Ceramic nanofiltration membrane for water treatment without intermediate layer and manufacturing method therefor

Abstract

The present invention relates to a ceramic nanofiltration membrane for water treatment without an intermediate layer and a manufacturing method therefor and, specifically, to a ceramic nanofiltration membrane for water treatment and a manufacturing method therefor, wherein MoS2 and PEI are attached onto the surface of the ceramic nanofiltration membrane by electrostatic attraction of H-S and C-S pairs between sulfur (S) and hydrogen (H) atoms and between sulfur (S) and carbon (C) atoms in each molecule. The ceramic nanofiltration membrane of the present invention has high mechanical stability while maintaining ion removal ability encompassing filtration amount, filtration recovery rate, and ion removal rate, can withstand extreme environments, such as semiconductor wastewater, through strong properties thereof, and allows for a small interlayer gap without the need for an intermediate layer, enabling the removal of fine contaminants, such as dissolved silica in semiconductor wastewater.

Description

Ceramic nanofiltration membrane for water treatment with intermediate layer removed and method for manufacturing the same

[0001] The present invention relates to a ceramic nanofiltration membrane, specifically, to a ceramic nanofiltration membrane for water treatment having a coating layer and a method for manufacturing the same.

[0002] As industrial development continues, the harmful effects of hazardous substances such as dust, soot, waste gases, smoke, and volatile organic compounds (VOCs) generated from various industrial processes are increasing. Consequently, some companies are using polymer filters to prevent the release of these pollutants. However, these filters suffer from poor heat resistance, chemical resistance, wear resistance, and flame retardancy.

[0003] Therefore, to solve these problems, ceramic filters have been developed. Ceramic filters have much better heat resistance, chemical resistance, and wear resistance than polymer filters. In particular, because of their excellent heat resistance, there is no need to install a separate cooling device within the exhaust device, which has the advantage of reducing installation and maintenance costs.

[0004] Conventional ceramic membranes consist of a three-layer structure: support, intermediate layer, and separation layer. The reason for the intermediate layer is as follows. If the separation layer were dip-coated on the support without an intermediate layer, the pores of the support would be larger than the particles forming the separation layer, so the separation layer particles would completely penetrate the pores of the support, blocking the pores and preventing the formation of a separation layer. Therefore, a intermediate layer composed of medium-sized particles is coated on the support with the largest particles, and a separation layer composed of the smallest particles is coated on top of that.

[0005]

[0006] Meanwhile, membrane filtration process using nanofiltration membrane (NF) is attracting attention as an advanced water purification process because it can maintain a relatively high membrane flux compared to the reverse osmosis (RO) membrane filtration process and has the advantage of being able to remove even low-molecular-weight organic substances.

[0007] The membrane materials primarily used in the nanofiltration membrane (NF) process are made of polymers, which are relatively inexpensive and easy to manufacture. However, they have the disadvantage of being vulnerable to high temperatures and organic solvents. To overcome this, research and technology development are actively being conducted, mainly in Japan, on ceramic nanofiltration membranes made of inorganic materials that have excellent heat, chemical, and pressure resistance and can be used semi-permanently. These membranes are made of various materials such as Al2O3, TiO2, and ZrO2. However, ceramic membranes are currently limited to microfiltration / ultrafiltration, and ceramic nanofiltration technology has not been developed much. In particular, ceramic nanofiltration technology is virtually non-existent in Korea.

[0008] Currently, ceramic filtration membranes are manufactured using silica, clay, and alumina as raw materials through consolidation and sintering. However, the sol-gel process, commonly used to manufacture ceramic membranes, requires smaller particles than conventional nanofiltration membranes. Furthermore, the production of defect-free ceramic membranes is a highly sensitive process requiring special technical attention. Furthermore, the production of defect-free ceramic nanomembranes presents manufacturing limitations, such as the requirement for high-quality supports and intermediate layers. Consequently, ceramic filtration membranes are currently manufactured only as microfiltration or ultrafiltration membranes with a relatively small average pore size.

[0009]

[0010] Recently, there has been a lot of research being conducted on modifying ultrafiltration membranes using nanomaterials such as TiO2 and carbon nanotubes to produce nanofiltration membranes (although examples of ceramic membranes are rare). One of the nanomaterials utilized in this is graphene oxide. Graphene oxide (GO) is a two-dimensional graphene oxide sheet containing carboxyl, hydroxyl, and epoxy groups. It is easily dispersed in water and easy to handle, so it is commonly used to modify the surface of membranes. By increasing the negative charge on the membrane surface, it can improve hydrophilicity, rejection capacity, and membrane fouling resistance. However, due to its high hydrophilicity, there is a problem that swelling occurs in water, which reduces the rejection capacity.

[0011] The present invention provides a ceramic nanofiltration membrane having improved chemical / thermal / mechanical stability, low operating pressure, long life, bacterial resistance, and ease of cleaning compared to conventional polymer membranes, and a method for manufacturing the same, which can be used in an advanced water purification process capable of maintaining a high membrane permeation flux and removing even low molecular weight organic substances.

[0012] In addition, the present invention provides a ceramic nanofiltration membrane for water treatment from which an intermediate layer has been removed and a method for manufacturing the same.

[0013] Meanwhile, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary knowledge in the technical field to which the present invention belongs from the description below.

[0014] To achieve the above purpose, the present invention provides a ceramic nanofiltration membrane for water treatment and a method for manufacturing the same, characterized in that MoS2 and PEI are attached to the surface of the ceramic nanofiltration membrane by electrostatic attractive interaction between the sulfur (S) of the MoS2 molecule and the hydrogen (H) and carbon (C) of the PEI molecule, and the HS and CS pairs.

[0015] The ceramic nanofiltration membrane of the present invention has high mechanical stability while maintaining ion removal ability including filtration amount, filtration recovery rate, and ion removal rate, and can withstand extreme environments such as semiconductor wastewater with strong physical properties, and can maintain a small interlayer gap by not requiring an intermediate layer, so it has the advantage of being able to remove fine contaminants such as dissolved silica in semiconductor wastewater.

[0016] However, the effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0017] FIG. 1 is a schematic diagram illustrating a ceramic nanofiltration membrane in which MoS2 and PEI are cross-coated on the ceramic nanofiltration membrane according to the present invention.

[0018] Figure 2 is a schematic diagram illustrating a method for manufacturing a ceramic nanofiltration membrane of the present invention.

[0019] Figure 3 illustrates a photograph of a filling device and a filled ceramic nanofiltration membrane of step 1 of the manufacturing method of the present invention.

[0020] Figure 4 shows a photograph of the device of steps 3 and 4 of the manufacturing method of the present invention and the obtained ceramic nanofiltration membrane.

[0021] Figure 5 illustrates a photograph of the device of step 5 of the manufacturing method of the present invention and the obtained ceramic nanofiltration membrane.

[0022] Figures 6a, 6b and 6c illustrate graphs and tables showing the evaluation results of NaF filtration, filtration recovery rate and removal performance of the present invention.

[0023] The significance of the features and advantages of the present invention will be better understood by reference to the accompanying drawings. However, it should be understood that the drawings are provided for illustrative purposes only and do not define the limitations of the present invention.

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily practice the present invention. However, since the description of the present invention is merely an embodiment for structural and functional explanation, the scope of the present invention should not be construed as being limited by the embodiment described in the text. That is, since the embodiment can be modified in various ways and can have various forms, the scope of the present invention should be understood to include equivalents that can realize the technical idea. In addition, the purpose or effect presented in the present invention does not mean that a specific embodiment must include all of it or only include such effects, and therefore the scope of the present invention should not be construed as being limited thereby.

[0025] In the present invention, singular expressions described should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as “comprise” or “have” should be understood to specify the presence of a described feature, number, step, operation, component, part, or combination thereof, and do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0026] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted to be consistent with their meaning within the context of the relevant technology, and should not be interpreted as having an idealized or overly formal meaning unless explicitly defined herein.

[0027]

[0028] One embodiment of the present invention provides a ceramic nanofiltration membrane for water treatment, which is cross-coated with MoS2 and PEI.

[0029] Specifically, as illustrated in FIG. 1, the ceramic nanofiltration membrane for water treatment of the present invention is characterized in that MoS2 and PEI are alternately coated on the surface of the ceramic nanofiltration membrane, and MoS2 and PEI are attached by electrostatic attraction between sulfur (S) and hydrogen (H) and carbon (C) of each molecule, HS and CS pairs, and in particular, the ceramic nanofiltration membrane for water treatment is characterized in that, in the presence of MoS2, PEI is attached by electrostatic attraction between sulfur (S) and hydrogen (H) and carbon (C) of each MoS2 molecule, HS and CS pairs, and thus does not require an intermediate crosslinker to combine MoS2 and PEI.

[0030]

[0031] Each component is described below.

[0032] The ceramic nanofiltration membrane is a porous ceramic nanofiltration membrane, and may have a porosity of 30% to 70% by volume, preferably 30% to 40% by volume, based on the total volume of the membrane. In addition, the pores of the ceramic nanofiltration membrane may be 1 to 10 nm. The pores of the membrane may function as channels. The channels refer to passages through which fluid or gaseous substances move within the membrane.

[0033] The ceramic nanofiltration membrane usable in the present invention is selected from the group consisting of titania, alumina, silica, and zirconia.

[0034]

[0035] In addition, MoS2 is a type of transition metal dichalcogenide (TMD or TMDC) compound composed of three molecular layers in the form of MX2 (where M represents a transition metal and X represents a Group 16 element such as oxygen or sulfur). Each layer of MoS2 typically has a thickness of about 0.65 nm, and its Young's modulus is about 0.33 TPa, showing mechanically flexible properties. In addition, it can be applied to various fields because it shows high stability in liquid or air, and the constituent layers can be easily separated into single layers because they have the characteristic of weak van der Waals forces.

[0036]

[0037] PEI is an abbreviation for polyethyleneimide, and is characterized by having an amine group (-NH2) as a terminal group. As can be seen in Fig. 1, the PEI of the present invention binds to the ceramic nanofiltration membrane through the bond between OH and NH2, which is stably fixed to the surface of the ceramic membrane by hydrogen bonding by heating. The PEI thus bound forms a bond through the electrostatic attraction of the HS and CS pairs between the sulfur (S) of MoS2 and the hydrogen (H) and carbon (C) of PEI. Through this reaction, the bond between MoS2 and PEI is very stable and does not require an intermediate linker. The MoS2 and PEI solution are deposited on the surface of the ceramic nanofiltration membrane by the electrostatic attraction to form a coating layer. As described above, since the present invention does not require an intermediate linker, it has the effect of reducing the process time and process cost.

[0038] The thickness of the coating layer composed of MoS2 and PEI of this structure may be 1 nm to 1,000 μm, preferably 10 nm to 100 μm, more preferably 100 nm to 10 μm. The coating layer may be porous having pores, and the average diameter of the pores of the coating layer may be 0.01 nm to 100 μm, preferably 0.1 nm to 1,000 nm.

[0039]

[0040] In addition, another embodiment of the present invention provides a method for manufacturing a ceramic nanofiltration membrane for water treatment in which MoS2 and PEI of the present invention are cross-coated.

[0041] Specifically, the manufacturing method of the present invention is as shown in Fig. 2,

[0042] A step of filling polyphenylene sulfite solid particles into the pores of a ceramic nanofiltration membrane (step 1);

[0043] A step of immersing the above solid particle-filled ceramic nanofiltration membrane in a PEI solution to form PEI on the ceramic surface (step 2);

[0044] Step of depositing a MoS2 / PEI multilayer thin film on a ceramic nanofiltration membrane (step 3);

[0045] A step of forming a ceramic coating layer by heating the above MoS2 / PEI multilayer thin film (step 4); and

[0046] It includes a step (step 5) of removing the filled polyphenylene sulfite solid particles by etching them with a sodium hydroxide (NaOH) solution.

[0047]

[0048] Below, each step is described in detail.

[0049] Step 1 is to fill the pores of a ceramic nanofiltration membrane with polyphenylene sulfite solid particles.

[0050] The ceramic nanofiltration membrane of the present invention has multiple pores and may have a porosity of 30 to 70% by volume, preferably 30 to 40% by volume, based on the total volume of the membrane to facilitate the movement of substances such as fluids and gases. The average diameter of the pores of the membrane may be 1 to 10 nm.

[0051] Pore ​​size can be typically measured using Mercury Intrusion Porosimetry, Liquid-Liquid Displacement (LLD), or a capillary flow porosimeter. That is, while sequentially changing the pressure of an unreacted inert gas, a wetting medium corresponding to the sample is infiltrated or extruded into the pores of the porous ceramic nanofiltration membrane. During this process, the pressure at a specific point, the weight of the medium, the gas flow rate, etc. are recorded. Thereafter, the pore size can be calculated using the Laplace equation (ASTM, F316-03, Standard test methods for pore size characteristics of membrane filters by bubble point and mean flow pore test). In the present invention, the pore size measured by the mercury intrusion method was used. In addition, the pore size of the ceramic nanofiltration membrane surface can be confirmed through SEM, the permeability of a fluid (liquid or gas) passing through the ceramic nanofiltration membrane at a certain pressure can be measured, and the pore size can be calculated inversely from the Hogen-Poiseuille equation.

[0052] The pores of the porous ceramic nanofiltration membrane of the present invention can function as channels. The channels refer to passages through which fluid or gaseous substances move within the porous ceramic nanofiltration membrane.

[0053] In the present invention, polyphenylene sulfite solid particles are used as the solid particles. These solid particles can be filled by a wet process using water or an organic solvent, or can be filled by a dry process without using a solvent (see Fig. 3). Examples include a dry rubbing method, a tapping method in which filled particles are placed on a support without a dispersion medium solvent and are evenly filled by applying constant vibration and force, or a vacuum method in which a vacuum is applied from the bottom of the support to partially penetrate the solid particles into the membrane pores and fill them. Preferably, the dry rubbing method can be used. When no solvent is used, it is more economical and suitable for mass production than the wet method. In addition, since the filled solid particles prevent the coating layer particles from deeply penetrating into the porous ceramic nanoparticle membrane, it has the advantage of having less influence on the membrane porosity.

[0054]

[0055] Step 2 is to immerse the solid particle filled ceramic nanofiltration membrane in a PEI solution to form PEI on the ceramic surface.

[0056] The concentration of the PEI solution may be 1,000 to 2,000 mg / L. Below the above range, a problem may arise in which the substance does not sufficiently contact the membrane, and above the above range, aggregation of solutes within the solution may occur.

[0057] The time for immersing the ceramic nanofiltration membrane in the PEI solution is preferably 6 to 24 hours, and most preferably 12 hours. If the time is less than the above range, there may not be enough time for the substance to be sufficiently adsorbed into the solution, and if the time exceeds the above range, the problem of the adsorbed substance resuspending may occur.

[0058]

[0059] Step 3 is to deposit a MoS2 / PEI multilayer film on a ceramic nanofiltration membrane. This process can be repeated until the thickness of the MoS2 / PEI multilayer film becomes 1 nm to 1,000 μm, preferably 10 nm to 100 μm, and more preferably 100 nm to 10 μm.

[0060]

[0061] Step 4 is to heat the MoS2 / PEI multilayer film to form a ceramic coating layer. At this time, the heating temperature may be 60 to 100°C. If it is below the above range, the MoS2 / PEI multilayer film may not be sufficiently fixed on the membrane, and if it exceeds the above range, the MoS2 / PEI multilayer film structure may be deformed.

[0062]

[0063] Step 5 involves removing the filled polyphenylene sulfite solid particles by etching them with a sodium hydroxide (NaOH) solution.

[0064]

[0065] The ceramic nanofiltration membrane of the present invention and the ceramic nanofiltration membrane manufactured by the manufacturing method first fill the pores of the ceramic nanofiltration membrane with polyphenylene sulfite solid particles, thereby preventing PEI from penetrating the pores and thus having less influence on the porosity of the ceramic nanofiltration membrane, and also has the advantage of being filled without a solvent, thereby having an advantage in terms of processability, and further, being easily removable through NaOH etching.

[0066] In addition, the ceramic nanofiltration membrane of the present invention is characterized by having the advantages of being able to form a multilayer thin film coating layer stably and easily by forming an electrostatic attraction of MoS2 / PEI, having excellent ion removal ability including filtration amount, filtration recovery rate, and ion removal rate, and having high mechanical stability.

[0067]

[0068] For example, the filtration amount, filtration recovery rate, and NaF rejection rate of the ceramic nanofiltration membrane of the present invention are specifically shown in FIGS. 6A to 6C. As can be seen in FIG. 6A, the initial filtration amount decreased due to the MoS2 and PPS layers, whereas the NaF and final distilled water filtration amounts were constant due to the effect of the layers. In addition, the filtration amount decreased as MoS2 and PPS were layered, but when NaF and the subsequent final distilled water were filtered, the filtration reduction was relatively lower than 1 kDa. In addition, as can be seen in FIG. 6B, the value of the MoS2 / PPS@1 kDa sample in terms of the initial to final distilled water filtration recovery rate was 94.0%, which was significantly greater than that of the MoS2@1 kDa and 1 kDa samples. Additionally, as can be seen from Fig. 6c, the MoS2 / PPS@1 kDa sample had the highest removal rate of 37.0% in terms of NaF removal rate.

[0069] In conclusion, the ceramic nanofiltration membrane of the present invention was very excellent in terms of filtration capacity, filtration recovery rate, and NaF removal rate, and in particular, the filtration recovery rate was significantly excellent through the combination of MoS2 and PPS.

[0070]

[0071] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not construed as being limited to the examples described below. The examples of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0072]

[0073] <Example 1> Manufacturing of the ceramic nanofiltration membrane of the present invention 1

[0074] Step 1: A small amount of polyphenylene sulfite solid particles having a particle size of 0.5 nm were placed on one surface of an alumina porous membrane having a pore size of 1 nm, and the polyphenylene sulfite solid particles were spread by applying pressure while rotating, rubbing, and pressing them in a circular motion from top to bottom by hand to fill the pores of the porous support. After sufficient filling, the surface of the porous support was wiped with a dry cloth or wipe-ol to remove excess polyphenylene sulfite.

[0075] It was confirmed by the difference in brightness that the pores were filled with polyphenylene sulfite solid (see Fig. 3).

[0076]

[0077] Step 2: The alumina porous membrane of Step 1 was immersed in a PEI solution (1,000 mg / L) for 1 hour to form PEI on the surface of the alumina porous membrane.

[0078]

[0079] Step 3: A MoS2 / PEI multilayer film (5 μm thick) was deposited on the alumina membrane (see Fig. 4).

[0080]

[0081] Step 4: The above MoS2 / PEI multilayer film was heated at 60°C for 12 hours to form an alumina coating layer, thereby manufacturing a porous alumina membrane coated with MoS2 / PEI (see Fig. 4).

[0082]

[0083] Step 5: The polyphenylene sulfite solid particles filled in Step 1 were removed by etching the porous alumina membrane of Step 6 with 100 mL of 2 M NaOH.

[0084] The surface of the porous alumina membrane appeared to be blurred with the naked eye, confirming that the polyphenylene sulfite solid particles were etched with NaOH (see Fig. 5).

[0085]

[0086] <Example 2> Manufacturing of the ceramic nanofiltration membrane of the present invention 2

[0087] The same procedure as in Example 1 was followed, except that one selected from the group consisting of titania, silica, and zirconia was used instead of the porous alumina membrane.

[0088]

[0089] <Experimental Example 1> Evaluation of NaF filtration, filtration recovery rate, and removal performance of the ceramic nanofiltration membrane of the present invention

[0090] This experimental example evaluated the NaF filtration, filtration recovery rate, and removal performance of the ceramic nanofiltration membrane of the present invention.

[0091] The remaining NaOH solution on the etched membrane before filtration was thoroughly washed with ultrapure water, and then the membrane was loaded onto the module to prepare for filtration. Ultrapure water was used for 3 hours before and after filtration of 1,000 mg / L NaF, and NaF was filtered for 1 hour. All filtrations were performed at a transmembrane pressure of 3 bar, and the filtration amount and recovery rate were calculated by measuring the weight of the filtered water in real time. In addition, the removal rate was calculated from the inlet / outlet NaF concentrations using ion chromatography.

[0092]

[0093] Figures 6a and 6b show the results for filtration amount and filtration recovery rate. As can be seen in Figure 6a, the initial filtration amount decreased due to the MoS2 and PPS layers, while the NaF and final distilled water filtration amounts remained constant due to the influence of the layers. Furthermore, the filtration amount decreased as the MoS2 and PPS layers were layered, but when NaF and the subsequent final distilled water were filtered, the filtration reduction was relatively low, less than 1 kDa.

[0094] Additionally, as can be seen in Fig. 6b, the value of the MoS2 / PPS@1 kDa sample in terms of the initial to final distilled water filtration recovery rate was 94.0%, which was significantly greater than that of the MoS2@1 kDa and 1 kDa samples.

[0095] Additionally, as can be seen from Fig. 6c, the MoS2 / PPS@1 kDa sample had the highest removal rate of 37.0% in terms of NaF removal rate.

[0096] In conclusion, the ceramic nanofiltration membrane of the present invention was very excellent in terms of filtration capacity, filtration recovery rate, and NaF removal rate.

[0097] The ceramic nanofiltration membrane of the present invention has high mechanical stability while maintaining ion removal ability including filtration amount, filtration recovery rate, and ion removal rate, and can withstand extreme environments such as semiconductor wastewater with strong physical properties, and can maintain a small interlayer gap by not requiring an intermediate layer, so it can remove fine contaminants such as dissolved silica in semiconductor wastewater, and thus has industrial applicability.

Claims

1. In a ceramic nanofiltration membrane for water treatment, MoS2 (Molybdenum disulfide) and PEI (Polyethyleneimine) are alternately coated on the surface of the above ceramic nanofiltration membrane. The above MoS2 and PEI are attached by electrostatic attraction between the HS and CS pairs between the sulfur (S) and hydrogen (H) and carbon (C) of each molecule, A ceramic nanofiltration membrane for water treatment, characterized by excellent ion filtration performance including filtration capacity, filtration recovery rate, and ion rejection rate.

2. A ceramic nanofiltration membrane for water treatment, characterized in that in the first paragraph, the PEI is attached by electrostatic attraction between the sulfur (S) and hydrogen (H) and carbon (C) pairs of HS and CS in the presence of MoS2, and thus does not require an intermediate linker (crosslinker) to combine MoS2 and PEI.

3. A ceramic nanofiltration membrane for water treatment, characterized in that, in the first or second paragraph, PEI is fixed by hydrogen bonding through heating.

4. A ceramic nanofiltration membrane for water treatment, characterized in that the thickness of the layer composed of MoS2 and PEI in the first paragraph is 1 nm to 1,000 ㎛.

5. A method for manufacturing a ceramic nanofiltration membrane of paragraph 1, A step of filling polyphenylene sulfite solid particles into the pores of a ceramic nanofiltration membrane (step 1); A step of immersing the above solid particle-filled ceramic nanofiltration membrane in a PEI solution to form PEI on the ceramic surface (step 2); Step of depositing a MoS2 / PEI multilayer thin film on a ceramic nanofiltration membrane (step 3); A step of forming a ceramic coating layer by heating the above MoS2 / PEI multilayer thin film (step 4); and A manufacturing method comprising a step (step 5) of removing the filled polyphenylene sulfite solid particles by etching them with a sodium hydroxide (NaOH) solution.

6. A manufacturing method according to claim 5, characterized in that the time for immersing the ceramic nanofiltration membrane in the PEI solution and the time for immersing the ceramic nanofiltration membrane with PEI fixed in the MoS2 solution are 6 to 24 hours.

7. A manufacturing method according to claim 5 or 6, characterized in that the concentration of the PEI solution is 1,000 to 2,000 mg / L and the concentration of the MoS2 solution is 1,000 to 2,000 mg / L.

8. A manufacturing method according to claim 5, characterized in that the heating temperature is 60 to 100°C.

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