Chlorination treatment actuated structural reconstitution and aggravated toxicity of molybdenum disulfide nanosheets...

The extensive application of molybdenum disulfide (MoS₂) nanosheets in various fields involving in water treatment inevitably results in their release into wastewater treatment plants, and eventually into aquatic environments following disinfection. However, little is known about the transformations and toxicity evolution of MoS₂ during chlorination. This study discovered that MoS₂ is unstable to NaClO exposure, and more soluble ions are released under UV/NaClO co-treatment due to the generation of •OH and chlorine radicals. Compared to NaClO alone, UV/NaClO treatment caused significant structural disorder and compositional alterations in MoS₂ (oxidation and chlorine incorporation), reducing its colloidal stability and hydrophilicity. Relative to pristine MoS₂, chlorinated MoS₂ showed stronger toxic effects against algae, including strengthened envelopment, morphological shrinkage and inner membrane collapse. Chlorination clearly intensified the abiotic and biotic ROS-dependent oxidative stress of MoS₂, leading to exacerbated cell growth (34.6 % at 10 μg/mL) and photosynthesis inhibition, and membrane damage. Metabolomics confirmed the aggravated toxicity of chlorinated MoS₂ in terms of the down-regulation of carbohydrates, amino acids, unsaturated fatty acids, and TCA cycle. This study underlines the significant role of chlorination processes in modifying MoS₂ ecotoxicity and proposes the necessity to systematically assess the risks of MoS₂-based nanomaterials while developing water treatment processes accordingly.