Effect of pH, temperature and co-existing anions on the Removal of Cr(VI) in groundwater by green synthesized nZVI/Ni

Low serum lipase levels in mothers of children with stunted growth indicate the possibility of low calcium absorption during pregnancy: A cross-sectional study in North Sumatra, Indonesia

Stunting is caused by various factors, including low nutritional intake in the first two years of life. This study aimed to investigate the differences in sociodemographic factors and mineral, vitamin, and enzyme parameters in mothers associated with the occurrence of stunting in children. We conducted a cross-sectional study from September to November 2020 on North Sumatra Island, Indonesia. The data collected included sociodemographic characteristics, pregnancy history, birth history, food intake, and laboratory examinations, including measurements of calcium, iron, zinc, vitamin D, pancreatic amylase, and serum lipase levels. This study included 50 healthy mothers aged 18-50 years old with children aged 2 to 60 months. There was a significant difference in serum calcium levels between the groups of mothers of children with normal and stunted growth (p = 0.03, mean difference±standard error (SE) = 0.23±0.12, 95% CI: 0.19-0.45). All of the study subjects were categorized as vitamin D deficient. The mean lipase level in the group of mothers of children with stunted growth was significantly lower than that in the group of mothers of children with normal growth (p = 0.02, mean difference±SE = 4.34±1.83, 95% CI: 0.62-8.06). The conclusion was that serum lipase levels were significantly lower in mothers of children with stunted growth compared to mothers of children with normal growth. Serum lipase levels this low are likely to indicate that a mother is unable to meet her child's calcium needs during pregnancy, increasing the child's risk of stunted growth.

Efficient removal of hexavalent chromium from water by Bacillus sp. Y2-7 with production of extracellular polymeric substances

Bioremediation is an environmentally friendly technology for the treatment of chromium-contaminated sites. Here, a hexavalent chromium [Cr(VI)]-resistant strain was isolated from oil-contaminated soil and designated as Bacillus sp. Y2-7 based on 16S rDNA sequence characterization. The effects of various factors including inoculation dose, pH value, glucose concentration, and temperature on Cr(VI) removal rates were then evaluated. Based on the response surface methodology, optimal Cr(VI) removal efficiency (above 90%) could be achieved at an initial Cr(VI) concentration of 155.0 mg·L-1, glucose concentration of 11.479 g·L-1, and pH of 7.1. The potential removal mechanisms of Cr(VI) by strain Y2-7 were also supposed. The contents of polysaccharide and protein in extracellular polymer (EPS) of strain Y2-7 decreased slowly after cultured with Cr(VI) of 15 mg·L-1 from 1 to 7 days. We thus inferred that EPS bonded with Cr(VI) and underwent morphological changes in water. Molecular operating environment (MOE) analysis suggested that macromolecular protein complexes in Bacillus sp. Y2-7 and hexavalent chromium could establish hydrogen bonds. Collectively, our findings indicate that Bacillus sp. Y2-7 is an excellent bacterial candidate for chromium bioremediation.

Green synthesis of nZVI-modified biochar significantly enhanced the removal of Cr(VI) from aqueous solution

Water contamination by hexavalent chromium (Cr(VI)) seriously jeopardizes human health, which is a pressing environmental concern. Biochar-loaded green-synthesized nZVI, as a green and environmentally friendly material, can efficiently reduce Cr(VI) to Cr(III) while removing Cr(VI) from water. Therefore, in this study, an efficient green-modified biochar material (TP-nZVI/BC) was successfully prepared using tea polyphenol (TP) and sludge biochar (BC) using a low-cost and environmentally friendly green synthesis method. The preparation conditions of TP-nZVI/BC were optimized using response surface methodology (RSM), revealing that the dosage of tea polyphenols plays a crucial role in the removal performance (R2 = 1271.09), followed by reaction time and temperature. The quadratic regression model proved accurate. The optimal preparation conditions are as follows: tea polyphenols (TP) dosage at 48 g/L, reaction temperature at 75 ℃, and a reaction time of 3 h. TP-nZVI/BC removed Cr(VI) from water at a rate 7.6 times greater than BC. The pseudo-second-order kinetic model (R2 = 0.987) accurately describes the adsorption process, suggesting that chemical adsorption predominantly controls the removal process. The adsorption of Cr(VI) by TP-nZVI/BC can be well described by the Langmuir model, and the maximum adsorption capacity reached 105.65 mg/g. FTIR and XPS analyses before and after adsorption demonstrate that nZVI plays a crucial role in the reduction process of Cr(VI), and the synergistic effects of surface adsorption, reduction, and co-precipitation enhance Cr(VI) removal. In summary, using green-modified biochar for Cr(VI) removal is a feasible and promising method with significant potential.

Tannic acid modified microscale zero valent iron (TA-mZVI) with enhanced anti-passivation capability for Cr(VI) removal

The removal of Cr(VI) from aqueous solutions using microscale zerovalent iron (mZVI) shows promising potential. However, the surface passivation of mZVI particles hinders its widespread application. In this study, we prepared tannic acid (TA) modified mZVI composite (TA-mZVI) by a simple sonication method. The introduction of TA allowing TA-mZVI composite to adsorb Cr(VI) rapidly under electrostatic forces attraction, guarantying TA-mZVI exhibited remarkable Cr(VI) removal capacity with a maximum adsorption capacity of 106.1 mg⋅g-1. At an initial pH of 3, it achieved a rapid removal efficiency of 96.2% within just 5 min, which was 7.7 times higher than that of mZVI. Various characterizations, including XPS and CV analysis, indicated that the formation of TA-Fe complexes accelerates electron transfer. In addition, TA endows functional groups to TA-mZVI, raising the dispersion and stability and serves as a protective layer hindering passivation. Further mechanistic analysis revealed that Cr(VI) removal by TA-mZVI followed an adsorption-reduction-precipitation mechanism, with TA mitigating the surface passivation of mZVI and facilitating the reduction of most Cr(VI) to Cr(III). Batch cyclic experiments revealed that TA-mZVI exhibited satisfactory performance, maintaining over 85% Cr(VI) removal even after five cycles and minimally affected by various coexisting ions. With notable advantages in cost-effectiveness, ease-synthesis and recovery, this work provides a great promise for developing efficient reactive adsorbent for addressing Cr(VI) contamination in aqueous solutions.

Coupling electrokinetic remediation with flushing using green tea synthesized nano zero-valent iron/nickel to remediate Cr (VI)

This study focuses on a flushing-electrokinetic remediation technology of hexavalent chromium from the chromium slag dump site. A suspension of nanoscale zero-valent iron/nickel fabricated from green tea (GT-nZVI/Ni), was employed as an eluent to degrade Cr (VI) and enhance the remediation effectiveness of a single EK. The removal efficiency of Cr (VI) was compared under different voltages, electrode spacings and pH values of the anolyte. The results demonstrated that the combined flushing and EK achieved a removal rate of Cr (VI) in the soil throughout all the experiments ranging from 83.08 to 96.97% after 120 h. The optimal result was obtained when the voltage was 28 V, the pH value of anolyte was 3 and the electrode spacing was 15 cm. The removal of Cr (VI) reached 91.49% and the energy consumption was 0.32606 kW·h·g-1. The underlying mechanisms responsible for the removal of Cr (VI) by GT-nZVI/Ni flushing-EK primarily involved electromigration, reduction and adsorption co-precipitation processes. The fractionation analysis of Cr (VI) concentration in the soil after remediation showed that the presence of GT-nZVI/Ni facilitated the conversion of Cr (VI) into oxidizable and residual states with low mobility and toxicity. The results of toxicity characteristic leaching procedure (TCLP) indicated that the leaching concentration of Cr (VI) was below 1 mg·L-1, complying with the standards set by the Environmental Protection Agency. Additionally, the phytotoxicity testing revealed that the germination index (GI) of the remediated soil reached 54.75%, indicating no potential harm to plants.

Cr(VI) removal from wastewater using nano zero-valent iron and chromium-reducing bacteria

Significant global efforts are currently underway to alleviate the presence of toxic metals in water bodies, aiming to encourage a sustainable environment. Nevertheless, the scientific community has yet to methodically inspect the performance and mechanisms underlying the interaction between nanomaterials and microorganisms in this context. Therefore, this study seeks to address this knowledge gap by developing a novel system that integrates nano zero-valent iron (nZVI) with chromium-reducing bacteria (CrRB) to efficiently remove Cr(VI) from water sources. The combined use of RBC600 and CrRB resulted in a Cr(VI) removal rate of 77.73%, displaying a substantial improvement of 17.61% compared to the use of CrRB alone. The efficacy of Cr(VI) elimination was observed to be affected by several factors within the system, such as the pH value, the quantity of nZVI added, the degree of CrRB inoculation, and the initial concentration of Cr(VI) at the onset of the experiment. When the pH was adjusted to 5, the complete removal of 200 mg/L Cr(VI) was achieved within 36 h. Increasing the dosage of nZVI to above 2 g/L resulted in the complete elimination of Cr(VI) from the solution within 72 h. This can be attributed to the availability of more reaction sites for the reduction of Cr(VI), facilitated by the higher nZVI dose. Additionally, the increased dose of nZVI allowed for the dissolution of more reactive Fe(II) ions. The characterization analysis, high-throughput sequencing, and fluorescence quantitative PCR results have established that CrRB and its extracellular polymer effectively reduce and complex Cr(VI). This process facilitated the dissolution of the passivated layer on the surface of nZVI, thus significantly enhancing the efficiency of nZVI in responding to Cr(VI). Additionally, the presence of nZVI created a favorable living environment for CrRB, resulting in increased richness and diversity within the CrRB community. These findings provide valuable preliminary insights into the mechanism underlying Cr(VI) elimination by the synergistic interaction between nZVI and CrRB. Therefore, this study establishes a solid theoretical foundations for the application of nano-bio synergy in the remediation of Cr(VI).

Removal of Nitrate Nitrogen in Groundwater by Attapulgite Loaded with Nano-Zero-Valent Iron

Nano-zero-valent iron (nZVI) can be used to remove nitrate nitrogen (NO3-N) from groundwater. However, it has low reduction efficiency owing to its oxidation and aggregation characteristics. Thus, nZVI-loaded material is used to alleviate these drawbacks. In this study, nZVI-coated attapulgite (ATP) was prepared for the removal of NO3-N from groundwater. ATP-nZVI was prepared using the chemical liquid deposition-coreduction method. The prepared materials were characterized by SEM, XRD, and XPS analyses, which confirmed that the aluminum silicate particles in the ATP structure are effective carriers of nZVI and effectively inhibit self-consumption caused by the oxidation and aggregation of nZVI. The batch experiments examined experimental samples containing 30 mg/L nitrate and analyzed the effects of various parameters, including the material, mass ratio, initial pH, initial temperature, and coexisting anions on the NO3-N removal efficiency. The results showed that the optimal removal rate of the composite was 78.61%, which is higher than that using the same amount of ATP, iron powder, and nZVI. When the mass ratio of ATP to nZVI was 1 : 1, the NO3-N removal efficiency was the highest. When the pH value increased from 3 to 9, the NO3-N removal rate decreased, while an increase in the reaction temperature promoted NO3-N removal. The order of the inhibitory effect of coexisting anions on NO3-N removal by various nanoions was PO43–>CO32–>SO42–>Cl–. The adsorption kinetic model fitting results indicated that the chemisorption of electron exchange between ATP and nZVI in NO3-N removal was the main rate-limiting step in the reaction. This study demonstrates the potential of the prepared ATP-nZVI composite for NO3-N removal from groundwater.

Review on the degradation of chlorinated hydrocarbons by persulfate activated with zero-valent iron-based materials

Chlorinated hydrocarbons (CHCs) are often used in industrial processes, and they have been found in groundwater with increasing frequency in recent years. Several typical CHCs, including trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), carbon tetrachloride (CT), etc., have strong cytotoxicity and carcinogenicity, posing a serious threat to human health and ecological environment. Advanced persulfate (PS) oxidation technology based on nano zero-valent iron (nZVI) has become a research hotspot for CHCs degradation in recent years. However, nZVI is easily oxidized to form the surface passivation layer and prone to aggregation in practical application, which significantly reduces the activation efficiency of PS. In order to solve this problem, various nZVI modification solutions have been proposed. This review systematically summarizes four commonly used modification methods of nZVI, and the theoretical mechanisms of PS activated by primitive and modified nZVI. Besides, the influencing factors in the engineering application process are discussed. In addition, the controversial views on which of the two (SO₄·^- and ·OH) is dominant in the nZVI/PS system are summarized. Generally, SO₄·^- predominates in acidic conditions while ·OH prefers neutral and alkaline environments. Finally, challenges and prospects for practical application of CHCs removal by nZVI-based materials activating PS are also analyzed.

Iron-sulphur transformation control for enhancing Cr(VI) removal in flake and nanoscale porous pyrrhotite (Fe7S8) added wastewater

Hexavalent chromium (Cr(VI)) contaminated wastewater should be addressed efficiently in the environmental field. In previous applications, nano iron sulfides amendment has not been well controlled for iron-sulfur transformation. In this study, the novel flake and nanoscale porous pyrrhotite (Fe₇S₈) (FNPP) amendment was synthesized. The iron-sulphur transformation of FNPP was controlled and optimized for enhancing Cr(VI) removal. The specific surface area and average pore diameter of the FNPP amendment reached 115.7 m²/g and 2.1 nm. The maximum adsorption capacity of total chromium reached 66.3 mg/g. The optimized iron-sulphur transformation condition was an initial FNPP and Cr(VI) molar ratio of 8, pH at 5.6, in which the Cr(VI) removal reached 96.5% and all producing S^2- was utterly consumed. It is confirmed that S^2- fast induced Fe³⁺/Fe²⁺ circulation and FNPP has a speedier adsorption rate for Cr(III) than Cr(VI). Fe²⁺ and S^2- mediated the Cr(VI) reduction to Cr(III), thus, much faster Cr(VI) removal was achieved. High efficiency removal mechanism of Cr(VI) was combined with surface adsorption/reduction and solution reduction/precipitation. The research demonstrated that controlling and optimizing the iron-sulphur transformation of Fe₇S₈ amendment can significantly enhance Cr(VI) removal.

Biochar-supported nZVI for the removal of Cr(VI) from soil and water: Advances in experimental research and engineering applications

Over the past decade, biochar-supported nZVI composites (nZVI/biochar) have been developed and applied to treat various pollutants due to their excellent physical and chemical properties, especially in the field of chromium (VI) removal. This paper reviewed the factors influencing the preparation and experiments of nZVI/biochar composites, optimization methods, column experimental studies and the mechanism of Cr(VI) removal. The results showed that the difference in raw materials and preparation temperature led to the difference in functional groups and electron transfer capabilities of nZVI/biochar materials. In the experimental process, pH and test temperature can affect the surface chemical properties of materials and involve the electron transfer efficiency. Elemental doping and microbial coupling can effectively improve the performance of nZVI/biochar composites. In conclusion, biochar can stabilize nZVI and enhance electron transfer in nZVI/biochar materials, enabling the composite materials to remove Cr(VI) efficiently. The study of column experiments provides a theoretical basis for applying nZVI/biochar composites in engineering. Finally, the future work prospects of nZVI/biochar composites for heavy metal removal are introduced, and the main challenges and further research directions are proposed.

Integrated green complexing agent and biochar modified nano zero-valent iron for hexavalent chromium removal: A characterisation and performance study

In this study, nano zero-valent iron (nZVI) was loaded on biochar (BC) prepared from recycled waste peanut shells. The loaded BC in the nZVI@BC composite was assumed to weaken the agglomeration of nZVI and the environmentally-friendly complexing agents sodium citrate (Cit) and sodium carboxymethyl cellulose (CMC) were used to establish Cit-nZVI@BC and CMC-nZVI@BC for the effective removal of Cr(VI) from aqueous environments. The characterisation results suggested that Cit and CMC not only inhibited the oxidation of nZVI, but also effectively improved its reactivity. The experimental results demonstrated that the Cr(VI) removal efficiency by nZVI was less than 20%, while CMC-nZVI@BC enhanced the Cr(VI) removal efficiency to 80.73%, because CMC was coated on the nZVI surface for anti-passivation and improved the surface activity of nanoparticles. In addition, the Cr(VI) removal efficiency reached almost 100% with Cit-nZVI@BC, and the citrate dissociated the passivation layer on the surface of the zero-valent iron particles to ensure the reactivity of the zero-valent iron. The reaction mechanism of Cit-nZVI@BC includes adsorption, reduction, and co-precipitation, whereas CMC-nZVI@BC also involves surface complexation reactions. The kinetic studies revealed that the removal of Cr(VI) by Cit-nZVI@BC and CMC-nZVI@BC followed the second-order reaction kinetic model, and the reaction rates of Cit-nZVI@BC and CMC-nZVI@BC were both higher than that of nZVI. The results indicate that the prepared systems are promising for Cr(VI) remediation in contaminated environments.

Sodium citrate and biochar synergistic improvement of nanoscale zero-valent iron composite for the removal of chromium (Ⅵ) in aqueous solutions

Sodium citrate (SC) is a widely-used food and industrial additive with the properties of complexation and microbial degradation. In the present study, nano-zero-valent iron reaction system (SC-nZVI@BC) was successfully established by modifying nanoscale zero-valent iron (nZVI) with SC and biochar (BC), and was employed to remove Cr(Ⅵ) from aqueous solutions. The nZVI, SC-nZVI and SC-nZVI@BC were characterized and compared using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses (TGA), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that nZVI was successfully loaded on the biochar, and both the agglomeration and surface passivation problems of nanoparticles were well resolved. The dosage of SC, C:Fe, initial pH and Cr(Ⅵ) concentration demonstrated direct effects on the removal efficiency. The maximum Cr(Ⅵ) removal rate and the removal capacity within 60 min were 99.7% and 199.46 mg/g, respectively (C:Fe was 1:1, SC dosage was 1.12 mol.%, temperature was 25°C, pH = 7, and the original concentration of Cr(Ⅵ) was 20 mg/L). The reaction confirmed to follow the pseudo-second-order reaction kinetics, and the order of the reaction rate constant k was as follows: SC-nZVI@BC > nZVI@BC > SC-nZVI > nZVI. In addition, the mechanism of Cr(Ⅵ) removal by SC-nZVI@BC mainly involved adsorption, reduction and co-precipitation, and the reduction of Cr(Ⅵ) to Cr(Ⅲ) by nano Fe⁰ played a vital role. Findings from the present study demonstrated that the SC-nZVI@BC exhibited excellent removal efficiency toward Cr(Ⅵ) with an improved synergistic characteristic by SC and BC.

Green synthesis of modified polyethylene packing supported tea polyphenols-NZVI for nitrate removal from wastewater: Characterization and mechanisms

Nano-zero-valent iron (NZVI), as an electron donor, performed excellence in the reduction and remove of nitrate. However, the easy agglomeration and poor antioxidation of NZVI declined the nitrate removal and limited the application in the field of wastewater treatment. Herein, a novel composite packing of tea polyphenol, NZVI and modified polyethylene carrier (TP-NZVI/PE) was prepared and characterized, the removal efficiency of nitrate was verified, and the preliminary removal mechanism was finally investigated. The results showed that the maximum iron loading on TP-NZVI/PE composite achieved under 50 °C, pH of 5.0, 4.0 g/L of Fe²⁺, and 7.2 g/L of TP, respectively, with 3.51 ± 0.12 mg/g. NZVI presented satisfactory antioxidation and anti-agglomeration via TP encapsulation. TP encapsulation of TP-NZVI/PE composite was easily degraded by microorganisms and NZVI was exposed to nitrate during wastewater treatment, which made the reduction of nitrate possible. The nitrate removal efficiency of TP-NZVI/PE composite with microorganism was 79.88 ± 0.17%, higher three times than that of TP-NZVI/PE (25.54 ± 0.21%). The oxidized NZVI was transformed to Fe²⁺/Fe³⁺, which were prone to adsorb nitrate and then co-precipitate. It was favorable for further removal of nitrate. Results suggested a novel approach for fast and eco-friendly preparation and efficient application of NZVI.

Highly efficient removal of Cr(VI) from aqueous solution by pinecone biochar supported nanoscale zero-valent iron coupling with Shewanella oneidensis MR-1

Nanoscale zero-valent iron (nZVI) has been extensively used to remove various pollutants. However, the rapid deactivation due to aggregation and surface passivation severely limits its practical application. In this study, a novel composite with nZVI supported by pinecone biochar (nZVI-PBC) was successfully synthesized and used for the removal of high concentration Cr(VI) from aqueous solution in the presence of Shewanella oneidensis MR-1 (MR-1). The results showed that the nZVI-PBC coupling with MR-1 (nZVI-PBC/MR-1) exhibited an excellent removal performance for high concentration Cr(VI) compared to the nZVI-PBC alone. Under optimal conditions, 100 mg/L Cr(VI) could be removed completely by nZVI-PBC/MR-1 within 48 h, while only 39.50% of Cr(VI) was removed by nZVI-PBC alone. The improvement of Cr(VI) removal is due to the dissolution of the surface passivation layer of nZVI-PBC, formation of sorbed Fe(II) in the presence of MR-1, and an important role of extracellular polymeric substance (EPS) derived from MR-1. X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near-edge structure spectra (XANES) confirmed that most Cr(VI) was reduced to insoluble Cr(III) and formed Cr₂O₃, Cr_xFe_1-x(OH)₃ and FeCr₂O₄ precipitates, and a small amount of unreduced Cr(VI) was immobilized through adsorption and complexation. The results suggest that nZVI-PBC/MR-1 can effectively overcome the limitations of nZVI and achieve highly efficient removal of high concentration Cr(VI).

Enhanced sequestration of Cr(VI) onto plant extract anchored on carbon-coated aluminium oxide composite

Aluminium oxide (ALU) and carbon-coated aluminium oxide modified with Kigelia africana leaf extract (KECA) were employed for the removal of toxic hexavalent chromium (Cr(VI)) from the aqueous phase. The adsorbents (ALU and KECA) were characterized by TGA, BET, FESEM, FTIR, Raman and XRD spectroscopic techniques. The potential of KECA and ALU to remove Cr(VI) from simulated wastewater was optimum at pH 2, sorbent dose of 0.025 g and a contact time of 200 min. Meanwhile, the uptake capacity of KECA and ALU was enhanced with an increase in sorbent dose, contact time and initial Cr(VI) concentration. The uptake of Cr(VI) onto the adsorbents ALU and KECA was kinetically best described by the pseudo-second-order and Elovich models, respectively. Besides, the equilibrium data acquired for ALU and KECA obeyed Freundlich and Langmuir isotherm models, respectively. ALU and KECA were observed to have optimum adsorption capacity of 56.45 mg g^-1 and 258.2 mg g^-1, respectively. The adsorption of Cr(VI) onto the adsorbents was thermodynamically feasible, endothermic in nature and entropy-driven. A decrease in efficiency was observed on regeneration of the absorbents, thus limiting their reusability. However, the presence of functional groups with reducing property in the extract of Kigelia africana leaves was noticed to enhance the capacity of the adsorbent to abstract Cr(VI) from the solution. Hence, this study demonstrates the potential of KECA to sequestrate Cr(VI) from an aqueous solution and provides a reference for its application to the treatment of Cr(VI)-laden industrial wastewater.

Synthesis of montmorillonite-supported nano-zero-valent iron via green tea extract: Enhanced transport and application for hexavalent chromium removal from water and soil

The nano-zero-valent iron composite (nZVI@TP-Mont) was successfully prepared using a low-cost and environmental-friendly green synthesis via tea leaves extract (tea polyphenols, TPs) and the montmorillonite (Mont). The batch and column experiments and characterization were conducted to investigate the transport behavior and Cr(VI) remediation by nZVI@TP-Mont in water/soil. Due to its particular surface characteristics and morphology (i.e., the Fe⁰ core wrapped by TPs, the doped sulfur, and interlayer structure), the nZVI@TP-Mont composite showed a great removal capacity of Cr(VI) and sufficient mobility under different soil conditions. We opine the increase in the Cr(VI) reduction of nZVI@TP-Mont was attributed to the tethering of Fe₂O₃ on the surface of Fe⁰ core by the support of Mont interlayer, especially the TP-coverage around nZVI@TP-Mont surface unwrapped, thereby increasing the regenerated reactive Fe²⁺ and the exposed reaction sites of Fe⁰ cores to Cr(VI). The increased transportability of nZVI@TP-Mont slightly depends on the heterogeneous soil properties (i.e., ionic strength, sand/soil ratio, and pH). The two-site kinetic attachment model fitting results suggest Cr(VI)/Cr(III) speciation associated with the agglomerated nZVI@TP-Mont were efficiently immobilized in soil. Therefore, this study would benefit the efficient application of the green-synthesized nZVI@TP-Mont in in-situ remediation of soils contaminated by Cr(VI).

Advances in metal(loid) oxyanion removal by zerovalent iron: Kinetics, pathways, and mechanisms

Metal(loid) oxyanions in groundwater, surface water, and wastewater can have harmful effects on human or ecological health due to their high toxicity, mobility, and lack of degradation. In recent years, the removal of metal(loid) oxyanions using zerovalent iron (ZVI) has been the subject of many studies, but the full scope of this literature has not been systematically reviewed. The main elements that form metal(loid) oxyanions under environmental conditions are Cr(VI), As(V and III), Sb(V and III), Tc(VII), Re(VII), Mo(VI), V(V), etc. The removal mechanisms of metal(loid) oxyanions by ZVI may involve redox reactions, adsorption, precipitation, and coprecipitation, usually with one of these mechanisms being the main reaction pathway and the other playing auxiliary roles. However, the removal mechanisms are coupled to the reactions involved in corrosion of Fe(0) and reaction conditions. The layer of iron oxyhydroxides that forms on ZVI during corrosion mediates the sequestration of metal(loid) oxyanions. This review summarizes most of the currently available data on mechanisms and performance (e.g., kinetics) of removal of the most widely studies metal(loid) oxyanion contaminants (Cr, As, Sb) by different types of ZVI typically used in wastewater treatment, as well as ZVI that has been sulfidated or combination with catalytic bimetals.

Highly efficient nano-Fe/Cu bimetal-loaded mesoporous silica Fe/Cu-MCM-41 for the removal of Cr(VI): Kinetics, mechanism and performance

Zero valent iron (Fe⁰) can reduce Cr(VI) in water, where Fe⁰ and Fe(Ⅱ) are possible electron donors, but passivation and aggregation easily occur to Fe⁰. To improve the performance of Fe⁰, a new hybridization strategy of Fe/Cu bimetal and silica-based mesoporous molecular sieve MCM-41 for the removal of Cr(VI) from water has been proposed. The results show that the two-dimensional mesoporous structure of MCM-41 can provide skeleton support for Fe⁰, improve the mass transfer rate, and overcome the aggregation bottleneck of Fe⁰. The Cr(VI) removal rate reached 98.98% (pH = 2) after 40 min. The analytical results revealed Cr(VI) removal process: Cr(VI) adsorbed onto Fe/Cu-MCM-41 by electrostatic attraction and other molecular inter-atomic forces. The second metal, Cu, can inhibit the passivation of Fe⁰ and promote Fe(Ⅱ)through the formation of Fe/Cu battery, thereby promoting the electron transfer. The resulting Cr(Ⅲ) is precipitated as FeCr₂O₄ and Cr_xFe_1-x(OH)₃.

Effects of green synthesized and commercial nZVI on crystal violet degradation by Burkholderia vietnamiensis C09V: Dose-dependent toxicity and biocompatibility

The increasingly common remedial application of nanoscale zero-valent iron (nZVI) to alleviate specific contaminant issues may inadvertently lead to nZVI accumulation in wastewater. This is a potential concern, because the effect of nZVI on the common microbes essential for wastewater biotreatment is not known. This is further complicated when there are many ways available to synthesize nZVI, which may interreact with bacteria differently. Thus, in this study, the different effects of nZVI synthesized by Eucalyptus leaves (EL-nZVI) and a commercially synthesized nZVI on the biodegradation of crystal violet by Burkholderia vietnamiensis C09V (B.V. C09V) was studied. At high dose (1000 mg/L), EL-nZVI and commercial nZVI both significantly inhibited the removal of crystal violet by B.V. C09V, decreasing removal rates by 10.5 and 13.1% respectively. Optical density (OD₆₀₀) and soluble protein assays indicated that the growth of B.V. C09V improved under low doses (100 mg/L), but remained inhibited under high doses (500 and 1000 mg/L) of both commercial and EL-nZVI. Enzymes were also sensitive to nZVI, where the commercial variant exerted a greater effect on both the activity of lactate dehydrogenase (LDH) and superoxide dismutase (SOD) than EL-nZVI, indicating that EL-nZVI was less toxic than commercial nZVI. LIVE/DEAD staining also showed that the number of apoptotic cells was significantly higher when exposed to commercial nZVI rather than EL-nZVI. Furthermore, scanning electron microscopy (SEM) confirmed that direct contact between nZVI and cells at 1000 mg/L nZVI caused cell membrane disruption. Whereas, at 100 mg/L EL-nZVI, B.V. C09V grew better due to the formation of dense biofilms around the suspended EL-nZVI at a. Fourier transform infrared spectra (FTIR), confirmed an abundance of oxygen-containing functional groups on the surface of EL-nZVI which provided better biocompatibility than commercial nZVI. Overall, while dose was the most significant factor influencing nZVI toxicity, surface composition and morphology was also important. These new findings suggest chemical synthesis of metal nanoparticles should be replaced by biosynthetic routes to maintain viable microbial pollution during wastewater treatment.

Pentaclethra macrophylla stem bark extract anchored on functionalized MWCNT-spent molecular sieve nanocomposite for the biosorption of hexavalent chromium

nsufficient innovative research on the sequestration of Cr(VI) from the aquatic ecosystem has made Cr(VI) a recalcitrant water contaminant that often affects water sources. In this work, a novel plant anchor-nanocomposite was fabricated from the spent molecular sieve, multi-walled carbon nanotubes, and the extract from the stem bark of Pentaclethra macrophylla. It was envisaged that due to the phytochemical constituent of the modifier, this nanocomposite could also act as potent adsorbents for the treatment of Cr(VI) polluted water. To the best of our knowledge, the application of Pentaclethra macrophylla stem bark extract as a modifier for the green fabrication of nanocomposite has not been reported. The resulting composites showed good uptake capacity for Cr(VI) as well as efficient reusability.

Removal of hexavalent chromium from wastewater by Cu/Fe bimetallic nanoparticles

Passivation of nanoscale zerovalent iron hinders its efficiency in water treatment, and loading another catalytic metal has been found to improve the efficiency significantly. In this study, Cu/Fe bimetallic nanoparticles were prepared by liquid-phase chemical reduction for removal of hexavalent chromium (Cr(VI)) from wastewater. Synthesized bimetallic nanoparticles were characterized by transmission electron microscopy, Brunauer-Emmet-Teller isotherm, and X-ray diffraction. The results showed that Cu loading can significantly enhance the removal efficiency of Cr(VI) by 29.3% to 84.0%, and the optimal Cu loading rate was 3% (wt%). The removal efficiency decreased with increasing initial pH and Cr(VI) concentration. The removal of Cr(VI) was better fitted by pseudo-second-order model than pseudo-first-order model. Thermodynamic analysis revealed that the Cr(VI) removal was spontaneous and endothermic, and the increase of reaction temperature facilitated the process. X-ray photoelectron spectroscopy (XPS) analysis indicated that Cr(VI) was completely reduced to Cr(III) and precipitated on the particle surface as hydroxylated Cr(OH)3 and CrxFe1-x(OH)3 coprecipitation. Our work could be beneficial for the application of iron-based nanomaterials in remediation of wastewater.

Thermodynamics, kinetics and isothermal studies of chromium (VI) biosorption onto Detarium senegalense stem bark extract coated shale and the regeneration potentials

A low-cost adsorbent (Detarium senegalense stem bark extract coated shale (DSMS)) comprising pristine shale (PSH) coated with D. senegalense stem bark extract was prepared and utilized for the adsorption of Cr(VI). The DSMS and PSH were characterized by the SEM, XRD, FTIR, EDX, TGA, and BET. The batch adsorption experiment results showed that DSMS exhibited an excellent ability to adsorb chromium with a maximum removal occurring at pH 2, dosage of 0.05 g and 180 min contact time. The adsorption process was best described by the pseudo-second-order for DSMS and Elovich model for PSH which depicts chemisorption as the major mechanism responsible for the uptake of Cr(VI) onto the adsorbents. Langmuir model provided the best fit to the isotherm analysis on both materials. The maximum adsorption capacity of DSMS and PSH were 64.98 mg g^-1 and 29.97 mg g^-1 respectively. The thermodynamics revealed that the adsorption of Cr(VI) was feasible, endothermic and entropy driven. Furthermore, after five cycles of reuse, both DSMS and PSH demonstrated effective regeneration and reusability for Cr(VI) uptake. The structural properties, reusability, and high adsorption capabilities of DSMS indicate that they could be used as low-cost adsorbents in large-scale Cr(VI) wastewater treatment. Novelty statement Plant extracts are packed with a variety of polyphenolic compounds, such as aldehydes, alcohols, carboxylics, ethers, ketones, and phenols which contains several functionalities useful in the adsorption of toxic metals. Despite this, research on the use of plant extracts in the modification of adsorbent materials for enhanced adsorption is rare. This study reports for the first time the use of Detarium senegalense stem bark extract coated shale adsorbent for the efficient uptake of Cr(VI) ion.

Column study of enhanced Cr(Ⅵ) removal and removal mechanisms by Sporosarcina saromensis W5 assisted bio-permeable reactive barrier

In this study, the performances of Sporosarcina saromensis W5 assisted bio-permeable reactive barrier, containing activated carbon (AC) or zero-valent iron (ZVI), were investigated by column experiments in removal of Cr(Ⅵ) from simulated groundwater. The enhanced Cr(Ⅵ) removal performances were observed in biotic columns. Cr(Ⅵ) was first detected in effluent on day 24 and day 85 in Bio-AC and Bio-ZVI columns, respectively whereas it breakthrough only on day 4 and day 15 in AC and ZVI columns. Additionally, Cr(Ⅵ) removal performances induced by biofilm in Bio-QZ columns were promoted with the increase of influent Cr(Ⅵ) concentrations. According to fluorescent images, activated carbon was found to be the best biofilm carrier. Fe⁰ may not be suitable for microbial colonization because biofilm depolymerization occurred on Fe⁰ surface. Moreover, high concentration of Cr(Ⅵ) would lag the evolution of biofilm. Magnetite generating was found on the Fe⁰ surface. X-ray photoelectron spectroscopy (XPS) analysis indicated that the removal mechanism of Cr(Ⅵ) in biotic columns was biotransformation of Cr(Ⅵ) to Cr(Ш) species. Our results may provide a new insight in Cr(Ⅵ) in-situ remediation from groundwater by Bio-PRB system.

Microscopic mechanism about the selective adsorption of Cr(VI) from salt solution on O-rich and N-rich biochars

The adsorption of Cr(VI) on biochars can be suppressed by coexisting anions, but the roles of O-containing functional groups and in particular N-containing functional groups are unclear. In this study, we combined spectroscopic and molecular simulation approaches to investigate the selective adsorption of Cr(VI) on the O-rich (PB, UB1) and N-rich (UB3, UB5) biochars under strong competition of anions. The elemental analysis and pyrolysis-gas chromatography/mass spectrometry indicated that the structures of PB and UB1 were similar, and so were the UB3 and UB5. Quantification of functional groups showed that for UB1, 75.3% of Cr(VI) removal was attributed to O-containing groups, while 53.3-72.7% of that was mediated by N-containing groups in UB3 and UB5. X-ray photoelectron spectra and density functional theory calculations confirmed that for O-rich biochars, surface complexation and strong H-bonds between carboxyl/hydroxyl and HCrO₄^- improved Cr(VI) removal in the presence of anions, while for N-rich biochars, Cr(VI) adsorption was depressed by coexisting anions in the order of Cl^->NO₃^- >SO₄^2- because of the weaker H-bond between protonated amino groups and HCrO₄^-. This study presents a novel approach for quantitative, molecular-level evaluation of the roles of biochar functional groups in the Cr(VI) removal from complex environmental systems.

FeS2 assisted degradation of atrazine by bentonite-supported nZVI coupling with hydrogen peroxide process in water: Performance and mechanism

In this study, bentonite-supported nZVI (B-nZVI) was used as a catalyst to activate H₂O₂ for atrazine (ATZ) degradation in the presence of FeS₂. Results indicated that ATZ degradation by B-nZVI/H₂O₂ process was significantly enhanced when FeS₂ was introduced, and nearly 98% of ATZ was degraded by B-nZVI/FeS₂/H₂O₂ process within 60 min under the optimum conditions. ATZ degradation of B-nZVI/FeS₂/H₂O₂ process was much higher than the sum of B-nZVI and FeS₂/H₂O₂ processes. The presence of HCO₃^-, PO₄^3- and F^- exhibited significant negative effects on the ATZ degradation, whereas both Cu²⁺ and Ni²⁺ exhibited positive effects on that. Both citric acid (CA) and ethylenediaminetetraacetic acid (EDTA) with lower concentration enhanced ATZ degradation rate, but significant suppression effects on that with higher concentration. The degradation of ATZ and 2,4-Dichlorophenol (2,4-DCP) could be simultaneously achieved in B-nZVI/FeS₂/H₂O₂ process under certain conditions. High soluble Fe²⁺ induced an excellent decomposition of H₂O₂ by B-nZVI and FeS₂. OH was dominant radical, and contributed to nearly 86% of the overall ATZ removal. A total of five intermediate products of ATZ were identified, and ATZ degradation was achieved via de-alkylation and hydroxylation processes. An enhanced reaction mechanism for ATZ degradation by B-nZVI/FeS₂/H₂O₂ process was proposed, and B-nZVI/FeS₂/H₂O₂ process exhibited an excellect catalytic performance within four successive runs.

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).

Remediation of hexavalent chromium in column by green synthesized nanoscale zero-valent iron/nickel: Factors, migration model and numerical simulation

In this work, green tea extracts synthesized nanoscale zero-valent iron/nickel (GT-nZVI/Ni) was prepared and the Cr(VI) contaminated soil column was remediated by GT-nZVI/Ni suspension. The influence factors including the concentration, pH value and flow rate of GT-nZVI/Ni suspension were studied. Under the conditions of pH = 4, concentration of 0.15 g/L and flow rate of 1.25 mL/h, GT-nZVI/Ni suspension had the best reduction and immobilization effect on Cr(VI) in the soil column. Na⁺ and Ca²⁺ can promote the immobilization of Cr (VI) in soil, while humic acid weakened the immobilization of Cr (VI). After GT-nZVI/Ni is injected into the soil column, the content of weak acid extractable and reduced chromium is significantly reduced, and the toxic hazard of hexavalent chromium in the soil is greatly reduced. The 1D-CDE model was used to fit the breakthrough curves of Fe(tot), Fe(aq) and Fe(0), and the migration of GT-nZVI/Ni in Cr(VI) contaminated soil was simulated and predicted. Compared with the inert solute Cl^-, the breakthrough curves of Fe (tot), Fe (aq) and Fe (0) in Cr (VI) contaminated soil column were significantly lagged, with delay coefficients of 2.465, 2.322 and 3.288, respectively. The reaction of GT-nZVI/Ni with Cr (VI) led to the decrease of Fe mobility. Finally, the outflow concentration of Fe (tot) was 0.064 g/L, and the loss was mainly due to reaction and retention in the soil. About 57.89% of GT-nZVI/Ni was retained in the soil.

Highly efficient remediation of groundwater co-contaminated with Cr(VI) and nitrate by using nano-Fe/Pd bimetal-loaded zeolite: Process product and interaction mechanism

Hexavalent chromium and nitrate co-contaminated groundwater remediation are attracting extensive attention worldwide. However, the transformation pathways of chromium and nitrate and the interplay mechanism between them remain unclear. In this work, zeolite-supported nanoscale zero-valent iron/palladium (Z-Fe/Pd) was synthesized and used for the first time to simultaneously remediate Cr(VI) and nitrate. Transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses confirmed that nanoscale zero-valent iron/palladium was successfully loaded onto zeolite and it exhibited good dispersibility and oxidation resistance. Results of batch experiments showed that the Cr(VI) and nitrate removal efficiencies decreased from 95.5% to 91.5% to 45% and 73%, respectively, with the initial solution pH increasing from 3.0 to 8.0. The removal rates and efficiencies of Cr(VI) and nitrate under anoxic conditions were higher than those under open atmosphere because the dissolved oxygen diminished the electron selectivity toward the target pollutants. Moreover, the presence of Cr(VI) inhibited nitrate reduction by forming Fe(III)-Cr(III) hydroxide to impede electron transfer. Cr(VI) removal was promoted by nitrate, within limits, by balancing the consumption and generation rate of Fe₃O₄, which enhanced electron migration from the Fe(0) core to the external surface. The removal capacities of Cr(VI) and nitrate reached 121 and 95.5 mg g^-1, respectively, which were superior to the removal capacities of similar materials. Results of product identification, XRD, and XPS analyses of spent Z-Fe/Pd indicated that the reduction of Cr(VI) was accompanied by adsorption and co-precipitation, whereas the reduction of nitrate was catalyzed by the synergism of Fe(0) and Pd(0). An alternative to the simultaneous remediation of Cr(VI) and nitrate from groundwater under anoxic conditions is provided.

Bottom-up approach synthesis of core-shell nanoscale zerovalent iron (CS-nZVI): Physicochemical and spectroscopic characterization with Cu(II) ions adsorption application

Single pot system in chemical reduction via bottom-up approach was used for the synthesis of core shell nanoscale zerovalent iron (CS-nZVI). CS-nZVI was characterized by a combination of physicochemical and spectroscopic techniques. Data obtained showed BET surface area 20.8643 m2/g, t-Plot micropore volume 0.001895 cm3/g, BJH volume pores 0.115083 cm3/g, average pore width 186.9268 Å, average pore diameter 240.753 Å, PZC 5.24, and pH 6.80. Surface plasmon Resonance from UV-Vis spectrophotometer was observed at 340 nm. Surface morphology from SEM and TEM revealed a spherical cluster and chain-like nanostructure of size range 15.425 nm -97.566 nm. Energy Dispersive XRF revealed an elemental abundance of 96.05% core shell indicating the dominance of nZVI. EDX showed an intense peak of nZVI at 6.2 keV. FTIR data revealed the surface functional groups of Fe-O with characteristics peaks at 686.68 cm-1, 569.02 cm-1 and 434 cm-1. In a batch technique, effective adsorption of endocrine disruptive Cu(II) ions was operational parameters dependent. Isotherm and kinetics studies were validated by statistical models. The study revealed unique characteristics of CS-nZVI and its efficacy in waste water treatment.

The comparative study of a homogeneous and a heterogeneous system with green synthesized iron nanoparticles for removal of Cr(VI)

Green iron nanoparticles (G-nZVI) were synthesized in situ by adding grape-seed extracts and Fe2+ solution simultaneously. The performances for the removal of Cr(VI) were compared in a homogeneous system by original G-nZVI (in suspension) with in a heterogeneous system by treated G-nZVI. The characterization of TEM, SEM, XRD, FTIR and XPS show that G-nZVI is the formation of Fe°-iron oxide core-shell nanoparticles with organic matters in the extracts as capping/stabilizing agents. The same excellent performances on the removal of Cr(VI) were observed in the both systems and the adsorption capacity was from 78.3 to 166.7 mg (Cr)·g-1 (Fe) with the increase of initial Fe2+ concentrations. The pseudo second-order model described the adsorption process excellently and both pseudo first-order and pseudo second-order models fit the reduction process well. It illustrated that the reaction included prompt adsorption and simultaneous redox process. Moreover, the results of thermodynamics study (ΔG° < 0, ΔH° > 0, ΔS° > 0) revealed that the adsorption was a spontaneous and endothermic process. It is obvious that the systhesis of original G-nZVI in the homogeneous system is more simple, rapid, cost-effective and suitable for in situ uses. It holds a great potential for remediation of soil and water.

Utilizing waste corn-cob in biosynthesis of noble metallic nanoparticles for antibacterial effect and catalytic degradation of contaminants

In the present study, cost-effective, and environmentally friendly fabrication of silver and gold nanoparticles was performed by using aqueous extract of waste corn-cob. The formation of the metallic nanoparticles (MNPs) was optimized by UV-Vis method. The phytoconstituents were responsible for reduction of silver and gold ions to silver nanoparticles (CC-AgNPs) and gold nanoparticles (CC-AuNPs) which were demonstrated by Fourier-transform infrared (FTIR) spectroscopy while formation of AgCl was attributed to the presence of chloride ions in the aqueous extract. The crystalline nature of the AgNPs, AgCl, and AuNPs was confirmed using the X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns. Morphological studies showed that the synthesized CC-AgNPs existed in spherical shape with the size ranging from 2 to 28 nm possessing an average value of 11 nm while CC-AuNPs were present in the multiple shapes with size ranging from 5 to 50 nm possessing an average value of 35 nm. For studies on bioactive application, the CC-AgNPs exhibited a high antibacterial activity against three bacterial strains including Salmonella typhimurium, Bacillus cereus, and Staphylococcus aureus. In addition, the catalytic efficiency of MNPs was investigated for reduction of o-, m-, p-nitrophenols, and degradation of organic dyes including Eosin Y and Rhodamine 6G. The rate constants calculated from the kinetical data revealed that the biosynthesized nanoparticles are excellent catalysts in potential applications for treatment of wastewater. Graphical abstract .

Polyethylene glycol-stabilized nano zero-valent iron supported by biochar for highly efficient removal of Cr(VI)

In this study, polyethylene glycol (PEG)-stabilized nano zero-valent iron (nZVI) supported by biochar (BC) (PEG-nZVI@BC) was prepared to remedy Cr(VI) with high efficiency. The morphology, functional groups, and crystalline structure of PEG-nZVI@BC composites were characterized, revealing that when PEG was added, a large number of -OH functional groups were introduced, and nZVI was effectively dispersed on the BC surface with a smaller particle size. The results of Cr(VI) remediation experiments showed Cr(VI) removal rate by PEG-nZVI@BC (97.38%) was much greater than that by BC-loaded nZVI (nZVI@BC) (51.73%). The pseudo second-order and Sips isotherm models provide the best simulation for Cr(VI) removal experimental data, respectively. The main remediation mechanism of Cr(VI) was reduction and co-precipitation of Cr-containing metal deposits onto PEG-nZVI@BC. Ecotoxicity assessment revealed PEG-nZVI@BC (1.00 g/L) has little influence on rice germination and growth, but resisted the toxicity of Cr(VI) to rice. The modified Community Bureau of Reference (BCR) sequential extraction showed pyrolysis could increase the percentage of oxidizable and residual Cr and diminish the environmental risk of Cr release from post-removal composites.

Effects of green synthesis, magnetization, and regeneration on ciprofloxacin removal by bimetallic nZVI/Cu composites and insights of degradation mechanism

In this study, nanoscale zerovalent iron (nZVI) with copper (Cu) bimetallic particles, whichare applied for degradation of Ciprofloxacin (CIP) under weak magnetic field (WMF), were synthesized using green tea extracts (GT-nZVI/Cu). The surface morphology and physicochemical properties of the novel catalytic materials were characterized. It was found that GT-nZVI was more stable and performed better in oxidation resistance than the nZVI synthesized by traditional chemical methods. Besides, the catalytic reactivity of GT-nZVI/Cu was measured with and without WMF, it is obvious from the experimental results the performance of GT-nZVI/Cu system was enhanced significantly with WMF. Moreover, WMF still had a certain effect even after being removed, which is called remanence effect. The mass spectrometry (MS) was utilized to analyze the degradation products of CIP, and the contribution of adsorption and Fenton/Fenton-like oxidation of GT-nZVI/Cu during CIP removal process was further evaluated. It was found that as the removal process progressed, the contribution ratio of Fenton/Fenton-like oxidation rose rapidly and exceeded adsorption after 20 min. Eventually, attempts have been made to regenerate GT-nZVI/Cu, in which physical recovery (ultrasonic) was the main route, and the CIP removal rate decreased as the regeneration times increased. This research provides new insights into the green synthesis and regeneration of nZVI and is expected to realize the practical application of nZVI.

Some Properties of Electron Beam-Irradiated Sheep Wool Linked to Cr(III) Sorption

We examined the characteristics of an electron beam irradiated wool with an absorbed dose of (21–410) kGy in comparison with natural wool with respect to the determination of the isoelectric point (IEP), zero charge point (ZCP), mechanism of Cr(III) sorption from higher concentrated solutions, and the modelling of the wool-Cr(III) interaction. The data of ZPC and IEP differed between natural and irradiated samples. Increasing the dose shifted the pH of ZPC from 6.85 for natural wool to 6.20 for the highest dosed wool, while the natural wool IEP moved very little, from pH = 3.35 to 3.40 for all of the irradiated samples. The sorption experiments were performed in a pH bath set at 3.40, and the determination of the residual Cr(III) in the bath was performed by VIS spectrometry under optimized conditions. The resulting sorptivity showed a monotonically rising trend with increasing Cr(III) concentration in the bath. Lower doses, unlike higher doses, showed better sorptivity than the natural wool. FTIR data indicated the formation of complex chromite salts of carboxylates and cysteinates. Crosslinks via ligands coming from different keratin chains were predicted, preferably on the surface of the fibers, but to a degree that did not yet inhibit the diffusion of Cr(III)-cations into the fiber volume. We also present a concept of a complex octahedral structure.

The degradation of decabromodiphenyl ether in the e-waste site by biochar supported nanoscale zero-valent iron /persulfate

Biochar supported nano zero-valent iron (BC-nZVI) synthesized through liquid phase reduction method was used to activate persulfate (PS) for the removal of decabromodiphenyl ether (BDE209) in the soil. The morphology, structure and composition of BC-nZVI were determined by SEM, XRD, XPS and FTIR. Batch experiments were carried out to investigate the effect of different factors, such as the molar ratio of PS to BC-nZVI, pH value of PS solution and reaction temperature, on the degradation efficiency of BDE209. Results showed that when the molar ratio of PS/BC-nZVI was 3:1, pH value was 3, reaction temperature was 40 °C, 82.06% of BDE209 could be removed within 240 min. The process fitted pseudo-first-order kinetics model well and the apparent activation energy (Ea) was 48.92 kJ mol^-1, indicating that the process was controlled by surface reaction. The quenching experiments showed that ·SO₄^- was predominate radical species in the degradation process in acid and neutral condition. However, ·OH played more important role in alkaline condition. GC-MS was used to determine the reaction products for inferring the degradation pathway of BDE209 in soil by BC-nZVI/PS system.

Aging effects on the stabilisation and reactivity of iron-based nanoparticles green synthesised using aqueous extracts of Eichhornia crassipes

Aging effects play a crucial role in determining applications of green-synthesised iron-based nanoparticles in wastewater treatment from laboratory scale to practical applications. In this study, iron-based nanoparticles (Ec-Fe-NPs) were synthesised using the extract of Eichhornia crassipes and ferric chloride. Scanning electron microscopy (SEM) revealed that the fresh Ec-Fe-NPs were spherical and had a narrow particle size range (50 to 80 nm). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) demonstrated that the Ec-Fe-NPs were mainly amorphous in nature and consisted of Fe⁰, FeO, Fe₂O₃ and Fe₃O₄. As they aged, the particle size of the liquid Ec-Fe-NPs gradually increased and then tended to stabilise. Ec-Fe-NPs that were aged for 28 days were only 19% less efficient than fresh material at removing Cr(VI). Extracts aged up to 28 days were also tested, and their antioxidant capacity was found to be 15.4% lower than that of the fresh extracts. Furthermore, the removal efficiency of Cr(VI) using iron-based nanoparticles synthesised with the aged extracts was 67.2%. Finally, the active components of the extracts, which were responsible for the reactivity and stability of the iron-based nanoparticles, were identified by liquid chromatography-mass spectrometry. Overall, green-synthesised iron-based nanoparticles show promise for Cr(VI) removal from wastewater in practical applications.

Bone-derived biochar and magnetic biochar for effective removal of fluoride in groundwater: Effects of synthesis method and coexisting chromium

The presence of fluoride in groundwater in excess of 1.5 mg L^-1 is a major environmental health concern, and biochar is a promising low-cost adsorbent for the treatment of such water. In the present study, pristine and magnetic biochars were synthesized by peanut hull and bovine bone for the adsorption of fluoride. The biochars were systematically characterized by SEM-EDS, BET, XRD, VSM, FT-IR, and XPS. The experiment results showed that the magnetic biochar prepared by soaking biomass in FeCl₃ solution and then pyrolyzing ("prepyrolysis") had a higher adsorption capacity than that prepared by mixing pristine biochar with Fe²⁺ /Fe³⁺ solution and then treating with NaOH ("postpyrolysis"). The bone-derived biochar and magnetic biochar exhibited high adsorption capacity of fluoride (>5 mg g^-1 ) due to the presence of hydroxyapatite (HAP) and γ-Fe₂ O₃ . The 0.1 M NaOH solution could be optimal desorption agent, and the adsorption-desorption experiments indicated the bone biochars maintained the reasonable adsorption capacity after several cycles. Moreover, the coexisting Cr(VI) and fluoride could be removed simultaneously by bone-derived biochars. It is suggested that bovine bone-derived pristine and magnetic biochars can be used as preferential adsorbents for fluoride removal from contaminated groundwater. PRACTITIONER POINTS: Bone-derived pristine and magnetic biochars exhibit high adsorption capacity for fluoride in weakly alkaline solution. The presence of hydroxyapatite and γ-Fe₂ O₃ in bone-derived biochars plays an important role for fluoride adsorption. Magnetic biochars prepared by soaking biomass in FeCl₃ solution and then pyrolyzing ("prepyrolysis") perform better. The coexisting Cr(VI) and fluoride can be simultaneously removed in groundwater by bone biochars.

Hexavalent chromium remediation based on the synergistic effect between chemoautotrophic bacteria and sulfide minerals

Hexavalent chromium (Cr(VI)) is an environmental concern due to the carcinogenic and mutagenic effect on living organisms. Sulfide minerals based Cr(VI) reduction is an economical and efficient strategy for Cr(VI) remediation. In this study, Cr(VI) reduction through the synergistic effect between chemoautotrophic bacteria and sulfide mineral is systematically investigated. Sulfide minerals dissolution and Cr(VI) reduction performance highly depends on mineral acid soluble property. Cr(VI) reduction capacity of pyrrhotite, pyrite, marcasite and sphalerite was 50, 104, 104 and 44 mg/g (Cr(VI)/mineral) respectively in the biotic system. Acidithiobacillus ferrooxidans (A. ferrooxidans) significantly enhanced pyrite and marcasite based Cr(VI) reduction kinetic and capacity. Proton consumption, iron coprecipitation and the biological activity deficiency in the abiotic system significantly inhibited Cr(VI) reduction. Elemental sulfur and secondary iron mineral as the main composition of the passivation layer inhibited sustainable Cr(VI) reduction. A. ferrooxidans facilitated acid nonsoluble mineral dissolution and surface passivation layer removal, and promoted Cr(VI) reduction. Acid nonsoluble sulfide mineral disulfide bond rapture, S°/S_n^2- oxidization, and Fe(III)/Cr(III) dissolution were accelerated by A. ferrooxidans, which facilitated Cr(VI) reduction reactive sites regeneration. Our study demonstrated that chemoautotrophic bacterial accelerated Cr(VI) reduction reaction through promoting acid nonsoluble sulfide mineral dissolution. This research is of environmental and practical significance to remediate redox sensitive contaminant based on the synergistic effect between sulfide minerals and chemoautotrophic A. ferrooxidans.

Green synthesis of zero valent iron nanoparticle using mango peel extract and surface characterization using XPS and GC-MS

In this study, a novel form of zero valent iron nanoparticle (GMP-nZVI) was successfully synthesized using mango peel extracts. Iron on the surface of the synthesized particle was negligible. Surface structure and compositional analysis was carried out using XPS and FTIR whereby the characteristic feature of the analysis highlighted the role of few organic compounds in the synthesis of GMP-nZVI. Depth profiling of GMP-nZVI by XPS indicated increasing intensity of Fe0 while the portion of Fe+2/Fe+3 and the dominant species which were on the surface (i.e. C and O) were decreasing. The structural form of GMP-nZVI has a layer of polyphenol followed by the oxides and hydroxides of iron onto the metallic iron which has a shell structure of 'Fe+3/Fe+2-polyphenol' complex islands on the core metallic iron (graphical abstract). The use of mango peel in the synthesis is a low cost approach and economically viable which also provides new insight of waste recycling and nanoremediation.

Optimizing the removal of nitrate from aqueous solutions via reduced graphite oxide-supported nZVI: synthesis, characterization, kinetics, and reduction mechanism

Graphene has been considered an ideal absorbent and excellent carrier for nanoparticles. Reduced graphite oxide (rGO)-supported nanoscale zero-valent iron (nZVI@rGO) is an effective material for removing nitrate from water. nZVI@rGO nanocomposites were prepared by a liquid-phase reduction method and then applied for nitrate-nitrogen (NO₃^--N) removal in aqueous solution under anaerobic conditions. The experimental results showed that the stability and activity of the nZVI@rGO nanocomposites were enhanced compared with those of nZVI. The influence of the reaction conditions, including the initial concentration of NO₃^--N, coexisting anions, initial pH of the solution, and water temperature, on NO₃^--N removal was also investigated by batch experiments. In a neutral or slightly alkaline environment, 90% of NO₃^--N at a concentration less than 50 mg/L could be removed within 1 h, and nitrogen production was approximately 15%. The process of NO₃^--N removal by nZVI@rGO fits well with different reaction kinetics. In addition, magnetite was the main oxidation product. RGO-supported nZVI might become a promising filler in the permeable reactive barrier process for groundwater remediation.