A room temperature synthesized carbon dot and its application in detecting H2O2

Abstract

The present invention discloses a carbon dot synthesized at room temperature and its application in H₂O₂ detection. The carbon dot uses o-phenylenediamine and hydroquinone as precursor raw materials, and iron salt acts as a catalytic reagent and doping element, and is prepared at room temperature by means of oxidation / polymerization and Schiff base reaction. The carbon dot not only has excellent fluorescence properties, but also its preparation process does not require high-energy consumption steps such as high-temperature carbonization, nor does it require the intervention of strong acids, strong bases or oxidants, and has the advantages of energy saving, safe operation and cheap and readily available raw materials. There is no need to introduce complex enzyme-catalyzed reactions or additional co-reactants, and the fluorescence of the carbon dot can be significantly quenched by H₂O₂, thereby achieving direct fluorescence detection of H₂O₂, which has the characteristics of high sensitivity, good selectivity and rapid response. The present invention is of great significance to alleviating environmental pollution, reducing production costs, promoting large-scale production, and promoting the application of carbon dots in multiple fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterial preparation and analysis detection, and particularly relates to fluorescent carbon dots prepared at room temperature, and the use of the carbon dots for H2O2 detection. Background Art

[0002] Hydrogen peroxide (H2O2) is widely used as a bleaching agent, disinfectant, and preservative due to its strong antioxidant properties and easy decomposition. It is widely used in environmental protection, papermaking, textiles, food, and medical fields. H2O2 also regulates cell growth, differentiation, and apoptosis in plants and animals. Excessive H2O2 can induce genetic mutations in humans and lead to cancer. H2O2 also decomposes into hydroxyl radicals in the human body, causing damage to cell structure and potentially contributing to cardiovascular and diabetes diseases. In 2017, the World Health Organization's International Agency for Research on Cancer designated H2O2 as a carcinogen, making accurate and efficient H2O2 detection crucial. Currently, commonly used H2O2 detection methods include electrochemical, fluorescence, surface-enhanced Raman scattering, and colorimetry. Fluorescence has attracted considerable attention due to its high selectivity and sensitivity, simplicity, and low cost. Although there have been many reports on the use of organic small molecule fluorescent probes to detect H2O2 (ACS sensors, 2020, 6(1): 54-62; Analytical chemistry, 2021, 93(6): 3301-3307), their synthesis is difficult and cannot be easily mastered by some laboratories without a deep organic synthesis background. Therefore, it is extremely challenging to develop fluorescent materials with simple synthesis methods and excellent performance to achieve simple and rapid H2O2 detection.

[0003] As a powerful photoluminescent nanomaterial, carbon dots (CDs) have been widely used in optoelectronics, bioimaging, fluorescence sensing, medical treatment and catalysis due to their low toxicity, excellent optical behavior, excellent chemical stability, high photostability and good biocompatibility. So far, carbon dots can be prepared by hydrothermal method, solvothermal method, microwave method, electrochemical exfoliation and other methods. Although these methods can produce a large number of carbon dots with excellent performance, they have disadvantages such as high energy consumption and certain risks in operation. For example, the most commonly used hydrothermal synthesis method usually requires 150 ~ 230 ○C under high temperature and high pressure, which may lead to safety risks; some other preparation methods are cumbersome and have many side reactions, and some equipment is complex and expensive, especially when prepared under high energy consumption conditions, resulting in high cost and low efficiency. In addition, these methods are usually carried out in a sealed environment, making it difficult to monitor and control the reaction process. It is worth noting that although there are reports on the use of carbon dots as probes for H2O2 detection, most of them utilize the enzyme-mimicking activity of carbon dots and require the addition of enzyme substrates for detection (Sensors and Actuators B: Chemical, 2019, 287: 408-415; Journal of Alloys and Compounds, 2021, 862: 158323; ACS Applied Nano Materials, 2024, 7(15): 17795-17803), while there are few reports on methods for directly detecting H2O2 using the fluorescence properties of carbon dots. Summary of the Invention

[0004] In view of the shortcomings of the carbon dot synthesis method in the background technology, the present invention provides a carbon dot prepared at room temperature and normal pressure and its application in H2O2 detection. At room temperature, using hydroquinone and o-phenylenediamine as carbon sources, trivalent iron as a reaction catalyst and doping element, long-wavelength emitting iron-doped carbon dots are prepared by catalytic oxidation, cross-linking polymerization and Schiff base reaction. Doping metal elements in carbon dots is an effective method to improve the performance of carbon dots, and as a low-energy consumption method, room temperature synthesis of carbon dots has the characteristics of simple equipment, low energy consumption, high output, adjustable process and low cost, which meets the needs of energy-saving chemistry and solves the shortcomings of high energy consumption and high cost in traditional carbon dot preparation methods. In addition, H2O2 can directly quench the fluorescence of the carbon dots prepared by the present invention, and H2O2 can be detected without adding additional reagents, which has the advantages of simplicity, rapidity, high sensitivity and good selectivity.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] In a first aspect of the present invention, a room temperature synthesis method for carbon dots is provided, comprising the following steps: adding hydroquinone, o-phenylenediamine, iron salt, and ultrapure water to a beaker, ultrasonically treating the mixture to form a transparent uniform solution, stirring the mixture on a magnetic stirrer at room temperature and atmospheric pressure to obtain a brown suspension; centrifuging the obtained suspension, filtering the supernatant with a 0.22 µm filter membrane, dialyzing, and freeze-drying the resulting carbon dots.

[0007] Preferably, the mass ratio of hydroquinone to o-phenylenediamine is 1:1 to 1:3, the amount of iron salt is 0.01 to 0.05 g, the amount of ultrapure water is 10 to 20 mL, the reaction temperature is room temperature, and the reaction time is 18 to 24 h;

[0008] Preferably, the iron salt is ferric nitrate;

[0009] Preferably, the centrifugal treatment speed is 8000 r / min and the time is 5 to 15 min.

[0010] The second aspect of the present invention provides carbon dots prepared by the preparation method described in the above technical solution, characterized in that the carbon dots have a spherical structure, a particle size of about 8 nm, and excellent fluorescence properties.

[0011] The third aspect of the present invention provides the application of the carbon dots described in the above technical solution in H2O2 detection.

[0012] Preferably, the application includes:

[0013] 1) Add the carbon dots to a buffer solution to prepare a test solution. H2O2 solutions of varying concentrations are then added. The fluorescence intensity of the resulting mixture is measured before and after the reaction. A H2O2 standard curve is established based on the relationship between H2O2 concentration and fluorescence intensity changes.

[0014] 2) Add the sample to be tested to the carbon dot detection solution, measure the fluorescence intensity of the resulting mixture before and after the reaction, substitute it into the H2O2 standard curve, and calculate the H2O2 content in the sample to be tested.

[0015] Preferably, a citric acid-sodium citrate buffer system is used, the pH of the detection system is 6, and the H2O2 concentration in the H2O2 solution to be detected is ≥0.028 μmol / L.

[0016] The technical solution provided by the present invention has the following beneficial effects:

[0017] 1. The carbon dots provided by the present invention can be prepared at room temperature, are uniform in size, and exhibit good stability and resistance to photobleaching. Furthermore, they have the advantages of low energy consumption, low cost, environmental friendliness, ease of operation, readily available raw materials, and ease of large-scale preparation.

[0018] 2. H₂O₂ exhibits a significant fluorescence quenching effect on the carbon dots prepared by this invention, and the degree of quenching is related to the H₂O₂ concentration. This allows for direct quantitative detection of H₂O₂ without the introduction of additional auxiliary reagents. This method offers the advantages of simple operation, good selectivity, and high sensitivity, with a detection limit as low as 0.028 µmol / L.

[0019] 3. The detection method provided by the present invention has been applied to the detection of H2O2 in actual water samples and foods, showing good reproducibility, reliability and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The transmission electron microscopy image and particle size distribution diagram of carbon dots prepared in Example 1 of the present invention;

[0021] Figure 2 This is the UV-visible absorption spectrum of the carbon dots prepared in Example 1 of the present invention;

[0022] Figure 3 This is the infrared absorption spectrum of the carbon dots prepared in Example 1 of the present invention;

[0023] Figure 4 This is a high-resolution X-ray photoelectron spectrum of carbon dots prepared in Example 1 of the present invention;

[0024] Figure 5 The fluorescence excitation and emission spectra of the carbon dots prepared in Example 1 of the present invention are shown;

[0025] Figure 6 Fluorescence emission spectra of carbon dots prepared in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention;

[0026] Figure 7 The fluorescence emission spectra of the carbon dots prepared in Example 1 of the present invention in the presence of different concentrations of H2O2 are shown;

[0027] Figure 8 This is a linear relationship diagram between the fluorescence intensity of carbon dots prepared in Example 1 of the present invention and the H2O2 concentration;

[0028] Figure 9 This is a diagram showing the selectivity experimental test results of carbon dots prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] In order to more clearly and deeply illustrate the content of the present invention, some examples will be further listed below, but the present invention is not limited to the examples listed. If the specific experimental conditions or methods in the following examples are not specified, they are all carried out according to the conventional conditions or methods in this field. Example 1

[0030] Accurately weigh 0.035 g of hydroquinone, 0.10 g of o-phenylenediamine, and 0.030 g of ferric nitrate, respectively, and add 10 mL of ultrapure water. Ultrasonication is then performed to form a transparent, homogeneous solution. The mixture is then stirred at room temperature for 18 hours to yield a brown suspension. The resulting product is centrifuged at 8000 rpm for 10 minutes to remove the precipitate. The supernatant is filtered through a 0.22 µm filter, dialyzed, and freeze-dried to obtain carbon dots.

[0031] The carbon dots obtained in Example 1 were analyzed by transmission electron microscopy. Figure 1 As shown. Figure 1 It can be seen that the prepared carbon dots have a spherical structure and good dispersibility, with an average particle size of 8.0±0.1 nm.

[0032] The carbon dots obtained in Example 1 were detected by UV-visible spectroscopy. Figure 2 It can be seen that carbon dots have two absorption peaks at 250 nm and 430 nm, which are respectively generated by the π→π* transition and n→π* transition of the chemical bonds in the carbon dots.

[0033] The carbon dots obtained in Example 1 were analyzed by infrared spectroscopy. Figure 3 As shown, 3430 cm -1 It is caused by the stretching vibration of OH / NH. The stretching vibration of CH appears at 1622 cm -1 1512 cm -1 The absorption peak at 1460 cm is caused by the stretching vibration of C=N / C=C. -1 1389 cm -1 The absorption peak at 1225 cm is caused by the stretching vibration of -NO2. -1 The absorption peak at 1092 cm is caused by the stretching vibration of NH, and the stretching vibration absorption peak of CO appears at 1092 cm -1 The Fe-O stretching vibration absorption peak appears at 570 cm -1 , these absorption bands indicate the formation of multi-ring structures and the successful doping of Fe.

[0034] X-ray photoelectron spectroscopy analysis of the carbon dots obtained in Example 1 further investigated the chemical composition of the prepared carbon dots, indicating that the carbon dots had four peaks of C 1s, N 1s, O 1s, and Fe 2p, located at approximately 284 eV, 399 eV, 532 eV, and 741 eV, with relative element contents of 67.86%, 14.21%, 17.1%, and 0.83%, respectively. Figure 4 A shows the four fitting peaks of the high-resolution C1s spectrum of carbon dots: C=C / CC (284.4 eV), CN (285.1 eV), C-OH (286.0 eV), and C=N / CO (288.0 eV); Figure 4 B shows the three fitting peaks of the high-resolution N 1s spectrum of carbon dots: CN=C (399.1 eV), -NH2 (400.6 eV) and -NO2 (406.5 eV); Figure 4C shows two fitting peaks of the high-resolution O 1s spectrum of carbon dots: C=O (531.7 eV) and COC / C-OH (532.5 eV); Figure 4 D shows two fitting peaks of the high-resolution Fe 2p spectrum of carbon dots: Fe 2p 3 / 2 , (711.8 eV) and Fe 2p 1 / 2 (726.2 eV), indicating the successful doping of Fe ions.

[0035] The carbon dots obtained in Example 1 were subjected to fluorescence spectrum analysis, and the test results were as follows: Figure 5 .Depend on Figure 5 It can be seen that as the excitation wavelength increases, the emission wavelength of carbon dots remains unchanged, and its fluorescence intensity first increases and then decreases. The optimal excitation wavelength is 390 nm, and the maximum emission wavelength is 553 nm.

[0036] The carbon dots obtained in Example 1 were continuously irradiated with ultraviolet light. The fluorescence intensities of the fluorescent carbon dots after irradiation for 0, 5, 10, 20, 30, and 40 min were 1619, 1617, 1600, 1602, 1592, and 1586, respectively. The above measurement results show that the fluorescence intensity of the carbon dots remains basically unchanged after long-term irradiation, indicating that the obtained carbon dots have good resistance to photobleaching.

[0037] NaCl solutions of varying concentrations were mixed with the carbon dots obtained in Example 1, and the mixed solutions were subjected to fluorescence detection. The fluorescence intensity and fluorescence emission peak position of the carbon dots did not change significantly when the salt ion concentration varied between 10 mM and 500 mM, indicating that the obtained carbon dots maintained good chemical and optical stability even at higher ionic strengths. Example 2

[0038] Carbon dots were prepared in the same manner as in Example 1, except that the amount of ferric nitrate added was 0.010 g. Example 3

[0039] Carbon dots were prepared in the same manner as in Example 1, except that the amount of ferric nitrate added was 0.050 g.

[0040] Comparative Example 1

[0041] Carbon dots were prepared in the same manner as in Example 1, except that the amount of ferric nitrate added was 0.

[0042] Fluorescence detection was performed on the carbon dots obtained in Example 1, Example 2, Example 3 and Comparative Example 1. The detection results are as follows: Figure 6As shown, the fluorescence intensities when the ferric nitrate dosages were 0 mg, 0.010 mg, 0.030 mg, and 0.050 mg, respectively, were 1185, 1680, 1601, and 1324. When no ferric nitrate was added during the preparation process, the fluorescence of the carbon dots was weak. As the amount of ferric nitrate added increased, the fluorescence of the carbon dots first increased and then decreased. The carbon dots synthesized under the conditions of the present invention exhibited superior fluorescence intensity. Example 4

[0043] The carbon dots obtained in Example 1 were subjected to H₂O₂ detection using the following steps: 100 mL (1 mg / L) of carbon dot solution and 100 mL of H₂O₂ (100 mmol / L) were added to a 1.5 mL centrifuge tube, followed by 800 mL of citric acid-sodium citrate buffer solution (pH = 6, 0.1 M). After mixing thoroughly, the mixture was allowed to react for 5 minutes. Fluorescence detection was then performed at room temperature. During fluorescence detection, the excitation slit width was set to 5 nm, the emission slit width to 5 nm, the photomultiplier tube detector voltage was 700 V, the maximum excitation wavelength was 390 nm, and the maximum emission wavelength was 553 nm. ΔF represents the difference in fluorescence intensity after the addition of H₂O₂.

[0044] Comparative Example 2

[0045] The carbon dots obtained in Example 2, Example 3 and Comparative Example 1 were subjected to H2O2 detection, and the operating steps were the same as those in Example 4.

[0046] The change in fluorescence intensity ΔF before and after the addition of H2O2 in Example 4 and Comparative Example 2 was calculated. It was found that when the carbon dots obtained in Comparative Example 1, the carbon dots obtained in Example 2, the carbon dots obtained in Example 1, and the carbon dots obtained in Example 3 were used, respectively, after the addition of 100 mL of H2O2 (100 mmol / L), the ΔF values ​​of the systems were 106, 301, 346, and 185, indicating that the carbon dots obtained in Example 1 had the best quenching effect on H2O2.

[0047] Comparative Example 3

[0048] H2O2 detection was performed according to Example 4, except that the pH of the buffer solution in the detection system was 3, 4, 5, and 7, respectively.

[0049] The change in fluorescence intensity △F before and after adding H2O2 in Example 4 and Comparative Example 2 was recorded. The △F values ​​were 30 (pH=3), 134 (pH=4), 213 (pH=5), 352 (pH=6), and 128 (pH=7), respectively, indicating that the quenching effect of H2O2 was best when a buffer solution with a pH of 6 was used.

[0050] Comparative Example 4

[0051] H2O2 detection was performed according to Example 4, except that the buffer solution systems in the detection system were: acetate buffer system, phosphate buffer system, and Tris-HCl buffer system, respectively. The change in fluorescence intensity ΔF before and after the addition of H2O2 in Example 4 and Comparative Example 4 was calculated. The ΔF values ​​were 286 (acetate buffer system), 25 (phosphate buffer system), 349 (citrate buffer system), and 13 (Tris-HCl buffer system), respectively, indicating that the citrate buffer system had the best quenching effect on H2O2. Example 5

[0052] Following the steps of Example 4, a series of H2O2 standard solutions with different concentrations were added to the detection system consisting of the carbon dots obtained in Example 1 and a pH 6 citric acid-sodium citrate buffer solution, and the fluorescence changes were recorded. Figure 7 As shown in the figure, when the concentration of added H2O2 is between 1 μmol / L and 500 μmol / L, the fluorescence emission spectrum curve obtained shows that the fluorescence intensity gradually decreases with the increase of H2O2 concentration. Figure 8 for the reason Figure 7 The linear relationship between the obtained △F value and H2O2 concentration is fitted, and its linear equation is △F = 25.28 + 2.491 c (µmol / L), correlation coefficient R 2 =0.9967, and the detection limit was 0.028µmol / L (S / N=3). Example 6

[0053] In order to investigate the selectivity and anti-interference of the carbon dots obtained in Example 1 in the detection process of H2O2, common metal ions and organic matter were added to the detection system and the corresponding fluorescence responses were recorded (Na and H2O2 were added at the same concentration). + , K + 、Cu 2+ 、Mn 2+ , Pb 2+ , Ca 2+ Mg 2+ 、Zn 2+ 、 Fe 3+ , as well as glucose, fructose, humic acid, glycine, and malic acid). The blank control is the fluorescence intensity when no H2O2 is added (i.e., only carbon dots). The fluorescence response results are shown in Figure 9 shown by Figure 9 It can be seen that Na + , K + 、Mn 2+ , Pb 2+ , Ca 2+ Mg 2+ 、Zn 2+、 Fe 3+ , glucose, fructose, sucrose, humic acid, glycine, and malic acid had little effect on the fluorescence intensity of the system, while Cu 2+ It has a great influence on the determination of H2O2, but the addition of EDTA can mask Cu 2+ The results show that the carbon dots obtained by the present invention have good selectivity for H2O2 and are not affected by other interferences.

[0054] Application Example 1

[0055] To verify the practical application performance of the fluorescent carbon dots obtained in the present invention in H2O2 detection, tap water and pickled pepper chicken feet were tested, and spiked recovery tests were conducted. The recoveries were 97.5% to 103.8%. The results are shown in Table 1, indicating that this experimental method provides a wide linear detection range and a low detection limit, is suitable for on-site and rapid analysis and detection, and has great development prospects.

[0056] Table 1 Recovery test of H2O2 in water samples and food by the carbon dots obtained in the present invention (n=3).

[0057]

[0058] As can be seen from the above examples, the present invention uses hydroquinone and o-phenylenediamine as starting materials, adopts a simple room temperature stirring method, and synthesizes fluorescent carbon dots with excellent fluorescence properties by adding a certain amount of iron salt. H2O2 can significantly quench the fluorescence of the prepared carbon dots, thereby realizing direct fluorescence detection of H2O2 with high sensitivity and a detection limit as low as 0.028µmol / L. Moreover, the carbon dots prepared at room temperature by the present invention not only have good anti-photobleaching properties and stability, but also have mild reaction conditions, do not require high temperature and high pressure, are safe to operate, and can be synthesized on a large scale at low cost.

[0059] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing carbon dots synthesized at room temperature, characterized in that: The carbon dots were prepared by the following steps: hydroquinone, o-phenylenediamine, iron salt and ultrapure water were mixed at room temperature, ultrasonically treated to form a homogeneous solution, and then stirred on a magnetic stirrer for 18 to 24 hours at room temperature to obtain a brown suspension. The suspension was centrifuged, and the obtained supernatant was filtered, dialyzed and freeze-dried to obtain carbon dots.

2. The method for preparing carbon dots according to claim 1, wherein: The mass ratio of hydroquinone to o-phenylenediamine is 1:1 to 1:3, the amount of iron salt used is 0.01 to 0.05 mg, and the amount of ultrapure water used is 10 to 20 mL.

3. The method for preparing carbon dots according to claim 1, wherein: The iron salt is one or a combination of two or more of ferric nitrate, ferric sulfate, ferric chloride and ferric acetate.

4. The method for preparing carbon dots according to claim 1, wherein: The centrifugal speed is 8000 ~ 10000r / min, and the time is 5 ~ 15 minutes.

5. The method for preparing carbon dots according to claim 1, wherein: The filtration was performed using a 0.22 µm filter membrane, the molecular weight cut-off for the dialysis was 500, and the dialysis time was 12 to 24 h.

6. A carbon dot synthesized at room temperature, characterized in that: The carbon dots are prepared by the preparation method according to any one of claims 1 to 5, and have a spherical structure, an average particle size of 8.0±0.1 nm, and excellent fluorescence properties.

7. The use of carbon dots in detecting H2O2 according to claim 6, characterized in that: The following steps are involved: 1) adding the carbon dots described in claim 6 to a buffer solution to prepare a test solution, adding H2O2 solutions of varying concentrations, measuring the fluorescence intensity of the resulting mixture before and after the reaction, and establishing a H2O2 standard curve based on the relationship between H2O2 concentration and fluorescence intensity change; 2) Add the sample to be tested to the carbon dot detection solution, measure the fluorescence intensity of the resulting mixture before and after the reaction, substitute it into the H2O2 standard curve, and calculate the H2O2 content in the sample to be tested.

8. The use of carbon dots in detecting H2O2 according to claim 7, characterized in that: The buffer used was citric acid-sodium citrate buffer solution at pH 6.0; The mixed solution was allowed to stand for 5 to 10 minutes before fluorescence detection.

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