Cyclic voltammetric study of mixed monolayers of methylene blue and Triton X-100 formed spontaneously on mercury

Abstract

We studied the spontaneous formation of mixed monolayers of methylene blue (MB +) and Triton X-100 (TX) from aqueous solutions containing both substances and a fixed concentration of MB + of c MB = 2.5 × 10 −6 M. The voltammetric peak obtained under these conditions was typical of redox sites immobilized at the electrode and was ascribed to the reduction of MB + molecules dissolved in the aliphatic subphase of the surface film formed by the TX molecules. This phenomenon arises from the hydrophobic character of MB + molecules and gives rise to strong interactions between such molecules and the hydrophobic moiety of TX molecules. The voltammetric peak of MB + in the surface film is of a quasi-reversible nature. The transfer coefficients of the reduction and oxidation processes were found to be aα f n ⋍ 1 and α b n ⋍ 1.5, with n = 2. A plausible mechanism to account for the relationship α f n + α b n ≠ 2 is put forward.