1,720,995 research outputs found
Bio-char from dead Posidonia oceanica residues as adsorbent towards toxic metal ions
No full textRecently, the pyrolysis of biomass from different algal species and from the Mediterranean sea plant Posidonia oceanica have been proposed for renewable fuel production with a maximum oil yield of 54.97% at 500°C, and high heating values of 24-32 MJ kg−1. The pyrolysis produces a large amount of bio-char and the accumulation of this byproduct may cause solid waste pollution problems. Although the composition and properties of bio-char depend on the raw material and on the carbonization process, it is on average composed of amorphous carbon with a highly functionalized surface, which makes it reactive towards inorganic and organic compounds. Considering the reactivity of bio-char, this pyrolysis by-product could be converted in a high value added material by using it as adsorbent towards toxic metal ions and other organic and inorganic pollutants in decontamination processes. In this context, the bio-char coming from the pyrolysis of local waste biomass (the dead Posidonia oceanica residues) was chemically activated and investigated for potential use as adsorbent of toxic metal ions. The activated and non activated bio-chars were characterized by using different techniques. Then, their
adsorption ability towards several toxic metal ions was studied carrying out several experiments with metal ions solutions at pH = 5, containing NaNO3 or NaCl backgrounds, at different ionic strengths and temperatures. The residual metal concentration in aqueous solutions during the equilibrium experiments was measured by Differential Pulse Anodic Stripping Voltammetry (DP-ASV) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) techniques. Langmuir and Freundlich isotherm equations were used to fit the experimental data
Functionalized Halloysite for enhanced removal of toxic metal ions from aqueous solutions
No full textDuring the last years several nanomaterials have been extensively used in the heavy metal ions removal from aqueous solutions. Among them, clay minerals have gathered particular interest owing to their unique features (e.g., high specific surface area, low toxicity and natural availability at low price). Halloysite nanotubes (Hal) are particular clay minerals with a predominantly hollow tubular structure. In this work Hal and their derivatives, Hal-NH2 and Hal-SH, were used as adsorbent materials of lead(II) and mercury(II) ions from aqueous solutions. The adsorption ability of clay nanomaterials towards toxic metal ions has been studied takeing into account important variables of the metal ion solution (e.g., ionic medium, ionic strength, pH, etc.). The Kinetic and the thermodyamic of the metal adsorption were evaluated by using the Differential Pulse Anodic Stripping Voltammetry (DP-ASV) and the Inductively coupled plasma – optical emission specrtoscopy techniques to check the metal ion concentration in the solutions. Several equilibrium and kinetic equations were used to fit the experimental data. The speciation of metal ion solutions together with the characterization of the adsorbents were considered in order to establish the mechanism of metal ion removal. The collected data showed that the functionalization enhances the adsorption ability of Halloysite and makes the nanoclay mineral a good candidate as adsorbent of toxic metal ion from aqueous solutions
Thermodynamic and kinetic studies on REE ions recovery onto biochar of dead Posidonia oceanica leaves
No full textThe widespread use of rare earth elements (REE) in cutting-edge technologies has led to an increase in their consumption and the urgency of finding sustainable solutions for their recovery.The European Community included REE in the list of critical raw materials, i.e. the list of materials whose recovery is of strategic interest. Adsorption by using materials derived from biomass is considered one of the most promising recovery techniques being cost-effective and in line with the principles of environmental sustainability and of circular economy. In the present contribution are reported the results of the adsorption study of three REE cations, namely La3+, Nd3+ and Dy3+ onto a biochar coming from the pyrolysis of dead Posidonia oceanica (BCP), a marine plant whose leaves accumulate in abundance on the sicilian coast, and onto its chemically activated forms with KOH (BBCP) and with H3PO4 (ABCP). The biochars were characterized through elemental analysis, surface area and average pore size measurements, ATR-FTIR and XRF spectra, and potentiometric measurements for the pHpzc determinations.
At first, single batch adsorption experiments were carried out at different pH values below the pH of formation of low soluble hydrolytic species of REE (~ 6.5). Then, pH = 5.0 was chosen as the best pH in terms of REE recovery and kinetic and isotherm experiments were carried out at I → 0 mol L-1 and T = 298.15 K. The adsorption study of ABCP, the best REE adsorbent among those investigated, was therefore extended to evaluate the effect of ionic medium (NaNO3 0.1 mol L-1).
The recyclability of ABCP adsorbent was also evaluated through column experiments in which HNO3 and EDTA 0.1 mol L-1 were chosen as extractant solutions. Inductively Coupled Plasma Optical Emission Spectroscopy was used to measure the REE concentration in the suspensions
Activated Biochar From Posidonia Oceanica. A New Adsorbent Material of Hydrocarbons from Wastewater
No full textEnvironmental pollution by petroleum derivatives is a very current topic. In particular, low concentration of this kind of pollutants can seriously compromise the life of animals and plants of aquatic ecosystems (Yu, 2017). The current legislation provides that bilgewater, wastewater produced by boats, can be discharged directly into the sea only if the total hydrocarbon concentration not exceds 15 mg L-1. In this work, new activated carbons were tested as adsorbent materials of oil / hydrocarbons from wastewater. Moreover, an instrumental technique able to quickly measure the required low hydrocarbons concentration is also proposed. The new activated carbons were obtained from bio-oil production waste, a biochar produced by pyrolysis of Posidonia oceanica, a marine plant widespread in the Mediterranean sea. The biochar has been characterized and adsorption experiments were carried out with the pristine biochar (not activated) and with two chemically activated biochars (BCB and BCA) by means of acid or alkali treatments. Moreover, a commercial activated carbon (Filtrasorb 400) has been used for comparison purpose. Synthetic bilge waters were prepared following reference standards (MEPC, 2003) containing DMA (distillate marine fuel) and SDS (sodium lauryl sulfate). Batch adsorption isotherms were carried out without ionic medium and at different concentrations of NaCl in order to evaluate the effect of salinity on the adsorption ability of adsorbent materials. The same adsorbents were tested by column experiments. In particular, a bench pilot system was built and breakthrough curves were obtained changing amount of adsorbent material in column, flow rate, initial DMA and surfactant concentrations. Several instrumental techniques (turbidimetry, TOC, HPLC-FLD) have been used to measure surfactant and hydrocarbon concentrations in experimental samples. The batch experimental data were fitted with the most used isotherm models (Langmuir, Freundlich, Sips) and important considerations were made on the breakthrough curves of column experiments
Microplastics as vehicles for toxic metal ions: an adsorption study
Full text linkThe widespread occurrence of plastic waste in aquatic environments and its impact on animals and humans health is a major topic of scientific research worldwide. Plastics and bioplastic polymers dispersed in the environment undergo several degradation processes, resulting in significant changes in their morphological properties and in their very small particle sizes. Of greatest concern to the scientific community is the fact that so-called microplastics (MPs), i.e. polymeric particles with a diameter below 5 mm, enter in the food chain and can accumulate in the tissues and organs of humans and animals. The hazard of MPs is highlighted by its ability to adsorb pollutants from the surrounding aquatic environment, making it a vehicle of toxic substances. In this work we report the adsorption of Pb2+ ions on MPs of polystyrene (PS), of PS functionalized with carboxylic groups (PS-COOH) and of polylactic acid (PLA). The adsorption capacity of MPs toward Pb2+ ions were investigated at different experimental conditions, i.e. in water, in NaNO3 or NaCl 0.1 mol L-1 and with small amounts of the surfactant sodium dodecyl sulfate (SDS). Atomic spectroscopy and voltammetry were used to determine the concentration of Pb2+ ions. Electrochemical impedance spectroscopy (EIS), scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), ξ-potential and FT-IR measurements were performed to evaluate the mechanism of Pb2+ ions adsorption onto MPs. The results show that the adsorption capacities of MPs towards Pb2+ ions vary from a few hundred μg g-1 to a few mg g-1 as function of experimental conditions of aqueous suspensions
A critical approach to the toxic metal ion removal by hazelnut and almond shells
Full text linkThe adsorption capacity of ground hazelnut (HS) and almond (AS) shells towards Pb(II) and Cd(II) has been studied at pH = 5, in NaNO3 and NaCl ionic media, in the ionic strength range 0.05–0.5 mol L−1. Kinetic and equilibrium experiments were carried out by using the Differential Pulse Anodic Stripping Voltammetry technique to check the amount of the metal ion removed by HS and AS materials. Different kinetic and equilibrium equations were used to fit experimental data and a statistical study was done to establish the suitable model for the data fitting. A speciation study of the metal ions in solution was also done in order to evaluate the influence of the ionic medium on the adsorption process. TGA-DSC, FT-IR, and SEM-EDX techniques were used to characterize the adsorbent materials. The mechanism of metal ions adsorption was explained on the basis of the results obtained by the metal ions speciation study and the characterization of materials
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
One-pot synthesis of ZnO nanoparticles supported on halloysite nanotubes for catalytic applications
Full text linkA versatile catalyst based on halloysite and zinc oxide (HNT@ZnO) was prepared, for the first time, starting from ZnO commercial bulk form as Zn precursor source, in a one-pot procedure. This strategy gives the possibility to obtain small ZnO nanoparticles loaded on the HNT surface without the use of inorganic salts which envisage the removal of undesired anions and therefore a calcination process at high temperature. It was found that the presence of halloysite improved the UV–vis spectral absorption ability of ZnO. The hybrid was successful used as photocatalyst for the methylorange and rhodamine B degradation. In addition, after eight consecutive cycles for the methylorange photodegradation, the hybrid did not exhibit significant reduction in its photocatalytic performances confirming its stability. Based on trapping experiments and calculated energy bands we also proposed a photocatalytic mechanism. Furthermore, to evaluate the versatility of the synthetized HNT@ZnO hybrid, we used it as catalyst for biodiesel production from soybean oil, too. Also, in this case, the hybrid showed good catalytic performance and recyclability
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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