Iron-based photocatalytic composite film and preparation method thereof

Abstract

The application relates to the technical field of water treatment, in particular to an iron-based photocatalytic composite membrane and a preparation method thereof. co AA co VI) copolymer and polyvinylidene fluoride are mixed uniformly in an organic solvent, defoamed, prepared into a porous membrane through a phase inversion method, then coordinated in an acidic aqueous solution of iron ions, and hydrothermally converted to obtain the iron-based photocatalytic composite membrane. The iron-based photocatalytic composite membrane has the beneficial effects that PVDF is used as a film-forming matrix, polymers are used as ligands, nano-iron oxides are generated in situ through hydrothermal reaction, iron ions are uniformly anchored, the introduction of g-C3N4 expands the visible light response, a heterojunction is formed with the iron oxides, the photocatalytic efficiency is improved, halloysite provides adsorption enrichment, cooperates with photocatalysis, the treatment efficiency is improved, the composite membrane has good stability, is convenient to recycle and reuse, and has a long service life.

Description

Technical Field

[0001] This invention relates to the field of nano-photocatalytic materials for water treatment, specifically to an iron-based photocatalytic composite membrane and its preparation method. Background Technology

[0002] Antibiotics, widely used in the treatment of human and animal diseases, are frequently detected in natural water bodies due to their extensive use, posing a potential threat to the ecological environment and human health. The main sources of antibiotics in wastewater are not only pharmaceutical production wastewater, but also hospital wastewater, livestock and poultry farming wastewater, and domestic sewage. The problem of antibiotics in wastewater is not merely a simple pollution issue; it involves multiple levels of environmental, ecological, and health concerns, and carries long-term risks. Therefore, developing effective wastewater treatment technologies to reduce antibiotic pollution is of significant practical importance. Among these technologies, photocatalysis has attracted considerable attention in the field of advanced antibiotic wastewater treatment due to its high efficiency, green nature, and sustainability. However, single treatment technologies often fail to achieve ideal results. Combining adsorption methods to enrich pollutants in water bodies with rapid degradation using photocatalysis can improve treatment efficiency. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention uses polyvinylidene fluoride (PVDF) as the film-forming matrix, combined with metal ion polymer complexes and adsorbent particles to achieve a cyclic process of adsorption-enrichment-degradation-regeneration of the composite membrane, which greatly improves the processing efficiency and service life.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing an iron-based photocatalytic composite film includes the following steps: S1: Preparation of modified halloysite: Halloysite nanotubes were etched with alkali and modified with polyethyleneimine to obtain aminated modified halloysite; S2: Preparation of carbon nitride nanosheets: Urea or melamine is thermally polymerized and thermally oxidized to obtain ultrathin g-C3N4 nanosheets; S3: Preparation of copolymer: Using acrylonitrile, acrylic acid, and vinylimidazole as monomers, free radical polymerization was carried out in a molar ratio of 5:3~4:1~2 to obtain P(AN- What -AA- What -VI); S4: Preparation of casting solution: Combine the modified halloysite from step S1, the g-C3N4 nanosheets from step S2, and the P(AN-) from step S3. What -AA- What -VI) and polyvinylidene fluoride are mixed evenly in an organic solvent, and degassed to obtain a casting solution; S5: Film formation: The casting solution is used to prepare a porous membrane by phase inversion. S6: Iron ion anchoring: Immerse the membrane from step S5 in an acidic aqueous solution containing iron ions, so that the Fe... 3+ Coordinate with the carboxyl groups of the copolymer within the membrane, then remove and wash; S7: Hydrothermal Conversion: The membrane from step S6 is placed in a high-pressure reactor for hydrothermal reaction, so that the coordinated iron ions are converted into nano-iron oxide. After washing and drying, the iron-based photocatalytic composite membrane is obtained.

[0005] Furthermore, in S1, the alkaline etching was performed by treating with a 2 M sodium hydroxide solution at 80°C for 4 h, and the polyethyleneimine modification concentration was 1 wt%, with a reaction time of 2 h.

[0006] Furthermore, the preparation method of g-C3N4 nanosheets in S2 is as follows: urea is calcined at 550℃ for 4 h, and the resulting bulk g-C3N4 is thermally oxidized and exfoliated at 500℃ for 2 h in an air atmosphere to obtain nanosheets with a thickness of <5 nm.

[0007] Furthermore, the mass fractions of each component in the casting solution in S4 are as follows: 5-8 parts modified halloysite, 1-3 parts g-C3N4 nanosheets, 5-10 parts copolymer, 20-30 parts polyvinylidene fluoride, and 50-80 parts organic solvent.

[0008] Furthermore, the iron ion solution mentioned in S6 is an aqueous solution of 0.01~0.1 M Fe(NO3)3·9H2O, with the pH adjusted to 4~6 and the soaking time to 6~10 h.

[0009] Furthermore, the hydrothermal reaction conditions in S7 are 160~180℃ for 4~12 h, the reaction medium is water or dilute ammonia, and the pH is 5~7.

[0010] The present invention further provides an iron-based photocatalytic composite membrane prepared by the preparation method described above.

[0011] PVDF and macromolecular polymer P(AN- What -AA- What -VI) The polymer solution is completely dissolved in an organic solvent, forming a homogeneous solution. Solid fillers (modified halloysite, g-C3N4 nanosheets) are uniformly dispersed in the polymer solution by ultrasonication. A dense film is formed by rapid precipitation of the polymer at the interface via phase inversion, while the solid fillers are embedded or anchored within the polymer matrix during phase separation, partially exposed on the pore surface. This film is then immersed in an acidic aqueous solution containing iron ions. Due to P(AN- What -AA- What-VI) provides a large number of carboxyl groups, which form stable complexes with iron ions. After hydrothermal treatment, α-FeOOH or α-Fe2O3 nanoparticles are generated in situ. g-C3N4 nanosheets, as visible light responsive components, form heterojunctions with iron oxides, promote photogenerated electron transfer, and enhance ·OH generation. Modified halloysite provides multi-level channels and adsorption sites to enrich pollutants.

[0012] The beneficial effects of this invention are: PVDF is used as the film-forming matrix and the polymer is used as the ligand. Nano-iron oxides are generated in situ through hydrothermal processes, achieving uniform anchoring of iron ions. The introduction of g-C3N4 extends the visible light response and forms a heterojunction with the iron oxides, improving photocatalytic efficiency. Halloysite provides adsorption and enrichment, which works synergistically with photocatalysis to improve treatment efficiency. The composite membrane has good stability, is easy to recycle and reuse, and has a long service life. Detailed Implementation

[0013] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0015] Example 1: S1, Modified Halloysite: 5 g halloysite (HNTs) was added to 100 mL of 2 M NaOH, stirred at 80°C for 4 h, filtered and washed with water until neutral. Then it was dispersed in 100 mL of 1 wt% polyethyleneimine (PEI, Mw 750) aqueous solution, stirred at room temperature for 6 h, filtered, dried at 60°C, and ground for later use.

[0016] S2. Preparation of g-C3N4 nanosheets: 20 g of urea was placed in a covered alumina crucible and calcined in a muffle furnace at 550 °C for 4 h (heating rate 5 °C / min) to obtain yellow blocky g-C3N4. 5 g of the blocky g-C3N4 was spread evenly in a porcelain boat and thermally oxidized and exfoliated at 550 °C in air for 2 h to obtain pale yellow nanosheets with a thickness of about 3-5 nm.

[0017] S3. Copolymer synthesis: Weigh 10 g of monomers, 0.1 g of AIBN, and 60 mL of DMF in a molar ratio of AN:AA:VI = 5:3:2. Polymerize under nitrogen at 70℃ for 12 h, precipitate with methanol, and dry to obtain copolymer P(AN-AA-VI) with a carboxyl content of approximately 4.2 mmol / g.

[0018] S4. Preparation of casting solution: Take 6.5 g of modified halloysite, 1.5 g of g-C3N4 nanosheets, 8 g of copolymer, 24 g of PVDF, add 60 g of DMAc, stir at 60℃ for 12 h, and let stand to remove bubbles.

[0019] S5. Film Formation: The casting solution is coated onto a glass plate (200 μm thick) and immersed in a deionized water coagulation bath, where phase inversion occurs to form a porous membrane. After removal, the membrane is replaced with ethanol and stored in deionized water.

[0020] S6. Iron ion anchoring: Prepare a 0.05 M Fe(NO3)3·9H2O aqueous solution, adjust the pH to 5.0, immerse the membrane in this solution, and shake at room temperature for 8 h to allow the Fe ions to anchor. 3+ Fully coordinate with the carboxyl group. After removal, rinse the surface with deionized water until the washing solution is colorless.

[0021] S7. Hydrothermal Conversion: The membrane was placed in a high-pressure reactor, and deionized water was added to just submerge it. Ammonia was added to adjust the pH to 6.0, and the reaction was carried out at 180℃ for 8 hours. After natural cooling, the membrane was removed, washed with deionized water, and dried at 60℃ to obtain an iron-based photocatalytic composite membrane.

[0022] The resulting film was characterized by XRD, and characteristic diffraction peaks of α-Fe2O3 appeared at 2θ≈24.1°, 33.2°, and 35.6° (JCPDS No. 33-0664), proving that it was successfully converted into a hematite photocatalyst.

[0023] The membrane was installed in a cross-flow filtration unit with a feed water of 50 mg / L tetracycline solution, an operating pressure of 0.2 bar, a hydraulic residence time of 30 min, and irradiation with a 300 W xenon lamp (λ≥420 nm) without the addition of H2O2.

[0024] Photocatalytic performance tests showed that the membrane achieved a 94.5% removal rate of tetracycline after 2 hours. The removal rate remained at 92.2% after 48 hours of continuous operation. Free radical capture experiments confirmed that the main active species was ·OH.

[0025] In addition, compared with the removal rate of only 40% under no light conditions after 2 hours, the removal efficiency of tetracycline is low due to adsorption alone. Combined with photocatalytic degradation, the degradation efficiency can be effectively improved.

[0026] Example 2: Basically the same as Example 1 The difference lies in the preparation of S4 casting solution: Take 5 g of modified halloysite, 1 g of g-C3N4 nanosheets, 5 g of copolymer, 20 g of PVDF, add 69 g of DMAc, stir at 60℃ for 12 h, and let stand to remove bubbles.

[0027] Photocatalytic performance tests showed that the membrane achieved a 90.3% removal rate of tetracycline after 2 hours. After 48 hours of continuous operation, the removal rate remained at 89.6%, demonstrating good stability.

[0028] The reduced liquid solid content in the casting process resulted in a decrease in both adsorbent filler and ligand copolymers of iron ions, leading to lower adsorption and photocatalytic performance compared to Example 1.

[0029] Example 3: Basically the same as Example 1 The difference lies in the preparation of S4 casting solution: Take 8 g of modified halloysite, 3 g of g-C3N4 nanosheets, 10 g of copolymer, 29 g of PVDF, add 50 g of DMAc, stir at 60℃ for 12 h, and let stand to remove bubbles.

[0030] Photocatalytic performance tests showed that the membrane achieved a tetracycline removal rate of 89.4% after 2 hours. After 48 hours of continuous operation, the removal rate remained at 80.1%, indicating decreased stability.

[0031] The increased solid content in the casting liquid led to a relatively higher viscosity, making film formation more difficult than in Example 1. Slight agglomeration of inorganic fillers occurred, and the membrane pores became denser. Although the number of adsorbent materials and coordinable iron ions increased, the degradation performance was ultimately lower than in Example 1 due to the properties of the membrane, especially after 48 hours, the removal rate decreased significantly.

[0032] Comparative Example 1: Basically the same as Example 1 The difference lies in the preparation of S4 casting solution: take 8 g of g-C3N4 nanosheets, 8 g of copolymer, 24 g of PVDF, add 60 g of DMAc, stir at 60℃ for 12 h, and let stand to remove bubbles.

[0033] The modified halloysite is replaced by g-C3N4 nanosheets, meaning that all inorganic fillers are g-C3N4 nanosheets. The packing is more loose, which can increase water flux. However, the adsorption performance is lower, which affects the adsorption efficiency. It takes 3 hours to achieve a degradation rate of over 90%. After 48 hours of continuous operation, the removal rate is maintained at 82.1%, indicating relatively good stability.

[0034] Comparative Example 2: Basically the same as Example 1 The difference lies in the preparation of S4 casting solution: Take 8 g of modified halloysite, 8 g of copolymer, 24 g of PVDF, add 60 g of DMAc, stir at 60℃ for 12 h, and let stand to remove bubbles.

[0035] The g-C3N4 nanosheets were replaced with modified halloysite, meaning that all inorganic fillers were modified halloysite. This improved the adsorption performance, but prevented the formation of heterojunctions and reduced photocatalytic activity. Photocatalytic performance tests showed that the membrane had a 2-hour removal rate of only 68.9% for tetracycline, and after 48 hours of continuous operation, the removal rate remained at 81%.

[0036] Comparative Example 3: Basically the same as Example 1 The difference lies in the preparation of S4 casting solution: take 8 g of modified halloysite, 32 g of PVDF, add 60 g of DMAc, stir at 60℃ for 12 h, and let stand to remove bubbles.

[0037] Without the addition of copolymers, iron ions cannot be effectively deposited on the film surface and cannot form a photocatalyst. Tests show that the film has a 2-hour removal rate of only 42% for tetracycline, and after 48 hours of continuous operation, the removal rate is only 63%.

[0038] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing an iron-based photocatalytic composite membrane, characterized in that, Includes the following steps: S1: Preparation of modified halloysite: Halloysite nanotubes were etched with alkali and modified with polyethyleneimine to obtain aminated modified halloysite; S2: Preparation of carbon nitride nanosheets: Urea or melamine is thermally polymerized and thermally oxidized to obtain ultrathin g-C3N4 nanosheets; S3: Preparation of copolymer: Using acrylonitrile, acrylic acid, and vinylimidazole as monomers, free radical polymerization was carried out in a molar ratio of 5:3~4:1~2 to obtain P(AN- co -AA- co -VI); S4: Preparation of casting solution: Combine the modified halloysite from step S1, the g-C3N4 nanosheets from step S2, and the P(AN-) from step S3. co -AA- co -VI) and polyvinylidene fluoride are mixed evenly in an organic solvent, and degassed to obtain a casting solution; S5: Film formation: The casting solution is used to prepare a porous membrane by phase inversion. S6: Iron ion anchoring: Immerse the membrane from step S5 in an acidic aqueous solution containing iron ions, so that the Fe... 3+ Coordinate with the carboxyl groups of the copolymer within the membrane, then remove and wash; S7: Hydrothermal Conversion: The membrane from step S6 is placed in a high-pressure reactor for hydrothermal reaction, so that the coordinated iron ions are converted into nano-iron oxide. After washing and drying, the iron-based photocatalytic composite membrane is obtained.

2. The method for preparing the iron-based photocatalytic composite film according to claim 1, characterized in that, In S1, alkaline etching was performed by treating with 2M sodium hydroxide solution at 80°C for 4 h, and the polyethyleneimine modification concentration was 1 wt%, with a reaction time of 2 h.

3. The method for preparing the iron-based photocatalytic composite film according to claim 1, characterized in that, The preparation method of g-C3N4 nanosheets in S2 is as follows: urea is calcined at 550℃ for 4 h, and the resulting bulk g-C3N4 is thermally oxidized and exfoliated at 500℃ for 2 h in air atmosphere to obtain nanosheets with a thickness of <5 nm.

4. The method for preparing the iron-based photocatalytic composite film according to claim 1, characterized in that, The mass fractions of each component in the casting solution of S4 are as follows: 5-8 parts modified halloysite, 1-3 parts g-C3N4 nanosheets, 5-10 parts copolymer, 20-30 parts polyvinylidene fluoride, and 50-80 parts organic solvent.

5. The method for preparing the iron-based photocatalytic composite film according to claim 1, characterized in that, The iron ion solution mentioned in S6 is an aqueous solution of 0.01~0.1 M Fe(NO3)3·9H2O, with the pH adjusted to 4~6 and the soaking time to 6~10 h.

6. The method for preparing the iron-based photocatalytic composite film according to claim 1, characterized in that, The hydrothermal reaction conditions in S7 are 160~180℃ for 4~12 h, and the reaction medium is water or dilute ammonia water with pH=5~7.

7. An iron-based photocatalytic composite membrane prepared by any one of claims 1-6.