g-C₃N₄ quantum dots decorated on urchin-like TiO₂ nanostructures for the photoelectrochemical water splitting

This work employs a straightforward, simple and low-cost method to grow g-C₃N₄ quantum dots (QDs) on a distinctive morphology of urchin-like TiO₂ (u-TiO₂) nanostructures. u-TiO₂ on Ti foil was prepared by the hydrothermal method under the optimized experimental parameters, including hydrothermal time and temperature. Then, for the activation of u-TiO₂ under visible light irradiation, g-C₃N₄ quantum dots (g-C₃N₄ QDs) were decorated on u-TiO₂ by combining a wet pre-coating and subsequent thermal evaporation procedure. The experimental parameters of the process were examined to determine the optimized conditions for the highest photocurrent density (J_ph) in a photoelectrochemical (PEC) cell. g-C₃N₄ QDs were elucidated by transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). HRTEM results revealed a uniform distribution of anchored g-C₃N₄ QDs on the surface of u-TiO₂ with a mean size of about 10 nm. Optimized decoration of g-C₃N₄ QDs on the u-TiO₂ dramatically enhanced J_ph under simulated sunlight irradiation from 0.06 mA/cm² for pristine u-TiO₂ up to 0.12 mA/cm² for TiO₂/g-C₃N₄QDs photoanodes under the biased potential of 0.5 V versus Ag/AgCl. Based on the results, the type-II heterostructure of u-TiO₂/g-C₃N₄ facilitates electron–hole separation and charge carrier transfer, thereby improving the PEC performance of the proposed photoanode.