Self-assembled films of nickel hexacyanoferrate: Electrochemical properties and application in potassium ion sensing

Pressure-area isotherms of hexametaphosphate (HMP) stabilized nickel hexacyanoferrate (NiHCF) nanocrystals were studied under the surfactants dioctadecyl dimethylammonium bromide (DODA), octadecyl amine (ODA) and tetrahexadecyl ammonium bromide. A transition from liquid-expanded to liquid-condensed phase is observed for NiHCF under DODA and ODA. The higher stability is observed for the monolayer of NiHCF under DODA. Ultrathin films of NiHCF were prepared by multiple adsorption of sodium-HMP stabilized nickel hexacyanoferrate nanocrystals under a monolayer of DODA. Its electrochemical properties were analysed by cyclic voltammetry and AC impedance spectroscopy. The successive transfer of HMP-stabilized NiHCF–DODA layers was demonstrated by increase in the current measured by cyclic voltammetry as well as the decrease in the capacitance measured with increasing number of layers. The voltammetric response and capacitance response of the film with change in the potential and varying potassium ion concentration (from 0.0001 M to 1.5 M) was also demonstrated.