CN115430462B - Bi-based photocatalytic material loaded by PVDF (polyvinylidene fluoride) film as well as preparation method and application thereof - Google Patents

Abstract

The invention discloses a PVDF film supported Bi-based photocatalytic material, a preparation method and application thereof, wherein BiOCOOH, biOCOOH is a layered double-based oxide which is formed by inserting [ Bi ₂O₂]²⁺ fluorescent layer formic acid. Then, bi metal is compounded on BiOCOOH, so that the simple substance Bi is loaded on BiOCOOH, the combination of photo-generated electron-hole pairs of the simple substance Bi can be effectively improved, and the absorption intensity of visible light is improved. The invention adopts PVDF and photocatalyst to combine and prepare a novel porous hybrid membrane material so as to solve the problems of photocatalyst loss caused by difficult recovery of the photocatalyst and partial aggregation of the photocatalyst in the reaction process, thereby improving the degradation effect on ciprofloxacin in water.

Description

PVDF membrane-supported Bi-based photocatalytic material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of catalytic materials, and in particular relates to a PVDF film-loaded Bi-based photocatalytic material and a preparation method and application thereof.

Background Art

Water resources are the most important substance for human survival, but with the acceleration of industrialization, more and more water resources are polluted. Water pollution is potentially dangerous to human health and the environment; it has direct and indirect damage to the health of all organisms. Unlike traditional water treatment methods, such as chlorination, ozonation, biodegradation and ultraviolet irradiation, advanced oxidation technology provides a safer and more natural water treatment method. However, this method also has many disadvantages, such as high investment, high maintenance costs, large consumption of chemical reagents, and environmental problems caused by wastewater treatment.

Among many advanced oxidation technologies, photocatalytic technology is green and environmentally friendly, has no secondary pollution, is simple to operate, and has a fast reaction. It is one of the important ways to solve water pollution.

Photocatalysis is a catalytic reaction under the action of light, which mostly occurs on the surface of semiconductors or some adsorbed reactive small molecules. When the light energy exceeds the band gap energy of the conductor or semiconductor, electrons will be excited to jump from their valence band to the conduction band, and there will be the same number of holes in the valence band; the separated electrons-holes will migrate to the surface of the conductor or semiconductor, where they are captured by electron donors or electron acceptors to undergo redox reactions, ultimately achieving photocatalytic reactions.

Using natural solar energy, photocatalytic technology removes pollutants and decomposes hydrogen in water, which can not only reduce environmental pollution, but also solve the problem of energy shortage and has economic benefits. Since _TiO2 was reported in 1972, there have been a lot of research on photocatalysts, but the photocatalysts themselves also have defects, such as narrow light absorption range, easy recombination of electrons and holes, difficulty in recycling, and partial aggregation.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a PVDF membrane-loaded Bi-based photocatalytic material and a preparation method and application thereof, so as to solve the problem that the photocatalyst is not easy to recover in the prior art, resulting in reduced photocatalyst activity and partial aggregation of the photocatalyst during the reaction, thereby improving the utilization rate of the catalyst and the photocatalytic degradation effect, as well as the degradation effect of ciprofloxacin in water.

In order to achieve the above object, the present invention adopts the following technical solutions:

The preparation method of the Bi-based photocatalytic material supported by a PVDF film comprises the following steps:

Step 1, dissolving Bi(NO ₃ ) ₃ ·5H ₂ O in a mixed solvent of DMF and water, adding glycerol after dissolution, stirring to obtain a clear solution A, subjecting the clear solution A to a solvothermal reaction to obtain a reaction product B, washing the reaction product B and drying it to obtain BiOCOOH powder;

Step 2, dissolving Bi(NO ₃ ) ₃ ·5H ₂ O in ethylene glycol to obtain solution C; adding BiOCOOH powder to solution C to obtain reaction solution D; heating the reaction solution D for reaction, and washing the reaction product to obtain Bi/BiOCOOH nanocomposite material;

Step 3, dissolving PVP in DMF to obtain solution E, adding Bi/BiOCOOH nanocomposite material to solution E, stirring evenly to obtain mixed solution F, adding PVDF to mixed solution F, stirring to form film-forming solution G, forming the membrane solution into a film, and obtaining Bi-based photocatalytic material loaded on PVDF membrane.

A further improvement of the present invention is:

Preferably, in step 1, the mixing ratio of Bi(NO ₃ ) ₃ ·5H ₂ O, DMF and glycerol is: 4 mmol: 30 mL: 50 mL.

Preferably, in step 1, the solvent thermal reaction temperature is 160° C., and the solvent thermal reaction time is 24 h.

Preferably, in step 2, the added Bi(NO ₃ ) ₃ ·5H ₂ O accounts for 2% to 6% of the mass of the BiOCOOH powder.

Preferably, in step 2, the reaction solution D is heated to a reaction temperature of 150-180° C., and the reaction time is 8 h.

Preferably, in step 3, the mixing ratio of PVP and DMF is 0.3 g: (7.26-8) mL.

Preferably, in step 2, after the Bi/BiOCOOH nanocomposite material is added to solution E, the stirring temperature is 40 to 80° C. and the stirring time is 8 to 15 hours.

Preferably, the added amount of the Bi/BiOCOOH nanocomposite material is 1% to 7%.

A PVDF membrane-supported Bi-based photocatalytic material prepared by any one of the preparation methods described above comprises a PVDF membrane, on which flower-shaped BiOCOOH is supported, and on which BiOCOOH are supported Bi nanoparticles.

An application of the Bi-based photocatalytic material supported by the PVDF membrane to the degradation of antibiotics in water.

Compared with the prior art, the present invention has the following beneficial effects:

The invention discloses a preparation method of a Bi-based photocatalytic material supported by a PVDF film. The preparation method first prepares BiOCOOH, which is a layered double-base oxide formed by inserting a [Bi ₂ O ₂ ] ²⁺ fluorescent layer formic acid. Then, Bi metal is compounded on BiOCOOH. Semimetallic bismuth, as a direct plasma photocatalyst, has been proven to have good photocatalytic activity, and its surface plasmon resonance (SPR) effect has special electronic characteristics similar to precious metals. Therefore, loading Bi element on BiOCOOH can effectively improve the recombination of its photogenerated electron-hole pairs and increase the absorption intensity of visible light. However, since small-particle composite nanomaterials are easy to agglomerate, they are difficult to recycle in practical applications, affecting the photocatalytic performance of composite semiconductor materials and the reusability of photocatalysts. Combining a PVDF film with a small-particle photocatalyst makes it no longer easy for the granular photocatalyst to aggregate.

The present invention also discloses a Bi-based photocatalytic material supported by a PVDF membrane, wherein the catalytic material supports a Bi/BiOCOOH nanocomposite material on the PVDF membrane, so that the Bi/BiOCOOH nanocomposite catalytic material can fully exert its catalytic effect in water. SEM, TEM, XPS, and XRD characterize the successful preparation of the photocatalytic composite membrane, BET characterizes the pore size and pore volume of the composite membrane, UV-Vis, EIS, PC, and PL characterize the optical properties of the composite membrane, and EPR characterizes the main active substances. The optimal treatment conditions of the composite membrane are determined through experiments on pH and inorganic anions.

The present invention also discloses a PVDF film-supported Bi-based photocatalytic material for treating antibiotics in water. During the catalytic process, BiOCOOH will undergo electron transition when exposed to external light with an Eg greater than that of the BiOCOOH. The separated electrons will migrate to the conduction band, while holes equal to the number of electrons will remain in the valence band. The electrons in the conduction band of BiOCOOH can be quickly transferred to the elemental Bi, thereby significantly promoting the separation of electron-hole pairs. These separated electrons will react with dissolved oxygen in the system to generate ·O ₂ ^-free radicals, and the holes will directly react with water in the system to generate ·OH free radicals. The holes themselves will also oxidize ciprofloxacin. It is the presence of these active substances that causes ciprofloxacin to be degraded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a microscopic morphology of a material prepared by the present invention;

Figure A is the SEM image of BiOCOOH, Figure B is the SEM image of Bi/BiOCOOH; Figure C is the scanning energy spectrum

Figures D, E, and F are the mapping diagrams of Bi/BiOCOOH, respectively;

Figure 2 is the top and cross-sectional SEM images of Bi/BiOCOOH/PVDF with 0%, 1%, 3%, 5%, and 7% in Figures A-J;

Among them, Figures A-E are top SEM images of 0%, 1%, 3%, 5%, and 7%, and Figures F-J are cross-sectional SEM images of 0%, 1%, 3%, 5%, and 7%.

FIG3 is an XPS diagram, an XRD diagram and an analysis diagram of the present invention;

Among them, Figures A-D are XPS graphs of Bi/BiOCOOH/PVDF; Figure E is the XRD graph of different materials; Figures F-G are nitrogen adsorption-analysis graphs and pore size distribution graphs of Bi/BiOCOOH/PVDF.

Figure 4 is a diagram for exploring optical performance.

Among them, Figure A is the UV-vis diagram of different materials; Figure B is the band gap diagram of different materials;

Figure C is the valence band spectrum of Bi/BiOCOOH/PVDF; Figure D is the PL graph of different materials;

Figures E-F are EIS and PC graphs of different materials.

Figure 5 A and B are explorations of the optimal ratio; Figure C compares the photodegradation effects of three different catalysts;

Figures D-E explore the effects of inorganic anions and pH on the photodegradation of Bi/BiOCOOH/PVDF.

Figure 6 A and B detect active substances during the photocatalytic reaction. Figures C and D are diagrams of the reuse of Bi/BiOCOOH/PVDF;

Figure 7 is a mechanism diagram.

DETAILED DESCRIPTION

The steps of the present invention are further described in detail below with reference to the accompanying drawings and specific embodiments.

The present invention discloses a PVDF film-supported Bi-based photocatalytic material and a preparation method and application thereof. The preparation method of the catalytic material comprises the following steps:

Step 1. Synthesis of BiOCOOH via solvothermal method

Bi(NO ₃ ) ₃ ·5H ₂ O (4 mmol) (1.94 g) was dissolved in 20 mL DMF and 10 mL water under vigorous stirring. After dissolution, 50 mL of glycerol (propylene glycol) was added to the above solution and stirred evenly so that the solution became clear after each substance was dissolved, and a clear solution A was obtained. The obtained solution was poured into an autoclave with a volume of 100 mL, and a solvent thermal reaction was carried out at 160° C. for 24 hours to generate the initial product of BiOCOOH and obtain the reaction product B. After the reaction was completed, the collected reaction product B was washed 3 times with deionized water and ethanol, and finally transferred into an oven and dried at 60° C. for 15 hours to obtain BiOCOOH powder;

Step 2. Synthesis of Bi/BiOCOOH

Bi/BiOCOOH nanocomposites were prepared by a simple solvothermal method. The specific process is as follows:

Bi(NO ₃ ) ₃ ·5H ₂ O was ultrasonically dissolved in 65 mL of ethylene glycol (EG) to obtain solution C. BiOCOOH powder was then added to the above solution C, wherein the mass ratio of Bi(NO ₃ ) ₃ ·5H ₂ O in the BiOCOOH powder was in the range of 1% to 7%, and the mixture was uniformly stirred after ultrasonic dispersion to obtain reaction solution D, which was heated in a reactor at 150 to 180°C for 8 h. The obtained composite material was washed three times with deionized water and ethanol, and dried at 80°C for 12 h. A Bi/BiOCOOH nanocomposite material was prepared. The BiOCOOH in the composite material was composed of 3D flower-like microspheres of uniform size (Figure 3A-B).

3. Synthesis of Bi/BiOCOOH/PVDF

PVP (polyvinyl pyrrolidone) powder was dissolved in DMF (N, N-dimethylformamide) (ρ=0.950) solvent under mechanical stirring to obtain solution E; a certain amount of catalyst Bi/BiOCOOH was ground and put into solution E, and stirred evenly to obtain a mixed solution F;

PVDF (polyvinyl fluoride) powder is dissolved in the above mixed solution F and mechanically stirred at 40-80°C for 8-15h to form a membrane-forming solution G; the above solution is degassed at a constant temperature for 12h to eliminate bubbles, and then the solution is scraped onto a glass plate with a film scraper. The formed film is immersed in deionized water and washed with deionized water every 6h on the first day to remove residual solvent, and then stored in deionized water until use. After the membrane material is fully formed, use filter paper to absorb excess moisture and place it in a fresh-keeping bag for subsequent use. In this step, the weight of PVP, DMF, Bi/BiOCOOH and PVDF is 10g.

By the above method, a PVDF membrane-supported Bi-based photocatalytic material is prepared, which is a new type of porous hybrid membrane material. The material includes a PVDF membrane, Bi nanoparticles and flower-shaped BiOCOOH, and the specific structure is that the PVDF membrane is supported by flower-shaped BiOCOOH, and BiOCOOH is supported by Bi nanoparticles.

Table 1 Ratios of various materials when preparing thin film catalysts of different masses

Comparative Example

3 g of PVP (polyvinyl pyrrolidone) powder was dissolved in 8 mL of DMF (N,N-dimethylformamide) (ρ=0.950) solvent under mechanical stirring;

Dissolve 2.1g of PVDF (polyvinyl fluoride) powder in the above solution and mechanically stir at 50°C for 12h to form a solution; degas the above solution at constant temperature for 12h to eliminate bubbles, then use a film scraper to scrape the solution onto a glass plate, immerse the formed membrane in deionized water, wash with deionized water every 6h on the first day to remove residual solvent, and then store in deionized water until use. After the membrane material is fully formed, use filter paper to absorb excess moisture and place it in a fresh-keeping bag for subsequent use.

Example 1

Step 1. Synthesis of BiOCOOH via solvothermal method

Bi(NO ₃ ) ₃ ·5H ₂ O (4mmol) (1.94g) was dissolved in 20mL DMF and 10mL water under vigorous stirring. After dissolution, 50mL of glycerol (propylene glycol) was added to the above solution and stirred evenly so that each substance was dissolved and the solution became clear. The obtained solution was poured into an autoclave with a volume of 100mL and subjected to a solvothermal reaction at 160°C for 24h to generate the initial product of BiOCOOH. After the reaction was completed, the collected product was washed 3 times with deionized water and ethanol, and finally transferred into an oven and dried at 60°C for 15h to obtain BiOCOOH powder;

Step 2. Synthesis of Bi/BiOCOOH

Bi/BiOCOOH nanocomposites were prepared by a simple solvothermal method. The specific process is as follows:

0.021g Bi(NO ₃ ) ₃ ·5H ₂ O was ultrasonically dissolved in 65mL ethylene glycol (EG). Then 0.42g BiOCOOH powder was added to the above solution, wherein Bi(NO ₃ ) ₃ ·5H ₂ O accounted for 5% of the BiOCOOH powder by mass, and stirred evenly after ultrasonic dispersion, and heated at 180°C in a reactor for 8h. The obtained composite material was washed with deionized water and ethanol for 3 times, and dried at 80°C for 12h. Bi/BiOCOOH nanocomposite material was prepared.

3. Synthesis of Bi/BiOCOOH/PVDF

0.3 g of PVP (polyvinyl pyrrolidone) powder was dissolved in 7.89 mL of DMF (N,N-dimethylformamide) (ρ=0.950) solvent under mechanical stirring; 0.1 g of catalyst Bi/BiOCOOH was ground and put into the above solution, and stirred evenly so that the mass proportion of the catalyst in the above solution was 1%.

Dissolve 2.1g of PVDF (polyvinyl fluoride) powder in the above solution and mechanically stir at 50°C for 12h to form a solution; degas the above solution at constant temperature for 12h to eliminate bubbles, then use a film scraper to scrape the solution onto a glass plate, immerse the formed membrane in deionized water, wash with deionized water every 6h on the first day to remove residual solvent, and then store in deionized water until use. After the membrane material is fully formed, use filter paper to absorb excess moisture and place it in a fresh-keeping bag for subsequent use.

By the above method, a Bi-based photocatalytic material supported by a PVDF membrane was prepared, which was 1% Bi/BiOCOOH/PVDF.

Example 2

Step 1, Synthesis of BiOCOOH by Solvothermal Method

Bi(NO ₃ ) ₃ ·5H ₂ O (4 mmol) (1.94 g) was dissolved in 20 mL DMF and 10 mL water under vigorous stirring. After dissolution, 50 mL of glycerol (propylene glycol) was added to the above solution and stirred evenly so that each substance was dissolved and the solution became clear. The obtained solution was poured into an autoclave with a volume of 100 mL and subjected to a solvothermal reaction at 160°C for 24 hours to generate the initial product of BiOCOOH. After the reaction was completed, the collected product was washed 3 times with deionized water and ethanol, and finally transferred into an oven and dried at 60°C for 15 hours to obtain BiOCOOH powder;

Step 2. Synthesis of Bi/BiOCOOH

Bi/BiOCOOH nanocomposites were prepared by a simple solvothermal method. The specific process is as follows:

0.021g Bi(NO ₃ ) ₃ ·5H ₂ O was ultrasonically dissolved in 65mL ethylene glycol (EG). Then 0.42g BiOCOOH powder was added to the above solution, wherein Bi(NO ₃ ) ₃ ·5H ₂ O accounted for 5% of the mass fraction of BiOCOOH powder, and stirred evenly after ultrasonic dispersion, and heated at 180°C in a reactor for 8h. The obtained composite material was washed with deionized water and ethanol for 3 times, and dried at 80°C for 12h. Bi/BiOCOOH nanocomposite material was prepared.

3. Synthesis of Bi/BiOCOOH/PVDF

0.3 g of PVP (polyvinyl pyrrolidone) powder was dissolved in 7.68 mL of DMF (N,N-dimethylformamide) (ρ=0.950) solvent under mechanical stirring; 0.3 g of catalyst Bi/BiOCOOH was ground and put into the above solution, and stirred evenly so that the mass fraction of the catalyst in the solvent was 3%.

Dissolve 2.1g of PVDF (polyvinyl fluoride) powder in the above solution and mechanically stir at 50°C for 12h to form a solution; degas the above solution at constant temperature for 12h to eliminate bubbles, then use a film scraper to scrape the solution onto a glass plate, immerse the formed membrane in deionized water, wash with deionized water every 6h on the first day to remove residual solvent, and then store in deionized water until use. After the membrane material is fully formed, use filter paper to absorb excess moisture and place it in a fresh-keeping bag for subsequent use.

By the above method, a Bi-based photocatalytic material supported by a PVDF membrane was prepared, which was 3% Bi/BiOCOOH/PVDF.

Example 3

Step 1. Synthesis of BiOCOOH via solvothermal method

Bi(NO ₃ ) ₃ ·5H ₂ O (4mmol) (1.94g) was dissolved in 20mL DMF and 10mL water under vigorous stirring. After dissolution, 50mL of glycerol (propylene glycol) was added to the above solution and stirred evenly so that each substance was dissolved and the solution became clear. The obtained solution was poured into an autoclave with a volume of 100mL and subjected to a solvothermal reaction at 160°C for 24h to generate the initial product of BiOCOOH. After the reaction was completed, the collected product was washed 3 times with deionized water and ethanol, and finally transferred into an oven and dried at 60°C for 15h to obtain BiOCOOH powder;

Step 2. Synthesis of Bi/BiOCOOH

Bi/BiOCOOH nanocomposites were prepared by a simple solvothermal method. The specific process is as follows:

0.021g Bi(NO ₃ ) ₃ ·5H ₂ O was ultrasonically dissolved in 65mL ethylene glycol (EG). Then 0.42g BiOCOOH powder was added to the above solution, wherein Bi(NO ₃ ) ₃ ·5H ₂ O accounted for 5% of the BiOCOOH powder by mass, and stirred evenly after ultrasonic dispersion, and heated at 180℃ in a reactor for 8h. The obtained composite material was washed with deionized water and ethanol for 3 times, and dried at 80℃ for 12h. Bi/BiOCOOH nanocomposite was prepared. The BiOCOOH in the composite material is composed of 3D flower-like microspheres of uniform size (Figure 3A-B). The surface of 5% Bi/BiOCOOH has both uniform flower-like microsphere structure and some flaky structures, and these flaky structures may be formed by the destruction of some of the original flower-like microspheres after the BiOCOOH was subjected to secondary hydrothermal treatment.

3. Synthesis of Bi/BiOCOOH/PVDF

0.3 g of PVP (polyvinyl pyrrolidone) powder was dissolved in 7.47 mL of DMF (N,N-dimethylformamide) (ρ=0.950) solvent under mechanical stirring; 0.5 g of catalyst Bi/BiOCOOH was ground and put into the above solution and stirred evenly;

Dissolve 2.1g of PVDF (polyvinyl fluoride) powder in the above solution and mechanically stir at 50℃ for 8-15, 12h to form a solution; degas the above solution at constant temperature for 12h to eliminate bubbles, then use a film scraper to scrape the solution onto a glass plate, immerse the formed membrane in deionized water, wash with deionized water every 6h on the first day to remove residual solvent, and then store in deionized water until use. After the membrane material is fully formed, use filter paper to absorb excess moisture and place it in a fresh-keeping bag for subsequent use.

By the above method, a Bi-based photocatalytic material supported by a PVDF membrane was prepared, which was 5% Bi/BiOCOOH/PVDF.

Example 4

Step 1. Synthesis of BiOCOOH via solvothermal method

Bi(NO ₃ ) ₃ ·5H ₂ O (4mmol) (1.94g) was dissolved in 20mL DMF and 10mL water under vigorous stirring. After dissolution, 50mL of glycerol (propylene glycol) was added to the above solution and stirred evenly so that each substance was dissolved and the solution became clear. The obtained solution was poured into an autoclave with a volume of 100mL and subjected to a solvothermal reaction at 160°C for 24h to generate the initial product of BiOCOOH. After the reaction was completed, the collected product was washed 3 times with deionized water and ethanol, and finally transferred into an oven and dried at 60°C for 15h to obtain BiOCOOH powder;

Step 2. Synthesis of Bi/BiOCOOH

Bi/BiOCOOH nanocomposites were prepared by a simple solvothermal method. The specific process is as follows:

0.021g Bi(NO ₃ ) ₃ ·5H ₂ O was ultrasonically dissolved in 65mL ethylene glycol (EG). Then 0.42g BiOCOOH powder was added to the above solution, wherein the mass ratio of Bi(NO ₃ ) ₃ ·5H ₂ O in the BiOCOOH powder ranged from 1% to 7%, and the mixture was stirred evenly after ultrasonic dispersion, and heated at 180℃ in a reactor for 8h. The obtained composite material was washed with deionized water and ethanol for 3 times, and dried at 80℃ for 12h. A Bi/BiOCOOH nanocomposite was prepared. The BiOCOOH in the composite material was composed of 3D flower-like microspheres of uniform size (Figure 3A-B). The surface of 5% Bi/BiOCOOH had both uniform flower-like microsphere structures and some flaky structures, and these flaky structures may be formed by the destruction of some of the original flower-like microspheres after the BiOCOOH was subjected to secondary hydrothermal treatment.

3. Synthesis of Bi/BiOCOOH/PVDF

PVP (polyvinyl pyrrolidone) powder was dissolved in DMF (N, N-dimethylformamide) (ρ=0.950) solvent under mechanical stirring; 0.7 g Bi/BiOCOOH was ground and put into the above solution and stirred evenly;

PVDF (polyvinyl fluoride) powder is dissolved in the above solution and mechanically stirred at 40-80,50℃ for 8-15,12h to form a solution; the above solution is degassed at constant temperature for 12h to eliminate bubbles, and then the solution is scraped onto a glass plate with a film scraper. The formed membrane is immersed in deionized water, washed with deionized water every 6h on the first day to remove residual solvent, and then stored in deionized water until use. After the membrane material is fully formed, use filter paper to absorb excess moisture and place it in a fresh-keeping bag for subsequent use.

By the above method, a Bi-based photocatalytic material supported by a PVDF membrane was prepared, which was 7% Bi/BiOCOOH/PVDF.

The morphology of BiOCOOH and 5% Bi/BiOCOOH was observed by scanning electron microscopy (Figure 1). It can be clearly seen from Figure 1 that BiOCOOH is composed of 3D flower-like microspheres of uniform size (A-B in Figure 1). The surface of 5% Bi/BiOCOOH has both uniform flower-like microsphere structures and some flaky structures, and these flaky structures may be formed by the destruction of some of the original flower-like microspheres after BiOCOOH was subjected to secondary hydrothermal treatment. Comparing BiOCOOH (Figure 3A) and 5% Bi/BiOCOOH (Figure 3B), it can be found that there are some particulate material accumulations on the flower-like microspheres in 5% Bi/BiOCOOH, which is likely to be the formation of elemental bismuth. This can be proved from the re-transmission image. In addition, the EDS mapping images (Figures 3C-F) show the Bi, C and O elements in the 5% Bi/BiOCOOH nanoparticles.

The top morphology of the membrane catalyst can be seen from Figure 2 (A, B, C, D, E). As the amount of catalyst increases, the pores on the membrane surface become fewer and fewer, and fragments and wrinkles appear on the surface. This is because the amount of catalyst increases, and some are stacked together to form microscopic flakes. In addition, when the membrane catalyst is degassed at rest, some catalysts may precipitate downward. The catalyst content of solutions at different heights is different. During the scraping process, cracks and wrinkles appear on the membrane surface. It can be seen from the cross-sectional diagram 2 (F, G, H, I, J) of the membrane catalyst that the top layer is a thin and dense layer, which forms the activity and selectivity of the membrane. The bottom layer is a finger-like structure with larger holes, which supports the surface of the membrane, which is conducive to the transmission of light. As the amount of catalyst increases, the holes in the membrane hardly change, and the original structural characteristics of the membrane are maintained.

The elemental composition and binding energy of 5% Bi/BiOCOOH/PVDF can be demonstrated by XPS graphs (Figure 3A-D). The full XPS spectrum shows the coexistence of Bi, O and C elements, which is consistent with the sample composition of the photocatalyst. The high-resolution C1s XPS spectrum (Figure 3B) shows that the peak at 284.3eV may be related to adventitious carbon, while the peaks at 285.7eV and 290.2eV belong to the carbon in the carboxyl group. In the O1s XPS spectrum (Figure 3C), the two peaks at 529.8eV and 531.6eV belong to the Bi-O bond and the oxygen in -COOH, respectively. The high-resolution Bi 4f XPS spectrum (Figure 3D) shows that the two peaks at 158.5eV and 163.7eV belong to Bi 4f _7/2 and Bi4f _5/2 , while the two peaks at 157.4eV and 162.6eV belong to semi-metallic bismuth. These results are consistent with the XRD characterization and also indicate that BiOCOOH and Bi exist simultaneously in 5%Bi/BiOCOOH/PVDF.

From XRD (Figure 3E), we can see the crystallinity and crystalline phase of BiOCOOH, 5%Bi/BiOCOOH, PVDF, and 5%Bi/BiOCOOH/PVDF. The diffraction peak position of BiOCOOH is consistent with the standard card of BiOCOOH (JCPDS No.35-0939), among which 24.33°, 28.82°, 32.52°, 35.06°, 41.86°, 46.53°, 53.44° and 55.69° correspond to (101), (102), (110), (103), (113), (200), (211) and (212) crystal planes, respectively, proving that this material has been successfully prepared. The diffraction peak position of 5%Bi/BiOCOOH is consistent with that of BiOCOOH. The diffraction peaks at 24.33°, 37.9° and 39.62° correspond to the diffraction peaks of (012), (104) and (110) crystal planes, respectively, which are consistent with the diffraction peaks of the standard card (JCPDS No.85-1329) of single substance Bi. The (110) crystal plane at 20.16° is the characteristic diffraction peak of PVDF. The diffraction peaks of 5%Bi/BiOCOOH/PVDF are also almost consistent with the characteristic diffraction peaks of the standard card (JCPDS No.35-0939), (JCPDS No.85-1329) and PVDF. This can also prove that the composite material has been successfully prepared.

As shown in Figure 3F, the _N2 absorption-desorption type IV isotherms of BiOCOOH, 5% Bi/BiOCOOH and 5% Bi/BiOCOOH/PVDF all show type IV curves for H3 hysteresis loops, indicating the presence of mesopores (2-50nm), which may be due to the narrow slit-like pores formed by the flower-like microsphere morphology. In addition, the corresponding pore size distribution curve (Figure 3G) shows that most of the pores are distributed from 2-30nm, which is consistent with the results of the nitrogen adsorption-desorption isotherm, confirming the existence of mesopores. The sharp peak of all samples is about 2.5nm, which may be attributed to the narrow slit-like pores formed by the flower-like microsphere morphology of BiOCOOH and the presence of voids between nanoparticles (observed in the SEM image). According to relevant reports, the mesoporous structure of the catalyst can provide an effective transport pathway for photogenerated carriers and reactants, which is beneficial to improve the photocatalytic activity.

The light absorption properties of BiOCOOH, 5% Bi/BiOCOOH and 5% Bi/BiOCOOH/PVDF were revealed by UV-visible diffuse reflectance spectroscopy (UV-vis DRS) (Figure 4A). Pure BiOCOOH has a very low light absorption intensity in the visible light wavelength range. 5% Bi/BiOCOOH and 5% Bi/BiOCOOH/PVDF have enhanced light absorption intensity, and the maximum absorption peak position moves toward the red wave direction, which can be attributed to the surface plasmon resonance effect of single Bi, which helps to improve the optical properties of BiOCOOH and is beneficial to improve the utilization of light in photocatalytic reactions. In addition, the corresponding band gap energy (Eg) value is calculated using the Tauc/David-Mott model, and the formula is as follows:

αhv＝A(hv-E _g ) ⁿ²

Where α, h, ν, A and Eg are absorption coefficient, Planck constant, vibration frequency, proportionality constant and band gap energy respectively. The calculated band gap energies of BiOCOOH, 5%Bi/BiOCOOH and 5%Bi/BiOCOOH/PVDF are 2.9eV, 3.2eV and 3.34eV respectively.

The corresponding valence band energy level analysis was measured by XPS valence band spectrum (Figure 4C). The VB of 5% Bi/BiOCOOH/PVDF is 1.38 eV. In addition, the CB value of 5% Bi/BiOCOOH/PVDF can be calculated by the following formula:

E _g = E _VB - E _CB

Where E _CB and E _VB are the CB and VB of the semiconductor, respectively, and Eg is the band gap of the material. The CB of 5% Bi/BiOCOOH/PVDF is calculated to be -1.82 eV.

The recombination rate of photogenerated electron-hole pairs was studied. The photoluminescence (PL) spectra of BiOCOOH, 5% Bi/BiOCOOH and 5% Bi/BiOCOOH/PVDF are shown in Figure 4D. The PL intensity of 5% Bi/BiOCOOH and 5% Bi/BiOCOOH/PVDF is lower than that of BiOCOOH, which means a low recombination rate of photogenerated carriers, improving the defect of easy recombination of photogenerated carriers in BiOCOOH.

The separation and transfer efficiency of carriers are key factors affecting the photocatalytic efficiency. As can be seen from Figure 4E, 5% Bi/BiOCOOH has a high current density, indicating that it has better carrier separation efficiency. At the same time, Figure 4F shows that the arc radius of 5% Bi/BiOCOOH is the smallest, which also proves that it has excellent photogenerated carrier characteristics, which is consistent with the results of Figure 4E, proving that BiOCOOH modified with single substance Bi has excellent photocatalytic activity.

As can be seen from Figure 5A, 5% Bi/BiOCOOH has the best catalytic effect. As can be seen from Figure 5B, 5% Bi/BiOCOOH/PVDF has the best photocatalytic effect. Comparing the three different catalysts, Figure 5C shows that the 5% Bi/BiOCOOH/PVDF photocatalyst loaded with a polymer film has almost the same degradation effect on ciprofloxacin as the 5% Bi/BiOCOOH photocatalyst, which can indicate that the polymer film has almost no negative impact on photocatalytic degradation, that is, it also shows that the photocatalyst loaded with a polymer film has excellent photocatalytic performance. As can be seen from Figures 5D and E, SO ₄ ^2- and pH 7 have the least effect on photocatalytic degradation.

In order to explore the possible mechanism of photocatalytic degradation of ciprofloxacin, free radical detection experiments were performed to analyze the free radicals that play a major role in the degradation of ciprofloxacin tablets. From Figure 6A and Figure 6B, it can be seen that the active species that play a major role in the photocatalytic degradation process are ·O ^2- and ·OH. The structure and stable performance of the catalyst are also very important in the photocatalytic degradation process. Under the same test conditions, the Bi/BiOCOOH/PVDF photocatalytic material was tested for photocatalytic performance after four cycles (as shown in Figure 6C). With the increase in the number of uses, the photocatalytic degradation ability of the photocatalytic material decreased slightly. The degradation efficiency of the first cycle was 89%, and the degradation efficiency after four cycles was 87%. This shows that the polymer film-loaded catalyst has almost no change in the photocatalytic degradation process (as shown in Figure D). After four cycles, it still has a high degradation efficiency for the photocatalytic degradation of ciprofloxacin, indicating that the composite material has good stability.

Based on the above research, a possible photocatalytic mechanism is proposed as shown in Figure 7. When BiOCOOH is irradiated by external light greater than its Eg, it will undergo electron transitions. The separated electrons will migrate to the conduction band, while the valence band will leave holes equal to the number of electrons. The electrons in the conduction band of BiOCOOH can be quickly transferred to the elemental Bi, which significantly promotes the separation of electron-hole pairs. These separated electrons will react with the dissolved oxygen in the system to generate ·O ₂ ^- free radicals, and the holes will directly react with the water in the system to generate ·OH free radicals. Moreover, the holes themselves will also oxidize ciprofloxacin. It is the presence of these active substances that causes ciprofloxacin to be degraded.

Example 5

In this embodiment, the mass ratio of Bi(NO ₃ ) ₃ ·5H ₂ O in the BiOCOOH powder is 1%, and the rest is the same as in the first embodiment.

Example 6

In this embodiment, the mass ratio of Bi(NO ₃ ) ₃ ·5H ₂ O in the BiOCOOH powder is 3%, and the rest is the same as in the first embodiment.

Example 7

In this embodiment, the mass ratio of Bi(NO ₃ ) ₃ ·5H ₂ O in the BiOCOOH powder is 5%, and the rest is the same as in the first embodiment.

Example 8

In this embodiment, the mass ratio of Bi(NO ₃ ) ₃ ·5H ₂ O in the BiOCOOH powder is 7%, and the rest is the same as in the first embodiment.

Embodiment 9

In step 2 of this embodiment, the reaction temperature in the reactor is 150° C., the reaction time is 8 h, and the remaining parameters and steps are the same as those in embodiment 1.

Example 10

In step 2 of this embodiment, the reaction temperature in the reactor is 180° C., the reaction time is 8 h, and the remaining parameters and steps are the same as those in embodiment 1.

Embodiment 11

In step 2 of this embodiment, the reaction temperature in the reactor is 160° C., the reaction time is 8 h, and the remaining parameters and steps are the same as those in embodiment 1.

Example 12

In step 2 of this embodiment, the reaction temperature in the reactor is 170° C., the reaction time is 8 h, and the remaining parameters and steps are the same as those in embodiment 1.

Example 13

In step 3 of this embodiment, the mechanical stirring temperature is 40° C. and the mechanical stirring time is 15 h.

Embodiment 14

In step 3 of this embodiment, the mechanical stirring temperature is 50° C. and the mechanical stirring time is 12 h.

Embodiment 15

In step 3 of this embodiment, the mechanical stirring temperature is 70° C. and the mechanical stirring time is 10 h.

Example 16

In step 3 of this embodiment, the mechanical stirring temperature is 80° C. and the mechanical stirring time is 8 h.

BiOCOOH, as an active ultraviolet light driven (ULD) photocatalyst, has the advantages of high chemical stability, low consumption, strong photoredox driving force and high activity. However, the wide band gap of BiOCOOH (e.g., = 3.4 eV) severely limits its practical application, so it needs to be modified to improve its photocatalytic performance. Semiconductors modified with noble metals such as Au, Ag, Pt, and Pd to form metal-semiconductor hybrids have been widely studied and used to accelerate charge separation and solar spectrum absorption. Considering the high cost of these noble metals, some low-cost and easily available metals have been developed.

However, since small particles of composite nanomaterials are easy to agglomerate, they are difficult to recycle in practical applications, affecting the photocatalytic performance of composite semiconductor materials and the reusability of photocatalysts. The hybrid photocatalytic membrane materials have outstanding recycling performance and good light transmittance and porosity. Immobilizing photocatalysts on porous polymers has gradually attracted people's attention. Polyvinylidene fluoride (PVDF) has become a common film-building material due to its unique antioxidant properties and film-forming properties. At the same time, polyvinylidene fluoride is also a common electrochemical auxiliary substrate. On the basis of preparing a new photocatalyst, PVDF is combined with a photocatalyst to prepare a new porous hybrid membrane material to solve the problem of reduced photocatalyst activity caused by the difficulty in recycling photocatalysts and partial aggregation of photocatalysts during the reaction, thereby improving the degradation effect of ciprofloxacin in water.

Photocatalytic thin film materials with good photocatalytic performance and easy to reuse were prepared by hydrothermal method (150℃-180℃, 20h-30h) and phase conversion method (40℃-80℃, 8h-15h)

The wide band gap of BiOCOOH (Eg = 3.4 eV) severely limits its practical application. The utilization rate of visible light is low, and the photogenerated electron-hole pairs are easy to recombine, so the efficiency of degrading antibiotic wastewater is poor. However, semimetallic bismuth, as a direct plasma photocatalyst, has been proven to have good photocatalytic activity. Its surface plasmon resonance (SPR) effect has special electronic properties, similar to precious metals, which can improve the shortcomings of BiOCOOH. The recycling and reuse rate of powdered nanomaterials is low and the economy is poor. On the basis of preparing a new photocatalyst, PVDF is combined with the photocatalyst to prepare a new porous hybrid membrane material to solve the problem of photocatalyst loss caused by the difficulty in recovering the photocatalyst and the partial aggregation of the photocatalyst during the reaction, thereby improving the degradation effect of ciprofloxacin in water.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A method for preparing a Bi-based photocatalytic material supported on a PVDF membrane, characterized in that it comprises the following steps: Step 1, dissolving Bi(NO ₃ ) ₃ ·5H ₂ O in a mixed solvent of DMF and water, adding glycerol after dissolution, stirring to obtain a clear solution A, subjecting the clear solution A to a solvothermal reaction to obtain a reaction product B, washing the reaction product B and drying it to obtain BiOCOOH powder; Step 2, dissolving Bi(NO ₃ ) ₃ ·5H ₂ O in ethylene glycol to obtain solution C; adding BiOCOOH powder to solution C to obtain reaction solution D, heating reaction solution D for reaction, washing the reaction product to obtain Bi/BiOCOOH nanocomposite material; the added Bi(NO ₃ ) ₃ ·5H ₂ O accounts for 2% to 6% of the mass of BiOCOOH powder; Step 3, dissolving PVP in DMF to obtain solution E, adding Bi/BiOCOOH nanocomposite material to solution E, stirring to obtain mixed solution F, adding PVDF to mixed solution F, stirring to form film-forming solution G, forming the film solution into a film, and obtaining Bi-based photocatalytic material supported by PVDF film; the addition amount of Bi/BiOCOOH nanocomposite material is 1% to 7%; The mixing ratio of PVP and DMF is 0.3 g: (7.26-8) mL; After adding Bi/BiOCOOH nanocomposite into solution E, the stirring temperature is 40-80°C and the stirring time is 8-15h; The PVDF membrane-supported Bi-based photocatalytic material is used to degrade antibiotics in water. 2 . The method for preparing a PVDF membrane-supported Bi-based photocatalytic material according to claim 1 , wherein in step 1, the mixing ratio of Bi(NO ₃ ) ₃ ·5H ₂ O, DMF and glycerol is: 4 mmol: 30 mL: 50 mL. 3. The method for preparing a PVDF membrane-supported Bi-based photocatalytic material according to claim 1, characterized in that in step 1, the solvothermal reaction temperature is 160°C and the solvothermal reaction time is 24 hours. 4. The method for preparing a PVDF membrane-supported Bi-based photocatalytic material according to claim 1, characterized in that in step 2, the reaction solution D is heated to a reaction temperature of 150-180°C and the reaction time is 8 hours. 5. A PVDF membrane-supported Bi-based photocatalytic material prepared by the preparation method according to any one of claims 1 to 4, characterized in that it comprises a PVDF membrane, on which flower-shaped BiOCOOH is supported, and on which BiOCOOH are supported Bi nanoparticles. 6. Use of the Bi-based photocatalytic material supported by the PVDF membrane as claimed in claim 5 for the degradation of antibiotics in water.