Preparation method and application of SiO2-loaded carbon quantum dot-doped delta-MnO2 nanoflower catalyst

Abstract

The invention discloses a preparation method and application of a SiO2-loaded carbon quantum dot-doped delta-MnO2 nanoflower catalyst, and belongs to the field of preparation of advanced oxidation catalysts. The delta-MnO2 nanoflower structure doped with the carbon quantum dots is synthesized in situ on the surface of the SiO2 carrier rich in Si-OH groups,-OH with lone pair electrons can easily form hydrogen bonds with nitrogen atoms, oxygen atoms or sulfur atoms in antibiotic molecules, and the adsorption capacity is improved. Carbon quantum dots are added to regulate and control the morphology and the structure of the catalyst, a delta-MnO2 nanoflower structure which preferentially grows along crystal faces (111), (201) and (020) and is controllable in size is prepared, then the specific surface area of the catalyst is increased, more surface active sites can be exposed, and the catalyst is used for activating PMS to degrade antibiotics and shows excellent catalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of advanced oxidation catalyst preparation, specifically relating to a method for preparing and applying a SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst. Background Technology

[0002] Antibiotics are widely used in the pharmaceutical and aquaculture industries due to their excellent antibacterial properties. In recent years, large quantities of antibiotic-treated wastewater from hospitals, livestock farms, and aquaculture have been discharged into natural water bodies, causing severe water pollution and accelerating the emergence of drug-resistant bacteria, posing a threat to human health. Therefore, the development of efficient new technologies for treating antibiotic wastewater is urgently needed.

[0003] Advanced oxidation technologies based on persulfate (PMS) degrade and mineralize organic pollutants by activating PMS to generate highly oxidizing sulfate radicals (SO₄•–). These technologies offer advantages such as mild reaction conditions, strong oxidizing power, and environmental friendliness, making them a promising approach. Transition metals are preferred catalytic materials for activating PMS because they can provide electrons to activate the SO bonds in PMS and accelerate their breakage to generate free radicals. Among these, MnO₂, with its abundant reserves, low cost, and environmental friendliness, shows great promise in catalysis. Of the various MnO₂ crystal forms, δ-MnO₂ possesses a two-dimensional layered structure, providing a large specific surface area and abundant active sites during catalytic reactions, which is beneficial for reactant adsorption and reaction. Carbon quantum dots (CQDs) are zero-dimensional carbon-based nanomaterials with a particle size of less than 10 nanometers. Their surfaces are rich in functional groups such as hydroxyl and carboxyl groups, demonstrating unique potential in the preparation of high-performance catalysts. To meet the complex environmental requirements of practical applications, doping carbon quantum dots into δ-MnO2 is expected to yield a highly efficient catalyst for activating PMS to degrade antibiotics. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying a SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst, in order to solve the problems existing in the prior art.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The first technical objective of this invention is to provide a method for preparing a SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst, comprising the following steps:

[0007] S1. Dissolve citric acid in deionized water and sonicate for 10 min to disperse it evenly. Then place it in a reaction vessel for hydrothermal reaction. After the reaction is completed, cool to room temperature, filter with a filter membrane, and take the filtrate to obtain a carbon quantum dot (CQDs) solution.

[0008] S2. A certain volume of tetraethyl orthosilicate was added to anhydrous ethanol and ultrasonically dispersed for 10 min. NaOH solution was slowly added dropwise and stirred continuously for 4 h. The solid product was then separated by centrifugation, washed with water until neutral, and dried under vacuum to obtain SiO2.

[0009] S3. Dissolve KMnO4 in deionized water, add SiO2 and disperse by ultrasonication to obtain SiO2 dispersion;

[0010] S4. Add the CQDs solution prepared in step S1 to the SiO2 dispersion and stir until homogeneous. Then add MnSO4 solution dropwise and stir for 30 min to obtain a mixed solution.

[0011] S5. The mixed solution obtained in step S4 is transferred to a hydrothermal reactor for reaction. After the reaction is completed, it is cooled to room temperature, and the solid product is separated by centrifugation. After washing with water, washing with alcohol and drying, SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst is obtained.

[0012] Preferably, in step S1, the concentration of the citric acid aqueous solution is 1.0~3.0 mol / L, and the reaction temperature is 180~220°C. o C, the reaction time is 4~8h.

[0013] Preferably, in step S3, the concentration of KMnO4 is 0.015~0.030 mol / L, the mass ratio of KMnO4 to SiO2 is (4~9):1, and the stirring time is 30 min.

[0014] Preferably, in step S4, the mass ratio of KMnO4 to MnSO4 is (3.5~5.5):1, and the volume-mass ratio of CQDs solution to KMnO4 is (0.25~0.65) mL:1g.

[0015] Preferably, the hydrothermal reaction temperature in step S5 is 120~150°C. o C, the reaction time is 4~8h.

[0016] Preferably, the SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst has a δ-MnO2 nanoflower size of 100~300nm and a carbon quantum dot size of 5~8nm.

[0017] The second technical objective of this invention is to provide an application of a SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst.

[0018] Preferably, the SiO2-supported doped carbon quantum dot δ-MnO2 nanoflower catalyst is used in the activation of PMS to degrade antibiotic wastewater.

[0019] Preferably, the antibiotic is a quinolone, macrolide, sulfonamide, or tetracycline.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0021] (1) By adding carbon quantum dots to regulate the morphology of the catalyst, more dispersed δ-MnO2 nanoflowers are obtained, thereby increasing the specific surface area of ​​the catalyst and exposing more surface active sites.

[0022] (2) By adding carbon quantum dots to regulate the structure of the catalyst, δ-MnO2 structures that preferentially grow along the (111), (201) and (020) crystal planes were prepared, which significantly improved the PMS activation ability.

[0023] (3) δ-MnO2 nanoflower structures doped with carbon quantum dots were synthesized in situ on the surface of SiO2 support rich in Si-OH groups. The –OH with lone pair electrons is easy to form hydrogen bonds with nitrogen, oxygen or sulfur atoms in antibiotic molecules, thus improving adsorption capacity. Attached Figure Description

[0024] Figure 1 This is a SEM image of CQDs@δ-MnO2 / SiO2-1 obtained in Example 1 of this invention.

[0025] Figure 2 This is a SEM image of δ-MnO2 / SiO2 prepared in Comparative Example 1 of this invention.

[0026] Figure 3 This is the nitrogen adsorption-desorption curve and pore size distribution diagram of CQDs@δ-MnO2 / SiO2-1 prepared in Example 1 of the present invention.

[0027] Figure 4 This is the nitrogen adsorption-desorption curve and pore size distribution diagram of δ-MnO2 / SiO2 prepared in Comparative Example 1 of this invention.

[0028] Figure 5 This is a SEM image of CQDs@δ-MnO2 / SiO2-2 obtained in Example 2 of this invention.

[0029] Figure 6 This is the nitrogen adsorption-desorption curve and pore size distribution diagram of CQDs@δ-MnO2 / SiO2-2 prepared in Example 2 of the present invention.

[0030] Figure 7 This is a graph showing the performance of the catalysts prepared in Comparative Examples 1, 2, 1, and 2 of this invention in activating PMS to degrade levofloxacin.

[0031] Figure 8 This is a graph showing the performance of the catalysts prepared in Comparative Examples 3, 2, 3 and 4 of this invention in activating PMS to degrade levofloxacin.

[0032] Figure 9 This is a graph showing the performance of the catalysts prepared in Comparative Examples 1, Examples 1, 2, and 5 of this invention in activating PMS to degrade levofloxacin. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, the present invention is not limited to these embodiments.

[0034] Example 1

[0035] (1) Dissolve 10g of anhydrous citric acid in 25mL of deionized water, stir ultrasonically for 10min, then transfer the solution to a 50mL hydrothermal reactor and heat at 210°C. o The reaction was carried out at C for 5 hours; after natural cooling, the solution was filtered using a 0.45 μm aqueous filter membrane, and the filtrate was a solution rich in CQDs.

[0036] (2) Add 5 mL of tetraethyl orthosilicate to 40 mL of anhydrous ethanol and sonicate for 10 min; slowly add 8 mL of 0.1 mol / L NaOH solution and stir continuously for 4 h; centrifuge the obtained product, wash with water until neutral, and then... o SiO2 was obtained by vacuum drying at C.

[0037] (3) Weigh 0.286g of KMnO4 and dissolve it in 50mL of deionized water. Then add 0.07g of SiO2 and sonicate for 30min to disperse it.

[0038] (4) Add 37 μL of CQDs solution to the SiO2 dispersion while stirring. After stirring for 10 min, add 10 mL of MnSO4 solution with a concentration of 0.035 mol / L and continue stirring for 30 min to obtain a mixed solution.

[0039] (5) Transfer the mixed solution to an 80 mL PTFE-lined stainless steel high-pressure reactor and heat it at 140 °C. o Incubate at C for 6 hours, cool to room temperature, separate the product, wash twice with water and twice with ethanol, and then at 70°C. o The SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst was obtained by vacuum drying and denoted as CQDs@δ-MnO2 / SiO2-1.

[0040] Example 2

[0041] The only difference from Example 1 is that 150 μL of CQDs solution is added in step (4), and the resulting catalyst is denoted as CQDs@δ-MnO2 / SiO2-2.

[0042] Example 3

[0043] The only difference from Example 1 is that 0.023 g of SiO2 is added in step (3) and 150 μL of CQDs solution is added in step (4). The catalyst obtained is denoted as CQDs@δ-MnO2 / SiO2-3.

[0044] Example 4

[0045] The only difference from Example 1 is that 0.15g of SiO2 is added in step (3) and 150μL of CQDs solution is added in step (4). The catalyst obtained is denoted as CQDs@δ-MnO2 / SiO2-4.

[0046] Example 5

[0047] The only difference from Example 1 is that 75 μL of CQDs solution was added in step (4), and the resulting catalyst was denoted as CQDs@δ-MnO2 / SiO2-5.

[0048] Comparative Example 1

[0049] The only difference from Example 1 is that CQDs solution is not added in step (4), and the resulting catalyst is denoted as δ-MnO2 / SiO2.

[0050] Comparative Example 2

[0051] (1) Weigh 0.286g of KMnO4 and add it to 50mL of deionized water to dissolve. After stirring for 10min, add 10mL of MnSO4 solution with a concentration of 0.035mol / L and continue stirring for 30min to obtain a mixed solution.

[0052] (2) Transfer the mixed solution to an 80 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, and heat at 140 °C. o Incubate at C for 6 hours, cool to room temperature, separate the product, wash twice with water and twice with ethanol, and then at 70°C. o Vacuum drying yielded δ-MnO2 nanoflower catalyst, denoted as δ-MnO2.

[0053] Comparative Example 3

[0054] The only difference from Example 1 is that SiO2 is not added in step (3), and the resulting catalyst is denoted as CQDs@δ-MnO2.

[0055] SEM images of CQDs@δ-MnO2 / SiO2-1 prepared in Example 1 and δ-MnO2 / SiO2 prepared in Comparative Example 1 are shown below. Figure 1 and Figure 2 As shown. By Figure 2 It can be seen that δ-MnO2 exhibits a flower-like structure formed by the assembly of nanosheets, with a diameter of 300-400 nm. Figure 1 It can be seen that the CQDs@δ-MnO2 / SiO2-1 catalyst prepared by adding carbon quantum dot solution still maintains the nanoflower structure, but the original tight cluster structure is more dispersed, and the nanoflower size is reduced to 200~300nm.

[0056] The nitrogen adsorption-desorption curves and pore size distributions of CQDs@δ-MnO2 / SiO2-1 prepared in Example 1 and δ-MnO2 / SiO2 prepared in Comparative Example 1 are shown below. Figure 3 and Figure 4 As shown, the specific surface area of ​​the δ-MnO2 / SiO2 catalyst is 44.5 m². 2 / g, while the specific surface area of ​​CQDs@δ-MnO2 / SiO2 is 82.5 m². 2 / g indicates that the addition of carbon quantum dots can significantly increase the specific surface area of ​​the catalyst.

[0057] from Figure 5 It can be seen that with the increase of carbon quantum dot dosage, the size of δ-MnO2 nanoflowers in the CQDs@δ-MnO2 / SiO2-2 catalyst further decreases to 100~200 nm. From... Figure 5 It can be seen that its specific surface area further increased to 171.5 m². 2 / g.

[0058] Application Example 1

[0059] The catalysts prepared in Examples 1, 2, Comparative Example 1, and Comparative Example 2 were tested for their performance in degrading levofloxacin-containing organic wastewater using activated PMS. The specific reaction conditions were as follows: 7.5 mg of catalyst was added to 40 mL of a 20 mg / L levofloxacin solution. After ultrasonication to ensure uniform dispersion, a magnetic stirrer was added at a stirring rate of 300 r / min. The mixture was first stirred for 20 min without PMS to reach adsorption-desorption equilibrium, and then 200 μL of a 0.1 mol / L PMS solution was added to initiate the reaction. Samples were taken every 5–10 min, filtered through a filter membrane, and the absorbance of the solution was measured at 287 nm using a UV spectrophotometer. The absorbance was then converted to levofloxacin concentration based on a standard curve, and the levofloxacin degradation rate was calculated. The results are shown in [Figure number missing]. Figure 7It can be seen that the degradation rate of levofloxacin in organic wastewater by the CQDs@δ-MnO2 / SiO2 catalyst is much higher than that by δ-MnO2. Among them, the degradation rate of levofloxacin by the CQDs@δ-MnO2 / SiO2-2 catalyst prepared according to Example 2 can reach 94.6% within 50 min.

[0060] Application Example 2

[0061] The catalysts prepared in Examples 2, 3, 4, and Comparative Example 3 were tested for their performance in degrading levofloxacin-containing organic wastewater using activated PMS. The results are shown in the table below. Figure 8 It can be seen that, within 50 minutes, the catalysts prepared according to Examples 2 and 3 both outperformed the catalyst prepared in Comparative Example 3.

[0062] Application Example 3

[0063] The catalysts prepared in Examples 1, 2, 5, and Comparative Example 1 were tested for their performance in degrading levofloxacin-containing organic wastewater using activated PMS. The results are shown in the figure. Figure 9 It can be seen that the catalysts prepared according to Examples 1, 2 and 5 all have better performance than the catalyst prepared in Comparative Example 1, which indicates that the performance of the catalysts increases with the amount of carbon quantum dots.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A method for preparing a SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst, characterized in that, Includes the following steps: S1. Dissolve citric acid in deionized water and sonicate for 10 min to disperse it evenly. Then place it in a reaction vessel for hydrothermal reaction. After the reaction is completed, cool to room temperature, filter with a filter membrane, and take the filtrate to obtain a carbon quantum dot (CQDs) solution. S2. A certain volume of tetraethyl orthosilicate was added to anhydrous ethanol and ultrasonically dispersed for 10 min. NaOH solution was slowly added dropwise and stirred continuously for 4 h. The solid product was then separated by centrifugation, washed with water until neutral, and dried under vacuum to obtain SiO2. S3. Dissolve KMnO4 in deionized water, add SiO2 and disperse by ultrasonication to obtain SiO2 dispersion; S4. Add the CQDs solution prepared in step S1 to the SiO2 dispersion and stir until homogeneous. Then add the MnSO4 solution dropwise and stir for 30 min to obtain a mixed solution. S5. The mixed solution obtained in step S4 is transferred to a hydrothermal reactor for reaction. After the reaction is completed, it is cooled to room temperature, and the solid product is separated by centrifugation. After washing with water, washing with alcohol and drying, SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst is obtained.

2. The preparation method according to claim 1, characterized in that: In step S1, the concentration of the citric acid aqueous solution is 1.0~3.0 mol / L, and the reaction temperature is 180~220°C. o C, the reaction time is 4~8h.

3. The preparation method according to claim 1, characterized in that: In step S3, the concentration of KMnO4 is 0.015~0.030 mol / L, the mass ratio of KMnO4 to SiO2 is (4~9):1, and the stirring time is 30 min.

4. The preparation method according to claim 1, characterized in that: In step S4, the mass ratio of KMnO4 to MnSO4 is (3.5~5.5):1, and the volume-mass ratio of CQDs solution to KMnO4 is (0.25~0.65) mL:1g.

5. The preparation method according to claim 1, characterized in that: The hydrothermal reaction temperature in step S5 is 120~150℃. o C, the reaction time is 4~8h.

6. The SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst prepared by the method according to any one of claims 1 to 5.

7. The SiO2-supported carbon quantum dot δ-MnO2 nanoflower catalyst according to claim 6, characterized in that: The size of δ-MnO2 nanoflowers is 100~300nm, and the size of carbon quantum dots is 5~8nm.

8. The application of the SiO2-supported doped carbon quantum dot δ-MnO2 nanoflower catalyst according to claim 6 or 7 in the activation of PMS for antibiotic degradation wastewater.

9. The application according to claim 8, characterized in that: The antibiotics are quinolones, macrolides, sulfonamides, or tetracyclines.

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