Besides their adjustable optical, electronic and photoelectrochemical properties, which are of interest in view of applications in biosensors and other nanodevices, gold nanoparticles have been attracting much attention because they can enhance the photocatalytical properties of TiO₂ due to a more efficient charge separation of the generated electron-hole pairs and an increase of their lifetime.
Transparent mesoporous TiO₂ films (MT) prepared by the EISA (evaporation-induced self-assembly) process offer very high porosities and thus potentially a higher number of catalytic centers [1]. Pure mesoporous TiO₂ films, however, show a low photocatalytic conversion of NO of only 3 % caused by a poor crystallinity of the TiO₂ framework and a film thickness of only about 200 nm currently reachable with the preparation method, which is significant lower than that for powder catalysts.
In this study we have prepared gold nanowires inside the mesoporous TiO₂ films by pulsed cathodic electrodeposition from HAuCl4 solution (Figure 1 A). The length and density of the nanowires could be controlled by the number and potential of the applied pulses. Individual gold nanoparticles were prepared by self-assembled anchoring on thiol groups and reduction with NaBH4 (Figure 1 B).
The gold nanoparticles (AuNP-MT) and nanowires (AuNW-MT) within the film increase considerably the NO oxidation to 16 % and 30 %, respectively (Figure 1 C). Because the growth of the nanowires appears from the conductive ITO layer this avoids blocking effects and ensures good accessibility of the pore system.

[1] M. Wark et al., Micropor. Mesopor. Mater. 84 (2005) 247.