Hydrothermal synthesis method for regulating and controlling morphology of titanium phosphate without template agent

Abstract

The invention discloses a hydrothermal synthesis method for regulating and controlling the morphology of titanium phosphate without a template agent and an obtained product, and belongs to the technical field of preparation of inorganic functional materials. The method does not use any organic surfactant or hard template agent, and comprises the following steps: dissolving a titanium source in water containing concentrated sulfuric acid, and heating and refluxing to obtain a precursor solution; at least one of sulfuric acid, citric acid or acetic acid can be selectively added as a second acid; and then adding a phosphoric acid solution, and carrying out hydrothermal reaction post-treatment to obtain titanium phosphate powder. Controllable preparation of the microstructure of the titanium phosphate can be realized under the template-free condition by regulating and controlling the addition amount of the phosphoric acid and whether the second acid is added or not. The obtained titanium phosphate is in a pure phase, and the morphology of the titanium phosphate comprises nanosheets, nanoparticles, flower-shaped microspheres assembled by the nanosheets and the like. The method disclosed by the invention is simple in process and low in cost, avoids generation of impure phases caused by high-temperature calcination, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of titanium phosphate preparation technology, and more specifically, to a hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agents. Background Technology

[0002] Titanium phosphate is an important class of inorganic functional materials with layered or open framework structures. It has attracted widespread attention in recent years due to its promising application potential in ion storage, proton conduction, heterogeneous catalysis, and selective adsorption. Related studies have shown that the macroscopic properties of titanium phosphate materials, such as electrochemical performance, mass transfer performance, and interfacial reactivity, largely depend on their microstructure and morphology. Therefore, achieving controllable preparation of the microstructure of titanium phosphate materials is a crucial prerequisite for improving their overall performance and expanding their application areas.

[0003] In existing technologies, the synthesis methods of titanium phosphate mainly include the traditional reflux method, hydrothermal method, or solvothermal method. Among them, the traditional reflux method has relatively simple process conditions, but it usually has a long reaction cycle, and the resulting product has low crystallinity and insufficient phase purity, making it difficult to meet the material structure requirements of high-performance applications. In contrast, the hydrothermal method can provide a high temperature and pressure environment in a closed system, which is conducive to the full growth and rearrangement of crystals. Therefore, it has significant advantages in shortening reaction time, improving crystallinity and phase purity, and has become one of the important technical routes for the preparation of titanium phosphate.

[0004] In the morphology control of titanium phosphate, existing research mainly focuses on introducing templates to guide the directional growth of crystals. Specifically, template-guided methods typically involve adding soft templates (including surfactants, polymers, etc.) or hard templates (porous inorganic materials) to induce titanium phosphate to grow along a specific direction, thereby obtaining specific morphologies such as nanosheets, nanorods, and microspheres. This type of method can achieve a certain degree of morphology design at the laboratory scale and is therefore widely used in related research.

[0005] However, the aforementioned morphology control strategies relying on template agents still have many shortcomings in practical applications: hard template methods typically involve multiple steps such as template preparation and removal, resulting in complex processes that are difficult to scale up efficiently and at low cost. Furthermore, the organic template agents used in soft template methods often require removal through high-temperature calcination after the reaction, and titanium phosphate materials are prone to phase transitions at high temperatures, transforming into thermodynamically more stable impurity phases such as titanium pyrophosphate (TiP2O7), leading to decreased product phase purity and even loss of original functional properties. In addition, the introduction of template agents may also lead to impurity residues and increased environmental burden, further limiting its industrial application prospects. Although hydrothermal methods have advantages in improving the crystallinity of titanium phosphate, existing research focuses more on the influence of hydrothermal conditions on crystal form or crystallinity. There is still a lack of in-depth research and mature technical solutions on how to fully explore the controllability potential of the hydrothermal system itself and achieve the systematic and controllable synthesis of titanium phosphate morphology without relying on template agents. Currently, there is no single method for preparing titanium phosphate that is simple in process, has clearly defined control variables, and can balance morphology controllability with scalability.

[0006] Therefore, developing a hydrothermal system-based technique that does not require the introduction of external template agents and enables the controlled synthesis of titanium phosphate remains a pressing technical problem to be solved in this field. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agents, so as to solve the problems of template dependence leading to complex process, high cost, difficult post-processing, and easy introduction of titanium pyrophosphate impurity phase, poor morphology controllability and insufficient reproducibility in the prior art.

[0008] To overcome the shortcomings of the prior art, this invention provides a hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agents. The method does not use organic surfactants or hard template agents and includes the following steps: S1: Disperse the titanium source in water, add a first acid solution to inhibit hydrolysis, and carry out a dissolution reaction under heating conditions to obtain a titanium source precursor solution. The titanium source is selected from at least one of titanium chloride, titanium sulfate, titanium oxysulfate, titanium citrate, and tetrabutyl titanate. S2: Add phosphoric acid solution with a concentration of 1-14.6 mol / L dropwise to the titanium source precursor solution, stir the reaction, and obtain the pre-reaction solution; S3: Place the pre-reaction liquid in a sealed container and carry out a hydrothermal reaction at 150-180 ℃; S4: After the reaction is complete, the product is subjected to solid-liquid separation, washing and drying to obtain titanium phosphate powder.

[0009] Compared with existing technologies, the hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agents of the present invention has the following advantages: The method of the present invention does not introduce any organic surfactants or hard template agents throughout the synthesis process, eliminating the additional steps of template preparation / introduction, loading, and removal commonly found in template methods, making the process simpler, lower in cost, and easier to scale up; furthermore, the product obtained by the method of the present invention does not require high-temperature calcination or strong oxidation treatment for template removal, significantly reducing the probability of titanium phosphate undergoing dehydration condensation under high temperature or harsh conditions, thereby generating impurities such as titanium pyrophosphate, thus making it easier to obtain titanium phosphate powder with high phase purity; in step S1, a first acid solution is added to the aqueous system... Inhibiting the hydrolysis of titanium source and promoting dissolution allows titanium species to enter the reaction system in a more stable and controllable ionic / coordination form, avoiding uncontrolled nucleation caused by disordered hydrolysis precipitation. In step S2, a high-concentration phosphoric acid solution is added dropwise and stirred thoroughly to ensure uniform release of the phosphorus source and controlled reaction with the titanium species, thus providing a homogeneous pre-reaction liquid for the subsequent hydrothermal process. In step S3, under hydrothermal conditions of 150-180℃, the system completes controlled nucleation and crystal growth in a closed environment, thereby forming a reproducible titanium phosphate solid phase. Subsequently, titanium phosphate powder can be directly obtained by separation, washing, and drying in step S4. This invention achieves the technical effects of simple process, low risk of impurity phases, high product phase purity, and good preparation stability through the combined effects of acid inhibition of hydrolysis to obtain a stable precursor, dropwise addition of phosphoric acid to form a homogeneous pre-liquid, and gentle hydrothermal crystallization without the need for template removal and calcination. This solves the problems of complexity and uncontrollable impurity phases / morphology caused by template routes in the background technology.

[0010] In one possible implementation, in step S1, the first acid solution is concentrated sulfuric acid, and the heating conditions are at a temperature of 50-80 °C and a reaction time of at least 30 min.

[0011] Compared with existing technologies, the above-mentioned technical solution can significantly suppress the instantaneous hydrolysis and colloidalization of titanium sources in an aqueous system by using the high acidity provided by concentrated sulfuric acid and the coordination / ionic strength effect of sulfate ions. Under the driving force of heating at 50-80℃, the dissolution and homogenization process of titanium sources is accelerated, so that titanium species exist in a more stable and dispersed precursor form. The reaction time of at least 30 minutes ensures that the system completes the full dissolution and acidification equilibrium, avoiding the disordered process of precipitation followed by dissolution caused by local undissolved particles or local pH fluctuations. In this way, a titanium source precursor solution with more uniform composition and more controllable activity can be obtained, providing consistent starting conditions for controlled nucleation during subsequent addition of phosphoric acid and reducing the probability of impurities and coarse agglomerates.

[0012] In one possible implementation, after step S1 ends and before step S2 begins, the following is further included: S1.5: Add at least one second acid solution selected from sulfuric acid, citric acid or acetic acid to the titanium source precursor solution and mix thoroughly.

[0013] Compared with existing technologies, the above-mentioned technical solution, without introducing a template agent, changes the coordination environment and polymerization state of titanium species through further acidification and complexation regulation of the titanium species by a second acid: sulfuric acid tends to maintain strong acidity and increase ionic strength, citric acid has a stronger multidentate complexation ability, and acetic acid provides a relatively mild coordination / buffering effect. The above effects can affect the nucleation rate, the number of crystal nuclei and the competition for crystal face growth when phosphoric acid is added later, so that the pre-reaction liquid has a controllable precursor chemical state before entering the hydrothermal stage, thereby improving the adjustability of morphology control and reducing the problems of agglomeration and widening of size distribution caused by excessively rapid local reactions.

[0014] In one possible implementation, in step S1.5, the second acid solution is added dropwise to the titanium source precursor solution, and the stirring time for mixing after addition is more than 30 minutes.

[0015] This embodiment further transforms the introduction of the second acid from abrupt acidification to gradual acidification by adding it dropwise. This avoids the local aggregation or salting out of titanium species caused by a sudden increase in local acid concentration, thus making the complexation / acidification reaction more uniform in the system. After addition, stirring is continued for more than 30 minutes to ensure that the complexation exchange, ion distribution and acid-base balance between the second acid and titanium species are fully completed, eliminating the micro-gradient of the system. This results in a precursor system with a more uniform chemical environment and higher stability, making the nucleation process during the subsequent addition of phosphoric acid more synchronous and controllable.

[0016] In one possible implementation, in step S1.5, the titanium source precursor solution is transferred to room temperature before adding the second acid solution.

[0017] Compared with existing technologies, the above-mentioned technical solution, by adding the second acid at room temperature, allows for a smoother coordination exchange and polymerization process of titanium species, avoiding instantaneous local aggregation, thickening, or uneven microgels caused by excessively fast reaction rates at higher temperatures. At the same time, room temperature conditions are more conducive to the controllability and reproducibility of the dropwise addition process, making the precursor system after the introduction of the second acid more stable and uniform, providing a more consistent reaction window for the subsequent dropwise addition of phosphoric acid, and reducing the risk of agglomeration and morphology drift.

[0018] In one possible implementation, the stirring reaction in step S2 takes at least 30 minutes.

[0019] Compared with existing technologies, the above-mentioned technical solution, after the phosphoric acid solution is added dropwise, allows the complexation, condensation and initial nucleation processes of titanium species and phosphate ions in the system to proceed fully through continuous stirring for at least 30 minutes. This enables the ion concentration, acidity and precursor distribution of the reaction system to reach a stable state, avoiding the problems of particle agglomeration, widened particle size distribution or uncontrollable morphology in local high phosphoric acid concentration areas caused by insufficient stirring.

[0020] In one possible implementation, in step S3, the hydrothermal reaction time is 3-24 h; and the filling volume of the pre-reaction liquid in the sealed container does not exceed 70%.

[0021] Compared with existing technologies, the above-mentioned technical solution can provide a sufficient kinetic window for titanium phosphate from initial nucleation to crystal growth and crystal phase perfection through a hydrothermal reaction time of 3-24 h. When the reaction time is within the range of 3-24 h, the system can complete the transformation from amorphous or low-crystallinity intermediates to crystallized titanium phosphate, and promote grain growth and structural rearrangement. This avoids insufficient crystallization, loose products, or inclusion of intermediate phases caused by too short a reaction time. At the same time, controlling the filling volume to no more than 70% can reserve sufficient gas phase space for the closed hydrothermal system, reduce the safety risks caused by rapid pressure rise during the heating process, improve the convection and heat and mass transfer conditions in the reactor, make the temperature field and concentration field of the reaction system more uniform, and reduce morphological drift caused by local overheating or local oversaturation.

[0022] In one possible implementation, in step S4, the washing is performed with water until the pH of the washing solution is greater than 5; the drying temperature is 120-150 °C, and the drying time is 6-12 h.

[0023] Compared with the prior art, in this embodiment, residual acid and soluble ions (including free phosphate, sulfate and unreacted salts) are effectively removed by washing the product to pH>5, which reduces the impact of product surface acidity and ion residue on subsequent storage stability and performance consistency, and avoids secondary reactions or agglomeration of particles caused by residual acid during the drying process; at the same time, the drying conditions of 120-150℃ and maintained for 6-12 h are used to fully remove pore water and adsorbed water without introducing the risk of high temperature phase change, so that the moisture content of the powder is stable, the flowability is better, and the agglomeration, weighing error or decrease in dispersibility caused by insufficient drying are reduced.

[0024] The present invention also provides titanium phosphate, which is prepared by the template-free hydrothermal synthesis method described above.

[0025] In one possible implementation, the titanium phosphate has any of the following morphologies: a sheet-like structure, a granular structure, or a three-dimensional microstructure assembled from sheet-like structures.

[0026] Compared with the prior art, the titanium phosphate of the present invention has the following advantages: By adjusting the amount of phosphoric acid added and coordinating with different acidic environments, the morphology of titanium phosphate can be controlled without introducing any template agent, so that the obtained titanium phosphate exhibits a lamellar structure, a granular structure, or a three-dimensional microstructure assembled from lamellar structures; The present invention avoids the problems of process complexity, increased cost, and easy transformation of titanium phosphate to titanium pyrophosphate caused by the introduction of template agents and subsequent high-temperature calcination to remove the template. By utilizing the regulating effect of phosphoric acid dosage on the hydrolysis and coordination behavior of titanium species, and through the synergistic influence of different acidic conditions on the crystal nucleation and growth process, the crystal morphology can be predictably controlled. The titanium phosphate prepared by the present invention not only has the characteristics of high crystallinity, stable phase composition, and uniform morphology, but also has a simple process, good repeatability, and is suitable for scale-up preparation. It solves the technical problems of titanium phosphate morphology control relying on template agents, difficulty in scaling up, and easy occurrence of unfavorable phase transitions in the prior art. Attached Figure Description

[0027] Figure 1 The image shows a scanning electron microscope (SEM) image of titanium phosphate prepared in Example 1. Figure 2 The image shows a scanning electron microscope (SEM) image of titanium phosphate obtained in Example 2. Figure 3 The image shows a scanning electron microscope (SEM) image of titanium phosphate prepared in Example 3. Figure 4 The image shows a scanning electron microscope (SEM) image of titanium phosphate obtained in Example 4. Figure 5 The image shows a scanning electron microscope (SEM) image of titanium phosphate obtained in Example 5. Figure 6 The image shows a scanning electron microscope (SEM) image of titanium phosphate obtained in Example 6. Figure 7 The image shows a scanning electron microscope (SEM) image of titanium phosphate prepared in Example 7. Figure 8 The X-ray diffraction (XRD) patterns of titanium phosphate obtained in Examples 2 and 7 are shown. Detailed Implementation

[0028] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0029] In the following embodiments, concentrated sulfuric acid refers to sulfuric acid with a mass fraction ≥95%, and glacial acetic acid refers to acetic acid with a mass fraction ≥99%. Those skilled in the art can make appropriate adjustments.

[0030] This invention provides a template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate. The method does not use organic surfactants or hard templates and includes the following steps: S1: Disperse the titanium source in water, add a first acid solution to inhibit hydrolysis, and carry out a dissolution reaction under heating conditions to obtain a titanium source precursor solution. The titanium source is selected from at least one of titanium chloride, titanium sulfate, titanium oxysulfate, titanium citrate, and tetrabutyl titanate. S2: Add phosphoric acid solution with a concentration of 1-14.6 mol / L dropwise to the titanium source precursor solution, stir the reaction, and obtain the pre-reaction solution; S3: Place the pre-reaction liquid in a sealed container and carry out a hydrothermal reaction at 150-180 ℃; S4: After the reaction is complete, the product is subjected to solid-liquid separation, washing and drying to obtain titanium phosphate powder.

[0031] As a preferred embodiment, in step S1, the first acid solution is concentrated sulfuric acid, and the heating conditions are at a temperature of 50-80 ℃ and a reaction time of at least 30 min.

[0032] As a preferred embodiment, after step S1 ends and before step S2 begins, the following steps are further included: S1.5: Add at least one second acid solution selected from sulfuric acid, citric acid or acetic acid to the titanium source precursor solution and mix thoroughly.

[0033] As a preferred embodiment, in step S1.5, the second acid solution is added dropwise to the titanium source precursor solution, and the stirring time for mixing after addition is more than 30 minutes.

[0034] As a preferred embodiment, in step S1.5, the titanium source precursor solution is transferred to room temperature before adding the second acid solution.

[0035] As a preferred embodiment, in step S2, the stirring reaction time is at least 30 minutes.

[0036] As a preferred embodiment, in step S3, the hydrothermal reaction time is 3-24 h; and the filling volume of the pre-reaction liquid in the sealed container does not exceed 70%.

[0037] As a preferred embodiment, in step S4, the washing is performed with water until the pH of the washing solution is greater than 5; the drying temperature is 120-150 ℃, and the drying time is 6-12 h.

[0038] This invention provides a titanium phosphate, which is prepared by the template-free hydrothermal synthesis method described above.

[0039] As a preferred embodiment, the titanium phosphate has any of the following morphologies: a sheet-like structure, a granular structure, or a three-dimensional microstructure assembled from sheet-like structures.

[0040] The method described in this invention requires no introduction of any soft or hard template agents, thus avoiding the cumbersome and costly processes associated with template methods. Furthermore, since subsequent high-temperature calcination is unnecessary to remove the template, the risk of uncontrollable transformation of titanium phosphate into titanium pyrophosphate impurities under high-temperature conditions is effectively avoided, ensuring high phase purity in the final product. Moreover, this invention further discovers that the amount of phosphoric acid is a key regulatory factor determining the morphology evolution of the product, and based on this, a clear and efficient dual-pathway morphology control strategy is established: when the phosphoric acid dosage is high, only the type of auxiliary acid (including sulfuric acid and citric acid) needs to be adjusted. By using phosphoric acid (such as acetic acid), precise and predictable switching of morphologies such as nanoparticles, nanosheets, and microspheres can be achieved within the same reaction system. When the phosphoric acid dosage is reduced to a lower level, the reaction system will proceed along a different morphology evolution path, thus obtaining novel structures significantly different from those under high phosphoric acid conditions. In the method of this invention, the entire morphology control process relies only on two simple, inexpensive, and easily precisely controlled liquid-phase chemical variables: the amount of phosphoric acid and the type of auxiliary acid (secondary acid). No special equipment or expensive additives are required, the process steps are simple, post-processing is convenient, and it possesses good process robustness and scalability potential. This method can stably prepare titanium phosphate materials with various regular morphologies, yielding products with high crystallinity, uniform morphology, and good dispersibility, demonstrating potential application value.

[0041] Example 1 This embodiment provides a template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate, and the titanium phosphate obtained by this method. The method includes the following steps: S1: Slowly add 2 mL of concentrated sulfuric acid to 18 g of deionized water, stirring continuously with a glass rod during the addition. Weigh 2 g of titanium sulfate and add it to a 50 mL round-bottom flask, then add the acidified deionized water mentioned above. Place the flask in an oil bath at 70°C under reflux and stir magnetically for 30 min. After the titanium sulfate is completely dissolved, pour the clear and transparent solution into a 100 mL beaker, transfer it to room temperature, and stir magnetically at 500 rpm to obtain the titanium source precursor solution, denoted as solution A.

[0042] S2: Slowly add 2 mL of 85 wt% phosphoric acid (original concentration 14.6 mol / L) to 18 g of deionized water, stirring continuously with a glass rod during the addition process, to obtain a phosphoric acid solution, denoted as solution B (the phosphoric acid concentration of solution B is approximately 1.37 mol / L). Then, add solution B dropwise to solution A using a dropper to obtain a mixed solution, denoted as solution C. Continue stirring solution C for 30 min to obtain the initial solution before the reaction.

[0043] S3: Transfer the pre-reaction liquid to a 50 mL hydrothermal reactor and heat it in an oven at 180 °C for 12 h.

[0044] S4: After the reaction is complete, centrifuge to separate the solid precipitate. Wash the precipitate with water until the pH of the washing solution is greater than 5. Collect the precipitate and dry it to obtain white titanium phosphate powder.

[0045] The scanning electron microscope (SEM) image of titanium phosphate obtained through this embodiment is as follows: Figure 1 As shown.

[0046] From Figure 1 As can be seen from the figures, the obtained titanium phosphate exhibits a regular hexagonal elongated sheet morphology with good overall dispersion and no obvious agglomeration was observed. The hexagonal sheet structure has a relatively clear edge outline and high morphological uniformity. Further measurements from the figures show that the width of the titanium phosphate nanosheets is approximately 500 nm and the length is approximately 3 μm, indicating that a sheet-like titanium phosphate structure with obvious anisotropic growth characteristics can be obtained under the conditions of this embodiment.

[0047] Example 2 This embodiment provides a template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate, and the titanium phosphate obtained by this method. The method includes the following steps: S1: Slowly add 1 mL of concentrated sulfuric acid to 10 g of deionized water while stirring. Weigh 2 g of titanium oxysulfate and add it to a 50 mL round-bottom flask, then add the acidified deionized water mentioned above. Place the flask in an oil bath at 50 °C under reflux and stir magnetically for 30 min. After the titanium oxysulfate is completely dissolved, pour the clear solution into a 100 mL beaker, transfer it to room temperature, and stir magnetically at 500 rpm to obtain the titanium source precursor solution.

[0048] S2: Using a dropper, 8 mL of 85 wt% phosphoric acid (14.6 mol / L) was added dropwise to the titanium source precursor solution. During the addition, a white precipitate was initially formed, which dissolved as phosphoric acid was added, and the solution became clear and transparent. The mixture was stirred for another 30 min to obtain the unreacted solution.

[0049] S3: Transfer the pre-reaction liquid to a 50 mL hydrothermal reactor and heat it in an oven at 180 ℃ for 24 h.

[0050] S4: Centrifuge to separate the solid precipitate, wash the precipitate with water until the pH of the washing solution is greater than 5, collect the precipitate and dry it to obtain white titanium phosphate powder.

[0051] The scanning electron microscope (SEM) image of titanium phosphate obtained through this embodiment is as follows: Figure 2 As shown.

[0052] Depend on Figure 2 As can be seen, the obtained titanium phosphate exhibits a short hexagonal nanosheet morphology with a relatively uniform particle distribution and no obvious large-sized blocky impurities. Compared with Example 1, the size of the titanium phosphate sheet structure in this example is significantly reduced; further measurements in the figure show that the size of the short hexagonal nanosheets is mainly distributed in the range of 300-500 nm, showing good size consistency, indicating that small-sized hexagonal sheet titanium phosphate can be stably obtained under the conditions of this example.

[0053] Example 3 This embodiment provides a template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate, and the titanium phosphate obtained by this method. The method includes the following steps: S1: Slowly add 0.5 mL of concentrated sulfuric acid to 6 g of deionized water while stirring. Weigh 2 g of titanium oxysulfate and add it to a 50 mL round-bottom flask, then add the acidified deionized water mentioned above. Place the flask in an oil bath at 50 °C under reflux and stir magnetically for 30 min. After dissolution, pour the clear solution into a 100 mL beaker, transfer it to room temperature, and stir magnetically at 500 rpm to obtain the titanium source precursor solution.

[0054] S1.5: Weigh 1 g of citric acid monohydrate, add 5 g of deionized water to dissolve it, and obtain a citric acid solution; add the citric acid solution to the titanium source precursor solution, stir for 30 min, and obtain a mixed solution.

[0055] S2: Use a dropper to transfer 3 mL of 85 wt% phosphoric acid (14.6 mol / L) dropwise into the mixed solution, and continue stirring for 30 min to obtain the solution before reaction.

[0056] S3: Transfer the pre-reaction liquid to a 50 mL hydrothermal reactor and heat it in an oven at 180 ℃ for 6 h.

[0057] S4: Centrifuge to separate the precipitate, wash with water until the pH of the washing solution is greater than 5, collect the precipitate and dry it to obtain white titanium phosphate powder.

[0058] The scanning electron microscope (SEM) image of titanium phosphate obtained through this embodiment is as follows: Figure 3 As shown.

[0059] From Figure 3 As can be seen from the figure, the obtained titanium phosphate mainly exhibits a short hexagonal sheet structure with a relatively regular overall morphology and a certain degree of dispersion between the sheets. Compared with Example 2, the lateral dimension of the titanium phosphate sheets obtained in this example is increased; further measurements from the figure show that the size of the sheets is approximately 1 μm, indicating that the obtained titanium phosphate has obvious two-dimensional sheet structure characteristics under the condition of introducing a second acid.

[0060] Example 4 This embodiment provides a template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate, and the titanium phosphate obtained by this method. The method includes the following steps: S1: Slowly add 2 mL of concentrated sulfuric acid to 18 g of deionized water while stirring. Weigh 2 g of titanium sulfate and add it to a 50 mL round-bottom flask, then add the acidified deionized water mentioned above. Place the flask in an oil bath at 70 °C under reflux and stir magnetically for 30 min. After dissolution, pour the clear solution into a 100 mL beaker, transfer it to room temperature, and stir magnetically at 500 rpm to obtain the titanium source precursor solution.

[0061] S1.5: Use a dropper to slowly add 10 mL of concentrated sulfuric acid to the titanium source precursor solution, mix well, and obtain a mixed solution.

[0062] S2: Then, 8 mL of 85 wt% phosphoric acid (14.6 mol / L) was added dropwise to the mixed solution using a dropper, and the mixture was stirred for 30 min to obtain the pre-reaction solution.

[0063] S3: Transfer the pre-reaction liquid to a 50 mL hydrothermal reactor and heat it in an oven at 150 ℃ for 6 h.

[0064] S4: Centrifuge to separate the precipitate, wash with water until the pH of the washing solution is greater than 5, collect the precipitate and dry it to obtain white titanium phosphate powder.

[0065] The scanning electron microscope (SEM) image of titanium phosphate obtained through this embodiment is as follows: Figure 4 As shown.

[0066] Depend on Figure 4It can be seen that the obtained titanium phosphate no longer exhibits a sheet-like structure, but is mainly composed of approximately spherical nanoparticles with relatively uniform distribution among the particles. No obvious large-sized sheet-like or rod-like structures were observed. Further measurements from the figure show that the particle size of the nanoparticles is approximately 100 nm, indicating that titanium phosphate nanoparticles with small particle size and relatively uniform morphology can be obtained under the conditions of this embodiment.

[0067] Example 5 This embodiment provides a template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate, and the titanium phosphate obtained by this method. The method includes the following steps: S1: Slowly add 2 mL of concentrated sulfuric acid to 18 g of deionized water while stirring. Weigh 2 g of titanium oxysulfate and add it to a 50 mL round-bottom flask, then add the above-mentioned acidified deionized water. Place the flask in an oil bath at 50 °C under reflux and stir magnetically for 30 min. After dissolution, pour the clear and transparent solution into a 100 mL beaker, transfer it to room temperature, and stir magnetically at 500 rpm to obtain the titanium source precursor solution.

[0068] S1.5: Use a dropper to slowly add 10 mL of glacial acetic acid to the titanium source precursor solution, mix well, and obtain a mixed solution.

[0069] S2: Then, 8 mL of 85 wt% phosphoric acid (14.6 mol / L) was added dropwise to the mixed solution using a dropper, and the mixture was stirred for 30 min to obtain the pre-reaction solution.

[0070] S3: Transfer the pre-reaction liquid to a 50 mL hydrothermal reactor and heat it in an oven at 150 ℃ for 6 h.

[0071] S4: Centrifuge to separate the precipitate, wash with water until the pH of the washing solution is greater than 5, collect the precipitate and dry it to obtain white titanium phosphate powder.

[0072] The scanning electron microscope (SEM) image of titanium phosphate obtained through this embodiment is as follows: Figure 5 As shown.

[0073] From Figure 5 As can be seen from the figure, the obtained titanium phosphate exhibits a three-dimensional flower-like microsphere structure, which is formed by the stacking and assembly of a large number of nanosheets. The overall outline of the flower-like microspheres is relatively clear and the structure is complete. Further measurements from the figure show that the overall size of the three-dimensional flower-like structure is about 2 μm, indicating that under the conditions of this embodiment, titanium phosphate can be further assembled from two-dimensional nanosheets to form a three-dimensional microstructure with hierarchical structural features.

[0074] Example 6 This embodiment provides a template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate, and the titanium phosphate obtained by this method. The method includes the following steps: S1: Slowly add 1 mL of concentrated sulfuric acid to 10 g of deionized water while stirring. Weigh 2 g of titanium oxysulfate and add it to a 50 mL round-bottom flask, then add the acidified deionized water mentioned above. Place the flask in an oil bath at 50 °C under reflux and stir magnetically for 30 min. After the titanium oxysulfate is completely dissolved, pour the clear solution into a 100 mL beaker, transfer it to room temperature, and stir magnetically at 500 rpm to obtain the titanium source precursor solution.

[0075] S2: Slowly add 4 mL of 85 wt% phosphoric acid (stock concentration 14.6 mol / L) to 4 g of deionized water, stirring continuously with a glass rod during the addition, to obtain a dilute phosphoric acid solution (concentration approximately 7.45 mol / L). Use a dropper to add this dilute phosphoric acid dropwise to the titanium source precursor solution. A white precipitate initially forms during the addition, but dissolves as phosphoric acid is added, and the solution becomes clear and transparent. Continue stirring for 30 min to obtain the initial reaction solution.

[0076] S3: Transfer the pre-reaction liquid to a 50 mL hydrothermal reactor and heat it in an oven at 180 ℃ for 24 h.

[0077] S4: Centrifuge to separate the solid precipitate, wash the precipitate with water until the pH of the washing solution is greater than 5, collect the precipitate and dry it to obtain white titanium phosphate powder.

[0078] The scanning electron microscope (SEM) image of titanium phosphate obtained through this embodiment is as follows: Figure 6 As shown.

[0079] Depend on Figure 6 As can be seen, the basic building blocks of the obtained product are still short sheet-like / polygonal sheet-like structures, with an overall morphology similar to the titanium phosphate obtained in Example 2. This indicates that sheet-like titanium phosphate structures can still be formed under the condition of using diluted phosphoric acid (approximately 7.45 mol / L) as the phosphorus source in this example. Compared with Example 2, the stacking and aggregation of sheet-like units are enhanced in this example, with relatively dense clusters forming in local areas. Based on the 3 μm scale bar in the figure, the lateral dimensions of the clusters are mainly distributed in the range of approximately 0.5–2 μm, and their interiors are composed of stacked sheet-like units on the order of hundreds of nanometers. The above results show that, under the premise of maintaining the formation of sheet-like structures, changes in phosphoric acid concentration affect the assembly and dispersion state of sheet-like units, resulting in different aggregation characteristics in the microstructure.

[0080] Example 7 (Scale-up Synthesis of Titanium Phosphate) This embodiment provides a template-free hydrothermal synthesis method (scale-up synthesis) for controlling the morphology of titanium phosphate, and the titanium phosphate obtained by this method. The method includes the following steps: S1: Slowly add 40 mL of concentrated sulfuric acid to 400 g of deionized water while stirring. Weigh 80 g of titanium oxysulfate and add it to a 2 L round-bottom flask, then add the above acidified deionized water. Place the flask in an oil bath at 50 °C under reflux and stir magnetically for 45 min. After dissolution, pour the clear solution into a 2 L beaker, transfer it to room temperature, and stir magnetically at 500 rpm to obtain the titanium source precursor solution.

[0081] S2: Using a dropper, 320 mL of 85 wt% phosphoric acid (14.6 mol / L) was added dropwise to the titanium source precursor solution. During the addition, a white precipitate was initially formed, which dissolved as phosphoric acid was added, and the solution became clear and transparent. The mixture was stirred for another 30 min to obtain the unreacted solution.

[0082] S3: Transfer the pre-reaction liquid to a 2 L hydrothermal reactor and heat it in an oven at 180 ℃ for 24 h.

[0083] S4: After the reaction is complete, filter the solid precipitate, wash with water until the pH of the washing solution is greater than 5, collect the precipitate and dry it to obtain white titanium phosphate powder.

[0084] The X-ray diffraction (XRD) pattern of titanium phosphate obtained in this embodiment is as follows: Figure 8 As shown. It can be seen from... Figure 8 As can be seen, the diffraction peak positions of the product obtained under the scaled-up synthesis conditions are consistent with those of the product obtained in Example 2, indicating that the titanium phosphate obtained after scaled-up synthesis is still α-type titanium phosphate, and its crystal structure has not changed due to the expansion of the reaction scale.

[0085] Furthermore, the scanning electron microscope (SEM) image of titanium phosphate obtained through this embodiment is as follows: Figure 7 As shown; by Figure 8 It can be seen that the morphology of titanium phosphate obtained under the scale-up synthesis conditions is basically consistent with that of the product under the small-scale conditions in Example 2, still exhibiting a short hexagonal nanosheet structure, indicating that the method of the present invention has good scale-up feasibility and morphology reproducibility.

[0086] As can be seen from the above embodiments, the present invention can stably prepare titanium phosphate powder without using organic surfactants or hard template agents. Furthermore, by introducing a first acid to inhibit hydrolysis during the formation stage of the titanium source solution and by optionally introducing different types of second acids (S1.5) before the addition of phosphoric acid, the system can form different nucleation / growth and assembly paths under hydrothermal conditions, thereby obtaining titanium phosphate with various morphologies, including sheet-like structures, nanoparticle structures, and three-dimensional flower-like microstructures assembled from nanosheets. At the same time, the scale-up results of Example 7 show that the product still maintains the same crystal form and morphology as the small-scale test after the reaction is scaled up, proving that the method of the present invention has good reproducibility and scale-up applicability.

[0087] This invention regulates the hydrolysis and complexation state of titanium source in an acidic environment, and forms a controllable precipitation-dissolution-re-nucleation process during the dropwise addition of phosphoric acid, thereby achieving directional crystal growth and structural reconstruction under hydrothermal conditions. The type and addition method of the second acid can alter the coordination / ionic strength environment and nucleation rate of the system, resulting in different morphological characteristics of the product at different scales. The process route of this invention is simple, requires no template agent, uses readily available raw materials, operates under mild conditions, and is easy to scale up. The obtained product has adjustable morphology and good consistency, making it suitable for the large-scale preparation and subsequent application development of titanium phosphate materials.

[0088] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. 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. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0089] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A template-free hydrothermal synthesis method for controlling the morphology of titanium phosphate, characterized in that, The method includes the following steps: S1: Disperse the titanium source in water, add a first acid solution to inhibit hydrolysis, and carry out a dissolution reaction under heating conditions to obtain a titanium source precursor solution. The titanium source is selected from at least one of titanium chloride, titanium sulfate, titanium oxysulfate, titanium citrate, and tetrabutyl titanate. S2: Add phosphoric acid solution with a concentration of 1-14.6 mol / L dropwise to the titanium source precursor solution, stir the reaction, and obtain the pre-reaction solution; S3: Place the pre-reaction liquid in a sealed container and carry out a hydrothermal reaction at 150-180 ℃; S4: After the reaction is complete, the product is subjected to solid-liquid separation, washing and drying to obtain titanium phosphate powder.

2. The hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agent according to claim 1, characterized in that, In step S1, the first acid solution is concentrated sulfuric acid, and the heating conditions are at a temperature of 50-80 ℃ and a reaction time of at least 30 min.

3. The hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agent according to claim 1, characterized in that, After step S1 ends and before step S2 begins, the following is also included: S1.5: Add at least one second acid solution selected from sulfuric acid, citric acid or acetic acid to the titanium source precursor solution and mix thoroughly.

4. The hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agent according to claim 3, characterized in that, In step S1.5, the second acid solution is added dropwise to the titanium source precursor solution, and the stirring time for mixing after addition is more than 30 minutes.

5. The hydrothermal synthesis method for controlling the morphology of titanium phosphate without template agent according to claim 4, characterized in that, In step S1.5, before adding the second acid solution, the titanium source precursor solution is transferred to room temperature.

6. The hydrothermal synthesis method for modulating the morphology of titanium phosphate without template agent according to claim 1, characterized in that, In step S2, the stirring reaction time is at least 30 minutes.

7. The hydrothermal synthesis method according to claim 1, characterized in that, In step S3, the hydrothermal reaction takes 3-24 hours; and the volume of the liquid before reaction in the sealed container does not exceed 70%.

8. The hydrothermal synthesis method according to claim 1, characterized in that, In step S4, the washing is performed with water until the pH of the washing solution is greater than 5; the drying temperature is 120-150 ℃ and the drying time is 6-12 h.

9. A titanium phosphate, characterized in that, The titanium phosphate is prepared by the template-free hydrothermal synthesis method according to any one of claims 1-8.

10. The titanium phosphate according to claim 9, characterized in that, The titanium phosphate has any of the following morphologies: a sheet-like structure, a granular structure, or a three-dimensional microstructure assembled from sheet-like structures.

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