1,721,034 research outputs found
Effects of metal nanoparticles deposition on the photocatalytic oxidation of ammonia in TiO2 aqueous suspensions
No full textTiO2 powders modified through the deposition of surfactant-stabilized preformed metal (Pt, Pd, Au and Ag) nanoparticles (NPs) were tested as photocatalysts for batch ammonia photo-oxidation in aqueous suspension, under UVA irradiation. NH3 conversion and the selectivity toward mildly oxidized N2 and highly oxidized nitrite and nitrate anions were monitored during the runs, in order to study the effects of noble metal NPs deposition on the reaction mechanism. This involves parallel and consecutive paths, also depending on the type of metal deposited on TiO2, as also highlighted by the nitrite photo-oxidation tests performed in the present study. Metal NPs acted as electron traps ensuring better separation of the photoproduced charge couples and consequently higher rates of hole-mediated oxidation reactions. Apart from Au/TiO2, the metal-modified powders exhibited higher photoactivity with respect to that of naked titania, with Ag/TiO2 being the best performing photocatalyst in terms of ammonia conversion. On the other hand, Pd NPs on TiO2 ensured a considerable increase of the selectivity toward N2 and may thus be considered the best co-catalysts of TiO2 for environmentally friendly photocatalytic NH3 abatement
TOWARDS THE PHOTOCATALYTIC PRODUCTION OF SOLAR FUELS - NANOSTRUCTURED TITANIUM DIOXIDE FOR PHOTOCATALYSIS & PHOTO-ELECTROCHEMISTRY
Get PDFIn spite of many efforts given during the last decades to find new alternative photocatalytic materials, titanium dioxide (TiO2) still represents the most widely employed semiconductor for photocatalytic applications, being photoactive, cheap, easily available, non-toxic, inert and, most of all, chemically stable. However, although exhibiting a powerful combination of extraordinary and attractive physico-chemical properties, it suffers from some issues, common to all semiconductors, related to the dynamic of the charge carriers. Precisely, trapping and recombination of valence band holes and conduction band electrons occur at a certain extent, anyway resulting in a drop of the process efficiency. Therefore, in view of limiting these detrimental phenomena, the charge transfer and the electric conductivity of a semiconductor can be enhanced, thus leading to an overall improvement of the photocatalyst performance.
In the first part of the work, homemade and commercial TiO2 powders were studied as photocatalysts for different applications, including the liquid-phase photocatalytic oxidation of ammonia and formic acid, and the H2 production through photocatalytic reforming of water-methanol vapors. In this context, a dopant (NH4F) was used during the sol-gel synthesis of the semiconductor to stabilize the formation of the TiO2 anatase phase (typically more active than rutile TiO2 because of its higher electron mobility), especially when crystallization of the amorphous oxides was performed at high temperature (700 ̊C). Furthermore, the effects induced by noble metal nanoparticles deposition on TiO2 anatase powders were also investigated. In situ electron spin resonance spectroscopy was employed to determine the amount of electrons and holes trapping centers formed under irradiation, in the absence and in the presence of noble metal co-catalysts at the surface of TiO2, hence assessing also the ability of Au and Pt nanoparticles in trapping conduction band electrons. The results were of great usefulness not only to interpret the different H2 production rates but also to understand some mechanistic aspects concerning the selectivity towards the different oxidation products in the methanol photo-steam reforming reaction.
In the second part of the work, the nanostructuring of the semiconductor was explored by fabricating TiO2 nanotube arrays through electrochemical anodization. The anodic oxides were employed for both photocatalytic and photo-electrochemical H2 production. In view of large-scale application, the anodization approach was studied on wide Ti substrate surfaces, in order to assess the feasibility of the scale up. Moreover, TiO2 nanotubes were also grown on Ti-based alloys. When fabricating the nanotubes under optimized conditions on Ti-Ta alloys, highly photoactive Ta-doped TiO2 nanotubes were obtained, exhibiting superior water splitting ability. When anodizing Ti-Au alloys, the TiO2 nanotubes resulted decorated with Au nanoclusters. These Au-decorated TiO2 nanotube arrays were used as efficient photocatalyst for H2 production from ethanol-water solutions. Finally, the fabrication of short TiO2 nanotube layers exhibiting an unprecedented level of self-ordering was achieved through an innovative anodization approach. The highly ordered topography allowed the subsequent self-ordering dewetting of Au, leading to Au nanoparticles of controllable size and distribution. These short, Au nanoparticles-filled TiO2 nanotubes exhibited advanced photoactivity ascribed to their reaction vessel-like geometry, fulfilling the requirements in terms of solid state charge carriers diffusion and liquid phase diffusion of oxidizing radicals
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Effect of metal nanoparticles deposition on the photocatalytic oxidation of ammonia in aqueous suspensions
No full textTiO2 powders modified through the deposition of surfactantstabilized
preformed metal (Pt, Pd, Au and Ag) nanoparticles
(NPs) were tested as photocatalysts in NH3 photo-oxidation in
aqueous suspension. Mildly oxidized N2, together with nitrite
and nitrate anions, were the main reaction products; their amount
was monitored during the runs, together with the residual NH3
concentration in the aqueous phase. The effects induced by the
type and amount of deposited metal NPs on both ammonia
conversion (XNH3%) and on products selectivities (S%) were thus
investigated systematically. Apart from Au-modified TiO2, the
metal-modified powders exhibited increased photoactivity with
respect to that of the naked semiconductor oxide, with Ag/TiO2
resulting the best performing photocatalyst in this reaction
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
