Perovskite nanocrystals doped with nickel ions and their application in rapid detection of moisture in edible oil

Abstract

The application discloses a kind of perovskite nanocrystals doped with nickel ions and its application in rapid detection of moisture in edible oil, the chemical formula of the perovskite nanocrystals is CsPb (1‑x) Ni x Br3, x represents the molar ratio of nickel ions and lead ions, x=0.05-0.23;The application provides a kind of perovskite nanocrystals doped with nickel ions, nanometer size is uniform, fluorescence signal is enhanced, structure is more stable;The perovskite nanocrystals doped with nickel ions can be dispersed with ethyl acetate as solvent, used for the detection of moisture content in edible oil, solve the problem that existing method uses toxic liquid such as toluene as solvent, improve safety.In addition, the detection method of the application is rapid (can be completed within 10 min), sensitive, accurate, and the detection limit is as low as 0.006% (v / v).

Description

(I) TECHNICAL FIELD

[0001] The present application relates to a nickel ion-doped perovskite nanocrystal and its application in rapid detection of water content in edible oil. (II) BACKGROUND

[0002] Moisture content is an important indicator of the quality and safety of edible oil, and significantly affects its processing and storage quality (Mishra, et al. 2021). The water content in edible oil should generally be controlled between 0.05%-0.2% (Wang, 2022; Xie, 2018). High moisture content in edible oil will on the one hand promote the hydrolysis of oil and increase the acid value, and the generated free fatty acids are relatively unstable and more prone to oxidation, causing the peroxide value to increase; on the other hand, high moisture content will increase the dissolved oxygen content, thereby accelerating the oxidation and hydrolysis of oil. At the same time, high moisture content in edible oil may promote the growth of microorganisms (especially Aspergillus flavus), bringing new food safety hazards (J. Chen, Zhang, Li, Zhang, Gao, & Yu, 2021; Zhao, Xu, Shi, & Fan, 2021). Therefore, rapid and sensitive evaluation of the moisture content in edible oil has important economic value and social significance for oil damage reduction and ensuring the quality and safety of edible oil.

[0003] Currently, the main methods for detecting the moisture content in edible oil include oven drying method (GB 5009.236-2016), distillation method, Karl Fischer titration (KFT) (Felgner, 2008; Popescu, et al., 2020), gas chromatography (GC) (Xie, 2018), infrared spectroscopy (Cifuentes Cabezas, 2023; Saleh, 2021; Ye, 2023), etc. As an official method, the oven drying method is simple and convenient to operate, but is easily disturbed by external factors, has large errors, and is time-consuming. The distillation method is time-consuming and generally suitable for samples with water content of 0.05% or more. KFT is the gold standard for water analysis, with high accuracy and low detection limit, but the KFT reagent used for titration has high preservation requirements, and is not suitable for on-site rapid detection. Direct quantification by mid-infrared spectroscopy (FTIR) is mainly based on the absorption of hydroxyl groups at 3500 cm -1 , but the absorption is weak, generally requires extraction by a polar solvent before measurement, and is easily affected by hydroxyl groups or hydrogen bonds, with poor sensitivity. The later developed quantification method based on 1640 cm -1 -OH bending vibration significantly improves the accuracy and detection limit of the analysis method, but the wavelet operation still increases the complexity of the method. NIR technology based on chemometrics algorithms has the advantages of non-destructive and green, but the quantitative model requires a large amount of data fitting.

[0004] Halide perovskite nanocrystals (CsPbBr3 NCs) as a new advanced fluorescent material, with high fluorescence quantum yield, stable luminescence, tunable fluorescence emission peak, etc., is becoming a hot material for rapid detection research (Huang, et al., 2021; Kailasa, 2021). And partial substitution of metal ions can improve the fluorescence characteristics of CsPbBr3 NCs, thereby further improving the detection performance (Swarnkar, 2018; van der Stam, 2017). Considering the instability of the structure of CsPbBr3 NCs to water, and the structure damage will be accompanied by changes in fluorescence intensity or wavelength, therefore, CsPbBr3 NCs can be used to rapidly and sensitively evaluate trace water in edible oil. Zhao et al. prepared mesoporous silica coated CsPbBr 1.5 I 1.5 NCs, and developed a ratiometric fluorescence sensor for water determination based on the material, with a LOD of 0.45% (Zhao, 2021). Wang et al. used terephthalic acid dimethyl ester to modify CsPbBr3 NCs, and constructed a dual-emission CsPbBr3 NCs, which showed sensitive fluorescence on / off and wavelength shift to water, with a LOD of 0.006% (Wang, 2022). However, the reaction system of the two methods is carried out in highly toxic toluene, and the method is complex to operate.

[0005] Therefore, there is a lack of rapid, accurate, sensitive oil moisture detection methods, especially intuitive on-site detection methods. (Three) Summary of the Invention

[0006] The purpose of the present application is to provide a kind of perovskite nanocrystals doped with nickel ions and its application in rapid detection of edible oil moisture, the prepared perovskite nanocrystals doped with nickel ions are uniform in nanometer size, fluorescence signal is enhanced, and the structure is more stable, which can be used as edible oil moisture sensor to rapidly, sensitively, accurately and low detection limit detect moisture in edible oil.

[0007] The technical scheme adopted by the present application is:

[0008] The present application provides a kind of perovskite nanocrystals doped with nickel ions, the chemical formula of the perovskite nanocrystals is CsPb (1-x) Ni x Br3, x represents the molar ratio of nickel ions to lead ions, x=0.05-0.23, preferably x=0.05.

[0009] The application also provides a preparation method of the nickel ion doped perovskite nanocrystal, which is carried out according to the following steps: mixing Pb-TOPO stock solution with Ni-TOPO stock solution, TOPO stock solution and n-hexane, injecting Cs-DOPA stock solution at the same time under the condition of intense stirring at 1000-2000 rpm (preferably 1500 rpm), adding lecithin stock solution after incubation at room temperature for 1-10 min (preferably 5 min), adding anti-solvent acetone after stirring for 20-50 s (preferably 30 s), and finally centrifuging, collecting the precipitate and obtaining the nickel ion doped perovskite nanocrystal which is stored after being redispersed in n-hexane;

[0010] The Pb-TOPO stock solution is prepared from PbBr2, trioctylphosphine oxide (TOPO > 90%), n-octane and n-hexane; the mass ratio of PbBr2 to trioctylphosphine oxide is 1:2-8; the volume of n-octane is 2-8 L / mol based on the mass of PbBr2, and the volume of n-hexane is 10-30 L / mol based on the mass of PbBr2;

[0011] The Ni-TOPO stock solution is prepared from NiBr2, trioctylphosphine oxide (TOPO), n-octane and n-hexane; the mass ratio of NiBr2 to trioctylphosphine oxide is 1:2-8; the volume of n-octane is 5-15 L / mol based on the mass of NiBr2, and the volume of n-hexane is 20-50 L / mol based on the mass of NiBr2;

[0012] The Cs-DOPA stock solution is prepared from Cs2CO3, 3-[2s-3,6-dioxopiperazin-2-yl]propionic acid (DOPA), n-octane and n-hexane; the volume of DOPA is 5-15 mL / g based on the mass of Cs2CO3; the volume of n-octane is 10-30 mL / g based on the mass of Cs2CO3; and the volume of n-hexane is 200-300 mL / g based on the mass of Cs2CO3;

[0013] The TOPO stock solution is prepared from TOPO and n-hexane; the volume of n-hexane is 2-8 L / mol based on the mass of TOPO;

[0014] The lecithin stock solution is prepared from lecithin and n-hexane; the volume of n-hexane is 10-30 mL / g based on the mass of lecithin; and all the stock solutions are filtered through a 0.45 μm filter membrane before use.

[0015] Further, the amount of Pb-TOPO stock solution is 0.04 mol / L, the amount of Ni-TOPO stock solution is 0.04 mol / L, the amount of Cs-DOPA stock solution is 0.01 mol / L, the amount of TOPO stock solution is 0.2 mol / L, the amount of lecithin stock solution is 0.66 g / mmol, the amount of n-hexane is 2 L / mmol, and the amount of acetone is 6 L / mmol.

[0016] Further, the Pb-TOPO stock solution is prepared by mixing PbBr2 and tri-n-octylphosphine oxide (TOPO>90%) and dispersing into n-octane, stirring and heating to 120℃, adding n-hexane after complete dissolution to obtain a 0.04 mol / L Pb-TOPO stock solution; the mass ratio of PbBr2 to tri-n-octylphosphine oxide is 1:5; the volume of n-octane is 5 L / mol, and the volume of n-hexane is 20 L / mol.

[0017] Further, the Ni-TOPO stock solution is prepared by dispersing NiBr2 and tri-n-octylphosphine oxide (TOPO) into n-octane, and then adding n-hexane; the mass ratio of NiBr2 to tri-n-octylphosphine oxide is 1:5; the volume of n-octane is 10 L / mol, and the volume of n-hexane is 40 L / mol.

[0018] Further, the Cs-DOPA stock solution is prepared by mixing Cs2CO3 and DOPA, heating to 120℃, then adding n-octane, and finally diluting with n-hexane to obtain a 0.01 mol / L Cs-DOPA stock solution; the volume of DOPA is 10 mL / g of Cs2CO3, the volume of n-octane is 20 mL / g of Cs2CO3, and the volume of n-hexane is 270 mL / g of Cs2CO3.

[0019] Further, the TOPO stock solution is prepared by dissolving TOPO in n-hexane to obtain a 0.2 mol / L TOPO stock solution; the volume of n-hexane is 5 L / mol.

[0020] Further, the lecithin stock solution: weigh lecithin and dissolve it in n-hexane to obtain a 50 mg / mL lecithin stock solution; the volume of n-hexane is 20 mL / g based on the mass of lecithin; all stock solutions are filtered through a 0.45 μm filter membrane before use.

[0021] The application also provides a use of the nickel ion-doped perovskite nanocrystal in detecting the moisture content of edible oil, which comprises adding the nickel ion-doped perovskite nanocrystal solution into the edible oil to be detected, standing at room temperature for 5-20 min (preferably 10 min), detecting the characteristic absorption value (preferably 516 nm) of the fluorescence spectrum in the range of 400-700 nm, and obtaining the moisture content in the edible oil to be detected according to the moisture standard curve; the moisture standard curve is obtained by taking the moisture mass concentration of edible oil as the abscissa, and taking the ratio of the difference between the fluorescence characteristic absorption value after adding the perovskite nanocrystal into the edible oil containing water and the fluorescence characteristic absorption value after adding the perovskite nanocrystal into the edible oil not containing water to the fluorescence characteristic absorption value after adding the perovskite nanocrystal into the edible oil not containing water as the ordinate.

[0022] Further, the solvent of the nickel ion-doped perovskite nanocrystal solution comprises ethyl acetate, cyclohexane or n-hexane, and ethyl acetate is preferred.

[0023] Further, the concentration of the nickel ion-doped perovskite nanocrystal solution is 1 mg / mL, and the volume ratio of the solution to the edible oil to be detected is 1:0.1-1, preferably 1:0.22.

[0024] Further, the moisture standard curve is obtained by mixing edible oil with different moisture mass contents and the nickel ion-doped perovskite nanocrystal solution, standing at room temperature for 10 min, detecting the fluorescence characteristic absorption value (preferably 516 nm) in the range of 400-700 nm, taking the edible oil not containing moisture as the control group, taking the fluorescence characteristic absorption as I0, taking (I0-I) / I0 as the ordinate, and taking the moisture mass concentration as the abscissa to draw the standard curve; the solvent of the nickel ion-doped perovskite nanocrystal solution is ethyl acetate, the concentration is 1 mg / mL, and the volume ratio of the solution to the edible oil to be detected is 1:0.1-1, preferably 1:0.22.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] The application provides a perovskite nanocrystal doped with nickel ions, which is uniform in nanometer size, has enhanced fluorescence signal and is more stable in structure; the perovskite nanocrystal doped with nickel ions can be dispersed by using ethyl acetate as a solvent, and is used for detecting the moisture content in edible oil, so that the problem of using toxic liquid such as toluene as a solvent in the prior art is solved, and the safety is improved. In addition, the detection method is rapid (can be completed within 10 min), sensitive, accurate, and the detection limit is as low as 0.006% (v / v). (V)DETAILED DESCRIPTION

[0027] Figure 1 CsPb (1-x) Ni x The fluorescence spectrum of CsPb

[0028] Figure 2 CsPb 0.95 Ni 0.05 The high-resolution transmission electron micrograph of CsPb

[0029] Figure 3 CsPb 0.95 Ni 0.05 The XPS spectrum of CsPb

[0030] Figure 4 The fluorescence spectrum (A) and the fitted moisture quantitative standard curve (B) of CsPb 0.95 Ni 0.05 Br3 NCs in edible oil with a moisture content of 0-0.5%. (V)DETAILED DESCRIPTION

[0031] The application will be further described below in combination with specific embodiments, but the protection scope of the application is not limited to this:

[0032] Preparation of reagents used in the embodiments of the application:

[0033] (1) Pb-TOPO stock solution: 0.1 mol of PbBr2 and 0.5 mol of trioctylphosphine oxide (TOPO > 90%) are weighed and mixed and dispersed into 0.5 L of n-octane, and then stirred and heated to 120 DEG C; after dissolution, 2 L of n-hexane is used for dilution to obtain a Pb-TOPO stock solution of 0.04 mol / L.

[0034] (2) Ni-TOPO stock solution: 0.05 mol of NiBr2 and 0.25 mol of TOPO were weighed into 0.5 L of n-octane, heated to 120 °C with stirring until completely dissolved, and then diluted with 2 L of n-hexane to obtain a Ni-TOPO stock solution of 0.02 mol / L.

[0035] (3) Cs-DOPA stock solution: 10 g of Cs2CO3 and 100 mL of DOPA were mixed and heated to 120 °C, then 200 mL of n-octane was added, and finally 2.7 L of n-hexane was added to dilute it to obtain a Cs-DOPA stock solution of 3.33 g / L (0.01 mol / L).

[0036] (4) TOPO stock solution: 0.4 mol of TOPO was dissolved in 2 L of n-hexane to obtain a TOPO stock solution (0.2 mol / L).

[0037] (5) Egg phospholipid stock solution: 10 g of egg phospholipid was dissolved in 200 mL of n-hexane to obtain an egg phospholipid stock solution of 50 mg / mL. All stock solutions were filtered through a 0.45 μm filter before use.

[0038] The room temperature of the present application refers to 25-30 °C.

[0039] Example 1-5: CsPb (1-x) Preparation of NixBr3 NCs

[0040] (1) CsPbBr3 NCs: 8 mL of Pb-TOPO stock solution and 24 mL of TOPO stock solution were mixed with 0.6 L of n-hexane, and 4 mL of Cs-DOPA stock solution was injected while stirring at 1500 rpm. After incubation at room temperature for 5 min, 4 mL of egg phospholipid stock solution was added, and after stirring for 30 s, 1.8 L of anti-solvent acetone was added. Finally, centrifugation was performed at 8000 rpm for 5 min, and the precipitate was dried at room temperature under ventilation to obtain 1.5 g of CsPbBr3 NCs as a control group.

[0041] (2) CsPbBr3 NCs: (1-x) NixBr3 NCs:

[0042] 7.6 mL of Pb-TOPO stock solution and 0.8 mL of Ni-TOPO stock solution were mixed with 24 mL of TOPO stock solution and 0.6 L of n-hexane, and 4 mL of Cs-DOPA stock solution was injected while stirring at 1500 rpm. After incubation at room temperature for 5 min, 4 mL of egg phospholipid stock solution was added, and after stirring for 30 s, 1.8 L of anti-solvent acetone was added. Finally, centrifugation was performed at 8000 rpm for 5 min, and the precipitate was dried at room temperature under ventilation to obtain 1.5 g of CsP 0.95 Ni0.05 Br3 NCs.

[0043] By adjusting the adding ratio of Pb-TOPO stock solution and Ni-TOPO stock solution (as shown in Table 1), other substance adding amount in relation to the total amount of Pb+Ni substance, the CsPb Figure 1 Br3 NCs were prepared. (1-x) NixBr3 NCs (x = 0-0.23), respectively, were CsPb 0.93 Ni 0.07 Br3 NCs, CsPb 0.91 Ni 0.09 Br3 NCs, CsPb 0.88 Ni 0.12 Br3 NCs, CsPb 0.77 Ni 0.23 Br3 NCs.

[0044] The fluorescence spectrum of 400-700 nm after 365 nm laser excitation was determined using a multifunctional enzyme marker (Synergy H1, Bioteck, USA), and the results are shown in Figure 2 and Table 1. Figure 1 The results show that the doping of nickel ions basically does not change the characteristic fluorescence wavelength (516 nm) of CsPbBr3 NCs, but significantly improves the fluorescence intensity of CsPbBr3 NCs, thereby improving the sensitivity and detection limit of the method for detecting moisture. When the doping amount of Ni ions increases from 0 to 0.12, the fluorescence intensity of CsPb (1-x) Ni x The excitation fluorescence wavelength of CsPbBr3 NCs increases from 70180 a.u. to 71095-88952 a.u. When 5% of Pb ions are replaced by Ni ions, the fluorescence of the quantum dots is the strongest, which is 88952 a.u. However, when 23% of Pb ions are replaced by Ni ions, the fluorescence of the nanocrystals decreases.

[0045] The microstructure (i.e. particle size) and surface lattice structure (i.e. lattice stripe distance) of CsPbBr3 NCs were determined using a high-resolution transmission electron microscope (Tecnai G2 F30 STWIN, Netherlands). 0.95 Ni 0.05 The results are shown in Figure 3 and Table 2. Figure 2 The results show that the CsPbBr3 NCs have a uniform crystalline distribution on the surface, with a particle size of about 8.7±0.14 nm and a lattice stripe distance of about 0.26 nm. 0.95 Ni 0.05 The results show that the CsPbBr3 NCs have a uniform crystalline distribution on the surface, with a particle size of about 8.7±0.14 nm and a lattice stripe distance of about 0.26 nm.

[0046] CsP was measured using X-ray photoelectron spectroscopy (XPS, AXIS Ultra DLD, Kratos, Japan) at 1000–0 eV, 745–715 eV, 150–130 eV, and 80–60 eV. 0.95 Ni 0.05 Br3 NCs( Figure 3 (A), Cs 3d ( Figure 3 (B), Pb 4f( Figure 3 (C) and Br 3d( Figure 3 The broad spectrum of CsP (in D) indicates that CsP 0.95 Ni 0.05 Five significant characteristic peaks appeared in Br3NCs, namely Cs 3d, O 1s, C 1s, Pb 4f, and Br 3d peaks.

[0047] Table 1 Nickel ion doped CSPb (1-x) Ni x Stock solution ratio and fluorescence intensity of Br3 NCs

[0048]

[0049] Example 6: Solvent-CsP 0.95 Ni 0.05 Effect of Br3 NCs fluorescence intensity

[0050] A suitable solvent should have good solubility for oils and fats, while also allowing for the uniform distribution of polar nanocrystals to effectively promote contact and reaction between the nanocrystals and water. Furthermore, the fluorescence intensity of the dispersed nanocrystals should not decrease to ensure the sensitivity of fluorescence signal monitoring.

[0051] 1 mg of CsPb prepared in Example 1 was used. 0.95 Ni 0.5 Br3 NCs were dispersed in 1 mL of solvents (toluene, chloroform, n-hexane, cyclohexane, ethyl acetate, ethanol, acetone) at a concentration of 1 mg / mL. The fluorescence spectra of 400-700 nm were detected using the method in Example 1, and the characteristic fluorescence absorption and intensity in each solvent were obtained, as shown in Table 2.

[0052] Table 2, CsP 0.95 Ni 0.05 Fluorescence intensity of Br3 NCs in different solvents

[0053]

[0054] The data in Table 2 shows that the fluorescence of the perovskite nanocrystals doped with nickel in the commonly used toluene, cyclohexane, n-hexane, ethyl acetate dispersion solvents is stable, and the intensity is relatively high, between 60549-71474 a.u. The highest is ethyl acetate, followed by n-hexane, but ethanol, acetone and the like are not good. Considering the high toxicity of traditional dispersion solvents toluene and chloroform, it is surprising that the fluorescence intensity of perovskite nanocrystals doped with nickel in ethyl acetate is the highest (71474 a.u.), combined with its low toxicity safety (relative to toluene, chloroform and the like strong carcinogenicity) and balanced solubility to oil and water, and therefore it is the most ideal dispersion and reaction solvent.

[0055] Example 7, CsPb 0.95 Ni 0.5 Construction of standard curve for detecting moisture in oil by CsPb

[0056] 0.22 mL of soybean oil with moisture content of 0-0.5% (0, 0.0125, 0.025, 0.075, 0.1, 0.125, 0.15, 0.175, 0.2, 0.3, 0.5%) were respectively taken, and 1 mg / mL CsPb 0.95 Ni 0.05 Br3 NCs ethyl acetate solution 1 mL was added, fully mixed, and placed at room temperature for 10 min, and the fluorescence absorption spectrum of the product between 400-700 nm after 365 nm laser excitation was detected by the method of Example 1. Figure 4 A), and the characteristic fluorescence absorption value at 516 nm was recorded, denoted as I, and the fluorescence absorption of the control group (moisture content of 0) was recorded as I0. Taking the moisture content as the independent variable X and (I0-I) / I0 as the dependent variable Y, a quantitative standard curve Y=kx+B was fitted and constructed, and k=2.63, the intercept B was -0.013, and R 2 =0.991 Figure 4 B), the detection limit LOD=3SD / k was 0.006%, showing good linear relationship and low detection limit (60 ppm).

[0057] Example 8, CsPb 0.95 Ni 0.5 Detection of moisture content in different edible oils by CsPb

[0058] Commercially available camellia oil, olive oil, flaxseed oil, coconut oil, hazelnut oil, sesame oil, gardenia oil, and Japanese nutmeg oil were selected as the samples to be tested. 0.22 mL of the sample to be tested was taken, and 1 mg / mL CsPb 0.95 Ni 0.05Br3 NCs ethyl acetate solution 1 mL, fully mixed, room temperature for 10 min, the product was detected by the method of Example 1 after 365 nm laser excitation, the fluorescence absorption spectrum between 400-700 nm was recorded, the characteristic fluorescence absorption value I of 516 nm was recorded, and the fluorescence absorption of the control group (soybean oil with water content of 0) was recorded as I0, according to the standard curve of Example 7, the water content in the sample was obtained, and the results are shown in Table 3.

[0059] At the same time, the standard Karl Fischer method was used for comparison, and the relative deviation of the detection results was calculated, and the results are shown in Table 3.

[0060] Table 3 CsPb 0.95 Ni 0.05 Br3 NCs method for determining water content of different edible oils

[0061]

[0062] Table 3 shows that the CsPb 0.95 Ni 0.05 Br3 NCs is suitable for water detection of various edible oils, and the error compared with the gold standard Karl Fischer method is between 2-6%, and the average error is 5.18%, which reflects the high accuracy, sensitivity and low detection limit of the new method, especially the simple and rapid method, which saves the chemical reagent solvent of high toxicity pyridine, chloroform and toluene, and the result is intuitive, especially suitable for on-site rapid detection.

Claims

1. A method for preparing nickel-doped perovskite nanocrystals, characterized in that, The chemical formula of the perovskite nanocrystals is CsPb. (1-x) Ni x Br3,x represents the molar ratio of nickel ions to lead ions, x = 0.05-0.23; The perovskite nanocrystals were prepared according to the following steps: Pb-TOPO reserve solution was mixed with Ni-TOPO reserve solution, TOPO reserve solution and n-hexane, and Cs-DOPA reserve solution was injected simultaneously under vigorous stirring at 1000-2000 rpm. After incubation at room temperature for 1-10 min, lecithin reserve solution was added, and after stirring for 20-50 seconds, acetone was added. Finally, the mixture was centrifuged and the precipitate was collected to obtain nickel-doped perovskite nanocrystals. The Pb-TOPO stock solution is prepared from PbBr2, trioctylphosphine oxide, n-octane, and n-hexane; the molar ratio of PbBr2 to trioctylphosphine oxide is 1:2-8; the volume of n-octane used is 2-8 L / mol based on the amount of PbBr2, and the volume of n-hexane used is 10-30 L / mol based on the amount of PbBr2. The Ni-TOPO stock solution is prepared from NiBr2, trioctylphosphine oxide, n-octane, and n-hexane; the molar ratio of NiBr2 to trioctylphosphine oxide is 1:2-8; the volume of n-octane used is 5-15 L / mol based on the amount of NiBr2, and the volume of n-hexane used is 20-50 L / mol based on the amount of NiBr2. The Cs-DOPA stock solution is prepared from Cs₂CO₃, 3-[2s-3,6-dioxoperazin-2-yl]propionic acid, n-octane, and n-hexane; the volume of 3-[2s-3,6-dioxoperazin-2-yl]propionic acid is 5-15 mL / g based on the mass of Cs₂CO₃; the volume of n-octane is 10-30 mL / g based on the mass of Cs₂CO₃; and the volume of n-hexane is 200-300 mL / g based on the mass of Cs₂CO₃. The TOPO stock solution is prepared from trioctylphosphine oxide and n-hexane; the volume of n-hexane used is 2-8 L / mol based on the molar amount of trioctylphosphine oxide. The lecithin stock solution is prepared from lecithin and n-hexane; the volume of n-hexane used is 10-30 mL / g based on the mass of lecithin.

2. The preparation method according to claim 1, characterized in that, The amount of Pb-TOPO stock solution used is based on the amount of Pb, the amount of Ni-TOPO stock solution used is based on the amount of Ni, the amount of Cs-DOPA stock solution used is based on the amount of Cs, the amount of TOPO stock solution used is based on the amount of TOPO, and the amount of lecithin stock solution used is based on the mass of lecithin. The molar ratio of Pb to Ni is 0.95:0.05-0.77:0.23; the molar ratio of Pb to Cs is 1:0.01-0.5; the molar ratio of Pb to TOPO is 1:1-20; the amount of lecithin used is 0.1-1 g / mmol based on the amount of Pb; the volume of n-hexane used is 1-5 L / mmol based on the amount of Pb; and the volume of acetone used is 1-10 L / mmol based on the amount of Pb.

3. The preparation method according to claim 1, characterized in that, The Pb-TOPO stock solution is prepared by mixing and dispersing PbBr2 and trioctylphosphine oxide in n-octane, stirring and heating to 120°C until completely dissolved, and then diluting with n-hexane to obtain a 0.04 mol / L Pb-TOPO stock solution. The molar ratio of PbBr2 to trioctylphosphine oxide is 1:

5. The volume of n-octane used is 5 L / mol based on the amount of PbBr2, and the volume of n-hexane used is 20 L / mol based on the amount of PbBr2. The Ni-TOPO stock solution is prepared by dispersing NiBr2 and trioctylphosphine oxide in n-octane and then adding n-hexane; the molar ratio of NiBr2 to trioctylphosphine oxide is 1:5; the volume of n-octane used is 10 L / mol based on the amount of NiBr2, and the volume of n-hexane used is 40 L / mol based on the amount of NiBr2. The Cs-DOPA stock solution is prepared by mixing Cs₂CO₃ and 3-[2s-3,6-dioxadiazin-2-yl]propionic acid and heating to 120°C, then adding n-octane and mixing, and finally diluting with n-hexane to obtain a 0.01 mol / L Cs-DOPA stock solution; the volume of 3-[2s-3,6-dioxadiazin-2-yl]propionic acid used is 10 mL / g based on the mass of Cs₂CO₃; the volume of n-octane used is 20 mL / g based on the mass of Cs₂CO₃; and the volume of n-hexane used is 270 mL / g based on the mass of Cs₂CO₃. The TOPO stock solution: Weigh out a 0.2 mol / L TOPO stock solution obtained by dissolving trioctylphosphine oxide in n-hexane; The volume of n-hexane used is 5 L / mol based on the amount of trioctylphosphine oxide. The lecithin stock solution: Lecithin was weighed and dissolved in n-hexane to obtain a lecithin stock solution of 50 mg / mL; the volume of n-hexane used was 20 mL / g based on the mass of lecithin. All stock solutions were filtered through a 0.45 μm filter membrane before use.

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