One-pot photo-synthesis and in-situ generation of hydrogen by silver/strontium titanate photocatalyst under visible or near-UV light and role of midgap states: Experiment and DFT computations

We report one-pot photo-synthesis of nanocrystalline Ag(0)/SrTiO3 photocatalysts in aqueous suspension followed by in-situ testing in the same suspension to generate hydrogen under visible (lambda >400 nm) or near-UV/visible (lambda > 366 nm) light. The Ag(0)/SrTiO3 showed a significant increase of the photocatalytic rate vs. SrTiO3 i) under near-UV/visible light with very small amount of silver promoter at Ago.001/SrTiO3 and ii) under visible light with Ag-0.05/SrTiO3. The Ag(0)/SrTiO3 was characterized by several complementary structural and spectroscopic methods; no bandgap narrowing in the nanocrystalline Ag(0)/SrTiO3 has been observed. Mechanism of photocatalytic hydrogen generation with Ag(0)/SrTiO3 under visible light involves relaxation of excited electron through the set of distinct electronic midgap states and includes preferential quenching of one of the two specific midgap transitions. The DFT computations of SrTiO3 with small cluster model for TiO2- and SrO-terminated surfaces result, for the first time, in optical bandgaps very close to experimental values. Geometry and binding energies were calculated for silver clusters attached to TiO2- and SrO-terminated surfaces. The DFT calculations suggest the mechanism of operation of Ag(0)/SrTiO3 under the UV light. (C) 2017 Elsevier B.V. All rights reserved.