Synergistic Effect of Hydrogenation and Thiocyanate Treatments on Ag-Loaded TiO2 Nanoparticles for Solar-to-Hydrogen Conversion

Abstract

H-2 evolution rate enhanced by Ag-loading on 25 nm TiO2 anatase nanopatticles (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 A To(STH) conversion using a. simulating light source, Ag/TiO2 shows an enhanced visible absorption with 4-5 tiine increase in H-2 evolutioh 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 Ag/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 02 mM gave [H-2] 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 H-2, HCOOH, and CH3OH as hydrogenation sources at 300 degrees C and the efficacies of CH3OH, C2H5OH, and sucrose as sacrificial agent to facilitate the separation of the electron from the hole.