Resumo em Inglês:

Abstract Macusanite is a volcanic glass extracted from the volcanic field Macusani – Peru, formed by the fast cooling of magma. This study shows physical and chemical characterization of Macusanite samples to better understand its molecular structure, elemental composition as well as to investigate the presence of natural inclusions. The characterization of the natural glass can give valuable geological information about the magma composition, the eruption intensity and age of volcanism activity. Moreover, the use of different characterization techniques can help in mineral prospecting. Macusanite was characterized by X-Ray Diffraction/Fluorescence (XRD/XRF), Optical Microscopy, Scanning Electron Microscopy (SEM) and micro-Raman spectroscopy. The latter suggests the presence of andalusite mineral incorporated in the glass structure, while the Energy-Dispersive X-ray Spectroscopy (EDS) analysis indicates the presence of some rich calcium inclusion. Moreover, XRD shows the glass characteristic amorphous band and that the sample is in the glassy stage.

Resumo em Inglês:

Abstract The photocatalytic activity and stability of TiO2 thin films deposited by reactive sputtering were evaluated through many cycles of aqueous methylene blue solutions photodegradation. Tests were performed in TiO2 films deposited onto silica, silicon, and lanthanum aluminate substrates under UV light irradiation. The dye degradation was determined using the optical absorbance spectra at pre-established exposure times. After 16 cycles of reaction, 180 minutes each, no systematic losses in the photocatalytic activity were observed in the samples. The best activity was observed on films deposited onto silica glass. The results indicate that the TiO2 samples deposited by the sputtering technique are stable concerning the UV degradation of methylene blue.

Resumo em Inglês:

Abstract Recently, there has been growing interest in the incorporation of particles in plasma deposited thin films to creation of multifunctional surfaces. In this work a new hybrid methodology based on the plasma enhanced chemical vapor deposition (PECVD) of hexamethyldisiloxane combined to the reactive sputtering of TiO2 is proposed for the preparation of SiOxCyHz-TiO2 composite films. Specifically, the effect of the proportion of O2 in the plasma environment on the morphology, chemical structure, elemental composition, wettability, thickness and surface roughness, of the films was studied. Agglomerates of TiO2 (16-83 μm) were detected into the organosilicon matrix with the concentration of particulates growing with the percentage of oxygen in the feed. In general, there was elevation in the angle of contact of the surfaces as the oxygen supply increased. Interpretation is proposed in terms of the influence of the oxygen supply on the TiO2 sputtering rate and in the oxidation of plasma species.

Resumo em Inglês:

Abstract 1,4-dihydro-1,2,4,5-tetraarylpyrrolo[3,2-b]pyrroles are a versatile class of materials with simple synthesis and promising application in organic electronic devices. In this work we present a method of synthesis of new 1,4-dihydro-1,2,4,5-tetraarylpyrrolo[3,2-b]pyrrole derivatives, with ester and carboxylic acid groups as anchoring groups, by multicomponent reactions using niobium pentachloride as catalyst. The new materials were structurally and optically characterized. Also, it was compared the bonding of different moieties to the titanium dioxide mesoporous film. The preliminary tests as dyes in standard configuration in dye-sensitized solar cells have shown a potential performance in the energy conversion.

Resumo em Inglês:

Abstract This study processed and characterized the biphasic ceramics Na2Ti3O7/Na2Ti6O13 that were obtained from semi-crystalline nanoparticles synthesized using sonochemical methods. Structural characterization techniques, such as X-ray diffraction and Raman spectroscopy, were used to identify the crystalline phases present. The Rietveld refinement revealed, among other structural parameters, the presence of two crystalline phases in compositions of 55.90% and 44.10% for sodium hexatitanate and trititanate, respectively. Via Raman spectroscopy, the presence of the main vibrational modes that correspond to the phases present in biphasic ceramics was confirmed. Finally, by using complex impedance spectroscopy, a decrease in the electrical resistance of both the grain (106 Ω-104 Ω) and its boundary (108 Ω -105 Ω) under increasing temperature was identified.

Resumo em Inglês:

Abstract There is a great demand to develop different techniques for the continuous removal, immobilization, and remediation of metallic ions from contaminated water. Human contamination by metallic ions could even occur by ingestion of seafood causing carcinogenic and mutagenic activities. In this study, a nanofibrous membrane of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) produced by electrospinning technique and coated with polyaniline (PAni) was tested for the removal of chromium in low-concentration solutions. The viability of ZFL cells (zebrafish liver cells) was performed to evaluate the water quality enhancement after chromium adsorption. The results indicated that the nanofibrous membrane successfully adsorbed the chromium species in low-concentration (Qe= 2.44 mg/g, at pH 4.5, room temperature (RT) and 24h) by Freundlich model and followed a pseudo-second-order kinetics model indicating a possible chemisorption in multilayers, at pH 4.5, RT and [CrVI] = 5.0 mg/L. At pH 2.0 (24h, RT and [CrVI] = 5.0 mg/L), the membrane adsorbed around 91.64% of CrVI contaminants. The thermodynamic studies revealed that the process was spontaneous and exothermic. The cells viability demonstrated the efficiency of the membrane tested in the aquatic ecosystem protection; the viability increased 19.2% in 5.0 mg/L CrVI solution. Thus, the results of this study shows that the nanofibrous membrane can be an alternative to remove low concentration of CrVI from aqueous solutions.

Resumo em Inglês:

The present work aims to prepare and characterize very thin films of poly(fullerene)s in order to investigate their electrical properties and the influence of xylene and chloroform solvents on these materials. The fullerenes studied were phenyl-C61-butyric acid methyl ester (PCBM), oligo{(phenyl-C61-butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene]} (OPCBMMB) and poly{[bispyrrolidino(phenyl-C61-butyric acid methyl ester)]-alt-[2,5-bis(octyloxy) benzene]} (PPCBMB), along with poly(3-hexylthiophene) (P3HT). The Langmuir-Schaeffer technique was used to prepare films, which were deposited on interdigitated gold substrates, and electrically characterized, with emphasis on the study of transport, conductivity and mobility mechanisms with respect to the solvents used. We found that the addition of P3HT significantly increased the conductivity of these materials. The xylene cast PPCBM, in both pure and mixed forms under dark conditions, presented the best conductivity results with respect to the other materials. However, when chloroform was used, it was found that OPCBMMB in both pure and mixed forms under light, exhibited the best conductivities. This is the first treatment, to our knowledge, of the impact of solvents on the electronic properties of poly(fullerene)s.

Resumo em Inglês:

Abstract Because of its excellent properties, carbon steel is a material widely used in several sectors. However, it is easily corroded when exposed to the environment. Seeking to remedy this problem, the possibility of coating carbon steel with SiOx/SiOxCyHz films generated by deposition and oxidation in low-pressure plasmas was investigated. Specifically, the effects of excitation power of the oxidation plasma on layer thickness, chemical structure, elemental composition, and barrier properties of the obtained coatings were investigated. The coating of the steel with the SiOxCyHz film, generated by plasma in an atmosphere of hexamethyldisiloxane (HMDSO), increased the total resistance to the passage of electric current, measured by electrochemical impedance spectroscopy. However, under the condition of moderate power oxidation (50 W), the results point to the creation of a bilayer system with high resistance to electrochemical attack compared to the SiOxCyHz film, even though its thickness is less than this.

Resumo em Inglês:

Abstract Target molecules adsorbed onto metallic nanoparticles can have their Raman and/or fluorescence signals enhanced, leading to the called surface-enhanced [resonance] Raman scattering (SE[R]RS) or surface-enhanced fluorescence (SEF). Here we have applied Au nanorods (AuNRs) coated with a surfactant bilayer leading to a positive surface charge to investigate the role played by these AuNRs in colloidal suspension on SERRS and SEF effects of charged molecules. In the case of the anionic nickel (II) tetrasulfonated phthalocyanine (NiTsPc), besides achieving SERRS with an enhancement factor (EF) of ca. 105, the AuNRs allowed the analytical application of the SERRS effect for the NiTsPc between 8.3x10-6 and 4.0x10-5 mol L-1. The limit of detection of 4.8x10-7 mol L-1 (at 752 cm-1) and 1.3x10-6 mol L-1 (at 1338 cm-1) was found. In the case of the cationic methylene blue, the SEF effect was achieved reaching an EF of ca. 10. Besides, fundamental discussions are carried out considering the results presented here.

Resumo em Inglês:

Abstract Copper sulfides are materials with different technological applications due to different possibilities of phases, which result in different properties. Thus, obtaining particles with different stoichiometry of the materials is of great interest. Two simple chemical routes were used to obtain copper sulfides (Cu2-xS) particles of different phases and stoichiometry. One of the obtained powders was used for thin film deposition through resistive evaporation and characterized. From scanning electron microscopy the particle size was found as around 500 nm. The second route leads to non-stoichiometric powder with characteristic CuS, Cu9S5 and Cu2S planes detected in the XRD diffractograms. Thin films from this route were also obtained by resistive evaporation. The amorphous film obtained after evaporation was submitted to thermal annealing at 200 ° C/2h, becoming semi-crystalline. The deposited film showed good adhesion to the substrate and low roughness, in addition to a bandgap of 2.5 ± 0.1 eV and a resistivity of 1x10-2 Ω.cm, values ​​in good agreement with those reported in the literature. The techniques used here proved to be of good quality for deposition of copper sulfide films, and can be used as a simpler alternative in addition to commonly used for deposition of copper sulfide films.

Resumo em Inglês:

Abstract Titanium dioxide (TiO2) and zinc oxide (ZnO) are among the most used catalysts in photodegradation. Paracetamol and salicylic acid are widely used as pharmaceutical drugs. We found that paracetamol is less susceptible to photodegradation compared to salicylic acid. From a chemical perspective, this was not expected since paracetamol is more vulnerable to chemical oxidation. Aiming the comprehension of this phenomenon, studies were performed comparing the efficiency of photodegradation of paracetamol versus salicylic acid and acetophenone versus 4-aminoacetophenone. The presence of amino/amide group decreased the efficiency of degradation significantly. It was also found that salicylic acid improved the degradation of paracetamol when both compounds were present in the reaction medium. The lower efficiency of photodegradation of the amino-based compounds seems to be related to the deactivation of the excited states of the TiO2 and ZnO. Theoretical calculations at the TD-PBE0/6-311++G(3df,2p) high level were performed and corroborated our proposal.

Resumo em Inglês:

Thin a-C:H:Si:F:N films were studied as a function of the partial pressure of SF6 in plasma feed, RSF, together with tetramethylsilane and N2. Deposition rates varied from ~4 to ~19 nm.min-1. Surface roughnesses were typically less than 35 nm. Surface contact angles with water droplets, measured using goniometry, were all around 90°. Scanning electron micrography revealed surface particles, probably formed in the gas phase, of typical diameters ~8 μm. As revealed by Fourier transform infrared spectroscopy and energy dispersive x-ray spectroscopy, the films are plasma polymers with a carbon and silicon network. Most of the films contain ~ 60 at.% C, ~ 10 at.% Si, 20 at.% O and ~5 to 14 at.% N. Film doping with F rises to ~2 at.% as RSF is increased. The Tauc gap, calculated from ultraviolet-visible near infrared spectroscopic data, is controllable in the range of ~3.5 to 4.1 eV by a suitable choice of RSF. Fluorination causes the films to be softer and less stiff. Total deformation and stored energies are reduced compared to those of the film deposited at RSF = 0%. The modulus of dissipation increases from ~8% to a maximum of ~65% for the fluorinated films.

Resumo em Inglês:

Glass-ceramic materials were obtained by heat treatment (960 ºC for 2, 4, and 6 hs) of glasses with CaCO3 47.50 wt%-TiO2 23.75 wt%-SiO2 23.75-Al2O3 5.00 wt% formulation produced by the melt-quenching technique (melting at 1650 ºC and subsequent annealing at 650 ºC). The materials’ structural characterization and crystallization kinetics (Kissinger method) indicate the presence of CaTiO3, CaSiO3, and CaTiSiO5 crystalline phases with activation energies 217, 281, and 446 kJ/mol, respectively. The structure refinement (Rietveld method) suggests metastability for the CaSiO3 and CaTiSiO5 phases as a function of the heat treatment time. The increase in time favors CaTiO3 crystallization, from 62.97 wt%, in the 2 hs treated sample, to 79.21 wt%, in the 6 hs treated sample. EDS and microstructure analyses confirm the glass-ceramic production and indicate segregation of the CaTiO3 phase for longer heat treatment times.

Resumo em Inglês:

Abstract This paper investigated the formation of crosslinks in natural rubber compounds in the vulcanization systems: conventional (CV), semi-efficient (SEV), and efficient (EV), processed with three types of accelerators: MBTS (dibenzothiazole disulfide), TMTD (tetramethylthiuram disulfide) and CBS (n-cyclohexyl 2-benzothiazole sulfenamide). The cross-linked densities were determined by organic solvent swelling, dynamic mechanical analysis (DMA), stress vs strain, and low-field nuclear magnetic resonance, the latter being the reference technique for comparison with the other results. It was found that the choice of accelerator type influences the processing time and the cross-linked density of the vulcanizate. The four techniques showed close values of cross-linked density for natural rubber compounds, demonstrating that the analytical techniques studied can be applied to determine cross-linked density.

Resumo em Inglês:

Abstract Thin AZO films were grown by RF magnetron sputtering for different deposition times in argon plasmas. Optical, structural, and morphological properties, together with elemental composition, were studied and correlated with the observed effects on the electrical properties and compared with two models of mobility scattering (ionized impurities and grain boundaries). The results suggest that the carrier density in the studied case is limited to below 15% owing to the low ionization efficiency caused by the formation of neutral impurities as homologous phases. While the spread in the mobility during the initial stages of film growth is strongly influenced by grain boundaries, in thicker films the limitation on ion efficiency becomes more significant.

Resumo em Inglês:

Abstract A derivation of the sol-gel-dip-coating deposition technique is proposed, where the precursor solution exhibits two separated liquid phases, reaching an equilibrium state in a heterogeneous solution. Structural, optical and photocatalytic properties of TiO2 films grown from the proposed two phases method are shown and discussed, along with the properties of films deposited when the top phase present distinct lengths, which are observed through SEM images and optical transmittance spectra. The dominant crystalline phase is anatase for all the films prepared. Films are tested towards their efficiency for photocatalysis, using methylene blue as dye degradation agent. It has been found that films deposited through the two phase method are more efficient on the photocatalyitic degradation of methylene blue.

Resumo em Inglês:

Abstract This work presents the results obtained in the production of poly (vinyl alcohol) (PVA) nanofibers with different concentrations of polypyrrole (PPy) doped with dodecylbenzene sulfonic acid (DBSA) - PPy.DBSA. The morphology of the nanofibers was studied by scanning electron microscopy (SEM) technique. The nanofibers were deposited on interdigitated electrodes (IDEs) for direct current electrical characterization (DC) and tested as ammonia gas sensors. The results showed a rapid detection of ammonia gas for higher concentrations of PPy.DBSA and for several alternating cycles in atmospheric N2.

Resumo em Inglês:

Abstract This work reports a study of the room-temperature synthesis of a SnO2/ZnO bilayer by magnetron sputtering. Morphological, optical, and electrical properties of the bilayer were investigated for different thicknesses of SnO2. Morphology was studied using profilometry and field emission scanning electron microscopy. The optical transmittances of the ZnO films and of the SnO2/ZnO combination were high (about 80%) in the visible, and the SnO2 film did not alter the optical properties of the ZnO, which would act as a transparent contact electrode in a perovskite solar cell.

Resumo em Inglês:

Abstract Here we report the production and characterization of a low-cost supercapacitor with electrodes based on colloidal graphite. We characterized the as-prepared device in terms of cyclic voltammetry (CV), Galvanostatic charge/discharge (GCD), and impedance spectroscopy. The supercapacitor exhibited good electrochemical performance with a high capacitance of 22 F g-1 for a discharge current of 2 mA. Long-term cyclability tests show that the device can keep about 85% of its capacitance after 500 cycles, even without encapsulation. We found power and energy densities of 110 W kg-1 and 3 Wh kg-1, respectively. All the experimental results indicate that the colloidal graphite Aquadag® is a promising material for application in supercapacitors.

Resumo em Inglês:

Abstract This paper evaluated the influence of the incorporation of the coinitiator Ethyl 4-(dimethylamino) benzoate (EDB) in Filtek Z250 XT resin in the reduction of the polymerization time and its behavior in halogen light and LED (Light Emitting Diode) light. The samples were subjected to thermal and spectroscopic analysis. The TG/DTG-DTA curve showed that both samples studied have a thermal stability temperature similar to the other polymers in the monomer blend. Morphological features were analyzed by SEM. By the MIR analysis, the degree of conversion using halogen light showed a better result compared to the LED light. The polymerization time applied to the specimens was 10 seconds, reducing the original resin time by half.

Resumo em Inglês:

Fullerene is considered to be the third carbon allotrope after diamond and graphite. The study of fullerene derivatives has been growing due to their exceptional electron affinity. This work proposes th study of three different fullerene derivatives, being phenyl-C61-butyric acid methyl ester (PCBM), oligo {(phenyl-C61-butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene]} (OPCBMMB) and poly {[bispyrrolidino(phenyl-C61-butyric acid methyl ester)]-alt-[2,5-bis(octyloxy)benzene]} (PPCBMB), and their application as NH3 sensors. Experimental results showed that these materials have a reproducible response to NH3, with PCBM resulting in the highest observed current peak, followed by OPCBMMB and PPCBMB. These results imply that PCBM, OPCBMMB and PPCBMB can be used to produce NH3 sensors.

Resumo em Inglês:

A tight-binding model is fitted to density-functional calculations of the electronic structure of the MoS2 monolayer. The model involves 13 atomic orbitals per unit cell: the 4d orbitals of the molybdenum atom plus the 3s and 3p orbitals of each sulfur atom. The hopping and overlap couplings of each atom with its first nearest neighbors in each crystalline sublattice are considered. Different values are allowed for the intraplane and interplane S-S hopping integrals. A closed-form expression is given for the effective-mass tensor at stationary points. The isotropy of the valence and conduction bands near the edges of the fundamental gap is proven. The role played by the orbital overlapping as well as the crystal-field splitting of the molybdenum 4d level is discussed.

Resumo em Inglês:

Abstract Carbon Nanotubes (CNTs) are materials of wide applicability, either due to their physical stability, rigidity of the structure and/or high electrical conductivity. These nanotubes can be manipulated using different techniques, as long as their idiosyncrasy and possible advantages of proper processing are known. One way to organize and manipulate this material is in the form of thin films, which despite the low solubility in organic solvents, when functionalized, the CNTs allow for satisfactory handling. In this work, we aimed to analyze the behavior of CNTs in an aqueous subphase, controlling the quality of the produced films. For that, it was observed the level of aggregation and rigidity of Langmuir films and carried out analyses of the monolayer reorganization and interaction of the mixture between CNTs and Stearic Acid. Quantitative estimations of the aforementioned features were done through an in-situ study that was performed using the Langmuir technique including analysis of isotherms, compressibility module, Gibbs interaction, and Brewster Angle Microscopy. In order to compare the monolayer after its removal from the Langmuir trough, UV-vis spectroscopy was carried out. The results showed that they form non-ideal mixtures, but they favor a better organized and less agglomerated film comparing to the pure CNT.

Resumo em Inglês:

Abstract Titanium is one of the most utilized metals for orthopedic implants. This element has excellent mechanical and biological properties. As a strategy to develop a new system of alloys that do not cause health problems to the patient, such as the Ti-6Al-4V alloy, a new group of alloys has been designed to meet these expectations. Molybdenum, when associated with titanium, reduces the transition temperature from α to the β phase. Zirconium increases the corrosion resistance, decreases the melting point, and improves the alloy's biocompatibility. The alloys with the beta phase's predominance are the most desirable for biomedical applications due to their higher mechanical compatibility with the bone tissue. This paper presents the preparation of as-cast Ti-10Mo-xZr (x= 30, 40, and 50 wt%) alloys and their characterization by measurements of density, energy dispersive spectrometry (EDS), x-ray diffraction, optical and scanning electron microscope (SEM). The density values were higher than that of pure titanium due to the zirconium and molybdenum. The EDS measurements reveal a suitable stoichiometry of the elements and no impurities contamination. In the x-ray diffraction and microscopy measurements, it was observed only peaks of the beta phase. This new system of Ti-alloys is promising for biomedical applications.