CN114590794A - Compressible carbon nanofiber aerogel, and preparation method and application thereof - Google Patents

Compressible carbon nanofiber aerogel, and preparation method and application thereof Download PDF

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CN114590794A
CN114590794A CN202210222740.4A CN202210222740A CN114590794A CN 114590794 A CN114590794 A CN 114590794A CN 202210222740 A CN202210222740 A CN 202210222740A CN 114590794 A CN114590794 A CN 114590794A
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aerogel
carbon nanofiber
bacterial cellulose
nanofiber aerogel
corundum crucible
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俞书宏
李超
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University of Science and Technology of China USTC
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/0091—Preparation of aerogels, e.g. xerogels
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
    • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
    • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
    • D01F9/16—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from products of vegetable origin or derivatives thereof, e.g. from cellulose acetate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13—Energy storage using capacitors

Abstract

The invention provides a preparation method of a compressible carbon nanofiber aerogel, which comprises the following steps: A) soaking the bacterial cellulose to obtain soaked hydrogel; B) placing the impregnated hydrogel on a metal plate at the temperature of between 20 ℃ below zero and 80 ℃ below zero for oriented freezing, and then performing freeze drying to obtain the bacterial cellulose aerogel; C) and pyrolyzing the bacterial cellulose aerogel to obtain the carbon nanofiber aerogel. The application also provides the compressible carbon nanofiber aerogel prepared by the method and application thereof. The preparation process of the carbon nanofiber aerogel does not need inert gas protection, the cost is reduced, the yield of the obtained carbon nanofiber aerogel is high, the macro and micro appearances are kept intact, and the carbon nanofiber aerogel has excellent compression recovery performance and temperature stability.

Description

Compressible carbon nanofiber aerogel, and preparation method and application thereof
Technical Field
The invention relates to the technical field of nano materials, in particular to a compressible carbon nanofiber aerogel electrode material, and a preparation method and application thereof.
Background
With the growing population, industrial development and increased water pollution, water shortage has become a serious problem worldwide and a challenge for social and economic development. Most of water resources on the earth exist in the form of seawater or brackish water, so that the desalination of the seawater and the brackish water becomes an important way for solving the problem of water resource shortage. The development of economic and effective desalination technology has important significance, and people have developed desalination technologies such as distillation, reverse osmosis and electrodialysis for many years. The Capacitive Deionization (CDI) technology is a low-cost and high-efficiency desalination technology developed in recent years, and the basic principle is to remove salt ions in water by applying an electrostatic field to force the ions to move to an electrode with opposite charges, so that the salt ions are adsorbed on the surface of the electrode.
In order to improve the efficiency of capacitive deionization, the electrode material should have the characteristics of high specific surface area, high porosity, high conductivity, stable property and the like. Besides the perfect conformity of the nano carbon aerogel to these requirements, the nano carbon material has other excellent characteristics, such as low apparent density, good mechanical properties, stable chemical properties and environmental compatibility. Therefore, the nano carbon aerogel is an ideal capacitive deionization electrode material.
Among the carbon aerogels commonly used at present, thermosetting polymer-derived carbon aerogels generally use toxic precursors (such as resorcinol and formaldehyde) as raw materials, and the carbon aerogels assembled by graphene and carbon nanotubes require complicated equipment and technology (such as a CVD method), and meanwhile, the fatigue resistance of the compression recovery of the carbon aerogels is poor, and the limitations indicate that the preparation method of the carbon aerogels has a large exploration space. The bacterial cellulose is used as a biomass material, has the advantages of low price, wide source, environmental friendliness, large-scale preparation and the like, is converted into the carbon nanofiber aerogel with high mechanical strength after pyrolysis, and is expected to become an ideal raw material for manufacturing the compressible carbon nanofiber aerogel electrode material.
Disclosure of Invention
The invention solves the technical problem of providing a preparation method of the compressible carbon nanofiber aerogel, and the carbon nanofiber aerogel prepared by the method can be compressed and recovered and has fatigue resistance; furthermore, the carbon nanofiber aerogel can be used as an electrode material, and the capacitance performance of the electrode material is improved.
In view of the above, the present application provides a method for preparing a compressible carbon nanofiber aerogel, comprising the following steps:
A) soaking the bacterial cellulose to obtain soaked hydrogel;
B) placing the impregnated hydrogel on a metal plate at the temperature of-20 to-80 ℃ for oriented freezing, and then performing freeze drying to obtain bacterial cellulose aerogel;
C) and pyrolyzing the bacterial cellulose aerogel to obtain the carbon nanofiber aerogel.
Preferably, the soaking is firstly carried out in water and then is carried out in an inorganic ammonium salt aqueous solution; the inorganic ammonium salt aqueous solution is an aqueous solution of ammonium dihydrogen phosphate, ammonium chloride or ammonium sulfate, the concentration of the inorganic ammonium salt aqueous solution is 0.1-1000 mmol/L, the temperature is 50-100 ℃, and the soaking time is 3-7 days.
Preferably, the concentration of the aqueous solution of ammonium dihydrogen phosphate is 10-100 mmol/L, the concentration of the aqueous solution of ammonium sulfate is 10-50 mmol/L, and the concentration of the aqueous solution of ammonium chloride is 10-50 mmol/L.
Preferably, the lower end of the metal plate is immersed in liquid nitrogen, so that the upper surface of the metal plate is kept at-20 to-80 ℃; the orientation freezing time is 10-30 min, and the freeze drying time is 3-5 days.
Preferably, the pyrolysis is carried out in a muffle furnace, and the pyrolysis atmosphere is an air atmosphere; the heating rate of pyrolysis is 5-20 ℃/min, the temperature of pyrolysis is 500-1500 ℃, and the time is 1-3 h.
Preferably, the pyrolysis process specifically comprises:
placing the bacterial cellulose aerogel in a first corundum crucible, and then placing the first corundum crucible in a second corundum crucible; and the pores between the first corundum crucible and the second corundum crucible are completely filled with activated carbon particles, and the top of the first corundum crucible and the top of the second corundum crucible are respectively covered with a corundum plate which is well sealed.
Preferably, the bacterial cellulose is (10-50) × (8-20) mm3The carbon nanofiber aerogel is (8-45) × (5-10) mm in sheet shape3The sheet-like shape of (1).
The application also provides the compressible carbon nanofiber aerogel prepared by the preparation method, wherein the carbon nanofibers in the carbon nanofiber aerogel comprise 40-99 wt% of carbon, 0.1-10 wt% of hydrogen, 0.5-50 wt% of oxygen, 0.1-10 wt% of nitrogen and 0.1-10 wt% of phosphorus or sulfur.
The application also provides an electrode material which is obtained by infiltrating the electrolyte into the compressible carbon nanofiber aerogel, wherein the compressible carbon nanofiber aerogel is the compressible carbon nanofiber aerogel prepared by the preparation method of the scheme or the compressible carbon nanofiber aerogel.
Preferably, the electrolyte is selected from a sodium chloride solution, a potassium sulfate solution, a sulfuric acid solution or a potassium hydroxide solution.
The application provides a preparation method of a compressible carbon nanofiber aerogel, which comprises the steps of taking bacterial cellulose as a raw material, and performing soaking, oriented freezing, freeze drying and pyrolysis on the bacterial cellulose to obtain the carbon nanofiber aerogel; in the preparation process, the bacterial cellulose aerogel is pyrolyzed by using a closed system, and the intermediate product is fully utilized to be fixed into carbon, so that the yield of the carbon aerogel is effectively improved; the pyrolysis process does not need inert atmosphere protection, reduces the cost, and the carbon nanofiber aerogel microstructure of finally preparing keeps good, has excellent mechanical properties, can compress and recover and has fatigue resistance, can be used as the compressible electrode of electric capacity deionization device or ultracapacitor system. According to the invention, in the process of preparing the compressible carbon nanofiber aerogel, heteroatoms such as nitrogen, phosphorus, sulfur and the like can be doped, so that the capacitance performance of the electrode material is improved, and different requirements can be met.
Drawings
Fig. 1 is a digital photograph of a carbon nanofiber aerogel prepared from pure bacterial cellulose in example 1 of the present invention, wherein the left side is the bacterial cellulose aerogel, and the right side is the carbon nanofiber aerogel;
fig. 2 is a scanning electron micrograph of the carbon nanofiber aerogel obtained in example 1 of the present invention;
fig. 3 is a compressive stress-strain curve of the carbon nanofiber aerogel obtained in example 1 of the present invention at 30%, 60%, and 90% compression, and the inner drawing is an enlarged view;
fig. 4 is a graph of stress change and shape change of the carbon nanofiber aerogel obtained in example 1 of the present invention after 90% compression for a plurality of cycles;
fig. 5 is a capacitance deionization performance curve of the carbon nanofiber aerogel electrode obtained in example 1 of the present invention;
fig. 6 is a digital photograph of a carbon nanofiber aerogel prepared by doping an aerogel with ammonium sulfate in example 2 of the present invention, where the left side is the ammonium sulfate doped aerogel and the right side is the carbon nanofiber aerogel;
fig. 7 is a scanning electron micrograph of the carbon nanofiber aerogel obtained in example 2 of the present invention;
fig. 8 is a compressive stress-strain curve of the carbon nanofiber aerogel obtained in example 2 of the present invention at 30%, 60%, and 90% compression, and the inner drawing is an enlarged view;
fig. 9 is a capacitance deionization performance curve of the carbon nanofiber aerogel electrode obtained in example 2 of the present invention;
fig. 10 is a digital photograph of a carbon nanofiber aerogel prepared by doping ammonium dihydrogen phosphate with an aerogel in example 3 of the present invention, wherein the left side is the ammonium dihydrogen phosphate-doped aerogel, and the right side is the carbon nanofiber aerogel;
fig. 11 is a scanning electron micrograph of the carbon nanofiber aerogel obtained in example 3 of the present invention;
fig. 12 is a compressive stress-strain curve of the carbon nanofiber aerogel obtained in example 3 of the present invention at 30%, 60%, and 90% compression, and the inner drawing is an enlarged view;
fig. 13 is a capacitance deionization performance curve of the carbon nanofiber aerogel obtained in example 3 of the present invention.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
In view of the poor fatigue resistance of the carbon nanofiber aerogel during compression recovery and the performance requirements of electrode materials in the prior art, the application provides the preparation method of the carbon nanofiber aerogel, the carbon nanofiber aerogel is prepared by using bacterial cellulose as a precursor, and the raw materials are cheap and easy to obtain; the pyrolysis process does not need the protection of inert atmosphere, thus reducing the cost and being easy for large-scale preparation; the bacterial cellulose aerogel is pyrolyzed by using a closed system, and the intermediate product is fully utilized to be fixed into carbon, so that the yield of the carbon aerogel is effectively improved; the prepared carbon nanofiber aerogel has a good microstructure, excellent mechanical properties, compression recovery and fatigue resistance, and can be used as a compressible electrode of a capacitor deionization or super capacitor; furthermore, in the preparation process, nitrogen, phosphorus, sulfur and other heteroatoms can be doped in the carbon nanofiber aerogel, so that the capacitance performance of the electrode material is improved, and different requirements can be met. Specifically, the embodiment of the invention discloses a preparation method of a compressible carbon nanofiber aerogel, which comprises the following steps:
A) soaking the bacterial cellulose to obtain a soaked hydrogel;
B) placing the impregnated hydrogel on a metal plate at the temperature of between 20 ℃ below zero and 80 ℃ below zero for oriented freezing, and then performing freeze drying to obtain the bacterial cellulose aerogel;
C) and pyrolyzing the bacterial cellulose aerogel to obtain the carbon nanofiber aerogel.
In the preparation process of the carbon nanofiber aerogel, firstly, soaking and washing bacterial cellulose in deionized water to obtain bacterial cellulose hydrogel with impurities removed; then soaking in deionized water for storage, or additionally soaking in inorganic ammonium salt water solution; in the application, the soaking is firstly carried out in water and then in an inorganic ammonium salt water solution, so that the yield of the carbon nanofiber aerogel is improved. The inorganic ammonium salt aqueous solution is ammonium dihydrogen phosphate, ammonium chloride or ammonium sulfate aqueous solution, the concentration of the inorganic ammonium salt aqueous solution is 0.1-1000 mmol/L, the temperature is 50-100 ℃, and the soaking time is 3-7 days; in a specific embodiment, the concentration of the aqueous solution of ammonium dihydrogen phosphate is 10-100 mmol/L, the concentration of the aqueous solution of ammonium sulfate is 10-50 mmol/L, and the concentration of the aqueous solution of ammonium chloride is 10-50 mmol/L. According to the invention, stirring is carried out simultaneously during the soaking.
Placing the impregnated hydrogel on a metal plate at the temperature of-20 to-80 ℃ for oriented freezing, and then performing freeze drying to obtain the bacterial cellulose aerogel; the oriented freezing is to enter the lower end of the metal plate into liquid nitrogen, keep the upper surface of the metal plate at-20 to-80 ℃, freeze for 10 to 30min, and freeze-dry for 3 to 5 days. The orientation freezing enables the ice crystals to grow orderly into an array shape or a plane shape, so that the obtained bacterial cellulose aerogel has a hierarchical network structure and is beneficial to enhancing the mechanical performance.
According to the invention, then, pyrolyzing the bacterial cellulose aerogel to obtain carbon nanofiber aerogel; the pyrolysis is carried out in a muffle furnace, an air atmosphere is used, the temperature rise rate of the pyrolysis is 5-20 ℃/min, the temperature is 600-1200 ℃, the time is 1-3 days, in the specific embodiment, the temperature rise rate of the pyrolysis is 8-15 ℃/min, and the temperature is 800-1000 ℃. In the application, the bacterial cellulose aerogel is firstly placed in a corundum crucible and then is placed in a muffle furnace for pyrolysis, specifically, the bacterial cellulose aerogel is placed in a first corundum crucible, and then the first corundum crucible is placed in a second corundum crucible; and the pores between the first corundum crucible and the second corundum crucible are completely filled with activated carbon particles, and the top of the first corundum crucible and the top of the second corundum crucible are respectively covered with a corundum plate which is well sealed. Under the condition, the intermediate product can be fully utilized to be fixed into carbon by pyrolysis, the yield of the carbon aerogel is effectively improved, and the carbon aerogel has good structure retentivity.
In the preparation process of the carbon nanofiber aerogel, the bacterial cellulose is (10-50) × (8-20) mm3The carbon nanofiber aerogel is (8-45) × (5-10) mm in sheet shape3The sheet-like shape of (1).
The application also provides the carbon nanofiber aerogel prepared by the method, which consists of carbon nanofibers, wherein the carbon nanofibers comprise 40-99 wt% of carbon, 0.1-10 wt% of hydrogen, 0.5-50 wt% of oxygen, 0.1-10 wt% of nitrogen and 0.1-10 wt% of phosphorus or sulfur; the diameter of the fiber is 10-100 nm, cross-linking nodes are arranged among the fibers and fixed, and the surface of the fiber is of an amorphous carbon structure.
The application still provides the electrode material that above-mentioned carbon nanofiber aerogel formed, it is got by carbon nanofiber aerogel infiltration electrolyte, carbon nanofiber aerogel can select to use plasma cleaning machine to wash, the time is 1 ~ 5min, then soak in electrolyte, it is different according to the application demand, can select like multiple electrolyte such as sodium chloride solution, potassium sulfate solution, sulfuric acid solution or potassium hydroxide solution, place vacuum oven in when soaking for the first time, get rid of the gas in the carbon nanofiber aerogel, later soak time is 6h ~ 24h, then directly assemble to corresponding device, electrode material can compress the recovery.
Experimental results show that the density of the carbon nanofiber aerogel electrode material is 1-40 mg-cm-3The conductivity is 0.01 to 20 S.cm-1The specific surface area is 200-1000 m2·g-1(ii) a The carbon nanofiber aerogel electrode material can completely recover the original shape after being compressed by 90 percent and can bear more than ten thousand compression cycles.
For further understanding of the present invention, the following examples are given to illustrate the preparation method of carbon nanofiber aerogel provided by the present invention, and the scope of the present invention is not limited by the following examples.
The reagents used in the following examples are all commercially available, wherein the bacterial cellulose is purchased from Hainan food GmbH.
Example 1
Taking 320X 240X 8mm for commercial purchase3Soaking large bacterial cellulose sheet in deionized water for 7 days, replacing deionized water every day, cutting the deacidified large bacterial cellulose sheet into 40 × 15 × 8mm pieces3The small pieces are ready for use;
placing the metal plate in a foam box filled with liquid nitrogen, and contacting the lower end of the metal plate with the liquid nitrogen for five minutes to completely cool the metal plate; then flatly spreading a small piece of bacterial cellulose, and attaching the small piece of bacterial cellulose to the upper surface of a metal plate; continuously adding liquid nitrogen during the period to ensure the low temperature of the metal plate, and controlling the temperature of the metal plate to be near minus 40 ℃; transferring the frozen bacterial cellulose small pieces to a freeze dryer for drying for 3 days, wherein the temperature of a cold trap is-53 ℃, and the pressure is 40 Pa; obtaining white bacterial cellulose aerogel after freeze drying is finished, as shown in figure 1;
placing the bacterial cellulose aerogel obtained by freeze drying in a corundum crucible, completely filling the corundum crucible, and covering a corundum plate with good sealing performance above the corundum crucible; placing the corundum crucible in a corundum crucible with a larger volume, wherein gaps around and above the corundum crucible are completely filled with activated carbon particles, and a corundum plate with good sealing is covered above the outer-layer corundum crucible;
placing the corundum crucible in a muffle furnace at 5 deg.C for min-1Heating at 800 ℃ for 2h, and then naturally cooling to room temperature to obtain black carbon nanofiber aerogel, as shown in fig. 1. The yield of the carbon nanofiber aerogel was 20.5%.
The carbon nanofiber aerogel obtained in example 1 was observed by using a field emission scanning electron microscope, and the result is shown in fig. 2. As can be seen from FIG. 2, the carbon nanofiber aerogel obtained in example 1 is composed of carbon nanofibers with diameters of 15 to 100nm, and many cross-linked structures are formed between the fibers.
Mechanical testing is performed on the carbon nanofiber aerogel obtained in example 1, and fig. 3 shows the compressive stress-strain curves of 30%, 60% and 90% of the compression of the carbon nanofiber aerogel provided in this embodiment, so that the aerogel can be recovered. Fig. 4 is a compressive stress-strain curve of the carbon nanofiber aerogel provided in example 3, which can withstand 10 ten thousand compression cycles with only 8% change in shape and 87% of the maximum stress remaining, at 90% of the strain compression cycle, indicating that it has good compression recovery performance.
Soaking the carbon nanofiber aerogel in deionized water, placing the carbon nanofiber aerogel in a vacuum oven to remove air, standing and soaking for 12 hours to be used as an electrode in a capacitive deionization deviceThe material was tested for its capacitive deionization performance and, as shown in FIG. 5, the desalting efficiency was 9.0mg g-1。
Example 2
Taking 320X 240X 10mm for commercial purchase3Soaking large bacterial cellulose sheet in deionized water for 7 days, replacing deionized water every day, cutting the deacidified large bacterial cellulose sheet into 50 × 15 × 10mm pieces3A tablet of (2); preparing 10mmol/L ammonium sulfate aqueous solution, soaking the bacterial cellulose tablet in the aqueous solution for 5 days, and stirring the solution every day during the soaking;
placing the metal plate in a foam box filled with liquid nitrogen, and contacting the lower end of the metal plate with the liquid nitrogen for five minutes to completely cool the metal plate; then flatly spreading a small piece of bacterial cellulose, and attaching the small piece of bacterial cellulose to the upper surface of a metal plate; continuously adding liquid nitrogen during the period to ensure the low temperature of the metal plate, and controlling the temperature of the metal plate to be near minus 40 ℃; transferring the frozen bacterial cellulose chips into a freeze dryer for drying for 3 days, wherein the temperature of a cold trap is-53 ℃, and the pressure is 40 Pa; obtaining a white bacterial cellulose aerogel after freeze drying is finished, as shown in fig. 6;
placing the bacterial cellulose aerogel obtained by freeze drying in a corundum crucible, completely filling the corundum crucible, and covering a corundum plate with good sealing performance above the corundum crucible; placing the corundum crucible in a corundum crucible with a larger volume, wherein gaps around and above the corundum crucible are completely filled with activated carbon particles, and a corundum plate with good sealing is covered above the outer-layer corundum crucible;
placing the corundum crucible in a muffle furnace at 5 deg.C for min-1Heating at 900 ℃ for 2h, and then naturally cooling to room temperature to obtain black carbon nanofiber aerogel, as shown in fig. 6. The yield of the carbon nanofiber aerogel was 32.0%.
The carbon nanofiber aerogel obtained in example 2 was observed by using a field emission scanning electron microscope, and the result is shown in fig. 7. As can be seen from FIG. 7, the carbon nanofiber aerogel obtained in example 2 is composed of carbon nanofibers with diameters of 30 to 150nm, and many cross-linked structures are formed between the fibers.
Mechanical testing is performed on the carbon nanofiber aerogel obtained in example 2, and fig. 8 shows the compressive stress-strain curves of 30%, 60% and 90% of the compression of the carbon nanofiber aerogel provided in this embodiment, so that the aerogel can be recovered.
Soaking the carbon nanofiber aerogel in deionized water, placing the carbon nanofiber aerogel in a vacuum oven to remove air, standing and soaking for 12 hours to be used as an electrode material in a capacitive deionization device, and testing the capacitive deionization performance of the carbon nanofiber aerogel, wherein the desalting efficiency is 13.1mg g-1。
Example 3
Taking a commercially purchased piece of 320X 240X 10mm3Large pieces of bacterial cellulose were soaked in deionized water for 10 days and the deionized water was changed daily. Cutting the deacidified bacterial cellulose into 50 × 15 × 10mm pieces3The small blocks are used for standby; preparing 20mmol/L ammonium dihydrogen phosphate aqueous solution, soaking the bacterial cellulose in the aqueous solution for 5 days, and continuously stirring the solution during the soaking;
placing the metal plate in a foam box filled with liquid nitrogen, and enabling the lower end of the metal plate to be in contact with the liquid nitrogen for five minutes to completely cool the metal plate; then flatly spreading small pieces of bacterial cellulose, and attaching the small pieces of bacterial cellulose to the upper surface of a metal plate; continuously adding liquid nitrogen during the period to ensure that the metal plate is at low temperature, and controlling the temperature of the metal plate to be near-40 ℃; transferring the frozen bacterial cellulose small pieces to a freeze dryer for drying for 3 days, wherein the temperature of a cold trap is-53 ℃, and the pressure is 40 Pa; obtaining a white bacterial cellulose aerogel after freeze drying is completed, as shown in fig. 10;
placing the bacterial cellulose aerogel obtained by freeze drying in a corundum crucible, completely filling the corundum crucible, and covering a corundum plate with good sealing performance above the corundum crucible; placing the corundum crucible in a corundum crucible with a larger volume, wherein gaps around and above the corundum crucible are completely filled with activated carbon particles, and a corundum plate with good sealing is covered above the outer-layer corundum crucible;
and (3) placing the corundum crucible in a muffle furnace, raising the temperature of the muffle furnace to 1000 ℃ at the speed of 5 ℃/min, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain black carbon nanofiber aerogel, wherein the yield of the carbon nanofiber aerogel is 30.7%, and is shown in fig. 10.
The carbon nanofiber aerogel obtained in example 3 was observed by using a field emission scanning electron microscope, and the result is shown in fig. 11. As can be seen from FIG. 11, the carbon nanofiber aerogel obtained in example 3 is composed of carbon nanofibers with diameters of 30 to 200nm, and many cross-linked structures are formed between the fibers.
Mechanical testing is performed on the carbon nanofiber aerogel obtained in example 3, and fig. 12 shows the compressive stress-strain curves of 30%, 60% and 90% of the compression of the carbon nanofiber aerogel provided in this example, so that the aerogel can be recovered.
The carbon nanofiber aerogel obtained in example 3 was subjected to plasma cleaning for 5min, then soaked in deionized water, placed in a vacuum oven to remove air, and then left to stand and soak for 12h to be used as an electrode material in a capacitive deionization device, and the capacitive deionization performance of the carbon nanofiber aerogel was tested, as shown in fig. 13, the desalination efficiency was 8.1mg g-1。
Comparative example 1
The same preparation method as that of example 1, except for the way of oriented freezing, was carried out in the following three ways:
(1) the bacterial cellulose is immersed in liquid nitrogen for freezing, and the bacterial cellulose is cracked due to the rapid growth and random direction of ice crystals, so that the bacterial cellulose aerogel with a regular shape cannot be obtained.
(2) The bacterial cellulose is put into a refrigerator for freezing, and because the temperature in the refrigerator is far higher than that of liquid nitrogen, the growth speed of ice crystals is too slow, the moisture in the bacterial cellulose hydrogel is separated from a fiber network, the shape is shrunk, and the bacterial cellulose aerogel with a regular shape cannot be obtained.
(3) Immersing the bacterial cellulose into ethanol or acetone for 3 days, continuously replacing corresponding solvents during the 3 days, fully exchanging the solution in the bacterial cellulose, performing supercritical drying on the bacterial cellulose subjected to solvent replacement to obtain bacterial cellulose aerogel, and performing pyrolysis to obtain the carbon nanofiber aerogel. The carbon nanofiber aerogel obtained by supercritical drying has an isotropic cross-linked network structure and a non-hierarchical structure, cannot be restored when bearing 90% compressive strain, and has poor mechanical properties.
Comparative example 2
The bacterial cellulose is impregnated by flame retardants such as ammonium dihydrogen phosphate, ammonium chloride and the like, so that the content of solid carbon in a product can be increased, and the yield of the carbon nanofiber aerogel is improved. The appearance and the property of the product carbon nanofiber aerogel are influenced by different concentrations of the flame retardant solution.
Taking 320X 240X 8mm for commercial purchase3Soaking large bacterial cellulose tablets in deionized water for 7 days, and replacing the deionized water every day; cutting the deacidified bacterial cellulose into large pieces of 40 × 15 × 8mm3The small pieces are ready for use; the subsequent soaking was carried out again in the same manner as in example 1:
(1) preparing 10mmol/L, 50mmol/L and 100mmol/L ammonium dihydrogen phosphate aqueous solution, and soaking the bacterial cellulose in the aqueous solution for 5 days while continuously stirring the solution;
freezing bacterial cellulose by using an oriented freezing method, then freezing and drying to obtain ammonium dihydrogen phosphate-impregnated bacterial cellulose aerogel, and pyrolyzing the bacterial cellulose aerogel at 800 ℃ in a closed system to obtain carbon nanofiber aerogel which is marked as CNFA-NHP-10, CNFA-NHP-50 and CNFA-NHP-100;
the carbon aerogel yield CNFA-NHP-10< CNFA-NHP-50< CNFA-NHP-100 proves that the flame retardant has the function of improving the carbon yield, and the volume retention rate CNFA-NHP-10> CNFA-NHP-50> CNFA-NHP-100, the CNFA-NHP-10 property is kept the most complete, because the flame retardant is excessive and the melting surface tension occurs during pyrolysis to cause the atrophy of the aerogel structure.
According to the above results, when a sample with larger porosity is needed, 10mmol/L ammonium dihydrogen phosphate solution is selected for treatment; when comprehensive character and yield factors are needed, 20mmol/L ammonium dihydrogen phosphate solution is selected for treatment.
(2) Preparing 10mmol/L, 20mmol/L and 50mmol/L ammonium chloride aqueous solution, and soaking the bacterial cellulose in the aqueous solution for 5 days while continuously stirring the solution;
and (3) freezing the bacterial cellulose by using an oriented freezing method, then freezing and drying to obtain ammonium chloride-impregnated bacterial cellulose aerogel, and pyrolyzing the bacterial cellulose aerogel at 1600 ℃ in a closed system to obtain carbon nanofiber aerogel which is marked as CNFA-NC-10, CNFA-NC-20 and CNFA-NC-50.
The shape atrophy of CNFA-NC-20 and CNFA-NC-50 is severe, while the CNFA-NC-10 shape remains intact.
From the above results, when comprehensive character and productivity factors are required, 10mmol/L ammonium chloride solution is selected for treatment.
Comparative example 3
When the carbon aerogel is prepared by using a closed system, oxygen in air is consumed by required fillers in a crucible to protect a carbon material at a high temperature; the activated carbon as a carbon material can react with oxygen at high temperature to provide an oxygen-free environment for the sample in the crucible. In addition, the activated carbon has higher specific surface area and can adsorb volatile substances in the reaction; the nano-structure carbon material with higher quality is obtained by low-cost activated carbon.
Taking 320X 240X 8mm for commercial purchase3Soaking large bacterial cellulose tablets in deionized water for 7 days, and replacing the deionized water every day; cutting the deacidified bacterial cellulose into large pieces of 40 × 15 × 8mm3The small pieces are ready for use; obtaining the bacterial cellulose aerogel by an oriented freezing-freeze drying method; the pyrolysis process adopts the following methods respectively:
(1) placing the bacterial cellulose aerogel in a corundum crucible, completely filling the corundum crucible, and covering a corundum plate with good sealing performance above the corundum crucible; placing the corundum crucible in a corundum crucible with a larger volume, wherein gaps around and above the corundum crucible are completely filled with activated carbon particles, and a corundum plate with good sealing is covered above the outer-layer corundum crucible;
and (3) placing the corundum crucible in a muffle furnace, heating the muffle furnace to 800 ℃ at the speed of 5 ℃/min, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain the black carbon nanofiber aerogel, wherein the yield is 21.5%.
(2) Placing the bacterial cellulose aerogel in a corundum crucible, completely filling the corundum crucible, and covering a corundum plate with good sealing performance above the corundum crucible; placing the corundum crucible in a corundum crucible with a larger volume, wherein gaps around and above the corundum crucible are completely filled with coal powder, and a corundum plate with good sealing is covered above the outer-layer corundum crucible;
and (3) placing the corundum crucible in a muffle furnace, heating the muffle furnace to 800 ℃ at the speed of 5 ℃/min, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain the black carbon nanofiber aerogel, wherein the yield is 15.6%.
(3) Placing the bacterial cellulose aerogel in a corundum crucible, completely filling the corundum crucible, and covering a sealed corundum plate above the corundum crucible; placing the corundum crucible in a corundum crucible with a larger volume, wherein gaps around and above the corundum crucible are completely filled with sea sand, and a corundum plate with good sealing is covered above the outer-layer corundum crucible;
placing the corundum crucible in a muffle furnace, heating the muffle furnace to 800 ℃ at the speed of 5 ℃/min, keeping the temperature for 2 hours, and then naturally cooling to room temperature, wherein no sample is left in the crucible; since sea sand does not provide an oxygen-free environment, carbon aerogels are completely oxidized at high temperatures.
(4) Placing the bacterial cellulose aerogel in a corundum crucible, completely filling the corundum crucible, and covering a corundum plate with good sealing performance above the corundum crucible; placing the corundum crucible in a corundum crucible with larger volume, and covering a corundum plate with good sealing above the outer-layer corundum crucible;
the corundum crucible is placed in a muffle furnace, the temperature of the muffle furnace is raised to 800 ℃ at the speed of 5 ℃/min, the temperature is kept for 2 hours, and then the temperature is naturally reduced to the room temperature.
The comparative test uses air, no sample remains in the crucible, and the necessity of air barriers such as activated carbon is proved.
(5) Filling gaps around and above a corundum crucible with a larger volume of bacterial cellulose aerogel into the corundum crucible, and covering a sealed corundum plate above the outer corundum crucible;
and (3) placing the corundum crucible in a muffle furnace, heating the muffle furnace to 800 ℃ at the speed of 5 ℃/min, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain the black carbon nanofiber aerogel, wherein the shape of the black carbon nanofiber aerogel is flattened, and the edge of the black carbon nanofiber aerogel is irregular. Although bacterial cellulose aerogel and carbon aerogel have strong mechanical properties, aerogel can be softened in the pyrolysis process and flattened by activated carbon, and the original regular shape cannot be maintained.
The high-temperature preparation process of the carbon nanofiber aerogel does not need inert gas protection, the cost is favorably reduced, the yield of the obtained carbon nanofiber aerogel is high, the macro-morphology and the micro-morphology are kept intact, the compression recovery performance and the temperature stability are excellent, the obtained carbon nanofiber aerogel has high specific surface area and high porosity and contains heteroatoms such as nitrogen and phosphorus, and the carbon nanofiber aerogel can be used for adsorbing materials, sensor materials, catalyst frameworks, electrode materials and polymer composite materials, so that the carbon nanofiber aerogel has potential industrial application.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, it is possible to make various improvements and modifications to the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A method for preparing a compressible carbon nanofiber aerogel comprising the steps of:
A) soaking the bacterial cellulose to obtain soaked hydrogel;
B) placing the impregnated hydrogel on a metal plate at the temperature of between 20 ℃ below zero and 80 ℃ below zero for oriented freezing, and then performing freeze drying to obtain the bacterial cellulose aerogel;
C) and pyrolyzing the bacterial cellulose aerogel to obtain the carbon nanofiber aerogel.
2. The method according to claim 1, wherein the soaking is carried out by soaking in water and then in an aqueous solution of an inorganic ammonium salt; the inorganic ammonium salt aqueous solution is an aqueous solution of ammonium dihydrogen phosphate, ammonium chloride or ammonium sulfate, the concentration of the inorganic ammonium salt aqueous solution is 0.1-1000 mmol/L, the temperature is 50-100 ℃, and the soaking time is 3-7 days.
3. The method according to claim 2, wherein the concentration of the aqueous solution of ammonium dihydrogen phosphate is 10 to 100mmol/L, the concentration of the aqueous solution of ammonium sulfate is 10 to 50mmol/L, and the concentration of the aqueous solution of ammonium chloride is 10 to 50 mmol/L.
4. The method for preparing the alloy material according to claim 1, wherein the lower end of the metal plate is immersed in liquid nitrogen so that the upper surface of the metal plate is maintained at-20 to-80 ℃; the orientation freezing time is 10-30 min, and the freeze drying time is 3-5 days.
5. The method according to claim 1, wherein the pyrolysis is carried out in a muffle furnace, and an atmosphere of the pyrolysis is an air atmosphere; the heating rate of pyrolysis is 5-20 ℃/min, the temperature of pyrolysis is 500-1500 ℃, and the time is 1-3 h.
6. The preparation method according to claim 1 or 5, characterized in that the pyrolysis process is in particular:
placing the bacterial cellulose aerogel in a first corundum crucible, and then placing the first corundum crucible in a second corundum crucible; and the pores between the first corundum crucible and the second corundum crucible are completely filled with activated carbon particles, and the top of the first corundum crucible and the top of the second corundum crucible are respectively covered with a corundum plate which is well sealed.
7. The method according to claim 1, wherein the bacterial cellulose is (10-50) x (8-20) mm3The carbon nanofiber aerogel is (8-45) × (5-10) mm in sheet shape3The sheet-like shape of (1).
8. The compressible carbon nanofiber aerogel prepared by the preparation method of any one of claims 1 to 7, wherein the carbon nanofibers in the carbon nanofiber aerogel comprise 40 to 99 wt% of carbon, 0.1 to 10 wt% of hydrogen, 0.5 to 50 wt% of oxygen, 0.1 to 10 wt% of nitrogen, and 0.1 to 10 wt% of phosphorus or sulfur.
9. An electrode material, which is obtained by soaking a compressible carbon nanofiber aerogel in an electrolyte, wherein the compressible carbon nanofiber aerogel is the compressible carbon nanofiber aerogel prepared by the preparation method of any one of claims 1 to 7 or the compressible carbon nanofiber aerogel of claim 8.
10. The electrode material of claim 9, wherein the electrolyte is selected from a sodium chloride solution, a potassium sulfate solution, a sulfuric acid solution, or a potassium hydroxide solution.
CN202210222740.4A 2022-03-09 2022-03-09 Compressible carbon nanofiber aerogel, and preparation method and application thereof Pending CN114590794A (en)

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