The adsorptive behavior of quaternary ammonium Gemini surfactants at bare gold electrode

Abstract

The adsorptive behavior of three cationic Gemini surfactants (C 16H33(CH3)2N-C4H 8-N(CH3)2C16H33 (C 16-C4-C16), C12H 25(CH3)2N-C4H8N(CH 3)2C12H25 (C12-C 4-C12), C8H17(CH3) 2N-C4H8-N(CH3)2C 8H17 (C8-C4-C8)) at bare gold electrode has been studied with cyclic voltammetry, alternating current impedance spectra(ACIS), and quartz crystal microbalance (QCM). It is found that the electrochemical probe catechol (CC) can exhibit two pairs of redox peaks in the range of 0-0.8 V (vs SCE) in 0.3 mol·L-1 KNO3 solutions. When some cationic Gemini surfactants are introduced into the solutions, the first pair of peaks decreases, but the second pair of peaks increases. At the same time, the anodic peaks move in positive direction and the cathodic peaks shift in negative direction. For the three Gemini surfactants, their influence on the voltammetric behavior of CC follows such order as C 8-C4-C8 < C12-C 4-C12 < C16-C4-C16. ACIS shows that in the presence of Gemini surfactants, the impedance of the electrode interface grows. For those surfactants, the impedance rises with increasing alkyl-chain length. Similar result is obtained in QCM experiment. Namely, when the alkyl-chain is longer, the Gemini surfactant makes the frequency change more. The adsorption modes of those Gemini surfactants are estimated according to the change of the first anodic peak area of CC. It is found that their adsorption belongs to Langmuir adsorption. © Editorial office of Acta Physico-Chimica Sinica.