Preparation method and application of a CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst

Abstract

The present invention discloses a method for preparing a CoFe Prussian blue analog @ nitrogen-doped carbon quantum dots (CoFe PBA@N-CD) composite photocatalyst, comprising the following steps: (1) using citric acid as a carbon source and urea as a nitrogen source to prepare N-CD by a simple hydrothermal reaction; (2) adding the prepared N-CD to a K3[Fe(CN)6] aqueous solution, slowly adding and mixing it with a CoSO4·7H2O aqueous solution at the same rate, stirring, standing, filtering, and drying to obtain a CoFe PBA@N-CD composite photocatalyst. The present invention also discloses an application of the CoFe PBA@N-CD composite photocatalyst obtained using the preparation method in the photocatalytic degradation of aflatoxin B1. The present invention prepares the CoFePBA@N-CD composite photocatalyst in two steps, has a simple preparation process, low production cost, and the prepared CoFe PBA@N-CD composite photocatalyst has excellent light absorption and photocatalytic performance, and the efficiency of degrading aflatoxin B1 under visible light irradiation reaches 90.9%.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and in particular relates to a preparation method and application of a CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst. Background Art

[0002] Photocatalytic technology is a gentle, green, and environmentally friendly technology. It utilizes free radicals generated by photocatalysis and highly oxidizing holes produced by photogenerated electron-hole separation to oxidize and decompose difficult-to-degrade organic pollutants into small molecules. This technology can effectively and rapidly detoxify organic pollutants to a certain extent. Currently, photocatalytic technology has been successfully applied to the degradation of pesticides, organic dyes, mycotoxins, and other products.

[0003] Prussian blue and its analogs (PB / PBA) are a traditional class of metal-organic frameworks (MOFs). These cyanide coordination polymers are formed by the reaction of metal ions with transition metal cyanometalates. They possess not only a porous framework structure and good chemical stability, but also simple preparation and low cost. Due to their tunable metal active sites and uniform catalytic centers, PB / PBAs hold great promise for application in photocatalysis. However, low light energy utilization and high recombination rates of photogenerated electron-hole pairs have severely limited their development in photocatalysis. Summary of the Invention

[0004] One of the objectives of the present invention is to provide a method for preparing a CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots (N-CD) composite photocatalyst. The introduction of N-CD solves the problem of high recombination rate of photogenerated electron-hole pairs in CoFe PBA.

[0005] The second object of the present invention is to provide the application of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst in the photocatalytic degradation of aflatoxin B1 (AFB1).

[0006] The present invention provides a method for preparing a CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst, comprising the following steps:

[0007] S1. Preparation of N-CD: Ultrasonic treatment of an aqueous solution containing a carbon source and a nitrogen source is performed, followed by a hydrothermal reaction. After the reaction is completed, the solution is cooled to room temperature and filtered, and the filtrate is filtered again using a filter membrane. The filtered solution is dialyzed and freeze-dried to obtain N-CD.

[0008] S2. Preparation of CoFe PBA@N-CD: N-CD obtained in step S1 is added to a K3[Fe(CN)6] aqueous solution and ultrasonically treated to obtain solution A; a CoSO4·7H2O aqueous solution is ultrasonically treated to obtain solution B; solution A and solution B are dropwise added and mixed at the same preset rate under stirring, and the suspension obtained after mixing is further stirred, allowed to stand, filtered, and dried to obtain the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst.

[0009] Furthermore, in step S1, the carbon source is citric acid, and the nitrogen source is urea; in the aqueous solution containing the carbon source and the nitrogen source, the concentration of citric acid is 0.17-0.5 mol / L, and the concentration of urea is 0.83-1.2 mol / L.

[0010] In step S1, the ultrasonic reaction time is 10 to 15 minutes, the hydrothermal reaction time is 3 to 5 hours, and the temperature is 180 to 200° C.; the pore size of the filter membrane is 0.22 μm; the freeze-drying temperature is -45 to -55° C., and the time is 24 to 36 hours.

[0011] The dialysis treatment time is 12 to 36 hours, and the molecular weight cut-off of the dialysis bag for the dialysis treatment is 500 to 1000 Da.

[0012] Furthermore, in step S2, the concentration of the K3[Fe(CN)6] aqueous solution is 0.01 to 0.02 mol / L; the amount of N-CD added is 0.33 to 0.67 g / L; the ultrasonic treatment time for preparing solution A and preparing solution B is 10 to 15 minutes; the concentration of the CoSO4·7H2O aqueous solution is 0.01 to 0.02 mol / L;

[0013] During the mixing process of solution A and solution B, the stirring rate is 400-500 rpm; the suspension is stirred for 1-3 hours and then allowed to stand for 6-18 hours.

[0014] The present invention also provides an application of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst in photocatalytic degradation of aflatoxin B1 (AFB1).

[0015] Furthermore, the light in the photocatalytic degradation is visible light with a wavelength greater than or equal to 420 nm.

[0016] The application is specifically as follows: the photocatalytic degradation of aflatoxin B1 by the CoFe Prussian blue analogue @ nitrogen-doped carbon quantum dot composite photocatalyst needs to be carried out in a solution; the ratio of the composite photocatalyst to aflatoxin B1 in the solution is (35-45):1; and the photocatalytic reaction needs to be stirred under light for 0-120 minutes.

[0017] Beneficial effects of the present invention:

[0018] The present invention utilizes the matching band structures of CoFe PBA and N-CD to construct a Z-type heterostructure composite photocatalyst, which features a simple preparation process and low production cost. Under light excitation, the catalyst's electrons and holes separate, and electrons in the N-CD conduction band and holes in the CoFe PBA valence band form an internal electric field. This allows the highly oxidizing holes in the N-CD valence band and the highly reducing electrons in the CoFe PBA conduction band to form conditions for the generation of reactive oxygen free radicals. Under visible light irradiation (λ ≥ 420 nm), the composite photocatalyst can achieve rapid and effective photocatalytic degradation of AFB1, with a degradation efficiency of 90.9%, which is 2.7 times and 4.8 times that of CoFe PBA and N-CD alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the preparation of CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst and the photocatalytic degradation of AFB1;

[0020] Figure 2 UV-visible spectra of CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst before and after photocatalytic degradation of AFB1;

[0021] Figure 3 This is the feasibility result of photocatalytic degradation of AFB1 by CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst;

[0022] Figure 4 This is a comparison chart of the efficiency of the CoFe Prussian blue analog @ nitrogen-doped carbon quantum dots composite photocatalyst and the separate CoFePBA and N-CD in photocatalytic degradation of AFB1 under visible light irradiation in the embodiment. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to specific embodiments.

[0024] Example 1 Preparation of N-CD

[0025] like Figure 1 As shown, 60 mL of a mixed aqueous solution containing 0.33 mol / L citric acid and 1.0 mol / L urea was ultrasonically treated for 10 min, transferred to a 100 mL hydrothermal reactor, and hydrothermally reacted at 180°C for 4 h; the solution was then cooled to room temperature and filtered, and the filtrate was filtered again using a 0.22 μm filter membrane; the filtered solution was dialyzed using a dialysis bag with a molecular weight cutoff of 500 Da for 24 h, and finally freeze-dried at -50°C to obtain yellow powder N-CD.

[0026] Example 2 Preparation of CoFe PBA@N-CD

[0027] 0.03 g of N-CD prepared in Example 1 was added to 30 mL of 0.013 mol / L K3[Fe(CN)6] aqueous solution and ultrasonically treated for 10 min to obtain solution A. 30 mL of 0.013 mol / L CoSO4·7H2O aqueous solution was ultrasonically treated for 10 min to obtain solution B. Solutions A and B were slowly added dropwise at the same rate at 400 rpm to obtain a brick-red suspension. After continuous stirring for 2 h, the suspension was allowed to stand for 12 h. The brick-red precipitate was then collected by vacuum filtration and washed three times with deionized water. Finally, it was dried in an oven at 60°C to obtain CoFe PBA@N-CD ( Figure 1 ).

[0028] Comparative Example 1 Preparation of CoFe PBA

[0029] Compared with Example 2, N-CD was not added to solution A, and the remaining steps were exactly the same as in Example 2 to obtain CoFePBA.

[0030] Example 3 Feasibility Experiment of Photocatalytic Degradation of AFB1

[0031] N-CD, CoFe PBA, and CoFePBA@N-CD were used in the photocatalytic degradation of AFB1. The specific steps were as follows: 4.0 mg of N-CD, CoFe PBA, and CoFe PBA@N-CD catalysts were accurately weighed and added to 10 mL of a 10 mg / L AFB1 solution. Before irradiation, the solution was stirred in the dark for 30 minutes to allow adsorption equilibrium to be reached between AFB1 and the catalyst. A xenon lamp (λ≥420 nm) was used for illumination for 2 hours. 500 μL of the solution was collected every 10 minutes, centrifuged, and the supernatant was collected. The absorbance at 365 nm was measured using a UV-visible spectrophotometer to observe the changes in the characteristic absorption peaks before and after AFB1 degradation, as shown in Figure 3. Figure 2 The degradation of AFB1 using CoFePBA@N-CD catalyst is shown in FIG.

[0032] The above steps were used to investigate the feasibility of photocatalytic degradation of AFB1 by CoFe PBA@N-CD. The degradation rate of AFB1 = C0-C / C0, where C0 is the initial concentration of AFB1 (mg / L) and C is the concentration of AFB1 after degradation for t minutes (mg / L). The concentration of AFB1 after degradation for t minutes is calculated as follows: 500 μL of the degraded solution is taken, centrifuged, and the supernatant is taken. The absorbance at 365 nm is measured using a UV-visible spectrophotometer. The concentration of AFB1 after degradation for t minutes can be calculated based on the relationship curve between the concentration of the AFB1 standard solution and the corresponding absorbance. Figure 3As shown in the figure, when no catalyst is added, the self-degradation rate of AFB1 under visible light irradiation is very low, only about 1.5%; when CoFe PBA@N-CD is added to the AFB1 solution, but no visible light irradiation is used, the degradation rate of AFB1 is only 2.4%, indicating that the adsorption of AFB1 by the material is not the reason for the decrease in the concentration of AFB1 in the solution; only under visible light irradiation, CoFePBA@N-CD shows a significant degradation effect on AFB1. This is because under light conditions, the CoFePBA@N-CD composite photocatalyst is excited, electrons undergo transitions, and photogenerated electron-hole pairs are generated. The active oxygen free radicals generated through a series of chemical reactions degrade AFB1 into fragment products. Figure 4 After 2 hours of visible light irradiation, the degradation rates of AFB1 by N-CD, CoFe PBA, and CoFePBA@N-CD were 18.9%, 33.2%, and 90.9%, respectively. Compared to single materials N-CD and CoFe PBA, the composite CoFePBA@N-CD significantly improved its efficiency in photocatalytic degradation of AFB1. This is because the introduction of N-CD forms a heterogeneous interface with CoFePBA, enhancing its light absorption capacity and improving the separation efficiency of electron-hole pairs, resulting in a significant improvement in photocatalytic performance.

[0033] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. Application of a CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst, characterized in that: The application is specifically the use of a CoFe Prussian blue analogue @ nitrogen-doped carbon quantum dot composite photocatalyst in the photocatalytic degradation of aflatoxin B1; the preparation method of the CoFe Prussian blue analogue @ nitrogen-doped carbon quantum dot composite photocatalyst comprises the following steps: S1. Preparation of N-CD: An aqueous solution containing a carbon source and a nitrogen source is sonicated, followed by a hydrothermal reaction. After the reaction is completed, the solution is cooled to room temperature and filtered, and the filtrate is filtered again using a membrane filter. The filtered solution is dialyzed and freeze-dried to obtain N-CD. S2. Preparation of CoFe PBA@N-CD: N-CD obtained in step S1 was added to a K3[Fe(CN)6] aqueous solution and ultrasonically treated to obtain solution A; a CoSO4·7H2O aqueous solution was ultrasonically treated to obtain solution B; solution A and solution B were dropwise added and mixed at the same preset rate under stirring. The suspension obtained after mixing was further stirred, allowed to stand, filtered, and dried to obtain the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dot composite photocatalyst.

2. The use of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst according to claim 1, characterized in that: In step S1, the carbon source is citric acid, and the nitrogen source is urea; in the aqueous solution containing the carbon source and the nitrogen source, the concentration of citric acid is 0.17~0.5 mol / L, and the concentration of urea is 0.83~1.2 mol / L.

3. The use of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst according to claim 1, characterized in that: In step S1, the ultrasonic reaction time is 10-15 minutes, the hydrothermal reaction time is 3-5 hours, and the temperature is 180-200°C; the pore size of the filter membrane is 0.22 μm; the freeze-drying temperature is -45-55°C, and the time is 24-36 hours.

4. The use of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst according to claim 1, characterized in that: The dialysis treatment time is 12 to 36 hours, and the molecular weight cut-off of the dialysis bag is 500 to 1000 Da.

5. The use of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst according to claim 1, characterized in that: In step S2, the concentration of the K3[Fe(CN)6] aqueous solution is 0.01~0.02 mol / L; the amount of N-CD added is 0.33~0.67 g / L; the ultrasonic time for preparing solution A and solution B is 10~15 min; the concentration of the CoSO4•7H2O aqueous solution is 0.01~0.02 mol / L.

6. The use of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst according to claim 1, characterized in that: In step S2, during the mixing of solution A and solution B, the stirring rate is 400-500 rpm; the suspension is stirred for 1-3 h and then allowed to stand for 6-18 h.

7. The use of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst according to claim 1, characterized in that: The photocatalytic degradation uses visible light with a wavelength greater than or equal to 420 nm.

8. The use of the CoFe Prussian blue analogue@nitrogen-doped carbon quantum dots composite photocatalyst according to claim 1, characterized in that: The specific application is: the photocatalytic degradation of aflatoxin B1 by the CoFe Prussian blue analog @ nitrogen-doped carbon quantum dot composite photocatalyst needs to be carried out in solution; the ratio of the composite photocatalyst to aflatoxin B1 in the solution is (35~45):1; the photocatalytic reaction needs to be stirred under light for 0~120 minutes, and the illumination time is not 0.

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