In situ nitrogen-doped hollow-TiO2/g-C3N4 composite photocatalysts with efficient charge separation boosting water reduction under visible light

Visible-light-driven water splitting process is highly attractive for alternative energy utilization, while developing efficient, earth-abundant, and environmentally friendly photocatalysts for hydrogen evolution reaction has remained a major challenge. Herein, heterostructured photocatalysts composed of hollow N-doped TiO2 and g-C3N4 (N-TiO2/g-C3N4) were developed by an in situ impregnation calcination method. N-TiO2 and N-TiO2/g-C3N4 heterostructures with different ratios of N-TiO2 and g-C3N4 were synthesized by simply varying the amount of cyanamide (CY) as the g-C3N4 precursor. Using N-TiO2/g-C3N4 as a H-2 evolution photocatalyst, the largest rate of 296.4 mmol g(-1) h(-1) was obtained under visible light irradiation (lambda >= 420 nm) without any noble metal co-catalyst, which is 25.8 times larger than that of pure g-C3N4 (11.5 mmol g(-1) h(-1)). Femtosecond time-resolved diffuse reflectance spectroscopy was used to evaluate the lifetime of photogenerated electrons and electron transfer dynamics in N-TiO2/g-C3N4. It is suggested that an additional decay pathway exists for the photogenerated electrons in N-TiO2/gC(3)N(4), in which N-TiO2 acts as an electron trapping site, leading to higher photocatalytic H2 evolution activity than pure g-C3N4. The present work not only provides a facile method for preparing doped materials and heterostructures with efficient photocatalytic activity, but also deepens the understanding of charge transfer dynamics in heterostructured photocatalysts.