The development of electrochemical methods for determining nanoparticles in the environment. Part I. Voltammetry and in-situ electrochemical scanning tunnelling microscopy (EC-STM) study of FeS in sodium chloride solutions

Abstract

Environmental context The dramatic change in physical and chemical characteristics that substances experience at reduced length scales (1–100nm), together with a potential risk of ecotoxicity, are two of the reasons for the scientific interest in nanoparticles. The current understanding of the behaviour and fate of nanoparticles in natural waters is limited because of a lack of efficient methods for their characterisation. Electrochemistry is a promising tool for the determination and characterisation of nanoparticles in the natural environment. Abstract In-situ electrochemical scanning tunnelling microscopy (EC-STM) has been used for the characterisation and determination of FeS nanoparticles (NPs) at a Au(111) electrode in NaCl solutions oversaturated with FeS. In parallel, voltammetric measurements in different electrode systems (Hg and Au) have been conducted. Particle deposition was studied in relation to variations in applied and scanning electrode potentials over a range of 0.1 to –1.5V v. Ag/AgCl. EC-STM images obtained on the Au(111) electrode revealed the presence of FeS NPs, accompanied by a drastic transformation in the electrode’s surface topography during scanning from 0.1 to –1.2V. A majority of FeS NPs (diameter 2–5nm) were detected in the potential range of –0.15 to –0.25V v. Ag/AgCl. The EC-STM results are in very good agreement with previous voltammetric measurements at Hg and Au electrodes. The combination of in-situ EC-STM and cyclic voltammetry complementary techniques appears to be a powerful tool for the characterisation of complex electrochemical systems such as chalcogenide NPs in aqueous solutions.