Degradation of scarlet 4BS in aqueous solution using bimetallic Fe/Ni nanoparticles

Highly improved dechlorination of 2,4-dichlorophenol in aqueous solution by Fe/Ni nanoparticles supported by polystyrene resin

2,4-dichlorophenol (2,4-DCP) is a typical chlorophenol that has been widely used in industrial production and caused serious pollution to the environment. In this study, the performance of Fe/Ni bimetallic nanoparticles supported on polystyrene cation exchange resin (Fe/Ni-D072) to remove 2,4-DCP was evaluated. The effects including the doping amount of Ni, the dosage of Fe/Ni-DCP, the initial concentration of 2,4-DCP, and pH value of the solution on the removal efficiency were also investigated. The results showed that when the initial concentration of 2,4-DCP was 20 mg/L and pH = 7.3, 90% of 2,4-DCP could be dechlorinated by Fe/Ni-D072 (Ni% = 30 wt%, dosage: 6.7 g/L) after 12 h reaction. The dechlorination process followed a pseudo-first-order model, and the reaction constant was 0.252 h^-1. In addition, the effects of humic acid and common coexisting ions on dechlorination were studied. The results showed that humic acid with a low concentration (5 mg/L) and CO₃^2- restrained the degradation of 2,4-DCP. The dechlorination products of 2,4-DCP were identified by HPLC and the result showed phenol was the main product with a slight amount of 2-CP as the dechlorination intermediate, and 4-CP was barely detected. These results suggest that Fe/Ni-D072 was a promising catalytic material for the removal of chlorophenol and has great application prospects in groundwater remediation.

Application of iron/aluminum bimetallic nanoparticle system for chromium-contaminated groundwater remediation

When the nanoscale zero valent iron (nZVI) is used for the reduction of hexavalent chromium (Cr⁶⁺) to trivalent chromium (Cr³⁺) in groundwater, the reduction efficiency is decreased due to the passivation of reactive sites by precipitation. The bimetallic nanoparticle (BNP) can be created with the addition of the second metal to achieve a higher activity and reduce the occurrence of the ferrous/ferric hydroxide precipitation. In this study, the iron-coated aluminum (Fe/Al) BNP and aluminum-coated iron (Al/Fe) BNP systems were designed for remediating Cr⁶⁺-contaminated groundwater. The chemical liquid-phase deposition and co-reduction method was applied to produce BNPs. Cr⁶⁺ removal rate by Fe/Al BNPs was directly proportional to the saturation concentration and reactive sites, which caused a higher Cr⁶⁺ removal rate. The pseudo-first-order kinetic model could be used to describe the Cr⁶⁺ adsorption mechanism by Fe/Al BNPs. Results show that Fe/Al BNPs and Al/Fe BNPs could reduce Cr⁶⁺ to Cr³⁺, and the removal efficiencies for Cr⁶⁺ were 1.47 g/g BNP and 0.07 g/g BNP, respectively. Detection of Cr³⁺ in the aqueous phase was observed during the Cr⁶⁺ removal process. Results from X-ray diffraction (XRD) analysis confirmed that Cr(OH)₃ was present on the surface of BNPs. Main mechanisms caused Cr⁶⁺ removal included reduction, precipitation, and adsorption. The reduction of Cr⁶⁺ produced OH^-, which created alkaline environment and facilitated the formation of chromium hydroxide precipitates [Cr(OH)₃]. Thus, the migration of Cr³⁺ was prevented and the environmental risk was reduced. BNP had a higher activity and stability, and it was applicable for Cr⁶⁺-contaminated site remediation.

Zero-Valent Iron Nanoparticles for Soil and Groundwater Remediation

Zero-valent iron has been reported as a successful remediation agent for environmental issues, being extensively used in soil and groundwater remediation. The use of zero-valent nanoparticles have been arisen as a highly effective method due to the high specific surface area of zero-valent nanoparticles. Then, the development of nanosized materials in general, and the improvement of the properties of the nano-iron in particular, has facilitated their application in remediation technologies. As the result, highly efficient and versatile nanomaterials have been obtained. Among the possible nanoparticle systems, the reactivity and availability of zero-valent iron nanoparticles (NZVI) have achieved very interesting and promising results make them particularly attractive for the remediation of subsurface contaminants. In fact, a large number of laboratory and pilot studies have reported the high effectiveness of these NZVI-based technologies for the remediation of groundwater and contaminated soils. Although the results are often based on a limited contaminant target, there is a large gap between the amount of contaminants tested with NZVI at the laboratory level and those remediated at the pilot and field level. In this review, the main zero-valent iron nanoparticles and their remediation capacity are summarized, in addition to the pilot and land scale studies reported until date for each kind of nanomaterials.

A new insight into the main mechanism of 2,4-dichlorophenol dechlorination by Fe/Ni nanoparticles

Three possible dechlorination mechanisms of chloroorganics by nanoscale zero-valent iron (n-ZVI) have been proposed and widely accepted, however, the main mechanism is still controversial and not verified by experimental results. In this study, 2,4-dichlorophenol (2,4-DCP) was selected as the target pollutant and the experiments were carried out for the screening of the main mechanism of 2,4-DCP dechlorination by n-ZVI and Fe/Ni nanoparticles (n-Fe/Ni). The results indicated that >95% of 2,4-DCP could be dechlorinated to phenol by n-Fe/Ni within 120 min, while 2,4-DCP could hardly be dechlorinated by n-ZVI particles. The active hydrogen atom (H*) that transformed from H₂ under the catalysis of Ni was responsible for >90% of 2,4-DCP dechlorination by n-Fe/Ni and <10% of the dechlorination was attributed to the direct electron transfer from ZVI. Fe²⁺ was not able to dechlorinate 2,4-DCP. Correspondently, Ni in n-Fe/Ni mainly acted as a catalyst, while the acceleration of electron transfer from ZVI by Ni had a positive effect on 2,4-DCP dechlorination. The investigations on the relative importance of these three mechanisms are essential to iron-based remediation technology.

Synthesis of nanoscale zero-valent iron loaded chitosan for synergistically enhanced removal of U(VI) based on adsorption and reduction

In this study, chitosan (CS) loading well-dispersed nanoscale zero-valent iron (NZVI/CS) was successfully prepared via the liquid-phase reduction method. Characterizations of the NZVI/CS with high-resolution transmission electron microscopy and X-ray diffraction suggested that the as-prepared NZVI/CS comprised numerous dispersed Fe⁰ nanoparticles. Synergistic adsorption and reduction occurred during the removal process based on X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Influence of pH, contract time and temperature on U(VI) removal were investigated. The high removal capacity and rapid removal kinetics were predominately ascribed to the existence of well-distributed NZVI, which could rapidly reduce U(VI) into U(IV). The removal process could be better depicted by the Langmuir isotherm model and the pseudo-second-order kinetic model. The thermodynamic parameters showed that the removal process was exothermic. These findings indicate that the synthesized NZVI/CS composites have potential application for the removal of U(VI) from the sewage water.

The humic acid influenced the behavior and reactivity of Ni/Fe nanoparticles in the removal of deca-brominated diphenyl ether from aqueous solution

The removal of contaminants by iron-based nanomaterials was inevitably affected by the natural organic matter (NOM), which is one of the most abundant material on earth and exists in natural waters. This study was performed to investigate the main influence of humic acid (HA, representing NOM) on the behavior and reactivity of Ni/Fe nanoparticles in the removal of deca-brominated diphenyl ether (BDE209). Generally, the inhibitory effect of HA on the removal of BDE209 by Ni/Fe showed greater significance with an increase of HA concentration. The zeta potential and sedimentation experiments showed that the HA enhanced the dispersion and stabilization of Ni/Fe particles; however, the removal of BDE209 was found to be inhibited. Moreover, the corrosion capacity of the Ni/Fe nanoparticles showed a positive correlation with the effect of HA on the reactivity of Ni/Fe nanoparticles. Meanwhile, typical quinone compounds in HA had an adverse effect on the removal of BDE209. Additionally, the competitive adsorption experiments and characterization illustrated that the adsorption of HA by Ni/Fe nanoparticles was superior to BDE209. Overall, it was proposed that the corrosion of Ni/Fe was reduced as the contact between the nanoparticles and H₂O was hindered due to the surface of Ni/Fe was occupied by the adsorbed HA, and thus inhibited the reactivity of Ni/Fe nanoparticles in the removal of BDE209.

Synergistic effect and degradation mechanism on Fe-Ni/CNTs for removal of 2,4-dichlorophenol in aqueous solution

Fe-Ni bimetallic nanoparticles supported on CNTs (Fe-Ni/CNTs) were synthesized, characterized, and applied for removal of 2,4-dichlorophenol (2,4-DCP) in aqueous solution. The removal performance was enhanced drastically on Fe-Ni/CNTs with respect to monometallic Fe/CNTs. The synergistic effect between Fe-Ni nanoparticles and CNTs has been studied in detail. The research results indicated that the doping of Ni played an important role in promoting the catalytic degradation of 2,4-DCP. And the presence of CNTs not only could effectively reduce the aggregation of nanoparticles but also facilitate the mass transfer of 2,4-DCP and the formation of active atomic hydrogen during the catalytic process. In addition, the removal kinetics of 2,4-DCP by Fe-Ni/CNTs were in agreement with a pseudo-first-order model, and the rate constants were dependent on a number of factors including the initial concentration of 2,4-DCP, the dosage of Fe-Ni/CNTs, pH value of the solution, and doping amount of Ni. The degradation mechanism involved the adsorption by CNTs and catalytic reduction by Fe under the stimulating of Ni, and the preferred dechlorination followed the order of para-Cl > ortho-Cl. The study confirmed that Fe-Ni/CNTs had a potential to be a promising catalytic material for removal of chlorophenol and had a great prospect for practical application.

Core–shell magnetic nano-powders with an excellent decolorization effect on dye wastewater

In recent years, zero-valent nano-iron (nZVI) has received extensive attention due to its excellent decolorization effect on dye wastewater. In this paper, zero-valent nano-iron-nickel (nZVIN) powders were prepared by a simple, efficient and non-polluting method. The powder has a unique core–shell structure and excellent oxidation resistance. Hence the problem that nZVI powders are easily oxidized and difficult to store is solved. Due to the addition of Ni, the magnetic properties of the nZVIN powders are enhanced, which facilitates the recycling of the powders using a magnetic field after sewage treatment. In the decolorization treatment of dye wastewater simulated with Congo red (CR) dye, nZVIN powders can maintain a removal rate of more than 90% for CR solutions with different pH values (7.0–11.5) and an initial dye concentration (50–200 mg L⁻¹). The research results show that nZVIN powders have broad application prospects in the treatment of azo dye wastewater.

In recent years, zero-valent nano-iron (nZVI) has received extensive attention due to its excellent decolorization effect on dye wastewater.

Highly efficient removal of chromium(VI) by Fe/Ni bimetallic nanoparticles in an ultrasound-assisted system

Highly active Fe/Ni bimetallic nanocomposites were prepared by using the liquid-phase reduction method, and they were proven to be effective for Cr(VI) removal coupled with US irradiation. The US-assisted Fe/Ni bimetallic system could maintain a good performance for Cr(VI) removal at a wide pH range of 3-9. Based on the characterization of the Fe/Ni nanoparticles before and after reaction, the high efficiency of the mixed system could attribute to the synergistic effects of the catalysis of Ni(0) and US cavitation. Ni(0) could facilitate the Cr(VI) reduction through electron transfer and catalytic hydrogenation. Meanwhile, US could fluidize the Fe/Ni nanoparticles to increase the actual reactive surface area and clean off the co-precipitated Fe(III)-Cr(III) hydroxides to maintain the active sites on the surface of the Fe/Ni nanoparticles. Thus, compared with shaking, the US-assisted Fe/Ni system was more efficient on Cr(VI) removal, which achieved 94.7% removal efficiency of Cr(VI) within 10 min. The pseudo-first-order rate constant (kobs) in US-assisted Fe/Ni system (0.5075 min(-1)) was over 5 times higher than that under shaking (0.0972 min(-1)). Moreover, the Fe/Ni nanoparticles still have a good performance under US irradiation after 26 days aging as well as regeneration.

Performance of iron nano particles and bimetallic Ni/Fe nanoparticles in removal of amoxicillin trihydrate from synthetic wastewater

In the present study, the degradation of amoxicillin trihydrate (AMT), using synthesized nanoscale zero-valent iron (nZVI) and bimetallic Fe and Ni nanoparticles stabilized with chitosan (Cs-Fe/Ni), in water was investigated. A central composite design combined with response surface methodology and optimization was utilized for maximizing the AMT reduction by the nanoparticles-water system. The importance of the various variables and their interactions were analyzed using analysis of variance and t-test. The effects of independent parameters were tested and the results showed that the initial concentration of AMT, pH, and nanoparticles dosage were all significant factors. Field-emission scanning electron microscopy images indicated that chitosan acts as a stabilizer preventing the agglomeration of nanoparticles. Also, chitosan and Ni increased the specific surface area of Cs-Fe/Ni. X-ray diffraction confirmed the existence of Fe(0) in fresh samples and the presence of Fe(II) and Fe(III) after the reaction with AMT. This study demonstrates that the nZVI technology could be a promising approach for antibiotic wastewater treatment.

Functional kaolinite supported Fe/Ni nanoparticles for simultaneous catalytic remediation of mixed contaminants (lead and nitrate) from wastewater

Kaolinite supported bimetallic Fe/Ni nanoparticles (K-Fe/Ni) demonstrated capacity for simultaneous removal of both cationic and anionic contaminants such as Pb (II) and NO3(-). The dispersion of Fe/Ni nanoparticles was improved when kaolinite was used as a stabilizer, and also enhanced the reactivity of K-Fe/Ni. The adsorption of Pb (II) onto the kaolinite and the consequent simultaneous catalytic reduction of Pb (II) and NO3(-) kaolinite were confirmed by SEM, BET, EDS, XRD and batch adsorption-reduction test. Orthogonal method showed that initial concentrations of Pb (II) and NO3(-), as well the dosage of K-Fe/Ni showed the most significant impact on the removal rates, where 86.3% of Pb (II) and 73.6% of NO3(-) was removed at optimized conditions. In addition, K-Fe/Ni could be stored for 15 days in dry air without losing reactivity. Reusability test of K-Fe/Ni indicated that the removal efficiency decreased by 12.5% for Pb (II) and 27.2% for NO3(-) after using 3 times successively. Two electroplating wastewater samples were tested and showed K-Fe/Ni could remove more than 96% of Pb (II) and NO3(-) under the optimized conditions.

Investigation of PAA/PVDF-NZVI hybrids for metronidazole removal: synthesis, characterization, and reactivity characteristics

For the first time, the removal process of metronidazole (MNZ) from aqueous solutions over nano zerovalent iron (NZVI) encapsulated within poly(acrylic acid) (PAA)/poly(vinylidene fluoride) (PVDF) membranes was reported. The resultant composite (PPN) demonstrated high reactivity, excellent stability and reusability over the reaction course. Such excellent performance might be attributed to the presence of the charged carboxyl groups in PVDF membrane support, which could enhance NZVI dispersion and improve its longevity. Results showed that a lower initial concentration and higher reaction temperature facilitated the removal of MNZ by PPN, and that the acidic and neutral conditions generally exhibited more favorable effect on MNZ removal than the alkaline ones. Kinetics of the MNZ removal by PPN was found to follow a two-parameter pseudo-first-order decay model well, and the activation energy of the MNZ degradation by PPN was determined to be 30.49kJ/mol. The presence of chloride ions slightly enhanced the reactivity of PPN with MNZ, whereas sulfate ions inhibited its reactivity. In addition, MNZ degradation pathways by PPN were proposed based on the identified intermediates. This study suggests that PPN composite possessing excellent performance may be a promising functional material to pretreat antibiotic wastewaters.

Impact of iron-based nanoparticles on microbial denitrification by Paracoccus sp. strain YF1

This study investigates the effects of Fe and Fe/Ni nanoparticles on biological denitrification when using Paracoccus sp. strain YF1. Results show that adding Fe and Fe/Ni nanoparticles to the cells decreased their growth and denitrification rate. Compared to that of free cells (control 89.47%), a decrease (64.33%) in the presence of 1000 mg/L Fe/Ni nanoparticles was observed, while a small decline in the denitrification rate (76.36%) was obtained when the concentration of Fe nanoparticles was 1000 mg/L. These were further confirmed by adding Fe(2+), Fe(3+), Fe3O4, Fe(2+)/Ni(2+) and Fe(3+)/Ni(2+) individually to the free cell system. Furthermore, Fe and Fe/Ni nanoparticles influenced the nitrate removal and bacterial growth under different pH and temperature conditions. SEM, XRD and EDS demonstrated that iron oxides formed as a result of nanoparticles corrosion in biological medium. Finally the presence of nanoparticles around some bacteria was observed.

Impact of Fe and Ni/Fe nanoparticles on biodegradation of phenol by the strain Bacillus fusiformis (BFN) at various pH values

The Bacillus fusiformis (BFN) strain and its biodegradation of phenol when iron-based nanoparticles such as nanoscale zero-valent iron (nZVI) and Ni/Fe nanoparticles (Ni/Fe) were present at different pH values (6.0, 8.0, and 3.0) were investigated. The growth of BFN and its biodegradation of phenol accelerated in the presence of nZVI and Ni/Fe both at pH 8.0 and pH 6.0. The H2 generated by the corrosion of iron can be used as an electron donor and source of energy for growing BFN. However, only nZVI improved the biodegradation of phenol at pH 3.0, which is most likely due to the increasing medium pH value resulting from the generation of OH(-) as a result of iron corrosion. The images from scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) demonstrated that these iron-based nanoparticles adhered to the surface of BFN, but no significant change in the morphology of BFN was observed.