Oxidation Of Hydrogen Sulfide Research Articles

Authigenic carbonate and native sulfur formation in Messinian (upper Miocene) marine sediments: Sedimentological, petrographical and geochemical constraints

Carbonate concretions accompanied by elemental sulfur were found in an early Messinian (Late Miocene) marine succession of NW Italy. The rocks were studied with an integrated approach including sedimentological, petrographical, stable isotope (carbon, oxygen, and multiple sulfur isotopes), and lipid biomarker analyses. Unlike other examples from Messinian strata of the Mediterranean area, the studied carbonate and sulfur concretions did not derive from the diagenetic replacement of sulfate minerals. Three lithofacies were distinguished: a) laminated lithofacies representing aphotic carbonate stromatolites enclosing fossils of filamentous sulfide-oxidizing bacteria; b) brecciated lithofacies deriving from the brecciation of carbonate stromatolites by mud injections; c) sulfur-bearing lithofacies deriving from the precipitation of thin laminae of elemental sulfur at or close to the sediment-water interface. The carbon and oxygen stable isotope composition of authigenic carbonate minerals and lipid biomarkers indicate that the initial formation of the laminated lithofacies was favored by organoclastic sulfate reduction in the shallow subsurface close to the sediment-water interface, producing sulfide that sustained dense microbial mats of sulfide-oxidizing bacteria at the seafloor. Calcification of the mats and consequent formation of stromatolites were possibly favored by nitrate-driven sulfide oxidation at the seafloor. The subsequent brecciation of the stromatolites was apparently the consequence of sulfate-driven anaerobic oxidation of methane (SD-AOM) in an underlying sulfate-methane transition zone (SMTZ). Focused fluid flow from below, possibly resulting from destabilization of gas hydrates, was not only responsible for the brecciation of the stromatolites, but also for the delivery of bicarbonate ions and the consequent precipitation of additional, 13C-depleted calcite (δ13C values as low as −52‰). Along with bicarbonate, also hydrogen sulfide was produced by SD-AOM at the SMTZ and was transported upwards. The oxidation of hydrogen sulfide at or close to the seafloor promoted the formation of elemental sulfur characterized by δ34S values and Δ33S values close to coeval seawater sulfate.

Insight into the effective electrocatalytic sulfide removal from aqueous solutions using surface oxidized stainless-steel anode and its desulfurization mechanism

The electrochemical oxidation of hydrogen sulfide (H2S) has shown its potential for the real application of H2S emission control in wastewater treatment. In this study, a surface corrosion treatment of stainless steel (SS) was optimized by regulate Ni content in the oxide film on the SS AISI 304 surface for sulfide removal. The X-ray photoelectron spectroscopy and linear sweeping voltammetry results indicated a higher Ni content in the oxide film of surface-oxidized stainless steel (SOSS) attributed to a higher sulfide removal potential. Sulfide removal experiment results showed that SS-150 (with 150 s anodic pretreatment) anodes achieved the highest Ni content of 69% with the best sulfide removal efficiency, i.e., 97% within 48 h, which increased by 20% compared to the untreated SS. This study also demonstrated a strategy for in situ removal of deposited sulfur on the anodes by cathodic treatment at −0.38 V vs. RHE to alleviate the common issue of sulfur passivation. Density functional theory (DFT) calculation revealed that NiOOH was the major active species in SS-150 oxide film for a faster sulfide removal rate. The study developed a SS surface modification process for Ni content regulation that contributed to better sulfide removal efficiency.

Engineering bifunctional sites in covalent polymers for boosting photocatalytic H2S oxidation

The development of catalyst for photocatalytic hydrogen sulfide (H2S) oxidation with excellent efficiency and regeneration properties is a significant challenge. Herein, the pyridine units as bifunctional sites are incorporated in covalent polymers (CPs) by CN coupling reaction, which exhibit photocatalytic H2S selective oxidation to sulfur conversion (95 %) under visible light in a continuous flow system, more than twice that of the pristine sample (40 %). Meanwhile, the photocatalytic H2S conversion rate had a linear function relationship with pyridinic N content, demonstrating the substantial role of pyridine in photocatalytic H2S oxidation process. According to experimental results, the pyridine unit not only acted as the structural base site to improve the H2S chemisorption, but also served as electron withdrawing unit to construct electron donor-acceptor (D-A) structure with benzene, which optimized the light absorption, charge separation and migration. In addition, series in-situ measurements and electron density difference simulations revealed the significant role of electron D-A structure in H2S adsorption and activation process. By exploring the effect of pyridine unit in CPs on H2S conversion process, this work provides a new idea for the subsequent study of photocatalytic H2S oxidation.

Sulfide catabolism in hibernation and neuroprotection

The mammalian brain is exquisitely vulnerable to lack of oxygen. However, the mechanism underlying the brain's sensitivity to hypoxia is incompletely understood. In this narrative review, we present a case for sulfide catabolism as a key defense mechanism of the brain against acute oxygen shortage. We will examine literature on the role of sulfide in hypoxia/ischemia, deep hibernation, and leigh syndrome patients, and present our recent data that support the neuroprotective effects of sulfide catabolism and persulfide production. When oxygen levels become low, hydrogen sulfide (H2S) accumulates in brain cells and impairs the ability of these cells to use the remaining, available oxygen to produce energy. In recent studies, we found that hibernating ground squirrels, which can withstand very low levels of oxygen, have high levels of sulfide:quinone oxidoreductase (SQOR) and the capacity to catabolize hydrogen sulfide in the brain. Silencing SQOR increased the sensitivity of the brain of squirrels and mice to hypoxia, whereas neuron-specific SQOR expression prevented hypoxia-induced sulfide accumulation, bioenergetic failure, and ischemic brain injury in mice. Excluding SQOR from mitochondria increased sensitivity to hypoxia not only in the brain but also in heart and liver. Pharmacological agents that scavenge sulfide and/or increase persulfide maintained mitochondrial respiration in hypoxic neurons and made mice resistant to ischemic injury to the brain or spinal cord. Drugs that oxidize hydrogen sulfide and/or increase persulfide may prove to be an effective approach to the treatment of patients experiencing brain injury caused by oxygen deprivation or mitochondrial dysfunction.

Oxidation of hydrogen sulfide and CO2 mixtures: Laser-based multi-speciation and kinetic modeling

Hydrogen sulfide (H2S), encountered in sour natural gas and in fossil fuel refineries, has adverse health and environmental impacts, but also the potential to be a source of clean hydrogen. This work addresses knowledge gaps and inconsistencies in H2S oxidation measurements and model predictions, emphasizing the scarcity of detailed kinetic modeling of H2S oxidation in the presence of carbon dioxide (CO2), a significant component of acid gas. This study leverages a shock tube coupled with laser absorption techniques to investigate the oxidation of mixtures of acid gas (H2S and CO2) with high H2S concentrations, equivalence ratios between 1.5 and 3.0, over the temperature range of 1300 – 1900 K and pressure near 1.3 bar. A detailed kinetic mechanism is proposed and validated through the measurement of time-histories of SO2, H2O, and CO, during fuel-rich acid gas oxidation. For the species measurements, we first conducted a comprehensive wavelength analysis for interference-free detection of the target species, providing new temperature-dependent absorption cross-section measurements of SO2 at its strongest IR band; moreover, we proposed a new laser-based thermometry technique for temperature time-history measurements behind reflected shock waves. The proposed kinetic mechanism is updated based on our recently calculated rate constants for reactions involving sulfurous species using high-level quantum chemistry and master equation calculations. The model outperforms former models at predicting measured time histories across the range of experimental conditions and elucidates different stages of the formation of target species. Important reactions in the new kinetic model are identified and discussed with reference to literature models, highlighting the reasons for the differences in model predictions.

Oxidation of Hydrogen Sulfide to Polysulfide and Thiosulfate by a Carbon Nanozyme: Therapeutic Implications with an Emphasis on Down Syndrome (Adv. Mater. 10/2024)

Oxidation of Hydrogen Sulfide to Polysulfide and Thiosulfate by a Carbon Nanozyme: Therapeutic Implications with an Emphasis on Down Syndrome (Adv. Mater. 10/2024)

Adsorption and partial catalytic oxidation of hydrogen sulfide to elemental sulfur using facilely prepared materials derived from sludge of groundwater treatment

AbstractRealizing the use of biogas as fuel or a gas engine, it is needed to upgrade to natural gas standards when it comes to pure biomethane, meaning impurities must be removed to a certain low concentration. Among these tasks, hydrogen sulfide (H2S) removal steadfastly gets the most attention. In the present work, partial catalytic oxidation was used to convert H2S to less harmful forms. Adsorbents/catalysts applied to this process were prepared from the sludge of a groundwater treatment plant using a simple combination of drying and calcination methods. As a relevant result, the as‐prepared sample (dried at 105°C for 24 h) exhibited high activity, with 90 ± 2% H2S conversion after 120 min of reaction time, while the sample calcined at about 500°C for 5 h (TP‐500) showed the highest H2S conversion (96 ± 2%); the lowest 28 ± 1% belonged to the case of TP‐700. The main compositions of the TP‐500 sample were crystalline calcite and amorphous iron oxides. The average size of calcite crystallites was ~45 nm, with a specific surface area of ~76 m2/g. Moreover, the presence of oxygen in the catalytic process and the “self‐outflow process” of sulfur desorption were the vital keys that allowed the partial H2S oxidation to take place continuously. After a reaction time of 2 h, the adsorption capacity of the best sample was 460.8 mg/g. Thus, it is obvious that inexpensive catalysts derived from sludge precursors can be effectively used for H2S removal from mixtures with air, supporting the treatment of raw biogas in the coming time.

From microbial heterogeneity to evolutionary insights: A strain-resolved metagenomic study of H2S-induced changes in anaerobic biofilms

The hidden layers of genomic diversity in microbiota of biotechnological interest have been only partially explored and a deeper investigation that overcome species level resolution is needed. CO2-fixating microbiota are prone to such evaluation as case study. A lab-scale trickle-bed reactor was employed to successfully achieve simultaneous biomethanation and desulfurization on artificial biogas and sulfur-rich biogas, and oxygen supplementation was also implemented. Under microaerophilic conditions, hydrogen sulfide removal efficiency of 81% and methane content of 95% were achieved. Methanobacterium sp. DTU45 emerged as predominant, and its metabolic function was tied to community-wide dynamics in sulfur catabolism. Genomic evolution was investigated in Gammaproteobacteria sp. DTU53, identified as the main contributor to microaerophilic desulfurization. Positive selection of variants in the hydrogen sulfide oxidation pathway was discovered and amino acid variants were localized on the sulfide entrance channel for sulfide:quinone oxidoreductase. Upon oxygen supplementation strain selection was the primary mechanism driving microbial adaptation, rather than a shift in species dominance. Selective pressure determined the emergence of new strains for example on Gammaproteobacteria sp. DTU53, providing in depth evidence of functional redundancy within the microbiome.

Geochemical transformations of sulfur and their role in the formation of different types and subtypes of saline lakes in Southeastern Transbaikalia

This study focused on the chemistry and isotopes of sulfur in lakes. The bottom sediments and water columns of lakes were found to contain reduced forms of sulfur, including hydrogen sulfide ions, elemental sulfur, and thiosulfate ions, along with sulfate ions. It was determined that elemental sulfur in lakes is present mainly in the form of suspensions and colloids, and the proportion of elemental sulfur in polysulfides increases with increasing water pH. It was shown that sulfate reduction results in the greatest isotope fractionation, with a light sulfur isotope accumulating in hydrogen sulfide ions and a heavy sulfur isotope accumulating in sulfate ions. It was confirmed that the abiotic reaction of hydrogen sulfide with oxygen yields a mixture of products that are depleted in 34S and enriched in 34S in hydrogen sulfide. In contrast, the microbial oxidation of HS− → S0 yields zerovalent sulfur, which is 2–4‰ heavier than the initial product. It was shown that the loss of sulfate ions due to bacterial reduction is most significant in subtype-I and subtype-III chloride and soda lakes. In contrast, in subtype-II sulfate and soda lakes, an increase in sulfate ions was noted due to the oxidation of hydrogen sulfides in water-bearing rocks and bacterial hydrogen sulfide. This finding indicated that in addition to evaporation, the formation of a particular type and subtype of saline lake involves the processes of aluminosilicate hydrolysis, sulfate reduction and hydrogen sulfide oxidation.

Quantum chemistry and kinetics of hydrogen sulphide oxidation.

A fundamental understanding of the acid gas (H2S and CO2) chemistry is key to efficiently implement the desulphurisation process and even the production of clean fuels such as hydrogen or syngas. In this work, we developed a new kinetic model for the pyrolysis and oxidation of hydrogen sulphide by merging two previously reported models with the goal of covering a wider range of conditions and including the effect of carbon dioxide. The resulting model, which consists of 75 species and 514 reactions, was used to conduct rate of production and sensitivity analysis in plug flow reactor simulations, and the results were used to determine the most prominent reactions in which hydrogen sulphide, molecular hydrogen, and sulphur monoxide are involved. The resulting list of important reactions was screened and the kinetics of three of them, i.e., SO2 + S2 → S2O + SO, S2O + S2 → S3 + SO, and SO + SH → S2 + OH, was found to warrant further investigation. With the goal of improving the accurancy of our new kinetic model, we carried out a robust quantum chemistry and Rice-Ramsperger-Kassel-Marcus master equation study to obtain, for the first time, the forward and reverse rate constants for those three reactions at temperatures and pressures of interest for combustion and atmospheric chemistry. This work is the first step of a kinetic study that is aimed at improving the understanding of the chemistry of the pyrolysis and oxidation of H2S, highlighting the importance of sulphur-sulphur interactions and providing a fundamental basis for future kinetic models of H2S not only in the field of combustion, but also in atmospheric chemistry.

Highly Dispersed FeAg-MCM41 Catalyst for Medium-Temperature Hydrogen Sulfide Oxidation in Coke Oven Gas.

The traditional hydrolysis-cooling-adsorption process for coke oven gas (COG) desulfurization urgently needs to be improved because of its complex nature and high energy consumption. One promising alternative for replacing the last two steps is selective catalytic oxidation. However, most catalysts used in selective catalytic oxidation require a high temperature to achieve effective desulfurization. Herein, a robust 30Fe-MCM41 catalyst is developed for direct desulfurization at medium temperatures after hydrolysis. This catalyst exhibits excellent stability for over 300 h and a high breakthrough sulfur capacity (2327.6 mgS gcat-1). Introducing Ag into the 30Fe-MCM41 (30Fe5Ag-MCM41) catalyst further enhances the H2S removal efficiency and sulfur selectivity at 120 °C. Its outstanding performance can be attributed to the synergistic effect of Fe-Ag clusters. During H2S selective oxidation, Fe serves as the active site for H2S adsorption and dissociation, while Ag functions as the catalyst promoter, increasing Fe dispersion, reducing the oxidation capacity of the catalyst, improving the desorption capacity of sulfur, and facilitating the reaction between active oxygen species and [HS]. This process provides a potential route for enhancing COG desulfurization.

Fe2TiO5-based photoanodes application in expanded photoelectrochemistry derived from the construction of heterojunction with the co-catalyst role

The Fe2TiO5 photoelectrode is limited in photoelectrochemical field (PEC) due to the slow charge transfer kinetics, short carrier diffusion distances and low separation efficiency. Hence, the Fe2TiO5/NiCo-LDH photoelectrodes with dual roles of co-catalyst and heterojunction are constructed, in which the photogenerated carriers are effectively separated and the conductivity is enhanced. At the same time, the surface state of the Fe2TiO5-based photoanode is modulated by the co-catalyst, which drives charge transfer into the electrolyte. With the synergistic effect of inhibiting photogenerated carrier complexation and accelerating charge transfer, the OER photocurrent density of Fe2TiO5/NiCo-LDH photoelectrode is enhanced to 2.42 mA/cm2, which is 3.4 folds higher than that of pristine Fe2TiO5. Specifically, Fe2TiO5/NiCo-LDH photoanode exhibits good stability and photoelectrochemical performance in hydrogen sulfide oxidation reaction (SOR). Similar to the OER, the sulphur oxidation photocurrent density of Fe2TiO5/NiCo-LDH photoelectrodes is enhanced to 0.21 mA/cm2, which is 2 folds higher than that of pristine Fe2TiO5. This work provides a new idea for the modification of Fe2TiO5 photoanodes and also explores a pioneering demonstration for the photoelectrochemical decomposition of hydrogen sulfide.

Oxidation of Hydrogen Sulfide to Polysulfide and Thiosulfate by a Carbon Nanozyme: Therapeutic Implications with an Emphasis on Down Syndrome.

Hydrogen sulfide (H2 S) is a noxious, potentially poisonous, but necessary gas produced from sulfur metabolism in humans. In Down Syndrome (DS), the production of H2 S is elevated and associated with degraded mitochondrial function. Therefore, removing H2 S from the body as a stable oxide could be an approach to reducing the deleterious effects of H2 S in DS. In this report we describe the catalytic oxidation of hydrogen sulfide (H2 S) to polysulfides (HS2+n - ) and thiosulfate (S2 O3 2- ) by poly(ethylene glycol) hydrophilic carbon clusters (PEG-HCCs) and poly(ethylene glycol) oxidized activated charcoal (PEG-OACs), examples of oxidized carbon nanozymes (OCNs). We show that OCNs oxidize H2 S to polysulfides and S2 O3 2- in a dose-dependent manner. The reaction is dependent on O2 and the presence of quinone groups on the OCNs. In DS donor lymphocytes we found that OCNs increased polysulfide production, proliferation, and afforded protection against additional toxic levels of H2 S compared to untreated DS lymphocytes. Finally, in Dp16 and Ts65DN murine models of DS, we found that OCNs restored osteoclast differentiation. This new action suggests potential facile translation into the clinic for conditions involving excess H2 S exemplified by DS.

Seagrass Thalassia hemprichii and associated bacteria co-response to the synergistic stress of ocean warming and ocean acidification

Seagrass meadows play vital ecological roles in the marine ecosystem. Global climate change poses considerable threats to seagrass survival. However, it is unclear how seagrass and its associated bacteria will respond under future complex climate change scenarios. This study explored the effects of ocean warming (+2 °C) and ocean acidification (−0.4 units) on seagrass physiological indexes and bacterial communities (sediment and rhizosphere bacteria) of the seagrass Thalassia hemprichii during an experimental exposure of 30 days. Results demonstrated that the synergistic effect of ocean warming and ocean acidification differed from that of one single factor on seagrass and the associated bacterial community. The seagrass showed a weak resistance to ocean warming and ocean acidification, which manifested through the increase in the activity of typical oxidoreductase enzymes. Moreover, the synergistic effect of ocean warming and ocean acidification caused a significant decrease in seagrass's chlorophyll content. Although the bacterial community diversity exhibited higher resistance to ocean warming and ocean acidification, further bacterial functional analysis revealed the synergistic effect of ocean warming and ocean acidification led to significant increases in SOX-related genes abundance which potentially supported the seagrass in resisting climate stress by producing sulfates and oxidizing hydrogen sulfide. More stable bacterial communities were detected in the seagrass rhizosphere under combined ocean warming and ocean acidification. While for one single environmental stress, simpler networks were detected in the rhizosphere. In addition, the observed significant correlations between several modules of the bacterial community and the physiological indexes of the seagrass indicate the possible intimate interaction between seagrass and bacteria under ocean warming and ocean acidification. This study extends our understanding regarding the role of seagrass associated bacterial communities and sheds light on both the prediction and preservation of the seagrass meadow ecosystems in response to global climate change.

Elemental Sulfur and Its Isotopic Composition in the Black Sea Water

As one of the main intermediate products of hydrogen sulfide oxidation, elemental sulfur plays an important indicator role in understanding the oxidative cycle of sulfur in the water of anoxic basins. The distribution of elemental sulfur in the water column of the Black Sea at stations located in the area of the continental slope is considered. For the first time, the concentration distributions of two forms of elemental sulfur depending on the depth in the Black Sea water were obtained: suspended elemental sulfur with a fraction of more than 0.45 μm (S0) and zero-valency sulfur (ZVS), which includes the sum of elemental sulfur (suspended and colloidal) and polysulfide sulfur. In the upper anoxic waters, the concentration of S0 noticeably increases (almost 200 times relative to the depth of 400 m) with an increase in the concentration of hydrogen sulfide and the density of water. At depths of more than 250 m, the concentration of both forms of sulfur remains almost constant (ZVS = 0.21 ± 0.03 µmol/kg, S0 = 0.05 ± 0.01 µmol/kg). A sharp increase in the concentration of S0 at the depths of 150–250 m is associated with the oxidation of hydrogen sulfide due to bacterial anoxygenic photosynthesis after sampling. The value of δ34S(ZVS) was determined in the waters of two stations Ash-26 and 149 at the depths of 450 and 600 m, respectively, which turned out to be +2.2‰ higher than δ34S(Н2S) from the same depths, which indicates the bacterial origin of elemental sulfur.

ELEMENTAL SULFUR AND ITS ISOTOPIC COMPOSITION IN THE BLACK SEA WATER

As one of the main intermediate products of hydrogen sulfide oxidation, elemental sulfur plays an important indicator role in understanding the oxidative cycle of sulfur in the water of anoxic basins. The distribution of elemental sulfur in the Black Sea water column at stations located in the area of the continental slope is considered. For the first time, the concentration distributions of two forms of elemental sulfur depending on the depth in the Black Sea water were obtained: suspended elemental sulfur with a fraction of more than 0.45 μm (S0) and zero valency sulfur (ZVS), which includes the sum of elemental sulfur (suspended and colloidal) and polysulfide sulfur. In the upper anoxic waters, the concentration of S0 noticeably increases (almost 200 times relative to the 400 m depth) with an increase in the concentration of hydrogen sulfide and the density of water. At depths of more than 250 m, the concentration of both forms of sulfur remains almost constant (ZVS = 0.21 ± ± 0.03 µmol/kg, S0 = 0.05 ± 0.01 µmol/kg). A sharp increase in the concentration of S0 at the depths of 150–250 m is associated with the oxidation of hydrogen sulfide due to bacterial anoxygenic photosynthesis after sampling. The value of δ34S(ZVS) was determined in the waters of two stations Ash-26 and 149 at the depths of 450 and 600 m respectively, which turned out to be +2.2‰ higher than δ34S(Н2S) from the same depths, which indicates the bacterial origin of elemental sulfur.

Heavy and less common metals in rainwater and the kinetics of the oxidation of hydrogen sulfide by oxygen in rainwater medium.

As a sequel to our recent study on the oxidation by O2, i. e., autoxidation of dissolved hydrogen sulfide, H2S, in aqueous medium, we present here the results of a similar study in rain water medium. The rainwater sampling was done sequentially for four years (2016-2019). In all 67 samples of rainwater were collected on event basis during monsoon period (June-October) in and around the Campus of University of Rajasthan, Jaipur (26°50̛ N-75°52̛ E), which is situated in a semi-arid region adjacent to the Thar Desert in the North-Western part of the India having an annual average rainfall of 54cm. ICP-MS technique was used in the analysis of rainwater and more than 30 metals were detected, which included transition metals, rare earths, less common metals. Beryllium, vanadium, silver, selenium, manganese, cerium, gallium, yttrium, barium, cesium, copper, rubidium, arsenic, lanthanum, cadmium, lead, uranium and bismuth were common to all rain water samples.H2S oxidation by dissolved oxygen was studied in rainwater as well as in laboratory water media for comparison. The kinetics rate law was: -d[O2]/dt = k1K1[H+][S][O2]t/( [H+]2 + K1[H+] + K1K2), where K1 is first dissociation constant of H2S and k1 is the rate constant for the dominant reaction step:HS- + O2 → products.

Two modes of gypsum replacement by carbonate and native sulfur in the Lorca Basin, SE Spain

Organoclastic sulfate reduction and bacterial sulfide oxidation have been suggested to explain the formation of authigenic carbonate and native sulfur replacing gypsum in the Lorca Basin, Spain. To gain more insight into the nature of this replacement, two types of sulfur-bearing carbonate (laminated and brecciated) from the late Miocene Lorca Basin were studied. Petrographic observations revealed that a sulfur-bearing laminated carbonate consists of clay-rich and dolomite-rich laminae with carbonate and native sulfur pseudomorphs after gypsum. Positive δ18Ocarbonate values in the laminae (δ18O = 2.6‰) and lipid biomarkers of halophilic archaea (e.g., extended archaeol) suggest formation under hypersaline conditions. Bacterial sulfate reduction, evidenced by biomarkers such as iso-C15, iso-C16, and iso-C17 fatty acids, produced hydrogen sulfide inducing the abiotic formation of organic sulfur compounds. Gypsum in the laminated carbonate likely dissolved due to undersaturation as evidenced by a low content of carbonate-associated sulfate (3,668 ppm) and 34S-enriched native sulfur (δ34S = 22.4‰), reflecting sulfate limitation. Such 34S-enrichment implies limited fluid flow, which probably restricted the supply of molecular oxygen required for native sulfur formation through oxidation of hydrogen sulfide. Alternatively, sulfate-reducing bacteria may have mediated native sulfur formation directly as a stress response to environmental conditions. The formation of sulfur-bearing calcite in brecciated carbonates is due to post-depositional alteration. Negative δ18O values of the calcite (δ18O = −1.5‰) and a tenfold decrease in carbonate-associated sulfate content (752 ppm) suggest gypsum dissolution and subsequent calcite precipitation from meteoric water. Relatively 34S-depleted native sulfur (δ34S = 13.1‰) leaves it ambiguous whether meteoric water influx could have supplied sufficient molecular oxygen for oxidation of hydrogen sulfide. In case of the brecciated carbonate, methanogenesis, anaerobic oxidation of methane, and bacterial sulfate reduction apparently mediated the formation of secondary minerals as indicated by 13C-depleted lipid biomarkers representative for the respective metabolisms. This study reveals that the conditions and timing of gypsum replacement are variable–taking place 1) during or shortly after gypsum deposition or 2) significantly after sedimentation–and suggests that methanogens in addition to anaerobic methanotrophic archaea and sulfate-reducing bacteria may be involved in the mineral-forming processes in the sedimentary subsurface.

Nozzle Electrode Point Discharge-Enhanced Oxidation and Portable Gas Phase Molecular Fluorescence Spectrometry for Sensitive Field Detection of Sulfide

It is still a challenge to accurately determine dissolved sulfide due to its susceptibility to contamination and loss during transportation, storage, and analysis in the laboratory, thus highlighting the necessity for its sensitive field analysis. Herein, a robust nozzle electrode point discharge (NEPD) enhanced oxidation coupling with chemical vapor generation (CVG) is described for the highly efficient and flameless conversion of sulfide (S2-) to SO2. Subsequently, a portable and low-power consumption gas phase molecular fluorescence spectrometry (GP-MFS) was constructed for the highly selective and sensitive determination of the generated SO2 via detecting its molecular fluorescence excited by a zinc hollow cathode lamp. Under optimal conditions, a limit of detection (LOD) of 0.1 μM was obtained for dissolved sulfide with a relative standard deviation (RSD, n = 11) of 2.6%. The accuracy and practicability of the proposed method were validated by the analyses of two certified reference materials (CRMs) and several river and lake water samples with satisfactory recoveries of 99%-107%. This work confirms that NEPD enhanced oxidation is a low energy consumption yet highly efficient method for the flameless oxidation of hydrogen sulfide and thus is suitable for the easy field detection of dissolved sulfide in environmental water by CVG-GP-MFS.

Different Magmatic‐Hydrothermal Fluids at the Same Magma Source Support Distinct Microbial Communities: Evidence From In Situ Detection

AbstractSubmarine magmatic‐hydrothermal systems are dominated by volcanism and generate unique biocenoses. However, the relationships between the microbial communities and the broad range of chemical and physical variability within the systems are poorly understood. Here, a high‐precision in situ Raman quantitative technique was used for the hydrothermal fluids at the Onsen site and a newly found site named Faxian in a magmatic‐hydrothermal system at the DESMOS caldera, Manus back‐arc basin. The maximum in situ H2 concentration (8.56 mmol/kg) at the Onsen site is the highest value ever reported in similar hydrothermal systems. In contrast, the diffuse fluid at the Faxian site was characterized by rich H2S (7.78 mmol/kg) but without H2. The differences in mixing contents of seawater induced different geochemical reactions and fluxes of hydrogen and hydrogen sulfide. Furthermore, the existence of hydrogen‐ and sulfide‐oxidizing genes suggests that the oxidation of hydrogen and hydrogen sulfide are the energy sources of the microbial communities at the two sites even within the same magma source. The in situ quantitative analyses of different types of fluids provide implications on the materials fluxes in the magmatic‐hydrothermal system, and the relationships between widespread submarine volcanic activities and life in early Earth.