Dominant Role of Digestate Biochar-Modified Zero-Valent Iron Interfacial Structure in Regulating Nitrobenzene Reduction Efficiency
Zero-valent iron (ZVI) suffers from surface passivation and low electron utilization in reductive removal of nitrobenzene (NB). To address these issues, a ball-milled iron/digestate biochar composite (BM-Fe/DBC) was prepared and compared with a physically mixed counterpart (PM-Fe/DBC). Characterization revealed that ball milling tightly embedded ZVI particles into the carbon matrix, forming Fe–C chemical bonds and a strong interfacial coupling structure that established efficient electron transfer channels. This structure significantly enhanced the micro-galvanic effect between iron and carbon, yielding superior reduction performance across a wide pH range (3–9). Under optimal conditions (Fe:C mass ratio 2:1, dosage 1.0 g·L−1, pH 5), BM-Fe/DBC achieved 79.9% NB removal, and the generation of aniline (AN) was 1.85 times that of PM-Fe/DBC. Mechanistic studies indicated that the intimate Fe–C interfacial coupling promoted sustained ZVI corrosion and enhanced the production of indirect reducing species, including adsorbed Fe(II) and atomic hydrogen (H*). Electrochemical analyses showed that BM-Fe/DBC exhibited a lower corrosion potential, a higher corrosion current density (approximately 2.15 times higher), and lower charge transfer resistance, kinetically confirming its superior electron transfer capability. These findings reveal that constructing strong interfacial coupling in iron–carbon composites via mechanochemical methods can effectively overcome key limitations of ZVI in reduction reactions, providing a theoretical basis and practical pathway for designing high-performance water treatment materials.