Less is more: Enhancement of photocatalytic activity of g-C3N4 nanosheets by site-selective atomic layer deposition of TiO2

Zero-dimensional/two-dimensional (0D/2D) TiO2/g-C3N4 heterostructural photocatalysts were fabricated via ALD technique. TiO2 nanoparticles were site-selectively grown on g-C3N4 nanosheets and the surface modification induced band engineering of the composite photocatalysts. Thus, the redox properties of the photocatalysts were fine tuned. Under visible light, since only g-C3N4 was excited, TiO2 was acting as the electron transport channel in the optimized interfacial structures. They effectively suppressed the recombination and facilitated the transfer of photogenerated charges, improving the photocatalytic activity. When both the components were excited under UV-vis light, the dynamic equilibrium of the conduction band positions on these n-n type semiconductor heterojunctions led to the increased recombination rate of charges, decreasing the reactivity for H-2 evolution. However, the photocatalytic degradation of organic pollutants by these composite photocatalysts exhibited enhanced activities, resulting from the photogenerated holes on VB of TiO2 which could promote oxidation of organic pollutants with strong oxidation potentials. Furthermore, TiO2/g-C3N4 photocatalysts with limited numbers of deposition cycles exhibited optimal photocatalytic activity under visible light. In contrast, excessive deposition cycles on g-C3N4 for TiO2/g-C3N4 led to continuous film and increased thickness of TiO2, resulting in the attenuation of the reactivity. We verified this TiO2/g-C3N4 photocatalysts with less massloading, but more enhanced photocatalytic activity.