Nanoscale Zero-valent Iron Research Articles

Anchoring nanoscale zero-valent iron within bacterial cellulose particles for boosting efficient adsorption of Co(II) and Sr(II) from seawater: Dual system and varying adsorption mechanisms

Increasing attention has been paid to radioactive wastewater to direct discharge in Japan or accidental leaks. Strontium-90 (90Sr) and Cobalt-60 (60Co) are the most hazardous nuclides in waste discharged form nuclear reactors. Because of their high solubility and long half-lives, these radioisotopes can persist for hundreds of years before decaying to negligible levels. Herein, a green and biodegradable material nanoscale zero-valent iron (nZVI) supported by bacterial cellulose particles (BCP-nZVI) is constructed for the first time to adsorb Co2+ and Sr2+ in single and binary systems. BCP-nZVI shows superior adsorption capacities of Co2+ and Sr2+in a single system within a wide range of pH values from 5 to7, while the coexistence of Co2+ adsorption inhibits the Sr2+ in binary system. Pseudo-second-order dynamics model and Langmuir isothermal model can be indicated the BCP-nZVI adsorption progress with 107.10 mg/g (Co2+) and 64.96 mg/g (Sr2+) maximum adsorption capacity. BCP-nZVI has outstanding stability, allowing it to be stored for more than one month with compromising its performance. More importantly, BCP-nZVI exhibits exceptional removal efficiency of Co2+(92.53%) and Sr2+(58.62%) removal in natural seawater systems. The mechanism investigation illustrates the high adsorption capacity of BCP-nZVI for Co2+ is controlled by redox and hydroxyl complexation. While Sr2+ is controlled by hydroxyl complexed adsorption, thus it has weak against interference by cations like Na+, Ca2+, etc. BCP-nZVI exhibits the advantages of high adsorption capacity, wide pH range, strong stability, and good applicability in natural seawater, which has excellent potential for application in radioactive ions removal.

Enhanced removal of antibiotic-resistant genes by sodium persulfate catalyzed by nanoscale zero-valent iron modified by Ginkgo biloba L. leaf

ABSTRACT In this study, nanoscale zero-valent iron (nZVI) modified by Ginkgo biloba L. leaf (G-nZVI), as an effective catalyst, exhibited excellent activation of sodium persulfate (PS), which could achieve higher removal efficiency of antibiotic-resistant genes (ARGs) in the Fen River than PS + nZVI system. This study utilizes forestry waste to address the limitations of using Fe2+/nZVI as an activator for the removal of ARGs. This approach adheres to the principle of employing waste to treat waste. The technology converts G. biloba L. leaf into plant extracts that are rich in a variety of bioactive components, rather than purifying natural biomolecules, which decreases operational complexity. In addition, the G-nZVI + PS system demonstrates superior removal performance to single components in the system. Consequently, the mechanism underlying the G-nZVI + PS treatment is attributed to peroxidation induced by radicals. In this context, the results of ARG removal by G-nZVI + PS with different G. biloba L. leaf /FeSO4·7H2O volume ratios indicated that the G. biloba L. leaf enhanced the conversion of Fe3+ to Fe2+, thereby generating more radicals through electron transfer between the biomass and G-nZVI. This research underscores the advantages of modifying G. biloba L. leaf for improved catalytic efficiency and the role of the components within the system.

Efficient co-removal of aqueous Cr(VI) and ciprofloxacin by alkali lignin-derived carbon supported nanoscale zero-valent iron via adsorption and redox synergistic mechanisms

Developing an efficient co-removal strategy is crucial for the treatment of combined contaminants with heavy metals and antibiotics due to their great threat to sustainable advancement and ecological preservation. Herein, the efficient co-removal of aqueous hexavalent chromium (Cr(VI)) and ciprofloxacin (CIP) is achieved via a newly developed composite of nanoscale zero-valent iron particles embedded into alkali lignin-derived carbon (nZVI/ALC) without external assistance (such as light, advanced oxidants). nZVl/ALC demonstrates superior co-removal efficiencies of Cr(VI) (99.9 %) and CIP (89.9 %) with high removal kinetic rate constants of 1.595 and 0.779 min−1, respectively. The underlying mechanisms involving the co-removal of Cr(VI) and CIP verify that Cr(VI) ions are adsorbed onto the skeleton of nZVI/ALC originating from the electrostatic interaction, and CIP molecules adsorbed on nZVl/ALC act as a bridge, complexing with the Cr(VI) ions to promote Cr(VI) removal. Meanwhile, the CIP adsorption by nZVI/ALC involves hydrogen bonding, π-π interaction, and complexation. The coexisting Cr(VI) ions are transformed into Cr(III) components with abundant electron transfer, leading to the generation of more •O2– radicals, thus the self-generating reactive oxygen species (•OH, •O2– and 1O2) in ambient-air condition promote CIP degradation in the binary system. The CIP molecules’ degradation pathways mainly include piperazine ring cracking, piperazine epoxidation, quinolone ring opening and defluorination according to the analysis of HPLC-MS and FuKui function, along with the gradual reduction in toxicity throughout the degradation process of CIP molecules. This study offers a new insight on the co-removal of Cr(VI) and CIP, which would provide promising guidance for the remediation of compound wastewater with heavy metals and antibiotics.

Magnet-assisted nanoscale zerovalent iron soil washing in chlorpyrifos-contaminated soil remediation: Proof of concept

Chlorpyrifos (CPF)––a widely used organophosphate pesticide––is banned in many countries due to its persistence in the environment and high toxicity. Residue levels often vastly exceed safety thresholds, posing significant risks to human health and ecosystems. This persistent contamination challenges farmers, especially those transitioning to organic practices. Here, we propose magnet-assisted soil washing with nanoscale zerovalent iron (nZVI) for the rapid remediation of CPF-contaminated soil. Soil mixed with water and nZVI facilitates CPF adsorption and degradation, with the CPF-sorbed nZVI being magnetically separated. We tested various nZVI conditions (inactivated [IZ] and activated [AZ], with and without hydrogen peroxide [H2O2]) against controls, including untreated soil and conventionally washed soil. The control experiments showed that conventional washing without nZVI removed 50.54 ± 3.48 % of the CPF via volatilization, leaving CPF residues in the soil (25.44 ± 2.12 %) that were above the maximum contamination level (MCL). Inactivated nZVI increased the removal by 24.38 ± 0.78 % via CPF sorption, but the MCL was still exceeded. However, AZ or nZVI with H2O2 achieved complete CPF removal (>99.95 %) within 180 min, reducing its concentration to below the MCL (<0.03 mg/kg). Thus, CPF sorption followed by either reductive dechlorination or oxidative degradation proved effective. Additionally, nZVI demonstrated reusability for three rounds while mitigating CPF toxicity, improving seed germination and plant growth. This method offers a promising solution for rapid soil decontamination, supporting the transition to organic farming.

Sulfidized nanoiron-loaded carbon for efficient removal of Cr(VI) from wastewater

With the advancement of industrial development, the threat of chromium (Cr) pollution in the aquatic environment has escalated significantly. So, it is essential to develop economically and environmentally friendly means to remove Cr(VI). In this experiment, a novel material, activated carbon loaded sulfidized nanoscale zero-valent iron (S-nZVI@AC) was prepared by sulfide modification and activated carbon (AC) loading modification. According to the data, the most effective material was found to have a S/Fe molar ratio of 0.07 and an S-nZVI@AC mass ratio of 3:1, with a removal rate (RR%) was as high as 99.9% at 60 min. The RR% of the dosage of 0.8 g/L was 99.9% and demonstrated good economic efficiency. The RR% of S-nZVI@AC for Cr(VI) was higher at pH = 3 or 7, reaching 99.8% and 99.6%, respectively. The presence of coexisting ions significantly impacted the RR%, with SO42−, K+, and high concentration of Na+ promoting removal, while PO43−, CO32− and Ca2+ had an inhibitory effect. Of these, PO43− could even reduce the RR% to about 10%, whereas a low concentration of Na+ had minimal impact. S-nZVI@AC also exhibited good resistance to aging, maintaining approximately 80% removal after being soaked in water for 10 days. Furthermore, using kinetic and thermodynamic studies, the pseudo-first-order kinetic model, Freundilch, and Elovich models were found to suit the experimental data better. Cr(VI) was eliminated by S-nZVI@AC via a combination of adsorption, reduction, co-precipitation. In summary, it is concluded that S-nZVI@AC was a new material that showed promise in the treatment of Cr(VI) effluent.

Application of central composite design for the simultaneous removal of tetracycline and cefixime using nanoscale zero-valent iron modified by montmorillonite and graphene oxide

Application of central composite design for the simultaneous removal of tetracycline and cefixime using nanoscale zero-valent iron modified by montmorillonite and graphene oxide

The beginning of iron corrosion - high-resolution visualization with 3D electron tomography

Understanding the genesis and early-phase reactions of iron corrosion is essential for the early detection, mitigation and prevention of metal degradation. In this work, high-resolution 3D tomography of metallic iron oxidation was acquired using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In particular, dendritic capillaries (<0.5 nm) were observed during the initial oxidation of fresh nanoscale zero-valent iron due to the differential oxygen diffusion and iron atoms migration. This observation led to the proposal of a nanoscale “pothole” model for early-phase corrosion, wherein hollowing out of the metal nanoparticle and formation of nanovoids beneath the iron/oxide interface through Kirkendall effect. Coalescence of the nanocapillaries results in the ultimate collapse of metal structure and/or functional failure. Using nanoscale zero-valent iron as a research model, this work provides unprecedented insights into the nano- and atomic-scale mechanisms of iron oxidation, paving the way for advanced detection and prevention strategies for iron corrosion.

Simultaneous removal of Cd(II) and phosphate by nanoscale zero-valent iron from solution: Co-sorption and implication of corrosion

Nanoscale zero-valent iron (nZVI) has been extensively utilized in environmental remediation, but its reactivity in the presence of co-contaminants requires further investigation for effective application in complex environments. Here, we conducted batch removal experiments to systematically investigate the co-removal behaviors of Cd(II) and phosphate by nZVI. Results showed that nZVI can synergistically remove Cd(II) and phosphate in solution, with the removal efficiency of Cd(II) and phosphate in the binary system being approximately 2 and 5 times higher than those in the single system, respectively. Sequential removal experiments combined with characterization analysis revealed the co-sorption of Cd(II) and phosphate onto the corrosion product of nZVI mainly by forming the ternary complexes (≡Fe–P–Cd). The Fe(OH)2 formed as the initial nZVI corrosion product provides numerous active sites for immobilization of Cd(II) and phosphate. Such effective co-sorption of Fe(OH)2 inhibits its subsequent phase transformation to Fe3O4. Overall, our work sheds light on how nZVI, Cd(II), and phosphate interact in solution as well as highlights the influence of phase transformation on co-removal, which can broaden the potential applications of nZVI in the practical environment.

Highly efficient removal of 1,1,1-trichloroethane from simulated groundwater by polydopamine-modified iron/polylactic acid/biochar composite coupling with Shewanella oneidensis MR-1

Biochar (BC) loaded with nanoscale zero-valent iron (nZVI) has been extensively used to remove chlorinated hydrocarbons from groundwater through biotic/abiotic reductive dechlorination. However, the rapid deactivation due to surface passivation, hydrophobicity, and inadequacy of carbon sources severely limits its practical application. Herein, a novel polydopamine (PDA)-modified iron/polylactic acid (PLA)/biochar composite (PDA@OBC-nZVI) was successfully synthesized to address this issue. Its effect and mechanism for 1,1,1-trichloroethane (1,1,1-TCA) removal from simulated groundwater coupling with Shewanella oneidensis MR-1 (MR-1) were investigated. Results showed that nZVI and PLA particles were uniformly dispersed on the BC surface, being smoother after PDA coating. The composite coupling with MR-1 exhibited efficient and long-term performances for 1,1,1-TCA removal. Under the experimental conditions comprising 10 % PLA mass fraction in the composite, 10 g·L−1 composite dosage and 20 mL·L−1 MR-1 inoculum volume, 83.14 % of 100 mg·L−1 1,1,1-TCA was removed by PDA@OBC-nZVI + MR-1 within 360 h, compared to only 48.12 % by PDA@OBC-nZVI alone. The primary removal pathways included the rapid chemical reductive dechlorination and the long-term microbial dissimilatory iron reduction. The synergistic dechlorination mechanism was manifested in the composite providing sustained carbon sources, accelerating electron transfer, raising sorbed Fe(II) level, and promoting cytochrome c secretion by MR-1. The novelty of this study is enhancing the hydrophilicity and redox activity of carbon-iron composites by PDA modification for the first time in 1,1,1-TCA removal. Overall, the results suggest that PDA@OBC-nZVI + MR-1 can effectively promote the reductive dechlorination process, being great potential for the remediation of chlorinated hydrocarbon-contaminated groundwater.

Unraveling the interplay of common groundwater ions in arsenic removal by sulfide-modified nanoscale zerovalent iron.

Sulphidation of nZVI (S-nZVI) has shown to significantly improve the arsenic removal capacity of nZVI, concurrently modifying the sequestration mechanism. However, to better apply S-nZVI for groundwater arsenic remediation, the impact of groundwater coexisting ions on the efficacy of arsenic uptake by S-nZVI needs to be investigated. This present study evaluates the potential of S-nZVI to remove arsenic in the presence of typical groundwater coexisting ions such as Cl-, HA, HCO3-, PO43- and SO42- through batch adsorption experiments. Individually, PO43- and HA had a dominant inhibition effect, while SO42- promoted As(III) removal by S-nZVI. Conversely, for As(V) removal, HCO3- and SO42- impeded the removal process. X-ray spectroscopic investigation suggests that the coexisting ions can either compete with arsenic for the adsorption sites, influence the S-nZVI corrosion rates and/or generate distinct corrosion products, thereby interfering with arsenic removal by S-nZVI. To investigate the cumulative effects of these ions, a 25-1 Fractional Factorial Design of experiments was employed, wherein the concentration of all the ions were varied simultaneously in an optimized manner, and their impact on arsenic removal by S-nZVI was observed. Our results shows that when these ions are present concurrently, PO43-, SO42- and HA still exerted a dominant influence on As(III) removal, whereas HCO3- was the main ions affecting As(V) removal, although the combined influence of the ions was not merely a summation of their individual effects. Overall, the finding of our study might provide valuable insight for predicting the actual performance of S-nZVI in field-scale applications for the remediation of arsenic-contaminated groundwater.

Interfacial interactions of nanoscale zero-valent iron particles with clay minerals in the aquatic environments: Experimental and theoretical calculation study

The environmental transport and fate of nanoscale zero-valent iron particles (nZVI) in soil and groundwater can be altered by their hetero-aggregation with clay mineral particles (CMP). This study examines the interactions between bare or carboxymethyl cellulose (CMC)-coated nZVI with typical CMP, specifically kaolinite and montmorillonite. Methods include co-settling experiments, aggregation kinetic studies, electron microscopy, Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO (EDLVO) energy analysis, and density functional theory calculations, focusing on the pH dependency of these interactions. The EDLVO theory effectively described the interactions between nZVI and CMP in aquatic environments. Under acidic conditions (pH 3.5), the interfacial interaction between bare nZVI and kaolinite is regulated by van der Waals forces, while complexation, van der Waals forces, and electrostatic attraction govern the interaction of bare nZVI with montmorillonite, primarily depositing on the SiO face. In contrast, the positively charged AlO face and edge of CMP are the main deposition sites for CMC-coated nZVI through hydrogen bonding, van der Waals forces, and electrostatic attraction. At neutral (pH 6.5) and alkaline (pH 9.5) conditions, both bare and CMC-coated nZVI predominantly attach to the AlO face and edge, facilitated by complexation or hydrogen bonding, alongside van der Waals forces. The attachment of CMC-coated nZVI to CMP surfaces shows reversible aggregation or deposition due to the steric repulsion from the CMC coating. These findings hold significant implications for the environmental applications and risk of nZVI.

Pectin-nano zero valent iron nanocomposites for efficient heavy metal removal and bactericidal action against waterborne pathogens — Innovative green solution towards environmental sustainability

This study investigated the effectiveness of a pectin-nano zero-valent iron-based nanocomposite in adsorbing heavy metals in bimetallic form (chromium‑lead mixture), along with assessing its antibacterial properties. The nanocomposite was synthesized using a straightforward dispersion method, employing eco-friendly components like biocompatible pectin sourced from banana peels and nano-scale zero-valent iron. Analytical characterization confirmed the formation of stable, nano-crystalline particles with active interactions between the functional groups of pectin and nano iron. Batch adsorption experiments optimized various parameters such as pH, adsorbent dosage, contact time, metal ion concentration, and temperature to enhance bimetal removal from water. The optimal conditions were determined as pH 8.0, a temperature of 40 °C, 1.0 g/L adsorbent dosage, 75 mg/l initial bimetal concentration, and a contact time of 30 min. Further assessments revealed that the nanocomposite did not induce phytotoxic or ecotoxic effects, confirming its non-toxicity and environmental safety. Biocompatibility studies conducted using zebrafish models showed no adverse effects on hatching, survival, or heart rate. These findings underscore the potential of the nanocomposite as a sustainable and efficient solution for heavy metal remediation in water treatment process.

Polydopamine-modified biochar supported polylactic acid and zero-valent iron affects the functional microbial community structure for 1,1,1-trichloroethane removal in simulated groundwater

In-situ enhanced bioreduction by functional materials is a cost-effective technology to remove chlorinated hydrocarbons in groundwater. Herein, a novel polydopamine (PDA)-modified biochar (BC)-based composite containing nanoscale zero-valent iron (nZVI) and poly-l-lactic acid (PLLA) (PB-PDA-Fe) was synthesized to enhance the removal of 1,1,1-trichloroethane (1,1,1-TCA) in simulated groundwater with actual site sediments. Its impact on functional microbial community structure in system was also investigated. The typical characterizations revealed uniform dispersion of PLA and nZVI particles on the BC surface, being smoother after PDA coating. The composite exhibited a significantly higher performance on 1,1,1-TCA removal (82.38%, initial concentration 100 mg/L) than Fe-PDA and PB-PDA treatments. The diversity and richness of the microbial community in the composite treatment consistently decreased during incubation due to a synergistic effect between PLLA-BC and nZVI. Desulfitobaterium, Pedobacter, Sphaerochaeta, Shewanella, and Clostridium were identified as enriched genera by the composite through DNA-stable isotope probing (DNA-SIP), playing a crucial role in the bioreductive dechlorination process. All the above results demonstrate that this novel composite selectively enhances the activity of microorganisms with extracellular respiration functions to efficiently dechlorinate 1,1,1-TCA. These findings could contribute to understanding the responsive microbial community by carbon-iron composites and expedite the application of in-situ enhanced bioreduction for effective remediation of chlorinated hydrocarbon-contaminated groundwater.

New insights into removal efficacy of perfluoroalkyl substances by layered double hydroxide and its composite materials

Though the use of per-and polyfluoroalkyl substances (PFAS) is strictly restricted worldwide, PFAS have been increasingly detected in aqueous environment with high human exposure risk. Effective PFAS remediation requires the simultaneous concentration and decomposition of these compounds from dilute solutions, presenting a significant challenge. The present work evaluated the suitability of layered double hydroxide (LDH) materials, promising adsorbents for anionic pollutants, for the removal of long-chain and short-chain PFAS in micro-polluted water. Additionally, it explored their potential for PFAS degradation after modification. The results suggested that LDH adsorbents have limited ability to extract short-chain PFAS such as perfluorobutane sulfonate (PFBS) from water matrices, especially in dilute solutions. Although organic modification of LDHs could enhance their uptake efficacy on PFAS, it cannot improve the decomposition of PFAS. Innovatively, a composite featuring zero-valent iron (ZVI) particles coupled with LDH was developed, in which the nanoscale ZVI core is coated with LDH to adsorb and decompose perfluorooctanoic acid (PFOA) synergistically. Characterization of the composite showed that LDH coating not only hinders the aggregation of ZVI particles, but also reduces the passivation of ZVI. The PFOA removal efficacy of the composite can be further facilitated in acid environment. By-product analysis revealed that the composite decomposed PFOA mainly through decarboxylation and formation of unstable alcohol.

Iron Nanostructure Primes Arbuscular Mycorrhizal Fungi Symbiosis Tightly Connecting Maize Leaf Photosynthesis via a Nanofilm Effect.

It is crucial to clarify how the iron nanostructure activates plant growth, particularly in combination with arbuscular mycorrhizal fungi (AMF). We first identified 1.0 g·kg-1 of nanoscale zerovalent iron (nZVI) as appropriate dosage to maximize maize growth by 12.7-19.7% in non-AMF and 18.9-26.4% in AMF, respectively. Yet, excessive nZVI at 2.0 g·kg-1 exerted inhibitory effects while FeSO4 showed slight effects (p > 0.05). Under an appropriate dose, a nano core-shell structure was formed and the transfer and diffusion of electrons between PS II and PS I were facilitated, significantly promoting the reduction of ferricyanide and NADP (p < 0.05). SEM images showed that excessive nZVI particles can form stacked layers on the surface of roots and hyphae, inhibiting water and nutrient uptake. TEM observations showed that excessive nanoparticles can penetrate into root cortical cells, disrupt cellular homeostasis, and substantially elevate Fe content in roots (p < 0.05). This exacerbated membrane lipid peroxidation and osmotic regulation, accordingly restricting photosynthetic capacity and AMF colonization. Yet, appropriate nZVI can be adhered to a mycelium surface, forming a uniform nanofilm structure. The strength of the mycelium network was evidently enhanced, under an increased root colonization rate and an extramatrical hyphal length (p < 0.05). Enhanced mycorrhizal infection was tightly associated with higher gas exchange and Rubisco and Rubisco enzyme activities. This enabled more photosynthetic carbon to input into AMF symbiont. There existed a positive feedback loop connecting downward transfer of photosynthate and upward transport of water/nutrients. FeSO4 only slightly affected mycorrhizal development. Thus, it was the Fe nanostructure but not its inorganic salt state that primed AMF symbionts for better growth.

Synchronous or selective removal of nitrate and Cr(VI) by montmorillonite supported sulfidized nanoscale zerovalent iron: Role of Fe(II) and S0

The reduction process of Cr(VI) and NO3−-N by sulfidized nanoscale zerovalent iron (S-nZVI) under coexistence conditions has yet to be investigated. This study innovatively confirmed that NO3−-N and Cr(VI) could be reduced synchronously or selectively by synthesizing diverse montmorillonite-supported S-nZVI (S-nZVI@MMT) to meet different remediation requirements. Concretely speaking, S-nZVI@MMT at low S/Fe could synchronously reduce NO3−-N and Cr(VI) to NH4+-N and Cr(III). S-nZVI@MMT at high S/Fe selectively removed Cr(VI). The vital roles of Fe(II) and S0 in S-nZVI@MMT were clearly revealed. Fe(II) mainly involved in the generation of Fe3O4 during the reaction at low S/Fe, while participating in the transformation of amorphous phases of Fe3O4, FeS, and FeS2 at high S/Fe. The Fe0 and converted Fe3O4 were the primary reactive sites for the synchronous removal of NO3−-N and Cr(VI) while the surface-bound Fe(II) and converted amorphous phases of Fe3O4 and FeSx determined the selective removal of Cr(VI). Meanwhile, the high contents of S0 in S-nZVI@MMT at high S/Fe mediated the generation of FeSx during the reaction and blocked the adsorption and reduction of NO3−-N which was critical for the selective removal of Cr(VI). The variations in the reactive species of S-nZVI@MMT at different S/Fe led to discrepant Cr(VI) reaction pathways. The findings provided new insights and strategies for the practical applicability of S-nZVI. SynopsisStudy provides a new insight into the synchronous/selective removal of Cr(VI) and NO3−-N by S-nZVI to meet the remediation requirements for different application scenarios.

The performance and mechanism of sulfidated nano-zero-valent iron for the simultaneous stabilization of arsenic and cadmium

Co-contamination of soil and groundwater with arsenic (As) and cadmium (Cd) is widespread. Sulfidized Nanoscale Zero-Valent Iron (S-nZVI) is effective in removing As and Cd from contaminated environments. However, the mechanisms governing As and Cd removal from systems containing both species are still unclear. This study investigated the effectiveness of S-nZVI in the simultaneous removal of Cd(II) and As(III) from contaminated solutions and their interaction mechanisms. Adsorption experiments were conducted under aerobic conditions to investigate the effect of Cd(II) and As(III) on their co-immobilisation at different As(III) and Cd(II) concentrations. S-nZVI was characterised before and after the reaction to elucidate the mechanism of its simultaneous immobilisation of As(III) and Cd(II). Batch experiments revealed that the presence of Cd(II) and As(III) together considerably promotes the passivation of S-nZVI. The adsorption of Cd(II) at Cd:As = 1:3 was 198.37 mg/g, which was 27.6 % higher than that in Cd(II)-only systems, and the adsorption of As(III) at As:Cd = 1:3 was 204.05 mg/g, which was 175 % higher than that in As(III)-only systems. The results of X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy indicated that the removal of Cd(II) and As(III) by S-nZVI involves electrostatic adsorption, complexation and oxidation reactions, amongst which electrostatic adsorption and ternary-complex generation are responsible for the synergistic effect. As and Cd ions can form two types of surface complexes with FeOH or FeS on the outer layer of S-nZVI: anionic bridging to form Fe–As–Cd and cationic bridging to form Fe–Cd–As. This investigation elucidates the synergistic action of Cd(II) and As(III) during their removal using S-nZVI. Thus, S-nZVI is a promising material for the combined removal of Cd(II) and As(III), which can mitigate environmental pollution.

Feasibility of simultaneous optimization of Anammox start-up and nitrogen removal performance by intermittent dosing of nanoscale zero-valent iron

The long acclimation period and sensitivity to environmental conditions of Anammox are the bottlenecks for its promotion and application. An innovative strategy was adopted to accelerate functional microbial enhancement and improve nitrogen removal performance by inoculating cryopreserved Anammox sludge and activated sludge with intermittent dosing of nanoscale zero-valent iron (nZVI). The acclimation time was shortened by 76 days with nitrogen removal efficiency (NRE) reaching up to 91.07 %. Anammox, NDFO (nitrate/nitrite-dependent Fe(II) oxidation), Feammox (Fe(III) reduction coupled with anaerobic ammonium oxidation) and abiotic reactions were coupled in the system with nZVI, contributing to 69.79 %, 15.14 %, 9.84 % and 0.25 % of nitrogen removal, respectively. Further microbial analysis demonstrated significant enrichment of functional microorganisms, such as Candidatus Jettenia, Acidovorax and Comamonas. High-efficient nitrogen removal was attribute to the increase of functional genes involved in Anammox, electronic transfer, heme C synthesis and iron metabolism. This work provides an inspiring idea for the mainstream Anammox application.

N-nitrosodimethylamine removal by a novel silver/sulfur-coated nanoscale zero-valent iron/activated carbon composite: Adsorption kinetics, mechanisms, and degradation pathways

The removal of disinfection by-products from water is of critical importance to achieve the water purification. N-nitrosodimethylamine (NDMA), an emerging nitrogenous disinfection by-product produced by the chlorine-ammonia disinfection, remains significantly hazardous even at low concentrations. Herein, an activated carbon (AC)-supported nanoscale zero-valent iron (nZVI) coated with sulfur (S) and silver (Ag) composite (Ag@S-nZVI/AC) was synthesized, characterized via several techniques and evaluated for NDMA removal performance. The results demonstrated that crystalline Ag and mackinawite (FeS) coated amorphous nZVI spheres were successfully anchored on AC. The removal of NDMA at ultra-lower concentrations by the Ag@S-nZVI/AC composite was better fitted by pseudo-second-order (PSO) kinetic and Freundlich isotherm models. NDMA was chemically adsorbed in multiple layers on heterogeneous surface of the Ag@S-nZVI/AC composite via spontaneous endothermic process. The adsorption constant (KF) of NDMA removal by Ag@S-nZVI/AC at T=298 K was 9.89 times greater than that of NDMA removal by pristine AC. The van der Waals forces, hydrogen bonds and surface-mediated electron transfer were the main mechanisms responsible for the highly effective remediation of ultra-lower concentrations of NDMA from drinking water. The decomposition of NDMA was significantly enhanced by Ag@S-nZVI/AC, resulting in the generation of more dimethylamine (DMA), ammonium and the nitrogen-containing compounds. The decomposition process involved the oxidation of FeS, S and Fe0 surface as well as the hydrogenation of Ag. The post-leaching concentrations of Fe, Ag and S in treated drinking water were lower than the standard permissible limits.

Quantifying remediation of chlorinated volatile compounds by sulfidated nano zerovalent iron treatment using numerical modeling and CSIA

Sulfidated nanoscale zerovalent iron (S-nZVI) has demonstrated promising reactivity and longevity for remediating chlorinated volatile compounds (cVOC) contaminants in laboratory tests. However, its effectiveness in field applications remains inadequately evaluated. This study provides the first quantitative evaluation of the long-term effectiveness of carboxymethyl cellulose-stabilized S-nZVI (CMC-S-nZVI) at a cVOC-contaminated field site. A reactive transport model-based numerical approach delineates the change in cVOC concentrations and carbon isotope values (i.e., δ13C from compound-specific stable isotope analysis (CSIA)) caused by dissolution of dense non-aqueous phase liquid, sorption, and pathway-specific degradation and production, respectively. This delineation reveals quantitative insights into remediation effectiveness typically difficult to obtain, including extent of degradation, contributions of different degradation pathways, and degradation rate coefficients. Significantly, even a year after CMC-S-nZVI application, degradation remains an important process effectively removing various cVOC contaminants (i.e., chlorinated ethenes, 1,2-dichloroethanes, and chlorinated methanes) at an extent varying from 5 %-62 %. Although the impacts of CMC-S-nZVI abundance on degradation vary for different cVOC and for different sampling locations at the site, for the primary site contaminants of tetrachloroethene and trichloroethene, their predominance of dichloroelimination pathway (≥ 88 %), high degradation rate coefficient (0.4–1.7 d-1), and occurrence at locations with relatively high CMC-S-nZVI abundance strongly indicate the effectiveness of abiotic remediation. These quantitative assessments support that CMC-S-nZVI supports sustainable ZVI-based remediation. Further, the novel numerical approach presented in this study provides a powerful tool for quantitative cVOC remediation assessments at complex field sites where multiple processes co-occur to control both concentration and CSIA data.