A lead-free perovskite x-ray shielding composite material and a preparation method and application thereof

Abstract

The application belongs to the field of new materials, and discloses a lead-free perovskite X-ray shielding composite material and a preparation method and application thereof, and comprises the following steps: mixing ANF / DMSO dispersion liquid with ethanol to obtain re-protonated ANF dispersion liquid; mixing the re-protonated ANF dispersion liquid, CsI powder and ethanol, and stirring to obtain two portions of the same CsI / ANF dispersion liquid; mixing re-protonated ANF, Cs3Bi2I9 powder and ethanol, and stirring to obtain Cs3Bi2I9 / ANF dispersion liquid; sequentially filtering the first portion of CsI / ANF dispersion liquid, the Cs3Bi2I9 / ANF dispersion liquid and the second portion of CsI / ANF dispersion liquid by using a gel-gel method, and vacuum hot-pressing to obtain a composite gradient film with a biomimetic symmetrical structure, which is used as a lead-free perovskite X-ray shielding composite material; and the application realizes continuous and efficient X-ray shielding effect, and can improve the mechanical flexibility and thermal stability of the material.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, and specifically relates to a lead-free perovskite X-ray shielding composite material, its preparation method, and its application. Background Technology

[0002] X-rays, as a type of high-energy ionizing radiation, are widely used in fields such as medicine, industry, scientific research, and safety. For example, in the medical field, X-rays are often used for medical imaging diagnosis; in the industrial field, they can be used for non-destructive testing or materials analysis. However, the high-energy nature of X-rays can cause atomic ionization, and long-term exposure can cause irreversible damage to human tissues, DNA structures, and precision electronic equipment. Therefore, in order to reduce the hazards of X-rays, shielding materials are needed to block or reduce X-ray radiation.

[0003] Traditional lead-based shielding materials are widely used in the field of X-ray shielding. However, due to the presence of lead, traditional lead-based shielding materials have defects such as high toxicity, high density, and poor flexibility, making it difficult to meet the requirements of lightweight and flexible wearable materials. In addition, lead-based shielding materials have a weak absorption region in the energy range of 40-80keV, which cannot provide comprehensive and effective protection.

[0004] Currently, in order to overcome the shortcomings of traditional lead-based shielding materials, research has been conducted on replacing lead with high atomic number elements such as bismuth (Bi) and tungsten (W) and blending them with polymers to prepare novel X-ray shielding materials. This composite method improves the performance of the material to a certain extent. However, simply physically blending high atomic number elements such as bismuth (Bi) and tungsten (W) with polymers can easily lead to filler agglomeration and uneven distribution, resulting in an uneven internal structure of the shielding material. This causes inconsistent X-ray propagation paths within the material, making it impossible to form a continuous and efficient shielding effect, thus affecting the overall shielding performance. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a lead-free perovskite X-ray shielding composite material, its preparation method and application, to solve the technical problem that the internal structure of existing novel X-ray shielding materials is not uniform, which makes the propagation path of X-rays in the material inconsistent and unable to form a continuous and efficient shielding effect.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing a lead-free perovskite X-ray shielding composite material, comprising: The ANF / DMSO dispersion was mixed with ethanol and protonated to obtain a reprotonated ANF dispersion. CsI ​​and BiI3 were added to DMSO and stirred to dissolve. Ethanol was added as an antisolvent while stirring continuously to obtain a red precipitate. The red precipitate was dried to obtain Cs3Bi2I9 powder. Two identical CsI / ANF dispersions were obtained by mixing reprotonated ANF dispersion, CsI powder, and ethanol and stirring. A Cs3Bi2I9 / ANF dispersion was obtained by mixing reprotonated ANF, Cs3Bi2I9 powder, and ethanol and stirring. Using the gel-gel method, with a pre-set filter membrane as support, the first CsI / ANF dispersion, the Cs3Bi2I9 / ANF dispersion and the second CsI / ANF dispersion were sequentially filtered to obtain a symmetrical gel-like composite film. Vacuum hot pressing was performed on a symmetrical gel-like composite film to obtain a composite gradient film with a biomimetic symmetrical structure, which can be used as a lead-free perovskite X-ray shielding composite material.

[0007] Furthermore, the mass fraction of CsI in both CsI / ANF dispersions was 50 wt%, and the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion was 65 wt%-95 wt%.

[0008] Furthermore, using the gel-gel method, with a pre-set filter membrane as support, the first CsI / ANF dispersion, the Cs3Bi2I9 / ANF dispersion, and the second CsI / ANF dispersion were sequentially filtered to obtain a symmetrical gel-like composite film, as follows: Under vacuum conditions, a first CsI / ANF dispersion is poured onto a pre-set filter membrane for filtration to form a moist gel-like bottom layer on the surface of the pre-set filter membrane. Then, while the gel-like bottom layer is not completely dry, a Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer. After that, a second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thereby obtaining a symmetrical gel-like composite film.

[0009] Furthermore, the preset filter membrane is a microporous filter membrane with a pore size of 0.22 μm.

[0010] Furthermore, CsI and BiI3 were added to DMSO and stirred to dissolve; while continuously stirring, ethanol was added as an antisolvent to obtain a red precipitate, as follows: CsI ​​and BiI3 were added to DMSO in a molar ratio of 3:2 and stirred to dissolve. Ethanol was added while stirring continuously to obtain a red precipitate. The volume ratio of ethanol to DMSO was (1-3):(300-400).

[0011] Further, the process of drying the red precipitate to obtain Cs3Bi2I9 powder is as follows: The red precipitate was dried in the dark for 8-12 hours at a temperature of 60-80℃ to obtain Cs3Bi2I9 powder.

[0012] Furthermore, in the process of vacuum hot pressing the symmetrical gel-like composite film to obtain a composite gradient film with a biomimetic symmetrical structure, the hot pressing temperature is 75-105℃.

[0013] Furthermore, the mass fraction of Cs3Bi2I9 in the composite gradient thin film with biomimetic symmetry structure is 65wt%-95wt%.

[0014] The present invention also provides a lead-free perovskite X-ray shielding composite material, which is prepared by the preparation method of the lead-free perovskite X-ray shielding composite material; The composite gradient thin film with a biomimetic symmetric structure includes a surface layer of CsI / ANF, a middle layer of Cs3Bi2I9 / ANF, and a bottom layer of CsI / ANF, with the surface layer of CsI / ANF and the bottom layer of CsI / ANF symmetrically distributed on both sides of the middle layer of Cs3Bi2I9 / ANF.

[0015] The present invention also provides an application of a lead-free perovskite X-ray shielding composite material, which is used in the field of X-ray shielding.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for preparing lead-free perovskite X-ray shielding composite material provided by this invention is based on biomimetic principles and multi-scale structural design to obtain a composite gradient film with a biomimetic symmetrical structure, thereby achieving continuous and efficient X-ray shielding effect, while significantly improving the material's mechanical flexibility, toughness, and thermal stability. Specifically, the material is designed as a symmetrical gradient structure of "surface CsI / ANF - middle layer Cs3Bi2I9 / ANF - bottom layer CsI / ANF" to accurately simulate the mechanism of energy transfer and efficient dissipation in the photosynthetic system of green sulfur bacteria, so that X-ray photons sequentially pass through the CsI / ANF surface layer, Cs3Bi2I9 / ANF, and Cs3Bi2I9 / ANF during penetration. The 2I9 / ANF intermediate layer and the CsI / ANF bottom layer achieve stepwise attenuation and multiple shielding effects for X-rays across the entire 20-70 keV spectrum, significantly improving overall shielding efficiency while effectively suppressing secondary radiation. Specifically, the surface CsI / ANF preferentially absorbs photons below 16.4 keV and attenuates photons from 35.9-70 keV through the photoelectric effect and Compton scattering. Because the intermediate Cs3Bi2I9 / ANF layer is rich in Cs3Bi2I9, it strongly absorbs photons from 16.4-35.9 keV. The remaining scattered photons below 16.4 keV are dispersed by the bottom CsI / ANF layer through strong light... The material exhibits complete electro-absorption and capture. Secondly, a gel-gel method is employed to achieve the layer-by-layer ordered assembly of a symmetrical gradient structure of "CsI / ANF-Cs3Bi2I9 / ANF-CsI / ANF". This gel-gel method, through interfacial fusion in the gel state, significantly enhances interlayer bonding, avoiding filler agglomeration and structural defects caused by traditional physical blending, and ensuring uniform composite and continuous transition of each functional layer at the molecular or nanoscale. Furthermore, the symmetrical design of the surface and bottom CsI / ANF layers not only endows the material with dual-sided usability, effectively expanding its application flexibility, but also enhances the overall structural stability through mechanical complementarity. This invention utilizes flexible and high-strength aramid nanofibers (ANF) as a matrix to successfully encapsulate and disperse brittle lead-free perovskite fillers, Cs3Bi2I9 and CsI. While ensuring the high X-ray blocking capability of high atomic number elements, it significantly improves the material's flexibility, bending resistance, and thermal stability, meeting the practical needs of lightweight, wearable protective equipment. By introducing Cs3Bi2I9 material components, integrating biomimetic structural design with gel-gel processes, this invention achieves synergistic optimization of environmental friendliness, high-efficiency shielding, structural stability, and practical flexibility, providing a promising technical path for the industrialization of safe, high-performance X-ray protection materials.

[0017] The lead-free perovskite X-ray shielding composite material prepared by this invention possesses all the advantages of the aforementioned preparation method of the lead-free perovskite X-ray shielding composite material. Attached Figure Description

[0018] Figure 1The image shows a surface SEM image of the lead-free perovskite X-ray shielding composite material prepared in Example 1. Figure 2 The image shows a cross-sectional SEM image of the lead-free perovskite X-ray shielding composite material prepared in Example 1. Figure 3 The diagram shows the X-ray shielding efficiency of the lead-free perovskite X-ray shielding composite material prepared in this invention. Detailed Implementation

[0019] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0020] This invention provides a method for preparing a lead-free perovskite X-ray shielding composite material, comprising the following steps: Step 1: Mix chopped para-aramid fibers (PPTA), potassium hydroxide (KOH), deionized water, and dimethyl sulfoxide (DMSO), and stir continuously until the aramid fibers decompose to obtain a translucent, red, viscous ANF / DMSO dispersion; wherein the concentration of the ANF / DMSO dispersion is 0.002-0.008 g / mL.

[0021] Step 2: Mix the ANF / DMSO dispersion with ethanol and protonate it to obtain a reprotonated ANF dispersion. Specifically, add ethanol to the ANF / DMSO dispersion and let it stand for 1-2 hours to protonate the ANF; repeat the ethanol addition process 4-6 times until a white gel is formed to obtain reprotonated ANF; wherein the volume ratio of ethanol to ANF / DMSO dispersion added each time is (5-7):(1-2); redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion; wherein the concentration of reprotonated ANF in the reprotonated ANF dispersion is 0.001-0.002 g / mL.

[0022] Step 3: Add CsI and BiI3 to DMSO at a molar ratio of 3:2 and stir for 24 hours to initially dissolve, obtaining a CsI-BiI3 DMSO dispersion; then, while continuously stirring, inject ethanol as an antisolvent into the CsI-BiI3 DMSO dispersion, and filter to obtain a red precipitate; wherein, the volume ratio of ethanol to DMSO is (1-3):(300-400); transfer the red precipitate to a vacuum drying oven and dry it in the dark at a temperature of 60-80℃ for 8-12 hours to obtain Cs3Bi2I9 powder.

[0023] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 65wt%-95wt%.

[0024] Step 5: Using the gel-gel method, with a pre-set filter membrane as a support, sequentially filter the first CsI / ANF dispersion, the Cs3Bi2I9 / ANF dispersion, and the second CsI / ANF dispersion to obtain a symmetrical gel-like composite film. Preferably, the pre-set filter membrane is a microporous filter membrane with a pore size of 0.22 μm.

[0025] Specifically, the sequential filtering process is as follows: Under vacuum conditions, a first CsI / ANF dispersion is poured onto a pre-set filter membrane for filtration to form a moist gel-like bottom layer on the surface of the pre-set filter membrane. Then, while the gel-like bottom layer is not completely dry, a Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer. After that, a second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thereby obtaining a symmetrical gel-like composite film.

[0026] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 75-105℃ to obtain a composite gradient film with a biomimetic symmetrical structure, which serves as a lead-free perovskite X-ray shielding composite material; wherein the thickness of the composite gradient film with a biomimetic symmetrical structure is 0.157-0.164mm and the mass is 0.241-0.248g.

[0027] In this invention, the biomimetic symmetrical composite gradient film includes a surface layer CsI / ANF, an intermediate layer Cs3Bi2I9 / ANF, and a bottom layer CsI / ANF, with the surface layer CsI / ANF and the bottom layer CsI / ANF symmetrically distributed on both sides of the intermediate layer Cs3Bi2I9 / ANF. The biomimetic symmetrical composite gradient film is denoted as SGF-x, where x represents the actual mass fraction of the intermediate layer Cs3Bi2I9. Preferably, the value of x is 65-95, that is, the mass fraction of Cs3Bi2I9 in the biomimetic symmetrical composite gradient film is 65wt%-95wt%.

[0028] Preparation principle: The preparation method of the lead-free perovskite X-ray shielding composite material of this invention, by drawing on the energy transfer mechanism of the green sulfur bacteria photosynthetic system, constructs a symmetrical gradient structure of "surface CsI / ANF - middle layer Cs3Bi2I9 / ANF - bottom layer CsI / ANF". It utilizes the preferential absorption of photons below 16.4 keV by the surface CsI and the photoelectric effect and Compton scattering attenuation of photons from 35.9-70 keV, combined with the strong absorption characteristics of photons from 16.4-35.9 keV by the middle layer Cs3Bi2I9, and the complete capture of the remaining scattered photons below 16.4 keV through strong photoelectric absorption by the bottom CsI / ANF, achieves 2 The system achieves graded capture and stepped energy dissipation of X-rays across the 0-70 keV spectrum. Specifically, the strong absorption region of Cs and I precisely covers the weak absorption region of Bi in the 40-90 keV range, compensating for the spectral shielding shortcomings of traditional lead-based materials and conventional bismuth and tungsten-based composites, thus forming a continuous and efficient shielding effect. Secondly, lead-free CsI and Cs3Bi2I9 are selected as shielding fillers, eliminating lead at the raw material level and completely solving the problem of high toxicity in traditional lead-based materials. Simultaneously, flexible aramid nanofibers (ANF) with excellent mechanical properties are used as the matrix, uniformly filling brittle perovskite particles, significantly improving the material's flexibility and toughness while ensuring high shielding performance. Thermal stability meets the application requirements of lightweight and flexible wearables. Furthermore, the gel-gel method employs a pre-set filter membrane for layer-by-layer sequential filtration, followed by vacuum hot pressing, resulting in a strong interfacial bond in the composite film under gel conditions. The tight interlayer bonding with no obvious voids allows for uniform composite formation of Cs3Bi2I9 nanocrystals, CsI, and the ANF matrix at the molecular or nanoscale. This effectively avoids the problems of filler agglomeration and uneven distribution in conventional physical blending processes, ensuring the integrity and stability of the gradient structure and solving the technical defect of inconsistent X-ray propagation paths caused by uneven internal material structure. In addition, by designing a symmetrical gradient structure, the composite material possesses unique properties on both sides. The surface usability breaks through the limitations of traditional shielding materials that can only be used on one side. At the same time, the symmetrical gradient structure, arranged in an orderly manner in the longitudinal direction, creates an effective way to attenuate X-rays and absorb secondary radiation, which significantly suppresses the risk of secondary radiation while improving shielding effectiveness. The selection of all-inorganic lead-free perovskite and the composite design of the ANF matrix take into account both the environmental friendliness and mechanical properties of the material. The gel-gel method also provides a feasible path for the large-scale and stable preparation of the material. The final composite material provides a high-quality material solution for the development of advanced, safe and lightweight X-ray protection equipment, which can be widely adapted to the X-ray protection needs of medical, industrial and scientific research fields.

[0029] The following specific embodiments further explain the preparation method of the lead-free perovskite X-ray shielding composite material provided by the present invention: Example 1 This embodiment 1 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.002 g / mL.

[0030] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 1 hour to protonate the ANF. Repeat the ethanol addition process 4 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 5:2. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.001 g / mL.

[0031] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve the CsI-BiI3 in DMSO to obtain a CsI-BiI3 DMSO dispersion. Then, while stirring continuously, inject 300 mL of ethanol as an antisolvent into the CsI-BiI3 DMSO dispersion and filter to obtain a red precipitate. Transfer the red precipitate to a vacuum drying oven and dry it at 60 °C in the dark for 8 h to obtain Cs3Bi2I9 powder.

[0032] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 75 wt%.

[0033] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0034] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 85℃ to obtain a composite gradient film with a biomimetic symmetrical structure; wherein, the mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 75wt%, denoted as SGF-75, as a lead-free perovskite X-ray shielding composite material; the thickness of the composite gradient film with a biomimetic symmetrical structure is 0.158mm and the mass is 0.243g; Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-75 prepared in Example 1 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-75 achieved an X-ray attenuation efficiency of 58.6%-70.7% in the range of 20-70 keV, and the tensile strength was 61.7 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-75 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0035] As attached Figure 1-2 As shown, attached Figure 1 The surface SEM image of the lead-free perovskite X-ray shielding composite material prepared in Example 1 is shown in the attached image. Figure 2 The attached image shows a cross-sectional SEM image of the lead-free perovskite X-ray shielding composite material prepared in Example 1; from the attached image... Figure 1-2 As can be seen from the results, the lead-free perovskite X-ray shielding composite material prepared in Example 1 has a smooth and dense film surface with no obvious particle protrusions or agglomeration. The surface and bottom layers of the film cross-section are dense and robust, while the middle layer exhibits a stacked structure resembling "bricks and mortar." Notably, the excellent structural density and interfacial bonding of the composite material enable it to possess good X-ray shielding performance and mechanical strength. The smooth and dense surface reduces scattering loss during X-ray penetration, which helps to improve the attenuation efficiency of X-rays. The density of the surface and bottom layers enhances the mechanical strength and weather resistance of the material, ensuring its structural stability during long-term use.

[0036] Example 2 This embodiment 2 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.004 g / mL.

[0037] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 2 hours to protonate the ANF. Repeat the ethanol addition process 6 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 7:1. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.002 g / mL.

[0038] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve, obtaining a DMSO dispersion of CsI-BiI3; then, while stirring continuously, inject 600 mL of ethanol as an antisolvent into the DMSO dispersion of CsI-BiI3, and filter to obtain a red precipitate; transfer the red precipitate to a vacuum drying oven and dry it at 80 °C in the dark for 8 h to obtain Cs3Bi2I9 powder.

[0039] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 65 wt%.

[0040] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0041] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 75℃ to obtain a composite gradient film with a biomimetic symmetrical structure; wherein, the mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 65wt%, denoted as SGF-65, as a lead-free perovskite X-ray shielding composite material; the thickness of the composite gradient film with a biomimetic symmetrical structure is 0.164mm and the mass is 0.248g; Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-65 prepared in Example 2 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-65 achieved an X-ray attenuation efficiency of 52.6%-64.7% in the range of 20-70 keV, and the tensile strength was 78.3 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-65 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0042] Example 3 This embodiment 3 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.006 g / mL.

[0043] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 2 hours to protonate the ANF. Repeat the ethanol addition process 5 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 7:2. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.001 g / mL.

[0044] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve the CsI-BiI3 in DMSO to obtain a CsI-BiI3 DMSO dispersion. Then, while stirring continuously, inject 400 mL of ethanol as an antisolvent into the CsI-BiI3 DMSO dispersion and filter to obtain a red precipitate. Transfer the red precipitate to a vacuum drying oven and dry it at 60 °C in the dark for 12 h to obtain Cs3Bi2I9 powder.

[0045] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 65 wt%.

[0046] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0047] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 75℃ to obtain a composite gradient film with a biomimetic symmetrical structure; wherein, the mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 65wt%, denoted as SGF-65, as a lead-free perovskite X-ray shielding composite material; the thickness of the composite gradient film with a biomimetic symmetrical structure is 0.162mm and the mass is 0.244g; Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-65 prepared in Example 3 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-65 achieved an X-ray attenuation efficiency of 52.9%-66.2% in the range of 20-70 keV, and the tensile strength was 74.4 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-65 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0048] Example 4 This embodiment 4 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.002 g / mL.

[0049] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 1 hour to protonate the ANF. Repeat the ethanol addition process 5 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 5:2. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.001 g / mL.

[0050] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve, obtaining a DMSO dispersion of CsI-BiI3; then, while stirring continuously, inject 300 mL of ethanol as an antisolvent into the DMSO dispersion of CsI-BiI3, and filter to obtain a red precipitate; transfer the red precipitate to a vacuum drying oven and dry it at 80 °C in the dark for 9 h to obtain Cs3Bi2I9 powder.

[0051] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 75 wt%.

[0052] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0053] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 95℃ to obtain a composite gradient film with a biomimetic symmetrical structure. The mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 75wt%, denoted as SGF-75, which serves as a lead-free perovskite X-ray shielding composite material. The thickness of the composite gradient film with a biomimetic symmetrical structure is 0.157mm, and the mass is 0.242g.

[0054] Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-75 prepared in Example 4 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-75 achieved an X-ray attenuation efficiency of 57.1%-69.3% in the range of 20-70 keV, and the tensile strength was 61.8 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-75 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0055] Example 5 This embodiment 5 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.008 g / mL.

[0056] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 2 hours to protonate the ANF. Repeat the ethanol addition process 6 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 7:2. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.001 g / mL.

[0057] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve the CsI-BiI3 in DMSO to obtain a CsI-BiI3 DMSO dispersion. Then, while stirring continuously, inject 500 mL of ethanol as an antisolvent into the CsI-BiI3 DMSO dispersion and filter to obtain a red precipitate. Transfer the red precipitate to a vacuum drying oven and dry it at 80 °C in the dark for 8 h to obtain Cs3Bi2I9 powder.

[0058] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 85 wt%.

[0059] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0060] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 95℃ to obtain a composite gradient film with a biomimetic symmetrical structure. The mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 85wt%, denoted as SGF-85, which serves as a lead-free perovskite X-ray shielding composite material. The thickness of the composite gradient film with a biomimetic symmetrical structure is 0.159mm, and the mass is 0.245g.

[0061] Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-85 prepared in Example 5 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-85 achieved an X-ray attenuation efficiency of 61.3%-75.6% in the range of 20-70 keV, and the tensile strength was 46.5 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-85 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0062] Example 6 This embodiment 6 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.002 g / mL.

[0063] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 1 hour to protonate the ANF. Repeat the ethanol addition process 6 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 5:1. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.002 g / mL.

[0064] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve, obtaining a DMSO dispersion of CsI-BiI3; then, while stirring continuously, inject 600 mL of ethanol as an antisolvent into the DMSO dispersion of CsI-BiI3, and filter to obtain a red precipitate; transfer the red precipitate to a vacuum drying oven and dry it at 60 °C in the dark for 12 h to obtain Cs3Bi2I9 powder.

[0065] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 85 wt%.

[0066] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0067] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 105℃ to obtain a composite gradient film with a biomimetic symmetrical structure. The mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 85wt%, denoted as SGF-85, which serves as a lead-free perovskite X-ray shielding composite material. The thickness of the composite gradient film with a biomimetic symmetrical structure is 0.161mm, and the mass is 0.247g.

[0068] Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-85 prepared in Example 6 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-85 achieved an X-ray attenuation efficiency of 61.1%-75.2% in the range of 20-70 keV, and the tensile strength was 47.3 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-85 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0069] Example 7 This embodiment 7 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.006 g / mL.

[0070] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 1 hour to protonate the ANF. Repeat the ethanol addition process 4 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 5:1. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.001 g / mL.

[0071] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve the CsI-BiI3 in DMSO to obtain a CsI-BiI3 DMSO dispersion. Then, while stirring continuously, inject 500 mL of ethanol as an antisolvent into the CsI-BiI3 DMSO dispersion and filter to obtain a red precipitate. Transfer the red precipitate to a vacuum drying oven and dry it at 70 °C in the dark for 8 h to obtain Cs3Bi2I9 powder.

[0072] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 95 wt%.

[0073] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0074] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 95℃ to obtain a composite gradient film with a biomimetic symmetrical structure; wherein, the mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 95wt%, denoted as SGF-95, as a lead-free perovskite X-ray shielding composite material; the thickness of the composite gradient film with a biomimetic symmetrical structure is 0.166mm and the mass is 0.244g.

[0075] Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-95 prepared in Example 7 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-95 achieved an X-ray attenuation efficiency of 613.4%-78.1% in the range of 20-70 keV, and the tensile strength was 31.5 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-95 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0076] Example 8 This embodiment 8 provides a method for preparing a lead-free perovskite X-ray shielding composite material, including the following steps: Step 1: Mix PPTA, KOH, deionized water and DMSO and stir until the aramid fibers decompose to obtain a semi-transparent, red, viscous ANF / DMSO dispersion with a concentration of 0.002 g / mL.

[0077] Step 2: Add ethanol to the ANF / DMSO dispersion and let it stand for 1 hour to protonate the ANF. Repeat the ethanol addition process 4 times until a white gel is formed to obtain reprotonated ANF. The volume ratio of ethanol to ANF / DMSO dispersion added each time is 5:2. Redisperse the reprotonated ANF in ethanol to obtain a reprotonated ANF dispersion with a concentration of 0.002 g / mL.

[0078] Step 3: Add 5.4 mmol of CsI and 3.6 mmol of BiI3 to 3 mL of DMSO and stir for 24 h to initially dissolve, obtaining a DMSO dispersion of CsI-BiI3; then, while stirring continuously, inject 300 mL of ethanol as an antisolvent into the DMSO dispersion of CsI-BiI3, and filter to obtain a red precipitate; transfer the red precipitate to a vacuum drying oven and dry it at 60 °C in the dark for 10 h to obtain Cs3Bi2I9 powder.

[0079] Step 4: Mix the reprotonated ANF dispersion, CsI powder, and ethanol, and mechanically stir to obtain two identical homogeneous CsI / ANF dispersions; wherein the mass fraction of CsI in both CsI / ANF dispersions is 50 wt%; mix the reprotonated ANF, Cs3Bi2I9 powder, and ethanol, and stir to obtain a Cs3Bi2I9 / ANF dispersion; wherein the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersion is 95 wt%.

[0080] Step 5: Using the gel-gel method, with a microporous filter membrane with a pore size of 0.22 μm as support, under vacuum conditions, the first CsI / ANF dispersion is poured onto the preset filter membrane for filtration to form a moist gel-like bottom layer on the surface of the preset filter membrane; then, when the gel-like bottom layer is not completely dry, the Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer; then, the second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thus obtaining a symmetrical gel-like composite film.

[0081] Step 6: Vacuum hot pressing is performed on the symmetrical gel-like composite film at a hot pressing temperature of 105℃ to obtain a composite gradient film with a biomimetic symmetrical structure. The mass fraction of Cs3Bi2I9 in the prepared composite gradient film with a biomimetic symmetrical structure is 95wt%, denoted as SGF-95, which serves as a lead-free perovskite X-ray shielding composite material. The thickness of the composite gradient film with a biomimetic symmetrical structure is 0.162mm, and the mass is 0.241g.

[0082] Shielding performance test: The shielding performance of the lead-free perovskite X-ray shielding composite material SGF-95 prepared in Example 5 was tested. The test results showed that the lead-free perovskite X-ray shielding composite material SGF-95 achieved an X-ray attenuation efficiency of 63.4%-78.1% in the range of 20-70 keV, and the tensile strength was 30.8 MPa. Therefore, the lead-free perovskite X-ray shielding composite material SGF-95 has good X-ray shielding performance and mechanical strength, and excellent comprehensive performance.

[0083] As attached Figure 3 As shown, attached Figure 3 The accompanying document presents the X-ray attenuation efficiency curves of the lead-free perovskite X-ray shielding composite materials prepared in Examples 1, 2, 5, and 8 in the range of 20-70 keV; from the appendix... Figure 3 As can be seen, the shielding efficiency of the lead-free perovskite X-ray shielding composite material significantly improves with decreasing tube voltage. This is because low-energy X-rays are more easily absorbed by the material, while high-energy X-rays have stronger penetrating power. Furthermore, compared with pure ANF film, the shielding attenuation capability is significantly improved after adding Cs3Bi2I9 filler, and the attenuation capability of the lead-free perovskite X-ray shielding composite material continuously increases with the Cs3Bi2I9 content increasing from 65% to 95%. In particular, within the tube voltage range of 20-70 keV, the AE of the lead-free perovskite X-ray shielding composite material SGF-95 is as high as 63.4%-78.1%.

[0084] The preparation method of the lead-free perovskite X-ray shielding composite material of the present invention draws on the energy transfer mechanism of the green sulfur bacteria photosynthetic system and designs a symmetrical gradient structure of "surface CsI / ANF - middle layer Cs3Bi2I9 / ANF - bottom layer CsI / ANF". Through functional partitioning of each layer, it achieves hierarchical capture and attenuation of X-rays in the full spectrum of 20-70 keV, and suppresses secondary radiation. Among them, the surface CsI / ANF preferentially absorbs photons below 16.4 keV and attenuates photons of 35.9-70 keV through photoelectric effect and Compton scattering; the middle layer Cs3Bi2I9 / ANF is rich in Cs3Bi2I9 and can strongly absorb photons of 16.4–35.9 keV; the remaining scattered photons below 16.4 keV are completely captured by the bottom layer CsI / ANF through strong photoelectric absorption, thereby achieving effective shielding of X-rays in the full spectrum.

[0085] This invention addresses the core issues of traditional X-ray shielding materials, such as insufficient full-spectrum shielding, high risk of secondary radiation, conflict between environmental protection and practicality, structural instability, and limited application scenarios. It symmetrically distributes the surface CsI / ANF and bottom CsI / ANF layers on both sides of the intermediate Cs3Bi2I9 / ANF layer. This symmetrical design of the surface and bottom CsI / ANF layers provides the film with usability on both sides, overcoming the limitation of traditional materials being used only on one side. Lead-free, high atomic number CsI and Cs3Bi2I9 are selected as shielding fillers, with ANF as the matrix, balancing environmental friendliness and mechanical properties. Flexible aramid nanofibers with excellent mechanical properties are used as the matrix, composited with Cs3Bi2I9 and CsI fillers. A biomimetic symmetrical gradient film is prepared using a gel-gel method, achieving strong interfacial bonding through layer-by-layer assembly in a gel state, thus improving the structural stability of the material.

[0086] In this invention, an all-inorganic lead-free perovskite Cs3Bi2I9 is ​​selected as the core shielding component. The strong absorption regions of Cs and I precisely cover the weak absorption region of Bi in the 40-90 keV range, thus achieving broad-spectrum and efficient attenuation of continuous-spectrum X-rays. Inspired by biomimicry, a symmetrical gradient structure guides photons through multiple physical processes via longitudinally ordered arrangement, achieving a stepwise dissipation of energy. This significantly suppresses secondary radiation while improving shielding effectiveness, providing both positive and negative protection. Layer-by-layer assembly using a gel-gel method ensures a strong interfacial bond in the layered film under gel conditions, guaranteeing the integrity and stability of the gradient structure. Furthermore, a flexible ANF substrate is used to support the brittle... The perovskite Cs3Bi2I9 particles are uniformly filled within the material, significantly improving its mechanical flexibility, toughness, and thermal stability while maintaining high shielding performance, thus meeting the demand for lightweight and flexible shielding materials in wearable devices. The lead-free perovskite X-ray shielding composite material prepared in this invention has tight interlayer bonding with no obvious voids. Cs3Bi2I9 nanocrystals, CsI, and the ANF matrix are uniformly composited at the molecular or nanoscale. By constructing a symmetrical gradient distribution of elements, an effective pathway for attenuating X-rays and absorbing secondary radiation is established within the material, while maintaining excellent flexibility. This provides a very promising material solution for developing advanced, safe, lightweight, and flexible protective equipment.

[0087] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A method for preparing a lead-free perovskite X-ray shielding composite material, characterized in that, include: The ANF / DMSO dispersion was mixed with ethanol and protonated to obtain a reprotonated ANF dispersion. CsI ​​and BiI3 were added to DMSO and stirred to dissolve. Ethanol was added as an antisolvent while stirring continuously to obtain a red precipitate. The red precipitate was dried to obtain Cs3Bi2I9 powder. Two identical CsI / ANF dispersions were obtained by mixing reprotonated ANF dispersion, CsI powder, and ethanol and stirring. A Cs3Bi2I9 / ANF dispersion was obtained by mixing reprotonated ANF, Cs3Bi2I9 powder, and ethanol and stirring. Using the gel-gel method, with a pre-set filter membrane as support, the first CsI / ANF dispersion, the Cs3Bi2I9 / ANF dispersion and the second CsI / ANF dispersion were sequentially filtered to obtain a symmetrical gel-like composite film. Vacuum hot pressing was performed on a symmetrical gel-like composite film to obtain a composite gradient film with a biomimetic symmetrical structure, which can be used as a lead-free perovskite X-ray shielding composite material.

2. The method for preparing a lead-free perovskite X-ray shielding composite material according to claim 1, characterized in that, The mass fraction of CsI in both CsI / ANF dispersions was 50 wt%, and the mass fraction of Cs3Bi2I9 in the Cs3Bi2I9 / ANF dispersions ranged from 65 wt% to 95 wt%.

3. The method for preparing a lead-free perovskite X-ray shielding composite material according to claim 1, characterized in that, The process of sequentially filtering a first CsI / ANF dispersion, a Cs3Bi2I9 / ANF dispersion, and a second CsI / ANF dispersion using a gel-gel method with a pre-set filter membrane as support to obtain a symmetrical gel-like composite film is as follows: Under vacuum conditions, a first CsI / ANF dispersion is poured onto a pre-set filter membrane for filtration to form a moist gel-like bottom layer on the surface of the pre-set filter membrane. Then, while the gel-like bottom layer is not completely dry, a Cs3Bi2I9 / ANF dispersion is poured onto the surface of the gel-like bottom layer for filtration to form a gel-like middle layer on the surface of the gel-like bottom layer. After that, a second CsI / ANF dispersion is poured onto the surface of the gel-like middle layer for filtration to form a gel-like top layer on the surface of the gel-like middle layer, thereby obtaining a symmetrical gel-like composite film.

4. The method for preparing a lead-free perovskite X-ray shielding composite material according to claim 1, characterized in that, The preset filter membrane is a microporous filter membrane with a pore size of 0.22μm.

5. The method for preparing a lead-free perovskite X-ray shielding composite material according to claim 1, characterized in that, The process of adding CsI and BiI3 to DMSO and stirring to dissolve them, followed by adding ethanol as an antisolvent while continuously stirring to obtain a red precipitate, is as follows: CsI ​​and BiI3 were added to DMSO in a molar ratio of 3:2 and stirred to dissolve. Ethanol was added while stirring continuously to obtain a red precipitate. The volume ratio of ethanol to DMSO was (1-3):(300-400).

6. The method for preparing a lead-free perovskite X-ray shielding composite material according to claim 1, characterized in that, The process of drying the red precipitate to obtain Cs3Bi2I9 powder is as follows: The red precipitate was dried in the dark for 8-12 hours at a temperature of 60-80℃ to obtain Cs3Bi2I9 powder.

7. The method for preparing a lead-free perovskite X-ray shielding composite material according to claim 1, characterized in that, In the process of vacuum hot pressing a symmetrical gel-like composite film to obtain a composite gradient film with a biomimetic symmetrical structure, the hot pressing temperature is 75-105℃.

8. The method for preparing a lead-free perovskite X-ray shielding composite material according to claim 1, characterized in that, The mass fraction of Cs3Bi2I9 in the composite gradient thin film with biomimetic symmetry structure is 65wt%-95wt%.

9. A lead-free perovskite X-ray shielding composite material, characterized in that, The lead-free perovskite X-ray shielding composite material was prepared using the preparation method described in any one of claims 1-9. The composite gradient thin film with a biomimetic symmetric structure includes a surface layer CsI / ANF, a middle layer Cs3Bi2I9 / ANF, and a bottom layer CsI / ANF, with the surface layer CsI / ANF and the bottom layer CsI / ANF symmetrically distributed on both sides of the middle layer Cs3Bi2I9 / ANF.

10. The application of the lead-free perovskite X-ray shielding composite material as described in claim 9, characterized in that, The lead-free perovskite X-ray shielding composite material is used in the field of X-ray shielding.

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