Effect of Ag loading position on the photocatalytic performance of TiO2 nanocolumn arrays

Abstract

Plasmonic metal/semiconductor composites have attracted great attention for efficient solar energy harvesting in photovoltaic and photocatalytic applications owing to their extremely high visible-light absorption and tuned effective band gap. In this work, Ag-loaded TiO₂ nanocolumn (Ag-TNC) arrays were fabricated based on anodic aluminum oxide (AAO) template by combining atomic layer deposition (ALD) and vacuum evaporation. The effects of the Ag loading position and deposition thickness, and the morphology, structure and composition of Ag-deposited TNC arrays on its optical and photocatalytic properties were studied. The Ag-filled TiO₂ (AFT) nanocolumn arrays exhibited higher removal efficiency of methylene blue (MB) compared with Ag-coated TiO₂ (ACT) nanocolumn arrays and pure TiO₂ nanocolumns arrays. Both experimental and theoretical simulation results demonstrated that the enhanced photocatalytic performance of AFT nanocolumn arrays was attributed to the surface plasmon resonance (SPR) of Ag and the absorption of light by TiO₂. These results represent a promising step forward to the development of high-performance photocatalysts for energy conversion and storage.

Keywords: anodic aluminum oxide template; nanocolumn arrays; photocatalysis; surface plasmon resonance.

Figure 1

Schematic diagram of the preparation process of the different Ag–TiO₂ nanocolumn structures. (1) Structure of samples ACT1, ACT2, and ACT3; (2) structure of samples AFT1, AFT2, and AFT3.

Figure 2

SEM images of the top view of different samples: (a) AAO template, (b) TNC, (c) EDS of TNC, (d) AFT1, (e) AFT2, (f) AFT3, (g) ACT1, (h) ACT2, and (i) ACT3.

Figure 3

SEM cross section of samples with AAO and Al substrate. (a) Observation sketch, (b) AAO template, (c) TNC, (d) AFT1, (e) AFT2, and (f) AFT3.

Figure 4

TEM images of nanocolumn structures. a) TNC nanocolumn TEM image, b) TNC TEM diffraction pattern, c) AFT1 TEM image, d) AFT1 nanocolumn high-resolution TEM image, where the insets show the image processed by the software in the selected areas of the red-dotted line frames.

Figure 5

XPS spectrum of AFT3: (a) Survey spectrum, and details of the regions related to (b) O 1s, (c) Ti 2p, (d) Ag 3d.

Figure 6

(a,b) UV–vis absorption spectra and (c,d) bandgaps of the different samples.

Figure 7

Photocatalytic activity for the degradation of MB: (a) UV–vis absorption spectra for the photocatalytic degradation of MB in the presence of AFT1 sample, (b) photocatalytic degradation rate of MB by different samples and pure MB under UV–vis light, (c) kinetics of different samples, (d) recycling of AFT3 and ACT3.

Figure 8

FDTD simulations of the electric field distribution of Ag-loaded TiO₂ nanocolumns with different structures. a1) Wavelength 457 nm TNC cross section, a2) wavelength 320 nm TNC cross section, a3) wavelength 457 nm TNC longitudinal section, a4) wavelength 320 nm TNC longitudinal section, b1) wavelength 457 nm ACT3 cross section, b2) wavelength 320 nm ACT3 cross section, b3) wavelength 457 nm ACT3 longitudinal section, b4) wavelength 320 nm ACT3 longitudinal section, c1) wavelength 457 nm AFT3 cross section, c2) wavelength 320 nm AFT3 cross section, c3) wavelength 457 nm AFT3 longitudinal section, c4) wavelength 320 nm AFT3 longitudinal section.

Figure 9

(a) Schematic diagram of electron–hole separation and energy conversion of Ag–TiO₂ structures under UV–vis illumination. b) AFT structure light absorption diagram. c) Schematic diagram of energy conversion in the case of excessive Ag-coated TiO₂. d) ACT structure light absorption diagram.