1,720,961 research outputs found
Biogeochemical effects of zerovalent iron on mercury methylation and bioaccumulation in rice paddy system
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Tunichrome mimetic matrix, its perspective in abatement for carcinogenic hexavalent chromium and specific coordination behavior
No full textInspired by naturally occurring metal chelation strategy by pyrogallol moiety of tunichromes of marine tunicates, a strong retention of carcinogenic chromium (Cr-VI) is described by mimicking tunichrome matrix as a proof-of-concept investigation in water treatment applications. Harvesting tunichromes tailored with the pyrogallol moiety are extremely difficult owing to aerial sensitivity and purification difficulties, thus proving a challenging synthesis problem. Despite significant interest, knowledge of specific metal coordination in tunicate's matrix is still ambiguous, hindering study scope. We planned to fabricate a promising tunichrome matrix (TM) tailored with pyrogallol moieties from the Earth-abundant raw materials (gallic acid and chitin nanofiber) at mass scale without artificial aid. Specifically, we aimed at atomistic understanding of contaminant and pyrogallol moiety of TM by examining the structural parameters (redox change, geometrical distortion, coordination bond). Cr K-edge extended X-ray absorption fine structure (EXAFS) corresponds well to nontoxic Cr-III (average four Cr-O bond lengths of 1.91 angstrom) and a small fraction of Cr-VI (average two Cr-O bond lengths of 1.62 angstrom). A coupled reductive complexation mechanism was identified by combining near edge X-ray absorption fine structure (NEXAFS) and linear combination fits. From the viewpoint of practical utility and effective performance (nearly 119 mg chromium per g weight of TM), the impacts of water chemistry conditions were investigated from a variety of contaminated waters, showing a distinct improvement compared to conventional popular materials. The gained knowledge would be beneficial for utilizing a pyrogallol moiety as an alternative greener and sustainable scavenger, specifically for toxic chromium. (C) 2017 Elsevier B.V. All rights reserved.112sciescopu
Mechanically combined persulfate on zerovalent iron: Mechanistic insights into reduction and oxidation processes
No full textPersulfate (S2O82-; PS) has been used with zerovalent iron (ZVI) for the remediation of various contaminants. However, the passive layer of commercial ZVI limitates the corrosion of ZVI and reaction with PS. In our initial attempt, we mechanically combined Na2S2O8 and micro-sized ZVI by simple ball milling to improve the reaction of PS and ZVI. The synthesized composite (PSZVIbm) was compared to the system in which Na2S2O8 was separately injected with ball-milled ZVI (ZVIbm/PS). The reaction in ZVIbm/PS depended on surface-bound Fe(II) to initiate PS consumption. Conversely, the PS immediately destroyed the passive layer and enhanced the corrosion of ZVI in PSZVIbm. Therefore, PSZVIbm reduced nitrobenzene rapidly with higher efficiency in deionized water (94.2%) compared to that of ZVIbm/PS (73.1%). Furthermore, PSZVIbm was less affected by the real groundwater matrix and removed nitrobenzene with higher efficiency (64.7%) than ZVIbm/PS (10.3%). Due to the different PS consumption rates and radical species, PSZVIbm removed phenol with lower efficiency (22.7%) than ZVIbm/PS (61.5%), showing the different effects of surface-bound Na2S2O8 on the reduction/oxidation capacities of ZVI. This study suggests a new scalable method to control the reactivity of ZVI without the use of toxic chemicals and wastewater generation.11Nsciescopu
Comparative study of peroxide oxidants activated by nZVI: Removal of 1,4-Dioxane and arsenic(III) in contaminated waters
No full textIn this study, we investigated the performance of nanoscale zerovalent iron (nZVI) in the presence of the common oxidants, persulfate (PS), peroxymonosulfate (PMS) and hydrogen peroxide (HP), for the removal of 1,4-dioxane (1,4-D) and As(III) in contaminated waters. PS/nZVI showed the highest removal of both 1,4-D and As(III), followed by HP/nZVI and PMS/nZVI in order. The removal increased as the oxidant dosage increased, whereas only As(III) removal was enhanced with increasing nZVI dosage. The maximum removal occurred at pH 3 and only PS/nZVI could remove As(III) as the pH increased from 3 to 7. Radicals such as center dot OH and SO4 center dot- were produced from the oxidant/nZVI system and the radicals contributed more to the removal of 1,4-D than As(III). The removal of As species was significantly influenced by nZVI dissolution, which consequently caused adsorption and co-precipitation as the main removal mechanisms. For environmental applications, the PS/nZVI system efficiently treated a real groundwater contaminated by 1,4-D and As(III), respectively. The basic knowledge gained from this study could help in selecting a proper oxidant to use with nZVI to purify surface and groundwaters contaminated by organic and inorganic contaminants at the same time.11Nsciescopu
Tunichrome-Inspired Gold-Enrichment Dispersion Matrix and Its Application in Water Treatment: A Proof-of-Concept Investigation
No full textTunicate, a filter-feeder in seawater, is able to accumulate high amount of metals using intracellular polymer matrices. The woven pyrogallol structures of tunichrome, a small peptide contained in tunicate's blood;Cells, is believed to, be responsible for selective. metal sequestration in tunicates from seawater. However, the intriguing tunichrome matrix is difficult both to harvest from the tunicate and to synthesize massively due to the-extreme oxidation sensitivity of the pyrogallol, moiety which limits the study scope. Here, we succeeded to mimic tunichrome by conjugating two cheap and naturally occurring components: pyrogallol-5-carboxylic acid (gallic acid) and chitin. nanofiber A tunicate-mimetic infiltration matrix of surface-tailored chitin nanofibers with pyrogallol moieties (CGa) demonstrated the versatility of this strategy in generation of ingenious filtration material, especially for unprecedented fine and-Clean gold recovery inside of the tunicate-mimetic infiltration matrix (>99%, 533 mg gold per gram weight), which exceeds that of the,presently most popular materials. Complexation between pyrogallol on the nanofiber and gold-was similar to that of a tunichrome's metal sequestration. Extended X-ray absorption fine Structure, (EXAFS); spectroscopy and data-fitting, elucidated the decreased coordination numbers for Au-Au nearest neighbors, demonstrating that gold coordinated to pyrogallol units, followed by an intramolecular association of Au-0. A catalytic reduction of 4-nitrophenol mediated by the-tunicate-mimetic matrix with harvested gold revealed excellent recyclability up to 30 cycles (similar to 95% reduction), which together with methylene-blue reduction and antimicrobial performances indicates the versatile characteristics,of sustainable processes by the tunichrome mimetics. This strategy opens the door for fast-developing new biomimetic alternatives for precious metal recovery, which is not restricted to gold and can offer a tool for multifaceted soft/hard nanomaterials..112sciescopu
Going 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
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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
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