Process for preparing dispersions of tio2 in the form of nanoparticles, and dispersions obtainable with this process and fuctionalization of surfaces by application of tio2 dispersions

The present invention relates to the field of methods for preparing compounds in the form of nanoparticlees, especially TiO in the form of nanoparticles.₂On how to prepare the dispersion of.

Titanium dioxide is used as a white pigment with good dyeing power, especially in paints and paper products and synthetic rubber products. Recent uses of titanium dioxide have been due to its photocatalytic activity, i.e. its generated capacity, the action of ultraviolet light, toxic or toxic substances such as benzene, dioxane and other organic pollutants, and discomfort such as rust and bacteria. We are developing radical species that can catalyze the oxidative decomposition reaction of infectious substances. Their use extends from the fight against pollutants in the environmental sector to the areas of cleaning and sterilization.

For the utilization of titanium dioxide, the treated one is used as a coating on the surface in order to maximize the photocatalytic effect. This crystal form of titanium dioxide, ie anatez, is this because in addition to being chemically stable and readily available, it has greater photocatalytic activity than the other two crystal forms, rutile and brookite. Preferred for seed utilization.

On the one hand, the overlap of titanium dioxide absorption spectra, including the solar spectrum, is not very good, even in its anatased shape, and exhibits low photocatalytic efficiency. Thus, for example, by preparing the compound doped with another metal or in the form of nanoparticles, modified TiO₂Various attempts have been made to make the surface area and photocatalytic efficiency in this way.

Anate's TiO₂Although various steps are known to prepare even the nanoparticulate form, but as far as the applicant knows, all these steps are obtained powdered TiO₂Connected to.

The method for preparing a suspension of nanoparticles in a high boiling point alcohol is, for example, the polyhydric alcohol method described in C. Feldmann's "Polyhydric alcohol for establishing the synthesis of nanoscale functional materials", and has been very active for a long time. It makes it possible to obtain a stable suspension, but contrary to currently required methods, it uses mineral acids as inhibitors of polycondensation (see also Patent Document 1 for this association).

This powdery material, which can be used to prepare photocatalytic coatings, should be dispersed in a suitable solvent and will probably be formed with additives to improve coating adhesion. However, this makes it impossible to maintain the activity and photocatalytic efficiency of the microparticle material and causes the titanium dioxide particles to coagulate. Furthermore, TiO being dispersed in these over time₂The particles tend to slowly descend to the bottom of the container in which they are stored, causing stability problems during storage.<patcit num="1"><text>International Publication No. 99/62822 Pamphlet</text></patcit>

<p> Therefore, it was felt that it was necessary to provide a method capable of stably preparing the nanoparticle dispersion of titanium dioxide in the anatez shape.</p>

<p> Applicant is now anatas-shaped TiO₂We have devised a method that gives the nanoparticles, already dispersed in a suitable solvent, which can be used directly in the preparation of photocatalytic coatings. The dispersion obtained by the method of the invention does not lead to a particle coagulation phenomenon even after prolonged storage, allowing the prepared coating to maintain the photocatalytic activity of the particulate material thanks to the uniform dispersion.</p><p> Therefore, the present invention is derived from the following steps: i) reacting the titanium alkoxide with an appropriate compositing solvent; ii) distilling the solution derived from step i) until the volume is reduced; iii) step ii). The solution comprises adding the complexing solvent together with water and one or more polycondensation inhibitors and then heating the reaction mixture under reflux to obtain the desired nanoparticles dispersion with water. Anatez TiO in a mixture with a suitable compositing solvent₂Provided is a method for preparing a dispersion of nanoparticles.</p><p> Titanium dioxide, TiO₂Another method of obtaining a suspension of nanoparticles of is the hydrolysis of titanium alkoxides such as titanium methoxydo, titanium ethoxydo, titanium normal propoxide, titanium isopropoxide, titanium normal butoxide and titanium isobutoxide. Titanium isopropoxide is preferred for the same reasons mentioned above.</p><p> Titanium isopropoxide is added with a hot aqueous solution containing a mineral acid (such as hydrochloric acid or nitric acid) and a nonionic surfactant (such as Triton X-100). The hydrolysis method maintains reflux for 24 hours.</p><p> Furthermore, the invention can be obtained by the method described above, anatez TiO in a mixture of water and a suitable complexing solvent.₂They are used to provide a nanoparticulate dispersion and to prepare photocatalytic surface coatings for antibacterial activity, photocatalytic purification of gases and liquids, and preparation of cosmetic formulations that protect the skin from sunlight.</p>

The properties and advantages of the invention will be illustrated in detail in the following description.

Anatez-shaped TiO that occurs directly in the water / complexing solvent mixture used in step i) by the method of the invention.₂The chemical formation of TiO at the end of the method is between 3 and 20 nm in size.₂Obtain a dispersion of particles. Particle size measurement is a specialty of this technology, such as XRD (X-ray diffraction), FEG-SEM (field emission electron gun-scanning electron microscope), TEM (transmission electron microscope) and DLS (dynamic light scattering). Attempted with a different technique famous for the house. These dispersions, in contrast to those prepared by dispersing the nanopowder in a solution mixture, clump the chemicals even after prolonged storage of the dispersion, and the coagulation and sedimentation reactions. Neither is shown.

The advantages of this type of dispersion are obvious and are related to the homogeneity of the coatings that can be prepared on it and the effectiveness of the photocatalyst. The multi-dispersion index of the dispersion available in the method of the invention, measured by DLS (Dynamic Light Scattering) technology, is less than 0.3 and therefore the dispersion of the invention is obtained by the traditional method of preparing nanoparticulate powder. Distinguish from what is possible, and then disperse it in solvent. A typical TEM image of our nanoparticle dispersion is shown in Figure 2.

The titanium alkoxide used as the starting product in the method can be selected from the group consisting of, for example, titanium methoxydo, titanium ethoxydo, titanium normal propoxide, titanium isopropoxide, titanium normal butoxide and titanium isobutoxide. ..

Among these products, titanium isopropoxide is the preferred starting compound for this method for a variety of reasons. It is the least expensive of the titanium compounds available and has the best reactivity under the conditions of the method; in addition, its use is the isopropyl obtained as a by-product of step ii). Combined with alcohol, the product is easily recoverable from the methods of invention and is valued for its widespread use in the detergent industry.

Complex solvents typically used in this method are, for example, ethylene glycol, diethylene glycol and polyethylene glucose having a molecular weight of 200-600. Long-chain polyethylene glucose with a molecular weight of up to 10,000 can also be used. In this case, at the end of the method and subsequent cooling, TiO in the liquid₂Instead of dispersion, TiO₂Nanoparticles are obtained by dispersing in a solid substrate. The final product is TiO₂Conserved in nano-dimensions, and a low polydispersity index is observed due to liquid dispersion. A preferred complexing solvent is diethylene glycol.

Excellent results were obtained by carrying out the reaction step i) using titanium isopropoxide and diethylene glycol in a molar ratio of 1: 3.

Within the scope of the present invention, a mixture containing at least one mineral acid and one organic acid is typically the term "hypercondensation inhibitor" means, where the mineral acid is, for example, hydrochloric acid, nitrate, sulfuric acid, perchlorine. It can be selected from the group consisting of acid, hydrobromic acid and hydroiodic acid, and the organic acid is preferably acetic acid.

According to a particularly preferred embodiment of the method, the polycondensation inhibitor is a mixture of hydrochloric acid and acetic acid.

The amount of polycondensation inhibitor is added so that the amount of mineral acid is 0.1-10% by volume of the total volume of the reaction mixture, while the amount of organic acid is 1-20% by volume of the total volume of the reaction mixture.

Mixtures of water / complexing solvents used in accordance with the invention provide photocatalytic coatings, even for practical use in certain types, even in the cosmetic or textile fields where the coating product is destined to come into contact with the skin. It can be used directly to prepare.

When they are used for coating preparation, this dispersion is an additive commonly used in the field of surface coatings, such as agents that improve adhesion or solvents such as water or ethanol to obtain the desired dilution. And can be formed with a diluent.

When they are used instead to purify liquid or gas products, the dispersion provides good adhesive properties on silica gel carriers or on glass, ceramics, porous ceramics, fibers, textiles, etc. Each is adsorbed on another suitable inorganic carrier provided, which is then either intact or diluted and immersed in or placed in a liquid to foam the purified gas that has passed through the vessel.

Carriers to which the coatings prepared with this dispersion may be applied on the surface range from those of finished textiles on rolls to ceramic products, glass, metal or mirror carriers and the like. Wide.

The photocatalytic activity of the surface coating according to the invention is suitable for wavelengths, typically 388 nm, for the coating itself to produce a surface with antibacterial, bacterial growth inhibitory and superhydrophilic properties as a result of exposure to UV light. Shown after exposure to less than light. TiO₂The coated carrier demonstrates a complete lack of water repellency known as hyperhydrophilicity, thereby TiO₂Gives self-cleaning of the treated surface.

In addition, a very small TiO₂Given the particle size, the dispersions are almost transparent, whereby the appearance of the surface on which they are utilized remains unchanged. Their transparency also makes them suitable for use in the cosmetic field for the preparation of highly protective UV solar filters.

A further advantage of this dispersion is their behavior at high temperatures. In this regard, even if a surface coating is applied on a ceramic carrier that requires high temperature treatment on the carrier to which the dispersion has been applied, the dispersion does not change the appearance of the anatez crystal shape and the coating prior to heating. The nanoparticle properties are maintained.

According to a special embodiment of the method, the doping of Ti is carried out in step i) or alternative step iii) of the method by the addition of one of those salts to the transition metals, especially Ag, Cu. Alternatively, it can be achieved with a metal selected from Ce. In this method, the process is Ag, Cu or Ce-doped TiO.₂It results in the formation of dispersions and can exhibit its catalytic activity even without UV light irradiation.

Some examples of the invention, which are not limited, are listed below.

Example 1 Anatese TiO in water / diethylene glycol starting with Ti isopropoxide₂Preparation of Nanoparticle Dispersion of Diethylene glycol 5.53 liters is poured into a 20 liter flask and 5.54 liters of titanium isopropoxide is added. The reaction mixture is maintained under stirring for 5 minutes and then heated to 120 ° C until small volumes to distill off isopropyl alcohol from the composition. Add 11.1 liters of diethylene glycol, 125 ml of 32-33% w / w hydrochloric acid, 2.07 liters of glacial acetic acid and 125 ml of deionized water. The temperature reaches 180 ° C and the mixture is maintained under reflux for 2 hours.

The resulting product is characterized as follows:

First, TiO in the final product₂Concentrations were measured using radio frequency inductively coupled plasma atomic emission (ICP) techniques according to standard methodologies. From this analysis, TiO in dispersion₂The amount was found to be equal to 5.7% by weight of the total weight of the dispersion.

The dispersion sample obtained as described above was dried in an oven at 200 ° C. for 12 hours until the solvent was completely evaporated. The resulting powder was then X-RD-analyzed using a Philips X'Pert PRO diffractometer to understand its crystal structure: as shown by the differential gram, which can be seen in Figure 1. The position and peak intensity are typical of anatase.

From the diffractogram in Figure 1, and especially the width of the major peaks, TiO₂The average size of the particles was calculated by applying Sherrer's equation and appeared to be equal to the average diameter value of 4.5 nm.

This value was also confirmed by transmission electron microscopy of the dispersion sample obtained as described above after being diluted 1: 100 with ethanol.

Example 2 Anatez TiO in water / diethylene glycol starting with Ti ethoxide₂Preparation of Nanoparticle Dispersion of Diethylene glycol 5.53 liters is poured into a 20 liter flask and 3.76 liters of titanium ethoxydo is added. The reaction mixture is maintained under stirring for 5 minutes and then heated to 130 ° C. to distill and remove ethanol from the composition. Add 11.1 liters of diethylene glycol, 125 ml of 32-33% w / w hydrochloric acid, 2.07 liters of glacial acetic acid and 125 ml of deionized water. The temperature reaches 180 ° C and the mixture is maintained under reflux for 2 hours.

This product was characterized in the same way as given in Example 1 to obtain particles of the same crystalline phase and similar dimensions. In addition, the resulting product was used to perform the same tests described above in order for Examples 2, 3 and 4 with similar results to obtain the product prepared as in Example 1. Was done.

Example 3 Anates TiO in water starting with Ti isopropoxide₂Preparation of Nanoparticle Dispersion of Hydrochloric Acid To obtain mixed water with 100 gr of hydrochloric acid and 80 gr of Triton X-100 1% w / w solution in water, 18.720 kg of aqueous solution was poured into a 20 liter flask. The reaction mixture was heated to 50 ° C. 1.280 kg of titanium isopropoxide was added. The reaction mixture is maintained under reflux at 50 ° C for 24 hours. The resulting product is characterized as follows:

First, TiO in the final product₂Concentrations were measured using radio frequency inductively coupled plasma atomic emission (ICP) techniques according to standard methodologies. From this analysis, TiO in dispersion₂The amount was found to be equal to 1.8% by weight of the total weight of the dispersion.

The dispersion sample obtained as described above was dried in an oven at 100 ° C. for 12 hours until the solvent was completely evaporated. The resulting powder was then X-RD analyzed using a Philips X'Pert PRO diffractometer to understand its crystal structure.

Example 4 TiO in water / diethylene glycol₂25 ml of deionized water was added to 75 ml of the dispersion prepared as in Example 1 above, so that the dispersion was diluted and placed in a bowl. A 20 cm x 60 cm piece of cotton fabric was soaked in a bowl for 10 seconds, then removed and passed between two rollers of silicone material to remove excess solvent. The fabric is then oven dried, machine washed, dried again, and the UV protection factor (UPF) exhibited by the coated fabric is compared to standard spectrophotometry for this type of measurement. , UPF 35.40 was seen.

Example 5 TiO in water / diethylene glycol₂25 ml of deionized water was added to 75 ml of the dispersion prepared as in Example 1 above, so that the dispersion was diluted and placed in a bowl. A 20 cm x 60 cm piece of woolen fabric was soaked in a bowl for 10 seconds, then removed and passed between two rollers of silicone material to remove excess solvent. The fabric was then dried in the oven, washed in the washing machine and dried again. Tested on this wool fabric, it had antibacterial properties as observed by AATCC TM 100: 99 standard. The results of the test are reported in the following table.

<tables num="1"><img file="JP2008522931A_D0001.tif" /></tables>

Example 6 TiO in water / diethylene glycol₂25 ml of deionized water was added to 75 ml of the dispersion prepared as in Example 1 above, so that the dispersion was diluted and placed in a bowl. .. The cotton thread was soaked in a bowl, dried in an oven, and wound onto a spool. A fabric knitted with this yarn was obtained and tested to show the UV protection factor (UPF) by the coated fabric. This property was compared to standard spectrophotometry and UPF 30.20 was found.

Example 7 TiO in water / diethylene glycol₂Utilization of Nanoparticle Dispersion on Ceramic Surface-Study on Adhesion and Resistance to High Temperature The nanoparticle dispersion prepared as described above in Example 1 has a low melting point in order to promote adhesion of titanium dioxide to the carrier. 5% by weight of frit was added and used to make a photocatalytic coating on a low gloss grease carrier. The frit used has a relatively low temperature range, equal to 700 ° C, and has the following chemical composition:

SiO₂ 48.32% CaO 6.95% Al₂O₃ 2.22% MgO 1.94% K₂O 0.049% Li₂O 13.9% Na₂O 0.06% ZnO 4.05% B₂O₃ 22.55% The dispersion of Example 1 was applied by dipping coating the carrier and exposed to both 700 ° C and 600 ° C thermal cycles. After the calcination, the carrier maintained its original appearance, and the coating and substrate demonstrated good adhesion.

The behavior of this coating at high temperatures was investigated by a high temperature powder diffractometer (XRD-HT). As a result, it is observed that the phase transition from anatez to rutile begins only at about 800 ° C, and it appears completely at about 900 ° C. By applying Cherel's equation, the size of nanocrystals at various temperatures was also calculated.

In Table 1 below, the 2θ angle obtained by the measurement, the peak width of the half height when inserted into the Cherel's equation for calculating the crystal size, the crystal size, and the temperature related to the size. Is given.

<tables num="2"><img file="JP2008522931A_D0002.tif" /></tables>

The same method was used to assess an increase in crystallite size at constantly maintained frit firing temperatures, but at different firing times, and in this case good coating adhesions were found even with extended firing times, over time. However, the crystallite size is increased to the extent that it is available without reducing the effectiveness of the coating photocatalyst.

To confirm the adhesion of the coating to the substrate, all samples were exposed to ultrasonic cycles for different times (5 and 60 minutes) in ethanol and acetone, and wiped with different wearable cloths. Was repeated. After the entire ultrasonic cycle, an XRD analysis was performed to see how much the amount of anatez present in the coating was reduced, however, the treatment performed was TiO.₂It was found that it did not affect either the crystal shape of the coating or the amount of the coating adhered to the carrier.

Example 8 TiO in water / diethylene glycol₂Utilization of Nanoparticle Dispersion on Ceramic Surfaces-Photocatalytic Efficacy Two samples of white photoslip, of the same grease, were "stained" in the same amount as a solution containing 10 ppm methylene blue. Only one of the two samples was pre-coated with the dispersion of the invention as described in Example 4.

The two samples were then exposed to light from UV lamps for various times of 10 minutes, 30 minutes, 60 minutes, 90 minutes and 120 minutes. No change in methylene blue staining was observed in the untreated sample, while a gradual disappearance of the blue staining was observed in the dispersion-coated sample of the invention. The same experiment was repeated with non-wipeable marker staining, and after 45 minutes of exposure to UV light, the disappearance of stains was observed only on the coated sample.

The above two experiments were repeated in sunlight instead of UV lamps and the same results were obtained.

Example 9 TiO in water / diethylene glycol₂Use of Nanoparticle Dispersion on Glass The dispersion of Example 1 was applied by dipping coating or spraying the carrier and exposed to a thermal cycle of 200 ° C for 30 minutes and 500 ° C for 30 minutes. After the calcination, the carrier maintained its original appearance, and the coating and substrate demonstrated good adhesion.

This sample was "stained" with a solution containing 10 ppm methylene blue. The sample was then exposed to light from a UV lamp, and a gradual disappearance of the blue stain was observed. This experiment was repeated in sunlight instead of with a UV lamp, and the same results were obtained.

Example 10 TiO in water / diethylene glycol₂Utilization of Nanoparticle Dispersion on Glass-Ceramic Surface The dispersion of Example 1 was applied by dipping coating or spraying the carrier and exposed to a thermal cycle of 200 ° C for 30 minutes and 700 ° C for 30 minutes. .. After the calcination, the carrier maintained its original appearance, and the coating and substrate demonstrated good adhesion.

This sample was "stained" with a solution containing 10 ppm methylene blue. The sample was then exposed to light from a UV lamp, and a gradual disappearance of the blue stain was observed. This experiment was repeated in sunlight instead of with a UV lamp, and the same results were obtained.

Example 11 TiO in water / diethylene glycol₂Utilization of nanoparticulate dispersion on various surfaces (glass, glass-ceramic, flat glass, body grease) In the dispersion of Example 1, a surfactant, eg, a nonionic surfactant that improves spreading on the surface ( Add 0.01-10% (such as Triton X-100). The solution is applied by dipping coating or spraying the carrier and exposed to a heat cycle of 200 ° C for 30 minutes and 500 ° C for glass or 700 ° C for glass-ceramic, flat glass and body grease for 30 minutes. Was done. After the calcination, the carrier maintained its original appearance, and the coating and substrate demonstrated good adhesion.

This sample was "stained" with a solution containing 10 ppm methylene blue. The sample was then exposed to light from a UV lamp, and a gradual disappearance of the blue stain was observed. This experiment was repeated in sunlight instead of with a UV lamp, and the same results were obtained.

Example 12 TiO in water₂50 ml of deionized water was added to 50 ml of the dispersion prepared as in Example 1 above, so that the dispersion was prepared. It was diluted and placed in a spray gun. This sample was sprayed onto the surface of the composite and then maintained at 100 ° C for 1 hour.

This sample was "stained" with a solution containing 10 ppm methylene blue. The sample was then exposed to light from a UV lamp, and a gradual disappearance of the blue stain was observed. This experiment was repeated in sunlight instead of with a UV lamp, and the same results were obtained.

<figref num="1">The differential gram obtained from the XRD analysis after drying the product obtained in Example 1 at 200 ° C. for 12 hours is shown.</figref><figref num="2">TiO₂It is a TEM photograph (90,000 times) of nanoparticles.</figref><figref num="3">It is a differential gram obtained from the XRD analysis of the product obtained in Example 8.</figref>