FeS Particles Research Articles

Efficient removal of Cr(VI) containing tunnel wastewater by sludge biochar loaded with ferrous sulfate

The ease of agglomeration reduced the removal of pollutants by FeS particles. Hence, sludge biochar was employed as a support to produce FeS-loaded biochar composites (FeS@BC) using a solvothermal method, for removing Cr(VI) from wastewater. The performance and mechanism of Cr(VI) removal on FeS@BC were investigated through adsorption experiments and characterization techniques. The adsorption tests revealed that under optimal conditions of solution pH of 3 and dosage of 40 mg, FeS@BC achieved a removal efficiency of over 97 % for 50 mg/L Cr(VI). The presence of Cl- and NO-3 did not affect Cr(VI) removal, whereas sulfate, phosphate, and carbonate inhibited the removal process. Low concentrations of humic acid (1–5 mg/L) held a negligible influence on removing, but elevated concentrations of humic acid inhibited Cr(VI) removal. The behavior of FeS@BC in removing Cr(VI) complied with to the pseudo-second-order and the Langmuir model. At 308.15 K, the largest removal capability of FeS@BC for Cr(VI) reached 185.874 mg/g. Thermodynamic studies confirmed that the Cr(VI) removing processes on FeS@BC were a spontaneous, entropy-driven, endothermic chemical adsorption. The primary mechanism for removing Cr(VI) on FeS@BC included reduction, electrostatic adsorption, complexation, and precipitation, with the reduction process playing a crucial role. This indicated that sludge biochar loaded with FeS was an ideal material for removing Cr(VI) from wastewater.

In situ-grown nitrogen-sulfur co-doped carbon nanotubes encapsulated with FeS particles as cathode materials for zinc-air batteries

Transition metal sulfides as ideal oxygen reduction reaction (ORR) catalysts have great potential to regulate multiple reaction pathways and understand their corresponding internal reaction mechanisms at cathode in zinc-air batteries (ZABS), effectively. This work adopted a facile one-pot synthesis method based on chemical vapor deposition (CVD), which utilizes the synergistic effect of zeolite imidazolium ester skeleton (ZIF-8) and polypyrrole (PPY) to grow nitrogen-sulfur co-doped carbon nanotubes (NS-CNT) in the shape of colonic with a relatively uniform size and encapsulated with FeS nanoparticles as the main active sites. The synthesized purpose catalyst noted as FeS-NS-CNT-900, in which that the FeS nanoparticles were tightly encapsulated in carbon nanotubes, and this special structure ensures that the FeS particles do not detach during the reaction, thus greatly enhancing their electrochemical activity and stability. As expected, the FeS-NS-CNT-900 catalyst exhibited a half-wave potential of 0.877 V which is higher than that of commercial platinum charcoal (0.847 V), at 0.1 mol KOH. More importantly, the formation of abundant FeS catalytic active sites, the optimal conditions for NS-CNT growth, and the covered mechanisms of the enhanced ORR reaction activity of FeS-NS-CNT-900 were thoroughly investigated. Additionally, whileFeS-NS-CNT-900 was used as an air cathode material for the assembly of a zinc-air battery, it exhibited a peak power density and specific capacity of 123 mW cm−2 and 785.81 mA h g−1, respectively, which were significantly better than that of platinum-carbon cathode (92.8 mW cm−2 and 740.4 mA h g−1). And surprisingly, the battery with FeS-NS-CNT-900 cathode exhibited (delivered/showed) a high cycle stability of 260 h at 5 mA cm−2. Conclusively, present work provides a feasible method for in situ growth of sulfur and nitrogen co-doped carbon nanotube encapsulated transition metal sulfide nanoparticle catalysts, which may pave a new avenue for the preparation of high ORR performance air cathode material for ZABS.

Yolk-shell FeS@N-doped carbon nanosphere as superior anode materials for sodium-ion batteries

Iron sulfides have shown great potential as anode materials for sodium-ion batteries (SIBs) because of their high sodium storage capacity and low cost. Nevertheless, iron sulfides generally exhibit unsatisfied electrochemical performance induced by sluggish electron/ion transfer and severe pulverization upon the sodiation/desodiation process. Herein, we constructed a yolk-shell FeS@NC nanosphere with an N-doped carbon shell and FeS particle core via a simple hydrothermal method, followed by in-situ polymerization and vulcanization. The FeS particles intimately coupled with N-doped carbon can accelerate the electron transfer, avoid severe volume expansion, and maintain structural stability upon repeated sodiation/desodiation process. Furthermore, the small particle size of FeS can shorten ion-diffusion distance and facilitate ion transportation. Therefore, the FeS@NC nanosphere shows excellent cycling performance and superior rate capability that it can deliver a high capacity of 520.1 mAh g−1 over 800 cycles at 2.0 A g−1 and a remarkable capacity of 625.9 mAh g−1 at 10.0 A g−1.

Bioelectrochemical treatment of acid mine drainage: Microbiome synergy influences sulfidogenesis and acetogenesis

Bioelectrochemical systems (BES) are emerging as potential technologies that can remediate acid mine drainage (AMD) by cathodic reduction of sulfates to metal sulfides. This study evaluated bioelectrochemical remediation of sulfate rich AMD at two applied cathode potentials; BES-1: −1.0 V and BES-2: −0.8 V. Sulfate reducing bacteria were selectively enriched to be used as biocatalyst in BES. Initially, lactate was fed as carbon source and switched to chemolithoautotrophy with only CO2-fed conditions. Both BESs were operated at 3±0.2 g/l of sulfate with synthetic AMD (SAMD) fed first, and gradually changed to 50% AMD from mining site with 50% SAMD. Sulfate reduction was relatively higher with BES-1: 82% than BES-2: 76% coupled with sulfidogenesis. Interestingly, acetogenesis (BES-1: 2.12±0.2 g/l, BES-2: 1.9±0.2 g/l) was also noticed with high reduction currents (BES-1&2: >-70 mA). Microbiome community analysis revealed the dominant presence of sulfate reducers, acetogens, syntrophic bacteria and Methanobacterium, probing microbial synergy aiding sulfate reduction. An added advantage was the iron-sulfide (FeS) particles formation on cathode, which might have contributed to increased reduction currents. This study reveals insights into microbial synergy for autotrophic sulfate reduction within mixed microbiome communities along with the impact of FeS particles as conducive facilitator for electron transfer in BES, thereby enhancing electrosynthetic acetate production.

Study on the effectiveness of sulfate-reducing bacteria to remove Pb(II) and Zn(II) in tailings and acid mine drainage.

In view of water and soil getting polluted by Pb(II), Zn(II), and other heavy metals in tailings and acid mine drainage (AMD), we explored the removal effect of sulfate-reducing bacteria (SRB) on Pb(II), Zn(II), and other pollutants in solution and tailings based on the microbial treatment technology. We used the scanning electron microscope-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray fluorescence (XRF), to reveal the mechanism of SRB treatment of tailings. The results showed that SRB had a strong removal capacity for Zn(II) at 0-40 mg/L; however, Zn(II) at 60-100 mg/L inhibited the growth of SRB. Similarly, SRB exhibited a very strong ability to remove Pb(II) from the solution. At a Pb(II) concentration of 10-50 mg/L, its removal percentage by SRB was 100%. SRB treatment could effectively immobilize the pollutants leached from the tailings. With an increase in the amount of tailings added to each layer, the ability of SRB to treat the pollutants diminished. When 1 cm of tailingssand was added to each layer, SRB had the best effect on tailing sand treatment. After treatment, the immobilization rates of , Fe(III), Mn(II), Pb(II), Zn(II), Cu(II), and total Cr in the leachate of #1 tailing sand were 95.44%, 100%, 90.88%, 100%, 96.20%, 86.23%, and 93.34%, respectively. After the tailings were treated by SRB, although the tailings solidified into a cohesive mass from loose granular particles, their mechanical strength was <0.2 MPa. Desulfovibrio and Desulfohalotomaculum played the predominant roles in treating tailings by mixing SRB. The S2- and carbonate produced by mixing SRB during the treatment of tailings could metabolize sulfate by combining with the heavy metal ions released by the tailings to form FeS, MnS, ZnS, CuS, PbS, Cr2S3, CaCO3, MnCO3, and other precipitated particles. These particles were attached to the surface of the tailings, reducing the environmental pollution of the tailings in the water and soil around the mining area.

EDA/PANI derived FeNxC with Fe-Nx active sites as room temperature hydrogen storage material

FeNxC is explored as an efficient and cost-effective hydrogen storage material. Fe/Ethylenediamine (EDA) complex formed initially is protected by (Polyaniline) PANI polymer that gets converted to FeNxC through two-step pyrolysis process. In the first pyrolysis, (Iron sulfide) FeS particles are formed, which get converted to Fe3O4 nanoparticles in second pyrolysis. Fe-Nx active sites get exposed in micro/mesoporous carbon matrix after oxide removal through acid wash. Hydrogen adsorption studies are conducted at 25–100 °C temperature, 5–30 bar pressure. The maximum hydrogen storage capacity is observed as 2.83 wt% at 26 bar, 25 °C for the two-step calcined, acid-washed FeNxC-900–800 A, which possesses large surface area of 995 m2/g, pore volume of 0.711 cm3/g when compared to FeNxC-900–800 and FeNxC-900. The adsorption mechanism, spillover occurring at covalently bonded Fe-Nx active sites and subsequent migration, diffusion to get physisorbed within porous carbon surface, leads to the enhancement in the hydrogen adsorption.

Effect of Gas-Phase Passivation Technology on Spontaneous Combustion Characteristic Stage and Reaction Kinetics of FeS During Particle Size Fragmentation

ABSTRACT To investigate the mechanism of inhibition of spontaneous combustion of reactive FeS by gas-phase passivation, this paper used liquid-phase synthesis to prepare reactive FeS which were divided into five particle size ranges by crushing and grinding and then passivated those by low-oxygen gas. This paper analyzed the effect of gas-phase passivation on the characteristic parameters of the characteristic stages of crushed FeS from the perspective of thermodynamics, and used the KAS and FWO methods to calculate the apparent activation energy of the different characteristic stages of the FeS oxidation heating process. Inhibition mechanism of FeS spontaneous combustion reaction kinetics during particle size fragmentation by gas-phase passivation was revealed. The results indicate that in the spontaneous combustion stage at room temperature (RT), the exothermic heat of passivated FeS was significantly reduced to below 5 J/g, and the apparent activation energy rose up to 116 kJ/mol, which was significantly increased by about 50% compared to the activated FeS. The essence of gas-phase passivation is that the low oxygen concentration gas reacts with FeS to produce a passivation protective film, blocking the reaction and pushing the oxidation process backwards as a whole. In the weight gain stage of oxygen absorption, the weight gain of passivation FeS is reduced to less than 2.2%, and the heat release is reduced to 2.8J/g. The particle size of the passivated FeS decreased, and the apparent activation energy increased by 20 kJ/mol in the decomposition and combustion stage. With the decrease of FeS particle size, the gas-phase passivation is more effective and the inhibition effect of spontaneous combustion of FeS is more obvious.

The effect of FeS on the fate of Cr(VI) in the presence of organic matters under dynamic anoxic/oxic conditions.

The reduction of Cr(VI) by FeS under anoxic conditions has been studied extensively. However, when the redox environments alternate from anoxic to oxic, the effect of FeS on the fate of Cr(VI) in the presence of organic matters still remains unknown. Therefore, this study investigated the effect of FeS coupled with humic acids (HA) and alga on the transformation of Cr(VI) under dynamic anoxic/oxic conditions. HA could promote the reduction of Cr(VI) from 86.6% to 100% under anoxic conditions due to the enhancement of the dissolution and dispersibility of FeS particles by HA. However, the strong complexing and oxidizing properties of alga inhibited the reduction of FeS. Reactive oxygen species (ROS) generated from FeS oxidation under oxic conditions could oxidize 3.80μM of Cr(III) to aqueous Cr(VI) at pH 5.0, while aqueous Cr(VI) reached to 4.83μM in the presence of HA, which was ascribed to the increasing amount of free radicals. In addition, acidic conditions and excess FeS would increase strong reducing Fe(II) and S(-II) species, and improve the efficiency of Fenton reaction. The findings provided new insights into the fate of Cr(VI) in aquatic systems containing FeS and organic matters under dynamic anoxic/oxic conditions.

Two metabolic stages of SRB strain Desulfovibrio bizertensis affecting corrosion mechanism of carbon steel Q235

Desulfovibrio bizertensis (D. bizertensis), an SRB isolated and cultured from the rust layer of the South China Sea, is widespread in the corrosive microbial communities on steel surface. Although the corrosion mechanism of SRB was widely studied, the mechanism of different metabolic stages inducing corrosion was still unclear. In this work, D. bizertensis was used to study the corrosion process of carbon steel Q235 at different metabolic stages by surface analysis and electrochemical methods. Combined with the metabolic process of SRB, corrosion pits of carbon steel could be influenced by two stages. In the first stage, the rapid growth of planktonic D. bizertensis cells in culture medium was accompanied by quick consumption of the electron donor (lactate) till complete consumption. D. bizertensis cells began to adhere to Q235 surface and promote anodic dissolution of iron. In the second stage, the growth of planktonic cells was suppressed, thus the colonized D. bizertensis cell in the pitting could obtain energy directly from Fe(0) through DET, which would further aggravate pitting corrosion and the maximum depth of the pits approached 15.7 µm. Sulfides produced by D. bizertensis metabolism would accumulate on steel coupon and form FeS coverage. Thus D. bizertensis could survive for a long time in this conductive FeS particles network. Electrochemical results showed the promotion effect of D. bizertensis on cathodic reaction, and the values of Rct in the SRB medium were much lower than that in the sterile medium.

Influence of Fe2O3‐FeS on the structure of iron‐containing clusters in aluminosilicate melts

AbstractIron compounds addition on the melt is a more complex issue. Uncertainties in industrial applications are caused by crystallization and depolymerization phenomena. Most of the current studies have discussed FeO and Fe2O3, ignoring the influence of FeS in the glass structure. This study designed and simulated artificial ash close to coal ash to interact with the glass melt at high temperatures. Coulomb titration, X‐ray diffraction (XRD), and Raman analyses were carried out to determine the percentage and composition of crystalline and noncrystalline materials in the glass. Samples of FeS‐Fe2O3 were subjected to the enumeration of the glass structure and quantitative calculations of the degree of polymerization. The results showed that 15‐wt% Fe2O3 promoted crystallization in the system and accelerates the depolymerization of FeS. The introduction of FeS increases the amorphous materials, and the obtained amorphous materials are Si dominated network structures and [SiO4]‐[FeO4]‐[SiO4] clusters. The network tends to change from [FeOn] and [AlO4] to [SiO4]. In addition, aluminosilicate may enter FeS particles and unreacted FeS may deposit on the aluminosilicate surface.

Remediation of Cr(VI) contaminated soil by chitosan stabilized FeS composite and the changes in microorganism community

In-suit immobilization is one of the major strategies to remediate heavy metals contaminated soil with the effectiveness largely depends on the characteristics of the added chemical reagents/materials. In this study, chitosan stabilized FeS composite (CS–FeS) was prepared to evaluate the performance of remediating the high and toxic hexavalent chromium contaminated soil from the effectiveness and microbial response aspects. The characterization analysis confirmed the successful preparation of composite, and the introduction of chitosan successfully stabilized FeS to protect it from rapid oxidation as compared to bare FeS particles. With the addition dosage at 0.1%, about 85.6% and 81.3% of Cr(VI) was reduced in 3 d based on toxicity characteristic leaching procedure (TCLP) and CaCl2 extraction, and the reduction efficiency increased to 96.6% and 94.8% in 7 d, respectively. The Cr(VI) was non-detected in the TCLP leachates with increase the CS-FeS composites to 0.5%. The percentages of HOAc-extractable Cr decreased from 25.17% to 6.12% accompanied with the increase in the residual Cr from 4.26% to 13.77% and improvement of soil enzyme activity under CS-FeS composites addition. Cr(VI) contamination reduced the diversity of microbial community in soil. Three dominate prokaryotic microorganisms, namely Proteobacteria, Actinobacteria and Firmicutes, were observed in Cr-contaminated soil. The addition of CS-FeS composites increased the microbial diversity especially for that in relative lower abundance. The relative abundance of Proteobacteria and Firmicute related to Cr-tolerance and reduction increased in CS-FeS composites added soils. Taking together, these results demonstrated the potential and promising of using the CS-FeS composites for Cr(VI) polluted soil remediation.

Growth mechanism of metal iron particles with sulfur additives in direct reduction: First-principles calculations and experiments

Sulfur additive can greatly promote iron particles growth in direct reduction. However, promotion mechanism for metallic iron particles growth is unclear. FeS was found as the thermodynamic stable sulfur phase in reduction, intensifying in metal iron particles growth. Therefore, microstructure evolution and phase transition of metallic iron growth with FeS was investigated by reduction experiments. There were three stages in reduction. Firstly, liquid FeS was found, and Fe was produced around pore. Secondly, Fe was wetted and wrapped by liquid phase (Fe-FeS). Thirdly, Fe migrated to even in liquid phase, then irregular fine Fe particles gradually transformed and aggregated to sphere. Furthermore, controlling mechanisms in each stage were identified. The first stage was driven by reduction reaction. For second stage, interfacial interaction was found as the driving force. As wettability is macroscopic manifestation of interfacial interaction, wetting experiments was used. The best wettability was found in Fe/FeS interface followed wetting order: Fe/FeS(1200 °C) > FeS/SiO2(1200 °C) > Fe/SiO2 (1570 °C) with contact angle of 1.86°, 71.5° and 100°, respectively. First-principles calculations further revealed that the strongest interfacial interaction between Fe/FeS drive second stage due to its combining ionic and covalent bonding, and the highest interfacial separation work in Fe(200)/FeS(110) which was 1.998 J/m2. Meanwhile, the well wettability of Fe/FeS also provides a well kinetic basis for third stage, and the huge Fe concentrations difference in FeS and irregular fine particles interfacial energy are combined to drive the stage. Summary, the growth mechanisms of metallic iron particles in direct reduction with sulfur is systematic established.

Surfactant-assisted RGO limited spherical FeS with superior stability and high capacity as an anode for lithium-ion batteries

The realization of high cycling stability and high reversible capacity of lithium-ion storage is the critical factor to promote the development of lithium-ion batteries. Here, a composite of spherical FeS particles distributed on the surface of graphene (FeS/rGO-60) has been designed by cetyltrimethylammonium bromide (CTAB)-assisted synthesis. The surface of graphene is activated by the surface activity of CTAB so that it can better anchor FeS. In the FeS/rGO-60 composite, spherical FeS particles of about 1 μm are uniformly distributed on the graphene surface, and no agglomeration occurs, thus resulting in excellent electrochemical properties. As a candidate anode, FeS/rGO-60 composite electrode exhibits ultra-high specific capacity and excellent cycling stability (1300 mAh g−1 over 1100 cycles at 1 A g−1), superior to those FeS-based anode materials reported so far. Even at higher current densities of 5 A g−1, the resulting electrode still maintains a high capacity of 432.9 mAh g−1 and its initial morphology after 900 cycles, confirming its superior rate performance and stability. The LiFePO4//FeS/rGO-60 full cell showed a high energy density of 797 Wh kg−1 at a power density of 824.2 W kg−1. At a 0.5 A g−1, the LiFePO4//FeS/rGO-60 full battery exhibited a remarkable cycling capacity with 488.6 mAh g−1 after 80 cycles. The creative idea in this work provides a new way to construct stable metal sulfide/rGO composite electrode materials for high Lithium storage performance.

Characterization of Fe-containing particles in Chengdu, southwest China, using single-particle aerosol mass spectrometry

Single-particle aerosol mass spectrometry was used to study the characteristics of Fe-containing particles during winter in Chengdu, southwest China. The mass concentrations of PM2.5 and PM10 during the study period were 64 ± 38 and 89 ± 49 µg/m3, respectively, and NO2 and particulate matter were high compared with most other regions of China. The Fe-containing particles were divided into seven categories with different mass spectra, sources and aging characteristics. The highest contribution was from Fe mixed with carbonaceous components (Fe-C, 23.1%) particles. Fe was more mixed with sulfate than nitrate and therefore the contribution of Fe mixed with sulfate (Fe-S, 20.7%) particles was higher than that of Fe mixed with nitrate (Fe-N, 12.5%) particles. The contributions from Fe-containing particles related to primary combustion were high in the small particle size range, whereas aged Fe-containing particles and dust-related particles were mostly found in the coarse particle size range. The air masses mainly originated from the west and east of Chengdu, and the corresponding PM2.5 concentrations were 79 ± 36 and 55 ± 36 µg/m3, respectively. The west and east air masses showed stronger contributions of Fe-containing particles related to biomass burning (Fe-B) and fossil fuel combustion (Fe-C and Fe-S) particles, respectively. The southwest area contributed the most Fe-containing particles. Future assessments of the effects of Fe-containing particles during heavy pollution period should pay more attention to Fe-C and Fe-S particles. Emission-reduction of Fe-containing particles should consider both local emissions and short-distance transmission from the surrounding areas.

Morphology and structure of in situ FeS affect Cr(VI) removal by sulfidated microscale zero-valent iron with short-term ultrasonication

The properties of sulfidated zero-valent iron (S-ZVI) are considered to be determined by the entire structure of Fe0 and FexSy as a whole, but few studies focus on the influence of the morphology and structure of the external FexSy layer on the performance of S-ZVI. In this study, after the sulfidation of microscale ZVI in acetate (HAc-NaAc) and 2-(N-morpholino) ethanesulfonic acid (MES) buffer solution, the S-mZVIHAc-NaAc surface presented the in situ growth of the FeS nanosheet, while the S-mZVIMES surface was dominated by agglomerated FeS sub-micron particles. Under short-term ultrasonication, S-mZVIHAc-NaAc was superior to removing Cr(VI) than S-mZVIMES, and the clearance of the passivation layer by ultrasound maximized the conductivity of the FeS nanosheet to strengthen the sulfidation contribution. However, agglomerated FeS particles were easily separated from S-mZVIMES by ultrasonication, resulting in the suppression of its sulfidation contribution. The removal of Cr(VI) by S-ZVI increased linearly with FeS content, and the chemical combination of FeS with ZVI had more significant synergy than their physical mixture. The FeS nanosheet with excellent conductivity and large vertical space benefited the generation of dissolved and surface-associated Fe(II) as electron donors and structural Fe(II) as the electron shuttle. Understanding the relationship between FeS structure and S-ZVI performance will pave a way for optimizing the synthesis of S-ZVI.

Preparation and properties of lead-free copper matrix composites by electroless plating and mechanical alloying

Based on the concept of green design and development, FeS/Cu–Bi lead-free copper matrix composites were prepared by using FeS and Bi powder as lubricating phase to replace the lead in CuPb alloy. Surface modification of FeS powder by electroless plating and mechanical alloying of mixed powder by high-energy ball milling are effective strategies for preparing lead-free copper matrix composites. The effects of surface modification and mechanical alloying on the mechanical and tribological properties of the materials are studied. Results show that electroless nickel plating improves the mechanical locking and metallurgical bonding between mixed powder particles; enhances the interface bonding between FeS particles and copper matrix; and increases the hardness, impact toughness, and crushing strength by 29.7%, 19.4%, and 13%, respectively. The density and hardness of the composite prepared by electroless nickel plating combined with mechanical alloying increases by 11.4% and 40.6%, respectively, average friction coefficient decreases from 0.44 to 0.28, and wear rate decreases by 62%. Electroless plating and mechanical alloying reduce the microploughing and material transfer on the worn surface of the composites, and the abrasive wear and adhesive wear are remarkably improved.

Characterization of biospheric bacterial community on reduction and removal of chromium from tannery contaminated soil using an integrated approach of bio-enhanced electrokinetic remediation

Intensive research efforts on different methods focus on reducing toxic Cr(VI) to less toxic Cr(III). However, most methods end up in improper removal, recurrence or subsequent pollutant generation. Therefore, our study focuses on the reduction and removal of Cr with no recurrence possibilities. So, the indigenous biospheric bacterial community is characterized by Metagenomics using EPI2ME 16S workflow Bioinformatics tool. The obtained metagenome raw data has been submitted in NCBI database with reference to the Bio Project ID PRJNA679434. Based on this data, the possible bio-mechanisms behind the reduction of Cr(VI) to Cr(III) by FeS particles generated by the biospheric microbes (4.5 × 103) was elucidated. Electrokinetic (EK) experiments further removed the reduced Cr(III) by Bio-enhanced electrokinetic remediation (BEER) approach. The presence of Mn (3.54%) in the soil was found to oxidize the reduced Cr(III) to Cr(IV), thus ruling out the Cr(VI) recurrence. The integrated approach of BEER showed an effective removal of Cr and Fe in the contaminated soil. Physico-chemical parameters such as chemical oxygen demand (COD) was assessed and found to show a drastic removal efficiency of 70% after the EK treatment. Thus, the presence of sulphide content (122 mg/L) generated by the biospheric microbial community was found to enhance the Cr(VI) reduction and Cr(III) removal significantly, thus proving the effectiveness of the BEER approach to overcome the drawback of Cr recurrence in heavy metal contaminated soil environments.

Synthesis of FeS-impregnated heteroatom-doped carbon nanofibers assisted by one-step vulcanization for superior sodium storage

Severe volume changes during sodiation/desodiation and the sluggish sodium reaction kinetics of FeS limit its applications in high-performance sodium-ion batteries (SIBs). To solve these problems, free-standing FeS nanocrystallites-impregnated porous N, S-doped carbon nanofibers (FeS@CNFs) is fabricated through an electrospinning technique combined with one-step vulcanization. During the vulcanization, the Fe precursor containing as-spun film is carbonized and sulfurated, and the carbon matrix is functionalized by S-containing oxygen groups meanwhile. The obtained free-standing and flexible FeS@CNFs film can be directly used as anode for SIBs without slurry-casting. The film exhibits prominent electrochemical property because low electronic conductivity and aggregation of FeS particles are resolved by introducing well-distributed FeS nanocrystallites into the conductive carbon nanofibers network. In addition, the film exhibits good structural stability with limited volume changes during cycling due to the buffer effects of CNFs. The film shows a high specific capacity of 530 mA h g−1 at 0.2 A g−1 with a high initial Coulombic efficiency of 86.2%. Additionally, with enhanced surface-dominant pseudocapacitive redox reactions, which facilitate charge transfer and ion diffusion, the FeS@CNFs delivers capacities of 367 and 278 mA h g−1 at 10 and 30 A g−1, respectively, maintaining long cycling stability with a high capacity retention rate of 87.6% after 700 cycles at 10 A g−1.

Effect of Copresence of Zerovalent Iron and Sulfate Reducing Bacteria on Reductive Dechlorination of Trichloroethylene.

Sulfur amendment of zerovalent iron (ZVI) materials has been shown to improve the reactivity and selectivity of ZVI toward a select group of organohalide contaminants in groundwater, most notably trichloroethene (TCE). In previous studies, chemical or mechanochemical sulfidation methods were used; however, the potential of using sulfate-reducing bacteria (SRB) to enable sulfur amendment has not been closely examined. In this study, lab-synthesized nanoscale ZVI (nZVI) and Peerless iron particles (ZVIPLS) were treated in a sulfate-reducing monoculture (D. desulfuricans) and an enrichment culture derived from freshwater sediments (AMR-1) prior to reactivity assessments with TCE as the model contaminant. ZVI conditioned in both cultures exhibited higher dechlorination efficiencies compared to unamended ZVIs. Remarkably, nZVI and ZVIPLS exposed to AMR-1 attained similar TCE dechlorination rates as their counterparts receiving chemical sulfidation (i.e., S-nZVI) using previously reported method. Product distribution data show that, in the SRB-ZVI system, abiotic dechlorination is the dominant TCE reduction pathway. In addition to dissolved sulfide, biogenic or synthesized FeS particles can enhance nZVI reactivity even as nZVI and FeS were not in direct contact, implying that SRB may influence the reactivity of ZVI via multiple mechanisms in different remediation situations. A shift in Archaea abundance in AMR-1 with nZVI amendment was observed but not with ZVIPLS. Overall, the synergy exhibited in the SRB-ZVI system may offer a valuable remediation strategy to overcome limitations of standalone biological or abiotic dechlorination approaches for chlorinated solvent abatement.

Adsorption and reduction of Cr(VI) by a novel nanoscale FeS/chitosan/biochar composite from aqueous solution

The purpose of this study was to synthesize FeS/chitosan/biochar composite (FSBC) to remove Cr(VI). Results indicate that the modification of FeS particles and chitosan to biochar provided large specific surface area and more active adsorption sites. FSBC(1:1:1) have an enhanced Cr(VI) adsorption capacity of 103.93 mg g-1 at 0.01 g per 50 mL Cr(VI) solution compared with 19.97 mg g−1 for FeS particles and 22.45 mg g−1 for biochar. Increasing temperature promote Cr(VI) removal. By contrast, increasing Cl- and SO42- concentrates and solution pH prevented Cr(VI) adsorption. Cr(VI) removal could attribute to surface adsorption, reduction and precipitation. XPS results indicated that 76.07% of Cr(VI) removal was due to reduction or precipitation, and 23.93% could be ascribed to surface adsorption. After adsorption-desorption cycle, Cr(VI) removal capacities are 70.42, 65.33 and 11.67 mg g−1 for FSBC(1:1:1), FSBC(1:1:5) and FSBC(5:5:1), respectively. The study demonstrated that FSBC were high-effective adsorbents for Cr(VI) removal in the water environment.