Preparation and application of a covalent organic framework composite material

Abstract

The application belongs to the field of material preparation, and particularly relates to a preparation method and application of CNT@TpBD composite material, wherein CNT@TpBD composite material is synthesized by self-assembling TpBD on the surface of CNT-NH2 through a simple and rapid one-pot method. The obtained composite material has the characteristics of high specific surface area and rich pores (micropores and mesopores). The composite material contains rich delocalized π bonds, amino groups, hydroxyl groups and carboxyl groups, and indole rings, benzene rings, carboxyl groups and amino groups in stress hormones and auxins, so that strong hydrophobic interaction, electrostatic interaction, π-π interaction and hydrogen bonding interaction can be generated between the two, further enhancing the enrichment effect. The adsorption mechanism research shows that the hydrophobic interaction and electrostatic interaction are the main adsorption forces. The composite material is used as an adsorbent of a dispersive solid-phase extraction method, and is used for enrichment and high-sensitivity detection of plant stress hormones and plant auxins.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation, specifically relating to the preparation of a carbon nanotube-modified covalent organic framework composite material and its application in the efficient adsorption and sensitive detection of plant stress hormones and auxins. Background Technology

[0002] Covalent organic frameworks (COFs) are a novel class of porous organic crystalline materials that have attracted widespread attention as novel extraction materials in the field of sample pretreatment. Among them, imine COFs are formed by the condensation of aldehyde and amine groups through Schiff base reactions. β-ketoenamine-linked COFs based on irreversible enol-ketone tautomerization (including the TpPa and TpBD series) possess excellent structural stability and mild synthesis conditions, making them the most widely used class of COFs. TpBD is a typical representative of imine COFs. On the other hand, carbon nanotubes (CNTs), with their large specific surface area, abundant aromatic structures, high chemical stability, and good adsorption capacity, are also widely used as adsorbents to enrich target analytes. Using CNTs as the substrate material for TpBD growth and crystallization can prevent spontaneous aggregation during the synthesis process, increase the contact area between TpBD and the target analyte, and fully utilize the independent tubular morphology and structural characteristics of CNTs. The resulting composite material (CNT@TpBD) may exhibit even better adsorption performance.

[0003] Plant growth depends on and adapts to its environment, and unfavorable environments are called stress. Endogenous plant hormones not only significantly regulate plant growth and development but also serve as key signaling factors in plant responses to various environmental stresses. Literature reviews have revealed that several hormones, including auxin, abscisic acid (ABA), ethylene, brassinolide, jasmonic acid, and salicylic acid, participate in stress responses and are crucial for enhancing plant resilience and adaptability. Plant ecological adaptation to adversity is based on the physiological regulation of stress hormones. Abscisic acid (ABA) is the most typical representative of stress hormones. When plants are under stress, ABA levels surge, triggering the plant's own stress mechanisms (including growth inhibition, dormancy promotion, and stomatal closure). Jasmonic acid (JA) is a lipid plant hormone that regulates plant growth and responses to external stimuli. Its effects are similar to ABA; at higher concentrations, it inhibits plant growth differentiation and induces stomatal closure. Auxins are among the earliest and most important plant hormones studied, typically found in vigorously growing parts of plants, and play a positive regulatory role in plant growth and development. Indoleacetic acid (IAA) is the most typical representative of auxins and is closely related to abiotic stress. It promotes growth at low concentrations and inhibits growth at high concentrations, demonstrating the "dual nature" of IAA. Plants accumulate stress hormones as a beneficial and harmful response to resist adversity and ensure survival. However, most current research focuses on exploring the molecular mechanisms of individual plant hormones involved in stress, while research on the cross-involvement of multiple plant hormones in stress remains relatively scarce. Therefore, it is necessary to integrate several major hormones, such as abscisic acid (ABA), jasmonic acid (JA), and indoleacetic acid (IAA), to study the interactions and synergistic effects among various stress hormones.

[0004] Quantitative analysis of the aforementioned plant hormones requires both sensitive detection methods and simple, efficient sample pretreatment techniques. Dispersive solid-phase extraction (dSPE) is a green and environmentally friendly sample pretreatment method. It has advantages such as low solvent consumption, short operation time, and wide applicability, while avoiding problems such as adsorbent filling and extraction column clogging. It has been widely used in the purification and enrichment of various organic compounds. In dSPE technology, the choice of adsorbent is a key factor, directly affecting the purification and enrichment effect of the method. Research on the use of COF composite materials for the enrichment and separation of plant hormones is limited, indicating significant untapped potential. A hollow tubular CNT@TpBD composite material was synthesized at room temperature using a rapid and simple one-pot method. The unique tubular morphology provides more adsorption sites, thereby increasing the contact area between the material and the target analyte, which is beneficial for the adsorption and extraction of stress hormones and auxins. Summary of the Invention

[0005] This invention aims to provide a method for preparing a covalent organic framework composite material. A simple and rapid one-pot method is used to self-assemble TpBD on the surface of CNT-NH2 to obtain the CNT@TpBD composite material, which is then used as an adsorbent material in a dispersion solid-phase extraction (dSPE) pretreatment method for the enrichment and extraction of several plant hormones. This CNT@TpBD composite material contains a large number of delocalized π bonds, amino, hydroxyl, and carboxyl groups. Several hormones contain active sites such as indole rings, benzene rings, carboxyl groups, and amino groups, thus generating strong hydrophobic interactions, electrostatic interactions, π-π interactions, and hydrogen bonding between them, resulting in a significant enrichment effect. Simultaneously, CNT@TpBD possesses a micro-mesoporous layered porous structure and a unique tubular morphology, further improving the material's specific surface area utilization and overall adsorption efficiency. Using this composite material as an adsorbent for dSPE, the efficient enrichment of trace plant hormones in complex plant samples is achieved through a simple and rapid extraction process, and it is expected to find wider applications in sample pretreatment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A CNT@TpBD composite material is disclosed, using CNT-NH2 as the substrate material for the growth and crystallization of imine-based COFs. At room temperature, Tp and BD ligands are added to an ethanol solution containing NH2-CNTs. The large delocalized π bonds on the outer surface of CNT-NH2 and the conjugated TpBD molecules are non-covalently linked through π-π stacking. The CNT@TpBD composite material is prepared by self-assembling TpBD on the CNT-NH2 surface using a simple and rapid one-pot cooking method, and is used as an adsorbent in the dSPE method. The resulting composite material has a specific surface area and pore volume of 200.7 m². 2 / g and 0.37 cm 3 The pore sizes are mainly distributed at 0.68 nm, 1.27 nm and 2.73 nm, indicating that the composite material has a high specific surface area and abundant micro-mesoporous structure, making it suitable as a potential dSPE adsorbent for subsequent extraction experiments.

[0008] The preparation method of the CNT@TpBD composite material specifically includes the following steps:

[0009] (a) At room temperature, 1,3,5-tricarboxymethyl phloroglucinol (Tp, 0.3 mmol, 63.04 mg) and benzidine (BD, 0.45 mmol, 82.91 mg) were dissolved in 20 mL of ethanol respectively; the above solutions were then slowly added at a rate of 20 mL / min to 20 mL of ethanol solution containing 100 mg of aminated carbon nanotubes (CNT-NH2) (BD was added first, followed by Tp).

[0010] (b) The mixed solution was stirred thoroughly at room temperature (magnetic stirring at 400 rpm for 45 min), the precipitate was centrifuged (centrifuged at 10000 rpm for 3 min), the residue was washed multiple times with N,N-dimethylformamide and ethanol to remove unreacted residual Tp and BD, and finally vacuum dried at 60 °C to obtain the dark green CNT@TpBD composite material.

[0011] (c) Bright yellow TpBD material was synthesized by the same preparation method without the addition of aminated carbon nanotubes CNT-NH2.

[0012] Furthermore, the obtained CNT@TpBD composite material was used as an adsorbent for dispersive solid-phase extraction (dSPE) for the enrichment and detection of trace plant stress hormones (abscisic acid (ABA), jasmonic acid (JA), and indoleacetic acid (IAA)). All adsorption and extraction experiments were performed in 30.0 mL plastic centrifuge tubes. The specific procedures were as follows: First, the pH of the sample solution (standard solution or crude plant extract) was adjusted to 5.0 with 1 mM hydrochloric acid. Then, 5.0 mg of the CNT@TpBD composite material was uniformly dispersed in 20.0 mL of the above solution. To promote sufficient contact between CNT@TpBD and the three target compounds, the mixture was shaken on a shaker at 300 r / min for 15 min, centrifuged, and the supernatant was removed. Next, 1.0 mL of acetonitrile was added as the eluent to elute the adsorbed composite material, and the mixture was vortexed vigorously for 5 min to desorb the target components from the CNT@TpBD material. The eluent was collected and dried under mild nitrogen at room temperature. Finally, the target analyte was redissolved in 0.2 mL of 80% methanol solution and placed in an autosampler vial for subsequent HPLC-MS / MS analysis.

[0013] Furthermore, the obtained CNT@TpBD composite material was used as an adsorbent for dispersive solid-phase extraction (dSPE) for the enrichment and detection of trace plant auxins (3-indoleacetic acid (IAA), 3-indolebutyric acid (IBA), and 3-indolepropionic acid (IPA)). All adsorption and extraction experiments were performed in 30.0 mL plastic centrifuge tubes. The specific procedures were as follows: First, the pH of the sample solution (standard solution or crude plant extract) was adjusted to 5.0 with 1 mM hydrochloric acid. Then, 5.0 mg of the CNT@TpBD composite material was uniformly dispersed in 20.0 mL of the above solution. To promote sufficient contact between CNT@TpBD and the three target auxins, the mixture was shaken at 300 r / min for 15 min on a shaker, centrifuged, and the supernatant was removed. Next, 1.0 mL of acetonitrile was added as the eluent to elute the adsorbed composite material, and the mixture was vortexed vigorously for 5 min to desorb the auxins from the CNT@TpBD material. The eluent was collected and dried under mild nitrogen at room temperature. Finally, the target analyte was redissolved in 0.2 mL of 80% methanol solution and placed in an autosampler vial for subsequent HPLC-MS / MS analysis.

[0014] The CNT@TpBD composite material prepared by a one-pot room temperature synthesis method uses CNT-NH2 as the substrate material for the growth and crystallization of imine-based COFs, effectively reducing the spontaneous aggregation of COF nanoparticles during the synthesis process. This modification method increases the contact area between the CNT@TpBD composite material and stress hormones and plant growth regulators, improving the specific surface area utilization and the target analyte capture ability of the material.

[0015] The advantages of this invention are:

[0016] (1) The CNT@TpBD composite material prepared by the method of the present invention has a tubular morphology and a high specific surface area and total pore volume (220.6 cm³). 3 / g, 0.37 cm 3 The material is rich in microporous structures (0.68 nm, 1.27 nm and 2.73 nm), which improves the specific surface area utilization rate of the material and increases the effective contact area between the material and the target plant hormone.

[0017] (2) The CNT@TpBD composite material prepared by the method of the present invention has abundant hydrophobic benzene rings, C=C and C=N functional groups. Several types of plant hormones contain active sites such as benzene rings, indole rings, carboxyl groups and amino groups. Therefore, strong hydrophobic interaction, electrostatic interaction, π-π interaction and hydrogen bonding interaction can be generated between the two, which further enhances the enrichment effect.

[0018] (3) The synthesized CNT@TpBD composite material was used as an adsorbent for dSPE, which enabled efficient extraction and enrichment of three stress hormones and three auxins. The pretreatment method was simple and rapid (adsorption for 15 min, desorption for 5 min), with good reproducibility (RSD between batches ≤ 2.4%) and high sensitivity (lowest LOD of 2.0 pg / mL).

[0019] (4) The CNT@TpBD composite material prepared by the method of the present invention was applied to the sample pretreatment of three stress hormones and three auxins in plants. Combined with liquid chromatography-triple quadrupole mass spectrometry detection technology, the whole method has good selectivity and high repeatability, and has good effect. Attached Figure Description

[0020] Figure 1 The image shown is a scanning electron microscope image of CNT@TpBD obtained in Example 1.

[0021] Figure 2 The diagram shows the specific surface area and pore size distribution of the CNT@TpBD composite material obtained in Example 1.

[0022] Figure 3 The chemical stability of the CNT@TpBD composite material obtained in Example 1.

[0023] Figure 4 The CNT@TpBD composite material obtained in Example 1 was applied to the analysis of different plant samples.

[0024] Figure 5 The CNT@TpBD composite material obtained in Example 1 was applied to the analysis of different parts of a rice sample.

[0025] Figure 6 This is a comparison chart showing the adsorption effect of auxin on the CNT@TpBD composite material obtained in Example 1.

[0026] Figure 7 The mechanism of auxin adsorption by the CNT@TpBD composite material obtained in Example 1 is shown. (a) Static contact angle of CNT-NH2 and CNT@TpBD materials; (b) Zeta potential of CNT@TpBD under different pH conditions; (c) Effect of pH value on auxin recovery rate. Detailed Implementation

[0027] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0028] Example 1

[0029] (a) At room temperature, 1,3,5-tricarboxymethyl phloroglucinol (Tp, 0.3 mmol, 63.04 mg) and benzidine (BD, 0.45 mmol, 82.91 mg) were dissolved in 20 mL of ethanol respectively; the above solutions were then slowly added at a rate of 20 mL / min to 20 mL of ethanol solution containing 100 mg of aminated carbon nanotubes (CNT-NH2) (BD was added first, followed by Tp).

[0030] (b) The mixed solution was stirred thoroughly at room temperature (magnetic stirring at 400 rpm for 45 min), the precipitate was centrifuged (centrifuged at 10000 rpm for 3 min), the residue was washed multiple times with N,N-dimethylformamide and ethanol to remove unreacted residual Tp and BD, and finally vacuum dried at 60°C to obtain the dark green CNT@TpBD composite material.

[0031] (c) Bright yellow TpBD material was synthesized by the same preparation method without the addition of CNT-NH2.

[0032] The scanning electron microscope image of the CNT@TpBD composite material obtained in Example 1 shows that the material has a fine tubular morphology and a slightly rough surface. Figure 1 The specific surface area and total pore volume are 220.6 cm³. 3 / g and 0.37 cm 3 / g and rich in microporous structures (0.68 nm, 1.27 nm and 2.73 nm, Figure 2 The aforementioned structural features can increase the effective contact area between the material and the target plant hormone, thereby improving the adsorption effect. Furthermore, the material was immersed in methanol, acetonitrile, acetone, water, 0.1 mol / L hydrochloric acid, and 0.1 mol / L sodium hydroxide solutions for 48 h, and infrared spectroscopy characterization revealed… Figure 3 Despite treatment with different solvents, the main chemical bonds of the CNT@TpBD composite material remained intact, demonstrating good chemical stability.

[0033] Application Example 1

[0034] Using CNT@TpBD obtained in Example 1 as the adsorbent material for dSPE, and combining liquid chromatography-triple quadrupole mass spectrometry, the changes in the content of several major stress hormones (abscisic acid (ABA), jasmonic acid (JA), and indoleacetic acid (IAA)) in seedlings of several plants under biological stress (pathogen infestation and insect infestation) were investigated. Actual plant samples were divided into: a rice control group and a rice group treated with pathogens for 12 days; a tomato control group and a tomato group treated with the chewing insect *Spodoptera litura* for 8 hours; and a corn control group and a corn group treated with the chewing insect *Pseudomonas aeruginosa* for 8 hours. The specific steps are as follows:

[0035] (1) Plant sample pretreatment: Small amounts of leaves from three plant seedlings (rice, tomato, and corn) were rapidly ground into powder in liquid nitrogen. 400 mg of the sample powder was accurately weighed into a centrifuge tube, and 20.0 mL of pre-cooled acetonitrile was added. The mixture was extracted by sonication in ice water for 40 min, and then placed in a 4°C refrigerator for overnight extraction. The next day, the mixture was centrifuged at 10,000 rpm for 10 min, and the supernatant was collected. 15.0 mL of pre-cooled acetonitrile was added to the residue for a second extraction. The two supernatants were combined, dried under nitrogen, and diluted with 20.0 mL of water to obtain the crude plant extract.

[0036] (2) dSPE adsorption-extraction operation: CNT@TpBD composite material was used as the adsorbent for dSPE. 5.0 mg of CNT@TpBD composite material was uniformly dispersed in 20.0 mL of the above crude plant extract (pH pre-adjusted to 5.0 with 1 mol / L hydrochloric acid). The mixture was shaken on a shaker at 300 r / min for 15 min, centrifuged at 10000 rpm for 10 min, the supernatant was removed, 1.0 mL of acetonitrile solution was added as the eluent, and the mixture was vortexed vigorously for 5 min to completely desorb the three stress hormones from the CNT@TpBD composite material. The eluent was collected and dried under mild nitrogen at room temperature. Finally, it was reconstituted with 0.2 mL of 80% methanol solution, filtered, and used for subsequent HPLC-MS / MS analysis.

[0037] (3) Instruments and analytical conditions: HPLC-MS / MS analysis was performed using a Scientific Accela high-performance liquid chromatography system coupled with a TSQ Quantum Access Max™ triple quadrupole mass spectrometer. Chromatographic separation conditions: The chromatographic column was a HypersilGOLD™ column (5 μm particle size, 150 × 2.1 mm); mobile phase A was an aqueous solution containing 0.05% formic acid (v / v), and mobile phase B was methanol. The gradient elution program was as follows: 0 min, 50% B; 5 min, 50% B; 6 min, 55% B; 9 min, 50% B; 10 min, 55% B; 12 min, 50% B, with a total run time of 12 min. The column temperature was controlled at room temperature; the injection volume was 10 μL; and the flow rate was 200 μL / min. -1 Mass spectrometry analysis conditions: ESI source, positive ion mode; spray voltage 3000V; ion source temperature 300℃; capillary temperature 290℃; nitrogen as sheath gas and auxiliary gas, pressures 40 and 12, respectively; collision gas as high-purity argon (≥99.999%); quantitative analysis mode selected reaction monitoring (SRM).

[0038] (4) Quantitative analysis and actual sample determination: Under optimal conditions, a dSPE-HPLC-MS / MS detection method based on CNT@TpBD was established. The linear range for the three stress hormones was 3.0-500 pg / mL, and the limit of detection (LOD) range was 2.0-5.0 pg / mL. The experiment determined the levels of the three stress hormones in the leaves of rice, tomato, and maize seedlings after feeding by pathogens or moths. Figure 4 ).

[0039] The basic conclusions are as follows: (1) All control group samples contained the above three endogenous stress hormones in their leaves, with contents ranging from ABA (2.6-402.7 mg / g), IAA (4.1-16.4 mg / g), and JA (59.4-127.8 mg / g); (2) After treatment with fungal and insect pests, the contents of ABA, IAA, and JA in the experimental group were higher than those in the normal control group, namely ABA (7.7-481.9 mg / g), IAA (20.3-39.4 mg / g), and JA (44.9-350.6 mg / g). This conclusion is consistent with the principle that the above plant stress hormones, as trace signaling molecules of the plant itself, participate in the regulation of emergency mechanisms. Within a certain range, plants have a spontaneous ability to compensate for damage and a stress mechanism, which is to alleviate the stress effect of adverse factors on plants by regulating the contents of various hormones (mainly stress hormones) in the body. Furthermore, the contents of the above hormones in different parts of rice samples (control group, namely stem, root, leaf, leaf sheath, etc.) were quantitatively analyzed. Experimental results ( Figure 5The study found that the content of IAA and JA in the stem was higher than that in other parts, while the content of ABA in the normal growth cycle was not significantly different in different parts. This is consistent with the fact that ABA, as a typical stress hormone, usually increases significantly under adverse conditions or when plants are aging.

[0040] Application Example 2

[0041] The CNT@TpBD obtained in Example 1 was used as the adsorbent material for dSPE. Combined with liquid chromatography-triple quadrupole mass spectrometry, the changes in the content of three auxins (indoleacetic acid (IAA), indolepropionic acid (IPA), and indolebutyric acid (IBA)) in several plant seedlings under biological stress (pathogen and insect infestation) were investigated. Actual plant samples were divided into: a rice control group and a rice group treated with pathogens for 12 days; a tomato control group and a tomato group treated with the chewing insect *Spodoptera litura* for 8 hours; and a corn control group and a corn group treated with the chewing insect *Pseudomonas aeruginosa* for 8 hours. The specific steps are as follows:

[0042] (1) Plant sample pretreatment: Small amounts of leaves from three plant seedlings (rice, tomato, and corn) were rapidly ground into powder in liquid nitrogen. 400 mg of the sample powder was accurately weighed into a centrifuge tube, and 20.0 mL of pre-cooled acetonitrile was added. The mixture was extracted by sonication in ice water for 40 min, and then placed in a 4°C refrigerator for overnight extraction. The next day, the mixture was centrifuged at 10,000 rpm for 10 min, and the supernatant was collected. 15.0 mL of pre-cooled acetonitrile was added to the residue for a second extraction. The two supernatants were combined, dried under nitrogen, and diluted with 20.0 mL of water to obtain the crude plant extract.

[0043] (2) dSPE adsorption-extraction operation: CNT@TpBD composite material was used as the adsorbent for dSPE. 5.0 mg of CNT@TpBD composite material was uniformly dispersed in 20.0 mL of the above crude plant extract (pH pre-adjusted to 5.0 with 1 mol / L hydrochloric acid). The mixture was shaken on a shaker at 300 r / min for 15 min, centrifuged at 10000 rpm for 10 min, the supernatant was removed, 1.0 mL of acetonitrile solution was added as the eluent, and the mixture was vortexed vigorously for 5 min to completely desorb the three auxins from the CNT@TpBD composite material. The eluent was collected and dried under mild nitrogen at room temperature. Finally, it was reconstituted with 0.2 mL of 80% methanol solution, filtered, and used for subsequent HPLC-MS / MS analysis.

[0044] (3) Instruments and analytical conditions: HPLC-MS / MS analysis was performed using a Scientific Accela high-performance liquid chromatography system coupled with a TSQ Quantum Access Max™ triple quadrupole mass spectrometer. Chromatographic separation conditions: The chromatographic column was a HypersilGOLD™ column (5 μm particle size, 150 × 2.1 mm); mobile phase A was an aqueous solution containing 0.05% formic acid (v / v), and mobile phase B was methanol. The gradient elution program was as follows: 0 min, 50% B; 5 min, 50% B; 6 min, 55% B; 9 min, 50% B; 10 min, 55% B; 12 min, 50% B, with a total run time of 12 min. The column temperature was controlled at room temperature; the injection volume was 10 μL; and the flow rate was 200 μL / min. -1 Mass spectrometry analysis conditions: ESI source, positive ion mode; spray voltage 3000V; ion source temperature 300℃; capillary temperature 290℃; nitrogen as sheath gas and auxiliary gas, pressures 40 and 12, respectively; collision gas as high-purity argon (≥99.999%); quantitative analysis mode selected reaction monitoring (SRM).

[0045] (4) Quantitative analysis and actual sample determination: Under optimal conditions, a dSPE-HPLC-MS / MS detection method based on CNT@TpBD was established. The linear range of the three auxins was 3.0-1000 pg / mL, and the limit of detection (LOD) was 2.0 pg / mL. The experiment determined the three auxins in the leaves of rice and tomato seedlings after they were fed by pathogens or moths. The results showed that IAA was successfully detected in the leaves of all six plant seedlings after dSPE extraction, with concentrations ranging from 4.4 to 78.8 ng / g. At the same time, the IAA content in the leaves of plants treated with pathogens and fed by insects was higher than that in the leaves that had not undergone any treatment. This conclusion is consistent with the law that plant hormones, as trace signaling molecules of plants, participate in the regulation of emergency mechanisms.

[0046] The adsorption effects of CNT@TpBD, CNT-NH2, and TpBD on three auxins were compared. Figure 6The results showed that the extraction capacity of the CNT@TpBD composite material was significantly better than that of the single material, confirming that using CNT-NH2 as the substrate material for TpBD growth and crystallization, this functionalization modification method can fully utilize the advantages of both materials and increase the contact area between the CNT@TpBD composite material and the target material by virtue of its special fine tubular morphology and pore structure, thus achieving a more significant extraction effect. Furthermore, the adsorption mechanism of the CNT@TpBD composite material for three auxins was investigated. Contact angle tests showed that the static contact angles of the substrate CNT-NH2 and the CNT@TpBD composite material were 30.6° and 93.7°, respectively. Figure 7 Figure A in the diagram shows that the more hydrophobic surface of the CNT@TpBD composite material is mainly attributed to the abundant hydrophobic benzene rings introduced into the TpBD shell. To investigate the electrostatic interaction between the CNT@TpBD composite material and auxin, the zeta potential and recovery rate of three auxins were examined within the pH range of 2.0–12.0. Figure 7 (See Figures B and C). When pH < 5.0, the recovery rate of auxin increases with increasing solution pH, reaching a peak at pH = 5.0 and remaining relatively stable until pH = 9.0. When pH > 9.0, the recovery rates of all substances decrease sharply, indicating that excessively high or low pH conditions are unfavorable for the extraction of auxin by CNT@TpBD. Simultaneously, within the pH range of 5.0-8.0, the Zeta potential of the CNT@TpBD composite material is positive, while the carboxyl groups in the auxin structure give it a negative charge. Therefore, the high recovery rate of auxin is related to the electrostatic interaction between the positively charged CNT@TpBD material and the negatively charged auxin molecules. Furthermore, auxin contains active sites such as indole rings, carboxyl groups, and amino groups, while the CNT@TpBD composite material possesses functional groups such as benzene rings, C=C, and C=N. Therefore, it is inferred that there is also π-π stacking and hydrogen bonding between CNT@TpBD and auxin molecules.

[0047] Based on the above analysis, the main mechanism by which CNT@TpBD enriches auxin involves hydrophobic interactions, electrostatic interactions, π-π interactions, and hydrogen bonding between the two. Among these, hydrophobic interactions and electrostatic interactions are the main adsorption forces.

[0048] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. The application of carbon nanotube-doped covalent organic framework (CNT@TpBD) composite materials in the enrichment and detection of plant stress hormones, characterized by: CNT@TpBD composites were synthesized on the surface of CNT-NH2 via a simple and rapid one-pot method for self-assembly of TpBD, specifically including the following steps: (a) At room temperature, 0.3 mmol 63.04 mg 1,3,5-tricarboxymethyl phloroglucinol Tp and 0.45 mmol 82.91 mg benzidine BD were dissolved in 20 mL of ethanol respectively; the above solutions were then slowly added to 20 mL of ethanol solution containing 100 mg of aminated carbon nanotubes CNT-NH2 at a rate of 20 mL / min. (b) The mixed solution was thoroughly stirred, precipitated, and centrifuged. The residue was washed with N,N-dimethylformamide and ethanol to remove unreacted residual Tp and BD. Finally, it was vacuum dried at 60°C to obtain the dark green CNT@TpBD composite material. The plant stress hormones are abscisic acid, jasmonic acid, and indoleacetic acid; the specific surface area and total pore volume of the CNT@TpBD composite material are 200.7 m². 2 / g and 0.37 cm 3 It contains 0.68 nm, 1.27 nm and 2.73 nm microporous structures.

2. The application according to claim 1, characterized in that: The order in which the two monomers Tp and BD described in step (a) are added to the CNT-NH2 solution is: BD is added first, followed by Tp.

3. Use according to claim 1, characterized in that: The ethanol mentioned in step (a) is anhydrous ethanol, and CNT-NH2 is aminated multi-walled carbon nanotubes.

4. Use according to claim 1, characterized in that: The specific conditions for stirring and centrifugation in step (b) are: magnetic stirring at 400 rpm for 45 min at room temperature; and centrifugation at 10,000 rpm for 3 min.

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