Stable nano titania sols and a process for their production

Stable nano titanium dioxide sol and preparation method thereof

The summary of the present disclosure is about stable concentrated nano-titanium dioxide sol and its preparation method and application. For example, the present disclosure is about stable concentrated nano-titanium dioxide sol in the mild pH range (4.0-10.0) and its preparation method and use.

Titanium dioxide (Titania or titanium dioxide) (TiO₂) Usually exists in the market as either of the two main polymorphs, anatase or rutile, and has an average particle size of 150 nm to 250 nm. Due to its high refractive index, negligible color and inertness, titanium dioxide can be used as a sunscreen agent in paints, paper, plastics, ceramics, inks, etc. Titanium dioxide with a small average particle size (for example, an average particle size between 1 nm and 150 nm) is called nano-titanium dioxide. It has been found that nano-titanium dioxide can be used in cosmetics, personal care products, plastics, surface coatings, self-cleaning surfaces and photovoltaic applications because of its: i) translucency combined with photoprotective properties; ii) photocatalysis And iii) conductivity combined with high surface area.

The problems with the nano-titanium dioxide products supplied in powder form include: i) the difficulty in dispersing the product to the required size; and ii) the dust/handling problems caused by the fineness of the nano-titanium dioxide powder. Nano-titanium dioxide products supplied in the form of stable concentrated sols will solve these major problems.

There have been reports of stable aqueous nano-TiO2 sols in the literature. However, its preparation is limited to very low (<pH 2) or very high (>pH 10) pH regions or low concentrations (<300 gpl).

In US Patent No. 2,448,683, a method of first neutralizing hydrated titanium dioxide and then using HCl to perform peptization to form a colloidal titanium dioxide sol is described. The colloidal titanium dioxide sol is then neutralized, dried and calcined at a temperature between about 500°C and 600°C, and then the calcined product is dispersed again.

In US Patent Publication No. 2006/0110319, rutile nano-grade titanium dioxide sol is prepared by hydrolyzing titanium tetraisopropoxide in an aqueous solution containing hydrogen peroxide, and then at a temperature of 50°C-120°C Under implementation of hot water treatment.

U.S. Patent Publication No. 2009/0062111 describes a method for forming nanoscale titanium dioxide sol, which comprises precipitating hydrated titanium dioxide from a titanium isopropoxide solution, and using α-hydroxycarboxylic acid pair at a temperature of 70°C-150°C Hydrated titanium hydroxide implements peptization for an extended period of time.

US Patent Publication No. 2009/0061230 also describes a method for forming a stable nano-scale titanium dioxide sol by reacting a halide-containing titanium compound with water in the presence of a polyhydric alcohol.

In US Patent No. 5,840,111, nano-scale titanium dioxide sol is prepared by the following method: adding a solution of sulfuric acid and titanyl sulfate to an alkaline reaction medium to form titanium dioxide nanoparticles, and adding a monobasic acid to flocculate the nanoparticles , And then separate the flocs by filtration.

Therefore, the industry is still very much looking forward to an alternative way of preparing highly stable nano-scale titanium dioxide sol, and in particular, a way to prepare highly stable concentrated nano-scale titanium dioxide sol.

The present disclosure provides a method for preparing concentrated aqueous nano-titanium dioxide sol, which includes:

(a) Contact the acidic nano-titanium dioxide sol with a dispersing agent and an alkalizing agent, the dispersing agent including at least one of water-soluble carboxylic acid, water-soluble carboxylate, water-soluble polycarboxylic acid, phosphate or silicate , Wherein the pH of the nano-titanium dioxide sol after contact is between about 4.0 and about 10.0; and

(b) Subject the pH-adjusted nano-titanium dioxide sol to membrane filtration, preferably cross-flow filtration or cross-flow filtration and vibration, and continue membrane filtration until the nano-titanium dioxide sol contains more than 300 g TiO₂Nano particles/dm³until.

The present disclosure also provides a method for preparing concentrated aqueous nano-titanium dioxide sol, which includes:

(a) Provide acidic nano-titanium dioxide sol;

(b) Contacting the acidic nano-titanium dioxide sol with a dispersing agent and an alkalizing agent, the dispersing agent including at least one of a water-soluble carboxylic acid, a water-soluble carboxylate, a water-soluble polycarboxylic acid, a phosphate or a silicate Wherein the pH of the nano-titanium dioxide sol after the contact is between about 4.0 and about 10.0; and

(c) Subject the pH-adjusted nano-titanium dioxide sol to membrane filtration, preferably cross-flow filtration or cross-flow filtration and vibration, and continue membrane filtration until the nano-titanium dioxide sol contains more than 300 g TiO₂Nano particles/dm³until.

In another embodiment, preferably, before starting to concentrate the nano-titania sol, during step (b) of the method described in paragraph [0013] or step (c) of the method described in paragraph [0014], The pH-adjusted nano-titanium dioxide sol can be contacted with a detergent to remove soluble salts from the nano-titanium dioxide sol.

According to another embodiment, the nano-titanium dioxide sol may be subjected to a coating treatment before, during or after any of the steps of the above method.

The concentrated aqueous nano-titanium dioxide sol of the present disclosure is suitable for various applications, including providing UV protection and photochemically degrading or passivating pollutants.

In the scope of this specification and the accompanying patent application, mention should be understood as many terms with the following meanings.

The term "nano-titania sol" refers to TiO with a particle size of less than 150 nm, preferably less than 100 nm₂A colloidal suspension of nano particles. TiO₂Nanoparticles can be anatase, rutile or amorphous or mixtures thereof.

The terms "cross-flow filtration" and "cross-flow filtration and vibration" refer to the following filtration methods: a suspension of solid particles in a fluid medium flows tangentially across the membrane surface, and at the same time, it is subjected to a fluid medium that is easy to cause the suspension to flow through. The pressure of the membrane, the membrane can permeate the fluid medium but not solid particles. By passing the suspension across the membrane surface, any excessive accumulation of solids on the membrane surface can be minimized. The mechanical vibration of the membrane surface can be used to reduce the clogging or fouling of the membrane. This method is described in, for example, US Patent No. 4,952,317, the content of which is expressly incorporated herein by reference.

The present disclosure provides a method for preparing concentrated aqueous nano-titanium dioxide sol. In an embodiment of the present disclosure, a concentrated aqueous nano-titanium dioxide sol is prepared by a method including the following steps:

(a) Contact the acidic nano-titanium dioxide sol with a dispersing agent and an alkalizing agent, the dispersing agent including at least one of water-soluble carboxylic acid, water-soluble carboxylate, water-soluble polycarboxylic acid, phosphate or silicate , Wherein the pH of the nano-titanium dioxide sol after contact is between about 4.0 and about 10.0; and

(b) Subject the pH-adjusted nano-titanium dioxide sol to membrane filtration, preferably cross-flow filtration or cross-flow filtration and vibration, and continue membrane filtration until the nano-titanium dioxide sol contains more than 300 g TiO₂Nano particles/dm³until.

In another embodiment of the present disclosure, the concentrated aqueous nano-titanium dioxide sol is prepared by a method including the following steps:

(a) Provide acidic nano-titanium dioxide sol;

(b) Contacting the acidic nano-titanium dioxide sol with a dispersing agent and an alkalizing agent, the dispersing agent including at least one of a water-soluble carboxylic acid, a water-soluble carboxylate, a water-soluble polycarboxylic acid, a phosphate or a silicate Wherein the pH of the nano-titanium dioxide sol after the contact is between about 4.0 and about 10.0; and

(c) Subject the pH-adjusted nano-titanium dioxide sol to membrane filtration, preferably cross-flow filtration or cross-flow filtration and vibration, and continue membrane filtration until the nano-titanium dioxide sol contains more than 300 g TiO₂Nano particles/dm₃until.

Essentially all steps of the method of the present invention can be implemented at a temperature lower than 100°C, thereby making the commercial setup of the method simpler and more economical. The concentrated aqueous nano-titanium dioxide sol prepared by the method of the present invention exhibits exceptional stability in a wide pH range, especially a mild pH range of 4.0-10.0 (for example, 6.0-8.0), making the sol environmentally safer and easier use. In addition, the concentrated aqueous nano-titanium dioxide sol does not exhibit agglomeration and therefore does not require a grinding step to exhibit excellent translucency. In addition, although the nano-titanium dioxide sol is relatively dense, it still has a low viscosity, making it particularly suitable for transportation and direct application.

According to an embodiment, an acidic nano titanium dioxide sol is provided. The acidic nano-titanium dioxide sol can be provided by any method, as long as the sol contains TiO₂An acidic colloidal suspension of nano particles is sufficient. TiO suspended in colloidal form₂Nanoparticles can be anatase, rutile or amorphous TiO prepared by any suitable method₂Make preparations. Typical methods may involve hydrolysis of a suitable titanium compound (e.g., titanium tetrachloride, titanyl sulfate, or organic or inorganic titanate), or oxidation of an oxidizable titanium compound (e.g., in a vapor state).

In one embodiment, the TiO obtained by the precipitation step in the sulfate process₂To prepare acidic nano-titanium dioxide sol. After precipitation, the obtained titanium dioxide hydrate is filtered, washed so as to be free of impurities, and contacted with an aqueous alkali solution to form a suspension with a pH of approximately neutral. The sulfate ions are then removed from the neutralized suspension by filtration and washing. In one aspect, the filter cake obtained after filtration is washed until the SO of the filtrate is washed₄^2-The content is less than 0.1 g/l (this can be measured by barium chloride solution titration). The washed filter cake is then slurried in water to prepare an aqueous suspension of titanium dioxide hydrate substantially free of sulfate ions, and then a strong monobasic acid is used to adjust the pH to about 2.0 or lower, preferably pH It is about 1.5 to peptize it to provide acidic nano-titanium dioxide sol.

Then, the acidic nano-titanium dioxide sol is contacted with a dispersing agent and an alkalizing agent. The acidic nano-titanium dioxide sol can be contacted with the dispersing agent and the alkalizing agent in any order or combination order.

According to an embodiment, the acidic nano-titanium dioxide sol is first contacted with the dispersant. The dispersant includes at least one of a water-soluble carboxylic acid, a water-soluble carboxylate, a water-soluble polycarboxylic acid, a phosphate, or a silicate. In one embodiment, the water-soluble carboxylic acid is an α-hydroxy carboxylic acid. The alpha-hydroxy carboxylic acid may include one, two, or three carboxylic acid groups, and include (not limited to) lactic acid, glycolic acid, malic acid, tartaric acid, mandelic acid, and citric acid. In another embodiment, the water-soluble carboxylic acid is β-hydroxycarboxylic acid. In another embodiment, the water-soluble polycarboxylic acid is a dicarboxylic acid or tricarboxylic acid. In other embodiments, the dispersant includes one or more salts of the aforementioned acids. In other embodiments, the dispersant includes the above-mentioned acids and salts, in combination with phosphates and silicates.

The acidic nano-titanium dioxide sol can be contacted with the dispersing agent by any suitable means (such as conventional mixing in a container) for a period of at least about 0.1 hours, preferably at least about 0.25 hours, and more preferably at least about 0.5 hours. In another embodiment, the acidic nano-titanium dioxide sol can be contacted with the dispersing agent for a period of less than about 24 hours, preferably less than about 12 hours, and more preferably less than about 3 hours. In yet another embodiment, the acidic nano-titanium dioxide sol can be contacted with the dispersing agent for a period of at least about 0.5 hours to less than about 3 hours.

The acidic nano-titanium dioxide sol is also brought into contact with an alkalizing agent. In one embodiment, the acidic nano-titanium dioxide sol is contacted with an alkalizing agent after being contacted with a dispersing agent. Examples of alkalizing agents include alkanolamines (preferably water-soluble alkanolamines, such as isopropanolamine) and choline hydroxide. The time of contact between the acidic nano-titanium dioxide sol and the alkalizing agent is a time sufficient to adjust the pH of the acidic nano-titanium dioxide sol to a pH between about 4.0 and about 10.0.

Then the pH-adjusted nano-titanium dioxide sol is subjected to membrane filtration, preferably cross-flow filtration or cross-flow filtration under vibration, so as to obtain at least 300 g of TiO₂Nano particles/dm³The concentrated nano-titanium dioxide sol. In other embodiments, the nano-titanium dioxide sol is subjected to membrane filtration to obtain a concentrated nano-titanium dioxide sol, which contains at least 500 g of TiO₂Nano particles/dm³, Preferably at least 550 g TiO₂Nano particles/dm³, And better at least 600 g TiO₂Nano particles/dm³, And even better at least 700 g TiO₂Nano particles/dm³. Preferably, the viscosity of the concentrated nano-titanium dioxide sol at 20° C. is about 0.001 Pa s to about 0.2 Pa s. The solid content of the pH-adjusted nano-titania sol used as the raw material for membrane filtration is usually less than about 350 g TiO₂Nano particles/dm³. Therefore, in one embodiment, the solid content of the pH-adjusted nano titania sol raw material is at least about 100 g TiO₂Nano particles/dm³To less than about 350 g TiO₂Nano particles/dm³between.

Optionally, at any time during the membrane filtration step, the pH-adjusted nano-titanium dioxide sol can be brought into contact with a detergent (such as water, preferably demineralized water) to remove a portion or substantially of the nano-titanium dioxide sol All soluble salts. In one embodiment, before concentrating the nano-titanium dioxide sol, the pH is adjusted during step (b) of the method described in paragraph [0021] or step (c) of the method described in paragraph [0022] The titanium dioxide sol is in contact with the detergent. In another embodiment, after concentrating the nano-titanium dioxide sol, the pH-adjusted nano-titanium dioxide sol is brought into contact with the detergent. Reducing the water-soluble salt in the nano-titanium dioxide sol will help to prepare a concentrated nano-titanium dioxide sol with the desired low conductivity. In one aspect, during step (b) of the method described in paragraph [0021] or step (c) of the method described in paragraph [0022], the nano-titanium dioxide sol is brought into contact with the detergent, and the contact time should be It is sufficient to reduce the conductivity of the nano-titania sol to less than 10 mS/cm, preferably less than 5 mS/cm, and more preferably less than 2 mS/cm.

In another aspect, the nano-titanium dioxide sol may be coated with the coating agent if necessary. The coating treatment can be performed before, during, or after any of the steps of the above-mentioned method. In one embodiment, in step (a) of the method described in paragraph [0021] or step (b) of the method described in paragraph [0022], the acidic nano-titanium dioxide sol is combined with a dispersant and an alkalinizing agent After the contact, a coating treatment is applied. In another embodiment, during step (b) of the method described in paragraph [0021] or step (c) of the method described in paragraph [0022], it is preferable that the pH-adjusted nano-titanium dioxide sol has been combined with After the detergent is contacted to remove the soluble salt from the nano-titania sol but before the concentration, a coating treatment is performed. Suitable coating agents include alkaline or acidic coating agents, for example, they are commonly used to coat inorganic oxides or hydrated oxides on TiO₂Those on the surface of the nanoparticle. Typical inorganic oxides and hydrated oxides include one or more oxides and/or hydrated oxides of silicon, aluminum, titanium, zirconium, magnesium, zinc, cerium, phosphorus, or tin. Relative to TiO₂The weight of nano particles, coated on TiO₂The coating amount on the surface of the nanoparticle may be between about 0.1 wt% and 50 wt.% of inorganic oxide and/or hydrated oxide. Examples of alkaline coating agents include sodium silicate, potassium silicate, sodium aluminate or mixtures thereof. Examples of acidic coating agents include aluminum chloride, aluminum sulfate, or mixtures thereof.

Cation exchange resins can also be used during the coating process to ensure that the ionic strength of the nano-titanium dioxide sol is maintained low during the process and the colloidal stability is maintained. In this embodiment, the nano-titanium dioxide sol is brought into contact with an alkaline coating agent (preferably sodium silicate) and a cation exchange resin in a batch tank. Control the addition rate of sodium silicate and cation exchange resin to maintain the pH of the sol in the batch tank between about 4.0 and about 10.0. In another embodiment, the sol and the alkaline coating agent are passed through the column or carrier containing the cation exchange resin at a certain rate, so that the pH of the effluent is maintained between about 4.0 and about 10.0. Any cation exchange resin can be used, including those generally known, such as strong acid cation exchange resins containing sulfonic acid groups, weak acid cation exchange resins containing carboxylic acid groups, or mixtures thereof. In some embodiments, if it is desired to remove the cation exchange resin, techniques known in the art can be used to facilitate this removal.

Anion exchange resins can also be used during the coating process. In this embodiment, the nano-titanium dioxide sol is brought into contact with the acid coating agent and the anion exchange resin in a batch tank. The addition rate of the acid coating agent and the anion exchange resin is controlled to maintain the pH of the sol in the batch tank between about 4.0 and about 10.0. In another embodiment, the sol and the acidic coating agent are passed through a column or carrier containing an anion exchange resin at a certain rate, so that the pH of the effluent is maintained between about 4.0 and about 10.0. Any anion exchange resin is applicable, including those generally known, such as strong base anion exchange resins containing hydroxide or quaternary ammonium groups, weak base anion exchange resins containing primary or secondary amine groups, or their mixture.

The prepared concentrated aqueous nano-titanium dioxide sol exhibits exceptional stability and translucency. The currently known methods involve drying the nano-titania sol (which causes partial inter-particle bonding) and subsequent grinding steps. The method of the present invention can avoid the use of drying and grinding and still provide a well-dispersed sol. Therefore, a nano-dispersion can be achieved in a compounding system containing the concentrated nano-titanium dioxide sol prepared by the method of the present invention. In addition, the present invention provides a sol with an improved physical form (ie, colloidal suspension vs. low-density bonding powder), which greatly facilitates the subsequent operation and processing of the nano-titanium dioxide sol.

The concentrated aqueous nano-titanium dioxide sol prepared according to the present invention is suitable for use as a coating or in an article. For example, concentrated aqueous nano-titanium dioxide sol can be used in the following: personal care products and cosmetic formulations, such as sunscreens, moisturizers, color foundation creams, lipsticks, lipsticks, foot care products and ointments; coatings and Masonry formulations, such as automotive coatings, wood coatings, architectural coatings, roofing slag, roof coverings, building side panels, floors, swimming pool surfaces, and cement or concrete; catalysts or photocatalysts or carriers in catalyst products ; Photovoltaic cells; plastic parts, films, and resin systems, including agricultural films, food packaging films, molded automotive plastic parts, and engineering polymer resins; rubber-based products, including silicone rubber; used in fabrics and non-woven fabrics Textile fibers in application, including polyamide, polyaramide, and polyimide fiber products and non-woven sheet products; ceramics; glass products, including architectural glass, automotive glass, and industrial glass; flame retardants; and Electronic components.

According to another embodiment, concentrated aqueous nano-titanium dioxide sol can be used in the method of the present invention to provide UV protection to the surface of the substrate. The method includes applying concentrated aqueous coated nano-titanium dioxide sol to the surface of the substrate as a film in the presence or absence of a binder medium. Various application techniques can be used to apply the sol, such as dipping, spraying, spin coating, dipping, brushing, and knife coating. Preferably, the concentrated coated nano-titanium dioxide sol is applied to a thickness of about 0.001 mm to about 0.2 mm, as measured in a liquid state. The applied film then forms a protective coating on the surface of the substrate. The film can be dried as needed. The substrate may include, but is not limited to, textile fibers, furniture, paper, paving materials, tiles, concrete, cement, wood, ceramics, polymers, leather, asphalt, building exteriors, and glass. In another embodiment, a concentrated aqueous nano-titanium dioxide sol is introduced into a cosmetic and the mixture is applied to the skin surface as described above to provide UV protection.

According to another embodiment, a catalytic composition is provided, which includes a concentrated aqueous nano-titanium dioxide sol prepared by the method of the present disclosure. The catalytic composition containing concentrated nano-titanium dioxide sol can be used to promote various reactions, and may be characterized by the conversion rate achieved by the chemical reaction when the reactant of the chemical reaction contacts the catalytic composition. In one embodiment, the catalytic composition is present on the support. Examples of carrier materials include glass, ceramics, metals, plastics, cement, concrete, asphalt, textiles, and paper. The support can be a porous or non-porous support. Examples of porous supports include fiber felts, zeolites, or porous membranes. The term "on the support" means that the catalytic composition is located on at least a part of the surface of the support. For porous supports, the term "on the support" further means that the catalytic composition is additionally present in the pores of the support.

In one embodiment, the catalytic composition can be mixed with the reactant fluid and irradiated with visible light to chemically react one or more components of the reactant fluid. The catalytic composition can then be recovered from the fluid and recycled for use in another portion of the reactant fluid. Catalytic compositions can be used instead of common metal catalysts, such as cobalt, nickel, copper, gold, iridium, lanthanum, nickel, osmium, platinum, palladium, rhodium, ruthenium, silver, strontium, yttrium, zirconium, and tin.

In another embodiment, the catalytic composition is present on the carrier, and the reactant fluid can flow to contact the carrier and the composition, and when light is irradiated, this can make one or more components of the reactant fluid A chemical reaction occurred. In this configuration, the catalytic composition can be exposed to a continuous flow of fluid and there is no need to separate the catalytic composition and the fluid after performing the reaction. For example, the catalytic composition can be applied to a carrier, such as an automobile exhaust system, where the exhaust system is equipped with a visible or UV light source, such as a fiber optic light source or an LED light source. Irradiation of the catalytic composition during the operation of the automobile engine can degrade the organic matter and other contaminants produced in the engine into environmentally acceptable substances.

In another embodiment, the catalytic composition may be present on surfaces that are in contact with various environmental pollutants or contaminants, such as dust, grease, and other organic and inorganic contaminants and contaminants. The catalytic composition, optionally including the formulation of the catalytic composition, is applied to the surface, and the surface is irradiated with UV/visible light while the contaminants or contaminants contact the surface. After exposure to UV/visible light, the surface becomes "self-cleaning" and degrades or passivates contaminants or contaminants. For example, self-cleaning glass may have a transparent or translucent coating of the catalytic composition applied to one or both sides of the glass. When the glass is exposed to UV/visible light, the contaminants that come into contact with the glass can then be degraded. It may be desirable for the self-cleaning glass to have a hydrophilic surface to use water to rinse any remaining degradation products from the glass.

In another embodiment, the catalytic composition may be present on surfaces exposed to microorganisms (such as bacteria and fungi, and/or viruses). After being exposed to UV/visible light, this surface can become a "disinfected surface" by destroying or inactivating microorganisms or viruses present on the surface. For example, a surface in a residential, commercial or hospital environment can have a coating of catalytic composition applied to the surface. When the surface is exposed to UV/visible light, the microorganisms and/or viruses that contact the surface can then be destroyed or inactivated. Examples of surfaces that can be made into sterile surfaces include countertops, floors, walls, handles, switches, handles, keyboards, telephones, and medical device surfaces.

The catalytic composition can also be applied to the surface to temporarily disinfect the surface. For example, the catalytic composition can be incorporated into the cleaning composition. The cleaning composition can be in the form of a liquid, foam or lotion. By applying the cleaning composition to the surface and then exposing the surface to UV/visible light, the microorganisms or viruses present on the surface can be destroyed or inactivated. These cleansing compositions can be formulated for use on the skin to provide disinfecting personal care products.

The catalytic composition containing concentrated nano-titanium dioxide sol can also be used for air and/or water purification. For example, the catalytic composition can be mixed with polluted air or water and irradiated with UV/visible light. The pollutants in the air or water can be degraded into volatile substances or more easily separated from the air or water. For example, pollutants containing organic substances and halogenated substances can be degraded into carbon dioxide and halide ions, and then the carbon dioxide and halide ions can be separated from air or water. In the case of air purification, pollutants (such as NO and NO₂(Single or together) and VOC) degradation can also produce cleaner air and can control the air odor.

In another embodiment, the catalytic composition can be used to sense gas. Because of TiO₂The conductivity of nano particles varies depending on the chemical composition of the environment, so the variable conductivity can be used to use TiO₂Nanoparticles are used to measure the type and/or amount of one or more gases. TiO can be measured in a certain environment₂Nano particles or contain TiO₂The resistance of the nanoparticle material is compared with the resistance in the control environment. The difference between the measured resistance and the control resistance can be correlated with the amount and/or identification of the gas in the environment. Examples of gases that can be identified and/or measured include hydrogen, carbon monoxide, hydrogen sulfide, and water. Preferably, a gas sensor including a catalytic composition is used to sense gas under ambient conditions.

In another embodiment, a catalytic composition can be used to generate hydrogen and oxygen from water. When water is irradiated with UV/visible light, the water containing the catalytic composition can be decomposed into hydrogen and oxygen by photocatalysis. This decomposition can also be implemented in a photoelectrochemical cell, which has a photoanode containing a quaternary oxide. It may be desirable to use a photoelectrochemical cell, so hydrogen and oxygen can be collected separately from the cell.

In another embodiment, the catalytic composition can be used to generate electricity from solar radiation, and in particular, it contains the catalytic composition and is used to sensitize TiO₂Nanoparticles of dye molecules are carried out in solar cells. For example, when the dye molecules are excited by exposure to light, an electric current can be generated. The excited dye molecules transfer electrons to the conduction band of the nanoparticle, and the nanoparticle guides the electron into the current collector connected to the circuit with the load.

In another embodiment, the catalytic composition can be used in composite materials, including polymer composites, textiles and non-woven materials. For example, the catalytic composition can be incorporated into a textile fabric along with the fibers. When exposed to UV/visible light, these fabrics can degrade the contaminants in contact with the fabric, thereby obtaining self-cleaning or disinfecting fabrics.

In another embodiment, the catalytic composition can be used as a bioactive agent. TiO irradiated by UV/visible light in an aqueous environment (such as in an organism)₂Nanoparticles can produce hydroxyl ions (OH^-), superoxide ion (O₂^-), and/or hydrogen peroxide. TiO exposed to UV/visible light₂Nanoparticles can create a toxic environment that can damage or kill cells when they are located in or in contact with cells. Therefore, the catalytic composition can be used as an anticancer agent when delivered to tumor cells. It may be desirable to couple the catalytic composition with a target agent that is selectively taken up by tumor cells. The light can be delivered laparoscopically to the cells containing the catalytic composition, thereby causing cell death or reducing cell growth or reproduction.

The present invention will be further explained by considering the following examples, which are intended as exemplary examples of the present invention. Unless otherwise stated, all parts and percentages in these examples are by weight.

<b>Instance</b>

<b>Example 1.</b>The ilmenite is cooked with concentrated sulfuric acid to obtain a digestion cake. The cooking cake is dissolved in water to form a crude liquid, which contains iron sulfate, titanium sulfate and some suspended insoluble substances. Then the iron in the form of ferric iron is chemically reduced and the liquid is filtered to remove insoluble materials. The liquid is then concentrated by vacuum treatment, and hydrolyzed by heating and adding a nucleating agent to precipitate hydrated titanium dioxide. The hydrated titanium dioxide is separated from impurities by washing and filtering, and then the titanium dioxide hydrate suspension is obtained by mixing the hydrated filter cake and demineralized water. Then use ammonia to neutralize the titanium dioxide hydrate suspension (pH&lt;2) to a pH of 7.05, filter and wash with water to remove sulfate compounds, where the filtrate wash has &lt;100 ppm SO₄^2-, And then make a slurry again in water. Then, the pH of the slurry was brought to pH 1.50 by adding hydrochloric acid, and mixed for 30 minutes to prepare an acidic nano-titanium dioxide sol with 33% solids. Then the acidic nano-titanium dioxide sol was contacted with citric acid by mixing in a container (1.0 g citric acid and 10.0 g TiO₂) About 20 minutes. Then, the pH of the sol was adjusted to 8.00 by mixing in a container to contact the sol with monoisopropanolamine for a sufficient time. Then the pH-adjusted nano-titanium dioxide sol was subjected to cross-flow filtration by the following method: first the sol was contacted with water to remove soluble salts to achieve a conductivity of 4.64 mS/cm, and then the cross-flow filtration was continued until the sol contained 673 g TiO2 nano particles/dm³(Based on the total weight of the aqueous sol). The resulting sol has a viscosity of 0.035 Pa s (measured using a Brookfield viscometer with a No. 2 rotor at 19.3° C. and 100 rpm). The modal particle size measured by the CPS disc centrifuge is 43 nm. The pH of the sol is 8.2.

<b>Example 2.</b>The stabilized nano-titanium dioxide sol prepared in Example 1 was incorporated into the semi-gloss acrylic emulsion with a dry film pigment volume concentration of 18.23%. Then the coating was applied to 125 um polyester film with a coating wet film thickness of 150 μm. After curing, the resulting coating has an absorbance of 1.546 at a wavelength of 550 nm. A comparative coating containing commercial anatase and having the same TiO2 concentration has an absorbance of 2.489 at a wavelength of 550 nm.

<b>Prophetic example A.</b>The acidic nano titanium dioxide sol was obtained as described in Example 1. Then by mixing in a container, the acidic nano-titanium dioxide sol was contacted with citrate (1.0 g citric acid and 10.0 g TiO₂) About 30 minutes. The sol is then contacted with monoisopropanolamine by mixing in a container until the pH of the sol is about 8.0. Then the TiO suspended in the pH-adjusted sol₂Nanoparticles are heated to 75°C and coated with silica by co-adding sodium silicate and cation exchange resin (in TiO₂20% by weight SiO on the₂), thereby maintaining the pH of the sol between about 5.0 and about 10.0. Then use the following method to make TiO containing coated silicon dioxide₂The nano-titanium dioxide sol of nano particles is subjected to cross-flow filtration. The sol is first contacted with water to remove soluble salts, and then the cross-flow filtration is continued until the sol contains more than 30% by weight of coated TiO₂Nanoparticles (based on the total weight of the sol).

<b>Prophetic example B.</b>A sample of the concentrated aqueous nano-titanium dioxide sol prepared in Prophetic Example A was made into a light-shielding composition containing the following components:

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The subject matter disclosed above should be regarded as illustrative rather than restrictive, and the scope of the attached patent application is intended to cover all such modifications, improvements and other embodiments within the true scope of the present invention. Therefore, to the maximum extent permitted by law, the scope of the present invention will be determined by the broadest permissible interpretation of the scope of the following patent applications and their equivalent scope, and should not be limited or restricted by the above detailed description.