Effect of Growth Parameters on the Photocatalytic Performance of TiO2 Films Prepared by MOCVD

Abstract

The present study evaluated the main factors that influence the photocatalytic activity of titanium dioxide (TiO 2 ) films grown by metalorganic chemical vapor deposition (MOCVD) at 400 and 500 °C, in different growth times. The photocatalytic behavior was analyzed by measuring the methyl orange dye degradation at different pH values. Structural and morphological characteristics, and the recyclability of the catalysts for several cycles were also investigated. Anatase phase was identified in all films. The higher photodegradation performances were obtained at acidic pH. The results demonstrated that the photocatalyst thickness is an important parameter in heterogenous photocatalysis. The best photocatalytic result occurred for the 395 nm-thick TiO 2 film grown at 400 °C, which presented 65.3% of the dye degradation under UV light. The recyclability experiments demonstrated that the TiO 2 films grown by MOCVD present a great stability after several photocatalytic cycles, which allows their practical application for water treatment with high efficiency.

Thickness Effect on Photocatalytic Activity of TiO2 Thin Films Fabricated by Ultrasonic Spray Pyrolysis

“…A similar increase in photocatalytic activity within the thickness range of 100 to 500 nm has also been reported for DC magnetron sputtered TiO 2 films [6]. However, Marcello et al [13] reported an optimum thickness of 395 nm for MOCVD-deposited TiO 2 films, whereas Yong-Ick Cho et al [14] reported, for MOCVD-deposited TiO 2 coatings, increases in photocatalytic activity between the thickness range of 110 nm to 5 µm, which remain constant for thicker films between 5 and 15 µm. According to these studies, the photocatalytic activity of the TiO 2 films improves with increasing film thickness until a limit, dominantly in the range of 130-500 nm, from which the degradation reaction remains almost constant or decreases.…”

“…When the film is very thin, only a small portion of incident light is absorbed in the catalyst. Thus, the films with low thickness are incapable of high photocatalytic performance [13,17]. The photocatalytic activity increases with the film thickness from 50 to 200 +/− 30 nm, which can be attributable to the increase in the amount of TiO 2 , and thus higher light absorption (Figure 6), providing more photogenerated carriers for the reaction.…”

“…In the case of photocatalytic self-cleaning surfaces, it is important to define in which thickness the catalyst layer shows the highest photocatalytic activity and transparency in the visible spectral range in order to provide the required self-cleaning activity while retaining the visual appearance of the 2 of 13 coated surface. The effect of thickness on photocatalytic activity has been studied for nanocrystalline TiO 2 thin films, for example, obtained by atomic layer deposition (ALD) [9,10], sputtering [6,11,12], metal-organic chemical vapor deposition (MOCVD) [13,14], and sol-gel methods [15][16][17][18][19].…”

Visible-light photocatalytic activity and recyclability of N-doped TiO2 films grown by MOCVD

“…Nevertheless, film thickness plays an important role in photocatalytic activity. As shown in our previous study [21], TiO 2 films have an ideal thickness in which they perform better in removing dyes from water.…”

“…Pure TiO 2 and N-doped TiO 2 obtained by MOCVD exhibited different growth rates due to the presence of gaseous ammonia in the atmosphere [43]. The growth time for undoped and N-doped TiO 2 films were 30 and 60 min, respectively, to achieve the film thickness of around 360 nm, an appropriate thickness for photocatalytic application [21]. All films were grown at 400 °C under a pressure of 50 mbar.…”