engleski

Humic acid adsorption on the Au(111) and Au polycrystalline electrode surface

The aim of the paper was to investigate the adsorption of humic acid (HA) on the Au(111) and Au polycristalline electrode, as well as the adsorption competition between HA and chloride anion. The investigations are relevant to the situation encountered in estuaries, where HA interacts with increasing concentrations of inorganic salts from sea water. The adsorption of HA was investigated using cyclic voltammetry, differential capacitance measurements, chronocoulometry and electrochemical quartz crystal microbalance measurements. The investigations were performed in NaClO4 and NaCl solutions at pH 5 and 2. HA adsorbs on the Au(111) surface practically in the whole double layer potential region (the potential region in which the faradaic current is negligable), from about -0.6 V (SCE) through all measured positive potentials. Gibbs surface excess of HA increases with positive potentials. In the presence of NaCl two contrary effects are encountered: Na+ ions neutralize negative charges on HA and thus enhance its adsorption, while Cl- compete with HA for the adsorption sites on Au(111). Ratio of HA to NaCl concentration, electrode potential, and structural transitions of the Au(111) surface dictate which of the two effects shall predominate.

humic acid (HA); adsorption; Au(111) and Au polycrystalline electrode

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