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São Carlos, Brazil

Bakar S.A.,Federal University of Sao Carlos | Ribeiro C.,Embrapa CNPDIA
Journal of Photochemistry and Photobiology C: Photochemistry Reviews | Year: 2016

TiO2 material has gained attention as the most studied semiconductor material for photocatalytic purposes, including their use in devices for clean energy production, such as solar cells and water splitting systems. However, the wide band gap of this material limits applications to UV light, which also confines the use of solar irradiation as the energy source. Much research in the last years is showing the ability of N doping into TiO2 to promote light absorption in the visible range but, to date, it is still controversy if this doping is beneficial to the photocatalytic process, as well as the synthetic methods are not well stabilized yet. Then, this paper summarizes the recent advancement in the structural design perspective of N-doped TiO2 photocatalyst, in a critical analysis of its application for environmental purposes. We reported the dimensionality effect associated with modified N-doped TiO2 structure for its characteristics properties and photocatalytic performance; counting more specifically its charge transportation, surface area, adhesion, reflection and absorption properties. A concise view of the doping effect over morphology in 0, 1, 2 and 3-dimensional ranges was provided, in order to understand which effects are also occurring on the materials besides the photocatalytic response. Furthermore, selected recent and significant advances in the area of renewable energy applications for modified N-doped TiO2 were assessed with the particular importance given towards the electricity generation by dye-sensitized solar cells and lithium-ion batteries rechargeable for electric energy storage. © 2016 Elsevier B.V. Source

Bakar S.A.,Federal University of Sao Carlos | Ribeiro C.,Embrapa CNPDIA
Journal of Molecular Catalysis A: Chemical | Year: 2016

Photocatalytic degradation of pollutant molecules delivered great challenges for sustainable development of green energy in the field of environmental science. For this purpose, growing interests have been made to witness the fast development of new photocatalysts with improved catalytic efficiency and to monitor the reaction mechanism at the atomic and molecular levels. Therefore, doping of semiconductor metal oxide (e.g. TiO2) with main group elements, especially with sulfur atoms (S), has gained much interest due to the introduction of a localized band between the conduction bands (CB) and valence bands (VB) that increase the absorbance in the visible light region. More interestingly, photocatalytic practices of the S-doped TiO2 material are of pronounced significance due to photon-to-carrier conversion ability of S-doping beneath the band gap energy region of pure TiO2. Therefore, visible-light-activated S-doped TiO2 photocatalysts were prepared via template free and low-temperature oxidant peroxide method (OPM) assisted hydrothermal treatments. Experimental findings have revealed the successful incorporation of sulfur atoms into TiO2 crystal lattice and, as a result, substitution of Ti4+ by S6+ to form Ti-O-S bonds for cationic S-doping was observed. Whereas, in the case of anionic S-doping, substitution of S2- by O2- to form O-Ti-S bonds was achieved. More evidence was observed for the presence of chemisorbed sulfate groups on the surface of S-doped TiO2 samples and inhibition of crystallite size growth by S-doping, and obviously, upsurge the absorbance in the visible light region. The photocatalytic activity of as-prepared 1-D nanorods shaped photocatalysts and the mechanism involved for the photodegradation of organic molecules (methyl orange and phenol) under visible-light irradiation were investigated by adding different scavengers into the system solution to capture active species. It was found that in cationic S-doped TiO2 photocatalysts, chemisorbed hydroxyls (OHads-) and photoinduced holes (h+) played a major role in photocatalysis. Whereas, in the case of anionic S-doped TiO2 photocatalysts, electrons (e-) and photoinduced holes (h+) played the nearly equal role in photocatalysis. © 2016 Elsevier B.V. All rights reserved. Source

Bakar S.A.,Federal University of Sao Carlos | Ribeiro C.,Embrapa CNPDIA
RSC Advances | Year: 2016

In recent years, growing concerned has been raised to the global problem of the drainage of organic pollutants into water steams. Therefore, a great demand has been raised for the development of efficient technologies for the treatment of wastewater pollution. The photocatalytic oxidation of organic pollutants under visible-light irradiation has several advantages for the remediation of wastewater compared to other conventional adsorption techniques. This study reports a rapid and morphology controlled synthesis of anionic 1D S-doped TiO2 photocatalysts by a facile and efficient oxidant peroxide route (OPM), followed by crystallization through a hydrothermal method. In particular, S-doping into the TiO2 crystal lattice and the formation of S-Ti-O bonds were confirmed by structural characterization of the as-prepared samples with the help of X-ray photoelectron spectroscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The as-prepared S-doped TiO2 photocatalysts showed enhanced photocatalytic activity for the liquid phase degradation of an organic compound (methyl orange) under visible-light irradiation (>420 nm) compared to the undoped TiO2. To extend the viability for the photocatalytic activity of the as-prepared S-doped TiO2 nanorods, other organic compounds (RhB and phenol) were also tested in photodegradation experiments. The promising effects of OPM treatment for S-doping and the enhanced photocatalytic performance were observed to be due to the large porous channels of nanorods, pure anatase phase crystallization, the high surface area, excellent stability from photocorrosion, enhanced absorbance shifts toward the visible-light region, improved effective interfacial charge transfer, and enhanced efficiency for the separation of photoinduced electron-hole pairs. The optimum photocatalytic activity was achieved for the ATO-3 sample for the degradation of the organic compounds under visible-light irradiation and was ∼8.12 times higher for MO compared to undoped TiO2. The synergistic effect and role of the active species, i.e., superoxide radical anions (O2 -) and holes (h+), on the photocatalysis mechanism for the degradation of organic pollutants are discussed in detail. This journal is © The Royal Society of Chemistry 2016. Source

The practice of agriculture and cattle raising produces waste, and as a result it can create environmental impacts. Therefore, it is necessary to assess, predict, and lessen the environmental impact for the sustainability of this activity and protection of ecosystems with the intention to fulfil such needs, the Brazilian Agricultural Research Agency (EMBRAPA) has proposed a system, the Environmental Impact Assessment of Agricultural Technology Innovations (Ambitec-Agro). Among countless technological innovations, the agriculture animal husbandry integration was selected which aims to improve the production of farming products in deteriorated areas; intensifying the use of land; and reclaming and renovating agricultural areas and pastures to guarantee agricultural sustainability. Based on a case study, this work aimed to make the assessment of the environmental impact caused by technology innovation of the animal husbandry integration in unirrigated and irrigated areas by applying the Ambitec-Agro system. The assessment of the environmental impact of animal husbandry integration, in the environmental conservation aspect was satisfactory, thus significative and positive indices were obtained in relation to water quality, soil quality and biodiversity in the scope of the studied establishment. Source

De Mendonca V.R.,Federal University of Sao Carlos | Ribeiro C.,Embrapa CNPDIA
Applied Catalysis B: Environmental | Year: 2011

Morphologically different TiO2 nanocrystals were prepared by oxidant-peroxo method (OPM) synthesis. Morphological characterization was performed with the use of field emission gun-scanning electron microscope, X-ray diffraction and low temperature N2 adsorption. The photocatalytic behavior of synthesized TiO2 powders was studied in the reaction of Rhodamine B photodegradation in water. The trials showed that synthesis performed at pH value around 8 generated materials with higher photoactivities than at other pH values. Zeta potential, Fourier transform infrared spectroscopy, X-ray absorption near edge structure part of the absorption spectra, photoluminescence spectroscopy and high resolution-transmission electron microscopy measurements were performed to investigate why the materials had different photoactivities. Two dominant particle characteristics, which came from synthesis environment, interfered in the photoactivity of materials. These characteristics were surface hydroxylation, which had a positive effect on photocatalysis, and crystalline defects due to crystal growth, which had a deleterious effect on photocatalysis. Both characteristics increased with an increase in synthesis pH value. Dye degradation mechanism in water, an oxidation by hydroxyl radicals, was used to explain the different photoactivities and the optimum synthesis pH. © 2011 Elsevier B.V. Source

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