M. R. D. Bomio

Influence of variables on the synthesis of CoFe2O4 pigment by the complex polymerization method

Synthetic inorganic pigments are most widely used in ceramic applications due to their excellent chemical and thermal stability and their lower toxicity to both human and environment as well. In the present work, black ceramic pigment CoFe2O4 has been synthesized by the complex polymerization method (CPM) with good chemical homogeneity. In order to study the influence of variables on the process of obtaining pigment through CPM, 2(5-2) fractional factorial design with resolution III was used. The variables studied in the mathematical modeling were: citric acid/metal concentration, pre-calcination time, calcination temperature, calcination time, and calcination rate. Powder pigments were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible (UV-Vis) spectroscopy. Based on the results, the formation of cobalt ferrite phase (CoFe2O4) with spinel structure was verified. The color of pigments obtained showed dark shades, from black to gray. The model adjusted to the conditions proposed in this study due to the determination coefficient of 99.9% and variance (R2) showed that all factors are significant at the confidence level of 95%.

Effect of different starting materials on the synthesis of Ba 0.8 Ca 0.2 TiO 3

Literature has reported the synthesis of barium calcium titanates by various synthesis methods such as solid state reaction, co-precipitation and polymer precursors. These compounds are usually obtained using calcium carbonate (CaCO3), barium carbonate (BaCO3) and titanium oxide as starting materials. This study investigated the effect of different starting reagents on the synthesis of Ba0.8Ca0.2TiO3 (BCT) by complex polymerization method (CPM). Two sets of starting precursors were used: titanium citrate, CaCO3 and BaCO3, and titanium citrate and Ba1−xCaxCO3 solid solution precursor. Samples were crystallized at a temperature range from 400 °C to 700 °C for different time. The obtained powders were characterized by X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), and Raman and infrared spectroscopy. The infrared spectroscopy indicated that the chelation processes of Ba, Ca, Ti and CA ions are very similar. The results showed that the use of CaCO3 and BaCO3 or Ba1−xCaxCO3 solid solution as precursors does not affect the final properties of BCT powders obtained by CPM.

Experimental statistic design applied for obtaining Zn:xCe by microwave-assisted hydrothermal method with photocatalytic property

In this study, the nanostructures of pure ZnO and ZnO:xCe3+ were prepared using statistic design—factorial design 3(3−1)−3-level and mixed-level factorials and fractional with replicates in the central point, totaling 11 experiments. The experiments were performed using the microwave-assisted hydrothermal (MAH) method with Ce3+ concentration of 2 and 4 mol% at 60, 110, and 160 °C for 10, 20, and 30 min. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical diffuse reflectance were used to characterize the products. The fractional factorial design indicated the optimal design area, and the studies were continued by ridge analysis. The analysis of variance (ANOVA), the Pareto, and the model adjusted to the conditions proposed in this study due to the determination coefficient of 99.9%, variance (R2), and response surface generated were satisfactory, thus having an optimization in the process of obtaining ZnO doped with Ce.

Microstructural, structural and optical properties of nanoparticles of PbO-CrO3 pigment synthesized by a soft route

PbCrO4 and Pb2CrO5 particles were synthesized by the polymeric precursor method. Structural and microstructural properties of the particles were characterized by scanning electron microscopy with field emission gun, X-ray diffraction, and Raman spectroscopy techniques. The diffuse reflectance technique was employed to study the optical properties in the 400-700 nm range. The optical bandgap of the samples was obtained indirectly. Colorimetric coordinates L*, a*, b* were calculated for the pigment powders as a function of the heat treatment (400-700 oC). The powders displayed colors ranging from green to red. X-ray diffraction patterns showed the presence of monoclinic PbCrO4 phase in green samples, while red powders had a monoclinic Pb2CrO5 phase structure. The Raman spectra of the PbCrO4 and Pb2CrO5 powders were in good agreement with those reported in the literature. The synthesized compounds can be used as green and red pigments with high thermal stability.

Efeito do Pr2O3 nas propriedades elétricas de varistores à base de SnO2

The purpose of this work was to study and prepare SnO2-based dense ceramics doped with CoO and Ta2O5 and different concentrations of Pr2O3. The systems displayed high values of relative density and nonohmic properties. The addition of Pr2O3 caused the number of effective barriers of the systems to increase, improving the value of the nonlinear coefficient, and increasing the breakdown electric field. The height and the width of the potential barriers, which were determined by impedance spectroscopy measurements, indicated that the results are in agreement with the direct current response.

Photocatalytic Properties under Sunlight of Heterostructures AgCl/CuO Obtained by Sonochemical Method

AgCl/CuO heterostructures were synthesized via a sonochemical method. AgCl/CuO molar compositions of 1:1 and 2:1 were prepared, respectively. Such compositions were prepared using three distinct routes. The particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM-FEG) and UV-Vis spectroscopy (UV-Vis). In order to analyze the applicability of the heterostructure, photocatalytic tests were performed under sunlight and UV-Vis radiation for the degradation of the methylene blue dye. The results of the X-ray diffraction confirmed the formation of the AgCl/CuO heterostructure in all samples, with no evidence of doping or formation of deleterious phases. SEM images indicate a cubic-like morphology for the AgCl particles, forming Ag0 on its surface, the CuO particles have a leaf appearance. The results of the photocatalytic activity indicate that the increase of the AgCl molar ratio from 1:1 to 2:1 accelerates the degradation of methylene blue for both the radiations and shows that sunlight decreases by at least 55% for the degradation of the methylene blue, depending on the composition, to the heterostructure.

Effects of MnO 2 /In 2 O 3 thin films on photocatalytic degradation 17 alpha-ethynylestradiol and methylene blue in water

In recent years, there has been a growing concern about some substances in the aquatic environment such as methylene blue dye (MB) and 17α-ethynylestradiol (EE2) hormone, mainly from waste textile and pharmaceutical industries, respectively. This waste, which is not effectively treated, generates large amounts of contaminated effluents. Textile industries, which use dyes mainly in their dyeing and finishing processes, generate a lot of effluent contamination by dyes. The 17α-ethynylestradiol hormone which is used in different contraceptive pills and in hormone replacement therapy, is the main substance found in the aquatic environment because of its high resistance to biodegradation. It is known that conventional water treatment processes, which involve the steps of coagulation, flocculation and sedimentation among others, have been reported to be ineffective in the removal of dyes and hormones. The heterogeneous photocatalysis has attracted great interest from many research groups around the world due to its potential application as a pollutant degradation method. For this purpose, the present work evaluated the performance of MnO2/In2O3 thin films in the degradation process of the blue methylene and 17α-ethynylestradiol in aqueous solutions. The degradation processes were monitored by UV–Vis spectroscopy and HPLC chromatography. From these analyzes, the concentration of the solutions was evaluated and it was possible to infer that the MnO2/In2O3 thin films significantly promoted a degradation of 89% of 17α-ethynylestradiol, however, the degradation of the methylene blue was not efficient.

Nanofitas de óxido de estanho: controle do estado de oxidação pela atmosfera de síntese

Tin oxide nanobelts in different states of oxidation were produced by carbothermal reduction at 1260 oC. The nanostructures were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The state of oxidation of the nanostructures was controlled by the synthesis atmosphere inside the furnace. The materials obtained in atmospheres without oxygen were SnO and SnO2 nanobelts, while atmospheres with oxygen (about 10%) only allowed for the growth of SnO2 nanobelts.