Filtration membrane and method for producing same

Abstract

To provide a filtration membrane and a method for manufacturing the same.SOLUTION: The filtration membrane comprises a porous membrane comprising a polymer and a derivatized polydopamine layer disposed on one or both sides of the porous membrane. The derivatized polydopamine layer is disposed on the porous membrane in the presence of an oxidizing agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to filtration membranes and methods for making same. In particular, the disclosure is applicable to the production of high purity chemicals used in the semiconductor manufacturing industry, as well as the water, food, and pharmaceutical industries. [Background technology]

[0002] In the semiconductor manufacturing industry, process chemicals, including liquids, are used throughout the manufacturing process, for example, in lithography, coating, cleaning, stripping, etching, and chemical-mechanical planarization (CMP) processes. Such chemicals include, for example, acids, solvents, photoresists, antireflective materials, developers, removers, slurries, and cleaning solutions. Due to the continuing reduction in critical dimensions required for advanced semiconductor devices, it is becoming increasingly important that process chemicals be provided in ultra-high purity form. However, even in purified form, process chemicals typically contain trace amounts of metals, such as iron, sodium, nickel, copper, calcium, magnesium, and potassium, among others. The presence of metals in process chemicals can be harmful, for example, resulting in patterning defects and altered electrical properties of formed devices, thereby affecting device reliability and product yield. Sources of such metal impurities can originate from raw materials used in the chemical manufacturing process or may be otherwise introduced during the manufacturing and packaging processes.

[0003] The reduction of metal and other impurities from process chemicals, raw materials, and precursors is traditionally achieved through the use of ion exchange and / or filtration processes. Ion exchange purification systems have many drawbacks. Many ion exchange resins have highly chemically reactive functional groups, making them unsuitable for acid-sensitive raw materials. Resins are also prone to decomposition and leaching of organic impurities, which can cause quality issues similar to metallic impurities.

[0004] Therefore, it would be desirable to develop improved filtration membranes and methods for making and using the same that address one or more of the problems associated with the prior art. Furthermore, filtration is an essential part of the manufacturing process for semiconductor-grade chemicals and formulations to remove particulate impurities. A filtration process that can remove both particulate and ionic impurities would be ideal. Summary of the Invention [Means for solving the problem]

[0005] The filtration membrane includes a porous membrane containing a polymer and a derivatized polydopamine layer disposed on one or both sides of the porous membrane in the presence of an oxidizing agent.

[0006] The method for coating a porous membrane includes placing the porous membrane in a solution containing dopamine monomer, a buffer, an oxidizing agent, and a solvent in a reactor. The dopamine monomer, buffer, and oxidizing agent are gradually added to the reactor to form a polydopamine layer on the porous membrane. The polydopamine layer is derivatized with an amine, a thiol, a carboxylic acid, or a combination thereof.

[0007] A method for purifying a liquid includes passing the liquid through a filtration membrane, the filtration membrane including a porous membrane and a derivatized polydopamine layer disposed on one or both sides of the porous membrane, the derivatized polydopamine layer being disposed on the porous membrane in the presence of an oxidizing agent, and removing ionic and particulate impurities from the liquid. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a bar graph showing metal nanoparticle removal for untreated and polydopamine-coated membranes. [Figure 2] 1 is a bar graph showing metal nanoparticle removal for untreated and polydopamine-coated membranes. [Figure 3]1 is a bar graph showing metal nanoparticle removal for untreated and polydopamine-coated membranes. DETAILED DESCRIPTION OF THE INVENTION

[0009] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms "a," "an," and "the" are intended to include the singular and plural unless the context indicates otherwise.

[0010] Autopolymerization refers to the process by which monomers form large chain molecules (i.e., polymers) without the need for a chemical initiator. In this case, oxygen dissolved in the solvent is thought to play a role similar to that of an initiator in the polymerization process. This process can be accelerated by adding a chemical oxidant, which can result in improved coatings.

[0011] Nominal pore size refers to the approximate size of the pores in a filter or membrane and represents the diameter of the pores that are expected to remove the majority of particles. Unlike absolute pore sizes, which specify a precise cutoff value, nominal pore size is a more general measure and is often expressed as the size at which a certain percentage (e.g., 90% or 95%) of particles are retained by the filter.

[0012] Disclosed herein are filtration membranes coated with polydopamine or its derivatives. The polydopamine or derivatives form a stable coating on one or both sides of the membrane. In one embodiment, an oxidizing agent is added to the precursor solution used to prepare the polydopamine. The use of an oxidizing agent increases polydopamine loading on the membrane, which correlates with improved metal removal capabilities. In another embodiment, the polydopamine membrane is subsequently functionalized with an amine. This subsequent functionalization improves metal removal from contents that come into contact with the membrane. These contents can include, for example, acids, solvents, polymers, photoresists, antireflective materials, developers, removers, slurries, and cleaning solutions.

[0013] Also disclosed herein is a method for forming a filter by coating one or more surfaces of a membrane with a polydopamine layer, optionally including a step of derivatizing the polydopamine layer. The method includes dissolving a dopamine-containing monomer and a buffer in a solvent to form a reaction solution, and then applying the reaction solution to one or more surfaces of the membrane to form a coating. The buffer promotes polymerization of the dopamine-containing monomer to form polydopamine.

[0014] In one embodiment, a filter can be formed by coating both opposing sides of a membrane with a layer of polydopamine, where the polydopamine layer on one or both sides may be derivatized as needed.

[0015] film In one embodiment, the membrane can comprise an organic polymer. The organic polymer is preferably a thermoplastic, non-aromatic hydrocarbon polymer having a linear carbon-carbon skeletal molecular structure containing only non-aromatic substituents and having multiple free hydrogen atoms bonded to carbon atoms in the polymer chain. These polymers can be extruded, blown, or cast to form membranes. In one embodiment, the membrane comprises a polyolefin, a fluoropolymer, or a combination thereof. Examples of these thermoplastic extrusion-grade or moldable-grade organic polymers include homopolymers of ethylene, propylene, isobutylene, methylpentene-1, butene-1, vinyl chloride, vinylidene chloride, and acrylonitrile, copolymers of the aforementioned monomers; chlorinated polyethylene and chlorinated polypropylene; fluoropolymers such as polytetrafluoroethylene and perfluoroalkoxy polymers; polyamides, polyimides, polyesters, polystyrene, polysulfones, and blends of the aforementioned monomers and copolymers. High- and low-density polyethylene, polypropylene, ethylene / propylene copolymers, ethylene / 1-butene copolymers, and blends thereof are particularly important.

[0016] In one embodiment, the membrane is porous. The membrane may have a porosity of 10 to 90 volume percent, preferably 30 to 70 volume percent, based on the total volume of the membrane. The membrane has a nominal pore size of 0.5 nanometers to 5 micrometers, preferably 5 nanometers to 200 nanometers. These "nominal" pore sizes are determined by methods such as bubble point tests and nanoparticle retention tests.

[0017] Preparation of reaction solution The reaction to form polydopamine can be carried out in a reactor into which the membrane is later immersed. The reactants (dopamine-containing monomer and buffer), preferably along with a solvent, are added directly to a vessel where they undergo a reaction to form the polydopamine coating.

[0018] The polydopamine layer is made by polymerizing a dopamine-containing monomer in a reaction solution using a buffer. The dopamine-containing monomer, buffer, solvent, oxidant, and any additional components are added to a reactor to form a reaction solution. The dopamine-containing monomer undergoes autopolymerization to form polydopamine.

[0019] The dopamine-containing monomer is typically in the form of a salt. In such cases, dopamine is preferably present in its protonated form with a halide counterion, such as Cl, Br, F, or I. In a preferred embodiment, the dopamine-containing monomer is dopamine hydrochloride.

[0020] The dopamine-containing monomer is typically present in the reaction solution in an amount of 0.01 to 10 weight percent (wt %), based on the total weight of the reaction solution. The dopamine-containing monomer is preferably present in the reaction solution in an amount of 0.02 to 5 wt %, 0.02 to 1 wt %, or 0.05 to 0.20 wt %, based on the total weight of the reaction solution.

[0021] The buffer is primarily used to adjust the pH of the solution to be in a range that promotes the autopolymerization of the dopamine-containing monomer. The buffer preferably has a pKa of 7.0 to 9.0.

[0022] Examples of buffers include Tris buffer (tris(hydroxymethyl)aminomethane), sodium dihydrogen phosphate, potassium dihydrogen phosphate, or a combination thereof. Tris buffer (tris(hydroxymethyl)aminomethane) is a preferred buffer. However, it may be replaced by any other buffer with a pKa of 7.0 to 9.0, such as sodium dihydrogen phosphate or potassium dihydrogen phosphate.

[0023] The buffer is typically present in the reaction solution in an amount of 0.01 to 5 wt % based on the total weight of the reaction solution, and preferably in an amount of 0.01 to 3 wt %, 0.05 to 1 wt %, or 0.10 to 0.30 wt % based on the total weight of the reaction solution.

[0024] The oxidizing agent promotes an increase in the amount of polydopamine deposited on the membrane surface, particularly compared to a reaction solution without the oxidizing agent. This increased presence of dopamine improves the metal removal capacity from the solution in contact with the membrane. The oxidizing agent is preferably water-soluble and includes, for example, hydrogen peroxide, organic peroxides, nitrates, permanganates, periodates, persulfates, dichromates, chlorates, perborates, or combinations thereof. Examples of suitable oxidizing agents include alkali metal metaperiodates (e.g., sodium metaperiodate, potassium metaperiodate, lithium metaperiodate, or combinations thereof), alkali metal perchlorates (e.g., lithium perchlorate, sodium perchlorate, potassium perchlorate, or combinations thereof), ammonium salts (e.g., ammonium persulfate, ammonium nitrate, ammonium dichromate, ammonium persulfate, ammonium perchlorate, ammonium periodate, or combinations thereof), or combinations thereof.

[0025] In one embodiment, controlled, gradual addition of the oxidizing agent to the reaction solution can result in improved membrane coating compared to adding the oxidizing agent all at once to the reaction solution. This is because the oxidizing agent significantly accelerates the coating reaction, allowing polydopamine particles to form in the solution without depositing on the membrane. By gradually adding the oxidizing agent, the reaction rate can be controlled to maximize the amount of polydopamine coated onto the filter membrane.

[0026] In one embodiment, one or more of the dopamine monomer, buffer, and oxidizing agent can be added gradually to the reaction solution. If the reagent concentrations (especially the oxidizing agent concentration) are too high, polydopamine formation can occur too quickly, potentially resulting in the precipitation of small polydopamine particles in the solution. This reduces the amount of polydopamine successfully coated onto the membrane. By gradually adding one or more of the dopamine monomer, buffer, and oxidizing agent, the concentrations of the reagents are maintained within an optimal range, thereby maximizing the slow, controlled deposition of polydopamine onto the membrane and minimizing rapid particle formation.

[0027] In one embodiment, the buffer and dopamine-containing monomer are added to the reactor over a period of 1 to 12 hours, preferably 4 to 8 hours, hi another embodiment, the oxidizing agent is added to the reactor over a period of 2 to 24 hours, preferably 12 to 16 hours.

[0028] In one embodiment, the molar ratio of electrons received by the oxidizing agent (if used) to the electron-donating dopamine-containing monomer is 2:1 to 8:1, preferably 3:1 to 5:1. The oxidizing agent, if used, is typically present in the solution in an amount of 0.001% to 10% by weight, based on the total weight of the reaction solution. More preferably, it is present in an amount of 0.01% to 5% by weight, or 0.1 to 0.5% by weight, based on the total weight of the reaction solution.

[0029] The solvent present in the reaction solution should be capable of dissolving the dopamine-containing monomer and any other solid components of the solution. The solvent forms the remainder of the reaction solution. Examples of suitable solvents are water, organic solvents such as alcohols, or combinations thereof. Particularly preferred solvents include ethanol and / or water.

[0030] The solvent is typically present in the reaction solution in an amount of 90 to 99.99 wt %, based on the total weight of the reaction solution, and preferably in an amount of 95 to 99.99 wt %, 98 to 99.90 wt %, or 99.50 to 99.85 wt %, based on the total weight of the reaction solution.

[0031] In one embodiment, dopamine monomer, an oxidizing agent, and a buffer (to adjust the pH to a range where dopamine self-polymerizes), as well as any additional components, are dissolved in a solvent in a reactor to form a reaction solution. A color change indicates the onset of self-polymerization. For example, the color may be observed to change to a light orange color, then begin to darken, and finally become black, indicating polymerization to high molecular weight polydopamine has occurred. The reaction solution is stirred at a temperature of 10 to 50°C, preferably 18 to 40°C, for 0.5 to 96 hours, preferably 5 to 80 hours, and more preferably 10 to 30 hours, to form a polydopamine coating solution.

[0032] The membrane to be coated with the polydopamine layer is preferably hydrophobic and requires prewetting with a water-miscible organic solvent followed by flushing (e.g., rinsing) with water to remove the solvent. Examples of such water-miscible solvents include alcohols (e.g., methanol, ethanol, isopropanol, ethylene glycol, or combinations thereof), ketones (e.g., acetone, methyl ethyl ketone, cyclohexanone, or combinations thereof), acetonitrile, dimethyl sulfoxide, tetrahydrofuran, glycerol, N-methyl-2-pyrrolidone, etc., or combinations thereof.

[0033] After flushing with water, the membrane is immersed in the polydopamine-containing solution in a reactor or other vessel. The membrane can be introduced into the reaction solution immediately after mixing the components or at any time after the self-polymerization has been initiated. The polydopamine-containing solution is allowed to contact the membrane for 2 to 20 hours, preferably 8 to 19 hours, and more preferably 12 to 16 hours, to promote the deposition of polydopamine on the membrane. The coated membrane is referred to as a polydopamine-coated membrane.

[0034] In one embodiment, both sides of the membrane can be coated with polydopamine. In another embodiment, one side of the membrane can be covered with a removable mask before immersion in the reaction solution. After the polydopamine layer is placed on the membrane, the mask can be removed, allowing only one side of the membrane to be coated. During this coating process, the polydopamine in the vessel or reactor can be gently agitated. Once deposition is complete, the remaining solution is discarded, leaving behind a polydopamine-coated membrane. The polydopamine-coated membrane is washed with water to remove any traces of the reaction solution and other loose particles from the membrane.

[0035] Derivatization of polydopamine In one embodiment, polydopamine-coated membranes can be functionalized after polymerization to form polydopamine derivatives. Derivatized polydopamines can exhibit improved effectiveness for removing metals from the contents of a container. Functionalizing agents that can be used to functionalize polydopamine include, for example, primary amines, secondary amines, tertiary amines, as well as carboxylic acid-containing moieties functionalized with amines and / or thiols, or combinations thereof. The amines can be, for example, linear or cyclic amines. Preferred amines are primary amines, secondary amines, or combinations thereof.

[0036] Examples of primary amines include methylamine, ethylamine, propylamine, ethylenediamine, monoethanolamine, etc., or combinations thereof. Examples of secondary amines include dialkylamines such as dimethylamine, diethylamine, dipropylamine, dibutylamine, diethanolamine, etc., or combinations thereof.

[0037] In one embodiment, amine-functionalized carboxylic acids can be used as functionalizing agents. The carboxylic acids present in these functionalizing agents promote additional metal removal capabilities compared to functionalizing agents containing only primary or secondary amines. Examples include iminodiacetic acid, aspartic acid, ethylenediaminetetraacetic acid, aminopolycarboxylic acids (APCAs) such as hyaluronic acid, or combinations thereof.

[0038] In one embodiment, polydopamine can be derivatized with a functionalizing agent containing a thiol and a carboxylic acid. An example of a functionalizing agent containing both a thiol and a carboxylic acid is mercaptosuccinic acid. Also, functionalizing agents containing both a thiol and an amine can be used to facilitate the removal of metals from the contents of the container.

[0039] In one embodiment, amine- and / or thiol-containing functionalizing agents containing sulfonic acid groups can also be used to facilitate removal of metals from the contents of the container. Examples of such functionalizing agents are sulfamic acid, 3-mercapto-1-propanesulfonic acid, or a combination thereof.

[0040] The amine can be added to the amination solution in whole or in part in the form of its hydrochloride salt rather than the free base, for example, dimethylamine hydrochloride can be used in place of dimethylamine, or more preferably a mixture of the two (dimethylamine and dimethylamine hydrochloride), to adjust the pH to the desired range.

[0041] In a preferred embodiment, during functionalization of polydopamine-coated membranes, an acid is added to the amination solution (if an amine is used to functionalize the polydopamine coating) to adjust the pH to an optimal range. Adjusting the pH allows for the use of higher concentrations of amine, which would otherwise be too high and dissolve the polydopamine coating. The acid can be an inorganic acid, such as hydrochloric acid, but can also be an aminocarboxylic acid, aminophosphonic acid, or aminosulfonic acid, all of which provide additional functional groups to the membrane by deposition with the free-base amine.

[0042] The derivatization of the polydopamine coating is preferably carried out after the formation of the polydopamine coating on the membrane. The functionalizing agent can be dissolved in the second solvent before immersing the polydopamine-coated membrane in the second solvent. The second solvent is preferably water, an alcohol, or a combination thereof. A preferred alcohol is ethanol. A preferred second solvent is water.

[0043] In one embodiment, the functionalizing agent is present in the solution in an amount of 0.01 to 10 wt %, based on the total weight of the functionalization solution, hi another embodiment, the functionalizing agent is present in the solution in an amount of 0.5 to 5.0 wt %, based on the total weight of the functionalization solution.

[0044] In a preferred embodiment, the membrane with the polydopamine coating thereon is then exposed to an amine. Amination of the polydopamine coating is optional, but it significantly improves metal removal performance. The polydopamine-coated membrane is immersed in an aqueous solution of an amine and agitated for 12 to 16 hours. The amine found to significantly improve metal removal performance is dimethylamine.

[0045] An optional pickling step may be used to remove residual metals that may impair membrane performance. The membrane is immersed in a dilute aqueous solution of acid, preferably trace metals grade (e.g., hydrochloric acid), and stirred for several hours. A water-miscible alcohol, such as isopropyl alcohol, may be used as a co-solvent. The pickling step can be performed after the polydopamine coating step, after the amination step, or after both steps.

[0046] After the pickling step, the membrane may be thoroughly washed with water before use. If the membrane is to be used in the purification of non-aqueous solvents or formulations, residual water must be removed by drying at elevated temperatures or by flushing with a non-aqueous solvent to displace the water. After the water-washing step, a drying / thermal curing step may optionally be performed, which improves the stability of the derivatized coating. The membrane is dried at 50-100°C, more preferably 70-80°C. The drying step lasts for 2-16 hours, more preferably 3-12 hours. In one embodiment, the drying step is performed under vacuum at an absolute pressure of 0.001-0.50 atmospheres, more preferably 0.005-0.10 atmospheres.

[0047] The derivatized polydopamine coating can exhibit a greater overall ability to extract ionic impurities from solutions filtered using polydopamine-coated membranes, hi one embodiment, the derivatized polydopamine coating can extract at least 5% more, preferably at least 10% more, and more preferably 15% more by weight of ionic impurities than a non-derivatized polydopamine coating of the same thickness.

[0048] Therefore, the membrane can be used in filtration processes to remove ionic impurities in a fluid passing through the membrane. Dead-end filtration (where the fluid enters the membrane directly at right angles) and cross-flow filtration (where the fluid passes tangentially across the membrane surface) can be used to remove ionic and nanoparticles.

[0049] The polydopamine and derivatized polydopamine coatings detailed herein and their methods of manufacture are illustrated by the following non-limiting examples. [Example]

[0050] Example 1 A piece of ultra-high molecular weight polyethylene (UPE) membrane (47 mm diameter, 50 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (25.4 mg), placed in a PFA (perfluoroalkoxy) filter holder, and flushed with 200 g of isopropyl alcohol (IPA) at a rate of approximately 3 g / min. The filter holder is a grid with 1-2 mm diameter holes for fluid passage and is held within a PFA housing with fluid inlet and outlet ports. The IPA was then replaced by flushing with 200 g of deionized water (DI). The filter membrane piece was then removed and placed in a 120 mL low-density polyethylene (LDPE) bottle containing 112.06 g of deionized water, 4.09 g of a 15 mg / mL Tris buffer (tris(hydroxymethyl)aminomethane) solution, and 4.03 g of a 15 mg / mL dopamine hydrochloride solution. The bottle was placed on a roller and rolled overnight, after which the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50°C. The final mass was 26.8 mg, representing 1.4 mg of polydopamine coated onto the membrane.

[0051] The polydopamine-coated membrane was rewetted with propylene glycol methyl ether acetate (PGMEA) and then placed back into the filter holder. It was then flushed with a PGMEA solution spiked with a custom multi-element standard containing Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, K, Na, Sn, Ti, and Zn ions (hereafter referred to as "contaminated PGMEA") at a flow rate of 1.5 g / min. Samples of the contaminated PGMEA were taken after 5, 40, and 75 minutes of continuous flushing and analyzed for metal content using an Agilent 7700 single quadrupole inductively coupled plasma mass spectrometer (ICP-MS). The contaminated PGMEA was continuously flushed through the filter without recirculation. Samples were taken from the membrane outlet after 5, 40, and 75 minutes.

[0052] The results, in parts per billion (ppb), along with those for the contaminated PGMEA control sample, are shown in Table 1. The results show a decrease in the amount of each metal in the sample (compared to the control) over time.

[0053] [Table 1]

[0054] Example 2 A piece of ultra-high molecular weight polyethylene (UPE) membrane (47 mm diameter, 50 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (25.7 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle, which was then charged with 72.06 g of deionized water, 4.07 g of the same 15 mg / mL Tris buffer solution as in Example 1, 4.01 g of a 15 mg / mL dopamine hydrochloride solution, and 40.09 g of a 6 mg / mL sodium metaperiodate solution. The bottle was placed on a roller and rolled overnight. The membrane was then removed, washed several times with deionized water, and dried in a vacuum oven at 50°C. The final mass was 34.5 mg, indicating that 8.8 mg of polydopamine had been coated onto the membrane.

[0055] The membrane was rewetted with propylene glycol methyl ether acetate (PGMEA) and then placed back into the filter holder and flushed with the contaminated PGMEA solution (described in Example 1) at a flow rate of 1.5 g / min. Samples of the contaminated PGMEA were taken after 9, 40, and 76 minutes of continuous flushing and analyzed for metal content using an Agilent 7700 single quadrupole inductively coupled plasma mass spectrometer (ICP-MS). Results for the contaminated PGMEA control sample, along with those obtained after continuous flushing, are shown in Table 2 below. Results are in parts per billion (ppb).

[0056] [Table 2]

[0057] Example 3 A piece of ultra-high molecular weight polyethylene (UPE) membrane (47 mm diameter, 50 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (24.3 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle containing 112.10 g of deionized water, 4.04 g of the 15 mg / mL Tris buffer solution from Example 1, and 4.03 g of the 15 mg / mL dopamine hydrochloride solution. The bottle was placed on a roller overnight, after which the dopamine-coated membrane was removed and washed with deionized water. The polydopamine-coated membrane was then functionalized (aminated) by placing it back in the bottle with 120.04 g of an aqueous solution containing 20 mg / mL dimethylamine (Fisher Scientific) and 0.5 mg / mL Tris buffer and adjusting the pH to 10 using hydrochloric acid. The jar was placed on a roller and rolled overnight. The membrane was then removed and the functionalized polydopamine-coated membrane was washed several times with deionized water. The coated membrane was then dried in a vacuum oven at 50 °C. The final mass was 24.4 mg, indicating that 0.1 mg of polydopamine coating remained on the membrane.

[0058] The membrane was rewetted with propylene glycol methyl ether acetate (PGMEA) and then placed back into the filter holder and flushed at a flow rate of 1.5 g / min with a PGMEA solution spiked with the custom multi-element standard (10 ppb per metal) described in Example 1. Samples were taken after 5, 40, and 75 minutes and analyzed for metal content using an Agilent 7700 single quadrupole inductively coupled plasma mass spectrometer (ICP-MS). Results for the contaminated PGMEA control sample, along with those obtained after successive flushes, are shown in Table 3 below. Results are in parts per billion (ppb).

[0059] [Table 3]

[0060] Example 4 A piece of ultra-high molecular weight polyethylene (UPE) membrane filter (47 mm diameter, 50 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (24.9 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle containing 72.09 g of deionized water, 4.01 g of 15 mg / mL Tris buffer solution (Fisher Scientific), 4.04 g of 15 mg / mL dopamine hydrochloride solution (Fisher Scientific), and 40.01 g of 6 mg / mL sodium metaperiodate solution (Fisher Scientific). The bottle was placed on a roller overnight, after which the membrane was removed and washed with deionized water. This was then functionalized by placing it back in the bottle with 120.08 g of an aqueous solution containing 20 mg / mL dimethylamine (Fisher Scientific) and 0.5 mg / mL Tris buffer and adjusting the pH to 10 using hydrochloric acid. The bottle was placed on a roller and rolled overnight, after which the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50°C. The final mass was 30.3 mg, indicating that 5.4 mg of coating remained on the membrane.

[0061] The polydopamine-coated membrane was rewetted with propylene glycol methyl ether acetate (PGMEA) and then placed back into the filter holder. It was then flushed at a flow rate of 1.5 g / min with a PGMEA solution spiked with a custom multi-element standard containing ions of Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, K, Na, Sn, Ti, and Zn (hereafter, "spiked PGMEA"). Samples of the spiked PGMEA were taken after 5, 40, and 75 minutes of continuous flushing and analyzed for metal content using an Agilent 7700 single quadrupole inductively coupled plasma mass spectrometer (ICP-MS). The results for the spiked PGMEA control sample, along with those obtained after continuous flushing, are shown in Table 4. Results are in parts per billion (ppb).

[0062] [Table 4]

[0063] Example 5 A piece of ultra-high molecular weight polyethylene (UPE) membrane filter (47 mm diameter, 50 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (27.7 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle with 0.404 g of dopamine hydrochloride solution, 0.163 g of Tris base (from Example 1), and 135.20 g of deionized water. The bottle was placed on a roller and rolled overnight. After that, the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50°C. The membrane was noticeably darker in color than before coating. The final mass was 38.3 mg, indicating that 10.6 mg of polydopamine had been coated onto the membrane.

[0064] A dispersion of maleic anhydride-functionalized iron(II,III) oxide nanoparticles (30 nm, Sigma-Aldrich) was diluted to 10 ppb with a 0.1% aqueous solution of Triton X-100 surfactant (Dow). This dispersion was passed through the coated membrane at 0.6 g / min. After a sample was taken, the remaining dispersion (approximately 400 g) was recirculated through the filter for 22 hours (equivalent to approximately two tank revolutions), after which another sample was taken at the filter holder outlet. The experiment was repeated using an untreated UPE membrane.

[0065] The iron content in the samples was determined by ICP-MS and compared to an unfiltered control sample to determine the nanoparticle rejection rate. The results are shown in Figure 1, which is a bar graph showing the iron nanoparticle rejection rate for an untreated UPE membrane and a polydopamine-coated membrane.

[0066] Example 6 A piece of ultra-high molecular weight polyethylene (UPE) membrane filter (47 mm diameter, 20 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (32.3 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle with 0.405 g of dopamine hydrochloride, 0.168 g of the Tris base from Example 1, and 135.01 g of deionized water. The bottle was placed on a roller and rolled overnight, after which the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50°C. The final mass of the polydopamine-coated membrane was 41.7 mg, indicating that 9.4 mg of polydopamine had been coated onto the membrane.

[0067] A dispersion of maleic anhydride-functionalized iron(II,III) oxide nanoparticles (average particle size 30 nm) was diluted to 10 ppb with a 0.1% aqueous solution of Triton X-100 surfactant (Dow). This dispersion was passed through the coated membrane at 0.6 g / min. After a sample was taken, the remaining dispersion (approximately 400 g) was recirculated through the filter for 22 hours, after which another sample was taken at the filter holder outlet. The experiment was repeated using an untreated control UPE membrane.

[0068] The iron content of the samples was determined by ICP-MS (as detailed in Example 1) and nanoparticle rejection was determined compared to an unfiltered control sample. The results are shown in Figure 2, which is a bar graph showing the iron nanoparticle rejection of untreated UPE membranes and polydopamine-coated membranes.

[0069] Example 7 A piece of ultra-high molecular weight polyethylene (UPE) membrane (47 mm diameter, 10 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (32.4 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle with 0.404 g of dopamine hydrochloride solution, 0.162 g of Tris base, and 135.46 g of deionized water. The bottle was placed on a roller and rolled overnight, after which the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50°C. The final mass was 43.8 mg, indicating that 11.4 mg of polydopamine had been coated onto the membrane.

[0070] A dispersion of maleic anhydride-functionalized iron(II,III) oxide nanoparticles (average particle size 30 nm) was diluted to 10 ppb with a 0.1% aqueous solution of Triton X-100 surfactant (Dow). The dispersion was initially passed through the coated membrane at 0.6 g / min, but was reduced to 0.2 g / min due to a large pressure drop (approximately 26 psig). After a sample was taken, the remaining dispersion (approximately 400 g) was recirculated through the filter for 70 hours, after which another sample was taken at the filter holder outlet. The experiment was repeated using an untreated control UPE membrane.

[0071] The iron content in the samples was determined by ICP-MS and compared to an unfiltered control sample to determine the nanoparticle rejection rate. The results are shown in Figure 3. Figure 3 is a bar graph showing the iron nanoparticle rejection rate for an untreated UPE membrane and a polydopamine-coated membrane.

[0072] Example 8 A piece of ultra-high molecular weight polyethylene (UPE) membrane (47 mm diameter, 30 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (28.1 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle containing 48.26 g of deionized water, 6.00 g of a 15 mg / mL Tris buffer solution (see Example 1), 5.99 g of a 15 mg / mL dopamine hydrochloride solution, and 60.38 g of a 28 mmol / L sodium metaperiodate solution. The bottle was placed on a roller overnight, after which the membrane was removed and washed with deionized water. It was then placed back in the bottle with 120.21 g of an aqueous solution containing 20 mg / mL dimethylamine and 0.5 mg / mL Tris buffer, adjusted to pH 10 using hydrochloric acid. The jar was placed on a roller and rolled overnight, after which the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50° C. The final mass was 38.6 mg, indicating that 10.5 mg of coating remained on the membrane.

[0073] The membrane was rewetted with propylene glycol methyl ether acetate (PGMEA) and then placed back into the filter holder and flushed at a rate of 1.5 g / min with a PGMEA solution spiked with the custom multi-element standard (10 ppb per metal) described in Example 1. Samples were taken at 8, 42, 77, and 112 minutes and analyzed for metal content, along with a control sample of contaminated PGMEA, using an Agilent 7700 single quadrupole inductively coupled plasma mass spectrometer (ICP-MS). The results, in ppb, are shown below in Table 5.

[0074] [Table 5]

[0075] Example 9 A piece of ultra-high molecular weight polyethylene (UPE) membrane (47 mm diameter, 30 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (28.7 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle containing 48.05 g of deionized water, 6.06 g of a 15 mg / mL Tris buffer solution, 6.03 g of a 15 mg / mL dopamine hydrochloride solution, and 60.25 g of a 28 mmol / L ammonium persulfate solution. The bottle was placed on a roller overnight, after which the membrane was removed and washed with deionized water. It was then placed back in the bottle with 120.11 g of an aqueous solution containing 20 mg / mL dimethylamine and 0.5 mg / mL Tris buffer, and the pH was adjusted to 10 using hydrochloric acid. The jar was placed on a roller and rolled overnight, after which the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50° C. The final mass was 30.8 mg, indicating that 2.1 mg of coating remained on the membrane.

[0076] The membrane was rewetted with propylene glycol methyl ether acetate (PGMEA) and then placed back into the filter holder and flushed at a flow rate of 1.4 g / min with a PGMEA solution spiked with the custom multi-element standards (10 ppb per metal) described in Example 1. Samples were taken after 5, 60, and 108 minutes and analyzed for metal content, along with a control sample of contaminated PGMEA, using an Agilent 7700 single quadrupole inductively coupled plasma mass spectrometer (ICP-MS). The results, in ppb, are shown below in Table 6.

[0077] [Table 6]

[0078] Example 10 A piece of ultra-high molecular weight polyethylene (UPE) membrane (47 mm diameter, 30 nanometer (nm) nominal pore size) was weighed to determine a baseline mass (25.6 mg). It was then placed in a PFA filter holder and flushed with IPA and water as described in Example 1. The filter membrane piece was then removed and placed in a 120 mL LDPE bottle containing 48.07 g of deionized water, 6.03 g of a 15 mg / mL Tris buffer solution (Example 1), 6.03 g of a 15 mg / mL dopamine hydrochloride solution, and 60.02 g of a 28 mmol / L lithium perchlorate solution (oxidizer). The bottle was placed on a roller overnight, after which the membrane was removed and washed with deionized water. It was then placed back in the bottle with 120.83 g of an aqueous solution containing 20 mg / mL dimethylamine (aminating agent) and 0.5 mg / mL Tris buffer, and the pH was adjusted to 10 using hydrochloric acid. The jar was placed on a roller and rolled overnight, after which the membrane was removed, washed several times with deionized water, and dried in a vacuum oven at 50° C. The final mass was 27.2 mg, indicating that 1.6 mg of coating remained on the membrane.

[0079] The membrane was rewetted with propylene glycol methyl ether acetate (PGMEA) and then placed back into the filter holder and flushed at a flow rate of 1.4 g / min with a PGMEA solution spiked with the custom multi-element standard (10 ppb per metal) described in Example 1. Samples were taken after 5, 50, and 125 minutes and analyzed for metal content, along with a control sample of contaminated PGMEA, using an Agilent 7700 single quadrupole inductively coupled plasma mass spectrometer (ICP-MS). The results, in ppb, are shown below in Table 7.

[0080] [Table 7]

Claims

1. a porous membrane comprising a polymer; a derivatized polydopamine layer disposed on one or both sides of the porous membrane; wherein the derivatized polydopamine layer is disposed on the porous membrane in the presence of an oxidizing agent. filtration membrane.

2. 10. The filtration membrane of claim 1, wherein the polydopamine layer is derivatized with an amine, a thiol, a carboxylic acid, or a combination thereof.

3. The filtration membrane of claim 1 , wherein the polymer comprises a polyolefin or a fluoropolymer.

4. 10. The filtration membrane of claim 1, wherein the porous membrane has a nominal pore size of 1 to 5000 nanometers.

5. 3. The filtration membrane of claim 2, wherein the amine is dimethylamine.

6. 2. The filtration membrane of claim 1, wherein the polydopamine layer has a thickness of 1 to 100 nm.

7. 10. The filtration membrane of claim 1, wherein the oxidizing agent comprises a periodate, a perchlorate, a persulfate, or a combination thereof.

8. 2. The filtration membrane of claim 1, wherein the periodate is sodium metaperiodate.

9. 1. A method for coating a porous membrane, comprising: placing the porous membrane in a solution comprising dopamine monomer, a buffer, an oxidizing agent, and a solvent in a reactor, wherein the dopamine monomer, the buffer, and the oxidizing agent are gradually added to the reactor; forming a polydopamine layer on the porous membrane; and derivatizing the polydopamine layer with an amine, a thiol, a carboxylic acid, or a combination thereof; A method comprising:

10. 1. A method for purifying a liquid, comprising: Passing a liquid through a filtration membrane, the filtration membrane comprising: a porous membrane; a derivatized polydopamine layer disposed on one or both sides of the porous membrane, wherein the derivatized polydopamine layer is disposed on the porous membrane in the presence of an oxidizing agent; and removing ionic and particulate impurities from said liquid; A method comprising:

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