PVDF / rGO / fe(ii) composite film as electro-fenton cathode, preparation method, application and membrane filtration reactor

Abstract

The application relates to a PVDF / rGO / Fe(II) composite film as an electro-Fenton cathode, a preparation method, application and membrane filtration reactor. The preparation method comprises the following steps: firstly, preparing a PVDF film by adopting a phase inversion method, covering reduced graphene oxide on the surface of the PVDF film by a suction filtration method to obtain a PVDF / rGO double-layer film; then, dispersing siderite powder in an organic solvent, adding a pore former and PVDF, and stirring and heating to prepare a uniform casting solution; finally, coating the casting solution on the surface of the PVDF / rGO double-layer film to obtain the PVDF / rGO / Fe(II) composite film; the composite film is applied to an organic pollutant and bacteria filtration system or a membrane biological reactor as an electro-Fenton cathode, has excellent anti-pollution effect and bacteria killing capacity, can significantly inhibit the formation of biofilm on the membrane surface, and has a wide application prospect in the aspect of anti-membrane pollution.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane separation technology in water treatment, and particularly relates to a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode, a preparation method, application and membrane filtration reactor. BACKGROUND

[0002] With the increasing demand for water treatment, the membrane separation industry has developed rapidly and become an important new force in the field of water treatment in China. Organic membranes in membrane separation materials, such as polyvinylidene fluoride (PVDF) membranes, are most widely used in industry, but such materials are easily contaminated due to their strong hydrophobicity. Membrane contamination often leads to an increase in transmembrane pressure difference and a decrease in filtration flux, increasing energy consumption, feed pressure and membrane cleaning frequency, shortening the service life of the membrane, and thus increasing the operation and maintenance cost of the system. Membrane bioreactor (MBR) as a combination of membrane filtration technology and sewage biological treatment process is also plagued by membrane contamination. Membrane contamination not only leads to an increase in MBR membrane cleaning frequency, but also accelerates the aging of the membrane module, thus further increasing the operating cost. Therefore, research on membrane contamination control methods has received widespread attention in the industry.

[0003] Traditional membrane contamination control techniques mainly include adding a grid / screen interception unit or chemical cleaning, but such methods not only increase energy consumption and chemical consumption, but also shorten the service life of the membrane material. Domestic and foreign scholars have found that using membrane modification methods to endow the membrane material with special anti-pollution properties is a direct and effective means to inhibit membrane contamination. Common membrane modification methods mainly obtain modified membranes by introducing antibacterial materials or hydrophilic substances on the surface of the membrane material. However, the anti-pollution properties of the above modified membranes will gradually weaken with the continuous release of the surface antibacterial or hydrophilic materials, not only poor in durability and stability, but also the released materials will inhibit the metabolic activity of functional microorganisms in the system, reducing the water treatment effect. Therefore, developing environmentally friendly and sustainable anti-pollution modified membranes based on membrane modification methods, which have both antibacterial and in-situ degradation properties of membrane pollutants, has become a key technical problem that needs to be broken through in the field of membrane contamination control.

[0004] As a typical advanced oxidation technology, electro-Fenton technology utilizes electrochemical reaction to continuously generate H2O2 at the cathode, which reacts with Fe(II) in the solution to generate a large amount of strong oxidizing ·OH; the generated ·OH can effectively degrade organic pollutants in water and inactivate bacteria; the accompanied Fe(III) can be reduced to Fe(II) at the cathode, thereby realizing the continuous regeneration of Fe(II). The membrane electrode electro-Fenton technology constructed by using a modified membrane as an electrocatalytic cathode is a high-efficiency and environmentally friendly membrane fouling control technology. In this technology, H2O2 is generated on the surface of the membrane, and the ·OH generated by the reaction of H2O2 with Fe(II) can directly inactivate bacteria on the surface of the membrane and degrade membrane pollutants, thereby effectively reducing membrane fouling. However, the Fe(II) in the currently reported membrane electrode electro-Fenton system is mainly derived from external addition or release of a pure Fe anode, which is difficult to ensure that ·OH is generated only on the surface of the modified membrane, thereby reducing the inhibition efficiency of ·OH on membrane fouling and causing adverse effects on functional microorganisms. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application provides a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode, a preparation method, an application and a membrane filtration reactor, which has excellent anti-fouling and anti-bacterial effects and can effectively inhibit membrane fouling.

[0006] To achieve the above-mentioned purpose, the technical scheme provided by the present application is as follows:

[0007] In a first aspect, the present application provides a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode, which comprises a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, wherein the substrate layer comprises a polyvinylidene fluoride (PVDF) membrane, and the electro-Fenton active layer comprises a PVDF membrane doped with siderite.

[0008] Optionally, the pore size of the electro-Fenton active layer is larger than that of the substrate layer.

[0009] Optionally, the conductive layer is a reduced graphene oxide (rGO) membrane.

[0010] Optionally, the PVDF membrane is prepared by a phase inversion method, and the pore size of the PVDF membrane is 0.1-0.3 μm, and the thickness of the PVDF membrane is 100-200 μm.

[0011] In a second aspect, the present application further provides a preparation method of the PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to the first aspect, which comprises the following steps:

[0012] 1) dispersing reduced graphene oxide in deionized water, using a substrate membrane to suction filter the reduced graphene oxide dispersion liquid, so that the reduced graphene oxide covers the substrate membrane, and then drying to obtain a PVDF / rGO double-layer membrane;

[0013] 2) ultrasonic dispersion of siderite powder in an organic solvent, addition of a pore-forming agent and polyvinylidene fluoride, heating and stirring to obtain a casting solution;

[0014] 3) coating the casting solution after vacuum degassing on one side of the reduced graphene oxide of the PVDF / rGO double-layer film, standing, then immersing in a coagulation bath to coagulate into a film, taking out after the film falls off and immersing in water, drying to obtain the PVDF / rGO / Fe(II) composite film.

[0015] Optionally, the number of layers of the reduced graphene oxide is ≤5, and the added amount of the reduced graphene oxide per unit area of the base film is 2-10 g / m 2 .

[0016] Optionally, the reduced graphene oxide is dispersed in deionized water under ultrasonic action, and the ultrasonic time is 30-60 min.

[0017] Optionally, in step 2), the casting solution is prepared from the following components by weight: organic solvent 76-80 parts, polyvinylidene fluoride 13-17 parts, pore-forming agent 3-6 parts, and siderite powder 2-3 parts.

[0018] Optionally, the particle size of the siderite powder is 20-60 μm.

[0019] Optionally, in step 3), the standing is standing in air for 5-15 s.

[0020] Optionally, in step 3), the immersion time of taking out after the film falls off and immersing in water is 24-48 h.

[0021] Optionally, in step 3), the coating thickness of the casting solution is 100-200 μm.

[0022] Optionally, in step 1), the drying condition is drying at 40-50℃ for 4-5 h.

[0023] Optionally, in step 3), the drying is natural air drying.

[0024] In a third aspect, the application further provides a PVDF / rGO / Fe(II) composite film as the cathode of the electro-Fenton in the application of membrane surface bacteria inactivation and membrane surface organic matter degradation.

[0025] In a fourth aspect, the application also provides a membrane filtration reactor, which comprises the PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode of the first aspect, the PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode is connected to the negative pole of a direct current power supply, and an electro-Fenton anode material is arranged in parallel on both sides of the electro-Fenton cathode, and the electro-Fenton anode material is connected to the positive pole of the power supply.

[0026] The PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode of the application can be used in an organic pollutant and / or bacteria filtration device or a membrane bioreactor (MBR), and under a certain current density condition, the inactivation of bacteria on the surface of the composite membrane and the degradation of organic pollutants on the surface of the membrane can be realized, so as to inhibit the membrane pollution phenomenon. The method for realizing the organic pollution resistance and bacteria resistance in the membrane filtration reactor and the membrane pollution resistance in the long-term operation of the MBR by using the PVDF / rGO / Fe(II) composite membrane of the application under a certain current density condition is as follows:

[0027] A membrane filtration reactor device is constructed, the PVDF / rGO / Fe(II) composite membrane is fixed on a flat plate membrane module and installed in the membrane filtration reactor, and is connected to the negative pole of a direct current power supply as the electro-Fenton cathode; an electro-Fenton anode material with the same area as the composite membrane is installed on both sides of the flat plate membrane module, the negative pole and the positive pole are arranged in parallel and opposite to each other, the distance between the negative pole and the positive pole is kept at 0.5-1.5 cm, the anode material is connected to the positive pole of the power supply; a stirring device is arranged below the electrodes at the bottom of the reactor; the constant current density is set to 0.2-0.4 mA / cm 2 .

[0028] When the organic pollutant solution is prepared in the reactor to form a pollutant filtration system, after the pollutant solution is filtered by the PVDF / rGO / Fe(II) composite membrane, the filtrate flows out from the water outlet of the membrane module, and the PVDF / rGO / Fe(II) composite membrane can realize the inhibition of the organic pollution on the surface of the membrane under the condition of constant current density and continuous stirring; when the bacterial suspension is prepared in the reactor to form a bacteria filtration system, the PVDF / rGO / Fe(II) composite membrane can realize the inactivation of the bacteria on the surface of the membrane under the condition of constant current density and continuous stirring; when the sludge-water mixture is added to the reactor to form an MBR, the PVDF / rGO / Fe(II) composite membrane can realize the membrane pollution control under the condition of constant current density and continuous stirring.

[0029] Optionally, the organic pollutants include proteins represented by bovine serum albumin, polysaccharides represented by sodium alginate and humic substances represented by humic acid; the bacteria include gram-negative bacteria represented by Escherichia coli and gram-positive bacteria represented by Staphylococcus aureus; and the sludge in the sludge-water mixture includes anaerobic ammonia oxidation sludge, aerobic activated sludge and anaerobic digestion sludge.

[0030] The PVDF / rGO / Fe(II) composite film as the electro-Fenton cathode of the application can generate H2O2 on the film by reducing H2O and O2 under constant low current density conditions, and then react with Fe(II) dissolved from the siderite particles on the surface of the film to generate non-selective and strong oxidizing ·OH, which can effectively oxidize and decompose organic pollutants adhered to the surface of the film, inactivate bacteria attached to the surface of the film, delay the formation of biofilm, and thus inhibit membrane pollution.

[0031] In the application, the electro-Fenton active layer on the PVDF / rGO / Fe(II) composite film is prepared by doping siderite with FeCO3 as the main component. Siderite is not only cheap and easy to obtain, but also can slowly release Fe(II) during membrane filtration, ensuring the in-situ generation of ·OH on the surface of the membrane, thereby improving the utilization efficiency of ·OH in inhibiting membrane pollution and avoiding the adverse effects of ·OH on functional microorganisms in the membrane filtration system. Fe(III) associated with the electro-Fenton reaction can be reduced to Fe(II) on the surface of the cathode membrane, thereby ensuring the sustainability of the anti-membrane pollution process.

[0032] The rGO conductive layer in the composite film solves the problem of poor conductivity of PVDF high molecular material. rGO has extremely strong conductivity, H2O and O2 on the surface of the film can be reduced to H2O2 on the rGO conductive layer by the electrons of the electro-Fenton cathode, and rapidly contact and react with Fe(II) of the active layer, further ensuring the in-situ generation of ·OH on the surface of the membrane. In addition, the separation of the electro-Fenton active layer and the substrate layer can avoid direct contact of ·OH with the substrate layer, which can cause oxidation of the membrane material; the rGO conductive layer further separates the substrate layer from ·OH, which can protect the substrate layer; the membrane pores of the electro-Fenton active layer are larger than those of the substrate layer, which avoids the decline of the water permeability of the membrane caused by the coverage of the electro-Fenton active layer. The PVDF / rGO / Fe(II) composite film provided by the application has high hydrophilicity, strong water permeability, good electro-Fenton activity, and can effectively reduce the blockage of the membrane pores caused by organic pollutants such as proteins represented by bovine serum albumin, polysaccharides represented by sodium alginate, and humic substances represented by humic acid under constant current density, and has good killing effect on gram-negative bacteria represented by Escherichia coli and gram-positive bacteria represented by Staphylococcus aureus, can significantly inhibit the formation of biofilm on the surface of the membrane, has excellent simultaneous anti-pollution and antibacterial effect, and has great application potential in MBR.

[0033] Compared with the prior art, the application has at least the following beneficial effects:

[0034] 1) The PVDF / rGO / Fe(II) composite film provided by the application as the electro-Fenton cathode has higher hydrophilicity than traditional PVDF modified films, and has significant electro-Fenton anti-pollution performance; the siderite in the electro-Fenton active layer can gradually release Fe(II) during the membrane filtration process, directly react with H2O2 generated by electrochemistry, and make ·OH generated in situ on the surface of the composite film, thereby improving the utilization efficiency of ·OH and avoiding the adverse effects of ·OH on functional microorganisms; the PVDF / rGO / Fe(II) composite film has good synchronous anti-pollution and antibacterial effects, and can effectively reduce membrane pollution and delay the decline rate of membrane flux.

[0035] 2) The PVDF / rGO / Fe(II) composite film provided by the application as the electro-Fenton cathode has stronger conductivity and stability; the rGO conductive layer in the middle endows the composite film with excellent conductivity, accelerates the in-situ generation of H2O2 on the membrane surface, and isolates the base layer from the electro-Fenton active layer, thereby avoiding the direct oxidation of the base layer by ·OH and ensuring the durability and stability of the membrane material.

[0036] 3) The method for preparing the PVDF / rGO / Fe(II) composite film provided by the application is a phase inversion method combined with a blending modification method, the layers of the film are tightly combined, the composite film is not easy to peel off during long-term filtration and anti-pollution, the siderite in the electro-Fenton active layer is not easy to flow away with water and is slowly dissolved, and the composite film has a long anti-pollution service life.

[0037] 4) The method for preparing the PVDF / rGO / Fe(II) composite film provided by the application is simple and easy to operate, the siderite as the electro-Fenton active material is low in cost, and the reaction conditions are mild, so the method can be widely applied to the preparation of modified membrane materials as the electro-Fenton cathode. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Figure 1 is a diagram of the anti-pollution mechanism of the PVDF / rGO / Fe(II) composite film prepared in Example 1;

[0039] Figure 2 Figure 2 is an electron paramagnetic resonance (EPR) spectrum of the PVDF / rGO / Fe(II) composite film prepared in Example 1 in Na2SO4 solution and deionized water by DMPO spin trapping detection of ·OH;

[0040] Figure 3 Figure 3 is a curve of the relative flux of the PVDF / rGO / Fe(II) composite film prepared in Example 1 and the PVDF film in a membrane filtration reactor under the conditions of occurrence and non-occurrence of the electro-Fenton reaction in filtering bovine serum albumin (BSA) solutions; Figure 3 a), sodium alginate (SA) solutions ( Figure 3 b), and humic acid (HA) solutions ( Figure 3 c) with time;

[0041] Figure 4 Inactivation of E. coli and S. aureus by PVDF / rGO / Fe(II) composite membrane prepared in Example 1 and PVDF membrane in membrane filtration reactor under conditions with and without electro-Fenton reaction;

[0042] Figure 5 Inactivation of E. coli and S. aureus by PVDF / rGO / Fe(II) composite membrane prepared in Example 1 and PVDF membrane in membrane filtration reactor under conditions with and without electro-Fenton reaction; Figure 5 a and 5c) and PVDF membrane (b and 5d) in membrane filtration reactor after filtering E. coli (a and 5b) and S. aureus (c and 5d); Figure 5 a and 5c) and PVDF membrane (b and 5d) in membrane filtration reactor after filtering E. coli (a and 5b) and S. aureus (c and 5d); Figure 5 a and 5c) and PVDF membrane (b and 5d) in membrane filtration reactor after filtering E. coli (a and 5b) and S. aureus (c and 5d); Figure 5 a and 5c) and PVDF membrane (b and 5d) in membrane filtration reactor after filtering E. coli (a and 5b) and S. aureus (c and 5d);

[0043] Figure 6 Change of transmembrane pressure difference of PVDF / rGO / Fe(II) composite membrane prepared in Example 1 as electro-Fenton cathode and PVDF membrane in MBR during 190 days of operation. DETAILED DESCRIPTION

[0044] The application will be further described in detail below with reference to the accompanying drawings:

[0045] The experimental methods used in the examples of the present application are all conventional methods unless otherwise specified.

[0046] The reagent materials used in the examples can be routinely purchased, and the quantitative experiments involved in the examples are all set up with at least three repeated experiments, and the results are averaged.

[0047] Raw materials: single-layer rGO: particle size of 0.2-10 μm; few-layer rGO: layer number of 3-5 layers, particle size of 5-50 μm.

[0048] Example 1

[0049] A polyvinylidene fluoride (PVDF) membrane with a pore size of 0.2 μm and a thickness of 150 μm was prepared using a phase inversion method. Single-layer reduced graphene oxide (rGO) was weighed according to the ratio of 8 g of reduced graphene oxide per square meter of PVDF, added to deionized water, and dispersed ultrasonically for 45 min. The rGO dispersion was then filtered through the PVDF membrane to coat the membrane surface with rGO. After drying in an oven at 45℃ for 5 h, a PVDF / rGO bilayer membrane was obtained. 3 g of siderite powder with a particle size of 20-40 μm (pre-dried in an oven at 70℃ for 12 h) was ultrasonically dispersed in 78 g of N,N-dimethylacetamide, along with 5 g of dried polyvinylpyrrolidone porogen and 14 g of dried PVDF. The mixture was heated and stirred at 85℃ for 18 h to prepare a uniform casting solution. The casting solution was then degassed in a vacuum drying oven for 5 minutes. After h, the casting solution was coated onto the rGO side of the above PVDF / rGO bilayer membrane using a coating tool on a coating machine, with a coating thickness of 150 μm, to form a liquid membrane; the PVDF / rGO bilayer membrane coated with the liquid membrane was left to stand in the air for 10 s and then immersed in a coagulation bath of deionized water to solidify into a membrane. After the membrane was detached, it was taken out and soaked in deionized water for 36 h. After natural air drying, the PVDF / rGO / Fe(II) composite membrane was obtained.

[0050] Figure 1 This is a diagram illustrating the antifouling mechanism of the PVDF / rGO / Fe(II) composite membrane prepared in this embodiment. The PVDF / rGO / Fe(II) composite membrane consists of a lower PVDF substrate layer, a middle rGO conductive layer, and an upper electro-Fenton active layer. Electrons provided by the electro-Fenton cathode are conducted through the rGO conductive layer to reduce H2O and O2 to H2O2. H2O2 then reacts with Fe(II) dissolved from the siderite on the Fe(II) active layer to generate ·OH, thereby degrading organic pollutants on the membrane surface and inactivating bacteria, thus achieving the purpose of inhibiting membrane fouling.

[0051] Figure 2 The EPR graphs of the PVDF / rGO / Fe(II) composite membrane prepared in this embodiment, obtained by DMPO spin capture detection of ·OH in Na2SO4 solution and deionized water, are shown below. Figure 2 It can be seen that the PVDF / rGO / Fe(II) composite film acts as an electro-Fenton cathode with a flux density of 0.3 mA / m. 2 When the current is applied, strong characteristic peaks with an intensity ratio of 1:2:2:1 corresponding to DMPO-‧OH can be observed in both Na2SO4 solution and deionized water, indicating that H2O2 generated on the surface of the composite membrane is successfully converted into‧OH, thus confirming the antifouling potential of the composite membrane.

[0052] The method for achieving resistance to organic fouling and antibacterial activity in a membrane filtration reactor and resistance to membrane fouling during long-term operation of an MBR using the PVDF / rGO / Fe(II) composite membrane prepared in this embodiment as an electro-Fenton cathode is as follows:

[0053] Construction of the membrane filtration reactor: A PVDF / rGO / Fe(II) composite membrane was fixed on a flat-sheet membrane module and installed inside the membrane filtration reactor, serving as the electro-Fenton cathode and connected to the negative terminal of a DC power supply; an iron mesh of the same area as the composite membrane was installed on both sides of the flat-sheet membrane module, with the anode and cathode parallel and opposite each other, maintaining a distance of 1 cm, and the iron mesh was connected to the positive terminal of the power supply; a stirring device was installed below the bottom electrode of the reactor; the constant current density was set to 0.3 mA / cm². 2 .

[0054] BSA, SA, and HA solutions were prepared in the reactor to form a pollutant filtration system. After the pollutant solution was filtered through the PVDF / rGO / Fe(Ⅱ) composite membrane, the filtrate flowed out from the outlet of the membrane module. After a constant current was applied, the membrane was continuously stirred to examine its ability to resist organic pollutants. Figure 3 The PVDF / rGO / Fe(II) composite membrane prepared for this embodiment, along with a PVDF membrane (using the same substrate material), was used in a membrane filtration reactor to filter BSA under conditions with and without the occurrence of an electro-Fenton reaction. Figure 3 a), SA ( Figure 3 b) and HA ( Figure 3 c) Curves showing the relative flux of the solution over time. The results showed that after 120 min of filtration, the relative flux decrease rates of the composite membrane that underwent the electro-Fenton reaction for filtering BSA, SA, and HA solutions were reduced by 7.3%, 14.4%, and 4.7%, respectively, compared to the PVDF membrane. This indicates that the composite membrane prepared in this embodiment exhibits good resistance to organic pollutants when used as an electro-Fenton cathode. Furthermore, the relative flux decrease rates of the composite membrane that did not undergo the electro-Fenton reaction for filtering BSA, SA, and HA solutions were also significantly higher than those of the PVDF membrane, indicating that the water permeability and resistance to pollutant adhesion of the composite membrane prepared in this embodiment were also improved.

[0055] A bacterial filtration system was formed in a reactor by preparing suspensions of Escherichia coli and Staphylococcus aureus. After connecting a constant current, the system was continuously stirred to examine the antibacterial ability of the composite membrane. Figure 4The PVDF / rGO / Fe(II) composite membrane prepared in this example and the PVDF membrane were used in the membrane filtration reactor under the conditions of occurrence and non-occurrence of electro-Fenton reaction to inactivate Escherichia coli and Staphylococcus aureus. The results showed that the PVDF membrane and the composite membrane without electro-Fenton reaction had no antibacterial effect, and the inactivation rates of the composite membrane with electro-Fenton reaction on Escherichia coli and Staphylococcus aureus were 90.4% and 86.2% respectively, indicating that the composite membrane prepared in this example had no toxicity to microorganisms, but had good antibacterial effect on gram-negative bacteria and gram-positive bacteria when used as electro-Fenton cathode.

[0056] Figure 5 The PVDF / rGO / Fe(II) composite membrane prepared in this example was used as electro-Fenton cathode to inactivate Escherichia coli and Staphylococcus aureus in the membrane filtration reactor. Figure 5 a and 5c)and the PVDF membrane( Figure 5 b and 5d)were used to filter Escherichia coli( Figure 5 a and 5b)and Staphylococcus aureus( Figure 5 c and 5d)in the membrane filtration reactor. The bacterial morphology on the membrane surface after filtration was observed by scanning electron microscopy. As shown in Figure 5 , the cell structure of bacteria on the PVDF membrane was complete, while the cell integrity of bacteria on the surface of the composite membrane after electro-Fenton reaction was destroyed, causing the cell contents to flow out and leading to cell death, proving that the composite membrane prepared in this example as electro-Fenton cathode produced ·OH on the surface, which achieved the inactivation of bacteria by destroying the cell integrity.

[0057] The sludge-water mixture of anaerobic ammonia oxidation sludge was added to the reactor to form MBR, and continuous stirring was carried out after connecting the constant current, and the anti-pollution ability of the composite membrane in the long-term operation of MBR was investigated. Figure 6 The PVDF / rGO / Fe(II) composite membrane prepared in this example as electro-Fenton cathode and the PVDF membrane were used in the MBR to investigate the change of transmembrane pressure difference during 190 days of operation. The results showed that after the start of electro-Fenton reaction, the average pollution period of the composite membrane (31.4 d) was twice that of the PVDF membrane (15.7 d), indicating that the composite membrane prepared in this example degraded the adhered pollutants and inactivated the attached bacteria by producing ·OH on its surface during the operation of MBR, alleviated the formation of biofilm on the membrane surface and the blockage of membrane pores, and significantly prolonged the membrane pollution period.

[0058] Example 2:

[0059] A PVDF membrane with a pore size of 0.15 μm and a thickness of 130 μm is prepared by a phase inversion method. A small amount of few-layer reduced graphene oxide (few-layer rGO) corresponding to 6 g of PVDF per square meter is weighed, added to deionized water, and dispersed under ultrasonic for 40 min. The rGO dispersion is filtered by suction using a PVDF membrane to cover the membrane surface. After drying in an oven at 42°C for 4.3 h, a PVDF / rGO double-layer membrane is prepared. 2.7 g of siderite powder with a particle size of 20-30 μm (previously dried in an oven at 65°C for 10 h) is ultrasonically dispersed in 77.3 g of N, N-dimethylacetamide, 4 g of dried polyethylene glycol pore former and 16 g of dried PVDF are added, and the mixture is heated and stirred at 83°C for 16 h to prepare a uniform casting solution. The casting solution is degassed in a vacuum drying oven for 4 h, and then coated on the rGO side of the PVDF / rGO double-layer membrane using a doctor blade on a film applicator to form a liquid film with a coating thickness of 120 μm. The PVDF / rGO double-layer membrane coated with the liquid film is left to stand in air for 8 s, then immersed in a coagulation bath of deionized water. After the membrane falls off, it is taken out and immersed in deionized water for 30 h, and then naturally air-dried to obtain a PVDF / rGO / Fe(II) composite membrane.

[0060] The PVDF / rGO / Fe(II) composite membrane prepared as the electro-Fenton cathode in this example realizes the method of resisting organic pollution and bacteria and resisting membrane fouling in the long-term operation of MBR under constant low current density conditions as follows:

[0061] A membrane filtration reactor is constructed. The PVDF / rGO / Fe(II) composite membrane is fixed on a flat membrane module and installed in the membrane filtration reactor, and connected to the negative electrode of a direct current power supply as an electro-Fenton cathode. Iron sheets with the same area as the composite membrane are installed on both sides of the flat membrane module, with the negative and positive electrodes parallel to each other and a distance of 0.5 cm. The iron sheets are connected to the positive electrode of the power supply. A stirring device is arranged below the electrodes at the bottom of the reactor. The constant current density is set to 0.2 mA / cm 2 .

[0062] The BSA, SA and HA solutions were prepared in the reactor to form a pollutant filtration system. After the pollutant solution was filtered through the PVDF / rGO / Fe(II) composite membrane, the filtrate flowed out from the water outlet of the membrane module, and constant current was connected for continuous stirring to investigate the ability of the composite membrane to resist organic pollutants. The results showed that after 120 min of filtration, the relative flux decline rate of the composite membrane filtering BSA, SA and HA solutions in the electro-Fenton reaction was reduced by 5.5%, 13.0% and 4.5% compared with the PVDF membrane, indicating that the composite membrane prepared in this embodiment has good anti-organic pollutant performance as an electro-Fenton cathode. In addition, the relative flux decline rate of the composite membrane filtering BSA, SA and HA solutions without electro-Fenton reaction was also significantly higher than that of the PVDF membrane, indicating that the water permeability and anti-pollutant adhesion properties of the composite membrane prepared in this embodiment were also improved.

[0063] The E. coli and S. aureus suspensions were prepared in the reactor to form a bacteria filtration system, and constant current was connected for continuous stirring to investigate the antibacterial ability of the composite membrane. The results showed that the PVDF membrane and the composite membrane without electro-Fenton reaction had no antibacterial effect, and the inactivation rate of the composite membrane in the electro-Fenton reaction to E. coli and S. aureus reached 89.1% and 83.5%, respectively, indicating that the composite membrane prepared in this embodiment had no toxicity to microorganisms, but had good antibacterial effect on gram-negative bacteria and gram-positive bacteria as an electro-Fenton cathode.

[0064] The sludge-water mixture of aerobic activated sludge was added to the reactor to form an MBR, and constant current was connected for continuous stirring to investigate the anti-pollution ability of the composite membrane in the long-term operation of the MBR. The results showed that after the electro-Fenton reaction started, the average pollution period of the composite membrane (29.6 d) was 1.9 times that of the PVDF membrane (15.4 d), indicating that the composite membrane prepared in this embodiment degraded the adhered pollutants and inactivated the attached bacteria by generating ·OH on its surface during the operation of the MBR, alleviated the formation of biofilm on the membrane surface and the blockage of the membrane pores, and significantly prolonged the membrane pollution period.

[0065] Example 3:

[0066] A PVDF membrane with a pore size of 0.25 μm and a thickness of 170 μm was prepared by a phase inversion method. 10 g / m 2The single layer of rGO of the PVDF membrane was dispersed in deionized water for 50 min by ultrasonic dispersion, and the rGO dispersion was filtered by suction using the PVDF membrane to make the rGO cover the surface of the membrane. The PVDF / rGO double-layer membrane was prepared after drying in an oven at 48°C for 4.8 h. 2.5 g of siderite powder with a particle size of 20-50 μm (previously dried in an oven at 75°C for 14 h) was ultrasonically dispersed in 80 g of N, N-dimethylacetamide, 4.5 g of dry cetyltrimethylammonium bromide porogen and 13 g of dry PVDF were added, and the mixture was heated and stirred at 87°C for 14 h to prepare a uniform casting solution. The casting solution was degassed in a vacuum drying oven for 3 h, and then the casting solution was coated on the rGO side of the above-mentioned PVDF / rGO double-layer membrane using a doctor blade on a film applicator to form a liquid film with a coating thickness of 170 μm. The PVDF / rGO double-layer membrane coated with the liquid film was immersed in a coagulation bath of deionized water after standing in the air for 12 s, and then taken out after the membrane fell off and immersed in deionized water for 42 h. The PVDF / rGO / Fe(II) composite membrane was obtained after natural air drying.

[0067] The PVDF / rGO / Fe(II) composite membrane prepared in this embodiment as an electro-Fenton cathode realizes the method of resisting organic pollution and resisting bacteria in the membrane filtration reactor and resisting membrane fouling in the long-term operation of MBR under constant low current density conditions as follows:

[0068] A membrane filtration reactor device was constructed, the PVDF / rGO / Fe(II) composite membrane was fixed on the flat membrane module and installed in the membrane filtration reactor, and was connected to the negative electrode of the direct current power supply as the electro-Fenton cathode. Iron mesh with the same area as the composite membrane was installed on both sides of the flat membrane module, the negative and positive electrodes were parallel to each other with a distance of 1.5 cm, and the iron mesh was connected to the positive electrode of the power supply. A stirring device was arranged below the electrode at the bottom of the reactor. The constant current density was set to 0.4 mA / cm 2 .

[0069] BSA, SA and HA solutions were prepared in the reactor to form a pollutant filtration system. After the pollutant solution was filtered through the PVDF / rGO / Fe(II) composite membrane, the filtrate flowed out from the water outlet of the membrane module, and constant stirring was carried out after connecting the constant current to investigate the ability of the composite membrane to resist organic pollutants. The results showed that after 120 min of filtration, the relative flux decline rate of the composite membrane subjected to electro-Fenton reaction when filtering BSA, SA and HA solutions was reduced by 6.7%, 11.6% and 4.2% compared with the PVDF membrane, indicating that the composite membrane prepared in this embodiment has good resistance to organic pollutants when used as an electro-Fenton cathode. In addition, the relative flux decline rate of the composite membrane without electro-Fenton reaction when filtering BSA, SA and HA solutions was also significantly higher than that of the PVDF membrane, indicating that the water permeability and anti-pollutant adhesion properties of the composite membrane prepared in this embodiment were also improved.

[0070] The E. coli and S. aureus suspensions were prepared in the reactor to form a bacterial filtration system, and constant current was connected for continuous stirring to investigate the antibacterial ability of the composite membrane. The results showed that the PVDF membrane and the composite membrane without electro-Fenton reaction had no antibacterial effect, and the inactivation rates of the composite membrane with electro-Fenton reaction on E. coli and S. aureus were 92.2% and 87.3% respectively, indicating that the composite membrane prepared in this example had no toxicity to microorganisms, but as an electro-Fenton cathode, it had good antibacterial effect on gram-negative bacteria and gram-positive bacteria.

[0071] The sludge-water mixture of anaerobic digestion sludge was added to the reactor to form an MBR, and constant current was connected for continuous stirring to investigate the anti-pollution ability of the composite membrane in the long-term operation of the MBR. The results showed that after the electro-Fenton reaction started, the average pollution period of the composite membrane (34.2 d) was 2.1 times that of the PVDF membrane (16.0 d), indicating that the composite membrane prepared in this example degraded the adhered pollutants and inactivated the attached bacteria on its surface by generating ·OH during the MBR operation, alleviated the formation of biofilm on the membrane surface and the blockage of the membrane pores, and significantly prolonged the membrane pollution period.

[0072] Example 4:

[0073] A PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode includes a substrate layer, an electro-Fenton active layer, and a conductive layer arranged between the substrate layer and the electro-Fenton active layer. The substrate layer is a polyvinylidene fluoride membrane, and the electro-Fenton active layer is a polyvinylidene fluoride membrane doped with siderite. The pore size of the electro-Fenton active layer is larger than that of the substrate layer. When the composite membrane is used as an electro-Fenton cathode under the action of current, H2O2 and ·OH are generated on the surface of the active layer to achieve membrane pollution control.

[0074] The preparation method of the PVDF / rGO / Fe(II) composite membrane includes the following steps:

[0075] 1) PVDF membrane was prepared by phase inversion method. 2 g / m 2 The few-layer rGO was ultrasonically dispersed in deionized water for 30 min, and the rGO dispersion liquid was pumped and filtered using the PVDF membrane to cover the rGO on the surface of the PVDF membrane. After drying, a PVDF / rGO double-layer membrane was prepared.

[0076] 2) The siderite powder was ground and dried, and 2.2 g of dried siderite powder with a particle size of 20-30 μm was ultrasonically dispersed in 79.8 g of N, N-dimethylacetamide. 3 g of sodium dodecyl sulfate porogen and 15 g of PVDF were added, and the mixture was heated and stirred to form a uniform casting solution.

[0077] 3) A coater on a film applicator is used to coat the casting solution on the rGO side of the PVDF / rGO double-layer film to a thickness of 100 μm to form a liquid film;

[0078] 4) The PVDF / rGO double-layer film coated with the liquid film is left to stand in air for 5 s and then immersed in a coagulation bath of water. After the film is peeled off, it is taken out and soaked in water. After natural air drying, a PVDF / rGO / Fe(II) composite film is obtained.

[0079] The PVDF / rGO / Fe(II) composite film as an electro-Fenton cathode is applied to membrane surface bacteria inactivation and membrane surface organic matter degradation.

[0080] Example 5:

[0081] A PVDF / rGO / Fe(II) composite film as an electro-Fenton cathode comprises a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer. The substrate layer is a polyvinylidene fluoride film, and the electro-Fenton active layer is a polyvinylidene fluoride film doped with siderite. The pore size of the electro-Fenton active layer is larger than that of the substrate layer. When the composite film is used as an electro-Fenton cathode under the action of current, H2O2 and ·OH are generated on the surface of the active layer to achieve membrane fouling control.

[0082] The preparation method of the PVDF / rGO / Fe(II) composite film comprises the following steps:

[0083] 1) A PVDF film is prepared by a phase inversion method. 5 g / m 2 The single-layer rGO of the PVDF film is ultrasonically dispersed in deionized water for 55 min. The rGO dispersion liquid is pumped and filtered using the PVDF film to cover the surface of the PVDF film. After drying, a PVDF / rGO double-layer film is prepared.

[0084] 2) Siderite powder is ground and dried. Siderite powder with a particle size of 20-60 μm is screened. The siderite powder is ultrasonically dispersed in 77 g N, N-dimethylacetamide. 3.5 g of propyl alcohol is added as a pore former, and 16.7 g of PVDF is added. The mixture is heated and stirred to prepare a uniform casting solution.

[0085] 3) A coater on a film applicator is used to coat the casting solution on the rGO side of the PVDF / rGO double-layer film to a thickness of 200 μm to form a liquid film;

[0086] 4) The PVDF / rGO double-layer film coated with the liquid film is left to stand in air for 15 s and then immersed in a coagulation bath of water. After the film is peeled off, it is taken out and soaked in water. After natural air drying, a PVDF / rGO / Fe(II) composite film is obtained.

[0087] The PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode is applied in membrane surface bacteria inactivation and membrane surface organic matter degradation.

[0088] Embodiment 6:

[0089] A PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode, the composite membrane comprises a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, the substrate layer is a polyvinylidene fluoride membrane, and the electro-Fenton active layer is a polyvinylidene fluoride membrane doped with siderite. The pore size of the electro-Fenton active layer is larger than that of the substrate layer. When the composite membrane is used as an electro-Fenton cathode under the action of current, H2O2 and ·OH are generated on the surface of the active layer to achieve membrane pollution control.

[0090] The preparation method of the PVDF / rGO / Fe(II) composite membrane comprises the following steps:

[0091] 1) PVDF membrane is prepared by phase inversion method, 7 g / m 2 The few-layer rGO is ultrasonically dispersed in deionized water for 60 min, the rGO dispersion liquid is pumped and filtered by using the PVDF membrane, the rGO is covered on the membrane surface, and the PVDF / rGO double-layer membrane is prepared after drying;

[0092] 2) After the siderite powder is ground and dried, 2 g of the siderite powder with a particle size of 20-40 μm is screened and ultrasonically dispersed in 76.3 g of N, N-dimethylacetamide, 4.7 g of polyvinylpyrrolidone pore former and 17 g of PVDF are added, and the mixture is heated and stirred to prepare a uniform casting solution;

[0093] 3) The casting solution is coated on the rGO side of the above PVDF / rGO double-layer membrane by using a doctor blade on a film casting machine, the coating thickness is 160 μm, and a liquid film is prepared;

[0094] 4) The PVDF / rGO double-layer membrane coated with the liquid film is placed in air for 13 s and then immersed in a coagulation bath of water, and after the membrane is taken out after falling off, it is fully immersed in water, and after natural air drying, the PVDF / rGO / Fe(II) composite membrane is obtained.

[0095] The PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode is applied in membrane surface bacteria inactivation and membrane surface organic matter degradation.

[0096] The foregoing description of the embodiments has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed. Modifications and variations are possible in light of the above teachings or can be acquired from practice of the application. As well, the description is presented in the context of the preferred embodiments as a number of alternatives. It is not intended to limit the application to the precise form described.

Claims

1. A PVDF / rGO / Fe(II) composite film as an electro-Fenton cathode, characterized in that, The PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode comprises a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, the substrate layer comprises a polyvinylidene fluoride membrane, and the electro-Fenton active layer comprises a polyvinylidene fluoride membrane doped with siderite. The preparation method of the PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode comprises the following steps: 1) The reduced graphene oxide is dispersed in deionized water, and a substrate membrane is used to suck and filter the reduced graphene oxide dispersion liquid, so that the reduced graphene oxide is covered on the substrate membrane, and a PVDF / rGO double-layer membrane is prepared after drying; 2) The siderite powder is ultrasonically dispersed in an organic solvent, and a pore former and polyvinylidene fluoride are added and heated and stirred to obtain a casting solution; 3) The casting solution after vacuum degassing is coated on one side of the reduced graphene oxide of the PVDF / rGO double-layer membrane, and then immersed in a coagulation bath to coagulate into a film after standing, and the film is taken out after falling off and soaked in water, and dried to obtain the PVDF / rGO / Fe(II) composite membrane.

2. The PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode according to claim 1, characterized in that, The pore size of the electro-Fenton active layer is larger than that of the substrate layer.

3. The PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode according to claim 1, characterized in that, The conductive layer is a reduced graphene oxide membrane.

4. A method for preparing the PVDF / rGO / Fe(II) composite film as the electro-Fenton cathode according to any one of claims 1-3, characterized in that, The preparation method comprises the following steps: 1) The reduced graphene oxide is dispersed in deionized water, and a substrate membrane is used to suck and filter the reduced graphene oxide dispersion liquid, so that the reduced graphene oxide is covered on the substrate membrane, and a PVDF / rGO double-layer membrane is prepared after drying; 2) The siderite powder is ultrasonically dispersed in an organic solvent, and a pore former and polyvinylidene fluoride are added and heated and stirred to obtain a casting solution; 3) The casting solution after vacuum degassing is coated on one side of the reduced graphene oxide of the PVDF / rGO double-layer membrane, and then immersed in a coagulation bath to coagulate into a film after standing, and the film is taken out after falling off and soaked in water, and dried to obtain the PVDF / rGO / Fe(II) composite membrane.

5. The method for preparing PVDF / rGO / Fe(II) composite film as electro-Fenton cathode according to claim 4, characterized in that, The reduced graphene oxide has a layer number of less than or equal to 5, and the added amount of the reduced graphene oxide per unit area of the base film is 2-10 g / m 2 .

6. The method for preparing PVDF / rGO / Fe(II) composite film as electro-Fenton cathode according to claim 4, characterized in that, In step 2), the casting solution is prepared from the following components by weight: organic solvent 76-80 parts, polyvinylidene fluoride 13-17 parts, pore former 3-6 parts, and siderite powder 2-3 parts.

7. The method for preparing PVDF / rGO / Fe(II) composite film as electro-Fenton cathode according to claim 4, characterized in that, The polyvinylidene fluoride membrane is prepared by phase inversion method, and the pore size of the polyvinylidene fluoride membrane is 0.1-0.3 μm, and the thickness is 100-200 μm.

8. The method for preparing PVDF / rGO / Fe(II) composite film as electro-Fenton cathode according to claim 4, characterized in that, In step 3), the coating thickness of the casting solution is 100-200 μm.

9. The PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode according to any one of claims 1-3 is applied to membrane surface bacteria inactivation and membrane surface organic matter degradation.

10. A membrane filter reactor, characterized by The PVDF / rGO / Fe(II) composite membrane as the electro-Fenton cathode according to any one of claims 1-3 is applied to membrane surface bacteria inactivation and membrane surface organic matter degradation.

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