A novel cation-binding TiO2 nanotube substrate for electro- and bioelectro-catalysis

Bavykin, D.V., Milsom, E.V., Marken, F., Kim, D.H., Marsh, D.H., Riley, D.J., Walsh, F.C., El-Abiary, K.H. and Lapkin, A.A. , Walsh, FC (ed.) (2005) A novel cation-binding TiO2 nanotube substrate for electro- and bioelectro-catalysis. Electrochemistry Communications, 7 (10), 1050-1058. (doi:10.1016/j.elecom.2005.07.010).

Abstract

TiO2 nanotubes (8–20 nm outer diameter and 3–5 nm inner diameter) grown via alkaline hydrothermal synthesis are characterised and compared to 6 nm diameter TiO2 (anatase) nanoparticles. Zeta potential, voltammetric, and titration experiments reveal that, in contrast to anatase nanoparticles (p.z.c. ca. 6), TiO2 nanotubes carry a stronger negative surface charge (p.z.c. ca. 3, acidic protons ca. 2 × 10?3 mol g?1, electrostatic cation adsorption sites in neutral solution ca. 7 × 10?5 mol g?1) and, under neutral conditions, offer electrostatic binding sites for cations.
When immobilised onto an inert boron-doped diamond substrate, TiO2 nanotubes show electrochemical reactivity due to reversible Ti(IV) reduction, which is very similar to that observed for anatase nanoparticles. Three cationic redox systems, Meldola’s blue, Ni2+, and cytochrome c, are immobilised on the TiO2 nanotube surface; the binding ability and the number of binding sites are quantified voltammetrically. Redox proteins, such as cytochrome c, adsorb readily and irreversibly. Well-defined voltammetric signals for the immobilised protein are observed in an aqueous buffer. TiO2 nanotubes are shown to be novel, inert substrates for both inorganic and biological electrocatalysts.

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