Intelligent Metal Frame - Conductive Polymer Anticorrosion Coating and Preparation Method Thereof, Application

Abstract

The present invention discloses an intelligent metal framework-conductive polymer anti-corrosion coating and its preparation method and application. The preparation method includes: preparing metal-organic framework ZIFs by a room-temperature synthesis method; formulating a mixed electrolyte for electrodepositing a composite coating; using a three-electrode system by a potentiostatic method, using the mixed solution prepared in step (2) as the electrolyte, and electrodepositing a composite coating on the surface of the working electrode to obtain an electrochemically deposited metal-organic framework-conductive polymer anti-corrosion coating. The coating raw materials in the present invention are easily obtained and low-toxic, can form a film directly, quickly and over a large area on the surface of a metal substrate, are not restricted by factors such as the shape and surface morphology of the substrate, and effectively avoid the defects of poor adhesion and unstable service performance of the existing conductive polymer coatings, and have good application prospects in stainless steel materials and fuel cell metal plates serving in acidic soil, seawater splash zones, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of metal corrosion protection, and particularly to an intelligent metal frame - conductive polymer anti - corrosion coating and its preparation method and application. Background Art

[0002] Corrosion is a natural phenomenon in which metals react chemically or electrochemically with media in a certain environment, resulting in metal deterioration or reduced performance. Metal corrosion can cause irreversible damage to ships, bridges, pipelines, public buildings, household appliances, etc., seriously threatening public safety and causing huge economic losses and environmental pollution. Stainless steel, as a commonly used metal material in industry, has very wide applications in fields such as construction, ships, petrochemical industry, and fuel cell plates. However, in the presence of corrosion media such as chloride ions and sulfur - containing compounds, the corrosion process of stainless steel materials during long - term service is still inevitable. It is estimated that about 20% of stainless steel rusts every year. In the actual environment, the corrosion of stainless steel cannot be completely stopped, but the corrosion rate of stainless steel can be reduced by various means to make the corrosion process controllable, thereby prolonging the service life of stainless steel materials and reducing their application costs. Currently, there are many methods to prevent the corrosion of stainless steel, and among them, the coating anti - corrosion method is one of the most important methods to improve the corrosion resistance of stainless steel.

[0003] Traditional anti - corrosion coatings are mainly resin - based organic coatings, and the anti - corrosion mechanism is to form a physical barrier on the surface of the metal substrate to isolate corrosive substances. However, due to the inherent defects of the film - forming substances, there are usually micropores in the constructed coating structure, which cannot play a long - term corrosion protection role. In recent years, the construction of intelligent anti - corrosion coatings has received extensive attention, and it is expected to overcome the bottleneck problem that the single protection mechanism of coatings cannot meet the long - term and stable protection of stainless steel. Conductive polymers (CPs) are a special type of polymer material. After doping, CPs can change from an insulating state to a conductive state. As a coating material, it can not only isolate the corrosion environment, but also form an oxide film at the coating / metal interface, maintaining the corrosion potential of the protected metal in the passivation zone and further strengthening the corrosion protection effect of the coating (anodic protection function). However, CPs coatings usually have defects such as micropores and cracks, and the de - doping of anions during long - term service can cause CPs to gradually return to the insulating state, weakening the anodic protection effect of the coating and making the coating gradually fail. Therefore, the stability of CPs coatings during long - term service greatly limits their practical applications in the field of corrosion protection.

[0004] Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials with intramolecular pores formed by the self-assembly of organic ligands and metal ions or clusters through coordination bonds. Due to their highly tunable porosity, large pore volume, and abundant active sites, they are widely used in the fields of biosensing, drug delivery, and catalysis. Currently, it has been reported that MOF materials are used as nano-microcapsule sealed corrosion inhibitors to enhance the anti-corrosion performance of coatings.

[0005] In the prior art, the invention patent with the application publication number CN110387548A discloses a composite of metal-organic framework encapsulated corrosion inhibitor, its preparation method and application. A novel corrosion inhibition system is constructed by encapsulating a corrosion inhibitor in a MOF nano-shell, which is suitable for the corrosion environment in the seawater splash zone. Utilizing the characteristic that the MOF material ZIF-67 is sensitive to acidic environments, the encapsulated corrosion inhibitor is rapidly released to act on the corrosion area. However, this composite acts in the acidic corrosion environment in the form of a corrosion inhibitor, which limits its application scope. The invention patent with the application publication number CN112521837A discloses a filler of MOF loaded with a corrosion inhibitor, a self-healing anti-corrosion coating and its preparation method. The corrosion inhibitor is encapsulated in hmt-MOF and used as a filler for epoxy resin to construct a protective coating, endowing the coating with self-healing performance. However, the dispersion problem of the MOFs encapsulating the corrosion inhibitor as a filler in the coating substrate also limits its corrosion inhibition performance. Summary of the Invention

[0006] Aiming at the problems mentioned in the background art, the present invention provides an intelligent metal framework-conductive polymer anti-corrosion coating, its preparation method and application to overcome the deficiencies that the existing anti-corrosion coatings cannot meet long-term and stable corrosion protection, and the defects and shortcomings existing in the existing intelligent anti-corrosion technologies. The intelligent metal-organic framework-conductive polymer anti-corrosion coating of the present invention is composed of metal-organic framework materials ZIFs with corrosion inhibition functions and CPs materials such as polyaniline (PANI) and polypyrrole (PPY). By exerting the synergistic effect of CPs and MOFs, targeted intelligent corrosion protection of metal materials such as stainless steel in acidic service environments is achieved.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions:

[0008] A preparation method of a metal framework-conductive polymer anti-corrosion coating includes the following steps:

[0009] Step (1): Prepare metal-organic framework ZIFs by a room-temperature synthesis method. The ZIFs include at least ZIF-67 and / or ZIF-8;

[0010] Step (2), prepare a mixed electrolyte for electrodepositing a composite coating: Disperse a conductive polymer monomer and a sodium dodecyl sulfate anionic surfactant in deionized water, then add the ZIFs prepared in step (1), and stir evenly by ultrasonic wave in sequence to obtain a mixed solution;

[0011] Step (3), use a three-electrode system by the potentiostatic method, use the mixed solution prepared in step (2) as the electrolyte, and electrodeposit a composite coating on the surface of the working electrode to obtain an electrochemically deposited metal-organic framework-conductive polymer anti-corrosion coating.

[0012] Preferably, in step (1), the ZIFs material uses a metal salt to provide a central metal ion and an imidazole organic compound to provide an organic ligand.

[0013] Preferably in any of the above solutions, the metal salt is Zn(NO3)2·6H2O and / or Co(NO3)2·6H2O, and the imidazole organic compound is 2-methylimidazole.

[0014] Preferably in any of the above solutions, in step (1), the preparation method of the ZIFs material is: dissolve at least one or both of the mixed metal salts of Zn(NO3)2·6H2O and Co(NO3)2·6H2O in water or methanol to obtain component A, dissolve the 2-methylimidazole organic ligand in water or methanol to obtain component B. After components A and B are fully dissolved, quickly pour component B into component A and stir to mix the two. After standing and reacting at room temperature, centrifuge to separate to obtain a precipitate, and after repeatedly washing with methanol, dry the precipitate to obtain the metal-organic framework crystal materials ZIF-67 and ZIF-8.

[0015] Preferably in any of the above solutions, the mixing and stirring time of components A and B is 30 min, the standing and reacting time at room temperature after mixing is 12 - 48 h, the centrifugation separation time after the reaction is 10 - 30 min, and the precipitate is washed 3 - 5 times with methanol and then vacuum dried. The drying temperature is 50 - 80 °C and the drying time is 12 - 48 h.

[0016] In the above steps, the standing and reacting time at room temperature after mixing components A and B is any value within the range of 12 - 48 h, such as 12 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 48 h; the centrifugation separation time after the reaction is any value within the range of 10 - 30 min, such as 10 min, 20 min, 30 min; the precipitate is washed 3 - 5 times with methanol and then vacuum dried, and the drying temperature is any value within the range of 50 - 80 °C, such as 50 °C, 60 °C, 70 °C, 80 °C; the drying time is any value within the range of 12 - 48 h, such as 12 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 48 h.

[0017] Preferably, in any of the above solutions, in step (1), during the preparation of ZIF-67 and ZIF-8, the molar ratios of the central ions to the ligands are 1:58 and 1:70, respectively.

[0018] Preferably, in any of the above solutions, in step (1), during the preparation of ZIF-67 and ZIF-8, the centrifugation speed for separating the product is 8000 rmp, the separation time is 10 - 20 min, and the methanol washing time for each centrifugation is 10 - 20 min. The product centrifugation separation time can be any value within the range of 10 - 20 min, such as 10 min, 15 min, or 20 min; the methanol washing time for each centrifugation is any value within the range of 10 - 20 min, such as 10 min, 15 min, or 20 min.

[0019] Preferably, in any of the above solutions, in step (1), the polymer monomer (CPs monomer) includes at least one of polyaniline (PANI) and polypyrrole (PPY).

[0020] Preferably, in any of the above solutions, in step (2), the mixed solution includes pyrrole or aniline monomer with a concentration of 0.1 - 0.5 mol / L, sodium dodecyl sulfate with a concentration of 0.05 - 0.3 mol / L, and ZIFs with a concentration of 0.5 - 2 mg / mL.

[0021] The concentration of pyrrole or aniline monomer can be any value within the range of 0.1 - 0.5 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, or 0.5 mol / L; the concentration of sodium dodecyl sulfate can be any value within the range of 0.05 - 0.3 mol / L, such as 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, or 0.3 mol / L. The concentration of ZIFs can be any value within the range of 0.5 - 2 mg / mL, such as 0.5 mg / mL, 1 mg / mL, 1.5 mg / mL, or 2 mg / mL.

[0022] Preferably, in any of the above solutions, in step (2), the mixed solution is ultrasonicated for 10 - 20 min and then continuously magnetically stirred for 10 - 30 min to obtain a homogeneous mixed electrolyte solution.

[0023] In this step, the ultrasonic time of the mixed solution can be any value within the range of 10 - 20 min, such as 10 min, 15 min, or 20 min; the magnetic stirring time can be any value within the range of 10 - 30 min, such as 10 min, 15 min, 20 min, 25 min, or 30 min.

[0024] Preferably, in any of the above solutions, in step (3), in the three-electrode deposition system, the reference electrode and the counter electrode are an Ag / AgCl electrode and a platinum sheet electrode respectively, the working electrode is the stainless steel substrate that needs corrosion protection, and the electrochemical deposition process is carried out by potentiostatic method with an electrodeposition time of 10 - 30 min.

[0025] Preferably, in any of the above solutions, in the method of potentiostatic electrodeposition, for aniline and pyrrole monomers, the deposition voltages are -1.3 V and 1.4 V respectively, the electrodeposition time is 10 - 30 min, the drying temperature of the prepared coating is 30 - 50 °C, and the drying time is 3 - 5 h. In this step, the electrodeposition time is any value within the range of 10 - 30 min, such as 10 min, 15 min, 20 min, 25 min, 30 min; the drying temperature of the prepared coating is any value within the range of 30 - 50 °C, such as 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, and the drying time is any value within the range of 3 - 5 h, such as 3 h, 4 h, 5 h.

[0026] Preferably, in any of the above solutions, during the electrodeposition process, the working electrode is the stainless steel substrate that needs anti-corrosion treatment, and the surface of the stainless steel substrate is a surface with any shape.

[0027] Preferably, in any of the above solutions, before preparing the coating, the non-coating deposition surface of the stainless steel is encapsulated with epoxy resin, its deposition surface is polished, and then it is successively cleaned with deionized water, acetone, and ethanol.

[0028] Preferably, in any of the above solutions, in step (3), after electrochemical deposition, the metal-organic framework - conductive polymer anti-corrosion coating is washed with deionized water and dried, the drying temperature is 30 - 50 °C, and the drying time is 3 - 5 h.

[0029] The present invention also provides a metal-organic framework - conductive polymer anti-corrosion coating prepared by the method according to any one of the above.

[0030] The present invention also provides an application of the metal-organic framework - conductive polymer anti-corrosion coating prepared by the method according to any one of the above in the corrosion protection of stainless steel in an acidic environment.

[0031] Preferably, in any of the above solutions, the acidic environment is a 0.1 - 0.5 mol / L sulfuric acid or hydrochloric acid solution.

[0032] The anti-corrosion effect in the acidic corrosion environment is characterized by electrochemical testing. The electrochemical testing is carried out through a three-electrode system, where the sample to be tested is the working electrode, the platinum sheet electrode is the counter electrode, and the Ag / AgCl electrode is the reference electrode.

[0033] Preferably, in any of the above solutions, the specific electrochemical tests include potentiodynamic polarization tests, open-circuit potential tests, and electrochemical impedance spectroscopy tests.

[0034] Beneficial effects

[0035] (1) As a representative class of MOFs, zeolitic imidazolate frameworks (ZIFs) are tetrahedral framework materials with imidazolate esters as organic ligands. As an anti-corrosion material, ZIFs have stability and acid-sensitivity characteristics that other types of MOFs do not have, and the imidazole-based ligands in the structure endow ZIFs with natural corrosion inhibition functions. Therefore, in-situ composite construction of anti-corrosion coating materials using ZIFs and CPs can give full play to the advantages of both. The self-healing property of the coating can be imparted through the designability of the structure and function of ZIFs, while CPs adhere to the surface and pores of ZIFs to form a laminated conductive network, giving full play to the anodic protection effect and physical barrier function, strengthening the anti-corrosion performance of the coating, and ultimately achieving intelligent protection of metals.

[0036] (2) The preparation method of the metal-organic framework-conductive polymer anti-corrosion coating provided by the present invention is simple in process, safe, environmentally friendly, low in energy consumption, and not limited by the shape of the stainless steel substrate. A functional metal-organic framework-conductive polymer anti-corrosion coating can be rapidly deposited on the stainless steel surface. The present invention strictly controls the concentrations of CPs monomers, sodium dodecyl sulfate dopants, and ZIFs, as well as the electrodeposition conditions, effectively inserting the dopants into the main chain of CPs and achieving the combination of ZIFs and CPs.

[0037] (3) The present invention constructs an intelligent composite anti-corrosion coating system, overcoming the problem of poor anti-corrosion stability in existing passive anti-corrosion coating technologies. The present invention endows the coating with a self-healing function using special metal-organic framework compounds ZIFs, and composites with conductive polymers to strengthen the anodic protection performance and physical barrier effect of the coating. ZIFs are assembled from metal center ions such as Zn and Co and 2-methylimidazole organic ligands with corrosion inhibition functions, with rich active sites, which are conducive to binding with conductive polymers and have good compatibility. The constructed composite coating can interact with the protected metal substrate to form metal-N / O coordination bonds, hydrogen bonds, etc., which is conducive to improving the adhesion of the coating and preventing the penetration of corrosive substances to the coating / substrate interface.

[0038] (4) The main working principle of this application is as follows: The ZIFs material composed of organic ligands with corrosion inhibition properties exhibits water stability, acid dissociation properties, and is sensitive to pH changes. In an acidic corrosive medium, the physical barrier formed by the composite coating constructed by the combination of CPs and ZIFs on the surface of the metal material can effectively prevent the inward penetration of corrosive substances. Under the condition that no corrosion occurs, CPs can fully exert their anodic protection performance, effectively reducing the corrosion potential of the substrate metal material to make it in a passivated state, while ZIFs remain in a stable state, avoiding the environmental degradation of the corrosion inhibitor active groups therein. When the continuous attack of corrosive substances causes local damage to the coating, while CPs play an anodic protection role, the stimulation of the coordination bonds in ZIFs by the pH change in a small range caused by the corrosion reaction can promote the dissociation of ZIFs, releasing the ligand corrosion inhibitor to act on the damaged area of the coating, thereby achieving the targeted delivery of the corrosion inhibitor at the corrosion-induced site and achieving the self-repair effect of the coating.

[0039] (5) The coating raw materials in the present invention are easily available, low-toxic, and easy to prepare. They can form a film directly, quickly, and over a large area on the surface of the metal substrate, without being restricted by factors such as the shape and surface morphology of the substrate, effectively avoiding the defects of poor adhesion and unstable service performance of the existing conductive polymer coatings. It has good application prospects in stainless steel materials and fuel cell metal plates serving in acidic soil, seawater splash zones, etc. The intelligent metal-organic framework-conductive polymer anti-corrosion coating material prepared in the present invention realizes the organic combination of the anti-corrosion advantages of metal-organic frameworks and conductive polymers. The stable and reliable anti-corrosion performance of the coating has been verified by electrochemical experiments, and it is suitable for the corrosion protection of stainless steel materials in acidic environments such as acidic soil, inside fuel cells, and seawater splash zones. The technical route of the present invention is reasonable, the coating preparation process is simple and environmentally friendly, the product performance is excellent, and the application prospect is broad. Description of the Drawings

[0040] Figure 1 is the preparation flow chart of the intelligent metal-organic framework-conductive polymer anti-corrosion coating of the present invention;

[0041] Figure 2 is the morphology diagram of the ZIF-67 nanoparticles synthesized in Example 1 of the present invention;

[0042] Figure 3 is the morphology diagram of the coatings in Example 2 and Comparative Example 2 of the present invention, where a is the morphology diagram of the ZIF-67-PPY anti-corrosion coating in Example 2, and b is the surface morphology diagram of the PPY anti-corrosion coating in Comparative Example 2;

[0043] Figure 4The following figure shows the variation of the Nyquist plots of the electrochemical impedance spectra of Example 2 and Comparative Example 2 of the present invention with service time in an acidic corrosion environment (0.1 mol / L HCl). Among them, a is the Nyquist plot of the ZIF-67-PPY anti-corrosion coating in Example 2, and b is the Nyquist plot of the PPY anti-corrosion coating in Comparative Example 2;

[0044] Figure 5 The following figure shows the variation curve of the open circuit potential of Example 2 and Comparative Example 2 of the present invention with the service time of the sample during long-term service, and the potentiodynamic polarization curves of Example 2, Comparative Example 2, and 430 stainless steel bare steel;

[0045] Figure 6 The following figure shows the surface morphology of the ZIF-8 nanoparticles synthesized in Example 4 of the present invention. Detailed implementation mode

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with 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. All other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention. Without special instructions, the relevant materials appearing in the subsequent embodiments are prepared and obtained in the previous embodiments.

[0047] A preparation method of an intelligent metal-organic framework-conductive polymer anti-corrosion coating of the present invention, the preparation process is as Figure 1 shown, including the following steps:

[0048] (1) Prepare MOF materials of two imidazole ligands, ZIF-67 and ZIF-8, by the room temperature synthesis method;

[0049] (2) Disperse CPs monomers aniline or pyrrole, sodium dodecyl sulfate anion dopant, and ZIFs in deionized water to prepare a uniform mixed solution;

[0050] (3) Use a three-electrode system to electro-deposit a coating in the mixed solution to obtain the metal-organic framework-conductive polymer anti-corrosion coating.

[0051] Among them, the ZIFs prepared by the room-temperature synthesis method are ZIF-67 and ZIF-8 materials, and the specific processes include crystal growth, centrifugation, washing, vacuum drying, etc. The more specific process of ZIF-67 crystal growth is as follows: A certain amount of Co(NO3)2·6H2O is added to 50 - 100 mL of water or methanol to obtain component A, and a certain amount of 2-methylimidazole is added to 50 - 100 mL of water or methanol to obtain component B. After A and B are fully stirred and dissolved, B is quickly poured into A and stirred and mixed. The molar ratio of metal ions to imidazole ligands is 1:58. After the mixed solution is stirred at room temperature for 30 min, it is left to react for 12 - 48 h to grow crystals. The rotation speed for centrifugal separation is 8000 rmp, centrifugation is carried out for 10 - 30 min, and it is centrifugally washed with methanol 3 - 5 times. The lower-layer precipitate after washing is vacuum dried at 50 - 80 °C for 12 - 48 h; The more specific process of ZIF-8 crystal growth is as follows: The nitrate providing the central metal ion is replaced with Zn(NO3)2·6H2O, and the molar ratio of metal ions to imidazole ligands is 1:70, and the remaining steps are the same as those of ZIF-67.

[0052] Example 1

[0053] An intelligent metal framework-conductive polymer composite conductive anti-corrosion coating, specifically a ZIF-67-PANI composite coating, and the preparation method specifically includes the following steps:

[0054] First step: Preparation of ZIF-67 by room-temperature synthesis method: Take 2.70 g of Co(NO3)2·6H2O and add it to 50 mL of methanol to obtain component A, and take 44.24 g of 2-methylimidazole and add it to 100 mL of methanol to obtain component B. After A and B are fully stirred and dissolved, B is quickly poured into A and stirred and mixed. After stirring at room temperature for 30 min, it is left to react for 48 h to grow crystals. Subsequently, centrifugation is carried out at 8000 rmp for 10 min, the precipitate is collected, and it is centrifugally washed with methanol 5 times, 10 min each time. The lower-layer precipitate after washing is vacuum dried at 70 °C for 24 h to obtain ZIF-67 nanoparticles. In this example, the surface morphology of the ZIF-67 nanoparticles is as shown in the appendix Figure 2 and presents a rhombic dodecahedron structure with a size of 200 - 400 nm.

[0055] Second step: Treatment of the stainless-steel substrate: Use epoxy resin to encapsulate the non-deposited surface of the bulk 430 stainless steel, leaving a deposition area of 1×1 cm 2 and an electrode clip contact area. The deposition area is polished successively with 240, 800, and 1500-mesh metallographic sandpapers, and then the deposition area is washed successively with deionized water, acetone, and ethanol, and finally dried.

[0056] Step 3: Prepare a metal-organic framework-conductive polymer coating through one-pot electrodeposition. Add aniline monomer, sodium dodecyl sulfate, and ZIF-67 into 100 mL of deionized water, ultrasonicate for 15 min, and magnetically stir for 30 min to prepare a homogeneous mixed solution, where the concentration of aniline monomer is 0.25 mol / L, the concentration of sodium dodecyl sulfate is 0.3 mol / L, and the concentration of ZIF-67 is 0.5 mg / mL. The treated stainless-steel substrate serves as the working electrode, the platinum plate electrode serves as the counter electrode, and the Ag / AgCl electrode serves as the reference electrode. A coating is electrodeposited on the stainless-steel surface by the potentiostatic method for 15 minutes at a deposition voltage of -1.3 V, and the obtained coating is marked as the ZIF-67-PANI coating.

[0057] The coating product obtained in this example has a dense structure and uniform morphology, mainly presenting the morphology of wrinkled PANI. Potentiodynamic polarization testing can judge the corrosion behavior occurring on the electrode surface, characterize the corrosion tendency and degree of the material, and thus reflect the anti-corrosion ability of the sample after applying the coating. Compared with the 430 stainless-steel substrate without the deposited coating, the self-corrosion voltage of the coating sample obtained in this example increased by 310 mV in the corrosion environment simulated by 0.3 mol / L sulfuric acid, indicating a significant improvement in the corrosion resistance of 430 stainless steel.

[0058] Comparative Example 1

[0059] The difference from Example 1 is as follows:

[0060] Add aniline monomer and sodium dodecyl sulfate into 100 mL of deionized water, ultrasonicate for 15 min, and magnetically stir for 30 min to prepare a homogeneous mixed solution, where the concentration of aniline monomer is 0.25 mol / L and the concentration of sodium dodecyl sulfate is 0.3 mol / L;

[0061] Other conditions are the same as those in Example 1, and a PANI coating is obtained by electrodeposition with the potentiostatic method.

[0062] The PANI coating prepared in this comparative example has a loose structure, showing many micropores and microcracks.

[0063] Example 2

[0064] An intelligent metal framework-conductive polymer composite conductive anti-corrosion coating, specifically a ZIF-67-PPY composite coating. The preparation method specifically includes the following steps:

[0065] Step 1: Preparation of ZIF-67 by room-temperature synthesis method: Take 2.70 g of Co(NO3)2·6H2O and add it to 25 mL of water to obtain component A. Add 44.24 g of 2-methylimidazole to 160 mL of water to obtain component B. After A and B are fully stirred and dissolved, quickly pour B into A and stir to mix. Stir at room temperature for 30 min and then let it stand for reaction for 24 h to allow crystal growth. Subsequently, centrifuge at 8000 rmp for 15 min, collect the precipitate, wash it by centrifugation with methanol 3 times, 10 min each time. The washed lower-layer precipitate is vacuum-dried at 60 °C for 24 h to obtain ZIF-67 nanoparticles. In this example, the morphology of the ZIF-67 product is similar to that of Figure 2 and presents a rhombic dodecahedron structure with a size of 200 - 300 nm.

[0066] Step 2: Treatment of the stainless-steel substrate: Use epoxy resin to encapsulate the non-deposition surface of the 430 stainless-steel sheet, leaving a deposition area of 1×1 cm 2 and the electrode clip contact area. Grind the deposition area successively with 240, 800, and 1500-mesh metallographic sandpapers, and then wash the deposition area successively with deionized water, acetone, and ethanol, and finally dry it.

[0067] Step 3: Preparation of a metal-organic framework-conductive polymer coating by one-pot electrodeposition method. Add pyrrole monomer, sodium dodecyl sulfate, and ZIF-67 to 100 mL of deionized water, ultrasonicate for 10 min, and stir magnetically for 20 min to prepare a homogeneous mixed solution, where the concentration of pyrrole monomer is 0.4 mol / L, the concentration of sodium dodecyl sulfate is 0.15 mol / L, and the concentration of ZIF-67 is 1 mg / mL. The treated stainless-steel substrate is used as the working electrode, a platinum sheet electrode is used as the counter electrode, and an Ag / AgCl electrode is used as the reference electrode. Coatings are electrodeposited on the stainless steel surface by the potentiostatic method, where the electrodeposition time is 10 min and the deposition voltage is 1.4 V. The obtained coating is marked as the ZIF-67-PPY coating.

[0068] In this example, the obtained metal-organic framework-conductive polymer coating product has a dense structure and uniform morphology, as shown in Figure 3 (a).

[0069] Electrochemical impedance spectroscopy can semi-quantitatively evaluate the physical barrier performance of the coating system against the corrosion environment and the interfacial corrosion kinetics process, thereby reflecting the anti-corrosion ability of the coating and the kinetics process of coating damage. The Nyquist diagram of the electrochemical impedance spectroscopy of this example in a corrosion environment simulated by 0.1 mol / L HCl within 600 h of service is shown in Figure 4(a) As shown, it can be seen that within the first 240 h of service of this embodiment, the impedance has been showing an increasing trend. After 240 h of service, although the impedance slightly decreases, it is still significantly higher than that at the initial stage of service. This is because PPY and ZIF-67 can play a synergistic role through the implementation of anodic protection performance and the release of corrosion inhibitors, endowing the coating with intelligent active protection ability, and still maintaining a high anti-corrosion effect when the coating has minor defects during long-term service.

[0070] Comparative Example 2

[0071] Preparation of PPY coating

[0072] The difference from Example 2 is as follows:

[0073] Pyrrole monomer and sodium dodecyl sulfate were added to 100 mL of deionized water, ultrasonicated for 10 min, and magnetically stirred for 20 min to prepare a homogeneous mixed solution, where the concentration of pyrrole monomer was 0.4 mol / L and the concentration of sodium dodecyl sulfate was 0.15 mol / L;

[0074] Other conditions were the same as those in Example 2, and a PPY coating was obtained by potentiostatic electrodeposition.

[0075] The morphology of the PPY coating prepared in this comparative example is as shown in the appendix Figure 3 (b). The coating is composed of cauliflower-like PPY particles, and there are micropores between the particles. The Nyquist diagram of the electrochemical impedance spectrum of this embodiment within 600 h of service in a corrosion environment simulated by 0.1 mol / L HCl is as shown in the appendix Figure 4 (b). It can be seen that the impedance of this comparative example reaches the maximum at 48 h of service, indicating that the coating has excellent corrosion resistance in a harsh corrosion environment during the service time of 0 - 48 h. However, after 48 h of service of the coating, the impedance shows a linear decreasing trend. As can be seen from the enlarged inset, the impedance at 600 h of service is even lower than the impedance value at the initial stage of service, indicating that the coating fails, and this coating does not have a stable corrosion protection effect, and the anti-corrosion effect is significantly inferior to that of the coating in Example 2.

[0076] The change of the open circuit potential (OCP) of the coating during long-term service in a corrosion environment can evaluate the spontaneous reaction, the formation of the steady-state potential and its stability occurring in the environment in the form of passivation or activation, and further reflect the anti-corrosion performance of the coating. Appendix Figure 5(a) is the curve of the OCP value of Example 2 and Comparative Example 2 varying with the service time. It can be seen that within the service time of 600 h, for Example 2 of the present invention, that is, the coating material constructed by ZIF-67, PPY, and sodium dodecyl sulfate, has a higher OCP value compared to Comparative Example 2, and basically maintains a relatively stable value throughout the service period, indicating that Example 2 has excellent corrosion resistance, and the coating can provide long-term, stable, and excellent corrosion protection for stainless steel.

[0077] Attachment Figure 5 (b) is the potentiodynamic polarization curve of Example 2, Comparative Example 2, and the bare stainless steel without coating in the acidic corrosion environment simulated by 0.1 mol / L HCl. It can be seen that Example 2 of the present invention has the highest self-corrosion potential and the lowest self-corrosion current density. Compared with the bare stainless steel, the self-corrosion voltage has increased by 495 mV. From the above electrochemical test results, it can be seen that Example 2 has higher corrosion protection efficiency, which is related to the dense structure of the coating (as shown in Attachment Figure 3 (a)), and also benefits from the synergistic effect of CPs, dopants, and MOFs. By giving full play to their respective advantages, the coating is endowed with intelligent active protection ability, effectively improving the corrosion resistance of stainless steel.

[0078] Example 3:

[0079] An intelligent metal frame-conductive polymer composite conductive anti-corrosion coating, specifically a ZIF-8-PANI composite coating. The preparation method includes the following steps:

[0080] The first step: Preparation of ZIF-8 by the room-temperature synthesis method: Take 1.17 g of Zn(NO3)2·6H2O and add it to 100 mL of water to obtain component A. Add 22.70 g of 2-methylimidazole to 100 mL of water to obtain component B. After A and B are fully stirred and dissolved, quickly pour B into A and stir and mix. Stir at room temperature for 30 min and then let it stand and react for 36 h to allow crystal growth. Subsequently, centrifuge at 8000 rmp for 20 min, collect the precipitate, wash it by centrifugation with methanol 4 times, 10 min each time. The lower-layer precipitate after washing is vacuum dried at 50 °C for 48 h to obtain ZIF-8 nanoparticles. In this example, the morphology of the ZIF-8 nanoparticles is in the shape of a rhombic dodecahedron structure, with a size of 100-150 nm.

[0081] The second step: Treatment of the stainless steel substrate: Use epoxy resin to encapsulate the non-deposited surface of the massive 304 stainless steel, leaving a deposition area of 1×1 cm 2 and the electrode clip contact area. Polish the deposition area successively with 240, 800, and 1500-mesh metallographic sandpapers, and then wash the deposition area successively with deionized water, acetone, and ethanol, and finally dry it.

[0082] Step 3: Prepare a metal-organic framework-conductive polymer coating by one-pot electrodeposition method. Add aniline monomer, sodium dodecyl sulfate, and ZIF-8 into 100 mL of deionized water, ultrasonicate for 20 min, and magnetically stir for 20 min to prepare a homogeneous mixed solution, where the concentration of aniline monomer is 0.5 mol / L, the concentration of sodium dodecyl sulfate is 0.25 mol / L, and the concentration of ZIF-8 is 2 mg / mL. The treated stainless steel substrate is used as the working electrode, a platinum sheet electrode is used as the counter electrode, and an Ag / AgCl electrode is used as the reference electrode. A coating is electrodeposited on the stainless steel surface by potentiostatic method for 30 minutes at a deposition voltage of -1.3 V. The obtained coating is marked as ZIF-67-PANI coating.

[0083] The morphology of the coating product obtained in this example is similar to that of the coating in Example 1 shown in Figure 3 (a). It has a dense structure, uniform morphology, and presents a more complex micro-morphology. Compared with the stainless steel substrate without the deposited coating, its self-corrosion voltage in the corrosion environment simulated by 0.5 mol / L hydrochloric acid increases by 298 mV.

[0084] Comparative Example 3

[0085] The difference from Example 3 is that:

[0086] Add aniline monomer and sodium dodecyl sulfate into 100 mL of deionized water, ultrasonicate for 20 min, and magnetically stir for 20 min to prepare a homogeneous mixed solution, where the concentration of aniline monomer is 0.5 mol / L and the concentration of sodium dodecyl sulfate is 0.25 mol / L;

[0087] Under other conditions the same as those in Example 3, a PANI coating is obtained by potentiostatic electrodeposition.

[0088] The PANI coating prepared in this comparative example has a loose structure, showing many micropores and microcracks.

[0089] Example 4

[0090] A preparation method of an intelligent metal framework-conductive polymer composite conductive anti-corrosion coating, specifically a ZIF-8-PPY composite coating, includes the following steps:

[0091] Step 1: Preparation of ZIF-8 by room-temperature synthesis method: 1.17 g of Zn(NO3)2·6H2O was added to 20 mL of methanol to obtain component A, and 22.70 g of 2-methylimidazole was added to 100 mL of methanol to obtain component B. After A and B were fully stirred and dissolved, B was quickly poured into A and stirred and mixed. After stirring at room temperature for 30 min, the mixture was left to react for 24 h to allow crystal growth. Subsequently, centrifugation was carried out at 8000 rmp for 15 min, the precipitate was collected, and it was centrifugally washed with methanol 3 times, 15 min each time. The washed lower-layer precipitate was vacuum dried at 60 °C for 48 h to obtain ZIF-8 nanoparticles. In this example, the morphology of the ZIF-8 nanoparticles is as shown in Figure 6 , and the product has a rhombic dodecahedron structure with a size of 70-100 nm.

[0092] Step 2: Treatment of the stainless-steel substrate: The non-deposition surface of a 304 stainless-steel sheet was encapsulated with epoxy resin, leaving a deposition area of 1×1 cm 2 and an electrode clip contact area. The deposition area was polished successively with 240-, 800-, and 1500-mesh metallographic sandpapers, and then the deposition area was washed successively with deionized water, acetone, and ethanol, and finally dried.

[0093] Step 3: Preparation of a metal-organic framework-conductive polymer coating by one-pot electrodeposition. Pyrrole monomer, sodium dodecyl sulfate, and ZIF-8 were added to 100 mL of deionized water, ultrasonicated for 10 min, and magnetically stirred for 20 min to prepare a homogeneous mixed solution, where the concentration of pyrrole monomer was 0.2 mol / L, the concentration of sodium dodecyl sulfate was 0.1 mol / L (SDS), and the concentration of ZIF-8 was 1.5 mg / mL. The treated stainless-steel substrate was used as the working electrode, a platinum sheet electrode was used as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. A coating was electrodeposited on the stainless steel by the potentiostatic method, where the electrodeposition time was 20 minutes and the deposition voltage was 1.4 V, and the obtained coating was labeled as the ZIF-8-PPY coating.

[0094] In this example, the obtained metal-organic framework-conductive polymer coating product has a dense structure and uniform morphology. Compared with the 304 stainless-steel substrate without the deposited coating, its self-corrosion voltage in the corrosion environment simulated by 0.5 mol / L sulfuric acid increased by 463 mV.

[0095] Comparative Example 4

[0096] The difference from Example 4 is that:

[0097] Add pyrrole monomer and sodium dodecyl sulfate into 100 mL of deionized water, ultrasonicate for 10 min, and magnetically stir for 20 min to prepare a homogeneous mixed solution, where the concentration of pyrrole monomer is 0.2 mol / L and the concentration of sodium dodecyl sulfate is 0.1 mol / L;

[0098] Under other conditions the same as those in Example 1, a PPY coating was obtained by potentiostatic electrodeposition.

[0099] The morphology of the PPY coating prepared in this comparative example is similar to that of Comparative Example 2 shown in Figure 3 (b). The coating is composed of cauliflower-like PPY particles, and there are micropores between the particles.

[0100] It can be seen from Examples 1 to 4 that the preparation method of the intelligent metal-organic framework-conductive polymer anti-corrosion coating material of the present invention is simple and has low energy consumption. A composite coating structure with a dense structure and uniform morphology can be obtained by adjusting the ratio of each component. Moreover, the construction of the coating is not limited by the morphology and shape of the metal substrate. The obtained coating material not only has a good physical barrier effect, but also can give full play to the advantages of conductive polymers and metal-organic frameworks, providing anodic protection for the substrate metal and an intelligent self-healing function at the micro-damaged parts of the coating. Therefore, in an acidic corrosion environment, the intelligent metal-organic framework-conductive polymer anti-corrosion coating in the present invention can provide stable and long-term protection for stainless steel materials. The present invention has great significance for the corrosion protection of stainless steel materials in acidic environments such as acidic soil, inside fuel cells, and the splash zone of seawater.

[0101] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An application of a metal framework-conductive polymer anti-corrosion coating to the corrosion protection of stainless steel in an acidic environment, characterized in that: The preparation method of the metal framework-conductive polymer anti-corrosion coating comprises the following steps: Step (1): Prepare metal-organic frameworks ZIFs by the room-temperature synthesis method, and the ZIFs include at least ZIF-67 and / or ZIF-8; Step (2): Prepare a mixed electrolyte for electrodepositing a composite coating: Disperse a conductive polymer monomer and a sodium dodecyl sulfate anionic surfactant in deionized water, and then add the ZIFs prepared in step (1), and stir evenly by ultrasonic wave in sequence to obtain a mixed solution. The conductive polymer monomer is aniline or pyrrole, the concentration of the pyrrole or aniline monomer is 0.1-0.5 mol / L, the concentration of sodium dodecyl sulfate is 0.05-0.3 mol / L, and the concentration of the ZIFs is 0.5-2 mg / mL; Step (3): Use a three-electrode system by the potentiostatic method, use the mixed solution prepared in step (2) as the electrolyte, and electrodeposit a composite coating on the surface of the working electrode to obtain an electrochemically deposited metal-organic framework-conductive polymer anti-corrosion coating. The working electrode is a stainless steel sample.

2. Use of the metal frame-conductive polymer anti-corrosion coating according to claim 1 for corrosion protection of stainless steel in an acidic environment, characterized in that: In step (1), the central metal ions of the ZIFs material are provided by a metal salt, and the organic ligand is provided by an imidazole organic compound.

3. Use of the metal frame-conductive polymer anti-corrosion coating according to claim 2 for corrosion protection of stainless steel in an acidic environment, characterized in that: The metal salt is Zn(NO3)2·6H2O and / or Co(NO3)2·6H2O, and the imidazole organic compound is 2-methylimidazole.

4. The application of the metal frame-conductive polymer anti-corrosion coating according to claim 1 to the corrosion protection of stainless steel in an acidic environment, characterized in that: In step (1), the preparation method of the ZIFs material is: dissolve at least one or two of Zn(NO3)2·6H2O and Co(NO3)2·6H2O in water or methanol to obtain component A, dissolve the 2-methylimidazole organic ligand in water or methanol to obtain component B. After components A and B are fully dissolved, quickly pour component B into component A and stir to mix the two. After standing and reacting at room temperature, centrifuge to separate to obtain a precipitate, and after repeatedly washing with methanol, dry the precipitate to obtain the metal-organic framework crystal material ZIF-67 and / or ZIF-8.

5. The application of the metal frame-conductive polymer anti-corrosion coating according to claim 4 to the corrosion protection of stainless steel in an acidic environment, characterized in that: The mixing and stirring time of components A and B is 30 min, the standing and reacting time at room temperature after mixing is 12-48 h, the centrifugal separation time after the reaction is 10-30 min, and the precipitate is washed 3-5 times with methanol and then vacuum dried. The drying temperature is 50-80 °C, and the drying time is 12-48 h; in the preparation process of ZIF-67 and ZIF-8, the molar ratios of the central ion to the ligand are 1:58 and 1:70 respectively.

6. The application of the metal frame-conductive polymer anti-corrosion coating according to claim 1 to the corrosion protection of stainless steel in an acidic environment, characterized in that: In step (3), the reference electrode and the counter electrode in the three-electrode deposition system are an Ag / AgCl electrode and a platinum sheet electrode respectively. The electrochemical deposition process is carried out by the potentiostatic method, and the electrodeposition time is 10-30 min.

7. The application of the metal frame-conductive polymer anti-corrosion coating according to claim 1 to the corrosion protection of stainless steel in an acidic environment, characterized in that: In step (3), the electrochemically deposited metal-organic framework-conductive polymer anti-corrosion coating is washed with deionized water and dried. The drying temperature is 30-50 °C, and the drying time is 3-5 h.

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