MX2008009883A

MX2008009883A - Method for the preparation of aqueous dispersions of tio2 in the form of nanoparticles, and dispersions obtainable with this method

Info

Publication number: MX2008009883A
Application number: MXMX/A/2008/009883A
Authority: MX
Inventors: Baldi Giovanni; Bitossi Marco; Barzanti Andrea
Original assignee: Baldi Giovanni; Barzanti Andrea; Bitossi Marco; Colorobbia Italia Spa
Priority date: 2006-02-01
Filing date: 2008-07-31
Publication date: 2008-10-03

Abstract

The invention relates to a method for the preparation of aqueous dispersions of TiO2in the crystalline form anatase, as well as the dispersions obtained with said method, useful for the preparation of photocatalytic coatings for surfaces, and for the photocatalytic decontamination of gases and liquids.

Description

METHOD FOR THE PREPARATION OF DISPERSIONS TIOUS ACIDS, IN THE FORM OF NANOPARTICLES. AND DISPERSIONS OBTAINED WITH THIS METHOD Field of the Invention The present invention relates to the field of methods for the preparation of compounds in the form of nanometric particles, and in particular, to a method related to a way to prepare the Ti02 dispersions in the form of nanoparticles. BACKGROUND OF THE INVENTION Titanium dioxide is a white pigment with a very strong coverage capacity used in particular in paints, and in the production of paper and synthetic rubber. Among the most recent applications of titanium dioxide is the attempt to use its photocatalytic activities to obtain a better advantage, that is through the action of ultraviolet light, to use this capacity to generate radical species capable of catalyzing the oxidative degradation of harmful substances or toxic, such as benzene, dioxin, and other organic pollutants, but also unpleasant and disease-causing substances such as mold and bacteria. These applications are therefore used in broad environmental fields ranging from combating detergent pollutants and sterilizing products.

For these applications, titanium dioxide is used as a coating on the surfaces to be treated to maximize the photocatalytic effect. The crystalline form of titanium dioxide called "anatase" is the most popular for this type of application because, as they are chemically stable and readily available, they also have a photocatalytic activity that is higher than the other two crystalline forms, rutile and brooquita. On the other hand, the superposition of the absorption spectrum of titanium dioxide, even in the form of anatase, in the solar spectrum, is not very large, and results in low levels of photocatalytic efficiency. For this reason several attempts have been made to modify Ti02, for example, by altering with other metals, or by preparing the compound based on the shape of the nanoparticles; in fact this increases the surface area enormously and therefore, also the photocatalytic efficiency. There are several methods to prepare the anatase of Ti02, including in the form of a nanoparticle, which provide Ti02 in powder form. For the preparation of the photocatalytic coatings to be convenient, this powder must be dispersed in an appropriate solvent and formulated with other possible additives to improve the adhesion of the coating, but this causes the coagulation of the titanium dioxide particles which makes it impossible to maintain the efficiency and photocatalytic activity of the particulate material. On the other hand, over a period of time, the Ti02 particles in these dispersions tend to settle in the bottom of the containers where they are stored, creating stability problems during storage. In addition, Patent Application No. FI2004A252 of the patent application (of the same Applicant), describes a method that allows the preparation of dispersions of stable nanoparticles of titanium dioxide in the anatase form, where the water and the solvents forming Suitable complexes are used as solvents. Brief Description of the Invention The Applicant recently created a method for obtaining nanoparticles of titanium dioxide in the form of anatase already dispersed in water only, and directly usable for the preparation of photocatalytic coatings. The dispersions obtained with the method according to the invention did not cause particle coagulation even after prolonged storage, thus allowing the preparation of coatings that maintain the photocatalytic activity of the particulate material due to the homogeneity of the dispersion. Therefore, the object of the present invention is a method for preparing dispersions of titanium dioxide nanoparticles in anatase form in water, wherein a titanium alkoxide is made to react under heat in water in the presence of mineral acid and a non-ionic surfactant and when necessary, the solution is finally reduced to a small volume. A further object of the invention is the use of dispersions of titanium dioxide nanoparticles in anatase form in water, obtained using this method, as well as their use for the preparation of photocatalytic surface coatings, for the photocatalytic decontamination of gases and liquids, and for the preparation of formula for cosmetics that provide a protective action against sun rays for human skin. The features and advantages of the invention will be illustrated in detail in the following description. Brief Description of the Figure Figure 1 shows a diffractogram of dry product powder, where the y-axis shows the intensity of the radiation while the x-axis shows the amplitude of the radiation incidence angle. This analysis shows how crystalline titanium dioxide in anatase form is obtained using this method. Detailed Description of the Invention The method of the present invention can produce Ti02 in anatase form directly in water, and obtain a dispersion of Ti02 particles at the end of the process with a size between 30-50 nm. Particle measurement was performed using several methods well known to those skilled in the art, such as XRD (X-ray diffraction), FEG-SEM (field emission cannon - scanning electron microscopy), TEM (transmission electron microscopy) ) and DLS (light scattering) dynamic). Unlike the nanoscale dispersion powders prepared in the solvent or water mixtures, these dispersions show no sign of conglomeration or coagulation or solid precipitation, even after prolonged storage periods of the dispersion product. The advantages that will be obtained with the dispersions of this type are obvious and are associated with the efficiency and photocatalytic uniformity of the coatings that can be prepared with the dispersions. The dispersion index obtainable with the method according to the present invention, measured with DLS (dynamic light scattering) techniques, is less than 0.3, and therefore the dispersion according to the invention is different from that obtained using the previous methods integrated by the preparation of the nanoparticle powder, subsequently dispersed in the solvent. The titanium alkoxide used as the starting product in this method may be chosen from the group consisting of titanium methoxide, ethoxide, normal propoxide, iso-propoxide, normal butoxide, and isobutoxide. Particularly preferable is titanium isopropoxide since it is more economical and reacts better under conditions used in the present method. Nonionic surfactants are surfactants composed of an apolar part and a polar function, ether non-ionizable, ester, ether-ester; particularly preferred is Triton X-100 (TX-100). The term "mineral acid" according to the invention refers, for example, to an acid selected from the group consisting of: hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, hydrobromic acid and hydrogen iodide; preferably, halogen acids, and particularly hydrochloric acid, are used.

The molar ratio of the titanium alkoxide / mineral acid alcoholate is between 0.005 and 15, and preferably between 5 and 6. The reaction temperatures range between 15 ° C and 95 ° C, preferably between 45 ° C and 55 ° C. The reaction times range from 12 h to 72 h, and preferably 24 h. When necessary, when used for coating preparations, the present dispersions can possibly be formulated using the additives and diluents commonly used in the field of surface coatings, such as improved adhesion agents or solvents such as water or ethanol for example. , to obtain the required level of dilution. On the other hand, when used to decontaminate liquid or gaseous products, the present dispersions are respectively absorbed in a silica gel support, or in some other suitable inorganic support with adsorbent characteristics, which is then immersed in the liquid, or placed in its current state or diluted, in the containers in which the gas that is purify is bubbled through the wash. The supports in which the surface coatings prepared with the present dispersion can be applied, vary widely, from fiber products, woven fibers in rolls or already made in garments, to ceramic products, as well as supports in glass, metal, mirror , and similar materials. The photocatalytic activity of the surface coating according to the present invention is explained as a result of exposure of the coating based on light with a suitable wavelength, commonly less than 388 nm, which produces a surface with the properties resistant to bacteria, bacteriostatic and super-hydrophilic after exposure to UV light. In fact, the Ti02 coated supports show a total lack of water repellent capacity, called super-hydrophilic capacity, which gives the surfaces treated with Ti02 the ability to self-clean. On the other hand, due to the extremely small size of the Ti02 particles, the present dispersions are practically transparent, leaving the appearance of the surface on which they are applied, totally unchanged. This transparency also makes the product suitable for use in cosmetic fields for the preparation of sun filters with high levels of UV protection. An additional advantage of the present dispersions is their behavior at high temperatures. In fact, the application of the surface coating on ceramic supports requires the high-temperature processing of the support where the dispersion is applied and the present dispersions maintain exactly the same appearance, the anatase crystalline form and the nature of the nanoparticles of the coating before the heating process. According to a particular embodiment of the present method, Ti can be altered with a metal selected from the series of transition metals, and in particular Ag, Cu and Ce by the addition of a salt of one of these metals to the solution Of start. In this way, the method will lead to the formation of a dispersion of Ti02 altered with Ag, Cu or Ce, which can perform its catalytic activities even without UV light rays. Below some examples of the invention are provided as illustrations but without being considered as limiting. Example 1 5 grams of concentrated HCl, 7.5 grams of TX-100, and water to a total weight of 750 grams, are placed in a 2-liter reactor heated by diathermic oil circulating in the outer shell. The temperature rises to 50 ° C. At this point 50 grams of Ti [OCH (CH3) 2] 4 (TIP) are added very quickly and a multiple white precipitate can be observed immediately. After 7 hours a very transparent transparent solenoid is formed stable. Characterization The characterization occurs determining the concentration of titanium dioxide present in the solution (ICP technique) and determining the size of the particles (DLS technique). Concentration: 1.5% by weight of Ti02 Size: 36.67 nm with a polydispersity index of = 0. 282 Example 2 5 grams of concentrated HCl, 7.5 grams of TX-100, and water to a total weight of 750 grams, are placed in a 2-liter reactor heated by diathermic oil circulating in the outer shell. The temperature rises to 50 ° C. At this point 50 grams of TIP are added very quickly and a multiple white precipitate can be observed immediately. After 24 hours a very stable transparent solenoid is formed. Characterization Concentration: 1.45% by weight of Ti02 Size: 30.26 nm with a polydispersity index of = 0. 216 Example 3 500 cc of product obtained through the synthesis of hydrolysis, place in the rotary evaporator and concentrate. The bathroom heated to 40 ° C and an oil-driven vacuum pump creates a vacuum in the bathroom. 110 cc of solution are obtained. Characterization Concentration: 6.69% by weight of Ti02 Size: 26.72 nm with a polydispersity index of = 0. 269 Example 4 5 grams of concentrated HCl, 1.0 grams of TX-100 ,. and water up to a total weight of 936 grams, are placed in a 2 liter reactor heated by diathermic oil circulating in the outer jacket. The temperature rises to 50 ° C. At this point 64 grams of TIP are added very quickly and a multiple white precipitate can be observed immediately. After 24 hours a very stable transparent solenoid is formed. Characterization Concentration: 1.8% by weight of Ti02 Size: 49.62 nm with a polydispersity index of = 0. Example 5 5 grams of concentrated HCl, and water to a total weight of 936 grams, are placed in a 2-liter reactor heated by diathermic oil circulating in the outer shell. The temperature rises to 50 ° C. At this point 64 grams of TIP are added very quickly and a multiple white precipitate can be observed immediately. After 24 hours a very stable transparent solenoid is formed.

Characterization Concentration: 1.8% by weight of Ti02 Size: 52.71 nm with a polydispersity index of = 0. 216 Example 6 Application of Ti02 nanoparticle dispersion in water on fabric The suspension obtained as described in examples 1-5 can be used to treat fabrics and have them absorb ultraviolet radiation which is harmful to the skin, therefore reduces the risk of developing skin cancer. 15 kg of 0.5M of sodium acetate solution and 0.5 kg of Pimasil (siloxane resin) are added to 13 Kg of the product prepared in water and concentrated to 6%. The obtained compound is applied to a cloth using a cushioning technique followed by Rameuse drying. The fabric obtained in such a way has a UPF value comparable to 20 times the value of an untreated fabric of the same type.

Example 7 Application of the dispersion of Ti02 nanoparticles in water on ceramic or glass surfaces The suspension obtained as described in examples 1-5 can be applied to ceramic or glass surfaces (using airbrush or dip coating techniques) in the current or diluted concentration (with water or alcohol). The surface obtained maintains its initial characteristics because the applied coating is completely transparent. The surface assumes all functions with photocatalytic characteristics: self-cleaning, resistant to bacteria, degradation capacity of organic pollutants.

Claims

1. The method for the preparation of nanoparticle dispersions of Ti02 in anatase form, where a titanium alkoxide is made to react under heat in water in the presence of mineral acids and a nonionic surfactant, the solution obtained in such a way is reduced possibly at a small volume if necessary.

2. Method according to claim 1, wherein the titanium alkoxide is selected from a group consisting of titanium methoxide, ethoxide, normal propoxide, iso-propoxide, normal butoxide, and isobutoxide.

3. Method according to claim 2, wherein the titanium alkoxide is titanium iso-propoxide.

4. Method according to claims 1-3, wherein the mineral acid is a halogen acid.

5. Method according to claim 4, wherein the halogen acid is HCI.

6. Method according to claims 1-5, wherein the nonionic surfactants possess the polar function of an ether or ester type.

7. Method according to claim 6, wherein the non-ionic surfactant is Triton X-100 (TX-100).

8. Method according to claims 1-7, wherein the molar ratio of titanium alkoxide / halogen acid is between 0.005 and 15. Method according to claim 8, wherein the molar ratio of titanium alkoxide / halogen acid is between 5 and 6. The method according to claims 1-9, wherein The reaction temperature is between 15 ° C and 95 ° C, and the reaction times are between 12 and 72 hours. The method according to claim 10, wherein the reaction temperature is between 45 ° C and 55 ° C, and the reaction time is 24 hours. 12. Method according to claims 1-11, wherein a metal salt of Ag, or Cu or Ce, is added to the solution containing titanium alkoxide, mineral acid, and surfactant. 13. Dispersions of Ti02 nanoparticles in anatase form in water, obtainable using the method as defined in claims 1-11. 14. Dispersions of Ti02 nanoparticles in water, where Ti is altered with a metal selected from the series of transition metals, obtainable using the method according to claim 12. 15. Dispersions according to claim 14, wherein the transition metal is selected from the group consisting of: AG, Cu and Ce. 16. Use of the Ti02 nanoparticle dispersions according to claims 13-15, for the preparation of photocatalytic coatings on surfaces that require treatment. 17. Use according to claim 16, wherein the surfaces are selected from the surfaces of fabric, metal, ceramic and enameled textile products. 18. Use of the Ti02 nanoparticle dispersions according to claims 13-15, for the photocatalytic decontamination of gases and liquids. 1

9. Use of the nanoparticle dispersions of Ti02 according to claims 13-15, for the preparation of cosmetics with a protective action for human skin against sun rays.