Preparation of Biochar-Supported Zero-Valent Iron/Iron Carbide Composites and Their Application in TCPA Removal
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.