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In this study, the role of iron sulfide (FeS) content on the structural and optical properties of graphene/polyvinyl alcohol (Gr/PVA) blend has been examined for environmental-friendly applications. Gr/PVA blend filled with FeS (0 to 10 wt%) were equipped using the casting technique. The prepared samples were studied via a scanning electron microscope, X-ray diffractometer, FT-IR and UV–visible-NIR spectrophotometers. XRD analysis shows that the crystallinity increases with increasing FeS concentration in the host Gr/PVA blend. UV–visible-NIR analysis shows that the direct optical bandgap of composite blends shrinks from 5.37 to 4.68 eV as FeS content is increased to 10 wt%. Also, it confirms that the refractive index and optical conductivity of Gr/PVA blend could be significantly enhanced via FeS filling. FeS filled Gr/PVA blends are recommended eco-friendly applications.

Nickel-iron sulfide has shown attractive activity in electrocatalytic oxygen evolution reaction (OER). However, the effects of low valence sulfur (S 2− ) and metal species on OER in binary nickel-iron sulfide have rarely been systematically studied. Works based on post-catalysis characterization have led to the assumption that the real active species are nickel-iron oxyhydroxide, and that nickel-iron sulfide acts only as a precatalyst. Therefore, to study the role of S, Ni, and Fe for the development of nickel-iron sulfide catalyst is of self-evident importance. Herein, a facile solvothermal method is used to synthesize acetylene black coated with nickel-iron sulfide nanosheets. Electrochemical tests show that the presence of low valence S species makes the catalyst have faster OER kinetics, larger active area, and intermediate active species adsorption area. Therefore, the present study reveals the enhancing effect of low valence sulfur species (S 2− ) on OER in binary nickel-iron sulfide. In situ Raman spectroscopy shows that the generation of γ-NiOOH intermediate is essential and Fe does not directly participate in the oxygen production. Density functional theory (DFT) calculation shows that Ni-OH deprotonation is a rate-determining step for both binary nickel-iron sulfide and nickel sulfide. The addition of Fe into NiS x lightly increases the charge transfer of Ni atom to O atom, which makes deprotonation easier and thereby improves the OER performance.

Pathological aspects of metal sulfide nanoparticles are lacunae in nanometal bioapplications. The present study is one of its own kind involving sonochemical synthesis and the phytopathological effect of aqua dispersed nanoparticles of ferrous sulfide (FeS-NPs) against the economically important fungus Fusarium verticillioides. In vitro antifungal evaluation against F. verticillioides showed the significant biopotential at 18 μg/ml, with deca-fold higher efficiency than the standard fungicide, carbendazim. Visible symptoms of conidial inhibition as well as membrane disruption in SEM nanographs rationalized the fungal inhibition. In vivo seed treatment on rice (Oryzae sativa) at 30 μg/ml revealed a significant reduction in seedling blight (76.08%) which is deca-fold greater than carbendazim (32.60% at 2000 μg/ml) with a comparable reduction in seed rot (82.12% for FeS-NPs and 80.76% for carbendazim). There were no morphologically visible signs of phytotoxicity at concentrations as high as 30 μg/ml giving a favorable edge to this novel FeS-NPs sample as antifungal nanopriming agent.

In this study, we investigated the removal of hexavalent chromium (Cr(VI)) through an innovative approach, which employed iron sulfide nanoparticles synthesized via a green chemistry technique, utilizing extracts derived from date palm seeds (referred to as ds-FeS). Batch studies, which were well represented by the Langmuir isotherm model, were conducted to determine the maximum removal capacities (qm) of ds-FeS nanoparticles at three different initial pH conditions (pH = 3, 7, and 9). Additionally, batch kinetic studies were conducted under varying conditions of initial Cr(VI) load (3.5, 9, 27, and 38 mg/g of nanoparticles), nanoparticle dose (25, 37, 50, and 75 g/g of Cr(VI)), and initial pH (3, 5, 7, and 9). Results demonstrated the positive impact of acidic pH during Cr(VI) removal by ds-FeS wherein the highest qm of 31.3 mg/g and initial rate of 6.95 mg/g·min (pseudo-second order kinetics) were observed at pH 3. Conversely, with an increase in pH to neutral and alkaline conditions, a decline in both qm and initial rates was observed. Measurements of solution pH, total chromium, and particle surface chemistry using X-ray diffraction and Fourier transform infrared spectrometry techniques revealed the crucial roles of reduction, surface precipitation, and complexation processes in Cr(VI) removal by ds-FeS nanoparticles. Overall, this study demonstrates the promising potential of environmentally friendly, date palm seed–derived iron sulfide nanoparticles for Cr(VI) removal.

Porous FeS nanofibers with numerous nanovoids for use as anode materials for sodium-ion batteries were prepared by electrospinning and subsequent sulfidation. The post-treatment of the as-spun Fe（acac）3-polyacrylonitrile composite nanofibers in an air atmosphere yielded hollow Fe2O3 nanofibers due to Ostwald ripening. The ultrafine Fe2O3 nanocrystals formed at the center of the fiber diffused toward the outside of the fiber via Ostwald ripening. On sulfidation, the Fe2O3 hollow nanofibers were transformed into porous FeS nanofibers, which contained numerous nanovoids. The formation of porosity in the FeS nanofibers was driven by nanoscale Kirkendall diffusion. The porous FeS nanofibers were very structurally stable and had superior sodium-ion storage properties compared with the hollow Fe2O3 nanofibers. The discharge capacities of the porous FeS nanofibers for the Ist and 150th cycles at a current density of 500 mA.g-1 were 561 and 592 mA.h-g-1, respectively. The FeS nanofibers had final discharge capacities of 456, 437, 413, 394, 380, and 353 mA-h.g-1 at current densities of 0.2, 0.5, 1.0, 2.0, 3.0, and 5.0 A.g-1, respectively.

Electroplating sludge (ES) containing large quantities of heavy metals is regarded as a hazardous waste in China. This paper introduced a simple method of treating ES using environmentally friendly fixatives biochar (BC) and iron sulfide (FeS), respectively. After 3 days of treatment with FeS at a FeS-to-ES mass ratio of 1:5, the toxicity characteristic leaching procedure (TCLP)-based leachability of total Cr (TCr), Cu(II), Ni(II), Pb(II), and Zn(II) was decreased by 59.6, 100, 63.8, 73.5, and 90.5 %, respectively. After 5 days of treatment with BC at a BC-to-ES mass ratio of 1:2, the TCLP-based leachability was declined by 35.1, 30.6, 22.3, 23.1, and 22.4 %, respectively. Pseudo first-order kinetic model adequately simulated the sorption kinetic data. Structure and morphology analysis showed that adsorption, electrostatic attraction, surface complexation, and chemical precipitation were dominant mechanisms for heavy metals immobilization by BC, and that chemical precipitation (formation of metal sulfide and hydroxide precipitates), iron exchange (formation of CuFeS 2 ), and surface complexation were mainly responsible for heavy metals removal by FeS. Economic costs of BC and FeS were 500 and 768 CNY/t, lower than that of Na 2 S (940 CNY/t). The results suggest that BC and FeS are effective, economic, and environmentally friendly fixatives for immobilization of heavy metals in ES before landfill disposal.

Expanding the basic knowledge required for improved understanding of hydrogen sulfide (H2S) corrosion of mild steel is needed. When it comes to even the most basic chemical descriptors of aqueous H2S systems such as H2S solubility, water chemistry, polymorphism of iron sulfide, the formation or dissolution of iron sulfide scale, and its protectiveness, many open questions persist and more investigation is required. Inconsistencies in prevailing expressions for H2S solubility constant (KH2S), the first dissociation constant (Ka,1), and the second dissociation constant (Ka,2) are reviewed here. By comparing with experimental data, the best prediction model for H2S solubility and dissociation in an H2S–H2O system was identified. Occurrence of iron sulfide polymorphs was experimentally investigated and it was found that, in short-term exposures, mackinawite formed at 25°C, while greigite and pyrite were detected at 60°C. The solubility limits for these iron sulfides were determined. Simplified Pourbaix diagrams for the H2S–H2O–Fe system have been constructed with different meta-stable and stable iron sulfides (mackinawite, pyrrhotite, greigite, and pyrite) to predict the corrosion products in H2S corrosion of mild steel.

Acetogenesis and methanogenesis have attracted attention as CO2-fixing reactions. Humin, a humic substance insoluble at any pH, has been found to assist CO2-fixing acetogenesis as the sole electron donor. Here, using two CO2-fixing consortia with acetogenic and methanogenic activities, the effect of various parameters on these activities was examined. One consortium utilized humin and hydrogen (H2) as electron donors for acetogenesis, either separately or simultaneously, but with a preference for the electron use from humin. The acetogenic activity was accelerated 14 times by FeS at 0.2 g/L as the optimal concentration, while being inhibited by MgSO4 at concentration above 0.02 g/L and by NaCl at concentrations higher than 6 g/L. Another consortium did not utilize humin but H2 as electron donor, suggesting that humin was not a universal electron donor for acetogenesis. For methanogenesis, both consortia did not utilize extracellular electrons from humin unless H2 was present. The methanogenesis was promoted by FeS at 0.2 g/L or higher concentrations, especially without humin, and with NaCl at 2 g/L or higher concentrations regardless of the presence of humin, while no significant effect was observed with MgSO4. Comparative sequence analysis of partial 16S rRNA genes suggested that minor groups were the humin-utilizing acetogens in the consortium dominated by Clostridia, while Methanobacterium was the methanogen utilizing humin with H2.

Nanostructured FeS dispersed onto N, S dual-doped carbon nanotube–graphene composite support (FeS/N,S:CNT–GR) was prepared by a simple synthetic method. Annealing an ethanol slurry of Fe precursor, thiourea, carbon nanotube, and graphene oxide at 973 K under N2 atmosphere and subsequent acid treatment produced FeS nanoparticles distributed onto the N, S-doped carbon nanotube–graphene support. The synthesized FeS/N,S:CNT–GR catalyst exhibited significantly enhanced electrochemical performance in the oxygen reduction reaction (ORR) compared with bare FeS, FeS/N,S:GR, and FeS/N,S:CNT with a small half-wave potential (0.827 V) in an alkaline electrolyte. The improved ORR performance, comparable to that of commercial Pt/C, could be attributed to synergy between the small FeS nanoparticles with a high activity and the N, S-doped carbon nanotube–graphene composite support providing high electrical conductivity, large surface area, and additional active sites.

Localized corrosion of carbon steel pipelines in oilfield environments is a serious concern. In environments containing both CO2 and H2S gases, pitting corrosion of carbon steel is considered to be a common occurrence which is particularly complex and still not fully understood. This paper presents a parametric study investigating the pitting corrosion behavior of carbon steel in CO2-H2S-containing environments. The work presented is divided into two parts. Part one focuses on understanding the impact of changes in three key process parameters (namely: temperature, absence/presence of 10% H2S, and absence/presence of CO2 in the gas phase) on FeS film formation process and overall the corrosion behavior of carbon steel with emphasis on general corrosion of carbon steel in a 3.5 wt% NaCl brine at 30°C and 80°C. Part two focuses on understanding the early and later stages of the pitting corrosion process, with consideration afforded to general corrosion and iron sulfide (FeS) film formation mechanisms, kinetics, and characteristics. The experiments were conducted based on short-term (7 h) and long-term tests (168 h) to investigate the early and later stages of evolution of pitting corrosion. Corrosion film properties and morphology are studied through a combination of electrochemical and surface analysis techniques which include scanning electron microscopy and x-ray diffraction. The extent of corrosion damage of the carbon steel is evaluated through the implementation of surface interferometry to study pit depth and geometry. The results show that early stages of pitting corrosion are more likely to occur with the formation of mackinawite at both 30°C and 80°C in H2S systems than in CO2 systems after 7 h. However, at 80°C extensive uniform corrosion is dominant, leading to the competing effect of iron sulfide (FeS) formation, continuous evolution of pitting corrosion, and continuous ferrite dissolution in the presence of CO2. Results from 168 h tests showed a buildup of FeS on the corroding steel surface with time with the increase in temperature and presence of CO2 in the gas phase. The buildup of FeS in H2S-CO2-containing environments is enhanced by ferrite dissolution. The FeS formed after 168 h is composed mainly of mackinawite at 30°C, and mackinawite and pyrrhotite at 80°C after 168 h. The combination of mackinawite (with a different morphology) and pyrrhotite is shown to promote more pitting and localized corrosion at 80°C than for mackinawite alone at 30°C.