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Voltammetry of Sulfide Nanoparticles and the FeS(aq) Problem

Voltammetry at Hg drop electrodes is a promising method for detecting sulfide nanoparticles in natural waters. Recent research suggests that such nanoparticles might affect organisms in unforeseen ways. Sulfide nanoparticles diffusing to Hg surfaces are captured selectively even from unfiltered waters that contain larger amounts of other nanoscale materials, such as organic macromolecules or clay minerals. Optimum size sensitivity for capture is roughly 5-100 nm at Hg drop electrodes. Sulfide nanoparticles are stabilized at Hg surfaces by transformation to adlayers, whose accumulation can be quantified electrochemically. Study of FeS adlayers has led to new insights regarding the puzzling -1.1 V vs. Ag/AgCl signal observed in sulfidic natural waters. This signal has been attributed previously to Fe sulfide clusters or complexes. New evidence shows that it arises from reduction of Fe2+ at FeS adlayers formed by sorption of FeS nanoparticles on Hg electrodes. Partial coverage of Hg with FeS creates in essence two electrodes. These reduce Fe2+ at separate potentials.

FeS(aq), voltammetry, anoxic conditions

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