Aqueous synthesis and optical study of undoped and Gd-doped ZnS semiconductor nanoparticles (Zn1-3xGd2xS): Environmental toxicity assessment

Abstract

Using the nucleation-doping strategy, bare ZnS and ZnS/Gd nanoparticles (NPs) have been elaborated at 80 °C in a basic aqueous solution. Different samples including Gd: ZnS NPs with 3, 5 and 10 % Gd doping were prepared and characterised by different techniques such as X-ray diffraction, infrared absorption and photoluminescence (PL) spectroscopy. The morphology of the obtained nanoparticles was established by transmission electron microscopy coupled with high resolution microscopy (HRTEM). The energy gap (E_g) of the samples were calculated using the classic UV–Visible technique coupled with the Tauc equation. The PL response of both ZnS and ZnS/Gd NPs showed a broad emission in the visible range shifted with the increasing the Gd percentage. The chemical species of crystalline growth were identified using Fourier transform. It is important to obtain NPs that meet the requirements of the application, but their toxicity to the environment needs to be investigated. The main objective of this study is to explain the filtration capacity (FC) and the induction of oxidative stress in the digestive gland and in the gills of the Mediterranean mussel (Mytilus galloprovincialis). The activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT)) and AChE have been measured in the digestive gland after exposure to the following substances to 50 mg/L and 100 mg/L of ZnS, ZnS: Gd (3 %), ZnS: Gd (5 %) and ZnS: Gd (10 %). Undoped ZnS and Gd-doped ZnS (3 and 5 %) do not show a significant effect indicating a minimal interaction between these nanoparticles and the non target organisms. In contrast, Gd-doped ZnS (10 %) increases the activities of SOD, CAT and AChE. These findings provide the first evidence for the formation of ZnS NPs using an aqueous method and highlight the importance of understanding the biological targets of NPs when assessing their prospective impact on environmental model organisms.