In-situ etching zif nanoparticle modified reverse osmosis membrane and preparation method thereof

Abstract

The application discloses an in-situ etching ZIF nanoparticle modified reverse osmosis membrane and a preparation method thereof. The reverse osmosis membrane is composed of an ultrafiltration membrane support layer, a polyamide layer, ZIF nanoparticles and nanogaps obtained after in-situ etching of the ZIF nanoparticles. First, an oil phase solution containing an acyl chloride monomer and ZIF nanoparticles is spread on the ultrafiltration membrane support layer treated by an amine monomer aqueous solution, and interfacial polymerization is carried out to obtain a membrane material containing ZIF nanoparticles. Then, a dimethylphenol orange disodium salt solution with a certain pH value is used to in-situ etch the ZIF nanoparticles in the membrane material to obtain the in-situ etching ZIF nanoparticle modified reverse osmosis membrane. The membrane material with the introduced ZIF nanoparticles is in-situ etched and modified, the prepared reverse osmosis membrane has high flux and high salt rejection performance, the preparation method is simple and easy to operate, and the reverse osmosis membrane has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reverse osmosis membranes, in particular to a reverse osmosis membrane modified by in-situ etching of ZIF nanoparticles and a preparation method thereof. BACKGROUND

[0002] In the existing development technology, the reverse osmosis (RO) based fresh water treatment technology is a key technology for producing fresh water from seawater / brackish water, which has the advantages of low energy consumption and simple operation, and has obtained wide attention.

[0003] The reverse osmosis membrane with polyamide as the selective functional layer obtained by interfacial polymerization of amine monomers and acyl chloride monomers on a porous support layer not only has advantages in separation performance, but also has good physical and chemical stability, and occupies a dominant position in the reverse osmosis membrane market. In order to improve the separation selectivity of the membrane, researchers try to embed titanium dioxide, silicon dioxide, metal-organic framework (MOF) and other nanoparticles in the polyamide layer to improve the water permeability of the membrane.

[0004] During the interfacial polymerization process, ZIF nanoparticles are introduced, which have good interfacial compatibility with polyamide and are not easy to produce non-selective defects. However, the water permeability and rejection performance of the reverse osmosis membrane always have a trade-off effect, so it is necessary to develop a modification method that can improve both the rejection performance and the water permeability of the membrane. SUMMARY

[0005] The purpose of the present application is to improve the performance of the original reverse osmosis membrane, and to provide a reverse osmosis membrane modified by in-situ etching of ZIF nanoparticles and a preparation method thereof.

[0006] The reverse osmosis membrane is composed of an ultrafiltration membrane support layer, a polyamide layer, ZIF nanoparticles and nanovoids obtained by in-situ etching of the ZIF nanoparticles. First, an oil phase solution containing acyl chloride monomers and ZIF nanoparticles is spread on the ultrafiltration membrane support layer treated with an amine monomer aqueous solution, and interfacial polymerization is carried out to obtain a membrane material containing ZIF nanoparticles. Then, a dimethylphenol orange disodium salt solution with a certain pH value is used to etch the ZIF nanoparticles in the above-mentioned membrane material in-situ, to produce more nanovoids in the polyamide membrane, and introduce defect ZIF-8 structures at the same time, thereby obtaining a reverse osmosis membrane modified by in-situ etching of ZIF nanoparticles.

[0007] The technical scheme of the present application is as follows:

[0008] A preparation method of a reverse osmosis membrane modified by in-situ etching of ZIF nanoparticles, the steps are as follows:

[0009] (1) After the ultrafiltration membrane support layer is cleaned with deionized water and dried, an aqueous solution containing an amine monomer is spread on the surface of the support layer, and kept for 1-10 min, then poured out and dried;

[0010] The ultrafiltration membrane support layer is prepared from one or more of polysulfone, polyethersulfone, polyether ketone, polyaryl sulfone, polyacrylonitrile, polyvinylidene fluoride;

[0011] The mass fraction of the amine monomer in the aqueous phase solution is 1-4wt%; the amine monomer is selected from one or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 4,4-diamino diphenyl ether, 4,4-diamino diphenyl methane, o-biphenyl methylamine, 1,2-propanediamine, 1,3-propanediamine, 2,4-diaminotoluene, 4,5-dichloro-o-phenylenediamine, m-phenyl triamine and derivatives thereof; and the aqueous phase solvent is water.

[0012] (2) The membrane material treated in step (1) is immersed in an organic phase solution containing acyl chloride monomers and ZIF nanoparticles for 10s-8min, and then taken out and dried;

[0013] The mass fraction of the acyl chloride monomer in the organic phase is 0.05-0.5wt%; the acyl chloride monomer is selected from one or more of m-phthaloyl chloride, p-phthaloyl chloride, o-phthaloyl chloride, trimesoyl chloride, polybasic aromatic sulfonyl chloride and derivatives thereof;

[0014] The organic phase solvent is a mixture of one or more of n-hexane, cyclohexane, toluene, benzene, ethyl acetate, dodecane, the drying temperature is 30-120℃, and the drying time is 2-30min.

[0015] The mass fraction of the ZIF nanoparticles is 0.01%-0.4wt%; the ZIF nanoparticles are one or more of ZIF-7, ZIF-8, ZIF-9, ZIF-67 and derivatives thereof;

[0016] Synthesis of ZIF nanoparticles: the metal precursor solution is mixed with the organic ligand solution, reacted at a certain temperature for 0.5-16h, then the nanoparticles are collected by centrifugation, washed, centrifuged and dried to obtain the ZIF nanoparticles; the metal precursor is selected from one or more of zinc chloride, zinc nitrate, zinc acetate, zinc oxide, cobalt chloride, cobalt nitrate, cobalt acetate, and the organic ligand is selected from one or more of 2-methylimidazole, benzimidazole and derivatives thereof; the molar ratio of the metal precursor to the organic ligand is 1:2-1:20, the solvent used is one or more of deionized water, methanol and DMF, and the reaction temperature is 10-80℃.

[0017] The drying temperature is 30-120℃, and the drying time is 2-30min.

[0018] (3) submerging the membrane material treated in step (2) in a dimethylphenol orange disodium salt solution with a certain pH value for a period of time, and then taking out and cleaning, to obtain a reverse osmosis membrane with ZIF nanoparticles in-situ etching modification;

[0019] The mass concentration of the dimethylphenol orange disodium salt is 0.5-3wt%, the pH value is 1.5-9, the pH value is regulated by hydrochloric acid, and the solvent is water.

[0020] Using the dimethylphenol orange disodium salt aqueous solution with a certain pH value can protonate the 2-methylimidazole ligand on the ZIF-8, thereby breaking the Zn-N bond and preferentially etching the

[100] and

[211] crystal planes with high density of Zn-MeIM bonds. Etching the ZIF-8 nanoparticles in the polyamide membrane using the dimethylphenol orange disodium salt aqueous solution can eliminate the crystal planes with high density of Zn-MeIM bonds in the ZIF-8, thereby generating more free volumes in the membrane and improving the membrane flux. At the same time, due to the p KfZn-XO = 6.15, the dimethylphenol orange disodium salt is easy to complex with the released zinc ions to form stable small fragment Zn-XO complexes retained in the membrane, thereby improving the salt rejection effect of the reverse osmosis membrane.

[0021] The present application in-situ etches and modifies the membrane material with introduced ZIF nanoparticles, introduces additional nano voids without causing defects in the polyamide layer, and regulates the ion rejection of the composite membrane by introducing defective ZIF-8 structures, thereby further improving the sodium chloride rejection rate while improving the water permeability.

[0022] The reverse osmosis membrane with in-situ etching modification of ZIF nanoparticles of the present application not only maintains high rejection rate, but also has a water flux of 39.78 LMH, which is increased by nearly 60% compared with the unmodified reverse osmosis membrane, and the salt rejection rate is also slightly improved.

[0023] The present application has the following beneficial effects:

[0024] On the basis of introducing ZIF nanoparticles into the reverse osmosis membrane, the nanoparticles in the membrane are further etched, so that the modified membrane has more nano voids, and the defective ZIF-8 affects the ion diffusion in the membrane, thereby further improving the sodium chloride rejection rate while improving the water permeability. The prepared reverse osmosis membrane has high flux and high salt rejection performance, and the preparation method is simple and easy to operate, and can be applied to the fields of domestic water purification, industrial wastewater treatment, seawater desalination, etc., and has good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a preparation flowchart of the membrane;

[0026] Figure 2are the plane scanning electron micrographs of Example 2 and Comparative Example 1. It can be observed that the surface of Comparative Example 1 has the typical leaf-like structure of aromatic polyamide reverse osmosis membranes, while the surface of Example 2 has a weakened leaf-like structure and is more smooth;

[0027] Figure 3 are the zinc element EDS scanning graphs of Example 2 and Comparative Example 2. It can be observed that the surface of Example 2 has less zinc element than Comparative Example 2, indicating that Example 2 etched away part of the ZIF-8;

[0028] Figure 4 are the reverse osmosis performance comparison graphs of the examples and the comparative examples. Referring to Comparative Example 1, the water flux and the rejection rate of the examples are both increased, while the water flux of Comparative Example 2 is increased, but at the same time, the salt rejection rate is decreased. DETAILED DESCRIPTION

[0029] The present application will be further described by specific examples, but the protection scope of the present application is not limited to this. Any changes within the content and scope of the present application shall be included in the technical scope of the present application.

[0030] The preparation environment of all the reverse osmosis membranes in the examples is: temperature 25℃, relative humidity 40-60%, normal pressure.

[0031] Example 1: In-situ etching of ZIF-8 nanoparticles to modify reverse osmosis membranes

[0032] (1) 3g of zinc acetate and 11.2g of 2-methylimidazole were dissolved in 50ml of deionized water respectively, and after stirring and mixing for a few seconds, they were left to stand at room temperature 25℃ for 3.5h, centrifuged, washed and dried to obtain powder-like ZIF-8 nanoparticles for standby use.

[0033] (2) 2.4wt% m-phenylenediamine aqueous solution was spread on a polysulfone ultrafiltration membrane (purchased from Hangzhou Water Treatment Technology Research and Development Center) with a polyester support layer, and after immersion for 3min, the solution was poured off and the excess solution was removed by air blowing;

[0034] (3) 0.12wt% of trimesoyl chloride n-hexane solution containing 0.06wt% of ZIF-8 nanoparticles was spread on the above treated membrane material, and after interfacial polymerization for 60s, the membrane was placed in a 60℃ oven for 10min and taken out;

[0035] (4) The obtained membrane was etched in a 1wt% dimethylphenol orange disodium salt solution with pH=2.5 for 6h, taken out, washed clean and stored in deionized water until testing.

[0036] The membrane obtained in Example 1 was analyzed and tested:

[0037] The reverse osmosis membrane prepared in this example was installed in a membrane performance testing device, and the experimental conditions were: 1.6 MPa, pre-pressing for 1 h, 2000 ppm NaCl salt solution; the test results were: water flux: 39.78 LMH, salt rejection: 98.88%.

[0038] Example 2

[0039] With reference to Example 1, the difference is that the etching time in step (3) is changed to 9 h.

[0040] The membrane testing conditions are the same as in Example 1, and the test results are: water flux: 37.29 LMH, salt rejection: 99.25%.

[0041] Comparative Example 1

[0042] (1) A 2.4 wt% aqueous m-phenylenediamine solution was spread on a polysulfone ultrafiltration membrane with a polyester support layer, and after immersion for 3 min, the solution was poured off and the excess solution was removed by air blowing;

[0043] (2) A 0.12 wt% trimesoyl chloride n-hexane solution was spread on the above-processed membrane material, and after interfacial polymerization for 60 s, the membrane was placed in a 60°C oven for 10 min, and then taken out to obtain a blank control membrane;

[0044] The membrane testing conditions are the same as in Example 1, and the test results are: water flux: 24.75 LMH, salt rejection: 98.83%.

[0045] Comparative Example 2

[0046] With reference to Comparative Example 1, the difference is that in step (2), the 0.12 wt% trimesoyl chloride n-hexane solution is replaced by a 0.12 wt% trimesoyl chloride n-hexane solution containing 0.06 wt% ZIF-8 nanoparticles.

[0047] The membrane testing conditions are the same as in Example 1, and the test results are: water flux: 34.66 LMH, salt rejection: 98.36%.

[0048] Comparative Example 3

[0049] With reference to Comparative Example 1, the difference is that the membrane obtained in step (2) is placed in a 1 wt% xylenol orange disodium salt solution with a pH of 2.5 for 6 h, taken out, washed clean, and stored in deionized water until testing.

[0050] The membrane testing conditions are the same as in Example 1, and the test results are: water flux: 25.38 LMH, salt rejection: 98.98%.

Claims

1. A method for preparing a reverse osmosis membrane modified with ZIF nanoparticles through in-situ etching, characterized in that, Includes the following steps: (1) Synthesis of ZIF nanoparticles: The metal precursor solution and the organic ligand solution were mixed and reacted for 0.5-16 h. Then, the nanoparticles were collected by centrifugation, washed, centrifuged, and dried to obtain ZIF nanoparticles. The metal precursor solution contains a metal precursor selected from one or more of zinc chloride, zinc nitrate, zinc acetate, and zinc oxide, and the organic ligand solution contains an organic ligand selected from one or more of 2-methylimidazole and its derivatives. (2) Preparation of reverse osmosis membrane by interfacial polymerization reaction: Amine monomers are dissolved in deionized water to prepare an aqueous solution, acyl chloride monomers and ZIF nanoparticles prepared in step (1) are dissolved in an organic solvent to prepare an oil solution, the aqueous solution is spread on the ultrafiltration membrane support layer for 1-10 min, the excess solution on the surface is poured out and removed, the oil solution is spread on the membrane material for interfacial polymerization for 10 s-8 min, the excess solution is poured out and dried to obtain a reverse osmosis membrane doped with ZIF nanoparticles; (3) In-situ etching of ZIF nanoparticles in the membrane: The reverse osmosis membrane doped with ZIF nanoparticles obtained in step (2) is immersed in a solution of disodium xylenol orange for 1-18 hours, taken out, cleaned and stored in deionized water to obtain a reverse osmosis membrane modified by in-situ etching of ZIF nanoparticles.

2. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 1, characterized in that, The in-situ etched ZIF nanoparticle modified reverse osmosis membrane is composed of an ultrafiltration membrane support layer, a polyamide layer, ZIF nanoparticles, and nanopores, wherein the nanopores are obtained by in-situ etching of the ZIF nanoparticles in the membrane.

3. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 2, characterized in that, The ultrafiltration membrane support layer is made of one or more of the following: polysulfone, polyethersulfone, polyetherketone, polyarylsulfone, polyethylene, polyacrylonitrile, and polyvinylidene fluoride. The polyamide layer is obtained by interfacial polymerization of aqueous amine monomers and oil-phase acyl chloride monomers. The ZIF nanoparticles are one or more of ZIF-8 and its derivatives; The nanopores are obtained by in-situ etching of ZIF nanoparticles in the film using an etching solution.

4. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 1, characterized in that, In step (2), the molar ratio of the metal precursor to the organic ligand is 1:2-1:20, the solvent used is one or more of deionized water, methanol, and DMF, and the reaction temperature is 10-80℃.

5. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 1, characterized in that, In step (2), the amine monomer is selected from one or more combinations of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 4,4-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, o-phenylenediamine, 1,2-propanediamine, 1,3-propanediamine, 2,4-diaminotoluene, 4,5-dichloro-o-phenylenediamine, pyromellitic triamine and their derivatives, and the aqueous solvent is water.

6. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 1, characterized in that, In step (2), the acyl chloride monomer is selected from one or more of isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, trimesoyl chloride, polyaryl aromatic sulfonyl chloride and their derivatives; The organic solvent is one or a mixture of several of the following: n-hexane, cyclohexane, toluene, benzene, ethyl acetate, and dodecane.

7. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 1, characterized in that, In step (2), the mass fraction of ZIF nanoparticles in the oil phase solution is 0.01~0.4 wt%.

8. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 1, characterized in that, In step (2), the drying temperature is 30-120℃ and the drying time is 2-30 min.

9. The method for preparing an in-situ etched ZIF nanoparticle-modified reverse osmosis membrane as described in claim 1, characterized in that, In step (3), the mass fraction of disodium xylenol in the xylenol orange disodium salt aqueous solution is 0.5-3 wt%, and the pH of the xylenol orange disodium salt aqueous solution is adjusted by hydrochloric acid, with a pH value of 1.5-9.

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