Preparation method and application of photocatalytic membrane loaded on basis of biochar-based g-C3N4 material

Abstract

The invention discloses a preparation method and application of a photocatalytic membrane loaded on the basis of a charcoal-based g-C3N4 material. The invention relates to a preparation method of a photocatalytic membrane loaded on the basis of a charcoal-based gC3N4 material, which comprises the following steps: 1) dispersing PBC-gC3N4 in water, and carrying out ultrasonic treatment for 20-30 minutes; and (2) enabling the PBC-gC3N4 mixed aqueous solution in the step (1) to continuously pass through a PVDF (Polyvinylidene Fluoride) membrane with the pore diameter of 0.45 mu m by using a vacuum pump until the PBC-gC3N4 is firmly fixed on the surface of the PVDF membrane, and drying in a drying oven at 50-60 DEG C to obtain the photocatalytic membrane loaded with the biochar-based gC3N4 material. The photocatalytic membrane has adsorption and degradation capabilities and is applied to removal of pesticides and antibiotics.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control and membrane separation technology, specifically relating to an integrated photocatalysis-membrane separation membrane material, and more particularly to a method for preparing and applying a photocatalytic membrane supported on biochar-based g-C3N4 material. Background Technology

[0002] The excessive use of pesticides and antibiotics has led to their frequent detection in surface and groundwater, posing a serious environmental risk. Traditional water treatment technologies (such as adsorption, ozone oxidation, and coagulation sedimentation) often suffer from high energy consumption, incomplete treatment, or secondary pollution. Photocatalysis technology has attracted attention due to its mild conditions, visible light response, and environmental friendliness. g-C3N4, as a metal-free visible light-responsive photocatalyst, exhibits high stability and environmental compatibility. However, its low specific surface area and easy electron-hole recombination result in limited catalytic efficiency. Powdered photocatalysts are difficult to recover and reuse in actual wastewater treatment, and particle loss is common, limiting their engineering applications. On the other hand, PVDF membranes are widely used in membrane separation due to their high mechanical strength and good chemical stability, but they suffer from serious membrane fouling problems, manifested as organic pollutant deposition leading to a decrease in membrane flux. Combining photocatalytic materials and PVDF membranes can solve the problem of the difficulty in recovering and reusing powdered photocatalysts in actual wastewater treatment, and can also utilize the excellent degradation performance of photocatalytic materials to improve the decontamination performance and self-cleaning ability of PVDF membranes. Therefore, it is particularly important to study how to combine g-C3N4 material and PVDF membrane into a high-performance photocatalytic membrane and apply it to the removal of pesticide and antibiotic pollution in water. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a method for preparing a photocatalytic membrane supported on biochar-based g-C3N4 material. This method solves the problems of difficulty in recovering existing photocatalysts and the susceptibility of PVDF membranes to fouling, achieving efficient removal of pollutants such as pesticides and antibiotics, and enabling the membrane to self-clean.

[0004] Based on this, the present invention provides a method for preparing a photocatalytic membrane supported on biochar-based g-C3N4 material and its application. The method for preparing a photocatalytic membrane supported on biochar-based (PBC) g-C3N4 material provided by this invention includes the following steps: 1) Disperse PBC-g-C3N4 (biochar-based g-C3N4) in water and sonicate for 20-30 min; 2) Using a vacuum pump, the PBC-g-C3N4 mixed aqueous solution from step 1 is continuously passed through a PVDF membrane with a pore size of 0.45 μm (the PVDF membrane is a common commercial membrane) until the PBC-g-C3N4 is firmly fixed on the surface of the PVDF membrane. After drying in an oven at 50-60℃, a photocatalytic membrane supported on biochar-based gC3N4 material is obtained.

[0005] In step (1), the ratio of PBC-g-C3N4 to water is (10-50) mg: 200 mL.

[0006] In step 2), a vacuum pump is used to continuously pass the PBC-g-C3N4 mixed aqueous solution from step 1 through a PVDF membrane with a pore size of 0.45 μm (the PVDF membrane is a common commercial membrane) until the PBC-g-C3N4 is firmly fixed on the surface of the PVDF membrane. After drying in an oven at 50-60℃, a photocatalytic membrane supported on biochar-based g-C3N4 material is obtained. The photocatalytic membrane prepared by the method based on biochar-based g-C3N4 material is also within the scope of protection of this invention.

[0007] The photocatalytic membrane based on biochar-based g-C3N4 material has a biochar-based g-C3N4 material loading of 0.29-1.45 mg / cm², preferably 1.16 mg / cm².

[0008] The biochar-based g-C3N4 material used in this invention is a composite material obtained by combining biochar and gC3N4. The biochar is H3PO4-activated biochar obtained through H3PO4 modification, specifically a photocatalyst (PBC-gC3N4) obtained by combining H3PO4-modified peanut shell biochar and gC3N4. The mass ratio of biochar to gC3N4 is (0.05-0.3):1; preferably 0.15:1.

[0009] The preparation method can be found in CN118179570A. Specifically, the method for combining biochar and gC3N4 involves adding H3PO4 activated biochar and gC3N4 to deionized water, stirring to disperse them evenly, ultrasonically treating for 4-12 hours, drying the mixture in an oven at 80-110℃, grinding it after drying, placing the ground mixture in a tube furnace, purging with nitrogen, heating it to 550℃ at a rate of 5℃ / min, maintaining it at this temperature for 2 hours, washing with water, and drying to obtain the PBC-gC3N4 composite material. Preferably, the preparation method of H3PO4 activated biochar is as follows: peanut shells are washed, dried, crushed using a crusher, and passed through a 2mm sieve for later use. 20g of crushed peanut shells are soaked in 100ml of a 1M phosphoric acid solution. Soak peanut shells for 12-24 hours, then dry them in an oven at 105℃ for 8-16 hours. After drying, transfer the peanut shells to a corundum boat, place the corundum boat in a tube furnace, purge with nitrogen, and heat to 450℃ at a rate of 5℃ / min, maintaining this temperature for 1 hour. Allow to cool naturally, remove the modified biochar, wash it with water until neutral, dry it in an oven, and grind it to obtain H3PO4 activated biochar. Preferably, the preparation method of gC3N4 is as follows: using melamine as a synthesis precursor, take an appropriate amount of melamine into a corundum boat, place it in a tube furnace, purge with nitrogen, and heat to 550℃ at a rate of 5℃ / min, maintaining this temperature for 4 hours; allow to cool naturally, remove the prepared gC3N4, wash it repeatedly with deionized water, dry it in an oven, grind it, and store it in a brown bottle for later use.

[0010] The beneficial effects of this invention are: This invention utilizes a simple vacuum filtration method to load PBC-g-C3N4 onto a common commercial PVDF membrane. The preparation process is simple and yields excellent results. The method of this invention produces a photocatalytic membrane that possesses both adsorption and degradation capabilities. The prepared photocatalytic membrane is simple to prepare and, when applied to the removal of pesticides and antibiotics, significantly improves the removal rate of these substances. Attached Figure Description

[0011] Figure 1 This is a bar chart showing the removal rate of azoxystrobin by various photocatalytic membranes under different preparation methods in Example 1 of the present invention.

[0012] Figure 2 The images are scanning electron microscope images of the surface and cross-section of the PVDF membrane and the BCN-PVDF photocatalytic membrane in Example 2 of this invention. a is the surface of the PVDF membrane; b is the surface of the BCN-PVDF membrane; c is the cross-section of the PVDF membrane; and d is the cross-section of the PVDF membrane.

[0013] Figure 3 This is a bar chart showing the removal rate of azoxystrobin by the supported photocatalytic membrane prepared in Example 3 of the present invention under different loading conditions.

[0014] Figure 4 This is a comparison curve of the atrazine removal effects of the supported photocatalytic membrane and the PVDF membrane under light / dark conditions in Example 4 of the present invention.

[0015] Figure 5 This is a graph showing the removal efficiency of the supported photocatalytic membrane of Example 5 of the present invention on tetracycline, chlorofloxacin, atrazine, and sulfadiazine.

[0016] Figure 6 This is a graph showing the removal effect of the supported photocatalytic membrane of Embodiment 6 of the present invention on pollutants in different water bodies such as urban sewage, Taihu Lake water, Yangtze River water, Yellow River water, seawater and farmland water. Detailed Implementation

[0017] Unless otherwise specified, the methods described in the following embodiments are conventional methods.

[0018] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art, and the reagents used are all commercially available products.

[0019] The photocatalyst used in this invention is a composite material obtained by combining biochar and gC3N4. The biochar is H3PO4-activated biochar obtained by H3PO4 modification, specifically a photocatalyst composed of H3PO4-modified peanut shell biochar and gC3N4 (PBC-gC3N4). The mass ratio of biochar to gC3N4 is (0.05-0.3):1; preferably 0.15:1.

[0020] The preparation method can be found in CN118179570A (application number (2024104461674)). Specifically, the method for compounding biochar and gC3N4 involves adding H3PO4 activated biochar and gC3N4 to deionized water, stirring to disperse them evenly, ultrasonically treating for 4-12 hours, drying the mixture in an oven at 80-110℃, grinding it after drying, placing the ground mixture in a tube furnace, purging with nitrogen, heating it to 550℃ at a rate of 5℃ / min, maintaining it at this temperature for 2 hours, washing with water, and drying to obtain the PBC-gC3N4 composite material. Preferably, the preparation method of H3PO4 activated biochar is as follows: peanut shells are washed, dried, crushed with a crusher, and passed through a 2mm sieve for later use. 20g of crushed peanut shells are soaked in 100ml of 1M solution. The peanut shells are soaked in phosphoric acid solution for 12-24 hours. After soaking, the peanut shells are dried in an oven at 105°C for 8-16 hours. After drying, the peanut shells are transferred to a corundum boat, which is then placed in a tube furnace. Nitrogen gas is introduced, and the temperature is increased to 450°C at a rate of 5°C / min, and maintained at this temperature for 1 hour. After natural cooling, the modified biochar is removed, washed with water until neutral, dried in an oven, and ground to obtain H3PO4 activated biochar. Preferably, the preparation method of gC3N4 is as follows: using melamine as a precursor, an appropriate amount of melamine is placed in a corundum boat, placed in a tube furnace, and nitrogen gas is introduced. The temperature is increased to 550°C at a rate of 5°C / min, and maintained at this temperature for 4 hours. After natural cooling, the prepared gC3N4 is removed and repeatedly washed with deionized water. It is then dried in an oven, ground, and stored in a brown bottle for later use.

[0021] The PBC-gC3N4 (0.15:1) prepared in Example 1 of CN118179570A is used in the following examples.

[0022] Example 1: Preparation method of the photocatalytic membrane of the present invention and verification of its effect I. Preparation of photocatalytic membrane (BCN-PVDF) Method 1: Preparation of photocatalytic PVDF membranes by vacuum filtration 40 mg of PBC-g-C3N4 was dispersed in 200 mL of water and sonicated for 20-30 min. The PBC-gC3N4 aqueous solution was continuously passed through a PVDF membrane with a pore size of 0.45 μm (a commercially available PVDF membrane) using a vacuum pump until the PBC-gC3N4 was firmly fixed on the PVDF membrane surface. After drying in an oven at 50-60℃, a photocatalytic membrane (BCN-PVDF-A) loaded with biochar-based gC3N4 material was obtained, with a PBC-gC3N4 powder loading of 1.16 mg / cm². By adjusting the amount of PBC-g-C3N4 added, photocatalytic PVDF membranes with PBC-gC3N4 powder loadings of 0.29 mg / cm², 0.58 mg / cm², 0.87 mg / cm², and 1.45 mg / cm² were prepared using the same method.

[0023] Method 2: Preparation of photocatalytic PVDF membranes by cross-linking modification 40 mg of PBC-g-C3N4 was weighed and dispersed in 100 mL of DMF, and sonicated for 20–30 min to form a uniform dispersion. Glutaraldehyde (1% of the total mass of the solution) was added as a crosslinking agent, and a suitable amount of triethylamine was added dropwise to promote the crosslinking reaction. Subsequently, a 0.45 μm PVDF membrane (a commercially available PVDF membrane) was immersed in this dispersion and reacted at 50–60 °C for 2–4 h, allowing the crosslinking agent to form a crosslinked network on the PVDF surface and within the pores, anchoring the PBC-gC3N4 particles. The PBC-gC3N4 powder loading was 1.16 mg / cm². The membrane was removed and washed with plenty of deionized water until the washing solution was odorless, removing unreacted substances and residual solvent. Finally, it was vacuum dried at 50 °C for 12 h to obtain a crosslinked photocatalytic composite membrane (denoted as BCN-PVDF-B).

[0024] Method 3: Wet preparation of photocatalytic PVDF membranes 100 mg of PBC-g-C3N4 was dispersed in 200 mL of N,N-dimethylformamide (DMF) solvent and ultrasonically dispersed for 20–30 min to form a uniform dispersion. Then, 10 g of polyvinylidene fluoride (PVDF) resin was added, and the mixture was magnetically stirred in a 60–70 °C water bath for 4–6 h until completely dissolved and a transparent, uniform casting solution was formed. After the resulting solution was allowed to stand at room temperature for 2 h to degas, it was uniformly coated onto a clean glass plate. The coating thickness was controlled to be approximately 300 μm. The glass plate was then slowly immersed in a deionized water coagulation bath for phase inversion, and allowed to stand for 2–4 h to form a porous membrane. Finally, the membrane was removed, washed sequentially with deionized water to remove residual solvent, and vacuum dried at 40–50 °C for 12 h to obtain an integrated photocatalytic composite membrane (named BCN-PVD-C) with a PBC-g-C3N4 powder loading of 1.16 mg / cm².

[0025] Method 4: Light-transmitting modified photocatalytic PVDF membrane The BCN-PVD-C photocatalytic membrane prepared by method 3 was immersed in a photomodifier consisting of a mixture of polydimethylsiloxane (PDMS), hydrogen-containing polysiloxane (PDMS), and n-hexane, wherein the concentration of PDMS was 15-30 g / L and the ratio of PDMS to PDMS was 1:10. After ten minutes, the photocatalytic membrane was removed and vacuum dried for 6 hours to obtain a light-transmitting modified photocatalytic PVDF membrane (named CN-PVD-D). The loading of PBC-g-C3N4 powder was 1.16 mg / cm².

[0026] II. Applications of Photocatalytic Membranes Using azoxystrobin as the target pollutant, the removal efficiency of different types of photocatalytic membranes prepared by four different methods was evaluated according to the following operating procedures.

[0027] BCN-PVDF with a PBC-g-C3N4 powder loading of 1.16 mg / cm² prepared by methods 1-4 was cut into membranes with a diameter of 7 cm. Catalytic removal experiments of 500 μg / L pesticides and antibiotics were conducted using a continuous flow system. The catalytic membrane was placed in a glass filter reactor and tightly sealed with O-rings to prevent leakage. A visible light source was placed 10 cm above the reactor. The light source was a 300W xenon lamp equipped with a UV cutoff filter (λ > 400 nm). Catalytic removal experiments were conducted on 500 μg / L aqueous solutions of pollutants at pH 7.0 ± 0.5. Simulated wastewater was stored in a 2.5 L amber glass bottle and continuously pumped into the membrane module at a flow rate of 1 mL / min using a peristaltic pump. 0.2 mL of effluent samples were collected at specified time intervals and mixed with 0.8 mL of HPLC-grade methanol. After filtration through a 0.22 μm polytetrafluoroethylene membrane, the sample was transferred to a vial, and the concentration of contaminants was determined by HPLC-MS / MS analysis. The contaminant removal efficiency was calculated using the following formula:

[0028] in, The values ​​represent the pollutant removal efficiency, where C0 and C represent the initial reaction time and the pollutant concentration (mg / L) at a specific reaction time, respectively. All experiments were repeated three times to improve the accuracy and reproducibility of the data.

[0029] The results are as follows Figure 1 As shown, after 12 hours of continuous removal, the supported photocatalytic membrane prepared by method one showed the best removal effect of azoxystrobin, with a removal rate of approximately 91%. The light-transmitting modified photocatalytic PVDF membrane and the photocatalytic PVDF membrane prepared by cross-linking modification also exhibited excellent removal performance, with removal rates reaching 73% and 80%, respectively.

[0030] Example 2: Microstructure characterization of supported photocatalytic membranes The microstructure of the PVDF membrane and the supported photocatalytic membrane prepared by method one in Example 1 of this invention were observed using scanning electron microscopy (SEM). The results are as follows: Figure 2 As shown in the figure. Figure 2 a is a surface morphology diagram of the PVDF membrane, showing a typical porous structure, while the BCN-PVDF membrane surface is uniformly covered with photocatalyst particles. Figure 2 b); In terms of cross-sectional structure, the PVDF membrane exhibits a layered characteristic of a dense layer and a support layer ( Figure 2 c), while the BCN–PVDF film forms a photocatalyst layer with a thickness of approximately 25 μm on its surface ( Figure 2d), the layer is tightly bonded to the substrate, demonstrating the stable loading effect of the photocatalyst in the film.

[0031] Example 3: Screening of photocatalytic membranes with optimal loading ratio Using azoxystrobin as the target pollutant, the removal efficiency of photocatalytic membranes with different loading ratios (0.29-1.45 mg / cm²) prepared in Method 1 was evaluated according to the procedure described in Example 1. Figure 3 It can be seen that the removal rate of azoxystrobin by the photocatalytic membrane gradually increases with the increase of the loading: the removal rate is about 50% at 0.29 mg / cm², while it increases to about 75% and 82% when the loading is increased to 0.58 mg / cm² and 0.87 mg / cm², respectively. Further increasing the loading to 1.16 mg / cm², the removal rate further increases to over 90%, and then the removal effect tends to stabilize with further increases in catalyst loading. Therefore, a loading of 1.16 mg / cm² is selected as the optimal loading.

[0032] Example 4: Comparative Experiment of Different Photocatalytic Films under Light / Dark Conditions Under optimal loading ratio (1.16 mg / cm²), using 500 μg / L azoxystrobin as a model pollutant, the removal performance of the BCN-PVDF photocatalytic membrane prepared by method one in Example 1 was compared under light and dark conditions, with a pure PVDF membrane as a control. The operation method for applying the photocatalytic membrane in Example 1 was followed. The results are as follows: Figure 4 As shown, under illumination, the BCN-PVDF photocatalytic membrane maintained a removal rate of over 90% for 12 hours of continuous removal of 500 μg / L azoxystrobin pollutants. Under dark conditions, the removal efficiency of the BCN-PVDF photocatalytic membrane decreased significantly, falling below 20% after 12 hours. The pure PVDF membrane showed almost no removal effect under dark conditions, with a removal rate of approximately 30%. These results indicate that illumination is a key factor in membrane performance, and the high removal efficiency of the BCN-PVDF membrane is mainly due to its photocatalytic effect.

[0033] Example 5: Evaluation of the removal performance of BCN-PVDF photocatalytic membrane for typical pesticides and antibiotics Under the optimal loading ratio, following the operating method of the photocatalytic membrane application in Example 1, tetracycline, ofloxacin, atrazine, and sulfadiazine at a concentration of 500 μg / L were selected as representative pollutants to evaluate the removal capacity of the photocatalytic membrane. The results are shown in [Figure 1]. Figure 5For tetracycline and cloxacin, the photocatalytic membrane achieved a removal rate of nearly 100% within 12 hours, demonstrating excellent broad-spectrum antibiotic removal capabilities. For atrazine and sulfadiazine, the removal rate decreased slightly over time, but remained around 70%–75% after 12 hours. This indicates that the photocatalytic membrane not only exhibits rapid and thorough degradation of antibiotics but also maintains good removal efficiency for typical pesticides.

[0034] Example 6: Suitability evaluation in different water bodies To verify the application potential of the photocatalytic membrane prepared by method 1 in Example 1 in complex aquatic environments, urban sewage, Taihu Lake water, Yangtze River water, Yellow River water, seawater, and farmland water were selected as substrates to prepare 500 μg / L aqueous solutions of azoxystrobin-polluted substances. The removal performance was investigated according to the operating method of the photocatalytic membrane application in Example 1. The results are shown in […]. Figure 6 In urban sewage, Taihu Lake water, and Yangtze River water, the removal rate decreased slightly, but remained at 70%–80% after 12 hours; in Yellow River water, seawater, and farmland water, the removal rate was relatively stable, maintaining at 60%–70% after 12 hours. The results indicate that the photocatalytic membrane of this invention exhibits good stability and broad-spectrum adaptability in various complex water bodies.

Claims

1. A method for preparing a biochar-based g-C3N4 material loaded photocatalytic membrane, comprising the following steps: 1) dispersing PBC-g-C3N4 in water and ultrasonicating for 20-30 min; 2) using a vacuum pump to continuously pass the PBC-g-C3N4 mixed aqueous solution in step 1 through a PVDF membrane with a pore size of 0.45 μm until the PBC-g-C3N4 is firmly fixed on the surface of the PVDF membrane, and then drying in a 50-60°C oven to obtain a biochar-based g-C3N4 material loaded photocatalytic membrane; wherein In step (1), the ratio of PBC-g-C3N4 to water is (10-50) mg: 200 mL.

2. The method of claim 1, wherein: In the step 2), using a vacuum pump to continuously pass the PBC-g-C3N4 mixed aqueous solution in step 1 through a PVDF membrane with a pore size of 0.45 μm until the PBC-g-C3N4 is firmly fixed on the surface of the PVDF membrane, and then drying in a 50-60°C oven to obtain a biochar-based g-C3N4 material loaded photocatalytic membrane.

3. The biochar-based g-C3N4 material loaded photocatalytic membrane prepared by the method of claim 1 or 2.

4. The biochar-based g-C3N4 material loaded photocatalytic membrane according to claim 3, wherein the biochar-based g-C3N4 material loading of the photocatalytic membrane is 0.29-1.45 mg / cm2.

5. The biochar-based g-C3N4 material loaded photocatalytic membrane according to claim 4, wherein the optimal biochar-based g-C3N4 material loading of the photocatalytic membrane is 1.16 mg / cm2.

6. The use of the biochar-based g-C3N4 material loaded photocatalytic membrane of claim 1 for removing azoxystrobin, atrazine, tetracycline, ofloxacin and / or sulfadiazine in water.

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