Sulfide-modified Nanoscale Zerovalent Iron Research Articles

Activation of H2O2 via sulfide-modified nanoscale zero-valent iron for tetracycline removal: Performance and mechanism

Tetracycline (TC) is widely detected in various environments and promotes bacterial resistance. In the present research, sulfide-modified nanoscale zero-valent iron (S-nZVI) was fabricated and used as activator of hydrogen peroxide (H2O2) for TC degradation. Sulfidation could improve the hydrophobicity of nZVI and its reactivity for TC degradation by up to 260 %. The reaction rate constant of the S-nZVI/H2O2 system was 16 times faster than that of the S-nZVI system. The quenching experiments results proved that •OH was the predominant radical involved in TC degradation. •OH played a significant role in ferryl ion (Fe(IV)) formation under acid conditions, while TC plays crucial roles under neutral pH condition in Fe(IV) formation by accelerating Fe(III) oxidation into Fe(IV). The possible degradation pathways were analyzed, and the toxicity analysis confirmed that the S-nZVI/H2O2 system is an effective method for degrading, and thus reducing the toxicity of TC. Therefore, this study suggests the possibility of an S-nZVI/H2O2 system for the efficient degradation of TC.

Degradation of 2-Chlorophenol in Aqueous Solutions Using Persulfate Activated by Biochar Supported Sulfide-Modified Nanoscale Zero-Valent Iron: Performance and Mechanisms

In this work, soybean biochar-supported sulfide-modified nanoscale zero-valent iron (BC@S-nZVI) was synthesized and used to activate persulfate (PS) to degrade 2-chlorophenol (2-CP) in aqueous solutions. Batch experiments were carried out to investigate the degradation effects under different conditions, including initial mass ratios among 2-CP, PS, and BC@S-nZVI, initial pH values, temperature, and anions. The results showed that the mass ratio of PS to 2-CP equal to 70 and the mass ratio of BC@S-nZVI to PS equal to 0.4 were the optimum mass ratios in the degradation system. The degradation efficiency of 2-CP was higher under acidic and alkaline conditions than the neutral condition, and the effect was best at a pH of 3; meanwhile, it increased with the increase in temperature. Moreover, the degradation rate was restrained with the addition of Cl−, promoted with the addition of NO3− and CO32−. Both free radical and material functions played leading roles in the degradation of 2-CP, and the stability of BC@S-nZVI was better than nZVI and S-nZVI. The experimental results showed that it was promising to remove 2-CP and other organic pollutants from groundwater by PS activated with BC@S-nZVI.

Persulfate activation by sulfide-modified nanoscale zero-valent iron for metronidazole degradation: Mechanism, major radicals and toxicity assessment

Sulfide-modified nanoscale zero-valent iron (SnZVI) is considered to be an effective method for persulfate (PS) activation. Here, the catalytic activity was evaluated in view of the potential influencing factors, including the sulfidation regent, Fe/S molar ratio, initial solution pH value, catalyst dosage, PS dosage, initial MNZ concentration and common anion species. The complete removal was obtained when Na2S was chosen at Fe/S molar ratio of 0.05 with 1.5 g·L−1 SnZVI and 1.5 mM PS. SnZVI exhibited a promising application owing to the high pH adaptation and the outstanding reusability. The high and persistent release of Fe2+ and FexSy generated on the surface, which accelerated the electron transfer rate for PS activation. The main reactive oxygen species, including OH, SO4−, O2− and 1O2, were further determined. However, OH rather than SO4− was the dominant reactive radical in our study. Finally, the degradation products and possible pathways were predicted based on the intermediate analysis. The T.E.S.T theoretical calculation indicated that the ecotoxicity of the various intermediate products of MNZ were greatly reduced. These results demonstrated that SnZVI/PS was a promising strategy for practical application in the remediation of MNZ contaminated water.

Removal of nitrate nitrogen from wastewater by green synthetic hydrophilic activated carbon supported sulfide modified nanoscale zerovalent Iron: Characterization, performance and mechanism

In this study, A green reducing agent green tea extract is used instead of traditional sodium borohydride and porous activated carbon was supported to prepare nano-zero valent iron (nZVI) combined with sulfate (GT-PAC-nZVI/S) to remove Nitrate Nitrogen (NO3–-N) in wastewater. SEM-EDS, BET, XRD and FTIR characterization results confirmed that effective preparation of porous and high specific surface area and successful loading of sulfide nZVI on PAC. Batch experiments were conducted to measure the effects on the removal of nitrate nitrogen of different parameters including pH, temperature, dosage, interfering agents, carbon-iron ratio and iron-sulfur ratio. The experimental results demonstrate that GT-PAC-nZVI/S has a high nitrate nitrogen removal rate and reduction product gaseous nitrogen can reach 93.00% and 22.10%, respectively, at pH = 7, the dosage of GT-PAC-nZVI/S = 4 g/L, temperature of 60 ℃, iron-sulfur ratio = 1:0.3 and time of 95 min. And interfering ion HPO42- have the strong inhibition for NO3–-N degradation. The adsorption isotherm and kinetic data for GT-PAC-nZVI/S was fitted well with the Langmuir and pseudo-second order model, respectively, indicating that the adsorption process for nitrate was chemisorption. Furthermore, GT-PAC-nZVI/S enhanced the removal of nitrate nitrogen through complexation, redox, and adsorption co-precipitation. This work highlights the efficient remediation of nitrate-nitrogen water pollution by porous activated carbon loaded with sulfide nZVI.

Sulfide-modified nanoscale zero-valent iron as a novel therapeutic remedy for septic myocardial injury

IntroductionMyocardial injury is a serious complication in sepsis with high mortality. Zero-valent iron nanoparticles (nanoFe) displayed novel roles in cecal ligation and puncture (CLP)-induced septic mouse model. Nonetheless, its high reactivity makes it difficult for long-term storage. ObjectivesTo overcome the obstacle and improve therapeutic efficiency, a surface passivation of nanoFe was designed using sodium sulfide. MethodsWe prepared iron sulfide nanoclusters and constructed CLP mouse models. Then the effect of sulfide-modified nanoscale zero-valent iron (S-nanoFe) on the survival rate, blood routine parameters, blood biochemical parameters, cardiac function, and pathological indicators of myocardium was observed. RNA-seq was used to further explore the comprehensive protective mechanisms of S-nanoFe. Finally, the stability of S-nanoFe-1d and S-nanoFe-30 d, together with the therapeutic efficacy of sepsis between S-nanoFe and nanoFe was compared. ResultsThe results revealed that S-nanoFe significantly inhibited the growth of bacteria and exerted a protective role against septic myocardial injury. S-nanoFe treatment activated AMPK signaling and ameliorated several CLP-induced pathological processes including myocardial inflammation, oxidative stress, mitochondrial dysfunction. RNA-seq analysis further clarified the comprehensive myocardial protective mechanisms of S-nanoFe against septic injury. Importantly, S-nanoFe had a good stability and a comparable protective efficacy to nanoFe. ConclusionsThe surface vulcanization strategy for nanoFe has a significant protective role against sepsis and septic myocardial injury. This study provides an alternative strategy for overcoming sepsis and septic myocardial injury and opens up possibilities for the development of nanoparticle in infectious diseases.

Insights into enhanced removal of Cd2+ from aqueous solutions by attapulgite supported sulfide-modified nanoscale zero-valent iron.

The sulfidation of nanoscale zerovalent iron (nZVI) has received increasing attention for reducing the oxidizability of nZVI and improving its reactivity toward heavy metal ions. Here, a sulfide (S)-modified attapulgite (ATP)-supported nanoscale nZVI composite (S-nZVI@ATP) was rapidly synthesized under acidic conditions and used to alleviate Cd2+ toxicity from an aqueous solution. The degree of oxidation of S-nZVI@ATP was less than that of nZVI@ATP, indicating that the sulfide modification significantly reduced the oxidation of nZVI. The optimal loading ratio was at an S-to-Fe molar ratio of 0.75, and the adsorption performance of S-nZVI@ATP for Cd2+ was significantly improved compared with that of nZVI@ATP. The removal of Cd2+ by S-nZVI@ATP was 100% when the adsorbent addition was 1 g/L, the solution was 30 mL, and the adsorption was performed at 25 °C for 24 h with an initial Cd2+ concentration of 100 mg/L. Kinetics studies showed that the adsorption process of Cd followed the pseudo-second-order model, indicating that chemisorption was the dominant adsorption mechanism. The adsorption of Cd2+ by S-nZVI @ATP is dominated by the complexation between the iron oxide or iron hydroxide shell of S-nZVI and Cd2+ and the formation of Cd(OH)2 and CdS precipitates.

Hydrogen Peroxide Activated by Biochar-Supported Sulfidated Nano Zerovalent Iron for Removal of Sulfamethazine: Response Surface Method Approach.

Biochar (BC)-supported sulfide-modified nanoscale zerovalent iron (S-nZVI/BC) was prepared using the liquid-phase reduction method for the application of the removal of sulfamethazine (SMZ) from water. The reaction conditions were optimized by the Box–Behnken response surface method (RSM). A model was constructed based on the influence factors of the removal rate, i.e., the carbon-to-iron ratio (C/Fe), iron-sulfur ratio (Fe/S), pH, and hydrogen peroxide (H2O2) concentration, and the influence of each factor on the removal efficiency was investigated. The optimal removal process parameters were determined based on theoretical and experimental results. The results showed that the removal efficiency was significantly affected by the C/Fe ratio and pH (p < 0.0001) but relatively weakly affected by the Fe/S ratio (p = 0.0973) and H2O2 concentration (p = 0.022). The optimal removal process parameters were as follows: 0.1 mol/L H2O2, a pH of 3.18, a C/Fe ratio of 0.411, and a Fe/S ratio of 59.75. The removal rate of SMZ by S-nZVI/BC was 100% under these conditions. Therefore, it is feasible to use the Box–Behnken RSM to optimize the removal of emerging pollutants in water bodies by S-nZVI/BC.

Co-Removal Effect and Mechanism of Cr(VI) and Cd(II) by Biochar-Supported Sulfide-Modified Nanoscale Zero-Valent Iron in a Binary System.

This study aimed to explore the co-removal effect and mechanism of Cr(VI) and Cd(II) with an optimized synthetic material. The toxicity and accumulation characteristics of Cr(VI) and Cd(II) encountered in wastewater treatment areas present significant challenges. In this work, a rational assembly of sulfide-modified nanoscale zero-valent iron (SnZVI) was introduced into a biochar (BC), and a Cr(VI)–Cd(II) binary system adsorbent with high efficiency was synthesized. When the preparation temperature of the BC was 600 °C, the molar ratio of S/Fe was 0.3, the mass ratio of BC/SnZVI was 1, and the best adsorption capacities of BC-SnZVI for Cr(VI) and Cd(II) in the binary system were 58.87 mg/g and 32.55 mg/g, respectively. In addition, the adsorption mechanism of BC-SnZVI on the Cr(VI)-Cd(II) binary system was revealed in depth by co-removal experiments, indicating that the coexistence of Cd(II) could promote the removal of Cr(VI) by 9.20%, while the coexistence of Cr(VI) could inhibit the removal of Cd(II) by 43.47%. This work provides a new pathway for the adsorption of Cr(VI) and Cd(II) in binary systems, suggesting that BC-SnZVI shows great potential for the co-removal of Cr(VI) and Cd(II) in wastewater.

Removal of cadmium(II) from aqueous solutions by a novel sulfide-modified nanoscale zero-valent iron supported on kaolinite: Treatment efficiency, kinetics and mechanisms

Nano zero-valent iron (nZVI) had great potential in water pollution remediation, but the instability and easy agglomeration limited its application. To improve the dispersion and antioxidant properties of the nZVI, kaolinite-supported sulfide-modified nZVI (S-nZVI@Kaol) was synthesized for the removal of cadmium (II) (Cd(II)) in aqueous solution. The structure and morphology of the samples were characterized by field emission scanning electronic microscopy (FE-SEM) and X-ray diffraction (XRD), the elemental distribution and microstructure of the S-nZVI@Kaol were accomplished by transmission electron microcopy (TEM) and energy dispersive X-Ray spectroscopy (EDX), Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS). The results showed that S-nZVI was successfully loaded on kaolinite with a “core–shell” structure. The S-nZVI had higher specific surface area and lower magnetism compared with nZVI. The adsorption process of S-nZVI@Kaol for Cd(II) conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm model better, and the maximum adsorption capacity was 104.7 mg·g−1. When the S/Fe molar ratio (MS/Fe) was 0.3, and the Fe/Kaol mass ratio (mFe/Kaol) was 50:50, S-nZVI@Kaol had the best removal efficiency for Cd(II). A higher solution pH (3.0–9.0) was beneficial for the removal of Cd(II). Adsorption thermodynamics studies showed that removing Cd(II) by composites was a spontaneous endothermic process. The mechanisms of the removal of Cd(II) involved electrostatic gravitation, chemical precipitation of CdS, and surface complexation.

Degradation mechanism of tetracycline using sulfidated nanoscale zerovalent iron driven peroxymonosulfate and metabolomic insights into environmental risk of intermediates products

• S-nZVI driven PMS exhibited an excellent performance to eliminate tetracycline. • Both SO 4 •− and •OH as dominant species were committed to degrading tetracycline. • Ten degradation intermediates were screened and determined by HRMS analysis. • Further intermediates products induced upmetabolism of carbohydrate, citrate cycle. • SO 4 •− based incomplete mineralization decreased the toxicity of tetracycline. Sulfide-modified nanoscale zerovalent iron (S-nZVI) has aroused increasing interest due to its excellent ability towards environmental decontamination. Heterogeneous catalytic degradation of tetracycline hydrochloride (TC-H) mediated by iron-based materials has been explored by previous researches. Yet, unknown role and degradation mechanism of tetracycline hydrochloride (TC-H) through S-nZVI driven peroxymonosulfate (PMS) need to be further investigated. In current research, the impacts of S-nZVI dosage, PMS dosage, initial pH, anions and humic acids were independently explored during TC-H degradation process. S-nZVI exhibited the high efficiency for activating PMS. TC-H degradation followed a pseudo-first order kinetics reaction with k obs at 0.1403 min −1 . HA, Cl − , HPO 4 2− , NO 3 − exhibited varied reduction of the reaction rates on TC-H removal. Besides, SO 4 •− and •OH were dedicated to degrading TC-H, and SO 4 •− was proved to be predominant one. The alteration of sulfide species from XPS analysis played a pivotal role in raising the electron transfer rate to improve TC-H degradation. Ten intermediates products were determined through HRMS and primary transformation mechanism involved in N-demethylation reaction, demethylation reaction, elimination reaction and hydrogenation reaction were proposed. Based on metabolomics analysis, up-regulated expression of carbohydrate metabolism, citrate cycle, CoA biosynthesis, fatty acid degradation and amino acid synthesis in Escherichia coli were significantly induced by the further products, whereas glutathione metabolism was significantly down-regulated, endorsing that potential toxicity induced by intermediates were weakened. To sum up, S-nZVI/PMS as a promising nano-water environmental remediation method could be feasible for emerging environment organic pollutants control.

Application of sulfide-modified nanoscale zerovalent iron electrodes for electrokinetic remediation of chromium-contaminated soil in a three-dimensional electrode system

A modified electrokinetic remediation (EKR) system was designed to remediate Cr-contaminated soil using sulfidated nano-scale zerovalent iron (S-nZVI) as the third electrode. This study systematically compared the technological parameters and remediation efficiencies of three-dimensional (3D) electrokinetic systems using different materials as the third electrodes. The comparative experiment showed that the 3D EKR could effectively increase current efficiency, balance voltage distribution, alleviate excessive acidification or alkalization of soils and effectively improve the removal efficiency of Cr. Compared with other 3D electrodes, the S-nZVI electrode led to the higher currents and the more uniform voltage distribution; additionally, the leaching toxicities were reduced by 50.0–66.7%, and the removal efficiencies of total Cr (Cr(tot)) and hexavalent Cr (Cr(VI)) were increased by at least 15.4% and 22.6%, respectively. Cr(VI) was removed mainly resulting from the electrokinetic migration. Meanwhile, a small amount of Cr(Ⅵ) was converted to FeCr2O4 and Cr3+OOH after reacting with S-nZVI in the middle region of the 3D EKR system. Due to the active layer of iron sulfides, S-nZVI was more stable and its electrokinetic efficiency was higher than other 3D electrodes, resulting in higher overall removal efficiencies. 3D EKR with S-nZVI can effectively decrease the toxicological effect of Cr contaminated soil at an experimental scale. The experimental findings from this study may provide a reference for guiding the development of more efficient methods for Cr-contaminated soil treatment.

Enhanced degradation of bisphenol S by persulfate activated with sulfide-modified nanoscale zero-valent iron.

Sulfide-modified nanoscale zero-valent iron (S-nZVI) has been considered an efficient material to remove heavy metals and organic contaminants. The experiments of bisphenol S (BPS) degradation by persulfate (PS) activated with S-nZVI (S-nZVI/PS) or nZVI (nZVI/PS) were carried out in this paper. The results show that, compared to the bare nZVI/PS system, the S-nZVI/PS system shows higher activity in BPS degradation, especially at high BPS concentration. The reaction rate constant kobs of BPS removal by the S-nZVI/PS system (0.142 min-1) was much higher than that in nZVI/PS system (0.089 min-1) because more oxidation species were generated in the S-nZVI/PS system. The results of electron paramagnetic resonance (EPR) and radical quenching tests show that both hydroxyl radical (·OH) and sulfate radical (SO4·-) were involved in the degradation of BPS and had a great contribution to BPS removal. Moreover, the effects of S/Fe molar ratio, S-nZVI dosage, initial pH, and initial concentration of PS or BPS on S-nZVI/PS were also studied. The results show that the S/Fe molar ratio has significant influence on the BPS degradation; over 97.7% of the removal efficiency was achieved at 0.035 of S/Fe molar ratio. And the removal efficiency of BPS degradation increased with the increase of the dosage of S-nZVI, PS concentration. Furthermore, BPS could be efficiently removed in solutions with a wide range of initial pH (3.13-9.35). The observed results show that it is promising in the removal of micro-pollutants from water by persulfate activated with S-nZVI.

Role of sulfide-modified nanoscale zero-valent iron on carbon nanotubes in nonradical activation of peroxydisulfate

Sulfamethoxazole (SMX) is highly persistent and difficult to remove, making it urgent to find an efficient method for alleviating the enormous environmental pressure of SMX. In this study, sulfide-modified nanoscale zero-valent iron on carbon nanotubes (S-nZVI@CNTs) was prepared to activate peroxydisulfate (PDS) for the degradation of SMX. The results showed that SMX was completely removed within 40 min (kobs=0.1058 min−1) in the S-nZVI@CNTs/PDS system. By analyzing quenching experiments and electron paramagnetic resonance (EPR), singlet oxygen (1O2) was the main active species of the S-nZVI@CNTs/PDS system. 1O2 might be mediated by the abundant carbonyl groups (CO) on carbon nanotubes through spectroscopic analyses. In addition, sulfur doping transitioned the activation pathway to a nonradical pathway. Spectroscopic analyses and electrochemical experiments confirmed that the formation of CNTs-PDS complexes and S-nZVI could promote electron transfer on the catalyst surface. Furthermore, the main degradation intermediates of SMX were identified, and five possible transformation pathways were proposed. The S-nZVI@CNTs/PDS system possessed advantages including high anti-interference (Cl-, NO3-, HA), a strong applicability, recyclability and a low PDS consumption, offering new insight into the degradation of antibiotic wastewater.

Removal of chloramphenicol by sulfide-modified nanoscale zero-valent iron activated persulfate: Performance, salt resistance, and reaction mechanisms

Herein, sulfide-modified nanoscale zero-valent iron (S-nZVI) was prepared by a liquid-phase reduction route and then applied to activate persulfate (PS) for the degradation of chloramphenicol (CAP). The effects of Fe/S molar ratio, catalyst dosage, PS concentration, initial pH, and co-existing ions (Cl−, SO42−, CO32−) on the catalytic performance of S-nZVI/PS system were investigated. Simultaneously, the fluctuations of solution pH, oxidation-reduction potential, dissolved oxygen, and Fe2+ concentration were also monitored during the reaction. Results shown that 98.8 % of CAP could be removed under the optimum reaction conditions (S-nZVI dosage = 0.1 g/L, PS concentration = 3 mM, initial pH = 6.86). Compared to the pristine nZVI, the sulfidation behavior could critically improve the removal efficiency of CAP, ascribe to the enhancements of hydrophobicity of nZVI, production of hydroxyl radicals, and salt resistance. Furthermore, possible degradation pathways of CAP in S-nZVI/PS system were inferred based on liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculations. This study proves that the S-nZVI is a more promising catalyst for activating PS than nZVI, especially in the field of saline pharmaceutical wastewater treatment.

Enhanced As(III) sequestration using nanoscale zero-valent iron modified by combination of loading and sulfidation: characterizations, performance, kinetics and mechanism.

Nanoscale zero-valent iron (nZVI) and sulfides have been confirmed to be effective in arsenic sequestration from aqueous solution. In this study, attapulgite supported and sulfide-modified nanoscale zero-valent iron (S-nZVI@ATP) are synthesized to realize the superposition effect of enhanced arsenic sequestration. The results indicated that nZVI clusters were well disaggregated and the BET specific surface area increased from 19.61 m2·g-1 to 46.04 m2·g-1 of S-nZVI@ATP, resulting in an enhanced removal efficiency of arsenic from 51.4% to 65.1% at 20 min. The sulfides in S-nZVI@ATP mainly exist as mackinawite (FeS) and this causes the spherical nanoparticles to exhibit a larger average particle size (94.6 nm) compared to bare nZVI (66.0 nm). In addition, S-nZVI@ATP exhibited a prominent ability for arsenic sequestration over a wide pH range of 3.0-6.0. The presence of anions SO42- and Cl- can enhance the arsenic removal whereas HCO3- inhibited it. The arsenic adsorption by S-nZVI@ATP could be explained by the pseudo-second-order kinetic model and the Langmuir model, with the maximum adsorption capacity of 193.8 mg·g-1. The mechanism of As(III) sequestration by S-nZVI@ATP involved multiple processes, mainly including precipitation conversion from FeS to As2S3, surface-complexation adsorption and co-precipitation.

Preparation of highly stable and easily regenerated sulfuretted nZVI via one-pot fast pyrolysis method for the removal of diclofenac

Sulfide-modified nanoscale zero-valent iron (S-nZVI) is a commonly used reductive agent in pollutant removal. However, the aggregation of S-nZVI can lower its reduction capacity in the water, and its regeneration remains challenging. To overcome these limitations, one-pot fast pyrolysis of FeSO4-loaded lignocellulosic biomass was proposed to obtain highly stable biochar-supported S-nZVI (S-nZVI/BC) nanoparticles. During this process, Fe2+ were reduced and sulfuretted in situ to form S-nZVI and subsequently covered by the freshly formed carbon film. A series of S-nZVI/BCs pyrolyzed at different temperatures (500–1000 °C) were prepared, among which S-nZVI/BC pyrolyzed at 800 °C (S-nZVI/BC-800) exhibited a fast and stable removal of diclofenac (DCF) via adsorption and reduction. The DCF removal efficiency of S-nZVI/BC-800 reached 80.1% within 4 h, with a particle dosage of 0.5 g/L and Fe dosage of 1 mmol/g. The adsorption and reduction efficiencies of DCF by S-nZVI/BC-800 were 43.2% and 36.9%, respectively. The improved reactivity of S-nZVI/BC-800 can be attributed to the formation of iron sulfides (i.e., FeS and Fe1−xS) in ZVI particles, which increased the electrical conductivity and improved the material selectivity for the reduction of DCF in the water. S-nZVI/BC-800 could be easily regenerated through pyrolysis, during which the carbon film could act as the electron donor. This study provides a facile and skillful method to prepare a highly stable and refreshable S-nZVI, which could be a promising permeable reactive bed material for the remediation of halogenated organic pollutants in contaminated water.

Kinetics and mechanism of arsenic removal using sulfide-modified nanoscale zerovalent iron

Sulphur modified nano zerovalent iron (S–nZVI) has shown considerable promise for removal of various aqueous contaminants. However studies utilizing S–nZVI for removal of aqueous inorganic arsenic (As) is relatively rare, which was studied in this work. Characterization of the synthesized S–nZVI showed typical core-shelled structure with distorted outer shell consisting of iron oxide and FeS. The removal rate of both As(III) and As(V) by S–nZVI was considerably enhanced compared to nZVI and highest As removal was observed at S/Fe ratio of 0.1 under acidic condition. Results showed slight decrease in As removal efficiencies for S–nZVI aged upto 48 h, with obvious drop in As removal efficiencies for longer aging time which although still exhibited higher reactivity than bare nZVI. Spectroscopic investigation showed sulphur amendment of nZVI completely altered the As sequestration mechanism compared to nZVI. While reduction of the adsorbed As(III) and As(V) was observed for bare nZVI, in contrast, uptake of As(III) and As(V) by S–nZVI involves adsorption as As(III) and As(V) oxyanion respectively with additional precipitation of As2S3. Overall, the study shows that incorporation of FeS on the surface of nZVI can be an effective modification strategy for efficient sequestration of As from contaminated water.

Removal of Ni(II) from aqueous solutions by sulfide-modified nanoscale zero-valent iron supported by hydroxyapatite(HAP/S-nZVI)

Removal of Ni(II) from aqueous solutions by sulfide-modified nanoscale zero-valent iron supported by hydroxyapatite(HAP/S-nZVI)

Enhanced molybdenum(VI) removal using sulfide-modified nanoscale zerovalent iron: kinetics and influencing factors.

The overall goal of this study is to investigate the effect of sulfidated nanoscale zerovalent iron (S-nZVI) on the removal of hexavalent molybdate (MoO42-) under different aquatic chemistry conditions. Surface analysis suggests that Mo(VI) is removed mainly by adsorption and co-precipitation onto the surface of S-nZVI and a small amount of Mo(VI) can be reduced to Mo(V) species. The results of batch tests show that Mo(VI) removal by S-nZVI are well described with the pseudo-second-order adsorption model. The removal rate increases with a decrease in solution pH (4.0-9.0) and is significantly affected by the S/Fe ratio of S-nZVI, with the optimal S/Fe ratio being 0.5. The presence of anions WO42- or CrO42- can reduce the Mo(VI) removal, which is likely because they compete for adsorption sites on the solid surfaces. The divalent cations Ni2+, Cu2+ and Co2+ also inhibit the removal of Mo(VI) whereas Zn2+, Ca2+ and Mg2+ enhance it. After being aged for 35 d in water, S-nZVI still exhibits high reactivity towards Mo(VI) removal (57.39%). The study demonstrates that S-nZVI can be used as an environmentally friendly material for effectively removing Mo(VI) from contaminated water.

Remediation of Trichloroethylene-Contaminated Groundwater by Sulfide-Modified Nanoscale Zero-Valent Iron Supported on Biochar: Investigation of Critical Factors

This study investigated the feasibility and mechanism of sulfide-modified nanoscale zero-valent iron supported on biochar (S-nZVI@BC) for the removal of TCE in the scenario of groundwater remediation. The effects of some critical factors, including pyrolysis temperature of biochar, mass ratio of S-nZVI to BC, initial pH, typical groundwater compositions, co-contaminants, and particle aging time, on the TCE removal were examined. The results revealed that the different pyrolysis temperatures could change physicochemical properties of BC, which influenced the TCE adsorption and degradation by S-nZVI@BC. The mass ratio of S-nZVI to BC could determine the extent of adsorption and degradation of TCE. The total removal of TCE was not significantly influenced by the initial pH (3.0–9.0), but the degradation of TCE was enhanced at higher pH. Notably, the typical anions (SO42−, HCO3−, and HPO42−), humic acid, and co-contaminants (Cr(VI) and NO3−) in groundwater all slightly influenced the total removal of TCE, but markedly inhibited its degradation. Additionally, after exposure to air over different times (5 days, 10 days, 20 days, and 30 days), the reactivity of S-nZVI@BC composites was apparently decreased due to surface passivation. Nevertheless, the aged S-nZVI@BC composites still maintained relative high removal and degradation of TCE when the reaction time prolonged. Overall, the results showed that the S-nZVI@BC, combining the high adsorption capacity of BC and the high reductive capacity of S-nZVI, had a much better performance than the single S-nZVI or BC, suggesting that S-nZVI@BC is one promising material for the remediation of TCE-contaminated groundwater.