Preparation method and application of multi-layer core-shell structure titanium dioxide-quantum dot-silica composite material

Abstract

This application belongs to the field of nanocomposite materials technology, specifically disclosing a method for preparing and applying a multilayer core-shell structured titanium dioxide-quantum dot-silica composite material. The preparation method includes: obtaining mercapto-modified titanium dioxide; dispersing mercapto-modified titanium dioxide and oleic acid ligand-coated quantum dots in a first organic solvent to obtain a first dispersion; mixing a silane coupling agent solution with terminal mercapto groups and an organic alkaline catalyst solution with the first dispersion to form a quantum dot-titanium dioxide composite; dispersing the quantum dot-titanium dioxide composite in a second organic solvent to obtain a second dispersion; mixing a silicate ester solution and a self-assembling monolayer forming agent solution with the second dispersion to obtain a mixed solution; adding an organic alkaline catalyst solution to the mixed solution to adjust it to a weakly alkaline state to obtain a multilayer core-shell structured composite material. This application solves the problems of weak bonding, easy detachment of quantum dots, and poor stability in traditional quantum dot composite materials.

Description

Technical Field

[0001] This application belongs to the field of nanocomposite materials technology, and more specifically, relates to a method for preparing and applying a multilayer core-shell structured titanium dioxide-quantum dot-silica composite material. Background Technology

[0002] Quantum dots (QDs), such as cadmium selenide (CdSe) quantum dots, have attracted widespread attention due to their excellent optical properties (such as size-tunable fluorescence emission, high quantum yield, and broad absorption spectrum). However, quantum dots themselves suffer from poor stability (easily photobleached and oxidized) and easy detachment of surface ligands, which limits their practical applications.

[0003] Titanium dioxide (TiO2) is an important wide-bandgap semiconductor material with excellent photocatalytic activity and electron transport capabilities. Combining quantum dots with titanium dioxide can construct highly efficient quantum dot-sensitized solar cells (QDSSCs) or photocatalyst systems. However, current common methods of directly combining quantum dots with titanium dioxide suffer from problems such as weak binding force, easy quantum dot detachment, and severe interfacial charge recombination.

[0004] Silica (SiO2) is chemically inert, highly stable, biocompatible, and has a tunable mesoporous structure, and is often used as a coating layer to protect the core material.

[0005] Currently, although a large number of studies are dedicated to the preparation of quantum dot-titanium dioxide or quantum dot-silica composite materials, how to construct a multi-layered core-shell structure that is structurally stable, has a high quantum dot loading rate, and can effectively protect quantum dots from environmental damage remains a technical challenge in this field. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this application is to provide a method for preparing and applying a multi-layer core-shell structured titanium dioxide-quantum dot-silica composite material, which aims to solve the technical problems of weak bonding force, easy detachment of quantum dots and poor stability of existing quantum dot composite materials.

[0007] To achieve the above objectives, in a first aspect, this application provides a method for preparing a multilayer core-shell structured titanium dioxide-quantum dot-silica composite material, comprising the following steps: Step S100: Obtain mercaptolated titanium dioxide; Step S200: The thiolized titanium dioxide and oleic acid ligand-coated quantum dots are dispersed in a first organic solvent to obtain a first dispersion; and a silane coupling agent solution with thiol groups at the end and an organic alkaline catalyst solution are mixed with the first dispersion to allow the quantum dots to adsorb onto the surface of titanium dioxide, forming a quantum dot-titanium dioxide composite. Step S300: The quantum dot-titanium dioxide composite is dispersed in a second organic solvent to obtain a second dispersion; the silicate ester solution, the self-assembled monolayer (SAM) forming agent solution are mixed with the second dispersion to obtain a mixture; an organic alkaline catalyst solution is added to the mixture to adjust it to a weakly alkaline state, so that the silicate ester is hydrolyzed and condensed on the surface of the quantum dot-titanium dioxide composite to form a silicon dioxide layer, thereby obtaining a multilayer core-shell structure composite material composed of titanium dioxide-quantum dot-silica.

[0008] As a further preferred option, the self-assembled monolayer forming agent is 6-mercapto-1-hexanol (6-MCH).

[0009] As a further preferred embodiment, the quantum dot is a II-VI or IV-VI group semiconductor quantum dot, preferably at least one of CdSe, CdS, CdTe, PbS, and ZnSe quantum dots.

[0010] As a further preferred embodiment, the first organic solvent is toluene; and / or the second organic solvent is ethanol.

[0011] As a further preferred embodiment, the silane coupling agent with a terminal thiol group is γ-mercaptopropyltrimethoxysilane.

[0012] As a further preferred embodiment, the organic basic catalyst is tetramethylammonium hydroxide; and / or the silicate ester is tetraethyl orthosilicate. As a further preferred embodiment, step S100 specifically includes: Titanium dioxide nanoparticles were dispersed in a third organic solvent to obtain a third dispersion, and the third dispersion was adjusted to acidity. A silane coupling agent solution with thiol groups at the end was mixed with the acidic third dispersion to obtain thiolized titanium dioxide.

[0013] As a further preferred embodiment, in step S200, the mass ratio of mercaptolated titanium dioxide to oleic acid ligand-coated quantum dots ranges from 5:1 to 10:1.

[0014] As a further preferred embodiment, in step S300, the volume ratio of the silicate ester solution to the second dispersion is in the range of 0.5:10 to 1:10. And / or the volume ratio of the silicate solution to the self-assembling monolayer forming agent solution is in the range of 10:1 to 5:1.

[0015] Secondly, this application provides a multi-layered core-shell structured titanium dioxide-quantum dot-silica composite material, which is prepared using the preparation method described in the first aspect.

[0016] Thirdly, this application provides an application of the multilayer core-shell structured titanium dioxide-quantum dot-silica composite material described in the second aspect above in optoelectronic devices, photocatalytic materials, or biofluorescent markers.

[0017] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages: This application provides a method for preparing and applying a multi-layered core-shell structured titanium dioxide-quantum dot-silica composite material. The material employs a three-layer structure of "core-QDs-shell," with the titanium dioxide core acting as an electron acceptor and framework, the quantum dot middle layer as a photoactive material, and the silica shell as a physical and chemical barrier. These three elements work synergistically to achieve functional integration. Modification of TiO2 using the silane coupling agent MPTMS introduces terminal thiol groups (-SH), forming a strong binding force with metal elements such as Cd in the QDs. This binding force is stronger and more stable than traditional physical or electrostatic adsorption methods, effectively preventing the quantum dots from detaching during use.

[0018] This application provides a method for preparing and applying a multi-layered core-shell structured titanium dioxide-quantum dot-silica composite material. The method involves bonding silica to the surface of quantum dots using 6-MCH. The addition of 6-MCH strengthens the bonding force between silica and the quantum dot surface, resulting in a denser outermost silica layer. This dense outermost silica shell effectively isolates the internal quantum dots from environmental factors such as water and oxygen, significantly improving the photostability and chemical stability of the quantum dots and extending the material's lifespan.

[0019] This application provides a method for preparing and applying a multilayer core-shell structured titanium dioxide-quantum dot-silica composite material. The entire preparation process is carried out at room temperature, under mild conditions, with low energy consumption, simple operation, and easy to scale up production. This method is applicable to quantum dots of different types and sizes (such as CdS, PbS, ZnSe, etc.) and titanium dioxide particles of different sizes, demonstrating excellent versatility. Attached Figure Description

[0020] Figure 1 This is a flowchart of the preparation method of the multilayer core-shell structured titanium dioxide-quantum dot-silica composite material provided in the embodiments of this application; Figure 2This is a schematic diagram of the process flow for preparing a multilayer core-shell structured titanium dioxide-quantum dot-silica composite material provided in the embodiments of this application; Figure 3 These are schematic TEM images of Embodiment 1 and its comparative example provided in this application; (a) shows the QDs-TiO2 surface without a SiO2 layer, and (b) shows the corresponding TiO2-QDs-SiO2 core-shell structure. Figure 4 These are schematic TEM images of Embodiment 2 provided in this application and its comparative example; (a) shows the QDs-TiO2 surface without a SiO2 layer, and (b) shows the corresponding TiO2-QDs-SiO2 core-shell structure; Figure 5 This is a schematic diagram of a transmission electron microscope (TEM) image of the TiO2-QDs-SiO2 core-shell composite material provided in the embodiments of this application; (a) is a SiO2 layer of the first thickness, and (b) is a SiO2 layer of the second thickness. Figure 6 This is a schematic TEM image of Embodiment 3 provided in this application; Figure 7 These are schematic TEM images of Example 1 and Comparative Example 4 provided in this application; (a) shows the TiO2-QDs-SiO2 core-shell structure of Comparative Example 4, and (b) shows the TiO2-QDs-SiO2 core-shell structure of Example 1. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] Furthermore, throughout this specification, references to "an embodiment"; "an embodiment," "an example," or similar language indicate that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. Therefore, the appearance of the phrase "in one embodiment;" throughout this specification, and similar language, may, but not necessarily, refer to the same embodiment.

[0024] A quantum dot composite material with a core-shell structure, particularly a composite material with titanium dioxide as the core, quantum dots as the intermediate layer, and silicon dioxide as the outer shell, and its preparation method, as well as its applications in optoelectronic devices (such as solar cells and LEDs), photocatalysis, and bioimaging.

[0025] The purpose of this application is to overcome the shortcomings of the prior art and provide a titanium dioxide-silica core-shell composite material (TiO2-QDs-SiO2) with stable structure, excellent optical properties and simple preparation method.

[0026] Specifically, the titanium dioxide-silicon dioxide core-shell structure composite material provided in this application comprises, from the inside out: 1. Core layer: composed of titanium dioxide (TiO2) nanoparticles; 2. Intermediate functional layer: A quantum dot layer that is bridged and tightly adsorbed onto the surface of the titanium dioxide core by a silane coupling agent; 3. Outer shell: A dense silicon dioxide (SiO2) protective layer that wraps around the quantum dot layer.

[0027] More specifically, this application also provides a method for preparing the above-mentioned titanium dioxide-silica core-shell composite material, including the following steps: Step S100: Obtain mercaptolated titanium dioxide; Among them, mercapto-modified titanium dioxide refers to a modified composite material formed by attaching mercapto (-SH) functional groups to the surface of titanium dioxide (TiO2) nanomaterials through chemical methods.

[0028] In step S200, the thiolized titanium dioxide and oleic acid ligand-coated quantum dots are dispersed in a first organic solvent to obtain a first dispersion; and the silane coupling agent solution with thiol groups at the end and the organic alkaline catalyst solution are mixed with the first dispersion to allow the quantum dots to adsorb onto the surface of titanium dioxide to form a quantum dot-titanium dioxide composite. The quantum dots can be II-VI or IV-VI semiconductor quantum dots, preferably at least one of CdSe, CdS, CdTe, PbS, and ZnSe quantum dots.

[0029] Furthermore, the first organic solvent mentioned above is toluene, where toluene is not easily decomposed, and the oleic acid ligand-coated quantum dots exhibit higher stability in toluene. If the organic solvent mentioned above is chloroform, under alkaline conditions, especially under light or heat, chloroform is easily oxidized by air to produce highly toxic phosgene (COCl2), and the oleic acid ligand-coated quantum dots cannot remain stable after the decomposition of chloroform.

[0030] In step S200 above, the strong interaction between the thiol groups on the surface of titanium dioxide (TiO2) nanomaterials and cadmium selenide quantum dots is utilized to make the quantum dots firmly adsorbed on the surface of titanium dioxide, forming a quantum dot-titanium dioxide composite (QDs-TiO2).

[0031] In step S300, the quantum dot-titanium dioxide composite is dispersed in a second organic solvent to obtain a second dispersion; the silicate ester solution, the self-assembly monolayer forming agent solution, and the second dispersion are mixed to obtain a mixture; an organic alkaline catalyst solution is added to the mixture to adjust it to a weakly alkaline state, so that the silicate ester is hydrolyzed and condensed on the surface of the quantum dot-titanium dioxide composite to form a silicon dioxide layer, thereby obtaining a multilayer core-shell structure composite material composed of titanium dioxide-quantum dot-silica.

[0032] In step S300 above, the above-mentioned silicate hydrolysis condensation refers to the removal of a water condensation bond between silicon dioxide particles, and then a large amount of silicon dioxide condenses to form a film. The self-assembled monolayer forming agent is responsible for connecting the silicon dioxide film and the quantum dots. After adding the self-assembled monolayer forming agent, the bonding force between silicon dioxide and the quantum dot surface is stronger, so the outermost silicon dioxide shell is more compact.

[0033] Furthermore, the self-assembly monolayer forming agent is 6-mercapto-1-hexanol.

[0034] Furthermore, the second organic solvent mentioned above is ethanol. When the second organic solvent is a mixture of toluene and ethanol, the above-mentioned toluene and ethanol mixture is polarly incompatible. Toluene is a non-polar solvent, while ethanol is a polar solvent. The two have poor solubility, and due to their different polarities, they may damage the ligands on the surface of the quantum dots and form aggregates.

[0035] In some embodiments, the silane coupling agent with a terminal thiol group is γ-mercaptopropyltrimethoxysilane.

[0036] In some embodiments, the above-mentioned organic basic catalyst is tetramethylammonium hydroxide, which is less basic and causes less damage to quantum dots.

[0037] In some embodiments, the silicate ester described above is tetraethyl orthosilicate (TEOS). Specifically, in an ethanol system, the reaction byproduct ethanol of TEOS does not introduce impurities compared to the reaction byproduct methanol of tetramethyl orthosilicate (TMOS), thus enabling the above-mentioned multilayer core-shell composite material composed of titanium dioxide-quantum dot-silica to have better purity.

[0038] For example, in step S200 above, the mass ratio of mercaptolated titanium dioxide to oleic acid ligand-coated quantum dots ranges from 5:1 to 10:1.

[0039] For example, in step S300 above, the volume ratio of the silicate ester solution to the second dispersion ranges from 0.5:10 to 1:10; The volume ratio of silicate solution to self-assembled monolayer forming agent solution ranges from 10:1 to 5:1.

[0040] In some more specific embodiments, step S100 specifically includes: Titanium dioxide nanoparticles were dispersed in a third organic solvent to obtain a third dispersion, and the third dispersion was adjusted to acidity. A silane coupling agent solution with thiol groups at the end was mixed with the acidic third dispersion to obtain thiolized titanium dioxide.

[0041] The third organic solvent can be methanol.

[0042] For example, the steps for silanization modification of titanium dioxide surface are as follows: titanium dioxide nanoparticles are dispersed in methanol solvent, the pH of the system is adjusted to 3-4 with acid, silane coupling agent γ-mercaptopropyltrimethoxysilane (MPTMS) is added, and the reaction is stirred at room temperature for 10-14 hours; after the reaction is completed, the mixture is centrifuged, washed, and dried to obtain modified titanium dioxide (TiO2-SH) with thiol (-SH) groups on the surface, i.e. thiolized titanium dioxide.

[0043] Preferably, the titanium dioxide nanoparticles have a particle size of 50 nm to 200 nm; the mass ratio of the silane coupling agent to titanium dioxide is 1:2 to 1:4.

[0044] Furthermore, the hydrolysis reaction formula of the above MPTMS is as follows:

[0045] The reaction formula for silanization modification of titanium dioxide surface is:

[0046] The surface structure of mercapto-modified titanium dioxide is as follows: .

[0047] In some more specific embodiments, step S200 specifically includes: The modified titanium dioxide (TiO2-SH) obtained in step S100 was co-dispersed with quantum dots (QDs) in toluene solvent, and silane coupling agent MPTMS and alkaline catalyst tetramethylammonium hydroxide were added simultaneously. The mixture was stirred at room temperature for 1-2 hours. The strong interaction between the mercapto groups and cadmium selenide quantum dots enabled the quantum dots to be firmly adsorbed onto the surface of titanium dioxide, forming a quantum dot-titanium dioxide composite (QDs-TiO2). Preferably, the mass ratio of the modified titanium dioxide to quantum dots is 5:1 to 10:1.

[0048] In some more specific embodiments, step S300 specifically includes: The quantum dot-titanium dioxide composite (QDs-TiO2) obtained in step S200 was washed and redispersed in ethanol solvent. Tetraethyl orthosilicate (TEOS) was added, along with a catalytic amount of tetramethylammonium hydroxide-ethanol solution. The system was adjusted to a weakly alkaline state (pH 8-9), and the reaction was stirred at room temperature for 10-12 hours. This allowed TEOS to hydrolyze and condense on the surface of the composite to form a dense silica protective layer. After the reaction was completed, the composite was centrifuged and dried to obtain the final core-shell structure composite material (TiO2-QDs-SiO2).

[0049] Preferably, the amount of silicon source TEOS used is 500μL-1000μL per 10mL of solvent.

[0050] The process flow diagram of the above preparation method can be found in [reference needed]. Figure 2 As shown.

[0051] The following detailed description of the solution described in this application is provided in conjunction with specific embodiments: Example 1 1. Surface modification of TiO2: 15 mL of methanol was placed in a 50 mL round-bottom flask, and the pH was adjusted to 3.5 with dilute nitric acid. 500 mg of titanium dioxide (TiO2) powder with an average particle size of 100 nm was added and ultrasonically dispersed for 10 minutes. Subsequently, 200 μL of MPTMS silane coupling agent was added, and the mixture was reacted at room temperature for 12 hours under magnetic stirring. After the reaction was completed, the mixture was centrifuged, washed three times with anhydrous ethanol, and dried in a vacuum oven at 60 °C for 0.5 hours to obtain a white powder product, TiO2-SH.

[0052] 2. Adsorption of quantum dots: 200 mg of TiO2-SH powder and 25 mg of CdSe QDs prepared in step 1 were co-dispersed in 30 mL of toluene. 1 mL of MPTMS and 100 μL of tetramethylammonium hydroxide were added, and the mixture was magnetically stirred at 300 rpm for 1 hour at room temperature. After centrifugation, the mixture was washed twice with anhydrous ethanol to remove unadsorbed quantum dots and toluene, yielding the solid product QDs-TiO2.

[0053] 3. SiO2 shell coating: The QDs-TiO2 obtained in step 3 was redispersed in 30 mL of anhydrous ethanol and sonicated to ensure uniform dispersion. 1.5 mL of tetraethyl orthosilicate (TEOS), 200 μL of 6-MCH, 1 mL of deionized water, and 200 μL of tetramethylammonium hydroxide were added as an alkaline catalyst. The reaction was carried out under weakly alkaline conditions (pH ~ 8.5) at room temperature with stirring for 10 hours. After the reaction was complete, the mixture was centrifuged, washed three times with ethanol, and dried to obtain the final product, TiO2-QDs-SiO2 powder.

[0054] Comparative Example 1 Step 3 is omitted, and only the QDs-TiO2 composite material is prepared.

[0055] Effect test The samples prepared in Example 1 and Comparative Example 1 were tested: 1. TEM characterization: such as Figure 3 As shown in (a), Comparative Example 1 has no covering layer. Figure 3 As shown in (b), the product of Example 1 exhibits a clear core-shell structure. TEOS hydrolysis forms a SiO2 layer on the surface of QDs-TiO2, with a dense SiO2 shell surrounding the TiO2 core. Quantum dots are distributed between the two layers. The core (TiO2), intermediate layer (QDs, which may be dark spots or a single layer in the figure), and outer layer (SiO2, light-colored halo) structure can be clearly observed.

[0056] 2. Fluorescence stability test: Both samples were placed in an oven and baked continuously at 85°C. The fluorescence of the comparative sample (without SiO2 coating) decreased by more than 20% in PLQY within 10 hours, while the fluorescence intensity of the sample in Example 1 decreased by less than 5% under the same conditions, demonstrating the excellent protective effect of the SiO2 shell.

[0057] Example 2 1. Surface modification of TiO2: 15 mL of methanol was placed in a 50 mL round-bottom flask, and the pH was adjusted to 3.5 with dilute nitric acid. 500 mg of titanium dioxide (TiO2) powder with an average particle size of 100 nm was added and ultrasonically dispersed for 10 minutes. Subsequently, 200 μL of MPTMS silane coupling agent was added, and the reaction was carried out at room temperature for 12 hours under magnetic stirring. After the reaction was completed, the mixture was centrifuged, washed three times with methanol, and dried in a vacuum oven at 60 °C for 0.5 hours to obtain a white powder product, TiO2-SH.

[0058] 2. Adsorption of quantum dots: 200 mg of TiO2-SH powder and 40 mg of CdSe QDs prepared in step 1 were dispersed together in 30 mL of toluene. 1 mL of MPTMS and 100 μL of tetramethylammonium hydroxide were added, and the mixture was magnetically stirred at 300 rpm for 1 hour at room temperature. After centrifugation, the mixture was washed twice with anhydrous ethanol to remove unadsorbed quantum dots and toluene, yielding the solid product QDs-TiO2.

[0059] 3. SiO2 shell coating: The QDs-TiO2 obtained in step 3 was redispersed in 40 mL of anhydrous ethanol and sonicated to ensure uniform dispersion. 2 mL of tetraethyl orthosilicate (TEOS), 200 μL of 6-MCH, 1 mL of deionized water, and 200 μL of tetramethylammonium hydroxide were added as an alkaline catalyst. The reaction was carried out under weakly alkaline conditions (pH ~ 8.5) at room temperature with stirring for 10 hours. After the reaction was complete, the mixture was centrifuged, washed three times with ethanol, and dried to obtain the final product, TiO2-QDs-SiO2 powder.

[0060] Comparative Example 2 Step 3 is omitted, and only the QDs-TiO2 composite material is prepared.

[0061] Effect test TEM tests were performed on the samples prepared in Example 2 and Comparative Example 2: TEM characterization: such as Figure 4 As shown in (a), Comparative Example 2 has no coating layer. Figure 4 As shown in (b), the product of Example 2 exhibits a clear core-shell structure, with the core (TiO2), intermediate layer (QDs, which may be dark spots or a single layer in the figure), and outer layer (SiO2, light-colored halo) clearly observable. The product of Example 2 achieved a higher quantum dot concentration and a thinner coating layer by controlling the amount of reactants.

[0062] Figure 5These are TEM images of the TiO2-QDs-SiO2 core-shell composite material prepared in Example 2 of this application. The core (TiO2), intermediate layer (QDs, which may be dark spots or a single layer in the image), and outer layer (SiO2, light-colored halo) structure can be clearly observed. Images (a) and (b) show silica coatings of different thicknesses, respectively.

[0063] Example 3 1. Surface modification of TiO2: 15 mL of methanol was placed in a 50 mL round-bottom flask, and the pH was adjusted to 3.5 with dilute nitric acid. 500 mg of titanium dioxide (TiO2) powder with an average particle size of 100 nm was added and ultrasonically dispersed for 10 minutes. Subsequently, 200 μL of MPTMS silane coupling agent was added, and the reaction was carried out at room temperature for 12 hours under magnetic stirring. After the reaction was completed, the mixture was centrifuged, washed three times with methanol, and dried in a vacuum oven at 60 °C for 0.5 hours to obtain a white powder product, TiO2-SH.

[0064] 2. Adsorption of quantum dots: 200 mg of TiO2-SH powder and 20 mg of CdSe QDs prepared in step 1 were dispersed together in 30 mL of toluene. 1 mL of MPTMS and 100 μL of tetramethylammonium hydroxide were added, and the mixture was magnetically stirred at 300 rpm for 1 hour at room temperature. After centrifugation, the mixture was washed twice with anhydrous ethanol to remove unadsorbed quantum dots and toluene, yielding the solid product QDs-TiO2.

[0065] 3. SiO2 shell coating: The QDs-TiO2 obtained in step 3 was redispersed in 40 mL of anhydrous ethanol and sonicated to ensure uniform dispersion. 4 mL of tetraethyl orthosilicate (TEOS), 800 μL of 6-MCH, 1 mL of deionized water, and 200 μL of tetramethylammonium hydroxide were added as an alkaline catalyst. The reaction was carried out under weakly alkaline conditions (pH ~ 8.5) at room temperature with stirring for 10 hours. After the reaction was complete, the mixture was centrifuged, washed three times with ethanol, and dried to obtain the final product, TiO2-QDs-SiO2 powder.

[0066] Comparative Example 3 Step 3 is omitted, and only the QDs-TiO2 composite material is prepared.

[0067] TEM characterization: such as Figure 6 As shown, the product of Example 3 exhibits a clear core-shell structure, with the core (TiO2), intermediate layer (QDs, which may be dark spots or a single layer in the figure) and outer layer (SiO2, light-colored halo) structure clearly observable.

[0068] Comparative Example 4 This comparative example uses a different preparation method, as detailed below: S100: Silanization modification of titanium dioxide surface.

[0069] 15 mL of methanol was placed in a 50 mL round-bottom flask, and the pH was adjusted to 4.0 with dilute nitric acid. 500 mg of titanium dioxide (TiO2) powder with an average particle size of 100 nm was added and ultrasonically dispersed for 10 minutes. Then, 167 μL of MPTMS silane coupling agent (silane coupling agent to titanium dioxide mass ratio 1:3) was added, and the mixture was reacted at room temperature for 14 hours with magnetic stirring. After the reaction was complete, the mixture was centrifuged (8000 r / min, 10 minutes), washed three times with methanol, and dried in a vacuum oven at 60 °C for 0.5 hours to obtain a white powdery product, TiO2-SH.

[0070] S200: Quantum dot ligand exchange.

[0071] Take 600 μL of a 0.9 g / mL CdS quantum dot solution with oleic acid ligand (chloroform) and dilute with 10 mL of chloroform. Then add 7 mL of 3-mercaptopropionic acid (MPA) solution and stir magnetically at room temperature for 6 hours. After the reaction, centrifuge and discard the supernatant (10000 r / min, 15 min). Wash the precipitate three times with anhydrous ethanol to obtain MPA-modified quantum dots (MPA-CdS QDs).

[0072] S300: Quantum dot adsorption.

[0073] All TiO2-SH powder prepared by S100 and all MPA-CdS QDs prepared by S200 were co-dispersed in 15 mL of chloroform and magnetically stirred at room temperature for 4 hours. After centrifugation (8000 r / min, 10 min), the mixture was washed twice with chloroform to remove unadsorbed quantum dots, yielding the solid product QDs-TiO2.

[0074] In this embodiment, considering that the oleic acid ligands are long chains that would hinder the coating of the silica shell, ligand exchange is performed first to replace the long chains with short chains. However, in Embodiments 1-3, since step S300 uses 6-MCH, the influence of the long oleic acid chains can be avoided, thus the quantum dot ligand exchange step can be omitted. Furthermore, the solvents used in the above embodiments ensure that the quantum dots coated with oleic acid ligands remain in a stable state, resulting in a stable and uniform TiO2-QDs-SiO2 core-shell structure.

[0075] S400: Silicon dioxide shell coating.

[0076] The QDs-TiO2 obtained from S300 was redispersed in 15 mL of chloroform and sonicated to ensure uniform dispersion. 400 μL of TMOS was added (400 μL per 15 mL solvent), followed by dropwise addition of 10 μL of a catalyst diluted 1:1 (v / v) with concentrated ammonia and anhydrous ethanol. The reaction was carried out under weakly alkaline conditions (pH 9.0) at room temperature with stirring for 18 hours. After the reaction was complete, the mixture was centrifuged (8000 r / min, 10 min), washed three times with ethanol, and dried in a vacuum oven at 60 °C for 0.5 hours to obtain the final product, TiO2-QDs-SiO2 powder.

[0077] See Figure 7 In the figures, (a) is a TEM image of Comparative Example 4 above, and (b) is a TEM image of Example 1. It can be seen that the preparation method provided in this application can obtain a denser silica shell layer, making the outermost denser silica shell layer more effective in isolating the internal quantum dots from environmental factors such as water and oxygen. It is evident that the core-shell structure prepared in this application shows improved photostability and chemical stability of the corresponding quantum dots compared to the core-shell structure prepared by the method in Comparative Example 4 above.

[0078] Furthermore, the aforementioned multilayered core-shell structured titanium dioxide-quantum dot-silica composite material can be applied to optoelectronic devices, photocatalytic materials, or biofluorescent markers. It is understood that the optoelectronic devices used in this application could be quantum dot-sensitized solar cells or light-emitting diodes.

[0079] In summary, this application successfully prepared a novel and stable core-shell composite material, which exhibits significant advantages in photostability and has promising application prospects.

[0080] This application is not limited to the specific embodiments described above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this application should also fall within the protection scope of this application.

[0081] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a multilayered core-shell structured titanium dioxide-quantum dot-silica composite material, characterized in that, Includes the following steps: Step S100: Obtain thiolized titanium dioxide; Step S200: The thiolized titanium dioxide and oleic acid ligand-coated quantum dots are dispersed in a first organic solvent to obtain a first dispersion; and a silane coupling agent solution with thiol groups at the end and an organic alkaline catalyst solution are mixed with the first dispersion to allow the quantum dots to adsorb onto the surface of titanium dioxide, forming a quantum dot-titanium dioxide composite. Step S300: The quantum dot-titanium dioxide composite is dispersed in a second organic solvent to obtain a second dispersion; the silicate ester solution, the self-assembly monolayer forming agent solution are mixed with the second dispersion to obtain a mixture; an organic alkaline catalyst solution is added to the mixture to adjust it to a weakly alkaline state, so that the silicate ester is hydrolyzed and condensed on the surface of the quantum dot-titanium dioxide composite to form a silicon dioxide layer, thereby obtaining a multilayer core-shell structure composite material composed of titanium dioxide-quantum dot-silica.

2. The preparation method according to claim 1, characterized in that, The quantum dot is a II-VI or IV-VI group semiconductor quantum dot, preferably at least one of CdSe, CdS, CdTe, PbS, and ZnSe quantum dots.

3. The preparation method according to claim 1, characterized in that, The first organic solvent is toluene; and / or the second organic solvent is ethanol.

4. The preparation method according to claim 1, characterized in that, The silane coupling agent with a terminal thiol group is γ-mercaptopropyltrimethoxysilane; and / or the self-assembling monolayer forming agent is 6-mercapto-1-hexanol.

5. The preparation method according to claim 1, characterized in that, The organic basic catalyst is tetramethylammonium hydroxide; and / or the silicate ester is tetraethyl orthosilicate.

6. The preparation method according to claim 1, characterized in that, Step S100 specifically includes: Titanium dioxide nanoparticles were dispersed in a third organic solvent to obtain a third dispersion, and the third dispersion was adjusted to acidity. A silane coupling agent solution with thiol groups at the end was mixed with the acidic third dispersion to obtain thiolized titanium dioxide.

7. The preparation method according to claim 1, characterized in that, In step S200, the mass ratio of mercaptolated titanium dioxide to oleic acid ligand-coated quantum dots ranges from 5:1 to 10:

1.

8. The preparation method according to claim 1, characterized in that, In step S300, the volume ratio of the silicate ester solution to the second dispersion ranges from 0.5:10 to 1:

10. And / or the volume ratio of the silicate solution to the self-assembling monolayer forming agent solution is in the range of 10:1 to 5:

1.

9. A multilayered core-shell structured titanium dioxide-quantum dot-silica composite material, characterized in that, The titanium dioxide-quantum dot-silica composite material is prepared by the preparation method described in any one of claims 1 to 8.

10. The application of the multilayer core-shell structured titanium dioxide-quantum dot-silica composite material of claim 9 in optoelectronic devices, photocatalytic materials or biofluorescent markers.

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