Preparation method and application of formic acid protonated MXene / ANF / Pd aerogel composite membrane

Abstract

The invention provides a preparation method of a formic acid protonated MXene / ANF / Pd aerogel composite membrane and application of the formic acid protonated MXene / ANF / Pd aerogel composite membrane in the field of electromagnetic shielding. The precious metal Pd is quickly reduced from the precious metal waste liquid by utilizing rich reducing active sites on the surface of the MXene nanosheet and is uniformly loaded on the surface of the MXene nanosheet, so that the formic acid protonated MXene / ANF / Pd aerogel composite membrane with enhanced performance is generated. The electromagnetic shielding effectiveness of the product prepared by the method is gt in the X wave band; the high-shielding-requirement scene such as military, communication, industry and the like is suitable for the high-shielding-requirement scene; pd is extracted and recovered from the Pd-containing noble metal waste liquid, so that the method has the industrial popularization advantages of low cost, low energy consumption, high selectivity, high economic effect and environment friendliness; the preparation process is good in repeatability and low in instrument requirement, and the aerogel film is high in mechanical flexibility and high in shielding effectiveness and has great application potential in the field of flexible electromagnetic shielding protection.

Description

Technical Field

[0001] This invention belongs to the field of flexible aerogel membrane material preparation and electromagnetic shielding application, specifically relating to a method for preparing a formic acid protonated MXene / ANF / Pd aerogel composite membrane and its application in the field of electromagnetic shielding. Background Technology

[0002] With the rapid development of information technology, wireless communication, intelligent electronic devices, and electric vehicles, electromagnetic waves are increasingly widely used in various scenarios. However, the resulting electromagnetic pollution problem is also becoming increasingly serious. Electromagnetic radiation sources include high-frequency communication equipment, microwave electronic components, power transmission lines, and industrial equipment. The electromagnetic waves they generate propagate through space, causing signal interference to communication systems, malfunctions in precision electronic instruments, and even potential harm to human health. Furthermore, in fields such as defense and aerospace, electromagnetic leakage can also lead to information security risks. Therefore, developing efficient, lightweight, and environmentally friendly electromagnetic shielding materials to suppress or absorb electromagnetic interference has become a crucial guarantee for the reliable operation of electronic devices and the safety of human life.

[0003] Among numerous emerging electromagnetic shielding materials (conductive polymers, carbon-based materials, metal composites, and novel two-dimensional materials, etc.), MXene has attracted widespread attention due to its excellent electrical conductivity, high specific surface area, layered structure, and good mechanical flexibility. MXene is typically obtained by selectively etching the A-layer elements of a MAX phase precursor, and its surface is rich in... The presence of functional groups endows it with excellent dispersibility and interface control capabilities. MXene's high conductivity enables it to effectively reflect incident electromagnetic waves, while its multilayer structure and internal interface scattering help enhance multiple reflections and absorption of electromagnetic waves, thereby significantly improving electromagnetic shielding performance.

[0004] However, pure MXene materials are prone to oxidative degradation during long-term use, leading to a decline in conductivity and structural stability. Simultaneously, the tendency for MXene sheets to stack and the confined pore structure hinder the multiple scattering and absorption processes of electromagnetic waves. To address these shortcomings, researchers have proposed various modification strategies, including polymer composites, heterostructure construction, carbonization / nitridation regulation, and metal or non-metal doping. Among these, the construction of MXene-based aerogel membranes has become a research hotspot in recent years. Aerogel structures possess ultra-low density, high porosity, and a three-dimensional continuous conductive network, which can significantly improve multiple reflection and absorption capabilities while maintaining lightweight and flexible properties, thus exhibiting excellent specific shielding effectiveness (SE value) and stability in electromagnetic shielding applications. MXene-based aerogel membranes not only achieve a synergistic effect of efficient electromagnetic wave reflection and absorption but also show ideal performance in applications such as flexible wearable devices, aerospace protection, and smart electronic packaging.

[0005] This invention addresses the shortcomings of existing MXene aerogel membranes in terms of conductivity stability and resource utilization by protonating a formic acid-based MXene / ANF / Pd aerogel composite membrane. This method utilizes ANF to stabilize MXene, inhibiting its oxidation and enhancing its toughness; it leverages the reprotonation effect of formic acid to introduce hydrogen bonding interactions to regulate the interfacial interactions of the material; and it uses waste liquid containing Pd (palladium) metal ions as a metal source, achieving in-situ reduction and extraction of Pd metal through a green chemical approach, resulting in uniform distribution of metal nanoparticles within the MXene-based aerogel framework. This strategy not only endows the aerogel membrane with higher conductivity and interfacial polarization capabilities, thereby improving electromagnetic shielding performance, but also effectively inhibits the oxidative deactivation of MXene, enhancing the material's environmental stability and service life. Compared with traditional processes such as exogenous metal salt addition or vapor deposition, this method offers significant advantages such as low cost, low energy consumption, high selectivity, and environmental friendliness, achieving an organic combination of waste liquid resource utilization and functional material preparation. Meanwhile, the electronic synergistic effect between the metal and MXene can form multi-scale conductive channels and interfacial polarization centers, generating multiple reflection, absorption, and dissipation effects during electromagnetic wave propagation, thereby achieving excellent shielding efficiency and energy loss capability. This invention not only provides a new technical approach for the green preparation of high-performance electromagnetic shielding materials, but also offers a solution with promotional potential for realizing the reuse of electronic waste liquid and environmental sustainability. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a formic acid protonated MXene / ANF / Pd aerogel composite membrane and its application in the field of electromagnetic shielding. This method, based on the preparation of a formic acid protonated MXene / ANF aerogel composite membrane, utilizes the abundant active sites on the surface of MXene nanosheets to rapidly reduce metal particles from a Pd metal precursor solution through simple contact and uniformly load them onto the MXene nanosheet surface, generating a performance-optimized formic acid protonated MXene / ANF / Pd aerogel composite membrane. This invention not only has significant economic value for the recovery and reuse of Pd-containing precious metal waste liquid, but the Pd loading also simultaneously improves the performance of the formic acid protonated MXene / ANF aerogel composite membrane in electromagnetic shielding and other applications. The preparation process of this invention has good repeatability, low instrument requirements, and produces a highly flexible and effective aerogel membrane. Simultaneously, the loading of precious metals anchors the recovery and reuse of Pd-containing waste liquid, and the reduction and extraction are highly selective, simple to operate, and environmentally friendly and pollution-free. It has the advantages of both high performance and high economic value for industrial application.

[0007] Technical solution: A formic acid protonated MXene / ANF / Pd aerogel composite membrane is characterized by: based on the formic acid protonated MXene / ANF aerogel composite membrane, utilizing the abundant active sites on the surface of MXene nanosheets, rapidly and in-situ reducing and extracting the noble metal Pd from waste liquid and uniformly loading it onto the surface of MXene nanosheets to generate a performance-enhanced formic acid protonated MXene / ANF / Pd aerogel composite membrane; the formic acid protonated MXene / ANF / Pd aerogel composite membrane exhibits an electromagnetic shielding effectiveness >55 dB in the X-band.

[0008] A method for preparing the formic acid protonated MXene / ANF / Pd aerogel composite membrane, characterized by the following steps: Step 1: Add aramid fibers (AR) and potassium hydroxide (KOH) together to a dimethyl sulfoxide (DMSO) solution to obtain a mixture; stir the mixture at room temperature and wash it several times until neutral to obtain a dark red and uniformly dispersed aramid nanofiber (ANF) / DMSO suspension, which is defined as suspension A; The mixture is prepared in a mass ratio of AR:KOH:DMSO of 1:0.5~2:50~100; The mixture was continuously magnetically stirred at room temperature for 24-72 h, and then washed multiple times with ultrapure water and anhydrous ethanol until neutral to obtain suspension A. Step 2: Use liquid phase etching to etch Ti3AlC2MAX ceramic powder to obtain multilayer Ti3C2T x After MXene precipitation, centrifugation and washing were performed, followed by exfoliation using a shaking method to obtain exfoliated Ti3C2T. x MXene / H2O dispersion; then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to multiple centrifugation-dispersion cycles to finally obtain an MXene / DMSO dispersion, which was defined as dispersion B. Step 3: Add suspension A to dispersion B and sonicate for 3-5 min to obtain a homogeneous black mixed MXene / ANF dispersion system, which is defined as mixture C; In the mixture C, the ANF / DMSO suspension A and the MXene / DMSO dispersion B were prepared according to a solute mass ratio of ANF:MXene = 40 wt%: 60 wt%.

[0009] Step 4: Transfer the mixture C to a mold, inject a 5-10 M formic acid protonated solvent, and perform a reprotonation treatment for 10-20 h to form a black gel with a metallic luster; then obtain a formic acid protonated MXene / ANF aerogel composite membrane by rinsing and freeze drying, which is defined as aerogel membrane D. Step 5: Immerse the aerogel membrane D in a 5-20 mM solution containing Pd precursor and let it stand for 5-10 min. After removing it and drying it after the solution is completely absorbed, the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E, is obtained.

[0010] The Pd precursor solution is a variety of recyclable waste liquids containing +2 valence Pd metal, including electroplating solution, mirror making solution, diamond and jewelry grinding waste liquid, and industrial production waste liquid containing Pd metal.

[0011] The etching agent for the Ti3AlC2MAX ceramic powder in step 2 is HF acid or HCl acid / LiF mixture.

[0012] In step 2, the etching temperature using liquid phase etching is set to 25-40°C. o C, the etching time is set to 24~36 h.

[0013] Step 2, multilayer Ti3C2T x The centrifugal washing conditions for MXene precipitate are: washing with ultrapure water 6-9 times, at a speed of 3000-5000 rpm, for 3-5 minutes.

[0014] The preparation conditions for the MXene / H2O dispersion by the shaking method in step 2 are 20 min of hand shaking or 30 min of mechanical shaking.

[0015] The centrifugation-dispersion conditions for preparing dispersion B by solvent replacement in step 2 are as follows: first, centrifuge the above MXene / H2O dispersion at 10000 rpm for 10 min to collect the precipitate, and then redisperse it in DMSO. Repeat the above centrifugation-dispersion process 2 to 5 times to completely replace the water.

[0016] The freeze-drying conditions for the aerogel membrane D in step 4 are -50°C. o Vacuum drying was carried out at a low temperature of C for 6-10 hours.

[0017] An application of the formic acid protonated MXene / ANF / Pd aerogel composite membrane is characterized in that: the formic acid protonated MXene / ANF / Pd aerogel composite membrane has an electromagnetic shielding effectiveness of >55 dB in the X-band, i.e., 8.2~12.4 GHz, and is suitable for high shielding requirements, especially for flexible electromagnetic shielding protection fields where the aerogel membrane has strong mechanical flexibility and high shielding effectiveness requirements.

[0018] Beneficial effects This invention provides a method for preparing a formic acid protonated MXene / ANF / Pd aerogel composite membrane and its application in the field of electromagnetic shielding. The beneficial effects of this invention are: (1) It innovatively utilizes the abundant reducing active sites on the surface of MXene nanosheets to rapidly reduce the noble metal Pd from the noble metal waste liquid and uniformly load it onto the surface of MXene nanosheets to generate a performance-enhanced formic acid protonated MXene / ANF / Pd aerogel composite membrane; (2) The product prepared by this invention has an electromagnetic shielding effectiveness of >55 dB in the X-band (8.2~12.4 GHz), which is suitable for high shielding requirements in military, communication, and industrial applications; (3) This invention extracts and recovers Pd from Pd-containing noble metal waste liquid, which has the advantages of low cost, low energy consumption, high selectivity, high economic efficiency, and environmental friendliness for industrial promotion; (4) The preparation process of this invention has good repeatability, low instrument requirements, strong mechanical flexibility of the aerogel membrane, and high shielding effectiveness, which has great application potential in the field of flexible electromagnetic shielding protection. Attached Figure Description

[0019] Figure 1 Photograph of protonated MXene / ANF / Pd aerogel composite membrane Figure 2 The XRD pattern of the formic acid protonated MXene / ANF / Pd aerogel composite membrane prepared under the conditions of Example 1 according to the present invention. Figure 3 The image above shows the SEM image of the formic acid protonated MXene / ANF / Pd aerogel composite membrane prepared under the conditions of Example 1 according to the present invention. Figure 4 This is a comparison chart showing the electromagnetic shielding performance of the formic acid protonated MXene / ANF / Pd aerogel composite membrane prepared under the conditions of Example 1 of this invention, and the comparative formic acid protonated MXene / ANF aerogel composite membrane. Detailed Implementation The present invention will now be further described in conjunction with the embodiments and accompanying drawings: The technical solution of the present invention is as follows: 1) Aramid fibers (AR) and potassium hydroxide (KOH) were added together to a dimethyl sulfoxide (DMSO) solution, wherein the mass ratio of AR:KOH:DMSO was 1:(0.5~2):(50~100). The mixture was then continuously magnetically stirred at room temperature for 24~72 h, and then washed repeatedly with ultrapure water and anhydrous ethanol until neutral, to obtain a dark red and uniformly dispersed aramid nanofiber (ANF) / DMSO suspension, defined as suspension A.

[0020] The AR mentioned here mainly refers to Kevlar-type aramid fibers.

[0021] 2) Obtain multilayer Ti3C2T by etching Ti3AlC2MAX ceramic powder using liquid phase etching method. x After MXene precipitation, centrifugation and washing were performed, followed by exfoliation using a shaking method to obtain exfoliated Ti3C2T. x MXene / H2O dispersion. Then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to multiple centrifugation-dispersion cycles to finally obtain an MXene / DMSO dispersion, which was defined as dispersion B.

[0022] The etching agent for the Ti3AlC2MAX ceramic powder can be HF acid or an HCl acid / LiF mixture, and the etching temperature is set to 25~40℃. o C, the etching time is set to 24~36 h. The multilayer Ti3C2T... x The centrifugal washing conditions for MXene precipitate are: washing 6-9 times with ultrapure water at a speed of 3000-5000 rpm for 3-5 minutes. The preparation conditions for the MXene / H2O dispersion obtained by the shaking method are: 20 minutes of hand shaking or 30 minutes of mechanical shaking.

[0023] The centrifugation-dispersion conditions for preparing dispersion B by solvent replacement method are as follows: first, centrifuge the above MXene / H2O dispersion at 10000 rpm for 10 min to collect the precipitate, and then redisperse it in DMSO. Repeat the above centrifugation-dispersion process 2 to 5 times to completely replace the water.

[0024] 3) Add suspension A to dispersion B according to the solute ratio of ANF:MXene = 40 wt%: 60 wt%, and sonicate for 3-5 min to obtain a homogeneous black mixed MXene / ANF dispersion system, which is defined as mixture C.

[0025] 4) Transfer the mixture C to a mold, immediately inject a 5-10 M formic acid protonated solvent, and perform a reprotonation treatment for 10-20 h to form a black gel with a metallic luster. Finally, obtain the formic acid protonated MXene / ANF aerogel composite membrane by rinsing with ultrapure water and freeze-drying, which is defined as aerogel membrane D.

[0026] The freeze-drying conditions for aerogel membrane D are -50°C. o Vacuum drying was carried out at a low temperature of C for 6-10 hours.

[0027] 5) Immerse the aerogel membrane D in a 5-20 mM solution containing Pd precursor, let it stand for 5-10 min, then remove it and wait for the solution to be completely absorbed and dried to obtain the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E.

[0028] The Pd-containing precursor solutions used are various palladium-containing metal solutions, including but not limited to electroplating solutions, mirror-making solutions, diamond and jewelry polishing waste solutions, and various industrial waste solutions containing palladium.

[0029] Example 1: 1) Add 2 g of AR and KOH together to a DMSO solution, wherein the mass ratio of AR:KOH:DMSO is 1:1.5:50. Then, the mixture is continuously magnetically stirred at room temperature for 72 h, and then washed multiple times with ultrapure water and anhydrous ethanol until neutral, to obtain a dark red and uniformly dispersed ANF / DMSO suspension A.

[0030] 2) Use 20 mL of HCl acid / LiF mixture as etching agent, and continuously stir at 40 ℃ for 24 h to etch Ti3AlC2MAX ceramic powder to obtain multilayer Ti3C2T x MXene precipitate was centrifuged in ultrapure water at 4000 rpm for 3 min, and washed repeatedly 8 times. The washed precipitate was then subjected to hand-shaking for 20 min to obtain exfoliated Ti3C2T. x MXene / H2O dispersion. Then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to three centrifugation-dispersion cycles to finally obtain MXene / DMSO dispersion B.

[0031] 3) Add suspension A to dispersion B according to the solute ratio of ANF:MXene = 40 wt%: 60 wt%, and sonicate for 5 min to obtain homogeneous black mixed MXene / ANF solution C.

[0032] 4) Transfer the mixture C to a mold, immediately inject a 10 M formic acid protonated solvent, and perform a 20-hour reprotonation treatment to form a black gel with a metallic luster. Finally, obtain the formic acid protonated MXene / ANF aerogel composite membrane D by rinsing with ultrapure water and freeze-drying.

[0033] 5) Immerse the aerogel composite membrane D in a 5 mM H2PdCl4 solution, let it stand for 10 min, then remove it and wait for the solution to be completely absorbed and dried to obtain the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E.

[0034] Example 2: 1) Add 2 g of AR and KOH together to a DMSO solution, wherein the mass ratio of AR:KOH:DMSO is 1:2:50. Then, the mixture is continuously magnetically stirred at room temperature for 48 h, and then washed multiple times with ultrapure water and anhydrous ethanol until neutral, to obtain a dark red and uniformly dispersed ANF / DMSO suspension A.

[0035] 2) Using 20 mL of HF acid as an etchant, the Ti3AlC2MAX ceramic powder was etched by continuous stirring at 35 °C for 24 h to obtain multilayer Ti3C2T x MXene precipitate was centrifuged in ultrapure water at 3500 rpm for 3 min, and washed repeatedly 9 times. The washed precipitate was then subjected to mechanical vibration for 30 min to obtain exfoliated Ti3C2T. x MXene / H2O dispersion. Then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to four centrifugation-dispersion cycles to finally obtain MXene / DMSO dispersion B.

[0036] 3) Add suspension A to dispersion B according to the solute ratio of ANF:MXene = 40 wt%: 60 wt%, and sonicate for 4 min to obtain homogeneous black mixed MXene / ANF solution C.

[0037] 4) Transfer the mixture C to a mold, immediately inject a 5 M formic acid protonated solvent, and perform a 10-hour reprotonation treatment to form a black gel with a metallic luster. Finally, obtain the formic acid protonated MXene / ANF aerogel composite membrane D by rinsing with ultrapure water and freeze-drying.

[0038] 5) Immerse the aerogel composite membrane D in a 10 mM Na2PdCl4 solution, let it stand for 8 min, then remove it and wait for the solution to be completely absorbed and dried to obtain the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E.

[0039] Example 3: 1) Add 1 g of AR and KOH together to a DMSO solution, wherein the mass ratio of AR:KOH:DMSO is 1:2:100. Then, the mixture is continuously magnetically stirred at room temperature for 24 h, and then washed multiple times with ultrapure water and anhydrous ethanol until neutral, to obtain a dark red and uniformly dispersed ANF / DMSO suspension A.

[0040] 2) Using 20 mL of HF acid as an etchant, the Ti3AlC2MAX ceramic powder was etched by continuous stirring at 40 °C for 24 h to obtain multilayer Ti3C2T xMXene precipitate was centrifuged in ultrapure water at 5000 rpm for 3 min, and washed repeatedly 7 times. The washed precipitate was then subjected to mechanical vibration for 30 min to obtain exfoliated Ti3C2T. x MXene / H2O dispersion. Then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to three centrifugation-dispersion cycles to finally obtain MXene / DMSO dispersion B.

[0041] 3) Add suspension A to dispersion B according to the solute ratio of ANF:MXene = 40 wt%: 60 wt%, and sonicate for 5 min to obtain homogeneous black mixed MXene / ANF solution C.

[0042] 4) Transfer the mixture C to a mold, immediately inject a 10 M formic acid protonated solvent, and perform a 15-hour reprotonation treatment to form a black gel with a metallic luster. Finally, obtain the formic acid protonated MXene / ANF aerogel composite membrane D by rinsing with ultrapure water and freeze-drying.

[0043] 5) Immerse the aerogel composite membrane D in a 15 mM H2PdCl4 solution, let it stand for 5 min, then remove it and wait for the solution to be completely absorbed and dried to obtain the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E.

[0044] Example 4: 1) Add 1 g of AR and KOH together to a DMSO solution, wherein the mass ratio of AR:KOH:DMSO is 1:1:50. Then, the mixture is continuously magnetically stirred at room temperature for 36 h, and then washed multiple times with ultrapure water and anhydrous ethanol until neutral, to obtain a dark red and uniformly dispersed ANF / DMSO suspension A.

[0045] 2) Using 20 mL of HCl / LiF mixture as the etching agent, the Ti3AlC2MAX ceramic powder was etched by stirring continuously at 35 °C for 36 h to obtain multilayer Ti3C2T x MXene precipitate was centrifuged in ultrapure water at 3000 rpm for 5 min, and washed repeatedly 8 times. The washed precipitate was then subjected to hand-shaking for 20 min to obtain exfoliated Ti3C2T. x MXene / H2O dispersion. Then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to 5 centrifugation-dispersion cycles to finally obtain MXene / DMSO dispersion B.

[0046] 3) Add suspension A to dispersion B according to the solute ratio of ANF:MXene = 40 wt%: 60 wt%, and sonicate for 3 min to obtain homogeneous black mixed MXene / ANF solution C.

[0047] 4) Transfer the mixture C to a mold, immediately inject a 5 M formic acid protonated solvent, and perform a 20-hour reprotonation treatment to form a black gel with a metallic luster. Finally, obtain the formic acid protonated MXene / ANF aerogel composite membrane D by rinsing with ultrapure water and freeze-drying.

[0048] 5) Immerse the aerogel composite membrane D in a mixture of 5 mM H2PdCl4 solution and 5 mM Na2PdCl4 solution, let it stand for 10 min, and then take it out. After the solution is completely absorbed and dried, the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E, is obtained.

[0049] Example 5: 1) Add 1 g of AR and KOH together to a DMSO solution, wherein the mass ratio of AR:KOH:DMSO is 1:0.5:50. Then, the mixture is continuously magnetically stirred at room temperature for 60 h, and then washed multiple times with ultrapure water and anhydrous ethanol until neutral, to obtain a dark red and uniformly dispersed ANF / DMSO suspension A.

[0050] 2) Using 20 mL of HCl / LiF mixture as the etching agent, the Ti3AlC2MAX ceramic powder was etched by stirring continuously at 25 °C for 36 h to obtain multilayer Ti3C2T x MXene precipitate was centrifuged in ultrapure water at 3500 rpm for 5 min, and washed repeatedly 9 times. The washed precipitate was then subjected to hand-shaking for 20 min to obtain exfoliated Ti3C2T. x MXene / H2O dispersion. Then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to four centrifugation-dispersion cycles to finally obtain MXene / DMSO dispersion B.

[0051] 3) Add suspension A to dispersion B according to the solute ratio of ANF:MXene = 40 wt%: 60 wt%, and sonicate for 4 min to obtain homogeneous black mixed MXene / ANF solution C.

[0052] 4) Transfer the mixture C to a mold, immediately inject a 10 M formic acid protonated solvent, and perform a 10 h reprotonation treatment to form a black gel with a metallic luster. Finally, obtain the formic acid protonated MXene / ANF aerogel composite membrane D by rinsing with ultrapure water and freeze-drying.

[0053] The aerogel composite membrane D was immersed in a mixture of 10 mM H2PdCl4 solution and 10 mM Na2PdCl4 solution, and after standing for 5 min, it was taken out and dried after the solution was completely absorbed to obtain the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E.

[0054] Figure 1 This is a photograph of the formic acid protonated MXene / ANF / Pd aerogel composite membrane prepared under the conditions of Example 1 according to the present invention. It can be seen that the product is a black aerogel with extremely high flexibility. It can withstand multiple bending and twisting without any damage to its mechanical properties.

[0055] Figure 2 The image shows the XRD pattern of the formic acid protonated MXene / ANF / Pd aerogel composite membrane prepared under the conditions of Example 1 according to the present invention. Strong Pd metal diffraction peaks appear in the image, demonstrating that the formic acid protonated MXene / ANF composite aerogel membrane can effectively reduce and extract a large amount of Pd metal.

[0056] Figure 3 This is a SEM image of the formic acid protonated MXene / ANF / Pd aerogel composite membrane prepared under the conditions of Example 1 according to the present invention. It can be seen that rapidly reduced Pd metal nanoflowers are uniformly dispersed on the wrinkled MXene nanosheets.

[0057] Figure 4 This is a comparison of the electromagnetic shielding performance of the formic acid protonated MXene / ANF / Pd aerogel composite membrane prepared under the conditions of Example 1, and the comparative formic acid protonated MXene / ANF aerogel composite membrane. It can be seen that, compared to the comparative formic acid protonated MXene / ANF aerogel composite membrane without Pd metal nanoflowers, the formic acid protonated MXene / ANF / Pd aerogel composite membrane exhibits superior electromagnetic shielding effectiveness in the X-band (8.2~12.4 GHz).

Claims

1. A formate protonated MXene / ANF / Pd aerogel composite membrane, characterized in that: Based on the formic acid protonated MXene / ANF aerogel composite membrane, the noble metal Pd is rapidly and in-situ reduced and extracted from waste liquid and uniformly loaded onto the surface of MXene nanosheets by utilizing the abundant active sites on the surface of MXene nanosheets, thereby generating a performance-enhanced formic acid protonated MXene / ANF / Pd aerogel composite membrane; the formic acid protonated MXene / ANF / Pd aerogel composite membrane has an electromagnetic shielding effectiveness of >55 dB in the X-band.

2. A method for preparing the formic acid protonated MXene / ANF / Pd aerogel composite membrane according to claim 1, characterized in that... The steps are as follows: Step 1: Add aramid fibers (AR) and potassium hydroxide (KOH) together to a dimethyl sulfoxide (DMSO) solution to obtain a mixture; stir the mixture at room temperature and wash it several times until neutral to obtain a dark red and uniformly dispersed aramid nanofiber (ANF) / DMSO suspension, which is defined as suspension A; The mixture is prepared in a mass ratio of AR:KOH:DMSO of 1:0.5~2:50~100; The mixture was continuously magnetically stirred at room temperature for 24-72 h, and then washed multiple times with ultrapure water and anhydrous ethanol until neutral to obtain suspension A. Step 2: Use liquid phase etching to etch Ti3AlC2MAX ceramic powder to obtain multilayer Ti3C2T x After MXene precipitation, centrifugation and washing were performed, followed by exfoliation using a shaking method to obtain exfoliated Ti3C2T. x MXene / H2O dispersion; then, using a solvent displacement method, the above Ti3C2T... x The MXene suspension was redispersed in DMSO and subjected to multiple centrifugation-dispersion cycles to finally obtain an MXene / DMSO dispersion, which was defined as dispersion B. Step 3: Add suspension A to dispersion B and sonicate for 3-5 min to obtain a homogeneous black mixed MXene / ANF dispersion system, which is defined as mixture C; In the mixture C, the ANF / DMSO suspension A and the MXene / DMSO dispersion B were prepared at a solute mass ratio of ANF:MXene = 40 wt%: 60 wt%. Step 4: Transfer the mixture C to a mold, inject a 5-10 M formic acid protonated solvent, and perform a reprotonation treatment for 10-20 h to form a black gel with a metallic luster; then obtain a formic acid protonated MXene / ANF aerogel composite membrane by rinsing and freeze drying, which is defined as aerogel membrane D. Step 5: Immerse the aerogel membrane D in a 5-20 mM solution containing Pd precursor and let it stand for 5-10 min. After removing it and drying it after the solution is completely absorbed, the final product, formic acid protonated MXene / ANF / Pd aerogel composite membrane E, is obtained.

3. The method according to claim 2, characterized in that: The Pd precursor solution is a variety of recyclable waste liquids containing +2 valence Pd metal, including electroplating solution, mirror making solution, diamond and jewelry grinding waste liquid, and industrial production waste liquid containing Pd metal.

4. The method according to claim 2, characterized in that: The etching agent for the Ti3AlC2MAX ceramic powder in step 2 is HF acid or HCl acid / LiF mixture.

5. The method according to claim 2, characterized in that: In step 2, the etching temperature using liquid phase etching is set to 25-40°C. o C, the etching time is set to 24~36 h.

6. The method according to claim 2, characterized in that: Step 2, multilayer Ti3C2T x The centrifugal washing conditions for MXene precipitate are: washing with ultrapure water 6-9 times, at a speed of 3000-5000 rpm, for 3-5 minutes.

7. The method according to claim 2, characterized in that: The preparation conditions for the MXene / H2O dispersion by the shaking method in step 2 are 20 min of hand shaking or 30 min of mechanical shaking.

8. The method according to claim 2, characterized in that: The centrifugation-dispersion conditions for preparing dispersion B by solvent replacement in step 2 are as follows: first, centrifuge the above MXene / H2O dispersion at 10000 rpm for 10 min to collect the precipitate, and then redisperse it in DMSO. Repeat the above centrifugation-dispersion process 2 to 5 times to completely replace the water.

9. The method according to claim 2, characterized in that: The freeze-drying conditions for the aerogel membrane D in step 4 are -50°C. o Vacuum drying was carried out at a low temperature of C for 6-10 hours.

10. An application of the formic acid protonated MXene / ANF / Pd aerogel composite membrane according to claim 1, characterized in that: The formic acid protonated MXene / ANF / Pd aerogel composite film has an electromagnetic shielding effectiveness of >55 dB in the X-band (8.2~12.4 GHz), making it suitable for high shielding requirements, especially for flexible electromagnetic shielding protection applications where the aerogel film has strong mechanical flexibility and high shielding effectiveness requirements.

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