Fluorescent carbon quantum dot as well as preparation method and application thereof
By calcining waste latex or tung gloves and synthesizing fluorescent carbon quantum dots and hydrothermal method, the problems of long synthesis, low fluorescent quantum yield and environmental pollution in the prior art are solved, and efficient, low-cost and environmentally friendly fluorescent carbon quantum dot preparation is achieved.
Patent Information
- Application Number
- CN202510208339.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-25
- Publication Date
- 2025-06-20
AI Technical Summary
The prior art when synthesizing fluorescent carbon quantum dots, the preparation takes a long time, the fluorescent quantum yield is low, and a large amount of organic solvents are required, resulting in environmental pollution and high costs.
Use discarded latex or nitrile gloves as raw materials to synthesize fluorescent carbon quantum dots through calcination and hydrothermal methods, avoid the use of organic solvents, and simplify the process flow.
The synthesis of fluorescent carbon quantum dots with high fluorescent quantum yields has been achieved, which reduces preparation costs, reduces environmental pollution, and can be applied to anti-counterfeiting printing and information encryption without additional modification.
Smart Images
Figure CN120173601A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to fluorescent carbon nanomaterials, in particular to a fluorescent carbon quantum dot and its preparation method and application. Background Art
[0002] Carbon quantum dots (CQDs) are a novel zero-dimensional carbon-based nanomaterial, with unique fluorescent properties, low toxicity, excellent biocompatibility, good hydrophilicity, and easy surface modification. They have shown great application prospects in the fields of fluorescent anti-counterfeiting printing, fluorescent sensing, biomedicine, optoelectronic devices, photoelectrocatalysis, etc. In particular, they exhibit advantages such as fluorescent anti-counterfeiting, multi-factor anti-counterfeiting, invisible ink, high-resolution printing, environmental friendliness, stability, and intelligent response in anti-counterfeiting printing, and are suitable for high-security fields such as currency, certificates, and luxury labels.
[0003] The synthesis methods of CQDs are generally divided into top-down and bottom-up strategies. The CQDs obtained by the top-down method have low quantum yields and poor water solubility, and need to be modified to improve their optical properties. The bottom-up method is the commonly used method for researchers to synthesize CQDs. It uses polymerizable functional groups in precursor molecules to create larger carbon-based structures. The precursor materials for synthesizing CQDs include carbohydrates, organic acids, biomass, carbon materials, organic small molecules, and amino acids and proteins.
[0004] However, when synthesizing CQDs by the bottom-up method using the reported precursor materials, it is necessary to synthesize in the liquid phase, which takes a long time to prepare, the obtained CQDs have low fluorescence quantum yields and need further modification. At the same time, a large amount of organic solvents need to be used, which not only increases the preparation cost, but also generates a large amount of difficult-to-treat waste liquid, causing potential environmental pollution risks. Therefore, developing a green and efficient method for synthesizing fluorescent CQDs still faces great challenges.
[0005] In China, there are many waste latex gloves and nitrile gloves from medical institutions, laboratories, industries, and daily life every year. These waste gloves degrade slowly in nature and exist in the environment for a long time, leading to soil pollution and water pollution. If incinerated, harmful gases are released, causing air pollution. In addition, industrial gloves may contain chemical residues that are harmful to the environment and human health. Therefore, promoting the recycling and transformation of waste latex gloves and nitrile gloves is an important way to achieve resource recycling and environmental protection, and is of great significance for promoting green transformation and development. Summary of the Invention
[0006] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a kind of fluorescent carbon quantum dots and their preparation method and application. Using waste latex and nitrile gloves as raw materials to synthesize fluorescent carbon quantum dots not only has the advantages of low cost and environmental friendliness, but also the synthesized fluorescent carbon quantum dots have a high fluorescence quantum yield and can be used for anti-counterfeiting printing and information encryption.
[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:
[0008] A preparation method of fluorescent carbon quantum dots, comprising the following steps:
[0009] Step 1: Pretreat the waste latex or nitrile gloves to obtain clean fragments. Take 3 - 4 g of clean fragments and put them into a ceramic crucible. Place the ceramic crucible in a tube furnace. In an air atmosphere, calcine at a temperature of 255 - 295 °C for 4 - 6 h. After cooling, grind to obtain a black powder;
[0010] Step 2: Add 30 mL of pure water to 4 - 6 mL of phosphoric acid solution with a mass fraction of 85% to obtain a diluted phosphoric acid solution. Add 0.1 - 0.15 g of the black powder to the diluted phosphoric acid solution, stir evenly, and then transfer it to a hydrothermal autoclave. Place the hydrothermal autoclave in an oven at 245 °C and heat for 10 - 12 h to obtain a black liquid. Filter several times to obtain a yellowish-brown transparent aqueous solution of fluorescent carbon quantum dots;
[0011] Step 3: Freeze-dry the aqueous solution of fluorescent carbon quantum dots to obtain a powder of fluorescent carbon quantum dots.
[0012] Further, the process of the pretreatment in Step 1 is: first cut the waste latex or nitrile gloves into fragments smaller than 0.5 cm × 0.5 cm, then wash them clean with water, and then dry them to obtain clean fragments.
[0013] Further, the stirring in Step 2 is magnetic stirring for 1 - 2 h.
[0014] Further, the volume of the hydrothermal autoclave in Step 2 is 50 mL.
[0015] Further, the filtration in Step 2 is carried out using a 50 nm organic filter membrane and filtering 4 times.
[0016] A kind of fluorescent carbon quantum dots with a fluorescence quantum yield of 41.2%.
[0017] An application of the fluorescent carbon quantum dots, where the aqueous solution of the fluorescent carbon quantum dots is used as a fluorescent ink for anti-counterfeiting printing and information encryption.
[0018] Compared with the existing technology, the present invention has the following technical effects:
[0019] The present invention uses waste latex and nitrile gloves as raw materials, combines calcination and hydrothermal methods to synthesize fluorescent carbon quantum dots (CQDs) with a high fluorescence quantum yield, and has the following advantages: 1) Using waste latex or nitrile gloves as raw materials significantly reduces the preparation cost and realizes the resource utilization of waste latex and nitrile; 2) The reaction process does not require any organic solvents, reduces the generation of by-products, simplifies the post-treatment steps, and can effectively prevent the loss of CQDs caused by the cumbersome post-treatment process; 3) The obtained CQDs do not require additional modification and have a high fluorescence quantum yield of 41.2% in the aqueous solution state. In short, the method for synthesizing CQDs in the present invention has the advantages of simplicity, green safety, high fluorescence quantum yield, and low cost, providing an effective strategy for the large-scale production of fluorescent CQDs and the recycling of waste latex, nitrile gloves, and even various latex and nitrile waste materials.
[0020] The CQDs synthesized in the present invention have rich oxygen-containing groups on the surface, endowing the CQDs with good hydrophilicity and fluorescence properties. When applied to fluorescent anti-counterfeiting printing inks, different anti-counterfeiting patterns printed all show high fluorescence color development ability. Therefore, the fluorescent carbon quantum dots prepared in the present invention can be used as fluorescent anti-counterfeiting inks for anti-counterfeiting printing and information encryption. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1(a) and FIG. 1(b) are TEM photos of the fluorescent carbon quantum dots prepared in Example 2 of the present invention at different magnifications;
[0022] FIG. 1(c) is a particle size distribution diagram of the fluorescent carbon quantum dots prepared in Example 2 of the present invention;
[0023] Figure 2 is the fluorescence spectrum diagram of the aqueous solution of the fluorescent carbon quantum dots prepared in Example 2 of the present invention;
[0024] Figure 3 is a photo of the aqueous solution of the fluorescent carbon quantum dots prepared in Example 2 of the present invention under daylight and 365 nm ultraviolet light;
[0025] Figure 4 are photos of different patterns printed on cardboard as fluorescent inks with the aqueous solutions of the fluorescent carbon quantum dots prepared in Example 1 and Example 2 of the present invention under daylight and ultraviolet light respectively. DETAILED DESCRIPTION OF THE INVENTION
[0026] The following further elaborates on the specific content of the present invention in detail in combination with examples.
[0027] Example 1
[0028] Step 1: Cut the waste nitrile gloves into pieces smaller than 0.5 cm × 0.5 cm, wash them clean with water, and then dry them to obtain clean pieces. Take 3 g of the clean pieces and put them into a ceramic crucible. Place the ceramic crucible in a tube furnace and calcine it at a temperature of 295 °C in an air atmosphere for 4 h. After cooling, grind it to obtain a black powder.
[0029] Step 2: Add 30 mL of pure water to 4 mL of a phosphoric acid solution with a mass fraction of 85% to obtain a diluted phosphoric acid solution. Add 0.1 g of the black powder to the diluted phosphoric acid solution, stir magnetically for 1 h, and then transfer it to a 50 mL hydrothermal autoclave. Place the hydrothermal autoclave in an oven at 245 °C and heat it for 10 h to obtain a black liquid. Filter it 4 times using a 50 nm organic filter membrane to obtain a yellowish-brown transparent aqueous solution of fluorescent carbon quantum dots.
[0030] Step 3: Freeze-dry the aqueous solution of fluorescent carbon quantum dots to obtain a fluorescent carbon quantum dot powder.
[0031] Example 2
[0032] Step 1: Cut the waste latex gloves into pieces smaller than 0.5 cm × 0.5 cm, wash them clean with water, and then dry them to obtain clean pieces. Take 3.5 g of the clean pieces and put them into a ceramic crucible. Place the ceramic crucible in a tube furnace and calcine it at a temperature of 270 °C in an air atmosphere for 5 h. After cooling, grind it to obtain a black powder.
[0033] Step 2: Add 30 mL of pure water to 5 mL of a phosphoric acid solution with a mass fraction of 85% to obtain a diluted phosphoric acid solution. Add 0.12 g of the black powder to the diluted phosphoric acid solution, stir magnetically for 1.5 h, and then transfer it to a 50 mL hydrothermal autoclave. Place the hydrothermal autoclave in an oven at 245 °C and heat it for 11 h to obtain a black liquid. Filter it 4 times using a 50 nm organic filter membrane to obtain a yellowish-brown transparent aqueous solution of fluorescent carbon quantum dots.
[0034] Step 3: Freeze-dry the aqueous solution of fluorescent carbon quantum dots to obtain a fluorescent carbon quantum dot powder.
[0035] Figure 1(a) and Figure 1(b) are TEM photos of the fluorescent carbon quantum dots prepared in Example 2 at different magnifications. It can be seen that the particles of the fluorescent carbon quantum dots are spherical-like, and the particles are completely dispersed without any agglomeration.
[0036] Figure 1(c) is the particle size distribution diagram of the fluorescent carbon quantum dots prepared in Example 2. It can be seen that the particle size distribution range of the fluorescent carbon quantum dots is 1.5 - 9.5 nm, and the average particle size is 3.2 nm.
[0037] Figure 2Fluorescence spectra of the aqueous solution of fluorescent carbon quantum dots prepared in Example 2, where: (a) is the fluorescence spectrum at different excitation wavelengths, and (b) is the optimal excitation and emission spectra. As can be seen from Figure (a), when the excitation wavelength gradually increases from 350 nm to 440 nm, the intensity of the corresponding emission spectrum first increases and then decreases, and gradually redshifts with the increase of the excitation wavelength, showing obvious excitation-dependent fluorescence properties; as can be seen from Figure (b), the optimal excitation spectrum is located at 392 nm, and the corresponding optimal fluorescence emission spectrum is located in the blue light region at 462 nm.
[0038] The aqueous solution of fluorescent carbon quantum dots prepared in Example 2 was placed under daylight and ultraviolet light for observation respectively, and the results are as Figure 3 shown. The aqueous solution of fluorescent carbon quantum dots appears transparent brown-yellow under daylight, and emits bright blue fluorescence under the irradiation of a 365 nm ultraviolet lamp, which is consistent with the Figure 2 fluorescence spectrum.
[0039] The aqueous solutions of fluorescent carbon quantum dots prepared in Example 1 and Example 2 were respectively filled into the ink cartridges of a printer, and two different patterns of "1953" and "SUST" were printed on the cardboard respectively, where Figure 4 (a) is a photo of the cardboard printed with the number "1953" under a daylight lamp, Figure 4 (c) is a photo of the cardboard printed with the letter "SUST" under a daylight lamp. It can be seen that the numbers and letters are hardly visible; Figure 4 (b) and Figure 4 (d) are photos of the cardboard printed with different patterns under a 365 nm ultraviolet lamp. The letters and numbers can be clearly seen, indicating that the fluorescent carbon quantum dots prepared in Example 1 and Example 2 have good fluorescence properties and can be used as fluorescent anti-counterfeiting inks for anti-counterfeiting printing and information encryption.
[0040] Using quinine sulfate as a fluorescence reference, the fluorescence quantum yield of the aqueous solution of fluorescent carbon quantum dots prepared in Example 2 was determined to be 41.2% at the optimal excitation wavelength of 392 nm by the reference method.
[0041] Example 3
[0042] Step 1: Cut the waste latex gloves into pieces smaller than 0.5 cm × 0.5 cm, wash them clean with water, and then dry them to obtain clean pieces. Take 4 g of clean pieces and put them into a ceramic crucible. Place the ceramic crucible in a tube furnace and calcine it at a temperature of 255 °C for 6 h in an air atmosphere. After cooling, grind it to obtain a black powder;
[0043] Step 2: Add 30 mL of pure water to 6 mL of phosphoric acid solution with a mass fraction of 85% to obtain a diluted phosphoric acid solution. Add 0.15 g of black powder to the diluted phosphoric acid solution, stir magnetically for 2 h, then transfer it to a 50 mL hydrothermal reactor. Place the hydrothermal reactor in an oven at 245 °C and heat for 12 h to obtain a black liquid. Filter it 4 times using a 50 nm organic filter membrane to obtain a yellow-brown transparent aqueous solution of fluorescent carbon quantum dots;
[0044] Step 3: Freeze-dry the aqueous solution of fluorescent carbon quantum dots to obtain fluorescent carbon quantum dot powder.
[0045] Comparative example
[0046] Step 1: Cut waste latex gloves into pieces smaller than 0.5 cm × 0.5 cm, wash them with clean water, and then dry them to obtain clean pieces. Take 3.5 g of clean pieces and put them into a ceramic crucible. Place the ceramic crucible in a tube furnace and calcine it at 270 °C for 5 h in an air atmosphere. After cooling, grind it to obtain black powder;
[0047] Step 2: Add 0.12 g of black powder to 35 mL of pure water, stir magnetically for 1.5 h, then transfer it to a 50 mL hydrothermal reactor. Place the hydrothermal reactor in an oven at 245 °C and heat for 11 h to obtain a black liquid. Filter it 4 times using a 50 nm organic filter membrane to obtain a yellow-brown transparent aqueous solution of fluorescent carbon quantum dots;
[0048] Step 3: Freeze-dry the aqueous solution of fluorescent carbon quantum dots to obtain fluorescent carbon quantum dot powder.
[0049] Using quinine sulfate as a fluorescence reference, at the optimal excitation wavelength of 345 nm, the fluorescence quantum yield of the aqueous solution of fluorescent carbon quantum dots prepared in the comparative example was measured to be only 9.81% by the reference method, which is much lower than the fluorescence quantum yield of 41.2% of the aqueous solution of fluorescent carbon quantum dots prepared in Example 2. The reason why the aqueous solution of fluorescent carbon quantum dots prepared in Example 2 has a high fluorescence quantum yield is as follows: On the one hand, the phosphorus atom in the phosphoric acid molecule is connected to the surface of the carbon quantum dots in the form of chemical bonds during the hydrothermal reaction, introducing functional groups with specific electronic properties, which enables the formation of new electronic structures and energy levels on the surface of the carbon quantum dots. These can participate in the electron transition process and generate fluorescence, and interact with the fluorescence of the carbon quantum dots itself to synergistically improve the overall fluorescence quantum yield. On the other hand, there are usually some unsaturated bonds or active sites on the surface of the carbon quantum dots. These sites may become non-radiative recombination centers, leading to fluorescence quenching. The modification with phosphorus can fill the surface dangling bonds and reduce surface defects and non-radiative transition channels, enabling more excited-state electrons to return to the ground state through radiative transition and release fluorescence, thereby increasing the fluorescence quantum yield of the carbon quantum dots in the hydrothermal reaction in the presence of phosphoric acid.
Claims
1. A method for preparing fluorescent carbon quantum dots, characterized in that: The steps include: Step 1, pre-treating the discarded latex or nitrile gloves to obtain clean fragments, taking 3 to 4 g of the clean fragments and putting them into a ceramic crucible, placing the ceramic crucible in a tube furnace, calcining for 4 to 6 hours at a temperature of 255 to 295° C. in an air atmosphere, and grinding after cooling to obtain a black powder; Step 2, add 30mL of pure water to 4-6mL of 85% phosphoric acid solution to obtain a diluted phosphoric acid solution, add 0.1-0.15g of black powder to the diluted phosphoric acid solution, stir evenly, and then transfer to a hydrothermal kettle, place the hydrothermal kettle in an oven at 245°C, heat for 10-12h, obtain a black liquid, filter several times, and obtain a yellow-brown transparent fluorescent carbon quantum dot aqueous solution; Step 3: freeze-dry the fluorescent carbon quantum dot aqueous solution to obtain fluorescent carbon quantum dot powder.
2. The method for preparing fluorescent carbon quantum dots according to claim 1, characterized in that: The pretreatment process of step 1 is: firstly cut the discarded latex or nitrile gloves into fragments smaller than 0.5 cm×0.5 cm, then wash them with clean water, and then dry them to obtain clean fragments.
3. The method for preparing fluorescent carbon quantum dots according to claim 1, characterized in that: The stirring in step 2 is magnetic stirring for 1 to 2 hours.
4. The method for preparing fluorescent carbon quantum dots according to claim 1, characterized in that: The volume of the hydrothermal kettle in step 2 is 50 mL.
5. The method for preparing fluorescent carbon quantum dots according to claim 1, characterized in that: The filtration in step 2 is performed using a 50 nm organic filter membrane and filtered 4 times.
6. A fluorescent carbon quantum dot prepared by the method according to any one of claims 1 to 5, characterized in that: The fluorescence quantum yield of the fluorescent carbon quantum dots aqueous solution is 41.2%.
7. The use of fluorescent carbon quantum dots according to claim 6, characterized in that: Fluorescent carbon quantum dot aqueous solution is used as fluorescent ink for anti-counterfeiting printing and information encryption.