Effect of metal ion dopants on photochemical properties of anatase TiO2 films synthesized by a modified sol-gel method

doi:10.1016/j.tsf.2007.02.101

Thin Solid Films

Volume 515, Issue 18, 25 June 2007, Pages 7091-7095

https://doi.org/10.1016/j.tsf.2007.02.101 Get rights and content

Abstract

Anatase TiO₂ films were successfully synthesized by a modified sol-gel method wherein peroxo titanic acid solution was derived from TiCl₄/ethanol/water solution at room temperature. The as-prepared films were further surface-doped by photodeposited Fe₂O₃ and Cr₂O₃ to improve its physicochemical properties. The phase and structure of the films were investigated by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The physicochemical properties of the films were also measured. The results show that both hydrophilicity and photocatalytic activity of the films were remarkably improved by doping transition metal ion Fe³⁺. In case of Cr³⁺ doped films, hydrophilicity was also significantly enhanced but photocatalytic activity for methyl orange under UV irradiation was still comparable with the undoped films.

Introduction

Titanium dioxide (TiO₂) is of great importance owing to its widely industrial applications related to photo-splitting of water [1], photocatalyst [2], photovoltaic devices [3], etc., mostly attributed to the optical and electronic properties, low cost, chemical stability and non-toxicity of nano-crystallined TiO₂ films. A large variety of methods have been developed to prepare TiO₂ films in which dip-coating of TiO₂ sol-gel method is most widely used due to its facility to prepare films onto wide-area bodies at low temperatures [4], [5]. However, the application of sol-gel method is often hindered by the usage of organometallic compounds which are expensive and intractable because of their hydrolysis with water in air [4], [5], [6], [7]. Also, the sol prepared by this method is unstable and acidic which limited metals to apply in this system.

Ichinose et al. [8] have reported the preparation of TiO₂ films by using peroxo titanic acid (PTA) solution and peroxo-modified sol. Compared with the conventional sol-gel methods, the method possesses many merits. For example, PTA is neutral and can be easily coated onto various materials even pure metal. Moreover, PTA is stable in air and its preparation is both simple and cost-efficient. However, the PTA solution has to be derived from TiCl₄ aqueous solution and the operations have to be done at a lower temperature 0–5 °C in the ice-water bath, which increases the difficulty of this method in applying on large industry scale.

In the present paper, a modified method has been attempted to prepare TiO₂ films in which PTA was derived from TiCl₄/ethanol/water solution at room temperature [9]. It was reported that different transition metal ions deposited onto the surface of the semiconductors could improve the separation of photoproduced electron-hole pairs, resultantly enhance the photocatalytic activity of TiO₂ [10]. The films prepared by modified PTA method were further coated by some transition metal ions (chromium, iron) via photodeposition. The effects of the dopants on physicochemical and photocatalytic of TiO₂ films were also investigated.

Section snippets

Preparation of the photocatalysts

TiCl₄ (0.05 mol) was dissolved in 200 ml ethanol with vigorously stirring till yielding a homogeneous solution, then diluted by 300 ml water. Afterwards, ammonia solution was dropped into the TiCl₄/ethanol/water solution to keep the pH value of the solution around 8. Then titanic acid gel was precipitated. The gel was rinsed, separated by decantation and centrifugation until Cl⁻ ions could not be detected. Then 80 ml H₂O₂ solution (30 wt.%) was added into the titanic acid gel and the yellow,

Phase composition

XRD patterns of as-prepared and doped TiO₂ films were shown in Fig. 1. Sharp diffraction peaks appear at 25° and 63°, indicating clearly the films are anatase phase. No obvious difference was observed between the undoped and doped TiO₂ films, which are attributed to quantity of the metal oxide that deposited on the surface of the TiO₂ films is too small to be detected by XRD. However, the intensity of the diffraction peaks of the films increased after doping. This should result from that the

Conclusions

A modified sol-gel method was successfully developed to synthesis anatase TiO₂ films and photodepositing method was used to dope the as-prepared films by Fe³⁺ and Cr³⁺. The films doped by Fe³⁺ and Cr³⁺ possess the improved wettability and became superhydrophilic under UV irradiation. The photocatalytic activity of Fe³⁺ doped films were significantly enhanced, whereas the photocatalytic activity of Cr³⁺ doped films were similar even lower than undoped those. The anatase films doped from Fe(NO₃)₃

Acknowledgments

The present work has been supported by the National Nature Science Foundation of China (No. 50474043). The authors are grateful to Prof. Fumitaka Tsukihashi (Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, Japan) for his contributions during many fruitful discussions on this subject.

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Effect of metal ion dopants on photochemical properties of anatase TiO2 films synthesized by a modified sol-gel method

Abstract

Introduction

Section snippets

Preparation of the photocatalysts

Phase composition

Conclusions

Acknowledgments

Thin Solid Films

Appl. Surf. Sci.

Nature

Nature

Chem. Rev.

J. Sol-Gel Sci. Technol.

J. Mater. Sci. Lett.

J. Mater. Sci.

J. Ceram. Soc. Jpn.

Effect of metal ion dopants on photochemical properties of anatase TiO₂ films synthesized by a modified sol-gel method