Xylan-based carbon dots with multicolor fluorescence and preparation method thereof

Abstract

The application discloses xylan-based carbon dots with multicolor fluorescence and a preparation method thereof. The carbon dots take xylan and p-phenylenediamine as precursors, are dissolved in different solvents at a certain ratio, are uniformly mixed, are reacted in a hydrothermal reaction kettle, are separated and purified by extraction after being cooled to room temperature, and four kinds of powder carbon dots can be obtained after drying. The four kinds of fluorescent carbon dots are dispersed in an ethanol solution, under a 365nm ultraviolet lamp, the carbon dots can emit blue, green, yellow and red fluorescence respectively. The fluorescent carbon dots have multiple fluorescence characteristics such as excitation independence, excitation dependence, solvent dependence and concentration dependence. The application realizes preparation of the multicolor fluorescent carbon dots with xylan as the precursor, the preparation method is simple in operation, convenient and fast in separation and purification, and low in cost. The prepared multicolor carbon dots have wide application prospects in the fields of biological labeling, cell imaging, fluorescent anti-counterfeiting, LED lighting and the like, and meanwhile, high-value utilization of xylan is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of xylan resource utilization, and relates to preparation of a luminescent carbon nanomaterial, in particular, to a preparation method of multi-color fluorescent xylan-based carbon dots. BACKGROUND

[0002] Agricultural and forestry residues are a kind of renewable resources, which are composed of cellulose, hemicellulose and lignin. Among them, carbon-rich hemicellulose is an ideal precursor for preparing carbon dots. Carbon dots are a new type of photoluminescent nanomaterials, which have the characteristics of tunable photoluminescence, good biocompatibility, low toxicity, low cost and easy functionalization. They show great application potential in photoluminescent devices, biological imaging and ion detection. Xylan is the main component of hemicellulose. Compared with lignin and cellulose, the molecular chain of xylan is shorter, and the intermolecular and intramolecular hydrogen bonds are weaker, which makes it more sensitive to thermochemistry and is also conducive to the preparation of xylan-based carbon dots and the regulation of fluorescent properties. Based on these advantages, people have successfully converted xylan into carbon dots and used them for electrochemical sensing and heavy metal ion detection.

[0003] However, in some existing studies, xylan-based (even most of the agricultural and forestry residue-based) carbon dots emit strong blue-green fluorescence under ultraviolet (UV) excitation. Emission in the long wavelength range, especially red fluorescence, is rarely seen. In addition, the commonly used separation and purification methods for carbon dots are dialysis and column chromatography. Both methods have the problems of complex operation and long time required for purification. The dialysis bag required for dialysis carbon dots has a small molecular weight cut-off and is expensive, which seriously limits the actual production and application of carbon dots. In this study, xylan-based carbon dots were prepared using xylan from agricultural and forestry residues as raw material, and multi-color xylan-based carbon dots including blue-green-yellow-red fluorescence were obtained by rapid separation and purification using extraction method. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of xylan-based carbon dots with multi-color fluorescence, which widens the high-value utilization way of xylan and provides a new method for the preparation of multi-color carbon dots.

[0005] The purpose of the present application is achieved by the following technical solutions.

[0006] A kind of xylan-based carbon dots with multi-color fluorescence, using xylan and p-phenylenediamine as materials, mixing uniformly and then reacting in a hydrothermal kettle, cooling to room temperature and then separating and purifying by extraction method, obtaining four different carbon dots (blue, green, yellow and red carbon dot fluorescent carbon dots), and the multi-color fluorescent xylan-based carbon dots are obtained after drying.

[0007] The preparation method of the xylan-based carbon dots with multi-color fluorescence of the present application, the multi-color fluorescence in the present application refers to blue, green, yellow and red fluorescence, and the preparation method comprises the following steps:

[0008] (1) Preparation of blue, green and yellow fluorescent xylan-based carbon dots:

[0009] a. Weigh 0.5-1 g of xylan and disperse it in 10-20 mL of deionized water. Weigh 0.5-1 g of p-phenylenediamine and dissolve it in 10-20 mL of deionized water. Mix and stir the two solutions evenly.

[0010] b. Transfer the mixed solution to an autoclave and react at 200-260°C for 6-24 hours. After the reaction is complete, cool the autoclave to room temperature in a natural environment to obtain a brown carbon dot solid-liquid mixture.

[0011] c. Centrifuge the obtained carbon dot mixture at a speed of 8000-10000 rpm to obtain supernatant and precipitate.

[0012] d. Extract the supernatant with xylene, then mix the extracted organic phase with ethanol and perform rotary evaporation to obtain blue fluorescent carbon dots (B-CD).

[0013] e. Wash the precipitate with deionized water three times, then add ethyl acetate to the precipitate. The part dissolved in ethyl acetate is green fluorescent carbon dots (G-CDs).

[0014] f. Finally, dissolve the part not dissolved in ethyl acetate in ethanol and perform rotary evaporation to obtain yellow fluorescent carbon dots (Y-CDs).

[0015] The reaction temperature in step b is preferably 200-230°C, and the reaction time is preferably 12-24h;

[0016] (2) Preparation of red fluorescent xylan-based carbon dots:

[0017] a. Weigh 0.5-1 g of xylan and disperse it in 10-20 mL of DMF. Weigh 0.5-1 g of p-phenylenediamine and dissolve it in 10-20 mL of DMF. Mix and stir the two solutions evenly.

[0018] b. Transfer the mixed solution to an autoclave and react at 200-260°C for 6-12 hours. After the reaction is complete, cool the autoclave to room temperature in a natural environment to obtain a purple-red carbon dot solution.

[0019] c. Centrifuge the obtained carbon dot solution at a speed of 8000-10000 rpm to obtain supernatant.

[0020] d. Extract the supernatant with xylene, then mix the extracted organic phase with ethanol and perform rotary evaporation to obtain red fluorescent carbon dots (R-CD).

[0021] Further preferably, the reaction temperature in step b is preferably 230-260 DEG C, and the reaction time is preferably 6-12 h.

[0022] The xylan-based carbon dots with multicolor fluorescence are prepared by the preparation method of the xylan-based carbon dots with multicolor fluorescence.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) The carbon dots are synthesized by using xylan and p-phenylenediamine as materials, the carbon source is cheap and abundant;

[0025] (2) The one-step hydrothermal method is adopted for preparation, the process is simple, the equipment requirement is low, the preparation cost is low, and the method is suitable for large-scale production;

[0026] (3) The separation and purification of the carbon dots are completed by the extraction step, the separation is more simple and fast, and the method is suitable for large-scale production;

[0027] (4) The synthesized carbon dots have four fluorescent colors including red, and have multiple fluorescence characteristics such as excitation dependence, excitation independence, concentration dependence and solvent dependence; BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is an effect diagram of the multicolor carbon dots respectively dissolved in ethanol and excited by sunlight and 365nm ultraviolet light.

[0029] Figure 2 is a TEM image of the carbon dots.

[0030] Figure 3 is a normalized emission spectrum diagram of four kinds of carbon dot solutions with anhydrous ethanol as a solvent under the excitation of a 365nm excitation wavelength;

[0031] Figure 4 In the figures, a, b, c and d are fluorescence emission spectrum diagrams of blue, green, yellow and red carbon dots, respectively, wherein, Figure 4 the a figure in the figures is a fluorescence emission spectrum diagram of blue carbon dots, Figure 4 the b figure in the figures is a fluorescence emission spectrum diagram of green carbon dots, Figure 4 the c figure in the figures is a fluorescence emission spectrum diagram of yellow carbon dots, Figure 4 the d figure in the figures is a fluorescence emission spectrum diagram of red carbon dots. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0033] Embodiment 1

[0034] 0.5 g of xylan was weighed and dispersed in 20 mL of deionized water, and 0.5 g of p-phenylenediamine was weighed and dissolved in 20 mL of deionized water, and the two were mixed and stirred uniformly. The above mixed solution was transferred to an autoclave, and reacted at 260°C for 24 hours. After the reaction was completed, the autoclave was cooled to room temperature in a natural environment, and a brown carbon dot solid-liquid mixture was obtained. The obtained carbon dot mixture was centrifuged at a speed of 10,000 rpm to obtain supernatant and precipitate. The supernatant was extracted with xylene, and then the extracted organic phase was mixed with ethanol and rotary evaporated to obtain blue fluorescent carbon dots (B-CDs). The precipitate was washed with deionized water three times, and then ethyl acetate was added to the precipitate. The part dissolved in ethyl acetate was green fluorescent carbon dots (G-CDs). Finally, the part not dissolved in ethyl acetate was dissolved in ethanol and rotary evaporated to obtain yellow fluorescent carbon dots (Y-CDs).

[0035] 0.5 g of xylan was weighed and dispersed in 20 mL of DMF, and 0.5 g of p-phenylenediamine was weighed and dissolved in 20 mL of DMF, and the two were mixed and stirred uniformly. The above mixed solution was transferred to an autoclave, and reacted at 260°C for 6 hours. After the reaction was completed, the autoclave was cooled to room temperature in a natural environment, and a purple-red carbon dot solution was obtained. The obtained carbon dot solution was centrifuged at a speed of 10,000 rpm to obtain supernatant. The supernatant was extracted with xylene, and then the extracted organic phase was mixed with ethanol and rotary evaporated to obtain red fluorescent carbon dots (R-CDs). The photos of the four carbon dots in ethanol solution and the fluorescence pictures under 365 nm ultraviolet excitation are shown in Figure 1 , and the transmission electron microscopy (TEM) images are shown in Figure 2 , and the prepared carbon dots have uniform particle size distribution. Figure 3 The normalized emission spectra of the four carbon dots are shown, and the prepared carbon dots almost cover the entire visible light region. Figure 4 a, b, c, d respectively show the emission spectra of blue, green, yellow, and red fluorescent carbon dots.

[0036] Embodiment 2

[0037] Take 1 g of xylan and disperse it in 20 mL of deionized water, take 0.5 g of p- phenylenediamine and dissolve it in 20 mL of deionized water, mix and stir them evenly. Transfer the above mixed solution to an autoclave, react at 230°C for 12 hours, after the reaction is completed, the autoclave is cooled to room temperature in the natural environment, and a brown carbon dot solid-liquid mixture is obtained. The obtained carbon dot mixture is centrifuged at a speed of 10,000 rpm to obtain supernatant and precipitate respectively. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain blue fluorescent carbon dots (B-CD). The precipitate is washed with deionized water three times, then ethyl acetate is added to the precipitate, and the part dissolved in ethyl acetate is green fluorescent carbon dots (G-CDs). Finally, the part not dissolved in ethyl acetate is dissolved in ethanol and rotary evaporated to obtain yellow fluorescent carbon dots (Y-CDs).

[0038] Take 1 g of xylan and disperse it in 20 mL of DMF, take 0.5 g of p-phenylenediamine and dissolve it in 20 mL of DMF, mix and stir them evenly. Transfer the above mixed solution to an autoclave, react at 230°C for 3 hours, after the reaction is completed, the autoclave is cooled to room temperature in the natural environment, and a purple-red carbon dot solution is obtained. The obtained carbon dot solution is centrifuged at a speed of 10,000 rpm to obtain supernatant. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain red fluorescent carbon dots (R-CD).

[0039] Example 3

[0040] Take 1 g of xylan and disperse it in 20 mL of deionized water, take 0.25 g of p- phenylenediamine and dissolve it in 20 mL of deionized water, mix and stir them evenly. Transfer the above mixed solution to an autoclave, react at 200°C for 24 hours, after the reaction is completed, the autoclave is cooled to room temperature in the natural environment, and a brown carbon dot solid-liquid mixture is obtained. The obtained carbon dot mixture is centrifuged at a speed of 10,000 rpm to obtain supernatant and precipitate respectively. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain blue fluorescent carbon dots (B-CD). The precipitate is washed with deionized water three times, then ethyl acetate is added to the precipitate, and the part dissolved in ethyl acetate is green fluorescent carbon dots (G-CDs). Finally, the part not dissolved in ethyl acetate is dissolved in ethanol and rotary evaporated to obtain yellow fluorescent carbon dots (Y-CDs).

[0041] Take 1 g of xylan and disperse it in 20 mL of DMF, take 0.25 g of p-phenylenediamine and dissolve it in 20 mL of DMF, mix and stir them evenly. Transfer the above mixed solution to the hydrothermal kettle, react at 260°C for 6 hours, after the reaction is completed, the hydrothermal kettle is cooled to room temperature in the natural environment, and a purple red carbon dot solution is obtained. The obtained carbon dot solution is centrifuged at a speed of 10,000 rpm to obtain a supernatant. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain red fluorescent carbon dots (R-CD).

[0042] Example 4

[0043] Take 1 g of xylan and disperse it in 20 mL of deionized water, take 1 g of p-phenylenediamine and dissolve it in 20 mL of deionized water, mix and stir them evenly. Transfer the above mixed solution to the hydrothermal kettle, react at 260°C for 12 hours, after the reaction is completed, the hydrothermal kettle is cooled to room temperature in the natural environment, and a brown carbon dot solid-liquid mixture is obtained. The obtained carbon dot mixture is centrifuged at a speed of 10,000 rpm to obtain a supernatant and a precipitate, respectively. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain blue fluorescent carbon dots (B-CD). The precipitate is washed with deionized water three times, then ethyl acetate is added to the precipitate, and the part dissolved in ethyl acetate is green fluorescent carbon dots (G-CDs). Finally, the part not dissolved in ethyl acetate is dissolved in ethanol and rotary evaporated to obtain yellow fluorescent carbon dots (Y-CDs).

[0044] Take 0.5 g of xylan and disperse it in 20 mL of DMF, take 0.5 g of p-phenylenediamine and dissolve it in 20 mL of DMF, mix and stir them evenly. Transfer the above mixed solution to the hydrothermal kettle, react at 290°C for 6 hours, after the reaction is completed, the hydrothermal kettle is cooled to room temperature in the natural environment, and a purple red carbon dot solution is obtained. The obtained carbon dot solution is centrifuged at a speed of 10,000 rpm to obtain a supernatant. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain red fluorescent carbon dots (R-CD).

[0045] Example 5

[0046] Take 0.5 g xylan dispersed in 20 mL deionized water, take 1 g p-phenylenediamine dissolved in 20 mL deionized water, mix and stir them evenly. Transfer the mixed solution above to an autoclave, react at 260°C for 12 hours, after the reaction is completed, the autoclave is cooled to room temperature in the natural environment, and a brown carbon dot solid-liquid mixture is obtained. The obtained carbon dot mixture is centrifuged at a speed of 10,000 rpm to obtain supernatant and precipitate. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain blue fluorescent carbon dots (B-CD). The precipitate is washed with deionized water three times, then ethyl acetate is added to the precipitate, and the part dissolved in ethyl acetate is green fluorescent carbon dots (G-CDs). Finally, the part not dissolved in ethyl acetate is dissolved in ethanol and rotary evaporated to obtain yellow fluorescent carbon dots (Y-CDs).

[0047] Take 1 g xylan dispersed in 20 mL DMF, take 1 g p-phenylenediamine dissolved in 20 mL DMF, mix and stir them evenly. Transfer the mixed solution above to an autoclave, react at 260°C for 12 hours, after the reaction is completed, the autoclave is cooled to room temperature in the natural environment, and a purple-red carbon dot solution is obtained. The obtained carbon dot solution is centrifuged at a speed of 10,000 rpm to obtain supernatant. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain red fluorescent carbon dots (R-CD).

[0048] It should be understood that the above detailed description of the technical solutions of the present application by means of the optimization examples is illustrative rather than limiting, and the specific embodiments of the present application cannot be limited to this. For ordinary skilled persons in the technical field to which the present application belongs, modifications to the technical solutions described in the embodiments, or equivalent replacement of part of the technical features, without departing from the concept of the present application, should be considered to belong to the scope of patent protection determined by the claims submitted by the present application.

[0049] The above embodiments of the present application are merely examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For ordinary skilled persons in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A method for preparing xylan-based carbon dots with multicolor fluorescence, characterized in that, The multi-color fluorescence refers to blue, green, yellow and red fluorescence; The method comprises the following steps: (1) Preparation of blue, green and yellow fluorescent xylan-based carbon dots: a. Xylan is weighed and dispersed in deionized water, and p-phenylenediamine is weighed and dissolved in deionized water, and the two are mixed uniformly to obtain a mixed solution; b. The mixed solution is transferred to a hydrothermal kettle, and hydrothermal reaction is carried out at 200-260°C. After the reaction is completed, the hydrothermal kettle is cooled to room temperature in a natural environment to obtain a brown carbon dot solid-liquid mixture; c. The obtained carbon dot mixture is centrifuged and purified to obtain supernatant and precipitate, respectively; d. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain blue fluorescent carbon dots (B-CD); e. The precipitate is washed with deionized water three times, and then ethyl acetate is added to the precipitate. The part dissolved in ethyl acetate is green fluorescent carbon dots (G-CDs); f. Finally, the part not dissolved in ethyl acetate is dissolved in ethanol and rotary evaporated to obtain yellow fluorescent carbon dots (Y-CDs); (2) Preparation of red fluorescent xylan-based carbon dots: a. Xylan is weighed and dispersed in DMF, and p-phenylenediamine is weighed and dissolved in DMF, and the two are mixed and stirred uniformly to obtain a mixed solution; b. The mixed solution is transferred to a hydrothermal kettle, and hydrothermal reaction is carried out at 200-260°C. After the reaction is completed, the hydrothermal kettle is cooled to room temperature in a natural environment to obtain a purple-red carbon dot solution; c. The obtained carbon dot solution is centrifuged and purified to obtain supernatant; d. The supernatant is extracted with xylene, and then the extracted organic phase is mixed with ethanol and rotary evaporated to obtain red fluorescent carbon dots (R-CD).

2. The production method according to claim 1, characterized by, In step (1), in step a, the mass of the xylan is 0.5-1 g, and the xylan is dispersed in 10-20 mL of deionized water; the mass of the p-phenylenediamine is 0.5-1 g, and the p-phenylenediamine is dissolved in 10-20 mL of deionized water.

3. The preparation method according to claim 1, characterized in that, In step (1), in step b, the hydrothermal reaction time is 6-24 h.

4. The preparation method according to claim 1, characterized in that, In steps (1) and (2), in step c, the centrifugal speed is 8000-10000 rpm.

5. The preparation method according to claim 1, characterized in that, In step (1), in step d, the reagent used for extracting the supernatant is xylene.

6. The preparation method according to claim 1, characterized in that, In step (1), in step e, the reagent used for dissolving the precipitate is ethyl acetate.

7. The preparation method according to claim 1, characterized in that, In step (2), the hydrothermal reaction time in step b is 6-24 h.

8. The method of claim 1, wherein, In step (2), in step a, the mass of the xylan is 0.5-1 g, and the xylan is dispersed in 10-20 mL of DMF; the mass of the p-phenylenediamine is 0.5-1 g, and the p-phenylenediamine is dissolved in 10-20 mL of DMF.

9. The method of claim 1, wherein, In step (2), in step b, the hydrothermal reaction time is 6-12 hours.

10. The xylan-based carbon dots with multi-color fluorescence prepared by the preparation method of any one of claims 1-9.

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