SI22672A - PREPARATION OF TiO2/SiO2 SOLS AND THEIR USE FOR APPLICATION OF SELF-CLEANING AND ANTI-FOGGING COATINGS - Google Patents

Abstract

The subject of the invention relates to a procedure of low temperature preparation of TiO2/SiO2 sols and their use for application of thin optically transmissive coatings with self-cleaning and anti-fogging properties. The preparation according to the invention is characterised in that the procedure consists of preparation of an acidic water sol containing photochemically active TiO2 nanoparticles, addition of SiO2 precursor followed by the hydrolysis/condensation of SiO2 and organically modified SiO2, addition of amorphous TiO2 hydrolysate, addition of colloidal SiO2, dilution of the prepared sol with water and/or organic solvents, application of the prepared sol to the substrate, evaporation of solvent and, in case of condensation reactions at the room temperature, formation of a thin and uniform TiO2/SiO2 layer with self-cleaning properties.

Description

Preparation of TiCVSiC ^ salts and their use for self-cleaning and anti-corrosion coatings

The subject of the invention relates to the process of low-temperature preparation of TiO ₂ / SiO2 salts and their use for the application of thin, optically permeable coatings with self-cleaning and antifouling properties. The invention therefore provides the preparation of optically permeable and persistent thin coatings with photocatalytic and hydrophilic properties from TiO ₂ / SiO ₂ colloidal solutions, i.e. salts.

On surfaces exposed to atmospheric influences and atmospheric pollution due to human activity, over time, various macroscopic particles and individual molecules of organic and inorganic origin are adsorbed. Dirt that accumulates on surfaces is both aesthetically pleasing and, in some cases, a safety issue. Dirt is most disturbing on substrates that are permeable to visible light, that is, on various glass and transparent organic polymers. Cleaning such surfaces is often a time-consuming and dangerous task, and chemicals are used for cleaning, which represents both a financial and environmental burden.

One way to keep surfaces clean for a long time is to use thin protective coatings applied to the substrate. There are two options: hydrophobic and hydrophilic coatings. The hydrophobic surfaces are characterized by the fact that the contact angle between the applied water droplet and the substrate is very large (> 150 °) and the circular water droplet with dirt consequently does not adhere to the substrate. Several methods are known for the preparation of hydrophobic surfaces using special polymers or waxes, which coat the surface by physical methods, i.e., by compression of polymer droplets, or by ion etching or chemical methods, e.g. chemical vapor deposition - KPO. Although the resulting surfaces have good self-cleaning properties, disadvantages in the preparation and stability of the resulting surfaces, this is a costly coating of the substrates, the coatings are often misty, the durability of the coatings is limited in time, preventing their wider applicability.

Another possible solution is hydrophilic coatings, which are often various semiconductor oxides of transition metals, e.g. ZnO, ZrO ₂ , TiO ₂ , WO3, etc. In the presence of UV radiation and water molecules, chemical changes occur on their surface, which in turn become very hydrophilic; contact angle between the surface and the water droplet below 5 °. High hydrophilicity increases adhesion

-2 water, so that water easily flushes out poorly adsorbed inorganic particles, such as e.g. sand.

However, hydrophilicity is not the only reason for the self-cleaning properties of semiconductor oxides. Another important self-cleaning property is photocatalytic efficiency. When a particle of a semiconductor absorbs a photon of electromagnetic wave of suitable energy, most often photons of the UV part of the spectrum, a transition of the valence electron into the conduction band occurs. The resulting positive gap is a strong oxidant, and the electron plays the role of a reducing agent. Both can react with molecules adsorbed on the surface of a particle, resulting in the oxidation of the molecules by the positive gap and the reduction of the molecules by the electrons. Thus, the complete mineralization of organic molecules gradually leads to CO2, H ₂ O and inorganic acids. Anatase TiO ₂ has proven to be the most suitable photocatalyst of all the oxides studied so far, because it is non-toxic, chemically and physically stable, inexpensive, etc. Only nanocrystalline TiO ₂ is useful for window cladding, since only nanocrystalline coatings can be made sufficiently optically permeable for commercial use. The classic preparation of anatase TiO ₂ requires firing from salts of prepared powders or thin layers above 350 ° C. At lower temperatures, the anatase crystalline phase is not formed, which is crucial for photocatalytic efficiency. This required high temperature limits the applicability of that method. Such methods can only be used in specialized factories, e.g. in glass manufacturing companies. The commercial product for high temperature heat treatment is Pilkington Activ (TM). It is a glass coated with a 20-30 nm thick layer of nanocrystalline anatase TiO ₂ . The layer is mechanically stable, photocatalytically active with extremely high transmittance in the visible part of the spectrum. Floating glass KPO techniques are used in the coating.

For wider use of self-cleaning TiO _2, it is necessary to prepare TiO ₂ salt, which can be applied to surfaces under normal atmospheric conditions, which does not require additional thermal treatment and which results in optically transparent and solid coatings. In an article by Ichinose, H.; Terasaki, M.; Katsuki, H. J Sol-Gel Sci Technol 2001, 22, 33-40 describes the preparation of a peroxo-modified anatase salt useful for low-temperature photocatalytic coating preparation. The prepared glass coated glasses are photocatalytically active and the adhesion of the coatings to the substrate is satisfactory. However, the optical quality of the prepared coatings is not reported. The downside is also the rather demanding preparation of salt, using a considerable number of chemicals.

-3In an article by Matsuda, A.; Matoda, T.; Kotanim Y .; Kogure, T.; Tatsumisago, M.; Minami, T. J Sol-Gel Sci Technol 2003, 26, 517-521 describes the preparation of nanocrystalline coatings on glass and on organic optically permeable polymers, achieving crystallization of TiO ₂ into anatases by treating hot water coatings. Due to the higher strength of the coating, its salts also contain SiO ₂ precursors. The coatings are photocatalytically active, the adhesion to the surface of the substrate and the hardness of the coating are satisfactory. The downside of film making is the impractical treatment of boiling water coatings for commercial use.

U.S. Patent 5,149,519 discloses the preparation of a low-temperature salt containing crystalline anatase TiO ₂ and does not use the prepared salt to prepare thin TiO ₂ layers.

In article Yun, YJ; Chung, JS; Kirn, S.; Hahn, SH; Kirn, EJ Mater Lett 2004, 58, 37033706 describes the preparation of a nanocrystalline TiO ₂ coating on ordinary sodium glass at low temperatures, with Yun et al. prepared a titanium tetraisopropoxide salt in acidic aqueous solutions, which was refluxed for several hours to obtain crystallization of amorphous TiO ₂ . The method of salt preparation using conventional chemicals and technologically simple process as well as the ease of applying the prepared salt to different substrates are advantages of the system under study. By design, it is also closest to the present invention, which in our case further comprises an additional SiO ₂ component to achieve better mechanical and hydrophilic properties of the coatings.

EP 0 913 447 discloses the preparation of self-cleaning liquids for various substrates using commercially available TiO ₂ and SiO ₂ salts. In the preparation of self-cleaning liquids, they also use various additives, such as surfactants, organic solvents, silicones. The coatings are photocatalytically active and the adhesion to the surface of the substrate and the hardness of the coatings are good in certain cases. A disadvantage of the invention is the use of commercially available TiO ₂ and SiO ₂ salts. In the patent EP 1 544 269, the invention is made of commercial TiO ₂ nanocrystalline particles and SiO ₂ colloidal solutions, thereby adding a binder made of hydrolyzed titanium alkoxide. The coatings thus obtained have good mechanical and hydrophilic properties even in the dark.

EP 0 826 633 discloses the preparation of aqueous dispersion and a thin transparent TiO ₂ coating in the low temperature route of T1CI4, which is a much cheaper raw material than any titanium alkoxide, but the removal of chloride ions by electrodialysis is required in this process. In the patent document WO 2004/060555, the invention is based on titanium peroxide salts and nanoanatase particles with the addition of urethane acrylic polymers to improve the wettability of the coating surface and to reduce the contribution of the yellow coloration in thin layers by the peroxide process. Inputs of non-volatile organic additives have, in addition to the good sites, the bad with

-4view of the additional chemical in the synthesis and the associated additional cost and in view of the questionability of the long-term integrity of such thin layers due to the degradation of organic matter in the photocatalysis process. There are more patent documents, e.g. WO 2004/108846 and WO 2004/005577 dealing with the preparation of photocatalytically active hybrid organic-inorganic thin films based on siloxanes and TiO ₂ dispersions or salts.

A technical problem that has not been satisfactorily solved so far is thin optically permeable coatings with self-cleaning and anti-scouring properties, which will be based on a simple process of preparing salts from accessible and not expensive chemicals, where it will be an easy way to apply salt to the substrate without further hardening the layers with thermal treatment where there will be a good relationship between the mechanical strength and the photocatalytic effect of the thin coating, where there will be high optical transmittance of the coating over the entire visible spectrum and high hydrophilicity of the coating in the presence of UV radiation.

The object of the invention is such a process of low-temperature preparation of TiO ₂ / SiO ₂ salts and their use for the application of thin, optically permeable coatings with self-cleaning and antifouling properties, which will be based on the simple process of preparing salts from accessible and not expensive chemicals, which will be an easy way of applying salt to the substrate without further hardening of the layers by thermal treatment, where there will be a good ratio of mechanical strength to the photocatalytic effect of the thin coating, where there will be high optical transmittance of the coating over the entire visible spectrum and high hydrophilicity of the coating in the presence of UV radiation.

According to the invention, the problem is solved by the process of preparing TiO ₂ / SiO ₂ salts and their use for applying thin coatings according to independent claims.

The invention will be described by way of embodiments and illustrations showing:

Figure 1: X-ray diffractograms of a sample prepared from thin TiO ₂ / SiO ₂ layers according to the procedure in Example 7.

Figure 2: Demonstration of photocatalytic activity of prepared self-cleaning layers.

Figure 3: UV-Vis spectrum of TiO ₂ / SiO ₂ thin layers on glass compared to glass itself.

According to the invention, the preparation of the anatase TiO ₂ salt is first carried out, followed by the preparation of the photocatalytically active liquid and its application to different surfaces.

The first part of the invention is a modification of the process for preparing an anatase TiO ₂ salt made in acidic aqueous media at temperatures up to 100 ° C. As a basis, we used the process of preparation of low-temperature TiO ₂ sol, published in 2004 by Yun et al. By modifying their process, we were able to prepare a stable salt with weakly aggregated TiO ₂ particles, in which the anatase crystalline phase was demonstrated by X-ray diff action. The prepared TiO _{2 is} very easily dispersed in aqueous solutions to give stable salts.

(i) Titanium tetrachloride (TiCfi), titanium oxysulphate (TiOSCfi) or various titanium alkoxides may be used as the source of TiO ₂ . Preferably titanium tetraisopropoxide TTIP is used. TTIP (5 to 45 mL) was added while stirring at room temperature to absolute ethanol (between 1 and 10 mL). Immediately thereafter, the resulting liquid mixture was added dropwise with an aqueous acid solution while stirring at room temperature. In the presence of acid, the hydrolysis reaction of the titanium compounds takes place, leaving a weakly soluble, amorphous titanium oxide from the reaction mixture. The inorganic acids used are conc. HNO ₃ , conc. HCIO4, conc. HC1 and conc. H2SO4, the organic acids used are formic, ethanoic, propanoic. Aqueous acid solution was prepared by mixing water (between 30 and 100 mL) and concentrated acid (between 0.1 and 10 mL). The preferred acid concentration is between 1 and 3 mL of acid in 90 mL of water. Too low and high acid concentrations lead to the aggregation of TiO ₂ particles, which is an undesirable process if we want to produce as transparent a coating as possible. HC1O ₄ has been shown to be the preferred acid.

(ii) TiO ₂ is photocatalytically active in crystalline form, be it anatase or rutile. The anatase crystalline form is more photocatalytically active than rutile. Crystallization of amorphous TiO ₂ into crystalline form is achieved by heating the salt. The advantages of the present invention are: a) crystallization is already achieved by heating to a temperature below 100 ° C; b) crystallization and dispersion of TiO ₂ particles is achieved directly in the aqueous salt, ie without additional stages of separation and resuspension of TiO ₂ . The resulting suspension from (i) is refluxed for 2 to 100 hours. The optimum reflux time is between 30 and 60 hours. The shorter reflux time is reflected in the unfinished crystallization of TiO ₂ , but the longer time does not lead to a significant increase in the activity of sol or. the resulting coatings. After refluxing, a basic colloidal solution of crystalline TiO ₂ (basic TiO ₂ salt) is obtained. The basic TiO ₂ salt is stable at room temperature for at least 1 year. The weight fraction of TiO ₂ in the salt is between 2 and 10%. The size of TiO ₂ particles in the sol obtained from dynamic light scattering measurements (3D DLS SLS apparatus) is between 15 and 80 nm.

The second part of the invention relates to the preparation of a photocatalytically active liquid consisting of (i) anatase TiO ₂ particles; (ii) a binder made by hydrolysis and condensation of silicon alkoxide and / or organosilane; and / or (iii) a binder made by hydrolysis and condensation of titanium alkoxide; (iv) colloidal SiO ₂ ; (v) organic solvent and (vi) water. The process for preparing a photocatalytically active liquid is as follows. To the metered volume of TiO ₂ aqueous salt (i) is added a SiO ₂ precursor (ii) and / or hydrolyzate TiO ₂ and epoxysilane (iii) and / or already prepared colloidal SiO ₂ salt (iv). It is stirred at room temperature for 1 to 24 hours, thereby achieving hydrolysis and condensation of the SiO ₂ precursor. Water (vi) and organic solvent (v) are then added to the prepared salt. All phases are carried out between 15 and 30 ° C.

(i) The aqueous TiO ₂ salt described in the first object of the invention is used as the source of the anatase TiO ₂ particles. TiO ₂ is a mandatory component of the photocatalytically active liquid. Without this, no self-cleaning coating or coating can be prepared because TiO ₂ is the component that has self-cleaning properties (both superhydrophilicity and photocatalytic activity). The water content of the aqueous TiO ₂ salt in the final liquid is between 0.5 and 50%. Too low TiO ₂ concentration leads to the formation of optically high quality and completely permeable coatings, which, due to the low TiO ₂ concentration, have a low photocatalytic activity. Too high concentration of TiO ₂ in the final fluid leads to photocatalytically very active coatings, which do not meet optical standards.

(ii) SiO ₂ hydrolyzate is prepared in situ in an aqueous TiO ₂ salt by adding to the 5 mL aqueous TiO ₂ salt between 0 and 1 mL of tetraalkoxysilane containing alkoxy groups of 1 to 4 carbon atoms. Examples of tetraalkoxysilanes are tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane ... The most preferred tetraalkoxysilane is tetraethoxysilane (TEOS). SiO ₂ hydrolyzate increases 1) the strength and abrasion resistance of the final coating, 2) increases and prolongs the superhydrophilic effect of the final coating. In addition to tetraalkoxysilanes, various organosilanes may be used which have an unsaturated carbon-carbon bonded organic group instead of one alkoxide group. Such a group may be epoxy or acrylic in nature. The most preferred organic silane is 3-glycidoxypropyl trimethoxysilane (GPMS). The function of organically modified silanes is to increase the strength of the prepared thin film as a result of polymerization reactions between organic groups. The initiation of such polymerization does not require radical conditions, but can be carried out at slightly elevated room temperature with the aid of catalysts or the reaction can be initiated by UV radiation. With the above organosilanes thus

-7we further solidify the thin layer of photocatalyst at low temperatures. Too high a hydrolyzate concentration in the final photocatalytically active liquid reduces the photocatalytic activity of the prepared self-cleaning coating because it reduces the density of the photocatalytically active T1O2 particles in the final self-cleaning coating. Too low concentration of S1O2 hydrolyzate reduces the strength of self-cleaning coatings. The molar ratio of Ti from the anatase T1O2 sol to Si from the hydrolyzate S1O2 is between 3: 1 to 0.5: 1, the preferential ratio ranges from 2: 1 to 1: 1.

(iii) T1O2 hydrolyzate has the function of a binder of colloidal S1O2 and colloidal T1O2 particles and has the function of a catalyst for the polymerization of epoxy organic silanes. It is not a condition that both the S1O2 hydrolyzate and the T1O2 hydrolyzate are present in the self-cleaning fluid. Titanium alkoxides whose alkoxy groups contain from 1 to 4 carbon atoms are used as the precursor of T1O2. Examples of titanium tetraalkoxides used are titanium tetramethoxide, titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, titanium tetrabutoxide. For the sake of affordability and sufficiently high stability, titanium tetraisopropoxide (TTIP) is the most suitable candidate. Due to the higher reactivity of titanium alkoxides compared to silicon alkoxides, titanium alkoxides cannot be added directly to the aqueous T1O2 salt, since in this case uncontrolled hydrolysis and condensation of amorphous T1O2 occur. Therefore, T1O2 hydrolyzate must be prepared separately. It is prepared so that in a mixture of water (between 0.5 and 2 mL), the conc. HNO3 (between 0.5 and 2 mL) and an organic solvent (between 4 and 10 mL) were added dropwise a mixture of titanium alkoxide (between 10 and 30 mL) and an organic solvent (between 5 and 15 mL). The optimum molar ratio of water to titanium alkoxide must be between 1: 1 and 3: 1, and in any case less than 4: 1. A higher molar ratio of water to titanium alkoxide leads to complete hydrolysis and condensation of titanium alkoxide. Fully condensed titanium alkoxide loses the function of the binder. The resulting mixture was stirred at room temperature for between 2 and 10 hours to achieve hydrolysis and condensation of titanium alkoxide. The prepared hydrolyzate does not contain crystalline T1O2, which is different from the T1O2 sol (i). Finally, dilute the prepared hydrolyzate with an organic solvent to give a final T1O2 weight fraction of between 1 and 5%. The monoalkyl ethers of various glycols having good wettability of partially hydrophobic surfaces, such as e.g. glass. 2-methoxyethanol, propylene glycol butyl ether, 2-propoxyethanol have been shown to be an organic solvent. The prepared T1O2 hydrolyzate is added to T1O2 salt (s) so that the molar ratio of Ti in the anatase T1O2 grains (i) and Ti in the T1O2 (iii) hydrolyzate is between 5: 1 and 1: 1.

-8 (iv) Colloidal SiO ₂ is a colloid prepared by dispersion of very pure SiO ₂ in aqueous medium. The average size of SiO ₂ particles must be between 1 and 200 nm in order to avoid visible light scattering on the particles. The advantage of colloidal SiO ₂ SiO ₂ hydrolysates from their greater stability in water. Namely, the SiO ₂ hydrolyzate can be slowly dissolved in water because the hydrolysis and condensation reactions are not yet complete. Otherwise, the colloidal silica nanoparticles are completely condensed and therefore have a higher water resistance. The main functions of colloidal silica in the final photocatalytic fluid are 1) to increase the abrasive resistance of the self-cleaning coating; 2) increase in the superhydrophilicity of the self-cleaning coating. The patent described here uses commercially available colloidal silica, namely Levasil 200/30% (manufactured by HC Starck GmbH) and Snowtex IPA-ST (manufactured by Nissan Chemical Industries, Ltd.). Colloidal silica is added to mixture (i) and (ii) or mixture (i) and (iii) or mixture (i), (ii) and (iii) while stirring at room temperature. The molar ratio of Ti of the anatase TiO ₂ sol (i) to Si of colloidal silica (iv) is between 3: 1 to 0.1: 1.

(v) Unless an organic solvent is added to a self-cleaning liquid (otherwise based on water), the prepared salt cannot be uniformly applied to the substrate, since after the solvent has evaporated, a thin, thin TiO ₂ layer remains. The main function of the organic solvent is thus to increase the wettability of the self-cleaning liquid on various substrates, especially hydrophobic ones (glass and polymeric substrates such as polyacrylates, polycarbonates, polyethylene, polypropylene, polystyrene ...). As the wettability of the substrate is increased with the use of organic solvents, the proper selection of more viscous solvents makes it very easy to apply a thicker layer of self-cleaning fluid to the substrate, which is reflected in the higher photocatalytic activity. The organic solvents used must not be too volatile to allow them to evaporate at room temperature for a short period of time at the same time as they must not have a boiling point below 100 ° C to prevent them from evaporating from the surface before water. The organic solvents used must be at least partially soluble in water because the self-cleaning liquid contains a high proportion of water. Furthermore, the solvents used must not cause the aggregation of TiO ₂ anatase grains. A further condition is the non-toxicity of the compounds used and the low flammability. Monoalkoxy ethers of various glycols and mixtures of monoalkoxy ethers of glycols and primary alcohols with less than 4 carbon atoms have proved to be an appropriate choice. The best combination were 2-propoxyethanol in combination with 1-butanol, 2-methoxyethanol in combination with 1-butanol, propylene glycol butyl ether and propylene glycol butyl ether in combination with 1-butanol. The volume fraction of the sum of organic solvents in the final photocatalytic fluid must be less than 0.8. If higher, TiO ₂ aggregation occurs. If the proportion of organic solvents is too low, the problem is how

-9 Apply a thick layer of TiCh / SiCh evenly to the surface - The optimum volume fraction of the sum of organic solvents is between 0.5 and 0.8.

(vi) Water is added to the final photocatalytic fluid to cheapen the product and to maintain the stability of the prepared photocatalytically active liquid. Too much organic solvents lead to salt destabilization, resulting in the aggregation and deposition of TiCh- This product is no longer useful. The water content of the final photocatalytically active liquid must be between 0.7 and 0.2.

A third part of the invention is the deposition of photocatalytically active fluids on various surfaces. Surfaces can be transparent to visible light, such as. glass, polypropylene, polyethylene, polystyrene, various polyacrylates, polycarbonate ... The self-cleaning fluid can also be applied to light-tight surfaces: concrete, tiles, ceramic tiles, wood, brick ... The surface to which the self-cleaning fluid should be applied must be clean and dry. Different application methods are used: (i) spraying the liquid with the help of sprays; (ii) application of the fluid by means of a roller; (iii) application of a liquid by brush; (iv) application of a liquid by means of a cloth; (v) immersion of the object in self-cleaning fluid.

(i) Pour the resulting self-cleaning fluid into a sprayer, which can be manual or electric, and spray on the desired surface until a homogeneous layer of liquid is formed on the surface.

(ii) The roller is immersed in a self-cleaning fluid and then applied to the surface, leaving a homogeneous layer of liquid behind the roller which dries at room temperature.

(iii) Soak the brush in self-cleaning fluid and then coat the surface, leaving a homogeneous layer of liquid behind the brush that dries at room temperature.

(iv) Removing the cloth over the surface leaves a very thin trace of salt behind the cloth, which dries quickly and hardens. The resulting layer is very thin.

(v) Immerse the object to be coated with the self-cleaning layer in the self-cleaning liquid. The object is then uniformly withdrawn from the liquid, with the excess fluid draining off, and the remaining self-cleaning fluid on the object is dried at room temperature and cured.

In all the above cases, after application, a thin liquid layer is left on the surface of the substrate, which dries at room temperature to form a solid, semi-crystalline self-cleaning coating which is transparent to visible light. Its thickness is less than 100 nm, and in most deposition methods it is less than 20 nm, which, given its high optical quality, is also sufficient for a good self-cleaning effect.

-10The coating does not need to be (but can be) further cured by heating. The coating is temperature resistant (X-ray diffractograms show the persistence of the anatase phase up to 1000 ° C and only then begins to transition to rutile), has proven self-cleaning properties, its hydrophilicity is expressed in the dark, and further increases under the influence of UV radiation.

Such coatings are also useful on surfaces where we have problems with fogging. This prevents various mirrors (such as car rearview mirrors, bathroom mirrors, saunas) and lenses (such as prescription glasses) from blurring.

The invention is explained, but by no means limited, by the following embodiments.

Example 1

TTIP (15 mL) was dissolved in absolute ethanol (2.5 mL). Particularly, 70% perchloric acid (1 mL) and water (90 mL) were mixed. This solution was added dropwise to TTIP solution while stirring. An exothermic reaction of uncontrolled hydrolysis and condensation of TTIP takes place, resulting in a white precipitate of hydrated, amorphous TiC ^. The resulting mixture was refluxed for 48 hours, crystallizing and deaggregating T1O2. After heating, a stable basic salt is obtained.

Example 2

TTIP (15 mL) was dissolved in absolute ethanol (2.5 mL). 65% nitric acid (1) and water (90 mL) were mixed separately. This solution was added dropwise to TTIP solution while stirring. An exothermic reaction of uncontrolled hydrolysis and condensation of TTIP takes place, resulting in a white precipitate of hydrated, amorphous T1O2. The resulting mixture was refluxed for 48 hours, crystallizing and deaggregating T1O2. After refluxing, the salt was cooled and filtered through filter paper. Discard the insoluble residue on the filter paper.

Example 3

The basic anatase T1O2 salt was prepared by the same procedure as described in Example 1, except to change the ratio of TTIP, HCIO4 to water. In this case, 15 mL TTIP, 45 mL water, and 3 mL HCIO4 were used.

-11Example 4

The basic anatase T1O2 salt was prepared by the same procedure as described in Example 1, except to change the ratio of TTIP, HCIO4 to water. In this case, 15 mL TTIP, 45 mL water, and 1 mL HCIO4 were used.

Example 5

The basic anatase T1O2 salt was prepared according to the same procedure as described in Example 1, except to change the reflux time. In this case, the salt was refluxed for 24 hours.

Example 6

Remove the base salt from Example 1 (5 mL) and add TEOS (400 pL). A two-phase system is formed because TEOS is poorly soluble in aqueous medium. It is stirred at room temperature, resulting in the gradual hydrolysis and condensation of TEOS. After 12 hours, TEOS as the basic precursor is no longer present, and the salt still retains its stability. To the prepared mixed salt, 40 mL of water was added and stirred well. In the salt thus prepared, the molar ratio of Ti to Si is 1.3: 1, and the concentration of T1O2 in the salt is approximately 4.2 mg / L. The salt is stable at room temperature for at least 6 months.

To prepare the thin layers, we take the cleaned glass surface. Soak the cotton cloth in dilute salt, then very thinly coat the glass with this cloth. When the solvent evaporates from the applied salt, a very thin layer of photocatalytically active coating remains on the glass.

Example 7

The basic salt of Example 1 (5 mL) was removed and TEOS (450 pL) was added. A two-phase system is formed because TEOS is poorly soluble in aqueous medium. It is stirred at room temperature, resulting in the gradual hydrolysis and condensation of TEOS. After 12 hours, TEOS as the basic precursor is no longer present, and the salt still retains its stability. To the prepared mixed salt was added 40 mL of water, 85 mL of 2-methoxyethanol and 85 mL of 1-butanol and stirred well. In the salt thus prepared, the molar ratio of Ti to Si is 1: 1, and the concentration of T1O2 in the salt is approximately 0.9 mg / L. The salt is stable at room temperature for at least 6 months.

To prepare the thin layers, we take the cleaned glass surface. The prepared salt is applied to the surface of any material using one of the described procedures (cloth, spray, brush, dipping ...).

-12Example 8

Remove the basic salt (5 mL) from Example 1 and add TEOS (450 pL). A two-phase system is formed because TEOS is poorly soluble in aqueous medium. It is stirred at room temperature, resulting in the gradual hydrolysis and condensation of TEOS. After 12 hours, TEOS as the basic precursor is no longer present, and the salt still retains its stability. 40 mL of water, 140 mL of propylene glycol butyl ether and 30 mL of 1-butanol were added to the prepared mixed salt and stirred well. In the salt thus prepared, the molar ratio of Ti to Si is 1: 1, and the concentration of TiO ₂ in the salt is approximately 0.9 mg / L.

To prepare the thin layers, we take the cleaned glass surface. The prepared salt is applied to the surface of any material using one of the described procedures (cloth, spray, brush, dipping ...).

Example 9

Mixtures of water (0.30 mL), conc. HNO3 (0.84 mL) and 2-propoxyethanol (4.1 mL) were added dropwise to a mixture of TTIP (4.7 mL) and 2-propoxyethanol (9.5 mL). The resulting mixture was stirred at room temperature for 4 hours to achieve hydrolysis and condensation of titanium alkoxide. Finally, dilute the prepared hydrolyzate with 2-propoxyethanol (35 mL). The percentage by weight of TiO ₂ in the prepared hydrolyzate is 2.5%.

Example 10

Remove the base salt (5 mL) from Example 1 and add the colloidal SiO ₂ salt Levasil 200/30% (0.47 g), which was previously mixed with 415 pL GPMS and 10 ml 2-methoxyethanol. Mix for 2 hours. To this was added partially hydrolyzed TTIP (TiO ₂ hydrolyzate) (4.1 mL) prepared according to the procedure described in Example 9. The salt maintained its stability. To the prepared mixed salt was added 40 mL of water, 75 mL of 2-methoxyethanol and 85 mL of 1-butanol and stirred well. The salt thus prepared contains 1.3 mg / L TiO ₂ per liter of salt, the molar ratio of anatase Ti, non-crystalline Ti from hydrolyzate, Si from GPMS and Si from colloid is 1: 0.5: 1: 1.

The prepared salt is applied to the surface of any material using one of the described procedures (cloth, spray, brush, dipping ...). The prepared thin layer is heated at 90 ° C for half an hour.

-13Characterization

The formation of the anatase crystalline phase was confirmed by X-ray diffraction (Figure 1). The anatase crystalline phase, which is present in the powder sample obtained from thicker coatings by means of a sharp scraper, still prevails over rutile after drying at room temperature and even after thermal treatment of the sample at 1000 ° C. It is only at higher temperatures that the anatase phase becomes fully rutile. It should be emphasized that, according to scientific literature, this is one of the widest, if not the widest, thermal window of thermal stability of the photocatalytically active anatase phase (from room temperature to 1000 ° C). The photocatalytic function of the coating is thus ensured even at extremely high temperatures. This could be the case if a coating is applied to the object, e.g. brick or ceramic tile that must still be heat treated at high temperature in the process to the finished product.

Figure 1 shows X-ray diffractograms of a sample prepared from thin TiCh / SiCh layers, which were made according to the procedure described in Example 7, namely a thermally untreated sample and a thermally treated sample at different temperatures.

The photocatalytic activity of the prepared coatings was demonstrated by attempting to discolour the resazurin dye. The procedure is described in an article by Evans, P.; Mantke, S.; Mills, A.; Robinson, A.; Sheel, DW J Photochem Photobiol A Chem 2007, 188, 387–391. In Figure 2, the left photo shows the state at 0 min and the right photo shows 45 mW of UVA light with a flux of 4 mW / cm ² . In the experiment, a self-cleaning glass coated with the self-cleaning coating of Example 7 and a resazurin-containing layer was used. The change from blue to pink is a sign of the photocatalytic activity of the surface under the dye.

Figure 2 demonstrates the photocatalytic activities of prepared self-cleaning layers on glass in the decomposition of resazurin dye deposited between the slide and the slide. The left sample in each photo shows glass coated with a thin layer of TiC1 / SiCh prepared according to the procedure described in Example 7, the right sample in each photo shows glass without T1O2. The left photo shows the condition before irradiation with UVA light, the right photo shows the condition after 45 min of irradiation.

The hydrophilicity of the resulting coatings was confirmed by measuring contact angles. Measurement of the angle between the drop of water and the surface of the coating of Example 7 on a conventional window glass at 0 min is

-14 between 30 and 40 ° and at 20 min of UVA irradiation with a flux of 0.004 W / cm ² , the contact angle drops from the initial value to 8 to 9 °, demonstrating the high hydrophilicity of the coating in the presence of UV radiation.

The high transmittance of the self-cleaning coating of Example 7 in the entire field of visible light is evidenced by the UV-VIS spectrum of the coating applied to sodium glass (Figure 3). All types of coatings, prepared according to the various procedures described above, allow more than 95% of visible light. Figure 3 shows the UV-Vis spectrum of the sample compared to the glass substrate alone.

Claims (10)

Patent claims 1. Preparation of TiO ₂ / SiO ₂ salts and their use for the application of thin, optically permeable coatings with self-cleaning and anti-rust properties, characterized in that the process consists of: - preparation of an acidic aqueous salt containing photochemically active TiO ₂ nanoparticles, - adding a SiO ₂ precursor with the following hydrolysis / condensation of SiO ₂ , - addition of epoxysilanes by subsequent polymerization to polyethers - the addition of an amorphous TiO ₂ hydrolyzate acting as a binder, - addition of colloidal SiO ₂ , - dilution of the prepared salt with water and / or with organic solvents, - application of prepared salt to the substrate, - solvent evaporation and condensation reactions at room temperature, - the formation of a thin, uniform TiO ₂ / SiO ₂ layer having self-cleaning properties. Device according to claim 1, characterized in that HCI 4 acid is used to prepare the acidic aqueous salt. Device according to claim 1, characterized in that TEOS is used as the precursor of SiO ₂ . Device according to claim 1, characterized in that TEOS is added to the cooled, undiluted base salt. Device according to claim 1, characterized in that GPMS is used as epoxysilane. Device according to claim 1, characterized in that the mixed TiO ₂ / SiO ₂ salt is diluted with water or with various mixtures of the listed organic solvents. 7. TiO ₂ / SiO ₂ salts, prepared according to the preceding claims. Use of TiO ₂ / SiO ₂ salts according to claim 7, characterized in that the prepared salt is applied to the surface of the substrate by means of a cloth, brush, sprayer, immersion of the sample in the salt. Use of TiO ₂ / SiO ₂ salts according to claim 7, characterized in that glass, concrete, ceramics or various polymeric materials are used as a base. Use of TiO ₂ / SiO ₂ salts according to claim 7, characterized in that no additional thermal or chemical treatment of the resulting coating is required.