Boron-doped carbon quantum dot as well as preparation method and application thereof

Abstract

The invention relates to the field of heavy metal detection, in particular to a boron-doped carbon quantum dot and a preparation method and application thereof. In order to realize synchronous detection of dichromate radicals and permanganate radicals, curcumin and m-phenylenediamine are used as a carbon source and a nitrogen source, boric acid is used as a boron element doping agent, and the boron-doped carbon quantum dots are obtained by adopting a one-step solvothermal method. Wherein curcumin and m-phenylenediamine are used as precursors, boric acid is used as a boron element doping agent, and the boron-doped carbon quantum dots are synthesized. The preparation method is simple, and the prepared B-N-CDs has blue-green fluorescence, shows excellent biocompatibility and photobleaching resistance, is successfully applied to detection of Cr2O7 < 2-> and MnO4 <-> in water, is successfully applied to the field of fluorescent ink, and has potential value in the aspect of anti-counterfeiting marks.

Description

Technical Field

[0001] The present invention relates to the field of heavy metal detection, and in particular to boron-doped carbon quantum dots, a preparation method thereof, and applications thereof. Background Art

[0002] The presence of toxic metals in the environment is considered a major risk to human health.

[0003] Chromate mainly comes from industrial wastewater and waste discharge, and chromium-containing compounds are used in many industrial processes. When these substances enter the water body, they will cause water pollution and endanger the aquatic ecosystem, thereby damaging the survival and reproduction of aquatic organisms and the ecological balance. At the same time, dichromate can also pose a serious threat to human health. When the concentration is low, it can induce genetic defects, allergic reactions and cancer. Permanganate is highly oxidizing and toxic to aquatic organisms. It can cause oxidative stress reactions in organisms and affect the growth and reproduction of organisms. When the concentration of permanganate is high, it is toxic to the human body and can cause lung dysfunction, Parkinson's disease, bronchitis, and hinder the intellectual development and normal growth of infants. Therefore, there is an urgent need to construct a dichromate (Cr2O7 2- ) and permanganate (MnO4 - ) Synchronous detection system to meet the precise quantification needs in environmental monitoring and industrial process control. Summary of the Invention

[0004] In view of the above problems, the present invention provides a boron-doped carbon quantum dot and a preparation method thereof, as well as a method for preparing the same in Cr2O7 2- and MnO4 - Application in visual detection.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing boron-doped carbon quantum dots, comprising the following steps:

[0007] Step 1, dissolving curcumin, m-phenylenediamine and boric acid in anhydrous ethanol and performing a hydrothermal reaction;

[0008] Step 2: After the hydrothermal reaction is completed, centrifugation, filtration, and rotary evaporation are performed in sequence, and the obtained viscous liquid is dispersed in ultrapure water and freeze-dried to obtain the boron-doped carbon quantum dots.

[0009] Furthermore, in step 1, the molar ratio of curcumin, m-phenylenediamine and boric acid is 1:5:3-20.

[0010] Furthermore, the temperature of the hydrothermal reaction in step 1 is 220° C. and the time is 6 hours.

[0011] Furthermore, the centrifugal speed in step 2 is 10000 rpm and the time is 10 min.

[0012] Furthermore, filtration was performed using a 0.22 μM microporous filter membrane.

[0013] Furthermore, the temperature of rotary evaporation concentration was 60° C. and the time was 1.5 h.

[0014] Furthermore, the freeze-drying temperature is -50°C and the time is 24 hours.

[0015] In a second aspect, the present invention provides boron-doped carbon quantum dots prepared by the preparation method.

[0016] In the third aspect, the present invention provides an application of boron-doped carbon quantum dots, which successfully applies BN-CDs to Cr2O7 in water. 2- With MnO4 - This synthesis method has the advantages of simple process and controllable conditions. It effectively regulates the electronic structure of carbon quantum dots by element doping, significantly enhancing the fluorescence performance and chemical stability of the material.

[0017] In a fourth aspect, the present invention provides an application of boron-doped carbon quantum dots, which are applied in the field of fluorescent ink and have potential value in anti-counterfeiting marking.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention uses curcumin and m-phenylenediamine as carbon and nitrogen sources, boric acid as a boron dopant, and a one-step solvent thermal method to obtain the boron-doped carbon quantum dots. Curcumin and m-phenylenediamine are used as precursors, and boric acid is used as a boron dopant to synthesize boron-doped carbon quantum dots (BN-CDs). The preparation method is simple, and the prepared BN-CDs have blue-green fluorescence, excellent biocompatibility and anti-photobleaching properties, and can be successfully applied to Cr2O7 2- and MnO4 - It has applications in heavy metal ion detection and can be successfully applied to the field of fluorescent ink, and has potential value in anti-counterfeiting labeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The effect of material ratio on the fluorescence of carbon dots under the synthesis conditions.

[0021] Figure 2 In the figure, a is the TEM image of BN-CDs, the inset is HR-TEM, b is the particle size distribution of BN-CDs, and c is the FT-IR spectrum of BN-CDs.

[0022] Figure 3In the figure, a is the full XPS spectrum of BN-CDs, b is the C spectrum, c is the N spectrum, d is the B spectrum, e is the O spectrum, and f is the Raman spectrum.

[0023] Figure 4 In the figure, a is the effect of different salt ion concentrations on the fluorescence intensity of BN-CDs, b is the effect of different pH on the fluorescence intensity of BN-CDs, and c is the effect of xenon lamp irradiation time on the fluorescence intensity of BN-CDs.

[0024] Figure 5 In the figure, a is the UV and fluorescence spectra of BN-CDs, b is the CIE coordinate diagram of BN-CDs, and c is the emission spectra of BN-CDs at different excitation wavelengths.

[0025] Figure 6 The selectivity of BN-CDs to metal ions in different pH buffers and secondary water.

[0026] Figure 7 The effects of different pH on the interaction between BN-CDs and metal ions Cr2O7 2- With MnO4 - The impact of reaction time.

[0027] Figure 8 In the equation, a is different Cr2O7 2- Effect of the fluorescence spectrum of BN-CDs, b is ΔF and Cr2O7 2- Nonlinear fitting diagram of concentration, c is ΔF and Cr2O7 2- The linear fitting diagram of the concentration, d is the anti-interference ability of BN-CDs.

[0028] Figure 9 In the equation, a is different MnO4 - Effect of concentration on the fluorescence spectrum of BN-CDs, b is ΔF and MnO4 - Nonlinear fitting diagram of concentration, c is ΔF and MnO4 - The linear fitting diagram of the concentration, d is the anti-interference of BN-CDs.

[0029] Figure 10 In the figure, a is the effect of different AA concentrations on BN-CDs+Cr2O7 2- b is the nonlinear fitting diagram of ΔF and AA concentration, and c is the linear fitting diagram of ΔF and AA concentration.

[0030] Figure 11 In the figure, a is the fluorescence lifetime, b is the fluorescence spectrum of BN-CDs and Cr2O7 2- 、MnO4 - UV absorption spectrum, c is UV-visible absorption spectrum, d is zeta potential, e is different concentrations of MnO4- Absorption spectrum after dropping BN-CDs solution, f is MnO 4- The Stern-Volmer curve of

[0031] Figure 12 In the figure, a is the anti-counterfeiting color development of N-CDs and BN-CDs, and b is the fluorescence color development of the BN-CDs pattern after treatment at different temperatures. DETAILED DESCRIPTION

[0032] In order to further illustrate the technical solution of the present invention, the present invention is further described below through examples.

[0033] Fluorescence spectrophotometry, particularly fluorescent probes, has attracted widespread attention due to its high sensitivity, cost-effectiveness, practicality, rapid response, and simplicity. CDs, as environmentally friendly fluorescent nanomaterials, possess low toxicity, good water solubility, and superior optical properties compared to traditional quantum dots. In particular, moderate doping with heteroatoms (such as nitrogen, sulfur, and boron) can alter their surface structure and electron distribution, leading to changes in the physicochemical properties of CDs, thereby increasing quantum yield and improving fluorescence properties. Consequently, they are widely used for the detection of heavy metal ions in the environment.

[0034] A first aspect of the present invention provides a method for preparing boron-doped carbon quantum dots, comprising the following steps:

[0035] Dissolve curcumin, m-phenylenediamine and boric acid in anhydrous ethanol and perform a hydrothermal reaction;

[0036] After the hydrothermal reaction is completed, filtration and freeze-drying are carried out in sequence to obtain the boron-doped carbon quantum dots.

[0037] In a preferred embodiment of the present invention, the molar ratio of curcumin, m-phenylenediamine and boric acid is 1:5:15.

[0038] In a preferred embodiment of the present invention, the hydrothermal reaction temperature is 220°C and the time is 6 hours.

[0039] The molar ratio of curcumin, m-phenylenediamine and boric acid is the best to achieve a higher quantum yield B - N - The key to CDs preparation is to obtain BN-CDs with the best fluorescence performance by maintaining the optimal temperature at 220℃ and the optimal time for 6 hours, and only changing the single variable of the material ratio of the reaction substrate to control the optimal emission fluorescence intensity and quantum yield of BN-CDs. Figure 1As shown, the fluorescence intensity corresponding to the optimal emission reaches its maximum when the curcumin:m-phenylenediamine:boric acid ratio is 1:5:15. Table 1 shows the effect of different material ratios on quantum yield. It can be seen that the highest quantum yield (7.64%) is achieved when the curcumin:m-phenylenediamine:boric acid ratio is 1:5:15. Therefore, the best performance of the synthesized B-CDs is achieved when the reaction temperature is 220°C, the reaction time is 6 hours, and the curcumin:m-phenylenediamine:boric acid ratio is 1:5:15.

[0040] The solution was filtered through a 0.22 μm filter membrane, and the filtrate was concentrated by rotary evaporation (60 °C, 1.5 h). The resulting viscous liquid was dispersed in ultrapure water (20 mL) and freeze-dried (-50 °C, 24 h) to obtain carbon dot powder.

[0041] Table 1 Effect of material ratio on quantum yield

[0042] Curcumin: m-phenylenediamine: boric acid Quantum yield 1:5:3 7.38% 1:5:5 7.58% 1:5:10 6.55% 1:5:15 7.64% 1:5:20 7.60%

[0043] The second aspect of the present invention provides boron-doped carbon quantum dots prepared according to the above preparation method. The BN-CDs have excellent salt resistance, acid and alkali resistance, and photobleaching resistance.

[0044] The third aspect of the present invention provides the boron-doped carbon quantum dots for detecting Cr2O7 in water environment. 2- and MnO4 - and its application in anti-counterfeiting color development.

[0045] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0046] Example 1

[0047] Curcumin (36.8 mg, 0.1 mmol), m-phenylenediamine (54 mg, 0.5 mmol), and boric acid (92.7 mg, 1.5 mmol) were dissolved in anhydrous ethanol (20 mL) at a molar ratio of 1:5:15 and ultrasonically treated (40 kHz, 10 min) to achieve uniform dispersion. The mixed solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and reacted at 220°C in a forced air drying oven for 6 h. After cooling naturally to room temperature, the reaction solution was centrifuged at high speed (10,000 rpm, 10 min), the supernatant was filtered through a 0.22 μM microporous membrane, and the filtrate was concentrated by rotary evaporation (60°C, 1.5 h). The resulting viscous solution was dispersed in ultrapure water (20 mL) and freeze-dried (-50°C, 24 h) to obtain carbon dot powder BN-CDs.

[0048] The BN-CDs prepared in Example 1 were characterized and their performance tested as follows:

[0049] 1. B - N - Morphological characterization of CDs

[0050] The morphology, particle size and dispersibility of the synthesized BN-CDs were characterized by TEM. Figure 2 As shown in (a), TEM images show that most BN-CDs are uniformly dispersed single spheres. Figure 2 The inset in Figure a is a high-resolution transmission electron micrograph of BN-CDs, showing clear lattice fringes with a lattice spacing of 0.20 nm. This lattice spacing corresponds to the (100) graphite plane, indicating that BN-CDs have a graphite-like crystal structure. Statistical analysis of the particle sizes of 100 random nanoparticles was performed, and a bar chart was drawn ( Figure 2 Figure (b) shows that the particle size distribution of BN-CDs ranges from 1.5 to 3.6 nm, with an average diameter of 2.43 ± 0.028 nm. Compared to N-CDs, BN-CDs have larger particle sizes. This may be due to the weaker bonding ability of B (the B–C bond energy is lower than that of N–C), resulting in a dominant particle growth phase and ultimately a larger particle size.

[0051] 2. Structural characterization of carbon dots

[0052] The surface functional groups of BN-CDs were measured by FT-IR. Figure 2 As shown in c. From 3251 to 3499 cm -1 The broad absorption band of BN-CDs indicates that there are a large number of amino groups (-NH) or hydroxyl groups (-OH) on the surface of BN-CDs. The FT-IR spectrum of BN-CDs has a peak at 2966 cm -1 The peak at 783 cm is the stretching vibration peak of CH. -1 and 1431cm -1 The absorption peaks at 692 cm are BC and BO. -1 The aromatic vibration peak of 1618cm indicates that the carbon dots have a graphitized or graphene-like aromatic conjugated system. -1 The absorption peak at 1029 cm is the stretching vibration peak of C=O. -1 and 1165 cm -1 The two peaks shown at are attributed to the stretching vibrations of CO and CC.

[0053] In addition, XPS was used to analyze the surface elements and chemical bonds of BN-CDs. Figure 3 (a) confirms the presence of B, N, C and O spectra in BN-CDs. C1s high-resolution XPS spectrum ( Figure 3b) There are three peaks at 285.23 eV, 283.81 eV, and 283.23 eV, which are attributed to C-O / CN, CC, and BC structures, respectively. N1s XPS spectrum ( Figure 3 The B1s XPS spectrum (c) shows three peaks, indicating that the N element exists in the form of pyridinic N, pyrrolic N and amino N, corresponding to the peaks at 397.73 eV, 398.35 eV and 398.95 eV respectively. Figure 3 Middle d) shows the presence of BO (191.25 eV) and BC bonds (190.75 eV), which is consistent with the 783 cm-1 peak in the infrared spectrum. -1 and 1431 cm -1 The absorption peaks at correspond to each other, indicating that boron has been successfully incorporated into carbon dots, forming BC chemical bonds and partially oxidized boron structures. O1s XPS spectrum ( Figure 3 (e) Two peaks at 530.85 and 531.92 eV are attributed to the CO / OB and C=O bonds, respectively. Combining XPS and FT-IR results, it can be inferred that BN-CDs were successfully prepared. Figure 3 f is the Raman spectrum of BN-CDs, 1360 cm -1 and 1580 cm -1 The broad peaks at and correspond to the D band and G band, respectively. Their intensity is higher than that of D / I G It is 0.92, indicating that the material has abundant active sites and retains some graphitized structure.

[0054] 3. Stability of carbon dots

[0055] The stability of BN-CDs is an important indicator for evaluating the performance of BN-CDs fluorescence sensors. Therefore, the stability of BN-CDs was evaluated from three aspects: salt ion solution, pH buffer solution, and xenon lamp irradiation time. Figure 4 As shown in Figure a, the intensity of BN-CDs remained basically unchanged when the salt ion concentration increased from 0.01 μM to 1 M. Figure 4 As shown in Figure b, the emission spectrum changes under 405 nm excitation under different pH conditions. As the pH continues to increase, the emission site of BN-CDs red-shifts. At the same time, the fluorescence intensity of BN-CDs in acidic environment is significantly better than that in alkaline environment. This may be because BN-CDs can improve the luminescence performance of carbon dots through charge regulation, defect passivation and solvent synergy in acidic environment, while under alkaline and neutral conditions, functional group deprotonation or charge neutralization can easily induce aggregation or non-radiative recombination, resulting in performance degradation. Figure 4Figure c shows the fluorescence intensity of BN-CDs after 60 minutes of continuous xenon lamp irradiation. The fluorescence intensity of BN-CDs shows little decrease with increasing xenon lamp irradiation time, remaining essentially constant, demonstrating their relatively good resistance to photobleaching and long-term stability. These results demonstrate the excellent photostability of BN-CDs, ensuring their successful applications in biosensing and environmental applications.

[0056] 4. Optical properties of carbon dots

[0057] The UV-visible absorption and fluorescence spectra of B - N - The optical characteristics of CDs were evaluated. Figure 5 As shown in Figure a, the absorption spectrum of BN-CDs in secondary water has two obvious absorption peaks. The higher peak at 290nm corresponds to the π-π* transition of the aromatic conjugated structure in the carbon quantum dots, and the peak at 406nm corresponds to the n-π* transition. Figure 5 As shown in b, the luminescence of BN-CDs under sunlight and ultraviolet light can be clearly observed in B - N - The solution of CDs appears yellow under natural light and bright green under ultraviolet light. The chromaticity and brightness of BN-CDs are accurately described using the CIE coordinate diagram, and its coordinates are (0.221, 0.421), which is consistent with the results of its fluorescence emission. The optimal excitation and emission spectra of BN-CDs in secondary water are as follows. Figure 5 As shown in Figure a, it can be seen that the maximum excitation wavelength (λex) of BN-CDs is 405 nm, and the corresponding emission wavelength (λem) is 531 nm. The excitation wavelength increases from 365 nm to 435 nm at intervals of 10 nm ( Figure 5 In Figure (c), it can be seen that as the excitation wavelength continues to increase, the peak position at the maximum emission wavelength undergoes a red shift, and the intensity shows a trend of first increasing and then decreasing. The fluorescence intensity reaches its optimum when the excitation wavelength is 405 nm. The reason for this may be that the electron-richness of N and the electron-deficient nature of B synergistically change the band structure of CDs, forming multi-level surface states and enhancing the excitation wavelength dependence. In addition, using coumarin 365 as a reference standard, the relative quantum yield of BN-CDs was calculated to be 7.64% at room temperature. Compared with N-CDs, the quantum yield of BN-CDs has been improved, which may be because boron doping improves the quantum yield of carbon quantum dots through mechanisms such as surface passivation, electronic structure optimization, and carbon core ordering.

[0058] 5. BN-CDs to Cr2O7 2- 、MnO4 - Selectivity

[0059] When using carbon dots as fluorescent markers to detect metal ions, their ability to identify specific metal ions is crucial. First, the selectivity of BN-CDs for metal ions under 405 nm excitation in secondary water was investigated. Figure 6 f). It can be seen that among the many ions, BN-CDs has the strongest effect on Cr2O7 2- With MnO4 - The fluorescence quenching effect of the two metal ions is the most significant, exceeding 70%, so Cr2O7 2- With MnO4 - Due to the effect of BN-CDs on Ag + There is also a partial quenching effect. At the same time, the pH of the detection environment has a great influence on the fluorescence intensity of BF-CDs. Therefore, the optimal pH is selected to improve the detection effect.

[0060] like Figure 6 As shown, B - Fluorescence quenching behavior of N-CDs in Cr2O7 2- and MnO4 - The system showed significant pH dependence. 2- , it exhibits efficient fluorescence quenching effect (quenching rate>75%) in the acidic range of pH 2-7, indicating that its binding mechanism with BN-CDs is less affected by protonation and may be dominated by electron transfer induced by strong oxidizing properties or surface coordination. In contrast, MnO4 - The fluorescence quenching efficiency of showed a clear pH gradient characteristic: the quenching rate was only 60% at pH 2-3, while it increased to more than 70% at pH 3-6. This phenomenon can be attributed to the following synergistic mechanisms: (1) Under low pH conditions, high concentrations of H + By protonating the amino groups (–NH2) and oxygen-containing functional groups on the surface of BN-CDs, the MnO4 - Competitive adsorption is formed, which significantly inhibits its binding efficiency; (2) As the pH increases (pH>3), the hydrogen ion concentration decreases, and MnO4 - The adsorption driving force of MO4 is enhanced, and the moderately increased ionic strength weakens the electrostatic repulsion between particles through the Debye screening effect, promoting the adsorption of MO4 - Interfacial binding with BN-CDs.

[0061] The time required for the reaction to reach equilibrium ( Figure 7 ) from the perspective of Cr2O7 2- With MnO4 -The fluorescence response time of the two showed regular differences with pH changes. At pH 2-3, the response time of both was extended to 60-90 s, while at pH 4-7 it was shortened to less than 30 s. This difference may be related to the following factors: (1) H+ occupation of surface active sites at low pH slowed down the adsorption kinetics; (2) high hydrogen ion concentration could induce B - N - The surface potential of CDs increases, which reduces the anion diffusion rate by enhancing electrostatic repulsion. It is worth noting that at pH 4, Cr2O7 2- With MnO4 - The fluorescence quenching efficiency of the Ag nanoparticles was 78.6% and 75.1% respectively, and the response time was less than 30 s. + The selectivity of BN-CDs is significantly better than other pH conditions. Taking into account the equilibrium time, selectivity and detection sensitivity, pH 4 was determined to be the optimal pH for BN-CDs to detect Cr2O7 2- With MnO4 - Optimization conditions.

[0062] 6. B - N - CDs to Cr2O7 2- Detection

[0063] Under the optimized detection conditions, - N - Gradient introduction of Cr2O7 into CDs system 2- (5-100μM), and its fluorescence response behavior was systematically investigated. 2- With the increasing concentration, the fluorescence emission peak of BN-CDs did not shift significantly, the intensity of BN-CDs showed a gradual downward trend, and the emission wavelength did not shift significantly ( Figure 8 (a) According to the change of its intensity and MO4 - The concentration was fitted with the Boltzmann equation ( Figure 8 In b), the fitting equation is Y=3810.952-714595.663 / (1+exp(X+3477.568) / 260.482)), R²=0.998. Further analysis shows that in the concentration range of 5-100μM, the change in fluorescence intensity is related to the Cr2O7 2- There was a significant linear relationship between the concentrations ( Figure 8 In Figure c), the linear regression equation is ΔF=6.232X+128.516, R2=0.990, and LOD=0.25μM. The reason why BN-CDs are less sensitive than N-CDs may be that the electron-deficient property of boron may form electron traps, interfere with the electron transfer path, and reduce the sensitivity of the reaction with Cr2O7. 2- and MnO4- The electron coupling efficiency.

[0064] In order to verify the practical application potential of BN-CDs, its anti-interference performance was further evaluated. Figure 8 As shown in Figure d, in the presence of interfering ions (including Ag + , Pb 2+ 、Cd 2+ 、Cu 2+ 、Hg 2+ Under the coexistence conditions of BN-CDs and Cr2O7 2- The fluorescence response of the probe was good, indicating that the probe has a good fluorescence response to Cr2O7 2- It has excellent selective recognition ability and can meet the needs of Cr2O7 in complex systems. 2- Specific detection needs.

[0065] 7. BN-CDs to MnO4 - Detection

[0066] Under the optimal detection conditions, different concentrations of MnO4 - Added to BN-CDs, and observed the change in fluorescence intensity. Figure 9 As shown in a, with the MnO4 - With the increasing concentration, the intensity of NB-CDs showed a trend of gradual decrease, and the emission wavelength had no obvious shift. - The concentration was fitted with the Boltzmann equation, and the results were as follows Figure 9 As shown in b, the fitting equation is Y=3117.004-38778.78 / (1+exp(X+864.898) / 343.754), R2=0.990. At the same time, MnO4 - In the concentration range of 0.5-40 μM, the fluorescence intensity changes with the 72 - The concentration changes linearly (e.g. Figure 9 In (c), the linear equation is Y=16.96X+61.19, the correlation coefficient R2=0.992, and the LOD is 0.21μM. Anti-interference performance is also an important feature for the practical application of BN-CDs. Figure 9 The fluorescence intensity of BN-CDs in the presence of different metal ions is shown in d. - Can effectively quench N - The fluorescence of CDs showed that BN-CDs could be used to treat MnO4 - It has strong selectivity and anti-interference ability.

[0067] 8. Based on BN-CDs / Cr2O72- AA detection

[0068] The fluorescence of BN-CDs was 2- By introducing AA as a reducing agent, a new type of "open-type" fluorescent probe was constructed to achieve the specific quenching of Cr2O7. 2- The indirect detection of Cr2O7 and the dynamic monitoring of new pollutants. Its mechanism of action is as follows: 2- It forms a non-fluorescent complex with BN-CDs through surface coordination and electron transfer (BN-CDs / Cr2O7 2- ), and AA can convert Cr2O7 2- Reduction to Cr 3+ , resulting in the dissociation of the complex and the restoration of the fluorescence signal of BN-CDs. This process showed a significant concentration dependence. When the AA concentration increased from 0 μM to 700 μM, the fluorescence intensity at 507 nm showed a gradient upward trend, indicating that AA effectively regulated the Cr2O7 2- The coordination state ( Figure 10 To further quantify the response behavior, the Boltzmann equation was used to fit the nonlinear relationship between the fluorescence intensity change and the AA concentration ( Figure 10 b), the fitting equation is:

[0069] ΔF=1556.96897-1570.11629 / 1+exp((X-290.08821) / 75.64241)), R²=0.992.

[0070] The model reveals the saturation response characteristics of the system, indicating that in the low concentration range (0.5-80 μM), the fluorescence intensity is significantly linearly related to the AA concentration ( Figure 10 In (c), the linear regression equation is ΔF=8.742X+12.369, R 2 =0.991, and the limit of detection (LOD) was 0.092 μM.

[0071] 9. Mechanism exploration

[0072] Due to the abundant functional groups on the surface of BN-CDs, they can specifically recognize target analytes through different mechanisms. Therefore, a series of experiments were conducted to study the effect of BN-CDs on Cr2O7 2- 、MnO4 - Reaction mechanism with AA. 2- In the case of B - Time-resolved fluorescence decay curves of N-CDs ( Figure 11 a). When adding Cr2O7 2-Under the condition of Cr2O7, the fluorescence lifetime of BN-CDs changes from 5.37 ns to 5.65 ns, with no significant change. This suggests that the quenching mechanism may be mainly static quenching or internal filter effect, rather than dynamic quenching. Dynamic quenching usually leads to a decrease in fluorescence lifetime, while static quenching or IFE does not affect the lifetime. 2- The strong absorption band at 350 nm partially overlaps with the excitation / emission spectra of BN-CDs ( Figure 11 b and c), indicating that it causes a decrease in apparent fluorescence intensity by competing to absorb incident light or emit photons. Figure 11 Where d is BN - CDs, BN-CDs+Cr2O7 2- 、BN-CDs+Cr2O7 2- 、BN-CDs+Cr2O7 2- +AA's zeta potential. Add Cr2O7 2- Before and after, the potential of BN-CDs is almost unchanged, so the combination Figure 11 It is speculated that BN-CDs has a great influence on Cr2O7 2- The quenching mechanism is the inner filter effect.

[0073] When adding MnO4 - In the case of B - N - The fluorescence lifetime of CDs changes from 5.37 ns to 5.12 ns, and its strong absorption band at 540 nm partially overlaps with the excitation / emission spectra of carbon dots ( Figure 11 In b), the zeta potential also changes significantly ( Figure 11 d), and according to Ster - The Volmer function can be used to obtain Ksv[MnO4 - ] is 4.63*10 3 L / mol( Figure 11 e), Kq is 8.5*10 12 L / mol / s. In summary, it is speculated that B - N - CDs on MnO4 - The quenching mechanism is caused by the synergistic effect of static quenching and inner filter effect.

[0074] Before and after adding AA, BN-CDs+ Cr2O7 2- The fluorescence lifetime and zeta potential of AA remain unchanged. - N - The mechanism of CDs fluorescence is also chemical reduction.

[0075] 10. Anti-counterfeiting applications

[0076] In order to intuitively verify the effectiveness of the doping strategy, the two carbon dots (N-CDs, BN-CDs) were compared in actual color development ( Figure 12 (a) Using solutions of N-CDs and BN-CDs at the same concentration (1 mg / mL), patterns were drawn on stone paper and compared. Under sunlight, both samples showed no noticeable color development. However, under 365 nm UV excitation, the BN-CDs-drawn areas exhibited bright blue-green fluorescence. This phenomenon confirms that the boron-nitrogen co-doping strategy significantly enhances the fluorescence quantum yield by manipulating the surface states and band structure of carbon quantum dots, resulting in superior color development at the same concentration. This provides experimental evidence for the development of anti-counterfeiting materials.

[0077] Temperature tolerance is a key factor in measuring the performance of anti-counterfeiting materials. We used a 1 mg / mL solution of BN-CDs to write the "Shanxi University" pattern. These patterns were then heated at 20°C, 40°C, 60°C, and 80°C for 10 minutes, followed by cooling to room temperature. We then illuminated these patterns with 365 nm and 254 nm UV light, recording and photographing the luminescence. Figure 12 (b) The experimental results show that the "Shanxi University" pattern treated at these four different temperatures showed no significant change in fluorescence color under the two UV light irradiations. This fully demonstrates that BN-CDs have excellent temperature stability and can effectively resist the impact of different temperature environments on their anti-counterfeiting performance. Therefore, they can be used as an excellent anti-counterfeiting material in real production and life.

[0078] The foregoing shows and describes the principal features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims, not the foregoing description, and all variations that come within the meaning and range of equivalents of the claims are intended to be embraced therein.

[0079] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing boron-doped carbon quantum dots, characterized in that: The following steps are involved: Step 1, dissolving curcumin, m-phenylenediamine and boric acid in anhydrous ethanol and performing a hydrothermal reaction; Step 2: After the hydrothermal reaction is completed, centrifugation, filtration, and rotary evaporation are performed in sequence, and the obtained viscous liquid is dispersed in ultrapure water and freeze-dried to obtain the boron-doped carbon quantum dots.

2. The method for preparing boron-doped carbon quantum dots according to claim 1, wherein: In the step 1, the molar ratio of curcumin, m-phenylenediamine and boric acid is 1:5:3-20.

3. The method for preparing boron-doped carbon quantum dots according to claim 1, wherein: The temperature of the hydrothermal reaction in step 1 is 220° C. and the time is 6 hours.

4. The method for preparing boron-doped carbon quantum dots according to claim 1, wherein: In step 2, the centrifugal speed is 10,000 rpm and the time is 10 min; the filtration uses a 0.22 μM microporous filter membrane, the rotary evaporation concentration temperature is 60° C. and the time is 1.5 h; the freeze-drying temperature is -50° C. and the time is 24 h.

5. Boron-doped carbon quantum dots prepared by the preparation method according to any one of claims 1 to 4.

6. The use of the boron-doped carbon quantum dots according to claim 5, characterized in that: For detection of Cr2O7 2- With MnO4 - .

7. The use of the boron-doped carbon quantum dots according to claim 5, characterized in that: As fluorescent ink, used for anti-counterfeiting marking.

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