Highly selective ultrathin polymer nanofilm composite membrane and its preparation method

Abstract

The present invention relates to a highly selective ultrathin polymer nanofilm, its composite membrane, and its preparation method. The composite membrane is prepared by interfacial polymerization of piperazine amine with a surface-active agent (SLS) added to the aqueous phase and reacted with trimesoyl chloride. The prepared ultrathin polymer nanofilm composite membrane exhibits a specific viscosity of 2 g / L under an applied pressure of 5 bar at 25 (±1) °C. -1 When tested using a supply of 47.9 to 59.6 Lm -2 h -1 bar -1 High water permeability ranges resulted in high rejection of Na2SO4 (91.77-98.47%); MgCl2 (3.2-10.0%); low rejection of NaCl (8.9-15.3%); 8.1-16.4 Lm -2 h -1 bar -1 The high water permeability range results in high rejection rates of Na2SO4 (99.81-99.99%), MgCl2 (96.7-98.4%), and NaCl (42.1-56.9%).

Description

[Technical Field]

[0001] The present invention relates to a highly selective ultrathin polymer nanofilm composite membrane, and more particularly to a method for preparing a highly selective ultrathin polymer nanofilm composite membrane. [Background technology]

[0002] Ultrathin polymer nanofilms and their composite membranes are used for higher liquid permeability and to achieve higher rejection rates of small solutes, including divalent and multivalent ions.

[0003] Nanofiltration membranes are 250-1000 g.mol -1 They are available with molecular weight cutoffs of 1000 and 1500. They are used for the removal of divalent and multivalent ions, small organic molecules, bacteria, and viruses. They are also used in wastewater treatment, chemical refining, food production, the chlorate and chlor-alkali industries, and in the pretreatment stage of reverse osmosis-based water treatment plants.

[0004] Nanofiltration membranes are used for the specific removal of divalent ions, including lead, mercury, iron, copper, magnesium, calcium, sulfate, and carbonate, with negligible or moderate removal of monovalent ions. Generally, nanofiltration membranes produce greater flux than reverse osmosis membranes at a given applied pressure.

[0005] There is a great need for highly selective membranes for desalination to produce high quality water. Increased water permeability at the expense of selectivity is not necessarily beneficial.

[0006] Sulfate ions are a common impurity in commercial salt produced from seawater, and methods for separating sulfate from NaCl are complicated.

[0007] Ion-selective thin-film composite membranes have been studied for over 30 years, and state-of-the-art nanofiltration membranes are made from semi-aromatic polyamides, which can separate sulfate from NaCl, with an ideal membrane selectivity (NaCl vs. Na2SO4) of approximately 20-100.

[0008] Highly selective nanofiltration membranes are used for improved brine recovery and sulfate removal in the chlorate and chloralkali industries.

[0009] In brine electrolysis plants, sodium chloride (300-350 g.L -1 NaCl) is used as a raw material to produce chlorine, sodium hydroxide, and hydrogen. The purity of NaCl brine is detrimental to product quality and can be up to 20g.L -1 of sulfate impurities is the limit to avoid operational problems.

[0010] Efficient removal of sulfate from NaCl and recovery of useful materials from the brine stream requires a highly selective separation method.

[0011] The composite nanofiltration membrane can be used to partially or completely remove amounts of undesirable compounds from aqueous solutions. The present invention also relates to the significant removal of sulfate, phosphate, chromium, calcium, mercury, lead, cadmium, magnesium, aluminum, and fluoride ions from brine solutions.

[0012] Thin-film composite (TFC) polyamide membranes are used in a variety of fluid separations, including separations in organic solvents, nanofiltration (NF), and reverse osmosis (RO) desalination processes. TFC is a type of membrane in which a thin film is fabricated or coated onto a porous support, which acts as the separation layer of the composite membrane. Interfacial polymerization is a technology that offers a simple route to fabricating composite membranes, and state-of-the-art NF and RO membranes are commercially manufactured using this technology and are available worldwide. They are produced by reacting polyfunctional amines (e.g., m-phenylenediamine, piperazine) with polyfunctional acyl halides (e.g., trimesoyl chloride) reactive molecules from immiscible solutions onto a porous support. Advances have been made to improve flux and / or rejection properties by incorporating / adding different chemicals / reagents into the reaction solution during interfacial polymerization.

[0013] Reference may be made to US Pat. No. 4,277,344A to JECadotte, which describes a method for producing superior reverse osmosis membranes or films or layers by condensation polymerization.

[0014] Reference can be made to US4259183A by JECadotte, which describes the use of a combination of difunctional and trifunctional acyl halide monomers, such as isophthalic acid chloride or terephthalic acid chloride, with trimesic acid chloride. The resulting poly(piperazinamide) NF membrane exhibits high rejection of divalent salts, especially magnesium sulfate, and produces a high flux.

[0015] Reference can be made to the paper by YJ. Tang et al., J. Membr. Sci. 498, 2016, 374-384, which reported the formation of piperazine-based polyamide membranes via interfacial polymerization with TMC by the addition of 2,2'-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4'-methylenedianiline (BHT™) in the aqueous phase. These membranes have a 79.1 Lm -2 h -1The catalyst showed a high pure water flux and 99.5% Na2SO4 rejection rate, with an ideal selectivity of 140 between NaCl and Na2SO4.

[0016] See J. Membr. Sci. 523, 2017, pp. 282–290, in which Y. Pan et al. reported the formation of poly(piperazine-amide) nanofiltration membranes by incorporating sericin into the active layer during interfacial polymerization between piperazine and TMC. They showed that after incorporating sericin (0.06% (w / v)) into a PIP aqueous solution, the permeability improved by 36.7%, the Na2SO4 rejection rate remained high at 97.5%, and the selectivity between NaCl and Na2SO4 in a mixed salt solution increased from 21.2 to 25.2.

[0017] See D. Hu et al., Desalination 301, 2012, pp. 75-81, which reported the formation of silica / polypiperazine-amide nanofiltration (NF) membranes by adding silica sol to a PIP aqueous solution and reacting it with a TMC solution. The incorporation of silica sol increased the water flux by up to 21.1%, but the ideal selectivity between NaCl and Na2SO4 decreased from 29.7 to 10.6.

[0018] See J. Membr. Sci. 343, 2009, pp. 219–228, which reported the formation of composite nanofiltration membranes by adding cationic cetyltrimethylammonium bromide (CTAB), nonionic (Triton X-100), and anionic sodium dodecyl sulfate (SDS) surfactants to the organic phase during interfacial polymerization of piperazine and TMC on a UF support. The membrane prepared using SDS additive in the organic phase exhibited higher flux than other membranes, with an ideal selectivity of 5.0 between NaCl and Na2SO4.

[0019] See the paper by BW. Zhou et al., Desalination 394, 2016, pp. 176-184, which reported the formation of TFC hollow fiber NF membranes through interfacial polymerization between a mixed diamine of PIP and 2,2'-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4'-methylenedianiline (BHT™) in the aqueous phase and TMC in the organic phase. Adding a second amine (BHT™) to the aqueous phase increased the Na2SO4 rejection rate to a maximum of 99.7%, and the ideal selectivity between NaCl and Na2SO4 increased to a maximum of 187%.

[0020] Reference may be made to the paper by J. Zhu et al., J. Mater. Chem. A6, 2018, pp. 15701-15709, which reports the synthesis of ultrathin polyamide nanofilms at the free aqueous-organic interface between an aqueous solution containing piperazine and an n-hexane solution containing trimesoyl chloride, and their direct transfer onto polydopamine-coated polymer substrates by vacuum filtration, which yielded a nanofilm thickness of 25.1 Lm -2 h -1 bar -1 It showed high water permeability and excellent divalent ion rejection, with a Na2SO4 rejection rate of 99.1% and an ideal selectivity between NaCl and Na2SO4 of over 80.

[0021] Reference can be made to the paper by Z. Wang et al., Nat. Commun. 9, 2018, 2004, which reported the formation of polyamide films on polydopamine-modified zirconium imidazole framework nanoparticles, which showed a maximum film thickness of 53.5 Lm -2 h -1 bar -1 The high water permeability of the membrane showed a 95% rejection rate of Na2SO4, and the ideal selectivity between NaCl and Na2SO4 was 18.6.

[0022] See Science 360, 2018, pp. 518-521 by Z. Tan et al., which reported the formation of piperazine-based polyamide membranes with controlled Turing structures via interfacial polymerization of TMC with polyvinyl alcohol in the aqueous phase. These membranes exhibited high water permeability and high water-salt separation. The ideality between NaCl and Na2SO4 was 126.

[0023] Reference may be made to US Pat. No. 5,152,901A by R.B. Hodgdon, which discloses polyamine-polyamide composite nanofiltration membranes for water softening with good separation of divalent and monovalent ions, prepared on a microporous substrate by interfacial polymerization between an aqueous phase containing piperazine or polyamine and an organic phase containing trimesoyl chloride or isophthaloyl chloride.

[0024] Reference can be made to US6833073B2 by AKA Garwal, which discloses the preparation of nanofiltration and reverse osmosis membranes via interfacial polymerization on porous substrates by using an aqueous amine solution containing an amine, an organic acid (e.g., propionic acid) and a non-amine base. These membranes have excellent MgSO4 rejection rates of up to 99.5% and a high water content of 100 gallons per cubic meter. -2 .day -1 This resulted in a flux of

[0025] Reference may be made to US4619767A by Y. Kamiyama et al., which describes the formation of composite semipermeable membranes for selective separation of ions by crosslinking polyvinyl alcohol with secondary diamines or higher amines on a porous support using a multifunctional crosslinking agent. These semipermeable membranes provided excellent water permeability and good solute rejection rates under low pressure.

[0026] Reference may be made to US Pat. No. 3,904,519A to J.R. McKinney et al., which discloses the preparation of reverse osmosis membranes with improved flux by crosslinking aromatic polyamide membranes using crosslinking agents and / or irradiation.

[0027] Reference can be made to CN101934201A, in which a composite nanofiltration membrane with high selectivity is prepared by reacting polyamines and / or amine polyalcohols with chlorine polyacyl on a porous support, and the membrane has a capacity of 19.69 gal.ft -2 .day -1 It results in high removal rates of MgSO4 (99.56%) and NaCl (80.82%) at a water flux of 1000 MPa.

[0028] Reference can be made to CN105435653A, which discloses the formation of a composite nanofiltration membrane by mixed cross-linking of aromatic amines and aliphatic amines on a polysulfone support, which has high selectivity for monovalent ions versus divalent ions, with a rejection rate of less than 40% for NaCl, more than 97% for MgCl, more than 98% for MgSO, and more than 93% for CaCl.

[0029] Reference can be made to CN104525000A, which discloses a method for preparing a highly selective polyvinyl alcohol nanofiltration membrane with high hydrophilicity and high retention, which provides high water flux and high separation of NaSO and MgCl.

[0030] Reference may be made to US6878278B2 by W.E. Mickols, which describes the addition of a wide range of complexing agents having binding cores selected from non-sulfur atoms of Groups IIIA-VIB and Periods 3-6 to acyl halide solutions to improve membrane flux and / or rejection.

[0031] Reference may be made to US20110049055A1 by H. Wang et al., which describes the preparation of composite membranes containing moieties derived from aromatic sulfonyl halides, heteroaromatic sulfonyl halides, sulfinyl halides; sulfenyl halides; sulfuryl halides; phosphoryl halides; phosphonyl halides; phosphinyl halides; thiophosphoryl halides, thiophosphonyl halides, isocyanates, ureas, cyanates, aromatic carbonyl halides, epoxides, or mixtures thereof, achieving improved boron selectivity.

[0032] Reference can be made to US Pat. No. 6,521,130 B1 by S. Kono et al., which describes the addition of carboxylic acids or carboxylic acid esters during polyamide formation to preserve high water permeability while maintaining the salt rejection of the membrane.

[0033] Reference can be made to US Pat. No. 5,576,057A, US Pat. No. 5,843,351A and US Pat. No. 6,024,873A to S. Kono et al., which disclose the use of alcohols, ethers, ketones, esters, halogenated hydrocarbons, and 8-14 (cal / cm 3 ) 1 / 2 The present invention describes a method for making a highly permeable composite membrane by adding to one of the coating solutions at least one compound selected from the group consisting of sulfur-containing compounds having a solubility parameter of

[0034] See US20090107922A1, which describes adding various "chain capping agents" (e.g., 1,3-propane sultone, benzoyl chloride, 1,2-bis(bromoacetoxy)ethane) and various surfactants to one or both of the coating solutions to increase water flux and reduce salt passage.

[0035] Reference can be made to the paper by W. Chen, J. Membr. Sci. 559, 2018, 98-106, which reported the fabrication of polyelectrolyte multilayer nanofiltration membranes using a layer-by-layer method by depositing a polycationic (poly(diallyldimethylammonium chloride), PDADMAC) and a polyanionic (poly(sodium 4-styrenesulfonate), PSS) layer onto a commercially available polyamide NF membrane. They reported that a PDADMAC-terminated membrane with 5.5 bilayers exhibited a high solubility in Na. + and Mg 2+ The selectivity between Mg and 2+ showed a removal rate of 97%.

[0036] Reference can be made to US6723422B1, which discloses the formation of a composite reverse osmosis membrane in which a surfactant is added to the aqueous phase to improve absorption of the aqueous solution into the porous support. The composite reverse osmosis membrane produced has high salt rejection (up to 99.5%) and high water permeability (up to 1.0 m 3 m -2 day -1 ) was shown.

[0037] Prior art membranes have only modest ion selectivity between monovalent and divalent anions or between monovalent and divalent cations, and many separation applications require much higher ion selectivity to make the process feasible. Thus, there is a need in the art for improved membranes with much higher ion selectivity and water permeability.

[0038] As is well known to those skilled in the art, interfacial polymerization is a type of three-dimensional network polymerization of two reactive molecules (monomers or polymers, or a combination thereof) that react at the interface between two immiscible liquid phases (typically an aqueous phase and an organic phase), each containing at least one of the reactive molecules, to produce a polymer thin film. In such polymerizations, at least one reactive molecule has low or no solubility in the other liquid phase, ensuring the controlled introduction of one reactive molecule into an excess of reactants in the other phase. The reaction rate is usually high and can be controlled by the diffusivity of one reactive molecule from one phase to the other. The concentration and diffusivity of the reactive molecule in the other phase determine the chemical structure of the high-molecular-weight network polymer formed at the interface. Summary of the Invention [Problem to be solved by the invention]

[0039] The primary objective of the present invention is to provide nanofilm composite membranes with higher permeability and / or higher selectivity for monovalent anions versus multivalent anions and / or monovalent cations versus multivalent cations depending on the anticipated end use.

[0040] Another object of the present invention is to provide a highly selective ultrathin polymer nanofilm composite membrane and a method for preparing the same, which can be most preferably employed to fabricate reverse osmosis and nanofiltration membranes.

[0041] Yet another object of the present invention is to control the thickness of polymer nanofilms prepared by interfacial polymerization to achieve higher permeability.

[0042] Yet another object of the present invention is to provide a nanofilm composite membrane that can operate at low pressures (e.g., less than 5 bar) and produce acceptable permeance and / or rejection rates.

[0043] Yet another object of the present invention is to provide a highly selective ultrathin polymer nanofilm composite membrane by interfacial polymerization on a porous support, wherein the nanofilm has a thickness of at least any one of 7 to 150 nm.

[0044] It is yet another object of the present invention to provide a method for isolating the ultrathin polymer nanofilm separation layer of a composite membrane.

[0045] It is yet another object of the present invention to provide a method for isolating a nanofilm separation layer of a composite membrane and transferring the free-standing nanofilm layer onto a different substrate while keeping the top surface of the nanofilm facing upward.

[0046] Yet another object of the present invention is to provide a method for preparing ultrathin polyamide nanofilm composite membranes by reacting piperazine (PIP) with trimesoyl chloride (TMC) via interfacial polymerization.

[0047] Yet another object of the present invention is to provide a method for preparing ultrathin polyamide nanofilm composite membranes used in nanofiltration applications by reacting PIP with TMC via interfacial polymerization.

[0048] Yet another object of the present invention is to provide a method for preparing ultra-thin polyamide nanofilm composite membranes for reverse osmosis applications by reacting m-phenylenediamine (MPD) with TMC via interfacial polymerization.

[0049] Yet another object of the present invention is to provide a method for the preparation of ultrathin polymer nanofilm composite membranes for separation applications in non-aqueous systems by interfacial polymerization.

[0050] Yet another object of the present invention is to provide a method for preparing ultrathin polymer nanofilm composite membranes with high water permeability.

[0051] Yet another object of the present invention is to provide a method for preparing an ultrathin polymer nanofilm composite membrane with high salt rejection.

[0052] Yet another object of the present invention is to provide a method for preparing ultrathin polymer nanofilm composite membranes with high ion selectivity.

[0053] Yet another object of the present invention is to provide a method for preparing ultrathin polymer nanofilm composite membranes with high ion rejection from mixed salt water.

[0054] It is yet another object of the present invention to provide an ultrathin polymer nanofilm composite membrane for selectively separating ions from seawater.

[0055] Yet another object of the present invention is to control the chemical structure of the polymer nanofilm to make the separation membrane selective between monovalent and divalent ions.

[0056] Yet another object of the present invention is to control the interfacial reaction and therefore the chemical structure of the polymer nanofilm formed at the interface by adding a surface active reagent (SAR), e.g., a surfactant, to at least one of the molecular solutions of the reactive molecules.

[0057] It is yet another object of the present invention to enhance ion selectivity by adding a surface active reagent (SAR), such as a surfactant, to at least one of the molecular solutions of the reactive molecules.

[0058] Yet another object of the present invention is to reduce organic fouling tendency. [Brief explanation of the drawings]

[0059] [Figure 1]Figure 1 shows the surface morphology of nanofilm composite membranes prepared on a hydrolyzed polyacrylonitrile (HPAN) support: (A) PIP 0.05%-SAR 0 mM / TMC 0.1%-hex-5 s, (B) PIP 0.01%-SAR 0 mM / TMC 0.1%-hex-5 s, (C) PIP 1.0%-SAR 0 mM / TMC 0.1%-hex-5 s, and (D) PIP 2.0%-SAR 0 mM / TMC 0.1%-hex-5 s.

[0060] [Figure 2] Figure 1 shows the surface morphology of nanofilm composite membranes prepared on a hydrolyzed polyacrylonitrile (HPAN) support. These membranes were reacted with 0.1% TMC for 5 seconds: (A) PIP 0.05%-SLS 1 mM hex-5 seconds, (B) PIP 0.1%-SLS 1 mM hex-5 seconds, (C) PIP 1.0%-SLS 1 mM hex-5 seconds, and (D) PIP 2.0%-SLS 1 mM hex-5 seconds.

[0061] [Figure 3] Figure 1 shows cross-sectional scanning electron microscope (SEM) images of nanofilm composite membranes prepared on porous alumina supports under different magnifications: (A) PIP 0.1%-SLS 1 mM-hex-5 s, (B) PIP 0.5%-SAR 0 mM-hex-5 s, and (C) PIP 2.0%-SAR 0 mM-hex-5 s.

[0062] [Figure 4] Atomic force microscopy (AFM) images and height profiles of free-standing nanofilm composite films transferred onto silicon wafers: (A and B) PIP 0.05%-SAR 0 mM / TMC 0.05%-hex-5 s, and (C and D) PIP 0.05%-SAR 0 mM / TMC 0.1%-hex-5 s. (A and C) AFM height images and (B and D) corresponding height profiles of the nanofilms.

[0063] [Figure 5]Figure 1 shows the change in water permeability of water or water / methanol mixtures as a function of the inverse viscosity and the pure water permeability as a function of increasing temperature (K). The membranes were prepared on a cross-linked polyacrylonitrile (HPAN) support.

[0064] [Figure 6] Figure 1 shows a comparison of fouling behavior, permeability reduction, and permeability recovery before and after adding BSA to the feed solution. After compressing the membrane with pure water and further compressing it with NaSO (2 g L) as the feed for at least 3 hours at 5 bar pressure and 25 (±1) °C, the foulant BSA (250 mg L) was added and the water permeability was recorded over time. After 24 hours, the membrane was washed with pure water, and then the water permeability was collected over time using NaSO solution as the feed at the same pressure and temperature.

[0065] [Figure 7] FIG. 10 shows the variation of Na2SO4 removal rate at feed concentrations ranging from 0.5 g L-1 to 40 g L-1.

[0066] [Figure 8] This figure shows the change in solute rejection rate with the molecular weight of solutes with different charges. Three different types of molecules were used as solutes in the feed solution: neutral molecules (glucose, sucrose, raffinose), negatively charged molecules (HNSA, Acid Orange 7, Orange G, Acid Fuchsin, Brilliant Blue R), and positively charged molecules (Chrysodine G, Toluidine Blue O, Basic Fuchsin, Crystal Violet, Rhodamine B).

[0067] [Figure 9] FIG. 1 shows the pure water flux of the nanofilm composite membrane measured at 25 (±1) °C with increasing pressure.

[0068] [Figure 10] Figure 1 shows the permeability of pure solvents through nanofilm composite membranes. The performance was tested at a cross-flow rate of 50 Lh-1 at 25 (±1) °C under an operating pressure of 5 bar.

[0069] [Figure 11] Figure 1 shows the acetone permeability and rejection of Acid Orange 7 before and after DMF activation of different nanofilm composite membranes. The performance was tested under an applied pressure of 5 bar at 25 (±1) °C using 200 mg L-1 of the dye dissolved in acetone as the feed.

[0070] [Figure 12] This diagram shows a fixture assembly for clamping PDMS rubber. The assembly was used to generate wrinkle patterns for free-standing nanofilms that were transferred onto the PDMS rubber, and the Young's modulus of the nanofilms was calculated. (Karan et al., Science 348, 1347, 2015)

[0071] [Means for solving the problem] Accordingly, the present invention provides a highly selective ultrathin polymer nanofilm composite membrane, comprising: a) a base layer of a porous polymer support membrane; b) top polymer nanofilm; Including, The present invention relates to a highly selective ultrathin polymer nanofilm composite membrane, in which the polymer nanofilm is prepared by interfacial polymerization in the presence of a surfactant in the range of 0.01 mg to 1 M, and the thickness of the nanofilm is in the range of 7 nm to 150 nm.

[0072] In one embodiment of the present invention, the base layer of the porous polymeric support membrane is selected from the group consisting of hydrolyzed polyacrylonitrile (HPAN), polysulfone (PSF), polyethersulfone (PES), P84, crosslinked P84, and polyacrylonitrile (PAN).

[0073] In another embodiment of the present invention, the surfactant is selected from the group consisting of anionic, cationic, zwitterionic and neutral surfactants.

[0074] In yet another embodiment of the present invention, the pure water permeability is 8.1 to 57.1 Lm -2 h -1 bar -1 The removal rate of Na2SO4 is over 98.0% up to 99.99%, and the removal rate of NaCl is between 15.3 and 56.9%.

[0075] In yet another embodiment of the present invention, the ideal salt selectivity for NaCl versus Na2SO4 is greater than 1 and is up to 4310.

[0076] In yet another embodiment of the present invention, the pure water permeability is 6.1 to 17.6 Lm -2 h -1 bar -1 The MgCl2 removal rate is over 97.0% to a maximum of 99.0%, and the NaCl removal rate is 38.4 to 61.2%.

[0077] In yet another embodiment of the present invention, the ideal salt selectivity for NaCl versus MgCl is greater than 1 and up to 40.

[0078] In yet another embodiment of the present invention, the ion selectivity between monovalent and divalent anions in the mixed salt feed material is greater than 1, up to 1460.

[0079] In yet another embodiment of the present invention, the membrane has a viscosity of 287 to 390 g.mol -1 The MWCO (molecular weight cutoff) ranges from 0.01 to 0.1.

[0080] In yet another embodiment of the present invention, when the polymer repeat units are selected from piperazine and trimesoyl chloride, the nanofilm has an elemental composition of 71.4-74.8 carbon, 7.5-12.8% nitrogen, and 12.4-21.1% oxygen.

[0081] In yet another embodiment, the present invention provides a method for preparing a highly selective ultrathin polymer nanofilm composite membrane, comprising the steps of: a) preparing a polymer support membrane on a nonwoven fabric by a phase inversion method; b) modifying the polymeric support membrane obtained in step (a) to obtain a hydrophilic support membrane; c) separately dissolving 0.01 to 5.0 w / w% of polyamine in an aqueous solvent to obtain solution A; d) separately dissolving 0.001 to 0.5 w / w % of a polyfunctional acid halide in an organic solvent to obtain a solution B; e) adding 0.01 mM to 1 M of a surface-active reagent to either solution A or B obtained in step (c) or step (d); f) pouring the solution A obtained in step (e) onto the hydrophilic support membrane of step (b), followed by immersion for 10 seconds to 1 minute; g) a step of discarding the aqueous solution from the hydrophilic support membrane, removing the remaining aqueous solution with a rubber roller, and then air-drying the membrane for 10 seconds to 1 minute; h) immediately contacting the solution B obtained in step (e) with the hydrophilic support membrane of step (g) for a period ranging from 5 seconds to 20 minutes for interfacial polymerization to obtain a nanofilm; i) removing excess organic solution, followed by removing any unreacted polyfunctional acid halide remaining on the nanofilm, and drying the film at room temperature for 10-30 seconds; j) Annealing the membrane at a temperature ranging from 40 to 90°C for a period ranging from 1 to 10 minutes to obtain a highly selective ultrathin polymer nanofilm composite membrane.

[0082] In yet another embodiment of the present invention, the organic solvent used in step (d) is selected from the group consisting of acyclic alkanes and isoalkanes (hexane, heptane, Isopar G), monocyclic cycloalkanes (cyclohexane, cycloheptane), aromatic hydrocarbons (benzene, toluene, xylene, mesitylene), esters (methyl acetate, ethyl acetate) alone or in mixtures thereof.

[0083] In yet another embodiment of the present invention, the polyamine used in step (c) is selected from the group consisting of piperazine (PIP), m-phenylenediamine (MPD), p-phenylenediamine (PPD), polyethyleneimine (PEI), 4-(aminomethyl)piperidine (AMP), 1,3-cyclohexanediamine (CDA13), 1,4-cyclohexanediamine (CDA14), 1,6-hexanediamine (HDA), ethylenediamine (EDA), resorcinol (RES), phloroglucinol (PHL), pentaerythritol (PET), quercetin (QCT), bisphenol A (BPA), and melamine (MM), alone or in combination.

[0084] In yet another embodiment of the present invention, the polyfunctional acid halide used in step (d) is selected from the group consisting of terephthaloyl chloride (TPC), 1,3,5 benzenetricarbonyl trichloride or trimesoyl chloride (TMC), alone or in combination.

[0085] In yet another embodiment of the present invention, when the two reactive molecule solutions A and B obtained in step (e) are contacted to form a liquid-liquid interface, a free-standing isolated polymer nanofilm is formed at the interface, which is then transferred onto a porous support to form a composite membrane.

[0086] In yet another embodiment of the present invention, nanofilms as free-standing entities are prepared by interfacial polymerization at the interface between two immiscible liquids and transferred onto a porous support to form a nanofilm composite membrane.

[0087] In yet another embodiment of the present invention, the nanofilm is intercalated with nanoparticles.

[0088] In yet another embodiment of the present invention, the nanofilms are disposed on top of each other in a layer-by-layer manner on a solid substrate.

[0089] In yet another embodiment of the present invention, the nanofilms are disposed on top of each other in a layer-by-layer manner on a porous support.

[0090] In yet another embodiment of the present invention, nanofilm composite membranes with tunable salt rejection properties, increased monovalent vs. multivalent ion selectivity, and reduced organic fouling are provided by adding additives to either of the reactive molecule solutions during interfacial polymerization.

[0091] In yet another embodiment of the present invention, when a surfactant is added to the aqueous solution during interfacial polymerization, the observed MWCO is between 287 and 390 g.mol -1 If the MWCO (molecular weight cut off) is between 0.5 and 1.0, the MWCO (molecular weight cut off) will decrease to a lower value. DETAILED DESCRIPTION OF THE INVENTION

[0092] The present invention relates to a highly selective ultrathin polymer nanofilm composite membrane, in which the nanofilm selective layer of the membrane has a thickness ranging from 7 to 150 nm, and a method for producing the highly selective ultrathin polymer nanofilm composite membrane by interfacial polymerization (IP) on a porous support.

[0093] The present invention provides a method for preparing highly selective ultrathin polymer nanofilm composite membranes by interfacial polymerization, in which at least two reactive molecules, separately dissolved in two immiscible solvents (phases), are brought into contact at either i) an interface created on a porous support, or ii) an interface between two immiscible bulk liquids.

[0094] In case i), the ultrafiltration porous support is immersed in a molecular solution of one reactive molecule, the excess solution is wiped off, and the support is then contacted with a molecular solution of the other reactive molecule, forming a nanofilm on the ultrafiltration porous support.

[0095] In case ii), when two solutions of reactive molecules are brought into contact to form a liquid-liquid interface, a free-standing polymer nanofilm is formed at the interface, which is then transferred onto a porous support to form a composite membrane.

[0096] The porous support is selected from the group consisting of polysulfone (PSf), polyacrylonitrile (PAN), hydrolyzed polyacrylonitrile (HPAN), polyimide (P84) and polyethersulfone (PES).

[0097] The present invention provides a method for preparing highly selective ultrathin polymer nanofilm composite membranes by interfacial polymerization, in which an amine (or polyamine) or hydroxyl-rich reactive molecule (as a single amine (or polyamine) or hydroxyl-rich reactive molecule or as a combination of amines (or polyamines) or hydroxyl-rich reactive molecules) is selected as the aqueous phase, and a polyfunctional acid halide (as a single polyfunctional acid halide molecule or a combination of polyfunctional acid halide molecules) is selected as the other reactive molecule in the organic phase.

[0098] A surface active reagent (SAR), such as a surfactant, is used together with at least one of the molecular solutions of the reactive molecules and / or is adsorbed onto the ultrafiltration support prior to interfacial polymerization.

[0099] A surfactant, selected from anionic, cationic, zwitterionic, and neutral (nonionic) surfactants, with a concentration ranging from 0.01 M to 1 M, is used together with at least one of the molecular solutions of the reactive molecules and / or adsorbed onto the ultrafiltration support prior to the addition of the aqueous phase. The use of surface-active reagents (SARs), such as surfactants, plays a role in regulating the structure and geometry of the template (interface) and therefore the polymer nanofilm formed at the interface of two immiscible liquids. The addition of surfactants controls the characteristics and morphology of the nanofilm, as well as the overall charge of the polymer nanofilm and therefore the degree of crosslinking.

[0100] In the present invention, defect-free polymer nanofilms, either fabricated as free-standing entities and transferred onto porous supports or fabricated directly onto porous supports to form nanofilm composite membranes, exhibit tunable salt rejection properties.

[0101] The amine- or hydroxyl-rich reagent is selected from the group consisting of piperazine (PIP), m-phenylenediamine (MPD), p-phenylenediamine (PPD), polyethyleneimine (PEI), 4-(aminomethyl)piperidine (AMP), 1,3-cyclohexanediamine (CDA), 1,4-cyclohexanediamine (CDA), 1,6-hexanediamine (HDA), ethylenediamine (EDA), resorcinol (RES), phloroglucinol (PHL), pentaerythritol (PET), quercetin (QCT), and bisphenol A (BPA), melamine (MM), at a concentration ranging from 0.01 to 5.0 w / w%.

[0102] The polyfunctional acid halide is selected as the reactive molecule from terephthalic acid chloride (TPC) and 1,3,5 benzenetricarbonyl trichloride or trimesic acid chloride (TMC) at a concentration ranging from 0.001 to 0.5 w / w%.

[0103] Polyamide nanofilms are developed on ultrafiltration supports through the interfacial polymerization reaction between piperazine (PIP) and trimesoyl chloride (TMC) by impregnating the porous support with an aqueous solution containing PIP and then reacting with a TMC solution dissolved in hexane, cyclohexane, heptane, toluene, octane, decane, or hexadecane.

[0104] The present invention provides a method for isolating a separation layer of an ultrathin polymer nanofilm composite membrane independent of a support in order to characterize its properties. The isolated free-standing polymer nanofilm layer is transferred to a different substrate while keeping the top surface of the nanofilm facing upward. The surface properties of the nanofilm are controlled by a combination of interfacial polymerization conditions and post-annealing treatment. The solvent permeability and ability to separate small solutes, including monovalent and multivalent ions, through the ultrathin polymer nanofilm composite membrane depend on the reactant concentrations used in the interfacial polymerization and the thickness of the polymer nanofilm.

[0105] The present invention further provides a method for preparing a polymer nanofilm composite membrane as defined herein: a. Free-standing polymer nanofilms are arranged on top of each other in a layer-by-layer manner on a solid substrate to form a composite material, wherein the thin films have a thickness of less than 10 nm.

[0106] b. The free-standing polymer nanofilms are arranged on top of each other in a layer-by-layer manner on a porous support to form a composite material, wherein the thin films have a thickness of less than 10 nm.

[0107] c. The free-standing polymer nanofilm and at least one additional material are vertically stacked or arranged as an in-plane heterostructure to form a composite film, wherein said film has a thickness of less than 10 nm.

[0108] d. The free-standing polymer nanofilm is intercalated with nanoparticles, said film having a thickness of less than 10 nm and the size of the nanoparticles being less than 100 nm.

[0109] The nanofilm layer is selected from the group consisting of polyamides, polyureas, polyurethanes, polyesters, polysulfonamides, polyphthalamides, polypyrrolidines, polysiloxanes, poly(amideimides), poly(etheramides), poly(esteramides), and poly(ureaamides).

[0110] The present invention provides a method for preparing highly selective ultrathin polymer nanofilm composite membranes by interfacial polymerization from an aqueous solution of PIP and a hexane solution of TMC, in which the resulting nanofilm composite membranes provide 99.99% divalent salt rejection in the presence of a surface-active reagent (SAR), e.g., a surfactant, in the aqueous solution.

[0111] The present invention provides a method for preparing highly selective ultrathin polymer nanofilm composite membranes by interfacial polymerization from an aqueous solution of PIP and a hexane solution of TMC, where the addition of a surface-active reagent (SAR), e.g., a surfactant, to the aqueous solution provides a composite membrane with reduced organic fouling.

[0112] The present invention provides the use of free-standing polymer nanofilms as defined herein for gas separations, insulating barrier layer thin films, transparent coatings with surface active groups, polar and non-polar thin film coatings, composite materials, separation membranes in aqueous and organic solvents, water purification and desalination.

[0113] Aqueous phase reactive molecules used in the present invention may contain any of the following functional groups: i. at least two primary aromatic amine groups (e.g., m-phenylenediamine, p-phenylenediamine, 1,3-bis(aminomethyl)benzene, m-phenylenediamine-4-methyl, 3,5-diamino-N-(4-aminophenyl)benzamide, and 1,3,5 benzenetriamine).

[0114] ii. at least two primary aromatic amine groups and at least one carboxylic acid group (e.g., 3,5-diaminobenzoic acid).

[0115] iii. at least two primary aromatic amine groups and at least one methyl group (eg, 2,4-diaminotoluene).

[0116] iv. at least two primary aromatic amine groups and at least one methoxy group (eg, 2,4-diaminoanisole).

[0117] v. At least two primary aromatic amine groups and at least one sulfonic acid group (e.g., 2,4-diaminobenzenesulfonic acid).

[0118] vi. At least two primary aliphatic amine groups (e.g., ethylenediamine, 2,2',2''-triaminotriethylamine, and polyethyleneimine).

[0119] vii. At least two primary amine groups in a cyclic or heterocyclic ring (e.g., melamine and 1,3-cyclohexanebis(methylamine)).

[0120] viii. At least two secondary amine groups in the cyclic or heterocyclic ring (eg, piperazine).

[0121] ix. At least two aromatic hydroxyl groups (e.g., resorcinol, phloroglucinol).

[0122] x. at least one aromatic primary amine and at least one aromatic hydroxyl group (e.g., 3-aminophenol, dopamine).

[0123] xi. at least two aliphatic hydroxyl groups (e.g., N-methyl-diethanolamine).

[0124] The polyfunctional acyl halide reactive molecule in the organic phase can contain at least two acyl halide groups. Preferably, the acyl halide groups are aromatic in nature and contain at least two. Most preferably, there are three acyl halide groups per molecule in the aromatic ring (e.g., trimesoyl chloride (TMC)).

[0125] As described herein, the surface active agents (SAR) used are anionic, cationic, zwitterionic and neutral (non-ionic) surfactants and may include: i. At least one anionic functional group derived from sulfates, alkyl ether sulfates, sulfonates, phosphates, and carboxylates (e.g., ammonium lauryl sulfate, sodium lauryl sulfate, sodium laureth sulfate, and sodium myreth sulfate, sodium lauroyl sarcosinate, perfluorononanoic acid, perfluorooctanoic acid).

[0126] ii. At least one cationic functional group derived from a primary amine, a secondary amine, a tertiary amine, and a quaternary ammonium salt (e.g., octenidine dihydrochloride, benzethonium chloride, cetyl-trimethyl-ammonium bromide, dimethyl-dioctadecyl-ammonium bromide, dimethyl-dioctadecyl-ammonium chloride, cetylpyridinium chloride, benzalkonium chloride).

[0127] iii. at least one cationic functional group derived from a primary amine, a secondary amine, a tertiary amine, and a quaternary ammonium salt, and at least one anionic functional group derived from a sulfate, an alkyl ether sulfate, a sulfonate, a phosphate, and a carboxylate (e.g., 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, dodecylphosphocholine (DPC), 3-(dodecyldimethylammonio)propanesulfonate (DPS), 2-[(3-dodecanamidopropyl)dimethylammonio]acetate, N,N-dimethyl-N-(3-cocamidopropyl)-3-ammonio-2-hydroxypropylsulfonate, phosphatidylserine, 1-oleoyl-2-palmitoyl-phosphatidylcholine, sphingomyelin); iv. Nonionic block copolymer chains composed of amines linked by a central hydrophobic block of poly(propylene glycol) or two hydrophilic blocks of poly(ethylene glycol), where each block may contain 2 to 100 hydrophilic polyether units (e.g., polyoxyethyleneamine, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), Pluronic® F-127, polyethylene glycol (15)-hydroxystearate, polyoxyethylene (20) sorbitan monolaurate).

[0128] v. At least one polymer chain comprising a hydrophilic polyether chain containing 2 to 100 units and a hydrophobic aromatic hydrocarbon group (e.g., polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100), 4-nonylphenyl-polyethylene glycol).

[0129] vi. At least one polymer chain containing an organosilane, organosiloxane group or dendrimer, and a hydrophilic polyether chain containing 2 to 100 units.

[0130] As used herein, the term "ultrathin polymer nanofilm composite membrane" refers to a composite membrane in which the polymer separation layer is at least 1-200 nm thick and is either i) fabricated at an interface on a porous support, or ii) fabricated by interfacial polymerization at the interface between two bulk liquids and transferred onto a porous support.

[0131] The ultra-thin polymer layer is polyamide with thicknesses varying from 7 nm to 150 nm.

[0132] The highly selective ultrathin polymer nanofilm of the nanofilm composite membrane has a thickness of less than 50 nm (e.g., 1 to 40 nm). Suitably, the highly selective ultrathin polymer nanofilm of the nanofilm composite membrane has a thickness of less than 20 nm. More suitably, the highly selective ultrathin polymer nanofilm of the nanofilm composite membrane has a thickness of less than 15 nm (e.g., less than 10 nm or 8 nm). The ultrathin polymer nanofilm has a thickness of less than 10 nm (e.g., 1 to 10 nm). More suitably, the ultrathin polymer nanofilm has a thickness of less than 8 nm (e.g., 7 nm).

[0133] The elemental composition (atomic %) of the nanofilms is as follows: 71.4–73.5% carbon, 7.5–10.6% nitrogen, and 15.9–21.1% oxygen.

[0134] The elemental composition (atomic %) of the nanofilms is as follows: 73.8–74.2% carbon, 7.9–9.2% nitrogen, and 16.6–18.2% oxygen.

[0135] The elemental composition (atomic %) of the nanofilms is as follows: 72.6–74.8% carbon, 11.1–12.8% nitrogen, and 12.4–16.3% oxygen.

[0136] The elemental composition (atomic %) of the nanofilms is as follows: 73.6 ± 0.9% carbon, 10.9 ± 0.8% nitrogen, and 15.5 ± 0.4% oxygen.

[0137] It will be appreciated that where the nanofilm includes nitrogen- and oxygen-containing moieties, such moieties form an integral part of the nanofilm's structure, rather than merely being surface contaminants.

[0138] The ultrathin polymer nanofilm composite membrane has a water contact angle value of 25.7 to 59.6°. Suitably, the ultrathin polymer nanofilm composite membrane has a water contact angle value of 25.7 to 56.9°. More suitably, the ultrathin polymer nanofilm composite membrane has a water contact angle value of 25.7 to 45.2°. Most suitably, the ultrathin polymer nanofilm composite membrane has a water contact angle value of 32.2 to 47.5°.

[0139] The ultrathin polymer nanofilm composite membrane has a zeta potential value of -12.2 to -23.4 mV measured at pH 7.0. Suitably, the ultrathin polymer nanofilm composite membrane has a zeta potential value of -12.2 to -27.2 mV measured at pH 7.0. Most suitably, the ultrathin polymer nanofilm composite membrane has a zeta potential value of -18.8 to -26.0 mV measured at pH 7.0.

[0140] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a low-concentration aqueous solution of PIP (0.01-0.05 w / w%) containing a surface-active agent (SAR), such as a surfactant, with a hexane solution of TMC. The ultrathin polymer nanofilm composite membrane fabricated on an HPAN support exhibited a selectivity of 2 g L at 25 (±1) °C under an applied pressure of 5 bar. -1 When tested with a feed solution of 16.9 to 59.0 L m , the maintenance of MgCl2 (2.7 to 94.6%) and NaCl (9.7 to 45.0%) removal rates was achieved. -2 h -1 bar -1 High water (pure water) permeability in the range of 9.5 to 1198% results in high rejection of Na2SO4 (91.43 to 99.95%). Ideal salt selectivity of NaCl / Na2SO4 in the range of 9.5 to 1198 is achieved.

[0141] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a moderately concentrated aqueous solution of PIP (0.1 w / w%) with the addition of a surface-active agent (SAR), e.g., a surfactant, and a hexane solution of TMC. The ultrathin polymer nanofilm composite membrane fabricated on an HPAN support exhibited a selectivity of 2 g L at 25 (±1) °C under an applied pressure of 5 bar. -1 When tested with a feed solution of 8.1 to 16.4 L m , the retention of high removal rates of MgCl2 (96.7 to 98.4%) and NaCl (42.1 to 56.9%) was achieved. -2 h -1 bar -1 High water (pure water) permeability in the range of 99.81-99.99% Na2SO4 rejection is achieved. Ideal salt selectivity of NaCl / Na2SO4 in the range of 296.3-4310 is achieved.

[0142] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a moderately concentrated aqueous solution of PIP (1 w / w%) with the addition of a surface-active agent (SAR), e.g., a surfactant, and a hexane solution of TMC. The ultrathin polymer nanofilm composite membrane fabricated on an HPAN support exhibited a selectivity of 2 g L at 25 (±1) °C under an applied pressure of 5 bar. -1 When tested with a feed solution of 6.1 to 13.7 L m , the retention of high removal rates of MgCl2 (89.5 to 99.0%) and NaCl (30.7 to 61.2%) was achieved. -2 h -1 bar -1 The high water (pure water) permeability range results in high rejection of Na2SO4 (32.55-91.73%). An ideal salt selectivity of NaCl / Na2SO4 of 4.7 is achieved.

[0143] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a highly concentrated aqueous solution of PIP (2 w / w%) with a surfactant, such as a surfactant, and a hexane solution of TMC. The ultrathin polymer nanofilm composite membrane fabricated on an HPAN support exhibited a selectivity of 2 g L at 25 (±1) °C under an applied pressure of 5 bar. -1When tested with a feed solution of 4.4 Lm, the retention of high removal rates of MgCl2 (98.4%) and NaCl (54.5%) was achieved. -2 h -1 bar -1 The water (pure water) permeability of 28.4 results in a low rejection of Na2SO4 (39.93%). An ideal salt selectivity of NaCl / MgCl2 of 28.4 is achieved.

[0144] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of different concentrations of PIP aqueous solutions (0.05-0.1 w / w%) with the addition of surface-active agents (SARs), such as surfactants, and a hexane solution of TMC. The ultrathin polymer nanofilm composite membranes fabricated on HPAN supports yielded ideal salt selectivities of NaCl / MgCl2 ranging from 2.2 to 35.3.

[0145] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a highly concentrated aqueous solution of PIP (1-2 w / w%) with the addition of a surface-active agent (SAR), such as a surfactant, and a hexane solution of TMC. The ultrathin polymer nanofilm composite membrane fabricated on an HPAN support exhibited ideal salt selectivity of NaCl / MgCl2 in the range of 6.6-38.8.

[0146] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a low-concentration aqueous solution of PIP (0.1 w / w%) containing a surface-active agent (SAR), such as a surfactant, with a hexane solution of TMC. The ultrathin polymer nanofilm composite membranes fabricated on PAN, P84, and PES supports exhibited a selectivity of 2 g L at 25 (±1) °C under an applied pressure of 5 bar. -1 When tested with a feed solution of 14.1 to 45.6 L m , the retention of high removal rates of MgCl2 (5.8 to 93.1%) and NaCl (11.3 to 42.8%) was achieved. -2 h -1 bar -1 High water (pure water) permeability in the range of 9.5 to 190.7 results in high rejection of Na2SO4 (90.65 to 99.70%). Ideal salt selectivity of NaCl / Na2SO4 in the range of 9.5 to 190.7 is achieved.

[0147] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a low-concentration aqueous solution of PIP (0.1 w / w%) containing a surface-active agent (SAR), such as a surfactant, with an organic solution of TMC. The ultrathin polymer nanofilm composite membranes were fabricated on an HPAN support, with the organic phase solvent selected from heptane, toluene, and cyclohexane. The membranes exhibited a selectivity of 2 g L at 25 (±1) °C under an applied pressure of 5 bar. -1 When tested with a feed solution of 13.3 to 15.3 L m , the retention of high removal rates of MgCl2 (89.4 to 97.7%) and NaCl (30.9 to 43.8%) was achieved. -2 h -1 bar -1 High water (pure water) permeability in the range of 1.6 to 267.6 results in high rejection of Na2SO4 (57.15 to 99.79%). The ideal salt selectivity for NaCl / Na2SO4 is achieved in the range of 1.6 to 267.6, and for NaCl / MgCl2 in the range of 6.5 to 25.4.

[0148] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a moderately concentrated aqueous solution of PIP (0.1 w / w%) with the addition of a surface-active agent (SAR), e.g., a surfactant, and a hexane solution of TMC. The ultrathin polymer nanofilm composite membranes fabricated on HPAN supports had a selectivity of 2–40 g / L at 25 (±1) °C under an applied pressure of 5–20 bar. -1 When tested using a mixed salt solution (Na2SO4 + NaCl; equal weight) of 12.9 to 16.4 Lm -2 h -1 bar -1 High water (pure water) permeability in the range of SO4 2- High removal rate (99.78-99.95%) and Cl - The Cl removal rate ranges from 476 to 1460 (-4.8 to 39.1%). - / SO4 2- The ion selectivity of the mixed salt is achieved.

[0149] Highly selective ultrathin polymer nanofilm composite membranes were fabricated by interfacial polymerization of a moderately concentrated aqueous solution of PIP (0.1 w / w%) with the addition of a surface-active agent (SAR), e.g., a surfactant, and a hexane solution of TMC. The ultrathin polymer nanofilm composite membranes fabricated on HPAN supports had a selectivity of 2–40 g / L at 25 (±1) °C under an applied pressure of 5–20 bar. -1 When tested using a mixed salt solution (Na2SO4 + MgSO4 + MgCl2 + NaCl; equal weights) of 12.9 to 16.4 Lm -2 h -1 bar -1 High water (pure water) permeability in the range of SO4 2- High removal rate (99.89-99.94%) and Cl - The Cl removal rate ranges from 636.4 to 1045 (30.0 to 48.5%). - / SO4 2- The ion selectivity of the mixed salt is achieved.

[0150] Highly selective ultrathin polymer nanofilms and their composite membranes were obtained with a capacity of 287-390 g.mol -1 and a decrease in the MWCO was observed when a surface active agent (SAR), such as a surfactant, was added to the aqueous solution during interfacial polymerization.

[0151] The highly selective, ultrathin polymer nanofilm composite membranes of the present invention offer numerous advantages over similar membranes known in the art. The composite membranes of the present invention exhibit improved ion selectivity compared to currently available membranes. By practicing the methods defined herein, highly selective, ultrathin polymer nanofilm composite membranes of the present invention can be reliably prepared with thicknesses less than 10 nm and ideal selectivities between NaCl and Na2SO4 of greater than 50 and up to 4310. Furthermore, the nanofilm composition offers advantages in the fields of separation / filtration technologies, organic synthesis in conjunction with membrane separation methods, catalyst recovery, and the pharmaceutical industry. [example] The following examples are given by way of illustration and therefore should not be construed as limiting the scope of the present invention. [Example 1] Preparation of ultrafiltration support membrane and cross-linking of support membrane Ultrafiltration polysulfone (PSf), polyethersulfone (PES), P84, and polyacrylonitrile (PAN) support membranes were prepared by the phase inversion method. The polyacrylonitrile (PAN) support membrane was prepared on a nonwoven fabric by using a continuous casting machine. First, PAN polymer powder was dried in a hot air oven at 70±1°C for 2 hours. The dried PAN was then dissolved in DMF in an airtight glass flask by continuous stirring at 70±1°C for several hours to produce a 13.0 wt% polymer solution. The polymer solution was then cooled to room temperature (25±1°C). Using a semi-continuous casting machine, a 60 m long, 0.32 m wide membrane sheet was continuously cast onto the nonwoven fabric by maintaining a gap (130-150 μm) between the casting knife and the nonwoven fabric at a speed of 4-7 m / min. During this process, the polymer film, along with the nonwoven fabric, was entrained in a water gelation bath maintained at 25 (±1) °C, where it underwent phase inversion to form an ultrafiltration membrane, and finally entrained in a winder roller. The distance between the knife position and the water gelation bath, i.e., the distance traveled in air, was 0.35 m. The membrane roll was washed with pure water by re-rotating it on another winder roller, cut into small pieces measuring 16 cm x 27 cm, and kept in pure water for 2 days before final storage at 10 (±1) °C in an isopropanol and water mixture (1:1 v / v). For crosslinking of the ultrafiltration support, several pieces (75 pieces) of PAN support were removed from the storage solution and thoroughly washed in pure water. The support was then immersed in 5 L of 1 M sodium hydroxide (NaOH) solution preheated to 60 (±1) °C for 2 hours, and this solution was then placed again in a hot air oven at 60 (±1) °C for 2 hours for hydrolysis. After crosslinking, the PAN membrane was washed with pure water and stored in pure water for several days. The pH of the water was checked regularly and replaced with pure water daily until the pH reached 7. Finally, the hydrolyzed PAN (HPAN) membrane pieces were stored in a mixture of isopropanol and water (1:1 v / v) at 10 (±1) °C.Similarly, a PSf polymer solution was prepared by dissolving 17 wt% PSf in NMP, a P84 polymer solution was prepared by dissolving 22 wt% P84 in DMF, and a PES polymer solution was prepared by dissolving 19 wt% PES with 3 wt% PVP in DMF. Support membranes were fabricated by the phase inversion method as described above. [Example 2] Preparation of nanofilm composite membranes in the presence of surface active agents [SAR] Nanofilm composite membranes were prepared by interfacial polymerization on HPAN, PAN, PSf, PES, and P84 support membranes. The support membranes were washed with ultrapure water to remove excess isopropanol and stored there. An aqueous solution containing reactive molecules selected from PIP, MPD, PPD, AMP, PEI, CDA13, CDA14, HDA, EDA, RES, PHL, PET, QCT, BPA, and MM at concentrations ranging from 0.01 to 5.0 w / w% was then poured onto the support and immersed for 20 seconds. The excess aqueous solution was then removed from the support with a rubber roller and gently air-dried for 10 seconds. An organic solution containing TMC at concentrations ranging from 0.001 to 0.5 w / w% was immediately contacted with the support for the specified time (5 seconds to 20 minutes) to initiate the interfacial polymerization reaction. The organic solvent used in the interfacial polymerization was selected from acyclic alkanes and isoalkanes (e.g., hexane, heptane, isopar G), monocyclic cycloalkanes (e.g., cyclohexane, cycloheptane), aromatic hydrocarbons (e.g., benzene, toluene, xylene, mesitylene), esters (e.g., methyl acetate, ethyl acetate), and / or mixtures thereof. During the interfacial polymerization, room temperature and relative humidity were maintained at 23-25°C and 25-35%, respectively. The excess organic solution containing TMC was removed immediately after the interfacial polymerization reaction, dried at room temperature for 10-30 seconds, and finally annealed in a hot air oven at designated temperatures between 40-90°C for 1-10 minutes. Unless otherwise noted, the organic solvent used in the interfacial polymerization, i.e., the TMC solution, was prepared in hexane. The drying time at room temperature after the interfacial polymerization was 10 seconds, and the annealing temperature was 70 (±1)°C for 1 minute.

[0152] Surface-active reagents (SARs), such as surfactants, were added to i) the aqueous phase containing reactive molecules, ii) the organic phase, and iii) the aqueous and organic phases. The surfactant concentrations ranged from 0.01 mM to 1 M. Unless otherwise specified, the additives were used in the aqueous phase, TMC was dissolved in a hexane solution for interfacial polymerization, the drying time at room temperature after interfacial polymerization was 10 seconds, and the annealing temperature was 70 (±1) °C for 1 minute. The preparation conditions are summarized in Table 1. Table 1: Preparation conditions for polymer nanofilm composite membranes by interfacial polymerization Post-treatment was performed by annealing the nanofilm composite membrane in a hot air oven at 70 (±1) °C for 1 minute. [Table 1-1] [Table 1-2] [Table 1-3] [Example 3] Method for isolating the polymer separation layer of a composite membrane and producing a free-standing nanofilm We used a nanofilm composite membrane fabricated by interfacial polymerization of PIP and TMC on a PAN support, a thin-film composite membrane prepared on a conventional support, prepared by interfacial polymerization of MPD and TMC on a PAN support, and a commercially available TFC nanofiltration membrane. The composite membranes were swollen in acetone by immersion for 30 minutes. The support membrane, along with the nanofilm / thin film, was peeled off from the nonwoven fabric with the aid of adhesive tape. The nonwoven fabric was peeled off by attaching adhesive tape to the top of the composite membrane (nanofilm side) from one end and pulling the ultrafiltration support (along with the nanofilm) away from the fabric. Acetone was added during this process to aid in layer separation. The nanofilm along with the support was then cut into small pieces and floated on the surface of DMF containing 2% water (v / v). During this time, the aqueous DMF solution slowly dissolved the polymer support, leaving only the nanofilm layer floating on the surface of the solution. The free-standing nanofilms were then transferred onto different supports, such as anodic alumina, silicon, or copper grids, with the backside of the nanofilm (facing the aqueous phase during interfacial polymerization) remaining on the support, and the topside (facing the organic phase during interfacial polymerization) remaining on the top side. Finally, the support containing the nanofilm was dried at room temperature, washed with methanol, and finally dried in a hot air oven at a temperature of 50 (±1) °C for 30 min before being used for characterization. [Example 4] Analysis of nanofilm surface morphology and thickness evaluation by scanning electron microscopy (SEM) A scanning electron microscope (SEM; JEOL, JSM 7100F) was used to analyze the surface morphology and cross-sectional images of the nanofilms and composite membranes. Prior to SEM testing, the sample surfaces were coated with a 2–5 nm thick gold-palladium coating sputtered from an EM ACE 200 (Leica Microsystems, GmbH, Germany). To avoid overestimation of thickness due to surface deposition caused by the coating, only relatively thick samples with thicknesses greater than 20 nm were analyzed by SEM. To measure the nanofilm thickness, free-standing polymer nanofilms were transferred onto porous alumina and / or silicon wafer supports and dried at room temperature. The nanofilms along with the supports were then washed in methanol by immersing them in methanol for 10 minutes and then dried in a hot air oven at 50 (±1) °C for 10 minutes. Small pieces along with the nanofilms were broken off from the supports and placed vertically in SEM sample stubs to observe the nanofilm cross-sections under SEM. [Example 5] Study of the surface morphology and thickness evaluation of nanofilms by atomic force microscopy (AFM) Nanofilm surface morphology, including roughness, and thickness were measured using an NT-MDT Spectrum Instruments NTEGRA Aura atomic force microscope (AFM) with a pizzo-type scanner equipped with an NSG10 series AFM cantilever. The cantilever length was 95 μm, width was 30 μm, and thickness was 2 μm. Typical resonant frequencies and force constants were 240 kHz and 11.8 N / m, respectively. A small number of samples were also characterized using a Bruker Dimension 3100, and images were captured in tapping mode using a PointProbe® Plus silicon-SPM probe. For thickness measurements, free-standing nanofilms were transferred onto silicon wafers, the wafer surface was exposed, and a scratch was created to measure the height from the silicon wafer surface to the top nanofilm surface. The step height was used to estimate the nanofilm thickness. A sampling resolution of 256 or 512 points / line and a speed of 0.5–1.0 Hz were used. Gwyddion 2.52 SPM data visualization and analysis software was used for image processing. [Example 6] Contact angle measurement of nanofilm composite membranes The contact angles of the composite films were measured with water using a drop shape analyzer (DSA100, KRUSS GmbH, Germany). At least five measurements were taken to determine the average value of the contact angle. [Example 7] Evaluation of nanofilm thickness by interferometry The thickness of the free-standing polymer nanofilm transferred onto the silicon wafer was measured using an optical interference technique. The thickness values ​​of the polymer nanofilms were measured from two different locations on the sample surface using a general-purpose film thickness measuring instrument (Filmetrics F20-UV, San Diego, USA). The results are shown in Table 2. [Example 8] Characterization of the elemental composition of nanofilms by X-ray photoelectron spectroscopy (XPS) The polymer nanofilm was free-standing and transferred onto a PLATYPUS™ gold-coated silicon wafer as described above. The gold-coated silicon wafer containing the nanofilm was then dried at room temperature, washed with methanol, and finally dried in a hot air oven at 50 (±1) °C for 10 minutes. XPS analysis was performed at the Central Science Services Office of the Indian Institute of Science and Technology (Kolkata, India) using an Omicron Nanotechnology Spectrometer using 300 watts of monochromated AlKα X-rays as the excitation source. Survey and core-level XPS spectra were recorded from at least three different spots on the sample. The analyzer was operated at a constant pass energy of 20 eV, and the Cl peak was set to BE 285 eV to overcome sample charging. Data processing was performed using CasaXps processing software (http: / / www.casaxps.com / ). Peak areas were measured after satellite subtraction and background subtraction according to the linear background or Shirley method. (DA Shirley, High-resolution X-ray photoelectron spectrum of the valence band of gold, Phys. Rev. B5, 4709, 1972). [Example 9] Surface morphology of nanofilm composite membrane observed under SEM The surface morphology of the membrane was analyzed using SEM, and the results are shown in Figures 1 and 2. Nanofilm membranes were prepared using PIP and TMC by interfacial polymerization on an HPAN support. Immediately after the reaction, the excess hexane solution containing TMC was removed, and unreacted TMC remaining on the nanofilm surface was further removed by washing with pure hexane and drying at room temperature for 10 seconds. The composite membrane was finally annealed in a hot air oven at 70 (±1) °C for 1 minute. SEM images of the nanofilm composite membrane were captured without removing the support. [Example 10] Measuring polymer nanofilm thickness by cross-sectional SEM The thickness of the free-standing nanofilms transferred onto the substrate was evaluated using SEM. The images are shown in Figure 3, and the results are summarized in Table 2. Nanofilms were prepared using PIP and TMC via interfacial polymerization on an HPAN substrate. [Example 11] Evaluation of surface morphology and thickness of free-standing nanofilms by AFM analysis The surface morphology and thickness of the free-standing nanofilms were determined from AFM analysis. Nanofilms with thicknesses preferably less than 20 nm were measured by this technique. The results are summarized in Table 2 and Figure 4. Table 2: Thickness measurements of free-standing nanofilms by using different measurement techniques:

[0153] [Table 2] [Example 12] Determination of surface charge of nanofilm composite membranes: The surface charge of the membranes was evaluated over a range of pH (pH 3 to pH 9) using a Zeta Cad streaming current and zeta potential meter (CAD Instruments, France). The results are shown in Table 3. Water-wet composite membrane samples were placed in a dedicated test cell. Zeta potential values ​​were recorded at different pH values ​​using an electrolyte of 1 mM KCl. Surface charge was measured using a pair of rectangular nanofilm composite membranes fabricated on an HPAN support. At least two sets of experiments were performed to obtain the mean and standard deviation of the measurements. Table 3. Zeta potential of membranes measured in electrolyte solutions of different pH. The pH of the electrolyte solution was adjusted using potassium hydroxide (KOH) as the base and hydrochloric acid (HCl) as the acid.

[0154] [Table 3] [Example 13] Determination of the elemental composition of nanofilms by XPS The elemental composition was evaluated by XPS studies of free-standing nanofilms transferred onto gold-coated silicon wafers. The results were obtained from survey spectra and are summarized in Table 4. Table 4: Elemental composition of free-standing polymer nanofilms.

[0155] [Table 4] [Example 14] Evaluation of desalination performance of nanofilm composite membranes The desalination performance of the nanofilm composite membrane was studied in a cross-flow desalination test unit consisting of an assembly of 12 SS316 cells, with four cells connected in series in each row. Each cell can accommodate a circular membrane coupon with a diameter of 0.043 m. The liquid flow rate was controlled to 50 Lh by controlling the rotation of the high-pressure pump connected to the assembly with a frequency drive control. -1 ~150Lh -1 The temperature of the feed solution was kept constant by a temperature controller and heat exchanger in the form of a cooling liquid jacket outside the feed tank. The solutes used in our studies include (i) salts (NaCl, KCl, MgCl2, CaCl2, MgSO4, K2SO4, and Na2SO4), (ii) carbohydrates (glucose, sucrose, and raffinose), and (iii) dyes (sodium-2-naphthol-6-sulfonate hydrate, acid orange 7, orange G, acid fuchsin, brilliant blue R, rhodamine B, crystal violet, toluidine blue O, basic fuchsin, and chrysodine G). Experiments were performed with 0.5 to 80 g L of feed solution under various applied pressures from 1 to 20 bar. -1 The salt concentrations were varied over a range of 100-150°C, and the feed temperature was maintained at 25 (±1)°C. All results were collected after the membranes were allowed to reach a steady state where the pure water permeability through the membrane was nearly constant. This was achieved by waiting 7 hours under cross-flow at 5 bar pressure and 3 hours under cross-flow at 20 bar pressure with pure water as the feed. The membrane permeability was calculated using the following equation:

[0156]

number

[0157] where V is the volume of permeate (liters) and A is the surface area of ​​the membrane (m 2 ) and t is time. The membrane rejection was calculated from the conductivity ratio between the difference between the feed and permeate concentrations and the feed concentration.

[0158]

number

[0159] In the formula, C p is the concentration of dissolved salts in the permeate, and C f is the concentration of dissolved salt on the supply side.

[0160] The selectivity of an ion (or salt) is expressed as follows:

[0161]

number

[0162] Double-pass RO treated water (conductivity <2 μS) was used to measure pure water permeability and prepare the feed solution. A conductivity meter (Eutech PC2700; CONSEN9201D with cell constant K = 0.530) was used to measure the conductivity of the samples in the range of several microsiemens (μS) to several millisiemens (mS). The conductivity of permeate samples with measured conductivities above 10 μS was measured together with the conductivity of the feed sample, and the salt rejection was calculated using equation (ii). The conductivity of permeate samples with measured conductivities below 10 μS was used to measure the ion concentrations in the samples using inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography (IC). Both the feed and permeate samples were analyzed by ICP-MS and IC after necessary dilution. The rejection and selectivity were determined using equations (ii) and (iii), respectively. [Example 15] Study of solvent (water) transport through polyamide nanofilm composite membranes at different viscosities and temperatures: The permeability of the polyamide composite membrane at different viscosities of the feed solution and different temperatures was recorded and is shown in Table 5 and Figure 5, respectively. Cross flow value 50 Lh -1 and operation was carried out in a cross-flow filtration system under an applied pressure of 5 bar. Table 5. Permeability of nanofilm composite membranes under different feed compositions with various viscosities.

[0163] [Table 5] [Example 16] Evaluation of the fouling behavior of nanofilm composite membranes BSA (250 mg L -1 The fouling behavior of the membrane during desalination of salt solutions was evaluated by the addition of NaSO (2 g L). The results are shown in Figure 6. Briefly, the membrane coupon was pressurized with pure water at a pressure of 5 bar and allowed to reach a steady state. Then, NaSO (2 g L) was added. -1 ) was added, and the mixture was left for another 3 hours, after which the NaSO removal rate and water permeability were measured. Then, 250 mg L of BSA was added. -1 The feed was added to a concentration of 0.01% NaSO4, and the system was operated continuously for 24 hours. The water permeability and NaSO4 rejection rate were recorded over time. The antifouling performance was determined by the permeability reduction rate (PR) and permeability recovery rate (PRR) according to the following equations (Equation iv and Equation v):

[0164]

number

[0165]

number

[0166] During the ceremony, J. o and J. t are the initial permeability (containing only salt in the feedwater) during desalination and the permeate flux at a given desalination time (containing salt in the BSA-contaminated feedwater), respectively. After 24 hours of operation with the BSA / salt solution, the membrane was washed with pure water for 30 minutes. The membrane permeability (J c ) and the removal rate were measured using Na2SO4 (2 g L -1 ) was used for measurement. [Example 17] Desalination performance of nanofilm composite membranes The desalination performance of the nanofilm composite membrane was studied using a pure salt feed, a mixed salt feed containing two salts, a mixed salt feed containing four salts, and a synthetic seawater feed. The pure water permeability, salt rejection, and ion selectivity (separation factor) were evaluated. The results are summarized in Tables 6–10. Table 6. Permeation behavior of polyamide nanofilm composite membranes fabricated on HPAN supports. The membranes were prepared at a salt concentration of 2 g L−1 under an operating pressure of 5 bar at 25 (±1) °C. -1 of feed and cross flow rate 50Lh -1 Tested with. [Table 6-1] [Table 6-2] [Table 6-3] [Table 6-4] [Table 6-5] [Table 6-6] Table 7. Permeation behavior of polyamide nanofilm composite membranes fabricated on different ultrafiltration supports. The membranes were loaded with 2 g L at 25 (±1) °C under an operating pressure of 5 bar. -1 of feed and cross flow rate 50Lh -1 Tested with.

[0167] [Table 7] Table 8. Performance of free-standing membranes prepared by interfacial polymerization at the aqueous-organic interface and then transferred onto HPAN supports. The membranes were polymerized at 25 (±1) °C under an operating pressure of 5 bar with 2 g L -1 of feed and cross flow rate 50Lh -1 Tested with.

[0168] [Table 8] Table 9. Pure water permeability, Na2SO4 and NaCl rejection (%), and ideal selectivity between NaCl and Na2SO4. The salt concentration used in the feed was 2 g L -1 The membrane was subjected to an applied pressure of 5 bar and a cross-flow rate of 50 Lh -1 Tested at 25(±1)°C. [Table 9-1] [Table 9-2] Table 10. Pure water permeability, MgCl2 and NaCl rejection (%), and ideal selectivity between NaCl and MCl2. The membranes were subjected to an applied pressure of 5 bar and a cross-flow rate of 50 Lh -1 Tested at 25(±1)°C.

[0169] [Table 10] [Example 18] Performance of nanofilm composite membranes with increasing feed salt concentration: The nanofiltration performance of the nanofilm composite membrane in terms of salt rejection rate with increasing salt concentration in the feed solution is shown in Figure 7. The salt concentration ranged from 0.5 to 40 g L -1 The measurements were carried out at a cross-flow rate of 50 L / h. -1 At 25 (±1) °C, 5 bar (0.5 to 8 g L -1 (for salt concentration), 10 bar (20 g L -1salt concentration) and 20 bar (40 g L -1 The analysis was carried out under the following conditions: [Example 19] Membrane performance at different concentrations of sodium lauryl sulfate used in the aqueous phase during interfacial polymerization: The membrane performance was studied in terms of pure water permeability, salt rejection, and salt selectivity. The membranes were prepared by adding different concentrations of sodium lauryl sulfate to the aqueous phase during interfacial polymerization, with the preferred polymerization time being 5 seconds. The polymerization reaction time was also varied from 5 seconds to 20 minutes to study the separation performance of the membranes. The results are shown in Table 6. [Example 20] Fluoride removal rate of nanofilm composite membrane: The nanofiltration performance of the membranes was evaluated using a sodium fluoride feed and the results are shown in Table 11. Table 11. Fluoride separation performance of nanofilm composite membranes under an applied pressure of 5 bar and a cross-flow rate of 50 Lh -1 At 25(±1)℃ and salt concentration 2gL -1 Measurements were carried out at.

[0170] [Table 11] [Example 21] Nanofiltration performance and ion selectivity using mixed salts where two salts are used in the feed Nanofiltration performance and ion selectivity results by using mixed salts where two salts are used as feed are summarized in Table 12. [Example 22] Nanofiltration performance and ion selectivity using mixed salts with four salts in the feed Nanofiltration performance and ion selectivity results using a mixed salt feed in which four salts were used are summarized in Table 13.

[0171] Table 12. Comparison of ion selectivity between single salts and mixed salts at different salt concentrations. Nanofiltration performance of single and mixed salts from low to high concentrations when two salts (Na2SO4 and NaCl) were used as a mixed salt with equal concentrations (1:1 in wt%). The membranes were treated at 25 (±1) °C and a cross-flow rate of 50 Lh -1 In order to overcome the osmotic pressure, the samples were tested under different pressures. [Table 12-1] [Table 12-2] Table 13. Nanofiltration performance at high salt concentrations using four salts (NaSO, MgSO, MgCl, and NaCl) as a mixed salt feed. The four salts were used at equal wt% in the feed solution. The membranes were run at 25 (±1) °C under different pressures higher than the osmotic pressure and at a cross-flow rate of 50 Lh. -1 Tested in.

[0172] [Table 13] [Example 23] Separation of charged and uncharged molecules and MWCO of different polyamide nanofilm composite membranes: The separation of charged and uncharged molecules and the MWCO of different polyamide membranes were measured, and the results are shown in Table 14 and Figure 8, respectively. Table 14. Permeability and rejection of different carbohydrates and dyes through polyamide nanofilm composite membranes fabricated on HPAN supports. The carbohydrate and dye feed concentrations used were 1 g L−1, respectively. -1 and 200 mg L -1 The carbohydrate removal rate was calculated from HPLC measurements, and the dye removal rate was calculated from UV-Vis absorbance. [Table 14-1] [Table 14-2] [Example 24] Performance of polyamide nanofilm composite membranes under different pressures: The performance of the nanofilm composite membrane under different pressures was measured and the results are shown in Figure 9. The membrane was allowed to reach a steady state at each applied pressure by pressing at the pressure for several hours. [Example 25] Solvent transport through polyamide nanofilm composite membranes: The solvent transport properties of pure solvents through the nanofilm composite membrane were investigated. First, the acetone permeability was measured, followed by the DMF permeability. The acetone permeability was recorded again to confirm the stability of the nanofilm composite membrane in DMF. After measuring the DMF permeability, an increase in acetone permeability (from 21 to 46%) was observed. This increase was attributed to the swelling of the polymer separation layer in DMF (e.g., activation effect) and subsequent rearrangement in acetone (Karan et al., Science 348, 1347, 2015). The permeabilities of THF, 2-propanol, and methanol were measured, with the highest permeability achieved for methanol. The results are shown in Figure 10. [Example 26] Solvent permeability and molecular separation studies of nanofilm composite membranes before and after DMF activation: The solvent permeability and molecular separation performance of the nanofilm composite membrane were investigated before and after DMF activation, and the results are shown in Figure 11. [Example 27] Wrinkle-based measurement of Young's modulus of nanofilms: The Young's modulus of the nanofilm was determined from a wrinkle-based experiment. The fixture assembly used for this experiment is shown in Figure 12. The front side of the nanofilm was placed on top of the PDMS. The measured Young's modulus values ​​ranged from 297 to 298 MPa. [Example 28] Measurement of mass and density of nanofilms by quartz crystal microbalance (QCM) The dry mass of the nanofilm was measured in both configurations: (i) the nanofilm front side up, and (ii) the nanofilm back side up. The dry mass density was calculated from the change in frequency and the known thickness of the nanofilm, Table 15 (Karan et al., Science 348, 1347, 2015). Table 15: Dry mass density of nanofilms measured by QCM.

[0173] [Table 15] [Effects of the invention]

[0174] Highly selective ultrathin polymer nanofilm composite membranes have the following advantages: 1. The nanofilm composite membranes presented herein are fabricated by interfacial polymerization, a method commonly used for large-scale industrial membrane manufacturing, and are used for desalination.

[0175] 2. The nanofilm composite membranes presented herein are fabricated using low-cost surface-active reagents.

[0176] 3. The nanofilm composite membranes presented herein are stable in organic solvents when the nanofilms are fabricated on a solvent-stable substrate of a porous polymer support membrane.

[0177] 4. The nanofilm composite membranes presented herein possess unique features with tunable salt rejection properties, enhanced monovalent vs. multivalent ion selectivity, and reduced organic fouling.

[0178] 5. The nanofilm composite membranes presented herein exhibit up to 99.99% rejection of divalent salts (Na2SO4) and exhibit monovalent to divalent ion selectivity of greater than 4000.

[0179] 6. The nanofilm composite membranes presented herein exceed the permeability-selectivity upper limits of state-of-the-art nanofiltration membranes, demonstrating performance that is 1-2 orders of magnitude higher than commercially available membranes. The inventions described in the original claims of this application are set forth below. [1] A highly selective ultrathin polymer nanofilm composite membrane, comprising: a) a base layer of a porous polymer support membrane; b) top polymer nanofilm; Including, The highly selective ultrathin polymer nanofilm composite membrane is prepared by interfacial polymerization in the presence of a surfactant at a concentration ranging from 0.01 mM to 1 M, and the thickness of the nanofilm is within the range of 7 nm to 150 nm. [2] The composite membrane of [1], wherein the base layer of the porous polymer support membrane is selected from the group consisting of hydrolyzed polyacrylonitrile (HPAN), polysulfone (PSf), polyethersulfone (PES), P84, crosslinked P84, and polyacrylonitrile (PAN). [3] The composite membrane according to [1], wherein the surfactant is selected from the group consisting of anionic, cationic, zwitterionic and neutral surfactants. [4] 8.1~57.1Lm -2 h -1 bar -1 Pure water permeability in the range of over 98.0% to max. 99.99% Na 2 SO 4 and a NaCl rejection rate between 15.3 and 56.9%. [5] NaCl vs. Na 2 SO 4 The composite membrane according to [1], wherein the ideal salt selectivity is greater than 1 and up to 4310. [6] 6.1~17.6Lm -2 h -1 bar -1 Pure water permeability in the range of over 97.0% to max. 99.0% MgCl 2 and a NaCl rejection rate between 38.4 and 61.2%. [7] NaCl vs MgCl 2 The composite membrane according to [1], wherein the ideal salt selectivity is greater than 1 and at most 40. [8] 10. The composite membrane according to claim 1, wherein the ion selectivity between monovalent anions and divalent anions in a mixed salt feed is greater than 1 and up to 1460. [9] 287-390 g.mol -1 The composite membrane according to [1], exhibiting a MWCO (molecular weight cut-off) in the range of

[10] [1] The composite film according to [1], wherein when the polymer repeat unit is selected from piperazine and trimesoyl chloride, the nanofilm has an elemental composition of 71.4 to 74.8% carbon, 7.5 to 12.8% nitrogen, and 12.4 to 21.1% oxygen.

[11] A method for preparing a highly selective ultrathin polymer nanofilm composite membrane, comprising the steps of: a) preparing a polymer support membrane on a nonwoven fabric by a phase inversion method; b) modifying the polymeric support membrane obtained in step (a) to obtain a hydrophilic support membrane; c) separately dissolving 0.01 to 5.0 w / w% of polyamine in an aqueous solvent to obtain solution A; d) separately dissolving 0.001 to 0.5 w / w % of a polyfunctional acid halide in an organic solvent to obtain a solution B; e) adding 0.01 mM to 1 M of a surface-active reagent to either solution A or B obtained in step (c) or step (d); f) pouring the solution A obtained in step (e) onto the hydrophilic support membrane of step (b), followed by immersion for 10 seconds to 1 minute; g) a step of discarding the aqueous solution from the hydrophilic support membrane, removing the remaining aqueous solution with a rubber roller, and then air-drying the membrane for 10 seconds to 1 minute; h) immediately contacting the solution B obtained in step (e) with the hydrophilic support membrane of step (g) for a period ranging from 5 seconds to 20 minutes for interfacial polymerization to obtain a nanofilm; i) removing excess organic solution, followed by removing any unreacted polyfunctional acid halide remaining on the nanofilm, and drying the film at room temperature for 10 to 30 seconds; j) annealing the membrane at a temperature ranging from 40 to 90°C for a time ranging from 1 to 10 minutes to obtain the highly selective ultrathin polymer nanofilm composite membrane.

[12] The method according to

[11] , wherein the organic solvent used in step (d) is selected from the group consisting of acyclic alkanes and isoalkanes (hexane, heptane, Isopar G), monocyclic cycloalkanes (cyclohexane, cycloheptane), aromatic hydrocarbons (benzene, toluene, xylene, mesitylene), esters (methyl acetate, ethyl acetate), alone or in mixtures thereof.

[13] 11. The method according to claim 11, wherein the polyamine used in step (c) is selected from the group consisting of piperazine (PIP), m-phenylenediamine (MPD), p-phenylenediamine (PPD), polyethyleneimine (PEI), 4-(aminomethyl)piperidine (AMP), 1,3-cyclohexanediamine (CDA13), 1,4-cyclohexanediamine (CDA14), 1,6-hexanediamine (HDA), ethylenediamine (EDA), resorcinol (RES), phloroglucinol (PHL), pentaerythritol (PET), quercetin (QCT), bisphenol A (BPA), and melamine (MM), either alone or in combination.

[14]

[11] The method according to

[11] , wherein the polyfunctional acid halide used in step (d) is selected from the group consisting of terephthaloyl chloride (TPC), 1,3,5-benzenetricarbonyl trichloride, or trimesoyl chloride (TMC), either alone or in combination.

[15] The method according to

[11] , wherein the two reactive molecule solutions A and B obtained in step (e) are brought into contact with each other to form a liquid-liquid interface, at which a free-standing isolated polymer nanofilm is formed, which is then transferred onto a porous support to form a composite membrane.

Claims

1. A highly selective ultrathin polymer nanofilm composite membrane, comprising: a) a base layer of a porous polymer support membrane; b) a top polymer nanofilm; Including, the polymer nanofilm is a polyamide having repeating units selected from piperazine (PIP) and trimesoyl chloride (TMC); the thickness of the polymer nanofilm is in the range of 7 nm to 150 nm; the polymer nanofilm has an elemental composition (atomic %) of 71.4-74.8% carbon, 7.5-12.8% nitrogen, and 12.4-21.1% oxygen; and The composite membrane is a highly selective ultrathin polymer nanofilm composite membrane having a zeta potential value in the range of −12.2 to −27.2 mV at pH 7.

0.

2. Young's modulus in the range of 297-298 MPa, 1.14-1.22 g.cm －３ 10. The composite membrane of claim 1 having a mass density in the range of 0.1 to 0.5, and a water contact angle value of 25.7 to 59.6 degrees.

3. 2. The composite membrane of claim 1, wherein the base layer of the porous polymer support membrane is selected from the group consisting of hydrolyzed polyacrylonitrile (HPAN), polysulfone (PSf), polyethersulfone (PES), polyimide (P84), crosslinked polyimide (P84), and polyacrylonitrile (PAN).

4. 8.1~57.1Lm －２ h －１ bar －１ Pure water permeability in the range of >98.0% to up to 99.99% Na ２ SO ４ 10. The composite membrane of claim 1, having a rejection of 0.1% to 0.5% of NaCl and a rejection of 0.5% to 0.5% of NaCl.

5. NaCl and Na ２ SO ４ 2. The composite membrane of claim 1, wherein the ideal salt selectivity between 0 and 1 is greater than 1 and a maximum of 4310.

6. 6.1~17.6Lm －２ h －１ bar －１ Pure water permeability in the range of >97.0% up to 99.0% MgCl ２ 10. The composite membrane of claim 1, having a rejection of 0.1% to 0.5% of NaCl and a rejection of 0.5% to 0.5% of NaCl.

7. NaCl and MgCl ２ 2. The composite membrane of claim 1, wherein the ideal salt selectivity between 0 and 1 is greater than 1 and at most 40.

8. 10. The composite membrane of claim 1, wherein the ion selectivity between monovalent and divalent anions in the mixed salt feed is greater than 1 and up to 1460.

9. 287-390g. mol －１ 10. The composite membrane of claim 1, which exhibits a molecular weight cutoff in the range of

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