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CN-121974354-A - Fluorine-free alkali etching MAX phase precursor method based on supercritical carbon dioxide medium

CN121974354ACN 121974354 ACN121974354 ACN 121974354ACN-121974354-A

Abstract

The invention discloses a method for etching a MAX phase precursor without fluorine base based on a supercritical carbon dioxide medium, which comprises the following steps of S1, placing a fluorine-free base etchant, an auxiliary agent and the MAX phase precursor in a supercritical reaction kettle according to a proportion, S2, introducing carbon dioxide into the reaction kettle, regulating and controlling the temperature and the pressure of the system to a preset supercritical state, maintaining the uniformity of a reaction system through stirring or a fluid circulation mode, and carrying out supercritical etching reaction for a preset time, S3, cooling the reaction system to room temperature after the supercritical etching reaction is finished, reducing the pressure to normal pressure, collecting a reaction product, and S4, sequentially centrifuging, washing and drying the collected reaction product to obtain a target product. The supercritical fluid synergistic fluorine-free etching method is adopted, so that the use of fluoride is completely avoided, the pollution risk is eliminated from the source, meanwhile, the rich polar groups such as-O, -OH and the like on the surface of MXene are reserved, and the material performance is improved.

Inventors

  • ZHANG HENGYU
  • LONG JIAJIE

Assignees

  • 苏州大学

Dates

Publication Date
20260505
Application Date
20260126

Claims (10)

  1. 1. A fluorine-free alkali etching MAX phase precursor method based on supercritical carbon dioxide medium is characterized by comprising the following steps: s1, placing a fluorine-free alkali etching agent, an auxiliary agent and a MAX phase precursor in a supercritical reaction kettle according to a proportion; S2, introducing carbon dioxide into the reaction kettle, regulating and controlling the temperature and the pressure of the system to a preset supercritical state, and simultaneously maintaining the uniformity of the reaction system in a stirring or fluid circulation mode to perform supercritical etching reaction for a preset time; s3, after the supercritical etching reaction is finished, cooling the reaction system to room temperature, reducing the pressure to normal pressure, and collecting a reaction product; S4, sequentially centrifuging, washing, oscillating and drying the collected reaction product to obtain a target product.
  2. 2. The method for etching MAX phase precursor based on supercritical carbon dioxide medium by using fluorine-free alkali as claimed in claim 1, wherein the fluorine-free etchant comprises inorganic alkali and organic alkali, the inorganic alkali is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, barium hydroxide, magnesium hydroxide, ammonium hydroxide, sodium carbonate and potassium carbonate, and the organic alkali is tetramethylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, methylamine, ethylamine, dimethylamine, triethylamine, ethylenediamine and hexamethylenediamine.
  3. 3. The method for etching MAX phase precursor without fluorine base based on supercritical carbon dioxide medium according to claim 1, wherein the auxiliary agent is water, ethanol, methanol, isopropanol, hydrogen peroxide or acetone, which is used for accelerating the reaction progress or increasing the interlayer spacing.
  4. 4. The method for etching MAX phase precursor based on supercritical carbon dioxide medium by using fluorine-free alkali according to claim 3, wherein the mass ratio of the fluorine-free etchant to the auxiliary agent is 15-80:100.
  5. 5. The method for fluorine-free alkali etching of MAX phase precursor based on supercritical carbon dioxide medium according to claim 1, wherein MAX phase is Ti 3 AlC 2 、Nb 2 AlC、Ti 2 AlC、Mo 2 GaC、Ti 4 AlN 3 or V 2 AlC.
  6. 6. The method for etching a MAX phase precursor without fluorine based on supercritical carbon dioxide medium according to claim 5, wherein the mass ratio of MAX phase to fluorine-free etchant is 1:10-50.
  7. 7. The method for etching MAX phase precursor based on supercritical carbon dioxide medium without fluorine according to claim 1, wherein the system temperature in the step S2 is 32-250 ℃ and the pressure is 7.4-30 Mpa.
  8. 8. The method for etching MAX phase precursor based on supercritical carbon dioxide medium without fluorine according to claim 1, wherein the stirring speed in the step S2 is 400-10000rpm, and the preset time is 1-168h.
  9. 9. The fluorine-free alkali etching MAX phase precursor method based on the supercritical carbon dioxide medium according to claim 1, wherein the centrifugation speed in the step S4 is 3000-12000 rpm, and the centrifugation time is 3-20 min.
  10. 10. The method for etching MAX phase precursor based on supercritical carbon dioxide medium without fluorine base according to claim 1, wherein the oscillation time in the step S4 is 0.5-2 h.

Description

Fluorine-free alkali etching MAX phase precursor method based on supercritical carbon dioxide medium Technical Field The invention belongs to the technical field of two-dimensional nanomaterial preparation, and particularly relates to a fluorine-free alkali etching MAX phase precursor method based on a supercritical carbon dioxide medium. Background MXene is used as a novel two-dimensional transition metal carbo/nitride, and has great application potential in the fields of energy storage, electromagnetic shielding, catalysis and the like by virtue of high conductivity, high specific surface area and adjustable surface chemical characteristics. The current industry mainly etches the A layer in the MAX phase through hydrofluoric acid or a fluoride salt system to prepare MXene, but the technical route has obvious defects, and the method has the following specific advantages that (1) fluorine is inevitably introduced into the surface of a MXene sheet layer to form an inert-F end group, so that the conductivity and electrochemical activity of the material are directly reduced, (2) hydrofluoric acid (HF) has extremely strong corrosiveness and high toxicity, forms serious threat to production equipment, operators and ecological environment, and has high waste liquid treatment cost, (3) has long reaction period, a few-layer MXene can be obtained through a subsequent ultrasonic or intercalation stripping process, the preparation efficiency is low, the yield is limited, and (4) fluoride waste liquid is difficult to meet the requirement of increasingly severe environmental regulations, and becomes a core bottleneck for restricting the large-scale application of MXene. To break through the bottleneck, the industry has explored fluorine-free preparation routes such as electrochemical etching, alkaline thermal method, molten salt method and the like, but all methods have inherent limitations. For example, patent CN114477181a proposes to prepare MXene in a supercritical carbon dioxide system in a large scale, but the etchant used is ammonium bifluoride, which still generates fluorine-containing byproducts, and is not completely free from fluorine dependence, patent CN114031078A and CN116588940a adopt solid alkali or molten salt to prepare fluorine-free MXene, but the preparation method of fluorine-free MXene quantum dot disclosed in patent CN114316971a needs to be performed at a high temperature above 300 ℃ and has high energy consumption and severe process requirements, and the intrinsic structure and performance of MXene can be destroyed. Therefore, developing a low-cost and scalable fluorine-free preparation technology has become a key core requirement for promoting the development of the MXene green industrialization. Disclosure of Invention Aiming at the technical problems, the invention provides a fluorine-free alkali etching MAX phase precursor method based on a supercritical carbon dioxide medium, which realizes the environment-friendly etching of MAX phase materials by utilizing the high diffusivity, low viscosity and excellent dissolving capacity of the supercritical carbon dioxide and cooperating with a fluorine-free etchant. The technical scheme is that the fluorine-free alkali etching MAX phase precursor method based on the supercritical carbon dioxide medium comprises the following steps: s1, placing a fluorine-free alkali etching agent, an auxiliary agent and a MAX phase precursor in a supercritical reaction kettle according to a proportion; S2, introducing carbon dioxide into the reaction kettle, regulating and controlling the temperature and the pressure of the system to a preset supercritical state, and simultaneously maintaining the uniformity of the reaction system in a stirring or fluid circulation mode to perform supercritical etching reaction for a preset time; s3, after the supercritical etching reaction is finished, cooling the reaction system to room temperature, reducing the pressure to normal pressure, and collecting a reaction product; S4, sequentially centrifuging, washing, oscillating and drying the collected reaction product to obtain a target product. Preferably, the fluorine-free etching agent comprises inorganic alkali and organic alkali, wherein the inorganic alkali is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, barium hydroxide, magnesium hydroxide, ammonium hydroxide, sodium carbonate and potassium carbonate, and the organic alkali is one or more of tetramethylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, methylamine, ethylamine, dimethylamine, triethylamine, ethylenediamine and hexamethylenediamine. Preferably, the auxiliary is water, ethanol, methanol, isopropanol, hydrogen peroxide or acetone, which acts to accelerate the reaction process or to increase the interlayer spacing. Further, the mass ratio of the fluorine-free etching agent to the auxiliary agent is 15-80:100. Preferably, the MAX phase is