A two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane, preparation method and application

Abstract

The present invention discloses a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane, a preparation method and an application thereof. The preparation method of the membrane includes the preparation of graphitic carbon nitride nanosheets, surface functionalization modification of chitosan, assembly of nanosheets into a membrane, preparation of ferric citrate complex and intercalation of ferric citrate complex. Compared with the existing preparation methods of two-dimensional material membranes, this method obtains a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane with a stable layered structure through intercalation of an environmentally friendly polymer network. It not only has good retention effect and high permeation flux for dye pollutants, but also can achieve enhanced photo-Fenton degradation of various pollutants under light conditions, has good self-cleaning and stable performance, and can realize long-term stable and efficient sewage treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material film preparation, and particularly relates to a two-dimensional graphitic carbon nitride-based photo-Fenton-like film, a preparation method and an application thereof. Background Art

[0002] Two-dimensional material films have unique layered structures and mass transfer modes, and have good separation efficiency in the film treatment process. Compared with traditional organic membranes that screen pollutants through membrane pores, two-dimensional material films achieve rapid water molecule transport and effective pollutant separation through in-plane slits and interlayer channels generated during the stacking process of nanosheets. However, it is very difficult to regulate the stacking process of nanosheets in an orderly manner, which results in the formation of in-plane defects of different sizes in the layered membrane structure. Although these in-plane defects provide additional channels for water molecule transport, they also cause pollutants to penetrate into the membrane structure through the defects. During the long-term separation process, pollutants gradually accumulate in the layered membrane structure through in-plane defects, forming irreversible membrane fouling that is difficult to remove, resulting in a significant decline in the separation performance and service life of the membrane.

[0003] Conventional physical flushing methods can only remove loosely attached pollutants on the surface and cannot remove irreversible fouling. Researchers have tried to construct self-cleaning membranes to achieve rapid degradation of membrane fouling. At present, the research on self-cleaning membranes mainly focuses on the field of hybrid membranes, and the composite membranes are made to have photocatalytic ability by blending inorganic semiconductor materials with the casting solution. There is less research on two-dimensional layered self-cleaning membranes. The classic two-dimensional materials such as graphene oxide GO, transition metal sulfides TMDs, MXene, etc. do not have outstanding photocatalytic performance themselves and are mostly used as co-catalyst carriers to composite with other semiconductor materials to construct photocatalytic self-cleaning membranes.

[0004] For example, Chinese Patent CN115106105B prepared a ternary heterojunction photocatalytic membrane by hydrothermal method and vacuum-assisted assembly of two-dimensional MXene material with BiOBr and Bi 2 MoO 6 Composite. Chinese Patent CN116422160A prepared a GO / CPU / PAA / TiO 2 Self-cleaning composite membrane by blending method. These membranes have certain photocatalytic self-cleaning ability through the construction of heterostructures. However, in the preparation process, a variety of dangerous reagents such as HF and concentrated H 2 SO 2 SO 4, which makes the preparation process complex and difficult to control. In addition, the compatibility between two-dimensional materials and three-dimensional materials is relatively low, and the layered structure formed during the stacking process is not obvious, resulting in weakened binding force and reduced selectivity of the membrane. Therefore, there is an urgent need to develop a two-dimensional material membrane with simple preparation, environmental friendliness, high throughput, and good self-cleaning performance. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the prior art, such as membrane fouling during the filtration process of two-dimensional material membranes, which leads to a decline in membrane performance, the destruction of the membrane layered structure caused by the blending of two-dimensional materials and three-dimensional materials, and the need to use a variety of hazardous reagents in the membrane preparation process. The present invention provides a preparation method and application of a graphite carbon nitride-based photo-Fenton-like membrane. This method obtains a stable membrane layered structure through environmentally friendly polymer network intercalation, with both high selectivity and high throughput, and at the same time has good self-cleaning performance for membrane fouling caused by various types of organic substances.

[0006] The present invention is realized through the following technical solutions.

[0007] According to one aspect of the present invention, a preparation method of a two-dimensional graphite carbon nitride-based photo-Fenton-like membrane is provided, including the following steps:

[0008] Prepare g-C 3 N 4 powder: Heat-treat the organic nitrogen-containing compound, and grind it after cooling to obtain g-C 3 N 4 powder;

[0009] Prepare g-C 3 N 4 nanosheets: Disperse the g-C 3 N 4 powder in hydrochloric acid solution, heat and stir, cool and wash, and perform ultrasonic treatment to obtain a crude dispersion. After centrifugation, take the supernatant as the g-C 3 N 4 nanosheet dispersion;

[0010] Prepare g-C 3 N 4 / chitosan nanosheets: Add chitosan solution to the g-C 3 N 4 nanosheet dispersion according to the mass ratio of (10 - 20):(80 - 90), and perform ultrasonic treatment to obtain the g-C 3 N 4 / chitosan nanosheet dispersion;

[0011] Prepare a ferric citrate complex solution: Mix citric acid and ferric salt according to the molar ratio of citric acid to ferric ion of 5 - 10:1 to prepare an aqueous solution of ferric citrate complex;

[0012] Preparation of two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane: Disperse the g-C 3 N 4 / chitosan nanosheet dispersion on a porous membrane substrate by suction filtration to obtain a g-C 3 N 4 / chitosan membrane; Filter the ferric citrate complex solution through the g-C 3 N 4 / chitosan membrane, form a composite membrane on the porous substrate, and dry it to obtain a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0013] According to an exemplary embodiment of the present invention, the organic nitrogen-containing compound is one of melamine, thiourea or dicyandiamide.

[0014] According to an exemplary embodiment of the present invention, the trivalent iron salt is ferric chloride or ferric sulfate.

[0015] According to an exemplary embodiment of the present invention, heat-treat the organic nitrogen-containing compound at a temperature of 500-700 °C for 2-4 h.

[0016] According to an exemplary embodiment of the present invention, disperse the g-C 3 N 4 powder in a hydrochloric acid solution with a concentration of 3-12 mol / L, heat and stir at 25-80 °C for 1-12 h; perform ultrasonic treatment at a power of 100-250 W for 1-2 h; the centrifugation speed is 3000-7000 r; the number of centrifugation times is 1-3 times.

[0017] According to an exemplary embodiment of the present invention, the concentration of citric acid is 0.05-0.15 mol / L; the volume of the ferric citrate complex solution is 50 mL.

[0018] According to an exemplary embodiment of the present invention, the porous substrate is a polyethersulfone membrane substrate or a nylon membrane substrate.

[0019] According to another aspect of the present invention, there is provided a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared by the above method.

[0020] According to still another aspect of the present invention, there is provided a self-cleaning method for the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane. Place the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane in a pressure filtration device, use an organic pollutant solution with a concentration of 10-100 mg / L as the feed liquid, filter it at a pressure of 1 bar at room temperature, and detect and calculate the flux and rejection rate of the membrane to the pollutants;

[0021] Take out the contaminated membrane and soak it in pure water. Irradiate it with a 300W xenon light source equipped with a 420nm cut-off filter at an irradiation distance of 10-20 cm for 10-30 min to complete the self-cleaning process of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0022] According to an exemplary embodiment of the present invention, the organic pollutant solution is one or more mixtures of dye, bovine serum albumin, humic acid, and sodium alginate solutions.

[0023] Due to the above technical solutions adopted by the present invention, it has the following beneficial effects:

[0024] 1. For the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared by the present invention, functionalizing the nanosheets with chitosan, the introduced oxygen-containing groups not only improve the hydrophilicity of the membrane structure but also strengthen the intermolecular forces, making the membrane structure more stable. In addition, the rich -NH2 and -OH in the chitosan backbone can accelerate the separation and transfer of charges, which helps to improve the efficiency of photocatalytic degradation of pollutants.

[0025] 2. For the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared by the present invention, a polymer network is formed between the layers of the two-dimensional g-C 3 N 4 nanosheet membrane by intercalating with iron citrate complex. This structure helps to open the narrow interlayer structure of the g-C 3 N 4 nanosheet membrane, and the expanded interlayer spacing provides an additional transport channel for the transmission of water molecules. At the same time, the iron citrate complex itself has the ability to degrade organic matter by photo-Fenton. After coupling with the inherent photocatalytic properties of g-C 3 N 4 nanosheets, the g-C 3 N 4 nanosheets, as electron donors, accelerate the cyclic transformation of iron ions in iron citrate through a rapid ligand-to-metal electron transfer (LMCT) process, inhibit the recombination of photo-generated electron-hole pairs, and can generate a variety of reactive oxygen species during this process, which can effectively achieve in-situ degradation of irreversible pollutants between membranes.

[0026] 3. The two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared by the present invention has excellent dye rejection rate and high water flux, and can achieve a fast and efficient water treatment process. It also has good stability and self-cleaning cycle performance, and can effectively degrade membrane fouling caused by various types of organic substances.

[0027] 4. The method for preparing the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane of the present invention is simple and controllable. The reagents used are all green, safe, and environmentally friendly reagents. The raw materials and precursors are easily available, the reaction conditions are mild, the cost is low, and it is suitable for actual large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are provided to further understand the present invention, form a part of this application, and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 It is a schematic flow chart of a method for preparing a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane provided for an example of the present invention;

[0030] Figure 2 It is a surface scanning electron microscope image of a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane;

[0031] Figure 3 It is a cross-sectional scanning electron microscope image of a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane;

[0032] Figure 4 It is a comparison graph of the separation performance of a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane for different dyes;

[0033] Figure 5 It is a self-cleaning effect diagram of a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane for different types of pollutants. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention will be described in detail below with reference to the drawings and specific embodiments. Here, the illustrative embodiments of the present invention and the description are used to explain the present invention, but not to limit the present invention.

[0035] An embodiment of the present invention provides a method for preparing a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane. The process is shown in Figure 1 as follows, and specifically includes the following steps:

[0036] Step 1, preparation of g-C 3 N 4 powder: Put an organic nitrogen-containing compound (one of melamine, thiourea, or dicyandiamide) into a muffle furnace and heat-treat it at 500-700 °C for 2-4 h. After cooling, grind it to obtain g-C 3 N 4 powder;

[0037] Step 2, preparation of g-C 3 N 4 nanosheets: The g-C 3 N 4The powder is dispersed in a hydrochloric acid solution with a concentration of 3 to 12 mol / L, heated and stirred at 25 to 80 °C for 1 to 12 h, cooled to room temperature, washed with deionized water multiple times and dispersed in water; ultrasonic treatment is carried out at a power of 100 to 250 W for 1 to 2 h to obtain a light yellow crude dispersion liquid. After centrifugation (centrifugation speed is 3000 to 7000 r, centrifugation times is 1 to 3 times), the supernatant is taken as the g-C 3 N 4 nanosheet dispersion liquid;

[0038] Step 3, preparation of g-C 3 N 4 / chitosan nanosheets: Add a chitosan solution to the g-C 3 N 4 nanosheet dispersion liquid obtained in step 2. The mass ratio of chitosan to g-C 3 N 4 nanosheets is 10 to 20 wt%, and ultrasonic treatment is carried out to obtain a g-C 3 N 4 / chitosan nanosheet dispersion liquid;

[0039] Step 4, preparation of ferric citrate complex: Dissolve citric acid and ferric salt (ferric chloride or ferric sulfate) in water. The concentration of citric acid is 0.05 to 0.15 mol / L, the molar ratio of citric acid to ferric ions is 5 to 10:1, the volume of the ferric citrate complex solution is 50 mL, and mix and stir at room temperature for 0.5 h to obtain a ferric citrate complex solution;

[0040] Step 5, preparation of two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane: The g-C 3 N 4 / chitosan nanosheet dispersion liquid is assembled on a polyethersulfone membrane or nylon membrane porous membrane substrate by suction filtration under a pressure of 1 bar to prepare a g-C 3 N 4 / chitosan membrane; then the ferric citrate complex solution obtained in step 4 is filtered through the g-C 3 N 4 / chitosan membrane to form a composite membrane on the porous substrate, and after drying, it is the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0041] The two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane includes chitosan-functionalized g-C 3 N 4 nanosheets and ferric citrate complex intercalation; the thickness of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane is 80 - 200 nm.

[0042] Next, the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared by the method of the present invention is detected.

[0043] Step 6: Place the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane obtained in Step 5 in a pressure filtration device. Use an organic pollutant solution (one or a mixture of dyes, bovine serum albumin, humic acid, and sodium alginate solutions) with a concentration of 10-100 mg / L as the feed liquid, and perform pressure filtration at 1 bar at room temperature. Detect and calculate the flux and rejection rate of the membrane to the pollutants.

[0044] Step 7: Take out the membrane that has been contaminated after the filtration in Step 6, soak it in pure water, and irradiate it with a 300-400 W xenon light source equipped with a 420 nm cut-off filter at an irradiation distance of 10-20 cm for 10-30 min to complete the self-cleaning process of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0045] The present invention will be further illustrated by specific examples below.

[0046] Example 1:

[0047] Step 1: Put melamine into a muffle furnace and heat-treat it at 550 °C for 4 h. After cooling, grind it to obtain g-C 3 N 4 powder.

[0048] Step 2: Disperse the powder obtained in Step 1 in a hydrochloric acid solution with a concentration of 12 mol / L, heat and stir it at 80 °C for 12 h. After cooling to room temperature, wash it 3 times with deionized water and disperse it in water. Ultrasonically treat it at a power of 250 W for 2 h to obtain a light yellow coarse dispersion. After centrifugation (centrifugation speed: 7000 r, centrifugation times: 3 times), take the supernatant as the g-C 3 N 4 nanosheet dispersion.

[0049] Step 3: Add a high-viscosity chitosan solution to the dispersion obtained in Step 2. The mass ratio of chitosan to g-C 3 N 4 nanosheets is 10 wt%. Ultrasonically treat it to obtain a g-C 3 N 4 / chitosan nanosheet dispersion.

[0050] Step 4: Dissolve citric acid and ferric chloride in water. The concentration of citric acid is 0.15 mol / L, the molar ratio of citric acid to iron ions is 10:1, and the volume of the ferric citrate complex solution is 50 mL. Mix and stir it at room temperature for 0.5 h to obtain a ferric citrate complex solution.

[0051] Step 5: Assemble the g-C 3 N 4 / chitosan nanosheet dispersion obtained in Step 3 on a polyethersulfone membrane porous membrane substrate by suction filtration under 1 bar pressure to prepare g-C 3 N4 / chitosan membrane; then, the iron citrate complex solution obtained in step 4 is filtered through the g-C 3 N 4 / chitosan membrane to form a composite membrane on a porous substrate, and after drying, it is a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0052] The surface scanning electron micrograph of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane is shown in Figure 2 the figure; the cross-sectional scanning electron micrograph of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane is shown in Figure 3 the figure.

[0053] Step 6, place the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane obtained in step 5 in a pressure filtration device, use an organic pollutant solution (one or a mixture of dyes, bovine serum albumin, humic acid, and sodium alginate solutions) at a concentration of 10 - 100 mg / L as the feed liquid, and filter at a pressure of 1 bar at room temperature, and detect and calculate the flux and rejection rate of the membrane to the pollutants.

[0054] Step 7, take out the membrane that has been contaminated after the filtration in step 6, soak it in pure water, and irradiate it with a 300 W xenon light source equipped with a 420 nm cut-off filter at an irradiation distance of 15 cm for 20 min to complete the self-cleaning process of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0055] The water flux of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared in this example is 230.51 L·m -2 ·h -1 ·bar -1 , the rejection rate of Evans blue is 95.94%, the flux recovery rate of the membrane pollution caused by dyes after self-cleaning is 99.54%, the flux recovery rate of the membrane pollution caused by bovine serum albumin is 74.41%, the flux recovery rate of the membrane pollution caused by sodium alginate is 99.62%, and the flux recovery rate of the membrane pollution caused by humic acid is 93.54%.

[0056] The comparison of the separation performance of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane for different dyes is shown in Figure 4 the figure, and the self-cleaning effect of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane on different types of pollutants is shown in Figure 5 the figure.

[0057] Example 2:

[0058] Step 1, put dicyandiamide into a muffle furnace and heat-treat it at 500 °C for 3 h, and grind it after cooling to obtain g-C 3 N 4 powder;

[0059] Step 2: Disperse the powder obtained in Step 1 in a hydrochloric acid solution with a concentration of 12 mol / L, heat and stir at 60 °C for 12 h. After cooling to room temperature, wash it with deionized water multiple times and disperse it in water, then perform ultrasonic treatment at a power of 100 W for 1 h to obtain a pale yellow coarse dispersion. After centrifugation (centrifugation speed: 6000 r, centrifugation times: 2 times), take the supernatant as the g-C 3 N 4 nanosheet dispersion;

[0060] Step 3: Add a high-viscosity chitosan solution to the dispersion obtained in Step 2. The mass ratio of chitosan to g-C 3 N 4 nanosheets is 12 wt%, and perform ultrasonic treatment to obtain the g-C 3 N 4 / chitosan nanosheet dispersion;

[0061] Step 4: Dissolve citric acid and ferric sulfate in water. The concentration of citric acid is 0.12 mol / L, the molar ratio of citric acid to ferric ions is 7:1, and the volume of the ferric citrate complex solution is 50 mL. Mix and stir at room temperature for 0.5 h to obtain the ferric citrate complex solution;

[0062] Step 5: Assemble the g-C 3 N 4 / chitosan nanosheet dispersion obtained in Step 3 on a polyethersulfone membrane porous membrane substrate by suction filtration under a pressure of 1 bar to prepare the g-C 3 N 4 / chitosan membrane; Then pass the ferric citrate complex solution obtained in Step 4 through the g-C 3 N 4 / chitosan membrane to filter and form a composite membrane on the porous substrate, and after drying, it is the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0063] Step 6: Place the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane obtained in Step 5 in a pressure filtration device, use an organic pollutant solution (one or a mixture of dyes, bovine serum albumin, humic acid, and sodium alginate solutions) with a concentration of 10 - 100 mg / L as the feed liquid, and perform pressure filtration at 1 bar at room temperature to detect and calculate the flux and rejection rate of the membrane to the pollutants;

[0064] Step 7: Take out the membrane that has been contaminated after the filtration in Step 6, soak it in pure water, and irradiate it with a 400 W xenon light source equipped with a 420 nm cut-off filter at an irradiation distance of 10 cm for 20 min to complete the self-cleaning process of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0065] The water flux of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared in this example is 180.75 L·m-2 ·h -1 ·bar -1 The rejection rate for Evans blue was 98.42%, the flux recovery rate for the membrane fouling caused by the dye after self-cleaning was 98.73%, the flux recovery rate for the membrane fouling caused by bovine serum albumin was 81.25%, the flux recovery rate for the membrane fouling caused by sodium alginate was 98.67%, and the flux recovery rate for the membrane fouling caused by humic acid was 90.31%.

[0066] Example 3:

[0067] Step 1: Put thiourea into a muffle furnace and heat-treat it at 600 °C for 1.5 h. After cooling, grind it to obtain g-C 3 N 4 powder;

[0068] Step 2: Disperse the powder obtained in Step 1 in a hydrochloric acid solution with a concentration of 10 mol / L, heat and stir at 80 °C for 6 h. After cooling to room temperature, wash it with deionized water multiple times and disperse it in water. Ultrasonically treat it at a power of 250 W for 1.5 h to obtain a light yellow coarse dispersion. After centrifugation (centrifugation speed: 7000 r, number of centrifugations: 1), take the supernatant as the g-C 3 N 4 nanosheet dispersion;

[0069] Step 3: Add a high-viscosity chitosan solution to the dispersion obtained in Step 2. The mass ratio of chitosan to g-C 3 N 4 nanosheets is 10 wt%. Ultrasonically treat it to obtain the g-C 3 N 4 / chitosan nanosheet dispersion;

[0070] Step 4: Dissolve citric acid and ferric sulfate in water. The concentration of citric acid is 0.08 mol / L, the molar ratio of citric acid to iron ions is 6:1, and the volume of the ferric citrate complex solution is 50 mL. Mix and stir at room temperature for 0.5 h to obtain a ferric citrate complex solution;

[0071] Step 5: Assemble the g-C 3 N 4 / chitosan nanosheet dispersion on a polyethersulfone membrane porous membrane substrate by suction filtration under a pressure of 1 bar to prepare a g-C 3 N 4 / chitosan membrane; Then, pass the ferric citrate complex solution obtained in Step 4 through the g-C 3 N 4 / chitosan membrane to filter and form a composite membrane on the porous substrate. After drying, it is a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0072] Step 6: Place the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane obtained in Step 5 in a pressure filtration device. Use an organic pollutant solution (one or a mixture of dyes, bovine serum albumin, humic acid, and sodium alginate solutions) with a concentration of 10-100 mg / L as the feed liquid, and perform pressure filtration at 1 bar at room temperature. Detect and calculate the flux and rejection rate of the membrane to the pollutants.

[0073] Step 7: Take out the contaminated membrane after the filtration in Step 6, soak it in pure water, and irradiate it with a 300 W xenon light source equipped with a 420 nm cut-off filter at an irradiation distance of 15 cm for 10-30 min to complete the self-cleaning process of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0074] In this example, the water flux of the prepared two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane is 304.28 L·m -2 ·h -1 ·bar -1 , the rejection rate to Evans blue is 88.61%, the flux recovery rate of the membrane fouling caused by dyes after self-cleaning is 99.23%, the flux recovery rate of the membrane fouling caused by bovine serum albumin is 72.17%, the flux recovery rate of the membrane fouling caused by sodium alginate is 98.99%, and the flux recovery rate of the membrane fouling caused by humic acid is 94.62%.

[0075] Example 4:

[0076] Step 1: Place melamine in a muffle furnace and heat-treat it at 500 °C for 3 h. After cooling, grind it to obtain g-C 3 N 4 powder;

[0077] Step 2: Disperse the powder obtained in Step 1 in a hydrochloric acid solution with a concentration of 9 mol / L, heat and stir it at 25 °C for 12 h. After cooling to room temperature, wash it with deionized water multiple times and disperse it in water, and perform ultrasonic treatment at a power of 150 W for 2 h to obtain a light yellow coarse dispersion. After centrifugation (centrifugation speed is 6500 r, centrifugation times is 2 times), take the supernatant as the g-C 3 N 4 nanosheet dispersion;

[0078] Step 3: Add a high-viscosity chitosan solution to the dispersion obtained in Step 2. The mass ratio of chitosan to g-C 3 N 4 nanosheets is 15 wt%, and perform ultrasonic treatment to obtain a g-C 3 N 4 / chitosan nanosheet dispersion;

[0079] Step 4: Dissolve citric acid and ferric chloride in water. The concentration of citric acid is 0.10 mol / L, the molar ratio of citric acid to ferric ions is 5:1, the volume of the ferric citrate complex solution is 50 mL, and mix and stir at room temperature for 0.5 h to obtain a ferric citrate complex solution;

[0080] Step 5: Disperse the g-C 3 N 4 / chitosan nanosheet dispersion on a polyethersulfone membrane porous membrane substrate by suction filtration under a pressure of 1 bar to prepare a g-C 3 N 4 / chitosan membrane; then pass the ferric citrate complex solution obtained in Step 4 through the g-C 3 N 4 / chitosan membrane to filter the composite membrane formed on the porous substrate, and after drying, it is a two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0081] Step 6: Place the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane obtained in Step 5 in a pressure filtration device, use an organic pollutant solution (one or a mixture of dyes, bovine serum albumin, humic acid, and sodium alginate solutions) with a concentration of 10 - 100 mg / L as the feed liquid, and filter under a pressure of 1 bar at room temperature, and detect and calculate the flux and rejection rate of the membrane to the pollutants;

[0082] Step 7: Take out the membrane that has been contaminated after the filtration in Step 6, soak it in pure water, and irradiate it with a 400 W xenon light source equipped with a 420 nm cut-off filter at an irradiation distance of 10 cm for 20 min to complete the self-cleaning process of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane.

[0083] In this example, the water flux of the prepared two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane is 210.32 L·m -2 ·h -1 ·bar -1 , the rejection rate for Evans blue is 98.22%, the flux recovery rate for the membrane pollution caused by dyes after self-cleaning is 97.37%, the flux recovery rate for the membrane pollution caused by bovine serum albumin is 69.31%, the flux recovery rate for the membrane pollution caused by sodium alginate is 91.26%, and the flux recovery rate for the membrane pollution caused by humic acid is 87.32%.

[0084] The following gives a comparison between the comparative example and the example of the present invention to further illustrate the effect of the present invention.

[0085] Comparative Example 1:

[0086] Step 1: g-C 3 N 4Preparation of powder: Urea was placed in a muffle furnace and heat-treated at 500 - 600 °C for 3 - 4 h in an argon atmosphere. After cooling, it was ground to obtain g-C 3 N 4 powder;

[0087] Step 2, preparation of g-C 3 N 4 nanosheets: The powder obtained in Step 1 was placed in a muffle furnace and further calcined at 500 - 600 °C for 1 - 3 h in an air atmosphere to obtain a light yellow powder, which was g-C 3 N 4 nanosheets.

[0088] Step 3, preparation of g-C 3 N 4 film: The g-C 3 N 4 nanosheets obtained in Step 2 were assembled on a polyacrylonitrile porous substrate under a pressure difference of 1 bar. After drying, g-C 3 N 4 film was obtained.

[0089] Step 4, preparation of g-C 3 N 4 composite film: 2 - 10 mL of a 0.1 - 1 wt% polyvinyl alcohol (PVA) solution was poured into the terminal membrane filtration module and evaporated in an oven at 40 - 80 °C for 0.5 - 1 h. Subsequently, the membrane was taken out and immersed in an aqueous glutaraldehyde (GA) solution for 0.5 - 2 h to form a stable coating at 40 - 80 °C.

[0090] The g-C 3 N 4 film obtained in this comparative example had a rejection rate of 81.2% for the dye solution and a water flux of 11.7 L·m -2 ·h -1 ·bar -1 , and the flux recovery rate for the membrane fouling caused by the dye was only 72.94%. After 3 cycles, the membrane structure was damaged to a certain extent.

[0091] It can be seen from the comparison of the above examples and comparative examples that the water flux of the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared by the method of the present invention is not less than 180.75 L·m -2 ·h -1 ·bar -1, the rejection rate of Evans blue is not less than 88.61%. After self-cleaning, the flux recovery rate of membrane fouling caused by dyes is not less than 97.37%, the flux recovery rate of membrane fouling caused by bovine serum albumin is not less than 69.31%, the flux recovery rate of membrane fouling caused by sodium alginate is not less than 91.26%, and the flux recovery rate of membrane fouling caused by humic acid is not less than 97.32%. It can be seen that the two-dimensional graphitic carbon nitride-based photo-Fenton-like membrane prepared by the present invention not only has good dye rejection rate and high water permeation flux, but also can effectively self-clean the membrane fouling caused by various pollutants to varying degrees, realizing a large-scale recovery of membrane flux, and is a two-dimensional separation membrane with good performance.

[0092] The present invention is not limited to the above embodiments. Based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and deformations of some technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional graphite phase carbon nitride-based photo-Fenton-like film, characterized in that: The steps include: Preparation of g-C3N4 powder: heat-treating an organic nitrogen-containing compound, cooling it, and grinding it to obtain g-C3N4 powder; the organic nitrogen-containing compound is one of melamine, thiourea or dicyandiamide; Preparation of g-C3N4 nanosheets: dispersing g-C3N4 powder in a hydrochloric acid solution, heating and stirring, cooling and washing, and ultrasonic treatment to obtain a coarse dispersion, and taking the supernatant after centrifugation as the g-C3N4 nanosheet dispersion; Preparation of g-C3N4 / chitosan nanosheets: adding chitosan solution to the g-C3N4 nanosheet dispersion at a mass ratio of 10-20:80-90, and ultrasonic treatment to obtain the g-C3N4 / chitosan nanosheet dispersion; Preparing a ferric citrate complex solution: mixing citric acid and trivalent iron salt according to a molar ratio of citric acid to iron ion of 5 to 10:1 to prepare a ferric citrate complex aqueous solution; Preparation of a two-dimensional graphite phase carbon nitride-based photo-Fenton-like membrane: assembling the g-C3N4 / chitosan nanosheet dispersion on a porous membrane substrate by suction filtration to obtain a g-C3N4 / chitosan membrane; filtering the ferric citrate complex solution through the g-C3N4 / chitosan membrane to form a composite membrane on the porous substrate, and drying to obtain a two-dimensional graphite phase carbon nitride-based photo-Fenton-like membrane.

2. The method for preparing a two-dimensional graphite phase carbon nitride-based photo-Fenton-like film according to claim 1, characterized in that: The trivalent iron salt is ferric chloride or ferric sulfate.

3. The method for preparing a two-dimensional graphite phase carbon nitride-based photo-Fenton-like film according to claim 1, characterized in that: The organic nitrogen-containing compound is heat treated at a temperature of 500-700°C for 2-4 hours.

4. The method for preparing a two-dimensional graphite phase carbon nitride-based photo-Fenton-like film according to claim 1, characterized in that: The g-C3N4 powder is dispersed in a hydrochloric acid solution with a concentration of 3-12 mol / L, heated and stirred at 25-80°C for 1-12 hours, ultrasonically treated at a power of 100-250 W for 1-2 hours, centrifuged at a speed of 3000-7000 r, and centrifuged 1-3 times.

5. The method for preparing a two-dimensional graphite phase carbon nitride-based photo-Fenton-like film according to claim 1, characterized in that: The concentration of citric acid is 0.05~0.15mol / L; the volume of the ferric citrate complex solution is 50mL.

6. The method for preparing a two-dimensional graphite phase carbon nitride-based photo-Fenton-like film according to claim 1, characterized in that: The porous substrate is a polyethersulfone membrane substrate or a nylon membrane substrate.

7. A two-dimensional graphite phase carbon nitride-based photo-Fenton-like film prepared by the method as described in any one of claims 1 to 6.

8. A self-cleaning method for a two-dimensional graphite-phase carbon nitride-based photo-Fenton-like film as claimed in claim 7, characterized in that: The two-dimensional graphene-phase carbon nitride-based photo-Fenton-like membrane was placed in a pressure filtration device, and a 10-100 mg / L organic pollutant solution was used as the feed solution. The membrane was filtered at a pressure of 1 bar at room temperature, and the flux and retention rate of the pollutants were detected and calculated. The contaminated membrane was taken out, immersed in pure water, and irradiated with a 300W xenon lamp light source equipped with a 420nm cutoff filter at a distance of 10-20cm for 10-30min to complete the self-cleaning process of the two-dimensional graphene phase carbon nitride-based photo-Fenton-like membrane.

9. The self-cleaning method of the two-dimensional graphite phase carbon nitride-based photo-Fenton-like film according to claim 8, characterized in that: The organic pollutant solution is one or more mixtures of dye, bovine serum albumin, humic acid and sodium alginate solution.

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