A method for preparing a nanofiltration membrane by using carbon nitride photo-generated charges to regulate interface polymerization

Abstract

The application provides a preparation method of a nanofiltration membrane by using carbon nitride photo-generated charges to regulate interface polymerization, and belongs to the technical field of water treatment membranes. The preparation method comprises the following steps: (1) adding carbon nitride membrane-forming sol into an aqueous solution of a polyamine monomer, and performing ultrasonic dispersion to obtain a mixed dispersion liquid; (2) preparing an organic phase monomer solution; (3) adding an ultrafiltration support base membrane into the mixed dispersion liquid, performing wetting, and then taking out and adding into the organic phase monomer solution to perform interface polymerization, so as to obtain a high-permeability membrane containing an ultrathin polyamide separation layer; wherein the wetting and the interface polymerization are both performed under light irradiation; and (4) performing heat treatment on the high-permeability membrane containing the ultrathin polyamide separation layer to obtain a nanofiltration membrane. The photoelectrochemical characteristics of carbon nitride are utilized, and under light irradiation, there is electrostatic repulsion between positive charges on the surface of carbon nitride and piperazine molecules, so that the interface polymerization rate is regulated, and then a high-permeability nanofiltration membrane with an ultrathin polyamide separation layer is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment membranes, and in particular relates to a method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride. Background Art

[0002] Membrane separation, with its low energy consumption and high separation efficiency, is an ideal means for removing pollutants and purifying water. As a typical low-pressure separation membrane, thin-layer composite nanofiltration membranes (TFCs) have become a preferred option for deep drinking water purification and industrial wastewater treatment. However, the separation performance of traditional nanofiltration membranes, represented by polyamide, is constrained by the trade-off between water flux and retention rate. Exploring effective methods to improve the separation performance of polyamide nanofiltration membranes has become a hot topic in nanofiltration technology research.

[0003] During the traditional interfacial polymerization process of nanofiltration membranes, the polyamine monomer piperazine molecules diffuse from the aqueous phase to the organic phase and undergo a violent condensation reaction with the organic phase monomer trimethylol chloride. This rapid reaction kinetic process induces local polymerization at the interface, and as the diffusion progresses along the thickness, it is very easy to form a dense and uneven membrane layer structure, which greatly restricts the water permeability of the formed polyamide nanofiltration membrane. Currently, most studies use the method of adding nanomaterials to the membrane-forming monomer solution. The construction of a hydrophilic interface has improved the water flux of the nanofiltration membrane to a certain extent. However, since the introduction of heterogeneous materials can easily lead to the formation of composite interface defects, the low amount of nanomaterial added has limited the improvement in membrane separation performance. Exploring more precise control methods for polymer membrane structure has become the key to obtaining selective layer materials with high water flux, good monovalent and polyvalent selectivity, and strong anti-fouling ability.

[0004] Carbon nitride nanosheets, due to their graphene-like two-dimensional layered structure, are ideal materials for selective permeation and separation at the sub-nanometer scale. Typically, researchers prepare carbon nitride-modified separation membranes by incorporating the exfoliated carbon nitride into a polymer matrix, primarily leveraging the intrinsic pores and hydrophilic sites on the two-dimensional plane to enhance nanofiltration membrane performance. As a new type of photosensitive semiconductor material, the application of carbon nitride's photoactive properties in nanofiltration membranes has only been disclosed for in-situ degradation of separated organic pollutants, and its potential for enhancing membrane separation performance through photogenerated charges remains to be explored. Summary of the Invention

[0005] Based on this, the present invention proposes a method for preparing a nanofiltration membrane by utilizing photogenerated charges of carbon nitride to regulate interfacial polymerization reaction to solve the above technical problems.

[0006] The present invention proposes a method for preparing a nanofiltration membrane by utilizing photogenerated charges of carbon nitride to regulate interfacial polymerization reaction, comprising the following steps:

[0007] (1) thermally polymerizing a nitrogen-containing precursor to obtain a bulk carbon-nitrogen compound, treating the bulk carbon-nitrogen compound in an acid solution to obtain a carbon nitride film-forming sol; adding the obtained carbon nitride film-forming sol to an aqueous solution of a polyamine monomer, and ultrasonically dispersing the resultant solution to obtain a mixed dispersion;

[0008] (2) dissolving the organic phase monomer in an organic solvent and stirring to obtain an organic phase monomer solution;

[0009] (3) adding the ultrafiltration support base membrane to the mixed dispersion to soak it, then taking it out and adding it to the organic phase monomer solution to carry out interfacial polymerization to obtain a high permeability membrane containing an ultrathin polyamide separation layer; wherein the soaking and interfacial polymerization are both carried out under light;

[0010] (4) After heat treatment of the above-mentioned high permeability membrane containing the ultrathin polyamide separation layer, a nanofiltration membrane based on the regulation of carbon nitride photogenerated positive charges is obtained.

[0011] Furthermore, in step (1), the nitrogen-containing precursor includes at least one of cyanamide, dicyandiamide, melamine, urea, and thiourea.

[0012] Furthermore, in step (1), the ratio of the bulk carbon and nitrogen compound to the acid solution is 1 g: 10 to 50 mL;

[0013] In step (1), the concentration of the obtained carbon nitride film-forming sol is 1.0 to 2.0 mg / ml;

[0014] In step (1), the concentration of carbon nitride in the aqueous solution of the polyamine monomer is 0.1 to 2.0 mg / mL.

[0015] Furthermore, in step (1), the polyamine monomer includes at least one of piperazine and its derivatives, o-phenylenediamine and its derivatives, m-phenylenediamine and its derivatives, diethylenetriamine, triethylenetetramine, polyethyleneimine, etc.

[0016] Furthermore, in step (2), the organic phase monomer includes at least one of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, pyromellitoyl chloride, cycloalkane polyacyl chloride, and polysulfonyl chloride;

[0017] In step (2), the concentration of the organic phase monomer in the organic solvent is 0.5 to 3 mg / mL.

[0018] Furthermore, in step (3), the illumination is formed by xenon lamp illumination; the intensity of the illumination is 100 to 300 mw / cm 2 .

[0019] Furthermore, in step (3), the soaking time is 30 to 180 seconds.

[0020] Furthermore, in step (3), the time of the interfacial polymerization reaction is 15 to 120 seconds, the temperature of the interfacial polymerization reaction is 20 to 30° C., and the humidity of the interfacial polymerization reaction is 45 to 70%.

[0021] Furthermore, in step (4), the heat treatment temperature is 40 to 70° C., and the heat treatment time is 10 to 60 minutes.

[0022] The present invention also provides a nanofiltration membrane prepared by any of the above-mentioned methods for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride.

[0023] The present invention has the following advantages:

[0024] This invention utilizes the photoelectrochemical properties of carbon nitride. Under illumination, the positive charge on the carbon nitride surface creates an electrostatic repulsion with piperazine molecules, thereby regulating the interfacial polymerization rate. This allows the fabrication of a highly permeable nanofiltration membrane with an ultrathin polyamide separation layer. The resulting nanofiltration membrane achieves the interception of divalent ions in water, while achieving a permeation flux that is more than three times higher than that of a polyamide membrane without carbon nitride. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a transmission electron microscope photograph of carbon nitride nanowires in Example 1 of the present invention.

[0027] Figure 2 Schematic diagram of pure water flux of Examples 1 to 4 of the present invention and Comparative Examples 1 to 4.

[0028] Figure 3 Schematic diagram of the brine flux and retention stability of sodium sulfate solution according to Example 4 of the present invention.

[0029] Figure 4 Schematic diagram of the brine flux and retention stability of sodium sulfate solution in Comparative Application Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. The embodiments of the present invention and the features in the embodiments can be combined with each other unless there is a conflict.

[0031] On the one hand, an embodiment of the present invention provides a method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride, comprising the following steps:

[0032] (1) thermally polymerizing a nitrogen-containing precursor to obtain a bulk carbon-nitrogen compound, treating the bulk carbon-nitrogen compound in an acid solution to obtain a carbon nitride film-forming sol; adding the obtained carbon nitride film-forming sol to an aqueous solution of a polyamine monomer, and ultrasonically dispersing the resultant solution to obtain a mixed dispersion;

[0033] (2) dissolving the organic phase monomer in an organic solvent and stirring to obtain an organic phase monomer solution;

[0034] (3) adding the ultrafiltration support base membrane to the mixed dispersion to soak it, then taking it out and adding it to the organic phase monomer solution to carry out interfacial polymerization to obtain a high permeability membrane containing an ultrathin polyamide separation layer; wherein the soaking and interfacial polymerization are both carried out under light;

[0035] (4) After heat treatment of the above-mentioned high permeability membrane containing the ultrathin polyamide separation layer, a nanofiltration membrane based on the regulation of carbon nitride photogenerated positive charges is obtained.

[0036] The embodiment of the present invention proposes a method for preparing a nanofiltration membrane by utilizing photogenerated charges of carbon nitride to regulate interfacial polymerization reactions. The method utilizes the photoelectrochemical properties of hydrophilic carbon nitride. The positively charged interface formed under light produces electrostatic repulsion with positively charged polyamine monomers, thereby regulating the diffusion rate of aqueous phase monomers and further regulating the rate of interfacial polymerization reactions, thereby obtaining a lower separation layer thickness and a controllable hydrophilic surface, thereby achieving the purpose of increasing water flux.

[0037] In one embodiment of the present invention, in step (1), the nitrogen-containing precursor includes at least one of cyanamide, dicyandiamide, melamine, urea, and thiourea.

[0038] In one embodiment of the present invention, in step (1), the thermal polymerization method is specifically: adding a nitrogen-containing precursor into a crucible and placing it in a muffle furnace for high-temperature calcination, and then grinding the calcined product into powder in a mortar to obtain a bulk carbonitride.

[0039] Furthermore, in step (1), the high-temperature calcination temperature is 500-600° C., and the high-temperature calcination time is 2-6 hours.

[0040] In one embodiment of the present invention, in step (1), the bulk carbon and nitrogen compound is placed in an acid solution for treatment, specifically: the bulk carbon and nitrogen compound is placed in a beaker containing the acid solution, stirred, and then the acid solution is removed by filtration, and the powder obtained by filtration is washed with deionized water until neutral, and the filtered carbon and nitrogen compound is diluted with deionized water, ultrasonicated, centrifuged, and the supernatant is collected to obtain a carbon nitride film sol.

[0041] Furthermore, the stirring temperature is 50-70° C., the stirring time is 3-8 hours, the ultrasonication time is 1-3 hours, the centrifugal speed is 3000-6000 rpm, and the centrifugal time is 10-50 minutes.

[0042] Preferably, the stirring temperature is 60° C., the stirring time is 5 h, the ultrasonication time is 2 h, the centrifugal speed is 5000 rpm, and the centrifugation time is 20 min.

[0043] Furthermore, in step (1), the acid solution includes at least one of concentrated hydrochloric acid, concentrated sulfuric acid or concentrated nitric acid.

[0044] Furthermore, in step (1), the ratio of the bulk carbon and nitrogen compound to the acid solution is 1 g: 10-50 mL. Preferably, the ratio of the bulk carbon and nitrogen compound to the acid solution is 1 g: 20 mL.

[0045] In one embodiment of the present invention, in step (1), the concentration of the obtained carbon nitride film-forming sol is 1.0-2.0 mg / ml. In step (1) of the embodiment of the present invention, the carbon nitride exists in the carbon nitride film-forming sol in the form of hydrophilic nanowires.

[0046] In one embodiment of the present invention, in step (1), the concentration of carbon nitride in the aqueous solution of the polyamine monomer is 0.1-2.0 mg / mL. In step (2), the concentration of the aqueous solution of the polyamine monomer is 1-6 mg / mL.

[0047] In one embodiment of the present invention, in step (1), the polyamine monomer includes at least one of piperazine and its derivatives, o-phenylenediamine and its derivatives, m-phenylenediamine and its derivatives, diethylenetriamine, triethylenetetramine, polyethyleneimine, etc. Preferably, the polyamine monomer is piperazine.

[0048] In one embodiment of the present invention, in step (2), the organic phase monomer comprises at least one of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, pyromellitoyl chloride, cycloalkane polyacyl chloride, and polysulfonyl chloride. Preferably, the organic phase monomer is trimesoyl chloride, i.e., 1,3,5-benzenetricarboxylic acid chloride.

[0049] Furthermore, in step (2), the concentration of the organic phase monomer in the organic solvent is 0.5 to 3 mg / mL.

[0050] Furthermore, in step (2), the organic solvent includes at least one of n-hexane, n-octane, n-heptane, dichloromethane, chloroform, carbon tetrachloride, benzene, toluene, xylene, pentane, and cyclohexane.

[0051] In one embodiment of the present invention, in step (3), the ultrafiltration supporting bottom membrane is a polycarbonate filter membrane, a polytetrafluoroethylene filter membrane, a polyethersulfone filter membrane, a polysulfone filter membrane or a polypropylene filter membrane.

[0052] In one embodiment of the present invention, in step (3), the illumination is provided by a xenon lamp. The intensity of the illumination is 100 to 300 mw / cm 2 .

[0053] In one embodiment of the present invention, in step (3), the soaking time is 30 to 180 seconds.

[0054] In one embodiment of the present invention, in step (3), the time of the interfacial polymerization reaction is 15 to 120 seconds, the temperature of the interfacial polymerization reaction is 20 to 30° C., and the humidity of the interfacial polymerization reaction is 45 to 70%.

[0055] Furthermore, step (3) further comprises: after the interfacial polymerization reaction, pouring out excess liquid and washing the treated surface of the ultrafiltration support membrane with an organic solvent to remove unreacted organic phase monomers.

[0056] In one embodiment of the present invention, in step (4), the heat treatment temperature is 40-70° C. and the heat treatment time is 10-60 min.

[0057] In an embodiment of the present invention, in step (4), the high permeability membrane containing the ultrathin polyamide separation layer is subjected to heat treatment to achieve further crosslinking. The nanofiltration membrane obtained after heat treatment can be immersed in water for storage.

[0058] On the other hand, the present invention also proposes a nanofiltration membrane prepared by the above-mentioned method for preparing a nanofiltration membrane by regulating the interfacial polymerization reaction using photogenerated charges of carbon nitride.

[0059] The present invention will be described in detail below with reference to embodiments and accompanying drawings.

[0060] Example 1:

[0061] A method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride comprises the following steps:

[0062] Step 1: Add 6g of melamine to a crucible and place it in a muffle furnace. Heat the temperature to 550℃ at a heating rate of 5℃ / min, calcine for 4h, and then grind the calcined product into powder in a mortar to obtain a bulk carbon nitride powder. Place 1g of bulk carbon nitride powder in a beaker containing 20mL of concentrated hydrochloric acid and stir at 60℃ for 5h. Then remove the concentrated hydrochloric acid by filtration and wash the powder with deionized water until neutral. Dilute the filtered carbon nitride with deionized water, sonicate for 2h, and then centrifuge at 5000rpm for 20min. Take the supernatant to obtain a carbon nitride film sol with a concentration of 2.0mg / mL.

[0063] Step 2: Prepare a 2 mg / mL piperazine aqueous solution, add carbon nitride film-forming sol to make the concentration of carbon nitride in the piperazine aqueous solution 0.5 mg / mL, and disperse it evenly by ultrasonication to obtain a mixed dispersion; take 5 ml of the mixed dispersion and add it dropwise to the surface of the polyethersulfone support base film and infiltrate it for 120 seconds, and remove the residual liquid on the surface; wherein, the infiltration is carried out under light, and the light is provided by irradiation with a xenon lamp, and the light intensity is 100 mW / cm 2 .

[0064] Step 3: Prepare a 2 mg / mL n-hexane solution of trimesoyl chloride, then immerse the surface of the ultrafiltration membrane in the n-hexane solution containing trimesoyl chloride to perform an interfacial polymerization reaction. After the reaction lasts for 30 seconds, remove the excess liquid, and then soak the resulting membrane in the n-hexane solution for 10 seconds to remove the unreacted acyl chloride monomer to obtain a high permeability membrane containing an ultrathin polyamide separation layer. The reaction temperature is 25°C and the reaction humidity is 60%. The reaction is carried out under light, and the light is formed by xenon lamp irradiation with an intensity of 100mw / cm 2 .

[0065] Step 4: The high permeability membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 min to obtain a fully polymerized nanofiltration membrane based on carbon nitride photogenerated positive charge regulation.

[0066] Example 2:

[0067] A method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride comprises the following steps:

[0068] Step 1: Add 6g of melamine to a crucible and place it in a muffle furnace. Heat the temperature to 550℃ at a heating rate of 5℃ / min, calcine for 4h, and then grind the calcined product into powder in a mortar to obtain a bulk carbon nitride powder. Place 1g of bulk carbon nitride powder in a beaker containing 20mL of concentrated hydrochloric acid and stir at 60℃ for 5h. Then remove the concentrated hydrochloric acid by filtration and wash the powder with deionized water until neutral. Dilute the filtered carbon nitride with deionized water, sonicate for 2h, and then centrifuge at 5000rpm for 20min. Take the supernatant to obtain a carbon nitride film sol with a concentration of 2.0mg / mL.

[0069] Step 2: Prepare a 4 mg / mL piperazine aqueous solution, add carbon nitride film-forming sol to make the concentration of carbon nitride in the piperazine aqueous solution 0.5 mg / mL, and disperse it evenly by ultrasonication to obtain a mixed dispersion; take 5 ml of the mixed dispersion and add it dropwise to the surface of the polyethersulfone support base film and infiltrate it for 120 seconds, and remove the residual liquid on the surface; wherein, the infiltration is carried out under light, and the light is provided by irradiation with a xenon lamp, and the light intensity is 100 mW / cm 2 .

[0070] Step 3: Prepare a 2 mg / mL n-hexane solution of trimesoyl chloride, then immerse the surface of the ultrafiltration membrane in the n-hexane solution containing trimesoyl chloride to perform an interfacial polymerization reaction. After the reaction lasts for 30 seconds, remove the excess liquid, and then soak the resulting membrane in the n-hexane solution for 10 seconds to remove the unreacted acyl chloride monomer to obtain a high permeability membrane containing an ultrathin polyamide separation layer. The reaction temperature is 25°C and the reaction humidity is 60%. The reaction is carried out under light, and the light is formed by xenon lamp irradiation with an intensity of 100mw / cm 2 .

[0071] Step 4: The high permeability membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 min to obtain a fully polymerized nanofiltration membrane based on carbon nitride photogenerated positive charge regulation.

[0072] Example 3:

[0073] A method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride comprises the following steps:

[0074] Step 1: Add 6g of melamine to a crucible and place it in a muffle furnace. Heat the temperature to 550℃ at a heating rate of 5℃ / min, calcine for 4h, and then grind the calcined product into powder in a mortar to obtain a bulk carbon nitride powder. Place 1g of bulk carbon nitride powder in a beaker containing 20mL of concentrated hydrochloric acid and stir at 60℃ for 5h. Then remove the concentrated hydrochloric acid by filtration and wash the powder with deionized water until neutral. Dilute the filtered carbon nitride with deionized water, sonicate for 2h, and then centrifuge at 5000rpm for 20min. Take the supernatant to obtain a carbon nitride film sol with a concentration of 2.0mg / mL.

[0075] Step 2: Prepare a 2 mg / mL piperazine aqueous solution, add carbon nitride film-forming sol to make the concentration of carbon nitride in the piperazine aqueous solution 1.0 mg / mL, and disperse it evenly by ultrasonication to obtain a mixed dispersion; take 5 ml of the mixed dispersion and add it dropwise to the surface of the polyethersulfone support base membrane and infiltrate it for 120 seconds, and remove the residual liquid on the surface, wherein the infiltration is carried out under light, and the light is provided by irradiation with a xenon lamp, and the light intensity is 100 mW / cm 2 .

[0076] Step 3: Prepare a 2 mg / mL n-hexane solution of trimesoyl chloride, then immerse the surface of the ultrafiltration membrane in the n-hexane solution containing trimesoyl chloride to carry out interfacial polymerization reaction. After the reaction lasts for 30 seconds, remove the excess liquid. Then, soak the obtained membrane in the n-hexane solution for 10 seconds to remove the unreacted acyl chloride monomer to obtain a high permeability membrane containing an ultrathin polyamide separation layer. The reaction temperature is 25°C and the reaction humidity is 60%. The reaction is carried out under light, and the light is formed by xenon lamp irradiation, and the intensity of the light is 100mw / cm 2 .

[0077] Step 4: The high permeability membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 min to obtain a fully polymerized nanofiltration membrane based on carbon nitride photogenerated positive charge regulation.

[0078] Example 4:

[0079] A method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride comprises the following steps:

[0080] Step 1: Add 6g of melamine to a crucible and place it in a muffle furnace. Heat the temperature to 550℃ at a heating rate of 5℃ / min, calcine for 4h, and then grind the calcined product into powder in a mortar to obtain a bulk carbon nitride powder. Place 1g of bulk carbon nitride powder in a beaker containing 20mL of concentrated hydrochloric acid and stir at 60℃ for 5h. Then remove the concentrated hydrochloric acid by filtration and wash the powder with deionized water until neutral. Dilute the filtered carbon nitride with deionized water, sonicate for 2h, and then centrifuge at 5000rpm for 20min. Take the supernatant to obtain a carbon nitride film sol with a concentration of 2.0mg / mL.

[0081] Step 2: Prepare a 4 mg / mL piperazine aqueous solution, add carbon nitride film-forming sol to make the concentration of carbon nitride in the piperazine aqueous solution 1.0 mg / mL, and disperse it evenly by ultrasonication to obtain a mixed dispersion; take 5 ml of the mixed dispersion and add it dropwise to the surface of the polyethersulfone support base film and infiltrate it for 120 seconds, and remove the residual liquid on the surface, wherein the infiltration is carried out under light, and the light is provided by irradiation with a xenon lamp, and the light intensity is 100 mW / cm 2 .

[0082] Step 3: Prepare a 2 mg / mL n-hexane solution of trimesoyl chloride, then immerse the surface of the ultrafiltration membrane in the n-hexane solution containing trimesoyl chloride to carry out interfacial polymerization reaction. After the reaction lasts for 30 seconds, remove the excess liquid. Then, soak the obtained membrane in the n-hexane solution for 10 seconds to remove the unreacted acyl chloride monomer to obtain a high permeability membrane containing an ultrathin polyamide separation layer. The reaction temperature is 25°C and the reaction humidity is 60%. The reaction is carried out under light, and the light is formed by xenon lamp irradiation, and the intensity of the light is 100mw / cm2 .

[0083] Step 4: The high permeability membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 min to obtain a fully polymerized nanofiltration membrane based on carbon nitride photogenerated positive charge regulation.

[0084] Comparative Example 1:

[0085] A method for preparing a conventional polyamide microfiltration membrane (no carbon nitride is added to the aqueous monomer solution, and neither the infiltration nor the interfacial polymerization reaction is performed under light) comprises the following steps:

[0086] Step 1: Use piperazine as the aqueous phase monomer and trimesoyl chloride as the organic phase monomer, dissolve them in water and n-hexane, respectively, to prepare a 4.0 mg / mL piperazine solution and a 2 mg / mL trimesoyl chloride n-hexane solution, respectively.

[0087] Step 2: Using polyethersulfone ultrafiltration membrane as the supporting base membrane and piperazine solution as the aqueous phase monomer, 5 ml of the solution was added dropwise to the surface of the polyethersulfone supporting base membrane for aqueous phase infiltration. After standing for 120 seconds, the polyethersulfone filter membrane was removed and the surface liquid was removed.

[0088] Step 3: Immerse the ultrafiltration membrane surface from step (3) in a hexane solution of trimesoyl chloride to conduct an interfacial polymerization reaction. After the reaction continues for 30 seconds, the excess liquid is removed. The resulting membrane is then immersed in the hexane solution for 10 seconds to remove unreacted acyl chloride monomer. The reaction temperature is 25°C and the reaction humidity is 60%.

[0089] Step 4: The microfiltration membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 minutes to obtain a fully polymerized traditional polyamide microfiltration membrane.

[0090] Comparative Example 2:

[0091] A method for preparing a conventional polyamide microfiltration membrane (no carbon nitride is added to the aqueous monomer solution, and both the infiltration and interfacial polymerization reactions are carried out under light) comprises the following steps:

[0092] Step 1: Use piperazine as the aqueous phase monomer and trimesoyl chloride as the organic phase monomer, dissolve them in water and n-hexane, respectively, to prepare a piperazine solution with a concentration of 4.0 mg / mL and a trimesoyl chloride solution with a concentration of 2 mg / mL.

[0093] Step 2: Using a polyethersulfone ultrafiltration membrane as the supporting base membrane and a piperazine solution as the aqueous phase monomer, 5 ml of the solution was dripped onto the surface of the polyethersulfone supporting base membrane for aqueous phase infiltration. After standing for 120 seconds, the polyethersulfone filter membrane was removed and the surface liquid was removed. The infiltration was carried out under light, and the light was formed by irradiation with a xenon lamp with an intensity of 100 mW / cm 2 .

[0094] Step 3: Immerse the surface of the ultrafiltration membrane in step (3) in a n-hexane solution of trimesoyl chloride to carry out interfacial polymerization reaction. After the reaction lasts for 30 seconds, remove the excess liquid. Then, soak the membrane in the n-hexane solution for 10 seconds to remove unreacted acyl chloride monomer. The reaction temperature is 25°C and the reaction humidity is 60%. The reaction is carried out under light, and the light is formed by xenon lamp irradiation, and the light intensity is 100mw / cm 2 .

[0095] Step 4: The microfiltration membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 minutes to obtain a fully polymerized traditional polyamide microfiltration membrane.

[0096] Comparative Example 3:

[0097] A method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride (carbon nitride is added to an aqueous monomer solution, but neither the wetting nor the interfacial polymerization reaction is carried out under light), comprising the following steps:

[0098] Step 1: Add 6g of melamine to a crucible and place it in a muffle furnace. Heat the temperature to 550℃ at a heating rate of 5℃ / min, calcine for 4h, and then grind the calcined product into powder in a mortar to obtain a bulk carbon nitride powder. Place 1g of bulk carbon nitride powder in a beaker containing 20mL of concentrated hydrochloric acid and stir at 60℃ for 5h. Then remove the concentrated hydrochloric acid by filtration and wash the powder with deionized water until neutral. Dilute the filtered carbon nitride with deionized water, sonicate for 2h, and then centrifuge at 5000rpm for 20min. Take the supernatant to obtain a carbon nitride film sol with a concentration of 2.0mg / mL.

[0099] Step 2: Prepare a 4 mg / mL piperazine aqueous solution and add carbon nitride membrane sol to make the concentration of carbon nitride in the piperazine aqueous solution 0.5 mg / mL. Ultrasonicate to disperse the carbon nitride uniformly to obtain a mixed dispersion. Take 5 ml of the mixed dispersion and add it dropwise to the surface of the polyethersulfone support membrane. Let it soak for 120 seconds, and remove any residual liquid on the surface.

[0100] Step 3: Prepare a 2 mg / mL hexane solution of trimesoyl chloride. Submerge the ultrafiltration membrane in this hexane solution to conduct interfacial polymerization. After the reaction continues for 30 seconds, remove the excess liquid and soak the resulting membrane in the hexane solution for 10 seconds to remove unreacted acyl chloride monomers. This yields a highly permeable membrane containing an ultrathin polyamide separation layer. The reaction temperature is 25°C and the humidity is 60%.

[0101] Step 4: The high permeability membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 min to obtain a fully polymerized nanofiltration membrane based on carbon nitride photogenerated positive charge regulation.

[0102] Comparative Example 4:

[0103] A method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride comprises the following steps:

[0104] Step 1: Add 6g of melamine to a crucible and place it in a muffle furnace. Heat the temperature to 550℃ at a heating rate of 5℃ / min, calcine for 4h, and then grind the calcined product into powder in a mortar to obtain a bulk carbon nitride powder. Place 1g of bulk carbon nitride powder in a beaker containing 20mL of concentrated hydrochloric acid and stir at 60℃ for 5h. Then remove the concentrated hydrochloric acid by filtration and wash the powder with deionized water until neutral. Dilute the filtered carbon nitride with deionized water, sonicate for 2h, and then centrifuge at 5000rpm for 20min. Take the supernatant to obtain a carbon nitride film sol with a concentration of 2.0mg / mL.

[0105] Step 2: Prepare a 4 mg / mL piperazine aqueous solution and add carbon nitride membrane sol to make the concentration of carbon nitride in the piperazine aqueous solution 1.0 mg / mL. Ultrasonicate to disperse the carbon nitride uniformly to obtain a mixed dispersion. Take 5 ml of the mixed dispersion and add it dropwise to the surface of the polyethersulfone support membrane. Let it soak for 120 seconds, and remove any residual liquid on the surface.

[0106] Step 3: Prepare a 2 mg / mL hexane solution of trimesoyl chloride. Submerge the ultrafiltration membrane surface in this hexane solution to allow interfacial polymerization. After the reaction continues for 30 seconds, remove the excess liquid. The resulting membrane is then immersed in the hexane solution for 10 seconds to remove unreacted acyl chloride monomers, resulting in a highly permeable membrane containing an ultrathin polyamide separation layer. The reaction temperature is 25°C and the humidity is 60%.

[0107] Step 4: The high permeability membrane obtained in step 3 is placed in an oven for heat treatment at 60° C. for 10 min to obtain a fully polymerized nanofiltration membrane based on carbon nitride photogenerated positive charge regulation.

[0108] Application Example 1:

[0109] The multifunctional nanofiltration membranes prepared in Examples 1 to 4 were subjected to membrane flux tests. Cross-flow filtration was used, and deionized water was used as the test fluid. The separation performance of the resulting nanofiltration membranes was tested at 4 bar. The test fluid temperature was 25°C. After pre-pressing at 4 bar for 60 minutes, the produced water was collected for 30 minutes. The permeability of the nanofiltration membranes was calculated based on the volume of water produced per unit time. The results are shown in Table 1. Figure 2 .

[0110] Comparative application example 1:

[0111] The multifunctional nanofiltration membranes prepared in Comparative Examples 1 to 4 were subjected to membrane flux tests. Using cross-flow filtration, deionized water was used as the test fluid. The separation performance of the resulting nanofiltration membranes was tested at 4 bar. The test fluid temperature was 25°C. After pre-pressing at 4 bar for 60 minutes, the produced water was collected for 30 minutes. The permeability of the nanofiltration membranes was calculated based on the volume of water produced per unit time. The results are shown in Table 1. Figure 2 .

[0112] Application Example 2:

[0113] The multifunctional nanofiltration membrane prepared in Example 4 was used to perform membrane separation tests on sodium sulfate aqueous solution. Cross-flow filtration was used, and 1g / L sodium sulfate solution was used as the test liquid. The separation performance of the obtained nanofiltration membrane was tested at 4 bar. The test liquid temperature was 25°C. After pre-pressing at 4 bar for 60 minutes, the produced water was collected for 30 minutes. The desalination rate of the nanofiltration membrane was calculated based on the conductivity values ​​of the produced water and the influent water. The brine flux of the nanofiltration membrane was calculated based on the volume of produced water per unit time. The results are shown in Figure 3 .

[0114] Comparative application example 2:

[0115] The multifunctional nanofiltration membrane prepared in Comparative Example 2 was subjected to membrane separation test on sodium sulfate aqueous solution. Cross-flow filtration was adopted, and 1g / L sodium sulfate solution was used as the test liquid. The separation performance of the obtained nanofiltration membrane was tested at 4 bar. The test liquid temperature was 25°C. After pre-pressing at 4 bar for 60 minutes, the produced water was collected for 30 minutes. The desalination rate of the nanofiltration membrane was calculated based on the conductivity values ​​of the produced water and the influent water. The brine flux of the nanofiltration membrane was calculated based on the volume of water produced per unit time. The results are shown in Figure 4 .

[0116] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride, characterized in that: The steps include: (1) thermally polymerizing a nitrogen-containing precursor to obtain a bulk carbon-nitrogen compound, treating the bulk carbon-nitrogen compound in an acid solution to obtain a carbon nitride film-forming sol; adding the obtained carbon nitride film-forming sol to an aqueous solution of a polyamine monomer, and ultrasonically dispersing the resultant solution to obtain a mixed dispersion; (2) dissolving the organic phase monomer in an organic solvent and stirring to obtain an organic phase monomer solution; (3) adding the ultrafiltration support base membrane to the above-mentioned mixed dispersion to soak it, then taking it out and adding it to the above-mentioned organic phase monomer solution to carry out interfacial polymerization reaction to obtain a high permeability membrane containing an ultrathin polyamide separation layer; wherein the soaking and interfacial polymerization reaction are both carried out under light; wherein the light is formed by xenon lamp irradiation; the intensity of the light is 100 to 300 mw / cm 2 ; (4) After heat treatment of the above-mentioned high permeability membrane containing the ultrathin polyamide separation layer, a nanofiltration membrane based on the regulation of carbon nitride photogenerated positive charges is obtained.

2. The method for preparing a nanofiltration membrane according to claim 1, wherein: In step (1), the nitrogen-containing precursor includes at least one of cyanamide, dicyandiamide, melamine, urea, and thiourea.

3. The method for preparing a nanofiltration membrane according to claim 1, wherein: In step (1), the ratio of the bulk carbon and nitrogen compound to the acid solution is 1 g: 10-50 mL; In step (1), the concentration of the obtained carbon nitride film-forming sol is 1.0 to 2.0 mg / ml; In step (1), the concentration of carbon nitride in the aqueous solution of the polyamine monomer is 0.1-2.0 mg / mL.

4. The method for preparing a nanofiltration membrane according to claim 1, wherein: In step (1), the polyamine monomer includes at least one of piperazine and its derivatives, o-phenylenediamine and its derivatives, m-phenylenediamine and its derivatives, diethylenetriamine, triethylenetetramine, and polyethyleneimine.

5. The method for preparing a nanofiltration membrane according to claim 1, wherein: In step (2), the organic phase monomer includes at least one of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, pyromellitoyl chloride, cycloalkane polyacyl chloride, and polysulfonyl chloride; In step (2), the concentration of the organic phase monomer in the organic solvent is 0.5-3 mg / mL.

6. The method for preparing a nanofiltration membrane according to claim 1, wherein: In step (3), the soaking time is 30-180s.

7. The method for preparing a nanofiltration membrane according to claim 1, wherein: In step (3), the time of the interfacial polymerization reaction is 15 to 120 seconds, the temperature of the interfacial polymerization reaction is 20 to 30° C., and the humidity of the interfacial polymerization reaction is 45 to 70%.

8. The method for preparing a nanofiltration membrane according to claim 1, wherein: In step (4), the heat treatment temperature is 40 to 70° C., and the heat treatment time is 10 to 60 minutes.

9. The nanofiltration membrane prepared by the method for preparing a nanofiltration membrane by regulating interfacial polymerization reaction using photogenerated charges of carbon nitride according to any one of claims 1 to 8.

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