CN109438980B

CN109438980B - Light absorber and preparation method thereof

Info

Publication number: CN109438980B
Application number: CN201811122872.XA
Authority: CN
Inventors: 徐挺; 张辉
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2018-09-26
Filing date: 2018-09-26
Publication date: 2021-06-25
Anticipated expiration: 2038-09-26
Also published as: CN109438980A

Abstract

The invention discloses a light absorber and a preparation method thereof, wherein the preparation method comprises the following steps: s1, preparing an aramid nanofiber solution by taking aramid as a raw material; s2, preparing a metal nanoparticle solution; s3, mixing the aramid fiber nanofiber solution prepared in the step S1 and the metal nanoparticle solution prepared in the step S2 to prepare a mixed solution; s4, removing the solvent from the mixed solution prepared in the step S3 to obtain a nano composite film light absorber; the light absorber takes aramid nano-fiber as a matrix, and the metal nano-particles are loaded on the aramid nano-fiber matrix. The optical absorber has super flexibility, has enough and lasting mechanical strength, and is beneficial to being widely applied to wearable and non-planar optical thermal devices; the high-efficiency, full-angle and broadband light absorption can be realized on visible light and near-infrared frequency; the preparation method is simple and efficient, and is easy for scale production.

Description

Light absorber and preparation method thereof

Technical Field

The invention relates to the technical field of composite materials, in particular to a light absorber and a preparation method thereof.

Background

The high absorption efficiency of an ideal light absorber with all directions (all angles) of light has always been a major goal of science and technology. In recent years, optical absorbers based on metamaterials (such as plasma optical absorbers) are widely researched and developed in many fields, and the metamaterials are artificial structural materials composed of sub-wavelength unit arrays and have excellent electromagnetic performance. The metamaterial wave-absorbing material can be generally divided into a narrow-band wave-absorbing material and a wide-band wave-absorbing material. Narrow band metamaterial absorbers always rely on the resonant effect of structures interacting with light of a particular frequency. In contrast, broadband metamaterial absorbers rely on a structure whose electromagnetic response is frequency independent and therefore can absorb light over a large bandwidth. Therefore, broadband metamaterial absorbers are very attractive for a wide range of photonic applications, such as solar-thermal energy collection, sensor platforms for full spectrum imaging and photodetection.

The implementation of broadband optical absorbers based on metamaterials has made tremendous progress. For example, nanopatterned anisotropic metamaterials with hyperbolic spatial dispersion have been demonstrated to have efficient optical absorption at visible and near-infrared frequencies. Metamaterials made from noble metal coated nanoporous templates also exhibit excellent broad band absorption properties. In addition, refractory materials such as titanium nitride and vanadium dioxide have recently been used to construct nanostructured broadband metamaterial absorbers. However, there are still some limitations that prevent the practical application of these metamaterial absorbers. First, nanostructured metamaterial absorbers are typically fabricated by top-down nanofabrication methods, such as Electron Beam Lithography (EBL) and Focused Ion Beam (FIB) milling, which inherently limit the maximum physical size and throughput of the absorber. Secondly, most of the broadband metamaterial wave-absorbing materials are prepared on a rigid substrate, such as glass and silicon wafers. This makes these devices inflexible and greatly limits their application in wearable and other optoelectronic systems having non-planar surfaces. Although some experimental attempts have been made at terahertz and optical frequencies, and the fabrication of metamaterials on flexible substrates has been successfully achieved, the strength and strain of the periodic metamaterial structures are inferior to those of flexible substrates, which reduces the overall mechanical performance of the device. Therefore, it remains challenging to produce flexible membranes with high performance, all-angle, and broadband light absorption using large area, high throughput bottom-up techniques.

Disclosure of Invention

In order to solve the problems, the invention provides a light absorber and a preparation method thereof, wherein the light absorber has super flexibility and can realize high-efficiency, full-angle and broadband light absorption on visible light and near-infrared frequency; the preparation method is simple and efficient, and is easy for scale production.

The preparation method of the light absorber provided by the invention comprises the following steps: s1, preparing an aramid nanofiber solution by taking aramid as a raw material; s2, preparing a metal nanoparticle solution; s3, mixing the aramid fiber nanofiber solution prepared in the step S1 and the metal nanoparticle solution prepared in the step S2 to prepare a mixed solution; s4, removing the solvent from the mixed solution prepared in the step S3 to obtain a nano composite film light absorber; the light absorber takes aramid nano-fiber as a matrix, and the metal nano-particles are loaded on the aramid nano-fiber matrix.

Preferably, the aramid fiber comprises Kevlar of dupont, the metal nanoparticles comprise one or more of gold nanoparticles, silver nanoparticles and copper nanoparticles, and the content of the metal nanoparticles in the nanocomposite film is more than 2.8%.

Preferably, the step S1 includes: s11, soaking aramid fiber in a solution for fiberization after vacuum drying, then fishing out, cleaning and vacuum drying to obtain fiberized aramid fiber; s12, uniformly mixing and stirring the fiberized aramid fiber obtained in the step S11, alkali and a solvent, and adding a treating agent after the solution is changed into a mauve oily solution from colorless to obtain an aramid fiber nano fiber solution.

More preferably, the vacuum drying conditions before the aramid fiber is fiberized in step S11 are: drying at 60-65 deg.C for 18-24 h; the vacuum drying condition after the fiberization is 60-70 ℃, and the drying is carried out for 48 hours. The alkali in the step S12 is potassium hydroxide, and the mass ratio of the potassium hydroxide to the aramid fiber is 1: 1-2: 1; the solvent is N, N-dimethyl sulfoxide; the treating agent is a mixed solution of phosphoric acid and water.

More preferably, the volume ratio of the phosphoric acid to the water is 1:2-2: 1; the volume of the treating agent accounts for 1.0-10% of the total volume of the mixed solution.

Preferably, the step S4 includes: and (5) carrying out suction filtration on the mixed solution prepared in the step S3 to obtain the nano composite film light absorber.

The present invention also provides a light absorber comprising: the nano-aramid fiber comprises an aramid nano-fiber matrix and metal nano-particles loaded on the aramid nano-fiber matrix.

Preferably, the aramid fiber comprises Kevlar (r) from dupont; the metal nanoparticles comprise one or more of gold nanoparticles, silver nanoparticles and copper nanoparticles; the content of the metal nanoparticles in the light absorber is more than 2.8%.

The invention has the beneficial effects that:

1. the invention selects aramid fiber as raw material, and prepares aramid fiber nano fibers (ANFs) as matrix, because the aramid fiber nano fiber matrix has excellent mechanical strength (high tensile strength, bending resistance and other properties), the film light absorber has super flexibility and sufficient and lasting mechanical strength, and is beneficial to being widely applied to wearable and non-planar photo-thermal devices.

2. Compared with the prior art which adopts a top-down preparation method, the method has the advantages that the aramid fiber nano-fiber solution and the metal nano-particle solution are mixed, and the solvent is removed to obtain the nano-composite film light absorber, so that the method is low in cost and easy to amplify. Meanwhile, the aramid fiber nano-fiber of the nano-composite film light absorber prepared by the method is self-assembled to form a porous three-dimensional matrix, and metal nano-particles are loaded on the nano-fibers and between the nano-fibers. The content and the diameter of metal nano particles doped in the film are optimized, and the high-dispersion metal nano particles realize excellent broadband, high-efficiency and omnidirectional light absorption due to the local surface plasmon resonance effect; compared with the light absorber in the prior art, the unit square of the metal nano particles is greatly reduced, and the cost of the light absorber is further reduced.

3. Based on the excellent chemical/thermal stability of the aramid nano-fiber, even if the surface temperature of the film is sharply increased under the action of high-efficiency light absorption and photo-thermal conversion, the light absorber can not burn or deform, and the physical property and the function of the light absorber can still be kept stable at high temperature.

Drawings

FIG. 1 is a schematic diagram of a specific process for preparing a light absorber (PMF) according to an embodiment of the present invention.

Fig. 2 is a schematic view of fiberization of an aramid yarn in an embodiment of the invention.

Fig. 3 is a schematic diagram of the nanocrystallization of the aramid fiber in the embodiment of the present invention.

Fig. 4 is a scanning electron microscope image of the aramid nanofibers obtained after treatment with different treatment agents in the embodiment of the present invention.

FIG. 5 shows the transmission electron microscope images of gold nanoparticles of different particle sizes prepared by the gold seed growing method in the embodiment of the present invention, wherein the particle size distribution a-b: 20nm, 30nm, 40nm, 60nm, 80nm, 110 nm.

FIG. 6 is a diagram of PMF real objects with different gold contents prepared by suction filtration in the embodiment of the present invention, wherein the gold contents a-h are respectively: 0, 1.4%, 2.8%, 4.3%, 5.7%, 7.1%, 8.6%, 9.9%.

Fig. 7 shows the influence of different gold nanoparticle particle sizes (a), different gold nanoparticle contents (B) and different incident angles (C) on the absorption in the ultra-flexible plasma optical absorber according to the embodiment of the present invention.

FIG. 8 is a scanning electron microscope image of the ultra-flexible plasma optical absorber and its surface topography in an embodiment of the present invention.

Fig. 9 shows flexibility test (a), bending property test (B) and young's modulus property test (C) of the ultra-flexible plasma optical absorber according to the embodiment of the present invention.

FIG. 10 is a study of the photothermal performance of the ultra-flexible plasma light absorber in the embodiment of the present invention.

Detailed Description

The invention provides the following specific embodiments and all possible combinations between them. For the sake of brevity, this application does not recite any particular combination of embodiments one by one, but it is to be understood that this application recites and discloses specifically all possible combinations of the described embodiments.

The invention provides an ultra-flexible nano composite film light absorber and a preparation method thereof, and the preparation method comprises the following steps: s1, preparing an aramid nanofiber solution by taking aramid as a raw material; s2, preparing a metal nanoparticle solution; s3, mixing the aramid fiber nanofiber solution prepared in the step S1 and the metal nanoparticle solution prepared in the step S2 to prepare a mixed solution; s4, removing the solvent from the mixed solution prepared in the step S3 and drying to obtain a nano composite film light absorber; the light absorber takes aramid nano-fiber as a matrix, and the metal nano-particles are loaded on the aramid nano-fiber matrix.

The aramid fiber is fully called poly phenylene terephthalamide, mainly comprises Twaron produced by imperial corporation and Kevlar produced by DuPont corporation, and has the excellent performances of ultrahigh strength, high modulus, high temperature resistance, acid and alkali resistance, light weight and the like.

In step S1, the aramid fiber is sequentially subjected to fiberization and hydrolysis to form nanofibers.

In step S2, the metal nanoparticles include one or more of gold nanoparticles, silver nanoparticles, and copper nanoparticles, and have a particle size of 1nm to 200nm and a particle size distribution of 20nm to 110 nm. The preparation of the metal nanoparticles can adopt any method for preparing the metal nanoparticles in the prior art.

In step S3, stirring the nanofiber solution prepared in step S1, heating to boiling, then adding the metal nanoparticle solution prepared in step S2, stirring uniformly, and stopping heating for later use;

in step S4, pressure filtration, freeze-drying, drying and supercritical CO are adopted₂Cleaning and the like to remove the solvent, and then drying at constant temperature to prepare the nano composite film.

The present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following embodiments, in which Kevlar (r) from dupont is used as the aramid, and gold (Au) nanoparticles are used as the metal nanoparticles. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.

The specific preparation process of the light absorber (PMF) is shown in FIG. 1, and the specific steps are as follows:

s11, fiberization of aramid fiber

Weighing 1.5g of aramid fiber, cutting the fiber into pieces by using scissors, and carrying out vacuum drying for 24h at the temperature of 60-65 ℃. The dried, chopped aramid is then placed in a solution of 100ml of anhydrous N-methyl pyrrolidone and soaked for about 48 hours (as shown in figure 2). And then taking out the fiber, continuously washing the fiber by using deionized water, removing the N-methylpyrrolidone solution contained in the fiber, and drying the washed fiber in a vacuum drying oven at 70 ℃ for about 48 hours. The obtained substance is a product of aramid fiber, and the dispersion degree of the fiber is higher than that of the fiber before and is easier to disperse in the solution of the subsequent hydrolysis step.

S12, hydrolysis of fiberized aramid

Firstly, weighing aramid fiber and potassium hydroxide, and adding the aramid fiber and the potassium hydroxide into a proper round-bottom flask, wherein the mass ratio of the potassium hydroxide to the aramid fiber is controlled to be 1:1 to 2: 1.

In this example, 1.0g each of aramid fiber and potassium hydroxide was weighed. The fibrillated aramid prepared in S11 was then transferred to the round bottom flask and 350ml of N, N-dimethyl sulfoxide (DMSO) was added to the flask. Next, the round-bottom flask containing the fiberized aramid fiber, potassium hydroxide and dimethyl sulfoxide is placed on a magnetic stirrer to be stirred, and the color of the material in the flask changes obviously along with the increase of the reaction time. As shown in fig. 3, the treatment agent was added to the round bottom flask as the solution changed from colorless to a uniform purplish red oily solution. The treating agent is: a mixed solution of phosphoric acid and water. Different treating agents are added to generate different influences on the final shape of the aramid nanofiber, as shown in fig. 4, the aramid nanofiber treated by the mixed solution of phosphoric acid (the phosphoric acid is purchased from the market, the mass concentration of the phosphoric acid is generally 85 percent, and the same below) and water has no blocky residue and no excessive hydrolysis, the thickness of the aramid nanofiber is uniform, the spatial three-dimensional structure is more three-dimensional, and the subsequent use is more facilitated; the uniformity of the aramid nano-fiber treated by phosphoric acid or water alone is not good than that of a mixed solution of phosphoric acid and water, as shown in fig. 4, the aramid nano-fiber treated by water is easy to excessively hydrolyze, and has large holes, and the spatial three-dimensional structure of the aramid nano-fiber treated by phosphoric acid is not three-dimensional enough.

Wherein, the volume ratio of the phosphoric acid to the deionized water is preferably 1:2-2:1, and most preferably 1:2, 2:2, 2: 1; the volume of the treating agent added is controlled to be 1.0-10% of the total volume of the solution in the round-bottom flask according to requirements.

It is worth noting that: compared with other strong bases (sodium hydroxide, barium hydroxide and the like), the ideal aramid nano-fiber can be obtained only by hydrolyzing potassium hydroxide with a fiberized aramid and DMSO solution and treating with a treating agent.

S2. preparation of gold (Au) nanoparticles

In this example, gold nanoparticles prepared by a gold seed method were mainly used. The particle size distribution mainly comprises: 20nm, 30nm, 40nm, 60nm, 80nm and 110nm, and the preparation method comprises the following steps:

s21, preparing seed liquid

19.0mL of high purity water was measured with a measuring cylinder and placed in the flask. Accurately measuring 0.17mL of tetrachloroauric acid solution (1 wt%) by using a pipette, adding the tetrachloroauric acid solution into a 50.0mL round-bottom flask, adjusting the rotation speed of a magnet to enable the solution to be stirred vigorously, accurately measuring 0.172mL of sodium citrate solution (0.75 wt%) by using the pipette, immediately and quickly adding 0.6mL of newly prepared sodium borohydride solution (0.1M), observing that the solution is quickly changed from colorless to yellowish red, timing, continuously stirring for 4 hours, then collecting the solution again, and putting the solution into a refrigerator to be kept in a dark place for later use.

It should be noted that: the seed liquid needs to be prepared fresh, the standing time cannot exceed 24 hours, aging can occur after the standing time is too long, the seeds slowly aggregate and grow up, the size and the regular morphology of the nano particles are controlled disadvantageously, and the amount of the required substances can be adjusted in equal proportion according to the amount of the required substances, so that the requirement of actual operation is met.

S22. seed crystal growth

A50.0 mL flask is erected with a device, a measuring cylinder measures 20mL of high-purity water and pours the high-purity water into the flask, then a magneton with a proper size is added, and a proper rotating speed is adjusted. 4.0mL of polyvinylpyrrolidone (PVP) solution, 2.0mL of ascorbic acid solution, 1.5mL of potassium iodide (KI) solution, and 5.1mL of chloroauric acid solution (1 wt%) were measured in this order by a pipette gun and charged into the flask. While keeping the solution well stirred, different volumes of seed solutions (0.018mL, 0.072mL, 0.144mL, 0.36mL, 1.44mL, 2.88mL) prepared in S21 were quickly added with a pipette to prepare gold nanoparticles of different particle size distributions (20nm, 30nm, 40nm, 60nm, 80nm, 110nm) with stirring for 10 min. After the reaction is finished, naturally cooling to room temperature, then transferring into a clean brown sample bottle, attaching label paper, and then placing into a refrigerator for storage in dark place. The sample was finally characterized by UV-Vis and TEM, as shown in fig. 5.

S3, preparation of nanofiber and nanoparticle mixed solution

In this embodiment, the nanofiber and nanoparticle mixed solution is prepared by mixing the aramid nanofiber solution and the gold nanoparticles prepared as above. The main preparation method comprises the following steps: a. adding 200ml of high-purity water (deionized water) into a round-bottom flask, continuously stirring, and heating to boil; b. and (3) measuring 20ml of the aramid nano-fiber solution prepared in the step S12 by using a measuring cylinder, continuously stirring and heating until the mixed solution boils again, quickly adding the mixed solution containing the gold nanoparticles prepared in the step S22 with a certain volume into the boiled mixed solution, and stopping heating for later use after the solution is stirred and mixed uniformly again.

S4, preparing the film material

As shown in FIG. 1, this example uses a reduced pressure filtration method to prepare an ultra-flexible, efficient, full-angle, broadband absorbing film. The preparation method comprises the following steps:

assembling a decompression suction filtration device, putting two layers of suction filtration paper into a suction filtration bottle, adding water for wetting, and turning on a power switch. And (4) quickly transferring the mixed solution prepared in the step S3 to a filter flask, slowly adding boiling water (the adding volume is about 20-50% of the mixed solution) into the Buchner funnel along the inner wall of the Buchner funnel when the filtrate in the Buchner funnel falls to the surface of the film, continuously carrying out suction filtration until no liquid flows out from the tail end of the Buchner funnel, and closing a power switch of a decompression suction filtration pump after carrying out suction filtration for 5 minutes. For the same grain size, films with different gold contents are prepared by the same method to test the influence of different gold contents on the absorption performance and the like of the material, and the prepared sample is shown in fig. 6, wherein the a-h gold contents are respectively as follows: 0, 1.4%, 2.8%, 4.3%, 5.7%, 7.1%, 8.6%, 9.9%, and the particle sizes are 58 nm.

Taking out the semi-finished film after suction filtration from a Buchner funnel, placing the semi-finished film in a drying box, and drying for 24 hours at the normal pressure of 65 ℃. And (5) peeling the film from the filter paper by using a knife after drying. Thus, the super-flexible plasma light absorber is prepared.

Compared with the common freeze-drying, drying and supercritical CO in the prior art₂The nano composite film prepared by the modes of cleaning and the like for removing the solvent and the modes of pressurizing and filtering has better flexibility and is more used for collection and transportation; in addition, the preparation method has low requirements on instruments and equipment, is simple and efficient, and has low processing cost.

Actual sample testing

For the light absorber prepared in this embodiment, the structural properties of the light absorber are further characterized and tested, which mainly includes: and (5) structural characterization and performance test.

First, the influence of the particle size, content and incident angle of gold nanoparticles in the light absorber on absorption was determined. As shown in fig. 7A, when the gold nanoparticle content is 5.7%, the influence of the particle size of the gold nanoparticles on the light absorption is different in the absorber. The light absorption of different light absorbers in a visible light region (380-780nm) and a near infrared short wave region (780-1100nm) can basically reach more than 95%, the light absorption is more than 85% even in a near infrared long wave region, and the effect of the gold nanoparticles with the particle size of 58nm is better than that of other particle sizes. As shown in fig. 7B, when the content of Au nanoparticles is above 2.8%, the absorption of light by the absorber reaches above 82%; when the content of the Au nano particles is more than 4.3%, the absorption of light reaches more than 90%. When the content of the gold nanoparticles reaches 5.7% or more, the light absorber has the best effect of absorbing light, the light absorber absorbs light by more than 99% in a visible light region (380-780nm) and a near-infrared short-wave region (780-1100nm), namely, the light absorption in the near-infrared long-wave region is more than 90%, and the absorption does not have obvious fluctuation along with the change of an incident light angle (figure 7C). The highly dispersed gold nanoparticles achieve effective optical absorption due to their localized surface plasmon resonance effect and the porous structure of the thin film material.

Secondly, the optical absorber also has excellent flexibility. As shown in fig. 9A, the film absorber can be folded and rolled for portability. Furthermore, the ultra-flexible plasma light absorber has good bending and stretching resistance, and as shown in fig. 9B and 9C, even after 800 times of stretching, the film still has good mechanical flexibility.

Finally, the photothermal properties of the ultra-flexible plasma light absorber were characterized to assess its potential in photothermal applications. As shown in FIG. 10, ultra-flexible plasma light absorbers are illuminated and live real-time using broadband laser sources with different output powersThe temperature was recorded. The diameter of an incident laser spot is 4mm, and the output power density range is from 4.7mW/mm²To 30.4mW/mm². It can be clearly seen that all of the heat generated is highly confined around the area of the incident laser spot. This is because the aramid nanofibers have low thermal conductivity (0.048W · m)^-1k^-1) The generated heat energy is not easily transferred to adjacent regions, so that the local temperature of the PMF may sharply rise. The power was turned on and off for 1 minute for each heating-cooling cycle, respectively (line graph). The temperature response of the ultra-flexible plasma light absorber is very fast both during heating and cooling. For example, when the ultra-flexible plasma light absorber is 30.4mW/mm²The laser output of (2) is only required to be heated from room temperature (20.5 ℃) to a stable temperature (147.2 ℃) for about 4.8 seconds. Once the light source is turned off, the cooling process of the ultra-flexible plasma light absorber back to room temperature is also less than 5 s. The stable temperature of the ultra-flexible plasma light absorber exposed by the laser light source collected with different output power shows good linear dependence that Ts (DEG C) is 3.69 XP (mW/mm)²) +31.85 where Ts and P represent the stable temperature and power supply output power, respectively. Determination of the coefficient (R)²) Is 0.9954. Linear correlation means that it is easy to control the temperature by adjusting the power of the power supply and vice versa. Thanks to gold (melting point: 1064 ℃) and aramid (decomposition temperature)>500 deg.C), the PMF can still keep the physical and functional stability at such high temperature.

The foregoing is a more detailed description of the invention in connection with specific/preferred embodiments and is not intended to limit the practice of the invention to those descriptions. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and these substitutions and modifications should be considered to fall within the scope of the invention.

Claims

1. A method of making a light absorber, comprising:

s1, preparing an aramid nanofiber solution by taking aramid as a raw material;

s2, preparing a metal nanoparticle solution; the metal nanoparticles comprise one or more of gold nanoparticles, silver nanoparticles and copper nanoparticles;

s3, mixing the aramid fiber nano-fiber solution prepared in the step S1 and the metal nano-particle solution prepared in the step S2 to prepare a mixed solution;

s4, removing the solvent from the mixed solution prepared in the step S3 to obtain the nano composite film light absorber; the light absorber takes aramid nano-fiber as a matrix, and the metal nano-particles are loaded on the aramid nano-fiber matrix;

the step S1 includes:

s11, soaking the aramid fiber in the solution for fiberization after vacuum drying, then fishing out, cleaning and vacuum drying to obtain the fiberized aramid fiber;

s12, uniformly mixing and stirring the fiberized aramid fiber obtained in the step S11, alkali and a solvent, and adding a treating agent after the solution is changed into a mauve oily solution from colorless to obtain an aramid fiber nano fiber solution; the treating agent is a mixed solution of phosphoric acid and water.

2. The method of claim 1, wherein the aramid fiber comprises Kevlar (r) from dupont; the content of metal nano particles in the nano composite film is more than 2.8%.

3. The preparation method according to claim 1, wherein the vacuum drying conditions before the aramid fiber is fiberized in the step S11 are as follows: drying for 18-24 h at 60-65 ℃; the vacuum drying condition after the fiberization is 60-70 ℃, and the drying is carried out for 48 hours.

4. The preparation method according to claim 1, wherein the alkali in the step S12 is potassium hydroxide, and the mass ratio of potassium hydroxide to the fiberized aramid fiber is 1: 1-2: 1; the solvent is dimethyl sulfoxide.

5. The method of claim 1, wherein the volume ratio of phosphoric acid to water is 1:2 to 2: 1; the volume of the treating agent accounts for 1.0-10% of the total volume of the mixed solution.

6. The method of claim 1, wherein the step S4 includes: and (5) carrying out suction filtration on the mixed solution prepared in the step S3 to obtain the nano composite film light absorber.

7. A light absorber, comprising: an aramid nanofiber matrix, and metal nanoparticles supported on the aramid nanofiber matrix; the light absorber is prepared by the method of any one of claims 1-6.