Search

Our society largely relies on inorganic semiconductor devices which are, so far, fabricated using expensive and complex processes requiring ultra‐high vacuum equipment. Here we report on the possibility of growing a p–n junction taking advantage of electrochemical processes based on the use of aqueous solutions. The growth of the junction has been carried out using the Electrochemical Atomic Layer Deposition (E‐ALD) technique, which allowed to sequentially deposit two different semiconductors, CdS and Cu2S, on an Ag(111) substrate, in a single procedure. The growth process was monitored in situ by Surface X‐Ray Diffraction (SXRD) and resulted in the fabrication of a thin double‐layer structure with a high degree of crystallographic order and a well‐defined interface. The high‐performance electrical characteristics of the device were analysed ex‐situ and show the characteristic feature of a diode. [ABSTRACT FROM AUTHOR]

Since 2013, 34 surveys of surface and ground waters within and outside the former Hg-mine of Abbadia San Salvatore (Italy), which is currently under remediation, were performed for determining Hg, As, Sb, and main and minor solutes. The water quality is rather poor since most waters show relatively high Hg concentrations (up to 695 µg/L). Differently, As and Sb only overcome the Italian law thresholds in a few sites. A high geochemical variability was observed for most groundwaters without any clear relationship between wet and dry periods. The main source of chalcophile elements is likely related to: (i) the interaction between meteoric waters and soils contaminated by the previous production of mercury; or (ii) the interaction between meteoric waters and the anthropic filling material of a former paleo-valley near the furnaces edifices. While the remediation is expected to be concluded in 2025, the aquifer contamination still remains a problem. Our investigation, including geochemical/hydrogeological modeling, is prodromal to future activities aimed at reducing the Hg content. Currently, the construction of a hydraulic barrier is apparently the most suitable solution to minimize the interaction processes between water–rock and man-made material, which are responsible for the 10-year concentration variability. [ABSTRACT FROM AUTHOR]

In this article, we present an in-situ and operando time-resolved X-ray Absorption Spectroscopy (XAS) technique which exploits a combination of Grazing Incidence XAS (GIXAS) and Fixed Energy X-ray Absorption Voltammetry (FEXRAV), the Grazing Incidence FEXRAV (GI-FEXRAV). A case-study is also outlined. Palladium ultra-low loadings were deposited above Au polycrystalline iso-oriented substrates adopting three different deposition methods: surface-controlled electrochemical methods, direct electrodeposition, and physical vapour deposition (PVD). These catalytical surfaces were prepared for the investigation by GI-FEXRAV of the Pd oxidation/dissolution phenomenon that could occur when the metal is used in the anodic compartment of Direct Alcohol Fuel Cells (DAFCs) or in electrochemical reformers. Moreover, we report a robust, low cost and versatile procedure to obtain wide and flat iso-oriented gold substrates that can mimic monocrystalline gold (1 1 1) in the electrochemical response. The use of GI-FEXRAV for the operando characterization of the catalysts, in conjunction with the designed experimental cell and our flexible Au-based electrochemical substrates show an invaluable potential in the operando study of fundamental phenomena in heterogeneous electrocatalysis model systems and, due to its versatility, paves the way to further studies on a wide selection of electrochemical systems. [ABSTRACT FROM AUTHOR]

Potential CO2 leakage from deep geologic reservoirs requires evaluation on a site-specific basis to assess risk and arrange mitigation strategies. In this study, a heterogeneous and realistic numerical model was developed to investigate CO2 migration pathways and uprising time in a shaly overburden, located in the Malaysian off-shore. Fluid flow and reactive transport simulations were performed by TOUGHREACT to evaluate the: (1) seepage through the caprock; (2) CO2-rich brine leakage through a fault connecting the reservoir with seabed. The effect of several factors, which may contribute to CO2 migration, including different rock types and permeability, Fickian and Knudsen diffusion and CO2 adsorption in the shales were investigated. Obtained results show that permeability mainly ruled CO2 uprising velocity and pathways. CO2 migrates upward by buoyancy without any important lateral leakages due to poor-connection of permeable layers and comparable values of vertical and horizontal permeability. Diffusive flux and the Knudsen flow are negligible with respect to the Darcy regime, despite the presence of shales. Main geochemical reactions deal with carbonate and pyrite weathering which easily reach saturation due to low permeability and allowing for re-precipitation as secondary phases. CO2 adsorption on shales together with dissolved CO2 constituted the main trapping mechanisms, although the former represents likely an overestimation due to estimated thermodynamic parameters. Developed models for both scenarios are validated by the good agreement with the pressure profiles recorded in the exploration wells and the seismic data along a fault (the F05 fault), suggesting that they can accurately reproduce the main processes occurring in the system. [ABSTRACT FROM AUTHOR]

The evaluation of caprock integrity and reservoir efficiency is critical for safe CO2 geological storage management. It is therefore important to investigate geochemical reactions between CO2-rich fluids and host rocks and their contribution in retaining CO2 at depth. This study deals with diffusive reaction experiments on shales and carbonate samples cored from an offshore structure in the Malaysian basin, a potential target for CO2-enhanced gas recovery. The aim is to evaluate the CO2 reaction front velocity in a typical shaly caprock and the mineral response of the reservoir. Rock samples were characterized in terms of texture, chemistry, and mineralogy by X-ray diffraction, electron microscopy (SEM), microanalysis (EDS), infrared spectroscopy (FT-IR), rock geochemistry (XRF), and mercury injection capillary permeability (MICP). Performed analyses show mineralogical alteration induced by CO2 as it penetrated into the samples. Carbonate dissolution and weathering of pyrite to form secondary carbonates belonging to siderite-ankerite series were observed along two reaction fronts. Estimated diffusion coefficients of CO2 are two orders of magnitude lower than CO2(aq) molecular diffusion in pure water and from half to an order of magnitude lower than diffusivity computed on unaltered sample, highlighting the important effect of gas–water–rock reactions on the CO2(aq) diffusivities in shales and carbonates. Results obtained in this study provide an insight regarding the effect of geochemical reactions on CO2 transport and represent a further discussion point on the diffusion coefficients. [ABSTRACT FROM AUTHOR]

The interpretation of low-temperature thermochronology (LTT) data in magmatic and metallogenic provinces requires a knowledge of the geothermal field through time. There, the challenge is differentiating rapid cooling following transient perturbations of the geotherms (reheating) from exhumational cooling induced by erosion during tectonic uplift or normal faulting. The Takab Range Complex (NW Iran) is a basement-cored range of the Arabia-Eurasia collision zone that experienced voluminous Eocene to Miocene magmatism and mineralization. Our new apatite and zircon (U-Th-Sm)/He and apatite fission track data, together with field observations, a dedicated numerical thermal model, and a re-evaluation of available geochronology data document the occurrence of a complex geological and thermal history including: (a) late Cretaceous-Paleocene exhumation possibly controlled by regional contractional deformation followed by Eocene deposition; (b) Oligocene to possibly early Miocene (29 to 22-20 Ma) exhumation of basement rocks from 13 to 8 km of depth, most likely through normal faulting during a thermal anomaly that led to migmatization and partial melting; (c) early to late Miocene (~22-20 or earlier to 11-10 Ma) regional subsidence with deposition of an up to ~2- to 3-km-thick Oligo-Miocene sedimentary sequence in association with the emplacement of shallow intrusions, which led to a partial to total reset of our LTT systems sometime between 18 and 13 Ma; and (e) erosional exhumation after 11-10 Ma with the development of a transpressional system and a master, right-lateral, strike slip fault (Chahartagh Fault). Our data highlights the impact of magmatic reheating on LTT ages in areas affected by intense magmatism. [ABSTRACT FROM AUTHOR]

Active hydrothermal travertine systems are ideal environments to investigate how abiotic and biotic processes affect mineralization mechanisms and mineral fabric formation. In this study, a biogeochemical characterization of waters, dissolved gases, and microbial mats was performed together with a mineralogical investigation on travertine encrustations occurring at the outflow channel of a thermal spring. The comprehensive model, compiled by means of TOUGHREACT computational tool from measured parameters, revealed that mineral phases were differently influenced by either abiotic conditions or microbially driven processes. Microbial mats are shaped by light availability and temperature gradient of waters flowing along the channel. Mineralogical features were homogeneous throughout the system, with euhedral calcite crystals, related to inorganic precipitation induced by CO2 degassing, and calcite shrubs associated with organomineralization processes, thus indicating an indirect microbial participation to the mineral deposition (microbially influenced calcite). The microbial activity played a role in driving calcite redissolution processes, resulting in circular pits on calcite crystal surfaces possibly related to the metabolic activity of sulfur‐oxidizing bacteria found at a high relative abundance within the biofilm community. Sulfur oxidation might also explain the occurrence of gypsum crystals embedded in microbial mats, since gypsum precipitation could be induced by a local increase in sulfate concentration mediated by S‐oxidizing bacteria, regardless of the overall undersaturated environmental conditions. Moreover, the absence of gypsum dissolution suggested the capability of microbial biofilm in modulating the mobility of chemical species by providing a protective envelope on gypsum crystals. [ABSTRACT FROM AUTHOR]

Total and leached Arsenic, Mercury and Antimony were determined in the topsoils developed on the mining waste dumping area of Le Lame (Mt. Amiata, central Italy) where the post-processing Hg-rich ore deposits from the mining area of Abbadia San Salvatore were stored. The concentrations of As, Hg and Sb were up to 610, 1910 and 1610 mg kg−1, respectively, while those in the leachates (carried out with CO2-saturated MilliQ water to simulate the meteoric water conditions) were up to 102, 7 and 661 μg·L−1, respectively. Most aqueous solutions were characterized by Hg content <0.1 μg·L−1. This is likely suggesting that the mine wastes (locally named "rosticci") were possibly resulting from an efficient roasting process that favored either the removal or inertization of Hg operated by the Gould furnaces and located in the southern sector of Le Lame. The highest values of total and leachate mercury were indeed mostly found in the northern portion where the "rosticci", derived by the less efficient and older Spirek-Cermak furnaces, was accumulated. The saturation index was positive for the great majority of leachate samples in Fe-oxy-hydroxides, e.g., ferrihydrite, hematite, magnetite, goethite, and Al-hydroxides (boehmite and gibbsite). On the other hand, As- and Hg-compounds were shown to be systematically undersaturated, whereas oversaturation in tripuhyte (FeSbO4) and romeite (Ca2Sb2O7) was evidenced. The Eh-pH diagrams for the three chalcophile elements were also constructed and computed and updated according to the recent literature data. [ABSTRACT FROM AUTHOR]

A new analytical method for the determination of the sulfur species ([SO.sub.2], [H.sub.2]S, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) in volcanic gases is proposed by revising, updating, and improving previous methods. The most significant advantages of the proposed procedure can briefly be summarized, as follows: (i) the reaction among sulfur species stops during the gas sampling by using preevacuated thorion-tapped vials with purified 0.15M [Cd(OH).sub.2] in 4 M NaOH to favor the precipitation of [H.sub.2]S as CdS; (ii) all the sulfur species ([SO.sub.2], [H.sub.2]S, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) are analyzed by ion chromatography, after conversion to [SO.sub.4], which allows the detection limit to be lowered significantly with respect to the previous studies; (iii) appropriate aliquots from intermediate steps may be used to determine other species commonly present in volcanic gases such as [CO.sub.2], HCl, HF, HBr, HI, and so forth; (iv) determination of all the other gas species is not jeopardized by the proposed method, i.e., one single vial can be used for analyzing the full chemical composition of a volcanic gas with the exception of [NH.sub.3]. Statistical parameters calculated from gas sampling data at the F5 crater fumarole in Vulcano Island (Aeolian Islands, southern Italy), suggest that the standard error of mean (s/[check] n) is higher for S (0.10), followed by [SO.sub.2], [H.sub.2]S, and [CO.sub.2] (0.04, 0.038, and 0.028, respectively). [SO.sub.2] shows the higher variation coefficient (12.1%) followed by [H.sub.2]S, S, and [CO.sub.2] (5.7, 1.5, and 0.8%, respectively). Furthermore, if the time dependence of sampling is taken into account, the measured values, instead of fluctuating in a random manner, tend to follow systematic patterns, out of statistical control, possibly suggesting a sort of natural fluctuation of the volcanic system. Other crater fumaroles from volcanic systems located in different geodynamical areas (Hawaii, USA, El Chichon, Mexico, Poas, Costa Rica) have been analyzed as well.

This study presents the results obtained by studying well integrity in the natural analogue for the geological storage of CO 2 of Sant’Albino, Southern Tuscany, which is affected by intense CO 2 degassing and where a thermal spa and a CO 2 production plant are present. Reaction Path Modeling (RPM) of cement hydration and carbonation as well as Reactive Transport Modeling (RTM) of cement alteration were used to investigate the processes occurring near a hypothetical average production well with a damaged leaking zone, affecting casing and cement, assuming a defined composition of class G Portland cement. It turns out that the advective flow of CO 2 from the damaged zone, first, leads to completion of cement carbonation and, second, promotes further cement alteration through considerable dissolution of carbonate minerals. These processes takes place in a relatively short time, in the order of some years. The ultimate consequence of these CO 2 -promoted comparatively fast chemical reactions is most likely CO 2 leakage to the surface. [ABSTRACT FROM AUTHOR]