Ultrasmall graphitic carbon nitride quantum dots decorated self-organized TiO₂nanotube arrays with highly efficient photoelectrochemical activity

In the present study, a novel graphitic carbon nitride quantum dots (CNQDs) modified TiO2nanotube arrays (NTAs) photoelectrode was successfully synthesized by a simple two-step method which includes an electrochemical anodization technique followed by a facile organic molecular linkage. The successful modification of TiO2by CNQDs was found to improve the photoelectrochemical activity significantly because of enhanced light absorption and improved separation of photo-generated electron-hole pairs. The optimized CNQDs/TiO2NTAs showed nearly 3.5-fold photocurrent of that from TiO2NTAs alone at 0.3V vs Ag/AgCl and the maximum photoconversion efficiency reaches up to 0.63% in neutral solution under simulated solar light irradiation. Furthermore, the prepared CNQD/TiO2NTAs demonstrated superior photoelectrocatalytic activity and stability in the degradation of RhB, with kinetic constants 3.0 times of that from TiO2NTAs. The hydroxyl and superoxide radicals were proved to be the dominant active radicals during pollutants degradation. Additionally, the prepared CNQD/TiO2sample was used as photoanodes for direct photoelectrochemical water splitting to produce H2and O2under simulated solar light illumination, achieving a H2production rate with 22.0μmolh-1cm-2at 0.3V vs Ag/AgCl.