Positively charged polythiourea composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of membranes, and discloses a positively charged polythiourea composite nanofiltration membrane as well as a preparation method and application thereof. The positively charged polythiourea composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polythiourea separation layer which are sequentially stacked, wherein the polythiourea separation layer comprises a quaternary ammonium salt structure as shown in a formula I and / or a formula II; wherein X is halogen; n is an integer from 0 to 10; and m is an integer of 2-10. The separation layer of the positively charged polythiourea composite nanofiltration membrane simultaneously contains a specific quaternary ammonium salt structure and a C = S group, and has good tolerance to H < + >, so that the nanofiltration membrane can keep structural stability in an acid environment, and the composite nanofiltration membrane can be used for improving the water flux of the membrane on the premise of keeping relatively high water flux. The composite material has excellent capability of intercepting divalent and high-valent metal cations, and is especially suitable for electroplating wastewater treatment under acidic working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membranes, in particular, to a positively charged polysulfide composite nanofiltration membrane and a preparation method and application thereof. BACKGROUND

[0002] Nanofiltration membranes have a wide range of applications in electroplating wastewater treatment. Through the nanofiltration process, the membrane material can accurately separate ions of different sizes and charge properties, effectively removing organic matter, heavy metal ions and other pollutants in wastewater, thereby improving the efficiency of wastewater treatment. This efficient electroplating wastewater treatment method not only improves the effect of wastewater treatment, but also effectively supports the development of electroplating wastewater treatment towards zero discharge and resource utilization, which has important significance. In some process design and working conditions, the electroplating wastewater contains acidic substances, which poses a challenge to the long-term stability of the nanofiltration membrane.

[0003] The commercial nanofiltration membranes on the current market are mainly polyamide nanofiltration membranes, which have the defect of poor acid resistance. The reason is that in an acidic environment, the C=O bond in the polyamide structure is easily attacked by the nucleophilic electrons of H + , leading to the hydrolysis of the amide bond and thus destroying the membrane structure, significantly reducing the rejection performance. In addition, the hydrolysis of the acid chloride groups on the surface of the polyamide membrane also generates a large number of carboxyl groups, making the membrane surface negatively charged. Due to the influence of the Donnan effect, the rejection efficiency of the membrane to divalent and high valence metal ions is reduced. In comparison, positively charged acid-resistant nanofiltration membranes can better meet the separation needs of electroplating wastewater.

[0004] Therefore, it is urgent to develop a simple preparation method to provide a positively charged nanofiltration membrane with excellent acid resistance and larger flux, to meet the growing industrial demand and promote the sustainable development of the industry. SUMMARY

[0005] The purpose of the present application is to overcome the problems of poor acid resistance and unsatisfactory rejection rate of divalent and high valence metal ions of the existing nanofiltration membranes, and to provide a positively charged polysulfide composite nanofiltration membrane and a preparation method and application thereof. The separation layer of the positively charged polysulfide composite nanofiltration membrane contains specific quaternary ammonium salt structures and C=S groups, which have good resistance to H+, so that the nanofiltration membrane can maintain structural stability in an acidic environment. In addition, the composite nanofiltration membrane has excellent rejection ability of divalent and high valence metal ions while maintaining a high water flux, and is particularly suitable for electroplating wastewater treatment under acidic working conditions.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a positively charged polysulfide composite nanofiltration membrane, wherein the nanofiltration membrane comprises a bottom layer, a porous support layer and a polysulfide separation layer which are sequentially stacked.

[0007] The polythiourea separation layer contains a quaternary ammonium salt structure represented by Formula I and / or Formula II.

[0008]

[0009] X is halogen; n is an integer of 0-10; and m is an integer of 2-10.

[0010] The second aspect of the present application provides a preparation method of a positively charged polythiourea composite nanofiltration membrane.

[0011] S1, preparing a porous support layer on a bottom layer;

[0012] S2, sequentially contacting the membrane layer obtained in step S1 with an aqueous phase containing a polyamine with a tertiary amine group for a first contact, and with an organic phase containing a polyisothiocyanate compound for a second contact, and then performing heat treatment to obtain a composite nanofiltration membrane containing a polythiourea separation layer;

[0013] S3, contacting the composite nanofiltration membrane with an organic solution containing a halogenated alkane and a catalyst, and then performing drying to obtain the positively charged polythiourea composite nanofiltration membrane.

[0014] The third aspect of the present application provides a positively charged polythiourea composite nanofiltration membrane prepared by the above preparation method.

[0015] The fourth aspect of the present application provides an application of the above positively charged polythiourea composite nanofiltration membrane in the field of water treatment and separation.

[0016] Through the above technical solution, the positively charged polythiourea composite nanofiltration membrane, the preparation method and the application provided by the present application have the following beneficial effects:

[0017] The polyamide separation layer of the positively charged polythiourea composite nanofiltration membrane provided by the present application contains specific quaternary ammonium salt structures and C=S groups at the same time, has good resistance to H+, enables the nanofiltration membrane to maintain structural stability in an acidic environment, and enables the composite nanofiltration membrane to have excellent rejection capability for divalent and high-valence metal cations on the premise of maintaining a relatively high water flux, and is particularly suitable for electroplating wastewater treatment under acidic working conditions.

[0018] In the preparation method of the positively charged polythiourea composite nanofiltration membrane provided by the present application, the halogenated alkane reacts with the tertiary amine in the polythiourea separation layer under the action of the alkaline catalyst, the tertiary amine is converted into a positively charged quaternary ammonium salt group, the rejection capability of the composite nanofiltration membrane for divalent and high-valence metal cations is improved through the repulsion effect between positive charges, and the composite nanofiltration membrane can also maintain a relatively high water flux. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1A surface infrared spectrum of the prepared composite nanofiltration membrane for Example 1 and Comparative Example 2 is compared.

[0020] Figure 2 A surface XPS sulfur element fine spectrum of the prepared composite nanofiltration membrane for Example 1.

[0021] Figure 3 A surface XPS nitrogen element fine spectrum of the prepared composite nanofiltration membrane for Example 1. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximations. The endpoints of the ranges and any values are understood to be approximate, and in actual practice, individual values will typically be understood to be within a range of values that are near to the stated value. Any numerical value, however, can be exact, where expressly stated.

[0023] The first aspect of the present application provides a positively charged polythiourea composite nanofiltration membrane, wherein the nanofiltration membrane comprises a bottom layer, a porous support layer and a polythiourea separation layer stacked in sequence.

[0024] The polythiourea separation layer comprises a quaternary ammonium salt structure represented by Formula I and / or Formula II.

[0025]

[0026] X is halogen; n is an integer of 0-10; and m is an integer of 2-10.

[0027] In the present application, the separation layer of the positively charged polythiourea composite nanofiltration membrane contains both a specific quaternary ammonium salt structure and a C=S group, which has good resistance to H+, so that the nanofiltration membrane can maintain structural stability in an acidic environment, and the composite nanofiltration membrane can have excellent rejection capability for divalent and high valence metal cations while maintaining a high water flux, and is particularly suitable for electroplating wastewater treatment under acidic working conditions.

[0028] In the present application, * refers to the position of the bond connecting the quaternary ammonium salt structure and the polythiourea separation layer.

[0029] Further, X is Cl, Br or I.

[0030] Further, n is an integer of 0-7; and m is an integer of 2-8.

[0031] According to the present application, the polythiourea separation layer comprises structural unit A from a polyamine and structural unit B from a polyisothiocyanide compound.

[0032] wherein the structural unit A and the structural unit B are connected by the structure shown in formula I wherein Ar1 is a residue after reaction of a compound containing a polyisothiocyanate group, and Ar2 is a residue after reaction of a polyamine.

[0033] In the present application, the C=S bond in the polysulfourea composite nanofiltration membrane can form a hydrogen bond, so that the composite nanofiltration membrane containing the C=S bond has excellent chemical stability, significantly improves the structural stability of the composite nanofiltration membrane in a strong acid environment, and improves the acid resistance of the composite nanofiltration membrane.

[0034] In the present application, the polyisothiocyanate compound refers to a compound containing at least two isothiocyanate groups (-N=C=S) in the compound.

[0035] According to the present application, the polyamine is a polyamine containing a tertiary amine group, preferably at least one selected from polyethyleneimine, polyethylene polyamine, 1-aminopiperazine, 1,4-diaminopiperazine, 1,4-piperazine diethylamine and 1,4-bisaminopropyl piperazine.

[0036] According to the present application, the polyisothiocyanate compound is at least one selected from 1,4-benzene diisothiocyanate, 1,3,5-triisothiocyanatobenzene, 1,2-benzene diisothiocyanate, 2,6-toluene diisothiocyanate and 1,3-propane diisothiocyanate.

[0037] Further, the polyisothiocyanate compound is selected from 1,4-benzene diisothiocyanate and / or 1,3,5-triisothiocyanatobenzene.

[0038] In the present application, the use of the above specific type of polyisothiocyanate compound can make the polysulfourea separation layer of the composite nanofiltration membrane contain both flexible segments and aromatic rigid segments, and by adjusting the molecular structure of the polysulfourea separation layer, the composite nanofiltration membrane can have excellent desalination rate and excellent acid permeability, and can simultaneously achieve efficient metal ion removal and waste acid recovery.

[0039] According to the present application, the content of the structural unit A on the membrane surface is 20-40wt%, and the content of the structural unit B on the membrane surface is 60-80wt%.

[0040] In the present application, when the content of the structural unit A and the structural unit B meets the above range, it indicates that the reaction between the structural unit A from the polyamine and the structural unit B from the polyisothiocyanate compound is sufficient, which can ensure that the surface of the composite nanofiltration membrane, especially the surface of the polysulfourea separation layer, is defect-free, thereby ensuring that the composite nanofiltration membrane has excellent separation performance.

[0041] Further, the content of the structural unit A on the surface of the membrane is 25-35wt%, and the content of the structural unit B on the surface of the membrane is 65-75wt%.

[0042] According to the application, the content of S atoms in the composite nanofiltration membrane is 1-5at.%.

[0043] In the application, when the content of S atoms in the composite nanofiltration membrane meets the above range, the density of C=S bonds in the polythiourea composite nanofiltration membrane is appropriate, which can form hydrogen bonds with H atoms in the molecular structure of polythiourea, so that the composite nanofiltration membrane has excellent chemical inertness, and under the premise of ensuring excellent separation performance of the composite nanofiltration membrane, the structural stability of the composite nanofiltration membrane in a strong acid environment is significantly improved.

[0044] Further, the content of S atoms in the composite nanofiltration membrane is 2-4at%.

[0045] According to the application, the content of N atoms in the quaternary ammonium salt group in the composite nanofiltration membrane is 0.5-5at.%.

[0046] In the application, when the content of nitrogen atoms in the quaternary ammonium salt structure meets the above range, it indicates that the positively charged polythiourea composite nanofiltration membrane contains more quaternary ammonium salt groups, which can make the composite nanofiltration membrane have a higher surface positive potential.

[0047] Further, the content of N atoms in the quaternary ammonium salt group in the composite nanofiltration membrane is 1-4at.%.

[0048] According to the application, the surface Zeta potential of the composite nanofiltration membrane is 0-35mV.

[0049] In the application, when the surface Zeta potential of the positively charged polythiourea composite nanofiltration membrane is in the above specified range, it indicates that the composite nanofiltration membrane has a higher surface potential. When it is applied to the separation of divalent and high valence metal cations, this high potential helps to more effectively repel metal cations, so that metal cations in the liquid are more difficult to penetrate the membrane, and thus stronger rejection performance for divalent and high valence metal cations is obtained.

[0050] In the application, the surface Zeta potential of the composite nanofiltration membrane refers to the surface Zeta potential at pH=7.

[0051] Further, the surface Zeta potential of the composite nanofiltration membrane is 5-25mV.

[0052] According to the application, the contact angle of the composite nanofiltration membrane is 20-80°.

[0053] When the contact angle of the nanofiltration membrane meets the above range, it indicates that the surface of the positively charged composite nanofiltration membrane has good hydrophilicity, thereby obtaining a higher water flux.

[0054] Further, the contact angle of the composite nanofiltration membrane is 30-60°.

[0055] According to the present application, the average pore size of the composite nanofiltration membrane is 0.2-0.5 nm.

[0056] In the present application, the average pore size of the composite nanofiltration membrane is tested by the PEG solute transfer method.

[0057] In the present application, when the average pore size of the nanofiltration membrane meets the above range, the positively charged polythiourea composite nanofiltration membrane exhibits appropriate compactness. This compactness endows the nanofiltration membrane with more superior performance, making it more effectively retain divalent and high-valent metal cations, forcing the metal cations in the liquid to be difficult to penetrate the membrane, thereby achieving more significant retention effect on divalent and high-valent metal cations.

[0058] Further, the average pore size of the composite nanofiltration membrane is 0.2-0.4 nm.

[0059] In the present application, the bottom layer and the porous support layer are not specifically limited and can be made of various existing materials having certain strength and capable of being used for nanofiltration and reverse osmosis membranes.

[0060] In the present application, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0061] In the present application, the porous support layer material can be at least one of polyether sulfone, polysulfone, poly (arylene ether), poly (benzimidazole), poly (ether ketone), poly (ether ether ketone), poly (acrylonitrile), poly (vinylidene fluoride), and poly (arylene ether ketone).

[0062] According to the present application, the thickness of the bottom layer, the porous support layer, and the polythiourea separation layer is not specifically limited and can be a conventional selection in the art, but in order to make the three layers play a better synergistic role, the resulting composite nanofiltration membrane can better have excellent divalent and high-valent metal cation retention capacity and higher water flux, preferably, the thickness of the bottom layer is 30-150 μm, preferably 50-120 μm; the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm; and the thickness of the polythiourea separation layer is 10-500 nm, preferably 50-150 nm.

[0063] The second aspect of the present application provides a preparation method of a positively charged polythiourea composite nanofiltration membrane, wherein the preparation method comprises:

[0064] S1, preparing a porous support layer on a bottom layer;

[0065] S2, sequentially contacting the film layer obtained in step S1 with an aqueous phase containing a polyamine having a tertiary amine group and an organic phase containing a polyisothiocyanide compound, and obtaining a composite nanofiltration membrane comprising a polysulfourea separation layer after heat treatment;

[0066] S3, contacting the composite nanofiltration membrane with an organic solution containing a halogenated alkane and a catalyst, and drying to obtain the positively charged polysulfourea composite nanofiltration membrane.

[0067] In the preparation method of the positively charged polysulfourea composite nanofiltration membrane provided by the application, the halogenated alkane reacts with the tertiary amine in the polysulfourea separation layer under the action of the alkaline catalyst to convert the tertiary amine into a positively charged quaternary ammonium salt group, thereby improving the rejection capacity of the composite nanofiltration membrane for divalent and high-valence metal cations through the repulsion effect between positive charges, and meanwhile enabling the composite nanofiltration membrane to maintain a relatively high water flux.

[0068] In the application, the method for preparing the porous support layer on the base layer is not particularly limited, and can be prepared by using a conventional method in the art, preferably by using a phase inversion method, specifically, coating a polymer solution of the porous support layer material on one surface of the base layer, and obtaining the porous support layer through phase inversion.

[0069] In the application, the phase inversion method can be preferably as follows: dissolving the support layer polymer material in a solvent to obtain a polymer solution with a concentration of 10-20 wt%, and defoaming at 20-40℃ for 10-180 min; then coating the polymer solution on the base layer to obtain an initial film, and immediately immersing it in water at a temperature of 10-30℃ for 10-60 min to obtain the support layer polymer porous film through phase inversion.

[0070] The solvent can be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0071] According to the application, the polyamine containing a tertiary amine group is selected from at least one of polyethyleneimine, polyethylene polyamine, 1-amino piperazine, 1,4-diamino piperazine, 1,4-piperazine diethylamine and 1,4-bis aminopropyl piperazine. Preferably, the polyamine containing a tertiary amine group is at least one of polyethyleneimine, polyethylene polyamine and 1,4-diamino piperazine.

[0072] According to the application, the concentration of the polyamine containing a tertiary amine group in the aqueous phase of the polyamine containing a tertiary amine group is 0.05-5 wt%.

[0073] In the application, when the concentration of the aqueous phase containing the polyamine is controlled to meet the above range, the porous support layer can be fully infiltrated by the aqueous phase monomer in the interfacial polymerization process, and monomer waste can be avoided, thereby ensuring effectiveness and economy.

[0074] Further, the concentration of the tertiary amine group-containing polyamine in the aqueous phase is 0.1-2.5 wt%.

[0075] According to the present application, the polyisothiocyanic compound is at least one selected from 1,4-phenylene diisothiocyanate, 1,3,5-triisothiocyanatobenzene, 1,2-phenylene diisothiocyanate, 2,6-toluene diisothiocyanate and 1,3-propane diisothiocyanate, preferably selected from 1,4-phenylene diisothiocyanate and / or 1,3,5-triisothiocyanatobenzene.

[0076] In one specific embodiment of the present application, the polyisothiocyanic compound is 1,4-phenylene diisothiocyanate and 1,3,5-triisothiocyanatobenzene, and the ratio of the amounts of the two is not particularly limited, as long as the total amount of the polyisothiocyanic compound satisfies the limitation of the present application, for example, the mass ratio of 1,4-phenylene diisothiocyanate to 1,3,5-triisothiocyanatobenzene is 0.1-10:1.

[0077] According to the present application, the concentration of the polyisothiocyanic compound in the organic phase containing the polyisothiocyanic compound is 0.025 wt%-1 wt%.

[0078] In the present application, when the concentration of the organic solution containing the polyisothiocyanic compound satisfies the above range, it can be ensured that the two-phase monomers are fully reacted in the interfacial polymerization process, and a uniform and dense polythiourea separation layer is obtained, and monomer waste is not caused, ensuring effectiveness and economy.

[0079] Further, the concentration of the polyisothiocyanic compound in the organic phase containing the polyisothiocyanic compound is 0.05-0.5 wt%.

[0080] In the present application, the type of the solvent of the organic phase is not particularly limited, as long as it can dissolve the polyisothiocyanic compound, and preferably, the solvent of the organic phase is one or more of n-hexane, dodecane, n-heptane, and alkane solvent oil (Isopar E, Isopar G, Isopar H, Isopar L and Isopar M).

[0081] According to the present application, the amounts of the aqueous phase containing the tertiary amine group-containing polyamine and the organic phase containing the polyisothiocyanic compound are such that the mass ratio of the tertiary amine group-containing polyamine to the polyisothiocyanic compound is 0.1-50:1.

[0082] In the present application, when the mass ratio of the polyamine and the polyisothiocyanic compound satisfies the above range, the polyamine and the polyisothiocyanic compound can be ensured to be fully reacted, and the polysulfourea separation layer prepared by the interfacial polymerization of the two has few defects, can ensure high retention efficiency of high-valence metal ions, and also maintains high water flux, so that ideal separation efficiency is obtained.

[0083] Further, the water phase of the polyamine containing a tertiary amine group and the organic phase containing the polyisothiocyanic compound are used in an amount such that the weight ratio of the polyamine containing a tertiary amine group and the polyisothiocyanic compound is 0.5-20:1.

[0084] According to the present application, the interfacial polymerization conditions of the polyamine containing a tertiary amine group and the polyisothiocyanic compound are not particularly limited, and can be carried out according to the conventional conditions in the art, but in order to make the three layers play a better synergistic role, so that the composite nanofiltration membrane can better have excellent acid resistance, acid permeability, high water flux and desalination rate, preferably, the first contact time is 5-100s, preferably 10-60s; the second contact time is 10-200s, preferably 20-120s; the heat treatment conditions include: the heat treatment temperature is 40-150℃, preferably 50-120℃; the heat treatment time is 0.5-20min, preferably 1-10min.

[0085] In the present application, in step S2, the volume ratio of the water phase of the polyamine containing a tertiary amine group to the membrane area of the membrane layer obtained in step S1 is 0.1-0.5mL / cm 2 , preferably 0.2-0.4mL / cm 2 .

[0086] In the present application, in step S2, the volume ratio of the organic phase containing the polyisothiocyanic compound to the membrane area of the membrane layer obtained in step S1 is 0.05-0.3mL / cm 2 , preferably 0.1-0.2mL / cm 2 .

[0087] According to the present application, in step S3, the halogenated alkane is selected from the halogenated alkane shown in formula III and / or the halogenated alkane shown in formula IV;

[0088]

[0089] wherein X1, X2 and X3 are each independently halogen; n is an integer of 0-10, and m is an integer of 2-10.

[0090] In the present application, the halogenated alkane with the specific structure mentioned above can further increase the positive charge density on the surface of the positively charged composite nanofiltration membrane, and further reduce the average pore size of the nanofiltration membrane.

[0091] Further, X1, X2 and X3 are each independently Cl, Br or I.

[0092] Further, n is an integer from 0 to 7; m is an integer from 2 to 8.

[0093] According to the present application, the halogenated alkane is at least one selected from the group consisting of methyl iodide, ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, heptyl iodide, octyl iodide, nonyl iodide, decyl iodide, cyclopropyl iodide, cyclobutyl iodide, cyclopentyl iodide, cycloheptyl iodide, cyclooctyl iodide, 1,2-diiodoethane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiodopentane, 1,6-diiodohexane, 1,7-diiodoheptane, 1,8-diiodooctane, methyl chloride, ethyl chloride, propyl chloride, butyl chloride, pentyl chloride, hexyl chloride, heptyl chloride, octyl chloride, nonyl chloride, decyl chloride, cyclopropyl chloride, cyclobutyl chloride, cyclopentyl chloride, cycloheptyl chloride, cyclooctyl chloride, 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane, 1,8-dichlorooctane, methyl bromide, ethyl bromide, propyl bromide, butyl bromide, pentyl bromide, hexyl bromide, heptyl bromide, octyl bromide, nonyl bromide, decyl bromide, cyclopropyl bromide, cyclobutyl bromide, cyclopentyl bromide, cycloheptyl bromide, cyclooctyl bromide, 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane and 1,8-dibromooctane.

[0094] In the present application, in order to ensure that the halogenated alkane can react with the residual amino group in the polysulfourea separation layer, preferably, the catalyst is a basic catalyst. Further, the catalyst is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, potassium tert-butoxide and sodium tert-butoxide, preferably selected from sodium hydroxide and / or sodium tert-butoxide.

[0095] According to the present application, the organic solution is an alcohol solvent. The specific type of alcohol solvent is not particularly limited, which can be one of methanol, ethanol, n-butanol and isopropyl alcohol, preferably methanol or ethanol.

[0096] According to the present application, in the organic solution in step S3, the concentration of the halogenated alkane is 1wt%-20wt%.

[0097] In the present application, when the concentration of the halogenated alkane in the organic solution in the control step S2 meets the above range, the halogenated alkane can be ensured to fully contact the polysulfide separation layer in the composite nanofiltration membrane, so that the tertiary amine groups remaining on the surface of the polysulfide separation layer can fully react with the halogenated alkane, and the reaction efficiency is high, and finally the prepared composite nanofiltration membrane contains more quaternary ammonium salt groups on the surface.

[0098] Further, in the organic solution, the concentration of the halogenated alkane is 5-10wt%.

[0099] According to the present application, the concentration of the catalyst in the organic solution is 0.01wt%-5wt%.

[0100] In the present application, when the concentration of the catalyst meets the above range, the halogenated alkane can be more fully reacted with the tertiary amine group on the surface of the composite nanofiltration membrane, and a specific content of quaternary ammonium salt group is introduced, and the catalyst is not wasted, and the economic benefit is improved.

[0101] Further, the concentration of the catalyst in the organic solution is 0.1wt%-1wt%.

[0102] According to the present application, the ratio of the volume of the organic solution to the membrane area of the composite nanofiltration membrane is 0.1-1mL / cm 2 ;

[0103] In the present application, by controlling the volume of the organic solution and the membrane area of the composite nanofiltration membrane to meet the above range, the halogenated alkane can be ensured to fully contact the polysulfide separation layer in the composite nanofiltration membrane, and the halogenated alkane can have high reaction efficiency with the tertiary amine groups of the polysulfide separation layer, and finally the prepared composite nanofiltration membrane contains more quaternary ammonium salt groups on the surface.

[0104] Further, the ratio of the volume of the organic solution to the membrane area of the composite nanofiltration membrane is 0.3-0.5mL / cm 2 .

[0105] According to the present application, the contacting conditions include that the contacting time is 1-120min.

[0106] In the present application, when the contacting time of the composite nanofiltration membrane and the organic solution containing the halogenated alkane and the catalyst meets the above range, the halogenated alkane can be fully reacted with the tertiary amine remaining on the surface of the polysulfide separation layer, and the reaction efficiency is high, so that the prepared positively charged composite nanofiltration membrane contains more quaternary ammonium salt groups on the surface.

[0107] Further, the contacting conditions include that the contacting time is 5-60min.

[0108] The temperature for the contacting is not particularly limited in the present application, and can be room temperature (20-30℃), for example.

[0109] According to the present application, the drying condition comprises: the drying temperature is 30-80℃; and the drying time is 0.5-5min.

[0110] Further, the drying condition comprises: the drying temperature is 40-60℃; and the drying time is 1-3min.

[0111] The third aspect of the present application provides a positively charged polythiourea composite nanofiltration membrane prepared by the above preparation method.

[0112] The fourth aspect of the present application provides an application of the above positively charged polythiourea composite nanofiltration membrane in the field of water treatment and separation.

[0113] The present application will be described in detail below through examples.

[0114] In the following examples and comparative examples:

[0115] (1) The water flux of the nanofiltration membrane is tested by the following method: the nanofiltration membrane is loaded into a membrane cell, and the water permeation amount of the nanofiltration membrane within a certain time is measured at 1.5MPa and 25℃, and the water flux is calculated by the following formula:

[0116] J=Q / (A·t) (1)

[0117] Wherein, J is the water flux, Q is the water permeation amount (L), A is the effective membrane area of the nanofiltration membrane (m 2 ), and t is the time (h).

[0118] (2) The desalination rate of the nanofiltration membrane is tested by the following method: the nanofiltration membrane is loaded into a membrane cell, and the raw water solution is 2000ppm copper chloride or 2000ppm nickel chloride, and after being pre-pressed at 1.5MPa for 0.5h, the permeate is obtained at a pressure of 1.5MPa, and the desalination rate is calculated by the following formula:

[0119] R=(C f -C p ) / C f ×100% (2)

[0120] Wherein, R is the desalination rate, %, C f is the concentration of copper chloride or nickel chloride in the raw solution, ppm, and C p is the concentration of copper chloride or nickel chloride in the permeate, ppm, both of which are measured by ion chromatography.

[0121] (3) The acid resistance test method of the nanofiltration membrane: the nanofiltration membrane sheet is soaked in a 20wt% HC1 solution for 30 days, after being taken out, it is washed thoroughly, and then the water flux of the nanofiltration membrane under neutral conditions and the desalination rate of copper chloride or nickel chloride are tested.

[0122] (4) The surface contact angle measurement of the composite nanofiltration membrane

[0123] The surface contact angle of the nanofiltration membrane sample is tested by using a DSA100 type surface contact angle measuring instrument produced by KRUSS Company in Germany by the static drop method. Before testing, the sample is dried in a 60°C vacuum oven for 30 min to remove the water on the surface and inside, and then the dried membrane is pasted on a flat glass slide with double-sided tape. During testing, the volume of each water drop is 2μL, the water drop is dropped on the membrane surface for 3s, and then the test is immediately performed. The final contact angle is determined by taking the average value of multiple measurements.

[0124] (5) The determination of the nitrogen atom content in the surface quaternary ammonium salt group of the composite nanofiltration membrane and the content of element S in the composite nanofiltration membrane:

[0125] Before measurement, the sample is dried to constant weight in an oven, and the Sigma Probe type X-ray photoelectron spectrometer produced by Thermo VG Company in the United Kingdom is used to determine the surface element composition of the nanofiltration membrane sample. For the sample containing quaternary ammonium salt groups, the molar content of nitrogen atoms in the quaternary ammonium salt groups is equal to the molar content of the corresponding halogen, and the content of nitrogen atoms in the quaternary ammonium salt groups is determined by the measured halogen content.

[0126] (6) The pore size test of the composite nanofiltration membrane: PEG solute transfer method is used, and the detailed steps are as follows:

[0127] (i) Test the rejection rate of the composite nanofiltration membrane to PEGs with different molecular sizes;

[0128] (ii) Linearly fit the PEG size and the rejection rate in the log-probability coordinate system, and the PEG size corresponding to the 50% rejection rate is the average pore size of the nanofiltration membrane.

[0129] (7) The surface Zeta potential test of the composite nanofiltration membrane: Surpass electrokinetic analyzer (Anton Paar) is used for determination, the circulating liquid is a dilute KCl aqueous solution, and the pH of the test solution is 7.

[0130] (8) The content test of structure unit A and structure unit B in the composite nanofiltration membrane adopts X-ray photoelectron spectroscopy (XPS, Escalab250, Thermo fisher, USA).

[0131] In addition, in the following examples and comparative examples:

[0132] Branched polyethyleneimine (weight average molecular weight of 25000 g / mol), polyethylene polyamine, 1,3,5-benzene tricarbonyl chloride, adipoyl chloride, 1,4-phenylene diisothiocyanate, 1,3,5-triisothiocyanatobenzene, halogenated alkane, etc. are purchased from Sigma-Aldrich, and other chemical reagents are purchased from Sinopharm Chemical Reagent Co., Ltd.

[0133] Preparation Example

[0134] The support layer is prepared by phase inversion method, and the specific steps are as follows:

[0135] A certain amount of polysulfone (number average molecular weight of 80000 g / mol) is dissolved in N,N-dimethylformamide to prepare a polysulfone solution with a concentration of 18 wt%, and the solution is degassed at 25°C for 120 min; then, the polysulfone solution is coated on a polyester non-woven fabric (thickness of 75 μm) using a doctor blade to obtain an initial film, which is then immersed in water at a temperature of 25°C for 60 min to allow the polysulfone layer on the surface of the polyester non-woven fabric to be phase-inverted into a porous membrane, and finally washed with water for 3 times to obtain a bottom-porous support layer with a total thickness of 115 μm.

[0136] Example 1

[0137] (1) At 25°C, the upper surface of the polysulfone support layer with an area of 400 cm 2 is contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine for the first time, and the liquid is drained after 60 s of contact; then the upper surface of the support layer after the first contact is contacted with 60 mL of an Isopar E solution containing 0.2 wt% 1,4-phenylene diisothiocyanate for the second time, and the liquid is drained after 60 s of contact; finally, the membrane after the two contacts is placed in an oven and heated at 70°C for 3 min to obtain a composite nanofiltration membrane A1; wherein the mass ratio of branched polyethyleneimine to 1,4-phenylene diisothiocyanate is 4.2:1.

[0138] (2) At 25°C, the obtained composite nanofiltration membrane A1 is immersed in 200 mL of a methanol solution containing 10 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide is 20:1) for the third time, taken out after 5 min, and dried at 70°C for 5 min to obtain a positively charged polysulfourea composite nanofiltration membrane N1.

[0139] Figure 1 The surface infrared spectrum of the composite nanofiltration membrane prepared in Example 1 and Comparative Example 2 is shown in the following figure. It can be seen that compared with the composite nanofiltration membrane D2 prepared in Comparative Example 2, the characteristic peak of quaternary ammonium group can be detected on the surface of the membrane N1 prepared in Example 1, which comes from the reaction of halogenated alkane with the tertiary amine group on the surface of the membrane, converting it into a quaternary ammonium group.

[0140] Figure 2 The surface XPS sulfur element fine spectrum of the composite nanofiltration membrane prepared in Example 1 was prepared, and four characteristic peaks were observed in the fine spectrum peak separation.

[0141] Due to the particularity of the electronic structure of sulfur element, the S2p peak separation shows closely adjacent spin-orbit splitting peaks. In other words, the adjacent two characteristic peaks correspond to one chemical state. The four characteristic peaks correspond to -N=C=S participating in the interfacial polymerization and -N=C=S not participating in the interfacial polymerization, respectively.

[0142] Figure 3 The surface XPS nitrogen element fine spectrum of the composite nanofiltration membrane prepared in Example 1 was prepared, and quaternary ammonium nitrogen on the membrane surface was found in the fine spectrum peak separation, which came from the reaction of halogenated alkane and tertiary amine group on the membrane surface.

[0143] Example 2

[0144] (1) At 25°C, the upper surface of the above-mentioned polysulfone support layer with an area of 400 cm 2 was subjected to first contact with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the liquid was discharged after 60 s of contact; then the upper surface of the support layer after the first contact was subjected to second contact with 60 mL of a solution of Isopar E containing 0.2 wt% 1,4-diisothiocyanate, and the liquid was discharged after 60 s of contact; finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A2; wherein the mass ratio of branched polyethyleneimine to 1,4-diisothiocyanate was 4.2:1.

[0145] (2) At 25°C, the obtained composite nanofiltration membrane A2 was immersed in 200 mL of a methanol solution containing 10 wt% chloropropane and 0.5 wt% potassium hydroxide to perform third contact, and was taken out after 5 min and dried at 70°C for 5 min to obtain a positively charged polysulfourea composite nanofiltration membrane N2.

[0146] Example 3

[0147] (1) At 25°C, the upper surface of the above-mentioned polysulfone support layer with an area of 400 cm 2 was subjected to first contact with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the liquid was discharged after 60 s of contact; then the upper surface of the support layer after the first contact was subjected to second contact with 60 mL of a solution of Isopar E containing 0.2 wt% 1,4-diisothiocyanate, and the liquid was discharged after 60 s of contact; finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A3; wherein the mass ratio of branched polyethyleneimine to 1,4-diisothiocyanate was 4.2:1.

[0148] (2) At 25°C, the obtained composite nanofiltration membrane A3 was immersed in 200 mL of methanol solution containing 10 wt% methyl iodide and 0.5 wt% potassium hydroxide for third contact, taken out after 5 min, and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N3.

[0149] Example 4

[0150] (1) At 25°C, the upper surface of a polysulfone support layer with an area of 400 cm2was subjected to first contact with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, the liquid was drained after 60 s of contact; then the upper surface of the support layer after first contact was subjected to second contact with 60 mL of Isopar E solution containing 0.2 wt% 1,4-diisothiocyanate, the liquid was drained after 60 s of contact; finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain a composite nanofiltration membrane A4; wherein the mass ratio of branched polyethyleneimine to 1,4-diisothiocyanate was 4.2:1. 2

[0151] (2) At 25°C, the obtained composite nanofiltration membrane A4 was immersed in 200 mL of methanol solution containing 10 wt% hexyl bromide and 0.5 wt% potassium hydroxide for third contact, taken out after 5 min, and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N4.

[0152] Example 5

[0153] (1) At 25°C, the upper surface of a polysulfone support layer with an area of 400 cm2was subjected to first contact with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, the liquid was drained after 60 s of contact; then the upper surface of the support layer after first contact was subjected to second contact with 60 mL of Isopar E solution containing 0.2 wt% 1,4-diisothiocyanate, the liquid was drained after 60 s of contact; finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain a composite nanofiltration membrane A5; wherein the mass ratio of branched polyethyleneimine to 1,4-diisothiocyanate was 4.2:1. 2

[0154] (2) At 25°C, the obtained composite nanofiltration membrane A5 was immersed in 200 mL of methanol solution containing 10 wt% hexyl iodide and 0.5 wt% potassium hydroxide for third contact, taken out after 5 min, and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N5.

[0155] Example 6

[0156] ​​(1) At 25°C, the upper surface of the above polysulfone support layer with an area of 400 cm 2 was subjected to first contact with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the liquid was drained after 60 s of contact; then the upper surface of the support layer after the first contact was subjected to second contact with 60 mL of a solution of Isopar E containing 0.2 wt% 1,4-diisothiocyanate, and the liquid was drained after 60 s of contact; finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A6; wherein the mass ratio of branched polyethyleneimine to 1,4-diisothiocyanate was 4.2:1.

[0157] (2) At 25°C, the obtained composite nanofiltration membrane A6 was subjected to third contact in 200 mL of a methanol solution containing 5 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 10:1), and was taken out after 5 min and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N6.

[0158] Example 7

[0159] (1) At 25°C, the upper surface of the above polysulfone support layer with an area of 400 cm 2 was subjected to first contact with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the liquid was drained after 60 s of contact; then the upper surface of the support layer after the first contact was subjected to second contact with 60 mL of a solution of Isopar E containing 0.2 wt% 1,4-diisothiocyanate, and the liquid was drained after 60 s of contact; finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A7; wherein the mass ratio of branched polyethyleneimine to 1,4-diisothiocyanate was 4.2:1.

[0160] (2) At 25°C, the obtained composite nanofiltration membrane A7 was subjected to third contact in 200 mL of a methanol solution containing 10 wt% bromoethane and 0.1 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 100:1), and was taken out after 5 min and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N7.

[0161] Example 8

[0162] (1) At 25°C, the upper surface of the above polysulfone support layer with an area of 400 cm 2The upper surface of the polysulfone support layer was first contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the liquid was drained after 60 s of contact. Then the upper surface of the support layer after the first contact was second contacted with 60 mL of a solution of Isopar E containing 0.2 wt% 1, 4-diisothiocyanatobenzene, and the liquid was drained after 60 s of contact. Finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A8. The mass ratio of branched polyethyleneimine to 1, 4-diisothiocyanatobenzene was 4.2:1.

[0163] (2) The obtained composite nanofiltration membrane A8 was third contacted with 200 mL of a methanol solution containing 10 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 20:1) at 25°C, taken out after 5 min, and dried at 60°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N8.

[0164] Example 9

[0165] (1) The upper surface of the polysulfone support layer with an area of 400 cm 2 was first contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C, and the liquid was drained after 60 s of contact. Then the upper surface of the support layer after the first contact was second contacted with 60 mL of a solution of Isopar E containing 0.2 wt% 1, 3, 5-triisothiocyanatobenzene, and the liquid was drained after 60 s of contact. Finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A9. The mass ratio of branched polyethyleneimine to 1, 3, 5-triisothiocyanatobenzene was 4.2:1.

[0166] (2) The obtained composite nanofiltration membrane A9 was third contacted with 200 mL of a methanol solution containing 10 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 20:1) at 25°C, taken out after 5 min, and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N9.

[0167] Example 10

[0168] (1) The upper surface of the polysulfone support layer with an area of 400 cm 2The upper surface of the polysulfone support layer was first contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the liquid was drained after 60 s of contact. Then the upper surface of the support layer after the first contact was second contacted with 60 mL of a solution of Isopar E containing 0.2 wt% 1,4-diisothiocyanatobenzene, and the liquid was drained after 60 s of contact. Finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A10. The mass ratio of branched polyethyleneimine to 1,4-diisothiocyanatobenzene was 4.2:1.

[0169] (2) The obtained composite nanofiltration membrane A10 was third contacted with 200 mL of a methanol solution containing 10 wt% bromoethane and 1 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 10:1) at 25°C, taken out after 5 min, and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N10.

[0170] Example 11

[0171] (1) The upper surface of the polysulfone support layer with an area of 400 cm 2 was first contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C, and the liquid was drained after 60 s of contact. Then the upper surface of the support layer after the first contact was second contacted with 60 mL of a solution of Isopar E containing 0.2 wt% 1,4-diisothiocyanatobenzene, and the liquid was drained after 60 s of contact. Finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain composite nanofiltration membrane A11. The mass ratio of branched polyethyleneimine to 1,4-diisothiocyanatobenzene was 4.2:1.

[0172] (2) The obtained composite nanofiltration membrane A11 was third contacted with 200 mL of a methanol solution containing 20 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 40:1) at 25°C, taken out after 5 min, and dried at 70°C for 5 min to obtain a positively charged polythiourea composite nanofiltration membrane N11.

[0173] Comparative Example 1

[0174] (1) The upper surface of the polysulfone support layer with an area of 400 cm 2The upper surface of the polysulfone support layer was first contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer was contacted again with 40 mL of a mixed solution of Isopar E containing 0.2 wt% 1,3,5-benzenetricarboxyl chloride and 10 mL of adipyl chloride containing 0.2 wt%, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 5 min to obtain the composite nanofiltration membrane B1. The mass ratio of branched polyethyleneimine to acyl chloride was 5:1.

[0175] (2) At 25°C, the obtained composite nanofiltration membrane B1 was immersed in 200 mL of a methanol solution containing 10 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 20:1) for the third contact. After 5 min, it was taken out and dried at 70°C for 5 min to obtain polyamide composite nanofiltration membrane D1.

[0176] Comparative Example 2

[0177] (1) At 25℃, the above area of ​​400cm² 2 The upper surface of the polysulfone support layer was first contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 60 mL of a solution containing 0.2 wt% 1,4-phenylenediisothiocyanate, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane D2. The mass ratio of branched polyethyleneimine to 1,4-phenylenediisothiocyanate was 4.2:1.

[0178] Comparative Example 3

[0179] (1) At 25℃, the above area of ​​400cm² 2 The upper surface of the polysulfone support layer was first contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 60 mL of a solution containing 0.2 wt% 1,4-phenylene diisothiocyanate, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane B3. The mass ratio of branched polyethyleneimine to 1,4-phenylene diisothiocyanate was 4.2:1.

[0180] (2) The obtained composite nanofiltration membrane B3 was immersed in 200 mL of a methanol solution containing 10 wt% of bromoethane at 25°C to perform a third contact, and was taken out after 5 min and dried at 70°C for 5 min to obtain a polythiourea composite nanofiltration membrane D3.

[0181] Comparative Example 4

[0182] (1) The upper surface of a polysulfone support layer having an area of 400 cm2 was contacted with 100 mL of an aqueous solution containing 0.5 wt% of ethylenediamine at 25°C to perform a first contact, and the liquid was drained after 60 s; then the upper surface of the support layer after the first contact was contacted with 60 mL of a solution of Isopar E containing 0.2 wt% of 1,4-diisothiocyanatobenzene to perform a second contact, and the liquid was drained after 60 s; finally, the membrane after the two contacts was placed in an oven and heated at 70°C for 3 min to obtain a composite nanofiltration membrane B4; wherein the mass ratio of ethylenediamine to 1,4-diisothiocyanatobenzene was 4.2:1. 2

[0183] (2) The obtained composite nanofiltration membrane B4 was immersed in 200 mL of a methanol solution containing 10 wt% of bromoethane and 0.5 wt% of potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 20:1) at 25°C to perform a third contact, and was taken out after 5 min and dried at 70°C for 5 min to obtain a polythiourea composite nanofiltration membrane D4.

[0184] The thickness of the separation layer, the content of each structural unit, the surface Zeta potential, the average pore size, the content of nitrogen atoms in the quaternary ammonium salt structure in the polythiourea separation layer, the content of sulfur atoms in the composite membrane, and the contact angle in the examples and comparative examples are shown in Table 1.

[0185] Table 1

[0186]

[0187]

[0188] a Sulfur atom content refers to the content of S atoms in the composite nanofiltration membrane;

[0189] b Nitrogen atom content refers to the content of N atoms in the quaternary ammonium salt structure in the polythiourea separation layer;

[0190] c Polyamine-derived structural unit content refers to the content of structural units derived from polyamines in the polyamide separation layer;

[0191] d Polyacyl chloride-derived structural unit content refers to the content of structural units derived from polyacyl chlorides in the polyamide separation layer.

[0192] ​The water flux, CuCl2 rejection rate, NiCl2 rejection rate and acid resistance of the composite membranes of the examples and the comparative examples were tested, and the results are shown in Table 2.

[0193] Table 2

[0194]

[0195]

[0196] As can be seen from Tables 1-2, the surface Zeta potential of the positively charged polythiourea composite nanofiltration membrane in the application is significantly increased, the average pore size is reduced, the contact angle is reduced, the acid resistance is excellent, the rejection performance of divalent metal ions is excellent, and the water flux is high.

[0197] As can be seen from Examples 1, 6 and 11, the halogenated alkane can be chemically grafted on the membrane surface at a suitable concentration, the surface charge density of the nanofiltration membrane is increased, the rejection rate of the nanofiltration membrane to divalent and high valence metal ions is increased, and the water flux is high; when the concentration of the halogenated alkane is reduced, the rejection rate shows a downward trend; when the concentration of the halogenated alkane is too large, the water flux is reduced.

[0198] As can be seen from Examples 1 and 9, by using different oil phase monomers and different thiocyanates to introduce C=S bonds in the nanofiltration membrane, the rejection rate of the membrane to divalent metal ions and the water flux are basically unchanged after strong acid treatment, which indicates that the composite nanofiltration membrane has good acid resistance. The composite nanofiltration membrane of Comparative Example 1 does not contain C=S bonds but only contains C=O bonds, and the membrane loses the rejection performance after strong acid treatment, which indicates that the membrane structure is damaged.

[0199] As can be seen from Examples 1 and 8, within a certain temperature range, a suitable drying temperature can promote the reaction of the halogenated alkane and the tertiary amine group on the surface of the composite nanofiltration membrane to be more sufficient, and improve the rejection rate and water flux of the composite nanofiltration membrane.

[0200] As can be seen from Examples 1, 7, 10 and Comparative Example 3, the catalyst can promote the reaction of the halogenated alkane and the tertiary amine group on the surface of the composite nanofiltration membrane to be more sufficient, and improve the rejection rate and water flux of the composite nanofiltration membrane; without the action of the catalyst, the reaction degree is reduced, the number of positive charges on the surface of the nanofiltration membrane is less, the water contact angle is large, and the rejection rate is low.

[0201] In Comparative Example 4, a binary amine is used as a polyamine monomer to prepare a composite nanofiltration membrane, and when the prepared composite nanofiltration membrane is contacted with a halogenated alkane and a catalyst, the composite nanofiltration membrane cannot be converted into a positively charged quaternary ammonium salt group, resulting in that the surface Zeta potential of the prepared polythiourea composite nanofiltration membrane is low, and the composite nanofiltration membrane cannot effectively separate divalent cations.

[0202] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A positively charged polythiourea composite nanofiltration membrane, characterized in that, The nanofiltration membrane comprises a bottom layer, a porous support layer and a polythiourea separation layer which are stacked in sequence; The polythiourea separation layer comprises a quaternary ammonium salt structure represented by Formula I and / or Formula II; X is Cl, Br or I; 2. The positively charged polythiourea composite nanofiltration membrane of claim 1, wherein, Preferably, n is an integer from 0 to 7, and m is an integer from 2 to 8. X is Cl, Br or I; 3. The positively charged polythiourea composite nanofiltration membrane according to claim 1 or 2, wherein, Preferably, n is an integer from 0 to 7, and m is an integer from 2 to 8. wherein the structural unit A and the structural unit B are connected through the structure shown in formula I wherein Ar1 is a residue after reaction of a compound containing a polyisothiocyanate group, and Ar2 is a residue after reaction of a polyamine; The polythiourea separation layer comprises structural unit A from a polyamine and structural unit B from a polyisothiocyanate compound; Preferably, the polyamine is a polyamine containing a tertiary amine group, preferably at least one selected from polyethyleneimine, polyethylene polyamine, 1-aminopiperazine, 1,4-diaminopiperazine, 1,4-piperazine diethylamine and 1,4-bisaminopropyl piperazine; 4. The positively charged polythiourea composite nanofiltration membrane according to claim 3, wherein, Preferably, the polyisothiocyanate compound is at least one selected from 1,4-phenylene diisothiocyanate, 1,3,5-triisothiocyanatobenzene, 1,2-phenylene diisothiocyanate, 2,6-toluene diisothiocyanate and 1,3-propane diisothiocyanate, preferably selected from 1,4-phenylene diisothiocyanate and / or 1,3,5-triisothiocyanatobenzene.

5. The positively charged polythiourea composite nanofiltration membrane according to any one of claims 1-4, wherein, The content of the structural unit A on the surface of the membrane is 20-40wt%, preferably 25-35wt%, and the content of the structural unit B on the surface of the membrane is 60-80wt%, preferably 65-75wt%. The content of S atoms in the composite nanofiltration membrane is 1-5at.%, preferably 2-4at.%; 6. The positively charged polythiourea composite nanofiltration membrane according to any one of claims 1-5, wherein, Preferably, the content of N atoms in the quaternary ammonium salt group in the composite nanofiltration membrane is 0.5-5at.%, preferably 1-4at.%. The surface Zeta potential of the composite nanofiltration membrane is 0-35mV, preferably 5-25mV; Preferably, the contact angle of the composite nanofiltration membrane is 20-80°, preferably 30-60°; 7. A method for preparing a positively charged polythiourea composite nanofiltration membrane, characterized in that, Preferably, the average pore size of the composite nanofiltration membrane is 0.2-0.5nm, preferably 0.2-0.4nm. The preparation method comprises: S1, preparing a porous support layer on the bottom layer; S2, sequentially contacting the membrane layer obtained in step S1 with an aqueous phase of a polyamine containing a tertiary amine group for the first contact, and with an organic phase containing a polyisothiocyanate compound for the second contact, and then heat treating to obtain a composite nanofiltration membrane comprising a polythiourea separation layer; 8. The production method according to claim 7, wherein S3, contacting the composite nanofiltration membrane with an organic solution containing a halogenated alkane and a catalyst, and then drying to obtain the positively charged polythiourea composite nanofiltration membrane. In step S2, the polyamine containing a tertiary amine group is at least one selected from polyethyleneimine, polyethylene polyamine, 1-aminopiperazine, 1,4-diaminopiperazine, 1,4-piperazine diethylamine and 1,4-bisaminopropyl piperazine; Preferably, the concentration of the polyamine containing a tertiary amine group in the aqueous phase of the polyamine containing a tertiary amine group is 0.05-5wt%, preferably 0.1-2.5wt%. Preferably, the polyisothiocyanic compound is selected from at least one of 1,4-phenylene diisothiocyanate, 1,3,5-triisothiocyanatobenzene, 1,2-phenylene diisothiocyanate, 2,6-toluene diisothiocyanate and 1,3-propane diisothiocyanate, preferably from 1,4-phenylene diisothiocyanate and / or 1,3,5-triisothiocyanatobenzene; Preferably, the concentration of the polyisothiocyanic compound in the organic phase containing the polyisothiocyanic compound is 0.025wt%-1wt%, preferably 0.05-0.5wt%; Preferably, the water phase containing the polyamine with a tertiary amine group and the organic phase containing the polyisothiocyanic compound are used in a mass ratio of 0.1-50:1, preferably 0.5-20:1; Preferably, the first contact is for 5-100s, preferably 10-60s; Preferably, the second contact is for 10-200s, preferably 20-120s; Preferably, the heat treatment is performed at a temperature of 40-150℃, preferably 50-120℃, for 0.5-20min, preferably 1-10min.

9. The production method according to claim 7 or 8, wherein In step S3, the halogenated alkane is selected from the halogenated alkane of formula III and / or the halogenated alkane of formula IV; wherein X1, X2and X3are each independently halogen; n is an integer of 0-10, and m is an integer of 2-10; Preferably, the halogenated alkane is selected from at least one of methyl iodide, ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, heptyl iodide, octyl iodide, nonyl iodide, decyl iodide, cyclopropyl iodide, cyclobutyl iodide, cyclopentyl iodide, cycloheptyl iodide, cyclooctyl iodide, 1,2-diiodoethane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiodopentane, 1,6-diiodohexane, 1,7-diiodoheptane, 1,8-diiodooctane, methyl chloride, ethyl chloride, propyl chloride, butyl chloride, pentyl chloride, hexyl chloride, heptyl chloride, octyl chloride, nonyl chloride, decyl chloride, cyclopropyl chloride, cyclobutyl chloride, cyclopentyl chloride, cycloheptyl chloride, cyclooctyl chloride, 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane, 1,8-dichlorooctane, methyl bromide, ethyl bromide, propyl bromide, butyl bromide, pentyl bromide, hexyl bromide, heptyl bromide, octyl bromide, nonyl bromide, decyl bromide, cyclopropyl bromide, cyclobutyl bromide, cyclopentyl bromide, cycloheptyl bromide, cyclooctyl bromide, 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane and 1,8-dibromooctane; Preferably, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, potassium tert-butoxide and sodium tert-butoxide, preferably from sodium hydroxide and / or sodium tert-butoxide; Preferably, the organic solution is an alcohol solvent.

10. The method of manufacturing according to any one of claims 7-9, wherein, In step S3, the concentration of the halogenated alkane in the organic solution is 1wt%-20wt%, preferably 5-10wt%; Preferably, the concentration of the catalyst in the organic solution is 0.01wt%-5wt%, preferably 0.1wt%-1wt%; Preferably, the ratio of the volume of the organic solution to the membrane area of the composite nanofiltration membrane is 0.1-1 mL / cm 2 , preferably 0.3-0.5 mL / cm 2 . Preferably, the contacting condition includes that the contacting time is 1-120min, preferably 5-60min; Preferably, the drying condition includes that the drying temperature is 30-80℃, preferably 40-60℃; the drying time is 0.5-5min, preferably 1-3min.

11. A positively charged polythiourea composite nanofiltration membrane prepared by the preparation method of any one of claims 7-10.

12. Use of the positively charged polythiourea composite nanofiltration membrane of any one of claims 1-6 and 11 in the field of water treatment separation.

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