Crystallization of titania in liquid media and photochemical properties of crystallized titania
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Crystallization of titania in liquid media and photochemical properties of crystallized titania Shu Yin, Yuichi Inoue, Satoshi Uchida, Yoshinobu Fujishiro, and Tsugio Satoa) Institute for Chemical Reaction Science, Tohoku University, Sendai 980-77, Japan (Received 11 September 1997; accepted 5 January 1998)
Titania gels in liquid media crystallized from amorphous to anatase at temperatures as low as 120 ±C, while the onset of crystallization in air was 370 ±C. The crystallization rate in water was much faster than in methanol and n-hexane, and the crystallite size of anatase prepared in water was larger than of those prepared in organic solvents. The crystallized powders were capable of efficient hydrogen evolution following band gap irradiation in the presence of a sacrificial hole acceptor such as methanol. The photocatalytic activity of powder crystallized in methanol was superior to those prepared in water and air.
I. INTRODUCTION
It is generally accepted that a critical parameter that affects final characteristics of ceramic materials is the state of agglomeration of the starting powder. Washing the powder with organic solvents is an effective way of avoiding the formation of hard agglomerates.1–5 It is proposed4,5 that agglomerate strength is determined by the extent to which water molecules, hydrogenbonded to surface hydroxyl groups, are able to form bridges between adjacent particles. Organic solvents can remove hydroxyl groups and water and leads to a reduction and/or elimination of hard agglomerates. In a previous paper6–8 it was reported that CeO2 –ZrO2 crystallized in methanol and dried by supercritical drying consisted of softly agglomerated fine powders and possessed excellent sinterability compared to those fabricated by hydrothermal crystallization and/or calcination in air. These results suggested that organic solvents played an important role to depress hard agglomeration and crystal growth during crystallization. The details of crystallization of ceramic powder in organic solvents, however, have not been clarified. In the present paper we described the crystallization behaviors of TiO2 gel in liquid media such as methanol, n-hexane, and water and photocatalytic properties of titania crystallized under different conditions. II. EXPERIMENTAL
Amorphous TiO2 gel was prepared by slowly adding 500 cm3 of i-propanol solution dissolving 0.66 mol of titanium tetraisopropoxide to the mixed solution of 50 cm3 of water to 500 cm3 of i-propanol at room tema)
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J. Mater. Res., Vol. 13, No. 4, Apr 1998
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perature. The gel was successively washed with 50 : 50 (vol %) water/methanol mixed solution and methanol, and dried at room temperature using a vacuum desiccator. Since the amount of water in the dried gel was determined at 30 wt. % by thermogravimetry, the chemical composition of the gel may be described as Ti(OH)4
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