Investigation of counterion effects of transition metal cations (Fe³⁺, Cu²⁺, Zn²⁺) on cetrimonium bromide using cyclic voltammetry

Surfactants manifest two important physical characteristics i.e., adsorption on interfaces and formation of self-assembled structures such as micelles. Due to their distinct chemical structures and differentiating affinities of the functional groups within the molecule, they may exhibit distinct electrochemistry. Herein, we report the electrochemical profiles of cetyltrimethylammonium bromide (CTAB) surfactant and its various forms with modified counterions (Fe³⁺, Cu²⁺, Zn²⁺), i.e., trichlorobromo cetyltrimethylammonium ferrate (CTAF), dichlorobromo cetyltrimethylammonium cupperate (CTAC) and dichlorobromo cetyltrimethylammonium zincate (CTAZ). Initially, conductivity (κ) measurements were undertaken in order to determine the critical micelle concentrations (CMC) of CTAB, CTAF, CTAC and CTAZ. Furthermore, CATB and its modified forms were investigated at the surface of glassy carbon electrode (GCE) using cyclic voltammetry (CV). CV responses of pre-micellar and post-micellar solutions of surfactants were investigated to understand redox behavior of CTAB and its modified forms under micellar effect at molecular level. The effect of potential sweep and concentration of surfactants were studied to evaluate the kinetic parameters namely surface adsorbed concentration (Г) and diffusion coefficient (D). The nature of redox processes occurring during cyclic voltammetry experiments were determined via Randles Sevcik and Reinmuth equations. The studies revealed that surfactants with modified counterions exhibited irreversible redox behavior in presence of modified counterions and shown their own redox signature.