Preparation method of carbon quantum dot corrosion inhibitor, prepared carbon quantum dot corrosion inhibitor and application

Abstract

The invention relates to the field of corrosion inhibitors, and discloses a preparation method of a carbon quantum dot corrosion inhibitor, the prepared carbon quantum dot corrosion inhibitor and application of the carbon quantum dot corrosion inhibitor. The preparation method comprises the steps that water serves as a solvent, a carbon source and a nitrogen and sulfur source containing a nitrogen element and a sulfur element are subjected to a hydrothermal reaction and then filtered, obtained filtrate is dialyzed, and the carbon quantum dot corrosion inhibitor is obtained. The carbon source comprises waste degradable plastic, the nitrogen-sulfur source comprises thioacetamide, the carbon quantum dot corrosion inhibitor prepared by the invention has hydrophilic groups and heteroatoms such as N and S groups, the heteroatom groups can form a stable chemical adsorption layer with the metal surface, the hydrophilic groups significantly enhance the hydrophilicity of the carbon quantum dots, and the metal surface has good corrosion resistance. Due to the synergistic effect, the prepared corrosion inhibitor has an excellent inhibition effect on hydrogen evolution corrosion of magnesium alloy in a neutral medium.

Description

Technical Field

[0001] The present invention relates to the field of corrosion inhibitors, and in particular to a method for preparing a carbon quantum dot corrosion inhibitor, the prepared carbon quantum dot corrosion inhibitor and applications thereof. Background Art

[0002] Due to its own advantages, magnesium alloys are widely used in the automotive industry, electronic communications, medical equipment, aerospace and other fields. However, due to the extremely high chemical activity of magnesium, its standard electrode potential is -2.37V, making it difficult for it to spontaneously form a stable passivation film on the interface. In addition, the potential difference (PD) between the magnesium matrix and other phases will further aggravate the problem of local corrosion, which to a certain extent limits the further development and wider application of magnesium alloys. In recent years, researchers have conducted a lot of research on the corrosion protection of pure magnesium and magnesium alloys, and developed some anti-corrosion technologies and materials, among which corrosion inhibitors are a simple and effective method.

[0003] Existing corrosion inhibitors include organic and inorganic types. Inorganic corrosion inhibitors are mainly composed of phosphates, silicates and molybdates, which can react with Mg produced during the corrosion process. 2+ Forming stable insoluble substances to protect the alloy matrix. Organic corrosion inhibitors mainly include organic amines, organic acids, Schiff bases, ionic liquids, and surfactants. They rely on heteroatoms such as N, S, and O or polar groups in their molecular structures to adsorb at the alloy / solution interface.

[0004] Although traditional corrosion inhibitors can provide certain protection for magnesium alloys, they generally have problems such as large dosage, high cost, poor water solubility and environmental pollution. Summary of the Invention

[0005] The present invention aims to overcome the environmental pollution problems associated with existing technologies and to provide a method for preparing a carbon quantum dot corrosion inhibitor, as well as the resulting carbon quantum dot corrosion inhibitor and its application. The preparation method provided by the present invention is simple, utilizes a wide range of raw materials, and meets environmental protection requirements. The resulting carbon quantum dot corrosion inhibitor has abundant functional groups containing N and S elements and exhibits excellent corrosion inhibition performance.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for preparing a carbon quantum dot corrosion inhibitor, wherein the preparation method comprises: using water as a solvent, hydrothermally reacting a carbon source and a nitrogen-sulfur source containing nitrogen and sulfur elements, then filtering, and dialyzing the obtained filtrate to obtain a carbon quantum dot corrosion inhibitor;

[0007] Wherein, the carbon source includes discarded degradable plastics, and the nitrogen and sulfur sources include thioacetamide.

[0008] Degradable plastics include bio-based degradable plastics (such as polylactic acid, polycaprolactone, polyhydroxyalkanoates, starch-based plastics, etc.), petroleum-based degradable plastics (such as polybutylene adipate terephthalate, polybutylene succinate, etc.), and other types of degradable plastics (such as polyvinyl alcohol, polypropylene carbonate, etc.). They have rich carbon sources. In the present invention, waste degradable plastics are used as precursors, and thioacetamide is used as the source of N and S for doping. Through a green and simple hydrothermal synthesis method, a carbon quantum dot corrosion inhibitor (denoted as N / S-CDs) is synthesized.

[0009] The raw materials of the present invention have a wide source, low cost, and meet the requirements of green environmental protection. The preparation method is simple and suitable for popularization and application. The prepared N / S-CDs have excellent anti-corrosion performance for magnesium alloys. This not only realizes the resource utilization of waste, but also provides a new direction for the search and design of magnesium alloy corrosion inhibitors.

[0010] The second aspect of the present invention provides a carbon quantum dot corrosion inhibitor prepared by the preparation method described in the first aspect of the present invention.

[0011] The third aspect of the present invention provides an application of the carbon quantum dot corrosion inhibitor prepared by the preparation method described in the first aspect of the present invention or the carbon quantum dot corrosion inhibitor described in the second aspect of the present invention in the anti-corrosion of magnesium alloys.

[0012] Magnesium alloys contain rich magnesium elements. Different from transition metals, the 2p orbitals of magnesium are completely occupied, with high stability. It is difficult to provide electrons for organic molecules to promote back bonding, and it can only accept lone pair electrons of molecules through higher energy level orbitals to form coordination covalent bonds. This requires corrosion inhibitor molecules to have high electron-donating ability to improve their corrosion inhibition performance, which makes it difficult for traditional corrosion inhibitors to meet the requirements of the anti-corrosion and slow-release ability of magnesium alloys.

[0013] The carbon quantum dot corrosion inhibitor prepared in the present invention has hydrophilic groups and heteroatoms such as N and S groups. Among them, the heteroatom groups can form a stable chemical adsorption layer on the metal surface, and the hydrophilic groups significantly enhance the hydrophilicity of the carbon quantum dots. This synergistic effect makes the prepared corrosion inhibitor show excellent inhibitory effect on the hydrogen evolution corrosion of magnesium alloys in neutral media.

[0014] The present invention synthesizes a carbon quantum dot corrosion inhibitor through a green and simple hydrothermal synthesis method. The raw materials have a wide source, low cost, and meet the requirements of green environmental protection. The preparation method is simple and suitable for popularization and application. The prepared N / S-CDs have excellent anti-corrosion performance for magnesium alloys. This not only realizes the resource utilization of waste, but also provides a new direction for the search and design of magnesium alloy corrosion inhibitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a process schematic diagram for preparing N / S-CDs;

[0016] Figure 2 They are the TEM, HRTEM, FTIR, and UV-Vis diagrams for the preparation of N / S-CDs;

[0017] Figure 3 They are the Tafel curves of magnesium alloy electrodes in 3.5 wt.% NaCl solutions containing different concentrations of N / S-CDs;

[0018] Figure 4 It is the equivalent circuit diagram for EIS analysis;

[0019] Figure 5 They are the SEM diagrams of magnesium alloy after immersion tests;

[0020] Figure 6 They are the AFM diagrams of magnesium alloy after immersion tests;

[0021] Figure 7 They are the XPS diagrams of magnesium alloy after immersion tests;

[0022] Figure 8 It is the corrosion inhibition mechanism diagram of magnesium alloy in 3.5 wt.% NaCl solutions with and without N / S-CDs. Specific Embodiments

[0023] The following further elaborates on the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0024] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without conflict, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0025] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0026] In addition, the term "and / or" in the specification and claims is used to describe the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0027] In the first aspect of the present invention, a preparation method of a carbon quantum dot corrosion inhibitor is provided. The preparation method includes: using water as a solvent, subjecting a carbon source and a nitrogen-sulfur source containing nitrogen and sulfur elements to a hydrothermal reaction, then filtering, and dialyzing the obtained filtrate to obtain a carbon quantum dot corrosion inhibitor.

[0028] Among them, the carbon source includes waste degradable plastics, and the nitrogen-sulfur source includes thioacetamide.

[0029] The nitrogen-sulfur source refers to a compound containing both nitrogen and sulfur elements.

[0030] Using waste degradable plastics can significantly reduce the reaction conditions. For example, carbonization can be carried out by the hydrothermal method, while non-degradable plastics cannot be carbonized by the hydrothermal method.

[0031] Preferably, the preparation method further includes pretreatment. After cutting the waste degradable plastics into small pieces with a length and width of 0.5 - 1 cm independently, the hydrothermal reaction is carried out.

[0032] Preferably, the mass ratio of the waste degradable plastics to the thioacetamide is 1:1 - 2. The mass ratio of the waste degradable plastics to the thioacetamide is related to the amount of doped N and S, and thus affects the slow-release performance of the prepared corrosion inhibitor. The mass ratio between the two can be any value between any two of 1:1, 1:1.5, and 1:2.

[0033] The present invention uses waste degradable plastics as raw materials, utilizing the oxygen-containing functional groups (such as ester groups and hydroxyl groups) rich in the molecular chains of waste degradable plastics. These functional groups are prone to breakage under hydrothermal or pyrolysis conditions, promoting the formation of small-molecule carbon structures, thereby significantly reducing the difficulty of the carbonization reaction (mainly reducing the reaction time required) and simplifying the preparation process.

[0034] Preferably, the temperature of the hydrothermal reaction is 150 - 250 °C, and the time is 4 - 6 h. The temperature of the hydrothermal reaction can be any value between any two of 150 °C, 180 °C, 200 °C, 230 °C, and 250 °C, and the time can be any value between any two of 4 h, 5 h, and 6 h.

[0035] Preferably, the mass-volume ratio of the nitrogen-sulfur source to the solvent is 1:20 - 40. The mass-volume ratio of the nitrogen-sulfur source to the solvent can be any value between any two of 1:20, 1:30, and 1:40.

[0036] Preferably, the filtration step includes: first performing rough filtration with filter paper, and then performing secondary filtration with a 0.2 - 0.25 μm filter. First, through rough filtration, large particle impurities are removed, and then through secondary filtration, small particle impurities are removed.

[0037] Preferably, the molecular cut-off of the dialysis is 500 - 1500 Da, and the dialysis time is 20 - 25 h. Through dialysis, substances with the target molecular weight can be retained to obtain the required corrosion inhibitor.

[0038] The second aspect of the present invention provides a carbon quantum dot corrosion inhibitor prepared by the preparation method described in the first aspect of the present invention.

[0039] Preferably, the carbon quantum dot corrosion inhibitor has a carbonized graphite core, and the core is connected with functional groups, and the functional groups include functional groups containing N element and functional groups containing S element.

[0040] The third aspect of the present invention provides an application of the carbon quantum dot corrosion inhibitor prepared by the preparation method described in the first aspect of the present invention or the carbon quantum dot corrosion inhibitor described in the second aspect of the present invention in the anti-corrosion of magnesium alloys.

[0041] Preferably, the anti-corrosion includes anti-corrosion by salt solution.

[0042] Preferably, the salt solution is a sodium chloride solution.

[0043] Preferably, based on the total amount of the salt solution, the concentration of the salt solution is 3 - 4 wt.%.

[0044] The carbon quantum dot corrosion inhibitor prepared by the present invention has stable adsorption performance, and its stable adsorption time in 3.5 wt.% NaCl solution is up to 5 h.

[0045] In the following examples and comparative examples, unless otherwise specified, for reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase. For those not indicating specific conditions in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer.

[0046] TEM (FEI Tecnai G2 F20) was used to observe the microscopic size and morphology of N / S-CDs.

[0047] HTEM (FEI Tecnai G2 F20) was used to observe the microscopic size and morphology of N / S-CDs.

[0048] The composition of N / S-CDs was analyzed by FTIR (Colet-iS50).

[0049] The absorbance of N / S-CDs was characterized by UV-vis (TU-1810).

[0050] The surface morphology of the alloy (0.5×0.5×0.5 cm 3 ) was observed by SEM (TM-1000).

[0051] The surface roughness of the alloy (1×1×0.1 cm 3 ) was measured by AFM (MFP-3D-BIO).

[0052] The alloy elements and bonding information were characterized by XPS (Thermo Scientific K-Al Alpha).

[0053] The corrosion inhibition effect of N / S-CDs on AZ31 magnesium alloy in 3.5 wt.% NaCl solution was studied using a CHI760E electrochemical workstation.

[0054] I. Preparation of the carbon quantum dot corrosion inhibitor, denoted as N / S-CDs

[0055] The schematic diagram of the preparation process of N / S-CDs is as Figure 1 shown.

[0056] The discarded degradable plastic bags were washed and dried, and then cut into small pieces (with a length and width of about 0.75±0.25 cm) with scissors to obtain plastic fragments for standby.

[0057] Weighed 2.0 g of thioacetamide and 2.0 g of plastic fragments with an analytical balance. First, dissolved 2.0 g of thioacetamide in 60 mL of ultrapure water, and ultrasonicated for 10 min to fully dissolve thioacetamide. Then added 2.0 g of plastic fragments, stirred with a glass rod to submerge the plastic fragments in the aqueous solution of thioacetamide, and finally transferred them to a 100 mL polytetrafluoroethylene reaction kettle. The sealed reaction kettle was transferred to a muffle furnace and kept at 200 °C for 5 h.

[0058] After heating, after natural cooling, all the liquid was transferred to a beaker, large particles were filtered out with a funnel, and the obtained crude filtrate was further filtered through a 0.22 μm needle filter. The filtrate was dialyzed with a dialysis bag with a molecular cut-off of 1000 Da for 24 h, and the water was changed every 4 h.

[0059] After dialysis, all the liquid in the dialysis bag was transferred to a 100 mL small beaker and refrigerated for one day. Finally, the refrigerated liquid was dried in a freeze dryer to remove moisture, and a yellow solid powder (N / S-CDs) was obtained.

[0060] II. Performance testing

[0061] Blank solution: Prepare a 3.5 wt.% NaCl solution.

[0062] Test solution: Prepare a series of 3.5 wt.% NaCl solutions, and successively add the required N / S-CDs at concentrations of 25, 50, 100, and 200 mg / L of N / S-CDs to form a series of test solutions.

[0063] Test sample: The magnesium alloy sample is a commercial AZ31 magnesium alloy, purchased from Dongguan Qiangsheng Metal Materials Co., Ltd.

[0064] 1. Electrochemical performance test method

[0065] Use the AZ31 magnesium alloy as the working electrode (the exposed area is delimited by an O-ring to be 1 cm 2 ), a saturated calomel electrode (SCE) as the reference electrode, and a platinum mesh as the auxiliary electrode to form a three-electrode system. The working electrode is polished successively with 400, 800, 1200, and 2000 grit SiC sandpaper until smooth and refined, then rinsed with ultrapure water, ethanol, and acetone, and dried with cold air.

[0066] Pour the corresponding test solution or blank solution into the flat corrosion test cell after encapsulating the pretreated working electrode, and conduct electrochemical tests at (25 °C ± 2 °C).

[0067] The electrochemical impedance spectroscopy (EIS) is measured at the open circuit potential. The test time for the open circuit potential (OCP) is 1000 s, the peak value of the AC excitation signal is 5 mV, and the frequency range is 10 5 ~10 -1 Hz.

[0068] The scanning rate of the polarization curve is 1 mV / s, and the scanning range is -0.5 V to +0.5 mV (relative to the open circuit potential).

[0069] Use Zsimpwin to fit and analyze the EIS curve to obtain the equivalent circuit diagram and related electrochemical parameters. All electrochemical tests are repeated at least three times to ensure repeatability. The corrosion inhibition efficiency of N / S-CDs can be calculated by formulas (1) and (2):

[0070]

[0071] Where: R0 and R ct are the charge transfer resistances corresponding to the blank solution and the test solution in the equivalent circuit diagram, respectively; and I corr are the corrosion current densities corresponding to the blank solution and the test solution, respectively.

[0072] 2. Surface corrosion analysis method

[0073] The AZ31 magnesium alloy samples were polished with SiC sandpapers of 400, 800, 1200, 2000, 3000, 5000, and 7000 successively by water grinding until smooth without fine scratches, and then cut into the required number of pieces (including two specifications, 0.5×0.5×0.5 cm 3 and 1×1×0.1 cm 3 ). Before use, they were ultrasonically cleaned with absolute ethanol for 30 min and then dried with cold air.

[0074] The pre-treated magnesium alloy was immersed in the blank solution or the test solution at 25°C. The morphology of the alloy (size 0.5×0.5×0.5 cm 3 ) surface was observed by scanning electron microscopy (SEM, TM-1000). The surface roughness of the alloy (size 1×1×0.1 cm 3 ) was measured by atomic force microscopy (MFP-3D-BIO). The elemental and bonding information was characterized by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Al Alpha).

[0075] 3. Test Results

[0076] (1) Characterization of the prepared N / S-CDs

[0077] The prepared N / S-CDs were observed by TEM, and further observed by high-resolution TEM, namely HRTEM. Then, FTIR and UV-vis scans were performed respectively, and the results are as Figure 2 shown. Figure 2 (a) is the TEM image, Figure 2 (b) is the HRTEM image, Figure 2 (c) is the FTIR image, Figure 2 (d) is the UV-vis image.

[0078] From Figure 2 (a), it can be seen that N / S-CDs have some polymer-like structures. It may be the influence of doping elements that leads to the polymerization and cross-linking of carbon quantum dots, forming a polymer-like network structure. From Figure 2 (b), it can be seen that the prepared N / S-CDs have obvious lattice fringes with a large area and the interplanar spacing is 0.21 nm, which can be attributed to the (100) crystal plane of graphite and has a graphite-like layered structure.

[0079] From Figure 2 (c), it can be seen that N / S-CDs have multiple absorption peaks. The broad peak at 3208 cm –1 corresponds to the stretching vibration of N-H or O-H; the peak at 2935 cm -1The absorption peak at [[]] corresponds to the stretching vibration of saturated C-H; the absorption peak at 1666 cm -1 corresponds to the stretching vibration of C=O, and the absorption peak at 1542 cm -1 may be the bending vibration of N-H or the stretching vibration of C=C; the absorption peaks at 1389 cm -1 , 1328 cm -1 may be the vibrations of C-N and C=N bonds; the absorption peak at 1084 cm -1 may be the absorption peak of C-O-C or C-OH bonds; the absorption peak at 1049 cm -1 may be the absorption peak of C-SO3; the absorption peak at 869 cm -1 corresponds to the bending vibration of aromatic compound C-H, and the absorption peak at 509 cm -1 may be the in-plane bending vibration of C-C=O.

[0080] From Figure 2 (d), it can be seen that there are two characteristic absorption peaks at 240 nm and 270 nm, corresponding to the π-π* transition of conjugated C=C bonds and the n-π* transition of C=O / C=N bonds, respectively.

[0081] In summary, N / S-CDs are composed of surface functional groups containing elements such as N and S and a carbonized graphite core.

[0082] (2) Analysis of polarization curve test data

[0083] The Tafel curves of AZ31 magnesium alloy electrodes in a series of 3.5 wt.% NaCl test solutions containing different concentrations of N / S-CDs and in a blank solution are as Figure 3 shown. In the figure, the anodic polarization curve represents the anodic oxidation of the magnesium alloy, while the cathodic curve represents the hydrogen evolution reaction by cathodic reduction of water.

[0084] As can be seen from the figure, there are no obvious inflection points and plateaus on the anodic polarization curve of the blank solution (Blank), while after adding the N / S-CDs inhibitor, an inflection point appears on the anodic polarization curve and there is a passivation plateau. The potential corresponding to the inflection point is the pitting potential, and the appearance of the passivation plateau indicates that N / S-CDs will form a protective film on the alloy surface to protect the magnesium alloy from corrosion. As the concentration of N / S-CDs increases, the passivation plateau increases significantly, probably because during the reaction, the density of the protective film formed on the anodic surface increases, slowing down the continuous corrosion of the magnesium anode. The cathodic polarization curves are similar in shape before and after adding N / S-CDs, meaning that the cathodic hydrogen evolution reaction process is similar, indicating that N / S-CDs may be an anodic inhibitor type that forms a protective film on the metal anode surface to prevent the continuous dissolution of the metal anode. Therefore, the N / S-CDs prepared in this invention is an anodic inhibitor.

[0085] By extrapolating the cathodic branch of the polarization curve to the corrosion potential E corr and the corrosion current density I corr , and further calculating the slow-release efficiency η according to formula (2), the results are shown in Table 1. In the 3.5 wt.% NaCl solution without N / S-CDs, I corr has a relatively large value of (46.3 μA / cm 2 ). After adding N / S-CDs, the value of I corr gradually decreases with the increase of the inhibitor concentration, and the minimum reaches (7.8 μA / cm 2 ), indicating that at high concentrations, a large amount of N / S-CDs adsorb on the surface of the magnesium alloy to form a dense adsorption film, thus inhibiting the corrosion of the magnesium alloy. When the concentration of N / S-CDs is 200 mg / L, the corrosion inhibition efficiency η value is 83.2%, indicating that the addition of N / S-CDs improves the corrosion resistance of AZ31 magnesium alloy in the open-circuit potential state.

[0086] Table 1 Tafel curve parameters

[0087]

[0088] (3) Analysis of EIS test data

[0089] The equivalent circuit diagram of EIS is as Figure 4 shown, and the obtained electrochemical parameters are shown in Table 2.

[0090] In Table 2, R s is the solution resistance, R ct is the charge transfer resistance, which are obtained by fitting. The middle frequency band is 100 - 1 Hz, and the low frequency band is 1 - 0.1 Hz; CPE is the constant phase element and C dl is the double-layer capacitance, which are obtained by calculation. The calculation formulas are as follows:

[0091]

[0092] C dl = Y0(ω max ) n-1

[0093] Among them, Z CPE is the impedance modulus value, Y0 is the CPE value, ω is the angular frequency, j is the imaginary unit, and the combination of jω characterizes the frequency-dependent phase behavior. n is a dimensionless exponent (0 ≤ n ≤ 1), which quantifies the non-ideality.

[0094] Table 2 EIS fitting data

[0095]

[0096] It can be seen from Table 2 that with the increase in the concentration of N / S-CDs, the inhibition efficiency IE also gradually increases.

[0097] (4) SEM characterization of AZ31 magnesium alloy after immersion test

[0098] At 298 K, the AZ31 magnesium alloy was immersed in 3.5 wt.% NaCl solution without and with 200 mg / L N / S-CDs. The SEM images after 20 h are as Figure 5 shown, where Figure 5 (a) is the SEM image of the AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution for 20 h, Figure 5 (b) is the SEM image of the AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution containing 200 mg / L N / S-CDs for 20 h.

[0099] It can be seen from the figure that after immersion in 3.5 wt.% NaCl solution without N / S-CDs, the surface of the magnesium alloy was severely corroded, with many wide and deep cracks, as well as a large number of pits and corrosion products. After adding N / S-CDs, the morphology of the magnesium alloy was relatively flat, and the grinding marks were still visible, and only slight granular corrosion was observed on the surface.

[0100] The results show that N / S-CDs can effectively prevent the corrosion of AZ31 magnesium alloy by NaCl solution.

[0101] (5) AFM characterization of AZ31 magnesium alloy after immersion test

[0102] At 298 K, the AFM images of the AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution without and with 200 mg / L N / S-CDs for 1 h were taken, and the contour maps were fitted according to the AFM images. The results are as Figure 6 shown, Figure 6 (a) From left to right are the AFM image, the diagonal image of the AFM, and the contour map of the AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution for 1 h, Figure 6 (b) From left to right are the AFM image, the diagonal image of the AFM, and the contour map of the AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution containing 200 mg / L N / S-CDs for 20 h.

[0103] As can be seen from the figure, in the 3.5 wt.% NaCl solution without the addition of N / S-CDs, the surface of the magnesium alloy sample was corroded into a shape similar to undulating mountains, with a drop of more than 400 nm between the peaks and valleys, and the average roughness of the entire magnesium alloy surface reached 115.2 nm. In the 3.5 wt.% NaCl solution with the addition of N / S-CDs, the surface of the magnesium alloy sample was relatively flat, with an average roughness of about 35.2 nm.

[0104] This experiment further demonstrates that N / S-CDs can effectively inhibit the corrosion of magnesium alloys in 3.5 wt.% NaCl solution.

[0105] (6) XPS analysis of AZ31 magnesium alloy after immersion test

[0106] At 298 K, the XPS spectra of AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution without and with 200 mg / L N / S-CDs for 24 h are shown as Figure 7 follows. Figures (b1-f1) are the curves of AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution without N / S-CDs, and figures (b2-f2) are the curves of AZ31 magnesium alloy immersed in 3.5 wt.% NaCl solution with the addition of 200 mg / L N / S-CDs.

[0107] Figure 7 (a) is the full-spectrum diagram. As can be seen from the figure, different from the surface composition of the magnesium alloy after immersion in the blank solution, the presence of a small amount of N and S elements after immersion in the experimental solution indicates the presence of carbon quantum dots on the alloy surface.

[0108] Figure 7 (b1) and 7(b2) are the XPS spectra of Mg 2p without and with the addition of N / S-CDs respectively. As can be seen from the figure, when immersed in 3.5 wt.% NaCl solution containing N / S-CDs, a much smaller shift of Mg 2p was observed, and weak metallic Mg was detected at 46.1 eV, which means that N / S-CDs formed a protective layer on the surface of the magnesium alloy.

[0109] Figure 7 (c1) and 7(c2) are the XPS spectra of C1s without and with the addition of N / S-CDs respectively. As can be seen from the figure, in Figure 7 (c2), the C-N peak is located at 284.6 eV, probably due to the presence of N / S-CDs.

[0110] Figure 7(d1) and 7(d2) are the O1s spectra of the magnesium alloy without and with N / S-CDs addition, respectively. It can be seen from the figure that compared with the magnesium alloy in 3.5 wt.% NaCl solution without N / S-CDs addition, the CDs-containing Figure 7 In the spectrum of (d2), in addition to the MgO peak at 531.2 eV, the Mg(OH)2 and O=C / C-O peaks at 531.9 ± 1 eV, an XPS peak of S=O also appears at 536 eV.

[0111] Figure 7 (e1) and 7(e2) are the XPS spectra of S2p of the magnesium alloy without and with N / S-CDs immersion, respectively. It can be seen from the figure that in the case of adding N / S-CDs Figure 7 The two peaks at 163.6 eV and 168.3 eV in (e2) are due to the presence of C-S / C-S(O) x -C and C=S.

[0112] Figure 7 (f1) and 7(f2) are the XPS spectra of N1s of the magnesium alloy without and with N / S-CDs immersion, respectively. It can be seen from the figure that in the case of adding N / S-CDs Figure 7 There are two weak peaks at 401.9 eV and 398.2 eV in (f2), indicating the presence of a small amount of C=NH and N-H bonds. An XPS peak of C-N / N-Mg appears at 399.9 ± 0.1 eV, indicating that N / S-CDs may be adsorbed on the surface of the magnesium alloy by forming a new skeleton, such as the presence of N-Mg bonds.

[0113] This application finds that the corrosion inhibition mechanism of N / S-CDs is as Figure 8 shown. Figure 8 As shown in (a), in the NaCl solution without N / S-CDs, a large amount of MgO and Mg(OH)2 are deposited on the surface of the magnesium alloy during corrosion, and they act as a film layer to protect the matrix. However, the film layer is unevenly distributed and prone to cracking, so it cannot provide effective protection. In the NaCl solution containing N / S-CDs, due to the doping of nitrogen and sulfur elements, N / S-CDs have rich active sites and improved electronic structures, enabling them to interact with the metal surface or oxide layer through electrostatic attraction (physical adsorption) and covalent bonding (chemical adsorption) as Figure 8 shown in (b), thereby protecting the metal from corrosion.

[0114] In summary, due to the doping of nitrogen and sulfur elements, N / S-CDs have rich active sites and improved electronic structures, enabling them to interact with the metal surface or oxide layer through electrostatic attraction (physical adsorption) and covalent bonding (chemical adsorption), protecting the metal from corrosion.

Claims

1. A preparation method of a carbon quantum dot corrosion inhibitor, characterized in that, The preparation method includes: using water as a solvent, subjecting a carbon source and a nitrogen-sulfur source containing nitrogen and sulfur elements to a hydrothermal reaction, then filtering, and dialyzing the obtained filtrate to obtain a carbon quantum dot corrosion inhibitor; wherein, the carbon source includes waste degradable plastics, and the nitrogen-sulfur source includes thioacetamide.

2. The preparation method according to claim 1, wherein The mass ratio of the waste degradable plastics to the thioacetamide is 1:1 - 2.

3. The preparation method according to claim 1 or 2, wherein, The temperature of the hydrothermal reaction is 150 - 250 °C, and the time is 4 - 6 h.

4. The preparation method according to claim 3, wherein, The mass-volume ratio of the nitrogen-sulfur source to the solvent is 1:20 - 40.

5. The preparation method according to claim 4, wherein, The filtering step includes: first performing rough filtration with filter paper, and then performing secondary filtration with a 0.2 - 0.25 μm filter.

6. The preparation method according to claim 5, wherein, The molecular cut-off for dialysis is 500 - 1500 Da, and the dialysis time is 20 - 25 h.

7. A carbon quantum dot corrosion inhibitor prepared by the preparation method according to any one of claims 1 - 6.

8. The carbon quantum dot corrosion inhibitor according to claim 7, wherein, The carbon quantum dot corrosion inhibitor has a graphitized carbon core, and functional groups are connected to the core, and the functional groups include functional groups containing N elements and functional groups containing S elements.

9. Application of a carbon quantum dot corrosion inhibitor prepared by the preparation method according to any one of claims 1 - 6 or a carbon quantum dot corrosion inhibitor according to any one of claims 7 - 8 in the anti-corrosion of magnesium alloys.

10. The application according to claim 9, wherein, The anti-corrosion includes anti-corrosion against salt solution corrosion. Preferably, based on the total amount of the salt solution, the concentration of the salt solution is 3 - 4 wt.%.

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