A synthesis method of monatomic doped C3N4 quantum dots with high catalytic activity and water solubility

Abstract

The application aims to provide a synthesis method of monatomic doped C3N4 quantum dots with high catalytic activity and water solubility, and belongs to the technical field of nanomaterial preparation. Metal ions are uniformly fixed in the C3N4 skeleton by polymerization of citric acid and urea under low temperature conditions, and high dispersion monatomic loading is realized. By adjusting the addition amounts of citric acid, urea and metal ions, the quantum dot particle size and metal doping amount can be accurately controlled, and the defects of the existing g-C3N4 monatomic material synthesis process, such as complex synthesis steps, high temperature, poor water solubility and the like, are compensated.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for synthesizing single-atom-doped C3N4 quantum dots with high catalytic activity and water solubility. Background Technology

[0002] In recent years, single-atom catalysis has become a research hotspot in materials science and catalysis due to its excellent atom utilization and unique catalytic activity. Single-atom catalysts, by stably loading individual metal atoms onto a support, can not only significantly improve catalytic efficiency but also achieve highly selective catalytic reactions by controlling the electronic structure and local coordination environment. They show broad application prospects, especially in energy conversion, environmental remediation, and biomedicine. However, traditional methods for preparing single-atom catalysts are complex, prone to metal agglomeration, and difficult to achieve highly dispersed single-atom loading. Furthermore, the preparation conditions are stringent, making it difficult to guarantee product uniformity and reproducibility.

[0003] Graphitic carbon nitride (C3N4) is an ideal support for single-atom loading due to its high thermal stability, abundant nitrogen coordination sites, and favorable electronic structure. By embedding single metal atoms into the cavities of C3N4, stable MN can be formed. x The active center significantly enhances its catalytic performance and electronic regulation capabilities. In existing technologies, most studies form single-atom-C3N4 catalysts by supporting metal single atoms on graphitic carbon nitride (g-C3N4). Although these materials exhibit high activity in catalysis, electrochemistry, and energy conversion, their preparation processes typically suffer from the following problems: first, the synthesis steps are complex, requiring multiple impregnation steps, high-temperature solid-state sintering, or template assistance; second, the reaction temperature is high, easily leading to metal atom aggregation, making it difficult to achieve true single-atom dispersion; and third, the product has poor water solubility, making it difficult to stably disperse in aqueous systems, thus limiting its application in biomedicine and aqueous catalysis. Summary of the Invention

[0004] This invention addresses the problems of complex synthesis, high reaction temperature, and poor water solubility of existing g-C3N4 supported single-atom materials. It provides a method for synthesizing single-atom doped C3N4 quantum dots with high catalytic activity and water solubility, focusing on factors such as material synthesis conditions, metal dispersion, aqueous phase stability, and particle size control. This method employs a low-temperature, one-step process to prepare C3N4 quantum dot single-atom materials. By polymerizing C3N4 quantum dots with citric acid and urea at 180°C, this invention simultaneously achieves uniform metal single-atom doping, resulting in small particle size, good dispersion, and excellent water solubility, thus promising high-efficiency applications in catalysis and biomedicine.

[0005] The present invention adopts the following technical solution: A method for synthesizing single-atom-doped C3N4 quantum dots with high catalytic activity and water solubility includes the following steps: S1. Weigh out citric acid and urea in proportion and grind them evenly in a clean agate mortar. S2. Add metal ion salt to the mixture of S1 and continue grinding to disperse it evenly to obtain a mixture; S3. Transfer the uniformly ground mixture to a sealed reaction vessel and place it in an oven for heating and reaction; S4. After the reaction is complete, the product is taken out and cooled to room temperature to obtain crude metal single-atom-C3N4 nanomaterials. S5. The crude Fe single-atom doped C3N4 material was dispersed in deionized water to prepare a dispersion, which was then transferred to a dialysis bag. The dialysis bag was placed in deionized water and magnetically stirred at room temperature for dialysis purification, during which the deionized water was replaced several times. After dialysis, the dispersion in the bag was transferred to a petri dish and dried to constant weight to obtain pure single-atom doped C3N4 material.

[0006] Furthermore, in S1, the molar ratio of citric acid to urea is 1:3.6-5.5.

[0007] Furthermore, in S2, the metal ion salt includes Fe. 3+ Fe 2+ Co 2+ Cu 2+ and Ni 2+ At least one of the following salts.

[0008] Furthermore, in S3, the heating rate is 5-10℃ / min, the heating temperature is 160-200℃, and the heating reaction time is 2-5h.

[0009] Furthermore, in S4, the metal single-atom-C3N4 nanomaterial contains metal that exists stably in the form of M-N2 or M-N4, where M represents a metal single atom.

[0010] The beneficial effects of this invention are as follows: This invention provides a one-step synthesis method for single-atom C3N4 quantum dot nanomaterials. The method utilizes the polymerization of citric acid and urea under low-temperature conditions to uniformly immobilize metal ions within the C3N4 framework, achieving highly dispersed single-atom loading. By adjusting the amounts of citric acid, urea, and metal ions, the quantum dot particle size and metal doping amount can be precisely controlled, overcoming the shortcomings of existing g-C3N4-loaded single-atom material synthesis methods, such as complex steps, high temperatures, and poor water solubility. The method of this invention is simple to operate, with mild reaction conditions, requiring no high-temperature sintering or template assistance, making it suitable for large-scale preparation. The prepared single-atom C3N4 nanomaterials exhibit uniform metal dispersion, stable structure, small particle size (0.5~10 nm), and good water solubility, possessing broad potential for catalytic, electrochemical, and biomedical applications. This method represents a rapid, efficient, and controllable preparation method for single-atom nanomaterials. Attached Figure Description

[0011] Figure 1 This is a transmission electron microscope (TEM) image of the Fe single-atom-C3N4 nanomaterial synthesized in Example 1 of the present invention.

[0012] Figure 2 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the Fe single-atom-C3N4 nanomaterial synthesized in Example 1 of the present invention, used to show the single-atom dispersion state.

[0013] Figure 3 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the single-atom C3N4 nanomaterial synthesized in Example 1 of this invention, revealing the metal coordination state.

[0014] Figure 4 This is a schematic diagram of the catalytic performance of the single-atom-C3N4 nanomaterial synthesized in Example 1 of the present invention.

[0015] Figure 5 This is a diagram showing the water solubility of the single-atom C3N4 nanomaterial synthesized in Example 1 of this invention.

[0016] Figure 6 The figure shows the electrochemical experimental results of the single-atom C3N4 nanomaterial synthesized in Example 1 of this invention.

[0017] Figure 7 This is a diagram showing the biomedical experimental results of the single-atom C3N4 nanomaterial synthesized in Example 1 of this invention. Detailed Implementation

[0018] The technical solutions involved in each embodiment will be clearly and comprehensively described below with reference to the accompanying drawings. Obviously, the embodiments described herein are only a part, not all, of the present invention. All other embodiments that can be obtained by those skilled in the art based on the above embodiments of the present invention without creative effort are included within the protection scope of the present invention.

[0019] Example 1 Take 0.081g of citric acid and 0.101g of urea (molar ratio 1:4.7), and add ferric chloride (to provide Fe). 3+ ), FeCl3 0.0182 g, together with the powder, were added to an agate mortar and ground manually for 15 min to obtain a uniform and fine mixed powder; Transfer the ground mixed powder to a 50mL polytetrafluoroethylene-lined reactor, and gently shake the reactor to spread the powder evenly on the bottom of the inner lining. Seal and secure the reactor, place it in a constant temperature oven, and heat it to 180°C at a rate of 8°C / min. Maintain the temperature for 3 hours. After the reaction was completed, the oven was closed and allowed to cool naturally to room temperature. The reaction vessel was then removed, the liner was opened, and the gray solid product was collected to obtain crude Fe single-atom doped C3N4 material. The crude Fe single-atom-doped C3N4 material was dispersed in deionized water to prepare a dispersion with a concentration of 10 mg / mL. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. The dialysis bag was placed in 200 mL of deionized water and purified by magnetic stirring at 400 r / min at room temperature for 12 h, with the deionized water being replaced every 5 h. After dialysis, the dispersion in the bag was transferred to a petri dish and dried in a 70 °C oven to constant weight to obtain pure Fe single-atom-doped C3N4 material.

[0020] Figure 1 This is a transmission electron microscope (TEM) image of the Fe single-atom-C3N4 nanomaterial synthesized in Example 1 of this invention. Figure 1 It can be known that: Transmission electron microscopy (TEM) images of Fe-C3N4 clearly show that the material has an ultra-small quantum dot morphology, which is a typical quantum dot structure with an average size of about 2 nm.

[0021] Figure 2 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the Fe single-atom-C3N4 nanomaterial synthesized in Example 1 of this invention. Figure 2It can be seen that atomic-scale structural information was obtained through aberration-corrected HAADF-STEM technology. Due to the high atomic number contrast, iron atoms appear as clear bright spots, directly proving that they are atomically dispersed in the C3N4 framework. No iron clusters or nanoparticles were observed. Magnified images show that iron atoms are stabilized through coordination with nitrogen sites in the C3N4 lattice.

[0022] Figure 3 This is the X-ray photoelectron spectroscopy (XPS) spectrum of the single-atom C3N4 nanomaterial synthesized in Example 1 of this invention, showing the metallic state. Figure 3 As can be seen, X-ray photoelectron spectroscopy (XPS) analysis directly confirmed the formation of the Fe-N coordination structure at the electronic level. Similarly, the full XPS spectrum of Fe-C3N4 confirmed the presence of C, N, O, and Fe elements. In the N·1s spectrum, an additional component appeared at 398.67 eV, which can be reasonably attributed to Fe-N coordination. Simultaneously, the characteristic peaks corresponding to the C=NC, NC, and CNH environments shifted towards lower binding energies, indicating that Fe induced electron redistribution within the C3N4 framework. A similar trend was observed in the C·1s spectrum, where the small shift of the fitted component further supports the modulation of the conjugated network by Fe-N coordination. In the Fe·2p spectrum, Fe·2p... 3 / 2 and Fe·2p 1 / 2 The peaks are located at 710.58 eV and 724.48 eV, respectively. These values ​​are slightly lower than the typical reported values ​​for Fe₂O₃, indicating a unique electronic environment for Fe species in the Fe-C₃N₄ system. This shift suggests that Fe is in an electron-rich state within the Fe-N coordination environment, which is favorable for reversible Fe... 3⁺ / Fe 2⁺ Redox conversion and rapid interfacial charge transfer.

[0023] Example 2 Take 0.06g of citric acid and 0.12g of urea (molar ratio 1:5.5), and add cobalt nitrate (providing Co). 2+ ), Co 2+ The dosage is 5% based on the mass of citric acid. Add it to the grinder and grind at 300 r / min for 20 min to obtain a uniform and fine mixed powder. Transfer the ground mixed powder to a 50mL polytetrafluoroethylene-lined reactor, and gently shake the reactor to spread the powder evenly on the bottom of the inner lining. Seal and secure the reactor, place it in a constant temperature oven, and heat it to 170°C at a rate of 10°C / min. Maintain the temperature for 4 hours. After the reaction was completed, the oven was closed and allowed to cool naturally to room temperature. The reaction vessel was then removed, the inner liner was opened, and the gray solid product was collected to obtain crude Co single-atom doped C3N4 material. The crude Co-doped C3N4 material was dispersed in deionized water to prepare a dispersion with a concentration of 8 mg / mL. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 8000 Da. The dialysis bag was placed in 200 mL of deionized water and purified by magnetic stirring at 350 r / min at room temperature for 18 h, with the deionized water being replaced every 4 h. After dialysis, the dispersion in the bag was transferred to a petri dish and dried in a 60 °C oven to constant weight to obtain pure Co-doped C3N4 material.

[0024] Example 3 Take 0.10g of citric acid and 0.09g of urea (molar ratio 1:3.8), and add nickel nitrate (providing Ni). 2+ ), Ni 2+ The dosage is 20% based on the mass of citric acid. Add it to the agate mortar and grind manually for 10 minutes to obtain a uniform and fine mixed powder. Transfer the ground mixed powder to a 50mL polytetrafluoroethylene-lined reactor, and gently shake the reactor to spread the powder evenly on the bottom of the inner lining. Seal and secure the reactor, place it in a constant temperature oven, and heat it to 190°C at a rate of 5°C / min. Maintain the temperature for 2.5 hours. After the reaction was completed, the oven was closed and allowed to cool naturally to room temperature. The reaction vessel was then removed, the liner was opened, and the gray solid product was collected to obtain crude Ni single-atom doped C3N4 material. The crude Ni single-atom-doped C3N4 material was dispersed in deionized water to prepare a dispersion with a concentration of 15 mg / mL. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 6000 Da. The dialysis bag was placed in 200 mL of deionized water and dialyzed at room temperature with magnetic stirring at 450 r / min for 10 h, during which the deionized water was replaced every 6 h. After dialysis, the dispersion in the bag was transferred to a petri dish and dried in an oven at 80 °C until constant weight, yielding pure Ni single-atom-doped C3N4 material.

[0025] Example 4 Take 0.12g of citric acid and 0.15g of urea (molar ratio 1:5.0), add copper chloride (providing Cu). 2+ Cu 2+ The dosage is 25% based on the mass of citric acid. Add the mixture to a planetary ball mill and grind at 400 r / min for 25 min to obtain a uniform and fine mixed powder. Transfer the ground mixed powder to a 50mL polytetrafluoroethylene-lined reactor, and gently shake the reactor to spread the powder evenly on the bottom of the inner lining. Seal and secure the reactor, place it in a constant temperature oven, and heat it to 200°C at a rate of 7°C / min. Maintain the temperature for 2 hours. After the reaction was completed, the oven was closed and allowed to cool naturally to room temperature. The reaction vessel was then removed, the inner liner was opened, and the gray solid product was collected to obtain crude Cu single-atom doped C3N4 material. The crude Cu single-atom-doped C3N4 material was dispersed in deionized water to prepare a dispersion with a concentration of 20 mg / mL. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 10000 Da. The dialysis bag was placed in 200 mL of deionized water and dialyzed at room temperature with magnetic stirring at 500 r / min for 24 h, during which the deionized water was replaced every 5 h. After dialysis, the dispersion in the bag was transferred to a petri dish and dried in a 90 °C oven to constant weight to obtain pure Cu single-atom-doped C3N4 material.

[0026] Example 5 Take 0.05g of citric acid and 0.08g of urea (molar ratio 1:3.6), add ferric sulfate (to provide Fe). 3+ ), Fe 3+ The dosage is 20% based on the mass of citric acid. Add it to the agate mortar and grind manually for 30 minutes to obtain a uniform and fine mixed powder. Transfer the ground mixed powder to a 50mL polytetrafluoroethylene-lined reactor, and gently shake the reactor to spread the powder evenly on the bottom of the inner lining. Seal and secure the reactor, place it in a constant temperature oven, and heat it to 160°C at a rate of 6°C / min. Maintain the temperature for 5 hours. After the reaction was completed, the oven was closed and allowed to cool naturally to room temperature. The reaction vessel was then removed, the liner was opened, and the gray solid product was collected to obtain crude Fe single-atom doped C3N4 material. The crude Fe single-atom-doped C3N4 material was dispersed in deionized water to prepare a dispersion with a concentration of 5 mg / mL. The dispersion was then transferred to a dialysis bag with a molecular weight cutoff of 3500 Da. The dialysis bag was placed in 200 mL of deionized water and purified by magnetic stirring at 300 r / min at room temperature for 8 h, with the deionized water being replaced every 4 h. After dialysis, the dispersion in the bag was transferred to a petri dish and dried in a 50 °C oven to constant weight to obtain pure Fe single-atom-doped C3N4 material.

[0027] Experimental Example 1 The experimental process for the catalytic properties of the single-atom C3N4 nanomaterial synthesized in Example 1 of this invention is as follows: Cyclic voltammetry (CV) measurements were performed on bare glassy carbon (GC) electrodes, pristine C3N4-modified electrodes, and Fe-C3N4-modified electrodes in pH 7.4 phosphate buffer (PBS) containing 1 mM Na2S (as an H2S donor) or without sodium sulfide, with a measurement potential window of -0.8 to 1.0 V (relative to Ag / AgCl) and a scan rate of 0.5 V·s⁻¹.

[0028] The results are as follows Figure 4 As shown, by Figure 4 It can be seen that, across the entire potential range, the bare GC electrode exhibits only a characteristic background current, indicating that its electrocatalytic activity for sulfide oxidation is negligible. Similarly, the electrode modified with the original C3N4 electrode shows only a slight increase in background current and no obvious redox characteristics, indicating that its adsorption and electrochemical activation capabilities for sulfides are limited. In contrast, the Fe-C3N4 electrode containing atomically dispersed iron sites shows a distinct anodic peak at approximately 0.018 V, and its oxidation current is much higher than that of the original C3N4. This behavior indicates that the introduction of single-atom iron centers significantly enhances sulfide oxidation.

[0029] Experimental Example 2 The water solubility experiment of the single-atom C3N4 nanomaterial synthesized in Example 1 of this invention is as follows: Accurately weigh 0.001 g of g-C3N4 powder and 0.001 g of Fe-C3N4 powder into two clean 10 mL centrifuge tubes. Add 1 mL of ultrapure water to each centrifuge tube to bring the final concentration of both samples to 1 mg / mL. Then, vortex the two centrifuge tubes at a frequency of 3000 r / min for 5 min to ensure that the samples are in full contact with the ultrapure water. After vortexing, place the two centrifuge tubes in a room temperature environment of 25 ℃ and observe and record the dissolution state and appearance changes of the two samples in ultrapure water. At the same time, take pictures to record the characterization data.

[0030] The results are as follows Figure 5 As shown in the figure, after static observation, the g-C3N4 sample exhibited obvious particulate matter in ultrapure water, with a large number of solid particles suspended in the solution and failing to dissolve effectively, resulting in an overall turbid solution. After standing for a period of time, the particles showed slight sedimentation. In contrast, the Fe-C3N4 sample, when mixed with ultrapure water, produced a clear and transparent solution with no obvious solid particle residue. No suspended matter or sedimentation was observed, indicating that Fe-C3N4 has superior dispersibility and solubility in ultrapure water. This difference may be related to the alteration of the surface electronic structure and hydrophilicity / hydrophobicity of C3N4 after Fe atom doping.

[0031] Experimental Example 3 A three-electrode system consisting of a Fe-C3N4 modified working electrode, a reference electrode, and a counter electrode was immersed in an electrochemical cell containing PBS buffer. A constant stirring rate was set, and a current-time (it) response test program was started using an electrochemical workstation to continuously record the current signal until the baseline reached a stable state (without significant drift) to eliminate background interference. Then, H2S was continuously introduced into the stabilized electrochemical system, and the dynamic changes in the current signal were recorded in real time.

[0032] The results are as follows Figure 6 As shown, when the Na₂S concentration gradually increases from 0.25 ppb, the current signal increases in a stepwise manner. The current at each concentration level remains stable, and the step height is consistent and repeatable, proving that under the selected operating conditions, the electrode's electrochemical response to sulfides is stable and controllable. The magnified image of the low-concentration region shows that after consecutively adding 0.01 ppb, 0.01 ppb, and 0.05 ppb of Na₂S, a clear and repeatable current increment is produced. The response deviation between two 0.01 ppb concentrations is less than 5%, indicating that the electrode has excellent response repeatability at sub-ppb levels, demonstrating superior ultra-low concentration detection capability. Experiment Example 4 The Fe-C3N4 modified working electrode was immersed in an electrochemical cell containing PBS buffer and equilibrated under stirring conditions, while continuously recording the current-time (it) response. After the baseline stabilized, the tissue homogenate supernatant was added and thoroughly mixed. Each group was measured in triplicate to ensure reproducibility. Under the same conditions, a homogenate prepared from muscle tissue of healthy mice was used as a blank control.

[0033] The results are as follows Figure 7 As shown, normal tissue homogenates produced a measurable amperometric response, indicating the presence of physiological levels of endogenous H2S. In contrast, tissue samples derived from bone metastases generally exhibited a higher current response, consistent with the trend of increased H2S levels. Clear and reproducible differences in electrochemical signals were observed between normal and metastatic tissues, demonstrating that even in complex biological matrices, the Fe-C3N4 modified electrode can resolve relative changes in H2S levels and distinguish between physiological and pathological states.

[0034] The foregoing has only described in detail the preferred embodiments of the present invention, but the scope of protection of the present invention is not limited to the above embodiments. Within the scope of conventional knowledge of those skilled in the art, various modifications and adjustments can be made as long as they do not depart from the core spirit of the present invention, and all such changes should be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing single-atom-doped C3N4 quantum dots with high catalytic activity and water solubility, characterized in that: Includes the following steps: S1. Weigh out citric acid and urea in proportion and grind them evenly in a clean agate mortar. S2. Add metal ion salt to the mixture of S1 and continue grinding to disperse it evenly to obtain a mixture; S3. Transfer the uniformly ground mixture to a sealed reaction vessel and place it in an oven for heating and reaction; S4. After the reaction is complete, the product is taken out and cooled to room temperature to obtain crude metal single-atom-C3N4 nanomaterials. S5. The crude Fe single-atom doped C3N4 material was dispersed in deionized water to prepare a dispersion, which was then transferred to a dialysis bag. The dialysis bag was placed in deionized water and magnetically stirred at room temperature for dialysis purification, during which the deionized water was replaced several times. After dialysis, the dispersion in the bag was transferred to a petri dish and dried to constant weight to obtain pure single-atom doped C3N4 material.

2. The method for synthesizing single-atom-doped C3N4 quantum dots with high catalytic activity and water solubility according to claim 1, characterized in that: In S1, the molar ratio of citric acid to urea is 1:3.6-5.

5.

3. The method for synthesizing single-atom-doped C3N4 quantum dots with high catalytic activity and water solubility according to claim 1, characterized in that: In S2, the metal ion salt includes Fe 3+ Fe 2+ Co 2+ Cu 2+ and Ni 2+ At least one of the following salts.

4. The method for synthesizing single-atom-doped C3N4 quantum dots with high catalytic activity and water solubility according to claim 1, characterized in that: In S3, the heating rate is 5-10℃ / min, the heating temperature is 160-200℃, and the heating reaction time is 2-5h.

5. The method for synthesizing single-atom-doped C3N4 quantum dots with high catalytic activity and water solubility according to claim 1, characterized in that: In S4, the metal single atom-C3N4 nanomaterial contains metal that exists stably in the form of M-N2 or M-N4, where M represents a metal single atom.

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