Charge Separation in layered Titanate Nanostructures: Effect of Ion Exchange induced Morphology Transformation*

Morphology changes induced by surface chemistry can provide important insights into photoexcitation processes on solids which are critical to photovoltaic and photocatalytic applications.$^{ }$We investigated charge separation processes on Na$_{2}$Ti$_{3}$O$_{7}$ nanowires and scrolled up H$_{2}$Ti$_{3}$O$_{7}$ nanotubes, two types of morphologies which by means of acid/base treatment can reversibly be transformed into each other. Some of the competitive processes photoexcited states undergo can be tracked by means of electron paramagnetic resonance and photoluminescence spectroscopy. A complementarity between efficient charge separation and radiative recombination of photoexcited states [1] was observed and clearly demonstrates the critical influence of morphology and interlayer composition on the photoelectronic properties of layered oxide nanostructures [2]. [1] Riss et al. Nano Lett. \textbf{2007, }7, 433-438. [2] Riss et al. Angew. Chem. Int Ed. \textbf{2007, a}nie.200703817, in press