Joanna Niedziolka

The electrochemical ion-transfer reactivity of porphyrinato metal complexes in 4-(3-phenylpropyl)pyridine | water systems

The transfer of ions between an aqueous and an organic phase is driven electrochemically at a triple phase junction graphite | 4-(3-phenylpropyl)pyridine | aqueous electrolyte. Tetraphenylporphyrinato (TPP) metal complexes (MnTPP+, FeTPP+, CoTPP) and hemin readily dissolve in the organic 4-(3-phenylpropyl)pyridine phase and undergo oxidation/reduction processes which are coupled to liquid | liquid ion transfer. In order to maintain charge neutrality, each one-electron oxidation (reduction) process is coupled to the transfer of one anion (here PF6−, ClO4−, SCN−, NO3−, OCN−, or CN−) from the aqueous (organic) into the organic (aqueous) phase. The range of anions studied allows effects of hydrophobicity and complex formation (association of the anion to the metal center) to be explored. A preliminary kinetic scheme is developed to quantify complex formation, facilitated anion transfer, and competing cation transfer processes. The effects of the organic solvent on the ion transfer processes are explored. Very strong binding and specific effects are observed for the reversible cyanide transfer process.

Hydrophobic silica sol–gel films for biphasic electrodes and porotrodes

Hydrophobic sol-gel films from methyltrimethoxysilane (MTMOS) are deposited onto glass and tin-doped indium oxide (ITO) coated glass substrates. Uniform and microporous films of ca. 200 nm thickness are obtained and investigated by scanning electron microscopy and by electrochemical techniques. From cyclic voltammograms for the oxidation of ferrocenedimethanol in aqueous 0.1 M KNO3 apparent diffusion coefficients and free volume data for processes within the film are derived and it is demonstrated that the film morphology can be controlled by the deposition timing. Two novel types of biphasic electrodes for observing liquid/liquid ion transfer reactions are introduced: (i) an ITO electrode coated with a hydrophobic sol-gel film and (ii) a hydrophobic sol-gel film on glass sputter-coated with 20 nm porous gold (porotrode). For the t-butylferrocene redox system deposited in the form of an organic liquid, very low and morphology dependent current responses are observed on modified ITO electrodes. However, the porotrode system allows biphasic electrode reactions to be driven with high efficiency and with no significant morphology effect of the hydrophobic sol-gel film. This type of nanofilm-modified electrode system will be of interest for biphasic sensor developments.

Solid electrolyte based on silicate matrix functionalised with tetraalkylammonium group solvated by organic solvent

Solid electrolyte composed of hybrid organic–inorganic silicate matrix functionalised with tetraalkylammonium group, solvated by viscous organic polar solvent (propylene carbonate (PC) or sulpholane (TMS)), was prepared by the sol–gel method under controlled drying conditions. Tetramethoxysilane (TMOS), N-trimethoxysilylpropyl-N,N,N-tributylammonium chloride (TMOSPTBACl) and organic solvent were principal sol components. Gel formed within 2 h and 2 days depending on substrate ratio and the solvent additive. The obtained material was transparent and it loosed about 15% of its mass during first 30 days of ageing. It was characterised by thermogravimetry (TGA), differential scanning calorimetry (DSC), NMR, FT-IR spectroscopy, small angle X-ray scattering (SAXS), and impedance spectroscopy. The transport of redox active molecules was studied by electrochemical methods. The porosity of samples dried in supercritical CO2 was also estimated. The shape of TGA and DSC curve appeared to be similar to that of pure solvent. The IR spectra indicated the silicate network formation with some silanol groups left. The NMR spectrum of the solution used to wash crushed sample indicated that all organic substrate is embedded in silicate matrix. The magnitude of electrical conductivity was close to 10 −4 to 10 −5 Sc m −1 , i.e. least more than one order of magnitude larger than that of TMOS based silicate matrix modified with a pure solvent. This conductivity is high enough for electrochemical experiments. Both conductivity and diffusion coefficient of redox probe-ferrocene (Fc) depended on time elapsed after gelation. Their most substantial decrease was observed during first 10 days after gelation and it correlated with mass loss.