CN116173986A - Surface composite photocatalytic film and its preparation method and application in water treatment - Google Patents

Abstract

The invention belongs to the technical field of photocatalytic film preparation, and particularly relates to a surface composite photocatalytic film, a preparation method thereof and application thereof in water treatment. In order to efficiently utilize a light source and stabilize a supported photocatalyst, the invention provides a novel film preparation strategy for preparing a surface composite photocatalytic film by coating the catalyst on the surface of a gel phase film through a submerged precipitation phase conversion process based on the gel characteristic of a polymer casting film liquid, and systematically researches the influence of an inorganic catalyst on the structural characteristics, permeability, photocatalytic performance and anti-pollution performance of an organic film in the phase conversion process. The surface composite photocatalytic film prepared by the strategy of the invention realizes the stable loading process of the inorganic catalyst on the surface of the organic separation film, and ensures the efficient utilization of the catalyst to the light source on the basis of improving the immobilization degree of the catalyst. Meanwhile, the two-phase interface effect of the inorganic catalyst and the organic separation membrane is used for realizing the regulation and control of the membrane structure and the performance, and providing a new idea for the combination of the advantages of photocatalysis and membrane separation technology.

Description

Surface composite photocatalytic film and its preparation method and application in water treatment

technical field

The invention belongs to the technical field of photocatalytic film preparation, and in particular relates to a surface composite photocatalytic film, a preparation method thereof and an application in water treatment.

Background technique

With the development of industry and the improvement of people's living standards, the increasing water pollution has caused a great threat to the ecological environment and human health. Membrane separation technology has been widely used in the field of sewage treatment due to the advantages of high efficiency, energy saving, and stable system operation. However, the membrane separation process can only achieve the separation and concentration of pollutants. The treatment of high-concentration concentrated wastewater is one of the inevitable problems in the application of membrane separation technology. 1. At the same time, the membrane fouling problem caused by the enrichment of pollutants on the membrane surface and membrane pores during the separation process will lead to problems such as attenuation of separation membrane flux, reduced service life, and increased maintenance costs, which have significantly hindered the application of membrane separation technology. .

Semiconductor photocatalysis technology is an advanced oxidation technology that combines the advantages of energy saving and environmental friendliness. Under the irradiation of light source, the semiconductor catalyst is excited to generate active free radicals to complete the process of converting light energy into chemical energy. Active free radicals have strong oxidative properties. , Thoroughly oxidize and decompose pollutants to reduce their harm to the environment, and the reaction process uses light energy to effectively avoid secondary consumption of energy and achieve the purpose of energy saving and emission reduction. Therefore, photocatalytic technology is an important technical means to solve the problem of environmental water pollution. At present, the common photocatalytic system is a suspension reaction system. Nano or micro catalysts participate in the reaction in a powder state, which is conducive to the mass transfer between substances in the system and obtains a good photocatalytic effect. However, the problem of separation, recovery and recycling of catalysts has become a limitation. The main obstacle to the engineering application of photocatalytic technology. The existing process achieves the separation and recovery of the catalyst through coagulation, flocculation, and precipitation processes in series after the photocatalytic system. However, the increase in energy consumption caused by the low separation efficiency and the leakage of the catalyst will cause secondary pollution to the environment and cause potential ecological problems. Environmental health risks; in addition, the powder catalyst agglomeration and its shielding effect on incident light during the photocatalytic reaction will have an adverse effect on the photocatalytic effect, and the problems that arise during the application of the powder catalyst will play an important role in taking advantage of the high efficiency, energy saving and environmental friendliness of photocatalytic technology had a negative impact.

In view of the defects of photocatalysis technology and membrane separation technology in the sewage treatment process, coupling photocatalysis and membrane separation technology to form a photocatalytic membrane is an effective way to simultaneously solve the problems of powder catalyst separation and reuse and membrane pollution. More and more The research focuses on immobilizing the catalyst on the surface of the separation membrane or in the pores of the membrane to prepare a photocatalytic membrane to participate in the reaction. On the basis of realizing the simultaneous separation process of the catalyst and the product, the pollutants accumulated on the membrane are degraded by the photocatalytic process to alleviate the membrane fouling. It provides the possibility for the separation membrane to run for a long time.

In the application process, the utilization of the light source and the mass transfer process between the pollutant and the catalyst are the key factors affecting the performance of the photocatalytic film. At present, researchers mainly use two methods of surface loading and bulk blending to prepare photocatalytic films. Surface loading methods such as surface deposition, dip coating, electron spraying, magnetron sputtering, and surface grafting are used to immobilize the catalyst on the surface of the film. prepared as a loaded photocatalytic film. Its advantage is that the catalytic layer is located on the membrane surface, which is beneficial for the catalyst to efficiently use the light source for photocatalytic reaction, and at the same time rely on photocatalytic degradation to hinder the formation of filter cake layer on the membrane surface to achieve the purpose of alleviating membrane pollution. However, based on the characteristics of the surface loading, the formation of the catalytic layer on the membrane surface will have a negative impact on the membrane flux. During the surface loading process, the catalysts are mainly physically adsorbed on the membrane surface or form hydrogen bonds with the membrane surface and other chemical bonds with low bond energy. Due to the weak interaction between the two, the shear force generated during the filtration process can easily convert the light to the surface. The catalytic layer is damaged, resulting in the loss of catalyst and the decrease of photocatalytic performance.

It is an effective way to improve the degree of catalyst immobilization by doping the catalyst in the bulk structure of the film to prepare the blended photocatalytic film. Relevant studies have found that the typical inorganic characteristics of catalysts can play an important role in the microscale combination of organic and inorganic components, and the two-phase interface will have a significant impact on the properties of the separation membrane. The addition of inorganic catalysts will affect the structure, hydrophilicity, roughness, mechanical strength and other characteristics of the separation membrane during the phase separation process to improve the performance of the separation membrane, but the catalyst is embedded in the membrane structure will inevitably lead to its impact on the light source. The reduction of utilization rate leads to the reduction of photocatalytic performance. At the same time, the incompatibility of inorganic materials and organic components will lead to uneven dispersion of catalysts, and the destruction of the film structure by active free radicals generated during the light and reaction processes is a blended photocatalytic process. Unavoidable problems in the process of membrane application.

Contents of the invention

Aiming at the above-mentioned technical deficiencies, the present invention provides a surface composite photocatalytic membrane, a preparation method thereof and an application in water treatment. In order to efficiently utilize the light source and stably load the photocatalyst, the present invention proposes a new film preparation strategy based on the gel properties of the polymer casting liquid, coating the catalyst on the surface of the gel phase film and preparing a surface composite photocatalytic film through the immersion precipitation phase inversion process , to systematically study the effects of inorganic catalysts participating in the phase inversion process on the structural characteristics, permeability, photocatalytic performance and antifouling performance of organic membranes. The surface composite photocatalytic membrane prepared by adopting the strategy of the invention realizes the stable loading process of the inorganic catalyst on the surface of the organic separation membrane, and ensures the efficient utilization of the catalyst for the light source on the basis of improving the immobilization degree of the catalyst. At the same time, relying on the two-phase interface effect of inorganic catalyst and organic separation membrane, the structure and performance of the membrane can be adjusted, which provides a new idea for the combination of the advantages of photocatalysis and membrane separation technology.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

The preparation method of the surface composite photocatalytic film comprises the following steps: dissolving the organic polymer film material and the porogen in an organic solvent to obtain a casting solution, leaving the casting solution to remove air bubbles, and then casting it into a gel Phase film, and then the photocatalyst is loaded on the surface of the gel phase film by surface coating, and then phase separation is carried out to obtain a surface composite photocatalytic film.

Preferably, the organic polymer membrane material includes but not limited to polyvinylidene fluoride, polysulfone, polyethersulfone;

The porogen includes but is not limited to polyvinylpyrrolidone, lithium chloride or a mixture of the two;

The organic solvent includes but not limited to N,N'-dimethylacetamide, N,N'-dimethylformamide, ethylene glycol methyl ether.

Preferably, when the porogen is selected from the mixture of polyvinylpyrrolidone and lithium chloride, in the casting solution, the mass ratio of the organic polymer membrane material, polyvinylpyrrolidone, lithium chloride and the organic solvent is 16 -18: 0.5-1: 1-2: 79-82.5; when the porogen is selected from polyvinylpyrrolidone or lithium chloride, the mass ratio of organic polymer membrane material, porogen and organic solvent is 16-18: 1.5-3:79-82.5.

Preferably, the phase separation method is as follows: after the catalyst is supported on the gel phase film, it is immersed in a constant temperature water bath at 40-60°C.

Preferably, the photocatalyst is a powder catalyst.

Preferably, the photocatalyst includes but not limited to ZnIn ₂ S ₄ catalyst, TiO ₂ catalyst, WO ₃ catalyst, ZnO catalyst, gC ₃ N ₄ catalyst.

Preferably, the ZnIn ₂ S ₄ catalyst is prepared according to the following steps:

Dissolve Zn(NO ₃ ) ₂ ·6H ₂ O, In(NO ₃ ) ₃ ·xH ₂ O and thioacetamide in deionized water, then react at 60-120°C for 6 hours, cool, wash and grind , to obtain ZnIn ₂ S ₄ catalyst;

Wherein, the mass ratio of Zn(NO ₃ ) ₂ ·6H ₂ O, In(NO ₃ ) ₃ ·xH ₂ O and thioacetamide is 1:2:16.

Preferably, the loading amount of the photocatalyst on the gel phase film is 0.2-2 mg/cm ² .

The invention also protects the surface composite photocatalytic film prepared by the above preparation method.

The present invention also protects the application of the surface composite photocatalytic film in the preparation of water treatment film, the method of water treatment is:

Soak the surface composite photocatalytic membrane in deionized water until there is no organic solvent residue on the surface, then fix the surface composite photocatalytic membrane in the membrane pool made of quartz glass, and use a diaphragm pump to pump the wastewater containing pollutants into the membrane pool In the process, membrane filtration and photocatalytic reaction process are carried out simultaneously under the condition of light, and the reaction is 2-8h.

Compared with prior art, the beneficial effect of the present invention is:

1. The present invention takes photocatalysts and organic polymer ultrafiltration membranes as objects, specifically ZnIn ₂ S ₄ and PVDF ultrafiltration membranes as objects, fully utilizes the gel properties of polymer casting liquid, and ZnIn ₂ S ₄ Catalyst Loaded on the surface of the gel phase film, the surface composite photocatalytic film is obtained through the process of immersion precipitation phase inversion, and a high-efficiency and stable photocatalytic film with the advantages of surface-loaded and bulk blended photocatalytic films is obtained.

2. In this study, ZnIn ₂ S ₄ and PVDF ultrafiltration membranes were used as the object to prepare surface composite photocatalytic membranes. SEM, XPS, XRD, UV-Vis, contact angle measurement and other technologies are used to analyze the structural features such as the morphology, element composition, crystal structure, optical properties and hydrophilicity of the composite photocatalytic film on the surface of different loads; the present invention Making full use of the gel properties of the polymer casting solution, the ZnIn ₂ S ₄ catalyst is loaded on the surface of the gel phase membrane, and the surface composite photocatalytic membrane is obtained through the process of immersion precipitation phase inversion, which has passed the pure water flux test, drug removal, and dye pollution. The permeability, photocatalytic performance and anti-pollution performance of the surface composite photocatalytic membrane with different loads were investigated experimentally. By analyzing the influence of inorganic catalysts participating in the phase separation process on the structure and performance of organic membranes, new ideas are provided for the combination of photocatalysis and membrane separation technology advantages; the main conclusions are as follows:

The surface composite photocatalytic membrane has a composite porous structure. With the increase of catalyst loading, the small pore structure of the upper layer is gradually occupied by ZnIn ₂ S ₄ to form a complete photocatalytic functional layer, and the absorption ability of ultraviolet-visible light is obviously enhanced. The formation of the photocatalytic functional layer effectively improves the hydrophilicity of the membrane surface and significantly increases the pure water flux of the surface photocatalytic membrane. The analysis results of elemental composition, crystal structure and optical properties show that the prepared surface composite photocatalytic membrane not only retains the chemical properties of PVDF ultrafiltration membrane, but also possesses the optical properties of absorbing light source energy for photocatalytic reaction, which is the basis for photocatalytic reaction. To provide basic guarantee.

Fluvastatin circulation filtration experiment results show that the catalyst is 1.2mg/cm ² , and the pure water flux of the surface composite photocatalytic membrane obtained under optimal conditions is as high as 628L/(m ² ·h), and the loading capacity is 1.2mg/cm ² The removal rates of fluvastatin and TOC reached 92.76% and 41.53% on the surface composite photocatalytic membrane, and remained basically stable during the cyclic reaction process. The surface composite photocatalytic film has good photocatalytic performance and stability. Compared with PVDF membrane, the permeability and photocatalytic performance are significantly enhanced, and it shows good photocatalytic stability during cyclic operation. The results of RhB continuous filtration experiments show that compared with PVDF ultrafiltration membranes, the flux of the surface composite photocatalytic membrane during operation is significantly improved, and it has excellent anti-pollution performance. The flux recovery rate of the surface composite photocatalytic membrane with a load of 1.2mg/cm ² was 80.50%. The photocatalytic functional layer can effectively degrade RhB adsorbed on the membrane surface or in the membrane pores and decompose it from the membrane pores so as to alleviate membrane fouling and improve membrane flux. During the filtration process, the photocatalytic functional layer degrades the pollutants adsorbed on the membrane surface or in the pores of the membrane to alleviate membrane fouling, and the stable flux and flux recovery rate of the surface composite photocatalytic membrane are significantly improved, indicating that it has excellent anti-pollution performance .

The research results confirmed that the optimal loading capacity of the composite photocatalytic film on the surface is 1.2mg/cm ² . Based on the gel properties of the polymer casting solution, the catalyst is loaded on the surface of the separation membrane and participates in the phase separation process to realize the stable loading process of the catalyst on the surface of the separation membrane. On the basis of improving the immobilization degree of the catalyst, the efficient utilization of the catalyst to the light source is guaranteed. At the same time, relying on the two-phase interface effect of the inorganic catalyst and the organic separation membrane, the membrane structure and performance are regulated, and a high-efficiency photocatalytic membrane with high flux, good catalytic performance, and strong anti-pollution performance is obtained, which is the combination of the advantages of photocatalysis and membrane separation technology. Provide new ideas.

Description of drawings

Fig. 1 is the SEM figure of surface composite photocatalyst film section structure (left figure) and surface structure (right figure) of embodiment 1-5 of the present invention; Wherein, M-0 is comparative example 1 sample, M-0.4, M-0.6 , M-0.8, M-1.2, M-1.7 are samples of embodiment 1-5 respectively;

Fig. 2 is the XPS spectrum of the surface composite photocatalyst film of the embodiment of the present invention 1-5 and comparative example 1: (a) full scan spectrum of the surface composite photocatalyst film; (b) M-1.2 film Zn element high resolution spectrum; (c ) high-resolution map of In elements in M-1.2 film; (d) high-resolution map of S elements in M-1.2 film;

Fig. 3 is the XRD spectrum of the surface composite photocatalyst film of the embodiment of the present invention 1-5 and comparative example 1;

Fig. 4 is the ultraviolet-visible diffuse reflectance spectrogram of the surface composite photocatalytic film of embodiment 1-5 of the present invention and comparative example 1;

Fig. 5 is the surface composite photocatalytic film contact angle figure of embodiment 1-5 of the present invention and comparative example 1;

Fig. 6 is the pure water flux figure of the surface composite photocatalytic membrane of the embodiment of the present invention 1-5 and comparative example 1;

Fig. 7 is the figure of removal effect of fluvastatin by the surface composite photocatalytic film of Examples 1-5 and Comparative Example 1 of the present invention: (a) darkness; (b) light;

8 is a TOC removal effect diagram of the surface composite photocatalytic film reaction system of Examples 1-5 of the present invention and Comparative Example 1;

Fig. 9 is the stability of the surface composite photocatalytic film of Example 4 of the present invention: (a) fluvastatin removal effect; (b) TOC removal effect diagram;

Fig. 10 is the flux attenuation curve figure of the surface composite photocatalytic membrane of the embodiment of the present invention 1-5 and comparative example 1 in the RhB filtration process;

Fig. 11 is the flux recovery rate of the surface composite photocatalytic membrane of Examples 1-5 and Comparative Example 1 of the present invention;

Fig. 12 is a schematic diagram of the preparation of the surface composite photocatalytic film of Example 1-5 of the present invention.

Detailed ways

Specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention. The experimental methods described in the various embodiments of the present invention are conventional methods unless otherwise specified.

Example 1

The preparation method of surface composite photocatalytic film comprises the following steps:

Dissolve 17wt.% polyvinylidene fluoride (PVDF), 0.5wt.% polyvinylpyrrolidone (PVP) and 2wt.% lithium chloride in 80.5wt.% N,N'-dimethylacetamide (DMAc) , Stir at a constant speed at 60°C until completely dissolved, then put it in a constant temperature drying oven for 12 hours to remove air bubbles, pour the defoamed casting solution on the top of a clean glass plate, and quickly spread it on the surface of the glass plate with a self-made scraping rod To form a gel phase film, a catalyst with a ZnIn ₂ S ₄ loading capacity of 0.4 mg/cm ² is loaded on the surface of the gel phase film by surface coating, and then the glass plate is horizontally immersed in a 45°C constant temperature water bath for phase separation. Surface composite photocatalytic film; soak the prepared surface composite photocatalytic film in deionized water for 4-7 days to remove residual organic solvents, then rinse the surface of the film repeatedly and soak it in deionized water for later use. The surface composite photocatalytic film is named M- 0.4.

Example 2

The preparation steps are the same as in Example 1, except that the loaded amount of ZnIn ₂ S ₄ is replaced by 0.6 mg/cm ² from 0.4 mg/cm ² , and the composite photocatalytic film on the surface is named M-0.6.

Example 3

The preparation steps are the same as in Example 1, except that the loaded amount of ZnIn ₂ S ₄ is replaced by 0.8 mg/cm ² from 0.4 mg/cm ² , and the composite photocatalytic film on the surface is named M-0.8.

Example 4

The preparation steps are the same as in Example 1, except that the loading of ZnIn ₂ S ₄ is replaced by 0.4 mg/cm ² to 1.2 mg/cm ² , and the surface composite photocatalytic film is named M-1.2.

Example 5

The preparation steps are the same as in Example 1, except that the loaded amount of ZnIn ₂ S ₄ is replaced by 0.4 mg/cm ² to 1.7 mg/cm ² , and the surface composite photocatalytic film is named M-1.7.

Example 6

The preparation method of surface composite photocatalytic film comprises the following steps:

Dissolve 16wt.% polysulfone and 1.5wt.% polyvinylpyrrolidone in 82.5wt.% N,N'-dimethylformamide, stir at a constant speed at 60°C until completely dissolved, and then place it in a constant temperature drying oven for 12 hours The bubbles were removed, and the defoamed casting solution was poured on the top of a clean glass plate, and quickly spread it on the surface of the glass plate with a self-made scraping rod to form a gel phase film. The _TiO2 catalyst loading was 2.0 mg/cm ² of the catalyst was loaded on the surface of the gel phase film and quickly immersed the glass plate horizontally in a 40°C constant temperature water bath for phase separation to obtain a surface composite photocatalytic film; the prepared surface composite photocatalytic film was placed in deionized water After soaking for 4-7 days to remove residual organic solvents, rinse the membrane surface repeatedly and soak in deionized water for later use.

Example 7

The preparation method of surface composite photocatalytic film comprises the following steps:

Dissolve 18wt.% polyethersulfone and 3wt.% lithium chloride in 79wt.% ethylene glycol methyl ether, stir at a constant speed at 60°C until completely dissolved, and then put it in a constant temperature drying oven for 12 hours to remove air bubbles. The final casting solution was poured on the top of a clean glass plate, and quickly spread it on the surface of the glass plate with a self-made scraping stick to form ^a gel _phase film. After the catalyst is loaded on the surface of the gel phase film, quickly immerse the glass plate horizontally in a 60°C constant temperature water bath for phase separation to obtain a surface composite photocatalytic film; soak the prepared surface composite photocatalytic film in deionized water for 4-7 days to remove After residual organic solvent, the surface of the membrane was rinsed repeatedly and soaked in deionized water for later use.

Comparative example 1

The gel phase film prepared in Example 1, that is, the PVDF film not loaded with ZnIn ₂ S ₄ , is named M-0.

Surface Composite Photocatalytic Film Characterization:

A MerlinCompact field emission scanning electron microscope (Carl Zeiss, Germany) was used to observe the surface and cross-section microstructure of the surface composite photocatalytic film. Before the characterization of the surface structure and cross-section structure, the sample needs to be sprayed with gold. Samples were extracted in liquid nitrogen. The element composition of the surface composite photocatalytic film was analyzed by K-Alpha X-ray photoelectron spectrometer (Thermoelectricity, USA). Ultiman Ⅳ X-ray diffractometer (Rigaku, Japan) was used to characterize the crystal structure of the surface composite photocatalytic film, with CuKα as the target source, the scanning range was 10°-80°, the step size was 0.02°, the scanning speed was 10°/min, and the voltage and The currents are 40kV and 40mA, respectively. The optical properties of the surface composite photocatalytic film were characterized by a U-4100 UV-Vis spectrophotometer (Hitachi, Japan) equipped with an integrating sphere, and the collection wavelength was 200nm-800nm. The contact angle of the surface composite photocatalytic film was measured by the static water drop method through the SL200B contact angle measuring instrument (Konuo, the United States). Five areas were selected for each sample, and each area was measured four times to eliminate experimental errors, and the average value was taken. Recorded as the contact angle of the sample.

Surface composite photocatalytic film performance test:

(1) Pure water flux test:

Fix a surface composite photocatalytic membrane at the bottom of the ultrafiltration cup, fill the ultrafiltration cup with deionized water and filter the deionized water with nitrogen pressure, first pre-press at 0.15Mpa for 30min, and then reduce the pressure to 0.1Mpa to continue Filtrate until the flux is stable, and the stable flux is recorded as the pure water flux. Record the filtrate quality in real time by an electronic balance (Sartorius, Germany) connected to a computer, and calculate the membrane flux according to formula (1):

In the formula, Jw represents pure water flux, L/(m ² h); V represents permeate volume, L; S represents effective filtration area, m ² ; t represents filtration time, h.

(2) Photocatalytic performance test

A photocatalytic membrane reaction system was used to test the photocatalytic performance of the surface composite photocatalytic membrane by means of circulating filtration. 1L of fluvastatin solution with an initial concentration of 10mg/L was used as the stock solution, which was transported to the photocatalytic membrane by a high-pressure diaphragm pump. In the tank, the system pressure is controlled at 0.1Mpa by adjusting the bypass valve. After the stock solution enters the membrane pool, it is filtered in a dead-end manner and the photocatalytic reaction is carried out at the same time. The filtrate is returned to the stock solution tank and mixed with the stock solution to continue to participate in the reaction. Take the filtrate sample at the same time interval and filter the concentration to be tested through a 0.22 μm filter membrane, and the removal rate of fluvastatin is calculated according to formula (2):

Where R is the removal rate of fluvastatin, %; C _t and C ₀ are the reaction time t and the concentration of fluvastatin in the stock solution, mg/L, respectively.

(3) Anti-pollution performance test

The photocatalytic membrane reaction system was used to test the anti-pollution performance of the surface composite photocatalytic membrane by means of continuous filtration. The rhodamine B solution with an initial concentration of 15mg/L was used as the original solution, which was transported to the membrane pool by a high-pressure diaphragm pump to maintain a pressure of 0.1Mpa, and was filtered by a dead-end method while performing photocatalytic reactions. Use an electronic balance connected to a computer to record the quality of the filtrate in real time and calculate the permeation flux. After the continuous filtration experiment, soak the polluted membrane with 95% ethanol for 30 minutes, then rinse the membrane surface repeatedly with deionized water and measure the pure water after cleaning the polluted membrane. flux. Calculate the pollution recovery rate (FRR) of the surface composite photocatalytic film according to formula (3):

Where J _W and J _C are the pure water flux of the new membrane and the pure water flux of the polluted membrane after cleaning, respectively, L/(m ² h).

Analytical method:

The concentration of fluvastatin is measured by high-performance liquid chromatography (Shimadzu, Japan), and the chromatographic column that uses is HPLCBetasilC18 analytical column (2.1mm * 150mm, 5 μ m, thermoelectric, U.S.), adopts 50% A phase (0.1% formic acid solution) and 50% Phase B (acetonitrile) as the mobile phase, the flow rate was set to 0.2 mL/min, the injection volume was set to 10 μL, the column temperature was set to 40 °C, and the detection wavelength was 234 nm.

The total organic carbon of the sample was analyzed by a TOC-LCPN total organic carbon analyzer (Shimadzu, Japan), the TOC concentration of the stock solution and the filtrate at different reaction times was measured, and the removal rate of TOC in the reaction system was calculated and evaluated according to formula (4) The salinity of the system during the reaction:

是反应体系TOC去除率，％；TOC_t和TOC₀分别是反应时间t及反应体系初始TOC浓度，mg/L。in

is the TOC removal rate of the reaction system, %; TOC _t and TOC ₀ are the reaction time t and the initial TOC concentration of the reaction system, mg/L, respectively.

Results and discussion

1. Microstructure analysis:

Figure 1 shows the surface and cross-sectional structure of the surface composite photocatalytic membrane characterized by SEM. It can be seen from the figure that the cross-sectional structure of PVDF ultrafiltration membrane is a typical asymmetric composite porous structure. The pore cortex and the lower layer are composed of loose finger-shaped pores, and the middle part is also dispersed with a drop-shaped mesopore structure. The formation of this structure is due to the instantaneous phase separation of the gel-state casting solution in the water bath. When the casting solution enters the water bath, the casting solution on the surface first contacts with water and solidifies rapidly to form a dense surface layer, while the casting solution at the middle and bottom forms pores with different pore sizes due to different solidification speeds. When ZnIn ₂ S ₄ was loaded on the surface of the gel phase film to participate in the phase separation process, the structure of the upper skin layer of the surface composite photocatalytic film section changed significantly, and the small pore structure was occupied by the catalyst to form a ZnIn ₂ S ₄ functional layer. Since the catalyst is loaded on the surface of the membrane, it has no obvious influence on the formation of the finger-like pore macroporous structure of the lower layer of the composite photocatalytic membrane on the surface. The small pore structure on the upper layer of the M-1.2 membrane section with a loading of 1.2 mg/cm ² has completely disappeared, forming a complete ZnIn ₂ S ₄ functional layer. However, when the catalyst loading increased to 1.7mg/ ^cm2 , the finger-shaped pores of the M-1.7 membrane were squeezed by the catalyst, resulting in a significant decrease in pore size, and some of the membrane pores were blocked, and the membrane pore structure of the surface composite photocatalytic membrane occurred. Seriously deformed. Wang et al.'s research on inorganic nanoparticles modified ultrafiltration membranes found that the pore size of ultrafiltration membranes will have a significant impact on the mass transfer of water molecules. Therefore, the change of the finger-like pore structure in the lower layer of the M-1.7 membrane may affect the mass transfer of water molecules in the membrane pores, thereby adversely affecting the membrane flux.

It can be seen from the surface SEM image that the surface of the PVDF ultrafiltration membrane is relatively smooth with a dense skin. With the increase of the loading amount, the ZnIn ₂ S ₄ functional layer gradually formed on the composite photocatalytic film surface, and ZnIn ₂ S ₄ could be covered by the surface skin layer during the phase separation process and firmly attached to the film surface. However, when the catalyst loading increased to 1.7 mg/cm ² , the excess ZnIn ₂ S ₄ on the surface of the M-1.7 membrane was agglomerated, which made it difficult to be completely covered by the surface skin and showed an open characteristic. It leads to the loss of the catalyst and affects the permeability of the separation membrane, so it is not conducive to the improvement of the membrane performance.

From the perspective of cross-section and surface structure, the M-1.2 membrane with a loading capacity of 1.2 mg/cm ² forms a complete and uniform ZnIn ₂ S ₄ functional layer and the finger-shaped pore structure does not undergo obvious deformation. In addition to the structural characteristics of the film itself, it also has the basic structural characteristics for photocatalytic reactions.

2. Elemental composition analysis:

The element composition of the surface composite photocatalytic film was analyzed by XPS. Figure 2 shows the XPS full-scan patterns of the surface composite photocatalytic film with different loads and the M-1.2 film with a load of 1.2 mg/cm ² Zn, In, S High-resolution XPS spectra of elements.

As shown in the full-scan spectrum of Figure 2(a), the PVDF ultrafiltration membrane has four distinct characteristic peaks at binding energies of 288.39eV, 402.89eV, 535.01eV and 691.08eV, which belong to C1s, N1s, O1s and F1s respectively. The characteristic peaks in the XPS full-scan pattern of ZnIn ₂ S ₄ belong to Zn2p, In3d and S2p, respectively. With the increase of ZnIn ₂ S ₄ loading, the characteristic peaks of PVDF ultrafiltration membrane in the full-scan spectrum of the surface composite photocatalytic membrane did not change significantly, and the characteristic peaks of Zn2p, In3d and S2p attributed to ZnIn ₂ S ₄ appeared and The response gradually increases. The results show that the surface composite photocatalytic membrane is composed of C, F, N, Zn, In, S and other elements, and ZnIn ₂ S ₄ can be supported on the surface of PVDF ultrafiltration membrane to form a ZnIn ₂ S ₄ functional layer by surface hybridization.

In order to further analyze the valence states of Zn, In, and S elements in the surface composite photocatalytic film, the high-resolution XPS spectrum scanning of Zn, In, and S elements was carried out by taking the M-1.2 film with a loading capacity of 1.2 mg/cm ² as an example. And compare it with the high-resolution XPS spectrum of powder ZnIn ₂ S ₄ , the results are shown in Figure 2(b)-(d). The characteristic peaks at binding energies of M-1.2 film at 162.38eV, 445.48eV, 453.18eV, 1022.98eV and 1046.07eV are closely related to S2p _3/2 , In3d _5/2 , In3d _3/2 , Zn2p ₃ of powdered ZnIn ₂ S _{4 /2} and Zn2p _1/2 characteristic peaks are exactly the same. The results show that the elements in ZnIn ₂ S ₄ supported on the surface composite photocatalytic film also exist as Zn ²⁺ , In ³⁺ and S ^2- . The preparation process of coating ZnIn ₂ S ₄ on the surface of the gel phase film and separating the phases in a water bath can not only successfully load ZnIn ₂ S ₄ on the film surface, but will not change the chemical composition and properties of ZnIn ₂ S ₄ . The surface composite photocatalytic film with ZnIn ₂ S ₄ functional layer can be successfully obtained by this method.

3. Crystal structure analysis:

The crystal structure of the surface composite photocatalytic film was analyzed by XRD, and the results are shown in Figure 3. PVDF has four phase types of α, β, γ and δ, among which α phase is the most common and stable phase state, and β phase plays an important role in practical application due to its good piezoelectric and pyroelectric properties. It can be seen from Figure 3 that the PVDF ultrafiltration membrane has obvious α-phase diffraction peaks at 36.8° and 40.0°, respectively, and the diffraction peak at 20.44° indicates the presence of β-phase. The diffraction peaks in the ZnIn ₂ S ₄ XRD pattern belong to the (006) crystal plane, (102) crystal plane, (105) crystal plane, (110) crystal plane and (202) crystal plane, respectively. The crystal form of ZnIn ₂ S ₄ For the hexagonal crystal single phase.

It can be observed from the figure that the characteristic diffraction peaks of α-PVDF, β-PVDF and hexagonal ZnIn ₂ S ₄ appear in the XRD spectrum of the composite photocatalytic film on the surface, and as the loading of ZnIn ₂ S ₄ increases, The characteristic diffraction peak responses attributed to ZnIn ₂ S ₄ are continuously enhanced, while the characteristic diffraction peak responses attributed to α-PVDF and β-PVDF are gradually decreased. The results showed that a ZnIn ₂ S ₄ functional layer was formed on the surface of the composite photocatalytic film.

4. Optical performance analysis:

The absorption performance of the surface composite photocatalytic film on ultraviolet-visible light can be reflected by the ultraviolet-visible diffuse reflectance spectrum, and the results are shown in Figure 4. It can be seen from the figure that the PVDF ultrafiltration membrane basically has no response in the ultraviolet-visible light region, indicating that the PVDF ultrafiltration membrane does not have optical properties. The response of the surface composite photocatalytic film to ultraviolet-visible light increases with the increase of the loading, indicating that the loading of ZnIn ₂ S ₄ effectively enhances the response ability of the surface composite photocatalytic film to light. Among them, M-1.2 film and M-1.7 film have good absorption capacity for ultraviolet-visible light. It has strong absorption for light with a wavelength of 200nm-500nm, and has a steep absorption edge at 500nm. In the range of 500nm-800nm, the light absorption performance gradually weakens with the increase of wavelength, which is similar to the ultraviolet light of ZnIn ₂ S ₄ - It can be seen that the diffuse reflectance spectrum is basically the same. The results show that the surface composite photocatalytic film has good absorption properties for ultraviolet and visible light, and has the basic conditions for photocatalytic reaction using light source energy, which provides a guarantee for the degradation of pollutants.

The above characterization results confirmed that the surface composite photocatalytic membrane formed a complete photocatalytic functional layer while retaining the chemical properties of the PVDF ultrafiltration membrane, and possessed the basic structure and optical properties for photocatalytic reactions. Therefore, it is effective to load ZnIn ₂ S ₄ on the film surface to form a surface composite photocatalytic film by means of surface hybridization.

5. Hydrophilicity and pure water flux analysis:

The hydrophilicity of the separation membrane is an important factor determining the flux and antifouling performance of the ultrafiltration membrane, which can be evaluated by the contact angle. In this study, the contact angle of the surface composite photocatalytic film was measured by the static droplet method, and the results are shown in Figure 5. It can be seen from the figure that the contact angle of the surface composite photocatalytic membrane is smaller than that of the PVDF ultrafiltration membrane, and it decreases with the increase of ZnIn ₂ S ₄ loading. The contact angle of PVDF ultrafiltration membrane is 76.94°, when the load increases to 1.2mg/cm ² , the contact angle of M-1.2 membrane decreases to 67.28°, but the load continues to increase, the contact angle of M-1.7 membrane is basically constant. The experimental results show that loading ZnIn ₂ S ₄ can improve the surface hydrophilicity of the separation membrane within a certain range. As a photocatalyst, ZnIn ₂ S ₄ has a large specific surface area and good hydrophilicity, which is beneficial to the mass transfer of water molecules, so loading it on the surface of the separation membrane is beneficial to enhance the hydrophilicity of the membrane surface. At the same time, during the phase inversion process, the hydrophilic inorganic catalyst located at the membrane-water interface can effectively reduce the interfacial energy and thus improve the surface hydrophilicity of the separation membrane. However, the surface roughness of the separation membrane will have a significant impact on the hydrophilicity of the membrane surface. The rougher the surface of the separation membrane, the larger the contact angle, and the poorer the wettability of water droplets on the membrane surface. It can be seen from the surface SEM images that the surface roughness of the composite photocatalytic film after loading ZnIn ₂ S ₄ increases with the increase of the catalyst loading, which has a negative impact on the improvement of the hydrophilicity of the film surface, resulting in M-1.7 The membrane contact angle no longer changes significantly.

The pure water flux of the surface composite photocatalytic membrane is shown in Fig. 6. It can be observed from the figure that the pure water flux of all surface composite photocatalytic membranes is significantly higher than that of the PVDF ultrafiltration membrane, and it first increases and then decreases with the increase of ZnIn ₂ S ₄ loading. Among them, the pure water flux of the PVDF ultrafiltration membrane is only 251.5L/(m ² ·h), while the pure water flux of the M-1.2 membrane with a loading capacity of 1.2mg/cm ² is as high as 628L/(m ² ·h). The results show that loading ZnIn ₂ S ₄ can significantly improve the pure water flux of the separation membrane. The hydrophilicity of the membrane surface and the membrane pore structure are the main factors affecting the flux of the separation membrane. From the microstructure characterization results in Section 5.3.1, it can be seen that the surface composite photocatalytic membrane has a composite porous structure. In the filtration process, the small pore structure of the upper layer of the composite porous structure plays a role in separation, while the permeability of the separation membrane is mainly determined by the macropore structure of the lower layer. As the load increases, the small pore structure of the upper layer is occupied to form a hydrophilic ZnIn ₂ S ₄ functional layer, which is beneficial to the mass transfer of water molecules and improves the flux, so the flux of pure water continues to increase. When the load increases to a certain level (1.7mg/cm ² ), excess ZnIn ₂ S ₄ enters the finger-shaped pore structure to block the membrane pores, and at the same time squeezes the finger-shaped pores, resulting in a decrease in pore diameter and a change in the cross-sectional structure. The obvious deformation has a negative impact on the permeability of the surface composite photocatalytic membrane. At the same time, the formation of the photocatalytic functional layer on the surface of the membrane leads to an increase in the thickness of the membrane, which adversely affects the transfer of water molecules and causes a decrease in the pure water flux of the composite photocatalytic membrane on the surface. Therefore, the pure water flux of the M-1.7 membrane was reduced compared with the M-1.2 membrane.

The results of hydrophilicity and pure water flux analysis show that loading ZnIn ₂ S ₄ on the surface of the gel phase film to participate in phase separation can significantly improve the hydrophilicity of the separation membrane and increase its pure water flux. The removal performance and anti-pollution performance have advantages.

6. Photocatalytic performance analysis:

6.1. Analysis of fluvastatin removal effect:

Fluvastatin was used as the target pollutant to investigate the catalytic performance of the surface composite photocatalytic film, and the removal effect of the surface composite photocatalytic film on fluvastatin was studied under dark conditions. The results are shown in Figure 7. As shown in Fig. 7(a), the removal ability of fluvastatin by the composite photocatalytic film on the surface is very limited under dark conditions. The removal rate of fluvastatin by PVDF ultrafiltration membrane is only 5.69%, and the removal rate of M-1.2 membrane with a loading capacity of 1.2mg/cm ² is 29.47%. The removal of fluvastatin by the composite photocatalytic membrane on the surface under dark conditions was mainly achieved through the physical sieving process. Due to the limited sieving capacity of the separation membrane, the removal rate of fluvastatin only increased significantly within 20 minutes of the beginning of the reaction, and did not change significantly after the filtration process. Due to the large pore size of the PVDF ultrafiltration membrane, the removal effect of fluvastatin with a relatively low molecular weight is poor. For the surface composite photocatalytic membrane, the formation of the photocatalytic functional layer can enhance the screening effect of the separation membrane, thereby improving the removal effect of the separation membrane on fluvastatin. However, excessive ZnIn ₂ S ₄ agglomeration led to obvious changes in the structure and morphology of the membrane surface, so the performance of the M-1.7 membrane to remove fluvastatin decreased.

As shown in Figure 7(b), the removal rate of fluvastatin in each system under light conditions was significantly higher than that under dark conditions, and the removal rate increased with the increase of reaction time. The removal rate of fluvastatin by PVDF ultrafiltration membrane was 58.24%. The removal effect of fluvastatin by surface composite photocatalytic membrane increases with the increase of loading, and the removal rate of fluvastatin in the M-1.2 membrane system is as high as 92.76%. Under the irradiation of xenon lamp, the ZnIn ₂ S ₄ photocatalytic functional layer is excited by incident light to generate ·O ₂ ^- and ·OH to degrade and remove fluvastatin in the reaction system. At the same time, the stronger polar OH can combine with water molecules to increase the membrane flux and accelerate the circulation rate of the reaction solution, further enhancing the removal effect. However, when the loading of ZnIn ₂ S ₄ increased to 1.7 mg/cm ² , a large amount of catalyst was transferred from the membrane to the pores of the membrane, reducing the utilization rate of the catalyst for incident light and affecting the photocatalytic effect. Therefore, the removal effect of M-1.7 membrane on fluvastatin is basically the same as that of M-1.2 membrane. In summary, compared with the PVDF ultrafiltration membrane, the surface composite photocatalytic membrane has a significantly enhanced removal effect on fluvastatin and has good photocatalytic performance.

6.2. TOC removal effect analysis:

The TOC removal effect in the surface composite photocatalytic film reaction system is shown in Figure 8. It can be seen from the results in the figure that the removal rate of TOC in the PVDF ultrafiltration membrane system is only 7.09% under dark conditions, and the removal rate of the M-1.2 membrane is 18.08%. Under the irradiation of xenon lamp, the removal effect of each system on TOC is obviously enhanced. The TOC removal rate of the PVDF ultrafiltration membrane system increased to 18.10%, while the TOC removal rate of the M-1.2 membrane reached 41.53%. The results showed that the light and catalyst loading significantly improved the removal capacity of the separation membrane for organic matter. Under light conditions, PVDF ultrafiltration membrane removes TOC in the reaction system through self-photolysis of fluvastatin absorbing photon energy. Due to the limited photon energy, fluvastatin can only undergo primary degradation and be decomposed into macromolecular products, resulting in a low removal rate of TOC. The formation of the photocatalytic functional layer can not only enhance the adsorption and sieving performance of the composite photocatalytic film on the surface, but also the strong oxidative active free radicals generated during the illumination process can degrade fluvastatin into small molecules, easily degradable products and eventually mineralize Complete removal of organic matter for H ₂ O and CO ₂ can significantly improve the removal rate of TOC.

From the above analysis results, it can be seen that compared with the PVDF ultrafiltration membrane, the surface composite photocatalytic membrane not only has excellent photocatalytic performance, but also can mineralize the organic matter in the reaction system, and truly realize the harmless of organic pollutants in the water body. treatment.

6.3. Stability analysis:

The stability of the catalyst in the separation membrane is an important factor affecting the performance of the photocatalytic membrane. The loss of the catalyst will not only adversely affect the performance of the photocatalytic membrane, but also cause certain harm to the water ecological environment. Stability studies are necessary.

Taking the M-1.2 film as an example, the stability of the surface composite photocatalytic film was evaluated by its removal effect on fluvastatin and TOC during continuous operation, and the results are shown in Figure 9. It can be seen from Figure 9(a) that the removal rate of fluvastatin can still reach 85.87% after 900 min of reaction in 5 cycles of experiments, which is only 6.89% lower than the removal rate after 180 min of reaction. The results show that the M-1.2 membrane always has a high removal rate of fluvastatin during the cycle operation, showing good photocatalytic stability. As shown in the results in Figure 9(b), the removal rate of TOC in the reaction system decreased during the cycle operation. The decrease of the removal effect of fluvastatin and TOC by the composite photocatalytic film on the surface is mainly due to the fact that fluvastatin and its intermediate products occupy the active sites of ZnIn ₂ S ₄ and cause catalyst deactivation, which affects the photocatalytic effect.

Overall, the surface composite photocatalytic film exhibited good photocatalytic stability during long-term operation. Compared with surface modification techniques such as surface deposition and surface grafting, using the gel properties of the casting solution to firmly adhere ZnIn ₂ S ₄ to the membrane surface can effectively improve the catalyst immobilization process and ensure the catalyst’s use of the light source. This method provides a guarantee for the excellent photocatalytic performance and good stability of the surface composite photocatalytic film, and is of great value in promoting the development of photocatalytic technology to the application level.

7. Analysis of anti-pollution performance:

The flux curve of the surface composite photocatalytic membrane with time during the continuous filtration of RhB is shown in Fig. 10. It can be seen from the figure that the membrane flux decays rapidly at the initial stage of filtration, and then gradually tends to be stable. The permeation flux of the surface composite photocatalytic membrane increases with the increase of catalyst loading at the same filtration time. The permeation flux of the PVDF ultrafiltration membrane after stable operation is 85.02L/(m ² h), and the stable flux of the surface composite photocatalytic membrane is significantly higher than the stable flux of the PVDF ultrafiltration membrane, in which the loading capacity is 1.2mg/cm ² 's M-1.2 membrane has a stable flux of 243.62L/(m ² ·h). Under light conditions, ZnIn ₂ S ₄ has a good photocatalytic degradation performance for RhB, and the active free radicals generated by the photocatalytic functional layer can degrade RhB adsorbed on the membrane surface and in the membrane pores into small molecular products and even mineralize into H ₂ O and CO ₂ are promoted to be decomposed from the membrane pores so as to alleviate membrane fouling and increase membrane flux. The OH produced by the photocatalytic reaction has strong polarity and can combine with water molecules through van der Waals force or hydrogen bonding, which is beneficial to improve the permeation flux of the membrane. In addition, related research results show that active free radicals can affect the membrane pore structure to improve membrane flux. The catalytic performance of surface composite photocatalytic membrane plays a very important role in reducing membrane fouling and improving membrane flux. Compared with the PVDF ultrafiltration membrane, the membrane fouling of the surface composite photocatalytic membrane is effectively alleviated, and the permeation flux during operation is significantly increased.

The pure water flux recovery rate of the surface composite photocatalytic membrane is shown in Fig. 11. The flux recovery rate of PVDF ultrafiltration membrane was 55.73%. The flux recovery rate of the surface composite photocatalytic film increased first and then decreased with the increase of ZnIn ₂ S ₄ loading, and the flux recovery rate of the M-1.2 film with the loading of 1.2mg/cm ² was as high as 80.50%. The results showed that the anti-fouling ability of the surface composite photocatalytic membrane was significantly enhanced compared with the PVDF ultrafiltration membrane, and the M-1.2 membrane had the best anti-fouling performance. In summary, the surface composite photocatalytic membrane prepared in this study has good anti-pollution performance and self-purification ability, which provides a new idea for solving the problem of separation membrane fouling.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations. The above-mentioned embodiments are only preferred embodiments for fully illustrating the present invention, and the scope of protection thereof is not limited thereto. The equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention, and the protection scope of the present invention shall be determined by the claims.

Claims (10)

1. The preparation method of surface composite photocatalytic film is characterized in that, comprises the steps: organic polymer membrane material, porogen are dissolved in organic solvent, obtains casting film liquid, and casting film liquid is left standstill to remove air bubble, Then, it is cast into a gel phase film, and then the photocatalyst is loaded on the surface of the gel phase film by surface coating, and then the phases are separated to obtain a surface composite photocatalytic film. 2. The preparation method of surface composite photocatalytic membrane according to claim 1, is characterized in that, described organic macromolecule membrane material comprises but not limited to polyvinylidene fluoride, polysulfone, polyethersulfone; The porogen includes but is not limited to polyvinylpyrrolidone, lithium chloride or a mixture of the two; The organic solvent includes, but is not limited to, N,N ^, -dimethylacetamide, N,N ^, -dimethylformamide, and ethylene glycol methyl ether. 3. The preparation method of the surface composite photocatalytic film according to claim 2, characterized in that, when the porogen is selected from the mixture of polyvinylpyrrolidone and lithium chloride, in the casting solution, the organic polymer The mass ratio of membrane material, polyvinylpyrrolidone, lithium chloride and organic solvent is 16-18:0.5-1:1-2:79-82.5; when the porogen is selected from polyvinylpyrrolidone or lithium chloride, organic high The mass ratio of molecular membrane material, porogen and organic solvent is 16-18:1.5-3:79-82.5. 4 . The preparation method of surface composite photocatalytic film according to claim 1 , characterized in that, the phase separation method is: after the catalyst is supported on the gel phase film, it is immersed in a 40-60° C. constant temperature water bath. 5. The preparation method of the surface composite photocatalytic film according to claim 1, characterized in that, the photocatalyst is a powder catalyst. 6. The preparation method of surface composite photocatalytic film according to claim 5, is characterized in that, described photocatalyst comprises but not limited to ZnIn _{2 S} catalyzer, _TiO catalyzer, WO ₃ catalyst, ZnO catalyst, gC ₃ N ₄ catalysts. 7. the preparation method of surface composite photocatalytic film according to claim 6, is characterized in that, described ZnIn ₂ S ₄ catalyst is prepared according to the following steps: Dissolve Zn(NO ₃ ) ₂ ·6H ₂ O, In(NO ₃ ) ₃ ·xH ₂ O and thioacetamide in deionized water, then react at 60-120°C for 6 hours, cool, wash and grind , to obtain ZnIn ₂ S ₄ catalyst; Wherein, the mass ratio of Zn(NO ₃ ) ₂ ·6H ₂ O, In(NO ₃ ) ₃ ·xH ₂ O and thioacetamide is 1:2:16. 8 . The method for preparing a surface composite photocatalytic film according to claim 1 , wherein the loading amount of the photocatalyst on the gel phase film is 0.2-2 mg/cm ² . 9. A surface composite photocatalytic film prepared by the preparation method according to any one of claims 1-8. 10. an application of the surface composite photocatalytic membrane according to claim 9 in the preparation of water treatment membrane, is characterized in that, the method for described water treatment is: Soak the surface composite photocatalytic membrane in deionized water until there is no organic solvent residue on the surface, then fix the surface composite photocatalytic membrane in the membrane pool, and use a diaphragm pump to pump the wastewater containing pollutants into the membrane pool. , Simultaneously carry out membrane filtration and photocatalytic reaction process, and react for 2-8h.

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