CN109103026B

CN109103026B - Preparation method of fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane

Info

Publication number: CN109103026B
Application number: CN201811011218.1A
Authority: CN
Inventors: 刘天西; 朱天宜; 张超; 刘思良
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2018-08-31
Filing date: 2018-08-31
Publication date: 2020-05-29
Anticipated expiration: 2038-08-31
Also published as: CN109103026A

Abstract

The invention relates to a preparation method of a fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane, which comprises the following steps: covering the bacterial cellulose film on ammonium fluoride, carbonizing, washing and drying to obtain the bacterial cellulose film. The invention well keeps the original fiber membrane appearance, thereby keeping partial flexibility and self-supporting performance of the bacterial cellulose and having good repeatability, and the content of fluorine and nitrogen can be adjusted and controlled along with the addition of ammonium fluoride. The method is simple, the doping is carried out in one step, the carbonization temperature is moderate, and the prepared fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane has the advantages of high specific mass capacity, good circulation stability and good conductivity. The bacterial cellulose is used as a renewable material, is green and environment-friendly, and has a good prospect in the application of the flexible super capacitor energy storage material.

Description

Preparation method of fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane

Technical Field

The invention belongs to the field of preparation of heteroatom co-doped carbon materials, and particularly relates to a preparation method of a fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane.

Background

With the rapid development of industry and the rapid increase of population, the global energy consumption is increasing at an incredible speed, and the energy shortage and environmental pollution become two major challenges facing the current human development. New low-cost, sustainable and environmentally friendly energy conversion and storage devices must therefore be vigorously developed to meet the development needs of modern society and to alleviate the increasingly prominent environmental problems. Carbon materials are first of all considered to be sustainable and environmentally friendly materials. The carbon material has rich source, inexhaustible carbon material and small chemical pollution.

The Bacterial Cellulose (BC) is natural cellulose without any impurities, and has many unique properties of fine network structure, higher mechanical strength, higher water absorption and retention performance, good biocompatibility and biodegradability and the like. Therefore, the cellulose with the best performance and the highest use value is considered to be one of the hot spots of international biomaterial research at present.

(1) The bacterial cellulose has higher purity and crystallinity. Compared with plant cellulose, the bacterial cellulose does not contain impurities such as hemicellulose, lignin and the like, and exists in the form of 100% cellulose.

(2) Fine network structure. The bacterial cellulose fiber is a fiber bundle with the thickness of 20-100 nm formed by combining microfibers with the diameter of 3-4 nm, and the fibers are mutually interwoven to form a developed hyperfine network structure.

(3) The controllability during synthesis. The cellulose obtained under different fermentation conditions has different structures and characteristics, and in order to improve the characteristics of the cellulose and make the cellulose more suitable for being applied to various fields, a modification method can be adopted to improve the properties of the cellulose.

(4) Degradability and reusability of bacterial cellulose. Under natural conditions, the microorganisms can degrade cellulose into micromolecular sugar, and environmental pollution can not be caused. The bacterial cellulose is a renewable and degradable biological resource and has great significance for building green and environment-friendly national economy.

(5) The extraction process is simple. The extraction process of the bacterial cellulose mainly comprises the steps of heating and soaking by using a low-concentration alkali solution, so that impurities such as thalli, culture medium and the like remained on the fiber can be completely removed, and the plant fiber can be heated and digested by using a high-concentration alkali solution to remove impurities such as hemicellulose, lignin and the like combined with the cellulose.

(6) Good hydrophilicity and air permeability. The bacterial cellulose has a large number of hydrophilic groups inside, and the molecules and the inside of the bacterial cellulose are connected with each other through hydrogen bonds, so that the bacterial cellulose is determined to be hydrogel, wherein the bound water accounts for the most part, and the free water accounts for only 10 percent. The purified cellulose network has many pores and can be well permeable to water and air, and due to the unique property, the bacterial cellulose is used for researching artificial skin.

(7) High tensile strength and young's modulus. After the bacterial cellulose is dried, the Young modulus can reach 10MPa, which is 4 times of that of the synthetic cellulose.

(8) Ultra-fine property. The diameter of the bacterial cellulose produced by the acetobacter xylinum is between 0.01 and 0.1 mu m, and the bacterial cellulose is a natural nano-grade material. Whereas plant cellulose has a diameter of about 10 μm, which is hundreds times larger than that of bacterial cellulose.

Doping is a common modification method, and the method is from initial single-component doping, modification of carbon materials by nitrogen, boron, phosphorus, sulfur and the like to multi-component co-doping in recent years. The nitrogen doping can inhibit the oxygen content, reduce the self-discharge behavior and the electronic contact resistance and improve the surface wettability of the carbon. Meanwhile, nitrogen-doped carbon has been widely reported because electronegativity of nitrogen (3.04) can induce charge redistribution of adjacent atoms on the surface of nitrogen-doped carbon, which greatly improves carbon electrocatalysis or faradaic reaction, and contributes to part of pseudocapacitance. Although nitrogen doping can effectively improve the electrochemical performance of the carbon material, excessive nitrogen can cause the resistance of the material to be increased, and nitrogen-containing functional groups block pores, so that the conductivity of the material is reduced. The most electronegative element in nature is fluorine, and since the great electronegativity is favorable for electrochemical performance, researchers naturally think of doping with fluorine. Therefore, many studies on co-doping of fluorine and nitrogen have been made in recent years. The fluorine and the nitrogen greatly improve the electrochemical performance of the carbon material by using the high electronegativity of the fluorine and the nitrogen and the synergistic effect of the fluorine and the nitrogen. The electrocatalytic performance, the capacitance and the stability are greatly improved. Doping carbon materials with fluorine invariably requires a large amount of fluorine source, which is quite difficult to dope into porous carbon substrates. Currently, ammonium fluoride is the most commonly used one, and ammonium fluoride is decomposed into ammonia gas and hydrogen fluoride gas at high temperature, so that the material is carbonized in the atmosphere and is codoped with fluorine and nitrogen.

Compared with the traditional fluorine and nitrogen codoping, the ammonium fluoride is used for carrying out double-element doping by a one-step method. The sodium fluoride can be decomposed by heating and slowly releases ammonia gas and hydrogen fluoride gas, and the bacterial cellulose membrane material is modified under the double-atmosphere. The complex steps of introducing ammonia gas and hydrogen fluoride atmosphere into the double pipelines are overcome, and a mild environment for slowly releasing the hydrogen fluoride atmosphere is provided.

Disclosure of Invention

The invention aims to solve the technical problem of providing a preparation method of a fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane, overcoming the complicated steps of introducing ammonia gas and hydrogen fluoride atmosphere into a double pipeline, and providing a mild environment for slowly releasing the hydrogen fluoride atmosphere.

The invention discloses a preparation method of a fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane, which comprises the following steps:

covering the bacterial cellulose membrane on ammonium fluoride, carbonizing, modifying the bacterial cellulose membrane by ammonia gas and ammonium fluoride, washing and drying to obtain the fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane.

The preferred mode of the above preparation method is as follows:

the mass ratio of the bacterial cellulose membrane to the ammonium fluoride is 1:5-40, and the mass ratio of the bacterial cellulose membrane to the ammonium fluoride is preferably 1: 20.

And carrying out vacuum filtration on the bacterial cellulose BC dispersion liquid, and pumping by using a vacuum pressure pump to form the bacterial cellulose membrane.

The solid content of the bacterial cellulose dispersion liquid is 0.60-0.70%.

The solid content of the bacterial cellulose BC dispersion is more preferably 0.65%.

The bacterial cellulose membrane has a mass of 6-7 mg and a thickness of about 2.5-3.5 μm.

It is further preferred that the extracted bacterial cellulose membrane is 6.5mg and is about 3 μm thick.

The carbonization is as follows: the carbonization is carried out in argon atmosphere, the carbonization temperature is 500-600 ℃, the heating rate is 3-5 ℃/min, and the heat preservation time is 0.5-2 h.

Further preferably, the carbonization is performed in an argon atmosphere; the carbonization temperature is 600 ℃, the heating rate is 5 ℃/min, and the heat preservation time is 2 h.

The ammonium fluoride NH₄F is crystalline particles.

The washing is as follows: firstly, acid soaking and washing are carried out for 1-3h by adopting dilute hydrochloric acid with the mass concentration of 5%, and a small amount of inorganic salt impurities are removed;

then washing with deionized water for 0.5-1 h.

The drying is drying for 6-12h in a vacuum oven at 60 ℃.

Further preferably, the drying is drying in a vacuum oven at 60 ℃ for 12 h.

The invention also provides a fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane prepared by the method.

The invention further provides an application of the fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane prepared by the method in an energy storage material of a flexible supercapacitor.

Advantageous effects

(1) According to the invention, the fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane prepared by carbonizing ammonium fluoride by pyrolysis in one step well keeps the original fiber membrane appearance, so that partial flexibility and self-supporting performance of the bacterial cellulose are kept, the repeatability is good, and the content of fluorine and nitrogen elements can be regulated and controlled along with the addition amount of ammonium fluoride;

(2) the method is simple, one-step doping is realized, the carbonization temperature is moderate, the complicated steps of introducing ammonia gas and hydrogen fluoride atmosphere into a double pipeline are overcome, and a mild environment for slowly releasing the hydrogen fluoride atmosphere is provided, so that the prepared fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane has very high specific mass capacity (the specific mass capacity of 350F/g is obtained under the current density of 1A/g in 1mol/L sulfuric acid electrolyte), has very good circulation stability, is green and environment-friendly as a renewable material, and has a very good prospect in the application of flexible supercapacitor energy storage materials.

Drawings

Fig. 1 is an SEM image of a BC film material subjected to fluorine and nitrogen co-doping, wherein (a) is a cross-sectional SEM image of the BC film material subjected to fluorine and nitrogen co-doping; (b) is a surface SEM image of a BC film material subjected to fluorine and nitrogen co-doping;

fig. 2 is an SEM image of a non-carbonized BC film material, wherein (a) is a cross-sectional view of the non-carbonized BC film material; (b) is a surface map of an uncarbonized BC film material;

FIG. 3 is a surface TEM image of the BC membrane material after fluorine and nitrogen co-doping;

FIG. 4 is an XRD pattern of the bacterial cellulose-derived carbon nanofiber films of examples 1 to 5 and comparative example;

FIG. 5 is a Raman diagram of the bacterial cellulose-derived carbon nanofiber membranes of examples 1 to 5 and comparative example;

FIG. 6 is a graph of specific surface area (BET) of the bacterial cellulose-derived carbon nanofiber membranes of example 1 and comparative example 1;

FIG. 7 is a pore size distribution diagram of the bacterial cellulose-derived carbon nanofiber membranes of example 1 and comparative example 1;

FIG. 8 is a CV cycle plot of the bacterial cellulose-derived carbon nanofiber membrane material of examples 1-5 and comparative example at a rate of 10 mV/s;

FIG. 9 is a charge-discharge curve of the bacterial cellulose-derived carbon nanofiber membrane material of examples 1-5 and the comparative example at a current density of 1A/g;

fig. 10 is a CV cycle chart of the fluorine and nitrogen co-doped bacterial cellulose-derived carbon nanofiber membrane material in example 1 at different scanning rates;

fig. 11 is a charge-discharge curve of the fluorine and nitrogen co-doped bacterial cellulose-derived carbon nanofiber membrane material in example 1 under different current densities.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

(1) Diluting commercial bacterial cellulose dispersion liquid with solid content of 0.65% by 10 times, taking 10ml of dispersion liquid, transferring the dispersion liquid to a vacuum filtration funnel, and pumping the dispersion liquid into a bacterial cellulose film through a vacuum pressure pump. The film was lyophilized by a lyophilizer, and 6.5mg was weighed to a thickness of 3 μm (the bacterial cellulose films used in the examples and comparative examples below are of this specification). The bacterial cellulose film after freeze-drying and taking down was mixed with 130mg of ammonium fluoride (BC: NH)₄F is 1:20) is placed in a graphite crucible, the temperature is raised to 600 ℃ at the heating rate of 5 ℃/min under the argon atmosphere, the temperature is kept for 2h, the obtained product is taken out and washed for 1-3h by hydrochloric acid with the concentration of 5%, deionized water is used for washing for 0.5-1h respectively, and finally vacuum drying is carried out at the temperature of 60 ℃ for 12h to obtain the bacterial cellulose derived carbon nanofiber membrane FN-BC-20.

(2) Mixing 70mg of the bacterial cellulose-derived carbon nanofiber membrane BC obtained in the step (1), 20mg of acetylene black and 10mg of PVDF binder with the concentration of 10%, grinding the mixture for 30min by using a mortar, adding 500 mu L of N-methyl pyrrolidone (NMP) for dilution, coating the active substance on carbon paper with known mass, and coating the carbon paper with the coating area of 1cm²And finally, vacuum drying for 6 hours at the temperature of 60 ℃, and weighing to calculate the mass of the active substance to be 1-1.5 mg.

(3) Two pieces of carbon paper with similar active mass are assembled into a double-electric-layer symmetrical capacitor, 1mol/L sulfuric acid solution is selected as electrolyte, and the electrochemical performance of the capacitor is tested by using a Shanghai Chenghua electrochemical workstation.

FIG. 1(a) shows: it is seen from the cross-sectional SEM image that the fluorine and nitrogen co-doped bacterial cellulose membrane of example 1 was partially melt-bonded after carbonization.

FIG. 1(b) shows: from the SEM image, the fiber morphology of the fluorine and nitrogen co-doped bacterial cellulose membrane in example 1 is well retained after carbonization, and a little adhesion exists.

FIG. 3 shows: it is clear from the TEM images that the fibers of example 1 have diameters below 50 nm and are closely stacked.

Fig. 8 and 9 show that: the specific capacity of the FN-BC-20 in the example 1 is calculated to be the highest through a charge-discharge diagram, the specific capacity reaches 350F/g, the maximum CV circulating area under the same current sweeping speed further indicates that the specific capacity is the maximum, and the nearly rectangular area of the material indicates that the material has good circulating stability and excellent rate capability.

The specific capacity of the electrolyte is 350F/g under the current density of 1A/g in 1mol/L sulfuric acid electrolyte.

Example 2

Preparation was carried out as in example 1, except that the ammonium fluoride was 32.5mg (BC: NH)₄F ═ 1:5), and obtaining the fluorine and nitrogen co-doped bacterial cellulose-derived carbon nanofiber membrane FN-BC-5.

The specific capacity of the electrolyte is 279F/g under the current density of 1A/g in 1mol/L sulfuric acid electrolyte.

Example 3

Preparation was carried out as in example 1, except that 65mg (BC: NH) of the ammonium fluoride was used₄F ═ 1:10), and a fluorine and nitrogen co-doped bacterial cellulose-derived carbon nanofiber membrane FN-BC-10 was prepared.

Has a specific capacity of 314F/g at a current density of 1A/g in a 1mol/L sulfuric acid electrolyte

Example 4

Prepared according to the method of example 1, except that the ammonium fluoride is 195mg (BC: NH)₄F ═ 1:30), and obtaining the fluorine and nitrogen co-doped bacterial cellulose-derived carbon nanofiber membrane FN-BC-30.

Has a specific capacity of 304F/g at a current density of 1A/g in a 1mol/L sulfuric acid electrolyte

Example 5

Preparation was carried out as in example 1, except that the ammonium fluoride was 260mg (BC: NH)₄F ═ 1:40), and obtaining the fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane FN-BC-40.

The specific capacity of the electrolyte is 261F/g under the current density of 1A/g in 1mol/L sulfuric acid electrolyte.

As can be seen from fig. 4, from XRD, as the amount of ammonium fluoride used increases, the broad peak at 25 ° is slightly shifted to the left, and the broad peak represents the 002 crystal face of amorphous carbon, indicating that carbon with a degree of graphitization occurs by carbonization.

As can be seen from FIG. 5, from the Raman spectrum, two peaks respectively represent the degree of graphitization disorder I_DAnd degree of graphitization orderI_GFrom I_D/I_GThe value of (a) is gradually increased, and the reduction of the graphitization order degree is seen because the order of graphite carbon is destroyed by doping fluorine and nitrogen heteroatom.

As can be seen from fig. 6, the BET spectrum shows that the specific surface area of the bacterial cellulose doped with fluorine and nitrogen in example 1 is increased compared with that of the bacterial cellulose not doped in comparative example 1.

As can be seen from fig. 7, as seen from the pore size distribution, the bacterial cellulose after co-doping with fluorine and nitrogen in example 1 has a hierarchical pore size distribution, and has a hierarchical pore structure with one micropore and one mesopore, and the pore size is wider in part than the undoped bacterial cellulose in comparative example 1.

As can be seen from fig. 8 and 9, the CV cycle diagrams of the examples and the comparative examples at 10mV/s illustrate that the example 1 has the highest electrochemical specific capacity through the ring specific area, which is attributed to the fact that the appropriate fluorine and nitrogen co-doping amount enables the electrolyte to have more C-F semiionic bonds with higher relative activity, and meanwhile, the appropriate heteroatom doping facilitates the wetting of the electrolyte and does not sacrifice the conductivity of the electrolyte.

As can be seen from FIGS. 10 and 11, the CV cycle diagrams of example 1 at different sweep rates are closed to approximate rectangles, which show good cycle stability and a specific capacity of 350F/g at a current density of 1A/g in 1mol/L sulfuric acid electrolyte.

Comparative example 1

Preparing a bacterial cellulose film according to the preparation method of the embodiment 1, except that the bacterial cellulose film which is freeze-dried and taken down is directly carbonized in an argon atmosphere; the carbonization temperature is 600 ℃, the heating rate is 5 ℃/min, and the heat preservation time is 2 h. And taking out, washing for 1-3h by using 5% hydrochloric acid, washing for 0.5-1h by using deionized water respectively, and finally drying in vacuum at 60 ℃ for 12h to obtain the undoped bacterial cellulose-derived carbon nanofiber membrane BC.

Has a specific capacity of 178F/g at a current density of 1A/g in a 1mol/L sulfuric acid electrolyte.

FIG. 2(a) shows: from the SEM image, it was seen that the non-carbonized bacterial cellulose membrane of comparative example 1 was approximately 3 μm thick and the fibers were dense.

FIG. 2(b) shows: from the SEM images, it is seen that the non-carbonized bacterial cellulose membrane of comparative example 1 had fibers that were tightly stacked.

Fig. 8 and 9 show that: the specific capacity of the undoped bacterial cellulose membrane material in the comparative example is poor, and the difference between the undoped bacterial cellulose membrane material and the bacterial cellulose membrane material doped with fluorine and nitrogen is obvious, which indicates that ammonium fluoride has a great effect on modification of the bacterial cellulose membrane.

Claims

1. A preparation method of a fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane comprises the following steps:

covering the bacterial cellulose membrane on ammonium fluoride, carbonizing, washing and drying to obtain a fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane; wherein the carbonization is: the carbonization is carried out in argon atmosphere, the carbonization temperature is 500-600 ℃, the heating rate is 3-5 ℃/min, and the heat preservation time is 0.5-2 h.

2. The preparation method according to claim 1, wherein the mass ratio of the bacterial cellulose membrane to the ammonium fluoride is 1: 5-40.

3. The method according to claim 1, wherein the bacterial cellulose membrane is specifically: and carrying out vacuum filtration on the bacterial cellulose dispersion liquid to form the bacterial cellulose membrane.

4. The method according to claim 3, wherein the bacterial cellulose dispersion has a solid content of 0.60 to 0.70%.

5. The method according to claim 1, wherein the bacterial cellulose membrane has a mass of 6 to 7mg and a thickness of 2.5 to 3.5 μm.

6. The method of claim 1, wherein the washing is: firstly, acid washing is carried out for 1-3h by using dilute hydrochloric acid with the mass concentration of 5%; then washing with deionized water for 0.5-1 h.

7. The preparation method according to claim 1, wherein the drying is drying in a vacuum oven at 60 ℃ for 6-12 h.

8. A fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane prepared by the method of claim 1.

9. The application of the fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber membrane prepared by the method in claim 1 in an energy storage material of a flexible supercapacitor.