Biocl nanosheet doped pvdf composite membrane and preparation method thereof

Abstract

The application relates to the technical field of photocatalysts, and discloses a BiOCl nanosheet doped PVDF composite film and a preparation method thereof. The preparation method of the nanosheet doped PVDF composite film is as follows: the nanosheet is surface-modified by using an alkenylated catechol type quaternary ammonium salt modifier to obtain an alkenylated nanosheet, wherein the nanosheet is any one of a BiOCl nanosheet, a Ni-BiOCl nanosheet and a Co-BiOCl nanosheet; a carbon-carbon double bond is formed through a dehydrofluorination reaction by alkali treatment to obtain modified PVDF powder; under the action of an initiator, the alkenylated nanosheet and the modified PVDF powder are subjected to a free radical polymerization reaction to obtain a composite film material; the composite film material is added into N,N-dimethylacetamide to form a casting solution; the casting solution is laid on a glass plate and is subjected to blade coating; and a nanosheet doped PVDF composite film is prepared through an immersion precipitation phase inversion method; and the film product can degrade methyl orange dye.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, and more particularly to BiOCl nanosheet-doped PVDF composite films and their preparation methods. Background Technology

[0002] BiOCl nanosheets are a novel photocatalyst with environmental friendliness, non-toxicity, temperature resistance, barrier properties, water resistance, and good chemical stability. Their unique layered structure gives them excellent light absorption capacity and high carrier migration efficiency. They can be used to degrade dyes through photocatalysis and can be applied to pollution control and the degradation of organic pollutants such as dyes.

[0003] Dyes play a vital role in many fields such as textile dyeing and printing, paint, plastics, leather, optoelectronic communications, and food. However, industrial dyes can cause organic solvent poisoning or polymer poisoning and can also cause environmental pollution. Existing technologies for treating waste dye wastewater mainly include biological methods, adsorption methods, extraction methods, photocatalytic decomposition methods, and membrane separation methods. Among them, photocatalysis is highly valued for its efficiency and good impurity removal effect.

[0004] Photocatalysis technology suffers from problems such as difficulty in recovering photocatalysts, easy secondary pollution from waste liquid, and accumulation of pollutant molecules leading to membrane fouling, which reduces membrane flux and shortens membrane lifespan. BiOCl, on the other hand, has limitations such as being able to absorb and utilize only ultraviolet light, having low efficiency in separating electrons and holes, and being difficult to recover and reuse in its powder form, thus restricting its application.

[0005] PVDF (polyvinylidene fluoride), which has advantages such as anti-aging, chemical resistance, weather resistance, and UV radiation resistance, is selected as the matrix membrane material. A composite membrane is prepared using BiOCl-doped PVDF for dye degradation. This not only maintains the process characteristics and treatment capacity of photocatalysis and membrane separation technology, but also achieves better degradation effect on dye wastewater. Furthermore, it generates a series of synergistic effects, thereby solving the defects of individual treatment processes. While the photocatalyst degrades the dye, it can also block unoxidized dyes and some intermediate products, thus better controlling the residence time of dyes in the reactor. Improving the photocatalytic degradation rate can also solve the problem of membrane flux decline caused by membrane fouling.

[0006] Research has found that doping with metal ions can alter the electronic structure of BiOCl, forming impurity energy levels that can effectively regulate the band gap of BiOCl, change the semiconductor band structure, broaden the photoresponse range, improve photocatalytic performance, and enhance dye degradation efficiency, thereby achieving better degradation results. Summary of the Invention

[0007] This invention proposes a nanosheet-doped PVDF composite film and its preparation method. Different types of BiOCl nanosheet photocatalysts are modified by an alkenylated catechol-type quaternary ammonium salt modifier to obtain alkenylated nanosheets. PVDF powder is used as the matrix film material and is subjected to alkali treatment to obtain modified PVDF powder containing carbon-carbon double bonds. Under the action of an initiator, the alkenylated nanosheets and modified PVDF powder undergo a free radical polymerization reaction. The nanosheet-doped PVDF composite film is then prepared by an immersion precipitation phase inversion method, which can be used to degrade methyl orange.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The preparation method of nanosheet-doped PVDF composite film includes the following steps:

[0010] Step 1: Preparation of alkenylated nanosheets: The surface of the nanosheets is modified by an alkenylated catechol-type quaternary ammonium salt modifier to obtain alkenylated nanosheets; wherein, the nanosheets are any one of BiOCl nanosheets, Ni-BiOCl nanosheets, and Co-BiOCl nanosheets; the mass ratio of alkenylated catechol-type quaternary ammonium salt modifier to nanosheets is 1-5:1;

[0011] Step 2: Preparation of modified PVDF powder: Modified PVDF powder is obtained by forming carbon-carbon double bonds through a defluorination reaction caused by alkali treatment;

[0012] Step 3: Preparation of casting solution: Under the action of an initiator, alkenylated nanosheets and modified PVDF powder undergo a free radical polymerization reaction to obtain a composite membrane material. The composite membrane material is then added to N,N-dimethylacetamide to form a casting solution; wherein the mass ratio of alkenylated nanosheets to modified PVDF powder is 1:1-2.

[0013] Step 4: Preparation of nanosheet-doped PVDF composite film: Spread the casting solution evenly on a glass plate, scrape the film, and obtain the nanosheet-doped PVDF composite film by immersion precipitation phase inversion method.

[0014] Preferably, the preparation method of the alkenylated catechol-type quaternary ammonium salt modifier is as follows:

[0015] In the presence of an activator and a catalyst, 1 molar equivalent of 1,3-diaminopropane and 1 molar equivalent of 3,4-dihydroxyphenylacetic acid undergo an amidation reaction via amino and carboxyl groups to prepare intermediate I.

[0016] One molar equivalent of intermediate I reacts with one molar equivalent of methacryloyloxyethyltrimethylammonium chloride via an amino-enyl addition reaction through an amino group and an α-β-unsaturated double bond to prepare intermediate II containing a secondary amine.

[0017] Under the action of triethylamine, 1 molar equivalent of intermediate II containing secondary amine reacts with 1 molar equivalent of allyl methacrylate via an amino-enyl addition reaction through amino and α-β unsaturated double bonds to prepare an alkenylated catechol-type quaternary ammonium salt modifier.

[0018] Preferably, the activator is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride or N,N-dicyclohexylcarbodiimide.

[0019] Preferably, the catalyst is N-hydroxysuccinimide or 4-dimethylaminopyridine.

[0020] Preferably, the initiator is benzoyl peroxide or azobisisobutyronitrile.

[0021] Preferably, the method for preparing the BiOCl nanosheets is as follows:

[0022] Bismuth chloride was added to hydrochloric acid solvent, dissolved and mixed evenly, and the pH value was adjusted to 10 to form a precipitate. The precipitate was washed and dried at a temperature of 155-165℃ for 10-15 hours. After grinding, BiOCl nanosheets were obtained.

[0023] Preferably, the method for preparing the Ni-BiOCl nanosheets is as follows:

[0024] Bismuth chloride and nickel chloride were added to hydrochloric acid solvent, dissolved and mixed evenly, and the pH value was adjusted to 10 to form a precipitate. The precipitate was washed and dried at a temperature of 155-165℃ for 10-15 hours. After grinding, Ni-BiOCl nanosheets were obtained. The molar equivalent ratio of bismuth chloride to nickel chloride was 2:1.

[0025] Preferably, the preparation method of the Co-BiOCl nanosheets is as follows:

[0026] Bismuth chloride and cobalt chloride were added to hydrochloric acid solvent, dissolved and mixed evenly, and the pH value was adjusted to 10 to form a precipitate. The precipitate was washed and dried at a temperature of 155-165℃ for 10-15 hours. After grinding, Ni-BiOCl nanosheets were obtained. The molar equivalent ratio of bismuth chloride to cobalt chloride was 3:1.

[0027] Preferably, the nanosheet-doped PVDF composite film is any one of BiOCl nanosheet-doped PVDF composite film, Ni-BiOCl nanosheet-doped PVDF composite film, and Co-BiOCl nanosheet-doped PVDF composite film.

[0028] Preferably, the nanosheet-doped PVDF composite film is used to degrade methyl orange dye.

[0029] The beneficial effects of this invention are as follows:

[0030] This invention prepares BiOCl nanosheets, Ni-BiOCl nanosheets, and Co-BiOCl nanosheets via a co-precipitation method.

[0031] An alkenylated catechol-type quaternary ammonium salt modifier containing catechol functional groups, quaternary ammonium salt functional groups, and double bond functional groups was designed and synthesized.

[0032] The catechol functional groups in alkenylated catechol-type quaternary ammonium salt modifiers possess adhesive properties and can form strong bonds with the surface of nanosheets, thus preparing alkenylated BiOCl nanosheets, alkenylated Ni-BiOCl nanosheets, and alkenylated Co-BiOCl nanosheets. The quaternary ammonium salt functional groups on the surface of the alkenylated nanosheets can adsorb the negatively charged anionic dye methyl orange. Under the action of an initiator, the alkenylated nanosheets can undergo a free radical polymerization reaction with modified PVDF powder that has undergone defluorination through alkali treatment to form carbon-carbon double bonds. Then, through the immersion precipitation phase inversion method, BiOCl nanosheet-doped PVDF composite films, Ni-BiOCl nanosheet-doped PVDF composite films, and Co-BiOCl nanosheet-doped PVDF composite films are prepared, realizing the loading and fixation of nanosheets on the surface of the membrane material. The prepared composite films have stable performance, and the nanosheets will not easily fall off, thus extending the service life of the composite films.

[0033] The experimental results show that the ability of the Ni-BiOCl nanosheet-doped PVDF composite film and the Co-BiOCl nanosheet-doped PVDF composite film prepared in this invention to degrade methyl orange dye is significantly improved. The Ni-BiOCl nanosheet-doped PVDF composite film has the best effect on degrading methyl orange dye. Although the Co-BiOCl nanosheet-doped PVDF composite film has a better performance in degrading methyl orange dye, Ni is more economical and environmentally friendly than Co, saving costs and raw materials. Attached Figure Description

[0034] Figure 1 Electron microscopy image of a BiOCl nanosheet-doped PVDF composite film;

[0035] Figure 2 Electron microscopy image of a Ni-BiOCl nanosheet-doped PVDF composite film;

[0036] Figure 3 Electron microscopy image of a Co-BiOCl nanosheet-doped PVDF composite film;

[0037] Figure 4 Electron microscopy image of Fe-BiOCl nanosheet-doped PVDF composite film;

[0038] Figure 5 Degradation curves of methyl orange by BiOCl nanosheet-doped PVDF composite film;

[0039] Figure 6 Degradation curves of methyl orange by Ni-BiOCl nanosheet-doped PVDF composite film;

[0040] Figure 7 Degradation curves of methyl orange by Co-BiOCl nanosheet-doped PVDF composite film;

[0041] Figure 8 Degradation curves of methyl orange by Fe-BiOCl nanosheet-doped PVDF composite film. Detailed Implementation

[0042] Example 1:

[0043] The synthesis mechanism of alkenylated catechol-type quaternary ammonium salt modifiers is as follows:

[0044] In the presence of an activator and a catalyst, 1 molar equivalent of 1,3-diaminopropane and 1 molar equivalent of 3,4-dihydroxyphenylacetic acid undergo an amidation reaction via amino and carboxyl groups to prepare intermediate I.

[0045] One molar equivalent of intermediate I reacts with one molar equivalent of methacryloyloxyethyltrimethylammonium chloride via an amino-enyl addition reaction through an amino group and an α-β-unsaturated double bond to prepare intermediate II containing a secondary amine.

[0046] Under the action of triethylamine, 1 molar equivalent of intermediate II containing secondary amine reacts with 1 molar equivalent of allyl methacrylate through an amino-enyl addition reaction via amino and α-β unsaturated double bonds to prepare an alkenylated catechol-type quaternary ammonium salt modifier.

[0047] The chemical structural formula of the alkenylated catechol-type quaternary ammonium salt modifier is as follows:

[0048] ;

[0049] The activator is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride or N,N-dicyclohexylcarbodiimide; the catalyst is N-hydroxysuccinimide or 4-dimethylaminopyridine; in this example, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are selected.

[0050] The specific experimental steps for preparing alkenylated catechol-type quaternary ammonium salt modifiers are as follows:

[0051] 1.6 g of 3,4-dihydroxyphenylacetic acid was added to 30 mL of methanol and stirred until homogeneous. Then, 0.3 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.2 g of N-hydroxysuccinimide were added and stirred until homogeneous. Finally, 0.7 g of 1,3-diaminopropane was added and reacted at room temperature for 8 h. The mixture was then distilled under reduced pressure, washed with deionized water, and dried to obtain intermediate I.

[0052] 2.4 g of intermediate I was added to 40 mL of dimethyl sulfoxide and stirred until homogeneous. Nitrogen gas was introduced for protection. 2.1 g of methacryloyloxyethyltrimethylammonium chloride was added, and the temperature was raised to 50 °C. After stirring and maintaining the temperature for 3 h, 0.1 g of triethylamine and 1 mL of allyl methacrylate were added, and the temperature was raised to 70 °C. After stirring and maintaining the temperature for 4 h, the mixture was cooled to room temperature, diluted with dichloromethane, washed with deionized water, and the organic phase was collected, dried with anhydrous magnesium sulfate, filtered, and the solvent was removed by rotary evaporation. After drying, the alkenylated catechol-type quaternary ammonium salt modifier was obtained.

[0053] The 1H NMR characterization results of the alkenylated catechol-type quaternary ammonium salt modifier are as follows:

[0054] 1 H NMR (400MHz, DMSO-D6, δ, ppm): 1.11-1.13 (d, 6H), 1.61-1.66 (m, 2H), 2.49-2.75 (m, 8H), 3.14-3.17 (m, 2H), 3.23 (s, 9H), 3.50 (s, 2H), 3.6 9-3.78 (m, 2H), 4.48-4.62 (m, 4H), 5.27-5.33 (m, 2H), 5.87-5.94 (m, 1H), 6.25 (s, 1H), 6.61-6.63 (t, 1H), 6.64-6.75 (m, 3H), 6.85 (s, 1H).

[0055] Example 2:

[0056] The specific experimental steps for preparing BiOCl nanosheets are as follows:

[0057] 8g of bismuth chloride was added to 30mL of 1mol / L hydrochloric acid solution and stirred continuously at 600rpm for 15min until dissolved and mixed evenly. Concentrated ammonia was then added to adjust the pH to 10, forming a precipitate. Stirring continued for 5min. After rinsing with deionized water, the precipitate was poured into a clean crucible and placed in an oven for reaction. It was ensured that samples from the same group were in the same position during the reaction to avoid poor sample repeatability due to temperature differences in different areas of the oven. The reaction temperature was set to 160℃ and the reaction time to 12h. After the program was completed, the crucible was allowed to cool to room temperature before being removed. The dried product was poured into an evaporating dish and ground thoroughly until it was entirely powder without any lumps of solid, thus obtaining BiOCl nanosheets.

[0058] The specific experimental steps for preparing Ni-BiOCl nanosheets are as follows:

[0059] 8 g of bismuth chloride and 1.64 g of nickel chloride were added to 30 mL of 1 mol / L hydrochloric acid solution and stirred continuously at 600 rpm for 15 min until dissolved and mixed evenly. Concentrated ammonia was then added to adjust the pH to 10, forming a precipitate. Stirring continued for 5 min. After rinsing with deionized water, the precipitate was poured into a clean crucible and placed in an oven for reaction. It was ensured that samples from the same group were reacted in the same location within the oven to avoid poor sample repeatability due to temperature differences in different areas. The reaction temperature was set to 160℃ and the reaction time to 12 h. After the program was completed, the crucible was allowed to cool to room temperature before being removed. The dried product was poured into an evaporating dish and ground thoroughly until it was entirely powder without any lumps of solid, thus obtaining Ni-BiOCl nanosheets.

[0060] The specific experimental steps for preparing Co-BiOCl nanosheets are as follows:

[0061] 8 g of bismuth chloride and 1.1 g of cobalt chloride were added to 30 mL of 1 mol / L hydrochloric acid solution and stirred continuously at 600 rpm for 15 min until dissolved and mixed evenly. Concentrated ammonia was then added to adjust the pH to 10, forming a precipitate. Stirring continued for 5 min. After rinsing with deionized water, the precipitate was poured into a clean crucible and placed in an oven for reaction. It was ensured that samples from the same group were reacted in the same location within the oven to avoid poor sample repeatability due to temperature differences in different areas. The reaction temperature was set to 160℃ and the reaction time to 12 h. After the program was completed, the crucible was allowed to cool to room temperature before being removed. The dried product was poured into an evaporating dish and ground thoroughly until it was entirely powder without any lumps of solid, thus obtaining Co-BiOCl nanosheets.

[0062] The specific experimental steps for preparing Fe-BiOCl nanosheets are as follows:

[0063] 8 g of bismuth chloride and 1.37 g of ferric chloride were added to 30 mL of 1 mol / L hydrochloric acid solution and stirred continuously at 600 rpm for 15 min until dissolved and mixed evenly. Concentrated ammonia was then added to adjust the pH to 10, forming a precipitate. Stirring continued for 5 min. After rinsing with deionized water, the mixture was poured into a clean crucible and placed in an oven for reaction. It was ensured that samples from the same group were reacted in the same location within the oven to avoid poor sample repeatability due to temperature differences in different areas. The reaction temperature was set to 160℃ and the reaction time to 12 h. After the program was completed, the crucible was allowed to cool to room temperature before being removed. The dried product was poured into an evaporating dish and thoroughly ground until it was entirely powder without any lumps of solid, thus obtaining Fe-BiOCl nanosheets.

[0064] Example 3:

[0065] The specific experimental steps for preparing alkenylated BiOCl nanosheets are as follows:

[0066] 0.5 parts by weight of BiOCl nanosheets were added to 50 parts by weight of N,N-dimethylformamide and ultrasonically dispersed for 30 min to form a uniform dispersion. 2 parts by weight of alkenylated catechol-type quaternary ammonium salt modifier were added to the dispersion. After stirring at room temperature for 12 h, the crude product was centrifuged, washed with deionized water and ethanol, and vacuum dried to obtain alkenylated BiOCl nanosheets.

[0067] The specific experimental steps for preparing alkenylated Ni-BiOCl nanosheets differ from those for alkenylated BiOCl nanosheets only in that 0.5 parts by weight of Ni-BiOCl nanosheets are used instead of 0.5 parts by weight of BiOCl nanosheets.

[0068] The specific experimental steps for preparing alkenylated Co-BiOCl nanosheets differ from those for alkenylated BiOCl nanosheets only in that 0.5 parts by weight of Co-BiOCl nanosheets are used instead of 0.5 parts by weight of BiOCl nanosheets.

[0069] The specific experimental steps for preparing alkenylated Fe-BiOCl nanosheets differ from those for alkenylated BiOCl nanosheets only in that 0.5 parts by weight of Fe-BiOCl nanosheets are used instead of 0.5 parts by weight of BiOCl nanosheets.

[0070] Example 4:

[0071] The method for preparing BiOCl nanosheet-doped PVDF composite films includes the following steps:

[0072] Step 1: Disperse 3 parts by weight of PVDF powder in 90 parts by weight of 2 mol / L sodium hydroxide solution, add 0.5 parts by weight of tetrabutylammonium bromide, react in a water bath at 50°C for 2 hours, filter, wash with deionized water, and vacuum dry to obtain modified PVDF powder.

[0073] Step 2: Add 0.6 parts by weight of dried alkenylated BiOCl nanosheets to 50 parts by weight of N,N-dimethylacetamide, and ultrasonically disperse for 20 min. Then slowly add 1 part by weight of modified PVDF powder and 0.2 parts by weight of benzoyl peroxide. Raise the temperature to 60°C and stir for 5 h. Continue to raise the temperature to 80°C and react for 4 h. Cool to room temperature, filter, wash with deionized water, and vacuum dry. Then add 20 parts by weight of N,N-dimethylacetamide, raise the temperature to 60°C, stir for 6 h, and let stand to remove bubbles to form a casting solution.

[0074] Step 3: Spread the casting solution evenly on the glass plate, manually scrape the film with a glass rod, and then immediately immerse the glass plate in 100 parts by weight of room temperature deionized water. After the film is formed, remove it and soak it in 100 parts by weight of deionized water for storage to obtain BiOCl nanosheet-doped PVDF composite film.

[0075] The specific method of Ni-BiOCl nanosheet doped PVDF composite film differs from that of BiOCl nanosheet doped PVDF composite film only in that 0.6 parts by weight of alkenylated Ni-BiOCl nanosheets are used instead of 0.6 parts by weight of alkenylated BiOCl nanosheets.

[0076] The specific method of Co-BiOCl nanosheet doped PVDF composite film differs from that of BiOCl nanosheet doped PVDF composite film only in that 0.6 parts by weight of alkenylated Co-BiOCl nanosheets are used instead of 0.6 parts by weight of alkenylated BiOCl nanosheets.

[0077] The specific method of Fe-BiOCl nanosheet doped PVDF composite film differs from that of Ni-BiOCl nanosheet doped PVDF composite film only in that 0.6 parts by weight of alkenylated Fe-BiOCl nanosheets are used instead of 0.6 parts by weight of alkenylated BiOCl nanosheets.

[0078] The surface morphology of the BiOCl nanosheet-doped PVDF composite film was observed using scanning electron microscopy, and the results are as follows: Figure 1 As shown;

[0079] The surface morphology of the Ni-BiOCl nanosheet-doped PVDF composite film was observed using scanning electron microscopy, and the results are as follows: Figure 2 As shown;

[0080] The surface morphology of the Co-BiOCl nanosheet-doped PVDF composite film was observed using scanning electron microscopy, and the results are as follows: Figure 3 As shown;

[0081] The surface morphology of the Fe-BiOCl nanosheet-doped PVDF composite film was observed using scanning electron microscopy, and the results are as follows: Figure 4 As shown.

[0082] Performance testing:

[0083] Degradation test of methyl orange dye

[0084] Preparation of methyl orange dye: 5 mg, 10 mg, and 20 mg of methyl orange powder were respectively placed into three 100 mL volumetric flasks, and 100 mL of hot water was added. The flasks were shaken well and then diluted to volume to obtain methyl orange dyes with concentrations of 50 mg / L, 100 mg / L, and 200 mg / L, respectively. The dyes were then stored in a dark place to prevent light decomposition and kept for later use.

[0085] BiOCl nanosheet-doped PVDF composite films, Ni-BiOCl nanosheet-doped PVDF composite films, Co-BiOCl nanosheet-doped PVDF composite films, and Fe-BiOCl nanosheet-doped PVDF composite films were cut to a size of 2.5 × 5 cm. Four 100 mL portions of 20 µg / L methyl orange dye were measured into beakers. The prepared BiOCl nanosheet-doped PVDF composite films, Ni-BiOCl nanosheet-doped PVDF composite films, Co-BiOCl nanosheet-doped PVDF composite films, and Fe-BiOCl nanosheet-doped PVDF composite films were then added to the beakers. The F composite membrane was placed in a beaker containing methyl orange dye. A 500W ultraviolet lamp was turned on, and under strong magnetic stirring, the degraded solution was taken after 0 min, 10 min, 20 min, 30 min, 60 min, 90 min, 120 min, 150 min, and 180 min, and its absorbance was measured at a wavelength of 464 nm. The change in the intensity of the absorption peak of the methyl orange solution at 464 nm, i.e. the change in the ratio of methyl orange concentration before and after the photochemical reaction, was used to characterize the speed of photodegradation and photocatalytic activity. The degradation curve of methyl orange dye by the composite membrane was plotted.

[0086] Test results: The degradation curve of methyl orange by the BiOCl nanosheet-doped PVDF composite film is shown below. Figure 5 As shown;

[0087] The degradation curve of methyl orange by the Ni-BiOCl nanosheet-doped PVDF composite film is shown below. Figure 6 As shown;

[0088] The degradation curve of methyl orange by the Co-BiOCl nanosheet-doped PVDF composite film is shown below. Figure 7 As shown;

[0089] The degradation curve of methyl orange by Fe-BiOCl nanosheet-doped PVDF composite film is shown below. Figure 8 As shown;

[0090] The following conclusions were drawn from the analysis of the test results:

[0091] 1. The degradation ability of BiOCl nanosheet-doped PVDF composite film on methyl orange dye is limited;

[0092] 2. The Ni-BiOCl nanosheet-doped PVDF composite film shows a significantly improved technical effect in terms of degradation ability of methyl orange dye compared with the BiOCl nanosheet-doped PVDF composite film;

[0093] 3. The Co-BiOCl nanosheet-doped PVDF composite film showed a significantly improved degradation ability of methyl orange dye compared with the BiOCl nanosheet-doped PVDF composite film, and the degradation ability was not much different from that of the Ni-BiOCl nanosheet-doped PVDF composite film.

[0094] 4. The degradation ability of Fe-BiOCl nanosheet-doped PVDF composite film on methyl orange dye is not obvious, which may be because Fe is not doped into BiOCl, resulting in an unsatisfactory degradation effect. We will improve and optimize the experimental method in the future.

[0095] In summary, the ability of the Ni-BiOCl nanosheet-doped PVDF composite film and the Co-BiOCl nanosheet-doped PVDF composite film prepared by this invention to degrade methyl orange dye is significantly improved. The Ni-BiOCl nanosheet-doped PVDF composite film has the best effect on degrading methyl orange dye. Although the Co-BiOCl nanosheet-doped PVDF composite film has a better performance in degrading methyl orange, Ni is more economical and environmentally friendly than Co, saving costs and raw materials.

Claims

1. A method for preparing a BiOCl nanosheet doped PVDF composite film, characterized in that, It comprises the following steps: Step one, surface modification of Ni-BiOCl nanosheets or Co-BiOCl nanosheets by alkenylated catechol type quaternary ammonium salt modifier, and the mass ratio of the modifier to the nanosheets is controlled to be 1-5:1, to obtain alkenylated nanosheets; The chemical structural formula of the alkenylated catechol type quaternary ammonium salt modifier is: ； Step two, dehydrofluorination reaction of PVDF powder by alkali treatment method to generate carbon-carbon double bond, to obtain modified PVDF powder; Step three, free radical polymerization reaction of alkenylated nanosheets and modified PVDF powder under the action of initiator, with the mass ratio of 1:1-2, to obtain composite membrane material, and the composite membrane material is added into N,N-dimethylacetamide to obtain casting solution; Step four, the casting solution is laid on a glass plate and scraped to form a film, and BiOCl nanosheet doped PVDF composite membrane is prepared by immersion precipitation phase inversion method; The preparation method of the alkenylated catechol type quaternary ammonium salt modifier is: Under the action of activator and catalyst, 1 mol equivalent of 1,3-diaminopropane and 1 mol equivalent of 3,4-dihydroxyphenylacetic acid are subjected to amidation reaction through amino and carboxyl to obtain intermediate I; 1 mol equivalent of intermediate I and 1 mol equivalent of methacryloyloxyethyl trimethyl ammonium chloride are subjected to amine-ene addition reaction through amino and α-β unsaturated double bond to obtain intermediate II containing secondary amine; Under the action of triethylamine, 1 mol equivalent of intermediate II containing secondary amine and 1 mol equivalent of allyl methacrylate are subjected to amine-ene addition reaction through amino and α-β unsaturated double bond to obtain the alkenylated catechol type quaternary ammonium salt modifier; The preparation method of the Ni-BiOCl nanosheet is: Bismuth chloride and nickel chloride are added into hydrochloric acid solvent, dissolved and mixed uniformly, the pH value is adjusted to 10, and a precipitate is formed, which is washed and dried, the drying temperature is 155-165℃, the time is 10-15h, and the Ni-BiOCl nanosheet is obtained after grinding; wherein, the molar equivalent ratio of bismuth chloride to nickel chloride is 2:1; The preparation method of the Co-BiOCl nanosheet is: Bismuth chloride and cobalt chloride are added into hydrochloric acid solvent, dissolved and mixed uniformly, the pH value is adjusted to 10, and a precipitate is formed, which is washed and dried, the drying temperature is 155-165℃, the time is 10-15h, and the Co-BiOCl nanosheet is obtained after grinding; wherein, the molar equivalent ratio of bismuth chloride to cobalt chloride is 3:

1.

2. The preparation method of BiOCl nanosheet doped PVDF composite film according to claim 1, characterized in that, The activator is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride or N,N-dicyclohexyl carbodiimide.

3. The preparation method of BiOCl nanosheet doped PVDF composite film according to claim 1, characterized in that, The catalyst is N-hydroxysuccinimide or 4-dimethylamino pyridine.

4. The preparation method of BiOCl nanosheet doped PVDF composite film according to claim 1, characterized in that, The initiator is dibenzoyl peroxide or azobisisobutyronitrile.

5. The BiOCl nanosheet doped PVDF composite membrane prepared according to the method of any one of claims 1-4, characterized in that, The nanosheet doped PVDF composite membrane is Ni-BiOCl nanosheet doped PVDF composite membrane or Co-BiOCl nanosheet doped PVDF composite membrane. 6.The BiOCl nanoplatelet-doped PVDF composite film according to claim 5, characterized in that, The BiOCl nanosheet doped PVDF composite membrane is used for degrading methyl orange dye.

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