Method for synthesizing fluorescent carbon quantum dots from carboxylated cellulose nanofibers

Abstract

The invention discloses a method for synthesizing fluorescent carbon quantum dots from carboxylated cellulose nanofibers, which comprises the following steps: adding carboxylated cellulose nanofibers into water, and carrying out oscillation and ultrasonic treatment to obtain a carboxylated cellulose nanofiber solution; placing the carboxylated cellulose nanofiber solution in a polytetrafluoroethylene reaction kettle for hydrothermal reaction; cooling the carboxylated cellulose nanofiber solution after the hydrothermal reaction to room temperature, centrifuging, and taking supernate; and performing dialysis treatment on the supernate by using a dialysis bag to obtain the carboxylated cellulose nanofiber carbon quantum dots. According to the method, carboxylated cellulose nanofibers are used as precursors, and the carbon quantum dots with blue fluorescence are prepared through a hydrothermal synthesis method and have photoluminescence characteristics and stability; the carboxylated cellulose nanofiber is wide in source, green, environment-friendly and renewable.

Description

Technical Field

[0001] The invention relates to the technical field of nanomaterials, and in particular to a method for synthesizing fluorescent carbon quantum dots from carboxylated cellulose nanofibers. Background Art

[0002] Carbon quantum dots (CQDs) are a class of carbon-based nanofluorescent materials with a size of less than 10 nm, consisting of a carbon core and surface functional groups (such as carboxyl, hydroxyl, and amino groups). Compared with traditional semiconductor quantum dots, CQDs have the advantages of adjustable fluorescence, high photostability, good biocompatibility, and low toxicity. They can also be synthesized from green precursors, which is in line with the concept of sustainable development. Their fluorescence properties can be regulated by size, surface chemical modification, and doping, and are widely used in bioimaging, environmental monitoring, optoelectronic devices, and food safety testing. In sensing detection, CQDs can highly selectively identify targets (such as metal ions, organic pollutants, etc.) based on fluorescence quenching or enhancement effects, making them a research hotspot for new nanosensing platforms.

[0003] The precursor materials for preparing CQDs are diverse, including inorganic carbon sources such as carbon black and graphite, as well as small organic molecules such as ammonium citrate and ethylenediamine. Although these precursors are relatively mature in the technology of synthesizing CQDs, their limitations are becoming increasingly apparent from the perspectives of environmental protection and economy. For example, CN108456519A uses a mixed system of carboxymethyl cellulose and ethylenediamine, and introduces toxic nitrogen source dopants such as ethylenediamine, which results in high raw material costs and insufficient environmental protection. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method for synthesizing fluorescent carbon quantum dots from carboxylated cellulose nanofibers. This method uses low-cost renewable raw materials as the core, has a simplified process, and does not require toxic reagents to synthesize carbon quantum dots, thereby achieving high fluorescence performance and wide applicability.

[0005] The embodiment of the present invention provides a method for synthesizing fluorescent carbon quantum dots from carboxylated cellulose nanofibers, which comprises the following steps:

[0006] Step 1, adding carboxylated cellulose nanofibers to water, shaking and ultrasonicating, to obtain a carboxylated cellulose nanofiber solution;

[0007] Step 2, placing the carboxylated cellulose nanofiber solution in a polytetrafluoroethylene reactor for hydrothermal reaction;

[0008] Step 3, cooling the carboxylated cellulose nanofiber solution after the hydrothermal reaction in step 2 to room temperature and then centrifuging it to collect the supernatant;

[0009] Step 4: dialyze the supernatant using a dialysis bag to obtain carboxylated cellulose nanofiber carbon quantum dots.

[0010] According to an embodiment of the present invention, a method for synthesizing fluorescent carbon quantum dots from carboxylated cellulose nanofibers is provided. The method uses carboxylated cellulose nanofibers as a precursor and, through a hydrothermal synthesis method, prepares carbon quantum dots with blue fluorescence, which have photoluminescence properties and stability. Carboxylated cellulose nanofibers are widely available, green, environmentally friendly, and renewable. The method is simple and efficient, does not require additional dopants, uses non-toxic reagents throughout the process, uses renewable raw materials, and has lower costs. The prepared carbon quantum dots can be used in many fields such as biomedicine, photoelectric conversion and sensing, ion detection, photoconversion membranes, information encryption and decryption, and the like.

[0011] Optionally, the hydrothermal reaction time in step 2 is 2 h to 12 h.

[0012] Optionally, the temperature of the hydrothermal reaction in step 2 is 160°C to 220°C.

[0013] Optionally, in step 4, dialysis is performed using a dialysis bag with a molecular weight cut-off of 500 Da.

[0014] Optionally, in step 4, the dialysis time is 24 hours, of which 12 hours are used for dialysis against water.

[0015] Optionally, in step 3, the centrifugation temperature is 20000 rcf and the centrifugation time is 20 min.

[0016] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the relative fluorescence intensity value of carbon quantum dots at 430 nm at different synthesis times according to an embodiment of the present invention;

[0018] Figure 2 is the relative fluorescence intensity value of carbon quantum dots at 430 nm at different synthesis temperatures according to an embodiment of the present invention;

[0019] Figure 3 is a transmission electron microscope image of carboxylated cellulose nanofibers according to an embodiment of the present invention;

[0020] Figure 4 A transmission electron microscopy image of carboxylated cellulose nanofiber carbon quantum dots according to an embodiment of the present invention;

[0021] Figure 5The UV-visible absorption spectrum of carboxylated cellulose nanofiber carbon quantum dots according to an embodiment of the present invention is shown in the insets, which are photos taken under natural light (left) and under UV light (right);

[0022] Figure 6 Graphs showing fluorescence emission spectra of carboxylated cellulose nanofiber carbon quantum dots at different excitation wavelengths according to an embodiment of the present invention;

[0023] Figure 7 This is an infrared spectrum of carboxylated cellulose nanofiber carbon quantum dots according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships, without substantially changing the technical content, should also be regarded as the scope of the present invention.

[0025] In order to better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0026] The test materials used in the present invention are all common commercial products and can be purchased in the market.

[0027] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way.

[0028] Example 1

[0029] Step 1: Add 1 g of carboxylated cellulose nanofibers to 120 mL of water, shake and ultrasonicate to obtain a uniformly mixed carboxylated cellulose nanofiber solution.

[0030] Step 2: placing the carboxylated cellulose nanofiber solution in a polytetrafluoroethylene reactor for hydrothermal reaction at 200° C. for different time periods (2 h to 12 h).

[0031] Step 3: After the hydrothermal reaction in step 2 is completed, the carboxylated cellulose nanofiber solution is cooled to room temperature and then centrifuged.

[0032] 20000rcf, 20min, take the supernatant.

[0033] Step 4: The supernatant was dialyzed using a dialysis bag with a molecular weight cutoff of 500 Da for 24 hours, wherein the dialysis water was replaced every 12 hours to obtain carboxylated cellulose nanofiber carbon quantum dots, which were stored at -4°C in the dark.

[0034] like Figure 1 The relative fluorescence intensity of carboxylated cellulose nanofiber carbon quantum dots synthesized at different times at 430 nm is shown. It can be seen that the fluorescence intensity increases with the increase of synthesis time, and the fluorescence intensity is basically the same when the synthesis time is 8h and 12h.

[0035] Example 2

[0036] Step 1: Add 1 g of carboxylated cellulose nanofibers to 120 mL of water, shake and ultrasonicate to obtain a uniformly mixed carboxylated cellulose nanofiber solution.

[0037] Step 2: placing the carboxylated cellulose nanofiber solution in a polytetrafluoroethylene reactor for hydrothermal reaction at different reaction temperatures (160° C. to 220° C.) for 8 hours.

[0038] Step 3: After the hydrothermal reaction in step 2 is completed, the carboxylated cellulose nanofiber solution is cooled to room temperature and then centrifuged.

[0039] 20000rcf, 20min, take the supernatant.

[0040] Step 4: The supernatant was dialyzed using a dialysis bag with a molecular weight cutoff of 500 Da for 24 hours, wherein the dialysis water was replaced every 12 hours to obtain carboxylated cellulose nanofiber carbon quantum dots, which were stored in a dark environment at 4°C.

[0041] like Figure 2 The relative fluorescence intensity of carboxylated cellulose nanofiber carbon quantum dots synthesized at different temperatures at 430nm is shown. It can be seen that with the increase of synthesis temperature, the fluorescence intensity is also increasing. When the synthesis temperature is 200℃ and 220℃, the fluorescence intensity is basically the same.

[0042] Example 3

[0043] Step 1: Add 1 g of carboxylated cellulose nanofibers to 120 mL of water, shake and ultrasonicate to obtain a uniformly mixed carboxylated cellulose nanofiber solution.

[0044] Step 2: placing the carboxylated cellulose nanofiber solution in a polytetrafluoroethylene reactor for hydrothermal reaction.

[0045] 00℃、8h.

[0046] Step 3: After the hydrothermal reaction in step 2 is completed, the carboxylated cellulose nanofiber solution is cooled to room temperature and then centrifuged.

[0047] 20000rcf, 20min, take the supernatant.

[0048] Step 4: The supernatant was dialyzed using a dialysis bag with a molecular weight cutoff of 500 Da for 24 hours, wherein the dialysis water was replaced every 12 hours to obtain carboxylated cellulose nanofiber carbon quantum dots, which were stored at -4°C in the dark.

[0049] like Figure 3 As shown in Figure 2, the precursor carboxylated cellulose nanofibers exhibited a fiber length of about 2 μm. The obtained carboxylated cellulose nanofiber carbon quantum dots were subjected to transmission electron microscopy scanning. The carbon quantum dot solution was dropped onto a copper mesh and dried before being subjected to transmission electron microscopy scanning. The results are shown in Figure 2. Figure 4 As shown in Figure 2, the prepared carboxylated cellulose nanofiber carbon quantum dots have excellent dispersibility and uniform particle size distribution, mainly concentrated around 2 nm. The obtained carboxylated cellulose nanofiber carbon quantum dots were subjected to UV-visible light absorption test with a scanning wavelength of 200-700 nm. Figure 5 As shown in Figure 2, carboxylated cellulose nanofiber carbon quantum dots exhibit a significant characteristic absorption peak at 255 nm, which originates from the n→π and π→π electron transitions of the C=C bond in the material, confirming the presence of unsaturated conjugated centers in its structure. 500 μL of the diluted carboxylated cellulose nanofiber carbon quantum dot solution was taken into a fluorescence cuvette and then placed in a fluorescence spectrophotometer to perform fluorescence spectrum analysis on the obtained carboxylated cellulose nanofiber carbon quantum dots, as shown in Figure 2. Figure 6 As shown in Figure 2, when the excitation wavelength gradually increases from 310nm to 370nm, the emission peak shows a regular blue shift phenomenon, and the fluorescence intensity reaches a maximum at an excitation wavelength of 340nm. The carboxylated cellulose nanofiber carbon quantum dot solution was freeze-dried and potassium bromide was added to press it into a sheet, and then Fourier transform spectroscopy was performed to reveal the surface chemical composition of the carboxylated cellulose nanofiber carbon quantum dots, as shown in Figure 2. Figure 7 As shown, 3377cm -1 The characteristic peak at 1604 cm corresponds to the stretching vibration of the OH / NH bond. -1 、2931cm -1 and 1412cm -1 The absorption peaks at 1213 cm-1 are attributed to the vibration of COOH and CH bonds, respectively, while the absorption peaks at 1213 cm-1 are attributed to the vibration of COOH and CH bonds, respectively. -1 and 1074cm -1The peak at is derived from the stretching vibration of the C-O-C and C-O bonds. These results fully demonstrate that the surface of the prepared carboxylated cellulose nanofiber carbon quantum dots is rich in various active functional groups such as hydroxyl, amino, and carboxyl groups, and is mainly composed of three elements: carbon, nitrogen, and oxygen.

[0050] In summary, according to the embodiments of the present invention, carboxylated cellulose nanofibers are used as precursors and a hydrothermal synthesis method is used to prepare carbon quantum dots with blue fluorescence, which have photoluminescence properties and stability. Carboxylated cellulose nanofibers are widely available, green, environmentally friendly, and renewable. The method is simple and efficient, does not require additional dopants, is non-toxic throughout the process, and uses renewable raw materials at a lower cost. The prepared carbon quantum dots can be used in many fields such as biomedicine, photoelectric conversion and sensing, ion detection, photoconversion membranes, information encryption and decryption, etc.

[0051] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0052] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for synthesizing fluorescent carbon quantum dots from carboxylated cellulose nanofibers, characterized in that: The following steps are involved: Step 1, adding carboxylated cellulose nanofibers to water, shaking and ultrasonicating, to obtain a carboxylated cellulose nanofiber solution; Step 2, placing the carboxylated cellulose nanofiber solution in a polytetrafluoroethylene reactor for hydrothermal reaction; Step 3, cooling the carboxylated cellulose nanofiber solution after the hydrothermal reaction in step 2 to room temperature and then centrifuging it to collect the supernatant; Step 4: dialyze the supernatant using a dialysis bag to obtain carboxylated cellulose nanofiber carbon quantum dots.

2. The method according to claim 1, wherein The hydrothermal reaction time in step 2 is 2 h to 12 h.

3. The method according to claim 1, wherein The temperature of the hydrothermal reaction in step 2 is 160°C to 220°C.

4. The method according to claim 1, wherein Step 4: Dialysis was performed using a dialysis bag with a molecular weight cut-off of 500 Da.

5. The method according to claim 1, wherein Step 4: The dialysis time is 24 hours, of which 12 hours are used for dialysis against water.

6. The method according to claim 1, wherein Step 3: Centrifuge at 20,000 rcf for 20 min.

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