Ultrasmall graphitic carbon nitride quantum dots decorated self-organized TiO₂ nanotube arrays with highly efficient photoelectrochemical activity

In the present study, a novel graphitic carbon nitride quantum dots (CNQDs) modified TiO₂ nanotube 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 TiO₂ by 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/TiO₂ NTAs showed nearly 3.5-fold photocurrent of that from TiO₂ NTAs 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/TiO₂ NTAs demonstrated superior photoelectrocatalytic activity and stability in the degradation of RhB, with kinetic constants 3.0 times of that from TiO₂ NTAs. The hydroxyl and superoxide radicals were proved to be the dominant active radicals during pollutants degradation. Additionally, the prepared CNQD/TiO₂ sample was used as photoanodes for direct photoelectrochemical water splitting to produce H₂ and O₂ under simulated solar light illumination, achieving a H₂ production rate with 22.0μmolh^-1cm^-2 at 0.3V vs Ag/AgCl.