Polyoxometalate composite n-doped carbon quantum dots and preparation method and application thereof
By synthesizing N-doped carbon quantum dots and polyoxometalates via a hydrothermal method, the problems of composite material stability and catalytic performance were solved, achieving efficient and stable photocatalytic performance suitable for large-scale applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA UNIVERSITY
- Filing Date
- 2026-04-30
- Publication Date
- 2026-05-29
Smart Images
Figure CN122098660A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of photocatalytic nanocomposite material preparation methods, specifically relating to a polyoxometalate composite N-doped carbon quantum dot, its preparation method, and its application. Background Technology
[0002] Photocatalysis is one of the core technologies for solving the energy crisis and environmental pollution problems. Its core lies in developing efficient, stable, and low-cost photocatalytic materials. Nitrogen-doped carbon quantum dots, as novel carbon-based nanomaterials, possess advantages such as high electron mobility, low toxicity, and easy surface functionalization, making them suitable as electron transfer media and photosensitizers in photocatalytic systems. However, single-doped carbon quantum dots suffer from insufficient catalytic active sites and limited redox capabilities, restricting their application in deep catalytic reactions.
[0003] Polyoxometalates (POMs) are a class of metal-oxygen cluster compounds with well-defined structures, rich in redox active sites, and capable of efficiently catalyzing reactions such as CO2 reduction and water splitting. However, pure POMs have small specific surface areas, are prone to aggregation, and have narrow light absorption ranges, resulting in low catalytic efficiency and stability when used alone. Combining POMs with N-doped carbon quantum dots can achieve synergistic performance improvements, enhancing the light absorption capacity, electron separation efficiency, and catalytic activity of the composite material, representing an effective approach to optimizing the performance of photocatalytic materials.
[0004] Currently, there are few methods for combining polyoxometalates with N-doped carbon quantum dots. Some methods suffer from weak bonding, loose interfacial contact, and easy agglomeration, resulting in poor composite material stability and rapid catalytic performance degradation. Other methods involve harsh reaction conditions, cumbersome steps, and high costs, making them difficult to scale up for application. Therefore, developing a simple, tightly bonded, and high-performance method for preparing polyoxometalate composites with N-doped carbon quantum dots has become an urgent technical problem to be solved. Summary of the Invention
[0005] In order to solve the problems mentioned in the background art, the purpose of this invention is to provide a polyoxometalate composite N-doped carbon quantum dot, its preparation method and application.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On one hand, the present invention provides a method for preparing polyoxometalate composite N-doped carbon quantum dots, comprising the following steps:
[0007] (1) Mix molybdate and water evenly to obtain an aqueous solution of molybdate; mix transition metal salt, hydrogen peroxide solution and water evenly to obtain a mixed solution; heat the aqueous solution of molybdate to boiling, and then add the mixed solution to the boiling aqueous solution of molybdate, and filter while hot to obtain a hot solution of polyoxometalate precursor;
[0008] (2) Mix and stir the hot solution of the polyoxometalate precursor and the aqueous solution of N-doped carbon quantum dots in step (1) to obtain a suspension; cool the suspension to room temperature and let it stand to obtain the composite crude product;
[0009] (3) Discard the supernatant of the composite crude product in step (2) to obtain a precipitate, wash and dry the precipitate to obtain the polyoxometalate composite N-doped carbon quantum dots.
[0010] Furthermore, the preparation method of the N-doped carbon quantum dots includes the following steps:
[0011] The carbon source, nitrogen-containing compound, and water are mixed thoroughly to obtain a mixed solution;
[0012] The mixed solution was subjected to a hydrothermal reaction. After the hydrothermal reaction was completed, it was cooled to room temperature, the pH was adjusted to 7, the supernatant was collected by centrifugation, and then the supernatant was filtered through a filter membrane, dialyzed, and freeze-dried to obtain N-doped carbon quantum dots.
[0013] Furthermore, the carbon source is selected from at least one of citric acid and glucose; citric acid and glucose are widely available and environmentally friendly carbon sources that can be efficiently converted into carbon quantum dots.
[0014] And / or, the nitrogen-containing compound is selected from at least one of urea and melamine; using urea or melamine as nitrogen-containing compounds results in high nitrogen doping efficiency, which can significantly improve the electron transfer capability and light absorption performance of carbon quantum dots;
[0015] And / or, the mass ratio of the carbon source to the nitrogen-containing compound is 3.46:3.24;
[0016] And / or, the temperature of the hydrothermal reaction is 160~220℃, and the time of the hydrothermal reaction is 6~12h;
[0017] And / or, the centrifugation speed is 8000~11000 r / min, and the centrifugation time is 10~20 min;
[0018] And / or, the pore size of the filter membrane is 0.22 μm;
[0019] And / or, the dialysis is performed using a dialysis bag with a molecular weight cutoff of 500-1000 Da, and the dialysis time is 24-48 hours;
[0020] And / or, the dialysis is performed in deionized water, with the deionized water being changed every 6-8 hours;
[0021] And / or, the freeze-drying temperature is -50 to -80°C, the freeze-drying vacuum degree is 10 to 30 Pa, and the freeze-drying time is 24 to 48 hours.
[0022] Furthermore, the reagent used to adjust the pH to 7 is 1 mol / L dilute hydrochloric acid.
[0023] Furthermore, the particle size of the N-doped carbon quantum dots is 2~10 nm.
[0024] Furthermore, the transition metal salt mentioned in step (1) is selected from at least one of cobalt sulfate heptahydrate and cobalt nitrate; the transition metal salt forms a stable metal-oxygen cluster structure with molybdate, giving the composite material excellent redox catalytic performance;
[0025] And / or, the molybdate mentioned in step (1) is selected from ammonium molybdate tetrahydrate; ammonium molybdate tetrahydrate has abundant active sites and good chemical stability;
[0026] And / or, the concentration of the hydrogen peroxide solution in step (1) is 10 wt%;
[0027] And / or, the mass ratio of molybdate, transition metal salt and hydrogen peroxide solution in step (1) is 30.9:4.2:4.4.
[0028] Further, in step (1), the ratio of molybdate to water in the molybdate aqueous solution is 30.9 g: 260 mL;
[0029] And / or, the ratio of transition metal salt, hydrogen peroxide solution and water in the mixed solution described in step (1) is 4.2g:4.4g:40mL.
[0030] Further, in step (2), the volume-to-mass ratio of N-doped carbon quantum dots in the polyoxometalate precursor hot solution and the N-doped carbon quantum dot aqueous solution is (1000~3000mL):1g;
[0031] And / or, the stirring time in step (2) is 10~15min, and the stirring speed is 100~2000r / min;
[0032] And / or, the settling time described in step (2) is 1 to 3 days.
[0033] Furthermore, the washing described in step (3) involves washing with deionized water 3 to 5 times;
[0034] And / or, the drying temperature in step (3) is 60°C and the drying time is 12~24h.
[0035] On the other hand, the present invention provides a polyoxometalate composite N-doped carbon quantum dot, which is prepared by any of the preparation methods described above.
[0036] On the other hand, the present invention provides an application of the above-described polyoxometalate composite N-doped carbon quantum dots in the photocatalytic carbon dioxide reduction reaction.
[0037] Furthermore, the polyoxometalate composite N-doped carbon quantum dots are combined with photosensitizer, acetonitrile, triethanolamine and deionized water to form a reaction system, which is then contacted with carbon dioxide under visible or ultraviolet light irradiation, with a reaction temperature of 15~25℃ and a reaction time of 1~4h.
[0038] Furthermore, the photosensitizer is tris(2,2′-bipyridine)ruthenium chloride, hexahydrate.
[0039] Furthermore, the ratio of the polyoxometalate composite N-doped carbon quantum dots, photosensitizer, acetonitrile, triethanolamine and deionized water is 1 mg: 8 mg: 8 mL: 2 mL: 2 mL.
[0040] Compared with the prior art, the present invention has the following beneficial effects:
[0041] (1) The present invention uses a hydrothermal method to synthesize N-doped carbon quantum dots in one step, and combines a stirring and static synergistic assembly process to achieve a close combination of polyoxometalates and N-doped carbon quantum dots. By adjusting the ratio of reactants, the structure and properties of the composite material can be precisely controlled.
[0042] (2) In the preparation of N-doped carbon quantum dots, the pH of the system is controlled to 7 to enable the polyoxometalate precursor to form a matching charge characteristic with the surface of N-doped carbon quantum dots. The surface of N-doped carbon quantum dots is rich in polar functional groups such as amino and hydroxyl groups. At this pH, they can form electrostatic interactions and hydrogen bonds with polyoxometalates (metal-oxygen cluster anions). At the same time, transition metal ions can coordinate with oxygen-containing functional groups on the surface of carbon quantum dots to form a stable interfacial bonding structure, avoiding the separation and shedding of components after recombination.
[0043] (3) The structure of the polyoxometalate composite N-doped carbon quantum dots of the present invention does not change before and after the photocatalytic reaction, and has excellent stability.
[0044] (4) The preparation method of the present invention is simple, convenient to operate, green and environmentally friendly. It does not require the use of toxic organic solvents, the raw material cost is low, and it is suitable for large-scale production.
[0045] (5) The N-doped carbon quantum dots prepared by the hydrothermal method of the present invention have a particle size controlled at 2~10 nm, and the nanoscale size has excellent dispersion stability. The polyoxometalate composite N-doped carbon quantum dots of the present invention do not agglomerate.
[0046] (6) In the preparation of N-doped carbon quantum dots in this invention, centrifugation, membrane filtration and dialysis are used to remove free unreacted impurities. Freeze drying is used to avoid particle agglomeration during the drying process. After the pure N-doped carbon quantum dots are prepared and combined with polyoxometalates, the resulting polyoxometalate composite N-doped carbon quantum dots can be stably dispersed in aqueous solution without obvious sedimentation or stratification, indicating that they have good dispersibility.
[0047] (7) The polyoxometalate composite N-doped carbon quantum dots of the present invention combine the spectral absorption characteristics of N-doped carbon quantum dots with the high catalytic activity sites of polyoxometalates, effectively promoting the separation and transport of photogenerated electron-hole pairs, inhibiting carrier recombination, and significantly enhancing photocatalytic performance; it can be used in the field of photocatalytic carbon dioxide reduction, with good market application prospects and economic value. In the photocatalytic carbon dioxide reduction reaction, the yield ratio of syngas CO and H2 in the carbon dioxide reduction products is 1.3:1, and the yield is >40000 μmol·g -1 ·h -1 . Attached Figure Description
[0048] Figure 1 The infrared spectra of the N-doped carbon quantum dots prepared in Example 1 of the present invention, the N-doped carbon quantum dots of the polyoxometalate composite prepared in Example 1, and the polyoxometalate prepared in Comparative Example 1 are shown.
[0049] Figure 2 X-ray diffraction patterns of N-doped carbon quantum dots prepared in Example 1 of the present invention, N-doped carbon quantum dots of polyoxometalate composite prepared in Example 1, and polyoxometalate prepared in Comparative Example 1.
[0050] Figure 3 The image shows the elemental surface scan of the polyoxometalate composite N-doped carbon quantum dots prepared in Example 1 of this invention.
[0051] Figure 4 This is a transmission electron microscope image of the polyoxometalate composite N-doped carbon quantum dots prepared in Example 1 of the present invention. The yellow circles in the image indicate the N-doped carbon quantum dots.
[0052] Figure 5 The graph shows the performance test results of the N-doped carbon quantum dots prepared in Example 1 of the present invention, the N-doped carbon quantum dots of the polyoxometalate composite prepared in Example 1, and the polyoxometalate prepared in Comparative Example 1 in the photocatalytic carbon dioxide reduction reaction.
[0053] Figure 6 The infrared contrast spectra of the polyoxometalate composite N-doped carbon quantum dots prepared in Example 1 of this invention before and after photocatalytic reaction are shown. Detailed Implementation
[0054] To better understand the content of this invention, the following detailed description is provided in conjunction with specific implementation methods. However, the scope of protection of this invention is not limited to the following embodiments.
[0055] Example 1
[0056] Preparation of N-doped carbon quantum dots: 3.46 g of citric acid and 3.24 g of urea were dissolved in 30 mL of deionized water and stirred at 800 r / min for 30 min until a homogeneous solution was formed. The solution was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and hydrothermally reacted at 180 °C for 8 h. After the hydrothermal reaction, the solution was allowed to cool naturally to room temperature. The pH was adjusted to 7 using 1 mol / L dilute hydrochloric acid. The supernatant was collected by centrifugation at 10000 r / min for 10 min. The supernatant was then filtered through a 0.22 μm filter membrane to remove impurities. The filtrate was transferred to a dialysis bag with a molecular weight cutoff of 500 Da and dialyzed in deionized water for 24 h, with the deionized water being replaced every 8 h. After dialysis, the solution was freeze-dried at -60 °C and a vacuum of 20 Pa for 24 h to obtain N-doped carbon quantum dots (NCQDs) with a particle size distribution of 2–10 nm.
[0057] Preparation of polyoxometalate composite N-doped carbon quantum dots:
[0058] (1) Mix 30.9g of ammonium molybdate tetrahydrate and 260mL of water to obtain an aqueous solution of ammonium molybdate tetrahydrate; mix 4.2g of cobalt sulfate heptahydrate, 4.4g of hydrogen peroxide solution (concentration of 10wt%) and 40mL of water to obtain a mixed solution; heat the aqueous solution of ammonium molybdate tetrahydrate to boiling, and then add the mixed solution to the boiling aqueous solution of ammonium molybdate tetrahydrate. After the addition is completed, filter while hot to obtain a hot solution of polyoxometalate precursor.
[0059] (2) Mix 300 mL of polyoxometalate precursor hot solution and N-doped carbon quantum dot aqueous solution (the N-doped carbon quantum dot aqueous solution contains 0.1 g N-doped carbon quantum dots), stir at 800 r / min for 10 min until a uniform suspension is formed, cool naturally to room temperature, and let stand for 2 days to obtain the composite crude product.
[0060] (3) The supernatant of the composite crude product was discarded to obtain a precipitate. The precipitate was washed three times with deionized water and then placed in an oven and dried at 60°C for 24 hours to obtain polyoxometalate composite N-doped carbon quantum dots (denoted as Anderson Co / NCQDs).
[0061] Comparative Example 1
[0062] Preparation of polyoxometalates:
[0063] 30.9 g of ammonium molybdate tetrahydrate and 260 mL of water were mixed evenly to obtain an aqueous solution of ammonium molybdate tetrahydrate. 4.2 g of cobalt sulfate heptahydrate, 4.4 g of hydrogen peroxide solution (concentration 10 wt%) and 40 mL of water were mixed evenly to obtain a mixed solution. The aqueous solution of ammonium molybdate tetrahydrate was heated to boiling, and then the mixed solution was added to the boiling aqueous solution of ammonium molybdate tetrahydrate. After the addition was completed, the solution was filtered while hot and cooled to room temperature to obtain a polyoxometalate solution. After standing for 2 days, crystals were obtained. After filtration, the crystals were dried in an oven at 60 °C for 24 h to obtain the polyoxometalate (denoted as Anderson Co).
[0064] Adding 0.1 g of polyoxometalate-based N-doped carbon quantum dots to 5 mL of deionized water and sonicating for 1 min revealed good monodispersity of the polyoxometalate-based N-doped carbon quantum dots in the deionized water. After standing, the system remained homogeneous and stable, exhibiting no visible sedimentation, stratification, or phase separation, demonstrating excellent aqueous dispersion capabilities. The synergistic effect of the surface functionalized structure of the N-doped carbon quantum dots and the electrostatic properties of the polyoxometalate effectively reduces van der Waals attraction between particles, enhances the spatial stability of the system, and enables the composite material to maintain a homogeneous dispersion in the aqueous phase for a long period, laying a solid foundation for its application in aqueous systems.
[0065] Fourier transform infrared spectroscopy was performed on the N-doped carbon quantum dots (NCQDs) prepared in Example 1, the polyoxometalate composite N-doped carbon quantum dots (Anderson Co / NCQDs) prepared in Example 1, and the polyoxometalate (Anderson Co) prepared in Comparative Example 1. The results are as follows: Figure 1 As shown. From Figure 1 As can be seen from the results, the N-doped carbon quantum dots of the polyoxometalate composite prepared in Example 1 have obvious infrared characteristic peaks of N-doped carbon quantum dots and polyoxometalates, indicating that the N-doped carbon quantum dots were successfully combined with polyoxometalates.
[0066] The N-doped carbon quantum dots (NCQDs) prepared in Example 1, the polyoxometalate composite N-doped carbon quantum dots (Anderson Co / NCQDs) prepared in Example 1, and the polyoxometalate (Anderson Co) prepared in Comparative Example 1 were tested using X-ray diffraction. The results are as follows: Figure 2 As shown. From Figure 2 As can be seen from the data, the polyoxometalate composite N-doped carbon quantum dots prepared in Example 1 have obvious XRD characteristic peaks of N-doped carbon quantum dots and polyoxometalates, indicating that N-doped carbon quantum dots were successfully composited with polyoxometalates.
[0067] Scanning electron microscopy (SEM) mapping tests were performed on the polyoxometalate composite N-doped carbon quantum dots (denoted as Anderson Co / NCQDs) prepared in Example 1. The resulting elemental surface scans are shown below. Figure 3 As shown. From Figure 3 As can be seen, the elements in the polyoxometalate composite N-doped carbon quantum dots are evenly distributed.
[0068] The polyoxometalate composite N-doped carbon quantum dots (denoted as Anderson Co / NCQDs) prepared in Example 1 were tested using transmission electron microscopy, and the results are as follows: Figure 4 As shown in the figure, the yellow circles mark N-doped carbon quantum dots. From Figure 4 As can be seen, N-doped carbon quantum dots were successfully combined with polyoxometalates, and the N-doped carbon quantum dots were uniformly distributed.
[0069] The N-doped carbon quantum dot catalyst prepared in Example 1 (denoted as NCQDs), the polyoxometalate composite N-doped carbon quantum dot catalyst prepared in Example 1 (denoted as Anderson Co / NCQDs), and the polyoxometalate prepared in Comparative Example 1 (denoted as Anderson Co / NCQDs) were compared. The performance of the Co catalyst in the photocatalytic reduction of carbon dioxide was tested. The specific procedure was as follows: In an 80 mL covered quartz reactor, using an MC-PF30-1 xenon lamp (300W, wavelength range 320~780nm) as the light source, 1 mg of catalyst, 2 mL of deionized water, 8 mg of tris(2,2′-bipyridine)ruthenium chloride hexahydrate, 2 mL of triethanolamine, and 8 mL of acetonitrile were added to the quartz reactor. Before illumination, ultra-high purity carbon dioxide (99.999%) was introduced into the quartz reactor for 15 min to ensure saturation of the reaction system and to remove air. The temperature of the reaction system was maintained at 15℃ using circulating water. Carbon dioxide was introduced to maintain a standard atmospheric pressure inside the quartz reactor. The reaction was carried out under illumination for 1 h. The products were analyzed by gas chromatography (Agilent GC-8860), and the results are as follows: Figure 5 As shown. From Figure 5 As can be seen, under the same test conditions, the polyoxometalate composite N-doped carbon quantum dots exhibit superior photocatalytic performance in reducing carbon dioxide to syngas (CO and H2). In the photocatalytic carbon dioxide reduction reaction, the yield ratio of syngas (CO) to H2 in the carbon dioxide reduction products is 1.3:1, and the yield is >40000 μmol·g. -1 ·h -1 .
[0070] After the photocatalytic carbon dioxide reduction reaction, centrifugation was performed at 10000 r / min for 10 min. The precipitate was collected, and this process was repeated three times. The precipitate was then washed three times alternately with deionized water and anhydrous ethanol, and finally dried in a vacuum oven at 60℃ for 12 h to obtain the reacted polyoxometalate composite N-doped carbon quantum dots. Fourier transform infrared spectroscopy was performed on both the reacted and unreacted polyoxometalate composite N-doped carbon quantum dots, and the results are shown below. Figure 6 As shown. From Figure 6 As can be seen, the structure of the polyoxometalate composite N-doped carbon quantum dots did not change before and after the reaction, indicating that the polyoxometalate composite N-doped carbon quantum dots have excellent stability.
[0071] The above description is only a specific embodiment of the present invention and not all embodiments. Any equivalent modifications made by those skilled in the art to the technical solutions of the present invention by reading the present invention specification are covered by the claims of the present invention.
Claims
1. A method for preparing N-doped carbon quantum dots from polyoxometalate composites, characterized in that, Includes the following steps: (1) Mix molybdate and water evenly to obtain an aqueous solution of molybdate; mix transition metal salt, hydrogen peroxide solution and water evenly to obtain a mixed solution; heat the aqueous solution of molybdate to boiling, and then add the mixed solution to the boiling aqueous solution of molybdate, and filter while hot to obtain a hot solution of polyoxometalate precursor; (2) Mix and stir the hot solution of the polyoxometalate precursor and the aqueous solution of N-doped carbon quantum dots in step (1) to obtain a suspension; cool the suspension to room temperature and let it stand to obtain the composite crude product; (3) Discard the supernatant of the composite crude product in step (2) to obtain a precipitate, wash and dry the precipitate to obtain the polyoxometalate composite N-doped carbon quantum dots.
2. The preparation method according to claim 1, characterized in that, The method for preparing the N-doped carbon quantum dots includes the following steps: The carbon source, nitrogen-containing compound, and water are mixed thoroughly to obtain a mixed solution; The mixed solution was subjected to a hydrothermal reaction. After the hydrothermal reaction was completed, it was cooled to room temperature, the pH was adjusted to 7, the supernatant was collected by centrifugation, and then the supernatant was filtered through a filter membrane, dialyzed, and freeze-dried to obtain N-doped carbon quantum dots.
3. The preparation method according to claim 2, characterized in that, The carbon source is selected from at least one of citric acid and glucose; And / or, the nitrogen-containing compound is selected from at least one of urea and melamine; And / or, the mass ratio of the carbon source to the nitrogen-containing compound is 3.46:3.24; And / or, the temperature of the hydrothermal reaction is 160~220℃, and the time of the hydrothermal reaction is 6~12h; And / or, the centrifugation speed is 8000~11000 r / min, and the centrifugation time is 10~20 min; And / or, the pore size of the filter membrane is 0.22 μm; And / or, the dialysis is performed using a dialysis bag with a molecular weight cutoff of 500-1000 Da, and the dialysis time is 24-48 hours; And / or, the freeze-drying temperature is -50 to -80°C, the freeze-drying vacuum degree is 10 to 30 Pa, and the freeze-drying time is 24 to 48 hours.
4. The preparation method according to claim 2, characterized in that, The particle size of the N-doped carbon quantum dots is 2~10 nm.
5. The preparation method according to claim 1, characterized in that, The transition metal salt mentioned in step (1) is selected from at least one of cobalt sulfate heptahydrate and cobalt nitrate; And / or, the molybdate described in step (1) is selected from ammonium molybdate tetrahydrate; And / or, the concentration of the hydrogen peroxide solution in step (1) is 10 wt%; And / or, the mass ratio of molybdate, transition metal salt and hydrogen peroxide solution in step (1) is 30.9:4.2:4.
4.
6. The preparation method according to claim 1, characterized in that, The volume-to-mass ratio of the N-doped carbon quantum dots in the polyoxometalate precursor hot solution and the N-doped carbon quantum dot aqueous solution in step (2) is (1000~3000mL):1g; And / or, the stirring time in step (2) is 10~15min, and the stirring speed is 100~2000r / min; And / or, the settling time described in step (2) is 1 to 3 days.
7. The preparation method according to claim 1, characterized in that, The washing described in step (3) involves washing with deionized water 3 to 5 times; And / or, the drying temperature in step (3) is 60°C and the drying time is 12~24h.
8. A polyoxometalate composite N-doped carbon quantum dot, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 7.
9. The application of the polyoxometalate composite N-doped carbon quantum dots according to claim 8 in the photocatalytic carbon dioxide reduction reaction.
10. The application according to claim 9, characterized in that, The polyoxometalate composite N-doped carbon quantum dots, photosensitizer, acetonitrile, triethanolamine and deionized water form a reaction system. The system is then exposed to carbon dioxide under visible or ultraviolet light irradiation at a temperature of 15-25°C for 1-4 hours.