Nanoscale Zero-valent Iron Research Articles

Azo-Enhanced Raman Scattering Probing Proton Transfer between Water and Nanoscale Zero-valent Iron.

The interaction between a solid and water at their interface, especially proton transfer, impacts molecular-scale catalysis, macroscopic environmental science, and geoscience. Although being highly desired, directly probing proton transfer between a solid and water is a great challenge, given the subnanometer to nanometer scale of the interface. The fundamental challenge lies in the lack of a measurement tool to sensitively observe local proton concentration without introducing an exogenous electrode or nanoparticle with a minimum size of tens of nanometers. Here, we demonstrate an azo-enhanced Raman scattering strategy to design a 2 nm long small-molecule pH probe with a chelating group anchoring to the solid surface. Empowered by the intramolecular Raman enhancing sensitivity, the probe directly observes proton transfer between water and nanoscale zero-valent iron (nZVI), a famous environmental material for pollution control. This molecular-scale interfacial probing methodology offers a powerful tool to pave the way for advanced environmental and geochemical discernment and management.

Significantly Enhanced Nitrate Removal by Nanoscale Zerovalent Iron–Reduced Graphene Oxide Composites via Biological Denitrification: Performance and Mechanism

Significantly Enhanced Nitrate Removal by Nanoscale Zerovalent Iron–Reduced Graphene Oxide Composites via Biological Denitrification: Performance and Mechanism

Unveiling trends in migration of iron-based nanoparticles in saturated porous media

Nanoscale zero-valent iron (nZVI) particles are routinely used for environmental remediation, but their transport dynamics in different settings remain unclear, hindering optimization. This study introduces a novel approach to predicting nZVI transport in saturated porous model environment. The method employs advanced long column devices for real-time monitoring via controlled magnetic susceptibility measurements. Numerical modeling with a modified version of the MNMs 2023 software was then used to predict nZVI and its derivatives mobility in field-like conditions, offering insights into the radius of influence (ROI) and shape factor (SF) of their distribution. A standard nZVI precursor was compared with its four major commercial derivatives: nitrided, polyacrylic acid-coated, oxide-passivated, and sulfidated nZVI. All these iron-based nanoparticles exhibited identical particle sizes, morphologies, surface areas, and phase compositions, isolating surface properties, dominated by charge, as the sole variable affecting their mobility. The study revealed optimal transport when the surface charge of nZVI and its derivatives was strongly negative, while rapid aggregation of nZVI derivatives due magnetic attraction reduced their mobility. Modeling predictions based on column scale-up, indicated that detectable concentrations of 20 g L⁻1 were found at distances ranging from 0.4 to 1.1 m from the injection well. Slightly sulfidated nZVI traveled farther than the nZVI precursor and ensured more homogenous particle distribution around the well. Organically modified nZVI migrated the longest distances but showed particle accumulation close to the injection point. The findings suggest that minimal sulfidation combined with organic modification of nZVI surfaces may effectively enhance radial and vertical nZVI distribution in aquifers. Such improvements increase the commercial viability of modified nZVI, reduce their adverse impacts, and boosts their practical applications in real-world scenarios.

Enhanced adsorption and reduction of Pb(II) from aqueous solution by sulfide-modified nanoscale zerovalent iron: characterization, kinetics and mechanisms

Nanoscale zerovalent iron (nZVI) was prone to aggregation and passivation, which limited its application. Here, sulfide-modified nZVI (S-nZVI) was synthesized to enhance Pb(II) removal, the transmission electron microscope and scanning electron microscope showed S-nZVI particles exhibited a core–shell structure, with Fe0 comprising the core and iron oxides in the shell, the generated iron sulfides (FeSx) were distributed over the iron oxides shell. The water contact angle results suggested S-nZVI was more hydrophobic than nZVI, which could prevent the oxidation of the inner Fe0 core with aqueous solution, furthermore, the electrochemical experiments demonstrated the FeSx improved the electron transfer efficiency from Fe0 core to contaminants, enhancing the reactivity of S-nZVI. Mechanism analysis confirmed that the electrostatic attraction, chemical precipitation, surface complexation and reduction occurred during the adsorption. S-nZVI with S/Fe molar ratio of 0.3 offered the best Pb(II) adsorption capacity, and higher pH value was favourable, the presence of co-existing cations (K+, Na+, Ca2+, Mg2+) all interfered the Pb(II) removal, followed as Ca2+ >Mg2+ > K+ > Na+. The pseudo-second-order kinetics and Langmuir model could well described the adsorption process, indicating that monolayer adsorption dominated the process. Thermodynamic results showed the adsorption was a spontaneous endothermic process, even after 4 cycles of recycling, the removal rate remained at 76.4 %, demonstrating S-nZVI had good reusability.

Hydrochar supported strategy for nZVI to remove bisphenol A and Cr(VI): Performance, synergetic mechanism, and life cycle assessment

To comprehensively overcome the shortcomings and extend the application of nanoscale zero-valent iron (nZVI), a promising hydrochar supported strategy was provided. nZVI/Eupatorium adenophorum hydrochar (nZVI/EaHC) composite was attained under relatively mild reaction condition, and life cycle assessment revealed that the greenhouse gases emission, ecotoxicity, and resource consumption of nZVI/EaHC fabrication processes largely reduced in comparison with nZVI and pyrolysis biochar supported nZVI (nZVI/EaBC). Moreover, nZVI/EaHC exhibited an outstanding potential in reduction and immobilization of Cr(VI) as well as degradation of bisphenol A (BPA) via Fenton-like system. The static experiment showed that the removal efficiency achieved 99.21 % within 1 h for Cr(VI) and 97.9 % within 1 min for BPA, which significantly exceeded the performance of nZVI/EaBC, accompanied by a significant detoxification to non-harmful level and mineralization of 87.9 % within 10 min. The dynamic continuous flow column experiment indicated that 90 % Cr(VI) was removed within 40 min and 90 % BPA within 180 min under ultra-low-dosage of catalyst and H2O2. Furthermore, hydrochar supported strategy may reduce the economic cost and avoid secondary pollution due to the outstanding stability under aerobic condition and recyclability in magnetic field. The synergetic mechanisms were further revealed, the abundant oxygen-containing functional groups on EaHC facilitated the generation of electron-rich/poor centers via chemical bond bridge (COFe) and Fe-π interaction, which further enhanced the electron transfer to reduce Cr(VI) or promote the production of multiple reactive species including OH, O2–, and 1O2 to degrade BPA, additionally, persistent free radicals on EaHC also contributed to the degradation of BPA. Therefore, this efficient, applicable, and sustainable strategy may have a greatly practical outlook on nZVI application together with a comprehensive control and utilization of biomass including invasive plants.

The carbon stability and energy characteristics of tea waste-derived biochar: Effects of pyrolytic temperature and co-pyrolysis with nanoscale zero-valent iron

Pyrolytic temperature and Fe addition are two typical factors widely used for modifying the characteristic of biochar, however, their co-effect on the C emission reduction (enhancing C stability) and fuel features of tea waste biochar remain unclear. Hence, this study systematically investigated the effects of pyrolytic temperature (300–900 °C) and nanoscale zero-valent iron (Fe) co-pyrolysis on the C stability and fuel features of TBC. Herein, H/C, (O + N)/C, FTIR spectrum, XRD spectrum, Ig/(Id + Ig) and DOC release suggested that pyrolytic temperature improvement decreased the aliphaticity, polarity and DOC content, but increased the aromaticity and graphitic degree for TBC. Meanwhile, Fe co-pyrolysis decreased the polarity and enhanced the graphitic degree of TBC at 800–900 °C. Thermogravimetric analysis indicated that Fe co-pyrolysis lowered the thermostability of C. Differently, H2O2 oxidization method indicated Fe co-pyrolysis significantly enhanced the chemical stability of C. Furthermore, Uv–vis and fluorescence spectrum indicated that pyrolytic temperature improvement decreased the aromaticity and molecular size of biochar-derived DOC. Fe co-pyrolysis increased the release of large molecular humic-like matters rather than small molecular protein-like matters. All the results suggested high pyrolytic temperature and Fe co-pyrolysis could improve the environmental (physico-chemical) C stability of TBC and the C emission reduction. Additionally, TBC presented a considerable energy densification ratio (EDR) ranges (1.355–1.450) of wood- and straw-derived biochars, indicating TBC could be a potential high-performance biofuel to alleviate the energy crisis. This study provides important information to optimize pyrolysis conditions to re-use of tea waste for C emission reduction and fuel substitute.

Relationships of ternary activities for the enhanced Cr(VI) removal by coupling nanoscale zerovalent iron with sulfidation and carboxymethyl cellulose

Nanoscale zerovalent iron (nZVI) has been extensively applied in water pollution control. However, the reactivity of nZVI toward contaminants is mainly limited by its corrosion and agglomeration. In this study, the nZVI modified by sulfidation coupled with carboxymethyl cellulose (CMC) (C-S-nZVI) was synthesized and characterized by TEM and electrochemical techniques. Taking Cr(VI) as the contaminant, it was found that the sulfidation could couple with CMC modification to not only enhance the reactivity of nZVI toward Cr(VI), but also regulate the sedimentation activity and corrosion activity of nZVI in water. Particularly, the optimal kobs (0.0816 min−1) obtained by the C-S-nZVIone-0.16 (i.e., one-step sulfidation and its S/Fe molar ratio was 0.16) was approximately 27.2 times higher than that by the nZVI (0.0030 min−1). Moreover, based on the correlation analysis of the ternary activities, this study confirmed that the reactivity of C-S-nZVI toward Cr(VI) was negatively correlated with its sedimentation activity (slope = −0.7623, R = 0.59) and corrosion activity (slope = −0.0171, R = 0.56), respectively. XPS and TEM results further revealed that CMC could couple with iron sulfides (FeSx) to enhance the mass transfer of Cr(VI) toward nZVI and subsequent electron transfer from Fe0 core to out, ultimately improving the reduction of Cr(VI) by nZVI. Overall, this study introduced a new evaluation method based on the ternary activity of nZVI, providing theoretical support for the practical application of nZVI-based technology.

Sustainable Abiotic-Biotic Dechlorination of Perchloroethene with Sulfidated Nanoscale Zero-Valent Iron as Electron Donor Source.

Combining organohalide-respiring bacteria with nanoscale zero-valent iron (nZVI) represents a promising approach for remediating chloroethene-contaminated aquifers. However, limited information is available regarding their synergistic dechlorinating ability for chloroethenes when nZVI is sulfidated (S-nZVI) under the organic electron donor-limited conditions typically found in deep aquifers. Herein, we developed a combined system utilizing a mixed culture containing Dehalococcoides (Dhc) and S-nZVI particles, which achieved sustainable dechlorination with repeated rounds of spiking with 110 μM perchloroethene (PCE). The relative abundance of Dhc considerably increased from 5.2 to 91.5% after five rounds of spiking with PCE, as evidenced by 16S rRNA gene amplicon sequencing. S-nZVI corrosion generated hydrogen as an electron donor for Dhc and other volatile fatty acid (VFA)-producing bacteria. Electron balance analysis indicated that 68.1% of electrons from Fe0 consumed in S-nZVI were involved in dechlorination, and 6.2, 1.1, and 3.2% were stored in formate, acetate, and other VFAs, respectively. The produced acetate possibly served as a carbon source for Dhc. Metagenomic analysis revealed that Desulfovibrio, Syntrophomonas, Clostridium, and Mesotoga were likely involved in VFA production. These findings provide valuable insights into the synergistic mechanisms of biotic and abiotic dechlorination, with important implications for sustainable remediation of electron donor-limited aquifers contaminated by chloroethenes.

Research progress of nanoscale zero-valent iron in synergistic combinations of denitrifying bacteria for nitrate removal

Nitrate (NO3--N) is a common inorganic nitrogen pollutant in water. Excessive NO3--N can lead to water eutrophication and threaten human health. Nanoscale zero-valent iron (nZVI) has attracted much attention in NO3--N removal due to its high specific surface and excellent electron donor properties. The combination of nZVI and denitrifying bacteria (DNB) demonstrates high efficiency in converting NO3--N into N2. This approach not only substantially enhances the removal rate of NO3--N but also exhibits superior environmental sustainability compared with conventional chemical denitrification methods. Accordingly, it holds substantial promise for mitigating NO3--N pollution and warrants further exploration in the pollution control. Therefore, it is necessary to understand the interaction mechanism between nZVI and DNB for NO3--N removal. This paper details the factors affecting the removal of NO3--N by nZVI combined with DNB, reviews the latest research progress in this field, elaborates on the interaction mechanism between nZVI and DNB for NO3--N removal, and discusses the challenges and future research directions of NO3--N removal by nZVI combined with DNB. This review aims to provide a theoretical basis for the development of efficient approaches for the remediation of NO3--N pollution.

Green synthesis of nanoscale zero-valent iron impregnated walnut shell biochar as efficient adsorbent for metal(loid)s purification: Performance and mechanism insight

The escalation of metal(loid) contamination in global water poses severe risks to ecological environment safety. Meeting the ‘pollution control with waste’ strategy, we utilized eco-friendly waste tea leaf extract and walnut shell to first fabricate a greenly synthesized nanoscale zero-valent iron impregnated walnut shell biochar (G-nZVI/WSB) for the simultaneous sequestration of cadmium (Cd), lead (Pb), and arsenic (As) from aqueous systems. Since the interactions among these metal(loid)s during adsorption on G-nZVI/WSB and their corresponding mechanisms remain unclear, we conducted a series of batch experiments coupled with characterization techniques. The optimal pyrolysis temperature and Fe/C ratio for G-nZVI/WSB were determined to be 650 °C and 20 %, respectively. Under optimal conditions (contact time = 24 h, pH = 6), G-nZVI/WSB exhibited theoretical maximum adsorption capacities for Cd(II), Pb(II), and As(III) of 52.96, 135.1, and 8.414 mg g−1, respectively, which were significantly higher than those of WSB carrier. In single and combined systems, the monolayer and chemical adsorption of metal(loid)s were predominant, with their competitive affinity for active sites following the order of Pb(II) > Cd(II) > As(III). Characterization analyses using FTIR, SEM, XRD, and XPS confirmed the specific adsorption mechanisms of G-nZVI/WSB for these metal(loid)s, including cation-π interactions, coprecipitation, oxidation, and coordinated complexation. Notably, G-nZVI/WSB exhibited excellent adsorption stability over five cycles of adsorption-desorption, which achieved the efficient purification of multi-contaminated actual wastewaters to meet the standards for wastewater discharge or drinking water. These findings demonstrate the significant potential of G-nZVI/WSB as an eco-friendly and promising nanocomposite for treating metal(loid)-contaminated wastewater.

A comparative study of different modification methods on zero-valent iron performance toward nitrate selective reduction to nitrogen

Although nanoscale zero-valent iron (nZVI) has been widely used for nitrate reduction, its application is always limited by the undesired generation of toxic ammonium. In this study, by selecting four commonly used nZVI modification methods (i.e., introducing Fe(II), activated carbon, Cu, and Pd), the roles of direct electron transfer and atomic hydrogen (H*) mediated reaction on nitrate selective reduction were examined. Results revealed that all the modification methods could enhance the reduction rates of nitrate with a promotion factor of 0.94–8.62, while the N2-selectivity could only be increased from ∼4.5 % to less than 25.7 % (in carbon amended system). The enhancing effect of these additives is determined to be highly associated with their ability to promote the direct electron transfer from Fe0 core to nitrate by forming galvanic couples or conductive magnetite layer. Unexpectedly, multiple lines of evidence suggested that H* was not the dominant reducing species responsible for nitrate reduction in Pd-modified nZVI system (and also the other tested systems), despite the presence of Pd could significantly accelerate H* generation. Correlation analysis further showed that there was no reasonable relationship between N2-selectivity and Fe0 corrosion tendency and hydrogen formation rates of different modified nZVI systems. All these finding could improve our understanding of nitrate selective reduction by Fe0.

Electrocatalytic Nitrate Reduction for Brackish Groundwater Treatment: From Engineering Aspects to Implementation

In recent years, nitrate has emerged as a significant groundwater pollutant due to its potential ecotoxicity. In particular, nitrate contamination of brackish groundwater poses a serious threat to both ecosystems and human health and remains difficult to treat. A promising, sustainable, and environmentally friendly solution when biological treatments are not applicable is the conversion of nitrate to harmless nitrogen (N2) or ammonia (NH3) as a nutrient by electrocatalytic nitrate reduction (eNO3R) using solar photovoltaic energy. This review provides a comprehensive overview of the current advances in eNO3R for the production of nitrogen and ammonia. The discussion begins with fundamental concepts, including a detailed examination of the mechanisms and pathways involved, supported by Density Functional Theory (DFT) to elucidate specific aspects of ammonium and nitrogen formation during the process. Furthermore, the integration of artificial intelligence (AI) and machine learning (ML) offers promising advancements in enhancing the predictive power of DFT, accelerating the discovery and optimization of novel catalysts. In this review, we also explore various electrode preparation methods and emphasize the importance of in situ characterization techniques to investigate surface phenomena during the reaction process. The review highlights numerous examples of copper-based catalysts and analyses their feasibility and effectiveness in ammonia production. It also explores strategies for the conversion of nitrate to N2, focusing on nanoscale zerovalent iron as a selective material and the subsequent oxidation of the produced ammonia. Finally, this review addresses the implementation of the eNO3R process for the treatment of brackish groundwater, discussing various challenges and providing reasonable opinions on how to overcome these obstacles. By synthesizing current research and practical examples, this review highlights the potential of eNO3R as a viable solution to mitigate nitrate pollution and improve water quality.

Investigation of small-strain shear modulus of marine sediment treated with different flocculants

Dredged sediments are typically found near coastal areas. Because of its high compressibility potential and low strength, multiple studies have tested various substances that can be mixed with the dredged materials to enhance the overall treatment process while minimizing post-construction settlement. Recent investigations indicated that combining flocculants such as cationic polyacrylamide (CPAM) with marine sediment improves the consolidation and permeability properties compared to untreated soil. Despite its importance, only a few studies have focused on the mechanical properties of marine sediment treated with various flocculant types. This study employs a bender element apparatus to examine the small-strain shear modulus (Gmax) variation of Macau marine sediment treated with three different flocculants: CPAM; chitosan; and nanoscale zero-valent iron (nZVI). The result revealed that the Gmax of natural marine sediment increases when blended with chitosan and CPAM with medium cationicity. Interestingly, no apparent change in Gmax values was observed when the marine sediment samples were treated using CPAM with high cationicity. In contrast, the Gmax values of soil samples treated with nZVI decreased. The comparison with existing empirical models reveals that the plasticity index is a significant parameter in determining the Gmax of Macau marine sediments. The findings from this study will support the identification of viable filling materials for future land reclamation projects in the Greater Bay Area of China.

Effective removal of nitrate by palygorskite-supported nanoscale zero-valent iron from aqueous solution

Nitrate nitrogen (NO3--N) has become an important pollutant in industrial and agricultural production processes in China. In this study, Palygorskite-supported nanoscale zero-valent iron (nZVI/PG) adsorbent was prepared using the liquid-phase reduction method for the removal of NO3--N from water. Benefiting from the good dispersion uniformity of nZVI on the Palygorskite carrier, the prepared nZVI/PG exhibited a significantly increased specific surface area compared to nZVI, with a noticeable reduction in nZVI aggregation. The Fe/PG mass ratio of 2:1 was found to be the optimal loading ratio for the removal of NO3--N by nZVI/PG, with a removal capacity of 24.36 mg/g and a removal efficiency of 81.23 %, with a nitrogen gas conversion rate of 40.92 %. The removal process of NO3--N by nZVI/PG followed a pseudo-second-order kinetic model, with the removal rate inversely proportional to the initial concentration of NO3--N and directly proportional to the dosage. nZVI/PG exhibited high removal efficiency for NO3--N within the pH range of 2 to 9, with the highest selectivity for NO3--N conversion to N2 observed at pH 5. The main mechanism for the removal of NO3--N by nZVI/PG was found to be adsorption and reduction, with the main products being NH4+-N, NO2--N, and N2.

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

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.

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.

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.

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.

Evaluation of a novel attapulgite loaded sulfidized nanoscale zero-valent iron for immobilization of Pb in sediment: Performance, microenvironmental response, and mechanisms

In recent years, industrial activities involving electroplating and mining have caused Pb to enter rivers and become over-enriched in sediments, posing a potential risk to aquatic organisms. Given this, in this study, attapulgite loaded sulfidized nZVI (S-nZVI@ATP) was prepared by sulfidized modification and ATP loading and applied for the first time to the remediation of Pb contaminated sediments. The immobilization effect and mechanism of S-nZVI@ATP on Pb contaminated sediments were comprehensively investigated, as well as the changes in the microenvironment during the remediation process were assessed. Characterization analysis revealed that S-nZVI was uniformly loaded on the surface of ATP, and the characteristic functional groups of ATP, such as Al/Mg-OH and Si-O, were successfully loaded. Incubation experiments demonstrated that S-nZVI@ATP significantly reduced the availability and leaching toxicity of sediment Pb with immobilization efficiencies as high as 94.08% and 73.15%, respectively (P < 0.05), meanwhile, it facilitated the conversion of acid soluble Pb to the residue state. This phenomenon suggested that S-nZVI@ATP displayed excellent performance in immobilizing Pb. The increase of sediment pH and the decrease of Eh were beneficial to the immobilization of Pb. The addition of S-nZVI@ATP changed the structure and composition of the sediment bacterial community, with Proteobacteria, Firmicutes, and Bacteroidota being the dominant phyla. Except for sucrase, urease and catalase activities were increased by 1.23 and 2.48 times, respectively. Correlation analysis highlighted the importance of pH, Eh, Proteobacteria phylum, and Firmicutes phylum in sediment Pb immobilization. Post-reaction material characterization indicated that the main mechanisms of S-nZVI@ATP for sediment Pb immobilization were adsorption, complexation, ion exchange, electrostatic attraction, reduction and precipitation.