A method for preparing large-area, highly conductive, and anti-oxidation MXene films

Abstract

The present invention discloses a large-area, highly conductive, and oxidation-resistant MXene film suitable for electromagnetic shielding. The method comprises the following steps: ① Mixing MAX ceramic M metal powder and its oxide or nitride in a certain proportion, adding an excess of Al powder, and thoroughly ball-milling and calcining to synthesize a MAX phase ceramic material; ② Etching the resulting MAX phase ceramic with hydrochloric acid and hydrofluoric acid, stirring thoroughly, and then repeatedly centrifuging with deionized water. After the final centrifugation, the supernatant is discarded to remove the precipitate, thereby obtaining a Ti3C2 multilayer precipitate. The precipitate is dispersed in a LiCl solution, stirred thoroughly, and then repeatedly centrifuged with deionized water until the supernatant reaches a pH of 6. At pH 6, the supernatant is centrifuged a final time and the supernatant is collected. ③ Dispersing the MXene film to the desired concentration in deionized water, then drop-coating the film onto a clean substrate and air-drying to obtain a film. ⑦ Preparation of a large-area film: Stretch a polyethylene film tightly over a flat substrate, then drop 60 mL of MXene solution onto the film, disperse evenly, and air-dry. Compared with MXene prepared by traditional methods, the MXene material of the present invention has the advantages of higher crystallinity, stronger antioxidant ability, higher conductivity, etc., and can produce large-area MXene films with good electromagnetic shielding effect.

Description

Technical Field

[0001] The present invention belongs to the field of nanomaterials, and specifically relates to a method for preparing a large-area, highly conductive, and anti-oxidation electromagnetic shielding MXene film. Background Art

[0002] MXene materials are a class of metal carbides and metal nitrides with a two-dimensional layered structure. Their appearance is similar to stacked potato chips. The chemical formula of MXene materials is M n+1 AX n , where (n = 1–3), M represents an early transition metal such as Sc, Ti, Zr, V, Nb, Cr, or Mo; A typically represents a Group III or Group IV element; and X represents a carbon or nitrogen element. MXenes, which share the metallic conductivity of transition metal carbides, have attracted significant attention in various research fields due to their superior properties.

[0003] Faisal Shahzad (corresponding author) of the Korea Institute of Science and Technology and Mohamed Alhabeb and Christine B. Hatter (co-corresponding authors) of Drexel University and others found that MXene and its polymer composites showed good performance in electromagnetic shielding. x The electromagnetic interference shielding effect of the film can reach 92dB, which is the best shielding performance of the synthetic materials manufactured so far. Such good performance is due to the Ti3C2T x Excellent electrical conductivity of the film and Ti3C2T in the unsupported film x Multiple internal reflections in thin sheets. MXenes and their composites can be used as shielding layers for objects of any shape due to their mechanical flexibility and ease of coating, while also maintaining their high electromagnetic interference shielding performance.

[0004] Recently, a research team led by Professor Joselito M. Razal of Deakin University in Australia has achieved the simple, large-scale, continuous preparation of self-supporting MXene films with both high strength and high conductivity using a blade-coating method without the use of any adhesives or film-forming additives. The conductive MXene flakes prepared using this method are highly ordered, with a 940 nm thick self-supporting film exhibiting a tensile strength of 568 ± 24 MPa, a Young's modulus of 20.6 ± 3.1 GPa, and an electrical conductivity of approximately 15,100 S cm-1 at a thickness of 214 nm. Furthermore, the MXene film exhibits excellent electromagnetic shielding performance (approximately 50 dB for a 940 nm thick film).

[0005] Recently, researchers from the Functional Materials Laboratory of the Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, successfully prepared macro-sized V4C3T using a top-down wet chemical method. x MXene two-dimensional materials. Related research results were published in the American Chemical Society journal Inorganic Chemistry under the title "Achieving Macroscopic V4C3Tx MXene by Selectively Etching Al from V4AlC3 Single Crystals."

[0006] The research group of Researcher Chen Feng from the Tenth People's Hospital affiliated to Tongji University, in collaboration with the research group of Professor Ma Mingguo from Beijing Forestry University and the research group of Researcher Wan Pengbo from Beijing University of Chemical Technology, have developed an ultra-thin flexible carbon nanotube / Ti3C2MXene / nanocellulose ternary composite electromagnetic shielding paper with gradient structure and "sandwich structure".

[0007] Northwestern Polytechnical University provides a three-dimensional layered MXene electromagnetic shielding foam and its preparation method in a Chinese patent application publication number CN108811478A.

[0008] Qingdao University provides a new method for preparing electromagnetic wave absorbing materials in its Chinese patent application publication number CN109152318A. Specifically, it relates to a new method for preparing electromagnetic wave absorbing materials, using ethanol or deionized water and Nb2AlC MAX as raw materials, and synthesizing Nb2C MXene nanosheets by HF (hafnium) etching and hydrothermal method. Summary of the Invention

[0009] The present invention provides a method for preparing a large-area, highly conductive, and anti-oxidation electromagnetic shielding MXene film, which specifically comprises the following steps:

[0010] 1.MAX phase is a general term for a class of ternary layered metal ceramic materials. This type of compound has a unified chemical formula M n+ 1AX n , where M is an early transition metal, A is a Group III or IV element, X is C or N, and n represents 1, 2, 3, etc. A ball mill was used to grind the metal powder represented by M, the corresponding carbide or nitride powder, and Al powder at a ratio of 1:2:1 (mass ratio) at 70 rpm for 18 hours. (One of the materials used in the experiment was Ti3AlC2).

[0011] 2.B. The ball-milled precursor powder was then placed in an alumina crucible, covered with graphite foil, and placed in a tube furnace. The furnace was purged with argon for 30 minutes at room temperature.

[0012] 3. Heat the precursor powder to 1380°C and hold it for 2 hours at an argon flow rate of approximately 100 sccm, with a heating and cooling rate of 3°C / min;

[0013] 4. The Al-Ti3AlC2 sintered block was then ground using a tin-plated drill bit to produce MAX powder, which was then cleaned using 9M HCl until no bubbles were generated.

[0014] 5. Filter the mixture through a vacuum filtration device, rinse with deionized water, and dry the filtered MAX in a vacuum oven at 80°C for at least 6 hours;

[0015] 6. Mix 6 mL of deionized water, 12 mL of 12 M hydrochloric acid, and 2 mL of 29 M hydrofluoric acid in a 60 mL high-density polyethylene bottle, stir, and heat to 35°C. Then, add 1 g of the MAX phase precursor prepared in step 1 and stir for at least 24 hours.

[0016] 7. Remove the solution, place it in a centrifuge tube and centrifuge at 3500 rpm, discard the supernatant, add deionized water to wash and centrifuge again, repeat the above steps until the pH of the supernatant reaches 6. After the pH reaches 6, centrifuge again, discard the supernatant and remove the precipitate;

[0017] 8. Disperse the removed Ti3C2 multilayer precipitate into 0.5M LiCl solution, heat to 25°C, and stir at 300 rpm for 24 hours for intercalation;

[0018] 9. Filter the MXene / LiCl mixture using a vacuum filtration device and rinse with deionized water;

[0019] 10. Disperse the precipitate in deionized water and then repeatedly centrifuge and wash with deionized water until the pH of the supernatant is 6. After the pH reaches 6, centrifuge again and take the last supernatant. DETAILED DESCRIPTION

[0020] Example 1:

[0021] 5g of Ti, 10g of Ti3C2, and 5g of Al powder were thoroughly ground in a grinding machine. The mixed powder was then placed in a crucible, heated to 1380°C in a tube furnace under argon, and removed after 20 hours to obtain a MAX phase precursor. The sintered agglomerate was ground into a powder and washed with 9M hydrochloric acid until bubbles disappeared. The mixture was then filtered using a vacuum filtration device and rinsed with deionized water. The filtered powder was dried in a vacuum oven for 6 hours to obtain a Ti3AlC2 precursor. 5g of the precursor powder was added to a mixture of 30mL of deionized water, 60mL of 12M hydrochloric acid, and 10mL of 29M hydrofluoric acid and stirred for 24 hours. After stirring, the solvent was removed using a vacuum filtration device and rinsed with deionized water. The resulting Ti3C2 multilayer precipitate was dispersed in a LiCl solution and stirred at 300 rpm for 24 hours. The solution is then placed in a centrifuge tube and centrifuged. The supernatant is discarded, deionized water is added, and centrifugation is repeated until the pH of the supernatant reaches 6. Once the pH reaches 6, centrifugation is repeated once more. After centrifugation, the supernatant is collected to obtain a MXene suspension. A polyethylene sheet is stretched tightly on a clean, flat substrate. The MXene suspension is adjusted to an appropriate concentration with deionized water and then drop-coated onto the polyethylene sheet. The suspension is evenly distributed and allowed to air dry to obtain a large-area, highly conductive, antioxidant, and electromagnetically shielding MXene film.

Claims

1. A method for preparing a large-area, highly conductive, and anti-oxidative MXene film that can be used for electromagnetic shielding, characterized in that: The following steps are involved: Step 1: Prepare MAX phase ceramic material precursor by adding excess aluminum powder; Step 2: Etch the prepared MAX phase ceramic with hydrochloric acid and hydrofluoric acid, wash it by centrifugation, and disperse it in LiCl. Centrifuge and take the upper liquid to obtain the desired MXene material. Step 3: Disperse the MXene material obtained in step 2 with deionized water to a suitable concentration, then drop-coat the MXene solution onto the hydrophobic film. Wait until the MXene solution is evenly dispersed and then air-dry naturally. The step 1 includes the following specific steps: A. MAX phase is a general term for a class of ternary layered metal ceramic materials. This type of compound has a unified chemical formula M n+1 AX n , wherein M is an early transition metal, A is a III or IV main group element, X is C or N, and n represents 1, 2, or 3; using a ball mill, grinding the metal powder represented by M, the carbide or nitride powder corresponding to M, and Al powder at a mass ratio of 1:2:1 at 70 rpm for 18 hours, wherein Al is in excess; then, the ground precursor powder is placed in an alumina crucible, covered with graphite foil, and then placed in a tube furnace, and the furnace is purged with argon at room temperature for 30 minutes; B. Heat the precursor powder to 1380°C and maintain it for 2 hours at an argon flow rate of 100 sccm, with a heating and cooling rate of 3°C / min; C. Al-M n+1 AX n The sintered block was then ground using a tinned drill bit to produce MAX powder, which was then washed with 9M HCl until no bubbles were generated. 500ml of 9M HCl was used to wash 50-60g of Al-M n+1 AX n ; D. Filter Al-M through vacuum filtration device n+1 AX n / HCl mixture, washed with deionized water, filtered through a 5-μm pore size membrane, and the filtered clear solution was dark purple. The filtered MAX was dried in a vacuum oven at 80°C for at least 6 hours; The step 2 includes the following specific steps: A. Mix 6 mL of deionized water, 12 mL of 12 M hydrochloric acid, and 2 mL of 29 M hydrofluoric acid in a 60 mL high-density polyethylene bottle, stir, and heat to 35°C. Then, add 1 g of the MAX phase precursor prepared in step 1 and stir for more than 24 hours. B. Remove the solution, place it in a centrifuge tube and centrifuge at 3500 rpm, discard the supernatant, add deionized water to wash and centrifuge again, repeat the above steps until the pH of the supernatant reaches 6. After the pH reaches 6, centrifuge again, discard the supernatant and remove the precipitate; C. Take out the M n+1 X n The multilayer precipitate was dispersed into 0.5 M LiCl solution, heated to 25 °C, and stirred at 300 rpm for 24 h for intercalation; D. Filter the MXene / LiCl mixture using a vacuum filtration device and wash with deionized water; E. Disperse the precipitate in deionized water and wash repeatedly by centrifugation with deionized water until the pH of the supernatant reaches 6. Centrifuge once more after the pH reaches 6 and take the last supernatant. The step 3 includes the following specific steps: Place a stretched polyethylene sheet on a clean flat substrate, disperse the MXene material obtained in step 2 with deionized water to an appropriate concentration, and then drop it onto the polyethylene sheet. Wait for the suspension to spread evenly and let it air dry naturally to obtain a large-area, highly conductive, anti-oxidation, and electromagnetic shielding MXene film.

2. The method for preparing a large-area, highly conductive, and anti-oxidative MXene film that can be used for electromagnetic shielding according to claim 1, characterized in that: In step 1, the M metal powder includes Sc, Ti, V, Cr, Zr, Nb, Hf or Ta; the MAX ceramic material includes Ti2AlC, Ti2AlN, V2AlC, V2AlN, Nb2AlC, NbAl2N, Ta2AlC, Ti3AlC2, Ti3AlN2, V3AlC2, Ta3AlC2, Ta3AlN2, Ti4AlC3, Ti4AlN3, Ta4AlC3, Ta4NAl3 or Nb4AlC3.

3. A large-area, highly conductive, anti-oxidation, electromagnetic shielding MXene film prepared by the method according to claim 1 or 2.