Reactivity Of nZVI Research Articles

Removal of ciprofloxacin by biosulfurized nano zero-valent iron (BP–S-nZVI) activated peroxomonosulfate: Influencing factors and degradation mechanism

Agglomeration and passivation restrict the using zero-valent iron nanoparticles (nZVI). Enhancing the reactivity of nZVI is often accomplished by sulfurization. In this work, nZVI was sulfurized using SRB to produce biosulfurized nano zero-valent iron (BP–S-nZVI), which was then utilized as a catalyst to investigating its performance in an advanced oxidation process based on activated peroxomonosulfate (PMS). When the S/Fe was 0.05, 0.4 g/L of catalyst and 0.5 mM PMS were added to a 20 mg/L ciprofloxacin solution. In 120 min, a 90.4% clearance rate was reached. When the initial pH of the solution was within the range of 3–11, all exhibited acceptable degradation performance and were minimally affected by co-existing anions. In this activation system, hydroxyl, superoxide and sulfate radicals (•OH, O2•− and SO4•−, respectively) have been proven to be the main active species. Seven intermediates in the degradation process of CIP were identified by LC-MS analysis and two possible degradation pathways were proposed. In addition, the degradation rate of CIP was still able to reach 87.0% after five cycles, and the removal rate remained unchanged in the CIP solution with actual water samples as background. This study demonstrated that BP-S-nZVI as a catalyst for the activation of PMS for CIP degradation can still show good reactivity, which provides more possibilities for the practical application of BP-S-nZVI in the degradation of pollutants.

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.

Carboxymethyl cellulose stabilization induced changes in particle characteristics and dechlorination efficiency of sulfidated nanoscale zero-valent iron

Polymer stabilization, exemplified by carboxymethyl cellulose (CMC), has demonstrated effectiveness in enhancing the transport of nanoscale zero-valent iron (nZVI). And, sulfidation is recognized for enhancing the reactivity and selectivity of nZVI in dechlorination processes. The influence of polymer stabilization on sulfidated nZVI (S-nZVI) with various sulfur precursors remains unclear. In this study, CMC-stabilized S-nZVI (CMC-S-nZVI) was synthesized using three distinct sulfur precursors (S2−, S2O42−, and S2O32−) through one-step approach. The antioxidant properties of CMC significantly elevated the concentration of reduced sulfur species (S2−) on CMC-S-nZVIs, marking a 3.1–7.0-fold increase compared to S-nZVIs. The rate of trichloroethylene degradation (km) by CMC-S-nZVIs was observed to be 2.2–9.0 times higher than that achieved by their non-stabilized counterparts. Among the three CMC-S-nZVIs, CMC-S-nZVINa2S exhibited the highest km. Interesting, while the electron efficiency of CMC-S-nZVIs surged by 7.9–12 times relative to nZVI, it experienced a reduction of 7.0–34% when compared with S-nZVIs. This phenomenon is attributed to the increased hydrophilicity of S-nZVI particles due to CMC stabilization, which inadvertently promotes the hydrogen evolution reaction (HER). In conclusion, the findings of this study underscores the impact of CMC stabilization on the properties and dechlorination performance of S-nZVI sulfidated using different sulfur precursors, offering guidance for engineering CMC-S-nZVIs with desirable properties for contaminated groundwater remediation.

Magnetic triiron tetraoxide/biochar–loaded nanoscale zero-valent iron for chromium(VI) removal from aqueous solution

BackgroundTo inhibit the agglomeration of nanoscale zero-valent iron (nZVI or Fe0), increase its stability and facilitate electron transfer, magnetic triiron tetraoxide/biochar (MBC) was used as the carrier to load nZVI. Consequently, a new pathway was created for electron transfer from nZVI to triiron tetraoxide (Fe3O4) and then to contaminants, thereby improving the chemical reactivity of nZVI. MethodsMagnetic triiron tetraoxide/biochar–loaded nanoscale zero-valent iron (nZVI@MBC) composites were prepared for chromium(VI) adsorption. Different influencing aspects were studied, including the loading percentage of nZVI, solution pH, co-existing anions(PO43−, SO42−, Cl−, NO3−), temperature and reusability. Furthermore, the adsorption isotherms, kinetics and thermodynamics for Cr(VI) removal were performed. Significant findingsnZVI@MBC exhibited an adsorption amount of 117.25 mg g−1 at the optimal conditions (dosage 0.4 g L−1, initial concentration 50 mg L−1, temperature 30 °C, nZVI loading percentage onto MBC 5.0 wt% and pH 2). The adsorption data obeyed the pseudo-second-order kinetics model and followed the Langmuir isotherm, thermodynamic characteristics revealed that Cr(VI) adsorption onto nZVI@MBC was a spontaneous endothermic process. After four recycles, the Cr(VI) removal efficiency remained higher than 70 %, exhibiting a good reusable ability. The mechanisms were confirmed to be physical adsorption, chemical reduction and co-precipitation processes.

Dynamic Shear Responses of Combined Contaminated Soil Treated with Nano Zero-Valent Iron (nZVI) under Controlled Moisture

Nano zero-valent iron (nZVI) technologies have gained recognition for the remediation of heavily contaminated sites and reused as backfilling soil. The moisture environment at these sites not only impacts the reactions and reactivity of nZVI but also the dynamic responses of compacted backfilled soils. The research explored the effects of different nZVI dosages (0.2%, 0.5%, 1%, 2%, and 5%) on Lead-Zinc-Nickel ions contaminated soil under a controlled-moisture condition. Cyclic triaxial tests were performed to evaluate the dynamic responses of treated soil samples prepared using a consistent moisture compaction method. Particle size distribution and Atterberg limits tests assessed changes in particle size and plasticity. The study revealed a minor reduction in the particle size, liquid limit, plastic limit, and plasticity index of the contaminated soil. Notably, increasing nZVI dosages in treated soils led to growing Atterberg limits. An increase in the specific sand fraction of treated soils was observed with nZVI, suggesting nanoparticles–soil aggregations favoring existing larger particles. Stepwise loading cyclic triaxial tests indicated an optimal dynamic response of soil treated with 1% nZVI under the controlled-moisture condition, proven by notable enhancements in the maximum shear modulus, maximum shear stress, less shear strain, and higher damping ratio within the small strain range. It should be noted that moisture content in treated soils declined significantly with higher nZVI dosages during preparation, potentially impeding effective aggregation and the formation of a solid soil skeleton. These findings advance the importance of considering the balanced nZVI dosage and moisture content when employing the safety assessment of practical applications in both nano-remediation techniques and soil mechanics.

Sulfide-modified nanozerovalent iron for rapid decontamination of Cu(Ⅱ) complexes in high-salinity wastewater

Heavy metal complexes receive less attention, but they are more difficult to remove than the free heavy metals. Moreover, the high-salinity wastewaters from various industries hinder the removal of heavy metal complexes. Removal of the metal complexes is a top priority but a challenging task. Herein, a new strategy for removing Cu-EDTA from high-salinity wastewater with sulfide-modified nanozerovalent iron (S-NZVI) was proposed. The S-NZVI exhibited a considerable adsorption capacity for Cu-EDTA (∼83 mg Cu/g) at a high salt concentration (25 g/L NaCl). Similarly, the S-NZVI maintained excellent adsorption performance (∼83 mg Cu/g) in the presence of CaCl2, MgCl2, Na2SO4, and NaNO3 (25 g/L). The S-NZVI showed extremely high efficiency for Cu-EDTA removal; 50 mg/L of Cu-EDTA was almost completely removed in 1 min, and the kobs was approximately 1.5 g/(mg min). The S-NZVI showed an extensive pH working range, and within the pH range of 2–9, the Cu-EDTA was removed completely within 5 min. The excellent removal performance of the S-NZVI was due to the high reactivity and high affinity of NZVI for Cu, as well as the special substitution of Fe2+ and the interfacial reactions between S-NZVI and the copper complexes. Compared with other studies of Cu complex removal, removal with S-NZVI was a simpler process with higher efficiency. In brief, S-NZVI efficiently removed Cu complexes from harsh water environments and was reused many times. The process was simple and efficient and has broad application prospects.

Adsorption of total petroleum hydrocarbon in groundwater by KOH-activated biochar loaded double surfactant-modified nZVI

Introduction: Crude oil and petroleum hydrocarbon contamination is commonly found in the soil and groundwater during the various processes of mining, processing, and utilization due to issues such as inefficient environmental management, random wastewater discharge, and storage tank leakage.To address this issue, we will use corn stalk biochar (SBC) and surfactants to improve the stability and chemical reactivity of nZVI, thereby enhancing its ability to remove pollutants, and explore the adsorption effect and mechanism of composite materials for petroleum hydrocarbons.Methods: Modified corn stalk biochar (SBC) was synthesized through high-temperature carbonization and KOH activation. Subsequently, the iron/carbon composite PN-nZVI@SBC (PNMSBC) was prepared by loading nano zero-valent iron modified with dual surfactants, and it was adopted to adsorb total petroleum hydrocarbons(TPH) in groundwater. The physical and chemical properties, surface patterns, and elemental mapping of PNMSBC particles were analyzed using SEM, EDS, TEM,XRD, BET, and FTIR spectroscopy. Kinetics and isotherm tests were performed to evaluate the adsorption properties of the composites. TPH adsorption was dependent on ionic strength, initial TPH concentration, as well as pH. The adsorption mechanism combining XPS and EPR spectroscopy was explored.Results: The characterization results by SEM and TEM showed that the particle size of nZVI particles modified by surfactants became smaller, and the dispersibility was enhanced. The characterization results by XRD and FTIR confirmed the successful preparation of the composites. The BET results showed that MSBC and PNMSBC were mesoporous structures. The characterization results indicated that Polyvinylpyrrolidone (PVP) and Sodium oleate (NaOA) inhibited the oxidation of nZVI while effectively improving its reactivity. The result of the experiments on adsorption showed that the removal of TPH by PNMSBC followed Freundlich isotherm and pseudo-second-order kinetic models, thus suggesting that the main adsorption processes comprise chemisorption and multilayer heterogeneous adsorption. The adsorption capacity of PNMSBC was increased by the abundance of macro and microporous structures. To be specific, a maximum Langmuir adsorption capacity (qm) was achieved as 75.26 g/g. The result of batch experiments indicated that PNMSBC continuously removed considerable TPH under a wide pH range from 2 to 6. The adsorption mechanism of PNMSBC includes surface adsorption, oxidation, complexation, and electrostatic interaction.Discussion: In brief, PNMSBC has a promising application for the adsorption of TPH in groundwater remediation.

Investigation of the adsorption and degradation of metronidazole residues in agricultural wastewater by nanocomposite based on nZVI on MXene

Metronidazole is a widely used antibiotic with powerful antimicrobial properties, but its presence in water can be detrimental to aquatic life and human health. To address this issue, we developed a novel composite material, zero-valent iron nanoparticles on alkalized Ti3C2Tx nanoflakes (NZVI/Ti3C2Tx), using an in-situ growth technique, aiming to efficiently adsorb and degrade metronidazole from aqueous solutions. The incorporation of Ti3C2Tx in NZVI/Ti3C2Tx resulted in enhanced dispersion, stability, and reactivity of NZVI. Our study demonstrated that NZVI/Ti3C2Tx exhibited the highest metronidazole removal efficiency (95.80%) within just 10 min of reaction time, outperforming NZVI and Ti3C2Tx alone. To optimize the removal process, we investigated the influence of various parameters on the degradation of metronidazole by NZVI/Ti3C2Tx, including the NZVI/Ti3C2Tx ratio, initial metronidazole concentration, pH, and reaction temperature. The highest removal rate was achieved with an NZVI/Ti3C2Tx ratio of 2:1 after 90 min of reaction time. As the initial concentration and pH of metronidazole increased, the removal efficiency decreased, while higher reaction temperatures improved the removal efficiency. Kinetic studies revealed that the degradation of metronidazole by NZVI/Ti3C2Tx followed a modified second-order parameter pseudo-first-order kinetic model, highlighting the effective reduction reaction. The unique properties of MXene nanosheets and NZVI synergistically contributed to the enhanced removal performance, with NZVI/Ti3C2Tx acting as an efficient adsorbent and reducing agent. Uur findings demonstrate the potential of the NZVI/Ti3C2Tx nanocomposite as an efficient and eco-friendly approach for the removal of metronidazole from agricultural wastewater. The combination of NZVI and Ti3C2Tx offers enhanced removal efficiency and stability, making it a promising material for water purification and environmental applications.

In situ prepared Chlorella vulgaris-supported nanoscale zero-valent iron to remove arsenic (III).

Nanoscale zero-valent iron (nZVI) has a high removal affinity toward arsenic (As). However, the agglomeration of nZVI reduces the removal efficiency of As and, thus, limit its application. In this study, we report an environmentally friendly novel composite of Chlorella vulgaris-supported nanoscale zero-valent iron (abbreviated as CV-nZVI) that exhibits a fast and efficient removal of As(III) from As-contaminated water. Scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometry (XRD), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) were used to characterize and analyze the CV-nZVI. These results indicated that the stabilization effect of C. vulgaris reduced the nZVI agglomeration and enhanced the reactivity of nZVI. The experiments showed a removal efficiency of 99.11% for As(III) at an optimum pH of 7.0. The adsorption kinetics and isotherms followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm with the superior maximum adsorption capacities of 34.11mg/g for As(III). The FTIR showed that the As(III) was adsorbed on the CV-nZVI surface by complexation reaction, and XPS indicated that oxidation reaction was also involved. After five reuse cycles, the removal efficiency of As(III) by CV-nZVI was 32.93%, suggesting that the CV-nZVI had some reusability and regeneration. Overall, this work provides a practical and highly efficient approach for As remediation in As-contaminated water, and simultaneously resolves the agglomeration problems of nZVI nanoparticles.

Performance and mechanism study of g-C3N4/rGO heterojunction enhanced NO3− reduction by nZVI under visible light irradiation

Zero valent iron (ZVI) is a low-cost, earth-abundant reactive metal, and it has a strong reducing ability with a standard redox potential of − 0.44 V. Therefore, it is an effective and widely used reducing agent for pollutant degradation. Since nanoscale zero valent iron (nZVI) shows a larger specific surface area which leads to the faster reaction rate and higher conversion efficiency, it has been widely used in NO3− nitrogen reduction reaction, however, it shows disadvantages of poor chemical stability, narrow applicable pH, and low total nitrogen (TN) removal efficiency. To solve these problems, in this paper, the nZVI nanoparticles were deposited on the g-C3N4/rGO composite, and its NO3− removal efficiency under visible light irradiation was investigated. The effects of nZVI loading, initial pH of solution, catalyst dosage and initial NO3− concentration on NO3− reduction performance were studied. The results showed that the g-C3N4/rGO/nZVI material achieved 100% of NO3− reduction efficiency in 60 min. And the TN removal efficiency of g-C3N4/rGO/nZVI was 82.8%, superior to nZVI and g-C3N4/nZVI (13.3% and 38.2%, respectively). Finally, the denitrification mechanism of g-C3N4/rGO/nZVI was proposed as follows: Under light irradiation, the photogenerated electrons on g-C3N4 transferred via rGO to the nZVI surface, thus improving the reactivity and stability of nZVI. The photogenerated electrons and active electrons on the surface of nZVI reduced NO3− to N2, NH4+, and other products, while the photogenerated holes further oxidized part of NH4+ to N2 and other gaseous products. During this process, the rGO material could inhibit the oxidation of nZVI by the photogenerated holes from g-C3N4.

Enhanced degradation of monobrominated diphenyl ether by sophorolipid modified nanoscale zerovalent iron: Reactivity, electron selectivity, and mechanism

Nanoscale zero-valent iron (nZVI) is regard as a promising reductant for halogenated organic compounds remediation, while it still suffers from low reactivity and poor electron selectivity toward monobrominated diphenyl ether. In this paper, the modified nZVI was successfully prepared via introducing sophorolipid during the synthesis of nZVI by a one-step method (SL-nZVI). The experimental results demonstrated that the degradation efficiency of SL-nZVI for BDE-3 could reach up to 99.96%, which was significantly higher than that of nZVI (59.60%). TEM and BET characterizations indicated that the modified nZVI possessed excellent dispersion properties and higher specific surface area, while the electrochemical tests results revealed that the sophorolipid modification reduced the charge transfer resistance of nZVI and favored the electron transfer. Besides, the introduced sophorolipid enhanced solubilization of hydrophobic organic contaminants via halogen bonding interaction also contributes to the increasement of BDE-3 degradation. More importantly, the experimental results also indicated that the utilization efficiency and electron selectivity of nZVI particles for the BDE-3 were significantly improved after sophorolipid modification (from 56.64% and 2.69% to 74.14% and 7.39%, respectively), and this could be owned to more accessible active sites, as well as the increased hydrophobicity of nZVI, which is not conducive to the adsorption of hydrophobic BDE-3 onto the nZVI surface, but reduces the occurrence of side reaction between nZVI and water. Those results demonstrate that the sophorolipid modification is an efficient strategy for nZVI in the remediation of hydrophobic BDE-3, and also highlight the promising prospects of sophorolipid in increasing the reactivity and electron selectivity of nZVI.

Supporting nanoscale zero-valent iron onto shrimp shell-derived N-doped biochar to boost its reactivity and electron utilization for selenite sequestration

Nanoscale zero-valent iron (nZVI) has been widely used in the reductive removal of contaminants from water, yet it still fights against the inherent passive cover and the raise of medium pH. In this study, nZVI was supported onto a nitrogen-doped biochar (NBC) that was prepared by pyrolyzing shrimp shell for efficiently sequestrating aqueous selenite (Se(IV)). The resultant composite (NBC-nZVI) revealed a higher reactivity and electron utilization efficiency (EUE) than the bare nZVI in Se(IV) sequestration because of the positive charge, the buffering effect and the good conductivity of NBC. The kinetic rate and EUE of NBC-nZVI were increased by 143.4% and 15.3% compared to the bare nZVI, respectively, at initial pH of 3.0. The high removal capacity of 605.4 mg g−1 for NBC-nZVI was obtained at Se(IV) concentration of 1000 mg L−1, initial pH of 3.0, NBC-nZVI dosage of 1.0 g L−1 and contact time of 12 h. Moreover, NBC-nZVI exhibited a strong tolerance to solution pHs and coexisting compounds (e.g., humic acid) and could reduce the Se(IV) concentration from 5.0 mg L−1 to below the limit of drinking water (50 μg L−1) in real-world samples. This work exemplified a utilization of shrimp shell-derived NBC to simultaneously enhance the reactivity and EUE of nZVI for reductively removing contaminants.

Efficient and comparative adsorption of trinitrotoluene on MOF MIL-100(Fe)-derived porous carbon/Fe composite adsorbents with rod-like morphology: Behavior, mechanism, and new perspectives

Porous carbon (PC) materials containing nanoscale zero-valent iron (nZVI) often exhibit higher removal efficiency for water pollutants due to the strong influence of nZVI reactivity. However, despite the advantages of nZVI, its presence can sometimes affect the adsorptive properties of the PC materials by blocking the pores and masking adsorption sites, thereby inhibiting efficient adsorption. Herein, we synthesized and used an iron-containing rod-like metal-organic framework, MIL-100(Fe), as a precursor to prepare PC rods with and without surface nZVI, namely, Fe-PCR and PCR, respectively. The prepared materials were characterized, and their adsorption properties for 2,4,6-trinitrotoluene (TNT) – an explosive contaminant – were studied. TNT adsorption onto Fe-PCR and PCR occurred rapidly within 10 min and reached equilibrium after 60 min. Moreover, the results from the kinetics studies showed that TNT adsorption process well-fitted the pseudo-second order (PSO) model due to the higher correlation value (R2 > 0.99), indicating a chemosorption process. The results from the adsorption isotherm and thermodynamic investigations revealed that TNT adsorption onto the prepared adsorbents occurred via a single-to-multilayer adsorption process in which exothermic chemisorption adsorption was dominant. The adsorption capacity of PCR reached 409.38 mg/g, which was significantly higher than Fe-PCR (249.97 mg/g) under ambient conditions. This revealed that the presence of surface-abundant nZVI in Fe-PCR limited the adsorption of TNT compared to PCR. Moreover, analysis of the TNT-loaded adsorbents revealed that TNT was not altered by nZVI but adsorbed onto the PC-rods surfaces via π-π EDA interactions, hydrogen bonding, and physical adsorption via pore filling. Thus, the improved structural properties of PCR due to Fe removal (SBET: 720 m2/g; Vpore: 1.76 cm3/g) compared to Fe-PCR (SBET: 408.72 m2/g; Vpore: 0.762 cm3/g) provided greater accessibility to adsorption sites, thereby resulting in better adsorption performance.

High-efficiency removal of tetracycline from water by electrolysis-assisted NZVI: mechanism of electron transfer and redox of iron.

A low-cost, stable and non-precious metal catalyst for efficient degradation of tetracycline (TC), one of the most widely used antibiotics, has been developed. We report the facile fabrication of an electrolysis-assisted nano zerovalent iron system (E-NZVI) that achieved TC removal efficiency of 97.3% with the initial concentration of 30 mg L-1 at an applied voltage of 4 V, which was 6.3 times higher than the NZVI system without an applied voltage. The improvement caused by electrolysis was mainly attributed to the stimulation of corrosion of NZVI, which accelerated the release of Fe2+. And Fe3+ in the E-NZVI system could receive electrons to reduce to Fe2+, which facilitated the conversion of ineffective ions to effective ions with reducing ability. Moreover, electrolysis assisted to expand the pH range of the E-NZVI system for TC removal. The uniformly dispersed NZVI in the electrolyte facilitated the collection and secondary contamination could be prevented with the easy recycling and regeneration of the spent catalyst. In addition, scavenger experiments revealed that the reducing ability of NZVI was accelerated in the presence of electrolysis, rather than oxidation. TEM-EDS mapping, XRD and XPS analyses indicated that electrolytic effects could also delay the passivation of NZVI after a long run. This is mainly due to the increased electromigration, implying that the corrosion products of iron (iron hydroxides and oxides) are not formed mainly near or on the surface of NZVI. The electrolysis-assisted NZVI shows excellent removal efficiency of TC and is a potential water treatment method for the degradation of antibiotic contaminants.

Removal of p-nitrophenol by double-modified nanoscale zero-valent iron with biochar and sulfide: Key factors and mechanisms

In this study, the mechanisms and key factors of p-nitrophenol (PNP) removal by biochar (BC) and sulfide double-modified nanoscale zero-valent iron (nZVI) were systematically investigated. The results showed that the residence time of the hydrothermal carbonization of waste bamboo chopsticks was the key factor affecting the removal of PNP by nZVI/BC. The biochar derived from waste bamboo chopsticks prepared at a hydrothermal temperature of 240 °C for 1 h was the most suitable nZVI loading material. The hydrophobicity of the biochar had a greater impact on S-nZVI/BC. Biochar effectively alleviated the agglomeration of nZVI and formed a miniature galvanic cell with nZVI to promote its corrosion. The effective reducing agents in the S-nZVI/BC system were Fe0, Fe2+, S2−, and S22−, and the system had stronger reducibility then nZVI. The reaction rate of S-nZVI/BC for PNP removal was 2.6 times higher than that of nZVI. In addition, the double modification of nZNI reduced the energy barrier of the PNP removal reaction and alleviated the surface passivation of nZVI. The apparent activation energy of the reaction under anaerobic conditions after sulfidation treatment was reduced by 23.7 %, while the PNP removal efficiency increased by 8 % under aerobic conditions. Density Function Theory (DFT) calculations revealed that PNP was more easily adsorbed and participated in the reaction on the surface of the sulfide shell layer than oxidized shell layer. This work confirms that biochar loading and surface sulfidation can enhance the reactivity and stability of nZVI.

Enhanced oxidation and removal of As(Ⅲ) from water using biomass-derived porous carbon-supported nZVI with high iron utilization and fast adsorption

Rapid and effective removal of As(III) from aqueous solutions is crucial and difficult due to its highly toxic and mobile properties. In this study, two kinds of carbonaceous supports, biomass-derived porous carbon (BPC) and biochar (BC), were fabricated for nZVI loading, and then served as adsorbent materials for As(III) removal from water. Characterization results indicated that BPC/nZVI showed more uniformly dispersed nZVI particles on the surface compared to BC/nZVI. Adsorption results showed that BPC/nZVI had highest adsorption capacity for As(III) with the fastest adsorption rate compared with BC/nZVI and pure nZVI. The porous structure and stronger electron accepting capacity for BPC enhanced the reactivity of loading nZVI compared to BC/nZVI. Batch experiments revealed that BPC/nZVI had the highest As(III) Langmuir adsorption capacity up to 177.8 mg/g at pH 7.0, and shorter adsorption equilibrium time within 90 min when compared to BC/nZVI and pure nZVI. The adsorption isotherm and adsorption kinetic of As(III) onto BPC/nZVI were described well by Langmuir model and the pesudo-second-order model, respectively. Additionally, BPC/nZVI exhibited excellent removal performance for As(III) in a broad pH and co-existing anions solution, and kept more than 80% As(III) removal rate after the fourth cycle. Our results indicate that oxidation and complexation are the dominant mechanisms and electrostatic interaction exists for As(III) removal by BPC/nZVI. This study indicates that BPC as supporting materials for nZVI loading is a promising strategy for efficient and fast remediation of As(III)-polluted wastewater.

Sophorolipid modification enables high reactivity and electron selectivity of nanoscale zerovalent iron toward hexavalent chromium

Nanoscale zero-valent iron is considered to be a promising nanostructure for environmental remediation, while increasing the electron selectivity of nanoscale zerovalent iron (nZVI) during target contaminant removal is still a challenge (electron selectivity, defined as the percentage of electrons transferred to the target contaminants over the number of electrons donated by nZVI). In this study, the strategy for increasing the reactivity and electron selectivity of nZVI via sophorolipid (SL-nZVI) modification was proposed. The results showed that the removal efficiency and electron selectivity of SL-nZVI toward Cr(VI) was 99.99% and 56.30%, which was higher than that of nZVI (61.16%, 25.91%). Meanwhile, the particles were well characterized and the mechanism for enhanced reactivity and electron selectivity was investigated. Specially, both the morphology and BET specific surface area characterization suggested that stability against aggregation was higher in SL-nZVI nanoparticles than in nZVI. Besides, X-ray photoelectron spectroscopy (XPS), Tafel polarization curves, and Electrochemical impedance spectroscopy also indicated that the introduction of sophorolipid successfully prevent the nanoparticles from oxidation and benefit the electron transferring. In addition, a water contact angle test revealed that SL-nZVI nanoparticles were less hydrophilic (contact angle = 34.8°) than nZVI (contact angle = 23.9°). Therefore, in terms of reactivity, sophorolipid modification inhibited the aggregation of the nanoparticles and enhanced the electrical conductivity. For electron selectivity, the introduction of sophorolipid not only benefited Cr(VI) adsorption and the electron transfer from Fe0 to the surface-adsorbed Cr(VI) that followed but also reduced the possibility of side reactions between Fe0 and H2O. This study demonstrates that the introduction of sophorolipid is an effective strategy for developing a highly efficient nZVI-based nanocomposite system and highlights the potential role of sophorolipid in improving the electron selectivity of nZVI.

Shewanella oneidensis MR-1 for enhanced the reactivity of FA-stabilized nZVI toward Cr(VI) removal

In present work, nanoscale zero-valent iron (nZVI) was successfully stabilized using fulvic acid (nZVI-FA). Shewanella oneidensis MR-1 (MR-1) was used to enhance the reactivity of the nZVI-FA. The results demonstrated that nZVI-FA combined with the MR-1 (nZVI-FA/MR-1) system could effectively solve the aggregation and surface passivation of nZVI, thereby significantly enhancing the reactivity of nZVI forCr(VI) removal. The Cr(VI) removal efficiency of the nZVI-FA/MR-1 system (100 %) within 24 h was apparently higher than that of the ZVI-FA system (64.43 %). The enhancement of Cr(VI) removal is because fulvic acid (FA) FA can stabilize nZVI against aggregation; MR-1 could rapidly reduce the Fe(III) (hydr)oxides (FeHOs) passivation layers on the surface of nZVI-FA to biogenic Fe(II) [bio-Fe(II)], which in turn reduced Cr(VI). X-ray photoelectron spectroscopy (XPS) analysis revealed that the Fe(II)/Fe(III) ratio (1.20) and Cr(III)/Cr(VI) ratio (2.53) of the precipitates in the nZVI-FA/MR-1 system were much higher than that those in the nZVI-FA system (0.55 and 1.40, respectively). Three-dimensional excitation-emission matrix (3D-EEM) spectral analysis confirmed that tyrosine, tryptophan, and protein-like substances in extracellular polymeric substances (EPSs) from MR-1 are vital for the removal of Cr(VI). The mechanism analysis demonstrated that most Cr(VI) was reduced to Cr(III); Cr(III) existed as Cr2O3, FeCr2O4 and CrxFe1-x(OH)3 precipitates, and some of the Cr(VI) was removed from the solution by adsorption and complexation. This study offers alow-cost, efficient, and environmentally friendly strategy to enhance the reactivity of nZVI for Cr(VI) removal, which has broad prospective applications.

Adsorption of chromium, copper, lead and mercury ions from aqueous solution using bio and nano adsorbents: A review of recent trends in the application of AC, BC, nZVI and MXene

Recent trends in adsorption of Chromium (Cr), Copper (Cu), Lead (Pb) and Mercury (Hg) in wastewater using (i) carbonaceous materials including activated carbon (AC) and biochar (BC), and (ii) nanomaterials including nano zero-valent iron (nZVI) and MXenes have been discussed in this paper. It has been found that adsorption capacity depends largely on the adsorbent modification technique, initial pH of wastewater, dosage of adsorbent, contact time and initial concentration of the pollutants. The pH value ranges for maximum removal of Cr, Cu, Pb and Hg have been reported as 2–4, 5–6, 5–8 and 3–8, respectively. Up to 99% removal of metals has been reported using AC, BC, nZVI and MXene. The mechanism involves the reduction and chemical adsorption of metals. AC and BC have a higher surface area (up to 5000 m2/g) compared to nZVI (up to 500 m2/g) and MXene (up to 67.66 m2/g). However, the higher reactivity and regeneration capacity of nZVI and MXene make them suitable adsorbents. From a practical point of view the application of adsorbents for real effluents, cost analysis, regeneration capability and reuse of heavy metals are some aspects that need attention in future studies. The removal efficiencies of AC and BC are comparable to the nZVI and MXene. The cost analysis may be an attractive aspect to decide the future application of these adsorbents at large scale.

Humic acid addition sequence and concentration affect sulfur incorporation, electron transfer, and reactivity of sulfidated nanoscale zero-valent iron

Nanoscale zero-valent iron (nZVI) is extensively used in field remediation and can be sulfidated in situ with sulfide or sulfate-reducing bacteria to enhance its performance. Humic acid (HA) widely exists in nature, but its influence on both the sulfidation process of nZVI and the reactivity of sulfidated nZVI (S-nZVI) has been rarely reported. Herein, we first synthesized S-nZVI by one-pot (S1-nZVI) and two-step (S2-nZVI) approaches with adding HA before (pre-added) or after (post-added) FexSy generation, respectively. Then, we evaluated their reactivity on Cr(VI) removal and analyzed the effects of HA on sulfidation regarding electron transfer resistance, sulfur incorporation, and structure characterization. Pre-added HA inhibited the Cr(VI) removal by S1-nZVI more seriously than by S2-nZVI and nZVI, and stronger inhibition was observed at higher HA concentrations. The inhibitory effect can be attributed mainly to the adsorbed HA increasing the impedance of the material and the free HA impeding the generation and deposition of FexSy. Different from the inhibition of pre-added HA at all studied HA concentrations, the Cr(VI) removal by both S1-nZVI and S2-nZVI with post-added HA was enhanced at specific HA concentrations. The reason for this phenomenon was that the dispersion and specific surface area of S-nZVI were improved, thereby offsetting the inhibition from both impedance increase and sulfur loss. This work suggests that the presence of HA can affect the sulfidation process and the property of S-nZVI, which is conducive to evaluating the performance of S-nZVI produced both by injection and in situ in the subsurface contaminant remediation.