Síntese e caracterização de hidroxiapatita natural extraída de escamas de pirarucu (Arapaima gigas)

A hidroxiapatita integra o grupo de biomateriais cerâmicos sendo aplicada na área médica devido a sua biocompatibilidade e propriedade osteocondutora, o que a torna uma opção para tratamentos envolvendo recuperação de traumas ósseos. Os resíduos pesqueiros, os ossos e as escamas, podem ser utilizados como uma fonte barata para a produção de fosfatos de cálcio (hidroxiapatita). O objetivo do estudo foi o uso das escamas de pirarucu, resíduo não tóxico, para investigar a viabilidade de extrair hidroxiapatita natural e caracterizá-la por análises físico-químicas e estruturais a fim de comprovar a sua integridade. Primeiramente, foi realizado caracterização térmica para estabelecer as condições do tratamento térmico. Com isso, as escamas foram tratadas termicamente para a remoção dos compostos orgânicos. Após isso, o material foi homogeneizado, peneirado e purificado com reagentes, devido a possibilidade da amostra absorver impurezas durante o procedimento experimental. As caracterizações físico-químicas e estruturais foram realizadas para acompanhar e comprovar as etapas desenvolvidas e examinadas. Os resultados apresentam que o produto obtido apresentou 99% de fase de HAp natural e fase cristalina. Na região do infravermelho obteve-se a presença dos picos 3750-3500cm-1 e 610-560 cm-1, referentes aos íons OH- e PO4-3 respectivamente, apresentando os grupos funcionais hidroxila e fosfato que constituem a fórmula química da hidroxiapatita e, por meio da espectroscopia por energia dispersiva, as amostras apresentaram percentuais elementares de cálcio (37%), oxigênio (40%) e fósforo (13) que são compatíveis com a razão molar Ca/P da fase de hidroxiapatita. Palavras-chave: escamas, tratamento térmico, hidroxiapatita natural, grupos funcionais, fase cristalina

One-Step Sol-Gel Facile Synthesis and 3D Nanoscale Morphology Investigation of Bi0.5Na0.5TiO3-BaTiO3 Thin Films

Abstract: Bismuth sodium titanate, denoted as Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT), possessing a perovskite-like structure, has emerged as a highly prospective material in recent years. It is considered a prime contender for replacing PZT-based compounds due to its exceptional piezoelectric and ferroelectric properties, coupled with the presence of loosely bound pairs of chemically active electrons. This study delves into the micromorphological properties of BNT-BT thin film electrodes, fabricated using sol-gel spin-coating and subsequent annealing processes. Employing Atomic Force Microscopy (AFM), comprehensive 2D and 3D topographical maps were acquired, enabling the extraction of pivotal parameters crucial for surface characterization. Notably, the investigation encompasses Minkowski Functionals, which encompass normalized Minkowski volume, boundary, and connectivity analyses. In conjunction, various roughness parameters, encompassing arithmetic mean height, maximum peak height, maximum valley depth, arithmetic mean depth, and the ten-point height parameter, were quantified across these analyses to facilitate a comprehensive comparison of surface morphologies among distinct samples. The morphological analysis outcome underscores the potential for elucidating material performance through microstructural shape and quantitative roughness evaluation of respective surfaces. This holds significant promise for applications such as predictive assessment of functional behavior, including industrial quality control during sample manufacturing processes

Toward a new PTCR material based on the Na2Ti6O13/Na2Ti3O7 system

Mixed phases of sodium titanate ceramics are obtained using both conventional and laser sintering methods. It was observed a clear dependence on the structural, microstructural and electrical resistivity with the employed sintering method. The temperature dependence of the resistivity in the ceramics shows an increase of three orders of magnitude in a narrow range of temperatures, thereby indicating a noticeable positive temperature coefficient of resistivity (PTCR) effect. To explain this observed abnormal behavior, a model based on the structure of the Na2Ti6O13/Na2Ti3O7 composite is proposed. A new class of PTCR materials is reported.Postprint (author's final draft

Synthesis of CaNb₂O₆ with a Rynersonite-like Structure: Morphology, Rietveld Refinement, Optical, and Vibrational Properties

In this study, we report the easy and low-cost synthesis of calcium niobate (CaNb2O6) with the isomorphic structure of the Rynersonite mineral for CaTa2O6. The samples were prepared by the ball milling method at room temperature at a synthesis time of 0.5, 1, 2, 3, and 4 h. The structural analysis by XRD, Rietveld refinement, and vibrational Raman spectroscopy confirms all diffraction peaks and active mode characteristics of the pure phase of CaNb2O6 for the 3-h and 4-h samples, with a crystallite size of 22.5 and 23.2 nm, respectively. The optical band gap obtained was 3.18(2) eV (3-h sample), lower than the optical band gap for niobium oxide, characteristic of materials with strong photon absorption in the UVA region of the spectrum. The surface analysis by scanning electron microscopy reveals the obtention of several agglomerates of irregular particles ranging in the submicro and micro scales. Therefore, the present approach successfully obtained calcium niobate with the formula CaNb2O6 at a short synthesis time and room temperature

Temperature Dependence of the Electrical Properties of Na2Ti3O7/Na2Ti6O13/POMA Composites

The temperature dependence of the electrical properties of composites formed by biphasic sodium titanate and poly(o-methoxyaniline) (Na2Ti3O7/Na2Ti6O13/POMA) with different concentrations of POMA (0%, 1%, 10%, 15%, 35% and 50%) in the ceramic matrix was determined from measurements of complex impedance. The structural details were studied by means of X-ray diffraction, confirming the formation of the Na2Ti3O7/Na2Ti6O13/POMA composites. The displacement of the (200) reflection from 2θ = 10.45° to 11.15° in the composites with 10 and 15% of POMA suggested the partial replacement of H+ for Na+ in the Na2Ti3O7 structure. The thermal properties were investigated by Thermogravimetry and Differential Thermal Analysis. The Thermogravimetry curves of the composites with POMA content of 1, 10 and 15% presented profiles similar to that of pure sodium titanate sample. The composites with 35 and 50% of POMA showed a process at temperatures around 60–70 °C, which was associated with water absorbed by the polymer. The analysis of the complex impedance spectroscopy measurements revealed that the electrical resistivity of the composites in the range from 0 to 35% increased by two orders of magnitude, with different values for each concentration. This positive temperature coefficient of resistivity was less noticeable in the composite with highest POMA mass content (50%). The rapid increase in resistivity caused an increase in the relaxation time calculated from the time domain. The electrical response of the 50% of POMA compound changes in relation to what was observed in the other compounds, which suggests that there is a saturation limit in the increase in resistivity with POMA content

Head-to-Tail and Head-to-Head Molecular Chains of Poly(p-Anisidine): Combined Experimental and Theoretical Evaluation

Poly(p-anisidine) (PPA) is a polyaniline derivative presenting a methoxy (–OCH3) group at the para position of the phenyl ring. Considering the important role of conjugated polymers in novel technological applications, a systematic, combined experimental and theoretical investigation was performed to obtain more insight into the crystallization process of PPA. Conventional oxidative polymerization of p-anisidine monomer was based on a central composite rotational design (CCRD). The effects of the concentration of the monomer, ammonium persulfate (APS), and HCl on the percentage of crystallinity were considered. Several experimental techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), multifractal analysis, Nuclear Magnetic Resonance (13C NMR), Fourier-transform Infrared spectroscopy (FTIR), and complex impedance spectroscopy analysis, in addition to Density Functional Theory (DFT), were employed to perform a systematic investigation of PPA. The experimental treatments resulted in different crystal structures with a percentage of crystallinity ranging from (29.2 ± 0.6)% (PPA1HT) to (55.1 ± 0.2)% (PPA16HT-HH). A broad halo in the PPA16HT-HH pattern from 2θ = 10.0–30.0° suggested a reduced crystallinity. Needle and globular-particle morphologies were observed in both samples; the needle morphology might have been related to the crystalline contribution. A multifractal analysis showed that the PPA surface became more complex when the crystallinity was reduced. The proposed molecular structures of PPA were supported by the high-resolution 13C NMR results, allowing us to access the percentage of head-to-tail (HT) and head-to-head (HH) molecular structures. When comparing the calculated and experimental FTIR spectra, the most pronounced changes were observed in ν(C–H), ν(N–H), ν(C–O), and ν(C–N–C) due to the influence of counterions on the polymer backbone as well as the different mechanisms of polymerization. Finally, a significant difference in the electrical conductivity was observed in the range of 1.00 × 10−9 S.cm−1 and 3.90 × 10−14 S.cm−1, respectively, for PPA1HT and PPA16HT-HH

Morphology, microstructure, and electrocatalytical properties of sol-gel spin-coated Bi0.5Na0.5Ba(TiO3)2 thin films

Herein, we report, for the first time, the reduction reaction kinetics of ciprofloxacin organic molecules based on structural and micromorphological conditions of an electrocatalytic system of Bi05Na05Ba(TiO3)2 (BNT-BT) thin films. XRD analysis showed the coexistence of rhombohedral and tetragonal structures for the BNT-BT thin films annealed at 600, 650, and 700 degrees C, showing that the first one had a greater number of surface defects, which Raman spectroscopy confirmed. Analysis of the 3D micromorphological evaluation showed that an annealing temperature increase from 600 to 700 degrees C does not induce significant changes in the topographical profile. However, BNT-BT thin films annealed at 600 degrees C displayed more anisotropic surface microtexture, high spatial complexity, and low spatial frequencies. For the reactive surface of BNT-BT films, the electroanalytical assays showed that electrons from the conduction band are captured by oxygen adsorbed on the film surface, forming superoxide radicals that attack ciprofloxacin molecules, promoting their degradation. The best performance observed for the BNT-BT thin films annealed at 600 degrees C is attributed to their unique structural and micromor-phological properties compared to the films annealed at higher temperatures. Our results prove that the proposed thin film deposition process is promising for developing new electrocatalytic devices