Enhanced hydrogen evolution from water splitting using Fe-Ni codoped and Ag deposited anatase TiO₂ synthesized by solvothermal method

Graphical abstract: - Highlights: • Fe-Ni/Ag/TiO₂ nanocomposites displayed a higher hydrogen evolution rate. • TiO₂ showed well optical property of light absorption by Fe, Ni and Ag modified. • More surface vacancies on TiO₂ generated by the low cost metal introduced. • The separation rate of photoinduced electro-hole pairs was considerable improved. - Abstract: In this paper, the Fe-Ni co-doped and Ag deposited anatase TiO₂ (Fe-Ni/Ag/TiO₂) nanocomposites were successfully prepared by a simple one-pot solvothermal approach. The investigations indicated that all as-prepared TiO₂ samples were single anatase phase, and the impurity level was generated due to the Fe³⁺ or Ni²⁺ being located in the intrinsic band gap of TiO₂, while the Ag⁺ ions could be transformed into metallic silver due to the reduction reaction and then loaded onto the surface of TiO₂. Compared with pure TiO₂, Fe-Ni/Ag/TiO₂ composites with the sizes of Ag nanoparticles from 1.0 to 3.0 nm displayed the well optical property including higher visible light absorption activity and lower electron-hole pair recombination rate, and its absorption wavelength edge moved remarkably with a red shift to 700 nm. The photocatalytic water splitting was performed to produce H₂ over the samples, and the experimental results indicate that Fe-Ni/Ag/TiO₂ composites presented the highest H₂ evolution rate, it can reach up to 793.86 μmol h⁻¹ g_cat⁻¹ (λ > 400 nm for 6 h, energy efficiency is 0.25%), which was much higher than that of pure TiO₂ for 9.57 μmol h⁻¹ g_cat⁻¹. In addition, a tentative photocatalytic mechanism is proposed to understand the enhancement mechanism over Fe-Ni codoped and Ag deposited anatase TiO₂