A graphene-based quinone mediator membrane, and a preparation method and application thereof

Abstract

The application belongs to the field of water treatment, and particularly relates to a graphene-based quinone mediator membrane as well as a preparation method and application thereof. The graphene-based quinone mediator membrane comprises a membrane matrix and graphene, amino imidazo pyridine and humus dispersed in the membrane matrix; the material of the membrane matrix is polyvinylidene fluoride / butadiene, the polyvinylidene fluoride / butadiene is a random copolymer of vinylidene fluoride and butadiene, and an anthraquinone modification unit is connected to a butadiene structural unit of the random copolymer. The graphene-based quinone mediator membrane provided by the application has a high initial denitrification rate and a denitrification rate over time.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, specifically relating to a graphene-based quinone mediator membrane, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of industry and agriculture and the improvement of living standards, an increasing amount of nitrogen-containing domestic sewage, industrial wastewater, and farmland surface water has been discharged into natural water bodies. Nitrogen is essential for all living matter; it is an essential element for proteins, nucleic acids, enzymes, denitrifying bacteria, nitrifying bacteria, and ammonifying bacteria, and is indispensable for plant growth, photosynthesis, energy transfer, and fertilizer synthesis. However, excessive nitrogen release into water damages aquatic ecosystems, leading to eutrophication of amphibian systems, depletion of dissolved oxygen, and the death of fish and other marine life, disrupting the ecological balance and thus posing a serious water pollution problem.

[0003] High concentrations of nitrate nitrogen pollution in water bodies not only cause serious harm to the natural environment but also increasingly erode human health and safety, making various denitrification technologies increasingly important. Currently, the main denitrification methods for nitrogen removal from nitrogen-containing wastewater can be divided into physical, chemical, and biological methods. Physical methods include ion exchange, physical adsorption, and membrane separation. Chemical methods include chemical precipitation and breakpoint chlorination. However, physical and chemical treatment processes are relatively expensive and can cause secondary pollution, requiring further treatment. In biological denitrification methods, in addition to traditional biological methods, many new biological denitrification theories and processes have emerged both domestically and internationally in recent years. Biological methods use microorganisms to convert organic nitrogen and ammonia nitrogen in wastewater into NO. 2- and NO 3- Then, through ammoniation, nitrification, and denitrification, it is ultimately converted into N2, thus achieving the purpose of nitrogen removal. Compared with physical and chemical methods, biological nitrogen removal technology is more mature and makes up for the shortcomings and deficiencies of the two. It has the advantages of simple process operation and low operating cost, while being environmentally friendly and not causing secondary pollution. With the continuous deepening of research and application promotion at home and abroad, traditional biological nitrogen removal processes have gradually been upgraded and developed into various new nitrogen removal processes such as simultaneous nitrification and denitrification, short-cut nitrification and denitrification, and anaerobic ammonium oxidation.

[0004] Traditionally, nitrification and denitrification are thought to occur sequentially, not simultaneously. However, recent research advancements both domestically and internationally have overturned this notion, making simultaneous nitrification and denitrification (SND) a possibility. SND involves a biological nitrogen removal process where nitrification and denitrification reactions occur simultaneously in space and time, directly converting ammonia nitrogen into nitrogen gas. Because the two processes occur concurrently, SND significantly reduces the required reactor volume, saving space and energy. Furthermore, compared to traditional biological nitrogen removal processes, this technology requires minimal aeration and organic carbon, resulting in approximately a 30% reduction in sludge production.

[0005] The key to short-cut nitrification-denitrification processes lies in regulating the nitrification process to stop it at the nitrite stage. The basic principle is to control the reaction parameters to reduce NH4+. + -N is converted to NO2 - -N, and then undergo denitrification to remove NO2 - -N is directly reduced to N2. Compared with traditional nitrification-denitrification processes, this novel biological nitrogen removal technology significantly reduces costs due to its shorter process flow, decreasing aeration requirements by 25% and organic carbon source requirements by 40%. Studies have shown that controlling reaction temperature, pH, dissolved oxygen (DO) concentration, and sludge age can effectively regulate the growth conditions of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), thereby promoting NO2 production. - Accumulation of -N.

[0006] Anaerobic ammonia oxidation refers to the process of oxidizing nitrogen under strictly anaerobic conditions using NO2. - -N acts as an electron acceptor, NH4 + -N, acting as an electron donor, promotes NH4+ oxidation in anaerobic ammonia-oxidizing bacteria. + -N and NO2 - -N is directly converted to N2. The reaction equation is shown in equation (1-1). Therefore, anaerobic ammonium oxidation is very suitable for treating substances containing NH4+. + -N and NO2 - Wastewater with a nitrogen-to-carbon ratio (C / N) of -N is susceptible to anaerobic oxidation (AMO). Anaerobic ammonia oxidizing bacteria require strictly anaerobic conditions to survive, which helps save energy by reducing aeration requirements. Furthermore, AMO operates as an autotrophic process, requiring no additional organic carbon source, making it particularly suitable for denitrification in wastewater with a low C / N ratio. Therefore, compared to traditional activated sludge systems, AMO has been classified as one of the more cost-effective and environmentally friendly systems, consuming less oxygen for nitrogen removal. However, the sensitivity of AMO bacteria to changes in environmental conditions and their slow growth rate are major limitations restricting the application of AMO in large-scale wastewater treatment.

[0007] NH4 + +1.32NO2- +0.066HCO3 - +0.13H + →

[0008] 1.02N2 + 0.26NO3 - +0.066CH2O 0.5 N 0.15 +2.03H2O(1-1)

[0009] In recent years, redox mediators (RMs) have been widely used in catalytic biotransformation due to their unique redox properties and biocompatibility, especially RMs containing quinones and carbonyl compounds, which exhibit excellent redox capabilities. As an electron transfer mediator, RMs can lower the activation energy of reactions and accelerate the electron transfer rate, thereby increasing the reduction / oxidation rate of pollutants. Furthermore, they can still promote the biodegradation and transformation of target pollutants under low-temperature conditions. They can play a catalytic enhancement role in the anaerobic biotransformation and degradation of pollutants such as azo dyes, nitroaromatic amines, polyhalogenated compounds, perchlorates, and heavy metals. However, RMs are primarily water-soluble, and directly adding them to wastewater often leads to water runoff and secondary pollution, limiting their practical application. In addition, RMs such as anthraquinones may be reduced or degraded during denitrification, causing them to easily lose their catalytic activity. That is, the denitrification rate of RMs usually decreases with prolonged treatment time. Therefore, improving the initial and sustained denitrification rates of RMs has become an urgent technical problem to be solved. Summary of the Invention

[0010] The primary objective of this invention is to provide a novel graphene-based quinone mediator membrane (AQ-G / PVDF) that exhibits high denitrification efficiency, which remains at a high level even after a period of use; that is, it possesses both high initial denitrification rate and high denitrification rate over time.

[0011] A second objective of this invention is to provide a method for preparing the above-mentioned graphene-based quinone mediator membrane.

[0012] A third objective of this invention is to provide the application of the above-mentioned graphene-based quinone mediator membrane in wastewater denitrification.

[0013] The graphene-based quinone mediator membrane provided by the present invention includes a membrane matrix and graphene, aminoimidazopyridine and humic substances dispersed in the membrane matrix; the membrane matrix is ​​made of polyvinylidene fluoride / butadiene, wherein the polyvinylidene fluoride / butadiene is a random copolymer of vinylidene fluoride and butadiene, and anthraquinone modification units are bonded to the butadiene structural units of the random copolymer.

[0014] The method for preparing the graphene-based quinone mediator membrane provided by this invention includes:

[0015] S1. Vinylidene fluoride and butadiene are subjected to free radical polymerization in the presence of a free radical initiator to obtain a prepolymer;

[0016] S2. The prepolymer is reacted with mercaptoanthraquinone by addition reaction to obtain polyvinylidene fluoride / butadiene;

[0017] S3. Graphene, aminoimidazopyridine and humic substances are dissolved in an organic solvent. The resulting solution is mixed with glutaraldehyde until homogeneous. The resulting mixture is then mixed with polyvinylidene fluoride / butadiene until homogeneous and degassed. The resulting casting solution is then placed on a substrate and leveled with a scraper before being immersed in pure water to solidify into a film, thus obtaining the graphene-based quinone mediator membrane.

[0018] Anthraquinone, as an electron transport mediator, can enhance the reduction / oxidation rate of pollutants, primarily promoting denitrification through electron shuttle and redox mediator interactions. Graphene (G) exhibits excellent adsorption properties for organic pollutants and can enhance the extracellular electron transport capacity of anaerobic microorganisms, achieving denitrification mainly through adsorption and catalysis. In other words, anthraquinone and graphene achieve denitrification via two different pathways, and combining them can leverage their combined denitrification activity. However, on the one hand, anthraquinone is easily lost with water and is readily reduced and degraded, losing its catalytic activity. This leads to a decrease in denitrification rate over time during wastewater treatment. On the other hand, graphene inhibits the activity of denitrifying microorganisms (such as ammonia-oxidizing bacteria (AOB) and denitrifying bacteria), which play a crucial role in the denitrification process. This change in community structure negatively impacts the denitrification process, hindering the improvement of denitrification efficiency. In other words, although anthraquinone and graphene can achieve synergistic denitrification through two different pathways, the denitrification rate of both decreases with the extension of treatment time, that is, the denitrification rate will decrease over time.

[0019] Based on this, the inventors of the present invention modified the mediator membrane by using a random copolymer of vinylidene fluoride and butadiene as the membrane matrix and attaching anthraquinone modification units to the membrane matrix. In addition, graphene was added to the membrane matrix, and aminoimidazopyridine and humic substances were added. The resulting graphene-based quinone mediator membrane has a high initial denitrification rate and a high denitrification rate over time. The reasons for this are speculated to be as follows: Firstly, chemically linking anthraquinone to the membrane carrier can effectively reduce the loss of anthraquinone during denitrification with the effluent, thereby increasing the denitrification rate over time. Furthermore, using a random copolymer of vinylidene fluoride and butadiene as the carrier, with anthraquinone linked to the butadiene structural units, allows multiple anthraquinone molecules to be linked to each copolymer molecular chain, resulting in a uniform distribution of anthraquinone across the entire side chain of the random copolymer, endowing the graphene-based quinone mediator membrane with excellent denitrification capabilities. Secondly, the combined addition of aminoimidazopyridine and humic substances not only improves the chemical stability of anthraquinone, making it less prone to degradation and transformation, but also inhibits the adverse effects of graphene on the activity of denitrifying microorganisms, improves the composition and structure of the microbial community, and increases the abundance of denitrifying microorganisms, thus significantly improving the denitrification rate of the resulting graphene-based quinone mediator membrane over time. Detailed Implementation

[0020] The graphene-based quinone mediator membrane provided by this invention comprises a membrane matrix and graphene, aminoimidazopyridine, and humic substances dispersed in the membrane matrix. Preferably, the mass ratio of the membrane matrix, graphene, aminoimidazopyridine, and humic substances is 100:(10-20):(5-10):(2-10). This ratio allows for better synergistic effects among the substances, which is more conducive to improving both the initial and over-term denitrification rates. Specifically, based on 100 parts by weight of the membrane matrix, the graphene content is preferably 10-20 parts by weight, such as 10, 12, 14, 16, 18, 20 parts by weight, or any value between them; the aminoimidazopyridine content is preferably 5-10 parts by weight, such as 5, 6, 7, 8, 9, 10 parts by weight, or any value between them; and the humic substances content is preferably 2-10 parts by weight, such as 2, 4, 6, 8, 10 parts by weight, or any value between them.

[0021] In this invention, the membrane substrate is made of polyvinylidene fluoride / butadiene. The polyvinylidene fluoride / butadiene is a random copolymer of vinylidene fluoride and butadiene, and anthraquinone modifying units are bonded to the butadiene structural units of the random copolymer.

[0022] In this invention, the polyvinylidene fluoride / butadiene can be commercially available or prepared using various existing methods. In a preferred embodiment, the polyvinylidene fluoride / butadiene is prepared by the following method: S1. Vinylidene fluoride and butadiene are subjected to a free radical polymerization reaction in the presence of a free radical initiator to obtain a prepolymer; S2. The prepolymer is subjected to an addition reaction with mercaptoanthraquinone to obtain polyvinylidene fluoride / butadiene. The molar ratio of vinylidene fluoride to butadiene is preferably 1:(0.2–0.6), such as 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, or any value between them. From the perspective of raw material availability, the mercaptoanthraquinone is particularly preferably 1-amino-5-mercaptoanthraquinone. The preferred molar ratio of the mercaptoanthraquinone to butadiene is (0.8–1.2):1, such as 0.8:1, 0.82:1, 0.85:1, 0.88:1, 0.9:1, 0.92:1, 0.95:1, 0.98:1, 1:1, 1.02:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.15:1, 1.18:1, 1.2:1, or any value between them. The preferred conditions for the free radical polymerization reaction include a temperature of 50–90°C, such as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any value between them; a pressure of 0.05–1 MPa, such as 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, or any value between them; and a time of 0.5–10 h, such as 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, or any value between them. The preferred conditions for the addition reaction include a temperature of 70–90°C, such as 70°C, 75°C, 80°C, 85°C, 90°C, or any value between them; a pressure of 0.01–1 MPa, such as 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, or any value between them; and a time of 0.1–24 h, such as 0.1 h, 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h, 22 h, 24 h, or any value between them. In this invention, all pressures refer to gauge pressure.

[0023] In this invention, the aminoimidazopyridine is particularly preferably 6-aminoimidazo[1,2-A]pyridine, which has the structure described in formula (1).

[0024]

[0025] The method for preparing the graphene-based quinone mediator membrane provided by this invention includes:

[0026] S1. Vinylidene fluoride and butadiene are subjected to free radical polymerization in the presence of a free radical initiator to obtain a prepolymer;

[0027] S2. The prepolymer is reacted with mercaptoanthraquinone by addition reaction to obtain polyvinylidene fluoride / butadiene;

[0028] S3. Graphene, aminoimidazopyridine and humic substances are dissolved in an organic solvent. The resulting solution is mixed with glutaraldehyde until homogeneous. The resulting mixture is then mixed with polyvinylidene fluoride / butadiene until homogeneous and degassed. The resulting casting solution is then placed on a substrate and leveled with a scraper before being immersed in pure water to solidify into a film, thus obtaining the graphene-based quinone mediator membrane.

[0029] In the preparation process of the graphene-based quinone mediator membrane, in step S1, the molar ratio of vinylidene fluoride and butadiene is preferably 1:(0.2-0.6), such as 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6 or any value between them.

[0030] In the preparation process of the graphene-based quinone mediator membrane described above, in step S1, the free radical initiator can be at least one of azo initiators, peroxide initiators, and redox initiators. Examples of azo initiators include at least one of dimethyl azobisisobutyrate, azobisisobutyramidine hydrochloride, azodicarbonamide, azobisisopropylimidazoline hydrochloride, azoisobutylcyanoformamide, azodicyclohexylformonitrile, azobiscyanopentanoic acid, azobisisopropylimidazoline, azobisisobutyronitrile, azobisisovalerate, and azobisisoheptanenitrile. Examples of peroxide initiators include at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, benzoyl peroxide, and benzoyl tert-butyl peroxide. Examples of redox initiators include at least one of sulfate-sulfite, persulfate-thiourea, persulfate-organic salt, and ammonium persulfate-aliphatic amine. The sulfate-sulfite can be selected from at least one of sodium sulfate-sodium sulfite, potassium sulfate-potassium sulfite, and ammonium sulfate-ammonium sulfite; the persulfate-thiourea can be selected from at least one of sodium persulfate-thiourea, potassium persulfate-thiourea, and ammonium persulfate-thiourea; the persulfate-organic salt can be selected from at least one of sodium persulfate-potassium acetate, potassium persulfate-potassium acetate, and ammonium persulfate-ammonium acetate; the ammonium persulfate-aliphatic amine can be ammonium persulfate-N,N-tetramethylethylenediamine and / or ammonium persulfate-diethylamine.

[0031] In the preparation process of the graphene-based quinone mediator membrane described above, in step S2, the molar ratio of the mercaptoanthraquinone to butadiene is preferably (0.8–1.2):1, such as 0.8:1, 0.82:1, 0.85:1, 0.88:1, 0.9:1, 0.92:1, 0.95:1, 0.98:1, 1:1, 1.02:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.15:1, 1.18:1, 1.2:1, or any value between them.

[0032] In the preparation process of the graphene-based quinone mediator membrane described above, in step S3, the preferred mass ratio of polyvinylidene fluoride / butadiene, graphene, aminoimidazopyridine, and humic substances is 100:(10-20):(5-10):(2-10). Specifically, based on 100 parts by weight of polyvinylidene fluoride / butadiene, the preferred content of graphene is 10-20 parts by weight, such as 10, 12, 14, 16, 18, 20 parts by weight or any value between them; the preferred content of aminoimidazopyridine is 5-10 parts by weight, such as 5, 6, 7, 8, 9, 10 parts by weight or any value between them; and the preferred content of humic substances is 2-10 parts by weight, such as 2, 4, 6, 8, 10 parts by weight or any value between them. Furthermore, the preferred mass ratio of glutaraldehyde to polyvinylidene fluoride / butadiene is (1-5):100, such as 1:100, 2:100, 3:100, 4:100, 5:100 or any value between them.

[0033] In the preparation process of the above-mentioned graphene-based quinone mediator membrane, the preferred conditions for the free radical polymerization reaction include a temperature of 50–90°C, such as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any value between them; a pressure of 0.05–1 MPa, such as 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, or any value between them; and a time of 0.5–10 h, such as 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, or any value between them.

[0034] In the preparation of the graphene-based quinone mediator membrane described above, the conditions for the addition reaction preferably include a temperature of 70–90°C, such as 70°C, 75°C, 80°C, 85°C, 90°C, or any value between them; a pressure of 0.01–1 MPa, such as 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, or any value between them; and a time of 0.1–24 h, such as 0.1 h, 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h, 22 h, 24 h, or any value between them.

[0035] The present invention also provides a graphene-based quinone mediator membrane prepared by the above method.

[0036] Furthermore, the present invention also provides the application of the graphene-based quinone mediator membrane in wastewater denitrification.

[0037] The present invention will be described in detail below through embodiments.

[0038] In the following test cases:

[0039] (1) BTB (bromothymol blue) medium: KNO3 1.0g, agar 20g, KH2PO4 1.0g, FeCl2·6H2O 0.5g, CaCl2·7H2O 0.2g, MgSO4·7H2O 1.0g, sodium succinate 8.5g, BTB (1% dissolved in alcohol) 1mL, distilled water 1000mL, pH=7.2.

[0040] (2) Denitrification medium: KNO3 0.7218g, sodium succinate 2.2g, MgSO4·7H2O 0.2g, K2HPO4 0.5g, distilled water 1000mL, pH=7.2.

[0041] (3) LB medium: 25g LB broth, 1000mL distilled water, pH=7.2.

[0042] (4) Determination of nitrate nitrogen: Nitrate nitrogen (NO3) was determined using an ultraviolet spectrophotometer. - The concentration of NO3- (-N). Specifically, by quantitatively determining NO3- - NO3 was monitored by absorbance at a wavelength of 220 nm. - The concentration of -N is such that soluble organic matter absorbs at wavelengths of 220 nm and 275 nm, while NO3... - There was no absorption at a wavelength of 275 nm, so a second measurement was performed at 275 nm to correct for NO3. - The concentration of -N. The detection limit of this method is 0.08-4 mg / L. The specific operating steps are as follows:

[0043] ① Take an appropriate water sample and transfer it into a 50mL colorimetric tube. Dilute it appropriately according to the detection range and bring the volume to 50mL with distilled water. If the water sample is colored or turbid, add a suspension of 10% zinc sulfate and aluminum hydroxide to pre-treat the water sample by flocculation, and then centrifuge or take the supernatant.

[0044] ② Add 1 mL of 1 mol / L hydrochloric acid and 0.8% aminosulfonic acid to the colorimetric tube, then mix and shake well;

[0045] ③ Use the solution obtained by adding 1 mL of hydrochloric acid (1 mol / L) and 0.1 mL of aminosulfonic acid (0.8%) to 50 mL of distilled water as a blank reference, and measure the absorbance at wavelengths of 220 nm and 275 nm using a 10 mm quartz cuvette.

[0046] ④ Determine NO3 according to the above steps. - The absorbance at wavelengths of 220 nm and 275 nm when the concentrations of -N are 0.25 mg / L, 0.5 mg / L, 1 mg / L, 1.5 mg / L and 2 mg / L;

[0047] ⑤NO3 - The formula (1) for calculating the -N content is as follows:

[0048] A 校 =A 220 -2A 275 (1)

[0049] ⑥ NO3 in the water sample - The concentration of -N was determined by the standard curve (y = 0.2509x + 0.0006, where x is NO3-). - The concentration of -N (mg / L) and y (absorbance) are used to calculate the value.

[0050] Example 1: Graphene-based quinone mediator membrane and its preparation method

[0051] S1. Add 2L of N,N-dimethylacetamide solution and 1.1g of tetrahydrofurfuryl ether to a high-pressure reactor. Purge nitrogen into the high-pressure reactor to reduce the oxygen content to below 20ppm. Then, continuously purge vinylidene fluoride (VDF) and butadiene in a molar ratio of 1:0.6 into the high-pressure reactor. Raise the temperature in the high-pressure reactor to 50℃, add 1.1mmol of n-butyllithium, and control the pressure at 1MPa to initiate the reaction for 2h to obtain a solution containing the prepolymer.

[0052] S2. Add 1-amino-5-mercaptoanthraquinone to the solution containing the prepolymer obtained in step S1, and control the amount of 1-amino-5-mercaptoanthraquinone to be 0.8 times the molar amount of butadiene used in step S1. Then heat to 70°C and add 6.7 g of azobisisobutyronitrile and control the pressure at 1 MPa to initiate the reaction for 24 h to obtain a solution containing polyvinylidene fluoride / butadiene.

[0053] S3. Graphene, 6-aminoimidazo[1,2-A]pyridine, and humic substances were dissolved in N,N-dimethylacetamide solution. The resulting solution was mixed evenly with glutaraldehyde. The resulting mixture was then mixed evenly with a solution containing polyvinylidene fluoride / butadiene and degassed. The mass ratio of polyvinylidene fluoride / butadiene, graphene, aminoimidazopyridine, humic substances, and glutaraldehyde was 100:15:8:6:3, yielding a casting solution with a solid content of 18.2 wt%. The casting solution was poured onto a clean glass plate and leveled with a 5 mm clean scraper. The plate was then immersed in a pure water coagulation bath for 24 hours to solidify into a film. The solidified film was washed with deionized water to remove residual solvent, yielding a graphene-based quinone mediator membrane, denoted as M1.

[0054] Example 2: Graphene-based quinone mediator membrane and its preparation method

[0055] S1. Add 2L of N,N-dimethylacetamide solution and 1.1g of tetrahydrofurfuryl ether to a high-pressure reactor. Purge nitrogen gas into the high-pressure reactor to reduce the oxygen content to below 20ppm. Then, continuously purge vinylidene fluoride (VDF) and butadiene in a molar ratio of 1:0.2 into the high-pressure reactor. Raise the temperature in the high-pressure reactor to 90℃, add 1.1mmol of n-butyllithium, and control the pressure at 0.1MPa to initiate the reaction for 10h to obtain a solution containing the prepolymer.

[0056] S2. Add 1-amino-5-mercaptoanthraquinone to the solution containing the prepolymer obtained in step S1, and control the amount of 1-amino-5-mercaptoanthraquinone to be 1.2 times the molar amount of butadiene used in step S1. Then heat to 90°C and add 6.7 g of azobisisobutyronitrile and control the pressure at 0.1 MPa to initiate the reaction for 1 h to obtain a solution containing polyvinylidene fluoride / butadiene.

[0057] S3. Graphene, 6-aminoimidazo[1,2-A]pyridine, and humic substances were dissolved in N,N-dimethylacetamide solution. The resulting solution was mixed evenly with glutaraldehyde. The resulting mixture was then mixed evenly with a solution containing polyvinylidene fluoride / butadiene and degassed. The mass ratio of polyvinylidene fluoride / butadiene, graphene, aminoimidazopyridine, humic substances, and glutaraldehyde was 100:10:5:2:1, yielding a casting solution with a solid content of 16.5 wt%. The casting solution was poured onto a clean glass plate and leveled with a 5 mm clean scraper. The plate was then immersed in a pure water coagulation bath for 24 hours to solidify into a film. The solidified film was washed with deionized water to remove residual solvent, yielding a graphene-based quinone mediator membrane, denoted as M2.

[0058] Example 3: Graphene-based quinone mediator membrane and its preparation method

[0059] S1. Add 2L of N,N-dimethylacetamide solution and 1.1g of tetrahydrofurfuryl ether to a high-pressure reactor. Purge nitrogen gas into the high-pressure reactor to reduce the oxygen content to below 20ppm. Then, continuously purge vinylidene fluoride (VDF) and butadiene in a molar ratio of 1:0.4 into the high-pressure reactor. Raise the temperature in the high-pressure reactor to 70℃, add 1.1mmol of n-butyllithium, and control the pressure at 0.6MPa to initiate the reaction for 0.5h, obtaining a solution containing the prepolymer.

[0060] S2. Add 1-amino-5-mercaptoanthraquinone to the solution containing the prepolymer obtained in step S1, and control the amount of 1-amino-5-mercaptoanthraquinone to be 1 times the molar amount of butadiene used in step S1. Then heat to 70°C and add 6.7 g of azobisisobutyronitrile and control the pressure at 0.6 MPa to initiate the reaction for 5 h to obtain a solution containing polyvinylidene fluoride / butadiene.

[0061] S3. Graphene, 6-aminoimidazo[1,2-A]pyridine, and humic substances were dissolved in N,N-dimethylacetamide solution. The resulting solution was mixed evenly with glutaraldehyde. The resulting mixture was then mixed evenly with a solution containing polyvinylidene fluoride / butadiene and degassed. The mass ratio of polyvinylidene fluoride / butadiene, graphene, aminoimidazopyridine, humic substances, and glutaraldehyde was 100:20:10:10:5, yielding a casting solution with a solid content of 20.6 wt%. The casting solution was poured onto a clean glass plate and leveled with a 5 mm clean scraper. The plate was then immersed in a pure water coagulation bath for 24 hours to solidify into a film. The solidified film was washed with deionized water to remove residual solvent, yielding a graphene-based quinone mediator membrane, denoted as M3.

[0062] Comparative Example 1: Reference Graphene-based Quinone Mediator Membrane and its Preparation Method

[0063] The mediator membrane was prepared according to the method of Example 1, except that graphene, 6-aminoimidazo[1,2-A]pyridine, and humic substances were not added to the casting solution. The other conditions were the same as in Example 1. The specific steps are as follows:

[0064] S1. Same as Example 1;

[0065] S2. Same as Example 1;

[0066] S3. Glutaraldehyde was dissolved in N,N-dimethylacetamide solution. The resulting solution was mixed thoroughly with a solution containing polyvinylidene fluoride / butadiene, and then degassed. The mass ratio of polyvinylidene fluoride / butadiene to glutaraldehyde was 100:3, yielding a casting solution with a solid content of 18.2 wt%. The casting solution was poured onto a clean glass plate and leveled with a 5 mm clean doctor blade. The plate was then immersed in a pure water coagulation bath for 24 hours to solidify into a film. The solidified film was washed with deionized water to remove residual solvent, yielding a quinone mediator membrane, denoted as DM1.

[0067] Comparative Example 2: Reference Graphene-based Quinone Mediator Membrane and its Preparation Method

[0068] Graphene-based quinone mediator membranes were prepared according to the method of Example 1, except that 6-aminoimidazo[1,2-A]pyridine was replaced with the same amount of graphene by weight, and the other conditions were the same as in Example 1, to obtain a reference graphene-based quinone mediator membrane, denoted as DM2.

[0069] Comparative Example 3: Reference Graphene-based Quinone Mediator Membrane and its Preparation Method

[0070] A graphene-based quinone mediator membrane was prepared according to the method of Example 1, except that the humic substance was replaced with the same amount of graphene by weight, and the other conditions were the same as in Example 1, to obtain a reference graphene-based quinone mediator membrane, denoted as DM3.

[0071] Comparative Example 4: Reference Graphene-based Quinone Mediator Membrane and its Preparation Method

[0072] Graphene-based quinone mediator membranes were prepared according to the method of Example 1, except that butadiene was not added during the preparation of the support, and 1-amino-5-mercaptoanthraquinone was not attached to the support by an addition reaction bond, but was directly added to the casting solution. The other conditions were the same as in Example 1. The specific steps are as follows:

[0073] S1. Add 2L of N,N-dimethylacetamide solution and 1.1g of tetrahydrofurfuryl ether to a high-pressure reactor. Purge nitrogen into the high-pressure reactor to reduce the oxygen content to below 20ppm. Then, continuously purge polyvinylidene fluoride (VDF) into the high-pressure reactor. Raise the temperature in the high-pressure reactor to 50℃, add 1.1mmol of n-butyllithium, and control the pressure at 1MPa to initiate the reaction for 2h, to obtain a solution containing polyvinylidene fluoride.

[0074] S3. Graphene, 6-aminoimidazo[1,2-A]pyridine, humic substances, and 1-amino-5-mercaptoanthraquinone were dissolved in N,N-dimethylacetamide solution. The resulting solution was mixed evenly with glutaraldehyde. The resulting mixture was then mixed evenly with a solution containing polyvinylidene fluoride (PVDF) and degassed. The mass ratio of PVDF, graphene, aminoimidazopyridine, humic substances, and glutaraldehyde was 100:15:8:6:3. The molar ratio of PVDF to 1-amino-5-mercaptoanthraquinone consumed during PVDF production was 1:0.48, resulting in a casting solution with a solid content of 18.2 wt%. The casting solution was poured onto a clean glass plate and leveled with a 5 mm clean scraper. The plate was then immersed in a pure water coagulation bath for 24 hours to solidify into a film. The solidified film was washed with deionized water to remove residual solvent, yielding a graphene-based quinone mediator membrane, denoted as DM4.

[0075] Test case

[0076] 2g of activated sludge from the biochemical treatment tank of a sewage treatment plant in Longyan was added to sterilized LB medium. After sealing with sealing film, the medium was placed in a shaker at 36℃ and 120r / min for 48h. 10mL of the resulting culture solution was added to a new LB medium. The resulting culture solution was then spread and streaked on BTB medium and placed in a constant temperature incubator at 36℃ for 2d. Highly efficient nitrogen-degrading strains were screened and stored at -20℃.

[0077] The mediator membranes obtained in the above examples and comparative examples were respectively placed into 1000 mL serum bottles. The serum bottles were then filled with water samples to be treated. Following the above method, the selected high-efficiency nitrogen-degrading strains were inoculated into LB medium and activated for 48 h in a shaker at 36℃ and 120 rpm. The activated strains were then inoculated into liquid denitrification medium (initial concentration 100 mg / L) at a concentration of 3%, and then added to the serum bottles. The serum bottles were incubated in a shaker at 36℃ and 120 rpm for 24 h. Samples were taken at regular intervals and quantitatively diluted according to the detection range. The NO3 content in the diluted water samples was then measured using a UV spectrophotometer. - Substitute the absorbance value of -N into NO3 - The standard curve for -N (y = 0.2509x + 0.0006, where x is NO3) - The concentration of -N (mg / L) and y (absorbance) were obtained, and the degradation curve was plotted. The denitrification rate was calculated using the following formula (2):

[0078]

[0079] Where A0 is the initial nitrate nitrogen concentration (mg / L); A tt represents the nitrate nitrogen concentration (mg / L) after time t; r represents the denitrification rate (%). The results are shown in Table 1.

[0080] The graphene-based quinone mediator membrane was used to treat 10 batches of water samples in the manner described above. Each batch of water samples was treated continuously for 6 days. The denitrification rate of the first batch and the 10th batch of water samples after 24 hours of treatment was calculated according to the above method. The results are shown in Table 1.

[0081] Table 1

[0082]

[0083] The results above show that the graphene-based quinone mediator membrane provided by this invention has a high initial denitrification rate and a high denitrification rate over time.

[0084] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A graphene-based quinone mediator membrane, characterized in that, The graphene-based quinone mediator membrane includes a membrane matrix and graphene, aminoimidazopyridine, and humic substances dispersed in the membrane matrix; the membrane matrix is ​​made of polyvinylidene fluoride / butadiene, wherein the polyvinylidene fluoride / butadiene is a random copolymer of vinylidene fluoride and butadiene, and anthraquinone modification units are bonded to the butadiene structural units of the random copolymer.

2. The graphene-based quinone mediator membrane according to claim 1, characterized in that, The mass ratio of the membrane substrate, graphene, aminoimidazopyridine to humic substances is 100:(10~20):(5~10):(2~10).

3. The graphene-based quinone mediator membrane according to claim 1, characterized in that, The polyvinylidene fluoride / butadiene was prepared according to the following method: S1. Vinylidene fluoride and butadiene are subjected to free radical polymerization in the presence of a free radical initiator to obtain a prepolymer; S2. The prepolymer is reacted with mercaptoanthraquinone by addition reaction to obtain polyvinylidene fluoride / butadiene.

4. The graphene-based quinone mediator membrane according to claim 3, characterized in that, The molar ratio of vinylidene fluoride to butadiene is 1:(0.2~0.6).

5. The graphene-based quinone mediator membrane according to claim 3, characterized in that, The mercaptoanthraquinone is 1-amino-5-mercaptoanthraquinone.

6. The graphene-based quinone mediator membrane according to claim 3, characterized in that, The molar ratio of the mercaptoanthraquinone to butadiene is (0.8~1.2):

1.

7. The graphene-based quinone mediator membrane according to claim 3, characterized in that, The conditions for the free radical polymerization reaction include a temperature of 50~90℃, a pressure of 0.05~1MPa, and a time of 0.5~10h.

8. The graphene-based quinone mediator membrane according to claim 3, characterized in that, The conditions for the addition reaction include a temperature of 70~90℃, a pressure of 0.01~1MPa, and a time of 0.1~24h.

9. The graphene-based quinone mediator membrane according to claim 1, characterized in that, The aminoimidazopyridine is 6-aminoimidazo[1,2-A]pyridine.

10. A method for preparing a graphene-based quinone mediator membrane, characterized in that, The method includes: S1. Vinylidene fluoride and butadiene are subjected to free radical polymerization in the presence of a free radical initiator to obtain a prepolymer; S2. The prepolymer is reacted with mercaptoanthraquinone by addition reaction to obtain polyvinylidene fluoride / butadiene; S3. Graphene, aminoimidazopyridine and humic substances are dissolved in an organic solvent. The resulting solution is mixed with glutaraldehyde until homogeneous. The resulting mixture is then mixed with polyvinylidene fluoride / butadiene until homogeneous and degassed. The resulting casting solution is then placed on a substrate and leveled with a scraper before being immersed in pure water to solidify into a film, thus obtaining the graphene-based quinone mediator membrane.

11. The method for preparing the graphene-based quinone mediator membrane according to claim 10, characterized in that, The molar ratio of vinylidene fluoride to butadiene is 1:(0.2~0.6); the molar ratio of mercaptoanthraquinone to butadiene is (0.8~1.2):1; the mass ratio of polyvinylidene fluoride / butadiene, graphene, aminoimidazopyridine to humic substances is 100:(10~20):(5~10):(2~10); the mass ratio of glutaraldehyde to polyvinylidene fluoride / butadiene is (1~5):

100.

12. The method for preparing the graphene-based quinone mediator membrane according to claim 10, characterized in that, The conditions for the free radical polymerization reaction include a temperature of 50~90℃, a pressure of 0.05~1MPa, and a time of 0.5~10h; The conditions for the addition reaction include a temperature of 70~90℃, a pressure of 0.01~1MPa, and a time of 0.1~24h.

13. A graphene-based quinone mediator membrane prepared by the method according to any one of claims 10 to 12.

14. The application of the graphene-based quinone mediator membrane according to any one of claims 1 to 9 and 13 in wastewater denitrification.

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