Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Abstract

Cyclic voltammetry on the Hg electrode was used to investigate the electrochemical behavior of NaCl/NaHCO 3 electrolyte solutions supersaturated with respect to Zn sulfide phases. The voltammetric results clearly show how an Hg electrode, due to exchange between Hg 2+ from an HgS adlayer and Zn 2+ from solution, becomes the site for surface ZnS adlayer formation in the potential range −0.45 to −0.6 V. The exchange reaction is reversible, and the surface-formed ZnS adlayer persists at the Hg electrode surface until −1.3 V during cathodic scans. Near −1.3 V, it is reduced. In the same solution, evidence for reduction of bulk Zn sulfide species including nanoparticles was not obtained. The approach emphasized here can be readily extended to any other system consisting of metal electrode and chalcogenide anions, pointing to the importance of choosing experimental conditions (i.e., deposition potential, stirring, and accumulation times) to avoid artifacts and wrong interpretation of data due to surface formation of metal sulfide species.

On the nature of dissolved copper ligands in the early buoyant plume of hydrothermal vents

“…The signal is much lower but still visible in untreated samples ( Figure 3A). The peak likely corresponds to the dissolutionreduction of an HgS layer deposited on the mercury drop surface as reported in many studies [50][51][52][53][54][55] . Many sulfur species could contribute to the HgS layer deposition especially sulfides (HSand S 2-), but also dissolved elemental sulfur S 0 (< 0.2 μm), polysulfides (Sn 2-) [52,56] or metal sulfide nanoparticles [35][36][37]57,58] .…”

“…Such process has been shown to happen for many metal as Zn 2+ or Fe 2+ but only the formation of the CuS layer provides a signal at -0.1 V vs Ag/AgCl (e.g. E ~ -0.6 V for the FeS layer) [53,55] . Once deposited, the CuS layer will be reduced at -1.0 V vs Ag/AgCl [35][36][37]55] as described in reaction 4:…”

Electroanalytical methods in characterization of sulfur species in aqueous environment

“…1. The obtained peak, usually in our papers designated as C2, represents the wellknown dissolution/reduction of HgS layer on the Hg electrode surface [5][6][7][9][10][11][12][13][14][15][16][17]: (E = -0.2 V, t a = 120 s). The C2 peak increases with either sulfide or with S 0 addition and corresponds to 6.5 nM RSS NV in a) and to mM RSSv in b.…”

“…Some examples include: potentiometry, polarography, voltammetry, chronopotentiometry, chronoamperometry, etc. These electrochemical methods, especially voltammetry, have appropriate features to be used as monitoring methods (early warning tools) for assessment of water quality in aqueous systems in general and will be key methods for trace pollutant analyses (sulfur species [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], organic compounds [18][19][20], trace metals [2-4, 8, 21-26], engineered and natural nanoparticles [27][28][29][30][31][32][33][34]).…”

“…These NPs could play important role as mediators of the trace metal nutrition and toxicity. Using different electrochemical methods it is possible to measure a variety of soluble and particulate sulfur compounds [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]32].…”