EP2485838A2 - Copper ion-modified titanium oxide and process for producing the same, and photocatalyst - Google Patents

Copper ion-modified titanium oxide and process for producing the same, and photocatalyst

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Publication number
EP2485838A2
EP2485838A2 EP10807495A EP10807495A EP2485838A2 EP 2485838 A2 EP2485838 A2 EP 2485838A2 EP 10807495 A EP10807495 A EP 10807495A EP 10807495 A EP10807495 A EP 10807495A EP 2485838 A2 EP2485838 A2 EP 2485838A2
Authority
EP
European Patent Office
Prior art keywords
titanium oxide
copper ion
modified
modified titanium
mass
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP10807495A
Other languages
German (de)
French (fr)
Inventor
Kazuhito Hashimoto
Hiroshi Irie
Yasuhiro Hosogi
Yasushi Kuroda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Tokyo NUC
Resonac Holdings Corp
Original Assignee
Showa Denko KK
University of Tokyo NUC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Showa Denko KK, University of Tokyo NUC filed Critical Showa Denko KK
Publication of EP2485838A2 publication Critical patent/EP2485838A2/en
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/063—Titanium; Oxides or hydroxides thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/72—Copper
    • B01J35/30—
    • B01J35/39—
    • B01J35/393—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/031—Precipitation
    • B01J37/033—Using Hydrolysis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/77—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by unit-cell parameters, atom positions or structure diagrams
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer

Definitions

  • the present invention relates to a copper ion-modified titanium oxide which is suitable as a photocatalyst capable of exhibiting an activity by irradiation with a visible light and a process for producing the copper ion-modified titanium oxide, and further to a photocatalyst containing the copper ion-modified titanium oxide as a main component.
  • Titanium oxide is widely known as a photocatalyst, but exhibits no photocatalytic function unless it is used in a place where any ultraviolet rays are present. Therefore, at present, it has been attempted to impart a visible light absorbing property to titanium oxide.
  • One of the attempts for imparting a visible light absorbing property to titanium oxide is a method of doping a copper ion into titanium oxide.
  • a composite substance composed of the copper ion and titanium oxide is capable of exhibiting a photocatalytic activity under the irradiation with a visible light (for instance, refer to Patent Document l).
  • Patent Document l Japanese Patent Document 1
  • Non-Patent Document 1 has reported that titanium oxide modified with a copper ion is imparted with a visible light absorption band and a multi-electron reduction capability owing to an interfacial charge transfer so as to decompose isopropanol under the irradiation with a visible light.
  • study on application to only rutile-type titanium oxide has been made, and the method is therefore not applicable to anatase-type titanium oxide or brookite-type titanium oxide which is generally considered to have a high activity.
  • Patent Document l JP-A 9-192496
  • Patent Document 3 JP-A 6-65012
  • Non-Patent Document 1 Hiroshi IRIE, Shuhei MIURA, Kazuhide KAMIYA and Kazuhito HASHIMOTO, "Chemical Physics Letters", 457 (2008), pp. 202-205
  • an object of the present invention is to provide a copper ion-modified titanium oxide which is capable of exhibiting a good catalytic activity under the irradiation with a visible light when used as a photocatalyst, a process for producing the copper ion-modified titanium oxide, and a photocatalyst containing the copper ion-modified titanium oxide as a main component.
  • the present inventors have found that the above conventional problems can be solved by the following aspects of the present invention. That is, the present invention relates to the following aspects.
  • a copper ion-modified titanium oxide including titanium oxide whose surface is modified with a copper ion, and containing a brookite-type crystal.
  • a process for producing a copper ion-modified titanium oxide including: a hydrolysis step of subjecting a titanium compound capable of producing titanium oxide to hydrolysis in a reaction solution! and
  • a copper ion-modified titanium oxide which is capable of exhibiting a good catalytic activity under the irradiation with a visible light when used as a photocatalyst, a process for producing the copper ion-modified titanium oxide, and a
  • photocatalyst containing the copper ion-modified titanium oxide as a main component photocatalyst containing the copper ion-modified titanium oxide as a main component.
  • FIG. 1 is a view showing an X-ray diffraction pattern of the copper ion-modified titanium oxide obtained in Example 1.
  • the copper ion-modified titanium oxide of the present invention has a crystal structure at least a part of which is composed of a brookite-type crystal.
  • the copper ion- modified titanium oxide may also include hydrous titanium oxide, titanium hydroxide, titanic acid, an amorphous moiety, an anatase-type crystal, a rutile-type crystal, etc., as long as it contains the brookite-type crystal.
  • the presence of the brookite-type crystal in the copper ion-modified titanium oxide may be determined by powder X-ray diffraction using a Cu-Kal ray. More specifically, the presence of the brookite-type crystal is determined by satisfying the condition that in a lattice spacing d (A) as measured in the powder X-ray diffraction, a diffraction line is detected at least in the range of 2.90 ⁇ 0.02 A.
  • the content of the brookite-type crystal in the copper ion-modified titanium oxide can be measured by Rietveld analysis in which the titanium oxide is mixed with 10% by mass of nickel oxide as an internal standard substance.
  • the proportions of the respective crystal phases being present in the titanium oxide may be determined using a Rietveld analytical software in a program " ⁇ ' Pert High Score Plus" available from Panalytical Co., Ltd.
  • the content of the brookite-type crystal in the copper ion-modified titanium oxide is preferably not less than 14% by mass and not more than 60% by mass, and more preferably not less than 14% by mass and not more than 40% by mass.
  • the content of the brookite-type crystal of not less than 14% by mass is preferable because a dispersibility of the titanium oxide sol as well as an absorption of the copper ion into titanium oxide can be enhanced.
  • the copper ion-modified titanium oxide having a brookite-type crystal content of not less than 14% by mass can exhibit an excellent catalyst performance when used as a photocatalyst.
  • the content of the brookite-type crystal is not more than 60% by mass, the copper ion-modified titanium oxide is inhibited from exhibiting an excessively large crystallite size, so that the titanium oxide and the copper ion used for modifying the surface of the titanium oxide can maintain a good interaction therebetween.
  • the crystallite size of the brookite-type crystal is preferably 24 nm or less, more preferably 18 nm or less, still more preferably from 5 to 18 nm, further still more preferably from 5 to 12 nm, and most preferably from 9 to 12 nm.
  • the crystallite size of the brookite-type crystal is 24 nm or less, the interaction between the brookite-type crystal and the copper ion can be suitably improved, and further the resulting photocatalyst can exhibit a high visible light activity owing to occurrence of change in reactivity between the surface of the respective photocatalyst particles and the copper ion.
  • the crystallite size of the crystal can be calculated from the following Scherrer's formula wherein t represents a crystallite size (nm); ⁇ represents a wavelength (A) of X-ray BM represents a half value width of a sample; Bs represents a half value width of a reference (S1O2); and ⁇ represents a diffraction angle.
  • the surface of the titanium oxide is modified with the copper ion.
  • the copper ion include those derived from copper (II) chloride, copper (II) acetate, copper (II) sulfate, copper (II) nitrate, copper (II) fluoride, copper (II) iodide, copper (II) bromide, etc. Among them, from the viewpoints of a good
  • the copper ion derived from copper (II) chloride is preferred.
  • the copper ion is produced by subjecting the above precursor to chemical reactions such as decomposition and oxidation on the titanium oxide, or through physical change of the precursor such as precipitation, etc.
  • the amount of the copper ion used for modifying the titanium oxide is preferably from 0.05 to 0.3% by mass and more preferably from 0.1 to 0.2% by mass in terms of metallic copper (Cu) on the basis of the titanium oxide.
  • the amount of the copper ion used for the modification is 0.05% by mass or more, the resulting photocatalyst can exhibit a good photocatalytic performance.
  • the amount of the copper ion used for the modification is 0.3% by mass or less, the copper ion tends to be hardly aggregated together, so that the resulting photocatalyst can be prevented from undergoing
  • Non-Patent Document 1 The mechanism of the interaction between the copper ion and the rutile-type titanium oxide is described in the above Non-Patent Document 1 as follows, although it is not clearly known yet.
  • the above-mentioned mechanism is also applicable to the titanium oxide containing the brookite-type crystal having a smaller crystallite size according to the present invention. That is, according to the above mechanism, the titanium oxide containing the brookite-type crystal can be imparted with a high visible light-responsive property and further can be promoted in interaction with the copper ion owing to the difference in crystal structure therebetween, and as a result, can exhibit a more excellent photocatalytic activity than that of the conventional titanium oxides.
  • the two kinds of crystals i.e., the anatase-type crystal and the rutile-type crystal which are different in band gap from the brookite-type crystal
  • the two kinds of crystals i.e., the anatase-type crystal and the rutile-type crystal which are different in band gap from the brookite-type crystal
  • the charge separation between the electrons and holes can be promoted, which makes a large contribution to excellent properties of the brookite-type crystal-containing titanium oxide according to the present invention.
  • the process for producing a copper ion-modified titanium oxide according to the present invention includes a hydrolysis step of subjecting a titanium compound capable of producing titanium oxide to hydrolysis in a reaction solution? and a surface modification step of mixing a solution obtained after the hydrolysis with an aqueous solution containing a copper ion to modify a surface of the titanium oxide therewith.
  • an aqueous solution of a titanium compound capable of producing titanium oxide such as, for example, titanium chloride
  • a titanium compound capable of producing titanium oxide such as, for example, titanium chloride
  • the thus produced titanium oxide may have an optional crystal shape by varying conditions of the solution used upon the hydrolysis.
  • titanium oxide particles having a brookite content of from 7 to 60% by mass may be produced.
  • the crystal structure or crystallite size of the titanium oxide has a large influence on a mobility of a carrier produced by irradiation with light as well as on an interaction with the copper ion.
  • the rutile-type titanium oxide tends to be produced when the hydrolysis is carried out at a temperature of 80°C or lower.
  • the anatase-type titanium oxide tends to be produced when the hydrolysis is carried out at a temperature of from 80 to 90°C.
  • the brookite-type titanium oxide tends to be produced when the hydrolysis is carried out at a temperature of 95°C.
  • titanium compound examples include titanium tetrachloride, titanium trichloride, titanium sulfate, titanium tetraethoxide and titanium tetraisopropoxide.
  • titanium tetrachloride preferred are titanium tetrachloride and titanium trichloride.
  • the temperature of the reaction solution used upon the hydrolysis is preferably not lower than 70°C and not higher than a boiling point of the reaction solution.
  • reaction solution is preferably bubbled with oxygen or ozone to well control a crystal structure and crystallite size of the resulting titanium oxide.
  • the temperature used for the surface modification is preferably controlled to the range of from 80 to 95°C and more preferably from 90 to 95°C.
  • the surface modification temperature is controlled to the range of from 80 to 95°C, the surface of the titanium oxide can be modified with the copper ion in an efficient manner.
  • the surface modification with the copper ion may be carried out according to the method described in the above Non-Patent Document 1.
  • a method in which titanium oxide particles and copper chloride are mixed with each other in a suitable medium under heating, and then the resulting reaction mixture is washed with water to recover the aimed product (2) a method in which titanium oxide particles and copper chloride are mixed with each other in a suitable medium under heating, and then the resulting reaction mixture is subjected to evaporation to dryness to recover the aimed product, or the like.
  • the method (l) is preferred because counter anions can be removed from the reaction mixture without heat treatment.
  • the surface of the respective titanium oxide particles is modified with the copper ion.
  • the condition of the presence of the copper ion used for modifying the surface of the titanium oxide is hardly analyzed owing to a trace amount of the copper ion. For this reason, when subjecting the titanium oxide to diffused reflection spectrum analysis using an
  • any absorption band attributed to neither only titanium oxide nor only the copper ion is observed near the range of from 420 to 500 nm, it is deemed that such a case is involved in modification with the copper ion.
  • the properties and quantity of the copper ion may also be determined by ICP analysis.
  • the photocatalyst of the present invention contains the copper ion-modified titanium oxide as a main component.
  • the content of the copper ion-modified titanium oxide in the photocatalyst is 70% by mass or more and preferably 75% by mass or more on the basis of a total amount of the photocatalyst.
  • photocatalyst include amorphous titanium oxide and hydrous titanium oxide.
  • the photocatalyst of the present invention may be used with various shapes. However, the photocatalyst is preferably used in the form of a powder.
  • the photocatalyst of the present invention is capable of exhibiting a photocatalytic performance when irradiated with a light having a wavelength of 420 nm or shorter, but can also exhibit a photocatalytic performance even when irradiated with a light having a wavelength of 420 nm or longer.
  • the photocatalytic performance as used in the present invention may also include other performances such as an antimicrobial property, a
  • deodorizing property an anti-fouling property and environmental purification properties such as atmospheric purification property and water purification property.
  • environmental purification properties such as atmospheric purification property and water purification property.
  • the respective copper ion-modified titanium oxides obtained in the following Examples and Comparative Examples were subjected to XRD measurement to identify a crystal structure thereof and to determine proportions of various crystals being present therein as well as a crystallite size of a brookite-type crystal contained therein.
  • the XRD measurement was carried out using copper as a target and Cu-Kocl ray under the following conditions-
  • the apparatus used in the above XRD measurement was "X' pert PRO” available from Panalytical Co., Ltd.
  • a reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and 60 g of a titanium trichloride aqueous solution (20% by mass solution! density: 1.23 g/mL) were added dropwise into the reaction vessel at a rate of 1 g/min. Thereafter, while bubbling the contents of the reaction vessel with oxygen supplied through an ozone generator, the temperature in the reaction vessel was raised up to 101°C over 30 min, and then maintained at 101°C for 90 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 200 mL of the resulting slurry solution (powder content: 1.5 g) was added 0.5 mL of a copper chloride aqueous solution
  • a reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 95°C and held 10 068223 at the same temperature. Then, 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass; specific gravity: 1.52) were added
  • the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature.
  • the obtained reaction mixture was washed by centrifugal separation to recover a reaction product.
  • the thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a hght-yellow copper ion-modified titanium oxide containing 35% by mass of a brookite-type crystal according to the present invention.
  • a reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass? specific gravity: 1.52) were added dropwise into the reaction vessel at a rate of 1 g/min. Thereafter, the contents of the reaction vessel were heated up to 101°C, and then maintained at 101°C for 120 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4.
  • a reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 70°C and held at the same temperature. Then, 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass; specific gravity: 1.52) were added dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm. The reaction solution in the reaction vessel began becoming whitely turbid immediately after initiation of the dropping, but was maintained as such at its temperature. After completion of the dropping, the reaction solution was further heated to 75°C and maintained at the same temperature for 60 min.
  • Ti content 17.0% by mass
  • specific gravity specific gravity
  • the resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4.
  • the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature.
  • the obtained reaction mixture was washed by centrifugal separation to recover a reaction product.
  • the thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a light-yellow copper ion-modified titanium oxide containing 14% by mass of a brookite-type crystal.
  • a reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 95°C and held at the same temperature. Then, 60 g of a titanium trichloride aqueous solution (20% by mass solution; density: 1.23 g/mL) were added drop wise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm and further bubbling the contents of the reaction vessel with oxygen supplied through an ozone generator.
  • the bubbling with oxygen supplied through the ozone generator was terminated, and the reaction solution was maintained as such at its temperature.
  • the reaction solution was further heated to a temperature near a boiling point thereof and maintained at the same temperature for 60 min.
  • the resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4.
  • Into 150 mL of the resulting slurry solution (powder content ⁇ 1.5 g) was added 0.5 mL of a copper chloride aqueous solution
  • a reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 95°C and held at the same temperature. Then, 60 g of a titanium trichloride aqueous solution (20% by mass solution; density: 1.23 g/mL) were added dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm and further bubbling the contents of the reaction vessel with oxygen supplied through an ozone generator. The resulting reaction solution was maintained at its temperature. After completion of the dropping, the reaction solution was further heated to a temperature near a boiling point thereof and maintained at the same temperature for 60 min.
  • a titanium trichloride aqueous solution (20% by mass solution; density: 1.23 g/mL) were added dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm and further bubbling the contents of the reaction
  • the resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4.
  • the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature.
  • the obtained reaction mixture was washed by centrifugal separation to recover a reaction product.
  • the thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a light-yellow copper ion-modified titanium oxide containing 60% by mass of a brookite-type crystal according to the present invention.
  • a reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 80°C and held at the same temperature. Then, 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass! specific gravity: 1.52) were added dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm. The reaction solution in the reaction vessel began becoming whitely turbid immediately after initiation of the dropping, but was maintained as such at its temperature. After completion of the dropping, the reaction solution was heated to 85°C and maintained at the same temperature for 60 min.
  • Ti content 17.0% by mass! specific gravity: 1.52
  • the resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4.
  • the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature.
  • the obtained reaction mixture was washed by centrifugal separation to recover a reaction product.
  • the thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a copper ion-modified titanium oxide composed of a rutile-type crystal only.
  • a suspension prepared by suspending 1.5 g of a commercially available titanium oxide composed mainly of an anatase-type crystal (tradename
  • a commercially available titanium oxide composed of an anatase-type crystal only (tradename "ST01" available from Ishihara Sangyo Kaisha, Ltd.) was modified with a copper ion in the same manner as in Comparative
  • Example 2 thereby obtaining a copper ion-modified titanium oxide.
  • a glass petri dish having a diameter of 1.5 cm was disposed in a closed-type glass reactor (capacity- 0.5 L), and 0.3 g of the respective titanium oxide particles obtained in the above Examples and Comparative Examples was placed in the petri dish.
  • An inside atmosphere of the reactor was replaced with a mixed gas containing oxygen and nitrogen at a volume ratio of 1-4, and the reactor was charged with 5.2 ⁇ of water (corresponding to a relative humidity of 50% (at 25°C)) and 5.0 mL of 5.1% acetaldehyde (a mixed gas with nitrogen " standard condition ' 25°C, 1 atm) and then sealed, followed by irradiating a visible light from outside of the reactor.
  • the irradiation with a visible light was carried out using a xenon lamp fitted with a filter for cutting an ultraviolet light having a wavelength of 420 nm or less (tradename "Y-44" available from Asahi Techno Glass Co., Ltd.) as a light source.
  • a xenon lamp fitted with a filter for cutting an ultraviolet light having a wavelength of 420 nm or less (tradename "Y-44" available from Asahi Techno Glass Co., Ltd.) as a light source.
  • the rate of reduction in amount of the acetaldehyde as well as the rate of generation of carbon dioxide as an oxidative decomposition product were measured with time by gas chromatography.
  • the true amount of carbon dioxide generated from the acetaldehyde was determined as the value obtained by subtracting the amount of carbon dioxide as measured immediately before the irradiation with a visible light from the amount of carbon dioxide generated as measured after 8 h from initiation of the irradiation with a visible light. The results are shown in Table 1.
  • the amount of carbon dioxide produced using the copper ion-modified titanium oxide containing a brookite-type crystal according to the present invention was from 1.3 to 2.4 times that produced using the copper ion-modified titanium oxide containing no brookite-type crystal. Therefore, it was apparently confirmed that the copper ion-modified titanium oxide according to the present invention was a photocatalyst having a high photocatalytic activity. In the copper ion-modified titanium oxide having a brookite-type crystal content of 40% by mass or less, as the brookite-type crystal content was increased, the photocatalytic activity thereof was enhanced correspondingly.
  • the photocatalytic activity thereof became lowered. That is, when the brookite-type crystal content in the copper ion-modified titanium oxide is not more than 40% by mass, the proportion of the brookite-type crystal particles in the titanium oxide is increased with the increase in the brookite-type crystal content, so that the photocatalytic activity thereof can be improved.
  • the proportion of the brookite-type crystal particles in the titanium oxide is increased with the increase in the brookite-type crystal content, so that the photocatalytic activity thereof can be improved.
  • brookite-type crystal content exceeds 40% by mass, the crystallite size of the brookite-type crystal becomes as large as up to about 20 nm, so that an interaction between the copper ion and the titanium oxide is lessened, resulting in a deteriorated photocatalytic activity of the copper ion-modified titanium oxide.

Abstract

The present invention relates to a copper ion-modified titanium oxide including titanium oxide whose surface is modified with a copper ion, and containing a brookite-type crystal; a process for producing a copper ion-modified titanium oxide, including a hydrolysis step of subjecting a titanium compound capable of producing titanium oxide to hydrolysis in a reaction solution, and a surface modification step of mixing a solution obtained after the hydrolysis with an aqueous solution containing a copper ion to modify a surface of the titanium oxide therewith; and a photocatalyst containing the copper ion-modified titanium oxide in an amount of 70% by mass or more.

Description

DESCRIPTION
COPPER ION-MODIFIED TITANIUM OXIDE AND PROCESS FOR
PRODUCING THE SAME, AND PHOTOCATALYST
TECHNICAL FIELD
[0001]
The present invention relates to a copper ion-modified titanium oxide which is suitable as a photocatalyst capable of exhibiting an activity by irradiation with a visible light and a process for producing the copper ion-modified titanium oxide, and further to a photocatalyst containing the copper ion-modified titanium oxide as a main component.
BACKGROUND ART
[0002]
Titanium oxide is widely known as a photocatalyst, but exhibits no photocatalytic function unless it is used in a place where any ultraviolet rays are present. Therefore, at present, it has been attempted to impart a visible light absorbing property to titanium oxide.
[0003]
One of the attempts for imparting a visible light absorbing property to titanium oxide is a method of doping a copper ion into titanium oxide. Such a composite substance composed of the copper ion and titanium oxide is capable of exhibiting a photocatalytic activity under the irradiation with a visible light (for instance, refer to Patent Document l). However, in the above method, it is not clearly known whether the metal added is present on a surface of titanium oxide or in a bulk portion thereof.
On the other hand, there has been proposed a method of modifying only a surface of titanium oxide with a copper ion for the purpose of enhancing an ultraviolet photoactivity or an antimicrobial property of titanium oxide.
However, in the method, no study has been made on a capability of
decomposing volatile organic compounds under the irradiation with a visible light (for instance, refer to Patent Documents 2 and 3).
[0004]
Aside from the above conventional art, Non-Patent Document 1 has reported that titanium oxide modified with a copper ion is imparted with a visible light absorption band and a multi-electron reduction capability owing to an interfacial charge transfer so as to decompose isopropanol under the irradiation with a visible light. However, in this report, study on application to only rutile-type titanium oxide has been made, and the method is therefore not applicable to anatase-type titanium oxide or brookite-type titanium oxide which is generally considered to have a high activity.
[Prior Documents]
[0005]
Patent Document l: JP-A 9-192496
Patent Document 2- JP-A 6-205977
Patent Document 3: JP-A 6-65012
Non-Patent Document 1- Hiroshi IRIE, Shuhei MIURA, Kazuhide KAMIYA and Kazuhito HASHIMOTO, "Chemical Physics Letters", 457 (2008), pp. 202-205
DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION
[0006]
In view of the above problems encountered in the art, an object of the present invention is to provide a copper ion-modified titanium oxide which is capable of exhibiting a good catalytic activity under the irradiation with a visible light when used as a photocatalyst, a process for producing the copper ion-modified titanium oxide, and a photocatalyst containing the copper ion-modified titanium oxide as a main component. MEANS FOR SOLVING THE PROBLEMS
[0007]
The present inventors have found that the above conventional problems can be solved by the following aspects of the present invention. That is, the present invention relates to the following aspects.
[0008]
[l] A copper ion-modified titanium oxide including titanium oxide whose surface is modified with a copper ion, and containing a brookite-type crystal.
[2] The copper ion-modified titanium oxide as described in the above aspect [l], wherein in a lattice spacing d (A) as measured by powder X-ray diffraction using a Cu-Kal ray, a diffraction line is detected at least in the range of 2.90±0.02 A.
[3] The copper ion-modified titanium oxide as described in the above aspect [l] or [2], wherein a content of the brookite-type crystal in the copper ion-modified titanium oxide is not less than 14% by mass and not more than 60% by mass as measured by Rietveld analysis using 10% by mass of nickel oxide as an internal standard substance.
[4] The copper ion-modified titanium oxide as described in any one of the above aspects [l] to [3], wherein the brookite-type crystal has a crystallite size of 24 nm or less as calculated from the Scherrer's formula.
[5] The copper ion-modified titanium oxide as described in any one of the above aspects [l] to [4], wherein the copper ion is derived from copper (II) chloride.
[6] The copper ion-modified titanium oxide as described in any one of the above aspects [l] to [5], wherein the titanium oxide is modified with the copper ion in an amount of from 0.05 to 0.3% by mass in terms of metallic copper.
[0009]
[7] A process for producing a copper ion-modified titanium oxide, including: a hydrolysis step of subjecting a titanium compound capable of producing titanium oxide to hydrolysis in a reaction solution! and
a surface modification step of mixing a solution obtained after the hydrolysis with an aqueous solution containing a copper ion to modify a surface of the titanium oxide therewith.
[8] The process for producing a copper ion-modified titanium oxide as described in the above aspect [7], wherein the titanium compound is titanium tetrachloride or titanium trichloride.
[9] The process for producing a copper ion-modified titanium oxide as described in the above aspect [7] or [8], wherein a temperature of the reaction solution upon the hydrolysis is not lower than 70°C and not higher than a boiling point of the reaction solution.
[10] The process for producing a copper ion-modified titanium oxide as described in any one of the above aspects [7] to [9], wherein the reaction solution is bubbled with oxygen or ozone upon the hydrolysis,
[ll] The process for producing a copper ion-modified titanium oxide as described in any one of the above aspects [7] to [lO], wherein in the surface modification step, a temperature used for the surface modification is controlled to the range of from 80 to 95°C.
[12] A copper ion-modified titanium oxide produced by the process as described in any one of the above aspects [7] to [ll].
[13] A hotocatalyst including the copper ion-modified titanium oxide as described in any one of the above aspects [l] to [6] and [12] in an amount of 70% by mass or more.
EFFECT OF THE INVENTION [0010]
In accordance with the present invention, there are provided a copper ion-modified titanium oxide which is capable of exhibiting a good catalytic activity under the irradiation with a visible light when used as a photocatalyst, a process for producing the copper ion-modified titanium oxide, and a
photocatalyst containing the copper ion-modified titanium oxide as a main component.
BRIEF DESCRIPTION OF THE DRAWING
[0011]
FIG. 1 is a view showing an X-ray diffraction pattern of the copper ion-modified titanium oxide obtained in Example 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0012]
[Copper Ion -Modified Titanium Oxide]
The copper ion-modified titanium oxide of the present invention has a crystal structure at least a part of which is composed of a brookite-type crystal.
The copper ion- modified titanium oxide may also include hydrous titanium oxide, titanium hydroxide, titanic acid, an amorphous moiety, an anatase-type crystal, a rutile-type crystal, etc., as long as it contains the brookite-type crystal.
[0013]
The presence of the brookite-type crystal in the copper ion-modified titanium oxide may be determined by powder X-ray diffraction using a Cu-Kal ray. More specifically, the presence of the brookite-type crystal is determined by satisfying the condition that in a lattice spacing d (A) as measured in the powder X-ray diffraction, a diffraction line is detected at least in the range of 2.90±0.02 A. [0014]
From the comparison between a peak observed at 2.90 A which is derived from the brookite-type crystal, a peak observed at 2.38 A which is derived from the anatase-type crystal and a peak observed at 3.25 A which is derived from the rutile-type crystal, it may be confirmed whether or not the respective crystal phases are present in the titanium oxide, or relative proportions between the respective crystal phases being present in the titanium oxide can be estimated. However, relative intensities of the three kinds of peaks are not completely consistent with the proportions between the respective crystal phases in the titanium oxide because the presence of the amorphous moiety is ignored in the former measurement. Therefore, the measurement for the contents of the respective crystal phases is preferably carried out by the Rietveld method using an internal standard substance.
[0015]
More specifically, the content of the brookite-type crystal in the copper ion-modified titanium oxide can be measured by Rietveld analysis in which the titanium oxide is mixed with 10% by mass of nickel oxide as an internal standard substance. Thus, the proportions of the respective crystal phases being present in the titanium oxide may be determined using a Rietveld analytical software in a program "Χ' Pert High Score Plus" available from Panalytical Co., Ltd.
[0016]
The content of the brookite-type crystal in the copper ion-modified titanium oxide is preferably not less than 14% by mass and not more than 60% by mass, and more preferably not less than 14% by mass and not more than 40% by mass.
The content of the brookite-type crystal of not less than 14% by mass is preferable because a dispersibility of the titanium oxide sol as well as an absorption of the copper ion into titanium oxide can be enhanced. In addition, the copper ion-modified titanium oxide having a brookite-type crystal content of not less than 14% by mass can exhibit an excellent catalyst performance when used as a photocatalyst. On the other hand, when the content of the brookite-type crystal is not more than 60% by mass, the copper ion-modified titanium oxide is inhibited from exhibiting an excessively large crystallite size, so that the titanium oxide and the copper ion used for modifying the surface of the titanium oxide can maintain a good interaction therebetween.
[0017]
The crystallite size of the brookite-type crystal is preferably 24 nm or less, more preferably 18 nm or less, still more preferably from 5 to 18 nm, further still more preferably from 5 to 12 nm, and most preferably from 9 to 12 nm. When the crystallite size of the brookite-type crystal is 24 nm or less, the interaction between the brookite-type crystal and the copper ion can be suitably improved, and further the resulting photocatalyst can exhibit a high visible light activity owing to occurrence of change in reactivity between the surface of the respective photocatalyst particles and the copper ion.
[0018]
Meanwhile, the crystallite size of the crystal can be calculated from the following Scherrer's formula wherein t represents a crystallite size (nm); λ represents a wavelength (A) of X-ray BM represents a half value width of a sample; Bs represents a half value width of a reference (S1O2); and Θ represents a diffraction angle.
[0019]
[0020]
In the copper ion-modified titanium oxide of the present invention, the surface of the titanium oxide is modified with the copper ion. Examples of the copper ion include those derived from copper (II) chloride, copper (II) acetate, copper (II) sulfate, copper (II) nitrate, copper (II) fluoride, copper (II) iodide, copper (II) bromide, etc. Among them, from the viewpoints of a good
availability and a high productivity, the copper ion derived from copper (II) chloride is preferred.
The copper ion is produced by subjecting the above precursor to chemical reactions such as decomposition and oxidation on the titanium oxide, or through physical change of the precursor such as precipitation, etc.
[0021]
The amount of the copper ion used for modifying the titanium oxide is preferably from 0.05 to 0.3% by mass and more preferably from 0.1 to 0.2% by mass in terms of metallic copper (Cu) on the basis of the titanium oxide.
When the amount of the copper ion used for the modification is 0.05% by mass or more, the resulting photocatalyst can exhibit a good photocatalytic performance. When the amount of the copper ion used for the modification is 0.3% by mass or less, the copper ion tends to be hardly aggregated together, so that the resulting photocatalyst can be prevented from undergoing
deterioration in its photocatalytic performance.
[0022]
The mechanism of the interaction between the copper ion and the rutile-type titanium oxide is described in the above Non-Patent Document 1 as follows, although it is not clearly known yet.
That is, it is described that when irradiated with light, electrons are directly transferred from a valence band of the rutile-type titanium oxide to the copper ion, so that the rutile-type titanium oxide modified with the copper ion can exhibit a photocatalytic activity even under the irradiation with a visible light.
[0023] It is considered that the above-mentioned mechanism is also applicable to the titanium oxide containing the brookite-type crystal having a smaller crystallite size according to the present invention. That is, according to the above mechanism, the titanium oxide containing the brookite-type crystal can be imparted with a high visible light-responsive property and further can be promoted in interaction with the copper ion owing to the difference in crystal structure therebetween, and as a result, can exhibit a more excellent photocatalytic activity than that of the conventional titanium oxides.
In particular, in the case where the two kinds of crystals, i.e., the anatase-type crystal and the rutile-type crystal which are different in band gap from the brookite-type crystal, are also included in the titanium oxide, there is a possibility that electrons and holes produced by the irradiation with light undergo a promoted charge separation from each other, resulting in an enhanced photocatalytic activity thereof. Thus, it is suggested that when the different kinds of titanium oxides which are different in band gap from each other are included together, the charge separation between the electrons and holes can be promoted, which makes a large contribution to excellent properties of the brookite-type crystal-containing titanium oxide according to the present invention.
[0024]
[Process for Producing Copper Ion-Modified Titanium Oxide]
The process for producing a copper ion-modified titanium oxide according to the present invention, includes a hydrolysis step of subjecting a titanium compound capable of producing titanium oxide to hydrolysis in a reaction solution? and a surface modification step of mixing a solution obtained after the hydrolysis with an aqueous solution containing a copper ion to modify a surface of the titanium oxide therewith.
In the followings, the respective steps are described.
[0025] (Hydrolysis Step)
In the hydrolysis step, an aqueous solution of a titanium compound capable of producing titanium oxide such as, for example, titanium chloride, is subjected to hydrolysis to obtain a slurry of titanium oxide. The thus produced titanium oxide may have an optional crystal shape by varying conditions of the solution used upon the hydrolysis. For example, upon the hydrolysis, titanium oxide particles having a brookite content of from 7 to 60% by mass may be produced. In addition, there may be selectively produced any of different kinds of titanium oxides which are different in crystallite size from each other, for example, over the range of from 9 to 24 nm, which is
determined from a half value width of X-ray diffraction peak and the
Scherrer's formula. The crystal structure or crystallite size of the titanium oxide has a large influence on a mobility of a carrier produced by irradiation with light as well as on an interaction with the copper ion.
More specifically, the rutile-type titanium oxide tends to be produced when the hydrolysis is carried out at a temperature of 80°C or lower. The anatase-type titanium oxide tends to be produced when the hydrolysis is carried out at a temperature of from 80 to 90°C. The brookite-type titanium oxide tends to be produced when the hydrolysis is carried out at a temperature of 95°C. By adding hydrochloric acid to the solution upon the hydrolysis, the content of the anatase-type crystal in the resulting titanium oxide may be reduced, whereas the contents of the brookite-type and rutile-type crystals therein may be increased, so that the titanium oxide containing the respective crystal phases at desired proportions may be selectively produced.
[0026]
Examples of the titanium compound include titanium tetrachloride, titanium trichloride, titanium sulfate, titanium tetraethoxide and titanium tetraisopropoxide. Among these titanium compounds, preferred are titanium tetrachloride and titanium trichloride. [0027]
The temperature of the reaction solution used upon the hydrolysis is preferably not lower than 70°C and not higher than a boiling point of the reaction solution. When controlling the temperature of the reaction solution upon the hydrolysis to the above-specified range, it is possible to synthesize a titanium oxide sol in an efficient manner.
[0028]
In addition, upon the hydrolysis, the reaction solution is preferably bubbled with oxygen or ozone to well control a crystal structure and crystallite size of the resulting titanium oxide.
[0029]
(Surface Modification Step)
In the surface modification step, the temperature used for the surface modification is preferably controlled to the range of from 80 to 95°C and more preferably from 90 to 95°C. When the surface modification temperature is controlled to the range of from 80 to 95°C, the surface of the titanium oxide can be modified with the copper ion in an efficient manner.
[0030]
The surface modification with the copper ion may be carried out according to the method described in the above Non-Patent Document 1. For example, there may be used (l) a method in which titanium oxide particles and copper chloride are mixed with each other in a suitable medium under heating, and then the resulting reaction mixture is washed with water to recover the aimed product, (2) a method in which titanium oxide particles and copper chloride are mixed with each other in a suitable medium under heating, and then the resulting reaction mixture is subjected to evaporation to dryness to recover the aimed product, or the like. Among these methods, the method (l) is preferred because counter anions can be removed from the reaction mixture without heat treatment. [0031]
In the copper ion-modified titanium oxide produced by the process of the present invention, the surface of the respective titanium oxide particles is modified with the copper ion. The condition of the presence of the copper ion used for modifying the surface of the titanium oxide is hardly analyzed owing to a trace amount of the copper ion. For this reason, when subjecting the titanium oxide to diffused reflection spectrum analysis using an
integrating-sphere spectrophotometer available from Shimadzu Seisakusho Corp., if any absorption band attributed to neither only titanium oxide nor only the copper ion is observed near the range of from 420 to 500 nm, it is deemed that such a case is involved in modification with the copper ion. The properties and quantity of the copper ion may also be determined by ICP analysis.
[0032]
[Photocatalyst]
The photocatalyst of the present invention contains the copper ion-modified titanium oxide as a main component. The term "main
component" as used herein means that the content of the copper ion-modified titanium oxide in the photocatalyst is 70% by mass or more and preferably 75% by mass or more on the basis of a total amount of the photocatalyst.
Examples of the other components which may be contained in the
photocatalyst include amorphous titanium oxide and hydrous titanium oxide.
The photocatalyst of the present invention may be used with various shapes. However, the photocatalyst is preferably used in the form of a powder.
[0033]
The photocatalyst of the present invention is capable of exhibiting a photocatalytic performance when irradiated with a light having a wavelength of 420 nm or shorter, but can also exhibit a photocatalytic performance even when irradiated with a light having a wavelength of 420 nm or longer.
The photocatalytic performance as used in the present invention may also include other performances such as an antimicrobial property, a
deodorizing property, an anti-fouling property and environmental purification properties such as atmospheric purification property and water purification property. Specific performances of the photocatalyst are illustrated below, although not particularly limited thereto.
In particular, when any substances having an adverse influence on ambient environments, for example, organic compounds such as aldehydes, are present together with the photocatalyst particles in the reaction system, reduction in concentration of the organic compounds as well as increase in concentration of carbon dioxide as a decomposed product of the organic compounds can be more remarkably recognized under the irradiation with light as compared to the case where the reaction system is present in a dark place.
EXAMPLES
[0034]
The present invention will be described in more detail below with reference to the following examples. However, these examples are only illustrative and not intended to limit the invention thereto.
Incidentally, the respective copper ion-modified titanium oxides obtained in the following Examples and Comparative Examples were subjected to XRD measurement to identify a crystal structure thereof and to determine proportions of various crystals being present therein as well as a crystallite size of a brookite-type crystal contained therein. The XRD measurement was carried out using copper as a target and Cu-Kocl ray under the following conditions-
Tube voltage : 45 kV> * tube current- 40 mAl measuring range : 2Θ = 20 to 80°; sampling width: 0.0167°; scanning speed: Ι. /min.
The apparatus used in the above XRD measurement was "X' pert PRO" available from Panalytical Co., Ltd.
[0035]
EXAMPLE 1
A reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and 60 g of a titanium trichloride aqueous solution (20% by mass solution! density: 1.23 g/mL) were added dropwise into the reaction vessel at a rate of 1 g/min. Thereafter, while bubbling the contents of the reaction vessel with oxygen supplied through an ozone generator, the temperature in the reaction vessel was raised up to 101°C over 30 min, and then maintained at 101°C for 90 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 200 mL of the resulting slurry solution (powder content: 1.5 g) was added 0.5 mL of a copper chloride aqueous solution
(corresponding to 0.1% by mass in terms of copper on the basis of TiO2). Next, the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature. The obtained reaction mixture was washed by centrifugal separation to recover a reaction product. The thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a light-yellow copper ion-modified titanium oxide containing 40% by mass of a brookite-type crystal according to the present invention.
Meanwhile, the X-ray diffraction patterns of the thus obtained copper ion-modified titanium oxide is shown in FIG. 1.
[0036]
EXAMPLE 2
A reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 95°C and held 10 068223 at the same temperature. Then, 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass; specific gravity: 1.52) were added
dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm. The reaction solution in the reaction vessel began becoming whitely turbid immediately after initiation of the dropping, but was maintained as such at its temperature. After completion of the dropping, the reaction solution was further heated to a temperature near a boiling point thereof and maintained at that temperature for 60 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 100 mL of the resulting slurry solution (powder content: 1.5 g) was added 0.5 mL of a copper chloride aqueous solution (corresponding to 0.1% by mass in terms of copper on the basis of T1O2). Next, the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature. The obtained reaction mixture was washed by centrifugal separation to recover a reaction product. The thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a hght-yellow copper ion-modified titanium oxide containing 35% by mass of a brookite-type crystal according to the present invention.
[0037]
EXAMPLE 3
A reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass? specific gravity: 1.52) were added dropwise into the reaction vessel at a rate of 1 g/min. Thereafter, the contents of the reaction vessel were heated up to 101°C, and then maintained at 101°C for 120 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 200 mL of the resulting slurry solution (powder content: 1.5 g) was added 0.5 mL of a copper chloride aqueous solution (corresponding to 0.1% by mass in terms of copper on the basis of T1O2). Next, the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature. The obtained reaction mixture was washed by centrifugal separation to recover a reaction product. The thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a light-yellow copper ion-modified titanium oxide containing 24% by mass of a brookite-type crystal according to the present invention.
[0038]
EXAMPLE 4
A reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 70°C and held at the same temperature. Then, 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass; specific gravity: 1.52) were added dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm. The reaction solution in the reaction vessel began becoming whitely turbid immediately after initiation of the dropping, but was maintained as such at its temperature. After completion of the dropping, the reaction solution was further heated to 75°C and maintained at the same temperature for 60 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 100 mL of the resulting slurry solution (powder content: 1.5 g) was added 0.5 mL of a copper chloride aqueous solution (corresponding to 0.1% by mass in terms of copper on the basis of T1O2). Next, the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature. The obtained reaction mixture was washed by centrifugal separation to recover a reaction product. The thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a light-yellow copper ion-modified titanium oxide containing 14% by mass of a brookite-type crystal.
[0039]
EXAMPLE 5
A reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 95°C and held at the same temperature. Then, 60 g of a titanium trichloride aqueous solution (20% by mass solution; density: 1.23 g/mL) were added drop wise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm and further bubbling the contents of the reaction vessel with oxygen supplied through an ozone generator.
Thereafter, the bubbling with oxygen supplied through the ozone generator was terminated, and the reaction solution was maintained as such at its temperature. After completion of the dropping, the reaction solution was further heated to a temperature near a boiling point thereof and maintained at the same temperature for 60 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 150 mL of the resulting slurry solution (powder content^ 1.5 g) was added 0.5 mL of a copper chloride aqueous solution
(corresponding to 0.1% by mass in terms of copper on the basis of T1O2). Next, the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature. The obtained reaction mixture was washed by centrifugal separation to recover a reaction product. The thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a light-yellow copper ion-modified titanium oxide containing 54% by mass of a brookite-type crystal according to the present invention.
[0040]
EXAMPLE 6
A reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 95°C and held at the same temperature. Then, 60 g of a titanium trichloride aqueous solution (20% by mass solution; density: 1.23 g/mL) were added dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm and further bubbling the contents of the reaction vessel with oxygen supplied through an ozone generator. The resulting reaction solution was maintained at its temperature. After completion of the dropping, the reaction solution was further heated to a temperature near a boiling point thereof and maintained at the same temperature for 60 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 150 mL of the resulting slurry solution (powder content: 1.5 g) was added 0.5 mL of a copper chloride aqueous solution (corresponding to 0.1% by mass in terms of copper on the basis of T1O2). Next, the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature. The obtained reaction mixture was washed by centrifugal separation to recover a reaction product. The thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a light-yellow copper ion-modified titanium oxide containing 60% by mass of a brookite-type crystal according to the present invention.
[0041]
COMPARATIVE EXAMPLE 1
A reaction vessel equipped with a reflux condenser was charged with 690 mL of distilled water, and the distilled water was heated to 80°C and held at the same temperature. Then, 60 g of a titanium tetrachloride aqueous solution (Ti content: 17.0% by mass! specific gravity: 1.52) were added dropwise into the reaction vessel at a rate of 1 g/min while continuously stirring the contents of the reaction vessel at a rate of 300 rpm. The reaction solution in the reaction vessel began becoming whitely turbid immediately after initiation of the dropping, but was maintained as such at its temperature. After completion of the dropping, the reaction solution was heated to 85°C and maintained at the same temperature for 60 min. The resulting sol was subjected to dechlorination treatment using an electrodialysis device until a pH value of the sol reached 4. Into 100 mL of the resulting slurry solution (powder content^ 1.5 g) was added 0.5 mL of a copper chloride aqueous solution (corresponding to 0.1% by mass in terms of copper on the basis of T1O2). Next, the resulting mixture was heat-treated while stirring at 90°C for 1 h, and then allowed to stand for cooling it to room temperature. The obtained reaction mixture was washed by centrifugal separation to recover a reaction product. The thus recovered reaction product was dried at 120°C for 24 h and then pulverized using an agate mortar, thereby obtaining a copper ion-modified titanium oxide composed of a rutile-type crystal only.
[0042]
COMPARATIVE EXAMPLE 2
A suspension prepared by suspending 1.5 g of a commercially available titanium oxide composed mainly of an anatase-type crystal (tradename
"SUPERTITANIA (registered trademark) F6" available from Showa Denko K.K.) in 200 mL of ion-exchanged water was treated with copper chloride in the same manner as in Example 1, thereby obtaining a copper ion-modified titanium oxide.
[0043]
COMPARATIVE EXAMPLE 3
A commercially available titanium oxide composed of an anatase-type crystal only (tradename "ST01" available from Ishihara Sangyo Kaisha, Ltd.) was modified with a copper ion in the same manner as in Comparative
Example 2, thereby obtaining a copper ion-modified titanium oxide.
[0044] (Measurement of Amount of Carbon Dioxide Generated)
A glass petri dish having a diameter of 1.5 cm was disposed in a closed-type glass reactor (capacity- 0.5 L), and 0.3 g of the respective titanium oxide particles obtained in the above Examples and Comparative Examples was placed in the petri dish. An inside atmosphere of the reactor was replaced with a mixed gas containing oxygen and nitrogen at a volume ratio of 1-4, and the reactor was charged with 5.2 μΐι of water (corresponding to a relative humidity of 50% (at 25°C)) and 5.0 mL of 5.1% acetaldehyde (a mixed gas with nitrogen" standard condition' 25°C, 1 atm) and then sealed, followed by irradiating a visible light from outside of the reactor. The irradiation with a visible light was carried out using a xenon lamp fitted with a filter for cutting an ultraviolet light having a wavelength of 420 nm or less (tradename "Y-44" available from Asahi Techno Glass Co., Ltd.) as a light source. The rate of reduction in amount of the acetaldehyde as well as the rate of generation of carbon dioxide as an oxidative decomposition product were measured with time by gas chromatography.
The true amount of carbon dioxide generated from the acetaldehyde was determined as the value obtained by subtracting the amount of carbon dioxide as measured immediately before the irradiation with a visible light from the amount of carbon dioxide generated as measured after 8 h from initiation of the irradiation with a visible light. The results are shown in Table 1.
[0045]
TABLE 1
Note * A: Anatase," R- Rutile! B: Brookite; Am: Amorphous
[0046]
From the above results, since the amount of carbon dioxide produced using the copper ion-modified titanium oxide containing a brookite-type crystal according to the present invention was from 1.3 to 2.4 times that produced using the copper ion-modified titanium oxide containing no brookite-type crystal. Therefore, it was apparently confirmed that the copper ion-modified titanium oxide according to the present invention was a photocatalyst having a high photocatalytic activity. In the copper ion-modified titanium oxide having a brookite-type crystal content of 40% by mass or less, as the brookite-type crystal content was increased, the photocatalytic activity thereof was enhanced correspondingly. However, once the brookite-type crystal content in the copper ion-modified titanium oxide exceeded 40% by mass, the photocatalytic activity thereof became lowered. That is, when the brookite-type crystal content in the copper ion-modified titanium oxide is not more than 40% by mass, the proportion of the brookite-type crystal particles in the titanium oxide is increased with the increase in the brookite-type crystal content, so that the photocatalytic activity thereof can be improved. However, when the
brookite-type crystal content exceeds 40% by mass, the crystallite size of the brookite-type crystal becomes as large as up to about 20 nm, so that an interaction between the copper ion and the titanium oxide is lessened, resulting in a deteriorated photocatalytic activity of the copper ion-modified titanium oxide.

Claims

1. A copper ion-modified titanium oxide comprising titanium oxide whose surface is modified with a copper ion, and containing a brookite-type crystal.
2. The copper ion-modified titanium oxide according to claim 1, wherein in a lattice spacing d (A) as measured by powder X-ray diffraction using a Cu-Kal ray, a diffraction line is detected at least in the range of 2.90±0.02 A.
3. The copper ion-modified titanium oxide according to claim 1, wherein a content of the brookite-type crystal in the copper ion-modified titanium oxide is not less than 14% by mass and not more than 60% by mass as measured by Rietveld analysis using 10% by mass of nickel oxide as an internal standard substance.
4. The copper ion-modified titanium oxide according to claim 1, wherein the brookite-type crystal has a crystallite size of 24 nm or less as calculated from the Scherrer's formula.
5. The copper ion- modified titanium oxide according to claim 1, wherein the copper ion is derived from copper (II) chloride.
6. The copper ion-modified titanium oxide according to claim 1, wherein the titanium oxide is modified with the copper ion in an amount of from 0.05 to 0.3% by mass in terms of metallic copper.
7. A process for producing a copper ion-modified titanium oxide, comprising- a hydrolysis step of subjecting a titanium compound capable of producing titanium oxide to hydrolysis in a reaction solution; and
a surface modification step of mixing a solution obtained after the hydrolysis with an aqueous solution containing a copper ion to modify a surface of the titanium oxide therewith.
8. The process for producing a copper ion-modified titanium oxide according to claim 7, wherein the titanium compound is titanium tetrachloride or titanium trichloride.
9. The process for producing a copper ion-modified titanium oxide according to claim 7, wherein a temperature of the reaction solution upon the hydrolysis is not lower than 70°C and not higher than a boiling point of the reaction solution.
10. The process for producing a copper ion-modified titanium oxide according to claim 7, wherein the reaction solution is bubbled with oxygen or ozone upon the hydrolysis.
11. The process for producing a copper ion-modified titanium oxide according to claim 7, wherein in the surface modification step, a temperature used for the surface modification is controlled to the range of from 80 to 95°C.
12. A copper ion-modified titanium oxide produced by the process as defined in claim 7.
13. A photocatalyst comprising the copper ion-modified titanium oxide as defined in claim 1 or 12 in an amount of 70% by mass or more.
EP10807495A 2009-10-08 2010-10-08 Copper ion-modified titanium oxide and process for producing the same, and photocatalyst Withdrawn EP2485838A2 (en)

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