Process for producing titanium oxide

Details Process for producing titanium oxide Process for producing titanium oxide

2001-03-29

2004-12-07

Silverman, Stanley S. (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Metal containing

C502S350000

Reexamination Certificate

active

06827922

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for producing a titanium oxide, specifically a process for producing a titanium oxide exhibiting a photocatalytic activity.
BACKGROUND OF THE INVENTION
Light irradiation to a photocatalyst generates electrons having a strong reduction activity and positive holes having a strong oxidation activity, to decompose a molecular species that comes in contact with the photocatalyst by an oxidation-reduction activity. Such an activity is called a photocatalytic activity. By the photocatalytic activity, NO
x
in the atmosphere is decomposed, bad-smelling substances, molds or the like in a living or working space are decomposed and removed, and environmental pollution substances such as organic solvents, agrochemicals and surfactants in water are decomposed and removed. In these days, a photocatalyst exhibiting the photocatalytic activity by irradiation of visible light has been researched from the point of general purpose and usage. It has been known that a certain titanium oxide can be utilized for such a photocatalyst.
Some processes for producing a titanium oxide exhibiting the photocatalytic activity have been proposed. For example, PCT International Application Laid-Open No. WO98/23374 discloses that a titanium oxide is treated in a microwave low-temperature plasma method so that a titania with a carbon deposit is formed thereon. In this method, however, there are problems in that a specific apparatus having a vacuum vessel such as a microwave low-temperature plasma generator is needed and the process thereof is complicated.
SUMMARY OF THE INVENTION
The objects of the present invention is to provide a process for easily producing a titanium oxide that shows sufficiently high photocatalytic activities by irradiation of visible light without utilizing a specific apparatus having a vacuum vessel.
The present inventors have studied on such a titanium oxide As a result, the present inventors have found that the titanium oxide can be easily produced by a process comprising a step of calcining a titanium compound under a specific condition, and have completed the present invention.
Thus, the present invention provides a process for producing a titanium oxide which comprises (i) a step of calcining a titanium compound in the presence of ammonia gas or (ii) steps of treating a titanium compound with heat in the presence of ammonia gas and calcining the heat-treated titanium compound.
DETAILED DESCRIPTION OF THE INVENTION
A titanium oxide in the present invention is produced by a process which comprises (i) a step of calcining a titanium compound in the presence of ammonia gas or (ii) steps of treating a titanium compound with heat in the presence of ammonia gas and calcining the heat-treated titanium compound.
Examples of the titanium compound used in the present invention include titanium hydroxides, titanic acids, other inorganic titanium compounds, organic titanium compounds, partially hydrolyzed inorganic titanium compounds and partially hydrolyzed organic titanium compounds. The partially hydrolyzed titanium compounds may be obtained by hydrolyzing the corresponding titanium compounds with smaller amount of water (which may be in a liquid state or vapor state) than that in a stoichiometric amount.
Examples of the titanium hydroxides and titanic acids include titanium hydroxide (II) (Ti(OH)
2
), titanium hydroxide (III) (Ti(OH)
3
), titanium hydroxide (IV) (Ti(OH)
4
), titanium oxyhydroxide (TiO(OH)
2
), &agr;-titanic acid (ortho-titanic acid (H
4
TiO
4
)), &bgr;-titanic acid (meta-titanic acid (H
2
TiO
3
)) and the like. Examples of other inorganic titanium compounds include titanium trichloride, titanium tetrachloride, titanium tetrabromide, titanium sulfate, titanium oxysulfate and the like. Examples of organic titanium compounds include tetra-alkoxy titanium compounds such as tetra-isopropoxy titanate, tetra-n-butoxy titanate, tetrakis(2-ethylhexyloxy) titanate and tetrasteariloxy titanate; titanium acylate compound; titanium chelate compounds such as di-isopropoxy-bis(acetylacetonato) titanium complex, isopropoxy(2-ethyl-1,3-hexandiorato) titanium complex, hydroxy-bis(lactato) titanium complex and the like.
In the present invention, the titanium hydroxides and the partially hydrolyzed organic titanium compounds are preferably used as the titanium compound. It is preferred that the titanium compound contains that having an amorphous phase. The more a rate containing amorphous titanium compound increases, the higher photocatalytic activity the resulting titanium oxide tends to exhibit when radiated with visible light. The ratio of the amorphous titanium compound to the whole titanium compound is measured in an X-ray diffraction method. The titanium hydroxide containing that of an amorphous phase may be obtained by hydrolyzing the above-described other inorganic titanium compound, the organic titanium compound or the like.
When a titanium hydroxide is utilized as the titanium compound in the present invention, it is preferred that the titanium hydroxide contains nitrogen or a nitrogen compound. When the titanium hydroxide containing nitrogen or the nitrogen compound in a larger amount is utilized, the resulting titanium oxide tends to exhibit a higher photocatalytic activity. The amount of nitrogen, the nitrogen compound or the like, which is contained in the titanium hydroxide, may be preferably about 0.2% by weight, more preferably about 1% by weight, much more preferably about 2.5% by weight in terms of nitrogen atom based on the titanium hydroxide. The amount of nitrogen, the nitrogen compound or the like may be measured by a melting method using a nitrogen analyzer.
The titanium hydroxide containing nitrogen or the nitrogen compound may be obtained in a method of adding an alkaline compound such as ammonia solution (ammonia water) or an alkali hydroxide into a titanium oxysulfate solution to precipitate a titanium hydroxide, or in a method of adding water or ammonia solution into a titanium chloride, to hydrolyze the titanium compound.
The titanium compound used in the present invention may be obtained after a mold processing. Examples of the shape of such a molded titanium compound include powdery shape, fibrous shape, thin-layer shape and the like. When the molded titanium compound having a designated shape formed by the mold processing is utilized in the present invention, the resulting titanium oxide exhibits sufficiently high photocatalytic activity as well as it has a designated shape. For example, when a fibrous-shaped titanium compound is used, a fibrous-shaped titanium oxide is provided. When a thin-layer-shaped titanium compound is used, a thin-layer-shaped titanium oxide is provided.
Alternatively, the above-described mold processing may be conducted in a method of dispersing a titanium compound in a solvent such as water or an alcohol to obtain a slurry, applying the slurry onto an uneven surface of a metal plate and drying the slurry. By such a method, a titanium hydroxide having a specific shape or a thin-layered shaped titanium hydroxide having a specific surface can be obtained.
In the case that an ammonia gas is present in calcinating a titanium compound, the ammonia gas may be allowed to be present by a method in which the titanium compound is treated with heat in the present of an ammonia gas and then calcined in a nitrogen atmosphere or in air, or by a method in which a compound which generates ammonia in calcination is allowed to come in contact with a titanium hydroxide before and/or in calcining the titanium hydroxide, or by a method in which an ammonia gas is introduced into a calcination furnace while calcining the titanium compound.
When a titanium compound is treated with heat in the presence of ammonia gas before calcining the titanium compound, such a heat treatment may be carried out by heating the titanium compound at a temperature of about 50° C. or higher, preferably about 100° C. or higher, and at a temperature of about 200° C. or lower, preferably about 150° C. or lower. In the h

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