Preparation and application of CDs@Fe3O4 nanoparticles, a type of peroxidase

Abstract

The application discloses a kind of peroxidase-like CDs@Fe3O4 nanoparticles and its preparation and application, which comprises: carbon source and nitrogen source are reacted by hydrothermal method, and nitrogen-doped carbon dot solution is prepared;Iron source is added to the nitrogen-doped carbon dot solution and stirred, after reaction at 150-300 DEG C, after separation, washing and drying, the peroxidase-like CDs@Fe3O4 nanoparticles are obtained.The CDs@Fe3O4 prepared by the application can catalyze hydrogen peroxide decomposition to produce hydroxyl radical to induce color change of chromogenic substrate, and Fe 3+ The linear response to chromogenic substrate is realized, and the visual monitoring of the damage depth of the protective layer of metal parts is realized.In the monitoring process, after the protective layer is slightly damaged, the CDs@Fe3O4 is exposed to make the chromogenic substrate develop color, and finally the protective layer is completely damaged to expose the metal, which can also induce the chromogenic substrate to develop color.At the same time, the application provides a convenient colorimetric method for detecting coating damage and metal corrosion using Python program.The method uses color difference as an index, and provides a simple and effective method for evaluating the degree of coating damage and metal corrosion.

Description

Technical Field

[0001] This invention relates to a nanoparticle, specifically to a peroxidase-like CDs@Fe3O4 nanoparticle and its preparation and application. Background Technology

[0002] Natural enzymes possess highly efficient catalytic activity and substrate specificity, making them widely used in industrial production. However, natural enzymes are subject to harsh environmental conditions and are prone to denaturation, resulting in low stability. Artificial enzymes, on the other hand, possess the catalytic activity of natural enzymes while avoiding their stringent environmental requirements. Compared to natural enzymes, they are easier to prepare, require less stringent storage conditions, and have lower production costs. Nanoparticles, due to their large specific surface area, high stability, and tunable size, can provide more catalytically active sites, making them an excellent material for artificial enzymes.

[0003] In recent years, safety issues arising from metal corrosion failure have attracted widespread attention. However, damage to the protective coating on metal parts is often difficult to detect. The aforementioned damage process proceeds from surface damage and microcrack formation to complete metal exposure. Therefore, timely and effective detection of the integrity and depth of damage to the protective coating of metal parts is crucial for preventing metal corrosion failure. However, current research on the extent of damage to the protective coating of metal parts is limited. While some literature has successfully monitored the width of damage to the protective coating, it cannot reflect the depth of damage in real time, leading to corrosion risks due to environmental exposure of the metal parts. Summary of the Invention

[0004] The purpose of this invention is to provide a peroxidase-like CDs@Fe3O4 nanoparticle, its preparation, and its application, solving the problem that existing technologies cannot reflect the damage depth of the protective layer in real time, leading to the risk of corrosion of metal parts due to environmental exposure. The CDs@Fe3O4 peroxidase can catalyze the decomposition of hydrogen peroxide to generate hydroxyl radicals that induce color change in the chromogenic substrate. Subsequently, by adding a reducing agent to decolorize the substrate, Fe... 3+ A linear response to the chromogenic substrate enables monitoring of iron ion concentration.

[0005] To achieve the above objectives, this invention provides a method for preparing peroxidase-like CDs@Fe3O4 nanoparticles, the method comprising:

[0006] (1) A nitrogen-doped carbon dot solution was prepared by reacting a carbon source and a nitrogen source using a hydrothermal method.

[0007] (2) The iron source was added to the nitrogen-doped carbon point solution and stirred. After reaction at 150-300℃, the peroxidase-like CDs@Fe3O4 nanoparticles were obtained by separation, washing and drying.

[0008] Preferably, in step (1), the carbon source is any one or more of glucose, citric acid, sodium alginate, cellulose, chitosan, dextran and lignin, and the nitrogen source is any one or more of ethylenediamine, ammonia, aniline, amino acids and L-arginine.

[0009] More preferably, the carbon source is glucose and the nitrogen source is L-arginine. Glucose has many hydroxyl groups, and L-arginine is more easily used for nitrogen atom doping. Other carbon and nitrogen sources are not easy to use for heteroatom doping, and the prepared material has low catalytic performance and cannot effectively catalyze hydrogen peroxide.

[0010] Preferably, in step (1), the mass of the carbon source is 10% to 90% of the mass of the nitrogen source; the concentrations of the carbon source and the nitrogen source are greater than 0 and less than 100%.

[0011] Preferably, in step (1), the hydrothermal reaction temperature is 150-250°C and the hydrothermal reaction time is 6-24 hours.

[0012] Preferably, in step (2), the iron source is any one or more of ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, iron(II,III) oxide, ferric bromide and ferric carbonate.

[0013] Preferably, in step (2), the mass of carbon dots in the nitrogen-doped carbon dot solution is 0 to 100% of the mass of the iron source, and is not 0; the pH value is greater than 0 and less than 14; and the reaction time at 150 to 300°C is 6 to 24 hours.

[0014] This invention provides peroxidase-like CDs@Fe3O4 nanoparticles prepared by the method described above.

[0015] This invention provides an application of the peroxidase-like CDs@Fe3O4 nanoparticles as described above in detecting the depth of damage to the protective layer of metal parts.

[0016] Preferably, the application involves inducing a color change in the chromogenic substrate through the peroxidase-like CDs@Fe3O4 nanoparticles, and Fe... 3+ The linear response of the colorimetric substrate was used to detect the depth of damage to the protective layer of the metal parts.

[0017] More preferably, the chromogenic substrate is tetramethylbenzidine, anthocyanin, or a peroxidase fluorescent probe; the material of the metal protective layer includes a base membrane and any one or two of the following (a) and / or (b):

[0018] (a) A coating on at least one side surface of a base film;

[0019] (b) Text and / or patterns located on the surface of the material;

[0020] The peroxidase-like CDs@Fe3O4 nanoparticles are added to at least one of the structures in the base film, coating, text, and / or pattern.

[0021] By adding peroxidase-like CDs@Fe3O4 nanoparticles to coatings, text, and / or patterns, the surface of the coating will display corresponding text or patterns when the coating is damaged, providing a relevant color response to the coating damage. The application of this invention lies not only in detecting whether a coating is damaged, but also in detecting the degree of coating damage and whether metal parts have been damaged.

[0022] The present invention relates to a peroxidase-like CDs@Fe3O4 nanoparticle, its preparation and application, which solves the problem that existing technologies cannot reflect the damage depth of the protective layer in real time, leading to the risk of corrosion of metal parts due to environmental exposure. It has the following beneficial effects:

[0023] 1. The CDs@Fe3O4 nanoparticles of this invention exhibit excellent catalytic activity. This is because Fe3O4 readily aggregates in water, while nitrogen-doped CDs create sufficient catalytic active sites on the Fe3O4 surface. The surface contains numerous C=N and C=O functional groups, which enhance the hydrophilicity of the Fe3O4 nanoparticles and strengthen electron transfer in the metal oxide. Compared to existing materials, the CDs@Fe3O4 nanoparticles of this invention have additional nitrogen elements on their surface, making electron transfer easier during catalysis, thereby significantly improving the catalytic activity of the material.

[0024] 2. Compared with existing technologies, this invention is the first to utilize the peroxidase-like properties of CDs@Fe3O4 nanoparticles, combined with Fe 3+ Linear colorimetric characteristics (CDs@Fe3O4 catalyzes the production of reactive oxygen species from hydrogen peroxide, thereby oxidizing the chromogenic substrate and causing the solution to develop color. Adding a reducing agent can block the oxidation of the chromogenic substrate or cause the oxidized substrate to fade. Meanwhile, Fe...) 3+ This invention utilizes a protective coating (primarily composed of epoxy resin and CDs@Fe3O4 nanoparticles) to detect the depth of damage to metal parts. This method is not only intuitive but also simple and rapid, requiring no large instruments or equipment, and can quickly and sensitively reflect the degree of damage to the protective coating of metal parts. (During monitoring, when the protective coating is intact, CDs@Fe3O4 peroxidase is not exposed, thus preventing color change of the chromogenic substrate. After slight damage, CDs@Fe3O4 peroxidase is exposed, causing the chromogenic substrate to develop color. Finally, when the protective coating is completely damaged, leading to metal exposure, the chromogenic substrate can be induced to develop color in the same way.)

[0025] 3. This invention proposes a convenient colorimetric method for detecting coating damage and metal corrosion using a Python program. This method utilizes color difference as an indicator, providing a simple and effective approach to assess the degree of coating damage and metal corrosion. Attached Figure Description

[0026] Figure 1 The absorption spectra of the materials prepared in Examples 1-3 and Comparative Examples 1-2 of this invention are shown.

[0027] Figure 2 This is a TEM image of the material prepared in Example 1 of the present invention.

[0028] Figure 3 The material prepared in Example 1 of this invention is effective against Fe. 3+ Selectivity plot.

[0029] Figure 4 This is an EDS image of the material obtained in Example 1 of the present invention.

[0030] Figure 5 This is an XPS image of the material obtained in Example 1 of the present invention.

[0031] Figure 6 This is an XPS image of the material obtained in Example 2 of the present invention.

[0032] Figure 7 This is an XPS image of the material obtained in Example 3 of the present invention.

[0033] Figure 8 These are structural characterization diagrams of the materials obtained in Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0034] Figure 9 This is a graph showing the relative catalytic activity of the material prepared in Example 1 of the present invention under different conditions.

[0035] Figure 10 The absorbance of the material prepared in Example 1 of this invention after the addition of methanol and isopropanol, hydroxyl radical scavengers, is shown in the image.

[0036] Figure 11 This is a steady-state dynamic diagram of the material obtained in Example 1 of the present invention (I).

[0037] Figure 12 This is the material steady-state dynamics diagram (II) obtained in Example 1 of the present invention.

[0038] Figure 13 The absorbance diagram is shown for the material prepared in Example 1 of this invention after the addition of 8-HQ reaction.

[0039] Figure 14SEM images of scratches of different depths generated in an epoxy coating containing 5% CDs@Fe3O4 (0.5) according to Example 1 of the present invention.

[0040] Figure 15 The images show magnified micrographs and color intensity diagrams of scratches of different depths produced in an epoxy coating containing 5% CDs@Fe3O4 (0.5) according to Example 1 of the present invention.

[0041] Figure 16 This is a magnified microscope image and color RGB diagram of scratches on an epoxy coating on a corroded steel plate according to Embodiment 1 of the present invention.

[0042] Figure 17 This is a schematic diagram illustrating the monitoring of coating damage and potential metal corrosion via a smartphone in Embodiment 1 of the present invention.

[0043] Figure 18 This is a process diagram of monitoring the degree of damage to the protective layer of metal parts in Embodiment 1 of the present invention. Detailed Implementation

[0044] Example 1

[0045] A method for preparing peroxidase-like CDs@Fe3O4 nanoparticles, the method comprising:

[0046] (1) Hydrothermal method: using glucose (C6H) 12 O6) is the carbon source, and L-arginine (C6H) is used as the carbon source. 14 Using N4O2 as the nitrogen source, 1g of glucose, 1g of L-arginine and deionized water were mixed and stirred for ten minutes. The solution was then transferred to a 100mL reaction vessel and heated at 160℃ for 10 hours. After cooling to room temperature, the carbon dot solution was filtered through a 0.22μm microporous membrane. The filtrate was collected to obtain the CDs solution, which was stored at 2–8℃.

[0047] (2) Solvent heat: 1g of FeCl3·6H2O and 4g of NaAC were added to 50mL of CDs solution and stirred for 15-20min to mix them thoroughly. The solution was then transferred to a 100mL reactor and heated at 200℃ for 10h. After cooling to room temperature, the solid nanomaterials in the solution were separated using a permanent magnet (1-1.5T). The nanomaterials were washed 6 times with a mixture of deionized water and anhydrous ethanol and dried at 50℃ in a drying oven to obtain the nanomaterials, which were denoted as CDs@Fe3O4(0.5).

[0048] If the mass of FeCl3·6H2O is less than 0.5g, the catalytic activity of the prepared nanoparticles is comparable to that of CDs@Fe3O4 nanoparticles prepared by adding 0.5g of FeCl3·6H2O. Therefore, a suitable amount of 0.5g of FeCl3·6H2O should be selected for preparation.

[0049] Example 2

[0050] The preparation method of a peroxidase-like CDs@Fe3O4 nanoparticle is basically the same as that in Example 1, except that:

[0051] In step (2), the mass of FeCl3·6H2O is adjusted from 0.5g to 0.8g;

[0052] Following the same remaining operations as in Example 1, the nanomaterial was obtained, denoted as CDs@Fe3O4(0.8).

[0053] Example 3

[0054] The preparation method of a peroxidase-like CDs@Fe3O4 nanoparticle is basically the same as that in Example 1, except that:

[0055] In step (2), the mass of FeCl3·6H2O is adjusted from 0.5g to 1.1g;

[0056] Following the same remaining operations as in Example 1, the nanomaterial was obtained, denoted as CDs@Fe3O4 (1.1).

[0057] Comparative Example 1

[0058] The preparation method of nanoparticles is basically the same as that in Example 1, except that:

[0059] Step (1) is missing;

[0060] In step (2), 25 mL of CDs solution was replaced with 25 mL of deionized water, and Fe3O4 was obtained by the same operation as in Example 1.

[0061] Comparative Example 2

[0062] The preparation method of nanoparticles is basically the same as that in Example 1, except that:

[0063] There is no step (2).

[0064] Experimental Example 1 Absorbance

[0065] 1. 30℃ test

[0066] In this invention, 3 mL of Na-AC (pH=3.6), 50 μL of TMB (concentration of 10 mM), 50 μL of H2O2 (concentration of 30%) and 50 μL of the catalyst material CDs@Fe3O4 (0.5) prepared in Example 1 were mixed and kept at 30 °C for 10 min, and the absorption spectrum was measured.

[0067] like Figure 1The images show the absorption spectra of the materials prepared in Examples 1-3 and Comparative Examples 1-2 of this invention, where the horizontal axis represents wavelength and the vertical axis represents absorbance. Figure 1 It can be seen that at 652 nm, TMB can only be oxidized in the presence of both H2O2 and CDs@Fe3O4. The catalytic activity of CDs and Fe3O4 alone is very low, while the catalytic activity of CDs@Fe3O4(0.5) material is the highest.

[0068] 2. Testing with cleaning agent

[0069] In this invention, 3 mL of Na-AC (pH=3.6), 50 μL of LMB (concentration of 10 mM), 50 μL of H2O2 (concentration of 30%) and 50 μL of the catalyst material CDs@Fe3O4 (0.5) prepared in Example 1 were mixed, and methanol and isopropanol, hydroxyl radical scavengers, were added. The mixture was kept at 45 °C for 10 min, and the absorbance was measured.

[0070] like Figure 10 As shown, the absorbance graph of the material prepared in Example 1 of this invention after the addition of hydroxyl radical scavengers methanol and isopropanol is presented. The vertical axis represents absorbance, and the horizontal axis represents the blank control group (BLANK), methanol (MA), and isopropanol (IPA). Figure 10 It can be seen that, compared with other groups, the absorbance of the group with the addition of IPA decreased significantly, indicating that CDs@Fe3O4 catalyzes the generation of ·OH from hydrogen peroxide, thereby oxidizing TMB.

[0071] 3. Reactions with 40mM or different concentrations of 8-HQ

[0072] In this invention, 3 mL of Na-AC (pH=3.6), 50 μL of LMB (10 mM), 50 μL of H2O2 (concentration of 30%) and 50 μL of CDs@Fe3O4 (0.5) prepared in Example 1 were mixed and kept at 45 °C for 10 min. Then, 50 μL of 8-HQ (40 mM or different concentrations) was added and reacted for 5 min. The absorbance was then measured.

[0073] like Figure 13 As shown, the absorbance graph of the material prepared in Example 1 of this invention after the addition of 8-HQ reaction is displayed, where A represents the reaction of 40mM 8-HQ for 5 min, followed by the addition of 100μLFe. 3+ (500mM) Absorbance was measured, with wavelength on the x-axis and absorbance on the y-axis; B was measured after a 5-minute reaction of 8-HQ at 0–40mM, with concentration on the x-axis and absorbance on the y-axis. Figure 13 As shown in A, the absorbance of the solution decreased significantly after the addition of 8-HQ, while the addition of Fe... 3+ The absorbance of the solution will recover somewhat afterward. Figure 13As the concentration of 8-HQ increases, the absorbance of the solution decreases in reaction B.

[0074] 4. Fe at different concentrations 3+ or metal ions

[0075] In this invention, 3 mL of Na-AC (pH = 3.6), 50 μL of TMB (10 mM), 50 μL of H2O2 (concentration 30%), and 50 μL of CDs@Fe3O4 (0.5) prepared in Example 1 were mixed and kept at 45 °C for 10 min. Then, 50 μL of 8-HQ (40 mM) was added and reacted for 5 min. Finally, 100 μL of Fe was added. 3+ The absorbance was measured using different concentrations or 100 μL of different metal ions (each metal ion concentration was 500 μM).

[0076] like Figure 3 As shown, the material obtained in Example 1 of this invention has a positive effect on Fe. 3+ The selectivity plot, where A is the selectivity of Fe 3+ The absorbance graphs at different concentrations are shown, with the horizontal axis representing iron ion concentration and the vertical axis representing absorbance; B represents the effect of different ions on Fe. 3+ The selectivity plot shows the concentration of various ions on the x-axis and the absorbance on the y-axis. Figure 3 From A, we know that the detection limit LOD is 0.066 μM; Figure 3 As can be seen from B, compared with other ions, it is more effective for Fe 3+ The selection is the best.

[0077] Analysis and structural characterization of Experiment Example 2

[0078] 1. Transmission electron microscopy analysis

[0079] The present invention performs TEM analysis on the material obtained in Example 1.

[0080] like Figure 2 The image shows a TEM image of the material obtained in Example 1 of this invention, where A is a TEM image with a 20 nm scale and B is a TEM image with a 5 nm scale. Figure 2 It can be seen that CDs and Fe3O4 are well combined to form a composite structure.

[0081] The TEM lattice spacing of the material prepared in Example 1 of this invention is 0.2548 nm, which belongs to the (311) crystal plane of the magnetite inverse spinel structure, and the lattice spacing of 0.2112 nm corresponds to the (100) crystal plane of graphite carbon.

[0082] 2. Energy Spectroscopy Analysis

[0083] The materials obtained in Examples 1-3 of this invention were subjected to energy dispersive spectroscopy (EDS) analysis, and the results are detailed in Table 1 and... Figures 4-7.

[0084] like Figure 4 As shown, the EDS diagrams of the materials obtained in Example 1 of this invention are as follows: A is the EDS diagram of each element; B is the EDS diagram of Fe; and C is the EDS diagram of N. Figure 4 It can be seen that carbon dots are uniformly distributed on the surface of iron oxide, forming a composite structure, nitrogen is uniformly distributed in the composite material of carbon dots and iron oxide, and CDs@Fe3O4 nanoparticles have good dispersibility.

[0085] like Figure 5 As shown, the XPS plots of the material obtained in Example 1 of this invention are as follows, where the horizontal axis represents binding energy and the vertical axis represents strength. A is the XPS plot of each element; B is the XPS plot of element C; C is the XPS plot of element O; D is the XPS plot of element N; and E is the XPS plot of element Fe. Figure 5 It can be seen that the C1s spectra at 284.8 eV, 286.3 eV, and 287.82 eV correspond to the CC, COC, and C=N functional groups, respectively; the O1s spectra at 529.38 eV and 530.89 eV correspond to the Fe-O and -OH functional groups, respectively; the N1s spectra at 399.65 eV correspond to the N-(C=O)- functional group; and the Fe2p spectra at 709.78 eV correspond to the Fe... 2+ 712.17 eV and 723.64 eV correspond to Fe 3+ .

[0086] Table 1 Comparison of XPS element content

[0087]

[0088] As shown in Table 1, with the increase of FeCl3·6H2O addition, the proportion of C element content continuously increases, while the proportions of O element and Fe element content continuously decrease. The proportion of nitrogen element is highest at 0.5g FeCl3·6H2O addition, while the proportions at 0.8g and 1.1g are roughly the same.

[0089] like Figure 6 As shown, the XPS plots of the material obtained in Example 2 of this invention are as follows, where the horizontal axis represents binding energy and the vertical axis represents strength. A is the XPS plot of each element; B is the XPS plot of element C; C is the XPS plot of element O; D is the XPS plot of element N; and E is the XPS plot of element Fe. Figure 6 It can be seen that the C1s spectra at 284.8 eV and 286.2 eV correspond to the CC and COC functional groups, respectively; the O1s spectra at 529.62 eV and 530.89 eV correspond to the Fe-O and -OH functional groups, respectively; the N1s spectra at 399.65 eV correspond to the N-(C=O)- functional group; and the Fe2p spectra at 710.14 eV correspond to the Fe2O3 functional group. 2+712.41 eV and 723.31 eV correspond to Fe 3+ .

[0090] like Figure 7 As shown, the XPS plots of the material obtained in Example 3 of this invention are displayed, where the horizontal axis represents binding energy and the vertical axis represents strength. A represents the XPS plots of each element; B represents the XPS plot of element C; C represents the XPS plot of element O; D represents the XPS plot of element N; and E represents the XPS plot of element Fe. Figure 7 It can be seen that the C1s spectra at 284.8 eV, 286.31 eV, and 288.50 eV correspond to the CC, COC, and OC=O functional groups, respectively; the O1s spectra at 529.77 eV, 531.32 eV, and 532.45 eV correspond to the Fe-O, -OH, and -CO functional groups, respectively; the N1s spectra at 399.78 eV correspond to the N-(C=O)- functional group; and the Fe2p spectra at 709.95 eV correspond to the Fe2O3 functional group. 2+ 712.72 eV and 723.02 eV correspond to Fe 3+ .

[0091] 3. Structural characterization

[0092] The present invention characterizes the structure of the materials obtained in Examples 1-3 and Comparative Examples 1-2.

[0093] like Figure 8 The diagrams shown depict the structural characterization of the materials obtained in Examples 1-3 and Comparative Examples 1-2 of this invention. A represents the room-temperature magnetization curves of CDs@Fe3O4(0.5) and pure Fe3O4, with the horizontal axis representing the field of influence and the vertical axis representing magnetization. B represents the XRD patterns of CDs@Fe3O4(0.5), CDs@Fe3O4(0.8), CDs@Fe3O4(1.1), and Fe3O4, with the horizontal axis representing 2θ and the vertical axis representing intensity. C represents the FTIR patterns of CDs@Fe3O4(0.5), CDs@Fe3O4(0.8), and CDs@Fe3O4(1.1), with the horizontal axis representing wavenumber and the vertical axis representing emission. D represents the TG pattern of CDs@Fe3O4(0.5), with the horizontal axis representing temperature and the vertical axis representing weight loss. Figure 8 As can be seen from A, the prepared CDs@Fe3O4 composite material has excellent magnetic properties. Figure 8 As can be seen from B, the prepared CDs@Fe3O4 composite material, when combined with Fe3O4 on the (220), (311), (400), (440), and (531) crystal planes, exhibits a broad peak corresponding to carbon points at approximately 20°. Figure 8 As can be seen from the C value, with the increase of FeCl3·6H2O addition, the functional groups on the surface of the composite material remain basically the same and do not change significantly. Figure 8As can be seen from D, the prepared CDs@Fe3O4 composite material is stable below 200℃.

[0094] Experiment Example 3 verifies the relative catalytic activity under different conditions

[0095] In this invention, 3 mL of Na-AC (pH=3.6), 50 μL of LTMB (10 mM), 50 μL of H2O2 (concentration of 30%) and 50 μL of CDs@Fe3O4 (0.5) prepared in Example 1 were mixed, and the relative catalytic activity was tested at different temperatures, pH and time.

[0096] like Figure 9 As shown, the relative catalytic activity diagrams of the material prepared in Example 1 of the present invention under different conditions are presented. A represents the relative catalytic activity diagram at different temperatures, with temperature on the horizontal axis and relative activity on the vertical axis; B represents the relative catalytic activity diagram at different pH values, with pH on the horizontal axis and relative activity on the vertical axis; C represents the relative catalytic activity diagram at different times, with time on the horizontal axis and relative activity on the vertical axis. Figure 9 It can be seen that the material in Example 1 exhibits the best catalytic activity at 45°C, pH=3.6, and a culture time of 10 min.

[0097] Experimental Example 4 Steady-state Dynamics

[0098] 1. Steady-state dynamics

[0099] In this invention, 3 mL of Na-AC (pH=3.6), 50 μL of LTMB (10 mM), 50 μL of H2O2 (concentration of 30%) and 50 μL of CDs@Fe3O4 (0.5) prepared in Example 1 were mixed and kept at 45 °C for 10 min to achieve steady-state kinetics.

[0100] like Figure 11 As shown, the steady-state kinetic diagram (I) of the material obtained in Example 1 of this invention is presented. The concentration of TMB was fixed at 10 mM, while the concentration of H2O2 was varied. A is the Michaelis-Menten curve; B is a double-reciprocal Lineweaver-Burk plot. Figure 11 It can be seen that the catalytic reaction rate increases continuously with the increase of H2O2 concentration, and the reaction rate gradually saturates after a certain concentration. Calculations show that Km = 2.53 and Vm = 4.77 x 10⁻⁶. -8 .

[0101] like Figure 12 As shown, the steady-state kinetic diagram (II) of the material obtained in Example 1 of this invention is presented. With a fixed H₂O₂ concentration of 30%, the TMB concentration was varied. A is the Michaelis-Menten curve; B is the double reciprocal Lineweaver-Burk plot. Figure 12It can be seen that the catalytic reaction rate increases continuously with the increase of TMB concentration, and the reaction rate gradually saturates after a certain concentration, Km = 5.011, Vmax = 4.356 x 10⁻⁶. -8 .

[0102] Experimental Example 5: Protective Layer for Metal Parts

[0103] The material obtained in Example 1 of this invention was used as a protective layer for metal parts to monitor the degree and depth of damage. Specifically, epoxy resin and curing agent were mixed at a weight ratio of 5:4. Hybrid nanoparticles CDs@Fe3O4(0.5) obtained in Example 1 were added to the mixture at different weight percentages. The thoroughly mixed suspension was then coated onto a steel plate using a micrometer-controlled scraper and cured at 50°C for 2 hours.

[0104] like Figure 14 As shown, SEM images of scratches of different depths were generated in an epoxy coating containing 5% CDs@Fe3O4(0.5) in Example 1 of the present invention, where A is a scratch depth of 18.6 μm; B is a scratch depth of 258.0 μm; and C is a scratch depth of 303.2 μm.

[0105] like Figure 15 As shown, Example 1 of the present invention presents magnified micrographs and color intensity diagrams of scratches of different depths generated in an epoxy coating containing 5% CDs@Fe3O4 (0.5). A represents deep scratches; B represents shallow scratches; and C represents the color intensity of the scratches. The horizontal axis, from left to right, represents the uncorroded coating, shallow scratches, 8-HQ treatment, and deep scratches, while the vertical axis represents color intensity. Figure 15 As can be seen from B, the shallow scratches exhibit a noticeable color change, indicating coating damage. Subsequently, upon introduction of 8-HQ, the TMB system's hue changed from blue to colorless. Without any scratch propagation, the signal remained inactive. However, by Figure 15 As shown in A, as the scratches deepen, the steel plate is exposed to the surrounding environment, and corrosion occurs due to the acidity of the TMB system. Therefore, the released Fe... 3+ This caused TMB's color to change from colorless to blue again. Figure 15 As can be seen from C, the presence of more CDs@Fe3O4(0.5) and Fe in the scratch indicates that... 3+ This results in the color intensity of the deep scratches on the exposed steel plate being higher than that of the shallow scratches.

[0106] like Figure 16As shown, in Embodiment 1 of the present invention, magnified microscope images and color RGB diagrams of scratches on epoxy coatings on corroded steel sheets are presented, where A is a magnified microscope image of the corroded sheet / deep scratches; B is a color RGB diagram of scratches on uncorroded and corroded sheets. Figure 16 As shown in A, compared to the uncorroded steel plate, its brightness is significantly darker. From... Figure 16 As shown in B, the RGB color matching diagram of scratches on the uncorroded and corroded boards shows that the blue intensity of the corroded board is significantly higher than that of the uncorroded board.

[0107] like Figure 17 As shown, this is a schematic diagram illustrating the monitoring of coating damage and potential metal corrosion via a smartphone in Embodiment 1 of the present invention. Figure 17 As can be seen, RGB colors are analyzed from digital images of the protective coating using a Python program. To eliminate the influence of observation time, photos should be taken at equal intervals, which can accurately estimate the color intensity at fixed times using a smartphone's built-in black box program. After calculating the color difference between the color swatch and the standard color chart, the degree of coating damage and potential underlying metal corrosion can be provided.

[0108] like Figure 18 As shown in the diagram, Embodiment 1 of the present invention is used for monitoring the degree of damage to the protective layer of metal parts, where A is a monitoring process diagram; B is a schematic diagram of the material surface. Figure 18 It is known that, firstly, CDs@Fe3O4(0.5) nanozymes are encapsulated within a polymer protective shell on a steel plate. When the coating is mechanically damaged, the exposed CDs@Fe3O4(0.5) nanozymes readily react with H2O2 to generate ·OH, resulting in the oxidation of TMB (colorless form) to oxTMB (colored form). In this way, an automatic display is made based on the color change of TMB. Furthermore, a secondary reaction defined between the color indicator system and 8-HQ can be introduced into the surrounding medium, reversibly deactivating the colored oxTMB to colorless TMB. This indicates that the CDs@Fe3O4(0.5) nanozymes can not only activate the signal and report the appearance of damage, but also deactivate the signal if the damage is not progressing or is healing. However, if the coating damage worsens, the TMB indicator system again displays a color change associated with metal corrosion at the damage point. The observable color shift of the TMB can accurately indicate coating damage and provide early warning of potential under-corrosion.

[0109] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. The application of peroxidase-like CDs@Fe3O4 nanoparticles in detecting the depth of damage to the protective layer of metal parts, characterized in that, These peroxidase CDs@Fe3O4 nanoparticles were prepared by the following method: (1) A nitrogen-doped carbon dot solution was prepared by reacting a carbon source and a nitrogen source using a hydrothermal method. (2) The iron source was added to the nitrogen-doped carbon dot solution and stirred. After reaction at 150~300℃, the peroxidase-like CDs@Fe3O4 nanoparticles were obtained by separation, washing and drying.

2. The application according to claim 1, characterized in that, In step (1), the carbon source is any one or more of glucose, citric acid, sodium alginate, cellulose, chitosan, dextran and lignin, and the nitrogen source is any one or more of ethylenediamine, ammonia, aniline and L-arginine.

3. The application according to claim 1, characterized in that, In step (1), the mass of the carbon source is 10% to 90% of the mass of the nitrogen source.

4. The application according to claim 1, characterized in that, In step (1), the hydrothermal reaction temperature is 150~250℃ and the hydrothermal reaction time is 6~24h.

5. The application according to claim 1, characterized in that, In step (2), the iron source is any one or more of ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, iron(II,III) oxide, ferric bromide and ferric carbonate.

6. The application according to claim 1, characterized in that, In step (2), the mass of carbon dots in the nitrogen-doped carbon dot solution is 0 to 100% of the mass of the iron source, and is not 0; the reaction time at 150 to 300°C is 6 to 24 hours.

7. The application according to claim 1, characterized in that, The application utilizes the peroxidase-like CDs@Fe3O4 nanoparticles to induce color change in the chromogenic substrate, and Fe... 3+ The linear response of the colorimetric substrate was used to detect the depth of damage to the protective layer of the metal parts.

8. The application according to claim 7, characterized in that, The chromogenic substrate is tetramethylbenzidine, anthocyanin, or a peroxidase fluorescent probe; the protective layer of the metal component includes a basement membrane and optionally the following (a) and / or (b): (a) A coating on at least one side surface of the basement membrane; (b) Text and / or patterns on the surface of the material; The peroxidase-like CDs@Fe3O4 nanoparticles are added at least to the base film, coating, text, and / or pattern.

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