A fluorescent probe for early corrosion detection of metal and a preparation method thereof

Abstract

The application relates to the technical field of metal ion detection, in particular to a fluorescent probe for early metal corrosion detection and a preparation method thereof. 35 H 33 N5O3.The application successfully develops a fluorescent small molecule Rhe-M sensitive to Fe 3+ response, which can be used as a fluorescent probe molecule capable of recognizing early corrosion sites of carbon steel, is applied to a surface layer of the carbon steel, and through irradiation of an ultraviolet lamp, corrosion sites and area sizes on the surface of the carbon steel can be directly observed; the method is simple in operation, sensitive in reaction, low in cost, strong in specific recognition ability, and is a high-efficiency method capable of detecting early metal corrosion sites.

Description

Technical Field

[0001] This invention relates to the field of metal ion detection technology, and in particular to a fluorescent probe for detecting early corrosion of metals and its preparation method. Background Technology

[0002] Corrosion is an irreversible chemical reaction between metals and their environment, leading to rust and pitting on metal surfaces. Corrosion is extremely harmful, damaging metal properties and impacting the environment. Anti-corrosion coatings are commonly used to protect metals from corrosion. However, over time, these coatings age or fail, allowing corrosive ions from the environment to penetrate the metal surface through cracks and pores, eventually causing severe corrosion. Detecting early-stage corrosion using simple and intuitive techniques can play a crucial role in protecting the metal. Applying fluorescent probes to the coating on the metal surface allows for the detection of Fe2+ generated during corrosion. 2+ This allows them to chelate with fluorescent probes, specifically generating characteristic fluorescent signals, thereby effectively identifying corrosion sites and regions. Compared to inorganic fluorescent materials and those containing heavy metals, organic small molecule fluorescent materials are not only environmentally friendly but also possess advantages such as strong chemical modification capabilities, low development costs, and a wide fluorescence emission range. Therefore, they are widely used in the detection of various metal ions. Through the construction of the molecular framework, metal cations (Fe2+) generated by metal surface corrosion are designed... 3+ and Fe 2+ Organic molecular fluorescent probes that can form chelates or metal complexes can generate strong fluorescent signals with metal ions, thereby enabling direct and efficient detection of early corrosion on steel surfaces.

[0003] Publication No.: CN114574070B A self-warning anti-corrosion coating for zeolite-doped fluorescent probes and its preparation method are disclosed. The method involves reacting rhodamine B with anhydrous hydrazine under anhydrous ethanol and reflux conditions to obtain a yellow precipitate, which is then centrifuged, washed, and dried to obtain rhodamine hydrazine fluorescent probe molecules. Zeolite powder is mixed with the prepared rhodamine hydrazine fluorescent probe molecules in a water-acetonitrile solution, and the reaction is continuously stirred to obtain zeolite-loaded fluorescent probe supramolecularly. The fluorescent probe is protected by loading it with zeolite micro / nano particles, achieving both protection and Fe2+ protection. 3+ The invention provides fluorescent warnings for coating damage and localized corrosion. However, the fabrication process is complex and the loading efficiency is limited.

[0004] Therefore, there is an urgent need to design a low-cost, simple-to-prepare fluorescent probe that can quickly and sensitively detect early corrosion sites and regions in carbon steel alloys. Summary of the Invention

[0005] In view of this, the present invention aims to propose a fluorescent probe for detecting early corrosion of metals and its preparation method, which solves the problems of the inability to quickly and sensitively detect early corrosion sites and areas of carbon steel alloys, as well as the high production cost and complex preparation methods of fluorescent probes in the prior art.

[0006] To address the challenges of efficient metal ion specificity recognition and early corrosion monitoring in practical applications of carbon steel alloys due to their susceptibility to moisture and corrosion in external environments, we designed and synthesized novel rhodamine-based organic small-molecule fluorescent probe molecules. These materials, added as fluorescence indicators to coatings, exhibit no fluorescence when no corrosion occurs; however, when corrosion does occur, the generated iron ions (Fe²⁺) produce fluorescence. 3+ It chelates with a fluorescent probe, generating fluorescence, thereby enabling rapid and sensitive detection of early corrosion sites and areas in carbon steel alloys.

[0007] Meanwhile, the probe Rhe-M of this application can be used as a chemical adsorption layer on the surface of carbon steel, which can delay the occurrence of corrosion to a certain extent and enhance the adsorption capacity of the coating.

[0008] The technical solution of this invention is implemented as follows:

[0009] The first objective of this invention is to disclose a fluorescent probe for detecting early corrosion of metals. The chemical name of this fluorescent probe is: N-[(Rhodamine-6G)lactamethylenediamine]-α-furan carboxaldehyde condensate, and its molecular formula is: C 35 H 33 N5O3, its structural formula is shown in formula (1):

[0010]

[0011] Furthermore, the fluorescent probe is used as follows: Rhe-M is added to L-6030 acrylic resin, and the mixture is stirred for 30 minutes to 1 hour using a magnetic stirrer or a high-speed stirrer to form a uniform coating. The coating is then evenly applied to the carbon steel surface, and the curing time is one week. The corrosion sites and area size on the carbon steel surface are observed by irradiation with an ultraviolet lamp.

[0012] Furthermore, Rhe-M on Fe 3+ The limit of detection (LOD) is 2.29 × 10⁻⁶. -6 M.

[0013] Another object of the present invention discloses a method for preparing a fluorescent probe for detecting early metal corrosion, which is used to prepare the fluorescent probe for detecting early metal corrosion as described in claim 1, comprising the following specific steps:

[0014] S1: Rhodamine 6G and ethylenediamine were added to a solvent and mixed under reflux conditions. The mixture was then cooled to room temperature to obtain the intermediate product Rhe.

[0015] S2: Purify the solid product Rhe obtained in step S1;

[0016] S3: Under reflux conditions, the intermediate product Rhe and α-furan carboxaldehyde were added to the solvent and mixed. After the reaction was complete, a brown powder Rhe-M was obtained.

[0017] Furthermore, in step S1, the molar ratio of Rhodamine 6G to ethylenediamine is 1:(0.8-1.4), and the reflux time is 4 hours.

[0018] Further, in step S2, the product is washed with a solvent, recrystallized with acetonitrile, and then dried under vacuum to obtain a white powder product Rhe.

[0019] Furthermore, in step S3, the molar ratio of the intermediate product Rhe to α-furan carboxaldehyde is 1:(1.1-1.5), and the mixture is refluxed for 8 hours.

[0020] Furthermore, in step S3, the molar ratio of the intermediate product Rhe to α-furan carbaldehyde is 1:(1.1-1.5).

[0021] Furthermore, in step S3, the reaction process is monitored using a TCL.

[0022] Furthermore, the solvent is one of methanol, ethanol, and dioxane.

[0023] Furthermore, the reaction temperature is 65-120℃, and the reaction time is 2-12h.

[0024] Compared with existing technologies, the method for preparing a fluorescent probe for early metal corrosion detection according to the present invention has the following advantages:

[0025] 1. This invention successfully synthesizes a substance for the treatment of Fe through a two-step organic synthesis. 3+ The responsive fluorescent small molecule Rhe-M, as a fluorescent probe molecule that can identify early corrosion sites in carbon steel, can be applied to the surface layer of carbon steel. By irradiating it with a UV lamp, the corrosion sites and their size on the carbon steel surface can be directly observed. This method is simple to operate, highly sensitive, low in cost, and has strong specific recognition ability, making it an efficient method for detecting early metal corrosion sites.

[0026] 2. This invention utilizes the unique "off-on" mechanism of the rhodamine lactone ring to regulate Fe... 3+ The limit of detection (LOD) is 2.29 × 10⁻⁶. -6M, detects the occurrence of early metal corrosion, significantly improving the ability to detect early metal corrosion.

[0027] 3. This invention, by introducing N and O heteroatoms, facilitates the physical and chemical adsorption of probe molecules on the carbon steel surface. Even after 4 days, the impedance value of the corrosion-sensitive coating remains as high as 3.47 × 10⁻⁶. 7 (Ω / cm 2 The addition of Rhe-M significantly improves the anti-corrosion performance of the coating. Attached Figure Description

[0028] 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:

[0029] Figure 1 This is a synthesis diagram of Rhe, the intermediate of this invention;

[0030] Figure 2 This is a synthesis diagram of the Rhe-M fluorescent small molecule of the present invention;

[0031] Figure 3 It is the fluorescent molecule Rhe-M of this invention. 1 H NMR spectrum;

[0032] Figure 4 This is the FT-IR spectrum of the fluorescent molecule Rhe-M of this invention.

[0033] Figure 5 This is the FT-IR spectrum of the fluorescent molecule Rhe-M of this invention.

[0034] Figure 6 This is the HRMS spectrum of the fluorescent molecule Rhe-M of this invention;

[0035] Figure 7 This is the fluorescence spectrum (λ) of Rhe-M (100 μmol / L) and different metal ions (100 μmol / L) of the present invention. ex =347nm);

[0036] Figure 8 This invention relates to Rhe-M (100 μmol / L) and 30 μL of Fe. 3+ Fluorescence intensity of other metal ions (100 μmol / L) added in the presence of 30 μL of 100 μmol / L;

[0037] Figure 9 This invention (a) uses different concentrations (0-250 mol / L) of Fe 3+(a) Comparison of fluorescence intensity after adding 100 μmol / L of the fluorescent molecule Rhe-M; (b) Fluorescence intensity under irradiation at an excitation wavelength of 347 nm compared with Fe 3+ Linear relationship of concentration; (c) Rhe-M with different concentrations (0-250 μmol / L) Fe under natural light and (d) UV lamp irradiation. 3+ Intuitive diagram;

[0038] Figure 10 The present invention (a) involves the fluorescent molecule Rhe-M reacting with (0-250 μmol / L) Fe. 3+ (a) Ultraviolet absorption spectrum, (b) Linear regression curve of ultraviolet absorption spectrum at excitation wavelength of 520 nm;

[0039] Figure 11 The adhesion of Rhe-M added at 1wt% and 2wt% according to this invention to L-6030 coating;

[0040] Figure 12 The present invention provides (a) the contact angle of the L-6030 coating; and (b) the contact angle diagram of the L-6030 coating with the Rhe-M probe added.

[0041] Figure 13 The images show the Nyquist curves of (a) L-6030 and (c) L-6030 coatings doped with Rhe-M (2wt%) over time in a 3.5% NaCl solution of the present invention; and the Bode plots of (b) L-6030 and (d) L-6030 coatings doped with Rhe-M (2wt%) over time.

[0042] Figure 14 The present invention includes (a) the Tafel polarization curve of the L-6030 coating immersed in 3.5 wt% NaCl solution; and (b) the Tafel polarization curve of the Rhe-M-doped L-6030 coating immersed in 3.5 wt% NaCl solution.

[0043] Figure 15 The images show (a) SEM images of the scratches on the L-6030 coating after immersion in 3.5% NaCl solution for 4 days; and (b) SEM images of the scratches on the L-6030 coating doped with Rhe-M after immersion in 3.5% NaCl solution for 4 days.

[0044] Figure 16 These are scratch corrosion images of the Rhe-M-doped L-6030 coating after immersion in 3.5wt% NaCl for (a) 0h, (b) 1h, (c) 2h, and (d) 4h under optical and fluorescence microscopes, respectively, under the same exposure parameters of this invention.

[0045] Figure 17This invention relates to the frontier orbital and electrostatic potential distribution of the fluorescent molecule Rhe-M. Detailed Implementation

[0046] To make the technical means and objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below with reference to specific illustrations.

[0047] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "lateral," "longitudinal," and "center," are only used to explain the relative positional relationships and connections between components in a specific state. They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0048] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0049] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0050] The first objective of this invention is to disclose a fluorescent probe for detecting early corrosion of metals. The chemical name of this fluorescent probe is: N-[(Rhodamine-6G)lactamethylenediamine]-α-furan carboxaldehyde condensate, and its molecular formula is: C 35 H 33 N5O3, its structural formula is shown in formula (1):

[0051]

[0052] This setup allows Rhe-M to exhibit high sensitivity to Fe, enabling the detection of low concentrations of Fe, effectively distinguishing it from other metal ions, reducing interference, and demonstrating high selectivity. Furthermore, Rhe-M exhibits rapid fluorescence response after binding with Fe, making it suitable for real-time detection. Additionally, Rhe-M demonstrates good biocompatibility and can be used in biological systems.

[0053] The second objective of this invention is to disclose a method for preparing a fluorescent probe for detecting early corrosion of metals, comprising the following specific steps:

[0054] S1: Rhodamine 6G and ethylenediamine were mixed and reacted under methanol and reflux conditions, and then cooled to room temperature to obtain the intermediate product Rhe;

[0055] S2: Purify the solid product Rhe obtained in step S1;

[0056] S3: Under methanol and reflux conditions, the intermediate product Rhe and α-furan carboxaldehyde were mixed and the reaction was completed to obtain a brown powder Rhe-M.

[0057] Rhodamine 6G and ethylenediamine react to form N-(rhodamine-6G)lactam ethylenediamine (Rhe). The introduction of ethylenediamine improves the water solubility of Rhe, making it more suitable for use in aqueous systems. Then, by removing unreacted raw materials and byproducts, the purity of the product is improved, ensuring its purity and fluorescence properties. Finally, through the reaction of Rhe and α-furanaldehyde, Fe... 3+ The probe Rhe-M has specific fluorescence properties and metal ion detection capabilities.

[0058] The preparation method described here has mild reaction conditions, moderate yield, simple overall operation, and good purity.

[0059] Preferably, the solvent is methanol, but it can also be replaced by ethanol or dioxane.

[0060] This setting provides flexibility in solvent selection, allowing you to choose the most suitable solvent based on specific experimental conditions and needs, thereby improving reaction efficiency and yield.

[0061] Specifically, the reaction temperature is 65-120℃ and the reaction time is 2-12 hours throughout the entire reaction process.

[0062] A temperature range of 65-120℃ provides sufficient energy to promote the reaction while avoiding excessively high temperatures that could lead to side reactions or reactant decomposition. A reaction time of 2-12 hours provides enough time for the reactants to fully contact and react, ensuring the complete reaction and improving the yield and purity of the product.

[0063] By rationally selecting and controlling these parameters, this setup can ensure the efficient conduct of the reaction, improve the yield and purity of the product, and meet the needs of early metal corrosion detection.

[0064] Specifically, in step S1, the molar ratio of rhodamine 6G to ethylenediamine is 1:(0.8-1.4).

[0065] In practice, to ensure the reaction proceeds completely, a reactant is usually added in slight excess. For example, if ethylenediamine is added in slight excess (e.g., 1.1 times), it ensures that all of the rhodamine 6G reacts with ethylenediamine, thereby increasing the completeness of the reaction, reducing side reactions, and ultimately increasing the yield of the target product.

[0066] Preferably, the molar ratio of rhodamine 6G to ethylenediamine is 1:1.2. For example, the mass of rhodamine 6G is 3g and the mass of ethylenediamine is 0.45g.

[0067] Specifically, in step S1, the condensation reflux time is 4 hours.

[0068] A 4-hour reflux time provides sufficient time for reactants to fully contact and react, ensuring complete reaction. The reflux device maintains the reaction system at a constant temperature, which helps stabilize reaction conditions and avoids incomplete reactions or side reactions caused by temperature fluctuations. A longer reflux time can increase the depth of the reaction, allowing more reactants to be converted into products, thereby increasing the yield. It also effectively recovers volatile solvents, reducing solvent loss and lowering costs.

[0069] Specifically, in step S2, the product is washed with a solvent, recrystallized with acetonitrile, and then dried under vacuum to obtain a white powdery product, Rhe.

[0070] Unreacted raw materials and byproducts are removed by washing with methanol and recrystallizing with acetonitrile, thereby improving the purity of the product. This allows for further purification of Rhe, ensuring its purity and fluorescence properties.

[0071] This setup ensures the purity of Rhe through multiple washing and recrystallization processes, improving the efficiency of subsequent reactions and the performance of the products. The overall process is relatively simple.

[0072] Specifically, in step S3, the molar ratio of the intermediate product Rhe to α-furan carbaldehyde is 1:(1.1-1.5).

[0073] By adding a slight excess of α-furanaldehyde, all Rhe can be ensured to react with α-furanaldehyde. The excess α-furanaldehyde can reduce side reactions and can also be removed through simple separation and purification steps, simplifying the post-processing.

[0074] This setup helps improve reaction completion, ensures the selectivity and purity of the target product, reduces total reaction time and post-processing steps, thereby lowering overall costs and achieving efficient, high-yield, and high-purity target products.

[0075] Specifically, in step S3, condensation reflux is performed for 8 hours.

[0076] An 8-hour reflux time provides sufficient time for reactants to fully contact and react, ensuring complete reaction. The reflux device maintains the reaction system at a constant temperature, which helps stabilize reaction conditions and avoids incomplete reactions or side reactions caused by temperature fluctuations. A longer reflux time can increase the depth of the reaction, allowing more reactants to be converted into products, thereby increasing the yield. It also effectively recovers volatile solvents, reducing solvent loss and lowering costs.

[0077] Specifically, in step S3, the reaction process is monitored using a TCL.

[0078] TLC is a rapid, simple, and sensitive analytical technique widely used in organic synthesis to monitor the progress of reactions, determine whether a reaction is complete, and assess the purity of products. TLC can complete a detection in a few minutes, making it ideal for frequent monitoring of reaction progress.

[0079] By periodically sampling and performing TLC analysis, we can monitor the consumption of reactants and the formation of products in real time, allowing for timely adjustments to reaction conditions. This helps prevent over-reaction, reduce the formation of byproducts, improve the purity of the target product, and determine whether the reaction has been completed.

[0080] This setup is simple to operate, requires no complex instruments, and presents TLC results in the form of spots, which are intuitive, easy to understand, and convenient for observation and recording.

[0081] Specifically, the fluorescent probe is used as follows: Rhe-M is added to L-6030 acrylic resin and stirred for 30 minutes to 1 hour using a magnetic stirrer or high-speed stirrer to form a uniform coating. The coating is then evenly applied to the carbon steel surface and cured for one week. The corrosion sites and area size on the carbon steel surface are observed by irradiation with a UV lamp.

[0082] The addition of Rhe-M significantly reduced the self-corrosion current density of the coating, from 1×10⁻⁶. -8 A / cm 2 Reduced to 1×10 - 10 A / cm 2This enhances the physical barrier effect of the coating, reduces the diffusion path of corrosive media, improves the coating's anti-permeability, and improves the adhesion between the coating and the substrate, making the coating more robust and less prone to peeling.

[0083] This setup significantly improves the corrosion resistance of coatings, reduces the formation of corrosion products, lowers environmental pollution, and is simple and easy to implement.

[0084] Preferably, 2 wt% of Rhe-M is added to L-6030 acrylic resin.

[0085] Preferably, the curing time is 4 days.

[0086] Specifically, Rhe-M affects Fe 3+ The limit of detection (LOD) is 2.29 × 10⁻⁶. -6 M.

[0087] Rhe-M on Fe 3+ The detection limit is 2.29 × 10⁻⁶. -6 M indicates that it has high sensitivity and can detect very low concentrations of Fe. 3+ Fe ions are detected in many applications, such as water quality monitoring and industrial process control, in the early stages. 3+ Ions are crucial for preventing potential problems, and Rhe-M is important for Fe. 3+ The specific response of ions ensures the accuracy of the detection results, while Rhe-M and Fe 3+ The ion binding reaction is rapid, and detection can be completed in a short time. It is suitable for rapid on-site detection, and the operation is simple, requiring no complicated pretreatment steps.

[0088] This setup, through fluorescence quenching and specific binding, enables Rhe-M to accurately and rapidly detect Fe. 3+ Ions ensure the reliability and accuracy of the detection results.

[0089] Example 1:

[0090] Preparation of Rhe-M

[0091] The synthesis reaction formula for Rhe is as follows: Figure 1 Rhodamine 6G (3.0 g, 6.26 mmol) and ethylenediamine (0.45 g, 7.51 mmol) were weighed and placed in a 100 mL round-bottom flask. 25 mL of methanol was added, and the mixture was refluxed for 4 h. After cooling to room temperature, the mixture was filtered. The product was washed with methanol, recrystallized from acetonitrile, and dried under vacuum to give 2.14 g of a white powder, Rhe (yield 74.8%).

[0092] The Rhe-M synthesis reaction formula is as follows: Figure 2Weigh the intermediate product Rhe (200.0 mg, 0.438 mmol) and α-furan carbaldehyde (48.0 mg, 0.525 mmol) into a 150 mL round-bottom flask, add 20 mL of methanol, reflux for 8 h, monitor the reaction progress with TCL, and wash with methanol after the reaction is complete to obtain 101 mg of brown powder Rhe-M (yield 43.2%).

[0093] Example 2

[0094] Rhodamine Fe 3+ Basic structural characterization of fluorescent probe small molecules

[0095] The prepared Rhe-M small molecules were dried in a vacuum drying oven for 24 hours. The solid sample was then subjected to 1H NMR spectroscopy. 1 H-NMR ( Figure 3 Fourier transform infrared spectroscopy ( Figure 4 ), ( Figure 5 ) and high-resolution mass spectrometry ( Figure 6 The correctness of the obtained product structure was verified by testing.

[0096] Example 3

[0097] Rhe-M Small Molecule Optical Sensing Performance Testing

[0098] Rhe-M ligand stock solution and Fe 3+ Preparation of stock solutions: Prepare a 100 μmol / L Rhe-M dichloromethane stock solution; prepare a 1 mol / L FeCl3·6H2O aqueous solution stock solution, and dilute FeCl3·6H2O at different concentrations (50 μmol / L, 100 μmol / L, 150 μmol / L, 200 μmol / L, 250 μmol / L). 3+ Stock solution. Fluorescence was measured using an excitation wavelength of 347 nm, with a wavelength range of 200-800 nm, to determine the fluorescence emission of Rhe-M in ethanol solution.

[0099] Example 4

[0100] Selectivity of ligand Rhe-M for different metal ions

[0101] Figure 7 To obtain the fluorescence spectrum of Rhe-M with metal ions, 30 μL of Fe was added. 3+ Adding Ag to a 100 μmol / L Rhe-M solution significantly enhanced fluorescence intensity, with an amplitude (1-I0 / I) reaching 95.14%. However, under the same conditions, adding an equal amount of Ag to the Rhe-M solution... + Ba 2+ Ca 2+ Cd2+ Co 2+ Cr 3+ In the same metal ion stock solution, the fluorescence of ligand Rhe-M remains essentially unchanged. Therefore, ligand Rhe-M has a high fluorescence intensity for Fe. 3+ It exhibits highly selective recognition capabilities, which may be attributed to the abundance of N, O, and other coordination sites in Rhe-M, which interact with Fe. 3+ Chelation occurs, leading to the ring-opening of the lactam and enhanced fluorescence of the system.

[0102] Example 5

[0103] Rhe-M-Fe 3+ Anti-interference test

[0104] Add 30 μL of Fe to a Rhe-M (100 μmol / L) EtOH solution. 3+ The stock solution was then sequentially supplemented with equal amounts of other metal ions (Ag). + Ba 2+ Ca 2+ Cd 2+ Zn 2+ Cr 3+ (etc.), fluorescence intensity changes such as Figure 8 The results showed that other metal ions did not affect Rhe-M-Fe. 3+ The fluorescence intensity is significantly affected, among which Fe 2+ Although the impact is significant, Fe 2+ Extremely unstable, it is easily oxidized to Fe. 3+ This indicates that Rhe-M-Fe 3+ Its selective recognition exhibits excellent anti-interference performance.

[0105] Example 6

[0106] Fe of different concentrations 3+ Fluorescence performance of ligand Rhe-M

[0107] Rhe-M and Fe were studied using fluorescence titration experiments. 3+ The relationship between concentration. Figure 9 -a indicates that, with Fe 3+ With increasing concentration, the fluorescence intensity of Rhe-M gradually increased, reaching its peak at 250 μmol / L. The solution turned red under natural light and exhibited yellow fluorescence under ultraviolet light. (The text then abruptly shifts to a seemingly unrelated topic about Fe...) 3+ A calibration curve was obtained by plotting the concentration of the complex on the x-axis and the fluorescence intensity I of the complex on the y-axis, yielding a linear equation: y = 2759.17x + 189.12, with R² = 0.998. Figure 9 -b). The calculated limit of detection (LOD) is 2.292 × 10⁻⁶. -6M indicates that Rhe-M affects Fe 3+ It has high sensitivity.

[0108] Example 7

[0109] Ultraviolet spectroscopy test

[0110] Figure 10 Rhe-M in different Fe 3+ The UV absorption spectra at concentrations (0-250 μmol / L) and the linear regression curves of the corresponding UV absorption intensity at an excitation wavelength of 520 nm show that the ligand Rhe-M exhibits strong UV absorption at 430 nm. This is attributed to the UV absorption of the -C=N- double bond on the Schiff base in Rhe-M. With the increase of Fe... 3+ As the concentration increased, a strong ultraviolet absorption peak appeared at 520 nm, which is attributed to the characteristic ultraviolet absorption peak after the ring opening of rhodamine spirolactam. Another absorption peak appeared at 353 nm, indicating that Fe... 3+ New substances are formed after interaction with the ligand. The linear equation of the regression line is y = 0.17446x + 0.0051, with a correlation coefficient R² = 0.96574. Ultraviolet absorption spectroscopy indicates that Rhe-M can be used as a detector for Fe. 3+ The probe has excellent performance.

[0111] Example 8

[0112] Adhesion performance test

[0113] L-6030 acrylic resin was evenly brushed onto the surface of Q235 carbon steel and allowed to cure for one week. The adhesion data of the fluorescent probe Rhe-M to the L-6030 coating are as follows: Figure 11 As shown, the L-6030 coating exhibits poor adhesion, averaging 3.192 N / cm². 2 The addition of Rhe-M significantly improved the L-6030 coating, with an average adhesion of 5.196 N / cm at a concentration of 2 wt%. 2 This indicates that the doping of Rhe-M improves the adhesion between the coating and the carbon steel substrate.

[0114] Example 9

[0115] Contact angle performance test

[0116] The contact angle of the prepared L-6030 composite coating was tested. Five points were randomly selected for parallel experiments to eliminate experimental errors. Figure 12As shown, the contact angle θ between the L-6030 coating and water is 69.6°, indicating that the L-6030 coating is hydrophilic and easily damaged by corrosive media in water. The L-6030 coating with added Rhe-M has a contact angle θ of 81.2°, which enhances the hydrophobicity of the coating and significantly improves its corrosion resistance.

[0117] Example 10

[0118] Electrochemical testing of coatings

[0119] Figure 13 These are the Nyquist curves and Bode plots for the L-6030 coating and the coating with added Rhe-M. Nyquist curves of (a) L-6030 and (c) L-6030 coating with 2wt% Rhe-M doping over time in 3.5% NaCl solution; Bode plots of (b) L-6030 and (d) L-6030 coating with 2wt% Rhe-M doping over time. With prolonged immersion time, the impedance arc radius in the Nyquist plot decreases, indicating a decline in the overall anti-corrosion performance of the coating. After immersion for 4 days, the impedance modulus |Z| of the coating with added Rhe-M increased from 5.93 × 10⁻⁶. 8 (Ω·cm 2 It decreased to 3.47 × 10 7 (Ω·cm 2 The impedance modulus of the blank L-6030 coating, |Z|, is 7.87 × 10⁻⁶. 5 (Ω·cm 2 It decreased to 4.14 × 10 4 (Ω·cm 2 The Rhe-M coating consistently exhibits an impedance modulus three orders of magnitude higher than the blank coating, thus enhancing the coating's corrosion resistance.

[0120] Figure 14 These are the Tafel polarization curves for the L-6030 coating and the coating with added Rhe-M. The self-corrosion potential of the L-6030 coating is -0.60V, while the corrosion potential of the L-6030 coating with added Rhe-M shifts positively to around -0.30V, significantly reducing the tendency of carbon steel plates to anodic corrosion. Corrosion current density refers to the corrosion current intensity per unit metal area; the lower the corrosion current value, the higher the degree of corrosion protection of the coating. The self-corrosion current density of the L-6030 coating is 1×10⁻⁶ at 2d. -8 A / cm 2 As the immersion time increased, the self-corrosion current density gradually decreased to 1×10⁻⁶. -6 A / cm 2 The self-corrosion current density of the L-6030 coating with added Rhe-M reaches 1×10⁻⁶. -10 A / cm2 This indicates that the L-6030 coating doped with Rhe-M has better corrosion resistance, which is consistent with the results obtained from the AC impedance test above.

[0121] Example 11

[0122] Microscopic morphology of the coating scratches (SEM image analysis)

[0123] Figure 15 SEM images of scratches on the L-6030 coating and the coating doped with Rhe-M (2wt%) are shown. Due to the entry of corrosive ions, the microscopic surface of the coating is mostly a fragmented resin layer, indicating that the coating begins to peel off and fail after corrosion. Compared with the coating doped with Rhe-M, we can clearly see that the coating has a more complete microstructure and fewer micropores, indicating that the doping with Rhe-M protects the L-6030 coating to some extent.

[0124] Example 12

[0125] Rhe-M's response to corrosion of L-6030 coating

[0126] Figure 16 Images of the Rhe-M-doped L-6030 coating under optical and fluorescence microscopes. After scratching the metal substrate, the exposed metal substrate beneath the scratches is clearly visible under an optical microscope. No significant changes were observed under a fluorescence microscope without immersion in NaCl solution. After immersion in a carbon steel sample for 1 hour… Figure 16 -b) When corrosion was observed on the coating scratches under an optical microscope, and faint dotted orange-yellow fluorescence could be seen at the scratches under a fluorescence microscope. 2 hours later ( Figure 16 -c) Under an optical microscope, a distinct pale pink color was observed at the scratch area. Under a fluorescence microscope, a clear orange-yellow fluorescence was observed at the scratch area, indicating that Fe was formed during metal corrosion. 3+ It reacts with the fluorescent probe Rhe-M and emits fluorescence. Soaking for 4 hours ( Figure 16 When -d), the fluorescence intensity weakens slightly, and the fluorescence tends to disappear at the scratch.

[0127] Example 13

[0128] Frontier orbital and electrostatic potential distribution of the fluorescent molecule Rhe-M

[0129] The relationship between Rhe-M and Fe was studied by analyzing and calculating HOMO and LUMO orbitals and electrostatic potential (ESP). 3+ Interactions between ions. For example... Figure 17As shown, the HOMO of Rhe-M is discretely distributed on the left benzene ring of the xanthracene, while the LUMO is mainly distributed at the -N=CH- group and the furan ring unit. After the addition of Fe, the distributions of HOMO and LUMO changed significantly. LUMO was more distributed at the open ring of the spirolactam and the furan ring, while HOMO was more concentrated at the aromatic ring of the xanthracene, essentially filling the entire band gap of the aromatic ring Rhe-M-Fe (ΔE=E). LUMO -E HOMO This indicates that the Rhe-M-Fe complex is more stable than Rhe-M, i.e., ΔE Rhe-M-Fe =2.22eV<ΔE Rhe-M =4.49eV).

[0130] Example 14

[0131] Through continuous experimentation and optimization by changing the feed ratio (Rhe: α-furanaldehyde), different solvents (methanol, ethanol, and dioxane), reaction temperature (65°C-120°C), and reaction time (2h to 12h), the optimal reaction conditions for developing Rhe-M were finally obtained. The optimized conditions are shown below:

[0132] S1 and S2: Research and purification of Rhe

[0133]

[0134] S3: Development of Rhe-M

[0135]

[0136] Fluorescence tests were performed on the prepared Rhe-M, and Fe was prepared at different concentrations (0-250 μmol / L). 3+ The fluorescence intensity was measured by adding the sample to a 100 μmol / L Rhe-M ethanol solution. The specific implementation method and results are shown in the table below:

[0137] Example 3: Fluorescence Intensity Test

[0138]

[0139]

[0140] This invention successfully synthesized the fluorescent small molecule Rhe-M, which is sensitive to Fe3+, through a two-step organic chemical reaction. Based on fluorescence sensing performance studies, the calculated limit of detection (LOD) was 2.292 × 10⁻⁶. -6 M indicates that Rhe-M affects Fe 3+It exhibits high sensitivity and good resistance to interference from other metal ions. Adding 2 wt% to L-6030 acrylic resin enabled the detection of early corrosion in carbon steel. Simultaneously, measurements of the corrosion resistance of the L-6030 coating showed that the probe Rhe-M can act as a chemisorption layer on the carbon steel surface, delaying corrosion to a certain extent. Therefore, Rhe-M's excellent early corrosion detection capability and corrosion resistance properties make it promising for broad applications and practical value in metal corrosion protection, the coatings industry, and shipbuilding.

[0141] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of a fluorescent probe for detecting early corrosion of metals in the field of metal corrosion prevention, characterized in that, The chemical name of this fluorescent probe is: N-[(Rhodamine-6G)lactamethylenediamine]-α-furan carboxaldehyde condensate, and its molecular formula is: C 35 H 33 N5O3, its structural formula is shown in formula (1): The fluorescent probe is added to L-6030 acrylic resin and stirred for 30 minutes to 1 hour using a magnetic stirrer or a high-speed stirrer to form a uniform coating. The coating is then evenly applied to the carbon steel surface.

2. The application according to claim 1, characterized in that, Rhe-M on Fe 3+ The limit of detection (LOD) is 2.29 × 10⁻⁶. -6 M.

3. The application according to claim 1, characterized in that, The preparation method of the fluorescent probe includes the following specific steps: S1: Rhodamine 6G and ethylenediamine were mixed and reacted in a solvent, which was one of methanol, ethanol and dioxane, under reflux conditions. The reaction temperature was 65-120℃ and the reaction time was 2-12h. After cooling to room temperature, the intermediate product Rhe was obtained. S2: Purify the solid product Rhe obtained in step S1; S3: Under reflux conditions, the intermediate product Rhe and α-furan carboxaldehyde were added to the solvent and mixed. After the reaction was complete, a brown powder Rhe-M was obtained.

4. The application according to claim 3, characterized in that, In step S1, the molar ratio of Rhodamine 6G to ethylenediamine is 1:(0.8-1.4), and the reflux time is 4 hours.

5. The application according to claim 3, characterized in that, In step S2, the product is washed with a solvent, recrystallized from acetonitrile, and then dried under vacuum to obtain a white powdery product, Rhe.

6. The application according to claim 3, characterized in that, In step S3, the molar ratio of the intermediate product Rhe to α-furan carboxaldehyde is 1:(1.1-1.5), and the mixture is refluxed for 8 hours.

7. The application according to claim 3, characterized in that, In step S3, the reaction process is monitored using a TCL.

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