Novel phosphorus doped carbon nitride modified TiO₂ nanotube arrays with improved photoelectrochemical performance

Novel phosphorus-doped graphitic-carbon nitride (P-C₃N₄) modified vertically aligned TiO₂ nanotube arrays (NTs) were designed and synthesized. They can significantly enhance the conduction and utilization of photogenerated charge carriers of TiO₂ NTs. The heterostructure was successfully fabricated through a three-step process: electrochemical anodization and wet-dipping followed by thermal polymerization. The prepared P-C₃N₄/TiO₂ NTs exhibit enhanced light-absorption characteristics and improved charge separation and transfer ability, thus resulting in a 3-fold photocurrent (1.98 mA cm^-2 at 0 V vs. Ag/AgCl) compared with that of pure TiO₂ NTs (0.66 mA cm^-2 at 0 V vs. Ag/AgCl) in 1 M NaOH solution. The prepared P-C₃N₄/TiO₂ NT photoelectrodes also present excellent photocatalytic and photoelectrocatalytic capabilities in the degradation of methylene blue (MB). The kinetic rate of P-C₃N₄/TiO₂ NTs in the photoelectrocatalytic process for MB is 2.7 times that of pristine TiO₂ NTs. Furthermore, the prepared sample was used as a photoanode for solar-driven water splitting, giving a H₂ evolution rate of 36.6 μmol h^-1 cm^-2 at 1.0 V vs. RHE under simulated solar light illumination. This novel structure with a rational design for a visible light response shows potential for metal free materials in photoelectrochemical applications.