Aqueous solution electrostatic spinning preparation method and application of microporous carbon fiber membrane

Abstract

The invention relates to an aqueous solution electrostatic spinning preparation method and application of a self-activated lignin-based microporous carbon fiber membrane. An industrial waste pollutant lignin is used as a carbon source, an organic solvent is abandoned, an electrostatic spinning method is used, a sodium hydroxide aqueous solution of the industrial lignin is used as a precursor, spinning, thermal stabilization and carbonization are carried out, and in-situ self-activation is carried out on carbon fibers by using sodium hydroxide in the heat treatment process; and preparing the flexible carbon fiber membrane material of which the surface micropore diameter is close to 0.45 nm (the formaldehyde gas molecule diameter). The problems of environmental pollution and energy consumption possibly generated in a traditional activation method are solved, meanwhile, the problem that a toxic organic solvent is used in electrostatic spinning is solved, and the method has the advantages of being low in raw material cost, large in formaldehyde adsorption capacity, good in adsorption selectivity and stability, capable of achieving one-step spinning forming and simple and environmentally friendly in process. The technology provides a novel solution for green preparation of the flexible microporous carbon fiber membrane, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon fiber preparation, and more specifically, relates to a method for preparing a microporous carbon fiber membrane by electrostatic spinning of an aqueous solution and an application thereof. Background Art

[0002] Formaldehyde is reproductively toxic, genotoxic, and carcinogenic. It primarily enters the human body through inhalation, but can also be absorbed through the skin or ingested. Even extremely low concentrations can pose health risks, making it considered one of the most threatening indoor air pollutants. Unlike other VOCs, formaldehyde's high vapor pressure (3883 mmHg at 25°C) and relatively low boiling point (-19.3°C) prevent it from being ideally removed by conventional adsorbents. Developing efficient formaldehyde removal technologies, pursuing higher adsorption capacities and improved adsorption stability, has become a research hotspot in the fields of environmental protection and public health.

[0003] While traditional adsorption materials such as activated carbon, zeolite, and silica gel possess considerable adsorption capacity, they also face limitations in terms of adsorption capacity, regeneration, and selectivity. In recent years, with the continued advancement of research into green and environmentally friendly materials, carbonaceous adsorption materials developed from biomass resources have become an emerging research direction. Among these, activated carbon fibers prepared from industrial lignin offer advantages such as low cost, reproducibility, and environmental friendliness, demonstrating significant potential for application in a variety of fields, including supercapacitors, adsorption materials, filters, and flexible electronic devices.

[0004] In the process of preparing activated carbon fibers, the activation step is crucial to the specific surface area and pore size distribution of the carbon fibers, which directly determines their application performance. Common activation methods include high-temperature gas activation and alkaline corrosion activation. Although these methods can increase the specific surface area and pore size of carbon fibers, they also bring certain problems such as energy consumption, environmental pollution, and increased production costs. Therefore, the development of a low-cost, green and environmentally friendly activation process has become a research focus in the production of lignin-based carbon fibers.

[0005] As an efficient fiber preparation method, electrospinning technology is capable of producing fiber membranes ranging from nanometer to micrometer scale. Due to its extremely high specific surface area and significant porosity, this membrane material exhibits unique performance advantages in fields such as filtration, sensors, and energy storage. However, traditional electrospinning technology usually relies on flammable, toxic or difficult-to-handle solvents. The use of these solvents not only poses safety risks, but may also bring about environmental pollution and energy consumption problems. Specifically, halogenated solvents (such as chloroform and trifluoroethanol) and toxic solvents (such as dimethylformamide) are the most commonly used solvents in electrospinning, which to a certain extent limits the promotion of this technology in large-scale commercial applications. In order to enhance the market competitiveness of electrospinning technology and improve its sustainable development potential, the development of aqueous solution electrospinning technology has become a more green, environmentally friendly and scalable ideal choice.

[0006] The present invention utilizes industrial waste pollutant lignin as a carbon source, abandons organic solvents, uses electrostatic spinning, uses sodium hydroxide aqueous solution of industrial lignin as a precursor, and undergoes spinning, thermal stabilization and carbonization. During the heat treatment process, sodium hydroxide is used to perform in-situ self-activation on the carbon fiber to prepare a flexible carbon fiber membrane material with a surface micropore diameter of nearly 0.45nm (formaldehyde gas molecule diameter). Due to the introduction of the self-activation process, the production cost is further reduced, and at the same time, the environmental pollution and energy consumption problems that may arise in the traditional activation method are avoided. It has the characteristics of low raw material cost, large formaldehyde adsorption capacity, good adsorption selectivity and stability, one-step spinning molding, green process, environmental protection, and sustainability. This technology provides a new solution for the green preparation of flexible microporous carbon fiber membranes and has broad application prospects. Summary of the Invention

[0007] In response to the problems of existing carbon fiber raw materials being expensive, organic solvents being used in spinning preparation, activation and pore formation being required, and weak adsorption capacity, the present invention provides a method for preparing a self-activated lignin-based flexible microporous carbon fiber membrane through aqueous solution electrospinning. The pore diameter of the membrane is concentrated at around 0.5 nm, which is close to the diameter of formaldehyde gas molecules (0.45 nm). This allows for more effective capture of formaldehyde, while improving adsorption stability and reducing secondary pollution.

[0008] Another object of the present invention is to protect the lignin-based flexible microporous carbon fiber membrane prepared by the method described in the present invention.

[0009] The last object of the present invention is to protect the application of the flexible microporous carbon fiber membrane of the present invention in the fields of supercapacitors, adsorption materials, filters and flexible electronic devices.

[0010] To achieve the above-mentioned purpose, the technical solution of the present invention is as follows:

[0011] (1) Lignin is spun into precursor (lignin) filaments through electrospinning technology.

[0012] In the presence of a spinning aid, lignin is dissolved in a solvent to prepare a spinning solution, which is then electrospun using a CO2 airflow-assisted process to obtain precursor (lignin) raw fibers.

[0013] The lignin is a by-product of kraft pulping and papermaking, namely, industrial-grade kraft lignin, and its biomass source includes at least one of softwood, hardwood, and herbaceous plants (such as pine, poplar, and corn stalks).

[0014] Preparation of the spinning dope: Excluding sodium hydroxide, the mass fraction of the spinning dope solute (industrial lignin and spinning aid) is 5-20%, with the mass ratio of the spinning aid polyethylene oxide (PEO) to lignin being 5-20:95-80. The solvent is deionized water or tap water. Sodium hydroxide is used as an activator, with a concentration in the spinning dope of 0.25-2 mol / L. The spinning dope is prepared using a one-pot method: industrial lignin, PEO, and sodium hydroxide are dissolved in the solvent at 40-70°C with stirring. Once fully dissolved, the spinning dope is cooled to room temperature, allowed to stand, and electrospinning is performed within 0-24 hours.

[0015] Electrospinning: CO2-assisted spinning is performed at a flow rate of 0.25 to 1.5 L / min. The spinning voltage is 12 to 20 kV, and the propulsion pump speed is 0.5 to 5 ml / h. Spinning is performed at room temperature with humidity below 60%. After spinning, the resulting fiber membrane is dried in an oven at 60 to 80°C overnight.

[0016] (2) The lignin precursor spun in step (1) is subjected to heat stabilization and carbonization treatment to obtain lignin-based flexible microporous carbon fibers. The present invention does not require any activation step, and self-activation pore formation is performed during the carbonization process. The obtained carbon fibers have a micropore diameter concentrated in the range of 0.4 to 0.6 nm, a high specific surface area, and a stable micro-nanostructure.

[0017] Thermal stabilization treatment: Place the dried fiber membrane in a tubular furnace or an atmosphere furnace, keep it at 250°C for 0.5 to 2 hours in an air atmosphere, and the heating rate is 2 to 5°C / min.

[0018] Carbonization: After thermal stabilization pretreatment, high-purity nitrogen is introduced into a tubular furnace, and the temperature is raised to 700-1000°C in a nitrogen atmosphere, and kept warm for 0.5-1h at a heating rate of 5-10°C / min; after cooling to room temperature after the insulation is completed, microporous carbon fibers can be obtained.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) Industrial-grade kraft lignin is a by-product of kraft pulping and papermaking. It is a high-value utilization of industrial by-products and solves the problem of high cost of carbon fiber raw materials from the source.

[0021] (2) The solvent for preparing the spinning solution is water, which can be directly used as tap water, completely solving the problem of organic solvent pollution in electrospinning.

[0022] (3) The one-pot method is used to prepare the spinning solution and in-situ activation is performed during the carbonization process, which greatly simplifies the production process and saves energy consumption.

[0023] (4) The use of CO2 airflow to assist electrospinning can effectively suppress the generation of electric sparks during the electrospinning process of aqueous solution, and at the same time solve the problem of spontaneous combustion of carbonized samples when exposed to air, fully ensuring the experimental safety and sample yield.

[0024] (5) The prepared microporous carbon fiber has excellent flexibility and is easy to device. The micropore diameter is concentrated at around 0.5 nm, which is close to the diameter of formaldehyde gas molecules (0.45 nm). It can capture formaldehyde more effectively, while improving adsorption stability and reducing secondary pollution. It is an ideal material for preparing air purification filter elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Scanning electron microscope (SEM) images of the carbon fiber membranes prepared in Examples 1-6;

[0026] Figure 2 Nitrogen adsorption-desorption curve and micropore size distribution of the carbon fiber membrane prepared in Example 6;

[0027] Figure 3 Dynamic formaldehyde performance test of Examples 1-6;

[0028] Among them, the formaldehyde background concentration is 12±1ppm, the air flow rate is 0.6L / min, and the mass of the carbon fiber adsorbent is 30mg;

[0029] Figure 4 Photo of spontaneous combustion of the carbon fiber membrane prepared in Comparative Example 1;

[0030] Figure 5 Microscope photo of the electrospinning product of the spinning solution prepared in Comparative Example 2;

[0031] Figure 6 Photo of flocculation of the spinning solution prepared in Comparative Example 3. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the embodiments.

[0033] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] In the examples, unless otherwise specified, all means used are conventional means in the art.

[0035] As used herein, the terms "comprise," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a listed element is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0036] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Example 1:

[0038] Raw material: Poplar kraft lignin.

[0039] Preparation of the spinning dope: Excluding sodium hydroxide, the mass fraction of the spinning dope solute (industrial lignin and PEO) is 10%, with a PEO:lignin mass ratio of 20:80. The solvent is tap water. The concentration of sodium hydroxide in the spinning dope is 0.25 mol / L. The spinning dope is prepared using a one-pot method: dissolve industrial lignin, PEO, and sodium hydroxide in the solvent at 70°C with stirring. Once fully dissolved, cool the spinning dope to room temperature and immediately proceed with electrospinning.

[0040] Electrospinning: CO2-assisted spinning was performed at a flow rate of 0.25 L / min, a spinning voltage of 20 kV, and a propeller pump speed of 0.5 ml / h. Spinning was performed at room temperature with humidity below 60%. After spinning, the resulting fiber membrane was dried in an oven at 60°C overnight.

[0041] Thermal stabilization treatment: Place the dried fiber membrane in a tubular furnace or atmosphere furnace, keep it at 250°C for 0.5h in an air atmosphere, and the heating rate is 2°C / min.

[0042] Carbonization: After thermal stabilization pretreatment, high-purity nitrogen was introduced into a tubular furnace, and the temperature was raised to 900°C in a nitrogen atmosphere, and the temperature was kept for 0.5 h at a heating rate of 5°C / min. After the temperature was held, the microporous carbon fiber membrane of Example 1 was obtained after cooling to room temperature. The scanning electron microscope image thereof was as shown in FIG. Figure 1 The pore size characteristics and specific surface area of the pores were measured and shown in Table 1.

[0043] Example 2:

[0044] Raw material: pine wood kraft lignin.

[0045] Prepare the spinning dope: Excluding sodium hydroxide, the mass fraction of the spinning dope solute (industrial lignin and PEO) is 5%, with a PEO:lignin mass ratio of 10:90. The solvent is tap water. The concentration of sodium hydroxide in the spinning dope is 1.0 mol / L. A one-pot method is used to prepare the spinning dope: industrial lignin, PEO, and sodium hydroxide are dissolved in the solvent at 70°C with stirring. Once fully dissolved, the spinning dope is cooled to room temperature and allowed to stand for 24 hours before electrospinning.

[0046] Electrospinning: CO2-assisted spinning was performed at a flow rate of 1 L / min, a spinning voltage of 18 kV, and a propulsion pump speed of 2 ml / h. Spinning was performed at room temperature with humidity below 60%. After spinning, the resulting fiber membrane was dried in an oven at 60°C overnight.

[0047] Thermal stabilization treatment: Place the dried fiber membrane in a tubular furnace or atmosphere furnace, keep it at 250°C for 1 hour in an air atmosphere, and the heating rate is 5°C / min.

[0048] Carbonization: After thermal stabilization pretreatment, high-purity nitrogen was introduced into a tube furnace, and the temperature was raised to 900°C in a nitrogen atmosphere, and the temperature was kept for 1 hour at a heating rate of 10°C / min. After the temperature was held, the microporous carbon fiber membrane of Example 2 was obtained after cooling to room temperature. The scanning electron microscope image thereof was as shown in FIG. Figure 1 The pore size characteristics and specific surface area of the pores were measured and shown in Table 1.

[0049] Example 3:

[0050] The difference from Example 2 is that the carbonization temperature is 700°C.

[0051] Example 4:

[0052] The difference from Example 2 is that the carbonization temperature is 1000°C.

[0053] Example 5:

[0054] Raw material: straw kraft lignin.

[0055] Prepare the spinning dope: Excluding sodium hydroxide, the mass fraction of the spinning dope solute (industrial lignin and PEO) is 10%, with a PEO:lignin mass ratio of 10:90. The solvent is tap water. The concentration of sodium hydroxide in the spinning dope is 1.5 mol / L. A one-pot method is used to prepare the spinning dope: industrial lignin, PEO, and sodium hydroxide are dissolved in the solvent at 40°C with stirring. Once fully dissolved, the spinning dope is cooled to room temperature and allowed to stand for 12 hours before electrospinning.

[0056] Electrospinning: CO2-assisted spinning was performed at a flow rate of 0.6 L / min, a spinning voltage of 16 kV, and a propeller pump speed of 3 ml / h. Spinning was performed at room temperature with humidity below 60%. After spinning, the resulting fiber membrane was dried in an oven at 80°C overnight.

[0057] Thermal stabilization treatment: Place the dried fiber membrane in a tubular furnace or atmosphere furnace, keep it at 250°C for 1 hour in an air atmosphere, and the heating rate is 5°C / min.

[0058] Carbonization: After thermal stabilization pretreatment, high-purity nitrogen was introduced into a tube furnace, and the temperature was raised to 900°C in a nitrogen atmosphere, and the temperature was kept for 1 hour at a heating rate of 10°C / min. After the temperature was held, the microporous carbon fiber membrane of Example 5 was obtained after cooling to room temperature. The scanning electron microscope image thereof was as shown in FIG. Figure 1 The pore size characteristics and specific surface area of the pores were measured and shown in Table 1.

[0059] Example 6:

[0060] Raw material: pine wood kraft lignin.

[0061] Preparation of the spinning dope: Excluding sodium hydroxide, the mass fraction of the spinning dope solute (industrial lignin and PEO) is 20%, with a PEO:lignin mass ratio of 5:95. The solvent is deionized water. The concentration of sodium hydroxide in the spinning dope is 2.0 mol / L. The spinning dope is prepared using a one-pot method: dissolve industrial lignin, PEO, and sodium hydroxide in the solvent at 40°C with stirring. Once fully dissolved, cool the spinning dope to room temperature and let it stand for 24 hours before electrospinning.

[0062] Electrospinning: CO2-assisted spinning was performed at a flow rate of 1.5 L / min, a spinning voltage of 12 kV, and a propeller pump speed of 5 ml / h. Spinning was performed at room temperature with humidity below 60%. After spinning, the resulting fiber membrane was dried in an oven at 80°C overnight.

[0063] Thermal stabilization treatment: Place the dried fiber membrane in a tubular furnace or atmosphere furnace, keep it at 250°C for 1 hour in an air atmosphere, and the heating rate is 5°C / min.

[0064] Carbonization: After thermal stabilization pretreatment, high-purity nitrogen was introduced into a tube furnace, and the temperature was raised to 900°C in a nitrogen atmosphere, and the temperature was kept for 1 hour at a heating rate of 10°C / min. After the temperature was held, the microporous carbon fiber membrane of Example 6 was obtained after cooling to room temperature. The scanning electron microscope image thereof was as shown in FIG. Figure 1 The nitrogen adsorption and desorption test was performed on it, and its pore size characteristics and specific surface area were measured as shown in Table 1. Its nitrogen adsorption and desorption curve and micropore size distribution are shown in Figure 2 .

[0065] Formaldehyde performance test: The dynamic formaldehyde performance test of Examples 1-6 is as follows Figure 3 The test used air as the carrier gas, the formaldehyde background concentration in the air was controlled at 12±1 ppm, the air flow rate was 0.6 L / min, and the carbon fiber adsorbent mass was 30 mg. The test showed that Examples 2, 3, and 6 had better formaldehyde penetration resistance. Based on this, it can be concluded that micropores larger than 0.45 nm and a larger micropore area play an important role in the process of resisting formaldehyde penetration.

[0066] Comparative Example 1:

[0067] The difference from Example 2 is that no CO2 airflow is used to assist the electrospinning process, and the airflow rate is 0 L / min. After the sample is carbonized, it will spontaneously combust when exposed to air. Figure 4 shown.

[0068] Comparative Example 2:

[0069] The difference from Example 2 is that when the spinning solution was prepared, the concentration of sodium hydroxide in the spinning solution was 0.2 mol / L. During electrospinning, droplets were ejected instead of fibers, and lignin precursors could not be successfully prepared. The optical microscope comparison photos are shown in Figure 2. Figure 5 shown.

[0070] Comparative Example 3:

[0071] The difference from Example 2 is that when the spinning solution was prepared, the concentration of sodium hydroxide in the spinning solution was 2.5 mol / L. During the spinning solution preparation process, flocculation occurred and the spinning could not be performed. The comparison photos of the spinning solution are shown in the figure below. Figure 6 shown.

[0072] According to the comparative example, CO2 airflow-assisted spinning is a necessary process for the successful carbonization of fibers, which is related to the thermal stability of sodium hydroxide and sodium carbonate. After the sodium hydroxide in the solution is converted into sodium carbonate using CO2 airflow-assisted spinning, the residual elemental sodium after carbonization can be effectively reduced, thereby reducing the occurrence of spontaneous combustion. At the same time, sodium hydroxide is used as an activator, and the concentration in the spinning solution is 0.25-2 mol / L. If it is too low or too high, normal spinning cannot be achieved. Finally, flexible microporous carbon fiber membranes can be successfully prepared at carbonization temperatures of 700-1000°C, but if a higher specific surface area is to be obtained, the carbonization temperature is preferably 900°C.

[0073] Table 1 shows the pore size characteristics and specific surface area of Examples 1-6

[0074]

[0075]

[0076] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a self-activated lignin-based microporous carbon fiber membrane by aqueous solution electrospinning and its application, characterized in that: The lignin is a byproduct of kraft pulping and papermaking - industrial-grade kraft lignin, which is used as the raw material for carbon fiber preparation. The process includes the following steps: (1) spinning lignin into precursor (lignin) raw fibers by aqueous solution electrospinning technology; wherein the spinning solution is prepared by a one-pot method, and industrial lignin, a spinning aid, and an activator are co-dissolved in a solvent; (2) The lignin precursor spun in step (1) is subjected to heat stabilization and carbonization treatment to obtain flexible microporous carbon fibers; wherein the micropore diameter of the carbon fibers is concentrated in the range of 0.4 to 0.6 nm, and the fibers have a high specific surface area and a gas formaldehyde molecule capture capability.

2. The preparation method according to claim 1, wherein: In step (1), the solvent of the spinning solution is deionized water or tap water; the activator is sodium hydroxide, and the concentration in the spinning solution is 0.25-2 mol / L; the spinning aid is polyethylene oxide (PEO), and the mass ratio of PEO to lignin is 5-20:95-80; excluding the activator, the mass fraction of the solute (industrial lignin and spinning aid) in the spinning solution is 5-20%.

3. The preparation method according to claim 1, wherein: In step (1), CO2 airflow is used to assist spinning, and the airflow rate is 0.25 to 1.5 L / min.

4. A lignin-based flexible microporous carbon fiber membrane, characterized in that: The method is prepared by any one of claims 1 to 3.

5. The lignin-based flexible microporous carbon fiber membrane according to claim 4, characterized in that: The micropore area accounts for 56% to 81% of the total specific surface area, and the micropore diameter is concentrated in the range of 0.4 to 0.6 nm. It has application potential in supercapacitors, adsorption materials, filters and flexible electronic devices.

6. Use of the preparation method according to any one of claims 1 to 4 or the lignin-based flexible microporous carbon fiber membrane according to claim 5.

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