Preparation method of red light carbon quantum dots and application thereof in detection of trivalent iron ions

Abstract

The application discloses a preparation method of red light carbon quantum dots. The preparation method comprises the following steps: (1) mixing evergreen and ethanol, and reacting in a reaction kettle at 100-150 DEG C for a certain time; (2) filtering the reaction solution, and dialyzing the filtrate to obtain the red light carbon quantum dots. Compared with the prior art, the method has the advantages of low raw material cost, green environmental protection and simple preparation operation, and the prepared red light carbon quantum dots have good selectivity to trivalent iron ions.

Description

Technical Field

[0001] This invention belongs to the field of carbon quantum dots, specifically relating to a method for preparing red-light carbon quantum dots and their application in the detection of ferric ions. Background Technology

[0002] Carbon quantum dots (CQDs), quasi-spherical nanoparticles, have been widely applied in various fields since their discovery. CQDs can be synthesized from a variety of green sources; therefore, various plant species, as renewable resources, are extensively used in their synthesis, with leaves, roots, and flowers being common components. Compared to semiconductor quantum dots and fluorescent organic agents, biomass carbon quantum dots possess significant advantages such as photostability, low cytotoxicity, and ease of surface functionalization, showing broad application prospects in fields such as bioimaging, chemical sensing, environmental monitoring, disease diagnosis, and photocatalysis.

[0003] For example, CN107764788A discloses a method for synthesizing carbon quantum dots, including (1) weighing 5g of fresh carrots, cutting them into small pieces, placing them in a 100mL round-bottom flask containing 50mL of water, heating to 110℃ and boiling, then continuing to heat for 15 minutes and stopping the heating; (2) taking out the carrots that have been heated above, grinding the carrots into a paste using a mortar and pestle, then taking 2g into another round-bottom flask, adding 20mL of pure water, and then adding 0.2g of citric acid and stirring for 10 minutes; (3) pouring the above mixture into a 25mL reaction vessel and reacting at 120℃ for 1h; then centrifuging the resulting mixture in a centrifuge for 15min, filtering it with a 0.22μm filter membrane, and finally dialyzing it with a dialysis bag for 24h to obtain carbon quantum dots, storing the synthesized carbon quantum dots in a refrigerator at 4℃ for later use. For example, CN106590641A discloses a method for preparing carbon quantum dots with fluorescent properties, including (1) washing and drying chrysanthemums, weighing chrysanthemums and distilled water and adding them to a reaction vessel with a polytetrafluoroethylene liner, the mass-volume ratio of chrysanthemums and distilled water being (0.5-3.0) g:(30-50) mL, reacting at 150-220℃ for 16-48 h, cooling to room temperature after the reaction, and separating the obtained brown-black product from the solid and liquid; (2) filtering the solution with a filter membrane, the resulting yellow or brown solution being carbon quantum dots with fluorescent properties. For example, CN105241854A discloses a method for preparing carbon quantum dots, including (1) preparing a dispersion of glucose and anhydrous ethanol with a mass ratio of 40:1 to 5:1; (2) placing the above mixed solution in a hydrothermal reaction vessel, placing the hydrothermal reaction vessel in an environment of 80-230℃ for 5-20 hours to obtain fluorescent quantum dots. The carbon quantum dots prepared by the above three methods all have good selectivity for ferric ions, and ferric ions can be detected by fluorescence quenching. However, the emission wavelengths of these carbon quantum dots are all in the blue light range.

[0004] CN115044370A discloses a heteroelement-doped red-light carbon dot method for detecting multiple metal ions. First, 0.1 g of lotus seed core, 0.6804 g of reduced glutathione, and 0.6106 g of o-phenylenediamine are dissolved in 20 mL of formamide, then transferred to a polytetrafluoroethylene (PTFE) reactor and reacted at 160 °C for 2 hours. After the reaction product cools to room temperature, it is centrifuged at 1000 rpm for 20 min, the supernatant is collected, and diluted 5 times with deionized water. The resulting solution is dialyzed through a 1000 Da molecular weight dialysis bag for one week, filtered through a 0.22 μm microporous filter, and finally freeze-dried to obtain a dark green heteroelement-doped red-light carbon dot powder. In this method, lotus seed core serves as the carbon source, and reduced glutathione and o-phenylenediamine serve as precursors for nitrogen and sulfur doping, respectively. Zinc ions significantly enhance the fluorescence of the carbon quantum dots, while divalent manganese ions significantly quench the fluorescence. Other metal ions, including trivalent iron ions, have a very weak effect on the fluorescence intensity of the carbon quantum dots.

[0005] CN115124999A discloses a method for preparing red fluorescent carbon dots using peony seed residue. The method involves dissolving peony seed residue and o-phenylenediamine in double-distilled water, fully dissolving them, and then pouring the solution into a high-temperature reaction vessel for reaction. The resulting solution is dialyzed using a dialysis bag, and the dialyzed solution is freeze-dried to obtain pure red fluorescent carbon dot powder. This fluorescent carbon dot is resistant to Fe. 3+ It has a significant identification function, but its preparation requires the use of toxic o-phenylenediamine. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing red carbon quantum dots that can be used for the detection of ferric ions by fluorescence quenching. This method has the advantages of being simple to operate and environmentally friendly.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing red-light carbon quantum dots, characterized by comprising the following steps: (1) Mix the evergreen plant with ethanol and react it in a reaction vessel at 100℃-150℃ for a certain period of time; (2) The reaction solution was filtered, and the filtrate was dialyzed to obtain the red carbon quantum dots.

[0008] Preferably, the evergreen plant is an evergreen leaf.

[0009] Preferably, the ratio of the *Aglaonema* plant to ethanol is 1:10 g / mL.

[0010] Preferably, the reaction time is 6-10 hours.

[0011] Preferably, the reaction solution is filtered using a 0.22 μm microporous membrane.

[0012] Preferably, the filtrate is dialyzed using a dialysis bag with a molecular weight cutoff of 1000 Da.

[0013] Preferably, the dialysis period is 7 days, with the water changed every 6 hours.

[0014] A method for preparing red-light carbon quantum dots based on the above method.

[0015] Preferably, the red-light carbon quantum dots have a carbon content of ≥89%, an oxygen content of ≤10%, and a silicon content of 0.6~0.7%.

[0016] The application of the above-mentioned red-light carbon quantum dots in the detection of ferric ions by fluorescence quenching method.

[0017] The beneficial effects of this invention are: Compared with existing technologies, the method of this invention uses evergreen as a carbon source and ethanol as a solvent, which has the advantages of low raw material cost, green and environmentally friendly, and simple preparation operation. The prepared red carbon quantum dots have good selectivity for ferric ions. Attached Figure Description

[0018] Figure 1 Transmission electron microscope image of the red-light carbon quantum dots prepared in this invention.

[0019] Figure 2 The infrared spectrum (FT-IR) of the red carbon quantum dots prepared in this invention.

[0020] Figure 3 The X-ray photoelectron spectrum (XPS) of the red carbon quantum dots prepared in this invention.

[0021] Figure 4 The X-ray diffraction (XRD) pattern of the red carbon quantum dots prepared in this invention.

[0022] Figure 5 The images show the fluorescence spectra of red carbon quantum dots prepared at different reaction temperatures according to the present invention.

[0023] Figure 6 For Fe 3+ The fluorescence quenching effect on red carbon quantum dots prepared with different solvents.

[0024] Figure 7 The graph shows the variation of fluorescence intensity of the red carbon quantum dots prepared in this invention at different pH values.

[0025] Figure 8 The graph shows the variation of fluorescence intensity of the red carbon quantum dots prepared in this invention under different KCl concentrations.

[0026] Figure 9 A dotted line graph showing the change in fluorescence intensity of the red carbon quantum dots prepared in this invention at different times.

[0027] Figure 10 The bar chart shows the change in fluorescence intensity of the red carbon quantum dots prepared in this invention under different interfering ions.

[0028] Figure 11 The fluorescence intensity of the red carbon quantum dots prepared in this invention varies under different concentrations of ferric ions.

[0029] Figure 12 The graph shows the linear relationship between the fluorescence intensity of the red carbon quantum dots prepared in this invention and the concentration of ferric ions. Detailed Implementation

[0030] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0031] Example 1 Preparation of Evergreen: Dry the fresh leaves of Evergreen and set aside.

[0032] Preparation of dialysis bags: First, cut the dialysis bags (molecular weight cutoff of 1000 Da) into small segments of appropriate length (10-20 cm). Then, boil the dialysis bags in 250 ml of 2% (w / v) sodium bicarbonate and 1 mmol / L disodium EDTA for 10 minutes. Thoroughly rinse the dialysis bags with distilled water. After that, boil the dialysis bags again in 500 ml of 1 mmol / L disodium EDTA for 10 minutes. After cooling, place them in 30% ethanol and store them in a refrigerator at 4°C. It is essential to ensure that the dialysis bags are always submerged in the solution. Gloves must be worn when handling the dialysis bags. Before use, fill the dialysis bags with water and then drain it to clean them thoroughly.

[0033] (1) Synthesis of red-light carbon quantum dots (R-CDs) Add 5g of *Aglaonema* to 50 mL of ethanol, stir for 5 min, then transfer to a reaction vessel and react at 120℃ for 8 h. After the product cools to room temperature, filter it using a 0.22 μm microporous membrane, then transfer the filtrate to a dialysis bag and dialyze it with deionized water at room temperature for 7 days, changing the water every 6 h to obtain red carbon quantum dots (denoted as R-CDs-ethanol).

[0034] Figure 1 This is a transmission electron microscope image of R-CDs-ethanol.

[0035] FT-IR of R-CDs-ethanol ( Figure 2 ) and XPS ( Figure 3The spectrum shows that the surface of R-CDs nanomaterials has abundant oxygen-containing functional groups, which is beneficial to the stable dispersion of the material in water; the XPS spectrum of red carbon quantum dots shows two main peaks of C1s at 284.8 eV and O1s at 531.3 eV, and a small amount of Si is also detected. Based on the peak area, the C content is calculated to be 89.69 wt%, the O content is 9.67 wt%, and the silicon content is 0.64 wt%.

[0036] XRD ( Figure 4 The results indicate that the prepared R-CDs-ethanol has a broad diffraction peak centered at about 20°, corresponding to the (002) lattice spacing of the carbon-based material, indicating that the carbon quantum dots have a layered structure.

[0037] With other synthetic conditions fixed, the fluorescence spectra of R-CDs prepared at different reaction temperatures (100℃, 120℃, 150℃) are shown below. Figure 5 As shown, the fluorescence intensity of R-CDs prepared at 120 degrees Celsius is relatively strong.

[0038] To compare the effect of solvent on carbon quantum dots, this invention, under the same synthesis conditions (reaction temperature 120℃), replaced the ethanol solvent with an ethanol-water solution (volume ratio 10:1) to prepare red-emitting carbon quantum dots (denoted as R-CDs-ethanol-water). Under the same conditions, the fluorescence quenching effect of the same concentration of ferric ions on the same concentration of carbon quantum dots was tested, and the results are as follows: Figure 6 As shown in the figure. It can be seen that with the addition of Fe... 3+ Subsequently, the fluorescence intensity decrease at 677 nm of red carbon quantum dots prepared with ethanol as the solvent (R-CDs-ethanol) was significantly greater than that of red carbon quantum dots prepared with aqueous ethanol as the solvent (R-CDs-ethanol-water), indicating that compared with R-CDs-ethanol-water, Fe... 3+ It has a better quenching effect on R-CDs-ethanol.

[0039] The changes in fluorescence intensity of R-CDs-ethanol at different pH values ​​are as follows: Figure 7 As shown, we can observe that the fluorescence intensity is relatively stable within the pH range of 1 to 11, but it decreases significantly in strongly alkaline environments with pH ≥ 12. This may be due to excessive H+. + / OH - Ions cause significant changes in functional groups.

[0040] The fluorescence intensity changes of R-CDs-ethanol at different KCl concentrations are as follows: Figure 8 As shown, the luminescence intensity of the red carbon dots varies with the KCl concentration.

[0041] The changes in fluorescence intensity of R-CDs-ethanol at different times are as follows: Figure 9As shown, the prepared red carbon dots are relatively stable.

[0042] (2) Fluorescence quenching of R-CDs-ethanol by different metal ions Take 300 μL of various interfering ions at 10 mM, then add 500 μL of R-CDs-ethanol and 1200 μL of phosphate-buffered saline (PBS) at pH 7. Detect the fluorescence intensity of each interfering ion using a fluorescence spectrometer. The results are as follows. Figure 10 As shown, compared with other interfering ions, ferric ions have a significant fluorescence quenching effect on the red carbon dots prepared in this invention, and can selectively detect ferric ions.

[0043] (3) Fe 3+ Detection Different amounts of ferric iron solution and 500 μl of R-CDs-ethanol were added to different amounts of pH=7 PBS, with the total solution volume fixed at 2 ml. The fluorescence intensity of the reaction solutions with different concentrations of ferric iron was detected using a fluorescence spectrometer under excitation at 425 nm, and the emission wavelength at 677 nm was observed. The results are as follows: Figure 11 As shown, the fluorescence intensity decreases with increasing concentration of ferric ions.

[0044] Figure 12 This is a linear relationship curve between the concentration of ferric ions and (F0-F) / F0 (F0 is the fluorescence intensity value without added ferric ions, and F is the fluorescence intensity value with different concentrations of ferric ions added). The linear equation is Y = 0.00393X - 0.01107, R 2 =0.9999, where Y is the concentration of ferric ions and X is (F0-F) / F0.

[0045] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of red-light carbon quantum dots in the detection of ferric ions by fluorescence quenching, characterized in that, The red-light carbon quantum dots are prepared by the following steps: (1) Mix the leaves of the evergreen tree with ethanol and react them in a reaction vessel at 100℃-150℃ for 6-10h; (2) The reaction solution was filtered, and the filtrate was dialyzed to obtain the red carbon quantum dots.

2. The application according to claim 1, characterized in that: The ratio of the leaves of the evergreen plant to the ethanol is 1:10 g / mL.

3. The application according to claim 1, characterized in that: The reaction solution was filtered using a 0.22 μm microporous membrane.

4. The application according to claim 1, characterized in that: The filtrate was dialyzed using a dialysis bag with a molecular weight cutoff of 1000 Da.

5. The application according to claim 4, characterized in that: The dialysis period is 7 days, with the water changed every 6 hours.

6. The application according to claim 1, characterized in that: The red-light carbon quantum dots have a carbon content of ≥89%, an oxygen content of ≤10%, and a silicon content of 0.6~0.7%.

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