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The fascinating world of mayenite (Ca12Al14O33) and its derivatives
Full text linkMayenite (12CaO·7Al2O3) is a mesoporous calcium aluminum oxide, with a characteristic crystalline structure. The framework of mayenite is composed of interconnected cages with a positive electric charge per unit cell that includes two molecules [Ca24Al28O64]4+, and the remaining two oxide ions O2−, often labelled “free oxygen”, are trapped in the cages defined by the framework. Starting from mayenite structure several derivatives have been prepared through advanced synthetic protocols by free oxygen substitution with various anions. Mayenite and its derivates have been intensively investigated in many applications which include catalysis (oxidation and reduction, ammonia synthesis, pinacol coupling), environmental sensors and CO2 sorbent materials. In this review, we summarize our recent results on the main applications of mayenite and its derivatives. © 2021, The Author(s)
STRATEGIE DI FITORISANAMENTO DI SITI CONTAMINATI DA SOLVENTI CLORURATI MEDIANTE L’IMPIEGO DELLA ZEA MAYS L.
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Phytoremediation performances of a maize cultivar grown on trichloroethylene polluted medium.
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Use of Zea mays L. in phytoremediation of trichloroethylene
No full textTrichloroethylene (TCE) is a chlorinated aliphatic organic compound often detected as pollutant in soils and ground water. “Green technologies” based on phytoremediation were proven to be effective to reclaim organic pollutants (e.g. TCE) and heavy metals from different environmental matrices. In this work, we use Zea mays L. for the removal of high TCE concentrations from medium cultures. In particular, we investigated a sealed bioreactor where the growth medium was contaminated with an increasing amount of TCE, in the range 55–280 mg/L; the removal capability of the maize plants was assessed by means of GC-MS and LC-MS analyses. An accurate mass balance of the system revealed that the plants were able to remove and metabolise TCE with an efficiency up to 20 %, depending on the total amount of TCE delivered in the bioreactor. Morphometric data showed that the growth of Z. mays is not significantly affected by the presence of the pollutant up to a concentration of 280 mg/L, while plants show significant alterations at higher TCE concentrations until the growth is completely inhibited for [TCE] ≃ 2000 mg/L. Finally, the presence of several TCE metabolites, including dichloroacetic and trichloroacetic acids, was detected in the roots and in the aerial part of the plants, revealing that Z. mays follows the green liver metabolic model. These results encourage further studies for the employment of this plant species in phytoremediation processes of soils and waters contaminated by TCE and, potentially, by many other chlorinated solvents
Phytoremediation performances of a maize cultivar grown on trichloroethylene polluted medium
No full textDetermination of the trichloroethylene diffusion coefficient in water
No full textTrichloroethylene (TCE) is a halogenated aliphatic organic compound frequently detected as pollutant in soils and ground water. To study the fate of TCE in water and to devise effective remediation strategies, a series of advection-diffusion (dispersion) models, where the diffusion coefficient of TCE (D-TCE) is an important parameter, have been developed. However, D-TCE in water has never been experimentally determined and only theoretical values ( similar or equal to 1x10-5 cm(2) s(-1) at 25 degrees C) are present in the literature. A new method based on the Taylor dispersion technique, which allows to measure D-TCE in a broad range of temperature and, in principle, in any solvent is presented. At 25 degrees C D-TCE= 8.16 +/- 0.06x10-6 cm(2) s(-1) and the value increases almost linearly with the temperature, while, in the limit of the experimental error, is independent from [TCE] for dilute solutions. From the temperature dependence of D-TCE, it was possible to calculate the specific TCE fitting constant in the well-known Wilke and Chang theoretical relation and the activation energy of the diffusion process through the Arrhenius plot
Enhanced solubility of trichloroethylene (TCE) by a poly-oxyethylene alcohol as green surfactant
No full textIn this paper we tested a commercially available synthetic fatty alcohol ethoxylated surfactant (synperonic 91/5, SYN), known to be a low-impact and biodegradable green surfactant, to improve the aqueous solubility of trichloroethylene (TCE). The alcohol is a non-ionic surfactant that easily forms O/W emulsions and it can emulsify several oils, waxes and solvents and it is also used as a wetting agent in a wide variety of applications, its biocompatibility and biodegradability have been tested in several conditions both in pharmaceutical and environmental fields. We measured the critical micelle concentration of the surfactant by means of the pyrene method; the dissolution of TCE into water solutions at increasing [SYN] was investigated by means of UV–VIS technique and the solubilization performances were evaluated in terms of WSR (Weight Solubilization Ratio) and MSR (Molar Solubilization Ratio). Finally, the dependence of TCE solubility upon temperature variation was also assessed. In the microemulsion regime the solubility of TCE was found to increase up to fifteen times with respect to pure water at 20° C, corresponding to a MSR of about 0.21. The MSR was found to increase at lower temperatures up to 0.24 at 4° C. Synperonic can thus be applied for TCE remediation from soils and groundwaters by taking advantage of techniques such as pump and treat and enhanced surfactant flushing
Integrated techniques for remediation of dense chlorinated solvents polluted sites
Full text link2016 - 2017Trichloroethylene (TCE) is a halogenated aliphatic organic compound frequently detected as pollutant in soils and ground
water.
A multidisciplinary approach is often required to remediate TCE polluted sites and this PhD thesis faces this problem blending together three main topics, namely surfactant co-solvent flushing, phytoremediation and catalytic oxidation, to develop an effective remediation strategy.
First of all we studied the diffusion mechanism of TCE in water to improve the models employed to describe the fate of the pollutant in the groundwater. In particular, we measured for the first time, the diffusion coefficient of TCE in water (8.16 ± 0.06 ×10-6 cm2s-1). Moreover, we tested a commercially available, low-impact and biodegradable green surfactant, namely Synperonic 91/5 (Syn 91/5), to enhance the aqueous solubility of trichloroethylene. The results showed that Syn 91/5 allowed to increase up to 15 times the TCE aqueous solubility. The aim of this part of the work is to improve surfactant co-solvent flushing technology using eco-compatible and low cost surfactants.
In a later stage, we investigated the use of the plant Zea mays L. for the removal of high TCE concentrations from a growing medium, intended to be a laboratory model for soils and water phytoremediation. In previous works, Mays plants were successfully used for the phytoextraction of heavy metals contaminated sites. The idea was to exploit the phytoremediation capability of Z. mays for the remediation of TCE polluted sites. The results showed that in 9 days of exposition, the plant was able to metabolize TCE with an efficiency ranging from 15 to 20 %, depending on the total amount of the pollutant added in the system.
Finally, we investigated a new green material to be used as catalyst for the total oxidation of TCE. Mayenite (C12A7) is a low cost material recently employed as active catalyst for several reactions. In this project we demonstrated that mayenite is able to oxidize TCE with better performances with respect to zeolites and other traditional catalysts. In particular, mayenite promoted the total oxidation of TCE in the temperature range 250-500° C, and the pollutant was converted in less harmful products such as CO2, CO and HCl.. [edited by Author]XXX cicl
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