Key Takeaways & Executive Findings
- •• • Cl-ZVIbm achieved a 76.5-fold increase in Cr(VI) removal kinetics (0.0306 min−1 vs. 0.0004 min−1 for ZVIbm), enabling complete removal of 2 mg·L−1 Cr(VI) within 120 min, a critical improvement for practical water treatment throughput. • • Chloride modification reduced Cr(VI) adsorption energy from –0.28 eV to –1.64 eV by switching to a bidentate binuclear configuration, enhancing surface affinity and facilitating subsequent reduction. • • Surface Fe(II) content increased by 26.9% (from 53.2% to 67.5%) due to Cl− electron-withdrawing effect, driving direct electron transfer that reduced 99.5% of Cr(VI) to Cr(III), ensuring high detoxification efficiency. • • Chloride leaching was only 0.0126 mmol·L−1, well below industrial discharge limits, confirming the material's environmental safety and potential for scale-up without secondary pollution.
Abstract
Conventional zero-valent iron (ZVI) suffers from limited electron transfer due to its dense surface oxide layer. This study introduces a mechanochemical ball-milling strategy incorporating sodium chloride (NaCl) with ZVI to fabricate chloride-modified ZVI (Cl-ZVIbm). Using hexavalent chromium (Cr(VI)) as a model pollutant, Cl-ZVIbm exhibited a 76.5-fold enhancement in removal kinetics (0.0306 min−1 vs. 0.0004 min−1) compared to ball-milled ZVI (ZVIbm), achieving complete removal of 2 mg·L−1 Cr(VI) within 120 min. Spectroscopic characterization and density functional theory (DFT) calculations revealed dual regulation mechanisms: (1) Cl− substitution of surface hydroxyl groups alters coordination environments, enabling Cr(VI) adsorption via a bidentate binuclear configuration with adsorption energy reduced from –0.28 eV to –1.64 eV; (2) The strong electron-withdrawing effect of Cl− drives directional electron migration from the iron core to the surface, increasing surface Fe(II) content by 26.9% (67.5% vs. 53.2%) and facilitating direct electron transfer to reduce 99.5% of Cr(VI) into low-toxicity Cr(III). Notably, chloride leaching during reactions was only 0.0126 mmol·L−1, far below industrial wastewater discharge standards, confirming environmental compatibility. This work provides atomic-scale insights into chloride-mediated electronic modulation on ZVI surfaces, offering novel principles for interfacial engineering of environmental functional materials and a theoretical basis for heavy metal remediation technologies.
1. Introduction
Conventional zero-valent iron (ZVI) has long been employed for reductive removal of heavy metals like hexavalent chromium (Cr(VI)) from industrial wastewater. However, its practical efficacy is severely hampered by a dense surface oxide layer that impedes electron transfer from the iron core to the contaminant, resulting in sluggish kinetics and incomplete reduction. Prior attempts to enhance ZVI reactivity, such as sulfidation or nanoscale engineering, often introduce complex synthesis steps or secondary contamination risks, limiting their industrial viability.
This study addresses the bottleneck by employing a simple mechanochemical ball-milling approach with sodium chloride (NaCl) to fabricate chloride-modified ZVI (Cl-ZVIbm). The chloride ions simultaneously restructure the surface coordination and induce a dual electron regulation effect, dramatically boosting Cr(VI) removal kinetics by 76.5-fold while maintaining environmental compatibility. This work not only provides a scalable modification strategy but also offers atomic-scale mechanistic insights, paving the way for rational design of high-performance ZVI-based remediation materials.
Loading authentic research manuscript (Pages 1–5)...
HU Chunlei, ZHANG Guangqin, HAO Chenglin, TAO Qingwen, WANG Zhuting, LI Meiqi, ZHANG Lizhi (2026). Chloride-Induced Dual Electron Regulation on Zero-Valent Iron Surface for Highly Efficient Reductive Removal of Cr(VI). Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025040401
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the underlying mechanism for the enhanced Cr(VI) removal kinetics observed with Cl-ZVIbm?
The enhancement is attributed to dual regulation by chloride ions: (1) Cl− substitutes surface hydroxyl groups, altering the coordination environment and enabling Cr(VI) adsorption via a bidentate binuclear configuration, which lowers adsorption energy from –0.28 eV to –1.64 eV; (2) The strong electron-withdrawing effect of Cl− drives electron migration from the iron core to the surface, increasing surface Fe(II) content by 26.9% (from 53.2% to 67.5%), thereby facilitating direct electron transfer to Cr(VI).
How does the chloride leaching from Cl-ZVIbm compare to environmental safety standards?
Chloride leaching during the reaction was measured at only 0.0126 mmol·L−1, which is significantly below typical industrial wastewater discharge limits (e.g., 0.5 mmol·L−1 for chloride in some standards). This confirms the material's environmental compatibility and suitability for practical water treatment applications.
What is the practical significance of the 76.5-fold increase in removal kinetics?
The 76.5-fold increase in kinetic rate constant (from 0.0004 min−1 to 0.0306 min−1) means that Cl-ZVIbm can achieve complete removal of 2 mg·L−1 Cr(VI) within 120 minutes, whereas conventional ball-milled ZVI would require over 150 hours. This dramatic improvement enables practical reactor designs with shorter hydraulic retention times, reducing capital and operational costs.
Can the Cl-ZVIbm synthesis be scaled up for industrial production?
The synthesis involves simple ball-milling of ZVI with NaCl, a low-cost and widely available reagent. The process is scalable using existing industrial ball-milling equipment, and the materials used are inexpensive. The low chloride leaching and high reactivity suggest that Cl-ZVIbm can be produced at scale for field applications, though further studies on long-term stability and performance under real wastewater conditions are recommended.
What are the potential limitations or challenges for applying Cl-ZVIbm in real wastewater?
Potential challenges include the presence of competing ions (e.g., nitrate, sulfate) that may interfere with Cr(VI) adsorption, and the need for pH control to maintain optimal reactivity. Additionally, the long-term stability of the chloride-modified surface under continuous flow conditions requires investigation. However, the current study demonstrates high efficiency in synthetic solutions, and ongoing research aims to address these real-world complexities.
Related Chinese Research & Cross-Citations
Exploring the Potential Molecular Mechanisms of Eight Environmental Pollutants in Lung Adenocarcinoma through Network Toxicology, Machine Learning, and Multi-Omics Analysis
Epidemiological studies have established a significant association between exposure to environmental pollutants (EP) and the risk of lung adenocarcinoma (LUAD). This study integrates network toxicology and multi-omics analysis to elucidate the EP-LUAD molecular regulatory network and identify key regulatory genes, thereby revealing novel mechanisms of environmental carcinogenesis. Transcriptomic data from GEO and TCGA databases yielded 4,971 and 4,488 disease-related targets, respectively. Integration of toxicology databases (TargetNet, Swiss Target Prediction, CTD, SEA) identified 24,860 potential targets for eight common pollutants (SO2, NO, CO, NO2, O3, benzene, toluene, and polycyclic aromatic hydrocarbons). Intersection of these datasets produced 1,536 EP-LUAD common target genes. Protein-protein interaction network analysis identified 247 core targets. Machine learning selected five key genes: AGER, CAV1, CD44, CEP55, and GNB3, which demonstrated robust diagnostic and prognostic efficacy. Their expression correlated with immune cell infiltration, including CD4+ memory T cells and macrophages. Single-cell RNA sequencing revealed epithelial cell-specific expression patterns. Molecular docking confirmed stable pollutant-target binding, with PAH showing highest affinity for CD44 (binding energy −9.32 kcal·mol−1) and GNB3 (−8.32 kcal·mol−1). These findings establish AGER, CAV1, CD44, CEP55, and GNB3 as core molecular mediators of pollution-related LUAD. The high-affinity binding of PAH to CD44 and GNB3 underscores its carcinogenic potential. This study constructs a multi-level regulatory network for EP-LUAD, revealing underlying molecular mechanisms and providing novel potential targets and theoretical basis for early warning and intervention.
Effects of Different Functionalized Nanoplastics on the Transformation of Extracellular Antibiotic Resistance Genes in Aquatic Environments
The rapid dissemination of antibiotic resistance genes (ARGs) in aquatic environments poses serious threats to public health and environmental safety under the 'One Health' framework. Nanoplastics (NPs), as co-occurring pollutants, can exacerbate ARG risks by promoting horizontal gene transfer (HGT), yet the influence of different functional groups on extracellular ARG (eARG) transformation remains unclear. This study investigated the effects of carboxy-modified polystyrene NPs (PS-COOH) and amino-functionalized polystyrene NPs (PS-NH2) compared to unmodified polystyrene NPs (PS) on the transformation of the extracellular resistance plasmid IE-V1955 (carrying an ampicillin resistance gene) into Escherichia coli DH5α. Results showed that PS-COOH exposure promoted plasmid transformation similarly to PS, with effects increasing over 0.1–20 mg·L−1. Low concentrations (0.1–0.5 mg·L−1) of PS-NH2 also enhanced transformation, with stronger effects than PS-COOH at equal doses, whereas high concentrations (1–20 mg·L−1) inhibited it. Mechanistically, PS-COOH (0.1–20 mg·L−1) and low PS-NH2 induced intracellular reactive oxygen species (ROS), increased cell membrane permeability, elevated the protein-to-polysaccharide ratio in extracellular polymeric substances (EPS), and promoted biofilm formation, thereby facilitating transformation. High PS-NH2 concentrations caused excessive ROS leading to cell lysis and formed aggregates with plasmids larger than membrane pores, blocking uptake. These findings provide a theoretical basis for assessing the combined environmental health risks of NPs and ARGs.
Cardiovascular Toxicity Induced by Micro/Nano-Plastics and Its Mechanisms
Micro/nano-plastics (MNPs) are emerging contaminants widely detected in human circulatory systems, including blood, heart, and vascular endothelium, raising concerns about cardiovascular health risks. This systematic review analyzed 61 peer-reviewed studies (2008–2024) to elucidate the cardiotoxic effects and molecular mechanisms of MNPs. Evidence indicates that MNPs exposure elevates risks of atherosclerosis, thrombosis, and arrhythmias through oxidative stress, inflammatory cascades, endothelial dysfunction, and metabolic dysregulation. Notably, co-exposure with persistent organic pollutants (POPs) or heavy metals may produce synergistic or antagonistic effects. Current research relies predominantly on animal and cell models, with critical gaps in low-dose, long-term exposure data and epidemiological evidence. Future studies should optimize experimental designs, integrate metabolomics and epigenetics, and explore transgenerational effects and combined toxicity mechanisms to inform pollution control policies and mitigate cardiovascular risks.
Body Burden of Polybrominated Diphenyl Ethers and Joint Effects on Thyroid Function in a Physical Examination Population in Shenzhen
This study characterized the body burden of polybrominated diphenyl ethers (PBDEs) in a physical examination population in Shenzhen and evaluated its impact on thyroid function. Serum samples from 368 residents were analyzed for eight PBDE congeners using atmospheric pressure gas chromatography-tandem mass spectrometry (APGC-MS/MS). The median concentration of ∑8PBDEs was 10.2 ng·g⁻¹ lipid weight (lw), ranging from 0.13 to 2089.4 ng·g⁻¹ lw, with BDE-209 predominating (59.7% of total). Multiple linear regression revealed that a 1.7-fold increase in serum BDE-153 was associated with a 0.4% increase in free triiodothyronine (FT3) (P<0.05), while a 1.7-fold increase in BDE-183 was associated with a 0.9% decrease in total triiodothyronine (T3) and a 0.7% decrease in FT3 (P<0.05). Bayesian kernel machine regression (BKMR) indicated a negative correlation between mixed PBDE exposure and thyroid-stimulating hormone (TSH) at high exposure levels. Weighted quantile sum (WQS) regression showed that mixed exposure was associated with decreased T3 levels and T3/FT3 ratio, with BDE-153 and BDE-183 as the primary contributors. These findings suggest that PBDE exposure may adversely affect thyroid function and disrupt thyroid hormone homeostasis, with BDE-183 and BDE-153 playing key roles. This study provides a scientific basis for PBDE health risk assessment and thyroid protection.
Mechanisms of Natural Organic Matter in Regulating Microplastic Aggregation and Transport in Soil-Groundwater Systems: A Review
Microplastics (MPs) are persistent emerging contaminants ubiquitously distributed in soil-groundwater environments, where their aggregation and transport critically govern pollutant fate and ecological risks. Natural organic matter (NOM), a complex assemblage of organic compounds, interacts with MPs and porous media via hydrogen bonding, π-π interactions, hydrophobic effects, and electrostatic binding, thereby modulating MP surface properties and environmental behavior. This review systematically synthesizes the mechanisms by which NOM influences MP aggregation and transport, with emphasis on the distinct roles of humic substances, proteins, and extracellular polymeric substances (EPS), and their synergistic modulation with solution chemistry (pH, ionic strength, ion type). Additionally, NOM accelerates MP aging and alters surface characteristics, consequently impacting transport capacity. Current research limitations are identified, and future directions are proposed to inform MP pollution risk assessment and management strategies. Key findings indicate that NOM generally enhances MP stability and mobility at low ionic strengths, while high ionic strengths may induce aggregation depending on NOM type and ion valence. Humic substances predominantly increase electrostatic repulsion, whereas proteins and EPS can bridge particles, promoting aggregation. Aging processes, accelerated by NOM photochemical activity, increase surface oxygen functionality and hydrophilicity, further altering transport. The review underscores the need for systematic studies under environmentally relevant conditions to predict MP fate accurately.
Neurotoxicity of Carboxyl-Modified Polystyrene Microplastics on Zebrafish at Early Developmental Stage
Carboxyl-modified polystyrene microplastics (PS-COOH) are negatively charged particles formed by surface oxidation and functional group modification of polystyrene microplastics (PS), widely used in biomedical and analytical chemistry. However, studies on their neurotoxic effects on aquatic organisms are scarce. This study employed zebrafish (Danio rerio) as a model organism, exposing embryos to environmentally relevant concentrations (0.1, 1, 10, 100 μg·L−1) of PS and PS-COOH. Neurotoxic effects were assessed by measuring tail coiling frequency at 24 hpf and swimming velocity under alternating light/dark cycles at 120 hpf. Results demonstrated that both PS and PS-COOH induced neurotoxicity, with PS-COOH significantly reducing tail coiling frequency and average swimming speed compared to PS (P<0.05). Exposure to 10 μg·L−1 PS-COOH disrupted neurotransmitter homeostasis, altering levels of acetylcholine (ACh), serotonin (5-HT), and γ-aminobutyric acid (GABA). Transgenic zebrafish Tg(huc:EGFP) fluorescence assays revealed that PS-COOH (0.1–100 μg·L−1) caused damage to central neurons. These findings indicate that PS-COOH exposure impairs cholinergic, serotonergic, and GABAergic neurotransmission, induces neuronal damage, and exerts neurotoxic effects on zebrafish larvae. This study provides a theoretical basis for assessing the ecological and health risks of modified microplastics.