A nanocomposite of carbon quantum dots and TiO2 nanotube arrays: enhancing photoelectrochemical and photocatalytic properties

A novel nanocomposite of carbon quantum dots (CQDs) and TiO2 nanotubes was fabricated and its enhanced photocatalytic and photoelectrochemical properties were demonstrated. Carbon quantum dots were obtained by electrochemical-etching graphite electrodes and TiO2 nanotubes arrays were prepared by anodization methods. Subsequently, CQDs were assembled on the surface of vertically aligned TiO2 nanotube arrays (CQDs/TiO2 nanotubes) and the as-prepared samples were characterized by field-emission scanning electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, photoelectrochemical and photocatalytic measurements. XPS measurement shows the presence of carbon species which come from CQDs. A red shift of light absorption edge and more absorption in the visible light region were observed for the resulting samples from the UV-vis diffuse reflectance spectra. An enhanced photocurrent and photopotential were demonstrated for the CQDs sensitized TiO2 nanotubes under visible light irradiation and the photocurrent density was 2.7 times larger than that of pristine TiO2 nanotubes. A solar cell was fabricated for further verifying the sensitization of CQDs over TiO2 nanotubes. Moreover, the photocatalytic activity of CQDs/TiO2 nanotubes towards the degradation of methylene blue was demonstrated and about 14% enhanced degradation efficiency was obtained with the presence of CQDs. This work developed a simple method to fabricate CQDs and demonstrated the introduction of CQDs to be a new approach for improving the utilization of visible light for TiO2 nanotube arrays.