Single chiral structure CNTs separation method based on PFO-Azo polymer

Abstract

The invention provides a single chiral structure CNTs separation method based on a PFO-Azo polymer, and relates to the technical field of nanometer material separation and preparation. The separation method of the single chiral structure CNTs based on the PFO-Azo polymer comprises the steps of CNTs dispersion, light-operated separation, target CNTs separation, PFO-Azo polymer recovery and the like. According to the method, the configuration of the PFO-Azo polymer is adjusted by using a light field, and the combination / release behavior of the PFO-Azo polymer to CNTs is dynamically controlled through the change of a photo-induced molecular structure, so that efficient separation of specific single chiral (6, 5) CNTs is realized, the purity of the PFO-Azo polymer reaches 98.5%, the recovery rate of the PFO-Azo polymer reaches 85.2%, the separation efficiency is remarkably improved, and the recycling capability of the polymer is ensured. According to the separation method, the separation cost of single chiral CNTs can be reduced, the separation energy consumption is reduced, and compared with a traditional process, the cost is reduced by about 70%.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial separation and preparation, and in particular to a method for separating single chiral structure CNTs based on PFO-Azo polymer. Background Art

[0002] Since their discovery, single-walled carbon nanotubes (SWCNTs) have rapidly become a research hotspot in condensed matter physics, nanomaterials, and devices, thanks to their one-dimensional nanostructure, quantum confinement, and unique physicochemical properties. Their electronic structure exhibits a high degree of tunability: the band gap can be manipulated via the chiral parameters (n, m), and carrier mobility is significantly higher than that of traditional semiconductor materials. Furthermore, SWCNTs are sensitive to light direction and exhibit significant nonlinear optical effects, offering promising applications in microelectronics, optoelectronics (such as infrared / visible light detectors), biosensing platforms, and catalytic supports.

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

[0004] At present, the chiral separation technology of SWCNTs is mainly based on the differences in physical and chemical properties, but both have certain shortcomings.

[0005] Ultracentrifugation separation methods utilize surfactants or polymers to modify SWCNTs, achieving stratification through density differences within the centrifugal field. For example, Patent Publication No. CN 115676807 A discloses a cascade ultracentrifugation purification method for single-chirality carbon nanotubes. The cascade ultracentrifugation purification method comprises: uniformly dispersing a polymer and single-walled carbon nanotube feedstock in a solvent to form a dispersion, centrifuging the dispersion to obtain a supernatant; and ultracentrifuging the supernatant to form a solid phase and a liquid phase system enriched in single-chirality carbon nanotubes, thereby obtaining high-purity single-chirality carbon nanotubes. Another example is Patent Publication No. CN 116062736 B, which discloses a method, reagent composition, and application for improving the extraction efficiency of single-chirality carbon nanotubes. The method comprises: mixing a reinforcing polymer, a chiral extracting polymer, a carbon nanotube feedstock, and a solvent, and then separating the resulting mixture to obtain a high-concentration single-chirality carbon nanotube solution. However, ultra-high-speed centrifugation separation methods rely on high-intensity centrifuges (>200,000g), which have high equipment costs, limited selectivity for chiral structures, and the separation products are still mixed.

[0006] The dielectrophoresis (DEP) method separates metallic and semiconducting SWCNTs based on the polarization difference in a non-uniform electric field. For example, patent publication number CN 118829330 A discloses a dielectrophoresis-based single-chirality carbon nanotube array film, preparation method, and application thereof. The preparation method comprises: preparing a high-purity single-chirality carbon nanotube solution; preparing an electrophoresis electrode structure, the electrophoresis electrode structure comprising a substrate with a plurality of electrophoresis electrodes etched thereon, and a plurality of devices etched between adjacent electrophoresis electrodes; connecting a sinusoidal voltage source to the electrophoresis electrodes, dripping the high-purity single-chirality carbon nanotube solution into the gaps between the electrophoresis electrodes, and performing electrophoresis to arrange the single-chirality carbon nanotubes in an array within the device's channels; after the electrophoresis is completed, the substrate surface is cleaned and dried to obtain a single-chirality carbon nanotube array film distributed within the device's channels within the electrophoresis electrode structure. However, the DEP method requires precise microelectrode design, resulting in high equipment complexity, difficulty in large-scale production, and limited production output.

[0007] Gel chromatography separates carbon nanotubes based on their adsorption capacity differences through gel chromatography columns. For example, the invention patent with publication number CN117486205 A discloses a method for separating single chiral carbon nanotube mirror images, which includes the following steps: (1) dispersing carbon nanotube raw materials into a solution of a composite surfactant to obtain a carbon nanotube dispersion; (2) using gel chromatography to perform step-by-step elution to separate the carbon nanotube dispersion, and collecting the separated products to obtain single chiral carbon nanotube mirror images; wherein the composite surfactant solution contains bile 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 lithocholic acid, sodium hyodeoxycholate and sodium chenodeoxycholate. However, gel chromatography relies on high-cost surfactants, and the elution process is complicated, and the separation efficiency is significantly affected by the solvent.

[0008] The polymer coating + replacement method uses the characteristics of a specific polymer (such as PFO, F8BT) to selectively coat the target chiral SWCNTs, and then removes impurities through solvent replacement. For example, the invention patent with publication number CN 112812507 A discloses a single chiral carbon nanotube-thiophene polymer composite material and its preparation method, by using a specific thiophene polymer to replace PFO-BP y PFO-BP on (6,5) SWCNTs y , successfully prepared a thiophene polymer / (6,5)SWCNT nanocomposite containing high-purity single-chiral carbon nanotubes. However, the polymer coating-replacement method is cumbersome and time-consuming, only suitable for laboratory use, requires large amounts of chemical solvents, and is less environmentally friendly.

[0009] As can be seen, existing technologies for separating single-chirality carbon nanotubes generally face challenges such as high cost, insufficient selectivity, difficulty in scalability, and environmental impact, which restrict the industrial application of carbon nanotubes. Therefore, developing a low-cost, high-throughput, and sustainable separation strategy to separate single-chirality carbon nanotubes is a pressing technical challenge in this field. Summary of the Invention

[0010] In view of this, the present invention provides a method for separating CNTs with a single chiral structure based on PFO-Azo polymer. This method uses the controllable configuration switching ability of PFO-Azo polymer and its binding-separation characteristics with CNTs to drive the adsorption-desorption process of CNTs, and by adjusting parameters such as illumination time and centrifugal rate, achieves high-purity and efficient separation of CNTs with a single chiral structure.

[0011] The present invention provides a method for separating CNTs with a single chiral structure based on PFO-Azo polymer, which specifically comprises the following steps:

[0012] S1. CNTs dispersion:

[0013] At room temperature, CNTs powder was added to a toluene solution containing PFO-Azo polymer, stirred at low speed until the CNTs were dispersed, and then irradiated with ultraviolet light to obtain a PFO-Azo polymer-CNTs mixture system;

[0014] S2, light control separation:

[0015] Irradiating a transparent centrifuge tube with light sources of different wavelengths at different heights in the vertical direction, then centrifuging the PFO-Azo polymer-CNTs mixture under the conditions of light irradiation, collecting the supernatant after the centrifugation to achieve the enrichment of the target chiral CNTs;

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

[0017] S3. Target CNTs separation:

[0018] The supernatant was irradiated with 450±1nm visible light for 3-8min to restore the trans configuration of the PFO-Azo polymer and release the target CNTs, which were then separated by centrifugation.

[0019] S4. PFO-Azo polymer recovery:

[0020] The supernatant in step S3 was irradiated under 470 nm blue light for 30-60 min, centrifuged at low speed, and the supernatant was collected to obtain a FO-Azo polymer solution.

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

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

[0023] Preferably, in step S1, the method for preparing the PFO-Azo polymer specifically comprises the following steps:

[0024] 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, Pd(PPh3)4, K2CO3 and a solvent are mixed and subjected to a Suzuki coupling reaction. After the reaction is completed, the mixture is cooled, precipitated, washed and purified to obtain a PFO-Azo polymer.

[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-diboric acid, 4,4'-dibromoazobenzene, and K2CO3 is (0.9-1.1): (0.9-1.1): (1.8-2.2), more preferably 1:1:2, and the amount of Pd(PPh3)4 is 4.8-5.2% of the total molar number of 9,9-dioctylfluorene-2,7-diboric acid, 4,4'-dibromoazobenzene, and K2CO3, more preferably 5%. The amount of the agent used is 8-10 times (mL) of the total molar sum of 9,9-dioctylfluorene-2,7-diboric acid, 4,4'-dibromoazobenzene, and K2CO3, more preferably 9 times; the Suzuki coupling reaction is carried out under a nitrogen atmosphere, the reaction conditions are 73°C-77°C oil bath, 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%), and the purification method is column chromatography, and the column chromatography uses a 100-200 mesh silica gel column.

[0026] Preferably, in step S2, the centrifuge tube is made of quartz or polycarbonate, and has a light transmittance of ≥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 invention has the following beneficial technical effects:

[0031] The present invention separates (6,5)CNTs using a dynamic separation method based on a light-responsive PFO-Azo polymer, avoiding traditional chemical modification and surfactant dependence, and achieving controllable, reversible, and efficient selective separation of (6,5)CNTs.

[0032] The present invention utilizes light fields to regulate the configuration of PFO-Azo polymers, dynamically controls the binding / release behavior of CNTs through light-induced molecular structural changes, and achieves efficient separation of (6,5) CNTs.

[0033] The present invention achieves efficient separation of specific single chiral (6,5) CNTs through light irradiation, achieving a purity of 98.5% and a PFO-Azo polymer recovery rate of 85.2%, significantly improving the separation efficiency and ensuring the recyclability of the polymer.

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

[0035] The present invention will be further described below with reference to the accompanying drawings.

[0036] Figure 1 The figure is a flow chart of the method for separating single chiral structure CNTs based on PFO-Azo polymer of the present invention. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] The present invention provides a method for separating CNTs with a single chiral structure based on a PFO-Azo polymer, which includes the steps of CNTs dispersion, light-controlled separation, target CNTs separation, and PFO-Azo polymer recovery.

[0039] The first step of the present invention is to disperse CNTs, which specifically includes the following steps:

[0040] At room temperature of 20°C-25°C, SWCNTs powder is added to a toluene solution containing a PFO-Azo polymer, stirred at a low speed until the CNTs are dispersed, and then irradiated with ultraviolet light to obtain a PFO-Azo polymer-CNTs mixture system.

[0041] The CNTs described in the present invention are synthesized by CVD method; the ratio of the CNTs, PFO-Azo polymer, and 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, the stirring time is 30-35 min, preferably 30 min; the ultraviolet light irradiation time is 58-62 min, preferably 60 min, the ultraviolet 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 present invention, after obtaining the PFO-Azo polymer-CNTs mixture system, it is enriched and separated by centrifugal classification or selective precipitation to further achieve pre-separation of CNTs with specific chiral structures, wherein the CNTs with specific chiral structures are (6,5)-type CNTs or (7,5)-type CNTs.

[0043] The PFO-Azo polymer described in the present invention is an orange-yellow solid with a structure of poly[(9,9-dioctylfluorene)-alt-(azo-phenylene)] and a molecular weight Mw of 30,000-80,000 Da. UV-Vis absorption spectra show that the PFO-Azo polymer has a significant reversible absorption peak shift between 365 nm and 450 nm. FTIR confirms the presence of -N=N- stretching vibration. The polymer has good solubility and is stably soluble in toluene and chloroform.

[0044] The present invention also provides a method for preparing the PFO-Azo polymer, which specifically comprises the following steps:

[0045] 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, Pd(PPh3)4, K2CO3 and solvent were mixed and subjected to Suzuki coupling reaction. After the reaction, the mixture was cooled, precipitated, washed and purified to obtain PFO-Azo polymer.

[0046] The solvent of the present invention 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 the 9,9-dioctylfluorene-2,7-diboric acid, 4,4'-dibromoazobenzene, and K2CO3 is (0.9-1.1): (0.9-1.1): (1.8-2.2), more preferably 1:1:2, and the amount of the Pd(PPh3)4 is 4.8-5.2% of the total molar number of the 9,9-dioctylfluorene-2,7-diboric acid, 4,4'-dibromoazobenzene, and K2CO3, more preferably 5%, and the The amount of solvent used is 8-10 times (mL) of the total molar sum of 9,9-dioctylfluorene-2,7-diboric acid, 4,4'-dibromoazobenzene, and K2CO3, more preferably 9 times; the Suzuki coupling reaction is carried out under a nitrogen atmosphere, the reaction conditions are 73°C-77°C oil bath, 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%), and the purification method is column chromatography, and the column chromatography uses a 100-200 silica gel column.

[0047] The present invention uses an azobenzene derivative as the core structure to form a PFO-Azo polymer, which is a π-conjugated polymer with a conjugated structure in the main chain and a side chain or main chain connected to an azobenzene structural unit. The PFO-Azo polymer of the present invention can be converted from a trans configuration to a cis configuration under 365nm ultraviolet light and reversibly recovers at a wavelength of 450-600nm, having a controllable configuration switching ability and being used to drive the adsorption-desorption process of CNTs. The present invention utilizes the characteristics of the PFO-Azo polymer, combines an LED ultraviolet light source (365nm) and a visible light source (450-600nm), dynamically adjusts the light during the centrifugation process, and achieves high-purity and efficient separation of target CNTs with the help of parameters such as illumination time and centrifugal rate.

[0048] The present invention gradually disperses CNTs into the solution by stirring at a low speed, and gradually forms a non-covalent π-π effect with the PFO-Azo polymer, thereby keeping the solution in a uniform and stable state. During the ultraviolet irradiation process after the stirring is completed, the azobenzene part on the PFO-Azo polymer structure gradually changes from the originally more stable trans structure to a more curved cis configuration under the action of ultraviolet light. This configuration change changes the softness of the PFO-Azo polymer chain and its swinging mode in space. As this structural adjustment occurs, the shape of the PFO-Azo polymer begins to fit the chiral CNTs, making it easier for the polymer to adsorb specific structures when the molecules come into contact, thereby allowing a biased selective binding to occur between the PFO-Azo polymer and the target chiral CNTs. This shows that the present invention relies on an external light field as a control means to construct a CNTs dispersion dynamic recognition mechanism that is essentially different from the traditional static coordination method.

[0049] The second step of the present invention is light-controlled separation, which specifically includes the following steps: irradiating a transparent centrifuge tube with light sources of different wavelengths at different heights in the vertical direction, then centrifuging the PFO-Azo polymer-CNTs mixture under the conditions of light illumination, and collecting the supernatant after the centrifugation to achieve enrichment of the target chiral CNTs;

[0050] The light source is set as follows:

[0051] 4-10cm from the bottom of the tube, 365±1nm ultraviolet light, irradiation intensity is 5-15mW / cm 2 Under UV light under these conditions, the azobenzene structure on the PFO-Azo polymer molecules in the solution will gradually change from its original trans state to its cis state. This configuration change will adjust the flexibility and spatial swinging mode of the PFO-Azo polymer chain segments. After the adjustment, the overall shape of the PFO-Azo polymer becomes more easily fitted to (6,5) CNTs, showing strong stability during the binding, allowing this type of complex to remain dispersed in the solution without aggregation;

[0052] 0-4cm from the bottom of the tube, 470±1nm blue light, irradiation intensity is 5-10mW / cm 2 When blue light shines on the PFO-Azo polymer that is already in the cis state, the PFO-Azo polymer will slowly revert to the trans structure. As the configuration returns to a more rigid state, the PFO-Azo polymer chain no longer maintains a tight bond with the non-target chiral CNTs. The CNTs begin to slowly desorb and gradually sink to the bottom under the action of gravity.

[0053] The present invention does not strictly limit the material of the centrifuge tube; any centrifuge tube that is light-transmissive and has a transmittance of ≥90% can be used for light-controlled separation. In some preferred embodiments of the present invention, the centrifuge tube is a quartz centrifuge tube or a polycarbonate centrifuge tube. The present invention does not strictly limit the specific method of setting the light source; in some specific embodiments of the present invention, the light-controlled separation can be achieved by means of a dual-wavelength LED light source module disposed outside the tube body. The LED light source is controlled by a programmable control unit for on / off, power, and illumination timing, and the light field forms a spatial configuration-induced gradient along the tube axis.

[0054] The present invention constructs a spatial gradient field of light-induced configurational transition by irradiating the upper and lower regions with light of different colors, thereby dividing the effect of PFO-Azo polymer configurational regulation into spatial positions. In this way, without applying additional centrifugal force, different types of CNTs can be separated inside the centrifuge tube, so that the PFO-Azo polymer region in the trans state releases non-target CNTs, while the region in the cis state continues to stably bind to the target CNTs, causing them to be enriched in the upper liquid. The centrifugal speed is 950-1050 rpm, preferably 1000 rpm, and the centrifugation time is 4.5-5.5 minutes, preferably 5 minutes.

[0055] The third step of the present invention is to separate the target CNTs, which specifically includes the following steps: irradiating the supernatant with 450±1nm visible light for 3-8min to restore the PFO-Azo polymer to the trans configuration, releasing the target CNTs, and centrifuging to separate the target CNTs; the centrifugation speed is 3000rpm and the centrifugation time is 5min.

[0056] The fourth step of the present invention is to recover the PFO-Azo polymer, which specifically includes the following steps: after the enrichment of the target chiral CNTs is completed, the remaining PFO-Azo polymer-CNTs complex in the system is enriched in the supernatant, so the supernatant is irradiated under 470nm blue light for 30-60min, which can restore the azobenzene side chain configuration in the PFO-Azo polymer from cis to trans state, weaken the π-π interaction between the PFO-Azo polymer and the CNT, and separate the two by low-speed centrifugation. The supernatant is collected to obtain a FO-Azo polymer solution, thereby achieving recovery; the centrifugal speed is 2950-3050rpm, preferably 3000rpm, and the centrifugation time is 4.5-5.5min, preferably 5min.

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

[0058] Unless otherwise specified, all experiments were repeated three times and the results were expressed as the mean value.

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

[0060] 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 and 40 mL solvent (deionized water:THF=1:3; v / v) were mixed and placed in an oil bath at 75°C for Suzuki coupling reaction for 12 hours. After the reaction was completed, the mixture was cooled and precipitated with 99.5% methanol, washed with 99.0% chloroform, and purified by column chromatography using a 200 mesh silica gel column to obtain a PFO-Azo polymer with a molecular weight Mw=45,000 Da.

[0061] Example 2: A method for extracting single chiral CNTs using FO-Azo polymer, comprising the following steps:

[0062] 1) At room temperature, 1 mg of SWCNTs prepared by CVD and 5 mg of PFO-Azo polymer prepared in Example 1 were added to 10 mL of toluene and stirred at 250 rpm for 30 min until the CNTs were fully dispersed. Then, 365 nm ultraviolet light was used at 10 mW / cm 2 The PFO-Azo polymer-CNTs mixture system was obtained by irradiation with an intensity of 1 h;

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

[0064] 3) Irradiating the collected supernatant with 450 nm visible light for 5 min, centrifuging (3000 rpm, 5 min) to separate the target CNTs;

[0065] 4) After the target chiral CNTs are enriched, the remaining PFO-Azo polymer-CNT complex in the system is enriched in the supernatant of step 3), and the supernatant is irradiated with 470 nm blue light for 45 minutes to revert the azobenzene side chain configuration in the PFO-Azo polymer from cis to trans, thereby weakening the π-π interaction between the PFO-Azo polymer and the CNT. The two are separated by low-speed centrifugation, and the supernatant is collected to obtain a PFO-Azo polymer solution;

[0066] The supernatant from step 2) was subjected to UV-Vis-NIR absorption testing, which revealed a clear (6,5) transition peak. Fluorescence spectroscopy showed enhanced fluorescence in the separated CNT sample, with the fluorescence intensity of (6,5) CNTs accounting for 98.5% of the total. Raman spectroscopy showed a G / D ratio >50, confirming low impurity carbon and high purity.

[0067] The PFO-Azo polymer recovered in step 4) was used as the raw material. The entire separation process was repeated 10 times. The purity of the target chiral CNTs and the recovery rate of the PFO-Azo polymer were statistically analyzed to evaluate the recyclability of the PFO-Azo polymer. The results are shown in Table 1.

[0068] Table 1 Test results of polymer recycling performance

[0069] Use times (6,5)CNTs purity (%) PFO-Azo polymer recovery rate (%) 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 invention remain basically stable after repeated use for more than 10 times, indicating that its photoresponsive configuration conversion process has good reversibility and material durability.

[0071] Comparative Example 1: Separation of CNTs by Density Gradient Centrifugation

[0072] Density gradients of iodixanol solutions with different concentrations were prepared (50%, 30%, 10%, 5%; w / v). Dilute iodixanol solution was added sequentially from the bottom of the centrifuge tube upwards. 1 mg of SWCNTs (same as in Example 1) was added to the top of the gradient in the centrifuge tube. The tube was centrifuged at 120,000 g for 3 h, and the target band was extracted and dialyzed to remove the agent.

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

[0074] It can be seen that the method of the present invention using a photoresponsive polymer to extract CNTs with a specific single chiral structure has significantly higher separation accuracy than the traditional method and has low equipment dependence.

[0075] Furthermore, statistical analysis of the separation time revealed that the separation method of the present invention significantly shortened the separation time compared to conventional separation methods, indicating that the separation method of the present invention significantly improved the separation efficiency of single-chiral CNTs.

[0076] Comparative Example 2

[0077] The difference from Example 2 is that the illumination time in step 1 is 30 minutes.

[0078] Testing revealed a purity of 78.4% for (6,5) CNTs, and a recovery of 62.7% for the PFO-Azo polymer after 10 reuses. This suggests that insufficient UV irradiation time can lead to incomplete conformational conversion of the PFO-Azo polymer, thereby affecting its selective binding to (6,5) CNTs and reducing separation efficiency.

[0079] Comparative Example 3

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

[0081] Testing revealed a purity of 84.2% for (6,5)CNTs, and a recovery of 75.3% for PFO-Azo polymer after 10 reuses. This suggests that deviations from the optimal centrifugal speed can affect the chromatographic distribution of (6,5)CNTs in solution, thereby reducing the efficiency of chiral selective enrichment.

[0082] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for separating single chiral CNTs based on PFO-Azo polymer, characterized in that: The following steps are involved: S1. CNTs dispersion: At room temperature, CNTs powder was added to the toluene solution containing PFO-Azo polymer and stirred at low speed until the CNTs were dispersed. Then, the solution was illuminated with a wavelength of 365±1nm and an intensity of 10±0.5mW / cm 2 Irradiate with ultraviolet light for 60±2 min to obtain a PFO-Azo polymer-CNTs mixture system; The method for preparing the PFO-Azo polymer comprises the following steps: 9,9-dioctylfluorene-2,7-diboronic acid, 4,4'-dibromoazobenzene, Pd(PPh3)4, K2CO3 and a solvent are mixed and subjected to a Suzuki coupling reaction. After the reaction is completed, the mixture is cooled, precipitated, washed and purified to obtain a PFO-Azo polymer. S2, light control separation: Irradiating a transparent centrifuge tube with light sources of different wavelengths at different heights in the vertical direction, then centrifuging the PFO-Azo polymer-CNTs mixture under the conditions of light irradiation, collecting the supernatant after the centrifugation to achieve the enrichment of the target chiral CNTs; The light source is set as follows: 4-10 cm from the bottom of the tube, 365±1 nm ultraviolet light, irradiation intensity of 5-15 mW / cm 2 ; 0-4cm from the bottom of the tube, 470±1nm blue light, irradiation intensity is 5-10mW / cm 2 ; S3. Target CNTs separation: The supernatant was irradiated with 450 nm visible light to restore the PFO-Azo polymer to the trans configuration, releasing the target CNTs, and then centrifuged to separate the target CNTs. S4. PFO-Azo polymer recovery: The supernatant obtained by centrifugation in step S3 was irradiated under 470 nm blue light for 30-60 min, centrifuged at low speed, and the supernatant was collected to obtain a FO-Azo polymer solution.

2. The separation method according to claim 1, wherein In step S1, the ratio of the CNTs, 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 according to claim 1, characterized in that In step S1, 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.

4. The separation method according to 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).

5. The separation method according to claim 1, characterized in that The molar ratio of 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).

6. The separation method according to claim 1, characterized in that The amount of Pd(PPh3)4 used is 4.8-5.2% of the total molar number of 9,9-dioctylfluorene-2,7-diboric acid, 4,4'-dibromoazobenzene and K2CO3.

7. The separation method according to claim 1, characterized in that The Suzuki coupling reaction was carried out under a nitrogen atmosphere, in an oil bath at 73° C.-77° C., and for 10-14 h.

8. The separation method according to claim 1, characterized in that In step S2, the centrifuge tube is made of quartz or polycarbonate.

9. The separation method according to claim 1, characterized in that In step S2, the light transmittance of the centrifuge tube is ≥90%.

10. The separation method according to claim 1, characterized in that In step S2, the centrifugal speed is 950-1050 rpm, and the centrifugal time is 4.5-5.5 min; 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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