Sulfur-nitrogen co-doped carbon quantum dot modified polyaspartic acid derivative as well as preparation method and application thereof

Abstract

The invention discloses a sulfur-nitrogen co-doped carbon quantum dot modified polyaspartic acid derivative as well as a preparation method and application thereof. The derivative is prepared by taking citric acid and L-cysteine as precursors, synthesizing sulfur-nitrogen co-doped carbon quantum dots (SN-CDs) with rich functional groups on the surface by adopting a hydrothermal method, and introducing the sulfur-nitrogen co-doped carbon quantum dots into a side chain of polyaspartic acid (PASP) through graft copolymerization. The derivative not only retains the complexing ability of polyaspartic acid with metal ions such as calcium and magnesium, but also has excellent scale and corrosion inhibition performance; the optical characteristics of the carbon quantum dots are inherited, and stable fluorescence can be emitted under the excitation of specific wavelength, so that in-situ and real-time concentration monitoring in an industrial circulating cooling water system by utilizing a fluorescence spectrum technology is supported. The product does not contain phosphorus, is environment-friendly, conforms to the development trend of a green water treatment technology, and provides an innovative material solution for intelligent monitoring and fine management of a circulating water system while improving the comprehensive performance of scale and corrosion inhibition.

Description

Technical Field

[0001] This invention relates to the field of industrial water treatment technology, specifically to a sulfur-nitrogen co-doped carbon quantum dot modified polyaspartic acid derivative, its preparation method, and its application. Background Technology

[0002] In industrial circulating cooling water systems, dissolved calcium, magnesium, carbonate, and sulfate ions in the water easily deposit on the surfaces of heat exchangers and pipes, forming insoluble scale layers such as calcium carbonate and calcium sulfate. This scale can cause corrosion of metal materials, leading to reduced heat transfer efficiency, increased energy consumption, and shortened equipment lifespan. Currently, adding chemical water treatment agents remains the most common and cost-effective control method.

[0003] Polyaspartic acid (PAA), as a biodegradable and environmentally friendly polymer scale inhibitor, has attracted widespread attention. However, its scale inhibition function is limited, and its corrosion inhibition performance is insufficient to cope with the complex and variable industrial water environment. Existing improvement methods usually involve introducing functional groups such as phosphorus or sulfonic acid groups into the PAA molecule. Although this can partially improve performance, it still faces problems such as potentially causing eutrophication or insufficient functional integration.

[0004] Carbon quantum dots, as an emerging nanomaterial, possess excellent water dispersibility, abundant surface functional groups, and tunable fluorescence properties. Studies have shown that carboxyl and amino groups on their surface can inhibit scale growth through adsorption and dispersion, and some functional groups also possess metal coordination capabilities, potentially endowing the material with certain corrosion inhibition functions. Furthermore, the inherent fluorescence properties of carbon quantum dots provide a new technical approach for in-situ, real-time monitoring of water treatment agent concentrations.

[0005] Against this backdrop, this invention proposes an innovative method: using citric acid and L-cysteine ​​as precursors, sulfur-nitrogen co-doped carbon quantum dots with surfaces rich in carboxyl, amino, and thiol groups are synthesized, and then these dots are covalently grafted onto a polyaspartic acid backbone. This method aims to combine the excellent dispersing and scale-inhibiting properties of polyaspartic acid with the multifunctional characteristics of carbon quantum dots, thereby developing a smart water treatment agent that simultaneously possesses highly efficient scale inhibition, corrosion inhibition, and fluorescence tracing capabilities. This addresses the problems of existing water treatment agents having limited functionality and difficulty in real-time monitoring of dosage concentration. Summary of the Invention

[0006] In view of the shortcomings of existing green water treatment agents, such as limited functionality and lack of process monitoring methods, the purpose of this invention is to provide a sulfur-nitrogen co-doped carbon quantum dot modified polyaspartic acid derivative, its preparation method and application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A polyaspartic acid derivative modified with sulfur-nitrogen co-doped carbon quantum dots (SN-CDs) is disclosed. The derivative is obtained by ring-opening modification of polysuccinimide (PSI) with SN-CDs. Its structure includes a polyaspartic acid peptide backbone and SN-CD functional fragments covalently linked to the backbone via amide bonds. The SN-CDs are synthesized via a hydrothermal method using citric acid and L-cysteine ​​as precursors.

[0009] The method for preparing the derivative includes the following steps:

[0010] (1) Synthesis of sulfur-nitrogen co-doped carbon quantum dots (SN-CDs): Citric acid and L-cysteine ​​were dissolved in water and reacted at 150~200℃ for 5~10 h. After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, and the filtrate was concentrated under reduced pressure to obtain sulfur-nitrogen co-doped carbon quantum dots (SN-CDs).

[0011] (2) Synthesis of polyaspartic acid derivative modified by SN-CDs: Polysuccinimide (PSI) and SN-CDs obtained in step (1) were dissolved in deionized water at a mass ratio of (10~40):1. The pH of the reaction solution was adjusted to weakly alkaline with sodium hydroxide solution under stirring. The reaction was stirred at 50~70℃. Sodium hydroxide solution was added dropwise during the reaction to maintain the pH of the system as weakly alkaline. After the reaction was completed, the product was dialyzed and then the solvent was evaporated to obtain the polyaspartic acid derivative modified by sulfur and nitrogen co-doped carbon quantum dots.

[0012] Furthermore, the molar ratio of citric acid to L-cysteine ​​is (1.5~3):1.

[0013] Furthermore, the concentration of the sodium hydroxide solution is 1-3 mol / L. The weakly alkaline pH is 8-9.

[0014] Furthermore, in step (1), 1 to 2 mL of water is required for every 1 mmol of L-cysteine; in step (2), 15 to 30 mL of water is required for every 10 to 30 mg of SN-CDs.

[0015] Furthermore, during dialysis, a dialysis bag with a molecular weight cutoff of 500-3000 Da is used, and dialysis is performed in deionized water until the conductivity of the system drops to 1.5-2.5 μS / cm.

[0016] Furthermore, the mass ratio of polysuccinimide to SN-CDs in step (2) is 30:1.

[0017] The above preparation method yields a sulfur-nitrogen co-doped carbon quantum dot-modified polyaspartic acid derivative.

[0018] The sulfur-nitrogen co-doped carbon quantum dot-modified polyaspartic acid derivative is used as a multifunctional water treatment agent with scale inhibition, corrosion inhibition, and fluorescence tracing functions, specifically for:

[0019] (1) As a scale inhibitor, it is used to inhibit the deposition of scale salts such as calcium carbonate and calcium sulfate;

[0020] (2) As a corrosion inhibitor, it is used to slow down the corrosion of metal materials such as carbon steel and copper;

[0021] (3) As a fluorescent tracer, its stable fluorescence properties can be used to achieve in-situ, real-time, and quantitative monitoring of the concentration of the drug in circulating water through a fluorescence spectrometer or online fluorescence monitoring equipment.

[0022] This invention optimizes the scale inhibition performance of the derivative by controlling the raw material ratio and polymerization conditions. The water treatment agent exhibits the best scale inhibition effect when the mass ratio of polysuccinimide to SN-CDs is 30:1. Simultaneously, the introduction of SN-CDs not only significantly improves the scale inhibition and corrosion inhibition performance of the material but also endows it with stable fluorescent properties, enabling it to possess tracer capabilities.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) For the first time, sulfur and nitrogen co-doped carbon quantum dots were combined with biodegradable polyaspartic acid to develop a water treatment agent that integrates scale inhibition, corrosion inhibition and real-time fluorescence monitoring, thus realizing the integration of "treatment" and "monitoring".

[0025] (2) The abundant functional groups (-COOH, -NH2, -SH) on the surface of SN-CDs work synergistically with the polyaspartic acid skeleton to enhance the scale inhibition effect through multiple coordination and dispersion mechanisms, and form a protective film on the metal surface with the help of nitrogen and sulfur groups, giving the material excellent corrosion inhibition performance.

[0026] (3) The product uses polyaspartic acid as a matrix, contains no phosphorus, and is environmentally friendly; its intrinsic fluorescence properties enable precise monitoring and intelligent dosing of reagent concentration without the need for external tracers, providing an innovative solution for intelligent management of circulating water systems.

[0027] (4) The preparation process is based on hydrothermal method and ring-opening amidation reaction. The raw materials are readily available, the steps are simple, and the conditions are mild, which has good feasibility for large-scale production and application prospects. Attached Figure Description

[0028] Figure 1 Fourier transform infrared (FT-IR) spectra of PASP, SN-CDs, and PASP-SN-30 prepared for this invention;

[0029] Figure 2The particle size distribution diagram of the SN-CDs prepared in this invention;

[0030] Figure 3 The proton nuclear magnetic resonance spectrum of polyaspartic acid (PASP) prepared in this invention (1H NMR spectrum) 1 H NMR spectrum;

[0031] Figure 4 A comparison of the scale inhibition effects of PASP and PASP-SN prepared in this invention on calcium carbonate scale.

[0032] Figure 5 A comparison of the scale inhibition effects of PASP and PASP-SN prepared in this invention on calcium sulfate scale;

[0033] Figure 6 In the figure: ac represents the variation of the scale inhibition performance of PASP and PASP-SN-30 prepared in this invention against calcium sulfate scale at a concentration of 4 mg / L with time, temperature and calcium ion concentration, respectively.

[0034] Figure 7 In the diagram: a is the Tafel curve of PASP prepared in this invention, b is the Tafel curve of PASP-SN-30, c is the Nyquist curve of PASP, d is the Nyquist curve of PASP-SN-30, e is the Bode curve and phase diagram of PASP, and f is the Bode curve and phase diagram of PASP-SN-30.

[0035] Figure 8 In the image: ab represents the fluorescence spectra of SN-CDs and PASP-SN-30 prepared in this invention, respectively. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to embodiments thereof. It should be understood that the embodiments described herein are only a part of the present invention, and are intended to help understand the essence and specific implementation methods of the present invention, rather than to limit the scope of protection of the present invention. Based on the content disclosed in this invention, any equivalent substitutions or modifications that can be conceived by those skilled in the art without creative effort should be included within the scope of protection of this invention.

[0037] Unless otherwise specified, all raw materials and reagents used in the following examples and comparative examples are commercially available reagents that can be directly purchased or prepared according to conventional techniques disclosed in the art.

[0038] The core raw material, polysuccinimide (PSI), is a product with a number average molecular weight of approximately 7,000-8,000, and is purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0039] Example 1

[0040] Preparation of SN-CDs-modified polyaspartic acid derivatives (PASP-SN)

[0041] (1) Synthesis of sulfur-nitrogen co-doped carbon quantum dots (SN-CDs)

[0042] Weigh 1.92 g (10.0 mmol) of citric acid and 0.605 g (5.0 mmol) of L-cysteine ​​into a 100 mL high-pressure reactor lined with polytetrafluoroethylene, add 50 mL of deionized water, and sonicate until completely dissolved. Seal the reactor and react in an oven at 180 ℃ for 8 hours. After the reaction, allow it to cool naturally to room temperature. Filter the resulting reaction solution through a 0.22 μm microporous membrane. Concentrate the filtrate under reduced pressure to obtain a brownish-yellow viscous oily substance, which is the crude sulfur-nitrogen co-doped carbon quantum dots (SN-CDs), stored at 4 ℃ for later use.

[0043] according to Figure 1 Infrared spectroscopy and Figure 2 The particle size analysis results showed that the synthesized sulfur-nitrogen co-doped carbon quantum dots (SN-CDs) had a particle size of 1710 cm⁻¹. -1 1562 cm -1 1495 cm -1 and 1202 cm -1 Characteristic absorption peaks appeared at the points, attributed to the C=O stretching vibration, amide II band (-CONH-), CH / CN vibration, and CO / CS stretching vibration, respectively. These characteristic peaks indicate that the SN-CDs surface is rich in functional groups such as carboxyl groups and amide bonds, and that sulfur and nitrogen elements have been successfully doped into the carbon dot structure. Meanwhile, particle size distribution analysis ( Figure 2 The results showed that the SN-CDs were concentrated at a size of approximately 1.75 nm, with a narrow distribution and uniform morphology. Infrared structure and particle size characterization together confirmed the successful preparation of surface-functionalized, uniformly sized sulfur-nitrogen co-doped carbon quantum dots using a hydrothermal method with citric acid and L-cysteine ​​as precursors.

[0044] (2) Preparation of PASP-SN

[0045] To determine the optimal raw material ratio, four parallel experiments were conducted, using the mass ratio of polysuccinimide (PSI) to SN-CDs as the variable. The feed ratio and feed amount for each experimental group are shown in Table 1.

[0046] Table 1 Feeding amounts for different PSI to SN-CDs mass ratios

[0047]

[0048] Weigh the corresponding masses of PSI and SN-CDs according to Table 1, and place them in four 100 mL round-bottom flasks. Add 20 mL of distilled water to each flask and stir until completely dissolved or uniformly dispersed. While stirring, add 2 mol / L NaOH solution dropwise to adjust the pH of the system to 8.5. Place the flasks in a 60 °C constant temperature water bath and stir continuously for 24 hours. Monitor the pH using a pH meter during the reaction, and add small amounts of 2 mol / L NaOH solution as needed to maintain the pH within the range of 8.5 ± 0.5.

[0049] After the reaction was completed, each reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 3000 Da and dialyzed against deionized water. The external solution was replaced every 6 hours until the conductivity of the external solution dropped to approximately 2 μS / cm. The retentate in the dialysis bag was concentrated under reduced pressure to obtain light brown solid products, which were labeled as PASP-SN-10 (PSI to SN-CDs mass ratio 10:1), PASP-SN-20 (PSI to SN-CDs mass ratio 20:1), PASP-SN-30 (PSI to SN-CDs mass ratio 30:1), and PASP-SN-40 (PSI to SN-CDs mass ratio 40:1), respectively.

[0050] In the infrared spectrum of PASP-SN-30 ( Figure 1 Characteristic absorption peaks similar to those of pure PASP can be observed, with its amide I band (C=O stretching vibration) located at 1619 cm⁻¹. -1 Nearby, the amide II band (coupled with NH bending vibration and CN stretching vibration) appears at 1542 cm⁻¹. -1 At this location, the symmetric stretching vibration of the carboxylate group shifts to 1395 cm⁻¹. -1 Left and right. The spectrum compared to pure PASP (1380 cm⁻¹). -1 and 1540 cm -1 Compared to the above, the characteristic peaks show a regular shift, indicating that SN-CDs were successfully grafted onto the PASP backbone through amide bonds, and a stable covalent connection was formed between the two, thus proving that the carbon dots have been effectively combined with polyaspartic acid.

[0051] (3) Synthesis of PASP

[0052] 0.984 g (10 mmol) of polysuccinimide (PSI) was dissolved in 10 mL of distilled water. 10 mL of 2 mol / L NaOH solution was slowly added dropwise with stirring, and the reaction was carried out in a 45 °C water bath for 24 hours. After the reaction was complete, the solution was placed in a dialysis bag with a molecular weight cutoff of 3000 Da and dialyzed until the conductivity of the external solution decreased to approximately 2 μS / cm. The retentate was evaporated to dryness under reduced pressure to obtain 1.05 g of PASP product, with a yield of 90.21%.

[0053] Figure 3 The ¹H NMR spectrum of the synthesized PASP shows characteristic peaks at δ 4.48 ppm and δ 2.65 ppm for the methylene and methine groups on the polyaspartic acid chain, respectively, confirming the successful synthesis of PASP.

[0054] Example 2

[0055] The scale inhibition performance of calcium carbonate in Example 1 was tested using the static scale inhibition method.

[0056] Referring to GB / T16632-2019 "Determination of scale inhibition performance of water treatment agents - calcium carbonate deposition method", the scale inhibition performance of the product prepared in Example 1 was tested using the static scale inhibition method.

[0057] (1) Take 7 250 mL conical flasks and number them from 1 to 7. Add 10 mL of 6 mg / mL CaCl2 aqueous solution, 10 mL of 3.8 g / L Na2B4O7·10H2O aqueous solution (adjust the initial pH to 9.0), and 10 mL of 18.3 mg / mL NaHCO3 solution to each flask.

[0058] (2) Then add a certain amount of 1 mg / mL PASP-SN aqueous solution to conical flasks 3-7 respectively, so that the final concentrations of PASP-SN in conical flasks 3-7 are 10, 20, 30, 40 and 50 mg / L respectively. At the same time, add distilled water to conical flasks 1-7 respectively to make the total volume of the solution 250 mL.

[0059] (3) Take 25 mL of the solution in bottle 1 and titrate it with 0.01 mol / L EDTA-2Na standard solution to standardize the Ca content. 2+ The concentration of the standard solution consumed is denoted as V0.

[0060] (4) Then, the conical flasks No. 2-7 were reacted in an 80 ℃ water bath for 10 h. After the reaction was completed, the mixture was filtered, and 25 mL of the filtrate was titrated with 0.01 mol / L EDTA-2Na standard solution to determine the Ca content. 2+ The concentration is denoted as V1, where the volume of standard solution consumed by the filtrate in bottle 2 is denoted as V2, and the volume of standard solution consumed by the filtrate in conical flasks 3-9 is denoted as V2.

[0061] (5) The scale inhibition efficiency ɧ (%) can be calculated according to formula (1):

[0062] Formula (1)

[0063] Repeat the above steps, replacing PASP-SN with PASP to test its scale inhibition effect on calcium carbonate scale as a control.

[0064] Figure 4 The results show a comparison of the scale inhibition rates of PASP and PASP-SN with different ratios for calcium carbonate scale. As shown in the figure, the scale inhibition rates of each PASP-SN sample tend to stabilize as the concentration increases. Among them, PASP-SN-30 (PSI to SN-CDs mass ratio 30:1) exhibits the best scale inhibition performance at all concentrations, and its scale inhibition effect is significantly better than that of pure PASP sample.

[0065] At a dosage concentration of 20 mg / L, PASP-SN-30 achieved a scale inhibition rate of approximately 80%, while pure PASP under the same conditions only achieved a scale inhibition rate of approximately 55%. The scale inhibition effects of PASP-SN-10 and PASP-SN-20 were essentially equivalent to those of pure PASP, while the average scale inhibition rate of PASP-SN-40 was approximately 10% higher than that of pure PASP. These results indicate that PASP-SN-30, prepared by grafting SN-CDs at a mass ratio of 30:1, exhibits the best calcium carbonate scale inhibition performance.

[0066] Example 3

[0067] The effect of the product in Example 1 on inhibiting calcium sulfate scale was tested using the static scale inhibition method.

[0068] The scale inhibition performance of Example 1 on calcium sulfate scale was determined using the static scale inhibition method in accordance with SY / T5673-2020 "General Technical Conditions for Scale Inhibitors for Oilfield Use".

[0069] (1) Take eight 250 mL conical flasks and number them from 1 to 8. Then add 50 mL of 7.35 mg / mL CaCl2 solution, 25 mL of 10.4 g / L Na2B4O7·10H2O solution, and 25 mL of 7.1 mg / mL Na2SO4 solution to each flask.

[0070] (2) Add a certain amount of 1 mg / mL PASP-SN aqueous solution to conical flasks 3-8 respectively, so that the final concentrations of PASP-SN in conical flasks 3-8 are 1, 2, 3, 4, 5, and 6 mg / L respectively. At the same time, add distilled water to conical flasks 1-8 respectively to make the total volume of the solution 250 mL.

[0071] (3) Take 5 mL of the solution in conical flask No. 1 and titrate it with 0.025 mol / L EDTA-2Na standard solution to standardize the Ca content. 2+ The concentration and the volume of standard solution consumed are denoted as V0.

[0072] (4) React the conical flasks No. 2-8 in a 70 ℃ water bath for 6 h. After filtration, take 5 mL of the filtrate and titrate it with 0.025 mol / L EDTA-2Na standard solution to determine the Ca content. 2+The concentration is recorded as follows: the volume of standard solution consumed by the filtrate in conical flask No. 2 is recorded as V1, and the volume of standard solution consumed by the filtrate in conical flasks No. 3-8 is recorded as V2.

[0073] (5) The scale inhibition efficiency ɧ (%) can be calculated according to formula (1) in Example 2.

[0074] Repeat the above steps, replacing PASP-SN with PASP to test its scale inhibition effect on calcium sulfate scale as a control.

[0075] Figure 5 This study compares the scale inhibition performance of PASP and PASP-SN at different concentrations for calcium sulfate scale. PASP-SN-30 exhibits significant advantages, especially at 4 mg / L, achieving a scale inhibition rate of 100%, while pure PASP only achieves approximately 60% under the same conditions. Based on this superior performance, the scale inhibition behavior of PASP-SN-30 and pure PASP at a dosage concentration of 4 mg / L was further investigated under time, temperature, and calcium ion concentration conditions. Figure 6 As shown in Figure a, even after 14 hours, PASP-SN-30 still maintains approximately 80% scale inhibition rate, significantly higher than the 20% of pure PASP; Figure 6 As shown in Figure b, under high temperature conditions of 70℃, the scale inhibition rate of PASP-SN-30 is close to 100%, while that of pure PASP decreases by about 60%; Figure 6 As shown in Figure c, when the calcium ion concentration increased to 2.2 mmol / L, the scale inhibition rate of PASP-SN-30 remained at around 95%, significantly better than the 50% of pure PASP. The results indicate that PASP-SN-30 exhibits optimal and stable calcium sulfate scale inhibition performance over a wide range of operating conditions and experimental formulations.

[0076] Example 4

[0077] The corrosion inhibition performance of the product in Example 1 was determined using an electrochemical method.

[0078] Electrochemical tests were conducted on the corrosion inhibition behavior of different concentrations of PASP-SN on carbon steel surfaces using a CHI 660E electrochemical workstation and a three-electrode system in 1 mol / L HCl solution. The specific experimental steps are as follows:

[0079] (1) Solution and electrode preparation: 1 mol / L HCl solution was used as the corrosive medium. The working electrode was made of No. 20 carbon steel, and its effective surface area exposed to the solution was 1 cm². 2 .

[0080] (2) Electrode pretreatment: The surface of the working electrode is polished to a mirror finish by using silicon carbide sandpaper of 400 to 2000 mesh in sequence. Then, it is ultrasonically cleaned in ethanol to remove oil stains, rinsed with deionized water, and air-dried for later use.

[0081] (3) Open circuit potential (OCP) stability: Immerse the treated working electrode in 500 mL of 1 mol / L HCl etching solution containing different concentrations of PASP-SN, and let it stand for about 1 hour under constant temperature of 298 K, and monitor its open circuit potential until it stabilizes.

[0082] (4) Potentiodynamic polarization curve test: After the open circuit potential stabilizes, a potentiodynamic polarization scan is performed in the range of -250 mV to +250 mV relative to the open circuit potential (EOCP), with a scan rate of 1 mV / s. The corrosion current density (Icorr) and corrosion potential (Ecorr) are obtained by extrapolating the Tafel curve.

[0083] (5) Data processing and corrosion inhibition efficiency calculation: Based on the corrosion current density obtained from the Tafel curve, the corrosion inhibition efficiency (η) is calculated using the following formula. p ) and surface coverage (θ):

[0084]

[0085]

[0086] (A cm -2 — Corrosion current density in blank corrosive medium (blank group: 500 mL of 1 mol / L HCl corrosive solution without PASP-SN, after 60 minutes of open circuit, impedance and polarization tests were performed).

[0087] (A cm -2 ) — Corrosion current density in corrosive media containing PASP-SN.

[0088] Repeat the above steps, replacing PASP-SN-30 with PASP to test its corrosion inhibition performance. The results are as follows: Figure 7 As shown in Table 2.

[0089] Table 2 Electrochemical polarization parameters of Tafel curves

[0090]

[0091] The corrosion inhibition properties of polyaspartic acid (PASP) and its modified product PASP-SN-30 were systematically studied using electrochemical methods. Figure 7As shown in Figures a and b, the corrosion current density and corrosion inhibition efficiency at different concentrations were calculated using the Tafel curve extrapolation method. The results show that within the concentration range of 0-100 mg / L, the corrosion inhibition efficiency of PASP-SN-30 significantly increases with increasing concentration, exhibiting a clear concentration dependence. When the concentration exceeds 100 mg / L, the corrosion inhibition efficiency decreases slightly before rebounding, reaching a maximum of 58.29% at 200 mg / L, approximately twice the corrosion inhibition efficiency of PASP at the same concentration.

[0092] The Nyquist curves further reveal the differences in the corrosion inhibition mechanisms of the two. From Figure 7 As can be seen from curve c, the arc-resistant radius of PASP remains basically consistent within the concentration range of 100 to 200 mg / L, indicating that the formation and coverage capacity of its corrosion-inhibiting film tends to saturate, which is consistent with the results of the polarization curve; while Figure 7 The results in Figure d show that PASP-SN-30 exhibits a larger capacitive arc radius at a concentration of 200 mg / L, indicating a significant increase in interfacial charge transfer resistance under this condition, and a stronger barrier effect of the corrosion-inhibiting film. Bode plot results further support these conclusions. Figure 7 As shown in Figures e and f in Figure 7, PASP-SN-30 maintains a high phase angle and a wider, gentler peak over a wider frequency range, indicating that it forms a denser and more stable protective film on the metal surface, thus providing more durable corrosion protection.

[0093] In summary, the electrochemical test results show that structural modification significantly improves the corrosion inhibition performance of PASP. PASP-SN-30 exhibits the best corrosion inhibition effect at 200 mg / L, and its mechanism is closely related to the enhancement of the integrity, stability and charge transfer resistance of the corrosion inhibition film.

[0094] Example 5

[0095] Fluorescence spectroscopy analysis of PASP-SN-30

[0096] The PASP-SN-30 sample prepared in Example 1 was analyzed by fluorescence spectrophotometry. The specific experimental steps are as follows:

[0097] (1) Weigh 10.0 mg of PASP-SN-30 and PASP control sample respectively, dissolve them in ultrapure water and make up to 100 mL to prepare a 100 mg / L stock solution; accurately measure an appropriate amount of stock solution with a pipette, and dilute and make up to 100 mL in a 50 mL volumetric flask according to the concentration gradient of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 mg / L, and shake well for later use.

[0098] (2) Take 50 mg / L of PASP-SN-30 and PASP solution and perform excitation wavelength scanning in the range of 200 nm-400 nm. The optimal excitation wavelength is 325 nm. The test settings are as follows: excitation wavelength 325 nm, emission scanning range 340 nm-650 nm; the excitation and emission slit widths of PASP-SN-30 are both set to 10 nm; the excitation and emission slit widths of PASP are both set to 2.5 nm.

[0099] (3) Using ultrapure water as a blank, put it into a quartz cuvette, perform baseline scanning and save the background.

[0100] (4) Take solutions of each gradient from low to high concentration and inject them into the cuvette. Scan the emission spectrum under 325 nm excitation and record the maximum emission wavelength and the corresponding fluorescence intensity. Each concentration sample is measured in parallel 3 times, and the average value is taken as the final fluorescence intensity value of that concentration. After each sample is measured, rinse the cuvette 3 times with ultrapure water and rinse it 2 times with the next sample to be tested to avoid cross-contamination.

[0101] (5) Plot a standard curve with concentration as the x-axis and fluorescence intensity (intensity value at the maximum emission wavelength) as the y-axis. Compare the emission spectra of PASP-SN-30 and PASP to observe the changes in fluorescence characteristics after carbon dot modification.

[0102] By comparing the fluorescence spectral characteristics of carbon dots (SN-CDs) and their product (PASP-SN-30) bound to polyaspartic acid, it was demonstrated that both possess excellent and stable optical activity. Within the test concentration range of 0-100 mg / L, the fluorescence intensity of both showed a significant linear correlation with concentration. Figure 8 Figures a and b show that the carbon dots retain their fluorescence properties after PASP modification, exhibiting a clear concentration-dependent relationship. This characteristic indicates that in practical industrial circulating cooling water systems, the characteristic emission intensity of water samples under 325 nm excitation can be directly measured using online fluorescence detection technology, enabling real-time, quantitative monitoring of PASP-SN-30 concentration. This method offers advantages such as high sensitivity, fast response, and no need for complex pretreatment, providing a reliable technical means for dynamic monitoring, intelligent feedback, and precise automatic dosing of water treatment agents. It is expected to improve the operating efficiency and treatment stability of circulating water systems while reducing the costs and risks associated with over- or under-dosing of reagents.

[0103] The above embodiments are only used to specifically illustrate the implementation of the present invention, and their descriptions are relatively detailed, but they should not be regarded as limiting the scope of protection of the present invention. Those skilled in the art can make several adjustments or improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. The scope of protection of the present invention is determined by the appended claims. The various embodiments and comparative examples belong to the same inventive concept, their contents complement each other, and any omissions can be referred to each other.

[0104] It should be noted that the above embodiments and comparative examples all belong to the same inventive concept. The descriptions of the embodiments and comparative examples have different focuses. Where the descriptions in the embodiments and comparative examples are not detailed, please refer to the descriptions in other embodiments and comparative examples.

Claims

1. A method for preparing a sulfur-nitrogen co-doped carbon quantum dot-modified polyaspartic acid derivative, characterized in that, Includes the following steps: (1) Dissolve citric acid and L-cysteine ​​in water and react at 150~200℃ for 5~10 h. After the reaction is completed, cool naturally to room temperature, filter, and concentrate the filtrate under reduced pressure to obtain sulfur-nitrogen co-doped carbon quantum dots. (2) The obtained sulfur-nitrogen co-doped carbon quantum dots and polysuccinimide were dissolved in water, and the pH of the reaction solution was adjusted to weak alkalinity with sodium hydroxide solution. The reaction was stirred at 50~70℃. During the reaction, sodium hydroxide solution was added dropwise to maintain the pH of the system as weak alkalinity. After the reaction was completed, the product was dialyzed and then the solvent was evaporated to obtain the polyaspartic acid derivative modified by sulfur-nitrogen co-doped carbon quantum dots.

2. The preparation method according to claim 1, characterized in that, The molar ratio of citric acid to L-cysteine ​​is (1.5~3):

1.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the polysuccinimide to the sulfur-nitrogen co-doped carbon quantum dots is (10~40):

1.

4. The preparation method according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 1-3 mol / L; the pH of the weakly alkaline solution is 8-9.

5. The preparation method according to claim 1, characterized in that, The dialysis is performed using a dialysis bag with a molecular weight cutoff of 500-3000 Da, and dialysis is performed in deionized water until the conductivity of the system drops to 1.5-2.5 μS / cm.

6. A polyaspartic acid derivative modified with sulfur and nitrogen co-doped carbon quantum dots, prepared by any one of claims 1 to 5.

7. The application of the sulfur-nitrogen co-doped carbon quantum dot-modified polyaspartic acid derivative as described in claim 6 as a multifunctional water treatment agent with scale inhibition, corrosion inhibition and fluorescence tracing functions.

8. The use of the sulfur-nitrogen co-doped carbon quantum dot-modified polyaspartic acid derivative as a scale inhibitor according to claim 6.

9. The application of the sulfur-nitrogen co-doped carbon quantum dot-modified polyaspartic acid derivative of claim 6 as a corrosion inhibitor.

10. The application of the sulfur-nitrogen co-doped carbon quantum dot-modified polyaspartic acid derivative of claim 6 as a fluorescent tracer.

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