Zero-valent Iron Research Articles

Activated carbon fiber loaded nano zero-valent iron for Microcystis aeruginosa removal: Performance and mechanisms

Cyanobacterial blooms caused by Microcystis aeruginosa threaten environmental safety and daily life. In this study, an activated carbon fiber-supported nano zero-valent iron composite (ACF-nZVI) was developed to remove Microcystis aeruginosa. The results showed that nZVI was evenly distributed on the activated carbon fibers, preventing aggregation and oxidation. ACF-nZVI achieved a removal efficiency of more than 90 % within a pH range of 3–7. During the reaction, H2O2, which was generated by Fe0, was activated to form ·OH and ·O–2, which dismantled antioxidant enzymes and induced lipid peroxidation. Additionally, ACF-nZVI destroyed the cell wall and membrane, resulting in protein and humus leakage and causing 92.34 % cell damage and death. In this study, an environmentally friendly and stable nanomaterial was developed, offering a novel approach for the safe, cost-effective, and efficient removal of cyanobacteria.

Roles of silica coating on nanosized zero-valent iron in sequential reduction–oxidation process in a system containing persulfate

A sequential reduction–oxidation process using silica-coated nanosized zero-valent iron (nZVI) particles (nZVI@SiO2) and persulfate for mineralizing recalcitrant compounds was developed, and the effects of the process on nitrobenzene were evaluated. This sequential process significantly enhanced contaminant mineralization, which could not be effectively achieved by reduction or oxidation alone. The nZVI@SiO2 rapidly reduced nitrobenzene to aniline, then the aniline concentration gradually decreased after persulfate had been added and initiated sequential oxidative degradation. The SiO2 coating on the nZVI@SiO2 limited outward mass transfer of reaction products and increased the efficiency with which nitrobenzene was converted into aniline. Slow release of Fe(II) caused by the coating caused persulfate activation and subsequent aniline oxidation to be more sustained and efficient than without the coating. The final nitrobenzene–aniline mineralization efficiency was higher for the nZVI@SiO2/persulfate system than the nZVI/persulfate system. The SiO2 coating of the nZVI@SiO2 particles was an excellent protective layer, protecting the particles from undesirable consumption through reactions with groundwater components. nZVI@SiO2 particle transformations during the sequential process were investigated, and the operating conditions were optimized to maximize the recalcitrant compound removal efficiency. The results indicated that nZVI@SiO2 and persulfate could be used to mineralize organic contaminants in groundwater through sequential reduction–oxidation.

Efficient Removal of Phosphate from Aqueous Solutions Using Kaolin-Supported Nanoscale Zero-Valent Iron Particles

Efficient Removal of Phosphate from Aqueous Solutions Using Kaolin-Supported Nanoscale Zero-Valent Iron Particles

Layered Double Hydroxides as Next-Generation Adsorbents for the Removal of Selenium from Water

This research paper provides a comprehensive overview of the use of layered double hydroxides (LDH) in the removal of selenium species from contaminated water sources. Key studies on sorption mechanisms and the impact of competing ions on selenium removal are presented, and the effectiveness of LDH is compared across different structures and compositions. Scholarly sources extensively document the application of conventional LDH for effective selenium removal, with notable advancements achieved through innovative synthesis approaches. Comparative studies between LDH synthesized through various methods reveal the potential of tailored LDH for enhanced selenium adsorption. The paper further explores the influence of competing anions on LDH efficacy, emphasizing the impact of sulfate on selenium removal. Additionally, investigations into calcined LDH and commercially available variants underscore the potential for industrial applications. Beyond conventional LDH, the paper delves into iron-based LDH, LDH with intercalated thiomolybdate anions, and layered rare earth hydroxides, exploring their effectiveness in separating different selenium species. The role of pH in the removal of selenium species and the impact of three-metal cation LDH are also discussed. The study extends to nanocomposites, combining LDH with zero-valent iron, carbon-based materials, and organic compounds, illustrating their potential for selenium species immobilization. The presented findings offer valuable insights for researchers and practitioners in environmental science, addressing the growing demand for efficient selenium remediation strategies.

Key role of sulfur in sulfidated zerovalent iron during persulfate activation for the dynamic equilibrium of oxidative radicals including SO4•- and •OH

Surface sulfidation has been widely investigated to effectively enhance the utilization and selectivity of iron electrons for enhanced pollutant reduction. However, there is relatively less knowledge on whether sulfidation facilitates the catalytic oxidation process and the mechanism of enhancement. Therefore, in this study, the role of surface sulfidation in modulating the oxidant decomposition pathway and reactive oxygen species generation was investigated with the sulfidated zerovalent iron (S-ZVI) activated persulfate (PS) system. The results revealed that sulfur on the surface of S-ZVI not only facilitates PS activation to generate more SO4•-, but also acts as an essential in the dynamic equilibrium between SO4•- and •OH. Specifically, the S-ZVI surface sulfide first forms sulfur monomers during catalysis, which promotes electron transfer to accelerate Fe3+ to Fe2+ cycling, prompting the generation of more SO4•- also generates SO32−. Then, SO32− is further reacted with •OH to generate the [O−-O-SO3-] intermediate of SO4•-, which leads to a dynamic equilibrium of SO4•- and •OH, mitigating the further conversion of SO4•- to •OH. These findings unveiled the dynamic variation of sulfur on the surface of S-ZVI during PS activation, elevating new insights for the sulfate radical-based efficient degradation.

Biological self-protection inspired engineering of nanomaterials to construct a robust bio-nano system for environmental applications.

Nanomaterials can empower microbial-based chemical production or pollutant removal, e.g., nano zero-valent iron (nZVI) as an electron source to enhance microbial reducing pollutants. Constructing bio-nano interfaces is critical for bio-nano system operation, but low interfacial compatibility due to nanotoxicity challenges the system performance. Inspired by microorganisms' resistance to nanotoxicity by secreting extracellular polymeric substances (EPS), which can act as electron shuttling media, we design a highly compatible bio-nano interface by modifying nZVI with EPS, markedly improving the performance of a bio-nano system consisting of nZVI and bacteria. EPS modification reduced membrane damage and oxidative stress induced by nZVI. Moreover, EPS alleviated nZVI agglomeration and probably reduced bacterial rejection of nZVI by wrapping camouflage, contributing to the bio-nano interface formation, thereby facilitating nZVI to provide electrons for bacterial reducing pollutant via membrane-anchoring cytochrome c. This work provides a strategy for designing a highly biocompatible interface to construct robust and efficient bio-nano systems for environmental implication.

The clogging effect of nanoscale zero valent iron corrosion in bicarbonate anaerobic water on porous media: A real-time pore-scale visualization

The corrosion-induced permeability changes of nanoscale zero-valent iron (NZVI) are one of the crucial factors constraining the successful application of NZVI in the remediation of contaminated groundwater. It is of great significance to study the dynamic evolution of corrosion products of NZVI after NZVI is injected into porous media and its influence on pore plugging effect from the pore scale. Micro computed tomography (Micro-CT) imaging technology, mineralogical characterization and theoretical calculations were used to understand the details of NZVI corrosion plugging porous media at the pore scale. This study reveals the factors of NZVI corrosion plugging porous media, namely, gas production (H2) in the early and middle stages of corrosion (before 90 days) and solid phase changes (NZVI volume increase and migration) in the later stages (after 90 days). The permeability loss rate of the porous media was 66.8%, 87.3%, 79.4%, and 53.6% at the corrosion times of 30, 60, 90, and 120 days, respectively. After 90 d of corrosion, the particle size of NZVI increases by 7.9%, and the secondary minerals formed by corrosion are mainly Fe3O4/γ-Fe2O3 and FeOOH. In addition, this study also found that the migration of NZVI after 90 d was due to its corrosion reducing the magnetic attraction between particles, dissociating into smaller particles or agglomerates under the action of fluid dynamics, resulting in its redistribution in the porous medium and causing blockage. This study clarifies that NZVI corrosion plays a vital influence in affecting the permeability and clogging of porous media, providing valuable guidance for optimizing NZVI-based remediation technologies.

Chemical aging of biochar-zero-valent iron composites in groundwater: Impact on Cd(II) and Cr(VI) co-removal

Biochar (BC), zero-valent iron (ZVI), and their composites are promising materials for use in permeable reactive barriers, although further research is needed to understand how their properties change during long-term aging in groundwater. In this study, BC, ZVI and their composites (4BC-1ZVI) were subjected to the chemical aging tests in five media (deionized water, NaCl, NaHCO3, CaCl2 and a mixture of CaCl2 and NaHCO3 solutions) for 20 days. After treatment, the microscopic analysis and performance tests for the co-removal of Cd(II) and Cr(VI) were carried out. The results indicated that the removal of Cd(II) by aged 4BC-1ZVI followed a pseudo-second-order model, whereas the removal of Cr(VI) was better fitted with a pseudo-first order model. The aging mechanism of 4BC-1ZVI was primarily governed by iron corrosion/passivation, the reduction of soluble components, and the formation of carbonate minerals. Less Fe3O4/ γ-Fe2O3 was formed during aging in deionized water, NaCl and CaCl2 solutions. The corrosion products, Fe3O4/ γ-Fe2O3, FeCO3 and α/γ-FeOOH, were observed after aging in NaHCO3 and a mixture of NaHCO3 and CaCl2 solutions. The decrease in the soluble components of biochar led to a decrease in cation exchange, while carbonate minerals contributed to Cd(II) precipitation. This work provides insights into the aging processes of BC-ZVI composites for long-term groundwater remediation applications.

Nanoscale zero-valent iron alleviated horizontal transfer of antibiotic resistance genes in soil: The important role of extracellular polymeric substances

Extracellular polymeric substances (EPS) are tightly related to the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs), but often neglected in soil. In this study, nanoscale zero-valent iron (nZVI) was utilized for attenuation of ARGs in contaminated soil, with an emphasis on its effects on EPS secretion and HGT. Results showed during soil microbe cultivation exposed to tetracycline, more EPS was secreted and significant increase of tet was observed due to facilitated HGT. Notably, copies of EPS-tet accounted for 71.39 % of the total tet, implying vital effects of EPS on ARGs proliferation. When co-exposed to nZVI, EPS secretion was decreased by 38.36–71.46 %, for that nZVI could alleviate the microbial oxidative stress exerted by tetracycline resulting in downregulation of genes expression related to the c-di-GMP signaling system. Meanwhile, the abundance of EPS-tet was obviously reduced from 7.04 to 5.12–6.47 log unit, directly causing decrease of total tet from 7.19 to 5.68–6.69 log unit. For the reduced tet, it was mainly due to decreased EPS secretion induced by nZVI resulting in inhibition of HGT especially transformation of the EPS-tet. This work gives an inspiration for attenuation of ARGs dissemination in soil through an EPS regulation strategy.

A novel catalyst based on zero-valent iron nanoparticles for assisting electro-fenton process applied to a toxic wastewater

A catalyst based on zero-valent iron nanoparticles (nZVI) supported by zeolite Y (zeolite Y-nZVI) was synthesized to improve the performance of the heterogeneous electro-Fenton-like process for treating a toxic pesticide wastewater with pH of 6. Central Composite Design (CCD) under Response Surface Methodology (RSM) was applied to design the experiments and find the optimal parameters including time, current intensity, hydrogen peroxide volume (or concentration) and the synthesized catalyst dosage. The results showed that the chemical oxygen demand (COD) removal under the optimal conditions (time of 125 min, current intensity of 272 mA, hydrogen peroxide volume (or concentration) of 0.19 ml (8.102 × 10−3 M), and zeolite Y-nZVI catalyst dosage of 1.78 g) was at 83.69 % for treating a wastewater with pH of 6 although this increased to 91.26 % at pH of 3 under the Fenton reactions. In fact, the synthesized catalyst could properly treat wastewater in a pH close to neutral one. Since electro-Fenton is as efficient technique for treating the hazardous pollutants such as pesticide, it can successfully be used by their manufacturing factories. Since it properly works in the acidic pHs, it is not as applied technique for most of industries. Therefore, catalytic electro-Fenton process can be performed in (or near) a neutral pH. Since electro-Fenton is basically associated with iron, a catalyst based on it (such as Fe°) was chosen and supported on an abundant and suitable material such as zeolite. The synthesized catalyst was initially synthesized and characterized, and then successfully applied in the electro-Fenton process to treat a real pesticide containing wastewater obtained from industry.

A novel strategy for enhancing high solid anaerobic digestion of fecal slag and food waste using percolate recirculation and dosage of nano zero-valent iron

To speed up reaching UN Sustainable Development Goal 6 for safe sanitation by 2030, integrating high-solid anaerobic digestion (HSAD) into decentralized systems could recycle fecal slag (FS) and food waste (FW), aiding a circular economy and toilet revolution. In this study, a percolate recirculation system and conductive material were used to improve mass transfer, stability, and enhance methane production in HSAD of FS and FW. This setup consists of a percolate tank and a digester tank, where nano-zero valent iron (nZVI) was dosed in the percolate tank (PnZVI in P) and the digester tank (PnZVI in D) and compared with a control with no additive (PControl). The highest cumulative methane yield of 519.43 mL/gVS was achieved in PnZVI in D, which was 4.52 and 3.59 times higher than that of PControl (144.59 mL/gVS) and PnZVI in P (114.96 mL/gVS). This finding demonstrates that the dosing strategy of PnZVI in D facilitated effective interaction among organic matter, microbial communities, and nZVI, resulting in organics removal efficiencies of 67.42 % (total solid) and 77.22 % (volatile solid). Moreover, microbial community analysis supported the efficacy of the PnZVI in D strategy, revealing the enrichment of Clostridium sensu stricto 1 (46.91 %), which potentially engaged in interspecies electron transport (Interspecies hydrogen transfer (IHT) and direct interspecies electron transfer (DIET)) with Methanobacterium (81.19 %) and Methanosarcina (17.11 %). These interactions contribute to enhanced methane yield and stability maintenance in the HSAD system with percolate recirculation. The findings of this study demonstrate that the implementation of HSAD of FS and FW, coupled with percolate recirculation and the addition of nZVI, holds promise for enabling sustainable sanitation practices in developing regions. Moreover, this approach not only facilitates resource recovery but also eliminates the requirement for water.

Mechanistic insights into Fe3O4-mediated inhibition of H2S gas production in sludge anaerobic digestion

The addition of iron-based conductive materials has been extensively validated as a highly effective approach to augment methane generation from anaerobic digestion (AD) process. In this work, it was additionally discovered that Fe3O4 notably suppressed the production of hazardous H2S gas during sludge AD. As the addition of Fe3O4 increased from 0 to 20 g/L, the accumulative H2S yields decreased by 89.2 % while the content of element sulfur and acid volatile sulfide (AVS) respectively increased by 55.0 % and 30.4 %. Mechanism analyses showed that the added Fe3O4 facilitated sludge conductive capacity, and boosted the efficiency of extracellular electron transfer, which accelerated the bioprocess of sulfide oxidation. Although Fe3O4 can chemically oxidize sulfide to elemental sulfur, microbial oxidation plays a major role in reducing H2S accumulation. Moreover, the released iron ions reacted with soluble sulfide, which promoted the chemical equilibrium of sulfide species from H2S to metal sulfide. Microbial analysis showed that some SRBs (i.e., Desulfomicrobium and Defluviicoccus) and SOB (i.e., Sulfuritalea) changed into keystone taxa (i.e., connectors and module hubs) in the reactor with Fe3O4 addition, showing that the functions of sulfate reduction and sulfur oxidation may play important roles in Fe3O4-present system. Fe3O4 presence also increased the content of functional genes encoding sulfide quinone reductase and flavocytochrome c sulfidedehydrogenase (e.g., Sqr and Fcc) that could oxidize sulfide to sulfur. The impact of other iron-based conductive material (i.e., zero-valent iron) was also verified, and the results showed that it could also significantly reduce H2S production. These findings provide new insights into the effect of iron-based conductive materials on anaerobic process, especially sulfur conversion.

Enhanced the removal of norfloxacin by oxalated zero-valent iron with rich surface Fe(II) sites activating the chlorite

Oxalic acid-modified ball-milled zero-valent iron (OA-ZVIbm) was employed to activate sodium chlorite (ClO2-) for the removal of norfloxacin (NOR). The complete removal of 20 mg/L NOR was achieved within 60 min by the OA-ZVIbm/ClO2- process. Compared with the ZVIbm/ClO2- process which was the ball-milled zero-valent iron (ZVIbm) activate sodium chlorite, the reaction activity of the OA-ZVIbm/ClO2- process was increased by 102.6 times. Through scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical testing, and density functional theory (DFT) calculations, which has been confirmed that the introduction of oxalic acid can significantly increase the surface Fe(II) content of OA-ZVIbm, and accelerate the electron transfer rate of iron nuclei, thereby improve the efficiency of ClO2- activation for the removal of NOR. The role of various active species in NOR removal, which were •O2-, 1O2, Fe(IV), ClO2, and •OH, was elucidated through free radical quenching experiments, electron paramagnetic resonance (EPR) spectroscopy, and quantitative detection of active species. These active species all participated in the reaction, while •O2- played a dominant role in the reaction because it could transform into other active species, such as (•OH, 1O2). Inorganic anions and natural organic matter have no significant effect on the removal of NOR in the OA-ZVIbm/ClO2- process. The protonation of oxalic acid ensured its good pH applicability range (pH = 2–11), thus exhibiting excellent performance in NOR removal in real water bodies. This further demonstrates that OA-ZVIbm prepared by oxalic acid ball milling modification is an efficient ClO2- activator, offering promising prospects for antibiotic removal technology.

Degradation mechanism and ecotoxicity analysis of levofloxacin by palladium-modified nano zero-valent iron doped coconut shell biochar

The palladium-modified nano zero-valent iron (nZVI) doped coconut shell biochar (Pd-nZVI/BC) was successfully obtained through bimetallic modification and liquid-phase reduction. The synthesized Pd-nZVI/BC was further enhanced by the addition of an H2O2 co-catalyst for the removal of antibiotic levofloxacin (LVF). Results demonstrated that removal of LVF by Pd-nZVI/BC accomplished 94.6 % under proper conditions. Adsorption and degradation processes were involved in the LVF removal, and the predominant free radicals were •OH and •O2-. Adsorption relied mainly on electrostatic interactions, π-π interactions, and hydrogen bonding. While demethylation, deamidation, quinolone ring aldolization, depiperazinylation, deacetylation, decarboxylation, dehydroxylation, and oxidative breakage of the piperazine ring occurred during the degradation processes. Based on the degradation pathways, the ecotoxicity of LVF and its degradation intermediates were compared and assessed. Results implied that majority of the antibiotic LVF pollutant was eliminated or mineralized, and the toxicity potential of LVF was reduced in the Pd-nZVI/BC system. Simultaneous biochar utilization and pollutants removal could be achieved.

Use of carbon-encapsulated zero-valent iron nanoparticles from waste biomass to hydrogen sulphide wet removal.

This study evaluates the use of carbon-encapsulated zero-valent iron nanoparticles for biogas upgrading in wet systems. The nanoparticles were produced by hydrothermal carbonization, using olive mill waste (OMW) or microalgae as carbon sources. The solids were characterized to investigate the specific surface area, total and zero-valent iron content, pHPZC and chemical and crystalline composition. Their adsorption performance towards hydrogen sulphide (H2S) was tested by treating two types of synthetic biogas with and without CO2. In both cases, the starting H2S concentration was approximately 60 ppm and the experiments lasted until the complete saturation of the nanoparticles. Optimal Fe/C ratios of 0.05 for OMW nanoparticles and 0.2 for microalgae nanoparticles demonstrated H2S-specific adsorption capacities of 9.66 and 9.55 , respectively, in a synthetic biogas without CO2. The addition of CO2 in biogas reduced adsorption, possibly due to system acidification. X-ray photoelectron spectroscopy analysis revealed surface compounds on the surface of the spent nanoparticles, including disulphides, polysulphides and sulphate. The saturated adsorbents were effectively regenerated with air, leading to the oxidation of sulphur species and desorption. The regeneration allowed a total adsorption capacity of 53.25 and 34.14 , after 10 consecutive cycles of adsorption/regeneration with a single batch of olive mill and microalgae nanoparticles, respectively.

Adsorption of nickel (II) from aqueous solutions with clay-supported nano-scale zero-valent iron synthesized from green tea extract

Nano zerovalent iron (nZVI) supported adsorbents have been reported as suitable candidates for adsorption of water contaminants. However, the role of and interplay between surface chemistry, functional group density and textural properties has largely been unexplored. In this work, green tea derived nano zerovalent iron (nZVI) supported clay hybrid material (CnZVI) was used as a novel adsorbent for the removal of Ni2+ ions from water. The unmodified natural clay (Arg) and the CnZVI composite were characterized using FTIR, SEM, TGA and BET techniques. Incorporation of nZVI ameliorated the specific surface area from 16.88 to 30.46 m2/g, translating to ∼80 % increase. This translated to ∼69 % increase in maximum adsorption capacity from 8.47 to 14.38 mg/g, respectively. The addition of nZVI in the clay decreased the affinity (KF) for Ni2+ by ∼48 %. The disparity between the percent increase in surface area (∼80 %) and the adsorption capacity (∼69 %) implies the adsorption of Ni2+ was significantly controlled by textural properties compensating for the antagonistic effects of functional group density. The kinetic rates were best predicted by the pseudo-first-order and Elovich’s models for the Arg and CnZVI, respectively, implicit evidence of the role of surface chemistry. A maximum adsorption capacity of 14 mg/g was achieved for 100 mg Ni2+/L in 120 min for CnZVI.

Antimony removal using zero-valent iron-manganese bimetallic nanomaterial: Adsorption behavior and mechanism

Although the effectiveness of zero-valent iron (ZVI) and zero-valent manganese (ZVMn) in heavy metal removal is well-established, their combined synergistic potential for antimony (Sb) remediation from wastewater has remained largely unexplored. Addressing this gap, this study introduced a magnetic zero-valent iron-manganese bimetallic material (ZVIM), synthesized via the borohydride reduction method, to investigate its capabilities and underlying mechanisms for Sb reduction and adsorption. The ZVIM, characterized by a high specific surface area of 220 m²/g, exhibited a high adsorption capacity (614.6 mg/g for Sb(III) and 241.7 mg/g for Sb(V)), facilitating over 96.7 % removal for both Sb(III) and Sb(V). The adsorption conformed to the pseudo-second-order kinetic model, and the isotherm data aligned with the Freundlich model, indicative of a heterogeneous adsorption process. The removal of Sb(III) predominantly occurred via surface complexation and electrostatic adsorption to the positively charged ZVIM surface, accompanied by a partial oxidation of Sb(III) to Sb(V). In contrast, the elimination of Sb(V) was primarily facilitated through surface complexation mechanism, encompassing both reduction and electrostatic adsorption. The outcomes of this study shed light on the intricate interactions between Sb species and the ZVIM, revealing the material as a promising candidate for the efficacious removal of Sb from wastewater.

Relevance of surface characterization of <i>Bambusa vulgaris</i> (l.) leaf extract doped iron nanoparticle

In the present study, green nano scaled zero-valent irons (nZVI) were synthesized from Bambusa vulgaris leaf extract at room temperature. The plant extract was evaluated for the presence of reducing agents (bioactive compounds) phytochemically using standard methods. nZVI was systematically characterized using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Ultraviolet-Visible (UV-Vis), and Fourier Transform Infra-Red (FT-IR) techniques. The SEM and XRD results showed that after the reduction process for 4 hr at 25oC, the iron powder obtained was a single phase of lamellar or platy α-Fe crystals with the presence of medium nanoparticles (10-100 nm) having crystal size, L ranging from 40-46 nm (42.2 nm) and particle size, D ranging from 53-70 nm (56.1 nm) for both 0.3 M and 0.9 M B. vulgaris-nZVI. It has been demonstrated that B. vulgaris leaf extract was capable of producing iron nanoparticles that shows good stability in solution and under the UV-Visible wavelength, nanoparticles exhibited quite good surface plasmon resonance behavior in the range of 220-740 nm. The FT-1R spectra revealed that the vibrational bands at 3722.76 cm-1 and 3706.4 cm-1 represented the O-H stretching due to the presence of polyphenol as a functional group in addition to tannins, saponins, and others which may be responsible for the eduction of ferrous ion (Fe3+) to zero-valent iron (Feo). This study reveals that B. vulgaris-nZVI possessing short-time synthesis protocol, anisotropism, and eco-benignity could be promising lowcost matrix for remediation (both soil and water), adsorption, catalysis, and other applications.

Effective removal of Cr(VI) from water by ball milling sulfur-modified micron zero-valent iron：Influencing factors and removal mechanism

To address the issues of ZVI's susceptibility to oxidation and aggregation, ball milling and Na2S·9H2O modification were employed on ZVI to enhance its efficiency in removing Cr(VI) from effluent. The characterization results expressed that S-mZVIbm had mesoporous and macroporous structures, enabling successful capture of Cr(VI). Moreover, S-mZVIbm had the highest adsorption capacity for Cr(VI) (350.04 mg/g) at pH = 2.00 and reached kinetic equilibrium within 420 min. Furthermore, the adsorption of Cr(VI) by S-mZVIbm conformed to the Avrami-fractional-order model, demonstrated that the adsorption process indicated a complex multi-adsorption process. Meanwhile, the adsorption also fit to Langmuir and Sips models, suggesting monolayer-level adsorption with heterogeneous sites located on S-mZVIbm. The S-mZVIbm could enhance Cr(VI) adsorption through various synergistic mechanisms, such as electrostatic interaction, chemical precipitation, surface complexation, and reduction. Overall, this research presented an innovative perspective for the modification of ZVI, and S-mZVIbm could be widely applied in the practical remediation of wastewater containing Cr(VI).

Sulfidation of Nanoscale Zero-Valent Iron by Sulfide: The Dynamic Process, Mechanism, and Role of Ferrous Iron.

Sulfidation of nanoscale zerovalent iron (nZVI) can enhance particle performance. However, the underlying mechanisms of nZVI sulfidation are poorly known. We studied the effects of Fe2+ on 24-h dynamics of nZVI sulfidation by HS- using a dosed S to Fe molar ratio of 0.2. This shows that in the absence of Fe2+, HS- rapidly adsorbed onto nZVI particles and reacted with surface iron oxide to form mackinawite and greigite (<0.5 h). As nZVI corrosion progressed, amorphous FeSx in solution deposited on nZVI, forming S-nZVI (0.5-24 h). However, in the initial presence of Fe2+, the rapid reaction between HS- and Fe2+ produced amorphous FeSx, which deposited on the nZVI and corroded the surface iron oxide layer (<0.25 h). This was followed by redeposition of colloidal iron (hydr)oxide on the particle surface (0.25-8 h) and deposition of residual FeSx (8-24 h) on S-nZVI. S loading on S-nZVI was 1 order of magnitude higher when Fe2+ was present. Surface characterization of the sulfidated particles by TEM-SAED, XPS, and XAFS verified the solution dynamics and demonstrated that S2- and S22-/Sn2- were the principal reduced S species on S-nZVI. This study provides a methodology to tune sulfur loading and S speciation on S-nZVI to suit remediation needs.