Dissolved Oxygen and Visible Light Irradiation Drive the Structural Alterations and Phytotoxicity Mitigation of...

Understanding environmental fate is a prerequisite for the safe application of nanoparticles. However, the fundamental persistence and environmental transformation of single-layer molybdenum disulfide (SLMoS₂, a 2D nanosheet attracting substantial attention in various fields) remain largely unknown. The present work found that the dissolution of SLMoS₂ was pH and dissolved oxygen dependent and that alterations in phase composition significantly occur under visible light irradiation. The 1T phase was preferentially oxidized to yield soluble species (MoO₄^2- and SO₄^2-), and the 2H phase remained as a residual. The transformed SLMoS₂ exhibited a ribbon-like and multilayered structure and low colloidal stability due to the loss of surface charge. Dissolved oxygen competitively captured the electrons of SLMoS₂ to generate superoxide radicals and accelerated the dissolution of nanosheets. Compared to pristine 1T-phase SLMoS₂, the transformed 2H-phase SLMoS₂ could not easily enter algal cells and induced a low developmental inhibition, oxidative stress, plasmolysis, photosynthetic toxicity and metabolic perturbation. The downregulation of amino acids and upregulation of unsaturated fatty acids contributed to the higher toxicity of 1T-phase SLMoS₂. The dissolved ions did not induce apparent phytotoxicity. The connections between environmental transformation (phase change and ion release) and phytotoxicity provide insights into the safe design and evaluation of 2D nanomaterials.