Enhanced visible light photocatalytic activity of Fe2O3 modified TiO2 prepared by atomic layer deposition

Abstract

In this work, commercial anatase TiO₂ powders were modified using ultrathin Fe₂O₃ layer by atomic layer deposition (ALD). The ultrathin Fe₂O₃ coating having small bandgap of 2.20 eV can increase the visible light absorption of TiO₂ supports, at the meantime, Fe₂O₃/TiO₂ heterojunction can effectively improve the lifetime of photogenerated electron-hole pairs. Results of ALD Fe₂O₃ modified TiO₂ catalyst, therefore, showed great visible light driven catalytic degradation of methyl orange compared to pristine TiO₂. A 400 cycles of ALD Fe₂O₃ (~ 2.6 nm) coated TiO₂ powders exhibit the highest degradation efficiency of 97.4% in 90 min, much higher than pristine TiO₂ powders of only 12.5%. Moreover, an ultrathin ALD Al₂O₃ (~ 2 nm) was able to improve the stability of Fe₂O₃-TiO₂ catalyst. These results demonstrate that ALD surface modification with ultrathin coating is an extremely powerful route for the applications in constructing efficient and stable photocatalysts.

Figure 1

The schematic diagram of coating TiO₂ powders by ALD Fe₂O₃.

Figure 2

XRD patterns of pristine TiO₂ and Fe₂O₃ coated TiO₂.

Figure 3

SEM images of (a) pristine TiO₂ and (b) TiO₂@400-Fe₂O₃. TEM images of (c) pristine TiO₂ and (d) TiO₂@400-Fe₂O₃.

Figure 4

XPS spectra of (a) Ti 2p and (b) O 1s for TiO₂ and TiO₂@400-Fe₂O₃, Fe 2p XPS spectra for (c) TiO₂@400-Fe₂O₃ and (d) Fe₂O₃ film.

Figure 5

(a) UV–Vis diffuse reflectance spectra and (b) Tauc plot of TiO₂ with and without 400 cycles Fe₂O₃ coating.

Figure 6

UV–vis absorption spectra of MO exposed to different irradiation time in the presence of (a) pristine TiO₂ and (b) TiO₂@400-Fe₂O₃ catalysts under visible light irradiation. The inserts are the photos of MO solution before and after irradiation. (c) Visible light photocatalytic degradation curves of MO and (d) −In(C/C₀) vs. time curves by using TiO₂ with and without Fe₂O₃ coating as catalysts.

Figure 7

(a) PL spectra and (b) photocurrent response curves of TiO₂ and Fe₂O₃ coated TiO₂.

Figure 8

(a) Valence band spectra of TiO₂ and Fe₂O₃–TiO₂. (b) Schematic illustration of energy band structure of Fe₂O₃ coated TiO₂ and proposed charge transfer mechanism during visible light irradiation.

Figure 9

(a) Three cycles of MO degradation for TiO₂@400-Fe₂O₃, TiO₂@800-Fe₂O₃ and 20 cycles Al₂O₃ coated TiO₂@400-Fe₂O₃ in 90 min. (b) Comparison of MO degradation curves for pristine TiO₂, TiO₂@400-Fe₂O₃, and 20 cycles Al₂O₃ coated TiO₂@400-Fe₂O₃.