Photo-Current Enhancement in Carbon Quantum Dots Functionalized Titania Nanotube Arrays

Highly aligned, vertically oriented, TiO2 nanotube arrays fabricated by electrochemical anodization were functionalised by carbon quantum dots (CQD) synthesized by an electrochemical reduction technique. Here, we report the photo-electrochemical properties of such TiO2 nanotubes array-CQD composite material and it has been found that the properties are significantly enhanced compared to that in pristine (bare) nanotubes. The TiO2 nanotubes were characterized by X-ray diffraction and scanning electron microscopy, whereas the CQD samples were characterized by transmission electron microscopy, optical absorption spectroscopy. CQDs synthesized under two different conditions showed a distinct size difference and corresponding absorption spectra revealed concominant shift in the absorption edges. Furthermore, the photo-electrochemical measurements were carried out with the help of photo-current, incident photon to current conversion efficiency (IPCE), Mott-Schottky plots and the impedance analysis. The photo-current data revealed 30% improvement in TiO2-CQD samples compared to bare TiO2 nanotubes samples. A higher photo-conversion efficiency was observed along with the shifting of the peak value towards visible wavelengths. The Mott-Schottky plots revealed shift in the flat-band potential in the CQD-TiO2 samples and corresponding lowering of the charge transfer resistance was observed through the impedance spectroscopy.