Preparation of hybrid films of an anionic Ru(II) cyanide polypyridyl complex with layered double hydroxides by the Langmuir–Blodgett method and their use as electrode modifiers

Abstract

Thin hybrid films of an amphiphilic anionic Ru(II) complex (K 2[Ru(CN) 4L]: L=4,4′-di- n-dodecylaminoyl-2,2′-bipyridyl) with Mg–Al–Cl or Ni–Al–Cl layered double hydroxides (LDHs) were prepared by the Langmuir–Blodgett (LB) method. A chloroform solution of K 2[Ru(CN) 4L] was spread onto an aqueous dispersion of the LDH. Hybridization proceeded through the adsorption of the positively charged LDH particles by the floating film of [Ru(CN) 4L] 2− at the air–water interface. The hybridized films were deposited onto mica by the vertical dipping method. Atomic force microscope (AFM) observation of the film surface confirmed that 15–50 nm thick LDH particles were combined with the string-like aggregates of the Ru(II) complex. Cyclic voltammograms of indium tin oxide (ITO) electrodes modified with the single layer of the hybrid films were recorded. No peak was observed in the potential range of 0–1200 mV (vs. SCE) for electrodes modified with [Ru(CN) 4L] 2−/Mg–Al–Cl LDH films. For electrodes modified with [Ru(CN) 4L] 2−/Ni–Al–Cl LDH films, oxidation–reduction peaks due to Ni(II)/Ni(III) couple in the LDH were observed, along with a peak attributed to the reduction of chemically oxidized [Ru(CN) 4L] −. This implies that the electrochemically produced Ni(III) sites in the LDH layers acted as mediator in oxidizing [Ru(CN) 4L] 2−. In this way, a cascade of electron flow from [Ru(CN) 4L] 2− to the electrode by way of Ni–Al–Cl LDH has been established.