Preparation method of biomass-derived magnetic porous carbon nanoparticles

Abstract

The invention discloses a preparation method of biomass-derived magnetic porous carbon nanoparticles, which comprises the following steps: by taking sodium alginate, polyvinyl alcohol, nickel acetate and the like as raw materials, preparing the magnetic porous carbon nanoparticles by adopting a wet solution spraying technology in combination with drying, low-temperature pre-oxidation treatment and a high-temperature carbonization technology. The magnetic porous carbon nanoparticles prepared by the method are uniform in size, large in specific surface area, high in metal loading capacity and strong in magnetism, and have great application prospects in the field of electromagnetic wave absorption. In addition, the wet solution spraying technology is simple to operate, low in cost, high in efficiency and easy for large-scale production.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of magnetic composite materials, porous materials, and biomass-derived carbon material preparation technology, and specifically relates to a method for preparing biomass-derived magnetic porous carbon nanoparticles. Background Technology

[0002] With the progress of the times and the rapid development of science and technology, while technology provides convenience for people's production and life, it also inevitably brings problems such as electromagnetic radiation and pollution. Electromagnetic radiation is a special form of matter that, although it cannot be directly observed or touched, truly exists in our living space. Electromagnetic radiation is a key factor affecting the performance of electronic devices and the stability of information transmission, especially in the fields of high-speed communication and precision electronics. It not only interferes with equipment operation and system stability but also causes electromagnetic pollution, threatening the ecological environment and potentially leading to limited plant growth and reduced biodiversity. More seriously, long-term exposure to high-intensity electromagnetic fields can harm human health and increase the risk of cancer. Therefore, the development of high-performance electromagnetic absorbing materials is of great significance for solving the problem of electromagnetic radiation.

[0003] In recent years, carbon materials have shown great promise for applications due to their high dielectric loss, low density, and excellent chemical stability. Zhang et al. (Zhang K, Gao X, Zhang Q, et al. Preparation and microwave absorption properties of asphalt carbon coated reduced graphene oxide / magnetic CoFe2O4 hollow particles modified multi-wall carbon nanotube composites[J]. Journal of Alloys and Compounds, 2017, 723: 912-921.) prepared carbon-coated reduced graphene oxide / magnetic CoFe2O4 hollow particle modified multi-wall carbon nanotube composites, which exhibited significant microwave absorption performance. The composite material demonstrated remarkable microwave absorption performance due to its unique nanostructure, additional void space, high surface area, and synergistic effect. At 11.6 GHz, with a thickness of 1.6 mm, the minimum reflection loss reached -46.8 dB. Although these materials exhibit excellent microwave absorption performance, most traditional carbon-based microwave absorbing materials rely on fossil resources for precursors, and their preparation process is limited by complex techniques. Biomass, as the most abundant carbon source in nature, possesses advantages such as diverse microstructures, low cost, and environmental friendliness, making it an important source for the preparation of carbon-based functional materials. Wu et al. (Wu Z, Tian K, Huang T, et al. Hierarchically porous carbons derived from biomasses with excellent microwave absorption performance[J].ACS Applied Materials & Interfaces, 2018, 10(13): 11108-11115.) successfully prepared various biomass-based carbon materials with two-level porous structures through a one-step carbonization process, utilizing the unique structure inherent in spinach. The minimum reflection loss value reached -62.2 dB, and the effective absorption bandwidth was 7.3 GHz. However, the electromagnetic wave loss mechanism of purely biomass-derived carbon materials is singular, often exhibiting impedance mismatch problems, leading to excessive reflection rather than absorption. A powerful solution is to combine biomass-derived carbon materials with magnetic materials to prepare magnetic carbon materials with multiple loss mechanisms.

[0004] Magnetic porous carbon nanoparticles, with their high specific surface area, rapid enrichment under magnetic fields, and effective magnetic loss capability, have been widely used in fields such as microwave absorption and adsorption separation. However, existing methods for preparing carbon nanoparticles still have some significant shortcomings in practical applications: such as large product size, small specific surface area, low magnetic metal content, poor controllability, complex preparation processes, and high costs. These limitations, to some extent, restrict the research and development of magnetic carbon nanoparticles and their large-scale commercial application. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing biomass-derived magnetic porous carbon nanoparticles, using green and biodegradable biomass materials as the carbon source. Furthermore, the method employs a wet solution spraying technique to prepare the magnetic porous nanoparticles, which is simple, controllable, low-cost, highly efficient, and easily scalable for mass production.

[0006] The present invention provides a method for preparing biomass-derived magnetic porous carbon nanoparticles, comprising the following steps:

[0007] (1) Preparation of stock solution

[0008] Sodium alginate (SA) aqueous solution and polyvinyl alcohol (PVA) aqueous solution are mixed in a certain proportion to obtain the stock solution; wherein the mass fraction of sodium alginate aqueous solution is 1-6 wt.%, the mass concentration of polyvinyl alcohol aqueous solution is 3-10 wt.%, and the mass ratio of SA to PVA is 1-5:10-18 (e.g. 1:5, 2:9, 3:14).

[0009] (2) Preparation of coagulation bath

[0010] The coagulation bath is a 0.05–0.2 mol / L metal salt solution, and the solvent for the metal salt solution is a mixture of water and ethanol.

[0011] (3) Preparation of magnetic porous carbon particles

[0012] The raw solution was sprayed into a coagulation bath using a wet solution spraying method to prepare primary particles; then the primary particles were separated from the coagulation bath by centrifugation and subsequently dried.

[0013] (4) The dried nascent particles are subjected to low-temperature pre-oxidation in a muffle furnace; then, the low-temperature pre-oxidized particles are subjected to high-temperature carbonization in a tube furnace under nitrogen or argon protective atmosphere to obtain magnetic porous nano-carbon particles.

[0014] Further, in step (1), the method for preparing the SA aqueous solution is as follows: under stirring conditions, sodium alginate (SA) is dissolved in deionized water to obtain an SA aqueous solution with a mass fraction of 1-6 wt.%; wherein, the stirring time is 4-12 h.

[0015] Further, in step (1), the PVA aqueous solution is prepared by dissolving PVA in deionized water under stirring conditions of water bath heating to obtain a PVA aqueous solution with a mass fraction of 3-10 wt.%; wherein the water bath heating temperature is 85-95℃ and the stirring time is 3-5h.

[0016] Furthermore, in step (2), the metal salt in the coagulation bath is one or a mixture of several of the following: ferric nitrate, ferric sulfate, ferric chloride, ferrous sulfate, ferrous chloride, ferrous carbonate, cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt chloride, nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 1 to 4:1.

[0017] Furthermore, in step (3), the needle used in the wet solution spraying technology is a dual-seat coaxial needle, with the core layer receiving the original solution and the skin layer receiving air. The inner diameter of the needle's inner shaft (core layer) is 0.2-0.4 mm and the outer diameter is 0.5-0.7 mm, while the inner diameter of the outer shaft (skin layer) is 1.5-2.0 mm and the outer diameter is 1.65-2.15 mm.

[0018] Furthermore, in step (3), the conditions for the wet solution spraying method are: the spray air pressure is 7-9 kPa, the receiving distance is 6-10 cm, the solution propulsion rate is 1-3 mL / min, and the rotor speed in the coagulation bath is set to 400-700 RPM.

[0019] Furthermore, in step (3), the nascent particles need to be soaked in a coagulation bath for 24 to 72 hours.

[0020] Furthermore, in step (3), the centrifugation is performed using a centrifuge, and the centrifuge speed is set to 8000-10000 RPM.

[0021] Furthermore, in step (3), the drying process can be carried out in a freezing, room temperature, or oven environment. The nascent particles can be first frozen in a low-temperature freezer and then freeze-dried in a freeze dryer; alternatively, the drying process can be carried out in a room temperature or oven environment. Specifically, when the drying process is carried out in a freezing environment, the nascent particles are first frozen and shaped in a low-temperature freezer at -50 to -15°C for 12 to 24 hours, and then dried in a freeze dryer at -60 to -40°C for 24 to 72 hours. When the drying process is carried out in an oven or at room temperature, the nascent particles can be directly dried in an oven or at room temperature. The oven drying temperature is 60 to 90°C, and the drying time is 12 to 20 hours. Drying at room temperature requires 5 to 7 days.

[0022] Furthermore, in step (3), the heating rate of the pre-oxidation treatment is 2-5℃ / min, the sintering temperature is 180-220℃, and the holding time is 1-4h. The heating rate of the high-temperature carbonization is 2-6℃ / min, the carbonization temperature is 800-1000℃, and the holding time is 2-8h.

[0023] The biomass-derived magnetic porous carbon particles prepared by the above method.

[0024] Compared with existing technologies for preparing magnetic porous carbon materials, this invention has the following advantages and outstanding effects:

[0025] (1) This method uses sodium alginate, a biomass material, as a carbon source. Sodium alginate is abundant and renewable, and has the characteristics of low cost and environmental friendliness. The preparation process utilizes the strong chelating ability of sodium alginate to metal ions, and then a metal salt coagulation bath with various metal compounds such as nickel acetate and ferric nitrate can be designed to prepare porous magnetic carbon nanoparticles.

[0026] (2) The method of this invention is an innovative wet solution jet preparation method based on the wet spinning method. This method has the characteristics of easy setup, simple operation, and controllable process, and is suitable for preparing magnetic metal / nanocarbon particles.

[0027] (3) The magnetic porous carbon nanoparticles prepared by this method have uniform size and large specific surface area (80-300m²). 2 g -1 The prepared Ni / C magnetic nanoparticles exhibit high metal loading (45-60 wt.%), strong magnetism (saturation magnetization 8-15 emu / g, coercivity 25-35 Oe), and excellent microwave absorption properties, showing great promise for applications in the field of electromagnetic wave absorption. The prepared Ni / C magnetic nanoparticles possess a spherical morphology and a specific surface area reaching 237.2 m². 2 g-1. Ni / C magnetic nanoparticles contain 55.81% Ni. The magnetic nanoparticles exhibit excellent absorption characteristics at a thickness of 3.5 mm, with an optimal reflection loss of -39.717 dB. Attached Figure Description

[0028] Figure 1 SEM image of Ni / C carbon nanoparticles prepared in Example 1;

[0029] Figure 2 TEM image of Ni / C carbon nanoparticles prepared in Example 1;

[0030] Figure 3 EDS image of Ni / C carbon nanoparticles prepared in Example 1;

[0031] Figure 4The specific surface area of ​​the Ni / C carbon nanoparticles prepared in Example 1;

[0032] Figure 5 The microwave absorption performance of Ni / C carbon nanoparticles prepared in Example 1 is shown in the figure.

[0033] Figure 6 The electrical conductivity of the Ni / C carbon nanoparticles prepared in Example 1;

[0034] Figure 7 The magnetic hysteresis curve of the Ni / C carbon nanoparticles prepared in Example 1. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, but the claims of the invention patent are not limited to the specific embodiments.

[0036] Example 1

[0037] The preparation method of Ni / C carbon nanoparticles includes the following steps:

[0038] (1) SA was dissolved in deionized water under stirring for 8 hours to obtain an aqueous solution with a mass fraction of 4 wt.%; PVA was dissolved in deionized water under water bath heating at 90°C and stirring for 4 hours to obtain an aqueous solution with a mass fraction of 8 wt.%; then the two solutions were mixed in proportion to obtain the preparation stock solution. The mass ratio of SA to PVA was 3:14.

[0039] (2) Add nickel acetate to the solvent and ultrasonically disperse for 4 hours to prepare a 0.1 mol / L nickel acetate solution. The solvent is a mixture of water and ethanol with a volume ratio of 3:1.

[0040] (3) The raw solution was sprayed into a coagulation bath using a wet solution spraying method to prepare nascent particles, which were then soaked in the coagulation bath for 48 hours. The preparation conditions were as follows: a coaxial needle was used, with liquid entering the core layer and air entering the skin layer; the inner diameter of the needle shaft (core layer) was 0.3 mm and the outer diameter was 0.6 mm; the inner diameter of the outer shaft (skin layer) was 2.0 mm and the outer diameter was 2.15 mm. The spray pressure was 8 kPa, the receiving distance was 8 cm, the solution propulsion rate was 2 mL / min, and the rotor speed in the coagulation bath was set to 500 RPM. Subsequently, the nascent particles were separated from the coagulation bath by centrifugation at 9000 RPM. They were then placed in a low-temperature freezer at -30℃ for 24 hours for freeze-drying, and then placed in a freeze dryer at -48℃ for 48 hours.

[0041] (4) The dried nascent particles were subjected to low-temperature pre-oxidation treatment in an air-atmosphere muffle furnace: the heating rate was 2℃ / min, the sintering temperature was 200℃, and the holding time was 2h. Finally, the pre-oxidized nascent particles were subjected to carbonization treatment in a tube furnace under a flowing nitrogen atmosphere: the heating rate was 5℃ / min, the carbonization temperature was 800℃, and the holding time was 2h, to obtain Ni / C nano-carbon particles. Their structural morphology is shown in […]. Figure 1 and Figure 2 SEM and TEM images revealed that the particles exhibited a spherical morphology with Ni particles attached to the surface, and the particle diameter ranged from 300 to 800 nm. Elemental spectrum of Ni / C carbon nanoparticles (…) Figure 3 This confirmed that C, Ni, and O elements were uniformly distributed, with Ni accounting for 55.81%. The specific surface area of ​​the sample was analyzed using BET testing, such as... Figure 4 As shown, the isotherms all exhibit the composite characteristics of Type IV curves, accompanied by obvious hysteresis loops, indicating the formation of mesoporous structures in the fiber matrix. Through systematic characterization, the specific surface area of ​​the Ni / C carbon nanoparticles was measured to be 237.2 m². 2 g-1. Figure 5 The microwave absorption performance of Ni / C nanoparticles was demonstrated, with an optimal reflection loss of -39.717 dB at a matching thickness of 3.5 mm and a frequency of 6.88 GHz. Figure 6 and Figure 7 The conductivity and magnetic properties of the sample are shown respectively. Its conductivity is 84.72 S / m, its saturation magnetization (Ms) is 8.86 emu / g, and its coercivity (Hc) is 31.11 Oe, which confirms that the sample has certain conductivity and magnetism.

[0042] Example 2

[0043] The preparation method of Fe / C carbon nanoparticles includes the following steps:

[0044] (1) SA was dissolved in deionized water under stirring for 4 hours to obtain an aqueous solution with a mass fraction of 2 wt.%; PVA was dissolved in deionized water under water bath heating at 85°C and stirring for 5 hours to obtain an aqueous solution with a mass fraction of 3 wt.%; then the two solutions were mixed in proportion to obtain the preparation stock solution. The mass ratio of SA to PVA was 2:9.

[0045] (2) Add ferric chloride to the solvent and ultrasonically disperse for 3 hours to prepare a 0.05 mol / L ferric chloride solution. The solvent is a mixture of water and ethanol, with a volume ratio of water to ethanol of 4:1.

[0046] (3) The raw solution was sprayed into a coagulation bath using a wet solution spraying method to prepare nascent particles, which were then soaked in the coagulation bath for 24 hours. The preparation conditions were as follows: a double-seat coaxial needle was used, with liquid entering through the core layer and air entering through the skin layer. The inner diameter of the needle shaft (core layer) was 0.3 mm and the outer diameter was 0.6 mm, while the inner diameter of the outer shaft (skin layer) was 2.0 mm and the outer diameter was 2.15 mm. The spray pressure was 7 kPa, the receiving distance was 8 cm, the solution propulsion rate was 3 mL / min, and the rotor speed in the coagulation bath was set to 400 RPM. Subsequently, the nascent particles were separated from the coagulation bath by centrifugation, with the centrifuge set to 8000 RPM. The nascent particles were then directly dried in an oven at 80℃ for 16 hours.

[0047] (4) The dried nascent particles were subjected to low-temperature pre-oxidation treatment in an air-atmosphere muffle furnace: the heating rate was 3℃ / min, the sintering temperature was 180℃, and the holding time was 2h. Finally, the pre-oxidized nascent particles were subjected to carbonization treatment in a tube furnace under a flowing nitrogen atmosphere: the heating rate was 5℃ / min, the carbonization temperature was 900℃, and the holding time was 3h, finally obtaining Fe / C nano-carbon particles.

[0048] Example 3

[0049] The preparation method of Co / C carbon nanoparticles includes the following steps:

[0050] (1) SA was dissolved in deionized water under stirring for 12 h to obtain an aqueous solution with a mass fraction of 3 wt.%; PVA was dissolved in deionized water under water bath heating at 95 °C and stirring for 5 h to obtain an aqueous solution with a mass fraction of 5 wt.%; then the two solutions were mixed in proportion to obtain the preparation stock solution. The mass ratio of SA to PVA was 1:5.

[0051] (2) Cobalt nitrate was added to a solvent and ultrasonically dispersed for 4 hours to prepare a 0.2 mol / L cobalt nitrate solution. The solvent was a mixture of water and ethanol, with a volume ratio of water to ethanol of 4:1.

[0052] (3) The raw solution was sprayed into a coagulation bath using a wet solution spraying method to prepare nascent particles, which were then soaked in the coagulation bath for 24 hours. The preparation conditions were as follows: a double-seat coaxial needle was used, with liquid entering through the core layer and air entering through the skin layer. The inner diameter of the needle shaft (core layer) was 0.3 mm and the outer diameter was 0.6 mm, while the inner diameter of the outer shaft (skin layer) was 2.0 mm and the outer diameter was 2.15 mm. The spray pressure was 9 kPa, the receiving distance was 8 cm, the solution propulsion rate was 1 mL / min, and the rotor speed in the coagulation bath was set to 600 RPM. Subsequently, the nascent particles were separated from the coagulation bath by centrifugation at 10000 RPM. They were then placed in a low-temperature freezer at -40℃ for 20 hours for freeze-drying, and then placed in a freeze dryer at -40℃ for 20 hours.

[0053] (4) The dried nascent particles were subjected to low-temperature pre-oxidation treatment in an air-atmosphere muffle furnace: the heating rate was 4℃ / min, the sintering temperature was 220℃, and the holding time was 2h. Finally, the pre-oxidized nascent particles were subjected to carbonization treatment in a tube furnace under a flowing nitrogen atmosphere: the heating rate was 5℃ / min, the carbonization temperature was 1000℃, and the holding time was 3h, finally obtaining Co / C nanocarbon particles.

Claims

1. A method for preparing biomass-derived magnetic porous carbon nanoparticles, characterized in that: Includes the following steps: (1) Preparation of stock solution A sodium alginate aqueous solution and a polyvinyl alcohol aqueous solution are mixed to obtain the preparation stock solution; wherein the mass fraction of the sodium alginate aqueous solution is 1-6 wt.%, the mass concentration of the polyvinyl alcohol aqueous solution is 3-10 wt.%, and the mass ratio of sodium alginate to polyvinyl alcohol is 1-5:10-18. (2) Preparation of coagulation bath The coagulation bath is a 0.05–0.2 mol / L metal salt solution, and the solvent for the metal salt solution is a mixture of water and ethanol. (3) Preparation of magnetic porous carbon particles The stock solution was sprayed into a coagulation bath using a wet solution spraying method to prepare primary particles; then, the primary particles were separated from the coagulation bath by centrifugation and subsequently dried. (4) The dried nascent particles are subjected to low-temperature pre-oxidation in a muffle furnace; then, the low-temperature pre-oxidized particles are subjected to high-temperature carbonization in a tube furnace under nitrogen or argon protective atmosphere to obtain magnetic carbon nanoparticles.

2. The preparation method according to claim 1, characterized in that: In step (1), the sodium alginate aqueous solution is prepared by dissolving sodium alginate in deionized water under stirring conditions to obtain a sodium alginate aqueous solution with a mass fraction of 1-6 wt.%. The method for preparing the polyvinyl alcohol aqueous solution is as follows: under stirring conditions of water bath heating, polyvinyl alcohol is dissolved in deionized water to obtain a polyvinyl alcohol aqueous solution with a mass fraction of 3-10 wt.%; wherein, the water bath heating temperature is 85-95℃.

3. The preparation method according to claim 1, characterized in that: In step (2), the metal salt in the coagulation bath is one or a mixture of several of the following: ferric nitrate, ferric sulfate, ferric chloride, ferrous sulfate, ferrous chloride, ferrous carbonate, cobalt nitrate, cobalt acetate, cobalt sulfate, cobalt chloride, nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the volume ratio of water to ethanol in the mixed solvent of water and ethanol is 1 to 4:

1.

4. The preparation method according to claim 1, characterized in that: In step (3), the needle used in the wet solution spraying technology is a double-seat coaxial needle. The inner diameter of the inner shaft of the needle is 0.2-0.4 mm and the outer diameter is 0.5-0.7 mm. The inner diameter of the outer shaft is 1.5-2.0 mm and the outer diameter is 1.65-2.15 mm. The inner shaft of the needle serves as the core layer and is used to inject the original solution, while the outer shaft of the needle serves as the outer layer and is used to inject air.

5. The preparation method according to claim 1, characterized in that: In step (3), the conditions for the wet solution spraying method are: the spray pressure is 7-9 kPa, the receiving distance is 6-10 cm, the solution propulsion rate is 1-3 mL / min, and the rotor speed in the coagulation bath is set to 400-700 RPM.

6. The preparation method according to claim 1, characterized in that: In step (3), the nascent particles are soaked in a coagulation bath for 24 to 72 hours.

7. The preparation method according to claim 1, characterized in that: In step (3), the centrifugation is performed using a centrifuge with a rotation speed of 8000 to 10000 RPM. The drying process is carried out under freezing, room temperature, or oven conditions.

8. The preparation method according to claim 7, characterized in that: When the drying process is carried out in a freezing environment, the specific steps are as follows: first, the nascent particles are frozen in a low-temperature freezer at -50 to -15°C for 12 to 24 hours, and then dried in a freeze dryer at -60 to -40°C for 24 to 72 hours. When the drying process is carried out in an oven environment, the oven drying temperature is 60-90℃ and the time is 12-20h; When the drying process is carried out at room temperature, the drying time at room temperature is 5 to 7 days.

9. The preparation method according to claim 1, characterized in that: In step (4), the heating rate of the low-temperature pre-oxidation treatment is 2-5℃ / min, the pre-oxidation temperature is 180-220℃, and the holding time is 1-4h; the heating rate of the high-temperature carbonization is 2-6℃ / min, the carbonization temperature is 800-1000℃, and the holding time is 2-8h.

10. Biomass-derived magnetic porous carbon particles prepared by the method according to any one of claims 1-9.

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