Degradation of Chloroform by Zerovalent Iron: Effects of Mechanochemical Sulfidation and Nitridation on the Kinetics and Mechanism

Iron pipe corrosion enhanced the transformation of iopamidol, a precursor of iodinated disinfection byproducts: The role of sulfate-reducing bacteria

Long-term use of iron pipes leads to inevitable corrosion due to chemical and biological processes, with sulfate-reducing bacteria (SRB) playing a significant role. The corrosion products generated will affect the transformation of micropollutants in pipe networks. This study investigated the effect of SRB-influenced corrosion (SIC) on the transformation of iodine-containing micropollutants, using iopamidol (IPM) as a model compound. The degradation rate of IPM in the presence of Febio (with SIC) was 2.3 times higher than that with Feabio (without SIC). This enhancement was primarily attributed to accelerated and selective electron transfer facilitated by FeSx formation in the SIC process. The enhancement was more pronounced in presence of an appropriate amount of SO42 (120 mg L-1), or under a weakly acidic condition (pH 6). The enhancement was further validated in real water, where the released iodide was converted into iodinated disinfection by-products (I-DBPs) and/or iodate (IO3-), depending on the disinfectant used. This study offers an insight into the interplay between SRB-driven iron corrosion and iodine-containing pollutant transformation, contributing to a deeper understanding of micropollutant fate in corroded iron pipe networks.

Co-incorporation of lattice S and P into nano zero-valent iron induces multiple Kirkendall effects for enhanced trichloroethylene reduction efficiently

Conventional zero-valent iron (ZVI) materials are limited by the constraints of reactivity-selectivity-stability trade-offs, so designing multi-heteroatom co-modified ZVI with synergistic effects is gradually gaining popularity. Herein, we developed a novel co-modified nZVI by simultaneously doping sulfur (S) and phosphorus (P) heteroatoms into nZVI using the one-step liquid-phase reduction method. In this case, the faster diffusion rate of core iron atoms compared to shell components triggeres multiple Kirkendall effects, causing the inward diffusion of vacancies with further coalescing into radial nanocracks. Regarding the reactivity and selectivity, sulfidation and phosphorylation co-modified nZVI exhibited the best performance, with a trichloroethylene (TCE) dechlorination rate (kobs,TCE) of 0.65 h-1 and an electron efficiency (εe) of 14.5 %, which are 20.9 and 13.8 times higher than those of unmodified nZVI. A series of characterizations and electrochemical analyses indicated that S and P doping significantly altered the physicochemical properties of the core and shell layers, generating distinctive "lemon slice" nanocracks that could be used as electron transport channels, and FeSX significantly reduced the availability of hydrogen evolution reaction (HER) active surface sites and attenuates the passivation of nZVI. In addition, the co-modified S/P-nZVI exhibited excellent stability in different groundwater conditions, indicating its strong potential for application.

Integrative Lattice and Surface Engineering of Nanoscale Fe0 for Superior Dechlorination of Trichloroethene in Groundwater: Coordination in Reactivity, Selectivity, and Stability

Nanoscale zero-valent iron (nFe0) materials hold great promise in environmental remediation, yet achieving high reactivity, selectivity, and stability in reduction remains a long-standing challenge. Here we address this challenge by employing Ni lattice and FeS surface engineering to fabricate novel nFe0-based nanomaterials (dubbed as FeNix@FeSy), featuring FeNi as the core and FeS as the shell. The FeNi5@FeS10 delivered approximately 242.7- and 81.2-times higher reactivity and selectivity, respectively, over unmodified nFe° for the remediation of trichloroethene (TCE; a notorious environmental pollutant), while maintaining high stability in groundwater remediation. We found that the core composition (i.e., Ni/Fe ratio) of FeNix@FeSy primarily determined reactivity, governed by a tradeoff between the galvanic effect and lattice strain, while shell properties mainly controlled selectivity, despite some interactions between them. Density functional theory (DFT) calculations revealed that the FeS surface served as a favorable adsorption site for TCE, and the low energy barriers (TS2, 0.19 eV) of FeNi5@FeS10 facilitated the cleavage of the first chlorine from TCE. Moreover, the core-shell structure promoted electron transfer from the core to the shell and TCE. This integrative lattice and surface engineering strategy provides a new avenue for designing advanced functional materials for environmental remediation and beyond.

Superior selectivity for efficiently reductive degradation of hydrophobic organic pollutants in strongly competitive systems

Highly toxic halo-/nitro-substituted organics, often in low concentrations and with high hydrophobicity, make it difficult to obtain electrons for reduction when strongly electron-competing substances (e.g., O2, H+/H2O, NO3-) coexist. To address this barrier, we devised a new strategy to modify microscale zero-valent aluminum (mZVAl) with graphene (GE) by one-pot ball-milling for GE@mZVAl, which exhibits 99 % selective removal of halo-/nitro-substituted organic pollutants (e.g., carbon tetrachloride (CT), trichloroethylene (TCE), p-nitrophenol (PNP) and p-nitrochlorobenzene (p-NCB)) in the presence of multiple competing inorganics (O2, H+/H2O, Cr(VI), NO3- and BrO3-) and interfering ions (Cl-, CO32-, SO42- and PO43-). Notably, due to the fact that the side-reaction of H2 evolution and second-passivation are significantly suppressed, the electron utilization efficiency for organics degradation reaches an impressive 96 %, even under harsh pH conditions (3-11). GE@mZVAl contains an Al-C interface with a high concentration of C-O, which can form active sites for organics and perform selective electron transfer. Meanwhile, the organophilic catalyst GE also hinders the exposure of AlOH+/Al0 sites to shield the competing and interfering of inorganic substances. As a highly selective reduction system, this work may yield innovative insights for the selective removal of hydrophobic refractory pollutants in complex water matrices.

Recent Progress in Molecular Oxygen Activation by Iron-Based Materials: Prospects for Nano-Enabled In Situ Remediation of Organic-Contaminated Sites

In situ chemical oxidation (ISCO) is commonly used for the remediation of contaminated sites, and molecular oxygen (O2) after activation by aquifer constituents and artificial remediation agents has displayed potential for efficient and selective removal of soil and groundwater contaminants via ISCO. In particular, Fe-based materials are actively investigated for O2 activation due to their prominent catalytic performance, wide availability, and environmental compatibility. This review provides a timely overview on O2 activation by Fe-based materials (including zero-valent iron-based materials, iron sulfides, iron (oxyhydr)oxides, and Fe-containing clay minerals) for degradation of organic pollutants. The mechanisms of O2 activation are systematically summarized, including the electron transfer pathways, reactive oxygen species formation, and the transformation of the materials during O2 activation, highlighting the effects of the coordination state of Fe atoms on the capability of the materials to activate O2. In addition, the key factors influencing the O2 activation process are analyzed, particularly the effects of organic ligands. This review deepens our understanding of the mechanisms of O2 activation by Fe-based materials and provides further insights into the application of this process for in situ remediation of organic-contaminated sites.

Electronic structure simulations in the cloud computing environment

The transformative impact of modern computational paradigms and technologies, such as high-performance computing (HPC), quantum computing, and cloud computing, has opened up profound new opportunities for scientific simulations. Scalable computational chemistry is one beneficiary of this technological progress. The main focus of this paper is on the performance of various quantum chemical formulations, ranging from low-order methods to high-accuracy approaches, implemented in different computational chemistry packages and libraries, such as NWChem, NWChemEx, Scalable Predictive Methods for Excitations and Correlated Phenomena, ExaChem, and Fermi-Löwdin orbital self-interaction correction on Azure Quantum Elements, Microsoft's cloud services platform for scientific discovery. We pay particular attention to the intricate workflows for performing complex chemistry simulations, associated data curation, and mechanisms for accuracy assessment, which is demonstrated with the Arrows automated workflow for high throughput simulations. Finally, we provide a perspective on the role of cloud computing in supporting the mission of leadership computational facilities.

Roles of varying carbon chains and functional groups of legacy and emerging per-/polyfluoroalkyl substances in adsorption on metal-organic framework: Insights into mechanism and adsorption prediction

Metal-organic frameworks (MOFs) are promising adsorbents for legacy per-/polyfluoroalkyl substances (PFASs), but they are being replaced by emerging PFASs. The effects of varying carbon chains and functional groups of emerging PFASs on their adsorption behavior on MOFs require attention. This study systematically revealed the structure-adsorption relationships and interaction mechanisms of legacy and emerging PFASs on a typical MOF MIL-101(Cr). It also presented an approach reflecting the average electronegativity of PFAS moieties for adsorption prediction. We demonstrated that short-chain or sulfonate PFASs showed higher adsorption capacities (μmol/g) on MIL-101(Cr) than their long-chain or carboxylate counterparts, respectively. Compared with linear PFASs, their branched isomers were found to exhibit a higher adsorption potential on MIL-101(Cr). In addition, the introduction of ether bond into PFAS molecule (e.g., hexafluoropropylene oxide dimeric acid, GenX) increased the adsorption capacity, while the replacement of CF2 moieties in PFAS molecule with CH2 moieties (e.g., 6:2 fluorotelomer sulfonate, 6:2 FTS) caused a decrease in adsorption. Divalent ions (such as Ca2+ and SO42-) and solution pH have a greater effect on the adsorption of PFASs containing ether bonds or more CF2 moieties. PFAS adsorption on MIL-101(Cr) was governed by electrostatic interaction, complexation, hydrogen bonding, π-CF interaction, and π-anion interaction as well as steric effects, which were associated with the molecular electronegativity and chain length of each PFAS. The average electronegativity of individual moieties (named Me) for each PFAS was estimated and found to show a significantly positive correlation with the corresponding adsorption capacity on MIL-101(Cr). The removal rates of major PFASs in contaminated groundwater by MIL-101(Cr) were also correlated with the corresponding Me values. These findings will assist with the adsorption prediction for a wide range of PFASs and contribute to tailoring efficient MOF materials.

Sodium salt promoted the generation of nano zero valent iron by carbothermal reduction: For activating peroxydisulfate to degrade antibiotic

Carbothermal reduction is a promising method for the industrial preparation of nano-zero-valent iron. Preparing it also involves very high pyrolysis temperatures, which leads to a significant amount of energy consumption. The temperature required for the preparation of nano-zero-valent iron by carbothermal reduction was reduced by 200 °C by the addition of sodium salt. Carbon-loaded nano zero-valent iron (Fe0/CB-Na) was prepared by carbothermal reduction through the addition of sodium salt. The results showed that Fe0/CB-Na@700 had the same activation performance as Fe0/CB@900 and the newly prepared nano-zero-valent iron. The addition of sodium salt promoted the transfer of oxygen from the iron oxide to the carbon structure during the roasting process so that the iron oxide was reduced to as much Fe0 as possible. Thus, sodium salts were optimized for the preparation of nano-zero-valent iron by carbothermal reduction through interfacial amorphization and oxygen transfer, thus reducing the preparation cost.

Carboxymethyl cellulose stabilization induced changes in particle characteristics and dechlorination efficiency of sulfidated nanoscale zero-valent iron

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.

Decoding the divalent cation effect on sulfidation of zero-valent iron: Phase evolution and FeSx assembly

The decontamination ability of sulfidated zero-valent iron (S-ZVI) can be enhanced by the effective assembly of iron sulfides (FeSx) on neglected heterogeneous surfaces by liquid-phase precipitation. However, S-ZVI preparation with the usual pickling is detrimental to orderly interfacial assembly and leads to an imbalance between electron transfer optimization and electron storage. In this work, S-ZVI was prepared in solutions containing trace divalent cation, and it removed Cr(VI) up to 323.25 times higher than ZVI. This result is achieved by surface sites protonation of divalent cations regulating the phase evolution on the ZVI surface and inducing FeSx chemical assembly. Regulation of divalent cation and S(-II) content further promotes FeSx targeted assembly and reduces electron storage consumption as much as possible. The barrier for FeSx assembly is found to lie at the ZVI interface rather than in the deposition between FeSx. Chemical assembly at heterogeneous interfaces is a prerequisite for the ordered assembly of FeSx. In addition, S-ZVI prepared in simulated groundwater showed extensive preparation pH and universality for remediation scenarios. These findings provide new insights into the development of in-situ sulfidation mechanisms with particular implications for S-ZVI applied to soil and groundwater remediation by the regulation of heterogeneous interfacial assembly.