Dissolved Oxygen and Visible Light Irradiation Drive the Structural Alterations and Phytotoxicity Mitigation of Single-Layer Molybdenum Disulfide

Abstract

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.

Influence of Size and Phase on the Biodegradation, Excretion, and Phytotoxicity Persistence of Single-Layer Molybdenum Disulfide

“…Rutile TiO 2 nanomaterials (>50 mg/L) induced persistent DNA fragmentation because of free radical generation, while the damage induced by anatase TiO 2 –cell interactions could be repaired . Furthermore, the metallic-phase SLMoS 2 with octahedral coordination (1T-SLMoS 2 ) showed a stronger preference for dissolution in an aqueous environment than semiconductive-phase SLMoS 2 with trigonal prismatic coordination (2H-SLMoS 2 ). , SLMoS 2 can also be degraded by horseradish peroxidase (HRP) . The different properties of NPs lead to their temporary or irreversible adverse effects. , Taken together, the sizes and phase of SLMoS 2 may be crucial for determining the persistence of SLMoS 2 phytotoxicity.…”

“…17 Furthermore, the metallic-phase SLMoS 2 with octahedral coordination (1T-SLMoS 2 ) showed a stronger preference for dissolution in an aqueous environment than semiconductive-phase SLMoS 2 with trigonal prismatic coordination (2H-SLMoS 2 ). 18,19 SLMoS 2 can also be degraded by horseradish peroxidase (HRP). 20 The different properties of NPs lead to their temporary or irreversible adverse effects.…”

Effects of MoS2 Layer Thickness on Its Photochemically Driven Oxidative Dissolution

“…According to the conduction band potential of MoS 2 nanosheets in reported literature, photo-excited electrons in MoS 2 nanosheets have enough negative potential to directly reduce dissolved oxygens to O 2 •– and H 2 O 2 in the aqueous media. However, • OH cannot be directly produced from the photoinduced holes in MoS 2 nanosheets because their valence band position is not sufficiently positive for oxidizing OH – to • OH. , Therefore, we expect that • OH could be generated by H 2 O 2 decomposition and Mo 6+ reduction under light illumination …”

DNA Cleavage by Chemically Exfoliated Molybdenum Disulfide Nanosheets

“…As the pH increased, a larger amount of O 2 – was produced. Previous studies revealed that the reaction MoS 2 + 9/2O 2 + 3H 2 O = MoO 4 2– + 2SO 4 2– + 6H + occurred in the aqueous ce-MoS 2 solution. − When the pH increased, the reaction would more likely move forward. Thus, the rate of electron transfer from molecular oxygen to form O 2 – under a higher pH could be faster than that under a lower pH .…”