Preparation method of pH-sensitive cationic covalent organic framework corrosion inhibitor as well as product and application of pH-sensitive cationic covalent organic framework corrosion inhibitor

Abstract

The invention discloses a preparation method of a pH-sensitive cationic covalent organic framework corrosion inhibitor as well as a product and application of the pH-sensitive cationic covalent organic framework corrosion inhibitor, and the preparation method comprises the following steps: mixing 1, 3, 5-tri (1h-imidazole-1-yl) benzene and 4-(bromomethyl) benzaldehyde, injecting N, N-dimethylformamide, magnetically stirring and heating; adding 3, 3 '-dihydroxybenzidine, dioxane, absolute methanol and water acetic acid, freezing, vacuumizing, and washing; and mixing with benzotriazole, dissolving, vacuumizing, centrifuging and filtering. The corrosion inhibitor is loaded into micropores of the two-dimensional layered pH-sensitive cationic covalent organic framework through physical and chemical adsorption, the corrosion inhibitor is prevented from being in direct contact with components such as water and cement in the concrete mixing stage, and a cationic carrier can adsorb corrosive ions such as chloride ions and carbonate ions in concrete through ion exchange; and the pH sensitive carrier shell releases the corrosion inhibitor by identifying a signal that the pH of the micro-area is reduced when the steel bar is corroded.

Description

Technical Field

[0001] The invention relates to a preparation method of a pH-sensitive cationic covalent organic framework rust inhibitor, a product and an application thereof, and belongs to the field of preparation and application of rust inhibitors. Background Art

[0002] In the process of failure of reinforced concrete structures, the concrete structure is often damaged due to corrosion and expansion of the steel bars. Therefore, preventing steel corrosion is an important means to improve the durability of concrete structures. Among them, adding rust inhibitors to concrete to inhibit steel corrosion is the most common method.

[0003] There are two ways to add rust inhibitors: internal mixing and migration. The internal mixing type is to add rust inhibitors during the concrete mixing process, while the migration type is to migrate the rust inhibitors to the surface of the steel bars through an external electric field after the steel bars in the concrete structure are obviously corroded. During the steel bar corrosion process, the pH of the corroded area will drop sharply from 13.5 to about 5. However, ordinary rust inhibitors cannot recognize changes in such internal environmental signals, and cannot exist stably for a long time in a highly alkaline concrete environment, making it difficult to improve the long-term corrosion resistance of the steel bars. In order to solve such problems, researchers often use a combination of functional carrier materials and high-performance rust inhibitors to give rust inhibitors the properties of precise release and long-term stability. This type of rust inhibitor is a carrier-loaded rust inhibitor.

[0004] Covalent Organic Frameworks (COFs) are a new class of crystalline porous materials assembled by reversible covalent bonds, with characteristics such as stable structure, adjustable pore size and large specific surface area. According to the molding dimension, COFs can be divided into two-dimensional (2D) layered structures and three-dimensional (3D) interpenetrating networks. In recent years, the periodic network structure, large specific surface area and high modifiability have made COFs widely used in the field of drug carriers. Among them, 2D COFs have more active sites and higher solvent stability than 3D COFs, and have a wider range of applications in more harsh environments.

[0005] However, the synthesis steps of COFs are strict, the functional design is complex, and COFs are rarely used as rust inhibitor carriers for corrosion protection in reinforced concrete. They are generally added to epoxy resins to enhance the surface corrosion protection of reinforced concrete. Therefore, in order to achieve long-term corrosion protection and multifunctional synergy of rust inhibitors, designing an internally mixed load-type rust inhibitor functional material is of great significance for the application and promotion of rust inhibitors in concrete. Summary of the invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a preparation method of a pH-sensitive cationic covalent organic framework rust inhibitor, its product and application, which solves the problems of single function and insufficient long-term rust inhibition of existing rust inhibitor technology. By compounding a pH-sensitive covalent organic framework with benzotriazole to form a two-dimensional layered hydrotalcite-like structure, the multiple effects of controlled release of the rust inhibitor, pH recognition, and long-term sustained release are achieved, thereby effectively improving the anti-corrosion performance of the rust inhibitor.

[0007] Technical solution: To solve the above technical problems, the present invention provides a method for preparing a pH-sensitive cationic covalent organic framework rust inhibitor, comprising the following steps:

[0008] (1) 1,3,5-tri(1h-imidazol-1-yl)benzene and 4-(bromomethyl)benzaldehyde are fully mixed, N,N-dimethylformamide is injected as a solvent under the protection of an inert gas, nitrogen is filled in and sealed, magnetic stirring and heating are performed; after the reaction is completed, the mixture is cooled to room temperature, filtered, washed with anhydrous ethanol, and dried to obtain the product 1,3,5-tri[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide;

[0009] (2) mixing the 1,3,5-tris[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide and 3,3'-dihydroxybenzidine prepared in step (1), adding dioxane, anhydrous methanol and aqueous acetic acid, evacuating and sealing after freeze degassing cycle under the action of liquid nitrogen, and after the reaction is completed, washing with anhydrous tetrahydrofuran and ethanol, and drying to obtain a pH-sensitive covalent organic framework;

[0010] (3) The pH-sensitive covalent organic framework prepared in step (2) is fully mixed with a benzotriazole-type rust inhibitor, dissolved in water, magnetically stirred, vacuumed, centrifuged, filtered, and dried to prepare a pH-sensitive covalent organic framework rust inhibitor.

[0011] Wherein, the molar ratio of 1,3,5-tri(1h-imidazol-1-yl)benzene to 4-(bromomethyl)benzaldehyde in step (1) is 1:4.5.

[0012] Wherein, the inert gas in step (1) is nitrogen, argon or helium.

[0013] Wherein, the rotation speed of the magnetic stirring in step (1) is 450-550 rpm.

[0014] The specific surface area of ​​the pH-sensitive covalent organic framework in step (2) is 40 to 55 m 2 / g, pore size is 4~5.2nm.

[0015] Wherein, the pH of the solution during the preparation of the pH-sensitive covalent organic framework in step (2) is 4-5.

[0016] The reaction temperature in step (2) is 120° C., the reaction time is 3 days, and after cooling to room temperature, the mixture is washed with tetrahydrofuran and ethanol three times, and then dried in vacuo at 80° C. for 24 hours.

[0017] Wherein, the molar ratio of 1,3,5-tris[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide to 3,3'-dihydroxybenzidine in step (2) is 1:1.5.

[0018] Wherein, the rotation speed of the magnetic stirring in step (3) is 50 to 70 rpm.

[0019] Wherein, the mass ratio of the covalent organic framework shell to benzotriazole in step (3) is 1:3.

[0020] Wherein, the centrifugal speed in step (3) is 5000 rpm, and the vacuum drying temperature after filtration is 40°C.

[0021] The invention also provides a pH-sensitive cationic covalent organic framework rust inhibitor prepared by the preparation method.

[0022] The present invention also provides application of the pH-sensitive cationic covalent organic framework rust inhibitor in inhibiting corrosion of reinforced concrete.

[0023] The pH-sensitive cationic covalent organic framework rust inhibitor is used to prevent ion corrosion of steel bars in reinforced concrete.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0025] 1. The rust inhibitor is loaded into the micropores of the two-dimensional layered pH-sensitive cationic covalent organic framework through physical and chemical adsorption to prevent the rust inhibitor from directly contacting with water, cement and other components during the concrete mixing stage. The cationic carrier can adsorb corrosive ions such as chloride ions and carbonate ions in the concrete through ion exchange. The pH-sensitive carrier shell releases the rust inhibitor by identifying the signal of pH drop in the micro-area when the steel bar is corroded.

[0026] 2. This composite rust inhibitor has pH recognition function and can quickly release the rust inhibitor components when pH ≤ 5. Compared with pH ≥ 12, the release rate ratio of the rust inhibitor in the first 5 hours reaches 3.5:1. It has the characteristics of rapid release in low pH environment and stability in high pH environment;

[0027] 3. This composite rust inhibitor has the function of chloride ion adsorption. After releasing the rust inhibitor, the cationic covalent organic framework adsorbs chloride ions through ion exchange, reducing the reaction between chloride ions and steel bars, thereby increasing the environmental pH.

[0028] 4. This composite rust inhibitor material has both pH response and ion exchange functions of a cationic covalent organic framework. In view of the characteristics of pH drop during steel corrosion caused by chloride ion invasion in reinforced concrete structures in coastal environments, it identifies the pH drop signal, actively releases rust inhibitors, and absorbs chloride ions and other corrosive ions through ion exchange without damaging the mechanical properties of the concrete structure. It can effectively prolong the sustained release time, improve the targeting of the sustained release effect, and achieve the purpose of synergistically enhancing the corrosion resistance of steel bars. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the SEM image of the pH-sensitive covalent organic framework shell;

[0030] Figure 2 This is the SEM image of the pH-sensitive covalent organic framework rust inhibitor;

[0031] Figure 3 This is the XRD pattern of pH-sensitive covalent organic framework rust inhibitor;

[0032] Figure 4 Schematic diagram of the release law of the rust inhibitor of the samples in Example 1 and Comparative 1 in the simulated pore solution of concrete;

[0033] Figure 5 The compressive strength of the blank sample and the mortar sample doped with the pH-sensitive cationic covalent organic framework rust inhibitor prepared in Example 1 at a concentration of 0.5 g / L;

[0034] Figure 6 This is the standard curve of BTA absorbance and concentration. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0036] Example 1 Preparation of pH-sensitive cationic covalent organic framework rust inhibitor

[0037] 1. Preparation of pH-sensitive cationic covalent organic framework shell materials:

[0038] The covalent organic framework is synthesized by a solvothermal method. The method is divided into two steps: the first step is to synthesize the precursor, and the second step is to synthesize the covalent organic framework.

[0039] In the first step, 1 mmol of 1,3,5-tri(1H-imidazol-1-yl)benzene and 4.5 mmol of 4-(bromomethyl)benzaldehyde are fully mixed, and then put into a 50 ml glass flask, and 5 ml of N,N-dimethylformamide is injected as a solvent under the protection of nitrogen gas. After nitrogen is filled, the flask is sealed, stirred in a magnetic stirring device and heated to 80°C and maintained for 24 hours. After the reaction is completed, the solution is cooled to room temperature, filtered, washed with anhydrous ethanol three times, and then dried in a vacuum drying oven at 60°C for 24 hours. The product is 1,3,5-tri[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide, with a yield of about 83%, in the form of a white solid;

[0040] In the second step, 0.08mmol of 1,3,5-tris[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide and 0.12mmol of 3,3'-dihydroxybenzidine obtained by the reaction were added to a heat-resistant glass tube. Subsequently, 1.6ml of dioxane, 0.4ml of anhydrous methanol, and 0.2ml of aqueous acetic acid (3M) were added to the heat-resistant glass tube. After three cycles of freeze degassing under liquid nitrogen, the tube was evacuated and sealed with a flame spray gun. The sealed glass tube was placed in an oven at 120°C and stored for 3 days. After the reaction was completed, the glass tube was opened to filter the sample, and it was washed three times with anhydrous tetrahydrofuran and ethanol respectively. The washed sample was dried in a vacuum oven at 80°C for 24 hours to obtain a yellow pH-sensitive covalent organic framework shell ( Figure 1 ).

[0041] 2. Preparation of pH sensitive cationic covalent organic framework rust inhibitor:

[0042] The prepared covalent organic framework shell material and the rust inhibitor benzotriazole were mixed thoroughly (the mass ratio of the covalent organic framework shell material to the rust inhibitor benzotriazole was 1:3) and then dissolved in water (the mass ratio of the mixture to water was 1:100). After magnetic stirring for 24 hours, the solution was placed in a vacuum box and the vacuum degree was maintained at -0.09Mpa for 15 minutes. After repeating this process 3 times, the solution was taken out and centrifuged at a speed of 5000rpm for 15 minutes. After filtering, it was vacuum dried at 40°C for 24 hours to prepare a pH-sensitive covalent organic framework rust inhibitor. SEM and XRD diagrams are shown in the figure. Figure 2 , 3 As shown, Figure 3 COF is the pH-sensitive covalent organic framework shell, BTA is the rust inhibitor benzotriazole, and COF+BTA is the pH-sensitive covalent organic framework rust inhibitor.

[0043] Comparative Example 1

[0044] The pH-sensitive cationic covalent organic framework shell was prepared. The specific implementation method was the same as the steps for preparing the pH-sensitive cationic covalent organic framework shell material in Example 1, and a covalent organic shell without benzotriazole was obtained.

[0045] Example 2 Performance Evaluation of pH Sensitive Covalent Organic Framework Rust Inhibitor

[0046] 1. Evaluation of rust resistance performance:

[0047] The rust resistance performance evaluation test was carried out in a concrete simulated pore solution (SCPs) containing NaCl. The composition of SCPs was 0.6M KOH+0.2M NaOH+Sat.Ca(OH)2, pH was 13.6, NaCl concentration was 3.5wt.%, and the material of the carbon steel electrode for the test was Q235 carbon steel. A pH-sensitive cationic covalent organic framework rust inhibitor prepared in Example 1, a single pH-sensitive cationic covalent organic framework, benzotriazole and an SCPs solution without rust inhibitor prepared in Comparative Example 1 (blank example) were set respectively, and the concentration was set to 0.5g / L. The corrosion inhibition ability was studied by electrochemical impedance spectroscopy (EIS) test, and the test age was up to 10 days. The rust resistance efficiency was obtained by fitting the data obtained by the above-mentioned experimental method test, and the results are shown in Table 1.

[0048] Table 1

[0049]

[0050] The addition of the pH-sensitive cationic covalent organic framework rust inhibitor prepared in Example 1 of the present invention can effectively improve the corrosion resistance of steel bars in concrete, and has long-term protection for steel bars; and the composite rust inhibitor can improve the rust inhibition efficiency by 53% compared with the pH-sensitive covalent organic framework shell that can only adsorb chloride ions. This is because the pH-sensitive cationic covalent organic framework rust inhibitor can identify the pH signal generated by the pitting micro-area in the solution, thereby controlling the release of the rust inhibition component to repair the pitting pit in time, and the cationic covalent organic framework can absorb chloride ions in the solution, reducing the tendency of steel bars to rust.

[0051] 2. Slow release process of rust inhibitor:

[0052] 50 mg of pH-sensitive cationic covalent organic framework rust inhibitor was dissolved in 100 mL of SCPs solution with pH values ​​of 5.2 and 13.5, respectively, and allowed to stand for a period of time, then centrifuged, and the supernatant was taken for absorbance test to obtain the release rate (%). A curve was drawn with time (t) as the horizontal axis and release rate (%) as the vertical axis. Figure 4This is the release kinetics trend diagram of the rust inhibitor. It can be seen that the pH-sensitive cationic covalent organic framework rust inhibitor has a sustained release effect in a strong alkaline environment and can be released quickly in a low pH environment.

[0053] 3. Compressive strength test:

[0054] The compressive strength test is carried out according to the provisions of GB / T17671-2021 "Test Method for Cement Mortar Strength", and the molding is 40×40×160mm 3 The mortar test block has a water-cement ratio of 0.5, a mortar-sand ratio of 1:3, and a concentration of rust inhibitor in the mixing water of 0.5 g / L. Figure 5 It can be seen from the results that there is no significant difference in compressive strength between the blank sample and the sample in Example 1, indicating that the pH-sensitive cationic covalent organic framework rust inhibitor has no obvious side effects on the mechanical properties of concrete.

[0055] Comparative Example 2

[0056] Three different covalent organic frameworks were prepared. The synthesis steps of the three covalent organic frameworks were divided into two steps: the first step was to synthesize the precursor in the same way as the first step in Example 1 to obtain 1,3,5-tris[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide; the second step was to introduce different functional groups into the covalent organic framework by changing the reactants in the imine condensation (see schematic diagram). Figure 1 ), benzidine, 3,3'-dihydroxybenzidine, and 3,3'-dicarboxybenzidine were selected to synthesize covalent organic frameworks with no functional groups, hydroxyl groups, and carboxyl groups, respectively, and they were named COF1, COF-OH, and COF-COOH.

[0057]

[0058] in:

[0059] The precursor is 1,3,5-tris[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide;

[0060] The reactants are benzidine, 3,3'-dihydroxybenzidine, and 3,3'-dicarboxybenzidine;

[0061] The reaction conditions, when the reactants are benzidine and 3,3'-dihydroxybenzidine, are the same as those in the second step of Example 1; when the reactant is 3,3'-dicarboxybenzidine, the amount of dioxane in the second step of Example 1 is increased to 2 ml, the amount of anhydrous methanol is increased to 0.6 ml, and the amount of acetic acid (3M) is reduced to 0.1 ml.

[0062] The prepared different types of covalent organic frameworks are loaded with BTA according to step 2 in Example 1. During the process, the supernatant after centrifugation is collected and marked for later use. Use a pipette to take 50uL of the supernatant and dilute it to 10mL, then measure its ultraviolet spectrum. Take the absorbance value at 259nm and bring it into the BTA absorbance and concentration standard curve to convert the free BTA content in the supernatant, and then obtain the drug loading rate of different functional groups. The BTA absorbance and concentration standard curve is as follows: Figure 6 shown.

[0063] Drug loading rate calculation formula:

[0064] in:

[0065] W1 represents the initial mass of BTA;

[0066] W2 represents the mass of BTA free in the solution;

[0067] W3 represents the total mass of COF loaded with BTA.

[0068] The drug loading rates of COF1, COF-OH, and COF-COOH were calculated according to the above formula, and the results are shown in Table 2:

[0069] Table 2

[0070]

[0071] Experiments have shown that the covalent organic framework introduced with hydroxyl functional groups has a higher drug loading rate, that is, the more BTA is loaded in the pH-sensitive cationic covalent organic framework rust inhibitor prepared in Example 1, the higher the rust inhibition efficiency.

Claims

1. A method for preparing a pH-sensitive cationic covalent organic framework rust inhibitor, characterized in that: The following steps are involved: (1) 1,3,5-tri(1h-imidazol-1-yl)benzene and 4-(bromomethyl)benzaldehyde are fully mixed, N,N-dimethylformamide is injected under the protection of an inert gas, nitrogen is filled in and sealed, magnetic stirring and heating are performed; after the reaction is completed, the mixture is cooled, filtered, washed and dried to obtain the product 1,3,5-tri[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide; (2) mixing the 1,3,5-tris[3-(4-formylbenzyl)-1h-imidazol-1-yl]benzyl bromide and 3,3'-dihydroxybenzidine prepared in step (1), adding dioxane, anhydrous methanol and aqueous acetic acid, evacuating and sealing after freeze degassing cycle under the action of liquid nitrogen, and washing and drying after the reaction is completed to obtain a pH-sensitive covalent organic framework; (3) The pH-sensitive covalent organic framework prepared in step (2) is fully mixed with the rust inhibitor benzotriazole and dissolved in water, magnetically stirred, vacuumed, centrifuged, filtered and dried to prepare a pH-sensitive covalent organic framework rust inhibitor.

2. The preparation method according to claim 1, characterized in that: The inert gas in step (1) is nitrogen, argon or helium.

3. The preparation method according to claim 1, characterized in that: The rotation speed of the magnetic stirring in step (1) is 450-550 rpm.

4. The preparation method according to claim 1, characterized in that: The rotation speed of the magnetic stirring in step (3) is 50 to 70 rpm.

5. The preparation method according to claim 1, characterized in that: The specific surface area of ​​the pH-sensitive covalent organic framework in step (2) is 40 to 55 m 2 / g, pore size is 4~5.2nm.

6. The preparation method according to claim 1, characterized in that: The pH of the solution during the preparation of the pH-sensitive covalent organic framework in step (2) is 4-5.

7. A pH-sensitive cationic covalent organic framework rust inhibitor prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the pH-sensitive cationic covalent organic framework inhibitor according to claim 7 in inhibiting corrosion of reinforced concrete.

9. The use according to claim 8, characterized in that: Used to prevent ion corrosion of steel bars in reinforced concrete.

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