Nano Zero-valent Iron Research Articles

Combination of polymer-stabilized nano zero-valent iron and biostimulated denitrifying bacteria for the removal of nitrate from groundwater

Polymer-stabilization of nano zero-valent iron (nZVI) is becoming a matter of research, although its effect on the reactivity towards targeted contaminants is not clear yet. Concurrently, combination of Abiotic Chemical Nitrate Reduction (ACNR) via nZVI and Heterotrophic Denitrification (HDN) to enhance nitrate (NO3−) removal and/or improve the end product distribution has also gained attention of researchers. The objective of this study was, on one hand, to compare the potential of nZVI stabilized with four different polymers (PAA, PAP, CMC or Tween80) to remove NO3− from groundwater via nZVI-mediated ACNR and, on the other hand, to assess the effect of combined supplementation of polymer-stabilized nZVI and acetate on NO3− reduction. The results showed that Tween80-stabilized nZVI over-performed those stabilized with PAA, PAP or CMC in removing NO3− from water. Furthermore, coupling Tween80 coated-nZVI and acetate enhanced both the overall NO3− removal (63%–95%) and the conversion of reduced NO3− to N2(g) (63%–80%) in comparison to when acetate or nZVI were applied alone (respectively 44%–62% and 30%–31%, with most of reduced NO3− converted to NO2− or NH4+). This study thus demonstrates that application of Tween80-stabilized nZVI has potential to make a significant contribution in remediating NO3−-contaminated groundwater.

Fabrication of Chitin microspheres supported sulfidated nano zerovalent iron and their performance in Cr (VI) removal

Sulfidated nanoscale zerovalent iron (S-nZVI) has been extensively studied for the reductive removal of Cr(VI), but its applicability is limited by agglomeration and unexpected efficiency reduction. In this study, chitin microsphere supported sulfidated nanoscale zero-valent iron (S-nZVI@Chi-M) was prepared by in-situ one-step reduction method and used to remove Cr(VI) from water. Compared to chitin and chitosan powder, Chi-M with nanofibrous structure and large surface area performed best in stabilizing S-nZVI with a Fe0 loading content of 3.01 wt%. The S-nZVI particles were homogeneously distributed on the surface of Chi-M, effectively avoiding agglomeration. Compared with bare nanoparticles and supported nZVI, S-nZVI@Chi-M showed significantly enhanced Cr(VI) removal capacity (924.5 mg Cr(VI) for per gram of effective Fe0). The influences of sulfidation degree, dosages, initial Cr(VI) concentration, pH, DO, humic acid and typical ions on Cr(VI) removal kinetics were further studied. S-nZVI@Chi-M could be recycled for at least 4 times with acceptable reactivity. The mechanism investigation results indicated that the Cr(VI) removal was a complex process of reduction, adsorption and co-precipitation under the synergistic effect of Chi-M and S-nZVI. This work provides new ideas for the continuous fabrication of highly reactive nanoparticles, hopefully expanding the application scope of biomass resources in pollution remediation.

Structure and properties of nanoscale zero-valent iron supported on multimorphologies kaolinite and its enhanced removal of Cr(VI) from water

Kaolinite has various morphologies, stable chemical properties, and abundant reserves. To broaden its application in the environment, kaolinite-based nano zero-valent iron composite (nZVI/Kaol) was synthesized for the removal of hexavalent chromium (Cr(VI)) in water. The results showed that the removal rate of Cr(VI) by nZVI/Kaol (the Fe/Kaol mass ratio was 30%) reached 91.7% after 60 min reaction in Cr(VI) solution with an initial concentration of 20 mg/L (pH=7), while the removal efficiencies of Cr(VI) by nZVI and kaolinite were 34.5% and 5.6%. The characterization showed the different morphologies of kaolinite led to nZVI particles with uneven sizes loaded on the surface, that the size of nZVI loaded on rodlike kaolinite (50–100 nm) tended to be smaller than flaky kaolinite (150–200 nm), so the utilization of various sizes of nZVI enhanced Cr(VI) removal. The removal process matched the pseudo-second-order kinetic model and Langmuir isothermal adsorption model better. The results of thermodynamic calculation verified the removal of Cr(VI) by nZVI/Kaol to be endothermic. FTIR and XPS analysis showed that the removal mechanism of Cr(VI) by nZVI/Kaol included adsorption, redox and co-precipitation.

A walnut shell biochar-nano zero-valent iron composite membrane for the degradation of carbamazepine via persulfate activation

In this study, novel walnut shell biochar-nano zero-valent iron nanocomposites (WSBC-nZVI) were synthesized using a combined pyrolysis/reduction process. WSBC-nZVI displayed a high removal efficiency (86 %) for carbamazepine (CBZ) compared with walnut shell biochar (70 %) and nano zero-valent iron (76 %) in the presence of persulfate (PS) (0.5 g/L catalyst, 10 mg/L CBZ, 1 mM persulfate). Subsequently, WSBC-nZVI was applied for the fabrication of the membrane using a phase inversion method. The membrane demonstrated an excellent removal efficiency of 91 % for CBZ in a dead-end system (2 mg/L CBZ, 1 mM persulfate). In addition, the effect of various operating conditions on the degradation efficiency in the membrane/persulfate system was investigated. The optimum pH was close to neutral, and an increase in CBZ concentration from 1 mg/L to 10 mg/L led to a drop in removal efficiency from 100 % to 24 %. The degradation mechanisms indicated that oxidative species, including 1O2, OH, SO4−, and O2−, all contribute to the degradation of CBZ, while the role of 1O2 is highlighted. The CBZ degradation products were also investigated, and the possible pathways and the predicted toxicity of intermediates were proposed. Furthermore, the practical use of the membrane was validated by the treatment of real wastewater.

Rapid removal of low concentration Hg(II) from water by iron nanoparticles: Excellent performance and unique mechanism

Mercury is highly toxic. It is a great threat to human health even with low-concentration mercury ingestion. Herein, we systematically explored the performances and mechanisms of nano zero-valent iron (nZVI) and sulfurized nano zero-valent iron (S-nZVI) for low concentration Hg(II). The S0 produced in the sulfidation process has a strong immobilization effect on Hg0 and reduces the volatilization of Hg0 into the air, which prevents secondary pollution. We discovered some unique mechanisms that occur only in the rapid treatment of low concentrations of mercury: the theory that sulfidation will inhibit the formation of FeOOH and thus enhance the reduction properties of S-nZVI was proposed for the first time; The formation of Fe(OH)x is no longer able to promote adsorption and coprecipitation for Hg(II) but instead hinders reduction on Hg(II). These findings provide insights into the purification of water containing low concentrations of Hg(II) by iron nanoparticles.

Enhancement of anaerobic digestion of ciprofloxacin wastewater by nano zero-valent iron immobilized onto biochar

The commonly used antibiotic ciprofloxacin (CIP) can significantly inhibit and interfere with the anaerobic digestion (AD) performance. This work was developed to explore the effectiveness and feasibility of nano iron-carbon composites to simultaneously enhance methane production and CIP removal during AD under CIP stress. The results demonstrated that when the nano-zero-valent iron (nZVI) content immobilized on biochar (BC) was 33% (nZVI/BC-33), the CIP degradation efficiency reached 87% and the methanogenesis reached 143 mL/g COD, both higher than Control. Reactive oxygen species analysis demonstrated that nZVI/BC-33 could effectively mitigate microorganisms subjected to the dual redox pressure from CIP and nZVI, and reduce a series of oxidative stress reactions. The microbial community depicted that nZVI/BC-33 enriched functional microorganisms related to CIP degradation and methane production and facilitated direct electron transfer processes. Nano iron-carbon composites can effectively alleviate the stress of CIP on AD and enhance methanogenesis.

Application of nanozero-valent iron to reduce toxicity and accumulation of chromium in lettuce (Lactuca sativa L.)

In past decades, nano zero-valent iron (nZVI) has been proven to be a promising approach for remediation of contaminated soils. A greenhouse study was conducted to evaluate the effect of nZVI on promoting plant growth and micronutrients uptake, reducing Cr availability in soil and rhizosphere as well as the accumulation and translocation of Cr in lettuce plant. The experiment was arranged in a randomized complete design in factorial manner with three replications. The treatments consisted of three levels of Cr (0, 25, and 50 mg kg−1) and three levels of nZVI (0, 5, and 10%). The results showed that the diethylene triaminepentacetic acid (DTPA)-extractable Cr in the soil and rhizosphere soil decreased significantly with increasing nZVI levels. The nZVI application significantly enhanced the leaves, stems and roots biomass as well as Fe, Mn, Zn, and Cu concentrations of leaves, whereas it reduced the Cr concentrations of plant tissues, bioaccumulation and translocation factor. These finding indicated that the applied nZVI levels did not exhibit inhibitory impact on the normal growth of plant but were effective in enhancing plant biomass and minimizing the Cr accumulation and translocation from the root to the edible parts of the lettuce plants.

Activation of persulfate by heterogeneous nano zero-valent iron/halloysite nanotubes: reaction behavior, mechanism, and implication for tetracycline hydrochloride degradation.

A novel composite (nZVI/HNTs) was prepared via incorporating nano zero-valent iron (nZVI) on halloysite nanotubes (HNTs) for degrading tetracycline hydrochloride (TCH) with existence of persulfate (PS). The adsorption process of nZVI/HNTs to TCH conformed to the Freundlich isotherm model and pseudo-second-order kinetic model, and its maximum adsorption capacity was 76.62mg·g-1. Furthermore, the nZVI/HNTs + PS system exhibited satisfactory degradation efficiency (84.21%) for TCH, and stable nZVI/HNTs (Fe leaching < 0.001mg·L-1) could be reused. When nZVI/HNTs dosage, PS dosage and temperature increased, TCH degradation could be enhanced. After four cycling, nZVI/HNTs + PS system had still 65.8% degradation for TCH. The quenching tests and EPR analysis evidenced that SO4•- was predominant instead of •OH in such system. Three possible pathways of TCH degradation were provided through the liquid chromatograph-mass spectrometer (LC-MS) determination. Meanwhile, the biological toxicity prediction analysis indicated that the nZVI/HNTs + PS system would be an environment friendly treatment method toward TCH pollution.

Effect of Grain Size Distribution of Soil on Immobilization of Cadmium and Nickel in Contaminated Soil Using Nano Zerovalent Iron: A Factorial Design and Response Surface Methodology Approach

Urban soils get contaminated due to the unscientific disposal of industrial effluents and solid waste, contaminating the soil with heavy metals. Contaminated soils need to be remediated to avoid the ingestion of toxic heavy metals. The immobilization of heavy metals is one of the methods to remediate contaminated soils. The primary purpose of this study was to explore the effect of grain size distribution (GSD) of soil on the efficiency of immobilization of toxic heavy metals in soil when nano zerovalent iron (nZVI) is used to immobilize the metals. Preliminary studies conducted with the 23 factorial design method confirmed that GSD is a significant factor along with the level of contamination and nZVI dosage in the immobilization of heavy metals in soil. Experiments were conducted with cadmium (Cd) and nickel (Ni), the toxic heavy metals, and three soils with different finer particles than 75 µm. Immobilization efficiency was obtained by comparing the leachability of contaminated and treated soil samples using the toxicity characteristic leaching procedure. Reduction in available fraction and variation in the speciation of heavy metals was observed through the sequential extraction procedure. The response surface methodology was adopted for analysis with three levels of GSD, contamination, and nZVI dosage. For Cd, a reduced cubic model was the best fit with a coefficient of determination (R-square) of 0.93, and for Ni, a quadratic model was the best fit with an R-square of 0.92. Both these models were validated experimentally. The efficiency variation followed an optimum curve concerning GSD, contamination level, and the nZVI dosage. For multimetal contamination, the immobilization efficiency gradually decreased from 10% finer to 90% finer soil, both in the case of Cd and Ni. It was observed that for both single metal and multimetal contamination, the interaction between soil and the nZVI plays a vital role in immobilization along with the factors considered.

Insights into the electron activation mechanisms at the micro level by nano zero-valent iron supported by molybdenum disulfide (nZVI@MD) from preparation to application

Both molybdenum disulfide (MoS2) and nano zero-valent iron (nZVI) exhibit excellent adsorption abilities. However, the constrained conductivity of MoS2 and the lack of selectivity of nZVI for electron transfer still pose challenges. In this study, we designed a series of novel nano zero-valent iron supported by molybdenum disulfide composites (nZVI@MD) with multiple electron-rich active sites, including iron dopant replacement, iron atom intercalation and exposed Mo4+, for effective removal of Cr(VI). Results showed that preparation temperature and the amount of MoS2 added were identified as the two most significant factors affecting the reduction properties of nZVI@MD. Systematic experiments revealed that the nZVI@MD exhibited good anti-interference performance, stability and reusability due to its excellent electron selectivity. Characterization results exhibited that iron atoms replaced the sulfur vacancies in MoS2 and inserted into an intercalation of MoS2 during the preparation process. The mechanisms underlying the uptake of Cr(VI) by nZVI@MD can be proposed as follows: (i) electrostatic interactions, (ii) reduction reaction, and (iii) co-precipitation involving Fe-O-Cr. Furthermore, nZVI@MD exhibited excellent electron activity, hydrophilicity and oxidation resistance, confirmed by density functional theory (DFT) calculations. This work provided new strategies and mechanistic insights for the rational design of adsorbents.

A green synthesized medicine residue carbon-based iron composite for the removal of chromium (VI) and cadmium (II): Performance, kinetics and mechanism.

Nowadays, clean-up of heavy metals from wastewaters using waste residue carbon-based material has received increasing attention. In this work, a novel Chinese medicine residue carbon-based nano zero-valent iron composite (CM-nZVI) had been successfully prepared using the combined Chinese medicine residue, FeCl3 and green tea extract. Cr(VI) and/ or Cd(II) removal in water by the CM-nZVI were systematacially investigated with a series of batch experiments. The most relevant findings indicated the adsorption efficiecy and capacity of Cr(VI) by CM-nZVI were respecitvely nearly 98% and 26mg/g under optimized reaction conditions. The negative influences of the cations on the Cr(VI) removal followed the order of Al3+ > Ca2+ > Mg2+ Na+ > K+, but the anions followed the order of HCO3- > PO43- > NO3- > Cl- > SO42-. Humic acid (HA) and ionic strength with high concentrations severely inhibited Cr(VI) removal. The Cr(VI) adsorption on CM-nZVI fitted well by the pseudo-second-order kinetic and Langmuir models. A monolayer endothermic chemisorption occurred on Cr(VI) adsorption over CM-nZVI, and Cr(VI) removal by CM-nZVI primarily involved in the absorption, reduction, precipitation and complexation processes. Both Cr(VI) and Cd(II) removals had been achieved by CM-nZVI at their low concentrations. This CM-nZVI showed a better reusability proprity for Cr(VI) and Cd(II) removal with the regeneration of CM-nZVI through simple pickling. The outcomes of this work show that CM-nZVI could be used an effective material for heavy metals removal from water.

The addition of nano zero-valent iron during compost maturation effectively removes intracellular and extracellular antibiotic resistance genes by reducing the abundance of potential host bacteria

Applying compost to soil may lead to the spread of antibiotic resistance genes (ARGs) in the environment. Therefore, removing ARGs from compost is critical. In this study, for the first time, nano zero-valent iron (nZVI) was added to compost during the maturation stage to remove ARGs. After adding 1 g/kg of nZVI, the abundance of total intracellular and total extracellular ARGs was decreased by 97.62% and 99.60%, and that of total intracellular and total extracellular mobile genetic elements (MGEs) was decreased by 92.39% and 99.31%, respectively. A Mantel test and network analysis indicated that the reduction in potential host bacteria and intI1 after nZVI treatment promoted the removal of intracellular and extracellular ARGs. The addition of nZVI during composting reduced the horizontal transfer of ARGs and improve the total nitrogen and germination index of compost, allowing it to meet the requirements for organic fertilizers.

Stimulation on microbial nitrogen metabolism by iron under PFAS exposure drives effective nitrogen removal in constructed wetland

Constructed wetlands (CWs) have been employed for treatment of perfluoroalkyl substances containing wastewater. However, suppression on operation performances of CWs was inevitable, particularly on nitrogen removal. In this study, 10–30 mg/L nano zero-valent iron (nZVI) was introduced into CWs because of its potential for driving effective nitrogen removal via promoting functional microbes. Perfluorooctanoic acid (PFOA) exposure led to reduction of ammonia (NH4+-N) transformation, but stimulated nitrate (NO3−-N) removal by up to 83.12 %. With PFOA exposure, 10 mg/L nZVI caused the most significant improvement on NH4+-N removal, with maximum increase of 3.65 %. By contrast, 30 mg/L nZVI was prone to alleviate NO3−-N accumulation by 14.19–24.22 % compared to control group. Lower dosage of nZVI (10–20 mg/L) increased activity of five nitrogen cycling enzymes by 31.42–315.18 % in maximum. Whereas, 30 mg/L nZVI led to limited promotion or even inhibition on these enzymes. Analogously, stimulation on nitrifying, anammox, and denitrifying bacteria, as well as functional key genes were more obvious by nZVI at lower concentration. Besides, nZVI reduced functional gene of dissimilatory nitrate reduction to ammonium and related bacteria, increasing NH4+-N removal indirectly. The most promotion on nitrate dependent Fe oxidation bacteria like Paracoccus could explain improvement on NO3−-N removal by 30 mg/L nZVI.

Modified nano zero-valent iron reduce toxicity of polystyrene microplastics to ryegrass (Lolium Perenne L.)

Microplastics pollution in environments has become a major concern and it has been proven to have adverse impacts on plants, so there is an urgent to find approaches to alleviate the detrimental effects of microplastics. In our study, we investigated the influence of polystyrene microplastics (PSMPs) on the growth, photosynthesis, and oxidative defense system changes of ryegrass, as well as the behavior of MPs at roots. Then three types of nanomaterials were applied to alleviate the adverse impact of PSMPs on ryegrass, which were nano zero-valent iron (nZVI), carboxymethylcellulose-modified-nZVI (C-nZVI) and sulfidated nZVI (S-nZVI), respectively. Our results suggested that PSMPs had significant toxicity to ryegrass, leading to decrease of shoot weight, shoot length and root length. Three nanomaterials regained the weight of ryegrass to a varying extent and made more PSMPs aggregate near roots. In addition, C-nZVI and S-nZVI facilitated the entrance of PSMPs into the root and promoted the chlorophyll a and chlorophyll b contents in leaves. Analysis of antioxidant enzymes and malondialdehyde content indicated that ryegrass coped well with the internalization of PSMPs, and all three types of nZVI could alleviate PSMPs-stress in ryegrass. This study elaborates the toxicity of MPs on plants and provides a novel insight into the fixing of MPs by plants and nanomaterials in environments, which needs to be further explored in future research.

Toward a better understanding of peroxymonosulfate and peroxydisulfate activation using a nano zero-valent iron catalyst supported on graphitized carbon: Mechanisms and application to the degradation of estrogenic compounds in different water matrix

In this study, we employed nano zero-valent iron catalysts supported on graphitized carbon (GC-nZVI) catalyst to efficiently degrade BPA under circumneutral pH conditions in both dark and UVA radiation. The GC-nZVI catalyst was characterized using specific techniques (XPS, FTIR, BET, etc.), and was used to activate both PS and PMS in solution. Although no significant BPA degradation constant (kBPA) was determined using PS/PMS or GC-nZVI alone, a significant synergistic effect was observed in the system. Under dark conditions, kBPA increased from 0.01 min−1 to 0.17 when PS was used, both in the dark and under UVA. Notably, when PMS was present in the system, the improvement was even higher with kBPA reaching 0.18 and 0.26 min−1 under dark and UVA conditions, respectively. To further support the synergistic effect, it was found that 80% of mineralization was achieved within 2 h of UVA exposure.Chemical quenching experiments were conducted using selective probes and kinetic modelling showed that the activation of PS/PMS produced sulfate radicals (SO4•−), hydroxyl radicals (•OH) and ferryl ions (FeIVO2+) in both systems. Additionally, GC-nZVI/PMS system demonstrated good stability in recycling experiments, with up to 70% of BPA still being degraded after 3 cycled in 1 h under UVA.In conclusion, the degradation efficiencies of GC-nZVI/PMS and GC-nZVI/PS systems under dark and UVA radiation were assessed for three different EDCs (BPA, E2, and EE2) in both tap and sewage treatment plant waters.This study has demonstrated that the highly efficient GC-nZVI/PS/UVA or GC-nZVI/PMS/UVA system has significant potential for application in different water matrix, and our findings provide insights into the design of heterogeneous Fenton-like and photo-Fenton-like catalysts.

Nano zero-valent iron enhances the absorption and transport of chromium in rice (Oryza sativa L.): Implication for Cr risks management in paddy fields

Chromium (Cr) accumulating in soil caused serious pollution to cultivated land. At present, nano zero-valent iron (nZVI) is considered to be a promising remediation material for Cr-contaminated soil. However, the nZVI impact on the behavior of Cr in the soil-rice system under high natural geological background value remains unknown. We studied the effects of nZVI on the migration and transformation of Cr in paddy soil-rice by pot experiment. Three different doses of nZVI (0, 0.001 % and 0.1 % (w/w)) treatments and one dose of 0.1 % (w/w) nZVI treatment without plant rice were set up. Under continuous flooding conditions, nZVI significantly increased rice biomass compared with the control. At the same time, nZVI significantly promoted the reduction of Fe in the soil, increased the concentration of oxalate Fe and bioavailable Cr, then facilitated the absorption of Cr in rice roots and the transportation to the aboveground part. In addition, the enrichment of Fe(III)-reducing bacteria and sulfate-reducing bacteria in soil provided electron donors for Cr oxidation, which helps to form bioavailable Cr that is easily absorbed by plants. The results of this study can provide scientific basis and technical support for the remediation of Cr -polluted paddy soil with high geological background.

Enhancement of 15% calcium oxide doped nano zero-valent iron on arsenic removal from high-arsenic acid wastewater.

Nano zero-valent iron (nZVI) has a great potential for arsenic removal, but it would form aggregates easily and consume largely by H+ in the strongly acidic solution. In this work, 15%CaO doped with nZVI (15%CaO-nZVI) was successfully synthesized from a simplified ball milling mixture combined with a hydrogen reduction method, which had a high adsorption capacity for As(V) removal from high-arsenic acid wastewater. More than 97% As(V) was removed by 15%CaO-nZVI under the optimum reaction conditions of pH 1.34, initial As(V) concentration 16.21g/L, and molar ratio of Fe/As (nFe/nAs) 2.5:1. The effluent pH solution was weakly acidic 6.72, and the secondary arsenic removal treatment reduced the solid waste and improved arsenic grade in slag from the mass fraction of 20.02% to 29.07%. Multiple mechanisms including Ca2+ enhanced effect, adsorption, reduction, and co-precipitation coexisted for As(V) removal from high-arsenic acid wastewater. Doping of CaO might lead to improving cracking channels which was benefit for electronic transmission and the confusion of atomic distribution. The in situ weak alkaline environment generated on the surface of 15%CaO-nZVI would increase the content of γ-Fe2O3/Fe3O4, which was in favor for As(V) adsorption. In addition, H+ in the strongly acidic solution could accelerate corrosion of 15%CaO-nZVI and abundant fresh and reactive iron oxides continuously generated, which would provide plenty specific reactive site and fast charge transfer and ionic mobility for arsenic removal.

Effect of external magnetic field on mass transport of reactive species in the reaction between nano zero valent iron and selenate anions in a simulated flue gas desulfurization wastewater

The mechanism involved in the reaction of regulated ions with nano Zero-Valent Iron (ZVI) in the presence of an applied weak magnetic field (WMF) was investigated. The WMF effect on mass transport of reacting ions and morphology and composition of the oxide layer in nano ZVI was elucidated using Electron Energy Loss Spectroscopy (EELS). The magnetic gradient force produced by ferromagnetic ZVI particles had a greater influence on the rate of selenate diffusion in solution than the Lorentz force due to the externally applied weak magnetic field. Moreover, the magnetic gradient force was suggested to suppress ZVI corrosion reactions. Despite changes in the iron oxide layer under the WMF influence, the rate of selenate reduction has not been significantly affected over short term lasting several hours. Most crucially, WMF had a negligible effect on the rate of mass transport of selenate anions, as compared to the dominant effect of forced convection.

Integrated application of green zero-valent iron and electrokinetic remediation of metal-polluted sediment.

In recent years, more focus has been placed on integrated metal removal processes. Electrokinetic (EK) treatment is superior to other technologies because it can be applied to a variety of mediums. Green nanoparticles, on the other hand, have the potential to significantly reduce pollutant concentrations in a short period of time. In this study, we investigated the possibility of combining green zero-valent iron (nZVI) with EK on Cd and Zn-contaminated sediment. For green synthesis, extracts of dry leaves of mulberry (ML-nZVI) and oak (OL-nZVI) were used, both abundantly present in the Republic of Serbia. The results show that, despite the fact that their availability was greatly reduced, the metals were concentrated and stabilized to a significant extent in the middle of the EK cell (z/L 0.5) after all treatments. When the results were compared, OL-nZVI proved to be a more effective nanomaterial even with smaller doses of OL-nZVI, which is important in terms of achieving better economic benefits. This study identified green nano zero-valent iron as a powerful tool for metal removal when combined with electrokinetic (EK) treatment, which improves green nZVI longevity and migration. This study of the combined green nZVI-EK remediation treatment, in particular, will have an impact on future research in this field, given the achieved efficiency.

Zero Valent Iron Impregnated Sodium Alginate Grafted (Acrylamide-Co-Acrylic Acid) Adsorbents for the Removal of Methylene Blue in Aqueous Systems

In this study sodium alginate (NaAlg) grafted acrylamide (AM)-co-acrylic acid (AA)) and nano zero-valent iron (nZVI) were synthesized by the microwave assisted and coprecipitation method, respectively. The nZVI was dispersed in NaAlg-g-(AM-co-AA) and the adsorbent was characterized by X-ray diffraction (XRD), proton nuclear magnetic resonance (1HNMR), and Fourier transform infrared spectroscopy (FTIR). In order to evaluate the effects of adsorbent dosage, contact time, pH, initial dye concentration and temperature, kinetic and thermodynamic tests were carried out on the adsorbents. The best dose of the NaAlg-g-(AM-co-AA)/nZVI with 0.5% nZVI needed to remove methylene blue (MB) dye (10 mg/L, 50 mL) was 0.2 g at 60 min. For NaAlg-g-(AM-co-AA)/nZVI to effectively remove a large portion of MB dye, pH 8.0 was ideal. To assess the adsorption data, Freundlich, Langmuir, and Dubinin-Radushkevich isotherm models were applied. The Langmuir isotherm performed best for MB adsorption, with an R2 of 0.975. The adsorption equilibrium’s kinetic process followed the pseudo-second-order model (R2=0.9988). The positive ΔGo values obtained from the thermodynamic studies showed that the adsorption processes were endothermic and non-spontaneous.