Molecule-Assembled Modulation of the Photocurrent Direction of TiO2 Nanotube Electrodes under the Assistance of the Applied Potential and the Excitation Wavelength

In this article, a type of molecule modulated electrode was assembled by conjugating TiO2 nanotubes with protocatechuic acid (PCA) and DNA linked PCA (DNA-PCA). We found that the photoelectrochemical behavior of the resulting PCA- and DNA-PCA-assembled TiO2 nanotube electrodes, especially the photocurrent direction, could be modulated by the assembled molecules under the assistance of an applied potential and excitation wavelength. Unlike bare TiO2 nanotube electrodes, which generate only anodic photocurrents, those assembled with PCA molecules and ssDNA-PCA molecules were found to generate anodic or cathodic photocurrents depending on the applied potential. Moreover, TiO2 nanotube electrodes assembled with dsDNA-PCA molecules generated either anodic or cathodic photocurrent depending on the specific applied potential and the excitation wavelength. The related photoexcited charge transfer processes discussed herein are influenced by the assembled molecules.