1,720,968 research outputs found
Toluene and n-hexane competitive adsorption on high-silica ZSM-5 zeolite
No full textFuel-based compounds, such as toluene and n-hexane, are common pollutants present in water and wastewater. Due
to their tendency to persist in air, water and soil and to bioaccumulate through the food chain, they are included among
the most hazardous compounds for human health and environment. Acquatic ecosystems are especially vulnerable
because of the frequent use of water bodies as recipients of potentially toxic liquids and solids from domestic,
agricultural and industrial wastes. Hence, the removal of fuel-based compounds, through adsorption onto inorganic
sorbents is of considerable interest. Due to their selectivity towards organic contaminant and fast adsorption kinetics, it
has been recently highlighted that High Silica Zeolites are hydrophobic sorbent materials suitable for adsorption
processes (Martucci et al., 2015; Pasti et al., 2016). The aim of this work is to determine the ZSM-5 zeolite degree of
selectivity and its structural changes when a competitive adsorption of toluene and n-hexane occurs. A sample of ZSM-
5 zeolite (MFI topology, SiO2/Al2O3 ratio=280), was provided by Tosoh Corporation and loaded with a binary mixture
of toluene and n-hexane. Kinetics and adsorption isotherm data were obtained via Headspace Solid Phase
Microextraction-GC. Powders patterns were collected before and after adsorption on a Bruker D8 Advance
diffractometer equipped with SOL-X detector. Thermal (TG and DTA) analysis were performed in air up to 900°C at
10°C/min. This multidisciplinary approach allowed us to: 1) measure the sorption capacity of zeolite materials weighed
against organic pollutants dissolved in water; 2) characterise the sorbent structure after pollutant adsorption; 3) localise
the organic species in the zeolite channel systems; 4) probe the interaction between the adsorbate and zeolite framework.
Rietveld refinements provide information about the relative position of molecules inside the structure after toluene, nhexane
and their mixture adsorption. Data reveal that 1) n-hexane and toluene are preferentially adsorbed whether as
single components than as binary mixture; 2) zeolite selectivity is higher towards the n-hexane than toluene. Differences
Fourier maps analysis shows that n-hexane, water, and toluene have been adsorbed at about 8.95%, 2.2%, and 1.59%,
respectively, in good agreement with both adsorption data and thermal analysis. As a matter of fact, ZSM-5 zeolite
preferably adsorbs n-hexane, even in presence of a competitor, such as toluene.
Martucci, A., Braschi, I., Bisio, C., Sarti, E., Rodeghero, E., Bagatin, R., Pasti, L. (2015): Influence of water on the retention of
methyl tertiary-butyl ether by high silica ZSM-5 and Y zeolites: a multidisciplinary study on the adsorption from liquid and gas
phase. RSC Adv., 5, 86997-87006.
Pasti, L., Rodeghero, E., Sarti, E., Bosi, V., Cavazzini, A., Bagatin, R., Martucci, A. (2016): Competitive adsorption of VOCs from
binary aqueous mixtures on zeolite ZSM-5. RSC Adv., 6, 54544-54552
High temperature characterization of Y-zeolite loaded with chlorobenzene
No full textDue to their widespread use in many industrial sectors, low solubility in water and their bioaccumulation tendency,
Volatile Organic Compounds (VOCs) are hazardous organic chemicals commonly present in water. Among this class of
pollutants, chlorobenzene (CB) is included as benzene (i.e., BTEX species) halogenated compound. Therefore, due to
its toxic effects on both human health and environmental systems, the removal of CB from water is a primary issue.
Recently, it has been highlighted that organophylic and hydrophobic zeolites are efficient as sorbent materials and
completely regenerable without showing remarkable changes in adsorption capacity and structural properties.
Nowadays, these zeolites features, combined with their high thermal stability, are exploited in regeneration processes
through thermal treatment in order to reuse regenerated zeolites in new adsorption processes (Rodeghero et al., 2016).
Therefore, the aim of the project is to investigate the desorption process of chlorobenzene (purchased by Sigma Aldrich
with a purity of 99.8%) Y (HSZ-390HUA code; 200 SiO2/Al2O3 ratio) system to: 1) determine the desorption
temperature of extraframework content; 2) characterize the structural modifications induced by high temperature
treatment and 3) highlight the temperature effects on the interactions between organic molecules and framework oxygen
atoms. With this purpose, Y-CB sample was prepared and characterized by chromatographic (via Headspace Solid
Phase Microextraction-GC) and thermal (TG and DTA) analysis. Desorption process was constantly monitored, through
synchrotron X-ray powder diffraction, at the high resolution Beamline ID22 (ESRF, Grenoble) from room temperature
to 590°C with a heating rate of 8°C/min. Rietveld refinements showed that chlorobenzene molecules are desorbed at
about 210°C. These results are in good agreement with thermal analysis, which suggest that all the extraframework
(H2O and CB molecules) content is completely released between 190 and 210°C. Hence, the detected desorption
temperature reveals an acceleration of desorption kinetics compared to that reported on a patent previously published
(Vignola et al., 2008). Moreover, structural refinements highlighted that both only slight memory effects in terms of
structural deformations are registered in 12MR channel geometry after regeneration process and the reactivated zeolite
regain the unit-cell parameters of the bare material almost perfectly. Furthermore, any significant crystallinity loss is
observed. Based on these results, the High Silica Y zeolite is potentially reusable in a new adsorption/desorption cycle.
Rodeghero, E., Martucci, A., Cruciani, G., Bagatin, R., Sarti, E., Bosi, V., Pasti, L. (2016): Kinetics and dynamic behaviour of
toluene desorption from ZSM-5 using in situ high-temperature Synchrotron X-ray diffraction and chromatographic techniques.
Catalysis Today, 277, 118-125.
Vignola, R. (2008): WO 2009/000429 A1, Eni S.p.A
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
Potential recovery of metal from plants: a combined XRD-Thermal study on Juncus acuts
No full textIn the Arburese mine district (SW Sardinia, Italy), centuries of mine exploitation addressed to the extraction
of Zn and Pb from sulphides and non-sulphides (calamine) deposits, left a widespread metal pollution. The
Juncus acutus, a halophyte pioneer plant, was able to adapt in this extreme environment and to affect metal
mobility thanks to its capacity to stabilize them in the external roots and rhizosphere.
A method for evaluating the potential of reuse of biomasses for economic purposes is here presented starting
from the specific case study of Juncus acutus. For this purpose, plants and rhizospheres, collected from the
banks of two streams (Rio Naracauli and Rio Irvi) impacted by past mining activity, were used to perform
Thermogravimetry and Differential Thermal analyses combined with X-ray Diffraction (XRD) carried out on
raw samples and on samples heated ex-situ (by a conventional diffractometer) or in-situ (by synchrotron-based
diffraction).
Results showed the presence of mainly quartz, phyllosilicates, and feldspars with minor amounts of
sulphides, sulphates, and Fe, Pb, and Zn carbonates concentrated in the rhizosphere of raw samples. The
mineral phases, Zn and Fe oxides and willemite, detected in internal roots and stems samples after heating,
indicated the presence of metals in the plant tissues. The ex-situ heating was found to be useful in determining
the occurrence of metal-bearing phases in plants especially if combined with thermal analyses in order to
reveal the temperature stages at which the significant reactions occur. Despite the high resolution proper of
a synchrotron light source, the in-situ heating resulted less effective in revealing minor phases in organic
samples, maybe due to the scarcity of oxygen within the sample holder that avoid sulphides oxidation and the
degradation of organic compounds (Fancello et al., 2019).
This method, if further developed, could be a useful tool in different application fields. The recognition
of metals in plant tissues, and the mineralogical form in which they transform after thermal treatment, is
an essential information for phytomining by hyperaccumulator plants. Likewise, biochar production from
vegetal masses would benefit from the knowledge of the mineral assemblage attainable under different thermal
conditions, to find the optimum temperature
Study of adsorption/desorption process of p-HBA into Y zeolite: a model system for water treatment contaminated by humic acids
No full textDue to their biological origin, humic monomers, such as p-hydroxybenzaldehyde (p-HBA), are usually present in
soils and water. Phenolic and aromatic compounds, such as p-HBA, arise from the degradation of natural organic matter
(NOM), which can assume different molecular structures creating natural and synthetic compounds. The removal of
these compounds from water is of increasing interest due to the possibility of negative interference with water
remediation systems. Indeed, they usually assume the role of intermediary or precursor of many hazardous
contaminants. Moreover, when high concentrations are present in water, they become phytotoxic for plants. It has been
highlighted that hydrophobic zeolites are eco-friendly materials, which can be exploited for their adsorption properties
in the removal of contaminants from water bodies and their possibility of regeneration through thermal treatment,
without changing their initial adsorption capacity (Braschi et al., 2016; Wang et al., 2016). Since the presence of natural
organic matter (NOM) can affect organic pollutants adsorption, the effect of lignin-derived phenolic monomers on the
adsorption properties was investigated. The aim of this work is to study the structural modifications induced by
adsorption/desorption process undergoing on a hydrophobic Y zeolite (HSZ-390HUA, SiO2/Al2O3 = 200, Tosoh
Corporation) loaded with p-HBA upon thermal treatment. To obtain this goal, chromatographic, diffractometric and
thermal (TG and DTA) analysis were carried out. Kinetics and adsorption isotherm batch data were obtained via
Headspace Solid Phase Microextraction-GC in order to quantify the amount of p-HBA adsorbed into zeolite channels
system.The desorption process was continuously monitored at the ID22 beamline (ESRF-Grenoble) as a function of
temperature (heating rate 20 °C/min, from room temperature to 600°C) to investigate high-temperature structural
modifications and probe the host-guest interactions. Experimental results confirm that p-HBA is highly adsorbed on
zeolites. Rietveld refinements reveal that the extraframework content is completely desorbed at about 570°C; these
results are in good agreement with the total weight loss registered by thermal analysis. After thermal treatment, zeolite
does not show any significant loss of crystallinity and non-equilibrium distortions in the framework are relaxed.
Moreover, the regenerated zeolites regain almost the same unit-cell parameters of the bare material and no relevant
structural deformations are registered in channel geometry.
Braschi, I., Blasioli, S., Buscaroli, E., Montecchio, D., Martucci, A. (2016): Physicochemical regeneration of high silica zeolite Y
used to clean-up water polluted with sulfonamide antibiotics. J. Environ. Sci., 43, 302-312.
Wang, X., Li, B.Q., Zhai, H.L., Xiong, M.Y., Liu, Y. (2016): An efficient approach to the quantitative analysis of humic acid in
water. Food Chem., 190, 1033-1039
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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