1,720,988 research outputs found
Short-range ordered 2D nanoholes: lattice-model and novel insight into the impact of coordination geometry and packing on their propagating-mode transmittance features
No full textOptically thin perforated gold films, fabricated using template colloidal masks self-assembled by following an elsewhere described simplified colloidal lithography protocol, are presented and discussed with the aim to develop a theory of short-range ordered nanoholes without straightforwardly extending concepts strictly related to periodic nanoholes. By Scanning Electron Microscopy (SEM) analysis of the evolution of nanohole short-range ordering and spatial coordination geometry under increasing interhole average spacing (d(NN)), unprecedented differences in the spectroscopic response are pointed out with respect to periodic systems. First, the dependence of the wavelength of a propagating plasmon mode on d(NN) is demonstrated to deviate from the linear relationship predicted by the grating-coupling picture developed for periodic arrays. Second, d(NN) cannot be straightforwardly interpreted as the counterpart of the lattice constant of periodic nanoholes, which demands to introduce a conceptually more rigorous periodicity-like length-scale. Once the impact of these findings on setting the operating parameters of a nanohole distribution is demonstrated, they are related, experimentally and by using a theoretical model developed by the authors, to the changes of the local coordination geometry (from quasi-hexagonal to quasi-square packing through mixed hexagonal–square coordination) induced by varying d(NN) over a wide interval. Autocorrelation analysis of SEM images is exploited to estimate a short-range periodicity-like length-scale, as a conceptual advance for laying the foundation of the concept of short-range ordered nanohole lattices and for deeper insight into the spectral response. As discussion is based on realistic, rather than simulated, evolution of colloidal arrangements, the formulated interpretative model accounts for realistic effects impacting transmission resonances
Accurate assessment of the oxygen reduction electrocatalytic activity of Mn/polypyrrole nanocomposites based on rotating disk electrode (RDE) measurements, complemented with multi-technique structural characterizations
No full textThis paper reports on the quantitative assessment of the oxygen reduction reaction (ORR) electrocatalytic activity of electrodeposited
Mn/polypyrrole (PPy) nanocomposites for alkaline aqueous solutions, based on the Rotating Disk Electrode (RDE)
method and accompanied by structural characterizations relevant to the establishment of structure-function relationships. The
characterization of Mn/PPy films is addressed to the following: (i) morphology, as assessed by Field-Emission Scanning Electron
Microscopy (FE-SEM) and Atomic Force Microscope (AFM); (ii) local electrical conductivity, as measured by Scanning Probe
Microscopy (SPM); and (iii) molecular structure, accessed by Raman Spectroscopy; these data provide the background against
which the electrocatalytic activity can be rationalised. For comparison, the properties of Mn/PPy are gauged against those of
graphite, PPy, and polycrystalline-Pt (poly-Pt). Due to the literature lack of accepted protocols for precise catalytic activity
measurement at poly-Pt electrode in alkaline solution using the RDE methodology, we have also worked on the obtainment of
an intralaboratory benchmark by evidencing some of the time-consuming parameters which drastically affect the reliability and
repeatability of the measurement
Block Copolymer and Cellulose Templated Mesoporous TiO2-SiO2 Nanocomposite as Superior Photocatalyst
Full text linkA dual soft-templating method was developed to produce highly crystalline and mesoporous TiO2-SiO2 nanocomposites. Pluronic F127 as the structure-directing agent and pure cellulose as the surface area modifier were used as the templating media. While Pluronic F127 served as the sacrificing media for generating a mesoporous structure in an acidic pH, cellulose templating helped to increase the specific surface area without affecting the mesoporosity of the TiO2-SiO2 nanostructures. Calcination at elevated temperature removed all the organics and formed pure inorganic TiO2-SiO2 composites as revealed by TGA and FTIR analyses. An optimum amount of SiO2 insertion in the TiO2 matrix increased the thermal stability of the crystalline anatase phase. BET surface area measurement along with low angle XRD revealed the formation of a mesoporous structure in the composites. The photocatalytic activity was evaluated by the degradation of Rhodamine B, Methylene Blue, and 4-Nitrophenol as the model pollutants under solar light irradiation, where the superior photo-degradation activity of Pluronic F127/cellulose templated TiO2-SiO2 was observed compared to pure Pluronic templated composite and commercial Evonik P25 TiO2. The higher photocatalytic activity was achieved due to the higher thermal stability of the nanocrystalline anatase phase, the mesoporosity, and the higher specific surface area
Accurate Assessment of the Oxygen Reduction Electrocatalytic Activity of Mn/Polypyrrole Nanocomposites Based on Rotating Disk Electrode Measurements, Complemented with Multitechnique Structural Characterizations
Full text linkThis paper reports on the quantitative assessment of the oxygen reduction reaction (ORR) electrocatalytic activity of electrodeposited Mn/polypyrrole (PPy) nanocomposites for alkaline aqueous solutions, based on the Rotating Disk Electrode (RDE) method and accompanied by structural characterizations relevant to the establishment of structure-function relationships. The characterization of Mn/PPy films is addressed to the following: (i) morphology, as assessed by Field-Emission Scanning Electron Microscopy (FE-SEM) and Atomic Force Microscope (AFM); (ii) local electrical conductivity, as measured by Scanning Probe Microscopy (SPM); and (iii) molecular structure, accessed by Raman Spectroscopy; these data provide the background against which the electrocatalytic activity can be rationalised. For comparison, the properties of Mn/PPy are gauged against those of graphite, PPy, and polycrystalline-Pt (poly-Pt). Due to the literature lack of accepted protocols for precise catalytic activity measurement at poly-Pt electrode in alkaline solution using the RDE methodology, we have also worked on the obtainment of an intralaboratory benchmark by evidencing some of the time-consuming parameters which drastically affect the reliability and repeatability of the measurement
Edge-melting: nanoscale key-mechanism to explain nanoparticle formation from heated TEM grids
No full textIn this study, we examine at both experimental and fundamental levels, the experimental evidence of nanoparticle formation in transmission electron microscopy (TEM) metal grids annealed at temperatures lower than the melting point of the corresponding metal bulk material. Our experimental investigation considers the most thermally unstable TEM grids (i.e. Cu-grids) and inspects the possible sources and mechanisms of contamination of thin films, conventionally deposited on carbon-coated Cu-grids. The investigations are supported by morphological–compositional analyses performed in different regions of the TEM sample. Then, a general model is formulated and discussed in order to explain the grid thermal instability, based on the critical role of edge-melting (i.e. melting initiated at edges and corners of th egrid bars), the enhanced rate of evaporation from a liquid surface and the polycristallinity of the grid bars.Hence, we totally disregard conventional arguments such as bulk evaporation and metal vapor pressure and, in order to emphasize and clarify the alternative point of view of our model, we also overview the nano-scale melting phenomenology relevant to our discussion and survey the discrepancies reported in the literature
Morphochemical evolution during ageing of pyrolysed Mn/polypyrrole nanocomposite oxygen reduction electrocatalysts: A study based on quasi-in situ photoelectron spectromicroscopy
No full textThis study dealswith themorphological and chemical-state changes caused by the degradation of nanocomposite
electrocatalysts – fabricated by pulsed potentiostatic co-electrodeposition and subsequently pyrolysed –
under oxygen reduction reaction (ORR) conditions in aqueous alkaline solution. Variations in shape, dimensions
and chemical state of theMn-centres were followed by quasi-in situ synchrotron-based scanning photoelectron
microscopy with submicron lateral resolution, combined with ex situ Raman measurements, in correspondence
of different cyclovoltammetric ageing stages. The decline of the electrocatalytic performance is accompanied by
size variations of theMnOx particles that are initially ~30nmin diameter, then shrink to ~10nmand subsequently
grow to ~45 nmafter prolonged ORR. Concerning chemical state, the pristine Mn0,II nanoparticles are converted
to MnIII,IV oxy-hydroxides as a result of a dissolution/redeposition process favoured by the oxygen
environment
NUMERICAL SIMULATION OF CSP BASED ON NANORECTENNA TECHNOLOGY
No full textConcentrated solar power (CSP) plants are one of several renewable energy technologies with significant potential to meet a part of our future energy demand. By now, CSP systems are used to supply photovoltaic or thermal power plant, but results on nanorectennas suggest the possibility to use this technology for direct energy conversion of solar radiation into electricity. A rectenna is a rectifying antenna that can be used to directly convert wave energy into DC electricity. Experiences in microwave applications have shown energy conversion efficiency in the order of 85%, and recently empirical tests have demonstrated that this technology can be used up to the infrared wavelength. The present paper, together with first preliminary results on the fabrication of the rectifier (the key element of a rectenna) and its electrical behavior, proposes the numerical simulation of a new CSP system where a receiver, heated by concentrated solar radiation, reemits infrared energy on the nanorectenna, which converts the incoming energy into electricity. In this way the receiver plays the role of a sunlight radiation converter to infrared energy.
The numerical simulation of the system consists of two steps. The first is a ray-tracing model to calculate the concentrator optical efficiency and the energy distribution on the focusing area of the parabolic mirror. The second step consists in the receiver temperature calculation as function of the incident solar radiation. The numerical procedure allows the calculation of the concentrator/receiver assembly performance which returns the energy incident on the nanorectenna as a function of external environmental conditions
Dy- and Tb-doped CeO 2 -Ni cermets for solid oxide fuel cell anodes: electrochemical fabrication, structural characterization, and electrocatalytic performance
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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