Classifications

• • 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
  • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
  • C01G23/0536—Producing by wet processes, e.g. hydrolysing titanium salts by hydrolysing chloride-containing salts
  • C01G23/0538—Producing by wet processes, e.g. hydrolysing titanium salts by hydrolysing chloride-containing salts in the presence of seeds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D9/0018—Evaporation of components of the mixture to be separated
  • B01D9/0031—Evaporation of components of the mixture to be separated by heating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D9/0036—Crystallisation on to a bed of product crystals; Seeding
• • B01J35/39—
• • 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
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20707—Titanium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/80—Type of catalytic reaction
  • B01D2255/802—Photocatalytic
• • 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
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area

Definitions

• Titanium dioxide product a process for production thereof, and use thereof as a photocatalyst
• the present invention relates to a process for the production of a titanium dioxide product, a product prepared by using the process, the use, as a photocatalyst, of the titanium dioxide product manufactured by using the process, a process for the production of a photocatalyst, as well as a photocatalyst, which comprises titanium dioxide prepared by using the process of the invention.
• the photocatalytic TiO 2 is a very interesting raw material for practical catalyst systems.
• TiO 2 can exist in three different crystal forms. Rutile is the stable form at higher temperatures. Anatase is the predominant form at lower temperatures. At lower temperatures, also the brookite form may exist, which is usually found among minerals showing an ortrhombic crystal form. Both rutile and anatase belong to a tetragonal crystal system. For example, TiO 2 , which is manufactured for the production of paints, is almost exclusively of the rutile form. It is commonly understood that the anatase form of TiO 2 is photocatalytically more active than the other crystal forms. Also, a good photocatalytic activity has been obtained with a mixture of anatase and rutile.
• the factors affecting the photocatalytic reaction include, among others, the specific surface of catalyst particles, porosity, and water adsorbed onto surfaces, as well as surface hydroxyl groups.
• Photocatalytically it is advantageous if the crystal size of titanium dioxide is small and its specific surface is large. These require- ments are fulfilled more often for anatase than for rutile, since anatase in known to be the predominant form at lower temperatures, where the crystal size is smaller.
• anatase absorbs water and hydroxyl groups to its surface to a higher extent than rutile. As it is well known, the preparation of mixtures of anatase and rutile is more easy than pure rutile.
• titanium dioxide in anatase form in the presence of so called rutilizing chemicals, such as, for example, zinc, results, even at lower temperatures, in the generation of a mixture of anatase and rutile.
• rutilizing chemicals such as, for example, zinc
• the marketed photocatalytic titanium dioxides are of anatase form or of a mixture of rutile and anatase, and are active within the UV-region, so that their activation requires, as a light source, UV bulb or sunlight, of which only 3-5% of the radiation reaching the earth can be exploited.
• EP 1 095 908 describes titanium dioxide, which has been characterized by determining, among others, spin concentration by employing an ESR spectrum (electron spin-resonance spectrum) and which is intended for use as a photocatalyst mainly within the visible region of light.
• ESR spectrum electron spin-resonance spectrum
• US-Patent 6 001 326 describes a process for producing monodisperse and crystalline titanium dioxide (TiO 2 ), wherein, according to the patent, a preferred titanyl chloride solution is produced, which makes possible the spontaneous precipitation of titanium dioxide out of the solution and thus also the control of the production of rutile and anatase form, among others, by the temperature and the length of precipitation.
• the process comprises of an initial preparation of a solution of 1.5 M titanium oxychloride, which is then diluted with water to 0.2-1.2 M, after which the precipitation of titanium dioxide out of solution is left to proceed spontaneously, without the addition of nucleating crystals, for example, at 15-70°C to obtain the rutile form, or at 70-155°C to enrich the anatase form.
• that patent refers generally to the use of titanium dioxide, among others, as a photocatalyst or pigment, but there is no mention of any photocatalytic activity possessed by the products prepared by the described process.
• rutile is produced in aqueous solution of titanium tetrachloride at any concentration at a temperature below 50°C, and predominantly anatase is produced at temperatures exceeding 80°C irrespective of the use of nucleating crystals.
• the hydrolysis reactions described by these authors are slow.
• titanium oxychloride solu- tion which was obtained by hydrolyzing titanium tetrachloride in an aqueous solu- tion (0.28 mol/l TiCI 4 corresponds to 22.4 g/l TiO 2 ) at a temperature of 95°C, during their precipitation with rutile nuclei, mostly anatase and only 35.5% rutile.
• nanorutile can be used, for example, as a UV absorbing agent in cosmetic products, pigments and plastics.
• EP 0 505 022 describes a process, which produces a titanium dioxide which is preferred for use in pigments.
• titanium dioxide crystal nuclei are added to an aqueous solution of titanic halide and the precipitation is performed in a closed vessel under pressure at a temperature of 150-300°C.
• the mixture is subjected to ultrasonic treatment during heating in order to improve pigmentary properties.
• rutile or anatase can be employed as crystal nuclei according to the desired form to be obtained.
• high temperature and pressure are preferred for the formation of pigmentary titanium dioxide particles.
• Catalysts within the visible region of light have been prepared by doping anatase with nitrogen or transition metals. There is, however, still need for efficient catalysts within the visible region of light suitable for industrial production. Furthermore, there is a need for a photocatalyst having a better performance, particularly for indoor use and for public and industrial spaces where fluorescent illumination is used.
• the object of the present invention is to provide a photocatalyst with excellent performance, which operates within the UV region and is preferably efficient also within the visible region of light.
• an object of the present invention is to provide a process for the preparation of titanium dioxide product, which is very useful as a photocatalyst, wherein easily obtainable and low-cost starting materials and simple process steps can be used. Further, there is provided a titanium dioxide product prepared by using this process.
• Figure 1 shows the equipment used for assaying the photoactivity in the context of the invention.
• Figure 2 shows excitation spectra of a fluorescent bulb (light output ratio, near-UV: 0.72 W/m 2 , VIS: 92 W/m 2 ) within the UV region and visible region of light (VIS), (shown as a continuous line in the plot), respectively, and the spectrum of a xenon bulb (light output ratio: near UV: 1.24 W/m 2 , VIS: 1080 W/m 2 ) cut off by using a 385 nm filter (shown as a dotted line in the plot).
• a fluorescent bulb light output ratio, near-UV: 0.72 W/m 2 , VIS: 92 W/m 2
• VIS visible region of light
• hydrated titanium dioxide TiO 2 xH 2 O
• TiO 2 xH 2 O hydrated titanium dioxide
• the process is characterized by the addition of the nucleating crystals to an aqueous solution of titanium oxychloride, having a content of more than 90 g TiO 2 in one litre of solution, calculated as titanium dioxide, and by performing the precipitation step at a temperature below the boiling point of the solution and at a normal pressure.
• titanium dioxide For the hydrated titanium dioxide, the common name titanium dioxide is also used, as usually known in the art.
• ambient pressure i.e., the precipitation step is not performed under pressure.
• the temperature below the boiling point can be varied without substantially affecting the crystal form of the precipitating product. It was found that, under these conditions, the addition of nucleating crystals is sufficient to drive the crystal form of the precipitating product primarily towards rutile. Even also in the presence of sulphate ions, surprisingly because sulphate is known to drive precipitation towards the anatase form.
• the aqueous solution of titanium oxychloride used for the precipitation of the invention can be prepared by any method known in the art, for example, from a commercial titanium tetrachloride and water.
• the starting materials, such as titanium tetrachloride, can be purified free of possible contaminants as needed.
• the process of the invention employs titanium oxychloride solutions with contents of over 90 g, such as 91 g, of TiO 2 in one litre of solution, calculated as titanium dioxide.
• the content of the aqueous solution of titanium oxychloride to be precipitated is 95-300 g of TiO 2 /l, preferably 100- 250 g TiO 2 /l, more preferably 150-230 g of TiO 2 /l.
• an aqueous solution of titanium oxychloride with a TiO 2 strength of 200 g /I would not precipitate hydrated titanium dioxide within a reasonable time.
• the solution of titanium oxychloride formed in the instant invention does not need further dilution with water in the precipitation step, whereby the water economy of the processes is improved.
• particulate titanium dioxide is added as crystal nuclei to solution of titanium dioxide, whereby, due to this addition, the crystal form of the precipitating product is driven under the conditions of the invention to a photocatalytically preferred direction.
• the amount of added crystal nuclei can also be varied in order to adjust the photoactivity of the product considering the various needs in end use applications.
• titanium dioxide particles can be added for example at 0.5-10% by weight, preferably at 1-7% by weight, more preferably at 1.5-5% by weight, such as at 2-5% by weight based on the calculated total titanium content of the titanium oxychloride solution expressed as TiO 2) depending on the desired photocatalytic activity for the finished product.
• the particles are added as a suspension, for example, an aqueous suspension, to the solution to be precipitated.
• the content of the suspension with respect to TiO 2 may be for example 5-100 g/l, preferably 10-80 g/l, more preferably 10-50 g/l, such as 15-40 g/l.
• the average crystal size (the average diameter) of the added nuclei is preferably in the range of 1-15 nm, for example 5-15 nm, as measured for example by X-ray diffraction method.
• the nucleating crystals used in the precipitation may be for example in rutile form or in anatase form and these may be prepared by using methods de- scribed in the literature.
• the rutile nuclei can be prepared, for example, by peptiz- ing a sodium titanate solution with hydrochloric acid, and anatase nuclei by hydro- lyzing a TiOSO 4 solution (Barksdale J., Titanium, its occurrence, chemistry, and technology, The Ronald Press Company, New York, 1949, p. 160 and p. 253).
• TiOSO 4 solution Balidation of TiOSO 4 solution
• crystal nuclei in excess of 20% in rutile are used.
• the temperature of the precipitated solution during the entire precipitation step is below the boiling point of the solution, preferably between 50-100°C, more preferably between 60 and below 100°C, still more preferably 70-98°C.
• the precipitation yield per unit time can be enhanced.
• the treatability of the titanium oxychloride solution with respect to the evaporating chloride fumes is enhanced.
• the precipitation step is carried out in the temperature range of 89-95°C.
• the length of precipitation depends on the concentration used in the aqueous solution, on the precipitation temperature and on the amount of added crystal nuclei. As a preferred example, 1-24 h, preferably 2-10 h, for example 2- 5 h, should be mentioned.
• the acidic precipitate obtained from the precipitation step is separated from the solution, whereby the precipitated product is typically filtered off and washed in a manner known in the art. Thus, washing allows the minimization of residual chlorides and cations in the product.
• the precipitated product which after isolation is in the form of hydrated titanium dioxide, is further neutralized to pH 6-10, preferably pH 7-9, more preferably pH 7-8.
• the neutralization is performed by using a base, such as sodium hydroxide or ammonia.
• the neutralization has again an advantageous influence on the catalytic properties of the final product, so as it may allow the enhancement of CO 2 conversion, if needed, and/or diminution of the percentage of the intermediates formed during the decomposition.
• the isolated and optionally neutralized product is optionally dried.
• the drying can be performed at a temperature that can vary between the ambient temperature and 500°C, preferably at 100-500°C, more preferably at 100-300°C, still more preferably at 100-250°C.
• the length of drying can be 0.5-5 h, for example 1-3 h.
• the product prepared by using the process is calcined in a manner known in the art by employing for example an oven, because of the unexpected finding that also calcination has further advantageous effects on the properties of the product, among others, on the crystal size and/or the crystal structure.
• an especially preferred photocatalytic activity is obtained for the precipitated product by calcining the product and performing the calcinations at a lower temperature, which can vary between the ambient temperature and a temperature below 700°C, preferably between 100-500°C, more preferably between 150-400°C, for example 150-300°C.
• the length of calcinations can be 0.5-5 h, preferably 1-3 h.
• the calcination step like the precipitation step, is also not performed under pressurized conditions but under normal pressure.
• the precipitated and optionally neutralized product may then be subjected separately to a drying and/or calcination step or these are employed as a one and the same step.
• a drying and/or calcination step or these are employed as a one and the same step.
• the drying and calcination is a one and the same step.
• the precipitated titanium dioxide product containing water of crystallization gives off water.
• the crystal size of the product of the invention can be varied within the limits of the process.
• the crystal size can be grown, among others, by using a calcination step.
• the average diameter of the precipitated crystals may vary in a range not exceeding 50 nm, for example, 1-50 nm, preferably 5-30 nm, more preferably 5-20 nm, for example 5-15 nm.
• the crystals may also agglomerate and they can be subjected to grinding as needed to obtain the desired particle size.
• the determination of the size can be performed, for example, by X-ray diffraction method.
• a photocatalytically active titanium dioxide product specific surface of which can vary, for example, in the range of 10-500 m 2 /g, preferably 10-300 m 2 /g, more preferably 15-200 m 2 /g, such as 15-100 m 2 /g, depending on, among others, the precipitation conditions, the calcination temperature, and/or the addition of sulphate.
• the specific surface of the product of the invention can be determined, for example, by means of nitro- gen absorption using the known BET technique.
• the process of the invention it is possible to produce a product having a photocatalytically very active crystal structure, and, furthermore, the process conditions can be varied in order to modify the photocatalytic properties of the product precipitated within the limits of the invention, for example, to obtain a product which has an efficient photocatalytic action within the UV region and which is also a substantially active photocatalyst within the visible region of light.
• the invention further provides a titanium dioxide product prepared by using the process, which has an excellent porous structure with a photocatalytic activity.
• the prepared TiO 2 product has a structure with a substan- tially better activity within the visible region of light than that prepared by processes known in the prior art.
• a titanium dioxide product wherein the crystal form is primarily rutile, preferably over 70%, more preferably over 80%, yet more preferably over 90%, in rutile.
• the specific surface of the precipitated titanium dioxide product is grown by adding sulphate either as a sulphate salt (as a solution or as a solid) or as sulphuric acid (as a solution) to the titanium oxychloride solution to be precipitated.
• Sulphate can be added for example at 1-5 % by weight, preferably at 1-3% by weight. The addition of sulphate was found to retard precipitation, like lowering the precipitation temperature. At the same time, the specific surface of the product grew.
• the crystals are precipitated at a temperature below the boiling point of the solution and at a normal pressure, and the hydrated titanium dioxide formed after the isolation, such as filtration and washing, as well as an optional neutralization, is preferably calcined as described above, whereby the formation of crystals can be controlled in two steps.
• the calcination is performed at temperatures mentioned above, preferably below a tem- perature of 400°C, such as 200-300°C.
• the product of the invention can convert harmful gases, for example formaldehyde, acetaldehyde and/or toluene, into carbon dioxide.
• harmful gases for example formaldehyde, acetaldehyde and/or toluene
• carbon dioxide Preferably, by using a measurement time of 1 hour and 15 minutes and a xenon bulb as a light source and a light filter at 385 nm (corresponding to daylight) in a measuring arrangement of Figure 1 , described in the Examples section, the conversion into carbon dioxide can be typically over 70%, for example 70-90%, preferably up to 100%.
• the invention provides the use of the titanium dioxide product produced according to the invention as a photocatalyst, preferably as a photocatalyst at least within the UV region, more preferably within the UV region and the visible region of light.
• the product produced according to the invention can be used for the photocatalytic purification of air and water, preferably for the purification of indoor air, such as indoor spaces open to public or indoor spaces in private surroundings, to remove harmful gases, for example formaldehyde, acet- aldehyde, or toluene in buildings and cars.
• indoor air such as indoor spaces open to public or indoor spaces in private surroundings
• harmful gases for example formaldehyde, acet- aldehyde, or toluene in buildings and cars.
• the product can be used in self-cleaning coatings.
• a photocatalyst which comprises, as a photocatalyst component, the titanium dioxide product produced according to the invention.
• the photocatalyst can comprise the product produced according to the invention as a sole catalyst component or in addition one or more other photocatalytically active agents and optionally one or more supports suitable for a photocatalyst, preferably an inert support.
• a manufacturing process for a photocatalyst wherein the titanium dioxide prepared according to the invention is further formulated into a form of a photocatalyst composition in a manner known in the art.
• the photocatalytic hydrated titanium dioxide prepared according to the invention can, for example, be ground into a powder or mixed into a coating slurry, for example, for a coating process.
• the photocatalyst can exist in the form of a powder or coat- ing.
• the coating can be composed of, for example, known coating mixtures useful in indoor spaces, into which mixtures the product of the invention and optionally other photocatalytically active agents or inert supports are added.
• the invention also provides a process for producing a coated product, wherein one or more surfaces of the product is coated at least in part with a photocatalyst prepared according to the invention. Furthermore, there is provided a product, such as a wall or a window, the surface of which is coated at least in part with the said photocatalyst, for example a photocatalyst coating.
• the activity of the photocatalytic product of the invention can be assessed by decomposing aldehyde and toluene simultaneously in the gaseous phase.
• the as- says are typically aimed to reflect maximally natural conditions. Actually, the air is never "clean and dry”. It always contains water vapour, carbon dioxide and solid particles.
• the air at room temperature and at normal pressure can be adjusted to an initial content of 400 ppm carbon dioxide and to a content of 10,000 ppm water.
• the decomposition of organic compounds and the generation of carbon dioxide can be monitored by a FTIR spectrometer.
• the titanium dioxide sample is ground in a mortar and mixed with water to form a slurry.
• the slurry is poured onto a Petri plate such that the TiO 2 -content on the plate is 10 g/m 2 .
• the Petri plate is placed in an oven at a temperature of 60°C over night.
• light sources there can be used, for example, a 300 W xenon bulb with a light filter at 385 nm, or a fluorescent bulb Dulux F 24W/830.
• the fluorescent bulb in question which is used in the assay, is used commonly in buildings open to the public.
• the illumination obtained with the xenon bulb equipped with a light filter at 385 nm can be thought to reflect daylight illumination. Typical excitation spectra are shown in Figure 2.
• the average rate of the formation of CO 2 was calculated based on the total amount of carbon dioxide formed.
• the rates of decomposition of acetaldehyde and toluene were fitted into a first order reaction kinetics equation as calculated on the basis of the removal of acetaldehyde and toluene from the gaseous phase. The results are expressed as relative figures.
• the efficiency of carbon dioxide formation is one of the most important variables, so that its value was regarded as a measure of the photocatalytic efficiency in the experiments performed.
• Photocatalytic hydrated titanium dioxide was prepared by precipitating from a volume of 500 ml of titanium oxychloride solution (236 g/l TiO 2 and 330 g/l HCI) with rutile nuclei (TiO 2 30 g/l), added at 3%, as calculated on the basis of TiO 2 .
• the mixture was stirred for three hours at 80°C, whereby the yield of hydrated TiO 2 was 98.3%.
• the acidic precipitate formed was filtered off and washed with excess of water.
• the acidic precipitate obtained was then neutralized with ammonia (200- 400 g/l) to a pH of 6, and the mixture stirred for half an hour.
• the precipitate was filtered and washed with warm distilled water.
• the precipitate was dried in air at 200°C for one hour.
• the rutile content of the product was more than 99.5% in rutile based on powder X-ray diffraction measurement.
• the crystal size of rutile was measured on the basis of the broadening of the peak of the X-ray diffraction pattern of rutile by using the Scherrer equation. The obtained crystal size was 10 nm.
• the specific surface was determined by the BET-technique on the basis of nitrogen absorption to be 126 m 2 /g.
• the product converted the starting materials totally into carbon dioxide within the measurement period (one hour and 15 minutes).
• the relative rate of formation of carbon dioxide was 205 ppm/h by using the 385 nm filter and the decomposition rate of aldehyde -10.7 and the decomposition rate of toluene -1.6.
• Photocatalytic hydrated titanium dioxide was prepared as in Example 1. However, the obtained precipitate was calcined at various temperatures for one hour. The temperatures chosen were 300°C, 400°C, 500°C, and 700°C. The measured properties and the photoactivity results are shown in Table 1.
• Photocatalytic hydrated titanium dioxide (5000 ml) was precipitated from a solution of titanium oxychloride (TiO 2 208.5 g/l) with nuclei (TiO 2 30 g/l), which were added at 2% calculated on the basis of TiO 2 .
• the mixture was stirred for three hours at 90°C, whereby the yield of TiO 2 was 96%.
• To the slurry was added 3 I of water and after the settling of the precipitate the overflow was discarded. Then, the precipitate was filtered off and washed with excess of water.
• the acidic precipitate was then neutralized with sodium hydroxide to pH 8 and the mixture was stirred for half an hour.
• the precipitate was filtered and washed with warm distilled water.
• the precipitate was dried at 270°C for four hours and the measured pH was 9.9.
• the measured properties and photoactivity results are shown in Table 1.
• Photocatalytic hydrated titanium dioxide was precipitated from a volume of 5000 ml of a solution of titanium oxychloride (TiO 2 214.5 g/l) with nuclei (TiO 2 30 g/l), which were added at 1.5% calculated on the basis of TiO 2 .
• the mixture was stirred for three hours and 45 minutes at 90°C, whereby the yield of TiO 2 was 94.2%.
• To the slurry was added 3 I of water and after the settling of the precipitate the overflow was discarded. Then, the precipitate was filtered off and washed with excess of water. Thereafter, the acidic precipitate was neutralized with sodium hydroxide to pH 10 and the mixture was stirred for half an hour. The precipitate was filtered and washed with warm distilled water. The precipitate was dried at 200°C for one hour.
• Table 1 The measured properties and photoactivity results are shown in Table 1.
• the photocatalytic hydrated titanium dioxide was precipitated as in Example 1 , but anatase nuclei were substituted for rutile nuclei. The length of precipitation was four hours and the yield 94.2%. The precipitate was neutralized and dried as in Example 1.
• the rutile content of the product was in excess of 79% in rutile on the basis of powder X-ray diffraction measurement.
• the other measured properties and photo- activity results are shown in Table 1.
• the photocatalytic hydrated titanium dioxide was precipitated as in Example 1 , but at the precipitation temperature of 70°C. The length of the precipitation was two hours and the yield 92.5%. The precipitate was neutralized as in Example 1 and dried at 300°C for one hour.
• the rutile content of the product was in excess of 99.5% in rutile on the basis of powder X-ray diffraction measurement.
• the other measured properties and photoactivity results are shown in Table 1.
• Photocatalytic hydrated titanium dioxide 700 ml was precipitated from a solution of titanium oxychloride (TiO 2 194 g/l) with nuclei (TiO 2 30 g/l), which were added at 5% calculated on the basis of TiO 2 .
• the mixture was stirred for two hours at 95°C, whereby the yield of TiO 2 was 96.8%.
• the precipitate was filtered off and washed with five litres of water. Thereafter, the acidic precipitate was neutralized with so- dium hydroxide to pH 7 and the mixture was stirred for half an hour at 40°C.
• the precipitate was filtered and washed with warm distilled water. The precipitate was dried at 200°C for one hour and the pH according to the measurement, was 8.1.
• the rutile content of the product was in excess of 99.5% rutile on the basis of powder X-ray diffraction measurement.
• the product converted the starting materi- als to CO 2 to an extent of 90% during the measuring period of the photoactivity assay.
• Other measured properties and photoactivity results are shown in Table 1.
• Photocatalytic hydrated titanium dioxide 700 ml was precipitated from the solution of titanium oxychloride (TiO 2 194 g/l), to which was added 3% SO 4 2" as sodium sulphate (200 g/l, Merck pro analysi) with nuclei (TiO 2 30 g/l), which were added at 4% calculated on the basis on TiO 2 .
• the mixture was stirred for two hours at 95°C, whereby the yield of TiO 2 was 97.5%.
• the precipitate was filtered off and washed with five litres of water. Thereafter, the acidic precipitate was neutralized with sodium hydroxide to pH 7 and the mixture was stirred for half an hour at 40°C.
• the precipitate was filtered and washed with warm distilled water. The precipitate was dried at 200°C for one hour and the pH was measured, and this was 7.9.
• the rutile content of the product was in excess of 99.5% in rutile on the basis of powder X-ray diffraction measurement.
• the sulphur content of the product was measured to be 0.37%.
• Other measured properties and photoactivity results are shown in Table 1.
• Photocatalytic hydrated titanium dioxide 700 ml was precipitated from the solution of titanium oxychloride (TiO 2 194 g/l), to which was added 5% SO 2" sulphuric acid solution (200 g/l, Merck pro analysi), with rutile nuclei (TiO 2 30 g/l), which were added at 4% calculated on the basis on TiO 2 .
• the mixture was stirred for two hours at 95°C, whereby the yield of TiO 2 was 95.5%.
• the precipitate was filtered off and washed with five litres of water. Thereafter, the acidic precipitate was neutralized with sodium hydroxide to pH 7 and the mixture was stirred for half an hour at 40°C. The precipitate was filtered and washed with warm distilled water. The precipitate was dried at 200°C for one hour and the pH was measured, and this was 7.4.
• the rutile content of the product was in excess of 88.5% in rutile on the basis of powder X-ray diffraction measurement.
• the sulphur content of the product was measured to be 0.67%.
• Other measured properties and photoactivity results are shown in Table 1.
• TiCI was diluted with water so that the strength of the solution calculated as the concentration of TiO 2 was 56 g/l.
• the solution was warmed to 50°C and stirred at that temperature for 4 hours. The yield was 94.6%.
• the precipitate was filtered off and washed with 1.7 litres of water. The cake was then neutralized to pH 7 by adding sodium hydroxide. Finally, the precipitate was filtered and washed with water and calcined at 200°C.
• the rutile content of the product was in excess of 88.5% in rutile on the basis of powder X-ray diffraction measurement. Other measured properties and photoactivity results are shown in Table 1.
• the solution was not warmed, but only stirred.
• the slurry contained 90 g/l TiO 2 and the measured concentration of hydrochloric acid was 10 g/l.
• the temperature was slowly increased to 80°C and the mixture was stirred at that temperature for 30 min.
• sodium hydroxide was added to the mixture so that the pH rose to 4,5. The precipitate was filtered off and washed with water.
• a commercial photocatalytic product Degussa P25, which is a mixture of anatase and rutile. The measured properties and photoactivity results are shown in Table 1.
• Decomposition of aldehyde (1 ⁇ l in a 25% aqueous solution) and toluene (0.2 ⁇ l) by the product of the invention resulted in the relative rate of formation of carbon dioxide of at least 130 ppm/h and in the relative decomposition rates for aldehyde and toluene of over 10 and 1.5, respectively, using the 385 filter.
• the relative rate of the formation of carbon dioxide was at least 160 ppm/h and the relative decomposition rates for aldehyde and toluene were over 15 and 2.5, respectively, using the 385 filter.
• the product of the instant invention is over 100%, preferably over 150% and most preferably over 250% more efficient photocatalyst in the conversion of toluene and aldehyde into carbon dioxide, as measured by using a xenon bulb and light passing a light filter at 385 nm.
• Example 8 Into each test tube filled with water were weighed, respectively, equal amounts of the product of Example 8, nitrogen-doped anatase, and a commercial anatase- rutile mixture. A drop of methylene blue was placed into each test tube. As a light source, a kitchen light (L 18 W-835 white super, Oy Airam AB) was used. The product of Example 8 decomposed methylene blue in a completely different manner as compared to the other samples. The blue test tube cleared in the case of Example 8 and the blue colour disappeared totally. In contrast, the other test tubes remained blue.
• Example 2 7.5 g of the product of Example 1 , 16.9 g of an aqueous dispersion of SiO 2 (30%, Ludox) and 20.8 g of ethanol were weighed out. The materials were mixed to- gether, and the laquer was applied by brushing onto a metal plate as a photocatalytic surface.
• the product of the invention was clearly at least 50% more efficient than the commercial anatase-rutile mixture products or nitrogen-doped anatase when assayed for photoactivity using a fluorescent bulb Osram Dulux® F 24W/830 as a light source.
• the advantage of the present invention over the prior art processes is that an industrially more advantageous solution of titanium oxychloride with a lower water content, and an industrially more advantageous length of precipitation can be used.
• the use of nuclei enhances safety.
• the combination of the given strength of precipitation solution, the use of nuclei, and the precipitation temperature below the boiling point can provide the precipitation of rutile with a clearly more efficient photocatalytic activity, which activity can be advantageously exploited also for indoor illumination conditions.

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• 2004
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• 2005
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