Visible-light-induced photocatalytic activity of TiO2−xNy prepared by solvothermal process in urea–alcohol system

doi:10.1016/j.jeurceramsoc.2005.05.012

Journal of the European Ceramic Society

Volume 26, Issue 13, 2006, Pages 2735-2742

https://doi.org/10.1016/j.jeurceramsoc.2005.05.012 Get rights and content

Abstract

Nitrogen-doped anatase, rutile and brookite titania photocatalyst TiO_2−xN_y which can be excited by visible light were prepared by mixing aqueous TiCl₃ solutions with urea ((NH₂)₂CO) and various type of alcohols followed by solvothermal treatment at 190 °C. The phase composition, crystallinity, microstructure and specific surface area of titania powders greatly changed depending on the pH and type of solvents. Violet, yellowish and grayish TiO_2−xN_y with excellent visible light absorption and photocatalytic activity were prepared. The TiO_2−xN_y powders prepared in urea–methanol solution showed excellent photocatalytic ability for the oxidative destruction of nitrogen monoxide under irradiation of visible light λ > 510 nm.

Introduction

Titania is the most effective photocatalyst and can be applied in decomposition of some pollute substances, such as nitrogen monoxide in atmosphere and/or organic pollutants in water under light irradiation.1, 2 However, titania can only be encouraged by UV light because of its large band gap value of ca. 3 eV. In order to utilize the solar energy effectively, it is necessary to develop a visible-light-reactive photocatalyst. In 2001, Asahi et al.3, 4 reported that nitrogen-doped titanium oxide with high visible-light photocatalytic activities could be prepared by sputtering TiO₂ in an N₂ (40%)/Ar gas mixture followed by annealing in N₂ gas at 550 °C or by treating anatase TiO₂ powder in the NH₃ (67%)/Ar atmosphere at 600 °C. They also pointed out that nitrogen doping leads to narrowing of band gap by mixing the N2p and O2p state and consequently induces the visible-light-responsive photocatalytic activity. It was also forecasted that other kind of anions such as C, S and F would result in the similar effect to nitrogen. Since then, many researchers paid their much attention on anion-doped photocatalysts.5, 6, 7, 8, 9, 10 Meanwhile, most methods are high temperature processes, using expensive precursors or preparation instruments. In our previous research, it was found that nitrogen, fluorine or sulfur-doped photocatalyst with high visible-light-induced photocatalytic activity could be prepared by a low-temperature mechanochemical doping process.11, 12, 13, 14 However, anion-doped titania in only rutile structure can be prepared by this process. In order to realize the phase-compositional and morphological control of anion-doped photocatalysts, a soft solution process is described in this paper, using various alcohol as reaction media. The effects of reaction conditions such as pH and type of solvents on phase composition, microstructure, specific surface area and photocatalytic activity were investigated in detail.

Section snippets

Experimental

Desired amount of urea ((NH₂)₂CO) and 21.5 cm³ of 20 wt.% TiCl₃ solution (Kanto Chem. Co. Inc., Japan) was introduced into 25 cm³ of distilled water or alcohols, the mixed solution was placed into a SUS 314 stainless steel autoclave attached with a Teflon tube of internal volume of 200 cm³. After that the chamber of autoclave was flushed by nitrogen gas three times. The autoclave was heated and kept at 90 °C for 1 h to realize the hydrolysis of urea, then heated at 190 °C for 2 h for crystallization.

Phase composition and physicochemical characterization

It is well known that the hydrolysis of urea produces CO₂ and NH₃ at above 85 °C. The ammonia react with TiCl₃ to form nitrogen contained TiO_2−xN_y·nH₂O precursor. Well-crystallized TiO_2−xN_y could be formed by the followed solvothermal treatment at 190 °C: $TiC l_{3} \overset{N H_{3}, H_{2} O, etc .}{⟶} Ti O_{2 - x} N_{y} \cdot n H_{2} O ⟶_{in autoclave}^{190 ° C} Ti O_{2 - x} N_{y}$

Fig. 1 shows the XRD patterns of the titania powders prepared in TiCl₃–urea aqueous solution and TiCl₃–urea–methanol solution at various pH and 190 °C for 2 h. It was found that the

Conclusions

Based on the above experimental results, the following conclusions might be drawn:

Nitrogen-doped titania photocatalyst TiO_2−xN_y with various phase composition was successfully prepared by solvothermal treatment of TiCl₃ solutions with urea and various alcohols at 190 °C. The TiO_2−xN_y powders showed various color and excellent visible light absorption and photocatalytic ability for the oxidative destruction of nitrogen monoxide under irradiation of visible light. In addition,

Acknowledgements

This research was partially supported by the Ministry of Education, Culture, Sports, Science and Technology, a Grant-in-Aid for the COE project (Giant Molecules and Complex Systems) and a Grant-in-Aid for Science Research (No. 14750660), the Steel Industry Foundation for the Advancement of Environmental Protection Technology and the JFE 21st Century Foundation.

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Visible-light-induced photocatalytic activity of TiO2−xNy prepared by solvothermal process in urea–alcohol system

Abstract

Introduction

Section snippets

Experimental

Phase composition and physicochemical characterization

Conclusions

Acknowledgements

J. Mol. Catal. A

J. Photochem. Photobio. A

Int. J. Inorg. Mater.

J. Photochem. Photobiol. A Chem.

J. Photochem. Photobiol. A Chem.

Chem. Phys. Lett.

J. Solid State Chem.

Electrochim. Acta

J. Solid State Chem.

Preparation, characterization, and reactivities of highly functional titanium oxide-based photocatalysts able to operate under UV–visible light irradiation: approaches in realizing high efficiency in the use of visible light

Bull. Chem. Soc. Jpn.

Visible-light photocatalysis in nitrogen-doped titanium oxides

Science

Band-gap narrowing of titanium dioxide by nitrogen doping

Jpn. J. Appl. Phys.

Designed self-doping titanium oxide thin films for efficient visible-light photocatalysis

Adv. Mater.

Efficient photochemical water splitting by a chemically modified n-TiO2

Science

Band-gap narrowing of titanium dioxide by sulfur doping

Appl. Phys. Lett.

Visible light-induced degradation of methylene blue on S-doped TiO2

Chem. Lett.

Visible-light-induced photocatalytic activity of TiO_2−xN_y prepared by solvothermal process in urea–alcohol system

Efficient photochemical water splitting by a chemically modified n-TiO₂

Visible light-induced degradation of methylene blue on S-doped TiO₂