Acylhydrazone-carbon nanotube gel as well as preparation method and application thereof

Abstract

The invention discloses acylhydrazone-carbon nanotube gel and a preparation method and application thereof.The acylhydrazone-carbon nanotube gel is prepared from a porphyrin compound containing four hydrazide groups, a compound containing at least two aldehyde groups and an aminated carbon nanotube as raw materials and has a porphyrin ring rigid plane structure, dense acylhydrazone bonds and the carbon nanotube keyed in the form of covalent bonds. And the gel has a cross-linked three-dimensional network structure, so that the gel can simultaneously realize good mechanical strength and a good adsorption effect on various heavy metals.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials technology, and particularly relates to an acylhydrazone-carbon nanotube gel, its preparation method and application. Background Technology

[0002] Heavy metal pollution, especially toxic heavy metal ions such as lead, cadmium, mercury, and copper in water bodies, poses a serious threat to the ecological environment and human health. These heavy metals are difficult to biodegrade and easily accumulate through the food chain; therefore, developing efficient and economical heavy metal adsorption materials has become a research hotspot in the field of environmental remediation. Currently, methods for treating heavy metal wastewater mainly include chemical precipitation, ion exchange, membrane separation, and adsorption. Among these, adsorption is considered one of the most promising technologies due to its simple operation, low cost, and recyclability. Traditional adsorption materials, such as activated carbon and zeolite, while possessing certain adsorption capacity, often suffer from limitations such as limited adsorption capacity, slow adsorption rate, poor selectivity, and difficulty in regeneration.

[0003] In recent years, nanomaterials have been widely studied for heavy metal adsorption due to their large specific surface area, unique nanotube structure, and excellent chemical stability. Studies have shown that nanomaterials have good adsorption potential for various heavy metal ions. However, raw nanomaterials are prone to aggregation, have poor dispersibility in water, and lack specific binding sites on their surfaces, resulting in a lack of selectivity in their adsorption of heavy metals, and there is still room for improvement in adsorption capacity. To improve these properties, researchers have attempted to covalently or non-covalently functionalize carbon nanotubes, among which grafting small organic molecules or polymers onto the surface of carbon nanotubes is a commonly used strategy.

[0004] Acylhydrazones are a class of Schiff bases formed by the condensation of acylhydrazides with aldehydes / ketones. Their molecular structures contain multiple nitrogen and oxygen coordinating atoms, enabling them to form stable five- or six-membered cyclic complexes with various heavy metal ions. Therefore, acylhydrazones are often used as excellent ligands for metal ions and have wide applications in chemical sensors and metal extraction. However, the combination of acylhydrazones / polymers with carbon nanotubes to construct composite gel materials with a three-dimensional network structure, achieving both high mechanical strength and high adsorption performance, has not yet been reported.

[0005] Therefore, how to provide an acylhydrazone gel that simultaneously achieves good mechanical strength and good adsorption effect on various heavy metals is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of the existing technology, an acylhydrazone-carbon nanotube gel is provided, along with its preparation method and applications. This acylhydrazone-carbon nanotube gel uses a porphyrin compound containing four acylhydrazine groups, a compound with at least two aldehyde groups, and aminated carbon nanotubes as raw materials. It has a rigid planar structure of porphyrin rings, dense acylhydrazone bonds, and carbon nanotubes covalently bonded together, and also possesses a cross-linked three-dimensional network structure. This gel can simultaneously achieve good mechanical strength and excellent adsorption effect on various heavy metals.

[0007] The first objective of this invention is to provide an acylhydrazone-carbon nanotube gel, the raw materials for which include a porphyrin compound containing four acylhydrazine groups, a compound with at least two aldehyde groups, and aminated carbon nanotubes.

[0008] In this invention, firstly, under mild reaction conditions, porphyrin compounds containing four hydrazide groups, compounds with at least two aldehyde groups, and aminated carbon nanotubes can form hydrazone / Schiff base bonds. That is, the raw materials for preparing the gel construct a three-dimensional network structure in the form of covalent bonds, providing a good structural basis for the gel to achieve good mechanical strength and stable heavy metal adsorption effect. Secondly, the rigid planar porphyrin ring structure in the gel not only provides a rigid structural basis to prevent the network structure of the gel from collapsing under external forces, but also provides four nitrogen atom coordination sites to achieve the adsorption of various heavy metals. Furthermore, the hydrazone bonds in the gel, on the one hand, have lone pairs of electrons in their nitrogen and oxygen atoms that can coordinate with heavy metals to achieve heavy metal adsorption; on the other hand, the hydrazone bonds have good structural stability, which is conducive to achieving the adsorption-desorption cycle of heavy metals. Finally, the carbon nanotubes uniformly dispersed in the gel and covalently bonded, on the one hand, have a huge specific surface area that provides sufficient physical space for heavy metal adsorption; on the other hand, their extremely high mechanical strength can also provide the tensile strength and toughness of the gel.

[0009] In some embodiments of the present invention, the molar ratio of the hydrazide group in the porphyrin compound containing four hydrazide groups to the aldehyde group in the compound containing at least two aldehyde groups is 1:1 to 2, for example, it can be 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, or 1:1.9. By controlling the molar ratio of the two groups within the above range, it is beneficial to control the reaction process for preparing the gel and obtain a gel with an appropriate degree of crosslinking.

[0010] In some embodiments of the present invention, the mass of the aminated carbon nanotubes is 0.1-2% of the sum of the masses of the porphyrin compound containing four hydrazide groups and the compound containing at least two aldehyde groups. By controlling the amount of carbon nanotubes within the above range, it is beneficial for the gel to simultaneously achieve good mechanical strength and good adsorption effect on various heavy metals. Furthermore, it is understood that the carbon nanotubes are multi-walled carbon nanotubes commonly used in industry.

[0011] In some embodiments of the present invention, the porphyrin compound containing four acylhydrazide groups is selected from 5,10,15,20-tetra(p-acylhydrazidephenyl)porphyrin.

[0012] In some embodiments of the present invention, the compound having at least two aldehyde groups is selected from at least one of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, hexanal, heptanedialdehyde, anthracenedialdehyde, terephthalaldehyde, o-phthalaldehyde, isophthalaldehyde, 2-bromomalondialdehyde, 4-hydroxyphenylglyoxal, 2-chloromalondialdehyde, 2,3-thiophenedialdehyde, 2,5-thiophenedialdehyde, 4,4'-biphenyldialdehyde, 2-(4-pyridine)malondialdehyde, 2,6-pyridinedialdehyde, pyromellitic tricarboxaldehyde, 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, tetra-(4-formylphenyl)methane, 1,3,6,8-tetra(4-formaldehydephenyl)pyrene, and 1,1'-ferrocenedialdehyde. Preferably, the compound with at least two aldehyde groups is selected from at least one of anthracene dialdehyde, 4,4'-biphenyl dicarboxaldehyde, 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, 1,3,6,8-tetra(4-carboxylphenyl)pyrene, and 1,1'-ferrocene dicarboxaldehyde, which can enhance the adsorption of heavy metals through cation-π interactions.

[0013] A second objective of this invention is to provide a method for preparing the aforementioned acylhydrazone-carbon nanotube gel, comprising the following steps:

[0014] S1. Dissolve the porphyrin compound containing four acylhydrazide groups and the compound containing at least two aldehyde groups in an organic solvent to obtain a pre-reaction solution;

[0015] S2. The aminated carbon nanotubes are added to the pre-reaction solution, a catalyst is added, the reaction is carried out, and post-treatment is performed to obtain the acylhydrazone-carbon nanotube gel.

[0016] In some embodiments of the present invention, the organic solvent in S1 is selected from dimethyl sulfoxide.

[0017] In some embodiments of the present invention, in the pre-reaction solution described in S1, the concentrations of the porphyrin compound containing four acylhydrazide groups and the compound containing at least two aldehyde groups are independently 0.03~0.06 mol·L⁻¹. -1 .

[0018] In some embodiments of the present invention, the catalyst in S2 is selected from acetic acid.

[0019] In some embodiments of the present invention, the temperature of the reaction in S2 is 25~80°C.

[0020] In some embodiments of the present invention, the reaction time in S2 is 1 to 24 hours.

[0021] In some embodiments of the present invention, the post-processing described in S2 includes the steps of sequential washing with DMSO, ethanol and subcritical CO2 extraction.

[0022] In some embodiments of the present invention, the subcritical CO2 extraction step is carried out in a high-pressure stainless steel solenoid extractor, with an extraction temperature of about 1±3℃, an extraction pressure of 5.8±1 MPa, and an extraction time of 20±4h.

[0023] In some embodiments of the present invention, after the subcritical CO2 extraction step, a step of slowly reducing the pressure to atmospheric pressure at room temperature is further included, preferably, reducing the pressure to atmospheric pressure within 2 to 3 hours.

[0024] A third objective of this invention is to provide the application of the aforementioned acylhydrazone-carbon nanotube gel in the adsorption of heavy metals.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The porphyrin compound containing four hydrazide groups, the compound with at least two aldehyde groups, and the aminated carbon nanotubes of the present invention can form hydrazone / Schiff base bonds under mild reaction conditions. That is, the raw materials for preparing the gel can form a three-dimensional network structure in the form of covalent bonds, which provides a good structural basis for the gel to achieve good mechanical strength and stable heavy metal adsorption effect.

[0027] (2) The rigid planar porphyrin ring of the present invention can not only provide a rigid structural foundation to prevent the network structure of the gel from collapsing under external force, but also provide four nitrogen atom coordination sites to achieve the adsorption of a variety of heavy metals;

[0028] (3) The acylhydrazone bond of the present invention, on the one hand, has lone pair electrons in its nitrogen and oxygen atoms that can coordinate with heavy metals to achieve adsorption of heavy metals; on the other hand, the acylhydrazone bond with good structural stability is conducive to achieving the adsorption-desorption cycle of heavy metals.

[0029] (4) The carbon nanotubes of the present invention are uniformly dispersed and covalently bonded. On the one hand, their huge specific surface area provides sufficient physical space for heavy metal adsorption. On the other hand, their extremely high mechanical strength can also provide the tensile strength and toughness of the gel. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0031] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0032] Example 1

[0033] This embodiment provides an acylhydrazone-carbon nanotube gel, the raw materials of which include 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 4,4'-biphenyldicarboxaldehyde in a molar ratio of 1:2.1, and aminated multi-walled carbon nanotubes in a mass ratio of 0.2 wt% relative to the sum of the mass of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 4,4'-biphenyldicarboxaldehyde. The preparation steps include:

[0034] S1. Weigh out 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 4,4'-biphenyldicarboxaldehyde according to the required amounts, dissolve them in dimethyl sulfoxide, and mix thoroughly to obtain a pre-reaction solution. The concentration of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin in this solution is approximately 0.03 mol·L⁻¹. -1 ;

[0035] S2. Add aminated multi-walled carbon nanotubes to the pre-reaction solution of S1 according to the specified dosage and mix thoroughly. Then add 30 μL of DMSO solution of acetic acid (3 mol·L⁻¹). -1 Mix thoroughly and let stand at 80°C for about 12 h to obtain an opaque gel. Let the obtained opaque gel stand at 80°C for another 24 h, cool to room temperature, and wash continuously with DMSO, changing the DMSO once a day for three days to obtain a wet gel. Then wash the wet gel with ethanol for three days using the same method. Place this solvent-exchanged gel in a 0.75 L high-pressure stainless steel solenoid extractor and extract with subcritical CO2 (l) (270 g) for 20 h at an extraction temperature of about 17°C (pressure 5.8 MPa). After completion, slowly reduce the pressure to ambient (about 2-3 h) at room temperature to obtain the acylhydrazone-carbon nanotube gel.

[0036] Example 2

[0037] This embodiment provides an acylhydrazone-carbon nanotube gel, the raw materials of which include 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine in a molar ratio of 1:1.6, and aminated multi-walled carbon nanotubes in a sum of 1.6 wt% relative to 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine. The preparation steps include:

[0038] S1. Weigh out 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine according to the required amounts, dissolve them in dimethyl sulfoxide, and mix thoroughly to obtain a pre-reaction solution. The concentration of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin in this solution is approximately 0.03 mol·L⁻¹. -1 ;

[0039] S2. Add aminated multi-walled carbon nanotubes to the pre-reaction solution of S1 according to the specified dosage and mix thoroughly. Then add 30 μL of DMSO solution of acetic acid (3 mol·L⁻¹). -1 Mix thoroughly and let stand at 80°C for about 12 h to obtain an opaque gel. Let the obtained opaque gel stand at 80°C for another 24 h, cool to room temperature, and wash continuously with DMSO, changing the DMSO once a day for three days to obtain a wet gel. Then wash the wet gel with ethanol for three days using the same method. Place this solvent-exchanged gel in a 0.75 L high-pressure stainless steel solenoid extractor and extract with subcritical CO2 (l) (270 g) for 20 h at an extraction temperature of about 17°C (pressure 5.8 MPa). After completion, slowly reduce the pressure to ambient (about 2-3 h) at room temperature to obtain the acylhydrazone-carbon nanotube gel.

[0040] Example 3

[0041] This embodiment provides an acylhydrazone-carbon nanotube gel, the raw materials of which include 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene in a molar ratio of 1:1.1, and aminated multi-walled carbon nanotubes in a total mass of 1.0 wt% relative to the sum of the masses of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene. The preparation steps include:

[0042] S1. Weigh out 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene according to the required amounts, dissolve them in dimethyl sulfoxide, and mix thoroughly to obtain a pre-reaction solution. The concentration of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin in this solution is approximately 0.03 mol·L⁻¹. -1 ;

[0043] S2. Add aminated multi-walled carbon nanotubes to the pre-reaction solution of S1 according to the specified dosage and mix thoroughly. Then add 30 μL of DMSO solution of acetic acid (3 mol·L⁻¹). -1 Mix thoroughly and let stand at 80°C for about 12 h to obtain an opaque gel. Let the obtained opaque gel stand at 80°C for another 24 h, cool to room temperature, and wash continuously with DMSO, changing the DMSO once a day for three days to obtain a wet gel. Then wash the wet gel with ethanol for three days using the same method. Place this solvent-exchanged gel in a 0.75 L high-pressure stainless steel solenoid extractor and extract with subcritical CO2 (l) (270 g) for 20 h at an extraction temperature of about 17°C (pressure 5.8 MPa). After completion, slowly reduce the pressure to ambient (about 2-3 h) at room temperature to obtain the acylhydrazone-carbon nanotube gel.

[0044] Example 4

[0045] This embodiment provides an acylhydrazone-carbon nanotube gel, the raw materials of which include 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and glutaraldehyde in a molar ratio of 1:2.2, and aminated multi-walled carbon nanotubes in a mass ratio of 1.0 wt% relative to the sum of the mass of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and glutaraldehyde. The preparation steps include:

[0046] S1. Weigh out 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and glutaraldehyde according to the required amounts, dissolve them in dimethyl sulfoxide, and mix thoroughly to obtain a pre-reaction solution. The concentration of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin in this solution is approximately 0.03 mol·L⁻¹. -1 ;

[0047] S2. Add aminated multi-walled carbon nanotubes to the pre-reaction solution of S1 according to the specified dosage and mix thoroughly. Then add 30 μL of DMSO solution of acetic acid (3 mol·L⁻¹). -1Mix thoroughly and let stand at 80°C for about 12 h to obtain an opaque gel. Let the obtained opaque gel stand at 80°C for another 24 h, cool to room temperature, and wash continuously with DMSO, changing the DMSO once a day for three days to obtain a wet gel. Then wash the wet gel with ethanol for three days using the same method. Place this solvent-exchanged gel in a 0.75 L high-pressure stainless steel solenoid extractor and extract with subcritical CO2 (l) (270 g) for 20 h at an extraction temperature of about 17°C (pressure 5.8 MPa). After completion, slowly reduce the pressure to ambient (about 2-3 h) at room temperature to obtain the acylhydrazone-carbon nanotube gel.

[0048] Comparative Example 1

[0049] This comparative example provides an acylhydrazone gel, the raw materials of which include 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene in a molar ratio of 1:1.1, and the preparation steps include:

[0050] S1. Weigh out 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene according to the required amounts, dissolve them in dimethyl sulfoxide, and mix thoroughly to obtain a pre-reaction solution. The concentration of 5,10,15,20-tetra(p-acylhydrazidophenyl)porphyrin in this solution is approximately 0.03 mol·L⁻¹. -1 ;

[0051] Add 30 μL of DMSO solution of acetic acid (3 mol·L⁻¹) to the pre-reaction solutions of S2 and S1. -1 Mix thoroughly, then add 30 μL of DMSO solution of acetic acid (3 mol·L⁻¹). -1 Mix thoroughly and let stand at 80°C for about 12 h to obtain an opaque gel. Let the obtained opaque gel stand at 80°C for another 24 h, cool to room temperature, and wash continuously with DMSO, changing the DMSO once a day for three days to obtain a wet gel. Then wash the wet gel with ethanol for three days using the same method. Place this solvent-exchanged gel in a 0.75 L high-pressure stainless steel solenoid extractor and extract with subcritical CO2 (l) (270 g) for 20 h at an extraction temperature of about 17°C (pressure 5.8 MPa). After completion, slowly reduce the pressure to atmospheric pressure at room temperature (about 2-3 h) and remove to obtain the acylhydrazone gel.

[0052] Comparative Example 2

[0053] This embodiment provides an imine-carbon nanotube gel, the raw materials of which include 5,10,15,20-tetra(p-aminophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene in a molar ratio of 1:1.1, and aminated multi-walled carbon nanotubes in a mass ratio of 1.0 wt% relative to the sum of the masses of 5,10,15,20-tetra(p-aminophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene. The preparation steps include:

[0054] S1. Weigh out 5,10,15,20-tetra(p-aminophenyl)porphyrin and 1,3,6,8-tetra(4-formaldehydephenyl)pyrene according to the required amounts, dissolve them in dimethyl sulfoxide, and mix thoroughly to obtain a pre-reaction solution. The concentration of 5,10,15,20-tetra(p-aminophenyl)porphyrin in this solution is approximately 0.03 mol·L⁻¹. -1 ;

[0055] S2. Add aminated multi-walled carbon nanotubes to the pre-reaction solution of S1 according to the specified dosage and mix thoroughly. Then add 30 μL of DMSO solution of acetic acid (3 mol·L⁻¹). -1 Mix thoroughly and let stand at 80°C for about 12 h to obtain an opaque gel. Let the obtained opaque gel stand at 80°C for another 24 h, cool to room temperature, and wash continuously with DMSO, changing the DMSO once a day for three days to obtain a wet gel. Then wash the wet gel with ethanol for three days using the same method. Place this solvent-exchanged gel in a 0.75 L high-pressure stainless steel solenoid extractor and extract with subcritical CO2 (l) (270 g) for 20 h at an extraction temperature of about 17°C (pressure 5.8 MPa). After completion, slowly reduce the pressure to ambient (about 2-3 h) at room temperature to obtain the imine-carbon nanotube gel.

[0056] Performance testing:

[0057] The gels of Examples 1-4 and Comparative Examples 1-2 were subjected to the following performance tests. The test methods and results are shown in Table 1.

[0058] (1) Mechanical properties: The gels of Examples 1-4 and Comparative Examples 1-2 were soaked in deionized water for 24 hours and then made into samples with a size of 30mm×5mm×5mm. The tensile strength was tested using a universal testing machine at a tensile rate of 50mm / min. The compressive strength was tested using a universal testing machine at a compression rate of 1mm / min.

[0059] (2) Adsorption performance: 20 mg of gels from Examples 1-4 and Comparative Examples 1-2 were added to 100 mL of different heavy metal ion solutions with a heavy metal ion concentration of 100 mg / L. The solutions were shaken for 3 h at a shaker speed of 200 rpm. The concentration of heavy metal ions after adsorption was measured using an atomic absorption spectrophotometer. The initial adsorption performance of the gel was evaluated according to the formula {(concentration of heavy metal ions before adsorption × volume of solution before adsorption - concentration of heavy metal ions after adsorption × volume of solution after adsorption) / 0.1 g}. The gel samples for initial adsorption performance evaluation were desorbed using 0.1 M HCl solution as the eluent. The desorbed gels were washed with water and ethanol for three days and then subjected to subcritical CO2 extraction and drying under the same conditions as in the aforementioned preparation method. The resulting gels were used for the second adsorption performance test, and this process was repeated for the third adsorption performance test. The secondary and tertiary adsorption performance of the gels were evaluated according to the aforementioned formula.

[0060] Table 1: Properties of the gels from Examples 1-4 and Comparative Examples 1-2

[0061]

[0062] As shown in Table 1, the acylhydrazone-carbon nanotube gels of Examples 1-4 of the present invention have good mechanical strength and good adsorption effect on a variety of heavy metals, especially stable repeated adsorption effect. In contrast, the acylhydrazone gel prepared in Comparative Example 1 has low mechanical strength and significantly reduced adsorption of Pd(II), and the imine-carbon nanotube gel of Comparative Example 2 has significantly reduced repeated adsorption effect on a variety of heavy metals, which cannot meet the needs of practical applications.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this application specification, they can still modify or make equivalent substitutions to the specific implementation of the present invention, but these modifications or changes do not depart from the protection scope of the pending claims of the present invention.

Claims

1. An acylhydrazone-carbon nanotube gel, characterized in that, The raw materials for its preparation include porphyrin compounds containing four acylhydrazine groups, compounds with at least two aldehyde groups, and aminated carbon nanotubes.

2. The acylhydrazone-carbon nanotube gel according to claim 1, characterized in that, The molar ratio of the acylhydrazine group in the porphyrin compound containing four acylhydrazine groups to the aldehyde group in the compound containing at least two aldehyde groups is 1:1 to 2.

3. The acylhydrazone-carbon nanotube gel according to claim 1, characterized in that, The mass of the aminated carbon nanotubes is 0.1 to 2% of the sum of the masses of the porphyrin compound containing four acylhydrazine groups and the compound containing at least two aldehyde groups.

4. The acylhydrazone-carbon nanotube gel according to claim 1, characterized in that, The porphyrin compound containing four acylhydrazide groups is selected from 5,10,15,20-tetra(p-acylhydrazidephenyl)porphyrin.

5. The acylhydrazone-carbon nanotube gel according to claim 1, characterized in that, The compound having at least two aldehyde groups is selected from at least one of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, hexanal, heptanedialdehyde, anthracenedialdehyde, terephthalaldehyde, o-phthalaldehyde, iso-phthalaldehyde, 2-bromomalondialdehyde, 4-hydroxyphenylglyoxal, 2-chloromalondialdehyde, 2,3-thiophenedialdehyde, 2,5-thiophenedialdehyde, 4,4'-biphenyldialdehyde, 2-(4-pyridine)malondialdehyde, 2,6-pyridinedialdehyde, pyromellitic tricarboxaldehyde, 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine, tetra-(4-formylphenyl)methane, 1,3,6,8-tetra(4-formaldehydephenyl)pyrene, and 1,1'-ferrocenedialdehyde.

6. The method for preparing the acylhydrazone-carbon nanotube gel according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Dissolve the porphyrin compound containing four acylhydrazide groups and the compound containing at least two aldehyde groups in an organic solvent to obtain a pre-reaction solution; S2. The aminated carbon nanotubes are added to the pre-reaction solution, a catalyst is added, the reaction is carried out, and post-treatment is performed to obtain the acylhydrazone-carbon nanotube gel.

7. The method for preparing acylhydrazone-carbon nanotube gel according to claim 6, characterized in that, The organic solvent mentioned in S1 is selected from dimethyl sulfoxide.

8. The method for preparing acylhydrazone-carbon nanotube gel according to claim 6, characterized in that, The reaction temperature described in S2 is 25~80℃.

9. The method for preparing acylhydrazone-carbon nanotube gel according to claim 6, characterized in that, The post-processing described in S2 includes the steps of washing with DMSO, ethanol and subcritical CO2 extraction in sequence.

10. The application of the acylhydrazone-carbon nanotube gel according to any one of claims 1 to 5 in the adsorption of heavy metals.

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