properties of bismuth(III) oxide with a monoclinic crystal structure (α-Bi2O3) have been explored in the past few years, methods of increasing PL emission intensity and information relating PL emission to structural defects are scarce. This research evaluated the effect of a pressure-assisted heat treatment (PAHT) on the PL properties of α-Bi2O3 with a needlelike morphology, which was synthesized via a microwave-assisted hydrothermal (MAH) method. PAHT caused an angular increase between the [BiO6]-[BiO6] clusters of α-Bi2O3, resulting in a significant increase in the PL emission intensity. The Raman and XPS spectra also showed that the α-Bi2O3 PL emissions in the low-energy region (below ∼2.1 eV) are attributed to oxygen vacancies that form defect donor states. The experimental results are in good agreement with first-principles total-energy calculations that were carried out within periodic density functional theory (DFT).

Effect of pressure-assisted thermal annealing on the optical properties of ZnO thin films

ZnO thin films were prepared by the polymeric precursor method. The films were deposited on silicon substrates using the spin-coating technique, and were annealed at 330 °C for 32 h under pressure-assisted thermal annealing and under ambient pressure. Their structural and optical properties were characterized, and the phases formed were identified by X-ray diffraction. No secondary phase was detected. The ZnO thin films were also characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, photoluminescence and ultraviolet emission intensity measurements. The effect of pressure on these thin films modifies the active defects that cause the recombination of deep level states located inside the band gap that emit yellow-green (575 nm) and orange (645 nm) photoluminescence.

Preparation of transparent hydrophobic polymeric films spray-deposited on substrates

ABSTRACT This paper describes the production of transparent hydrophobic polymeric films made of poly(vinyl chloride) and paraffin wax. A liquid polymeric solution was prepared and spray-deposited on silica glass and nonwoven fabric surfaces. The contact angle between water droplets and glass substrate was 102° while that between droplets and nonwoven fabric was 120°. The films exhibited hydrophobic behaviour regardless of the droplet size. Field emission gun scanning electron microscopy revealed complete adhesion of the film on the substrate and a film thickness of 0.16 µm. The atomic force microscopy micrographs showed a nanoscale rough film surface, which was responsible for air entrapment, preventing water from penetrating the film. This fact explains the high contact angle obtained. The raw materials also contributed to the film’s hydrophobicity because of their non-polarity, which prevents miscibility between water droplets and film. GRAPHICAL ABSTRACT

Optical Properties of the MoO3-TiO2 Particulate System and Its Use as a Ceramic Pigment

Mo-doped TiO2 powders were prepared using a dry mixture of TiO2 and MoO3 oxides with several compositions, followed by a calcination step at several temperatures. The resulting oxide system develops yellow and green tones. The XRD patterns showed only traces of MoO3; however, EDS results, combined with TG/DTA data, confirmed the presence of molybdenum ions, suggesting that the changes in optical properties of the oxide system is due to the incorporation of Mo ions into the TiO2 matrix, substituting Ti+4 with Mo+6 ions. The band gap decreased with increasing of MoO3 content; on the other hand, the band gap reached a maximum value at about 850°C to 910°C when plotted as a function of the calcination temperature. The glazes produced showed that the oxide system under study is a potential material for use as abinary ceramic pigment.

Bioactive Potential of 3D-Printed Oleo-Gum-Resin Disks: B. papyrifera, C. myrrha, and S. benzoin Loading Nanooxides—TiO2, P25, Cu2O, and MoO3

This experimental study investigates the bioactive potential of filaments produced via hot melt extrusion (HME) and intended for fused deposition modeling (FDM) 3D printing purposes. The oleo-gum-resins from benzoin, myrrha, and olibanum in pure state and also charged with 10% of metal oxide nanoparticles, TiO2, P25, Cu2O, and MoO3, were characterized by ultraviolet-visible (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray microanalysis (EDXMA), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Disks were 3D-printed into model geometries (10 × 5 mm) and the disk-diffusion methodology was used for the evaluation of antimicrobial and antifungal activity of materials in study against the clinical isolates: Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans. Due to their intrinsic properties, disks containing resins in pure state mostly prevent surface-associated growth; meanwhile, disks loaded with 10% oxides prevent planktonic growth of microorganisms in the susceptibility assay. The microscopy analysis showed that part of nanoparticles was encapsulated by the biopolymeric matrix of resins, in most cases remaining disorderly dispersed over the surface of resins. Thermal analysis shows that plant resins have peculiar characteristics, with a thermal behavior similar to commercial available semicrystalline polymers, although their structure consists of a mix of organic compounds.

Analytic Hierarchy Process Applied to the Choice of a Long-Life Tomato (Lycopersicon esculentum Mill) Drying System

Drying processes are widely employed to add quality and preserve and concentrate high-value foods and pharmaceutical products. However, most drying processes are highly energy and time consuming, which makes them costly, and also cause numerous changes in the product that may impair its quality. Several aspects must be considered in the choice of the type of dryer, because different parameters may imply different purchase costs, energy consumption, and effects on quality. In this study, to simplify the decision-making process, the application of the analytic hierarchy process (AHP) was tested and proved to be satisfactory.

High-Energy Mechanical Milling of Ultra-High Molecular Weight Polyethylene (UHMWPE)

Ultra-high molecular weight polyethylene (UHMWPE) is a polyethylene with a very long chain, which provides excellent features, however it makes the processing difficult due to high melt viscosity. Many studies intend to found out means to make its processing easier. Recently, the high-energy mechanical milling has been used for polymeric materials and it was detected that physical and chemical changes occur during milling. In such case, powder of UHMWPE was milled in three types of mills: SPEX, attritor e planetary, in different times of milling. The polymer was characterized by SEM and XRD. Thus, it was observed that the material processed in attritor mill showed larger phase transformation from orthorhombic to monoclinic. This is most likely due to the smaller milling temperature of attritor mill when compared with the other two mills and the high shear force generated during milling.

Synthesis of acicular α-Bi2O3 microcrystals by microwave-assisted hydrothermal method

ABSTRACT Materials based on bismuth(III) oxide are candidate to be used in optical and electronic devices because of their properties such as a variable band gap, photoconductivity, photoluminescence, high refractive index, and dielectric permittivity. These properties are dependent of several factors, e.g., present phases and crystal morphology. The microwave-assisted hydrothermal method (MAH) is a fast and efficient approach of synthesis to obtain semiconductor powders. However, the synthesis of monoclinic bismuth oxide (α-Bi2O3) with acicular morphology by MAH was not found in literature. In this paper, microcrystals of acicular α-Bi2O3 (monophasic) were successfully obtained by MAH using a synthesis temperature of 80°C for 0.5 h. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron, and transmission electron microscopies showed the formation of a monoclinic structure (space group P21/c) with acicular morphology that grew along the [001] direction. The temperature and time necessary to synthetize acicular microcrystals were significantly lower than those found for acicular microcrystals obtained by conventional hydrothermal method.

Energia de superfície para nanossuperfícies de TiO2 na direção (001)

In this work was made an investigation about bulk and surface models (at maximum 20 layers) of the TiO2 material in the (001) direction. TiO2 commercial sample was feature using XDR technique to determine phase and crystallites average size. Bulk and (001) surface models were simulated for TiO2 material using DFT/B3LYP and its results were used for calculating energy surface, electronic levels, superficial atomic displacement and charge maps. Atoms of the first and second layers of the slab model showed electronic densities very well organized in the form of chains or wires.

Modification of Complex Materials Using a Pressure-Assisted Heat Treatment

This chapter reports a physical method to modify materials structures using a pressure-assisted heat treatment (denoted PAHT). This method has attracted much attention to obtain of novel complex materials, mainly due to the use of the low-temperature and elevated gas (e.g., air) pressure. PAHT is performed into a hermetically closed chamber from specifically designed for this purpose. PAHT has been studied as a technique of thin film deposition and as an alternative treatment to modify the crystalline structure of novel complex materials. In the field of film deposition, PAHT uses crystalline powder of metal oxides to produce the films. Films obtained by PAHT are homogeneous and dense, with similar morphology to that found in the starting oxide particles. The fundamental mechanism of this PAHT is mainly based on the mass transfer from oxide particles to the substrate surface, which enables a strong thin film adhesion/interaction to the substrate surface. One of the greatest advantages of this methodology is the possibility of applying films on several kinds of substrates that include glasses, polymers, silicon, and so on. Hence, the PAHT causes structural modifications as well as creation of various types of defects in crystalline thin films and oxide powders. For example, ordered clusters can be disordered by the pressure action, leading to the significant changes in the physical and chemical properties of thin films and oxide powders. Furthermore, as will be shown in this chapter, the effect of air pressure on crystalline structures has opened up novel opportunities to the rational development of novel complex materials with tunable physical and chemical properties for a wide variety of technological applications of interest.