Graphene quantum dot / indium sulfide electromagnetic wave absorbing material and preparation method thereof

Abstract

The application discloses a graphene quantum dot / indium sulfide electromagnetic wave absorbing material and a preparation method thereof, and comprises the following steps: carrying out a hydrothermal reduction reaction on trinitro-pyrene and an alkaline solution to obtain graphene quantum dot powder rich in hydroxyl functional groups on the surface; and carrying out a hydrothermal reaction on a mixture of indium chloride tetrahydrate and thioacetamide and the graphene quantum dot powder to obtain a graphene quantum dot / indium sulfide heterojunction electromagnetic wave absorbing material with a sulfur vacancy concentration of 3.8% to 5.7%. The addition amount of the sulfur source is controlled by regulating the addition amount of the thioacetamide in the hydrothermal reaction process, the introduced sulfur vacancy concentration is accurately controlled, the In-O covalent bond is formed at the interface between the graphene quantum dot and the indium sulfide, the interface covalent bridging structure is formed, the interface charge transfer efficiency is accelerated, the built-in electric field in the interface is enhanced, stronger interface polarization loss is induced, and the performance of high absorption intensity and wide bandwidth of the composite wave absorbing material is realized.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically a graphene quantum dot / indium sulfide electromagnetic wave absorbing material and its preparation method. Background Technology

[0002] With the rapid iteration of modern electronic information technology and wireless communication technology, electromagnetic waves are increasingly used as information transmission carriers. However, the resulting electromagnetic radiation pollution and electromagnetic interference problems are becoming increasingly prominent. Electromagnetic waves not only interfere with the normal operation of precision electronic equipment and damage the electromagnetic compatibility environment, but also pose a potential threat to human health. In the defense field, they can even affect the stealth performance of equipment and information security. Therefore, high-performance electromagnetic wave absorbing materials have become a research hotspot and core demand in the field of materials science.

[0003] From a technical perspective, the core performance of electromagnetic wave absorbing materials depends on the efficiency of their loss mechanisms. Interface polarization loss, as a key loss path, directly determines the material's electromagnetic wave attenuation efficiency. Heterogeneous composite materials, due to their ability to integrate the physicochemical advantages of different components and achieve synergistic loss mechanisms, have become the mainstream development direction for high-performance microwave absorbing materials. The built-in electric field at the interface is the core factor controlling polarization loss and subsequent microwave absorption performance in various heterogeneous structures. Traditional theory holds that the strength of the built-in electric field at the interface is mainly determined by the Fermi level difference between the heterogeneous interfaces. The larger the Fermi level difference, the stronger the thermodynamic driving force of charge transfer, and the more significant the built-in electric field at the interface, thus improving polarization loss efficiency. Therefore, existing technologies generally increase the Fermi level difference through defect engineering (such as vacancy modulation) or element doping to strengthen the built-in electric field at the interface and optimize microwave absorption performance. However, existing technologies still have many insurmountable defects, resulting in performance that cannot meet the requirements of high-end applications. 1. Significant bottlenecks exist in the modulation of the built-in electric field at the interface. Existing technologies that rely on the Fermi level difference to modulate the built-in electric field at the interface have inherent limitations. Excessive defect concentration can lead to sulfide lattice distortion or even amorphization, resulting in the loss of Fermi level modulation capability. Element doping is limited by solid solubility and orbital hybridization saturation effects, and the adjustment range of the Fermi level difference is strictly constrained by the intrinsic electronic structure of the material, thus creating a bottleneck in enhancing the built-in electric field at the interface and preventing breakthrough improvements.

[0004] 2. Insufficient absorption performance. Due to the aforementioned issues, most sulfide or quantum dot materials generally suffer from the defects of "weak absorption and narrow bandwidth". The minimum reflection loss is only -20 dB to -30 dB, and the effective absorption bandwidth is less than 5 GHz, which cannot meet the core requirements of "high absorption intensity, wide effective bandwidth, and thin matching thickness" for advanced stealth, precision electronic protection and other scenarios.

[0005] The aforementioned defects are interconnected, with the core issue being the limited enhancement of the built-in electric field strength at the interface. Existing control technologies have failed to break through the control paradigm dependent on the Fermi level difference, ultimately making it difficult for the electromagnetic wave absorption intensity and effective absorption bandwidth of related materials to achieve a qualitative leap. Summary of the Invention

[0006] To address the limitations of existing electromagnetic wave absorbing materials, which rely on ΔEf to control the built-in electric field at the interface, resulting in insufficient absorption intensity and effective absorption bandwidth, this invention provides a graphene quantum dot (GQDs) / indium sulfide (In2S3) electromagnetic wave absorbing material and its preparation method. By precisely controlling the sulfur vacancy concentration of In2S3, the interface is driven from physical adsorption orientation to covalent bridging. By adding interface charge and dynamics, the built-in electric field at the interface is enhanced, thereby optimizing polarization loss and significantly improving the electromagnetic wave absorption intensity and effective absorption bandwidth of the material.

[0007] The present invention is achieved through the following technical solution.

[0008] One aspect of the present invention provides a method for preparing a graphene quantum dot / indium sulfide electromagnetic wave absorbing material, comprising: (a) Trinitropyrene was mixed with an alkaline solution at a mass ratio of (2~5):(300~800) and ultrasonically dispersed. The mixture was then subjected to hydrothermal reduction reaction, filtered, purified by dialysis, and freeze-dried to obtain graphene quantum dot powder with hydroxyl functional groups on its surface. (b) Indium chloride tetrahydrate with a molar ratio of 1:(1.40~1.50) was mixed with thioacetamide to obtain a mixture. The mixture was then dispersed with graphene quantum dot powder in deionized water at a mass ratio of (7~9):1. After being mixed evenly, a hydrothermal reaction was carried out. After washing and drying, a graphene quantum dot / indium sulfide electromagnetic wave absorbing material was obtained.

[0009] Preferably, in step (a), the preparation of trinitropyrene includes: adding pyrene to nitric acid at a mass ratio of (1~2):(50~90), refluxing and stirring at 60~90℃ for 10~12 h to carry out a nitration reaction to obtain trinitropyrene.

[0010] As a preferred method, trinitropyrene is ultrasonically treated with an alkaline solution for 2-10 hours, followed by hydrothermal reduction at 190℃-210℃ for 8-12 hours.

[0011] Preferably, the alkaline solution is a sodium hydroxide or potassium hydroxide solution.

[0012] Preferably, in step (a), after the hydrothermal reduction reaction, the product is filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da.

[0013] Preferably, in step (a), the product is freeze-dried at -60 °C.

[0014] Preferably, in step (b), the mixture and graphene quantum dot powder are dispersed in deionized water, with a solution concentration of 0.08~0.10 g / mL.

[0015] Preferably, in step (b), the hydrothermal reaction is carried out at 80~100℃ for 10~14 h; the product is dried in a vacuum drying oven at 50~70℃ for 12~24 h.

[0016] In another aspect, the present invention provides a graphene quantum dot / indium sulfide electromagnetic wave absorbing material prepared by the method described above.

[0017] The present invention, by adopting the above technical solution, has the following beneficial effects: 1. This invention prepares trinitropyrene and reacts it with an alkaline solution to obtain graphene quantum dot powder with a surface rich in hydroxyl functional groups. The hydroxyl functional groups can serve as subsequent interfacial reaction sites, and undergo coordination or bonding reactions with indium species during the hydrothermal composite process, promoting the formation of In-O covalent bonds between graphene quantum dots and indium sulfide.

[0018] 2. This invention involves the interfacial bonding of indium chloride, thioacetamide, and graphene quantum dot powder during a hydrothermal reaction, resulting in the uniform dispersion of graphene quantum dots on the surface of indium sulfide, thus forming an in-situ graphene quantum dot / indium sulfide composite structure. This stabilizes the sulfur vacancy concentration of indium sulfide in the resulting graphene quantum dot / indium sulfide electromagnetic wave absorbing material at 3.8%~5.7%, achieving a sulfur vacancy concentration of 3.8%~5.7% for indium sulfide. In-O covalent bonds are formed at the interface between the graphene quantum dots and indium sulfide, and the built-in electric field strength at the interface is (1.8~2)*10⁻⁶. -3 mV / nm. The effective absorption bandwidth of electromagnetic waves of graphene quantum dot / indium sulfide electromagnetic wave absorbing material was achieved in the range of 5.1-7.0 GHz, with a minimum reflection loss of -36.5 to -48.3 dB.

[0019] This invention can simultaneously meet the application requirements of electromagnetic wave absorbing materials for strong absorption and wide bandwidth, and is suitable for application scenarios such as anti-interference of electronic equipment, radar stealth, electromagnetic protection of communication base stations, and electromagnetic compatibility of automotive electronics. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings: Figure 1(a) and Figure 1(b) are schematic diagrams of the interface structure of the GQDs / In2S3 electromagnetic wave absorbing material provided by the present invention. Figure 1(a) is the interface structure of physical adsorption, and Figure 1(b) is the interface structure of In-O covalent bridging. Figure 2 These are scanning electron microscope (SEM) images of the graphene quantum dot / indium sulfide electromagnetic wave absorbing material provided by the present invention under different sulfur vacancy concentrations, wherein (a) is the SEM image of Example 4, (b) is the SEM image of Example 3, (c) is the SEM image of Example 2, and (d) is the SEM image of Example 1. Figure 3 This is a transmission electron microscope image and elemental distribution of graphene quantum dots / indium sulfide with a sulfur vacancy concentration of 5.7% provided in Example 1 of this invention; Figure 4 These are synchrotron radiation characterization diagrams of the graphene quantum dot / indium sulfide electromagnetic wave absorbing material provided by the present invention under different sulfur vacancy concentrations, wherein (a) is the synchrotron radiation characterization diagram of Example 4, (b) is the synchrotron radiation characterization diagram of Example 3, (c) is the synchrotron radiation characterization diagram of Example 2, and (d) is the synchrotron radiation characterization diagram of Example 1. Figure 5 These are test diagrams of the interface built-in electric field strength of electromagnetic wave absorbing materials in Examples 1-4 and Comparative Examples 1-8 of this invention, namely graphene quantum dots / indium sulfide, pure indium sulfide, and mixtures of graphene quantum dots and indium sulfide, under different sulfur vacancy concentrations. (a) is the interface built-in electric field strength test diagram of Examples 1-4, (b) is the interface built-in electric field strength test diagram of Comparative Examples 1-4, and (c) is the interface built-in electric field strength test diagram of Comparative Examples 5-8. Figure 6 The graphs show the absorption performance test results of the graphene quantum dot / indium sulfide electromagnetic wave absorbing material provided by the present invention under different sulfur vacancy concentrations. Among them, (a) is the absorption performance test result of Example 4, (b) is the absorption performance test result of Example 3, (c) is the absorption performance test result of Example 2, and (d) is the absorption performance test result of Example 1. Figure 7 These are test results of the absorption performance of the indium sulfide electromagnetic wave absorbing material provided by the present invention under different sulfur vacancy concentrations. Among them, (a) is the test result of the absorption performance of Comparative Example 1, (b) is the test result of the absorption performance of Comparative Example 2, (c) is the test result of the absorption performance of Comparative Example 3, and (d) is the test result of the absorption performance of Comparative Example 4. Figure 8The graphs show the absorption performance test results of the electromagnetic wave absorbing material of graphene quantum dots and indium sulfide mixture provided by the present invention under different sulfur vacancy concentrations. Among them, (a) is the absorption performance test result of Comparative Example 5, (b) is the absorption performance test result of Comparative Example 6, (c) is the absorption performance test result of Comparative Example 7, and (d) is the absorption performance test result of Comparative Example 8. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0022] The method for preparing graphene quantum dot / indium sulfide electromagnetic wave absorbing material provided by the present invention includes the following steps: S1, Preparation of graphene quantum dots: Add 1-2 g of pyrene to 50-90 mL of nitric acid and reflux and stir at 60-90 °C for 10-12 h to carry out the nitration reaction to obtain trinitropyrene. After the reaction is complete, allow the mixed solution to cool naturally to room temperature, dilute with 1 L of deionized water, and then filter through a 0.22 μm microporous membrane to collect the yellow 1,3,6-trinitropyrene powder (yield of about 90%).

[0023] 2–5 g of trinitropyrene powder was dispersed in 300–800 ml of 0.2 M sodium hydroxide or potassium hydroxide solution and sonicated at 500 W and 40 kHz for 2–10 h to ensure thorough dispersion. The dispersion was then transferred to a high-pressure reactor for hydrothermal reduction at 190–210 °C for 8–12 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried at -60 °C to obtain graphene quantum dot powder with a surface rich in -OH functional groups.

[0024] S2, Preparation of graphene quantum dot / indium sulfide electromagnetic wave absorbing materials with different sulfur vacancy concentrations: Indium chloride tetrahydrate and thioacetamide were mixed at a molar ratio of 1:(1.40~1.50) to obtain a mixture. The mixture was then dispersed in deionized water at a mass ratio of (7~9):1 with graphene quantum dot powder, and the concentration of the mixed solution was 0.08~0.10 g / mL. The mixed solution was transferred to a 50 mL high-pressure reactor for hydrothermal reaction at 80~100℃ for 10~14 h. After the reaction was completed, the high-pressure reactor was naturally cooled to room temperature, and the product was collected. The product was washed 3~5 times each with deionized water and ethanol to remove unreacted impurities. The product was then dried in a vacuum drying oven at 50~70℃ for 12~24 h to obtain indium sulfide powder graphene quantum dot / indium sulfide electromagnetic wave absorbing material with a sulfur vacancy concentration preferably of 3.8%~5.7%.

[0025] The electromagnetic wave absorbing material prepared by this invention is a heterostructure composite material formed by graphene quantum dots and indium sulfide. In this material, the graphene quantum dots are uniformly dispersed on the surface of indium sulfide, and the particle size of the graphene quantum dots is 1 nm to 10 nm. The indium sulfide has a hexagonal crystal structure.

[0026] This invention introduces pyrene into nitric acid to carry out a nitration reaction to prepare trinitropyrene. The introduction of active groups such as nitro groups into the pyrene molecule enhances its subsequent reactivity in an alkaline environment, which is beneficial for the formation of small-sized graphene quantum dot precursors rich in oxygen-containing functional groups during hydrothermal reduction.

[0027] Mixing trinitropyrene with an alkaline solution of sodium hydroxide or potassium hydroxide provides a suitable alkaline reaction environment, promoting the denitration, redox transformation, condensation and carbonization processes of trinitropyrene molecules, so that the surface of the resulting graphene quantum dots retains more hydroxyl functional groups.

[0028] Sonicating trinitropyrene with an alkaline solution ensures its full dispersion, reduces molecular or intermediate aggregation, and improves the uniformity of subsequent hydrothermal reactions. Controlling the hydrothermal reaction conditions ensures complete reduction and carbonization of trinitropyrene, forming structurally stable graphene quantum dots. This avoids insufficient carbonization and uneven functional group distribution due to excessively low reaction temperature or time, or excessive carbonization and reduction of surface hydroxyl functional groups due to excessively high temperature or time.

[0029] By employing microporous membrane filtration, large particles and unreacted agglomerates are removed, resulting in a more uniform particle size distribution of graphene quantum dots. Dialysis using dialysis bags with a molecular weight cutoff of 3500 Da removes residual inorganic salts, small molecule byproducts, and excess alkali, reducing the interference of impurities on subsequent interfacial recombination and electromagnetic parameters. Powdered graphene quantum dots are obtained through freeze-drying, which better preserves their dispersed structure and surface functional groups, avoiding particle agglomeration and loss of hydroxyl functional groups caused by conventional high-temperature drying.

[0030] The presence of -OH hydroxyl functional groups on the surface serves as a site for subsequent interfacial reactions, enabling coordination or bonding reactions with indium species during hydrothermal composite processes. This promotes the formation of In-O covalent bonds between graphene quantum dots and indium sulfide. This avoids the problem of weak interfacial bonding between graphene quantum dots and indium sulfide relying solely on physical adsorption, improving the dispersion uniformity and interfacial bonding stability of graphene quantum dots on the indium sulfide surface. Furthermore, it provides a structural basis for interfacial charge transfer, enhanced interfacial polarization, and the formation and enhancement of the built-in electric field at the interface.

[0031] In this embodiment of the invention, the mixing ratio of indium chloride tetrahydrate and thioacetamide is controlled to provide sufficient active sites for the interfacial reaction. The graphene quantum dot surface is rich in hydroxyl functional groups, which form active site pairs with sulfur vacancies in indium sulfide. The -OH groups on the graphene surface undergo a directional chemical reaction, forming In-O covalent bonds at the interface between the graphene quantum dots and indium sulfide, constituting an interfacial covalent bridging structure to build an atomic-level charge transport channel, thereby enhancing the dynamics of the built-in electric field at the interface. The minimum reflection loss is -36.5 to -48.3 dB in the frequency range of 2 GHz to 18 GHz, and the absorption bandwidth is 5.1 to 7.0 GHz.

[0032] By controlling the molar ratio of indium chloride tetrahydrate to thioacetamide to regulate the amount of sulfur source added, the sulfur vacancy concentration in indium sulfide was controllably adjusted, stabilizing the sulfur vacancy concentration of indium sulfide in the resulting graphene quantum dot / indium sulfide electromagnetic wave absorbing material at 3.8%–5.7%. This sulfur vacancy concentration range can form an appropriate number of defect sites and local charge inhomogeneity regions in the indium sulfide lattice, enhancing defect polarization. Simultaneously, it is beneficial for regulating the electronic structure of the indium sulfide surface, making it easier to promote interfacial In-O covalent coupling between indium sulfide and the hydroxyl-rich graphene quantum dots, resulting in a more significant charge redistribution at the interface, which is beneficial for subsequently improving the built-in electric field strength at the interface.

[0033] Under the combined influence of sulfur vacancy concentration, hydroxyl functional groups on the graphene quantum dot surface, and the interfacial covalent bonding structure, an effective redistribution of interfacial charge and directional charge transport are achieved between the graphene quantum dots and indium sulfide, resulting in an interfacial built-in electric field strength of (1.8~2.0)×10⁻⁶. 3 mV / nm. The enhanced interfacial built-in electric field can improve charge separation efficiency and directional migration capability, promote charge accumulation, relaxation and dissipation processes at the interface, thereby enhancing the interfacial polarization loss capability of the material and obtaining a stronger interfacial polarization response. This overcomes the problem that traditional heterostructure microwave absorbing materials mainly rely on Fermi level difference to control the interfacial built-in electric field, and significantly enhances the intensity of the interfacial built-in electric field.

[0034] A mixture of indium chloride tetrahydrate and thioacetamide, along with graphene quantum dot powder, was dispersed in deionized water at a specific ratio. The system concentration was controlled at 0.08–0.10 g / mL, ensuring sufficient contact between the indium source, sulfur source, and graphene quantum dots in the solution. This provides a suitable reaction environment for the in-situ nucleation and growth of indium sulfide on the graphene quantum dot surface. If the proportion of graphene quantum dots is too low, the number of heterointerfaces formed will be insufficient, resulting in limited interfacial polarization contribution. Conversely, if the proportion is too high, agglomeration or excessive conductive loss may occur, affecting impedance matching. By controlling the material ratio and reaction concentration, uniform loading or growth of indium sulfide around the graphene quantum dots is promoted, forming a uniformly dispersed composite structure with sufficient interfacial contact. Furthermore, mild hydrothermal conditions facilitate the slow release of the sulfur source from thioacetamide, allowing the indium species to gradually react with the sulfur source to generate indium sulfide, thereby achieving in-situ composite formation of indium sulfide on the graphene quantum dot surface.

[0035] By simultaneously introducing 3.8%-5.7% sulfur vacancy defect polarization, In-O covalent bridging interface polarization, and enhanced interface built-in electric field, the resulting composite material can enhance the interface polarization mechanism under the action of electromagnetic waves, thereby improving the dissipation capability of incident electromagnetic waves.

[0036] Under the influence of electromagnetic waves, the In-O covalent bridging interface promotes the accumulation and migration of interfacial charges, enhancing interfacial polarization loss. The enhanced built-in electric field at the interface further improves charge separation and directional migration capabilities, allowing electromagnetic energy to be more fully dissipated within the material. Simultaneously, the composite ratio and dispersion state of graphene quantum dots and indium sulfide can modulate the complex permittivity and impedance matching of the composite material, allowing more incident electromagnetic waves to penetrate the material interior rather than being directly reflected at the surface. At the corresponding absorption thickness, the effective absorption bandwidth of the graphene quantum dot / indium sulfide electromagnetic wave absorbing material is 5.1–7.0 GHz, with a minimum reflection loss of -36.5 to -48.3 dB, indicating that it not only significantly reduces electromagnetic wave reflection loss but also achieves effective absorption over a wide frequency range.

[0037] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments: Example 1 The specific steps for preparing a graphene quantum dot / indium sulfide (GQDs / In2S3) electromagnetic wave absorbing material with a sulfur vacancy concentration of 5.7% are as follows: S1. Add 1 g of pyrene to 80 mL of nitric acid and reflux and stir at 80 °C for 12 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, dilute with 1 L of deionized water and then filter through a 0.22 μm microporous membrane to obtain trinitropyrene powder.

[0038] 3.0 g of trinitropyrene powder was dispersed in 0.6 L of 0.2 M sodium hydroxide solution and sonicated for 2 h using an ultrasonic device at 500 W and 40 kHz to ensure thorough dispersion. The dispersion was then transferred to a high-pressure reactor and reacted at 200 °C for 10 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried at -60 °C to obtain GQDs powder with a surface rich in -OH functional groups.

[0039] S2, indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.41. The mixture was then mixed with graphene quantum dot powder at a mass ratio of 8:1 and dispersed in 50 mL of deionized water, resulting in a mixed solution concentration of 0.09 g / mL. The mixture was subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain a GQDs / In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 5.7%.

[0040] Example 2 In this embodiment, a GQDs / In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 3.8% was prepared.

[0041] S1. Add 1.5 g of pyrene to 50 mL of nitric acid and reflux and stir at 80 °C for 11 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, dilute with 1 L of deionized water and then filter through a 0.22 μm microporous membrane to obtain trinitropyrene powder.

[0042] 5.0 g of trinitropyrene powder was dispersed in 0.8 L of 0.2 M sodium hydroxide solution and sonicated for 2 h using an ultrasonic device at 500 W and 40 kHz to ensure thorough dispersion. The dispersion was then transferred to a high-pressure reactor and reacted at 210 °C for 8 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried at -60 °C to obtain GQDs powder with a surface rich in -OH functional groups.

[0043] S2, indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.44. The mixture was then mixed with graphene quantum dot powder at a mass ratio of 7:1 and dispersed in 50 mL of deionized water, resulting in a mixed solution concentration of 0.08 g / mL. The mixture was subjected to a hydrothermal reaction at 100 °C for 12 h. After cooling, the mixture was washed four times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 50 °C for 24 h to obtain a GQDs / In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 3.8%.

[0044] Example 3 In this embodiment, a GQDs / In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 2.5% was prepared.

[0045] S1. Add 2 g of pyrene to 90 mL of nitric acid and reflux and stir at 90 °C for 10 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, dilute with 1 L of deionized water and then filter through a 0.22 μm microporous membrane to obtain trinitropyrene powder.

[0046] 2.0 g of trinitropyrene powder was dispersed in 0.3 L of 0.2 M potassium hydroxide solution and sonicated for 10 h using a 500 W, 40 kHz ultrasonic device to ensure complete dispersion. The dispersion was then transferred to a high-pressure reactor and reacted at 190 °C for 12 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried at -60 °C to obtain GQDs powder with a surface rich in -OH functional groups.

[0047] S2, indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.47. The mixture was then mixed with graphene quantum dot powder at a mass ratio of 9:1 and dispersed in 50 mL of deionized water, resulting in a mixed solution concentration of 0.09 g / mL. The mixture was subjected to a hydrothermal reaction at 80 °C for 14 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 70 °C for 12 h to obtain a GQDs / In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 3.8%.

[0048] Example 4 In this embodiment, a GQDs / In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 0.6% was prepared.

[0049] S1. Add 1 g of pyrene to 70 mL of nitric acid and reflux and stir at 70 °C for 12 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, dilute with 1 L of deionized water and then filter through a 0.22 μm microporous membrane to obtain trinitropyrene powder.

[0050] 4.0 g of trinitropyrene powder was dispersed in 0.7 L of 0.2 M sodium hydroxide solution and sonicated for 5 h using a 500 W, 40 kHz ultrasonic device to ensure thorough dispersion. The dispersion was then transferred to a high-pressure reactor and reacted at 200 °C for 11 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried at -60 °C to obtain GQDs powder with a surface rich in -OH functional groups.

[0051] S2, indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.50. The mixture was then mixed with graphene quantum dot powder at a mass ratio of 7.5:1 and dispersed in 50 mL of deionized water, resulting in a mixed solution concentration of 0.10 g / mL. The mixture was subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain a GQDs / In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 3.8%.

[0052] The following comparative examples further illustrate the preparation effect of the present invention.

[0053] Comparative Example 1 Pure In2S3 electromagnetic wave absorbing material with a vacancy concentration of 0.6% Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.50. The mixture was dispersed in 50 mL of deionized water and subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 0.6%.

[0054] Comparative Example 2 Pure In2S3 electromagnetic wave absorbing material with a vacancy concentration of 2.5% Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.47. The mixture was dispersed in 50 mL of deionized water and subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 2.5%.

[0055] Comparative Example 3 Pure In2S3 electromagnetic wave absorbing material with a vacancy concentration of 3.8% Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.44. The mixture was dispersed in 50 mL of deionized water and subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 3.8%.

[0056] Comparative Example 4 Pure In₂S₃ electromagnetic wave absorbing material with a vacancy concentration of 5.7% Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.41. The mixture was dispersed in 50 mL of deionized water and subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 5.7%.

[0057] Comparative Example 5 A physical mixture of In2S3 and GQDs with a vacancy concentration of 0.6% was used as an electromagnetic wave absorbing material. S1, 1 g of pyrene was added to 80 mL of nitric acid and refluxed at 80 °C for 12 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, it was diluted with 1 L of deionized water and then filtered through a 0.22 μm microporous membrane. 3.0 g of trinitropyrene powder was dispersed in 0.6 L of 0.2 M sodium hydroxide solution and sonicated at 500 W and 40 kHz for 2 h to ensure complete dispersion of the powder. The dispersion was then transferred to a high-pressure reactor and reacted at 200 °C for 10 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried to obtain GQDs powder with a surface rich in -OH functional groups.

[0058] S2, Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.5, and the mixture was dispersed in 50 mL of deionized water. The mixture was subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 0.6%.

[0059] S3, pure indium sulfide powder with a sulfur vacancy concentration of 0.6% and graphene quantum dot powder were dispersed in 50 mL of deionized water at a mass ratio of 8:1 and stirred evenly. The product was then placed in a vacuum drying oven at 60℃ and dried for 12 h to obtain an electromagnetic wave absorbing material of In2S3 and GQDs physical mixture with a sulfur vacancy concentration of 0.6%.

[0060] Comparative Example 6 A physical mixture of In2S3 and GQDs with a vacancy concentration of 2.5% was used as an electromagnetic wave absorbing material. S1, 1 g of pyrene was added to 80 mL of nitric acid and refluxed at 80 °C for 12 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, it was diluted with 1 L of deionized water and then filtered through a 0.22 μm microporous membrane. 3.0 g of trinitropyrene powder was dispersed in 0.6 L of 0.2 M sodium hydroxide solution and sonicated at 500 W and 40 kHz for 2 h to ensure complete dispersion of the powder. The dispersion was then transferred to a high-pressure reactor and reacted at 200 °C for 10 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried to obtain GQDs powder with a surface rich in -OH functional groups.

[0061] S2, Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.47, and the mixture was dispersed in 50 mL of deionized water. The mixture was subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 2.5%.

[0062] S3, pure indium sulfide powder with a sulfur vacancy concentration of 0.6% and graphene quantum dot powder were dispersed in 50 mL of deionized water at a mass ratio of 8:1 and stirred evenly. The product was then placed in a vacuum drying oven at 60℃ and dried for 12 h to obtain an electromagnetic wave absorbing material of In2S3 and GQDs physical mixture with a sulfur vacancy concentration of 2.5%.

[0063] Comparative Example 7 A physical mixture of In2S3 and GQDs with a vacancy concentration of 3.8% was used as an electromagnetic wave absorbing material. S1, 1 g of pyrene was added to 80 mL of nitric acid and refluxed at 80 °C for 12 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, it was diluted with 1 L of deionized water and then filtered through a 0.22 μm microporous membrane. 3.0 g of trinitropyrene powder was dispersed in 0.6 L of 0.2 M sodium hydroxide solution and sonicated at 500 W and 40 kHz for 2 h to ensure complete dispersion of the powder. The dispersion was then transferred to a high-pressure reactor and reacted at 200 °C for 10 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried to obtain GQDs powder with a surface rich in -OH functional groups.

[0064] S2, Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.44. The mixture was dispersed in 50 mL of deionized water and subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 3.8%.

[0065] S3, pure indium sulfide powder with a sulfur vacancy concentration of 0.6% and graphene quantum dot powder were dispersed in 50 mL of deionized water at a mass ratio of 8:1 and stirred evenly. The product was then placed in a vacuum drying oven at 60℃ and dried for 12 h to obtain an electromagnetic wave absorbing material of In2S3 and GQDs physical mixture with a sulfur vacancy concentration of 3.8%.

[0066] Comparative Example 8 A physical mixture of In2S3 and GQDs with a vacancy concentration of 5.7% was used as an electromagnetic wave absorbing material. S1, 1 g of pyrene was added to 80 mL of nitric acid and refluxed at 80 °C for 12 h to carry out the nitration reaction to obtain trinitropyrene. After cooling, it was diluted with 1 L of deionized water and then filtered through a 0.22 μm microporous membrane. 3.0 g of trinitropyrene powder was dispersed in 0.6 L of 0.2 M sodium hydroxide solution and sonicated at 500 W and 40 kHz for 2 h to ensure complete dispersion of the powder. The dispersion was then transferred to a high-pressure reactor and reacted at 200 °C for 10 h. After the reaction, the product was filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da to remove impurity ions. Finally, the purified solution was freeze-dried to obtain GQDs powder with a surface rich in -OH functional groups.

[0067] S2, Indium chloride tetrahydrate and thioacetamide were mixed uniformly at a molar ratio of 1:1.41. The mixture was dispersed in 50 mL of deionized water and subjected to a hydrothermal reaction at 90 °C for 12 h. After cooling, the mixture was washed three times each with deionized water and ethanol. The product was then dried in a vacuum drying oven at 60 °C for 12 h to obtain pure In2S3 electromagnetic wave absorbing material with a sulfur vacancy concentration of 0.6%.

[0068] S3, pure indium sulfide powder with a sulfur vacancy concentration of 5.7% and graphene quantum dot powder were dispersed in 50 mL of deionized water at a mass ratio of 8:1 and stirred evenly. The product was then placed in a vacuum drying oven at 60℃ and dried for 12 h to obtain an electromagnetic wave absorbing material of In2S3 and GQDs physical mixture with a sulfur vacancy concentration of 0.6%.

[0069] Figures 1(a) and 1(b) illustrate the differences between physical adsorption and In-O covalent bonds at the interface structure. They demonstrate that the graphene quantum dot / indium sulfide electromagnetic wave absorbing material provided by this invention enhances the built-in electric field strength at the interface through atomic-level charge transport channels constructed via In-O covalent bonds.

[0070] Figure 2 These are scanning electron microscope images of Examples 1-4. All samples were found to exhibit a nano-flower-like shape, consistent with the traditional indium sulfide morphology. Figure 2 In the image, (a) is a scanning electron microscope (SEM) image of Example 4, (b) is a scanning electron microscope (SEM) image of Example 3, (c) is a scanning electron microscope (SEM) image of Example 2, and (d) is a scanning electron microscope (SEM) image of Example 1. Graphene quantum dots cannot be observed in the SEM images due to their small size.

[0071] Figure 3 The image shows a transmission electron microscope (TEM) image and elemental distribution of Example 1. The presence of In, S, C, and O can be observed, demonstrating the successful introduction of graphene quantum dots.

[0072] Figure 4 Synchrotron radiation (XAFS) characterization for Examples 1-4. Figure 4 In Figure (a), the synchrotron radiation characterization diagram is for Example 4; (b), for Example 3; (c), for Example 2; and (d), for Example 1. The interfaces of Examples 3 and 4 show no In-O covalent bond characteristic peaks, indicating predominantly physical adsorption. The interfaces of Examples 1 and 2 show obvious In-O covalent bond characteristic peaks, indicating predominantly covalent bond bridging. Comparative Examples 1-4 are pure indium sulfide, and Comparative Examples 5-8 are physical mixtures of graphene quantum dots and indium sulfide, which definitely do not contain In-O covalent bonds.

[0073] The built-in electric field strength at the interface was measured for Examples 1-4 and Comparative Examples 1-8. The method used was Kelvin probe force microscopy.

[0074] Figure 5 These are test diagrams of the interface built-in electric field strength of electromagnetic wave absorbing materials of graphene quantum dots / indium sulfide, pure indium sulfide, graphene quantum dots and indium sulfide mixture under different sulfur vacancy concentrations provided by the present invention in Examples 1-4 and Comparative Examples 1-8. Figure 5 (a) shows the interface built-in electric field strength of Examples 1-4 measured using Kelvin probe force microscopy. (b) shows the interface built-in electric field strength of Comparative Examples 1-4 measured using Kelvin probe force microscopy. (c) shows the interface built-in electric field strength of Comparative Examples 5-8 measured using Kelvin probe force microscopy. It can be seen that the interface built-in electric field strength of Examples 1-4 is generally one to two orders of magnitude greater than that of Comparative Examples 1-8, and the interface built-in electric field strength of Examples 1-2 is particularly prominent. This indicates that the interfacial covalent bonds generated by regulating the sulfur vacancy concentration contribute to the improvement of the interface built-in electric field strength.

[0075] For Examples 1-4 ( Figure 6 ) and Comparative Examples 1-8 ( Figure 7-8 Electromagnetic wave absorption performance was tested. The absorption performance of the samples at room temperature was measured using a vector network analyzer via the coaxial line method. Before testing, all samples were mixed into an epoxy resin-based cyclic material with an inner diameter of approximately 3 mm and an outer diameter of approximately 7 mm. The absorbing powder content of the samples was 40 wt.%.

[0076] The interface built-in electric field strength and absorption performance of Examples 1-4 and Comparative Examples 1-8 are summarized in Table 1.

[0077] Table 1

[0078] Figure 6 The electromagnetic wave absorption performance of Examples 1-4 is shown. It can be seen that... Figure 6Example 1 (d) exhibits the best absorption performance, including an ultra-low reflection loss of -48.3 dB and an ultra-wide effective absorption bandwidth of 7.0 GHz. Figure 6 The absorption performance of Example 2 in (c) is the second best, with a minimum reflection loss of -36.5 dB and an effective absorption bandwidth of 5.1 GHz. Figure 6 The microwave absorption performance of Examples 3-4 in (a)-(b) shows a significant decrease compared to Examples 1-2, indicating that although a heterogeneous interface was formed, In-O covalent bonding was not formed. Therefore, it was impossible to further trigger an efficient interface charge transfer mechanism and the built-in electric field strength of the interface, and thus the microwave absorption performance could not be effectively improved.

[0079] Figure 7 In Figures (a)-(d), the electromagnetic wave absorption performance of Comparative Examples 1-4 is shown. It can be seen that regardless of the vacancy concentration, the pure indium sulfide sample does not form a heterojunction, let alone a strong interfacial bond, and therefore has extremely poor wave absorption performance.

[0080] Figure 8 In the figures (a)-(d), the electromagnetic wave absorption performance of comparative examples 5-8 is shown. The physically mixed samples did not form an effective heterogeneous interface, let alone a chemically bonded heterogeneous interface. Therefore, they could not further trigger an efficient interface charge transfer mechanism and the built-in electric field strength at the interface, and thus could not effectively improve the absorption performance.

[0081] The above results indicate that by controlling the sulfur source content to regulate the sulfur vacancy concentration, the In-O covalent bonds generated in Examples 1-2 can construct atomic-level charge transport channels, which can strengthen the interface built-in electric field. The strong interface built-in electric field is expected to cause the interface charge to undergo severe polarization relaxation under electromagnetic wave irradiation, consume a large amount of electromagnetic wave energy, promote interface polarization loss, and ultimately improve electromagnetic wave absorption performance.

[0082] This invention has led to the fabrication of a series of graphene quantum dot-indium sulfide heterojunctions. By controlling the amount of sulfur source introduced during the reaction process, the sulfur vacancy concentration in In₂S₃ is precisely controlled. These vacancy sites act as unsaturated sites, driving the interface from physical adsorption orientation to covalent bridging. This enhances the built-in electric field at the interface, improving polarization loss and ultimately significantly improving the electromagnetic wave absorption performance of the material, including lower reflection loss and a wider effective absorption bandwidth. The materials prepared by this invention can be widely used in fields such as anti-interference of electronic equipment, radar stealth, electromagnetic protection of communication base stations, and electromagnetic compatibility of automotive electronics.

[0083] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for preparing a graphene quantum dot / indium sulfide electromagnetic wave absorbing material, characterized in that, include: (a) Trinitropyrene was mixed with an alkaline solution at a mass ratio of (2~5):(300~800) and ultrasonically dispersed. The mixture was then subjected to hydrothermal reduction reaction, filtered, purified by dialysis, and freeze-dried to obtain graphene quantum dot powder with hydroxyl functional groups on its surface. (b) Indium chloride tetrahydrate with a molar ratio of 1:(1.40~1.50) was mixed with thioacetamide to obtain a mixture. The mixture was then dispersed with graphene quantum dot powder in deionized water at a mass ratio of (7~9):

1. After being mixed evenly, a hydrothermal reaction was carried out. After washing and drying, a graphene quantum dot / indium sulfide electromagnetic wave absorbing material was obtained.

2. The method for preparing the graphene quantum dot / indium sulfide electromagnetic wave absorbing material according to claim 1, characterized in that, In step (a), the preparation of trinitropyrene includes: adding pyrene to nitric acid at a mass ratio of (1~2):(50~90), refluxing and stirring at 60~90℃ for 10~12 h to carry out the nitration reaction to obtain trinitropyrene.

3. The method for preparing the graphene quantum dot / indium sulfide electromagnetic wave absorbing material according to claim 1, characterized in that, Trinitropyrene was ultrasonically treated with an alkaline solution for 2-10 hours, followed by hydrothermal reduction at 190℃-210℃ for 8-12 hours.

4. The preparation method of the graphene quantum dot / indium sulfide electromagnetic wave absorbing material according to claim 1, characterized in that, The alkaline solution is a sodium hydroxide or potassium hydroxide solution.

5. The method for preparing the graphene quantum dot / indium sulfide electromagnetic wave absorbing material according to claim 1, characterized in that, In step (a), after the hydrothermal reduction reaction, the product is filtered through a 0.22 μm microporous membrane and then dialyzed for 2 days using a dialysis bag with a molecular weight cutoff of 3500 Da.

6. The method for preparing the graphene quantum dot / indium sulfide electromagnetic wave absorbing material according to claim 1, characterized in that, In step (a), the product is freeze-dried at -60 °C.

7. The method for preparing the graphene quantum dot / indium sulfide electromagnetic wave absorbing material according to claim 1, characterized in that, In step (b), the mixture and graphene quantum dot powder are dispersed in deionized water with a solution concentration of 0.08~0.10 g / mL.

8. The method for preparing the graphene quantum dot / indium sulfide electromagnetic wave absorbing material according to claim 1, characterized in that, In step (b), the hydrothermal reaction is carried out at 80~100℃ for 10~14 h; the product is dried in a vacuum drying oven at 50~70℃ for 12~24 h.

9. A graphene quantum dot / indium sulfide electromagnetic wave absorbing material prepared by the method according to any one of claims 1-8.

10. The application of the graphene quantum dot / indium sulfide electromagnetic wave absorbing material as described in claim 9 in the fields of anti-interference of electronic devices, radar stealth, electromagnetic protection of communication base stations, or electromagnetic compatibility of automotive electronics.

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