N, s co-doped melon seed shell carbon quantum dots-based corrosion inhibitor, preparation method and application thereof

Abstract

This invention provides a corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots, its preparation method, and its application. It relates to the technical field of corrosion inhibitors, specifically the reaction of sunflower seed shells and thiourea to obtain an N,S co-doped sunflower seed shell carbon quantum dot corrosion inhibitor. The inhibitor exhibits a carbon fiber structure, with its outermost layer containing hydrophilic and heteroatom groups. The N,S co-doped sunflower seed shell carbon quantum dot corrosion inhibitor prepared by reacting sunflower seed shells with thiourea exhibits good corrosion inhibition of copper in sulfuric acid. This is mainly because the N,S co-doped sunflower seed shell carbon quantum dot corrosion inhibitor possesses both hydrophilic and heteroatom groups. The heteroatom groups can combine with the metal surface to form a protective layer, thereby achieving corrosion inhibition. The hydrophilic groups enhance the hydrophilicity of the N,S co-doped sunflower seed shell carbon quantum dot corrosion inhibitor. This N,S co-doped carbon quantum dot corrosion inhibitor can effectively inhibit copper corrosion in 0.5M sulfuric acid.

Description

Technical Field

[0001] This invention relates to the field of corrosion inhibitor preparation technology, and more specifically, to corrosion inhibitors based on N,S co-doped sunflower seed shell carbon quantum dots, their preparation methods, and applications. Background Technology

[0002] Copper is one of the earliest unearthed metals and is widely used in various chemical, metallurgical, and electrical industries due to its excellent ductility, electrical conductivity, and thermal conductivity. However, copper is extremely susceptible to corrosion in humid environments. Acid pickling is the most common method for removing oxides from copper surfaces, with sulfuric acid being the most frequently used pickling agent. However, during acid pickling, copper often exhibits over-corrosion. Corrosion inhibitors are commonly used to suppress the corrosion of copper in sulfuric acid. Currently, there are many types of corrosion inhibitors, which can be classified into organic and inorganic inhibitors. However, copper corrosion inhibitors are usually organic compounds containing heteroatoms, and frequent use of these reagents can seriously cause environmental pollution, waste of resources, and poor inhibitory effects.

[0003] Numerous corrosion inhibitors have been reported to date, including imidazole derivatives, quinoline derivatives, and thiophene derivatives. However, the extensive use of these inhibitors would pollute the environment and be prohibitively expensive, failing to achieve the goals of green chemistry. Therefore, in line with the deeper principles of green chemistry, the development of a green and pollution-free corrosion inhibitor is urgently needed.

[0004] Carbon quantum dots have attracted attention from experts in various fields in recent years as corrosion inhibitors to suppress the corrosion behavior of metals in corrosive media. However, the synthesis of carbon quantum dots using traditional carbon sources (such as p-phenylenediamine, citric acid, imidazole and its derivatives) has disadvantages such as high cost, strong carbon source toxicity, and complex operation process. Summary of the Invention

[0005] One objective of this invention is to provide a corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots, which is prepared by reacting sunflower seed shells and thiourea. The main components of sunflower seed shells are cellulose and lignin. The main effective component of the prepared corrosion inhibitor is N,S co-doped sunflower seed shell carbon quantum dots (N,S-CQDs), which have a carbon fiber structure and contain hydrophilic groups and heteroatom groups on the outermost layer. During the bonding process between carbon quantum dots and copper surface, a protective layer with a thickness of 1-2 mm is formed, thereby reducing the contact between copper surface and corrosive medium, reducing reactive sites and thus affecting the diffusion of dissolved oxygen in solution to copper electrode anode. In addition, N,S-CQDs form coordination ions with Cu+ at cathode to prevent Cu+ from converting to Cu2+, thereby achieving the purpose of corrosion inhibition.

[0006] The reaction process is as follows:

[0007] Cathode reaction: 2O₂ + 4H₂ + +4e -→2H2O (1)

[0008] Anode reaction:

[0009]

[0010] Furthermore, the hydrophilic group is an oxygen-containing hydrophilic group such as -COOH or -OH.

[0011] The heteroatomic groups are -NH2 and -SO3.

[0012] The hydrophilic group enables it to dissolve better in water, and the heteroatom group can bind to the metal surface to form a protective layer, thereby preventing metal corrosion. The hydrophilic group and the heteroatom group complement each other and work synergistically.

[0013] One of the objectives of this invention is to provide a method for preparing a corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots, the specific operation of which is as follows:

[0014] After crushing the sunflower seed shells into powder, pass them through a 100-mesh standard sieve. The powder size is approximately 200mm in diameter.

[0015] Thiourea and sunflower seed shell powder were dissolved in a beaker containing pure water to obtain a suspension. During the reaction, thiourea served as both a nitrogen and sulfur source. The main components of sunflower seed shells are cellulose and lignin, and their composition includes C, H, and O elements.

[0016] The suspension was poured into a 100ml polytetrafluoroethylene-lined reactor and heated. The reaction temperature was adjusted to 150-220℃, and the reaction time was 8-12h. The optimal temperature was 200℃ and the reaction time was 10h. After the reaction, the suspension was allowed to cool naturally to obtain a carbon quantum dot mixed suspension. The carbon quantum dot mixed suspension has a carbon fiber structure. The external -COOH and -OH oxygen-containing hydrophilic groups can make it more soluble in water. The -NH2 and -SO3 heteroatom groups can bind to the metal surface to form a protective layer, thereby preventing metal corrosion.

[0017] The resulting carbon quantum impurity mixture suspension was filtered to obtain a carbon quantum dot mixture solution.

[0018] A carbon quantum dot solution was obtained by dialyzing a mixed solution of carbon quantum dots in pure water.

[0019] Carbon quantum dot powder was obtained by freeze-drying the carbon quantum dot solution.

[0020] To better realize the present invention, in the preparation process, the mass ratio of sunflower seed shells and thiourea is 1:1, and the amount of sunflower seed shells and thiourea weighed is further optimized to be 3.0g each, and the amount of pure water used for dissolution is 60ml.

[0021] To better realize the present invention, furthermore, in the process of filtering the obtained carbon quantum dot mixed suspension, it is selected to filter it through a funnel and then filter it with a 0.22μm needle filter.

[0022] To better realize the present invention, further, in dialysis, the dialysis molecule cutoff is 1000 Da, the dialysis time is 24 h, and the pure water is changed every 6 h during the period.

[0023] To better realize the present invention, the drying time is further 3 days during the freeze-drying process.

[0024] The third objective of this invention is to provide an application of a corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots in suppressing copper corrosion.

[0025] The beneficial effects of this invention are:

[0026] This invention discloses a corrosion inhibitor based on N,S co-doped carbon quantum dots from sunflower seed shells, prepared by reacting sunflower seed shells with thiourea. This inhibitor exhibits good corrosion inhibition in the process of copper corrosion in sulfuric acid. This is mainly because the N,S co-doped carbon quantum dot corrosion inhibitor possesses both hydrophilic and heteroatom groups. The heteroatom groups can combine with the metal surface to form a protective layer, thereby achieving corrosion inhibition. The hydrophilic groups enhance the hydrophilicity of the N,S co-doped carbon quantum dot corrosion inhibitor. These components work synergistically and are indispensable. Furthermore, this N,S co-doped carbon quantum dot corrosion inhibitor can effectively inhibit copper corrosion in 0.5M sulfuric acid.

[0027] This invention uses carbon quantum dots prepared from sunflower seed shells as a corrosion inhibitor, which has the advantages of wide material availability, low price and relatively novel composition. In addition, the preparation method of this invention is simple, the operation process is controllable and easy, which is more conducive to industrial preparation. Attached Figure Description

[0028] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 A flowchart illustrating the preparation method of the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots provided by this invention;

[0030] Figure 2 A schematic diagram illustrating the preparation of the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots provided by the present invention;

[0031] Figure 3 (a) and (b) are open circuit potential diagrams and potentiodynamic polarization curves of copper immersed in 0.5M sulfuric acid solution containing different concentrations of corrosion inhibitors, provided in the embodiments of the present invention.

[0032] Figure 4 (a) and (b) are Nyqusit and Bode diagrams of copper immersed in 0.5M sulfuric acid solution containing different concentrations of corrosion inhibitors, provided in the embodiments of the present invention.

[0033] Figure 5 This is an equivalent circuit diagram provided in the embodiments of the present invention for fitting electrochemical impedance spectroscopy data;

[0034] Figure 6 The following are surface morphology images of copper after immersion in a 200 mg / L corrosion inhibitor, provided by embodiments of the present invention: (a) copper is immersed in a 0.5 M sulfuric acid solution; (b) copper is immersed in a 0.5 M sulfuric acid solution containing a corrosion inhibitor.

[0035] Figure 7 The following are 3D morphology images of copper after immersion in a 200 mg / L corrosion inhibitor, provided in the embodiments of the present invention: (a) copper is immersed in a 0.5 M sulfuric acid solution; (b) copper is immersed in a 0.5 M sulfuric acid solution containing a corrosion inhibitor.

[0036] Figure 8 This is the Fourier transform infrared spectrum of N,S co-doped carbon quantum dots on a copper surface provided in an embodiment of the present invention.

[0037] Figure 9 This is a Langmuir adsorption diagram of N,S co-doped carbon quantum dots on a copper surface provided in an embodiment of the present invention.

[0038] Figure 10 This is the suppression mechanism of N,S co-doped carbon quantum dots on the copper surface provided in the embodiments of the present invention. Detailed Implementation

[0039] The technical solutions of the present invention will now be described with reference to the accompanying drawings.

[0040] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0041] Example:

[0042] Sunflower seed shells were completely pulverized in a grinder. 3.0g of sunflower seed shell powder and 3.0g of thiourea were weighed and dissolved in approximately 60ml of pure water. The solution was transferred to a 100ml polytetrafluoroethylene-lined reactor and heated to 200℃ for 10 hours. After natural cooling, the reddish-brown suspension was removed. Large particles were initially removed by funnel filtration, followed by removal of smaller impurities using a 0.22μm needle filter. The resulting solution was transferred to a dialysis bag (retention capacity ~1000Da). The dialysis bag was immersed in pure water for 24 hours to remove unreacted small particles. The pure water was changed every 6 hours. The liquid in the dialysis bag was then transferred to a beaker and placed in a refrigerator for 12 hours. Finally, it was dried in a freeze-drying oven. The resulting brown solid was a corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots, abbreviated as N,S-CQDs.

[0043] Analysis of its ingredients:

[0044] The main components of sunflower seed shells are cellulose and lignin, which are macromolecular polysaccharides. They primarily contain elements such as C, H, and O. Thiourea, as a nitrogen source and sulfur source, contains C, S, and N. After hydrothermal synthesis at 200℃ for 10 hours, the resulting N,S-CQDs exhibit a carbon fiber structure, such as... Figure 2 As shown, the presence of oxygen-containing hydrophilic groups such as -COOH and -OH on the outside enables it to dissolve better in water, while heteroatom groups such as -NH2 and -SO3 can bind to the metal surface to form a protective layer, thereby preventing metal corrosion.

[0045] In the preparation of N,S-CQDs, the heating temperature was 200℃ and the reaction time was 10h. This is because a higher hydrothermal temperature affects the degree of carbonization of sunflower seed shells, which in turn affects the degree of bond breaking between precursors such as cellulose and lignin. Experiments have shown that carbon quantum dots obtained at a hydrothermal temperature of 200℃ have a higher slow-release effect on copper than those obtained at a temperature of 160-180℃. This is because the hydrothermal time affects the size and content of oxygen-containing hydrophilic groups such as -COOH and -OH on the surface of the carbon quantum dots produced from sunflower seed shells. Smaller sizes make it easier for carbon quantum dots to disperse in water, and a reduction in oxygen-containing hydrophilic groups is beneficial. When carbon quantum dots are adsorbed on the substrate surface, fewer oxygen-containing hydrophilic groups on the carbon dot surface reduce the contact sites between the carbon quantum dots and the corrosive medium. This further explains why carbon dots with fewer hydrophilic groups are more hydrophobic than those with more hydrophilic groups, which explains why they are more effective at inhibiting the slow release of copper in corrosive solutions than carbon quantum dots with shorter reaction times.

[0046] The experimental process and results are as follows Figure 10As shown, the addition of carbon quantum dots forms a protective layer on the copper surface, thereby reducing the contact between the copper surface and the corrosive medium, which in turn reduces the reactive sites and further affects the diffusion of dissolved oxygen in the solution to the copper anode. At the same time, N,S-CQDs form coordination ions with Cu+ at the cathode to prevent Cu+ from converting to Cu2+, thus achieving corrosion inhibition.

[0047] Further electrochemical testing was conducted. Pure copper was used as the working electrode. During the electrochemical tests, the copper electrode was sealed with epoxy resin, exposing only one working surface (1 cm). 2 In corrosive media, the workstation used for electrochemical testing was a Chi760E, employing a three-electrode system: copper as the working electrode, platinum as the counter electrode, and a saturated calomel electrode as the reference electrode. Before electrochemical testing, the copper electrode was sequentially polished with 400, 800, 1200, and 2000 grit sandpaper until the entire electrode surface was smooth. The copper electrode was then ultrasonically treated with pure water and anhydrous ethanol, and subsequently dried in cold air. The first step was an open-circuit potential test, lasting 2400 seconds to allow the copper surface to reach a stable state. Following this, electrochemical impedance spectroscopy was performed, with a frequency range of 10... 5 Hz to 10 -2 The excitation signal was a sine wave of 0.01V. Finally, potentiodynamic polarization curves were measured, with the test interval being Eocp±0.25V and a scan rate of 0.001V / s. N,S co-doped sunflower seed shell carbon quantum dots were prepared at concentration gradients of 10 mg / L, 25 mg / L, 50 mg / L, 100 mg / L, and 200 mg / L. A 0.5M sulfuric acid solution was used as a blank control. Each experiment was performed three times to obtain good reproducibility. The corrosion inhibition efficiency was calculated using the polarization curves and electrochemical impedance spectroscopy formulas:

[0048]

[0049]

[0050] Among them, i corr,0 i represents the corrosion current density without corrosion inhibitor. corr R represents the corrosion current density when a corrosion inhibitor is present. p,0 R represents the polarization resistance without corrosion inhibitor. p This indicates the polarization resistance when a corrosion inhibitor is present.

[0051] The corrosion inhibitor mentioned in this embodiment refers to N,S co-doped sunflower seed shell carbon quantum dots.

[0052] See attached Figure 3 , attached Figure 3The figures show the open-circuit potential and potentiodynamic polarization curves of copper immersed in 0.5M sulfuric acid solution with different concentrations. It can be observed that after immersing copper in 0.5M sulfuric acid for 2400 s, the open-circuit potential curve remains stable but shifts significantly negatively with increasing concentration, indicating that the surface corrosion inhibitor can suppress the cathodic reaction. As shown in Figure (b), the corrosion current gradually decreases with increasing inhibitor concentration, indicating that the inhibitor adsorbs on the copper surface and inhibits copper corrosion. The parameters of the polarization curves fitted by Tafel extrapolation are shown in Table 1. Table 1 shows that the inhibition efficiency increases significantly with increasing concentration; when the concentration is 200 mg / L, the inhibition efficiency reaches 95.5%, indicating that N,S co-doped sunflower seed shell carbon quantum dots have a good corrosion inhibition effect on copper.

[0053] Table 1. Polarization curve parameters of copper immersed in 0.5M sulfuric acid solution containing different concentrations of corrosion inhibitor.

[0054]

[0055] See attached Figure 4 Figures (a) and (b) show the Nyqusit and Bode plots of copper immersed in sulfuric acid solutions containing different concentrations of corrosion inhibitors, respectively. As shown in Figure (a), the diameter of the capacitive arc gradually increases with increasing corrosion inhibitor concentration, indicating that N,S co-doped sunflower seed shell carbon quantum dots can effectively suppress charge transfer on the copper surface. (The last sentence appears to be incomplete and requires further context.) Figure 5 The data after fitting the electrochemical impedance spectrum to the equivalent circuit shown are shown in Table 2. When the amount of corrosion inhibitor added is 200 mg / L, the slow release effect reaches 99.9%.

[0056] Table 2. Electrochemical impedance spectroscopy fitting parameters of copper immersed in 0.5M sulfuric acid solutions containing different concentrations of corrosion inhibitors.

[0057]

[0058] The corrosion inhibitor mentioned in this embodiment refers to N,S co-doped sunflower seed shell carbon quantum dots.

[0059] This implementation will be 0.5×0.5×0.5cm 3 The copper samples were sequentially polished to a bright finish using water-based sandpaper of grits 400, 800, 1200, 2000, 3000, 5000, and 7000 grit, followed by ultrasonic cleaning with pure water and ethanol. After immersion in a 0.5M sulfuric acid solution containing or without N,S co-doped sunflower seed shell carbon quantum dots at 298K for 36 hours, the samples were removed and ultrasonically cleaned for 1 minute. The scanning electron microscope model was [model number missing].

[0060] See attached Figure 6Figures (a) and (b) show the surface morphology of copper after immersion in a blank sulfuric acid solution and a sulfuric acid solution containing a corrosion inhibitor for 36 hours, respectively. As shown in Figure (a), the surface of copper after immersion in sulfuric acid solution is very rough, with many corrosion pits and grooves, while in Figure (b), only a few corrosion pits are present, and the surface is relatively smooth. Therefore, it can be seen that N,S co-doped sunflower seed shell carbon quantum dots can effectively inhibit the corrosion of copper.

[0061] This implementation will be 1×1×1cm 3 The copper samples were sequentially polished to a bright finish using water-based sandpaper with grits of 400, 800, 1200, 2000, 3000, 5000, and 7000 grits, followed by ultrasonic cleaning with pure water and ethanol. After immersion in a 0.5M sulfuric acid solution containing or without N,S co-doped sunflower seed shell carbon quantum dots at 298K for 36 hours, the samples were removed and ultrasonically cleaned for 1 minute. The atomic force microscope used was an MFP-3D-BIO.

[0062] See attached Figure 7 Figures (a) and (b) show the 3D morphology of copper after immersion in a blank sulfuric acid solution and a sulfuric acid solution containing a corrosion inhibitor for 36 hours, respectively. As shown in Figure (a), the surface of copper after immersion in sulfuric acid solution is very rough, with a roughness of 130, while the surface in Figure (b) is relatively smooth, with a roughness of only 16.2. This experimental result is consistent with the SEM results, proving that N,S co-doped sunflower seed shell carbon quantum dots have a good corrosion inhibition effect.

[0063] In this embodiment, a Fourier transform infrared spectrometer (Nicoleti S50) was used to test the functional groups adsorbed on copper, with a test range of 4000 cm⁻¹. -1 up to 400cm -1 .

[0064] See attached Figure 8 , attached Figure 8 The image shows the ATR-FTIR spectrum of copper surface after immersion in a 0.5M sulfuric acid solution containing N,S co-doped sunflower seed shell carbon quantum dots for 24 hours. The 3380 cm⁻¹ region is shown in the image. 1 The broad peak at 1640 cm⁻¹ corresponds to the characteristic stretching vibration of OH or NH. -1 The peak value at 1160 cm⁻¹ represents the stretching vibrations at C=C, C=O, and C=N. -1 Caused by the stretching vibrations of COC and CO, 1050cm -1 The peak value at 877 cm⁻¹ may be caused by the stretching vibration of C-SO₃. -1 and 588cm -1 The peak value at that point is caused by the stretching vibration of CH.

[0065] See attached Figure 9 , attached Figure 9 This is a Langmuir adsorption curve. Based on the adsorption Gibbs free energy, it can be determined that the adsorption of N,S co-doped sunflower seed shell carbon quantum dots on the copper surface is a combination of physical and chemical adsorption.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots, characterized in that, The corrosion inhibitor comprises N,S co-doped carbon quantum dots of sunflower seed shells obtained by reacting sunflower seed shells and thiourea. The corrosion inhibitor has a carbon fiber structure and the outermost layer of the structure contains hydrophilic groups and heteroatom groups. The hydrophilic group is -COOH or -OH, an oxygen-containing hydrophilic group. The heteroatomic groups are -NH2 and -SO3; The mass ratio of sunflower seed shells to thiourea during the reaction process is 1:

1.

2. The method for preparing the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots according to claim 1, characterized in that, Includes the following steps: Thiourea and sunflower seed shell powder were dissolved in pure water to obtain a suspension; The mixed suspension is added to the reaction vessel and reacted at a temperature of 150-220℃ for 8-12 hours. After the reaction was completed, cooling yielded a mixed suspension of carbon quantum dots. A carbon quantum dot solution was obtained by dialysis of a carbon quantum dot impurity suspension in pure water. Carbon quantum dot solution was freeze-dried to obtain carbon quantum powder.

3. The method for preparing the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots according to claim 2, characterized in that, The mixed suspension was added to the reaction vessel and reacted at a temperature of 200℃ for 10 hours.

4. The post-preparation method of the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots according to claim 3, characterized in that: The process involves dialysis of a mixture of carbon quantum dot impurities in pure water, with a molecular cutoff of 1000 Da in the dialysis bag and a dialysis time of 24 hours. The pure water is replaced every 6 hours during the dialysis process.

5. The post-preparation method of the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots according to claim 4, characterized in that, Carbon quantum dot solution was freeze-dried to obtain carbon quantum powder, and the drying time was 3 days.

6. The post-preparation method of the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots according to claim 4, characterized in that, Before dialysis of the carbon quantum dot impurity mixture in pure water, it was filtered through a funnel and then filtered again through a 0.22μm needle filter to obtain a carbon quantum dot mixed solution.

7. The application of the corrosion inhibitor based on N,S co-doped sunflower seed shell carbon quantum dots according to claim 1 in inhibiting the corrosion of copper in sulfuric acid.

Images