Two-dimensional red phosphorus nanosheet, preparation of two-dimensional red phosphorus nanosheet and third-order nonlinear optical modulator comprising two-dimensional red phosphorus nanosheet

Abstract

The invention discloses a two-dimensional red phosphorus nanosheet, preparation of the two-dimensional red phosphorus nanosheet and a third-order nonlinear optical modulator comprising the two-dimensional red phosphorus nanosheet. The preparation method comprises the following steps: dissolving phosphorus halide in a low-boiling-point solvent, adding L-ascorbic acid, uniformly mixing, and removing the low-boiling-point solvent in vacuum at 20-50 DEG C to obtain a precursor; and heating the precursor in an inert atmosphere, so that the precursor is subjected to a pyrolytic reaction at an interface, and cooling, washing and freeze-drying to obtain the two-dimensional red phosphorus powder. By adopting the preparation method, a large amount of two-dimensional red phosphorus nanosheets with relatively thin layer thickness can be prepared at relatively low temperature, the operation is simple and convenient, and the synthesis period is short. The obtained two-dimensional red phosphorus nanosheet is used for preparing a third-order nonlinear optical modulator, the obvious solvent dependence effect is achieved, and modulation between saturated absorption and anti-saturated absorption can be achieved.

Description

Technical Field

[0001] The present invention relates to the fields of materials science and nonlinear optics. More specifically, it relates to a two-dimensional red phosphorus nanosheet, its preparation, and a third-order nonlinear optical modulator containing the same. Background Art

[0002] Since the discovery of graphene in 2004, two-dimensional materials have become a research hotspot. Since then, thousands of two-dimensional materials have been discovered, such as hexagonal boron nitride, graphene, silicene, and borophene. Among them, red phosphorus has attracted increasing attention in many fields due to its excellent optical and chemical properties. Compared with its allotrope black phosphorus, commercial amorphous red phosphorus has low cost and is non-toxic, which contributes to its wide application in large-scale production and practical applications, such as flame retardants, semiconductor dopants, and biotherapy. More importantly, red phosphorus has strong visible light response and adjustable band width (1.5 - 2.4 eV), making it very suitable for optical modulation. Red phosphorus can be divided into two types: crystalline and amorphous. Amorphous red phosphorus is a chain-like linear polymer that is disorderly arranged in space by intermolecular forces. When the growth in one direction is restricted, it is easy to form two-dimensional non-layered materials. Currently reported preparation methods of red phosphorus include soft template method, solvothermal method, pyrolysis method, ultrasonic method, etc. However, the existing public technologies have their respective defects. For example, the yield of the soft template method is low, the energy consumption of the pyrolysis method is high, and the thickness of two-dimensional red phosphorus prepared by the ultrasonic method is relatively thick. There is an urgent need to develop a new synthesis method with high synthesis yield, low reaction temperature, and high quality to prepare two-dimensional red phosphorus. Summary of the Invention

[0003] To solve the above problems, the first object of the present invention is to provide a preparation method of a two-dimensional red phosphorus nanosheet. This preparation method is simple to operate, has a short synthesis cycle, and can prepare a large number of two-dimensional red phosphorus nanosheets with a relatively thin sheet thickness at a relatively low temperature.

[0004] The second object of the present invention is the two-dimensional red phosphorus nanosheet prepared by using the above-mentioned preparation method.

[0005] The third object of the present invention is to provide a third-order nonlinear optical modulator.

[0006] In the present invention, the interface refers to the position where the coated phosphorus triiodide layer is in direct contact with L-ascorbic acid.

[0007] To achieve the above first object, the present invention adopts the following technical solutions:

[0008] The present invention discloses a preparation method of a two-dimensional red phosphorus nanosheet, comprising the following steps:

[0009] Dissolve phosphorus halide in a low-boiling solvent, add L-ascorbic acid, mix evenly, and then remove the low-boiling solvent under vacuum at 20 - 50 °C to obtain a precursor;

[0010] Under an inert atmosphere, heat the precursor to cause pyrolysis reaction of the precursor at the interface, and obtain two-dimensional red phosphorus powder after cooling, washing, and freeze-drying.

[0011] In the present invention, using L-ascorbic acid as a solid template, first disperse phosphorus halide dissolved in a low-boiling solvent around L-ascorbic acid. After the low-boiling solvent is completely evacuated by vacuum, the phosphorus halide uniformly coats the surface of L-ascorbic acid to obtain a precursor. Then, taking advantage of the poor thermal stability of phosphorus halide, control the heating temperature to cause pyrolysis reaction of the precursor at the interface, complete the removal of halogen, and then remove L-ascorbic acid and unreacted phosphorus halide or its intermediate state through post-treatment, finally obtaining two-dimensional red phosphorus nanosheets with relatively high purity.

[0012] Further, the phosphorus halide is selected from phosphorus tribromide and / or phosphorus triiodide, preferably phosphorus triiodide. Other phosphorus halides are not easy to complete pyrolysis below 100 °C to achieve the purpose of removing halogen;

[0013] The addition amount of the phosphorus halide is 0.1 - 1 g; the addition amount of the L-ascorbic acid is 1 - 20 g.

[0014] Further, the mass ratio of the phosphorus halide to the L-ascorbic acid is 1:20 - 80; exemplarily, the mass ratio of the phosphorus halide to the L-ascorbic acid can be 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, etc.

[0015] In the present invention, there are two limiting requirements when selecting a suitable low-boiling solvent: one is that the boiling point should not be too high, generally preferably below 100 °C. If the boiling point is too high, it is not easy to completely remove it by vacuum, which is not conducive to obtaining high-purity two-dimensional red phosphorus later; the other is that it cannot react with phosphorus halide. Especially, the activity of phosphorus triiodide is very high, and ethanol and water will react with it. In a specific embodiment, the low-boiling solvent is selected from one or more of cyclohexane (boiling point 81 °C), n-hexane (boiling point 69 °C), n-heptane (boiling point 98.4 °C), and petroleum ether (boiling point 40 - 80 °C).

[0016] When removing the low-boiling solvent by vacuum, technicians can adjust the removal method according to the difficulty of removing the low-boiling solvent. For example, they can pump vacuum for a period of time and then replenish nitrogen, and then pump vacuum again. Through this repeated alternate operation, nitrogen can be used to carry away the low-boiling solvent vapor. The present invention does not further limit the specific operation, as long as it is ensured that the low-boiling solvent is removed as completely as possible.

[0017] Further, when heating the precursor, controlling the heating conditions is also crucial, which directly affects the thickness of the final product. If the heating temperature is too high or the heating time is too long, the pyrolysis process will not only occur at the interface but also spread to the more outer-layer wrapped phosphorus halide, resulting in an overly thick two-dimensional red phosphorus. If the heating temperature is too low or the heating time is too short, the pyrolysis at the interface may not be completed, and thus it may be impossible to obtain qualified two-dimensional red phosphorus. In a specific embodiment, the heating conditions are a heating temperature of 50 - 90 °C and a heating time of 10 - 60 min.

[0018] Further, ethanol and deionized water can be used during washing to remove unreacted L-ascorbic acid, unreacted phosphorus halide or its intermediate state, for the purpose of purifying the sample.

[0019] To achieve the second above-mentioned purpose, the present invention adopts the following technical solution:

[0020] The present invention discloses a two-dimensional red phosphorus nanosheet prepared by using the preparation method as described above.

[0021] Further, the average thickness of the two-dimensional red phosphorus nanosheet is 1.2 - 100 nm, and the average size is 50 - 400 nm.

[0022] To achieve the third above-mentioned purpose, the present invention adopts the following technical solution:

[0023] The present invention discloses a third-order nonlinear optical modulator, which includes a dispersion prepared by using the two-dimensional red phosphorus nanosheet as described above.

[0024] Further, the third-order nonlinear optical modulator is prepared according to the following steps:

[0025] Disperse the two-dimensional red phosphorus nanosheets in a solvent to obtain a dispersion, and then place the dispersion in a cuvette, and that's it. Place the cuvette in the Z-scan optical path, and a nonlinear optical response can be presented;

[0026] Among them, the concentration of the dispersion is 0.001 - 0.1 mg / ml; exemplarily, the concentration of the dispersion can be 0.001 mg / ml, 0.002 mg / ml, 0.003 mg / ml, 0.004 mg / ml, 0.005 mg / ml, 0.006 mg / ml, 0.007 mg / ml, 0.008 mg / ml, 0.009 mg / ml, 0.01 mg / ml, 0.02 mg / ml, 0.03 mg / ml, 0.04 mg / ml, 0.05 mg / ml, 0.06 mg / ml, 0.07 mg / ml, 0.08 mg / ml, 0.09 mg / ml, 0.1 mg / ml, etc.

[0027] Further, the solvent is selected from one or more of methanol, ethanol, ethylene glycol, 1,2 - propylene glycol, 1,2,3 - glycerol, 1,2,4 - butanetriol, dimethyl sulfoxide, acetone, and water.

[0028] Further, the cuvette is made of quartz and has a thickness of 1 - 5 mm.

[0029] Further, the beam waist power density of the Z - scan optical path is 0.1 - 3 GW / cm 2 。

[0030] The beneficial effects of the present invention are as follows:

[0031] The present invention discloses a preparation method of two - dimensional red phosphorus nanosheets. This preparation method can prepare a large number of two - dimensional red phosphorus nanosheets with a relatively thin sheet thickness at a relatively low temperature. The operation is simple, the synthesis period is short, and the obtained two - dimensional red phosphorus nanosheets have a relatively thin thickness, with an average thickness of 1.2 - 100 nm and an average size of 50 - 400 nm.

[0032] The present invention also discloses a third - order nonlinear optical modulator prepared using the obtained two - dimensional red phosphorus nanosheets, which has an obvious solvent - dependent effect. By adjusting the solvent composition, modulation between saturated absorption and reverse - saturated absorption can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0034] Figure 1 Shows the scanning electron microscope image of two - dimensional red phosphorus in Example 1.

[0035] Figure 2 Shows the transmission electron microscope image of two - dimensional red phosphorus in Example 1.

[0036] Figure 3 Shows the atomic force microscope image of two - dimensional red phosphorus in Example 1.

[0037] Figure 4 Shows the open - aperture Z - scan curves of two - dimensional red phosphorus in Example 1 in different dispersion solvents (laser wavelength is 532 nm, beam waist power density is 1.132 GW / cm 2 )。

[0038] Figure 5 Shows the open - aperture Z - scan curve of two - dimensional red phosphorus prepared in Example 2 in ethanol (laser wavelength is 532 nm, beam waist power density 1.132 GW / cm 2 )。

[0039] Figure 6Shows the open-aperture Z-scan curve of two-dimensional red phosphorus in 1,2,3-glycerol in Example 3 (laser wavelength is 532 nm, beam waist power density is 2.264 GW / cm 2 ).

[0040] Figure 7 Shows the transmission electron microscope image of two-dimensional red phosphorus prepared in Comparative Example 1.

[0041] Figure 8 Shows the open-aperture Z-scan curve of two-dimensional red phosphorus prepared in Comparative Example 2 in ethanol (laser wavelength is 532 nm, beam waist power density is 1.132 GW / cm 2 ).

[0042] Figure 9 Shows the open-aperture Z-scan curve of commercial two-dimensional black phosphorus described in Comparative Example 3 in 1,2-propanediol (laser wavelength is 532 nm, beam waist power density is 1.132 GW / cm 2 ). Detailed implementation manners

[0043] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0044] Example 1

[0045] Step 1: Dissolve 0.5 g of phosphorus triiodide in cyclohexane and set aside.

[0046] Step 2: Add 15 g of L-ascorbic acid and the cyclohexane solution containing phosphorus triiodide obtained in Step 1 to a three-necked flask in sequence, and stir magnetically until evenly mixed.

[0047] Step 3: At 25°C, evacuate the three-necked flask to negative pressure, maintain the negative pressure for a period of time, then refill with nitrogen, and then evacuate to negative pressure again. Alternately cycle the above operations for a total of 120 min to completely remove cyclohexane to obtain a precursor, and then refill with nitrogen to return the three-necked flask to atmospheric pressure.

[0048] Step 4: In a nitrogen atmosphere, heat the three-necked flask to 70°C and maintain it for 20 min to cause the precursor to undergo a pyrolysis reaction at the interface.

[0049] Step 5: After the pyrolysis reaction ends, naturally cool to room temperature, and use ethanol and deionized water to centrifuge, wash, and purify the sample.

[0050] Step 6: Obtain the target product two-dimensional red phosphorus powder by freeze-drying.

[0051] Step 7: Take a total of 5 portions of the prepared two-dimensional red phosphorus powder, each portion being 0.05 mg. Using an ultrasonic cleaner, use 3 ml of 1,2-propanediol, 3 ml of 1,2,3-propanetriol, 3 ml of 1,2-propanediol + 3 ml of 1,2,3-propanetriol, 9 ml of 1,2-propanediol + 3 ml of 1,2,3-propanetriol, and 3 ml of 1,2-propanediol + 9 ml of 1,2,3-propanetriol as dispersion solvents to disperse the two-dimensional red phosphorus powder therein, obtaining 5 kinds of dispersions.

[0052] Step 8: Take a small amount of each of the above 5 kinds of dispersions and place them in different cuvettes. Under an ultraviolet-visible-near-infrared absorption spectrometer, sequentially adjust the transmittance at a laser wavelength of 532 nm to 60% by adding the same dispersion solvent.

[0053] Step 9: Place the cuvettes with the adjusted transmittance in Step 8 on the translation stage of the Z-scan optical path, and adjust the beam waist power density of the Z-scan optical path to 1.132 GW / cm 2 , thereby obtaining its nonlinear optical response, and the effect is as Figure 4 shown.

[0054] Figure 1 shows the scanning electron microscope image of the two-dimensional red phosphorus powder prepared in Example 1. It can be found that the sample morphology is uniform and the size is uniform.

[0055] Figure 2 shows the transmission electron microscope image of the two-dimensional red phosphorus powder prepared in Example 1. It can be obtained from Figure 2 that this material has obvious two-dimensional material characteristics.

[0056] Figure 3 shows the atomic force microscope image of the two-dimensional red phosphorus powder prepared in Example 1. It can be obtained from Figure 3 that the average thickness of this material is 1.62 nm and the average size is 112 nm.

[0057] Figure 4 shows the open-aperture Z-scan curve of the two-dimensional red phosphorus prepared in Example 1 in the dispersion solvent (laser wavelength is 532 nm, beam waist power density is 1.132 GW / cm 2 ). It can be found from the figure that by controlling the ratio of 1,2-propanediol and 1,2,3-propanetriol in the dispersion solvent, its conversion between saturated absorption and reverse saturated absorption can be modulated.

[0058] Example 2

[0059] Step 1: Dissolve 0.5 g of phosphorus triiodide fully in cyclohexane for standby.

[0060] Step 2: Add 15 g of L-ascorbic acid and the cyclohexane solution containing phosphorus triiodide obtained in Step 1 to a three-necked flask in sequence, and stir magnetically until evenly mixed.

[0061] Step 3: At 25 °C, evacuate the three-necked flask to negative pressure, maintain the negative pressure for a period of time, then refill with nitrogen, and then evacuate to negative pressure again. Alternately cycle the above operations for a total of 120 min to completely remove cyclohexane and obtain a precursor. Then refill with nitrogen to restore the three-necked flask to atmospheric pressure.

[0062] Step 4: In a nitrogen atmosphere, heat the three-necked flask to 70 °C and maintain for 20 min to cause the thermal decomposition reaction of the precursor at the interface.

[0063] Step 5: After the thermal decomposition reaction is completed, naturally cool to room temperature, and use ethanol and deionized water to centrifuge, wash, and purify the sample.

[0064] Step 6: Obtain the target product, two-dimensional red phosphorus powder, by freeze-drying.

[0065] Step 7: Take 0.05 mg of the two-dimensional red phosphorus powder prepared above, use an ultrasonic cleaner, and disperse the two-dimensional red phosphorus powder in 3 ml of ethanol as a dispersion solvent to obtain a dispersion.

[0066] Step 8: Take a small amount of the above dispersion and place it in a cuvette. Under an ultraviolet-visible-near-infrared absorption spectrometer, adjust its transmittance at a laser wavelength of 532 nm to 60% by adding ethanol.

[0067] Step 9: Place the cuvette with the adjusted transmittance in Step 8 on the translation stage of the Z-scan optical path, and adjust the beam waist power density of the Z-scan optical path to 1.132 GW / cm 2 , and its nonlinear optical response can be obtained, and the effect is as Figure 5 shown.

[0068] Figure 5 shows the open-aperture Z-scan curve of the two-dimensional red phosphorus prepared in Example 2 in ethanol (laser wavelength is 532 nm, beam waist power density is 1.132 GW / cm 2 ). It can be found from the figure that the two-dimensional red phosphorus exhibits the characteristic of saturated absorption in ethanol.

[0069] Example 3

[0070] Step 1: Dissolve 0.5 g of phosphorus triiodide in cyclohexane completely and set aside.

[0071] Step 2: Add 15 g of L-ascorbic acid and the cyclohexane solution containing phosphorus triiodide obtained in Step 1 to a three-necked flask in sequence, and stir magnetically until evenly mixed.

[0072] Step 3: At 25 °C, evacuate the three-necked flask to negative pressure, maintain the negative pressure for a period of time, then replenish nitrogen, and then evacuate to negative pressure again. Alternately cycle the above operations for a total of 120 min to completely remove cyclohexane and obtain the precursor. Then replenish nitrogen to restore the three-necked flask to atmospheric pressure.

[0073] Step 4: In a nitrogen atmosphere, heat the three-necked flask to 70 °C and maintain it for 20 min to cause the thermal decomposition reaction of the precursor at the interface.

[0074] Step 5: After the thermal decomposition reaction is completed, naturally cool to room temperature, and use ethanol and deionized water to centrifuge, wash, and purify the sample.

[0075] Step 6: Obtain the target product, two-dimensional red phosphorus powder, by freeze-drying.

[0076] Step 7: Take 0.05 mg of the two-dimensional red phosphorus powder prepared above, use an ultrasonic cleaner, and disperse the two-dimensional red phosphorus powder in 3 ml of 1,2,3-glycerol as a dispersion solvent to obtain a dispersion.

[0077] Step 8: Take a small amount of the above dispersion and place it in different cuvettes. Under an ultraviolet-visible-near-infrared absorption spectrometer, adjust the transmittance at a laser wavelength of 532 nm to 60% by adding 1,2,3-glycerol.

[0078] Step 9: Place the cuvettes with the adjusted transmittance in Step 8 on the translation stage of the Z-scan optical path, and adjust the beam waist power density of the Z-scan optical path to 2.264 GW / cm 2 , and its nonlinear optical response can be obtained, and the effect is as Figure 6 shown.

[0079] Figure 6 Shows the open-aperture Z-scan curve of the two-dimensional red phosphorus prepared in Example 3 in 1,2,3-glycerol (laser wavelength is 532 nm, beam waist power density 2.264 GW / cm 2 ). It can be found from the figure that the two-dimensional red phosphorus shows reverse saturation absorption in 1,2,3-glycerol, and when the beam waist power density increases, the modulation depth of the two-dimensional red phosphorus increases.

[0080] Comparative Example 1

[0081] Step 1: Dissolve 0.5 g of phosphorus triiodide in cyclohexane and set aside.

[0082] Step 2: Add 15 g of L-ascorbic acid and the cyclohexane solution containing phosphorus triiodide obtained in Step 1 to the three-necked flask in sequence, and magnetically stir until evenly mixed.

[0083] Step 3: At 70 °C, evacuate the three-necked flask to a negative pressure, maintain the negative pressure for a period of time, then refill with nitrogen, and then evacuate to a negative pressure again. Alternately cycle the above operations for a total of 120 min to completely remove cyclohexane to obtain a precursor. Then refill with nitrogen to return the three-necked flask to atmospheric pressure.

[0084] Step 4: In a nitrogen atmosphere, heat the three-necked flask to 70 °C and maintain it for 20 min to cause the precursor to undergo a pyrolysis reaction at the interface.

[0085] Step 5: After the pyrolysis reaction is completed, naturally cool to room temperature, and use ethanol and deionized water to centrifuge, wash, and purify the sample.

[0086] Step 6: Obtain the target product, two-dimensional red phosphorus powder, by freeze-drying.

[0087] Figure 7 The transmission electron microscope image of the two-dimensional red phosphorus prepared in Comparative Example 1 is shown. It can be found from the figure that due to the too high temperature during the removal of cyclohexane, the reaction occurred in the liquid phase, resulting in an increase in the thickness of the obtained two-dimensional red phosphorus lamellae.

[0088] Comparative Example 2

[0089] Step 1: Dissolve 0.5 g of phosphorus triiodide in cyclohexane and set aside.

[0090] Step 2: Add 15 g of L-ascorbic acid and the cyclohexane solution containing phosphorus triiodide obtained in Step 1 to the three-necked flask in sequence, and magnetically stir until evenly mixed.

[0091] Step 3: At 25 °C, evacuate the three-necked flask to a negative pressure, maintain the negative pressure for a period of time, then refill with nitrogen, and then evacuate to a negative pressure again. Alternately cycle the above operations for a total of 120 min to completely remove cyclohexane to obtain a precursor. Then refill with nitrogen to return the three-necked flask to atmospheric pressure.

[0092] Step 4: In a nitrogen atmosphere, heat the three-necked flask to 70 °C and maintain it for 20 min to cause the precursor to undergo a pyrolysis reaction at the interface.

[0093] Step 5: After the pyrolysis reaction is completed, naturally cool to room temperature, and use ethanol and deionized water to centrifuge, wash, and purify the sample.

[0094] Step 6: Obtain the target product, two-dimensional red phosphorus powder, by freeze-drying.

[0095] Step 7: Take 0.05 mg of the two-dimensional red phosphorus powder prepared above, use an ultrasonic cleaner, and disperse the two-dimensional red phosphorus powder in 3 ml of ethanol as a dispersion solvent to obtain a dispersion.

[0096] Step 8: Take a small amount of the above dispersion and place it in a cuvette. Under an ultraviolet-visible-near-infrared absorption spectrometer, adjust the transmittance at a laser wavelength of 532 nm to 100% by adding ethanol.

[0097] Step 9: Place the cuvettes with the adjusted transmittance in Step 8 on the translation stage of the Z-scan optical path respectively, and adjust the beam waist power density of the Z-scan optical path to 1.132 GW / cm 2 , and its nonlinear optical response can be obtained, and the effect is as Figure 8 shown.

[0098] Figure 8 shows the open-aperture Z-scan curve of the two-dimensional red phosphorus prepared in Comparative Example 2 in ethanol (laser wavelength is 532 nm, beam waist power density 1.132 GW / cm 2 ). When the transmittance is 100%, the solvent does not have a nonlinear optical effect under nanosecond laser.

[0099] Comparative Example 3

[0100] Step 1: Take 0.05 mg of commercial two-dimensional black phosphorus, use an ultrasonic cleaner, and disperse the two-dimensional black phosphorus in 3 ml of 1,2-propanediol as a dispersion solvent to obtain a dispersion.

[0101] Step 2: Take a small amount of the above dispersion in a cuvette. Under an ultraviolet-visible-near-infrared absorption spectrometer, adjust the transmittance at a laser wavelength of 532 nm to 60% by adding 1,2-propanediol.

[0102] Step 3: Place the cuvettes with the adjusted transmittance in Step 2 on the translation stage of the Z-scan optical path respectively, and adjust the beam waist power density of the Z-scan optical path to 1.132 GW / cm 2 , and its nonlinear optical response can be obtained, and the effect is as Figure 9 shown.

[0103] Figure 9 shows the open-aperture Z-scan curve of the commercial two-dimensional black phosphorus described in Comparative Example 3 in 1,2-propanediol (laser wavelength is 532 nm, beam waist power density 1.132 GW / cm 2 ). It can be found that the commercial two-dimensional black phosphorus is not as excellent as the two-dimensional red phosphorus prepared in the present invention in terms of modulation depth or initial nonlinear threshold.

[0104] Comparative Example 4

[0105] Step 1: Dissolve 0.5 g of phosphorus triiodide in cyclohexane and set aside.

[0106] Step 2: Add 1 g of L-ascorbic acid and the cyclohexane solution containing phosphorus triiodide obtained in Step 1 to a three-necked flask in sequence, and stir magnetically until evenly mixed.

[0107] Step 3: At 25°C, evacuate the three-necked flask to negative pressure, maintain the negative pressure for a period of time, then refill with nitrogen, and then evacuate to negative pressure again. Alternately cycle the above operations for a total of 120 min to completely remove cyclohexane and obtain a precursor. Then refill with nitrogen to restore the three-necked flask to atmospheric pressure.

[0108] Step 4: In a nitrogen atmosphere, heat the three-necked flask to 70°C and maintain for 20 min to cause the precursor to undergo a pyrolysis reaction at the interface.

[0109] Step 5: After the pyrolysis reaction is completed, naturally cool to room temperature, and use ethanol and deionized water to centrifuge, wash, and purify the sample.

[0110] Step 6: Obtain the target product, two-dimensional red phosphorus powder, by freeze-drying.

[0111] Since the amount of L-ascorbic acid used is small, most of the phosphorus triiodide is not at the interface, and the thickness of the prepared two-dimensional red phosphorus lamellae is relatively thick, which is not suitable for use in the preparation of nonlinear optical modulators.

[0112] Comparative Example 5

[0113] Step 1: Dissolve 0.5 g of phosphorus triiodide in cyclohexane and set aside.

[0114] Step 2: Add 15 g of L-ascorbic acid and the cyclohexane solution containing phosphorus triiodide obtained in Step 1 to the three-necked flask in sequence, and magnetically stir until evenly mixed.

[0115] Step 3: At 25°C, evacuate the three-necked flask to negative pressure, maintain the negative pressure for a period of time, then refill with nitrogen, and then evacuate to negative pressure again. Alternately cycle the above operations for a total of 120 min to completely remove cyclohexane and obtain a precursor. Then refill with nitrogen to restore the three-necked flask to atmospheric pressure.

[0116] Step 4: In a nitrogen atmosphere, heat the three-necked flask to 120°C and maintain for 20 min to cause the precursor to undergo a pyrolysis reaction at the interface.

[0117] Step 5: After the pyrolysis reaction is completed, naturally cool to room temperature, and use ethanol and deionized water to centrifuge, wash, and purify the sample.

[0118] Step 6: Obtain the target product, two-dimensional red phosphorus powder, by freeze-drying.

[0119] Due to the excessively high pyrolysis temperature, the phosphorus triiodide at non-interface locations decomposes, and the thickness of the prepared two-dimensional red phosphorus lamellae is relatively thick, which is not suitable for use in the suspension for nonlinear optical modulation.

[0120] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for preparing two-dimensional red phosphorus nanosheets, characterized in that, It includes the following steps: Dissolve phosphorus halide in a low-boiling solvent, add L-ascorbic acid, and after mixing evenly, remove the low-boiling solvent under vacuum at 20 - 50 °C to obtain a precursor; Under an inert atmosphere, heat the precursor to cause a pyrolysis reaction of the precursor at the interface, and obtain two-dimensional red phosphorus powder after cooling, washing, and freeze-drying.

2. The preparation method according to claim 1, characterized in that, The phosphorus halide is selected from phosphorus tribromide and / or phosphorus triiodide; The addition amount of the phosphorus halide is 0.1 - 1 g; the addition amount of the L-ascorbic acid is 1 - 20 g.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the phosphorus halide to the L-ascorbic acid is 1:20 - 80.

4. The preparation method according to claim 1, characterized in that, The low-boiling solvent is selected from one or more of cyclohexane, n-hexane, n-heptane, and petroleum ether.

5. The preparation method according to claim 1, characterized in that, The heating conditions are a heating temperature of 50 - 90 °C and a heating time of 10 - 60 min.

6. A two-dimensional red phosphorus nanosheet, characterized in that, It is prepared by using the preparation method described in any one of claims 1 - 5.

7. The two-dimensional red phosphorus nanosheet according to claim 6, characterized in that, The average thickness of the two-dimensional red phosphorus nanosheets is 1.2 - 100 nm, and the average size is 50 - 400 nm.

8. A third-order nonlinear optical modulator, characterized in that, It includes a dispersion prepared by using the two-dimensional red phosphorus nanosheets described in claim 6 or 7.

9. The third-order nonlinear optical modulator according to claim 8, characterized in that, The third-order nonlinear optical modulator is prepared according to the following steps: Disperse the two-dimensional red phosphorus nanosheets in a solvent to obtain a dispersion, and then place the dispersion in a cuvette, thus obtaining it; Among them, the concentration of the dispersion is 0.001 - 0.1 mg / ml.

10. The third-order nonlinear optical modulator according to claim 9, characterized in that, The solvent is selected from one or more of methanol, ethanol, ethylene glycol, 1,2-propanediol, 1,2,3-propanetriol, 1,2,4-butanetriol, dimethyl sulfoxide, acetone, and water.

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