New highly efficient 2D/1D HAp/g‒C3N4 photocatalyst thin film insight into crystal orientation and C‒vacancy effects.

The novel synthetic Sol‒EPD process of a thin film including of well decorated g‒C3N4 nanotubes on plate‒like hydroxyapatite (HAp) were applied. Using Sol‒EPD designable method anisotropic growth of HAp nanocrystals on the substrate were achieved. It has provided the orientation of the different crystal facets resulted in the photogenerated O‒vacancy from phosphate groups. Based on the studied XRD pattern, EPD deposited film of HAp was oriented along c‒plane that can improve the photocatalytic activity of the designed composited film. Systematic designing was applied for decoration of g‒C3N4 nanotubes on the HAp under thermal condensation of melamine coincide with calcination of HAp. This new designed HAp/g‒C3N4 nanofilm was shown high photocatalytic efficiency and completely degradation of persistent pollutant of 4‒nitrophenol in the aqueous solution. According to the electrochemical impedance spectroscopy and current density studies, the higher charge separation/low charge recombination results were obtained for composited g‒C3N4/HAp nano‒film comparing with the single films of HAp and urchin like g‒C3N4. This high separation of charge pairs should be also assigned to the special designed morphology. In addition, wrapped like structure of g‒C3N4 nanotubes with C‒vacancy around HAp nanoplates play key role in separation of photo‒induced charge pairs, light diffusion, and high light harvesting within hollow nanotube. It can be highlighted that the composite degraded more than 95% of 4‒nitrophenol during 90 min that after 5 runs the photocatalytic activity was not significantly changed.