The oxidative dissolution of citrate-capped silver nanoparticles (AgNPs, ∼50 nm diameter) is investigated herein by two electrochemical techniques: nano-impacts and anodic stripping voltammetry. Nano-impacts or single nanoparticle-electrode collisions allow the detection of individual nanoparticles. The technique offers an advantage over surface-immobilized methods such as anodic stripping voltammetry as it eliminates the effects of particle agglomeration/aggregation. The electrochemical studies are performed in different electrolytes (KNO , KCl, KBr and KI) at varied concentrations (≤20 mm). In nano-impact measurements, the AgNP undergoes complete oxidation upon impact at a suitably potentiostated electrode. The frequency of the nanoparticle-electrode collisions observed as current-transient spikes depends on the electrolyte identity, its concentration and the potential applied at the working electrode. The frequencies of the spikes are significantly higher in the presence of halide ions and increase with increasing potentials. From the frequency, the rate of AgNP oxidation as compared with the timescale the AgNP is in electrical contact with the electrode can be inferred, and hence is indicative of the relative kinetics of the oxidation process. Primarily based on these results, we propose the initial formation of the silver (I) nucleus (Ag , AgCl, AgBr or AgI) as the rate-determining process of silver oxidation on the nanoparticle.
It is commonly assumed that the use and application of electrochemical techniques to natural surface waters requires the presence of high electrolyte concentrations prior to measurement, so limiting the applicability of the technique. We report that even for the complex case of oxygen reduction, an analytically useful electrochemical signal is obtainable using a carbon fibre microcylinder electrode. It is shown to be the case even when using voltammetric signals recorded in potable water that has not been pre‐treated or had the addition of any ionic material. The magnitude of the redox wave gives a reliable measure of the oxygen content of these solutions which contain only few millimolar of ions and contains no pH buffer.
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