nZVI Particles Research Articles

Redox-active rGO-nZVI nanohybrid-catalyzed chain shortening of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)

Per- and polyfluoroalkyl substances (PFASs) are exceptionally stable chemicals due to their strong CF bonds. Nanoscale zero-valent iron (nZVI) particles have the potential to remove and degrade PFASs through redox activity. In this study, we deposited nZVI onto two-dimensional reduced graphene oxide (rGO) nanosheets and tested these synthesized rGO-nZVI nanohybrid (NH) for the treatment of a mixture of short- and long-chain PFASs in water with and without H2O2. All PFASs were removed at a higher efficiency by the rGO-nZVI NH than by the parent materials rGO and nZVI. Notably, the long-chain PFASs were removed at a faster rate than the short-chain PFASs. After a 10 min exposure to the rGO-nZVI NH without H2O2, the long-chain PFASs (perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)) were removed by 85 % and 39 %, respectively, while short-chain PFASs (perfluoropentane sulfonic acid and perfluoropentanoic acid) were removed by 19 % and 18 %, respectively. The addition of H2O2 enhanced the PFAS treatment performance by 10–18 %, which can be attributed to the generation of reactive oxygen species by the rGO-nZVI NH. Liquid chromatography high-resolution mass spectrometry analysis confirmed the formation of unique shorter chain and partially defluorinated PFAS-Fe complexes from both PFOS and PFOA.

Performance of lead ion removal by the three-dimensional carbon foam supported nanoscale zero-valent iron composite

The tendency to agglomeration and the difficulty in recycling of nano-zero-valent iron (nZVI) has been a major gap hindering its practical utilization. In this study, for the first time, nZVI particles were immobilized on carbon foam (CF) with a macroscopic three-dimensional (3D) network structure through an annealing process following NaBH4 reduction. The as-fabricated CF-nZVI exhibit a superior adsorption capacity of 335.4 mg g−1 for Pb2+ (conditions: 10 mg, 200 mg L−1, 25 °C and pH = 6), which is associated with the abundant adsorption sites (functional groups, i.e. –OH and –COOH) and effective mass transfer resulted from the interconnected porous network structure. The adsorption of Pb2+ by CF-nZVI can be described by the Langmuir isotherm adsorption model with R2 of 0.980, following the pseudo second-order kinetics with a linear correlation coefficient R2 of 0.988. A combination of multiple nanoparticles forms a novel vinca-like structure, which demonstrates a good dispersibility and avoids the massive reunion of nZVI. Given that advantages including low cost, excellent adsorption capacity and the facile separation of 3D porous monolith, CF-nZVI composites can be selected as a potential candidate for environmental remediation.

Single-loop octane enrichment.

The tendency to agglomeration and the difficulty in recycling of nano-zero-valent iron (nZVI) has been a major gap hindering its practical utilization. In this study, for the first time, nZVI particles were immobilized on carbon foam (CF) with a macroscopic three-dimensional (3D) network structure through an annealing process following NaBH4 reduction. The as-fabricated CF-nZVI exhibit a superior adsorption capacity of 335.4 mg g−1 for Pb2+ (conditions: 10 mg, 200 mg L−1, 25 °C and pH = 6), which is associated with the abundant adsorption sites (functional groups, i.e. –OH and –COOH) and effective mass transfer resulted from the interconnected porous network structure. The adsorption of Pb2+ by CF-nZVI can be described by the Langmuir isotherm adsorption model with R2 of 0.980, following the pseudo second-order kinetics with a linear correlation coefficient R2 of 0.988. A combination of multiple nanoparticles forms a novel vinca-like structure, which demonstrates a good dispersibility and avoids the massive reunion of nZVI. Given that advantages including low cost, excellent adsorption capacity and the facile separation of 3D porous monolith, CF-nZVI composites can be selected as a potential candidate for environmental remediation.

Interactions of iron-based nanoparticles with soil dissolved organic matter: adsorption, aging, and effects on hexavalent chromium removal

The interactions and mechanisms between soil dissolved organic matter (DOM) and three types of iron-based nanoparticles (NPs), i.e., nanoscale zero-valent iron (nZVI) particles, Fe2O3 NPs, and Fe3O4 NPs, were investigated in short-term exposure experiments. The adsorption results showed that soil DOM was rapidly adsorbed on the surface of the iron-based NPs with the adsorption rate varying according to Fe3O4 > Fe2O3 > nZVI. Spectral analysis results revealed that aromatic DOM fractions with high-molecular-weights were preferentially adsorbed. The binding mechanism was determined as hydrogen bonding and ligand exchange via Fourier transform infrared spectroscopy (FT-IR) analysis. Scanning electron microscopy, FT-IR, X-ray photoelectron spectroscopy, and X-ray diffraction were used to identify the corrosion products of the three iron-based NPs at the adsorption equilibrium. The results suggest that Fe3O4 and/or γ-Fe2O3 and α-FeOOH were the main corrosion products of nZVIs and α-FeOOH was obtained as an aged product of Fe3O4 NPs. Results of Cr(VI) removal tests suggest that the aged nZVI achieved 79.87% of Cr(VI) removal and the Cr(VI) removal efficiency was significantly improved by coating DOM onto Fe2O3 NPs. The overall data indicate the fate and transformation of iron-based NPs and the enhancement for Cr(VI) removal after interactions between DOM and NPs.

Stabilization of cadmium in polluted soil using palygorskite-coated nanoscale zero-valent iron

The palygorskite-coated nanoscale zero-valent iron (PAL-nZVI) was synthesized and used in the remediation of Cd-contaminated soils. The function of PAL-nZVI on fraction of Cd in soils, the growth, Cd translocation, and accumulation in corn (Zea mays L.) were investigated using a pot experiment. Cd-contaminated soils were amended with palygorskite, nanoscale zero-valent iron (nZVI), and PAL-nZVI (with varying mass ratios between PAL and nZVI) and with no amendment as control. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the changes in both the surface and the structure of stabilizers. CaCl2-extractable and toxicity characteristic leaching procedure (TCLP)-extractable Cd were measured in order to estimate the bioavailability and the stabilization efficiency. The Community Bureau of Reference (BCR) sequential extraction method was applied to evaluate the speciation change of Cd in soils stabilized by nZVI, PAL, and PAL-nZVI with different coating mass ratios of PAL to nZVI. The Cd accumulation in root and shoot fresh weight was measured to assess the stabilization efficiency. SEM and XRD indicated that nZVI particles were distributed uniformly and well fixed on the surface of palygorskite. After adding PAL-nZVI, the pH value of soil increased by 1 pH unit; CaCl2-extractable Cd decreased from 2.24 to 0.95 mg/kg; the residual Cd increased by 23.06% after 30-day incubation. The fresh weight of corn reached 43.02 g/plant, and the Cd contents in roots and shoots achieved minimum values of 1.50 and 0.73 mg/kg, respectively, when applying PAL-nZVI composite with a coating mass ratio of 2:1. The application of PAL-nZVI decreased the bioavailability and mobility of Cd in soils effectively. The stabilization showed a better effect when applying PAL-nZVI in Cd-contaminated soils than applying nZVI alone. Hence, it was a feasible and potential material that could be applied to amend the Cd-contaminated soil effectively, which would have a high and valuable utilization in field applications.

Sulfidated nano-scale zerovalent iron is able to effectively reduce in situ hexavalent chromium in a contaminated aquifer

In a number of laboratory studies, sulfidated nanoscale zero-valent iron (S-nZVI) particles showed increased reactivity, reducing capacity, and electron selectivity for Cr(VI) removal from contaminated waters. In our study, core-shell S-nZVI particles were successfully injected into an aquifer contaminated with Cr(VI) at a former chrome plating facility. S-nZVI migrated towards monitoring wells, resulting in a rapid decrease in Cr(VI) and Crtot concentrations and a long-term decrease in groundwater redox potential observed even 35 m downstream the nearest injection well. Characterization of materials recovered from the injection and monitoring wells confirmed the presence of nZVI particles, together with iron corrosion products. Chromium was identified on the surface of the recovered iron particles as Cr(III), and its occurrence was linked to the formation of insoluble chromium-iron (oxyhydr)oxides such as CrxFe(1−x)(OH)3(s). Injected S-nZVI particles formed aggregates, which were slowly transformed into iron (oxyhydr)oxides and carbonate green rust. Elevated contents of Fe0 were detected even several months after injection, indicating good S-nZVI longevity. The sulfide shell was gradually disintegrated and/or dissolved. Geochemical modelling confirmed the overall stability of the resulting Cr(III) phase at field conditions. This study demonstrates the applicability of S-nZVI for the remediation of a Cr(VI)-contaminated aquifer.

Catalytic degradation of ranitidine using novel magnetic Ti3C2-based MXene nanosheets modified with nanoscale zero-valent iron particles

Magnetic nanoscale zero-valent iron (nZVI)@Ti3C2-based MXene nanosheets were synthesized via an in-situ reductive deposition method, and were characterized as a novel Fenton-like catalyst for ranitidine degradation. The vast majority of ranitidine was found to be mineralized after 30 min of reaction time with 91.1 % of removal efficiency and the removal of 63.3 % of total organic carbon (TOC). Results showed that the nZVI@Ti3C2-based MXene nanosheets had a synergistic effect enhancing the catalyst chemical reactivity and stability. In particular, Ti3C2-based MXene was found to restrain the agglomeration of nZVI particles (nZVIPs) and promote electron transfer between magnetic particles with a diameter of approximately 10−40 nm. Ranitidine molecules were decomposed mainly by hydroxyl radicals (∙OH) attack especially the surface-bound ∙OHads. This study provided a completely new insight into the mode of surface inactivation of nZVIPs under different solution pH conditions, establishing that this novel catalyst was suitable for use under a wide pH range.

Experimental Study of the Relationship Between Dissolved Iron, Turbidity, and Removal of Cu(II) Ion From Aqueous Solutions Using Zero-Valent Iron Nanoparticles

In this study, nanoscale zero-valent iron has been prepared through the reduction method by sodium borohydride and then was used for removal of Cu(II) from aqueous solutions. The XRD analysis proved the high crystallinity of synthesized nZVI particles, and the calculated particle size was found to be 72 nm, which corresponds to a specific surface area of 10.68 m2/kg. The SEM analysis provided images about the morphologies of nZVI particles before/after Cu(II) adsorption, which revealed that the nZVI particles are spherical and tend to aggregate together in chain-like agglomerates. Besides, after Cu(II) adsorption, the SEM image evidenced a disparity in the structure of nZVI particles. The mineral composition of nZVI particles before/after Cu(II) adsorption was examined using XRF, which demonstrated that the nZVI particles were mainly composed of iron metal by up to 74.16%, and further proved the successful adsorption for Cu(II) onto nZVI particles. Kinetics, isotherms, and thermodynamics studies were showed that the adsorption process obeyed the pseudo-second-order, well-fitted to monolayer Langmuir isotherm with a maximum adsorption capacity of 54.35 mg/g, and have endothermic spontaneously nature, respectively. Both the released dissolved iron ions and the yielded turbidity that co-occurred along with the nZVI/Cu reaction were monitored. The dissolved iron concentrations recorded the highest value reached up to 106.3 mg/L at pH 1.0, while the turbidity dramatically increased to 32, and 35 NTU with increases in nZVI dosages and initial Cu(II) ion concentrations, respectively. Finally, some explanations have been suggested to represent the Cu(II) ion removal mechanisms onto nZVI particles.

Remediation of Lead and Nickel Contaminated Soil Using Nanoscale Zero-Valent Iron (nZVI) Particles Synthesized Using Green Leaves: First Results

Nanoscale zero-valent iron (nZVI) particles have proved to be effective in the remediation of chlorinated compounds and heavy metals from contaminated soil. The present study aimed to analyze the performance of nanoparticles synthesized from low-cost biomass (green leaves) as chemical precursors, namely Azadirachta indica (neem) and Mentha longifolia (mint) leaves. These leaves were chosen because huge amounts of them are present in the region of Vellore. These nanoparticles were used to remove lead and nickel from contaminated soil. Characterization of nZVI particles was conducted using the Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Brunauer–Emmett–Teller isotherm (BET) techniques. Remediation was performed on two different soil samples, polluted with lead or nickel at an initial metal concentration around 250 mg/kg of soil. The results revealed that after 30 days, the lead removal efficiency with 0.1 g of nZVI particles/kg of soil was 26.9% by particles synthesized using neem leaves and 62.3% by particles synthesized using mint leaves. Similarly, nickel removal efficiency with 0.1 g of particles/kg of soil was 33.2% and 50.6%, respectively, by particles using neem and mint leaves. When the nanoparticle concentration was doubled, Pb and Ni removal improved, with similar trends obtained at a lower dosage (0.1 g of particles/kg of soil). These first results evidenced that: (1) the nZVI particles synthesized using green leaves had the potential to remove Pb and Ni from contaminated soil; (2) the neem-derived particles gave better Ni removal efficiency than Pb one; (3) the mint-derived particles showed better Pb removal efficiency than Ni one; (4) the highest removal efficiency for both metals was achieved with the mint-derived particles; (5) double higher dosage did not greatly improve the results.

Nanoscale zero-valent iron-modified PVDF membrane prepared by a simple filter-press coating method can robustly remove 2-chlorophenol from wastewater

Abstract In recent years, nanoscale zero-valent iron (nZVI) has been considered an appealing alternative for halogenated organic compound removal for its advantages, such as its high activity. However, easy aggregation limits nZVI activity. In this study, functional nZVI-modified PVDF membranes (nZVI@PVDF membranes) were successfully prepared by a simple and easy-to-follow filter-press coating method and was applied in the ultrafiltration process to treat 2-chlorophenol (2-cp) wastewater. Scanning electron microscopy showed that nZVI particles were relatively uniformly distributed on the membrane surface and formed a fluffy and porous space-stacked structure. 2-cp ultrafiltration degradation results illustrated that nZVI@PVDF membranes revealed good 2-cp removal efficiencies ranged from 56.06% to74.62%. These 2-cp removal efficiencies were higher than those for Fe supported on powder materials and were relatively comparable to those for nZVI composite membranes prepared by complex methods (e.g., blend spinning and cross-linking methods). Furthermore, the 2-cp degradation efficiencies by nZVI@PVDF membranes were not affected much in the presence of natural organic matter and different ions, demonstrating a robust anti-interference ability of nZVI@PVDF membrane. The mechanism underlying its robust performance likely resulted from that nZVI was uniformly distributed and loaded layer by layer on the PVDF membrane surface with high loading capacity, which guaranteed high nZVI activity, layer-layer interception of pollutants and complete reaction between nZVI and pollutants. These findings provide key insights into how nZVI@PVDF membranes could be integrated into the treatment of wastewater containing refractory pollutants.

Does soluble starch improve the removal of Cr(VI) by nZVI loaded on biochar?

A novel material that nano zero valent iron (nZVI) loaded on biochar with stable starch stabilization (nZVI/SS/BC) was synthesized and used for the removal of hexavalent chromium [Cr(VI)] in simulated wastewater. It was indicated that as the pyrolysis temperature of rice straw increased, the removal rate of Cr(VI) by nZVI/SS/BC first increased and then decreased. nZVI/SS/BC made from biochar pyrolyzed at 600 °C (nZVI/SS/BC600) had the highest removal efficiency and was suitable for a wide pH range (pH 2.1–10.0). The results showed that 99.67% of Cr(VI) was removed by nZVI/SS/BC600, an increase of 45.93% compared to the control group, which did not add soluble starch during synthesis. The pseudo-second-order model and the Langmuir model were more in line with reaction. The maximum adsorption capacity for Cr(VI) by nZVI/SS/BC600 was 122.86 mg·g−1. The properties of the material were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) mapping, Brunauer-Emmett-Teller (BET), Fourier-transform infrared (FTIR), and X-ray diffraction (XRD). The results showed that the nZVI particles were uniformly supported on the biochar, and the BET surface areas of nZVI/SS/BC was 40.4837 m2·g−1, an increase of 8.79 times compared with the control group. Mechanism studies showed that soluble starch reduced the formation of metal oxides, thereby improving the reducibility of the material, and co-precipitates were formed during the reaction. All results indicated that nZVI/SS/BC was a potential repair material that can effectively overcome the limitations of nZVI and achieve efficient and rapid repair of Cr(VI).

Assessment of sulfamethoxazole removal by nanoscale zerovalent iron

Removal of pharmaceutical compounds, such as sulfamethoxazole (SMX) from the aquatic environments, is critical in order to mitigate their adverse environmental and human health effects. In this study, the effectiveness of nanoscale zerovalent iron (nZVI) particles for the removal of SMX was investigated under varying conditions of initial solution pH (3, 5, 7 and 11) and nZVI to SMX mass ratios (1:1, 5:1, 10:1, 13:1, 25:1). Batch kinetic studies, which were well represented using both pseudo-first-order and pseudo-second-order kinetic models (R2 > 0.98), showed that both solution pH and mass ratios strongly influenced SMX removal. At a fixed mass ratio of 10:1, removal efficiencies were higher in acidic conditions (83% to 91%) compared to neutral (29%) and alkaline (6%) conditions. A similar trend was observed for removal rates and removal amounts. For mass ratios between 1:1 and 10:1, an optimum pH existed (pH 5) wherein highest removal efficiencies were attained. Increasing the mass ratio above 10:1 resulted in virtually complete removal efficiencies at pH 3 and 5, and 70% at pH 7. Analysis of SMX speciation and zeta potential of nZVI particles provided insights into the role of pH on the efficiencies, rates and extents of SMX removal. Total organic carbon analysis and mass spectrometry measurements of SMX solution before and after exposure to nZVI particles suggested the transformation of SMX via redox reactions, which are likely the dominant process compared to adsorption. Five transformation products were observed at m/z 156 (TP1), 192 (TP2), 256 (TP3), 294 (TP4) and 296 (TP5). TP1, TP2 and TP3 were further identified using ion fragment analysis. Overall, results from this study indicate a strong potential for SMX removal by nZVI particles, and could be useful towards identifying reaction conditions for optimum SMX transformation.

Photocatalytic degradation of Congo Red under UV irradiation by zero valent iron nano particles (nZVI) synthesized using Shorea robusta (Sal) leaf extract.

In the present study, photo catalytic degradation of azo dye Congo Red was conducted using Fe nano particles (nZVI) in the presence of UV light. nZVI was biosynthesized using FeSO4.7H2O precursor and leaf extract of Shorea robusta (sal) as reducing agent under optimum condition of 1 mM concentration of precursor and a ratio of 1:1 Sal leaf extract to precursor. TEM and AFM images revealed formation of well dispersed spherical nano particles of 54-80 nm. SAED patterns of nZVI particles indicated its crystalline nature, while EDX result showed the presence of iron as the most abundant element. In batch experiments, optimum degradation of CR was 96% at 220 ppm CR with a dose of 1.2 g/L nZVI at pH 4 in 15 min following pseudo second order kinetics. The study suggested nZVI to be a potentially economic and ecofriendly technique for treatment of Congo Red.

Nitrate removal in potable groundwater by nano zerovalent iron under oxic conditions

Abstract Groundwater pollution by nitrate contamination has become a significant issue in some areas of Sri Lanka, giving rise to health concerns and a dearth in good quality potable water. In this study, the effectiveness of nano zerovalent iron (nZVI) for the removal of nitrate in potable groundwater under oxic conditions was investigated to meet the drinking water quality standards stipulated by World Health Organization (WHO) and Sri Lanka Standards Institution (SLSI) (nitrate level <50 mg/L). Under oxic conditions, the nZVI was synthesized and batch experiments were conducted using an artificial nitrate (150 mg/L) contaminated water sample. Our results corroborated that with an optimum nZVI dose of 1 g/L and optimum contact time of 30 minutes, 80% nitrate removal could be achieved and the remaining nitrate level was ≈ 30 mg/L as nitrate (<50 mg/L), which was equivalent to ≈ 7 mg/L as nitrate–N (≈21% of the total–N). Ammonium ions were the main product of nitrate reduction by nZVI and at 30 minutes contact time, ≈ 20 mg/L of ammonium as ammonium–N was detected (≈ 59% of the total–N). Ammonia stripping took place under the basic solution pH (pH > 9.5). At 30 minutes of contact time, ≈7 mg/L of ammonia as ammonia–N was accounted for ammonia stripping, which is 20% of the total–N. Ammonia stripping resulted in a decrease in nitrogen-containing species in the aqueous phase. The spent nZVI particles were recovered (99.9%) from the treated water using an external magnetic field. In conclusion, nZVI particles synthesized under oxic conditions are viable to successfully treat the nitrate-contaminated groundwater under aerobic conditions to reduce the nitrate levels to meet the WHO/SLSI drinking water quality standards.

The overlooked role of carbonaceous supports in enhancing arsenite oxidation and removal by nZVI: Surface area versus electrochemical property

Carbonaceous supports (e.g. biochar) have been widely applied to enhance the performance of nanoscale zero-valent iron (nZVI) for removing heavy metals (e.g. arsenic; As) due to their large surface areas (SSA) to alleviate nZVI particles aggregation, while their electrochemical properties are largely overlooked. Herein, the role of these two characteristics in enhancing As(III) removal has been systematically investigated through designing two parallel experiments to identify the effects of the two characteristics of biochar. Our results suggest that biochar with varying surface areas (33.38–470.36 m2/g) supported nZVI exhibits a substantially higher the As(III) oxidation rate (29.7–34.3%) and removal [295.5–371.5 mg/(g·nZVI)] efficiency compared to that by nZVI [27.1%; 192.7 mg/(g·nZVI)]. Despite the importance of SSA, the biochar with extremely low SSA of 33.38 m2/g appears to have comparable capacity of enhancing nZVI’s performance with a nZVI loading up to 50%. On the contrary, electrochemical analysis suggests that the oxidation and removal of As(III) are highly related to the electron accepting capacity of biochar, indicating a strong electrochemical effect of biochar in As(III) removal varying with pyrolysis temperature. Surface quinone moieties are found responsible for enhancing electron transfer between biochar [up to 0.25 mmol e·(g biochar)−1] and nZVI, promoting nZVI corrosion and the generation of reactive oxygen species (ROS; mainly ·O2-) for enhancing the As(III) oxidation and removal. These findings highlight the important role of electrochemical properties of carbonaceous supports rather than SSA in developing nZVI-based materials for further improving heavy metals removal.

The role of cellulose nanocrystals in stabilizing iron nanoparticles

Iron nanoparticles are strong reducing agents with a variety of applications. Their reactivity is governed by their valence state as well as their available surface. As such their widespread use is limited by their colloidal instability. This work investigated the role of cellulose nanocrystal stabilizers on the shape, size, density, and colloidal stability of iron nanoparticles. Colloidally-stable zero-valent iron nanoparticles (nZVI) were synthesized through a classical redox reaction of iron sulfate using cellulose nanocrystals (CNCs) as stabilizers. Spherical nZVI nanoparticles were formed with high surface roughness and mean size of ~ 130 nm. CNC:nZVI nanoparticles made with greater amounts of CNCs were measured to have lower solidity, indicating that these nanocomposite nanoparticles are less compact. Low solidity nanoparticles were observed to be irregular aggregates composed of ~ 10 nm nZVI particles stabilized on CNCs. CNC:nZVI nanoparticles remained colloidally stable after more than 40 days. Mobility studies confirmed both their colloidal stability under flow conditions as well as the strong interaction between CNCs and nZVI as demonstrated by achieving over 97% breakthrough within 2 pore volumes and no measurable particle retention, respectively. It was hypothesized that cellulose nanocrystals play a triple role in nZVI stability: as a foreign surface to encourage stable nucleation over fast aggregation, as a capping agent to control particle growth, and as a stabilizer to prevent iron nanoparticles from aggregating into colloids. Our results highlight the impact of the presence of CNCs on the rates of nucleation, growth, aggregation, and aging of nZVI particles, demonstrating that CNCs have the potential to act as nZVI stabilizers.

Drastically inhibited nZVI-Fenton oxidation of organic pollutants by cysteine: Multiple roles in the nZVI/O2/hv system

The influence of l-cysteine, a common aliphatic amino acid, on the zero-valent iron (nZVI)/O2 photo-Fenten degradation of rhodamine B (RhB) was investigated in this study. The oxidation rate of RhB in the nZVI/O2/hv system was 91.2% after 40 min under the illumination and oxygen conditions and pH of 3, but when cysteine was introduced into the system, the oxidization process was inhibited. The removal of RhB was only about 50% after 40 min at a cysteine concentration ≥50 μM. It was shown experimentally that, under dark conditions, only 40.5% and 19.8% RhB was removed by the nZVI/O2 and nZVI/O2/cysteine systems, respectively. Electron paramagnetic resonance (EPR) and iron dissolving experiments revealed that the addition of cysteine clearly reduced the production of hydroxyl radicals (OH) and Fe2+ and Fe3+. In addition, Fourier transform infrared spectroscopy (FTIR) demonstrated that cysteine could form hydrogen bonds on the iron surface. These results indicated that the main inhibition mechanism of cysteine was the alleviation of the oxidation of nZVI to Fe2+ and Fe3+ through wrapping the nZVI particles. Moreover, cystine (the oxidized form of CYS) could partly react with OH to regenerate cysteine, which resulted in competition with RhB for OH. Another possible reason for the inhibitory effect of cysteine was the prevention of light utilization. These findings indicate a non-negligible inhibitory trait for heterogeneous Fenton process in wastewater treatment when amino acids are present.

Green Synthesis of Kaolin-Supported Nanoscale Zero-Valent Iron Using Ruellia tuberosa Leaf Extract for Effective Decolorization of Azo Dye Reactive Black 5

Kaolin-supported nanoscale zero-valent iron (K-NZVI) was synthesized via a green synthesis method, in which leaf extract of Ruellia tuberosa was used as a reducing agent. The synthesized K-NZVI was used for decolorization of Reactive Black 5 (RB5), an azo dye widely used in textile industry. The XRD patterns of the K-NZVI particles show the characteristic peaks of Fe0, indicating that Fe0 nanoparticles (NZVI) were successfully synthesized on the kaolin surface. The SEM, TEM images and EDS elemental mapping show that the NZVI particles are well dispersed on the kaolin surface, thus, reducing the extent of NZVI aggregation. Batch experiments for decolorization of RB5 were carried out to investigate the effects of process parameters including solution pH, initial dye concentration and contact time. The results show that high decolorization efficiencies are obtained in acidic pH. Increasing initial dye concentration causes the decolorization efficiency to decrease, whereas increasing contact time results in higher efficiency. Furthermore, after five cycles of reuse of K-NZVI, the decolorization efficiency slightly decreases, indicating high reusability and stability of K-NZVI. The disappearance of the characteristic peaks of RB5 solution recorded by a UV–Vis spectrophotometer indicates cleavage of the azo bonds and, thus, the decomposition of RB5 in the solution. From a kinetic analysis performed at various RB5 concentrations, the decolorization process of RB5 by K-NZVI is well fit by the pseudo-first-order kinetic model.

Removal of hexavalent chromium from aqueous solution by fabricating novel heteroaggregates of montmorillonite microparticles with nanoscale zero-valent iron

This study fabricated novel heteroaggregates of montmorillonite (Mt) microparticles with nanoscale zero-valent iron (nZVI) (Mt-nZVI) and examined the removal of Cr(VI) by the Mt-nZVI through batch experiments. Spherical nZVI particles were synthesized by the liquid phase reduction method, which were then attached on the flat Mt surfaces in monolayer. The fabricated Mt-nZVI had similar removal efficiency for Cr(VI) compared to the monodispersed nZVI particles, but was much greater than that of nZVI aggregates. The removal efficiency of Mt-nZVI increased with decreasing its dosage and increasing initial Cr(VI) concentration, whereas had insignificant change with solution pH. The removal of Cr(VI) by Mt-nZVI was well described by the pseudo second-order kinetics and the Langmuir equilibrium model. The removal was spontaneous and exothermic, which was mainly due to chemsorption rather than intra-particle diffusion according to calculation of change in free energy and enthalpy and Weber–Morris model simulations. X-ray diffraction and X-ray photoelectron spectroscopy analysis revealed that the adsorption was likely due to reduction of Cr(VI) to Cr(III) by Fe(0) and co-precipitation in the form of oxide-hydroxide of Fe(III) and Cr(III). The fabricated Mt-nZVI showed the promise for in-situ soil remediation due to both high removal efficiency and great mobility in porous media.

Graphene-like carbon sheet-supported nZVI for efficient atrazine oxidation degradation by persulfate activation

Developing excellent carrier materials for supporting metal-based catalysts is challenging. Herein, a graphene-like carbon sheet (CS) was fabricated from a mixture of corn straw and potassium oxalate (K2C2O4) via a simple one-pot approach. The as-obtained sample possesses a 2D lamellar structure similar to graphene, which improves the specific surface area of the biochar. CS-supported nanoscale zero-valent iron (nZVI) composites (nZVI@CS) were designed to enhance atrazine removal by persulfate (PS) activation. The removal efficiencies of nZVI@CS-800 were higher than that of nZVI-PS, implying that the synergy between CS and nZVI was achieved and promoted the removal efficiency of atrazine. CS facilitates the dispersion of nZVI due to its vast SSA, which could prevent nZVI particles from self-aggregation. Simultaneously, the degradation may be by preferentially degrading the atrazine adsorbed on catalyst to promote adsorption. SO4− plays a more important role in the oxidative degradation of atrazine. CS can directly activate PS to generate SO4−, and as an electron shuttle, it can promote the conversion of Fe3+ to Fe2+ and improve the activity of the catalyst. The apparent mineralization rate of atrazine after reaction for 60 min is 38.65%, and degradation pathways include dealkylation, alkyl oxidation and dichlorination. Oxidative degradation of atrazine is favored at high temperature or low pH, while it is inhibited when the amount of PS or catalyst becomes excessive. And it may be impacted by organic compounds or anions in the environment. This study is of great significance for the practical application of nZVI@CS for in situ organic pollution remediation.