A dual-stimulus response corrosion self-warning coating and a preparation method thereof

Abstract

The present application relates to a kind of double stimulation response corrosion self-warning coating and its preparation method, belong to material technical field.The coating includes resin and sea urchin-like composite fluorescent probe, the composite fluorescent probe is with graphene oxide modified lanthanide metal organic framework material;The lanthanide metal organic framework material is based on central metal ion terbium (Tb 3+ ) And uniform benzene tricarboxylic acid (H3BTC) Ligand coordination constitutes;The fluorescent probe has the effect of fast, sensitive fluorescence quenching indication to pH or Fe 3+ , can be the reversible fluorescence response of pH;Meanwhile, it can also effectively block the penetration of corrosion medium;The coating is coated on the surface of metal matrix and can form corrosion self-warning coating, has the function of detecting and early warning to the early corrosion of metal matrix under coating.

Description

Technical Field

[0001] This invention relates to a dual-stimulus responsive corrosion self-warning coating and its preparation method, specifically, to a coating that responds to pH and Fe... 3+ The corrosion self-warning coating exhibiting fluorescence response to both stimuli and its preparation method belong to the field of materials technology. Background Technology

[0002] Organic coatings are crucial for protecting metal substrates from corrosion. However, over time, due to prolonged exposure to harsh environments such as sunlight and corrosive media, the corrosion resistance of organic protective coatings decreases, leading to corrosion of the underlying metal. This process is often difficult to detect during routine maintenance, and failure to detect and implement timely maintenance measures can result in significant economic losses and catastrophic events. Therefore, there is an urgent need for efficient and timely detection methods to track the early corrosion status of the metal under the coating, enabling effective maintenance measures to extend the coating's service life.

[0003] To address the limitations of traditional corrosion detection methods in timely, in-situ, and non-destructive detection of early-stage metal corrosion, smart coatings with corrosion early warning capabilities can solve this problem. Smart coatings contain fluorescent probes or color-changing dyes, which exhibit fluorescence or color responses to changes in pH, metal ions, and corrosion-induced electrochemical activity. This allows for a non-destructive, simple, and timely determination of the early corrosion status of the metal beneath the coating, enabling subsequent maintenance measures. Fluorescently responsive smart coatings, in particular, offer significant advantages due to their high detection sensitivity, as they are unaffected by background color interference. Therefore, developing fluorescent coatings with self-early warning capabilities is of considerable research importance.

[0004] Existing self-warning fluorescent coatings for early corrosion detection mostly exhibit a single fluorescent stimulus response and are only compatible with specific coating systems or metal substrates. Furthermore, the luminescent centers of most fluorescent probes used in coating detection are composed of organic fluorophores, resulting in short fluorescence lifetimes and a tendency to undergo aggregation-induced quenching during coating preparation (Haowen Xiao, et al., Progress in Organic Coatings, 177(2023)107418). Notably, existing fluorescent coatings are mostly disposable, failing upon exposure to metal ions or changes in ambient pH, requiring the construction of entirely new coatings for subsequent repairs, thus increasing the associated costs of fluorescent early warning corrosion coatings. For example, CN 110183569 A discloses a polymer coating material for early warning of metal corrosion, capable of detecting and reporting early corrosion of metals before any visible signs of corrosion appear. However, the fluorescent probes used are organic fluorophores with limited fluorescence lifetimes, and these responses do not optimize the sensitivity of the self-warning coating to corrosion, making it non-reusable and limiting its application.

[0005] Lanthanide metal-organic frameworks (Ln-MOFs) exhibit unique photoelectric properties as fluorescent probes, thanks to the abundant 4f electrons, large Stokes shift, narrow emission band, stable luminescence characteristics, and long luminescence lifetime of lanthanide ions. Therefore, some lanthanide MOFs have been used as luminescent indicators for metal ions, anions, gas molecules, and small molecules, commonly applied in environmental pollution and medical detection. However, due to their uncertain fluorescence response efficiency and corrosion resistance in coatings, the development of lanthanide MOFs in self-monitoring anti-corrosion coatings still faces challenges.

[0006] Navid Keshmiri et al. modified Ce-MOF with graphene oxide (GO) to obtain composite materials, which exhibited better oxidation resistance, stability, and dispersibility in the coating matrix (Navid Keshmiri, et al., Journal of Cleaner Production, 319(2021)128732). However, in this study, the modification of graphene oxide only improved the durability of the anti-corrosion coating and did not address the issues of detection efficiency and timeliness related to corrosion early warning. For fluorescent self-early warning coatings, the fluorescence response speed and efficiency for detecting corrosion are crucial. Graphene oxide modification usually alters the microstructure of MOFs, but the morphology of GO-modified MOFs is uncertain. Changes in morphology can significantly affect the distribution of active sites in the composite material, thereby affecting the response sensitivity and timeliness of the self-early warning coating. Summary of the Invention

[0007] Addressing the technical challenge of timely, repeatable, and rapid detection of under-coating metal corrosion in existing technologies, one objective of this invention is to provide a dual-stimulus-responsive corrosion self-warning coating. This coating contains a sea urchin-like composite fluorescent probe, which exhibits sensitivity to pH or Fe... 3+ It can rapidly and sensitively indicate fluorescence quenching and has a reversible fluorescence response to pH; at the same time, it can effectively block the penetration of corrosive media; the coating can form a corrosion self-warning coating when applied to the surface of the metal substrate, and has the function of detecting and warning of early corrosion of the metal substrate under the coating.

[0008] The second objective of this invention is to provide a method for preparing the dual-stimulus-responsive corrosion self-warning coating described in this invention.

[0009] To achieve the objectives of this invention, the following technical solutions are provided.

[0010] A dual-stimulus responsive corrosion self-warning coating, the coating comprising a resin and a composite fluorescent probe.

[0011] The composite fluorescent probe is a lanthanide metal-organic framework material modified with graphene oxide (GO); the lanthanide metal-organic framework material is based on the central metal ion terbium (Tb). 3+ It is composed of a ligand of pyromellitic acid (H3BTC) and is referred to as Tb-BTC; the composite fluorescent probe is referred to as GO@Tb-BTC.

[0012] Preferably, Tb 3+ The molar ratio of the compound to pyromellitic acid is 1:0.5 to 1.

[0013] Preferably, Tb 3+ The molar ratio of Tb to graphene oxide is 1:6 to 10; more preferably, Tb 3+ The molar ratio with graphene oxide is 1:7.

[0014] Preferably, in the coating, the mass fraction of the composite fluorescent probe is 0.2% to 0.5% of the resin mass.

[0015] Preferably, the resin is at least one of waterborne polyurethane and waterborne epoxy resin.

[0016] Whether the coating contains a curing agent can be determined based on the type of resin.

[0017] When the resin is waterborne polyurethane, the coating does not contain a curing agent.

[0018] When the resin is a water-based epoxy resin, the coating contains a curing agent; preferably, the curing agent is an amine curing agent; more preferably, the mass ratio of water-based epoxy resin to amine curing agent is 4 to 5:1.

[0019] The coating may also include additives in the art, such as dispersants, defoamers and leveling agents; preferably, the mass ratio of each additive to the resin is 1:40 to 50.

[0020] Preferably, the dispersant is at least one of BYK163 and BYK142 from BYK Chemicals (Germany); the defoamer is at least one of Deqian Chemicals defoamer 6800 or BYKA-530; and the leveling agent is BYK-301 or BYK75 from BYK Chemicals (Germany).

[0021] A method for preparing the dual-stimulus responsive corrosion self-warning coating of the present invention, the method comprising the following steps:

[0022] (1) The graphene oxide nanosheets were ultrasonically treated and mixed evenly in an ethanol aqueous solution to obtain a graphene oxide solution. Trimethylbenzene acid was added to the graphene oxide solution and mixed evenly to obtain a mixture. Then, while stirring, terbium nitrate aqueous solution was added dropwise to the mixture to carry out a coordination reaction. After the reaction was completed, the mixture was washed and dried to obtain a composite fluorescent probe.

[0023] Preferably, the coordination reaction time is 1 to 2 hours.

[0024] (2) Add the composite fluorescent probe prepared in step (1) to the resin and stir evenly to obtain a dual-stimulus-responsive corrosion self-warning coating.

[0025] It is preferable to disperse the composite fluorescent probe in water, so as to treat it with ultrasound to achieve uniform dispersion, and then add resin. This can make the composite fluorescent probe more uniformly dispersed in the coating.

[0026] An application of the dual-stimulus-responsive corrosion self-early warning coating of the present invention is to use the coating for visual detection of early corrosion of metallic materials under the coating; specifically, the application is as follows:

[0027] The coating is applied to the surface of a metal substrate and dried at room temperature to form a coating layer. When early corrosion occurs on the metal substrate under the complete coating and the scratched coating, the composite fluorescent probe in the coating undergoes rapid fluorescence quenching, enabling convenient tracking and timely maintenance of early corrosion under the coating.

[0028] Preferably, the metal matrix is ​​an iron-containing metal, and more preferably, a steel material.

[0029] Preferably, the coating is applied to the surface of the metal substrate by brushing to form a coating layer, and the dry film thickness of the coating layer is 60μm to 80μm.

[0030] Beneficial effects

[0031] (1) This invention provides a dual-stimulus responsive corrosion self-warning coating, wherein the coating contains a composite fluorescent probe with a sea urchin-like structure. This composite fluorescent probe is a novel terbium ion and trimesic acid-based fluorescent probe modified with graphene oxide. By using graphene oxide modification, the composite fluorescent probe exhibits a micro-nano sea urchin-like spherical structure. Compared to the rod-shaped fluorescent probes in the prior art, the specific surface area of ​​the composite fluorescent probe is significantly increased, and the contact sites with active substances are greatly increased, significantly improving the response efficiency and detection capability of the composite fluorescent probe. It can be used in pH or Fe... 3+ The composite fluorescent probe exhibits rapid and sensitive fluorescence quenching indication under dual stimulation; it also possesses reversible fluorescence response to pH; simultaneously, the composite fluorescent probe can effectively block the penetration of corrosive media through the shielding effect of graphene micro-nano fillers combined with the micro-nano sea urchin spherical structure; the composite fluorescent probe can be combined with various types of organic coatings to form a corrosion self-warning coating on the surface of a metal substrate, which has the function of detecting and warning of early corrosion of the metal substrate under the coating.

[0032] (2) This invention provides a dual-stimulus-responsive corrosion self-warning coating, the coating comprising a resin and a composite fluorescent probe; the coating is applied to the surface of a metal substrate to form a coating layer, the coating layer responding to pH changes in the metal substrate caused by corrosion and the corrosion product Fe 3+ It exhibits a synergistic fluorescence quenching response, which rapidly and accurately indicates the corrosion location of the metal substrate under the coating through fluorescence quenching.

[0033] When early corrosion occurs in the metal under an intact coating, pH changes in the corrosion microcathode and microanode disrupt the energy transfer between terbium ions and ligands in the coating, leading to fluorescence quenching at the corrosion site. This fluorescence change is reversible; because the fluorescent probes in the coating possess a reversible fluorescence response to pH, the fluorescence can exhibit an "on-off" pattern as the coating progresses from an intact state to localized corrosion, and then to pH recovery after repair. (Fe) 3+ The presence of [something] will also specifically quench green fluorescence; when early corrosion of the metal occurs at the damaged coating, the Fe produced by the corrosion anode [something] 3+ Can block Tb 3+ The antenna effect of the ligand leads to fluorescence quenching, which in turn rapidly indicates the location of the damage.

[0034] (3) The present invention provides a dual-stimulus-responsive corrosion self-warning coating. The fluorescence quenching in the coating formed by the coating is earlier than normal visual inspection and other electrochemical corrosion detection. It can quickly and accurately indicate the corrosion location under the intact and damaged coating before any visible corrosion signs and traditional electrochemical detection methods, thereby helping to accurately locate and repair coating / corrosion damage in a timely manner. At the same time, thanks to the reversible pH response of the composite fluorescent probe, it is possible to avoid repeatedly building new coatings, realize the reusability of the corrosion self-warning coating, and greatly reduce the cost of use.

[0035] (4) The present invention provides a dual-stimulus-responsive corrosion self-warning coating. The coating prepared by the coating contains a composite fluorescent probe, which can effectively block the transmission of corrosive media in the coating, thereby further improving the anti-corrosion performance of the coating and greatly extending the service life of the coating.

[0036] (5) This invention provides a dual-stimulus-responsive corrosion self-warning coating, wherein the composite fluorescent probe in the coating controls the mixing amount of graphene oxide and Tb-BTC, i.e., Tb 3+ The optimal molar ratio of terbium to graphene oxide is 1:6 to 10 to achieve the best fluorescence and corrosion resistance of the coating. When the terbium ion content is too high, the corrosion resistance of the coating will decrease, while when the terbium ion content is too low, the fluorescence detection efficiency will decrease.

[0037] (6) The present invention provides a method for preparing a self-early warning anti-corrosion coating. The method is simple, carried out at room temperature, under mild conditions, and does not require complex equipment or complex post-processing. It is suitable for large-area construction of components such as ships and bridges. Attached Figure Description

[0038] Figure 1 Fourier transform infrared spectra of the composite fluorescent probes prepared in Examples 1 and 2.

[0039] Figure 2 The X-ray photoelectron spectra of the composite fluorescent probes prepared in Examples 1 and 2 are shown.

[0040] Figure 3 The X-ray diffraction patterns of the composite fluorescent probes prepared in Examples 1 and 2 are shown.

[0041] Figure 4 Scanning electron microscope images of the composite fluorescent probes prepared in Examples 1 and 2.

[0042] Figure 5 The images show the electrochemical impedance spectroscopy of the coatings prepared in Example 1 and Comparative Examples 1 and 2.

[0043] Figure 6 The composite fluorescent probes prepared in Examples 1 and 2 for Fe3+ Fluorescence spectrum of the response.

[0044] Figure 7 The images show the fluorescence of the composite fluorescent probes prepared in Examples 1 and 2 under pH changes.

[0045] Figure 8 Electrochemical impedance spectroscopy and fluorescence photographs of the coating prepared in Example 1 after immersion for different times during scratch fabrication.

[0046] Figure 9 Electrochemical impedance and fluorescence images of the coating prepared in Example 2 after immersion for different times during scratch fabrication.

[0047] Figure 10 Fluorescent photographs of the coatings prepared in Examples 1 and 2 when immersed in their intact state. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the present invention.

[0049] In the following examples and comparative examples:

[0050] The curing agent is DY-105 from Shenyang Dongyan Coatings & Decoration Co., Ltd.

[0051] The waterborne polyurethane used is 3EAH0543W from Guangdong Tongde New Materials Co., Ltd.

[0052] Example 1

[0053] (1) 0.0139 g of graphene oxide nanosheets were ultrasonically treated in 10 mL of ethanol aqueous solution for 20 minutes to obtain a graphene oxide solution; 0.105 g of trimesic acid was added to the graphene oxide solution and mixed for 30 minutes to obtain a mixture; while stirring, 25 mL of 0.02 mmol / L Tb(NO3)3 aqueous solution was added dropwise to the mixture to make Tb 3 + The molar ratio with pyromellitic acid is 1:1; Tb 3+ The molar ratio of GO@Tb-BTC to graphene oxide is 1:7; a coordination reaction is carried out, and the reaction is stopped after 2 hours and allowed to stand for 1 day; the supernatant is removed, and the precipitate is washed 6 times alternately with ethanol and deionized water to obtain a purified precipitate, which is then dried in an oven at 60°C for one day to obtain urchin-shaped GO@Tb-BTC, which is a composite fluorescent probe of the present invention; wherein, the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1.

[0054] (2) Disperse 10 mg of the composite fluorescent probe obtained in step (1) in 1 mL of deionized water, sonicate for 30 minutes to disperse evenly to obtain a suspension, mix the suspension with 5 g of waterborne epoxy resin E20 (601), the mass of the composite fluorescent probe is 0.2% of the resin mass; stir for 30 minutes to ensure that the composite fluorescent probe is evenly dispersed in the waterborne epoxy resin; then add 0.1 g of Deqian Chemical defoamer 6800, 0.1 g of dispersant BYK-163 and 0.1 g of leveling agent BYK-301 and mix evenly to obtain a mixed slurry, then add 1 g of DY-105 curing agent, and stir for 10 minutes to completely cure the resin to obtain a dual-stimulation response corrosion self-warning coating of the present invention.

[0055] The dual-stimulus responsive corrosion self-warning coating prepared in step (2) was uniformly coated onto the surface of a carbon steel substrate using a thin-film coating machine. After drying and curing at room temperature for 3 days, a coating with a dry film thickness of 60 μm to 80 μm was formed. Under ultraviolet light irradiation, the coating exhibited bright green fluorescent luminescence.

[0056] Example 2

[0057] (1) 0.0139 g of graphene oxide nanosheets were ultrasonically treated in 10 mL of ethanol aqueous solution for 20 minutes to obtain a graphene oxide solution; 0.105 g of trimesic acid was added to the graphene oxide solution and mixed for 30 minutes to obtain a mixture; while stirring, 25 mL of 0.02 mmol / L Tb(NO3)3 aqueous solution was added dropwise to the mixture to make Tb 3 + The molar ratio with pyromellitic acid is 1:1; Tb 3+ The molar ratio of GO@Tb-BTC to graphene oxide is 1:7; a coordination reaction is carried out, and the reaction is stopped after 2 hours and allowed to stand for 1 day; the supernatant is removed, and the precipitate is washed 6 times alternately with ethanol and deionized water to obtain a purified precipitate, which is then dried in an oven at 60°C for one day to obtain urchin-shaped GO@Tb-BTC, which is a composite fluorescent probe of the present invention; wherein, the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1.

[0058] (2) Disperse 10 mg of the composite fluorescent probe obtained in step (1) in 1 mL of deionized water, sonicate for 30 minutes to disperse evenly to obtain a suspension, mix the suspension with 5 g of waterborne polyurethane, the mass fraction of the composite fluorescent probe is 0.2% of the resin mass; stir for 30 minutes to ensure that the composite fluorescent probe is evenly dispersed in the waterborne polyurethane; then add 0.1 g of Deqian Chemical defoamer 6800, 0.1 g of dispersant BYK-163 and 0.1 g of leveling agent BYK-301, mix evenly to obtain a mixed slurry, and obtain the dual-stimulation response corrosion self-warning coating of the present invention.

[0059] The dual-stimulus responsive corrosion self-warning coating prepared in step (2) was uniformly coated onto the surface of a carbon steel substrate using a thin-film coating machine. After drying and curing at room temperature for 3 days, a coating with a dry film thickness of 60 μm to 80 μm was formed. Under ultraviolet light irradiation, the coating exhibited bright green fluorescent luminescence.

[0060] Comparative Example 1

[0061] (1) 105 mg of 0.5 mmol trimellitic acid was completely dissolved in 25 ml of ethanol to prepare H3BTC solution; H3BTC solution was added to 25 ml of 0.02 mmol / L Tb(NO3)3 solution and stirred continuously for 2 h to obtain a solution containing white solid; the solution was centrifuged at 8000 r / min for 5 min to remove the supernatant, and the remaining precipitate was washed 6 times alternately with deionized water and ethanol to obtain solid product, which was dried at 60 °C for 1 day to obtain rod-shaped Tb-BTC, which is a fluorescent probe.

[0062] (2) Disperse 10 mg of the fluorescent probe obtained in step (1) in 1 mL of deionized water, sonicate for 30 minutes to disperse evenly to obtain a suspension, mix the suspension with 5 g of waterborne epoxy resin E20 (601), the mass fraction of the fluorescent probe is 0.2% of the resin mass, stir for 30 minutes to ensure that the fluorescent probe is evenly dispersed in the waterborne epoxy resin; then add 0.1 g of Deqian Chemical defoamer 6800, 0.1 g of dispersant BYK-163 and 0.1 g of leveling agent BYK-301 and mix evenly to obtain a mixed slurry, then add 1 g of DY-105 curing agent, stir for 10 minutes to allow the resin to be completely cured to obtain a coating.

[0063] The coating obtained in step (2) was uniformly applied to the surface of a carbon steel substrate using a thin film coating machine. After drying and curing at room temperature for 3 days, a coating with a dry film thickness of 60 μm to 80 μm was formed. Under ultraviolet light irradiation, the coating exhibited bright green fluorescent luminescence.

[0064] Comparative Example 2

[0065] Place 5g of waterborne epoxy resin E20(601) in a dispersion tank, then add 0.1g of Deqian Chemical defoamer 6800, 0.1g of dispersant BYK-163 (Germany), and 0.1g of leveling agent BYK-301 (Germany) and mix evenly to obtain a mixed slurry. Mix the mixed slurry and curing agent DY-105 evenly at a mass ratio of 5:1 to obtain a waterborne epoxy resin coating.

[0066] The water-based epoxy resin coating was applied to the surface of a carbon steel substrate and allowed to air dry at room temperature for three days, forming a coating with a dry film thickness of 60 μm to 80 μm. Under ultraviolet light irradiation, this coating did not exhibit fluorescent luminescence properties.

[0067] The probes and coatings in the above embodiments and comparative examples were tested as follows:

[0068] (1) Composition and structure testing of composite fluorescent probes

[0069] The composition and structure of the composite fluorescent probes prepared in Examples 1 and 2 were tested and characterized. Figure 1 The Fourier transform infrared spectra show that Tb-BTC and GO@Tb-BTC without graphene oxide modification have the same infrared characteristic peaks. Figure 2 The X-ray photoelectron spectroscopy (XPS) confirms the successful modification of Tb-BTC by graphene oxide. Figure 3 The X-ray diffraction pattern shows that the diffraction peaks in GO@Tb-MOF are similar to those in Tb-MOF and GO, indicating that GO has successfully modified Tb-MOF.

[0070] (2) Microscopic morphology observation of composite fluorescent probes

[0071] The microstructure of the composite fluorescent probes prepared in Examples 1 and 2 was observed using scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS). Figure 4 As shown, Figure 4 a is a scanning electron microscope image. Figure 4 b is the energy-dispersive X-ray surface distribution map of different elements. Observations show that the composite fluorescent probe is a lanthanide metal-organic framework material modified with graphene oxide, which is based on the coordination of the central metal ion terbium and trimesic acid. The composite fluorescent probe has a sea urchin-like structure and possesses a larger specific surface area and more reactive sites compared to the rod-shaped Tb-BTC probe prepared in Comparative Example 1.

[0072] (3) Corrosion resistance test

[0073] The coating was applied to a 10cm × 5cm × 0.1cm Q235 carbon steel plate for testing. A 3.6cm diameter, 5cm high PVC pipe was fixed to the coating surface of the examples and comparative examples using silicone sealant to prevent porosity. The testing apparatus used a quick-assembly electrolytic cell with a PVC pipe body. Simulated seawater, specifically a 3.5% (w / w) NaCl solution, was used as the electrolyte. A standard three-electrode system was employed, with a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, and the coating sample as the working electrode. The electrodes were placed 1cm apart. All electrochemical tests were performed at open-circuit potential, with an excitation voltage of 10mV / s and frequencies ranging from 100kHz to 0.01Hz. The corrosion resistance of the coatings obtained in the examples and comparative examples was evaluated using electrochemical impedance spectroscopy obtained from a 72-hour simulated seawater immersion test.

[0074] Results and Analysis:

[0075] The electrochemical impedance spectroscopy spectra of the fluorescent coatings prepared in Example 1 and Comparative Examples 1-2 are shown below. Figure 5 The results showed that in the 72-hour simulated seawater immersion test, Comparative Example 2, Figure 5 The coating in sample a exhibited a lower impedance value from the initial immersion stage, and its impedance decrease was more significant than the other two, resulting in the worst corrosion resistance among all samples. Comparative Example 1, Figure 5 Coating b exhibits enhanced corrosion resistance compared to the coating in Comparative Example 2, achieving a low-frequency impedance of 10 after 72 hours. 7 Ω·cm 2 , and Example 1, Figure 5 The low-frequency impedance of the coating in c reaches 10. 8 Ωcm 2 The values ​​around 100° indicate that the coating described in Example 1 exhibits excellent corrosion resistance. The coating prepared in Example 2 also shows significantly enhanced corrosion resistance compared to the polyurethane coating prepared using the Tb-BTC probe without GO modification. These results demonstrate that GO modification in the composite probe significantly improves the corrosion resistance of the coating.

[0076] (4) Fluorescence test

[0077] The luminescence of the coating was observed by irradiating it with a handheld ultraviolet lamp at a wavelength of 254 nm, and the fluorescence spectra of the composite fluorescent probes prepared in Examples 1 and 2 were then tested using a Hitachi F-7000 fluorescence spectrometer.

[0078] The composite fluorescent probes prepared in Examples 1 and 2 were tested using a fluorescence spectrometer in Fe. 3+ The fluorescence spectrum in its presence is shown in the following results. Figure 6 As shown. The concentration of the composite fluorescent probe was controlled at 1 mg / mL, with Fe... 3+As the concentration of Fe increased from 0 μM to 20 μM, the fluorescence gradually decreased. 3+ This almost completely quenched the fluorescence of the composite fluorescent probe. Furthermore, the rod-shaped Tb-BTC from Comparative Example 1 was used to quench the fluorescence of Fe... 3+ The fluorescence quenching behavior was compared with that of the composite fluorescent probe prepared in Example 1. The results showed that the urchin-shaped composite fluorescent probe in Example 1 exhibited better fluorescence quenching than Fe. 3+ The fluorescence response exhibits significantly improved fluorescence quenching efficiency and sensitivity, indicating that the change in morphology from rod-shaped to urchin-shaped can effectively enhance the probe's sensitivity to Fe. 3+ Detection efficiency.

[0079] The fluorescence of the composite fluorescent probes prepared in Examples 1 and 2 under alternating pH conditions was tested using a handheld ultraviolet lamp, and the results are as follows: Figure 7 As shown, GO@Tb-BTC dispersed in a neutral 3.5% NaCl solution exhibited stable and bright green fluorescence under UV light. When the pH was adjusted to pH=4 and pH=10, a significant fluorescence quenching occurred instantaneously. Upon further pH adjustment to return to neutral, the fluorescence resumed. This "on-off-on" fluorescence pattern is attributed to Tb... 3+ Antenna effect between ligands, when excess H + / OH - When present, the antenna effect is blocked; under neutral conditions, Tb 3+ Upon ligand reconstruction, the antenna effect is restored, and fluorescence is reactivated. This pH-responsive fluorescence mode enables the reuse of fluorescence warning coatings.

[0080] The coatings prepared in Examples 1 and 2 were used to create scratches on their surfaces using a blade to simulate coating defects, forming samples. These samples were then immersed in a corrosive medium, specifically a 3.5% (w / w) NaCl solution, to accelerate corrosion. The samples were then removed and irradiated under a UV lamp. Figure 8 and Figure 9 The left figures show the electrochemical impedance curves of the scratched area at different time periods, while the right figures show the fluorescence images of the coated sample in the scratched area. Figure 8 In the case of immersion in a corrosive medium for 2 hours, the coating prepared in Example 1 showed obvious fluorescence quenching at the defects, and the corrosion rate was earlier than that of the corresponding electrochemical impedance spectroscopy test, demonstrating the timeliness of the fluorescent coating in detecting corrosion. Figure 9In Example 2, the coating defects exhibited significant fluorescence quenching after immersion in the corrosive medium for 25 minutes. However, the electrochemical impedance spectroscopy showed that the scratched areas of the coating only showed signs of corrosion after immersion in the corrosive medium for 4 hours. This indicates that the coating's corrosion detection speed is superior to traditional electrochemical detection methods, achieving timely corrosion detection. Because the carbon steel substrate at the scratched area is exposed to the corrosive medium, the Fe generated at the anolyte... 3+ The rapid blocking of fluorescence from the composite fluorescent probe within the coating demonstrates the sensitivity and speed of the fluorescent early warning coating. This phenomenon can be used for the visual monitoring of coating defects, facilitating the early detection of micro-defects in the coating and enabling timely repair.

[0081] The coatings on the carbon steel substrates prepared in Examples 1 and 2 were immersed in a corrosive medium, namely a 3.5% NaCl solution, for 10 days. Afterward, they were removed and the early corrosion of the metal under the intact coating was observed under ultraviolet light. Figure 10 As shown, the circular area in the upper image is a digital photograph of the coating prepared in Example 1 under sunlight and ultraviolet light, and the rectangular area in the lower image is a digital photograph of the coating prepared in Example 2 under sunlight and ultraviolet light. Areas with severe corrosion are circled in the images. Corrosion cannot be directly observed in the coating under sunlight, but obvious fluorescence quenching points are visible under ultraviolet light. Pitting corrosion occurs in the metal beneath the coating, due to local pH changes or Fe... 3+ The formation of this substance leads to fluorescence quenching. This phenomenon can be used for visual monitoring of coating defects, which is beneficial for early detection of micro-defects in the coating and for evaluating the degree of coating aging.

[0082] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A dual-stimulus responsive corrosion self-warning coating, characterized in that: The coating comprises a resin and a composite fluorescent probe; The composite fluorescent probe is a lanthanide metal-organic framework material modified with graphene oxide; the lanthanide metal-organic framework material is based on the central metal ion Tb. 3+ Coordination with pyromellitic acid ligands; The composite fluorescent probe has a micro / nano urchin-like spherical structure, and it reacts with pH or Fe. 3+ It exhibits fluorescence quenching indication under dual stimulation and possesses a reversible fluorescence response to pH.

2. The dual-stimulus responsive corrosion self-warning coating according to claim 1, characterized in that: Tb 3+ The molar ratio with pyromellitic acid is 1:0.5~1; Tb 3+ The molar ratio with graphene oxide is 1:6~10.

3. A dual-stimulus responsive corrosion self-warning coating according to claim 1 or 2, characterized in that: In the coating, the mass fraction of the composite fluorescent probe is 0.2% to 0.5% of the resin mass.

4. The dual-stimulus responsive corrosion self-warning coating according to claim 1, characterized in that: The resin is at least one of waterborne polyurethane and waterborne epoxy resin; when the resin is waterborne polyurethane, the coating does not contain a curing agent; when the resin is waterborne epoxy resin, the coating contains a curing agent.

5. The dual-stimulus responsive corrosion self-warning coating according to claim 4, characterized in that: The curing agent is an amine-based curing agent; the mass ratio of waterborne epoxy resin to amine-based curing agent is 4~5:

1.

6. The dual-stimulus responsive corrosion self-warning coating according to claim 1, characterized in that: The coating also includes at least one of a dispersant, a defoamer, and a leveling agent as an additive; the mass ratio of each additive to the resin is 1:40~50.

7. A method for preparing a dual-stimulus responsive corrosion self-warning coating as described in any one of claims 1 to 6, characterized in that: The method steps are as follows: (1) Graphene oxide nanosheets were ultrasonically treated and mixed evenly in an ethanol aqueous solution to obtain a graphene oxide solution. Trimethylbenzene acid was added to the graphene oxide solution and mixed evenly to obtain a mixture. Then, terbium nitrate aqueous solution was added dropwise to the mixture while stirring to carry out a coordination reaction. After the reaction was completed, the mixture was washed and dried to obtain a composite fluorescent probe. (2) Add the composite fluorescent probe to the resin and stir evenly to obtain a dual-stimulus-responsive corrosion self-warning coating.

8. The method for preparing a dual-stimulus responsive corrosion self-warning coating according to claim 7, characterized in that: In step (1), the coordination reaction time is 1 to 2 hours; in step (2), the composite fluorescent probe is dispersed in water, ultrasonically treated to disperse it evenly, and then resin is added.

9. The application of a dual-stimulus responsive corrosion self-warning coating as described in any one of claims 1 to 6, characterized in that: The coating is used for visual detection of early corrosion in the metal substrate beneath the coating.

10. The application of the dual-stimulus responsive corrosion self-early warning coating according to claim 9, characterized in that: The coating is applied to the surface of a metal substrate and dried at room temperature to form a coating. When early corrosion occurs on the metal substrate under the complete coating and the scratched coating, the composite fluorescent probe in the coating undergoes rapid fluorescence quenching, enabling convenient tracking and timely maintenance of early corrosion under the coating. The metal matrix is ​​a metal containing iron ions; The coating is applied to the surface of a metal substrate by brushing to form a coating with a dry film thickness of 60 μm to 80 μm.

Images