Diffusion Of H2S Research Articles

Cu3(HHTP)2 decorated over rGO nanocomposites for flexible NH3 and H2S dual sensing at room temperature

Ammonia (NH3) and hydrogen sulfide (H2S) are both poisonous and corrosive gases, and timely detecting their leakage is thus required. Ideally, employing individual flexible sensor to simultaneously detect NH3 and H2S dual gases at room temperature would contribute to their miniaturization and integration, however, remains challenging. Here, flexible NH3 and H2S dual sensing at room temperature has been developed by utilizing Cu3(HHTP)2 decorated over reduced graphene oxide nanocomposites {Cu3(HHTP)2//rGO NCPs, HHTP=2,3,6,7,10,11-hexahydroxytriphenylene}, which have been synthesized via oxidation–reduction reaction of GO and Cu3(HHTP)2 metal–organic frameworks (MOFs). Typically, the Cu3(HHTP)2 MOFs are observed with spiny surface, and as-synthesized Cu3(HHTP)2//rGO NCPs present amorphous crystallization. Beneficially, Cu3(HHTP)2//rGO NCPs exhibit the NH3 and H2S dual sensing with the resistance-increasing response toward 10–50000 ppm NH3 and resistance-decreasing response to 0.1–20 ppm H2S. Further, the sensor prototype shows 40 days-long stability and 75 % high relative humidity tolerance, respectively. Remarkably, the ternary-NCPs show excellent flexibility, along with excellent sensing performance against various bendings. Theoretically, rGO with high specific surface ratio and Cu3(HHTP)2 MOFs with enriched adoption sites might contribute to NH3 and H2S diffusion and adsorption. Practically, the simulation utilizing Cu3(HHTP)2//rGO NCPs to monitor H2S and NH3 has been conducted with reliable sensing.

H2S induced in-situ formation of recyclable metal sulfide-based sorbent for elemental mercury sequestration in natural gas

Enlightened by the phenomenon that hydrogen sulfide (H2S) can readily decompose on metal oxides to generate sulfide species and the obtained metal sulfides are generally adopted as Hg-affine ligands for Hg0 capture, a urea modified copper oxide (U-CuO) was prepared via high-temperature calcination of the mixture of urea and copper nitrate for Hg0 removal in natural gas containing H2S. Benefitted from the decomposition of urea and the release of gaseous decomposition products, the as-synthesized U-CuO was enriched with abundant base sites and lattice oxygen, and characterized with developed textural features, which facilitates the diffusion and adsorption of H2S and subsequent sequestration of Hg0. The Hg0 adsorption capacity and uptake rate of U-CuO under simulated natural gas (N2 + 500 ppm H2S+8% H2O) reached as high as 134.06 mg g−1 and 58.32 μg g−1 min−1, respectively, which largely surpassed those of most CuS-based sorbents for Hg0 immobilization. Besides, U-CuO sorbent also exhibited satisfactory recyclability only through simple thermal treatment, the Hg0 removal efficiency of U-CuO maintained above 97 % even after ten adsorption-regeneration rounds. This preparation strategy not only provides valuable hints to guide the design and synthesis of Hg0 sorbents used for natural gas containing H2S but also inspires further investigation for the cost-effective performance enhancement of Hg0 sorbents.

Mechanism of WS2 Nanotube Formation Revealed by in Situ/ex Situ Imaging.

Multiwall WS2 nanotubes have been synthesized from W18O49 nanowhiskers in substantial amounts for more than a decade. The established growth model is based on the "surface-inward" mechanism, whereby the high-temperature reaction with H2S starts on the nanowhisker surface, and the oxide-to-sulfide conversion progresses inward until hollow-core multiwall WS2 nanotubes are obtained. In the present work, an upgraded in situ SEM μReactor with H2 and H2S sources has been conceived to study the growth mechanism in detail. A hitherto undescribed growth mechanism, named "receding oxide core", which complements the "surface-inward" model, is observed and kinetically evaluated. Initially, the nanowhisker is passivated by several WS2 layers via the surface-inward reaction. At this point, the diffusion of H2S through the already existing outer layers becomes exceedingly sluggish, and the surface-inward reaction is slowed down appreciably. Subsequently, the tungsten suboxide core is anisotropically volatilized within the core close to its tips. The oxide vapors within the core lead to its partial out-diffusion, partially forming a cavity that expands with reaction time. Additionally, the oxide vapors react with the internalized H2S gas, forming fresh WS2 layers in the cavity of the nascent nanotube. The rate of the receding oxide core mode increases with temperatures above 900 °C. The growth of nanotubes in the atmospheric pressure flow reactor is carried out as well, showing that the proposed growth model (receding oxide core) is also relevant under regular reaction parameters. The current study comprehensively explains the WS2 nanotube growth mechanism, combining the known model with contemporary insight.

Constructing ether-rich and carboxylate hydrogen bonding sites in protic ionic liquids for efficient and simultaneous membrane separation of H2S and CO2 from CH4

Removing H2S and CO2 is of great significance for natural gas purification. With excellent gas affinity and tunable structure, ionic liquids (ILs) have been regarded as nontrivial candidates for fabricating polymer-based membranes. Herein, we firstly reported the incorporation of protic ILs (PILs) having ether-rich and carboxylate sites (ECPILs) into poly(ether-block-amide) (Pebax) matrix for efficient separation H2S and CO2 from CH4. Notably, the optimal permeability of H2S reaches up to 4310 Barrer (40 °C, 0.50 bar) in Pebax/ECPIL membranes, along with H2S/CH4 and (H2S + CO2)/CH4 selectivity of 97.7 and 112.3, respectively. These values are increased by 1125%, 160.8% and 145.9% compared to those in neat Pebax membrane. Additionally, the solubility and diffusion coefficients of the gases were measured, demonstrating that ECPIL can simultaneously strengthen the dissolution and diffusion of H2S and CO2, thus elevating the permeability and permselectivity. By using quantum chemical calculations and FT-IR spectroscopy, the highly reversible multi-site hydrogen bonding interaction between ECPILs and H2S was revealed, which is responsible for the fast permeation of H2S and good selectivity. Furthermore, H2S/CO2/CH4 (3/3/94 mol%) ternary mixed gas can be efficiently and stably separated by Pebax/ECPIL membrane for at least 100 h. Overall, this work not only illustrates that PILs with ether-rich and carboxylate hydrogen bonding sites are outstanding materials for simultaneous removal of H2S and CO2, but may also provide a novel insight into the design of membrane materials for natural gas upgrading.

Microscopic simulation study on the penetration property of pure hydrogen sulfide gas in polyethylene and polyvinylidene fluoride

The H2S penetration in the nonmetallic biogas pipelines and reinforced thermoplastic composite pipelines can lead to severe environmental pollution and disrupt the regular operations of oil and gas fields. Thus, delving into and comprehending the H2S penetration in polyethylene (PE) or polyvinylidene fluoride (PVF2) holds immense significance for both environmental preservation and industrial progress. In this study, Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) are employed to investigate and contrast the H2S penetration property within PE and PVF2 at 300–360 K and 0.1–1.5 MPa. The results indicate the diffusion and penetration coefficients decrease with decreasing temperature and pressure, while the solubility coefficient increases with decreasing temperature. Compared to PE, PVF2 demonstrates stronger resistance to H2S penetration, mainly due to H2S is difficult to diffuse in PVF2. The relationship between penetration coefficient and temperature is consistent with Arrhenius law. In 0.1 MPa, the activation energy of H2S in PE and PVF2 are 31,911 and 42,247 J/mol, respectively. Moreover, the relationship between activation energy and pressure is power function. The study also reveals the H2S diffusion in both PE and PVF2 follows the leap mechanism. These research findings can offer valuable guidance for reducing environmental pollution and ensuring industrial development.

Improvement of mechanical properties of highly ZnO‐filled polyethylene composites by dual‐compatibilizer for hydrogen sulfide permeation inhibition

AbstractTransportation of acidic fluids containing hydrogen sulfide (H2S) by flexible reinforced thermoplastic pipes can cause safety problems due to diffusion of H2S in the pipe. Herein, high‐density polyethylene (HDPE) composites are prepared with a large amount of zinc oxide (ZnO) particles as absorbent fillers by melt‐mixing via introducing maleic anhydride‐grafted polyethylene (PE‐g‐MAH) and maleic anhydride‐grafted poly(ethylene‐co‐octene) (POE‐g‐MAH) as dual‐compatibilizer. By controlling the mass ratio of the two compatibilizers, ZnO particles can be encapsulated by PE‐g‐MAH and POE‐g‐MAH so that mechanical properties of the prepared HDPE/ZnO composites are improved owing to enhanced compatibility between the filler and the resin. By adding PE‐g‐MAH and POE‐g‐MAH with total 10 wt% in a mass ratio of 1/3, the HDPE/ZnO composite containing 50 wt% ZnO exhibits 37.3 ± 3.8 MPa of yield strength, 576 ± 16 MPa of flexural modulus, and 84.4 ± 1.4 kJ m−2 of notched Izod impact strength corrected to 311 ± 24.9 kJ m−2. After exposure in H2S at 0.1 MPa for 7 days, the diffusion distance of H2S in the composite is 659 ± 17 μm, demonstrating a high barrier ability on H2S via absorption. This study provides a feasible method for preparation of polymer composites with suitable mechanical properties for inhibiting H2S permeation in reinforced thermoplastic pipes.

Distribution of H2S in the 10103 excavation working face of the Baozigou coal mine

Based on the production conditions of the 10103 excavation working face of the Baozigou coal mine, this paper analyzes the potential sources of H2S and the expected emission concentrations of H2S in the working face. Considering the previous engineering practice for controlling H2S disasters in coal mine working faces, numerical simulations were conducted to investigate air flow and H2S migration and diffusion in the tunnel in the excavation working face. The migration and distribution of H2S in the coal seam mining face were studied, and the effects of outlet wind speed, duct location, and duct diameter on the H2S concentration distribution were explored. The higher the outlet wind speed, the more conducive to the emission of H2S gas, but too high a wind speed will be detrimental to the concentrated extraction and purification absorption of H2S; the closer the outlet position of the air duct is to the end of the working surface, the lower the H2S concentration in the vortex area at the corner; the air duct If the diameter is too small, the harmful gases released from hard-to-break coal cannot be entrained and taken away. When the diameter of the air duct is too large, the entrainment volume during the jet process will be expanded. To verify the field distribution of H2S concentration at the bottom, middle, and top of the boring machine, a CD4-type portable H2S instrument was used to analyze the distribution of H2S near the excavation working face.

Engineering highly reversible hydrogen bonding interaction in pebax/deep eutectic solvent blended membranes for efficient separation of H2S from CO2 and CH4

Removal of H2S and CO2 is a key step for natural gas upgrading. However, further separating H2S/CO2 remains challenging as they are both acid gas with similar kinetic diameters, incurring complex processes and high cost for recovering H2S as sulfur resource. Herein we reported for the first time the introduction of highly reversible hydrogen bonding into Pebax/deep eutectic solvent (DES) blended membranes comprising 1-ethyl-3-methylimidazolium chloride ([Emim]Cl)-based DESs for selectively separating H2S from CO2 and CH4. The successful fabrication of Pebax/DES membranes was confirmed by various characterizations. Benefitting from the highly reversible DES–H2S hydrogen bonding interaction, the H2S permeability, H2S/CO2 and H2S/CH4 selectivity for single gas tests are high up to 1829 Barrer, 14.35 and 242.0, respectively. Based on solution-diffusion data, the acidic [Emim]Cl/levulinic acid (Lev) DESs are found to be the most efficient owing to the moderate DES–H2S hydrogen bonding interaction and thus fast H2S diffusion, which was also confirmed by quantum chemical calculations coupled with visual study of weak interactions. Permeation test of mixed gas shows that Pebax/DES blended membranes can steadily and efficiently separate H2S/CO2/CH4 (3/3/94 vol%) ternary gas, with 1450 Barrer of H2S permeability, 34.5 of H2S/CO2 selectivity and 160 of H2S/CH4 selectivity obtained, which may indicates the applicability of these materials in desufuration of natural gas. To summarize, this work demonstrated the vital role of DES–H2S hydrogen bonding interaction in dominating H2S permeation, which may provide an easy but effective way for fabricating high-performance H2S sepration membranes.

H2S removal at downhole conditions using iron oxide nanoparticles

The objective of the present work is the study of H2S removal from heavy oil, using iron oxide nanoparticles in a controlled environment that simulates the pressure and temperature conditions of a reservoir and the aqua-thermolysis process during enhanced oil recovery with steam injection. Since molecular diffusion of H2S plays an important role during the removal process, its measurement through experimental tests was also a major goal. The research divides into three stages: 1) preparation of nanoparticles; 2) diffusion tests, and, 3) H2S removal tests. The procedure for nanoparticle preparation from a microemulsion and a metal precursor salt was successful in yielding nanoparticle sizes less than 100 nm. The diffusion coefficient of H2S in heavy oil, measured in a stainless steel PVT cell, varied between 8.3 × 10–9 and 8.9 × 10–9 m2s–1 over the range of test temperatures. Finally, over 65% of the H2S was removed when 500 ppm of nanoparticles were used.

Modelling the disease: H2S-sensitivity and drug-resistance of triple negative breast cancer cells can be modulated by embedding in isotropic micro-environment

Three-dimensional (3D) cell culture systems provide more physiologically relevant information, representing more accurately the actual microenvironment where cells reside in tissues. However, the differences between the tissue culture plate (TCP) and 3D culture systems in terms of tumour cell growth, proliferation, migration, differentiation and response to the treatment have not been fully elucidated. Tumoroid microspheres containing the MDA-MB 231 breast cancer cell line were prepared using either tunable PEG-fibrinogen (PFs) or tunable PEG-silk fibroin (PSFs) hydrogels, respectively named MDAPFs and MDAPSFs. The cancer cells in the tumoroids showed changes both in globular morphology and at the protein expression level. A decrease of both Histone H3 acetylation and cyclin D1 expression in all 3D systems, compared to the 2D cell culture, was detected in parallel to changes of the matrix stiffness. The effects of a glutathionylated garlic extract (GSGa), a slow H2S-releasing donor, were investigated on both tumoroid systems. A pro-apoptotic effect of GSGa on tumour cell growth in 2D culture was observed as opposed to a pro-proliferative effect apparent in both MDAPFs and MDAPSFs. A dedicated ad hoc 3D cell migration chip was designed and optimized for studying tumour cell invasion in a gel-in-gel configuration. An anti-cell-invasion effect of the GSGa was observed in the 2D cell culture, whereas a pro-migratory effect in both MDAPFs and MDAPSFs was observed in the 3D cell migration chip assay. An increase of cyclin D1 expression after GSGa treatment was observed in agreement with an increase of the cell invasion index. Our results suggest that the “dimensionality” and the stiffness of the 3D cell culture milieu can change the response to both the gasotransmitter H2S and doxorubicin due to differences in both H2S diffusion and changes in protein expression. Moreover, we uncovered a direct relation between the cyclin D1 expression and the stiffness of the 3D cell culture milieu, suggesting the potential causal involvement of the cyclin D1 as a bio-marker for sensitivity of the tumour cells to their matrix stiffness. Therefore, our hydrogel-based tumoroids represent a valid tunable model for studying the physically induced transdifferentiation (PiT) of cancer cells and as a more reliable and predictive in vitro screening platform to investigate the effects of anti-tumour drugs.

Removal of hydrogen sulfide by metal-free amine-functionalized mesoporous carbon at room temperature: Effect of amines

The introduction of nitrogen can effectively improve the alkalinity of carbon materials, introduce catalytic sites and active oxygen radicals, thus enhancing the desulfurization ability. However, the study on the effect of amine species and loading amount on the desulfurization properties is very limited. In this study, mesoporous carbon materials with large specific surface area and pore volume were prepared. Different amines were selected as impregnating agents to investigate the performance of amine-functionalized carbon catalysts for hydrogen sulfide (H2S) removal under various operating conditions. The synthesized carbon material has a large specific surface area of 989 m2/g, with an average pore diameter of 12.94 nm. The well-developed pores could not only provide the space for the dispersion of amine, but also facilitate the diffusion of H2S and the storage of sulfur products. Amine increase the alkalinity of carbon material and the reactivity of reaction sites located on the carbon skeleton. The desirable catalytic performance of catalysts impregnated by amines should be the compromise among spatial structure of the amine, the surface chemistry and porosity of catalysts. Among them, the polyethylene polyamine impregnated carbon catalyst with a high ratio of secondary and tertiary amine (80.54 %) showed the best catalytic performance of 1.58 g H2S/g-catalyst at 30 °C due to due to suitable steric hindrance and higher stability in the H2S adsorption–desorption cycle. This work further refines the previously proposed reaction mechanism and provides a possibility for the application of carbon-based catalysts with directional introduction of nitrogen elements by impregnation method in the removal of H2S.

Field investigation of temporal variation and diffusion of hydrogen sulfide on waste working face and intermediate landfill cover

This paper presents the study on the variation, influencing factors and diffusion regularity of hydrogen sulfide (H2S) concentration and surface flux on the working face and intermediate geomembrane cover of a landfill. Field investigations were conducted using static chambers at a large-scale municipal solid waste landfill in Hangzhou, China, from January 2019 to June 2021. The analytical models of H2S transport in the working face and intermediate cover were developed to investigate the surface flux under various conditions. The CALPUFF model was used to demonstrate the diffusion path. The H2S surface flux on the working face ranged from 7.1 × 10−3 to 1.7 mg/m2/h, whereas the range was found to be 1.5 × 10−4 to 0.9 mg/m2/h on the intermediate geomembrane cover. This observation indicated that the geomembrane can reduce H2S emissions. In addition, the H2S surface fluxes at the HDPE GMB seams and near the gas collecting wells were generally 1–2 orders of magnitude larger than that in the intact GMB. The analytical model estimates that the intact GMB exhibits a diffusion coefficient of H2S ranging from 2.7 × 10−11 to 2.2 × 10−10 m2/s. However, the diffusion coefficient increases significantly to a range of 3.3 × 10−11–9.8 × 10−7 m2/s on the GMB seams. According to CALPUFF results, only the H2S diffusion from the working face had areas exceeding the standard concentration.

Ratiometric Near-Infrared Fluorescence Liposome Nanoprobe for H2S Detection In Vivo

Accurate detection of H2S is crucial to understanding the occurrence and development of H2S-related diseases. However, the accurate and sensitive detection of H2S in vivo still faces great challenges due to the characteristics of H2S diffusion and short half-life. Herein, we report a H2S-activatable ratiometric near-infrared (NIR) fluorescence liposome nanoprobe HS-CG by the thin-film hydration method. HS-CG shows "always on" fluorescence signal at 816 nm and low fluorescence signal at 728 nm; the NIR fluorescence ratio between 728 and 816 nm (F728/F816) is low. Upon reaction with H2S, the fluorescence at 728 nm could be more rapidly turned on due to strong electrostatic interaction between enriched HS- and positively charged 1,2-dihexadecanoyl-sn-glycero-3-phosphocholine (DPPC) doped in the liposome nanoprobe HS-CG, resulting in a large enhancement of F728/F816, which allows for sensitive visualization of the tumor H2S levels in vivo. This study demonstrates that this strategy of electrostatic adsorption between HS- and positively charged molecules provides a new way to enhance the reaction rate of the probe and H2S, thus serving as an effective platform for improving the sensitivity of imaging.

Influence of the Interface Wettability of Membranes on Electrolysis Reduction of SO2 to H2S

Converting SO2 to H2S is an important process for sulfur recycling. In our previous study, electroreduction of SO2 to H2S was achieved by using a gas-permeable catalyst membrane. In this paper, the influence of the interface wettability of the membrane was investigated since it has a great effect on the conversion of SO2 to H2S. A 94% increase in the current density and a 189% increase in H2S flux were obtained after treating the membrane using NH3 plasma when the contact angle is 93°. A formula for H2S membrane flux was established, in which the contact angle θ and surface pH have a negative effect on H2S flux. The elevated wettability (smaller θ) increased the current density of H2S production but hindered H2S diffusion due to the increased immersion depth. The surface pH increase resulting from the current density increase had tiny effects on H2S separation.

Removal of Gaseous H2S by the Titanium Silicalite-1/H2O2 Wet Oxidation System

A wet oxidation system of titanium silicalite-1 (TS-1)/hydrogen peroxide (H2O2) was proposed for gaseous hydrogen sulfide (H2S) removal in this study, and the effects of the TS-1 dosage, H2O2 concentration, H2S concentration, reaction temperature, gas flow, and reaction time on the removal rate of H2S (η) were investigated. Samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and N2 adsorption–desorption. An experiment using isopropanol, benzoquinone, and butylated hydroxytoluene was carried out as well to verify the active substance in the TS-1/H2O2 system. The results show that η reached 86.3% when bubbling 160 ppm of H2S through a 500 mL solution (pH 4.21) containing TS-1 (0.5 g/L) and H2O2 (0.33 mol/L, 1.12 wt %) at 293 K and atmospheric pressure with a flow rate of 265 mL/min. Subsequently, the mechanism of the reaction was proposed. After the H2S diffuses onto the surface of TS-1, it is first oxidized by adsorbed H2O2 and eventually oxidized to H2SO4; this process is controlled by H2S diffusion. The final product of the process is sulfuric acid, which is pollution-free and can be recycled to achieve resource utilization. The removal of H2S by the TS-1/H2O2 system is a green, simple, low-cost, resource-saving, safe, and efficient method.

Review of Hydrogen Sulfide Removal from Various Industrial Gases by Zeolites

Hydrogen sulfide (H2S) removal from various industrial gases is crucial because it can cause huge damage to humans, the environment, and industrial production. Zeolite possesses huge specific surface area and well-developed pore structure, making it a promising adsorbent for H2S removal. This review attempts to comprehensively compile the current studies in the literature on H2S removal in gas purification processes using zeolites, including experimental and simulation studies, mechanism theory, and practical applications. Si/Al ratio, cations of zeolite, industrial gas composition and operating conditions, and H2S diffusion in zeolites affect desulfurization performance. However, further efforts are still needed to figure out the influence rules of the factors above and H2S removal mechanisms. Based on an extensive compilation of literature, we attempt to shed light on new perspectives for further research in the future.

Refining the early Cambrian marine redox profile by using pyrite sulfur and iron isotopes

It is widely accepted that the emergence of metazoans in the Ediacaran-Cambrian transition might be triggered by oxygenation of the atmosphere-ocean system. However, some Ediacaran and early Cambrian macroscopic fossils (such as multicellular algae) were preserved under sulfidic conditions, challenging the conventional view of the prohibition of eukaryotes in the presence of H2S. It was proposed that organisms might have lived in some episodic non-sulfidic intervals although the ocean was predominantly sulfidic. However, the hypothesized short-lived non-sulfidic intervals were hardly identified by traditional bulk sample analyses, which cannot provide sufficiently high temporal resolution to resolve the short-term oxygenation events. In this study, we analyzed pyritized sponge spicules and disseminated pyrites from black shales of the early Cambrian Shuijingtuo Formation in South China. We conducted in situ pyrite sulfur (δ34Spy) and iron (δ56Fepy) isotopes as well as bulk sample pyrite sulfur isotope analyses. The intra-crystal or intra-spicule δ34Spy variations reflect the evolution of seawater and porewater geochemistry during pyrite formation, providing a higher temporal resolution of redox fluctuation in the early Cambrian ocean. Our study indicates: (1) The bulk sample pyrite sulfur isotope and pyrite content data suggest diagenetic pyrite precipitation in sediment porewater with H2S diffusion from the overlying sulfidic seawater; (2) Limited intra-crystal and intra-spicule δ34Spy variations imply that both spicule and disseminate pyrites had a homogenous S source from sulfidic seawater, and dissimilatory sulfate reduction (DSR) in sediment porewater was negligible; (3) The in situ iron isotope analyses indicate active dissimilatory iron reduction (DIR) in sediment that generated excessive ferrous iron (Fe2+) to compensate for Fe2+ consumption by pyrite precipitation, allowing Fe2+ to accumulate in ferruginous porewater. Therefore, the early Cambrian ocean was characterized by active DSR in sulfidic seawater and DIR in ferruginous sediment porewater. In addition, our study demonstrates that the seawater might be persistently sulfidic, and does not support the presence of intermittent non-sulfidic intervals for the survival of organisms. If correct, it is hypothesized that some primitive sponges might have survived in sulfidic seawater, although the seawater H2S concentration remains unknown.

Removal of Gaseous Hydrogen Sulfide by a FeOCl/H2O2 Wet Oxidation System

The removal of gaseous hydrogen sulfide using FeOCl/H2O2 was studied. The effects of the FeOCl dosage, the H2O2 concentration, the reaction temperature, and the gas flow rate on the removal of H2S were investigated. The reaction products were analyzed, and the characterization of FeOCl was carried out by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. Furthermore, radical quenching experiments were carried out using butylated hydroxytoluene, isopropanol, and benzoquinone. It was found that the H2S removal rate for a H2S gas concentration of 160 ppm reached 85.6% when bubbling through 100 mL of an aqueous solution containing FeOCl (1 g/L) and H2O2 (0.33 mol/L) at 293 K with a flow rate of 135 mL/min. Although the dissolution of chlorine in FeOCl was found to result in reduced catalytic performance, the activity was restored after soaking the catalyst in concentrated hydrochloric acid (37%) and subsequent calcination. The mechanism of H2S removal was also discussed, and it was found that this process was controlled by H2S diffusion. FeOCl was found to activate H2O2 and produce radicals, such as •OH and •O2–, resulting in the formation of a water film rich in radicals on the FeOCl surface. Following the diffusion of H2S into the water film, it underwent oxidation by radicals to produce SO42–. Overall, the catalyst and the product can be effectively separated.

Complex iron and sulphate reducing Cretaceous sedimentary system revealed by extreme isotope values

AbstractThe iron and sulphur isotope compositions of sedimentary pyrites have been extensively used as a proxy for microbial metabolisms and redox evolution of the oceans. We illustrate the benefit of in‐situ and coupled study of Fe and S isotopes on sedimentary pyrites from late mid‐Cretaceous sediments from the Central Apennines, Italy. We report extremely low δ56Fe values for sedimentary pyrites (as low as −4.7‰) and unusual high δ34S values (as high as +88.9‰). We propose a model that explains these extreme values but also the large range of pyrite δ34S and δ56Fe values as well as the considerable microscale variations in this values. These isotopic compositions were likely produced by microbial dissimilatory iron reduction in the shelf sediment, transportation of Fe2+ via an iron shuttle, production of heavy SO4 by pyrite precipitation in the water column, diffusion and advection of SO4 and H2S, and finally bacterial sulphate reduction.

Predominant microbial iron reduction in sediment in early Cambrian sulfidic oceans

Microbial sulfate reduction (MSR) and microbial iron reduction (MIR) are two major anaerobic metabolic pathways, and account for the majority of anaerobic organic matter degradation in modern marine sediments. Because it is thermodynamically more favorable, the zone of porewater Fe2+ accumulation usually overlies the zone of porewater H2S accumulation in modern marine sediments. The sequence of redox reactions is collectively known as the ‘redox latter’, which has been used as a yardstick in reconstructing the marine redox landscape in Earth's history. To understand the redox profile in the early Cambrian oceans, here we analyzed syndepositional and diagenetic pyrite (FeS2) in carbonate concretions hosted in the black shale of the early Cambrian Shuijingtuo Formation in the Yangtze Block, South China. Syndepositional pyrite laminae, disseminated pyrite and diagenetic pyrite aggregates in the periphery of carbonate concretions have nearly identical sulfur isotope compositions, which cannot be resolved by quantitative reduction of seawater sulfate. Instead, a homogeneous H2S source from sulfidic (H2S-enriched) seawater might be the major sulfur source, and pyrite precipitation was sustained by H2S diffusion from sulfidic seawater. In addition, the homogeneous pyrite sulfur isotopes also imply negligible MSR in sediment porewater, reflecting low sulfate concentration in sulfidic seawater. On the other hand, the enrichment of Fe2+ in carbonate concretions implies deposition in ferruginous (Fe2+-enriched) porewater, resulting from active MIR that reduced detrital iron oxides to Fe2+. Thus, the early Cambrian sulfidic ocean might be characterized by extensive MSR in seawater and MIR in sediment porewater, which differs from the modern sulfidic ocean, such as the Black Sea, showing predominantly MSR in sediment. The development of such a reverse redox profile might be attributed to the terrestrial supply of particulate iron oxides that passed through the thermodynamically unstable sulfidic water column and low seawater sulfate concentration in sulfidic seawater that prohibited MSR in sediment. Finally, our study indicates that the redox profile might be diverse in the early Cambrian oceans.