KR20040052739A - Process of preparing a dispersed solution of photocatalyst - Google Patents

Abstract

PURPOSE: Provided is a method for preparing a photocatalyst dispersion, which combines a transition metal and a colloidal silica on the surface of ultra-fine titanium dioxide particles. CONSTITUTION: The method comprises steps of (a) after mixing water and acid in a molar ratio o 1 : 0.01-0.1, adding 0.01-0.1 mol of titanium alkoxide thereto and stirring at a temperature of 60-80 deg.C for 6-8 hours to prepare an anatase titanium dioxide dispersion having a particle size of 1-10 nanometer; (b) after respectively dissolving Na4EDTA and a transition metal compound in a molar ratio of 1 : 0.1-0.75 in water, mixing them with each other and stirring at a temperature of 40-60 deg.C for 1-10 hours to prepare a transition metal EDTA salt substituted by 1-3 transition metals instead of Na and (c) reacting the surface of the titanium oxide of the anatase titanium dioxide dispersion with the negatively charged colloidal silica having a surface area of 200-1,000 m¬2/g at a temperature of 30-60 deg.C for 1-2 hours to prepare a photocatalyst dispersion where the transition metal and the colloidal silica are combined to the surface of the titanium dioxide particles.

Description

Process of preparing a dispersed solution of photocatalyst

The present invention relates to a photocatalyst dispersion in which a transition metal and colloidal silica are bonded to a surface of ultrafine titanium dioxide particles, and to a manufacturing method thereof.

The present invention relates to a transition metal such as silver (Ag), platinum (Pt), palladium (Pd), tin (Sn), copper (Cu), iron (Fe), and the like on a nano-size ultrafine titanium dioxide particle surface. It relates to a method for producing a photocatalyst dispersion in which colloidal silica is bound.

The photocatalyst prepared according to the present invention combines a transition metal and colloidal silica on the surface of titanium dioxide particles by using an electrostatic interaction with an ethylene diamine tetra acetic acid (EDTA) compound. In addition, it is possible to overcome the disadvantages of the conventional photocatalyst by adding the sterilization function by the transition metal and the adsorption of contaminants by the colloidal silica having a large surface area.

In addition, by combining transition metal EDTA salt and colloidal silica with positively charged titanium dioxide particle surface without special treatment, it is possible to stabilize the pH of the dispersion to prevent aggregation of particles even when neutral, so that photocatalytic dispersion can be widely used. There is an advantage.

Photocatalyst electron (e ^-) to the surface absorbs light over the band gap (band gap) as a semiconductor material and holes (h ⁺⁾ are generated, and, thus generated electrons and studied the abundant around us water and oxygen to Is converted into hydroxyl radical (OH ·) or active oxygen (O ₂ ⁻ ) with very high oxidative activity, and these are harmful organic substances such as formaldehyde, volatile organic compounds, odor causing substances, pollutants, environmental hormones, etc. It has a function of oxidizing and decomposing and removing. In particular, general fungicides cannot remove toxins (endotoxins) that bacteria give off, but photocatalysts have the property of completely degrading even toxins.

There are various metal oxides and composite oxides such as titanium dioxide (TiO ₂ ), zinc oxide (ZnO), tin dioxide (SnO ₂ ), nickel oxide (NiO), and iron oxide (Fe ₂ O ₃ ). Among them, titanium dioxide has high photocatalytic activity, good acid / alkali resistance, harmless to human body, and is inexpensive, and is most commonly used. Titanium dioxide is anatase, rutile, and brookite depending on the crystal form. The anatase and rutile types can be used as photocatalysts, but anatase is known to have higher photocatalytic activity than rutile. In addition, transition metals such as platinum (Pt), rhodium (Rh), tin (Sn), nickel (Ni), and copper (Cu) or oxides thereof are added to titanium dioxide to reactivate the electrons and holes, thereby reducing the activity. By delaying, the activity of the photocatalyst can be increased. In addition, the photocatalytic particle size is smaller than several tens of nanometers (nm) or less to increase the photocatalytic activity due to the quantum size effect, and improve transparency and dispersibility.

As the functions of photocatalysts are gradually known, various methods for manufacturing them by increasing their activity and performance have been studied, and many patents have been filed. The method for producing a titanium dioxide photocatalyst is to oxidize a titanium compound such as titanium tetrachloride (TiCl ₄ ) or titanium alkoxide (Ti (OC _n H _{2n + 1} ) ₄ ) by spraying or evaporating with oxygen in a container maintained at high temperature to oxidize the same. It can be divided into two methods, a gas phase method of making a fine powder and a liquid sol-gel method of preparing a solution in which nano-sized titanium dioxide particles are dispersed by hydrolyzing and peptizing a titanium compound at a temperature of 60 to 80 ° C.

The photocatalyst can be manufactured and used in the form of a powder, a coating on a substrate, or a photocatalyst coating, depending on the situation.However, the photocatalyst is hardly used because it is difficult to collect the photocatalyst powder. The photocatalyst is coated on inorganic support such as beads, and the photocatalyst coating agent is mixed with 5-30 nm photocatalyst particles in dispersion such as water or alcohol. .

Although the activity of the photocatalyst itself or the selection of the dispersion solution is very important among the constituents of the photocatalyst coating agent, the use of a separate binder is also essential to increase the adhesion by coating the photocatalyst coating agent on the target material. Binders are organic binders, which are commonly used in daily life, and inorganic binders such as water glass, silane, and cement. As organic binders are decomposed due to photocatalytic action, inorganic binders such as water glass and silane are mainly used, and fluororesins are relatively stable to photocatalysts, but adhesives are relatively low and expensive, and cement is coated with a coating agent. If mixed, there is a disadvantage that it can not be solidified.

Titanium dioxide photocatalysts are only activated by light in a specific wavelength band (about 380 nm), so their use is severe in conditions such as nights and basements where there is no light. Recently, transition metals such as silver and copper have been scientifically proven to show strong sterilizing power, and have been applied to various products such as air purifiers and washing machines. Especially silver has been used in jewelry such as rings for a long time. Excellent sterilizing power compared to transition metals.

In order to use silver efficiently in life, many techniques for making nano-sized particles have been researched and developed. The method of making silver nanoparticles is an electrolysis method to make silver ions (Ag ⁺ ) by electrolyzing high-purity metallic silver rods under high voltage in water, and dissolving silver compounds such as silver nitrate or silver acetate into water to make an aqueous solution. It can be divided into alcohol reduction method which reduces to alcohol, such as methanol and ethanol, at 70 degreeC temperature. However, in both methods, nano-sized particles are initially formed, but after a certain time, silver particles aggregate and grow into large particles, and so on. To overcome this problem, various surfactants or hydrophilic polymers such as polyvinylpyrrolidone (PVP) or polyvinylalcohol (PVA) are used to prevent aggregation.

Attempts to overcome the shortcomings of photocatalysts that do not show activity in the absence of light have been proposed in various ways. However, by adding substances with high adsorption capacity to the surface of the photocatalyst, in the absence of light, contaminants are adsorbed and stored, Under certain conditions, it would be useful to decompose and remove stored contaminants.

EDTA is an anion chelate compound having four carboxyl groups and having a negative charge of four when dissolved in water, and atoms such as hydrogen, sodium, calcium and iron are generally bonded to the carboxyl group. The compound is known to be non-toxic and is used in small amounts in foods to retard food deterioration. Na ₄ EDTA contains Ca ²⁺ , Mg ²⁺ , and Fe ³⁺ ions in water, which interfere with the role of soap. It is added to detergents to remove, and is used in various purposes for removing calcium ions that serve to coagulate blood by adding a small amount to the heavy metal poisoning treatment such as lead and blood for transfusion.

According to the present invention, the titanium dioxide particle surface prepared by hydrolyzing and peptizing titanium alkoxide with water and acid at a temperature of 60 to 80 ° C. is strongly charged with positive charge under acidic conditions, and thus it is stably present as nanoparticles. When the pH is adjusted to neutral, agglomeration of large particles occurs in order to lose charge and stabilize.The pH is adjusted to neutral by reacting the transition metal EDTA salt, an anion, and colloidal silica, which has a negative charge on the surface, with titanium dioxide particles. It also prevents agglomeration and at the same time increases the activity and sterilization ability of photocatalyst control, adds the function of absorbing sterilization and pollutants in the absence of light and removing the adsorbed pollutants in the light environment. The purpose is to prepare a photocatalyst dispersion liquid having excellent adhesion by coating and drying the coating.

1 is a transmission electron micrograph of the photocatalyst dispersion prepared according to the present invention.

2 is an X-ray diffraction pattern of the photocatalyst dispersion prepared according to the present invention.

Figure 3 is an antimicrobial test photograph of the photocatalyst dispersion prepared according to the present invention.

Figure 4 is a methylene blue decomposition photo of glass beads coated with a photocatalyst dispersion prepared according to the present invention.

In the present invention, water and acid are mixed in a molar ratio of 1: 0.01 to 0.1, and 0.01 to 0.1 mole of titanium alkoxide is added thereto, followed by stirring for 6 to 8 hours at a temperature of 60 to 80 ° C. Dissolving and peptizing to prepare an anatase titanium dioxide dispersion having a particle size of 1 to 10 nm; The molar ratio of Na ₄ EDTA and the transition metal compound was dissolved in water at a ratio of 1: 0.1 to 0.75, respectively, and then mixed with each other and stirred for 1 to 10 hours at a temperature range of 40 to 60 ° C. to substitute 1 to 3 transition metals instead of Na atoms. Preparing a transition metal EDTA salt; A dispersion in which the transition metal EDTA salt is dissolved on the titanium dioxide surface of the anatase-type titanium dioxide dispersion and a colloidal silica having a surface area of 200 to 1,000 m ² / g and a negatively charged surface at 1 to 2 at 30 to 60 ° C A method of producing a photocatalyst dispersion comprising a transition metal and a colloidal silica coupled to a titanium dioxide particle surface, comprising the steps of preparing a photocatalyst dispersion comprising a transition metal and colloidal silica on the titanium dioxide particle surface by reacting with stirring for a time. It is about.

In the present invention, water is deionized water, acid is nitric acid (HNO ₃ ), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ) or acetic acid (CH ₃ COOH), titanium alkoxide is titanium propoxide, titanium Isopropoxide or titanium buthoxide. In the present invention, the transition metal is silver, copper, platinum, palladium, rhodium, ruthenium, tin, iron, cobalt or molybdenum. In the present invention, the amount of EDTA to titanium dioxide is 40 to 60% by weight. In the present invention, silver or copper is 10% by weight based on the weight ratio of titanium dioxide, and platinum, palladium, rhodium, ruthenium, tin, iron, cobalt, or molybdenum is 1 to 2% by weight. In the present invention, the colloidal silica is added in an amount of 50 to 150% by weight based on the weight ratio of titanium dioxide. In the present invention, the titanium dioxide photocatalyst dispersion has a pH of 6 to 8.

The present invention relates to a method for preparing a photocatalyst dispersion in which a transition metal and colloidal silica are bonded to a nano-sized ultrafine titanium dioxide particle surface, and the method will be described in detail below.

Step 1: preparing nano-sized titanium dioxide dispersion, in which water and acid are mixed at a molar ratio of 1: 0.01 to 0.1 in a ratio range, and 0.01 to 0.1 mole of titanium alkoxide is added thereto at a temperature of 6 to 8 at 60 to 80 ° C. After stirring for a time, the titanium alkoxide was hydrolyzed and peptized with water and an acid to prepare an anatase type titanium dioxide dispersion having a particle size of 10 nm or less. At this time, de-ionized water is preferable, and acid is nitric acid (HNO ₃ ), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ), acetic acid (CH ₃ COOH), etc. , Nitric acid and acetic acid are preferred, and titanium alkoxide is at room temperature, such as titanium propoxide, titanium isopropoxide, titanium butoxide, except titanium methoxide. Both liquid titanium alkoxides can be used.

Step 2: preparing a transition metal EDTA salt, dissolving the molar ratio of Na ₄ EDTA and the transition metal compound in water at a ratio of 1: 0.1 to 0.75, respectively, and mixing them with each other and stirring at a temperature range of 40 to 60 ° C. for at least 1 hour. To make a transition metal EDTA salt in which the transition metal is substituted for Na atom. In this case, since more transition metal atoms are substituted for four Na atoms in the Na ₄ EDTA molecule, they may be converted into insoluble compounds, so that the number of substitution of transition metal atoms does not exceed three per molecule of EDTA, preferably not more than two It is important to control the molar ratio of Na ₄ EDTA and the transition metal, and to control the water ratio so that the transition metal EDTA salt does not precipitate.

Types of transition metals may be silver, copper, or titanium dioxide, which are known to have bactericidal properties, and platinum, palladium, rhodium, ruthenium, tin, iron, cobalt, molybdenum, etc., which can be combined with a photocatalyst to enhance activity. It is possible to use a compound having a high solubility in water, and a form of -NO ₃ , -Cl, and some -OH which exist as a transition metal cation in water. The transition metal EDTA salt dispersion prepared as described above was not aggregated with each other even after standing for a long time.

Step 3: A final step of preparing a photocatalyst dispersion in which a transition metal and colloidal silica is combined on a titanium dioxide particle surface, and a two-step method on an anatase crystalline titanium dioxide surface having a particle size of 10 nm or less prepared by a one-step method. The dispersion prepared by dissolving the transition metal EDTA salt and the negatively charged colloidal silica having a large surface area of 200 m ² / g or more were reacted by stirring at a temperature of 30 to 60 ° C. for 1 to 2 hours.

In the bonding process, EDTA, which is partially substituted with a transition metal instead of four Na atoms, is dissolved in water and exists as an anion having four or less carboxyl groups (COO ⁻ ), and colloidal silica has a negatively charged surface. It is strongly bound and stabilized by electrostatic interaction with the positively charged titanium dioxide particle surface.

At this time, the amount of EDTA to titanium dioxide is suitable by 40 to 60% by weight, and the transition metal is 10% by weight of titanium or silver added for the purpose of increasing sterilization power, and the photocatalytic activity It is desirable that the other transition metal added to increase the content not to exceed 2%. The addition amount of colloidal silica is appropriate to add about 50 ~ 150% by weight ratio to titanium dioxide, but it is appropriately adjusted according to the irradiation time of light or application conditions of the photocatalyst.

Titanium dioxide photocatalyst dispersion combined with transition metal EDTA salt and colloidal silica is acidic, so it is desirable to adjust the pH to 6 to 8 so that it can be applied safely and widely regardless of the material of the target material to be coated. Organic / inorganic bases such as sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia water (NH ₄ OH), ethylenediamine (C ₂ H ₈ N ₂ ), and the like may be used.

After a certain time after coating the photocatalyst dispersion prepared by the above method, EDTA and other organic substances contained in the photocatalyst dispersion are decomposed by light, so that titanium dioxide particles and the transition metal are in close contact and the transition metal is oxidized to a transition metal oxide. To enhance the photocatalytic effect. In addition, the film coated with the photocatalyst powder prepared by the above method was tested by the pencil hardness method, and showed a hardness of H or more, thereby showing excellent adhesion.

<Example 1>

10 g of nitric acid (60%) was mixed with 350 g of deionized water, followed by stirring. 40 g of titanium isopropoxide was added thereto, the temperature was maintained at 70 ° C., and stirred for 8 hours to disperse about 3% of titanium dioxide. As a result of analyzing the characteristics of the prepared titanium dioxide by transmission electron microscope (TEM) and X-ray diffraction pattern (XRD) as shown in Figs. 1 and 2, the average particle size of titanium dioxide is about 8-10 It was in the order of nm and investigated as an anatase crystalline form.

<Example 2>

Dissolve 1.5 g of AgNO ₃ , 0.3 g of Fe (NO ₃ ) ₃ , and 0.4 g of Zn (NO ₃ ) _{2 in} 200 g of deionized water, completely dissolve 5 g of Na ₄ EDTA in 300 g of deionized water, mix and The reaction was carried out for 3 hours at 50 ℃ to prepare a transition metal EDTA salt solution. The transition metal EDTA salt thus prepared was added to the titanium dioxide dispersion prepared in Example 1 and stirred, with an average particle diameter of 12 nm produced by DuPont, 220 m ² / g, and a negative particle surface. The LUDOX HS-40 colloidal silica charged slowly was added while maintaining the temperature at 50 ° C. and reacted for 1 hour to prepare a photocatalyst dispersion in which the transition metal EDTA salt and the colloidal silica were attached to the titanium dioxide particle surface. pH was adjusted to 7.

<Example 3>

The performance of the photocatalyst dispersion prepared according to the method of Example 2 was evaluated by formaldehyde decomposition test. Formaldehyde decomposition evaluation method was injected into a 1 L container 10 × 10 cm glass plate coated with a photocatalyst and 2 μl of formaldehyde, and irradiated with 20 W black light, and measured by the gas detection tube method. Two hours after the start of the test, 83% of formaldehyde was removed.

<Example 4>

The performance of the photocatalyst dispersion prepared according to the method of Example 2 was evaluated through the antibacterial test of Staphyococcus aureus ATTC 6538 and Klebsiella pneumoniae ATTC 4352. In the antibacterial test, the concentration of bacteria was 1.3 × 10 ⁵ / ml, and the nonionic surfactant was tested by adding Tween 80 and 0.05% to the inoculated bacteria solution. As shown in Figure 3, Staphylococcus aureus was 99.9%, pneumococcal bacteria showed a 97.9% bacteriostatic rate.

Example 5

The glass beads coated with the photocatalyst dispersion were prepared, and a methylene blue decomposition experiment was performed. 20 ml of 20 ppm methylene blue solution was poured into each of two sares, and 20 g of glass beads coated with a photocatalyst dispersion and 20 g of uncoated glass beads were added thereto, and the light emitted from the 20 W black light was irradiated. In the early stage of the reaction, glass beads not coated with photocatalyst did not show any change, but glass beads coated with photocatalyst absorbed some methylene blue and turned the surface blue. 6 hours after irradiation with light, methylene blue mixed with glass beads not coated with photocatalyst remained blue, but methylene blue was decomposed to colorless in glass beads coated with photocatalyst.

The photocatalyst prepared according to the method of the present invention combines a transition metal and colloidal silica on a nano-sized fine titanium dioxide particle surface by using an electrostatic interaction with an EDTA compound, even in the absence of light. The sterilization function and the adsorption function of contaminants by the colloidal silica having a large surface area are added to overcome the disadvantages of the conventional photocatalyst.

In addition, by combining transition metal EDTA salt and colloidal silica with positively charged titanium dioxide particle surface without special treatment, it is possible to stabilize the pH of the dispersion to prevent aggregation of particles even when neutral, so that photocatalytic dispersion can be widely used. There is an advantage.

Claims (7)

Mix water and acid in a molar ratio of 1: 0.01 to 0.1 and add 0.01 to 0.1 mole of titanium alkoxide to the mixture and stir for 6 to 8 hours at a temperature of 60 to 80 ° C. to hydrolyze and bridge the titanium alkoxide with water and acid. Reacting to prepare an anatase type titanium dioxide dispersion having a particle size of 1 to 10 nm; The molar ratio of Na ₄ EDTA and the transition metal compound was dissolved in water at a ratio of 1: 0.1 to 0.75, respectively, mixed with each other, and stirred for 1 to 10 hours at a temperature range of 40 to 60 ° C. to substitute 1 to 3 transition metals instead of Na atoms. Preparing a transition metal EDTA salt; A dispersion in which the transition metal EDTA salt is dissolved on the titanium dioxide surface of the anatase-type titanium dioxide dispersion and a colloidal silica having a surface area of 200 to 1,000 m ² / g and a negatively charged surface at 1 to 2 at 30 to 60 ° C A method of producing a photocatalyst dispersion comprising a transition metal and a colloidal silica coupled to a titanium dioxide particle surface, comprising the steps of preparing a photocatalyst dispersion comprising a transition metal and colloidal silica on the titanium dioxide particle surface by reacting with stirring for a time. . The method of claim 1, wherein the water is deionized water, the acid is nitric acid (HNO ₃ ), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ) or acetic acid (CH ₃ COOH), and the titanium alkoxide is titanium propoxide ( Titanium propoxide), titanium isopropoxide (Titanium isopropoxide) or titanium butoxide (Titanium buthoxide) characterized in that the production method of the photocatalyst dispersion combined with a transition metal and colloidal silica on the surface of titanium dioxide particles. The photocatalyst dispersion of claim 1, wherein the transition metal is silver, copper, platinum, palladium, rhodium, ruthenium, tin, iron, cobalt or molybdenum. Manufacturing method. The method according to claim 1, wherein the amount of EDTA to titanium dioxide is 40 to 60% by weight in terms of weight ratio. The method of preparing a photocatalyst dispersion liquid in which a transition metal and colloidal silica are combined on a titanium dioxide particle surface. The method of claim 3, wherein the silver or copper is 10% by weight based on the titanium dioxide, titanium, palladium, rhodium, ruthenium, tin, iron, cobalt or molybdenum is titanium dioxide, characterized in that 1 to 2% by weight A method for producing a photocatalyst dispersion wherein a transition metal and colloidal silica are bonded to a particle surface. The method of claim 1, wherein the colloidal silica is added in an amount of 50 to 150% by weight based on the weight of titanium dioxide. The method of preparing a photocatalyst dispersion having a transition metal and colloidal silica coupled to a titanium dioxide particle surface. The method of claim 1, wherein the titanium dioxide photocatalyst dispersion has a pH of 6 to 8, wherein the transition metal and colloidal silica are bonded to the titanium dioxide particle surface.