1,354 research outputs found
Biogeochemical effects of zerovalent iron on mercury methylation and bioaccumulation in rice paddy system
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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 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
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
Tunichrome-inspired gold-enrichment dispersion matrix and its application in water treatment: A proof of concept investigation
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Decentralized Approximate Bayesian Inference for Distributed Sensor Network
No full textBayesian models provide a framework for probabilistic modelling of complex datasets. Many such models are computationally demanding, especially in the presence of large datasets. In sensor network applications, statistical (Bayesian) parameter estimation usually relies on decentralized algorithms, in which both data and computation are distributed across the nodes of the network. In this paper we propose a framework for decentralized Bayesian learning using Bregman Alternating Direction Method of Multipliers (B-ADMM).We demonstrate the utility of our framework, with Mean Field Variational Bayes (MFVB) as the primitive for distributed affine structure from motion (SfM).Peer reviewe
Fast ADMM Algorithm for Distributed Optimization with Adaptive Penalty
No full textWe propose new methods to speed up convergence of the Alternating Direction Method of Multipliers (ADMM), a common optimization tool in the context of large scale and distributed learning. The proposed method accelerates the speed of convergence by automatically deciding the constraint penalty needed for parameter consensus in each iteration. In addition, we also propose an extension of the method that adaptively determines the maximum number of iterations to update the penalty. We show that this approach effectively leads to an adaptive, dynamic network topology underlying the distributed optimization. The utility of the new penalty update schemes is demonstrated on both synthetic and real data, including an instance of the probabilistic matrix factorization task known as the structure-from-motion problem.Peer reviewe
Impact of surface modification on the toxicity of zerovalent iron nanoparticles in aquatic and terrestrial organisms
No full textNanoscale zerovalent iron (nZVI)-based materials are increasingly being applied in environmental remediation, thereby lead to their exposure to aquatic and terrestrial biota. However, little is known regarding the toxic effects of surface-modified nZVI on multiple species in the ecosystem. In this study, we systematically compared the toxicities of different forms of nZVIs, such as bare nZVI, carboxymethyl cellulose (CMC)-stabilized nZVI, tetrapolyphosphate (TPP)-coated nZVI and bismuth (Bi)-doped nZVI, on a range of aquatic and terrestrial organisms, including bacteria (Escherichia coil and Bacillus subtilis), plant (Arabidopsis thaliana), water flea (Daphnia magna) and earthworm (Eisenia fetida). The Bi- and CMC-nZVI induced adverse biological responses across all the test systems, except E. fetida, varying from cell death in E. coli and B. subtilis to inhibition of the physiological states in D. magna and A. thaliana. The particle characterization under exposure conditions indicated that the surface modification of nZVI played a significant role in their toxicities by changing their physicochemical properties. The underlying mechanisms by which nZVI induces toxicity might be a combination of oxidative stress and another mechanism such as cell membrane disruption, chlorosis and hypoxia. Overall, our findings could provide important implications for the development of environment-friendly nanomaterials and direct further ecotoxicological researches regarding interspecies exploration.11Nsciescopu
A Knowledge Distribution Model to Support an Author in Narrative Creation
No full textAdjusting the knowledge of characters and the reader is a critical task for an author in narrative creation. Throughout a narrative, both characters and the reader experience events according to their own timelines and perspectives. They interpret information accumulated through their experience and update knowledge to the narrative-world which the author constructed. In this paper, we present a Knowledge Distribution Model which supports an author in finely controlling the knowledge of characters and the reader. Within the model, the Knowledge Structure is constructed by connecting event, information, and knowledge. The Knowledge State is evaluated as the degree of belief under the knowledge structure. We adopted a probabilistic reasoning model to calculate the knowledge state. The change in knowledge state, defined as Knowledge Flow, is visually presented to the author. We designed a GUI prototype to implement the proposed modeling process, and demonstrated the knowledge flow with an actual cinematic narrative
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