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

Abstract

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 H₂ evolution photocatalyst, the largest rate of 296.4 μmol g⁻¹ h⁻¹ was obtained under visible light irradiation (λ ≥ 420 nm) without any noble metal co-catalyst, which is 25.8 times larger than that of pure g-C₃N₄ (11.5 μmol 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/g-C₃N₄, 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.