Fabrication of TiO₂ on porous g-C₃N₄ by ALD for improved solar-driven hydrogen evolution

Porous graphitic carbon nitride (P-g-C₃N₄) thin sheets were fabricated by a one-step calcination of a mixture of urea, melamine, and ammonia chloride at 550 °C. P-g-C₃N₄ showed 48% higher photocatalytic H₂ production from methanol aqueous solution than conventional urea-derived graphitic carbon nitride (g-C₃N₄) because the existence of numerous pores reduces the recombination rate of charge carriers. In order to further enhance the photocatalytic activity, TiO₂ was uniformly deposited on P-g-C₃N₄ by 60-300 cycles of atomic layer deposition (ALD) to form the TiO₂@P-g-C₃N₄ composite. They exhibited much higher photocatalytic hydrogen production rates than both TiO₂ and P-g-C₃N₄. Among all composites, the sample deposited with 180 ALD cycles of TiO₂ showed the highest H₂ production because of optimal diffusion length for electrons and holes. It also performed better than the sample of g-C₃N₄ deposited with 180 cycles of TiO₂.