New insights into the surface plasmon resonance (SPR) driven photocatalytic H2 production of Au–TiO2

Abstract

The Surface Plasmon Resonance (SPR) driven photocatalytic H₂ production upon visible light illumination (≥500 nm) was investigated on gold-loaded TiO₂ (Au–TiO₂). It has been clearly shown that the Au-SPR can directly lead to photocatalytic H₂ evolution under illumination (≥500 nm). However, there are still some open issues about the underlying mechanism for the SPR-driven photocatalytic H₂ production, especially the explanation of the resonance energy transfer (RET) theory and the direct electron transfer (DET) theory. In this contribution, by means of the EPR and laser flash photolysis spectroscopy, we clearly showed the signals for different species formed by trapped electrons and holes in TiO₂ upon visible light illumination (≥500 nm). However, the energy of the Au-SPR is insufficient to overcome the bandgap of TiO₂. The signals of the trapped electrons and holes originate from two distinct processes, rather than the simple electron–hole pair excitation. Results obtained by Laser Flash Photolysis spectroscopy evidenced that, due to the Au-SPR effect, Au NPs can inject electrons to the conduction band of TiO₂ and the Au-SPR can also initiate e⁻/h⁺ pair generation (interfacial charge transfer process) upon visible light illumination (≥500 nm). Moreover, the Density Functional Theory (DFT) calculation provided direct evidence that, due to the Au-SPR, new impurity energy levels occurred, thus further theoretically elaborating the proposed mechanisms.