Ultra-pure titanium dioxide and its preparation method and application

Abstract

This application provides an ultrapure titanium dioxide, its preparation method, and its application. The method includes the following steps: S1: Dissolving an inorganic titanium source and a composite weakly polydentate dynamic coordination molecule in an inert organic solvent to obtain a composite precursor solution; wherein the composite weakly polydentate dynamic coordination molecule contains two or more reversible coordination functional groups; S2: Adding water to the composite precursor solution to form a titanium-oxygen network precursor; S3: Performing solvothermal treatment on the titanium-oxygen network precursor to induce crystallization, obtaining a crystallization intermediate; S4: Performing a two-stage heat treatment on the crystallization intermediate to obtain ultrapure titanium dioxide. Through the above method, titanium dioxide materials with both ultra-high purity and strong photocatalytic activity can be prepared without relying on external ion doping or unstable post-reduction treatment.

Description

Technical Field

[0001] This application relates to the field of titanium dioxide technology, specifically to an ultrapure titanium dioxide, its preparation method, and its application. Background Technology

[0002] Titanium dioxide (TiO2), as a semiconductor material with a wide bandgap, is widely used in high-end self-cleaning optical components (such as photovoltaic module covers and optical lenses) due to its good chemical stability, excellent photoresponse characteristics, low cost, and environmental friendliness. These applications place dual demands on the material: on the one hand, it needs to possess highly efficient photocatalytic self-cleaning capabilities to achieve in-situ decomposition of surface organic contaminants; on the other hand, it must maintain extremely high optical transmittance. The introduction of any external impurities can increase light scattering and absorption, leading to decreased transparency and directly affecting device performance. These dual demands from these applications point to a common technical challenge: how to effectively improve the photocatalytic activity of titanium dioxide without introducing external impurities.

[0003] In existing technologies, the main approaches to improving the photocatalytic performance of titanium dioxide fall into two categories: one is through exogenous ion doping (such as metal ions Fe). 3+ Non-metallic ions N 3- One approach is to modify the band structure of the material to broaden its light absorption range; another is to introduce reduced-state sites on the material surface through post-treatment with strong reduction (such as high-temperature H2 treatment or plasma treatment) to improve charge separation. However, these methods all have obvious limitations: ion doping introduces modified elements but also introduces exogenous impurities. These impurity atoms may become new charge recombination centers, thus offsetting some of the gain effect and even impairing the chemical stability of the material under harsh environments; while post-reduction treatment can improve light absorption, the active sites introduced are mostly concentrated on the material surface, which are prone to deactivation in subsequent oxidation environments or long-term use, leading to catalytic performance degradation and insufficient stability.

[0004] In addition, some wet chemical synthesis methods (such as the sol-gel method) attempt to control the precursor hydrolysis process by adding organic ligands to optimize the material structure. However, commonly used strong chelating ligands often bind too firmly to titanium ions, which may not only cause compositional inhomogeneity in the precursor stage, but may also completely decompose during the subsequent high-temperature crystallization process. They cannot play a continuous regulatory role in the critical stage of crystal growth, and therefore it is difficult to achieve a precise and stable improvement in the final photocatalytic performance of the material.

[0005] Therefore, there is an urgent need in this field for an innovative synthesis strategy that can obtain titanium dioxide with both high purity and photocatalytic performance without relying on external impurity doping or introducing unstable surface states, in order to meet the growing demand for high-end photochemical applications. Summary of the Invention

[0006] This application provides an ultrapure titanium dioxide and its preparation method, aiming to regulate the coordination environment, hydrolysis process and crystal growth path of titanium ions by introducing composite weakly multidentate dynamic coordination molecules. In this way, titanium dioxide materials with both ultra-high purity and strong photocatalytic activity can be prepared without relying on external ion doping or unstable post-reduction treatment, so as to solve the contradiction between the difficulty of synergistically optimizing material purity and photocatalytic performance in the existing technology.

[0007] In a first aspect, this application provides a method for preparing ultrapure titanium dioxide, comprising the following steps: S1: Dissolve the inorganic titanium source and the composite weakly multidentate dynamic coordination molecule in an inert organic solvent to obtain a composite precursor solution; The composite weakly polydentate dynamic coordination molecule contains two or more reversible coordination functional groups, and the inert organic solvent includes at least one of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, or ether solvents. S2: Water is added to the composite precursor solution, and hydrolysis and condensation reactions are carried out through the competitive occupation of titanium ion coordination sites by water molecules to form a titanium-oxygen network precursor. S3: The titanium-oxygen network precursor is subjected to solvothermal treatment to crystallize it, and under the action of the composite weakly multidentate dynamic coordination molecules, intrinsic defects are formed in situ during the crystallization process to obtain a crystallization intermediate. S4: The crystallization intermediate is subjected to a first-stage heat treatment at 200~400℃ in a weakly reducing atmosphere and a second-stage heat treatment at 450~600℃ in an oxidizing atmosphere to remove organic residues and stabilize the crystal structure, thereby obtaining ultrapure titanium dioxide.

[0008] According to this application, the ultrapure titanium dioxide, by introducing composite weakly multidentate dynamic coordination molecules under an ultra-low impurity background, regulates the formation path of the titanium-oxygen network, causing intrinsic defects to be induced in situ in titanium dioxide during the process. This achieves synergistic regulation of high purity and defect structure simultaneously without introducing exogenous metal doping or relying on strong reduction treatment. This method, through the multiple synergistic effects of "dynamic coordination - restricted hydrolysis - crystallization path perturbation - stepwise heat treatment," changes the traditional technical path of titanium dioxide photocatalytic performance, which mainly depends on impurities or post-treatment introduction.

[0009] In step S1, the inorganic titanium source and the composite weakly multidentate dynamic coordination molecule are dissolved in an inert organic solvent to form a homogeneous and stable composite precursor solution. The coordination molecule contains two or more reversible coordination functional groups, and its interaction with titanium ions is moderate and reversible. In this step, the coordination molecule, through partial and temporary occupation of the coordination sites of titanium ions, acts as a "molecular template," effectively inhibiting the spontaneous and violent hydrolysis of the titanium source while maintaining the reactivity of the system. This constructs a homogeneous reaction starting point in a kinetically controllable state, laying the foundation for the regulation of subsequent steps.

[0010] In step S2, water is introduced into the composite precursor solution to initiate the hydrolysis and condensation reaction of the titanium source, forming a titanium-oxygen network precursor. Because the coordination interaction between the composite weakly polydentate dynamic coordination molecules and titanium ions is reversible, when water molecules enter the system, they competitively occupy the coordination sites of titanium ions, causing some weakly coordinating functional groups to reversibly dissociate, thereby exposing reactive titanium active sites. Guided by this competitive coordination mechanism, the hydrolysis reaction of the titanium source can occur gradually under localized and restricted conditions, reducing the disordered condensation and structural defect concentration caused by excessively rapid hydrolysis in traditional sol-gel systems. Simultaneously, the undissociated weakly coordinating molecules can still temporarily stabilize the unreacted titanium sites, allowing the entire hydrolysis and condensation process to exhibit a gradual and controllable characteristic, thus forming a uniformly structured titanium-oxygen network precursor.

[0011] In step S3, the titanium-oxygen network precursor is subjected to solvothermal treatment to induce crystallization. Under solvothermal conditions, the titanium-oxygen network begins to transform from an amorphous structure to crystalline titanium dioxide. During conventional crystallization, titanium ions tend to form a perfect six-coordinate [TiO6] octahedral structure, with an idealized lattice arrangement. While this perfection is beneficial for improving crystal quality, it results in a lack of tunable active sites, requiring subsequent external doping or strong reduction treatment to introduce defects. However, in this application, the composite weakly multidentate dynamic coordination molecule, due to its reversible coordination characteristics, can still repeatedly coordinate and dissociate with titanium ions in local regions during the crystallization stage. This dynamic coordination behavior is not an occasional local disturbance, but occurs continuously and synchronously throughout the entire titanium-oxygen network transformation process, generating uniform and continuous micro-perturbations on the formation sequence and connection mode of Ti-O-Ti bonds. This "dynamic perturbation" causes some lattice units to deviate more from the perfect [TiO6] octahedral configuration during rearrangement, thereby uniformly introducing localized crystal structure defects within the lattice. These structural features do not directly constitute photocatalytic active centers, but rather are pre-implanted into the lattice as a "structural basis" in a bulk-uniform distribution. Since these defects are formed naturally during crystal growth, rather than being artificially introduced through later reduction or doping, they do not depend on the presence of exogenous impurities.

[0012] In step S4, a stepwise thermal treatment strategy of weak reduction followed by oxidation is adopted. The first stage is carried out under a mild reducing atmosphere, which interacts with the local crystal structure defects formed in step S3, inducing the formation of defect structures that are beneficial to improving photocatalytic performance, while removing most of the organic components and initially consolidating the crystal framework of the material. Subsequently, the process is switched to an oxidizing atmosphere for a second stage treatment at a higher temperature to thoroughly remove residual carbon and ensure the ultra-high chemical purity of the product. This stepwise strategy achieves purification while uniformly constructing defect structures in the bulk titanium dioxide phase, ultimately yielding a titanium dioxide material with both high purity and photocatalytic performance.

[0013] By employing composite weakly multidentate dynamic coordination molecules, a restricted hydrolysis process, solvothermal crystallization, and stepwise heat treatment, this application achieves the regulation of the titanium dioxide lattice formation path under ultra-low impurity conditions, thereby enhancing the photocatalytic performance of titanium dioxide.

[0014] In some embodiments, the composite weakly polydentate dynamic coordination molecule includes an organic molecule containing an amide group and a phenolic hydroxyl group, a carbonyl group and an ether oxygen group, or a combination of an amide group and an ether oxygen group.

[0015] In some of the above embodiments, when organic molecules containing amide groups and phenolic hydroxyl groups, carbonyl groups and ether oxygen groups, or combinations of amide groups and ether oxygen groups are selected as composite weakly polydentate dynamic coordination molecules, the resulting ultrapure titanium dioxide exhibits better photocatalytic performance. This may be because these functional group combinations construct an ideal coordination environment that is "polydentate but with reversible and moderate strength," thereby regulating the entire formation path of titanium dioxide from molecular precursor to crystal. On one hand, these combined coordination molecules possess two or more potential coordination sites (i.e., "polydentate"), enabling them to interact with titanium ions from multiple directions. Even if some coordination sites undergo reversible dissociation, the molecule can still be held near the titanium ion or crystal surface through other coordination sites. This multi-point binding ability effectively disperses and stabilizes titanium ions in step S1, inhibiting their spontaneous aggregation and premature hydrolysis, providing a basis for forming a homogeneous and stable precursor solution.

[0016] On the other hand, and more importantly, the spatial arrangement of these functional groups makes it difficult for them to form rigid, stable chelate ring structures with the same titanium ion. Therefore, their binding force with the titanium ion remains moderate and reversible. This dynamic coordination characteristic plays a regulatory role throughout the synthesis process: in step S2, the reversibility of coordination creates conditions for the competitive intervention of water molecules, achieving "restricted hydrolysis," thereby forming a uniform titanium-oxygen network rich in potential reaction sites; during the solvothermal crystallization process in step S3, these molecules can continuously undergo reversible "binding-dissociation" at the crystal growth interface. This dynamic perturbation optimizes the crystal growth kinetics, guiding the formation of a crystal structure more conducive to the separation and transport of photogenerated charges, thus improving its macroscopic photocatalytic performance.

[0017] In some embodiments, the mass ratio of the composite weakly multidentate dynamic coordination molecule to the inorganic titanium source is (10~40):100.

[0018] In the above embodiments, the mass ratio of the composite weakly multidentate dynamic coordination molecule to the inorganic titanium source is controlled at (10~40):100. On the one hand, this allows the coordination molecule to form an effective "weakly constrained" network of titanium ions through sufficient reversible coordination functional groups, constructing a metastable precursor solution in step S1, laying the foundation for the entire controlled reaction, and reducing the violent hydrolysis and self-aggregation of the titanium source. On the other hand, if the ratio is too high, the ligand molecules will excessively occupy and shield the coordination and reaction sites of titanium ions, making it difficult for water molecules to effectively compete for coordination and hydrolysis in step S2, thus inhibiting the reactivity. This ratio allows the coordination molecule to be effectively competitively dissociated by water molecules in subsequent steps, while also retaining an appropriate amount of molecules to continuously exert dynamic perturbation during the solvothermal crystallization stage, thereby improving the photocatalytic performance of titanium dioxide crystals.

[0019] In some embodiments, step S1 includes: Under an inert atmosphere, 100 parts by mass of an inorganic titanium source and 10-40 parts by mass of a composite weakly multidentate dynamic coordination molecule are dispersed in 400-600 parts by mass of an inert organic solvent and stirred at 20-60°C for 0.5-4 hours to obtain a composite precursor solution.

[0020] In some of the above embodiments, the coordination environment and reactivity of titanium ions are regulated by controlling the mass ratio of the composite weakly multidentate dynamic coordination molecule to the inorganic titanium source to be (10~40):100. This ratio allows sufficient coordination functional groups to form an effective "weakly constrained" network for the titanium ions, inhibiting their spontaneous hydrolysis and aggregation, while avoiding excessive shielding of the active sites of titanium ions due to excessive ligand content, thus preventing inactivation. The amount of inert organic solvent is controlled at 400~600 parts by mass to construct a reaction system with a suitable concentration: this amount ensures sufficient dissolution and uniform dispersion of the reactants, preventing excessively high local concentrations that could lead to heterogeneous nucleation; it also maintains the necessary reactant concentration, providing favorable kinetic conditions for the "constrained hydrolysis" induced by water molecules in subsequent steps. These conditions collectively ensure that the precursor solution is in a metastable state of coordination saturation but controlled reactivity, thereby successfully constructing an initial coordination structure in which titanium ions are moderately "bound". This lays the foundation for the competitive intervention and controllable reaction of water molecules in the subsequent hydrolysis steps. On the other hand, the reversibility of the coordination bond also reserves space for the dynamic perturbation during crystal growth in step S3, which is the starting point for realizing photocatalytic properties.

[0021] In some embodiments, in step S2: 5-30 parts by weight of water are added to the composite precursor solution, and the mixture is stirred and reacted at 20-60°C for 2-12 hours to form a titanium-oxygen network precursor.

[0022] In some of the above embodiments, by controlling the amount of water added to 5-30 parts by mass, this range allows water molecules to act as competing ligands, sufficient to intervene in and partially replace the weak coordination bonds established in step S1, thereby initiating the reaction; at the same time, it reduces the violent, global, and uncontrollable hydrolysis caused by excessive water. Through these parameters, the hydrolysis reaction proceeds locally and in a controlled manner under the "weak constraint" of dynamically coordinated molecules, forming a uniform amorphous titanium-oxygen network precursor. This provides a uniform reaction basis for subsequent solvothermal crystallization, and its uniformity is also a structural prerequisite for ensuring subsequent photocatalytic performance.

[0023] In some embodiments, in step S3: the titanium-oxygen network precursor is subjected to solvothermal treatment at 120~220°C for 12~36 hours, and then naturally cooled to 20°C to obtain a crystallized intermediate.

[0024] In some of the above embodiments, by controlling the solvothermal treatment temperature at 120~220℃, sufficient thermodynamic driving force is obtained for the transformation of the amorphous network into crystalline titanium dioxide. Simultaneously, under this temperature condition, the composite weakly multidentate dynamically coordinated molecules from the precursor step do not completely decompose, allowing for continuous reversible coordination and dissociation behavior at the crystal growth interface, dynamically perturbing the Ti-O-Ti bond arrangement. Under these conditions, when crystal growth and dynamic perturbation occur simultaneously, a localized incomplete coordination structure is formed within the crystal lattice. Subsequent natural cooling to 20℃, compared to quenching, helps reduce internal stress that may be introduced by drastic temperature changes, thereby better maintaining the localized structural characteristics formed during the crystallization process. Through the synergy of the above process conditions, a structural basis conducive to the stable formation of intrinsic defects is pre-constructed in the crystallization intermediate, providing conditions for finally obtaining titanium dioxide materials with both high purity and photocatalytic performance.

[0025] In some embodiments, in step S4: the crystallization intermediate is heated to 200-400°C at a heating rate of 1-5°C / min under a weak reducing atmosphere with a flow rate of 50-200 mL / min, and held at that temperature for 1-4 hours. Subsequently, the atmosphere was switched to an oxidizing atmosphere, and the temperature was increased to 450-600°C at the same flow rate of 1-5°C / min, and held for 2-6 hours. After natural cooling, the ultrapure titanium dioxide was obtained.

[0026] In some of the above embodiments, a staged heat treatment strategy of "weak reduction followed by oxidation" is adopted, with precise control of the heating rate, treatment temperature, holding time, and gas flow rate, aiming to optimize the photocatalytic performance and stability of the final product. The first stage is carried out in a weak reducing atmosphere at 200-400°C. This treatment can interact with the locally incompletely coordinated structure formed in step S3, inducing the formation of defect structures that are beneficial to improving photocatalytic performance. The subsequent second stage switches to an oxidizing atmosphere at 450-600°C. The purpose is to use higher temperatures and sufficient oxygen to completely oxidize and remove the non-volatile carbonaceous impurities remaining from the first stage, thereby ensuring the ultra-high chemical purity of the material. The synergistic effect of these two stages ultimately achieves deep purification of the material while effectively constructing and stabilizing the defect structures, thus ensuring that the product possesses both high purity and photocatalytic performance.

[0027] In some embodiments, the inorganic titanium source includes at least one of tetraisopropyl titanate, tetraethyl titanate, or titanium tetrachloride. Based on the above embodiments, the reactivity of the selected titanium source can be effectively regulated by the composite weakly multidentate dynamic coordination molecule, which not only ensures the solution stability in step S1, but also provides a suitable starting reaction point for the controllable hydrolysis and condensation initiated by water molecules in step S2.

[0028] In some embodiments, the inert organic solvent includes at least one of benzene, toluene, xylene, n-hexane, cyclohexane, tetrahydrofuran, or 1,4-dioxane; as an example, toluene is selected as the inert organic solvent in one embodiment of this application.

[0029] In some embodiments, the weakly reducing atmosphere is a nitrogen-hydrogen mixture with a hydrogen content of 5%; based on the above embodiments, this concentration of nitrogen-hydrogen mixture can interact with the locally incompletely coordinated structure in the crystallization intermediate at a relatively low temperature of 200~400°C, inducing the formation of defect structures that are beneficial to improving photocatalytic performance.

[0030] In some embodiments, the oxidizing atmosphere is air. Based on the above embodiments, within a high-temperature window of 450~600°C, it can efficiently and completely oxidize the residual non-volatile carbonaceous impurities from the first stage into gaseous CO2 for removal, thereby achieving the goal of ultrapure purification.

[0031] Secondly, this application provides an ultrapure titanium dioxide prepared according to the method described in any embodiment of the first aspect.

[0032] According to this application, the titanium dioxide prepared by the method according to any embodiment of the first aspect has high purity and high optical catalytic performance.

[0033] Thirdly, this application provides the use of ultrapure titanium dioxide according to any embodiment of the first aspect in the preparation of functional optical glass coatings.

[0034] According to this application, since the ultrapure titanium dioxide provided in the first aspect possesses both ultra-high chemical purity and photocatalytic performance, when it is prepared as a coating on the surface of optical components, it can simultaneously endow the substrate with multiple functions: First, based on the high refractive index of titanium dioxide itself and the high dispersibility of the powder obtained by the preparation method, the coating can achieve efficient transmission and control of visible light; second, it enhances its visible light photocatalytic activity, enabling the coating to continuously degrade organic pollutants attached to the optical surface under ambient light, thereby achieving long-lasting self-cleaning and maintaining the high light transmittance of the optical components. Furthermore, the stable bulk defect structure ensures the durability of the coating function during long-term use.

[0035] Compared with the prior art, the beneficial effects of this application are at least as follows: This application provides ultrapure titanium dioxide, its preparation method, and its applications. The method introduces composite weakly multidentate dynamic coordination molecules to synergistically regulate the entire process of "dynamic coordination-restricted hydrolysis-crystallization path-stepwise heat treatment," constructing a stable active structure in situ within the bulk material without introducing exogenous impurities. Simultaneously, by precisely controlling the reaction parameters at each stage, the high chemical purity of the product is ensured. This method, while maintaining the intrinsic high transparency and stability of the material, endows it with high visible light photocatalytic activity. The ultrapure titanium dioxide provided in this application possesses high purity, high optical performance, and long-lasting photocatalytic function. Under long-term illumination and complex environmental conditions, it can serve as a functional coating material, enabling substrates such as optical glass to maintain high light transmittance and self-cleaning properties over a long period. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0037] Figure 1 This is a scanning electron microscope image of titanium dioxide obtained in one embodiment of this application. Detailed Implementation

[0038] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0039] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0041] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0042] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0043] Example 1 Preparation of ultrapure titanium dioxide: S1: In an argon-filled glove box, add 100 parts by mass of tetraisopropyl titanate, 25 parts by mass of a composite weakly multidentate dynamic coordination molecule (composed of equimolar amounts of benzamide and p-tert-butylphenol, providing amide and phenolic hydroxyl groups), and 500 parts by mass of toluene to a dry 250 mL three-necked flask. Stir the mixture magnetically at 500 rpm for 2 hours at 40 °C to obtain a composite precursor solution.

[0044] S2: Maintaining an inert atmosphere and stirring, slowly add 15 parts by mass of deionized water dropwise to the above solution using a microsyringe. After the addition is complete, continue stirring the reaction at 40°C for 8 hours to obtain the titanium-oxygen network precursor.

[0045] S3: The titanium-oxygen network precursor was solvothermal treated at 180°C for 24 hours. After treatment, it was naturally cooled to 20°C in an oven. The reaction product was removed, washed three times with ethanol and deionized water by centrifugation, and dried in an oven at 80°C for 12 hours to obtain the crystallized intermediate.

[0046] S4: The above-mentioned crystallization intermediate was placed in a quartz boat in a tube furnace. A nitrogen-hydrogen mixture with a hydrogen content of 5% was introduced at a flow rate of 100 mL / min. The furnace temperature was raised to 300°C at a heating rate of 3°C / min and held at this temperature for 2 hours. Subsequently, the atmosphere was switched to air, and the same gas flow rate was maintained. The temperature was then raised to 500°C at a rate of 3°C / min and held for 4 hours. Finally, the mixture was naturally cooled to 20°C in an air atmosphere to obtain ultrapure titanium dioxide, the scanning electron microscope image of which is shown below. Figure 1 As shown.

[0047] Example 2 Preparation of ultrapure titanium dioxide: S1: In an argon-filled glove box, add 100 parts by mass of tetraisopropyl titanate, 25 parts by mass of a composite weakly multidentate dynamic coordination molecule (ethyl 2-methoxybenzoate, providing carbonyl and ether oxygen), and 500 parts by mass of toluene to a dry 250 mL three-necked flask. Stir the mixture magnetically at 500 rpm for 2 hours at 40 °C to obtain a composite precursor solution.

[0048] S2: Maintaining an inert atmosphere and stirring, slowly add 15 parts by mass of deionized water dropwise to the above solution using a microsyringe. After the addition is complete, continue stirring the reaction at 40°C for 8 hours to obtain the titanium-oxygen network precursor.

[0049] S3: The titanium-oxygen network precursor was solvothermal treated at 180°C for 24 hours. After treatment, it was naturally cooled to 20°C in an oven. The reaction product was removed, washed three times with ethanol and deionized water by centrifugation, and dried in an oven at 80°C for 12 hours to obtain the crystallized intermediate.

[0050] S4: The above-mentioned crystallization intermediate was placed in a quartz boat in a tube furnace. A nitrogen-hydrogen mixture with a hydrogen content of 5% was introduced at a flow rate of 100 mL / min. The furnace temperature was raised to 300°C at a heating rate of 3°C / min and held at this temperature for 2 hours. Subsequently, the atmosphere was switched to air, and the same gas flow rate was maintained. The temperature was then raised to 500°C at a rate of 3°C / min and held for 4 hours. Finally, the mixture was naturally cooled to 20°C in an air atmosphere to obtain ultrapure titanium dioxide.

[0051] Example 3 Preparation of ultrapure titanium dioxide: S1: In an argon-filled glove box, add 100 parts by mass of tetraisopropyl titanate, 25 parts by mass of a composite weakly multidentate dynamic coordination molecule (N-(2-methoxyethyl)acetamide, providing amide groups and ether oxygen), and 500 parts by mass of toluene to a dry 250 mL three-necked flask. Stir the mixture magnetically at 500 rpm for 2 hours at 40 °C to obtain a composite precursor solution.

[0052] S2: Maintaining an inert atmosphere and stirring, slowly add 15 parts by mass of deionized water dropwise to the above solution using a microsyringe. After the addition is complete, continue stirring the reaction at 40°C for 8 hours to obtain the titanium-oxygen network precursor.

[0053] S3: The titanium-oxygen network precursor was solvothermal treated at 180°C for 24 hours. After treatment, it was naturally cooled to 20°C in an oven. The reaction product was removed, washed three times with ethanol and deionized water by centrifugation, and dried in an oven at 80°C for 12 hours to obtain the crystallized intermediate.

[0054] S4: The above-mentioned crystallization intermediate was placed in a quartz boat in a tube furnace. A nitrogen-hydrogen mixture with a hydrogen content of 5% was introduced at a flow rate of 100 mL / min. The furnace temperature was raised to 300°C at a heating rate of 3°C / min and held at this temperature for 2 hours. Subsequently, the atmosphere was switched to air, and the same gas flow rate was maintained. The temperature was then raised to 500°C at a rate of 3°C / min and held for 4 hours. Finally, the mixture was naturally cooled to 20°C in an air atmosphere to obtain ultrapure titanium dioxide.

[0055] Comparative Example 1 Preparation of ultrapure titanium dioxide: S1: In an argon-filled glove box, add 100 parts by mass of tetraisopropyl titanate, 25 parts by mass of a strongly coordinating molecule (citric acid, providing a tricarboxylic acid group), and 500 parts by mass of toluene to a dry 250 mL three-necked flask. Stir the mixture magnetically at 500 rpm for 2 hours at 40 °C to obtain a composite precursor solution.

[0056] S2: Maintaining an inert atmosphere and stirring, slowly add 15 parts by mass of deionized water dropwise to the above solution using a microsyringe. After the addition is complete, continue stirring the reaction at 40°C for 8 hours to obtain the titanium-oxygen network precursor.

[0057] S3: The titanium-oxygen network precursor was solvothermal treated at 180°C for 24 hours. After treatment, it was naturally cooled to 20°C in an oven. The reaction product was removed, washed three times with ethanol and deionized water by centrifugation, and dried in an oven at 80°C for 12 hours to obtain the crystallized intermediate.

[0058] S4: The above-mentioned crystallization intermediate was placed in a quartz boat in a tube furnace. A nitrogen-hydrogen mixture with a hydrogen content of 5% was introduced at a flow rate of 100 mL / min. The furnace temperature was raised to 300°C at a heating rate of 3°C / min and held at this temperature for 2 hours. Subsequently, the atmosphere was switched to air, and the same gas flow rate was maintained. The temperature was then raised to 500°C at a rate of 3°C / min and held for 4 hours. Finally, the mixture was naturally cooled to 20°C in an air atmosphere to obtain ultrapure titanium dioxide.

[0059] Comparative Example 2 Preparation of ultrapure titanium dioxide: S1: In an argon-filled glove box, add 100 parts by mass of tetraisopropyl titanate, 5 parts by mass of a composite weakly multidentate dynamic coordination molecule (composed of equimolar amounts of benzamide and p-tert-butylphenol, providing amide and phenolic hydroxyl groups), and 500 parts by mass of toluene to a dry 250 mL three-necked flask. Stir the mixture magnetically at 500 rpm for 2 hours at 40 °C to obtain a composite precursor solution.

[0060] S2: Maintaining an inert atmosphere and stirring, slowly add 15 parts by mass of deionized water dropwise to the above solution using a microsyringe. After the addition is complete, continue stirring the reaction at 40°C for 8 hours to obtain the titanium-oxygen network precursor.

[0061] S3: The titanium-oxygen network precursor was solvothermal treated at 180°C for 24 hours. After treatment, it was naturally cooled to 20°C in an oven. The reaction product was removed, washed three times with ethanol and deionized water by centrifugation, and dried in an oven at 80°C for 12 hours to obtain the crystallized intermediate.

[0062] S4: The above-mentioned crystallization intermediate was placed in a quartz boat in a tube furnace. A nitrogen-hydrogen mixture with a hydrogen content of 5% was introduced at a flow rate of 100 mL / min. The furnace temperature was raised to 300°C at a heating rate of 3°C / min and held at this temperature for 2 hours. Subsequently, the atmosphere was switched to air, and the same gas flow rate was maintained. The temperature was then raised to 500°C at a rate of 3°C / min and held for 4 hours. Finally, the mixture was naturally cooled to 20°C in an air atmosphere to obtain ultrapure titanium dioxide.

[0063] Test section Titanium dioxide content test: Weigh approximately 0.2 g (accurate to 0.0001 g) of the prepared ultrapure titanium dioxide powder sample and place it in an Erlenmeyer flask. Add appropriate amounts of sulfuric acid and ammonium sulfate, and heat until the sample is completely dissolved. After cooling, add hydrochloric acid and aluminum foil to reduce titanium(IV) in the solution to titanium(III). After cooling, immediately titrate with ammonium sulfate solution as an indicator using ferric ammonium sulfate standard titration solution until a stable purple-red endpoint is reached. A blank test is performed simultaneously.

[0064] The volume (mL) of ferric ammonium sulfate standard titration solution consumed in the V0 blank test. Volume (mL) of ferric ammonium sulfate standard titration solution consumed in the titration of sample V1. c. Concentration of the standard titration solution of ferric ammonium sulfate (mol / L); The molar mass of titanium dioxide (M) is 79.87 g / mol. m is the mass of the sample (g); Titanium dioxide content (%) Photocatalytic performance test: Weigh 20 mg of the ultrapure titanium dioxide sample to be tested and disperse it in 50 mL of methylene blue aqueous solution. Place the suspension in the photocatalytic reactor and stir continuously for 30 minutes in the dark. At this time, the concentration of methylene blue in the solution is C0. Then, turn on the xenon lamp source (equipped with a filter with λ>420 nm) for irradiation while maintaining continuous stirring. Take about 5 mL of sample every 20 minutes and immediately filter it through a microporous membrane (0.22 μm) to completely remove catalyst particles. Use a UV-Vis spectrophotometer to measure the absorbance of the filtrate at the characteristic absorption wavelength of methylene blue, 664 nm, and calculate its concentration (Ct) using a pre-plotted standard curve. The degradation rate (D) of the pollutant is calculated by the following formula: Degradation rate D(%) = [(C0-Ct) / C0] × 100% The test results are shown in Table 1 below. Table 1 According to the data in Table 1, the ultrapure titanium dioxide prepared in each embodiment of this patent is better in terms of titanium dioxide purity and photocatalytic activity compared with each comparative example and commercially available P25. This indicates that the preparation method provided in this application can improve the purity and photocatalytic performance of titanium dioxide. The reasons may be as follows: In Comparative Example 1, citric acid was used as a strong chelating agent, which formed a rigid and stable chelate structure with titanium ions. This strong coordination first interfered with the normal hydrolysis-condensation pathway of titanium ions, resulting in a non-uniform precursor. More importantly, it was difficult for it to undergo reversible dissociation during subsequent solvothermal crystallization, failing to dynamically disturb the crystal growth path. Simultaneously, the strong coordination resulted in significant residue of ligand molecules after heat treatment, leading to a decrease in titanium dioxide content and impairing purity and photocatalytic activity. In Comparative Example 2, although the preferred ligand combination of the present invention (benzamide and p-tert-butylphenol) was used, its dosage was too small, and the ligand molecules could not form an effective "weakly constrained" network for titanium ions. This resulted in insufficient dispersion and stabilization in step S1, leading to poor "restricted hydrolysis" in step S2 and a decrease in precursor uniformity. Therefore, the visible light photocatalytic activity of the final material was lower than that of Example 1. Blank titanium dioxide, while having high purity, had almost no photocatalytic activity due to the lack of any photocatalytic performance adjustment, resulting in the lowest degradation rate.

[0065] As shown in Examples 1-3, the specific functional group combination of the composite weakly polydentate dynamic coordination molecule has a certain influence on the final performance. When using the combination of amide group and phenolic hydroxyl group (Example 1) or amide group and ether oxygen group (Example 3), the resulting material has higher photocatalytic activity because it can construct the most ideal dynamic coordination environment in terms of strength and reversibility. When using the combination of carbonyl group and ether oxygen group (Example 2), its coordination dynamism is slightly inferior, so the performance index is slightly lower, but still higher than the comparative example.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing ultrapure titanium dioxide, characterized in that, Includes the following steps: S1: Dissolve the inorganic titanium source and the composite weakly multidentate dynamic coordination molecule in an inert organic solvent to obtain a composite precursor solution; The composite weakly polydentate dynamic coordination molecule contains two or more reversible coordination functional groups, and the inert organic solvent includes at least one of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, or ether solvents. S2: Water is added to the composite precursor solution, and hydrolysis and condensation reactions are carried out through the competitive occupation of titanium ion coordination sites by water molecules to form a titanium-oxygen network precursor. S3: The titanium-oxygen network precursor is subjected to solvothermal treatment to crystallize it, and under the action of the composite weakly multidentate dynamic coordination molecules, intrinsic defects are formed in situ during the crystallization process to obtain a crystallization intermediate. S4: The crystallization intermediate is subjected to a first-stage heat treatment at 200~400℃ in a weakly reducing atmosphere and a second-stage heat treatment at 450~600℃ in an oxidizing atmosphere to remove organic residues and stabilize the crystal structure, thereby obtaining ultrapure titanium dioxide.

2. The method according to claim 1, characterized in that, The composite weakly polydentate dynamic coordination molecule includes organic molecules containing amide groups and phenolic hydroxyl groups, carbonyl groups and ether oxygen groups, or combinations of amide groups and ether oxygen groups.

3. The method according to claim 1, characterized in that, The mass ratio of the composite weakly multidentate dynamic coordination molecule to the inorganic titanium source is (10~40):

100.

4. The method according to claim 1, characterized in that, Step S1 includes: Under an inert atmosphere, 100 parts by mass of an inorganic titanium source and 10-40 parts by mass of a composite weakly multidentate dynamic coordination molecule are dispersed in 400-600 parts by mass of an inert organic solvent and stirred at 20-60°C for 0.5-4 hours to obtain a composite precursor solution.

5. The method according to claim 1, characterized in that, In step S2: Add 5-30 parts by mass of water to the composite precursor solution and stir the reaction at 20-60°C for 2-12 hours to form a titanium-oxygen network precursor.

6. The method according to claim 1, characterized in that, In step S3: The titanium-oxygen network precursor was subjected to solvothermal treatment at 120~220℃ for 12~36 hours, and then naturally cooled to 20℃ to obtain a crystallized intermediate.

7. The method according to claim 1, characterized in that, In step S4: The crystallization intermediate was heated to 200-400°C at a heating rate of 1-5°C / min under a weak reducing atmosphere with a flow rate of 50-200 mL / min, and held at that temperature for 1-4 hours. Subsequently, the atmosphere was switched to an oxidizing atmosphere, and the temperature was increased to 450-600°C at the same flow rate of 1-5°C / min, and held for 2-6 hours. After natural cooling, the ultrapure titanium dioxide was obtained.

8. The method according to any one of claims 1 to 7, characterized in that, The raw materials meet at least one of the following conditions: 1) The inorganic titanium source includes at least one of tetraisopropyl titanate, tetraethyl titanate, or titanium tetrachloride; 2) The inert organic solvent includes at least one of benzene, toluene, xylene, n-hexane, cyclohexane, tetrahydrofuran, or 1,4-dioxane; 3) The weakly reducing atmosphere is a nitrogen-hydrogen mixture with a hydrogen content of 5%; 4) The oxidizing atmosphere is air.

9. An ultrapure titanium dioxide, characterized in that, Prepared by the method according to any one of claims 1 to 8.

10. A functional optical glass element, characterized in that, Its surface is provided with a functional coating comprising ultrapure titanium dioxide prepared according to any one of claims 1 to 9.

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