CN108485662A - Nitrogen, sulphur codope fluorescent carbon quantum dot material and preparation method thereof - Google Patents

Abstract

The present invention disclose a kind of nitrogen, sulphur codope fluorescent carbon quantum dot material and preparation method thereof, the preparation method includes the following steps：1）Citric acid and N acetyl L cysteine solids are weighed, is placed in beaker, mixing, 150 ~ 250 DEG C is heated to electric jacket；2）Hybrid solid gradually melts, and color becomes light yellow from colourless, eventually becomes brown, after heating 20 ~ 30min, rapidly pours into the solution of melting in ultra-pure water, and be constantly vigorously stirred；3）Then it is dialysed in deionized water 20 ~ 30 hours with 100 ~ 500D cellulose dialysis bag, it is 4.0 ~ 6.0 to use 1M NaOH to adjust pH later.To gained quantum point carry out vacuum freeze drying, with ultrapure water dissolution obtain nitrogen, sulphur codope fluorescent carbon quantum dot aqueous solution.The advantages that present invention is easy to get with raw material, environmentally protective, hypotoxicity, and the fluorescent carbon quantum dot good dispersion of gained, epigranular, with good stability and higher fluorescence quantum yield.

Description

Nitrogen, sulfur double-doped fluorescent carbon quantum dot material and preparation method thereof

technical field

The invention relates to a method for preparing a fluorescent carbon quantum dot material doped with nitrogen and sulfur, and belongs to the field of nanotechnology.

Background technique

Carbon quantum dots (carbon quantum dots, CQDs) are a class of environmentally friendly fluorescent nanomaterials with a particle size of less than 10 nm. They are mainly composed of carbon elements and do not contain heavy metal elements. They have the advantages of high biocompatibility and low cytotoxicity. , with little interference to biomolecules, it is expected to replace traditional quantum dots and be applied to the fields of optical imaging, biomedicine, and analysis and detection.

In recent years, scientists hope to find a simpler and cheaper method to prepare carbon quantum dots with excellent performance and high fluorescence quantum yield, and apply them in the fields of medicine, life science, optoelectronics and other fields. Recent studies have shown that the particle size and surface characteristics of carbon quantum dots have a crucial impact on their properties. Carbon quantum dots with small particle size have larger specific surface area and more surface luminescent sites. Therefore, the luminescence of carbon quantum dots with small particle size is stronger than that of carbon quantum dots with large particle size, which further indicates that the luminescence of carbon quantum dots is related to the surface. In addition, carbon quantum dots with a large number of oxygen-containing groups such as (hydroxyl, carboxyl, etc.) on the surface have good water solubility and are easy to achieve further functionalization. Therefore, fluorescent carbon quantum dots have unique physical and chemical properties, and have broad application prospects in magnetism, electricity, optics, catalysis, and chemical sensing, as well as biomedicine.

Many properties of carbon quantum dots mainly depend on the selected synthetic raw materials, the internal structure and surface activity of nanomaterials, and surface activity is the main factor determining the performance of carbon quantum dots. The functionalization of carbon quantum dots is the best way to improve the performance of carbon quantum dots, and it is mainly realized by surface modification and doping elements. Doping impurities in the semiconductor lattice has a great impact on the optical, electrical, magnetic and other physical properties of semiconductor quantum dots.

The invention uses citric acid (CA) and N-acetyl-L-cysteine (L-Cys) which can simultaneously provide carbon, nitrogen and sulfur as synthetic precursors, and adopts a simple one-step hydrothermal method to prepare water-soluble nitrogen , Sulfur double-doped fluorescent carbon quantum dots.

Contents of the invention

The object of the present invention is to provide a fluorescent carbon quantum dot material doped with nitrogen and sulfur and a preparation method thereof. The synthesis technology provided by the invention has a simple process, only two small molecular substances are needed to synthesize a precursor, the cost is low, and it is suitable for large-scale batch production.

In order to achieve the above object, the present invention adopts the pyrolysis method to prepare nitrogen and sulfur double-doped fluorescent carbon quantum dots with uniform particle size distribution, and its technical scheme is that citric acid and N-acetyl-L-cysteine solid powder Fluorescent carbon quantum dots were prepared by pyrolysis. A method for preparing a nitrogen-sulfur double-doped fluorescent carbon quantum dot material according to the present invention comprises the following steps: 1) Weighing citric acid and N-acetyl-L-cysteine, citric acid and N- The mass ratio of acetyl-L-cysteine is 1:1-1.4, put in a beaker, mix well, and heat to 150~250°C with a heating mantle; 2) The mixed solid gradually melts, and the color changes from colorless to light yellow , and finally turn brown, after heating for 20~30min, quickly pour the molten solution into ultrapure water, and keep stirring vigorously to obtain the pyrolysis product; 3) use the pyrolysis product obtained in step 2) with 100-500D fiber The plain dialysis bag was dialyzed in deionized water for 20-30 hours, then the pH was adjusted to 4.0-6.0 with NaOH, the obtained quantum dots were vacuum freeze-dried, and dissolved in ultrapure water to obtain an aqueous solution of fluorescent carbon quantum dots doped with nitrogen and sulfur. .

The fluorescent carbon quantum dot aqueous solution was subjected to rotary evaporation and vacuum drying to obtain a fluorescent carbon quantum dot solid powder, and the average particle size of the fluorescent carbon quantum dot was 3.82 nm.

The pyrolysis product obtained in step 2) was dialyzed in deionized water with a 100-500D cellulose dialysis bag for 24 hours, during which the dialyzed fluid was replaced every 4 hours.

After dialysis, adjust the pH with 1M NaOH, vacuum freeze-dry the obtained quantum dots, and dissolve the quantum dot aqueous solution with ultrapure water.

The fluorescent carbon quantum dots double-doped with nitrogen and sulfur prepared by the above-mentioned preparation method of the present invention are stored in the dark at 4° C. for future use.

The aqueous solution of the fluorescent carbon quantum dot material is brown and transparent, and after scanning the ultraviolet-visible absorption spectrum of the solution, the maximum absorption peak of the fluorescent carbon quantum dot solution is at 337nm.

The above fluorescent carbon quantum dots have an average particle size of 3.82 nm.

Specifically, the preparation method of nitrogen and sulfur double-doped fluorescent carbon quantum dots of the present invention comprises the following steps: 1) Weigh citric acid and N-acetyl-L-cysteine solids and place them in a beaker 2) The mixed solid gradually melted, and the color changed from colorless to light yellow, and finally to brown. After heating for 25 minutes, quickly pour the molten solution into ultrapure water. And keep stirring vigorously; 3) Then use a 100-500D cellulose dialysis bag to dialyze in deionized water for 24 hours, and then adjust the pH to 5.0 with 1M NaOH. The obtained quantum dots are subjected to vacuum freeze-drying, and are dissolved in ultrapure water to obtain an aqueous solution of fluorescent carbon quantum dots doped with nitrogen and sulfur.

The fluorescent carbon quantum dot aqueous solution was rotary evaporated and vacuum dried to obtain a fluorescent carbon quantum dot solid powder, and the average particle size of the fluorescent carbon quantum dot was 3.82 nm.

The preparation method of the fluorescent carbon quantum dot material doped with nitrogen and sulfur double, is characterized in that

1) Weigh citric acid and N-acetyl-L-cysteine solids, put them in a 10mL beaker, mix well, and heat to 200°C with a heating mantle;

2) The mixed solid obtained in step 1) was gradually melted, and the color changed from colorless to light yellow, and finally to brown;

3) After heating for 25 minutes, quickly pour the molten solution into ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

4) Dialyze the pyrolysis product obtained in step 3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

5) Adjust the pH to 5.0 with 1M NaOH after dialysis. The obtained quantum dots were subjected to vacuum freeze-drying, dissolved in ultrapure water to obtain an aqueous solution of nitrogen-sulfur double-doped fluorescent carbon quantum dots, and stored at 4°C in the dark for future use.

The heating temperature of the electric heating mantle in step 1) is preferably 200 °C, the mixed solid gradually melts, and the color changes from colorless to light yellow, and finally brown, and the time for continuous pyrolysis is preferably 25 minutes.

Fluorescent carbon quantum dots double-doped with nitrogen and sulfur prepared by the above-mentioned preparation method of the present invention.

The fluorescent carbon quantum dots doped with nitrogen and sulfur are characterized in that the aqueous solution of the fluorescent carbon quantum dot material is brown and transparent, and when the ultraviolet-visible absorption spectrum of the solution is scanned, the maximum absorption peak position of the fluorescent carbon quantum dot solution is at 337nm.

The fluorescent carbon quantum dots doped with nitrogen and sulfur are characterized in that the average particle size of the fluorescent carbon quantum dots is 3.82nm.

Specifically, the preparation method of nitrogen and sulfur double-doped fluorescent carbon quantum dots of the present invention, the method steps are:

Step 1: Weigh the solids of citric acid and N-acetyl-L-cysteine, put them in a beaker, mix well, and heat to 200°C with a heating mantle;

Step 2: gradually melt the mixed solid obtained in step 1), and the color changes from colorless to light yellow, and finally to brown;

Step 3: After heating for 25 minutes, quickly pour the molten solution into ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

Step 4: Dialyze the pyrolysis product obtained in step 3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

Step 5: Adjust the pH to 5.0 with 1M NaOH after dialysis. The obtained quantum dots were subjected to vacuum freeze-drying, dissolved in ultrapure water to obtain an aqueous solution of nitrogen-sulfur double-doped fluorescent carbon quantum dots, and stored at 4°C in the dark for future use.

The precursor citric acid and N-acetyl-L-cysteine do not need any pretreatment, and no other reagents need to be added in addition to the precursor citric acid and N-acetyl-L-cysteine during the reaction.

The obtained nitrogen-sulfur double-doped fluorescent carbon quantum dots had an average particle size of 3.82 nm.

The advantage of the present invention is: in the preparation process of the fluorescent carbon quantum dot material doped with nitrogen and sulfur, no other reagents need to be added except the precursor citric acid and N-acetyl-L-cysteine. Nitrogen-sulfur double-doped fluorescent carbon quantum dots can be obtained by a simple one-step pyrolysis method of the precursors citric acid and N-acetyl-L-cysteine. The method of the invention has the advantages of simple preparation process, low cost and environmental protection. The prepared fluorescent carbon quantum dots doped with nitrogen and sulfur have regular appearance, uniform particle size, good water solubility, high solution stability, easy storage and large-scale batch production.

Description of drawings

Figure 1 is a photo of nitrogen and sulfur double-doped fluorescent carbon quantum dot material aqueous solution under the irradiation of 365 nm ultraviolet lamp, and blue fluorescence can be observed.

Fig. 2 is an ultraviolet-visible absorption spectrum diagram of a fluorescent carbon quantum dot material doped with nitrogen and sulfur.

Fig. 3 is a fluorescence excitation and emission spectrum diagram of a nitrogen-sulfur double-doped fluorescent carbon quantum dot material.

Fig. 4 is a transmission electron microscope image of a fluorescent carbon quantum dot material doped with nitrogen and sulfur.

Fig. 5 is an X-ray photoelectron energy spectrum diagram of a fluorescent carbon quantum dot material doped with nitrogen and sulfur.

Fig. 6 is an infrared spectrum diagram of a fluorescent carbon quantum dot material doped with nitrogen and sulfur.

Figure 7 is a linear plot of the area integral of the emission spectrum versus the absorbance value.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

Example 1

(1) Accurately weigh 1.0001g of citric acid and 1.0003g of N-acetyl-L-cysteine solid, place in a 10mL beaker, mix well, and heat to 200°C with a heating mantle;

(2) The mixed solid obtained above was gradually melted, and the color changed from colorless to light yellow, and finally to brown;

(3) After heating for 25 minutes, quickly pour the molten solution into 70mL ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

(4) Dialyze the pyrolysis product obtained in step (3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

(5) After dialysis, adjust the pH to 5.0 with 1M NaOH. The obtained quantum dots were subjected to vacuum freeze-drying, and dissolved in ultrapure water to obtain a nitrogen-sulfur double-doped fluorescent carbon quantum dot aqueous solution with a concentration of 1.65 mg/mL. The photo of the solution under the irradiation of 365 nm ultraviolet lamp can be observed blue fluorescence (see Figure 1). Take a small amount of the solution and dilute it to a certain concentration, and scan its ultraviolet-visible absorption spectrum. The maximum absorption peak of the nitrogen-sulfur double-doped fluorescent carbon quantum dot solution is at 337 nm (see Figure 2).

Example 2

(1) Accurately weigh 1.0001g of citric acid and 1.0003g of N-acetyl-L-cysteine solid, place in a 10mL beaker, mix well, and heat to 200°C with a heating mantle;

(2) The mixed solid obtained above was gradually melted, and the color changed from colorless to light yellow, and finally to brown;

(3) After heating for 25 minutes, quickly pour the molten solution into 70mL ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

(4) Dialyze the pyrolysis product obtained in step (3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

(5) After dialysis, adjust the pH to 5.0 with 1M NaOH. The obtained quantum dots were subjected to vacuum freeze-drying, and dissolved in ultrapure water to obtain a nitrogen-sulfur double-doped fluorescent carbon quantum dot aqueous solution with a concentration of 1.65 mg/mL. Take a small amount of the solution and dilute it to a certain concentration, and scan its excitation spectrum and emission spectrum. It can be seen from the spectrum that the optimal excitation wavelength and optimal emission wavelength of the carbon quantum dot solution are 346 nm and 418 nm, respectively (see Figure 3).

Example 3

(1) Accurately weigh 1.0001g of citric acid and 1.0003g of N-acetyl-L-cysteine solid, place in a 10mL beaker, mix well, and heat to 200°C with a heating mantle;

(2) The mixed solid obtained above was gradually melted, and the color changed from colorless to light yellow, and finally to brown;

(3) After heating for 25 minutes, quickly pour the molten solution into 70mL ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

(4) Dialyze the pyrolysis product obtained in step (3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

(5) After dialysis, adjust the pH to 5.0 with 1M NaOH. The obtained quantum dots were subjected to vacuum freeze-drying, and dissolved in ultrapure water to obtain a nitrogen-sulfur double-doped fluorescent carbon quantum dot aqueous solution with a concentration of 1.65 mg/mL. The resulting solution was drip-coated on a copper grid for transmission electron microscopy detection. The fluorescent carbon quantum dots doped with nitrogen and sulfur were in a regular monodisperse spherical shape with an average particle size of 3.26 nm (see Figure 4).

Example 4

(1) Accurately weigh 1.0001g of citric acid and 1.0003g of N-acetyl-L-cysteine solid, place in a 10mL beaker, mix well, and heat to 200°C with a heating mantle;

(2) The mixed solid obtained above was gradually melted, and the color changed from colorless to light yellow, and finally to brown;

(3) After heating for 25 minutes, quickly pour the molten solution into 70mL ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

(4) Dialyze the pyrolysis product obtained in step (3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

(5) After dialysis, adjust the pH to 5.0 with 1M NaOH. The obtained quantum dots were subjected to vacuum freeze-drying, and dissolved in ultrapure water to obtain a nitrogen-sulfur double-doped fluorescent carbon quantum dot aqueous solution with a concentration of 1.65 mg/mL. The fluorescent carbon quantum dot solid powder doped with nitrogen and sulfur can be obtained after rotary evaporation and vacuum drying. The obtained powder was taken for X-ray photoelectron spectroscopy, and it can be seen from the spectrum that the surface of carbon quantum dots contains a large amount of C, O, N, and S elements (see Figure 5).

Example 5

(1) Accurately weigh 1.0001g of citric acid and 1.0003g of N-acetyl-L-cysteine solid, place in a 10mL beaker, mix well, and heat to 200°C with a heating mantle;

(2) The mixed solid obtained above was gradually melted, and the color changed from colorless to light yellow, and finally to brown;

(3) After heating for 25 minutes, quickly pour the molten solution into 70mL ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

(4) Dialyze the pyrolysis product obtained in step (3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

(5) After dialysis, adjust the pH to 5.0 with 1M NaOH. The obtained quantum dots were subjected to vacuum freeze-drying, and were dissolved in ultrapure water to obtain an aqueous solution of nitrogen and sulfur double-doped fluorescent carbon quantum dots with a concentration of 1.65 mg/mL. The fluorescent carbon quantum dot solid powder doped with nitrogen and sulfur can be obtained after rotary evaporation and vacuum drying. The obtained powder was taken for Fourier transform infrared (FTIR) spectroscopic measurement, which further confirmed the existence of oxygen-containing groups (O-H, -COO-, C=O) and C-S, C=C and C-N (see Figure 6).

Example 6

(1) Accurately weigh 1.0001g of citric acid and 1.0003g of N-acetyl-L-cysteine solid, place in a 10mL beaker, mix well, and heat to 200°C with a heating mantle;

(2) The mixed solid obtained above was gradually melted, and the color changed from colorless to light yellow, and finally to brown;

(3) After heating for 25 minutes, quickly pour the molten solution into 70mL ultrapure water, and keep stirring vigorously to obtain the pyrolysis product;

(4) Dialyze the pyrolysis product obtained in step (3) with a 100-500D cellulose dialysis bag in deionized water for 24 hours, during which the dialyzed fluid is replaced every 4 hours;

(5) Adjust the pH to 5.0 with 1M NaOH after dialysis. The obtained quantum dots were subjected to vacuum freeze-drying, and were dissolved in ultrapure water to obtain an aqueous solution of nitrogen and sulfur double-doped fluorescent carbon quantum dots with a concentration of 1.65 mg/mL. Taking quinine sulfate dissolved in 0.1MH ₂ SO ₄ as a reference (345nm is the excitation wavelength, the absorbance is selected at 360nm, QY=0.54), the different concentrations of N,S-CDs and quinine sulfate were respectively measured under the excitation wavelength of 346nm Gained emission spectrum and the ultraviolet absorption spectrum of corresponding concentration, take the absorbance value at 360nm place in the corresponding absorption spectrum under the same concentration as the X-axis, and the area integral of the emission spectrum is plotted as the Y-axis, calculate the slope of the curve, and then According to the equation:

Φx = ΦST (mx / mST) (ηx2 /ηST2 )

Calculate the relative fluorescence quantum yield, "Φ" represents the fluorescence quantum yield in the formula, "m" represents the slope of the curve obtained by plotting the area integral of the emission spectrum to the absorbance value, and "η" is the refractive index of the solvent (wherein quinine sulfate The refractive index of carbon dots is 1.33, and the refractive index of carbon dots dissolved in ultrapure water is 1.33), "ST" and "X" represent standard and sample solutions respectively. The results are shown in Figure 7, and the calculated relative fluorescence quantum yield of N,S-CDs is 74.08%.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications made within the spirit and principles of the present invention, equivalent replacements and improvements, etc., should be included in the protection of the present invention. within range.

Claims (7)

1. a kind of nitrogen, sulphur codope fluorescent carbon quantum dot material preparation method, include the following steps：1）Weigh citric acid and The mass ratio 1 of N-acetyl-L-cysteine, citric acid and N-acetyl-L-cysteine:1-1.4 is placed in beaker, mixing, is used Electric jacket is heated to 150 ~ 250 DEG C； 2）Hybrid solid gradually melts, and color becomes light yellow from colourless, eventually becomes brown, After heating 20 ~ 30min, the solution of melting is poured into ultra-pure water rapidly, and is constantly vigorously stirred, obtains thermal decomposition product；3）It will Step 2）The thermal decomposition product of acquisition is dialysed 20 ~ 30 hours in deionized water with 100-500D cellulose dialysis bag, Zhi Houyong It is 4.0 ~ 6.0 that NaOH, which adjusts pH, carries out vacuum freeze drying to gained quantum point, nitrogen, sulphur codope are obtained with ultrapure water dissolution Fluorescent carbon quantum dot aqueous solution.

2. nitrogen according to claim 1, sulphur codope fluorescent carbon quantum dot material preparation method, it is characterised in that institute It states fluorescent carbon quantum dot aqueous solution and acquires fluorescent carbon quantum dot solid powder, fluorescent carbon quantum dot after rotating, being dried in vacuo Average grain diameter is 3.82 nm.

3. nitrogen according to claim 1 or 2, sulphur codope fluorescent carbon quantum dot material preparation method, feature exists In

By step 2）The thermal decomposition product of acquisition is dialysed 24 hours in deionized water with 100-500D cellulose dialysis bag, during which every Replace extracellular fluid dialysis within 4 hours.

4. nitrogen according to claim 3, sulphur codope fluorescent carbon quantum dot material preparation method, it is characterised in that

PH is adjusted with 1M NaOH after dialysis, vacuum freeze drying is carried out to gained quantum point, dissolves quantum dot water with ultra-pure water Solution.

5. the fluorescent carbon quantum dot of nitrogen made from any preparation methods of claim 1-4, sulphur codope, 4 DEG C are protected from light guarantor It deposits spare.

6. the fluorescent carbon quantum dot of nitrogen according to claim 5, sulphur codope, it is characterised in that fluorescent carbon quantum dot material Aqueous solution is in amber transparent shape, the absorption maximum of fluorescent carbon quantum dot solution after scanning the ultraviolet-visible absorption spectroscopy of the solution Peak position is at 337nm.

7. the fluorescent carbon quantum dot of nitrogen according to claim 5 or 6, sulphur codope, it is characterised in that fluorescent carbon quantum dot Average grain diameter is 3.82 nm.