Preparation method of PVDF β-crystal piezoelectric ultrafiltration membrane

Abstract

The present invention provides a method for preparing a PVDF β - crystal strong piezoelectric ultrafiltration membrane, which comprises the following steps: adding an organic base to PVDF powder to obtain modified PVDF, adding the modified PVDF, carboxylated graphene oxide powder, catalyst, plasticizer, and pore - forming agent into a DMAC solution respectively, ultrasonically mixing them evenly, then performing phase inversion, and finally successively undergoing activation and strong - pressure polarization to obtain a PVDF β - crystal piezoelectric ultrafiltration membrane. The preparation method of the present invention can improve the uniformity, stability, and hydrophilicity of the membrane, greatly enhance the anti - fouling ability, and effectively combine the low - resistance water passage and the greatly improved desalination ability of water molecules. The obtained PVDF β - crystal piezoelectric ultrafiltration membrane has the advantages of low energy consumption, high - efficiency removal of humic acid under high concentration and low pollution conditions, and high desalination efficiency.

Description

Technical Field

[0001] The present invention relates to piezoelectric film materials and their preparation processes, and specifically relates to a strong piezoelectric - ultra - low pressure - high - throughput ultrafiltration membrane and its preparation method. Background Art

[0002] As the ultrafiltration membrane with the most extensive application and development at present, polyvinylidene fluoride (PVDF) has many advantages. Due to its good chemical stability and physical stability, it can produce filter membranes with high stability, high strength, high temperature resistance, and high corrosion resistance. However, due to the poor hydrophilicity of the PVDF membrane material itself, in the actual membrane separation process, it is easily contaminated by various organic substances in water, resulting in a decrease in membrane flux, an increase in energy consumption, and inability to operate stably for a long time, thus hindering its development and popularization in the membrane technology field. Therefore, how to improve the hydrophilic ability of PVDF membranes is an urgent problem to be solved in the current membrane separation field.

[0003] Polyvinylidene fluoride (PVDF) is a polymer material with excellent piezoelectric properties. Previous studies have shown that PVDF has high separation efficiency and stability as a nanofiltration membrane material. However, pure PVDF has certain limitations, such as limited permeability and corrosion resistance. Therefore, modifying PVDF to improve its performance for macromolecular substances has become an important research topic.

[0004] Piezoelectric ultrafiltration membranes are new nanofiltration membrane materials developed in recent years. They have excellent piezoelectric properties and high separation efficiency, and have broad application prospects in water treatment and purification. PVDF, as a polymer material with excellent chemical stability and biocompatibility, is a commonly used ultrafiltration membrane material. In recent years, many scholars have been committed to modifying PVDF materials to improve their performance in water treatment and purification. However, due to the deficiencies of the PVDF material itself, the corrosion resistance and mechanical properties of its nanofiltration membranes still have problems, and at the same time, its separation efficiency also needs to be further improved. In order to effectively alleviate the water - quality - type water shortage problem caused by water pollution and more widely apply the ultrafiltration membrane technology to micro - polluted water treatment on a large scale, and give full play to the actual advantages of membrane filtration compared with other water treatment technologies, the present invention uses a PVDF ultrafiltration membrane with excellent characteristics such as high mechanical strength, good flexibility, wear - resistance, high temperature stability, and high chemical corrosion resistance as the base membrane. The limitations of PVDF ultrafiltration membranes in the actual water treatment process are mainly reflected in poor hydrophilicity and low β - crystal content, resulting in insignificant piezoelectricity. If these two problems can be solved, it will provide favorable conditions for the reuse of the membrane and the treatment of micro - pollutants. Therefore, the research and development of a PVDF - based piezoelectric ultrafiltration membrane has important practical significance and application prospects for improving the separation efficiency and stability of nanofiltration membranes and realizing efficient and low - energy - consumption water treatment and purification. Summary of the Invention

[0005] The present invention aims to provide a preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane for solving the difficult problems of low piezoelectricity, limited permeability, too low removal efficiency of humic acid, and poor anti-pollution performance of traditional PVDF ultrafiltration membranes.

[0006] The technical solution of the present invention is realized as follows:

[0007] A preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane includes the following preparation steps:

[0008] (1) Preparation of modified PVDF: PVDF powder and an organic base are put into a reactor for reaction.

[0009] (2) The modified PVDF, carboxylated graphene oxide powder, catalyst, plasticizer, and pore-forming agent obtained in step (1) are added to the DMAC solution in batches. After each material is added to the DMAC solution, ultrasonic stirring is carried out. After all the materials are added, a composite base membrane casting solution is obtained;

[0010] (3) The composite base membrane casting solution obtained in step (2) is added to an ethanol-water solution or a methanol-water solution for phase inversion; a PVDF ultrafiltration membrane is obtained;

[0011] (4) The PVDF ultrafiltration membrane obtained in step (3) is mechanically stretched and activated, and then electrically polarized by a polarization device or sprayed by an electrostatic spray gun to obtain a PVDF β-crystal piezoelectric ultrafiltration membrane.

[0012] Further explanation: In step (1), the reaction temperature is 20 - 60 °C, the reaction time is 5 - 10 minutes, in step (4), the polarization voltage is 10 - 20 V, the polarization time is 1 - 15 min; the spraying pressure is 2 - 2.5 kV.

[0013] Further explanation: The organic base includes but is not limited to: methylamine, urea, ethylamine, ethanolamine, ethylenediamine, dimethylamine, trimethylamine, triethylamine, propylamine, isopropylamine, 1,3-propanediamine, 1,2-propanediamine, tripropylamine, triethanolamine, butylamine, isobutylamine, tert-butylamine, hexylamine, octylamine, aniline, benzylamine, cyclohexylamine, pyridine, hexamethylenetetramine, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, o-aminophenol, m-aminophenol, p-aminophenol, o-toluidine, m-toluidine, p-toluidine, 8-hydroxyquinoline (20 °C), diphenylamine, benzidine, n-butyllithium, LDA, KHMDS, NaHMDS, potassium tert-butoxide, sodium tert-butoxide.

[0014] Further illustration shows that the mass ratio of the modified PVDF, carboxylated graphene oxide powder, catalyst, plasticizer, and pore-forming agent is 10 - 14:5 - 8:5 - 10:5 - 9:71 - 81, and the time of ultrasonic treatment is 0.5 - 1 h.

[0015] Further illustration shows that the catalyst is one of 3 - aminopropyltriethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, or vinyltrisilane.

[0016] Further illustration shows that the plasticizer includes, but is not limited to, phthalate, aliphatic dibasic acid ester, fatty acid ester, benzene polyacid ester, polyol ester, epoxy hydrocarbon, and alkyl sulfonate.

[0017] Further illustration shows that the pore-forming agent includes, but is not limited to, polyethylene glycol, polyvinylpyrrolidone, sodium dodecyl sulfate, and cetyltrimethylammonium bromide.

[0018] The present invention also provides a PVDF β - crystal piezoelectric ultrafiltration membrane and its application in water treatment, including energy recovery and multi - stage continuous ultrafiltration desalination under the reuse of surplus pressure.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) Utilizing the unique organic and metal dual properties of 3 - aminopropyltriethoxysilane (APTES) etc., under certain induction conditions, the organic compatibility and fusion of CFGO (carboxylated graphene oxide) and PVDF can be achieved ( Figure 1 ), forming a composite material with both inorganic and organic properties, having advantages such as covalent bond binding and rich ligand sites, which can significantly improve the uniformity, stability, and hydrophilicity of the composite material, greatly enhance the anti - fouling ability, and effectively combine the low - resistance passage of water molecules and the substantial improvement of desalination ability.

[0021] (2) Through processes such as induction, activation, and polarization, the charge amount of the membrane body under external pressure is increased, promoting the rejection of Cl - etc. and enhancing the separation efficiency of small - molecule salts.

[0022] (3) The preparation method of the present invention requires simple experimental equipment, mild operating conditions, is simple and easy to implement, can effectively improve the piezoelectricity and separation efficiency of the nanofiltration membrane, reduce its preparation and operation costs, and make it a veritable strong piezoelectric ultrafiltration membrane.

[0023] The ultrafiltration membrane prepared by the present invention has low energy consumption, can efficiently remove humic acid under high concentration and low pollution, and the developed equipment will have advantages such as small floor area, low energy consumption, mobility, and high desalination efficiency. Therefore, it has important application prospects in urban and rural sewage treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the surface scanning electron microscope photograph of the PVDF β-crystal composite piezoelectric ultrafiltration membrane in Example 1 of the present invention; Detailed implementation manners

[0025] To better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0026] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0027] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can all be obtained from commercial channels.

[0028] Example 1

[0029] Put PVDF powder and 1,3-propanediamine into a reactor, react at 60 °C for 10 min to introduce conjugated double bonds to obtain modified PVDF; add the above-obtained modified PVDF, carboxylated graphene oxide powder, 3-aminopropyltriethoxysilane, phthalate, and sodium dodecyl sulfate in five materials into the DMAC solution in batches according to a mass ratio of 14:5:5:5:71. After each material is added to the DMAC solution, ultrasonic stirring is carried out for 1 h. After all the materials are added, a composite base membrane casting solution is obtained; add the obtained composite base membrane casting solution into an ethanol-aqueous solution for phase inversion; obtain a PVDF ultrafiltration membrane; subject the obtained PVDF ultrafiltration membrane to mechanical stretching activation, and then use a commercially available non-woven fabric as a support substrate, and spray the ultrafiltration membrane onto the substrate surface under negative pressure conditions using an electrostatic spray gun (2 kV) to obtain a PVDF β-crystal piezoelectric ultrafiltration membrane.

[0030] Example 2

[0031] Put PVDF powder and p-aminophenol into a reactor, react at 20 °C for 5 min to introduce conjugated double bonds to obtain modified PVDF; add the above-obtained modified PVDF, carboxylated graphene oxide powder, vinyltriethoxysilane, aliphatic dibasic acid ester, and polyvinylpyrrolidone in five materials into the DMAC solution in batches according to a mass ratio of 10:8:10:9:81. After each material is added to the DMAC solution, ultrasonic stirring is carried out for 0.5 h. After all the materials are added, a composite base membrane casting solution is obtained; add the obtained composite base membrane casting solution into an ethanol-aqueous solution for phase inversion; obtain a CFGO-PVDF ultrafiltration membrane; subject the obtained CFGO-PVDF ultrafiltration membrane to mechanical stretching activation, and then place it under an electric field polarization of 10 - 20 v in a polarization device for 1 - 15 min to obtain a CFGO-PVDF β-crystal piezoelectric ultrafiltration membrane.

[0032] Example 3

[0033] Example 3 is different from Example 1 in that the mass ratios of the five added materials are changed.

[0034] Put PVDF powder and 1,3-propanediamine into a reactor, react at 60 °C for 10 min to introduce conjugated double bonds to obtain modified PVDF; add the above-obtained modified PVDF, carboxylated graphene oxide powder, 3-aminopropyltriethoxysilane, phthalate, and sodium dodecyl sulfate in batches to the DMAC solution according to a mass ratio of 18:2:2:15:60. After each material is added to the DMAC solution, ultrasonic stirring is carried out for 1 h. After all the materials are added, a composite base membrane casting solution is obtained; add the obtained composite base membrane casting solution to an ethanol-aqueous solution for phase inversion; obtain a PVDF ultrafiltration membrane; mechanically stretch and activate the obtained PVDF ultrafiltration membrane, and then use commercially available non-woven fabric as a support substrate, and spray the ultrafiltration membrane onto the substrate surface under negative pressure conditions using an electrostatic spray gun (2 kv) to obtain a PVDF β-crystal piezoelectric ultrafiltration membrane.

[0035] Comparative Example 1

[0036] The difference between Comparative Example 1 and Example 1 is that no catalyst is added, and the remaining raw materials and preparation methods are the same as those in Example 1. Specifically:

[0037] Put PVDF powder and 1,3-propanediamine into a reactor, react at 60 °C for 10 min to introduce conjugated double bonds to obtain modified PVDF; add the above-obtained modified PVDF, carboxylated graphene oxide powder, phthalate, and sodium dodecyl sulfate in batches to the DMAC solution according to a mass ratio of 14:5:5:71. After each material is added to the DMAC solution, ultrasonic stirring is carried out for 0.5 - 1 h. After all the materials are added, a composite base membrane casting solution is obtained; add the obtained composite base membrane casting solution to an ethanol-aqueous solution for phase inversion; obtain a PVDF ultrafiltration membrane; mechanically stretch and activate the obtained PVDF ultrafiltration membrane, and then use commercially available non-woven fabric as a support substrate, and spray the ultrafiltration membrane onto the substrate surface under negative pressure conditions using an electrostatic spray gun (2 kV) to obtain a PVDF β-crystal piezoelectric ultrafiltration membrane.

[0038] Comparative Example 2

[0039] The main difference between Comparative Example 2 and Example 1 is that PVDF is not modified.

[0040] Specifically, PVDF, carboxylated graphene oxide powder, 3-aminopropyltriethoxysilane, phthalate, and polyvinylpyrrolidone were added to the DMAC solution in batches according to a mass ratio of 14:5:5:5:71. After each material was added to the DMAC solution, ultrasonic stirring was carried out for 1 h. After all the materials were added, a composite base membrane casting solution was obtained; the obtained composite base membrane casting solution was added to an ethanol-aqueous solution for phase inversion; a PVDF ultrafiltration membrane was obtained; the obtained PVDF ultrafiltration membrane was mechanically stretched and activated, and then a commercially available non-woven fabric was used as a support substrate. Under negative pressure conditions, the ultrafiltration membrane was sprayed onto the substrate surface using an electrostatic spray gun (2 kV) to obtain a PVDF β-crystal piezoelectric ultrafiltration membrane.

[0041] Comparative Example 3

[0042] The main difference between Comparative Example 3 and Example 1 is that the various materials were not added to the DMAC solution separately in batches, but were added simultaneously and mixed and stirred.

[0043] Specifically, PVDF powder and 1,3-propanediamine were placed in a reactor and reacted at 60 °C for 10 min to introduce conjugated double bonds to obtain modified PVDF; the above-obtained modified PVDF, carboxylated graphene oxide powder, 3-aminopropyltriethoxysilane, phthalate, and polyvinylpyrrolidone were added to the DMAC solution simultaneously according to a mass ratio of 14:5:5:5:71, and then ultrasonic stirring was carried out for 2.5 h to obtain a composite base membrane casting solution; the obtained composite base membrane casting solution was added to an ethanol-aqueous solution for phase inversion; a PVDF ultrafiltration membrane was obtained; the obtained PVDF ultrafiltration membrane was mechanically stretched and activated, and then a commercially available non-woven fabric was used as a support substrate. Under negative pressure conditions, the ultrafiltration membrane was sprayed onto the substrate surface using an electrostatic spray gun (2 kV) to obtain a PVDF β-crystal piezoelectric ultrafiltration membrane.

[0044] Performance Test

[0045] (1) Membrane water purification performance test

[0046] Humic acid solutions with a concentration of 5 mg / L were respectively prepared, the filtration pressure was adjusted to 0.05 MPa, and the strongly piezoelectric composite ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-3 were filtered and detected. The removal effect of the ultrafiltration membrane on humic acid was determined, and by measuring the mass of the permeate, the fluxes of the two membranes were calculated using F = J / A*t (F is the membrane flux; J is the sampling volume; A is the effective membrane area; t is the time). Using the same method, the humic acid concentration was adjusted to 50 mg / L, the pressures were adjusted to 0.5 MPa, 2.5 MPa, and 20 MPa respectively, and three commercially available ultrafiltration membranes with good performance (Hydranautics HYDRAcap® MAX40 ultrafiltration membrane, Dow SFD-2880 ultrafiltration membrane, MEMOS tubular ultrafiltration membrane) were selected for detection, and the removal rate and membrane flux were calculated.

[0047] (2) Piezoelectric property test

[0048] The piezoelectric properties of the ultrafiltration membranes prepared in Examples 1-3 and Comparative Examples 1-3, and three commercially available ultrafiltration membranes with good performance (Hydranautics HYDRAcap® MAX40 ultrafiltration membrane, Dow SFD-2880 ultrafiltration membrane, MEMOS tubular ultrafiltration membrane) were tested using a d33 quasi-static measuring instrument. The measurement was carried out in parallel three times, and the piezoelectric constant was recorded and averaged.

[0049] (3) Test results

[0050]

[0051] As can be seen from the above results, compared with the three commercially available ultrafiltration membranes with good performance, the PVDF β-crystal composite piezoelectric ultrafiltration membranes prepared in Examples 1-2 of the present invention achieved relatively high values for the removal rate of humic acid and the filtration flux at a low pressure of 0.05 MPa. The highest filtration flux reached 1800 L / m 2 ·h, and the highest removal rate reached 88%, and its piezoelectric constant far exceeded that of commercially available ultrafiltration membranes. It can be seen that the ultrafiltration membrane prepared by the preparation method of the present invention has the advantages of low energy consumption, high efficiency, strong filtration ability, etc. From Examples 3 and Comparative Examples 1-3, it can be seen that changing the material mass ratio, not adding a catalyst, not modifying PVDF, or changing the mixing method of raw materials during the preparation process will have a great impact on the performance of the material.

[0052] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane, characterized in that, It includes the following preparation steps: (1) Preparation of modified PVDF: React PVDF powder and organic base in a reactor; (2) Add the modified PVDF, carboxylated graphene oxide powder, catalyst, plasticizer, and pore former obtained in step (1) to the DMAC solution in batches. After each material is added to the DMAC solution, ultrasonic stirring is carried out. After all the materials are added, a composite base membrane casting solution is obtained; The catalyst is one or more of 3-aminopropyltriethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, or vinyltrisilane; (3) Add the composite base membrane casting solution obtained in step (2) to an ethanol-water solution or a methanol-water solution for phase inversion; A PVDF ultrafiltration membrane is obtained; (4) Mechanically stretch and activate the PVDF ultrafiltration membrane obtained in step (3), and then perform electric field polarization using a polarization device to obtain a PVDF β-crystal piezoelectric ultrafiltration membrane.

2. The preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane according to claim 1, characterized in that, In step (1), the reaction temperature is 20 - 60 °C, the reaction time is 5 - 10 minutes. In step (4), the polarization voltage is 10 - 20 V, and the polarization time is 1 - 15 min.

3. The preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane according to claim 1, characterized in that, The organic base includes one or more of methylamine, urea, ethylamine, ethanolamine, ethylenediamine, dimethylamine, trimethylamine, triethylamine, propylamine, isopropylamine, 1,3-propanediamine, 1,2-propanediamine, tripropylamine, triethanolamine, butylamine, isobutylamine, tert-butylamine, hexylamine, octylamine, aniline, benzylamine, cyclohexylamine, pyridine, hexamethylenetetramine, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, o-aminophenol, m-aminophenol, p-aminophenol, o-toluidine, m-toluidine, p-toluidine, 8-hydroxyquinoline, diphenylamine, benzidine, n-butyllithium, LDA, KHMDS, NaHMDS, potassium tert-butoxide, sodium tert-butoxide.

4. The preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane according to claim 1, characterized in that, The mass ratio of the modified PVDF, carboxylated graphene oxide powder, catalyst, plasticizer, and pore former is 10 - 14:5 - 8:5 - 10:5 - 9:71 - 81, and the ultrasonic time is 0.5 - 1 h.

5. The preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane according to claim 1, wherein, The plasticizer includes one or more of phthalate esters, aliphatic dibasic acid esters, fatty acid esters, benzene polycarboxylic acid esters, polyol esters, epoxy hydrocarbons, and alkyl sulfonates.

6. The preparation method of a PVDF β-crystal piezoelectric ultrafiltration membrane according to claim 1, characterized in that, The pore former includes one or more of polyethylene glycol, polyvinylpyrrolidone, sodium dodecyl sulfate, and cetyltrimethylammonium bromide.

7. A PVDF β-crystal piezoelectric ultrafiltration membrane, characterized in that, The PVDF β-crystal piezoelectric ultrafiltration membrane is prepared by the preparation method according to any one of claims 1 - 6.

8. The application of a PVDF β-crystal piezoelectric ultrafiltration membrane according to claim 7 in water treatment.

9. The application of the PVDF β-crystal piezoelectric ultrafiltration membrane according to claim 8 in water treatment, characterized in that, It includes energy recovery and multi-stage continuous ultrafiltration desalination under the reuse of surplus pressure.

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