Oxygen vacancies mediated in-situ growth of noble-metal (Ag, Au, Pt) nanoparticles on 3D TiO2 hierarchical spheres for efficient photocatalytic hydrogen evolution from water splitting

Abstract

Defect engineering is effective to extend the light absorption range of TiO2. However, the oxygen vacancy defects in TiO2 may serve as recombination centers, hampering the separation and transfer of photo-generated charges. Here, we present a strategy of in-situ depositing noble-metal (M = Ag, Au or Pt) nanoparticles (NPs) on defective 3D TiO2 hierarchical spheres (THS) with large surface area through the redox reaction between metal ions in solution and the electrons trapped at oxygen vacancies in THS. The oxygen vacancies at the THS surface are consumed, resulting in direct contact between TiO2 and noble-metal NPs, while the other oxygen vacancies in the bulk are retained to promote visible light absorption. The noble-metal NPs with well-controlled size and distribution throughout the porous hierarchical structure not only facilitate the generation of electron-hole pairs in THS due to the effect of surface plasmon-induced resonance energy transfer (SPRET) from noble-metal NPs to TiO2, but also expediate the electron transfer from TiO2 to noble-metal NPs due to the Schottky junction at the TiO2/M interface. Therefore, THS-M shows improved photocatalytic performance in water splitting compared to THS. The optimum performance is achieved on THS-Pt (13.16 mmol h−1g−1) under full-spectrum (UV–Vis) irradiation but on THS-Au (1.49 mmol h−1g−1) under visible-light irradiation. The underlying mechanisms are proposed from the surface plasmon resonance of noble-metal NPs as well as the Schottky junction at the TiO2/M interface.