Low Sulfide Concentrations Research Articles

Effect of sulfidogenesis on ferrihydrite geochemistry and associated arsenic fate.

The behavior of arsenic (As) in groundwater is closely related to the sulfidation of ferrihydrite. In the ternary ferrihydrite-As-sulfide system, ferrihydrite can either initially adsorb As before sulfide reduction or first encounter sulfide and then interact with the aqueous As, altering As fate. However, their relative contributions to the mineralogical transformation of ferrihydrite and subsequently associated As mobilization/redistribution remain poorly understood. Therefore, batch experiments combined with chemical, microscopic, and spectroscopic analyses were conducted to clarify the geochemistry of ferrihydrite and its influence on As behavior. Results indicated that in the pre-sorption groups, the secondary minerals were predominantly presented in amorphous phase due to the retardative effect of As. At low sulfide concentrations (S/Fe=0.04), the content of residual ferrihydrite was large, which favored As immobilization. At high sulfide concentrations (S/Fe=0.8), however, As was initially released into the solution and subsequently re-immobilized by secondary minerals. The adsorption capacity of the secondary minerals for As decreased with the increase in amorphous mackinawite formation. In the pre-sulfidation groups, rapid ferrihydrite reduction promoted the formation of crystalline minerals, significantly reducing their adsorption capacity. At low sulfide concentrations, the released As was partially adsorbed on the surface of crystalline goethite and lepidocrocite. At high sulfide concentrations, magnetite formed and favored As immobilization through its incorporation into magnetite particles. These results provide important insights into the geochemistry of Fe, S, and As in groundwater systems.

Potential for formation of methylated thioarsenates in geothermal environments

Geothermal waters typically have elevated arsenic (As) concentrations. Various As species have been identified, including methylated thioarsenates, which present a high environmental and health risk due to high mobility and toxicity. Upon discharge from hot springs, temperature and geogenic sulfide excess decrease, while redox potential increases. The combined effects of those parameters on activities of sulfate-reducing bacteria and methanogens and thereby on extent of As methylation versus thiolation is currently unknown. Here, we incubated sediments from alkaline hot springs and outflow channels at the Tengchong geothermal region in southwestern China, where inorganic and methylated thioarsenates had been detected, at temperatures between 20 to 90 °C with different initial aqueous As and sulfur species. Results from field samples and incubation experiments showed methylated thioarsenates, but no methylated oxyarsenates, implying quantitative thiolation even at low sulfide concentrations. Enrichment cultures derived from one sediment with quantitative formation of dimethyl-dithioarsenate (DMDTA) at 55 °C, showed a dominance of inorganic trithioarsenate at 35 °C and monomethylated thioarsenates at 55 °C when incubated with two other sediments. The rate-limiting step was microbially mediated As methylation from arsenite, which was not observed at 20 °C or >= 75 °C, in contrast to thiolation of already methylated arsenates. Addition of free sulfide and thiosulfate to incubation experiments promoted formation of inorganic or monomethylated high-thiolated arsenates, while sulfate promoted full methylation and formation of DMDTA, probably due to continuous low supply of microbially produced sulfide. Since DMDTA is more mobile and toxic than inorganic and monomethylated thioarsenates, understanding constraints to its formation is especially important for future risk assessment

Seasonal Sulfur Redox Cycling in Two Constructed Wetlands with Insight on How They Age.

Long-term metal remediation in wetland treatment systems (WTSs) involves facilitating dissimilatory sulfate reduction to produce sulfide and mineralize metals in deep sediments. We evaluated seasonal sulfur cycling in two constructed wetlands (Maintained WTS constructed in 2007, and the Unmaintained WTS constructed in 2000) on the Savannah River Site in Aiken, South Carolina, USA. Significant interactions in sulfide concentration were observed between sediment depth, season, and wetland (F = 4.64, df = 11, P = 3.28 × 10 - 5). In the Maintained WTS, dissimilatory sulfate reduction dominated the surface sediments during the warm season (0-2cm depth, t=-2.66, P = 9.70 × 10 - 3), unlike the Unmaintained system. Sulfate concentrations in pore waters increased in the warm season (F = 7.84, df = 1, P = 6.50 × 10 - 3), contrary to expectations. Sulfur limitation in the Unmaintained WTS during the warm season correlated with increased sulfur assimilation in giant bulrush. Lower sulfide concentrations in surface sediments of the Unmaintained WTS illustrated aging effects. The Maintained WTS shows potential for managing erosion, pH reduction, and sulfur limitation observed in the older Unmaintained WTS.

High-sensitive and fast-responsive In2O3 thin film sensors for dual detection of NO2 and H2S gases at room temperature

In this work, the room-temperature dual gas sensing characteristics of indium oxide (In2O3) thin films towards NO2 and H2S have been studied. In2O3 thin films were synthesized by the thermal oxidation of indium metal films of various thicknesses in the range of 50–250 nm deposited by thermal evaporation method. Grazing incidence X-ray diffraction (GI-XRD) revealed the change in preferred orientation of In2O3 thin films corresponding to varying thickness, while field-emission electron microscopy studies showcased evolving surface morphologies from individual grains to granular network with respect to the increase in film thickness. Investigations were made on the ability of In2O3 thin films to detect various low concentrations of nitrogen dioxide (NO2) and hydrogen sulfide (H2S) gases at ambient temperature. In2O3 thin films synthesized using 100 nm thick In films exhibited good sensing response of around 58 and 68 % towards NO2 and H2S gases of 5 ppm respectively, at room temperature (27 °C) with the response time of 36 and 18 s. Remarkably, the lower experimental detection limit of these toxic gases could be extended up to 100 ppb. Using X-ray photoelectron spectroscopy, a large presence of surface oxygen is observed on the In2O3 thin film. The sensor has demonstrated remarkable sensing abilities, including strong selectivity, quick sensing response, and good repeatability.

Influence of environmental settings, including vegetation, on speciation of the redox-sensitive elements in the sediments of monomictic Lake Kinneret

AbstractThe redox conditions in the littoral limnic sediments may be affected by the penetration of plant roots which provide channels for oxygen transport into the sediment while decomposition of the dead roots results in consumption of oxygen. The goal of this work was to study the impact of environmental parameters including penetration of roots of Cyperus articulatus L. into the sediments on cycling of the redox-sensitive elements in Lake Kinneret. We measured roots content, porosity, and chemical parameters including pH, sulfur, iron and manganese speciation in the sediments from the shore, littoral and sublittoral zones with and without vegetation. Our results show that at ≥ 12 m water depth, the upper 10 cm of the sediments are affected by the active sulfur cycling with concentrations of hydrogen sulfide > 70 μM near the sediment–water interface. Speciation of sulfur, iron, and manganese in the upper 10 cm of littoral sediments, which are covered by < 20 cm of water, are affected by their permeability and, to a lesser extent, by roots penetration. In the case when sediments are not covered by water, oxygen penetration to the sediments by desiccation is an additional important control of the redox zonation in the surface sediments. In the shore sediments, despite relatively high concentrations of sulfate in the pore-waters, sulfur cycling may be described as “cryptic” as expressed by very low concentrations of hydrogen sulfide in the pore-waters. This is most likely a result of its fast reoxidation by the abundant highly reactive Fe(III) and Mn(IV) phases.

Chemiresistive NH3 and H2S sensors based on thin films of vitamin B12 derivatives

Despite the large number of materials, e.g. semiconducting oxides, carbon nanomaterials, conducting polymers and others, that are used as active layers of chemiresistive sensors to ammonia and hydrogen sulfide, the search for new materials remains an urgent task. Special attention is paid to the search for environmentally friendly materials. Corrinoids are naturally occurring coordination complexes consisting of a central cobalt ion and a tetrapyrrole ligand called a corrin ring. Cobalamins and their derivatives are widely used as active layers of optical and electrochemical sensors. At the same time, vitamin B12 derivatives have not been studied as active layers of chemiresistive gas sensors. In this work, films of two vitamin B12 derivatives, viz. dicyanocobyrinic acid heptabutyl ester (DC) and its aquacyano form, aquacyanocobyrinic acid heptabutyl ester (AC), deposited by spin coating and drop casting techniques onto interdigitated electrodes, were tested for the first time as active layers of chemiresistive sensors for the detection of low concentrations of ammonia and hydrogen sulfide (1–50 ppm) in air. It was shown that films of both vitamin B12 derivatives demonstrated reversible sensor response to NH3 and H2S at room temperature. The limit of detection (LOD) of H2S was 0.1 ppm for both vitamin B12 derivatives, while LOD of ammonia was noticeably lower (0.06 ppm) in the case of AC films than in the case of DC films (0.4 ppm). Both sensors demonstrated a fairly low regeneration time, which did not exceed 180 s for 5 ppm of NH3 and 185 s for 5 ppm of H2S.

Research on hydrogen sulfide removal from water using a hydroejector

The war in Ukraine has significantly impacted the country's water resources, leading to deteriorated water quality, threats to drinking water supplies, and long-term environmental issues. Intensive pollution of surface water sources has necessitated increased use of groundwater for drinking purposes. The quality of groundwater in Ukraine varies greatly, often containing concentrations of iron, manganese, hardness salts, and hydrogen sulfide that exceed acceptable limits. Hydrogen sulfide concentrations in different regions range from 1 to over 20 mg/dm³, far exceeding the permissible limit of 0.05 mg/dm³ for drinking water. In the southern regions of Ukraine, such as Kherson, Mykolaiv, and Odesa oblasts, hydrogen sulfide levels exceed the norm by more than 100 times. Existing water purification methods for hydrogen sulfide require the construction of expensive aeration facilities with various loadings, biological reactors, and oxidation filters, which entail significant capital and operational costs. Moreover, these facilities do not always ensure the desired water quality. Therefore, developing new methods and technologies aimed at intensifying hydrogen sulfide removal from water, along with various devices and structures for their implementation, is a pressing issue related to supplying the population with quality water. Among the developed approaches, the use of aeration as an independent method for purification is notable; however, it is used for low hydrogen sulfide concentrations and is most effective at low water pH levels. This article presents the results of experimental studies on the purification of groundwater from hydrogen sulfide by aeration using a hydroejector. Optimal parameters for the hydrogen sulfide removal process, depending on its concentration and water pH, were determined. The effectiveness of water purification using the hydroejector was substantiated and investigated. The key operational parameters of the hydroejector were established.

Coupled redox cycling of arsenic and sulfur regulates thioarsenate enrichment in groundwater

High‑arsenic groundwater is influenced by a combination of processes: reductive dissolution of iron minerals and formation of secondary minerals, metal complexation and redox reactions of organic matter (OM), and formation of more migratory thioarsenate, which together can lead to significant increases in arsenic concentration in groundwater. This study was conducted in a typical sulfur- and arsenic-rich groundwater site within the Datong Basin to explore the conditions of thioarsenate formation and its influence on arsenic enrichment in groundwater using HPLC-ICPMS, hydrogeochemical modeling, and fluorescence spectroscopy. The shallow aquifer exhibited a highly reducing environment, marked by elevated sulfide levels, low concentrations of Fe(II), and the highest proportion of thioarsenate. In the middle aquifer, an optimal ∑S/∑As led to the presence of significant quantities of thioarsenate. In contrast, the deep aquifer exhibited low sulfide and high Fe(II) concentration, with arsenic primarily originating from dissolved iron minerals. Redox fluctuations in the sediment driven by sulfur‑iron minerals generated reduced sulfur, thereby facilitating thioarsenate formation. OM played a crucial role as an electron donor for microbial activities, promoting iron and sulfate reduction processes and creating conditions conducive to thioarsenate formation in reduced and high‑sulfur environments. Understanding the process of thioarsenate formation and the influencing factors is of paramount importance for comprehending the migration and redistribution of arsenic in groundwater systems.

Organic sulfur from source to sink in low‐sulfate Lake Superior

AbstractOrganic sulfur plays a crucial role in the biogeochemistry of aquatic sediments, especially in low sulfate (< 500 μM) environments like freshwater lakes and the Earth's early oceans. To better understand organic sulfur cycling in these systems, we followed organic sulfur in the sulfate‐poor (< 40 μM) iron‐rich (30–80 μM) sediments of Lake Superior from source to sink. We identified microbial populations with shotgun metagenomic sequencing and characterized geochemical species in porewater and solid phases. In anoxic sediments, we found an active sulfur cycle fueled primarily by oxidized organic sulfur. Sediment incubations indicated a microbial capacity to hydrolyze sulfonates, sulfate esters, and sulfonic acids to sulfate. Gene abundances for dissimilatory sulfate reduction (dsrAB) increased with depth and coincided with sulfide maxima. Despite these indicators of sulfide formation, sulfide concentrations remain low (< 40 nM) due to both pyritization and organic matter sulfurization. Immediately below the oxycline, pyrite accounted for 13% of total sedimentary sulfur. Both free and intact lipids in this same interval accumulated disulfides, indicating rapid sulfurization even at low concentrations of sulfide. Our investigation revealed a new model of sulfur cycling in a low‐sulfate environment that likely extends to other modern lakes and possibly the ancient ocean, with organic sulfur both fueling sulfate reduction and consuming the resultant sulfide.

Contrasting Intermediate-Temperature La0.7Sr0.3VO3.86-⸹ (LSV) Porous Catalyst Elevated Sulfur Tolerance Using Gaseous and Liquid Fuel Explored through Experimental and Modeling Characterization Over Time

The U.S. Army is investigating Solid Oxide Fuel Cells (SOFCs), which can produce clean, secure, and sustainable energy to replace existing power sources. Today SOFCs are known to provide high density, high efficiency power with long term stability at low cost and environmental impact, utilizing a variety of naturally sourced fuels such as hydrogen, hydrocarbons, and alcohols. This fuel flexibility makes SOFCs attractive for use with multiple applications and helps bridge the gap between current hydrogen-fueled SOFC technologies and future hydrocarbon-fueled based use. Despite this potential, many technical hurdles remain, such as thermal stress cracking and coarsening, delamination, and catalyst contamination. Catalyst contamination is of particular concern for the U.S. Army, which operates on JP-8 kerosene-based fuel via AR-70 single fuel policy, as sulfur impurities commonly found in naturally sourced hydrocarbon-based fuels, can poison the catalyst, permanently degrading SOFC system performance, even at low concentrations. As the U.S. Army begins to investigate SOFCs to enable additional capabilities like silent watch, advanced radios, and exportable power in their fleet, catalyst poisoning from sulfur presents a concerning technology gap that must be addressed, especially since it is also possible that sulfur contaminated fuel, scavenged in theater, may be used, and could contain elevated levels (>300ppm) of sulfur.While lower temperature SOFC operation is also actively being pursued to help alleviate physical material degradation issues, with the introduction of hydrocarbon-based fuels, catalyst development to reduce sulfur poisoning degradation also needs further exploration. This study continues to experimentally and theoretically investigate the response of sulfur tolerant anode catalyst La0.7Sr0.3VO3.86-⸹ (LSV) at currently targeted SOFC intermediate operating temperatures (400-600°C). We have previously investigated low and moderate hydrogen sulfide (H2S) concentrations (30ppm, 300ppm) in balance hydrogen and methane gas environments for up to 100 hours. In this work, LSV showed significant sulfur tolerance in hydrogen and methane balance gases when compared to the industry standard Ni-YSZ anode, where sulfur adsorption rates were 278-287x lower in some cases. The lowest rates occurred between 600-700°C, which is attributed to the cubic structure the material presents in this temperature range. Higher adsorption rates were observed in the monoclinic/tetragonal structure the material presents at temperatures between 400-500°C. Average adsorption rates were overall higher in methane. When compared against Ni-YSZ, which is known to accumulate sulfur from hydrogen sulfide via two-step dissociative adsorption, LSV was observed to accumulate sulfur through weak chemisorption (H2S*, 0.43 eV max) of molecular hydrogen sulfide on oxygen deficient surfaces and one-step dissociative adsorption (H2S*, 0.34 eV, max, HS*+H*, 8.34 eV, max) on oxygen sufficient surfaces. The weak chemisorption behavior on oxygen deficient surfaces is attributed to the reduced oxygen stoichiometry of the material, in which only vanadium V2+/3+ couples exist. Overall, molecular adsorption/dissociation was observed to occur near strontium defects on LaO/SrO terminations. The propensity of H2S adsorption on LSV surfaces was observed to be significantly less for oxygen deficient LSV, and significantly higher for oxygen sufficient LSV, when compared to H2S adsorption calculations on Ni (100) surfaces, which follow a two-step dissociative adsorption reaction (H2S* → HS*+H* → H*+S*), resulting in a strongly adsorbed S* species (5.96 eV, max).Under the Army’s single fuel policy, it is more likely SOFCs would be fueled using hydrogen and/or methane, which are both gases, however SOFCs in the future could also be directly fueled using liquid alcohol fuels, or as scavenged from theater. Typical small alcohol molecules (methanol or ethanol) do not contain high concentrations of sulfur; however, alcohols can be contaminated with sulfur-containing hydrocarbons. This work will investigate sulfur adsorption using methanol contaminated with 300ppm thiophene using the same operating temperature and heating duration conditions with hydrogen and methane. These results will be contrasted against the 300ppm H2S hydrogen and methane results previously reported. Figure 1

Dissolution Potential of Elemental Mercury in the Presence of Bisulfide and Implications for Mobilization.

Liquid elemental mercury (Hg0L) pollution can remain in soils for decades and, over time, will undergo corrosion, a process in which the droplet surface oxidizes soil constituents to form more reactive phases, such as mercury oxide (HgO). While these reactive coatings may enhance Hg migration in the subsurface, little is known about the transformation potential of corroded Hg0L in the presence of reduced inorganic sulfur species to form sparingly soluble HgS particles, a process that enables the long-term sequestration of mercury in soils and generally reduces its mobility and bioavailability. In this study, we investigated the dissolution of corroded Hg0L in the presence of sulfide by quantifying rates of aqueous Hg release from corroded Hg0L droplets under different sulfide concentrations (expressed as the S:Hg molar ratio). For droplets corroded in ambient air, no differences in soluble Hg release were observed among all sulfide exposure levels (S:Hg mole ratios ranging from 10-4 to 10). However, for droplets oxidized in the presence of a more reactive oxidant (hydrogen peroxide, H2O2), we observed a 10- to 25-fold increase in dissolved Hg when the oxidized droplets were exposed to low sulfide concentrations (S:Hg ratios from 10-4 to 10-1) relative to droplets exposed to high sulfide concentrations. These results suggest two critical factors that dictate the release of soluble Hg from Hg0L in the presence of sulfide: the extent of surface corrosion of the Hg0L droplet and sufficient sulfide concentration for the formation of HgS solids. The mobilization of Hg0L in porous media, therefore, largely depends on aging conditions in the subsurface and chemical reactivity at the Hg0L droplet interface.

Major contribution of sulfide-derived sulfur to the benthic food web in a large freshwater lake.

In freshwater systems, contributions of chemosynthetic products by sulfur-oxidizing bacteria in sediments as nutritional resources in benthic food webs remain unclear, even though chemosynthetic products might be an important nutritional resource for benthic food webs in deep-sea hydrothermal vents and shallow marine systems. To study geochemical aspects of this trophic pathway, we sampled sediment cores and benthic animals at two sites (90 and 50 m water depths) in the largest freshwater (mesotrophic) lake in Japan: Lake Biwa. Stable carbon, nitrogen, and sulfur isotopes of the sediments and animals were measured to elucidate the sulfur nutritional resources for the benthic food web precisely by calculating the contributions of the incorporation of sulfide-derived sulfur to the biomass and of the biogeochemical sulfur cycle supporting the sulfur nutritional resource. The recovered sediment cores showed increases in 34 S-depleted sulfide at 5 cm sediment depth and showed low sulfide concentration with high δ34 S in deeper layers, suggesting an association of microbial activities with sulfate reduction and sulfide oxidation in the sediments. The sulfur-oxidizing bacteria may contribute to benthic animal biomass. Calculations based on the biomass, sulfur content, and contribution to sulfide-derived sulfur of each animal comprising the benthic food web revealed that 58%-67% of the total biomass sulfur in the benthic food web of Lake Biwa is occupied by sulfide-derived sulfur. Such a large contribution implies that the chemosynthetic products of sulfur-oxidizing bacteria are important nutritional resources supporting benthic food webs in the lake ecosystems, at least in terms of sulfur. The results present a new trophic pathway for sulfur that has been overlooked in lake ecosystems with low-sulfate concentrations.

Research on the distribution of S species in the pressure oxidation leaching process of SrS solution

Strontium compounds apply extensively in a variety of domains. Commonly, strontium compounds are made by carbonization of SrS solution. H2S is readily generated in this process. To avoid H2S byproducing, a novel strategy for the pressure oxidation leaching process of SrS solution was used. The overoxidation of sulfides was restrained, and a higher separation efficiency of Sr and S was obtained, which was beneficial for synthesizing other strontium compounds. The effects of the oxidation pH environment, reaction temperature, initial total sulfide concentration and reaction time on the conversion ratio of S species were investigated. The results showed that S0 was preferably generated in a near-neutral, low-temperature and low initial total sulfide concentration oxidation environment. The optimum oxidation conditions were summarized experimentally: 48 mL/L HCl (pH = 7.11), 25 °C reaction temperature, 8.2 g/L initial total sulfide concentration and 60 min reaction time. The optimum conversion ratios were obtained under optimum oxidation conditions as follows: χsulfide 2.3%, χH2S 0.5%, χS0 81.5%, χinter 10.0% and χS - Sr 5.7%. SrCl2 crystal was recovered finally from the leachate. At last, the pressure oxidation mechanism of SrS was discussed.

Gold-nanoparticle-decorated Tin Oxide of a Gas Sensor Material for Detecting Low Concentrations of Hydrogen Sulfide

Gold-nanoparticle-decorated Tin Oxide of a Gas Sensor Material for Detecting Low Concentrations of Hydrogen Sulfide

Low sulfide concentration in Mercury’s smooth plains inhibits hollows

MESSENGER (Mercury, Surface, Space Environment, Geochemistry, and Ranging) mission to Mercury led to the discovery of hollows. These geological landforms have no close counterpart on other airless silicate bodies. Multispectral images and geochemical measurements by MESSENGER suggest that hollows are formed by the loss of volatile-bearing minerals. We investigated the mineralogical composition of the hollows using near-ultraviolet to near-infrared spectra obtained by MESSENGER. We compared reflectance spectra of hollows with laboratory spectra of Mercury's analogs: sulfides, chlorides, silicates, and graphite. The best candidates to reproduce the curvature of the hollow spectra are calcium sulfide, magnesium sulfide, and sodium sulfide. In addition, we performed spectral modeling with spectra obtained at the highest spectral and spatial resolution within the hollows. Our results show that the enrichment of sulfides in hollow material is up to two times higher than the sulfide concentration derived from chemical measurements of Mercury's high-reflectance smooth plains. This result explains the small percentage of hollows found within these plains.

Quantifying sulfidization and non-sulfidization in long-term in-situ microbial colonized As(V)-ferrihydrite coated sand columns: Insights into As mobility

Sulfide-induced reduction (sulfidization) of arsenic (As)-bearing Fe(III) (oxyhydro)oxides may lead to As mobilization in aquifer systems. However, little is known about the relative contributions of sulfidization and non-sulfidization of Fe(III) (oxyhydro)oxides reduction to As mobilization. To address this issue, high As groundwater with low sulfide (LS) and high sulfide (HS) concentrations were pumped through As(V)-bearing ferrihydrite-coated sand columns (LS-column and HS-column, respectively) being settled within wells in the western Hetao Basin, China. Sulfidization of As(V)-bearing ferrihydrite was evidenced by the increase in dissolved Fe(II) and the presence of solid Fe(II) and elemental sulfur (S0) in both the columns. A conceptual model was built using accumulated S0 and Fe(II) produced in the columns to calculate the proportions of sulfidization-induced Fe(III) (oxyhydro)oxide reduction and non-sulfidization-induced Fe(III) (oxyhydro)oxide reduction. Fe(III) reduction via sulfidization occurred preferentially in the inlet ends (LS-column, 31 %; HS-column, 86 %), while Fe(III) reduction via non-sulfidization processes predominated in the outlet ends (LS-column, 96 %; HS-column, 86 %), and was attributed to the metabolism of genera associated with Fe(III) reduction (including Shewanella, Ferribacterium, and Desulfuromonas). Arsenic was mobilized in the columns via sulfidization and non-sulfidization processes. More As was released from the solid of the HS-column than that of the LS-column due to the higher intensity of sulfidization in the presence of higher concentrations of dissolved S(-II). Overall, this study highlights the sulfidization of As-bearing Fe(III) (oxyhydro)oxides as an important As-mobilizing pathway in complex As-Fe-S bio-hydrogeochemical networks.

Hybrid material based on single walled carbon nanotubes and cobalt phthalocyanine bearing sixteen pyrene moieties as a sensing layer for hydrogen sulfide detection

We report on a sensor platform for the determination of hydrogen sulfide based on a new hybrid material obtained by the non-covalent functionalization of single-walled carbon nanotubes (SWCNT) with a novel cobalt phthalocyanine bearing 16 pyrene substituents (CoPc-Pyr). The structural features of the hybrid were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy, and thermogravimetric analysis (TGA). The sensor characteristics of SWCNT/CoPc-Pyr hybrid layers prepared by spin coating of its suspension in dichloromethane were studied against low concentrations of hydrogen sulfide (0.5–50 ppm) with the limit of detection (LOD) of 38 ppb and response and recovery time of 60 s and 80 s, respectively. This LOD value lies in the appropriate range and the prepared hybrid material is promising for the creation of the sensors for the detection of H2S, which can be used as an important biomarker of halitosis and asthma. It was shown that the SWCNT/CoPc-Pyr hybrid could be successfully used for the selective detection of H2S in the presence of carbon dioxide, hydrogen, ethanol, acetone, and dichloromethane.

Influence of hydrated Ca<sup>2+</sup> and Mg<sup>2+</sup> complexes on the sulfidization of smithsonite: Density functional based tight binding (DFTB+) study

Ca<sup>2+</sup> and Mg<sup>2+</sup> are the most dominating unavoidable ions in the smithsonite flotation. In this paper, the effect of Ca<sup>2+</sup> (Mg<sup>2+</sup>) on the surface of smithsonite sulfidization in a system where water molecules are present was investigated using density functional based tight binding (DFTB+) simulations for the first time. The results indicated that the adsorption of hydrated Ca<sup>2+</sup> complexes is stronger than that of hydrated Mg<sup>2+</sup> complexes on the hydrated smithsonite (101) surface. In addition, at low concentrations of sodium sulfide, there is no adsorption of HS- on the surface pre-adsorbed with hydrated Ca<sup>2+</sup> complexes, but only on the surface pre-adsorbed with hydrated Mg<sup>2+</sup> complexes. At high concentrations of Na<sub>2</sub>S, S<sup>2-</sup> weakens the adsorption of hydrated Ca<sup>2+</sup> complexes due to competitive adsorption, but the presence of S<sup>2-</sup> could desorb hydrated Mg<sup>2+</sup> complexes from the surface. The results compared the differences in effects of Ca<sup>2+</sup> and Mg<sup>2+</sup> on smithsonite sulfidization, which could provide an atomic scale basis for researching the surface sulfidization of oxide minerals.

Progressive expansion of seafloor anoxia in the Middle to Late Ordovician Yangtze Sea: Implications for concurrent decline of invertebrate diversity

The Great Ordovician Biodiversification Event (GOBE) achieved its peak during the Middle Ordovician, likely in association with climatic cooling and a rise of atmospheric O2. However, unstable redox states developed widely in contemporaneous epeiric seas, challenging previous assumptions about sustained oceanic oxygenation driven by deep-ocean ventilation in the aftermath of Ordovician cooling. Here, we investigate two Middle-Upper Ordovician shale-dominated successions from intra-shelf basin and slope settings of the Yangtze Sea, South China. Negative shifts in bulk δ15N and productivity proxies reveal temporal changes in the pattern of nutrient cycling under moderate-to-high productivity conditions, which were likely sustained by increased upwelling of cold and nutrient-rich deep waters in sync with contemporaneous climatic cooling. As a result, marine anoxia likely expanded in deep waters of the Yangtze Sea, as reflected in enrichments of highly reactive iron and redox-sensitive metals (Mo, U). Although moderate Mo abundances (25-50 ppm) and δ98/95Mo values (+0.4 to +0.8‰) within the euxinic interval suggest that bottom waters had low sulfide concentrations, the δ98/95Mo values are comparable with those of coeval euxinic facies (∼+0.6‰). Furthermore, our modeling results show that low δ98/95Mo can be produced when sulfidic sinks dominate Mo removal, suggesting that Middle-Late Ordovician oceans may have been less oxygenated than previously assumed, at least for the continental seas of South China, Baltica and Laurentia. These environmental changes may provide a new explanation for the ∼50% decline of invertebrate species following the peak of GOBE. Our findings thus link the progressive expansion of marine anoxia and climatic cooling to a profound biotic change during the Mid-Late Ordovician Period.

Comparison of Operating Atmosphere Impact on La0.7Sr0.3V3.86-⸹ (LSV) Intermediate-Temperature Solid Oxide Fuel Cell Sulfur Tolerance Explored Through Experimental and Modeling Characterization Over Time

Experts have long projected that in the future solid oxide fuel cells (SOFCs) could provide a viable path for the replacement of existing power sources and the production of clean, secure, and sustainable energy. Today, not only have SOFCs matured as a technology with a proven ability to provide high density, high efficiency power with long term stability at low cost and environmental impact, but with the theoretical capacity to utilize a variety of naturally sourced fuels. This theoretical capacity makes their potential use attractive in many additional applications and positions SOFCs to be the technology which can bridge the gap between current hydrocarbon fueled technologies and future hydrocarbon fueled electric technologies. That said, there remains many technical hurdles associated with the incorporation of naturally sourced fuels, to include thermal stress cracking and catalyst coarsening, delamination, and poisoning. Catalyst poisoning, specifically arising from sulfur impurities in naturally sourced fuels, remains one of the largest SOFC technical challenges, since their presence, even at low concentrations, have now shown permanent performance degradation. As the U.S. Army begins to investigate SOFCs to enable additional capabilities like silent watch, advanced radios, and exportable power in their fleet, catalyst poisoning from sulfur impurities presents a concerning technology gap which must be addressed, as the entire fleet operates on JP-8 kerosene-based fuel, which by specification can contain up to 3000 ppm of sulfur, via AR-70 single fuel policy.As SOFC technologies migrate to lower temperature operation to resolve physical degradation issues, the development catalysts materials with greater sulfur tolerance are being explored to resolve issues of chemical degradation related to sulfur poisoning. In this study, a previously reported, high temperature, sulfur tolerant SOFC catalyst, La0.7Sr0.3VO3.86-⸹ (LSV), was further experimentally investigated via Optical Microscopy, X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive Spectroscopy for its sulfur tolerance at currently targeted SOFC intermediate operating temperatures (400-600°C) in wide range of hydrogen sulfide (30ppm, 300ppm and 10vol%) balance hydrogen gas environments for up to 100 hours. When compared against the industry standard Ni-YSZ anode, LSV was observed to have significantly lower (287x) sulfur adsorption rates, with the lowest rates observed between 600-700°C. This behavior is attributed the cubic structure the material presents in this temperature range. Higher adsorption rates were observed in the monoclinic/tetragonal structure the material presents at temperatures between 400-500°C. This study was further supplemented by a theoretical investigation of hydrogen sulfide adsorption on low index LSV surfaces via periodic Density Functional Theory. When compared against Ni-YSZ, which is known to accumulate sulfur from hydrogen sulfide via two-step dissociative adsorption, LSV was observed to accumulate sulfur through weak chemisorption (0.43 eV max) of undissociated molecular hydrogen sulfide only. The weak chemisorption behavior is attributed to structural surface changes due to oxygen vacancies near strontium defects, wherein the strongest adsorption energies were observed, and in direct contrast to similar calculations of hydrogen sulfide adsorption with low index surfaces of LVO3, wherein no adsorption was observed.Since it is likely SOFCs will operate on hydrocarbon fuels, as well as compressed hydrogen gas in the future, this study is also currently experimentally investigating sulfur accumulation under the same operating conditions above with hydrogen sulfide mixtures in methane gas. Methane is a small hydrocarbon chain, which will help minimize the accumulation of carbon deposition. Initial comparisons of sulfur adsorption between hydrogen and methane gas mixtures, using low hydrogen sulfide concentrations, show they are statistically similar, although methane gas exposure was observed to result in the formation of two activation energies, which was not observed with hydrogen mixture previously. The methane gas was also observed to promote LSV to take the monoclinic/tetragonal structure at lower operating temperatures than hydrogen mixtures. This observation may lead to elevated sulfur adsorption rates at higher hydrogen sulfide concentrations. Finally, it was originally observed during experimental exposure experiments with hydrogen sulfide/hydrogen gas balance mixtures that higher concentrations of lattice oxygen, present at lower temperatures, had a positive correlation with sulfur accumulation in the LSV material. This study is therefore currently theoretically investigating the effect of lattice oxygen content on the LSVs structure via Density Functional Theory, which could lead to further derivation from optimal cubic configuration, which may lead to configurations which increase sulfur adsorption. Figure 1