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Manzoli A.,University of Sao Paulo | Manzoli A.,National Nanotechnology Laboratory for Agribusiness LNNA | Eguiluz K.I.B.,University of Sao Paulo | Eguiluz K.I.B.,Tiradentes University | And 3 more authors.
Materials Chemistry and Physics | Year: 2010

Semiconducting films of (n-type) ZnSe and (p-type) nitrogen-doped ZnSe were electrodeposited by a linear-sweep voltammetric technique on to a substrate of fluorine-tin oxide (FTO) glass ceramics. The films were characterized by scanning electron microscopy, energy-dispersive X-ray analysis and grazing-incidence X-ray diffraction. The results indicated that the material was deposited uniformly over the substrate, forming clusters when the Zn content of the bath was 0.1 mol L-1 and a film when it was 0.2 or 0.3 mol L-1. The effectiveness of doping the films with nitrogen by adding ammonium sulfate to the deposition solution was assessed by measuring the film-electrolyte interface capacitance (C) at various applied potentials (Eap) and plotting Mott-Schottky curves (C-2 vs Eap), whose slope sign was used to identify p-type ZnSe. © 2009 Elsevier B.V. All rights reserved.

Milao T.M.,University of Sao Paulo | de Mendonca V.R.,Federal University of Sao Carlos | Araujo V.D.,University of Sao Paulo | Avansi W.,Sao Paulo State University | And 3 more authors.
Science of Advanced Materials | Year: 2012

ZnO and doped M:ZnO (M = V, Fe and Co) nanostructures were synthesized by microwave hydrothermal synthesis using a low temperature route without addition of any surfactant. The transition metal ions were successfully doped in small amount (3% mol) into ZnO structure. Analysis by X-ray diffraction reveals the formation of ZnO with the hexagonal (wurtzite-type) crystal structure for all the samples. The as-obtained samples showed a similar flower-like morphology except for Fe:ZnO samples, which presented a plate-like morphology. The photocatalytic performance for Rhodamine B (RhB) degradation confirmed that the photoactivity of M:ZnO nanostructures decreased for all dopants in structure, according to their eletronegativity. Photoluminescence spectroscopy was employed to correlate M:ZnO structure with its photocatalytical properties. It was suggested that transition metal ions in ZnO lattice introduce defects that act as trapping or recombination centers for photogenerated electrons and holes, making it impossible for them reach the surface and promote the photocatalytical process. © 2012 by American Scientific Publishers.

Araujo V.D.,University of Sao Paulo | Avansi W.,University of Sao Paulo | De Carvalho H.B.,Federal University of Alfenas | Moreira M.L.,University of Sao Paulo | And 3 more authors.
CrystEngComm | Year: 2012

Ceria (CeO 2) plays a vital role in emerging technologies for environmental and energy-related applications. The catalytic efficiency of ceria nanoparticles depends on its morphology. In this study, CeO 2 nanoparticles were synthesized by a microwave-assisted hydrothermal method under different synthesis temperatures. The samples were characterized by X-ray diffraction, transmission electron microscopy, Raman scattering spectroscopy, electron paramagnetic resonance spectroscopy and by the Brunauer-Emmett-Teller method. The X-ray diffraction and Raman scattering results indicated that all the synthesized samples had a pure cubic CeO 2 structure. Rietveld analysis and Raman scattering also revealed the presence of structural defects due to an associated reduction in the valence of the Ce 4+ ions to Ce 3+ ions caused by an increasing molar fraction of oxygen vacancies. The morphology of the samples was controlled by varying the synthesis temperature. The TEM images show that samples synthesized at 80 °C consisted of spherical particles of about 5 nm, while those synthesized at 120 °C presented a mix of spherical and rod-like nanoparticles and the sample synthesized at 160 °C consisted of nanorods with 10 nm average diameter and 70 nm length. The microwave-assisted method proved to be highly efficient for the synthesis of CeO 2 nanoparticles with different morphologies. © 2012 The Royal Society of Chemistry.

Souza A.L.,University of Sao Paulo | Ceridorio L.F.,Federal University of Sao Paulo | Paula G.F.,National Nanotechnology Laboratory for Agribusiness LNNA | Mattoso L.H.C.,National Nanotechnology Laboratory for Agribusiness LNNA | Oliveira O.N.,University of Sao Paulo
Colloids and Surfaces B: Biointerfaces | Year: 2015

The disinfectant activity of poly(hexamethylene biguanide) (PHMB) has been explored in industrial applications, in agriculture and in food manipulation, but this biocide action is not completely understood. It is believed to arise from electrostatic interactions between the polyhexanide group and phosphatidylglycerol, which is the main phospholipid on the bacterial membrane. In this study, we investigated the molecular-level interactions between PHMB and dipalmitoyl phosphatidylglycerol (DPPG) in Langmuir monolayers that served as cell membrane models. PHMB at a concentration of 2×10-4gL-1 in a Theorell-Stenhagen at pH 3.0 and in a phosphate at pH 7.4 was used as a subphase to prepare the DPPG monolayers. Surface pressure-area isotherms showed that PHMB adsorbs and penetrates into the DPPG monolayers, expanding them and increasing their elasticity under both conditions examined. Results from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) indicated that PHMB induces disorder in the DPPG chains and dehydrates their CO groups, especially for the physiological medium. Overall, these findings point to hydrophobic interactions and dehydration being as relevant as electrostatic interactions to explain changes in membrane fluidity and permeability, believed to be responsible for the biocide action of PHMB. © 2015 Elsevier B.V.

Manzoli A.,National Nanotechnology Laboratory for Agribusiness LNNA | Steffens C.,National Nanotechnology Laboratory for Agribusiness LNNA | Paschoalin R.T.,National Nanotechnology Laboratory for Agribusiness LNNA | Correa A.A.,Federal University of ABC | And 4 more authors.
Sensors | Year: 2011

A low-cost sensor array system for banana ripeness monitoring is presented. The sensors are constructed by employing a graphite line-patterning technique (LPT) to print interdigitated graphite electrodes on tracing paper and then coating the printed area with a thin film of polyaniline (PANI) by in-situ polymerization as the gas-sensitive layer. The PANI layers were used for the detection of volatile organic compounds (VOCs), including ethylene, emitted during ripening. The influence of the various acid dopants, hydrochloric acid (HCl), methanesulfonic acid (MSA), p-toluenesulfonic acid (TSA) and camphorsulfonic acid (CSA), on the electrical properties of the thin film of PANI adsorbed on the electrodes was also studied. The extent of doping of the films was investigated by UV-Vis absorption spectroscopy and tests showed that the type of dopant plays an important role in the performance of these low-cost sensors. The array of three sensors, without the PANI-HCl sensor, was able to produce a distinct pattern of signals, taken as a signature (fingerprint) that can be used to characterize bananas ripeness. © 2011 by the authors; licensee MDPI, Basel, Switzerland.

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