Nanocomposite films based on layer-by-layer assembly of quantum dots and their applications

Abstract

The present invention relates to a nanocomposite film based on layer-by-layer quantum dot assembly and its applications, belonging to the technical field of nanofilm materials. Quantum dot materials are used as the main material, and an in-situ ligand exchange method is used to assemble the quantum dots layer by layer on a conductive substrate to obtain a multilayered, ordered nanocomposite film. Compared to other assembly methods, the in-situ ligand exchange method allows for precise control of size, shape, and composition, and can effectively improve the stability and mobility of the quantum dots.

Description

Technical Field

[0001] The invention relates to a nanocomposite film based on layer-by-layer assembly of quantum dots and application thereof, belonging to the technical field of nano film materials. Summary of the Invention

[0002] To address the common issues of chemical instability and low carrier transport efficiency in nanomaterials, this application uses quantum dots as the primary material and employs an in-situ ligand exchange method to assemble the dots layer by layer onto a conductive glass substrate, resulting in a multilayered, ordered nanocomposite film. Compared to other assembly methods, the in-situ ligand exchange method allows for precise control of size, shape, and composition, and effectively improves the stability and mobility of the quantum dots.

[0003] The technical solution of this application is as follows:

[0004] A nanocomposite film based on layer-by-layer assembly of quantum dots, wherein the preparation method of the nanocomposite film comprises the following steps:

[0005] (1) Preparation of the first layer of quantum dot deposition film: Add aqueous quantum dots and NaCl solution, and let it stand for deposition. This method can obtain a single-layer quantum dot deposition film with a certain coverage. Then soak it in ligand solution. According to the cyclic voltammetry test, after the vacant sites on the substrate are saturated, remove the substrate;

[0006] (2) Preparation of the second layer of quantum dot deposition film: using oil-soluble quantum dots wrapped with oleic acid ligands to perform in-situ replacement with the ligands of the first layer of quantum dots in step (1); determining the replacement time based on cyclic voltammetry testing, and removing the substrate;

[0007] The oil-soluble quantum dots are prepared by dissolving the oil-phase quantum dots in chloroform and adding dimethyl sulfoxide in a volume ratio of 1:1 to prepare a mixed solution;

[0008] (3) Preparation of the Nth layer of quantum dot deposition film: Repeat step (2) to prepare the third layer of quantum dot deposition film; repeat in sequence to obtain a multi-layer quantum dot deposition film.

[0009] Preferably, the quantum dots are CdS quantum dots, CdSe quantum dots or PbS quantum dots.

[0010] Preferably, the ligand solution in step (1) is: 3-MPA solution, DMSA solution or DMPS solution; and / or, in order to facilitate the subsequent cyclic voltammetry test, conductive glass is used as the substrate, with the conductive layer of the conductive glass facing upward.

[0011] Preferably, after removing the substrate in step (1), the substrate is slowly rinsed with methanol to rinse away free ligands on the surface; and / or, in step (2), the substrate is removed and excess ligands are slowly rinsed with methanol; and / or, the amount of chloroform used in step (2) is such that the first absorption peak is between 0.5±0.05 according to the optical path length of the colorimetric cell used in the test being 5 mm.

[0012] Preferably, the method for preparing oil-phase CdS quantum dots in step (2) comprises the following steps:

[0013] a. Sulfur dioxide and cadmium oxide shall be calculated according to Cd 2+ After mixing 3:S=3:1, oleic acid and octadecene were added and stirred under nitrogen atmosphere for reaction;

[0014] b. Dilute with n-hexane and centrifuge at a ratio of chloroform: n-hexane: methanol = 1:2:7. Take the precipitate and dissolve it in n-hexane. Add methanol to form layers. Add chloroform until the layers disappear and the solution turns yellow. Centrifuge and take the precipitate. Allow the precipitate to air dry naturally. Finally, add chloroform to dissolve it. Centrifuge again and take the upper liquid to obtain the oil-phase CdS quantum dots.

[0015] Furthermore, the method for preparing aqueous CdS quantum dots in step (1) comprises the following steps:

[0016] S1. Dissolve 2,3-dimercaptosuccinic acid sodium salt, 2,3-dimercaptopropanesulfonic acid sodium salt or 3-mercaptopropionic acid in dimethyl sulfoxide, add an appropriate amount of triethylamine to make the white turbid liquid clear; add oil-phase CdS quantum dots dissolved in chloroform solution, shake and perform ligand exchange;

[0017] S2. Add ethyl acetate to the ligand exchange solution of step S1, and centrifuge to obtain a precipitate; repeat the process to fully exchange the oil phase CdS quantum dots to obtain the water phase CdS quantum dots.

[0018] Preferably, the stirring reaction conditions in step a are: rapidly heating to 100±5°C under a nitrogen environment and stirring to dissolve, then heating to 210±10°C at a rate of 8±1°C / min, and maintaining the reaction temperature for 0.5-2 h. After the reaction is completed, naturally cooling to room temperature.

[0019] Preferably, the DMSA solution needs to be prepared and used immediately.

[0020] Preferably, the DMSA solution is prepared by dissolving sodium 2,3-dimercaptosuccinate in dimethyl sulfoxide, and then adding triethylamine to make the white turbid liquid clear.

[0021] Another object of the present invention is to protect the application of the above-mentioned nanocomposite film in photocatalytic degradation of dyes.

[0022] Furthermore, the dye is methylene blue, methyl green or acid fuchsin.

[0023] Beneficial effects of the present invention

[0024] (1) Based on the ligands of the first layer of quantum dots, this application prefers to use oil-phase quantum dots in the second layer of quantum dots for experiments, because the ligands of the first layer of quantum dots can easily replace the oleic acid ligands, thereby "grasping" the CdS quantum dots; the operating instruments used are more common and cheaper;

[0025] (2) It can be produced in large quantities during the preparation process; at the same time, it can realize the preparation of multilayer films according to needs and be applied to different application fields;

[0026] (3) Compared with other preparation methods, it more effectively improves the defects of quantum dot materials themselves. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the process in which the surface of the conductive glass is completely covered;

[0028] Figure 2 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the first layer of CdS quantum dots assembled in Example 1;

[0029] Figure 3 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the second layer of CdS quantum dots assembled in Example 1;

[0030] Figure 4 is the catalytic efficiency of different quantum dots with different layers for methylene blue in Example 1;

[0031] Figure 5 This is a bar graph showing the catalytic degradation rate of methylene blue by quantum dots with different layers in Example 1;

[0032] Figure 6 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the first layer of CdS quantum dots assembled in Example 2;

[0033] Figure 7 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the second layer assembly of CdS quantum dots in Example 2;

[0034] Figure 8 is the catalytic efficiency of different quantum dots for methyl green in Example 2;

[0035] Figure 9 This is a bar graph of the catalytic degradation rate of methyl green by CdS quantum dots with different numbers of layers in Example 2;

[0036] Figure 10 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the first layer of CdS quantum dots assembled in Example 3;

[0037] Figure 11 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the second layer assembly of CdS quantum dots in Example 3;

[0038] Figure 12 is the catalytic efficiency of different quantum dots for methyl green in Example 3;

[0039] Figure 13 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the first layer of CdSe quantum dots assembled in Example 4;

[0040] Figure 14 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the second layer assembly of CdSe quantum dots in Example 4;

[0041] Figure 15 is the catalytic efficiency of CdSe quantum dots with different layers for methyl green in Example 4;

[0042] Figure 16 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the first layer of PdS quantum dots assembled in Example 5;

[0043] Figure 17 The specific situation of the change of the cyclic voltammetry oxidation peak position over time of the second layer assembly of PdS quantum dots in Example 5;

[0044] Figure 18 The catalytic efficiency of PdS quantum dots with different numbers of layers for acid fuchsin in Example 5. DETAILED DESCRIPTION

[0045] The following further describes the preparation method of a nanocomposite film based on layer-by-layer assembly of quantum dots on a conductive glass substrate of the present invention with reference to the examples. All raw materials used were purchased from a reagent company and were of analytical grade or higher.

[0046] Reagents: nitrogen, cadmium oxide, sublimed sulfur, dimethyl sulfoxide, chloroform, n-hexane, triethylamine, oleylamine, oleic acid, acetone, methanol, potassium ferrocyanide, potassium ferrocyanide, potassium chloride, meso-2,3-dimercaptosuccinic acid sodium salt, 3-mercaptopropionic acid, 2,3-dimercaptopropanesulfonic acid sodium salt;

[0047] Main instruments: UV-2550 UV-visible spectrophotometer, ZW-3 multifunctional UV analyzer, LK2005 electrochemical workstation;

[0048] Solution configuration:

[0049] (1) K3[Fe(CN)6] / K4[Fe(CN)6] solution (containing 0.1 mol / L KCl solution), 0.1 mol / L NaCl solution, and a concentration of 8×10 -3 g / L methylene blue solution

[0050] (2) Preparation of ligand solution: Weigh 80 mg of ligand reagent (2,3-dimercaptosuccinic acid sodium salt (DMSA), 3-mercaptopropionic acid (3-MPA) or 2,3-dimercaptopropanesulfonic acid sodium salt (DMPS)) using an electronic balance, dissolve in 2 ml of dimethyl sulfoxide (DMSO), and then add an appropriate amount of triethylamine (TEA) to adjust the pH so that the white turbid liquid becomes clear. The solution should be prepared and used immediately to avoid deterioration due to long-term storage.

[0051] Example 1

[0052] Preparation of oil-phase CdS quantum dots:

[0053] a. Use an electronic balance to weigh 0.160 g of sulfur dioxide (S) and 1.920 g of cadmium oxide (CdO) and put them into a three-necked flask. 2+ :S=3:1, use a pipette to transfer 15 ml of oleic acid (OA) and 60 ml of octadecene (ODE), quickly heat to 95 °C under nitrogen environment and stir to dissolve, then heat to 200 °C at a rate of 7 °C / min and maintain the reaction temperature for 2 h. After the reaction is completed, naturally cool to room temperature.

[0054] b. Dissolve 1 ml of sample in 5 ml of n-hexane and centrifuge in a ratio of chloroform:n-hexane:methanol = 1:2:7. Collect the precipitate and dissolve it in 1 ml of a solution. Add 2 ml of methanol to separate the layers. Add an appropriate amount of chloroform until the layers disappear and the solution turns yellow. Centrifuge and collect the precipitate. Allow the precipitate to air dry, add 4 ml of chloroform, centrifuge again, and collect the supernatant. This will yield oil-phase CdS quantum dots for UV spectroscopy.

[0055] Preparation of aqueous CdS quantum dots:

[0056] S1 ligand exchange solution configuration:

[0057] Using an electronic balance, weigh 40 mg of the ligand reagent (DMSA) and dissolve it in 2 ml of dimethyl sulfoxide (DMSO). Add an appropriate amount of triethylamine (TEA) to adjust the pH until the turbid white liquid becomes clear. Add 3.5 ml of the CdS chloroform solution and shake for 5 minutes to fully exchange the ligand.

[0058] S2 synthesis of aqueous quantum dots:

[0059] Add 3.5 ml of ethyl acetate to the ligand exchange solution and centrifuge to obtain a precipitate. Repeat this process twice to fully exchange the oil-phase CdS quantum dots to obtain the aqueous phase quantum dots. Finally, dissolve the precipitate in 25 mmol / L NaCl buffer. For UV testing, dilute the solution until the peak of the first absorption peak is between 0.3 and 0.4 (using a 5 mm pathlength cell).

[0060] A method for preparing a nanocomposite film based on layer-by-layer assembly of quantum dots comprises the following steps:

[0061] (1) Using the above-mentioned aqueous phase CdS quantum dots, oil phase CdS quantum dots and related solutions;

[0062] (2) The first layer of CdS quantum dot coating

[0063] Place the pre-treated conductive glass in a clean glass dish. Use a multimeter to test the conductive surface of the glass, with the conductive side facing up. Add a mixture of 1 ml of aqueous CdS quantum dots and 1 ml of NaCl solution. Let it sit for 1 hour to allow the CdS quantum dots to adhere to the surface of the conductive glass. A monolayer of quantum dots will form on the glass surface. Then, soak the glass in DMSA solution to fully fill the undeposited quantum dot surfaces with DMSA ligand molecules. Perform rapid cyclic voltammetry tests at different soaking times to determine the optimal time for monolayer formation. Figure 1 This is a schematic diagram of the glass surface being completely covered by CdS quantum dots and DMSA molecules; it can be seen that it is a gradual covering process.

[0064] Take the standing time periods of 5, 10, 15, 20, and 25 min respectively, use clean tweezers to take out the conductive glass soaked in the DMSA solution for 5 minutes, and then gently rinse the conductive surface of the glass with distilled water 1-2 times to ensure that the excess ligands that are not bound by van der Waals forces are washed away. Then, after drying with a nitrogen flow, use 1 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6] solution as the electrolyte solution for cyclic voltammetry test, and read the peak potential of the highest peak of the cyclic voltammetry. According to the above steps, while trying to keep the area of ​​the conductive glass immersed in the solution consistent each time, read the peak potential of the highest peak position of the cyclic voltammetry for 10, 15, 20, and 25 minutes in turn. Plot the peak potential value against the standing time, as shown in Figure 2. Figure 2As shown in the figure, it can be seen that because the initial quantum dot deposition was insufficient to cover the entire conductive glass, the glass had a high number of vacant sites. The figure shows that the slope of the curve for the first 15 minutes is steep, and the peak shifts to the right at a rapid rate, indicating that DMSA fills the vacancies more quickly when there are more vacancies. However, during the 15-20 minute period, the curve becomes noticeably flatter, with a decreasing slope and a significantly lower rightward shift of the peak. This indicates that the DMSA filling rate is decreasing during this period, indicating that the vacancy sites on the glass are nearing saturation. Furthermore, during the 20-25 minute period, the curve becomes nearly parallel to the X-axis, and the peak no longer shifts to the right. This indicates that at approximately 20 minutes, the conductive glass can be considered completely covered with CdS quantum dots and DMSA. This time can be recorded as the DMSA deposition time T2.

[0065] (3) Second layer of CdS quantum dots

[0066] Based on the above experiment, the ligands of the first layer of quantum dots and the exposed glass surface are both DMSA. Therefore, the second layer of quantum dots should use oil-soluble quantum dots wrapped with oleic acid ligands to replace the DMSA ligands of the first layer of quantum dots in situ, and "grab" the CdS quantum dots through the coordination groups. This is also the experimental theoretical basis for laying the second layer of quantum dots.

[0067] The same rapid cyclic voltammetry method was used to determine the optimal time for complete exchange of the second layer of quantum dots. The standing time periods were 2, 4, 6, 8, and 10 min respectively. Use tweezers to pick up the conductive glass that has been standing in the DMSA solution for 20 min, and slowly rinse it with methanol 1-2 times to ensure that the free DMSA on its surface is completely rinsed off, and then transfer it to a mixed solution of oil-phase CdS quantum dots (dissolved in chloroform, the amount of chloroform used is based on the optical path of the colorimetric cell used in the test is 5 mm, so that the first absorption peak is between 0.45) and DMSO in a volume ratio of 1:1. Let it stand for a certain period of time, then take it out with tongs, and measure the peak potential corresponding to the highest peak current of the cyclic voltammetry. Plot the peak potential value against the standing time, as shown in the figure. Figure 3 As shown in the figure, the peak position changes in the voltammogram curves of the conductive glass after being in the oil-phase quantum dots and DMSO for 2, 4, 6, 8, and 10 minutes, with the first layer fully covered with quantum dots and DMSA. The figure shows that after a complete second layer of quantum dots is applied, the peak position changes by a total of 40 mV (from 312 to 360). Of this, the change in the first 6 minutes reaches 28 mV (from 312 to 356), accounting for 91% of the total change. Complete coverage is achieved after another 4 minutes. From these data, it is easy to conclude that 10 minutes is the ligand exchange time for the second layer of quantum dots, i.e., the second coating time.

[0068] (4) Exploration of the optimal number of layers for photodegradation efficiency

[0069] According to the above experimental conclusions, we can carry out experimental exploration of laying multiple layers of CdS quantum dots on conductive glass. First, complete the coating work of the first and second layers of quantum dots. Then, according to the principle of the second layer, lay 3, 4, and 5 layers of quantum dots on the glass surface in turn. Place the conductive glass with 1, 2, 3, 4, and 5 layers of quantum dots, a blank glass without quantum dots, and a control group with only methylene blue into 7 glass dishes, and use a pipette to transfer 5 ml of methylene blue solution into each. Place it under a UV analyzer and irradiate it with UV light for 40 minutes. The color of the methylene blue solution of the conductive glass with quantum dots becomes significantly lighter, indicating that the quantum dots have considerable photocatalytic ability. The seven groups of methylene blue samples are then measured for UV spectra, and it is seen Figure 4 .

[0070] Depend on Figure 4 According to the degradation rate formula:

[0071]

[0072] The following table is obtained:

[0073] Table 1 Degradation rate of methylene blue by quantum dots with different number of layers

[0074]

[0075] Figure 5 The catalytic degradation rate of methylene blue by different number of quantum dots is shown in Table 1. Figure 5 It can be concluded that the catalytic efficiency reaches a maximum of 41.5% at the third layer, so it can be concluded that the third layer is the optimal number of coating layers for CdS quantum dots.

[0076] Example 2

[0077] Preparation of oil-phase CdS quantum dots:

[0078] a. Use an electronic balance to weigh 0.160 g of sulfur dioxide (S) and 1.920 g of cadmium oxide (CdO) and put them into a three-necked flask. 2+ :S=3:1, use a pipette to transfer 15 ml of oleic acid (OA) and 60 ml of octadecene (ODE), quickly heat to 100 °C under nitrogen environment, stir and dissolve, then heat to 210 °C at a rate of 8 °C / min, and maintain the reaction temperature for 1 hour. After the reaction is completed, naturally cool to room temperature.

[0079] b. Dissolve 1 ml of sample in 5 ml of n-hexane and centrifuge in a ratio of chloroform:n-hexane:methanol = 1:2:7. Collect the precipitate and dissolve it in 1 ml of a solution. Add 2 ml of methanol to separate the layers. Add an appropriate amount of chloroform until the layers disappear and the solution turns yellow. Centrifuge and collect the precipitate. Allow the precipitate to air dry, add 4 ml of chloroform, centrifuge again, and collect the supernatant. This will yield oil-phase CdS quantum dots for UV spectroscopy.

[0080] Preparation of aqueous CdS quantum dots:

[0081] S1 ligand exchange solution configuration:

[0082] Weigh 40 mg of the ligand reagent (3-MPA) using an electronic balance and dissolve it in 2 ml of dimethyl sulfoxide (DMSO). Add an appropriate amount of triethylamine (TEA) to adjust the pH until the turbid white liquid becomes clear. Add 3.5 ml of CdS chloroform solution and shake for 5 minutes to fully exchange the ligand.

[0083] S2 synthesis of aqueous quantum dots:

[0084] Add 3.5 ml of ethyl acetate to the ligand exchange solution and centrifuge to obtain a precipitate. Repeat this process twice to fully exchange the oil-phase CdS quantum dots to obtain the aqueous phase quantum dots. Finally, dissolve the precipitate in 25 mmol / L NaCl buffer. For UV testing, dilute the solution until the peak of the first absorption peak is between 0.3 and 0.4.

[0085] A method for preparing a nanocomposite film based on layer-by-layer assembly of quantum dots comprises the following steps:

[0086] (1) Using the above-mentioned aqueous phase CdS quantum dots, oil phase CdS quantum dots and related solutions;

[0087] (2) The first layer of CdS quantum dot coating

[0088] Place the pre-treated conductive glass in a clean glass dish. Use a multimeter to test the conductive surface of the glass, with the conductive side facing upward. Add 1 ml of aqueous CdS quantum dots and 1 ml of NaCl solution. Let it sit for 1 hour to allow the CdS quantum dots to adhere to the conductive glass surface. A monolayer of quantum dots will form on the glass surface. Then, soak the glass in 3-MPA solution to ensure that the undeposited quantum dots are fully filled with 3-MPA ligand molecules. Perform rapid cyclic voltammetry tests at different soaking times to determine the optimal time for monolayer formation.

[0089] Take the standing time periods of 5, 10, 15, 20, 25, 30, and 35 min respectively, use clean tweezers to take out the conductive glass immersed in 3-MPA solution for 5 min, and then gently rinse the conductive surface of the glass with distilled water 1-2 times to ensure that the excess ligands that are not bound by van der Waals forces are washed away. Then, after drying with a nitrogen flow, use 1 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6] solution as the electrolyte solution for cyclic voltammetry test, and read the peak potential of the highest peak of the cyclic voltammetry. According to the above steps, while trying to keep the area of ​​the conductive glass immersed in the solution consistent each time, read the peak potential of the highest peak position of the cyclic voltammetry for 10, 15, 20, 25, 30, and 35 minutes in turn. Plot the peak potential value against the standing time, as shown in Figure 2. Figure 10 As shown in the figure, it can be seen that because the initial quantum dot deposition was insufficient to cover the entire conductive glass, there were many vacant sites on the glass. The slope of the curve for the first 25 minutes is steep, and the peak shifts rightward at a rapid rate, indicating that with a high number of vacancies, 3-MPA fills them quickly. During the 25-30 minute period, the curve becomes noticeably flatter, with a decreasing slope and a significantly lesser rightward shift in the peak. This indicates that the 3-MPA filling rate is decreasing during this period, indicating that the vacancy sites on the glass sheet are nearing saturation. Furthermore, during the 30-35 minute period, the curve becomes nearly parallel to the X-axis, and the peak no longer shifts rightward. This indicates that at approximately 30 minutes, the conductive glass can be considered completely covered with CdS quantum dots and 3-MPA. This time can be denoted as the 3-MPA deposition time, T2.

[0090] (3) Second layer of CdS quantum dots

[0091] Based on the above experiments, the ligand of the first layer of quantum dots is 3-MPA, so the second layer of quantum dots should be carried out using oil-phase quantum dots, because 3-MPA can easily replace oleic acid ligands, thereby "grasping" CdS quantum dots. This is also the experimental theoretical basis for laying the second layer of quantum dots.

[0092] The same rapid cyclic voltammetry method was used to determine the optimal time for complete exchange of the second layer of quantum dots. The standing time periods were 2, 4, 6, 8, 10, 12, and 14 min respectively. Use tweezers to pick out the conductive glass that has been standing in the 3-MPA solution for 20 min, slowly rinse it with methanol 1-2 times to ensure that the free 3-MPA on its surface is completely rinsed, and transfer it to a mixed solution of oil-phase CdS quantum dots (dissolved in chloroform, the amount of chloroform is based on the optical path of the colorimetric cell used in the test is 5 mm, so that the first absorption peak is between 0.5±0.05) and DMSO in a volume ratio of 1:1. Let it stand for a certain period of time, then take it out with tongs, and measure the highest peak voltage value of the cyclic voltammetry. The results are organized as follows. Figure 11 As shown in the figure, the peak position changes in the voltammogram curves of the conductive glass after being exposed to oil-phase quantum dots and DMSO for 2, 4, 6, 8, 10, 12, and 14 minutes, with the first layer fully covered with quantum dots and 3-MPA. The figure shows that after a complete second layer of quantum dots is applied, the total peak position change is 48 mV (from 288 to 336). The change in the first 10 minutes reaches 46 mV (from 288 to 334), accounting for 95% of the total change. Complete coverage is achieved after another 4 minutes. From these data, it is easy to conclude that 14 minutes is the ligand exchange time for the second layer of quantum dots, i.e., the second coating time.

[0093] (4) Exploration of the optimal number of layers for photodegradation efficiency

[0094] According to the above experimental conclusions, we can carry out experimental exploration of laying multiple layers of CdS quantum dots on conductive glass. First, complete the coating work of the first layer of quantum dots. Then, according to the principle of the second layer, lay 3, 4, and 5 layers of quantum dots on the glass surface in turn. Place the conductive glass with 1, 2, 3, 4, and 5 layers of quantum dots, a blank glass without quantum dots, and a control group with only methyl green into 7 glass dishes, and use a pipette to transfer 5 ml of methyl green solution into each. Place it under a UV analyzer and irradiate it with UV light for 40 minutes. The color of the methyl green solution of the conductive glass with quantum dots becomes significantly lighter, indicating that the quantum dots have considerable photocatalytic ability. The UV spectra of the seven groups of methyl green samples are then measured, as shown Figure 12 .

[0095] Depend on Figure 12 , according to the degradation rate formula:

[0096]

[0097] The following table is obtained:

[0098] Table 3 Degradation rate of methyl green by quantum dots with different number of layers

[0099]

[0100] Table 3 shows that the catalytic efficiency reaches a maximum of 46.57% at the third layer. Therefore, it can be concluded that the third layer is the optimal number of coating layers for CdS quantum dots.

[0101] Example 3:

[0102] Preparation of oil-phase CdS quantum dots:

[0103] a. Use an electronic balance to weigh 0.160 g of sulfur dioxide (S) and 1.920 g of cadmium oxide (CdO) and put them into a three-necked flask. 2+:S=3:1, use a pipette to transfer 15 ml of oleic acid (OA) and 60 ml of octadecene (ODE), quickly heat to 105 ℃ under nitrogen environment, stir and dissolve, then heat to 220 ℃ at a rate of 9 ℃ / min, and maintain the reaction temperature for 0.5h. After the reaction is completed, naturally cool to room temperature.

[0104] b. Dissolve 1 ml of sample in 5 ml of n-hexane and centrifuge in a ratio of chloroform:n-hexane:methanol = 1:2:7. Collect the precipitate and dissolve it in 1 ml of a solution. Add 2 ml of methanol to separate the layers. Add an appropriate amount of chloroform until the layers disappear and the solution turns yellow. Centrifuge and collect the precipitate. Allow the precipitate to air dry, add 4 ml of chloroform, centrifuge again, and collect the supernatant. This will yield oil-phase CdS quantum dots for UV spectroscopy.

[0105] Preparation of aqueous CdS quantum dots:

[0106] S1 ligand exchange solution configuration:

[0107] Using an electronic balance, weigh 40 mg of the ligand reagent (DMPS) and dissolve it in 2 ml of dimethyl sulfoxide (DMSO). Add an appropriate amount of triethylamine (TEA) to adjust the pH until the turbid white liquid becomes clear. Add 3.5 ml of the CdS chloroform solution and shake for 5 minutes to fully exchange the ligand.

[0108] S2 synthesis of aqueous quantum dots:

[0109] Add 3.5 ml of ethyl acetate to the ligand exchange solution and centrifuge to obtain a precipitate. Repeat this process twice to fully exchange the oil-phase CdS quantum dots to obtain the aqueous phase quantum dots. Finally, dissolve the precipitate in 25 mmol / L NaCl buffer. For UV testing, dilute the solution until the peak of the first absorption peak is between 0.3 and 0.4.

[0110] A method for preparing a nanocomposite film based on layer-by-layer assembly of CdS quantum dots comprises the following steps:

[0111] (1) Using the above-mentioned aqueous phase CdS quantum dots, oil phase CdS quantum dots and related solutions

[0112] (2) The first layer of CdS quantum dot coating

[0113] Place a piece of conductive glass in a clean glass dish. Use a multimeter to test the conductive surface of the glass, with the conductive side facing upward. Add 1 ml of aqueous CdS quantum dots and 1 ml of NaCl solution. Let it sit for 1 hour to allow the CdS quantum dots to adhere to the surface of the conductive glass. A monolayer of quantum dots will form on the surface of the glass. Then soak the glass in DMPS solution to fully fill the undeposited quantum dot surface with DMPS ligand molecules. Perform rapid cyclic voltammetry tests at different soaking times to determine the optimal time for monolayer formation.

[0114] Take the standing time periods of 5, 10, 15, 20, 25, and 30 min respectively, use clean tweezers to take out the conductive glass immersed in the DMPS solution for 5 min, and then gently rinse the conductive surface of the glass with distilled water 1-2 times to ensure that the excess ligands that are not bound by van der Waals forces are washed away. Then, after drying with a nitrogen flow, use 1 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6] solution as the electrolyte solution for cyclic voltammetry test, and read the peak potential of the highest peak of the cyclic voltammetry. According to the above steps, while trying to keep the area of ​​the conductive glass immersed in the solution consistent each time, read the peak potential of the highest peak position of the cyclic voltammetry for 10, 15, 20, 25, and 30 minutes in turn. Plot the peak potential value against the standing time, as shown in Figure 2. Figure 13 As shown in the figure, it can be seen that because the initial quantum dot deposition was insufficient to cover the entire conductive glass, the glass had a high number of vacant sites. The figure shows that the slope of the curve for the first 20 minutes is steep, and the peak shifts to the right at a rapid rate, indicating that DMPS fills the vacancies more quickly when there are more vacancies. However, during the 20-25 minute period, the curve becomes noticeably flatter, the slope decreases, and the rightward shift of the peak decreases significantly. This indicates that the DMPS filling rate is decreasing during this period, indicating that the vacancy sites on the glass sheet are nearing saturation. Furthermore, during the 25-30 minute period, the curve becomes nearly parallel to the X-axis, and the peak no longer shifts to the right. This indicates that at approximately 25 minutes, the conductive glass can be considered completely covered with CdS quantum dots and DMPS. This time can be recorded as the DMPS deposition time T2.

[0115] (3) Second layer of CdS quantum dots

[0116] Based on the above experiment, at this time, the ligand of the first layer of quantum dots is DMPS, so the second layer of quantum dots should be carried out using oil-phase quantum dots, because DMPS can also easily replace oleic acid ligands, thereby "grabbing" CdS quantum dots. This is also the experimental theoretical basis for laying the second layer of quantum dots.

[0117] The same rapid cyclic voltammetry method was used to determine the optimal time for complete exchange of the second layer of quantum dots. The standing time periods were 2, 4, 6, 8, 10, and 12 minutes respectively. Use tweezers to pick up the conductive glass that has been standing in DMPS for 25 minutes, slowly rinse it with methanol 1-2 times to ensure that the free DMPS on its surface is completely rinsed, and transfer it to a mixed solution of oil-phase CdS quantum dots (dissolved in chloroform) and DMSO with a volume ratio of 1:1. Let it stand for a certain period of time, then take it out with tongs and measure the highest peak voltage value of the cyclic voltammetry. The results are organized as follows Figure 14 As shown in the figure, the peak position changes in the voltammogram curves of the conductive glass after being exposed to oil-phase quantum dots and DMSO for 2, 4, 6, 8, 10, and 12 minutes, with the first layer fully covered with quantum dots and DMPS. The figure shows that after a complete second layer of quantum dots is applied, the total peak position change is 49 mV (from 289 to 338). The change in the first 8 minutes reaches 44 mV (from 289 to 333), accounting for 90% of the total change. Complete coverage is achieved after another 4 minutes. From these data, it is easy to conclude that 12 minutes is the ligand exchange time for the second layer of quantum dots, i.e., the second coating time.

[0118] (4) Exploration of the optimal number of layers for photodegradation efficiency

[0119] According to the above experimental conclusions, we can carry out experimental exploration of laying multiple layers of CdS quantum dots on conductive glass. First, complete the coating work of the first layer of quantum dots. Then, according to the principle of the second layer, lay 3, 4, and 5 layers of quantum dots on the glass surface in turn. Place the conductive glass with 1, 2, 3, 4, and 5 layers of quantum dots, a blank glass without quantum dots, and a control group with only methyl green into 7 glass dishes, and use a pipette to transfer 5 ml of methyl green solution into each. Place it under a UV analyzer and irradiate it with UV light for 40 minutes. The color of the methyl green solution of the conductive glass with quantum dots becomes significantly lighter, indicating that the quantum dots have considerable photocatalytic ability. The UV spectra of the seven groups of methyl green samples are then measured, as shown Figure 12 .

[0120] Depend on Figure 12 , according to the degradation rate formula:

[0121]

[0122] The following table is obtained:

[0123] Table 3 Degradation rate of methyl green by quantum dots with different number of layers

[0124]

[0125] Table 3 shows that the catalytic efficiency reaches a maximum of 47.36% at the third layer. Therefore, it can be concluded that the third layer is the optimal number of coating layers for CdS quantum dots.

[0126] Example 4

[0127] Preparation of oil-phase CdSe quantum dots:

[0128] a. To three-necked flask A, add 20 mmol of CdO powder, 9.6 mL of oleic acid, and 40 mL of liquid paraffin. Subsequently, add 1 mmol of selenium powder to three-necked flask B, which contains 50 mL of liquid paraffin. Before heating the mixtures in both flasks, flasks A and B are filled with nitrogen for 20 minutes. The solution in flask A is heated to approximately 150°C, and the reddish-brown CdO powder rapidly dissolves, forming a clear, pale yellow solution. When the solution in flask B is heated to approximately 170°C, the selenium powder begins to dissolve. As the temperature of flask B rises to 240°C, 5 mL of solution A and 2.5 mL of oleylamine are rapidly added to flask B while stirring vigorously. The resulting solution instantly turns orange-yellow. Stable CdSe quantum dots are synthesized by heating at 240°C for 20 minutes.

[0129] b. Dissolve 1 ml of sample in 5 ml of n-hexane and centrifuge in a ratio of chloroform:n-hexane:methanol = 1:2:7. Collect the precipitate and dissolve it in 1 ml of a solution. Add 2 ml of methanol to separate the layers. Add an appropriate amount of chloroform until the layers disappear and the solution turns yellow. Centrifuge and collect the precipitate. Allow the precipitate to air dry, add 4 ml of chloroform, centrifuge again, and collect the supernatant. This will yield oil-phase CdSe quantum dots for UV spectroscopy.

[0130] Preparation of aqueous CdSe quantum dots:

[0131] S1 ligand exchange solution configuration:

[0132] Using an electronic balance, weigh 40 mg of the ligand reagent (DMSA) and dissolve it in 2 ml of dimethyl sulfoxide (DMSO). Add an appropriate amount of triethylamine (TEA) to adjust the pH until the turbid white liquid becomes clear. Add 3.5 ml of the CdSe chloroform solution and shake for 5 minutes to fully exchange the ligand.

[0133] S2 synthesis of aqueous quantum dots:

[0134] Add 3.5 ml of ethyl acetate to the ligand exchange solution and centrifuge to obtain a precipitate. Repeat this process twice to fully exchange the oil-phase CdSe quantum dots to obtain the aqueous phase quantum dots. Finally, dissolve the precipitate in 25 mmol / L NaCl buffer. For UV testing, dilute the solution until the peak of the first absorption peak is between 0.3 and 0.4.

[0135] A method for preparing a nanocomposite film based on layer-by-layer assembly of quantum dots comprises the following steps:

[0136] (1) Using the above-mentioned aqueous CdSe quantum dots, oil-phase CdSe quantum dots and related solutions

[0137] (2) The first layer of CdSe quantum dot coating

[0138] Place the treated conductive glass in a clean glass dish. Use a multimeter to test the conductive surface of the glass, with the conductive side facing upward. Add 1 ml of aqueous CdSe quantum dots and 1 ml of NaCl solution. Let it sit for 1 hour to allow the CdSe quantum dots to adhere to the surface of the conductive glass. Since the quantum dots may not adhere to the entire surface, soak it in DMSA solution again to ensure that the glass surface is fully filled. Perform rapid cyclic voltammetry at different soaking times to determine the optimal time.

[0139] Take the standing time periods of 5, 10, 15, 20, and 25 min respectively, use clean tweezers to take out the conductive glass soaked in DMSA solution for 5 minutes, and then gently rinse the conductive surface of the glass with distilled water 1-2 times to ensure that the excess ligands that are not bound by van der Waals forces are washed away. Then, after drying with a nitrogen flow, use 1 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6] solution as the electrolyte solution for cyclic voltammetry test, and read the peak potential of the highest peak of the cyclic voltammetry. According to the above steps, while trying to keep the area of ​​the conductive glass immersed in the solution consistent each time, read the peak potential of the highest peak position of the cyclic voltammetry for 10, 15, 20, and 25 min in turn. Plot the peak potential value against the standing time, as shown in Figure 2. Figure 13 As shown, because the initial quantum dot deposition was insufficient to cover the entire conductive glass, the glass exhibited a high number of vacant sites. The graph shows that the slope of the curve for the first 15 minutes is steep, and the peak shifts to the right at a rapid rate, indicating that DMPS fills these vacancies more quickly when there are more vacancies. However, during the 15-20 minute period, the curve flattens significantly, with a decreasing slope and a significantly lower rightward shift of the peak. This indicates that the DMSA filling rate is decreasing during this period, indicating that the vacant sites on the glass sheet are nearing saturation. Furthermore, during the 20-25 minute period, the curve becomes nearly parallel to the X-axis, and the peak no longer shifts to the right. This indicates that at approximately 20 minutes, the conductive glass can be considered completely covered with CdSe quantum dots and DMSA. This time can be recorded as the DMSA deposition time, T2.

[0140] (3) Second layer of CdSe quantum dots

[0141] Based on the above experiment, at this time, the ligand of the first layer of quantum dots is DMSA, so the second layer of quantum dots should be carried out using oil-phase quantum dots, because DMSA can also easily replace oleic acid ligands, thereby "grabbing" CdSe quantum dots. This is also the experimental theoretical basis for laying the second layer of quantum dots.

[0142] The same rapid cyclic voltammetry method was used to determine the optimal time for complete exchange of the second layer of quantum dots. The standing time periods were 2, 4, 6, 8, and 10 minutes respectively. Use tweezers to pick up the conductive glass that has been standing in DMSA for 20 minutes, slowly rinse it with methanol 1-2 times to ensure that the free DMPS on its surface is completely rinsed, and transfer it to a mixed solution of oil-phase CdSe quantum dots (dissolved in chloroform) and DMSO with a volume ratio of 1:1. Let it stand for a certain period of time, then take it out with tongs and measure the highest peak voltage value of the cyclic voltammetry. The results are organized as follows Figure 14 As shown in the figure, the peak position changes in the voltammogram curves of the conductive glass after 2, 4, 6, 8, and 10 minutes of incubation in the oil-phase quantum dots and DMSO, with the first layer fully covered with quantum dots and DMSA. The figure shows that after a complete second layer of quantum dots is applied, the total peak position change is 44 mV (from 298 to 342). The change in the first 6 minutes reaches 28 mV (from 298 to 338), accounting for 95% of the total change. Complete coverage is achieved after another 4 minutes. From these data, it is easy to conclude that 10 minutes is the ligand exchange time for the second layer of quantum dots, i.e., the second coating time.

[0143] (4) Exploration of the optimal number of layers for photodegradation efficiency

[0144] According to the above experimental conclusions, we can carry out experimental exploration of laying multiple layers of CdSe quantum dots on conductive glass. First, complete the coating work of the first layer of quantum dots. Then, according to the principle of the second layer, lay 3, 4, and 5 layers of quantum dots on the glass surface in turn. Place the conductive glass with 1, 2, 3, 4, and 5 layers of quantum dots, a blank glass without quantum dots, and a control group with only methyl green into 7 glass dishes, and use a pipette to transfer 5 ml of methylene blue solution into each. Place it under a UV analyzer and irradiate it with UV light for 40 minutes. The color of the methyl green solution of the conductive glass with quantum dots becomes significantly lighter, indicating that the quantum dots have considerable photocatalytic ability. The UV spectra of the seven groups of methyl green samples are then measured, and it is seen Figure 15 .

[0145] Depend on Figure 15 , according to the degradation rate formula:

[0146]

[0147] The following table is obtained:

[0148] Table 4 Degradation rate of methyl green by different number of quantum dots

[0149]

[0150] Table 4 shows that the catalytic efficiency reaches a maximum of 48.41% at the third layer. Therefore, it can be concluded that the third layer is the optimal number of coating layers for CdSe quantum dots.

[0151] Example 5:

[0152] Preparation of oil-phase PdS quantum dots:

[0153] a. Add 15 ml of oleylamine and 4.9852 g of PdCl₂ powder to three-necked flask A. Pre-bubble nitrogen for 5 minutes, then maintain at 60°C with stirring for 2.5 hours to prepare a PbCl₂ solution. Under nitrogen, add 4.4 ml of oleylamine and 0.0241 g of sublimed sulfur to three-necked flask B. Rapidly heat to 120°C with stirring for 20 minutes, then cool to 60°C. Evacuate flask A for 5 minutes. Milky bubbles appear during evacuation. Evacuate at 80°C for 5 minutes, 90°C for 5 minutes, and 110°C for 5 minutes without noticeable bubbles. Once the temperature stabilizes at 120°C and the solution remains under vacuum, quickly inject the entire solution from flask B. After five minutes, remove the vacuum and allow the solution to grow for 10 minutes. After the sulfur solution is injected, the color gradually deepens, eventually turning dark gray, with a slight white upper layer. Then, 20 mL of frozen n-hexane was injected into the PbS solution, and the flask was placed in an ice-water bath and cooled to 20-30°C to obtain a crude solution of PbS quantum dots. Subsequently, 200% oleic acid was added to the crude solution of PbS quantum dots to disperse the solution and centrifuge it. The lower layer of precipitate was fully dissolved in n-hexane and centrifuged. The upper layer of black liquid was the oily PbS quantum dots.

[0154] b. Dissolve 1 ml of sample in 5 ml of n-hexane and centrifuge in a ratio of chloroform:n-hexane:methanol = 1:2:7. Collect the precipitate and dissolve it in 1 ml of a solution. Add 2 ml of methanol to separate the layers. Add an appropriate amount of chloroform until the layers disappear and the solution turns yellow. Centrifuge and collect the precipitate. Allow the precipitate to air dry, add 4 ml of chloroform, centrifuge again, and collect the supernatant. This will yield the oil-phase PdS quantum dots for UV spectroscopy.

[0155] Preparation of aqueous PdS quantum dots:

[0156] S1 ligand exchange solution configuration:

[0157] Using an electronic balance, weigh 40 mg of the ligand reagent (DMSA) and dissolve it in 2 ml of dimethyl sulfoxide (DMSO). Add an appropriate amount of triethylamine (TEA) to adjust the pH until the turbid white liquid becomes clear. Add 3.5 ml of the PdS chloroform solution and shake for 5 minutes to fully exchange the ligand.

[0158] S2 synthesis of aqueous quantum dots:

[0159] Add 3.5 ml of ethyl acetate to the ligand exchange solution and centrifuge to obtain a precipitate. Repeat this process twice to fully exchange the oil-phase PdS quantum dots to obtain the aqueous phase quantum dots. Finally, dissolve the precipitate in 25 mmol / L NaCl buffer. For UV testing, dilute the solution until the peak of the first absorption peak is between 0.3 and 0.4.

[0160] A method for preparing a nanocomposite film based on layer-by-layer assembly of quantum dots comprises the following steps:

[0161] (1) Using the above-mentioned aqueous phase PdS quantum dots, oil phase PdS quantum dots and related solutions

[0162] (2) The first layer of PdS quantum dot coating

[0163] Place a piece of conductive glass in a clean glass dish. Use a multimeter to test the conductive surface of the glass, with the conductive side facing upward. Add 1 ml of aqueous PdS quantum dots and 1 ml of NaCl solution. Let it sit for 1 hour to allow the PdS quantum dots to adhere to the glass surface. A monolayer of quantum dots will form on the glass surface. Then soak the glass in DMSA solution to fully fill the undeposited quantum dot surface with DMSA ligand molecules. Perform rapid cyclic voltammetry tests at different soaking times to determine the optimal time for monolayer formation.

[0164] Take the standing time periods of 5, 10, 15, 20, and 25 min respectively, use clean tweezers to take out the conductive glass soaked in DMSA solution for 5 minutes, and then gently rinse the conductive surface of the glass with distilled water 1-2 times to ensure that the excess ligands that are not bound by van der Waals forces are washed away. Then, after drying with a nitrogen flow, use 1 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6] solution as the electrolyte solution for cyclic voltammetry test, and read the peak potential of the highest peak of the cyclic voltammetry. According to the above steps, while trying to keep the area of ​​the conductive glass immersed in the solution consistent each time, read the peak potential of the highest peak position of the cyclic voltammetry for 10, 15, 20, and 25 min in turn. Use the peak potential value to plot the standing time. Figure 16Because the initial quantum dot deposition is insufficient to cover the entire conductive glass, the glass is prone to numerous vacancies. The figure shows that the slope of the curve for the first 15 minutes is steep, and the peak potential shifts significantly to the right. This indicates that with more vacancies, DMSA fills them more quickly. During the 15-20 minute period, the curve becomes noticeably flatter, with a decreasing slope and a significantly less rightward shift in the peak position. This indicates that the DMSA filling rate is decreasing during this period, indicating that the vacancies on the glass are nearing saturation. Furthermore, during the 20-25 minute period, the curve becomes nearly parallel to the X-axis, and the peak position no longer shifts to the right. This indicates that at approximately 20 minutes, the conductive glass can be considered completely covered with PbS quantum dots and DMSA. This time can be recorded as the DMSA deposition time, T2.

[0165] (3) Second layer of PbS quantum dots

[0166] Based on the above experiments, the ligands of the first layer of quantum dots and the exposed glass surface are both DMSA ligands. Therefore, the second layer of quantum dots should use oil-soluble quantum dots wrapped with oleic acid ligands to replace the DMSA ligands of the first layer of quantum dots in situ, and "grab" the PbS quantum dots through the coordination groups. This is also the experimental theoretical basis for laying the second layer of quantum dots.

[0167] The same rapid cyclic voltammetry method was used to determine the optimal time for complete exchange of the second layer of quantum dots. The standing time periods were 2, 4, 6, 8, and 10 min respectively. Use tweezers to pick up the conductive glass that has been standing in the DMSA solution for 20 min, slowly rinse it with methanol 1-2 times to ensure that the free DMSA on its surface is completely rinsed, and transfer it to a mixed solution of oil-phase PbS quantum dots (dissolved in chloroform, the amount of chloroform is based on the optical path of the colorimetric cell used in the test is 5 mm, so that the first absorption peak is between 0.5±0.05) and DMSO in a volume ratio of 1:1. Let it stand for a certain period of time, then take it out with tongs, and measure the highest peak voltage value of the cyclic voltammetry. The results are organized as follows. Figure 17 As shown in the figure, the peak position changes in the voltammogram curves of the conductive glass after being placed in the oil-phase quantum dots and DMSO for 2, 4, 6, 8, and 10 minutes, with the first layer fully covered with quantum dots and DMSA. The figure shows that after a complete second layer of quantum dots is applied, the total peak position change is 31 mV (from 316 to 347). Of this, the change in the first 6 minutes reaches 28 mV (from 316 to 344), accounting for 90% of the total change. Complete coverage is achieved after 4 minutes. From these data, it is easy to conclude that 10 minutes is the ligand exchange time for the second layer of quantum dots, i.e., the time it takes for the second film to assemble.

[0168] (4) Exploration of the optimal number of layers for photodegradation efficiency

[0169] According to the above experimental conclusions, we can carry out experimental exploration of laying multiple layers of PdS quantum dots on conductive glass. First, complete the coating work of the first layer of quantum dots. Then, according to the principle of the second layer, lay 3, 4, and 5 layers of quantum dots on the glass surface in turn. Place the conductive glass with 1, 2, 3, 4, and 5 layers of quantum dots, a blank glass without quantum dots, and a control group with only fuchsin into 7 glass dishes, and use a pipette to transfer 5 ml of acid fuchsin solution into each. Place it under a UV analyzer and irradiate it with UV light for 40 minutes. The color of the acid fuchsin solution of the conductive glass with quantum dots becomes significantly lighter, indicating that the quantum dots have considerable photocatalytic ability. The seven groups of acid fuchsin samples are then measured for UV spectra, as shown below. Figure 18 .

[0170] Depend on Figure 18 , according to the degradation rate formula:

[0171]

[0172] The following table is obtained:

[0173] Table 5 Degradation rate of methyl green by different number of quantum dots

[0174]

[0175] Table 5 shows that the catalytic efficiency reaches a maximum of 48.9% at the third layer. Therefore, it can be concluded that the third layer is the optimal number of coating layers for PdS quantum dots.

Claims

1. A nanocomposite film based on layer-by-layer assembly of quantum dots, characterized in that: The method for preparing the nanocomposite film comprises the following steps: (1) Preparation of the first layer of quantum dot deposition film: Add aqueous quantum dots and NaCl solution, and let it stand for deposition. This method can obtain a single-layer quantum dot deposition film with a certain coverage. Then soak it in ligand solution. According to the cyclic voltammetry test, after the vacant sites on the substrate are saturated, remove the substrate; (2) Preparation of the second layer of quantum dot deposition film: using oil-soluble quantum dots wrapped with oleic acid ligands to perform in-situ replacement with the ligands of the first layer of quantum dots in step (1); determining the replacement time based on cyclic voltammetry testing, and removing the substrate; The oil-soluble quantum dots are prepared by dissolving the oil-phase quantum dots in chloroform and adding dimethyl sulfoxide in a volume ratio of 1:1 to prepare a mixed solution; (3) Preparation of the Nth quantum dot deposition film: Repeat step (2) to prepare the third quantum dot deposition film; repeat in sequence to obtain a multi-layer quantum dot deposition film; The ligand solution is: 3-MPA solution, DMSA solution or DMPS solution; and / or, in order to facilitate the subsequent cyclic voltammetry test, a conductive glass is used as the substrate, with the conductive layer of the conductive glass facing upward; The quantum dots are CdS quantum dots, CdSe quantum dots or PbS quantum dots; The method for preparing aqueous CdS quantum dots described in step (1) comprises the following steps: S1. Dissolve 2,3-dimercaptosuccinic acid sodium salt, 2,3-dimercaptopropanesulfonic acid sodium salt or 3-mercaptopropionic acid in dimethyl sulfoxide, add an appropriate amount of triethylamine to make the white turbid liquid clear; add oil-phase CdS quantum dots dissolved in chloroform solution, shake and perform ligand exchange; S2. Add ethyl acetate to the ligand exchange solution of step S1, and centrifuge to obtain a precipitate; repeat the process to fully exchange the oil phase CdS quantum dots to obtain the aqueous phase CdS quantum dots; The method for preparing oil-phase CdS quantum dots in step (2) comprises the following steps: a. Sulfur dioxide and cadmium oxide shall be calculated according to Cd 2+ After mixing 3:S=3:1, oleic acid and octadecene were added and stirred under nitrogen atmosphere for reaction; b. Dilute with n-hexane and centrifuge at a ratio of chloroform: n-hexane: methanol = 1:2:

7. Take the precipitate and dissolve it in n-hexane. Add methanol to form layers. Add chloroform until the layers disappear and the solution turns yellow. Centrifuge and take the precipitate. Allow the precipitate to air dry naturally. Finally, add chloroform to dissolve it. Centrifuge again and take the upper liquid to obtain the oil-phase CdS quantum dots.

2. The nanocomposite film according to claim 1, characterized in that In step (1), after removing the substrate, the substrate is slowly rinsed with methanol to rinse away the free ligands on the surface; and / or, in step (2), the substrate is removed and the excess ligands are slowly rinsed with methanol; and / or, the amount of chloroform used in step (2) is such that the first absorption peak is between 0.5±0.05 when the optical path of the colorimetric cell used in the test is 5 mm.

3. The nanocomposite film according to claim 1, characterized in that The stirring reaction conditions in step a are as follows: rapidly heating to 100±5°C under a nitrogen environment and stirring to dissolve, then heating to 210±10°C at a rate of 8±1°C / min, and maintaining the reaction temperature for 0.5-2 h. After the reaction is completed, naturally cooling to room temperature.

4. The nanocomposite film according to claim 1, characterized in that The DMSA solution needs to be prepared and used immediately.

5. The nanocomposite film according to claim 4, characterized in that The preparation method of DMSA solution is as follows: dissolve 2,3-dimercaptosuccinic acid sodium salt in dimethyl sulfoxide, and then add triethylamine to make the white turbid liquid become clear.

6. Use of the nanocomposite film according to claim 1 in photocatalytic degradation of dyes.

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