Black phosphorus crystal treatment method based on controllable micro-oxidation

Abstract

The invention discloses a black phosphorus crystal treatment method based on controllable micro-oxidation and application of the black phosphorus crystal treatment method in liquid phase stripping. Firstly, black phosphorus crystals are pretreated in an inert atmosphere, vacuum drying is performed after water washing and alcohol washing, surface impurities are removed to improve oxidation uniformity, and the black phosphorus crystals are crushed to a certain size range for standby application. And then exposing the pretreated black phosphorus crystal in a low-concentration oxygen atmosphere for low-temperature micro-oxidation treatment, inducing the surface and layer edge of the crystal to form an extremely thin oxide layer, immediately quenching in an inert atmosphere after treatment, cooling to room temperature, terminating the oxidation reaction and stabilizing the structure of the oxide layer. And finally, dispersing the quenched black phosphorus sample in a specific solvent system for liquid-phase ultrasonic stripping, thereby effectively improving the stripping efficiency of the black phosphorus crystal and the quality of the black phosphorus nanosheet. Compared with a traditional preparation process, the black phosphorus crystal treatment method based on the controllable micro-oxidation technology realizes interlayer binding force optimization only through surface bonding reconstruction, does not destroy a black phosphorus main body structure, does not need to introduce additional substances, is simple to operate and easy to amplify, and is suitable for large-scale production. The method is suitable for liquid phase stripping large-scale controllable preparation of the high-quality black phosphorus nanosheet.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional materials technology, specifically relating to a method for processing black phosphorus crystals based on controllable micro-oxidation and its application in liquid phase exfoliation. By controlling the micro-oxidation treatment of black phosphorus crystals to optimize their interlayer bonding force, the exfoliation efficiency of black phosphorus crystals and the quality of black phosphorus nanosheets are effectively improved. Background Technology

[0002] Black phosphorus is the most stable allotrope of common elemental phosphorus. As a novel two-dimensional semiconductor material, it has many unique physicochemical properties and has broad application prospects in many fields such as optoelectronic devices, energy catalysis, fast-charging energy storage and biomedicine.

[0003] The superior properties of black phosphorus are often accompanied by precise control of material size effects, thus nanotechnology plays an important role in the practical application of black phosphorus. However, how to achieve the large-scale, high-quality production of black phosphorus nanosheets from laboratory pilot-scale preparation to industrial-scale production remains a key challenge restricting the commercial application of two-dimensional black phosphorus.

[0004] Current mainstream preparation processes mainly include mechanical exfoliation, liquid-phase ultrasonic exfoliation, and ion intercalation. Mechanical exfoliation (such as CN115611247B and CN106185849B), including methods like ball milling and shearing, uses external mechanical forces to prepare nanomaterials. While suitable for large-scale production, this method suffers from low controllability of the external force process, resulting in poor crystal quality and product uniformity. Liquid-phase ultrasonic exfoliation (such as CN107055497B and CN105600760B) generates significant energy that effectively breaks the weak van der Waals forces between black phosphorus layers, but has limited impact on the strong covalent bonds within the layers, thus resulting in low overall exfoliation efficiency. Ion intercalation methods (such as CN109368607B and CN115611247B) are improved liquid-phase exfoliation methods. They utilize ion insertion into the interlayer gaps of black phosphorus to weaken the van der Waals forces between the layers, and then prepare black phosphorus nanosheets by ultrasonic exfoliation. Although the exfoliation efficiency is improved, this method often requires the use of a large amount of intercalating agent during the exfoliation process. On the one hand, it introduces unnecessary impurities, and on the other hand, it also affects the physical structure and photoelectric properties of black phosphorus. Therefore, it only has a certain applicability in specific application fields.

[0005] In summary, current preparation processes primarily rely on various methods to weaken the interlayer forces of black phosphorus to achieve black phosphorus crystal exfoliation. However, it is difficult to improve exfoliation efficiency without damaging the main structure of black phosphorus or introducing additional substances. Therefore, developing a highly efficient and controllable preparation method to effectively improve both the exfoliation efficiency of black phosphorus crystals and the quality of black phosphorus nanosheets is of great value for broadening the applications of black phosphorus materials in optoelectronic devices, energy catalysis, and biomedicine. Summary of the Invention

[0006] This invention discloses a method for processing black phosphorus crystals based on controlled micro-oxidation and its application in liquid-phase exfoliation. Compared with traditional preparation processes, the black phosphorus crystal processing method based on controlled micro-oxidation technology in this invention optimizes interlayer bonding forces solely through surface bonding reconstruction, thereby effectively improving the exfoliation efficiency of black phosphorus crystals and the quality of black phosphorus nanosheets.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for treating black phosphorus crystals based on controlled micro-oxidation and its application in liquid-phase exfoliation includes the following steps: (1) Pretreatment. Under an inert atmosphere, black phosphorus crystals are washed with water and alcohol, then vacuum dried to remove surface impurities and improve oxidation uniformity. They are then crushed to a certain size range for later use. (2) Low-temperature micro-oxidation treatment. The pretreated black phosphorus crystals were exposed to a low-concentration oxygen atmosphere for low-temperature micro-oxidation treatment to induce the formation of an extremely thin oxide layer on the crystal surface and layer edges; (3) Quenching treatment. Immediately after the micro-oxidation treatment, the oxide layer is quenched in an inert atmosphere and cooled to room temperature to terminate the oxidation reaction and stabilize the oxide layer structure; (4) Liquid phase ultrasonic exfoliation treatment. The quenched black phosphorus sample was dispersed in a specific solvent system for liquid phase ultrasonic exfoliation, and finally high-yield, high-quality black phosphorus nanosheets were obtained.

[0008] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0009] In the above scheme, the pretreatment atmosphere is high-purity Ar with a purity greater than 99.999%.

[0010] In the above scheme, the water washing and alcohol washing refer to deionized water and anhydrous ethanol, respectively.

[0011] In the above scheme, the vacuum drying temperature is 60~80 ℃.

[0012] In the above scheme, the size of the black phosphorus crystals after crushing is 100~1000 μm.

[0013] Preferably, the size of the black phosphorus crystals after crushing is 200~500 μm.

[0014] Preferably, the mass of black phosphorus crystals subjected to a single low-temperature micro-oxidation treatment is 10~100 g.

[0015] In the above scheme, the low-temperature micro-oxidation treatment atmosphere is a high-purity Ar / O2 mixture with a purity greater than 99.999%, wherein the O2 concentration is 1%~5%.

[0016] Preferably, the O2 concentration in the high-purity Ar / O2 mixture is 2% to 4%.

[0017] Preferably, the low-temperature micro-oxidation treatment incorporates an oxygen regulation module to achieve real-time monitoring and precise control of oxygen concentration.

[0018] Preferably, the low-temperature micro-oxidation treatment includes a temperature control module to achieve real-time temperature monitoring and program control.

[0019] In the above scheme, the low-temperature micro-oxidation treatment temperature is 60~120℃, the heating rate to reach this temperature range is 1℃~5℃ / min, and the treatment time within this temperature range is 10~60 min.

[0020] Preferably, the low-temperature micro-oxidation treatment temperature is 80~100℃, the heating rate to reach this temperature range is 2℃~3℃ / min, and the treatment time within this temperature range is 20~40 min.

[0021] Preferably, the low-temperature micro-oxidation process is as follows: the pretreated black phosphorus crystals are heated to 80~100℃ in Ar atmosphere, then Ar / O2 mixed gas is introduced, and the treatment is carried out in this temperature range for 20~40 min. After the treatment is completed, the Ar / O2 mixed gas is introduced immediately, and the crystals are quenched in Ar atmosphere and cooled to room temperature.

[0022] In the above scheme, the thickness of the black phosphorus oxide layer after the low-temperature micro-oxidation treatment satisfies the empirical formula: ; 0.5 nm < d < 2 nm Preferably, this formula is only applicable to the initial oxidation stage of black phosphorus (0.5 nm < d < 2 nm). Black phosphorus oxidation is a surface-limited reaction and is not controlled by bulk diffusion. After the oxide layer exceeds 2 nm, it may grow in a self-limiting manner due to the formation of dense oxides, or it may cause the destruction of the main structure of black phosphorus due to excessive oxidation (such as the formation of unstable oxides such as P2O5).

[0023] in ; The thickness of the black phosphorus oxide layer needs to be controlled between 0.5 and 2 nm.

[0024] Based on oxidation kinetics theory and model fitting, where: Oxygen concentration ( ;%): The oxygen concentration is linearly dominant, and the oxygen partial pressure directly affects the oxidation reaction rate. The parameter a in the formula is taken as 1.0.

[0025] temperature( K): The rate constant of oxidation reactions usually follows the Arrhenius equation ( However, within a limited temperature range (e.g., 60–120 °C), it can be simplified to ,Right now Oxidation is accelerated by increasing temperature, but is inhibited by the self-limiting effect (d < 2 nm). The parameter b in the formula is taken as 0.5.

[0026] Time (t; min): The oxide layer thickness has a power-law relationship with time. The time exponent is determined by the reaction mechanism. Within the ultrathin oxide layer (d < 2 nm), the oxidation rate is mainly controlled by the interfacial reaction rate rather than the oxygen diffusion rate. Therefore, the time exponent is low, and the parameter c in the formula is taken as 0.3.

[0027] Empirical coefficient k ( ): k is 0.01.

[0028] Right now ; 0.5 nm < d < 2 nm.

[0029] Preferably, the thickness of the black phosphorus oxide layer after low-temperature micro-oxidation treatment is 0.5~2 nm.

[0030] In the above scheme, the quenching atmosphere is high-purity Ar with a purity of 99.999%, the quenching time is 120~240 min, and the temperature is cooled to room temperature.

[0031] Preferably, the quenching time is 150~200 min and then cooled to room temperature.

[0032] In the above scheme, the solvent is any one of pure water, N-methylpyrrolidone (NMP), N-vinylpyrrolidone (NVP), N-cycloethylpyrrolidone (CHP), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), methanol, ethanol, ethylene glycol, isopropanol, tert-butanol, acetone, 2-pentanone, and 3-pentanone.

[0033] Preferably, the solvent is any one of pure water, N-methylpyrrolidone (NMP), N-vinylpyrrolidone (NVP), N-cycloethylpyrrolidone (CHP), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), ethanol, and acetone.

[0034] In the above scheme, the concentration of the dispersion system is 1~20 mg / mL.

[0035] Preferably, the concentration of the dispersion system is 1~10 mg / mL.

[0036] In the above scheme, the ultrasonic treatment power density is 500~5000 W / L, the temperature is 10~25 ℃, and the time is 2~24 h; Preferably, the ultrasonic treatment power density is 1000~3000 W / L, the temperature is 10~15 ℃, and the time is 4~12 h.

[0037] This invention is based on controlled micro-oxidation treatment to form an extremely thin oxide layer (d<2nm) on the surface and edges of black phosphorus crystals. Through the synergistic effects of "chemical bond reconstruction," "stress defects," and "sacrificial layer mechanism" within the oxide layer, and by precisely controlling the oxide layer thickness, the interlayer bonding force is significantly reduced without damaging the crystal structure, thereby effectively improving the exfoliation efficiency of black phosphorus crystals and the quality of black phosphorus nanosheets. Compared with existing technologies, the beneficial effects of this invention are: (1) Reconstruction of chemical bonds in the oxide layer. The black phosphorus layer is bonded by strong covalent bonds (PP bonds), while the interlayer bonds are bonded by weaker van der Waals forces. The bond energy of PO bonds (360 kJ / mol) is significantly lower than that of PP bonds within the layer (490 kJ / mol), but higher than that of the interlayer van der Waals forces (1-10 kJ / mol). Micro-oxidation treatment introduces a small number of oxygen atoms on the crystal surface and layer edges, forming PO bonds or other oxidized phosphorus structures. The PO bonds formed locally in the oxide layer create "non-uniform bonding regions" at the interlayer interfaces, thereby reducing the interlayer bonding force and improving the crystal exfoliation efficiency.

[0038] (2) Stress defects in the oxide layer. During the micro-oxidation process, oxygen atoms embed into the black phosphorus interlayer through the layer edge, causing lattice expansion and generating local tensile stress at the interlayer interface. This stress induces dislocation defects in the internal structure of the crystal, thereby reducing the energy threshold required for peeling. In addition, the thin oxide layer forms a "buffer layer" structure between the layers, reducing the direct contact area between the original black phosphorus layers, thereby weakening the overall effect of van der Waals forces and improving the crystal peeling efficiency.

[0039] (3) Sacrificial layer mechanism of oxide layer. During the subsequent liquid phase exfoliation process, the oxide layer will fracture preferentially because its mechanical strength is lower than that of the original black phosphorus layer (oxidation leads to increased brittleness). This fracture provides an "initial crack propagation path" for the exfoliation process, thereby avoiding energy from acting directly on the main structure, reducing defect generation, and making it more conducive to improving the quality of black phosphorus nanosheet products.

[0040] (4) Oxide layer thickness control. For the first time, it is proposed to achieve precise control of sub-nanometer oxide layer thickness through the synergistic regulation of oxygen concentration, temperature and time. Through precise control of process parameters, an extremely thin oxide layer is formed only on the crystal surface and layer edge, without damaging the main structure. This maintains the intrinsic properties of black phosphorus and achieves interlayer weakening.

[0041] (5) Advantages compared to traditional processes. Traditional mechanical exfoliation processes, such as ball milling and shearing, have low controllability of the external force process, poor product uniformity, and are prone to introducing structural defects that damage the crystal structure, affecting product quality. Traditional liquid phase exfoliation processes have low exfoliation efficiency and low product yield, making it difficult to produce high-quality black phosphorus nanosheets on a large scale. Traditional chemical intercalation processes require the introduction of foreign ions / molecules, and residual impurities are difficult to remove, affecting product purity and performance. In contrast, the black phosphorus crystal processing method based on controllable micro-oxidation technology in this invention optimizes the interlayer bonding force only through surface bonding reconstruction. It does not damage the main structure of black phosphorus, nor does it require the introduction of additional substances. Moreover, it is simple to operate, easy to scale up, and suitable for the large-scale controllable preparation of high-quality black phosphorus nanosheets by liquid phase exfoliation. Attached Figure Description

[0042] Figure 1 This is a process flow diagram of a black phosphorus crystal treatment method based on controlled micro-oxidation.

[0043] Figure 2 This is a schematic diagram of micro-oxidation on the crystal surface and at the edge of the layers.

[0044] Figure 3 This is a TEM characterization image of the black phosphorus crystals obtained after low-temperature micro-oxidation treatment in Example 12.

[0045] Figure 4 The image shows the TEM characterization of the black phosphorus nanosheets obtained in Example 1.

[0046] Figure 5 The image shows the TEM characterization of the black phosphorus nanosheets obtained in Example 12. Detailed Implementation

[0047] A method for treating black phosphorus crystals based on controlled micro-oxidation and its application in liquid-phase exfoliation, the specific preparation steps are as follows: (1) Pretreatment. Under an Ar (99.999%) atmosphere, black phosphorus crystals were washed with water and alcohol, then vacuum dried at 60°C and crushed to 200~500 μm for later use; (2) Low-temperature micro-oxidation treatment. 20 g of pretreated black phosphorus crystals were placed in a tube furnace and heated at 2 °C / min under an Ar (99.999%) atmosphere. (°C), then an Ar / O2 mixture (99.999%, O2 concentration) is introduced. (%)), and at this temperature, a low-temperature micro-oxidation treatment of t (min) is performed to induce the formation of an extremely thin oxide layer on the crystal surface and layer edges; (3) Quenching treatment. Immediately after the micro-oxidation treatment is completed, the Ar / O2 mixed gas is stopped, and the mixture is quenched for 180 min in an Ar (99.999%) atmosphere and cooled to room temperature to terminate the oxidation reaction and stabilize the oxide layer structure; (4) Liquid phase ultrasonic exfoliation treatment. 500 mg of quenched black phosphorus sample was dispersed in 100 mL of N-methylpyrrolidone (NMP) for liquid phase ultrasonic exfoliation. The system concentration was 5 mg / mL, the ultrasonic power density was 2000 W / L, the temperature was 10℃, and the time was 10 h. Finally, high-yield and high-quality black phosphorus nanosheets were obtained.

[0048] (5) Calculation of exfoliation efficiency: The black phosphorus nanosheet dispersion obtained in (4) was centrifuged at a speed of 1000 r / min for 10 min. The resulting precipitate was vacuum dried and weighed, recorded as m (mg), and calculated using the following formula: Stripping efficiency = .

[0049] Specific implementation examples are shown in the table below:

[0050] Figure 1 This is a process flow diagram of a black phosphorus crystal treatment method based on controlled micro-oxidation. First, a certain mass of pretreated black phosphorus crystals is placed in a tube furnace and heated to the target temperature under an Ar atmosphere. Then, an Ar / O2 mixed gas is introduced, and low-temperature micro-oxidation is performed at this temperature to induce the formation of an extremely thin oxide layer on the crystal surface and layer edges. Immediately after treatment, the Ar / O2 mixed gas supply is stopped, and the crystals are quenched under an Ar atmosphere and cooled to room temperature to terminate the oxidation reaction and stabilize the oxide layer structure. A schematic diagram of the micro-oxidation of the crystal surface and layer edges is shown below. Figure 2 As shown.

[0051] Figure 3 This is a TEM image of the black phosphorus crystals obtained after low-temperature micro-oxidation treatment in Example 12. As can be seen from the image, the micro-oxidation region is mainly concentrated on the crystal surface and edge layer.

[0052] Figure 4 The image shows the TEM characterization of black phosphorus nanosheets obtained in Example 1 (without low-temperature micro-oxidation treatment). Figure 5This is a TEM image of the black phosphorus nanosheets obtained in Example 12 (the example with the highest yield after low-temperature micro-oxidation treatment). As can be seen from the image, both groups of samples are uniform in size and thickness, exhibiting high overall quality. The low-temperature micro-oxidation treatment did not affect the product quality. Here, uniformity mainly refers to the size being between 500 nm and 1 μm, with no significant difference in overall thickness.

[0053] By comparing the above embodiments, it can be found that through the ternary synergistic regulation of oxygen concentration, temperature, and time, based on the empirical formula: This allows for precise control of the oxide layer thickness at the sub-nanometer level. Compared with Example 1 and Example 2 without low-temperature micro-oxidation treatment, when the oxide layer thickness is controlled at 0.5~2 nm, the peeling efficiency is significantly improved. When the oxide layer thickness is controlled at 0.9~1.8 nm, the peeling efficiency is improved by more than 2 times, while the crystal quality is still well maintained.

Claims

1. A method for treating black phosphorus crystals based on controlled micro-oxidation, characterized in that, Includes the following steps: (1) Pretreatment: Under an inert atmosphere, black phosphorus crystals are washed with water and alcohol, then vacuum dried and crushed; (2) Low-temperature micro-oxidation treatment: The pretreated black phosphorus crystals are exposed to a low-concentration oxygen atmosphere for low-temperature micro-oxidation treatment to induce the formation of an extremely thin oxide layer on the crystal surface and layer edges; (3) Quenching treatment: After the micro-oxidation treatment is completed, the oxide layer is immediately quenched in an inert atmosphere and cooled to room temperature to terminate the oxidation reaction and stabilize the oxide layer structure. (4) Liquid phase ultrasonic exfoliation: The quenched black phosphorus sample was dispersed in a solvent and subjected to liquid phase ultrasonic exfoliation to obtain black phosphorus nanosheets.

2. The method for processing black phosphorus crystals according to claim 1, characterized in that, The pretreatment inert atmosphere in step (1) is high-purity Ar with a purity greater than 99.999%; the water washing and alcohol washing are deionized water and anhydrous ethanol, respectively; and the vacuum drying temperature is 60~80℃.

3. The method for processing black phosphorus crystals according to claim 1, characterized in that, The low-temperature micro-oxidation atmosphere described in step (2) is a mixture of high-purity Ar and high-purity O2, with the purity of high-purity Ar and high-purity O2 being greater than 99.999%, and the concentration of high-purity O2 being 1%~5%.

4. The method for processing black phosphorus crystals according to claim 1, characterized in that, The low-temperature micro-oxidation treatment in step (2) is at a temperature of 60~120℃, the heating rate to reach this temperature range is 1℃~5℃ / min, and the treatment time within this temperature range is 10~60 min.

5. The method for processing black phosphorus crystals according to claim 4, characterized in that, The low-temperature micro-oxidation treatment in step (2) is 80~100℃, the heating rate to reach this temperature range is 2℃~4℃ / min, and the treatment time within this temperature range is 20~40 min.

6. The method for processing black phosphorus crystals according to claim 1, characterized in that, The thickness of the black phosphorus oxide layer after the low-temperature micro-oxidation treatment described in step (2) satisfies the empirical formula: ;0.5 nm<d<2 nm in ; The thickness of the black phosphorus oxide layer needs to be controlled between 0.5 and 2 nm. Based on oxidation kinetics theory and model fitting, where: Oxygen concentration ( ;%): The oxygen concentration is linearly dominant, and the oxygen partial pressure directly affects the oxidation reaction rate. The parameter a in the formula is taken as 1.0; temperature( K): The rate constant of oxidation reactions usually follows the Arrhenius equation ( However, within a limited temperature range, it is simplified to ,Right now Increased temperature accelerates oxidation, but it is inhibited by the self-limiting effect, with d < 2 nm. The parameter b in the formula is taken as 0.

5. Time (t; min): The oxide layer thickness has a power-law relationship with time. ), where c is determined by the reaction mechanism. Within the ultrathin oxide layer, the oxidation rate is mainly controlled by the interfacial reaction rate rather than the oxygen diffusion rate, so the time exponent is low. The parameter c in the formula is taken as 0.

3. Empirical coefficient k ( k is 0.01; Right now ; 0.5 nm < d < 2 nm.

7. The method for processing black phosphorus crystals according to claim 1, characterized in that, The quenching atmosphere described in step (3) is high-purity Ar with a purity greater than 99.999%, and the quenching time is 120~240 min, followed by cooling to room temperature.

8. The method for processing black phosphorus crystals according to claim 1, characterized in that, The solvent mentioned in step (4) is any one of pure water, N-methylpyrrolidone, N-vinylpyrrolidone, N-cycloethylpyrrolidone, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, methanol, ethanol, ethylene glycol, isopropanol, tert-butanol, acetone, 2-pentanone, and 3-pentanone; the concentration of the dispersion system is 1~20 mg / mL.

9. The method for processing black phosphorus crystals according to claim 1, characterized in that, The ultrasonic treatment in step (4) has a power density of 500~5000 W / L, a temperature of 10~25 ℃, and a time of 2~24 h.

10. A black phosphorus crystal, characterized in that, The method according to any one of claims 1-9 forms an extremely thin oxide layer on the surface and edge of the black phosphorus crystals, with an oxide layer thickness of 0.5~2 nm, more preferably 0.9~1.8 nm; further, black phosphorus nanosheets are obtained by liquid-phase ultrasonic exfoliation.

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