Circularly polarized luminescent carbon quantum dot film composite material, and preparation method and application thereof

Abstract

The application provides a circularly polarized luminescent carbon quantum dot film composite material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing CNCs and deionized water, dispersing, heating and stirring to obtain CNCs suspension liquid; (2) dissolving FeCl3.6H2O and FeSO4.7H2O in distilled water, then adding the distilled water into the CNCs suspension liquid, reacting, then adding NH3.H2O aqueous solution, continuously reacting, and post-treating to obtain a Fe3O4 / CNC composite material; (3) mixing carbon quantum dot aqueous solution, Fe3O4 / CNC composite material aqueous solution and CNCs suspension liquid, dispersing to obtain a colloidal suspension liquid, placing the colloidal suspension liquid in a magnetic field, and evaporating and concentrating to obtain the circularly polarized luminescent carbon quantum dot film composite material. The application is based on magnetic field regulation and control to synthesize a composite material which is chiral and has circularly polarized fluorescence activity.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and relates to a circularly polarized luminescent carbon quantum dot film composite material and its preparation method and application, and in particular to a preparation method of a circularly polarized luminescent carbon quantum dot film composite material based on magnetic field regulation. Background Art

[0002] Circularly polarized luminescence (CPL) has a wide range of applications in nonlinear photonic devices, stereoscopic vision, optical storage devices, biosensors, asymmetric catalysis and synthesis, and security systems. Cellulose nanocrystals (CNCs) extracted from cellulose can self-assemble into a cholesteric phase when their concentration exceeds a critical value. The helical structure formed in the CNC film by evaporation-induced self-assembly (EISA) produces photonic properties, namely, the so-called selective reflection, which provides a universal method for constructing photonic materials without complex design and process technology. Li et al. reported a method for preparing chiral polymer nanowire arrays using CNC templates, and achieved CPL regulation by regulating the morphology of nanowires and the concentration of chiral molecules (ACS Nano, 12 (12), 12345-12350, 2018). Zheng et al. successfully obtained CPL composite films by encapsulating chiral fluorescent molecules and carbon dots in CNC to form chiral carbon dot nanomaterials with a helical superstructure (AOM., 6, 1801246, 2018). Xu et al. achieved the regulation of circularly polarized luminescence by dissolving semiconductor quantum dots in nanocrystalline films and regulating the structure and optical properties of the nanocrystalline films by adjusting the concentration of silicone oil (J.Am.Chem.C.7,13794,2019).

[0003] Methods such as optical resonators and polarizers can effectively control CPL, but they typically require complex experimental setup and adjustments. Optical resonators require precise control of the cavity size and resonant frequency, while polarizers require precise adjustment of the polarization direction and angle of the incident light. These operations may require specialized equipment and techniques, and increase the complexity and difficulty of the experiments, which limits the flexibility and applicability of these methods in practical applications.

[0004] Therefore, in the art, it is desired to develop a method for preparing a circularly polarized luminescent carbon quantum dot thin film composite material with simple operation and low cost. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to provide a circularly polarized luminescent carbon quantum dot film composite material, its preparation method, and application, and in particular, to provide a method for preparing a circularly polarized luminescent carbon quantum dot film composite material based on magnetic field regulation. The present invention combines a self-assembled helical structure formed by CNC evaporation and concentration with carbon quantum dots having photoluminescent properties to obtain a circularly polarized luminescent carbon quantum dot film composite material with excellent performance. The preparation method of the present invention is simple to operate and low in cost. Compared with the traditional method of regulating the helical pitch of the CNC helix by controlling the concentration of the doped fluorescent material, changing the pH value, ionic strength, or temperature, the present invention utilizes a magnetic field to regulate the helical pitch of the CNC helix, which is a non-invasive tuning method. That is, the present invention uses magnetic field regulation to influence the chiral sequence of the CNC composite film, and self-assembles to synthesize a chiral composite material with circularly polarized fluorescence activity.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a circularly polarized luminescent carbon quantum dot thin film composite material, the preparation method comprising:

[0008] (1) mixing cellulose nanocrystals (CNCs) and deionized water, dispersing, heating, and stirring to obtain a cellulose nanocrystal suspension;

[0009] (2) dissolving FeCl3·6H2O and FeSO4·7H2O in distilled water, and then adding them to the cellulose nanocrystal suspension obtained in step (1) to react, and then adding NH3·H2O aqueous solution to continue the reaction, and post-treating to obtain Fe3O4 / CNC composite material;

[0010] (3) mixing deionized water, phenylenediamine solution and FeCl3 solution, heating and stirring, and post-treating to obtain carbon quantum dots;

[0011] (4) The carbon quantum dot aqueous solution, the Fe3O4 / CNC composite material aqueous solution and the cellulose nanocrystal suspension are mixed and dispersed to obtain a colloidal suspension, the colloidal suspension is placed in a container, and placed under a magnetic field, evaporated and concentrated to obtain the circularly polarized luminescent carbon quantum dot thin film composite material.

[0012] The present invention modulates the pitch of the helical structure produced by CNC self-assembly by controlling the intensity of an external magnetic field. Simultaneously, a composite film with circularly polarized luminescence (CPL) is obtained through the self-assembly of multicolor luminescent carbon quantum dots and CNCs. Fe3O4 nanoparticles are assembled into a composite material with cellulose nanocrystals (CNCs). The composite material is then dispersed with the multicolor luminescent carbon quantum dots within pure cellulose nanocrystals. The composite interacts with the multicolor luminescent carbon quantum dots to form a self-assembled nanostructure within a colloidal suspension. This composite material then dries under different external magnetic field conditions to form a film with structural color. This film exhibits excellent circularly polarized luminescence (CPL) and has broad application prospects in nonlinear photonic devices, chiral sensing, and other fields.

[0013] By adjusting the external magnetic field intensity during the drying process of the colloidal suspension, the pitch of the CNC helical structure, and thus the reflected wavelength, can be successfully controlled. Compared with traditional methods such as changing pH, ionic strength, or temperature, using a magnetic field to adjust the structure is an effective non-invasive tuning method. Furthermore, carbon quantum dots, which have excellent luminescence, good biocompatibility, and low toxicity, are self-assembled with CNC to produce a well-preserved CPL photonic film.

[0014] Conventional regulation of the CNC cholesteric phase requires the use of a very strong magnetic field (≥5T), which limits the applicability of this method. Iron oxide (Fe3O4) has become an outstanding material due to its inherent superparamagnetism and strong photothermal effect. However, due to the high surface energy of nanoparticles, their poor dispersibility has always been an obstacle to their further development. In step (2) of the present invention, Fe 3+ and Fe 2+ The chemical hydrolysis of CNCs controls the formation of Fe3O4 nanoparticles on the surface of CNCs. 3+ ) and the electrostatic attraction between the abundant hydroxyl groups on the surface of CNC nanorods, which produces local areas of iron enrichment, promote the nucleation and growth of magnetic nanoparticles, so that Fe3O4 nanoparticles grow in situ on CNC to form Fe3O4 / CNC suspension. While avoiding the agglomeration of Fe3O4 nanoparticles, it also changes the magnetic field response behavior of pure CNC, causing it to respond to a magnetic field under a weak external magnetic field, and causing its helical pitch to change accordingly with the change of the external magnetic field (the helical pitch decreases with the increase of the external magnetic field strength), thereby affecting the chiral arrangement of the film.

[0015] The introduction of the Fe3O4 / CNC suspension (i.e., the Fe3O4 / CNC composite material) in step (4) of the present invention changes the magnetic field response behavior of CNC, making it more sensitive to the magnetic field. The present invention places the colloidal suspension of step (4) under four magnetic field intensities of no, weak, medium, and strong, and verifies the influence of the Fe3O4 / CNC composite material on the magnetic field response of CNC. After the carbon quantum dots and the CNC spiral structure are self-assembled, the dried and formed film has good CPL optical behavior. Finally, a multi-color adjustable, high quantum yield circularly polarized fluorescent film is synthesized through a simple co-assembly method.

[0016] Preferably, in the cellulose nanocrystal suspension in step (1), the mass fraction of cellulose nanocrystals is 1%-1.5%, for example, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0017] Preferably, the dispersion in step (1) comprises ultrasonic dispersion.

[0018] Preferably, the ultrasonic dispersion time is 5-15 min, for example, 5 min, 8 min, 10 min, 13 min, 15 min, etc.

[0019] Preferably, the heating in step (1) is heating to 60-80°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, etc.

[0020] Preferably, the stirring time in step (1) is 20-40 min, for example, 20 min, 25 min, 30 min, 35 min, 40 min, etc.

[0021] Preferably, the heating and stirring in step (1) are carried out under protective gas.

[0022] Preferably, the protective gas comprises nitrogen.

[0023] Preferably, the molar ratio of FeCl3·6H2O to FeSO4·7H2O is (1.5-2.5):1, and 1.5-2.5 can be, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc.

[0024] Preferably, in step (2), based on the amount of FeSO4·7H2O used being 0.1 g, the amount of distilled water used is 4-6 mL, for example, 4 mL, 5 mL, 6 mL, etc.

[0025] Preferably, the mass ratio of FeSO4·7H2O to cellulose nanocrystals is 1:(15-25), and 15-25 can be, for example, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, etc.

[0026] Preferably, the volume percentage of NH3·H2O in the NH3·H2O aqueous solution is 1%-3%, for example, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0027] Preferably, the volume ratio of distilled water to NH3·H2O aqueous solution in step (2) is 1:(3-5), where 3-5 can be, for example, 3, 3.5, 4, 4.5, 5, etc.

[0028] Preferably, the reaction time of step (2) is 20-40 min, for example, 20 min, 25 min, 30 min, 35 min, 40 min, etc.

[0029] Preferably, the reaction time in step (2) is 1-3 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc.

[0030] Preferably, the post-treatment in step (2) includes centrifugation and washing.

[0031] Preferably, the phenylenediamine includes any one of metaphenylenediamine (mPD), o-phenylenediamine (oPD) or p-phenylenediamine (pPD), or a combination of at least two thereof.

[0032] Preferably, the concentration of the phenylenediamine solution is 15-18 (eg, 15, 16, 17, 18, etc.) millimoles per liter.

[0033] Preferably, the concentration of the FeCl3 solution is 90-110 (e.g., 90, 95, 100, 105, 110, etc.) mmol / L.

[0034] Preferably, in step (3), the volume ratio of deionized water to phenylenediamine solution is (8-10):1, and 8-10 can be, for example, 8, 9, 10, etc.

[0035] Preferably, in step (3), the volume ratio of deionized water to FeCl3 solution is (1600-2000):1, and 1600-2000 can be, for example, 1600, 1700, 1800, 1900, 2000, etc.

[0036] Preferably, the heating in step (3) is heating to 80-100°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, etc.

[0037] Preferably, the stirring time in step (3) is 8-12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc.

[0038] Preferably, the post-treatment in step (3) includes centrifugation and removal of agglomerates.

[0039] Preferably, the carbon quantum dots in step (3) include any one of green carbon quantum dots, yellow carbon quantum dots, and red carbon quantum dots.

[0040] Preferably, in the carbon quantum dot aqueous solution of step (4), the concentration of carbon quantum dots is 0.1-0.2 mg / mL, for example, 0.1 mg / mL, 0.11 mg / mL, 0.12 mg / mL, 0.13 mg / mL, 0.14 mg / mL, 0.15 mg / mL, 0.16 mg / mL, 0.17 mg / mL, 0.18 mg / mL, 0.19 mg / mL, 0.2 mg / mL, etc.

[0041] Preferably, in the Fe3O4 / CNC composite material aqueous solution in step (4), the concentration of the Fe3O4 / CNC composite material is 3-4 mg / mL, for example, 3 mg / mL, 3.3 mg / mL, 3.5 mg / mL, 3.8 mg / mL, 4 mg / mL, etc.

[0042] Preferably, in the cellulose nanocrystal suspension in step (4), the mass fraction of cellulose nanocrystals is 2%-5%, for example, 2%, 3%, 4%, 5%, etc.

[0043] Preferably, in step (4), the mass ratio of carbon quantum dots to cellulose nanocrystals is (0.1-0.8):1, and 0.1-0.8 can be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc.

[0044] Preferably, in step (4), the volume ratio of the Fe3O4 / CNC composite material aqueous solution to the cellulose nanocrystal suspension is 1:(20-40), where 20-40 can be, for example, 20, 25, 30, 35, 40, etc.

[0045] Preferably, the dispersion in step (4) includes first ultrasonic dispersion, then stirring, and then continuing ultrasonic dispersion.

[0046] Preferably, the magnetic field strength in step (4) is 5-18 mT, for example, 5 mT, 6 mT, 7 mT, 8 mT, 9 mT, 10 mT, 11 mT, 12 mT, 13 mT, 14 mT, 15 mT, 16 mT, 17 mT, 18 mT, etc. The strength of the magnetic field can be controlled by adjusting the distance between the two parallel magnets.

[0047] Preferably, the evaporation concentration in step (4) is carried out at room temperature.

[0048] Preferably, the evaporation concentration in step (4) is carried out for 2-3 days, such as 2 days, 2.5 days, 3 days, etc.

[0049] In a second aspect, the present application provides a circularly polarized luminescent carbon quantum dot film composite material, which is prepared by the preparation method of the first aspect.

[0050] In a third aspect, the present application provides an application of the circularly polarized luminescent carbon quantum dot film composite material of the second aspect in a nonlinear photon device or chiral sensing.

[0051] Compared with the prior art, the present application has the following beneficial effects:

[0052] (1) The present application controls the formation of Fe3O4 nanoparticles on the surface of CNCs through the chemical hydrolysis of Fe 3+ and Fe 2+ , the local area of iron enrichment generated by the electrostatic attraction between the ferric ion (Fe 3+ ) and the abundant hydroxyl groups on the surface of CNC nanorods promotes the nucleation and growth of magnetic nanoparticles, and the Fe3O4 nanoparticles grow in situ on the CNCs to form a Fe3O4 / CNC composite material, which changes the magnetic field response behavior of pure CNCs while avoiding the agglomeration of Fe3O4 nanoparticles.

[0053] (2) The present application adopts a co-assembly method to form a colloidal suspension by compounding the achiral Fe3O4 / CNC composite material, carbon quantum dots, and CNCs, and then adjusts the pitch of the chiral nematic phase to decrease with the increase of the magnetic field strength through external magnetic field regulation during the drying process of the colloidal suspension, thereby affecting the chiral arrangement of the film composite material. Meanwhile, the carbon quantum dots of the present application have luminescent properties, thereby providing a circularly polarized luminescent carbon quantum dot film composite material. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 TEM image of the Fe3O4 / CNC composite material provided for step (2) of Example 1.

[0055] Figure 2 CD test result graph of the four circularly polarized luminescent carbon quantum dot film composite materials provided for Example 1.

[0056] Figure 3 SEM image of the circularly polarized luminescent carbon quantum dot film composite material formed at 7 mT provided for Example 1.

[0057] Figure 4This is a POM image of the circularly polarized luminescent carbon quantum dot thin film composite material formed at 7mT provided in Example 1.

[0058] Figure 5 This is a diagram showing the CD test results of the four circularly polarized luminescent carbon quantum dot film composite materials provided in Example 2.

[0059] Figure 6 This is a diagram showing the CD test results of the four circularly polarized luminescent carbon quantum dot film composite materials provided in Example 3. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0061] The cellulose nanocrystal CNCs suspension used in the examples and comparative examples of the present invention was purchased from Mujingling Nanocellulose Company and can be diluted according to actual needs.

[0062] The carbon quantum dots used in the examples and comparative examples of the present invention were prepared by Preparation Examples 1-3.

[0063] Preparation Example 1

[0064] This preparation example provides a green carbon quantum dot, and the preparation method is as follows:

[0065] 10 mL of 16 mM m-phenylenediamine (mPD) aqueous solution and 50 μL of 100 mM FeCl3 aqueous solution were added to 90 mL of deionized water, and the resulting mixture was stirred continuously at 90 ° C for 10 h. The crude product was then centrifuged at 12000 rpm for 15 min to remove large aggregates to obtain green carbon quantum dots.

[0066] Preparation Example 2

[0067] This preparation example provides a yellow carbon quantum dot, and the preparation method is as follows:

[0068] 10 mL of 16 mM o-phenylenediamine (oPD) aqueous solution and 50 μL of 100 mM FeCl3 aqueous solution were added to 90 mL of deionized water, and the resulting mixture was stirred continuously at 90 ° C for 10 h. The crude product was then centrifuged at 12000 rpm for 15 min to remove large agglomerates to obtain yellow carbon quantum dots.

[0069] Preparation Example 3

[0070] This preparation example provides a red carbon quantum dot, and the preparation method is as follows:

[0071] 10 mL of 16 mM p-phenylenediamine (pPD) aqueous solution and 50 μL of 100 mM FeCl3 aqueous solution were added to 90 mL of deionized water, and the resulting mixture was stirred continuously at 90 ° C for 10 h. The crude product was then centrifuged at 12000 rpm for 15 min to remove large agglomerates to obtain red carbon quantum dots.

[0072] Example 1

[0073] In this embodiment, a method for preparing a circularly polarized luminescent carbon quantum dot thin film composite material is provided, the preparation method comprising:

[0074] (1) 60 g of CNCs suspension and 120 g of deionized water were mixed and ultrasonicated for 10 min (power 50%, room temperature). The mixture was transferred into a three-necked flask and evacuated with nitrogen for three cycles, maintaining a nitrogen flow rate of 10 m / s. The mixture was preheated to 70°C and stirred for 30 min to obtain a cellulose nanocrystal suspension (mass fraction of CNCs was 1.21%).

[0075] (2) Dissolve 0.17 g of FeCl3·6H2O and 0.11 g of FeSO4·7H2O in 5 mL of distilled water and inject into a three-necked flask using a 5 mL syringe. Allow to react for 30 min. Then, dilute 400 μL of NH3·H2O to 20 mL with deionized water and slowly add dropwise using a 5 mL syringe. After reacting for 2 h, dismantle the apparatus and cool naturally to room temperature. Transfer to a 10 mL centrifuge tube and centrifuge at 10,000 rpm for 10 min. Subsequently, wash repeatedly with deionized water and anhydrous ethanol three times, and finally wash with anhydrous ethanol to obtain a Fe3O4 / CNC composite material, which is stored in ethanol at 5°C.

[0076] (3) 300 μL of a 0.125 mg / mL yellow carbon quantum dot aqueous solution, 100 μL of a 3.16 mg / mL Fe3O4 / CNC composite material aqueous solution, and 3 mL of a 3% mass fraction CNCs suspension were mixed, ultrasonicated for 10 min, stirred for 90 min, and ultrasonicated for 10 min to fully mix the mixed solution to obtain a colloidal suspension. Four identical colloidal suspensions were prepared according to the above steps and placed in polystyrene culture dishes with a diameter of about 35 mm. They were then placed in magnetic fields of 0 mT (i.e., no magnetic field), 7 mT (weak magnetic field strength), 12 mT (medium magnetic field strength), and 15 mT (strong magnetic field strength), respectively. The magnetic field strength was controlled by adjusting the distance between the two parallel magnets. The films were evaporated and concentrated at room temperature for 2 days to finally obtain four photonic crystal films with rainbow colors (i.e., circularly polarized luminescent carbon quantum dot film composite materials).

[0077] The Fe3O4 / CNC composite material obtained in step (2) of this embodiment was subjected to TEM (transmission electron microscopy) testing, and the results were as follows: Figure 1 As shown in the figure, it can be seen that Fe3O4 magnetic nanoparticles attach to CNC to nucleate and grow, eventually forming a new type of composite material.

[0078] The four circularly polarized luminescent carbon quantum dot film composite materials provided in this embodiment were subjected to circular dichroism spectroscopy analysis test (CD test), and the results are as follows: Figure 2 As shown in the figure, it can be seen that after the Fe3O4 / CNC composite material is introduced into pure CNC, the magnetic field responsiveness of CNC is changed. At the same doping concentration, as the external magnetic field increases, the obtained CD spectrum peak tends to blue-shift, which effectively shows that as the external magnetic field increases, the helical pitch of the CNC self-assembled helical structure gradually decreases.

[0079] The circularly polarized luminescent carbon quantum dot film composite material provided in this embodiment formed at 7mT was subjected to SEM testing, and the results were as follows: Figure 3 As shown in the figure, it can be seen that the orderly arranged layered structure proves that the three materials of carbon quantum dots, CNC and Fe3O4 / CNC have been successfully self-assembled.

[0080] The circularly polarized luminescent carbon quantum dot film composite material provided in this embodiment formed at 7mT was subjected to polarization optical microscope test (POM test), and the results are as follows: Figure 4 As shown in the figure, it can be seen that the film material has chirality.

[0081] Example 2

[0082] The only difference between this embodiment and embodiment 1 is that the yellow carbon quantum dot aqueous solution in step (3) is replaced by a green carbon quantum dot aqueous solution.

[0083] The four circularly polarized luminescent carbon quantum dot film composite materials provided in this embodiment were subjected to CD testing, and the results were as follows: Figure 5 As shown in the figure, it can be seen that after the Fe3O4 / CNC composite material is introduced into pure CNC, the magnetic field responsiveness of CNC is changed. At the same doping concentration, as the external magnetic field increases, the obtained CD spectrum peak tends to blue-shift, which effectively shows that as the external magnetic field increases, the helical pitch of the CNC self-assembled helical structure gradually decreases.

[0084] Example 3

[0085] The only difference between this embodiment and embodiment 1 is that the yellow carbon quantum dot aqueous solution in step (3) is replaced by a red carbon quantum dot aqueous solution.

[0086] The four circularly polarized luminescent carbon quantum dot film composite materials provided in this embodiment were subjected to CD testing, and the results were as follows: Figure 6 As shown in the figure, it can be seen that after the Fe3O4 / CNC composite material is introduced into pure CNC, the magnetic field responsiveness of CNC is changed. At the same doping concentration, as the external magnetic field increases, the obtained CD spectrum peak tends to blue-shift, which effectively shows that as the external magnetic field increases, the helical pitch of the CNC self-assembled helical structure gradually decreases.

[0087] Example 4

[0088] The only difference between this example and Example 1 is that the amount of the yellow carbon quantum dot aqueous solution with a concentration of 0.125 mg / mL used in step (3) is 100 μL. The results show that although all four films produced good structural color, the luminescence properties were poor. Under ultraviolet light, no obvious fluorescence was observed. The circularly polarized luminescence properties were also poor, the signal was weak, and the noise interference was large.

[0089] Example 5

[0090] The only difference between this embodiment and embodiment 1 is that the amount of the yellow carbon quantum dot aqueous solution with a concentration of 0.125 mg / mL in step (3) is 700 μL. The results show that all four films obtained have no structural color but a relatively dark yellow color, indicating that the assembly failed.

[0091] Comparative Example 1

[0092] In this comparative example, a method for preparing a circularly polarized luminescent carbon quantum dot thin film composite material is provided, and the preparation method comprises:

[0093] 300 μL of a 0.125 mg / mL yellow carbon quantum dot aqueous solution, 100 μL of a 3.16 mg / mL Fe3O4 aqueous solution, and 3 mL of a 3% mass fraction CNCs suspension were mixed. After ultrasonication for 10 minutes, the mixture was stirred for 90 minutes and then ultrasonicated for 10 minutes to fully mix the mixture to obtain a colloidal mixture. It was found that a large number of Fe3O4 particles were aggregated in the mixture. Four identical colloidal mixtures were prepared according to the above steps and placed in polystyrene culture dishes with a diameter of about 35 mm. Then, they were placed in magnetic fields with magnetic field strengths of 0 mT (i.e., no magnetic field), 7 mT, 12 mT, and 15 mT, respectively. The strength of the magnetic field was controlled by adjusting the distance between the two parallel magnets. The films were evaporated and concentrated at room temperature for 2 days. The results showed that the four films obtained were uneven and had obvious particle aggregation.

[0094] The applicant declares that the present invention uses the above-described embodiments to illustrate the circularly polarized luminescent carbon quantum dot thin film composite material, its preparation method, and its application. However, the present invention is not limited to the above-described embodiments, which does not necessarily mean that the present invention must rely on the above-described embodiments for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a circularly polarized luminescent carbon quantum dot film composite material, characterized in that: The preparation method comprises: (1) mixing cellulose nanocrystals and deionized water, dispersing, heating and stirring to obtain a cellulose nanocrystal suspension; (2) dissolving FeCl3·6H2O and FeSO4·7H2O in distilled water, and then adding them to the cellulose nanocrystal suspension obtained in step (1) to react, and then adding NH3·H2O aqueous solution to continue the reaction, and post-treating to obtain Fe3O4 / CNC composite material; (3) mixing deionized water, phenylenediamine solution and FeCl3 solution, heating and stirring, and post-treating to obtain carbon quantum dots; (4) mixing and dispersing the carbon quantum dot aqueous solution, the Fe3O4 / CNC composite material aqueous solution and the cellulose nanocrystal suspension to obtain a colloidal suspension, placing the colloidal suspension in a container, placing it under a magnetic field, and evaporating and concentrating it to obtain the circularly polarized luminescent carbon quantum dot thin film composite material; In the carbon quantum dot aqueous solution of step (4), the concentration of carbon quantum dots is 0.1-0.2 mg / mL; In the Fe3O4 / CNC composite material aqueous solution in step (4), the concentration of the Fe3O4 / CNC composite material is 3-4 mg / mL; In the cellulose nanocrystal suspension of step (4), the mass fraction of cellulose nanocrystals is 2%-5%; In step (4), the mass ratio of carbon quantum dots to cellulose nanocrystals is (0.1-0.8):1; In step (4), the volume ratio of the Fe3O4 / CNC composite material aqueous solution to the cellulose nanocrystal suspension is 1:(20-40).

2. The preparation method according to claim 1, characterized in that In the cellulose nanocrystal suspension in step (1), the mass fraction of the cellulose nanocrystals is 1%-1.5%.

3. The preparation method according to claim 1, characterized in that The dispersion in step (1) includes ultrasonic dispersion.

4. The preparation method according to claim 3, characterized in that The ultrasonic dispersion time is 5-15 minutes.

5. The preparation method according to claim 1, characterized in that The heating in step (1) is heating to 60-80°C.

6. The preparation method according to claim 1, characterized in that The stirring time in step (1) is 20-40 minutes.

7. The preparation method according to claim 1, characterized in that The heating and stirring in step (1) are carried out under protective gas.

8. The preparation method according to claim 1, characterized in that The molar ratio of FeCl3·6H2O to FeSO4·7H2O is (1.5-2.5):

1.

9. The preparation method according to claim 1, characterized in that In step (2), based on the amount of FeSO4·7H2O used being 0.1 g, the amount of distilled water used is 4-6 mL.

10. The preparation method according to claim 1, characterized in that The mass ratio of the FeSO4·7H2O to the cellulose nanocrystals is 1:(15-25).

11. The preparation method according to claim 1, characterized in that In the NH3·H2O aqueous solution, the volume percentage of NH3·H2O is 1%-3%.

12. The preparation method according to claim 1, characterized in that The volume ratio of the distilled water to the NH3·H2O aqueous solution in step (2) is 1:(3-5).

13. The preparation method according to claim 1, characterized in that The reaction time of step (2) is 20-40 minutes.

14. The preparation method according to claim 1, characterized in that The reaction time in step (2) is 1-3 hours.

15. The preparation method according to claim 1, characterized in that The post-processing in step (2) includes centrifugation and washing.

16. The preparation method according to claim 1, characterized in that The phenylenediamine includes any one of m-phenylenediamine, o-phenylenediamine or p-phenylenediamine, or a combination of at least two of them.

17. The preparation method according to claim 16, characterized in that The concentration of the phenylenediamine solution is 15-18 mmol per liter.

18. The preparation method according to claim 1, characterized in that The concentration of the FeCl3 solution is 90-110 mmol / L.

19. The preparation method according to claim 1, characterized in that In step (3), the volume ratio of deionized water to phenylenediamine solution is (8-10):

1.

20. The preparation method according to claim 1, characterized in that In step (3), the volume ratio of deionized water to FeCl3 solution is (1600-2000):

1.

21. The preparation method according to claim 1, characterized in that The heating in step (3) is heating to 80-100°C.

22. The preparation method according to claim 1, characterized in that The stirring time in step (3) is 8-12h.

23. The preparation method according to claim 1, characterized in that The post-processing in step (3) includes centrifugation and removal of agglomerates.

24. The preparation method according to claim 1, characterized in that The carbon quantum dots in step (3) include any one of green carbon quantum dots, yellow carbon quantum dots, and red carbon quantum dots.

25. The preparation method according to claim 1, characterized in that The dispersion in step (4) includes first ultrasonic dispersion, then stirring, and then continuing ultrasonic dispersion.

26. The preparation method according to claim 1, characterized in that The magnetic field strength in step (4) is 5-18 mT.

27. The preparation method according to claim 1, characterized in that The evaporation concentration in step (4) is carried out at room temperature.

28. The preparation method according to claim 1, characterized in that The time for the evaporation and concentration in step (4) is 2-3 days.

29. A circularly polarized luminescent carbon quantum dot film composite material, characterized in that: The circularly polarized luminescent carbon quantum dot thin film composite material is prepared by the preparation method according to any one of claims 1 to 28.

30. Use of the circularly polarized luminescent carbon quantum dot thin film composite material as claimed in claim 29 in nonlinear photonic devices or chiral sensing.

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