Zero-dimensional perovskite nanocrystal large-scale preparation method based on room-temperature self-assembly strategy

Abstract

The invention belongs to the technical field of nano material preparation, discloses a zero-dimensional perovskite nanocrystalline large-scale preparation method based on a room-temperature self-assembly strategy, and aims to solve the technical problems that in the prior art, the uniformity of a product is poor, high luminous efficiency and conductivity are difficult to achieve at the same time, and the wavelength cannot be accurately regulated and controlled. According to the method, a water-in-oil microemulsion system is adopted as a nanoreactor, and the high uniformity of nanocrystal growth is fundamentally guaranteed through a confinement reaction. The composition creatively comprises two ligands: one ligand is a pi-conjugated conductive main functional ligand with surface passivation and charge transfer functions, which solves the problem of poor conductivity caused by the traditional insulating ligand while ensuring high photoluminescence efficiency, and the other ligand is a competitive tuning ligand which forms dynamic competitive balance with the main ligand. The key problems of product uniformity, conductivity, wavelength controllability and the like are synergistically solved, and the prepared nanocrystal has high optical purity, high quantum yield and excellent conductivity.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy. Background Technology

[0002] In recent years, zero-dimensional all-inorganic lead halide perovskite nanocrystals have attracted widespread attention from the scientific and industrial communities as a novel optoelectronic functional material due to their outstanding optical properties. These materials typically possess extremely high photoluminescence quantum yields, size-tunable emission wavelengths covering the entire visible light spectrum, and extremely narrow emission full width at half maximum (FWHM), meaning they can produce high-brightness, high-purity light. These excellent properties make them demonstrate enormous application potential in fields such as high-definition displays, solid-state lighting, solar cells, and photoelectric detection.

[0003] However, despite the promising prospects, existing technologies still face a series of interconnected and profound challenges in the preparation and application of these high-performance materials. Current mainstream preparation methods, such as ligand-assisted reprecipitation, often involve extremely rapid and difficult-to-control reaction kinetics. This near-uncontrolled rapid crystallization inevitably leads to significant inhomogeneities in the size and morphology of the products. This inhomogeneity not only directly results in a decline in the macroscopic optical properties of the materials, but more seriously, it makes it difficult to reproducible between different batches, greatly hindering their large-scale, standardized practical applications.

[0004] To stabilize the nanocrystalline structure and achieve high luminescence efficiency, existing technologies generally rely on coating the nanocrystals with organic ligands such as long-chain alkylammonium salts. Unfortunately, these ligands themselves are electrically insulating, forming a dense insulating shell on the nanocrystal surface, much like wrapping each luminescent core in a "plastic film." This "film" severely hinders charge transport between nanocrystals, resulting in poor performance in applications requiring electrical injection. Therefore, existing technologies present an inherent contradiction between high luminescence efficiency and excellent conductivity; the necessary means to achieve high brightness is precisely the key bottleneck limiting their electrical applications.

[0005] Furthermore, existing technologies exhibit significant limitations in controlling the emission wavelength of the product. Typically, wavelength adjustment requires altering the halogen composition or strictly controlling reaction conditions in different batches to obtain nanocrystals of varying sizes—a discrete, trial-and-error approach. This method is not only cumbersome and costly, but also struggles to precisely target a specific wavelength, lacking effective means for in-situ, continuous fine-tuning within a single synthesis reaction, thus significantly reducing the flexibility and precision of the preparation process. Therefore, a novel preparation technology is needed to fundamentally and synergistically address the three core challenges of product uniformity, conductivity, and precise wavelength control. Summary of the Invention

[0006] The present invention aims to solve the technical problems in the prior art, such as the difficulty in precisely controlling the preparation process of zero-dimensional perovskite nanocrystals, poor product uniformity and batch consistency, and the difficulty in achieving both high luminous efficiency and excellent conductivity.

[0007] To address the aforementioned technical problems, the first aspect of this invention provides a method for the large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy. This method achieves high-precision preparation of zero-dimensional perovskite nanocrystals by constructing a microemulsion confined reaction platform and introducing a competitive ligand exchange mechanism and online control methods.

[0008] The preparation method provided by this invention specifically includes the following steps:

[0009] a. Preparation of the reaction system:

[0010] This step aims to prepare an aqueous phase containing the reactants and an oil phase containing the functional control molecules, respectively. Specifically:

[0011] Preparation of the aqueous phase: The perovskite precursor is dissolved in an aqueous solvent. In a preferred embodiment, the perovskite precursor comprises lead bromide and cesium bromide, and the molar ratio of cesium bromide to lead bromide is 4.0:1 to 4.5:1.

[0012] Preparation of the oil phase: The main functional ligand and the competing tuning ligand are co-dissolved in a nonpolar organic solvent. The main functional ligand is a π-conjugated conductive organic ammonium salt used to construct charge transport channels on the nanocrystal surface; the competing tuning ligand is an organic ammonium salt with a different structure than the main functional ligand, but capable of competitively adsorbing onto the nanocrystal surface. In a preferred embodiment, the main functional ligand is 4-(oligothienyl)-benzyltrimethylammonium bromide, and the competing tuning ligand is 4-(monothienyl)-benzyltrimethylammonium bromide. The total molar concentration of these two ligands in the oil phase is 80 mmol / L to 150 mmol / L, and their initial molar ratio is set to 10:1 to 4:1.

[0013] The preparation method of the competitively tuned ligand [4-(monothienyl)-benzyltrimethylammonium bromide] is as follows:

[0014] Step 1.1: Suzuki Coupling Reaction In a 500 mL three-necked flask equipped with a reflux condenser and a magnetic stirrer, 25.0 g (0.1 mol) of 4-bromobenzyl bromide, 14.1 g (0.11 mol) of thiophene-2-boronic acid, 2.3 g (2 mmol) of tetra(triphenylphosphine)palladium, and 41.4 g (0.3 mol) of anhydrous potassium carbonate were added sequentially. The reaction mixture was evacuated and purged with nitrogen three times to ensure an inert atmosphere. A mixed solvent of toluene (200 mL) and ethanol (50 mL) was then added. The reaction mixture was heated to 85 °C and stirred vigorously at this temperature for 12 hours.

[0015] After the reaction was complete, the mixture was cooled to room temperature. The reaction solution was filtered, and the filtrate was washed three times with saturated brine. The organic phase was dried over anhydrous magnesium sulfate. After filtration, the solvent was removed by rotary evaporation to obtain the crude product. The crude product was purified by silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 20:1) to give the intermediate 2-(4-(bromomethyl)phenyl)thiophene, a pale yellow solid.

[0016] Step 1.2: Quaternization Reaction. The intermediate 2-(4-(bromomethyl)phenyl)thiophene (13.4 g, 0.05 mol) obtained in Step 1.1 was dissolved in tetrahydrofuran (150 mL). This solution was cooled in an ice-water bath, and then excess trimethylamine gas was slowly passed into the solution, or a tetrahydrofuran solution of trimethylamine (33% wt, about 20 mL) was added. The ice bath was removed, and the reaction was sealed at room temperature for 24 hours, during which a large amount of white solid precipitated.

[0017] After the reaction was complete, the white solid product was collected by vacuum filtration and washed several times with a small amount of cold tetrahydrofuran to remove unreacted raw materials. The obtained solid was dried in a vacuum drying oven at 40°C for 12 hours to obtain the final product 4-(monothienyl)-benzyltrimethylammonium bromide.

[0018] The preparation method of the main functional ligand [4-(2,2'-bithiophen-5-yl)-benzyltrimethylammonium bromide]:

[0019] Step 2.1: Suzuki Coupling Reaction

[0020] In the same reaction apparatus as in Preparation Example 1, 25.0 g (0.1 mol) of 4-bromobenzyl bromide, 23.1 g (0.11 mol) of (2,2'-bithiophene)-5-boronic acid, 2.3 g (2 mol) of tetrakis(triphenylphosphine)palladium(O) (2.3 g, 2 mol) and 41.4 g (0.3 mol) of anhydrous potassium carbonate were added sequentially. Under an inert atmosphere, a mixed solvent consisting of toluene (250 mL) and ethanol (60 mL) was added. The reaction system was heated to 90 °C and stirred vigorously at this temperature for 16 hours.

[0021] The reaction and post-processing were similar to those in step 1.1. Finally, the intermediate 5-(4-(bromomethyl)phenyl)-2,2'-bithiophene was obtained by column chromatography (eluent: petroleum ether / dichloromethane = 10:1), which was a yellow needle-like crystal.

[0022] Step 2.2: Quaternization reaction

[0023] The intermediate 5-(4-(bromomethyl)phenyl)-2,2'-bithiophene (16.8 g, 0.05 mol) obtained in step 2.1 was dissolved in dichloromethane (200 mL). An ethanol solution of trimethylamine (33% wt, approximately 25 mL) was added to the solution. The reaction flask was sealed, and the reaction was stirred at 40 °C for 36 hours.

[0024] After the reaction was complete, the volume of the reaction liquid was concentrated to about one-third by rotary evaporation, and then excess diethyl ether was added to precipitate the product. The precipitated yellow solid product was collected by vacuum filtration and washed repeatedly with diethyl ether. The obtained solid was dried in a vacuum drying oven at 45°C for 24 hours to obtain the final product 4-(2,2'-bithiophene-5-yl)-benzyltrimethylammonium bromide.

[0025] b. Construction of the microemulsion system:

[0026] The aqueous phase prepared in step a is dispersed in the oil phase and subjected to high-energy physical methods, such as ultrasonic treatment with a power of 300W to 600W and a frequency of 20kHz to 40kHz, or shearing by a high-speed homogenizer, to form a water-in-oil (W / O) microemulsion. This microemulsion consists of countless uniformly sized nanoscale aqueous droplets encapsulated by the oil phase, forming an independent nanoreactor array.

[0027] c. Interface self-assembly reaction:

[0028] The constructed microemulsion system was allowed to react continuously at room temperature (25℃–30℃) for 45–90 minutes. During this process, perovskite precursor ions in the aqueous phase underwent a self-assembly reaction with the oriented main functional ligands and competing tuning ligands at the oil-water interface, forming uniformly sized initial zero-dimensional perovskite nanocrystals inside each nanoreactor.

[0029] d. In-situ tuning and programming of optical properties:

[0030] This is the core step of the invention. After self-assembly, a polar modifier, preferably an alcohol or ketone solvent such as isopropanol, is added dropwise to the microemulsion system at a uniform rate of 0.1 mL / min to 0.4 mL / min. During the dropwise addition, the photoluminescence spectrum of the nanocrystals is collected and monitored in real time using online monitoring equipment such as a fiber optic spectrometer. The addition of the polar modifier changes the solvent environment of the interfacial microregion, thereby disturbing and altering the adsorption-desorption dynamic equilibrium of the main functional ligand and the competing tuning ligand on the nanocrystal surface. This change in the microstructure of the ligand shell directly leads to a change in the quantum confinement effect of the nanocrystals, resulting in a continuous and smooth shift in their photoluminescence spectrum. When the spectrum shifts to the preset target wavelength, the addition of the polar modifier is stopped, thus precisely locking the optical properties of the nanocrystals.

[0031] e. Separation and purification of products:

[0032] The tunable microemulsion system was demulsified by adding an antisolvent, causing the product to precipitate. Subsequently, through centrifugation, solvent washing, and vacuum drying, high-purity zero-dimensional perovskite nanocrystal powder was obtained.

[0033] This invention provides a method for the large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy.

[0034] It has the following beneficial effects:

[0035] 1. This invention constructs a physically isolated and uniformly sized "nanoreactor array" for the growth of zero-dimensional perovskite nanocrystals by using a water-in-oil microemulsion method. This "dimensional reduction and confinement" reaction method fundamentally ensures that the microenvironment for nucleation and growth of each nanocrystal is highly consistent, overcoming the inherent defects of traditional solution methods, such as wide product size distribution and poor batch repeatability caused by uneven mass transfer and concentration. This lays the foundation for the large-scale and high-quality preparation of materials.

[0036] 2. This invention innovatively designs and uses a π-conjugated conductive organic ammonium salt as the main functional ligand. This ligand can not only effectively guide the self-assembly of nanocrystals and passivate their surface defects to ensure high luminescence efficiency, but its inherent π-conjugated structure can also build an effective charge transport path between nanocrystals, giving the final material excellent conductivity. This "functional integration" design solves the "charge island" effect caused by traditional insulating ligands, enabling the material to have both excellent optical and electrical properties.

[0037] 3. This invention constructs a closed-loop control system of "stimulus-response-feedback-lock" by introducing "competitive ligand pairs" into the composition and combining it with an online in-situ tuning step. This method enables the emission wavelength of the product to be actively and accurately "programmed" to any preset value based on the dynamic balance of the perturbation ligand on the nanocrystal surface according to the real-time monitored spectral data during a single synthesis process. This achieves "on-demand customization" of the optical properties of the material and greatly improves the flexibility and accuracy of the preparation process.

[0038] 4. The unique dual-ligand synergistic passivation strategy of this invention allows the π-conjugated conductive organic ammonium salt, which serves as the passivation host, to form a stable chemical bond with the nanocrystal surface, efficiently repairing surface defects and thus maximally suppressing non-radiative recombination channels. At the same time, the competitive tuning ligand, which serves as a fine-tuning aid, is introduced in an optimized ratio, ensuring the tunability of the system without damaging the high-quality passivation layer constructed by the host ligand. The synergistic effect of the two ensures the excellent luminescence performance of the final product.

[0039] 5. This invention combines sophisticated composition design with advanced process control concepts. The entire preparation process is logically clear and easy to control. In particular, the unique online tuning step transforms the traditional process of obtaining a specific wavelength product by relying on "trial and error" into a process that can achieve the goal within a batch. This significantly simplifies the process development process and ensures a high degree of repeatability of the final product performance. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1:

[0042] This embodiment aims to demonstrate a method for the large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy. The specific steps are as follows:

[0043] 1. Preparation of precursor solution:

[0044] Aqueous phase: 0.54 g lead bromide (PbBr2, 1.47 mmol) and 1.24 g cesium bromide (CsBr, 5.84 mmol) were dissolved in 3.0 mL of deionized water to obtain an aqueous solution with a PbBr2 concentration of 0.49 mol / L and a CsBr / PbBr2 molar ratio of 4.0:1.

[0045] Oil phase: 0.47 g of the main functional ligand A (4-(oligothienyl)-benzyltrimethylammonium bromide, molecular weight ~398 g / mol, 1.18 mmol / L based on bithienyl group) and 0.10 g of the competitive tuning ligand B (4-(monothienyl)-benzyltrimethylammonium bromide, molecular weight ~316 g / mol, 0.32 mmol / L) were dissolved together in 10 mL of cyclohexane. The total ligand concentration was 150 mmol / L, and the initial molar ratio of A / B was approximately 3.7:1.

[0046] 2. Microemulsion construction and self-assembly:

[0047] 1.5 mL of aqueous solution was injected into 300 mL of oil (oil:water = 200:1). The mixture was then treated with ultrasound at 450 W and 30 kHz for 12 minutes in an ice-water bath to form a microemulsion.

[0048] The microemulsion was gently stirred at 28°C for 60 minutes to complete the interface self-assembly. At this time, the initial photoluminescence peak was measured to be at 522nm.

[0049] 3. Online tuning:

[0050] Isopropanol was added dropwise to the reaction system at a rate of 0.25 mL / min using a syringe pump.

[0051] By monitoring the PL peak position in real time with an online spectrometer, it was observed that the peak position gradually blue-shifted with the addition of isopropanol.

[0052] When the PL peak shifts to 515.0 nm, stop adding isopropanol. Continue stirring for 30 minutes to allow the system to equilibrate.

[0053] 4. Product separation:

[0054] Add approximately 900 mL of ethanol to the system to demulsify and precipitate.

[0055] Collect the product by centrifugation at 8500 rpm for 12 minutes.

[0056] The product was washed twice with n-hexane and then dried under vacuum at 35°C for 18 hours to obtain the final product.

[0057] Example 2: Preparation of zero-dimensional perovskite nanocrystals

[0058] This embodiment aims to demonstrate a method for the large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy. The specific steps are as follows:

[0059] 1. Preparation of precursor solution:

[0060] Aqueous phase: Prepare an aqueous solution containing 0.2 mol / L PbBr2 and 0.8 mol / L CsBr (CsBr / PbBr2 molar ratio of 4.0:1).

[0061] Oil phase: Prepare a cyclohexane solution containing the main functional ligand A and the competing tuning ligand B. The total ligand concentration was 80 mmol / L, and the initial molar ratio of A / B was 4:1.

[0062] 2. Microemulsion construction and self-assembly:

[0063] Add 1.0 mL of the aqueous phase solution to 150 mL of the oil phase (oil phase:water = 150:1).

[0064] Microemulsion was formed by treating the sample with ultrasound at a power of 300W and a frequency of 20kHz for 8 minutes.

[0065] The microemulsion was stirred at 25°C for 45 minutes to complete self-assembly.

[0066] 3. Online tuning:

[0067] Isopropanol was added dropwise to the system at a rate of 0.1 mL / min.

[0068] Stop adding the reagent when the PL peak position displayed on the online spectrometer reaches the preset value. Continue stirring for 20 minutes.

[0069] 4. Product separation:

[0070] Add 450 mL of ethanol to precipitate.

[0071] Collect the product by centrifugation at 7000 rpm for 10 minutes.

[0072] Wash twice with n-hexane, then vacuum dry at 30°C for 12 hours.

[0073] Example 3: Preparation of zero-dimensional perovskite nanocrystals

[0074] This embodiment aims to demonstrate a method for the large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy. The specific steps are as follows:

[0075] 1. Preparation of precursor solution:

[0076] Aqueous phase: Prepare an aqueous solution containing 0.8 mol / L PbBr2 and 3.6 mol / L CsBr (CsBr / PbBr2 molar ratio of 4.5:1).

[0077] Oil phase: Prepare a cyclohexane solution containing the main functional ligand A and the competing tuning ligand B. The total ligand concentration was 150 mmol / L, and the initial molar ratio of A / B was 10:1.

[0078] 2. Microemulsion construction and self-assembly:

[0079] Add 1.0 mL of the aqueous phase solution to 300 mL of the oil phase (oil phase:water = 300:1).

[0080] Microemulsion was formed by treating the sample with 600W of ultrasound at a frequency of 40kHz for 15 minutes.

[0081] The microemulsion was stirred at 30°C for 90 minutes to complete self-assembly.

[0082] 3. Online tuning:

[0083] Isopropanol was added dropwise to the system at a rate of 0.4 mL / min.

[0084] Stop adding liquid when the PL peak position displayed on the online spectrometer reaches the preset value. Continue stirring for 40 minutes.

[0085] 4. Product separation:

[0086] Add 900 mL of ethanol to precipitate.

[0087] Collect the product by centrifugation at 10,000 rpm for 15 minutes.

[0088] Wash three times with n-hexane, then vacuum dry at 40°C for 24 hours.

[0089] Comparative Example

[0090] Comparative Example 1: The difference from Example 1 is that the microemulsion method was not used. Specifically, 1.5 mL of the aqueous solution prepared in Example 1 was directly mixed with 100 mL of the oil solution without high-energy ultrasonic treatment, and the reaction was completed by mechanical stirring at the same temperature.

[0091] Comparative Example 2: The difference from Example 1 is that the π-conjugated conductive main functional ligand is not used. Specifically, the main functional ligand A (4-(oligothienyl)-benzyltrimethylammonium bromide) in the oil phase of Example 1 is replaced with an equimolar amount of a conventional ligand without π-conjugated structure—octadecyltrimethylammonium bromide.

[0092] Comparative Example 3: The difference from Example 1 is that the reaction system does not contain a competing tuning ligand. Specifically, only the main functional ligand A is added during the preparation of the oil phase, and the competing tuning ligand B is not added.

[0093] Comparative Example 4: Compared with Example 1, the difference is that the online in-situ tuning step was omitted. Specifically, after the microemulsion construction and self-assembly steps were completed, the online tuning step was not performed, and the product separation step was directly initiated.

[0094] Comparative Example 5: Compared with Example 1, the difference is that the reaction system does not contain the main functional ligand. Specifically, when preparing the oil phase, only the competitive tuning ligand B is added, and the main functional ligand A is not added. Moreover, the amount of competitive tuning ligand B is the same as the total molar amount of the two ligands in Example 1.

[0095] Comparative Example 6: Compared with Example 1, the difference lies in that the initial molar ratio of the main functional ligand to the competing tuning ligand exceeds the specified range. Specifically, when preparing the oil phase, the initial molar ratio of the main functional ligand A to the competing tuning ligand B is set to 1:1.

[0096] Test Example 1: Comparative Test of the Uniformity of Optical Properties of Products

[0097] I. Experimental Instructions

[0098] This test aims to verify the effect of the microemulsion confined reaction method used in this invention in improving the uniformity of product performance by comparing the optical spectral properties of the products obtained in Example 1 and Comparative Example 1.

[0099] Experimental steps

[0100] 1. Sample Solution Preparation: Using an analytical balance with an accuracy of 0.1 mg, accurately weigh 10.0 mg each of the zero-dimensional perovskite nanocrystal dry powder prepared in Example 1 and Comparative Example 1. Place each sample into a separate, clean, and dry 10 mL volumetric flask. Add analytical grade cyclohexane to each volumetric flask to the mark, stopper the flasks, and then place them in an ultrasonic cleaner for 5 minutes to ensure that the nanocrystal powder is fully and uniformly dispersed in the solvent, forming a test stock solution with a concentration of 1.0 mg / mL for each sample. Take 1.0 mL from each stock solution and add it to a cuvette containing 3.0 mL of pure cyclohexane, gently shake to mix, and obtain the final solution for testing.

[0101] 2. Spectroscopic Testing: Turn on the fluorescence spectrometer and preheat for 30 minutes to stabilize the light source and detector. Set the spectrometer's test parameters: excitation wavelength fixed at 365 nm, emission spectral scanning range from 450 nm to 600 nm, scanning speed at 240 nm / min, and excitation and emission slit widths both set to 5.0 nm. Place the cuvette containing the sample from Example 1 in the sample chamber and perform photoluminescence spectroscopy testing. To ensure data reliability, empty the sample chamber, replace the cuvette, and repeat the test three times, recording the results as test batches 1, 2, and 3. Wash the cuvette three times with pure cyclohexane, dry it, and then replace it with the sample solution from Comparative Example 1. Repeat the above spectroscopic testing procedure under the exact same test parameters, recording the data three times as well.

[0102] 3. Data Analysis: From the six acquired spectral curves, two key parameters, the peak wavelength and full width at half maximum (FWHM), were extracted. All data were organized and recorded in a data table for subsequent comparative analysis.

[0103] Experimental data

[0104] Table 1: Comparison of optical performance test data between the products of Example 1 and Comparative Example 1

[0105] sample Test batch Emission peak wavelength (nm) Full width at half maximum (FWHM) (nm) Example 1 1 515.2 18.3 Example 1 2 514.9 19.1 Example 1 3 515.5 18.7 Comparative Example 1 1 528.1 35.7 Comparative Example 1 2 519.5 40.2 Comparative Example 1 3 535.4 38.9

[0106] III. Experiment Summary

[0107] As shown in Table 1, the product of Example 1 prepared by the method of the present invention exhibits a photoluminescence spectrum with emission peak wavelengths highly concentrated around 515 nm, and a full width at half maximum (FWHM) consistently below 19 nm, demonstrating extremely high optical performance uniformity. In contrast, the product of Comparative Example 1 prepared using the conventional solution method showed significant fluctuations in emission peak wavelengths exceeding 15 nm in three tests, while its FWHM was generally greater than 35 nm, significantly wider than that of the product of Example 1.

[0108] This significant difference reveals the crucial role of the microemulsion-confined reaction method in this invention. In the conventional solution reaction represented by Comparative Example 1, nucleation and growth occur in a macroscopic, disordered bulk solution. Inevitably, there are differences in local supersaturation, mass transfer rate, and stirring efficiency in different regions, leading to a broad distribution of the generated nanocrystals in terms of size and morphology. Since the optical properties of zero-dimensional materials directly depend on the quantum confinement effect brought about by their size, this physical dimensional inhomogeneity directly manifests as optical performance inhomogeneity, namely, a wider full width at half maximum (FWHM) and unstable emission peak positions.

[0109] In contrast, the microemulsion method employed in this invention transforms the reaction system into a "nanoreactor array" composed of countless physically isolated, uniformly sized nanodroplets using high-energy techniques. This "dimensional reduction and confinement" strategy ensures, from a physical mechanism perspective, a highly consistent growth environment for each nanocrystal, fundamentally solving the size distribution problem caused by environmental inhomogeneity in traditional methods. Therefore, the final product exhibits a very narrow size distribution and directly displays highly uniform and reproducible optical properties, namely stable, concentrated emission peak positions and extremely narrow full width at half maximum (FWHM). This fully demonstrates the significant advantages of the method of this invention in achieving high-performance, uniform preparation of zero-dimensional perovskite nanocrystals.

[0110] Test Example 2: Comparative Test of Electrical Properties of Products

[0111] I. Experimental Instructions

[0112] This test aims to verify the role of the functionally integrated bifunctional ligand system used in this invention in improving the electrical properties of the products by comparing the macroscopic electrical conductivity of the products obtained in Example 1 and Comparative Example 2.

[0113] Experimental steps

[0114] 1. Sample Tableting Preparation: Accurately weigh 200.0 mg of each of the dried powders obtained in Example 1 and Comparative Example 2. Evenly pack the 200.0 mg powder from Example 1 into a circular tableting mold with an inner diameter of 10 mm. Place the mold on a powder tableting machine and maintain pressure at 10 MPa for 5 minutes to obtain a circular tablet with a smooth surface and uniform thickness. Carefully remove the tablet and use a digital thickness gauge to measure its thickness at four different locations: the center and the edge. Record the five values ​​and calculate the average thickness. Using the same mold and identical pressing parameters, prepare circular tablets from the powder of Comparative Example 2, and measure and record their average thickness in the same manner.

[0115] 2. Electrical performance test: Turn on the four-probe tester and perform instrument calibration.

[0116] The thin-film sample prepared in Example 1 was placed in the center of the test platform, and four probes in a straight line were gently lowered, ensuring good ohmic contact between all probes and the sample surface. The test current was set to 100 nA, and the test program was started. The instrument automatically applied the current and measured the voltage drop through its internal voltmeter. Then, based on the preset sample size and thickness, the volume resistivity of the material was calculated and displayed. To ensure the reliability of the data, the sample was rotated 90 degrees and the test was repeated. This process was repeated four times, and four sets of volume resistivity data were recorded. The thin-film sample of Comparative Example 2 was then used, and the above four-probe test procedure was repeated under the exact same test parameters, with four sets of data recorded in the same manner.

[0117] 3. Data Analysis: The average volume resistivity of the samples from Example 1 and Comparative Example 2 was calculated for four tests. All raw data and average values ​​were compiled and recorded in a data table for subsequent comparative analysis.

[0118] Experimental data

[0119] Table 2: Comparison of Electrical Performance Test Data of Products from Example 1 and Comparative Example 2

[0120] sample Test batch Average thickness (mm) Volume resistivity (Ω·cm) Example 1 1 0.48 <![CDATA[1.83×10 7 ]]> Example 1 2 0.48 <![CDATA[2.09×10 7 ]]> Example 1 3 0.48 <![CDATA[1.77×10 7 ]]> Example 1 4 0.48 <![CDATA[1.94×10 7 ]]> Comparative Example 2 1 0.51 <![CDATA[3.15×10 12 ]]> Comparative Example 2 2 0.51 <![CDATA[4.02×10 12 ]]> Comparative Example 2 3 0.51 <![CDATA[2.98×10 12 ]]> Comparative Example 2 4 0.51 <![CDATA[3.56×10 12 ]]>

[0121] III. Experiment Summary

[0122] As shown in Table 2, the product of Example 1 prepared by the method of the present invention has a stable bulk resistivity of 10. 7The resistivity is on the order of Ω·cm. In stark contrast, the product of Comparative Example 2, prepared using traditional insulating ligands, has a bulk resistivity as high as 10⁻⁶. 12 The difference is on the order of Ω·cm, with a significant difference of up to five orders of magnitude. This result strongly demonstrates the substantial improvement in electrical performance resulting from the innovative composition design of this invention.

[0123] The fundamental difference in electrical properties stems from the fundamental difference in the ligand shells on the surfaces of the two products. In Comparative Example 2, the nanocrystal surface is completely coated with conventional saturated long-chain alkylammonium salts such as octadecyltrimethylammonium bromide. These ligand molecules do not contain freely moving electrons, forming a dense electrically insulating layer, much like wrapping each luminescent core with a "plastic film." This severely hinders the injection and transition of charge between the nanocrystals, resulting in a film composed of these nanocrystals exhibiting extremely high resistivity on a macroscopic scale, thus becoming a typical insulator.

[0124] This invention creatively designs and introduces a master functional ligand with π-conjugated conductive units. This ligand, while anchored to the nanocrystal surface via a quaternary ammonium salt head, provides stability, and its π-conjugated structure extends beyond the nanocrystal surface. When a large number of nanocrystals are tightly packed during tableting, the π-conjugated units on adjacent nanocrystal surfaces can interact through π-π stacking and other means, forming potential charge transport "bridges" or "pathways" between the nanocrystals. These pathways break the "charge island" effect caused by traditional insulating ligands, allowing charge to be transported relatively easily within the material, thereby significantly reducing the overall bulk resistivity of the material and exhibiting semiconductor characteristics. This opens up possibilities for applications requiring electrical actuation, such as electroluminescent devices.

[0125] Test Example 3: Comparative Test of the Tunability of Product Optical Properties

[0126] I. Experimental Instructions

[0127] This test aims to verify the decisive role of the "competitive ligand pair" composition designed in this invention in achieving online tuning of optical properties by comparing the spectral responses of Example 1 and Comparative Example 3 during the tuning process.

[0128] Experimental steps

[0129] 1. Reaction System Preparation and Online Monitoring Deployment: Following the steps of Example 1, the reaction system was prepared and the self-assembly step was completed to obtain a microemulsion containing initial nanocrystals. Following the steps of Comparative Example 3, another microemulsion containing initial nanocrystals was prepared and the self-assembly step was completed to obtain another microemulsion. The two completed microemulsions were placed in flasks equipped with magnetic stirrers, and the probes of fiber optic spectrometers were immersed below the liquid surface for online monitoring.

[0130] 2. Online Tuning Process and Spectral Acquisition: First, the system of Example 1 was tuned. Magnetic stirring was started, and the initial photoluminescence spectrum was recorded. Subsequently, the syringe pump was started, and isopropanol was added dropwise to the system at a rate of 0.25 mL / min. During the dropwise addition, a complete photoluminescence spectrum was immediately acquired and the emission peak wavelength was recorded whenever the cumulative amount of isopropanol added increased by 1.0 mL, until the cumulative amount added reached 5.0 mL. Next, the same operation was performed on the system of Comparative Example 3. Its initial photoluminescence spectrum was recorded, and isopropanol was added dropwise at the same rate and cumulative amount, with the emission peak wavelength also acquired and recorded at each 1.0 mL node.

[0131] 3. Data Analysis: The data on the change of PL emission peak wavelength with the amount of isopropanol added during the two experiments were compiled and recorded in a data table for intuitive comparative analysis.

[0132] Experimental data

[0133] Table 3: Comparison of optical performance changes during online tuning process between Example 1 and Comparative Example 3

[0134]

[0135] III. Experiment Summary

[0136] As shown in Table 3, during the uniform dropwise addition of the polar modifier, the photoluminescence peak of the reaction system in Example 1 exhibited a continuous, smooth, and significant blue shift, precisely tuned from the initial 522.1 nm to 515.0 nm. In stark contrast, the system in Comparative Example 3, lacking a competing tuning ligand, showed its emission peak position fluctuating irregularly around the initial 526 nm after undergoing the same identical operation, without any directional or meaningful shift. This comparative result irrefutably demonstrates the criticality of the composition design in this invention.

[0137] This strikingly different response behavior is rooted in the dynamic equilibrium of the ligand shell on the nanocrystal surface. In Example 1 of this invention, the main functional ligand and the competing tunable ligand coexist, forming a delicate competitive adsorption dynamic equilibrium on the nanocrystal surface. When a polar modifier is introduced into the oil phase, it alters the solvent polarity environment of the interfacial microregion. This perturbation actively disrupts the original equilibrium and, based on the subtle differences in the molecular structure and polarity of the two ligands, selectively affects their adsorption-desorption rates, leading to a gradual change in the composition of the ligand shell. This microscopic reconstruction of the ligand shell structure directly alters the intensity of the quantum confinement effect on the internal perovskite core, thus macroscopically manifesting as a continuous and controllable shift of the photoluminescence peak position.

[0138] Because the system contains only one main functional ligand, a relatively stable, non-competitive single ligand layer forms on the nanocrystal surface. While adding a polar modifier will also alter the solvent environment, the lack of a suitable "competitor" prevents effective ligand exchange, thus maintaining the ligand shell structure's basic stability and preventing significant changes in the quantum confinement effect; consequently, the emission wavelength is "locked." This comparison powerfully demonstrates that the online tuning capability of this invention does not stem from the simple addition of solvent, but rather from the innovative dynamic chemical equilibrium constructed by "competitive ligand pairs" that can be actively regulated by external stimuli, highlighting the core innovative value of the composition design of this invention.

[0139] Test Example 4: Comparative test of the control precision of product optical properties.

[0140] I. Experimental Instructions

[0141] This test aims to verify the decisive role of the online programming control method contained in this invention in achieving precise control of the optical properties of the product by comparing the optical properties of the final products obtained in Example 1 and Comparative Example 4.

[0142] Experimental steps

[0143] 1. Sample Acquisition:

[0144] Sample 1: The final product powder prepared and dried in Example 1 was used directly. According to the preparation record, the online tuning target wavelength of this batch of product was 515.0 nm, and its initial emission peak wavelength before tuning was 522.1 nm.

[0145] Sample 2: The final product powder prepared and dried in Comparative Example 4 was used directly. This sample underwent the same initial preparation process as Example 1, but the online tuning step was skipped.

[0146] 2. Sample solution preparation: Following the steps in Test Example 1, accurately weigh 10.0 mg of each of the two sample powders mentioned above, and prepare cyclohexane test solutions of consistent concentration and uniform dispersion.

[0147] 3. Spectroscopic Testing: The same fluorescence spectrometer and testing parameters as in Test Example 1 were used. Photoluminescence spectra were performed on the test solutions containing the products of Example 1 and Comparative Example 4, respectively. To ensure data accuracy, each sample was measured three times independently, and the final emission peak wavelength was recorded.

[0148] 4. Data Analysis: The emission peak wavelength data of the final products obtained from the two experiments, as well as the tuning target and initial wavelength of Example 1, were compiled and recorded in a data table for comparison.

[0149] Experimental data

[0150] Table 4: Comparison of optical properties of the final products of Example 1 and Comparative Example 4

[0151]

[0152] III. Experiment Summary

[0153] As clearly shown in Table 4, the final product of Example 1 exhibits emission peak wavelengths that precisely fall near the preset target value of 515.0 nm in all three measurements, demonstrating extremely high control precision. Conversely, Comparative Example 4, which omitted the online tuning step, shows that the emission peak wavelength of its final product remains essentially the same as before tuning, around 522 nm. This comparison directly demonstrates that the online in-situ tuning step in this invention is not optional, but rather the core and key to achieving "on-demand customization" of the product's optical performance.

[0154] This result profoundly reveals the innovativeness of the methodology of this invention. In the traditional synthesis path represented by Comparative Example 4, the optical properties of the product are "fixed" the moment self-assembly is completed, and its properties are passively determined entirely by the initial reactant ratio and conditions, without any subsequent active intervention. This is a static "manufacturing" process, and its product is fixed. This invention, however, introduces a dynamic, programmable "customization" step, namely the online tuning step.

[0155] The online tuning step of this invention essentially establishes a closed-loop control system of "stimulus-response-feedback-lock". By actively applying a perturbation variable to the system and monitoring its optical response in real time using an online spectrometer, the operator can proactively and predictively guide the properties of the product toward a preset target, much like "programming". When the monitored property perfectly matches the target, the property can be precisely "locked" by stopping the application of stimulation. This process elevates the preparation of nanocrystals from a passive, fixed-endpoint process to an active, selectable-endpoint, and highly flexible process, fully demonstrating the significant innovation and technological superiority of this invention in process control.

[0156] Test Example 5: Comparative Test of Product Luminescence Efficiency

[0157] I. Experimental Instructions

[0158] This test aims to verify the necessity of the synergistic effect of the main functional ligand and the competing tuning ligand in obtaining high-performance luminescent materials by comparing the photoluminescence quantum yields of the products obtained in Example 1 and Comparative Example 5.

[0159] Experimental steps

[0160] 1. Sample Solution Preparation: Weigh the dried powders obtained from Example 1 and Comparative Example 5, and prepare a series of dilute solutions using analytical grade cyclohexane. Use a UV-Vis spectrophotometer to measure the absorbance of each sample series at the excitation wavelength. From each series, select one solution with an absorbance value between 0.05 and 0.10 at 365 nm for subsequent testing to minimize errors caused by concentration and reabsorption effects. Record the precise absorbance value of the selected solution.

[0161] 2. Quantum Yield Test: The test was performed using a fluorescence spectrometer equipped with an integrating sphere. First, a cuvette containing pure cyclohexane solvent was placed in the center of the integrating sphere, and the spectrum of the excitation light was measured as a blank reference. Then, a cuvette containing the sample solution from Example 1 was placed in the cuvette, and under the same conditions, its emission spectrum and the spectrum of the excitation light transmitted through the integrating sphere were measured. The instrument software automatically calculated the photoluminescence quantum yield of the sample based on these three sets of data. To ensure data reliability, the sample was removed and reinserted, and the measurement was repeated three times, recording the PLQY values ​​three times. The sample solution from Comparative Example 5 was then used, and the above quantum yield test procedure was repeated under the exact same test parameters, with data recorded three times in the same manner.

[0162] 3. Data Analysis: The PLQY test data of the samples from Example 1 and Comparative Example 5 were compiled and recorded in a data table for comparative analysis.

[0163] Experimental data

[0164] Table 5: Comparison of photoluminescence quantum yield of products from Example 1 and Comparative Example 5

[0165] sample Test batch Absorbance (at 365nm) Photoluminescence quantum yield (PLQY) (%) Example 1 1 0.082 91.3 Example 1 2 0.082 88.9 Example 1 3 0.082 92.5 Comparative Example 5 1 0.091 5.7 Comparative Example 5 2 0.091 8.2 Comparative Example 5 3 0.091 6.5

[0166] III. Experiment Summary

[0167] As shown in Table 5, the product of Example 1 prepared by the method of this invention exhibits an extremely high photoluminescence quantum yield of nearly 90%. However, when the key main functional ligand is missing from the reaction system and self-assembly is completed only by competing tunable ligands, the quantum yield of the product drops sharply to less than 10%. This huge performance gap profoundly reveals that in the dual-ligand system designed in this invention, the two ligands each play an indispensable and complementary role.

[0168] The underlying mechanism of this phenomenon lies in the passivation quality of the ligand on the nanocrystal surface. The efficient luminescence of zero-dimensional perovskites presupposes that their surface defects must be effectively "healed" or "passivated" by ligand molecules to eliminate nonradiative recombination centers capable of trapping excitons. In the composition design of this invention, the main functional ligand is specifically designed as a highly efficient surface passivator. Its molecular structure can form a stable chemical bond with the nanocrystal surface, providing complete electronic and physical confinement, thereby maximally suppressing nonradiative recombination channels and ensuring that excitons can emit light efficiently through radiative recombination. This is fundamental to obtaining high quantum yield.

[0169] In contrast, the core design objective of competitively tunable ligands is not to provide optimal surface passivation, but to introduce a "variable" that can be controlled by the external environment to achieve fine-tuning of optical properties. When present alone, although it can guide the formation of nanocrystalline structures, its interaction forces with the nanocrystalline surface, steric hindrance, and coverage efficiency are not optimal, resulting in numerous defects in the formed ligand shell. These unpassivated surface defects become "traps" for exciton recombination, causing most excitons to be consumed through non-radiative pathways, ultimately leading to extremely low photoluminescence efficiency. Therefore, this invention is not a simple mixture of two ligands, but a synergistic strategy with efficient passivation as the primary focus and competitive fine-tuning as a secondary approach. The successful implementation of this strategy is the foundation for simultaneously achieving both high quantum yield and spectral tunability.

[0170] Test Example 6: Effect of Ligand Ratio on the Uniformity of Product Optical Properties

[0171] I. Experimental Instructions

[0172] This test aims to verify the importance of the ligand component ratio range defined in this invention for ensuring high product quality and high uniformity by comparing the optical spectral characteristics of the products obtained in Example 1 and Comparative Example 6.

[0173] Experimental steps

[0174] 1. Sample Acquisition:

[0175] Sample 1: The final product powder prepared and dried in Example 1 was used directly. According to the preparation record, the initial molar ratio of the main functional ligand A to the competing tuning ligand B in the oil phase was approximately 3.7:1.

[0176] Sample 2: The final product powder prepared and dried in Comparative Example 6 was used directly. According to the preparation record, the initial molar ratio of the main functional ligand A to the competing tuning ligand B in the oil phase was 1:1.

[0177] 2. Sample Solution Preparation and Spectroscopic Testing: Following the experimental procedures in Test Example 1, cyclohexane test solutions of identical concentrations were prepared for both sample powders. Using the same fluorescence spectrometer and test parameters as in Test Example 1, photoluminescence spectroscopy was performed on the test solutions containing the product of Example 1 and the product of Comparative Example 6, respectively. To ensure data reliability, each sample was measured three times independently.

[0178] 3. Data Analysis:

[0179] From all the acquired spectral curves, the full width at half maximum (FWHM) of the emission peaks was extracted as a key parameter. All data were organized and recorded in a data table for comparative analysis.

[0180] Experimental data

[0181] Table 6: Comparison of optical property uniformity between the products of Example 1 and Comparative Example 6

[0182] sample Ligand A / B molar ratio Test batch Full width at half maximum (FWHM) (nm) Example 1 3.7:1 1 18.3 Example 1 3.7:1 2 19.1 Example 1 3.7:1 3 18.7 Comparative Example 6 0.042361111 1 42.1 Comparative Example 6 0.042361111 2 45.8 Comparative Example 6 0.042361111 3 43.5

[0183] III. Experiment Summary

[0184] As shown in Table 6, the product of Example 1 prepared with the preferred ligand ratio consistently maintained a full width at half maximum (FWHM) of 19 nm below 19 nm, exhibiting excellent optical purity. However, when the ratio of the main functional ligand to the competing tunable ligand was adjusted to 1:1, significantly deviating from the preferred range of this invention, the FWHM of the product spectrum increased sharply to over 40 nm. FWHM is a direct indicator of the uniformity of nanocrystal size distribution; this significant difference in data reveals the scientific validity and necessity of limiting the ligand ratio in this invention.

[0185] The underlying mechanism of this phenomenon stems from the influence of the competitive dynamics of the two ligands during self-assembly on the nucleation and growth stages. In the preferred ligand ratio of this invention, the highly efficient passivating main functional ligand dominates in number. This ensures that during the critical periods of nanocrystal nucleation and growth, the vast majority of surface sites can be rapidly and stably covered and passivated by this high-quality ligand. The competing tunable ligands, as a minority of species, are present enough to establish the dynamic equilibrium required for subsequent tuning, but not enough to excessively interfere with the ordered passivation process of the main ligand during the initial growth stage, thus ensuring that the initially grown nanocrystals themselves possess high crystallinity and size uniformity.

[0186] In contrast, in Comparative Example 6, when the ratio of the two ligands is close to 1:1, their competition on the nanocrystal surface becomes exceptionally fierce and disordered. These two ligands, with their different molecular structures and properties, have different effects on the adsorption and assembly of precursor ions at the interface. This intense competition disrupts the originally ordered crystal growth kinetics, potentially leading to the formation of multiple nucleation centers, uneven growth rates, or even the formation of structurally mixed ligand shells. This disorder introduced at the very forefront of nanocrystal growth directly results in significant inhomogeneities in the final product's size, morphology, and surface state, inevitably manifesting macroscopically as an extremely broad full width at half maximum (FWHM). Therefore, the limitation on the ligand ratio in this invention is essentially aimed at achieving an optimal balance between "ensuring high initial crystal quality" and "constructing subsequent tunability," which is crucial for achieving the final high-performance product.

[0187] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy, characterized in that, Includes the following steps: a. Prepare an aqueous phase containing a perovskite precursor and an oil phase containing a main functional ligand and a competing tuning ligand; b. Disperse the aqueous phase from step a into the oil phase from step a to construct a water-in-oil microemulsion system; c. Perform a self-assembly reaction at the oil-water interface of the microemulsion formed in step b to form initial zero-dimensional perovskite nanocrystals. d. Add a polarity modifier to the microemulsion system formed in step b, and tune the optical properties in situ by monitoring the optical properties of the zero-dimensional perovskite nanocrystals online until the preset target is achieved. e. Separate and purify the zero-dimensional perovskite nanocrystals that were tuned in situ in step b.

2. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 1, characterized in that, In step a, the perovskite precursor in the aqueous phase includes a metal halide salt and an alkali metal halide salt, wherein the metal halide salt is lead bromide and the alkali metal halide salt is cesium bromide, and the molar ratio of cesium bromide to lead bromide is 4.0:1 to 4.5:

1. In step a, the main functional ligand is a π-conjugated conductive organic ammonium salt, and the competitive tuning ligand is an organic ammonium salt with a structure different from the main functional ligand and exhibiting competitive adsorption.

3. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 1, characterized in that, In step a, the main functional ligand and the competing tuning ligand are dissolved together in a nonpolar organic solvent; Specifically, the main functional ligand is 4-oligothienyl-benzyltrimethylammonium bromide, and the competitive tuning ligand is 4-monothienyl-benzyltrimethylammonium bromide. The total molar concentration of the main functional ligand and the competitive tuning ligand in the nonpolar organic solvent is 80 mmol / L to 150 mmol / L, and the initial molar ratio of the main functional ligand to the competitive tuning ligand is 10:1 to 4:

1.

4. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 1, characterized in that, In step b, the aqueous phase is dispersed in the oil phase using high-energy physical methods, including ultrasonic treatment or high-speed homogenizer shearing.

5. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 4, characterized in that, The ultrasonic treatment has a power of 300W to 600W and a frequency of 20kHz to 40kHz.

6. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 1, characterized in that, In step c, the temperature of the self-assembly reaction is 25℃~30℃, and the reaction time is 45 minutes~90 minutes.

7. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 1, characterized in that, In step d, the polarity modifier is an alcohol or ketone solvent, preferably isopropanol.

8. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 7, characterized in that, In step d, the polarity modifier is added dropwise to the microemulsion system at a rate of 0.1 mL / min to 0.4 mL / min using a syringe pump.

9. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 1, characterized in that, In step d, the online monitoring is achieved by acquiring the photoluminescence spectrum of the zero-dimensional perovskite nanocrystals in real time using a fiber optic spectrometer.

10. The method for large-scale preparation of zero-dimensional perovskite nanocrystals based on a room-temperature self-assembly strategy according to claim 1, characterized in that, The specific content of step e is as follows: An antisolvent was added to the microemulsion system to demulsify and precipitate the precipitate. The precipitate was collected by centrifugation, and then washed and vacuum dried.

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