Molten Ag₂ SO₄ -based Ion-Exchange Preparation of Ag_0.5 La_0.5 TiO₃ for Photocatalytic O₂ Evolution

Ag_0.5 La_0.5 TiO₃ with an ABO₃ perovskite structure was synthesized by a newly developed ion-exchange method. Molten Ag₂ SO₄ instead of traditional molten AgNO₃ was used as Ag⁺ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag⁺ for Na⁺ in Na_0.5 La_0.5 TiO₃ with a stable ABO₃ perovskite structure at a high ion-exchange temperature (700 °C). Under full-arc irradiation, the O₂ -evolution activity of Ag_0.5 La_0.5 TiO₃ was about 1.6 times that of Na_0.5 La_0.5 TiO₃ due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag⁺ for Na⁺ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light-response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag⁺ for Na⁺ induced a lattice distortion of the ABO₃ perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible-light irradiation, Ag_0.5 La_0.5 TiO₃ displayed notable O₂ evolution whereas Na_0.5 La_0.5 TiO₃ showed little O₂ evolution, thus demonstrating that the substitution of Ag⁺ for Na⁺ enabled the use of visible light to evolve O₂ photocatalytically. This work presents an effective route to explore novel Ag-based photocatalysts.