Preparation method and application of boron-nitrogen co-doped carbon quantum dots

Abstract

The invention provides a boron-nitrogen co-doped carbon quantum dot as well as preparation and application thereof, and comprises application of the boron-nitrogen co-doped carbon quantum dot in detection of the content of Co (II) in a water body and application of the boron-nitrogen co-doped carbon quantum dot in detection of the content of AA in fruits. The invention designs a novel method for detecting Co (II) and AA (Acrylic Acid) based on 'off / on' type fluorescence of boron-nitrogen co-doped carbon quantum dots (B, N-CDs). Co (II) reacts with amino groups on the surfaces of the B, N-CDs to form a non-fluorescent compound, and fluorescence linear quenching of the B, N-CDs is caused; the addition of ascorbic acid (AA) causes linear fluorescence recovery of B, N-CDs due to competitive coordination between ascorbic acid and Co (II). The detection is quick and sensitive; the selectivity is high.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot preparation technology, specifically relating to a boron-nitrogen co-doped carbon quantum dot and its preparation and application. Background Technology

[0002] Cobalt ions (Co(II)) are essential trace elements in living organisms, but excessive intake can harm human health, such as causing heart disease and nervous system damage. Vitamin C (also known as ascorbic acid, AA) is an important water-soluble vitamin with various physiological functions, including antioxidant and immune-boosting effects. Furthermore, the content of AA is an important indicator for evaluating the nutritional value of food. Therefore, developing a rapid, sensitive, and selective detection method for the simultaneous detection of Co(II) and AA has significant scientific value and practical application implications. Summary of the Invention

[0003] In view of this, the present invention provides a method for preparing boron-nitrogen co-doped carbon quantum dots and their application. The prepared boron-nitrogen co-doped carbon quantum dots can detect the content of Co(II) in water and the content of AA in fruits, with rapid, sensitive and highly selective detection.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an application of boron-nitrogen co-doped carbon quantum dots in detecting the content of Co(II) in water.

[0005] Preferably, the method for detecting the content of Co(II) in water is as follows: after mixing boron-nitrogen co-doped carbon quantum dot solution, HCl-NaOH solution and the water to be tested, the mixture is detected using a fluorescence spectrometer.

[0006] Preferably, the concentration of the boron-nitrogen co-doped carbon quantum dot solution is 55 mg / mL.

[0007] Preferably, the pH value of the HCl-NaOH solution is 8.

[0008] Secondly, this invention provides an application of boron-nitrogen co-doped carbon quantum dots in detecting the content of AA in fruits.

[0009] Preferably, the method for detecting the AA content in fruit is as follows: after mixing boron-nitrogen co-doped carbon quantum dot solution, HCl-NaOH solution, Co(II) solution and the fruit to be tested, the mixture is then detected using a fluorescence spectrometer.

[0010] Preferably, the concentration of the boron-nitrogen co-doped carbon quantum dot solution is 55 mg / mL, and the concentration of the Co(II) solution is 500 μg / mL.

[0011] Preferably, the pH value of the HCl-NaOH solution is 8.

[0012] Thirdly, the present invention provides a method for preparing boron-nitrogen co-doped carbon quantum dots, comprising the following steps: S1. Mix carbon powder, phenylboronic acid, ethylenediamine and methanol to obtain a mixture; S2. After heating the mixture, filter it to obtain a yellow liquid, namely a boron-nitrogen co-doped carbon quantum dot solution.

[0013] Preferably, in step S1, the molar ratio of phenylboronic acid to ethylenediamine is 1:9.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention presents a novel "off / on" fluorescence detection method for Co(II) and AA based on boron-nitrogen co-doped carbon quantum dots (B, N-CDs). Co(II) interacts with amino groups on the surface of B, N-CDs to form a non-fluorescent complex, causing linear quenching of the fluorescence of B, N-CDs; while the addition of ascorbic acid (AA) leads to linear recovery of the fluorescence of B, N-CDs due to the competitive coordination between ascorbic acid and Co(II). The detection is rapid, sensitive, and highly selective.

[0015] (2) This invention uses waste carbon powder as raw material, phenylboronic acid as boron source and ethylenediamine as nitrogen source for doping, and synthesizes boron-nitrogen co-doped carbon quantum dots with good fluorescence properties through a one-step solvothermal method. Attached Figure Description

[0016] Figure 1 The graph shows the effect of the amount of phenylboronic acid on the fluorescence intensity of B,N-CDs provided in Example 2 of the present invention. Figure 2 The bar chart shows the effect of the amount of ethylenediamine provided in Example 2 of this invention on the fluorescence intensity of B, N-CDs. Figure 3 This is a graph showing the effect of different solvents on the fluorescence intensity of B, N-CDs provided in Example 2 of the present invention. Figure 4 This is a property characterization diagram of B, N-CDs provided in Embodiment 2 of the present invention; Figure 5 This is another B, N-CDs property characterization diagram provided in Embodiment 2 of the present invention; Figure 6 The excitation (blue line), emission (black line), and ultraviolet-visible absorption (red line) spectra of B, N-CDs provided in Embodiment 2 of the present invention are shown in the inset, which is an aqueous solution of B, N-CDs under visible light and ultraviolet light irradiation. Figure 7This is a schematic diagram of the "off / on" type fluorescence detection of Co(II) and AA by B,N-CD provided in Embodiment 2 of the present invention; Figure 8 The graphs showing the effects of different pH values ​​on the detection of Co(II) by B, N-CDs and the detection of AA by B, N-CDs / Co(II) are provided in Example 2 of this invention. Figure 9 The graph shows the effect of the amount of B and N-CDs provided in Example 2 of the present invention on the detection of Co(II) and AA. Figure 10 The graph shows the effect of the response time of B, N-CDs on the detection of Co(II) and AA provided in Embodiment 2 of the present invention. Figure 11 The bar charts show the selectivity of the quenched fluorescence sensor B, N-CDs for detecting Co(II) and the enhanced fluorescence sensor B, N-CDs / Co(II) for detecting AA, provided in Embodiment 2 of the present invention. Figure 12 This is a mechanism verification diagram of the quenching fluorescence sensor B, N-CDs for detecting Co(II) and the enhanced fluorescence sensor B, N-CDs / Co(II) for detecting AA provided in Embodiment 2 of the present invention; Figure 13 The fluorescence spectrum and performance analysis diagram of B, N-CDs for detecting Co(II) provided in Example 2 of the present invention; Figure 14 The fluorescence spectrum and performance analysis diagram of B, N-CDs / Co(Ⅱ) for detecting AA provided in Example 2 of the present invention. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0018] Example 1 Sample Detection and Processing 1.1 Preparation of B, N-CDs 0.1 g of waste carbon powder, 0.12 g (1 mmol) of phenylboronic acid, 600 μL (9 mmol) of ethylenediamine, and 5 mL of methanol were thoroughly mixed and placed in a 25 mL hydrothermal reactor. The mixture was reacted at 200 °C for 12 hours. After the reactor cooled to room temperature, the mixture was filtered through a 0.22 μm aqueous filter, and the yellow liquid was retained to obtain B,N-CDs. Based on the original carbon source, the concentration of the mother liquor was calculated to be 1.1 × 10⁻⁶. -2 Store in a refrigerator (4℃) at a concentration of g / mL for later use.

[0019] 1.2 Quenching-type (off) fluorescence sensor B, N-CDs detection of Co(II) 80 μL of B, N-CDs (55 mg / mL) and 625 μL of HCl-NaOH solution (pH 8) were added sequentially to a 5 mL EP tube. Then, a series of Co(II) standard solutions of different concentrations were added, and the volume was adjusted to 4 mL with double-distilled water. After mixing at room temperature for 1 min, the B, N-CDs sensor was detected using a fluorescence spectrometer. The fluorescence ratio F0 / F of the B, N-CDs sensor at 405 nm under an excitation wavelength of 330 nm was recorded to prepare a standard curve.

[0020] 1.3 Enhanced (on) fluorescence sensor B, N-CDs / Co(II) detection of AA Add 80 μL of B, N-CDs (55 mg / mL), 625 μL of HCl-NaOH solution (pH 8), and 160 μL of Co(II) (500 μg / mL) standard solution to a 5 mL EP tube in sequence. Then add a series of AA standard solutions. Dilute to 4 mL with double-distilled water. Mix well at room temperature for 1 min. Detect the sample using a fluorescence spectrometer and record the fluorescence ratio F0 / F of the B, N-CDs / Co(II) sensor at 405 nm under an excitation wavelength of 330 nm to prepare a standard curve.

[0021] 1.4 Sample Pretreatment Water samples: Filter tap water (local tap water) and lake water (local Qingshan Lake water) through a 0.22μm filter, collect the filtrate and set it aside.

[0022] Fruit (local supermarket): Accurately weigh 20g each of kiwi, orange, and tangerine, stir and crush, centrifuge at 8000rpm for 10min, take the supernatant, filter it through a 0.22μm microporous membrane, collect the filtrate as the juice stock solution.

[0023] 1.5 Quenching-type (off) fluorescence sensor B, N-CDs for detecting Co(II) in water samples A certain volume of treated water sample was added to a mixture of 80 μL B, N-CDs (55 mg / mL) and 625 μL HCl-NaOH solution (pH 8), and the volume was adjusted to 4 mL with double-distilled water. After reacting for 1 min, the sample was detected using a fluorescence spectrometer. The fluorescence ratio F0 / F of the B, N-CDs sensor at 405 nm under an excitation wavelength of 330 nm was recorded. The Co(II) content in the actual water sample was calculated based on the obtained standard curve.

[0024] 1.6 Enhanced (on) fluorescence sensor B, N-CDs / Co(II) for detecting AA in fruits A certain volume of pre-treated fruit solution was added to a mixture of 80 μL B, N-CDs (55 mg / mL), 625 μL HCl-NaOH solution (pH 8), and 160 μL Co(II) (500 μg / mL). The mixture was then diluted to 4 mL with double-distilled water. After reacting for 1 min, the sample was detected using a fluorescence spectrometer. The fluorescence ratio F0 / F of the B, N-CDs / Co(II) sensor at 405 nm under an excitation wavelength of 330 nm was recorded. The content of AA in the actual sample was calculated based on the obtained standard curve.

[0025] Example 2: Condition Optimization, Performance Testing, and Results 2.1 Effect of phenylboronic acid dosage on the fluorescence intensity of B, N-CDs Phenylated acid is used as the boron source in the synthesis of B,N-CDs, and its amount affects the fluorescence properties of the product. Therefore, with fixed amounts of waste carbon powder, ethylenediamine, and methanol as solvents of 0.1 g, 600 mL, and 5 mL, respectively, the effect of different concentrations of phenylboronic acid on the fluorescence intensity of synthesized B,N-CDs was investigated. The results are as follows: Figure 1 As shown, the fluorescence intensity of B,N-CDs slowly increased with increasing phenylboronic acid dosage, and then tended to stabilize. Therefore, 1.0 mmol / L of phenylboronic acid was selected as the optimal dosage for the synthesis of B,N-CDs.

[0026] 2.2 Effect of ethylenediamine dosage on the fluorescence intensity of B,N-CDs Ethylenediamine is used as the nitrogen source in the synthesis of B,N-CDs, and its amount affects the fluorescence properties of the product. Therefore, with fixed amounts of waste carbon powder, phenylboronic acid, and methanol (0.1 g, 0.12 g, and 5 mL respectively), the effect of different concentrations of ethylenediamine on the fluorescence intensity of synthesized B,N-CDs was investigated. The results are as follows: Figure 2 As shown, with the gradual increase of ethylenediamine dosage, the fluorescence intensity of B,N-CDs showed a trend of first increasing and then decreasing, with the fluorescence intensity reaching its maximum when the ethylenediamine dosage was 600 μL. Therefore, the final dosage of ethylenediamine was selected as 600 μL.

[0027] 2.3 Effect of reaction solvent on the fluorescence intensity of B, N-CDs Considering the water solubility of waste carbon powder, the effect of the 5 mL reaction solvent was also taken into account. Therefore, the amounts of waste carbon powder, phenylboronic acid, and ethylenediamine were fixed at 0.1 g, 0.12 g, and 600 mL, respectively, and the effects of different solvent systems (water, methanol, and ethanol) on the fluorescence intensity of synthesized B, N-CDs were investigated. The results are as follows: Figure 3As shown, compared to water and ethanol solvents, B,N-CDs exhibited the strongest fluorescence intensity and a wavelength red-shifted by approximately 15 nm when methanol was used as the solvent. This is likely due to the better dispersibility of waste carbon powder in methanol. Therefore, methanol was chosen as the optimal solvent for the synthesis of B,N-CDs.

[0028] 2.4 Effects of temperature and time on the fluorescence intensity of B,N-CDs Since temperature and time are crucial factors affecting the hydrothermal synthesis of carbon dots, the effects of different reaction times (4 h, 8 h, 12 h, 16 h, and 24 h) and temperatures (160 °C, 180 °C, 200 °C, and 220 °C) on the fluorescence quantum yield of synthesized B,N-CDs were investigated. The results are shown in Table 1. When the reaction time is within 12 h, at the same reaction temperature, the fluorescence quantum yield gradually increases with increasing time. When the reaction time is greater than 12 h, the fluorescence quantum yield tends to stabilize or shows a decreasing trend. When the reaction time is the same, the fluorescence quantum yield reaches its maximum at 200 °C for all products. Therefore, considering all factors, the optimal reaction time and temperature for synthesizing B,N-CDs are 12 h and 200 °C, respectively, with the highest quantum yield reaching 25.4%.

[0029] Table 1. Effects of different reaction temperatures and times on the fluorescence quantum yield of synthesized B, N-CDs

[0030] The experimental and calculation formulas for quantum yield are explained below: Quinine sulfate was selected as a reference, and the UV-Vis absorption of B, N-CDs, and quinine sulfate was measured. Then, the fluorescence quantum yield was calculated from the integrated fluorescence intensity of the two, as shown in the following formula:

[0031] References, Ψ R Ψ represents the fluorescence quantum yield of quinine sulfate (reference solution), with a value of 0.54; AR and A represent the absorbance of quinine sulfate and B, N-CDs, respectively; IR and I represent the integrated fluorescence intensities of quinine sulfate and B, N-CDs, respectively; η represents the fluorescence quantum yield of B, N-CDs. R η and η are the refractive indices of quinine sulfate and B, N-CDs, respectively, both 1.33 here. The calculated QY values ​​for materials with and without phenylboronic acid are 25.4% and 19.6%, respectively.

[0032] 2.5 Material Characterization To verify the morphology, composition, structure and properties of the synthesized material, it was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray electron spectroscopy (XPS), X-ray powder diffraction (XRD), fluorescence spectroscopy and ultraviolet-visible absorption spectroscopy.

[0033] First, the material was characterized by TEM. Figure 4 (a) It can be seen that the material is spherical and uniformly dispersed. From the particle size distribution illustration, it can be seen that the average particle size is about 8.0 nm and the lattice fringe spacing is 0.323 nm, which is similar to the graphite 002 layer.

[0034] XRD characterization of materials Figure 4 (b) The results show that 2θ has obvious broad peaks at around 18.8° and 22.3°, indicating poor crystallinity, which corresponds to amorphous carbon particles, proving that carbon dots were successfully synthesized.

[0035] according to Figure 4 (c) FT-IR infrared characterization shows that at 3400 cm⁻¹ -1 The peak value corresponds to the stretching vibration caused by OH / NH, 1635 cm. -1 The peak value is attributed to the stretching vibration of C=O, 1399 cm⁻¹ -1 The peak value is attributed to the stretching vibration of CN, 1360 cm. -1 and 1060cm -1 The peak values ​​correspond to the stretching vibrations of -CB- and -B-OH in the boric acid group, respectively. The infrared spectra of phenylboronic acid and B, N-CDs were compared to further confirm the successful synthesis of B, N-CDs.

[0036] The chemical composition of the material was then characterized using XPS, such as... Figure 5 As shown, from the XPS full spectrum Figure 5(a) The scanning results show that the four strong peaks at 191.88, 284.88, 99.88, and 531.88 eV correspond to the signal peaks of B 1s, C 1s, N 1s, and O 1s, respectively, with contents of 3.15%, 77.38%, 5.88%, and 13.59%. The five peaks of the C 1s spectrum (5(b)) correspond to CC (285.1 eV), CNC (285.7 eV), OC=O (288.1 eV), CO (284.7 eV), and CB (283.6 eV). The two peaks of the N 1s spectrum (5(c)) correspond to NH (400.6 eV) and CN (399.8 eV). The three peaks in the O 1s spectrum (5(d)) correspond to BO (532.4 eV), C-OH / COC (533.0 eV), and C=O (531.7 eV), respectively. The two peaks in the B 1s spectrum (5(e)) correspond to OB (190.7 eV) and CB (191.1 eV), respectively. Combined TEM, XRD, and XPS characterization further confirms the successful synthesis of B, N-CDs.

[0037] Figure 6 The images show the excitation, emission, and UV-Vis absorption spectra of B and N-CDs, respectively. B and N-CDs exhibit excellent water solubility; the solution appears pale yellow under visible light and emits blue fluorescence under UV light. Figure 6 The emission spectrum of B, N-CDs exhibits two peaks, corresponding to the excitation of the intrinsic state at a high energy level and the excitation of the defect state at a low energy level, respectively. The UV absorption spectrum (red line) shows two absorption peaks: a sharp absorption peak at 230-250 nm attributed to the π-π* transition of the C=C bond; and a weak absorption peak at 280-290 nm attributed to the n-π* transition of the C=O bond. Figure 7 As can be seen from the data, the optimal excitation (blue line) and emission wavelength (black line) are 330nm and 405nm, respectively.

[0038] 2.6 Schematic diagram of "off / on" fluorescence detection of Co(II) and AA based on B, N-CDs Figure 7This diagram illustrates the mechanism of "off / on" type fluorescence detection of Co(II) and AA using B, N-CDs. First, using waste carbon powder as a precursor, ethylenediamine as a nitrogen source, and phenylboronic acid as a boron source, B, N-CDs with a quantum yield of 25.4% were synthesized via a one-pot solvothermal method at 200℃ for 12 h. Upon addition of Co(II), Co(II) reacts with the amino groups on the surface of B, N-CDs to form a non-fluorescent complex, resulting in static quenching and fluorescence quenching. Then, upon addition of ascorbic acid, due to the competitive complexation between AA and Co(II) in the non-fluorescent complex, B, N-CDs are released, leading to fluorescence recovery. This successfully constructed novel methods for "off" type B, N-CDs sensing of Co(II) and "on" type B, N-CDs / Co(II) sensing of AA.

[0039] 2.7 Optimization of conditions for detecting Co(II) with quenched (off) fluorescence sensor B and N-CDs / Co(II) fluorescence sensor B to detect AA. To optimize the detection of Co(II) by B,N-CDs and the detection of AA by B,N-CD / Co(II), the concentrations of B,N-CDs and AA were fixed at 33 μg / mL, Co(II) at 15 μg / mL, and AA at 100 μM. The effects of pH, Co(II) quenching efficiency, and AA recovery efficiency of the B,N-CDs / Co(II) fluorescence ratio in the HCl-NaOH and BR buffer systems were investigated. The results are as follows: Figure 8 As shown, the black line represents the quenching rate, and the red line represents the recovery rate. In the HCl-NaOH system, pH has little effect; within the pH range of 6-10, both the fluorescence quenching and recovery rates are good, reaching their optimal values ​​at pH 8 (8(a)). In the BR buffer system, as the pH value increases from 2 to 12, the quenching and recovery rates show a trend of first increasing and then decreasing. At pH 6, the fluorescence quenching rate of B,N-CDs reaches its maximum, while the fluorescence efficiency of B,N-CDs / Co(II) reaches its maximum at pH 8 (8(b)). However, the overall quenching and recovery rates are not as good as those of the HCl-NaOH system. Therefore, the HCl-NaOH system was ultimately selected, with pH 8 being the optimal value.

[0040] 2.8 Optimization of B, N-CDs dosage To obtain optimal sensitivity, the dosage of B and N-CDs was optimized. With the Co(II) concentration fixed at 15 μg / mL and the AA concentration at 100 μM, the effects of the dosage of B and N-CDs on the fluorescence efficiency of Co(II) quenching of B and N-CDs, and the fluorescence efficiency of B and N-CDs / Co(II) restored by AA, were investigated at pH 8. The results are as follows: Figure 9 As shown, with the increase of B and N-CDs dosage, the fluorescence quenching rate and recovery rate of the system did not change significantly. The optimal dosage of B and N-CDs was 33 μg / mL. Therefore, 33 μg / mL was selected as the optimal dosage of B and N-CDs.

[0041] 2.9 Optimization of Reaction Time To account for the effect of reaction time on detection, under optimal conditions, the effects of reaction time on the fluorescence efficiency of Co(II) quenching B,N-CDs and the fluorescence efficiency of AA recovery of B,N-CDs / Co(II) were investigated. The results are as follows: Figure 10 As shown, when Co(II) was added to B, N-CDs for 1 min, its fluorescence intensity remained essentially unchanged. However, when AA was added to B, N-CDs / Co(II), its fluorescence intensity showed an increasing trend followed by a slight decrease, reaching its maximum at 2 min, and then slightly decreasing with further time. Therefore, 2 min was ultimately chosen as the optimal reaction time for both systems.

[0042] 3.0 Selectivity of quenched (off) fluorescence sensor B, N-CDs for detecting Co(II) and enhanced (on) fluorescence sensor B, N-CDs / Co(II) for detecting AA The selectivity of the method is crucial for measurement accuracy. Therefore, under optimal conditions, the effects of common coexisting ions in actual water samples on the detection of Co(II) by B and N-CDs were investigated. These ions were K(I), Ca(II), Ba(II), Mn(II), Fe(II), Pb(II), Mg(II), Na(I), Ni(II), Hg(II), Fe(III), Al(III), Ag(I), Cu(II), Zn(II), and Co(II) (5 μg / mL). The results are as follows: Figure 11 As shown in (a), common metal ions have no significant effect on B and N-CDs, but exhibit good selectivity for Co(II).

[0043] Similarly, under optimal conditions, the effects of common coexisting substances in actual fruits on the detection of AA by B, N-CDs / Co(II) were also investigated. These substances were Na(I), K(I), Ca(II), Fe(II), Mg(II), Zn(II), Cu(II) (1 μg / mL), and HCO3-. - PO43- NH4 + (1 μg / mL), as well as malic acid, tartaric acid, oxalic acid, citric acid and amino acids that may be present in fruits, and individual small biological molecules such as vitamin B12 and glutathione (100 μM). F0 is the fluorescence intensity of B, N-CDs / Co(II) at 405 nm, and F is the fluorescence intensity of B, N-CDs / Co(II) with added interfering ions at 405 nm. The results are as follows: Figure 11 As shown in (b). These interfering ions have no significant effect, and the probe exhibits high selectivity for AA.

[0044] 3.1 Mechanism verification of the detection of Co(II) by the quenching (off) fluorescence sensor B, N-CDs and the detection of AA by the enhancement (on) fluorescence sensor B, N-CDs / Co(II). Figure 12 (a) shows the UV absorption spectra of B, N-CDs, Co(II), B, N-CDs / Co(II), and B, N-CDs / Co(II)+AA (the attached figure is an enlarged UV-Vis absorption spectrum of Co(II)). It can be seen that, compared to B, N-CDs and Co(II), a distinct absorption peak at 350 nm appears in the B, N-CDs+Co(II) system, indicating that B, N-CDs form a complex with Co(II), causing fluorescence quenching of B, N-CDs. Compared to B, N-CDs+Co(II), the absorption peak at 350 nm is weakened in the B, N-CDs / Co(II)+AA system. It is speculated that AA competitively complexes with Co(II) in the B, N-CDs / Co(II) complex, forming a new complex, thereby releasing B, N-CDs and leading to fluorescence recovery.

[0045] Figure 12 (b) is a graph showing the relationship between the fluorescence intensity of B, N-CDs and the concentration of Co(II) under different temperature conditions (288K, 298K, 308K) described by the Stern-Volmer equation. It was found that the quenching constant of the equation decreases with increasing temperature, which is static quenching. It is further speculated that B, N-CDs and Co(II) may form a non-fluorescent complex, leading to the fluorescence quenching of B, N-CDs.

[0046] Figure 12 (c) shows the infrared spectra of B, N-CDs, B, N-CDs+Co(II), AA, and B, N-CDs / Co(II)+AA, as shown in the figure. B, N-CDs are at 2069 cm⁻¹. -1 and 1530cm -1The absorption peaks at these locations belong to the NH stretching and bending vibrations, respectively. Compared to B,N-CDs, the addition of Co(II) to B,N-CDs results in a higher absorption peak at 1530 cm⁻¹. -1 The peak of the NH bending vibration disappears at 2069 cm⁻¹. -1 The peak shifted, which is speculated to be due to the interaction between -NH2 and Co(II) on the surface of B,N-CDs, producing a non-fluorescent complex.

[0047] Figure 12 (d) is the Co 2p scanning XPS characterization spectrum of B, N-CDs / Co(II), which shows that a Co-N bond appears at 781.5 eV, further indicating that the -NH2 on the surface of B, N-CDs interacts with Co(II) to produce a non-fluorescent complex.

[0048] Figure 12 (c) Ascorbic acid at 1760cm -1 and 1665cm -1 The absorption peak at [location] corresponds to the stretching vibration of C=O. Compared to B, N-CDs / Co(II), after the addition of AA to B, N-CDs / Co(II), the absorption peak at [location] in ascorbic acid, which originally appeared at [location] and [location], is [value]. -1 and 1665cm -1 The carbonyl stretching vibration peaks at 1635 cm⁻¹ have all shifted to lower wavenumbers, and can be observed at 1635 cm⁻¹. -1 Absorption peaks of the chelate rings C=C and C=O appeared at the chromatic anode, but the absorption peaks were mainly due to the C=O vibration. It is speculated that these peaks may be caused by the C=O vibration on the ascorbic acid chelate due to the interaction between ascorbic acid and Co(II). Further speculation suggests that there is a competitive interaction between AA and B, N-CDs / Co(II), which leads to the recovery of its fluorescence.

[0049] 3.2 Performance Analysis of Quenching (off) Fluorescence Sensor B, N-CDs for Co(II) Detection and Enhancement (on) Fluorescence Sensor B, N-CDs / Co(II) for AA Detection 3.2.1 Analytical performance of quenched (off) fluorescence sensor B, N-CDs in detecting Co(II) Under optimal conditions, the analytical performance of B,N-CDs fluorescence sensing in detecting Co(II) was studied, and the results are as follows: Figure 13 As shown, B,N-CDs exhibit good linearity in detecting Co(II). As the concentration of Co(II) increases, the fluorescence intensity of B,N-CDs gradually decreases. The linear equation is F0 / F = 0.1358c + 0.9465, with a linear range of 0.1-40 μg / mL and a detection limit of 0.023 μg / mL.

[0050] Table 2 compares this method with previously reported methods for detecting Co(II). The sensitivity of this method for detecting Co(II) is higher than that of Zhang et al. and Kang et al., and similar to the detection limits of Li et al. and Wang et al. Furthermore, this method has a wider detection range for Co(II) and is faster than the work of Zhang, Li, and Wang et al. Therefore, these B,N-CDs offer promising applications for the detection of Co(II).

[0051] Table 2 Comparison of this work with other fluorescence sensors for detecting Co(II)

[0052] 3.2.2 Analytical performance of enhanced (on) fluorescence sensor B, N-CDs / Co(II) for detecting AA Under optimal conditions, with a fixed Co(II) concentration of 20 μg / mL, the sensitivity and linear range of B,N-CDs / Co(II) fluorescence detection of AA were investigated by adding standard solutions of AA at different concentrations (0.3-120 μM). Figure 14 As shown, the fluorescence intensity of B, N-CDs / Co(II) gradually increases with increasing AA concentration, and the fluorescence recovery degree F / F0 shows a good linear relationship with the AA concentration. The linear equation is F / F0 = 0.0209c + 1.0069, the linear range is 0.3-120 μM, and the detection limit is 0.086 μM.

[0053] Table 3 compares the performance of this method with other reported methods for detecting AA. As can be seen from the table, the sensitivity of this method for detecting AA is slightly higher than that of Wang et al., Zhao et al., Chen et al., and Shi et al., but slightly lower than that of Li et al. However, this method requires only two minutes to detect AA, demonstrating a significant advantage in rapid detection. Furthermore, this method is economical, simple, and has good selectivity, making it more suitable for practical detection.

[0054] Table 3 Comparison of this work with other fluorescence sensors for detecting AA

[0055] 3.3 Actual Sample Testing Under optimal conditions, to verify the applicability of the method, we explored the practical applications of the quenched (off) fluorescence sensor B, N-CDs for detecting Co(II) in tap water and Qingshan Lake water, and the enhanced (on) fluorescence sensor B, N-CDs / Co(II) for detecting AA in kiwifruit, oranges, and tangerines. The detection results and spiked recoveries are shown in Tables 4-5. The spiked recoveries of Co(II) in water samples ranged from 96.4% to 102.0%, with relative standard deviations all less than 5%, indicating that the method has good feasibility and accuracy. Similarly, AA was detected in all positive samples, and the spiked recoveries were between 98.8% and 103.5%, which are satisfactory results.

[0056] Table 4. Analytical results of Co(II) in actual samples

[0057] Table 5. Analytical results of AA in actual samples

[0058] Unless otherwise specified, all raw materials used in this invention are existing substances that can be purchased directly from the market.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An application of boron-nitrogen co-doped carbon quantum dots in detecting the content of Co(II) in water.

2. The application according to claim 1, characterized in that, The method for detecting the Co(II) content in water is as follows: after mixing boron-nitrogen co-doped carbon quantum dot solution, HCl-NaOH solution and the water to be tested, the content is detected using a fluorescence spectrometer.

3. The application according to claim 2, characterized in that, The concentration of the boron-nitrogen co-doped carbon quantum dot solution was 55 mg / mL.

4. The application according to claim 2, characterized in that, The pH value of the HCl-NaOH solution is 8.

5. An application of boron-nitrogen co-doped carbon quantum dots in the detection of AA content in fruits.

6. The application according to claim 5, characterized in that, The method for detecting the AA content in fruits is as follows: after mixing boron-nitrogen co-doped carbon quantum dot solution, HCl-NaOH solution, Co(II) solution and the fruit to be tested, the results are detected using a fluorescence spectrometer.

7. The application according to claim 6, characterized in that, The concentration of the boron-nitrogen co-doped carbon quantum dot solution is 55 mg / mL, and the concentration of the Co(II) solution is 500 μg / mL.

8. The application according to claim 6, characterized in that, The pH value of the HCl-NaOH solution is 8.

9. A method for preparing boron-nitrogen co-doped carbon quantum dots, characterized in that, Includes the following steps: S1. Mix carbon powder, phenylboronic acid, ethylenediamine and methanol to obtain a mixture; S2. After heating the mixture, filter it to obtain a yellow liquid, namely a boron-nitrogen co-doped carbon quantum dot solution.

10. The preparation method according to claim 3, characterized in that, In step S1, the molar ratio of phenylboronic acid to ethylenediamine is 1:9.

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