"One-Pot" Synthesis and Photocatalytic Hydrogen Generation with Nanocrystalline Ag(0)/CaTiO3 and in Situ Mechanistic Studies

We describe a previously not reported "one-pot" synthesis of nanocrystalline Ag(0)/CaTiO3 in aqueous suspension and the following in situ photocatalytic testing in the same suspension to generate hydrogen. The Ag(0)/CaTiO3 showed an enhancement of photocatalytic hydrogen generation rate vs CaTiO3 precursor. The obtained Ag(0)/CaTiO3 photocatalyst was ex situ characterized by XPS, XRD, UV-vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy, and concluded to have metallic silver nanoparticles on the surface of calcium titanate nanocrystals. The three photocatalytic mechanisms in Ag(0)/CaTiO3 were considered: (a) bandgap narrowing in CaTiO3, (b) enhanced electron hole separation in CaTiO3, and (c) excitation of surface plasmon resonance (SPR) in metallic Ag nanoparticles. In mechanistic studies, photocatalytic suspensions with CaTiO3 precursor, with silver precursor, and with both CaTiO3 and Ag precursors to form Ag(0)/CaTiO3 were illuminated, flash-frozen to 77 K, and characterized by in situ "conventional" PL spectroscopy and in situ synchronous luminescence spectroscopy. On the basis of the complementary ex situ and in situ studies, an enhanced electron-hole separation in Ag(0)/CaTiO3 is suggested.