CN119819144B - Preparation method, product and application of polyaniline modified composite membrane - Google Patents
Preparation method, product and application of polyaniline modified composite membraneInfo
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Abstract
The invention relates to the technical field of high polymer materials, in particular to a preparation method, a product and application of a polyaniline modified composite membrane. The preparation method of the polyaniline modified composite membrane comprises the following steps of 1, activating and cleaning a polyvinylidene fluoride substrate, immersing the polyvinylidene fluoride substrate in a solution A, stirring, taking out the polyvinylidene fluoride substrate after stirring is finished, cleaning the polyvinylidene fluoride substrate to obtain a treated polyvinylidene fluoride substrate, 2, mixing the solution A with a solution B, filtering to obtain a mixed solution, 3, immersing the treated polyvinylidene fluoride substrate in the mixed solution, taking out the treated polyvinylidene fluoride substrate after immersing is finished, and drying to obtain the polyaniline modified composite membrane, wherein the solution A is a SiO 2 solution, and the solution B is a mixed solution of polyaniline and polyvinylpyrrolidone. The preparation method is simple and easy to operate, is beneficial to industrial production, and has high separation efficiency of the polyaniline modified composite membrane oil slick/water solution.
Description
Technical Field
The invention relates to the technical field of high polymer materials, in particular to a preparation method, a product and application of a polyaniline modified composite membrane.
Background
Mineral insulating oil is widely applied to large-scale power equipment such as transformers and reactors by virtue of excellent insulating and heat dissipation properties, and a special accident oil pool is arranged in a transformer substation for preventing pollution caused by oil injection and oil leakage of large-scale oil-filled electrical equipment such as a main transformer and high resistance. The accident oil pool stores oil leakage of power equipment and sewage of a transformer substation, and meanwhile, potential safety hazards of the transformer substation and a series of sewage leakage environmental protection problems are increased. Transformer waste oil contains a variety of toxic components such as polycyclic aromatic hydrocarbons, biphenyls, and heavy metals. Such transformer waste oils, if not treated thoroughly in time, can be a threat to animal and plant health and human health. Therefore, a scientific and efficient oil-water separation method is adopted, so that the treatment of the oily sewage at the sewage outlet of the accident oil pool is enhanced, and the discharge of the waste liquid meets the economic and environment-friendly requirements, and becomes an important problem for the current management of the waste liquid of the accident oil pool of the transformer substation.
Polyaniline is used as a conductive polymer, has good oxidation-reduction reversibility, conductivity and stability, and has potential advantages for oil-water separation. The existing oil-water separation technology is only suitable for specific types of oil-water mixtures, has poor separation effect on transformer oil-water mixtures, can generate byproducts or emissions harmful to the environment, and is difficult to maintain the separation performance for a long time. Therefore, how to enhance the adaptability, environmental protection and sustainability of the membrane is a technical problem to be solved at present when a new oil-water separation technology is developed.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a preparation method, a product and application of a polyaniline modified composite membrane; the method adopts a surface coating mode, and uses the polyvinylidene fluoride membrane as a substrate to prepare the polyaniline modified composite membrane with high separation efficiency, good water flux and long service life.
In order to achieve the above object, the present invention provides the following solutions:
According to one of the technical schemes, the preparation method of the polyaniline modified composite membrane comprises the following steps:
step 1, activating and cleaning a polyvinylidene fluoride substrate, immersing the polyvinylidene fluoride substrate in the solution A, stirring, and taking out the polyvinylidene fluoride substrate after stirring to clean the polyvinylidene fluoride substrate to obtain a treated polyvinylidene fluoride substrate;
step2, mixing the solution A with the solution B, and filtering to obtain a mixed solution;
step 3, immersing the treated polyvinylidene fluoride substrate in the mixed solution, and taking out and drying after the immersion is finished to obtain the polyaniline modified composite membrane;
the solution A is SiO 2 solution;
The solution B is a mixed solution of polyaniline and polyvinylpyrrolidone.
According to the second technical scheme, the polyaniline modified composite membrane prepared by the preparation method is provided.
In the third technical scheme of the invention, the polyaniline modified composite membrane is applied to oil-water separation.
The invention discloses the following technical effects:
The polyaniline modified composite membrane provided by the invention has higher membrane flux and good anti-fouling property and recycling property. The polyaniline modified composite membrane takes SiO 2, polyaniline and polyvinylpyrrolidone as main materials, achieves higher oil slick separation efficiency, has good anti-fouling property and recycling property, effectively reduces the harm of industrial wastewater to the environment, and has good environmental protection.
The polyaniline modified composite membrane has a membrane flux up to 458.48Lm -2h-1, a separation efficiency up to 98.73%, and a plurality of circulating tests are carried out, and the total organic carbon content of filtrate is detected to be 17.2mg/L, so that the national wastewater discharge standard is met.
The preparation method is simple and easy to operate, and is beneficial to industrial production.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an optical photograph of a PANI@PVDF-3 composite film prepared in example 3 of the present invention.
Fig. 2 is a FESEM view of PVDF film (a) and pani@pvdf-3 composite film (b, c) prepared in example 3 of the invention.
FIG. 3 is an AFM image of PVDF film (a, b) and PANI@PVDF-3 composite film (c, d).
FIG. 4 shows an oil-water separator used in the oil-water separation cycle test of the present invention.
Fig. 5 is a graph of experimental results of separation of oil slivers/water solutions of 5 pani@pvdf composite membranes prepared in example 1 to example 5 of the present invention.
FIG. 6 is a graph depicting membrane flux and total organic carbon content (TOC) of the PANI@PVDF-3 composite membrane prepared in example 3 of the present invention when the membrane is recycled.
Detailed Description
Various exemplary embodiments of the invention will now be described in detail, which should not be considered as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples of the present invention are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.
The first aspect of the invention provides a preparation method of a polyaniline modified composite membrane, comprising the following steps:
step 1, activating and cleaning a polyvinylidene fluoride substrate, immersing the polyvinylidene fluoride substrate in the solution A, stirring, and taking out the polyvinylidene fluoride substrate after stirring to clean the polyvinylidene fluoride substrate to obtain a treated polyvinylidene fluoride substrate;
step2, mixing the solution A with the solution B, and filtering to obtain a mixed solution;
step 3, immersing the treated polyvinylidene fluoride substrate in the mixed solution, and taking out and drying after the immersion is finished to obtain the polyaniline modified composite membrane;
the solution A is SiO 2 solution;
The solution B is a mixed solution of polyaniline and polyvinylpyrrolidone.
In some embodiments of the invention, the polyvinylidene fluoride substrate is activated by being placed in absolute ethyl alcohol, and the activation time is 0.5-3 h.
The main purpose of the membrane is to remove residual solvent and impurities on the surface of the membrane, clean pore channels, improve the pore structure of the membrane, and enhance the pore rate, thereby improving the permeability and hydrophilicity of the membrane. In addition, the activation treatment is beneficial to reducing the blockage of the pore canal of the membrane, promoting the uniform permeation of liquid and enhancing the stability and the subsequent use performance of the membrane. Through activation, the pore channel of the membrane is optimized, and a better foundation is laid for the oil-water separation or filtration process.
In some embodiments of the invention, the concentration of SiO 2 in the solution A is 2-10 g/L, the solvent of the solution A is dimethylformamide, and the particle size of SiO 2 in the solution A is 5-50 nm.
The concentration of SiO 2 in the solution A has an important influence on the performance of the polyaniline modified composite membrane. Too high a concentration of SiO 2 in solution a may cause a decrease in membrane porosity, a decrease in flux, and a membrane to become fragile and easily broken, while too low a concentration may cause a shortage in mechanical strength of the membrane, a decrease in separation efficiency, and an inferior effect particularly in treating wastewater with high oil concentration. Therefore, the concentration of SiO 2 should be kept within a proper range (2-10 g/L) to ensure the stability of the membrane and good separation performance.
At the same time, the SiO 2 particle size plays a critical role in the performance of the film. When the SiO 2 particle size is too large, the pore structure of the membrane is too large, the separation precision is reduced, the separation effect is poor, the surface of the membrane is rough and easy to be polluted, when the SiO 2 particle size is too small, the pore size of the membrane is too thin, the flux is reduced, the treatment efficiency is weakened, and the membrane is more easily polluted and blocked. Therefore, the SiO 2 particle size should be controlled between 5nm and 50nm to balance flux, separation efficiency and membrane stability.
In some embodiments of the invention, the solution A is prepared by dispersing SiO 2 powder with the particle size of 5-50 nm in dimethylformamide and stirring for 1-3 hours.
Dimethylformamide is a polar solvent, has good dispersibility on SiO 2, is favorable for forming a uniform dispersion system, improves the fluidity and formability of the uniform dispersion system in the subsequent processing process, and reduces the difficulty in preparing films.
If other polar solvents such as ethyl acetate, ethanol, acetone, tetrahydrofuran or dimethyl sulfoxide are used to replace Dimethylformamide (DMF), the performance of the polyaniline-modified composite membrane can be adversely affected. First, the poor dispersibility of ethyl acetate and ethanol results in uneven dispersion of SiO 2 particles, which in turn affects the uniformity and mechanical strength of the film. Acetone, although it is highly soluble, is unsuitable for dispersing SiO 2 and volatilizes at a high rate, affecting film formability and surface smoothness. Tetrahydrofuran (THF) can better disperse SiO 2, but interacts with polyaniline, affecting the electrical and mechanical properties of the film. In addition, THF is relatively volatile, resulting in uneven film formation. Dimethyl sulfoxide (DMSO) has strong dispersibility, but has high polarity, influences the hydrophilicity of the membrane, reduces the oil-water separation effect and has adverse effects on polyaniline.
In summary, although these solvents have a certain ability to disperse SiO 2, they result in uneven dispersion of SiO 2, difficulty in film formation, poor film stability, and influence on polyaniline compared to dimethylformamide. Dimethylformamide is therefore a more suitable choice.
In some embodiments of the present invention, the concentration of polyaniline in the solution B may be 5-15 g/L, specifically may be 5g/L, 10g/L, 15g/L, the concentration of polyvinylpyrrolidone in the solution B may be 2-10 g/L, specifically may be 2g/L, 3g/L, 4g/L, 5g/L, 8g/L, 10g/L, and the solvent of the solution B may be 0.5-1.5mol·L -1 hydrochloric acid solution.
In some embodiments of the invention, polyaniline (PANI) and polyvinylpyrrolidone are dissolved in hydrochloric acid solution at a concentration of 1mol·l -1, and in an acidic environment, the amino moiety (-NH) of polyaniline will bind with hydrogen ions (H +), pani+hcl→pani ++Cl-, thereby forming protonated polyaniline, increasing its solubility in the acidic environment. Meanwhile, polyvinylpyrrolidone is used as a water-soluble polymer, can form a compound or blend with polyaniline, and improves the dispersibility and uniformity of the compound or blend. The blend can enhance the conductivity and mechanical properties of the polyaniline modified composite membrane and simultaneously improve the physical and chemical stability of the polyaniline modified composite membrane.
If the concentrations of Polyaniline (PANI) and polyvinylpyrrolidone (PVP) in solution B are outside the above-described parameter ranges, the properties of the composite film are adversely affected, as follows:
Too high a concentration of polyaniline results in increased brittleness of the film, decreased mechanical strength of the film, and easy occurrence of cracks or fractures. In addition, too high a polyaniline concentration makes the membrane too conductive, affecting its application properties and resulting in a reduced flux of the membrane. Conversely, too low a polyaniline concentration may result in insufficient electrical properties of the film, and weak mechanical strength of the film, affecting the stability of the film.
Too high a polyvinylpyrrolidone concentration may result in enhanced swelling of the membrane, affecting the stability and structure of the membrane, and increasing the surface roughness, reducing the separation effect of the membrane. While too low a concentration may result in poor stability and insufficient hydrophilicity of the membrane, affecting the wettability and separation properties of the membrane, especially in water treatment applications.
In some embodiments of the invention, in the step 1, the stirring parameter is set to stir at a rotation speed of 400-600 r/min for 1-3 h at a temperature of 35-75 ℃.
The parameters of the agitation in step 1 (such as agitation speed and time) are critical to ensure uniformity of the solution and membrane performance.
If the stirring speed is too high, bubbles are introduced to affect the surface quality of the film, and the high shear force causes uneven dispersion of particles to affect the mechanical and electrical properties of the film. Conversely, too low stirring speed results in insufficient dispersion of the particles, uneven components in the solution, and influences the stability and separation effect of the membrane.
Too long stirring times cause elevated solution temperatures, affecting film formability, and even leading to degradation or excessive polymerization of the material. However, too short stirring time results in insufficient mixing of the solution, uneven dispersion of polyaniline and PVP, and further influences the mechanical strength and performance of the membrane.
Therefore, the stirring speed and time should be controlled within proper ranges to ensure uniformity of the solution and avoid adversely affecting the performance of the membrane.
In some embodiments of the present invention, in step 2, the step of stirring the solution B at a rotation speed of 400 to 600r/min for 3 to 5 hours at a temperature of 75 ℃ is further included before the step of mixing the solution B with the solution a.
The purpose of stirring the solution B for a certain time in the temperature range is to ensure that all components in the solution are uniformly dispersed and fully dissolved, avoid particle agglomeration and ensure the uniformity and stability of the film. In the stirring process, the temperature and time are controlled, so that the mechanical property, conductivity and separation efficiency of the membrane are optimized, the uniform reaction is promoted, and the final quality and performance of the membrane are ensured.
In some embodiments of the invention, in step 2, the volume ratio of the solution a to the solution B is 1:1.
In some embodiments of the invention, in the step 3, the soaking is specifically performed for 8-12 hours vertically, and the drying parameters are set to 80-120 ℃ for 15-30 minutes.
The purpose of the vertical soak is to ensure that the membrane material is in sufficient contact with the solution to form a uniform membrane layer and optimize its structure and performance. Soaking times outside the above parameters lead to excessive adsorption or deposition on the membrane surface, resulting in uneven membrane layer, inconsistent thickness, and even affecting the mechanical strength and separation effect of the membrane. At the same time, the change of the solution composition can also lead to bad change of the chemical structure of the film, thereby affecting the functionality of the film.
In the present invention, the parameter setting of the drying is adjusted based on the material properties of the film. The sensitivity of different membrane materials to temperature and time is different, and reasonable drying conditions are helpful for optimizing the microstructure of the membrane and improving the mechanical strength, the porosity and the separation performance of the membrane. In addition, the specific drying parameters (temperature and time) can avoid embrittlement, structural collapse or uneven pore size distribution of the membrane in the drying process, and ensure the stability and the functionality of the membrane.
The second aspect of the invention provides a polyaniline modified composite membrane prepared according to the preparation method.
The third aspect of the invention provides an application of the polyaniline modified composite membrane in oil-water separation.
The polyaniline modified composite membrane can effectively filter the oil-water solution of the transformer, is suitable for various oil-water mixtures, and has good adaptability.
The technical scheme of the invention is conventional in the field, and the reagents or raw materials are purchased from commercial sources or are disclosed.
The polyvinylidene fluoride (PVDF) substrate used in the embodiment of the invention has the pore diameter range of 0.1-0.5 mu m, and the polyvinylidene fluoride (PVDF) substrate with the pore diameter range of 0.1-0.5 mu m obtained by a commercial way is suitable for the invention.
The average particle size of the SiO 2 powder used in the examples according to the invention was 25nm.
The test method related to the embodiment of the invention comprises the following steps:
Microscopic topography analysis
The influence of polyaniline on film roughness was studied to investigate its influence on film wettability, so the influence of polyaniline on film roughness was analyzed by scanning electron microscopy and atomic force microscopy. The microscopic morphology of the different materials was observed using a field emission scanning electron microscope. And (3) carrying out metal spraying treatment on the prepared sample, wherein the voltage is 10kV, the metal spraying time is 90 seconds, and the accelerating voltage in the test is 5kV.
Analysis of surface chemical composition
The chemical composition of PVDF membranes before and after PANI modification was studied using ATR-FTIR and XPS measurement methods. And analyzing functional groups in the sample by using a Fourier transform infrared spectrometer, wherein the sample to be detected needs to be dried, and the scanning range is 500-4000 cm -1.
And (3) carrying out solid surface analysis on the sample by using an X-ray photoelectron spectroscopy analyzer, wherein the solid surface analysis comprises chemical composition of the surface of a fiber film, and the energy analysis range is 0-1500 eV so as to cover the binding energy of all element electrons which may exist.
And analyzing the phase structure by using an X-ray diffractometer, wherein the test range is 5-80 degrees, and the scanning speed is 5 degrees/min.
Analysis of mechanical Properties
The sample was cut into rectangular films of a certain area and set to a holding distance of 2cm. The fracture strength, young's modulus and fracture growth rate of each sample were measured by a texture analyzer, and three parallel measurements were performed for each test, and an average value was taken.
Calculation formula of separation efficiency
The oil content in the original solution and the filtrate is measured according to an infrared spectrophotometry, and the separation efficiency R (%) of the prepared film is calculated according to the formula (1):
Wherein, C 0 and C 1 represent the oil content in the original emulsion and the filtrate after filtration, respectively.
Membrane flux J (Lm -2h-1), which is calculated as formula (2):
wherein V represents the volume (L) of the filtrate, A (m 2) represents the effective area of the membrane, and T represents the separation time (h).
TOC content was measured by a total organic carbon analyzer and determined by non-dispersive infrared absorption.
The technical solutions provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
The embodiment of the invention provides a preparation method of a Polyaniline (PANI) modified composite membrane, which comprises the following steps:
s1, activating a polyvinylidene fluoride (PVDF) substrate for 0.5-3 hours;
S2, dispersing SiO 2 powder into 50mL of polar organic solution, stirring for 1-3 hours, and marking as solution A, wherein the concentration of SiO 2 in the solution A is 2-10 g/L;
S3, dissolving PANI and polyvinylpyrrolidone (PVP) in 50mL of acid solution, and marking the solution as solution B, wherein the concentration of PANI in the solution B is 5-15 g/L, and the concentration of PVP is 2-10 g/L;
s4, cleaning the activated PVDF substrate by using deionized water, immersing the PVDF substrate into the solution A, stirring at the temperature of 35-75 ℃ for 1-3 hours at the rotating speed of 400-600 r/min, taking out the PVDF substrate after stirring, and cleaning the PVDF substrate by using deionized water again;
s5, placing the solution B in a constant-temperature water bath at 75 ℃ and stirring for 3-5 hours, wherein the rotating speed is 400-600 r/min;
S6, mixing the solution A after the stirring in the step S4 and the solution B after the stirring in the step S5 according to a volume ratio of 1:1, filtering and precipitating the mixed solution, and vertically placing the PVDF substrate cleaned in the step S4 into the filtered mixed solution, and soaking for 8-12 h;
S7, taking out the soaked PVDF substrate, and drying in a drying oven at the temperature of 80-120 ℃ for 15-30 min to obtain the PANI modified composite film, which is named PANI@PVDF.
Example 1
A PANI modified composite membrane is named as PANI@PVDF-1, and the preparation method comprises the following steps:
s1, placing a PVDF substrate into absolute ethyl alcohol for activation for 2 hours;
S2, dispersing SiO 2 powder into 50mL of Dimethylformamide (DMF) solution, stirring for 2h, and marking as a solution A, wherein the concentration of SiO 2 in the solution A is 2g/L;
S3, dissolving PANI and PVP in 50mL of 1 mol.L -1 hydrochloric acid solution, namely a solution B, wherein the concentration of PANI in the solution B is 10g/L, and the concentration of PVP is 2g/L;
S4, cleaning the PVDF substrate activated in the step S1 by deionized water, immersing the PVDF substrate in the solution A, stirring at the temperature of 75 ℃ for 2 hours at the rotating speed of 500r/min, taking out the PVDF substrate after stirring, and cleaning the PVDF substrate by deionized water again;
s5, placing the solution B in a constant-temperature water bath at 75 ℃ and stirring for 4 hours, wherein the rotating speed is 500r/min;
s6, mixing the solution A after the stirring in the step S4 and the solution B after the stirring in the step S5 according to a volume ratio of 1:1, filtering and precipitating the mixed solution, and vertically placing the PVDF substrate cleaned in the step S4 into the filtered mixed solution, and soaking for 10 hours;
S7, taking out the soaked PVDF substrate, and drying in a drying oven at 100 ℃ for 20min to obtain the PANI@PVDF-1 composite film.
Through tests, the PANI@PVDF-1 composite membrane prepared in the embodiment has the breaking strength of 30.1MPa, the Young modulus of 2.4MPa, the breaking elongation of 29.8%, the membrane flux of 441.50Lm -2h-1 and the oil slick/water solution separation efficiency of 98.5%.
Example 2
A PANI modified composite membrane is named PANI@PVDF-2, and the preparation method comprises the following steps:
s1, placing a PVDF substrate into absolute ethyl alcohol for activation for 2 hours;
S2, dispersing SiO 2 powder in 50mL of DMF solution, stirring for 2h, and marking as solution A, wherein the concentration of SiO 2 in the solution A is 6g/L;
s3, dissolving polyaniline and PVP in 50mL of 1 mol.L -1 hydrochloric acid solution, namely a solution B, wherein the concentration of PANI in the solution B is 10g/L, and the concentration of PVP is 6g/L;
S4, cleaning the PVDF substrate activated in the step S1 by deionized water, immersing the PVDF substrate in the solution A, stirring at the temperature of 75 ℃ for 2 hours at the rotating speed of 500r/min, taking out the PVDF substrate after stirring, and cleaning the PVDF substrate by deionized water again;
s5, placing the solution B in a constant-temperature water bath at 75 ℃ and stirring for 4 hours, wherein the rotating speed is 500r/min;
s6, mixing the solution A after the stirring in the step S4 and the solution B after the stirring in the step S5 according to a volume ratio of 1:1, filtering and precipitating the mixed solution, and vertically placing the PVDF substrate cleaned in the step S4 into the filtered mixed solution, and soaking for 10 hours;
S7, taking out the soaked PVDF substrate, and drying in a drying oven at 100 ℃ for 20min to obtain the PANI@PVDF-2 composite film.
Through tests, the pani@PVDF-2 composite membrane prepared in the embodiment has the breaking strength of 55.2MPa, the Young modulus of 3.3MPa, the elongation at break of 23.5%, the membrane flux of 475.46Lm -2h-1 and the oil slick/water solution separation efficiency of 90%.
Example 3
A PANI modified composite membrane is named PANI@PVDF-3, and the preparation method comprises the following steps:
s1, placing a PVDF substrate into absolute ethyl alcohol for activation for 2 hours;
S2, dispersing SiO 2 powder in 50mL of DMF solution, stirring for 2h, and marking as solution A, wherein the concentration of SiO 2 in the solution A is 10g/L;
S3, dissolving polyaniline and PVP in 1 mol.L -1 of hydrochloric acid solution, namely a solution B, wherein the concentration of PANI in the solution B is 10g/L, and the concentration of PVP is 10g/L;
S4, cleaning the PVDF substrate activated in the step S1 by deionized water, immersing the PVDF substrate in the solution A, stirring at the temperature of 75 ℃ for 2 hours at the rotating speed of 500r/min, taking out the PVDF substrate after stirring, and cleaning the PVDF substrate by deionized water again;
s5, placing the solution B in a constant-temperature water bath at 75 ℃ and stirring for 4 hours, wherein the rotating speed is 500r/min;
s6, mixing the solution A after the stirring in the step S4 and the solution B after the stirring in the step S5 according to a volume ratio of 1:1, filtering and precipitating the mixed solution, and vertically placing the PVDF substrate cleaned in the step S4 into the filtered mixed solution, and soaking for 10 hours;
s7, taking out the soaked PVDF substrate, and drying in a drying oven at 100 ℃ for 20min to obtain the PANI@PVDF-3 composite film.
Through tests, the PANI@PVDF-3 composite membrane prepared in the embodiment has the breaking strength of 60.9MPa, the Young modulus of 3.1MPa, the elongation at break of 19.9%, the membrane flux of 458.48Lm -2h-1, the separation efficiency of oil slick/water solution of 98.73% and the most thorough separation. The optical photograph of the pani@pvdf-3 composite film prepared in this example is shown in fig. 1, the FESEM image is shown in fig. 2, and it can be seen from fig. 2 that compared with the unmodified PVDF film, the pani@pvdf-3 composite film has a coarser surface and a denser structure, which indicates that the polymerization of polyaniline increases the roughness of the fiber, and that the PANI and PVDF have good compatibility. Meanwhile, as can be seen from fig. 2, the pani@pvdf-3 membrane has a compact porous structure, and the compact structure enables the membrane to have better mechanical properties.
The surface roughness analysis of the film was performed using an atomic force microscope AFM. As shown in fig. 3, the surface of the base film exhibits a uniform concave-convex structure due to uniform film holes. The PANI@PVDF surface shows uneven concave-convex structure distribution because the adsorption and aggregation degrees of polyaniline nanofibers are different in different places. The surface roughness of the PVDF film and the PANI@PVDF-3 composite film is accurately measured by using an atomic force microscope, and the average roughness of the PVDF film is 8.9nm, which shows that the surface is relatively smooth, and compared with the surface, the average roughness of the PANI@PVDF composite film is obviously increased to 95.39nm, which is related to the adsorption and aggregation of polyaniline nanowires on the surface of the film.
Multiple oil-water separation cycle tests were performed using pani@pvdf-3 composite membrane as shown in fig. 6. The total organic carbon content of the filtrate is detected to be 17.2mg/L to meet the national wastewater discharge standard, which indicates that the PANI@PVDF-3 composite membrane prepared by the invention has good anti-fouling property and recycling property.
The test method of the oil-water separation cycle test is as follows:
1. Experimental device
Five different PANI@PVDF composite membranes are used as membrane materials, wherein the PANI@PVDF-3 composite membrane is used as the best choice, and the optimal separation effect is achieved.
The membrane is fixed in a sand core filter device with an inner diameter of 5cm and an effective separation area of 19.63cm 2. The oil-water separator used in the experiment is shown in the figure (fig. 4).
2. Preparation of oil/water solutions
Deionized water was mixed with an organic solvent (transformer oil concentrate) at a ratio V Deionized water /V Organic solvents = 100/1. After mixing, the mixture was poured into an upper glass tube, and oil-water separation was performed.
The mixed solution was filtered under a pressure of 0.07MPa to obtain an original solution containing an oil-water mixture and a filtrate.
3. Separation process and data recording
After each filtration, the oil content in the original solution and the filtrate was measured by infrared spectrophotometry, and used to calculate the separation efficiency R (%).
The membrane flux (J) is determined by calculating the volume (V) of filtrate, the effective area (a) of the membrane and the separation time (T).
4. Cyclic test procedure
In each cycling experiment, pani@pvdf-3 composite membranes were simply rinsed with water to restore membrane flux.
The experiment was performed in multiple cycles and the membrane flux and TOC content of the membrane was checked after each experiment.
TOC analysis TOC content in the filtrate was tested by a total organic carbon analyzer using a non-dispersive infrared absorption method to evaluate the durability of the oil-water separation effect.
5. Results of the cyclic experiments
After 5 cycles, the membrane flux was slightly reduced, but by simple rinsing, the membrane flux could be restored to near the original value.
After the fifth cycle, the TOC content in the filtrate is 17.2mg/L, which accords with the national wastewater discharge standard.
Experimental results show that the PANI@PVDF-3 composite membrane has good dirt resistance and recycling property, is suitable for repeated use and can maintain a good separation effect.
6. Summary
Through the cyclic test, the performance of the composite film after multiple uses can be evaluated. The flux of the membrane was slightly reduced after multiple filtration but could be recovered by simple rinsing. The TOC content accords with environmental protection standards, and the film has better anti-fouling property and recycling property.
Example 4
The procedure was different from example 3 except that stirring was performed at 35℃in step S4, and the other steps and parameters were the same as those in example 3, and the PANI modified composite film was obtained and was designated as PANI@PVDF-4.
Through tests, the membrane flux of the PANI@PVDF-4 composite membrane prepared in the embodiment is 339.62Lm -2h-1, and the oil slick/water solution separation efficiency is 95.5%.
Example 5
The procedure was different from example 3 except that stirring was performed at 55℃in step S4, and the other steps and parameters were the same as those in example 3, and the PANI modified composite film was obtained and was designated as PANI@PVDF-5.
Through tests, the membrane flux of the PANI@PVDF-5 composite membrane prepared in the embodiment is 407.54Lm -2h-1, and the oil slick/water solution separation efficiency is 98.5%.
FIG. 5 is a graph showing the results of experiments on oil/water solutions separated by 5 PANI@PVDF composite membranes prepared in examples 1-5, wherein in the graph, the ABCD bottle corresponds to the PANI@PVDF-2 composite membrane, the PANI@PVDF-4 composite membrane, the PANI@PVDF-1 composite membrane and the PANI@PVDF-5 composite membrane in sequence, and the PANI@PVDF-3 composite membrane is used as the E bottle. From fig. 5, it can be seen that the oil content after separation gradually decreases, the oil drops in bottle a are obvious, which indicates that the oil-water separation is incomplete, the B, C and the D bottles have a small amount of oil drops, the oil-water separation is incomplete, the E bottle has no visible oil drops basically, the oil-water separation is basically complete, the E bottle is the oil-water separation performed by pani@pvdf-3 composite membrane, which indicates that the membrane has the best separation effect when the heating temperature is 75 ° C, siO 2 and the concentration ratio of PVP to polyaniline is 1:1:1. The membrane flux of the original membrane is 390.5L m -2h-1, and the separation efficiency is 53.2%.
It was also verified that further increases in the temperature of stirring in step S4 of 80 ℃, 85 ℃ and 90 ℃ respectively on the basis of example 3 (i.e., only in the difference from example 3 in that stirring was performed at temperatures of 80 ℃, 85 ℃ and 90 ℃ respectively in step S4, and the remaining steps and parameters were the same as example 3), and as a result, it was revealed that as the temperature of stirring in step S4 was gradually increased from 35 ℃ to 90 ℃, the flux of the membrane was primarily increased although the high temperature helped to increase the fluidity of the solution, the resistance of the membrane was reduced, and the separation process was accelerated. However, too high a temperature may cause a change in the structure of the membrane, and particularly the pore structure of the membrane may be deformed by thermal expansion or contraction, thereby affecting the mechanical strength and stability of the membrane. The high temperature may also cause degradation or shedding of the membrane surface coating or modified materials (e.g., siO 2 and polyaniline), which may affect the hydrophilicity and wettability of the membrane, thereby resulting in a decrease in separation efficiency. In addition, stirring at too high a temperature for a long time can reduce the durability of the membrane, reduce the recycling capability of the membrane, and can cause the surface of the membrane to be more easily polluted, thereby affecting the cleaning effect. Therefore, the temperature should be kept within a suitable range to ensure long-term stability of the membrane and optimal separation.
Comparative example 1
A PANI modified composite membrane is named as PANI@PVDF-D1, and the preparation method comprises the following steps:
s1, placing a PVDF substrate into absolute ethyl alcohol for activation for 2 hours;
S2, dispersing SiO 2 powder in 50mL of DMF solution, stirring for 2h, and marking as solution A, wherein the concentration of SiO 2 in the solution A is 10g/L;
S3, dissolving polyaniline and PVP in 50mL of 1 mol.L -1 hydrochloric acid solution, namely a solution B, wherein the concentration of PANI in the solution B is 10g/L, and the concentration of PVP is 10g/L;
s4, stirring the solution A at the temperature of 75 ℃ for 2 hours at the rotating speed of 500r/min;
s5, placing the solution B in a constant-temperature water bath at 75 ℃ and stirring for 4 hours, wherein the rotating speed is 500r/min;
S6, mixing the solution A after the stirring in the step S4 and the solution B after the stirring in the step S5 according to a volume ratio of 1:1, filtering and precipitating the mixed solution, washing the PVDF substrate activated in the step S1 by deionized water, vertically placing the PVDF substrate into the filtered mixed solution, and soaking for 10 hours;
S7, taking out the soaked PVDF substrate, and drying in a drying oven at 100 ℃ for 20min to obtain the PANI@PVDF-D1 composite film. (i.e., the only difference from example 3 is that the step of immersing the PVDF substrate in the solution A is omitted)
The PANI@PVDF-D1 prepared in this comparative example was subjected to the same effect verification as in example 3, and the result showed that the PANI@PVDF-D1 had a breaking strength of 40.3MPa, a Young's modulus of 2.0MPa, an elongation at break of 28.7%, a membrane flux of 382.5Lm -2h-1 and a separation efficiency of oil slick/water solution of 83%.
Comparing comparative example 1 with example 3, it can be seen that omitting the step of immersing the PVDF substrate in solution a significantly reduces the performance of the composite film. And is characterized by deterioration of mechanical properties such as reduction of breaking strength and young's modulus, decrease of hydrophilicity and wettability due to insufficient surface roughness, and further, significantly lower separation efficiency and membrane flux than in example 3. Meanwhile, due to the lack of modification of the SiO 2 coating on the surface of the membrane, the oil content of the filtrate after oil-water separation is high, and the environment-friendly emission standard is difficult to reach.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.
Claims (10)
1. The preparation method of the polyaniline modified composite membrane is characterized by comprising the following steps of:
step 1, activating and cleaning a polyvinylidene fluoride substrate, immersing the polyvinylidene fluoride substrate in the solution A, stirring, and taking out the polyvinylidene fluoride substrate after stirring to clean the polyvinylidene fluoride substrate to obtain a treated polyvinylidene fluoride substrate;
step2, mixing the solution A with the solution B, and filtering to obtain a mixed solution;
step 3, immersing the treated polyvinylidene fluoride substrate in the mixed solution, and taking out and drying after the immersion is finished to obtain the polyaniline modified composite membrane;
the solution A is SiO 2 solution;
The solution B is a mixed solution of polyaniline and polyvinylpyrrolidone.
2. The preparation method of the polyaniline modified composite membrane according to claim 1, wherein the polyvinylidene fluoride substrate is activated by being placed in absolute ethyl alcohol, and the activation time is 0.5-3 h.
3. The preparation method of the polyaniline modified composite membrane according to claim 1, wherein the concentration of SiO 2 in the solution A is 2-10 g/L, the solvent of the solution A is dimethylformamide, and the particle size of SiO 2 in the solution A is 5-50 nm.
4. The preparation method of the polyaniline modified composite membrane according to claim 1, wherein the concentration of polyaniline in the solution B is 5-15 g/L, the concentration of polyvinylpyrrolidone is 2-10 g/L, and the solvent of the solution B is 0.5-1.5mol.L -1 of hydrochloric acid solution.
5. The method for preparing the polyaniline modified composite membrane according to claim 1, wherein in the step 1, the stirring parameters are set to be stirring at a rotation speed of 400-600 r/min for 1-3 hours at a temperature of 35-75 ℃.
6. The method for preparing a polyaniline modified composite membrane according to claim 1, wherein in step 2, the step of stirring the solution B at a rotation speed of 400 to 600r/min for 3 to 5 hours at a temperature of 75 ℃ is further included before the solution B is mixed with the solution a.
7. The method for preparing a polyaniline modified composite membrane according to claim 1, wherein in step 2, the volume ratio of the solution a to the solution B is 1:1.
8. The preparation method of the polyaniline modified composite membrane according to claim 1, wherein in the step 3, the soaking is performed for 8-12 hours vertically, and the drying parameters are set to 80-120 ℃ and dried for 15-30 min.
9. The polyaniline modified composite membrane prepared by the preparation method according to any one of claims 1 to 8.
10. The use of the polyaniline modified composite membrane according to claim 9 in oil-water separation.
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