1,720,960 research outputs found
Innovative Photoreactors to remove N-containing pollutants from water
No full textThe photooxidation of ammonia and photoreduction of nitrates have been investigated in semibatch mode, developing a suitable process to achieve the desired selectivity to innocuous N2. Proper photoreactor prototypes have been tested for both applications, together with process design.
1. Scope
The development of efficient processes in photocatalysis is a challenging task. In particular, N-containing pollutants1, such as inorganic ammonia, nitrites and nitrates, and some organic N-containing compounds (dyes, pesticides, drugs, etc.)2, are harmful contaminants for drinking water, inducing acute and/or chronic diseases, especially affecting infants and children. Furthermore, when released in waste waters, they contribute to eutrophication, or possibly contaminate ground water. This is particularly relevant in agriculturally intensive zones and in the case of some relevant industrial processes involving e.g. nitration reactions.
In the present work, we developed innovative photocatalytic processes for the abatement of N-compounds, focusing on selectivity towards innocuous N2, to be applied for the treatment of waste waters to meet legislative specifications. The photocatalytic performance of the samples, to be correlated with nanomaterials properties, has been checked for the photoreduction of nitrate ions and the photooxidation of ammonia and organic N-containing compounds by means of two semi-batch photoreactors, specifically designed and optimized for this application.
2. Results and discussion
Different photocatalysts have been tested and compared. TiO2 has been prepared in nanosized form by using an innovative flame pyrolysis (FP) approach, able to synthesise single or mixed oxide nanoparticles, characterized by homogeneous particle size and good phase purity. This method is suitable for continuous one-step synthesis of oxides3. The apparatus includes a nozzle/burner, which is co-fed with oxygen and with an organic solution of the oxide precursors. The organic solvent acts as fuel for the flame, whereas oxygen is the comburent and the dispersing agent. The TiO2 samples was prepared from a solution of Titanium(IV)-isopropylate (Aldrich, pur. 97 %) in xylene and propionic acid. The burner was fed with a flow rate of 2.2 mL/min of the solution and 5 L/min of O2. The pressure drop across the nozzle was set to 1.5 bar. Several metals such as Pd and Ag were added as co-catalysts with a 0.1-0.5 wt% concentration by wet impregnation from a solution of nitrate precursors.
Photocatalytic reduction of NO3− and oxidation of NH3/NH4+ in water were carried out in a specifically designed Pyrex reactor, with a top quartz window (Figure 1). The catalysts were suspended in an aqueous solution of NH4Cl (0.2M) or NaNO3 (0.006M) and the suspension was stirred using a magnetic stirrer. The reaction suspension was thoroughly degassed and then exposed to He. The reactor was operated in semi-batch mode: the solution containing the pollutant to be photoconverted was added at the beginning of the reaction in batch mode, whereas a gas stream continuously flowed through the reactor. The gas was composed by He during the conditioning-outgassing phase preliminary to every measurement. He was fed in continuous mode also during the nitrate photoreduction tests, whereas it was substituted by synthetic air (80 vol% He + 20 vol% O2) during the ammonia photooxidation experiments. A trap for ammonia, possibly stripped from the reactor, was placed downstream.
Comparison with commercial nanostructured TiO2 supports revealed several differences. The TiO2 sample prepared by FP exhibited higher activity with respect to the commercial sample, achieving ca. 20 % conversion after 5 h, without indication of decay or deactivation. By contrast, the commercial sample was less active and most of all its activity was rapidly ruled out. Some induction period was observed, due to the need of sample conditioning upon irradiation. The most interesting point is that no trace of nitrites or nitrates was observed, confirming a full selectivity to the desired product, i.e. molecular N2.
The photoreduction of nitrates was also tested over the same samples. Very low conversion (<5%) was achieved with pure TiO2 catalysts, whereas Pd doping improved conversion by ca. one order of magnitude under the same experimental conditions. The key problem remained process selectivity: 100% to the undesired NH3 for the undoped photocatalyst, max 30% for the Pd-doped sample prepared by FP.
Figure 1. Scheme of the photocatalytic plant set up
3. Conclusions
An innovative photoreactor has been set up allowing to achieve the photoreduction of nitrates and the photooxidation of ammonia in semibatch mode. Its configuration, to be further optimised as for geometry and mixing, is suitable for scale up, easily implements immobilised photocatalysts and is ready to use with direct sunlight. These first results on both reactions let us conclude that a two step process can be designed to cope with the insufficient selectivity to N2 during the nitrate photoreduction step. The ammonia produced is removed during a second, fully selective step of photooxidation. The flame pyrolysis procedure is a viable technique for the preparation of either bare or metal-doped semiconductors in nanosized form, to be used for the photocatalytic abatement of inorganic N-containing pollutants in waste or drinking waters. Even if a photoreactor with external irradiation is less efficient than one base on immersion lamps, it is much more suitable for scale up and most of all for the direct application with solar light. Sufficiently high ammonia conversion was achieved during photooxidation in semibatch confirguration, with 100 % selectivity to N2.
The financial support of Fondazione Cariplo (Italy) through the measure “Ricerca sull’inquinamento dell’acqua e per una corretta gestione della risorsa idrica”, project “DEN - Innovative technologies for the abatement of N-containing pollutants in water”, grant no. 2015-0186, is gratefully acknowledged.
References
1. Compagnoni, M.; Ramis, G.; Freyria, F. S.; Armandi, M.; Bonelli, B.; Rossetti, I. Photocatalytic Processes for the Abatement of N-Containing Pollutants from Waste Water. Part 1: Inorganic Pollutants. J. Nanosci. Nanotechnol. 2017, in press.
2. Freyria, F. S.; Armandi, M.; Compagnoni, M.; Ramis, G.; Rossetti, I.; Bonelli, B. Catalytic and Photocatalytic Processes for the Abatement of N-Containing Pollutants From Wastewater . Part 2 : Organic Pollutants. J. Nanosci. Nanotechnol., 2017, in press.
3. Compagnoni, M.; Lasso, J.; Di Michele, A.; Rossetti, I. Flame Pyrolysis Prepared Catalysts for the Steam Reforming of Ethanol. Catal. Sci. Technol. 2016, 6247-6256
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
- …
