Preparation method and application of nanoscale porous hydroxyapatite material

Abstract

The application provides a preparation method and application of a nanoscale porous hydroxyapatite material, and belongs to the field of inorganic material synthesis. The hydroxyapatite material with high crystallinity, nanoscale, microspherical morphology and multi-level pore structure of microporous and mesoporous is obtained through one reaction of a calcium source suspension liquid containing calcium acetylacetonate and a phosphorus solution containing a trisalt of phosphoric acid through a microchannel reactor, and then secondary crystallization through high-temperature calcination. The material particle size is 30-90nm, the pore size range is 0.5-50nm, heavy metal ion adsorption can be realized, the adsorption rate reaches more than 93.0% when the heavy metal ion concentration is 100-500mg / L, is 1.21 times of the adsorption rate of a hydroxyapatite material prepared by a simple chemical precipitation method, and has a wide application prospect in the field of heavy metal ion adsorption.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material synthesis, specifically relating to a method for preparing and applying nano-sized porous hydroxyapatite material. Background Technology

[0002] Hydroxyapatite (Ca 10 Hydroxyapatite (HAP) has gained popularity due to its prominent role in dental and bone tissues, as well as its excellent biocompatibility and bioactivity, and is widely regarded as a non-toxic and environmentally friendly bioceramic material. With the development of materials synthesis and engineering technology, the application of HAP-based materials has gradually expanded to more disciplines. Furthermore, due to its high chemical and thermal stability, the presence of both acid-base active sites, and tunable pore structure, hydroxyapatite has also become an ideal functional material with great application potential.

[0003] The particle size, crystallinity, and pore size of HAP materials have a significant impact on their physicochemical properties and application performance. Smaller particle size HAP has a larger specific surface area and is more widely used. Methods for controlling the particle size, pore size, and crystallinity of HAP include solvothermal methods, template methods, sol-gel methods, microemulsion methods, and high-temperature calcination methods. Among these methods, the solvothermal method controls the particle size of HAP by controlling the reaction temperature, time, and type of phosphorus source, but it cannot affect the pore size and crystallinity, and its control over particle size is limited. The template method uses surfactants such as polyethylene glycol and Tween 80 as template agents, which can improve the crystallinity of HAP and control the particle size and pore size of the material. However, most of the surfactants used are expensive and highly toxic, and they generate a lot of foam during the reaction, requiring multiple washes to remove residues and generating a lot of waste liquid, resulting in poor environmental performance. The sol-gel method often uses organic solvents as the reaction system, and the resulting products have high crystallinity, small particle size, and high dispersion. However, it has drawbacks such as expensive alkoxide raw materials, highly toxic organic solvents, and few synthesized samples (low yield). The microemulsion method usually produces nanoscale products, which can control the particle size of the product well. However, it requires the addition of organic solvents and surfactants during the reaction, and both organic solvents and surfactants are highly toxic. The high-temperature calcination method involves calcining the material at high temperatures. Although it can improve the crystallinity of the material, the material is prone to agglomeration at high temperatures, leading to larger particle size, and the pore structure may also collapse.

[0004] Chinese invention patent document CN118529701A discloses a method for synthesizing hydroxyapatite with uniform and controllable particle size. This method involves adding a particle size modifier and a charge interference agent to a calcium source reaction solution and a phosphorus source reaction solution. The particle size modifier is ethylene glycol, an organic solvent. As shown in Examples 2 and 7, the essence of this invention is to improve the dispersibility of hydroxyapatite and reduce its agglomeration by adding a second solvent. However, because this process uses ethylene glycol as an organic solvent, it causes environmental pollution. Furthermore, this process only uses hydroxyapatite obtained through wet chemical methods without secondary processing, resulting in low crystallinity of the product, which severely limits its application scenarios. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing nanoscale porous hydroxyapatite materials. This method can prepare microsphere hydroxyapatite materials with nanoscale, microporous, mesoporous, and hierarchical pore structures and high crystallinity in two steps. Compared with traditional preparation methods, it effectively overcomes the waste liquid problem caused by organic solvents and surfactants. At the same time, it also solves the problems of long reaction time and pore collapse during high-temperature calcination of traditional hydroxyapatite materials, so that the hydroxyapatite materials have excellent material properties and broad application prospects in the field of adsorption.

[0006] To address the above problems, the present invention provides a method for preparing nanoscale porous hydroxyapatite materials, specifically including the following steps:

[0007] (1) Mix calcium acetylacetonate, glacial acetic acid and water evenly to obtain a calcium source suspension; mix triphosphate, sugar alcohol solids, hydroxyapatite seeds and water evenly, and adjust the pH to 13-14 with alkaline solids to obtain a phosphorus source solution.

[0008] (2) The calcium source suspension and the phosphorus source solution were simultaneously fed into a microchannel reactor for mixing and reaction. The flow rate and temperature of the reactants were controlled to obtain the reaction solution. After solid-liquid separation and drying, crude hydroxyapatite was obtained.

[0009] (3) The crude hydroxyapatite was calcined at high temperature in an oxygen-containing atmosphere, and then washed and dried to obtain nano-sized porous hydroxyapatite.

[0010] Further, in step (1), the triphosphate is trisodium phosphate, tripotassium phosphate, or triammonium phosphate; the sugar alcohol solid is sorbitol or xylitol; and the alkaline solid is potassium hydroxide or sodium hydroxide.

[0011] Furthermore, in step (1), the hydroxyapatite seed crystals have a particle size of 10-40 nm.

[0012] Further, in step (1), the calcium salt concentration in the calcium source suspension is 1.67-1.72 mol / L, and the amount of glacial acetic acid added is 10%-20% of the total volume of the calcium source suspension; the ratio of triphosphate, sugar alcohol solids, hydroxyapatite seed crystals to water in the phosphorus source solution is 1 mol: 0.8-1.4 mol: 2-7 g: 1000 mL.

[0013] Furthermore, in step (2), the diameter of the microchannel reactor pipe is 8-10 mm; the total length of the pipe is 135-225 m; and the microchannel structure is a coil-type direct-flow channel.

[0014] Further, in step (2), the flow rate of the calcium source suspension and the phosphorus source solution is 0.05-0.2 L / min; the molar ratio of calcium to phosphorus in the calcium source suspension and the phosphorus source solution is 1.67-1.72:1; and the temperature of the reactants is 80-100℃.

[0015] Furthermore, in step (3), the high-temperature calcination conditions are: room temperature is raised to 400-800℃, the heating rate is 10-20℃ / min, and the holding time is 1-3h.

[0016] Furthermore, in step (3), the washing conditions are: washing with pure water one to three times; the drying conditions are: vacuum drying temperature 60-80℃ and drying time 1-3h.

[0017] Another technical problem this invention aims to solve is to provide an application of nanoscale porous hydroxyapatite material for the adsorption of heavy metal ion wastewater. The specific operation steps are as follows:

[0018] Nanoscale porous hydroxyapatite material was activated under vacuum at 100-120℃ for 4-6 hours. The activated nanoscale porous hydroxyapatite material was then added to heavy metal ion wastewater, and the mixture was stirred at room temperature for 1-3 hours. After the reaction, the wastewater was separated from the nanoscale porous hydroxyapatite material by filtration or centrifugation. The concentration of heavy metal ions in the wastewater was then analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The heavy metal ions were identified as Cr. 3+ or Pb 2+ The volume ratio of the nano-porous hydroxyapatite material added to the heavy metal ion wastewater is 0.5-1g:1000mL; the stirring speed is 200-400r / min.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) This invention employs microchannel continuous flow technology combined with a secondary crystallization process involving high-temperature calcination. By optimizing process parameters, nanoscale, microporous, mesoporous, and highly crystalline microspheres of hydroxyapatite are obtained. This process uses water as a solvent and does not employ organic solvents or surfactants, making it a green and environmentally friendly process. Furthermore, the process is simple to operate, has a short reaction time, and is suitable for large-scale production.

[0021] (2) In this invention, calcium acetylacetonate, which has a relatively slow hydrolysis rate, is used as the calcium source to control the release rate of calcium ions. Compared with the use of inorganic calcium salts such as calcium nitrate and calcium chloride in the prior art, this effectively slows down the nucleation rate of calcium in the calcium source suspension and phosphorus in the phosphorus source solution, avoids the rapid aggregation of hydroxyapatite, and provides conditions for obtaining nanoscale microsphere hydroxyapatite materials.

[0022] (3) The glacial acetic acid used in this invention contains abundant carboxyl groups. These carboxyl groups provide a low-energy nucleation pathway by stabilizing the initially formed, unstable calcium-phosphorus clusters, thereby reducing the critical nucleation free energy. Furthermore, the hydroxyapatite seed crystals provide a ready-made nucleation template, allowing for direct epitaxial growth on the existing crystal structure, lowering the nucleation energy barrier, and guiding the crystal's localized growth. Both work synergistically to promote hydroxyapatite nucleation, reduce reaction time, and also help shorten the pipe length of the microchannel reactor, saving on equipment investment costs.

[0023] (4) The microchannel reactor used in this invention has a tube diameter of 8-10 mm. The narrow channel allows for good interfacial contact between the calcium source and the phosphorus source, greatly improving mass and heat transfer efficiency. Compared with traditional batch reactors, it can reduce the instantaneous concentration of calcium source suspension and phosphorus source solution, avoid excessively rapid reaction and agglomeration, significantly reduce particle size, and shorten reaction time. At the same time, by adjusting the pipe length of the microchannel reactor, the purity of the product can be directly affected.

[0024] (5) The high-temperature calcination process used in this invention (heating from room temperature to 300-600℃ at a rate of 10-20℃ / min, and holding for 1-3 hours) achieves the improvement of microporous, mesoporous, hierarchical pore structure and crystallinity. First, under high-temperature calcination, hydroxyapatite undergoes secondary crystallization, causing the crystal structure to rearrange into crystals, thereby improving the crystallinity of the material. Second, in-situ pore formation is performed during calcination. The sugar alcohols adsorbed in the hydroxyapatite pores undergo a chemical in-situ reaction in an oxygen-containing atmosphere, producing carbon dioxide, which can form pores on the material surface, effectively inhibiting pore collapse during high-temperature processes, thus preparing hydroxyapatite materials with microporous, mesoporous, hierarchical pore structures. In addition, sugar alcohols act as dispersants, adsorbing on the surface of hydrocarbon-based apatite, which can prevent excessive agglomeration of hydroxyapatite particles, providing a guarantee for obtaining nano-sized hydroxyapatite materials. At the same time, sugar alcohols are environmentally friendly substances and are safe and harmless.

[0025] (6) The hydroxyapatite material prepared by this invention exhibits outstanding performance in the adsorption of heavy metal ions. It has a hierarchical pore structure with micropores and mesopores, with a particle size of 30-90 nm and a pore size range of 0.5-50 nm. The adsorption rate reaches over 93.0% at heavy metal ion concentrations of 100-500 mg / L, which is 1.21 times that of hydroxyapatite prepared by chemical precipitation without high-temperature calcination secondary treatment, and has good prospects for industrialization. Attached Figure Description

[0026] Figure 1 X-ray diffraction (XRD) patterns of the hydroxyapatite materials prepared in Example 1 and Comparative Examples 1, 4, 6, and 8.

[0027] Figure 2 Particle size determination of the hydroxyapatite material prepared in Example 1 using transmission electron microscopy (TEM);

[0028] Figure 3 The particle size was measured by scanning electron microscopy (SEM) of the hydroxyapatite material prepared in Comparative Example 2.

[0029] Figure 4 SEM particle size analysis of the hydroxyapatite material prepared in Comparative Example 3.

[0030] Figure 5 TEM particle size analysis of the hydroxyapatite material prepared in Comparative Example 5;

[0031] Figure 6 SEM particle size analysis of the hydroxyapatite material prepared in Comparative Example 7;

[0032] Figure 7 The image shows the XRD pattern of the hydroxyapatite material prepared in Comparative Example 9. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application. All technologies implemented based on the above content of the present invention are included within the scope of protection intended by the present invention. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by known methods.

[0034] In one specific embodiment of the present invention, the microchannel reactor used comprises a water-cooled temperature control system, an air-cooled temperature control system, a feeding system, a data acquisition system, and a premixing system. The microchannel reactor is model KX-P3-PRO, branded by Anhui Kexin Microfluidic Chemical Technology Co., Ltd., with an output voltage of 380V, a power of 11kW, a reaction temperature of 0-100℃, a coil-type direct-flow microchannel structure, a pipe length of 45-180m, and a pipe material of fluorinated ethylene propylene copolymer (FEP). Example 1

[0035] (1) Mix 16.9 mol calcium acetylacetonate, 1.5 L glacial acetic acid and 8.5 L pure water evenly to obtain a calcium source suspension; mix 10 mol trisodium phosphate, 12.0 mol sorbitol, 50 g 30 nm hydroxyapatite seed crystals and 10 L pure water evenly, and add solid sodium hydroxide powder to adjust the pH of the solution to 13.6 to obtain a phosphorus source solution;

[0036] (2) The calcium source suspension and the phosphorus source solution were simultaneously fed into a microchannel reactor with a diameter of 9 mm, a pipe length of 180 m, and a coiled direct-flow channel structure through the feeding system of the microchannel reactor for thorough mixing and reaction. The feed flow rates of the calcium source suspension and the phosphorus source solution were both 0.12 L / min. The molar ratio of calcium to phosphorus in the calcium source suspension and the phosphorus source solution was 1.69:1. The reaction temperature was controlled at 90 °C to obtain the reaction completed solution.

[0037] (3) The reaction liquid was separated into solid and liquid and dried to obtain crude hydroxyapatite. The crude hydroxyapatite was then placed in a muffle furnace and calcined in an air atmosphere. The calcination conditions were controlled as follows: room temperature to 500℃, heating rate of 15℃ / min, holding time of 2h. Finally, it was washed twice with pure water and vacuum dried at 70℃ for 2h to obtain nano-porous hydroxyapatite, which was recorded as the sample of Example 1. Example 2

[0038] (1) Mix 16.7 mol calcium acetylacetonate, 1 L glacial acetic acid and 9 L pure water evenly to obtain a calcium source suspension; mix 10 mol tripotassium phosphate, 8.0 mol xylitol, 20 g 10 nm hydroxyapatite seed crystals and 10 L pure water evenly, and add solid potassium hydroxide powder to adjust the pH of the solution to 13.0 to obtain a phosphorus source solution;

[0039] (2) The calcium source suspension and the phosphorus source solution were simultaneously fed into the microchannel reactor with a diameter of 8 mm, a pipe length of 135 m, and a coiled direct-flow channel structure through the feeding system of the microchannel reactor for thorough mixing and reaction. The feed flow rates of the calcium source suspension and the phosphorus source solution were both 0.05 L / min. The molar ratio of calcium to phosphorus in the calcium source suspension and the phosphorus source solution was 1.67:1. The reaction temperature was controlled at 100 °C to obtain the reaction completed solution.

[0040] (3) After the reaction liquid was separated into solid and liquid, crude hydroxyapatite was obtained. Then, the crude hydroxyapatite was placed in a muffle furnace and calcined in an air atmosphere. The calcination conditions were controlled as follows: room temperature was raised to 600℃, the heating rate was 20℃ / min, and the holding time was 1h. Finally, it was washed once with pure water and vacuum dried at 60℃ for 3h to obtain nano-sized porous hydroxyapatite, which was recorded as the sample of Example 2. Example 3

[0041] (1) Mix 17.2 mol calcium acetylacetonate, 2 L glacial acetic acid and 8 L pure water evenly to obtain a calcium source suspension; mix 10 mol triammonium phosphate, 14.0 mol sorbitol, 70 g 40 nm hydroxyapatite seed crystals and 10 L pure water evenly, and add solid sodium hydroxide powder to adjust the pH of the solution to 14.0 to obtain a phosphorus source solution;

[0042] (2) The calcium source suspension and the phosphorus source solution were simultaneously fed into a microchannel reactor with a diameter of 10 mm, a pipe length of 225 m, and a coiled direct-flow channel structure through the feeding system of the microchannel reactor for thorough mixing and reaction. The feed flow rates of the calcium source suspension and the phosphorus source solution were both 0.2 L / min, the molar ratio of calcium to phosphorus in the calcium source suspension and the phosphorus source solution was 1.72:1, and the reaction temperature was controlled at 80 °C to obtain the reaction completed liquid.

[0043] (3) The reaction liquid was separated into solid and liquid to obtain crude hydroxyapatite. The crude hydroxyapatite was then placed in a muffle furnace and calcined in an air atmosphere. The calcination conditions were controlled as follows: room temperature to 300°C, heating rate of 10°C / min, holding time of 3h. Finally, it was washed three times with pure water and vacuum dried at 80°C for 1h to obtain nano-porous hydroxyapatite, which was recorded as the sample of Example 3. Example 4

[0044] (1) Mix 16.8 mol calcium acetylacetonate, 1.2 L glacial acetic acid and 8.8 L pure water evenly to obtain a calcium source suspension; mix 10 mol trisodium phosphate, 13.0 mol sorbitol, 25 g 40 nm hydroxyapatite seed crystals and 10 L pure water evenly, and add solid sodium hydroxide powder to adjust the pH of the solution to 13.8 to obtain a phosphorus source solution;

[0045] (2) The calcium source suspension and the phosphorus source solution were simultaneously fed into the microchannel reactor with a diameter of 9 mm, a pipe length of 180 m, and a coiled direct-flow channel structure through the feeding system of the microchannel reactor for thorough mixing and reaction. The feed flow rates of the calcium source suspension and the phosphorus source solution were both 0.10 L / min. The molar ratio of calcium to phosphorus in the calcium source suspension and the phosphorus source solution was 1.68:1. The reaction temperature was controlled at 85 °C to obtain the reaction completed solution.

[0046] (3) After the reaction liquid was separated into solid and liquid, crude hydroxyapatite was obtained. Then, the crude hydroxyapatite was placed in a muffle furnace and calcined in an oxygen atmosphere. The calcination conditions were controlled as follows: room temperature was raised to 450°C, the heating rate was 15°C / min, and the holding time was 2h. Finally, it was washed twice with pure water and vacuum dried at 70°C for 2h to obtain nano-sized porous hydroxyapatite, which was recorded as the sample of Example 4. Comparative Example 1

[0047] The difference between Comparative Example 1 and Example 1 is that the addition of glacial acetic acid in step (1) and the high-temperature calcination treatment in step (3) are omitted, while the other steps remain unchanged. Comparative Example 2

[0048] The difference between Comparative Example 2 and Example 1 is that no sugar alcohol solids such as sorbitol were added in step (1) and no high-temperature calcination treatment was performed in step (3), while the other steps remained unchanged. Comparative Example 3

[0049] The difference between Comparative Example 3 and Example 1 is that the calcium source in step (1) is different. Calcium acetylacetone is replaced with calcium nitrate, while the other steps remain the same. Comparative Example 4

[0050] The difference between Comparative Example 4 and Example 1 is that the hydroxyapatite seed crystals in step (1) and the high-temperature calcination treatment in step (3) are omitted, while the other steps remain unchanged. Comparative Example 5

[0051] The difference between Comparative Example 5 and Example 1 is that the hydroxyapatite seed crystal size is different in step (1). The hydroxyapatite seed crystal size is replaced with 500 nm, while the other steps remain unchanged. Comparative Example 6

[0052] The difference between Comparative Example 6 and Example 1 is that the pipe length in step (2) is different and the high-temperature calcination treatment in step (3) is not performed. The pipe length is changed to 90m, while the other steps remain the same. Comparative Example 7

[0053] The difference between Comparative Example 7 and Example 1 is that the reactor in step (2) is different; the microchannel reactor is replaced with a reaction vessel, and the operating conditions are as follows:

[0054] 100 mL of calcium source suspension and 100 mL of phosphorus source solution were added to a 500 mL four-necked flask. The molar ratio of calcium to phosphorus in the calcium source suspension and phosphorus source solution was controlled at 1.69:1. The reaction temperature was controlled at 85 °C and the reaction time was controlled at 24 h. The reaction solution was obtained and then filtered to obtain crude hydroxyapatite.

[0055] The crude hydroxyapatite was placed in a muffle furnace and calcined in air. The calcination conditions were controlled as follows: the temperature was raised from room temperature to 600℃ at a rate of 15℃ / min and held for 2 hours. Finally, the hydroxyapatite was obtained by washing it twice with pure water and drying it under vacuum at 70℃ for 2 hours. Comparative Example 8

[0056] The difference between Comparative Example 8 and Example 1 is that there is no high-temperature calcination treatment in step (3), while the other steps remain unchanged. Comparative Example 9

[0057] The difference between Comparative Example 9 and Example 1 is that glacial acetic acid was not added in step (1), while the other steps remained the same.

[0058] Application Example 1

[0059] The nano-sized porous hydroxyapatite materials obtained in Examples 1-4 and the hydroxyapatite materials in Comparative Examples 7-8 were activated at 110°C in a vacuum for 5 hours. Then, 0.8 g of the activated nano-sized porous hydroxyapatite material or hydroxyapatite material was added to 1 L of Cr-containing solution with a concentration of 300 mg / L. 3+ In wastewater, a stirring adsorption reaction was carried out at room temperature for 2 hours, with the stirring speed controlled at 300 r / min. After the reaction was completed, the mixture was filtered to separate the adsorbed nano-sized porous hydroxyapatite material and the adsorbed Cr-containing material. 3+ Wastewater, and then the adsorbed Cr-containing 3+ Wastewater chromium (Cr) was analyzed using inductively coupled plasma mass spectrometry (ICP). 3+ The concentration and heavy metal ion adsorption test results are shown in Table 1.

[0060] The nanoscale porous hydroxyapatite materials obtained in Examples 1-4 and the hydroxyapatite materials obtained in Comparative Examples 7-8 were subjected to nitrogen adsorption-desorption test (N2-BET) to determine the pore size distribution (NLDFT model full pore distribution) and scanning electron microscopy (SEM) or transmission electron microscopy (TEM) to determine the particle size. The test results are shown in Table 1.

[0061] The heavy metal ion adsorption test analysis is as follows: The adsorption rate is calculated by the formula: X = (C0 - C1) / C0 × 100%, where X is the heavy metal ion adsorption rate (%), C0 is the concentration of heavy metal ions in the wastewater before adsorption by the nano-porous hydroxyapatite material (mg / L), and C1 is the concentration of heavy metal ions in the wastewater after adsorption by the nano-porous hydroxyapatite material (mg / L).

[0062] As shown in Table 1, the adsorption test results of the nano-porous hydroxyapatite materials in Examples 1-4 showed an adsorption rate of 93-97.5% for heavy metal ions, which is much higher than that of the hydroxyapatite materials in Comparative Examples 7-8. This is because the particle size and pore size of the two materials are different. Smaller particle size increases the unit contact area for heavy metal ions in wastewater, thereby improving the adsorption efficiency under the same adsorption time. A wider pore size range can adsorb more heavy metal ions, thus improving the adsorption efficiency.

[0063] As shown in Table 1, the pore size distribution test results of the nanoscale porous hydroxyapatite materials in Examples 1-4 have a pore size range of 0.5-50 nm, classifying them as microporous, mesoporous, hierarchical porous materials. Comparative Examples 7 and 8 have pore size ranges of 3.0-42 nm and 5.0-30 nm, respectively, classifying them as mesoporous materials. In the narrow channels, the fluid is in a laminar flow state, and the calcium and phosphorus sources have excellent interfacial contact reaction. The growth and aggregation of particles are precisely controlled, forming porous, loosely packed microspheres. High-temperature calcination causes an in-situ chemical reaction of sugar alcohol solids in the material channels, producing carbon dioxide. This effectively inhibits channel collapse during high-temperature processing, forming more pores on the material surface, thus achieving a wide range of micropore and mesopore coverage. Therefore, the hydroxyapatite materials prepared using a microchannel reactor and high-temperature calcination treatment have a wider pore size range.

[0064] As shown in Table 1, the particle size test results indicate that the nano-sized porous hydroxyapatite materials in Examples 1-4 have a particle size range of 30-90 nm, classifying them as nanoscale materials, while the particle size of Comparative Example 7 is 2 μm. Compared to a reaction vessel, the reactants in a microchannel reactor can be mixed rapidly and uniformly, allowing the entire system to instantly reach extremely high supersaturation, generating a large number of uniformly sized crystal nuclei, forming small and uniform nanoparticles. Therefore, the hydroxyapatite material prepared using a microchannel reactor has an even smaller particle size, classifying it as a nanoscale material.

[0065] Application Example 2

[0066] The nano-sized porous hydroxyapatite material from Example 1 was activated at 100°C under vacuum for 6 hours. Then, 0.5 g of the activated nano-sized porous hydroxyapatite material was added to 1 L of a Cr-containing solution with a concentration of 100 mg / L. 3+In wastewater, a stirred adsorption reaction was carried out at room temperature for 1 hour, with the stirring speed controlled at 200 r / min. After the reaction was completed, centrifugation was performed to obtain the adsorbed nano-sized porous hydroxyapatite material and the wastewater solution. Then, the Cr content in the wastewater solution was analyzed by ICP. 3+ Concentration, as tested, indicates that for heavy metal ions Cr 3+ The adsorption rate is 99.8%.

[0067] Application Example 3

[0068] The nano-sized porous hydroxyapatite material from Example 1 was activated at 120°C under vacuum for 4 hours. Then, 1.0 g of the activated nano-sized porous hydroxyapatite material was added to 1 L of a Cr-containing solution with a concentration of 500 mg / L. 3+ In wastewater, a stirred adsorption reaction was carried out at room temperature for 3 hours, with the stirring speed controlled at 300 r / min. After the reaction was completed, the mixture was filtered to separate the adsorbed nano-sized porous hydroxyapatite material and the wastewater solution. Then, the Cr content in the wastewater solution was analyzed by ICP. 3+ Concentration, as tested, indicates that for heavy metal ions Cr 3+ The adsorption rate is 96.5%.

[0069] Application Example 4

[0070] The difference between Application Example 4 and Application Example 3 lies in the different heavy metal ions; Cr-containing... 3+ Wastewater replaced with Pb 2 + Wastewater, everything else remains unchanged. Tests show that it is effective against the heavy metal ion Pb. 2+ The adsorption rate is 98.8%.

[0071] The results of heavy metal ion adsorption tests, N2-BET pore size distribution tests, and particle size tests of the samples from Examples 1-4, Comparative Examples 2, Comparative Examples 6-8, and Application Examples 2-4 are shown in Table 1.

[0072]

[0073] In summary, by comparing Example 1 with Comparative Examples 1, 4, and 6, and in conjunction with... Figure 1As shown in Table 1, glacial acetic acid and the length of the microchannel reactor affect the preparation of pure-phase hydroxyapatite materials, and whether the hydroxyapatite is pure-phase also affects the adsorption effect of heavy metal ions. Without the addition of glacial acetic acid, a mixed phase of dicalcium phosphate and hydroxyapatite is obtained. This is because glacial acetic acid and hydroxyapatite seed crystals promote the nucleation of hydroxyapatite, reducing reaction time and thus reducing the size of the microchannel reactor, saving investment. Furthermore, if the length of the microchannel reactor is too short, a mixed phase of hydroxyapatite and dicalcium phosphate is obtained, which reduces the adsorption effect on heavy metal ions. Therefore, the addition of glacial acetic acid and hydroxyapatite seed crystals, as well as the length of the microchannel reactor, are important influencing factors in this process.

[0074] A comparison of Example 1 with Comparative Examples 2 and 8, and in conjunction with Table 1, shows that sugar alcohol solids such as sorbitol affect not only particle size but also pore size. Without the addition of sorbitol, the resulting hydroxyapatite material has a larger size. This is because the sorbitol or xylitol solids, which have not fully participated in the in-situ chemical reaction of hydroxyapatite, have a dispersing effect, hindering excessive aggregation of nano-porous hydroxyapatite, thereby controlling the particle size. Simultaneously, with the addition of sorbitol and without high-temperature treatment, the resulting pore size range is narrower. This is because during the in-situ preparation of hydroxyapatite, some sorbitol or xylitol solids are adsorbed into the pores. When the material is calcined at high temperature in an oxygen-containing atmosphere, the sorbitol or xylitol solids undergo an in-situ chemical reaction to produce carbon dioxide gas. The generated CO2 gas not only inhibits pore collapse but also creates pores, thus contributing to the formation of a hierarchical porous structure of micropores and mesopores in hydroxyapatite. Therefore, high-temperature calcination with the addition of sorbitol is a key factor in the preparation of hierarchical pore structures in nanoscale porous hydroxyapatite materials. The pore size range affects the adsorption effect of heavy metal ions; the wider the pore size range, the better the adsorption effect.

[0075] A comparison of Example 1 with Comparative Examples 3, 5, and 7, and in conjunction with Table 1 and... Figure 2 , Figure 4 , Figure 5It is evident that the main factors influencing particle size are the calcium source, hydroxyapatite seed crystals, and the reactor configuration. Different calcium sources result in different particle sizes because they have varying hydrolysis rates. Calcium nitrate hydrolyzes too quickly, reacting rapidly with the phosphorus source to generate a large number of hydroxyapatite nuclei. These nuclei easily agglomerate, leading to larger particle sizes. Adding hydroxyapatite seed crystals of different sizes will produce hydroxyapatite of varying sizes. Appropriate control of the hydroxyapatite seed crystal size is crucial for preparing nanoscale hydroxyapatite. Simultaneously, the reactor configuration also affects the particle size of the hydroxyapatite material. This is because the instantaneous Ca / P concentration in a batch reactor is much higher than that in a microchannel reactor, resulting in a large number of hydroxyapatite nuclei and particle agglomeration, further increasing the particle size. Therefore, the calcium source, hydroxyapatite seed crystals, and reactor configuration are important factors affecting the particle size of hydroxyapatite. Particle size influences the adsorption effect of heavy metal ions; smaller particle sizes result in a larger contact area with the reaction substrate, leading to better adsorption.

[0076] By comparing Example 1 with Comparative Examples 1 and 9, and in conjunction with... Figure 1 and Figure 7 It is known that without the addition of glacial acetic acid and without high-temperature calcination, a mixed-phase product of dicalcium phosphate and hydroxyapatite is obtained, indicating that glacial acetic acid promotes the nucleation of hydroxyapatite and increases the reaction rate. Simultaneously, high-temperature calcination facilitates the decomposition of dicalcium phosphate in the mixed phase, promoting its transformation to tricalcium phosphate, and the resulting product is still a mixed phase of hydroxyapatite and tricalcium phosphate. Therefore, the purpose of the high-temperature treatment in this invention is twofold: first, to achieve secondary crystallization, enhancing the intensity of the hydroxyapatite diffraction peaks and improving the crystallinity of the material; and second, to obtain a hierarchical porous structure of micropores and mesopores from the sorbitol or xylitol solids within the pores of the hydroxyapatite material after calcination.

[0077] In summary, glacial acetic acid and pipe length affect the pure phase of hydroxyapatite; calcium source, hydroxyapatite seed crystals, sugar alcohol solids such as sorbitol or xylitol, and reactor configuration affect particle size; sugar alcohol solids such as sorbitol or xylitol also affect the pore size range of the material. The adsorption performance of heavy metal ion wastewater is limited by the particle size and pore size range of the material. Smaller particle sizes increase the specific surface area of ​​the material, thereby improving the contact efficiency and mass transfer rate with heavy metal ions and shortening the adsorption equilibrium time. Simultaneously, a wider pore size range provides more adsorption channels and sites for metal ions of different sizes, thus comprehensively improving the adsorption effect.

[0078] Figure 1The images show the X-ray diffraction (XRD) patterns of the hydroxyapatite materials prepared in Example 1 and Comparative Examples 1, 4, 6, and 8. As can be seen from the figures, Example 1 and Comparative Example 8 are single-phase hydroxyapatite, corresponding to standard card PDF#97-009-4822 (Ca...). 10 (PO4)6(OH)2), but the crystallinity of Comparative Example 8 is much lower than that of Example 1. This is mainly because the diffraction peak intensity of the material without high-temperature calcination is much lower than that of Example 1; Comparative Examples 1, 4, and 6 are all mixed phases of calcium hydrogen phosphate and hydroxyapatite, corresponding to standard cards PDF#97-000-0504 (CaHPO4) and PDF#97-009-4822 (Ca 10 (PO4)6(OH)2), thus it can be seen that hydroxyapatite seed crystals, glacial acetic acid, and pipe length all affect the preparation of single phase of hydroxyapatite materials.

[0079] Figure 2 The particle size of the hydroxyapatite material prepared in Example 1 is measured by transmission electron microscopy (TEM). As shown in the figure, the hydroxyapatite material prepared in Example 1 has a microsphere morphology of about 50 nm and a uniform morphology.

[0080] Figure 3 The particle size of the hydroxyapatite material prepared in Comparative Example 2 was measured by scanning electron microscopy (SEM). The figure shows that the hydroxyapatite material prepared without sorbitol is prone to agglomeration and is uneven, with a particle size of approximately 1.25 μm. This indicates that sorbitol has a dispersing effect, thereby inhibiting agglomeration and achieving the purpose of controlling particle size.

[0081] Figure 4 The particle size of the hydroxyapatite material prepared in Comparative Example 3 was measured by scanning electron microscopy (SEM). As shown in the figure, the particle size of the hydroxyapatite material prepared in Comparative Example 3 is about 1.2 μm, which is much larger than that of Example 1. However, the morphology is basically microspheres and is not uniform, indicating that different calcium sources will affect the particle size and morphological uniformity. It is important to select an appropriate calcium source.

[0082] Figure 5 TEM particle size analysis was performed on the hydroxyapatite material prepared in Comparative Example 5. As shown in the figure, the particle size of the hydroxyapatite material prepared in Comparative Example 5 is approximately 0.8 μm, which is significantly larger than the particle size of Example 1.

[0083] Figure 6 The SEM particle size distribution of the hydroxyapatite material prepared in Comparative Example 7 is shown in the figure. As can be seen from the figure, the particle size of the hydroxyapatite material prepared in Comparative Example 7 is approximately 2.0 μm, which is significantly larger than that of Example 1. This indicates that the type of reactor can affect the particle size, and a suitable reactor should be selected accordingly.

[0084] Figure 7 The image shows the XRD pattern of the hydroxyapatite material prepared in Comparative Example 9. As can be seen from the image, this hydroxyapatite is a miscible phase, specifically a mixture of hydroxyapatite and tricalcium phosphate, corresponding to standard card PDF#97-009-4822 (Ca...). 10 (PO4)6(OH)2) and PDF#86-1585 (Ca3(PO4)2) indicate that glacial acetic acid promotes the nucleation of hydroxyapatite, which can form a single hydroxyapatite phase and increase the reaction rate.

Claims

1. A method for preparing a nano-sized porous hydroxyapatite material, characterized in that, Includes the following steps: (1) Mix calcium acetylacetonate, glacial acetic acid and water to obtain a calcium source suspension; mix triphosphate, sugar alcohol solids, hydroxyapatite seeds and water, and adjust the pH to 13-14 to obtain a phosphorus source solution; (2) The calcium source suspension and the phosphorus source solution were simultaneously fed into a microchannel reactor to react and obtain the reaction completed liquid. After solid-liquid separation and drying, crude hydroxyapatite was obtained. (3) The crude hydroxyapatite was calcined at high temperature in an oxygen-containing atmosphere, and then washed and dried to obtain nano-sized porous hydroxyapatite. In step (1), the calcium salt concentration in the calcium source suspension is 1.67-1.72 mol / L, and the amount of glacial acetic acid added is 10%-20% of the total volume of the calcium source suspension; the ratio of triphosphate, sugar alcohol solids, hydroxyapatite seed crystals, and water in the phosphorus source solution is 1 mol: 0.8-1.4 mol: 2-7 g: 1000 mL; the particle size of the hydroxyapatite seed crystals is 10-40 nm. In step (2), the diameter of the microchannel reactor is 8-10 mm; the total length of the pipeline is 135-225 m; the flow rate of the calcium source suspension and the phosphorus source solution is 0.05-0.2 L / min; the molar ratio of calcium to phosphorus in the calcium source suspension and the phosphorus source solution is 1.67-1.72:1; and the temperature of the reactants is 80-100 °C. In step (3), the high-temperature calcination conditions are: room temperature is raised to 300-600℃, the heating rate is 10-20℃ / min, and the holding time is 1-3h.

2. The method for preparing nanoscale porous hydroxyapatite material according to claim 1, characterized in that, In step (1), the triphosphate is trisodium phosphate, tripotassium phosphate, or triammonium phosphate; the sugar alcohol solid is sorbitol or xylitol; and the pH is adjusted using potassium hydroxide or sodium hydroxide.

3. The method for preparing nanoscale porous hydroxyapatite material according to claim 1, characterized in that, In step (2), the channel structure of the microchannel reactor is a coil-type direct-flow channel.

4. The method for preparing nanoscale porous hydroxyapatite material according to claim 1, characterized in that, In step (3), the washing conditions are: washing with pure water one to three times; the drying conditions are: vacuum drying temperature 60-80℃ and drying time 1-3h.

5. The application of the nano-porous hydroxyapatite material prepared by the preparation method according to any one of claims 1-4, characterized in that, It was used for the adsorption of heavy metal ions in wastewater.

6. The application of the nanoscale porous hydroxyapatite material according to claim 5, characterized in that, Includes the following steps: The nano-sized porous hydroxyapatite material was activated in a vacuum at 100-120℃ for 4-6 hours. Then, the activated nano-sized porous hydroxyapatite material was added to the wastewater containing heavy metal ions and stirred at room temperature for 1-3 hours. After the reaction was completed, the nano-sized porous hydroxyapatite material was separated by filtration or centrifugation. Then, the concentration of heavy metal ions in the wastewater was analyzed by inductively coupled plasma mass spectrometry. The heavy metal ion is Cr. 3+ or Pb 2+ ; The volume ratio of the nano-porous hydroxyapatite material added to the heavy metal ion wastewater is 0.5-1g:1000mL; the stirring speed is 200-400r / min.

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