The mechanism of iron binding processes in erionite fibres

Fibrous erionite-Na from Rome (Oregon, USA) was K-exchanged and characterized from the structural point of view. In addition, the modifications experienced after contact with a Fe(II) source were investigated for evaluating if the large potassium ions, blocking off nearly all the erionite cavity openings, might prevent the Fe(II) binding process, which is currently assumed to be one of the reasons of the toxicity of erionite. The K-exchanged sample had a 95% reduction of the BET surface area indicating that it behaves as a mesoporous material. Exchanged K is segregated at K2 and at OW sites commonly occupied by H2O. The latter K cations provide a relevant contribution to the reduction of the surface area. Surprisingly, despite the collapse of its surface area the sample preserves the tendency to bind Fe(II). Therefore, yet in the case of a peculiar and potentially hostile structural environment the Fe(II) ion-exchange process has essentially the same kinetics observed in a typical erionite sample. This is a clear evidence of the very limited effect of the chemical composition of erionite on the Fe(II) binding process and reasonably it does not play a significant role in its toxicity

Characterizing biochar as alternative sorbent for oil spill remediation

Biochar (BC) was characterized as a new carbonaceous material for the adsorption of toluene from water. The tested BC was produced from pine wood gasification, and its sorption ability was compared with that of more common carbonaceous materials such as activated carbon (AC). Both materials were characterized in terms of textural features and sorption abilities by kinetic and equilibrium tests. AC and BC showed high toluene removal from water. Kinetic tests demonstrated that BC is characterized by faster toluene removal than AC is. Textural features demonstrated that the porosity of AC is double that of BC. Nevertheless, equilibrium tests demonstrated that the sorption ability of BC is comparable with that of AC, so the materials' porosity is not the only parameter that drives toluene adsorption. The specific adsorption ability (mg sorbed m-2 of surface) of the BC is higher than that of AC: toluene is more highly sorbed onto the biochar surface. Biochar is furthermore obtained from biomaterial thermally treated for making energy; this also makes the use of BC economically and environmentally convenient compared with AC, which, as a manufactured material, must be obtained in selected conditions for this type of application. © 2017 The Author(s)

Dalle formule di struttura di Lewis ai concetti di numero di ossidazione, carica formale e carica effettiva di un atomo in una molecola

Riassunto I concetti di elettronegatività assoluta e di durezza assoluta degli atomi liberi, nel loro stato elettronico fondamentale, e il principio di equalizzazione dell’elettronegatività degli atomi nelle molecole, sono qui utilizzati insieme alle formule di struttura di Lewis e al modello di Gillespie (VSEPR) per determinare la probabile geometria molecolare, per una didattica della Chimica generale coerente ed efficace che a partire da una semplice formula analitica, permette di introdurre i concetti di numero di ossidazione, di carica formale e di carica effettiva per ogni atomo in una molecola.Abstract The concepts of absolute electronegativity and absolute hardness of the free atoms, in their electronic ground state, and the principle of the electronegativity equalization for the atoms in molecules, are used together with the Lewis structures and the Gillespie model (VSEPR) for the definition of the molecular geometry, to present in the General chemistry course the concepts of oxidation number, of formal charge and effective charge for the atom in a molecule by means of a simple analytical formula

Enhancing methane production from food waste fermentate using biochar. The added value of electrochemical testing in pre-selecting the most effective type of biochar

Background: Recent studies have suggested that addition of electrically conductive biochar particles is an effective strategy to improve the methanogenic conversion of waste organic substrates, by promoting syntrophic associations between acetogenic and methanogenic organisms based on interspecies electron transfer processes. However, the underlying fundamentals of the process are still largely speculative and, therefore, a priori identification, screening, and even design of suitable biochar materials for a given biotechnological process are not yet possible. Results: Here, three charcoal-like products (i.e., biochars) obtained from the pyrolysis of different lignocellulosic materials, (i.e., wheat bran pellets, coppiced woodlands, and orchard pruning) were tested for their capacity to enhance methane production from a food waste fermentate. In all biochar-supplemented (25 g/L) batch experiments, the complete methanogenic conversion of fermentate volatile fatty acids proceeded at a rate that was up to 5 times higher than that observed in the unamended (or sand-supplemented) controls. Fluorescent in situ hybridization analysis coupled with confocal laser scanning microscopy revealed an intimate association between archaea and bacteria around the biochar particles and provided a clear indication that biochar also shaped the composition of the microbial consortium. Based on the application of a suite of physico-chemical and electrochemical characterization techniques, we demonstrated that the positive effect of biochar is directly related to the electron-donating capacity (EDC) of the material, but is independent of its bulk electrical conductivity and specific surface area. The latter properties were all previously hypothesized to play a major role in the biochar-mediated interspecies electron transfer process in methanogenic consortia. Conclusions: Collectively, these results of this study suggest that for biochar addition in anaerobic digester operation, the screening and identification of the most suitable biochar material should be based on EDC determination, via simple electrochemical tests. © 2017 The Author(s)

Different Erionite Species Bind Iron into the Structure: A Potential Explanation for Fibrous Erionite Toxicity

In this investigation, the crystal chemical characterization of one sample of woolly erionite-K (Lander County, NV, USA) was examined after suspension in a FeCl2 solution, in anaerobic conditions. The aim of this study was to determine the effect of the chemical composition of erionite on its efficiency to bind iron. Inductively coupled plasma (ICP) results showed that the sample bound Fe(II) through an ion-exchange mechanism mainly involving Ca. In addition, chemical and structural data indicated that Fe(II) is fixed at the Ca3 site, six-fold coordinated to water molecules. According to Brunauer–Emmett–Teller (BET) sample surface area the amount of Fe(II) bound by the fibers was comparable with that retrieved for fibrous erionite-Na sample from Rome (OR, USA) for which the ion-exchange process mainly affected Na. This finding provides clear evidence of a strong tendency of Fe(II) to bind to the erionite structure. Furthermore, considering that the woolly erionite-K from Langer County differs markedly from erionite-Na from Rome in the extra-framework cation content, our observations indicate that the Fe binding efficiency is not significantly modulated by the chemical composition. Notably, Fe ion-exchanged and/or accumulated on the fiber surface can generate hydroxyl radicals via the Fenton reaction, thus influencing the potential carcinogenicity of the different erionite species

SiO2 nanoparticles as new repairing treatments toward the Pietraforte sandstone in Florence renaissance buildings

In this work, the consolidation efficiency of SiO2 nanoparticles (synthesized in the Chemistry laboratories at the Tor Vergata University of Roma) was tested on Pietraforte sandstone surfaces belonging to the bell tower of San Lorenzo (Florence, Italy) and was fully investigated. Nanoparticles (synthesized in large-scale mass production) have been characterized by XRD—X-Ray Diffraction; Raman and FTIR—Fourier Transform Infrared spectroscopy; SEM—Scanning Electron Microscopy; while the Pietraforte sandstone morphology was examined by Porosimetry, capillary absorption test, surface hardness test, drilling resistance and tensile strength. The colorimetric measurements were also performed to characterize the optical modification exhibited by Pietraforte sandstones, especially after the SiO2 treatments. Our results show that applying to the Pietraforte, the new consolidating agent based on SiO2 nanoparticles, has several advantages, as they are more resistant to perforation, wear, and abrasion even long range (for long times of exposure and consolidating exercise against Florentine sandstone), compared to the CaCO3 nanoparticles (tested in our previous paper), which instead show excellent performance but only close to their first application. This means that over time, their resistance to drilling decreases, they wear much more easily (compared to SiO2 -treated sandstone), and tend to exhibit quite a significant surface abrasion phenomena. The experimental results highlight that the SiO2 consolidation efficiency on this kind of Florentine Pietraforte sandstone (having low porosity and a specific calcitic texture) seems to be higher in terms of water penetration protection, superficial cohesion forces, and an increase in surface resistance. Comparing the performance of SiO2 nanoparticles with commercial consolidants in solvents such as Estel 1000 (tested here), we demonstrate that: (A) the restorative effects are obtained with a consolidation time over one week, significantly shorter when compared to the times of Estel 1000, exceeding 21 days; (B) SiO2 nanoparticles perform better than Estel 1000 in terms of cohesion forces, also ensuring excellent preservation of the optical and color properties of the parent rock (without altering it after application)

Il nuovo Sistema Internazionale di unità di misura (SI). La nuova definizione della quantità di sostanza e della mole

Il 20 maggio 2019 è entrato in vigore il nuovo Sistema Internazionale di Unità di Misura (SI) nel quale le sette unità di misura fondamentali sono definite per mezzo di sette costanti di natura, con valore numerico fissato. Da un punto di vista pratico le grandezze fisiche fondamentali e le unità di misura sono rimaste le stesse del precedente SI, ma con il nuovo SI è stato realizzato un sistema completamente libero da quantità fisiche basate su artefatti. L’unità di massa, il kilogrammo, non è più basato su un lingotto di una lega platino-iridio conservato presso il Bureau International de Poids et Mesures (BIPM) a Sèvres (Francia). In questa nota riportiamo le definizioni delle sette unità di misura fondamentali e il valore delle costanti di natura che le caratterizzano, con particolare attenzione alla quantità di sostanza (quantità chimica) e alla sua unità di misura, la mole, che sono di importanza fondamentale per la Chimica, alla stesso livello della Tavola Periodica degli elementi.Starting from May 20th, 2019 the new International System of Units (SI) should be in use in all the Nations. In this new SI the seven base quantities are defined by means of seven constants of nature with fixed numerical values. From a practical point of view the base quantities and the base units are the same of the previous SI but in the new SI it is realized a system free from physical units based on artifacts. The mass unit, the kilogram, is no more based on a platinum-iridium ingot maintained at the International Bureau of Weights and Measures (BIPM) in Sèvres (France). In the present contribution we report the definitions of the seven base units and the numerical value of the seven constants of nature by which they are characterized. We devote particular attention to the amount of substance (chemical amount) and to its base unit, the mole, which are of fundamental importance for Chemistry, as well as the Periodic Table of the elements

Nota sul bilanciamento delle reazioni redox in soluzione acquosa

In relazione al metodo di bilanciamento delle reazioni redox in soluzione acquosa, nei manuali universitari di Chimica generale attualmente in commercio, solo alcuni seguono le indicazioni chiare e lineari riportate nei manuali di L. Pauling e di R.J. Gillespie et al. (non più in commercio da diversi anni). La maggioranza dei manuali esaminati (12 su 15) adottano metodologie a nostro parere di dubbio valore didattico che possono confondere sia gli studenti sia i docenti, in modo particolare i docenti delle scuole secondarie di secondo grado che assumono il manuale universitario come testo di riferimento standard.In most of commercial university General Chemistry textbooks (12 out of 15 taken into account) the balancing method of redox reactions in aqueous solution is not according to the correct method described by L. Pauling and R.J. Gillespie et al. in their textbooks no more commercially available. These alternative methods may induce confusion in both students and teachers, in particular chemistry teachers of the secondary school who consider the university textbook as the main point of reference

Characterization by x-ray absorption, x-ray powder diffraction, and magnetic susceptibility of Cu-Zn-Co-Al-containing hydroxycarbonates, oxycarbonates, oxides, and their products of reduction

Copper-zinc-cobalt-aluminium-containing crystalline hydroxycarbonates having hydrotalcite structure have been prepared by coprecipitation. X-ray powder diffraction (XRPD), magnetic susceptibility, and extended X-ray absorption fine structure (EXAFS) indicate that Cu2+, Zn2+, and Co2+ are present in an octahedral environment. Calcination of the hydroxycarbonates at 723 K produces quasi-amorphous oxycarbonates where Cu2+ and Co2+ still retain octahedral coordination and cobalt is almost completely oxidized to Co3+. The coordination of Zn2+, at this stage, is intermediate between the octahedral one of the precursors and the tetrahedral one of ZnO and Zn-based spinels. Further calcination at 973 K produces a mixture of crystalline oxides such as CuO, ZnO, CuAl2O4, ZnAl2O4, and ZnCo2O4. EXAFS analysis of these samples indicates that copper is mainly in a fourfold coordination (although two longer Cu-O distances are also detected), zinc is tetrahedral, and cobalt (as Co3+) is essentially octahedral. EXAFS and XANES investigations performed after in situ reduction (10% H2/N2, at 523 and 623 K) on the oxycarbonates and oxides reveal that the total Cu2+ → Cu0 reduction occurs only at 623 K in both series of samples, Co3+ is reduced to Co2+ only at 623 K in the oxycarbonates, and Zn2+ is never reduced. © 1996 Academic Press, Inc