KR102312961B1 - Piezoelectric membrane for membrane fouling reduction and its method - Google Patents

Abstract

The piezoelectric membrane for reducing membrane contamination according to an embodiment of the present invention includes a piezoelectric polymer nanofiber, and is characterized in that mechanical vibration is generated according to an applied voltage.

Description

Piezoelectric membrane for membrane fouling reduction and its method for manufacturing the same

The present invention relates to a piezoelectric membrane for reducing membrane contamination and a method for manufacturing the same, and more particularly, to a piezoelectric membrane for reducing membrane contamination that can improve antifouling properties through vibration induction by adjusting a solvent ratio, a tip-collector distance, and a heat treatment time and to a method for manufacturing the same.

Membrane technology for drinking water production and wastewater treatment has attracted attention due to various advantages such as relatively low operating cost, high efficiency and small formation area.

However, membrane technology suffers from fouling problems. Since the fouling is a phenomenon related to the adsorption and accumulation of contaminants, the working life of the membrane may be shortened, the membrane performance efficiency may be reduced, and the operating cost may increase.

To solve the above problems, many researchers are working on various methods to prevent fouling, such as pretreatment (coagulation, adsorption), membrane modification (functionalization, blending), washing, UV irradiation, and operating condition control.

In addition to the above method, a technique including fluid instability has also been reported, which is a technique to reduce the adhesion of contaminants to the membrane by generating a turbulent flow generated by sonication and a piezoelectric reaction on the membrane surface.

Techniques for generating turbulent flow generated by sonication can create turbulence through external ultrasonic waves. And a technique that creates a piezoelectric reaction on the membrane surface can create an unstable fluid due to the internal contrast between the piezoelectric materials.

A technology for generating a piezoelectric reaction on the membrane surface may use a commercially available polyvinylidene fluoride (PVDF) membrane or a lead zirconate titanate (PZT) ceramic membrane having piezoelectric properties.

In the case of PVDF or PZT formed to have the above piezoelectric properties, when a piezoelectric reaction occurs during the filtration process, the membrane may exhibit a lower flux reduction than when there is no piezoelectric reaction.

On the other hand, in the conventional membrane, piezoelectric properties are activated by a poling deoxidation method. The poling deoxidation method is a technique for polarizing PVDF and PZT molecules in the same direction by applying a high voltage to the membrane after the membrane is manufactured.

And as another method of forming the membrane, the piezoelectric film may be manufactured by the electrospinning technique. The above-described electrospinning technique can be used to simultaneously form a membrane and polarize the membrane because a high voltage is applied during the membrane manufacturing process.

In addition, the electrospun nanofiber membrane (pENM) formed by the electrospinning technique has been reported to have various advantages such as high surface area and high porosity.

Meanwhile, as another method of forming the membrane, an electrospun nanofiber membrane (ENM) may be prepared by the electrospinning technique.

Despite the huge potential of electrospun nanofiber membranes (ENMs) as water treatment membranes, their mechanical and geometrical properties remain significant drawbacks for field applications.

For example, one of the disadvantages of the electrospun nanofibers (ENMs) for use in liquid filtration applications is that the membrane cleaning by countercurrent is very difficult. In addition, when a high-pressure reverse fluid flows into the bottom of the electrospun nanofibers (ENM), the electrospun nanofibers (ENM) may be peeled off and not be used.

Another disadvantage of the electrospun nanofibers (ENM) is the weakness of membrane fouling. In general, if the roughness of the membrane surface is high, the possibility of membrane fouling may increase.

Since the electrospun nanofiber (ENM) has a very rough surface shape due to its nonwoven structure, there is a limit to its application to the actual field of the electrospun nanofiber (ENM). Maeng reports that fouling occurred in a short period of time when the electrospun nanofiber (ENM) was used as a membrane.

Therefore, in order to overcome the limitations of the electrospun nanofibers (ENM) described above, there is a need for a functional membrane for minimizing adhesion of the compressed material (foulant) on the membrane surface.

The technical problem to be achieved by the present invention is to provide a piezoelectric membrane for reducing membrane contamination capable of improving antifouling properties through vibration induction by adjusting a solvent ratio, a tip-collector distance (hereinafter, TCD), and a heat treatment time, and a method for manufacturing the same .

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. There will be.

This embodiment of the present invention comprises the steps of preparing a PVDF solution by mixing PVDF with acetone and NMP mixed solvent; preparing a nanofiber mat on a current collector by electrospinning the PVDF solution; removing the residual solvent by immersing the nanofiber mat in a deionized water bath; drying the nanofiber mat from which the residual solvent is removed; and manufacturing a piezoelectric membrane by heat-treating the dried nanofiber mat.
The PVDF solution is prepared by mixing the PVDF with a mixed solvent in which the acetone and the NMP are mixed in a volume ratio of 4: 6 to 6: 4.
In the manufacturing of the nanofiber mat, the PVDF solution is spun and electrospinning is performed to apply a voltage of 10 kV to 13 kV with a high voltage power supply device to prepare the nanofiber assembly, and the nanofiber assembly to an aluminum foil It is characterized in that the step of preparing the nanofiber mat by coating.
The nano-electrospinning of the step of preparing the nanofiber mat is characterized in that the TCD (tip to collector distance) is performed in the range of 15 cm to 20 cm.
Another embodiment of the present invention provides a piezoelectric membrane for reducing membrane contamination comprising PVDF piezoelectric polymer nanofibers, characterized in that mechanical vibration is generated according to an applied voltage.
The membrane is characterized in that the tensile strength is 0.5 MPa to 1.0 MPa.

The piezoelectric membrane for reducing membrane contamination and the method for manufacturing the same according to an embodiment of the present invention have the effect of improving antifouling properties through vibration induction by adjusting the solvent ratio, the tip-collector distance, and the heat treatment time.

It should be understood that the effects of the present invention are not limited to the above-described effects, and include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a schematic diagram of a piezoelectric membrane cross-flow system for forming a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
2 is a diagram illustrating the shape and crystal properties of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
3 is a graph showing characteristics of electrospun PVDF nanofibers according to a solvent ratio of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
4 is a diagram illustrating FE-SEM images when TCDs of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention are different.
5 is a graph showing the characteristics of electrospun PVDF nanofibers according to the TCD length of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
6 is an FE-SEM (left: 2000x, right: 10,000x) photograph of the piezoelectric membrane (pENM) for reducing membrane contamination according to the heat treatment time of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention; This is a photographed drawing.
7 is a graph showing the characteristics of the electrospun PVDF nanofibers according to the heating time of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
8 is a graph showing tensile strength according to heat treatment time of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
9 is a photograph of a piezo-response force microscopy (PFM) of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
10 is a graph showing the water permeability of 0.5 and a commercial MF membrane of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.
11 is a graph showing a decrease in the flux of pENM0.5 in a 10ppm alginate solution according to the presence or absence of a piezoelectric effect of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be embodied in several different forms, and thus is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is said to be “connected (connected, contacted, coupled)” with another part, it is not only “directly connected” but also “indirectly connected” with another member interposed therebetween. "Including cases where In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises" or "have" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The piezoelectric membrane for reducing membrane contamination according to an embodiment of the present invention includes a piezoelectric polymer nanofiber, and is characterized in that mechanical vibration is generated according to an applied voltage.

According to an embodiment of the present invention, a PVDF nanofiber membrane is typically prepared for the application of a piezoelectric microfiltration (MF) membrane. To form a PVDF nanofiber membrane, a piezoelectric membrane (pENM) for reducing membrane contamination is prepared by controlling the synthesis conditions, specifically the solvent ratio, the tip-collector distance (TCD), and the heat treatment time.

The performance measurement of the piezoelectric membrane (pENM) for membrane contamination reduction evaluates water permeability, particulate removal, and antifouling properties in the presence of organic matter.

First described is PVDF (average molecular weight 275,000 by GPC), N-methyl-2-pyrrolidone (NMP, anhydrous, 99.5%), acetone (ACS reagent, >99.5%), kaolin and sodium alginate salt from Sigma-Aldrich. It was purchased as a drug from

And, ethyl alcohol (99.5%) was purchased from SAMCHUN Chemical Korea, and deionized water was purified through a water purification system (Millipore, 18.2 MX cm, USA). All reagents were used without further purification.

Then, the electrospinning method was performed on the substrate prepared as described above to form a piezoelectric membrane (pENM) for reducing membrane contamination.

22 wt% PVDF solutions were prepared in various solvent ratios (acetone/NMP, 1/9-7/3). Acetone and NMP were thoroughly mixed at 200 rpm using a magnetic stirrer.

Voltages were applied in the range of 10-13 kV using a high voltage power supply. The polymer solution was ejected with a syringe pump at a feed rate of 0.5 ml/h. The nanofibers are laminated on the current collector and covered with aluminum foil.

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After the electrospinning was completed, the PVDF nanofiber mat was immersed in a water bath to remove residual solvent. Heat treatment was performed to enable mechanical properties for filtration. The prepared PVDF nanofiber membrane was completely dried at 50 °C. The membrane was sandwiched between two glass plates under low pressure. After that, heat treatment was performed at 150 °C for 0.5-5 h.

The average diameter of the piezoelectric membrane for reducing membrane contamination (pENM) formed of PVDF nanofibers formed by the electrospinning method as described above was observed.

The morphology of PVDF nanofibers was analyzed by field emission scanning electron microscopy (FE-SEM) (Hitachi S-4800, Japan, Jeol JSM-7001F, Japan). Image J 1.48v software (National Health of Health, USA) was used.

The crystalline phase of PVDF nanofibers was characterized with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy (Varian 660-IR, USA) in the range ^{of 600-1400 cm -1 .}

The tensile strength of the piezoelectric membrane for membrane fouling reduction (pENM) was measured using a universal testing machine (UTM) (Shimadzu AG-X, Japan) with a load cell of 50 kN capacity.

A piezoelectric membrane (pENM) for reducing membrane contamination was cut in a rectangular shape of 20 mm × 0.5 mm.

All samples were tested at a speed of 200 mm/min and compared with a heated piezoelectric membrane for reducing membrane fouling (pENM) to determine the effect of heat treatment time on mechanical properties.

A capillary flow pore analyzer (CFP-1500AE, Porous Materials Inc., USA) was used to analyze the pore size distribution of the piezoelectric membrane (pENM) for reducing membrane contamination before and after heat treatment. Galwick™ was used as the wetting liquid. All samples were cut to an effective diameter of 1.5 cm.

The porosity of the piezoelectric membrane (pENM) for reducing membrane contamination before and after heat treatment was measured using a mercury porosimeter (Autopore III 9420, Micrometrics, USA).

To investigate the piezoelectric properties, a multimode atomic force microscope (AFM) with a Pt/Ir-coated cantilever (MultiMode 8, Bruker, Germany) was used.

An AC signal of 3 V amplitude and 13 kHz was applied between the upper electrode (tip) and the lower electrode (metal plate) of the sample. All samples were coated with a 20-30 nm gold (Au) layer. Carbon-paste was used to attach the sample to the sample holder.

Membrane performance and antifouling properties of the piezoelectric membrane (pENM) for reducing membrane contamination according to the present invention were measured.

Before performing the water permeability test and the turbidity test, a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention and a commercial PVDF MF membrane (V0.2, Synder Membrane Technology, China) were soaked in ethanol for 1 hour. immersed. Then, the membrane was thoroughly washed with deionized water.

A commercial PVDF MF membrane of the membrane type was formed as a flat membrane having a pore size of 0.2 μm, and the water permeability test was performed using another filtration cell with a ^{filtration area of 28.7 cm 2 .}

The selected PVDF ENM has a storage tank of 5 liters and the filtration pressure is maintained by _{N 2 gas.}

The weight of the permeate was measured at 0.25, 0.5, 0.75, 1.0 and 1.25 bar for 15 seconds, and the water permeability was calculated by [Equation 1].

[Equation 1]

where m is the mass of the permeate (kg), t is the sampling time, A is the effective membrane area (m2), and p is the pressure (bar).

On the other hand, the turbidity test was performed to observe the rejection of particulates and the change in turbidity.

To evaluate the selectivity of ENM, kaolin particles with a particle size of 0.4 to 4.0 and an average particle size of 1.6 μm were used as target materials for the turbidity test.

A 0.1 g/L kaolin solution was prepared and the test was performed at room temperature and 0.25 bar using a dead-end filtration system.

Sampling of HpENM was performed at volumes of 0, 0.5 and 1 L, and commercial MF membranes were sampled at the end of filtration.

The turbidity of the sample was measured using a turbidimeter (TN-100, Eutech Instruments, USA), and the removal rate was calculated by [Equation 2].

[Equation 2]

where Ci is the initial value and Cf is the value of the permeate.

And, the flux decay test was performed to confirm the antifouling effect of the vibration generated by the piezoelectric effect.

A 10 ppm alginate solution was tested using a piezoelectric membrane cross flow system with an effective area of ^{18.36 cm 2} shown in Figure 1 with a cross flow rate of 400 mL/min at room temperature and 0.25 bar.

1 is a schematic diagram of a piezoelectric membrane cross-flow system for forming a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

The membrane was fitted with a stainless mesh to apply AC (500 Hz, 10 Vpp) while filtering.

The polarized PVDF membrane showed reduced fouling and the highest average flux when AC signals were 10V and 500Hz. AC signals (Agilent 33250A, Keysight Technologies Inc., USA) were used to generate AC signals.

2 is a diagram illustrating the shape and crystal properties of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention. Here, Figure 2 shows a piezoelectric membrane (pENM) for reducing membrane contamination (pENM) having a solvent ratio (acetone/NMP) different from each optimum voltage at a feed rate of 0.5 ml/h, a TCD of 20 cm, and a humidity of 44%, 22 wt% FE-SEM photograph (2000x) of electrospun PVDF nanofibers.

Specifically, (a) of FIG. 2 is a FE-SEM photograph having a voltage-solvent ratio of 10kV-7/3, and (b) of FIG. 2 is a FE-SEM having a voltage-solvent ratio of 10kV-6/4. A photograph, (c) of FIG. 2 is a FE-SEM photograph having a voltage-solvent ratio of 10 kV-5/5, and (d) of FIG. 2 is an FE-SEM having a voltage-solvent ratio of 11 kV-4/6. 2(e) is a FE-SEM photograph having a voltage-solvent ratio of 11.5kV-3/7, and FIG. 2(f) is a FE- having a voltage-solvent ratio of 13kV-2/8. It is an SEM photograph, and (g) of FIG. 2 is an FE-SEM photograph having a voltage-solvent ratio of 13 kV-1/9.

As can be seen in Fig. 2 (f, g), when the NMP was acetone/NMP ratio of 8 and 9, uniform nanofibers were not formed. It is considered that this is because the volatility of the solvent is low. That is, NMP is because the volatility of the solvent is very low.

When the polymer solution was pulled from the needle to the current collector, the NMP was not completely volatilized. Thus, nanofibers with beads were formed.

When the nanofiber diameter is 724 and 682 nm, solvent ratios of 7/3 and 6/4 (acetone/NMP) are required, respectively. Small diameter nanofibers were prepared compared to nanofibers prepared with a 5/5 solvent ratio. This result can be explained by the relationship between diameter and viscosity.

Increasing the acetone ratio decreased the viscosity of the polymer solution and thus decreased the diameter. When the ratio of acetone was decreased, the diameter decreased, contrary to the results for the 7/3 and 6/4 acetone/NMP ratios. This result occurred by increasing the voltage.

Hao Shao et al. reported that when the applied voltage was increased from 9 kV to 15 kV, the diameter of the nanofiber decreased. However, to analyze the results more accurately, the change in viscosity must be measured.

3 is a graph showing characteristics of electrospun PVDF nanofibers according to a solvent ratio of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

Here, (a) of FIG. 3 is an ATR-FTIR spectrum graph of the electrospun PVDF nanofiber according to the solvent ratio, and FIG. 3 (b) is a graph showing the β-phase ratio of the electrospun PVDF nanofiber according to the solvent ratio.

Figure 3(a) shows the ATR-FTIR spectra of PVDF nanofibers with different solvent ratios.

A phase oscillation band was detected at 766 cm-1. The absorption band or transmission band at 840 cm ⁻¹ _{was identified due to CH 2} locking/CF ₂ asymmetric stretching of the b-phase. In addition, the upper bound ratios were calculated with values of ^{766 cm -1} and 840 cm ^-1 using the absorption coefficients of Ka and Kb of phase b and phase a, respectively. The b phase ratio was calculated as in [Equation 3].

[Equation 3]

Here, Ab and Aa are absorbance values at ^{840 cm -1 and 766 cm -1 , respectively.} Ka and Kb are the absorption coefficients at ^{6.1×10 4} and 7.7× ^{10 4 cm 2} mol ^{−1 , respectively.}

The b-phase ratio is shown in Fig. 3(b) using Eq. (3). The highest b-phase ratio was observed at the 5/5 solvent ratio. When the proportion of acetone was increased from 5 to 7, the b-phase proportion decreased from 85% to 61%. Acetone is a very volatile solvent. Therefore, when the polymer solution was stretched, it was not completely formed due to the rapid evaporation of the solvent. When the proportion of acetone decreases from 5 to 9, the residual solvent interferes with nanofiber b phase formation, reducing the b phase proportion from 85% to 50%.

In conclusion, a 5/5 ratio of acetone/NMP was the most suitable solvent ratio to form the b phase. Different experiments were performed using a 5/5 acetone/NMP solvent ratio due to the highest b-phase formation at this solvent ratio.

4 is a diagram illustrating an FE-SEM image when the TCD of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention is different.

Specifically, FIG. 4 is a FE-SEM photograph (2000x) of 22 wt% electrospun PVDF nanofibers having different TCDs at a solvent ratio of 5/5 (acetone/NMP), a voltage of 10 kV, and a feed rate of 0.5 ml/h. More specifically, (a) of FIG. 4 is a photograph of a nanofiber having a TCD of 10 cm, (b) of FIG. 4 is a photograph of a nanofiber having a TCD of 15 cm, and (c) of FIG. 4 is a TCD of 20 cm is a photograph of the nanofiber having a , and Fig. 4 (d) is a photograph of the nanofiber having a TCD of 25 cm.

Referring to FIG. 4 , under all experimental conditions, fibers with some beads were prepared and they exhibited similar morphologies. When the distance was changed from 10 cm to 20 cm, the average fiber diameter decreased due to the increase of the instability period.

As the distance increased from 20 cm to 25 cm, the average fiber diameter increased by about 300–400 nm because the voltage intensity per unit distance decreased.

5 is a graph showing the characteristics of electrospun PVDF nanofibers according to the TCD length of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

Specifically, (a) of FIG. 5 is an ATR-FTIR spectrum graph of the electrospun PVDF nanofiber according to the TCD length, and FIG. 5 (b) is a graph showing the β-phase ratio of the electrospun PVDF nanofiber according to the TCD length. am

Fig. 5(a) shows ATR-FTIR spectra of PVDF nanofibers with different TCDs. In Fig. 5(b), the highest b-phase ratio was observed in the TCD of 20 cm.

6 is an FE-SEM (left: 2000x, right: 10,000x) photograph of the piezoelectric membrane (pENM) for reducing membrane contamination according to the heat treatment time of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention; This is a photographed drawing.

Referring to FIG. 6 , heat treatment of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention was performed to improve mechanical properties.

Here, (a1), (a2) of Figure 6 is a photograph of the nanofiber having a heating time of 0h, (b1), (b2) of Figure 6 is a photograph of the nanofiber having a heating time of 0.5h, Figure 6 (c1) and (c2) are photographs of nanofibers having a heating time of 1h, (d1), (d2) of FIG. 6 are photographs of nanofibers having a heating time of 3h, (e1) of FIG. , (e2) are photographs of nanofibers with a heating time of 5 h.

However, when a high energy input such as thermal energy near the melting temperature (Tm) is applied to phase b, phase b can be transformed into more stable phase a or phase c. Therefore, the heat treatment time was adjusted to minimize the crystal phase change.

Heat treatment was applied at 150 °C for 0.5, 1, 3 and 5 h. 6 shows the shape before and after heat treatment. The loose structure between the nanofibers can be observed in Fig. 6(a).

As shown in FIG. 6 (b, c, d, e), after heat treatment, a dense structure can be observed, and when heat treatment for 5 hours is applied, a network structure between the nanofibers can be observed. That is, the above results may affect the mechanical properties.

7 is a graph showing the characteristics of the electrospun PVDF nanofibers according to the heating time of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

Specifically, (a) of FIG. 7 is an ATR-FTIR spectrum graph of electrospun PVDF nanofibers according to heating time, and (b) of FIG. 7 is a graph showing the β-phase ratio of electrospun PVDF nanofibers according to heating time am.

Referring to Fig. 7, ATR-FTIR (Fig. 7(a)) was used to confirm the b-phase change. The b-phase ratio was calculated by equation (3). The results for the b-phase ratio are shown in Fig. 7(b). When the heat treatment time was increased from 0 hours to 5 hours, the b-phase ratio decreased from 85% to 71%.

As described above, since sufficient thermal energy was supplied to the polymer phase, the b-phase was changed to either the a-phase or the c-phase.

8 is a graph showing tensile strength according to heat treatment time of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

Referring to FIG. 8 , after heat treatment, the tensile strength was increased from 0.5 MPa to 1.0 MPa. These results can be caused by the formation of dense structures and networks between the nanofibers.

Here, referring to FIGS. 7 and 8, the membrane (HpENM) treated for 0.5 hour was selected in the next experiment because it produced the highest b-phase ratio among piezoelectric membranes (pENM) for reducing membrane contamination.

[Table 1] shows the pore size and porosity results of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

[Table 1]

The unheated pENM (pENM0) had a bubble point of 25.3788 μm and an average pore size of 0.6489 μm. HpENM had a bubble point of 12.6085 μm and an average pore of 0.5764 μm.

The pore size and porosity decreased. These results can be explained by the formation of dense nanofiber structures.

9 is a photograph of a piezo-response force microscopy (PFM) of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

Specifically, (a) of FIG. 9 is a PFM picture of HpENM locally, (b) of FIG. 9 is a PFM picture of HpENM with respect to phase, and (c) of FIG. 9 is a PFM picture of HpENM with respect to amplitude.

Referring to FIG. 9 , piezo-response force microscopy (PFM) was used to observe the piezoelectric response of a piezoelectric membrane (pENM) for reducing membrane contamination.

PFM is a special AFM technique that creates an image of the piezoelectric response as the sample expands or contracts. Piezoelectric response imaging was performed for a scan size of 5 μm x 5 μm with AC signals of 5 V and 15 kHz.

The image in Fig. 9 shows a PFM image of nanofibers on aluminum foil. In Fig. 9(a), the local image showed a slightly flattened shape. After heat treatment, the shape of the nanofiber was changed to a flat shape.

The PFM phase image in Fig. 9(b) shows the polarization direction. The bright regions inside the nanofibers show upward polarization, and the dark regions show downward polarization.

Fig. 9(c) is an amplitude image. The bright area shows a relatively higher piezoelectric response than other areas. These results indicate that the piezoelectric effect of HpENM was confirmed and that the piezoelectric reaction could contribute to the formation of turbulent flow on the membrane surface.

10 is a graph showing the water permeability of 0.5 of the piezoelectric membrane (pENM) for reducing membrane contamination and the commercial MF membrane according to an embodiment of the present invention.

Referring to FIG. 10, pure water flux, turbidity test and flux reduction test were performed to evaluate filtration properties. Commercial PVDF MF membranes were tested to compare water permeability and kaolin removal rates.

The piezoelectric membrane for membrane fouling reduction (pENM) showed three times greater water permeability than commercial MF membranes.

Table 2 is a table showing the removal performance of pENM0.5 and commercial MF membrane using 0.1g/L kaolin solution under 0.25bar pressure.

[Table 2]

As shown in Table 2, the kaolin removal rates can be similar between the two membranes. The high water permeability of the piezoelectric membrane (pENM) for reducing membrane fouling can be explained by its high porosity. Unlike a cast membrane having finger-shaped pores, a nanofiber membrane, which is a piezoelectric membrane (pENM) for reducing membrane contamination, may have an interconnected pore structure. Therefore, water can easily pass through the membrane.

The piezoelectric membrane for membrane fouling reduction (pENM) has a larger pore size than a commercial PVDF membrane, but the removal rate can be similar. This result is due to the high surface area to volume ratio. That is, the surface area to volume ratio can affect the entrapment of particulates.

Therefore, the piezoelectric membrane for membrane contamination reduction (pENM) can exhibit a high removal rate through the sieving effect according to the pore size and the lapping phenomenon due to the high surface area to volume ratio.

As described above, it becomes difficult to use because the period until the fouling is completed increases by about three times. Currently, the only paper on piezoelectric films is the MF level film reported by Darestani et al. They reported that the piezoelectric MF synthesized by the Pauling process showed a pure water flux of about 2600 LMH bar. However, they fabricated a piezoelectric membrane for membrane fouling reduction (pENM) that performed a 5573 LMH bar pure water flux without a polling process.

11 is a graph showing a decrease in the flux of pENM0.5 in a 10ppm alginate solution according to the presence or absence of a piezoelectric effect of a piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention.

Referring to FIG. 11 , the normalized flux for a piezoelectric membrane for membrane fouling reduction (pENM) at a cross flow rate of 400 ml/min at 25° C. and 0.25 bar is shown. To evaluate the antifouling effect of the piezoelectric effect, filtration was performed in the presence or absence of the piezoelectric effect.

AC of 10 Vpp and 500 Hz was applied to generate a piezoelectric effect. Frequency and voltage were determined with reference to previously reported research results.

The polarized PVDF membrane was reported to show the highest average flux and reduction of fouling with AC signals of 10 V and 500 Hz.

The 10ppm alginic acid removal efficiency of the piezoelectric membrane (pENM) for membrane contamination reduction was 51%, and the flux reduction was obtained.

The piezoelectric membrane for membrane contamination reduction (pENM) showed a difference in flux reduction depending on the presence or absence of the piezoelectric effect. The piezoelectric membrane for membrane contamination reduction (pENM) with piezoelectric effect showed 15% lower magnetic flux reduction than the piezoelectric membrane (pENM) for membrane contamination reduction without the piezoelectric effect, and this result is considered to be due to vibration.

Ultrasonic agitation generated by a piezoelectric transducer to overcome fouling during filtration has been described. It has been found that dimensional changes in thickness, length or width with resonant frequency are responsible for localized turbulence on the permeate side that is transmitted to the membrane.

Thus, vibrations generated by the piezoelectric effect can create a fluid unstable environment that retards film surface and film formation.

Despite the huge potential of ENM as a water treatment membrane, significant drawbacks remain for field applications in terms of fouling resistance.

This is because the fibrous membrane has a rougher membrane surface compared to the flat sheet membrane.

In order to overcome this limitation, the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention can minimize foulant adhesion on the membrane surface by vibration of the membrane generated by the piezoelectric effect. In addition, the piezoelectric membrane for reducing membrane fouling (pENM) may exhibit much higher water permeability than a flat sheet membrane, and the piezoelectric reaction may improve the antifouling property of the piezoelectric membrane for membrane fouling reduction (pENM).

As such, the membrane technology of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention is recognized as one of the most important technologies in water treatment.

However, this technique suffers from fouling phenomena that lead to higher operating pressures, reduced flow rates, frequent membrane replacements and ultimately higher operating costs.

Various methods have also been used to reduce the deposition of contaminants on the surface of the membrane and to maintain the flux. Among the various methods to reduce membrane fouling, membrane vibration can be a good candidate for limiting foulant accumulation. And a piezoelectric membrane, one of the vibrating membranes, will be a good alternative membrane material. In addition, the electrospun nanofiber membrane with piezoelectric properties can ensure high water productivity and flux maintenance.

The piezoelectric membrane for membrane fouling reduction (pENM) has shown high potential as a water treatment in terms of water flux and antifouling effect by experiments.

In conclusion, the optimized properties of the piezoelectric membrane for reducing membrane fouling (pENM) for water treatment applications were measured with FE-SEM, FT-IR, UTM, CFP and mercury porosimetry. It was measured with an acetone/NMP solvent ratio of 5/5, a TCD of 20 cm and a heat treatment time (HpENM) of 0.5 h.

The piezoelectric membrane for membrane fouling reduction (pENM) showed a water permeability of 5573.24 LMH/bar and a kaolin removal rate of 99%. This result was higher than that of commercial MF membranes due to the high porosity and surface area/volume ratio of the piezoelectric membrane (pENM) for reducing membrane contamination.

Manufacturing conditions such as solvent ratio and heat treatment directly or indirectly affect antifouling properties and filtration ability.

Piezoelectric ENM properties such as beta phase ratio and mechanical properties affect filtration performance or antifouling. In addition, the piezoelectric reaction improved the antifouling properties of HpENM. When the piezoelectric effect was applied, the flux reduction was reduced by 15% compared to the case without the piezoelectric effect.

Therefore, it is determined that the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention provides optimal manufacturing conditions for developing a piezoelectric membrane using electrospinning technology, and has strengths in terms of moisture generation and membrane contamination reduction do.

The improved performance of the piezoelectric membrane (pENM) for reducing membrane contamination according to an embodiment of the present invention may improve water treatment capability in water treatment applications.

The description of the present invention described above is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and likewise components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.

Claims (6)

preparing a PVDF solution by mixing PVDF with acetone and NMP mixed solvent;
preparing a nanofiber mat on a current collector by electrospinning the PVDF solution;
removing the residual solvent by immersing the nanofiber mat in a deionized water bath;
drying the nanofiber mat from which the residual solvent is removed; and
manufacturing a piezoelectric membrane by heat-treating the dried nanofiber mat; characterized in that it is configured to include,
The PVDF solution is prepared by mixing the PVDF with a mixed solvent in which the acetone and the NMP are mixed in a volume ratio of 4: 6 to 6: 4,
The manufacturing of the nanofiber mat comprises performing electrospinning in which the PVDF solution is spun and a voltage of 10 kV to 13 kV is applied to a high voltage power supply device. delete The method of claim 1, wherein the manufacturing of the nanofiber mat comprises:
Method for producing a piezoelectric membrane for reducing membrane contamination, characterized in that the step of manufacturing the nanofiber assembly by performing electrospinning while spinning the PVDF solution, and coating the nanofiber assembly with aluminum foil to prepare the nanofiber mat. According to claim 1,
The electrospinning of the step of preparing the nanofiber mat is a method for producing a piezoelectric membrane for reducing membrane contamination, characterized in that the TCD (tip to collector distance) is performed in the range of 15 cm to 20 cm. It is characterized in that it was manufactured according to the method for manufacturing a piezoelectric membrane for reducing membrane contamination of claim 1,
Contains PVDF piezoelectric polymer nanofibers,
A piezoelectric membrane for reducing membrane contamination, characterized in that mechanical vibration is generated according to an applied voltage. 6. The method of claim 5,
A piezoelectric membrane for reducing membrane fouling, characterized in that the tensile strength is 0.5 MPa to 1.0 MPa.

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