CN114180556A

CN114180556A - Three-dimensional porous modified carbon nanotube and preparation method and application thereof

Info

Publication number: CN114180556A
Application number: CN202111656783.5A
Authority: CN
Inventors: 苟珍琼; 黄川�; 周桂林; 徐丹
Original assignee: Chongqing University; Chongqing Technology and Business University
Current assignee: Chongqing University; Chongqing Technology and Business University
Priority date: 2021-12-30
Filing date: 2021-12-30
Publication date: 2022-03-15
Anticipated expiration: 2041-12-30
Also published as: CN114180556B

Abstract

The invention relates to a modified carbon nanotube with a three-dimensional porous structure, a preparation method and application thereof, belonging to the field of materials. The invention provides a modified carbon nanotube, which is prepared by taking a carbon nanotube, a polycation and a polyanion as raw materials and utilizing the covalent interaction between the polycation and the carbon nanotube and the electrostatic bridging interaction between the polyanion and the polycation. After the modified carbon nano tube obtained by the invention is introduced into the polymer matrix, the dispersibility of the modified carbon nano tube in the polymer matrix can be improved, and the comprehensive properties of the polymer matrix, such as thermal stability, strength and Young modulus, can be improved.

Description

Three-dimensional porous modified carbon nanotube and preparation method and application thereof

Technical Field

The invention relates to a modified carbon nanotube with a three-dimensional porous structure, a preparation method and application thereof, belonging to the field of materials.

Background

Carbon Nanotubes (CNTs), also known as buckytubes, are seamless cylindrical shell-structured Carbon materials formed by crimping single-or multi-layer graphite sheets around a central axis at a certain helical angle. Carbon nanotubes are classified into Single-wall carbon nanotubes (SWNTs) and Multi-wall carbon nanotubes (MWNTs) according to the number of layers. Compared with single-walled carbon nanotubes, multi-walled carbon nanotubes are widely used due to their low preparation cost.

Compared with other carbon materials, the carbon nanotube has more excellent mechanical, electrical, chemical, magnetic, optical, thermal and other properties. In addition, the carbon nanotube is not only an excellent reinforcing agent, but also has a larger specific surface area due to the curling action due to its porous structure, and is considered to be an excellent adsorbent.

However, the carbon nanotubes have smooth surfaces and strong hydrophobicity, are easily aggregated into bundles, which makes the carbon nanotubes difficult to disperse in solutions and matrixes, and have smooth and complete carbon structures, so that the interfacial interaction between the carbon nanotubes and substances is weak, and the carbon nanotubes are not satisfactory in terms of adsorption. Therefore, how to improve the dispersibility of the carbon nanotubes in the solution or the base material and enhance the interaction between the carbon nanotubes and the base material is a problem to be solved.

In addition, some physical methods such as ball milling, ultrasonic method, wrapping method and the like are adopted in the prior art to treat the carbon nano tube, but some physical methods are complex to operate and troublesome to clean, and the physical method is adopted, the acting force between molecules is weak, and the physically blended carbon nano tube is extremely easy to disperse after entering the solution, secondary agglomeration occurs, and the dispersion effect is not good. Some methods improve the dispersibility of the carbon nanotubes to a certain extent, but the adsorbability is not good, for example, the wrapping method modifies the carbon nanotubes, i.e. small molecules or polymers are wrapped on the surface of the carbon nanotubes, so as to improve the surface property of the carbon nanotubes and improve the dispersibility of the carbon nanotubes.

Disclosure of Invention

Aiming at the defects, the invention provides a three-dimensional porous modified carbon nanotube, which is prepared by covalently grafting a substance with excellent hydrophilic performance, such as Chitosan (CS), on carbon nanotubes (MWNTs) and introducing a polyanion, such as carboxymethyl cellulose (CMC), to prepare the three-dimensional porous modified carbon nanotube (such as CMC/MWNTs-CS); the hydrophilicity of CS and CMC and the electrostatic bridging effect between the CS and CMC are utilized to enable MWNTs, CS and CMC to form a modified carbon nano tube with a three-dimensional porous structure, thereby enhancing the dispersibility of MWNTs in aqueous solution and polymer base materials.

The technical scheme of the invention is as follows:

the first technical problem to be solved by the invention is to provide a modified carbon nanotube, which takes a carbon nanotube, a polycation and a polyanion as raw materials, and utilizes the covalent interaction between the polycation and the carbon nanotube and the electrostatic bridging interaction between the polyanion and the polycation to obtain the modified carbon nanotube.

Further, the modified carbon nanotube has a three-dimensional porous structure.

Further, the mass ratio of the polyanion to the polycation is as follows: 0.5-2: 1.

furthermore, the addition amount of the polycation is enough to ensure that the carbon nano tube can be completely grafted.

Further, the polycation is hydrophilic type polycation; specifically selected from: chitosan, quaternary ammonium group polysaccharide or seaweed polysaccharide. Polycations refer to "micelles of aggregated positive charge" in colloidal chemistry.

Further, the polyanionic body is selected from: one of sodium carboxymethylcellulose, carboxymethyl curdlan gum or corn fiber gum. Generally, the polyanionic entities refer to "colloidal particles of agglomerated negative charges" in colloidal chemistry.

Further, the carbon nanotubes are: multi-walled or single-walled carbon nanotubes, preferably multi-walled carbon nanotubes.

The second technical problem to be solved by the present invention is to provide a method for preparing the above modified carbon nanotube, wherein the method comprises: firstly, the polycation and the carbon nano tube are compounded to obtain a polycation/carbon nano tube compound, then the compound and the polyanion are uniformly blended, and the modified carbon nano tube with the three-dimensional porous structure is formed by utilizing the electrostatic bridging action of the polyanion and the polycation.

Further, the polycation and the carbon nano tube are compounded in a covalent grafting mode.

Further, when the polycation is chitosan and the polyanion is sodium carboxymethyl cellulose, the preparation method of the modified carbon nanotube comprises the following steps: covalently grafting chitosan to a carbon nano tube to form a chitosan grafted carbon nano tube; then adding chitosan grafted carbon nano tubes into the sodium carboxymethyl cellulose solution, and uniformly mixing by ultrasonic and stirring; finally, freeze drying to obtain the modified carbon nano tube.

The addition amount of the polycation is enough to ensure that the carbon nano tube can be completely grafted.

Further, the sodium carboxymethyl cellulose solution refers to a solution formed by dissolving sodium carboxymethyl cellulose in acetic acid.

The third technical problem to be solved by the invention is to provide a polymer-based composite material, wherein the composite material is prepared by introducing modified carbon nanotubes into a polymer matrix, and the modified carbon nanotubes are prepared by adopting the method.

Further, the polymer matrix is starch, chitosan or cellulose.

Further, the ratio of the polymer matrix to the modified carbon nanotube is as follows: 100 parts of a polymer matrix and 1-15 parts of modified carbon nanotubes.

The fourth technical problem to be solved by the present invention is to provide a method for improving the dispersibility of carbon nanotubes in a polymer matrix, wherein the method comprises: introducing a polycation and a polyanion into the carbon nano tube, and obtaining a modified carbon nano tube with a three-dimensional porous structure by utilizing the covalent action between the polycation and the carbon nano tube and the electrostatic bridging action of the polyanion and the polycation; and then introducing the obtained modified carbon nano tube into a high molecular matrix.

The invention has the beneficial effects that:

the modified carbon nano tube is obtained by introducing the polycation and the polyanion into the carbon nano tube, and forming a mesh-shaped pore structure by utilizing the covalent action between the polycation and the carbon nano tube and the electrostatic bridging action between the polyanion and the polycation; after the modified carbon nano tube is introduced into the polymer matrix, the dispersibility of the modified carbon nano tube in the polymer matrix can be improved, and the comprehensive properties of the polymer matrix, such as thermal stability, strength and Young modulus, can be improved.

Description of the drawings:

FIG. 1 is an infrared spectrum of MWNTs-CS and purified carboxylated carbon nanotubes and chitosan obtained in example 1 of the present invention.

FIG. 2 is a graph showing the results of the change of the UV absorption of MWNTs-CS and the pure carboxylated carbon nanotube according to example 1 of the present invention with time.

FIG. 3 is a microscopic topography of MWNTs-CS (FIG. 3a) and pure carboxylated carbon nanotubes (FIG. 3b) obtained in example 1 of the present invention.

FIG. 4 is a microscopic morphology of a starch-based composite film obtained in example 3 of the present invention.

FIG. 5 shows the results of thermogravimetric curves and thermogravimetric differential curves of the starch-based composite film obtained in example 4 of the present invention and the pure starch film (comparative example 1) and the comparative samples (comparative example 2 and comparative example 5).

FIG. 6 shows the mechanical properties of the starch-based composite films obtained in the examples of the present invention and the comparative examples, as well as the pure starch films and the comparative samples: FIG. 6(a) -Strength, FIG. 6(b) -Young's modulus; wherein different lower case letters a-f represent significant differences, P (significant difference) < 0.05.

Detailed Description

The invention can prepare the modified carbon nano tube by adopting the following method, which comprises the following steps: the method comprises the following steps: adopting a covalent grafting method to covalently graft CS of the polycationic polymer with MWNTs, and marking the MWNTs-CS as MWNTs; step two: mixing a certain amount of CMC with MWNTs-CS; further compounding to form the modified carbon nano tube with a three-dimensional porous structure. According to the invention, the carbon nano tube modified by covalent grafting of hydrophilic chitosan has more stable performance and is not easy to generate secondary agglomeration, chitosan is uniformly dispersed around the carbon nano tube and is in an amorphous state, the dispersing ability and stability of the carbon nano tube in a solution can be obviously improved, and then the carboxymethyl cellulose of a polyanion and chitosan of a polycation generate an electrostatic bridging effect to form a mesh pore structure, so that the dispersibility of the carbon nano tube in the solution and a polymer matrix is enhanced, and the comprehensive performance of the polymer matrix is improved.

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1

A method for obtaining the network structure and the comprehensive performance of a CMC/MWNTs-CS three-dimensional porous carbon nanotube-based composite material by adopting a covalent grafting method, such as improving the dispersibility of a carbon nanotube in a solution, comprises the following specific steps:

preparation of MWNTs-CS:

the first step is as follows: preparing anhydrous tetrahydrofuran and anhydrous N, N-dimethylformamide; firstly activating the 5A molecular sieve, namely putting the 5A molecular sieve into a muffle furnace to preheat for 1h at 150 ℃, and then heating to 400 ℃ and keeping for 3 h; taking out, immediately placing into dimethylformamide and tetrahydrofuran, drying, and standing for 2-3 days for later use;

the second step is that: preparing an acyl chlorinated carbon nanotube; 150mL of thionyl chloride was added to a 3.5g carbon nanotube made acetic acid, and the mixture was magnetically stirred at 70 ℃ for 24 hours in a fume hood, and then subjected to a silicon oil bath and reflux condensation. Repeatedly cleaning with anhydrous tetrahydrofuran after the reaction is finished, performing suction filtration, and performing vacuum drying to obtain solid powder;

the third step: preparing a chitosan covalent grafting carbon nanotube; adding 0.4g of carbon nanotube of acyl chloride and excessive chitosan into 160mLN, N-dimethylformamide and 8mL of pyridine, stirring for 96h at 100 ℃, carrying out silicon oil bath, and carrying out condensation reflux; and after the reaction is finished, repeatedly washing the mixture by using 2 (v/v)% of acetic acid solution, drying the mixture in vacuum and weighing the mixture to obtain solid powder, namely the product of the chitosan covalent grafting carbon nano tube, which is marked as MWNTs-CS.

And (3) performance testing:

and (3) infrared spectrum characterization:

a small amount of fully dried samples (chitosan powder, carboxylated carbon nanotubes and MWNTs-CS) were taken and mixed with potassium bromide thoroughly, ground and tableted, and examined using Spectrum 100 Fourier transform infrared spectrometer from Perkin Elmer, USA. The scanning range was set to 400cm^-1To 4000cm^-1. The existence and the change of the functional group in the sample are deduced by observing and analyzing the change of each characteristic peak.

And (3) ultraviolet testing:

the absorbance of the sample was measured by using a spectrophotometer model UV-2450 from Shimadzu corporation, Japan. The samples were dissolved in a 2 (v/v)% acetic acid solution before the test to prepare a solution having a concentration of 50mg/L with the wavelength set at 260nm, and the absorbance values were read after 10min intervals, respectively, and recorded.

Characterizing a field emission scanning electron microscope:

the sample powder was subjected to gold spraying and then tested using a JEM-2100 field emission scanning electron microscope (JEOL Ltd., Japan).

FIG. 1 is an infrared spectrum of MWNTs-CS and a pure carboxylated carbon nanotube and chitosan, FIG. 2 is a graph of a change result of ultraviolet absorption of MWNTs-CS and a pure carboxylated carbon nanotube with time, and FIG. 3 is a microscopic morphology graph of MWNTs-CS and a pure carboxylated carbon nanotube. The infrared spectrum and electron microscope scanning show that the carbon nano tube modified by the hydrophilic chitosan covalent grafting has more stable performance and is not easy to generate secondary agglomeration, and the chitosan is uniformly dispersed around the carbon nano tube and is in an amorphous state. Through ultraviolet analysis, the chitosan and the carbon nano tube in the MWNTs-CS are connected through a covalent bond, the bonding force between the chitosan and the carbon nano tube is strong, and the chitosan and the carbon nano tube have good stability after being dispersed in an acetic acid solution; compared with the unmodified carbon nanotube, the absorbance of the carboxylated carbon nanotube is reduced rapidly within 20min from the beginning of the test, the MWNTs-CS still maintains 91.00% of the absorbance after ultrasonic treatment for 80min through further modification of the hydrophilic polymer chitosan, and the color of the MWNTs-CS solution is not changed remarkably and almost has no precipitation after the ultrasonic treatment and standing for 24 h.

Example 2

Preparing the polymer composite film added with polyanion and polycation with different proportions.

Preparing a high-molecular composite film: the solution blending method is adopted and is correspondingly adjusted to prepare the material, and the preparation steps are as follows:

(1) preparing a solution: dissolving 3.5g of corn starch and 0.8g of glycerol in 100mL of deionized water;

(2) gelatinizing starch: heating the prepared solution in water bath at 75 deg.C and stirring; after the time is 1.5h, stopping heating;

(3) respectively dissolving 0.175g of MWNTs-CS (chitosan grafting degree is 85.9%) prepared in example 1 and 0.075g of sodium carboxymethylcellulose CMC in 2 (v/v)% of acetic acid solution, performing ultrasonic treatment for 30min, and adding into gelatinized starch solution; then stirring for 24h at room temperature by using a constant-temperature magnetic stirrer, ultrasonically treating for 1h, and standing for about 10 min; wherein the mass ratio of the sodium carboxymethylcellulose to the chitosan content in the MWNTs-CS is 0.5: 1.

(4) And (3) film pouring: pouring 25.0g and 10.0g of the mixed solution into a square culture dish (13 cm. times.13 cm) and a round culture dish (9 cm. times.9 cm), respectively;

(5) drying the film: setting the temperature of the oven at 50 ℃ and the film drying time to be 3-4 h; drying to obtain modified starch composite film (marked as PS/CMC/MWNTs-CS-0.5)

Example 3

The other procedures are the same as those in example 2, except that: changing the mass ratio of the sodium carboxymethylcellulose to the chitosan content in MWNTs-CS from 0.5:1 to 1: 1; the obtained starch composite membrane is marked as PS/CMC/MWNTs-CS-1.

Example 4

The other procedures are the same as those in example 2, except that: changing the mass ratio of the sodium carboxymethylcellulose to the chitosan content in MWNTs-CS from 0.5:1 to 2: 1; the obtained starch composite membrane is marked as PS/CMC/MWNTs-CS-2.

Comparative example

A pure starch film (comparative example 1, marked as PS) is obtained by adopting the same method as the example 2 and omitting the step 3; the filler adopted in the step 3 is MWNTs-CS to obtain a modified starch film (a comparative example 2, marked as PS/MWNTs-CS); adopting CMC with different contents in the step 3 to obtain modified starch films (comparative examples 3-5, respectively marked as PS/CMC-0.5, PS/CMC-1 and PS/CMC-2); adopting CMC and MWNTs in the step 3 to obtain a modified starch film (a comparative example 6, marked as PS/CMC/MWNTs-2); the raw material ratios of the respective examples and comparative examples are shown in table 1.

TABLE 1 component contents in examples and comparative examples

And (3) performance testing:

and (3) testing the machine performance:

according to the GB 1040 standard and improved, the measurement is carried out by using XLW-PC type intelligent electronic tension tester of the Jinnan optical electromechanical technology, Inc. The film was equilibrated for 24h in an environment with a relative humidity of 50% before the measurement. During measurement, the film is cut into strips with the size of 50mm multiplied by 10mm, the strips are fixed on a clamp of an intelligent electronic tensile tester, the tensile rate is set to be 25mm/min, and the tensile strength and the tensile rate of the composite film are measured. The average was taken 10 replicates per sample. Significance testing was performed using One-way ANOVA in SPSS19.0 statistical analysis software (significant differences were P < 0.05).

Characterizing a field emission scanning electron microscope: the obtained film sample powder was subjected to gold spraying treatment and then tested using a JEM-2100 field emission scanning electron microscope (JEOL Ltd., Japan).

And (3) thermogravimetric testing: before testing, the film samples were fully dried in a vacuum oven and tested using a TGAQ50 thermogravimetric analyzer from TA instruments, usa; the test process is carried out under the protection of nitrogen, the heating rate is 10 ℃/min, and the heating range is from 40 ℃ to 600 ℃.

Through mechanical property tests, it is found that the strength and Young modulus of the pure starch film are relatively poor as shown in FIGS. 6(a) and (b), and the strength and Young modulus of the starch film are remarkably improved (P <0.05) by adding MWNTs-CS and sodium carboxymethyl cellulose. Wherein, the strength and Young modulus of PS/CMC/MWNTs-CS-2 are highest and reach 39.30MPa and 1623.73GPa respectively, and are respectively improved by 1126.92 percent and 164891.91 percent compared with a pure starch film.

Effect of addition of sodium carboxymethyl cellulose alone on mechanical properties of starch films: as can be seen from fig. 6, the strength and young's modulus tended to increase with the increase in the content of sodium carboxymethylcellulose. The strength and Young modulus of the obtained starch composite membrane are both obviously higher than those of PS/CMC and PS/MWNTs-CS (P is less than 0.05) by simultaneously adding the two components (sodium carboxymethylcellulose and MWNTs-CS).

In addition, the comparison of the PS/CMC-2 composite membrane, the PS/CMC/MWNTs-2 composite membrane and the PS/CMC/MWNTs-CS-2 composite membrane shows that the strength and the Young modulus of the PS/CMC-2 composite membrane are respectively 8.48MPa and 401.50GPa, and the strength and the Young modulus of the PS/CMC/MWNTs-2 composite membrane are respectively 22.50MPa and 1007.30 Gpa; and the strength and Young modulus of PS/CMC/MWNTs-CS-2 are significantly higher than those of the PS/CMC/MWNTs-CS-2 (P <0.05) and are respectively as high as 39.30MPa and 1623.73 GPa. Further proves that the electrostatic bridging effect between the carboxymethyl cellulose and the chitosan enables stronger acting force between the nano particles and the starch matrix.

Scanning by an electron microscope to find that the CMC/MWNTs-CS three-dimensional porous carbon nanotube-based composite material is uniformly dispersed in the starch film; through thermogravimetry, the residue residual amount of the pure starch film at 490 ℃ is about 11.29 percent, and the residue residual amount of the composite starch film added with the CMC/MWNTs-CS three-dimensional porous carbon nanotube-based composite starch film is increased to 28.42 percent; this indicates that the simultaneous presence of MWNTs-CS and sodium carboxymethylcellulose is more helpful in improving the thermal stability of the starch film.

In conclusion, the invention adopts the chitosan covalent grafting carbon nano tube with excellent hydrophilic performance and the composite carboxymethyl cellulose to prepare the modified carbon nano tube, the carbon nano tube after the hydrophilic chitosan covalent grafting modification has more stable performance and is not easy to generate secondary agglomeration, the chitosan is uniformly dispersed around the carbon nano tube and is in an amorphous state, the dispersing ability and the stability of the carbon nano tube in the solution can be obviously improved, and then the carboxymethyl cellulose sodium of the polyanion and the chitosan of the polycation generate electrostatic bridging action to ensure that the three form a net-shaped pore structure, thereby enhancing the dispersibility of the carbon nano tube in the solution and the polymer matrix and improving the comprehensive performance of the polymer matrix, such as thermal stability, strength and Young modulus.

Claims

1. The modified carbon nanotube is characterized in that the modified carbon nanotube is prepared by taking a carbon nanotube, a polycation and a polyanion as raw materials and utilizing the covalent interaction between the polycation and the carbon nanotube and the electrostatic bridging interaction between the polyanion and the polycation.

2. The modified carbon nanotube according to claim 1, wherein said modified carbon nanotube has a three-dimensional porous structure.

3. The modified carbon nanotube according to claim 1 or 2, wherein the mass ratio of said polyanion to polycation is: 0.5-2: 1;

4. The modified carbon nanotube according to any one of claims 1 to 3, wherein the polycation is a hydrophilic type polycation; preferably: one of chitosan, quaternary ammonium group polysaccharide or algal polysaccharide;

further, the polyanionic body is selected from: one of sodium carboxymethylcellulose, carboxymethyl curdlan gum or corn fiber gum;

further, the carbon nanotubes are: multi-walled or single-walled carbon nanotubes; preferably multi-walled carbon nanotubes.

5. The method for producing the modified carbon nanotube according to any one of claims 1 to 4, wherein the method comprises: firstly, the polycation and the carbon nano tube are compounded to obtain a polycation/carbon nano tube compound, then the compound and the polyanion are uniformly blended, and the modified carbon nano tube is formed by utilizing the electrostatic bridging action of the polyanion and the polycation.

6. The method of claim 5, wherein when the polycation is chitosan and the polyanion is sodium carboxymethyl cellulose, the method comprises: covalently grafting chitosan to a carbon nano tube to form a chitosan grafted carbon nano tube; then adding chitosan grafted carbon nano tubes into the sodium carboxymethyl cellulose solution, and uniformly mixing by ultrasonic and stirring; finally, freeze drying to obtain the modified carbon nano tube.

7. The method for preparing modified carbon nanotubes according to claim 5 or 6, wherein the solution of sodium carboxymethyl cellulose is a solution of sodium carboxymethyl cellulose dissolved in acetic acid.

8. A polymer-based composite material, characterized in that the composite material is prepared by introducing modified carbon nanotubes into a polymer matrix, wherein the modified carbon nanotubes are the modified carbon nanotubes of any one of claims 1 to 4, or the modified carbon nanotubes prepared by the method of any one of claims 5 to 7.

9. The polymer-based composite material according to claim 8, wherein the polymer matrix is starch, chitosan or cellulose;

10. A method for improving the dispersibility of carbon nanotubes in a polymer matrix is characterized by comprising the following steps: introducing a polycation and a polyanion into the carbon nano tube, and obtaining a modified carbon nano tube with a three-dimensional porous structure by utilizing the covalent action between the polycation and the carbon nano tube and the electrostatic bridging action of the polyanion and the polycation; and then introducing the obtained modified carbon nano tube into a high molecular matrix.