Preparation method and application of modified layered double hydroxide

Abstract

This invention provides a method for preparing and applying a modified layered bimetallic hydroxide. The preparation method includes the following steps: Step 1, preparing a mixed solution of Ca(NO3)2 and Al(NO3)2, labeled as solution A, and preparing a mixed solution of NaNO3 and NaOH, labeled as solution B; Step 2, adding solution A dropwise to solution B to obtain a mixed slurry; Step 3, hydrothermal reaction; Step 4, cooling, centrifuging, washing, and drying for later use; Step 5, preparing a sodium tartrate solution and adjusting the pH; Step 6, mixing the solid sample obtained in Step 4 and the solution obtained in Step 5, and stirring; Step 7, centrifuging, washing, and drying. This invention enables the embedding of environmentally friendly tartrate ions into a calcium-aluminum layered bimetallic hydroxide. Chloride ions in a corrosive environment can enter the interlayer of the layered bimetallic hydroxide to reduce the concentration of free chloride ions in the system. Simultaneously, tartrate ions are released from the interlayer, forming an adsorption film on the surface of the metal substrate.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion materials technology, and more specifically, to a method for preparing and applying a modified layered bimetallic hydroxide. Background Technology

[0002] Layered bimetallic hydroxides are a common type of anionic layered compound, widely used in corrosion protection systems due to their unique layered structure, anion exchangeability, and controllable properties. According to literature review, layered bimetallic hydroxides can be used as corrosion inhibitor containers. When chloride ions in the corrosive medium invade, the chloride ions in the environment can exchange with the interlayer corrosion inhibitor anions of the layered bimetallic hydroxide, absorbing chloride ions while releasing corrosion inhibitor ions, thereby protecting the substrate and achieving the effect of corrosion inhibition (Coatings 12 (2022) 1631, Coatings 13 (2023) 1166).

[0003] Chinese patent CN110627097A discloses a method for preparing a MgAl-LDH material intercalated with an azole-based corrosion inhibitor, and adding it as a filler to a coating to prepare a high-performance water-based anti-corrosion coating for polar low-temperature environments. This coating exhibits good low-temperature resistance and low-temperature application performance, and can be used for corrosion protection of engineering facilities in low-temperature environments. However, the MgAl-LDH intercalated with the azole-based corrosion inhibitor released harmful substances during service, leading to environmental pollution. Therefore, developing an environmentally friendly modified layered bimetallic hydroxide is of great significance. Summary of the Invention

[0004] In view of this, the present invention aims to propose a method for preparing and applying modified layered bimetallic hydroxides, so as to solve the problem that modified layered bimetallic hydroxides cannot achieve green and environmentally friendly effects as corrosion inhibitors in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A method for preparing a modified layered metal hydroxide includes the following steps:

[0007] Step 1: Prepare a mixed solution of Ca(NO3)2 and Al(NO3)2, labeled as solution A; prepare a mixed solution of NaNO3 and NaOH, labeled as solution B.

[0008] Step 2: Add solution A dropwise into solution B to obtain a mixed slurry;

[0009] Step 3: Perform a hydrothermal reaction on the mixed slurry;

[0010] Step 4: After cooling to room temperature, wash the reaction product by centrifugation, dry it, and set it aside for later use.

[0011] Step 5: Prepare a sodium tartrate solution and adjust its pH.

[0012] Step 6: Mix the solid sample obtained in Step 4 and the solution obtained in Step 5, and then stir.

[0013] Step 7: Take out the product obtained in Step 6 by centrifugation, washing, drying and storing for later use.

[0014] Furthermore, in step one, the volume ratio of solution A to solution B is 2:1, the concentration of Ca(NO3)2 solution is 0.5 mol / L, the concentration of Al(NO3)2 solution is 0.25 mol / L, the concentration of NaNO3 solution is 2 mol / L, and the concentration of NaOH is 3 mol / L.

[0015] Furthermore, in step two, solution A is added drop by drop into solution B at a rate of one drop per second.

[0016] Furthermore, in step three, the hydrothermal reaction conditions are a temperature of 60~70℃ and a reaction time of 22~25h.

[0017] Furthermore, in step four, centrifugation is performed using a centrifuge at a speed of 7000~10000 r / min for a time of 4~6 min.

[0018] Furthermore, in step four, the drying temperature is 60~70℃, and the drying time is 45~50 hours.

[0019] Furthermore, in step five, the concentration of the sodium tartrate solution is 0.005~1.0 mol / L, and the pH value of the sodium tartrate solution is adjusted to 9~12 with NaOH.

[0020] Furthermore, in step six, the weight-to-volume ratio of the solid sample obtained in step four to the solution obtained in step five is 0.1~4g:100mL.

[0021] Furthermore, in step six, the stirring time is 10~48 hours.

[0022] The present invention also proposes the application of the modified layered bimetallic hydroxide prepared by the above preparation method in corrosive media environments.

[0023] Compared with existing technologies, the preparation method and application of the modified layered bimetallic hydroxide described in this invention have the following advantages:

[0024] (1) Sodium tartrate is an excellent phosphorus-free corrosion inhibitor with the advantages of being green, environmentally friendly, inexpensive and readily available. It utilizes calcium and aluminum to construct a layered structure, which facilitates the intercalation of more tartrate ions, thereby achieving a better slow-release effect. Moreover, it is green and pollution-free, and has high application potential.

[0025] (2) The present invention further adjusts the parameters so that tartrate can be embedded more and more tightly in the interlayer, thus playing a better and longer-lasting role.

[0026] (3) The tartrate-intercalated layered bimetallic hydroxide prepared by this invention can be used in corrosive media environments. Chloride ions in the corrosive environment can enter the interlayer of the calcium-aluminum layered bimetallic hydroxide to reduce the concentration of free chloride ions in the system and reduce the damage of chloride ions to the metal substrate. At the same time, the modified layered bimetallic hydroxide releases tartrate ions from the interlayer, forming an adsorption film on the surface of the metal substrate, further blocking the corrosive medium from harming the metal substrate and improving the corrosion resistance of the substrate. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 The XRD patterns of LDH obtained in Comparative Example 3 and TA-LDH-1 obtained in Example 1 are shown below.

[0029] Figure 2 a is the SEM image of LDH obtained in Comparative Example 3. Figure 2 b is the SEM image of TA-LDH-1 obtained in Example 1;

[0030] Figure 3 a is the Nyquist plot corresponding to the blank group of this invention. Figure 3 b is the Bode diagram corresponding to the blank group of this invention;

[0031] Figure 4 a is the Nyquist diagram corresponding to Embodiment 1 of the present invention. Figure 4 b is the Bode diagram corresponding to Embodiment 1 of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments. First, it should be noted that the data in the following experimental examples were obtained by the inventors through numerous experiments. Due to space limitations, only a portion of these data is shown in the specification, and those skilled in the art can understand and implement the present invention based on this data. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various modifications or alterations to the invention, and these modifications or alterations also fall within the scope of protection of this application.

[0033] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0034] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] A method for preparing a modified layered metal hydroxide according to the present invention includes the following steps:

[0036] Step 1: Prepare a mixed solution of Ca(NO3)2 and Al(NO3)2, labeled as solution A; prepare a mixed solution of NaNO3 and NaOH, labeled as solution B.

[0037] Step 2: Add solution A dropwise into solution B to obtain a mixed slurry;

[0038] Step 3: Perform a hydrothermal reaction on the mixed slurry;

[0039] Step 4: After cooling to room temperature, wash the reaction product by centrifugation, dry it, and set it aside for later use.

[0040] Step 5: Prepare a sodium tartrate solution and adjust its pH.

[0041] Step 6: Mix the solid sample obtained in Step 4 and the solution obtained in Step 5, and then stir.

[0042] Step 7: Take out the product obtained in Step 6 by centrifugation, washing, drying and storing for later use.

[0043] Specifically, in step one, the volume ratio of solution A to solution B is 2:1, the concentration of Ca(NO3)2 solution is 0.5 mol / L, the concentration of Al(NO3)2 solution is 0.25 mol / L, the concentration of NaNO3 solution is 2 mol / L, and the concentration of NaOH is 3 mol / L.

[0044] In step two, solution A is added drop by drop into solution B at a rate of one drop per second.

[0045] In step three, the hydrothermal reaction conditions are a temperature of 60-70℃ and a reaction time of 22-25 hours. Specifically, the hydrothermal temperature can be selected as 60℃, 63℃, 65℃, or 70℃, and the reaction time can be selected as 22 hours, 23 hours, 24 hours, or 25 hours.

[0046] In step four, centrifugation is performed using a centrifuge at a speed of 7000~10000 r / min for a time of 4~6 min. Specifically, the centrifuge speed can be selected as 7000 r / min, 8000 r / min, 9000 r / min, or 10000 r / min, and the centrifugation time can be selected as 4 min, 5 min, or 6 min.

[0047] In step four, the drying temperature is 60~70℃, and the drying time is 45~50h. Specifically, the drying temperature can be 60℃, 63℃, 65℃, or 70℃, and the drying time can be 45h, 46h, 48h, or 50h.

[0048] In step five, the concentration of sodium tartrate solution is 0.005~1.0 mol / L, and the pH value of sodium tartrate solution is adjusted to 9~12 with NaOH.

[0049] In step six, the weight-to-volume ratio of the solid sample obtained in step four to the solution obtained in step five is 0.1~4g:100mL.

[0050] In step six, the stirring time is 10~48 hours.

[0051] In step seven, centrifugation is performed using a centrifuge at a speed of 5000~11000 r / min for a time of 2~10 min.

[0052] In step seven, the drying temperature is 40~110℃, and the drying time is 12~72 hours.

[0053] The preparation method of this invention enables the embedding of tartrate ions into calcium-aluminum layered bimetallic hydroxides. This invention first prepares the calcium-aluminum layered bimetallic hydroxides via co-precipitation, and then intercalates sodium tartrate into the calcium-aluminum layered bimetallic hydroxides via anion exchange. The use of calcium and aluminum to construct the layered structure facilitates the intercalation of a larger number of tartrate ions, thereby achieving a better slow-release effect. Sodium tartrate is an excellent phosphorus-free corrosion inhibitor with the advantages of being environmentally friendly, inexpensive, and readily available.

[0054] This invention prepares a tartrate-intercalated layered bimetallic hydroxide, namely a modified layered bimetallic hydroxide, which can be used in corrosive environments. Chloride ions in corrosive environments can enter the interlayer of the calcium-aluminum layered bimetallic hydroxide, reducing the concentration of free chloride ions in the system and minimizing their damage to the metal substrate. Simultaneously, the modified layered bimetallic hydroxide releases tartrate ions from the interlayer, forming an adsorption film on the surface of the metal substrate, further preventing the corrosive medium from harming the substrate and improving its corrosion resistance. This invention is of great significance for improving the service life of substrates, reducing labor costs, enhancing facility safety, and promoting environmental sustainability.

[0055] The present invention further adjusts parameters, such as pH in step five, the weight-to-volume ratio of solid sample to solution in step six, and stirring time in step six, so that tartrate ions can be more and more tightly embedded in the interlayer, thereby exerting a better and longer-lasting effect.

[0056] Example 1

[0057] Step 1: Select 200 mL of a mixed solution of 0.5 mol / L Ca(NO3)2 and 0.25 mol / L Al(NO3)2 as the precursor solution and label it as solution A. Prepare 100 mL of a mixed solution of 2 mol / L NaNO3 and 3 mol / L NaOH and label it as solution B.

[0058] Step 2: Under room temperature conditions, solution A is added drop by drop to solution B at a rate of one drop per second to obtain a mixed slurry.

[0059] Step 3: Place the mixed slurry in a beaker for hydrothermal reaction at a temperature of 65°C for 24 hours.

[0060] Step 4: After the hydrothermal reaction is completed, cool to room temperature, centrifuge and wash the reaction product. The centrifuge speed is 8000 r / min and the centrifugation time is 5 min. Place the washed product in an oven to dry. The oven temperature is set to 65℃ and the drying time is set to 48 h. Label the obtained product as LDH.

[0061] Step 5: Prepare 100 mL of 0.1 mol / L sodium tartrate solution and adjust its pH to 10.8 with NaOH solution.

[0062] Step 6: Weigh 2g of the LDH obtained in Step 4 and place it in the solution obtained in Step 5. Stir vigorously at room temperature for 24 hours.

[0063] Step 7: The reaction product is then centrifuged and washed. The centrifuge speed is set to 8000 r / min and the centrifugation time is 5 min. The washed product is then placed in an oven for drying. The oven temperature is set to 65℃ and the drying time is set to 48 h. The final product is labeled as TA-LDH-1.

[0064] Example 2

[0065] Step 1: Select 200 mL of a mixed solution of 0.5 mol / L Ca(NO3)2 and 0.25 mol / L Al(NO3)2 as the precursor solution and label it as solution A. Prepare 100 mL of a mixed solution of 2 mol / L NaNO3 and 3 mol / L NaOH and label it as solution B.

[0066] Step 2: Under room temperature conditions, solution A is added drop by drop to solution B at a rate of one drop per second to obtain a mixed slurry.

[0067] Step 3: Place the mixed slurry in a beaker for hydrothermal reaction at a temperature of 65°C for 24 hours.

[0068] Step 4: After the hydrothermal reaction is completed, cool to room temperature, centrifuge and wash the reaction product at a speed of 10000 r / min for 6 min. Place the washed product in an oven to dry at a temperature of 70℃ for 50 h. Label the obtained product as LDH.

[0069] Step 5: Prepare 100 mL of 0.2 mol / L sodium tartrate solution and adjust its pH to 11.0 with NaOH solution.

[0070] Step 6: Weigh 42g of the LDH obtained in Step 4 and place it in the solution obtained in Step 5. Stir vigorously at room temperature for 36 hours.

[0071] Step 7: The reaction product is then centrifuged and washed. The centrifuge speed is set to 8000 r / min and the centrifugation time is 4 min. The washed product is then placed in an oven for drying. The oven temperature is set to 65℃ and the drying time is set to 48 h. The final product is labeled as TA-LDH-2.

[0072] Comparative Example 1

[0073] The preparation method of Comparative Example 1 is the same as that of Example 1, except that in step six, the stirring time is 50 hours.

[0074] Comparative Example 2

[0075] The preparation method of Comparative Example 2 is the same as that of Example 1, except that in step five, the pH value of the sodium tartrate solution is adjusted to 13 using NaOH solution.

[0076] Comparative Example 3

[0077] Comparative Example 3 is the LDH obtained in step four of Example 1.

[0078] The final product TA-LDH-1 obtained in Example 1 and the final product TA-LDH-2 obtained in Example 2 have the same XRD and SEM spectra. Due to space limitations, only the spectra of Example 1 will be used as an example in this invention.

[0079] XRD tests were performed on the LDH obtained in Comparative Example 3 and the TA-LDH-1 obtained in Example 1, and the results are as follows: Figure 1 As shown, SEM testing was performed, and the results are as follows. Figure 2 As shown. From Figure 1 It can be seen that TA-LDH-1 exhibits characteristic peaks on the (003) and (006) crystal planes, displaying a typical LDH structure, proving the successful synthesis of LDH. Furthermore, the leftward shift of the (003) crystal plane diffraction peak of TA-LDH-1 indicates that the tartrate anion was successfully intercalated into the LDH interlayer. Figure 2 It can be seen that the TA-LDH-1 crystals have a hexagonal structure, exhibiting a typical LDH structure, proving that LDH was successfully synthesized, and that the intercalation of tartrate did not change the morphology of LDH.

[0080] Equal amounts of the final products from Examples 1, 2, 1, 2, and 3 were added to 0.1 mol / L NaCl solution at a concentration of 5 g / L, and Q235 steel was immersed in the solution for 5 days. A blank control group was also set up, consisting of NaCl solution without added TA-LDH, in which Q235 steel was immersed for 5 days. The concentration and volume of the NaCl solution used in each group were consistent.

[0081] The corrosion inhibition performance was tested using EIS electrochemical testing. Q235 steel was immersed in NaCl solution without added TA-LDH for 5 days. The Nyquist and Bode plots of the blank group are shown below. Figure 3 a and Figure 3 As shown in b. The Nyquist and Bode plots of Q235 steel after immersion in a NaCl solution containing TA-LDH-1 prepared in Example 1 for 5 days are shown in Figures. Figure 4 a and Figure 4 As shown in b. After soaking for 5 days, |Z| from Example 1 was added. 10mHz The value remains at 10 4 Ω·cm 2This indicates that the corrosive medium has difficulty reaching the metal substrate, resulting in a long-lasting protective effect. The addition of TA-LDH-1 from Example 1 effectively delays corrosion and improves the corrosion resistance of the substrate. Furthermore, compared to the control group, the impedance arc of Example 1 is increased. Similarly, the addition of |Z| from Example 2... 10mHz The value is 10 4 Ω·cm 2 .

[0082] After adding Comparative Example 3, |Z| 10mHz The value is only 2.6 × 10 3 Ω·cm 2 After adding Comparative Example 1, although the impedance arc increased compared to the blank group, |Z| 10mHz The value is 7.5 × 10 3 Ω·cm 2 After adding Comparative Example 2, although the impedance arc increases compared to the blank group, |Z| 10mHz The value is 4.9 × 10 3 Ω·cm 2 The possible reasons are as follows: In Comparative Example 1, the stirring time was too long. After the exchange of nitrate ions between tartrate ions and LDH layers reached equilibrium, the calcium-aluminum layered bimetallic hydroxide remained in an alkaline environment for a considerable period, resulting in slight dissolution and disruption of the layered structure. This placed some intercalated tartrate ions in unfavorable positions, ultimately reducing the intercalation amount. Therefore, Comparative Example 1 released a limited amount of tartrate ions, resulting in a weaker ability to prevent corrosive media from eroding the metal substrate. In contrast, the higher pH sodium tartrate solution in Comparative Example 2 caused the calcium-aluminum layered bimetallic hydroxide to dissolve, accelerating localized damage to the layered structure and reducing the effective intercalation sites for tartrate ions. Consequently, the intercalation amount of tartrate ions in Comparative Example 2 was less than that in Examples 1 and 2, leading to a weaker ability to prevent corrosive media from eroding the metal substrate.

[0083] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a modified layered metal hydroxide, characterized in that, Includes the following steps: Step 1: Prepare a mixed solution of Ca(NO3)2 and Al(NO3)2, labeled as solution A; prepare a mixed solution of NaNO3 and NaOH, labeled as solution B. Step 2: Add solution A dropwise into solution B to obtain a mixed slurry; Step 3: Perform a hydrothermal reaction on the mixed slurry; Step 4: After cooling to room temperature, wash the reaction product by centrifugation, dry it, and set it aside for later use. Step 5: Prepare a sodium tartrate solution and adjust its pH. Step 6: Mix the solid sample obtained in Step 4 and the solution obtained in Step 5, and then stir. Step 7: Take out the product obtained in Step 6 by centrifugation and washing, dry it and store it for later use.

2. The preparation method according to claim 1, characterized in that, In step one, the volume ratio of solution A to solution B is 2:1, the concentration of Ca(NO3)2 solution is 0.5 mol / L, the concentration of Al(NO3)2 solution is 0.25 mol / L, the concentration of NaNO3 solution is 2 mol / L, and the concentration of NaOH is 3 mol / L.

3. The preparation method according to claim 1, characterized in that, In step two, solution A is added drop by drop into solution B at a rate of one drop per second.

4. The preparation method according to claim 1, characterized in that, In step three, the hydrothermal reaction conditions are a temperature of 60~70℃ and a reaction time of 22~25h.

5. The preparation method according to claim 1, characterized in that, In step four, centrifugation is performed using a centrifuge at a speed of 7000~10000 r / min for a time of 4~6 min.

6. The preparation method according to claim 1, characterized in that, In step four, the drying temperature is 60~70℃, and the drying time is 45~50 hours.

7. The preparation method according to claim 1, characterized in that, In step five, the concentration of sodium tartrate solution is 0.005~1.0 mol / L, and the pH value of sodium tartrate solution is adjusted to 9~12 with NaOH.

8. The preparation method according to claim 1, characterized in that, In step six, the weight-to-volume ratio of the solid sample obtained in step four to the solution obtained in step five is 0.1~4g:100mL.

9. The preparation method according to claim 1, characterized in that, In step six, the stirring time is 10~48 hours.

10. The application of the modified layered bimetallic hydroxide prepared by any one of the preparation methods of claims 1 to 9 in a corrosive media environment.

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