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Definitions

• the invention relates to a carbon-containing photocatalyst based on titanium dioxide, which is photoactive in the visible range, hereinafter also called vlp-TiO 2 .
• the invention further relates to a method for producing a carbon-containing titanium dioxide (vlp-TiO 2 ), which is effective as a photocatalyst when irradiated with visible light.
• vlp-TiO 2 carbon-containing titanium dioxide
• Photocatalytic materials are semiconductors in which electron-hole pairs are formed under the influence of light, which generate highly reactive free radicals on the surface of the material.
• Titanium dioxide is one such semiconductor. It is known that titanium dioxide can remove natural and artificial impurities in air and water by exposure to UV light by reducing atmospheric oxygen and oxidizing (mineralizing) the impurities to environmentally friendly end products. In addition, the surface of titanium dioxide becomes superhydrophilic due to the absorption of UV light. This is the basis for the anti-fog effect of thin titanium dioxide films on mirrors and windows.
• titanium dioxide A serious disadvantage of titanium dioxide is the fact that it only contains the UV component of sunlight, i.e. only 3 to 4% of the radiation, and is either not at all or only very weakly catalytically active in diffuse daylight.
• JP 11333304 A describes a titanium dioxide whose surface at least partially has a deposit of graphite, amorphous carbon, diamond-like carbon or hydrocarbons.
• EP 0 997 191 A1 reports a titanium dioxide, on the surface of which titanium carbide was applied by means of gas phase deposition.
• Photocatalytic materials in which titanium dioxide and others Containing nitrogen, sulfur, carbon or other elements as an anion are disclosed for example in EP 1 205 244 A1 and EP 1 205 245 A1.
• the anions are said to be located either at oxygen sites, at interstitial sites or at the grain boundaries of a polycrystalline titanium oxide particle. No information is given about the characterization of the material or about catalytic or physical properties. It is further known to produce titanium dioxide from titanium alcoholates by hydrolysis with hydrochloric acid and subsequent heating to 350 ° C., which contains 1.0 to 1.7% by weight of carbon (C. Lettmann et al., Applied Catalysis B 32 (2001) 215). The carbon here comes from the ligand of the titanium compound.
• the disadvantage of the known photocatalytic materials is that the processes for their production are not suitable for large-scale production. For technical reasons, the processes either cannot be implemented on a large scale or they would then no longer be economical. In addition, most of the products obtained show an insufficient photocatalytic activity in the degradation of pollutants in visible light in the range of ⁇ > 400 nm and only a slight light-induced increase in hydrophilicity. In addition, the products have so far only been optimized for their photocatalytic properties. The color and brightness, ie the optical properties, have so far been disregarded.
• the use of a very bright vlp-TiO 2 with low intrinsic color and high photocatalytic activity has advantages in all applications that tolerate no or only a small intrinsic color of vlp-TiO 2 , such as. B. when used in coating materials, especially in paints, varnishes and plasters.
• the object of the invention is to provide a daylight-active, highly effective photocatalyst based on a carbon dioxide-modified titanium dioxide and to provide an economical process for its production.
• the object is achieved by a carbon-containing titanium dioxide with a significant light absorption compared to pure titanium dioxide in the range of ⁇ > 400 nm (vlp-Ti0 2 ), the electron spin resonance spectrum (ESR) measured at a temperature of 5 K in the range of the g value from 1.97 to 2.05 has only one significant signal.
• the object is further achieved by a production process in which a titanium compound which has a specific surface area of at least 50 m 2 / g according to BET
• the vlp-TiO 2 according to the invention shows a higher photocatalytic activity than that in
• photoactivity The degradation of 4-chlorophenol by a defined amount of vlp-TiO 2 when exposed to light of wavelength> 455 nm for 120 minutes serves as a measure of the photocatalytic activity (hereinafter referred to as “photoactivity”).
• the photoactivity of the vlp-TiO 2 according to the invention is at least 20%, preferably at least 40%, in particular at least 50%.
• the carbon content is in the range from 0.05 to 4% by weight, based on TiO 2 , preferably
• titanium dioxide particles only contain carbon in one surface layer and are therefore referred to below as "carbon-modified” - in contrast to the volume-doped titanium dioxide produced according to Sakthivel and Kisch (2003)
• Carbon or the carbon compounds of the vlp-TiO 2 according to the invention are presumably primarily covalently bound via oxygen on the TiO 2 surface and can be leached out alkaline.
• the photocatalyst can additionally or alternatively contain nitrogen and / or sulfur.
• the vlp-TiO 2 according to the invention absorbs visible light of the wavelength ⁇ > 400 nm.
• the Kubelka-Munk function F (R ⁇ ) which is proportional to the absorbance, is approximately 50% at 500 nm and approximately 20 at 600 nm % of the value at 400 nm.
• the electron spin resonance spectrum (ESR) of the vlp-Ti0 2 according to the invention, measured at a temperature of 5 K, is characterized by a strong signal at a g-value of 2.002 to 2.004, in particular 2.003. No further signals occur in the range of the g values 1, 97 to 2.05.
• the intensity of the signal at g about 2.003 is increased by irradiation with light of wavelength ⁇ > 380 nm (UV-free 100W halogen lamp, cold light filter KG5) compared to the measurement in the dark.
• the X-ray photoelectron spectrum (XPS) of the vlp-Ti0 2 according to the invention is characterized by the occurrence of a strong absorption band at a binding energy of 285.6 eV based on the O1s band at 530 eV. It is also characteristic that the vlp-TiO 2, in contrast to the photocatalyst according to Sakthivel & Kisch (2003), shows neither carbonate bands in the X-ray photoelectron spectrum (XPS) nor in the infrared spectrum.
• the vlp-TiO 2 When irradiated with visible light, the vlp-TiO 2 has a water contact angle of approximately 8 °, while unmodified Ti0 2 shows a contact angle of approximately 21 °.
• the new photocatalyst enables pollutant degradation not only with artificial visible light, but also with diffuse daylight from inside. It can be used to break down contaminants and pollutants in liquids or gases, especially in water and air.
• the photocatalyst can advantageously be applied to various supports such as glass (normal and mirrored), wood, fibers, ceramics, concrete, building materials, SiO 2 , metals, paper and plastics as a thin layer. Together with the simple manufacture, this opens up application possibilities in diverse areas such as B. in the construction, ceramic and vehicle industry for self-cleaning surfaces or in environmental technology (air conditioners, devices for air purification and air sterilization and water purification, especially drinking water, for example, for antibacterial and antiviral purposes).
• the photocatalyst can be used in coatings for indoor and outdoor use such as paints, plasters, lacquers and glazes for application to masonry, plaster surfaces, paints, wallpapers and wood, metal, glass or ceramic surfaces or on components such as thermal insulation composite systems and curtains Facade elements are used, as well as in road surfaces and in plastics, plastic foils, fibers and paper.
• the photocatalyst can also be used in the production of precast concrete, Concrete paving stones, roof tiles, ceramics, tiles, wallpaper, fabrics, panels and cladding elements can be used for ceilings and walls indoors and outdoors.
• the light-induced increase in the hydrophilicity of the TiO 2 surface results in further applications such as B. fog-free mirrors and windows in the sanitary area or in the vehicle and construction industries.
• the photocatalyst is also suitable for use in photovoltaic cells and for water splitting.
• FIG. 1 shows the Kubelka-Munk function F (R ⁇ ) (arbitrary units) proportional to the relative absorbance for unmodified Ti0 2 and for C modified Ti0 2 (vlp-Ti0 2 ) as a function of the wavelength and reveals that the vlp -TiO 2 in contrast to unmodified titanium dioxide is absorbed in the visible spectral region.
• F (R ⁇ ) is about 50% at 500 nm and about 20% of the value at 400 nm at 600 nm.
• FIG. 2 shows the electron resonance spectra (ESR) of the vlp-Ti0 2 according to the invention (spectrum A) and of the TiO 2 (spectrum B) produced by Sakthivel & Kisch, recorded in the dark and at a temperature of 5 K.
• Spectrum A only shows a significant signal with a g-value of 2.003.
• spectrum B shows three further signals in the range of the g values 1.97 to 2.05.
• FIG. 3 contains the X-ray photoelectron spectra (XPS) of the vlp-TiO 2 according to the invention (spectrum A) and of the known TiO 2 according to Sakthivel & Kisch (spectrum B), which has been precipitated from titanium tetrachloride with tetrabutylammonium hydroxide.
• XPS X-ray photoelectron spectra
• the spectrum of vlp-Ti0 2 shows a pronounced C1s signal at a binding energy of 285.6 eV based on the O1s absorption band at 530 eV, which indicates elemental carbon.
• Spectrum B shows C1s signals for elemental carbon with a binding energy of 284.5 eV and additional bands at 289.4 eV and 294.8 eV, which indicate carbonate.
• Corresponding IR spectra also have typical carbonate bands at 1738, 1096 and 798 cm “1 .
• FIG. 4 illustrates the photocatalytic activity of vlp-TiO 2 compared to unmodified TiO 2 in the degradation of 4-chlorophenol (as a 2.5 ⁇ 10 "4 molar aqueous solution) artificial visible light ( ⁇ > 455 nm).
• the decrease in the total organic carbon (TO) content in the solution in relation to the initial value (TOC 0 ) is shown.
• TO total organic carbon
• FIG. 5 illustrates the photocatalytic activity of vlp-TiO 2 compared to unmodified TiO 2 in the degradation of 4-chlorophenol (as a 2.5 x 10 "4 molar aqueous solution) by the diffuse daylight of an interior.
• the decrease in the total content of organic is shown Carbon (TOC t ) in the solution in relation to the initial value (TOC 0 ).
• TOC t Carbon
• TOC 0 initial value
• Figure 6 illustrates the photocatalytic activity of vlp-Ti0 2 against unmodified TiO 2 in the degradation of benzene (5 vol .-%), acetaldehyde (2 vol .-%) and carbon monoxide (5 vol .-%) by the diffuse daylight interior.
• the decrease in the total organic carbon content (TOC t ) in the atmosphere is shown in relation to the initial value (TOC 0 ).
• FIG. 7 shows an X-ray powder diffractogram of vlp-TiO2, which has only anatase reflections.
• the crystallite size calculated according to the Scherrer method is 10 nm.
• FIG. 8 shows a picture of vlp-TiO 2 with the lattice lines of the crystallites taken by means of high resolution electron microscopy (HTEM).
• the crystallite size can be estimated on the order of 10 nm.
• FIG. 9 shows a carbon depth profile of the vlp-TiO 2 , represented as a C / Ti ratio. It was determined using ion bombardment (Ar + ) and ESCA analysis. The specified fire time of 5x10 3 seconds corresponds to a depth of about 5 nm.
• the process according to the invention is based on a titanium compound which is in the form of an amorphous, partially crystalline or crystalline titanium oxide or water-containing titanium oxide and / or a titanium hydrate and / or titanium oxyhydrate and which is referred to below as the starting titanium compound.
• the starting titanium compound can be produced, for example, in the production of titanium dioxide either by the sulfate process or by the chloride process. Titanium hydrate or titanium oxyhydrate or metatitanic acid is e.g. precipitated in the hydrolysis of titanyl sulfate or titanyl chloride.
• the starting titanium compound can be present as a fine-grained solid or in suspension with a corresponding solids content of at least 15% by weight, the specific
• Surface of the solid is at least 50 m 2 / g according to BET, preferably about 150 to 350 m 2 / g according to BET, in particular 150 to 250 m 2 / g according to BET.
• titanium compound titanium hydrate from the sulfate process.
• This titanium hydrate is advantageously pre-neutralized and washed by adherent
• the carbon-containing substance has a decomposition temperature of at most 400 ° C, better ⁇ 350 ° C, preferably ⁇ 300 ° C.
• Carbon-containing substances such as, for example, wood, soot or activated carbon, and in particular organic ones, have proven suitable Carbon compounds such as hydrocarbons with at least one functional group proven.
• the functional group can be: OH; CHO; COOH; NH X ; SH X ; COOR, where R is an alkyl or aryl radical.
• succinic acid, glycerin or ethylene glycol are suitable.
• Sugar or other carbohydrates can also be used, as can organoammonium hydroxides, in particular tetraalkylammonium. Mixtures of the compounds mentioned are also suitable.
• Water-soluble polyalcohols with a carbon / oxygen ratio of about 0.7 to 1.5, preferably of about 1, preferably pentaerythritol, are preferably used.
• the carbon compound can be used as a solid or as a solution or as a suspension.
• the organic carbon compound should have as high an affinity as possible for the surface of the starting titanium compound in order to be able to form an intimate connection with it.
• the starting titanium compound is intimately mixed with the organic carbon compound in such a way that the starting titanium compound is surface-coated with the carbon compound.
• the organic carbon compound can be physisorbed or chemisorbed on the surface of the starting titanium compound.
• the surface of the starting titanium compound can be covered by dissolving the carbon compound in the suspension of the starting titanium compound or by mixing the suspension of the carbon compound with the suspension of the
• initial titanium connection take place. Intensive mixing of the carbon compound with a previously dried powdered titanium compound is also possible. If titanium hydrate is used, the carbon compound can alternatively also be added to the solution to be hydrolyzed during the preparation of the titanium hydrate. In the finished mixture of starting titanium compound and carbon compound, the amount of carbon compound based on the starting titanium compound (as a solid) is 1 to 40% by weight.
• the finished mixture is in the form of a suspension, it can be dried to a powdery solid before further processing.
• Known methods such as spray drying or fluidized bed drying are suitable for this.
• the finished and optionally pre-dried mixture is treated thermally at a maximum temperature of 400 ° C.
• the thermal treatment is preferably carried out in an oxidizing atmosphere in air or in an oxygen-air mixture. This leads to the decomposition of the organic carbon compound on the surface of the starting titanium compound and the release of H 2 O, CO 2 and CO.
• the thermal treatment also in batch operation - for example in a commercially available laboratory furnace, a continuous process in which a certain temperature profile can be operated is preferred for economic reasons. All processes with which a corresponding temperature profile and the necessary dwell time can be realized are possible as continuous processes.
• Particularly suitable units are indirectly and directly heated rotary kilns. Continuously operated fluid bed reactors, fluidized bed dryers and heated ploughshare mixers can also be used. The last three units mentioned can also be operated in a batch mode.
• the thermal treatment is preferably carried out in such a way that a product (vlp-TiO 2 ) with a carbon content of 0.05 to 4.0% by weight, preferably 0.05 to 2.0% by weight, particularly preferably 0, 3 to 1.5 wt .-% and in particular 0.4 to 0.8 wt .-% arises.
• a color change from white to brown and finally to beige takes place.
• the end product is characterized by a beige to slightly yellowish-brown color. It is characterized in that the carbon is detectable in amorphous and polycrystalline areas of the surface layer as well as on the surface itself.
• the product is photoactive in visible light.
• the product is deagglomerated using known methods, for example in a pin mill, jet mill or counter jet mill.
• the thermal treatment usually leads to agglomerate-free products that do not require further grinding.
• the grain size to be achieved depends on the grain size of the starting titanium compound.
• the grain size or specific surface of the product is only slightly lower, but in the same order of magnitude as that of the educt.
• the desired grain size of the photocatalyst depends on the field of application of the photocatalyst. It is usually in the range as for TiO 2 pigments, but can also be below or above.
• the BET specific surface area is 100 to 250 m 2 / g, preferably 130 to 200 m 2 / g, in particular 130 to 170 m 2 / g.
• Example 1 The invention is described in more detail with the aid of the following examples, without the scope of the invention being restricted thereby.
• Example 1 Example 1 :
• An aqueous titanium oxyhydrate paste (35% by weight of solids) produced by the sulfate process is diluted with distilled water at room temperature until a stirrable suspension is formed.
• the solids content is 20 to 25%.
• Sufficient NaOH solution (36% by weight) is added until a pH between 6.0 and 7.0 is established.
• the suspension is then filtered and washed with distilled water until the S0 3 content measured on the dried residue is below 1% by weight.
• the titanium oxyhydrate neutralized and washed in this way is then again diluted to a stirrable suspension (25% solids) with distilled water and 12% by weight of succinic acid, based on the solids, is added.
• Succinic acid is added to the suspension as a solid and the suspension is stirred until the succinic acid has completely dissolved.
• the suspension is heated to approximately 60 ° C. to improve the solubility of succinic acid.
• the suspension prepared in this way is dried under a surface evaporator (IR radiator) with stirring until a paste-like mass is formed from the suspension.
• the pasty mass is then dried in a laboratory drying cabinet at 150 ° C. until the solids content is> 98%.
• 300 g of the dried titanium oxyhydrate / succinic acid mixture are finely comminuted (e.g. by mortar and sieving) and the powder obtained is placed in a quartz bowl with a lid at 290 ° C. in a laboratory oven.
• the quartz bowl is removed at intervals of 1 to 2 hours and the powder is mixed again. After 13 to 15 hours in the laboratory oven, the color of the powder changed from initially yellowish to gray-black to yellowish-brown.
• the thermal treatment for vlp-Ti0 2 is complete when the carbon content has decreased from an initial 5 to 5.5% by weight to approximately 0.65 to 0.80% by weight.
• the photocatalyst is then deagglomerated and analyzed for carbon content, optical properties, BET surface area and photoactivity.
• Example 2 The procedure is the same as in Example 1, with the difference that 12% by weight of pentaerythritol is added as a solid to the titanium oxyhydrate suspension.
• Example 4 The procedure is the same as in Example 2, with the difference that 5% by weight of pentaerythritol is added as a solid to the titanium oxyhydrate suspension.
• Example 4 The procedure is the same as in Example 2, with the difference that 5% by weight of pentaerythritol is added as a solid to the titanium oxyhydrate suspension.
• a titanium oxyhydrate / pentaerythritol suspension is produced using 5% by weight pentaerythritol as described in Example 1.
• the thermal treatment of the suspension thus obtained is carried out in a continuously operated rotary kiln as follows:
• the rotary kiln is operated in a counterflow process and heated directly by a gas burner.
• the open flame of the gas burner is protected by a flame tube and thus prevents direct contact with the product (vlp-Ti0 2 ).
• the heated furnace length is 7 m and the inside diameter is 0.3 m.
• the suspension is sprayed finely into the oven.
• the feed quantity of the suspension is 40 kg / h. Chain internals in the entry of the oven ensure good swirling and thus rapid drying and subsequent comminution of the dried material.
• the throughput time through the continuously operated rotary kiln is 1 hour.
• the furnace temperature in the outlet area is regulated to 260 ° C by the amount of gas on the burner.
• Vlp-Ti0 2 is obtained at the furnace outlet as a fine powder with a yellowish-brown color.
• the vlp-Ti0 2 is then deagglomerated in a laboratory mixer (Braun, MX 2050) and analyzed for carbon content, optical properties, BET surface area and photoactivity.
• Example 5 The procedure is the same as in example 4, with the difference that the furnace temperature in the outlet area is regulated to 280 ° C. by the amount of gas on the burner.
• a titanium oxyhydrate / pentaerythritol suspension is produced using 5% by weight pentaerythritol as described in Example 1.
• the suspension is predried to a powdery solid with a residual moisture content of 22% in an electrically heated oven.
• the thermal treatment of the pre-dried powdery feed is carried out in a continuously operated, indirectly heated rotary kiln as follows: The rotary kiln is operated in a direct current process and electrically heated in three zones.
• the total heated furnace length is 2700 mm and the inside diameter is 390 mm.
• the pulverulent solid is conveyed into the furnace entry via a dosing screw.
• the oven temperature is divided into three Heating zones controlled electrically. The temperature of each of the three heating zones can be individually adjusted. Vlp-Ti0 2 is obtained at the furnace outlet as a beige-colored fine powder. The vlp-Ti0 2 is then deagglomerated in a laboratory mixer (Braun, MX 2050) and analyzed for carbon content, optical properties, BET surface area and photoactivity.
• a Ti0 2 pigment (anatase) with a BET surface area of about 10 m 2 / g (commercial product
• Kronos 1000 is mixed with 12% pentaerythritol analogously to Example 2 and thermally treated.
• the table shows the analysis and photoactivity of vlp-Ti0 2 according to the invention.
• Vlp-Ti0 2 (Examples 1 to 6) made from titanium hydrate shows good optical values
• Example 7 5 g of titanium dioxide (commercial product TRONOX titanium hydrate-0 from Kerr-McGee Pigments GmbH) are suspended in 20 ml of distilled water at room temperature, mixed with 5 ml of ethylene glycol (commercial product from FLUKA AG) and in an ultrasonic bath (Sonorex Super RK.) For 30 minutes 106 from Bandelin Electronic, Berlin; 35 kHz, 120 W eff. RF power). After magnetic stirring overnight, the solvent is preferably removed in vacuo, the residue is dried at 100 to 200.degree. C., preferably at about 200.degree. C. for at least 12 hours, then heated to 300.degree. C. within an hour in a closed vessel and then three more Maintained at this temperature for hours.
• titanium dioxide commercial product TRONOX titanium hydrate-0 from Kerr-McGee Pigments GmbH
• the color of the powder changes from white to dark brown to beige. Prolonged heating leads to colorless, inactive powders. Elemental analysis of the product shows 2.58% by weight of carbon, 0.02% by weight of nitrogen and 0.40% by weight of hydrogen. Unmodified Ti0 2 contains 0.07% by weight of C and 0.0% by weight of N and 0.0% by weight of H.
• Example 8 To detach the surface carbon compound, 5 g of vlp-TiO 2 are stirred overnight in 100 ml of a 2 M sodium hydroxide solution (pH 12). A brown-yellow extract and a barely colored whitish residue are obtained by centrifugation, the latter being dried at 100.degree. The powder thus obtained shows no activity when 4-chlorophenol is broken down in visible light. If the powder is combined again with the extract and warmed up slightly, preferably to about 200 ° C., it has the same activity in the degradation reaction as the untreated (non-leached) vlp-Ti0 2 .
• a powder prepared according to Example 6 is suspended in a liquid such as methanol or ethanol in an ultrasound bath and the resulting suspension is applied as thinly as possible to the film using a spray bottle. After drying at 343 K, the coating can be
• plastic film instead of the plastic film, another carrier such as. B. paper (see experiment according to FIG. 6) or aluminum (see under test methods h): “dip coating”) can be used. measurement methods
• a) Determination of the optical values The method serves to determine the optical values brightness L *, tone a * and tone b * of the vlp-T ⁇ ' 0 2 .
• a powder compact is produced from the vlp-Ti0 2 to be tested under defined conditions using a hydraulic small press from MATRA, Frankfurt. With the HUNTERLAB Tristimulus Colorimeter, the reflectance values are then determined on the powder compact.
• the vlp-Ti0 2 is ground before the compact is produced. For this purpose, 100 g of the vlp-Ti0 2 obtained are placed in a commercial mixer (manufacturer: Braun, model: MX 2050) and ground 12 times for 5 seconds.
• the mixer is opened between each grinding step and the powder is mixed again.
• a base plate with a circular recess place a sheet of white matt paper on both sides and press a metal ring (height 4 cm, diameter 2.4 cm) into the recess with the press.
• About 25 g of the ground vlp-Ti0 2 are added to the metal ring with gentle shaking and tapping.
• the powder is pressed together with a pressure of 2 - 3 kN.
• the pressing process is repeated a second time until the desired operating pressure of 15 kN is reached.
• the paper between the base plate and ring is removed. In the ring there is now the pressure that is used for the measurement process on the HUNTERLAB colorimeter.
• the measured values L *, a *, b * are read directly on the colorimeter.
• 15 mg of vlp-Ti0 2 are dispersed in 15 ml of a 2.5 x 10 "4 molar solution of 4-chlorophenol in an ultrasonic bath for 10 minutes and then exposed in a water-cooled round cuvette on an optical bench.
• the exposures for determining the photoactivity are carried out with an Osram XBO 150 W xenon short-arc lamp installed in a focusing lamp housing (AMKO Mod. A1020, focal length 30 cm)
• the spectrum of this lamp is shown in Figure 10.
• the reactions are carried out in a 15 ml, water-cooled round cuvette with an inner diameter of 30 mm and a layer thickness of 20 mm.
• the reaction suspension can be stirred with a stirring motor and stirring magnet attached to the side.
• the round cuvette is shown in Figure 11.
• the cuvette is fixed in the focus of the lamp.
• the light is focused so that only the reaction space of the
• the cuvette is irradiated permanently mounted on an optical bench.
• an edge filter (from Schott) is introduced into the beam path, the permeability of which is ⁇ > 455 nm.
• an IR filter is also installed in the beam path. It is a cylinder filled with water (diameter 6 cm, length 10 cm).
• the determination is made as total organic carbon content (TOC) with the LECO C-200 carbon analyzer.
• the measurement method is based on the combustion of the organic substance contained in the Ti0 2 in an induction furnace under oxygen gas and the subsequent determination of the carbon dioxide formed by means of IR detection.
• the weight of Ti0 2 is approx. 0.4 g. t
• the BET surface area is measured with a Tristar 3000 from Micromeritics according to the static volumetric principle.
• the device Phi 5600 ESCA spectrometer (pass energy of 23.50 eV; AI standard; 300.0 W; 45.0 °) was used to measure the binding energies.
• a Bruker Elexys 580 spectrometer X- band (9.5 GHz) is used.
• the sample was evacuated to 10 "5 torr, filled with helium to a pressure of 10 " 2 torr and then melted.
• the measurement was carried out under the following conditions:
• the diffuse reflection spectra of the powders were measured with a Shimadzu UV-2401 PC UV / Vis spectrometer, which was equipped with an integrating sphere.
• the white standard used was barium sulfate, with which the powders were ground in a mortar before the measurement.
• the Kubelka-Munk function is proportional to the absorbance.

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