Nanocellulose hydrothermal carbon spheres, and preparation method and application thereof

Abstract

This invention discloses a hydrothermal carbon sphere made from nanocellulose, its preparation method, and its applications. The invention uses cellulose nanocrystals as raw material and glacial acetic acid solution as solvent, obtaining monodisperse micron-sized carbon spheres after high-temperature hydrothermal treatment. The main feature of this process is the use of inexpensive biomass raw material cellulose nanocrystals to generate hydrothermal carbon spheres with uniform particle size, high sphere formation rate, and good dispersibility through a one-step hydrothermal process. The resulting carbon spheres have a particle size range of 1–2 μm, which can be adjusted by changing experimental parameters such as substrate concentration, hydrothermal temperature, and hydrothermal time. This method exhibits excellent reproducibility and is environmentally friendly. The resulting carbon spheres have stable chemical properties and can be widely used in medicine, optics, and electromagnetics.

Description

Technical Field

[0001] This invention relates to the field of micro / nano carbon material preparation, and particularly to a nanocellulose hydrothermal carbon sphere, its preparation method, and its application. Background Technology

[0002] In recent years, carbon spheres have attracted widespread attention due to their regular morphology, high specific surface area, high mechanical strength, stable physicochemical properties, and good heat and acid / alkali resistance. Methods for preparing hydrothermal carbon spheres include hydrothermal methods, chemical vapor deposition (CVD), template methods, and arc discharge methods. Among these, CVD produces products with a high degree of graphitization, but it requires strict temperature control and has a low yield. Template methods offer controllable morphology and uniform particle size, but the process is cumbersome. Hydrothermal methods, due to their simplicity, low cost, low energy consumption, and environmental friendliness, have become the main method for preparing carbon spheres in recent years. During the hydrothermal reaction, the morphology and size of hydrothermal carbon microspheres can be controlled by adjusting parameters such as substrate concentration, reaction time, and temperature. Carbon spheres prepared by the hydrothermal method have a lower degree of carbonization and rich active groups on their surface, making them widely applicable in the preparation of functional composite materials.

[0003] Currently, many easily hydrolyzable small biomass molecules, such as monosaccharides (e.g., glucose, fructose, and xylose) and disaccharides (e.g., maltose and sucrose), are used as raw materials for preparing carbon spheres, and hydrothermal carbon spheres have been successfully prepared via a hydrothermal method. CN113648968A uses monosaccharides and disaccharides as carbon sources to prepare oxygen-rich ultrafine hydrothermal carbon spheres using a hydrothermal method. Compared to glucose, cellulose is a cheaper and more readily available raw material. Although there are reports on the carbonization of macromolecular biomass such as cellulose, starch, and chitosan into spheres, they require more stringent hydrothermal conditions because they must first undergo hydrolysis and molecular chain breakage to generate monosaccharides and oligosaccharides, and then further nucleate and grow into carbon spheres. CN115215322A uses a one-step high-temperature hydrothermal method to carbonize sodium carboxymethyl cellulose and polydopamine to prepare cellulose carbon spheres with good photothermal properties. CN115285968A mixes carboxymethyl cellulose and o-phenylenediamine to prepare cellulose nanocarbon spheres via a hydrothermal method. Because carboxymethyl cellulose has a large molecular weight and long molecular chains, the carbon spheres prepared by both methods have diameters of 10-30 μm. Excessively large diameters reduce the specific surface area of ​​the carbon spheres. Cellulose nanocrystals (CNC), also known as cellulose nanowhiskers (CNW), are obtained from renewable cellulose raw materials by acid hydrolysis to eliminate amorphous regions; they are short rod-shaped nanocellulose. Currently, there are very few reports on the preparation of carbon spheres using CNC. In a suitable solvent system, by controlling the solubility, we partially dissolved CNC into flexible monolayers, which then hydrolyzed to form nuclei. The remaining undissolved CNC grew tightly around the nuclei through hydrogen bonding to form carbon spheres. Due to the small size and aspect ratio of CNC, the carbon spheres prepared using this method have a dense structure and small particle size, resulting in higher activity and surface area in catalysis and adsorption applications. In addition, CNC raw materials are widely available. Currently, research has successfully produced CNC using biomass resources such as agricultural waste such as peach and palm fruit residue, sugarcane bagasse, wheat straw, and pea shells. This not only realizes the resource utilization of agricultural waste, but also avoids the secondary pollution to the environment caused by incineration.

[0004] CNC (carbon nanospheres) possess abundant hydroxyl groups and are highly modifiable. By adding other materials or altering reaction conditions during preparation, the chemical composition and physical properties of hydrothermal carbon microspheres can be further modified to meet diverse application requirements. The preparation of carbon microspheres using cellulose nanocrystals allows for the coating or composite formation of other functional materials (such as metals and polymers), endowing them with new properties and applications. This makes carbon microspheres promising for applications in energy storage, catalysts, sensors, and medicine.

[0005] Therefore, this invention is the first to utilize CNC as a carbon source, and by controlling parameters such as substrate concentration, dissolution medium concentration, hydrothermal temperature, and time, the optimal conditions for CNC carbonization into spheres were explored. Then, utilizing the abundant hydroxyl groups on CNC, it was thiolized and modified, and after hydrothermal carbonization, it was used as a carrier to composite with silver nanoparticles, thus preparing a carbon sphere / silver nanoparticle composite material with significant antibacterial effects. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing monodisperse hydrothermal carbon spheres using nanocellulose as a carbon source. This objective is achieved through the following technical solution.

[0007] Specifically, the steps include the following:

[0008] (1) Under stirring conditions, cellulose nanocrystals were dispersed in deionized water to obtain a dispersion;

[0009] (2) Add glacial acetic acid solution dropwise to the dispersion and mix well to obtain a mixed solution;

[0010] (3) Pour the mixed solution from step (2) into the reaction vessel for hydrothermal reaction;

[0011] (4) After the hydrothermal reaction is completed, the monodisperse hydrothermal carbon balls are obtained by centrifugation, washing and drying.

[0012] Further, in step (1), the cellulose nanocrystals have a fiber length of 500-600 nm and a diameter of 20-30 nm.

[0013] Further, in step (1), the cellulose nanocrystals are unmodified cellulose nanocrystals or thiol-modified cellulose nanocrystals.

[0014] Furthermore, in step (1), the concentration of cellulose nanocrystals in the dispersion is 2 wt%, or the concentration of thiol-modified cellulose nanocrystals in the dispersion is 0.5 wt%.

[0015] Furthermore, in step (2), the concentration of glacial acetic acid in the mixed solution is 1M.

[0016] Furthermore, in step (3), the reactor is heated by programmed temperature rise at a rate of 5 to 10 °C / min.

[0017] Furthermore, in step (3), the temperature of the hydrothermal reaction is 175-235°C, and the holding time of the hydrothermal reaction is 12-24h.

[0018] Further, in step (4), the centrifugation rate is 3500-4500 rpm and the centrifugation time is 5-20 min.

[0019] Furthermore, in step (4), the water used for washing is deionized water, and the washing step is repeated 3 to 4 times.

[0020] Furthermore, in step (4), the drying method is freeze drying, the drying temperature is -40 to -60°C, and the drying time is 18 to 24 hours.

[0021] This invention provides a nanocellulose hydrothermal carbon ball prepared by any of the above preparation methods.

[0022] The present invention also provides the application of the above-mentioned nanocellulose hydrothermal carbon spheres in the preparation of photothermal conversion materials and drugs.

[0023] Preferably, the drug is an antitumor drug or an antibacterial drug, and the nanocellulose hydrothermal carbon spheres are used as the loading material.

[0024] The hydrothermal carbon spheres prepared by the above method have small particle size, uniform distribution, high sphericity, and good dispersibility, making them excellent catalyst supports and electrode materials with wide applications in medicine, optics, and electromagnetics. Furthermore, the preparation method is simple, and the raw materials are inexpensive and readily available, providing a new approach for the high-value utilization of agricultural and forestry waste and the green production of hydrothermal carbon spheres.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) The cellulose nanocrystals used in this invention are abundant, inexpensive, readily available and pollution-free raw materials. After hydrothermal treatment, they are easily hydrolyzed into small molecules with a high carbonization rate.

[0027] (2) The preparation method of the present invention is simple, and the product can be obtained through a one-step reaction. The production energy consumption and cost are low, which is conducive to large-scale industrial production.

[0028] (3) The carbon spheres prepared by this invention have small particle size, uniform distribution and good dispersibility, which is beneficial for application in fields such as medicine, optics and electromagnetics.

[0029] (4) The raw materials and preparation methods used in this invention are environmentally friendly. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope (SEM) image of the hydrothermal carbon spheres prepared in Example 1 of this invention.

[0031] Figure 2 This is the Fourier Transform Infrared (FTIR) spectrum of the hydrothermal carbon spheres prepared in Example 1 of this invention.

[0032] Figure 3 These are scanning electron microscope (SEM) images of the hydrothermal carbon spheres prepared in Comparative Example 2 of this invention.

[0033] Figure 4 This is a scanning electron microscope (SEM) image of the hydrothermal carbon spheres prepared in Comparative Example 3 of this invention.

[0034] Figure 5 This is a scanning electron microscope (SEM) image of the hydrothermal carbon spheres prepared in Comparative Example 4 of this invention.

[0035] Figure 6 This is a scanning electron microscope (SEM) image of the hydrothermal carbon spheres prepared in Comparative Example 5 of this invention.

[0036] Figure 7 This is a scanning electron microscope (SEM) image of the hydrothermal carbon spheres prepared in Comparative Example 6 of this invention.

[0037] Figure 8 This is a scanning electron microscope (SEM) image of the hydrothermal carbon spheres prepared in Comparative Example 7 of this invention.

[0038] Figure 9 This is a scanning electron microscope (SEM) image of the hydrothermal carbon spheres prepared in Example 8 of this invention.

[0039] Figure 10 Image (a) is a scanning electron microscope (SEM) image of the hydrothermal carbon ball composite material Ag@CS prepared in Example 8 of the present invention, with a magnification of 3000x. Figure 10 Image (b) is a scanning electron microscope (SEM) image of the hydrothermal carbon ball composite material Ag@CS prepared in Example 8 of the present invention, with a magnification of 15,000. Figure 10 (c) is the transmission electron microscope and elemental distribution diagram of the hydrothermal carbon ball composite material Ag@CS prepared in Example 8 of the present invention.

[0040] Figure 11 This is an infrared (FTIR) image of the hydrothermal carbon ball composite material Ag@CS prepared in Example 8 of the present invention.

[0041] Figure 12 This is an XRD image of the hydrothermal carbon ball composite material Ag@CS prepared in Example 8 of the present invention.

[0042] Figure 13 This is an image of the antibacterial hydrothermal carbon ball composite material prepared in Example 8 of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the embodiments and protection scope of the present invention are not limited thereto.

[0044] Example 1

[0045] (1) Disperse 3g of unmodified cellulose nanocrystals in 15mL of aqueous solution and stir to obtain a uniform CNC dispersion; add 0.857mL of glacial acetic acid to the suspension (the concentration of CNC in the solvent system is 2wt% and the concentration of glacial acetic acid is 1M).

[0046] (2) The mixed solution from (1) was transferred into a reactor for hydrothermal reaction. The hydrothermal reaction temperature was 235℃, the holding time was 24h, and the heating rate was 5℃ / min.

[0047] (3) After the reaction was completed, the mixture was transferred to a 50 mL centrifuge tube, centrifuged at 4000 rpm for 5 min, the supernatant was discarded, and deionized water was added for further centrifugation and washing. This process was repeated 3 times. Finally, hydrothermal carbon spheres were obtained after freeze-drying at -60℃ for 24 h. SEM and infrared spectroscopy analysis showed that the carbon spheres under these conditions had a high sphericity, uniform morphology, and retained abundant oxygen-containing functional groups.

[0048] Comparative Example 2

[0049] (1) Disperse 1.5g of unmodified cellulose nanocrystals in 15mL of aqueous solution and stir to obtain a uniform CNC dispersion; add 0.857mL of glacial acetic acid to the suspension (the concentration of CNC in the solvent system is 1wt% and the concentration of glacial acetic acid is 1M).

[0050] (2) The mixed solution from (1) was transferred into a reactor for hydrothermal reaction. The hydrothermal reaction temperature was 235℃, the holding time was 24h, and the heating rate was 5℃ / min.

[0051] (3) After the reaction was complete, the mixture was transferred to a 50 mL centrifuge tube, centrifuged at 4000 rpm for 5 min, the supernatant was discarded, and deionized water was added for further centrifugation and washing. This process was repeated three times. Finally, hydrothermal carbon spheres were obtained after freeze-drying at -60℃ for 24 h. SEM analysis showed that reducing the substrate concentration resulted in non-uniform carbon sphere particle size, and the carbon block structure did not completely disappear.

[0052] Comparative Example 3

[0053] (1) Disperse 4.5g of unmodified cellulose nanocrystals in 15mL of aqueous solution and stir to obtain a uniform CNC dispersion; add 0.857mL of glacial acetic acid to the suspension (the concentration of CNC in the solvent system is 3wt% and the concentration of glacial acetic acid is 1M).

[0054] (2) The mixed solution from (1) was transferred into a reactor for hydrothermal reaction. The hydrothermal reaction temperature was 235℃, the holding time was 24h, and the heating rate was 5℃ / min.

[0055] (3) After the reaction was complete, the solution was transferred to a 50 mL centrifuge tube, centrifuged at 4000 rpm for 5 min, the supernatant was discarded, and deionized water was added for further centrifugation and washing. This process was repeated three times. Finally, hydrothermal carbon spheres were obtained after freeze-drying at -60℃ for 24 h. SEM analysis showed that increasing the substrate concentration reduced the diameter of the carbon spheres, but the dispersion was uneven. This is because when the substrate concentration is too high, the distance between the carbon nuclei decreases, causing them to interfere with each other during the formation of carbon spheres and making them prone to adhesion.

[0056] Comparative Example 4

[0057] (1) Disperse 3g of unmodified cellulose nanocrystals in 15mL of aqueous solution and stir to obtain a uniform CNC dispersion; add 0.428mL of glacial acetic acid to the suspension (the concentration of CNC in the solvent system is 2wt% and the concentration of glacial acetic acid is 0.5M).

[0058] (2) The mixed solution from (1) was transferred into a reactor for hydrothermal reaction. The hydrothermal reaction temperature was 235℃, the holding time was 24h, and the heating rate was 5℃ / min.

[0059] (3) After the reaction was completed, the mixture was transferred to a 50 mL centrifuge tube, centrifuged at 4000 rpm for 5 min, the supernatant was discarded, and deionized water was added for further centrifugation and washing. This process was repeated 3 times. Finally, hydrothermal carbon spheres were obtained after freeze-drying at -60℃ for 24 h. SEM analysis showed that reducing the concentration of glacial acetic acid did not completely hydrolyze the microcrystalline cellulose macromolecules, resulting in a low sphere formation rate of the prepared carbon spheres.

[0060] Comparative Example 5

[0061] (1) Disperse 3g of unmodified cellulose nanocrystals in 15mL of aqueous solution and stir to obtain a uniform CNC dispersion; add 1.714mL of glacial acetic acid to the suspension (the concentration of CNC in the solvent system is 2wt% and the concentration of glacial acetic acid is 2M).

[0062] (2) The mixed solution from (1) was transferred into a reactor for hydrothermal reaction. The hydrothermal reaction temperature was 235℃, the holding time was 24h, and the heating rate was 5℃ / min.

[0063] (3) After the reaction was complete, the mixture was transferred to a 50 mL centrifuge tube, centrifuged at 4000 rpm for 5 min, the supernatant was discarded, and deionized water was added for further centrifugation and washing. This process was repeated three times. Finally, hydrothermal carbon spheres were obtained after freeze-drying at -60℃ for 24 h. SEM analysis showed that increasing the concentration of glacial acetic acid promoted the hydrolysis of CNC and improved the sphere formation rate, but the resulting carbon spheres had uneven particle size.

[0064] Comparative Example 6

[0065] (1) Disperse 1.50g of thiol-functionalized CNC in 15mL of aqueous solution and stir to obtain a uniform CNC dispersion; add 0.857mL of glacial acetic acid to the suspension (the concentration of thiol-functionalized CNC in the solvent system is 1.0wt% and the concentration of glacial acetic acid is 1M).

[0066] (2) The mixed solution from (1) was transferred into a reactor for hydrothermal reaction. The hydrothermal reaction temperature was 235℃, the holding time was 24h, and the heating rate was 5℃ / min.

[0067] (3) After the reaction was complete, the mixture was transferred to a 50 mL centrifuge tube, centrifuged at 4000 rpm for 5 min, the supernatant was discarded, and deionized water was added for further centrifugation and washing. This process was repeated three times. Finally, hydrothermal carbon spheres were obtained after freeze-drying at -60℃ for 24 h. SEM analysis showed that a high substrate concentration resulted in a low sphere formation rate.

[0068] Comparative Example 7

[0069] (1) Disperse 0.30g of thiol-functionalized CNC in 15mL of aqueous solution and stir to obtain a uniform CNC dispersion; add 0.857mL of glacial acetic acid to the suspension (the concentration of thiol-functionalized CNC in the solvent system is 0.2wt% and the concentration of glacial acetic acid is 1M).

[0070] (2) The mixed solution from (1) was transferred into a reactor for hydrothermal reaction. The hydrothermal reaction temperature was 235℃, the holding time was 24h, and the heating rate was 5℃ / min.

[0071] (3) After the reaction was completed, the mixture was transferred to a 50 mL centrifuge tube, centrifuged at 4000 rpm for 5 min, the supernatant was discarded, and deionized water was added for further centrifugation and washing. This process was repeated 3 times. Finally, hydrothermal carbon spheres were obtained after freeze-drying at -60℃ for 24 h. SEM analysis showed that reducing the substrate concentration increased the sphere formation rate, but the resulting carbon spheres had uneven particle size.

[0072] Example 8

[0073] 0.75 g of thiol-functionalized CNC was dispersed in 15 mL of aqueous solution and stirred to obtain a homogeneous dispersion. 0.857 mL of glacial acetic acid was added to the suspension (the concentration of thiol-functionalized CNC in the solvent system was 0.5 wt%, and the concentration of glacial acetic acid was 1 M). The mixed solution was transferred to a hydrothermal reactor and reacted at 235 °C for 24 h. After the reaction was completed, the carbon spheres were obtained by centrifugation and washing.

[0074] Furthermore, the above product was dispersed in 15 ml of deionized water, and 1 ml of prepared silver ammonia solution and 0.9 g of sodium citrate were added dropwise. The resulting mixture was then placed in a microwave reactor and heated by microwave radiation (800 W) at 65 °C for 30 min. After the reaction, the system was allowed to cool naturally, washed several times with deionized water, and then freeze-dried at -60 °C for 24 h to obtain the composite material Ag@CS. The carbon spheres with a large specific surface area and abundant active sites serve as a good carrier for the silver nanoparticles. This composite material exhibits good antibacterial effects and biosafety, and can be applied in the medical field.

[0075] The microstructure and elemental distribution of the prepared cellulose carbon sphere composite sample Ag@CS were analyzed using high-resolution scanning electron microscopy and TEM-mapping. Figure 10 As shown, nanocellulose carbon spheres serve as an excellent carrier for nanosilver, fixing and loading it onto the surface of the carbon spheres.

[0076] The functional groups and chemical structure of Ag@CS were analyzed using FT-IR spectroscopy, such as... Figure 11 As shown, Ag@CS retains a large number of oxygen-containing groups, which play an important role in the immobilization and in-situ reduction of silver nanoparticles.

[0077] The material composition of Ag@CS was analyzed using XRD diffraction patterns, such as... Figure 12 As shown, the diffraction peaks at 38.1°, 44.2°, 64.5°, and 77.3° are attributed to the (111), (200), (220), and (311) crystal planes of AgNPs, respectively, indicating that the particles loaded on the surface of the carbon spheres are silver nanoparticles.

[0078] The antibacterial activity of the Ag@CS composite material was evaluated using the colony-forming unit (CFU) counting method. Ag@CS powder and bacterial suspension were co-cultured at 37°C. At predetermined time points, the bacterial suspension was diluted 10-1. 5 Take 100 μL of the diluted solution and transfer it to an agar plate. Incubate at 37°C for 24 hours and observe the colony units formed. Figure 13 As shown, compared with the control group, the number of colonies with Ag@CS added was significantly reduced, indicating that the carbon spheres loaded with silver nanoparticles have good antibacterial activity.

[0079] The above embodiments are merely preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. Any changes, substitutions, modifications, etc., made by those skilled in the art without departing from the spirit and essence of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing hydrothermal carbon nanospheres of cellulose nanoparticles, characterized in that, Specifically, the following steps are included: (1) Under stirring conditions, cellulose nanocrystals are dispersed in deionized water to obtain a dispersion; the concentration of cellulose nanocrystals in the dispersion is 2 wt%, or the concentration of thiol-modified cellulose nanocrystals in the dispersion is 0.5 wt%. (2) Add glacial acetic acid solution dropwise to the dispersion, mix well to obtain a mixed solution, wherein the concentration of glacial acetic acid in the mixed solution is 1 M; (3) Pour the mixed solution from step (2) into the reactor for hydrothermal reaction; the temperature of the hydrothermal reaction is 235°C and the holding time of the hydrothermal reaction is 24 h; (4) After the hydrothermal reaction is completed, the monodisperse hydrothermal carbon balls are obtained by centrifugation, washing and drying.

2. The production method according to claim 1, characterized by, In step (1), the cellulose nanocrystals have a fiber length of 500~600 nm and a diameter of 20~30 nm.

3. The preparation method according to claim 1, characterized in that, In step (1), the cellulose nanocrystals are unmodified cellulose nanocrystals or thiol-modified cellulose nanocrystals.

4. The method of claim 1, wherein, In step (3), the reactor is heated by programmed temperature rise at a rate of 5~10 ℃ / min.

5. The preparation method according to claim 1, characterized in that, In step (4), the centrifugation rate is 3500~4500 rpm and the centrifugation time is 5~20 min.

6. The method of claim 1, wherein, In step (4), the water used for washing is deionized water, and the washing step is repeated 3 to 4 times; in step (4), the drying method is freeze drying, the drying temperature is -40 to -60 ℃, and the drying time is 18 to 24 h.

7. A nanocellulose hydrothermal carbon ball prepared by the preparation method according to any one of claims 1-6.

8. The application of the nanocellulose hydrothermal carbon spheres according to claim 7 in the preparation of photothermal conversion materials and drugs.

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