7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Enhancing Photocatalytic Performance of Silver-Decorated Titanium Dioxide
via Nanocolumnar Thin Films Produced by Oblique Angle Deposition

L.C. Montefalcon1 and M.R. Vasquez Jr1
1
Department of Mining, Metallurgical, and Materials Engineering, University of the Philippines
Dilimane-mail (speaker): lcmontefalcon@up.edu.phTitanium dioxide (TiO2) has been widely studied invarious applications especially in photocatalysis due toits stability, non-toxicity and high photocatalytic activity.
Although it exhibits favorable properties, its activity isonly limited in the ultraviolet range due to its relatively
high band gap. [1] In general, sputter deposited TiO2 thinfilms offer good mechanical stability and high reusability
when it comes to wastewater treatment. However, therelatively dense characteristics of thin films limit thesurface area accessibility. Oblique angle deposition(OAD) provides a simple way to make nanostructurecolumnar films with high porosity. In this process, thesubstrate is placed at an angle large enough (~70o to 85o)to the direction of the coating vapor flux. During film
growth, line-of-sight shadowing prevents the subsequent
incoming atoms from impinging on the area directly
behind these initial nuclei. The result, tall columns growat the expense of smaller columns due to self-shadowing.
[2] In this work, visible light active silver-decorated TiO2
nanocolumnar thin films (Ag-TiO2 NCTFs) were
fabricated using a custom-built magnetron sputter
deposition using OAD technique followed by acalcination step to form a high surface area NCTFs. The
TiO2 NCTFs are then decorated with metallic Ag
nanoparticles through wet impregnation and subsequentplasma reduction to shift the activity of TiO2 films to thevisible light region.
The composition and crystalline phases of theNCTFs were identified using Raman spectroscopy.
Figure 1(a) presents the Raman spectra of the fabricated
NCTFs. No significant peaks were observed for asdeposited TiO2 NCTFs due to its amorphous structure.
Peaks observed at 145 cm-1, 197 cm-1, 396 cm-1, 515 cm-1,and 639 cm-1 for annealed NCTFs confirms the presenceof anatase characteristic peaks of TiO2. Incorporation ofAg shows an increase in intensity of the characteristic

peaks of anatase TiO2 due to surface plasmon resonance(SPR) phenomenon where the CB electrons on thesurface undergo oscillation when excited by light at a
specific wavelength, resulting in the strong scatteringand absorption of light. [3]Figure 1(b) shows the Raman Spectroscopy
measurements of TiO2 NCTFs tilted at different angles(0 ° and 85 ° ). Both films show anatase characteristicpeaks of TiO2 but intensity decreases as tilting angle isincreased due to differences in film thickness. Figure1(c) shows methylene blue (MB) photodegradation undervisible light irradiation. In comparison, NCTFs tilted at
850 show higher rate constant as compared to the untitledones. This suggests that more structured columnar films
with higher porosity are produced when tilting angle isset at 85o due to self-shadowing.
Degradation experiments also revealed that MB
removal efficiency of TiO2 NCTFs increased from 26%
to 79% upon decorating with Ag. The inset plot also
shows a decrease in band gap energy from 3.3 eV to 2.9
eV upon Ag decoration. This improvement was due toSPR effect in which electrons from the conduction band(CB) of Ag were efficiently transferred to the CB of TiO2
improving the oxidation-reduction process needed forphotocatalysis as well as the improvement of local
electric field near Ag-TiO2 for faster generation of charge
carriers.
References[1] D. Kim, N. Han, J. B. Lee, and H. T. Kim. Scripta
Materialia 54, p. 143–146, (2006).
[2] Y. P. He, Z. Y. Zhang, and Y. P. Zhao. JVST B 26, p.
1350 (2008)[3] A.S. Montallana and M.R. Vasquez. Res. in Phys. 25
p. 104205 (2021)Figure 1. (a) Raman Spectroscopy measurements of as deposited amorphous TiO 2 NCTFs, TiO2 NCTFs annealed at
450 ℃, and plasma-reduced Ag on TiO2 NCTFs. (b) Raman Spectroscopy measurements of TiO2 NCTFs tilted atdifferent angles (0° and 85°). (c) Plots of ln(Co/C) versus time and corresponding linear fits (inset: Tauc’s Plot derivedfrom UV-Vis Absorbance Spectra of annealed TiO2 and Ag-TiO2.