A method for separating single-handed structure cnts based on pfo-azo polymer

Abstract

The application provides a single chirality structure CNTs separation method based on PFO-Azo polymer, and relates to the technical field of nanometer material separation and preparation.The single chirality structure CNTs separation method based on PFO-Azo polymer comprises the steps of CNTs dispersion, light control separation, target CNTs separation, PFO-Azo polymer recovery and the like.The application utilizes a light field to adjust the configuration of PFO-Azo polymer, dynamically controls the combination / release behavior of the PFO-Azo polymer to CNTs through light-induced molecular structure change, realizes efficient separation of specific single chirality (6,5) CNTs, makes the purity of the CNTs reach 98.5%, and makes the recovery rate of the PFO-Azo polymer reach 85.2%, thereby significantly improving the separation efficiency and ensuring the recyclable use ability of the polymer.The separation method can reduce the separation cost of single chirality CNTs and reduce the separation energy consumption, and compared with a traditional process, the cost is reduced by about 70%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterial separation and preparation, and particularly relates to a single-handed structure CNTs separation method based on PFO-Azo polymer. BACKGROUND

[0002] Since the discovery of single-walled carbon nanotubes (SWCNTs), they have rapidly become a research hotspot in the fields of condensed matter physics, nanomaterials and devices due to their one-dimensional nanostructure, quantum confinement effect and unique physical and chemical properties. The electronic structure of SWCNTs exhibits high tunability: the band gap can be regulated by the chirality parameter (n, m), and the carrier mobility is significantly higher than that of traditional semiconductor materials. In addition, SWCNTs are sensitive to light direction and have significant nonlinear optical effects, which make them have broad application prospects in the fields of microelectronic devices, optoelectronics (such as infrared / visible light detectors), biosensing platforms and catalytic carriers.

[0003] The electronic behavior of SWCNTs is closely related to their chirality parameter (n, m). When m-n=3k (k∈Z), SWCNTs exhibit metallic properties and are suitable for conductive materials and nanointerconnections; when m-n≠3k, SWCNTs exhibit semiconducting properties and can be used in transistors, photodetectors and logic circuits. SWCNTs with different chirality have significant differences in properties such as band gap width and light absorption wavelength. However, existing synthesis technologies (such as chemical vapor deposition, CVD) are difficult to directly prepare SWCNTs with uniform chirality, and the products usually contain dozens of different chirality structures. This structural heterogeneity leads to fluctuations in material performance, which seriously restricts the application of SWCNTs in precision electronic / optical devices. Therefore, developing efficient and low-cost chirality separation technology is a core challenge to promote the practical application of SWCNTs.

[0004] At present, the chirality separation technology of SWCNTs mainly depends on the differences in physical and chemical properties, but all have certain deficiencies.

[0005] Ultra-high speed centrifugal separation method uses surfactants or polymers to modify SWCNTs, and separates them by density difference in the centrifugal field. For example, the invention patent with publication number CN 115676807 A discloses a gradient ultra-high speed centrifugal purification method for single-chiral carbon nanotubes. The gradient ultra-high speed centrifugal purification method includes: uniformly dispersing a polymer and single-walled carbon nanotube raw material in a solvent to form a dispersion liquid, and performing centrifugal treatment to obtain a supernatant of the dispersion liquid; and performing ultra-high speed centrifugal treatment on the supernatant of the dispersion liquid to form a solid and a liquid phase system enriched with single-chiral carbon nanotubes, thereby obtaining high-purity single-chiral carbon nanotubes. For another example, the invention patent with publication number CN 116062736 B discloses a method for improving the extraction efficiency of single-chiral carbon nanotubes, a reagent composition and an application. The method includes: mixing an enhanced polymer, a chiral extractive polymer, carbon nanotube raw material and a solvent, and then separating the obtained mixture to obtain a high-concentration single-chiral carbon nanotube solution. However, the ultra-high speed centrifugal separation method needs to rely on high-strength centrifuges (>200000g), which has high equipment cost, and the selectivity for chiral structure is limited, and the separation product still has mixed.

[0006] Dielectrophoresis (DEP) method separates metallic and semiconducting SWCNTs based on the polarization difference in a non-uniform electric field. For example, the invention patent with publication number CN 118829330 A discloses a single-chiral carbon nanotube array film based on dielectrophoresis method, preparation method and application thereof. The preparation method includes: preparing a high-purity single-chiral carbon nanotube solution; preparing an electrophoresis electrode structure, which includes a substrate, a plurality of electrophoresis electrodes are etched on the substrate, and a plurality of devices are etched between adjacent electrophoresis electrodes; connecting a sinusoidal voltage source to the electrophoresis electrodes, and adding the high-purity single-chiral carbon nanotube solution into the gap between the electrophoresis electrodes for electrophoresis, so that the single-chiral carbon nanotubes are arranged in an array in the channel of the device; after electrophoresis, the substrate surface is washed and dried to obtain a single-chiral carbon nanotube array film distributed in the channel of the electrophoresis electrode structure device. However, DEP method needs precise microelectrode design, which has high equipment complexity and is difficult to scale up production, and the yield is limited.

[0007] Gel chromatography separates carbon nanotubes by the adsorption capacity difference of the gel chromatography column. For example, the invention patent with publication number CN117486205 A discloses a method for separating single chiral carbon nanotube mirror bodies, which comprises the following steps: (1) dispersing carbon nanotube raw materials into a solution of a composite surfactant to obtain a carbon nanotube dispersion liquid; (2) using gel chromatography for step-by-step elution to separate the carbon nanotube dispersion liquid, and collecting the separation product to obtain single chiral carbon nanotube mirror bodies; wherein the solution of the composite surfactant comprises cholic acid, a first surfactant and an optional second surfactant, and a solvent; the first surfactant is selected from one or more of sodium octyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate and sodium n-hexadecyl sulfate; the second surfactant is selected from one or more of sodium cholate, sodium cholate hydrate, sodium dehydrocholate, sodium deoxycholate, sodium lithocholate, sodium hyodeoxycholate and sodium chenodeoxycholate. However, gel chromatography relies on high-cost surfactants, and the elution process is complex, and the separation efficiency is significantly affected by the solvent.

[0008] Polymer coating + replacement method takes advantage of the selective coating of specific polymers (such as PFO, F8BT) on target chiral SWCNTs, and then removes impurities by solvent replacement. For example, the invention patent with publication number CN112812507 A discloses a single chiral carbon nanotube-thiophene polymer composite material and a preparation method thereof, which successfully prepares a thiophene polymer / (6,5) SWCNT nanocomposite containing high-purity single chiral carbon nanotubes by using a specific thiophene polymer to replace PFO-BP y on PFO-BP y (6,5) SWCNT. However, the polymer coating + replacement method is complicated, time-consuming, only suitable for laboratory use, and requires a large amount of chemical solvents, which is not environmentally friendly.

[0009] Therefore, the existing single chiral carbon nanotube separation technology generally faces problems such as high cost, insufficient selectivity, difficulty in scaling up, and environmental burden, which restricts the industrial application of carbon nanotubes. Therefore, how to develop a low-cost and high-efficiency single chiral structure carbon nanotube separation method based on a low-cost, high-throughput and green and sustainable separation strategy is one of the technical problems to be solved in the field. SUMMARY

[0010] Therefore, the present application provides a single chiral structure CNTs separation method based on PFO-Azo polymer. The method takes advantage of the controllable configuration switching ability of PFO-Azo polymer and its combination-separation characteristics with CNTs to drive the adsorption-desorption process of CNTs, and adjusts the parameters such as light exposure time and centrifugal rate to realize high-purity and high-efficiency separation of single chiral structure CNTs.

[0011] The application provides a single-handed structure CNTs separation method based on a PFO-Azo polymer, and specifically comprises the following steps.

[0012] S1, CNTs dispersion:

[0013] At room temperature, CNTs powder is added into a toluene solution containing a PFO-Azo polymer, low-speed stirring is performed until the CNTs are dispersed, and then ultraviolet light is irradiated to obtain a PFO-Azo polymer-CNTs mixture system;

[0014] S2, light-controlled separation:

[0015] Different wavelengths of light sources are irradiated at different heights in the vertical direction of a transparent centrifugal tube, and then the PFO-Azo polymer-CNTs mixture is centrifuged under the condition of light source irradiation, supernatant is collected after centrifugation, and enrichment of target chiral CNTs is realized;

[0016] The light source is arranged as follows: 4-10 cm from the bottom of the tube, 365±1 nm ultraviolet light, and an irradiation intensity of 5-15 mW / cm 2 ; 0-4 cm from the bottom of the tube, 470±1 nm blue light, and an irradiation intensity of 5-10 mW / cm 2 ;

[0017] S3, target CNTs separation:

[0018] 450±1 nm visible light is irradiated on the supernatant for 3-8 min, the PFO-Azo polymer is restored to a trans configuration, target CNTs are released, centrifugation is performed, and target CNTs are separated;

[0019] S4, PFO-Azo polymer recovery:

[0020] The supernatant in step S3 is irradiated under 470 nm blue light for 30-60 min, low-speed centrifugation is performed, supernatant is collected, and a PFO-Azo polymer solution is obtained.

[0021] Preferably, in step S1, the ratio of the CNTs, the PFO-Azo polymer, and the toluene solution is (0.8-1.2) mg:(4.5-5.5) mg:(9.5-10.5) mL, and more preferably 1 mg:5 mg:10 mL; the low-speed stirring speed is 200-300 rpm, and the stirring time is 30-35 min, and more preferably 30 min; the ultraviolet light irradiation time is 58-62 min, and more preferably 60 min; the ultraviolet light wavelength is 365 nm, and the light irradiation intensity is 9.5-10.5 mW / cm 2 , and more preferably 10 mW / cm 2 .

[0022] Preferably, in step S1, the PFO-Azo polymer is an orange-yellow solid, with the structure of poly[(9,9-dioctylfluorene)-alt-(azo-phenylene)], a molecular weight Mw = 30,000-80,000 Da, and UV-Vis absorption spectrum showing a significant reversible absorption peak shift between 365 nm and 450 nm; FTIR confirms the presence of -N=N- stretching vibration, and it is well soluble in toluene, chloroform.

[0023] Preferably, in step S1, the PFO-Azo polymer preparation method specifically includes the following steps:

[0024] After mixing 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, Pd(PPh3)4, K2CO3 with a solvent, performing Suzuki coupling reaction, cooling, precipitating, washing, purifying after the reaction is completed, the PFO-Azo polymer is obtained;

[0025] The solvent is composed of deionized water and THF in a volume ratio of (0.9-1.1):(2.9-3.1), more preferably 1:3; the molar ratio of 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, K2CO3 is (0.9-1.1):(0.9-1.1):(1.8-2.2), more preferably 1:1:2; the amount of Pd(PPh3)4 is 4.8-5.2% of the total moles of 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, K2CO3, more preferably 5%; the amount of solvent is 8-10 times the volume (mL) of the total moles of 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, K2CO3, more preferably 9 times; the Suzuki coupling reaction is carried out under a nitrogen atmosphere, with the reaction condition being an oil bath at 73-77°C, more preferably 75°C, and the reaction time being 10-14h, more preferably 12h; the precipitating is performed using methanol (purity ≥99.5%), the washing is performed using chloroform (purity ≥99.0%), and the purification is performed by column chromatography using a 100-200 mesh silica gel column.

[0026] Preferably, in step S2, the material of the centrifuge tube is quartz or polycarbonate, with a transmittance ≥90%.

[0027] Preferably, in step S2, the centrifugal speed is 950-1050 rpm, more preferably 1000 rpm, and the centrifugal time is 4.5-5.5 min, more preferably 5 min.

[0028] Preferably, in step S3, the centrifugal speed is 2950-3050 rpm, more preferably 3000 rpm, and the centrifugal time is 4.5-5.5 min, more preferably 5 min.

[0029] Preferably, in step S4, the centrifugal speed is 2950-3050 rpm, more preferably 3000 rpm, and the centrifugal time is 4.5-5.5 min, more preferably 5 min.

[0030] Compared with the prior art, the present application has the beneficial technical effects of:

[0031] The present application separates (6,5) CNTs based on the dynamic separation method of photo-responsive PFO-Azo polymer, avoids traditional chemical modification and surfactant dependence, and realizes controllable, reversible and efficient selective separation of (6,5) CNTs.

[0032] The present application utilizes light field to adjust the configuration of PFO-Azo polymer, dynamically controls the binding / release behavior of CNTs through light-induced molecular structure change, and realizes efficient separation of (6,5) CNTs.

[0033] The present application realizes efficient separation of specific single chiral (6,5) CNTs through light irradiation, so that the purity of (6,5) CNTs reaches 98.5%, and the recovery rate of PFO-Azo polymer reaches 85.2%, which significantly improves the separation efficiency and ensures the recyclable use of the polymer.

[0034] The separation method of the present application can reduce the separation cost of single chiral (6,5) CNTs and reduce the energy consumption of centrifuges, and compared with the traditional process, the cost is reduced by about 70%. BRIEF DESCRIPTION OF DRAWINGS

[0035] The present application will be further described below in conjunction with the description of the drawings.

[0036] Figure 1 The present application is based on the single chiral structure CNTs separation method of PFO-Azo polymer. DETAILED DESCRIPTION

[0037] The technical solutions of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0038] The application provides a single chirality structure CNTs separation method based on a PFO-Azo polymer, which comprises the steps of CNTs dispersion, light-controlled separation, target CNTs separation and PFO-Azo polymer recovery.

[0039] The first step of the application is CNTs dispersion, which specifically comprises the following steps:

[0040] At room temperature of 20-25 DEG C, SWCNTs powder is added into a toluene solution containing the PFO-Azo polymer, and then low-speed stirring is conducted until the CNTs are dispersed, and then UV light is irradiated to obtain a PFO-Azo polymer-CNTs mixture system.

[0041] The CNTs are CVD synthesis products; the ratio of the CNTs, the PFO-Azo polymer and the toluene solution is (0.8-1.2) mg:(4.5-5.5) mg:(9.5-10.5) mL, preferably 1 mg:5 mg:10 mL; the low-speed stirring speed is 200-300 rpm, and the stirring time is 30-35 min, preferably 30 min; the UV light irradiation time is 58-62 min, preferably 60 min, the UV light wavelength is 365 nm, and the light irradiation intensity is 9.5-10.5 mW / cm 2 , preferably 10 mW / cm 2 .

[0042] In some specific embodiments of the application, after the PFO-Azo polymer-CNTs mixture system is obtained, it is enriched and separated through centrifugal classification or selective precipitation, so that the pre-separation of specific chirality structure CNTs is further realized, and the specific chirality structure CNTs are (6,5) type CNTs or (7,5) type CNTs.

[0043] The PFO-Azo polymer is an orange-yellow solid, the structure is poly[(9,9-dioctylfluorene)-alt-(azo-phenylene)], the molecular weight Mw is 30,000-80,000 Da, the UV-Vis absorption spectrum shows that the PFO-Azo polymer has obvious reversible absorption peak migration between 365 nm and 450 nm; the FTIR confirms that the -N=N- stretching vibration exists, and the solubility is good, and the PFO-Azo polymer can be stably dissolved in toluene and chloroform.

[0044] The application further provides a preparation method of the PFO-Azo polymer, which specifically comprises the following steps:

[0045] Suzuki coupling reaction is carried out after mixing 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, Pd(PPh3)4, K2CO3 with a solvent, and after the reaction is completed, cooling, precipitation, washing, purification are carried out to obtain the PFO-Azo polymer

[0046] The solvent is composed of deionized water and THF in a volume ratio of (0.9-1.1):(2.9-3.1), preferably 1:3; the molar ratio of 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, K2CO3 is (0.9-1.1):(0.9-1.1):(1.8-2.2), more preferably 1:1:2; the amount of Pd(PPh3)4 is 4.8-5.2% of the total moles of 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, K2CO3, more preferably 5%; the amount of the solvent is 8-10 times the volume (mL) of the total moles of 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, K2CO3, more preferably 9 times; the Suzuki coupling reaction is carried out under a nitrogen atmosphere, and the reaction conditions are an oil bath at 73-77°C, more preferably 75°C, and the reaction time is 10-14h, more preferably 12h; the precipitation is carried out using methanol (purity ≥99.5%); the washing is carried out using chloroform (purity ≥99.0%); the purification is carried out by column chromatography, and the column chromatography uses a 100-200 silica gel column.

[0047] The PFO-Azo polymer of the present application uses azobenzene derivatives as the core structure, and forms a π-conjugated polymer with azobenzene structural units in the side chain or main chain. The PFO-Azo polymer of the present application can be converted from the trans configuration to the cis configuration under 365nm ultraviolet light, and reversibly returns to the trans configuration at a wavelength of 450-600nm, and has controllable configuration switching capability, which is used to drive the adsorption-desorption process of CNTs. The present application utilizes the characteristics of the PFO-Azo polymer, combines LED ultraviolet light source (365nm) and visible light source (450-600nm), dynamically adjusts the light during centrifugation, and realizes high-purity and high-efficiency separation of target CNTs by means of light time, centrifugal rate and other parameters.

[0048] The present application gradually disperses the CNTs into the solution by low-speed stirring, and gradually forms a non-covalent type of π-π interaction between the CNTs and the PFO-Azo polymer, so that the solution remains uniform and stable. During the ultraviolet light irradiation after the stirring is completed, the azobenzene part on the structure of the PFO-Azo polymer gradually changes from the originally stable trans structure to the more curved cis configuration under the action of ultraviolet light. This configuration change changes the flexibility of the PFO-Azo polymer chain and the way it swings in space. With the occurrence of this structure adjustment, the shape of the PFO-Azo polymer begins to fit the chiral CNTs, so that the polymer is more easily adsorbed to a specific structure when the molecules contact, thereby producing selective binding between the PFO-Azo polymer and the target chiral CNTs with a bias. As can be seen, the present application relies on external light field as a control means, and constructs a CNTs dispersion dynamic recognition mechanism which is essentially different from the traditional static coordination method.

[0049] The second step of the present application is light-controlled separation, specifically comprising the following steps: irradiating light sources of different wavelengths at different heights in the vertical direction of the transparent centrifugal tube, and then centrifuging the PFO-Azo polymer-CNTs mixture under the condition of light irradiation, collecting the supernatant after centrifugation, and realizing the enrichment of the target chiral CNTs.

[0050] The light source is set as follows:

[0051] 4-10 cm from the bottom of the tube, 365±1 nm ultraviolet light, irradiation intensity is 5-15 mW / cm 2 Under the condition of ultraviolet light irradiation, the azobenzene structure on the PFO-Azo polymer molecule in the solution will gradually change from the original trans state to cis. This configuration change will adjust the flexibility and spatial swinging mode of the PFO-Azo polymer chain segment. After adjustment, the overall shape of the PFO-Azo polymer becomes more easily fitted to the (6,5) CNTs, and shows strong stability during combination, so that this kind of complex can remain dispersed in the solution without aggregation;

[0052] 0-4 cm from the bottom of the tube, 470±1 nm blue light, irradiation intensity is 5-10 mW / cm 2 When the blue light irradiates the PFO-Azo polymer which is in the cis state, the PFO-Azo polymer will slowly recover to the trans structure. With the configuration changing back to a higher rigidity state, the PFO-Azo polymer chain no longer maintains close combination with non-target chiral CNTs, and the CNTs begin to slowly detach and gradually sink to the bottom under the action of gravity.

[0053] The application is not strictly limited to the material of the centrifugal tube, and any centrifugal tube with light transmittance ≥ 90% can be used for light-controlled separation. In some preferred embodiments of the application, the centrifugal tube is a quartz centrifugal tube or a polycarbonate. The application is not strictly limited to the specific method of setting the light source. In some specific embodiments of the application, the light-controlled separation can be achieved by setting a dual-wavelength LED light source module outside the tube body. The LED light source is controlled by a programmed control unit to start and stop, power and irradiation timing. The light field forms a spatial configuration along the tube axis to induce a gradient.

[0054] The application constructs a spatial gradient field of light-induced configuration transition by irradiating the upper and lower regions with different colors of light, and further divides the action of PFO-Azo polymer configuration regulation into spatial positions. Thus, without additional centrifugal force, different types of CNTs can be separated in the centrifugal tube, the PFO-Azo polymer region in the trans state releases non-target CNTs, and the region in the cis state continues to stably bind the target tube type, so that they are enriched in the upper liquid. The centrifugal speed is 950-1050 rpm, preferably 1000 rpm, and the centrifugal time is 4.5-5.5 min, preferably 5 min.

[0055] The third step of the application is target CNT separation, which specifically includes the following steps: irradiating the supernatant with 450±1nm visible light for 3-8min to make the PFO-Azo polymer restore the trans configuration and release the target CNTs, and then centrifuging and separating the target CNTs; the rotation speed is 3000rpm, and the centrifugal time is 5min.

[0056] The fourth step of the application is PFO-Azo polymer recovery, which specifically includes the following steps: after the enrichment of the target chiral CNTs, the remaining PFO-Azo polymer-CNT complex in the system is enriched in the supernatant. Therefore, irradiating the supernatant with 470nm blue light for 30-60min can make the azobenzene side chain configuration of the PFO-Azo polymer return to the trans state, the π-π interaction between the PFO-Azo polymer and the CNTs is weakened, and the two are separated by low-speed centrifugation. Collecting the supernatant can obtain the FO-Azo polymer solution, and further realize the recovery; the centrifugal speed is 2950-3050rpm, preferably 3000rpm, and the centrifugal time is 4.5-5.5min, preferably 5min.

[0057] In order to further illustrate the application, the following examples are used for detailed description. The raw materials used in the following examples of the application are all commercially available.

[0058] Unless otherwise specified, all tests are repeated 3 times, and the results are expressed as the average value.

[0059] Example 1 Preparation of PFO-Azo polymer, the steps are as follows:

[0060] After mixing 1.0 mmol 9,9-dioctylfluorene-2,7-diboronic acid, 1.0 mmol 4,4'-dibromoazobenzene, 2 mmol K2CO3, 0.2 mmol Pd(PPh3)4 with 40 mL solvent (deionized water:THF = 1:3; v / v), oil bath at 75°C, Suzuki coupling reaction was carried out for 12 h, after the reaction was completed, it was cooled, precipitated with 99.5% methanol, washed with 99.0% chloroform, and purified by column chromatography with a 200 mesh silica gel column to obtain PFO-Azo polymer with a molecular weight Mw = 45,000 Da.

[0061] Example 2 Method for extracting single chiral structure CNTs using FO-Azo polymer, the steps are as follows:

[0062] 1) At room temperature, 1 mg of SWCNTs prepared by CVD method, 5 mg of PFO-Azo polymer prepared in Example 1 were added to 10 mL of toluene, and magnetically stirred at 250 rpm for 30 min to disperse the CNTs, then irradiated with 365 nm ultraviolet light at an intensity of 10 mW / cm 2 for 1 h to obtain a PFO-Azo polymer-CNTs mixture system;

[0063] 2) The PFO-Azo polymer-CNTs mixture system was transferred to a quartz transparent centrifuge tube with a transmittance of ≥90%, and different wavelengths of light were irradiated at different heights in the vertical direction of the centrifuge tube, specifically: 365 nm ultraviolet light at an intensity of 10 mW / cm 2 at a distance of 4-10 cm from the bottom of the tube, 470 nm blue light at an intensity of 8 mW / cm 2 at a distance of 0-4 cm from the bottom of the tube, then the PFO-Azo polymer-CNTs mixture was centrifuged (3000 rpm, 5 min) under the irradiation of the light source, and the supernatant was collected;

[0064] 3) The collected supernatant was irradiated with 450 nm visible light for 5 min, and then centrifuged (3000 rpm, 5 min) to separate the target CNTs;

[0065] 4) After the enrichment of the target chiral CNTs was completed, the remaining PFO-Azo polymer-CNT composite in the system was enriched in the supernatant of step 3), the supernatant was irradiated with 470 nm blue light for 45 min to make the azobenzene side chain configuration of PFO-Azo polymer return to the trans state from the cis state, the π-π interaction between PFO-Azo polymer and CNTs was weakened, and the two were separated by low-speed centrifugation, and the supernatant was collected to obtain a PFO-Azo polymer solution;

[0066] The supernatant of step 2) is subjected to UV-Vis-NIR absorption test, and clear (6, 5) transition peak appears; fluorescence spectrum shows that the fluorescence of the separated CNT sample is enhanced, and the fluorescence intensity of (6, 5) CNTs accounts for 98.5% of the total amount; the Raman spectrum measurement G / D ratio is greater than 50, confirming that the impurity carbon is low and the purity is high.

[0067] The PFO-Azo polymer recovered in step 4) is used as raw material, and the whole separation process is repeated for a total of 10 times, and the purity of the target chiral CNTs and the recovery rate of the PFO-Azo polymer are counted to evaluate the recycling performance of the PFO-Azo polymer, and the results are shown in Table 1.

[0068] Table 1: Polymer recycling performance test results

[0069] Number of uses (6,5) CNTs purity (%) PFO-Azo polymer recovery (%) Round 1 98.5 85.2 Round 5 97.8 83.9 Round 10 96.9 80.8

[0070] It can be seen that the dispersion ability and chiral selectivity of the PFO-Azo polymer of the present application remain stable after being used repeatedly for more than 10 times, indicating that the photoresponsive configuration conversion process has good reversibility and material durability.

[0071] Comparative Example 1: Density gradient centrifugation method for separating CNTs

[0072] Density gradient iodixanol solutions (50%, 30%, 10%, 5%; w / v) with different concentration gradients are prepared, and the dilute iodixanol solution is sequentially added from the bottom of the centrifuge tube, 1 mg of SWCNTs (same as Example 1) is added to the top of the gradient in the centrifuge tube, and 120,000 g centrifugation is carried out for 3 h, the target band is extracted, and the agent is removed by dialysis.

[0073] After detection, the Raman G / D ratio of the product is 30, the (6, 5) chiral peak purity in the UV-Vis spectrum is 90-93%, and the fluorescence intensity distribution is wide, and the side peak interference is obvious.

[0074] It can be seen that the method for extracting CNTs with a specific single chiral structure using a photoresponsive polymer of the present application is significantly higher in separation precision than the traditional method, and has low dependence on equipment.

[0075] In addition, by counting the separation time, it can be found that compared with the traditional separation method, the separation time is significantly shortened by using the separation method of the present application. It can be seen that the separation method of the present application significantly improves the separation efficiency of CNTs with a single chiral structure.

[0076] Comparative Example 2

[0077] The difference from Example 2 is that the light irradiation time of step 1 is 30 min.

[0078] The purity of (6,5)CNTs was 78.4% and the recovery rate of PFO-Azo polymer was 62.7% after being used for 10 times. It can be seen that the insufficient UV irradiation time can result in incomplete configuration transformation of PFO-Azo polymer, thus affecting the selective combination of (6,5)CNTs and reducing the separation effect.

[0079] Comparative Example 3

[0080] The difference from Example 2 is that the centrifugal speed in step 2 is 1500 rpm.

[0081] The purity of (6,5)CNTs was 84.2% and the recovery rate of PFO-Azo polymer was 75.3% after being used for 10 times. It can be seen that the deviation of centrifugal speed from the optimal parameter can affect the distribution chromatography effect of (6,5)CNTs in the solution, thus reducing the chiral selective enrichment efficiency.

[0082] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as the limitation of the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A method for separating single chiral structure CNTs based on PFO-Azo polymer, characterized in that, The method comprises the following steps: S1, dispersion of CNTs: At room temperature, the CNTs powder was added into the toluene solution containing PFO-Azo polymer, and stirred at low speed until the CNTs were dispersed, and then irradiated with ultraviolet light with a wavelength of 365±1 nm and an illumination intensity of 10±0.5 mW / cm 2 for 60±2 min to obtain a PFO-Azo polymer-CNTs mixture system; The preparation method of the PFO-Azo polymer comprises the following steps: Suzuki coupling reaction is performed after 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, Pd(PPh3)4, K2CO3 and a solvent are mixed, and then the reaction is cooled, precipitated, washed and purified to obtain the PFO-Azo polymer; The molar ratio of the 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene and K2CO3 is (0.9-1.1):(0.9-1.1):(1.8-2.2); the amount of the Pd(PPh3)4 is 4.8-5.2% of the total moles of the 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene and K2CO3; the Suzuki coupling reaction is performed under a nitrogen atmosphere, and the reaction conditions are an oil bath at 73-77 ℃ and a reaction time of 10-14 h; The structure of the PFO-Azo polymer is poly[(9,9-dioctylfluorene)-alt-(azo-phenylene)], and the molecular weight Mw is 30,000-80,000 Da; S2, light-controlled separation: Different wavelengths of light sources are irradiated at different heights in the vertical direction of a transparent centrifugal tube, and then the PFO-Azo polymer-CNTs mixture is centrifuged under the irradiation of the light sources, and the supernatant is collected after centrifugation to realize enrichment of the target chiral CNTs; the centrifugal speed is 950-1050 rpm, and the centrifugal time is 4.5-5.5 min; The light source is arranged as follows: 4-10 cm from the tube bottom, 365±1 nm ultraviolet light, illumination intensity of 5-15 mW / cm 2 ; 0-4 cm from the tube bottom, 470±1 nm blue light, illumination intensity of 5-10 mW / cm 2 ; S3, separation of the target CNTs: The supernatant is irradiated with 450 nm visible light to make the PFO-Azo polymer restore the trans configuration and release the target CNTs, which are then centrifuged and separated; S4, recovery of the PFO-Azo polymer: The supernatant obtained by centrifugation in step S3 is irradiated with 470 nm blue light for 30-60 min, and then low-speed centrifugation is performed to collect the supernatant to obtain a PFO-Azo polymer solution.

2. The separation method of claim 1, wherein, In step S1, the ratio of the CNTs, the PFO-Azo polymer and toluene solution is (0.8-1.2) mg:(4.5-5.5) mg:(9.5-10.5) mL.

3. The separation method of claim 1, wherein, The solvent is composed of deionized water and THF in a volume ratio of (0.9-1.1):(2.9-3.1).

4. The separation method of claim 1, wherein, In step S2, the centrifugal tube is made of quartz or polycarbonate.

5. The separation method of claim 1, wherein, In step S2, the transmittance of the centrifugal tube is ≥90%.

6. The separation method of claim 1, wherein, In step S3, the centrifugal speed is 2950-3050 rpm, and the centrifugal time is 4.5-5.5 min; in step S4, the centrifugal speed is 2950-3050 rpm, and the centrifugal time is 4.5-5.5 min.

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