Ion Adsorption on Modified Electrodes as Determined by Direct Force Measurements under Potentiostatic Control
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- 作者：Volodymyr Kuznetsov ; Georg Papastavrou
- 刊名：Journal of Physical Chemistry C
- 出版年：2014
- 出版时间：February 6, 2014
- 年：2014
- 卷：118
- 期：5
- 页码：2673-2685
- 全文大小：542K
- ISSN：1932-7455
文摘
Ion adsorption is a charging process that is of central importance for many hydrophobic surfaces, such as gas bubbles, oil drops, and cell membranes. This process has been studied by various techniques and different adsorption mechanisms have been proposed so far. However, different analytical methods seem to indicate the adsorptions of different types of ions, particularly hydroxyl or hydronium ions, at hydrophobic surfaces. In this work, we studied ion adsorption on modified electrodes by direct force measurements with the colloidal probe technique. The electrodes were modified with a self-assembled monolayer (SAM), and their potential was controlled externally by means of a potentiostat. Ion adsorption onto OH- or CH3-terminated SAMs was determined as a function of pH and background electrolyte concentration. Charge at the interface was found to result primarily from the adsorption of hydroxyl and hydronium ions, whereas the influence of the background electrolyte (KCl) can be neglected. For the hydronium and hydroxyl ions, we determined the adsorption constants by means of a simple semiquantitative model and found that the adsorption constant of hydroxyl ions is orders of magnitude larger than that of hydronium ions. Furthermore, ion adsorption was found to be much more pronounced for hydrophobic surfaces than for hydrophilic ones.