Walnut shell carbon quantum dots, preparation method thereof, and application in detecting iron ions in wastewater

Abstract

The present invention belongs to the technical field of iron ion detection, and provides a walnut shell carbon quantum dot and its preparation method and its application in detecting iron ions in wastewater. The preparation method of the present invention comprises: mixing walnut shell powder, potassium hydroxide and anhydrous ethanol and reacting them to obtain walnut shell carbon quantum dots. The walnut shell carbon quantum dots of the present invention are mixed with Fe 3+ The reaction occurs and the carbon dots are quenched. In Tris-HCl buffer solution, W-CDs react with Fe 3+ A reduction reaction occurs, and the functional groups in W-CDs react, resulting in fluorescence quenching. It is used to detect water samples from the Longtanyong sewage outlet and detect the average Fe 3+ The concentration was 0.39mmol / L, and the recovery rate was 88.9-117.5%. The linear range was 0.05-5.0mmol / L, the detection limit was 0.015mmol / L, and R 2 =0.9978, which has the advantages of being sensitive, specific, rapid and simple.

Description

Technical Field

[0001] The present invention relates to the technical field of iron ion detection, in particular to walnut shell carbon quantum dots, a preparation method thereof, and application thereof in detecting iron ions in wastewater. Background Art

[0002] Iron is abundant in nature and exists mainly in the form of trivalent iron in water, soil and other environments. 3+ When the standard is exceeded, the survival and development of microorganisms in the water will be inhibited, the self-purification ability of the water will be weakened, and the water quality will be irreversibly polluted. 3+ The detection and monitoring of the content is particularly important. At present, the main methods for detecting iron ions are: spectrophotometry, atomic absorption spectroscopy, electrochemical method, ICP-MS, etc. However, these methods and experimental conditions are not suitable for Fe 3+ The detection is relatively cumbersome and rigorous, therefore, it is particularly important to develop a new rapid detection technology.

[0003] Fluorescent carbon dots are synthesized using bio-based raw materials as a carbon source. These materials are inexpensive, renewable, and suitable for large-scale production, reducing or even eliminating contact with chemicals and being environmentally friendly. Furthermore, through controlled chemical treatments, fluorescent carbon dots connect organic and inorganic molecules, creating a rich surface structure. This holds great potential for applications in chemical detection, sensing, and bioimaging, as well as in emerging fields. Walnut shells, discarded as plant waste due to their inedible nature, contain over 80% lignin and cellulose, resulting in a significant waste of carbon resources.

[0004] Therefore, the rich carbon content and various functional groups of walnut shells are used to synthesize fluorescent carbon dots for Fe 3+ Rapid testing is of great significance. Summary of the Invention

[0005] The purpose of the present invention is to provide a walnut shell carbon quantum dot and a preparation method thereof and an application thereof in detecting iron ions in wastewater in order to overcome the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing walnut shell carbon quantum dots, comprising the following steps:

[0008] Walnut shell powder, potassium hydroxide and anhydrous ethanol are mixed and reacted to obtain walnut shell carbon quantum dots;

[0009] The mass volume ratio of the walnut shell powder, potassium hydroxide and anhydrous ethanol is 1.7-2.3 g:0.8-1.2 g:8-12 mL.

[0010] Preferably, the reaction temperature is 180-220° C., and the reaction time is 10-14 h.

[0011] Preferably, the walnut shells are washed, dried, crushed and sieved in sequence to obtain walnut shell powder; the drying temperature is 55-65° C., and the mesh number of the sieve used for sieving is ≥80 meshes.

[0012] Preferably, the product obtained after the reaction is completed is cooled and centrifuged in sequence, and the upper layer solution after centrifugation is filtered to obtain walnut shell carbon quantum dots.

[0013] Preferably, the centrifugal speed is 4500-5500 rpm, the centrifugal time is 8-12 min, and the pore size of the filter membrane used for filtration is 0.20-0.24 μm.

[0014] The present invention also provides walnut shell carbon quantum dots prepared by the preparation method.

[0015] The present invention also provides an application of the walnut shell carbon quantum dots in detecting iron ions in wastewater, which comprises reacting a dilution of the walnut shell carbon quantum dots, a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and an iron ion solution.

[0016] Preferably, the concentration of the walnut shell carbon quantum dot dilution solution is 0.9-1.1 mg / mL, the pH value of the tris hydrochloride buffer solution is 7.7-8.1, and the concentration of the iron ion solution is 0.009-0.011 mol / L.

[0017] Preferably, the volume ratio of the walnut shell carbon quantum dot dilution solution, tris(hydroxymethyl)aminomethane hydrochloride buffer solution and iron ion solution is 480-520:90-110:18-22.

[0018] Preferably, the reaction time is 4 to 6 minutes.

[0019] The beneficial effects of the present invention include the following:

[0020] 1) The walnut shell carbon quantum dots (W-CDs) of the present invention have multiple functional groups, and their hydroxyl, carboxyl and other functional groups provide good stability and water solubility. 3+ The reaction occurs and the carbon dots are quenched. In Tris-HCl buffer, W-CDs react with Fe 3+ A reduction reaction occurs, and the functional groups in W-CDs react to quench fluorescence. Based on this principle, a Fe 3+ Rapid detection method, which is used to detect trace Fe in polluted wastewater 3+ Detection.

[0021] 2) The walnut shell carbon quantum dots of the present invention were used to detect water samples from the Longtanyong sewage outlet, and the average Fe 3+ The concentration was 0.39mmol / L, and the recovery rate was 88.9-117.5%. The linear range was 0.05-5.0mmol / L, the detection limit was 0.015mmol / L, and R 2 =0.9978, the method of the present invention has the advantages of being sensitive, specific, rapid and simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the FTIR spectrum of the walnut shell carbon quantum dots in Example 1;

[0023] Figure 2 The UV-visible absorption spectrum and fluorescence spectrum of the walnut shell carbon quantum dots in Example 1 are shown;

[0024] Figure 3 This is a graph showing the carbon quantum dot concentration and iron ion concentration of Example 1;

[0025] Figure 4 This is the ion selectivity diagram of the walnut shell carbon quantum dots in Example 1;

[0026] Figure 5 This is a linear relationship diagram of the walnut shell carbon quantum dots detected by Example 1 for iron ion concentration;

[0027] Figure 6 This is an anti-interference test diagram of the walnut shell carbon quantum dots in detecting iron ions in Example 1. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing walnut shell carbon quantum dots, comprising the following steps:

[0029] Walnut shell powder, potassium hydroxide and anhydrous ethanol are mixed and reacted to obtain walnut shell carbon quantum dots;

[0030] The mass volume ratio of the walnut shell powder, potassium hydroxide and anhydrous ethanol is 1.7-2.3 g:0.8-1.2 g:8-12 mL.

[0031] In the present invention, the mass volume ratio of the walnut shell powder, potassium hydroxide and anhydrous ethanol is preferably 1.8-2.2 g:0.9-1.1 g:9-11 mL, more preferably 1.9-2.1 g:0.95-1.05 g:9.5-10.5 mL, and more preferably 2.0 g:1.0 g:10 mL.

[0032] In the present invention, the reaction temperature is preferably 180-220° C., more preferably 190-210° C., and more preferably 200° C.; the reaction time is preferably 10-14 h, more preferably 11-13 h, and more preferably 12 h.

[0033] In the present invention, the walnut shells are preferably washed, dried, crushed and sieved in sequence to obtain walnut shell powder; the drying temperature is preferably 55-65°C, more preferably 58-62°C, and more preferably 60°C; the mesh number of the sieve used for sieving is preferably ≥80 mesh, more preferably ≥85 mesh.

[0034] In the present invention, the product obtained after the reaction is completed is preferably cooled and centrifuged in sequence, and the upper layer solution after centrifugation is filtered to obtain walnut shell carbon quantum dots.

[0035] In the present invention, the centrifugal speed is preferably 4500-5500 rpm, more preferably 4800-5200 rpm, and more preferably 5000 rpm; the centrifugal time is preferably 8-12 min, more preferably 9-11 min, and more preferably 10 min; the pore size of the filter membrane used for filtration is preferably 0.20-0.24 μm, more preferably 0.21-0.23 μm, and more preferably 0.22 μm.

[0036] The present invention also provides walnut shell carbon quantum dots prepared by the preparation method.

[0037] The present invention also provides an application of the walnut shell carbon quantum dots in detecting iron ions in wastewater, which comprises reacting a dilution of the walnut shell carbon quantum dots, a tris-hydrochloride buffer solution (Tris-hydrochloric acid buffer solution) and an iron ion solution.

[0038] In the present invention, the concentration of the walnut shell carbon quantum dot dilution solution is preferably 0.9 to 1.1 mg / mL, more preferably 0.95 to 1.05 mg / mL, more preferably 1.0 mg / mL, the pH value of the Tris-hydrochloric acid buffer is preferably 7.7 to 8.1, more preferably 7.8 to 8.0, more preferably 7.9; the concentration of the iron ion solution is preferably 0.009 to 0.011 mol / L, more preferably 0.01 mol / L.

[0039] In the present invention, the volume ratio of the walnut shell carbon quantum dot dilution solution, Tris-hydrochloric acid buffer and iron ion solution is preferably 480-520:90-110:18-22, more preferably 490-510:95-105:19-21, and more preferably 500:100:20.

[0040] In the present invention, the reaction time is preferably 4 to 6 minutes, more preferably 5 minutes.

[0041] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] The electric blast drying oven was a 101-2B electric blast drying oven purchased from Zhejiang Shaoxing Supo Instrument Co., Ltd.; the U-3010 UV-visible spectrophotometer was purchased from Hitachi, Ltd.; the UV lamp was a UV 6W UV lamp (365 nm) purchased from Jacksman Electronics Co., Ltd.; the F-7000 fluorescence spectrophotometer was purchased from Hitachi, Ltd.; and the polytetrafluoroethylene reactor was purchased from Lichen Instrument Technology Co., Ltd.

[0043] Example 1

[0044] The walnut shells were washed with distilled water and dried in a 60°C electric forced air drying oven to a moisture content of 3%. The dried walnut shells were crushed into powder and sieved with an 80-mesh sieve. 2g of the sieved walnut shell powder and 1g of potassium hydroxide were placed in a polytetrafluoroethylene reactor. 10mL of anhydrous ethanol was added to the reactor as a solvent. The reactor was reacted at 200°C for 12h. After the autoclave was naturally cooled to room temperature, the reaction product was removed and centrifuged at 5000rpm for 10min. The upper layer solution was taken and filtered through a 0.22μm cellulose acetate filter to obtain walnut shell carbon quantum dots (W-CDs), which were stored at 4°C for later use.

[0045] The walnut shell carbon quantum dots of this embodiment exhibit blue light under ultraviolet light.

[0046] Example 2

[0047] The walnut shells were washed with distilled water and dried in a 58°C electric forced air drying oven to a moisture content of 3%. The dried walnut shells were crushed into powder and sieved with an 85-mesh sieve. 1.9 g of sieved walnut shell powder and 0.95 g of potassium hydroxide were placed in a polytetrafluoroethylene reactor. 9.5 mL of anhydrous ethanol was added to the reactor as a solvent. The reactor was reacted at 190°C for 13 hours. After the autoclave was naturally cooled to room temperature, the reaction product was taken out and centrifuged at 4800 rpm for 12 minutes. The upper layer solution was taken and filtered through a 0.21 μm cellulose acetate filter membrane to obtain walnut shell carbon quantum dots (W-CDs), which were stored at 4°C for later use.

[0048] The walnut shell carbon quantum dots of this embodiment exhibit blue light under ultraviolet light.

[0049] Example 3

[0050] The walnut shells were washed with distilled water and dried in a 62°C electric forced air drying oven to a moisture content of 3%. The dried walnut shells were crushed into powder and sieved with an 80-mesh sieve. 2.1g of sieved walnut shell powder and 1.05g of potassium hydroxide were placed in a polytetrafluoroethylene reactor. 10.5mL of anhydrous ethanol was added to the reactor as a solvent. The reactor was reacted at 210°C for 11 hours. After the autoclave was naturally cooled to room temperature, the reaction product was taken out and centrifuged at 5200rpm for 8 minutes. The upper solution was taken and filtered through a 0.23μm cellulose acetate filter membrane to obtain walnut shell carbon quantum dots (W-CDs), which were stored at 4°C for later use.

[0051] Structural characterization of walnut shell carbon quantum dots

[0052] The functional group structure of the walnut shell carbon quantum dots of Example 1 was analyzed by infrared spectroscopy. The FTIR spectrum of the walnut shell carbon quantum dots of Example 1 is as follows: Figure 1 The infrared groups are shown in Table 1.

[0053] Depend on Figure 1 As shown in Table 1, the carbon dots synthesized from walnut shells have a variety of functional groups. From the various absorption peaks, it can be seen that the binding bonds of the walnut shell carbon quantum dots of Example 1 contain functional groups such as -C=O, -OH, -NH, -NO2, -COOH, and Ar-NH (amino group connected to a benzene ring).

[0054] Table 1 Infrared groups of W-CDs of Example 1

[0055]

[0056] Calculation of the yield of walnut shell carbon quantum dots

[0057] The absorbance of W-CDs and quinine sulfate in Example 1 was measured using a U-3010 UV-visible spectrophotometer. The measurement method was in accordance with the T / CSTM 00197-2021 standard. The data was recorded when the absorbance A was <0.05 and transferred to a 96-well plate at the same time. The data were tested three times in parallel. The average value of the three integrated peak areas within the emission peak range of 320 to 550 nm measured under the UV-visible spectrophotometer was taken, and the measurement was performed at the excitation wavelength of 366 nm.

[0058] The UV-visible absorption spectrum and fluorescence spectrum of the walnut shell carbon quantum dots of Example 1 are shown in FIG. Figure 2 As shown. Figure 2 It can be seen that the optimal excitation wavelength of W-CDs is 280 nm, the optimal fluorescence emission wavelength is 370 nm, and it exhibits sky blue fluorescence. The calculated fluorescence quantum yield (QY) is 8.36%.

[0059] Application Example 1: Detection of iron ions in wastewater using walnut shell carbon quantum dots

[0060] 500 μL of walnut shell carbon quantum dots (Example 1) dilution, 100 μL of Tris-hydrochloric acid buffer with a pH value of 7.9, and 20 μL of iron ion solution (ferric chloride hexahydrate solution) were reacted, and the concentrations of the walnut shell carbon quantum dots dilution were 2.0 mg / mL, 1.67 mg / mL, 1.25 mg / mL, 1.1 mg / mL, 1.0 mg / mL, 0.50 mg / mL, and 0.33 mg / mL, respectively; the concentrations of the iron ion solution were 0, 0.01 mmol / L, 0.05 mmol / L, 0.1 mmol / L, 0.5 mmol / L, 1 mmol / L, and 2 mmol / L, respectively.

[0061] In the present invention, when the total amount of W-CDs is constant, the higher the concentration, the smaller the solution volume, and the more Fe 3+ When the concentration of the W-CDs dilution solution is 2.0 mg / mL, 1.67 mg / mL, 1.25 mg / mL and 1.1 mg / mL, the carbon quantum dot concentration and iron ion concentration curve of Example 1 are as shown in FIG. Figure 3 As shown. Figure 3 It can be seen that there is an inflection point or fault phenomenon between the carbon quantum dot concentration and the iron ion concentration curve. This is because when the carbon quantum dot concentration is too high, the solution color is too dark, which masks the mild quenching and causes the fluorescence intensity to increase, thus deviating from the linear relationship. When the concentration of the W-CDs diluent is 0.33 mg / mL, the reaction quenching is not thorough enough. When the concentration of the W-CDs diluent is 0.50 mg / mL and 1.0 mg / mL, as the iron ion concentration increases, the fluorescence intensity is sequentially quenched and shows a certain gradient attenuation. However, the detection range is too large at 0.50 mg / mL. Considering the practicality, detection limit and linear lower limit of actual sample detection, the W-CDs diluent concentration of 1.0 mg / mL is the optimal reaction concentration.

[0062] Application Example 2 Ion Selectivity Test of Walnut Shell Carbon Quantum Dots

[0063] After mixing 500 μL of the walnut shell carbon quantum dot dilution (concentration of 1.0 mg / mL) prepared in Example 1 and 100 μL of Tris-hydrochloric acid buffer with a pH value of 7.9, 20 μL of 0.01 mol / L ion solution (the ion solution was zinc chloride solution, anhydrous magnesium chloride solution, monohydrated manganese sulfate solution, sodium chloride solution, sodium nitrate solution, potassium chloride solution, barium chloride solution, calcium nitrate solution, sodium nitrite solution, aluminum nitrate nonahydrate solution, sodium fluoride solution, hydrochloric acid with a mass concentration of 38%, ferric chloride hexahydrate solution, anhydrous sodium carbonate solution, and sodium bicarbonate solution) were added and the reaction was continued for 5 min until the reaction was complete. At an excitation wavelength of 280 nm, an F-7000 fluorescence spectrophotometer was used for detection and analysis, and its peak value change was recorded, and then its different ion quenching conditions were plotted.

[0064] The ion selectivity of the walnut shell carbon quantum dots of Example 1 is as follows Figure 4 As shown. Figure 4 It can be seen that W-CDs has a great influence on Fe 3+ The selectivity of Na is good, with a quenching rate of 88.57%. The quenching rates of other ions are less than 40%, which may cause mild quenching, but the quenching effect is not obvious. + The quenching rate of walnut shell carbon quantum dots to Fe 3+ The quenching effect of Fe 3+ It can almost completely quench the fluorescence of carbon dots, indicating that W-CDs can 3+ The selectivity is good and higher than that of other ions. The results show that the walnut shell carbon quantum dots of the present invention have the ability to qualitatively detect Fe 3+ ability.

[0065] Application Example 3: Determining the linear relationship

[0066] The ordinate is (F0-F) / F0, which represents the fluorescence quenching change rate. 3+ The concentration of the stock solution is 10mmol / L, and Fe 3+ The concentrations of the working solutions were 0, 0.05 mmol / L, 0.5 mmol / L, 1 mmol / L, 2 mmol / L, and 5 mmol / L, respectively. 600 μL of the W-CDs dilution (at a concentration of 1.0 mg / mL) prepared in Example 1 was thoroughly mixed with 100 μL of Tris-HCl buffer solution at a pH of 7.9, and the fluorescence peak was recorded. The complete linear lower limit was further determined based on the calculated limit of detection (LOD), and the linear upper limit of the walnut shell carbon quantum dots was obtained as 50% of its quenching rate. The linear range was determined to further determine the linear relationship and used for actual sample detection.

[0067] The linear relationship of the walnut shell carbon quantum dots in Example 1 in detecting iron ion concentration is as follows: Figure 5 As shown. Figure 5 It can be seen that the walnut shell carbon quantum dots have a good linear relationship in detecting iron ion concentration (R 2 =0.9978), the detection limit (LOD) of W-CDs was calculated to be 0.015mmol / L. From these results, it can be seen that the Fe 3+ Good and stable sensing, can be used for materials containing trace amounts of Fe 3+ Analysis of samples.

[0068] Application Example 4: Anti-interference Test

[0069] 500 μL of the diluted solution of walnut shell carbon quantum dots prepared in Example 1 (concentration of 1.0 mg / mL) was mixed with 100 μL of Tris-HCl buffer with a pH value of 7.9, and 20 μL of interfering ions (Na2CO3) with a concentration of 0.01 mol / L was added. + 、Ba 2+ Mg 2+ , Ca 2+ 、Mn 2+ 、Zn 2+ 、Al 3+ 、NO3 - 、NO2 - , K + , F-) and 20 μL of 0.01 mol / L iron ion solution. The blank control was to replace the interfering ion solution with pure water. They were mixed evenly and reacted. The retention value of the W-CDs peak was taken to indicate the degree of fluorescence quenching under the interference degree.

[0070] The anti-interference test of walnut shell carbon quantum dots prepared in Example 1 for detecting iron ions is as follows Figure 6 As shown. Figure 6 It can be seen that interfering ions have a great influence on W-CDs-Fe 3+ The quenching effect of FeCl2 was relatively small or negligible, with the maximum quenching rate of 92.31% and the minimum quenching rate of 82.65% both being between the blank control. This is because some ions may form a competitive relationship with each other or with FeCl2. 3+ Chelation or reaction occurs, which reduces the quenching rate, that is, the fluorescence intensity increases, such as Mn 2+ 、Zn 2+ 、F - ; Some ions react slightly with W-CDs to quench, causing the W-CDs content to decrease, Fe 3+ The content remains unchanged, so the quenching rate decreases, that is, the fluorescence intensity becomes lower, such as Na + 、Ba 2+ Mg 2+ 、Al3+ 、NO3 - 、NO2 - , K + , but the quenching rate amplitude RSD is 4.35%, indicating that W-CDs-Fe 3+ The anti-interference performance is good.

[0071] Application Example 5: Wastewater Sample Testing

[0072] 600 μL of the diluted solution of W-CDs prepared in Example 1 (concentration of 1.0 mg / mL) was thoroughly mixed with 100 μL Tris-HCl buffer with a pH value of 7.9 to obtain a mixed solution, which was then mixed with 50 μL of unspiked water sample (corresponding to Fe 3+ Original concentration) and 50 μL spiked water sample (Fe 3+ The spiked values ​​are shown in Table 2) were mixed and allowed to react for 5 min. 200 μL was transferred to a 96-well plate and measured in parallel 3 times. The water sample was the outlet water sample of Longtanyong wastewater. Fe 3+ The results of spike recovery are shown in Table 2. The average Fe 3+ The content is 0.39mmol / L, the spike recovery is 88.9~117.5%, which is a good result, and the RSD is between 5.1% and 9.7%, which shows that the accuracy of the result is good. 3+ Water samples have the advantages of being fast, simple and having reliable test results, and can be used for Fe 3+ Contaminated wastewater detection.

[0073] Table 2 Detection of Fe in water samples by W-CDs 3+ Spike recovery

[0074]

[0075]

[0076] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An application of walnut shell carbon quantum dots in detecting iron ions in wastewater, characterized in that: The diluted solution of walnut shell carbon quantum dots, tris(hydroxymethyl)aminomethane hydrochloride buffer solution and iron ion solution are reacted; The preparation method of walnut shell carbon quantum dots comprises the following steps: Walnut shell powder, potassium hydroxide and anhydrous ethanol are mixed and reacted to obtain walnut shell carbon quantum dots; The mass volume ratio of the walnut shell powder, potassium hydroxide and anhydrous ethanol is 1.7-2.3 g: 0.8-1.2 g: 8-12 mL.

2. The use according to claim 1, characterized in that The reaction temperature is 180-220° C., and the reaction time is 10-14 hours.

3. The use according to claim 1 or 2, characterized in that The walnut shells are washed, dried, crushed and sieved in sequence to obtain walnut shell powder; the drying temperature is 55-65° C., and the mesh number of the sieve used for sieving is ≥80 meshes.

4. The use according to claim 2, characterized in that The product obtained after the reaction is completed is cooled and centrifuged in sequence, and the upper layer solution after centrifugation is filtered to obtain walnut shell carbon quantum dots.

5. The use according to claim 4, characterized in that The centrifugal speed is 4500-5500 rpm, the centrifugal time is 8-12 min, and the pore size of the filter membrane used for filtration is 0.20-0.24 μm.

6. The use according to claim 1, characterized in that The concentration of the walnut shell carbon quantum dot dilution solution is 0.9-1.1 mg / mL, the pH value of the tris(hydroxymethyl)aminomethane hydrochloride) buffer solution is 7.7-8.1, and the concentration of the iron ion solution is 0.009-0.011 mol / L.

7. The use according to claim 6, characterized in that The volume ratio of the walnut shell carbon quantum dot dilution solution, tris(hydroxymethyl)aminomethane hydrochloride buffer solution and iron ion solution is 480-520:90-110:18-22.

8. The use according to claim 1, characterized in that The reaction time is 4 to 6 minutes.

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