HK1104569B - Carbon-containing, titanium dioxide-based photocatalyst, and process for producing the same - Google Patents

Description

Carbon-containing titanium dioxide photocatalyst and preparation method thereof

The invention relates to a titanium dioxide-based photocatalyst containing carbon, which is optically active in the visible range and is also referred to below as vlp-TiO₂。

The invention also relates to a method for producing carbon-containing titanium dioxide (vlp-TiO)₂) The method of (1), which functions as a photocatalyst under irradiation of visible light.

Photocatalytic materials are semiconductors in which electron-hole pairs are formed under the action of light, which generate highly reactive 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 ultraviolet irradiation, wherein oxygen is reduced by air and impurities are oxidized (mineralized) to be environmentally friendly end products. Further, the surface of titanium dioxide becomes super-hydrophilic by absorbing ultraviolet rays. The anti-deposition effect of titanium dioxide films on mirrors and windows is based on this.

A serious disadvantage of titanium dioxide is the fact that only the ultraviolet part of the sunlight, i.e. only 3-4% of the light is available, and in diffuse natural light there is no or only very weak catalytic activity.

For this reason, it has long been investigated to modify titanium dioxide so that the phenomenon can also be produced using the major part of the photochemically acting sunlight, the visible region of the spectrum from about 400 to about 700 nm.

Make TiO react₂One way to show photocatalytic activity for natural light is to dope with metal ions such as V, Pt, Cr, Fe, and the like. Another possibility is by reduction of Ti⁴⁺In the TiO region₂Oxygen vacancies are created in the crystal lattice. Both developments require costly production techniques such as ion implantation or plasma processing. Numerous patents describe nitrogen-modified titanium dioxide which has a photocatalytic effect under irradiation in the visible region (for example EP 1178011A 1, EP 1254863A 1).

It is also known that the photocatalytic activity of titanium dioxide under visible light irradiation is improved by modification with carbon. For example, JP 11333304 a discloses a titanium dioxide having at least a part of its surface with graphite, amorphous carbon, diamond-like carbon or hydrocarbon precipitates. EP 0997191 a1 relates to a titanium dioxide, on the surface of which titanium carbide is applied by vapour deposition. Photocatalytic materials in which titanium dioxide contains, in particular, nitrogen, sulfur, carbon or other elements as anions are disclosed, for example, in EP 1205244 a1 and EP 1205245 a 1. These anions are located at the oxygen sites, the interstitial sites, or the grain boundaries of the polycrystalline titanium oxide particles. No material properties or catalytic or physical properties are specified.

It is also known that titanium dioxide can be made from titanium alcoholates by hydrolysis with hydrochloric acid and subsequent heating to 350 ℃ and that contains 1.0-1.7% by weight of carbon (C.Lettmann et al, applied catalysis B32 (2001) 215). Here, the carbon is derived from a ligand of a titanium compound.

According to another publication, it was found that hydrolysis of titanium tetrachloride with tetrabutylammonium hydroxide followed by calcination at 400 ℃ for one hour produced a titanium dioxide product containing 0.42 wt% carbon (s.saktive & h.kisch, angelw.chem.int.ed.42 (2003) 4908). In this case, the carbon comes from the precipitant and is mostly distributed more uniformly in the volume (volume-doping).

A disadvantage of the known photocatalytic materials is that their preparation is not suitable for large-scale industrial production. These processes are either not suitable for large-scale use for technical reasons or are uneconomical. In addition, in the degradation of harmful substances, the products obtained often exhibit inadequate photocatalytic activity in the visible region with lambda ≥ 400nm, with only minor increase in hydrophilicity due to photoinduction. Moreover, the photocatalytic performance of the product has only been optimized to date. Color and brightness, i.e. optical properties, have not attracted attention so far. In contrast, no or only a small amount of vlp-TiO can be tolerated₂All areas of inherent colour, such as in coatings, in particular in inks, lacquers and plasters, use very bright vlp-TiO with low inherent colour and high photocatalytic activity₂Has the advantages.

The object of the present invention is to provide a natural-light-active and highly efficient photocatalyst based on titanium dioxide modified with carbon and to provide an economical process for the preparation of this catalyst.

According to the invention, this object is achieved by a carbon-containing titanium dioxide which, compared with pure titanium dioxide, has a lambda ≧ 400nm (vlp-TiO)₂) The region has obvious light absorption, and only one obvious light absorption is in the range of g value of 1.97-2.05 in electron spin resonance spectrum (ESR) measured at the temperature of 5KA signal. The object is also achieved by a process for the preparation of a composition having a particle size of at least 50m²A titanium compound having a BET (Brunauer-Emmett-Teller) specific surface area is intimately mixed with a carbon-containing substance and the mixture is heat treated at a temperature of up to 400 ℃. Further advantageous embodiments of the invention are given in the dependent claims.

Product(s)

The inventive vlp-TiO₂Exhibit a higher photocatalytic efficiency than the types described in the prior art. Irradiating with light having a wavelength of 455nm or more for 120 minutes by a determined amount of vlp-TiO₂The amount of 4-chlorophenol degradation caused was used as a measure of the photocatalytic efficiency (hereinafter referred to as "photoactivity"). The measurement method is described in detail below. Under the measuring conditions, the inventive vlp-TiO₂Is at least 20%, preferably at least 40%, especially at least 50%.

Carbon content in TiO₂0.05 to 4 wt.%, preferably 0.05 to 2.0 wt.%, particularly preferably 0.3 to 1.5 wt.%. The best results are obtained with a carbon content of 0.4 to 0.8% by weight.

The titanium dioxide particles contain carbon only in the surface layer and are therefore referred to below as "carbon-modified", in contrast to the volume-doped titanium dioxide produced according to Saktive and Kisch (2003). The inventive vlp-TiO₂May first be bonded to the TiO by oxygen conjugation₂On the surface and can be washed off with alkali.

The photocatalyst may additionally or alternatively contain nitrogen and/or sulfur. With unmodified TiO₂In contrast, the present invention is a vlp-TiO₂Absorb visible light with the wavelength lambda being more than or equal to 400 nm. Kubelka-Munk function F (R) proportional to the absorption rate_∞) About 50% of the value at 500nm and about 20% of the value at 400nm at 600 nm.

Inventive vlp-TiO measured at 5K₂The electron spin resonance spectroscopy (ESR) of (1) is characterized by a strong signal at a g value of 2.002 to 2.004, particularly 2.003.No other signals appear in the range of g value of 1.97-2.05. The signal intensity at g of about 2.003 is increased by irradiation with light of wavelength λ ≧ 380nm (100W halogen lamp without ultraviolet, luminescence filter KG5) compared to the intensity measured in the dark.

The inventive vlp-TiO₂Is characterized by the appearance of a strong absorption band at a bond energy of 285.6eV, as measured by the 01 s-band at 530 eV.

Another feature is that unlike the photocatalysts made according to Saktive and Kisch (2003), the vlp-TiO₂Neither in X-ray photoelectron spectroscopy (XPS) nor in infrared spectroscopy shows carbonate bands.

Under the irradiation of visible light, vip-TiO₂Has a water contact angle of about 8 DEG, while unmodified TiO₂The contact angle shown is about 21.

This novel photocatalyst makes not only can use artificial visible light, can make harmful substance degradation with indoor diffuse natural light moreover. Can be used for degrading impurities and harmful substances in liquid or gas, especially water and air.

The photocatalyst can advantageously be applied in thin layers on various supports such as glass (normal and specular), wood, fibers, ceramics, concrete, building materials, SiO₂Metal, paper and plastic. Together with simple preparation, the use possibilities in numerous fields are thus also disclosed, for example in the construction industry, the ceramic industry and the automobile industry for self-cleaning surfaces or in environmental technology (air conditioners, devices for air purification and air disinfection, and water purification devices, in particular drinking water, for example for antibacterial and antiviral purposes).

The photocatalyst can be used in coatings for indoor and outdoor use, such as inks, plasters, paints and glazes (Lasuren), for coating walls, plaster surfaces, coverings, wallpapers and wood surfaces, metal surfaces, glass surfaces or ceramic surfaces, or for coating components, such as heat-insulating composite systems and suspended facade decorations, and in pavements and plastics, plastic films, fibers and paper. The photocatalyst may also be used to produce concrete parts, concrete-paving tiles, roofing tiles, ceramics, tiles, wallpaper, fabrics, fire-resistant bricks and secondary linings (Verkleidung) parts for indoor and outdoor roofs and walls.

By photoinduced TiO₂The increased hydrophilicity of the surfaces also leads to deposition-free mirrors and windows in other applications, such as in the hygiene sector or in the automotive and construction industry.

The photocatalyst is also suitable for use in photovoltaic cells and for decomposing water.

The present invention will be described in detail with reference to FIGS. 1 to 9₂。

FIG. 1 shows the Kubelka-Munk function F (R) proportional to the relative absorption rate_∞) (optional Unit) represents an unmodified TiO₂And TiO modified with C₂(vlp-TiO₂) As a function of wavelength, it can be seen that, unlike unmodified titanium dioxide, vlp-TiO₂Absorbing the visible spectrum. F (R)_∞) The value is about 50% of the value at 500nm and about 20% of the value at 400nm at 600 nm.

FIG. 2 shows a plot of the inventive vlp-TiO recorded in the dark at a temperature of 5K₂(spectra A) and TiO prepared according to Saktive and Kisch₂(spectrum B) electron resonance spectrum (ESR). Spectrum a shows only one significant signal at a g value of 2.003. Spectrum B shows three other signals in the range of g values of 1.97 to 2.05, in addition to the main signal shown when g is about 2.003.

FIG. 3 includes a present invention of vlp-TiO₂(spectra A) and the TiO precipitated from titanium tetrachloride with tetrabutylammonium hydroxide according to Saktive and Kisch already known₂X-ray photoelectron spectroscopy (XPS) (Spectrum B). vlp-TiO₂Has an outstanding Cls-signal at a bond energy of 285.6eV, as evidenced by a 0 ls-absorption band at 530eVIs the element carbon. In contrast, spectrum B shows the Cls-signal of elemental carbon at a bond energy of 284.5eV, as well as bands at 289.4eV and 294.8e.V, indicating carbonate. Corresponding IR spectra at 1738, 1096 and 798cm^-1There are also typical carbonate bands.

FIG. 4 illustrates the vlp-TiO₂Relative to unmodified TiO₂Degradation of 4-chlorophenol (as 2.5X 10) by artificial visible light (lambda. gtoreq.455 nm)^-4Aqueous M solution). The graph shows The Organic Carbon (TOC) in solution_t) Relative to the initial value (TOC)₀) And (4) descending. With vl-TiO₂Complete degradation after 3 hours.

FIG. 5 illustrates the reaction with unmodified TiO₂In contrast, vlp-TiO₂Degradation of 4-chlorophenol (as 2.5X 10) by natural light diffused indoors^-4Aqueous M solution). The graph shows The Organic Carbon (TOC) in solution_t) Relative to the initial value (TOC)₀) And (4) descending. Even in the case of weak intensity of diffused natural light (7-10W/m in the range of 400-1200 nm)²) Lower, vlp-TiO₂Causing 80% degradation in six hours. Even in the case of diffuse natural light of very low intensity (1.6 to < 1W/m)²) In contrast to the commercially available TiO₂Photocatalyst (Degussa P25, Kemira UV-Titan, Sachtleben Hombikat, Tayca MT-100SA), vl-TiO₂Also exhibits significant photoactivity. As described above, 2.5X 10 was measured^-4Degradation rate of M4-chlorophenol solution.

a) Light intensity: 1.6W/m²(ii) a Time: 12h

Catalyst and process for preparing same BET surface area Rate of degradation

vlp-TiO₂ 170m²/g 16％

P25 50m²/g 4％

UV-titanium 20m²/g 5％

Hombikat 240m²/g 9％

MT-100SA 50m²/g 5％

b) Light intensity: < 1W/m²(ii) a Time: 24h

Catalyst and process for preparing same BET surface area Rate of degradation

vlp-TiO₂ 170m²/g 18％

Hombikat 240m²/g 3％

FIG. 6 illustrates the reaction with unmodified TiO₂In contrast, vlp-TiO₂Photocatalytic efficiency when benzene (5 vol%), acetaldehyde (2 vol%) and carbon monoxide (5 vol%) were degraded by natural light diffused in the room. A 1-liter round-bottom flask was used as a reactor equipped with a paper-round filter coated with 12mg of titanium dioxide (d ═ 15 cm). The graph shows The Organic Carbon (TOC) in the atmosphere_t) Relative to the initial value (TOC)₀) And (4) descending. The curves show benzene, acetaldehyde and carbon monoxide being reacted by the inventive vlp-TiO₂Degradation and unmodified TiO of acetaldehyde₂And (4) degrading.

FIG. 7 shows vlp-TiO₂X-ray powder diffraction pattern of (2), only anatase reflection. The crystal size calculated according to the Scherrer method was 10 nm.

FIG. 8 shows the generation of vlp-TiO by high resolution electron microscopy (HTEM)₂Figure, gridlines with crystals. The crystal size can be estimated to be in the order of 10 nm.

FIG. 9 shows the vlp-TiO expressed as C/Ti ratio₂Carbon-depth curve of (a). By ion bombardment (Ar)⁺) And ESCA assay. Bombardment time indicated 5X 10³Seconds correspond to a depth of about 5 nm.

Preparation of

The process of the invention starts from a titanium compound which is present as amorphous, partially crystalline or crystalline titanium oxide or hydrous titanium oxide and/or in the form of titanium hydrate and/or titanium hydrate, hereinafter referred to as starting titanium compound.

The starting titanium compound is formed, for example, in the preparation of titanium dioxide according to the sulfate process or according to the chloride process. Titanium hydrate or titanyl hydrate or metatitanic acid is produced, for example, in the hydrolysis of titanyl sulfate or titanyl chloride.

The starting titanium compound may be present as a finely divided solid or in a suspension having a corresponding solids content of at least 15% by weight, the solids having a BET specific surface area of at least 50m²A BET of about 150 to 350m is preferred²A BET of 150 to 250m²/g。

For industrial use of the process according to the invention, titanium hydrate from the sulfate process is preferred as starting titanium compound for economic reasons. The titanium hydrate is advantageously first freed of adhering sulfuric acid by neutralization and washing, SO that the sulfate content of the solid after drying is < 1% by weight, expressed as SO₃And (6) counting.

The decomposition temperature of the carbonaceous material is at most 400 ℃, preferably < 350 ℃, preferably < 300 ℃. Carbon-containing substances which have proven suitable are, for example, wood, carbon black or activated carbon, in particular organic carbon compounds, such as hydrocarbons which contain at least one functional group. The functional group may be: OH; CHO; COOH; NH (NH)_x；SH_x(ii) a COOR, wherein R is alkyl or aryl. Suitable are, for example, succinic acid, glycerol or ethylene glycol. Sugars or other carbohydrates may also be used, as may organic ammonium hydroxides, especially tetraalkylammonium. Mixtures of the compounds mentioned are also suitable. Water-soluble polyols having a carbon/oxygen ratio of about 0.7 to 1.5, preferably about 1, especially pentaerythritol, are preferably used. The carbon compound may be used as a solid or as a solution or suspension.

The organic carbon compound should have as high an affinity as possible for the surface of the starting titanium compound so that an intimate bond can be produced therewith.

The starting titanium compound is intimately mixed with the organic carbon compound in such a way that the surface of the starting titanium compound is coated with the carbon compound. The organic carbon compound may be present on the surface of the starting titanium compound by physical adsorption or chemical adsorption. Coating the surface of the starting titanium compound can be achieved by dissolving the carbon compound in a suspension of the starting titanium compound or by mixing a suspension of the carbon compound with a suspension of the starting titanium compound. It is likewise possible to subject the carbon compound to intensive mixing with the powdery starting titanium compound which has been dried beforehand. In the case of using titanium hydrate, alternatively, the carbon compound may be mixed as early as the preparation of titanium hydrate into a hydrolyzable solution. In the obtained mixture of the starting titanium compound and the carbon compound, the amount of the carbon compound in the starting titanium compound (as a solid) is 1 to 40% by weight.

If the mixture is present as a suspension, it is dried to a powdery solid before further processing. Known methods, such as spray drying or fluidized-bed drying, are used for this purpose.

The resulting, optionally pre-dried mixture is subjected to a heat treatment at a temperature of up to 400 ℃. The heat treatment is carried out in an oxidizing atmosphere, preferably in air or an oxygen-air mixture. At this time, the organic carbon compound is decomposed on the surface of the starting titanium compound and releases H₂O、CO₂And CO. Although the heat treatment can also be carried out in a (discontinuous) batch operation, for example in a commercially available laboratory oven, a continuous process which can be carried out with defined temperature characteristics is preferred for economic reasons. All methods which make it possible to achieve the corresponding temperature profile and the necessary retention time are conceivable as continuous methods. Particularly suitable apparatuses are indirect and direct-heated rotary kilns. Continuously operating fluidized bed reactors, fluidized bed dryers and heated ploughshare mixers may also be used. The latter three devices may also be operated in a discontinuous mode of operation.

The heat treatment is preferably carried out so that the resultant carbon content is 0.05 to 4.0 wt%% by weight, preferably 0.05 to 2.0% by weight, particularly preferably 0.3 to 1.5% by weight, in particular 0.4 to 0.8% by weight, of the product (vlp-TiO)₂). During the heat treatment, the color changes from white to grey and then to beige. The final product showed a beige to pale grayish yellow color. Characterized in that carbon is detectable both in the amorphous and polycrystalline range of the surface layer and in the surface itself. The product is photoactive in visible light.

After the heat treatment, the product is deagglomerated by known methods, for example in a rod mill, jet mill or back-jet mill. For powdered pre-dried mixtures, heat treatment mostly results in an agglomerate-free product, which does not require further grinding. The particle size to be achieved depends on the particle size of the starting titanium compound. The particle fineness or specific surface area of the product is very small, but of the same order of magnitude as the educts. The particle size to be achieved by the photocatalyst depends on the field of use of the photocatalyst. Usually in the presence of, for example, TiO₂Within the range of the pigment, but may be below or above. A specific surface area according to BET of 100 to 250m²A concentration of 130 to 200m²A specific volume of 130 to 170m²/g。

Examples

The invention is described in detail with the aid of the following examples, without limiting the scope of the invention thereto.

Example 1:

aqueous titanyl hydrate slurry (35% by weight solids) was prepared according to the sulfate method and diluted with distilled water at room temperature to form a stirrable suspension. The solid content is 20-25%. NaOH solution (36 wt%) was added until the pH was adjusted to 6.0-7.0. The suspension is then filtered and washed with distilled water until the SO measured as dry residue₃The content is less than 1 wt%.

The titanyl hydrate neutralized and washed in this way is subsequently diluted again with distilled water to a stirrable suspension (25% solids) and 12% by weight of succinic acid, calculated as solids, are added. Succinic acid was added to the suspension as a solid and the suspension was stirred until the succinic acid was completely dissolved. To improve the solubility of succinic acid, the suspension was heated to about 60 ℃. The suspension prepared in this way is dried under stirring in a surface evaporator (IR light source) until the suspension is slurried. The slurry was then dried in a laboratory drying oven at 150 ℃ until the solids content was > 98%.

300g of the dried titanyl hydrate/succinic acid mixture is finely comminuted (for example by means of a mill and sieve) and the powder obtained is placed in a quartz cup with a lid in a laboratory oven at 290 ℃. Taking out the quartz cup after 1-2 hours, and mixing the powder again. After 13-15 hours in the laboratory oven, the powder changed color from initially yellow to gray-yellow through gray-black. Final heat treatment to vl p-TiO₂The carbon content is reduced from the initial 5-5.5 wt% to about 0.65-0.80 wt%.

The photocatalyst was then de-agglomerated and analyzed for carbon content, optical properties, BET surface area and photoactivity.

Example 2

The procedure is carried out analogously to example 1, with the difference that 12% by weight of pentaerythritol is added as a solid to the titanyl hydrate suspension.

Example 3

The procedure is carried out analogously to example 2, with the difference that 5% by weight of pentaerythritol is added as solid to the titanyl hydrate suspension.

Example 4

The titanyl hydrate/pentaerythritol-suspension was prepared as described in example 1 using 5 wt% pentaerythritol. In contrast to example 1, the suspension thus obtained was subjected to a heat treatment in a continuously operated rotary kiln as follows:

the rotary kiln is operated in countercurrent and is heated directly by gas burners. The flame of the gas burner is protected by the flame tube and is thus protected fromProduct of neutralization (vip-TiO)₂) In direct contact. The heated furnace had a length of 7m and an internal diameter of 0.3 m. The suspension was finely sprayed at the entrance of the furnace. The amount of suspension fed was 40 kg/h. The chain internals of the furnace inlet provide good turbulence and thus rapid drying, followed by comminution of the dried material. The operation time of the continuously operated rotary kiln was 1 hour. The furnace temperature in the outlet zone was controlled at 260 c by the amount of gas passed through the burner. vlp-TiO producing a fine gray-yellow powder at the furnace exit₂. Then the vlp-TiO₂Deagglomeration was carried out in a laboratory mixer (Braun, MX2050) and analyzed for carbon content, optical properties, BET surface area and photoactivity.

Example 5

The procedure was carried out similarly to that of example 4 except that the furnace temperature of the outlet zone was controlled at 280 ℃ by the gas amount of the burner.

Example 6

The titanyl hydrate/pentaerythritol-suspension was prepared as described in example 1 using 5 wt% pentaerythritol. In contrast to example 1, the suspension was pre-dried in an electric furnace to a powdery solid with a residual moisture content of 22%. In a continuously operating indirectly heated rotary furnace, the pre-dried, powdery starting material is heat-treated as follows:

the rotary kiln was operated in concurrent flow and electrically heated in three zones. The heated furnace had a total length of 2700mm and an internal diameter of 390 mm. The powdered solids are fed into the inlet of the furnace by a quantitative screw conveyor. The chain internals provide an even distribution in the furnace over the entire length of the rotating tube and prevent adhesion to the furnace walls. The amount fed was 25kg solids per hour. The operation time of the continuously operated rotary kiln was 0.5 hour. The furnace temperatures of the three heating zones are electrically controlled. The respective temperatures of the three heating zones are individually adjustable. Fine powder of velum-TiO generated at the furnace exit₂. Then the vlp-TiO₂Deagglomeration was carried out in a laboratory mixer (Braun, MX2050) and analyzed for carbon content, optical properties, BET surface area and photoactivity.

Counter example

Analogously to example 2, the BET surface area is approximately 10m²Per g of TiO₂Pigment (anatase) (commercial Kronos 1000) was mixed with 12% pentaerythritol and heat treated.

Examples	Organic matter	Thermal treatment		vlp-TiO2Analysis of					Photoactive component
										℃	Time (h)	Content of C	PLV testing			BET	Degradation of 4-CP (%) within 120 minutes
		(％)	L*	b*	a*	m2/g
								1	Succinic acid			290	13	0.79	85.4	9.85	1.63	164	48
2	Pentaerythritol	290	28	0.75	86.9	10.08	1.53			158	50
								3	Pentaerythritol			290	10	0.76	83.7	10.03	1.59	140	63
4	Pentaerythritol	260*	1**	0.92	85.1	11.7	1.2			152	58
								5	Pentaerythritol			280*	1**	0.50	85.8	9.4	2.2	160	68
6	Pentaerythritol	300***	0.5**	0.78	83.0	11.0	2.6			167	86
								Counter example	Pentaerythritol			290	42	0.82	74.7	9.12	2.50	11.6	＜5

Maximum temperature measured at the outlet of the rotary kiln

Running time of feed through rotary kiln

Temperature of three heating zones measured across the heating element

The table summarizes the vip-TiO of the invention₂Analytical value and photoactivity of (a).

vlp-TiO from titanium hydrate₂Examples 1 to 6 show excellent photocatalytic efficiency in the visible region while showing good optical values (PLV test). The use of anatase pigments instead of titanium hydrate as the starting titanium compound leads to products which have no noteworthy photoactivity (counterexample).

Example 7

5g of titanium dioxide (commercially available from Kerr-McGee Pigments GmbH, TRONOXTitanhydratat-0) were suspended in 20ml of distilled water at room temperature, mixed with 5ml of ethylene glycol (commercially available from FLUKA AG), and treated in an ultrasonic bath (Sonorex Super RK 106 from Bandelin electronic, 35kHz, 120W eff. Hf-Leistung) for 30 minutes. After magnetic stirring overnight, the solvent is removed, preferably in vacuo, and the residue is dried at 100-200 ℃, preferably at about 200 ℃, for at least 12 hours, then heated to 300 ℃ in a closed vessel for one hour and held at this temperature for a further three hours. The powder was found to change color from white through dark gray to beige. Longer heating times produced a colorless, inactive powder.

Elemental analysis of the product gave 2.58 wt% carbon, 0.02 wt% nitrogen and 0.40 wt% hydrogen. Unmodified TiO₂Containing 0.07 wt% C and 0.0 wt% N and 0.0 wt% H.

Example 8

For separating the carbon compounds on the surface, 5g of vlp-TiO₂In 100ml of 2M sodium hydroxide solution (pH12) were stirred overnight. The extract was obtained by centrifugation as a pale yellow colour and as an almost colourless white residue, which was dried at 100 ℃. The resulting powder showed no activity in degrading 4-chlorophenol under visible light. If the powder is combined with the extract again and heated slightly, preferably to about 200 ℃, there is an untreated (non-alkaline) vlp-TiO in the degradation reaction₂The same activity.

Example 9

For coating plastic films, the powder prepared according to example 6 is suspended in a liquid, such as methanol or ethanol, in an ultrasonic bath and the resulting suspension is applied as thinly as possible to the film by means of a spray bottle. After subsequent drying at 343K, the coating is repeated until the desired layer thickness is reached.

Instead of a plastic film, other supports can also be used, such as paper (see experiment in fig. 6) or aluminum (see test method h below): "dip coating").

Measuring method

a) Determination of the optical value (PLV test)

The method is used for finding out the vlp-TiO₂The optical values of (a) brightness L, hue a and hue b. Under defined conditions, the test is carried out on the vlp-TiO using a micro-hydraulic press from FrankfurMATRA₂A powder compact was prepared. The powder compaction is then determined with a colorimeter of the HUNTERLAB trichromeEmission value of the article.

Grinding of the vlp-TiO before the preparation of the compacts₂. For this purpose, 100g of the resulting vlp-TiO are mixed₂Was added to a commercially available mixer (manufacturer: Braun, model: MX2050) and ground 12 times for 5 seconds. The mixer was opened between each grinding step and the powders were mixed again. A piece of white paper, matt on both sides, was laid on a base plate with an annular groove and a metal ring (4 cm in height, 2.4cm in diameter) was pressed in the groove with a press. About 25g of ground vlp-TiO were mixed with gentle shaking and tapping₂Is added into the metal ring. The powder was compressed with a pressure of 2-3 kN. The pressing process was repeated a second time until the desired operating pressure of 15kN was reached.

The metal ring is separated from the base plate by carefully rotating and pulling the metal ring. The paper between the base plate and the ring is removed. Now there is a compact in the ring for the measurement process on the HUNTERLAB colorimeter.

The measured values L, a, b are read directly on the colorimeter.

b) Determination of photoactivity (hazardous substance degradation)

Under artificial visible light:

in an ultrasonic bath, 15mg of vlp-TiO₂In 15ml 2.5X 10^-4M in 4-chlorophenol solution for 10 minutes, and then exposed on an optical bench in a water-cooled round sample cell. To determine photoactivity, exposures were performed with an Osram XBO 150W xenon arc lamp mounted in a focusing lamp housing (AMKO model A1020, focal length 30 cm). The spectrum of the lamp is plotted in fig. 10. The reaction was carried out in a 15ml embedded, water-cooled round cuvette (internal diameter 30mm, layer thickness 20 mm). The reaction suspension can be stirred with a stirring motor and magnetic stirrer mounted on one side. A round sample cell is drawn in fig. 11. The sample cell is fixed at the focus of the lamp. The light is focused such that only the reaction chambers of the sample cell are illuminated. All components are fixedly mounted on the optical bench. In order to eliminate ultraviolet rays, a slit filter (Schott Corp.) having a permeability of lambda.gtoreq.455 nm was installed in the light path. To prevent reactionThe chamber may be heated by exposure to light and an IR filter is also installed in the optical path. Here a water-filled cylinder (diameter 6cm, length 10 cm).

The decrease in the concentration of 4-chlorophenol is followed by ultraviolet spectroscopy (λ 224nm) or, in the case of degradation (oxidation), by measuring the total content of organic carbon (TOC value).

Among natural light diffused indoors:

50mg of vlp-TiO in an ultrasonic bath₂In 50ml 2.5X 10^-4M in 4-chlorophenol solution 10, and then irradiated with room natural light while stirring in an Erlenmeyer flask (100 ml).

Degradation of acetaldehyde gas, benzene vapor and carbon monoxide:

two double-coated vlp-TiO substrates were placed in a round-bottomed flask (1 liter) filled with air-saturated acetaldehyde gas (2 vol.%) or benzene vapor (5 vol.%) or carbon monoxide₂Round filters (paper, d 15cm, 12mg catalyst/filter).

The flask was then exposed to natural light in the laboratory and the reduction of harmful substances and the formation of carbon dioxide was followed by IR spectroscopy.

c) Determination of carbon content

Total organic carbon content (TOC) was determined using a carbon analyzer LECO C-200. The measurement method is based on the combustion of TiO in an induction furnace under oxygen₂And then the carbon dioxide formed is determined by IR detection. TiO 2₂The initial weight was about 0.4 g.

d) Determination of BET (Brunauer-Emmett-Teller) specific surface area

The BET surface area is determined according to the statistical volume principle using Tristar3000 from Micromeritics.

e) XPS measurement

To measure the bond energy, an instrument Phi 5600 ESCA spectrometer (23.50eV pass energy; A1 standard; 300.0W; 45.0 deg.) was used.

f) ESR measurement

For measurement of electron resonance spectra, a Bruker elexyz 580 spectrometer X-band (9.5GHz) was used. The sample is evacuated to 10^-5At torr, fill with helium until the pressure is 10^-2Torr, then melted. The measurements were carried out under the following conditions:

the magnetic field was adjusted to 100 Hz. RF power: 0.0002-1 mW. Field: 3340 3500G. Scanning width: 100 and 500G. Switching time: 81.92 ms. Time constant: 40.96 ms. Width of the finish: 0.2-13G, temperature: 5K. The g value was determined by Hall-Sonde.

g) Measurement of the diffuse reflectance Spectrum (Kubelka-Munk-function)

The diffuse reflectance spectrum of the powder was measured using a Shimadzu UV-2401 PC UV/Vis spectrometer equipped with Ulbrich balls. The powder was ground together with barium sulfate in a mill before measurement using barium sulfate as white standard. The Kubelka-Munk-function is proportional to the absorption rate.

h) Super hydrophilic property

To measure the contact angle of water, vlp-TiO₂And unmodified TiO₂Suspended in distilled water, respectively, and applied by "dip coating" to an aluminum plate of 5X 5cm size and calcined at 400 ℃ for 1 hour. The contact angle of the unmodified titanium dioxide after storage under natural light was measured to be 21 °, whereas the contact angle of the vlp-Ti02 was only 8 °. The contact angle of the uncoated aluminium plate was 91 °.

Claims (32)

1. A photocatalyst containing carbon based on titanium dioxide, which has a significant light absorption in the lambda region ≥ 400nm, relative to pure titanium dioxide, characterized by an electron spin resonance spectrum ESR, measured at a temperature of 5K, which has only a significant signal in the g-value range 1.97-2.05, and by carbon being present only in the surface layer of the titanium dioxide particles, characterized in that it has a carbon content of 0.05-4 wt.%.

2. The photocatalyst according to claim 1, wherein the signal appears at a g value of 2.002 to 2.004 in an ESR spectrum.

3. The photocatalyst according to claim 1, characterized in that in X-ray photoelectron spectroscopy XPS there is a strong absorption band at a bond energy of 285.6eV, calculated as O1 s-band at 530 eV.

4. Photocatalyst according to claim 1, characterized in that the Kubelka-Munk function F (R) is proportional to the absorbance_∞) 50% of the value at 400nm at 500nm and 20% of the value at 400nm at 600 nm.

5. A photocatalyst as claimed in claim 1, characterized in that the photoactivity is at least 20%.

6. The photocatalyst according to claim 1, wherein the carbon content is 0.3 to 1.5% by weight.

7. The photocatalyst according to claim 1, characterized in that a carbonate band is not exhibited in neither X-ray photoelectron spectroscopy (XPS) nor in infrared spectroscopy.

8. The photocatalyst as claimed in claim 1, wherein the BET specific surface area is 100 to 250m²/g。

9. A process for preparing titanium dioxide-based carbon-containing photocatalysts having a pronounced light absorption in the lambda ≥ 400nm region relative to pure titanium dioxide, characterized in that they have a refractive index of at least 50m²A titanium compound having a BET specific surface area/g is uniformly mixed with a carbon-containing substance, and the mixture is heat-treated at a temperature of up to 400 ℃ with carbon being present only in the surface layer of titanium dioxide particles, characterized in that the carbon content is 0.05 to 4% by weight.

10. The process according to claim 9, characterized in that the titanium compound is amorphous, partially crystalline or crystalline titanium oxide or hydrous titanium oxide or titanium hydrate.

11. The process according to claim 10, characterized in that the titanium compound is a titanium hydrate produced by the sulfate process.

12. A method according to claim 11, characterized in that the titanium hydrate is first neutralized and washed SO that the SO of the solid after drying is obtained₃The content is less than 1 wt%.

13. A method according to claim 9, characterized in that the decomposition temperature of the carbonaceous material is at most 400 ℃.

14. The method of claim 9, wherein the carbonaceous material is a hydrocarbon containing at least one functional group.

15. The method according to claim 14, characterized in that the functional group is one of the following groups: OH, CHO, COOH, NH_x、SH_xCOOR, wherein R is alkyl or aryl.

16. The method according to claim 9, characterized in that a compound selected from the group consisting of ethylene glycol, glycerol, carbohydrates, organic ammonium hydroxides, or mixtures thereof is used as the carbon-containing substance.

17. The method of claim 9, wherein the carbonaceous material is wood, activated carbon, or carbon black.

18. The method as claimed in claim 9, characterized in that the heat treatment is carried out in a continuously operating calcining apparatus.

19. The process according to claim 9, characterized in that the heat treatment is carried out in a rotary kiln or in a fluidized bed.

20. Method according to claim 9, characterized in that the heat treatment is carried out in an oxidizing atmosphere.

21. The method according to claim 9, characterized in that the heat treatment is carried out in air or in an oxygen-air mixture.

22. A method according to claim 9, characterized in that a separate pre-drying is carried out before the heat treatment.

23. The method according to claim 22, characterized in that the pre-drying is carried out in a spray dryer or a fluidized bed dryer.

24. A photocatalyst prepared according to the method of claim 9.

25. Use of a photocatalyst according to any one of claims 1 to 8 or 24 for plastics, fibres, paper and pavements.

26. Use of a photocatalyst according to any one of claims 1 to 8 or 24 in a plastic film.

27. Use of a photocatalyst according to any one of claims 1 to 8 or 24 in the construction industry for the production of components, and in the automotive industry.

28. Use according to claim 27 for the production of concrete parts, ceramics, wallpaper, textiles, and secondary linings for indoor and outdoor roofs and walls.

29. Use according to claim 27 for the production of concrete-paving bricks, roof bricks, ceramic tiles, refractory bricks.

30. Use of a photocatalyst according to any one of claims 1 to 8 or 24 in an air conditioner, a device for air purification and air disinfection, and a water purification device.

31. Use according to claim 30 for antibacterial or antiviral purposes.

32. Use of a photocatalyst according to any one of claims 1 to 8 or 24 in photovoltaic cells and for the decomposition of water.