A broadband light-absorbing material and its preparation method

Abstract

This invention relates to a light-absorbing material and its preparation method, disclosing a broadband light-absorbing material and its preparation method. The broadband light-absorbing material, with the molecular formula AB2, is a porous particle. The solar energy absorption rate of this broadband light-absorbing material in the 0.3–2.5 μm wavelength range is 0.891–0.909. It is prepared by dissolving any five of the following six metal raw materials—Co(NO3)3·6H2O, Ni(NO3)2·6H2O, Cr(NO3)2·9H2O, Cu(NO3)2·3H2O, FeSO4·7H2O, and Mn(NO3)2 solution—in deionized water that has been purged with nitrogen or an inert gas to obtain a salt solution. Then, an aqueous solution of NaBH4 is dissolved in the same deionized water to obtain an aqueous solution of sodium borohydride. The solution is then reacted, filtered, frozen, and dried. The preparation method is easy, highly reproducible, and has high production efficiency, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to a light-absorbing material and its preparation method, particularly a high-entropy boride and its preparation method. Background Technology

[0002] With the increasing severity of global energy and environmental issues, solar thermal utilization has become a focus of widespread attention. Light-absorbing materials are the most crucial component of solar thermal conversion devices, decisively influencing their conversion efficiency. The energy of the solar spectrum in different wavelength bands is mainly concentrated in the ultraviolet region (0.30–0.38 μm), the visible region (0.38–0.78 μm), and the near-infrared region (0.78–2.5 μm), accounting for 98% of total solar radiation. Typically, the absorptivity (α) in the 0.3–2.5 μm band is used to characterize the coating's ability to convert sunlight into heat.

[0003] Light absorption is a prerequisite for photothermal conversion. When the energy of an incident photon exceeds the band gap, it can induce electrons in the valence band to transition to the conduction band. Thanks to the localization of d-electrons in transition metals, particularly their strong interband transitions, they are frequently used in light-absorbing materials, and their light absorption intensity is related to the d-band distribution near the Fermi level. However, due to their electronic structures, different transition metals exhibit strong interband transitions only within specific spectral ranges, which is detrimental to absorption across the entire solar spectrum. Theoretically, by combining multiple transition metals, the d-band distribution near the Fermi level can be filled, thereby achieving absorption and utilization of the entire solar spectrum.

[0004] The multi-principal element design of high-entropy alloys enhances the d-band distribution near the Fermi level, promoting interband transitions across the entire spectrum and improving light absorption. Simultaneously, the high configurational entropy resulting from the multi-principal element design overcomes the adverse effects of enthalpy, lowering the Gibbs free energy and contributing to structural stability. Furthermore, its glass transition, microcrystalline structure, and single-phase characteristics provide favorable conditions for improving the corrosion resistance of high-entropy alloys. Therefore, high-entropy alloys are ideal light-absorbing materials.

[0005] Barbarossa et al. successfully prepared a bulk high-entropy diboride for solar energy utilization, demonstrating its potential application in light absorption (Simone Barbarossa, Roberto Orrù, Giacomo Cao, et al. Optical properties of bulk high-entropy diborides for solar energy applications[J]. Journal of Alloys and Compounds, 2023, 935:167965). Their research indicates that the study of innovative high-entropy diborides (HEBs), belonging to the more general category of ultra-high temperature ceramics (UHTC), is entirely limited to fabricating or characterizing them from the perspectives of microstructure, mechanics, and oxidation resistance. This paper evaluates (Hf... 0.2 Zr 0.2 Ta 0.2 Mo 0.2 Ti 0.2 B2 and (Hf) 0.2 Nb 0.2 Ta 0.2 Mo 0.2 Ti 0.2 The optical properties of two members of HEB2 were investigated to evaluate their applications in the field of solar thermal energy. Bulk samples (densities 96.5% and 97.4%, respectively) were obtained as single-phase products by spark plasma sintering (1950 °C 20 min / 20 MPa), starting from powders previously synthesized via self-propagating high-temperature synthesis (SHS). The results are discussed by comparing HEBs with individual borides, demonstrating their inherent spectral selectivity and low thermal emissivity.

[0006] However, the powder was prepared by a self-propagating method under an argon atmosphere. The reaction rate was fast, difficult to control, and the preparation conditions were quite harsh. Furthermore, bulk high-entropy borides were prepared by spark plasma sintering technology. The reflectance spectra showed that the absorption rates of the two different bulk materials were only 0.4 and 0.38, which were far from meeting the needs of solar energy utilization.

[0007] Chinese patents CN112408409A and CN112521911A disclose a method for preparing high-entropy borides by vacuum high-temperature calcination, mainly for electromagnetic wave absorption. However, the preparation process used is similar to other patents involving the preparation of high-entropy boride powders, requiring extremely high calcination temperatures and a vacuum or inert environment. These stringent conditions place extremely high demands on the production equipment.

[0008] Chinese patent CN11793781A discloses a ternary boride cermet solar selective absorption composite coating and its preparation method. This method uses Mo, B, Cr, and Co or Ni as raw materials to prepare the composite coating, obtaining CoMoB, CoMo2B2, or NiMo2B2 ternary borides through in-situ reactions. At room temperature (25℃), the absorption rates of the MoB / CoCr and MoB / NiCr coatings are 0.96-1.12 and 1.10-1.16, respectively, indicating good optical absorption. However, XRD patterns reveal that this patent obtains a composite coating of boride-doped oxides and metals, achieving excellent absorption. However, this multiphase structure is prone to forming galvanic cells, making it susceptible to corrosion; furthermore, the different phases have different coefficients of thermal expansion, leading to cracking during heating and poor thermal stability.

[0009] In summary, finding a high-entropy boride that can fill the d-band distribution near the Fermi level, overcome the adverse effects of enthalpy, reduce the Gibbs free energy, stabilize the structure, and thus improve the broadband light absorption rate has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0010] Obviously, among the many transition metals, selecting multiple transition metals to form high-entropy borides with boron, thereby enhancing the d-band distribution near the Fermi level, and determining the appropriate ratio to form a multi-principal-element structure are the technical problems to be solved by this invention. In addition, this invention also needs to find a method to facilitate the preparation of such high-entropy borides.

[0011] The technical solution adopted by the present invention to solve its technical problem is:

[0012] A broadband light-absorbing material with the general molecular formula AB2, wherein A is selected from five metals: Co, Ni, Cr, Cu, Fe and Mn, and the five metals are in equimolar ratio, and the material is a porous particle. The broadband light-absorbing material has a solar energy absorption rate of 0.891 to 0.909 in the 0.3 to 2.5 μm wavelength range.

[0013] The metals in the broadband light-absorbing materials are derived from Co(NO3)3·6H2O, Ni(NO3)2·6H2O, Cr(NO3)3·9H2O, Cu(NO3)2·3H2O, FeSO4·7H2O powder and Mn(NO3)2 solution, respectively, while the boron raw material is derived from sodium borohydride.

[0014] The preparation method of this broadband light-absorbing material is as follows:

[0015] (1) Prepare raw materials: Weigh the metal powder or solution according to the standard of equimolar ratio of metals, add them to deionized water that has been purged with nitrogen or inert gas beforehand and dissolve them to obtain a salt solution for later use; dissolve NaBH4 in deionized water that has been purged with nitrogen or inert gas beforehand to obtain a sodium borohydride aqueous solution for later use.

[0016] (2) Reaction: Sodium borohydride aqueous solution is slowly added to salt solution to carry out the reaction. After 20 to 40 minutes of reaction, a suspension is obtained.

[0017] (3) Vacuum filtration: The suspension after reaction is vacuum filtered to obtain the filter material, and the filter material is repeatedly washed with deionized water and anhydrous ethanol alternately.

[0018] (4) Freezing: Freeze the filter material at -18°C for 6 to 12 hours;

[0019] (5) Drying: The frozen filter material is dried for 8 to 12 hours at a temperature of -48 to 63°C and a vacuum of 30 to 43 Pa to obtain high-entropy boride powder.

[0020] The deionized water used as a solvent for the metal raw materials is deionized water that has been purged with nitrogen or an inert gas for 30 to 60 minutes. The inert gas is helium, neon, argon, krypton, xenon, or radon, and the mass ratio of the four powders to water is 1.459 to 1.618:120.

[0021] The deionized water used to dissolve the NaBH4 aqueous solution is deionized water that has been purged with nitrogen or an inert gas for 30 to 60 minutes. The inert gas is helium, neon, argon, krypton, xenon, or radon. The mass ratio of sodium borohydride to deionized water in the NaBH4 aqueous solution is 0.757:50.

[0022] The dissolution of metal raw materials and the dissolution of NaBH4 aqueous solution are carried out under stirring at a speed of 300–500 r / min.

[0023] The filter material is washed 3 to 6 times with alternating deionized water and anhydrous ethanol, with each wash lasting 1 minute.

[0024] The frozen filter material is in a loose powder state.

[0025] The moisture content of the freeze-dried powder is not higher than 2.5%.

[0026] The beneficial effects of this invention are:

[0027] Considering that different transition metals exhibit strong interband transitions only within specific spectral ranges due to their electronic structures, which is detrimental to the absorption of the entire solar spectrum, the inventors, through extensive experiments, developed this invention using an equimolar ratio of five metals—Co, Ni, Cr, Cu, Fe, and Mn—to form high-entropy borides. By combining multiple transition metals to fill the d-band distribution near the Fermi level, the absorption and utilization of the entire solar spectrum can be achieved. Furthermore, these materials are common light-absorbing materials, with abundant reserves, low cost, and easy solubility.

[0028] Another advantage of this invention is that it requires simple equipment, is easy to prepare, has high repeatability, and high production efficiency, making it suitable for large-scale industrial production. The prepared broadband light-absorbing material exhibits a solar energy absorptivity of 0.891–0.909 in the 0.3–2.5 μm wavelength range and demonstrates excellent thermal stability in air, making it widely applicable to solar thermal conversion materials.

[0029] Optical performance

[0030] Absorption spectra of high-entropy borides in the range of 0.3–2.5 μm were obtained using a PerkinElmer Lambda 950 UV / Vis / NIR spectrophotometer (equipped with a 150 mm integrating sphere) and a Bruker Tensor 27 infrared spectrometer (including an integrating sphere). Solar energy absorptivity was then calculated according to the national standard GB / T 26974-2011. The calculated absorptivity of the high-entropy borides prepared in this invention is 0.891–0.909.

[0031] Thermal stability performance

[0032] The high-entropy borides were placed in a box furnace and subjected to a thermal stability test at 600°C in air for 168 hours. The results showed that the high-entropy boride material prepared in this invention has a stable structure and a solar energy absorption rate fluctuation of only 0.01 to 0.05, which can meet the operating requirements of CSP systems. Attached Figure Description

[0033] Figure 1 This is the absorption spectrum of the (CoNiCuFeMn)B2 broadband light-absorbing material powder in Example 1;

[0034] Figure 2 This is a SEM image of the (CoNiCuFeMn)B2 broadband light-absorbing material powder in Example 1;

[0035] Figure 3 This is the XRD pattern of the (CoNiCuFeMn)B2 broadband light-absorbing material powder in Example 1;

[0036] Figure 4 This is the absorption spectrum of the (CoNiCrFeMn)B2 broadband light-absorbing material powder in Example 2;

[0037] Figure 5 This is the absorption spectrum of the (CuNiCrFeMn)B2 broadband light-absorbing material powder in Example 3;

[0038] Figure 6 This is the absorption spectrum of (CoNi)B2 powder in Comparative Example 1;

[0039] Figure 7 This is the absorption spectrum of CoNiCu)B2 powder in Comparative Example 2;

[0040] Figure 8 This is the absorption spectrum of (CoMnCuFe)B2 powder in Comparative Example 3. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] Example 1:

[0043] Weigh out 0.291 g (1 mmol) of four powdered raw materials: Co(NO3)3·6H2O, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, and FeSO4·7H2O, as well as 0.358 g (2 mmol) of a 50% Mn(NO3)2 solution.

[0044] The weighed metal raw material was added to 120g of deionized water that had been purged with nitrogen for 30min before dissolving. The dissolution process was carried out by stirring with a mechanical stirrer at a speed of 300r / min for 30min to obtain a salt solution.

[0045] 0.757 g (20 mmol) of NaBH4 was dissolved in 50 g of deionized water that had been purged with nitrogen for 60 min to obtain an aqueous solution of sodium borohydride. It should be noted that excess sodium borohydride was added during the reaction to ensure complete reaction.

[0046] Sodium borohydride aqueous solution was slowly added to the salt solution using a syringe, and the reaction was allowed to proceed for 30 minutes. The resulting solution was then filtered by vacuum filtration. During the filtration process, the sample was washed three times alternately with deionized water and anhydrous ethanol, with each wash lasting one minute. The filtered sample was then frozen for 12 hours and placed in a freeze dryer at -48°C and a vacuum of 43 Pa for 12 hours to obtain (CoNiCuFeMn)B2 broadband light-absorbing material powder.

[0047] Figure 1 The absorption spectrum of the prepared (CoNiCuFeMn)B2 broadband light-absorbing material powder was obtained. The absorbance of the powder in the 0.3-2.5 μm band was measured to be 0.909, indicating that the material has a high absorbance in the solar spectrum.

[0048] Table 1 shows the EDS results of the prepared (CoNiCuFeMn)B2 broadband light-absorbing material powder, indicating that the molar ratio of each metal element in the broadband light-absorbing material conforms to the original composition design and is a typical high-entropy compound state.

[0049] Table 1. EDS results of (CoNiCuFeMn)B2 broadband light-absorbing material powder

[0050] element Wt% mole percentage B 21.08 59.16 Mn 14.15 7.80 Fe 14.11 7.66 Co 13.92 7.16 Ni 17.34 8.96 Cu 19.40 9.26 Total 100 100

[0051] (Note: Due to errors in the experimental and testing process, the EDS results appear to be approximately equal molar ratios, but still satisfy the concept of high entropy.)

[0052] Figure 2 The SEM image of the prepared (CoNiCuFeMn)B2 broadband light-absorbing material powder shows that the prepared material is composed of porous particles.

[0053] Figure 3 The XRD pattern of the prepared (CoNiCuFeMn)B2 broadband light-absorbing material powder shows obvious peaks belonging to high-entropy alloy borides (100), (101), (110), and (210).

[0054] Example 2:

[0055] Weigh out 0.291 g (1 mmol) of four powdered raw materials: Co(NO3)3·6H2O, Ni(NO3)2·6H2O, Cr(NO3)2·9H2O, and FeSO4·7H2O, as well as 0.358 g (2 mmol) of a 50% Mn(NO3)2 solution.

[0056] The weighed metal raw material was dissolved in 50g of deionized water that had been purged with nitrogen for 60min. The dissolution process was carried out by stirring with a mechanical stirrer at a speed of 500r / min for 30min to obtain a salt solution.

[0057] 0.757 g (20 mmol) of NaBH4 was dissolved in 50 g of deionized water that had been purged with nitrogen for 30 min to obtain an aqueous solution of sodium borohydride. It should be noted that excess sodium borohydride was added during the reaction to ensure complete reaction.

[0058] Sodium borohydride aqueous solution was slowly added to the salt solution using a syringe, and the reaction was allowed to proceed for 40 minutes. The resulting solution was then filtered by vacuum filtration. During the filtration process, the sample was washed five times alternately with deionized water and anhydrous ethanol, with each wash lasting one minute. The filtered sample was then frozen for 6 hours and placed in a freeze dryer at -60°C and a vacuum of 30 Pa for 8 hours to obtain (CoNiCrFeMn)B2 broadband light-absorbing material powder.

[0059] Figure 4 The absorption spectrum of the prepared (CoNiCrFeMn)B2 broadband light-absorbing material powder was obtained. The absorbance of the powder in the 0.3-2.5 μm band was measured to be 0.896, indicating that the material has a high absorbance in the solar spectrum.

[0060] Example 3:

[0061] Weigh out 0.4 g (1 mmol) of Cr(NO3)2·9H2O, 0.291 g (1 mmol) of Ni(NO3)2·6H2O, 0.242 g (1 mmol) of Cu(NO3)2·3H2O, and 0.278 g (1 mmol) of FeSO4·7H2O, as well as 0.358 g (2 mmol) of a 50% Mn(NO3)2 solution.

[0062] The weighed metal raw material was dissolved in 120g of deionized water that had been purged with nitrogen for 40min. The dissolution process was carried out by stirring with a mechanical stirrer at a speed of 400r / min for 30min to obtain a salt solution.

[0063] 0.757 g (20 mmol) of NaBH4 was dissolved in 50 g of deionized water that had been purged with nitrogen for 50 min to obtain an aqueous solution of sodium borohydride. It should be noted that excess sodium borohydride was added during the reaction to ensure complete reaction.

[0064] Sodium borohydride aqueous solution was slowly added to the salt solution using a syringe, and the reaction was allowed to proceed for 35 minutes. The resulting solution was then filtered by vacuum filtration. During the filtration process, the sample was washed six times alternately with deionized water and anhydrous ethanol, with each wash lasting one minute. The filtered sample was then frozen for 12 hours and placed in a freeze dryer at -55°C and a vacuum of 40 Pa for 10 hours to obtain (CuNiCrFeMn)B2 broadband light-absorbing material powder.

[0065] Figure 5 The absorption spectrum of the prepared (CuNiCrFeMn)B2 broadband light-absorbing material powder was obtained. The absorbance of the powder in the 0.3-2.5 μm band was measured to be 0.891, indicating that the material has a high absorbance in the solar spectrum.

[0066] Comparative Example 1:

[0067] Weigh out 0.291 g (1 mmol) of Co(NO3)3·6H2O and 0.291 g (1 mmol) of Ni(NO3)2·6H2O powders respectively. Add the weighed powders to 48 g of deionized water that has been purged with nitrogen for 30 min before dissolving. The dissolution process is carried out by stirring with a mechanical stirrer at a speed of 300 r / min for 30 min to obtain a salt solution.

[0068] Dissolve 0.303 g (8 mmol) of NaBH4 in 20 g of deionized water that has been purged with nitrogen for 60 min to obtain an aqueous solution of sodium borohydride. It should be noted that excess sodium borohydride is added during the reaction to ensure complete reaction.

[0069] Sodium borohydride aqueous solution was slowly added to the salt solution using a syringe, and the reaction was allowed to proceed for 30 minutes. The resulting solution was then filtered by vacuum filtration, during which it was washed three times alternately with deionized water and anhydrous ethanol. The sample obtained after filtration was first frozen for 12 hours, and then placed in a freeze dryer at -50°C and a vacuum of 47 Pa for 8 hours to obtain (CoNi)B2 powder.

[0070] Figure 6 The absorption spectrum of the prepared (CoNi)B2 powder was obtained. The absorbance of the powder in the 0.3-2.5 μm band was measured to be 0.6127, which is lower than that of the pentagonal high-entropy boride material proposed in this invention.

[0071] Comparative Example 2:

[0072] Weigh out 0.291 g (1 mmol) of Co(NO3)3·6H2O, 0.242 g (1 mmol) of Cu(NO3)2·3H2O, and 0.291 g (1 mmol) of Ni(NO3)2·6H2O, respectively. Add the weighed powder raw materials to 72 g of deionized water that has been purged with nitrogen for 30 min to dissolve them. The dissolution process is carried out by stirring with a mechanical stirrer at a speed of 350 r / min for 30 min to obtain a salt solution.

[0073] 0.454 g (12 mmol) of NaBH4 was dissolved in 30 g of deionized water that had been purged with nitrogen for 60 min to obtain an aqueous solution of sodium borohydride. It should be noted that excess sodium borohydride was added during the reaction to ensure complete reaction.

[0074] Sodium borohydride aqueous solution was slowly added to the salt solution using a syringe, and the reaction was allowed to proceed for 30 minutes. The resulting solution was then filtered by vacuum filtration, during which it was washed four times alternately with deionized water and anhydrous ethanol. The filtered sample was first frozen for 12 hours, and then placed in a freeze dryer at -53°C and a vacuum of 45 Pa for 9 hours to obtain (CoNiCu)B2 powder.

[0075] Figure 7 The absorption spectrum of the prepared (CoNiCu)B2 powder was obtained. The absorbance of the powder in the 0.3-2.5 μm band was measured to be 0.6188, which is lower than that of the pentagonal high-entropy boride material proposed in this invention.

[0076] Comparative Example 3:

[0077] Weigh out 0.291 g (1 mmol) of Co(NO3)3·6H2O, 0.242 g (1 mmol) of Cu(NO3)2·H2O, 0.278 g (1 mmol) of FeSO4·7H2O, and 0.358 g (2 mmol) of 50% Mn(NO3)2 solution. Add the weighed three powder raw materials and Mn(NO3)2 solution to 96 g of deionized water that has been purged with nitrogen for 30 min before dissolving. The dissolution process is carried out by stirring with a mechanical stirrer at a speed of 400 r / min for 30 min to obtain a salt solution.

[0078] 0.606 g (16 mmol) of NaBH4 was dissolved in 40 g of deionized water that had been purged with nitrogen for 60 min to obtain an aqueous solution of sodium borohydride. It should be noted that excess sodium borohydride was added during the reaction to ensure complete reaction.

[0079] Sodium borohydride aqueous solution was slowly added to the salt solution using a syringe, and the reaction was allowed to proceed for 40 minutes. The resulting solution was then filtered by vacuum filtration, during which it was washed four times alternately with deionized water and anhydrous ethanol. The filtered sample was first frozen for 12 hours, and then placed in a freeze dryer at -51°C and a vacuum of 45 Pa for 10 hours to obtain (CoMnCuFe)B2 powder.

[0080] Figure 8The absorption spectrum of the prepared (CoMnCuFe)B2 powder was obtained. The absorption rate of the powder in the 0.3-2.5 μm band was measured to be 0.7415, which is lower than that of the pentagonal high-entropy boride material proposed in this invention.

[0081] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A broadband light-absorbing material, characterized in that: The general molecular formula of this broadband light-absorbing material is AB2, where A is selected from five metals: Co, Ni, Cr, Cu, Fe, and Mn, and the five metals are in equimolar ratio.

2. The broadband light-absorbing material according to claim 1, characterized in that: This broadband light-absorbing material is a porous particle.

3. The broadband light-absorbing material according to claim 1, characterized in that: The solar energy absorption rate of this broadband light-absorbing material is 0.891 to 0.909 in the 0.3 to 2.5 μm wavelength range.

4. The broadband light-absorbing material according to claim 1, characterized in that: The metals in the samples are derived from Co(NO3)3·6H2O, Ni(NO3)2·6H2O, Cr(NO3)3·9H2O, Cu(NO3)2·3H2O, FeSO4·7H2O powders and Mn(NO3)2 solution.

5. The broadband light-absorbing material according to claim 1, characterized in that: The boron raw material used comes from sodium borohydride.

6. The method for preparing the broadband light-absorbing material according to claim 1, characterized in that... Includes the following steps: (1) Preparation of raw materials: Weigh Co(NO3)3·6H2O, Ni(NO3)2·6H2O, Cr(NO3)3·9H2O, Cu(NO3)2·3H2O, FeSO4·7H2O powder and Mn(NO3)2 solution according to the standard of metal equimolar ratio, add them to deionized water that has been purged with nitrogen or inert gas beforehand and dissolve them to obtain a salt solution for later use; dissolve NaBH4 in deionized water that has been purged with nitrogen or inert gas beforehand to obtain sodium borohydride aqueous solution for later use; (2) Reaction: Sodium borohydride aqueous solution is slowly added to salt solution to carry out the reaction. After 20-40 minutes of reaction, a suspension is obtained. (3) Vacuum filtration: The suspension after the reaction is vacuum filtered to obtain the filter material, and the filter material is repeatedly washed with deionized water and anhydrous ethanol alternately. (4) Freezing: Freeze the filter material at -18 °C for 6 to 12 hours; (5) Drying: The frozen filter material is dried for 8 to 12 hours at a temperature of -48 to 63 °C and a vacuum of 30 to 43 Pa to obtain high-entropy boride powder.

7. The method for preparing the broadband light-absorbing material according to claim 6, characterized in that: The deionized water used as a solvent for the metal raw materials is deionized water that has been purged with nitrogen or an inert gas for 30 to 60 minutes. The inert gas is helium, neon, argon, krypton, xenon, or radon. The mass ratio of the metal raw materials to water is 1.459 to 1.618:

120.

8. The method for preparing the broadband light-absorbing material according to claim 6, characterized in that: The deionized water used to dissolve the NaBH4 aqueous solution is deionized water that has been purged with nitrogen or an inert gas for 30 to 60 minutes. The inert gas is helium, neon, argon, krypton, xenon, or radon. The mass ratio of sodium borohydride to deionized water in the NaBH4 aqueous solution is 0.757:

50.

9. The method for preparing the broadband light-absorbing material according to claim 7 or 8, characterized in that: The dissolution of metal raw materials and the dissolution of NaBH4 aqueous solution are carried out under stirring at a speed of 300–500 r / min.

10. The method for preparing the broadband light-absorbing material according to claim 6, characterized in that: The filter material is washed 3-6 times with alternating deionized water and anhydrous ethanol, with each wash lasting 1 minute.

11. The method for preparing the broadband light-absorbing material according to claim 6, characterized in that: The frozen filter material is in a loose powder state.

12. The method for preparing the broadband light-absorbing material according to claim 6, characterized in that: The moisture content of the dried powder is not higher than 2.5%.

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