Cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) have been used for studying the binding of protons and cadmium(II) ions by 8-mercaptooctanoic acid monolayer that was assembled on an Au surface. Binding of the cations by the monolayer affected the kinetics of electron transfer to negatively charged species, i.e., IrCl63-, in the solution. Increasing the pH of the solution causes the CV of IrCl63- to become less reversible and the feedback current of the SECM to decrease as the distance between the microelectrode and the surface decreases. On the other hand, addition of Cd 2+ to the solution at pH 6.8 increases the CV reversibility and the feedback current of the SECM as a result of neutralizing the negative charge of the monolayer by the metallic ions. A model based on the Frumkin correction was used to account for these findings and for extracting the heterogeneous association constant of Cd2+ by the monolayer.
Bibliographical noteFunding Information:
This study was supported by the American Israeli Binational Science Foundation (BSF, Grant No. 97/00198) and by the Israel Science Foundation (Grant No. 200/02).
- Metal ion binding
- Scanning electrochemical microscope
- Self assembled monolayers