Direct evidence and enhancement of surface plasmon resonance effect on Ag-loaded TiO2 nanotube arrays for photocatalytic CO2 reduction

Surface plasmon resonance (SPR) effect has been utilized in many solar conversion applications because of its ability to convert visible photons into "hot electron" energy. However, the direct evidence and enhancement of this unique effect are still great challenges, limiting its practical applications. Here we present the direct evidence and enhancement of SPR effect using TiO2 nanotube arrays (TNTAs) loaded with Ag nanoparticles (NPs) as a proof-of-concept example. Particularly, electrochemical deposition method is applied to deposit Ag NPs into the inner space of TNTAs for enhancing SPR effect of Ag NPs, as demonstrated by Raman and light absorption spectroscopies. This enhanced SPR effect is because multiscattered light within TNTAs can be effectively utilized by Ag NPs in the inner space of TNTAs. Moreover, combining synchronous-illumination X-ray photoelectron and electrochemical impedance spectroscopy characterization, we confirm that the SPR effect of Ag NPs can enhance photocatalytic performance of TNTAs mainly from two aspects: (i) injection of " hot electrons" from Ag NPs to TNTAs and (ii) acceleration of charge carrier migration on the TNTAs through a unique near field effect. The direct evidence and enhancement of SPR effect open new perspectives in design of functional plasmonic nanomaterials with high solar conversion efficiency. (C) 2017 Elsevier B.V. All rights reserved.