Tania Regina Giraldi

Anatase-to-rutile transition in co-doped TiO2 pigments

In this paper, cobalt-doped titanium dioxide green ceramic pigments were synthesized by the polymeric precursor method. In order to investigate the obtainment of a crystalline rutile phase and particles in nanoscale, a chromophore doping was made with fixed concentrations of 1, 2, and 4 mol%, utilizing a calcination temperature of 600oC. The products were investigated by thermal analysis, X-ray diffraction, diffuse reflectance, scanning and transmission electron microscopies. The titanium dioxide:cobalt crystallite size was about 65–100 nm. A broad reflectance band around 540 nm (green region) was observed for all doped samples, indicating the appearance of a deep green pigment. Furthermore, the results have shown that cobalt-doped titanium dioxide promotes greater phase conversion of anatase to rutile. Samples submitted at a temperature of 600 °C, pure titanium dioxide contains 22% rutile, whereas titanium dioxide: 4% of cobalt contains 78% rutile. The mechanism of phase transition in presence of cobalt is attributed to the lower valences of the dopant (II or III) when compared to the titanium valence (IV). Ionic substitution leads to the generation of oxygen vacancies that promote phase transitions at lower temperatures than expected in pure titanium dioxide.Graphical Abstract

Photocatalytic Degradation of Rhodamine B Dye through Zinc Oxide Obtained by High Energy Milling

The heterogeneous photocatalysis has been developed to treatment of recalcitrant organic effluents such as the dyes. The chemical reactions occur on a semiconductor surface exposed to electromagnetic radiation. The objective of this study was evaluate the high energy milling as a mechanism to obtain fine powders of ZnO to utilization in photocatalysis. Raw ZnO was characterized by X-Ray diffraction, BET, sedigraph and Helium pycnometry and it was milled during four and ten hours in dry and wet media. The milled powders were characterized by X-Ray diffraction and they were evaluated in photocatalytic degradation of Rhodamine B dye. The results showed high purity of the powders before and after milling and the photocatalytic efficiency was function of processing conditions. The average half-life time for the dye varied between of 990.2 and 7.6 min wherein the powder obtained by four hours in dry media milling showed the best results of photodegradation.

Synthesis and Photocatalytic Evaluation of Nanocrystalline ZnO Obtained by High Energy Milling

Photocatalytic processes have been applied to treatment of organic effluents through the mineralization of these pollutants on a semiconductor surface. Obtaining nanosemiconductors is desirable for the increasing of particle surface area and improvement in photocatalytic efficiency. In this paper, it was evaluated the influence of High Energy Milling (HEM) as a technique to produce nanocrystalline zinc oxide. The photocatalytic activity of the milled powders to degrade Rhodamine-B dye when exposed to ultraviolet and visible radiation also was investigated. The powders were milled during 4 and 10 hours by dry media milling and 10 hours by wet media milling. The results indicated that there were no detectable powder contamination during the millings and the reduction of crystallite size was function of time and media of milling. All of the assessed samples demonstrate high degradation of the dye, which corroborates with the potentiality of this technique to photocatalysts production. The material milled during 10 hours by dry media milling showed the best results under the experimental conditions.

WO3:TiO2 Particle Characterization Obtained by High Energy Milling for Application in Photocatalysis

Effective ways to treat textile industrial effluents have been studied in attempt to find alternatives to reduce the imminent risk of water resources contamination. The heterogeneous photocatalysis stands out in this scenario working in the organic waste mineralization, such as dyes. The objectives of this study were to investigate the obtaining of fine powders of the WO3:TiO2 (the investigated proportions in this work were 0: 100; 30:70; 50:50; 70:30; 100:0) using the high energy milling technique and to evaluate the photocatalytic efficiency of the Rhodamine B dye in this system. The oxides precursors were characterized by X-ray diffraction, BET and Helium pycnometry. After dry milling for 4 hours, the obtained powders were characterized by X-ray diffraction and tested to the photocatalysis in UV-C. The results indicate that the milling process has a direct influence on the photocatalytic properties of the investigated systems, and that the greater presence of titania in the mixture leads to a greater catalytic effect.

Utilização de partículas de ZnO:Mn para a degradação do azul de metileno por processo de fotocatálise

The management of water use in the agricultural environment is a key factor to build new environmentally sustainable productive methods. Photocatalysis is a promising method for water decontamination. This research paper aimed to evaluate the photocatalytic potential of pure and Mn-doped ZnO particles. The materials were obtained by the polymeric precursor method, and characterized by X-ray diffraction, N2 adsorption in low temperature, infrared and ultraviolet spectroscopy, and photoluminescence. In order to evaluate ZnO:Mn particles photoefficiency, experiments were carried out by applying the methylene blue dye solution to photodegradation under UVC exposure. The particles had ZnO single-phase, but low specific surface area. The sample ZnO:0.25% Mn presented higher efficiency in the methylene blue photocatalytic degradation test. This efficiency was related to a higher band gap energy value and a lower rate of electron recombination, which allows greater formation of hydroxyl radicals, which are responsible for dye degradation.