Monodisperse hexagonal bismuth photothermal nanoparticles and a preparation method thereof

Abstract

The application relates to the technical field of nanomaterial synthesis, and particularly discloses monodisperse hexagonal crystal bismuth photothermal nanoparticles and a preparation method thereof. The nanoparticles have a core-shell structure, the core is hexagonal crystal metal bismuth, and the shell is a polyvinylpyrrolidone film. The particle size of the nanoparticles is 60-80 nm. The polyol solvothermal method is used to complete the synthesis of the bismuth nanoparticles under low-temperature conditions of 80 DEG C, without special equipment such as a high-temperature and high-pressure reaction kettle, and without special energy input such as microwaves and lasers. Compared with the traditional hydrothermal method (usually requiring high temperature above 100 DEG C) and the solvothermal method (usually requiring high temperature and high pressure), the reaction conditions of the application are more moderate, the energy consumption and equipment cost are significantly reduced, and the application is conducive to large-scale industrial production and popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial synthesis technology, specifically relating to a monodisperse hexagonal bismuth photothermal nanoparticle and its preparation method. Background Technology

[0002] Photothermal therapy is an emerging cancer treatment strategy. Its basic principle is to utilize nanomaterials with photothermal conversion capabilities as photothermal agents. Under irradiation with excitation light of a specific wavelength, the absorbed light energy is converted into heat energy, raising the local temperature to a level capable of ablating tumor cells. Compared with traditional surgical treatments, radiotherapy, and chemotherapy, photothermal therapy has significant advantages such as ease of operation, short treatment time, minimal trauma, and rapid recovery. Furthermore, photothermal therapy is non-invasive or minimally invasive, has good biocompatibility, and has the potential to treat a wide range of tumor types, thus attracting widespread attention in the field of cancer treatment. With the rapid development of nanomedicine, photothermal therapy is no longer limited to a single treatment modality but is gradually developing towards multimodal combined therapy and integrated diagnosis and treatment. Researchers are committed to constructing combined treatment platforms integrating multiple therapeutic functions such as photothermal therapy, photodynamic therapy, chemodynamic therapy, and sonodynamic therapy. Simultaneously, they are combining photothermal agents with functional components such as imaging contrast agents, targeted ligands, and therapeutic drugs to develop integrated diagnostic and therapeutic nanoplatforms. Under this research trend, the development of novel photothermal agents is of great scientific significance and application value for promoting the development of photothermal therapy and constructing multifunctional drug delivery systems;

[0003] Bismuth is considered a green metallic element with good biocompatibility, and its compounds, such as bismuth subsalicylate and bismuth subnitrate, have long been developed as clinical treatments for gastrointestinal diseases. In recent years, research has discovered that bismuth nanoparticles possess excellent photothermal conversion properties, exhibiting strong absorption and high photothermal conversion efficiency in the near-infrared region, making them a highly promising novel photothermal agent material. Furthermore, bismuth has a high X-ray attenuation coefficient, making it suitable as a contrast agent in computed tomography imaging, providing a natural advantage for constructing integrated diagnostic and therapeutic nanoplatforms. Therefore, developing methods for synthesizing bismuth nanoparticles with controllable morphology, uniform particle size, and good dispersibility has significant research value and application prospects.

[0004] Currently, the main methods for synthesizing bismuth nanoparticles include hydrothermal synthesis, solvothermal synthesis, ionothermal synthesis, sol-gel synthesis, microemulsion synthesis, chemical reduction synthesis, microwave-assisted synthesis, and sonochemical and laser-mediated synthesis. Hydrothermal synthesis is typically carried out under high temperature and high pressure conditions, with crystal growth occurring in a sealed high-pressure reactor using water as the solvent; the reaction temperature usually exceeds 100°C. Solvothermal synthesis is similar to hydrothermal synthesis, but uses organic solvents instead of water as the reaction medium. Commonly used organic solvents include toluene, decahydronaphthalene, and octadecene. The size and morphology of the nanocrystals can be controlled by adjusting the reaction temperature and the concentration of the bismuth precursor. Ionothermal synthesis uses ionic liquids as the solvent medium, utilizing the low interfacial tension and high nucleation rate of ionic liquids to prepare ultrafine nanoparticles. However, all three of the above-mentioned thermal synthesis methods have certain limitations: hydrothermal and solvothermal methods typically require high reaction temperatures and pressures, placing special demands on reaction equipment and safe operation; the use of toxic organic solvents in solvothermal methods increases the risk of environmental pollution and biosafety hazards; ionic thermal methods involve high costs of ionic liquids and complex post-processing, hindering large-scale industrial production. The sol-gel method is commonly used to prepare metal oxide nanomaterials and can be used to synthesize composites of bismuth and other metal oxides, but this method usually requires high-temperature calcination to remove organic residues during post-processing, resulting in high energy consumption. The microemulsion method encapsulates nano-sized water droplets in surfactants and disperses them in an organic phase, using an aqueous microreactor to synthesize nanoparticles. This method also involves the use of large amounts of organic solvents, posing environmental pollution problems. Chemical reduction methods include polyol reduction, electrochemical reduction, and photochemical reduction. Among these, the polyol process is a soft chemical reduction technique for preparing metal nanoparticles, using polyols as both solvents and reducing agents. It has advantages such as mild reaction conditions, simple operation, low cost, and ease of scale-up production, making it a relatively ideal strategy for bismuth nanoparticle synthesis. Although microwave-assisted synthesis, as well as sonochemical and laser-mediated synthesis, can be carried out at room temperature and pressure without the need for high temperature and high pressure conditions, they require special instruments and equipment, which is not conducive to widespread promotion and large-scale production.

[0005] In summary, existing bismuth nanoparticle synthesis technologies still have many shortcomings: high-temperature and high-pressure reaction conditions require sophisticated equipment and consume a lot of energy; the use of toxic organic solvents poses environmental risks and biosafety hazards; and reliance on specialized instruments and equipment limits the universality of the methods and their capacity for large-scale production. Summary of the Invention

[0006] The purpose of this invention is to provide a monodisperse hexagonal bismuth photothermal nanoparticle and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A monodisperse hexagonal bismuth photothermal nanoparticle has a core-shell structure, with a core of hexagonal metallic bismuth and a shell of polyvinylpyrrolidone film; the nanoparticle has a particle size of 70 nm to 90 nm.

[0009] A method for preparing the above-described monodisperse hexagonal bismuth photothermal nanoparticles includes the following steps:

[0010] (1) Mix the bismuth source, surfactant and solvent evenly to form a reaction precursor solution;

[0011] (2) Heat the precursor solution to the reaction temperature, add the reducing agent, and react for a certain time;

[0012] (3) After the reaction is terminated, the nanoparticles are obtained by centrifugation, washing and drying.

[0013] Preferably, the bismuth source is bismuth nitrate pentahydrate, the surfactant is glucose monohydrate and polyvinylpyrrolidone, the solvent is 1,2-propanediol, and the reducing agent is morpholine borane.

[0014] Preferably, the reducing agent is morpholine borane, with CAS number 4856-95-5, and is prepared into a solution with a concentration of 0.5 mol / L using 1,2-propanediol.

[0015] Preferably, the bismuth nitrate pentahydrate is prepared into a solution with a concentration of 0.25 mol / L using 1,2-propanediol.

[0016] Preferably, the glucose monohydrate is of type D, with CAS number 5996-10-1 and purity of analytical grade.

[0017] Preferably, the polyvinylpyrrolidone has an average molecular weight of 58,000, a CAS number of 9003-39-8, and an analytical purity.

[0018] Preferably, the reaction temperature is 80°C and the reaction time is 1 min.

[0019] Preferably, in the centrifugation step, the initial centrifugation condition is 8000 rcf for 30 min, and the subsequent centrifugation condition is 8000 rcf for 20 min; anhydrous ethanol is used in the washing step; and the drying step is carried out in an 80°C constant temperature drying oven.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The present invention uses a polyol solvothermal method to synthesize bismuth nanoparticles at a low temperature of 80°C. It does not require special equipment such as high temperature and high pressure reactors, nor does it require special energy input such as microwaves or lasers. Compared with the traditional hydrothermal method (which usually requires a high temperature of over 100°C) and solvothermal method (which often requires high temperature and high pressure), the reaction conditions of the present invention are milder, significantly reducing energy consumption and equipment costs, which is conducive to large-scale industrial production and application.

[0022] (2) This invention uses 1,2-propanediol as a solvent, which has good biocompatibility and low toxicity, and is widely used in the food, pharmaceutical, and cosmetic fields. Morpholine borane, the reducing agent, efficiently reduces the bismuth source during the reaction, and its byproducts can be effectively removed through a washing step. The surfactants polyvinylpyrrolidone and glucose monohydrate also have good biocompatibility; polyvinylpyrrolidone is a recognized pharmaceutical excipient, and glucose monohydrate is a naturally occurring sugar in organisms. The entire synthesis process avoids the use of toxic organic solvents, reducing environmental pollution risks and biosafety hazards.

[0023] (3) This invention achieves precise control over the particle size and morphology of bismuth nanoparticles by adjusting the ratio of surfactants. Transmission electron microscopy characterization results show that the obtained nanoparticles are nearly hexagonal or nearly spherical, with a particle size distribution in the range of 70 nm to 90 nm. There is no aggregation between particles, and the monodispersity is good. By adjusting the amount of polyvinylpyrrolidone and glucose monohydrate, the size and morphology of nanoparticles can be controlled while maintaining crystal form and dispersibility.

[0024] (4) The hexagonal bismuth nanoparticles prepared in this invention exhibit a significant photothermal effect under 808 nm near-infrared laser irradiation, with a significantly higher temperature rise than the pure water control group, indicating that they have good photothermal conversion capabilities. Combined with the inherent biocompatibility of bismuth, the nanoparticles obtained in this invention can serve as an ideal photothermal agent for application in the field of tumor photothermal therapy. Furthermore, their uniform particle size and good dispersibility make them suitable for constructing targeted delivery systems. Attached Figure Description

[0025] Figure 1 The X-ray diffraction pattern of the monodisperse hexagonal bismuth photothermal nanoparticles prepared in Example 1 of this invention;

[0026] Figure 2 This is a transmission electron microscope image of monodisperse hexagonal bismuth photothermal nanoparticles prepared in Example 1 of the present invention.

[0027] Figure 3 This is a transmission electron microscope image of the monodisperse hexagonal bismuth photothermal nanoparticles prepared in Example 2 of the present invention.

[0028] Figure 4 This is a transmission electron microscope image of the monodisperse hexagonal bismuth photothermal nanoparticles prepared in Example 3 of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] Please see Figures 1-2 As shown, this embodiment aims to prepare a monodisperse hexagonal bismuth photothermal nanoparticle.

[0032] First, prepare the precursor solutions required for the two reactions. Weigh 2.524 g of analytical grade morpholinoborane and dissolve it completely in 40 mL of analytical grade 1,2-propanediol. After complete dissolution, transfer the resulting solution to a 50 mL volumetric flask and dilute to 50 mL with analytical grade 1,2-propanediol to obtain a morpholinoborane reducing agent solution with a concentration of 0.5 mol / L.

[0033] Take 3.032 g of bismuth nitrate pentahydrate with analytical purity and dissolve it completely in 20 mL of analytical grade 1,2-propanediol. After complete dissolution, transfer the resulting solution to a 25 mL volumetric flask and dilute to 25 mL with analytical grade 1,2-propanediol to obtain a bismuth source solution with a concentration of 0.25 mol / L.

[0034] In the construction stage of the reaction system, the following reagents were added sequentially to a 100 mL single-necked round-bottom flask: 15.7 mL of analytical grade 1,2-propanediol was measured as the reaction solvent, 800 μL of the above-prepared bismuth nitrate pentahydrate solution was added, 180 mg of glucose monohydrate reagent was weighed as the surfactant, and 3 g of polyvinylpyrrolidone with an average molecular weight of 58,000 was weighed as the stabilizer.

[0035] The mixture was placed on a magnetic stirrer and thoroughly mixed to completely dissolve the solid reagent and form a homogeneous reaction precursor system.

[0036] The above round-bottom flask was placed in an oil bath magnetic stirrer equipped with a thermocouple, and the magnetic rotor speed was set to 350 rpm. Heating was started at room temperature.

[0037] When the temperature of the reaction system rises to 80℃, quickly add 3.5 mL of a pre-prepared 0.5 mol / L morpholinoborane solution and start timing immediately;

[0038] After the reducing agent was added, the reaction system began to undergo a reduction reaction, and the solution color gradually changed, indicating that the bismuth nanoparticles began to nucleate and grow. After the reaction proceeded for 1 minute, 40 mL of analytical grade anhydrous ethanol pre-cooled to -20 °C was immediately added to the flask, and the mixture was stirred at 350 rpm to quickly reduce the system temperature and dilute the concentration of the reactants, thereby terminating the reaction.

[0039] The obtained product needs to be centrifuged and washed multiple times to remove unreacted reagents and byproducts. Before the first centrifugation, add 50 mL of room temperature analytical grade anhydrous ethanol to the reaction solution, mix well, and centrifuge at 8000 rcf for 30 min. After centrifugation, carefully discard the supernatant waste liquid, add 10 mL of room temperature analytical grade anhydrous ethanol to the precipitate at the bottom of the centrifuge tube, use an ultrasonic cleaner to ultrasonically disperse and resuspend the precipitate, and then centrifuge at 8000 rcf for 20 min, and discard the supernatant.

[0040] Repeat the washing steps once, that is, after the second wash, centrifuge at 8000 rcf for 20 min, discard the supernatant, and obtain the cleaned nanoparticle precipitate.

[0041] After the final centrifugation, 2 mL of room temperature analytical grade anhydrous ethanol was added to the centrifuge tube. The nanoparticles were fully resuspended and dispersed by ultrasonic cleaning. The resulting dispersion was transferred to a suitable container and dried in an 80°C constant temperature drying oven to obtain monodisperse hexagonal bismuth photothermal nanoparticle solid product.

[0042] The product obtained in this embodiment was characterized as follows:

[0043] X-ray diffraction patterns (such as...) Figure 1 As shown in the figure, the diffraction peaks of the obtained nanoparticles are in good agreement with the standard card of hexagonal bismuth, indicating that the product has a hexagonal crystal structure.

[0044] Transmission electron microscope images (e.g.) Figure 2 As shown in the figure, the obtained nanoparticles have a near-hexagonal or near-spherical morphology, uniform particle size distribution, and a size range of 60 nm to 80 nm. The particles are well dispersed and there is no obvious aggregation.

[0045] Example 2:

[0046] This embodiment adjusts the amount of surfactant polyvinylpyrrolidone based on Example 1;

[0047] First, prepare the precursor solutions required for the two reactions using the same method as in Example 1: Weigh 2.524 g of analytical grade morpholinoborane, completely dissolve it in 40 mL of analytical grade 1,2-propanediol, transfer it to a 50 mL volumetric flask and dilute to the mark to obtain a morpholinoborane reducing agent solution with a concentration of 0.5 mol / L.

[0048] Another 3.032 g of analytical grade bismuth nitrate pentahydrate was completely dissolved in 20 mL of analytical grade 1,2-propanediol, then transferred to a 25 mL volumetric flask and diluted to the mark to obtain a bismuth source solution with a concentration of 0.25 mol / L.

[0049] In the construction stage of the reaction system, the following reagents were added sequentially to a 100 mL single-necked round-bottom flask: 15.7 mL of analytical grade 1,2-propanediol was measured as the reaction solvent; 800 μL of the prepared bismuth nitrate pentahydrate solution was added; 180 mg of glucose monohydrate was weighed as the auxiliary surfactant; and 2.4 g of polyvinylpyrrolidone with an average molecular weight of 58,000 was weighed as the main surfactant and stabilizer. Compared with Example 1, the amount of polyvinylpyrrolidone in this example was adjusted from 3 g to 2.4 g, while the remaining components remained unchanged.

[0050] The mixture was placed on a magnetic stirrer and stirred thoroughly to completely dissolve the solid reagent and form a homogeneous reaction precursor system.

[0051] The above round-bottom flask was placed in an oil bath magnetic stirrer equipped with a thermocouple, and the magnetic rotor speed was set to 350 rpm. Heating was started at room temperature.

[0052] When the temperature of the reaction system rises to 80℃, 3.5 mL of a pre-prepared morpholinoborane solution with a concentration of 0.5 mol / L is quickly added, and timing is started immediately. After the addition of the reducing agent, the reaction system begins to undergo a reduction reaction, and the color of the solution gradually changes, indicating that bismuth nanoparticles begin to nucleate and grow.

[0053] After the reaction proceeded for 1 minute, 40 mL of analytical grade anhydrous ethanol pre-cooled to -20 °C was immediately added to the flask. The mixture was stirred at 350 rpm to rapidly reduce the system temperature and dilute the reactant concentration, thereby terminating the reaction.

[0054] The obtained product needs to be centrifuged and washed multiple times to remove unreacted reagents and byproducts. Before the first centrifugation, add 50 mL of room temperature analytical grade anhydrous ethanol to the reaction solution, mix well, and centrifuge at 8000 rcf for 30 min. After centrifugation, carefully discard the supernatant waste liquid.

[0055] Add 10 mL of room-temperature analytical-grade anhydrous ethanol to the precipitate at the bottom of the centrifuge tube, and resuspend the precipitate by ultrasonic dispersion using an ultrasonic cleaner. Then centrifuge at 8000 rcf for 20 min and discard the supernatant. Repeat the above washing steps once, i.e., after the second wash, centrifuge at 8000 rcf for 20 min and discard the supernatant to obtain a clean nanoparticle precipitate.

[0056] After the final centrifugation, 2 mL of room temperature analytical grade anhydrous ethanol was added to the centrifuge tube. The nanoparticles were fully resuspended and dispersed by ultrasonic cleaning. The resulting dispersion was transferred to a suitable container and dried in an 80°C constant temperature drying oven to obtain monodisperse hexagonal bismuth photothermal nanoparticle solid product.

[0057] The product obtained in this embodiment was characterized as follows:

[0058] Transmission electron microscope images (e.g.) Figure 3 As shown in the figure, when the amount of polyvinylpyrrolidone was reduced to 2.4 g, the resulting nanoparticles still maintained good dispersibility and uniform particle size distribution, with the particle size range remaining between 60 nm and 80 nm. However, the particle morphology changed compared to Example 1, with some particles exhibiting a more spherical morphology and a reduced near-hexagonal characteristic. This result indicates that by adjusting the amount of polyvinylpyrrolidone, the morphology of nanoparticles can be controlled to a certain extent while maintaining particle size uniformity.

[0059] X-ray diffraction pattern (and) Figure 1 (Similarly, not shown again) It is confirmed that the product obtained in this embodiment still maintains the hexagonal crystal structure, indicating that the change in the amount of polyvinylpyrrolidone did not affect the crystal form of metallic bismuth.

[0060] Example 3:

[0061] This embodiment adjusts the amount of auxiliary surfactant hydrated glucose based on Embodiment 1;

[0062] First, prepare the precursor solutions required for the two reactions using the same method as in Example 1: Weigh 2.524 g of analytical grade morpholinoborane, completely dissolve it in 40 mL of analytical grade 1,2-propanediol, transfer it to a 50 mL volumetric flask and dilute to the mark to obtain a morpholinoborane reducing agent solution with a concentration of 0.5 mol / L.

[0063] Another 3.032 g of analytical grade bismuth nitrate pentahydrate was completely dissolved in 20 mL of analytical grade 1,2-propanediol, transferred to a 25 mL volumetric flask, and diluted to the mark to obtain a bismuth source solution with a concentration of 0.25 mol / L.

[0064] In the construction stage of the reaction system, the following reagents were added sequentially to a 100 mL single-necked round-bottom flask: 15.7 mL of analytical grade 1,2-propanediol was measured as the reaction solvent, 800 μL of the above-prepared bismuth nitrate pentahydrate solution was added, 225 mg of glucose monohydrate was weighed as the auxiliary surfactant, and 3 g of polyvinylpyrrolidone with an average molecular weight of 58,000 was weighed as the main surfactant and stabilizer. Compared with Example 1, this example only adjusted the amount of glucose monohydrate from 180 mg to 225 mg, while keeping the amount of polyvinylpyrrolidone unchanged at 3 g.

[0065] The mixture was placed on a magnetic stirrer and stirred thoroughly to completely dissolve the solid reagent and form a homogeneous reaction precursor system.

[0066] The round-bottom flask was placed in an oil bath magnetic stirrer equipped with a thermocouple. The magnetic rotor speed was set to 350 rpm, and heating was started at room temperature. When the temperature of the reaction system reached 80°C, 3.5 mL of a pre-prepared 0.5 mol / L morpholinoborane solution was quickly added, and the timing was started immediately.

[0067] The reaction system began to undergo a reduction reaction after the addition of the reducing agent, and the solution color gradually changed, indicating that bismuth nanoparticles began to nucleate and grow. After 1 minute of reaction, 40 mL of analytical grade anhydrous ethanol pre-cooled to -20°C was immediately added to the flask, and the mixture was stirred at 350 rpm to rapidly lower the system temperature and dilute the reactant concentration, thereby terminating the reaction.

[0068] The obtained product needs to be centrifuged and washed multiple times to remove unreacted reagents and byproducts. Before the first centrifugation, add 50 mL of room temperature analytical grade anhydrous ethanol to the reaction solution, mix well, and centrifuge at 8000 rcf for 30 min. After centrifugation, carefully discard the supernatant. Add 10 mL of room temperature analytical grade anhydrous ethanol to the precipitate at the bottom of the centrifuge tube, use an ultrasonic cleaner to ultrasonically disperse and resuspend the precipitate, and then centrifuge at 8000 rcf for 20 min. Discard the supernatant.

[0069] Repeat the washing steps once, that is, after the second wash, centrifuge at 8000 rcf for 20 min, discard the supernatant, and obtain the cleaned nanoparticle precipitate.

[0070] After the final centrifugation, 2 mL of room temperature analytical grade anhydrous ethanol was added to the centrifuge tube. The nanoparticles were fully resuspended and dispersed by ultrasonic cleaning. The resulting dispersion was transferred to a suitable container and dried in an 80°C constant temperature drying oven to obtain monodisperse hexagonal bismuth photothermal nanoparticle solid product.

[0071] The product obtained in this embodiment was characterized as follows:

[0072] Transmission electron microscope images (e.g.) Figure 4 As shown in the figure, when the amount of glucose monohydrate increased to 225 mg, the obtained nanoparticles still maintained good dispersibility and uniform particle size distribution, but the average particle size increased compared to Example 1, with a particle size range of approximately 70 nm to 90 nm, and the particle morphology was still mainly near-hexagonal. This result indicates that the particle size of nanoparticles can be controlled by adjusting the amount of glucose monohydrate while maintaining crystal form and dispersibility. Combining the results of Example 1 and Example 2, it can be seen that the ratio of surfactant has a significant impact on the morphology and size of the product. By optimizing the amount of glucose and polyvinylpyrrolidone, the size and morphology of bismuth nanoparticles can be controlled.

[0073] X-ray diffraction pattern (and) Figure 1 (Similarly, not shown again) It is confirmed that the product obtained in this embodiment still maintains the hexagonal crystal structure, indicating that the change in the amount of glucose monohydrate does not affect the crystallization characteristics of metallic bismuth.

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A monodisperse hexagonal bismuth photothermal nanoparticle, characterized in that, The nanoparticles have a core-shell structure, with a hexagonal crystalline metallic bismuth core and a polyvinylpyrrolidone membrane as the outer shell; the particle size of the nanoparticles is 70 nm to 90 nm.

2. A method for preparing monodisperse hexagonal bismuth photothermal nanoparticles as described in claim 1, characterized in that, Includes the following steps: (1) Mix the bismuth source, surfactant and solvent evenly to form a reaction precursor solution; (2) Heat the precursor solution to the reaction temperature, add the reducing agent, and react for a certain time; (3) After the reaction is terminated, the nanoparticles are obtained by centrifugation, washing and drying.

3. The method for preparing monodisperse hexagonal bismuth photothermal nanoparticles according to claim 2, characterized in that: The bismuth source is bismuth nitrate pentahydrate, the surfactant is glucose monohydrate and polyvinylpyrrolidone, the solvent is 1,2-propanediol, and the reducing agent is morpholinoborane.

4. The method for preparing monodisperse hexagonal bismuth photothermal nanoparticles according to claim 2, characterized in that: The reducing agent is morpholine borane, CAS number 4856-95-5, which is prepared into a 0.5 mol / L solution using 1,2-propanediol.

5. The method for preparing monodisperse hexagonal bismuth photothermal nanoparticles according to claim 2, characterized in that: The bismuth nitrate pentahydrate was prepared into a solution with a concentration of 0.25 mol / L using 1,2-propanediol.

6. The method for preparing monodisperse hexagonal bismuth photothermal nanoparticles according to claim 2, characterized in that: The glucose monohydrate is of type D, with CAS number 5996-10-1 and a purity of analytical grade.

7. The monodisperse hexagonal bismuth photothermal nanoparticles and their preparation method according to claim 2, characterized in that: The polyvinylpyrrolidone has an average molecular weight of 58,000, CAS number 9003-39-8, and is of analytical grade.

8. The method for preparing monodisperse hexagonal bismuth photothermal nanoparticles according to claim 2, characterized in that: The reaction temperature is 80℃ and the reaction time is 1 min.

9. The method for preparing monodisperse hexagonal bismuth photothermal nanoparticles according to claim 2, characterized in that: In the centrifugation step, the initial centrifugation condition is 8000 rcf for 30 min, and the subsequent centrifugation condition is 8000 rcf for 20 min; anhydrous ethanol is used in the washing step; The drying process is carried out in a constant temperature drying oven at 80°C.

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