CN115029867A

CN115029867A - Preparation method of extracellular polymer composite nanofiber membrane

Info

Publication number: CN115029867A
Application number: CN202210713324.4A
Authority: CN
Inventors: 曹达啟; 韩佳霖; 唐凯; 刘辉; 刘小旦; 郝晓地
Original assignee: Beijing University of Civil Engineering and Architecture
Current assignee: Beijing University of Civil Engineering and Architecture
Priority date: 2022-06-22
Filing date: 2022-06-22
Publication date: 2022-09-09

Abstract

The invention relates to a preparation method of an extracellular polymeric substance composite nanofiber membrane, which comprises a substrate layer, a middle layer and an upper sealing layer, wherein the preparation method comprises the following steps: s1, weighing polyvinylidene fluoride powder, drying in an oven, adding the dried polyvinylidene fluoride powder into an organic solvent mixed by dimethylacetamide and acetone, and then heating and stirring to obtain polyvinylidene fluoride spinning solution; s2: preparing a substrate layer by an electrostatic spinning machine; s3: adding polyvinyl alcohol particles into deionized water to prepare a polyvinyl alcohol solution; s4: adding extracellular polymer powder into deionized water, heating and stirring, adding polyvinyl alcohol solution, and preparing extracellular polymer/polyvinyl alcohol spinning solution; s5: preparing the intermediate layer by an electrostatic spinning machine; s6: and pumping the prepared polyvinylidene fluoride spinning solution into an injector, and preparing an upper sealing layer through an electrostatic spinning machine to further prepare the extracellular polymeric substance composite nanofiber membrane.

Description

Preparation method of extracellular polymer composite nanofiber membrane

Technical Field

The invention relates to a preparation method of an extracellular polymer composite nanofiber membrane.

Background

With the promotion of urbanization in China and the improvement of sewage treatment facilities, according to published data statistics of 'annual book for urban and rural construction statistics in 2020', the urban sewage treatment scale is over 2.3 hundred million m after 2020 ³ D, the amount of sludge produced by the method reaches 6163 ten thousand meters ³ Year (calculated as water content 80%). The sludge treatment and disposal process not only generates a large amount of energy consumption and drug consumption, but also causes a large amount of greenhouse gas emission approaching the 'useless' end landfill disposal mode, which is contrary to the 'double carbon' purpose. However, as an important byproduct of sewage treatment, besides a large amount of organic matters and pollutants in sewage, a large amount of potential resources are also stored in excess sludge. For example, the energy consumption requirement of 60-80% of sewage treatment plants can be met by recycling biomass energy and resources of sludge in European and American countries. The method increases carbon compensation by energy recovery and product utilization, converts sludge treatment into energy and resource manufacturing, and is undoubtedly a low-carbon sustainable inevitable choice.

Extracellular Polymeric Substance (EPS) is an important component of excess sludge which is a by-product of sewage treatment, accounts for about 10% to 40% of the dry weight of sludge, is usually derived from cell autolysis, cell secretion, cell surface shedding and the like of microorganisms, and mainly comprises polysaccharides, proteins, nucleic acids, lipids, metal ions and the like. The substances form a compact network structure through electrostatic acting force, hydrogen bond combination, ion attraction, biochemistry and other actions, can be used as a protective layer of microorganisms, resists the invasion of external heavy metals, toxic compounds and the like, and has good biodegradability, biocompatibility and bioactivity. The complex structures with different combination modes are obtained through different combination modes, can be used as heavy metal adsorbents, fireproof materials, biological flocculants, soil conditioners and the like, and has extremely high utilization value. Meanwhile, the removal of EPS can improve the dehydration property of sludge so as to be beneficial to subsequent sludge treatment and disposal, and a breakthrough is opened for the difficulty in handling huge sludge amount. Therefore, the method replaces the high polymer industrially synthesized in the market with the extracted and recycled matter of the excess sludge, is an excellent strategy for realizing the regeneration of the sludge waste to the high value-added matter nirvana, and powerfully promotes the sludge resource utilization.

EPS has a density close to that of water and is in a colloidal state after being dissolved in water, so that the EPS has limitation in practical application. For example, when used as a heavy metal adsorbing material, the colloidal substance formed after adsorbing heavy metals in water is difficult to separate from water; when applied to fire-retardant coating film materials, EPS is difficult to bond with building materials. Therefore, it is necessary to promote the high value-added application of EPS by other polymer modification or mosaic carrier forms and widen the practical application field. On the other hand, EPS is an important component of excess sludge which is a by-product of sewage treatment, and is a renewable substance which has good biological property and is derived from a wide range and low cost. Taking the heavy metal adsorbent as an example, compared with various emerging nano adsorbents, although the latter can achieve high-efficiency adsorption effect, the heavy metal adsorbent is difficult to leave a laboratory in a short period due to high cost and extremely complex synthesis or extraction process.

In the field of bioengineering, membrane technology has been widely used in the research of separation and concentration of substances, filtration and adsorption of toxic and harmful substances, and the like. Meanwhile, as a good carrier, in recent years, many researches have been made on film modification and film development by introducing chitosan, graphene oxide, carbon nanotubes and new nanoparticles in the forms of embedding in a film matrix, embedding, surface coating, grafting and the like, so as to impart characteristics of an additive to the base film and enhance the specificity of a functional film.

The electrostatic spinning technology is a mature and novel film-making method. Under the action of a high-voltage electrostatic field, the prepared nanofiber membrane has a three-dimensional through structure, so that the membrane impedance is reduced, the membrane pollution is reduced, and the special structure and the free nanometer gap formed by transverse and longitudinal overlapping of the nanofibers provide conditions for specific modification of the surface and the interior of the membrane. Based on the electrostatic spinning technology, the invention develops the extracellular polymeric substance composite nanofiber membrane by using the natural high polymer material EPS, and realizes high-value utilization of sludge byproducts.

Disclosure of Invention

In view of the above problems in the prior art, the main object of the present invention is to provide a method for preparing an extracellular polymeric substance composite nanofiber membrane.

The technical scheme of the invention is as follows:

a preparation method of an extracellular polymeric compound nanofiber membrane, which comprises a substrate layer, a middle layer and an upper sealing layer, the preparation method comprising the following steps:

s1, weighing a certain amount of polyvinylidene fluoride (PVDF) powder, drying the PVDF powder in a 60 ℃ oven for 2 hours, removing excessive moisture, adding the dried PVDF powder into an organic solvent mixed by dimethylacetamide and acetone, then placing the mixture in a water bath constant-temperature heating pot for heating and stirring until the PVDF powder is completely dissolved and the solution is transparent and clear, and obtaining a homogeneous PVDF spinning solution, wherein the mass percentage of PVDF is 10-25%;

s2: starting an electrostatic spinning machine, preheating, setting experiment temperature and experiment humidity, sucking 1/2 volume of the prepared PVDF spinning solution into an injector, fixing the injector on a solution feeding device of the electrostatic spinning machine, selecting a corresponding injection needle for injection, and preparing a substrate layer through the electrostatic spinning machine;

s3: adding a certain amount of polyvinyl alcohol (PVA) particles into deionized water, placing the mixture into a water bath heating pot, heating and stirring the mixture at a constant temperature until the PVA particles are completely dissolved, and obtaining a uniform PVA solution;

s4: adding a certain amount of EPS powder into deionized water, placing the EPS powder into a water bath heating pot, heating and stirring at a constant temperature until the EPS powder is completely dissolved, adding the prepared PVA solution, continuing heating and stirring at a constant temperature in the water bath heating pot, and then placing the mixture in a vacuum environment for degassing treatment to obtain an EPS/PVA spinning solution;

s5: starting an electrostatic spinning machine, preheating, setting an experiment temperature and an experiment humidity, pumping the prepared EPS/PVA spinning solution into an injector, fixing the injector on a solution feeding device of the electrostatic spinning machine, selecting a 20G injection needle for injection, and preparing an intermediate layer through the electrostatic spinning machine;

s6: and pumping the residual 1/2 volume amount of the prepared PVDF spinning solution into an injector, fixing the injector on a solution feeding device of an electrostatic spinning machine, selecting a corresponding injection needle for injection, preparing an upper sealing layer through the electrostatic spinning machine, and further preparing the EPS composite nanofiber membrane.

The intermediate layer can also be prepared by adopting a coating method, and specifically comprises the following steps: preheating a film coating machine to 35 ℃, pouring EPS/PVA spinning solution to one side of a base layer paved on the film coating machine, selecting a 10-micrometer wire bar as a coating bar, operating at a speed of 20mm/s and a running distance of 300mm of the length of the base layer, pushing the EPS/PVA spinning solution from one side of the base layer to the other side at a constant speed, and drying in a 70 ℃ oven for 30min to obtain an intermediate layer of the EPS composite nanofiber membrane prepared by the film coating method.

The intermediate layer can also be prepared by adopting a suction filtration method, and the preparation method specifically comprises the following steps: fixing the base layer on a sand core of a filter flask, fixing a Buchner funnel by using a fixing clamp, starting a vacuum pump to vacuumize, pouring the EPS solution into the Buchner funnel, and depositing the EPS solution on the surface and in the hole of the base layer through vacuum filtration; and after the suction filtration is finished, placing the base layer deposited with the EPS in a 70 ℃ drying oven for drying for 30min to obtain the intermediate layer of the EPS composite nanofiber membrane prepared by the suction filtration method.

In the step S1, when the organic solvent is placed in a water bath constant temperature heating pot for heating and stirring, the heating temperature is 60 ℃, and the stirring speed and the stirring time are 350rpm and 4h respectively.

In the step S2, the experiment temperature is 21.5-26.5 ℃, and the experiment humidity is 38-42%.

In the step S3, a certain amount of PVA is added into deionized water, and the mixture is placed in a water bath heating pan for heating and stirring at a constant temperature, wherein the heating temperature is 80 ℃, and the stirring speed and the stirring time are respectively 500rpm and 2 h.

In the step S4, a certain amount of EPS powder is added into deionized water, and the mixture is placed in a water bath heating pan for heating and stirring at a constant temperature, wherein the heating temperature is 30 ℃, and the stirring speed and the stirring time are 500rpm and 2h, respectively.

In the step S4, the prepared PVA solution is added, and while heating and stirring are continuously performed in a water bath heating pan at a constant temperature, the heating temperature is 30 ℃, and the stirring speed and the stirring time are 500rpm and 3 hours, respectively.

In the step S5, the experimental temperature is 35 ℃ and the experimental humidity is 30%.

In the EPS/PVA spinning solution, the mass percent of the EPS is 1.0%, and the mass percent of the PVA is 10%.

In the step S2, when the base layer of the EPS composite nanofiber membrane is prepared by using the electrostatic spinning machine, the working parameters of the electrostatic spinning machine are as follows: the spinning time is 1.25h, the plug flow speed is 4mL/h, the translation speed is 500mm/min, the receiving distance is 20cm, the rotating speed of a receiver is 100/min, and the positive/negative voltage is +8.0kV/-2.5 kV.

In the step S5, when the EPS/PVA intermediate layer is prepared by the electrostatic spinning machine, the working parameters of the electrostatic spinning machine are as follows: the spinning time is 2.5h, the plug flow speed is 4mL/h, the translation speed is 300mm/min, the receiving distance is 15cm, the rotating speed of a receiver is 140/min, and the positive/negative voltage is +22.5kV/-2.5 kV.

In the step S6, when the upper sealing layer of the EPS composite nanofiber membrane is prepared by the electrostatic spinning machine, the working parameters of the electrostatic spinning machine are the same as those in the step S2.

The invention has the following advantages and beneficial effects: according to the preparation method of the EPS composite nanofiber membrane provided by the embodiment of the invention, the base layer and the upper sealing layer of the extracellular polymer composite nanofiber membrane are prepared by an electrostatic spinning method, namely, the EPS is embedded by a high-porosity nanofiber carrier, and a sufficient exchange channel is provided for material transmission by virtue of a net structure formed by nanofibers, so that the material characteristics of the EPS are greatly exerted.

Drawings

Fig. 1 is a flow chart of a preparation process of an extracellular polymeric substance composite nanofiber membrane provided by an embodiment of the present invention.

Fig. 2 is a schematic diagram of an intermediate layer of an extracellular polymeric substance composite nanofiber membrane prepared by a coating method according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of an intermediate layer of an extracellular polymeric substance composite nanofiber membrane prepared by a suction filtration method according to an embodiment of the present invention.

Fig. 4 is a schematic diagram illustrating a pure water flux of the extracellular polymeric substance composite nanofiber membrane according to an embodiment of the present invention.

Fig. 5 is a schematic diagram of a water contact angle of a nanofiber membrane provided in an embodiment of the present invention.

Fig. 6 is a schematic diagram of a water contact angle of the extracellular polymeric substance composite nanofiber membrane provided by an embodiment of the present invention.

Fig. 7 is a schematic diagram of pore size distribution of a nanofiber membrane and an extracellular polymeric substance composite nanofiber membrane provided by an embodiment of the present invention.

FIG. 8 shows Pb in the extracellular polymeric substance composite nanofiber membrane prepared by using the unmodified nanofiber membrane and the electrospinning method, the coating method and the suction filtration method in the embodiment of the invention ²⁺ Schematic diagram of the removal rate of (a).

FIG. 9 shows Pb accompanying filtration in the case of using the unmodified nanofiber membrane and the extracellular polymeric substance composite nanofiber membrane prepared by the electrospinning method, the coating method and the suction filtration method according to the embodiment of the present invention ²⁺ Schematic of the cumulative adsorption amount of (a).

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should also be noted that, unless otherwise explicitly stated or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The invention will be further described with reference to the drawings and specific embodiments.

As shown in fig. 1 to 9: the preparation method of the extracellular polymeric substance composite nanofiber membrane comprises a substrate layer, a middle layer and an upper sealing layer, and comprises the following steps:

the method comprises the following steps: firstly, preparing spinning solution of a basal layer and an upper sealing layer of the extracellular polymeric substance composite nanofiber membrane. Weighing a certain amount of PVDF powder, drying in an oven at 60 ℃ for 2h, and removing excessive water. Mixing a fiber solvent dimethylacetamide and an organic solvent acetone according to a certain volume ratio, adding dried PVDF powder into the mixed organic solvent, adjusting the material ratio to 10-25 wt%, and stirring for 4 hours at a set heating temperature of 60 ℃ and 350rpm in a water bath constant-temperature heating pot. Completely dissolving the PVDF powder, and obtaining a homogeneous PVDF spinning solution by transparent and clear solution; controlling the pH, conductivity, viscosity, surface tension, etc. of the casting solution. And removing bubbles in the spinning solution by using a circulating water type multipurpose vacuum pump.

The spinning solution determines the basic performance of the membrane, so that high-molecular polymers are selected, including synthetic polymers such as PVDF, PVA and polysulfone, and natural polymers such as EPS and sodium alginate. Meanwhile, the corresponding fiber solvent is selected, and the material proportion and the optimal conditions of the casting solution are optimized.

Step two: and (4) preparing a substrate layer by electrostatic spinning. And starting the electrostatic spinning machine, preheating for 30min, and setting the experiment temperature and humidity. Taking the spinning solution prepared in the step one, drawing 1/2 volume into an injector, fixing the injector on a liquid feeding device, selecting a needle head with a proper size (for example, a 20G needle head with an inner diameter of 0.6mm can be replaced by a 22-24G needle head), and fixing a high-voltage electrostatic clamp at the needle head. The push flow speed of the injector, the translation speed of the liquid feeder, the rotating speed of the roller receiver, the receiving distance, and the high-voltage electrostatic voltages of the anode and the cathode are set, and specific operating parameters are shown in table 1. The electrostatic spinning process is the key for preparing the high-flux and high-mechanical-strength fiber membrane, and the relationship between the spinning parameters and the diameters of the nano fibers and the pore diameters of the nano fiber membrane should be optimized.

Preparing a multi-channel base layer with certain mechanical strength through the first step and the second step so as to bear EPS. Therefore, appropriate polymers and organic solvents are optimally selected to prepare a stable substrate, and spinning parameters are optimized to regulate and control the aperture of the substrate film; thus, a higher water flux is ensured and the loss of EPS is prevented. A suitable commercial fiber film may also be selected as the substrate layer.

Step three: an EPS doped interlayer is prepared. The EPS doping process can be realized by various means, such as an electrostatic spinning method, a suction filtration method, a coating method, a hot pressing method and the like. The specific operation is as follows:

firstly, preparing EPS/PVA spinning solution. Adding 2.25g of PVA into 10mL of deionized water, heating and stirring for 2h at 500rpm in a water bath heating pot at a constant temperature of 80 ℃ until PVA particles are completely dissolved to obtain a uniform PVA solution. 0.225g of EPS powder is added into 10mL of deionized water, and the mixture is heated and stirred for 2h at 500rpm in a water bath heating pot at a constant temperature of 30 ℃ until the EPS powder is completely dissolved. Mixing the two solutions in a water bath heating pot, keeping the temperature constant at 30 ℃, and mixing and stirring at 500rpm for 3 hours. A large amount of bubbles are easily stirred into the EPS/PVA mixed solution in the stirring process, so the EPS/PVA mixed solution is subjected to degassing treatment in a vacuum environment before spinning. Another 10mL syringe is taken to inject the spinning solution, the syringe is fixed on a liquid feeder, a 20G needle is selected, the needle is fixed by a high-voltage electrostatic clamp, the temperature of the spinning environment is changed to 30 ℃, the humidity is 50%, and the parameters of the rest electrostatic spinning machines are shown in the table 1.

TABLE 1 electrospinning machine spinning parameters

The scheme focuses on the configuration of the EPS spinning solution. Because the polarity of acetone easily causes protein to be dehydrated, the dielectric constant is reduced, and the interaction between charges is increased to cause protein precipitation, so that the original hydrogen bond in the protein is damaged, and the protein is denatured, and the high temperature for preparing the spinning solution even accelerates the denaturation process, so that the structures and characteristic functional groups of protein, polysaccharide and the like in EPS can be damaged to a certain extent, and the developed membrane is not favorable for ion adsorption and other applications. Therefore, a proper polymer is selected as a thickening agent, and the PVA selected here can be replaced by other water-soluble polymers. Because the spinning process is greatly influenced by the viscosity of the spinning solution, not only how to successfully compound the EPS needs to be considered, but also the viscosity and the conductivity of the mixed solution need to be focused, and appropriate spinning parameters are adjusted through the properties of the solution.

Step four: and preparing an upper sealing layer. And (4) drawing 1/2 volume spinning solution remained in the step one into an injector, adjusting parameters of the electrostatic spinning machine, and spinning the upper seal layer according to the step two. The step aims to solidify the EPS and ensure that the EPS can be firmly embedded in the electrostatic spinning film. Because EPS has water solubility, and is covered by the nanofiber membrane with certain porosity, the EPS can be prevented from being dissolved in water to cause loss in the actual application process.

And (4) preparing the EPS composite nanofiber membrane through the steps from the first step to the fourth step by a layer-by-layer superposition method. It is worth noting that in the third step and the fourth step, the EPS is embedded between PVDF nanofiber layers through an electrostatic spinning method, and filtration and adsorption are taken as application scenes of the EPS composite nanofiber membrane. In addition, other film modification means for compounding EPS and nano fibers can be selected, such as a coating method, a suction filtration method, a hot pressing method, surface grafting and the like.

The intermediate layer of the patent embodiment of the invention can also be prepared by two modes of a coating method and a suction filtration method, and the specific operation method comprises the following steps:

coating method: the coating machine is preheated to 35 ℃ to prevent the casting solution from being solidified too fast. As shown in fig. 2, the EPS/PVA mixed casting solution (i.e., EPS/PVA spinning solution) was poured onto one side of the base layer tiled on the film coating machine, the coating rod was a 10 μm wire rod, the running speed was 20mm/s, the running distance was 300mm, the EPS/PVA mixed casting solution was pushed from one side of the base layer to the other side at a uniform speed, and dried in a 70 ℃ oven for 30min to obtain the intermediate layer of the EPS composite nanofiber membrane prepared by the film coating method.

And (3) suction filtration: as shown in fig. 3, the substrate layer is fixed on a sand core of a filtration bottle, a buchner funnel is fixed by a fixing clamp, a vacuum pump is opened for vacuumizing, an EPS solution (10mL, 1.0g/L) is poured into the buchner funnel, and the EPS solution is deposited on the surface and in the hole of the substrate layer by vacuum filtration; and after the suction filtration is finished, placing the base layer deposited with the EPS in a 70 ℃ drying oven for drying for 30min to obtain the intermediate layer of the EPS composite nanofiber membrane prepared by the suction filtration method.

The preparation method of the extracellular polymeric substance composite nanofiber membrane provided by the embodiment of the invention has the following outstanding advantages:

1. the EPS has wide sources and low cost: EPS is derived from residual sludge which is a by-product of sewage treatment, and has huge, wide and reliable yield; the recovered EPS not only improves the value of the excess sludge, but also can be used for carbon compensation of a sewage plant and neutralizing carbon emission generated by energy consumption and material consumption of the sewage plant.

2. Ecological sustainable and no secondary pollution: the EPS is a natural high molecular substance which is autolyzed, secreted and shed by microbial cells, has abundant material characteristics due to different microbial sources, can replace industrial petroleum-based products in various fields, can be automatically degraded in the ecological environment, and cannot cause secondary pollution to the environment.

3. Nanometer characteristics, great development and design potential: the EPS is embedded by taking the nano-fiber as a substrate, so that the composite material has the nano characteristics of high porosity, large specific surface area, light weight, macroscopic particle tunnel and the like, and has great innovation potential after being doped with the EPS.

4. The influence on bioactive substances is small: the normal temperature electrostatic spinning is a non-thermal processing technology, namely the EPS is effectively embedded on the premise of not damaging the structure and the composition of a substance; meanwhile, the nanofiber has a certain slow release effect under strong acid, strong alkali and extremely severe environmental conditions, and the functional characteristics of bioactive substances in the EPS are prevented from being damaged.

5. The water-soluble EPS can be effectively sealed by virtue of high-flux, three-dimensional through and disordered pores formed by the nano fibers, and the loss of the EPS in the application process is avoided.

6. The reticular structure formed by the nano-fibers provides a great exchange channel for material transmission, and the embedding formed by the high-porosity carrier can fully exert the material characteristics of EPS.

7. Compared with the dispersed EPS, the preparation method for fixing the EPS among the nano fibers or among the nano fiber layers in a doping manner plays an effective fixing role on the EPS; particularly, when the EPS is used for removing heavy metal ions in wastewater, the separation and recovery processes after the EPS adsorbent is treated can be avoided, so that the practical application of the EPS can be assisted.

8. EPS and a thickening agent are mixed to prepare an EPS spinning solution, so that EPS is suspended on the nano-fibers to form microspheres, the microspheres are uniformly dispersed, and the specific surface area of adsorption is enlarged.

Example 1

The EPS composite nanofiber membrane prepared by the electrostatic spinning layer-by-layer stacking method is subjected to pure water flux test at room temperature and under the filtering pressure of 20kPa by a pressure filtering device, and the result is shown in FIG. 4. As can be seen, the water flux is up to 1442.58L/(m) ² H) and the membrane filtration impedance was calculated to be 49.3X 10 ⁹ m ^-1 Much less than the filtration impedance of commercial 10kDa ultrafiltration membranes (244X 10) ⁹ m ^-1 ) Therefore, the method has great advantages. Meanwhile, due to the addition of EPS, the water contact angle of the membrane increased from 109.5 ° to 90.1 °, as shown in fig. 5, so that the hydrophilicity of the membrane material increased.

The results of mercury intrusion method on the pore size distribution and porosity of the membrane are shown in fig. 6. The porosity of the EPS composite nanofiber membrane is improved from 52.46% to 61.58%, and the distribution situation contrast shows that the pore size distribution of the nanofiber membrane (ENM) is basically between 20nm and 5 micrometers, the pore size distribution of the EPS composite nanofiber membrane (EPS @ ENM) is basically between 120nm and 20 micrometers, the small pores are extruded or blocked in the EPS composite process, and the large pores larger than 5 micrometers come from the space between the nanofibers and the EPS membrane layer, so that the porosity of the EPS composite nanofiber membrane is improved, the large pores are increased, and the small pores among nano voids are reduced.

Example 2

In order to test the adsorption capacity of the EPS composite nanofiber membrane (also called EPS composite membrane for short) to heavy metal, 180mL of 10 mu MPb is subjected to pressure filtration by a pressure filtration device ²⁺ The solution was subjected to dead-end filtration at 20 kPa. And collecting the filtrate by a beaker placed on a balance, reading the weight of the filtrate in real time, and measuring the concentration of metal ions in the filtrate by using an inductively coupled plasma instrument. The filtration experiment was carried out using unmodified nanofiber membranes and EPS composite membranes (10mg EPS addition) prepared by electrospinning, coating and suction filtration, and the cumulative volume of filtrate filtered per unit membrane area was 1cm ³ /cm ² Is aligned with Pb ²⁺ The removal rate of (2) is shown in FIG. 7. As shown in FIG. 8, four membrane pairs of Pb ²⁺ The removal rates of the nano-fiber membrane are respectively 11.3%, 80.1%, 72.9% and 40.3%, namely the EPS composite nano-fiber membrane prepared by the electrostatic spinning method has Pb-free performance ²⁺ The removal efficiency is optimal.

Various films change with time vs. Pb ²⁺ The cumulative adsorption amount of (2) is as shown in fig. 9. As can be seen from FIG. 9, the EPS composite nanofiber membrane prepared by the electrospinning method has the maximum adsorption rate and the maximum cumulative adsorption amount, and the cumulative volume of the filtrate filtered per unit membrane area is 9cm ³ /cm ² In time, the membrane is affected compared to unmodified nanofiber membranesThe adsorption capacity is increased from 0.43 mu mol to 0.97 mu mol; furthermore, as can be seen from fig. 9, the adsorption curve still shows a linear rising trend, which indicates that the adsorption saturation capacity of the EPS composite membrane is not reached.

According to the preparation method of the extracellular polymeric substance composite nanofiber membrane provided by the embodiment of the invention, the doping substances are not limited to EPS extracted from excess sludge, and can also cover EPS generated by algae, bacteria and other substances and all high molecular substances, such as alginate, protein, polysaccharide, cellulose and the like. And the method is not limited to the byproducts of sewage treatment plants, and can also be derived from agriculture and animal husbandry, marine organisms and the like.

According to the preparation method of the extracellular polymeric substance composite nanofiber membrane provided by the embodiment of the invention, the raw materials of the electrostatic spinning nanofiber basement membrane are not limited to PVDF, but also include all substances which can be prepared through high-voltage static electricity, such as cellulose acetate, cellulose triacetate, polysulfone, polyethersulfone, polyacrylonitrile, polyethylene terephthalate and the like.

The embodiment of the invention provides a preparation method of an extracellular polymeric substance composite nanofiber membrane, the preparation method of the nanofiber membrane comprises but is not limited to the formation of nanofibers through a high-pressure electrostatic method, and all solution spinning methods capable of solidifying a polymer solution to form polymer fibers are within the protection scope of the patent.

The preparation method of the extracellular polymeric substance composite nanofiber membrane provided by the embodiment of the invention is not limited to an electrostatic spinning method, and a coating method, a suction filtration method, a hot pressing method and the like all belong to the protection scope of the patent.

Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of an extracellular polymeric substance composite nanofiber membrane is characterized in that the extracellular polymeric substance composite nanofiber membrane comprises a substrate layer, a middle layer and an upper sealing layer, and the preparation method comprises the following steps:

s1, weighing a certain amount of polyvinylidene fluoride powder, drying the polyvinylidene fluoride powder in an oven at 60 ℃ for 2 hours, removing excessive moisture, adding the dried polyvinylidene fluoride powder into an organic solvent mixed by dimethylacetamide and acetone, and then placing the mixture in a water bath constant-temperature heating pot for heating and stirring until the polyvinylidene fluoride powder is completely dissolved and the solution is transparent and clear, so as to obtain a homogeneous polyvinylidene fluoride spinning solution, wherein the mass percentage of polyvinylidene fluoride is 10-25%;

s2: starting an electrostatic spinning machine, preheating, setting experiment temperature and experiment humidity, sucking 1/2 volume of the prepared polyvinylidene fluoride spinning solution into an injector, fixing the injector on a solution feeding device of the electrostatic spinning machine, selecting a corresponding injection needle for injection, and preparing a substrate layer through the electrostatic spinning machine;

s3: adding a certain amount of polyvinyl alcohol particles into deionized water, placing the mixture into a water bath heating pot, heating and stirring the mixture at a constant temperature until the polyvinyl alcohol particles are completely dissolved, and obtaining a uniform polyvinyl alcohol solution;

s4: adding a certain amount of extracellular polymer powder into deionized water, placing the mixture into a water bath heating pot, heating and stirring at constant temperature until the extracellular polymer powder is completely dissolved, adding the prepared polyvinyl alcohol solution, continuing to heat and stir the mixture in the water bath heating pot at constant temperature, and then placing the mixture in a vacuum environment for degassing treatment to obtain an extracellular polymer/polyvinyl alcohol spinning solution;

s5: starting an electrostatic spinning machine, preheating, setting experiment temperature and experiment humidity, pumping the prepared extracellular polymer/polyvinyl alcohol spinning solution into an injector, fixing the injector on a solution feeding device of the electrostatic spinning machine, selecting a 20G injection needle for injection, and preparing an intermediate layer by using the electrostatic spinning machine;

s6: pumping the residual 1/2 volume of the prepared polyvinylidene fluoride spinning solution into an injector, fixing the injector on a liquid feeding device of an electrostatic spinning machine, selecting a corresponding injection needle for injection, preparing an upper sealing layer through the electrostatic spinning machine, and further preparing the extracellular polymer composite nanofiber membrane.

2. The method for preparing the extracellular polymeric substance composite nanofiber membrane as claimed in claim 1, wherein the intermediate layer is prepared by a coating method, and the method comprises the following steps: preheating a film coating machine to 35 ℃, pouring extracellular polymer/polyvinyl alcohol spinning solution to one side of a base layer paved on the film coating machine, selecting a 10-micrometer wire rod as a coating rod, operating at the speed of 20mm/s and the operating distance of 300mm, pushing the extracellular polymer/polyvinyl alcohol spinning solution from one side of the base layer to the other side at a constant speed, and drying in a 70 ℃ drying oven for 30min to obtain the intermediate layer of the extracellular polymer composite nanofiber membrane prepared by the film coating method.

3. The preparation method of the extracellular polymeric substance composite nanofiber membrane as claimed in claim 1, wherein the intermediate layer can be prepared by a suction filtration method, and specifically comprises the following steps: fixing the substrate layer on a sand core of a filter flask, fixing a Buchner funnel by using a fixing clamp, opening a vacuum pump for vacuumizing, pouring the extracellular polymeric substance solution into the Buchner funnel, and depositing the extracellular polymeric substance solution on the surface and in the hole of the substrate layer by vacuum filtration; and after the suction filtration is finished, placing the basal layer deposited with the extracellular polymeric substance in a 70 ℃ drying oven for drying for 30min to obtain the intermediate layer of the extracellular polymeric substance composite nanofiber membrane prepared by the suction filtration method.

4. The method for preparing an extracellular polymeric substance composite nanofiber membrane according to claim 1, wherein in the step S2, the test temperature is 21.5-26.5 ℃, and the test humidity is 38-42%.

5. The method for preparing the extracellular polymeric substance composite nanofiber membrane according to claim 1, wherein in the step S4, a certain amount of extracellular polymeric substance powder is added into deionized water, and the deionized water is placed in a water bath heating pot for heating and stirring at a constant temperature, wherein the heating temperature is 30 ℃, and the stirring speed and time are 500rpm and 2h respectively.

6. The method for preparing an extracellular polymer composite nanofiber membrane according to claim 1, wherein in step S4, the prepared polyvinyl alcohol solution is added while heating and stirring are continued in a water bath heating kettle at a constant temperature, wherein the heating temperature is 30 ℃, and the stirring speed and the stirring time are 500rpm and 3h, respectively.

7. The method for preparing an extracellular polymer composite nanofiber membrane according to claim 1, wherein in the step S5, the test temperature is 35 ℃ and the test humidity is 30%.

8. The method for preparing an extracellular polymer composite nanofiber membrane according to claim 1, wherein the extracellular polymer/polyvinyl alcohol spinning solution contains 1.0% by mass of the extracellular polymer and 10% by mass of the polyvinyl alcohol.

9. The method for preparing an extracellular polymeric substance composite nanofiber membrane according to claim 1, wherein in step S2, when the substrate layer is prepared by an electrospinning machine, the working parameters of the electrospinning machine are as follows: the spinning time is 1.25h, the plug flow speed is 4mL/h, the translation speed is 500mm/min, the receiving distance is 20cm, the rotating speed of a receiver is 100/min, and the positive/negative voltage is +8.0kV/-2.5 kV.

10. The method for preparing an extracellular polymeric substance composite nanofiber membrane according to claim 1, wherein in step S5, when the extracellular polymeric substance/polyvinyl alcohol intermediate layer is prepared by an electrospinning machine, the operating parameters of the electrospinning machine are as follows: the spinning time is 2.5h, the plug flow speed is 4mL/h, the translation speed is 300mm/min, the receiving distance is 15cm, the rotating speed of a receiver is 140/min, and the positive/negative voltage is +22.5kV/-2.5 kV.