Effect of LSPR, temperature and electric field on reduction of CO2 in H2O vapor using photocatalytic TiO2-nanowires with Ag nanoparticles extruded from Ag-Nb-N-O film

Abstract

This paper reports on the formation and study of Ag-Nb-N-O/TiO2 nanowires (NWs) for photocatalytic reduction of CO2. Firstly, the Ag-Nb-N-O thin film was grown by simultaneous magnetron sputtering of Ag and Nb targets in an atmosphere of Ar and N2. Subsequently, the Ag-Nb-N-O thin film was coated with TiO2 NWs, which were presynthesized by a hydrothermal method and then annealed at 500 °C. Before photocatalytic tests, the Ag-Nb-N-O/TiO2 NW samples were subjected to heat treatment at 350 °C. A morphology of the fresh and 350 °C-annealed Ag-Nb-N-O/TiO2 NWs was comprehensively studied by SEM, TEM, EDXS, and XRD. Heating was found to facilitate the extrusion of Ag particles from the bulk of the Ag-Nb-N-O film to its surface. In addition, the heat treatment led to partial evaporation of silver and its further redeposition on the surface of TiO2 NWs in the form of Ag nanoparticles. The Ag-Nb-N-O/TiO2 NWs subjected to the 350 °C heating possessed a remarkable photocatalytic activity in the synthesis of methanol from CO2, which was 3 times over that of the pure TiO2 NWs. This is associated with the contribution of localized surface plasmon resonance of Ag particles to generation of the charge carriers. Moreover, we demonstrate that LSPR-induced heating of Ag nanoparticles, confirmed by IR imaging, plays a crucial role in charge carrier separation. The thermoelectromotive force generated by the temperature gradient facilitates electron transfer from TiO2 to Ag, thereby improving CO2 reduction efficiency. Additionally, we revealed that an external electric field enables an improvement of the Ag-Nb-N-O/TiO2 NW photocatalytic activity providing an additional increase in the methanol yield by 60 %.