Key Takeaways & Executive Findings
- •• • SL-FeC2O4-800 °C achieved 98% TCPA removal within 2 minutes across pH 3–9, demonstrating rapid kinetics and broad pH applicability critical for real wastewater streams with fluctuating pH. • • The composite maintained high activity over five cycles, with degradation efficiencies of 98.54%, 80.94%, 64.88%, 46.79%, and 40.36%, indicating a 59% loss after five uses—highlighting the need for regeneration strategies to extend catalyst lifespan. • • Mechanistic studies confirmed that TCPA removal involves biochar adsorption, direct reduction by zero-valent iron, and oxidation by ROS generated via oxygen activation, with surface-bound iron species playing a pivotal role in ROS formation—this multi-pathway mechanism enhances robustness against varying water chemistries. • • The synthesis uses activated sludge (waste biomass) and ferrous oxalate, offering a cost-effective and sustainable approach for producing high-performance iron-based composites, aligning with circular economy principles and waste valorization.
Abstract
Chloropyridine compounds, widely used as pesticide intermediates in China, pose significant risks to aquatic ecosystems and human health due to their high toxicity, persistence, and frequent detection in water bodies. This study addresses the removal of 3,4,5,6-tetrachloropyridine-2-carboxylic acid (TCPA), a representative chloropyridine contaminant, using a novel composite material. Biochar-supported zero-valent iron/iron carbide composites (SL-FeC2O4-800 °C) were synthesized via a high-temperature carbothermal process, employing activated sludge as the carbon source and ferrous oxalate (FeC2O4) as the iron precursor. The composite exhibited rapid and efficient TCPA degradation across a wide pH range (3–9), achieving 98% removal within 2 minutes. Mechanistic studies using scavenging experiments revealed that TCPA removal proceeds through synergistic pathways: adsorption onto biochar, direct reduction by zero-valent iron, and oxidation by reactive oxygen species (ROS) generated via oxygen activation. Surface-bound iron species were identified as critical for ROS formation. The material demonstrated reusability over five cycles, with degradation efficiencies decreasing from 98.54% to 40.36%, indicating gradual deactivation due to iron consumption and surface passivation. This work not only provides an efficient and environmentally sustainable method for removing persistent and highly toxic pollutants like TCPA but also offers a novel strategy for sludge resource utilization. The low-cost raw materials, simple preparation, and high activity position this composite as a promising candidate for industrial wastewater treatment, particularly in pesticide manufacturing effluents.
1. Introduction
Chloropyridine compounds, integral to pesticide manufacturing, are produced and used on a massive scale in China. Their high water solubility and weak soil adsorption facilitate leaching into groundwater, posing chronic health risks. Among these, 3,4,5,6-tetrachloropyridine-2-carboxylic acid (TCPA) is particularly recalcitrant due to its chemical stability and high toxicity, resisting conventional biological and Fenton treatments. Existing remediation technologies often suffer from slow kinetics, narrow pH tolerance, or secondary pollution, necessitating the development of efficient, green, and cost-effective alternatives.
This study introduces a biochar-supported zero-valent iron/iron carbide composite (SL-FeC2O4-800 °C) synthesized via carbothermal reduction of activated sludge and ferrous oxalate. The composite leverages the adsorptive capacity of biochar, the reducing power of zero-valent iron, and the catalytic generation of reactive oxygen species to achieve rapid TCPA degradation. By utilizing waste sludge as a carbon source, this approach not only addresses pollutant removal but also offers a sustainable route for sludge valorization, tackling two environmental challenges simultaneously.
Loading authentic research manuscript (Pages 1–5)...
SHI Shaojie, LI Na, ZHAO Rusong, NIU Hongyun, CAI Yaqi (2026). Preparation of Biochar-Supported Zero-Valent Iron/Iron Carbide Composites and Their Application in TCPA Removal. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025042101
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 optimal iron-to-carbon ratio for synthesizing SL-FeC2O4-800 °C, and how does it affect TCPA degradation performance?
The optimal mass ratio of FeC2O4 to activated sludge is 1:1, yielding the composite SL-FeC2O4-800 °C (1:1). This formulation achieved 98% TCPA removal within 2 minutes at pH 3–9. Ratios deviating from 1:1 likely result in lower iron loading or insufficient carbon support, reducing reactive sites and overall degradation efficiency.
What are the primary deactivation mechanisms during cyclic use, and how can catalyst longevity be improved?
Cyclic tests showed degradation efficiency dropped from 98.54% (cycle 1) to 40.36% (cycle 5). Deactivation is attributed to the consumption of zero-valent iron (Fe0) as an electron donor and the accumulation of inert iron oxides on the surface, which block active sites. Regeneration strategies such as acid washing or electrochemical reduction could restore activity, but further research is needed to enhance stability.
How does the composite achieve TCPA removal across a wide pH range (3–9) without pH adjustment?
The composite operates effectively across pH 3–9 due to multiple removal pathways: biochar adsorption is pH-independent, zero-valent iron reduction is favored under acidic conditions, and ROS generation via oxygen activation occurs over a broad pH range. This synergy ensures consistent performance without the need for pH pre-conditioning, a significant advantage for treating industrial effluents with variable pH.
What is the role of surface-bound iron species in ROS generation, and how does this contribute to TCPA oxidation?
Scavenging experiments revealed that surface-bound iron species are crucial for ROS formation. These iron sites catalyze the activation of dissolved oxygen to produce reactive oxygen species (e.g., hydroxyl radicals), which oxidize TCPA and its degradation intermediates. This oxidative pathway complements direct reduction by Fe0, ensuring complete mineralization or transformation to less toxic products.
What are the scalability prospects for this synthesis method using activated sludge as a precursor?
The synthesis is straightforward and uses low-cost, readily available materials (activated sludge and ferrous oxalate). The carbothermal process is amenable to scale-up, though careful control of temperature and atmosphere is required to achieve consistent iron carbide formation. The dual benefit of waste sludge valorization and pollutant removal makes this approach economically attractive for industrial adoption, particularly in regions with abundant sludge generation.
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.