1,721,018 research outputs found
The importance of mechanistic studies in the development of cold plasma-based degradation of persistent organic pollutants in water
Full text linkAn overview is given of major recent advancements in cold plasma-based water treatment, with specific focus on the degradation mechanisms of organic pollutants. Mechanistic insight is indeed a powerful tool for process optimization considering the treatment duration, its products, and energy costs as it provides guidelines for the design of optimized reactors and the selection of best experimental conditions. The cases considered emphasize the importance of matching the plasma composition in terms of reactive species with the reactivity of the target pollutant(s), and of identifying and understanding the reciprocal effects of different pollutants as well as those of complex aqueous matrices. Harnessing the chemistry activated by the plasma to achieve the desired goal is the key to treatment success. A general strategy is outlined for designing the best plasma experimental set-up and for predicting possible byproducts
Air non-thermal plasma treatment of the herbicides mesotrione and metolachlor in water
No full textThe goals of this research were to i) test the ability of air non-thermal plasma to promote the degradation in
water of two widespread herbicides, mesotrione and metolachlor, ii) determine the process efficiency and
products for each herbicide treated individually, iii) detect and investigate any possible reciprocal effects when
the two herbicides, which are often used in combination, are treated together in the same solution. The experiments
were carried out using a dielectric barrier discharge (DBD) reactor to generate a strongly oxidizing
non-thermal plasma above the liquid surface and induce the advanced oxidation of dissolved organic chemicals.
The results of extensive HPLC (UV, MS and MS/MS) and TOC analyses show that air non-thermal plasma efficiently
decomposes both herbicides, that mesotrione is considerably more reactive than metolachlor and that
complete mineralization of both is achieved at sufficiently long treatment times. Treatment of metolachlor was
also performed in tap water, a closer model for environmental systems, achieving the same results as found in
deionized water. Detailed product and kinetic studies failed to reveal any effect attributable to reciprocal influence
of mesotrione and metolachlor when treated together in the same solution
Plasma Treatment and Ozonation of Binary Mixtures: The Case of Maleic and Fumaric Acids
Full text linkWith respect to ozonation, plasma treatment involves direct contact between the discharge
and the contaminated water therefore benefting, in addition to ozone, also of short-lived
reactive species. This paper focuses on mechanistic aspects of water treatment based on
plasma activation (in-situ discharge) and ozonation (ex-situ discharge), using maleic acid
and fumaric acid as model substrates and dielectric barrier discharges (DBDs) for producing plasma and ozone. Both types of experiments were carried out at diferent pH values and degradation profles of residual concentration vs treatment time were compared in
experiments in which each acid was treated individually and in mixture with the other. It
was found that, under all conditions examined, plasma treatment was more efcient than
ozonation for both acids, and that fumaric acid was always more reactive than maleic acid.
Peculiar S-shaped degradation curves were obtained for the decay of maleic acid when
treated in mixture with fumaric acid under acidic and neutral pH conditions in ozonation
and in plasma experiments. This efect was not observed when maleic acid was treated
in mixture with phenol instead of fumaric acid. The experimental data are nicely ftted
with a simple kinetic model which assumes that a single reactive species, in steady state
concentration, is responsible for the attack initiating the pollutants degradation. Based on
the complete set of results obtained the conclusion is reached that, in the DBD reactor
used, under acidic and neutral pH conditions ozone plays a major role in the degradation of
maleic and fumaric acids also in direct plasma treatment
Highly efficient degradation of PFAS and other surfactants in water with atmospheric RAdial plasma (RAP) discharge
Full text linkAtmospheric plasma offers a viable approach to new water remediation technologies, best suited for the degradation of persistent organic pollutants such as PFAS, per- and polyfluoroalkyl substances. This paper reports on the remarkable performance of a novel RAdial Plasma (RAP) discharge reactor in treating water contaminated with PFAS surfactants, notably the ubiquitous perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). RAP proved to be versatile and robust, performing very well over a wide range of pollutants concentrations. Thus, PFOA degradation was most satisfactory with regard to all critical indicators, kinetics (≥99% PFOA conversion in less than 2.5 min and 30 min in solutions with initial concentrations of 41 μg/L and 41 mg/L, respectively), byproducts, and energy efficiency (G50 greater than 2000 mg/kWh for 41 μg/L - 4.1 mg/L PFOA initial concentrations). Likewise for PFOS as well as for Triton X-100, a common fluorine-free non-ionic surfactant tested to explore the scope of applicability of RAP to the degradation of surfactants in general. The results obtained with RAP compare most favourably with those reported for state-of-art plasma systems in similar experiments. RAP's excellent performance is attributed to the dense network of radial discharges it generates, randomly spread over the entire exposed surface of the liquid thus establishing an extended highly reactive plasma-liquid interface with both strongly reducing and oxidizing species. Mechanistic insight is offered based on the observed degradation products and on available literature data on the surfactants properties and on their plasma induced degradation investigated in previous studies
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
Atmospheric Pressure Non-thermal Plasma for Air Purification: Ions and Ionic Reactions Induced by dc+ Corona Discharges in Air Contaminated with Acetone and Methanol
Full text linkAtmospheric pressure mass spectrometry (APCI-MS) was used to investigate the positive ions in air containing acetone (A), methanol (M) and mixtures thereof (A + M), subjected to +dc corona discharges. The results of experiments with isotopically labelled analogues, perdeuterated acetone Adeu and methanol Mdeu, and relevant thermochemical data found in the literature allowed us to identify the main ionic reactions occurring in single component systems (A or M) and in binary mixtures (A + M). It is concluded that, thanks to its significantly higher proton affinity, A is very efficient in quenching M-derived ions at atmospheric pressure. These conclusions provide a rationale for interpreting the results of a parallel investigation on the reciprocal effects of M and A when treated together in air at atmospheric pressure with +dc corona in a non-thermal plasma reactor developed previously in our laboratory. Specifically, we observed a marked drop in the degradation efficiency of methanol when it was treated in the presence of an equivalent amount of acetone. This effect is attributed to acetone interfering with ion-initiated degradation processes of methanol, and supports the conclusion that ions and ionic reactions are important in dc+ corona induced oxidation of volatile organic pollutants in air
Nitrogen-containing organic products from the treatment of liquid toluene with plasma-activated N2 gas
Full text linkThis proof-of-principle study explored the possibility to form nitrogen-containing organic products via exposure of liquid toluene to a flow of molecular nitrogen, at room temperature and atmospheric pressure, activated by dielectric barrier discharges. N-containing organic compounds indeed formed under these conditions, including benzonitrile, a high-value chemical that is industrially synthesized from toluene under demanding conditions. Toluene-derived higher hydrocarbons, as well as oxygen-containing derivatives, were also detected, the latter due to efficient reactions of residual oxygen in the system. A mechanistic description of the observed chemistry is provided, together with guidelines for increasing the selectivity for C–N forming reactions and the development of this approach into a novel synthetic approach for high-value organic N-containing chemicals
Efficiency, products and mechanisms of ethyl acetate oxidative degradation in air non-thermal plasma
Full text linkEthyl acetate (EA) is a popular solvent and diluent in many products and one of the most ubiquitous organic pollutants of indoor air. Although EA's ascertained toxicity is classified as low, exposure to its vapors at concentrations 400 ppm causes serious problems in humans. EA is thus a frequent target in testing novel technologies for air purification. We report here an investigation of EA oxidative degradation in air at room temperature and atmospheric pressure induced by corona discharges. Three corona regimes, dc-, dc+ and pulsed +, were tested in the same reactor under various experimental conditions with regard to EA initial concentration (C 0) and the presence of humidity in the system. The EA degradation process was monitored by gas chromatography (GC)-flame ionization detection, GC-mass spectrometry and Fourier transform infrared spectroscopy analysis of the treated gas. These analyses yielded the concentration of residual EA (C) and those of its major products of oxidation (CO2, CO) and revealed a few organic reaction intermediates formed along the oxidation chain. The process energy efficiency was determined as energy constant, k E (kJ-1 l) and as energy yield, EY (g kW-1 h-1). The efficiency depends on the type of corona (pulsed + >dc- >dc+), on the presence of humidity in the air (improvement in the case of dc-, little or no effect for dc+) and on C 0 (k E increases linearly with 1/C 0). CO2 and CO were the major carbon containing products, confirming the strong oxidizing power of air non-thermal plasma. Acetic acid and acetaldehyde were detected in very small amounts as reaction intermediates. The experimental results obtained in this work support the conclusion that different reactive species are involved in the initial step of EA oxidation in the case of dc- and dc+ corona air non-thermal plasma
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
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