Novel core-shell sulfidated nano-Fe(0) particles for chromate sequestration: Promoted electron transfer and Fe(II) production

Tea saponin co-ball milled commercial micro zero-valent iron for boosting Cr(VI) removal

Tea saponins (TS), a natural biosurfactant extracted from tea trees, were co-ball milled with commercial micro zero-valent iron (mZVI) to produce TS modified mZVI (TS-BZVI) for efficient hexavalent chromium (Cr(VI)) removal. The findings demonstrated that TS-BZVI could nearly remove 100% of Cr(VI) within 2 h, which was 1.43 times higher than that by ball milled mZVI (BZVI) (70%). Kinetics analysis demonstrated a high degree of compatibility with the pseudo-second-order (PSO), revealing that TS-BZVI exhibited a 2.83 times faster Cr(VI) removal rate involved primarily chemisorption. Further, X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) measurements indicated that the TS co-ball milling process improved the exposure of Fe(II) and Fe(0) on mZVI, which further promoted the Cr(VI) reduction process. Impressively, the introduction of TS increased the hydrophobicity of ZVI, effectively inhibiting the H2 evolution by 95%, thus improved electron selectivity for efficient Cr(VI) removal. Ultimately, after operating for 10 days, a simulated permeable reactive barrier (PRB) column experiment revealed that TS-BZVI had a higher Cr(VI) elimination efficiency than BZVI, indicating that TS-BZVI was promising for practical environment remediation.

Integrated influence of sulfide modification on the reactivity of nanoscale zero-valent iron towards decabromodiphenyl ether under an electromagnetic field

Individual application of sulfide modification and electromagnetic field (EMF) can enhance the reactivity of nanoscale zero-valent iron (nZVI), yet the potential of both in combination is not clear. This work found that the reactivity of nZVI towards decabromodiphenyl ether was significantly enhanced by the combined effect of sulfidation and EMF. The specific reaction rate constant of nZVI increased by 7 to 10 times. A series of characterization results revealed that the sulfidation level not only affects the inherent reactivity but also the magnetic-induced heating (MIH) and corrosion (MIC) of nZVI. These collectively influence the degradation efficiency of nZVI under EMF. Sulfidation generally diminished the MIH effect. The low degree of sulfidation (S/Fe = 0.1) slightly reduced the MIC effect by 21.4%. However, the high degree of sulfidation (S/Fe = 0.4) led to significantly enhanced MIC effect by 107.1%. For S/Fe = 0.1 and 0.4, the overall enhancement in the reactivity resulting from EMF was alternately dominated by the contributions of MIH and MIC. This work provides valuable insights into the MIH and MIC effects about the sulfidation level of nZVI, which is needed for further exploration and optimization of this combined technology.

In-situ precipitation zero-valent Co on Co2VO4 to activate oxygen vacancies and enhance bimetallic ions redox for efficient detection toward Hg(II)

Despite the widespread utilization of variable valence metals in electrochemistry, it is still a formidable challenge to enhance the valence conversion efficiency to achieve excellent catalytic activity without introducing heterophase elements. Herein, the in-situ precipitation of Co particles on Co2VO4 not only enhanced the concentration of oxygen vacancies (Ov) but also generated a greater number of low-valence metals, thereby enabling efficient reduction towards Hg(II). The electroanalysis results demonstrate that the sensitivity of Co/Co2VO4 towards Hg(II) was measured at an impressive value of 1987.74 μA μM-1 cm-2, significantly surpassing previously reported results. Further research reveals that Ov acted as the main adsorption site to capture Hg(II). The redox reactions of Co2+/Co3+ and V3+/V4+ played a synergistic role in the reduction of Hg(II), accompanied by the continuous supply of electrons from zero-valent Co to expedite the valence cycle. The Co/Co2VO4/GCE presented remarkable selectivity towards Hg(II), with excellent stability, reproducibility, and anti-interference capability. The electrode also exhibited minimal sensitivity fluctuations towards Hg(II) in real water samples, underscoring its practicality for environmental applications. This study elucidates the mechanism underlying the surface redox reaction of metal oxides facilitated by zero-valent metals, providing us with new strategies for further design of efficient and practical sensors.

Iron Nanoparticle-Incorporated Laser-Induced Graphene Filters for Environmental Remediation via an In Situ Electro-Fenton Process

Laser-induced graphene (LIG) has garnered much attention due to its facile and chemically free fabrication technique. Metal nanoparticle incorporation into the LIG matrix can improve its electrical and catalytical properties for environmental application. Here, we demonstrate the fabrication of nanoscale zerovalent iron (nZVI) nanoparticle-incorporated LIG (Fe-LIG) and sulfidized-nanoscale zerovalent iron (S-nZVI) nanoparticle-incorporated LIG (SFe-LIG) surfaces. The sheets were first fabricated to investigate nanoparticle loading, successful incorporation in the LIG matrix, and electrochemical performance as electrodes. Fe-LIG and SFe-LIG sheets showed ∼3-3.5 times more charge density as compared with the control LIG sheet. The XPS and its deconvolution confirmed the presence of nZVI and S-nZVI in the Fe-LIG and SFe-LIG surfaces, which can generate in situ hydroxyl radical (•OH) via iron activation of electrogenerated hydrogen peroxide (H2O2) in short in situ electro-Fenton process. After confirmation of the successful incorporation of iron-based nanoparticles in the LIG matrix, filters were fabricated to demonstrate the application in the flow-through filtration. The Fe-LIG and SFe-LIG filters showed ∼10-30% enhanced methylene blue removal under the application of 2.5 V at ∼1000 LMH flux. The Fe-LIG and SFe-LIG filters also showed complete 6-log bacteria and virus removal at 2.5 and 5 V, respectively, while the LIG filters showed only ∼4-log removal. Such enhanced removal by the Fe-LIG and SFe-LIG filters as compared to LIG filters is attributed to the improved charge density, electrochemical activity, and in situ electro-Fenton process. The study shows the potential to develop catalytic LIG-based surfaces for various applications, including contaminant removal and microbial inactivation.

Accelerated Cr (VI) removal by a three-dimensional electro-Fenton system using green iron nanoparticles

Green-synthesized iron nanoparticles (GAP-FeNP) were used as particle electrodes in a three-dimensional electro-Fenton (3DEF) process to accelerate the removal of hexavalent chromium [Cr (VI)]. Removal was evaluated by varying the pH (3.0, 6.0, and 9.0) and initial Cr (VI) concentrations (10, 30, and 50 mg/L) at 5 and 25 min. These results demonstrated that GAP-FeNP/3DEF treatment achieved more than 94% Cr (VI) removal under all tested conditions. Furthermore, it was observed that Cr (VI) removal exceeded 98% under pH 9.0 in all experimental parameters tested. The results of the response surface methodology (RSM) determined two optimal conditions: the first, characterized by a pH of 3.0, Cr (VI) concentration at 50 mg/L, and 25 min, yielded a Cr (VI) removal of 99.7%. The second optimal condition emerged at pH 9.0, with Cr (VI) concentrations of 10 mg/L and 5 min, achieving a Cr (VI) removal of 99.5%. This study highlights the potential of the GAP-FeNP to synergistically accelerate Cr (VI) removal by the 3DEF process, allowing faster elimination and expansion of the alkaline (pH 9.0) applicability. PRACTITIONER POINTS: The required time for >99% of Cr (VI) removal by the GAP-FeNP/3DEF process was shortened from 25 to 5 min. EF process with GAP-FeNP reduces the time necessary for Cr (VI) removal, which is 67% faster than conventional methods. EF process using GAP-FeNP removed >94% of Cr (VI) after 25 min for all initial Cr (VI) concentrations and pH treatments. Cr (VI) removal by the GAP-FeNP/3DEF process was >98% at a pH of 9.0, widening the solution pH applicability.

Recent advances in sulfidized nanoscale zero-valent iron materials for environmental remediation and challenges

Over the past decade, sulfidized nanoscale zero-valent iron (S-nZVI) has been developed as a promising tool for the remediation of contaminated soil, sediment, and water. Although most studies have focused on applying S-nZVI for clean-up purposes, there is still a lack of systematic summary and discussion from its synthesis, application, to toxicity assessment. This review firstly summarized and compared the properties of S-nZVI synthesized from one-step and two-step synthesis methods, and the modification protocols for obtaining better stability and reactivity. In the context of environmental remediation, this review outlined an update on the latest development of S-nZVI for removal of heavy metals, organic pollutants, antibiotic resistance genes (ARGs), and antibiotic resistant bacteria (ARB) and also discussed the underlying removal mechanisms. Environmental factors affecting the remediation performance of S-nZVI (e.g., humic acid, coexisting ions, S/Fe molar ratio, pH, and oxygen condition) were highlighted. Besides, the application potential of S-nZVI in advanced oxidation processes (AOP), especially in activating persulfate, was also evaluated. The toxicity impacts of S-nZVI on the environmental microorganism were described. Finally, the future challenges and remaining restrains to be resolved for better applicability of S-nZVI are also proposed. This review could provide guidance for the environmental remediation with S-nZVI-based technology from theoretical basis and practical perspectives.

Fabrication of Chitin microspheres supported sulfidated nano zerovalent iron and their performance in Cr (VI) removal

Sulfidated nanoscale zerovalent iron (S-nZVI) has been extensively studied for the reductive removal of Cr(VI), but its applicability is limited by agglomeration and unexpected efficiency reduction. In this study, chitin microsphere supported sulfidated nanoscale zero-valent iron (S-nZVI@Chi-M) was prepared by in-situ one-step reduction method and used to remove Cr(VI) from water. Compared to chitin and chitosan powder, Chi-M with nanofibrous structure and large surface area performed best in stabilizing S-nZVI with a Fe0 loading content of 3.01 wt%. The S-nZVI particles were homogeneously distributed on the surface of Chi-M, effectively avoiding agglomeration. Compared with bare nanoparticles and supported nZVI, S-nZVI@Chi-M showed significantly enhanced Cr(VI) removal capacity (924.5 mg Cr(VI) for per gram of effective Fe0). The influences of sulfidation degree, dosages, initial Cr(VI) concentration, pH, DO, humic acid and typical ions on Cr(VI) removal kinetics were further studied. S-nZVI@Chi-M could be recycled for at least 4 times with acceptable reactivity. The mechanism investigation results indicated that the Cr(VI) removal was a complex process of reduction, adsorption and co-precipitation under the synergistic effect of Chi-M and S-nZVI. This work provides new ideas for the continuous fabrication of highly reactive nanoparticles, hopefully expanding the application scope of biomass resources in pollution remediation.

The Effects of Nanoparticles- Zerovalent Iron on Sustainable Biomethane Production through Co-Digestion of Olive Mill Wastewater and Chicken Manure

The impacts of nanoparticles-zerovalent iron (NP-ZVI) on anaerobic co-digestion (AcoD) were assessed. The production of biogas and methane (CH4), as well as the removal efficiency of volatile solids (VS) and contaminants were investigated in the AcoD of chicken manure (CM) and olive mill wastewater (OMWW) with the addition of NP-ZVI at different concentrations (10–50 mg/g VS) and different sizes resulting from various mixing volume ratios (MVR) of NaBH4:FeSO4.7H2O. The results show that NP-ZVI ≤ 30 mg/g VS at MVR-2:1, MVR-4:1, and MVR-6:1 improves the AcoD. In contrast to 40–50 mg/g VS of NP-ZVI, which caused an inhibitory impact in all of the AcoD stages, as well as a decrease in the contaminant’s removal efficiency, the concentration of 10–30 mg NP-ZVI/g VS at MVR-4:1 achieved a maximum improvement of CH4 by 21.09%, 20.32%, and 22.87%, respectively, and improved the biogas by 48.14%, 55.0%, and 80.09%, respectively, vs. the 0 additives. Supplementing AcoD with NP-ZVI at a concentration of 30 mg/g VS at MVR-4:1 resulted in maximum enhancement of the contaminant removal efficiency, with a total oxygen demand (TCOD) of up to 73.99%, turbidity up to 79.07%, color up to 53.41%, total solid (TS) up to 59.57%, and volatile solid (VS) up to 74.42%. It also improved the hydrolysis and acidification percentages by up to 86.67% and 51.3%, respectively.

Integration of two-stage anaerobic digestion process with in situ biogas upgrading

High impurity concentration of biogas limits its wide commercial utilization. Therefore, the integration of two-stage anaerobic digestion process with in situ biogas upgrading technologies is reviewed, with emphasis on their principles, main influencing factors, research success, and technical challenges. The crucial factors that influence these technologies are pH, alkalinity, and hydrogenotrophic methanogenesis. Hence, pH fluctuation and low gas-liquid mass transfer of H₂ are some major technical challenges limiting the full-scale application of in situ upgrading techniques. Two-stage anaerobic digestion integration with various in situ upgrading techniques to form a hybrid system is proposed to overcome the constraints and systematically guide future research design and advance the development and commercialization of these techniques. This review intends to provide the current state of in situ biogas upgrading technologies and identify knowledge gaps that warrant further investigation to advance their development and practical implementation.

Elemental sulfur generated in situ from Fe(III) and sulfide promotes sulfidation of microscale zero-valent iron for superior Cr(VI) removal

Herein, we compared the effect of different extra iron and sulfur precursors on the sulfidation efficiency, physicochemical properties, and reactivity of post-sulfidated microscale zero-valent iron (S-ZVI). S⁰@ZVI was synthesized from in situ S⁰ generated via reaction of Fe(III) with S^2-, which resulted in 23-fold higher Cr(VI) removal compared with S⁰_com/ZVI synthesized using commercial S⁰. The direct formation of FeS_x film via reaction between S⁰ and ZVI played a crucial role in enhancing the removal of Cr(VI) by S⁰@ZVI, with 16- and 12-fold faster rates compared with FeS@ZVI and FeS₂@ZVI prepared via precipitated reaction of Fe(II) with S^2- and sulfur mixtures, respectively. The incorporated sulfur, sulfidation sequence, and sulfidation time determined the performance of S⁰@ZVI. A combination of batch experiments and kinetic models was used to determine the chemical composition of reduced Cr(VI) products. S⁰@ZVI immobilized Cr(VI) as Fe_0.5Cr_0.5(OH)₃ via surface heterogeneous reactions, and partial Cr(VI) was homogeneously reduced to soluble Cr(acetate)₃ or Fe_0.75Cr_0.25(OH)₃(aq) by dissolved Fe(II). The insights gained from this study will facilitate the fabrication of highly reactive S-ZVI and elucidate the mechanism of Cr(VI) removal.

Hydrogen Peroxide Activation with Sulfidated Zero-Valent Iron for Synchronous Removal of Cr(VI) and BPA

In this work, the synchronous removal of Cr(VI) and bisphenol A (BPA) in a heterogeneous Fenton process with sulfidated nanoscale zero-valent iron (S-nZVI) as the reductant and catalyst was systematically evaluated. Compared to other systems including S-nZVI or H2O2 alone, a simultaneous BPA degradation and Cr(VI) removal could be achieved in the S-nZVI/H2O2 system at an optimum pH of 3. It was, interestingly, found that 7.8% of BPA and 98.2% of Cr(VI) were removed within 60 min in presence of S-nZVI alone, whereas, correspondingly, 98.2% of BPA and 96.9% of Cr(VI) were eliminated in the S-nZVI/H2O2 system. Specifically, humic acid (HA) and H2PO4− inhibited the deterioration of BPA but posed no significant effect on Cr(VI) removal. NO3− had a slight lifting effect on the removal of BPA and Cr(VI), while HCO3− showed a relatively weak prohibition. Experiments with EPR and radical probe tests also provide direct evidence that hydroxyl radicals was monitored in the S-nZVI/H2O2 system, which not only degraded BPA but also inhibited the reduction of Cr(VI). It could not be ignored that FeS accelerated Fe0 corrosion to release Fe2+. In, addition, Fe0, Fe2+ and S2+ could react with Cr(VI) while the most of produced Cr(III) was co-precipitated in the form of CrxFe1−xOOH film. The study confirmed that it was feasible for S-nZVI/H2O2 system to remove synchronously organic pollutants and heavy metal.