Bare Nanoscale Zero-valent Iron Research Articles

Can polymeric surface modification and sulfidation of nanoscale zerovalent iron (NZVI) improve arsenic-contaminated agricultural soil restoration via ex situ magnet-assisted soil washing?

Environmental context Arsenic (As) contamination in agricultural soil threatens safe agricultural production. Therefore, an ex situ magnet-assisted soil washing, using different types of nanoscale zerovalent iron was tested as a remediation option in soil restoration. Uncoated nanoparticles was the best tested option, with As removal at 45.5% and the nanoparticles were reusable up to four times. Rationale Arsenic (As) contamination in agricultural soil threatens safe food and medicinal herb production for millions of people. Methodology Therefore, ex situ magnet-assisted soil washing of metal-contaminated soil using bare nanoscale zerovalent iron (NZVI) is proposed as a novel remediation alternative. Conceptually, metal-contaminated soil is mixed with water and bare NZVI, and metals in the soil are transferred to the bare NZVI. The metal-sorbed NZVI is then retrieved from the soil slurry through magnetic separation, leaving behind treated soil. This study evaluated if advanced surface modification can improve ex situ soil restoration efficacy including polymeric coating and sulfidation of NZVI, proven beneficial in situ NZVI application. Sulfur and carboxymethylcellulose (CMC) at various S/Fe and CMC/NZVI ratios were used to modify NZVI via sulfidation and physisorption. Result Results revealed that sulfidised NZVI (S-NZVI) performed poorer (41.0%) than bare NZVI (45.5%) in As removal, even at the optimised S/Fe ratio of 0.31. This could be due to acid release via oxidative dissolution of FeS2 on the S-NZVI surface driven by O2. The incidental acid-dissolved NZVI sorption sites decreased As removal efficacy. Similarly, CMC-modified NZVI failed to improve As removal efficacy (11.0%) because it reduced NZVI reactivity and blocked As accessibility to NZVI sorptive sites. Discussion Nevertheless, S-NZVI and CMC-modified NZVI promoted non-phytoavailable As fractions in the treated soil. Overall, bare NZVI performed the best for As removal but moderately transformed As into more non-phytoavailable fractions. Bare NZVI can be reused for four cycles of soil washing. In every case, mobile As in treated soil was lower than the maximum contamination level.

Coupling adsorption and reduction for tellurium recovery by hierarchical porous nanoscale zero-valent iron (NZVI) /LDOs composites

The efficient recovery of tellurium from aqueous solution is essential from the viewpoint of non-ferrous metal resource exploitation and environmental protection. In this work, Mg–Al LDOs (layered double oxides) was synthesized by a facile biotemplate method, and then loaded with NZVI to realize coupling adsorption and reduction for tellurium recovery. Through the SEM, TEM, XRD, and BET tests, the morphology and crystal structure of this NZVI/LDOs composites were determined, and it was found that NZVI can be distributed on the surface of the LDOs sheet uniformly with large specific surface area of 134.04 m2/g and pore size of 10.15 nm. The prepared NZVI/LDOs composites exhibited excellent tellurium adsorption capacity (the removal rate can reach more than 99%) and pH, adsorption concentration and temperature are controlled to find the optimal adsorption conditions. The XPS analysis confirmed that the reduced tellurium adhered to the LDOs surface in elemental form, demonstrating the feasibility of the method. The combination of NZVI and Mg–Al LDOs solved the defects of bare NZVI and greatly improved the adsorption performance which has a good application prospect in the future recovery of tellurium.

Experimental study of the effect of nanoscale zero-valent iron injected on the permeability of saturated porous media

Abstract In a comparison of modified nanoscale zero-valent iron (NZVI), bare NZVI used to remediate deep contaminated groundwater source areas has more advantages. However, the influence of injected bare NZVI deposition on the permeability of aquifer remains unclear, together with which are still the key factors of engineering cost and contamination removal. Hence, this study sought to assess a method of measuring hydraulic conductivity with a constant head device and to examine the permeability loss mechanism of NZVI injected into different saturated porous media, using column tests. The results showed that it was feasible to determine hydraulic conductivity by the constant head device. The permeability loss caused by NZVI injection increased with a decrease in the grain size of the porous media, and was determined by the amount and distribution of NZVI deposition. The NZVI distribution area had a good linear correlation with dispersivity of the porous media. Additionally, although surface clogging occurred in all porous media, the amount of NZVI deposition at the injection point was largest in fine sand, so that its permeability loss was the most; this was more likely to cause hydraulic fracturing and expand the area of the contaminant source zone. These results have implications for NZVI field injection for successful groundwater remediation.

Re-recognizing micro locations of nanoscale zero-valent iron in biochar using C-TEM technique

Biochar supported nanoscale zero-valent iron (NZVI/BC), prepared commonly by liquid reduction using sodium borohydride (NaBH4), exhibits better reduction performance for contaminants than bare NZVI. The better reducing ability was attributed to attachment of nanoscale zero-valent iron (NZVI) on biochar (BC) surface or into the interior pores of BC particles due to observations by scanning electron microscopy (SEM) and plan transmission electron microscopy (P-TEM) techniques in previous studies. In this study, cross-sectional TEM (C-TEM) technique was employed firstly to explore location of NZVI in NZVI/BC. It was observed that NZVI is isolated from BC particles, but not located on the surface or in the interior pores of BC particles. This observation was also supported by negligible adsorption and precipitation of Fe2+/Fe3+ and iron hydroxides on BC surface or into interior pores of BC particles respectively. Precipitation of Fe2+ and Fe3+, rather than adsorption, is responsible for the removal of Fe2+ and Fe3+ by BC. Moreover, precipitates of iron hydroxides cannot be reduced to NZVI by NaBH4. In addition to SEM or P-TEM, therefore, C-TEM is a potential technique to characterize the interior morphology of NZVI/BC for better understanding the improved reduction performance of contaminants by NZVI/BC than bare NZVI.

Comparative study of arsenic removal by iron-based nanomaterials: Potential candidates for field applications

Graphene oxide supported magnetite (GM) and graphene oxide supported nanoscale zero-valent iron (GNZVI) nanohybrids were compared for arsenic removal at a wide pH range (3‐9). While already published work reported high process efficiency for GM and GNZVI, they cannot be compared one-on-one given the non-identical experimental conditions. Each researcher team used different initial arsenic concentration, solution pH, and adsorbent dose. This study evaluated GM and GNZVI, bare magnetite (M), and bare nanoscale zero-valent iron (NZVI) for aqueous arsenic removal under similar experimental conditions. GNZVI worked more efficiently (>90%) in a wide pH range (3–9) for both As(III) and As(V), while GM was efficient (>90%) only at pH 3 for As(V) and As(III) removal was maximum of ~80% at pH 9. GNZVI also exhibited better aqueous dispersibility with a zeta potential of −21.02 mV compared to other adsorbents in this experiment. The arsenic removal based on normalized iron content indicated that the nanohybrids recorded improved arsenic removal compare to bare nanoparticles, and GNZVI worked the best. In NZVI-based nanomaterials (GNZVI and NZVI), electrostatic attraction played a limited role while surface complexation was dominant in removal of both the arsenic species. In case of M-based nanomaterials (GM and M), As(V) removal was controlled by electrostatic attraction while As(III) adsorption was ligand exchange and surface complexation. GNZVI has the potential for field application for drinking water arsenic removal.

Integrating starch encapsulated nanoscale zero-valent iron for better chromium removal performance

Hexavalent chromium removal from wastewater is a major challenge for researchers. The study attempts to use starch-modified nanoscale zero-valent iron for hexavalent chromium removal. Starch was used to reduce the agglomeration tendency of nanoparticle, which was evident in SEM micrographs. The effects of various process variables were investigated, including pH, nanoparticle dosage, initial chromium concentration, mixing rate, temperature. The results showed that all these variables, except pH, were positively correlated with removal efficiency. The pH played a vital role in Cr(VI) removal performance. The removal performance of bare nanoscale zero-valent iron was below 50 % for chromium concentration 50 mg/l. The starch encapsulated nanoscale zero-valent iron worked well for lower chromium concentration, but at higher concentration (50 mg/l), the performance stagnated to around 65 %. In order to improve the performance for higher chromium concentration, the nanoparticle was integrated with various other remedial methods like ultrasonication, irradiation, aeration, and Fenton system. All these remedial techniques generate reactive oxygen species in the system, which, together with nanoscale zero-valent iron, greatly enhance the removal performance. It was seen that among various systems created, the removal performance for US/nZVI system, UV/nZVI system, aeration/nZVI system, and Fenton/nZVI system increased to 92 %, 86.7 %, 91 %, 93 % respectively. The removal efficiency was seen to be strongly correlated with parameters like ORP and final pH of the system and thus can be used for monitoring removal performance.

Activation of sulfite by different Fe0-based nanomaterials for oxidative removal of sulfamethazine in aqueous solution

In this work, bare nanoscale zero-valent iron (NZVI) and the modified NZVI (sulfide-modified NZVI, Ni/NZVI and activated carbon supported NZVI) were utilized to activate sulfite for the removal of the target pollutant sulfamethazine (SMT). Some critical factors influencing the removal process were investigated, including dosage of sulfite and nanoparticles (NPs), ratios of modifier/NZVI, dissolved oxygen, initial pH values, groundwater components and aging time of NPs. Under the optimal conditions, in terms of the dosage of sulfite/NPs and the ratio of modifier/NZVI, all the modified NZVI showed a better performance than the bare NZVI. Dissolved oxygen was determined to be an essential factor for producing reactive radicals in all the activation processes. The active radicals were identified to be SO4· and HO·, and HO· was evidenced as the principal reactive species. Initial pH value significantly affected the SMT removal, which was obviously inhibited under alkaline condition. In such case, Ni/NZVI showed a better performance than the other NPs due to the catalysis effect of Ni. It was also found that the groundwater components (e.g., HCO3−, Ca2+, SO42−, and humic acid) could restrain the removal process because of the buffering effect, the radical scavenging effect and some other effects (e.g., surface precipitation). Spectroscopic analysis of the fresh and aged (30 d) NPs illustrated that both bare and modified NZVI were slightly oxidized in the air, and could still be employed for the activation of sulfite.

Phytotoxicity of iron-based materials in mung bean: Seed germination tests

Environmental applications and potential risks of iron-based materials have attracted increasing attention. However, most previous studies focused on a single material. Comparative research using different iron-based materials under the same experimental conditions is still lacking. Here, six iron-based materials, including micro-sized and nanoscale Fe3O4 (i.e., mFe3O4 and nFe3O4), bulk and bare nanoscale zero-valent iron (i.e., mZVI and B-nZVI), starch-supported nZVI (S-nZVI), and activated carbon-supported nZVI (A-nZVI), were studied to compare their phytotoxicity in mung bean grown in suspensions with doses of 0, 300, 600 and 1000 mg/L. Taking the four toxicology parameters (seed germination rate, germination index, seedling elongation and biomass) together, the iron-based materials except mFe3O4 generally produced no significant phytotoxicity to mung bean even at 1000 mg/L. nFe3O4 and B-nZVI showed no higher phytotoxicity than their micro-sized counterparts (mFe3O4 and mZVI). All the materials resulted in increased Fe concentrations in seedlings particularly in roots, and mZVI and B-nZVI produced more significant effects. However, the Fe in the roots was difficultly translocated to the shoots. Compared to B-nZVI, nFe3O4 had lower bioavailability and bioaccumulation potential. XRD results confirmed that most Fe3O4 and B-nZVI remained unchanged during seedling growth, while support materials accelerated the corrosion and transformation of S-nZVI and A-nZVI. In conclusion, the tested nanoscale iron-based materials generally possess no obvious phytotoxicity within the dose range, but cause excess Fe accumulation in seedlings. Introduction of support materials may reduce such risk, allowing safer applications of these iron-based materials.

Investigating the design parameters for a permeable reactive barrier consisting of nanoscale zero-valent iron and bimetallic iron/copper for phosphate removal

There is a growing interest in deploying nanoscale zero valent iron (NZVI) in permeable reactive barriers (PRBs) for groundwater remediation. In the present study a series of packed-column experiments were conducted in order to investigate the effectiveness of phosphorus removal from groundwater using NZVI and bimetallic NZVI/Cu as reactive materials within PRBs. Seven sets of packed-column experiments were conducted in order to study the effect of different design parameters for PRB; including delivery approach of NZVI into porous media, PRB's configuration, coexisting groundwater ions and change in flowrate. Results implied that doping NZVI surface with copper had an anti-aggregation effect and enhanced its performance in terms of phosphorus removal 2.2 times higher than bare NZVI. Moreover, the lower flowrate (10 ml/min) demonstrated improved phosphorus removal by 22% compared with higher flowrate (60 ml/min). Additionally, groundwater ions barely interfered phosphorus removal process with only ±6%. Overall, geochemical properties and characteristics of the supporting materials were key parameters in the removal process of phosphorus by NZVI/Cu.

Improved longevity of nanoscale zero-valent iron with a magnesium hydroxide coating shell for the removal of Cr(VI) in sand columns

Nanoscale zero-valent iron (NZVI) has been engineered as an attractive tool for in-situ groundwater remediation. However, the poor mobility and aqueous corrosion of NZVI in the porous subsurface have hindered its practical applications. In this research, the NZVI surface was coated with a novel Mg(OH)2 shell (NZVI@Mg(OH)2) to improve the feasibility of NZVI for remediation. In the column tests for continuous removal of Cr(VI) from the flowing water, the Mg(OH)2 shell greatly improved the delivery of NZVI into the sand columns. Coating NZVI with Mg(OH)2 shell also showed considerably greater chemical stability than bare NZVI and thus greater resistance to aqueous corrosion. In addition, the dissolution of Mg(OH)2 allowed the reactivity to be gradually recovered along the sand column for Cr(VI) reduction. As a result, compared to bare NZVI in the columns, NZVI@Mg(OH)2 significantly prolonged the breakthrough period of Cr(VI) and hence increased the columns’ Cr(VI) removal capacity. Moreover, the Cr(III) produced was effectively immobilized by NZVI@Mg(OH)2, even under an acidic condition (pH 4.0). The results show that Mg(OH)2 coating is a promising technique to improve the longevity and capacity of NZVI for full-scale in-situ soil and groundwater remediation.

Modified tapioca starch for iron nanoparticle dispersion in aqueous media: potential uses for environmental remediation

Synthesis of cost-effective surface-modified nanoscale zero-valent iron (NZVI) for use in environmental remediation is a challenge. Herein, we report the synthesis of modified tapioca starch-coated NZVI (CNZVI) particles and their application for effective aqueous nitrate remediation. We used 2-octen-1-ylsuccinic anhydride (OSA) to modify the native starch and, thus introduced carboxyl and ester groups for effective binding of the starch to the NZVI surface. Coating NZVI (3 g L−1) with 35% OSA-modified tapioca starch (10 g L−1) significantly improved colloidal stability of CNZVI in deionized (DI) water compared to bare (unmodified) NZVI (p = 0.000). Approximately 66% of CNZVI remained suspended till 2 h as compared to 4% of bare NZVI. Nitrate removal studies (20, 40, and 60 mg $${\text{NO}}_{3}^{ - }$$ –N L−1 and 1 g L−1 of nanoparticles) showed CNZVI removed nitrate effectively (54–71% removal). The nitrate removal by CNZVI followed second-order reactions with surface normalized reaction rate constants ranging from 0.003 to 0.007 L m−2 h−1. Shelf life of the coated nanoparticles was found to be 3 months. High biochemical oxygen demand was expressed during respirometric biodegradation studies indicating ease of biodegradation of the CNZVI particles. Coating NZVI particles with OSA-modified tapioca starch is expected to have widespread scientific and industrial application potentials for ex situ as well as in situ contaminant remediation. The authors opine that the use of tapioca starch as the raw material for coated nanoparticle synthesis will be a value addition for the crop, and thus, nanotechnology will contribute to agricultural economy.

A comparative study on the activation of persulfate by bare and surface-stabilized nanoscale zero-valent iron for the removal of sulfamethazine

In this study, bare nanoscale zero-valent iron (NZVI) and that modified by starch, carboxymethyl cellulose (CMC) and sodium dodecyl benzene sulfonate (SDBS) were compared for their ability in activating persulfate to degrade sulfamethazine (SMT) in aqueous solution. The influencing factors, i.e., mass ratio of stabilizer/NZVI, pH, groundwater components (e.g., Ca2+, HCO3−, SO42− and humic acid) and particle aging, on SMT removal were examined. The results showed that there was an optimal mass ratio of stabilizer/NZVI for the stabilized NZVI (50 wt%, 0.1 wt% and 0.5 wt%, respectively, for starch-, SDBS- and CMC-stabilized NZVI) in order to achieve a faster removal rate of SMT than the bare NZVI. There was no significant difference among different nanoparticles in SMT removal in pure water at pH 5 and 9. While in simulated groundwater, the SMT removal in the bare NZVI system was more inhibited than the stabilized NZVI system. Compared with that in pure water, the removal rate of SMT was markedly decreased in simulated groundwater, especially at pH 9, which might be due to the radical scavenging effect of groundwater components (e.g., HCO3−, humic acid, SO42−) and the buffering effect of HCO3−. The aging of nanoparticles decreased the reaction rate. After aging for 15 d, SMT removal was decreased from 71.6%, 83.2%, 81.9% and 72.4% to 58.8%, 61%, 59.1% and 52.9%, respectively, for bare, starch-, SDBS- and CMC-stabilized NZVI in the first 5 min. However, SMT could still be completely removed in all systems when the reaction time was prolonged to 1 h. XRD analysis of the aged nanoparticles indicated that both bare and stabilized NZVI were not significantly oxidized in the air, and could still be employed for the activation of persulfate.

Oxidation resistance of nanoscale zero-valent iron supported on exhausted coffee grounds

In this study, nanoscale zero-valent iron (NZVI) was supported by exhausted coffee grounds. Exhausted coffee grounds are a crucial waste generated in enormous amounts. Since supported nanoscale particles have a lower free energy than bare particles, oxidation resistance of supported NZVI on coffee grounds (NZVI-Coffee ground) is postulated. The main aim of this study was to ascertain the enhanced oxidation resistance of NZVI-Coffee ground. Synthesized materials were dried and stored in the air at temperatures of 4, 20, and 35 °C. Changes in the surface characteristics and cadmium removal efficiency of the supported NZVI were investigated. Fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy showed that supported NZVI underwent less oxidation compared to bare NZVI. Cadmium removal efficiencies of supported NZVI did not deteriorate with age, while those of bare NZVI decreased by 9.5 ± 0.1, 13.0 ± 0.1, and 18.3 ± 0.2% compared to their initial removal efficiencies when stored 8 weeks at 4, 20, and 35 °C, respectively. This is because the surface free energy of the NZVI decreased via strong interaction with the functional groups of the coffee grounds. According to the results, exhausted coffee grounds are an effective supporting material for NZVI to enhance its storage stability.

Ceria accelerated nanoscale zerovalent iron assisted heterogenous Fenton oxidation of tetracycline

The development of an ultra-efficient heterogeneous Fenton catalyst that has practical application and can be easily separated is of great importance. In this study, a novel nanocomposite, Fe0/CeO2, was successfully synthesised and applied for Fenton oxidation of tetracycline. The results show that Fe0/CeO2 significantly enhanced the removal of pollutants, which suggests a synergistic effect between nanoscale zero-valent iron and CeO2. Furthermore, the composite catalyst exhibited ideal reusability and wide pH adaptation. A radical identification experiment revealed that surface-bounded OH (OHads) played a critical role in Fenton reaction, and compared with bare nanoscale zero-valent iron, Fe0/CeO2 remarkably promoted the generation of OH in the Fenton system, mostly because CeO2 not only increased the adsorption properties of the catalyst, it also accelerated electron transfer to promote the decomposition of H2O2 due to the abundance of surface oxygen vacancies. A reasonable degradation pathway was also proposed for tetracycline on the basis of the detected intermediates. Our findings help to understand the mechanism of tetracycline degradation by heterogeneous Fenton-like, and also provide an efficient system for organic wastewater treatment.

Preparation of nano-Fe0 modified coal fly-ash composite and its application for U(VI) sequestration

The nanoscale zero valent iron (NZVI) modified coal fly ash (CFA) magnetic composites (NZVI/CFA) were synthesized from the waste CFA and applied for the high-efficiency sequestration of U(VI) ions from water solution. The sequestration capacity of U(VI) ions on NZVI/CFA (0.62 mmol·g−1) was larger than that on bare CFA (0.25 mmol·g−1) or NZVI (0.38 mmol·g−1). The sequestration of U(VI) on NZVI and NZVI/CFA was primary controlled by outer-sphere surface complexation at low pH, and by inner-sphere surface complexation at high pH. According to the thermodynamic data and the adsorption isotherms' analysis, the U(VI) sorption process to the NZVI/CFA was spontaneous and endothermic. The main reaction mechanism was that, most of the soluble U(VI) ions were firstly adsorbed to NZVI/CFA and then the surface adsorbed U(VI) was partly reduced to U(VI) on the porous NZVI/CFA composites, and this synergistically affected U(VI) removal from solution to NZVI/CFA. The results of DFT calculation indicated that the NZVI/CFA had a strong sequestration capacity towards U(VI) and U(IV) ions, and the binding energy of U(IV) species was larger than that of U(VI) species, which evidenced the higher sorption of U(IV) than U(VI) on NZVI/CFA. The results showed that NZVI/CFA was an appropriate material for U(VI) sequestration from large volumes of actual effluent in wastewater cleanup.

Characteristics of Aggregate Size Distribution of Nanoscale Zero-Valent Iron in Aqueous Suspensions and Its Effect on Transport Process in Porous Media

Bare nanoscale zero-valent iron (NZVI) particles in aqueous suspensions aggregate into micron to submicron sizes. The transport process of enlarged aggregates or multi-sized aggregates is different from that of nanoparticles. In this work, we performed aggregate size distribution analysis of NZVI suspension using a laser grain size analyzer and conducted a series of continuous injection column experiments with different injected NZVI concentrations. The results show that aggregates in NZVI suspensions range from submicron to submillimeter size and are mainly distributed around 5–9 μm and 50–100 μm. Quantitative calculation of iron transport and retention showed that the retained iron linearly correlates with injected concentration. The cross-section images revealed that clogging weakened from inlet to outlet. Furthermore, larger aggregates (>40 μm) appeared more often in the rising-declining stages of breakthrough curves, whereas small aggregates (<30 μm) dominated the steady stage. Indeed, relatively preferential flow facilitated the transport and discharge of both large and small iron aggregates. Straining of glass beads especially for the large iron aggregates resulted in a decline in breakthrough. Moreover, the blocking of attached and plugged iron prevented later retention of iron, resulting in a certain concentration of iron in the effluents. Our study provides greater insight into the transport of NZVI.

PREPARATION METHOD OF NZVI-PVDF HYBRID FILMS WITH CATION-EXCHANGE FUNCTION FOR REDUCTIVE TRANSFORMATION OF CR(VI)

Poly (vinylidene fluoride) (PVDF) microporous film was successfully synthesized and functionalized by poly acrylic acid (PAA) for immobilization of nanoscale zero-valent iron (NZVI). PAA was innovatively introduced onto PVDF film via in situ polymerization of acrylic acid (AA) and followed by ion exchange procedure. The as-prepared PAA/PVDF-NZVI hybrids (PPN) were characterized in terms of morphology (SEM) and surface functional groups (FTIR). FTIR spectra confirms the functionalization of PVDF film by coating of PAA within its micropores. And SEM images suggested that NZVI were well immobilized onto the surface of the support. Over the reaction course, the resultant PPN hybrids demonstrated high reactivity, excellent stability and reusability for Cr(VI) removal. Results showed that lower pH and initial concentration facilitated the removal of Cr(VI) by PPN. Compared with bare NZVI, PAA/PVDF film-immobilized NZVI resulted in a lower activation energy for Cr(VI) removal, indicating that Cr(VI) reduction process with PPN is a surfacecontrolled chemical reaction. Moreover, a two-parameter pseudo-first-order model was provided and well-described the reaction kinetics of Cr(VI) over PPN under various conditions.

Highly reactive and stable nanoscale zero-valent iron prepared within vesicles and its high-performance removal of water pollutants

Nanoscale zero-valent iron particles have large specific surface area and high reaction activity, and have been increasingly used for the degradation of environmental contaminants. However, rapid aggregation and deactivation hinder their wide applications. In this work, nanoscale zero-valent iron (NZVI) particles were prepared in vesicles, which were formed by self-assembly of amphiphilic block copolymer poly(1-vinylpyrrolidone-co-vinylacetate) (PVV) in aqueous tetrahydrofuran medium, and characterized with the aid of XRD, FTIR, SEM-EDX, TEM, XPS and DLS techniques. It was found that the NZVI particles were well encapsulated in the vesicles, and they could be stored directly in the air as solids, but the dried NZVI particles could be easily released from the vesicles once they were put in water. These NZVI particles showed some unique features, such as uniform nanometer size distribution (from 70 to 100nm), vesicle-like morphology, and good dispersion. Activity and stability of the NZVI in vesicles were examined by using Cr(VI) and nitrobenzene as the model pollutants, and compared with the bare NZVI particles synthesized with the same procedures but without PVV. A dramatic difference in activity and stability was observed for the two different NZVI particles. The NZVI in vesicles showed a good chemical stability in the air, and still maintained its high reactivity in water. Such excellent performance might be attributed to the encapsulation of the NZVI by vesicles, which could impede well the strong agglomeration of metal particles in water and prevent metal particles from being oxidized in the air.

Reductive dechlorination of trichloroethylene by polyvinylpyrrolidone stabilized nanoscale zerovalent iron particles with Ni

We developed a novel stabilized nanoscale zerovalent iron (NZVI) particles with Ni using an electron conducting polymer, polyvinylpyrrolidone (PVP), to selectively dechlorinate trichloroethylene (TCE) to non-toxic intermediates. The size of the PVP stabilized NZVI-Ni ((PVP-NZVI-Ni), average diameter: ∼20nm) is smaller than that of bare NZVI (50–80nm) due to the prevention of agglomeration of the resultant iron particles by PVP. PVP-NZVI-Ni showed a complete removal of TCE in 1h with superior dechlorination kinetics (kobs=5.702h−1) and ethane selectivity (98%), while NZVI-Ni showed 5 times slower dechlorination kinetics (1.218h−1). Other PVP-NZVI-metals (i.e., Cu, Sn, Co, and Mn) also enhanced the TCE dechlorination, but they were much slower (kobs=0.024−0.411h−1) than that of PVP-NZVI-Ni. In column test, PVP-NZVI-Ni exhibited better mobility (95% of PVP-NZVI-Ni recovery in the eluent) than NZVI-Ni (1%). In addition, PVP-NZVI-Ni reductively transform TCE to ethane even under 10 cycles of repeated TCE dechlorination treatment.

Enhanced removal of Ni(II) by nanoscale zero valent iron supported on Na-saturated bentonite

Nanoscale zero valent iron (NZVI) can remove Ni(II) from wastewater through surface adsorption and then reduction into lower-toxic Ni0, but the reduction is often blocked by the iron oxide shell of NZVI. In this study, the negatively charged Na-saturated bentonite (Na-bent) with high adsorption capacity to Ni(II) was used to support NZVI for improving the removal and reduction of Ni(II), and the functions of Na-bent were investigated by X-ray photoelectron micro-spectroscopy (XPS), transmission electron microscope (TEM) and Fe(II) determination. The results showed that Na-bent as a carrier could enrich Ni(II) on the reaction surface, protect the surface of NZVI from oxidation, prevent the aggregation of NZVI particles, and decrease the iron oxides products on NZVI surface by pH buffering. Therefore, NZVI/Na-bent not only showed much higher removal efficiency of Ni(II) (98.5%) than the sum (48.8%) of those by bare NZVI removal (41.9%) and by Na-bent adsorption (6.9%), but also greatly enhanced the reduction efficiency of Ni(II) into Ni0 by facilitating the electron transfer from Fe0 core to the surface-adsorbed Ni(II). In general, the unique property of bentonites will provide effective solutions to support NZVI for enhancing the removal and transformation of various environmental contaminants.