The Enhancement of Hydrogenation and Thiocyanate Treatments on Ag-Loaded TiO₂ Nanoparticles for Hydrogen Evolution
Yan-Gu Lin1, Liang-Ching Hsu1*, Ming-Chang Lin2
1Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan
* Presenter:Liang-Ching Hsu,
H₂ evolution rate enhanced by Ag-loading on 25 nm TiO₂ anatase nanoparticles (denoted as Ag/TiO₂), Ag-loaded on hydrogenated TiO₂ NPs (Ag/H:TiO₂), as well as by the treatment of both NPs with potassium thiocyanate (KSCN) solution have been systematically investigated in conjunction with quantum-chemical calculations and XANES and EXAFS analyses with synchrotron radiation. We have observed a cumulative enhancement effect of these fabrication processes on solar to hydrogen (STH) conversion using a simulating light source. Ag/TiO₂ shows an enhanced visible absorption with 4–5 time increase in H₂ evolution over that of TiO₂ or H:TiO₂ prepared under mild hydrogenation conditions, while Ag/H:TiO₂ exhibits an even greater UV–visible absorption, similar to that of AgSCN/H:TiO₂, with 3.1 times higher STH than that of Ag/TiO₂. The treatment of Ag/TiO₂ and Ag/H:TiO₂ NPs with 0.1 mM KSCN solution further increases their STHs by 3.6 and 2.8 times, respectively. Optimization of KSCN concentration up to 0.2 mM gave [H₂] production rate rise to 2.75 mmol h–1 g–1 under Xe lamp illumination for the AgSCN/H:TiO₂ system, which has also been tested for its durability, showing a notable robustness. The observed synergistic effect of TiO₂ hydrogenation and SCN treatment of the Ag/H:TiO₂ NPs has been corroborated by the results of quantum chemical elucidation of H₂ production mechanism and the photocatalytic effects of Ag/H:TiO₂ and AgSCN/H:TiO₂ NPs revealed by appearances of new sub-band states within the TiO₂ bandgap, as well as by the result of XANES and EXAFS analyses which support the electron-pulling effect of the SCN group attached to Ag. Finally, we have also compared the efficacies of H₂, HCOOH, and CH₃OH as hydrogenation sources at 300 °C and the efficacies of CH₃OH, C₂H₅OH, and sucrose as sacrificial agent to facilitate the separation of the electron from the hole.

Keywords: TiO2, Potassium thiocyanate, Hydrogenation, H2 evolution