A carbon fiber membrane for wastewater treatment and its preparation method

Abstract

This invention discloses a carbon fiber membrane for wastewater treatment and its preparation method, relating to the field of polymer materials technology. In preparing the carbon fiber membrane for wastewater treatment, triethyl phosphate is first hydrolyzed and then added to calcium, magnesium, and iron solutions to form a magnesium-iron doped tricalcium phosphate sol. The magnesium-iron doped tricalcium phosphate sol, biochar, and polyacrylonitrile are mixed and electrospun. After hot stretching, pre-oxidation, carbonization, and alkali washing, a doped carbon fiber membrane is obtained. The doped carbon fiber membrane is then electrodeposited onto polyamic acid in a polyamic acid emulsion to obtain the carbon fiber membrane for wastewater treatment. The carbon fiber membrane for wastewater treatment prepared by this invention has the advantages of high mechanical strength, high biofilm formation rate, and fast biofilm formation speed.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a carbon fiber membrane for wastewater treatment and its preparation method. Background Technology

[0002] The ecological cycle of water can be mainly divided into natural and social cycles. Natural cycles are usually unaffected by human intervention, while social cycles are closely related to our production and daily life. In the social cycle of water, the discharge of wastewater often contains a large amount of pollutants. When the content of these pollutants is too high and exceeds the self-purification capacity of the water body, it will cause water quality deterioration and disrupt the ecological balance of the water body. Therefore, wastewater treatment is one of the most urgent problems to be solved and a major measure to alleviate water pollution.

[0003] Biofilm technology is widely used in water environment management and is one of the more reliable methods for nitrogen and phosphorus removal from wastewater. Its green nature, lack of secondary pollution, and low cost have garnered significant attention from the wastewater treatment industry both domestically and internationally. The core of this method is the formation of a high-performance biofilm, and the growth and reproduction of microorganisms within the biofilm are prerequisites for the remediation of eutrophic water bodies. All of these are closely related to the biofilm carrier. Carbon fiber, due to its strong adsorption capacity and microbial affinity, can achieve both adsorption and biofilm remediation functions. Based on bioremediation, it combines physical, chemical, and biological processes to achieve a composite environmental management technology, which has been extensively studied in the field of river and lake ecological restoration. Further research has shown that, compared to other carriers such as carbon fiber, bio-rope, microfiber three-dimensional artificial aquatic plants, three-dimensional elastic materials, and polyethylene plastics, carbon fiber exhibits faster biofilm formation, higher efficiency, and better nitrogen removal efficiency. Therefore, carbon fiber is an ideal carrier material for biofilm remediation technology.

[0004] As a crucial component of biofilm remediation technology, the carrier serves as the transfer medium between microorganisms and pollutants within the biofilm. By loading the biofilm, it provides a growth and metabolic site for aerobic, anaerobic, and facultative anaerobic microorganisms, forming the foundation for bioremediation and playing a vital role in improving biofilm treatment efficiency. While carbon fiber possesses a rough surface with numerous pores and depressions, untreated virgin carbon fiber exhibits high surface inertness, low levels of active functional groups, and numerous surface defects, thus limiting its high performance. Therefore, surface modification is necessary to further enhance its activity. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon fiber membrane for wastewater treatment and its preparation method, so as to solve the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A carbon fiber membrane for wastewater treatment is prepared by electrodepositing a polyamic acid layer onto a doped carbon fiber membrane in a polyamic acid emulsion.

[0008] The doped carbon fiber film is prepared by electrospinning a mixture of magnesium-iron doped tricalcium phosphate sol, polyacrylonitrile, and biochar with N,N-dimethylformamide, followed by hot stretching, pre-oxidation, carbonization, and alkali washing.

[0009] The magnesium-iron doped tricalcium phosphate sol is prepared by hydrolyzing triethyl phosphate and then adding calcium, magnesium, and iron solutions for aging.

[0010] As an optimization, the polyamic acid emulsion is prepared by reacting 4,4'-diaminodiphenyl ether with pyromellitic anhydride and then adding triethylamine and methanol.

[0011] As an optimization, the thickness of the polyamic acid layer is 100~200nm.

[0012] As an optimization, the biochar is obtained by carbonizing biomass raw materials.

[0013] As an optimization, the biomass raw materials include one or more of the following: rice straw, corn straw, wheat straw, peanut shells, walnut shells, coffee grounds, sugarcane bagasse, tea leaves, sawdust, fallen leaves, bamboo processing residues, algae, and distiller's grains.

[0014] A method for preparing a carbon fiber membrane for wastewater treatment includes the following preparation steps:

[0015] (1) Mix pure water, ethanol and triethyl phosphate evenly, seal and stir at room temperature, add ammonia water, seal and stir, add calcium solution, magnesium solution and iron solution, stir after addition, and then let stand to age to obtain magnesium iron doped tricalcium phosphate sol.

[0016] (2) Magnesium iron doped tricalcium phosphate sol, polyacrylonitrile, biochar and N,N-dimethylformamide are mixed evenly, stirred, sonicated and defoamed to obtain spinning solution; after electrospinning, the film is collected from the collecting roller, dried, stretched, pre-oxidized, carbonized, cooled, alkali washed and dried to obtain carbon fiber doped film.

[0017] (3) Using polyamic acid emulsion as electrolyte, doped carbon fiber membrane as positive electrode and graphite as negative electrode, electrodeposition and drying are performed to obtain carbon fiber membrane for sewage treatment.

[0018] As an optimization, in step (1), the amount of pure water added is 4 to 6 parts by mass, ethanol is 10 to 15 parts, triethyl phosphate is 13.48 to 20.22 parts, and ammonia is 0.14 to 0.21 parts.

[0019] As an optimization, the molar ratio of triethyl phosphate to calcium ions in calcium solution, magnesium ions in magnesium solution, and iron ions in iron solution in step (1) is 1:(1.35~1.4):(0.08~0.12):(0.02~0.03).

[0020] As an optimization, the addition rate of the calcium solution, magnesium solution and iron solution in step (1) is 0.8~1.2 ml / min.

[0021] As an optimization, the content of metal ions in the calcium solution, magnesium solution and iron solution in step (1) is 1 mol / L, and the solvent is anhydrous ethanol.

[0022] As an optimization, the preparation process of the magnesium-iron doped tricalcium phosphate sol in step (1) is as follows:

[0023] By mass, 4-6 parts of pure water, 10-15 parts of ethanol, and 13.48-20.22 parts of triethyl phosphate are mixed evenly and stirred at 200-300 rpm for 20-24 hours in a sealed container at room temperature. Then, 0.14-0.21 parts of ammonia water are added, and the mixture is stirred at 300-400 rpm for 20-24 hours in a sealed container at 70-80°C. Finally, calcium, magnesium, and iron solutions are added at 0.8-1.2 ml / min at 300-400 rpm at 0-4°C. After the addition is complete, the mixture is stirred at 300-400 rpm for 2-3 hours in a sealed container at 0-4°C. The mixture is then allowed to stand and age for 7 days to obtain magnesium-iron doped tricalcium phosphate sol.

[0024] As an optimization, the mass concentration of the ammonia water is 20%~25%.

[0025] As an optimization, in step (2), the amount of magnesium-iron doped tricalcium phosphate sol added is 0.3~0.4 parts by mass, polyacrylonitrile is 2~3 parts, biochar is 0.5~0.7 parts, N,N-dimethylformamide is 25~35 parts, the stirring temperature is 50~60℃, the stirring time is 8~12h, and the ultrasonic time is 2~3h.

[0026] As an optimization, the electrospinning process parameters in step (2) are: voltage 17~18kV, flow rate 1.2~1.4ml / h, receiving distance 15~16cm, roller speed 800~1000rpm, temperature 25~35℃, humidity 35%~45%, and duration 10~12h.

[0027] As an optimization, the process parameters for stretching in step (2) are: stretching along the parallel direction of fiber arrangement, stretching temperature of 130~140℃, stretching time of 5~10min, and stretching force of 0.75~1.25N.

[0028] As an optimization, the process parameters for the pre-oxidation in step (2) are: under an air atmosphere, the temperature is increased to 260~270℃ at a heating rate of 1~1.2℃ / min for 90~120min for pre-oxidation.

[0029] As an optimization, the carbonization process parameters in step (2) are as follows: under a nitrogen atmosphere, the temperature is increased to 900-1000℃ at a heating rate of 5-6℃ / min for 3-4 hours.

[0030] As an optimization, the process parameters for alkaline washing in step (2) are: immersing in sodium carbonate solution, soaking at 70~80℃ and 100~150r / min for 2~3h, filtering, and washing until neutral.

[0031] As an optimization, the preparation process of biochar in step (2) is as follows:

[0032] Biomass raw materials are crushed and washed using a pulverizer, and dried at 80-100℃ to obtain biomass powder. 3-4 parts by mass of biomass powder and 37-49 parts by mass of concentrated sulfuric acid are mixed evenly and stirred at 100-200 rpm for 30-40 minutes at room temperature. Hydrogen peroxide is added at a volume ratio of 3:(0.9-1.1) under ice-water bath conditions at 400-500 rpm at a rate of 2-3 ml / min. After addition, the mixture is stirred under ice-water bath conditions for 3-4 hours. After the reaction cools to room temperature, the mixture is washed with pure water until neutral, then centrifuged to remove the liquid. The mixture is dried at 60-80℃ for 20-30 hours and ball-milled at 100-150 rpm for 6-8 hours. The resulting biochar is obtained by passing the mixture through a 400-mesh sieve.

[0033] As an optimization, the preparation process of the doped carbon fiber film in step (2) is as follows:

[0034] By weight, 0.3-0.4 parts of magnesium-iron-doped tricalcium phosphate sol, 2-3 parts of polyacrylonitrile, 0.5-0.7 parts of biochar, and 25-35 parts of N,N-dimethylformamide are mixed evenly and stirred at 50-60℃ and 300-400 r / min for 8-12 hours, followed by ultrasonication for 2-3 hours to remove bubbles, thus obtaining the spinning solution. Electrospinning is performed at a voltage of 17-18 kV, a flow rate of 1.2-1.4 ml / h, a receiving distance of 15-16 cm, a drum speed of 800-1000 rpm, a temperature of 25-35℃, and a humidity of 35%-45% for 10-12 hours. The film is collected from the collecting drum and vacuum dried at 60-70℃ for 10-12 hours. The film is then distributed along the fiber arrangement. The carbon fiber membrane is drawn in the direction of stretching at a temperature of 130-140℃ for 5-10 minutes and a stretching force of 0.75-1.25N. After naturally cooling to room temperature, it is removed and pre-oxidized at 260-270℃ for 90-120 minutes in air at a heating rate of 1-1.2℃ / min. After naturally cooling to room temperature, it is carbonized at 900-1000℃ for 3-4 hours in nitrogen at a heating rate of 5-6℃ / min. After naturally cooling to room temperature, it is immersed in sodium carbonate solution at 70-80℃ and 100-150 r / min for 2-3 hours. After filtration, it is washed with pure water until neutral and dried at 80-100℃ for 10-12 hours to obtain the doped carbon fiber membrane.

[0035] As an optimization, the solvent for the sodium carbonate solution is water with a concentration of 15 wt%.

[0036] As an optimization, the electrodeposition voltage in step (3) is 40~50V and the time is 8~12min.

[0037] As an optimization, the polyamic acid emulsion in step (3) is prepared by mixing 1.84~2.76 parts of 4,4'-diaminodiphenyl ether and 30~40 parts of N,N-dimethylacetamide by mass, stirring at room temperature until completely dissolved, adding 2~3 parts of pyromellitic anhydride, stirring at 200~300 r / min in an ice-water bath for 8~10 h, stirring at 200~300 r / min at room temperature for 10~12 h, adding triethylamine at a molar ratio of (2~3):1 to the remaining carboxyl group, stirring at 200~300 r / min at room temperature for 60~90 min, adding 80~100 parts of methanol, and continuing to stir at 200~300 r / min at room temperature for 60~80 min.

[0038] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0039] In preparing carbon fiber membranes for wastewater treatment, the present invention first carbonizes biomass raw materials to produce biochar; hydrolyzes triethyl phosphate and adds calcium, magnesium, and iron solutions for aging to obtain magnesium-iron doped tricalcium phosphate sol; mixes the magnesium-iron doped tricalcium phosphate sol, polyacrylonitrile, and biochar with N,N-dimethylformamide, then electrospins the mixture, followed by hot stretching, pre-oxidation, carbonization, and alkali washing to obtain a doped carbon fiber membrane; and electrodeposits the doped carbon fiber membrane onto a polyamic acid layer in a polyamic acid emulsion to obtain the carbon fiber membrane for wastewater treatment.

[0040] First, biochar and magnesium-iron-doped tricalcium phosphate sol were prepared. Biochar has high porosity and high surface area, and has good adsorption properties. After being incorporated into carbon fibers, it combines with carbon fibers to become the main body and provides more loading space to assist the deposition of magnesium-iron-doped tricalcium phosphate sol. Using fully hydrolyzed triethyl phosphate as the phosphate source, calcium is the main component, with small amounts of magnesium and iron doped into it, a magnesium-iron-doped tricalcium phosphate precursor was obtained.

[0041] Secondly, magnesium-iron-doped tricalcium phosphate sol, polyacrylonitrile, and biochar were mixed with N,N-dimethylformamide and electrospun. The mixture was then subjected to hot stretching, pre-oxidation, carbonization, and alkali washing to obtain a doped carbon fiber membrane. The magnesium-iron-doped tricalcium phosphate sol and biochar were electrospun together with polyacrylonitrile to obtain a fiber membrane. During electrospinning, a high-speed rotating collecting roller was used for initial orientation. Subsequently, hot stretching was performed parallel to the fiber arrangement to further improve the orientation of the fibers within the membrane. This effectively improved the mechanical properties of the carbon fibers after carbonization. Following pre-oxidation and high-temperature carbonization, the polyacrylonitrile carbonized to form the carbon fiber matrix, while the biochar adsorbed a large amount of magnesium-iron-doped tricalcium phosphate sol and was encapsulated or loaded within the polyacrylonitrile matrix. At high temperatures, the magnesium-iron-doped tricalcium phosphate sol gradually transformed its crystal form, forming tricalcium phosphate crystals with a β-TCP structure. Magnesium and iron ions replaced some calcium ions and entered the crystal interior, forming magnesium-iron-doped tricalcium phosphate crystals that were loaded or encapsulated within the carbon fiber matrix. Subsequently, the carbon fibers are washed with sodium carbonate solution to remove carbonized impurities and expand the pores, thereby improving the surface pore structure of the carbon fibers and increasing their adsorption surface area. A polyacrylonitrile-based carbon fiber material, i.e., a doped carbon fiber membrane, loaded with biochar particles and magnesium-iron doped tricalcium phosphate crystals was prepared. The introduction of biochar particles into the doped carbon fiber membrane not only improves the initial adsorption of magnesium-iron doped tricalcium phosphate sol but also provides numerous adsorption sites due to its porous structure, which is beneficial for the adsorption of nitrogen and phosphorus in wastewater and improves the biofilm formation rate and amount of microorganisms. Magnesium-iron doped tricalcium phosphate crystals exhibit biocompatibility at appropriate concentrations. These crystals can slowly degrade under the action of microorganisms, releasing calcium ions for their growth. Furthermore, magnesium ions at concentrations below 24 mg / L and iron ions at concentrations below 3 mg / L effectively promote the increase and formation rate of extracellular polymers in the biofilm, thereby promoting biofilm adhesion to the doped carbon fiber membrane. However, the sudden release of magnesium and iron ions can easily lead to excessively high local metal ion concentrations. Excessive magnesium and iron ion concentrations can have an inhibitory effect, inhibiting microbial adhesion and reducing biofilm formation rate and amount. Therefore, it is necessary to control their release rate.

[0042] Finally, a polyamic acid layer was electrodeposited onto the doped carbon fiber membrane in a polyamic acid emulsion to obtain a carbon fiber membrane for wastewater treatment. Using electrodeposition technology, polyamic acid was deposited onto the doped carbon fiber membrane. In the polyamic acid emulsion, the carboxyl groups in the polyamic acid segments formed salts under the action of triethylamine, allowing it to be used for electrodeposition and obtaining a uniform thin film layer, namely the polyamic acid layer. The polyamic acid layer possesses excellent biocompatibility, facilitating microbial attachment and rapid biofilm formation on the wastewater treatment carbon fiber membrane, effectively improving biofilm formation speed and quantity. Furthermore, the polyamic acid layer contains a large number of carboxyl and amide groups, exhibiting good metal chelating properties. After coating the doped carbon fiber membrane, it can effectively chelate released calcium, magnesium, and iron metal ions to achieve a slow-release effect, avoiding abnormal increases in local metal ion concentration caused by sudden release. This allows for the loading of as many magnesium-iron-doped tricalcium phosphate crystals as possible onto the carbon fiber membrane, providing a longer period of metal ion nutrient release, maintaining the daily consumption of the biofilm, and increasing its treatment capacity for nitrogen and phosphorus in wastewater. This resulted in a carbon fiber membrane for wastewater treatment that can slowly release calcium, magnesium, and iron ions and has excellent biocompatibility. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] The following information is provided for the raw materials used in all the following embodiments and comparative examples:

[0045] Biomass raw material: rice straw;

[0046] Biochar: Biomass raw materials are crushed and washed using a pulverizer, and dried at 90℃ to obtain biomass powder. 3.5 parts by mass of biomass powder and 43 parts by mass of concentrated sulfuric acid are mixed evenly and stirred at 150 r / min for 35 min at room temperature. Hydrogen peroxide is added at 2.5 ml / min at 450 r / min under ice-water bath conditions, according to a volume ratio of concentrated sulfuric acid to hydrogen peroxide of 3:1. After the addition is completed, the mixture is stirred under ice-water bath conditions for 3.5 h. After the reaction is cooled to room temperature, it is washed with pure water until neutral, then centrifuged to remove the liquid, dried at 70℃ for 25 h, ball-milled at 150 rpm for 7 h, and passed through a 400-mesh sieve to obtain biochar.

[0047] Concentrated sulfuric acid: 98 wt%

[0048] Hydrogen peroxide: concentration 30 wt%;

[0049] Polyacrylonitrile: weight average molecular weight 100,000, purchased from Taian Yingshun Chemical Co., Ltd.

[0050] Calcium solution: The solute is calcium nitrate, the solvent is anhydrous ethanol, and the concentration of calcium ions is 1 mol / L;

[0051] Magnesium solution: solute is magnesium nitrate, solvent is anhydrous ethanol, and the concentration of magnesium ions is 1 mol / L;

[0052] Iron solution: the solute is ferric chloride, the solvent is anhydrous ethanol, and the concentration of iron ions is 1 mol / L;

[0053] Ammonia solution: concentration 25 wt%;

[0054] Sodium carbonate solution: concentration 15wt%.

[0055] Example 1:

[0056] A method for preparing a carbon fiber membrane for wastewater treatment, the method comprising the following preparation steps:

[0057] (1) By mass, 4 parts of pure water, 10 parts of ethanol and 13.48 parts of triethyl phosphate were mixed evenly, sealed at room temperature and stirred at 200 r / min for 24 h. 0.14 parts of ammonia water were added, sealed at 70℃ and stirred at 300 r / min for 24 h. At 0℃, at 300 r / min, calcium solution, magnesium solution and iron solution were added at 0.8 ml / min according to the molar ratio of triethyl phosphate to calcium ions in calcium solution, magnesium ions in magnesium solution and iron ions in iron solution of 1:1.35:0.12:0.03. After the addition was completed, the mixture was stirred at 0℃ and 300 r / min for 3 h. Then it was allowed to stand and age for 7 days to obtain magnesium iron doped tricalcium phosphate sol.

[0058] (2) By mass fraction, 0.3 parts of magnesium-iron doped tricalcium phosphate sol, 2 parts of polyacrylonitrile, 0.5 parts of biochar, and 25 parts of N,N-dimethylformamide were mixed evenly and stirred at 50℃ and 300 r / min for 12 h, followed by sonication for 2 h to remove bubbles, to obtain the spinning solution; electrospinning was performed at a voltage of 17 kV, a flow rate of 1.2 ml / h, a receiving distance of 15 cm, a drum speed of 800 rpm, a temperature of 25℃, and a humidity of 35% for 12 h, and the film was collected from the collecting drum and vacuum dried at 60℃ for 12 h along the parallel direction of fiber arrangement. The carbon fiber membrane was prepared by stretching at 130℃ for 10 min with a stretching force of 1.25 N. After naturally cooling to room temperature, the membrane was removed and pre-oxidized at 260℃ for 120 min in air at a heating rate of 1℃ / min. After naturally cooling to room temperature, the membrane was carbonized at 900℃ for 4 h in nitrogen at a heating rate of 5℃ / min. After naturally cooling to room temperature, the membrane was immersed in sodium carbonate solution at 70℃ and 100 r / min for 3 h. After filtration, the membrane was washed with pure water until neutral and dried at 80℃ for 12 h to obtain the doped carbon fiber membrane.

[0059] (3) By mass, 1.84 parts of 4,4'-diaminodiphenyl ether and 30 parts of N,N-dimethylacetamide were mixed evenly and stirred at room temperature until completely dissolved. 2 parts of pyromellitic anhydride were added and stirred at 200 r / min for 10 h in an ice-water bath. Then, the mixture was stirred at 200 r / min for 12 h at room temperature. Triethylamine was added at a molar ratio of 2:1 to the remaining carboxyl group. The mixture was stirred at 200 r / min for 90 min at room temperature. 80 parts of methanol were added and the mixture was stirred at 200 r / min for 80 min at room temperature to obtain a polyamic acid emulsion.

[0060] (4) Using polyamic acid emulsion as electrolyte, doped carbon fiber membrane as positive electrode, graphite as negative electrode, voltage of 40V, electrodeposition for 12min, and vacuum drying at 50℃ for 12h, carbon fiber membrane for sewage treatment is obtained.

[0061] Example 2:

[0062] A method for preparing a carbon fiber membrane for wastewater treatment, the method comprising the following preparation steps:

[0063] (1) By mass, 5 parts of pure water, 12.5 parts of ethanol and 16.85 parts of triethyl phosphate were mixed evenly, sealed at room temperature and stirred at 200 r / min for 24 h. 0.18 parts of ammonia water were added, sealed at 75℃ and stirred at 350 r / min for 22 h. At 2℃ and 350 r / min, the calcium solution, magnesium solution and iron solution were added at 1 ml / min according to the molar ratio of triethyl phosphate to calcium ions in calcium solution, magnesium ions in magnesium solution and iron ions in iron solution of 1:1.375:0.1:0.025. After the addition was completed, the mixture was stirred at 2℃ and 350 r / min for 2.5 h. Then it was allowed to stand and age for 7 days to obtain magnesium iron doped tricalcium phosphate sol.

[0064] (2) By mass fraction, 0.35 parts of magnesium-iron doped tricalcium phosphate sol, 2.5 parts of polyacrylonitrile, 0.6 parts of biochar, and 30 parts of N,N-dimethylformamide were mixed evenly and stirred at 55℃ and 350 r / min for 10 h, followed by ultrasonication for 2.5 h to remove bubbles, thus obtaining the spinning solution. Electrospinning was performed for 11 h at a voltage of 17.5 kV, a flow rate of 1.3 ml / h, a receiving distance of 15 cm, a drum speed of 900 rpm, a temperature of 30℃, and a humidity of 40%. The film was collected from the collecting drum and vacuum dried at 65℃ for 11 h, along the parallel fiber arrangement. The carbon fiber film was prepared by stretching in the following directions at a temperature of 135℃ for 8 minutes and a stretching force of 1N. After naturally cooling to room temperature, the film was removed and pre-oxidized at 265℃ for 105 minutes in air at a heating rate of 1.1℃ / min. After naturally cooling to room temperature, the film was carbonized at 950℃ for 3.5 hours in nitrogen at a heating rate of 5.5℃ / min. After naturally cooling to room temperature, the film was immersed in sodium carbonate solution at 75℃ and 125r / min for 2.5 hours. After filtration, the film was washed with pure water until neutral and dried at 90℃ for 11 hours to obtain the doped carbon fiber film.

[0065] (3) By mass, 2.3 parts of 4,4'-diaminodiphenyl ether and 35 parts of N,N-dimethylacetamide were mixed evenly and stirred at room temperature until completely dissolved. 2.5 parts of pyromellitic anhydride were added and stirred at 250 r / min for 9 h in an ice-water bath. Then, the mixture was stirred at 250 r / min for 11 h at room temperature. Triethylamine was added at a molar ratio of 2.5:1 to the remaining carboxyl group. The mixture was stirred at 250 r / min for 75 min at room temperature. 90 parts of methanol were added and the mixture was stirred at 250 r / min for 70 min at room temperature to obtain a polyamic acid emulsion.

[0066] (4) Using polyamic acid emulsion as electrolyte, doped carbon fiber membrane as positive electrode, graphite as negative electrode, voltage of 45V, electrodeposition for 10min, and vacuum drying at 55℃ for 11h, carbon fiber membrane for sewage treatment is obtained.

[0067] Example 3:

[0068] A method for preparing a carbon fiber membrane for wastewater treatment, the method comprising the following preparation steps:

[0069] (1) By mass, 6 parts of pure water, 15 parts of ethanol and 20.22 parts of triethyl phosphate were mixed evenly, sealed at room temperature and stirred at 300 r / min for 20 h. 0.21 parts of ammonia water were added, sealed at 80℃ and stirred at 400 r / min for 20 h. At 4℃ and 400 r / min, calcium solution, magnesium solution and iron solution were added at 1.2 ml / min according to the molar ratio of triethyl phosphate to calcium ions in calcium solution, magnesium ions in magnesium solution and iron ions in iron solution of 1:1.4:0.08:0.02. After the addition was completed, the mixture was stirred at 4℃ and 400 r / min for 2 h. Then it was allowed to stand and age for 7 days to obtain magnesium iron doped tricalcium phosphate sol.

[0070] (2) By mass fraction, 0.4 parts of magnesium-iron doped tricalcium phosphate sol, 3 parts of polyacrylonitrile, 0.7 parts of biochar, and 35 parts of N,N-dimethylformamide were mixed evenly and stirred at 60℃ and 400 r / min for 8 h, followed by sonication for 3 h to remove bubbles, thus obtaining the spinning solution. Electrospinning was performed for 10 h at a voltage of 18 kV, a flow rate of 1.4 ml / h, a receiving distance of 16 cm, a drum speed of 1000 rpm, a temperature of 35℃, and a humidity of 45%. The film was collected from the collecting drum and vacuum dried at 70℃ for 10 h. The film was then processed along the parallel direction of the fiber arrangement. The carbon fiber film was prepared by stretching at 140℃ for 5 min with a stretching force of 0.75 N and then naturally cooling to room temperature. It was then pre-oxidized in air at 270℃ for 90 min at a heating rate of 1.2℃ / min, and naturally cooled to room temperature. In a nitrogen atmosphere, it was carbonized at 1000℃ for 3 h at a heating rate of 6℃ / min, and then naturally cooled to room temperature. The film was then immersed in a sodium carbonate solution at 80℃ and 150 r / min for 2 h, filtered, washed with pure water until neutral, and dried at 100℃ for 10 h.

[0071] (3) By mass, 2.76 parts of 4,4'-diaminodiphenyl ether and 40 parts of N,N-dimethylacetamide were mixed evenly and stirred at room temperature until completely dissolved. 3 parts of pyromellitic anhydride were added and stirred at 300 r / min for 8 h in an ice-water bath. Then, the mixture was stirred at 300 r / min for 10 h at room temperature. Triethylamine was added at a molar ratio of 3:1 to the remaining carboxyl group. The mixture was stirred at 300 r / min for 60 min at room temperature. 100 parts of methanol were added and the mixture was stirred at 300 r / min for 60 min at room temperature to obtain a polyamic acid emulsion.

[0072] (4) Using polyamic acid emulsion as electrolyte, doped carbon fiber membrane as positive electrode, graphite as negative electrode, voltage of 50V, electrodeposition for 8min, and vacuum drying at 60℃ for 10h, carbon fiber membrane for sewage treatment is obtained.

[0073] Comparative Example 1:

[0074] The difference between the preparation method of the carbon fiber membrane for wastewater treatment in Comparative Example 1 and Example 2 lies in step (1). Step (1) is modified as follows: 5 parts of pure water, 12.5 parts of ethanol, and 16.85 parts of triethyl phosphate are mixed evenly by mass, sealed at room temperature, and stirred at 200 r / min for 24 h. 0.18 parts of ammonia water are added, and the mixture is sealed at 75°C and stirred at 350 r / min for 22 h. At 2°C and 350 r / min, calcium and iron solutions are added at a rate of 1 ml / min, based on a molar ratio of 1:1.475:0.025 between triethyl phosphate and calcium ions in the calcium solution and iron ions in the iron solution. After addition, the mixture is stirred at 2°C and 350 r / min for 2.5 h, and then allowed to stand for 7 days to obtain magnesium-iron doped tricalcium phosphate sol. The remaining steps are the same as in Example 2.

[0075] Comparative Example 2:

[0076] The difference between the preparation method of the carbon fiber membrane for wastewater treatment in Comparative Example 2 and that in Example 2 lies in step (1). Step (1) is modified as follows: 5 parts by mass of pure water, 12.5 parts by mass of ethanol, and 16.85 parts by mass of triethyl phosphate are mixed evenly, sealed at room temperature, and stirred at 200 r / min for 24 h. Then, 0.18 parts by mass of ammonia water are added, sealed at 75°C, and stirred at 350 r / min for 22 h. At 2°C, at 350 r / min, calcium and magnesium solutions are added at a rate of 1 ml / min, based on a molar ratio of 1:1.4:0.1 between triethyl phosphate and calcium ions in the calcium solution and magnesium ions in the magnesium solution. After the addition is complete, the solution is stirred at 2°C, at 350 r / min for 2.5 h, and then allowed to stand for 7 days to obtain magnesium-iron doped tricalcium phosphate sol. The remaining steps are the same as in Example 2.

[0077] Comparative Example 3:

[0078] The preparation method of carbon fiber membrane for wastewater treatment in Comparative Example 3 differs from that in Example 2 in that step (1) is omitted, and step (2) is modified as follows: 2.5 parts by mass of polyacrylonitrile, 0.6 parts by mass of biochar, and 30 parts by mass of N,N-dimethylformamide are mixed evenly, stirred at 55°C and 350 r / min for 10 h, and sonicated for 2.5 h to remove bubbles to obtain a spinning solution; electrospinning is performed at a voltage of 17.5 kV, a flow rate of 1.3 ml / h, a receiving distance of 15 cm, a drum speed of 900 rpm, a temperature of 30°C, and a humidity of 40% for 11 h; the membrane is collected from the collecting drum and vacuumed at 65°C. After drying for 11 hours, the fibers were drawn along the parallel direction of their arrangement at a temperature of 135°C for 8 minutes and a force of 1 N. After natural cooling to room temperature, the fibers were removed and pre-oxidized at 265°C for 105 minutes at a heating rate of 1.1°C / min in air. After natural cooling to room temperature, the fibers were carbonized at 950°C for 3.5 hours at a heating rate of 5.5°C / min in nitrogen atmosphere. After natural cooling to room temperature, the fibers were immersed in a sodium carbonate solution at 75°C and 125 r / min for 2.5 hours. The solution was then filtered, washed with pure water until neutral, and dried at 90°C for 11 hours to obtain the doped carbon fiber membrane. The remaining steps were the same as in Example 2.

[0079] Comparative Example 4:

[0080] The difference between the preparation method of the carbon fiber membrane for wastewater treatment in Comparative Example 4 and Example 2 lies in the different step (2). Step (2) is modified as follows: 0.35 parts by mass of magnesium-iron doped tricalcium phosphate sol, 2.5 parts by mass of polyacrylonitrile, and 30 parts by mass of N,N-dimethylformamide are mixed evenly, stirred at 55°C and 350 r / min for 10 h, and sonicated for 2.5 h to obtain a spinning solution after defoaming; electrospinning is performed at a voltage of 17.5 kV, a flow rate of 1.3 ml / h, a receiving distance of 15 cm, a drum speed of 900 rpm, a temperature of 30°C, and a humidity of 40% for 11 h, and the film is collected from the collecting drum. The fiber was vacuum dried at 5℃ for 11 hours, then drawn along the parallel direction of the fiber arrangement at a drawing temperature of 135℃ for 8 minutes with a drawing force of 1 N. After naturally cooling to room temperature, it was removed and pre-oxidized at 265℃ for 105 minutes in air at a heating rate of 1.1℃ / min. After naturally cooling to room temperature, it was carbonized at 950℃ for 3.5 hours in nitrogen at a heating rate of 5.5℃ / min. After naturally cooling to room temperature, it was immersed in sodium carbonate solution at 75℃ and 125 r / min for 2.5 hours, filtered, washed with pure water until neutral, and dried at 90℃ for 11 hours to obtain the doped carbon fiber membrane. The remaining steps were the same as in Example 2.

[0081] Comparative Example 5:

[0082] The difference between the preparation method of the carbon fiber membrane for wastewater treatment in Comparative Example 5 and Example 2 lies in the difference in step (2). Step (2) is modified as follows: 0.35 parts by mass of magnesium-iron doped tricalcium phosphate sol, 2.5 parts by mass of polyacrylonitrile, 0.6 parts by mass of biochar, and 30 parts by mass of N,N-dimethylformamide are mixed evenly, stirred at 55°C and 350 r / min for 10 h, and sonicated for 2.5 h. After defoaming, a spinning solution is obtained; the spinning solution is prepared at a voltage of 17.5 kV, a flow rate of 1.3 ml / h, a receiving distance of 15 cm, a drum speed of 900 rpm, and a temperature of 3... Electrospinning was performed at 0°C and 40% humidity for 11 hours. The film was collected from the collecting drum and vacuum dried at 65°C for 11 hours. Pre-oxidation was carried out in air at a heating rate of 1.1°C / min to 265°C for 105 minutes, followed by natural cooling to room temperature. Carbonization was then carried out in nitrogen at a heating rate of 5.5°C / min to 950°C for 3.5 hours, followed by natural cooling to room temperature. The film was then immersed in a sodium carbonate solution at 75°C and 125 rpm for 2.5 hours, filtered, washed with pure water until neutral, and dried at 90°C for 11 hours to obtain the doped carbon fiber film. The remaining steps were the same as in Example 2.

[0083] Comparative Example 6:

[0084] The preparation method of carbon fiber membrane for wastewater treatment in Comparative Example 6 differs from that in Example 2 in that steps (3) and (4) are omitted, and step (2) is modified as follows: 0.35 parts by mass of magnesium-iron doped tricalcium phosphate sol, 2.5 parts by mass of polyacrylonitrile, 0.6 parts by mass of biochar, and 30 parts by mass of N,N-dimethylformamide are mixed evenly, stirred at 55°C and 350 r / min for 10 h, and sonicated for 2.5 h to remove bubbles to obtain a spinning solution; electrospinning is performed at a voltage of 17.5 kV, a flow rate of 1.3 ml / h, a receiving distance of 15 cm, a drum speed of 900 rpm, a temperature of 30°C, and a humidity of 40% for 11 h, and the solution is collected from the collecting drum. The film was vacuum dried at 65°C for 11 hours, then stretched along the parallel direction of the fiber arrangement at a stretching temperature of 135°C for 8 minutes with a stretching force of 1 N. After naturally cooling to room temperature, it was removed and pre-oxidized at 265°C for 105 minutes in air at a heating rate of 1.1°C / min. After naturally cooling to room temperature, it was carbonized at 950°C for 3.5 hours in nitrogen at a heating rate of 5.5°C / min. After naturally cooling to room temperature, it was immersed in a sodium carbonate solution at 75°C and 125 r / min for 2.5 hours, filtered, washed with pure water until neutral, and dried at 90°C for 11 hours to obtain a carbon fiber membrane for wastewater treatment. The remaining steps were the same as in Example 2.

[0085] Test Example 1:

[0086] Mechanical strength and biofilm attachment performance testing: The tensile strength and biofilm attachment amount of the prepared carbon fiber membrane for wastewater treatment were tested to evaluate its mechanical strength and biofilm attachment performance. The specific test methods are as follows:

[0087] Tensile strength: The tensile strength of the prepared carbon fiber membrane for wastewater treatment was tested in accordance with the standard GB / T 1040.3-2006. The prepared carbon fiber membrane for wastewater treatment was cut into type 2 specimens with a length of 150 mm and a width of 10 mm. The tensile strength was tested at room temperature on an Instron-1121 universal testing machine at a test speed of 5 mm / min. Five specimens were tested in parallel for each group, and the average value was recorded.

[0088] Biofilm formation: The prepared carbon fiber membrane for wastewater treatment was cut into 10cm long and 1cm wide samples to form carbon fiber membrane bundles with a mass of 2g. Thirty carbon fiber membrane bundles were fixed on a wooden stick and then immersed in activated sludge suspension. The bundles were cultured at 25℃ with aeration. The carbon fiber membrane bundles were removed, dried, and weighed at 24h and 7 days. The average mass of biofilm formation per gram of carbon fiber membrane for wastewater treatment was calculated. Five carbon fiber membrane bundles were taken for each sampling and weighed. The average value was recorded. The bundles were not returned after each weighing.

[0089] Preparation of activated sludge suspension: Activated sludge was taken from the bottom of the Fenhe River and cultured in simulated organic wastewater. It was cultured in a constant temperature container at 25℃ with aeration for one month. The solid concentration of the activated sludge suspension was adjusted to 4000 mg / L and the pH was adjusted to 7.8. The simulated organic wastewater composition was: peptone 0.48 g / L, beef extract 0.32 g / L, urea 0.08 g / L, sodium chloride 0.024 g / L, sodium dihydrogen phosphate 0.08 g / L, and potassium chloride 0.011 g / L.

[0090] The results are shown in Table 1.

[0091] Table 1

[0092] Tensile strength / MPa <![CDATA[24-hour film-forming amount / g·g -1 > <![CDATA[7-day film hanging amount / g·g -1 > Example 1 684.84 3.14 5.73 Example 2 691.28 3.21 5.86 Example 3 678.55 3.18 5.82 Comparative Example 1 685.44 2.91 5.43 Comparative Example 2 686.72 2.93 5.49 Comparative Example 3 702.19 2.52 4.84 Comparative Example 4 694.37 2.72 5.13 Comparative Example 5 584.26 3.19 5.79 Comparative Example 6 681.45 1.51 2.93

[0093] A comparison of the experimental data of Examples 1-3 and Comparative Examples 1-6 in Table 1 reveals that the carbon fiber membrane for wastewater treatment prepared by this invention has good tensile strength, high biofilm formation rate, and fast biofilm formation speed.

[0094] By comparing the data in the table, the data in Comparative Examples 1 and 2 show that the doping of magnesium and iron in tricalcium phosphate crystals promotes biofilm growth and the formation and attachment of extracellular polymers, thereby increasing the biofilm formation rate and amount.

[0095] By comparing the data in the table, the data in Comparative Example 3 shows that although the loading of magnesium-iron-doped tricalcium phosphate crystals in the doped carbon fiber membrane slightly reduces the mechanical strength of the carbon fiber membrane, it significantly improves biocompatibility, biofilm formation rate and amount, and promotes biofilm formation.

[0096] By comparing the data in the table, the data in Comparative Example 4 shows that the addition of biochar to the doped carbon fiber membrane improves the loading and coating of magnesium-iron doped tricalcium phosphate crystals, enhances the loading effect, reduces free loss, improves the amount of biofilm attached, and promotes the formation of biofilm.

[0097] By comparing the data in the table, the data in Comparative Example 5 shows that the hot stretching process of the fiber membrane obtained after electrospinning improves its orientation, makes it denser, and effectively improves its tensile strength.

[0098] By comparing the data in the table, the data in Comparative Example 6 shows that the deposition and coating of the polyamic acid layer effectively improves biocompatibility while avoiding the negative effects of increased local metal ion concentration caused by sudden release of metal ions on microbial adhesion and growth, thus further promoting the increase of biofilm.

[0099] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A carbon fiber membrane for wastewater treatment, characterized in that, The carbon fiber membrane for wastewater treatment is prepared by electrodepositing a polyamic acid layer onto a doped carbon fiber membrane in a polyamic acid emulsion. The doped carbon fiber film is prepared by electrospinning a mixture of magnesium-iron doped tricalcium phosphate sol, polyacrylonitrile, and biochar with N,N-dimethylformamide, followed by hot stretching, pre-oxidation, carbonization, and alkali washing. The magnesium-iron doped tricalcium phosphate sol is prepared by hydrolyzing triethyl phosphate and then adding calcium, magnesium, and iron solutions for aging.

2. The carbon fiber membrane for wastewater treatment according to claim 1, characterized in that, The polyamic acid emulsion is prepared by reacting 4,4'-diaminodiphenyl ether with pyromellitic anhydride and then adding triethylamine and methanol. The thickness of the polyamic acid layer is 100~200nm.

3. The carbon fiber membrane for wastewater treatment according to claim 1, characterized in that, The biochar is obtained by carbonizing biomass raw materials; The biomass raw materials include one or more of the following: rice straw, corn straw, wheat straw, peanut shells, walnut shells, coffee grounds, sugarcane bagasse, tea leaves, sawdust, fallen leaves, bamboo processing residues, algae, and distiller's grains.

4. A method for preparing a carbon fiber membrane for wastewater treatment according to any one of claims 1 to 3, characterized in that, The preparation steps include the following: (1) Mix pure water, ethanol and triethyl phosphate evenly, seal and stir at room temperature, add ammonia water, seal and stir, add calcium solution, magnesium solution and iron solution, stir after addition, and then let stand to age to obtain magnesium iron doped tricalcium phosphate sol. (2) Magnesium iron doped tricalcium phosphate sol, polyacrylonitrile, biochar and N,N-dimethylformamide are mixed evenly, stirred, sonicated and defoamed to obtain spinning solution; after electrospinning, the film is collected from the collecting roller, dried, stretched, pre-oxidized, carbonized, cooled, alkali washed and dried to obtain carbon fiber doped film. (3) Using polyamic acid emulsion as electrolyte, doped carbon fiber membrane as positive electrode and graphite as negative electrode, electrodeposition and drying are performed to obtain carbon fiber membrane for sewage treatment.

5. The method for preparing a carbon fiber membrane for wastewater treatment according to claim 4, characterized in that, In step (1), the amount of pure water added is 4 to 6 parts by mass, ethanol is 10 to 15 parts, triethyl phosphate is 13.48 to 20.22 parts, and ammonia is 0.14 to 0.21 parts; The molar ratio of triethyl phosphate to calcium ions in calcium solution, magnesium ions in magnesium solution, and iron ions in iron solution is 1:(1.35~1.4):(0.08~0.12):(0.02~0.03); The calcium solution, magnesium solution, and iron solution are added at a rate of 0.8~1.2 ml / min.

6. The method for preparing a carbon fiber membrane for wastewater treatment according to claim 4, characterized in that, In step (2), the amount of magnesium-iron doped tricalcium phosphate sol added is 0.3-0.4 parts by mass, polyacrylonitrile is 2-3 parts, biochar is 0.5-0.7 parts, N,N-dimethylformamide is 25-35 parts, the stirring temperature is 50-60℃, the stirring time is 8-12h, and the ultrasonic time is 2-3h.

7. The method for preparing a carbon fiber membrane for wastewater treatment according to claim 4, characterized in that, The electrospinning process parameters in step (2) are: voltage 17~18kV, flow rate 1.2~1.4ml / h, receiving distance 15~16cm, roller speed 800~1000rpm, temperature 25~35℃, humidity 35%~45%, and duration 10~12h.

8. The method for preparing a carbon fiber membrane for wastewater treatment according to claim 4, characterized in that, The process parameters for stretching in step (2) are: stretching along the parallel direction of fiber arrangement, stretching temperature of 130~140℃, stretching time of 5~10min, and stretching force of 0.75~1.25N; The pre-oxidation process parameters are as follows: under an air atmosphere, the temperature is increased to 260-270℃ at a heating rate of 1-1.2℃ / min for 90-120 min for pre-oxidation; The carbonization process parameters are as follows: under a nitrogen atmosphere, the temperature is increased to 900-1000℃ at a heating rate of 5-6℃ / min for 3-4 hours; The alkaline washing process parameters are as follows: immersion in sodium carbonate solution at 70~80℃ and 100~150r / min for 2~3 hours, followed by filtration and washing until neutral.

9. The method for preparing a carbon fiber membrane for wastewater treatment according to claim 4, characterized in that, The electrodeposition voltage in step (3) is 40~50V and the time is 8~12min.

10. The method for preparing a carbon fiber membrane for wastewater treatment according to claim 4, characterized in that, The polyamic acid emulsion in step (3) is prepared by mixing 1.84-2.76 parts of 4,4'-diaminodiphenyl ether and 30-40 parts of N,N-dimethylacetamide by mass, stirring at room temperature until completely dissolved, adding 2-3 parts of pyromellitic anhydride, stirring in an ice-water bath for 8-10 hours, stirring at room temperature for 10-12 hours, adding triethylamine at a molar ratio of (2-3):1 to the remaining carboxyl group, stirring at room temperature for 60-90 minutes, adding 80-100 parts of methanol, and continuing to stir at room temperature for 60-80 minutes.