A high-stability bismuth-based core-shell heterojunction nanomaterial and a preparation method thereof

Abstract

This invention belongs to the field of nanomaterial preparation technology and discloses a highly stable bismuth-based core-shell heterojunction nanomaterial (Bi@Bi2X3) and its preparation method. The method uses a non-aqueous composite electrolyte as a medium to construct an electrochemical system to achieve simultaneous exfoliation and in-situ coating of the material. Powdered Bi@Bi2X3 nanomaterials are precisely synthesized through separation and washing, chemical reduction enhancement, and freeze-drying processes. The process described in this invention is not only simplified and has mild reaction conditions, but also possesses excellent large-scale preparation capabilities. More importantly, the resulting heterojunction material, through its unique core-shell structure design, effectively overcomes the easy oxidation defect of traditional bismuth-based materials, exhibiting excellent air stability.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, specifically to a highly stable bismuth-based core-shell heterostructure nanomaterial and its preparation method. Background Technology

[0002] Bismuth (Bi)'s inherent layered crystal structure provides a natural advantage for preparing nanomaterials through physical exfoliation techniques. Given the tunable transition of its electronic band structure from a half-metallic to a semiconductor state, coupled with its unique topological physics and excellent nonlinear optical response, bismuth nanomaterials show broad application prospects in cutting-edge fields such as next-generation micro / nanoelectronic devices, ultrafast photonics, high-efficiency energy conversion, and biomedical diagnostics. However, the lack of environmental stability constitutes a key technological bottleneck restricting the practical application and commercialization of bismuth nanomaterials. Especially in humid environments or aqueous media, the extremely high specific surface area of ​​bismuth nanomaterials, combined with the high chemical reactivity of edge dangling bonds, makes them highly susceptible to oxidation-induced chemical degradation. In-depth mechanistic studies show that dissolved oxygen tends to preferentially attack edge active sites, forming a surface oxide layer; subsequently, water molecules weaken interlayer van der Waals forces and disrupt lattice integrity through intercalation and hydration, ultimately leading to severe morphological collapse and semiconductor performance degradation in a short period.

[0003] Existing protection strategies primarily rely on physical coating with polymers. However, this non-covalent physical adsorption layer has weak bonding, increasing interfacial contact resistance and easily detaching in complex solution environments, failing to achieve durable and hermetic protection of the bismuth core. Furthermore, a patent titled "A Method for Constructing Electron Migration Channels on the Surface of a Bismuth-Based Anode Material" (patent number: 202211647968.4) reports a bismuth-based anode material of Bi2X3 / Bi@CNT@PANI, mentioning Bi2X3 / Bi nanomaterials. These materials use Bi2X3 as a precursor, with only a small amount of Bi nanostructures on their surface. Clearly, this material is a derivative of Bi2X3 and not a Bi-based material. Therefore, current strategies do not truly address the chemical stability of Bi materials. It should be noted that nanoscale Bi materials fall under the semiconductor field; when modifying them, the impact of modification on their electronic structure must be fully considered, aiming to impart functionality to the material while simultaneously addressing its stability.

[0004] Given the high chemical reactivity of Bi, developing a preparation process that can construct a highly stable chemically bonded protective layer in situ is crucial for realizing the application of bismuth nanomaterials in energy, biology, and semiconductor-related aquatic fields. Summary of the Invention

[0005] In view of this, the present invention provides a highly stable bismuth-based core-shell heterostructure nanomaterial and its preparation method.

[0006] A method for preparing a highly stable bismuth-based core-shell heterostructure nanomaterial includes the following steps:

[0007] (1) Preparation of non-aqueous composite electrolyte: Anhydrous dimethyl sulfoxide (DMSO), a non-aqueous solvent, is introduced into a dry electrolytic cell, followed by the addition of an intercalating agent, a precursor salt, and a surfactant. The precursor salt is selected from sodium tellurite, sodium selenite, or a mixture thereof. The surfactant is polyvinylpyrrolidone. Under continuous stirring, the mixture is ultrasonically dispersed until all components are completely dissolved or uniformly dispersed to obtain the composite electrolyte.

[0008] (2) Assembly of the electrochemical stripping system: A block of high-purity bismuth is fixed with a platinum sheet electrode clamp as the working electrode and a platinum wire is used as the counter electrode. The bismuth working electrode is connected to the negative electrode (cathode) of the DC power supply, and the platinum counter electrode is connected to the positive electrode (anode) of the DC power supply. The two electrodes are then immersed in the composite electrolyte prepared in step (1) in parallel and opposite directions.

[0009] (3) Electrochemical stripping and in-situ coating: A constant DC voltage was applied between the bismuth working electrode and the platinum counter electrode to carry out an electrochemical stripping reaction, resulting in a black Bi@Bi2X3 nanomaterial mixed suspension.

[0010] (4) Separation and washing of the product: The mixed suspension obtained in step (3) is centrifuged, the bottom precipitate is collected and washed multiple times to completely remove the residual electrolyte. Then, the purified product is redispersed in anhydrous ethanol and ultrasonically treated to form a uniform alcohol dispersion.

[0011] (5) Chemical reduction enhancement treatment: Add hydrazine hydrate, a reducing agent, to the alcohol dispersion obtained in step (4) and carry out chemical reduction reaction by stirring continuously under constant temperature conditions to eliminate surface defects of the material and enhance the stability of the crystal structure. After the reaction is completed, centrifuge to separate the precipitate and wash it again.

[0012] (6) Freeze-drying: The wet precipitate washed in step (5) is placed in liquid nitrogen for liquid nitrogen quenching, and then vacuum freeze-drying is performed to obtain powdered Bi@Bi2X3 nanomaterials, namely the highly stable bismuth-based core-shell heterostructure nanomaterials.

[0013] Further, in step (1), 20 mL of non-aqueous solvent anhydrous dimethyl sulfoxide is introduced into a dry electrolytic cell, followed by the sequential addition of 20 mg-2 g intercalating agent, 1 mg-50 mg sodium tellurite and / or 1 mg-50 mg sodium selenite and 0 mg-100 mg surfactant.

[0014] Furthermore, in step (1), the intercalating agent is a quaternary ammonium salt intercalating agent, wherein the general formula is: [R1R2R3R4]X - Where R1-R4 is C1–C 20 Alkyl, substituted alkyl, allyl, benzyl, aralkyl or combinations thereof; X - It is a halide ion, fluoroborate ion, hexafluorophosphate ion, tetrafluoroborate ion or bis(trifluoromethanesulfonyl)imide electrolyte anion; or an imidazole ionic liquid, pyridine ionic liquid or quaternary ammonium salt ionic liquid; or a mixture of two or more of the above intercalating agents.

[0015] Furthermore, in step (1), the intercalating agent is tetrabutylammonium bromide or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0016] Furthermore, in step (1), the stirring speed is 50 rpm-1000 rpm, the ultrasonic power is 100 W-1000 W, and the ultrasonic time is 1-30 minutes.

[0017] Furthermore, in step (2), the two electrodes are immersed in the composite electrolyte prepared in step (1) in parallel relative to each other, and the electrode spacing is controlled to be 1.0-1.5 cm.

[0018] Furthermore, in step (3), a constant DC voltage of -6V to -14V is applied between the bismuth working electrode and the platinum counter electrode to carry out an electrochemical stripping reaction for a reaction time of 0.2-12 hours.

[0019] Furthermore, in step (4), the centrifugation speed is 10000 rpm and the centrifugation time is 1-10 minutes; the ultrasonic power is 100W-1000 W and the ultrasonic time is 1-30 minutes.

[0020] Further, in step (5), the volume ratio of alcohol dispersion to hydrazine hydrate is (10-100mL):1mL, and each 30mL alcohol dispersion contains 10-100mg of purified product; the reaction is stirred at a constant temperature of 20-100℃ for 0.5-2 hours, the stirring speed is 50 rpm-1000rpm, and the product is collected by centrifugation at 10000rpm for 1-30 minutes.

[0021] Further, in step (6), the final cleaned product precipitate is placed in liquid nitrogen for rapid freezing for 1 to 10 minutes, and then transferred to a freeze dryer for freeze drying under vacuum conditions for 12 to 72 hours. The vacuum degree is below 100 Pa and the freezing temperature is from -10 degrees Celsius to -100 degrees Celsius to obtain powdered Bi@Bi2X3 nanomaterials.

[0022] The present invention also provides a highly stable bismuth-based core-shell heterojunction nanomaterial, which is prepared by the aforementioned preparation method.

[0023] The beneficial effects of the present invention are as follows: The present invention provides a bismuth-based heterojunction material with a simple process, mild conditions, large-scale preparation capability, and high chemical stability of the product in air, while possessing a special structure.

[0024] The Bi@Bi2X3 obtained in this invention (where Bi is the substrate framework structure and Bi2X3 is the surface and / or edge modification layer, X=Se, Te or Se-Te) has several beneficial effects in terms of structure and function: (1) Unique core-shell microstructure: Bi is the substrate framework structure and is the main phase structure; Bi2X3 (X=Se, Te or Se-Te) is the surface or edge modification structure and is the auxiliary phase structure; (2) Narrow bandgap-narrow bandgap heterojunction structure: the bandgap of Bi monolayer is 0.5-0.8 eV, the bandgap of Bi2Se3 monolayer is 0.35-0.5 eV, and the bandgap of Bi2Te3 monolayer is 0.3-0.4 eV. Since the Bi2Se3 and Bi2Te3 with narrower band gaps are formed on the Bi surface, the absorption range of light by Bi@Bi2X3 will be significantly improved, the carrier concentration will be increased, and the electron-phonon coupling efficiency will be greatly improved, thus having excellent photothermal conversion efficiency; (3) Permanent chemical stability: Since the dangling bonds on the Bi surface are greatly reduced by the covalent bonds of Te and Se atoms, Bi@Bi2X3 can exist in water for a long time.

[0025] This invention utilizes an electrochemical method to in-situ exfoliate and modify bismuth nanomaterials, preparing Bi@Bi2X3 nanomaterials (where Bi is the substrate framework structure, and Bi2X3 is the surface and / or edge modification layer, X = Se, Te, or Se-Te). The reaction mechanism of these nanomaterials is as follows:

[0026] Electrolyte type: 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (imidazolium-based ionic liquid) is used as the intercalating agent, and DMSO is used as the solvent. The imidazolium cation and the bis(trifluoromethanesulfonyl)imide anion form solvation layers with the solvent, resulting in a homogeneous system. To modify Bi, sodium tellurite and sodium selenite are added to the system as reactants. Due to the limited solubility of the inorganic salts sodium tellurite and sodium selenite in DMSO, the resulting mixture is a suspension, in which the majority of sodium tellurite and sodium selenite exist as tiny particles.

[0027] Electrochemical exfoliation and modification: Bi bulk materials are typical van der Waals layered structures; the directional movement of anions and cations driven by an electric field (i.e., the intercalation behavior of Bi) helps to weaken van der Waals forces, forming Bi-based superlattice precursor materials with ion / molecular intercalation. At this point, the material's macroscopic volume expands due to the insertion of charged particles. In this invention, a negative voltage (such as -10V) drives the imidazole cations of the ionic liquid to intercalate into the interlayer spacing of Bi. With the assistance of the solvent DMSO, the interlayer spacing of Bi significantly increases, and it subsequently detaches into the solution. The newly exfoliated Bi nanomaterials have a very large surface area and high surface activity, undergoing an in-situ reaction with surrounding sodium tellurite and sodium selenite to form Bi₂X₃ (X=Se, Te). This patent application speculates that defects and edges on the Bi surface are the main sites for this chemical reaction. Since the amount of dissolved or dissolved sodium tellurite and sodium selenite in the solution system is relatively small, and the Bi nanomaterials serve as the reaction site, the final Bi₂X₃ is attached to the surface of the Bi nanomaterials.

[0028] Further processing with hydrazine hydrate: Hydrazine hydrate is a strong reducing agent. At 60°C, it can rapidly reduce unreacted selenite and tellurite ions adsorbed on the bismuth surface to highly reactive zero-valent or divalent ions. The newly generated selenium / tellurium atoms have extremely high reactivity; they immediately react with neighboring bismuth surface atoms in high-energy states (especially dangling bonds at the edges) to form Bi₂X₃ compounds. Furthermore, hydrazine hydrate ensures that the aqueous phase reaction at this step is a possible oxidation of Bi.

[0029] The Bi@Bi2X3 nanomaterials prepared by this invention are expected to be applied in optoelectronic devices, catalysis, energy and biomedicine. Attached Figure Description

[0030] Figure 1 In the figure, (a) shows the newly prepared Bi2X3 nanomaterial dispersion; (b) shows the Bi@Bi2X3 dispersion after standing in a water environment at room temperature for 10 days; (c) shows the newly prepared pure Bi nanomaterial; and (d) shows the pure Bi nanomaterial dispersion after standing for 10 days under the same conditions.

[0031] Figure 2 This is a comparison of Raman spectra.

[0032] Figure 3 The image shows the HAADF image and elemental distribution map of Example 1.

[0033] Figure 4 The results show the stability of the dispersions in different examples. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0035] Example 1

[0036] A method for preparing highly stable bismuth-based core-shell heterojunction nanomaterials includes the following steps:

[0037] (1) Preparation of non-aqueous composite electrolyte:

[0038] In a dry and well-ventilated environment, the electrolytic cell was pre-dried in a forced-air drying oven at 70°C for 30 minutes. Then, 20 mL of anhydrous dimethyl sulfoxide was injected into the electrolytic cell. Subsequently, the solutes were weighed: 200 mg of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]), 11.08 mg of sodium tellurite (Na2TeO3), 8.65 mg of sodium selenite (Na2SeO3), and 5.0 mg of polyvinylpyrrolidone (PVP) were accurately weighed using an analytical balance and added to the dried electrolytic cell. Under continuous stirring, the mixture was ultrasonically dispersed for 10 minutes at an ultrasonic power of 600 W to obtain the composite electrolyte.

[0039] (2) Assembly of the electrochemical stripping system:

[0040] Electrode pretreatment: A block of high-purity bismuth is held and fixed as the working electrode using a platinum sheet electrode clamp, and a platinum wire is used as the counter electrode. Before assembly, the electrode and electrode clamp are ultrasonically cleaned in high-purity water and anhydrous ethanol for 5 minutes each, with an ultrasonic power of 600W, to remove surface oil and impurities. They are then dried in a forced-air drying oven at 70°C for 30 minutes.

[0041] System connection: A dual-electrode system is adopted, with the bismuth working electrode connected to the negative terminal (cathode) of the DC power supply and the platinum counter electrode connected to the positive terminal (anode) of the DC power supply.

[0042] The two electrodes are immersed in the composite electrolyte obtained in step (1) in parallel and opposite directions, the electrode spacing is controlled to be 1.0-1.5 cm, and the electrode material is ensured to be submerged in the electrolyte;

[0043] (3) Electrochemical stripping and in-situ coating:

[0044] A constant DC voltage of -10V was applied between the working electrode and the counter electrode to carry out an electrochemical stripping reaction for 2 hours.

[0045] Reaction phenomena: During the reaction, bubbles are generated on the surface of the working electrode (originating from the reduction and intercalation of ionic liquid cations), causing the bulk bismuth to expand and peel off; at the same time, the solution color gradually deepens, eventually yielding a black Bi@Bi2X3 nano-mixed suspension.

[0046] (4) Separation and washing of the products:

[0047] Preliminary separation: Transfer the mixed suspension after reaction into a centrifuge tube, centrifuge at 10,000 rpm for 10 minutes, discard the supernatant, and collect the bottom precipitate;

[0048] Alternating washing: The precipitate is redispersed in the solvent and washed four times in the order of "ethanol-water-ethanol-water". Each washing process is as follows: first, add solvent and sonicate for 5 minutes, then centrifuge at 10,000 rpm for 10 minutes, and finally discard the supernatant.

[0049] Dispersion preparation: After the final washing, the product is dispersed in 30 mL of ethanol and sonicated at 600 W for 5 minutes to obtain a uniform dispersion, i.e., ethanol dispersion.

[0050] (5) Chemical reduction enhancement treatment:

[0051] Add 1 mL of hydrazine hydrate to 30 mL of the alcohol dispersion obtained in step (4), and stir the mixture at a constant temperature of 60 °C for 1 hour at a stirring speed of 500 rpm to fully reduce any possible oxides on the surface and consolidate the shell structure. After the reaction is complete, collect the product by centrifugation at 10,000 rpm for 10 minutes, and wash it once with anhydrous ethanol and once with deionized water.

[0052] (6) Freeze-drying:

[0053] The final cleaned product precipitate was rapidly frozen in liquid nitrogen for 10 minutes, and then transferred to a freeze dryer for freeze drying under vacuum conditions of 50 Pa and -50 °C for 48 hours, finally obtaining powdered Bi@Bi2X3 nanomaterials.

[0054] Figure 1 In the figure, (a) shows the newly prepared Bi@Bi2X3 nanomaterial dispersion in Example 1; (b) shows the Bi@Bi2X3 nanomaterial dispersion after standing in a water environment at room temperature for 10 days; (c) shows the newly prepared pure Bi nanomaterial; and (d) shows the pure Bi nanomaterial dispersion after standing for 10 days under the same conditions.

[0055] Compared with Example 1, the pure Bi nanomaterials had the same solute content except that the composite electrolyte did not contain the precursor salts sodium selenite and sodium tellurite. Product separation and washing: three ethanol washes.

[0056] Figure 2 The images show a comparison of the Raman spectra of Bulk Bi, Bi Nanosheet (Comparative Example 1), Bi@TeSe-1X (Example 1), and Bi@TeSe-2X (Example 2).

[0057] Figure 3 This is the HAADF image and elemental distribution map of Example 1.

[0058] Figure 1 This paper visually demonstrates the comparative evaluation results of the chemical stability of the Bi@Bi2X3 core-shell heterojunction nanomaterials prepared in the embodiments of the present invention and the comparative example (pure bismuth nanomaterials) in an aqueous medium. (Refer to...) Figure 1 Figure (a) shows that the fresh Bi@Bi2X3 nanomaterials prepared in this invention can form a uniform and stable black colloidal dispersion in the aqueous phase. Figure 1 As shown in Figure (b), even after aging at room temperature and under natural light for 10 days (240 hours), the dispersion retained its initial deep black color without any visible fading. This excellent macroscopic stability strongly demonstrates that the in-situ grown Bi2X3 shell not only structurally completely encapsulates the bismuth core but also acts as a robust chemical barrier, effectively isolating it from water and oxygen erosion and endowing the material with excellent chemical inertness in aquatic environments. In stark contrast, the dispersion of pure bismuth nanomaterials, although initially also black (…),… Figure 1 (Figure (c) in the text), but after undergoing the same 10-day aging process, its macroscopic state underwent a fundamental reversal. For example... Figure 1 As shown in Figure (d), the solution completely transforms from its original deep black color to a milky white suspension. This drastic color change reveals a catastrophic failure of the microstructure: due to the lack of a surface protective barrier, the low-dimensional metallic bismuth with high surface energy suffers severe oxidation, corrosion, and hydrolysis in the aqueous environment, causing its nanoframework to collapse and transform into wide-bandgap oxides or basic salt species (appearing milky white), thus completely losing its original low-dimensional structural characteristics and functional advantages.

[0059] Depend on Figure 2 The Raman spectra show that bulk bismuth exhibits a highly distinctive sharp Bi-E spectrum. g and Bi-A 1g Characteristic peaks, which perfectly match the structural features of bulk rhombohedral bismuth crystals. In contrast, the pure bismuth nanomaterial Bi-A... 1gA significant redshift was observed in the mode. This frequency shift is attributed to the phonon confinement effect at the nanoscale, strongly confirming that the electrochemical exfoliation process has successfully transformed bulk materials into low-dimensional nanostructures. For the core-shell structured product prepared using standard proportions, its spectrum exhibits new characteristic vibrational modes compared to pure bismuth nanomaterials: located at 122 cm⁻¹. -1 The peak at that location belongs to the A of the Te-Te bond. 1g Breathing model, 140 cm -1 The peak at that point corresponds to the E of the Bi-Te bond. g The model, located at 170 cm - The broad peak near ¹ originates from the A of the Bi-Se bond. 1g Vibrations. The appearance of these specific chemical bond vibration signals provides direct spectroscopic evidence that Te and Se elements are not physically adsorbed through weak interactions, but rather anchored to the bismuth surface through strong covalent bonds, thus confirming the successful in-situ synthesis of the bismuth chalcogenide (Bi2X3) shell. Further increasing the precursor concentrations of sodium selenite and sodium tellurite (as shown by the green curve in the spectrum, twice the concentration of the standard ratio), at 170 cm⁻¹... -1 The peak shape at this location is sharper than that of the standard sample (blue curve), reflecting an increase in selenium content in the system. Crucially, with the increase in shell-related signals (120-180 cm⁻¹),... -1 The region (A) dominates the spectrum, and the A region, which originally belonged to the bismuth nucleus, is dominant. 1g The relative intensity of the characteristic peaks decreased significantly. This reversal of signal intensity indicates that the outer shell has grown to a considerable thickness, thus effectively shielding the Raman signal of the internal bismuth core.

[0060] like Figure 3 The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images clearly reveal the elemental distribution characteristics of the nanoparticles. The Bi element signal intensity exhibits a significant enrichment peak in the geometric center region of the particles, confirming that metallic Bi constitutes the core of this nanocomposite material. Simultaneously, the Bi element signal is not confined to the center but shows a tendency to extend radially outward to the particle edges, exhibiting a high degree of spatial co-localization with the signals of Se and Te. This microscopic morphological characterization result is consistent with… Figure 2The spectroscopic analyses corroborated each other, strongly supporting the successful construction of the Bi@Bi2X3 core-shell heterojunction structure. In-depth elemental distribution analysis revealed a crucial structural detail: compared to Te, the Se element distribution area more tightly surrounds and is adjacent to the Bi core in space. This differential spatial distribution is attributed to the significant difference in atomic radii between Se and Te, leading to different interfacial diffusion kinetics on the Bi core surface. This phenomenon indicates that within the in-situ generated Bi2X3 shell, a single homogeneous solid solution is not formed, but rather a fine compositional gradient structure.

[0061] Figure 4 The results show the stability of the dispersions in different examples. Compared to Example 1, except... Figure 4 The process parameters are different, but the other steps and parameters are the same. The results show that only one of sodium selenite and sodium tellurite needs to be added to achieve the desired effect, and the effect of both is better.

[0062] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a highly stable bismuth-based core-shell heterostructure nanomaterial, characterized in that, Includes the following steps: (1) Preparation of non-aqueous composite electrolyte: Anhydrous dimethyl sulfoxide, a non-aqueous solvent, is introduced into a dry electrolytic cell, followed by the addition of an intercalating agent, a precursor salt, and a surfactant. The precursor salt is selected from sodium tellurite, sodium selenite, or a mixture thereof. The surfactant is polyvinylpyrrolidone. Under continuous stirring, the mixture is ultrasonically dispersed until all components are completely dissolved or uniformly dispersed to obtain the composite electrolyte. (2) Assembly of the electrochemical stripping system: A block of high-purity bismuth is fixed with a platinum sheet electrode clamp as the working electrode and a platinum wire is used as the counter electrode. The bismuth working electrode is connected to the negative terminal of the DC power supply, and the platinum counter electrode is connected to the positive terminal of the DC power supply. The two electrodes are immersed in the composite electrolyte prepared in step (1) in parallel and opposite directions. (3) Electrochemical stripping and in-situ coating: A constant DC voltage was applied between the bismuth working electrode and the platinum counter electrode to carry out an electrochemical stripping reaction, resulting in a black Bi@Bi2X3 nanomaterial mixed suspension. (4) Separation and washing of the product: The mixed suspension obtained in step (3) is centrifuged, the bottom precipitate is collected and washed multiple times to completely remove the residual electrolyte. Then, the purified product is redispersed in anhydrous ethanol and ultrasonically treated to form a uniform alcohol dispersion. (5) Chemical reduction enhancement treatment: Add hydrazine hydrate, a reducing agent, to the alcohol dispersion obtained in step (4) and carry out chemical reduction reaction by stirring continuously under constant temperature conditions to eliminate surface defects of the material and enhance the stability of the crystal structure. After the reaction is completed, centrifuge to separate the precipitate and wash it again. (6) Freeze-drying: The wet precipitate washed in step (5) is placed in liquid nitrogen for liquid nitrogen quenching, and then vacuum freeze-drying is performed to obtain powdered Bi@Bi2X3 nanomaterials, namely the highly stable bismuth-based core-shell heterostructure nanomaterials. Where X = Se, Te or Se-Te.

2. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (1), 20 mL of anhydrous dimethyl sulfoxide (DMSO), a non-aqueous solvent, is introduced into a dry electrolytic cell, followed by the addition of 20 mg to 2 g of intercalating agent, 1 mg to 50 mg of sodium tellurite and / or 1 mg to 50 mg of sodium selenite and 0 mg to 100 mg of surfactant.

3. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (1), the intercalating agent is one or a mixture of several of the following: quaternary ammonium salt intercalating reagent, imidazole ionic liquid, pyridine ionic liquid, or quaternary ammonium salt ionic liquid. The general formula for the quaternary ammonium salt intercalating reagent is: [R1R2R3R4]X - Where R1-R4 is C1–C 20 Alkyl, substituted alkyl, allyl, benzyl, aralkyl or combinations thereof; X - It is a halide ion, fluoroborate ion, hexafluorophosphate ion, tetrafluoroborate ion, or bis(trifluoromethanesulfonyl)imide electrolyte anion.

4. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (1), the stirring speed is 50 rpm-1000 rpm, the ultrasonic power is 100 W-1000 W, and the ultrasonic time is 1-30 minutes.

5. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (2), the two electrodes are immersed in the composite electrolyte prepared in step (1) in parallel relative to each other, and the electrode spacing is controlled to be 1.0-1.5 cm.

6. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (3), a constant DC voltage of -6V to -14V is applied between the bismuth working electrode and the platinum counter electrode to carry out an electrochemical stripping reaction for a reaction time of 0.2-12 hours.

7. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (4), the centrifugation speed is 10000 rpm and the centrifugation time is 1-10 minutes; the ultrasonic power is 100 W-1000 W and the ultrasonic time is 1-30 minutes.

8. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (5), the volume ratio of alcohol dispersion to hydrazine hydrate is (10-100mL):1mL, and each 30mL alcohol dispersion contains 10-100mg of purified product; the reaction is carried out under constant temperature of 20-100℃ for 0.5-2 hours with stirring speed of 50 rpm-1000rpm, and the product is collected by centrifugation at 10000rpm for 1-30 minutes.

9. The method for preparing a highly stable bismuth-based core-shell heterojunction nanomaterial according to claim 1, characterized in that, In step (6), the final cleaned product precipitate is placed in liquid nitrogen for rapid freezing for 1 to 10 minutes, and then transferred to a freeze dryer for freeze drying under vacuum conditions for 12 to 72 hours. The vacuum degree is below 100 Pa and the freezing temperature is from -10 degrees Celsius to -100 degrees Celsius to obtain powdered Bi@Bi2X3 nanomaterials.

10. A highly stable bismuth-based core-shell heterostructure nanomaterial, characterized in that, The highly stable bismuth-based core-shell heterojunction nanomaterial is prepared by the preparation method described in any one of claims 1-9.

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