Influence of solution chemistry on the properties of hydrothermally grown TiO2 for advanced applications

doi:10.1016/j.cattod.2009.02.009

Catalysis Today

Volume 144, Issues 1–2, 15 June 2009, Pages 172-176

https://doi.org/10.1016/j.cattod.2009.02.009 Get rights and content

Abstract

It is demonstrated that the properties of hydrothermally deposited titanium (IV) oxide (TiO₂) films are greatly affected by the solution chemistry. Anatase TiO₂ films grown using i-PrOH presented the best reversible photoinduced hydrophilic response, reaching a contact angle (CA) of 15° and 83% photocatalytic activity as well as measurable photoconductivity. Inclusion of as low as 0.02 M NaOH in the solution resulted in films probably consisted of sodium titanate exhibiting good photoinduced properties, which makes it a promising candidate for various applications. In contrast, rutile TiO₂ films prepared using EtOH as a solvent showed weak photoinduced activity. The correlation of solution chemistry with the morphology and the photoinduced properties of the materials are discussed.

Introduction

Titanium (IV) oxide (TiO₂) or titania is one of the most promising semiconductors for applications in various technologies such as solar cells [1] photocatalysis [2], anti-fogging and self-cleaning or anti-bacterial coatings [3] having the added advantage of being a non-toxic and low-cost material [4]. The photoinduced properties involved in these applications can be regulated by controlling the TiO₂ crystallographic structure and morphology [5]. In addition, transparent conducting applications can already be realised for TiO₂ by doping with Nb [6].

Anatase and rutile TiO₂ have been widely studied as photocatalysts [7], anatase exhibiting a higher activity than rutile due to its particular band structure [8]. Furthermore, surface roughness is an important parameter for the photocatalytic activity of this material [5]. Photocatalysis takes place on the surface of the film under the presence of adsorbed water molecules. The wider is the exposed surface of the films the higher is expected to be the number of photocatalytic events. The efficiency of the effect per unit of film area will thus be enhanced by a corresponding increase of the ratio of the actual surface of the films to the deposited area. Such an increase is the natural consequence of surface roughness.

TiO₂ with such properties can be developed using several techniques such as sputtering [9], chemical vapour deposition (CVD) [10], hydrolysis [11], sol–gel methods [12] and hydrothermal synthesis [13], [14], [15], most of them requiring costly equipment and/or vacuum and/or high temperatures and/or hazardous chemicals. Hydrothermal synthesis is a “one pot” process, requiring non-hazardous chemicals, low temperatures and atmospheric pressure. Moreover, it can be expanded to large substrates with the only shortcoming being the long preparation times needed for full coverage. Finally, with this method, the structural and morphological characteristics of the samples can be tailored by simply controlling the solution chemistry (precipitation/dispersion conditions affecting the thermodynamic stabilization of the system) [16]. Therefore, hydrothermal synthesis seems to be a rather attractive technique for the deposition of TiO₂.

The aim of the present work is to provide insight on the correlation of solution chemistry with morphology and photoinduced properties of hydrothermally grown titanium oxide, at 95 °C on Corning 7059 substrates. It is noteworthy that under appropriate conditions, it is possible to grow sodium titanate with good reversible photoinduced hydrophilic and photocatalytic activity.

Section snippets

Experimental

The growth of titanium oxide on Corning 7059 was performed by the hydrothermal method using as precursors three different solutions: (series 1) TTIP (Ti[(OCH(CH₃)₂)]₄), propanol (i-PrOH, (CH₃)₂CHOH)) and MilliQ water, (series 2) TTIP, ethanol (EtOH, CH₃CH₂OH) and MilliQ water and (series 3) TTIP, i-PrOH, MilliQ water and 0.02 M NaOH/i-PrOH solution. For growth using i-PrOH as solvent, the solution preparation involved initially the stirring of 12 M i-PrOH with 0.1 M MilliQ H₂O, followed by the

Results and discussion

Since growth times shorter than 20 h resulted in TiO₂ films with no photoinduced response, a range of deposition periods 20–50 h was chosen for our studies. Propanol was selected based on considerations of similar procedures reported in the literature [17], [18], while ethanol was used for the control of the morphological characteristics of the films via the alteration of precipitation rate of the solution [19]. Regarding the choice of using sodium hydroxide in these experiments, this was based

Conclusion

The results presented in this paper reveal that under suitable deposition conditions, it is possible to control the phase of hydrothermally grown titanium oxide thin films. Depending on the solution chemistry, Raman analysis indicated that the formation of anatase, rutile or Na₂Ti₃O₇ is possible, the corresponding photoinduced properties strongly depending on the phase of the film. Anatase films grown for a deposition period of 20 h using i-PrOH were found to simultaneously exhibit optimum

Acknowledgements

This work was co financed by 75% from the European Regional Development Fund and by 25% from national Greek resources (INTERREG IIIA Greece-Cyprus).

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Influence of solution chemistry on the properties of hydrothermally grown TiO2 for advanced applications

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgements

Surf. Coat. Technol.

Appl. Catal. A

Appl. Surf. Sci.

J. Cryst. Growth

Powder Technol.

J. Colloid Interface Sci.

Thin Solid Films

Thin Solid Films

Colloid Surf. A: Physicochem. Eng. Aspects

J. Colloid Interf. Sci.

Chem. Phys. Lett.

J. Photochem. Photobiol. A: Chem.

J. Photochem. Photobiol. A: Chem.

J. Non-Cryst. Solids

Thin Solid Films

Nature

J. Phys. Chem.

Influence of solution chemistry on the properties of hydrothermally grown TiO₂ for advanced applications