A Plasmonic Photocatalyst Consisting of Silver Nanoparticles Embedded in Titanium Dioxide. Ryan Huschka LANP Seminar February 19, 2008

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1 A Plasmonic Photocatalyst Consisting of Silver Nanoparticles Embedded in Titanium Dioxide Ryan Huschka LANP Seminar February 19, 2008

2 TiO 2 Applications White Pigment Photocatalyst

3 Previous methods to improving activity 1. Improve quantum yield Crystal structure, the presence of hydroxyl groups on the surface, and the presence of oxygen deficiencies affect the photocatalytic activity. 2. Extend light Absorption from the UV region into the visible region Nitrogen-doped titanium oxide (TiO x N y ) 3. Suppress the recombination of electron-hole pairs in TiO 2 Deposited platinum particles on TiO2 act as electron traps aiding electron-hole separation

4 Plasmonic Photocatalysis TiO2 in the anatase phase is a semiconductor with bandgap of 3.26 ev UV irradiation excites pairs of electrons and holes Near Ag nanoparticles the near-field enhancement caused by the localized surface plasmon could boost excitation of electron-hole pairs in TiO 2 thus increase efficiency of photocatalysis.

5 Experimental Setup Ag NPs core with silica shell to inhibit the oxidation of Ag by TiO 2 into AgO Resonance wavelength blue shifts with increasing SiO 2 shell thickness 50 nm shell thickness shifts resonance wavelength to 390 nm. Ag NPs covered with TiO 2 (~90nm) Monitored methylene blue trihydrate on TiO 2 photocatalytic decomposition by optical absorption spectroscopy

6 Scattering Response Figure 1. Scattering response. The extinction cross section for a spherical Ag nanoparticle (NP) of 50 nm diameter as a function of the wavelength and the thickness of a SiO2 shell. The core-shell structure is surrounded by TiO2. White denotes a large value, and black, a low value

7 Near-field Amplitude Figure 2. Near-field amplitude. Amplitude enhancement inside a TiO2 substrate was shown at the interface to a SiO2 substrate where a Ag NP with a diameter of 40 nm is embedded. The center of the coordinate system coincides with the center of the NP. The sketched sphere does not possess the correct dimensions but merely serves to indicate the geometrical situation that was simulated. The y-polarized illuminating plane wave propagates in the z-direction.

8 Sample Setup Figure 3. SEM observations. (a) Top view of Ag NPs on a SiO2 substrate. The 2.5- nm-thick Ag film was annealed at 800 C for 5 min to generate Ag NPs. (b) Top view of Ag NPs embedded in a SiO2 layer deposited by sputtering. (c) Crosssectional view of TiO2 film on Ag-core-SiO2-shell on a SiO2 substrate. The TiO2 film was deposited by spin coating with a coating solution, followed by heating at 500 C for 30 min

9 Sample Setup (c) Cross-sectional view of TiO2 film on Agcore-SiO2-shell on a SiO2 substrate. The TiO2 film was deposited by spin coating with a coating solution, followed by heating at 500 C for 30 min Figure 4. TEM view. Cross section of TiO2 film on Ag/ SiO2 core-shell on a SiO2 substrate [the same structure is as shown in Figure 2c].

10 Absorption Spectra Figure 5. Optical absorption spectra. (a) TiO2 thin film, (b) Ag NP embedded in TiO2, and (c) Ag NPs covered with SiO2 layer embedded in TiO2.

11 Varying Silica Shell Thickness Figure. S2: Optical absorption spectra. SiO2 was deposited on Ag NPs with thickness of 5 nm (a), 10 nm (b), 20 nm (c) and 30 nm (d) followed by deposition of 90 nm thick TiO2. Spectrum for SiO2 deposited on Ag NPs is shown in (e) for comparison.

12 Methylene Blue Decomposition (a) A TiO2 film on a SiO2 substrate. (b) A TiO2 film on a Ag/SiO2 core-shell structure on a SiO2 substrate. (c) A TiO2 film on a Ag/SiO2 coreshell structure with SiO2 thickness of 5 nm on a SiO2 substrate. SiO2 thickness for (a) and (b) was 20 nm.

13 Supporting Information Figure. S1: SEM observations. Ag NPs were deposited on SiO2 substrates followed by deposition of a SiO2 layer with a thickness of 5 nm (a), 10 nm (b), 20 nm (c) and 30 nm (d).

14 Supporting Information Figure. S3: Spectra before and after MB coating were shown with black and blue lines, respectively. After exposure of near UV for every one minute, optical absorption spectra were measured. Gray line presented the spectrum after 16 min illumination.

15 Plasmonic Photocatalyst