Preparation Method and Application of LDH Nanonetwork-Assisted Polyamide Nanofiltration Membrane

Abstract

The present invention belongs to the technical field of separation composite membranes, and specifically relates to a preparation method and application of an LDH nano-network assisted polyamide nanofiltration membrane. The preparation method of the LDH nano-network assisted polyamide nanofiltration membrane comprises the following steps: (1) regionally coating a porous substrate membrane with a coating; (2) obtaining a precursor solution, and then immersing the porous substrate membrane in the precursor solution for reaction to obtain an LDH membrane; (3) cleaning and soaking the LDH membrane with an organic solvent, and drying the LDH membrane to obtain a dried LDH membrane; (4) under vacuum conditions, immersing the dried LDH membrane in a mixed aqueous solution of piperazine and LDH nanosheets, filtering with suction, and drying to obtain an LDH network membrane; (5) immersing the LDH network membrane in a solution of trimesoyl chloride in n-hexane for polymerization reaction, washing and drying to obtain an LDH nano-network assisted polyamide nanofiltration membrane. The nanofiltration membrane obtained by the present invention has a large water flux and a high rejection rate, and can be widely used in the field of water treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation composite membranes, and particularly relates to a preparation method and application of an LDH nano-network assisted polyamide nanofiltration membrane. Background Art

[0002] The direct discharge of wastewater generated by human activities has caused the rapid deterioration of the water ecosystem, which has attracted wide attention worldwide. Among them, the problem of water eutrophication has received the most attention. The increasing phosphorus content in wastewater has caused the eutrophication of lake water bodies, which in turn induces algal blooms and destroys the ecosystem. At present, the commonly used phosphorus removal methods include biological phosphorus removal, chemical precipitation, electrochemistry and adsorption. However, these methods have disadvantages such as large infrastructure, low efficiency and high cost. Therefore, choosing a more economical and efficient deep phosphorus removal method is an important research direction for water source treatment at present. As a rapidly developing high-tech, membrane separation technology has been widely used in the field of water treatment, with the characteristics of simple process, easy operation, good selective filtration and high efficiency and low cost.

[0003] Among various pressure-driven membranes, nanofiltration membranes can effectively filter divalent ions, multivalent ions or substances with a molecular weight greater than 200, and have broad application prospects, including water treatment and resource recovery. Nanofiltration membranes generally consist of a porous support layer and a dense layer. Among them, the dense layer composed of polyamide serves as the selective functional layer, which determines the separation performance of the membrane. The preparation of a large-area defect-free polyamide layer is mostly carried out through an interfacial polymerization reaction. A typical interfacial polymerization reaction includes the diffusion of amine monomers from water to the organic phase and the Schotten-Baumann reaction of acid chloride monomers at the interface. However, the diffusion and reaction processes of amine monomers are fast and uncontrollable, which easily lead to changes in the layer thickness, resulting in uneven pore sizes and unable to improve both rejection and permeability simultaneously. All along, the research on water treatment membranes still focuses on the difficult-to-overcome trade-off effect, that is, to achieve a two-way improvement in permeability and selectivity.

[0004] Chinese Patent CN113578066A discloses a method for preparing a modified nanofiltration membrane based on MXene, which includes the following steps: (1) Using a polysulfone membrane as the base membrane, performing pretreatment, uniformly spraying a solution containing MXene nanosheets onto the pretreated polysulfone membrane, and standing still after spraying to completely evaporate the moisture; (2) Pouring an aqueous solution onto the base membrane obtained in step (1), standing still and then pouring out the excess aqueous solution, and drying the residual solution on the surface of the base membrane; (3) Pouring an oil-phase solution onto the base membrane obtained in step (2), standing still for reaction, and then taking out the obtained nanofiltration membrane; (4) Soaking the nanofiltration membrane obtained in step (3) in deionized water to remove residual reagents to obtain a modified nanofiltration membrane. However, the transport channels of the two-dimensional intermediate layer assembled in parallel in this patent are voids interconnected in the vertical and horizontal directions, showing a "zigzag" transmission, which is extremely tortuous and several orders of magnitude longer than the thickness of the stacked nanosheets, making it limited in improving permeability.

[0005] Chinese Patent CN109012187A discloses a method for in-situ growing a layered double metal oxide nanofiltration membrane, belonging to the field of nanofiltration membrane separation. Its steps include: performing pretreatment on a porous base membrane to remove surface impurities; dissolving metal salts, urea, and ammonium fluoride in a solvent and stirring evenly until the oil phase disappears; placing the prepared solution in a reaction kettle, sealing and assembling the reaction kettle; at a certain temperature, metal ions in-situ grow in the reaction kettle to form a layered double metal hydroxide nanofiltration membrane on the surface of the base membrane, and then preparing an LDO composite membrane by means of high-temperature calcination. The rejection rate and flux of this nanofiltration membrane for 0.1 g / L of Eriochrome Black T are 99.2% and 5.4 L·m -2 ·h -1 ·bar -1 respectively. The water flux of the membrane in this patent is still at a relatively low level among the reported nanofiltration membranes, and it only has a good rejection effect on large-size dyes - Eriochrome Black T and does not have the rejection performance for small-size molecules.

[0006] Chinese Patent CN111686588A discloses a composite nanofiltration membrane with a layered double metal hydroxide as a modified template and a preparation method, relating to the technical field of separation membranes. First, load the layered double metal hydroxide modified by polyphenol molecules on a support base membrane to form a modified support base membrane. Then, perform an interfacial polymerization reaction on the modified support base membrane. During the interfacial polymerization process, the loaded modified layered double metal hydroxide is beneficial to form an active separation layer with an ultra-thin thickness and a large effective area. This patent utilizes the hydrophilicity of LDH to form an ultra-thin and large-effective-area active layer. However, the method of loading LDH powder particles by suction filtration will inevitably make the surface structure of the base membrane uneven, resulting in the polyamide layer showing nano-scale inhomogeneity in the depth distribution, and thus will affect the permeability and rejection rate of the composite nanofiltration membrane. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the problems to be solved by the present invention are as follows: to provide a preparation method of a LDH nanonetwork-assisted polyamide nanofiltration membrane, to improve the properties of the polyamide nanofiltration membrane through the LDH nanonetwork, and to obtain a nanofiltration membrane with excellent filtration effect; the present invention also provides the application of the LDH nanonetwork-assisted polyamide nanofiltration membrane.

[0008] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0009] The preparation method of the LDH nanonetwork-assisted polyamide nanofiltration membrane of the present invention includes the following steps:

[0010] (1) Regionally coat a porous substrate membrane with a coating material;

[0011] (2) Dissolve a metal ion salt, urea, and ammonium fluoride in water and stir to obtain a precursor solution, then immerse the porous substrate membrane in the precursor solution for reaction to obtain a LDH membrane;

[0012] (3) Wash and soak the LDH membrane with an organic solvent, and dry the LDH membrane to obtain a dried LDH membrane;

[0013] (4) Under vacuum conditions, immerse the dried LDH membrane in a mixed aqueous solution of piperazine and LDH nanosheets, filter by suction, and dry to obtain a LDH network membrane;

[0014] (5) Immerse the LDH network membrane in a solution of trimesoyl chloride in n-hexane for polymerization reaction, and then wash and dry to obtain a LDH nanonetwork-assisted polyamide nanofiltration membrane.

[0015] Wherein:

[0016] In the step (1), the coating material is glass glaze, the porous substrate membrane is an ultrafiltration membrane or a microfiltration membrane, the membrane material is one of alumina, titanium oxide, or zirconium oxide, and the pore size of the porous substrate membrane is 0.1 - 1.0 μm.

[0017] In the step (2), the metal ions in the metal ion salt include divalent metal ions and trivalent metal ions. The divalent metal ions include one of Ni 2+ , Zn 2+ , Co 2+ , Cu 2+ , Ca 2+ , Mn 2+ or Mg 2+ , and the trivalent metal ions include one of Cr 3+ , Fe 3+ or Al 3+ .

[0018] In step (2), the stirring time is 30 - 50 min, the total metal ion concentration of the precursor solution is 30 - 80 mmol / L, the urea concentration is 50 - 140 mmol / L, the ammonium fluoride concentration is 100 - 200 mmol / L, the reaction temperature is 110 - 120 °C, and the reaction time is 24 - 36 h.

[0019] In step (3), the organic solvent is absolute ethanol, the soaking time is 10 - 15 h, and the drying is carried out in an oven at 30 - 50 °C.

[0020] In step (4), the concentration of piperazine in the mixed aqueous solution of piperazine and LDH nanosheets is 0.5 - 2 wt.%, and the concentration of LDH nanosheets is 0.025 - 0.1 wt.%; the suction filtration time is 5 - 20 min, and the drying is carried out at room temperature.

[0021] In step (5), the concentration of trimesoyl chloride in the trimesoyl chloride n - hexane solution is 0.15 - 0.5 wt.%, the polymerization reaction temperature is 35 - 65 °C, the polymerization reaction time is 15 - 30 min, and the washing is carried out 3 - 5 times with n - hexane solution; the drying is carried out by air knife drying and then placed in an oven and dried at 50 - 70 °C for 5 - 20 min.

[0022] The LDH nanonetwork - assisted polyamide nanofiltration membrane prepared by the method for preparing an LDH nanonetwork - assisted polyamide nanofiltration membrane is used for filtering phosphorus - containing substances, including the following steps:

[0023] (a) Prepare a phosphorus - containing solution;

[0024] (b) Install the LDH nanonetwork - assisted polyamide nanofiltration membrane on a terminal filtration device and filter the phosphorus - containing solution.

[0025] In step (a), the phosphorus includes one or more of H 2 PO 4 - , HPO 4 2- or PO 4 3- , and the concentration of the phosphorus - containing solution is 20 - 1000 mgP / L.

[0026] In step (b), the filtration pressure is 0.2 - 0.6 MPa.

[0027] The basic principle of the present invention is:

[0028] First, a hydrothermal method is used to in-situ grow an interlaced network of LDH nanowires on the surface of a porous base membrane. The porous base membrane is placed in an LDH precursor solution. At a certain temperature and pressure, an interlaced LDH nanowire network is in-situ grown on the surface of the porous base membrane, so that the LDH nanowire network completely covers the surface of the porous base membrane. At this time, the LDH nanowire network is distributed in a honeycomb shape as a whole. The structure of the LDH nanowire network will affect the morphology of the polyamide membrane. The LDH layer structure is regulated by controlling the reaction temperature, reaction time, ion species of the LDH precursor solution and the pore size of the porous membrane. Subsequently, the small-sized LDH nanosheets wrapped with piperazine monomers are filtered into the pores of the LDH nanowire network by a vacuum-assisted method. LDH nanosheets with a size smaller than the pores on the surface of the LDH nanowires can pass through the surface and deposit in the interconnected cavities, forming a multi-dimensional pore structure of longitudinal macropores and micropores, which serves as a template material for the subsequent formation of a honeycomb polyamide membrane. Hydrophilic LDH and fluoride-containing ions have hydrogen bonding, which can slow down the diffusion rate of fluoride-containing ions to the oil phase interface during interfacial polymerization, making interfacial polymerization controllable. Finally, the LDH nano-membrane was placed in a trimesoyl chloride n-hexane solution, interfacial polymerization was performed to form a nanofiltration membrane, and then immersed in a trimesoyl chloride n-hexane solution, and nano-interfacial polymerization was performed on the LDH nano-membrane to form a honeycomb LDH nano-network-assisted polyamide nanofiltration membrane.

[0029] The beneficial effects of the present invention are as follows:

[0030] The present invention forms an LDH nano-network-assisted polyamide nanofiltration membrane through the porous basement membrane, the LDH nano-membrane and the polyamide layer, which can effectively intercept phosphorus in the water ecosystem. LDH grows on the surface of the porous basement membrane in the form of nanowires to form a staggered network, and piperazine-wrapped LDH nanosheets are added to the pores of the LDH nano-network to form a multi-dimensional pore structure, control the surface morphology of the polyamide layer, and increase the effective filtration area of ​​the membrane. In the present invention, the LDH nano-membrane forms a staggered network, stores amine monomers through space and hydrogen bonding, makes the interfacial polymerization reaction controllable, and provides a porous rapid transmission channel, which significantly improves the phosphorus removal efficiency of the membrane.

[0031] The LDH nano-network-assisted polyamide nanofiltration membrane prepared by the present invention has a high rejection rate and a large water flux, is highly practical, and can effectively treat phosphorus-containing wastewater. The staggered LDH nanowire network is synthesized in situ on a porous substrate, and when in use, it can be performed without any complex equipment; the morphology and surface properties of the LDH nano-network membrane can control the uniform release of piperazine, thereby affecting the interfacial polymerization reaction, and the prepared LDH nano-network-assisted polyamide nanofiltration membrane has a special honeycomb structure, which improves the permeability and selectivity of the nanofiltration membrane. The present invention introduces nanochannels in the polyamide layer to provide additional water transport paths and reduce the packing density of the polyamide molecular chains, which can effectively overcome the trade-off effect.

[0032] The preparation steps of the present invention are simple. The obtained nanofiltration membrane has a large water flux and a high rejection rate, can maintain long-term filtration stability, has strong practicability, and can be widely used in the field of water treatment. Description of the Drawings

[0033] Figure 1 SEM image of the surface of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 1;

[0034] Figure 2 SEM image of the surface of the LDH composite membrane prepared in Comparative Example 1;

[0035] Figure 3 SEM image of the surface of the LDH composite membrane prepared in Comparative Example 2. Detailed Description of the Invention

[0036] The present invention will be further described below in conjunction with examples.

[0037] Example 1

[0038] (1) Use glass glaze to perform regional coating on an Al porous ultrafiltration membrane with an outer diameter of 12 mm and a pore diameter of 0.5 μm, and the coating area is 11.3 cm; 2 O 3 ; 2 ;

[0039] (2) Dissolve zinc nitrate, aluminum nitrate, urea and ammonium fluoride in water and stir to obtain a precursor solution, where the total ion concentration of zinc nitrate and aluminum nitrate is 30 mmol / L (the molar ratio of Zn / Al is 3.43), the urea concentration is 70 mmol / L, and the ammonium fluoride concentration is 100 mmol / L. Stir for 30 min, then fix the Al porous substrate membrane with polytetrafluoroethylene and immerse it in the precursor solution, and then place it in an oven at 120 °C for hydrothermal reaction for 24 h to obtain an LDH membrane; 2+ / Al 3+ molar ratio is 3.43), the urea concentration is 70 mmol / L, the ammonium fluoride concentration is 100 mmol / L, stir for 30 min, and then fix the AlO porous substrate membrane with polytetrafluoroethylene and immerse it in the precursor solution, and then place it in an oven at 120 °C for hydrothermal reaction for 24 h to obtain an LDH membrane; 2 O 3 porous substrate membrane through polytetrafluoroethylene and immerse it in the precursor solution, and then place it in an oven at 120 °C for hydrothermal reaction for 24 h to obtain an LDH membrane;

[0040] (3) Wash the LDH membrane with absolute ethanol, soak it for 12 h, and dry the LDH membrane in an oven at 30 °C to obtain a dried LDH membrane;

[0041] (4) Under vacuum conditions, immerse the dried LDH membrane in a mixed aqueous solution of 1 wt.% piperazine and 0.025 wt.% LDH nanosheets, filter for 5 min, and dry at room temperature to obtain an LDH nanonetwork membrane;

[0042] (5) Immerse the LDH nanomesh in a 0.15 wt.% solution of trimesoyl chloride in n - hexane, then carry out a polymerization reaction at 65 °C for 15 min. After the reaction, wash it 3 times with n - hexane solution, dry it with an air knife and then place it in an oven, and dry it at 60 °C for 10 min to obtain the LDH nanofiber - assisted polyamide nanofiltration membrane.

[0043] Example 2

[0044] (1) Use glass glaze to perform regional coating on a porous Al base membrane with an outer diameter of 12 mm and a pore diameter of 0.2 μm 2 O 3 with a coating area of 11.3 cm 2 ;

[0045] (2) Dissolve cobalt nitrate, aluminum nitrate, urea, and ammonium fluoride in water and stir to obtain a precursor solution, where the total ion concentration of cobalt nitrate and aluminum nitrate is 60 mmol / L (Co 2+ / Al 3+ molar ratio is 3.43), the urea concentration is 140 mmol / L, the ammonium fluoride concentration is 200 mmol / L, stir for 50 min, and then fix the Al 2 O 3 porous base membrane with polytetrafluoroethylene and immerse it in the precursor solution, then place it in an oven at 110 °C for hydrothermal reaction for 30 h to obtain the LDH membrane;

[0046] (3) Wash the LDH membrane with absolute ethanol, soak it for 15 h, and place the LDH membrane in an oven at 50 °C for drying to obtain a dried LDH membrane;

[0047] (4) Under vacuum conditions, immerse the dried LDH membrane in a mixed aqueous solution of 0.5 wt.% piperazine and 0.1 wt.% LDH nanosheets, carry out suction filtration for 20 min, and dry it at room temperature to obtain the LDH nanomesh;

[0048] (5) Immerse the LDH nanomesh in a 0.2 wt.% solution of trimesoyl chloride in n - hexane, then carry out a polymerization reaction at 35 °C for 30 min. After the reaction, wash it 5 times with n - hexane solution, dry it with an air knife and then place it in an oven, and dry it at 70 °C for 5 min to obtain the LDH nanofiber - assisted polyamide nanofiltration membrane.

[0049] Example 3

[0050] (1) Use glass glaze to perform regional coating on a porous Al base membrane with an outer diameter of 12 mm and a pore diameter of 1.0 μm 2 O 3 with a coating area of 11.3 cm 2 ;

[0051] (2) Dissolve nickel nitrate, chromium nitrate, urea, and ammonium fluoride in water and stir to obtain a precursor solution, where the total ion concentration of nickel nitrate and cobalt nitrate is 80 mmol / L (Ni 2+ / Cr 3+ molar ratio is 3.43), the urea concentration is 50 mmol / L, the ammonium fluoride concentration is 110 mmol / L, stir for 40 min, and then fix the Al 2 O 3 porous substrate membrane with polytetrafluoroethylene and immerse it in the precursor solution, then place it in an oven at 120 °C for hydrothermal reaction for 36 h to obtain the LDH membrane;

[0052] (3) Wash the LDH membrane with absolute ethanol, soak it for 10 h, and dry the LDH membrane in an oven at 40 °C to obtain a dried LDH membrane;

[0053] (4) Under vacuum conditions, immerse the dried LDH membrane in a mixed aqueous solution of 2 wt.% piperazine and 0.05 wt.% LDH nanosheets, filter it for 15 min, and dry it at room temperature to obtain the LDH nano-network membrane;

[0054] (5) Immerse the LDH nano-network membrane in a 0.5 wt.% trimesoyl chloride n-hexane solution, then carry out a polymerization reaction at 55 °C for 20 min. After the reaction, wash it 3 times with n-hexane solution, dry it with an air knife and then place it in an oven, dry it at 50 °C for 20 min to obtain the LDH nano-network assisted polyamide nanofiltration membrane.

[0055] Comparative Example 1

[0056] The LDH membrane obtained in step (3) is not immersed in the mixed aqueous solution of piperazine and LDH nanosheets, nor is it immersed in the trimesoyl chloride n-hexane solution. The remaining steps are the same as in Example 1 to obtain the LDH composite membrane.

[0057] Comparative Example 2

[0058] Do not add LDH nanosheets to the mixed aqueous solution in step (4), and the remaining steps are the same as in Example 1 to obtain the LDH composite membrane.

[0059] Comparative Example 3

[0060] Do not add piperazine to the mixed aqueous solution in step (4), and the remaining steps are the same as in Example 1 to obtain the LDH composite membrane.

[0061] Apply the LDH nano-network assisted polyamide nanofiltration membranes prepared in Examples 1-3 and the LDH composite membranes prepared in Comparative Examples 1-3 to the filtration experiments of phosphorus-containing substances respectively.

[0062] (1) Prepare 6 portions of KH 2 PO 4Solution, and set the filtration pressure to 0.2 MPa.

[0063] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 1 is 98.95%, and the flux is 48.20 L·m -2 ·h -1 ·bar -1 。

[0064] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 2 is 97.89%, and the flux is 55.92 L·m -2 ·h -1 ·bar -1 。

[0065] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 3 is 98.67%, and the flux is 48.26 L·m -2 ·h -1 ·bar -1 。

[0066] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 1 is 4.57%, and the flux is 189.57 L·m -2 ·h -1 ·bar -1 。

[0067] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 2 is 25.73%, and the flux is 113.74 L·m -2 ·h -1 ·bar -1 。

[0068] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 3 is 2.42%, and the flux is 254.78 L·m -2 ·h -1 ·bar -1 。

[0069] (2)Prepare 6 portions of KH 2 PO 4 solution with a concentration of 1000 mg P / L, and set the filtration pressure to 0.6 MPa.

[0070] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 1 is 99.01%, and the flux is 46.94 L·m -2 ·h -1 ·bar -1 。

[0071] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 2 is 97.33%, and the flux is 52.75 L·m 2 ·h -1 ·bar -1 。

[0072] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 3 is 98.89%, and the flux is 50.61 L·m -2 ·h -1 ·bar -1 。

[0073] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 1 is 2.64%, and the flux is 228.38 L·m -2 ·h -1 ·bar -1 。

[0074] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 2 is 22.38%, and the flux is 106.41 L·m -2 ·h -1 ·bar -1 。

[0075] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 3 is 2.97%, and the flux is 185.27 L·m -2 ·h -1 ·bar -1 。

[0076] (3)Prepare 6 portions of KH 2 PO 4 solution with a concentration of 500 mg P / L, and set the filtration pressure to 0.4 MPa.

[0077] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 1 is 97.55%, and the flux is 54.13 L·m 2 ·h -1 ·bar -1 。

[0078] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 2 is 97.17%, and the flux is 56.71 L·m -2 ·h -1 ·bar -1 。

[0079] The phosphorus rejection rate of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared in Example 3 is 97.98%, and the flux is 48.63 L·m -2 ·h -1 ·bar-1 。

[0080] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 1 was 5.47%, and the flux was 191.41 L·m -2 ·h -1 ·bar -1 。

[0081] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 2 was 27.13%, and the flux was 110.63 L·m -2 ·h -1 ·bar -1 。

[0082] The phosphorus rejection rate of the LDH composite membrane prepared in Comparative Example 3 was 3.42%, and the flux was 231.82 L·m -2 ·h -1 ·bar -1 。

[0083] The SEM image of the surface of the LDH nano-network assisted polyamide nanofiltration membrane prepared in Example 1 is shown in Figure 1 , and the SEM image of the surface of the LDH composite membrane prepared in Comparative Example 1 is shown in Figure 2 , and the SEM image of the surface of the LDH composite membrane prepared in Comparative Example 2 is shown in Figure 3 。

[0084] From the above experimental data, it can be seen that the present invention constructs an LDH nano-membrane network system by a hydrothermal method, so that the polymerization of the polyamide layer becomes controllable, and the prepared LDH nano-network assisted polyamide nanofiltration membrane has a higher phosphorus rejection rate for phosphorus-containing substances and a better interception effect, and can effectively solve the problem of excessive phosphorus-containing substances in the current water ecosystem.

Claims

1. A method for preparing a LDH nanonetwork-assisted polyamide nanofiltration membrane, characterized in that: The following steps are involved: (1) Using coating to seal the porous base membrane; (2) dissolving metal ion salt, urea and ammonium fluoride in water and stirring to obtain a precursor solution, and then immersing the porous base membrane in the precursor solution to react to obtain an LDH membrane; (3) using an organic solvent to clean and soak the LDH membrane, and drying the LDH membrane to obtain a dry LDH membrane; (4) Under vacuum conditions, immersing the dried LDH membrane in a mixed aqueous solution of piperazine and LDH nanosheets, filtering, and drying to obtain an LDH mesh membrane; The piperazine concentration in the mixed aqueous solution of piperazine and LDH nanosheets is 0.5-2wt.%, and the LDH nanosheet concentration is 0.025-0.1wt.%; (5) The LDH network membrane is immersed in a hexane solution of trimesoyl chloride to carry out a polymerization reaction, and then washed and dried to obtain an LDH nanonetwork-assisted polyamide nanofiltration membrane.

2. The method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 1, characterized in that: In step (1), the coating is glass glaze, the porous base membrane is an ultrafiltration membrane or a microfiltration membrane, the membrane material is one of aluminum oxide, titanium oxide or zirconium oxide, and the pore size of the porous base membrane is 0.1-1.0 μm.

3. The method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 1, characterized in that: The metal ions in the metal ion salt in step (2) include divalent metal ions and trivalent metal ions, wherein the divalent metal ions include Ni 2+ 、Zn 2+ 、Co 2+ , Cu 2+ , Ca 2+ , Mn 2+ or Mg 2+ One of the trivalent metal ions, including Cr 3+ , Fe 3+ or Al 3+ One of them.

4. The method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 1, characterized in that: In step (2), the stirring time is 30-50 min, the total metal ion concentration of the precursor solution is 30-80 mmol / L, the urea concentration is 50-140 mmol / L, the ammonium fluoride concentration is 100-200 mmol / L, the reaction temperature is 110-120° C., and the reaction time is 24-36 h.

5. The method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 1, characterized in that: In step (3), the organic solvent is anhydrous ethanol, the soaking time is 10-15 hours, and the drying is oven drying at 30-50°C.

6. The method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 1, characterized in that: In step (4), the filtration time is 5-20 minutes, and the drying is done at room temperature.

7. The method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 1, characterized in that: In step (5), the concentration of trimesoyl chloride in the n-hexane solution of trimesoyl chloride is 0.15-0.5wt.%, the polymerization reaction temperature is 35-65°C, the polymerization reaction time is 15-30min, the washing is 3-5 times of n-hexane solution washing; the drying is carried out by air knife drying and then placing in an oven, drying at 50-70°C for 5-20min.

8. An application of an LDH nanonetwork-assisted polyamide nanofiltration membrane prepared by the method for preparing an LDH nanonetwork-assisted polyamide nanofiltration membrane according to any one of claims 1 to 7, characterized in that: The LDH nano-network-assisted polyamide nanofiltration membrane is applied to the filtration of phosphorus-containing substances, comprising the following steps: (a) preparing a phosphorus-containing solution; (b) The LDH nanonetwork-assisted polyamide nanofiltration membrane is installed on the terminal filtration device to filter the phosphorus-containing solution.

9. Use of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared by the method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 8, characterized in that: In step (a), phosphorus includes H2PO4 - 、HPO4 2- or PO4 3- One or more of the above, the concentration of phosphorus solution is 20-1000 mgP / L.

10. Use of the LDH nanonetwork-assisted polyamide nanofiltration membrane prepared by the method for preparing the LDH nanonetwork-assisted polyamide nanofiltration membrane according to claim 8, characterized in that: The filtration pressure in step (b) is 0.2-0.6 MPa.

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