Preparation method of wurtzite nanosheet and wurtzite nanosheet

Abstract

This application provides a method for preparing wurtzite nanosheets and the wurtzite nanosheets themselves. The method for preparing wurtzite nanosheets includes: mixing a metal source with a solvent to obtain a cationic precursor solution, wherein the solvent comprises, by volume fraction, 30%–100% amine solvent; mixing an anionic source, arylphosphine, and a solvent to obtain an anionic precursor solution; and mixing and reacting the cationic and anionic precursor solutions at a preset temperature to obtain wurtzite nanosheets. The preparation method of this application introduces a specific arylphosphine ligand to inhibit the activity of the (0001) crystal plane while maintaining the activity of the (1120) crystal plane, thereby achieving controllable growth of wurtzite nanosheets and solving the problem in existing technologies where the morphology of nanosheets cannot be well controlled.

Description

Technical Field

[0001] This application relates to the field of materials synthesis technology, and in particular to a method for preparing wurtzite nanosheets and wurtzite nanosheets. Background Technology

[0002] Colloidal semiconductor nanocrystals are important semiconductor materials with great potential applications in optoelectronic devices, fluorescent materials, microwave absorbing materials, solar cells, and photocatalysis. Compared to common zero-dimensional quantum dots, two-dimensional II-VI group colloidal semiconductor nanocrystals (hereinafter referred to as nanosheets) possess unique optical, electrical, and magnetic properties, and are expected to significantly improve the efficiency of optoelectronic devices. Currently synthesized wurtzite nanosheets exhibit large lateral dimensions and high aspect ratios. Summary of the Invention

[0003] This application provides a method for preparing wurtzite nanosheets and wurtzite nanosheets, which can achieve the synthesis of nanosheets with small lateral size and high symmetry morphology.

[0004] In a first aspect, embodiments of this application provide a method for preparing wurtzite nanosheets, comprising: mixing a metal source with a solvent to obtain a cationic precursor solution, wherein, by volume fraction, the solvent comprises: 30% to 100% amine solvent; mixing an anionic source, arylphosphine with a solvent to obtain an anionic precursor solution; and mixing and reacting the cationic precursor solution and the anionic precursor solution at a preset temperature to obtain wurtzite nanosheets.

[0005] According to an embodiment of the first aspect of this application, the metal source includes one or more of zinc salts and cadmium salts; and / or, the zinc salt includes one or more of zinc formate, zinc acetate, zinc propionate, zinc butyrate, zinc chloride, zinc bromide, and zinc nitrate; and / or, the cadmium salt includes one or more of cadmium formate, cadmium acetate, cadmium propionate, zinc chloride, and cadmium nitrate; and / or, the anion source includes elemental or compound elements of the same group such as selenium powder, selenoamide, sodium selenide, lithium selenide, sulfur powder, hydrogen sulfide, sodium sulfide, lithium sulfide, tellurium powder, hydrogen telluride, and lithium telluride.

[0006] According to an embodiment of the first aspect of this application, the concentration of zinc cation in the cationic precursor solution is 0.01 mol / L to 5 mol / L; the concentration of selenium ion in the anionic precursor solution is 0.01 mol / L to 5 mol / L; and the molar ratio of cation to anion is adjusted to a range of 1:5 to 5:1.

[0007] According to the embodiments of the first aspect of this application, the amine solvent includes one or more of oleylamine, butylamine, octylamine, decaamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, dioctylamine, and trioctylamine; and / or, the arylphosphine includes one or more of phenylphosphine, diphenylphosphine, triphenylphosphine, diethylphenyl, ethyldiphenylphosphine, diphenylmethylphosphine, and dimethylphenylphosphine.

[0008] According to an embodiment of the first aspect of this application, the ratio of the anion source to arylphosphine is 1:0 to 1:3.

[0009] According to an embodiment of the first aspect of this application, in the step of obtaining wurtzite nanosheets, the preset temperature for the reaction between the cationic precursor solution and the anionic precursor solution is 100°C to 180°C.

[0010] According to an embodiment of the first aspect of this application, the solvent further includes at least one of alkane solvent and olefin solvent, ranging from 0 to 30%.

[0011] According to an embodiment of the first aspect of this application, in the step of obtaining the cation precursor solution, the metal source and the solvent are mixed and dissolved in a temperature range of 30°C to 250°C.

[0012] According to an embodiment of the first aspect of this application, in the step of obtaining the cation precursor solution, after the metal source is mixed and dissolved with the solvent, the solution is further kept at a temperature of about 0 to 120 minutes.

[0013] Secondly, embodiments of this application provide a wurtzite nanosheet prepared by the above-described preparation method.

[0014] Compared with the prior art, this application has at least the following beneficial effects:

[0015] This application achieves controllable growth of wurtzite nanosheets by introducing specific arylphosphine ligands to significantly suppress the activity of the (0001) crystal plane, thus solving the problem of poor morphological control in existing technologies. The wurtzite nanosheets prepared by the method of this application can achieve lengths and widths of 5 nm and 4 nm, respectively. Furthermore, arylphosphine can act as a reducing agent, accelerating the activation of anionic precursors, avoiding lengthy precursor preparation and activation processes, significantly reducing reaction time, and increasing experimental and production efficiency. Simultaneously, due to the electron-withdrawing effect of phenyl groups, arylphosphine has a lower binding affinity to chalcogens than alkylphosphines, thus avoiding the binding of phenyl groups to chalcogens. Complete suppression of crystal planes results in granular products. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0017] Figure 1 These are transmission electron microscope images of the zinc selenide nanosheets obtained in Example 1;

[0018] Figure 2 The absorption spectrum of the wurtzite zinc selenide nanosheets obtained in Example 1;

[0019] Figure 3 The absorption spectrum of the wurtzite zinc selenide nanosheets obtained in Example 4 is shown. Detailed Implementation

[0020] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0021] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0022] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0023] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0024] Wurtzite nanosheets have high research and application value, but current technologies cannot effectively control their morphology. This is mainly reflected in two aspects: firstly, the lateral dimensions of the nanosheets are too large, and secondly, the aspect ratios are too large. Nanosheets synthesized using existing technologies often have lateral dimensions greater than 50 nanometers and aspect ratios greater than 2.

[0025] Increasing the lateral size reduces the dispersibility of nanosheets, making them prone to aggregation and difficult to process. Simultaneously, excessively large lateral sizes increase the specific surface area of ​​the nanosheets, raising the number of defect states and causing a decrease in optical properties such as fluorescence quantum yield. Furthermore, excessively large lateral sizes hinder the subsequent growth of inorganic heterostructures with passivating defect effects, leading to uneven surface growth and increased fluorescence half-width at half-maximum (FWHM). Therefore, the synthesis of wurtzite nanosheets with small lateral sizes has significant application value and scientific research significance.

[0026] Although shortening the reaction time in existing technologies can reduce the length and width of nanosheets, the aspect ratio of the nanosheets remains relatively large, and undissolved byproducts are often present. For example, in some typical zinc selenide nanosheet synthesis methods, reducing the reaction time to 4 minutes can reduce the width to about 6 nanometers, but the length can still reach 20 nanometers, and the upper surface area is still 120 square nanometers. This asymmetric growth makes it difficult for the subsequently grown inorganic heterostructures to form uniform defect passivation, resulting in a reduction in optical properties.

[0027] In view of the above problems, this application provides a method for preparing wurtzite nanosheets and wurtzite nanosheets. The technical solution provided in this application is described in detail below.

[0028] Preparation method of wurtzite nanosheets

[0029] In a first aspect, embodiments of this application provide a method for preparing wurtzite nanosheets, comprising: mixing a metal source with a solvent to obtain a cationic precursor solution, wherein, by volume fraction, the solvent comprises: 30% to 100% amine solvent; mixing an anionic source, arylphosphine with a solvent to obtain an anionic precursor solution; and mixing and reacting the cationic precursor solution and the anionic precursor solution at a preset temperature to obtain wurtzite nanosheets.

[0030] The inventors of this application have noted that the inability of existing technologies to effectively control the lateral dimensions of nanosheets is primarily due to the strong asymmetry of the surface energies of wurtzite crystal planes. In the wurtzite structure, the surface energies of the crystal planes are ordered as follows: Higher surface energy leads to higher surface activity. This causes the nanosheets to grow much faster along the

[0001] direction than along the

[0001] direction. and The growth rate, and along The growth rate in the (0001) direction is the slowest, ultimately resulting in nanosheets with a high aspect ratio. Therefore, suppressing the activity of the (0001) crystal plane is crucial for achieving controllable growth of nanosheets. This application significantly suppresses the activity of the (0001) crystal plane by introducing specific arylphosphine ligands, achieving controllable growth of wurtzite nanosheets and solving the problem of the inability to effectively control the lateral dimensions of nanosheets in existing technologies.

[0031] In this embodiment, a cationic precursor solution and anionic precursor solution are first prepared, and then wurtzite nanosheets are obtained by mixing and reacting the cationic and anionic precursor solutions at a preset temperature.

[0032] The wurtzite nanosheets prepared by the method of this application have a hexagonal wurtzite crystal form; their morphology is sheet-like, meaning that the size in one direction is significantly smaller than in the other two directions. Typical morphologies have a thickness dimension of 0.3 nm to 10 nm, while the size in the other two directions is 4 nm to 100 nm. Furthermore, the wurtzite nanosheets prepared by the method of this application are colloidal semiconductor crystals, possessing common properties of colloidal semiconductor crystals, such as… Figure 2 The absorption peaks for hole-electron transitions are shown.

[0033] In the step of obtaining the cationic precursor solution, a metal source is mixed with a solvent, the metal source being a compound comprising transition metal cations, and the solvent comprising 30% to 100% by volume an amine solvent, which facilitates the dissolution of the metal source.

[0034] In some embodiments, the metal source includes one or more of zinc salts and cadmium salts. The metal source may include only zinc salts, only cadmium salts, or a mixture of zinc and cadmium salts. Exemplarily, the zinc salt includes one or more of zinc formate, zinc acetate, zinc propionate, zinc butyrate, zinc chloride, zinc bromide, and zinc nitrate; the cadmium salt includes one or two of cadmium formate, cadmium acetate, cadmium propionate, cadmium butyrate, zinc chloride, cadmium bromide, and cadmium nitrate.

[0035] In the step of obtaining the anion precursor solution, the anion source, arylphosphine, and solvent are mixed. The anion source is a compound including a Group 6 nonmetallic element. The arylphosphine, acting as an arylphosphine ligand, significantly suppresses the activity of the (0001) crystal plane while maintaining... The activity of the crystal facets enables the controllable growth of wurtzite nanosheets, thus solving the problem of the inability to effectively control the lateral size of nanosheets in existing technologies. Amine solvents possess reducing properties, which facilitates the dissolution of the anion source.

[0036] In this application, the solvents used in the step of obtaining the cationic precursor solution and the solvents used in the step of obtaining the anionic precursor solution both independently comprise 30% to 100% amine solvents, and may be the same or different. When they are different, the solvent used in the step of obtaining the cationic precursor solution can be regarded as the first solvent, and the solvent used in the step of obtaining the anionic precursor solution can be regarded as the second solvent.

[0037] In some embodiments, the anion source includes elemental or compound elements of the same group such as selenium powder, selenoamide, sodium selenide, lithium selenide, sulfur powder, hydrogen sulfide, sodium sulfide, lithium sulfide, tellurium powder, hydrogen telluride, and lithium telluride.

[0038] The inventors of this application have also noted the problem of long reaction times in existing technologies. These long reaction times are mainly due to the complex preparation of precursors and the extended reaction duration. Taking a typical zinc selenide nanosheet synthesis method as an example, the mixture needs to be held at 110°C for 30 minutes to fully activate the precursor. Even considering a minimum reaction time of 10 minutes without byproducts, the entire synthesis cycle of a typical zinc selenide nanosheet requires at least 40 minutes. This long reaction time extends the work cycle, thereby increasing the cost of experiments and production.

[0039] To address this issue, the arylphosphine used in this application acts as a reducing agent to accelerate the activation of the anionic precursor, and the highly reactive zinc salt is used in conjunction to reduce the activation time required for the cationic precursor, thus significantly reducing the synthesis time. Due to the sufficient activation of the anionic precursor, this application also significantly reduces the number of unreacted anionic precursors.

[0040] In some embodiments, the concentration of metal cations in the cation precursor solution is 0.01 mol / L to 5 mol / L, preferably 0.5 mol / L.

[0041] In some embodiments, the concentration of Group 6 element anions in the anionic precursor solution is 0.01 mol / L to 5 mol / L, preferably 0.066 mol / L.

[0042] In some embodiments, the molar ratio of cations to anions is adjusted to a range of 1:5 to 5:1. Exemplarily, the molar ratio of cations to anions is 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or a range consisting of any two of the above ratios. Preferably, the molar ratio is 1:1.

[0043] Existing technologies also suffer from the presence of numerous unreacted anionic precursors during synthesis. In typical zinc selenide nanosheet synthesis methods, the molar ratio of cations to anions is 1:3. During the reaction, these unreacted anionic precursors act as reaction sites, hindering the doping of other elements in the same group. For example, elemental selenium reacts with lithium telluride, preventing tellurium from being incorporated into the nanosheets. After the reaction, the unreacted elemental selenium requires extraction using trioctylphosphine, increasing production costs.

[0044] This application utilizes arylphosphine as a reducing agent to accelerate the activation of the anionic precursor and combines it with highly reactive zinc salts to reduce the activation time required for the cationic precursor, thus significantly reducing the synthesis time. Due to the sufficient activation of the anionic precursor, this application also significantly reduces the amount of unreacted anionic precursor. Nanosheets can be synthesized with an equimolar ratio of cations and anions, greatly improving the utilization rate of the synthesized material and avoiding the situation where unreacted precursors act as redundant reaction sites, thereby achieving high reaction purity.

[0045] In some embodiments, the amine solvent includes one or more of oleylamine, butylamine, octylamine, decaamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, dioctylamine, and trioctylamine.

[0046] In some embodiments, it includes one or more of phenylphosphine, diphenylphosphine, triphenylphosphine, diethylphenyl, ethyldiphenylphosphine, diphenylmethylphosphine, and dimethylphenylphosphine.

[0047] In some embodiments, the molar ratio of the anion source to the arylphosphine is 1:0 to 1:3. Exemplarily, the molar ratio of the anion source to the arylphosphine is 1:0.5, 1:0.8, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, or 1:3. Preferably, the molar ratio is 1:1.1.

[0048] Not intending to be limited by any theory or explanation, the inventors discovered in experiments that different ratios of arylphosphine to anion source affect the final morphology of the product. When the ratio of anion source to arylphosphine is 1:0 to 1:3, wurtzite nanosheets can be obtained.

[0049] In some embodiments, in the step of obtaining wurtzite zinc selenide nanosheets, the preset temperature for the reaction between the cationic precursor solution and the anionic precursor solution is 100°C to 180°C.

[0050] Within this temperature range, wurtzite nanosheets can be obtained through reaction. The inventors discovered in their experiments that the order of injection of the cationic and anionic precursors has no significant effect on the final product. Therefore, this application does not limit the order of addition of the cationic and anionic precursors; the cationic precursor solution can be injected into the anionic precursor solution, or vice versa.

[0051] In some embodiments, the solvent further includes 0-30% of at least one of alkane solvents and olefin solvents.

[0052] Through extensive research, the inventors discovered that the solvent also includes at least one of alkane solvents and olefin solvents, which helps to regulate the morphology of wurtzite nanosheets. A certain amount of alkane solvent or olefin solvent can reduce by-products and particulate products.

[0053] For example, the volume fraction of alkane solvent in the solvent is 0, 2%, 4%, 6%, 8%, 9%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or any combination of two of the above values.

[0054] In some embodiments, in the step of obtaining the cationic precursor solution, the metal source and solvent are mixed and dissolved in a temperature range of 30°C to 250°C.

[0055] For example, the metal source and solvent are mixed and dissolved at 30°C, 60°C, 90°C, 100°C, 120°C, 150°C, 180°C, 200°C, 210°C, 220°C, 240°C or 250°C, or at a temperature range consisting of any two of the above values.

[0056] Secondly, embodiments of this application provide a wurtzite nanosheet prepared by the above-described preparation method.

[0057] The wurtzite nanosheets of this application enable the synthesis of nanosheets with small lateral dimensions and high symmetry morphology. The wurtzite nanosheets of this application have a thickness of 0.3 nm to 5 nm, a length and width of less than 20 nm, and an aspect ratio of 1:1 to 2:1.

[0058] The wurtzite nanosheets of this application can be dispersed in organic solvents (such as n-hexane, n-octane, toluene, chloroform, etc.) to form a homogeneous and stable mixture, thus obtaining a colloid.

[0059] Example

[0060] The following embodiments describe the disclosure of this application in more detail. These embodiments are for illustrative purposes only, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly or purified as needed. The instruments used in the embodiments are also commercially available.

[0061] Example 1

[0062] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0063] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0064] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0065] When the anionic precursor solution is heated to 180°C, 2 mL of the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0066] After the insulation is completed, the mixture is cooled to room temperature.

[0067] Example 2

[0068] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0069] Preparation of cationic precursor solution: Mix 1 mmol zinc propionate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0070] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0071] When the anionic precursor solution is heated to 180°C, 2 mL of the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0072] After the insulation is completed, the mixture is cooled to room temperature.

[0073] Example 3

[0074] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0075] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL octylamine, dissolve at 180 °C, keep warm for 5 minutes and then cool.

[0076] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol triphenylphosphine, 5 mL dodecylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0077] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0078] After the insulation is completed, the mixture is cooled to room temperature.

[0079] Example 4

[0080] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0081] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0082] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol diphenylphosphine and 10 mL oleylamine and dissolve at 100 °C.

[0083] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0084] After the insulation is completed, the mixture is cooled to room temperature.

[0085] Example 5

[0086] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0087] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0088] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0089] When the anionic precursor solution is heated to 130°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0090] After the insulation is completed, the mixture is cooled to room temperature.

[0091] Example 6

[0092] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0093] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0094] Preparation of anionic precursor solution: Mix 1 mmol selenoamide, 1.1 mmol triphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0095] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0096] After the insulation is completed, the mixture is cooled to room temperature.

[0097] Example 7

[0098] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0099] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0100] Preparation of anionic precursor solution: Dissolve 1 mmol selenium powder, 3 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene at 100 °C.

[0101] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0102] After the insulation is completed, the mixture is cooled to room temperature.

[0103] Example 8

[0104] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0105] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0106] Preparation of anionic precursor solution: Dissolve 1 mmol selenium powder, 1.5 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene at 100 °C.

[0107] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0108] After the insulation is completed, the mixture is cooled to room temperature.

[0109] Example 9

[0110] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0111] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0112] Preparation of anionic precursor solution: Dissolve 1 mmol selenium powder, 2 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene at 100 °C.

[0113] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0114] After the insulation is completed, the mixture is cooled to room temperature.

[0115] Example 10

[0116] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0117] Preparation of cationic precursor solution: Mix 5 mmol zinc acetate and 10 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0118] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0119] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0120] After the insulation is completed, the mixture is cooled to room temperature.

[0121] Example 11

[0122] A zinc selenide nanosheet made of wurtzite is prepared by the following steps:

[0123] Preparation of cationic precursor solution: Mix 1 mmol zinc acetate and 2 mL oleylamine, dissolve at 60 °C, keep warm for 120 minutes and then cool.

[0124] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0125] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0126] After the insulation is completed, the mixture is cooled to room temperature.

[0127] Example 12

[0128] A wurtzite zinc sulfide nanosheet is prepared by the following steps:

[0129] Preparation of cationic precursor solution: Mix 1 mmol of zinc nitrate and 2 mL of oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0130] Preparation of anionic precursor solution: Mix 1 mmol sulfur powder, 1.1 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0131] When the anionic precursor solution is heated to 180°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 6 minutes.

[0132] After the insulation is completed, the mixture is cooled to room temperature.

[0133] Example 13

[0134] A wurtzite cadmium selenide nanosheet is prepared by the following steps:

[0135] Preparation of cationic precursor solution: Mix 1 mmol cadmium chloride and 2 mL oleylamine, dissolve at 60 °C, keep warm for 5 minutes and then cool.

[0136] Preparation of anionic precursor solution: Mix 1 mmol selenium powder, 1.1 mmol diphenylphosphine, 5 mL oleylamine, 5 mL octylamine, and 5 mL octadecene, and dissolve at 100 °C.

[0137] When the anionic precursor solution is heated to 100°C, the above-mentioned cationic precursor solution is injected into the anionic precursor solution and kept at this temperature for 30 minutes.

[0138] After the insulation is completed, the mixture is cooled to room temperature.

[0139] Comparative Example 1

[0140] The preparation process is similar to that in Example 1, except that diphenylphosphine is not added in the step of preparing the anionic precursor solution.

[0141] Comparative Example 2

[0142] The preparation process is similar to that in Example 1, except that the amount of diphenylphosphine added is changed to 5 mmol in the step of preparing the anionic precursor solution.

[0143] Comparative Example 3

[0144] The preparation process is similar to that in Example 1, except that diphenylphosphine is not added in the step of preparing the anionic precursor solution, but 1.1 mmol of tributylphosphine is added.

[0145] Comparative Example 4

[0146] The preparation process is similar to that in Example 1, except that the reaction temperature is 220°C in the step of obtaining wurtzite zinc selenide nanosheets.

[0147] Comparative Example 5

[0148] Similar to the preparation process in Example 1, the molar ratio of anions and cations was 1:6.

[0149] Comparative Example 6

[0150] The preparation process is similar to that in Example 1, except that the temperature is kept at 300°C in the step of obtaining the cationic precursor solution.

[0151] Results Analysis

[0152] Figure 1 The image shows the transmission electron microscope structure of the wurtzite zinc selenide nanosheets obtained in Example 1. The average length is about 5 nanometers and the average width is about 4 nanometers, with an aspect ratio close to 1:1. Figure 2The absorption spectrum of the wurtzite zinc selenide nanosheets obtained in Example 1 shows a clear splitting of the light / heavy hole-electron transition absorption peak, indicating that the obtained sample has a sheet-like morphology. In contrast, the heavy hole-electron transition absorption peak of Example 1 is at 341 nm, a blue shift of 7 nm compared to 348 nm in the literature. This small blue shift indicates a reduction in lateral size, also suggesting that the thickness of the nanosheets has not changed, remaining consistent with the literature at 1.4 nm. Therefore, the absorption spectrum will be used later to determine whether the sample is a wurtzite zinc selenide nanosheet and its relative lateral size. Specifically, zinc selenide and cadmium selenide nanosheets can be identified by the presence or absence of light / heavy hole-electron transition absorption peak splitting, and their lateral size can be determined by the degree of blue shift of the heavy hole-electron transition absorption peak, which is generally within 30 nm. Due to their inherent energy level characteristics, zinc sulfide nanosheets do not exhibit obvious splitting of light / heavy hole-electron transition absorption peaks. Therefore, whether a sample is a zinc sulfide nanosheet and its lateral size can be determined by the degree of blue shift of the heavy hole-electron transition absorption peak. If a blue shift is observed and is less than 10 nanometers, the sample is considered to be a zinc sulfide nanosheet with a reduced lateral size.

[0153] The light / heavy hole-electron absorption peaks of Examples 1 to 13 and Comparative Example 1, and the blue shift of the heavy hole-electron absorption peak relative to the corresponding large-size nanosheets, are collected in Table 1 below.

[0154] Table 1

[0155]

[0156] The heavy hole-electron transition absorption peak of Comparative Example 1 is at 346 nm, a 5 nm redshift compared to Example 1, indicating that its lateral size is larger than that of Example 1. The samples obtained from Comparative Examples 2, 3, 4, 5, and 6 all lacked the characteristic light / heavy hole-electron absorption peak splitting of wurtzite nanosheets, indicating that wurtzite zinc selenide nanosheets were not obtained in any of them. Please refer to... Figure 3 In Example 4, not only did the characteristic light / heavy hole-electron absorption peaks of wurtzite zinc selenide nanosheets appear, but also the absorption peaks of by-products appeared at around 300 nm. The analysis compared with Example 1 showed that olefins and alkanes helped to eliminate by-products.

[0157] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing wurtzite nanosheets, characterized in that, include: A metal source is mixed with a solvent to obtain a cationic precursor solution, wherein, by volume fraction, the solvent comprises: 30%~100% amine solvent; the metal source comprises one or more of zinc salts and cadmium salts; the zinc salt comprises one or more of zinc formate, zinc acetate, zinc propionate, zinc butyrate, zinc chloride, zinc bromide, and zinc nitrate; the cadmium salt comprises one or two of cadmium formate, cadmium acetate, cadmium propionate, cadmium butyrate, cadmium chloride, cadmium bromide, and cadmium nitrate. An anion source, arylphosphine, and the solvent are mixed to obtain an anion precursor solution; the arylphosphine includes one or more of phenylphosphine, diphenylphosphine, triphenylphosphine, diethylphenylphosphine, ethyldiphenylphosphine, diphenylmethylphosphine, and dimethylphenylphosphine; the anion source includes elemental sulfur, selenium, and tellurium or compounds. The cationic precursor solution and the anionic precursor solution are mixed and reacted at a preset temperature to obtain wurtzite nanosheets, wherein the preset temperature is 100°C to 180°C.

2. The preparation method according to claim 1, characterized in that, The anion source includes selenium powder, selenoamide, sodium selenide, lithium selenide, sulfur powder, hydrogen sulfide, sodium sulfide, lithium sulfide, tellurium powder, hydrogen telluride, or lithium telluride.

3. The preparation method according to claim 1 or 2, characterized in that, The concentration of metal cations in the cationic precursor solution is 0.01 mol / L to 5 mol / L; The concentration of Group 6 element anions in the anion precursor solution is 0.01 mol / L to 5 mol / L. The molar ratio of cations to anions can be adjusted within the range of 1:5 to 5:

1.

4. The preparation method according to claim 1, characterized in that, The amine solvent includes one or more of oleylamine, butylamine, octylamine, decaamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, dioctylamine, and trioctylamine, and the general structural formula of the arylphosphine is PPh. x R 2-x P represents phosphorus, Ph represents phenyl, R represents alkyl or hydrogen atom, and x represents an integer from 0 to 2.

5. The preparation method according to claim 1 or 4, characterized in that, The ratio of the anion source to the arylphosphine is 1:0 to 1:

3.

6. The preparation method according to claim 1, characterized in that, The solvent also includes 0-30% of at least one of alkane solvents and olefin solvents.

7. The preparation method according to claim 1, characterized in that, In the step of obtaining the cationic precursor solution, the metal source is mixed with the solvent and dissolved in a temperature range of 30°C to 250°C.

8. The preparation method according to claim 7, characterized in that, In the step of obtaining the cation precursor solution, after the metal source is mixed and dissolved with the solvent, the solution is further kept at a temperature of 0 to 120 minutes.

9. A wurtzite nanosheet, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

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