A method for preparing intrinsic semiconductor carbon nanotubes

Abstract

The application discloses a preparation method of intrinsic semiconductor carbon nanotube material. By using degradable conjugated polymer to replace commonly used separation polymer, separation and purification of semiconductor carbon nanotube and removal of surface polymer can be realized. The polymer used in the application can be quickly degraded under weak acid condition on the basis of ensuring the separation yield and high purity of the semiconductor carbon nanotube, and is decomposed into small molecules, so that the semiconductor carbon nanotube can show its intrinsic performance. Therefore, the semiconductor carbon nanotube material with intrinsic performance can be prepared by using the method of the application, the process is simple, the condition is mild, and the method is stable, efficient and can be widely applied to the carbon-based electronic field.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube electronics, and more specifically to a method for preparing intrinsic semiconductor carbon nanotubes. Background Technology

[0002] Single-walled semiconducting carbon nanotubes are widely used in field-effect transistors, sensors, and other applications due to their excellent electrical properties. However, commercially available single-walled carbon nanotubes are a mixture of metallic and semiconducting carbon nanotubes. Therefore, the methods and technologies for separating and purifying semiconducting carbon nanotubes are of paramount importance.

[0003] Among existing methods for the separable preparation of semiconductor carbon nanotubes, the conjugated polymer encapsulation method offers advantages such as high efficiency, high purity, and mass production capability. Commonly used conjugated polymers include polyfluorene, polycarbazole, and polythiophene. The widely accepted mechanism for separating semiconductor carbon nanotubes using the conjugated polymer encapsulation method is that the π-π interaction between the conjugated structure of the polymer backbone and the carbon nanotubes causes dispersion, while the metallic carbon nanotubes aggregate due to stronger dipole interactions. Under centrifugal force, these aggregates, along with other impurities, settle to the bottom of the centrifuge tube, and the supernatant becomes a high-purity semiconductor carbon nanotube solution. This method is relatively simple, and the extracted high-purity semiconductor carbon nanotube solution can be used to fabricate various devices. However, the polymer encapsulating the surface of the semiconductor carbon nanotubes is tightly bound to the carbon nanotubes and difficult to remove, preventing them from exhibiting their excellent intrinsic properties and thus affecting the fabrication and performance of subsequent transistor devices.

[0004] In existing carbon-based electronic fabrication processes, post-processing methods such as solvent cleaning and immersion, hot steam cleaning, and annealing are used to remove polymers adhering to the surface of carbon nanotubes as much as possible to improve transistor performance. Solvent cleaning and immersion, and hot steam cleaning utilize the interaction between good solvents and polymers to remove polymers from the carbon nanotube surface, while annealing is often carried out under high temperature and vacuum conditions to break down the polymer molecular chains. These methods are all effective means of removing polymers from the surface of carbon nanotubes, but they require multiple, long-term, and high-temperature processes, which can easily introduce defects into the carbon nanotubes; moreover, the removal effect on tightly packed polymers is limited. Therefore, how to stably and effectively remove polymers from the surface of semiconductor carbon nanotubes to obtain carbon nanotube materials with intrinsic properties is an urgent problem to be solved, which is of great significance for the fabrication of high-performance carbon nanotube transistor devices. Summary of the Invention

[0005] To address the above problems, this invention proposes a method for preparing intrinsic semiconductor carbon nanotubes using a biodegradable conjugated polymer, specifically comprising the following steps:

[0006] Step 1: Dissolve the biodegradable conjugated polymer in organic solvent 1, then add carbon nanotube raw material, ultrasonically crush and centrifuge to obtain a high-purity semiconductor carbon nanotube solution.

[0007] Step 2: Centrifuge the high-purity carbon nanotube solution obtained in Step 1 multiple times to obtain an ultra-high-purity semiconductor carbon nanotube solution.

[0008] Step 3: Add an acidic solution to the ultra-high purity semiconductor carbon nanotube solution obtained in Step 2 to precipitate carbon nanotubes and obtain intrinsic semiconductor carbon nanotubes.

[0009] The molecular backbone structure of the aforementioned biodegradable conjugated polymer includes fluorenyl groups, bipyridines, and imine bonds (C=N).

[0010] Among them, the above-mentioned biodegradable conjugated polymers have the general formula (1):

[0011]

[0012] In general formula (1), n ​​is the number of repeating units in the polymer, and Ar1 and Ar2 are selected from one or more of the following aromatic structures:

[0013]

[0014] Among them, one of Ar1 and Ar2 is Q1, and the other is selected from Q2, Q3 or Q4, and R1 or R2 is C. n H 2n+1 Where 0≤n≤30, preferably 0≤n≤12.

[0015] When Ar1 is Q1, Ar2 is any one of Q2, Q3, or Q4; when Ar2 is Q1, Ar1 is any one of Q2 or Q3.

[0016] The mass ratio of the biodegradable conjugated polymer to the carbon nanotube raw material is 0.5:1-3:1, preferably 1:1-2:1, and more preferably 1:1.

[0017] In step two above, the single centrifugation step involves centrifuging the high-purity carbon nanotube solution for an extended period and collecting the precipitate. The precipitate is then dispersed in organic solvent two. This single centrifugation step is repeated 2-4 times to achieve a mass ratio of degradable conjugated polymer to carbon nanotubes in the precipitate of 3:1 to 1:1, preferably 1:1. The precipitate obtained from the last centrifugation is then dispersed in organic solvent three to obtain an ultra-high purity semiconducting carbon nanotube solution.

[0018] In step three above, after the carbon nanotube precipitate is formed, the carbon nanotube precipitate is collected and washed with organic solvent four to obtain intrinsic semiconductor carbon nanotubes.

[0019] Wherein, the above-mentioned organic solvent one, organic solvent two and organic solvent four are selected from any one or more of toluene, xylene, dimethylformamide, tetrahydrofuran, chloroform, dichloromethane, dichloroethane or trichloroethane.

[0020] The three organic solvents mentioned above are selected from one or more of toluene, xylene, tetrahydrofuran, or chloroform.

[0021] The acidic solution mentioned above is selected from one of trifluoroacetic acid, trifluoromethanesulfonic acid, acetic acid, hydrofluoric acid, hydrochloric acid, sulfuric acid, or nitric acid.

[0022] This invention enables the efficient extraction of high-purity semiconductor carbon nanotubes and the removal of polymers from the surface of carbon nanotubes, yielding intrinsic semiconductor carbon nanotube materials that meet the requirements of high-performance carbon-based electronics for clean carbon nanotube surfaces. Through molecular structure and synthetic process design, an intrinsically biodegradable conjugated polymer was prepared to replace commonly used separation polymers for the separation and purification of semiconductor carbon nanotubes and the removal of surface-coated polymers. Specifically, imine bonds are introduced into the polymer backbone, with C=N directly connected to aromatic heterocycles, ensuring the conjugated structure of the polymer backbone and guaranteeing the separation yield and high purity of the semiconductor carbon nanotubes. Furthermore, the C=N bonds can be chemically degraded into small molecule monomers under weakly acidic conditions. This means that the polymer coating on the surface of the semiconductor carbon nanotubes can be destroyed by washing with a mild acidic solvent, followed by washing with a good solvent containing the monomers to completely remove residual impurities from the carbon nanotube surface, thus preparing intrinsic semiconductor carbon nanotubes. Attached Figure Description

[0023] The above and other objects, features and advantages of the present invention will become clearer from the following description of the technical solution of the present invention with reference to the accompanying drawings, in which:

[0024] Figure 1 This is a flowchart illustrating the steps involved in preparing intrinsic semiconductor carbon nanotubes according to the present invention.

[0025] Figure 2 This is a schematic diagram of the nucleophilic addition reaction of fluorene diamine and bipyridine dialdehyde in this invention;

[0026] Figure 3 The NMR spectrum of the biodegradable conjugated polymer prepared in this invention;

[0027] Figure 4 The molecular weight and distribution spectrum of the conjugated polymer prepared in this invention;

[0028] Figure 5The UV-Vis absorption spectra of the conjugated polymer prepared for the invention before and after acid addition;

[0029] Figure 6 The absorption spectrum of the conjugated polymer in the invention in the separated semiconductor carbon nanotube solution;

[0030] Figure 7 TEM image of the carbon nanotube material prepared in this invention before acid addition;

[0031] Figure 8 TEM image of the carbon nanotube material prepared in this invention after acid addition; Detailed Implementation

[0032] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the drawings, the same elements are represented by the same reference numerals, and the various parts in the drawings are not drawn to scale. Furthermore, some well-known parts may not be shown.

[0033] This invention provides a method for preparing intrinsic semiconductor carbon nanotubes using a biodegradable conjugated polymer, specifically including the following steps:

[0034] Step 1: Dissolve the biodegradable conjugated polymer in toluene. In other embodiments, the biodegradable conjugated polymer can also be dissolved in one or more of xylene, dimethylformamide, dichloromethane, and chloroform. Then, add the carbon nanotube raw material, ultrasonically break it up, and centrifuge it. The ultrasonic power is 50-300W, the time is 10-60 min, the duty cycle is 20%-80%, the temperature is -50 to 40 degrees Celsius, the centrifugal force is 10000g-50000g, the time is 20 min-120 min, and the temperature is -10 to 30 degrees Celsius. The mass ratio of the biodegradable conjugated polymer to the carbon nanotube raw material is 1:1. In other embodiments, the mass ratio can be in the range of 0.5:1-3:1. After centrifugation, take 90% of the supernatant to obtain a high-purity semiconductor carbon nanotube solution.

[0035] Among them, the molecular backbone structure of the above-mentioned biodegradable conjugated polymer includes fluorenyl, bipyridine and imine C=N bonds, and the biodegradable conjugated polymer has the general formula (1):

[0036]

[0037] In general formula (1), n ​​is the number of repeating units in the polymer, and Ar1 and Ar2 are selected from one or more of the following aromatic structures:

[0038]

[0039] Among them, one of Ar1 and Ar2 is Q1, and the other is selected from Q2, Q3 or Q4, and R1 or R2 is C. n H 2n+1 Where 0≤n≤30, preferably 0≤n≤12.

[0040] When Ar1 is Q1, Ar2 is any one of Q2, Q3, or Q4; when Ar2 is Q1, Ar1 is any one of Q2 or Q3.

[0041] In this embodiment, the above-mentioned degradable conjugated polymer can be prepared by the following method: a nucleophilic addition reaction of fluorene diamine and bipyridine dialdehyde in an organic solvent is carried out to prepare the degradable conjugated polymer. Figure 2 This is a schematic diagram of the nucleophilic addition reaction of fluorene diamine and bipyridine dialdehyde. As can be seen, to ensure the conjugated structure of the main chain, this embodiment designs a main chain structure containing fluorene and bipyridine, and introduces meta-imine bonds into the main chain. Compared to the ortho-structure, this structure has a more compliant and regular structure, which is beneficial for the entanglement of polymer molecular chains with carbon nanotubes. The preparation method of the biodegradable conjugated polymer in this embodiment specifically includes the following steps:

[0042] Under nitrogen atmosphere and at room temperature, in a three-necked flask equipped with a magnetic stirrer, thermometer, and condenser, 212.2 mg (1 mmol) of 2,2'-bipyridine-5,5'-dicarboxaldehyde (M2) and 30 g of toluene were added and stirred until completely dissolved. In other embodiments, 2,2'-bipyridine-5,5'-dicarboxaldehyde can also be added to xylene, dimethylformamide, dichloromethane, or chloroform and stirred until dissolved. 420.69 mg (1 mmol) of 2,7-diamino-9,9'-n-octylfluorene (M1) was added, with an initial solid content of 2 wt%. After complete dissolution, 2 g of anhydrous lithium chloride was added as a desiccant. In other embodiments, the desiccant can also be selected from anhydrous calcium chloride, sodium bicarbonate, or molecular sieves.

[0043] In this embodiment, the molar ratio of M1 to M2 is 1:1. In other embodiments, the molar ratio of M1 and M2 is 1:1.

[0044] The molar ratio of M2 is (0.95-1.02):1, and the initial solid content is 1%-10%. After stirring the above solution at room temperature for 12 hours, 3 mg of salicylaldehyde is added, and the solution is heated to 110°C and refluxed for 4 hours. In other embodiments, the stirring time at room temperature can be 2-24 hours, and the heating and stirring time during reflux is 1-12 hours.

[0045] After the reaction, lithium chloride was removed by filtration through a membrane filter, yielding a clear yellow filtrate. An equivalent amount of methanol was added to the filtrate, followed by stirring and standing. Recrystallization was then carried out to precipitate a yellow precipitate, which was then filtered through a membrane filter and vacuum dried to obtain a yellow powder, which is the biodegradable conjugated polymer P1. In other embodiments, recrystallization can be performed by rotary evaporation of the filtrate.

[0046] Degradability test: P1 obtained above was dissolved in toluene to obtain a yellow solution. After adding 3% trifluoroacetic acid (TFA), the solution color rapidly lightened to almost colorless, indicating that the surface polymer decomposed.

[0047] In another embodiment, a biodegradable conjugated polymer can be prepared by nucleophilic addition reaction of equimolar amounts of fluorene dialdehyde and bipyridine diamine in an organic solvent, with subsequent steps consistent with those described above. In other embodiments, the bipyridine diamine can be ortho-, meta-, or para-bipyridine diamine.

[0048] Figure 2 This is the NMR spectrum of P1. 1 H NMR (300MHz, Chloroform-d), 10.19 (s,

[0049] 1H),8.88-8.85(m,1H),8.65-8.62(m,1H),8.38-8.35(m,1H),8.05-8.03(m,2H),7.79 -7.76(m,2H),7.39-7.38(m,4H),2.05-1.89(m,4H),1.25-0.97(m,20H),0.82 -0.78(m,10H); Figure 3 This is a graph showing the molecular weight and its distribution, where M... n =27848 g / mol, M w =55121 g / mol, PDI = 2. As can be seen from the figure above, the high molecular weight target polymer was finally obtained.

[0050] Figure 4 The figures show the UV-Vis absorption spectra of the polymer P1 dissolved in toluene, the absorption spectrum of the solution after adding TFA for 1 minute, and the absorption spectra of the two monomers M1 and M2 required for the preparation of P1 dissolved in toluene. The figures show that the P1 solution has an absorption peak at 430 nm, which disappears rapidly after the addition of TFA, and two absorption peaks appear near 300 nm and 320 nm, indicating that P1 has degraded under acid washing conditions. The toluene solutions of M1 and M2 have absorption peaks at 300 nm and 320 nm, respectively, corresponding to the two main decomposition products of P1, indicating that P1 has degraded into monomers and can be recovered after post-treatment.

[0051] Step 2: The high-purity carbon nanotube solution obtained in Step 1 is centrifuged multiple times to obtain an ultra-high-purity semiconductor carbon nanotube solution. Each centrifugation step involves prolonged centrifugation of the high-purity carbon nanotube solution and collection of the precipitate. The precipitate is then dispersed in toluene. The ultrasonic power is 10W-100W, the ultrasonic time is 2-10 minutes, the duty cycle is 20%-80%, the temperature is -50 to 40 degrees Celsius, the centrifugation weight is 30,000g-300,000g, the time is 10-30 hours, and the temperature is -10 to 30 degrees Celsius. In other embodiments, the precipitate may also be dispersed in one or more of xylene, dimethylformamide, dichloromethane, or chloroform.

[0052] The above single centrifugation step is repeated 2-4 times to achieve a 1:1 mass ratio of biodegradable conjugated polymer to carbon nanotubes in the precipitate. In other embodiments, the mass ratio of biodegradable conjugated polymer to carbon nanotubes can be in the range of 3:1 to 1:1. The precipitate obtained from the last centrifugation is dispersed in toluene to obtain an ultra-high purity semiconducting carbon nanotube solution of >99.99%. In other embodiments, the precipitate may also be dispersed in one or more of xylene, tetrahydrofuran, or chloroform.

[0053] Step 3: Add 0.3 vol% trifluoroacetic acid to the ultra-high purity semiconductor carbon nanotube solution obtained in Step 2 as an acidic solution to precipitate carbon nanotubes. Collect the carbon nanotube precipitate. In other embodiments, the acidic solution may also be one of trifluoroacetic acid, trifluoromethanesulfonic acid, acetic acid, hydrofluoric acid, hydrochloric acid, sulfuric acid, or nitric acid. Then, use toluene as a cleaning agent to clean the solution and obtain intrinsic semiconductor carbon nanotubes. In other embodiments, the cleaning agent may also be one or more of xylene, dimethylformamide, dichloromethane, or chloroform.

[0054] Figure 6 This is the absorption spectrum of the solution obtained by separating arc-discharged carbon nanotubes from conjugated polymers. It can be seen that no absorption peak appears in the carbon nanotube solution between 600-800 nm, while an absorption peak appears between 800-1200 nm in the arc-discharged raw material containing semiconductor carbon nanotubes (S). 22 The typical absorption peak indicates that the separated semiconductor carbon nanotube solution has high semiconductor purity.

[0055] Figure 7 and Figure 8 These are TEM images of the carbon nanotube material prepared in this embodiment before and after acid addition. It can be seen that before acid addition, the carbon nanotube wall was covered with a large amount of polymer, while after acid addition, the carbon nanotube wall was not covered with polymer and was clearly visible.

[0056] The preparation method of this invention enables efficient extraction of high-purity semiconductor carbon nanotubes and meets the requirements of high-performance carbon-based electrons for clean carbon nanotube surfaces. Through molecular structure and synthesis process design, this invention uses an intrinsically biodegradable conjugated polymer to replace commonly used separation polymers to achieve the separation and purification of semiconductor carbon nanotubes and the removal of surface-coated polymers. By introducing imine bonds into the polymer backbone, C=N directly connects to aromatic heterocycles, ensuring the conjugated structure of the polymer backbone and guaranteeing the separation yield and high purity of semiconductor carbon nanotubes. Furthermore, the C=N bonds can be chemically degraded into small molecule monomers under weakly acidic conditions. That is, the polymer coated on the surface of the semiconductor carbon nanotubes can be destroyed by washing with a mild acidic solvent, and then the residual impurities on the carbon nanotube surface can be completely removed by washing with a good solvent of the monomers, thereby preparing intrinsically semiconductor carbon nanotubes.

[0057] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing intrinsic semiconductor carbon nanotubes, characterized in that, Includes the following steps: Step 1: Dissolve the biodegradable conjugated polymer in organic solvent 1, then add carbon nanotube raw material, ultrasonically crush and centrifuge to obtain a high-purity semiconductor carbon nanotube solution. The ultrasonic crushing power is 50-300W, the time is 10-60min, the duty cycle is 20%-80%, and the temperature is -50~40 degrees Celsius. The centrifugation force is 10000g-50000g, the time is 20min-120min, and the temperature is -10~30 degrees Celsius. Step 2: The high-purity semiconductor carbon nanotube solution obtained in Step 1 is centrifuged multiple times to obtain an ultra-high-purity semiconductor carbon nanotube solution. Each centrifugation step involves centrifuging the high-purity carbon nanotube solution at a centrifugal force of 30,000 g-300,000 g for 10-30 h at a temperature of -10 to 30 degrees Celsius and collecting the precipitate. The precipitate is then dispersed in organic solvent two. This single centrifugation step is repeated 2-4 times to achieve a mass ratio of degradable conjugated polymer to carbon nanotubes of 3:1-1:1 in the precipitate. The precipitate obtained from the final centrifugation is then dispersed in organic solvent three to obtain an ultra-high-purity semiconductor carbon nanotube solution. Step 3: Add an acidic solution to the ultra-high purity semiconductor carbon nanotube solution obtained in Step 2 to precipitate carbon nanotubes. Collect the carbon nanotube precipitate and wash it with organic solvent IV to obtain intrinsic semiconductor carbon nanotubes; wherein the biodegradable conjugated polymer has the general formula (1): （1） In general formula (1), n ​​is the number of repeating units in the polymer, and Ar1 and Ar2 are selected from one or more of the following aromatic structures: wherein R1or R2is C n H 2n+1 wherein 0n30; when Ar1structure is Q1, Ar2structure is any one of Q2, Q3, Q4structure, when Ar2structure is Q1, Ar1structure is any one of Q2, Q3structure.

2. The method of producing intrinsic semiconductor carbon nanotubes according to claim 1, wherein R1or R2is C n H 2n+1 wherein 0 < n < 12.

3. The method for preparing intrinsic semiconductor carbon nanotubes according to any one of claims 1-2, characterized in that, The mass ratio of the biodegradable conjugated polymer to the carbon nanotube raw material is 0.5:1-3:

1.

4. The method of producing intrinsic semiconductor carbon nanotubes according to claim 3, wherein The mass ratio of the biodegradable conjugated polymer to the carbon nanotube raw material is 1:1-2:

1.

5. The method for preparing intrinsic semiconductor carbon nanotubes according to claim 1, characterized in that, Organic solvent one and organic solvent two are selected from any one or more of toluene, xylene, dimethylformamide, tetrahydrofuran, chloroform, dichloromethane, dichloroethane, or trichloroethane; organic solvent three is selected from any one or more of toluene, xylene, tetrahydrofuran, or chloroform.

6. The method for preparing intrinsic semiconductor carbon nanotubes according to claim 1, characterized in that, The organic solvent is selected from any one or more of toluene, xylene, dimethylformamide, tetrahydrofuran, chloroform, dichloromethane, dichloroethane, or trichloroethane.

7. The method for preparing intrinsic semiconductor carbon nanotubes according to claim 1, characterized in that, The acidic solution is selected from one of the following: trifluoroacetic acid, trifluoromethanesulfonic acid, acetic acid, hydrofluoric acid, hydrochloric acid, sulfuric acid, and nitric acid.

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