Method for microwave-assisted preparation of hydroxy calcium phosphate and application

Abstract

The invention provides a microwave-assisted hydroxy calcium phosphate preparation method and application. According to the method, hydroxy calcium phosphate is cooperatively prepared with a chitosan molecular template under the assistance of a microwave heat effect. The molecular chain of chitosan can be stretched through the microwave heat effect, so that amino groups and calcium ions form a stable complex, free diffusion of the calcium ions is inhibited, and the nucleation rate of hydroxyl calcium phosphate crystals is regulated and controlled. Local high temperature generated by microwaves can accelerate hydrolysis of diammonium hydrogen phosphate and promote rapid combination of phosphate ions and calcium ions. Under the coordination action of chitosan molecules and calcium ions, the chitosan molecules selectively adsorb on the crystal face (001) of the hydroxyl calcium phosphate crystal, the growth of the crystal face is inhibited, and the hydroxyl calcium phosphate is promoted to preferentially grow along the crystal faces (100) and (010) to form a sheet structure; meanwhile, the grain size and impurity content of crystal growth are also controlled. The method is short in preparation time, low in preparation temperature and suitable for mass production, and energy consumption is reduced. The hydroxyl calcium phosphate prepared by the method is used for in-vivo implantation and fluorine-containing wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydroxyapatite preparation, and relates to a method for preparing hydroxyapatite assisted by microwave and its application. Background Art

[0002] Hydroxyapatite [Ca 10 (PO4)6(OH)2] is a biodegradable inorganic material with good biocompatibility and bioactivity, and is the main component of bones and teeth. Hydroxyapatite can chemically bond with body tissues at the interface, release ions harmless to the body, participate in body metabolism, stimulate or induce osteoproliferation, promote the repair of defective tissues, and can be applied to fields such as bone defect repair, skin filling, moderate to severe wrinkles of facial skin and subcutaneous tissues, and hand rejuvenation.

[0003] The purity and crystallinity of hydroxyapatite are the main factors affecting the mechanical properties and safety of the material, and the synthesis method of biomedical hydroxyapatite needs to take into account the product purity, morphology controllability and process greenness. The patent with the publication number CN1039567A discloses a method for preparing hydroxyapatite for special use in defluorination of mineral water. This method uses the coprecipitation method to prepare hydroxyapatite. Although large-scale production can be achieved, the impurity content of the product is >2%, the purity is insufficient, and the grains are prone to agglomeration. Additional dispersants such as polyethylene glycol need to be added, resulting in high costs and great difficulty in post-treatment. The patent with the publication number CN108689394A discloses a method for preparing nano calcium hydrogen phosphate. This method uses the hydrothermal method for preparation, and the preparation temperature is 180 - 220°C, the preparation pressure is 5 - 10 MPa, and the preparation time is >12 hours or even 24 hours. Therefore, this preparation method has high energy consumption, large equipment investment, and a long reaction cycle, which limits industrial application. The patent with the publication number CN110721348A discloses a natural silk-reinforced hydroxyapatite / chitosan composite membrane and its preparation method. This method relies on natural templates such as eggshell membranes and silk proteins to prepare hydroxyapatite, but when removing the template, a calcination temperature of >500°C is required, resulting in sintering and agglomeration of hydroxyapatite grains, and the template source is unstable, making it difficult to produce standardized products. The patent with the publication number CN103771381A discloses a method for producing nano calcium hydrogen phosphate. This method uses the ultrasonic radiation method to prepare nano calcium hydrogen phosphate. Although it can refine the grains, it needs to use an inverse emulsion system such as Span-80 / Tween-80, and the residual organic matter will affect the biocompatibility of the product, and the energy consumption of the ultrasonic equipment is relatively high.

[0004] In summary, the existing methods for preparing hydroxyapatite have a long preparation time and a high impurity content in the product. Summary of the Invention

[0005] The object of the present invention is to provide a method and application for microwave-assisted preparation of calcium hydroxyphosphate, so as to solve the problems of high impurity content and long preparation time of calcium hydroxyphosphate prepared by existing preparation methods.

[0006] To achieve the above object, the present invention adopts the following technical solutions: The present application provides a method for microwave-assisted preparation of calcium hydroxyphosphate, and the method includes: S01: Adding a calcium source to a chitosan solution, and performing ultrasonic treatment at room temperature to form a complex solution, wherein the Ca 2+ concentration in the complex solution is 0.3 ± 0.02 M.

[0007] Dissolve chitosan with a deacetylation degree ≥ 90% and a molecular weight of 50 - 100 kDa in an aqueous acetic acid solution with a concentration of 1% to prepare a chitosan solution with a mass concentration of 0.5 - 1.5%. In the present application, chitosan is used as a complexing agent for calcium ions to disperse the calcium source, thereby regulating the crystal growth rate of calcium hydroxyphosphate. If the concentration of chitosan is too high, it is easy to lock the calcium source, slow down the reaction rate, and result in a lower conversion rate. Therefore, in the present application, the mass concentration of the chitosan solution is 0.5 - 1.5%, accurate to 0.01%. More preferably, the mass concentration of the chitosan solution is 0.8%.

[0008] Add the calcium source to the chitosan solution, and magnetically stir until the calcium source is completely dissolved. After complete dissolution, perform ultrasonic treatment at room temperature with an ultrasonic power of 100 - 200 W for 15 - 25 min to form a uniform and stable chitosan-Ca 2+ complex solution.

[0009] In the present application, when the Ca 2+ concentration is relatively high, it is difficult to control the reaction rate, and it is easy to cause crystal inclusion, which in turn easily leads to a lower product purity. Therefore, it is necessary to strictly control the Ca 2+ concentration to be 0.3 ± 0.02 M.

[0010] In the present application, the calcium source is an inorganic water-soluble calcium such as calcium nitrate, calcium chloride or calcium carbonate. More preferably, the calcium source is calcium nitrate, the ultrasonic power is 200 W, and the ultrasonic time is 15 min.

[0011] S02: Adding a diammonium hydrogen phosphate solution and ammonia water to the complex solution to form a mixed solution; wherein, during the dropping process, the Ca / P molar ratio is maintained at 1.67, and the pH is maintained at 9.0 - 9.5.

[0012] Under constant stirring at 300 rpm, a diammonium hydrogen phosphate solution with a molar concentration of 0.14 - 0.18 M was added dropwise to the complex solution at a dropping rate of 1 - 10 ml / min. During the dropping process, the Ca / P molar ratio was maintained at 1.67. While adding the diammonium hydrogen phosphate solution, 25% ammonia water with a mass concentration was added dropwise to the complex solution at a dropping rate of 0.2 - 2 ml / min. During the dropping process, the pH was maintained at 9.0 - 9.5 to form a mixed solution.

[0013] Since hydroxyl groups, phosphate groups, and calcium ions can form a wide variety of double salts according to different ratios, in this application, the Ca / P molar ratio and pH are strictly controlled to form uniform calcium hydroxyphosphate.

[0014] S03: The mixed solution was reacted for 15 - 25 min under the conditions of a temperature of 60 - 70 °C and a microwave power of 200 - 400 W, and calcium hydroxyphosphate was obtained after filtration, washing, vacuum drying, and pulverization.

[0015] The mixed solution was transferred to a microwave reactor with a polytetrafluoroethylene inner lining and reacted for 15 - 25 min under the conditions of a temperature of 60 - 70 °C and a microwave power of 200 - 400 W. During the reaction process, the reaction temperature was monitored in real time by an infrared thermometer to ensure that the temperature fluctuation ≤ ±2 °C to avoid the generation of impurities. After the reaction, the reaction product was filtered using a double-layer membrane filter, and the filter cake was washed 3 times with deionized water, and ultrasonic dispersion was carried out for 5 min during each washing process. The filter cake obtained after washing was placed in a vacuum drying oven at -0.1 MPa and dried at 60 °C for 8 h, and finally, calcium hydroxyphosphate was obtained after grinding and pulverization with an agate.

[0016] In this application, under the action of microwaves, the microwave thermal effect can cause the molecular chains of chitosan to stretch, enabling the amino group to form a stable complex with calcium ions, thereby inhibiting the free diffusion of calcium ions and regulating the nucleation rate of calcium hydroxyphosphate crystals. The instantaneous microwave temperature can reach 120 °C, and this locally high temperature generated can accelerate the hydrolysis of diammonium hydrogen phosphate and promote the rapid combination of phosphate ions and calcium ions.

[0017] In addition, through the coordination of chitosan molecules with calcium ions, the selective adsorption of chitosan molecules on the (001) crystal plane of calcium hydroxyphosphate crystals is achieved, inhibiting the growth of this crystal plane and promoting the preferential growth of calcium hydroxyphosphate along the (100) and (010) crystal planes to form a flaky structure; at the same time, the particle size and impurity content of crystal growth are also controlled.

[0018] In this application, the calcium hydroxyphosphate is flaky calcium hydroxyphosphate. By adjusting the chitosan concentration and microwave power, the particle size, thickness, and specific surface area of calcium hydroxyphosphate can be adjusted so that the particle size is 30 - 400 nm, the thickness is 10 - 50 nm, and the specific surface area ≥ 50 m2 / g.

[0019] The calcium hydroxyphosphate prepared in this application is used for in vivo implantation and treatment of fluoride-containing wastewater.

[0020] The present invention has the following beneficial effects: (1) In this application, microwave thermal effect is used to assist and chitosan molecular template is used to synergistically prepare calcium hydroxyphosphate. The microwave thermal effect can make the molecular chain of chitosan stretch, enabling the amino group to form a stable complex with calcium ions, thereby inhibiting the free diffusion of calcium ions and regulating the nucleation rate of calcium hydroxyphosphate crystals. In addition, the local high temperature generated by microwave can also accelerate the hydrolysis of diammonium hydrogen phosphate and promote the rapid combination of phosphate ions and calcium ions.

[0021] (2) In this application, through the coordination of chitosan molecules and calcium ions, the selective adsorption of chitosan molecules on the (001) crystal plane of calcium hydroxyphosphate crystals is achieved, inhibiting the growth of this crystal plane and promoting the preferential growth of calcium hydroxyphosphate along the (100) and (010) crystal planes to form a flaky structure; at the same time, the particle size and impurity content of crystal growth are also controlled.

[0022] (3) The preparation time of calcium hydroxyphosphate in this application is 15 - 25 min, which is only 1 / 36 of the preparation time of the traditional hydrothermal method, greatly shortening the preparation time and significantly reducing the production temperature, which reduces energy consumption and is suitable for mass production.

[0023] (4) The method of using microwave thermal effect to assist and chitosan molecular template to prepare calcium hydroxyphosphate can precisely control the reaction kinetics and crystal growth path, realizing the efficient synthesis of nano-scale medical calcium hydroxyphosphate, and is applicable to biomedical materials such as bone repair scaffolds and drug carriers, as well as environmental protection adsorbent fields such as treatment of fluoride-containing wastewater. Description of the Drawings

[0024] Figure 1 It is the SEM image of the calcium hydroxyphosphate prepared in Example 1 of this application; Figure 2 It is the XRD image of the calcium hydroxyphosphate prepared in Example 1 of this application. Detailed Embodiments

[0025] The technical solutions of the present invention will be further explained and illustrated below through specific embodiments.

[0026] Example 1 The embodiment of this application provides a method for microwave-assisted preparation of calcium hydroxyphosphate, and this method includes: S101: Dissolve chitosan with a deacetylation degree of ≥90%, a molecular weight of 80 kDa, and a mass of 0.8 g in an acetic acid aqueous solution with a concentration of 1% and a volume of 100 mL to prepare a chitosan solution with a mass concentration of 0.8%. Slowly add 4.92 g (30 mmol) of calcium nitrate to the chitosan solution and stir magnetically until the calcium source is completely dissolved. After complete dissolution, perform ultrasonic treatment for 15 min at room temperature with an ultrasonic power of 200 W to form a uniform and stable chitosan-Ca 2+ complex solution.

[0027] S102: Under constant stirring at 300 rpm, add a diammonium hydrogen phosphate solution with a mass of 2.38 g and a molar concentration of 0.18 M to the complex solution at a dropping rate of 5 ml / min. During the dropping process, maintain the Ca / P molar ratio at 1.67. While adding the diammonium hydrogen phosphate solution, add 25% ammonia water with a mass concentration at a dropping rate of 0.5 ml / min to the complex solution. During the dropping process, maintain the pH at 9.2 ± 0.2 to form a mixed solution.

[0028] S103: Transfer the mixed solution to a microwave reactor with a PTFE liner and react for 20 min at a temperature of 65°C and a microwave power of 300 W. During the reaction process, monitor the reaction temperature in real time through an infrared thermometer to ensure that the temperature fluctuation is ≤±2°C to avoid the generation of impurities. After the reaction, filter the reaction product using a double-layer membrane filter. Wash the filter cake 3 times with deionized water, and perform ultrasonic dispersion for 5 min during each washing process. Place the filter cake obtained after washing in a vacuum drying oven at -0.1 MPa and dry at 60°C for 8 h. Finally, obtain flaky calcium hydroxyphosphate after grinding and pulverizing with an agate.

[0029] Example 2 The embodiment of the present application provides a method for microwave-assisted preparation of calcium hydroxyphosphate, which includes: S201: Dissolve chitosan with a deacetylation degree of ≥90%, a molecular weight of 50 kDa, and a mass of 0.6 g in an acetic acid aqueous solution with a concentration of 1% and a volume of 80 mL to prepare a chitosan solution with a mass concentration of 0.75%. Add 3.94 g (24 mmol) of calcium nitrate to the chitosan solution and stir magnetically until the calcium source is completely dissolved. After complete dissolution, perform ultrasonic treatment for 15 min at room temperature with an ultrasonic power of 100 W to form a uniform and stable chitosan-Ca 2+ complex solution.

[0030] S202: Under the condition of constant-speed stirring at 300 rpm, the ammonium hydrogen phosphate solution with a mass of 1.90 g and a molar concentration of 0.144 M was added dropwise to the complex solution at a dropping rate of 1 ml / min. During the dropping process, the Ca / P molar ratio was maintained at 1.67. While adding the ammonium hydrogen phosphate solution dropwise, the ammonia water with a mass concentration of 25% was added dropwise to the complex solution at a dropping rate of 0.2 ml / min. During the dropping process, the pH was maintained at 9.0 ± 0.2 to form a mixed solution.

[0031] S203: Transfer the mixed solution to a microwave reactor with a polytetrafluoroethylene inner lining and react for 25 min under the conditions of a temperature of 65°C and a microwave power of 250 W. During the reaction process, the reaction temperature was monitored in real time by an infrared thermometer to ensure that the temperature fluctuation ≤ ±2°C to avoid the generation of impurities. After the reaction, the reaction product was filtered using a double-layer membrane filter, and the filter cake was washed 3 times with deionized water, and ultrasonic dispersion was carried out for 5 min during each washing process. The filter cake obtained after the washing was placed in a vacuum drying oven at -0.1 MPa and dried at 60°C for 8 h. Finally, it was ground and crushed with agate to obtain flaky calcium hydroxyphosphate.

[0032] Example 3 The embodiment of the present application provides a method for preparing calcium hydroxyphosphate assisted by microwave, and the method includes: S301: Dissolve 0.5 g of chitosan with a deacetylation degree ≥ 90%, a molecular weight of 100 kDa in 100 mL of acetic acid aqueous solution with a concentration of 1% to prepare a chitosan solution with a mass concentration of 0.5%. Add 3.336 g (30 mmol) of calcium chloride to the chitosan solution and stir magnetically until the calcium source is completely dissolved. After complete dissolution, ultrasonic treatment was carried out for 25 min at room temperature and an ultrasonic power of 100 W to form a uniform and stable chitosan-Ca 2+ complex solution.

[0033] S302: Under the condition of constant-speed stirring at 300 rpm, the ammonium hydrogen phosphate solution with a mass of 2.377 g and a molar concentration of 0.18 M was added dropwise to the complex solution at a dropping rate of 10 ml / min. During the dropping process, the Ca / P molar ratio was maintained at 1.67. While adding the ammonium hydrogen phosphate solution dropwise, the ammonia water with a mass concentration of 25% was added dropwise to the complex solution at a dropping rate of 2 ml / min. During the dropping process, the pH was maintained at 9.5 ± 0.2 to form a mixed solution.

[0034] S303: Transfer the mixed solution to a microwave reactor with a polytetrafluoroethylene lining, and react for 15 min at a temperature of 70 °C and a microwave power of 400 W. During the reaction, monitor the reaction temperature in real time through an infrared thermometer to ensure that the temperature fluctuation ≤ ±2 °C to avoid the generation of impurities. After the reaction, filter the reaction product using a double-layer membrane filter. Wash the filter cake 3 times with deionized water, and perform ultrasonic dispersion for 5 min during each washing process. Place the filter cake obtained after washing in a vacuum drying oven at -0.1 MPa and dry it at 60 °C for 8 h. Finally, obtain flaky calcium hydroxyphosphate through grinding and pulverization with an agate mortar.

[0035] Comparative Example 1 The comparative example of this application provides a method for preparing calcium hydroxyphosphate by a hydrothermal method, which includes: D101: Mix 4.91 g (30 mmol) of calcium nitrate with 2.39 g (18 mmol) of diammonium hydrogen phosphate solution. During the reaction, slowly add 25% ammonia water dropwise, and maintain the pH at 9.2 ± 0.2 during the dropping process to form a mixed solution.

[0036] D102: Carry out a hydrothermal reaction on the mixed solution at 180 °C for 12 h. After the reaction, centrifuge, wash the precipitate 3 times with deionized water, place the filter cake obtained after washing in a vacuum drying oven at -0.1 MPa and dry it at 60 °C for 8 h. Finally, obtain massive calcium hydroxyphosphate through grinding and pulverization with an agate mortar.

[0037] Perform SEM and XRD tests on the flaky calcium hydroxyphosphate prepared in Example 1 respectively, and obtain Figure 1 、 2 . From Figure 1 , it can be seen that the calcium hydroxyphosphate prepared in Example 1 of this application is flaky, with a particle size of 30 - 400 nm and a thickness of 10 - 50 nm. From Figure 2 , it can be seen that the crystallinity of the calcium hydroxyphosphate prepared in Example 1 is relatively high; compared with the standard spectrum, the characteristic peaks of the XRD of the calcium hydroxyphosphate prepared in Example 1 are obvious, and there are no other obvious impurity peaks, indicating that the content of the impurity phase of the prepared calcium hydroxyphosphate is relatively low.

[0038] Perform measurements on the shape, pH value, specific surface area, crystallinity, and impurity content of the calcium hydroxyphosphate prepared in Examples 1 - 3 and Comparative Example 1 respectively, and obtain Table 1.

[0039] Table 1: Detection data of Examples 1 - 3 and Comparative Example 1 As can be seen from Table 1, the Ca / P molar ratios in Examples 1-3 were controlled to be 1.67-1.69. The specific surface area and crystallinity of the hydroxyapatite prepared were much greater than those of the hydroxyapatite in Comparative Example 1, and the impurity content was much less than that of the hydroxyapatite in Comparative Example 1. This indicates that the method provided in the embodiments of the present application can improve the specific surface area and crystallinity of hydroxyapatite and reduce the impurity content.

[0040] After immersing the hydroxyapatite prepared in Example 1 of the present application and Comparative Example 1 in SBF simulated body fluid for 7 days respectively, the deposition amount of apatite was measured. After measurement, the deposition amounts of apatite of the hydroxyapatite in Example 1 and Comparative Example 1 were 0.85 mg / cm 2 and 0.42 mg / cm 2 respectively. This indicates that the hydroxyapatite prepared in Example 1 has higher biocompatibility in vivo, is more conducive to tightly binding with surrounding tissues after being implanted in vivo, and promotes the growth and repair of bone tissues.

[0041] In addition, equal masses of the hydroxyapatite prepared in Example 1 of the present application and commercially available activated alumina were respectively placed in equal volumes of fluoride-containing wastewater. After adsorption for the same period of time, the maximum adsorption capacity of the hydroxyapatite prepared in Example 1 of the present application was 38 mg / g, and the maximum adsorption capacity of the commercially available activated alumina was 25 mg / g. This indicates that the hydroxyapatite prepared in the embodiments of the present application can effectively treat fluoride-containing wastewater.

[0042] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing calcium hydroxyphosphate by microwave assistance, characterized in that, Comprising: Add a calcium source to the chitosan solution and perform ultrasonic treatment at room temperature to form a complex solution, where the Ca 2+ concentration in the complex solution is 0.3 ± 0.02 M; Adding a diammonium hydrogen phosphate solution and ammonia water to the complex solution to form a mixed solution; wherein, during the dropping process, the Ca / P molar ratio is maintained at 1.67 and the pH is maintained at 9.0 - 9.5; The mixed solution reacts for 15 - 25 min under the conditions of a temperature of 60 - 70 °C and a microwave power of 200 - 400 W, and hydroxyapatite is obtained after filtration, washing, vacuum drying, and pulverization.

2. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, characterized in that, The preparation method of the chitosan solution comprises: dissolving chitosan in an acetic acid aqueous solution with a concentration of 1% to form a chitosan solution with a mass concentration of 0.5 - 1.5%.

3. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, wherein The calcium source includes calcium nitrate, calcium chloride, or calcium carbonate.

4. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, wherein, The ultrasonic power is 100 - 200 W and the ultrasonic time is 15 - 25 min.

5. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, wherein The dropping rate of the diammonium hydrogen phosphate solution is 1 - 10 ml / min, and the dropping rate of ammonia water is 0.2 - 2 ml / min.

6. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, wherein, The molar concentration of the diammonium hydrogen phosphate solution is 0.14 - 0.18 M, and the mass concentration of ammonia water is 25%.

7. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, characterized in that, The temperature fluctuation during the microwave reaction of the mixed solution is ≤ ±2 °C.

8. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, wherein Filter using a double-layer membrane filter, and wash the filter cake 3 times with deionized water, and perform ultrasonic dispersion for 5 min during each washing process.

9. The method for preparing calcium hydroxyphosphate by microwave assistance according to claim 1, wherein The vacuum drying pressure is -0.1 MPa and the drying temperature is 60 °C.

10. The hydroxyapatite prepared by the method according to any one of claims 1 - 9 is used for treating fluoride-containing wastewater.

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