Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders

Oxide based diluted magnetic semiconductor (DMS) materials have been a subject of increasing interest due to reports of room temperature ferromagnetism in several systems and their potential use in the development of spintronic devices. However, concerns on the stability of the magnetic properties of different DMS systems have been raised. Their magnetic moment is often unstable, vanishing with a characteristic decay time of weeks or months, which precludes the development of real applications. This paper reports on the ferromagnetic properties of two-year-aged Ti1-xCoxO2-δ reduced anatase nanopowders with different Co contents (0.03≤x≤0.10). Aged samples retain rather high values of magnetization, remanence and coercivity which provide strong evidence for a quite preserved long-range ferromagnetic order. In what concern Co segregation, some degree of metastability of the diluted Co doped anatase structure could be inferred in the case of the sample with the higher Co content.

A new chemical route to synthesise TM-doped (TM = Co, Fe) TiO2 nanoparticles

Since the discovery of ferromagnetism well above room temperature in the Co-doped TiO2 system, diluted magnetic semiconductors based on TiO2 doped with transition metals have generated great interest because of their potential use in the development of spintronic devices. The purpose of this paper is to report on a new and swift chemical route to synthesise highly stable anatase single-phase Co- and Fe-doped TiO2 nanoparticles, with dopant concentrations of up to 10 at.-% and grain sizes that range between 20 and 30 nm. Complementary structural, microstructural and chemical analyses of the different nanopowders synthesised strongly support the hypothesis that a homogeneous distribution of the dopant element in the substitutional sites of the anatase structure has been achieved. Moreover, UV/Vis diffuse reflectance spectra of powder samples show redshifts to lower energies and decreasing bandgap energies with increasing Co or Fe concentration, which is consistent with n-type doping of the TiO2 anatase matrix. Films of Co-doped TiO2 were successfully deposited onto Si (100) substrates by the dip-coating method, with suspensions of Ti1-xCOxO2 nanoparticles in ethylene glycol. ((C)Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Microstrip antenna array for multiband dedicated short range communications systems

Dedicated Short Range Communications (DSRC) is the key enabling technology for the present and future vehicular communication for various applications, such as safety improvement and traffic jam mitigation. This paper describes the development of a microstrip antenna array for the roadside equipment of a DSRC system, whose characteristics are according with the vehicular communications standards. The proposed antenna, with circular polarization, has a wide bandwidth, enough to cover the current European DSRC 5.8 GHz band and the future 5.9 GHz band for next generation DSRC communications. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 2794-2796, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26394

Phase growth control in low temperature PLD Co: TiO2 films by pressure

This paper reports on the structural and optical properties of Co-doped TiO2 thin films grown onto (0001)Al2O3 substrates by non-reactive pulsed laser deposition (PLD) using argon as buffer gas. It is shown that by keeping constant the substrate temperature at as low as 310 degrees C and varying only the background gas pressure between 7 Pa and 70 Pa, it is possible to grow either epitaxial rutile or pure anatase thin films, as well as films with a mixture of both polymorphs. The optical band gaps of the films are red shifted in comparison with the values usually reported for undoped TiO2, which is consistent with n-type doping of the TiO2 matrix. Such band gap red shift brings the absorption edge of the Co-doped TiO2 films into the visible region, which might favour their photocatalytic activity. Furthermore, the band gap red shift depends on the films' phase composition, increasing with the increase of the Urbach energy for increasing rutile content. (C) 2012 Elsevier B.V. All rights reserved.

A multiresidue method for the analysis of carbamate and urea pesticides from soils by microwave-assisted extraction and liquid chromatography with photodiode array detection

A multiresidue approach using microwave-assisted extraction and liquid chromatography with photodiode array detection was investigated for the determination of butylate, carbaryl, carbofuran, chlorpropham, ethiofencarb, linuron,metobromuron, and monolinuron in soils. The critical parameters of the developed methodology were studied. Method validation was performed by analyzing freshly and aged spiked soil samples. The recoveries and relative standard deviations reached using the optimized conditions were between 77.0 ± 0.46% and 120 ± 2.9% except for ethiofencarb (46.4 ± 4.4% to 105 ± 1.6%) and butylate (22.1 ± 7.6% to 49.2 ± 11%). Soil samples from five locations of Portugal were analysed.

Screening of grapes and wine for azoxystrobin, kresoxim-methyl and trifloxystrobin fungicides by HPLC with diode array detection

The Quinone outside Inhibitors (QoI) are one of the most important and recent fungicide groups used in viticulture and also allowed by Integrated Pest Management. Azoxystrobin, kresoxim-methyl and trifloxystrobin are the main active ingredients for treating downy and powdery mildews that can be present in grapes and wines. In this paper, a method is reported for the analysis of these three QoI-fungicides in grapes and wine. After liquid–liquid extraction and a clean-up on commercial silica cartridges, analysis was by isocratic HPLC with diode array detection (DAD) with a run time of 13 min. Confirmation was by solid-phase micro-extraction (SPME), followed by GC/MS determination. The main validation parameters for the three compounds in grapes and wine were a limit of detection up to 0.073mg kg-1, a precision not exceeding 10.0% and an average recovery of 93% ±38.

Structural modification of TiO2 nanorod films with an influence on the photovoltaic efficiency of a dye-sensitized solar cell (DSSC).

TiO2 nanorod films have been deposited on ITO substrates by dc reactive magnetron sputtering technique. The structures of these nanorod films were modified by the variation of the oxygen pressure during the sputtering process. Although all these TiO2 nanorod films deposited at different oxygen pressures show an anatase structure, the orientation of the nanorod films varies with the oxygen pressure. Only a very weak (101) diffraction peak can be observed for the TiO2 nanorod film prepared at low oxygen pressure. However, as the oxygen pressure is increased, the (220) diffraction peak appears and the intensity of this diffraction peak is increased with the oxygen pressure. The results of the SEM show that these TiO2 nanorods are perpendicular to the ITO substrate. At low oxygen pressure, these sputtered TiO2 nanorods stick together and have a dense structure. As the oxygen pressure is increased, these sputtered TiO2 nanorods get separated gradually and have a porous structure. The optical transmittance of these TiO2 nanorod films has been measured and then fitted by OJL model. The porosities of the TiO2 nanorod films have been calculated. The TiO2 nanorod film prepared at high oxygen pressure shows a high porosity. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO2 nanorod films prepared at different oxygen pressures as photoelectrode. The optimum performance was achieved for the DSSC using the TiO2 nanorod film with the highest (220) diffraction peak and the highest porosity.

Electrochemical determination of the herbicide bentazone using a carbon nanotube b-Cyclodextrin modified electrode

An electrochemical sensor has been developed for the determination of the herbicide bentazone, based on a GC electrode modified by a combination of multiwalled carbon nanotubes (MWCNT) with b-cyclodextrin (b-CD) incorporated in a polyaniline film. The results indicate that the b-CD/MWCNT modified GC electrode exhibits efficient electrocatalytic oxidation of bentazone with high sensitivity and stability. A cyclic voltammetric method to determine bentazone in phosphate buffer solution at pH 6.0, was developed, without any previous extraction, clean-up, or derivatization steps, in the range of 10–80 mmolL 1, with a detection limit of 1.6 mmolL 1 in water. The results were compared with those obtained by an established HPLC technique. No statistically significant differences being found between both methods.

Non-uniform microstrip antenna array for RX DSRC communications

The urgent need to mitigate traffic problems such as accidents, road hazards, pollution and traffic jam have strongly driven the development of vehicular communications. DSRC (Dedicated Short Range Communications) is the technology of choice in vehicular communications, enabling real time information exchange among vehicles V2V (Vehicle-to-Vehicle) and between vehicles and infrastructure V2I (Vehicle-Infrastructure). This paper presents a receiving antenna for a single lane DSRC control unit. The antenna is a non-uniform array with five microstrip patches. The obtained beam width, bandwidth and circular polarization quality, among other characteristics, are compatible with the DSRC standards, making this antenna suitable for this application. © 2014 IEEE.

The impact of different power dividers used in a non-uniform planar antenna array

Wireless communications are widely used for various applications, requiring antennas with different features. Often, to achieve the desired radiation pattern, is necessary to employ antenna arrays, using non-uniform excitation on its elements. Power dividers can be used and the best known are the T-junction and the Wilkinson power divider, whose main advantage is the isolation between output ports. In this paper the impact of this isolation on the overall performance of a circularly polarized planar antenna array using non-uniform excitation is investigated. Results show a huge decrease of the array bandwidths either in terms of return loss or in polarization, without resistors. © 2014 IEEE.

Aplicação de compósitos de TiO2 em carvão activado na fotodegradação do fenol com luz ultravioleta

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia Química e Bioquímica

Porta substratos para um sistema de pulverização catódica. Aplicação na obtenção de TiO2.

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Física

Implementação de um Array de detetores de radiação ionizante

Atualmente, as radiações ionizantes desempenham um papel fundamental nas áreas de diagnóstico e terapia, estando omnipresentes em ambientes hospitalares. Contudo, devido aos efeitos biológicos adversos da radiação, torna-se essencial a protecção dos profissionais de saúde e pacientes. Consequentemente, um array de detetores capazes de produzir um sinal acústico, aquando da presença de radiação ionizante excedendo determinados valores limite e transmissão via wireless das leituras para um sistema central _e de grande interesse prático. Nesta dissertação, foi implementado um sistema capaz de alimentar um array de sensores de radiação para monitorização de diferentes espaços e transmissão das leituras efetuadas via wireless. A aquisição de dados foi realizada, recorrendo à utilização de um conversor analógico-digital. Vários testes de validação foram realizados, através de vários passos para alcançar a concretização do sistema final, nomeadamente testes relativos ao circuito de detecção, módulos de comunicação wireless, bem como o uso de diferentes ambientes de desenvolvimento integrados (IDE). Os resultados destes testes mostram a visualização e gravação adequadas dos dados relativos aos níveis de radiação, bem como a transmissão de dados de forma viável, permitindo a monitorização de espaços sujeitos à presença de radiação ionizante. Desta forma, um array de contadores Geiger-Müller, ligados a módulos wireless XBee open-source e uma placa Arduino, possibilitou a implementação de um sistema viável e de baixo custo para monitorização de radiação ionizante e registar esses mesmos dados para posterior análise.

Growth of the [110] oriented TiO2 nanorods on ITO substrates by sputtering technique for dye-sensitized solar cells

TiO2 films have been deposited on ITO substrates by dc reactive magnetron sputtering technique. It has been found that the sputtering pressure is a very important parameter for the structure of the deposited TiO2 films. When the pressure is lower than 1 Pa, the deposited has a dense structure and shows a preferred orientation along the [101] direction. However, the nanorod structure has been obtained as the sputtering pressure is higher than 1 Pa. These nanorods structure TiO2 film shows a preferred orientation along the [110] direction. The x-ray diffraction and the Raman scattering measurements show both the dense and the nanostructure TiO2 films have only an anatase phase, no other phase has been obtained. The results of the SEM show that these TiO2 nanorods are perpendicular to the ITO substrate. The TEM measurement shows that the nanorods have a very rough surface. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO2 nanorod films prepared at different sputtering pressures as photoelectrode. And the effect of the sputtering pressure on the properties of the photoelectric conversion of the DSSCs has been studied.

Experimental study of the mechanical properties and durability of self-compacting mortars with nano materials (SiO2 and TiO2)

Resumo: Cement, as well as the remaining constituents of self-compacting mortars, must be carefully selected, in order to obtain an adequate composition with a granular mix as compact as possible and a good performance in the fresh state (self-compacting effect) and the hardened state (mechanical and durability-related behavior). Therefore in this work the possibility of incorporating nano particles in self-compacting mortars was studied. Nano materials are very reactive due mostly to their high specific surface and show a great potential to improve the properties of these mortars, both in mechanical and durability terms. In this work two nano materials were used, nano silica (nano SiO2) in colloidal state and nano titanium (nano TiO2) in amorphous state, in two types of self-compacting mortars (ratio binder:sand of 1:1 and 1:2). The self-compacting mortar mixes have the same water/cement ratio and 30% of replacement of cement with fly ashes. The influence of nano materials nano-SiO2 and nano-TiO2 on the fresh and hardened state properties of these self-compacting mortars was studied. The results show that the use of nano materials in repair and rehabilitation mortars has significant potential but still needs to be optimized. (C) 2015 Elsevier Ltd. All rights reserved.