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Nanoscale zerovalent iron (nZVI) has garnered significant attention as an efficient advanced oxidation activator, but its practical application is hindered by aggregation and oxidation. Coating nZVI with carbon can effectively addresses these issues. A simple and scalable production method for carbon-coated nZVI composite is highly desirable. The anti-oxidation and catalytic performance of carbon-coated nZVI composite merit in-depth research. In this study, a highly stable carbon-coated core-shell nZVI composite (Fe0@RF-C) was successfully prepared using a simple method combining phenolic resin embedding and carbothermal reduction. Fe0@RF-C was employed as a heterogeneous persulfate (PS) activator for degrading 2,4-dihydroxybenzophenone (BP-1), an emerging contaminant. Compared to commercial nZVI, Fe0@RF-C exhibited superior PS activation performance and oxidation resistance. Nearly 95% of BP-1 was removed within 10 min in the Fe0@RF-C/PS system. The carbon layer promotes the enrichment of BP-1 and accelerates its degradation through singlet oxygen oxidation and direct electron transfer processes. This study provides a straightforward approach for designing highly stable carbon-coated nZVI composite and elucidates the enhanced catalytic performance mechanism by carbon layers.

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It is crucial to clarify how the iron nanostructure activates plant growth, particularly in combination with arbuscular mycorrhizal fungi (AMF). We first identified 1.0 g·kg-1 of nanoscale zerovalent iron (nZVI) as appropriate dosage to maximize maize growth by 12.7-19.7% in non-AMF and 18.9-26.4% in AMF, respectively. Yet, excessive nZVI at 2.0 g·kg-1 exerted inhibitory effects while FeSO4 showed slight effects (p > 0.05). Under an appropriate dose, a nano core-shell structure was formed and the transfer and diffusion of electrons between PS II and PS I were facilitated, significantly promoting the reduction of ferricyanide and NADP (p < 0.05). SEM images showed that excessive nZVI particles can form stacked layers on the surface of roots and hyphae, inhibiting water and nutrient uptake. TEM observations showed that excessive nanoparticles can penetrate into root cortical cells, disrupt cellular homeostasis, and substantially elevate Fe content in roots (p < 0.05). This exacerbated membrane lipid peroxidation and osmotic regulation, accordingly restricting photosynthetic capacity and AMF colonization. Yet, appropriate nZVI can be adhered to a mycelium surface, forming a uniform nanofilm structure. The strength of the mycelium network was evidently enhanced, under an increased root colonization rate and an extramatrical hyphal length (p < 0.05). Enhanced mycorrhizal infection was tightly associated with higher gas exchange and Rubisco and Rubisco enzyme activities. This enabled more photosynthetic carbon to input into AMF symbiont. There existed a positive feedback loop connecting downward transfer of photosynthate and upward transport of water/nutrients. FeSO4 only slightly affected mycorrhizal development. Thus, it was the Fe nanostructure but not its inorganic salt state that primed AMF symbionts for better growth.

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Nano zero-valent iron (nZVI) is an advanced environmental functional material for the degradation of tetrabromobisphenol A (TBBPA). However, high surface energy, self-agglomeration and low electron selectivity limit degradation rate and complete debromination of bare nZVI. Herein, we presented biomass-derived cellulose nanocrystals (CNC) modified nZVI (CNC/nZVI) for enhanced TBBPA removal. The effects of raw material (straw, filter paper and cotton), process (time, type and concentration of acid hydrolysis) and synthesis methods (in-situ and ex-situ) on fabrication of CNC/nZVI were systematically evaluated based on TBBPA removal performance. The optimized CNC-S/nZVI(in) was prepared via in-situ liquid-phase reduction using straw as raw material of CNC and processing through 44 % H2SO4 for 165 min. Characterizations illustrated nZVI was anchored to the active sites at CNC interface through electrostatic interactions, hydrogen bonds and FeO coordinations. The batch experiments showed 0.5 g/L CNC-S/nZVI(in) achieved 96.5 % removal efficiency at pH = 7 for 10 mg/L initial TBBPA. The enhanced TBBPA dehalogenation by CNC-S/nZVI(in), involving in initial adsorption, reduction process and partial detachment of debrominated products, were possibly attributed to elevated pre-adsorption capacity and high-efficiency delivery of electrons synergistically. This study indicated that fine-tuned fabrication of CNC/nZVI could potentially be a promising alternative for remediation of TBBPA-contaminated aquatic environments.

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Polymer stabilization, exemplified by carboxymethyl cellulose (CMC), has demonstrated effectiveness in enhancing the transport of nanoscale zero-valent iron (nZVI). And, sulfidation is recognized for enhancing the reactivity and selectivity of nZVI in dechlorination processes. The influence of polymer stabilization on sulfidated nZVI (S-nZVI) with various sulfur precursors remains unclear. In this study, CMC-stabilized S-nZVI (CMC-S-nZVI) was synthesized using three distinct sulfur precursors (S2-, S2O42-, and S2O32-) through one-step approach. The antioxidant properties of CMC significantly elevated the concentration of reduced sulfur species (S2-) on CMC-S-nZVIs, marking a 3.1-7.0-fold increase compared to S-nZVIs. The rate of trichloroethylene degradation (km) by CMC-S-nZVIs was observed to be 2.2-9.0 times higher than that achieved by their non-stabilized counterparts. Among the three CMC-S-nZVIs, CMC-S-nZVINa2S exhibited the highest km. Interesting, while the electron efficiency of CMC-S-nZVIs surged by 7.9-12 times relative to nZVI, it experienced a reduction of 7.0-34% when compared with S-nZVIs. This phenomenon is attributed to the increased hydrophilicity of S-nZVI particles due to CMC stabilization, which inadvertently promotes the hydrogen evolution reaction (HER). In conclusion, the findings of this study underscores the impact of CMC stabilization on the properties and dechlorination performance of S-nZVI sulfidated using different sulfur precursors, offering guidance for engineering CMC-S-nZVIs with desirable properties for contaminated groundwater remediation.

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Gas nanobubbles used for water treatment and recovery give rise to great concern for their unique advantages of less byproducts, higher efficiency, and environmental friendliness. Nanoscale zerovalent iron (nZVI), which has also been widely explored in the field of environmental remediation, can generate gas hydrogen by direct reaction with water. Whether nanoscale hydrogen bubbles can be produced to enhance the pollution removal of the nZVI system is one significant concern involved. Herein, we report direct observations of in situ generation of hydrogen nanobubbles (HNBs) from nZVI in water. More importantly, the formed HNBs can enhance indeed the reduction of Se(IV) beyond the chemical reduction ascribed to Fe(0), especially in the anaerobic environment. The possible mechanism is that HNBs enhance the reducibility of the system and promote electron transport in the solution. This study demonstrates a unique function of HNBs combined with nZVI for the pollutant removal and a new approach for in situ HNB generation for potential applications in the fields of in situ remediation agriculture, biotechnology, medical treatment, health, etc.

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Whether it's necessary to extra chemical synthesis steps to modify nZVI in peroxymonosulfate (PMS) activation process are worth to further investigation. The 56 mg/L nZVI/153.65 mg/L PMS and 56 mg/L sulfidated nZVI (S-nZVI) (S/Fe molar ratio = 1:5)/153.65 mg/L PMS) processes could effectively attain 97.7% (with kobs of 3.7817 min-1) and 97.0% (with kobs of 3.4966 min-1) of the degradation of 20 mg/L sulfadiazine (SDZ) in 1 min, respectively. The nZVI/PMS system could quickly achieve 85.5% degradation of 20 mg/L SDZ in 1 min and effectively inactivate 99.99% of coexisting Pseudomonas. HLS-6 (5.81-log) in 30 min. Electron paramagnetic resonance tests and radical quenching experiments determined SO4•-, HO•, 1O2 and O2•- were responsible for SDZ degradation. The nZVI/PMS system could still achieve the satisfactory degradation efficiency of SDZ under the influence of humic acid (exceeded 96.1%), common anions (exceeded 67.3%), synthetic wastewater effluent (exceeded 90.7%) and real wastewater effluent (exceeded 78.7%). The high degradation efficiency of tetracycline (exceeded 98.9%) and five common disinfectants (exceeded 96.3%) confirmed the applicability of the two systems for pollutants removal. It's no necessary to extra chemical synthesis steps to modify nZVI for PMS activation to remove both chemical and biological pollutants.

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Nanoscale zerovalent iron (Fe0)-based materials have been demonstrated to be a effective method for the U(VI) removal. However, limited research has been conducted on the long-term immobilization efficiency and mechanism of Fe0-based materials for U(VI), which are essential for achieving safe handling and disposal of U(VI) on a large scale. In this study, the prepared carboxymethyl cellulose (CMC) and sulfurization dual stabilized Fe0 (CMC-Fe0/FeS) exhibited excellent long-term immobilization performances for U(VI) under both anoxic and oxic conditions, with the immobilization efficiencies were respectively reached over 98.0 % and 94.8 % after 180 days of aging. Most importantly, different from the immobilization mechanisms of the fresh CMC-Fe0/FeS for U(VI) (the adsorption effect of -COOH and -OH groups, coordination effect with sulfur species, as well as reduction effect of Fe0), the re-mobilized U(VI) were finally re-immobilized by the formed FeOOH and Fe3O4 on the aged CMC-Fe0/FeS. Under anoxic conditions, more Fe3O4 was produced, which may be the main reason for the long-term immobilization U(VI). Under oxic conditions, the production of Fe3O4 and FeOOH were relatively high, which both played significant roles in re-immobilizing U(VI) through surface complexation, reduction and incorporation effects.

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The cracked phosphorylated nanoscale zerovalent iron (p-nZVI) has a strong electron selectivity towards the reductive removal of many heavy metal ions in waters. However, the unintended environmental risk after interactions with impurities or wastewater are not involved. Therefore, in this study, the phosphate group was successfully adsorbed into p-nZVI, and the cracked p-nZVI was successfully prepared with an optimal P/Fe ratio of 0.5%. The dosages of p-nZVI and temperatures were positively correlated with the removal rates. The removal process of Cr(VI) was more suitable by the Langmuir isothermal model（R2 > 0.99). The process of Cr (VI) (10, 20 and 40 mg/L) removal more fitted the pseudo first-order reaction model, while the process of Cr (VI) (60, 80 mg/L) removal more fitted the pseudo second-order reaction model. The Cr (VI) removal rates gradually decreased when the pH was increased. Dissolved oxygen slowed nanoiron reaction rates. The order of inhibition on the reactivity towards Cr(VI) was SiO32- > SO42- > PO43- > NO3- > HCO3-.The facilitation followed the order of Cd2+>Cu2+>Mg2+>Mn2+>Ca2+. Ca2+ showed an inhibitory effect, but all other cations showed different degrees of facilitation. The promotion effect is relatively similar in presence of Mn2+ or Mg2+. HA had a significant inhibitory effect. Environmental friendly p-nZVI had a good effect in simulated groundwater, seawater, river water and secondary effluent of the urban sewage treatment plant. The main pathway to remove Cr (VI) was in situ reduction by p-nZVI. The improved adsorption and reduction effect of p-nZVI on heavy metal ions in water was due to the structural change and the phosphate group.

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In recent years, there has been a growing focus on treating textile wastewater due to its escalating threat to aquatic ecosystems and exposed communities. The present study investigates the adsorption efficacy of biopolymer functionalized nanoscale zero-valent iron (CS@nZVI) composite for the treatment of textile wastewater using the RSM-CCD model. The structure and morphology of CS@nZVI were characterized using XRD, FTIR, FESEM, and EDX. CS@nZVI was then evaluated for its adsorption potential in removing COD, color, and other physico-chemical parameters from textile wastewater. The results showed the high efficacy of CS@nZVI for COD and color removal from textile wastewater. Under optimal conditions (pH 6, contact time 60 min, and 1.84 g CS@nZVI), COD removal reached a maximum of 85.53%, and decolorization efficiency was found to be 89.73%. The coefficient of determination R2 (0.98) and AIC (269.75) values suggested quadratic model as the best-fitted model for optimizing the process parameters for COD removal. Additionally, the physico-chemical parameters were found to be within permissible limits after treatment with CS@nZVI. The influence of coexisting ions on COD removal followed the order PO43- > SO42- > Cl- >Na+ > Ca2+. The kinetics data fitted well with the pseudo-first-order reaction, indicating physisorption as the primary mechanism. The thermodynamic study revealed the endothermic nature of the removal process. Reusability tests demonstrated that great regeneration capacity of spent CS@nZVIafter five consecutive cycles. Furthermore, toxicological studies showed reduced toxicity in treated samples, leading to improved growth of Vigna radiata L. These findings suggest that CS@nZVI bionanocomposites could serve as an efficient, cost-effective, and eco-friendly remediation agent for the treatment of textile effluents, presenting significant prospects for commercial applications.

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Iron-based heterogeneous catalysts due to the environmental friendliness have been widely studied for activation of peracetic acid (PAA) for abatement of organic contaminants in the water and wastewater treatment. However, the slow reduction from Fe(III) to Fe(II) of the iron-based catalysts as the rate-limiting step results in the low PAA activation efficiency. With regard to the excellent electron-donating capability of the reductive sulfur species, sulfidized nanoscale zerovalent iron is proposed for PAA activation (simplified as the S-nZVI/PAA process) and the tetracycline (TC) abatement efficacy and mechanism of this process are elucidated. The optimal sulfidation ratio (S/Fe) of S-nZVI is 0.07, which exhibits superior performance in PAA activation for TC abatement with the efficiency of 80-100% in the pH range of 4.0-10.0. The radical quenching experiments and oxygen release measurements confirm that acetyl(per)oxygen radicals (CH3C(O)OO•) are the main radical contributing to TC abatement. The influence of sulfidation on the crystalline structure, hydrophobicity, corrosion potential, and electron transfer resistance of S-nZVI is evaluated. The main sulfur species on the S-nZVI surface are identified as ferrous sulfide (FeS) and ferrous disulfide (FeS2). The analysis by X-ray photoelectron spectroscopy (XPS) and Fe(II) dissolution suggest that the reductive sulfur species can accelerate the conversion from Fe(III) to Fe(II). In summary, the S-nZVI/PAA process exhibits application prospects for the abatement of antibiotics in the aquatic environments.

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Sulfidized nanoscale zerovalent iron (S-nZVI) was a promising material for degrading halogenated contaminants, but the easy aggregation limits its application for in-situ groundwater remediation. Hence, S-nZVI was decorated onto modified biochar (mBC) to obtain better dispersity and reactivity with florfenicol (FF), a widely used antibiotic. Uniform dispersion of S-nZVI particles were achieved on the mBC with plentiful oxygen-containing functional groups and negative surface charge. Thus, the removal rate of FF by S-nZVI@mBC was 2.5 and 3.1 times higher than that by S-nZVI and S-nZVI@BC, respectively. Adsorption and dechlorination of FF showed synergistic effect under appropriate mBC addition (e.g., C/Fe mass ratio = 1:3, 1:1), probably due to the enrichment of FF facilitates its reduction. In contrast, the contact between FF and S-nZVI could be hindered under more mBC addition, significantly decrease the reduction rate of FF and the reduction capacity of per unit Fe0. In addition, sulfur dose altered the surface species of surface Fe and S, and removal rates of FF correlated well with surface reductive species, i.e., FeS (r = 0.90, p < 0.05) and Fe0 (r = 0.98, p < 0.01). These mechanistic insights indicate the importance of rational design for biochar supported S-nZVI, which can lead to more efficient FF degradation.

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Since contamination of xenobiotics in water bodies has become a global issue, their removal is gaining ample attention lately. In the present study, nZVI was synthesized using chitosan for removal of two such xenobitic dyes, Bromocresol green and (BCG) and Brilliant blue (BB), which have high prevalence in freshwater and wastewater matrices. nZVI functionalization prevents nanoparticle aggregation and oxidation, enhancing the removal of BCG and BB with an efficiency of 84.96% and 86.21%, respectively. XRD, FESEM, EDS, and FTIR have been employed to investigate the morphology, elemental composition, and functional groups of chitosan-modified nanoscale-zerovalent iron (CS@nZVI). RSM-CCD model was utilized to assess the combined effect of five independent variables and determine the best condition for maximum dye removal. The interactions between adsorbent dose (2-4 mg), pH (4-8), time (20-40 min), temperature (35-65 0C), and initial dye concentration (40-60 mg/L) was modeled to study the response, i.e., dye removal percentage. The reaction fitted well with Langmuir isotherm and pseudo-first-order kinetics, with a maximum qe value of 426.97 and 452.4 mg/g for BCG and BB, respectively. Thermodynamic analysis revealed the adsorption was spontaneous, and endothermic in nature. Moreover, CS@nZVI could be used up to five cycles of dye removal with remarkable potential for real water samples.

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Multiple reactive intermediates have been proposed to be involved in peroxydisulfate (PDS) activation by zerovalent iron (ZVI), including sulfate radical (SO4·-) produced via iron-oxide shell mediated electron transfer, ferryl ion species (Fe(IV)) formed from Fe(II)-PDS interaction, and hydroxyl radical (·OH) generated by ZVI aerobic oxygenation. In this study, evolution of the relative role of these intermediates in microscale and nanoscale ZVI (mZVI vs. nZVI) activated PDS processes is comparatively investigated by using a methyl phenyl sulfoxide (PMSO) probe that selectively reacts with Fe(IV) to produce methyl phenyl sulfone (PMSO2). Interestingly, during PMSO transformation by mZVI/PDS process, yields of PMSO2 (η(PMSO2)) exhibit three-stage behavior that they first increase to a maximum (∼80% but lower than 100%) (Stage I) and then plateau for a period (Stage II) followed by a decrease phase (Stage III). Accordingly, the relative role of Fe(IV) in PMSO transformation is unceasingly improved in Stage I and subsequently reaches equilibrium with that of free radicals in Stage II, while it finally decreases in Stage III. Similar η(PMSO2) evolution trends are obtained in nZVI/PDS process, except that the η(PMSO2) increase in Stage I is negligible, possibly due to the exceptional fast nZVI dissolution. It was further clarified by tert-butyl alcohol scavenging assay that, in addition to Fe(IV), the free radical involved in Stages I and II is SO4·-, while ·OH was dominant in Stage III. Moreover, studies on O2 effect reveal that ZVI aerobic oxygenation participates in mZVI corrosion during the entire process, while it is only involved in nZVI corrosion when PDS content is reduced to a low concentration, indicating that the reactivities of PDS and O2 are similar in mZVI corrosion, but differ greatly in nZVI corrosion. Additionally, effects of reactant dose and pH on η(PMSO2) evolution are also explored. Dynamics of the relative role of different reactive oxidants should be taken into account in further applications of ZVI/PDS in situ chemical remediation technology considering their different chemistries.

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While nanoscale zero-valent iron modified biochar (nZVI-BC) have been widely investigated for the removal of heavy metals, the corrosion products of nZVI and their interaction with heavy metals have not been revealed yet. In this paper, nZVI-BC was synthesized and applied for the removal of Cr(VI). Batch experiments indicated that the adsorption of Cr(VI) fit Langmuir isotherm, with the maximum removal capacity at 172.4 mg/g at pH 2.0. SEM-EDS, BET, XRD, FT-IR, Raman and XPS investigation suggested that reduction of Cr(VI) to Cr(III) was the major removal mechanism. pH played an important role on the corrosion of nZVI-BC, at pH 4.5 and 2.0, FeOOH and Fe3O4 were detected as the major iron oxide, respectively. Therefore, FeOOH-BC and Fe3O4-BC were further prepared and their interaction with Cr were studied. Combining with DFT calculations, it revealed that Fe3O4 has higher adsorption capacity and was responsible for the effective removal of Cr(VI) through electrostatic attraction and reduction under acidic conditions. However, Fe3O4 will continue to convert to the more stable FeOOH, which is the key to for the subsequent stabilization of the reduced Cr(III). The results showed that the oxide corrosion products of nZVI-BC were subjected to the environment, which will eventually affect the fate and transport of the adsorbed heavy metal.

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Biochar (BC)-supported sulfide-modified nanoscale zerovalent iron (S-nZVI/BC) was prepared using the liquid-phase reduction method for the application of the removal of sulfamethazine (SMZ) from water. The reaction conditions were optimized by the Box−Behnken response surface method (RSM). A model was constructed based on the influence factors of the removal rate, i.e., the carbon-to-iron ratio (C/Fe), iron-sulfur ratio (Fe/S), pH, and hydrogen peroxide (H2O2) concentration, and the influence of each factor on the removal efficiency was investigated. The optimal removal process parameters were determined based on theoretical and experimental results. The results showed that the removal efficiency was significantly affected by the C/Fe ratio and pH (p < 0.0001) but relatively weakly affected by the Fe/S ratio (p = 0.0973) and H2O2 concentration (p = 0.022). The optimal removal process parameters were as follows: 0.1 mol/L H2O2, a pH of 3.18, a C/Fe ratio of 0.411, and a Fe/S ratio of 59.75. The removal rate of SMZ by S-nZVI/BC was 100% under these conditions. Therefore, it is feasible to use the Box−Behnken RSM to optimize the removal of emerging pollutants in water bodies by S-nZVI/BC.

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Using chicken manure as raw material to prepare activated carbon as a dispersant, a novel biochar-loaded nano-zerovalent iron composite (nZVI@CMBC) was developed and applied to remove hexavalent chromium, i.e., Cr(VI), in wastewater. The dispersion of nano-zerovalent iron (nZVI) particles on the surface of chicken manure-derived biochar (CMBC) successfully inhibited the aggregation of magnetic iron particles and effectively reduced the size of nZVI particles. The results demonstrated that under acidic conditions, the removal efficiency of Cr(VI) by the nZVI@CMBC composite could reach 124.12 mg g-1. The pseudosecond-order kinetic model had a good agreement with the adsorption kinetics of the nZVI@CMBC composite, implying that the adsorption of Cr(VI) is based on the multi-layer chemical adsorption. Therefore, this study provides a new clue and strategy for removing Cr(VI) in wastewater.

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1,2-dichloroethane (1,2-DCA) is a chlorinated hydrocarbon used for polyvinyl chloride plastic production. As such, 1,2-DCA is a common persistent contaminant in saturated zones. While nanoscale zerovalent iron (NZVI) is considered an effective reductant for removing a wide range of chlorinated hydrocarbons, 1,2-DCA is resistant to reduction by NZVI as well as by modified forms of NZVI (e.g., sulfidated-NZVI). Hydroxyl radicals produced in Fenton's reaction can effectively degrade 1,2-DCA, but Fenton's reaction requires the acidification of saturated zones to achieve a groundwater pH of 3 to facilitate the catalytic reaction. To overcome this problem, this study has developed a sequential treatment process using an NZVI-induced Fenton-like reaction that can effectively degrade 1,2-DCA at an initially neutral pH range. The experiments were conducted using a high 1,2-DCA concentration (2000 mg/L) to evaluate the feasibility of using the treatment process at source zones. The process degraded 99% of 1,2-DCA with a pseudo-first-order rate constant of 0.49 h-1. Unlike the single-stage treatment process, the sequential treatment can control the used H2O2 concentration in the system, thus sustaining the reaction and resulting in more efficient 1,2-DCA degradation. To mimic subsurface conditions, batch experiments were conducted to remove 1,2-DCA sorbed in contaminated soil. The results show that 99% removal of 1,2-DCA was obtained within 16 h. Additionally, this study suggests that the NZVI can be used for at least three consecutive 1,2-DCA degradation cycles while maintaining high removal efficiency.

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This study conducted laboratory column experiments to systematically examine the transport of novel heteroaggregates of montmorillonite (Mt) microparticles with nanoscale zerovalent irons (nZVIs) in saturated sand at solution ionic strengths (ISs) ranging from 0.001 to 0.2 M. Spherical nZVIs were synthesized using the liquid phase reduction method and were attached on the plate-shaped Mt surfaces in monolayer. While complete deposition occurred for nZVIs in sand, significant transport was observed for Mt-nZVI heteroaggregates at IS ≤ 0.01 M despite the transport decrease with an increasing loading concentration of nZVIs on Mt. The increased mobility of Mt-nZVI heteroaggregates was because the attractions between nZVIs and sand collectors were reduced by the electrostatic repulsions between the Mt and the collector surfaces, which led to a decreased deposition in the sand columns. Complete deposition occurred for the Mt-nZVI heteroaggregates at IS ≥ 0.1 M due to a favorable deposition at Derjaguin-Landau-Verwey-Overbeek (DLVO) primary energy minima. Interestingly, a large fraction of the deposited heteroaggregates was released by reducing IS because of a monotonic decrease of interaction energy with separation distance for the heteroaggregates at low ISs (resulting in repulsive forces), in contrast to the irreversible deposition of nZVIs. Therefore, the fabricated heteroaggregates could also have high mobility in subsurfaces with saline pore water through continuous capture and release using multiple injections of water with low ISs. Our study was the first to examine the transport of heteroaggregates of a plate-like particle with spherical nanoparticles in porous media; the results have important implications in the use of nanoscale zerovalent iron for in situ soil and groundwater remediation.

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Cadmium (Cd) contamination in soils is of great concern, and therefore the development of effective remediation technologies for cadmium contamination is urgent. In our study, nano zero-valent iron (NZVI) supported by metal-organic framework (MOF) materials (MOF-NZVI) were prepared using NaBH4 and FeCl3 to try to solve the soil Cd remediation problem. Herein, the effects and the mechanism of MOF-NZVI for the immobilization of Cd in contaminated soil was investigated. The results showed that MOF-NZVI was capable of converting Cd in soil from weak acid extractable and reducible fractions to oxidizable and residual states, thus effectively reducing the toxicity of Cd in soil. FTIR and XRD analysis confirmed that the dominant reaction mechanism between MOF-NVZI and Cd is adsorption with complexation, and the stabilization of Cd is achieved by the formation of compounds such as FeOCdOH.

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Sulfidized nanoscale zerovalent iron (SNZVI) with desirable properties and reactivity has recently emerged as a promising groundwater remediation agent. However, little information is available on how the molecular structure of chlorinated ethenes (CEs) affects their dechlorination by SNZVI or whether the sulfur content of SNZVI can alter their dechlorination pathway and reactivity. Here, we show that the reactivity (up to 30-fold) and selectivity (up to 70-fold) improvements of SNZVI (compared to NZVI) toward CEs depended on the chlorine number, chlorine position, and sulfur content. Low CEs (i.e., vinyl chloride and cis-1,2-dichloroethene) and high CEs (perchloroethene) tended to be dechlorinated by SNZVI primarily via atomic H and direct electron transfer, respectively, while SNZVI could efficiently and selectively dechlorinate trichloroethene and trans-1,2-dichloroethene via both pathways. Increasing the sulfidation degree of SNZVI suppressed its ability to produce atomic H but promoted electron transfer and thus altered the relative contributions of atomic H and electron transfer to the CE dechlorination, resulting in different reactivities and selectivities. These were indicated by the correlations of CE dechlorination rates and improvements with CE molecular descriptors, H2 evolution rates, and electron transfer indicators of SNZVI. These mechanistic insights indicate the importance of determining the structure-specific properties and reactivity of both SNZVI materials and their target contaminants and can lead to a more rational design of SNZVI for in situ groundwater remediation of various CEs.

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