High-light-resistance titanium dioxide and preparation method thereof

Abstract

The invention discloses high-light-resistance titanium dioxide and a preparation method. The titanium dioxide comprises a titanium dioxide base material and a coating layer located on the surface of titanium dioxide, the film coating layer comprises an aluminum phosphate film layer doped with lanthanide elements and an aluminum oxide film layer from inside to outside; the aluminum oxide film layer is obtained by adopting an organic aluminum source for coating and then calcining to remove an organic ligand. The lanthanide-doped aluminum phosphate film layer is coated on the surface of the titanium dioxide, and the organic aluminum source is adopted for aluminum oxide coating, so that the existence of bound water can be reduced, the stability of the coating layer is improved, the photocatalytic activity of the titanium dioxide is effectively inhibited, and the light resistance of the titanium dioxide is further remarkably improved; the requirement on high light resistance of the titanium dioxide in the fields of papermaking and the like is met.

Description

Technical Field

[0001] This invention belongs to the field of titanium dioxide preparation technology, specifically relating to a high lightfast titanium dioxide and its preparation method. Background Technology

[0002] Titanium dioxide, a core white pigment in coatings and plastics, directly determines the lifespan and appearance stability of end products due to its lightfastness. However, currently, titanium dioxide is prone to yellowing and chalking in outdoor or long-term light exposure environments due to insufficient lightfastness. The core issue lies in the bound water remaining on the surface of titanium dioxide. This bound water (water molecules bound by surface hydroxyl groups through hydrogen bonds or chemical adsorption) is a key hidden danger leading to decreased lightfastness. Under ultraviolet light irradiation, the bound water will react with the titanium dioxide to create photo-generated holes (…). ) react to generate hydroxyl radicals ( These highly oxidizing free radicals accelerate the degradation of surrounding media (such as coating resins); simultaneously, the presence of bound water weakens the structural stability of surface coating layers (such as aluminum phosphate and alumina). Water permeates into the coating layer through hydrogen bonds, causing microcracks due to swelling or hydrolysis, exposing the titanium dioxide to ultraviolet light and further enhancing photocatalytic activity. This creates a vicious cycle of "bound water accumulation → coating failure → intensified photocatalysis," ultimately leading to a significant decrease in the lightfastness of titanium dioxide.

[0003] Existing single coating or simple modification methods are insufficient to completely resolve the chain reaction caused by bound water. Therefore, developing high-light-resistant titanium dioxide and its preparation method that can efficiently reduce bound water and enhance the stability of the coating layer has become the key to meeting the performance requirements of high-end coatings, outdoor building materials and other fields. Summary of the Invention

[0004] The purpose of this invention is to provide a high lightfast titanium dioxide and its preparation method to overcome the shortcomings of the prior art.

[0005] The objective of this invention is achieved through the following technical solution: A high-light-resistant titanium dioxide includes a titanium dioxide substrate and a coating layer on the surface of the titanium dioxide; the coating layer, from the inside to the outside, includes a lanthanide-doped aluminum phosphate film layer and an aluminum oxide film layer; The alumina film is obtained by coating with an organic aluminum source and then removing the organic ligands by calcination.

[0006] Preferably, the lanthanide-doped aluminum phosphate film is prepared by the following steps: Phosphoric acid source, lanthanide element source and inorganic aluminum source are added to titanium dioxide-based material slurry, and then aluminum phosphate is deposited by adjusting pH.

[0007] Preferably, the amount of the lanthanide-doped aluminum phosphate film coating, calculated as aluminum phosphate, is 2-5% of the mass of the titanium dioxide substrate; The doping amount of the lanthanide elements, calculated as lanthanide oxides, is 0.05~0.15% of the mass of the titanium dioxide substrate.

[0008] Preferably, the coating amount of the alumina film, calculated as alumina, is 3.0 to 5.0% of the mass of the titanium dioxide substrate.

[0009] This application also provides a method for preparing the high lightfastness titanium dioxide as described above, comprising the following steps: S1. Preparation of titanium dioxide-based material slurry; S2. Apply aluminum phosphate coating with lanthanide doping; S3. Perform organic aluminum source coating; S4. Calcination to remove organic ligands.

[0010] Preferably, step S2 further includes: Phosphoric acid source, lanthanide element source and inorganic aluminum source are added to the slurry, and then aluminum phosphate is deposited by adjusting the pH. The amount of phosphoric acid source added, calculated as P2O5, is 1.0~3.0% of the mass of the titanium dioxide substrate; The amount of lanthanide source added, calculated as lanthanide oxides, is 0.05~0.15% of the mass of the titanium dioxide substrate; The amount of the inorganic aluminum source added, calculated as Al2O3, is 0.7~2.3% of the mass of the titanium dioxide substrate; Preferably, the pH is adjusted to 5.0~6.0.

[0011] Preferably, step S3 further includes: Adjust the pH of the slurry to 3.0~5.0, then add an organic aluminum source and pH adjuster in parallel flow, maintaining the pH at 3.0~5.0 in parallel flow, and allow it to mature.

[0012] Preferably, the organoaluminum source is added in solution form, and the solvent is anhydrous ethanol; Preferably, the organoaluminum source is at least one selected from alkoxyaluminum and organocarboxylic acid aluminum.

[0013] Preferably, the step between step S3 and step S4 further includes: Adjust the pH of the slurry to 5.0-6.0, and then mature it.

[0014] Preferably, step S4 calcination adopts gradient calcination, first holding at 220~280℃ for 0.5~1.5h, then holding at 350~450℃ for 0.5~1.5h, and finally calcining at 550~650℃ for 1.5~2.5h; Preferably, vacuum drying is performed before calcination at a temperature of 60-80°C for 3-5 hours.

[0015] This application reduces the presence of bound water and improves the stability of the coating layer by coating the surface of titanium dioxide with a lanthanide-doped aluminum phosphate film and using an organic aluminum source for alumina coating. This effectively inhibits the photocatalytic activity of titanium dioxide and significantly improves the lightfastness of titanium dioxide, meeting the high lightfastness requirements of titanium dioxide in papermaking and other fields. Detailed Implementation

[0016] This application provides a high lightfast titanium dioxide, comprising a titanium dioxide substrate and a coating layer on the surface of the titanium dioxide; the coating layer, from the inside to the outside, includes a lanthanide-doped aluminum phosphate film layer and an aluminum oxide film layer; The alumina film is obtained by coating with an organic aluminum source and then removing the organic ligands by calcination.

[0017] This invention first coats the surface of titanium dioxide with a lanthanide-doped aluminum phosphate film. Lanthanide ions have abundant redox potentials and 4f orbital energy levels, which can act as "electron traps." Taking lanthanide ions as an example, the photogenerated electrons generated by titanium dioxide ( ) can be Capture and Restored to Light-generating holes (h) + )quilt The neutralization of lone pairs of electrons directly blocks the recombination of electron-hole pairs (recombination is the core driving force for oxidation reactions); compared to aluminum phosphate alone (which has almost no carrier trapping ability), lanthanide doping can reduce the carrier recombination rate, thus inhibiting photocatalytic activity at the source. Lanthanide ions (ionic radius 0.08~0.11nm) and phosphate ions ( The coordination ability of ) is stronger than It can fill the lattice defects of aluminum phosphate film, forming a denser "lanthanum-aluminum-phosphorus" three-dimensional network structure (La-OP bonds and Al-OP bonds intertwined), reducing cracks in the film caused by light / humidity; improving the temperature resistance and hydrolysis resistance of the film, and increasing the integrity retention rate of the film by more than 40% under long-term light exposure.

[0018] The outermost layer uses an organoaluminum source (such as aluminum isopropoxide or aluminum sec-butoxide) to deposit an alumina film. The alumina precursor generated by the organoaluminum source deposition (such as amorphous aluminum hydroxide) reacts with the hydroxyl groups on the surface of titanium dioxide. ) can be achieved through condensation reaction ( The formation of covalent bonds results in a tighter interfacial bond, reducing water molecules adsorbed at the interface due to weak interactions (such as van der Waals forces). This allows for the formation of a continuous, non-porous, and dense film on the titanium dioxide surface. This dense film not only has fewer pores but also covers the hydroxyl sites on the titanium dioxide surface, further reducing the chance of water binding to the titanium dioxide. The hydrolysis reaction of organoaluminum salts is more thorough, and during subsequent calcination, the slow volatilization of organic ligands provides a "spatial buffer" for the orderly arrangement of alumina particles. The crystallization process occurs through van der Waals forces and chemical bonds between particles. This achieves "close packing," significantly reducing the pores formed by the volatilization of organic ligands, and producing alumina ( The residual hydroxyl groups in ) The amount of hydroxyl content is significantly lower than that of inorganic aluminum source coating products. The resulting alumina film has the characteristics of low hydroxyl content and more stable bonding with the titanium dioxide surface, thereby reducing the bound water adsorbed on the film and titanium dioxide surface (i.e., water molecules that are bound to titanium dioxide / alumina through hydrogen bonds or coordination bonds), thus improving lightfastness.

[0019] Therefore, this application reduces the presence of bound water, improves the stability of the coating layer, effectively inhibits the photocatalytic activity of titanium dioxide, and significantly improves the lightfastness of titanium dioxide by coating the surface of titanium dioxide with a lanthanide-doped aluminum phosphate film and using an organic aluminum source for alumina coating. This meets the high lightfastness requirements of titanium dioxide in papermaking and other fields.

[0020] As those skilled in the art will understand, each film layer requires a certain amount of coating to achieve complete coverage of the titanium dioxide surface and to exert its due function. At the same time, the coating amount cannot be too large. Preferably, the coating amount of the lanthanide-doped aluminum phosphate film, calculated as aluminum phosphate, is 2-5% of the mass of the titanium dioxide substrate; the doping amount of the lanthanides, calculated as lanthanide oxides, is 0.05-0.15% of the mass of the titanium dioxide substrate. The coating amount of the alumina film, calculated as alumina, is 3.0-5.0% of the mass of the titanium dioxide substrate.

[0021] Preferably, the lanthanide-doped aluminum phosphate film is obtained by wet coating, which can improve coating uniformity and stability compared to other coating methods (such as dry coating).

[0022] Furthermore, the lanthanide-doped aluminum phosphate film is prepared through the following steps: Phosphoric acid source, lanthanide element source and inorganic aluminum source are added simultaneously to titanium dioxide-based material slurry, and then aluminum phosphate is deposited by adjusting the pH.

[0023] Another aspect of this application provides a method for preparing the high lightfastness titanium dioxide as described above, comprising the following steps: S1. Preparation of titanium dioxide-based material slurry; S2. Apply aluminum phosphate coating with lanthanide doping; S3. Add an organic aluminum source to the slurry and allow it to mature; S4. Calcination to remove organic ligands.

[0024] As those skilled in the art will understand, using a certain high temperature for coating can improve the coating effect. Preferably, the coating temperature in steps S2 and S3 is 70~90℃.

[0025] The calcination temperature and time should be such that the organic ligands are decomposed and completely removed, but not too high to avoid over-burning the titanium dioxide. Preferably, gradient calcination is used to allow the organic ligands to volatilize slowly, avoiding excessively rapid volatilization that could affect the film density. Specifically, the film is first held at 220~280℃ for 0.5~1.5h, then at 350~450℃ for 0.5~1.5h, and finally calcined at 550~650℃ for 1.5~2.5h.

[0026] More preferably, the process includes a vacuum drying step before calcination. More preferably, the drying temperature is 60-80°C, and the drying time is 3-5 hours. If the titanium dioxide is calcined directly without vacuum drying, the rapid temperature increase can easily lead to cracking of the aluminum hydroxide film, thus affecting the uniformity and density of the alumina film after calcination.

[0027] Titanium dioxide substrates can be produced using either the chlorination or sulfuric acid process. The preferred slurry concentration for titanium dioxide-based materials is 300-350 g / L, as this concentration provides good slurry dispersibility and is suitable for coating.

[0028] Preferably, step S2 further includes: Simultaneously, a phosphoric acid source, a lanthanide element source, and an inorganic aluminum source are added, and then aluminum phosphate is deposited by adjusting the pH. As those skilled in the art will understand, this pH is the pH that allows aluminum phosphate to precipitate, preferably 5.0 to 6.0. After adjustment, the mixture is aged for 40 to 80 minutes to ensure complete precipitation of aluminum phosphate.

[0029] The preferred addition time for the phosphoric acid source, lanthanide element source, and inorganic aluminum source is 40-60 min, followed by aging for 20-40 min to ensure thorough mixing of the raw materials.

[0030] The amount of phosphoric acid source added, calculated as P2O5, is 1.0~3.0% of the mass of the titanium dioxide substrate; the amount of lanthanide source added, calculated as oxides of lanthanides, is 0.05~0.15% of the mass of the titanium dioxide substrate; and the amount of inorganic aluminum source added, calculated as Al2O3, is 0.7~2.3% of the mass of the titanium dioxide substrate.

[0031] Phosphoric acid source, lanthanide element source, inorganic aluminum source, and organoaluminum source are preferably added in solution form and can be uniformly added to the slurry. The solution concentration, based on their respective oxides, is 100~150 g / L. Water is used as the solvent for the phosphoric acid source, lanthanide element source, and inorganic aluminum source, while anhydrous ethanol or other solvents capable of dissolving the organoaluminum source are used as the solvent.

[0032] Preferably, step S3 further includes: The pH of the slurry is adjusted to 3.0~5.0, and then an organic aluminum source and pH adjuster are added in parallel to maintain the pH at 3.0~5.0. Under this pH condition, the organic aluminum salt (such as aluminum isopropoxide) undergoes controlled hydrolysis. The generated aluminum hydroxyl species form an amorphous aluminum hydroxide film on the surface of titanium dioxide through ordered adsorption and chemical bonding (Al-O-Ti). This film has the characteristics of dense structure and strong adhesion, which can effectively isolate the titanium dioxide matrix from external environmental erosion.

[0033] More preferably, the pH adjustment time is 20-40 min, followed by maturation for 20-60 min to stabilize the slurry pH, and then the organoaluminum source and pH adjuster are added in parallel. The preferred time for the parallel addition of the organoaluminum source and pH adjuster is 60-120 min, followed by maturation for 20-40 min.

[0034] Preferably, the amount of organic aluminum source added, calculated as Al2O3, is 3 to 5% of the mass of the titanium dioxide substrate.

[0035] Preferably, the phosphoric acid source can be phosphoric acid, sodium dihydrogen phosphate, sodium hexametaphosphate, etc., the lanthanide element source can be nitrates or sulfates of lanthanum, cerium, praseodymium, neodymium, etc., and the inorganic aluminum source can be aluminum sulfate, aluminum chloride, aluminum nitrate, etc.

[0036] Preferably, the organoaluminum source is at least one selected from alkoxyaluminum and organocarboxylic acid aluminum. Alkoxyaluminum can be aluminum isopropoxide, aluminum sec-butoxide, and aluminum triethanolamine, etc., while organocarboxylic acid aluminum can be aluminum acetate, aluminum stearate, etc.

[0037] Preferably, to facilitate washing and adapt to downstream product requirements, the step between step S3 and step S4 further includes: Adjust the pH of the slurry to 5.0-6.0, and then mature it for 1-3 hours.

[0038] Preferably, as those skilled in the art will understand, the process before calcination generally includes steps of pressing and filtering the slurry, washing it with water, and flash drying it to remove inorganic salts adhering to the surface of the titanium dioxide. The process after calcination generally includes a powdering step, where the coated titanium dioxide is micronized to obtain the finished titanium dioxide product.

[0039] Example 1 Pour the slurry with the qualified particle size from the sand mill into a coating tank, controlling the slurry concentration at 300 g / L (calculated as TiO2), and simultaneously raise the temperature to 70℃; within 40 min, add a mixed solution of 1.44% aluminum sulfate (calculated as alumina), 2.0% phosphoric acid (calculated as phosphorus pentoxide), and 0.05% lanthanum nitrate (calculated as lanthanum oxide) based on the mass of the titanium dioxide substrate, and mature for 30 min; within 60 min, adjust the pH of the slurry to 5.0 with dilute NaOH solution, and mature for another 60 min; adjust with dilute H2SO4 solution... The slurry pH was adjusted to 3.0 over 30 minutes, followed by maturation for 30 minutes. Within 120 minutes, an ethanol solution of aluminum isopropoxide (3.0% by mass of the titanium dioxide substrate) and an H2SO4 solution were slowly added in parallel flow, maintaining the pH at 3.0, and then maturated for another 30 minutes. Within 60 minutes, the pH was adjusted to 5.0 with dilute NaOH, followed by maturation for another 120 minutes. The slurry was then filtered, washed with water, vacuum dried at 70℃ for 4 hours, held at 250℃ for 1 hour, 400℃ for 1 hour, and 600℃ for 2 hours. After steam drying, the product was obtained.

[0040] Example 2 Pour the slurry with the qualified particle size from the sand mill into a coating tank, controlling the slurry concentration at 300 g / L (based on TiO2), and simultaneously raise the temperature to 80℃. Within 40 minutes, add a mixed solution of 1.44% aluminum sulfate, 2.0% phosphoric acid, and 0.05% lanthanum nitrate (based on the mass of the titanium dioxide substrate), and allow it to mature for 30 minutes. Within 60 minutes, adjust the pH of the slurry to 5.0 with dilute NaOH solution and allow it to mature for another 60 minutes. Finally, adjust the pH of the slurry to 4.0 with dilute H2SO4 solution and allow it to mature for 30 minutes. After adjusting the pH, let it mature for 30 minutes. Then, slowly add an ethanol solution of aluminum sec-butoxide (3.0% by mass of the titanium dioxide substrate) and an H2SO4 solution in parallel flow over 120 minutes, controlling the pH at 4.0. Let it mature for another 30 minutes. Adjust the pH to 6.0 with dilute NaOH over 60 minutes, then mature for another 120 minutes. After pressure filtration, washing with water, vacuum drying at 70℃ for 4 hours, holding at 250℃ for 1 hour, 400℃ for 1 hour, and 600℃ for 2 hours, then pulverize to obtain the product.

[0041] Example 3 Pour the slurry with the qualified particle size from the sand mill into a coating tank, controlling the slurry concentration at 300 g / L (based on TiO2), and simultaneously raise the temperature to 90℃. Within 40 minutes, add a mixed solution of aluminum sulfate (2.15% by mass of the titanium dioxide substrate), phosphoric acid (3.0%), and lanthanum nitrate (0.1%), and allow it to mature for 30 minutes. Within 60 minutes, adjust the pH of the slurry to 5.0 with dilute NaOH solution and allow it to mature for another 60 minutes. Finally, adjust the pH of the slurry to 3.0 with dilute H2SO4 solution. After adjusting the pH for 30 minutes, the product was cured for 30 minutes. Within 120 minutes, an ethanol solution of aluminum isopropoxide (4.0% by mass of titanium dioxide substrate) and an H2SO4 solution were slowly added in parallel flow, controlling the pH at 3.0. The product was then cured for another 30 minutes. Within 60 minutes, the pH was adjusted to 5.0 with dilute NaOH. The product was then cured for another 120 minutes. The product was then filtered, washed with water, vacuum dried at 70℃ for 4 hours, kept at 250℃ for 1 hour, 400℃ for 1 hour, and 600℃ for 2 hours. After drying, the product was obtained.

[0042] Example 4 Pour the slurry with qualified particle size from the sand mill into a coating tank, controlling the slurry concentration at 300 g / L (based on TiO2), and simultaneously raise the temperature to 90℃. Within 40 minutes, add a mixed solution of 2.15% aluminum sulfate, 3.0% phosphoric acid, and 0.15% lanthanum nitrate (based on the mass of the titanium dioxide substrate). Within 60 minutes, adjust the pH of the slurry to 5.0 with dilute NaOH solution and allow it to mature for 60 minutes. Finally, adjust the pH of the slurry to 3.0 with dilute H2SO4 solution and allow it to mature for 30 minutes. After completion, it was cured for 30 minutes; within 120 minutes, an ethanol solution of aluminum isopropoxide (5.0% by mass of titanium dioxide substrate) and H2SO4 solution were slowly added in parallel flow, controlling the pH of the parallel flow to 3.0, and then cured for 30 minutes; within 60 minutes, the pH was adjusted to 5.0 with dilute NaOH, and then cured for 120 minutes; after pressure filtration and washing with water, vacuum drying at 70℃ for 4 hours, it was kept at 250℃ for 1 hour, 400℃ for 1 hour, and 600℃ for 2 hours, and then the product was obtained after steaming.

[0043] Comparative Example 1 (aluminum phosphate coating and alumina coating using an inorganic aluminum source) Pour the slurry with qualified particle size from the sand mill into a coating tank, control the slurry concentration at 300 g / L (based on TiO2), and simultaneously raise the temperature to 90℃; adjust the pH of the slurry to 5.0 within 20 min, and mature for 30 min; within 60 min, simultaneously add 3.0% H3PO4 solution and NaAlO2 solution (based on the mass of the titanium dioxide substrate), maintaining a co-current pH of 5.0. The amount of NaAlO2 solution added should be adjusted to maintain the co-current pH, and mature for 30 min; within 20 min, use dilute NaO... The pH of the slurry was adjusted to 8.0 with H2SO4 solution and aged for 30 min. NaAlO2 solution and dilute Al2(SO4)3 solution were added within 120 min, maintaining a parallel flow pH of 8.0. The total amount of NaAlO2 solution and dilute Al2(SO4)3 added was 4% of the mass of the titanium dioxide substrate, based on alumina. The slurry was then aged for 30 min. The pH was adjusted to 5.0 with dilute H2SO4 for 60 min, and the slurry was aged for 120 min. The slurry was then filtered, washed with water, flash-evaporated, and steam-powdered to obtain the product.

[0044] Comparative Example 2 (Titanium phosphate, aluminum phosphate coating, and alumina coating using an inorganic aluminum source) Pour the slurry with the qualified particle size from the sand mill into a coating tank, control the slurry concentration at 300 g / L (based on TiO2), and simultaneously raise the temperature to 90℃; add 0.5% TiOCl2 (based on TiO2) by mass of the titanium dioxide substrate within 40 min, and simultaneously add 0.6% Na4P2O7 solution by mass of the titanium dioxide substrate, and mature for 60 min; adjust the pH of the slurry to 5.0 with dilute NaOH solution, adjust for 30 min, and mature for 30 min; add 3% H2O solution by mass of the titanium dioxide substrate within 60 min. The slurry was prepared by mixing 3PO4 solution and NaAlO2 solution, maintaining a co-current pH of 5.0, with the amount of NaAlO2 solution added to maintain the co-current pH, and then maturing for 30 min. The pH of the slurry was then adjusted to 8.0 with dilute NaOH solution for 30 min, followed by maturing for another 30 min. Within 120 min, NaAlO2 solution and dilute Al2(SO4)3 solution were added, maintaining a co-current pH of 8.0, with the total amount of NaAlO2 solution and dilute Al2(SO4)3 added being 4% of the mass of the titanium dioxide substrate (calculated as alumina), and maturing for another 30 min. The pH was then adjusted to 5.5 with dilute H2SO4 for 60 min, and maturing for another 120 min. The product was obtained by washing with water, flash evaporation, and steam condensation.

[0045] Comparative Example 3 (Lanthanum-doped aluminum phosphate coating and aluminum oxide coating using an inorganic aluminum source) The slurry with qualified particle size from sand milling is poured into a coating tank, and the slurry concentration is controlled at 300 g / L (calculated as TiO2). At the same time, the temperature is raised to 90℃. Within 40 min, a mixed solution of aluminum sulfate (2.15%), phosphoric acid (3.0%), and lanthanum nitrate (0.1%) is added, accounting for 2.15% of the mass of the titanium dioxide substrate. Within 60 min, the pH of the slurry is adjusted to 5.0 with dilute NaOH solution, and the slurry is matured for 60 min. Within 20 min, the pH of the slurry is adjusted to 8.0 with dilute NaOH solution, and the slurry is matured for 30 min. Within 120 min, NaAlO2 solution and dilute Al2(SO4)3 solution are added, maintaining a parallel flow pH of 8.0. The total amount of NaAlO2 solution and dilute Al2(SO4)3 added is 4% of the mass of the titanium dioxide substrate, calculated as alumina, and the slurry is matured for 30 min. Within 60 min, the pH is adjusted to 5.0 with dilute H2SO4, and the slurry is matured for 120 min. After washing with water, flash evaporation, and steam pulverization, the product is obtained.

[0046] Comparative Example 4 (aluminum phosphate coating and alumina coating using an organic aluminum source) Pour the slurry with qualified particle size from the sand mill into a coating tank, controlling the slurry concentration at 300 g / L (based on TiO2), and simultaneously raise the temperature to 90℃; adjust the pH of the slurry to 5.0 with dilute NaOH solution for 30 min, and then mature for 30 min; within 60 min, add 3% H3PO4 solution and NaAlO2 solution (based on the mass of the titanium dioxide substrate), maintaining a co-current pH of 5.0. The amount of NaAlO2 solution added should be adjusted to maintain the co-current pH, and then mature for 30 min; adjust with dilute H2SO4 solution... The slurry pH was adjusted to 3.0 over 30 minutes, followed by maturation for 30 minutes. Within 120 minutes, an ethanol solution containing 4.0% aluminum isopropoxide (by mass of the titanium dioxide substrate) and an H2SO4 solution were slowly added in parallel flow, maintaining the pH at 3.0, and then maturated for another 30 minutes. Within 60 minutes, the pH was adjusted to 5.0 with dilute NaOH, followed by maturation for another 120 minutes. The slurry was then filtered, washed with water, vacuum dried at 70℃ for 4 hours, held at 250℃ for 1 hour, 400℃ for 1 hour, and 600℃ for 2 hours, and then pulverized to obtain the final product.

[0047] The samples obtained in Examples 1-3 and Comparative Examples 1-4 were subjected to moisture content and lightfastness testing using conventional methods in the art. The moisture content testing method is as follows: Test the moisture content of the sample; ② Take a crucible, wash and dry it until constant weight, and record the weight G1; ③ Weigh about 10 grams of titanium dioxide (weight G2), place it in a crucible and put it in a muffle furnace at 950~1000℃. After calcining for 4 hours, take it out, put it in a desiccator to cool and keep it at constant weight, and record the weight G3.

[0048] The calculation method is as follows:

[0049] The lightfastness testing method is as follows: 1. Pulping: Weigh 33g of pulp, tear it into small pieces, and put it into a fiber separator. Add 2L of water and use a standard fiber separator at 40,000 rpm to decompose the pulp. After decomposition, pour the pulp into a filter screen to remove the water, put it into a 2L measuring cup and weigh it to 300g. Stir well and put it into a refiner. Spread the pulp as evenly as possible on the wall of the refiner. Then refine the pulp at 7,000 rpm. After refining, remove the pulp and set it aside for later use. 2. Dispersion of pulp and titanium dioxide: Take 30g of titanium dioxide sample and 260g of pulp, add about 2L of water, and dissociate them using a standard fiber dissociator at 40,000 rpm; 3. Volume adjustment: Transfer the pulp from the standard fiber dissociator to a 5L bucket, adjust the volume to 3000g, stir at 700rpm on a stirrer, add 1g of wet strength agent, adjust the pH to 7.0, stir for 10min, and take 170g of paper for each batch. 4. Impregnation and pressing; 5. Place the pressed cardboard in a xenon lamp aging chamber and expose it for 120 hours. Measure the L, a, and b values ​​before and after exposure, and calculate the color difference, which is the lightfastness ΔE.

[0050] The results are shown in Tables 1 and 2:

[0051] Table 1 Results of Loss on Ignition

[0052] Table 2 Results of lightfastness test

[0053]

[0054] As can be seen from the above data, the titanium dioxide prepared in the embodiments of the present invention has a significantly lower bound water content than the comparative example, and its lightfastness in papermaking is better than that of the comparative example.

[0055] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A high-light-fastness titanium dioxide, characterized in that, It includes a titanium dioxide substrate and a coating layer on the surface of the titanium dioxide; the coating layer, from the inside to the outside, includes a lanthanide-doped aluminum phosphate film layer and an aluminum oxide film layer; The alumina film is obtained by coating with an organic aluminum source and then removing the organic ligands by calcination.

2. The high lightfastness titanium dioxide as described in claim 1, characterized in that, The lanthanide-doped aluminum phosphate film is prepared by the following steps: Phosphoric acid source, lanthanide element source and inorganic aluminum source are added to titanium dioxide-based material slurry, and then aluminum phosphate is deposited by adjusting pH.

3. The high lightfastness titanium dioxide as described in claim 1, characterized in that, The amount of the lanthanide-doped aluminum phosphate film coating, calculated as aluminum phosphate, is 2-5% of the mass of the titanium dioxide substrate. The doping amount of the lanthanide elements, calculated as lanthanide oxides, is 0.05~0.15% of the mass of the titanium dioxide substrate.

4. The high lightfastness titanium dioxide as described in claim 1, characterized in that, The coating amount of the alumina film, calculated as alumina, is 3.0 to 5.0% of the mass of the titanium dioxide substrate.

5. A method for preparing high-light-fastness titanium dioxide as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Preparation of titanium dioxide-based material slurry; S2. Apply aluminum phosphate coating with lanthanide doping; S3. Perform organic aluminum source coating; S4. Calcination to remove organic ligands.

6. The method for preparing high-light-resistant titanium dioxide as described in claim 5, characterized in that, Step S2 further includes: Phosphoric acid source, lanthanide element source and inorganic aluminum source are added to the slurry, and then aluminum phosphate is deposited by adjusting the pH. The amount of phosphoric acid source added, calculated as P2O5, is 1.0~3.0% of the mass of the titanium dioxide substrate; The amount of lanthanide source added, calculated as lanthanide oxides, is 0.05~0.15% of the mass of the titanium dioxide substrate; The amount of the inorganic aluminum source added, calculated as Al2O3, is 0.7~2.3% of the mass of the titanium dioxide substrate; Preferably, the pH is adjusted to 5.0~6.

0.

7. The method for preparing high-light-resistant titanium dioxide as described in claim 5, characterized in that, Step S3 further includes: Adjust the pH of the slurry to 3.0~5.0, then add an organic aluminum source and pH adjuster in parallel flow, maintaining the pH at 3.0~5.0 in parallel flow, and allow it to mature.

8. The method for preparing high-light-resistant titanium dioxide as described in claim 7, characterized in that, The organoaluminum source is at least one selected from alkoxyaluminum and organocarboxylic acid aluminum.

9. The method for preparing high-light-resistant titanium dioxide as described in claim 5, characterized in that, The interval between steps S3 and S4 also includes: Adjust the pH of the slurry to 5.0-6.0, and then mature it.

10. The method for preparing high-light-resistant titanium dioxide as described in claim 5, characterized in that, The calcination in step S4 is a gradient calcination, first held at 220~280℃ for 0.5~1.5h, then held at 350~450℃ for 0.5~1.5h, and finally held at 550~650℃ for 1.5~2.5h. Preferably, vacuum drying is performed before calcination at a temperature of 60-80°C for 3-5 hours.

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