Synthesis method and application of redox cation covalent organic framework

Abstract

The invention discloses a synthesis method and application of a redox cation covalent organic framework, and belongs to the technical field of functional adsorption materials. 2, 5-dihydroxy benzaldehyde and triamino guanidine chloride are used as reaction monomers, a covalent organic framework is constructed through a Schiff alkali condensation reaction, guanidyl cation sites are synchronously introduced, hydroxyl redox active groups are reserved, and a redox cation covalent organic framework (AGS-TPA-OH) uniformly-distributed high-density guanidyl salt cation and hydroquinone active unit is prepared. Cr2O7 < 2-> is efficiently captured through electrostatic interaction. The synthesis method is green and efficient, the adsorption capacity of the obtained AGS-TPA-OH on Cr2O7 < 2-> reaches 4377.25 mg / g, the removal rate in 50 minutes exceeds 98%, an innovative solution is provided for efficient treatment and resource recycling of hexavalent chromium in industrial wastewater, and the method has remarkable environmental and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials, and particularly relates to a synthesis method and application of a redox cationic covalent organic framework. Background Art

[0002] Heavy metal pollution poses a serious threat to the ecological environment and human health. Among them, hexavalent chromium Cr(VI) exists widely in industrial wastewater in the form of dichromate ions Cr2O7 2- and has high toxicity, strong carcinogenicity and high mobility. Traditional treatment methods such as chemical precipitation, ion exchange and activated carbon adsorption have certain effects, but face problems such as low adsorption capacity, poor selectivity and secondary pollution. In recent years, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have become research hotspots for efficient adsorbents due to their designable pores and functionalization sites. For example, ZIF-8 can capture Cr(VI) through electrostatic interaction, but its hydrothermal stability and antioxidant property are insufficient, and it is prone to structural collapse under strong acid / alkali conditions. Although some cationic COFs have achieved selective adsorption of Cr(VI) through quaternary ammonium groups, they lack redox active sites and are difficult to reduce highly toxic Cr(VI) to low-toxicity Cr(III), resulting in the need for additional treatment steps after adsorption. In addition, existing redox materials such as zero-valent iron or sulfides can directly reduce Cr(VI), but are prone to aggregation and oxidation inactivation, and it is difficult to synergize with the adsorption function. Cationic polymer networks (CPNs) have a high specific surface area and adjustable charge density, but their post-synthesis modification often leads to uneven distribution of functional groups, and cationic units such as imidazolium salts are prone to hydrolysis under strong alkaline conditions, restricting their practical applications. Therefore, there is an urgent need to develop redox cationic covalent organic frameworks with high stability, high selectivity, high adsorption capacity and fast adsorption kinetics for the efficient removal of dichromate ions and achieve deep purification of Cr(VI). Summary of the Invention

[0003] To solve the above problems, the present invention provides a synthesis method and application of a redox cationic covalent organic framework, which are achieved through the following technical solutions.

[0004] A synthesis method of a redox cationic covalent organic framework includes the following steps:

[0005] S1, using 2,5-dihydroxybenzaldehyde and guanidine triamine hydrochloride as reaction monomers, adding THF, water and acetic acid thereto, wherein the volume ratio of tetrahydrofuran to water is 3.4:0.6, and then obtaining a reaction mixture through ultrasonic treatment, and the THF is tetrahydrofuran;

[0006] S2. Place the reaction mixture in a quartz tube for degassing treatment. The degassing process is liquid nitrogen bath freezing - vacuum pumping - thawing, and this process is cycled three times. After the degassing treatment is completed, flame seal the quartz tube. The sealed quartz tube is heated at 120 °C for 3 days, filter the heated reaction mixture and collect the product;

[0007] S3. Wash the product collected by filtration with THF, DMF and absolute ethanol. The washed product is dried overnight at 120 °C, and the DMF is N,N - dimethylformamide;

[0008] S4. Filter and separate the dried product, and the product after filtration and separation is post - treated to obtain the redox cationic covalent organic framework.

[0009] Furthermore, in the step S1, the molar ratio of 2,5 - dihydroxybenzaldehyde to guanyl chloride triamine as the reaction monomers is 3:2.

[0010] Furthermore, in the step S1, in the reaction mixture, the volume range of THF, water and acetic acid is 4.0 - 4.6 mL.

[0011] Furthermore, in the step S4, the post - treatment is to wash the solid product obtained by filtration with THF, DMF and absolute ethanol in sequence, and the washed product is dried under vacuum.

[0012] The present invention also provides an application of the redox cationic covalent organic framework in adsorbing dichromate ions:

[0013] Add the redox cationic covalent organic framework prepared by the above - mentioned preparation method into the solution to be treated containing dichromate ions to obtain a suspension.

[0014] Furthermore, the ion concentration in the solution to be treated containing dichromate ions is 0 - 600 mg / L, and the addition amount of the redox cationic covalent organic framework in the solution to be treated is

[0015] Furthermore, before the solution to be treated containing dichromate ions is mixed with the redox cationic covalent organic framework, it also includes adjusting its pH to 2 - 6 by using a pH regulator.

[0016] Furthermore, the addition amount of the redox cationic covalent organic framework in the solution to be treated is Before the solution to be treated containing dichromate ions is mixed with the redox cationic covalent organic framework, its pH is adjusted to 4 by using a pH regulator.

[0017] Further, it also includes filtering the suspension after adsorption with a 0.22 μm nylon membrane filter.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention uses 2,5-dihydroxybenzaldehyde and triaminoguanidine chloride as reaction monomers to construct a covalent organic framework through Schiff base condensation reaction, synchronously introducing guanidinium cation sites and retaining hydroxyl redox active groups, and preparing a redox cationic covalent organic framework (AGS-TPA-OH) with uniformly distributed high-density guanidinium salt cations and hydroquinone active units. It can efficiently capture Cr2O7 through electrostatic interaction 2- , and can in-situ reduce Cr(VI) to low-toxicity Cr(III) through electron transfer of hydroxyl groups. The electron-rich nitrogen and oxygen groups provide effective coordination sites to achieve a "adsorption-reduction-coordination" synergistic mechanism. It can improve the adsorption kinetics and adsorption selectivity of the material for dichromate ions, thereby realizing the highly selective and ultrafast removal of dichromate ions in water. The method for synthesizing the cationic covalent organic framework in the present invention is simple, has a stable structure, is environmentally friendly, can be used for the rapid removal and highly selective recovery of dichromate ions, and has good application prospects. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the following description of the specific embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0021] Figure 1 It is a schematic diagram of the synthesis route of the redox cationic covalent organic framework AGS-TPA-OH.

[0022] Figure 2 It is the Fourier transform infrared spectroscopy (FT-IR) diagram of AGS, TPA-OH, and AGS-TPA-OH.

[0023] Figure 3 It is the solid-state 13 13C cross-polarization / magic angle spinning NMR spectrum of AGS-TPA-OH.

[0024] Figure 4 It is the nitrogen adsorption-desorption isotherm of AGS-TPA-OH.

[0025] Figure 5 It is the effect of AGS-TPA-OH on the removal efficiency of Cr2O7 at different solid-liquid ratios 2- ​

[0026] Figure 6 The influence of AGS-TPA-OH on the removal efficiency of Cr2O7 2- at different pH values.

[0027] Figure 7 The adsorption thermodynamic curve of AGS-TPA-OH for Cr2O7 2-

[0028] Figure 8 The adsorption kinetic curve of AGS-TPA-OH for Cr2O7 2- Specific embodiments

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0030] A synthesis method of a redox cationic covalent organic framework, comprising the following steps:

[0031] S1, using 2,5-dihydroxybenzaldehyde and guanidine trichloride triamine as reaction monomers, adding THF, water and acetic acid thereto, wherein the volume ratio of tetrahydrofuran to water is 3.4:0.6, and then obtaining a reaction mixture through ultrasonic treatment, where THF is tetrahydrofuran;

[0032] S2, placing the reaction mixture in a quartz tube for degassing treatment, and the degassing treatment process is liquid nitrogen bath freezing - vacuum pumping - thawing. The degassing treatment process is cycled three times. After the degassing treatment is completed, the quartz tube is flame-sealed, and the sealed quartz tube is heated at 120 °C for 3 days. The heated reaction mixture is filtered and the product is collected;

[0033] S3, washing the product collected by filtration with THF, DMF and absolute ethanol, and drying the washed product overnight at 120 °C, where DMF is N,N-dimethylformamide;

[0034] S4, filtering and separating the dried product, and the product after filtration and separation is post-treated to obtain the redox cationic covalent organic framework.

[0035] Specifically, in step S1, the molar ratio of 2,5-dihydroxybenzaldehyde and guanidine trichloride triamine as reaction monomers is 3:2.

[0036] Specifically, in step S1, in the reaction mixture, the volume range of THF, water and acetic acid is 4.0 - 4.6 mL.​​

[0037] Specifically, in step S4, the post-treatment is to wash the solid product obtained by filtration with THF, DMF, and absolute ethanol in sequence, and then vacuum-dry the washed product.

[0038] The present invention also provides an application of a redox cationic covalent organic framework in adsorbing dichromate ions:

[0039] Add the redox cationic covalent organic framework prepared by the above preparation method into the solution to be treated containing dichromate ions to obtain a suspension.

[0040] Specifically, the ion concentration in the solution to be treated containing dichromate ions is 0 - 600 mg / L, and the addition amount of the redox cationic covalent organic framework in the solution to be treated is

[0041] Specifically, before the solution to be treated containing dichromate ions is mixed with the redox cationic covalent organic framework, it also includes adjusting its pH to 2 - 6 using a pH regulator.

[0042] Specifically, the addition amount of the redox cationic covalent organic framework in the solution to be treated is Before the solution to be treated containing dichromate ions is mixed with the redox cationic covalent organic framework, its pH is adjusted to 4 using a pH regulator.

[0043] Specifically, it also includes filtering the suspension after adsorption using a 0.22 μm nylon membrane filter.

[0044] Example 1:

[0045] AGS-TPA-OH was synthesized by a Schiff base reaction of 2,5-dihydroxybenzaldehyde (TPA-OH, 0.3 mmol, 49.8 mg) and aminoguanidine chloride (AGS, 0.2 mmol, 28.9 mg) in 4 mL of tetrahydrofuran (THF) / water (3.4:0.6, v / v) with the addition of acetic acid (3 M, 0.6 mL). The synthesized product was placed in a quartz tube, and the mixture was degassed three times by freeze-pumping-thaw cycles under liquid nitrogen, and then the quartz tube was sealed with a screw cap and heated at 120 °C for 3 days. Then the product was collected by filtration, and the filtered product was washed with THF, N,N-dimethylformamide (DMF), and absolute ethanol, and then dried overnight at about 100 °C. After drying overnight, the redox cationic covalent organic framework AGS-TPA-OH was obtained through post-treatment.

[0046] Figure 1 It is a schematic diagram of the synthesis route of the redox cationic covalent organic framework AGS-TPA-OH.

[0047] The redox cationic covalent organic framework AGS-TPA-OH was characterized by infrared spectroscopy,

[0048] Figure 2 which are the Fourier transform infrared spectroscopy (FT-IR) spectra of AGS, TPA-OH, and AGS-TPA-OH.

[0049] Figure 3 The solid-state 13 13C cross-polarization / magic angle spinning NMR spectrum of the redox cationic covalent organic framework AGS-TPA-OH further confirmed that AGS-TPA-OH showed an obvious characteristic peak at ~150 ppm, which was attributed to the sp 2 hybrid carbon atoms in the imine bond.

[0050] Figure 4 The nitrogen adsorption-desorption isotherm of the redox cationic covalent organic framework AGS-TPA-OH is shown. According to the nitrogen-desorption isotherm at 77 K, the BET specific surface area of the redox cationic covalent organic framework AGS-TPA-OH was determined to be 60.2 m 2 g -1 .

[0051] Example 2: Application of a Redox Cationic Covalent Organic Framework in the Removal of Dichromate Ions

[0052] Figure 5 shows the effect of AGS-TPA-OH on the removal efficiency of Cr2O7 at different solid-liquid ratios. 2- As can be seen from Figure 5 , within the range of solid-liquid ratios of , AGS-TPA-OH showed the optimal removal efficiency at .

[0053] Figure 6 shows the effect of AGS-TPA-OH on the removal efficiency of Cr2O7 at different pH values. 2- As can be seen from Figure 5 , AGS-TPA-OH still maintained excellent removal efficiency within the pH range of 2-6, showing high acid resistance stability. Among them, AGS-TPA-OH had the best removal efficiency for Cr2O7 at pH = 4. 2-

[0054] 3 mg of AGS-TPA-OH was added to a solution containing Cr2O7 2-In a solution of (0 - 600 ppm), the pH value of the solution was adjusted to 4.0 with nitric acid or sodium hydroxide solution, the mixture was stirred at 300 rpm, and the suspension was filtered through a 0.22 μm microporous membrane filter. The remaining Cr2O7 in the filtrate was measured by inductively coupled plasma mass spectrometry 2- The concentration of, and finally the adsorption capacity of AGS - TPA - OH for Cr2O7 2- was calculated to be 4377.25 mg / g, which is higher than that of most existing materials. For example, the adsorption capacity of TzDa - COF is 1866 mg / g, that of CF - COF is 1794 mg / g, and that of TpDa - COF is 982.5 mg / g. The adsorption capacity calculation formula is as follows: q e =(C0 – C e ) / m×V, where V is the volume of the mixed solution in L; m is the dosage of the cationic covalent organic framework in g; C0 is the initial concentration of Cr2O7 2- in mg / L; C e is the equilibrium concentration of Cr2O7 2- in mg / L.

[0055] Figure 7 is the adsorption thermodynamic curve of AGS - TPA - OH for Cr2O7 2- .

[0056] Figure 8 is the adsorption kinetic curve of AGS - TPA - OH for Cr2O7 2- . The results show that the adsorption of AGS - TPA - OH for Cr2O7 2- reaches dynamic equilibrium within 50 min. This can be attributed to the cationic guanidine fragment of AGS - TPA - OH and the hydroquinone molecules on the framework providing high - affinity Cr(VI) binding sites, thus greatly improving the adsorption capacity for Cr2O7 2- . The experimental results conform to the pseudo - second - order kinetic model, indicating that the adsorption of AGS - TPA - OH for Cr2O7 2- is mainly chemisorption.

[0057] It can be seen that the redox cationic covalent organic framework AGS - TPA - OH prepared by the method of the present invention has excellent stability and extremely high chromium adsorption capacity, and can be used as an efficient adsorbent for dichromate ions.

[0058] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments only. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for synthesizing a redox cationic covalent organic framework, characterized in that, It includes the following steps: S1. Using 2,5-dihydroxybenzaldehyde and guanidine triamine chloride as reaction monomers, adding THF, water and acetic acid thereto, wherein the volume ratio of tetrahydrofuran to water is 3.4:0.6, and then obtaining a reaction mixture through ultrasonic treatment, and the THF is tetrahydrofuran; S2. Placing the reaction mixture in a quartz tube for degassing treatment, and the degassing treatment process is liquid nitrogen bath freezing - vacuum pumping - thawing. The degassing treatment process is cycled three times. After the degassing treatment is completed, the quartz tube is flame-sealed. The sealed quartz tube is heated at 120°C for 3 days, and the heated reaction mixture is filtered and the product is collected; S3. The product after filtration and collection is washed with THF, DMF and absolute ethanol, and the washed product is dried overnight at 120°C, and the DMF is N,N-dimethylformamide; S4. The dried product is filtered and separated, and the product after filtration and separation is post-treated to obtain a redox cationic covalent organic framework.

2. The synthesis method of a redox cationic covalent organic framework according to claim 1, characterized in that: In the step S1, the molar ratio of 2,5-dihydroxybenzaldehyde to guanidine triamine chloride as reaction monomers is 3:

2.

3. The synthesis method of a redox cationic covalent organic framework according to claim 1, characterized in that: In the step S1, in the reaction mixture, the volume range of THF, water and acetic acid is 4.0 - 4.6 mL.

4. The synthesis method of a redox cationic covalent organic framework according to claim 1, characterized in that: In the step S4, the post-treatment is to wash the solid product obtained by filtration with THF, DMF and absolute ethanol in sequence, and the washed product is dried in vacuum.

5. Application of a redox cationic covalent organic framework, which is synthesized by the method described in any one of claims 1-4, characterized in that: It is used for removing dichromate ions.

6. The application of a redox cationic covalent organic framework according to claim 5, characterized in that, Adding the redox cationic covalent organic framework to a solution to be treated containing dichromate ions to obtain a suspension.

7. Use of a redox cationic covalent organic framework according to claim 6, characterized in that, The ion concentration in the solution to be treated containing dichromate ions is 0 - 600 mg / L, and the addition amount of the redox cationic covalent organic framework in the solution to be treated is 8. Use of a redox cationic covalent organic framework according to claim 7, characterized in that, Before the solution to be treated containing dichromate ions is mixed with the redox cationic covalent organic framework, it further includes adjusting its pH to 2 - 6 by using a pH regulator.

9. Use of a redox cationic covalent organic framework according to claim 8, characterized in that, The addition amount of the redox cationic covalent organic framework in the solution to be treated is ; before the solution to be treated containing dichromate ions is mixed with the redox cationic covalent organic framework, its pH is adjusted to 4 by using a pH regulator.

10. The application of a redox cationic covalent organic framework according to claim 6, wherein It further includes filtering the suspension after adsorption by using a 0.22 μm nylon membrane filter.

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