Nano Zero-valent Iron Composites Research Articles

Synergistic adsorption and degradation of sulfonylurea herbicides by biochar-supported nano zero-valent iron composites in in-situ soil remediation

The extensive and continuous application of sulfonylurea herbicide is crucial for weed management but has resulted in widespread non-point source pollution. In this study, nano zero-valent iron/biochar (nZVI/BC) was synthesized by using FeCl3-impregnated corn stalks under anoxic pyrolysis conditions, which was applied in the in-situ remediation of bensulfuron methyl (BSFM) and sulfometuron methyl (SMTM) polluted soil. The results show that nZVI/BC with a 2.7 ratio of Fe/C had the highest efficiency in removing sulfonylurea herbicides. The removal efficiencies of BSFM and SMTM by nZVI/BC were negatively correlated to initial concentrations of sulfonylurea herbicides and positively correlated to nZVI/BC addition amount in the soil. Moreover, nZVI/BC could remove 53 % of BSFM and 72 % of SMTM at the concentration of 5 mg/kg after 21 d, which was much higher than that of BC. Notably, the removal efficiency of BSFM by nZVI/BC reached 36 % within 7 d, while the removal efficiency of SMTM by nZVI/BC was up to 68 % even within 3 d. The adsorption of herbicides by nZVI/BC was mainly driven by chemical processes involving multilayer adsorption. Furthermore, the removal mechanisms of BMTM and SMTM by nZVI/BC also involved C = O and C–O groups and oxidation of nZVI to FeO and Fe3O4 along with the cleavage of the sulfonylurea bridge. This study provides a promising application of nZVI/BC in in-situ remediating sulfonylurea herbicide- polluted soil.

Carbothermally synthesized, lignin biochar-based, embedded and surface deposited nano zero-valent iron composites: Comparative material characterization, selective gas adsorption and nitroaromatics remediation

Biochar (BC) with nanoscale zero valent iron (nZVI) incorporation offers advantageous materials for water purification. Even though the most common approach for nZVI incorporation is the deposition on the carrier surface, embedding in the support matrix has also been reported. However, the behavior of the embedded material in contaminant removal has not been adequately studied while characteristics and the remediation capabilities of the two materials have not been compared. Present study focuses on preparing and extensively characterizing two materials: nZVI embedded in (Lig-e-nZVI) and surface deposited on (Lig-s-nZVI) lignin BC with subsequent comparative study of remedial action for two nitroaromatics, p-nitroaniline (pNA) and p-nitrophenol (pNP). The synthesis of Lig-e-nZVI and Lig-s-nZVI involved simultaneous and subsequent pyrolysis of lignin and carbothermal reduction of the iron salt, respectively. Lig-e-nZVI showed enhanced porosity. XRD confirmed the formation of Fe0. HR-TEM images proved the core-shell structure of nZVI, and an interlayer spacing of 0.36nm of the shell verified that the Fe0 particles are encapsulated with graphene while an iron carbide inner layer was also observed, thinner in Lig-e-nZVI and thicker in Lig-s-nZVI. Band gap energy of 2.54eV suggested a photocatalytic activity of both materials. Best fitted Sips isotherms showed 23.1 and 13.1mgg-1 capacities for Lig-s-nZVI in pNP and pNA adsorption respectively. Highest stability was portrayed by Lig-e-nZVI over 4 regeneration cycles. The physicochemical features of the developed materials further enable selective gas adsorption. Findings provide new insights into physicochemical characteristics and remedial actions of differently synthesized nZVI-BC composites.

Enhanced methylene blue degradation by graphene oxide-encapsulated nano zero-valent iron composites: Optimization, mechanistic insights, and environmental implications

Methylene blue (MB) in textile dye wastewater poses a significant environmental challenge due to its high chemical stability and resistance to biodegradation. This study investigates the use of a novel graphene oxide-encapsulated nano zero-valent iron (GO/nZVI) composite for the efficient and sustainable degradation of MB. The GO/nZVI composite was synthesized via hydrothermal co-precipitation and self-assembly methods and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Under optimized conditions, the composite achieved an impressive 99.99 % degradation of MB within 40 min, demonstrating substantial improvements in stability and reusability. The composite retained over 84.5 % of its catalytic activity after five cycles, underscoring its potential for practical wastewater treatment applications. The optimization of reaction conditions through response surface methodology (Box-Behnken design, BBD) facilitated the formation of a core-shell structure, which significantly enhanced electron transfer and radical generation, crucial for MB oxidation. Radical quenching experiments confirmed hydroxyl radicals (·OH) as the primary active species, and gas chromatography-mass spectrometry (GC-MS) analysis elucidated the degradation pathway. This study presents a scalable and environmentally friendly solution for the treatment of recalcitrant organic pollutants, marking a significant advancement in water purification technologies.

Removal and stabilization of As and Cd in water/soil using silicate-supported nano zero-valent iron composites: Preparation, behavior, mechanism and cost analysis

A novel silicate-supported nano zero-valent iron composite material (nZVI@SS) for the removal and stabilization of arsenic (As) and cadmium (Cd) in water/soil had been developed through the modification of low-grade oolitic iron ore (OI) by reduction, while refinery sludge (RS) as reductant, manganese carbonate (MC) as additive in this work. The As and Cd adsorption capacity of nZVI@SS reached 93.91 mg·g−1 and 265.81 mg·g−1, respectively. Its specific surface area and pore volume increased by 19.28 m2·g−1 and 0.24 cm3·g−1, respectively when compared with unmodified OI. In the actual soil leaching process, using 2 % nZVI@SS for 30 days, the leaching concentrations of As and Cd decreased by 87.86 % and 85.51 % respectively, while their bioavailable contents were reduced by 15.59 mg·kg−1 and 1.40 mg·kg−1, correspondingly. The formation of chemical precipitates as Fe-As, Ca-As compounds, and Cd(OH)2 was the main mechanism of their adsorption process. Therefore, HMs adsorbed by nZVI@SS were difficult to desorb, making it more suitable for passivation/stabilization of HMs in groundwater/soil. Furthermore, the production cost of nZVI@SS was approximately 50 $/T, below the average market value of comparable adsorption materials. This method made low-grade minerals into environmentally friendly materials with high added value, significantly reduced the environmental risk of HMs in water/soil, and provided a new approach for the development of sustainable environmentally friendly materials using hazardous waste RS as a resource.

Zr4+-modified chitosan coated nZVI enhance the removal of Cr(VI) by adsorption-reduction interaction

In order to solve the problems of poor mechanical properties and stability of chitosan and easy agglomeration and oxidation of nano zero-valent iron, Zr4+ crosslinked chitosan-coated nano zero-valent iron composites (CS-Zr@nZVI) were prepared for Cr(VI) removal from wastewater. The Zr-O, Zr-N and chitosan characteristic peaks in FTIR spectrum and the nZVI characteristic peaks in XRD pattern confirmed its successful synthesis. SEM and TEM showed that nZVI was dispersed on the surface of CS-Zr@nZVI, which solved the problem of easy agglomeration of nZVI. CS-Zr@nZVI has a wide operating pH range (pH= 2.0–10.0), high pHpzc, good stability and regeneration ability. The removal of Cr(VI) by CS-Zr@nZVI accords with pseudo-second-order kinetic model and Langmuir isotherm model, and it is a spontaneous, disordered and endothermic process. The maximum adsorption capacity was 344.82 mg g−1 at 318 K and pH = 2.0. At the dosage of 1.0 g L−1, CS-Zr@nZVI can treat 134.56 mg L−1 chromium-containing wastewater (pH = 3.5) to meet the discharge standard, which proves that CS-Zr@nZVI has the application prospect of removing Cr(VI). The main mechanisms of Cr(VI) removal by CS-Zr@nZVI are electrostatic interaction, ion exchange, reduction, complexation and co-precipitation. XPS analysis showed that 84.87 % of Cr(VI) was reduced to Cr(III). The above results provide a reference for the design of efficient Cr(VI) removal materials.

Green construction of MBI corrosion-resistant interfaces modified NZVI@MOFs-regulated 3D PAN cryogel film to enhance Cr(VI) removal

Nano zero-valent iron (NZVI) is an ideal material for treating chromium (VI). However, the NZVI's low loading and corrosion susceptibility in acidic Cr-containing industrial wastewater is the most pressing issue. Therefore, it is necessary to explore a method to construct novel NZVI composites with high loading, corrosion resistance, and outstanding activity. In this study, green 2-mercaptobenzimidazole (MBI) was employed for the first time as a corrosion inhibitor for NZVI to form a protective coating through chemisorption, thus blocking the corrosion of NZVI by reaction medium. Meanwhile, a novel multiphase green crystallization-assisted pore formation freeze-drying method was constructed to synthesize UiO-66-NH2 regulated 3D network porous polyacrylonitrile (PAN) cryogel film for stabilizing NZVI, which is intended to remove Cr(VI) effectively and without secondary contamination. The synthesized MBI-Fe0@MOF/PAN possessed prominent activity, corrosion resistance, and considerable NZVI loading (45.9 mg/g). The Cr(VI) removal could still reach 82.7 % after 6 cycles, and the level of total dissolved iron ions was lowered to 0.255 mg/L. MBI-Fe0@MOF/PAN for rapid removal of Cr(VI) may be ascribed to the synergistic reaction of rapid protonation of MBI and strong reduction of NZVI. This study constructed the MBI corrosion-resistant interface and 3D PAN cryogel film concepts not only to broaden the horizons of designing efficient NZVI catalytic materials but also to promote the development of treatment technologies for acidic Cr-containing industrial wastewater.

Boron-doped biochar-nano loaded zero-valent iron to activate persulfate for the degradation of oxytetracycline

Oxytetracycline has posed a serious environmental nuisance, and seeking environmental decontamination materials is the priority task to deal with antibiotic water contamination. Herein, boron-doped biochar loaded nano zero-valent iron composites (nZVI/BBC) were fabricated as activators of PDS for oxidative degradation of oxytetracycline hydrochloride (OTC), and the main removal mechanism was explored in detail. The results showed that Boron-doped biochar with borate ester structure (BC2O) and degree of defects are the main active sites for improving PDS activation properties. BBC could effectively prevent nZVI agglomeration and reduce nZVI passivation. The effects of calcination temperature of BBC, loading ratio and dosage of nZVI/BBC, PDS concentration, initial solution pH, pollutant concentration, and interfering ions on OTC removal by nZVI/BBC were also systematically investigated, and the optimal reaction conditions were screened: 10 wt% loading of nZVI in the composite, 1 g/L dosage of nZVI/BBC, 1 mM dosage of PDS and solution pH= 5. The cycling test showed that the removal rate of OTC by nZVI/BBC decreased from 95.3% to 70.2% after five cycles, indicating that there is excellent stability of this material. Among them, the catalyst of 10%nZVI/BBC displayed the optimal PDS activation performance, owing to the synergistic adsorption-double oxidation system, BBC as well as nZVI. The free radical quenching experiment and free radical trapping experiment proved that the degradation of OTC mainly followed the free radical pathway and SO4•− and •OH were the primary active species in the catalytic system. This study provides a practical reference for the treatment of actual antibiotic wastewater.

Persulfate activation using leonardite char-supported nano zero-valent iron composites for styrene-contaminated soil and water remediation

Effective in-situ technology to treat carcinogenic compounds in contaminated areas poses a major challenge. Our objective was to load nano-zero-valent iron (nZVI) onto leonardite char (LNDC), an alternative carbon source from industrial waste, for use as a persulfate (PS) activator for styrene treatment in soil and water. By adding a surfactant during synthesis, cetyltrimethylammonium bromide (CTAB) promotes a flower-like morphology and the nZVI formation in smaller sizes. Results showed that nZVI plays a crucial role in PS activation in both homogeneous and heterogeneous reactions to generate reactive oxygen species (ROS), which can remove 98% of styrene within 20 min. Quenching experiments indicated that singlet oxygen (1O2), superoxide radicals (O2•–), and sulfate radicals (SO4•–) were the main species working together to degrade styrene. XPS analysis also revealed a role of surface oxygen-containing groups (i.e., CO, C–OH) in activating PS for SO4•– and 1O2 generation. The possible reaction mechanism of PS activation by LNDC-CTAB-nZVI composite and factors affecting treatment efficiency (i.e., PS concentration, catalyst dosage, pH, and humic acid) were illustrated. The molarity/molality ratio of PS to nZVI should be set greater than 1 for effective styrene removal. GC-MS analysis showed that styrene was degraded to a less toxic benzaldehyde intermediate. However, the excessive use of PS and catalysts can harm plant growth, requiring a combining approach to achieve safer use for real applications. Overall results supported the use of the LNDC-CTAB-nZVI/PS system as an efficient in-situ treatment technology for soil and water remediation.

Remediation and its biological responses to Cd(II)-Cr(VI)-Pb(II) multi-contaminated soil by supported nano zero-valent iron composites

Multi-metal contaminated soil has received extensive attention. The biochar and bentonite-supported nano zero-valent iron (nZVI) (BC-BE-nZVI) composite was synthesized in this study by the liquid-phase reduction method. Subsequently, the BC-BE-nZVI composite was applied to immobilize cadmium (Cd), chromium (Cr), and lead (Pb) in simulated contaminated soil. The simultaneous immobilization efficiencies of Cd, Cr(VI), Crtotal, and Pb were achieved at 70.95 %, 100 %, 86.21 %, and 100 %, respectively. In addition, mobility and bioavailabilities of Cd, Cr, and Pb were significantly decreased and the risk of iron toxicity was reduced. Stabilized metal species in the contaminated soil (e.g., Cd(OH)2, Cd-Fe-(OH)2, CrxFe1-xOOH, CrxFe1-x(OH)3, PbO, PbCrO4, and Pb(OH)2) were formed after the BC-BE-nZVI treatment. Thus, the immobilization mechanisms of Cd, Cr, and Pb, including adsorption, reduction, co-precipitation, and complexation co-exist with the metals. More importantly, bacterial richness, bacterial diversity, soil enzyme activities (dehydrogenase, urease, and fluorescein diacetate hydrolase), and microbial activity were enhanced by applying the BC-BE-nZVI composite, thus increasing the soil metabolic function. Over all, this work applied a promising procedure for remediating multi- metal contaminated soil by using the BC-BE-nZVI composite.

Vitamin C mediates the activation of green tea extract to modify nanozero-valent iron composites: Enhanced transport in heterogeneous porous media and the removal of hexavalent chromium

Both green tea (GT) extract and vitamin C (VC) were used for the reduction of Fe3+ to Fe0 using a green synthesis method. Modified nanozero-valent iron (GT-nZVI@VC nanocomposites) was successfully obtained and characterized as α-Fe0-iron oxide/VC by multiple analytical methods. The GT-nZVI@VC nanocomposites showed better transportability than nZVI, in that transport behavior was slightly dependent on various ratios of sand/soil in water-saturated heterogeneous porous media. Breakthrough curves of GT-nZVI@VC nanocomposites in paddy soil exhibited “blocking effects” and were well described using a first-order straining coefficient (k2) on site 2 obtained from a two-site kinetic attachment model. In particular, GT-nZVI@VC (VC/Fe = 0.6) showed higher Cr(VI) removal (especially reducibility) in both paddy soil and water compared to that of nZVI and VC. It is likely that the synergistic effects of VC (ascorbic acid) and tea polyphenols can increase the released free electrons into solution, favoring the high reduction of Cr(VI) into Cr(III) (i.e., FeOCr2O3, Cr(OH)3 and Cr2O3), where Cr(III) is prone to be immobilized by the nanocomposites in soil. This research highlights that VC can mediate the activation of GT extract to successfully modify nZVI, which could be beneficial for efficient transport in subsurface and remediation of Cr(VI)-contaminated soil and underground water.

Facile fabrication of nano zerovalent iron – Reduced graphene oxide composites for nitrate reduction in water

Nano zerovalent iron is used to destruct a wide range of organic and inorganic contaminants in water. However, its performance is limited due to rapid aggregation and surface passivation. To minimise aggregation, we fabricated nano zerovalent iron on the reduced graphene oxide sheets using green tea derived polyphenols (hereafter rGO-nZVI-P) or borohydride ions (hereafter rGO-nZVI-B). Both rGO-nZVI-P and rGO-nZVI-B composites were characterised by electron microscopic, molecular spectroscopic and electrochemical methods. The spherical nZVI particulates (e.g. ~4–15 mm diameter) are well dispersed among rGO sheets. Polyphenols act as a capping agent for Fe (0) to prevent its aggregation. The X-ray diffraction and X-ray photon spectroscopic results show an admixture of Fe (0) with rGO and Fe oxides (e.g. FeOOH, Fe2O3, and Fe3O4 phases). The association of Fe (0) on the reduced graphene oxide matrix is believed to occur via π–π framework thus minimising surface passivation. The reduction efficiency of the nano zerovalent iron composites was determined using nitrate as index ion. When compared with rGO-nZVI-B, the rGO-nZVI-P reduces 70% of 0.8064 mM nitrate within an hour. Although traces of NO and NO2− are observed, ammonia is the dominant product that accounts for 95% nitrogen mass balance. The nitrate reduction by the rGO-nZVI composites follows pseudo-second-order kinetics. Fe (0) or its oxidation products are environmentally benign. The rGO-nZVI-P also has the potential to destruct excess nitrate in water remediation.

Effects of humic acid on enhanced removal of lead ions by polystyrene-supported nano-Fe (0) nanocomposite

Polymer-supported nanozero-valent iron composites (D001-nZVI) were fabricated for the removal of lead ions from aqueous solutions by embedding nZVI into the porous polystyrene anion exchanger D001. Humic acid (HA) was selected as a model species because of its ubiquitous existence to gain insight into the influencing factors in the actual application process. The iron contents of the composites were approximately 11.2%, and the smallest ZVI particle size was ~ 5 nm. The experimental results showed that the effect of HA on the reduction of lead ions by D001-nZVI was a concentration-dependent process. At low HA concentrations, the surface-competitive adsorption of HA and Pb2+ dominated; therefore, the removal efficiency of Pb2+ by D001-nZVI decreased from 97.5 to 90.2% with an increasing HA concentration. When the HA concentration increased to 30 mg/L or more, the lead ions removal remained constant with the following possible cooperation mechanism: the competitive adsorption of HA and Pb2+ on the nZVI surface and the well-dispersed particles were caused by electrostatic interactions between the HA coating and the nZVI surface. In addition, the adsorption complexation between HA and Pb2+ also had a positive effect on the removal of Pb2+ at higher concentrations of HA.

Turning date palm waste into carbon nanodots and nano zerovalent iron composites for excellent removal of methylthioninium chloride from water

Novel carbon nanodots (nCD-DBC) and nano zero-valent iron composites (nZVI-DBC) were synthesized using date palm waste-derived biochar (DBC). The synthesized materials were analyzed for chemical and structural composition by using FTIR, SEM, XRD, and TGA, and evaluated for their methylthioninium chloride dye (MB) removal efficiency from contaminated aqueous solutions. pH 7.0 was found optimum for the highest MB removal in sorption batch studies. Kinetics sorption of MB onto the sorbents was best described by pseudo-second-order (R2 = 0.93–0.99) and Elovich models (R2 = 0.86–0.97) implying that sorption was being controlled by chemisorption. Langmuir model predicted maximum sorption capacities for nCD-DBC, nZVI-DBC, and DBC were 1558.66, 1182.90, and 851.67 mg g−1, respectively, which correlated with the results of kinetics sorption. Likewise, nCD-DBC yielded the highest partition coefficient (7067 mL g−1), followed by nZVI-DBC (1460 mL g−1), and DBC (930 mL g−1). Post-sorption XRD, FTIR, and SEM analyses depicted the binding of MB onto the sorbents. It was suggested that electrostatic interactions, π–π electron donor-accepter interactions, degradation, and diffusion were responsible for MB removal by the synthesized materials. Therefore, the nCD-DBC, nZVI-DBC, and DBC can potentially be used for scavenging MB dye from contaminated aqueous solutions.

Efficient photocatalysis of CrVI and methylene blue by dispersive palygorskite-loaded zero-valent iron/carbon nitride

Our previous study reported that a more dispersed palygorskite (Pal) with a multiparous structure can be fabricated from rigid nano-rods by ion beam bombardment. In this study, the new multiparous structure of Pal (MPal) was used to carry a nanocomposite prepared from graphitic carbon nitride (CN) and nano zero-valent iron (NZVI) following a simple thermopolymerisation method for the first time. The as-prepared sample (MPal/NZVI/CN) achieved broader light absorption in the visible light region and low recombination, according to the characterisation results of the UV–vis diffuse reflectance and photoluminescence (PL) spectra of the photocatalysts. The photocatalysis of CrVI and methylene blue (MB) in an aqueous solution by MPal/NZVI/CN revealed that the MPal/NZVI/CN-1:5:6 composites exhibited superior catalytic activity, with CrVI and MB removal efficiencies of 98.48% and 99.2% in 120 min, respectively. Additionally, the reaction rate constants (kCr and kMB) of MPal/NZVI/CN were much higher than those of CN, NZVI/CN, and MPal/CN because the formation of MPal and NZVI composites with CN promoted the separation of photo-generated electron-hole pairs. After four cycles, MPal/NZVI/CN exhibited great photoactivity, which could not only be attributed to the improved dispersion of MPal, but also to the ability of the photo-generated electrons of CN to reduce the FeIII/FeII to Fe0. This study opens new opportunities for modifying photocatalysts using the inorganic nanomaterials readily formed by physical irradiation.

Carboxymethyl nanocellulose stabilized nano zero-valent iron: an effective method for reduction of hexavalent chromium in wastewater

The present work describes a novel material, carboxymethyl nanocellulose (CMNc) and its use for stabilization of nano zero-valent iron (nZVI) composites. The CMNc stabilized nano zero-valent iron composite was further utilized for effective reduction of hexavalent chromium [Cr(VI)] in aqueous media. The FTIR studies showed peaks corresponding to the nanocellulose and carboxymethylation of nanocellulose (CMNc). The x-ray diffraction pattern of CMNc-stabilized nZVI composites was confirmed the presence of nZVI nanoparticles. The morphology of nanocomposites was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The thermograms of thermogravimetric analysis showed that thermal stability of the CMNc-stabilized nZVI composites was much improved as compared to bare nZVI. The maximum adsorption capacity of CMNc-stabilized nZVI composites for Cr(VI) was 87.71 mg g−1 as determined by Langmuir and Freundlick adsorption isotherms. At a constant dose of 0.015 g, CMC-stabilized nZVI nanoparticles were able to reduce almost 100% of 15 mg l−1 of Cr(VI) in 90 min. Therefore, the CMNc-stabilized nZVI composites material showed a promising potential for the adsorption of Cr(VI) in wastewater and can impel advancements in CMNc-based nanomaterials for their application in environmental remediation of heavy metals.

Facile synthesis of graphene nano zero-valent iron composites and their efficient removal of trichloronitromethane from drinking water.

Halonitromethanes (HNMs), as an emerging class of disinfection by-products containing nitrogen (N-DBPs) in drinking water, have possessed public health concerns. Two most studied materials, graphene and nanometer-sized zero-valent iron, have been successfully combined into binary nanocomposites (G-nZVI) via facile carbonization and calcinations of glucose and ferric chloride, which was used in the removal of HNMs from drinking water in this study. When the Fe/C mass ratio was 1:5, the as-prepared G-nZVI hybrids comprised numerous dispersed Fe(0) nanoparticles with a range of 5-10 nm in diameter. Batch experimental results indicated that the as-prepared G-nZVI could effectively remove trichloronitromethane (TCNM), a dominant in the group of HNMs from drinking water. About 99% of initial TCNM could be adsorbed and degraded under 60 mg/L G-nZVI dosage within 120 min. Kinetic studies indicated that the removal of TCNM by G-nZVI followed a pseudo first order rate (R(2) > 0.9). The degradation pathways of TCNM by G-nZVI nanocomposites might include dechlorination and denitration of TCNM. The Fe was in the form of iron oxides in the graphene material shape which was then restored to Fe(0) again via calcinations. These results indicated that the synthesized G-nZVI nanocomposites could be a powerful material to remove HNMs from drinking water.