Boron-doped lignin-based carbon dots, preparation method thereof and application thereof in detection of Fe < 3 + >

Abstract

The invention discloses a boron-doped lignin-based carbon dot as well as a preparation method and Fe < 3 + > detection application thereof, and belongs to the technical field of preparation and application of nano carbon materials. Sodium lignin sulfonate is used as a carbon source, boric acid is used as a boron source, and the boron-doped lignin-based carbon dots are prepared by a hydrothermal synthesis method. Compared with lignin-based carbon dots (LCDs) which are not doped with boron, the boron-doped carbon dots (B-LCDs) have excellent water solubility and richer surface functional groups, have better fluorescence detection selectivity on Fe < 3 + >, and are wide in Fe < 3 + > detection concentration range (0-1000 [mu] M, R2gt, 0.99) and low in detection limit (0.94 [mu] M). Compared with the prior art, the method has the advantages of low lignin-based raw material cost, environment friendliness, simplicity and convenience in operation and the like, and has huge application potential in actual detection.

Description

Technical Field

[0001] This invention relates to the fields of carbon nanomaterial preparation, ion detection, and physicochemical research. Specifically, it relates to a controllable preparation method for heteroatom-doped carbon dots based on biomass precursors, particularly a lignin-based carbon dot method that achieves surface charge reversal through boron doping, and systematically studies its interaction with Fe. 3+ Interactive fluorescence quenching mechanism. Background Technology

[0002] Carbon dots (CDs), as a new type of carbon-based fluorescent nanomaterials, have shown broad application prospects in environmental monitoring, bioimaging, and optoelectronic devices due to their excellent optical properties, low toxicity, good biocompatibility, and ease of functionalization. Utilizing renewable biomass resources to prepare carbon dots aligns with the principles of green chemistry and sustainable development. Lignin, the most abundant aromatic polymer in nature, with its high carbon content, abundant functional groups (hydroxyl and methoxy groups), and aromatic structure, makes it an ideal precursor for carbon dot preparation.

[0003] In recent years, lignin-based carbon dots (LCDs) have been explored for metal ion detection. For example, Jiang et al. prepared N-doped lignin carbon dots (N-LCDs) using alkali lignin and deep eutectic solvent (DES) as raw materials, and successfully applied them to Fe... 3+ The fluorescence detection limit was 0.44 μM. However, existing research has mostly focused on nitrogen doping, and the preparation of boron-doped lignin-based carbon dots (B-LCDs) and their application in Fe... 3+ There is a lack of systematic reports on its application in detection.

[0004] Boron doping can effectively modulate the electronic structure, surface states, and band gap of B-LCDs, thereby enhancing their fluorescence performance and introducing new recognition sites. Studies have shown that boron (nitrogen) co-doping can achieve the modulation of Fe through mechanisms such as photoinduced electron transfer (PET) or surface state modification. 3+ High selectivity and high sensitivity detection. However, using sodium lignin sulfonate as the carbon source and boric acid as the boron source alone, boron-doped lignin-based carbon dots (B-LCDs) were prepared and used for Fe... 3+ The preparation methods for quantitative detection and the fluorescence quenching mechanism have not yet been systematically studied.

[0005] Therefore, this invention provides a method for preparing boron-doped lignin-based carbon dots (B-LCDs) using sodium lignin sulfonate and boric acid as raw materials via a hydrothermal / solvothermal method. This preparation process is simple, uses renewable raw materials, operates under mild conditions, and yields B-LCDs with uniform particle size, good fluorescence properties, and high quantum yield. Furthermore, it can be used as a fluorescent probe for Fe... 3+The detection results showed a good linear relationship over a wide range, with low detection limits (down to the nanomolar level), and good performance for Fe. 3+ It exhibits high selectivity. Through systematic research on Fe... 3+ The fluorescence quenching effect of B-LCDs, combined with characterization of UV-absorbing power, fluorescence lifetime, and Zeta potential, revealed its quenching mechanism—static quenching—which is related to the quenching of boron-doped lignin-based carbon dots in environmental water by Fe. 3+ This provides a theoretical and technological foundation for rapid and sensitive detection. Summary of the Invention

[0006] The purpose of this invention is to provide a simple and controllable method for preparing boron-doped lignin-based carbon dots (B-LCDs). Boron-doped lignin-based carbon dots (B-LCDs) with a characteristic strongly positively charged surface are obtained by the above method, and their performance is compared with that of undoped boron samples (LCDs). Furthermore, Fe... 3+ Using B-LCDs as model analytes, we systematically studied and elucidated their fluorescence quenching mechanism, revealing the surface charge reversal and the role of boron doping sites in their interaction with Fe. 3+ The specific roles in the interaction process and the quenching type (static / dynamic) are identified, thereby revealing the impact of boron doping at the mechanistic level.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing boron-doped lignin-based carbon dots, which achieves intervention in the properties of carbon dots from the synthesis source by precisely controlling the boron doping ratio. The method includes the following steps: Step S1: Sodium lignosulfonate and boric acid are mixed at a mass ratio of (4:0) to (4:9), ultrapure water is added, and the mixture is ultrasonically dispersed to form a uniform precursor solution; Step S2: Transfer the precursor solution to the reactor and carry out a hydrothermal reaction at 140-180°C for 3-24 hours to ensure that carbonization and boron doping are completed simultaneously. Step S3: The reaction solution is cooled, filtered, and the filtrate is purified by dialysis. Step S4: Freeze-dry the dialysate to obtain boron-doped lignin-based carbon dots (B-LCDs); when the mass of boric acid is 0, boron-free lignin-based carbon dots (LCDs) are obtained; store the carbon dots for later use.

[0008] Furthermore, in step S1, the carbon source is sodium lignosulfonate, and the boron source is selected from boric acid, phenylboronic acid, 1,4-phenyldiboronic acid, or naphthaleneboronic acid, more preferably boric acid.

[0009] Furthermore, in step S1, the mass ratio of sodium lignosulfonate to boric acid is 4:5.

[0010] Furthermore, the duration of the ultrasonic treatment in step S1 is 3 to 10 minutes.

[0011] Furthermore, in step S2, the hydrothermal reaction temperature is 160°C and the reaction time is 6 hours.

[0012] Furthermore, the solvent in step S3 is ultrapure water. The dialysis is performed using a dialysis bag with a molecular weight cutoff of 1000 Da, for a duration of 3 days, at a frequency of 3 times per day.

[0013] Furthermore, the boron-doped lignin-based carbon dots (B-LCDs) synthesized in step S4 are stored at 4°C for later use.

[0014] A boron-doped lignin-based carbon dot (B-LCDs) prepared by the above method. The surface of the carbon dots is rich in heteroatom functional groups such as boron, oxygen, and sulfur. Its zeta potential is measured to be +51 mV to +57 mV near pH=7, while the zeta potential of the control carbon dots without boron doping is negative (about -38 mV).

[0015] Furthermore, the optimal excitation wavelength of the carbon dots is approximately 330 nm, and the optimal emission wavelength is located in the blue light region.

[0016] Furthermore, the carbon dots on Fe 3+ It exhibits a static fluorescence quenching effect, with a quenching rate exceeding 90%, while exhibiting a quenching effect on other common metal ions (such as Na+). + , K + Ca 2+ Mg 2+ Al 3+ Cu 2+ Zn 2+ The fluorescence response of (etc.) is weak, showing extremely high selectivity.

[0017] The above-mentioned boron-doped lignin-based carbon dots (B-LCDs) are used in the preparation of Fe... 3+ Applications in fluorescent probes. Further, the application involves preparing the carbon quantum dots into an aqueous solution with a concentration of 20~1000 μg / mL as a detection reagent.

[0018] Furthermore, Fe was detected. 3+ The linear range is 0–200 μM, the limit of detection (LOD) is 0.94 μM, and it maintains good linearity in the range of 0–1000 μM (R0). 2 >0.99).

[0019] Furthermore, the detection can be performed in the pH range of 1 to 13, and its performance is most stable in a near-neutral pH environment.

[0020] The beneficial effects of adopting the above technical solution are: The beneficial effects of this invention are reflected in: (1) Achieving control of carbon dot surface properties: By simple boric acid doping, the surface charge of lignin-based carbon dots is reversed from -38mV to +51mV, providing a highly operable surface modification method.

[0021] (2) Elucidating the complete chain of “doping-structure-property-mechanism”: linking boron doping with particle size control and surface charge reversal, further clarifying the direct relationship between surface charge and “static quenching”, with significant scientific depth.

[0022] (3) Excellent detection performance: The detection limit is as low as 0.94 μM, which is far superior to that of undoped carbon dots (4.9 μM); for Fe 3+ It has extremely high selectivity and valence state recognition ability, strong anti-interference ability, wide pH adaptability and antioxidant stability.

[0023] (4) The preparation process is green and environmentally friendly: sodium lignosulfonate, an industrial by-product, is used as the carbon source and water as the solvent. It is synthesized in one step by hydrothermal method, without the need for complicated post-processing, and is easy to scale up for production, which is in line with the concept of green chemistry.

[0024] (5) Sufficient mechanistic evidence: combining zeta potential, fluorescence lifetime, K SV Temperature dependence and ultraviolet absorption spectroscopy were used to cross-validate the quenching mechanism from multiple dimensions, and the conclusions are reliable. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1Characterization images of carbon dots prepared for embodiments of this application; (a) Transmission electron microscopy (TEM) images and particle size distribution of LCDs; (b) High-resolution transmission electron microscopy (HRTEM) images and selected area diffraction (SAD) ring patterns of LCDs; (c) Atomic force microscopy (AFM) images of LCDs; (d) Transmission electron microscopy (TEM) images and particle size distribution of B-LCDs; (e) High-resolution transmission electron microscopy (HRTEM) images and selected area diffraction (SAD) ring patterns of B-LCDs; (f) Atomic force microscopy (AFM) height curves of B-LCDs; (g) X-ray diffraction (XRD) patterns of LCDs and B-LCDs; (h) Raman spectra of LCDs and B-LCDs; (i) Fourier transform infrared (IR) spectra of LCDs and B-LCDs.

[0027] Figure 2 The image shows the B 1s XPS spectrum of the carbon dot B-LCDs prepared in Example 1 of this application.

[0028] Figure 3 The ultraviolet-visible absorption spectrum (UV-vis) of the carbon dot B-LCDs prepared in Example 1 of this application.

[0029] Figure 4 The fluorescence emission spectrum (λ) of the carbon dot B-LCDs prepared in Example 1 of this application ex =282 nm).

[0030] Figure 5 The photoluminescence (PL) emission spectra of the carbon dot B-LCDs prepared in Example 1 of this application under different excitation wavelengths.

[0031] Figure 6 Study on the metal ion selectivity of carbon dot B-LCDs prepared in Example 1 of this application.

[0032] Figure 7 The PL emission spectra of carbon dot B-LCDs prepared in Example 1 of this application at different pH values.

[0033] Figure 8 Fluorescence spectra of carbon dot B-LCDs prepared in Example 1 of this application at different concentrations (0.1-1 mg / mL).

[0034] Figure 9 Fluorescence spectra of carbon dot B-LCDs prepared in Example 1 of this application at different concentrations (0-80 μg / mL).

[0035] Figure 10 The effect of hydrogen peroxide (H2O2) concentration on the PL intensity of carbon dot B-LCDs prepared in Example 1 of this application (λ) ex =330 nm).

[0036] Figure 11 The effect of oxidation time (10 mM H2O2) on the PL intensity of the carbon dot B-LCDs prepared in Example 1 of this application (λ) ex =330 nm).

[0037] Figure 12 Carbon dot B-LCDs and Fe prepared in Example 1 of this application 3+ The UV-Vis absorption spectra of the compound and its complex.

[0038] Figure 13 The fluorescence lifetime decay curve of the carbon dot B-LCDs sample prepared in Example 1 of this application.

[0039] Figure 14 Carbon dots B-LCDs+Fe prepared in Example 1 of this application 3+ Fluorescence lifetime decay curve of (200 μM) sample.

[0040] Figure 15 The carbon dot B-LCDs prepared for Example 1 of this application were subjected to different Fe values ​​at 15°C. 3+ Stern-Volmer curves for concentrations (0-200 μM).

[0041] Figure 16 The carbon dot B-LCDs prepared for Example 1 of this application were subjected to different Fe values ​​at 25°C. 3+ Stern-Volmer curves for concentrations (0-200 μM).

[0042] Figure 17 The carbon dot B-LCDs prepared in Example 1 of this application were subjected to different Fe values ​​at 35°C. 3+ Stern-Volmer curves for concentrations (0-200 μM).

[0043] Figure 18 Fe was added to the carbon dot B-LCDs prepared in Example 1 of this application. 3+ Fluorescence intensity of samples after (0-1000 μM).

[0044] Figure 19 Fe was added to the carbon dot B-LCDs prepared in Example 1 of this application. 3+ Analysis of fluorescence quenching efficiency after (0-1000 μM).

[0045] Figure 20 Fe was added to the carbon dot B-LCDs prepared in Example 1 of this application. 3+ Analysis of fluorescence quenching efficiency after (0-200 μM). Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0047] It should be understood that the following terms contained herein may be for ease of description and simplification, or are based solely on the relationships shown in the illustrations, and do not indicate or imply any specific relationship that must be referred to. Those skilled in the art need to interpret them broadly in conjunction with the entire text, and they should not be construed as limitations on this technical solution.

[0048] Example 1 The synthesis method of boron-doped lignin-based carbon dots (B-LCDs) includes the following steps: (1) Weigh 500 mg of sodium lignosulfonate and 625 mg of boric acid (mass ratio 4:5) and place them in a 50 mL polytetrafluoroethylene liner. Add 20 mL of ultrapure water and stir with a glass rod until initially dissolved. Then sonicate for 5 minutes to form a uniform brownish-yellow precursor solution. Place the liner into a stainless steel reactor; (2) Place the above-treated reactor in an oven at 160 °C and react for 6 hours; (3) After the reaction is complete, allow it to cool naturally to room temperature. Filter the reaction solution and collect the filtrate; (4) The filtrate was injected into a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed in ultrapure water for 3 days, with the water changed every 3 hours. Finally, the dialysate was pre-frozen at -80 ℃ and then freeze-dried in a freeze dryer for 72 hours to obtain a dark brown solid powder with a metallic luster, which is B-LCDs, and dried and stored at 4 ℃.

[0049] Comparative Example 1: The method for synthesizing undoped lignin-based carbon dots (LCDs) includes the following steps: Except for the absence of boric acid, the remaining steps were exactly the same as in Example 1, and LCDs were obtained and dried and stored at 4 °C.

[0050] Example 2 Structural and performance characteristics of boron-doped lignin-based carbon dots (B-LCDs) and their comparative undoped lignin-based carbon dots (LCDs): (1) Characterization of LCDs and B-LCDs: Figure 1In Figures (a) and (d), the prepared LCDs and B-LCDs are respectively obtained by transmission electron microscopy (TEM) and particle size distribution. The LCDs are approximately spherical and uniformly dispersed, with an average particle size of 3.00 ± 0.45 nm. The B-LCDs also have a spherical dispersion structure, with an average particle size reduced to 2.09 ± 0.32 nm. This indicates that boron doping may have played a "scissoring" role, limiting the excessive growth of carbon cores or promoting the formation of smaller nanoparticles.

[0051] Figure 1 Images (b) and (e) show high-resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) images of the prepared carbon dots. The HRTEM images show that the lattice spacing of both L-CDs and B-LCDs is 0.21 nm, corresponding to the crystal planes of amorphous carbon. The diffuse ring-shaped spots in the SAED images also verify the amorphous carbon structure of L-CDs and B-LCDs. This indicates that boron doping does not change the basic crystal type of the carbon dots, but only modulates the surface / carbon core growth process.

[0052] Figure 1 Figures (c) and (f) show the height curves of the prepared carbon dot atomic force mirror (AFM), which show that the height of B-LCDs (1.9 nm) is significantly lower than that of L-CDs (2.5 nm), further verifying the "scissor" effect of boron doping.

[0053] Figure 1 The image (g) shows the X-ray diffraction (XRD) pattern of the prepared carbon dot powder. It can be seen from the figure that both LCDs and B-LCDs have obvious broad absorption peaks near θ=22°, which further confirms that they have the same crystal form.

[0054] Figure 1 (h) represents the I of the prepared carbon dot Raman spectroscopy display LCDs. D / I G =0.94, indicating that LCDs participate in the construction of sp. 2 The presence of more hybrid orbitals and fewer defect states indicates that the sp structure of the undoped boron-carbon dotted carbon is more robust. 2 The orderliness is relatively high; while the I of B-LCDs is... D / I G =1.04, a significantly increased ratio, indicating that boron doping introduces more carbon defects—direct evidence that B atoms replace carbon framework atoms and change the electronic structure.

[0055] Figure 1 Image (i) shows the Fourier transform infrared (IR) spectrum of the prepared carbon quantum dots; both L-CDs and B-LCDs can be visualized at ~3400 cm⁻¹. -1 NH / -OH stretching vibrations were observed at ~2900 cm⁻¹. -1The signal peak is from CH stretching vibration, ~2000-1000 cm⁻¹ -1 The observed stretching vibration peaks are C=O, C=C, C=C, -CH2, CN, and COC, indicating that the two have similar basic crystal types. However, the C=C stretching vibration peak of B-LCDs is relatively reduced compared to that of LCDs, suggesting that B and C are combined.

[0056] Figure 2 The prepared B-LCDs B1s XPS; B was successfully doped into the carbon dots, forming new BO bonds, BC bonds and BN bonds.

[0057] (2) Surface charge: Table 1 lists the carbon dots prepared in the embodiments of this application and the results of Fe addition. 3+ The quenching zeta potential comparison table shows that in an aqueous dispersion system near pH=7, the zeta potential of undoped B LCDs is approximately -38 mV, while the zeta potential of B-LCDs is approximately +51 mV, achieving complete reversal of surface charge.

[0058] Table 1. Carbon dots prepared in the examples and those with added Fe 3+ Comparison table of quenched Zeta potentials (3) Optical properties: Figure 3-5 The results indicate that the aqueous solution of B-LCDs has a maximum UV absorption peak at 282 nm, the optimal excitation wavelength is 330 nm (in the 220-420 nm range), and the optimal emission wavelength is located in the blue light region. Using quinine sulfate (0.1 mol / L H2SO4, PLQY=55%) as a reference, the PLQY of B-LCDs was measured to be approximately 1%. The fluorescence response of B-LCDs to 21 different metal salts, including but not limited to: Na... + , K + Ca 2+ Mg 2+ Al 3+ Cu 2+ Zn 2+ Cd 2+ Co 2+ Ni 2+ , Cr 3+ Ag + Hg 2+ Fe 2+ And various rare earth ions, etc. Only Fe 3+ The fluorescence intensity decreased sharply (quenching rate >90%), while the fluorescence changes caused by most other ions were less than 10%, indicating that B-LCDs have a significant effect on Fe.3+ It has extremely high selectivity. Figure 6 Of particular note is the effect on Fe. 2 + The response was also much lower than that of Fe. 3+ This enabled the control of Fe 3+ Valence state specificity identification.

[0059] Figure 7 The results showed that B-LCDs exhibited stable autofluorescence over a wide pH range of 2-11 and were also resistant to Fe. 3+ The quenching efficiency remains at a high level, indicating its potential for application in the detection of various real-world water bodies.

[0060] B-LCDs showed increased fluorescence intensity with increasing concentration in the range of 0-80 μg / mL; however, in the range of 100-1000 μg / mL, the fluorescence intensity decreased until quenching with increasing concentration (maximum intensity at 100 μg / mL). Figure 8-9 When mixed with 10 mM hydrogen peroxide, the fluorescence intensity showed no significant decay within 120 minutes. Fluorescence emission spectra were measured every 20 minutes, revealing stable fluorescence intensity, indicating that B-LCDs possess excellent antioxidant stability. Figure 10-11 ).

[0061] Example 3 Figure 12-17 This demonstrates through multi-dimensional experiments that B-LCDs are compatible with Fe... 3+ The interaction is a result of static quenching: Pure carbon dots B-LCDs, Fe 3+ Comparison of UV-Vis absorption spectra of the solution and its mixture () Figure 12 The display shows "B-LCDs+Fe". 3+ "The absorption spectrum of the system is not a simple superposition of the two; the absorbance at 250 nm and 275 nm is significantly lower than the theoretical superposition value, confirming the formation of the ground-state complex. Fluorescence lifetime spectrum of pure B-LCDs (...") Figure 13 B-LCDs+Fe 3+ Fluorescence lifetime spectrum ( Figure 14 The core of dynamic quenching is the significant shortening of t1 and t2 at all luminescent sites, and a substantial decrease in both A1 and A2; while the changes in t1 and t2 before and after quenching in B-LCDs are within the range of instrument error. The increase in A1 and the decrease in A2 are due to the long-lived sites being quenched by Fe. 3+ In static quenching, only the change in the proportion of sites due to luminescence from short-lived sites remains, rather than a shortening of the site's own lifetime—this is a typical lifetime characteristic of static quenching, directly ruling out dynamic quenching. The temperature characteristics of dynamic quenching: as temperature increases, molecular diffusion speed accelerates, collision probability increases, and K...SV Significantly increased; while as shown in the data above, K at 15~35℃ SV Almost no change ( Figure 15-17 ), indicating Fe 3+ The interaction with carbon dots is a ground-state stable coordination (static quenching) rather than an excited-state collision (dynamic quenching) – temperature has a negligible effect on the stability of the ground-state complex, matching the temperature response law of static quenching.

[0062] Example 4 Fe 3+ Detection applications: Detection performance: Using an aqueous solution of B-LCDs as the detection reagent, at an excitation wavelength of 330 nm, the fluorescence intensity ratio (F0 / F) and Fe... 3+ The concentration exhibits good linearity in the 0-200 μM range, with the linear equation (F0 / F⁻¹) = 0.02625x + 0.79684 (R² = 0.99785), and the detection limit is 0.94 μM. The detection limit remains consistent in the 0-1000 μM range. 2 A linear relationship >0.99 for Fe 3+ The fluorescence quenching rate exceeds 90%, and it is effective against 21 common metal ions (including Fe). 3+ The quenching rate of Fe was less than 10%, achieving Fe 3+ Valence state specificity identification ( Figure 18-20 ).

[0063] in conclusion This invention successfully prepared a novel boron-doped lignin-based carbon dots (B-LCDs). Boron doping not only altered the synthesis process (the "boron scissors" effect), but more importantly, it completely reversed the surface charge of the carbon dots and introduced specific binding sites, thereby endowing them with resistance to Fe. 3+ This method offers unprecedented high selectivity and sensitivity. It uses environmentally friendly raw materials and involves a simple process, making it a promising candidate for applications in environmental monitoring and industrial wastewater analysis.

[0064] 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 invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0065] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing boron-doped lignin-based carbon dots, characterized in that, Includes the following steps: Step S1: Mix sodium lignosulfonate and boric acid at a mass ratio of (4:0) to (4:9), add ultrapure water, and disperse by ultrasonication for 3 to 10 minutes to form a uniform precursor solution; Step S2: Transfer the precursor solution to the reactor and carry out a hydrothermal reaction at 140-180°C for 3-24 hours to ensure that carbonization and boron doping are completed simultaneously. Step S3: The reaction solution is cooled, filtered, and the filtrate is purified by dialysis. Step S4: Freeze-dry the dialysate to obtain boron-doped lignin-based carbon dots (B-LCDs); when the mass of boric acid is 0, boron-free lignin-based carbon dots (LCDs) are obtained; store the carbon dots for later use.

2. The preparation method according to claim 1, characterized in that, The boron source is selected from boric acid, phenylboronic acid, 1,4-phenyldiboronic acid or naphthaleneboronic acid; preferably boric acid.

3. The preparation method according to claim 1, characterized in that, The mass ratio of sodium lignosulfonate to boric acid is selected from the range of 4:0, 4:1, 4:2, 4:3, 4:4, 4:5, and 4:6; preferably, the mass ratio is 4:

5.

4. The preparation method according to claim 1, characterized in that, The hydrothermal reaction was carried out at a temperature of 160°C for 6 hours.

5. The preparation method according to claim 1, characterized in that, The dialysis was performed using a dialysis bag with a molecular weight cutoff of 1000 Da, for a duration of 3 days, at a frequency of 3 hours per session.

6. The boron-doped lignin-based carbon dots prepared by any one of the preparation methods according to claims 1 to 5, characterized in that, Its solid powder is a brownish-yellow color with a metallic luster, with an average particle size of 2.09±0.32 nm, and a Zeta potential of +51 mV to +57 mV in an aqueous dispersion system at pH=7.

7. The boron-doped lignin-based carbon dots according to claim 6, characterized in that, It is used to detect Fe 3+ At that time, within the concentration range of 0~200μM, the fluorescence intensity ratio (F0 / F) and Fe 3+ The concentration showed a linear relationship, with a detection limit (LOD) below 1.0 μM; and it was effective against Fe... 3+ The fluorescence quenching rate exceeds 90%, while for Na + , K + Ca 2+ Mg 2+ Al 3+ Cu 2+ Zn 2+ Fe 2+ The fluorescence quenching rate of any of the plasmas is less than 10%.

8. The boron-doped lignin-based carbon dot according to any one of claims 6-7, characterized in that, In the preparation of samples with potential for detecting Fe 3+ Applications in detection devices or reagent kits.

Images