A supported BiVO4 / NF photocatalyst, its preparation method and application

Abstract

The application discloses a supported BiVO4 / NF photocatalyst and a preparation method and application thereof, and the method comprises the following steps: in step one, NF is pretreated to obtain an NF carrier; in step two, a BiVO4 precursor solution is prepared; in step three, the NF carrier is vertically fixed in a polytetrafluoroethylene lining in a hydrothermal reaction kettle, then the BiVO4 precursor solution is transferred into the reaction kettle, and then is placed into an oven for heat preservation; in step four, after the reaction kettle is cooled to room temperature, the NF carrier loaded with BiVO4 is taken out, washed with ethanol and ultrapure water for several times, and then is placed into a vacuum drying box for vacuum drying, and finally is placed into a muffle furnace for calcination, so as to obtain the supported BiVO4 / NF photocatalyst. The application solves the problems that the photocatalyst is not easy to recover, thereby causing the loss of the photocatalyst, and the photocatalyst is accumulated in the reaction process, thereby causing slow ion diffusion, and thus the degradation effect on TCH in water is improved.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a supported BiVO4 / NF photocatalyst, its preparation method, and its application. Background Technology

[0002] Most antibiotics possess good structural stability, which leads to their difficulty in degradation in the natural environment. In the long run, antibiotics accumulated in the environment can enter the human body through aquatic products, fruits and vegetables, and drinking water, threatening human health. Antibiotic removal methods mainly include biological, physical, and chemical methods. Commonly used chemical methods include advanced oxidation techniques such as Fenton oxidation, electrochemical oxidation, photocatalysis, and persulfate oxidation. Advanced oxidation technologies offer a safer and more natural water treatment method. However, these methods also have many drawbacks, such as high investment costs, high maintenance costs, large consumption of chemical reagents, and environmental problems caused by wastewater treatment.

[0003] Among the many advanced oxidation technologies, photocatalysis is an advanced solar-based photocatalytic oxidation process that uses low-cost semiconductors as catalysts. It is also a more environmentally friendly and cost-effective pollutant treatment technology.

[0004] Photocatalysis is a technology in which, under visible light irradiation, a photocatalyst absorbs photon energy, causing photogenerated electrons to transition from the valence band to the conduction band, generating photogenerated electron-hole pairs, i.e., photogenerated charge carriers. These photogenerated electrons and holes migrate to the surface of the photocatalytic material and undergo photooxidation and photoreduction reactions with the surface active sites. The photogenerated electrons reduce dissolved oxygen on the semiconductor surface to generate •O2. - Holes oxidize water to produce hydroxyl radicals (•OH). Holes, •O2 - •OH decomposes pollutants in water into CO2 and H2O, thereby achieving photocatalytic degradation of wastewater.

[0005] In most studies, catalysts exist in powder form. Common methods for immobilizing powdered photocatalysts include granulation, sol-gel, and freeze-drying. These three methods are relatively cumbersome and unsuitable for large-scale industrial applications. Industrial applications often require catalysts with macroscopic structures and larger dimensions; immobilizing powdered photocatalysts on a support significantly improves their industrial usability. In practical applications, supported photocatalysts, with their monolithic structure, offer significantly improved hydrodynamics and heat and mass transfer compared to powdered, packed catalysts. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a supported BiVO4 / NF photocatalyst, its preparation method and application, so as to solve the problems of photocatalyst loss due to difficulty in recycling and slow ion diffusion due to photocatalyst accumulation during the reaction process, thereby improving the degradation effect of TCH in water.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for preparing a supported BiVO4 / NF photocatalyst includes the following steps:

[0009] Step 1: Cut the NF and immerse it in dilute hydrochloric acid, ethanol and ultrapure water in sequence for ultrasonic treatment. Then put the NF into a vacuum drying oven to dry it and obtain the NF carrier.

[0010] Step 2: Add Bi(NO3)3•5H2O to (CH2OH)2 and stir until dissolved. Then add NH4VO3 and continue stirring to obtain BiVO4 precursor solution.

[0011] Step 3: The NF carrier pretreated in Step 1 is vertically fixed in the polytetrafluoroethylene liner of the hydrothermal reactor. Then, the BiVO4 precursor solution stirred until completely dissolved in Step 2 is transferred into the reactor and then placed in an oven for heat preservation.

[0012] Step 4: After the reactor cools to room temperature, remove the NF support loaded with BiVO4, wash it several times with ethanol and ultrapure water, place it in a vacuum drying oven for vacuum drying, and finally calcine it in a muffle furnace to obtain the supported BiVO4 / NF photocatalyst.

[0013] The present invention further illustrates that the NF is nickel foam. Nickel foam is a low-cost, highly active 3D porous material that can be used as a catalyst.

[0014] In this invention, NF is first pretreated, and then BiVO4 is composited on the NF support. NF has advantages such as abundant active contact sites, high thermal conductivity, and high mechanical strength, and will not reduce the activity and durability of the supported catalyst. In addition, the active components can be more uniformly distributed in NF, avoiding the problem of insufficient chemical contact. Immobilizing the powdered photocatalyst on a porous three-dimensional NF substrate, compared with traditional two-dimensional structure materials, the use of NF support greatly reduces the spatial stacking of BiVO4, and BiVO4 can be uniformly covered on the NF surface, which solves the problem of slow ion diffusion caused by photocatalyst stacking. In step two of this invention, under normal circumstances, the synthesis of BiVO4 requires 1 mmol Bi(NO3)3•5H2O dissolved in 10 ml (CH2OH)2.

[0015] The method of this invention is further described in that, in step one, the NF cutting size is 10*10 mm; and the concentration of the dilute hydrochloric acid is 1 mmol·L⁻¹. -1 The ethanol used is anhydrous ethanol; the ultrasonic treatment time is 20 minutes. A 10*10 mm NF size is chosen for its regularity, which is beneficial for subsequent scale-up experiments, and this size allows for sufficient exposure of active sites. Ultrasonic treatment is used to remove the oxide layer on the surface of the nickel foam.

[0016] The method of this invention further illustrates that, in step two, the molar ratio of Bi(NO3)3•5H2O to NH4VO3 is 0.5–3. Preferably, the molar ratio of Bi(NO3)3•5H2O to NH4VO3 is 1:1, which is beneficial for the formation of monoclinic bismuth vanadate. Monoclinic bismuth vanadate has a relatively narrow band gap and exhibits good photocatalytic effect.

[0017] The method described in this invention further illustrates that, in step three, the oven temperature is 180°C, and the holding time is 2 hours. 180°C is a commonly used reaction temperature in hydrothermal synthesis processes, aimed at promoting the chemical reaction of the BiVO4 precursor solution. At this temperature, the reaction proceeds more efficiently, the reactants dissolve and react more easily, generating the desired BiVO4. The high temperature under hydrothermal conditions contributes to the growth and uniform distribution of BiVO4 crystals, ensuring that the morphology and structure of the material meet the requirements of the catalyst.

[0018] The method of this invention further illustrates that, in step four, the holding temperature of the vacuum drying oven is 60°C, and the holding time is 2 hours; the calcination temperature of the muffle furnace is 450°C, the heating rate is 10°C / min, the heating time is 45 minutes, and the holding time is 30 minutes. After hydrothermal synthesis, the product usually contains a certain amount of organic solvents (such as (CH2OH)2) and other byproducts generated during the reaction process. These organic substances need to be removed by calcination. The high temperature of 450°C helps to completely remove these impurities and avoid their negative impact on the performance of the catalyst. Calcination can also further promote the optimization of the crystal structure of BiVO4. Through high-temperature treatment, the lattice structure of the catalyst becomes more stable, forming an active phase with good catalytic performance. High-temperature calcination helps to improve the thermal stability of the BiVO4 / NF catalyst, enabling it to withstand higher temperatures and longer operating times in practical applications.

[0019] The present invention also provides a supported BiVO4 / NF photocatalyst, which is prepared by the above method.

[0020] The supported BiVO4 / NF photocatalyst of this invention further illustrates that the NF support contains nanosphere-shaped BiVO4 crystals. This catalytic material, with BiVO4 supported on the NF support, allows the supported BiVO4 / NF photocatalyst to fully exert its catalytic effect in water. The successful preparation of the photocatalyst was characterized by XRD and SEM.

[0021] This invention also proposes the application of a supported BiVO4 / NF photocatalyst, which is used for the degradation of antibiotics in water; in particular for the degradation of tetracycline hydrochloride (TCH) in water.

[0022] Under visible light (λ > 420 nm) irradiation, the photocatalyst absorbs photon energy, causing photogenerated electrons to transition from the valence band to the conduction band, thus generating photogenerated electrons (ep). - )-hole (h + Yes, that is, photogenerated carriers; e - h + They migrate to the BiVO4 surface and undergo photo-oxidation and photo-reduction reactions with the surface active sites, respectively. - •O2 is generated from dissolved oxygen on the semiconductor surface. - h + Oxidation of water produces hydroxyl radicals (•OH), h + •O2 - •OH decomposes TCH in water into CO2 and H2O, thereby achieving photocatalytic degradation of wastewater.

[0023] Advantages of this invention:

[0024] 1. This invention uses nickel foam (NF) as a support, which is a low-cost, highly active 3D porous material that can be used as a catalyst. It has the advantages of abundant active contact sites, strong thermal conductivity and high mechanical strength, and will not reduce the activity and durability of the supported catalyst. In addition, the active component BiVO4 can be more uniformly distributed in NF, which will not lead to the problem of insufficient chemical contact. Moreover, compared with traditional two-dimensional structure materials, the use of NF support greatly reduces the stacking of BiVO4 in the spatial structure. BiVO4 can be uniformly covered on the surface of NF, which solves the problem of slow ion diffusion caused by photocatalyst stacking.

[0025] 2. In this invention, the NF support is immersed in the BiVO4 precursor solution and then subjected to a hydrothermal reaction, so that the photocatalyst crystals nucleate and grow on the support surface. The supported BiVO4 / NF photocatalyst prepared by this one-step hydrothermal method has higher loading strength and higher distribution uniformity, and the process is also simpler.

[0026] 3. This invention uses a hydrothermal method to prepare a supported BiVO4 / NF photocatalyst to solve the problems of photocatalyst loss due to difficulty in recovery and slow ion diffusion caused by photocatalyst accumulation during the reaction process, thereby improving the degradation effect of tetracycline hydrochloride (TCH) in water. Attached Figure Description

[0027] Figure 1 The XRD spectra of NF, BiVO4, and BiVO4 / NF of this invention are shown below.

[0028] Figure 2 The images show the microstructure of the materials prepared according to this invention; wherein, image A is a SEM image of the NF support, and image B is a SEM image of BiVO4 / NF.

[0029] Figure 3 The graph shows the photocatalytic degradation efficiency of TCH by NF, BiVO4, and BiVO4 / NF according to the present invention; wherein, the reaction conditions are: TCH concentration 5 mg·L. -1 The size of BiVO4 / NF is 10*10mm.

[0030] Figure 4 To investigate the effect of initial pH of the BiVO4 / NF / Vis solution on the degradation rate of TCH; the reaction conditions were: TCH concentration 5 mg·L⁻¹. -1 The size of BiVO4 / NF is 10*10mm.

[0031] Figure 5 This is a diagram of the cyclic degradation experiment of the present invention; wherein, the reaction conditions are: TCH concentration 5 mg·L⁻¹. -1 The size of BiVO4 / NF is 10*10mm.

[0032] Figure 6 This invention provides experiments on the degradation of various organic pollutants. Detailed Implementation

[0033] The invention will be further described below with reference to the accompanying drawings.

[0034] Example: A supported BiVO4 / NF photocatalyst, the preparation method of which includes the following steps:

[0035] The first step is to cut NF (nickel foam) into 10*10mm pieces and immerse them in 1 mmol·L⁻¹ solution. -1 The NF was ultrasonically treated in dilute hydrochloric acid, anhydrous ethanol, and ultrapure water for 20 min, and then dried in a vacuum drying oven for 12 h to obtain the NF carrier for later use.

[0036] In the second step, 0.9701g Bi(NO3)3•5H2O was added to 30mL of (CH2OH)2 and stirred until dissolved. Then, 0.2340g NH4VO3 was added and stirring was continued to obtain the BiVO4 precursor solution.

[0037] The third step involves vertically fixing the pretreated NF carrier within the polytetrafluoroethylene liner of the hydrothermal reactor, then transferring the completely dissolved BiVO4 precursor solution into the reactor, and subsequently placing it in an oven at 180°C for 2 hours.

[0038] Fourth step: After the reactor is cooled to room temperature, the NF loaded with BiVO4 is taken out, washed several times with ethanol and ultrapure water, and then placed in a vacuum drying oven at 60°C for 12 hours. The obtained product is then placed in a muffle furnace and calcined at 450°C for 30 minutes to obtain the supported BiVO4 / NF photocatalyst.

[0039] A supported BiVO4 / NF photocatalyst was prepared using the above method, wherein the NF support is loaded with nanosphere-shaped BiVO4 crystals.

[0040] The crystal structure of the catalyst was studied using XRD. Figure 1 ).like Figure 1 As shown, the diffraction peaks of BiVO4 match well with those of monoclinic scheelite BiVO4 (JCPDS No. 14-0688). The XRD patterns of BiVO4 / NF and NF show almost identical diffraction peak positions, with the peaks at 44.5°, 51.8°, and 76.4° corresponding to the (111), (200), and (220) crystal planes of Ni in the NF substrate (JCPDS No. 03-1051). For BiVO4 / NF, the weak diffraction peak at 28.8° corresponds to the (121) crystal plane of BiVO4. The XRD patterns demonstrate that BiVO4 can be successfully grown on the NF surface via a one-step hydrothermal method.

[0041] The morphology of the synthesized catalyst was observed by scanning electron microscopy. SEM images of the BiVO4 catalyst grown on the NF surface are shown below. Figure 2 As shown. NF ( Figure 2 A) It possesses a 3D porous framework and a smooth outer surface, which is beneficial for the growth of BiVO4. For example... Figure 2 As shown in Figure B, the 3D framework of the BiVO4 / NF sample is encapsulated with dense BiVO4 crystals. BiVO4 is a nanosphere structure with a diameter of approximately 600 nm, confirming that BiVO4 is firmly grown on NF.

[0042] Figure 3The degradation results of TCH under different conditions show that the supported BiVO4 / NF exhibits a significantly enhanced degradation effect on TCH. Under visible light irradiation, the supported BiVO4 / NF achieved a TCH degradation rate of 95.2% after 90 minutes, which is 5.73 times that of BiVO4 alone and 11.92 times that of NF alone. Meanwhile... Figure 3 This indicates that BiVO4 / NF exhibits poor degradation efficiency for TCH under dark conditions. This suggests that BiVO4 / NF cannot effectively degrade TCH in the absence of visible light.

[0043] The effect of different initial pH values ​​on TCH degradation efficiency was studied, and the results are as follows: Figure 4 As shown, when the pH value is below 7, the degradation efficiency increases with increasing pH value. This is because acidic solutions have a higher concentration of activated hydrogen atoms, which improves the solvation efficiency of the photocatalyst. Conversely, when the pH value is above 7.0, the removal efficiency of TCH decreases with increasing pH. The results show that the TCH removal rate is the highest at pH 5.0, reaching 98.2%. When the pH value increases to 9.0, the degradation rate of TCH is significantly inhibited, decreasing to 50.7% after 90 min. This is because when the pH value is greater than 7.7, both TCH and BiVO4 / NF carry negative charges, which creates a strong repulsive force between them, hindering the adsorption of TCH by BiVO4 / NF. Overall, BiVO4 / NF maintains a high degradation rate of TCH in both acidic and neutral solutions.

[0044] The stability and recyclability of the supported BiVO4 / NF were evaluated through cyclic experiments. Using BiVO4 / NF as a photocatalyst, no further treatment was required after each photocatalytic experiment; the BiVO4 / NF was directly reused for TCH degradation experiments. The experimental results are as follows: Figure 5 As shown, the degradation rate of TCH by BiVO4 / NF still reaches 80% after five cycles. After five cycles, the degradation rate of TCH slightly decreases, which can be attributed to residual TCH and a small amount of BiVO4 photocatalyst shedding from the NF surface during photocatalysis. The cycling experiments confirm the stability of BiVO4 / NF, and the cycling process, which requires no additional chemical treatment, promises to reduce catalyst recovery costs in practical applications.

[0045] To test its general applicability, supported BiVO4 / NF was used to degrade various dyes and antibiotics. Only the types of pollutants used were varied while keeping other conditions constant. The experimental results are as follows: Figure 6As shown, BiVO4 / NF achieved a 100% degradation rate of methyl orange (MO) within 60 min and a 100% degradation rate of rhodamine B (RhB) within 90 min. The degradation rates of TCH, oxytetracycline (OTC), and levofloxacin (LEV) within 90 min were 95.2%, 94.0%, and 78.7%, respectively, demonstrating that the supported BiVO4 / NF exhibited excellent photocatalytic degradation effects on these organic pollutants. This proves that BiVO4 / NF is a promising photocatalyst for the degradation of various organic pollutants in wastewater.

[0046] Obviously, the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description; it is neither necessary nor possible to exhaustively list all possible implementations; however, obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. An application of a supported BiVO4 / NF photocatalyst, characterized in that: The supported BiVO4 / NF photocatalyst is used to degrade tetracycline hydrochloride in water; The supported BiVO4 / NF photocatalyst was prepared by the following steps: Step 1: Cut the NF and immerse it in dilute hydrochloric acid, ethanol and ultrapure water in sequence for ultrasonic treatment. Then put the NF into a vacuum drying oven to dry it and obtain the NF carrier. The NF is nickel foam; the NF is cut to a size of 10*10 mm; the concentration of the dilute hydrochloric acid is 1 mmol·L⁻¹. -1 The ethanol is anhydrous ethanol; the ultrasonic treatment time is 20 minutes. Step 2: Add Bi(NO3)3•5H2O to (CH2OH)2 and stir until dissolved. Then add NH4VO3 and continue stirring to obtain a BiVO4 precursor solution. The molar ratio of Bi(NO3)3•5H2O to NH4VO3 is 0.5 to 3. Step 3: The NF carrier pretreated in Step 1 is vertically fixed in the polytetrafluoroethylene liner of the hydrothermal reactor. Then, the BiVO4 precursor solution stirred until completely dissolved in Step 2 is transferred into the reactor and then placed in an oven for heat preservation. The oven is kept at a temperature of 180°C for 2 hours. Step 4: After the reactor cools to room temperature, the NF support loaded with BiVO4 is removed, washed several times with ethanol and ultrapure water, and then placed in a vacuum drying oven for vacuum drying. Finally, it is calcined in a muffle furnace to obtain the supported BiVO4 / NF photocatalyst; the NF support is loaded with nanosphere-shaped BiVO4 crystals. The vacuum drying oven has a holding temperature of 60℃ and a holding time of 2 hours; the muffle furnace has a calcination temperature of 450℃, a heating rate of 10℃ / min, a heating time of 45 minutes, and a holding time of 30 minutes.

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