Altering the adsorptive and electronic properties of Pt through poly(vinyl alcohol) adsorption

In the present paper we investigated the effect of adsorbed PVA on Pt electrodes on classic electrochemical processes such as hydrogen UPD, oxygen reduction and CO electro-oxidation. Upon adsorption PVA blocks roughly 50% of the hydrogen sites and can not be removed from the Pt surface through cycling in the potential range of 0.05-1.0 V vs. RHE. Potentiodynamic experiments under controlled hydrodynamic conditions provided by rotating disk electrode experiments showed a negative impact of the adsorbed PVA on the oxygen reduction reaction (ORR). Cyclic-voltammetry results revealed that not even CO was able to remove PVA from the Pt surface. Regarding the oxidation of CO, the adsorbed polymer positively shifted the CO oxidation peak potential, therefore higher potentials are required to free the Pt surface from CO poisoning. In situ Fourier transform infrared spectroscopy evidenced that the presence of PVA shifted the linearly bound CO frequency toward higher wavenumbers, a process found to be independent of the Pt surface orientation. In situ electrochemical X-ray absorption spectroscopy results showed that PVA also impacted the electronic properties of platinum by decreasing the occupancy of the Pt conducting 5d band. Our findings clearly support the efforts toward understanding the nature of the interaction between polymers and metallic surfaces as well as the impact on technological applications (e.g. in PEMFCs). © 2013 Elsevier Ltd. All rights reserved.

Interface formation of nanostructured heterojunction SnO 2:Eu/GaAs and electronic transport properties

Thin films of tin dioxide (SnO2) are deposited by the sol-gel-dip-coating technique, along with GaAs layers, deposited by the resistive evaporation technique. The as-built heterojunction has potential application in optoelectronic devices, combining the emission from the rare-earth doped transparent oxide (Eu3+-doped SnO2 presents very efficient red emission) with a high mobility semiconductor. The advantage of this structure is the possibility of separation of the rare-earth emission centers from the electron scattering, leading to a strongly indicated combination for electroluminescence. Electrical characterization of the heterojunction SnO2:Eu/GaAs shows a significant conductivity increase when compared to the conductivity of the individual films, and the monochromatic light irradiation (266 nm) at low temperature of the heterojunction GaAs/SnO2:Eu leads to intense conductivity increase. Scanning electron microscopy (SEM) of the heterojunction cross section shows high adherence and good morphological quality of the interfaces substrate/SnO2 and SnO2/GaAs, even though the atomic force microscopy (AFM) image of the GaAs surface shows disordered particles, which increases with sample thickness. On the other hand, the good morphology of the SnO2:Eu surface, shown by AFM, assures the good electrical performance of the heterojunction. The observed improvement on the electrical transport properties is probably related to the formation of short conduction channels at the semiconductors interface, which may exhibit two-dimensional electron gas (2DEG) behavior. © 2012 Elsevier B.V. All rights reserved.

Effect of structural anisotropy on electrical and magnetic properties of polyaniline conducting films

It is shown that highly conducting films of polyaniline protonated with di-esters of sulfosuccinic and sulfophthalic acids which contain alkyl- or alkoxy-type substituents exhibit highly anisotropic structural, electrical and magnetic properties. The layered-like structure of these films can be described as consisting of polyaniline chains which are mainly oriented parallel to the plane of the film and form regular out-of-plane stacks. These stacks are separated by bilayers of the dopant anions. Accordingly, the main anisotropy observed for solution cast films implies in-plane and out-of-plane measurements. An electrical anisotropy of about 80 is found for the in-plane and out-of-plane electronic conductivities at 5 K. The temperature dependences of the in-plane and out-of-plane conductivities are qualitatively similar and have been fitted as a series combination of variable-range-hopping-type and power law contributions. A maximum is observed in the temperature dependence of the electrical anisotropy at low temperature. The films also show a clear anisotropy of magnetization whose temperature and field characteristics depend on the chemical structure of the dopant anion. © 2013 Elsevier B.V.

Effect of chemical modifications on the electronic structure of poly(3-hexylthiophene)

The widespread use of poly(3-hexylthiophene) (P3HT) in the active layers of organic solar cells indicates that it possesses chemical stability and solubility suitable for such an application. However, it would be desirable to have a material that can maintain these properties but with a smaller bandgap, which would lead to more efficient energy harvesting of the solar spectrum. Fifteen P3HT derivatives were studied using the Density Functional Theory. The conclusion is that it is possible to obtain compounds with significantly smaller bandgaps and with solubility and stability similar to that of P3HT, mostly through the binding of oxygen atoms or conjugated organic groups to the thiophenic ring. © 2013 Wiley Periodicals, Inc.

Effect of ionic strength solution on the stability of chitosan-DNA nanoparticles

Chitosan-DNA nanoparticles employed in gene therapy protocols consist of a neutralised, stoichiometric core and a shell of the excess of chitosan which stabilises the particles against further coagulation. At low ionic strength, these nanoparticles possess a high stability; however, as the ionic strength increases, it weakens the electrostatic repulsion which can play a decisive part in the formation of highly aggregated particles. In this study, new results about the effect of ionic strength on the colloidal stability of chitosan-DNA nanoparticles were obtained by studying the interaction between chitosans of increasing molecular weights (5, 10, 16, 29, 57 and 150 kDa) and calf thymus DNA. The physicochemical properties of polyplexes were investigated by means of dynamic light scattering, static fluorescence spectroscopy, optic microscopy, transmission electronic microscopy and gel electrophoresis. After subsequent addition of salt to the nanoparticles solution, secondary aggregation increased the size of the polyplexes. The nanoparticles stability decreased drastically at the ionic strengths 150 and 500 mM, which caused the corresponding decrease in the thickness of the stabilising shell. The morphologies of chitosan/DNA nanoparticles at those ionic strengths were a mixture of large spherical aggregates, toroids and rods. The results indicated that to obtain stable chitosan-DNA nanoparticles, besides molecular weight and N/P ratio, it is quite important to control the ionic strength of the solution. © 2013 Copyright Taylor and Francis Group, LLC.

Preparação de catalisadores de reforma de glicerol para células a combustível de eletrólito sólido

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Síntese e caracterização do sistema vítreo (1-x) NaPO 3 – (x)WO 3

Pós-graduação em Ciência dos Materiais - FEIS

Reação de redução de oxigênio sobre perovskitas La1-xSrxFeyCo1-yO3-δ, para células a combustível de óxido sólido (SOFC)

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Electronic data interchange in port management: the experience of the port of Barcelona

Every port is unique. Although all ports exist for the same basic purpose (to act as an interface in the transfer from one mode of transport to another), no two are ever organized in the same way.Ports may be classified according to: Physical conditions: location (geographical position, man-made or natural harbour, estuary location, difficult weather conditions, tides, etc.) and size (large, small or medium-sized). Use: commercial (general cargo, bulk solids, bulk liquids, oil, break bulk, mixed), passenger, sport and leisure, fishing, mixed, etc. Ownership: private, municipal, regional or State-owned. The Port Authority's role in management of the port: Overall control, i.e. the Port Authority plans, sets up and operates the whole range of services. Facilitator, i.e. the Port Authority plans and sets up the infrastructure and the superstructure, but services are provided by private companies. Landlord, i.e. the Port Authority allows private companies to be responsible for the superstructure and provide port services. Different combinations of port types will therefore give rise to different kinds of organization and different information flows, which means that the associated information systems may differ significantly from port to port. Since this paper relates to the port of Barcelona, with its own specific characteristics, the contents may not always be applicable to other ports.

Síntese e caracterização da cerâmica 'Ti IND. x''('Sm IND. 0,2''Ce IND. 0,8') IND. (1-x)''O IND. (2-Б) para aplicação como anodo em células a combustível de óxido sólido

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Investigação do processo de fixação biológica de N2 atmosférico na fermentação de fécula de mandioca

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Estudo eletroquímico da corrosividade de biodiesel para aço carbono e outros materiais metálicos usados em veículos automotores

Pós-graduação em Química - IQ

Análise experimental da reforma a vapor de etanol: aspectos técnicos, econômicos e ecológicos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo de mecanismos de transporte em nanofios de óxido de índio dopado com estanho

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

First-Principles Study of Pressure-Induced Phase Transitions and Electronic Properties of Ag2MoO4

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)