Preparation method and application of near-infrared light response carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst

Abstract

The invention provides a preparation method and application of a near-infrared response carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst. According to the material, levofloxacin is taken as a precursor, nitrogen-fluorine-doped carbon dots with an up-conversion characteristic are synthesized through a hydrothermal method, and the nitrogen-fluorine-doped carbon dots are compounded with a NiO nanosheet and a BiVO4 precursor which are prepared in advance by adopting a one-step hydrothermal strategy. Due to the up-conversion characteristic of the carbon dots, near-infrared light can be converted into visible light, spectral response is widened, and light capture efficiency is improved; meanwhile, the electron transmission capability of the material is cooperated with the built-in electric field of the BiVO4 / NiO p-n heterojunction, a multi-dimensional transmission channel is constructed, and carrier recombination is inhibited, so that the generation efficiency of active oxygen is remarkably improved, and the photocatalytic material with near-infrared light response characteristics, excellent antibiotic degradation performance and high stability is finally obtained.

Description

Technical Field

[0001] This invention relates to a method for preparing a near-infrared light-responsive carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst and its application in the photocatalytic degradation of antibiotics, belonging to the field of photocatalysis technology. Background Technology

[0002] Antibiotic residues in water bodies pose a serious threat to ecosystem balance and human health. Traditional water treatment methods have limitations in removing antibiotics. Photocatalysis, as a green and environmentally friendly technology that uses solar energy to drive reactions to degrade pollutants, has shown great potential in the field of environmental governance. However, currently widely used photocatalytic materials (such as TiO2) are limited by their wide bandgap characteristics, only responding to ultraviolet light, which accounts for about 4% of the solar spectrum, while being almost unable to utilize near-infrared light (NIR), which accounts for more than 53% of the solar spectrum, resulting in a significant limitation on solar energy conversion efficiency.

[0003] Bismuth vanadate (BiVO4), as a semiconductor photocatalyst with visible light response, has expanded the range of light utilization to some extent, but still faces inherent defects such as high recombination rate of photogenerated carriers and low quantum efficiency. Nickel oxide (NiO), as a p-type semiconductor, is inexpensive and easy to prepare. When combined with n-type semiconductor BiVO4 to construct a pn heterojunction, it can form a built-in electric field, promote interfacial charge separation, and improve catalytic performance in the visible light region. However, its light response range is still limited by the intrinsic band gap of the constituent semiconductors, and it cannot effectively utilize the near-infrared light band.

[0004] Carbon dots (CDs) have attracted widespread attention due to their unique photochemical properties. Their upconversion characteristics enable them to absorb low-energy near-infrared photons and emit high-energy visible photons, thus significantly broadening the spectral response range of photocatalytic materials. At the same time, the excellent electronic conductivity of carbon dots can serve as efficient electronic mediators, synergizing with BiVO4 / NiOp-n heterojunctions to construct multidimensional charge transport channels, further suppressing the recombination of photogenerated electron-hole pairs and improving the efficiency of interfacial charge separation. Summary of the Invention

[0005] This invention provides a method for preparing and applying a near-infrared light-responsive carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst. Using levofloxacin as a precursor, nitrogen-fluorine doped carbon dots with upconversion properties are synthesized via a hydrothermal method. These carbon dots are then composited with pre-prepared NiO nanosheets and a BiVO4 precursor using a one-step hydrothermal strategy. The upconversion properties of the carbon dots convert near-infrared light into visible light, broadening the spectral response and improving light-harvesting efficiency. Simultaneously, their electron transport capability synergizes with the built-in electric field of the BiVO4 / NiO pn heterojunction to construct multidimensional transport channels, suppressing carrier recombination and significantly improving the generation efficiency of reactive oxygen species. Ultimately, a photocatalyst material with near-infrared light-responsive properties, excellent antibiotic degradation performance, and high stability is obtained.

[0006] Based on the above objectives, the technical solution adopted by the present invention is as follows:

[0007] Firstly, specifically, the preparation process of the near-infrared light-responsive carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst includes the following steps:

[0008] The first step involves adding a certain amount of levofloxacin (LVX) to water and stirring to dissolve it. The solution is then transferred to a polytetrafluoroethylene high-pressure reactor for a closed hydrothermal reaction. After the reaction is complete, carbon dots are obtained by dialysis.

[0009] The second step involves adding a certain amount of nickel chloride and urea to a mixed solution of water and anhydrous ethanol and stirring to dissolve them. The solution is then transferred to a polytetrafluoroethylene high-pressure reactor for a closed hydrothermal reaction. After the reaction, the solution is filtered, washed, and dried, and then calcined at high temperature in a muffle furnace to obtain NiO nanosheets.

[0010] In the third step, a certain amount of bismuth nitrate pentahydrate, ammonium metavanadate, and sodium dodecyl sulfate were added to water and stirred to dissolve. Then, the carbon dot aqueous solution prepared in the first step and the NiO nanosheets prepared in the second step were added to the above mixed solution and stirred to ensure thorough dispersion and mixing. The mixture was then transferred to a polytetrafluoroethylene high-pressure reactor for a closed hydrothermal reaction. After the reaction, it was filtered, washed, and dried to obtain a carbon dot composite bismuth vanadate / nickel oxide heterojunction material.

[0011] Furthermore, in the first step, the ratio of levofloxacin to water is 0.5g:20ml to 0.5g:40ml.

[0012] Furthermore, in the first step, the hydrothermal temperature is 180–200℃, and the hydrothermal time is 4–6 hours.

[0013] Furthermore, in the second step, the molar ratio of nickel oxide to urea is 1:1 to 1:1.2.

[0014] Furthermore, in the second step, the volume ratio of water to anhydrous ethanol is 1:3 to 1:4.

[0015] Furthermore, in the second step, the hydrothermal temperature is 120–140°C, and the hydrothermal time is 10–12 hours.

[0016] 2. Furthermore, in the second step, the calcination temperature is 450–550℃, the calcination time is 3±1h, and the heating rate is 2±1℃ / min.

[0017] Furthermore, in the third step, the molar ratio of bismuth nitrate pentahydrate, ammonium metavanadate, and sodium dodecyl sulfate is 40:40:7 to 42:42:9, and the volume of water is 60 to 80 ml.

[0018] Furthermore, in the third step, the ratio of carbon dot solution to nickel oxide is 5 ml: 0.02 mmol to 5 ml: 0.1 mmol.

[0019] Furthermore, in the third step, the hydrothermal temperature is 180–200℃, and the hydrothermal time is 16–18 hours.

[0020] Secondly, the present invention provides a carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst material prepared by the above method.

[0021] Thirdly, this invention seeks protection for the application of the above-mentioned carbon dot composite bismuth vanadate / nickel oxide heterojunction composite photocatalyst in the photocatalytic degradation of antibiotics.

[0022] Beneficial technical effects:

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1) Achieved efficient utilization of near-infrared light: Most existing photocatalysts (such as pure BiVO4 or its heterojunctions) cannot utilize near-infrared light, which accounts for the majority of the solar spectrum's energy. This invention, by introducing carbon dots and utilizing their unique upconversion effect, successfully converts near-infrared light into visible light that the catalyst can effectively utilize, significantly broadening the light response range and improving the overall utilization efficiency of solar energy.

[0025] 2) A synergistic charge separation system was constructed: Compared with a single heterojunction, this invention constructs a more efficient electron transport channel through the synergistic interaction of carbon dots, BiVO4, and NiO. Carbon dots, as excellent electron acceptors and mediators, work synergistically with the built-in electric field of the pn heterojunction to greatly promote the separation and migration of photogenerated electron-hole pairs, thereby improving the photocatalytic degradation efficiency.

[0026] 3) The catalyst has a stable structure, high catalytic degradation activity and cycle stability, and has high application prospects in the field of antibiotic degradation. Attached Figure Description

[0027] Figure 1 XRD patterns of the products of Example 1 and Comparative Example 1;

[0028] Figure 2 The FTIR spectra of the products of Example 1 and Comparative Example 1 are shown below.

[0029] Figure 3 SEM images of the products of Example 1 and Comparative Example 1;

[0030] Figure 4 Here is an HRTEM image of the product from Example 1;

[0031] Figure 5 The graphs show the photocatalytic degradation performance of tetracycline by the products of Example 1 and Comparative Example 1.

[0032] Figure 6 This is a cycle test diagram of the photocatalytic degradation of tetracycline by the product of Example 1. Specific implementation methods

[0033] The present invention will be further described below with reference to specific embodiments. However, the scope of protection of the present invention is not limited to the following embodiments. Any non-essential adjustments and modifications made to the present invention based on the above description shall still fall within the scope of protection of the present invention.

[0034] Example 1

[0035] (1) Accurately weigh 0.5 g of levofloxacin using an electronic balance and add it to 20 mL of deionized water. Stir to disperse the mixture. Place the mixture into a 50 mL polytetrafluoroethylene-lined high-pressure reactor and heat it in an oven at 180 °C for 4 h. After cooling to room temperature, filter to remove larger particles of residue and then transfer it to a dialysis bag with a molecular weight cutoff of 1000 Da. Dialyze for 48 h to obtain the CDs solution.

[0036] (2) Dissolve 2 mmol of nickel chloride and 2 mmol of urea in a mixture of 10 mL of deionized water and 30 mL of ethanol, and stir at room temperature for 0.5 h. Transfer the mixture to a 50 mL polytetrafluoroethylene high-pressure reactor and heat in an oven at 120 °C for 10 h. After cooling to room temperature, wash several times with water and ethanol, and dry at 80 °C for 12 h to obtain the NiO precursor. Grind the NiO precursor and calcine it in a muffle furnace at 450 °C for 3 h at a heating rate of 2 °C / min. After natural cooling, grind to obtain NiO nanosheets.

[0037] (3) Add 4 mmol of bismuth vanadate pentahydrate, 4 mmol of ammonium metavanadate, and 0.2 g of sodium dodecyl sulfate to 60 mL of deionized water and stir to dissolve. Add 0.02 mmol of NiO nanosheets and 5 mL of LVX-derived carbon dot aqueous solution and stir at room temperature for 1 h. Transfer the mixed suspension to a 100 mL polytetrafluoroethylene high-pressure reactor and heat in an oven at 180 °C for 16 h. After cooling to room temperature, wash several times with water and ethanol, and dry at 80 °C for 12 h to obtain the carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst, named CDs-BN.

[0038] Comparative Example 1

[0039] (1) Dissolve 2 mmol of nickel chloride and 2 mmol of urea in a mixture of 10 mL of deionized water and 30 mL of ethanol, and stir at room temperature for 0.5 h. Transfer the mixture to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and heat in an oven at 120 °C for 10 h. After cooling to room temperature, wash several times with water and ethanol, and dry at 80 °C for 12 h to obtain the NiO precursor. Grind the NiO precursor and calcine it in a muffle furnace at 450 °C for 3 h at a heating rate of 2 °C / min. After natural cooling, grind to obtain NiO nanosheets.

[0040] (2) 4 mmol of bismuth vanadate pentahydrate, 4 mmol of ammonium metavanadate, and 0.2 g of sodium dodecyl sulfate were added to 60 mL of deionized water and stirred to dissolve. 0.02 mmol of NiO nanosheets were added, and the mixture was stirred at room temperature for 1 h. The mixed suspension was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and heated in an oven at 180 °C for 16 h. After cooling to room temperature, the mixture was washed several times with water and ethanol, and dried at 80 °C for 12 h to obtain the bismuth vanadate / nickel oxide heterojunction photocatalyst, named BN.

[0041] Figure 1 The XRD patterns of the products of Example 1 and Comparative Example 1 are shown. The characteristic diffraction peaks of BN match well with the standard diffraction peaks of BiVO4 (PDF#14-0688) and NiO (PDF#44-1159). The characteristic peaks of CDs-BN still correspond to the standard diffraction peaks of BiVO4 and NiO, indicating that the carbon dot modification has not destroyed the main crystal phase of the heterojunction. Due to the interfacial interaction between the carbon dots and the heterojunction, the characteristic peaks of CDs-BN show changes such as peak broadening and intensity attenuation compared to BN.

[0042] Figure 2 The images show the FTIR spectra of the products from Example 1 and Comparative Example 1. Compared to BN, CDs-BN exhibits COC bonds (1048 cm⁻¹). -1 The peak of ) and the VO bond (746 cm⁻¹) -1 The peak vibration of -OH (3424 cm⁻¹) is enhanced.-1 ) and C=O(1655cm -1 The peak intensity of the carbon dots decreased. This not only indicates that the carbon dots were successfully incorporated into the bismuth vanadate / nickel oxide heterojunction system, but also that the carbon dots, through interfacial interactions, modulated the vibrational behavior of the intrinsic functional groups (-OH, C=O) and chemical bonds (VO, Ni-O) of the heterojunction.

[0043] Figure 3 SEM images of the products from Example 1 and Comparative Example 1. Figure 3 It can be seen that BN has a spherical structure, and the modification of CDs did not change the structure of the composite material.

[0044] Figure 4 This is a HETEM diagram of Example 1. (From...) Figure 4 It can be seen that CDs were successfully composited on the BN surface and uniformly distributed.

[0045] Performance testing

[0046] The method for evaluating the degradation performance of the products of Example 1 and Comparative Example 1 on antibiotics provided by the present invention is as follows:

[0047] Weigh 40 mg each of the products from Example 1 and Comparative Example 1, and add them to a 0.5 mg / L tetracycline (TC) solution. Maintain the reaction temperature at 20°C using circulating cooling water, and stir the suspension with a magnetic stirrer. Stir for 30 min in the dark to reach adsorption equilibrium. Irradiate the sample in the beaker using a 300W Xe lamp with an 800 nm filter. After a specified time, remove 1 mL of solution and filter it using a syringe with a 0.45 μm filter. Then, analyze the concentration of the remaining TC using high-performance liquid chromatography (HPLC, Shimadzu 2030C). After the reaction is complete, centrifuge and wash the catalyst, and perform a cycle stability test.

[0048] Figure 5 The images show the photocatalytic degradation performance of tetracycline in Example 1 and Comparative Example 1. Figure 5 It can be seen that, under near-infrared light irradiation, CDs-BN exhibits higher catalytic degradation efficiency for TC compared to BN.

[0049] Figure 6 This is a cycle test diagram of the photocatalytic degradation of tetracycline by the product of Example 1. It can be seen that CDs-BN exhibits good reusability and cycle stability.

[0050] Although the present invention has been described in detail through the above preferred examples, it should be understood that the above description should not be considered as a limitation of the present invention.

Claims

1. A method for preparing a near-infrared light responsive carbon dot composite bismuth vanadate / nickel oxide heterojunction photocatalyst, characterized in that, The method comprises the following steps: In the first step, a certain amount of levofloxacin is added to water and stirred to dissolve, and the solution is transferred to a polytetrafluoroethylene high-pressure reaction kettle for a sealed hydrothermal reaction. After the reaction, the carbon dots are obtained after dialysis. In the second step, a certain amount of nickel chloride and urea is added to a mixed solution of water and anhydrous ethanol, stirred to dissolve, and transferred to a polytetrafluoroethylene high-pressure reaction kettle for a sealed hydrothermal reaction. After the reaction, the NiO nanosheet is obtained after filtration, washing and drying, and then placed in a muffle furnace for high-temperature calcination. In the third step, a certain amount of bismuth nitrate pentahydrate, ammonium metavanadate and sodium dodecyl sulfate is added to water and stirred to dissolve. Subsequently, the carbon dot aqueous solution prepared in the first step and the NiO nanosheet prepared in the second step are added to the above mixed solution and stirred to fully disperse and mix. The mixture is transferred to a polytetrafluoroethylene high-pressure reaction kettle for a sealed hydrothermal reaction. After the reaction, the carbon dot composite bismuth vanadate / nickel oxide heterojunction material is obtained after filtration, washing and drying.

2. The preparation method of the carbon dot composite BiVO4 / NiO heterojunction photocatalyst according to claim 1, characterized in that, In the first step, the ratio of levofloxacin to water is 0.5g:20ml-0.5g:40ml, the hydrothermal temperature is 180-200℃, and the hydrothermal time is 4-6h.

3. The method for preparing the carbon dot composite BiVO4 / NiO heterojunction photocatalyst according to claim 1, characterized in that, In the second step, the molar ratio of nickel oxide to urea is 1:1-1:1.

2.

4. The method for preparing the carbon dot composite BiVO4 / NiO heterojunction photocatalyst according to claim 1, characterized in that, In the second step, the volume ratio of water to anhydrous ethanol is 1:3-1:4, the hydrothermal temperature is 120-140℃, and the hydrothermal time is 10-12h.

5. The method for preparing the carbon dot composite BiVO4 / NiO heterojunction photocatalyst according to claim 1, characterized in that, In the second step, the calcination temperature is 450-550℃, the calcination time is 3±1h, and the heating rate is 2±1℃ / min.

6. The method for preparing the carbon dot composite BiVO4 / NiO heterojunction photocatalyst according to claim 1, characterized in that, In the third step, the molar ratio of bismuth nitrate pentahydrate, ammonium metavanadate and sodium dodecyl sulfate is 40:40:7-42:42:9, the volume of water is 60-80ml, the ratio of carbon dot solution to nickel oxide is 5ml:0.02mmol-5ml:0.1mmol, the hydrothermal temperature is 180-200℃, and the hydrothermal time is 16-18h. 7.A method for preparing a near-infrared light responsive carbon dot composite BiVO4 / NiO heterojunction photocatalyst, characterized in that, The composite material is prepared by the preparation method of any one of claims 1-6.

8. The application of the carbon dot-containing composite bismuth vanadate / nickel oxide heterojunction photocatalyst in antibiotic degradation according to claim 7.

9. Use according to claim 8, characterized in that, The antibiotic includes tetracycline.

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