Fermi-level shift, electron separation, and plasmon resonance change in Ag nanoparticle-decorated TiO₂ under UV light illumination

Abstract

A method was developed to use in situ photoconductance to determine the Fermi-level and electron distribution in Ag/TiO2, and the photoinduced plasmon shift was studied by the in situ photoinduced absorption and XPS.

Kinetic pathways of sub-bandgap induced electron transfer in Ag/TiO2 and the effect on isopropanol dehydrogenation under gaseous conditions

“…However, the photoconductance relaxations are almost apparently independent of temperatures for Ag/TiO 2 , featuring a non-thermal activation; this agrees with that obtained under the super-bandgap light illumination. 18 Similar results were also seen for the photoconductance relaxations measured under 532 nm laser illumination (Fig. 9(c) and (d)) for the two samples.…”

“…Independent of the laser wavelengths, it is seen that the photoconductances of the bare TiO 2 are much higher, so the electron accumulation in the TiO 2 was greatly decreased after the Ag decoration because of the significant increase in the electron relaxation (see Section 3.5); this agrees well with the case of super-bandgap (UV) light illuminations. 18,19 In the case of the bare TiO 2 , the 450 nm laser-induced photoconductances are much higher than that caused by the 532 nm laser illumination; 17 this is also the same for the Ag/TiO 2 , which might relate to the exponentially distributed gap states. Differently from the undecorated sample, the photoconductances of the Ag/TiO 2 are related to the electron generation through both the pathways and the electron consumption on the TiO 2 surfaces and via the Ag nanoparticles.…”

“…The Ag-decorated TiO 2 (Ag/TiO 2 ) was prepared using the photodeposition method as per our previous study. 18 92.7 mL of 0.1 M AgNO 3 aqueous solution was added to 50 mL of aqueous solution containing 20% (v/v) methanol, and then 0.2 g of pre-milled P25 TiO 2 powder was added. The mixed solution was continuously stirred for 40 min in the dark and was then irradiated with a 500 W Xe lamp for 2 h under a constant flow of pure N 2 .…”

“…Because no electrons can accumulate in TiO 2 , the above results also indicate that the Ag nanoparticles increase the relaxation of the electrons generated in TiO 2 ; this also agrees with that observed under super-bandgap light illumination. 18 To show whether the plasmon-assisted Ag oxidation is related to the electron transfer from the Ag nanoparticles to TiO 2 , the effect of different wavelength laser illuminations on the absorption spectra of Ag/a-Al 2 O 3 were also measured in the methanol-containing air atmosphere, as shown in Fig. 8.…”

“…We had previously revealed that bare undecorated TiO 2 exhibited wavelength-dependent conductance, absorption, and isopropanol dehydrogenation under sub-bandgap (visible) light illumination; 17 we have shown that Ag decoration increased the transfer of photogenerated electrons in TiO 2 to O 2 under super-bandgap (UV) light illumination. 18,19 However, the increase in electron transfer to O 2 mainly contributed to recombination assisted with O 2 photoinduced adsorption-desorption cycling. Therefore, it is thus possible that Ag decoration might also have the same effect under sub-bandgap light illumination.…”