Asencios Y.J.O.,University of Sao Paulo |
Rodella C.B.,Brazilian Synchrotron Light Laboratory (LNLS) |
Assaf E.M.,University of Sao Paulo
Applied Catalysis B: Environmental | Year: 2013
Catalysts composed of NiO/Y2O3/ZrO2 mixtures were synthesized by the polymerization method in a single step. They were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), physisorption of N2 (BET) and X-ray photoelectron spectroscopy (XPS) and then tested in the oxidative reforming of a model biogas (1.5CH4:1CO2) in the presence of oxygen (1.5CH4+1CO2+0.25O2) at 750°C for 6h. It was observed that the catalysts Ni20YZ and Ni40YZ performed better in catalytic processes than NiO/ZrO2 and NiO/Y2O3, synthesized under the same conditions. The formation of Y2O3-ZrO2 and NiO-Y2O3 solid solutions increased the rates of conversion of the reactants (CH4 and CO2) into synthesis gas (H2+CO). The formation of oxygen vacancies (in samples containing ZrO2 and Y2O3) seemed to promote removal of the coke deposited on the nickel surface during the oxidative reforming of model biogas. The H2/CO ratios in the reaction products formed on the best catalysts were 1:1, which is desirable for their direct use in the STD and in the Fischer-Tropsch processes. © 2012.
Pontes R.B.,University of Sao Paulo |
Rocha A.R.,Federal University of ABC |
Sanvito S.,Trinity College Dublin |
Fazzio A.,University of Sao Paulo |
And 2 more authors.
ACS Nano | Year: 2011
By performing ab initio density functional theory (DFT) calculations and electronic transport simulations based on the DFT nonequilibrium Green's functions method we investigate how the conformational changes of a benzene-1,4-dithiol molecule bonded to gold affect the molecular transport as the electrodes are separated from each other. In particular we consider the full evolution of the stretching process until the junction breaking point and compare results obtained with a standard semilocal exchange and correlation functional to those computed with a self-interaction corrected method. We conclude that the inclusion of self-interaction corrections is fundamental for describing both the molecule conductance and its stability against conformational fluctuations. © 2011 American Chemical Society.
Shiroma L.Y.,University of Campinas |
Santhiago M.,University of Campinas |
Gobbi A.L.,Brazilian Synchrotron Light Laboratory (LNLS) |
Kubota L.T.,University of Campinas
Analytica Chimica Acta | Year: 2012
The present work describes the construction and application of a simple, low cost and sensitive microfluidic paper-based device with electrochemical detection for the detection of paracetamol and 4-aminophenol. The separation channels of a width of 2.0mm were created on paper using a wax printing process to define the regions of the device. A baseline separation level of the analytes can be obtained in 0.1molL -1 acetate buffer solution at pH 4.5 and by injecting 500nL of the standard solutions at 12mm from the working electrode. The electrochemical detection system was created at the end of the channels through a process known as sputtering. The previously separated analytes were detected at the end of the hydrophilic separation channel by applying a potential of 400mV vs. pseudo Au on the working electrode. Experimental variables such as type of paper (cation exchanger and n1), pH, sample volume, applied potential and distance of sample injection were evaluated and, under the conditions of higher response, it was possible to obtain detection limits of 25.0 and 10.0μmolL -1 for paracetamol and 4-aminophenol, respectively. © 2012 Elsevier B.V..
Westfahl Jr H.,Brazilian Synchrotron Light Laboratory (LNLS) |
Cardoso M.B.,Brazilian Synchrotron Light Laboratory (LNLS)
Journal of Applied Crystallography | Year: 2011
Most melt-crystallized polymers present a lamellar nanostructure of alternating crystalline and amorphous lamellae which is coherent enough to display a broad interference peak in small-angle X-ray scattering experiments (SAXS). Nascent semi-crystalline polymers, on the other hand, though highly crystalline, hardly show an interference peak. This has long been attributed either to the formation of extended chain crystals or to a highly incoherent lamellar stacking. Here it is shown that a coherent lamellar order is shaded by a large scattering contribution from the air/grain interface. This is revealed by a SAXS contrast variation technique that suppresses the air/grain interface scattering and leaves only the scattering contribution from the internal lamellae. © 2011 International Union of Crystallography.
Wender H.,Brazilian Synchrotron Light Laboratory (LNLS) |
Migowski P.,Federal University of Rio Grande do Sul |
Feil A.F.,Federal University of Rio Grande do Sul |
Feil A.F.,National Renewable Energy Laboratory |
And 2 more authors.
Coordination Chemistry Reviews | Year: 2013
Nanoparticles (NPs) have recently attracted significant attention from the materials science community due to their promise to play an important role in developing new technologies. Indeed, NPs with small sizes, narrow size distributions and various shapes have been prepared via the reduction of organometallic compounds with molecular hydrogen, the decomposition of transition-metal complexes in the zero-valent state, metal bombardment or the simple transfer of previously prepared NPs from one liquid to another. This review paper will discuss the simple and quick method of sputtering deposition over liquid substrates to generate stable colloidal NPs. Initially, the sputtering phenomena will be presented in more detail, as well as the state-of-the-art in sputter deposition over both solid and liquid substrates. Then, special attention will be paid to sputtering onto ionic liquids (ILs), silicon oil and vegetable oils, and some selected results and the current mechanisms of NP formation will be discussed. Finally, applications of this new approach to synthesizing colloidal NPs will be shown. © 2013 Elsevier B.V..
Tischer P.C.S.F.,Federal University of Paraná |
Sierakowski M.R.,Federal University of Paraná |
Westfahl H.,Brazilian Synchrotron Light Laboratory (LNLS) |
Tischer C.A.,Federal University of Paraná
Biomacromolecules | Year: 2010
In this work, bacterial cellulose was subjected to a high-power ultrasonic treatment for different time intervals. The morphological analysis, scanning electron microscopy, and atomic force microscopy revealed that this treatment changed the width and height of the microfibrillar ribbons and roughness of their surface, originating films with new nanostructures. Differential thermal analysis showed a higher thermal stability for ultrasonicated samples with a pyrolysis onset temperature of 208 °C for native bacterial cellulose and 250 and 268 °C for the modified samples. The small-angle X-ray scattering experiments demonstrated that the treatment with ultrasound increased the thickness of the ribbons, while wide-angle X-ray scattering experiments demonstrated that the average crystallite dimension and the degree of crystallinity also increased. A model is proposed where the thicker ribbons and crystallites result from the fusion of neighboring ribbons due to cavitation effects. © 2010 American Chemical Society.
Padilha J.E.,University of Sao Paulo |
Fazzio A.,University of Sao Paulo |
Da Silva A.J.R.,University of Sao Paulo |
Da Silva A.J.R.,Brazilian Synchrotron Light Laboratory (LNLS)
Physical Review Letters | Year: 2015
In this Letter, we study the structural and electronic properties of single-layer and bilayer phosphorene with graphene. We show that both the properties of graphene and phosphorene are preserved in the composed heterostructure. We also show that via the application of a perpendicular electric field, it is possible to tune the position of the band structure of phosphorene with respect to that of graphene. This leads to control of the Schottky barrier height and doping of phosphorene, which are important features in the design of new devices based on van der Waals heterostructures. © 2015 American Physical Society.
Cardoso M.B.,Brazilian Synchrotron Light Laboratory (LNLS) |
Westfahl Jr. H.,Brazilian Synchrotron Light Laboratory (LNLS)
Carbohydrate Polymers | Year: 2010
Advances in the structural understanding of the lamellar organization of starch obtained through small-angle X-ray scattering (SAXS) technique are presented. An accurate starch sample preparation followed by appropriate background subtraction and Lorentz correction were able to evidence the second harmonic SAXS peak. Interface distribution functions (IDF) were generated from SAXS data to obtain dimensions and distributions of starch lamellae without any constraints or predefined assumptions. Dimensions and distributions of crystalline and amorphous lamellae were consistent with the molecular architecture of amylopectin. IDF fit results clearly indicate that amorphous and crystalline lamellae present different degrees of paracrystallinity, i.e. peak width/peak position ratios. The results of lamellar domain boundary are interpreted as a consequence of enzymatic trimming required to generate order in the amorphous lamellae for subsequent synthesis of the crystalline lattice. Amylose content seems to affect amorphous and crystalline lamellar distributions while the allomorph-type content is only reflected within the distribution of crystalline lamellae. © 2010 Elsevier Ltd. All rights reserved.
Chiaramonte T.,University of Campinas |
Tizei L.H.G.,University of Campinas |
Tizei L.H.G.,Brazilian Synchrotron Light Laboratory (LNLS) |
Ugarte D.,University of Campinas |
Cotta M.A.,University of Campinas
Nano Letters | Year: 2011
InP nanowire polytypic growth was thoroughly studied using electron microscopy techniques as a function of the In precursor flow. The dominant InP crystal structure is wurtzite, and growth parameters determine the density of stacking faults (SF) and zinc blende segments along the nanowires (NWs). Our results show that SF formation in InP NWs cannot be univocally attributed to the droplet supersaturation, if we assume this variable to be proportional to the ex situ In atomic concentration at the catalyst particle. An imbalance between this concentration and the axial growth rate was detected for growth conditions associated with larger SF densities along the NWs, suggesting a different route of precursor incorporation at the triple phase line in that case. The formation of SFs can be further enhanced by varying the In supply during growth and is suppressed for small diameter NWs grown under the same conditions. We attribute the observed behaviors to kinetically driven roughening of the semiconductor/metal interface. The consequent deformation of the triple phase line increases the probability of a phase change at the growth interface in an effort to reach local minima of system interface and surface energy. © 2011 American Chemical Society.
News Article | November 4, 2016
Two major scientific facilities being built in Brazil are facing delays after failing to receive any the funds allocated to them for 2016. The Sirius synchrotron light source and the Brazilian Multipurpose Research Reactor (RMB) have both been hit by federal budget cuts caused by the recent economic slowdown in the country. Any further funding delays could lead to both facilities being put back a number of years. Sirius, costing $290m, is being built at the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas, some 100 km north-west of São Paulo, and is expected to begin operation in 2018. As a fourth-generation synchrotron light source, it will generate coherent, high-brightness X-rays that scientists will use to study the structure and properties of materials in unprecedented detail. LNLS director Antônio José Roque da Silva says that officials at the synchrotron have not received the money they were promised for 2016 and are still using 2015 funds. Cash for 2016 was expected to be $87.4m, but that has now been cut to $57.7m by the National Congress of Brazil. "Even though this budget is well below our needs, at this moment the critical point is whether we will in fact receive the funds," says da Silva. He says it is critical that funding is maintained to allow officials to order equipment. "To keep the planned activities, it is indispensable to receive funds allocated for this year and have the assurance that no new cuts will threaten the $116m [allocated] for 2017," warns da Silva. "Otherwise it won't be possible to meet the schedule." da Silva adds that even if this funding is received, Sirius will still require an additional $76m to make sure it is open by 2018. The RMB, meanwhile, is located at Iperó, about 130 km east of São Paulo. Costing $500m, the reactor was expected to open this year. By generating radioisotopes, it promises to ensure Brazil does not depend on other countries for supplying radioisotopes for diagnosing and treating cancer. The RMB will also be used for neutron scattering and will carry out irradiation testing for nuclear fuels and materials. While cash has been spent obtaining the necessary permits for the RMB, including an environmental licence, officials are still waiting for the release of funds to begin construction. RMB's budget was supposed to be $47.6m from 2014 to 2016, but only $10.6m has so far been allocated. "The prediction was that the reactor would be ready this year, but, in this saga of precarious disbursements and insufficient funds, our time frame will have to be extended," says RMB technical co-ordinator José Perotta, who is research director at the National Nuclear Energy Commission. Brazil's Ministry of Science, Technology, Innovation and Communications maintains that funds for 2016 for Sirius and RMB are "secure". The ministry says that the cash for next year has been included in the country's annual budget, although it has yet to be approved by the country's national congress.