Impact of sulfhydryl ligands on the transformation of silver ions by molybdenum disulfide and their combined toxicity to freshwater algae

Abstract

The transformation of silver ions (Ag⁺) mediated by engineered nanomaterials (ENMs) influences the biosafety of Ag-containing products in natural environments. Actually, modification of biomolecules to ENMs in aquatic ecosystems alters their interactions with Ag⁺. This study discovered that surface functionalization of glutathione (GSH, a sulfhydryl compound ubiquitous in natural waters) on molybdenum disulfide (MoS₂) nanoflakes suppressed the redox reaction between 1 T components and Ag⁺, inhibiting the MoS₂-mediated reduction of Ag⁺ to Ag nanoparticles (AgNPs) in aqueous phase in the dark. However, AgNPs formation (from 2.32 ± 0.35-3.25 ± 0.29 mg/L per day, pH 7.0) and oxidation of MoS₂ were remarkably accelerated after GSH binding under light conditions. The dominant electron donator of MoS₂ to Ag⁺ was transformed from the electron-hole pairs to surface ligands driven by the introduction of chromophoric groups was authenticated as the cause for the elevated Ag⁺ reduction. These processes also occurred between Ag⁺ and MoS₂ at low levels (50 μg/L). Additionally, the joint algal toxicity of GSH-modified MoS₂ with Ag⁺ was weaker than that of pristine MoS₂ due to increased retention of free Ag⁺ and AgNPs formation. Our findings improve the understanding of the interaction between ENMs and Ag⁺ in aquatic ecosystems.

Keywords: Environmental risk; Freshwater algae; Molybdenum disulfide; Silver transformation; Surface functionalization.