Preparation method of nanofiber composite membrane for removing various pollutants in water

Abstract

The invention discloses a preparation method of a nanofiber composite membrane for removing various pollutants in water. Non-woven fabric is used as a substrate, and a polymer nanofiber membrane is deposited on the surface of the non-woven fabric to serve as a supporting layer by adopting an electrostatic spinning technology. The nanofiber composite membrane for removing various pollutants in water is obtained by depositing nanofibers on the surface of a polymer nanofiber membrane supporting layer by using a mixed aqueous solution of an auxiliary spinning agent / sodium alginate / diammonium hydrogen phosphate by adopting an electrostatic spinning technology and sequentially crosslinking through aqueous solutions of calcium ions and cobalt ions. The in-situ generated calcium phosphate improves the strength and swelling resistance of the hydrogel nanofiber. The obtained nanofiber composite membrane is good in hydrophilicity and resistant to pollution, emulsified oil in sewage is removed through interception, heavy metal ions in the sewage are removed through adsorption, peroxide is added into the sewage, and free radicals are generated under catalysis of cobalt ions in the nanofiber composite membrane to degrade organic pollutants in the water. The method has a good application prospect.

Description

Technical Field

[0001] The present invention relates to a method for preparing a nanofiber composite membrane for removing various pollutants in water, belonging to the fields of wastewater and sewage treatment and functional materials. Background Art

[0002] With the all-round development of industry and agriculture and the acceleration of the urbanization process, the components of pollutants in wastewater have gradually become more complex, the types of pollutants in water bodies have increased, posing a threat to the ecological system and increasing the treatment difficulty. Water pollution control has become an important research direction in the field of environmental protection. Among them, oily wastewater, as one of the main pollution sources, widely exists in industrial wastewater, domestic sewage and petrochemical emissions, seriously threatening the ecological system and human health.

[0003] Many treatment methods widely used for the separation of oil-water mixtures, including gravity separation, adsorption, flotation, biological treatment and electrochemical treatment, consume a large amount of energy during the separation process and have low separation efficiency. Therefore, there is an urgent need for innovative and sustainable methods to address the ongoing challenges associated with the treatment of emulsified oil wastewater. Membrane separation technology is a process that utilizes the selective permeability of a membrane to achieve the separation, concentration or purification of different substances under the action of an external driving force. Its basic principle is based on effects such as molecular size, solution diffusion and electrostatic repulsion, enabling the target substance to selectively permeate or be retained, thereby achieving the separation purpose. Due to its advantages such as high efficiency, energy conservation and sustainability, membrane separation technology has been widely applied in fields such as wastewater treatment, seawater desalination and biopharmaceuticals. However, traditional membrane materials are prone to pollutant adsorption or deposition during long-term use, resulting in membrane fouling, reducing the service life and increasing the operating cost. Therefore, the development of environmentally friendly membrane materials with excellent anti-fouling performance has become the focus of current research.

[0004] Manufacturing thin films using electrospinning technology has many significant advantages. Electrospun nanofiber membranes are high-flux membranes at low pressure due to their fully interconnected pore structure; they are known for their high porosity and controllable pore size distribution from sub-micron to micron. In addition, electrospun nanofibers can be functionalized to improve separation performance. However, the irreversible fouling of electrospun filtration membranes made of traditional materials often clogs the pores and reduces the flux. Superhydrophilic membranes provide a promising approach to improving the efficiency of the oily wastewater purification process. Hydrogels have received extensive attention due to their unique three-dimensional network structure, high hydrophilicity, biocompatibility and environmental friendliness

J.J.Membr.Sci.,2023,679:11

[0005] Heavy metals in sewage mainly enter water bodies through forms such as human pollution, geological erosion, and weathering. They are not easily metabolized in the biological chain and are easily bioaccumulated, seriously threatening the survival of humans and aquatic organisms and being key factors in teratogenesis and carcinogenesis. Currently, the main methods for treating heavy metal ions in water are: chemical methods, biological methods, and physicochemical methods [China Resources Comprehensive Utilization, 2008, 26(2): 22 - 25], etc. Zhao Kongyin et al. used sodium alginate and carboxymethyl chitosan as the main raw materials, dissolved them together with polymers for assisting spinning, pore formers, and reinforcing agents in water to prepare a spinning solution. Electrospinning technology was used to obtain nanofibers, which were crosslinked and formed with calcium ions to obtain porous nanofibers for heavy metal ion extraction [ZL201610546869.5].

[0006] Organic waste is a major aspect causing water pollution. There are various types and complex components of sulfamethazine in water bodies, which pose great harm to the environment and human beings. Traditional wastewater treatment methods include physical adsorption, chemical methods, biological methods, electrochemistry methods, etc. However, the treatment of refractory organic wastewater is currently very difficult and can no longer meet the increasingly high environmental protection and process requirements. The advanced oxidation process based on persulfate (PS-AOPs) has received extensive attention from researchers due to its excellent oxidation efficiency. PS-AOPs activates persulfate through radical oxidation (such as SO4· - ) and non-radical oxidation (such as singlet oxygen and direct electron transfer), which can effectively destroy the structure of sulfamethazine. Due to the advanced oxidation process based on persulfate, its longer radical lifetime (30 - 40 μs), higher oxidation potential (2.5 - 3.1 V), and wider pH response range, it is regarded as a highly potential technology. Single-atom catalysts (SACs) have the highest utilization efficiency for each metal atom and have excellent catalytic activity and selectivity in persulfate activation. Chen Min et al. first proposed a method for removing sulfamethazine by combining an alginate-based heterogeneous catalytic hydrogel membrane with cross-flow activation of peroxymonosulfate

Advanced Materials, 2024, 2311416

[0007] Aiming at problems such as traditional filter membranes being easily contaminated, resulting in a decline in separation efficiency, one membrane being unable to remove multiple pollutants simultaneously, and the low mechanical strength of alginate hydrogel nanofibers, the present invention reports a preparation method of a nanofiber composite membrane for removing multiple pollutants in water. The present invention uses non-woven fabric as the substrate and deposits a polymer nanofiber membrane on its surface as the support layer by electrospinning technology. The mixed aqueous solution of the co-spinning agent / sodium alginate / diammonium hydrogen phosphate is deposited on the surface of the polymer nanofiber membrane support layer by electrospinning technology to form nanofibers, and then cross-linked successively with aqueous solutions of calcium ions and cobalt ions to obtain a nanofiber composite membrane for removing multiple pollutants in water. The in-situ generated calcium phosphate improves the strength and anti-swelling performance of the hydrogel nanofibers. The nanofiber composite membrane obtained in the present invention has good hydrophilicity and anti-pollution performance. It intercepts and removes emulsified oil in sewage, adsorbs and removes heavy metal ions in sewage, and adds peroxides to the sewage. Under the catalysis of cobalt ions in the nanofiber composite membrane, free radicals are generated to degrade organic pollutants in water.

[0008] Adding a support layer can improve the overall mechanical properties and durability of the hydrogel film, preventing it from deforming or breaking during use. The nanofiber composite film obtained in the present invention has excellent anti-pollution performance, can effectively remove emulsified oil, heavy metal ions and various organic pollutants in water, and has good application prospects in the field of wastewater and sewage treatment. Summary of the Invention

[0009] Aiming at the problems that traditional filtration membranes are easily contaminated, resulting in a decrease in separation efficiency, one membrane cannot remove multiple pollutants at the same time, and the mechanical strength of alginate hydrogel nanofibers is low. The technical solution of the present invention for the above existing problems and deficiencies is to provide a preparation method of a nanofiber composite membrane for removing multiple pollutants in water.

[0010] A preparation method of a nanofiber composite membrane for removing multiple pollutants in water according to the present invention is characterized by including the following steps:

[0011] a) Modify the non-woven fabric by using plasma surface treatment technology to introduce hydrophilic functional groups on its surface to improve the hydrophilicity of the non-woven fabric; prepare a spinning solution of a polymer with dimethylformamide as the solvent, and use electrospinning technology to deposit a layer of polymer nanofiber membrane on the surface of the hydrophilic non-woven fabric treated by plasma as a support layer;

[0012] b) Dissolve sodium alginate with a mass percentage concentration of 0.2% - 3.0%, diammonium hydrogen phosphate with a mass percentage concentration of 0.1% - 5.0% and an auxiliary spinning agent with a mass percentage concentration of 0.2% - 5.0% together in deionized water, disperse evenly by ultrasonic wave, and obtain a spinning solution after degassing. Use electrospinning technology to deposit a layer of nanofiber membrane on the surface of the support layer obtained in step a);

[0013] c) Prepare an aqueous solution of soluble calcium salt with a mass percentage concentration of 0.5% - 5.0% as coagulation bath 1, and prepare an aqueous solution of cobalt chloride with a mass percentage concentration of 0.5% - 2.0% as coagulation bath 2;

[0014] d) Immerse the nanofiber membrane containing the support layer obtained in step b) into the coagulation bath 1 obtained in step c). Calcium ions coordinate with the carboxyl groups on sodium alginate to form calcium alginate hydrogel. Calcium ions react with diammonium hydrogen phosphate to in-situ generate calcium hydrogen phosphate in the calcium alginate hydrogel. The in-situ generated calcium hydrogen phosphate improves the strength and anti-swelling performance of the hydrogel nanofiber membrane;

[0015] e) Take out the hydrogel nanofiber membrane obtained in step d), wash away the residual calcium ions on the membrane surface with deionized water, and soak it in the coagulation bath 2 obtained in step c). Cobalt ions are loaded into the hydrogel nanofiber membrane through ion exchange and adsorption to obtain a nanofiber composite membrane for removing various pollutants in water, with a water contact angle of 1 to 10 degrees and good hydrophilicity;

[0016] f) Prepare an aqueous mixture solution containing emulsified oil with a mass percentage concentration of 0.1% - 5%, heavy metal ions with a mass percentage concentration of 0.01% - 0.5%, and sulfamethazine with a mass percentage concentration of 0.01% - 0.5% as complex sewage;

[0017] g) Assemble the nanofiber composite membrane obtained in step e) into a cross - flow filtration device. The rejection rate of emulsified oil in the complex sewage reaches 70% - 99.9%, and the flux reaches 1000 - 5000L m -2 h -1 bar -1 , thereby efficiently removing emulsified oil in the sewage. At the same time, the adsorption and removal rate of heavy metal ions by the nanofiber composite membrane in the cross - flow filtration device reaches 70 - 96%. After eluting the heavy metal ions from the nanofiber composite membrane adsorbed with heavy metal ions with dilute hydrochloric acid, it can be cross - linked again with calcium chloride aqueous solution and reused for the removal of emulsified oil and heavy metal ions;

[0018] h) Add peroxide to the complex sewage mainly containing sulfamethazine after removing emulsified oil and heavy metal ions, assemble the nanofiber composite membrane obtained in step e) into a cross - flow filtration device to filter the sewage. The peroxide generates free radicals under the catalysis of cobalt ions in the nanofiber composite membrane to degrade sulfamethazine in the sewage, and the degradation rate of sulfamethazine reaches 70% - 99.9% in 2 - 15 minutes.

[0019] The non - woven fabric in the present invention is any one of polyester non - woven fabric, polypropylene non - woven fabric, polyamide non - woven fabric, and polytetrafluoroethylene non - woven fabric; the polymer is any one of polyacrylonitrile, polyvinylidene fluoride, polyester, and polyhydroxybutyrate; the auxiliary spinning agent is any one of polyethylene oxide ether, polyvinyl alcohol, water - soluble cellulose, and sericin. The soluble calcium salt is any one or a mixture of two or more of calcium chloride, calcium dihydrogen phosphate, and calcium nitrate; the heavy metal ions are any one or a mixture of two or more of lead ions, copper ions, cadmium ions, and chromium ions; the sulfamethazine is one or more of sulfamethazine, methylisothiazolinone, tetracycline, and bisphenol A; the peroxide is one or more of hydrogen peroxide, peroxysulfate, persulfate, and peracetic acid. Detailed implementation mode

[0020] The specific embodiments of the present invention are described below, but the present invention is not limited by the embodiments.

[0021] Example 1.

[0022] a) The polyester non-woven fabric is modified by plasma surface treatment technology to introduce hydrophilic functional groups on its surface to improve the hydrophilicity of the polyester non-woven fabric; a spinning solution of polyacrylonitrile is prepared with dimethylformamide as the solvent, and an electrostatic spinning technology is used to deposit a layer of polyacrylonitrile nanofiber membrane on the surface of the hydrophilic polyester non-woven fabric after plasma treatment as a support layer;

[0023] b) Sodium alginate with a mass percentage concentration of 0.2%, diammonium hydrogen phosphate with a mass percentage concentration of 0.1%, and polyoxyethylene ether with a mass percentage concentration of 0.2% are dissolved in deionized water together, ultrasonically dispersed evenly, and degassed to obtain a spinning solution. An electrostatic spinning technology is used to deposit a layer of nanofiber membrane on the surface of the support layer obtained in step a);

[0024] c) Prepare an aqueous calcium chloride solution with a mass percentage concentration of 0.5% as coagulation bath 1, and prepare an aqueous cobalt chloride solution with a mass percentage concentration of 0.5% as coagulation bath 2;

[0025] d) The nanofiber membrane containing the support layer obtained in step b) is immersed in the coagulation bath 1 obtained in step c), and calcium ions coordinate with the carboxyl groups on sodium alginate to form calcium alginate hydrogel. Calcium ions react with diammonium hydrogen phosphate to in-situ generate calcium hydrogen phosphate in the calcium alginate hydrogel. The in-situ generated calcium hydrogen phosphate improves the strength and anti-swelling performance of the hydrogel nanofiber membrane;

[0026] e) Take out the hydrogel nanofiber membrane obtained in step d), wash the residual calcium ions on the membrane surface with deionized water, and immerse it in the coagulation bath 2 obtained in step c). Cobalt ions are loaded into the hydrogel nanofiber membrane through ion exchange and adsorption to obtain a nanofiber composite membrane for removing various pollutants in water. Its water contact angle is 1 degree and it has good hydrophilicity;

[0027] f) Prepare a mixture aqueous solution containing emulsified oil with a mass percentage concentration of 0.1%, lead ions with a mass percentage concentration of 0.01%, and sulfamethazine with a mass percentage concentration of 0.01% as complex sewage;

[0028] g) Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device. The interception rate of emulsified oil in the complex sewage reaches 70%, and the flux reaches 5000L m -2 h -1 bar -1, thus efficiently removing emulsified oil in sewage; meanwhile, the adsorption and removal rate of lead ions by the nanofiber composite membrane in the cross-flow filtration device reaches 70%. After eluting the lead ions from the nanofiber composite membrane adsorbed with lead ions with dilute hydrochloric acid, it can be cross-linked again with an aqueous calcium chloride solution and reused for the removal of emulsified oil and lead ions;

[0029] h) Add hydrogen peroxide to the complex sewage mainly containing sulfamethazine after removing emulsified oil and lead ions, assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device to filter the sewage. Hydrogen peroxide generates free radicals under the catalysis of cobalt ions in the nanofiber composite membrane to degrade sulfamethazine in the sewage, and the degradation rate of sulfamethazine reaches 70% in 15 minutes.

[0030] Example 2.

[0031] a) Modify the polypropylene non-woven fabric by plasma surface treatment technology to introduce hydrophilic functional groups on its surface to improve the hydrophilicity of the polypropylene non-woven fabric; prepare a spinning solution of polyvinylidene fluoride with dimethylformamide as the solvent, and use electrospinning technology to deposit a layer of polyvinylidene fluoride nanofiber membrane on the surface of the hydrophilic polypropylene non-woven fabric treated by plasma as the support layer;

[0032] b) Dissolve sodium alginate with a mass percentage concentration of 3.0%, diammonium hydrogen phosphate with a mass percentage concentration of 5.0%, and polyvinyl alcohol with a mass percentage concentration of 2.0% in deionized water, ultrasonically disperse evenly, and obtain a spinning solution after defoaming. Use electrospinning technology to deposit a layer of nanofiber membrane on the surface of the support layer obtained in step a);

[0033] c) Prepare an aqueous solution of calcium dihydrogen phosphate with a mass percentage concentration of 5.0% as coagulation bath 1, and prepare an aqueous solution of cobalt chloride with a mass percentage concentration of 2.0% as coagulation bath 2;

[0034] d) Immerse the nanofiber membrane containing the support layer obtained in step b) into the coagulation bath 1 obtained in step c). Calcium ions coordinate with the carboxyl groups on sodium alginate to form calcium alginate hydrogel, and calcium ions react with diammonium hydrogen phosphate to in-situ generate calcium hydrogen phosphate in the calcium alginate hydrogel. The in-situ generated calcium hydrogen phosphate improves the strength and anti-swelling performance of the hydrogel nanofiber membrane;

[0035] e) Take out the hydrogel nanofiber membrane obtained in step d), wash the residual calcium ions on the membrane surface with deionized water, and immerse it into the coagulation bath 2 obtained in step c). Cobalt ions are loaded into the hydrogel nanofiber membrane through ion exchange and adsorption to obtain a nanofiber composite membrane for removing various pollutants in water, with a water contact angle of 10 degrees and good hydrophilicity;

[0036] f) Prepare an aqueous solution of a mixture containing emulsified oil with a mass percentage concentration of 5%, copper ions with a mass percentage concentration of 0.5%, and methylisothiazolinone with a mass percentage concentration of 0.5% as complex sewage;

[0037] g) Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device. The rejection rate of emulsified oil in the complex sewage reaches 99.9%, and the flux reaches 1000 L m -2 h -1 bar -1 , thereby efficiently removing emulsified oil from the sewage. At the same time, the adsorption and removal rate of copper ions by the nanofiber composite membrane in the cross-flow filtration device reaches 96%. After eluting the copper ions adsorbed on the nanofiber composite membrane with dilute hydrochloric acid, it can be cross-linked again with an aqueous calcium chloride solution and reused for the removal of emulsified oil and copper ions;

[0038] h) Add persulfate to the complex sewage mainly containing methylisothiazolinone after removing emulsified oil and copper ions. Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device to filter the sewage. Persulfate generates free radicals under the catalysis of cobalt ions in the nanofiber composite membrane to degrade methylisothiazolinone in the sewage, and the degradation rate of methylisothiazolinone reaches 99.9% in 15 minutes.

[0039] Example 3.

[0040] a) Modify the polyamide non-woven fabric using plasma surface treatment technology to introduce hydrophilic functional groups on its surface to improve the hydrophilicity of the non-woven fabric. Prepare a spinning solution of polyester using dimethylformamide as a solvent, and deposit a layer of polyester nanofiber membrane on the surface of the hydrophilic polyamide non-woven fabric treated by plasma using electrospinning technology as a support layer;

[0041] b) Dissolve sodium alginate with a mass percentage concentration of 1.0%, diammonium hydrogen phosphate with a mass percentage concentration of 1.5%, and water-soluble cellulose with a mass percentage concentration of 1.0% in deionized water, disperse evenly by ultrasonic treatment, and obtain a spinning solution after degassing. Deposit a layer of nanofiber membrane on the surface of the support layer obtained in step a) using electrospinning technology;

[0042] c) Prepare an aqueous solution of calcium nitrate with a mass percentage concentration of 3.0% as coagulation bath 1, and prepare an aqueous solution of cobalt chloride with a mass percentage concentration of 1.0% as coagulation bath 2;

[0043] d) Immerse the nanofiber membrane containing the support layer obtained in step b) into the coagulation bath 1 obtained in step c). Calcium ions coordinate with the carboxyl groups on sodium alginate to form calcium alginate hydrogel. Calcium ions react with diammonium hydrogen phosphate to in-situ generate calcium hydrogen phosphate in the calcium alginate hydrogel. The in-situ generated calcium hydrogen phosphate improves the strength and anti-swelling performance of the hydrogel nanofiber membrane;

[0044] e) Take out the hydrogel nanofiber membrane obtained in step d), wash the residual calcium ions on the membrane surface with deionized water, and immerse it into the coagulation bath 2 obtained in step c). Cobalt ions are loaded into the hydrogel nanofiber membrane through ion exchange and adsorption to obtain a nanofiber composite membrane for removing various pollutants in water. Its water contact angle is 4 degrees and it has good hydrophilicity;

[0045] f) Prepare an aqueous mixture solution containing 0.5% by mass concentration of emulsified oil, 0.2% by mass concentration of cadmium ions and 0.05% by mass concentration of tetracycline as complex sewage;

[0046] g) Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device. The rejection rate of emulsified oil in the complex sewage reaches 98%, and the flux reaches 4000L m -2 h -1 bar -1 , thereby efficiently removing emulsified oil in the sewage. At the same time, the adsorption removal rate of cadmium ions by the nanofiber composite membrane in the cross-flow filtration device reaches 92%. After eluting cadmium ions from the nanofiber composite membrane adsorbed with cadmium ions with dilute hydrochloric acid, it can be cross-linked again with calcium chloride aqueous solution and reused for the removal of emulsified oil and cadmium ions;

[0047] h) Add persulfate to the complex sewage mainly containing tetracycline after removing emulsified oil and cadmium ions. Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device to filter the sewage. Persulfate generates free radicals under the catalysis of cobalt ions in the nanofiber composite membrane to degrade tetracycline in the sewage, and the degradation rate of tetracycline reaches 95% in 2 minutes.

[0048] Example 4.

[0049] a) Modify the polytetrafluoroethylene non-woven fabric by plasma surface treatment technology to introduce hydrophilic functional groups on its surface to improve the hydrophilicity of the non-woven fabric. Prepare a spinning solution of polyhydroxybutyrate with dimethylformamide as the solvent, and deposit a layer of polyhydroxybutyrate nanofiber membrane on the surface of the plasma-treated hydrophilic polytetrafluoroethylene non-woven fabric as the support layer by electrospinning technology;

[0050] b) Dissolve sodium alginate with a mass percentage concentration of 2.0%, diammonium hydrogen phosphate with a mass percentage concentration of 1.0%, and sericin with a mass percentage concentration of 2.0% together in deionized water, ultrasonically disperse them evenly, and obtain a spinning solution after defoaming. Use the electrospinning technique to deposit a nanofiber membrane on the surface of the support layer obtained in step a);

[0051] c) Prepare an aqueous solution of calcium chloride and calcium nitrate with a mass percentage concentration of 3.0% as coagulation bath 1, and prepare an aqueous solution of cobalt chloride with a mass percentage concentration of 2.0% as coagulation bath 2;

[0052] d) Immerse the nanofiber membrane containing the support layer obtained in step b) into the coagulation bath 1 obtained in step c). Calcium ions coordinate with the carboxyl groups on sodium alginate to form calcium alginate hydrogel. Calcium ions react with diammonium hydrogen phosphate to in-situ generate calcium hydrogen phosphate in the calcium alginate hydrogel. The in-situ generated calcium hydrogen phosphate improves the strength and anti-swelling performance of the hydrogel nanofiber membrane;

[0053] e) Take out the hydrogel nanofiber membrane obtained in step d), wash the residual calcium ions on the membrane surface with deionized water, and immerse it into the coagulation bath 2 obtained in step c). Cobalt ions are loaded into the hydrogel nanofiber membrane through ion exchange and adsorption to obtain a nanofiber composite membrane for removing various pollutants in water. Its water contact angle is 2 degrees, showing good hydrophilicity;

[0054] f) Prepare a mixed aqueous solution containing emulsified oil with a mass percentage concentration of 0.5%, chromium ions with a mass percentage concentration of 0.1%, and bisphenol A with a mass percentage concentration of 0.01% as complex sewage;

[0055] g) Assemble the nanofiber composite membrane obtained in step e) into a crossflow filtration device. The rejection rate of emulsified oil in the complex sewage reaches 99%, and the flux reaches 4000L m -2 h -1 bar -1 , thereby efficiently removing emulsified oil in the sewage. At the same time, the adsorption and removal rate of chromium ions by the nanofiber composite membrane in the crossflow filtration device reaches 96%. After eluting the chromium ions from the nanofiber composite membrane adsorbed with chromium ions with dilute hydrochloric acid, it can be crosslinked again with calcium chloride aqueous solution and reused for the removal of emulsified oil and chromium ions;

[0056] h) Add peracetic acid to the complex sewage mainly containing bisphenol A after removing emulsified oil and chromium ions. Assemble the nanofiber composite membrane obtained in step e) into a crossflow filtration device to filter the sewage. Peracetic acid generates free radicals under the catalysis of cobalt ions in the nanofiber composite membrane to degrade bisphenol A in the sewage, and the degradation rate of bisphenol A reaches 90% in 2 minutes.

[0057] Example 5.

[0058] a) The polytetrafluoroethylene non-woven fabric is modified by plasma surface treatment technology to introduce hydrophilic functional groups on its surface to improve the hydrophilicity of the non-woven fabric; a spinning solution of polyhydroxybutyrate is prepared with dimethylformamide as the solvent, and a layer of polyhydroxybutyrate nanofiber membrane is deposited on the surface of the hydrophilic polytetrafluoroethylene non-woven fabric after plasma treatment by electrospinning technology as a support layer;

[0059] b) Sodium alginate with a mass percentage concentration of 1.0%, diammonium hydrogen phosphate with a mass percentage concentration of 1.0%, and polyoxyethylene ether with a mass percentage concentration of 2.0% are dissolved in deionized water together, ultrasonically dispersed evenly, and degassed to obtain a spinning solution. A layer of nanofiber membrane is deposited on the surface of the support layer obtained in step a) by electrospinning technology;

[0060] c) An aqueous solution of calcium chloride with a mass percentage concentration of 3.0% is prepared as coagulation bath 1, and an aqueous solution of cobalt chloride with a mass percentage concentration of 2.0% is prepared as coagulation bath 2;

[0061] d) The nanofiber membrane containing the support layer obtained in step b) is immersed in the coagulation bath 1 obtained in step c). Calcium ions coordinate with the carboxyl groups on sodium alginate to form calcium alginate hydrogel. Calcium ions react with diammonium hydrogen phosphate to in-situ generate calcium hydrogen phosphate in the calcium alginate hydrogel. The in-situ generated calcium hydrogen phosphate improves the strength and anti-swelling performance of the hydrogel nanofiber membrane;

[0062] e) The hydrogel nanofiber membrane obtained in step d) is taken out, and the residual calcium ions on the membrane surface are washed away with deionized water. It is immersed in the coagulation bath 2 obtained in step c), and cobalt ions are loaded into the hydrogel nanofiber membrane through ion exchange and adsorption to obtain a nanofiber composite membrane for removing various pollutants in water. Its water contact angle is 5 degrees, and it has good hydrophilicity;

[0063] f) A mixture aqueous solution containing 0.5% by mass of emulsified oil, 0.1% by mass of chromium ions, 0.1% by mass of lead ions, 0.01% by mass of methylisothiazolinone, and 0.01% by mass of bisphenol A is prepared as complex sewage;

[0064] g) The nanofiber composite membrane obtained in step e) is assembled into a cross-flow filtration device, and the interception rate of emulsified oil in the complex sewage reaches 98%, and the flux reaches 4500L m -2 h -1 bar -1, thus efficiently removing emulsified oil in sewage; at the same time, the adsorption and removal rate of chromium ions by the nanofiber composite membrane in the cross-flow filtration device reaches 95%, and the adsorption and removal rate of lead ions reaches 96%. After eluting the nanofiber composite membrane adsorbed with chromium ions and lead ions with dilute hydrochloric acid, it can be cross-linked again with an aqueous calcium chloride solution and reused for the removal of emulsified oil, chromium ions and lead ions;

[0065] h) Add persulfate and peracetic acid to the complex sewage mainly containing bisphenol A and methylisothiazolinone after removing emulsified oil, chromium ions and lead ions. Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device to filter the sewage. Persulfate and peracetic acid generate free radicals under the catalysis of cobalt ions in the nanofiber composite membrane to degrade bisphenol A and methylisothiazolinone in the sewage. The degradation rate of bisphenol A reaches 95% and the degradation rate of methylisothiazolinone reaches 96% in 5 minutes.

Claims

1. A preparation method of a nanofiber composite membrane for removing various pollutants in water, characterized in that It includes the following steps: a) Modify the non-woven fabric by using plasma surface treatment technology to introduce hydrophilic functional groups on its surface to improve the hydrophilicity of the non-woven fabric; prepare a spinning solution of polymer with dimethylformamide as the solvent, and deposit a layer of polymer nanofiber membrane on the surface of the hydrophilic non-woven fabric after plasma treatment as the support layer by using electrospinning technology; b) Dissolve sodium alginate with a mass percentage concentration of 0.2% - 3.0%, diammonium hydrogen phosphate with a mass percentage concentration of 0.1% - 5.0%, and an auxiliary spinning agent with a mass percentage concentration of 0.2% - 5.0% together in deionized water, disperse evenly by ultrasonic treatment, and obtain a spinning solution after degassing. Deposit a layer of nanofiber membrane on the surface of the support layer obtained in step a) by using electrospinning technology; c) Prepare an aqueous solution of soluble calcium salt with a mass percentage concentration of 0.5% - 5.0% as coagulation bath 1, and prepare an aqueous solution of cobalt chloride with a mass percentage concentration of 0.5% - 2.0% as coagulation bath 2; d) Immerse the nanofiber membrane containing the support layer obtained in step b) into the coagulation bath 1 obtained in step c). Calcium ions coordinate with the carboxyl groups on sodium alginate to form calcium alginate hydrogel. Calcium ions react with diammonium hydrogen phosphate to in-situ generate calcium hydrogen phosphate in the calcium alginate hydrogel. The in-situ generated calcium hydrogen phosphate improves the strength and anti-swelling performance of the hydrogel nanofiber membrane; e) Take out the hydrogel nanofiber membrane obtained in step d), wash the residual calcium ions on the membrane surface with deionized water, and immerse it into the coagulation bath 2 obtained in step c). Cobalt ions are loaded into the hydrogel nanofiber membrane through ion exchange and adsorption to obtain a nanofiber composite membrane for removing various pollutants in water, with a water contact angle of 1 - 10 degrees and good hydrophilicity; f) Prepare a mixture aqueous solution containing emulsified oil with a mass percentage concentration of 0.1% - 5%, heavy metal ions with a mass percentage concentration of 0.01% - 0.5%, and organic pollutants with a mass percentage concentration of 0.01% - 0.5% as complex sewage; g) Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device, with the rejection rate of emulsified oil in complex sewage reaching 70% - 99.9% and the flux reaching 1000 - 5000 L m -2 h -1 bar -1 , thereby efficiently removing emulsified oil from sewage; meanwhile, the adsorption and removal rate of heavy metal ions by the nanofiber composite membrane in the cross-flow filtration device reaches 70 - 96%. After eluting the heavy metal ions from the nanofiber composite membrane adsorbed with heavy metal ions with dilute hydrochloric acid, it can be cross-linked again with an aqueous calcium chloride solution and reused for the removal of emulsified oil and heavy metal ions; h) Add hydrogen peroxide to the complex sewage from which emulsified oil and heavy metal ions have been removed and mainly contains organic pollutants. Assemble the nanofiber composite membrane obtained in step e) into a cross-flow filtration device to filter the sewage. Hydrogen peroxide generates free radicals under the catalysis of cobalt ions in the nanofiber composite membrane to degrade the organic pollutants in the sewage, and the degradation rate of organic pollutants reaches 70% - 99.9% in 2 - 15 minutes.

2. The preparation method of a nanofiber composite membrane for removing various pollutants in water according to claim 1, characterized in that The non-woven fabric is any one of polyester non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and polytetrafluoroethylene non-woven fabric.

3. The preparation method of a nanofiber composite membrane for removing multiple pollutants in water according to claim 1, characterized in that The polymer is any one of polyacrylonitrile, polyvinylidene fluoride, polyester, and polyhydroxybutyrate.

4. The preparation method of a nanofiber composite membrane for removing various pollutants in water according to claim 1, characterized in that The auxiliary spinning agent is any one of polyoxyethylene ether, polyvinyl alcohol, water-soluble cellulose, and sericin.

5. The preparation method of a nanofiber composite membrane for removing multiple pollutants in water according to claim 1, characterized in that The soluble calcium salt is any one of calcium chloride, calcium dihydrogen phosphate, calcium nitrate, or a mixture of two or more of them.

6. The preparation method of the nanofiber composite membrane for removing various pollutants in water according to claim 1, characterized in that The heavy metal ions are any one of lead ions, copper ions, cadmium ions, chromium ions, or a mixture of two or more of them.

7. The preparation method of a nanofiber composite membrane for removing multiple pollutants in water according to claim 1, characterized in that The organic pollutants described are one or more of sulfamerazine, methylisothiazolinone, tetracycline, and bisphenol A.

8. The preparation method of a nanofiber composite membrane for removing various pollutants in water according to claim 1, characterized in that The peroxides described are one or more of hydrogen peroxide, monopersulfate, dipersulfate, and peracetic acid.