Plasmonic photocatalyst of Au nanoparticle-decorated hollow mesoporous TiO2 with 0, 0.1, 0.25, 0.5, and 1% Au content was successfully synthesized by a hydrothermal method. Controlling the particle size of Au coated on TiO2 hollow microspheres (AuTHMSs) is expected to improve the photocatalytic ability. Our results of X-ray absorption spectroscopy (XAS) indicated that the coated Au ions are nulvalent and cause a lattice distortion as well as a variation in Ti 3d orbital orientation. It is also inferred that TiO6 octahedral symmetry is significantly affected by the Au incorporation, giving rise to an increase in the Ti 3d t2g unoccupied state. UV–visible absorption spectra and I–V measurements were performed to examine localized surface plasmon resonance (LSPR) effect and photoelectrocatalytic (PEC) ability. We present the first in situ XAS measurements on AuTHMS system, which enabled us to correlate the electronic structure and photocatalytic property of the material. An analysis of the results showed an LSPR effect triggered by the Au nanoparticles that provided a conductive path to the excited charge carriers, resulting in an enhanced photocurrent due to the charge transfer from Au 5d to Ti 3d orbitals under solar illumination. The photocurrent density of AuTHMSs showed an increase with Au content with a maximum for 0.5% Au, whereas in the case of 1% Au the photocurrent profile was similar to the 0% Au. Furthermore, a comparison of the XAS and PEC performance implied that the lattice distortion and the corresponding symmetry changes together with the size of Au particle substantially influenced the rate of hot electron charge transfer, resulting in the variation of PEC activity of AuTHMS samples with a higher activity for 0.5% Au. Our studies are expected to fabricate chemically stable innovative structures with enhanced surface area that would boost the photocatalytic efficiency, which is a vital factor for environmental and energy applications.
The Journal of Physical Chemistry 122(12), p.6955-6962