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SIMONE POLLASTRI

Ricercatore t.d. art. 24 c. 3 lett. A
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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Pubblicazioni

2024 - Comprehensive study of nanostructured Bi2Te3 thermoelectric materials - insights from synchrotron radiation XRD, XAFS, and XRF techniques [Articolo su rivista]
Imam, N. G.; Elyamny, S.; Aquilanti, G.; Pollastri, S.; Gigli, L.; Kashyout, A. E. B.
abstract

In this contribution, a comprehensive study of nanostructured Bi2Te3 (BT) thermoelectric material was performed using a combination of synchrotron radiation-based techniques such as XAFS, and XRF, along with some other laboratory techniques such as XRD, XPS, FESEM, and HRTEM. This study aims to track the change in morphological, compositional, average and local/electronic structures of Bi2Te3 of two different phases; nanostructure (thin film) and nanopowders (NPs). Bi2Te3 nanomaterial was fabricated as pellets using zone melting process in a one step process, while Bi2Te3 thin film was deposited on sodalime glass substrate using a vacuum thermal evaporation technique. Synchrotron radiation-based Bi LIII-edge fluorescence-mode X-ray absorption fine structure (XAFS) technique was performed to probe locally the electronic and fine structures of BT thin film around the Bi atom, while transmission-mode XAFS was used for BT NPs distributed in the PVP matrix. The structural features of the collected Bi LIII XANES spectra of thin film and powder samples of BT are compared with the simulated XANES spectrum of BT calculated using FDMNES code at 5 Å cluster size. Combining different off-line structural characterization techniques (XRD, FESEM, XPS, and HRTEM), along with those of synchrotron radiation-based techniques (XAFS and XRF) is necessary for complementary and supported average crystal, chemical, morphological and local electronic structural analyses for unveiling the variation between Bi2Te3 in the nanostructure/thin film and nanopowder morphology, and then connecting between the structural features and functions of BT in two different morphologies. After that, we measured the Seebeck coefficient and the power factor values for both the BT nanopowder and thin film.

2024 - Influence of sulfur ions on the glass-forming ability and structure of silicate-phosphate glasses [Articolo su rivista]
Sułowska, J.; Szumera, M.; Berezicka, A.; Olejniczak, Z.; Stępień, J.; Pollastri, S.; Olivi, L.
abstract

2024 - Potentially toxic elements speciation in bottom ashes from a municipal solid waste incinerator: A combined SEM-EDS, µ-XRF and µ-XANES study [Articolo su rivista]
De Matteis, C.; Pollastri, S.; Mantovani, L.; Tribaudino, M.
abstract

Bottom Ashes from Municipal Solid Waste Incinerators and Waste to Energy plants represent an interesting source of secondary raw materials for many applications, like urban mining and inclusion in concrete, and road pavement. However, Bottom Ashes may contain potentially toxic elements, whose actual toxicity depends essentially on their oxidation state and mineralogical environment. For this reason, a representative sample of bottom ashes from Parma Waste to Energy plant has been selected to investigate the chemical speciation of Cr, Ni, Pb, Co, Zn and Cu by means of complementary techniques: Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS), micro X-Ray Fluorescence (µ-XRF) mapping and X-Ray Absorption Near Edge Structure (XANES) measurements by synchrotron radiation. This multi-technique approach allowed to obtain a general image of the mineralogical and chemical environment in which these elements are found. SEM-EDS analyses show the presence of Zn and Pb both in minerals and in glass matrix. Cr has been detected in the form of oxide and in spinel structure (chromite) whereas Co and Cu are found as alloy or metal inclusions. µ-XRF mapping reveals that Cu, Ni and Cr are generally associated to Na, K and Si suggesting their presence in glass matrix. XANES investigations exhibit that Cu has a variable oxidation state that suggesting its presence in the form of oxide, hydroxide, acetate and metal. Zn is mainly found as +II and in a number of different phases (including Zn-carbonates, in agreement with SEM-EDS data). Cr has been found only as +III, with XANES features resembling those of chromite, whereas as +VI was never identified. Ni and Co were found either as metal form and oxides. Pb spectra show a good match with oxides.

2023 - Adsorption and diffusion of selenite on Boda Claystone Formation [Articolo su rivista]
Czompoly, O.; Fabian, M.; Koranyi, T. I.; Nagy, G.; Horvath, Z. E.; Zizak, I.; Pollastri, S.; Aertsens, M.; Osan, J.
abstract

This study provides adsorption and diffusion data of selenite on Boda Claystone Formation (BCF) which is a potential host rock of a deep geological disposal of high-level radioactive waste. The experiments were performed on two diverse core samples: one albitic claystone sample characteristic for the entire BCF and one pyrite containing sample sparsely occurring in BCF. The experiments were carried out under atmospheric conditions. Batch experiments were carried out to study the kinetics of adsorption at a high initial concentration (1.2 × 10−3 M), the adsorption isotherms and reversibility were investigated in the 10−10–10−3 M concentration range. Adsorption onto petrographic thin sections was done to study the elemental distribution on the microscale and the oxidation state of selenium. The maximum of the distribution coefficient was found as Kd ≈ 200 L/kg and a decrease was experienced around 10−6–10−7 M equilibrium concentration, which showed similarities to other argillaceous rocks. Isotopic exchange experiments revealed reversibility of selenite adsorption. Diffusion was studied with through-diffusion and in-diffusion experiments. Using X-ray fluorescence, despite a low initial concentration of 2.3 × 10−5 M in the in-diffusion experiment, a meaningful diffusion profile of selenium could be obtained, from which the selenite apparent diffusion coefficient Dappselenite = (1.5–4.3) × 10−14 m2/s and the selenite rock capacity factor αselenite = 1.4–2.2 were determined. As selenium species are redox sensitive the oxidation state of adsorbed species was studied with X-ray absorption near edge structure spectroscopy on Se–K edge. Adsorbed selenium remained in +IV oxidation state, however reduction was experienced on the pyritic sample.

2023 - Defect Engineering of Ta3N5 Photoanodes: Enhancing Charge Transport and Photoconversion Efficiencies via Ti Doping [Articolo su rivista]
Wagner, L. I.; Sirotti, E.; Brune, O.; Grotzner, G.; Eichhorn, J.; Santra, S.; Munnik, F.; Olivi, L.; Pollastri, S.; Streibel, V.; Sharp, I. D.
abstract

While Ta3N5 shows excellent potential as a semiconductor photoanode for solar water splitting, its performance is hindered by poor charge carrier transport and trapping due to native defects that introduce electronic states deep within its bandgap. Here, it is demonstrated that controlled Ti doping of Ta3N5 can dramatically reduce the concentration of deep-level defects and enhance its photoelectrochemical performance, yielding a sevenfold increase in photocurrent density and a 300 mV cathodic shift in photocurrent onset potential compared to undoped material. Comprehensive characterization reveals that Ti4+ ions substitute Ta5+ lattice sites, thereby introducing compensating acceptor states, reducing the concentrations of deleterious nitrogen vacancies and reducing Ta3+ states, and thereby suppressing trapping and recombination. Owing to the similar ionic radii of Ti4+ and Ta5+, substitutional doping does not introduce lattice strain or significantly affect the underlying electronic structure of the host semiconductor. Furthermore, Ti can be incorporated without increasing the oxygen donor content, thereby enabling the electrical conductivity to be tuned by over seven orders of magnitude. Thus, Ti doping of Ta3N5 provides a powerful basis for precisely engineering its optoelectronic characteristics and to substantially improve its functional characteristics as an advanced photoelectrode for solar fuels applications.

2023 - Hexavalent chromium release over time from a pyrolyzed Cr-bearing tannery sludge [Articolo su rivista]
Ghezzi, L.; Mugnaioli, E.; Perchiazzi, N.; Duce, C.; Pelosi, C.; Zamponi, E.; Pollastri, S.; Campanella, B.; Onor, M.; Abdellatief, M.; Franceschini, F.; Petrini, R.
abstract

Pyrolysis in an inert atmosphere is a widely applied route to convert tannery wastes into reusable materials. In the present study, the Cr(III) conversion into the toxic hexavalent form in the pyrolyzed tannery waste referred to as KEU was investigated. Ageing experiments and leaching tests demonstrated that the Cr(III)–Cr(VI) inter-conversion occurs in the presence of air at ambient temperature, enhanced by wet environmental conditions. Microstructural analysis revealed that the Cr-primary mineral assemblage formed during pyrolysis (Cr-bearing srebrodolskite and Cr-magnetite spinel) destabilized upon spray water cooling in the last stage of the process. In the evolution from the higher to the lower temperature mineralogy, Cr is incorporated into newly formed CrOOH flakes which likely react in air forming extractable Cr(VI) species. This property transforms KEU from an inert waste to a hazardous material when exposed to ordinary ambient conditions.

2023 - In-situ/operando characterization of FeOx-based chemiresistive sensor of acetone vapours by X-ray absorption spectroscopy [Articolo su rivista]
Ivančo, J.; Pollastri, S.; Hofbauerová, M.
abstract

2023 - Insights into the morphological structure of remineralized dentin obtained by synchrotron radiation and micro-PIXE [Articolo su rivista]
Karrari, S. Z.; Afarideh, H.; Kermanshah, H.; Aquilanti, G.; Agha Aligol, D.; Shahidi, Z.; Pollastri, S.; Oliveira de Souza, D.
abstract

This in vitro study has evaluated the effect of OrthoMTA as a commercially available dental bioactive cement on artificial demineralized dentine through indirect pulp capping (IPC), using complementary analysis techniques. The concentration of elements in de/remineralized regions and ions diffusion has been observed using synchrotron radiation X-ray fluorescence (SR-XRF) and micro-proton-induced X-ray emission (µ-PIXE) images, respectively. The model compounds (Ca10(PO4)6(OH)2) and calcium phosphate were compared using X-ray absorption near-edge structure (XANES) measurements on de/remineralized dentin regions. XANES analysis showed that the calcium environment at remineralized dentin has a structure with mixed features between HA and calcium phosphate, showing that effectively OrthoMTA application can recover the Ca species of the original tooth. Our results show that the use of OrthoMTA, in addition to being used in direct pulp capping, can also be used on the surface of artificial demineralized dentin for remineralization of affected dentin which extends its application in IPC procedures.

2023 - Mechanism of complexation of toxic arsenate, selenate, and molybdate with hydrotalcites [Articolo su rivista]
Gomez, M. A.; Ma, X.; Chen, Y.; Wang, S.; Pollastri, S.; Aquilanti, G.; Cui, Y.; Yao, S.; Xiao, T.
abstract

Wastewater from the uranium mining industry contains toxic arsenate (AsO43–), selenate (SeO42–), and molybdate (MoO42–) that can be removed by complexation with MgAlFe(III)CO3SO4 hydrotalcites, yet underlying mechanisms are poorly known. Here, we studied complexation by K–edge Extended X-ray Absorption Fine Structure Spectroscopy, Density Functional Theory, Powder X-ray Diffraction, and Infrared and Raman Spectroscopy. We found that single shell paths with a coordination number of 4 and bond lengths of As–O = 1.69 Å, Se–O = 1.65 Å and Mo–O = 1.76 Å were best fitted for As–MgAlFe, Se–MgAlFe, and Mo–MgAlFe hydrotalcites. We observed a single antisymmetric υ3 band with no splitting at 821 cm−1 for AsO43–, 856 cm−1 for SeO42–, and 852 cm−1 for MoO42–. In all cases, basal (d003) and interlayer (d006) spacings before and after anion adsorption varied by less than 0.1 Å. Therefore, our findings demonstrate that arsenate, selenate, molybdate form outer-sphere-like complexes with MgAlFe hydrotalcite, and that these complexes are surface-bound and not intercalated.

2023 - Mono-, bi- and tri-metallic platinum group metal-free electrocatalysts for hydrogen evolution reaction following a facile synthetic route [Articolo su rivista]
Mirshokraee, Seyed Ariana; Muhyuddin, Mohsin; Orsilli, Jacopo; Berretti, Enrico; Capozzoli, Laura; Lavacchi, Alessandro; Lo Vecchio, Carmelo; Baglio, Vincenzo; Galli, Anna; Zaffora, Andrea; Di Franco, Francesco; Santamaria, Monica; Olivi, Luca; Pollastri, Simone; Santoro, Carlo
abstract

2023 - Quantification and speciation of lead in air particulate matter collected from an urban area in Amman, Jordan [Articolo su rivista]
Sa'Adeh, H.; Chiari, M.; Pollastri, S.; Aquilanti, G.
abstract

Lead (Pb) is a carcinogenic element, and it originates in the atmosphere from various natural and anthropogenic sources. This work aims to provide further insights about the presence of lead in Amman's atmosphere. Air particulate matter (PM) samples were collected in two fractions (PM2.5 and PM10) simultaneously on Teflon filters in an urban area in Amman, Jordan. Elemental quantification and chemical speciation of Pb were performed using particle-induced X-ray emission (PIXE) and X-ray absorption near-edge structure (XANES) techniques, respectively. Elemental quantitative analysis using PIXE showed that Pb concentrations increased during workdays regardless of the aerosol particle size fraction. The average Pb concentration was 2.9 ± 1.7 ng/m3 and 3.9 ± 2.0 ng/m3 in PM2.5 and PM10, respectively. Based on XANES measurements, it was shown that both PM2.5 and PM10 in Amman contain divalent lead (Pb (II)), most likely as PbSO4, PbS and PbO compounds.

2023 - Revealing the Formation Mechanism and Optimizing the Synthesis Conditions of Layered Double Hydroxides for the Oxygen Evolution Reaction [Articolo su rivista]
Chen, Z.; Wang, X.; Han, Z.; Zhang, S.; Pollastri, S.; Fan, Q.; Qu, Z.; Sarker, D.; Scheu, C.; Huang, M.; Colfen, H.
abstract

Layered double hydroxides (LDHs), whose formation is strongly related to OH− concentration, have attracted significant interest in various fields. However, the effect of the real-time change of OH− concentration on LDHs’ formation has not been fully explored due to the unsuitability of the existing synthesis methods for in situ characterization. Here, the deliberately designed combination of NH3 gas diffusion and in situ pH measurement provides a solution to the above problem. The obtained results revealed the formation mechanism and also guided us to synthesize a library of LDHs with the desired attributes in water at room temperature without using any additives. After evaluating their oxygen evolution reaction performance, we found that FeNi-LDH with a Fe/Ni ratio of 25/75 exhibits one of the best performances so far reported.

2023 - Structure Evolution of Ge-Doped CaTiO3 (CTG) at High Pressure: Search for the First 2:4 Locked-Tilt Perovskite by Synchrotron X-ray Diffraction and DFT Calculations [Articolo su rivista]
Ardit, M.; Conte, S.; Belmonte, D.; Menescardi, F.; Pollastri, S.; Cruciani, G.; Dondi, M.
abstract

This research investigates the high-pressure behavior of the Ca(Ti0.95Ge0.05)O3 perovskite, a candidate of the locked-tilt perovskite family (orthorhombic compounds characterized by the absence of changes in the octahedral tilt and volume reduction under pressure controlled solely by isotropic compression). The study combines experimental high-pressure synchrotron diffraction data with density functional theory (DFT) calculations, complemented by the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), to understand the structural evolution of the perovskite under pressure. The results show that CTG undergoes nearly isotropic compression with the same compressibility along all three unit-cell axes (i.e., Ka0 = Kb0 = Kc0, giving a normalized cell distortion factor with pressure dnorm(P) = 1). However, a modest increase in octahedral tilting with pressure is revealed by DFT calculations, qualifying CTG as a new type of GdFeO3-type perovskite that exhibits both isotropic compression and nonlocked tilting. This finding complements two existing types: perovskites with anisotropic compression and tilting changes and those with isotropic compression and locked tilting. The multimethod approach provides valuable insights into the structural evolution of locked-tilt perovskites under high pressure and establishes a protocol for the efficient study of complex high-pressure systems. The results have implications for the design of new functional materials with desirable properties.

2023 - Unexpected silicon localization in calcium carbonate exoskeleton of cultured and fossil coccolithophores [Articolo su rivista]
Bordiga, M.; Lupi, C.; Langer, G.; Gianoncelli, A.; Birarda, G.; Pollastri, S.; Bonanni, V.; Bedolla, D. E.; Vaccari, L.; Gariani, G.; Cerino, F.; Cabrini, M.; Beran, A.; Zuccotti, M.; Fiorentino, G.; Zanoni, M.; Garagna, S.; Cobianchi, M.; Di Giulio, A.
abstract

Coccolithophores, marine calcifying phytoplankton, are important primary producers impacting the global carbon cycle at different timescales. Their biomineral structures, the calcite containing coccoliths, are among the most elaborate hard parts of any organism. Understanding the morphogenesis of coccoliths is not only relevant in the context of coccolithophore eco-physiology but will also inform biomineralization and crystal design research more generally. The recent discovery of a silicon (Si) requirement for crystal shaping in some coccolithophores has opened up a new avenue of biomineralization research. In order to develop a mechanistic understanding of the role of Si, the presence and localization of this chemical element in coccoliths needs to be known. Here, we document for the first time the uneven Si distribution in Helicosphaera carteri coccoliths through three synchrotron-based techniques employing X-ray Fluorescence and Infrared Spectromicroscopy. The enrichment of Si in specific areas of the coccoliths point to a targeted role of this element in the coccolith formation. Our findings mark a key step in biomineralization research because it opens the door for a detailed mechanistic understanding of the role Si plays in shaping coccolith crystals.

2023 - Use of copper carbonate as corrosion inhibitor for carbon steel in post combustion carbon capture [Articolo su rivista]
Skountzos, Epameinondas; Price, Cameron A.; Alsalem, Mustafa M.; Booth, Samuel G.; Pollastri, Simone; Cussen, Serena A.; Parlett, Christopher M. A.; Sedransk Campbell, Kyra L.
abstract

The realisation of post-combustion CO2 capture (PCCC) at industrial scale remains limited; one challenge is the concerns around capital costs and another concern is corrosion of the system itself. Corrosion resistance and mitigation against the amine solvent monoethanolamine (MEA) was studied, using the inhibitor copper (II) carbonate basic (CC). Carbon steel (C1018) was tested in CO2 loaded, 5M aqueous MEA solution, alone and in the presence of CC, to assess the corrosivity of the solution. Immersion testing used mass loss, Fe and Cu ion concentration in solution via ICP-MS, imaging (SEM) and analytical techniques (XRD and EDX) to investigate the effect of corrosion. Generally, the use of CC improved C1018 corrosion resistance relative to C1018 alone. Even at low concentrations (0.9 mM), CC was effective in inhibiting corrosion against CO2 loaded MEA, as the observed corrosion rate was effectively zero and no dissolved Fe was detected in solution. There was no evidence of copper surface adsorption. To clarify the solution chemistry resulting in corrosion inhibition, the local chemical environment of Fe and Cu were probed by Cu and Fe K-edge X-ray Absorption Spectroscopy, respectively. The Cu K- edge HERFD-XANES spectra reveal that a Cu2+ amine complex forms, critical to understanding the structure which is promoting significant corrosion inhibition.

2022 - Characterization of innovative Pt-ceria catalysts for PEMFC by means of ex-situ and operando X-Ray Absorption Spectroscopy [Articolo su rivista]
Pollastri, S.; Bogar, M.; Fiala, R.; Amenitsch, H.; Yakovlev, Y.; Lavacchi, A.; Aquilanti, G.; Matolin, V.
abstract

As the demand for energy is rising, the role of batteries and fuel cells in everyday life is undeniable, but fuel cell systems are still currently not employed worldwide mainly because of their cost, which is due to the large amount of Pt used in catalyst layers. Recently, it was demonstrated that catalysts composed by low Pt loading (around 10 μg/cm2) onto ceria (CeOx) matrix are a promising alternative, showing comparable performances with respect to catalysts made by Pt only. Indeed, a strong metal to support interaction between Pt and ceria has been already observed and exploited for application in direct methanol fuel cells. In this context, the aim of the present study is to investigate the stability of innovative Pt-CeOx anode catalyst deposited on two different supports and characterized by means of X-ray Absorption Spectroscopy (XAS). The XANES ex-situ data collected at the Ce L3-edge highlighted the stability of ceria when directly deposited onto the nano-Gas Diffusion Layer (nGDL) whereas it is particularly unstable when deposited onto the so-called Carbon Ionomer Layer (CIL), where Ce was found irreversibly reduced to Ce3+ upon contact with the air. These behaviors are confirmed also by preliminary test experiments conducted in operando conditions, using a modified fuel cell designed on purpose. In addition, EXAFS data collected ex-situ at the Pt L3-edge evidenced an increase in the fraction of Pt2+ as the overall amount of Pt (or the Pt/Ce ratio) is decreasing, in agreement with existing literature. Our results provide an extended picture about characterization of Pt-CeOx catalyst, focusing on the effects of the hosting support, in order to improve the fabrication of more stable Membrane Electrode Assemblies (MEAs) with low Pt contents to be employed with PEMFCs.

2022 - Comprehensive Analysis of Two H13-Type Starting Materials Used for Laser Cladding and Aerosol Particles Formed in This Process [Articolo su rivista]
Peter, L.; Osan, J.; Kugler, S.; Groma, V.; Pollastri, S.; Nagy, A.
abstract

Laser cladding with H13 steel powders was performed and the related material transformations were studied for the particles emitted during this process. Fractions of various sizes of the aerosol particles formed during the laser cladding were collected on a cascade impactor, while the electromobility and the aerodynamic size of the particles were measured using a scanning mobility particle spectrometer and an aerodynamic particle sizer, respectively. The aerosol particles deposited onto the impactor plates were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy, as well as total-reflection X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Both the concentration and mean oxidation state of the major components were correlated with the aerosol particle size. The ultrafine aerosol particles (with a diameter less than about 100 nm) were predominantly oxidized and formed as the result of an evaporation–oxidation–condensation process sequence. The larger particles (>200 nm in geometric diameter) were primarily the residues of the original metal powder and exhibited a composition change as compared to the as-received metal powder. Correlations between the changes in the concentration ratio of the components were detected and explained.

2022 - Controlling the selectivity of high-surface-area Ru/TiO2 catalysts in CO2 reduction - modifying the reaction properties by Si doping of the support [Articolo su rivista]
Cisneros, S.; Chen, S.; Fauth, C.; Abdel-Mageed, A. M.; Pollastri, S.; Bansmann, J.; Olivi, L.; Aquilanti, G.; Atia, H.; Rabeah, J.; Parlinska-Wojtan, M.; Bruckner, A.; Behm, R. J.
abstract

The influence of Si doping of high specific-surface-area Ru/TiO2 catalysts with similar structural properties on the CO2 reduction reaction was systematically investigated by kinetic measurements, combined with microscopic and spectroscopic methods for ex situ and in situ /operando catalyst characterization. While for undoped Ru/TiO2 a high-temperature treatment (350 °C) in reaction atmosphere results in a pronounced change of the selectivity from methanation to CO formation via the reverse water-gas shift (RWGS) reaction, CH4 formation is stabilized by Si doping of the catalyst support. For doping levels around 8 wt%, almost 100% CH4 selectivity is maintained. Comprehensive catalyst characterization is employed to identify trends in the physical and chemical properties with increasing Si doping and thus physical reasons responsible for the distinct differences in catalyst performance and stability. This work opens a route for improving the stability and selectivity of Ru/TiO2 catalysts in the CO2 hydrogenation reaction, a highly relevant application.

2022 - Heavy metals concentrations and speciation of Pb and Ni in airborne particulate matter over two residential sites in Greater Cairo - reflection from synchrotron radiation [Articolo su rivista]
Monged, M. H. E.; Imam, N. G.; Aquilanti, G.; Pollastri, S.; Rashad, A. M.; Osan, J.
abstract

Synchrotron radiation-based techniques [X-ray absorption near-edge structure (XANES) and X-ray fluorescence (XRF)] combined with inductively coupled plasma-mass spectrometry (ICP-MS) were used for the assessment of heavy metals concentrations as well as lead (Pb) and nickel (Ni) speciation in airborne particulate matter (PM10) over two residential sites in Greater Cairo. Nineteen 24 h high-volume samples collected at Giza (G) Square and Helwan (H) University (Egypt) were selected for this study. Mean concentrations of heavy metals in PM10 at both sites were found to have the same descending order of Pb > Cu > Ni > Cd > Co > As, of which concentrations of Pb, Cu, Ni and Cd in H samples were higher than those in G samples. For Pb, synchrotron-based XRF results were in good agreement with concentrations obtained by ICP-MS. The XANES spectra of PM10 at the Pb L 2-edge and Ni K-edge were compared with those of Pb and Ni in model standard compounds to provide information on the potential oxidation states as well as the chemical forms of those elements. The data show that Pb has similar chemical environments in both series G and H with the predominance of Pb2+oxidation state. Nickel was found as Ni(OH)2, NiO and Ni metal in the analyzed samples. However, the content of Ni in the background filter shows a very strong interference with that of the collected PM10. Carcinogenic and non-carcinogenic risks resulting from the inhalation of the studied heavy metals were assessed for children and adult residents and were found below the safe limits, at both sites.

2022 - Insight into the interdependence of Ni and Al in bifunctional Ni/ZSM-5 catalysts at the nanoscale [Articolo su rivista]
Vu, H. -T.; Arcon, I.; De Souza, D. O.; Pollastri, S.; Drazic, G.; Volavsek, J.; Mali, G.; Zabukovec Logar, N.; Novak Tusar, N.
abstract

Catalyst design is crucial for improving catalytic activity and product selectivity. In a bifunctional Ni/ZSM-5 zeolite type catalyst, catalytic properties are usually tuned via varying Al and Ni contents. While changes in acid properties associated with Al sites are usually closely investigated, Ni phases, however, receive inadequate attention. Herein, we present a systematic structural study of Ni in the Ni/ZSM-5 materials by using Ni K-edge XANES and EXAFS analyses, complemented by XRD and TEM, to resolve the changes in the local environment of Ni species induced by the different Al contents of the parent ZSM-5 prepared by a “green”, template free technique. Ni species in Ni/ZSM-5 exist as NiO crystals (3-50 nm) and as charge compensating Ni2+ cations. The Ni K-edge XANES and EXAFS results enabled the quantification of Ni-containing species. At a low Al to Si ratio (nAl/nSi ≤ 0.04), the NiO nanoparticles predominate in the samples and account for over 65% of Ni phases. However, NiO is outnumbered by Ni2+ cations attached to the zeolite framework in ZSM-5 with a high Al to Si ratio (nAl/nSi = 0.05) due to a higher number of framework negative charges imparted by Al. The obtained results show that the number of highly reducible and active NiO crystals is strongly correlated with the framework Al sites present in ZSM-5 zeolites, which depend greatly on the synthesis conditions. Therefore, this kind of study is beneficial for any further investigation of the catalytic activities of Ni/ZSM-5 and other metal-modified bifunctional catalysts.

2022 - Low temperature epitaxy of in situ Ga doped Si1-xGex: dopant incorporation, structural and electrical properties [Relazione in Atti di Convegno]
Rengo, G.; Porret, C.; Hikavyy, A.; Coenen, G.; Ayyad, M.; Morris, R. J. H.; Pollastri, S.; De Souza, D. O.; Grandjean, D.; Loo, R.; Vantomme, A.
abstract

The effect of the growth temperature and the Ga precursor flow on the epitaxy of Si1-xGex:Ga is studied. These parameters are found to have a significant impact on the Ga surface segregation behavior. In particular, Ga in situ doping impacts the growth rate of the epilayer, the Si1-xGex alloy composition, and the onset of strain relaxation. The growth temperature can be used to modulate the Ga segregation, enabling the deposition of materials with enhanced dopant concentrations and improved electrical properties. The Ga local atomic environment was studied in both a Si0.4Ge0.6:Ga and a Ge:Ga sample by X-ray absorption fine structure. The local environment of the Ga determined confirmed that the majority of dopants occupy a substitutional position within the lattice.

2022 - Photoluminescence intensity of Cu-doped ZnO modulated via defect occupancy by applying electric bias [Articolo su rivista]
Ho, L. -P.; Younas, M.; Borgersen, J.; Khan, R. T. A.; Rezvani, S. J.; Pollastri, S.; Akhtar, M. J.; Nadeem, M.; Huang, D.; Shi, Y. -L.; Kuznetsov, A.; Ling, F. C. -C.
abstract

Discovering multifunctional materials is of paramount importance for advancing the science and technology. Herein, we report on an optical phenomenon modulated by an electrical process that happened at the metal-ZnO:Cu junction, for which the light emission intensity from the photoluminescence is tuned reversibly by applying electric bias to the junction. Importantly, these observations were correlated with the x-ray absorption measurements, detecting prominent flips in Cu+/Cu2+ oxidation state occupations in ZnO:Cu film as a function of the resistive switching. Moreover, further analysis of the x-ray absorption data revealed an additional prominent correlation - the signals interpreted as the Zn-O bond fingerprints also exhibited the modulations. By considering the whole set of data, we propose a scenario explaining the modulation phenomena.

2022 - Solubilization and coordination of the HgCl2 molecule in water, methanol, acetone, and acetonitrile: an X-ray absorption investigation [Articolo su rivista]
Busato, M.; Fazio, G.; Tavani, F.; Pollastri, S.; D'Angelo, P.
abstract

X-ray absorption spectroscopy (XAS) has been employed to carry out structural characterization of the local environment around mercury after the dissolution of the HgCl2 molecule. A combined EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) data analysis has been performed on the Hg L3-edge absorption spectra recorded on 0.1 M HgCl2 solutions in water, methanol (MeOH), acetone and acetonitrile. The Hg-Cl distance determined by EXAFS (2.29(2)-2.31(2) Å) is always comparable to that found in the HgCl2 crystal (2.31(2) Å), demonstrating that the HgCl2 molecule dissolves in these solvents without dissociating. A small sensitivity of EXAFS to the solvent molecules interacting with HgCl2 has been detected and indicates a high degree of configurational disorder associated with this contribution. XANES data analysis, which is less affected by the disorder, was therefore carried out for the first time on these systems to shed light into the still elusive structural arrangement of the solvent molecules around HgCl2. The obtained results show that, in aqueous and MeOH solutions, the XANES data are compatible with three solvent molecules arranged around the HgCl2 unit to form a trigonal bipyramidal structure. The determination of the three-body Cl-Hg-Cl distribution shows a certain degree of uncertainty around the average 180° bond angle value, suggesting that the HgCl2 molecule probably vibrates in the solution around a linear configuration.

2022 - Thermal Decomposition Pathways of ZnxFe3- xO4Nanoparticles in Different Atmospheres [Articolo su rivista]
Kuciakowski, J.; Stepien, J.; Zukrowski, J.; Lachowicz, D.; Zywczak, A.; Gajewska, M.; Przybylski, M.; Pollastri, S.; Olivi, L.; Sikora, M.; Kmita, A.
abstract

This article shows how initial composition and thermal treatment of nonstoichiometric zinc ferrite nanoparticles (nZFN) can be chosen to adjust the structure and cation distribution and enhance magnetism in the resulting nanoscale material. It also provides insight into new prospects regarding the production and design of nanoscale materials. Investigations were conducted before and after heating of nZFN in an inert atmosphere and a vacuum up to temperature of 1170 °C. Annealing leads to partial reduction of Fe ions, enhanced magnetism, and an increase in the size of the particles independent of the atmosphere. Use of the inert atmosphere delivers a solid solution of magnetite and zinc ferrite with a reduced Zn content in the structure as a result of sublimation of newly formed ZnO and reduction of Fe, and it favors crystallization. A preference for normal-spinel phase and enhancement of magnetic saturation from 20 Am2/kg up to 101 Am2/kg was observed. Vacuum annealing with high probability produces ZnO, Fe3O4, and Fe2O3 multiphase system with signs of amorphization, mainly on the surface. A large fraction of Fe ions is reduced and the volume ratio of Fe3O4 to Fe2O3 increases with heating time. The final solid product from a complete decomposition of ZFN is magnetite.

2022 - Unraveling the low-temperature activity of Rh-CeO2 catalysts in CO oxidation: probing the local structure and Red-Ox transformation of Rh3+ species [Articolo su rivista]
Fedorova, E. A.; Kardash, T. Y.; Kibis, L. S.; Stonkus, O. A.; Slavinskaya, E. M.; Svetlichnyi, V. A.; Pollastri, S.; Boronin, A. I.
abstract

The local structure of the active sites is one of the key aspects of establishing the nature of the catalytic activity of the systems. In this work, a detailed structural investigation of the Rh-CeO2 catalysts prepared by the co-precipitation method was carried out. The application of a variety of physicochemical methods such as XRD, Raman spectroscopy, XPS, TEM, TPR-H2, and XAS revealed the presence of highly dispersed Rh3+ species in the catalysts: Rh3+ single ions and RhOx clusters. The substitution of Ce4+ ions by Rh3+ species, which provided a strong distortion of the CeO2 lattice, is shown. XAS data ensured the refinement of the Rh local structure. It was shown that single Rh3+ sites located next to each other can merge the formation of RhOx clusters with Rh local environment close to the one in Rh2O3 and CeRh2O5 oxides. The distortion of the CeO2 lattice around single and cluster rhodium species had a beneficial effect on the catalytic activity of the samples in low-temperature CO oxidation (LTO-CO). TEM, XAS, and in situ XRD data allowed establishing the structural transformations of the catalysts under Red-Ox treatments. The reduction treatment led to Rhn metallic cluster formation localized on defects of the reduced CeO2−δ. The reduced sample demonstrated efficient CO conversion at 0 °C. However, this system was not stable: its contact with air led to ceria reoxidation and partial reoxidation of Rh to highly dispersed Rh3+ species at room temperature, while heating in an oxidizing atmosphere resulted in the complete reoxidation of metallic rhodium species. The results of the work shed light on the structural aspects of the reversibility of the Rh-CeO2 catalysts based on the highly dispersed Rh3+ species under treatment in the reaction conditions.

2022 - Unraveling the nature of sulfur-bearing silicate-phosphate glasses: Insights from multi-spectroscopic (Raman, MIR, 29Si, 31P MAS-NMR, XAS, XANES) investigation [Articolo su rivista]
Berezicka, A.; Szumera, M.; Sulowska, J.; Jelen, P.; Olejniczak, Z.; Stepien, J.; Zajac, M.; Pollastri, S.; Olivi, L.
abstract

Herein, we investigate silicate-phosphate glasses from the SiO2–P2O5–K2O–MgO–SO3 system enriched with various amounts of sulfur, as a nutrient indispensable for the proper development of plants, in order to gain a profound understanding of the structure of such materials. An inherent capability of glasses from the studied system to incorporate sulfate groups into the vitreous matrix was discussed on the basics of the results from XRF, XRD and internal Al2O3 standard techniques. It has been found, that as much as 3 mol.% of SO3 can be loaded into the glass batches to obtain fully amorphous material, while beyond this limit K2SO4 crystallizes within the matrix. Comprehensive spectroscopic investigation, comprising Raman, Middle Infrared (MIR), 29Si and 31P MAS-NMR, X-ray absorption spectroscopy (XANES and XAS) techniques, has been implemented in order to determine an impact of sulfur on silicate-phosphate glass framework. On this basics, it has been concluded, that sulfur exists in the vitreous matrix in the form of specific domains, in which [SO4]2- anions are surrounded by the shell of charge-compensating K+ cations. Such sulfate groupings maintain their individuality without direct bonding to silico-oxygen or phospho-oxygen subnetwork. Spectroscopic results revealed also, that the presence of sulfur affects silico-oxygen subnetwork to a significantly greater extent than the phospho-oxygen one. It has been demonstrated, that along with SO3 addition, the more polymerized QSi3 units increase in abundance at the expense of less polymerized QSi2 groups. Results of the present study are believed to contribute to a greater understanding of the nature of sulfur-bearing oxide glasses.

2021 - A multidisciplinary study unveils the nature of a Roman ink of the I century AD [Articolo su rivista]
Sibilia, M.; Stani, C.; Gigli, L.; Pollastri, S.; Migliori, A.; D'Amico, F.; Schmid, C.; Licen, S.; Crosera, M.; Adami, G.; Barbieri, P.; Plaisier, J. R.; Aquilanti, G.; Vaccari, L.; Buson, S.; Gonzato, F.
abstract

A multi-instrumental approach combining highly sensitive Synchrotron Radiation-based techniques was used to provide information on the real composition of a dry black ink powder found in a bronze inkwell of the first century AD. The presence of Pb, Cu and Fe in the powder, revealed by XRF and ICP-OES data, leads to raise several hypotheses on their origin. The inkpot and its lid were also investigated by Hand-Held XRF, revealing a bronze alloy (Cu-Sn) with a certain amount of Fe and Pb. The lid was found to be particularly enriched in lead. XRPD, XAS and FTIR measurements showed a substantial presence of silicates and common clay minerals in the ink along with cerussite and malachite, Pb and Cu bearing-carbonates, respectively. These evidences support the hypothesis of an important contamination of the ink sample by the burial environment (soil) and the presence of degradation products of the bronze inkpot. The combined use of IR, Raman, and GC-MS evidenced that the black ink is mainly composed of amorphous carbon deriving from the combustion of organic material mixed with a natural binding agent, Arabic gum.

2021 - Associating High Oxide-Ion Conductivity and Conduction Mechanisms with Local Atomic Environments in Na0.5Bi0.5- xTi1- yMgyO3-δ [Articolo su rivista]
Santhoshkumar, B.; Priolkar, K. R.; Pollastri, S.; Oliveira De Souza, D.; Carlomagno, I.; Bera, A. K.; Yusuf, S. M.; Pahari, B.
abstract

Oxide-ion conductors are of high interest in electrochemical devices such as solid-oxide fuel cells, oxygen sensors, and separation membranes. In this paper, high oxide-ion conductivity and associated ion conduction mechanism in perovskite-type oxides Na0.5Bi0.5-xTi1-yMgyO3-1.5x-y (for x = 0.0 and y = 0.0, x = 0.01 and y = 0.02, x = 0.01 and y = 0.04) are investigated systematically. Na0.5Bi0.5TiO3 ceramic is a poor conductor, whereas Na0.5Bi0.49Ti0.98Mg0.02O2.965 and Na0.5Bi0.49Ti0.96Mg0.04O2.945 ceramics are excellent oxide-ion conductors at 500 °C. While the Rietveld refinements of powder X-ray diffraction data using the monoclinic Cc space group and the rhombohedral R3c space group showed reasonably similar quality of fits, extended X-ray absorption fine structure (EXAFS) data could be fitted only with the monoclinic Cc structure at room temperature for all three ceramics. Extensive EXAFS investigations have also been used to probe the local environments of Bi and Ti atoms directly and reveal the ordering of Bi3+/Na+, displacements of the cations, oxygen-vacancy generation, and their migration pathways. Our EXAFS results demonstrate Bi- and Na-rich planes formation due to short-range ordering of Bi3+/Na+ in the perovskite units. Oxygen vacancies were found to be located in the Bi-rich planes. 23Na magic-angle spinning NMR experiments indicate that the local environments of Na atoms are disordered. The present work also provides an insight into the dramatically improved conducting behavior of Na0.5Bi0.49Ti0.98Mg0.02O2.965 and Na0.5Bi0.49Ti0.96Mg0.04O2.945 ceramics in terms of the local, long-range, and microstructure, which can be exploited to develop design principles for the syntheses of related oxides with even improved properties.

2021 - Cement-stabilized contaminated soil: Understanding Pb retention with XANES and Raman spectroscopy [Articolo su rivista]
Contessi, S.; Dalconi, M. C.; Pollastri, S.; Calgaro, L.; Meneghini, C.; Ferrari, G.; Marcomini, A.; Artioli, G.
abstract

Cement-based stabilization is a widespread technique used for the treatment of contaminated soils. Despite its established application, the mechanisms involved in the stabilization of contaminants are not fully understood yet. This work aims to elucidate the fate of a real Pb contaminated soil amended with different binders, by studying Pb local environment prior and after the stabilization process. The study of a complex historically contaminated soil was coupled with the investigation of simplified artificial systems, developed to model Pb local structure in the unknown newly formed hybrid systems of soil and binders. The use of synchrotron-based element-specific X-ray absorption spectroscopy (XAS) permitted to probe the actual transformation of Pb environment in the real contaminated soil after the stabilization process. With the support of the model systems, we can propose as the main mechanism involved in Pb retention in sulfated soil treated with cement, the incorporation and/or adsorption of Pb on calcium silicate hydrates and ettringite.

2021 - Characterization of the ultrafine and fine particles formed during laser cladding with the Inconel 718 metal powder by means of X-ray spectroscopic techniques [Articolo su rivista]
Kugler, S.; Nagy, A.; Osan, J.; Peter, L.; Groma, V.; Pollastri, S.; Czitrovszky, A.
abstract

Additive manufacturing is a rapidly growing industrial technology. Still, there is a lack of knowledge regarding the fine particle emission and new particle formation during the processes and their consequences on the performance of the operation and the operator's health as well. Therefore, we studied the properties of the emitted particles during the 3D printing process using the Inconel 718 (Ni-based) superalloy. The number and the mass concentrations were measured with a Scanning Mobility Particle Counter and Sizer. Size-fractionated samples were collected by a cascade impactor, and the elemental composition of the particles was determined by total-reflection X-ray fluorescence analysis, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and microscopic X-ray fluorescence analysis in the different size fractions. The oxidation states of the metals (Cr, Mn, Fe, Ni) in the samples were determined with the X-ray absorption near-edge structure (XANES) method. Most of the particles were found in the ultrafine region with a size below 100 nm, and the mass size distribution had the maximum at 85 nm. In the original powder, Ni was dominating with appr. 52 wt%, and the proportion of Cr was around 20 wt%, and Mn was below 1 wt%. In the released particles, the Ni content decreased to appr. 26 wt%, the Cr content increased to appr. 47 wt% and Mn increased to around 10 wt% for particles with a size between 0.07 and 10 μm. According to the XANES results, Cr, Mn and Fe were found to be oxidized significantly, whereas Ni remained in the metallic form in the total emitted aerosol containing mostly ultrafine particles. The enrichment and oxidation of metals were correlated with each other.

2021 - Characterization of unique aerosol pollution episodes in urban areas using TXRF and TXRF-XANES [Articolo su rivista]
Czompoly, O.; Borcsok, E.; Groma, V.; Pollastri, S.; Osan, J.
abstract

Identifying sources of unique, short-time aerosol pollution episodes in urban areas is a difficult task since they could last only for a couple of hours. With the combination of size-fractioned sampling with May-type cascade impactor and total-reflection X-ray fluorescence (TXRF) in addition to X-ray absorption near-edge structure spectroscopy various sources could be identified in samples collected in Budapest (Hungary) and Cassino (Italy). Using short-time (1–4 h), size-fractionated (70 nm up to 10 μm into 7 stages) sampling method, TXRF is capable of detecting transition metals in the order of 0.1 ng/m3. The present study discusses pollution episodes with Cu and Br concentrations in the range of 1–40 ng/m3. The contribution of both exhaust and non-exhaust type traffic-related emission sources were found to be dominant in the Cu species. Wear products of brake system were identified in coarse particles in addition to resuspension of roadside dust. The ratio of organic/inorganic Br could be determined for a pollution episode with elevated Br concentration.

2021 - Copper Oxide Nanomaterial Fate in Plant Tissue: Nanoscale Impacts on Reproductive Tissues [Articolo su rivista]
Marmiroli, M.; Pagano, L.; Rossi, R.; De La Torre-Roche, R.; Lepore, G. O.; Ruotolo, R.; Gariani, G.; Bonanni, V.; Pollastri, S.; Puri, A.; Gianoncelli, A.; Aquilanti, G.; D'Acapito, F.; White, J. C.; Marmiroli, N.
abstract

A thorough understanding of the implications of chronic low-dose exposure to engineered nanomaterials through the food chain is lacking. The present study aimed to characterize such a response in Cucurbita pepo L. (zucchini) upon exposure to a potential nanoscale fertilizer: copper oxide (CuO) nanoparticles. Zucchini was grown in soil amended with nano-CuO, bulk CuO (100 mg Kg-1), and CuSO4 (320 mg Kg-1) from germination to flowering (60 days). Nano-CuO treatment had no impact on plant morphology or growth nor pollen formation and viability. The uptake of Cu was comparable in the plant tissues under all treatments. RNA-seq analyses on vegetative and reproductive tissues highlighted common and nanoscale-specific components of the response. Mitochondrial and chloroplast functions were uniquely modulated in response to nanomaterial exposure as compared with conventional bulk and salt forms. X-ray absorption spectroscopy showed that the Cu local structure changed upon nano-CuO internalization, suggesting potential nanoparticle biotransformation within the plant tissues. These findings demonstrate the potential positive physiological, cellular, and molecular response related to nano-CuO application as a plant fertilizer, highlighting the differential mechanisms involved in the exposure to Cu in nanoscale, bulk, or salt forms. Nano-CuO uniquely stimulates plant response in a way that can minimize agrochemical inputs to the environment and therefore could be an important strategy in nanoenabled agriculture.

2021 - Effect of germanium incorporation on the electrochemical performance of electrospun Fe2O3 nanofibers-based anodes in sodium-ion batteries [Articolo su rivista]
Petrovicova, B.; Ferrara, C.; Brugnetti, G.; Ritter, C.; Fracchia, M.; Ghigna, P.; Pollastri, S.; Triolo, C.; Spadaro, L.; Ruffo, R.; Santangelo, S.
abstract

Fe2O3 and Fe2O3:Ge nanofibers (NFs) were prepared via electrospinning and thoroughly characterized via several techniques in order to investigate the effects produced by germanium incorporation in the nanostructure and crystalline phase of the oxide. The results indicate that reference Fe2O3 NFs consist of interconnected hematite grains, whereas in Fe2O3:Ge NFs, constituted by finer and elongated nanostructures developing mainly along their axis, an amorphous component coexists with the dominant α-Fe2O3 and γ-Fe2O3 phases. Ge4+ ions, mostly dispersed as dopant impurities, are accommodated in the tetrahedral sites of the maghemite lattice and probably in the defective hematite surface sites. When tested as anode active material for sodium ion batteries, Fe2O3:Ge NFs show good specific capacity (320 mAh g-1 at 50 mA g-1) and excellent rate capability (still delivering 140 mAh g-1 at 2 A g-1). This behavior derives from the synergistic combination of the nanostructured morphology, the electronic transport properties of the complex material, and the pseudo-capacitive nature of the charge storage mechanism.

2021 - Large scale synthesis of copper nickel alloy nanoparticles with reduced compressibility using arc thermal plasma process [Articolo su rivista]
Das, S. K.; Das, A.; Gaboardi, M.; Pollastri, S.; Dhamale, G. D.; Balasubramanian, C.; Joseph, B.
abstract

Among the various methods employed in the synthesis of nanostructures, those involving high operating temperature and sharp thermal gradients often lead to the establishment of new exotic properties. Herein, we report on the formation of Cu-Ni metallic alloy nanoparticles with greatly enhanced stiffness achieved through direct-current transferred arc-thermal plasma assisted vapour-phase condensation. High pressure synchrotron X-ray powder diffraction (XRPD) at ambient temperature as well as XRPD in the temperature range 180 to 920 K, show that the thermal arc-plasma route resulted in alloy nanoparticles with much enhanced bulk modulus compared to their bulk counterparts. Such a behaviour may find an explanation in the sudden quenching assisted by the retention of a large amount of local strain due to alloying, combined with the perfect miscibility of the elemental components during the thermal plasma synthesis process.

2021 - Local structural evolution in the anionic solid solution ZnSex S1-x [Articolo su rivista]
Dan, T.; Mohanty, A.; Dutta, A.; Varma, R. M.; Sarkar, S.; Di Marco, I.; Eriksson, O.; Welter, E.; Pollastri, S.; Olivi, L.; Priolkar, K. R.; Sarma, D. D.
abstract

The century-old Vegard's law has been remarkably accurate in describing the evolution of the lattice parameters of almost all solid solutions. Contractions or expansions of lattice parameters of such systems depend on the size of the guest atom being smaller or larger than the host atom it replaces to form the solid solution. This has given rise to the concept of "chemical pressure"in analogy to the physical pressure. We have investigated using EXAFS the evolution of the local structure in terms of atom-pair distances extending up to the third-nearest neighbors in the family of compounds, ZnSexS1-x as an example of an anionic solid solution, in contrast to all previous studies focusing on cationic solid solutions. Our results establish several common features between these two types of solid solutions, while strongly suggesting that the concept of a chemical pressure is inaccurate and misleading. Most interestingly, we also find a qualitative difference between the cationic solid solutions, reported earlier, and the anionic solid solution.

2021 - Solubilization properties and structural characterization of dissociated HgO and HgCl2 in deep eutectic solvents [Articolo su rivista]
Migliorati, V.; Fazio, G.; Pollastri, S.; Gentili, A.; Tomai, P.; Tavani, F.; D'Angelo, P.
abstract

A synergic approach combining X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies together with quantum mechanical (QM) calculations on cluster models has been used to investigate the solvation properties of the HgCl2 salt and of HgO dissolved in deep eutectic solvents (DESs). Choline chloride (ChCl)-based DESs were prepared using different hydrogen bond donors, namely 1:2 mixtures of ChCl and either urea, acetylsalicylic acid (ASA) or sesamol (SES) and a 1:1 mixture of ChCl and pyrogallol (PYR). The XANES results show that both HgCl2 and HgO molecules are completely dissociated in all the investigated DESs and the Hg2+ first coordination shell is composed only of Cl− anions in all the systems, with a local structure of Cl− ligands around the Hg2+ ion that is the same independently of the DES solvent and of the nature of the dissolved species. By applying a deconvolution procedure on the Hg L3-edge raw XANES experimental data and carrying out fitting procedures of the deconvolved XANES data using different coordination models for the Cl− anions surrounding Hg2+, we were able to unambigously determine the coordination number and the geometry of the Hg2+ first shell complex, namely a [HgCl4]2− tetrahedral coordination model. The analysis of the EXAFS spectra of HgCl2 salt in ChCl-Urea, ChCl-ASA, ChCl-SES and ChCl-PYR and of HgO dissolved in ChCl-ASA allowed us to obtain a very accurate determination of the Hg[sbnd]Cl first shell average distance (2.47–2.48 Å), in agreement with the XANES determinations. Moreover, ab initio calculations of different [HgCln](2−n)+ clusters carried out both in vacuum and simulating bulk solvent effects by means of the SMD solvation model strongly support the experimental findings that, in DESs, Hg2+ forms a complex with four chloride ions arranged in a tetrahedral geometry. The Cl− ion is thus shown to form such strong interactions with Hg2+ that none of the DES hydrogen bond donors is able to compete with it and act as a ligand for Hg2+. The strong solvation ability of the Cl− anions towards metal ions can be at the origin of the high solubility of metal oxides in chloride-based DESs, which is crucial in several important processes such as metal winning, corrosion remediation and catalyst preparation.

2021 - Structural defects responsible for the strain glassy transition in Ni50+x Ti50-x [Articolo su rivista]
Nevgi, R.; Pollastri, S.; Aquilanti, G.; Priolkar, K. R.
abstract

The strain glassy phase is produced by doping a small percentage of impurity in a martensitic alloy. Its ground state is conceived to consist of martensitic nanodomains spatially separated from each other by a defect phase. The present study, by probing the local structure around the Ni and Ti in martensitic and strain glassy compositions of Ni50+xTi50-x, identifies the defect phase that is responsible for inhibiting the long range ordering of the elastic strain vector leading to the formation of the strain glassy phase.

2021 - The Missing Piece: The Structure of the Ti3C2TxMXene and Its Behavior as Negative Electrode in Sodium Ion Batteries [Articolo su rivista]
Ferrara, C.; Gentile, A.; Marchionna, S.; Quinzeni, I.; Fracchia, M.; Ghigna, P.; Pollastri, S.; Ritter, C.; Vanacore, G. M.; Ruffo, R.
abstract

The most common MXene composition Ti3C2Tx (T = F, O) shows outstanding stability as anode for sodium ion batteries (100% of capacity retention after 530 cycles with charge efficiency >99.7%). However, the reversibility of the intercalation/deintercalation process is strongly affected by the synthesis parameters determining, in turn, significant differences in the material structure. This study proposes a new approach to identify the crystal features influencing the performances, using a structural model built with a multitechnique approach that allows exploring the short-range order of the lamella. The model is then used to determine the long-range order by inserting defective elements into the structure. With this strategy it is possible to fit the MXene diffraction patterns, obtain the structural parameters including the stoichiometric composition of the terminations (neutron data), and quantify the structural disorder which can be used to discriminate the phases with the best electrochemical properties.

2020 - Coupling nickel chemical speciation and isotope ratios to decipher nickel dynamics in the Rinorea cf. bengalensis-soil system in Malaysian Borneo [Articolo su rivista]
Zelano, I. O.; Cloquet, C.; van der Ent, A.; Echevarria, G.; Gley, R.; Landrot, G.; Pollastri, S.; Fraysse, F.; Montarges-Pelletier, E.
abstract

Abstract: Aims. Rinorea cf. bengalensis is a Ni hyperaccumulator which occurs in Sabah (Malaysia), on Borneo Island, that is able to accumulate considerable amounts of Ni and influences the Ni cycle in surface soil layers, both in terms of Ni concentration and Ni isotopic composition. In this study, the biogeochemical processes underpinning Ni isotopic fractionation in the soil-plant system and the mechanisms regulating Ni homeostasis in R. cf. bengalensis plants were elucidated. Methods: Two specimens of R. cf. bengalensis of different ages and associated surface soils were collected from ultramafic soils in Sabah. Soil mineralogy, Ni concentrations, speciation and isotopic signatures were subsequently determined in plant and soil samples. Results: Nickel in R. cf. bengalensis leaves is mainly complexed with citrate. Soil Ni available fractions have different δ60Ni values depending on the Ni bearing phases. Rinorea cf. bengalensis specimens take up lighter Ni isotopes and a pronounced isotopic fractionation within the plant is observed, especially in the young specimen. Conclusions: The results suggest that the observed fractionation in the young plant can be attributable to kinetic effects (lighter isotopes move faster), which become less evident in the older specimen, as Ni is redistributed and homogenized through phloem loading and unloading processes.

2020 - Insights on Ga-zeolite catalysts: X-ray powder diffraction and absorption spectroscopy characterization at ambient conditions [Articolo su rivista]
Beltrami, G.; Chenet, T.; Pasti, L.; Gigli, L.; Pollastri, S.; Martucci, A.
abstract

Gallium substituted L, mordenite and ferrierite zeolites, obtained through wet impregnation, were characterized combining adsorption isotherms, X-ray powder diffraction (XRPD) and X-ray absorption spectroscopy (XAS) to elucidate nature and structure of the Ga+3 sites of the materials. The saturation capacity of L was higher than those of mordenite and ferrierite. Rietveld refinements on saturated materials confirm the presence of Ga+3 within the zeolites pores system. Besides, the analysis of the structural features (i.e., lightening of tetrahedral bond distances and narrowing of interthetraedral angles) suggest that small fractions of metal cation have been also incorporated in tetrahedral sites. This is corroborated by XAS analysis, which confirms the effective inclusion of gallium into the zeolites frameworks, thus indicating that the incorporation of Ga+3 from wet impregnation within the zeolite structures occurs in both framework and non-framework positions.

2020 - Large isotropic negative thermal expansion in water-free Prussian blue analogues of ScCo(CN)6 [Articolo su rivista]
Gao, Q.; Sun, Y.; Shi, N.; Milazzo, R.; Pollastri, S.; Olivi, L.; Huang, Q.; Liu, H.; Sanson, A.; Sun, Q.; Liang, E.; Xing, X.; Chen, J.
abstract

We first found that ScCo(CN)6 of Prussian blue analogues has a large isotropic negative thermal expansion which occurs in a wide temperature range from 25K to 600K. More intriguingly, the present material of ScCo(CN)6 exhibits the merits of the facile fabrication via chemical coprecipitation and the good environment stability of water-free, which are very important for the applications. The transverse vibration of C and N atoms is critical for the occurrence of negative thermal expansion, which is confirmed by the atomic mean square relative displacements. The present new material of ScCo(CN)6 will be promising for the applications.

2020 - Leveraging Cu/CuFe2O4-Catalyzed Biomass-Derived Furfural Hydrodeoxygenation: A Nanoscale Metal-Organic-Framework Template Is the Prime Key [Articolo su rivista]
Koley, P.; Chandra Shit, S.; Joseph, B.; Pollastri, S.; Sabri, Y. M.; Mayes, E. L. H.; Nakka, L.; Tardio, J.; Mondal, J.
abstract

Enormous efforts have been initiated in the production of biobased fuels and value-added chemicals via biorefinery owing to the scarcity of fossil resources and huge environmental synchronization. Herein, non-noble metal-based metal/mixed metal oxide supported on carbon employing a metal-organic framework as a sacrificial template is demonstrated for the first time in the selective hydrodeoxygenation (HDO) of biomass-derived furfural (FFR) to 2-methyl furan (MF). The aforementioned catalyst (referred to as Cu/CuFe2O4@C-A) exhibited extraordinary catalytic proficiency (100% selectivity toward MF) compared with the conventional Cu/CuFe2O4@C-B catalyst which was prepared by the wet impregnation method. High-resolution transmission electron microscopy and synchrotron X-ray diffraction studies evidenced the existence of both metal (Cu) and mixed metal oxide (CuFe2O4) phases, in which the metal could help in hydrogenation to alcohol and metal oxide could assist in the hydroxyl group removal step during HDO reaction. The stabilization of encapsulated metal/metal oxide nanoparticles in the carbon matrix, modulation of the electronic structure, and regulation of geometric effects in the Cu/CuFe2O4@C-A are thought to play an important role in its excellent catalytic performance, confirmed by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy investigations. Furthermore, the structure and activity interconnection was confirmed by in situ attenuated total reflection-IR studies, which manifested the strong interfacial interaction between FFR and the Cu/CuFe2O4@C-A catalyst. This finding was further supported by NH3 temperature-programmed desorption analysis, which suggested that the presence of more Lewis/weak acidic sites in this catalyst was beneficial for the hydrogenolysis step in HDO reaction. Additionally, H2 temperature-programmed reduction studies revealed that the adsorption of H2 was stronger on the Cu/CuFe2O4@C-A than that over the conventional Cu/CuFe2O4@C-B catalyst; thus, the former catalyst promoted activation of H2. A detailed kinetic analysis which demonstrated the lower activation energy barrier along with dual active sites attributed for the activation of the two separate reactions in the HDO process on the Cu/CuFe2O4@C-A catalyst. This work has great implication in developing a highly stable catalyst for the selective upgradation of biomass without deactivation of metal sites in extended catalytic cycles and opens the door of opportunity for developing a sustainably viable catalyst in biomass refinery industries.

2020 - Local structure displacements in La1−xCexOBiSSe as a function of Ce substitution [Articolo su rivista]
Pugliese, G. M.; Stramaglia, F.; Capone, F. G.; Hacisalihoglu, M. Y.; Kiyama, R.; Sogabe, R.; Goto, Y.; Pollastri, S.; De Souza, D. O.; Olivi, L.; Mizokawa, T.; Mizuguchi, Y.; Saini, N. L.
abstract

We have investigated the local structure of layered La1−xCexOBiSSe system by Bi L3-edge extended X-ray absorption fine structure (EXAFS) measurements for different Ce substitutions. Ce L3-edge X-ray absorption spectroscopy (XAS) has been used to evaluate the Ce valence responsible for the self-doping in this system. We have found that the local distortion, determined by the separation between two Bi-Ch distances within the BiCh2-layer (Ch=S,Se), is quickly suppressed by Ce substitution while the axial Bi-S2 bond elongates. Ce L3-edge XAS reveals a coexistence of Ce3+ and Ce4+ in which the Ce4+ weight decreases, an indication of a partial breaking of RE-S-Bi (RE=La/Ce) charge transfer channel with Ce substitution. The results suggest that interaction between REO spacer layer and BiCh2 layer, dictated by the out-of-plane Bi-S2 distance, has a significant role in triggering superconductivity in the title system, with the in-plane distortion controlling the charge mobility within the BiCh2-layer.

2020 - Raising the COx Methanation Activity of a Ru/γ-Al2O3 Catalyst by Activated Modification of Metal–Support Interactions [Articolo su rivista]
Chen, S.; Abdel-Mageed, A. M.; Dyballa, M.; Parlinska-Wojtan, M.; Bansmann, J.; Pollastri, S.; Olivi, L.; Aquilanti, G.; Behm, R. J.
abstract

Ru/Al2O3 is a highly stable, but less active catalyst for methanation reactions. Herein we report an effective approach to significantly improve its performance in the methanation of CO2/H2 mixtures. Highly active and stable Ru/γ-Al2O3 catalysts were prepared by high-temperature treatment in the reductive reaction gas. Operando/in situ spectroscopy and STEM imaging reveals that the strongly improved activity, by factors of 5 and 14 for CO and CO2 methanation, is accompanied by a flattening of the Ru nanoparticles and the formation of highly basic hydroxylated alumina sites. We propose a modification of the metal–support interactions (MSIs) as the origin of the increased activity, caused by modification of the Al2O3 surface in the reductive atmosphere and an increased thermal mobility of the Ru nanoparticles, allowing their transfer to modified surface sites.

2020 - Realistic dielectric response of high temperature sintered ZnO ceramic: A microscopic and spectroscopic approach [Articolo su rivista]
Ibadat, S.; Younas, M.; Shahzada, S.; Nadeem, M.; Ali, T.; Akhtar, M. J.; Pollastri, S.; Rehman, U. -U.; Yousef, I.; Ali Khan, R. T.
abstract

High temperature sintering (1200-1400 °C) has been performed on ZnO ceramics. An X-ray Absorption Fine Structure (XAFS) study shows that high sintering temperature introduces a constant amount of VO and VZn defects without any significant effect on the crystal or electronic structure of Wurtzite ZnO. The combined effects of grain boundaries and voids are considered responsible for the apparent colossal dielectric constant (ϵ′) > 104 at low frequency (∼102 Hz) for all the sintered ZnO ceramics. The superior contact among grains of the ZnO-1200 sample enhances both the interfacial and orientational polarization of the Zn2+-VO dipoles, which results in the increase of low and high frequency dielectric constants (ϵ′) and the corresponding dielectric loss (tan δ) also increases. On the other hand, high temperature sintering of ZnO at 1300 °C and 1400 °C introduces voids at the expense of reduced grain and grain boundary contact areas, thus affecting both the interfacial and orientational polarization with corresponding reduction of dielectric constant (ϵ′) and dielectric loss. Orientational polarizations due to Zn2+-VO dipoles are suggested to remain fixed and it is the microstructure which controls the dielectric properties of high temperature sintered ZnO ceramics. This journal is

2019 - Experimental quantification of the Fe-valence state at amosite-asbestos boundaries using acSTEM dual-electron energy-loss spectroscopy [Articolo su rivista]
Vigliaturo, R.; Pollastri, S.; Giere, R.; Gualtieri, A.; Drazic, G.
abstract

Determination of the oxidation state and coordination geometry of iron in Fe-bearing minerals expands our knowledge obtained by standard mineralogical characterization. It provides information that is crucial in assessing the potential of minerals to interact with their surrounding environment and to generate reactive oxygen species, which can disrupt the normal function of living organisms. Aberration-corrected scanning transmission electron microscopy dual-electron energy-loss spectroscopy (acSTEM Dual-EELS) has only rarely been applied in environmental and medical mineralogy, but it can yield data that are essential for the description of near-surface and surface mechanisms involved in many environmental and health-related processes. In this study, we have applied the energy loss near-edge structure (ELNES) and L2,3 white-line intensity-ratio methods using both the universal curve and progressively larger integrating windows to verify their effectiveness in satisfactorily describing the valence state of iron at amosite grain boundaries, and, at the same time, to estimate thickness in the same region of interest. The average valence state obtained from acSTEM Dual-EELS and from a simplified geometrical model were in good agreement, and within the range defined by the bulk and the measured surface-valence states. In the specific case presented here, the use of the universal curve was most suitable in defining the valence state of iron at amosite grain boundaries. The study of ELNES revealed an excellent correspondence with the valence state determined by the L2,3 white-line intensity-ratio method through the use of the universal curve, and it seems that the spectra carry some information regarding the coordination geometry of Fe. The combination of visual examination, reconstruction of the grain boundaries through a simple geometrical model, and Dual-EELS investigation is a powerful tool for characterizing the grain boundaries of hazardous minerals and foreseeing their potential activity in an organism, with the possibility to describe toxic mechanisms in a stepwise fashion.

2018 - Assessment of the potential hazard represented by natural raw materials containing mineral fibres—The case of the feldspar from Orani, Sardinia (Italy) [Articolo su rivista]
Gualtieri, Alessandro F.; Gandolfi, Nicola Bursi; Pollastri, Simone; Rinaldi, Roberta; Sala, Orietta; Martinelli, Giovanni; Bacci, Tiziana; Paoli, Federica; Viani, Alberto; Vigliaturo, Ruggero
abstract

This work describes the nature of the potentially hazardous fibrous amphibole found in the Orani's feldspar mine (Sardinia, Italy). To identify its nature, a protocol of analysis including morphometric, chemical and crystallographic characterizations was applied. Thanks to this approach, it was possible to classify the observed fibres as tremolite after comparing chemical data, SEM/TEM observations, FTIR/ Raman spectra and X-ray diffraction data with those reported for a standard sample. The unit cell parameters of the investigated tremolite phase are a = 9.82(1) Å, b = 18.08(3) Å, c = 5.27(1) Å, and the angle β corresponds to 104.4(1)°. The mean concentration of asbestos tremolite in the Orani's feldspar is 0.28 wt%. Most of the fibres (0.26 wt%) are respirable ‘regulated’ fibres, representing a potential hazard. Because the total amount of tremolite in the sample is 0.6 wt%, a large fraction of it has a crystal habit other than fibrous-asbestiform or acicular. The obtained results allowed us to suggest possible solutions for a safe exploitation and mineral processing of the Orani's mine. The procedure proposed herein may be a general tool suitable to identify the mineralogical nature of fibrous minerals in raw materials and assess if they may represent a potential health/environmental hazard.

2018 - Cu-Pd bimetallic nanoalloy anchored on a N-rich porous organic polymer for high-performance hydrodeoxygenation of biomass-derived vanillin [Articolo su rivista]
Shit, S. C.; Singuru, R.; Pollastri, S.; Joseph, B.; Rao, B. S.; Lingaiah, N.; Mondal, J.
abstract

The structural composition, particle size on the nanoscale, phase state, and surface property have a significant impact on the performance of nanoalloy catalysts. Here we report a bimetallic Cu3Pd nanoalloy anchored on a N-rich porous organic polymer (BBA-1), Cu3Pd@BBA-1, which shows enhanced catalytic activity for the hydrodeoxygenation of vanillin, a typical compound of lignin-derived bio-oil. The prepared Cu3Pd @BBA-1 bimetallic nanocatalyst exhibits highly efficient catalytic performance in promoting biomass refining compared with its monometallic counterparts, providing 99.3% conversion of vanillin with an exclusive selectivity of 93.6% for the hydrogenolysis product 2-methoxy-4-methylphenol. This catalyst is also found to have superior stability (reproducible conversion values upon several cycles), which represents a significant step forward in promoting biomass refining. The Cu3Pd@BBA-1 and related Cu and Pd based catalysts with varying metallic molar ratios were synthesized by a polyol method using NaBH4 as a strong reducing agent. The specific textural and chemical characteristics of the as-synthesized nanohybrid materials were comprehensively investigated by performing X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, synchrotron powder diffraction, X-ray absorption fine structure spectroscopy, 13C cross polarization magic angle spinning nuclear magnetic resonance, nitrogen physisorption, high resolution transmission electron microscopy, and high angle annular dark field scanning transmission electron microscopy with the corresponding elemental mapping. The catalytic performance of Cu3Pd on other commercial supports such as Al2O3, TiO2 and N-doped carbon is found to be inferior to that on BBA-1, revealing the important role of the nitrogen-rich porous organic polymer matrix. The performance of a 3:1 mixture of the monometallic nanoalloys was substantially lower than that of Cu3Pd@BBA-1. These results and the inputs from the experimental probes used for the characterization indicate that in Cu3Pd@BBA-1, alloying leads to improved surface conditions on the nanoscale and brings about a synergetic electronic effect, thus enabling an enhanced catalytic activity and good recyclability.

2018 - In vitro acellular dissolution of mineral fibres: A comparative study [Articolo su rivista]
Gualtieri, Alessandro F.; Pollastri, Simone; Bursi Gandolfi, Nicola; Gualtieri, Magdalena Lassinantti
abstract

The study of the mechanisms by which mineral fibres promote adverse effects in both animals and humans is a hot topic of multidisciplinary research with many aspects that still need to be elucidated. Besides length and diameter, a key parameter that determines the toxicity/pathogenicity of a fibre is biopersistence, one component of which is biodurability. In this paper, biodurability of mineral fibres of social and economic importance (chrysotile, amphibole asbestos and fibrous erionite) has been determined for the first time in a systematic comparative way from in vitro acellular dissolution experiments. Dissolution was possible using the Gamble solution as simulated lung fluid (pH = 4 and at body temperature) so to reproduce the macrophage phagolysosome environment. The investigated mineral fibres display very different dissolution rates. For a 0.25 μm thick fibre, the calculated dissolution time of chrysotile is in the range 94-177 days, very short if compared to that of amphibole fibres (49-245 years), and fibrous erionite (181 years). Diffraction and SEM data on the dissolution products evidence that chrysotile rapidly undergoes amorphization with the formation of a nanophasic silica-rich fibrous metastable pseudomorph as first dissolution step whereas amphibole asbestos and fibrous erionite show minor signs of dissolution even after 9-12 months.

2018 - Infra red spectroscopy of the regulated asbestos amphiboles [Articolo su rivista]
Della Ventura, Giancarlo; Vigliaturo, Ruggero; Gieré, Reto; Pollastri, Simone; Gualtieri, Alessandro F.; Iezzi, Gianluca
abstract

Vibrational spectroscopies (Fourier Transform Infra Red, FTIR, and Raman) are exceptionally valuable tools for the identification and crystal–chemical study of fibrous minerals, and asbestos amphiboles in particular. Raman spectroscopy has been widely applied in toxicological studies and thus a large corpus of reference data on regulated species is found in the literature. However, FTIR spectroscopy has been mostly used in crystal–chemical studies and very few data are found on asbestos amphiboles. This paper is intended to fill this gap. We report new FTIR data collected on a suite of well-characterized samples of the five regulated amphibole species: anthophyllite, amosite, and crocidolite, provided by the Union for International Cancer Control (UICC) Organization, and tremolite and actinolite, from two well-known occurrences. The data from these reference samples have been augmented by results from additional specimens to clarify some aspects of their spectroscopic features. We show that the FTIR spectra in both the OH-stretching region and in the lattice modes region can be effective for rapid identification of the asbestos type.

2018 - Is fibrous ferrierite a potential health hazard? Characterization and comparison with fibrous erionite [Articolo su rivista]
Gualtieri, Alessandro F.; Gandolfi, Nicola Bursi; Passaglia, Elio; Pollastri, Simone; Mattioli, Michele; Giordani, Matteo; Ottaviani, Maria Francesca; Cangiotti, Michela; Bloise, Andrea; Barca, Donatella; Vigliaturo, Ruggero; Viani, Alberto; Pasquali, Luca; Gualtieri, Magdalena Lassinantti
abstract

Fibrous erionite is classified by the International Agency for Research on Cancer (IARC) as carcinogenic substance to humans (Group 1). In the areas where it is present in the bedrock, it may cause environmental exposure, and both professional and environmental exposures are possible when the bedrock is used for industrial applications (e.g., building materials). For health and environment protection, prevention is a priority action. In this framework, the recent guidelines of the Consensus Report of the Weinman International Conference on Mesothelioma suggest identifying locations where potentially hazardous mineral fibers (like erionite) are found in the environment, to prevent environmental exposure. The present study will show that one such potentially hazardous mineral fiber might be fibrous ferrierite. Here, the mineralogy, chemical-physical properties, and surface activity of a hydrothermal fibrous ferrierite from Monte Lake British Columbia (Canada) and a diagenetic fibrous ferrierite from Lovelock, Nevada (U.S.A.), were investigated using a combination of "state of the art" experimental methods including optical microscopy, electron microscopy and microprobe analysis, laser ablation-inductively coupled plasma-mass spectrometry (for the trace elements), vibrational spectroscopy, electron paramagnetic resonance, and synchrotron powder diffraction. The chemical-physical properties of these fibrous ferrierites (morphometric parameters, specific surface area, chemical composition with special attention to metals, mainly iron) that prompted adverse effects in vivo were compared to those of the positive carcinogenic standard fibrous erionite-Na from Jersey, Nevada (U.S.A.). The results of our study have demonstrated that, although there are differences in the crystal chemistry and genetic environment, ferrierite samples exhibit outstanding similarities with fibrous erionite samples: both fibrous erionite and fibrous ferrierite may occur in large amounts as microcrystalline fibrous-asbestiform phases in diagenetic rocks with fibers of breathable sizes. For both zeolites, iron is not structural but is associated with impurities lying at the surface of the fibers. Moreover, data useful to understand the surface activity of these fibrous ferrierites were collected. As far as hydrothermal sample is concerned, the EPR data indicate the presence of hydrophilic (SiO-, AlO-, SiOH) and hydrophobic (Si-O-Si) interacting surface groups able to bind the charged CAT1 probes at close sites and attract the probes in the water pools formed into the fiber aggregates. A high percentage of CAT1 probes weakly interacting with the surface due to competition with metal ions were observed for surface of the diagenetic sample. CAT8 probes were less adsorbed by its surface if compared to the diagenetic sample but the more charged surface provided a stronger binding strength for the diagenetic sample compared to the hydrothermal one. In summary, the results of this study indicate that fibrous ferrierite may represent a potential health hazard and, applying the precautionary principle, it should undergo a procedure of toxicity testing.

2017 - Bulk spectroscopy of mineral fibres [Relazione in Atti di Convegno]
Andreozzi, G. B.; Pollastri, S.
abstract

Spectroscopic methods are utilized widely for characterizing minerals and other geomaterials in terms of electronic, vibrational and nuclear properties. The basics and applications of spectroscopic methods in mineralogy were reported comprehensively by Hawthorne (1988), and later discussed carefully and updated by Burns (1993) and Clark (1999), by Beran and Libowitzky (2004) and more recently by Henderson et al. (2014). These esteemed books and reviews focused generally on topics of immediate mineralogical interest, but nevertheless contain stimulating parallel excursions into the fields of geology and materials sciences. This chapter is built on the shoulders of those giants and is devoted specifically to exploring spectroscopic investigations of electronic and nuclear properties of mineral fibres, a topic not reviewed previously. A number of spectroscopies (though not all) will be mentioned without covering in detail their physical bases (which can be found easily in the books and reviews mentioned above), because this chapter is intended to serve as a review of their contribution to increasing comprehension of the bulk properties of mineral fibres.

2017 - New insights into the toxicity of mineral fibres: A combined in situ synchrotron μ-XRD and HR-TEM study of chrysotile, crocidolite, and erionite fibres found in the tissues of Sprague-Dawley rats [Articolo su rivista]
Gualtieri, Alessandro F.; Bursi Gandolfi, Nicola; Pollastri, Simone; Burghammer, Manfred; Tibaldi, Eva; Belpoggi, Fiorella; Pollok, Kilian; Langenhorst, Falko; Vigliaturo, Ruggero; Gorandražić,
abstract

Along the line of the recent research topic aimed at understanding the in vivo activity of mineral fibres and their mechanisms of toxicity, this work describes the morpho-chemical characteristics of the mineral fibres found in the tissues of Sprague-Dawley rats subjected to intraperitoneal/intrapleural injection of UICC chrysotile, UICC crocidolite and erionite-Na from Nevada (USA). The fibres are studied with in situ synchrotron powder diffraction and high resolution transmission electron microscopy to improve our understanding of the mechanisms of toxicity of these mineral fibres. In contact with the tissues of the rats, chrysotile fibres are prone to dissolve, with leaching of Mg and production of a silica rich relict. On the other hand, crocidolite and erionite-Na fibres are stable even for very long contact times within the tissues of the rats, showing just a thin dissolution amorphous halo. These findings support the model of a lower biopersistence of chrysotile with respect to crocidolite and erionite-Na but the formation of a silica-rich fibrous residue after the pseudo-amorphization of chrysotile may justify a higher cytotoxic potential and intense inflammatory activity of chrysotile in the short term in contact with the lung tissues.

2017 - The crystal structure of mineral fibres. 2. Amosite and fibrous anthophyllite [Articolo su rivista]
Pollastri, Simone; Perchiazzi, Natale; Gigli, Lara; Ferretti, Paolo; Cavallo, Alessandro; Bursi Gandolfi, Nicola; Pollok, Kilian; Gualtieri, Alessandro F.
abstract

This study reports for the frst time crystal-structure data for amosite and fibrous anthophyllite. The chemical composition of the two fibre species was determined from EMPA. Crystal structures were refned using powder-diffraction data, using both laboratory sources and synchrotron radiation. Results were compared with the available literature data for the non-fibrous varieties grunerite and anthophyllite, respectively. The calculated site-occupancies for all samples are in agreement with the chemical compositions calculated from EMPA. The existing structure models of grunerite and orthorhombic anthophyllite also applies to the corresponding fibrous varieties amosite and fibrous anthophyllite, respectively. In amosite, both Fe 2+ and Fe 3+ atoms are found at the sites M(1), M(2) and M(3) and Fe 2+ ions is the only atomic species found at site M(4). Mg is disordered over the C sites with a preference for site M(2). Minor Ca and Na have been assigned to the A site. In fibrous anthophyllite, Mg is the only atomic species found at the M1, M2 and M3 sites. Fe 2+ , Mg (and minor Mn) have been assigned to the M4 site, whereas minor Ca has been assigned to the A site. In both structures, the environment at the M(4) site in amosite and M4 site in fibrous anthophyllite is highly distorted. This work can be considered a basis for studies aimed at understanding the potential toxicity/pathogenicity of these mineral fibres.

2017 - The crystal structure of mineral fibres. 3. Actinolite asbestos [Articolo su rivista]
Pollastri, Simone; Gigli, Lara; Ferretti, Paolo; Andreozzi, Giovanni B.; Bursi Gandolfi, Nicola; Pollok, Kilian; Gualtieri, Alessandro F.
abstract

The present work reports chemical and structural data of actinolite asbestos from Aurina Valley, Bolzano (Italy). The chemical composition was determined using EMPA and TG analysis, and the Fe3+/Fetot ratio was accurately evaluated with independent 57Fe Mössbauer spectroscopy. Morphology and crystallinity were also investigated through SEM and TEM investigations. Crystal structure was refined using high-resolution synchrotron XRPD data. The iron content of Aurina Valley sample is lower compared to two representative asbestiform actinolite samples (with structure refinement) taken from the literature (FeOtot 7.77 wt% against 12÷13 wt%, respectively), accounting for the reduced cell volume here measured (910.29 ų against 912÷918 ų, respectively). Refined site scattering values of Aurina Valley sample are in agreement with those calculated from chemical compositions, and the optimized structural formula is: K0.02Na0.05(Na0.08Ca1.92)Ʃ=2.00(Mg3.80Fe2+0.79Fe3+0.11Al0.20Mn0.05Ni0.02Cr0.01)Ʃ=4.98(Si7.67Al0.25)Ʃ=7.92O21.69(OH)2.31. The C sites M(1), M(2) and M(3) are occupied by Mg and Fe in a proportion of ~4:1, whereas the M(4) site contains mainly Ca and a very small amount of Na. Iron exclusively occupies the octahedral C sites, with Fe 2+ ions occurring at the M(1,2,3) sites and the small amount of Fe 3+ (13% of Fe tot) ordered at the M(2) site. The refined crystal structure and cation distribution are fully consistent with results previously obtained on asbestiform and non-asbestiform samples belonging to the tremolite-actinolite-ferro– actinolite substitutional series.

2016 - Assessment of asbestos body formation by high resolution FEG-SEM after exposure of Sprague-Dawley rats to chrysotile, crocidolite, or erionite [Articolo su rivista]
Bursi gandolfi, N.; Gualtieri, A. F.; Pollastri, S.; Tibaldi, E.; Belpoggi, F.
abstract

This work presents a comparative FEG-SEM study of the morphological and chemical characteristics of both asbestos bodies and fibres found in the tissues of Sprague-Dawley rats subjected to intraperitoneal or intrapleural injection of UICC chrysotile, UICC crocidolite and erionite from Jersey, Nevada (USA), with monitoring up to 3 years after exposure.Due to unequal dosing based on number of fibres per mass for chrysotile with respect to crocidolite and erionite, excessive fibre burden and fibre aggregation during injection that especially for chrysotile would likely not represent what humans would be exposed to, caution must be taken in extrapolating our results based on instillation in experimental animals to human inhalation. Notwithstanding, the results of this study may help to better understand the mechanism of formation of asbestos bodies.For chrysotile and crocidolite, asbestos bodies are systematically formed on long asbestos fibres. The number of coated fibres is only 3.3% in chrysotile inoculated tissues. In UICC crocidolite, Mg, Si, and Fe are associated with the fibres whereas Fe, P and Ca are associated with the coating. Even for crocidolite, most of the observed fibres are uncoated as coated fibres are about 5.7%. Asbestos bodies do not form on erionite fibres. The crystal habit, crystallinity and chemistry of all fibre species do not change with contact time, with the exception of chrysotile which shows signs of leaching of Mg.A model for the formation of asbestos bodies from mineral fibres is postulated. Because the three fibre species show limited signs of dissolution in the tissue, they cannot act as source of elements (primarily Fe, P and Ca) promoting nucleation and growth of asbestos bo dies. Hence, the limited number of coated fibres should be due to the lack of nutrients or organic nature.

2016 - In situ synchrotron powder diffraction study of the setting reaction kinetics of magnesium-potassium phosphate cements [Articolo su rivista]
Viani, A.; Peréz-Estébanez, M.; Pollastri, S.; Gualtieri, A. F.
abstract

This work reports a kinetic study of the formation of magnesium-potassium phosphate cements accomplished using in-situ synchrotron powder diffraction. The reaction: MgO + KH 2 PO 4 + 5H 2 O → MgKPO 4 · 6H 2 O was followed in situ in the attempt of contributing to explain the overall mechanism and assess the influence of periclase (MgO) grain size and calcination temperature (1400-1600 °C) on the reaction kinetics. Numerical kinetic parameters for the setting reaction have been provided for the first time. The best fit to the kinetic data was obtained using a weighted nonlinear model fitting method with two kinetic equations, representing two consecutive, partially overlapping processes. MgO decomposition could be described by a first order (F1) model followed by a Jander diffusion (D3) controlled model. Crystallization of the product of reaction was modelled using an Avrami model (A n ) followed by a first order (F1) chemical reaction. A reaction mechanism accounting for such results has been proposed.

2016 - Stability of mineral fibres in contact with human cell cultures. An in situ μXANES, μXRD and XRF iron mapping study [Articolo su rivista]
Pollastri, Simone; Gualtieri, Alessandro F.; Vigliaturo, Ruggero; Ignatyev, Konstantin; Strafella, Elisabetta; Pugnaloni, Armanda; AlessandroCroce,
abstract

Relevant mineral fibres of social and economic importance (chrysotile UICC, crocidolite UICC and a fibrous erionite from Jersey, Nevada, USA) were put in contact with cultured diploid human non-tumorigenic bronchial epithelial (Beas2B) and pleural transformed mesothelial (MeT5A) cells to test their cytotoxicity. Slides of each sample at different contact times up to 96 h were studied in situ using synchrotron XRF, μ-XRD and μ-XAS (I18 beamline, Diamond Light Source, UK) and TEM investigations. XRF maps of samples treated for 96 h evidenced that iron is still present within the chrysotile and crocidolite fibres and retained at the surface of the erionite fibres, indicating its null to minor mobilization in contact with cell media; this picture was confirmed by the results of XANES pre-edge analyses. μ-XRD and TEM data indicate greater morphological and crystallinity modifications occurring in chrysotile, whereas crocidolite and erionite show to be resistant in the biological environment. The contact of chrysotile with the cell cultures seems to lead to earlier amorphization, interpreted as the first dissolution step of these fibres. The formation of such silica-rich fibre skeleton may prompt the production of HO in synergy with surface iron species and could indicate that chrysotile may be much more reactive and cytotoxic in vitro in the (very) short term whereas the activity of crocidolite and erionite would be much more sluggish but persistent in the long term.

2016 - The crystal structure of mineral fibres. 1. Chrysotile [Articolo su rivista]
Pollastri, Simone; Perchiazzi, Natale; Lezzerini, Marco; Plaisier, Jasper R.; Cavallo, Alessandro; Chiara Dalconi, Maria; Bursi Gandolfi, Nicola; Gualtieri, Alessandro F.
abstract

This work reports the results of the structural study of three representative chrysotile samples of different provenance (Canadian UICC, and Italian Balangero and Valmalenco). Chemical composition was determined using EMPA and TG data. An innovative wet cryo-milling procedure was used to powder the flexible and durable chrysotile fibres. X-ray powder diffraction patterns were collected using both conventional and nonconventional sources. Collected data were used for Rietveld structural refinements and results were compared with available literature data. The three samples display similar structure models, although small differences were detected in the position of the oxygen atoms. Both the structural refinements and spectroscopic investigations confirms that Fe 2+ and Fe 3+ atoms in chrysotile are located in the octahedral cavities only, substituting for Mg 2+ . Regarding the atom coordinates, UICC chrysotile is the closest to the model reported by Falini et al. (2004). About the lattice parameters, the Valmalenco chrysotile is the closest, if compared with the Balangero and UICC, to both the model proposed by Whittaker (1956a,b) and Falini et al. (2004). This work is intended as a basis for subsequent studies aimed at understanding the toxicity of these mineral fibres.

2016 - Trace elements in hazardous mineral fibres [Articolo su rivista]
Bloise, A.; Barca, D.; Gualtieri, A. F.; Pollastri, S.; Belluso, E.
abstract

Both occupational and environmental exposure to asbestos-mineral fibres can be associated with lung diseases. The pathogenic effects are related to the dimension, biopersistence and chemical composition of the fibres. In addition to the major mineral elements, mineral fibres contain trace elements and their content may play a role in fibre toxicity. To shed light on the role of trace elements in asbestos carcinogenesis, knowledge on their concentration in asbestos-mineral fibres is mandatory. It is possible that trace elements play a synergetic factor in the pathogenesis of diseases caused by the inhalation of mineral fibres. In this paper, the concentration levels of trace elements from three chrysotile samples, four amphibole asbestos samples (UICC amosite, UICC anthophyllite, UICC crocidolite and tremolite) and fibrous erionite from Jersey, Nevada (USA) were determined using inductively coupled plasma mass spectrometry (ICP-MS). For all samples, the following trace elements were measured: Li, Be, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Sb, Cs, Ba, La, Pb, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U. Their distribution in the various mineral species is thoroughly discussed. The obtained results indicate that the amount of trace metals such as Mn, Cr, Co, Ni, Cu and Zn is higher in anthophyllite and chrysotile samples, whereas the amount of rare earth elements (REE) is higher in erionite and tremolite samples. The results of this work can be useful to the pathologists and biochemists who use asbestos minerals and fibrous erionite in-vitro studies as positive cyto- and geno-toxic standard references.

2016 - Where is iron in erionite? A multidisciplinary study on fibrous erionite-Na from Jersey (Nevada, USA) [Articolo su rivista]
Gualtieri, A. F.; Nicola Bursi, Gandolfi; Simone, Pollastri; Kilian, Pollok; Falko, Langenhorst
abstract

Fibrous erionite is a mineral fibre of great concern but to date mechanisms by which it induces cyto- and geno-toxic damage, and especially the role of iron associated to this zeolite species, remain poorly understood. One of the reasons is that we still don’t know exactly where iron is in natural erionite. This work is focused on fibrous erionite-Na from Jersey (Nevada, USA) and attempts to draw a general model of occurrence of iron in erionite and relationship with toxicity mechanisms. It was found that iron is present as 6-fold coordinated Fe3+ not part of the zeolite structure. The heterogeneous nature of the sample was revealed as receptacle of different iron-bearing impurities (amorphous iron-rich nanoparticles, micro-particles of iron oxides/hydroxides, and flakes of nontronite). If iron is not part of the structure, its role should be considered irrelevant for erionite toxicity, and other factors like biopersistence should be invoked. An alternative perspective to the proposed model is that iron rich nano-particles and nontronite dissolve in the intracellular acidic environment, leaving a residue of iron atoms at specific surface sites anchored to the windows of the zeolite channels. These sites may be active later as low nuclearity groups.

2016 - XANES and micro-Raman spectroscopy study of the barium titanosilicates BaTiSi2O7 and BaTiSi4O11 [Articolo su rivista]
Viani, A.; Pollastri, S.; Macova, P.; Palermo, A.; Peréz-Estébanez, M.; Gualtieri, A. F.
abstract

The coordination environment around Ti4+ in the photoluminescent compound BaTiSi2O7 and in BaTiSi4O11 was investigated with X-ray absorption near-edge structure spectroscopy and micro-Raman spectroscopy. The presence of VTi in TiO5 pyramidal units with one short Ti–O bond involving the apical oxygen was detected in both compounds. Interpretation of the vibrational signal from the silicate framework suggested that BaTiSi4O11 is a metasilicate containing building units of SiO4 tetrahedra, which are larger than in other barium titanosilicates. These results confirmed the same structural environment of Ti4+ as recently disclosed by structure refinement of BaTiSi2O7 and provided new insights into the unknown structure of BaTiSi4O11 in the light of the study of its physical properties as potential functional material.

2015 - Inorganic polymers from laterite using activation with phosphoric acid and alkaline sodium silicate solution: Mechanical and microstructural properties [Articolo su rivista]
Gualtieri, Eva Magdalena; Romagnoli, Marcello; Pollastri, Simone; Gualtieri, Alessandro
abstract

Geopolymers from laterite, an iron-rich soil available in developing countries, have great potential as building materials. In this work, laterite from Togo (Africa) was used to prepare geopolymers using both phosphoric acid and alkaline sodium silicate solution. Microstructural properties were investigated by scanning electron microscopy, X-ray powder diffraction and mercury porosimetry, whereas thermal properties were evaluated by thermal analyses. The local environment of iron was studied by X-ray Absorption Spectroscopy (XANES region). The mechanical properties were determined. Modulus of Rupture and Young's modulus fell in the ranges 3.3–4.5 MPa and 12–33 GPa, respectively, rendering the materials good candidates for construction purposes. Heating above 900 °C results in weight-gain, presumably due to iron redox reactions. X-ray Absorption Spectroscopy data evidence changes in the chemical and structural environments of iron following thermal treatment of geopolymers. These changes indicate interaction between the geopolymer structure and iron during heating, possibly leading to redox properties.

2015 - Investigation of setting reaction of magnesium-potassium phosphate ceramics by qualsi-elastic neutron scattering [Banca dati]
Viani, A; Gualtieri, A; Pollastri, S; Zbiri, M
abstract

2015 - Study of the asbestos bodies and chemical-physical modification of mineral fibres in rat histological tissues using electron microscopy and micro-Raman spetroscopy [Abstract in Atti di Convegno]
Bursi Gandolfi, N; Pollastri, S; Viani, A; Gualtieri, Af
abstract

2015 - The chemical environment of iron in mineral fibres. A combined X-ray absorption and Mössbauer spectroscopic study [Articolo su rivista]
Pollastri, Simone; D’Acapito, Francesco; Trapananti, Angela; Colantoni, Ivan; Andreozzi, Giovanni B.; Gualtieri, Alessandro F.
abstract

Although asbestos represents today one of the most harmful contaminant on Earth, in 72% of the countries worldwide only amphiboles are banned while controlled use of chrysotile is allowed. Uncertainty on the potential toxicity of chrysotile is due to the fact that the mechanisms by which mineral fibres induces cyto- and geno-toxic damage are still unclear. We have recently started a long term project aimed at the systematic investigation of the crystal-chemistry, bio-interaction and toxicity of the mineral fibres. This work presents a systematic structural investigation of iron in asbestos and erionite (considered the most relevant mineral fibres of social and/or economic-industrial importance) using synchrotron X-ray absorption and Mössbauer spectroscopy. In all investigated mineral fibres, iron in the bulk structure is found in octahedral sites and can be made available at the surface via fibre dissolution. We postulate that the amount of hydroxyl radicals released by the fibers depends, among other factors, upon their dissolution rate; in relation to this, a ranking of ability of asbestos fibres to generate hydroxyl radicals, resulting from available surface iron, is advanced: amosite > crocidolite ≈ chrysotile > anthophyllite > tremolite. Erionite, with a fairly high toxicity potential, contains only octahedrally coordinated Fe3+. Although it needs further experimental evidence, such available surface iron may be present as oxide nanoparticles coating and can be a direct cause of generation of hydroxyl radicals when such coating dissolves.

2014 - Determination of the concentration of asbestos minerals in highly contaminated mine tailings: An example from abandoned mine waste of Cretaz and Emarese (Valle d'Aosta, Italy) [Articolo su rivista]
Gualtieri, Alessandro; Pollastri, Simone; Ronchetti, Francesco; Gandolfi, N. B.; Albonico, C.; Cavallo, A.; Zanetti, G.; Marini, P.; Sala, O.
abstract

For the first time, this work reports concentration maps of asbestos minerals in contaminated mine tailings drawn using the results of Rietveld quantitative phase analysis (QPA). The investigated sites are located in the Valle d’Aosta region (Italy): Crètaz, the most important Italian magnetite mine, active until 1979 and Emarèse, one the most important chrysotile asbestos mines in Italy, active until 1968. The results of the study permit to draw the spatial distribution of the asbestos (chrysotile and tremolite in this specific case) concentration, useful to plan reclamation of the sites, with priority given to the areas with the highest asbestos concentration. Because of the complexity of the mineral assemblage, which includes, among the others, antigorite, chlorite, talc, and tremolite, the concentration of chrysotile was cross-checked using different experimental techniques such as X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), polarized light optical microscopy (PCOM), and differential thermal analysis (DTA). The accuracy of the results was validated by analyzing standard samples with known concentrations of chrysotile and tremolite. The comparison allowed to point out the advantages and disadvantages of each experimental method. At Crètaz, chrysotile ranges from 4.4 to 22.8 wt% and tremolite from 1.0 to 10.3 wt%, whereas at Emarèse the concentration of chrysotile varies from 3.3 to 39.5 wt% and tremolite from 5.9 to 12.4 wt%. Antigorite and chlorite are the major accompanying phases with variable amounts of other accessory minerals including magnetite, carbonates, talc, olivine, pyroxene, talc, and brucite. The results of our study are of key importance for the local environmental policies as the knowledge of the spatial distribution of the asbestos concentration allows to plan a detailed reclamation agenda of the contaminated sites. The spots with the highest surface contamination of both chrysotile and tremolite were identified and classified as priority areas in the reclamation plan.

2014 - The concept of 'end of waste' and recycling of hazardous materials: In depth characterization of the product of thermal transformation of cement-asbestos [Articolo su rivista]
Croce, A.; Allegrina, M.; Trivero, P.; Rinaudo, C.; Viani, A.; Pollastri, S.; Gualtieri, A. F.
abstract

Selected samples of asbestos-containing material (ACM) with different Ca/Si ratios have been treated thermally at 1200°C for 15 min to obtain an 'end of waste geo-inspired material'. Before and after treatment, micro-Raman spectroscopy allowed the investigation of both powdered and massive samples by directing the laser beam onto crystals with elongated morphology, thin fibres and the matrix. In the raw samples, chrysotile and/or crocidolite were detected. After the thermal treatment, no asbestos phases were identified in the Raman spectra collected on fibrous or fibre-like morphologies. The scanning electron microscopy/energy dispersive spectroscopy investigations confirmed the onset of a pseudomorphic process during annealing, leading to the complete transformation of asbestos minerals into non-hazardous magnesium or calcium magnesium silicates such as forsterite, monticellite, åkermanite and merwinite. The identification of such mineral assemblages was inspired by the close inspection of a natural counterpart, the high-temperature contact metamorphic imprint due to the intrusion of a sill into carbonate rocks. The process turned out to occur largely at the solid state and involved substantial mobilization of Ca and Mg to form a spinel phase (namely MgFe2O4) which was recognized in the matrix and within, or close to elongated morphologies.

2014 - The zeta potential of mineral fibres [Articolo su rivista]
Pollastri, Simone; Gualtieri, Alessandro; Gualtieri, Eva Magdalena; Hanuskova, Miriam; Cavallo, Alessandro; Gaudino, Giovanni
abstract

For the first time, the zeta (ξ) potential of pathogenic mineral fibres (chrysotiles, amphiboles and erionite) was systematically investigated to shed light on the relationship between surface reactivity and fibre pathogenicity. A general model explaining the zeta potential of chrysotile, amphiboles and erionite has been postulated. In double distilled water, chrysotiles showed positive values while crocidolite and erionite showed negative values. In contact with organic solutions, all fibres exhibited negative values of zeta potential. The decrease of the surface potential is deemed to be a defensive chemical response of the macrophage cells to minimize hemolytic damage. Negatively charged surfaces favour the binding of collagen and redox activated Fe-rich proteins, to form the so-called asbestos bodies and prompt the formation of HO via the reaction with peroxide (H2O2+e(-)→HO+HO(-)). An additional mechanism accounting for higher carcinogenicity is possibly related to the Ca(2+) sequestration by the fibres with surface negative potential, impairing the mitochondrial apoptotic pathway. It was also found that with a negative zeta potential, the attractive forces prevailed over repulsions and favoured processes such as agglomeration responsible of a tumorigenic chronic inflammation.

2014 - Transformations through pseudomorphosis of asbestos minerals in thermally processed asbestos-containing materials investigated through SEM/EDS and micro-Raman spectroscopy: implications for recycling of hazardous wastes [Abstract in Atti di Convegno]
Viani, A; Gualtieri, Af; Macova, P; Pollastri, S
abstract

Asbestos-containing materials, extensively used in the past in many European countries, are now considered hazardous wastes of great concern. It has been proved that inertization can be obtained via thermal treatment above 1100 °C. This solution relies upon the scientific evidence that all asbestos minerals at high temperature transform into stable crystalline silicates via a solid state recrystallization process [1]. Asbestos fibres preserve the same external crystal habit although a complete modification of the structure at a molecular scale occurred. This phenomenon is called pseudomorphosis. With increasing the temperature of the thermal treatment above 650-750 °C, the transformation sequence of chrysotile asbestos predicts the crystallization of forsterite (Mg2SiO4) and enstatite (MgSiO3 ) [1]. In a system high in Ca, such as cement-asbestos, crystallization of cement phases such as larnite (Ca2SiO4), ferrite (ideally Ca4Al2Fe2O10), and Al-,Ca-,Mg-rich silicates, such as akermanite (ideally Ca2MgSi2O7) and merwinite (ideally Ca3MgSi2O8), occurs. In this work, analytical and spectroscopic techniques coupled with microscopy allowed for the study of individual residual pseudo-morphosed fibre bundles, in cement-asbestos samples heat treated at 1200 °C. Phases detected were mainly monticellite (CaMgSiO4) or akermanite. They likely formed through the reactions: CaO + MgSiO3 (en) -> CaMgSiO4 (mtc), and CaMgSiO4 (mtc) + CaO + SiO2 -> Ca2MgSiO7 (ake). This suggests that, although transformation reactions occurred largely at the solid state, a substantial mobilisation of Ca and Mg resulted. Such a process is essential for the attainment of the bulk mineralogical composition predicted by the phase diagrams in the system CaO-MgO-SiO2 [2]; however, because of crystallization under non equilibrium conditions, departures from the expected bulk phase composition are still observed. This study contributes to the definition of factors conditioning the recycling of transformed cement-asbestos as secondary raw material [2-3].

2013 - Crystal chemistry of the high temperature product of transformation of cement-asbestos [Articolo su rivista]
Viani, Alberto; Gualtieri, Alessandro; Pollastri, Simone; Rinaudo, Caterina; Croce, Alessandro; Urso, Giancarlo
abstract

In this work, the high-temperature inertization product of a representative batch of samples of cement-asbestos (CA) from different localities in Italy have been characterized with a multidisciplinary approach. All the raw CA samples were heated at 1200°C for 15 min. After firing, they underwent a series of solid state reactions leading to global structural changes of the matrix. Effects of annealing time and temperature on the crystallization kinetics were thoroughly investigated. Both factors acted in favour of equilibrium. Three classes of CA were identified with the aid of phase diagrams and of specific plots relating chemical and mineralogical parameters. This result was considered of importance in view of the potential use of transformed cement-asbestos as a secondary raw material. In principle, the content of CA packages removed from the environment and their corresponding heat-treated products can be classified simply using XRF. This method allows for the selection of appropriate fractions in function of the most suitable recycling solution adopted. Samples belonging to the class called larnite-rich, turned out to be of great interest as possible candidate for substituting a fraction of cement in many building materials and innovative green cement productions.

2013 - THE CONCEPT OF END OF WASTE IN VIEW OF DEVELOPING SUSTAINABLE SECONDARY RAW MATERIALS [Abstract in Atti di Convegno]
Gualtieri, Af; Viani, A; Pollastri, S
abstract

The concept of end of waste, adopted by the European Commission on December 2005, regards under which conditions a waste could cease to be waste and could be regarded as a non-waste material. This is a revolutionary way to think of wastes not just as refuse to be dismissed but as secondary raw material to be exploited, with an enormous social and economic impact. In this scenario, the creativity of materialsscientists is highly stimulated and the key to success is the development of innovative and sustainable means to transform a waste into a secondary raw material of potential economic value. To this aim, stimulus comes from the so called geo-inspiring materials. This contribution presents the results of a long-term project aimed to recycle asbestos containing materials (ACMs), into secondary raw materials for various industrial applications. The high temperature product of transformation of ACM can be successfully recycled in clay bricks, rock-wool, glass–ceramics, ceramic pigments[1], geopolymers [2], concrete [3], and recently also for innovative formulations of calcium sulfoaluminate cement clinkers [4 ] and magnesium phosphate cements [5].

2012 - CRYSTAL CHEMISTRY OF CEMENT-ASBESTOS AND ITS HIGH TEMPERATURE PRODUCTS [Abstract in Atti di Convegno]
Viani, A; Gualtieri, Af; Pollastri, S; Rinaudo, C; Croce, A; Cruciani, G
abstract

Asbestos-containing materials (ACM) are an example of hazardous waste which has become matter of greatconcern due to its widespread diffusion. Cement asbestos (CA) are the most represented ACM. Recently, anindustrial process for the thermal destruction of CA wastes was developed [1] in compliance with the Europeandirectives and Italian legislation. Sealed packages of CA slates undergo prolonged annealing in the temperaturerange 1200-1300 C, during which both serpentine and amphibole asbestos minerals are completely transformedinto newly-formed silicates.The potential of this product as secondary raw material relies on the effectiveness and reproducibility of theinertization process at the industrial scale, and on the choice of suitable recycling solutions. At the scope, is of greatinterest to investigate how the high temperature transformed product is affected by the chemistry and mineralogyof the starting CA material. Literature data on CA slates are scarce and incomplete, and a comprehensive picturewith emphasis on areal distribution and compositional variability at a large scale is lacking.In this work, 27 CA samples coming from different localities in Italy, and their high-temperature inertizationproducts were characterized with a combination of analytical techniques, including XRF, XRPD, SEM/EDS, FTIRand micro-Raman. Raw materials revealed a complex mineralogy comprising cement hydrated phases, a residualnon-hydrated component, and a relevant fraction attributable to various processes of alteration. The industrialinertization process was reproduced at the laboratory scale by heat treating small chunks of cement-asbestosat 1200 C. A series of solid state reactions leading to global structural changes of the matrix with completetransformation of asbestos minerals was observed. Chemical gradients due to limited ionic diffusion testifiedrecrystallization under non-equilibrium conditions. This didn’t prevented the use of the CaO-SiO2-MgO phasediagram in order to relate the mineralogy of thermally treated samples with their chemistry. Effects of annealingtime and temperature on the crystallization kinetics were investigated with further thermal treatments. With theaid of thermodynamic calculations both factors were considered to act in favour of equilibrium. Three classes ofheat-treated CA, showing distinct chemical and mineralogical fingerprints, were identified. XRF data allow forthe content of CA packages, and thus, the corresponding heat-treated products, to be quickly classified. Analysescould be carried out indifferently before or after the thermal treatment. This result is of importance in view of thepotential recycling applications. Classes of transformed product can be selected and eventually mixed in functionof the solution adopted. This is the case of larnite-rich products, already recognized as larnite-rich cements highin magnesium, potential constituent of green cements, and tested as substitute for cement in commercial concrete[2].