Fluorescent probe for detecting permanganate ions and preparation method thereof

Abstract

The invention relates to a preparation method of a fluorescent probe for detecting permanganate ions, which comprises the following steps: dissolving purslane powder and o-phenylenediamine (OPD) in ethanol, uniformly mixing, carrying out heating reaction, and cooling to room temperature to obtain a suspension; filtering and dialyzing the suspension to obtain a purified solution; carrying out rotary evaporation on the purified solution in a water bath to obtain a solute; and dissolving the solute in ultrapure water, and freeze-drying to obtain carbon quantum dot fluorescent probe powder. According to the invention, purslane is used as a precursor, o-phenylenediamine is used as a nitrogen doping agent, and the nitrogen-doped carbon nanodots (N-CDs) are synthesized through a solution heat reaction in ethanol. The obtained N-CDs shows excellent oxidation resistance, and shows excellent fluorescence stability under the conditions of extreme pH, salt concentration and continuous ultraviolet radiation. Meanwhile, the N-CDs have good selectivity on MnO4 <-> ions, the N-CDs and the MnO4 <-> ions are in a linear relation within the concentration range of 0.5-168 mu M, and the lowest detection limit reaches 41.8 nM.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorescent probes, and particularly relates to a fluorescent probe for detecting permanganate ions and a preparation method thereof. Background Art

[0002] Permanganate ion (MnO4 - or Mn(VII) ion) is widely used in environmental water treatment due to its strong oxidizing property, mainly used to oxidize organic matter and metal ions such as iron and manganese in water. However, MnO4 - Excessive residual ions in environmental water bodies will pose a serious threat to the ecosystem and may even cause the death of aquatic organisms. - The residual amount of ions is an important indicator for water quality monitoring. According to the National Drinking Water Standard (GB 5749-2006), the residual amount of MnO4 in drinking water in China is - The residual limit of ions is 0.05 mg / L; according to the "Industrial Wastewater Discharge Standard" (GB 8978-1996), MnO4 - The emission limit of MnO4 in natural water is 5 mg / L. - The specific residual limit of ions varies according to the water type, such as 2 mg / L for Class I water and 5 mg / L for Class II water.

[0003] At present, the detection of MnO4 in water - There are four common methods for measuring residual ions. Among them, the spectrophotometric method is to use xylene and MnO4 - The ions react to form a purple product, and the absorbance is measured to determine its concentration. Titration method uses a reducing agent such as sodium sulfite to titrate MnO4 - ions, the color change (from purple to colorless) indicates the endpoint and determines its concentration. - The behavior of ions on the electrode surface is analyzed, and the colorimetric method is based on the reaction of specific reagents with MnO4 - The reaction produces a color change to determine its concentration. However, these methods all have certain limitations. First, spectrophotometry and titration methods have weak anti-interference capabilities and are easily affected by other oxidizing substances in water, thus affecting the accuracy of the test results. Second, electrochemical methods require complex sample pretreatment, expensive equipment, and the operation process requires professionals to have a high level of technical skills. Finally, colorimetry is used to detect MnO4 - The sensitivity of the ion is low, and the accuracy of the test results is easily interfered by pH value, salt concentration and other oxidizing substances in the water sample. -The ideal fluorescent probe of ions should have the following characteristics: (a) Excellent selectivity, which can effectively distinguish MnO4 - ions and other common highly oxidizing ions; (b) inherent antioxidant properties, which can reduce the interference of other oxidizing substances; (c) low detection limit, preferably lower than the 0.05 mg / L residue limit specified in the Chinese drinking water standard; (d) stable fluorescence performance in complex environments such as different pH values ​​and high salt concentrations; (e) simple operation, high cost-effectiveness, easy to popularize and good environmental sustainability.

[0004] Zero-dimensional carbon dots (CDs) are a new class of functional nanomaterials that have been widely used in the field of environmental monitoring due to their simple preparation process, adjustable photoluminescence properties, and excellent resistance to fluorescence photobleaching. Studies have shown that CDs can be used as fluorescent probes to detect MnO4 in environmental water samples. - Significant progress has been made in ion residues. First, Jayaweera S, Yin K, Hu X, et al (2019) Fluorescent N / Al co-doped carbon dots from cellulose biomass for sensitive detection of manganese (VII). J Fluoresc 29: 1291-1300. CDs were synthesized using durian shell, urea and aluminum nitrate to achieve MnO4 - ions (46.8 nM). However, this study has not yet explored how to convert MnO4 - ions are distinguished from other common strong oxidizing ions, and the antioxidant properties of CDs themselves have not been studied. Secondly, Mohammed A, Gugulothu Y, Bandi R, et al (2021) Ultraspeed synthesis of highlyfluorescent N-doped carbon dots for the label-free detection of manganese (VII). J Chin Chem Soc (Weinheim, Ger.) 68: 1514-1521. CDs were synthesized using threonine and guanidine hydrochloride, but this study also lacked MnO4 - ions and other strong oxidizing ions, and its MnO4 -The detection limit of the ion is 0.66μM, which exceeds the Chinese drinking water standard (0.361μM, based on KMnO4). Finally, Newar R, SultanaN, Das S, et al (2024) Development of FRET-based optical sensors using N-doped carbon dots for detection of chromium (VI) and manganese (VII) in water for asustainable future. J Environ Chem Eng 12: 111721. CDs were synthesized using Alstonia scholaris leaves and ethylenediamine. The CDs were effective in distinguishing MnO4 - ions and other common oxidizing ions. However, the fluorescence stability of these CDs in different pH solutions is poor, and their antioxidant properties have not been explored. - The detection limit of the ion is 0.394 μM, which is higher than the Chinese drinking water standard. Therefore, it is urgent to develop a new type of CDs that can efficiently and sensitively detect MnO4 in environmental water. - ions, and has higher selectivity, stability and antioxidant properties to meet the needs of environmental water monitoring. Summary of the invention

[0005] The purpose of the present invention is to provide a fluorescent probe for detecting permanganate ions and a preparation method thereof, which can efficiently and sensitively detect MnO4 in environmental water. - ion;

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a fluorescent probe for detecting permanganate ions comprises the following steps:

[0008] Purslane powder and o-phenylenediamine are dissolved in ethanol, mixed evenly, heated for reaction, and then cooled to room temperature to obtain a suspension; the suspension is filtered and dialyzed to obtain a purified solution; the purified solution is rotary evaporated in a water bath to obtain a solute; the solute is dissolved in ultrapure water, and freeze-dried to obtain a carbon quantum dot fluorescent probe powder.

[0009] Preferably, the mass volume ratio of the purslane powder, o-phenylenediamine and ethanol is: 0.15-0.25 g: 0.08 g: 8-12 mL.

[0010] Preferably, the heating reaction temperature is 190-210° C., and the reaction time is 9.5-10.5 h.

[0011] Another aspect of the present invention provides a fluorescent probe for detecting permanganate ions prepared according to the above-mentioned preparation method.

[0012] In another aspect, the present invention provides a method for detecting permanganate ions using the fluorescent probe described above, comprising the following steps:

[0013] (1) Add the fluorescent probe powder to ultrapure water and fully dissolve it by ultrasonication to obtain an N-CDs stock solution;

[0014] (2) Add the N-CDs stock solution to the sample to be tested, and measure the change in the fluorescence intensity of N-CDs at 486 nm in the sample to be tested. Substituting it into the linear equation, the MnO4 in the sample can be obtained. - Ion content;

[0015] Preferably, in step (1), the concentration of the N-CDs stock solution is 5 mg / mL.

[0016] Preferably, the linear equation is obtained by diluting the N-CDs stock solution with ultrapure water, recording the fluorescence value of N-CDs at 486 nm as F0 under the excitation of 358 nm; then adding different volumes of MnO4 - ions, recording N-CDs and MnO4 - The fluorescence value of the ion mixture is F; through linear fitting, we get MnO4 - Linear relationship between ion concentration and fluorescence intensity of N-CDs.

[0017] Preferably, within the linear range of 0.5-168uM, the linear equation is: F0-F=3.2039Log c (MnO4-) +30.6872, R 2 =0.9916.

[0018] Another aspect of the present invention provides the use of the fluorescent probe for detecting permanganate ions described above in detecting permanganate ions in environmental water.

[0019] The present invention uses purslane as a precursor and o-phenylenediamine (OPD) as a nitrogen doping agent to synthesize nitrogen-doped carbon nanodots (N-CDs) by solvothermal reaction in ethanol. The obtained N-CDs exhibit excellent antioxidant properties and excellent stability under extreme pH, salt concentration and continuous ultraviolet irradiation conditions. At the same time, N-CDs have a strong antioxidant effect on MnO4 - The ion has good selectivity and reacts with MnO4 in the concentration range of 0.5 to 168 μM. - The ions showed a linear relationship and the minimum detection limit was 41.8nM.

[0020] The precursor purslane in the present invention is widely distributed, cheap and easy to obtain, and o-phenylenediamine (OPD) and ethanol are common reagents and easy to purchase. The preparation method of the fluorescent probe is simple, does not require expensive instruments, and can quickly and efficiently detect MnO4 - The prepared fluorescent probe has stable performance, strong anti-interference ability, high accuracy and sensitivity.

[0021] In conclusion, compared with other detection methods of MnO4 - Compared with the ion method, this method has several advantages: (a) excellent selectivity, which can effectively distinguish MnO4 - ions and other common highly oxidizing ions; (b) inherent antioxidant properties, which can reduce the interference of other oxidizing substances; (c) stable fluorescence performance in complex environments such as different pH and high salt concentrations; (d) simple operation, high cost-effectiveness, easy to popularize and good environmental sustainability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 a is the ultraviolet spectrum and fluorescence spectrum of the N-CDs prepared by the present invention, and b is the excitation wavelength dependence spectrum.

[0023] Figure 2 There are 15 typical anions (Br - ,I - ,F - ,Cl - ,CO3 2- ,C2O4 2- ,S2O3 2- ,SO3 2- ,SO4 2- ,SCN - ,NO2 - ,H2PO4 2- ,NO3 - ,ClO4 - ,MnO4 - ) Detection of MnO4 on N-CDs - Figure 2. Ion selectivity and anti-interference test results.

[0024] Figure 3 In the figure a, the fluorescence stability of the N-CDs prepared by the present invention in different pH, salt concentration (KCl), H2O2 solutions and under continuous UV irradiation.

[0025] Figure 4 To utilize MnO4 - Ion titration of N-CDs solution, the change curve of N-CDs fluorescence intensity and MnO4 - Linear plot of ion concentration and fluorescence intensity of N-CDs. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0027] 1. Preparation and characterization of N-CDs

[0028] (1) Hydrothermal reaction: Weigh 0.2 g of purslane powder and 0.08 g of o-phenylenediamine (OPD) into 10 mL of ethanol and mix them thoroughly in a 50 mL beaker. Then transfer the mixture into a polytetrafluoroethylene-lined autoclave, place it in a constant temperature incubator, and heat it at 200 °C for 10 h.

[0029] (2) Purification: After the reactor was cooled naturally to room temperature (about 25°C), a dark brown suspension (crude product) was obtained; then, the suspension was filtered with a 0.45 μm filter paper to remove insoluble matter and larger particles; then, the suspension was dialyzed with a 500 Da dialysis bag (Spectra / Por 6, Spectra Laboratories, USA) to eliminate unreacted molecules and ions to obtain a purified solution; finally, the purified solution obtained above was rotary evaporated in a 50°C water bath to remove ethanol to obtain a refined product;

[0030] (3) Precipitation: The prepared N-CDs are dissolved in ultrapure water, and the carbon quantum dot fluorescent probe, i.e., N-CDs solid powder, is obtained by freeze-drying.

[0031] The purslane powder used above was obtained as follows: First, air-dried purslane was purchased from Taiyuan Tongrentang Co., Ltd., China, and then it was crushed and sieved through a 200-mesh sieve to finally obtain the purslane powder.

[0032] The o-phenylenediamine (OPD) used in the above was purchased from Aladdin Reagent Co., Ltd. (Shanghai, China) and was reagent grade with a purity of 99.5%.

[0033] The ethanol used above is commercially available analytical grade ethanol with a purity of 100%.

[0034] N-CDs stock solution: Weigh 50 mg of N-CDs solid powder and add 10 mL of ultrapure water. Ultrasonicate for 15 min to completely dissolve it to obtain a 5 mg / mL N-CDs stock solution.

[0035] Characterization of properties Figure 1 The N-CDs aqueous solution exhibits bright light blue fluorescence under 358nm ultraviolet light and transparent light pink under visible light (see Figure 1a illustration). The UV-visible absorption of N-CDs shows a strong peak at 245 nm, which may be caused by the π-π* transition of aromatic CC bonds and C=C bonds (see Figure 1 a). The maximum emission wavelength of N-CDs is 486nm and the excitation wavelength is 358nm (see Figure 1 a). When the excitation wavelength changes from 308nm to 408nm, the emission band moves to the red side (from 473nm to 497nm), showing a typical excitation-dependent fluorescence phenomenon (see Figure 1 b).

[0036] 2. MnO4 - Selectivity and anti-interference experiments of ion detection

[0037] Step 1: weigh 50 mg of N-CDs solid powder, add 10 mL of ultrapure water, and sonicate for 15 min to completely dissolve it to obtain a N-CDs stock solution with a concentration of 5 mg / mL.

[0038] Step 2: Prepare 15 typical anions (Br - ,I - ,F - ,Cl - ,CO3 2- ,C2O4 2- ,S2O3 2- ,SO3 2- ,SO4 2- ,SCN - ,NO2 - ,H2PO4 2- ,NO3 - ,ClO4 - ,MnO4 - ), the concentration was 100mM.

[0039] Step 3: Take 20 μL of the above N-CDs stock solution and each test solution into a quartz cup, then dilute with ultrapure water to a final volume of 2 L, mix well, incubate for 1 min, and record the fluorescence spectrum value at an excitation wavelength of 358 nm.

[0040] Step 4: Add MnO4 to the N-CDs solution - ions and other test solutions (all 1 mM). After incubation for 1 min, the fluorescence spectrum of each sample was monitored at an excitation wavelength of 358 nm to check whether the presence of other test solutions had an effect on the MnO4 - The quenching effect of ions has a significant impact.

[0041] MnO4 - The results of the selectivity and anti-interference experiments of ion detection show that adding MnO4- ions, while the fluorescence of 14 typical anions did not or almost did not cause fluorescence changes ( Figure 2 a). With MnO4 - Compared with the quenching effect of ions, the effect of coexisting substances is almost negligible ( Figure 2 b), indicating that N-CDs have an effect on MnO4 - It has good selectivity and anti-interference in ion detection.

[0042] 3. Fluorescence stability of N-CDs in different environmental solutions

[0043] Step 1, prepare pH solutions of different strengths: dilute concentrated hydrochloric acid (12M) with deionized water step by step, measure the solution pH with a pH agent, determine the dilution end point, and obtain an acidic solution with a pH of 1-6. Then mix 0.1M sodium dihydrogen phosphate (NaH2PO4) and disodium hydrogen phosphate (Na2HPO4) solutions, measure and adjust with a pH agent, and obtain a neutral solution with a pH of 7. Finally, dilute NaOH (1M) step by step with deionized water, measure and adjust with a pH agent, and obtain an alkaline solution with a pH of 8-12.

[0044] Step 2, prepare KCl solutions of different concentrations: weigh 745.5 mg of KCl powder and add it to 10 mL of deionized water to obtain a KCl solution with a concentration of 1 M. Then dilute it in multiples to gradually obtain a KCl solution with a concentration of 0.8-0.2 M.

[0045] Step 3, prepare H2O2 solutions of different concentrations: purchase 100 mL of commercially available 30% (w / w) H2O2 stock solution, use a pipette to draw 1.133 mL of H2O2 stock solution into a volumetric flask, then dilute to 10 mL with deionized water to obtain a 1 M H2O2 solution. Then dilute by multiples to gradually obtain a 0.8-0.2 M H2O2 solution.

[0046] Step 4: Take 20 μL of the above N-CDs stock solution in a quartz cup, then add different concentrations of pH, KCl solution and H2O2 solution to a final volume of 2 L, mix well, incubate for 1 min, and record the fluorescence spectrum value at an excitation wavelength of 358 nm.

[0047] Step 5: Take 20 μL of the above N-CDs stock solution in a quartz cup, then dilute the solution with deionized water to a final volume of 2L, mix well, place it under a 365nm ultraviolet lamp, and then record the fluorescence spectrum value at an excitation wavelength of 358nm, record once every 15 minutes, for a total of 120 minutes. The experimental results are shown in Figure 3 d.

[0048] The results showed that in acidic solutions (pH 2-6), the fluorescence intensity of N-CDs remained almost unchanged. In alkaline solutions (pH 7-10), the fluorescence intensity of N-CDs gradually decreased, with a decrease of less than 10%, which may be due to the protonation of the carboxyl groups on the surface of N-CDs under alkaline conditions ( Figure 3 a). In addition, N-CDs exhibited stable fluorescence intensity under high ionic strength (0.2-1.0 M NaCl) and high concentration of H2O2, indicating that they have strong salt tolerance and antioxidant capacity ( Figure 3 bc). Finally, under the continuous irradiation of UV light, the fluorescence of N-CDs gradually decreased, and the fluorescence intensity only decreased by 15% after 120 minutes, indicating that N-CDs have a strong ability to resist photobleaching ( Figure 3 d) In summary, N-CDs have strong acid and alkali resistance, salt resistance, antioxidant and photobleaching ability, and are suitable for MnO4 - Detection.

[0049] 4. MnO4 - Linear equation of ion concentration and N-CDs fluorescence intensity

[0050] Step 1: Fluorescence titration method is used, that is, 200 μL of N-CDs stock solution is diluted to 2L with ultrapure water, and under the excitation of 358 nm, the fluorescence value of N-CDs at 486 nm is recorded as F0.

[0051] Step 2: Add different volumes of MnO4 to the above solution. - ions (1mM), recording N-CDs and MnO4 - The fluorescence value of the ion mixture is F, and the change of fluorescence intensity is shown in Figure 4 a.

[0052] Step 3: Through linear fitting of Origin software, we can get MnO4 - The linear relationship between ion concentration and N-CDs fluorescence intensity is shown in Figure 4 b.

[0053] The results show that: With the increase of MO4 - As the ion concentration increases from 0 to 249 μM, the fluorescence intensity of the N-CDs emission peak (about 486 nm) decreases ( Figure 4 a). When the linear range is 0.5-168μM, the linear equation is: R 2 =0.9916, the minimum detection limit is 41.8nM ( Figure 4 b).

[0054] 5. MnO4 in actual samples -Ion content detection

[0055] The actual samples were tap water (from the 302 laboratory of the Institute of Biomedicine of Shanxi University) and local river water (Fen River, Taiyuan, China).

[0056] Step 1: Add 20ul N-CDs stock solution to 2mL ultrapure water. The concentration of N-CDs is 5μg·mL. -1 , measure the fluorescence intensity at 486 nm and record it as F0.

[0057] Step 2: Centrifuge the water sample at 8000 rpm for 5 min, then filter it with a 0.22 μm filter membrane for later use; finally, add 20 μL of N-CDs stock solution to 2 mL of tap water and river water respectively, and the concentration of N-CDs is 5 μg mL -1 , measure the fluorescence intensity at 486nm, record it as F, calculate F0-F, and substitute it into the linear equation: The calculated MnO4 in the actual sample - Ion concentration.

[0058] The results are shown in Table 1. It can be seen that N-CDs can be used to detect MnO4 in actual samples. - ion content, and the relative standard deviation was less than 2.15%, with good reproducibility.

[0059] Table 1. MnO4 in two actual samples - Ion content

[0060]

[0061] 6. MnO4 in actual samples - Ion spike recovery experiment

[0062] Step 1: weigh 50 mg of N-CDs solid powder into a beaker, add 10 mL of ultrapure water, and sonicate to fully dissolve it to obtain a N-CDs mother solution with a concentration of 5 mg / mL.

[0063] Step 2: Weigh 1.5804 mg of potassium permanganate powder, add it to 10 mL of distilled water, and sonicate to fully dissolve it to obtain a concentration of 1 mM MnO4 - Ion stock solution.

[0064] Step 3: Add 20 μL of N-CDs stock solution to 2 mL of ultrapure water. The concentration of N-CDs is 5 μg mL -1 , measure the fluorescence intensity at 486 nm and record it as F0.

[0065] Step 4: Add 20 μL of N-CDs stock solution to 2 mL of tap water. The concentration of N-CDs is 5 μg mL -1 , measure the fluorescence intensity at 486 nm and record it as F.

[0066] Step 5: Add 20 μL of N-CDs stock solution to 2 mL of tap water, and then add 5 μM, 10 μM, and 20 μM of MnO4 - Ion spike stock solution, the concentration of N-CDs is 5 μg mL -1 , measure the fluorescence intensity at 486 nm and record it as F.

[0067] Step 6: Add 20 μL of N-CDs stock solution to 2 mL of river water. The concentration of N-CDs is 5 μg mL -1 , measure the fluorescence intensity at 486 nm and record it as F.

[0068] Step 7: Add 20 μL of N-CDs stock solution to 2 mL of river water, and then add 5 μM, 10 μM, and 20 μM of MnO4 - Ion spike stock solution, the concentration of N-CDs is 5 μg mL -1 , measure the fluorescence intensity at 486 nm and record it as F.

[0069] Step 8: Substitute F0-F into the linear equation to calculate the MnO4 in the three actual samples. - The spike recovery of ions.

[0070] The results are shown in Table 2. The MnO4 - The recoveries of the spiked ions ranged from 95.67% to 103.42%, and the relative standard deviation was less than 5.23% (see Table 2), indicating that N-CDs can be used to identify MnO4 in actual samples. - The spiked detection of ions is not interfered by other substances in the actual sample and has good recovery results and reproducibility.

[0071] Table 2. MnO4 in two actual samples - Results of ion spike recovery experiments

[0072]

Claims

1. A method for preparing a fluorescent probe for detecting permanganate ions, characterized in that: The following steps are involved: Purslane powder and o-phenylenediamine are dissolved in ethanol, mixed evenly, heated for reaction, and then cooled to room temperature to obtain a suspension; the suspension is filtered and dialyzed to obtain a purified solution; the purified solution is rotary evaporated in a water bath to obtain a solute; the solute is dissolved in ultrapure water, and freeze-dried to obtain a carbon quantum dot fluorescent probe powder.

2. The preparation method according to claim 1, characterized in that: The mass volume ratio of the purslane powder, o-phenylenediamine and ethanol is: 0.15-0.25 g: 0.08 g: 8-12 mL.

3. The preparation method according to claim 1, characterized in that: The heating reaction temperature is 190-210° C., and the reaction time is 9.5-10.5 hours.

4. A fluorescent probe for detecting permanganate ions prepared according to the preparation method according to any one of claims 1 to 3.

5. The method for detecting permanganate ions using the fluorescent probe according to claim 4, characterized in that: The steps include: (1) Add the fluorescent probe powder to ultrapure water and fully dissolve it by ultrasonication to obtain an N-CDs stock solution; (2) Add the N-CDs stock solution to the sample to be tested, and measure the change in the fluorescence intensity of N-CDs at 486 nm in the sample to be tested. Substituting it into the linear equation, the MnO4 in the sample can be obtained. - The content of ions.

6. The method according to claim 5, characterized in that In step (1), the concentration of the N-CDs stock solution is 5 mg / mL.

7. The method according to claim 5, characterized in that The linear equation is obtained by diluting the N-CDs stock solution with ultrapure water, recording the fluorescence value of N-CDs at 486 nm as F0 under the excitation of 358 nm; then adding different volumes of MnO4 - ions, recording N-CDs and MnO4 - The fluorescence value of the ion mixture is F; through linear fitting, we get MnO4 - Linear relationship between ion concentration and fluorescence intensity of N-CDs.

8. The method according to claim 5 or 7, characterized in that: In the linear range of 0.5-168uM, the linear equation is: F0-F=3.2039Log c (MnO4-) +30.6872, R 2 =0.9916.

9. Use of the fluorescent probe for detecting permanganate ions according to claim 4 in detecting permanganate ions in environmental water.

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