Mechanical ball milling-constructed Z-scheme oxalate-nZVI/MoS₂ heterojunction for efficient photocatalytic tetracycline degradation

To address tetracycline (TC) contamination in aquatic environments, a novel Z-scheme heterojunction photocatalyst (OA-nZVI/MoS₂) was synthesized via mechanical ball milling. This composite integrates oxalate-modified nano zero-valent iron (OA-nZVI) with nanoflower-structured molybdenum disulfide (MoS₂), significantly enhancing visible-light-driven photocatalytic activity. The optimized OA-nZVI/MoS₂ achieved 92.71 % TC degradation within 90 min, exhibiting a 14.52-fold increase in kinetic rate constant compared to pristine MoS₂. Quenching experiments and electron spin resonance (ESR) analysis confirmed efficient charge separation and the dominant role of hydroxyl radicals (•OH) in the degradation mechanism. The ferrous oxalate shell stabilized nZVI, ensuring excellent recyclability and adaptability across diverse environmental conditions, including varying pH, coexisting ions, temperature, and humic acid. High-performance liquid chromatography-mass spectrometry (HPLC-MS) identified major degradation pathways, while the Toxicity Estimation Software Tool (TEST) revealed substantially reduced toxicity of intermediates post-treatment. This work provides a novel material design for stable, efficient photocatalytic systems to address antibiotic pollution.