Metal organic framework nanosheet interlayer forward osmosis membrane and method of making same

Abstract

The application discloses a kind of metal organic framework nanosheet sandwich positive osmosis membranes and preparation method thereof, the metal organic framework nanosheet sandwich positive osmosis membrane is the sandwich structure of base film, Zr-BTB metal organic framework nanosheet and polyamide layer;Wherein, the surface of the base film is loaded with the Zr-BTB metal organic framework nanosheet, the surface of the Zr-BTB metal organic framework nanosheet is polymerized with the polyamide layer.The technical scheme of the present application, the existence of sandwich can slow down the diffusion rate of amine monomer, avoid the collapse of separation layer, beneficial to form thin and defect-free separation layer;In addition, large-size metal organic framework nanosheet with uniform porosity as sandwich has the advantages of 3D nanomaterial and 2D nanomaterial, which can ensure that the sandwich material remains stable during the formation of the separation layer, and can also utilize the unique hydrophilic functional groups on the material to form more water channels in the separation layer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane separation, and particularly relates to a metal organic framework nanosheet sandwich forward osmosis membrane and a preparation method thereof. BACKGROUND

[0002] With the great change of energy use, electricity becomes the main power source in the future, which significantly improves the application value of lithium in the energy field.

[0003] The lithium reserves in salt lake brine are rich, but the development is insufficient; this is mainly due to the generally low lithium concentration in the brine, and the lithium product can be obtained by precipitation only after further concentration treatment after preliminary purification of the brine, and the development is difficult. Based on the above situation, lithium concentration directly affects the product quality and the overall cost, and is the key bottleneck for lithium extraction from low-grade lithium brine; breaking through the bottleneck of lithium extraction from brine and accelerating lithium resource development have great significance for promoting effective utilization of resources. In recent years, forward osmosis technology has developed rapidly and attracted widespread attention. Compared with traditional pressure-driven membrane separation technology, it has the characteristics of low energy consumption and low pollution, and has potential application value in the lithium extraction and concentration stage of brine.

[0004] The FO membrane currently studied is mainly a thin film composite (TFC) membrane, which is prepared by cross-linking polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) on a base film to form a dense polyamide layer (separation layer). The existing conventional forward osmosis membrane is composed of a support layer and a separation layer, and the separation layer which plays a key role in separation and concentration is generally formed by cross-linking reaction of amine monomers in water phase and acyl chloride organic phase on the surface of the support layer.

[0005] In the formation process of the separation layer of the above-mentioned conventional forward osmosis membrane, the amine monomers on the surface of the support layer can quickly diffuse to the organic phase and react with the acyl chloride monomers without hindrance; it is proved by the Freger kinetic model that the third power of the diffusion rate of the amine monomers is proportional to the thickness of the separation layer; therefore, the rapid diffusion of the amine monomers causes the formation of a thick separation layer of the conventional forward osmosis membrane, the water molecule permeation resistance increases, and the water flux is low. In addition, the formed separation layer is easy to collapse at the large-size pores of the support layer, forming non-selective defects, which causes the reduction of lithium ion recovery rate.

[0006] In view of the above prior art defects, constructing a nanomaterial interlayer is the key to regulating the diffusion rate of amine monomers and obtaining an ultra-thin defect-free forward osmosis membrane; however, 1D and 3D nanomaterials (for example, SiO2, MOFs, etc.) as the interlayer, the spatial structure of the material determines the limited contact area with the support layer and the separation layer, making it difficult for the interlayer to maintain stability in the separation membrane, and the separation layer is prone to collapse during the formation of the separation layer, thereby causing defects in the separation layer; typical 2D nanomaterials (for example, GO, MXene, etc.) have higher stability in the separation membrane due to their larger surface size, but their surfaces do not have water molecule permeation channels, which adversely affect the water permeability of the separation membrane. SUMMARY

[0007] The purpose of the present application is to provide a metal organic framework nanosheet interlayer forward osmosis membrane and a preparation method thereof to solve one or more of the above technical problems.

[0008] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0009] The metal organic framework nanosheet interlayer forward osmosis membrane provided by the present application is a sandwich structure composed of a base film, Zr-BTB metal organic framework nanosheets and a polyamide layer.

[0010] The surface of the base film is loaded with the Zr-BTB metal organic framework nanosheets, and the surface of the Zr-BTB metal organic framework nanosheets is polymerized with the polyamide layer.

[0011] The preparation method of the metal organic framework nanosheet interlayer forward osmosis membrane provided by the present application comprises the following steps:

[0012] Obtain an aqueous solution of a small molecule diamine monomer, an organic phase solution of a polyacyl chloride and a base film with Zr-BTB metal organic framework nanosheets deposited on the surface;

[0013] Soak the base film with Zr-BTB metal organic framework nanosheets deposited on the surface in the aqueous solution of the small molecule diamine monomer for a first predetermined time, remove the excess liquid and air dry to obtain an air-dried base film;

[0014] Soak the air-dried base film in the organic phase solution of the polyacyl chloride for a second predetermined time to form a polyamide layer through interfacial polymerization, and obtain a metal organic framework nanosheet interlayer forward osmosis membrane.

[0015] The further improvement of the preparation method is that,

[0016] In the aqueous solution, the small molecule diamine monomer is m-phenylenediamine, piperazine or dopamine;

[0017] The polybasic acid chloride in the organic phase solution is trimesoyl chloride, and the organic solvent is n-hexane.

[0018] The material of the base film is nylon, polyether sulfone or polyvinylidene fluoride.

[0019] The further improvement of the preparation method is that,

[0020] The mass percentage concentration of the small molecule diamine monomer in the aqueous phase solution is 1.5% to 3%;

[0021] The mass percentage concentration of the polybasic acid chloride in the organic phase solution is 0.15% to 0.3%;

[0022] In the base film with the Zr-BTB metal organic framework nanosheet deposited on the surface, the content of the Zr-BTB metal organic framework nanosheet is 0.003980 mg / cm 2 ~ 0.015923 mg / cm 2 ;

[0023] The first preset time length is 3 min to 10 min;

[0024] The second preset time length is 45 s to 60 s.

[0025] The further improvement of the preparation method is that, after the base film after airing is soaked in the organic phase solution of the polybasic acid chloride and kept for a second preset time length to occur an interfacial polymerization reaction to form a polyamide layer and obtain a metal organic framework nanosheet sandwiched forward osmosis membrane, the method further includes:

[0026] The metal organic framework nanosheet sandwiched forward osmosis membrane is heat treated at 45 DEG C to 85 DEG C for 1 min to 6 min to obtain a final metal organic framework nanosheet sandwiched forward osmosis membrane.

[0027] The further improvement of the preparation method is that, the obtaining step of the base film with the Zr-BTB metal organic framework nanosheet deposited on the surface includes:

[0028] Obtaining Zr-BTB metal organic framework nanosheet;

[0029] Based on the aqueous solution of Zr-BTB metal organic framework nanosheet, the Zr-BTB metal organic framework nanosheet is deposited on the surface of the base film by vacuum filtration to obtain the base film with the Zr-BTB metal organic framework nanosheet deposited on the surface;

[0030] The step of obtaining Zr-BTB metal organic framework nanosheet includes:

[0031] The benzoic acid is dissolved in dimethylformamide at room temperature, and then zirconium tetrachloride, 1,3,5-tricarboxybenzene benzoic acid and ultrapure water are added after ultrasonic treatment for the first time, and a mixed solution is obtained after ultrasonic treatment for the second time;

[0032] The obtained mixed solution is placed at a temperature of 85-175 DEG C for 14-52 hours to obtain an initial metal organic framework nanosheet accumulation body;

[0033] The initial metal organic framework nanosheet accumulation body is washed and peeled off by ultrasonic treatment and centrifugation to obtain Zr-BTB metal organic framework nanosheets.

[0034] Further improvement of the preparation method is that, in the step of depositing the Zr-BTB metal organic framework nanosheets on the surface of the base film by vacuum filtration to obtain the base film with the Zr-BTB metal organic framework nanosheets deposited on the surface, the pressure of vacuum filtration is 0.01-0.06 MPa.

[0035] Further improvement of the preparation method is that, in the step of dissolving the benzoic acid in dimethylformamide at room temperature, adding zirconium tetrachloride, 1,3,5-tricarboxybenzene benzoic acid and ultrapure water after ultrasonic treatment for the first time, and obtaining a mixed solution after ultrasonic treatment for the second time,

[0036] The mass ratio of zirconium tetrachloride to benzoic acid is 1:(35-75);

[0037] The volume ratio of ultrapure water to dimethylformamide is greater than 0 and less than or equal to 0.19;

[0038] The mass ratio of zirconium tetrachloride to 1,3,5-tricarboxybenzene benzoic acid (H3BTB) is 1:(1-1.5);

[0039] The ultrasonic treatment time for the first time is 1-2 hours;

[0040] The ultrasonic treatment time for the second time is 15-45 minutes.

[0041] Further improvement of the preparation method is that, in the step of washing and peeling off the initial metal organic framework nanosheet accumulation body by ultrasonic treatment and centrifugation to obtain Zr-BTB metal organic framework nanosheets, the step includes:

[0042] The first-stage washing includes: dispersing the initial metal organic framework nanosheet accumulation body in dimethylformamide, and washing by ultrasonic treatment and centrifugation to obtain a washed accumulation body;

[0043] The second stage washing comprises: placing the washed accumulation body in a methanol solution, washing through ultrasonic and centrifugation, and obtaining a clean accumulation body;

[0044] The peeling comprises: placing the clean accumulation body in a methanol solution, peeling the nanosheet through ultrasonic and centrifugation, and obtaining a metal organic framework nanosheet;

[0045] In the first stage washing, the form of the dimethylformamide dispersion liquid is replaced repeatedly for multiple times.

[0046] The further improvement of the preparation method of the application is that, in the steps of the first stage washing, the second stage washing and the peeling, the ultrasonic time is 45 min to 60 min, the ultrasonic power is 15000 Hz to 24000 Hz, the centrifugal speed is 3500 r / min to 8000 r / min, and the centrifugal time is 3 min to 10 min.

[0047] Compared with the prior art, the metal organic framework nanosheet sandwiched positive osmosis membrane has the advantages at least including:

[0048] The metal organic framework nanosheet sandwiched positive osmosis membrane provided by the application has the advantages that, on one hand, the existence of the sandwiched layer slows down the diffusion rate of the amine monomer, avoids the collapse of the separation layer, and is beneficial to the formation of a thin and defect-free separation layer; on the other hand, the large-size metal organic framework nanosheet with uniform pores as the sandwiched layer has the advantages of both 3D nanomaterials and 2D nanomaterials, can ensure that the sandwiched layer material remains stable during the formation of the separation layer, and can form more water channels in the separation layer by using the unique hydrophilic functional groups on the material.

[0049] The separation layer of the traditional positive osmosis membrane is formed on the surface of the support layer with large pore size, and the separation layer has the disadvantages of high thickness and many non-selective pores. In the preparation method of the application, a sandwiched layer of nanosheet-shaped material is formed on the surface of the support layer with large pore size by pre-depositing the metal organic framework nanosheet on the surface of the support layer, so as to reduce the disadvantages of the non-selective pores of the positive osmosis membrane. Similarly, the interlayer spacing between the nanosheet-shaped materials can better store the amine monomer, and the ultra-small porosity can better control the release rate of the amine monomer and thus control the thickness of the separation layer. In summary, the metal organic framework nanosheet is added in the membrane preparation method of the application, the preparation process is simple, convenient and low in cost, the prepared positive osmosis membrane significantly improves the water flux and the ion recovery performance, can solve the problems of low water flux and poor ion recovery performance of the existing traditional positive osmosis membrane, and avoids the disadvantage of insufficient stability of the traditional 3D sandwiched positive osmosis membrane.

[0050] In the present application, the metal organic framework nanosheet as the interlayer has uniform pores, intercepts ions while allowing water molecules to pass through, and is conducive to improving water flux; the metal organic framework nanosheet has a uniform pore structure, with a zirconium metal cluster as a center and 1,3,5-tris(carboxyphenyl)benzoic acid (H3BTB) as a ligand The ultra-small pore structure ensures that the prepared metal organic framework nanosheet interlayer composite membrane has a suitable and uniform pore size, which not only ensures that water molecules and lithium ions can smoothly pass through the membrane pores, but also ensures that other impurity ions are intercepted, thereby ensuring a higher lithium ion concentration function and a greater water flux. The metal organic framework nanosheet prepared in the present application has a high aspect ratio; the large-size metal organic framework nanosheet ensures that the material has a larger contact area with the support layer under the condition of a small amount of material addition, thereby avoiding the problem of positive osmosis membrane defects caused by the collapse of the separation layer; the stability and specific functional groups of the metal organic framework nanosheet can be used to regulate the interfacial polymerization process, thereby greatly reducing the thickness of the separation layer under the premise of ensuring the integrity of the separation layer; the effective contact area of the larger separation layer and the support layer is increased, and compared with the three-dimensional interlayer material which is prone to agglomeration and causes a large change in thickness, thereby causing a large spacing between the separation layer and the support layer, the positive osmosis membrane prepared by the method greatly improves the interlayer stability. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following briefly introduces the drawings needed to be used in the embodiments or prior art description; obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0052] Figure 1 is a flowchart of a method for preparing a metal organic framework nanosheet interlayer positive osmosis membrane for ion concentration provided by an embodiment of the present application;

[0053] Figure 2 is an atomic force microscope picture of a nanosheet material in an embodiment of the present application;

[0054] Figure 3 is a scanning electron microscope picture of a membrane in Comparative Example 1;

[0055] Figure 4 is a scanning electron microscope picture of a membrane in Example 2 of the present application. DETAILED DESCRIPTION

[0056] The present application will be further described below in conjunction with specific embodiments, and it should be understood that these embodiments are only used to illustrate the present application and not to limit the protection scope of the present application.

[0057] Those skilled in the art will readily understand from the disclosure herein the advantages and benefits of the present application. The present application can be practiced in additional and / or different ways than those specifically described herein without departing from the spirit of the present application, and the full scope of equivalents made to the claims is intended to be covered.

[0058] It should be noted that the process equipment or device not specifically mentioned in the following examples is the conventional equipment or device in the art.

[0059] It should be understood that the one or more method steps mentioned in the present application do not exclude the presence of other method steps before and after the combination step or the insertion of other method steps between the explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between the one or more devices / apparatuses mentioned in the present application does not exclude the presence of other devices / apparatuses before and after the combination device / apparatus or the insertion of other devices / apparatuses between the two explicitly mentioned devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool to identify each method step, and is not intended to limit the arrangement order of each method step or to limit the scope of the present application, and the change or adjustment of the relative relationship, without substantial change of the technical content, is also considered as the scope of the present application.

[0060] The metal organic framework nanosheet sandwich forward osmosis membrane for ion concentration in the embodiment of the present application is a sandwich structure, comprising a base film, Zr-BTB metal organic framework nanosheets loaded on the surface of the base film, and a PA (polyamide) layer polymerized on the surface of the Zr-BTB metal organic framework nanosheets. In the preferred scheme, the Zr-BTB metal organic framework nanosheets are 1-3 layers.

[0061] In the embodiment of the present application, the metal organic framework nanosheet is used as a sandwich layer, which has uniform pores, intercepts ions and allows water molecules to pass through, which is beneficial to improve water flux.

[0062] Please refer to Figure 1 The preparation method of the metal organic framework nanosheet sandwich forward osmosis membrane for ion concentration provided in the embodiment of the present application comprises the following steps:

[0063] Step 1, obtaining a water phase solution of small molecule diamine monomers, an organic phase solution of polyacyl chloride and a base film with metal organic framework nanosheets deposited on the surface; wherein in the water phase solution, the small molecule diamine monomers are m-phenylenediamine, piperazine or dopamine; the mass percentage concentration of the small molecule diamine monomers is 1.5% to 3%; in the organic phase solution, the polyacyl chloride is trimesoyl chloride, and the organic solvent is n-hexane; the mass percentage concentration of the polyacyl chloride is 0.15% to 0.3%; the material of the base film is nylon, polyether sulfone or polyvinylidene fluoride; in the base film with metal organic framework nanosheets deposited on the surface, the material content of the metal organic framework nanosheet Zr-BTB nanomaterial is 0.003980 mg / cm 2 ~ 0.015923 mg / cm 2 ;

[0064] Step 2, soaking the base film with metal organic framework nanosheets deposited on the surface in the water phase solution of small molecule diamine monomers for a first preset time, removing excess liquid and air-drying to obtain an air-dried base film; for example, the first preset time can be 3 min to 10 min, and the air-drying can be air-drying in air;

[0065] Step 3, soaking the air-dried base film in the organic phase solution of polyacyl chloride for a second preset time to occur interfacial polymerization and form a separation layer, and obtaining a metal organic framework nanosheet sandwiched forward osmosis membrane for ion concentration; for example, the second preset time can be 45 s to 60 s. For explanation, the time is set to ensure that the organic phase solution fully soaks and wets the membrane under the condition of reducing the interfacial polymerization time with the water phase solution.

[0066] In a further preferred technical solution of the embodiment of the application, after step 3, it further comprises:

[0067] Step 4: heat treating the membrane after interfacial polymerization in step 3 at 45℃ to 85℃ for 1 min to 6 min to promote the interfacial polymerization reaction to be more rapid and stable. For explanation, this step is to increase the molecular thermal motion and accelerate the interfacial polymerization reaction; the control time ensures that the newly formed PA layer reduces the influence of temperature and produces defects.

[0068] The embodiment of the present application is specifically exemplified, in step 1, the obtaining step of the base film on which the metal organic framework nanosheet is deposited includes: mixing the nanomaterial into an aqueous solution, stripping the metal organic framework nanosheet into supernatant by ultrasonic centrifugation and pre-depositing on the surface of the base film by vacuum suction filtration; the pressure of the vacuum suction filtration can be 0.01-0.06 Mpa. Specifically, an appropriate amount of metal organic framework nanosheet can be dispersed in 100 ml of ultrapure water, and the mixed solution is ultrasonically dispersed at 15000 Hz-24000 Hz for 30 min to uniformly disperse the nanomaterial in the solution.

[0069] In the embodiment of the present application, the step of obtaining the metal organic framework nanosheet includes:

[0070] In step 1, benzoic acid is dissolved in dimethylformamide at room temperature, and ultrasonic is performed once; zirconium tetrachloride, 1,3,5-tris(carboxyphenyl) benzoic acid (H3BTB) and ultrapure water are added, and ultrasonic is performed twice to obtain a mixed solution; wherein the mass ratio of zirconium tetrachloride to benzoic acid is 1:(35-75); the volume ratio of ultrapure water to dimethylformamide is (0, 0.19]; the mass ratio of zirconium tetrachloride to 1,3,5-tris(carboxyphenyl) benzoic acid (H3BTB) is 1:(1-1.5); specifically, the first ultrasonic time is 1 h-2 h, and the second ultrasonic time is 15 min-45 min;

[0071] In step 2, the obtained mixed solution is placed at 85℃-175℃, and reacted for 14 h-52 h to obtain an initial metal organic framework nanosheet accumulation body; preferably, after the heating process is completed, the material can be taken out from the oven only after the oven temperature is reduced to room temperature, so as to avoid the generation of defective materials due to large temperature change;

[0072] Step 3, the initial metal organic framework nanosheet accumulation body is dispersed into dimethylformamide, ultrasonic, centrifugal washing is carried out once, and the washed accumulation body is obtained, this step can be repeated multiple times by changing the form of dimethylformamide dispersion liquid; the washed accumulation body is placed in a methanol solution, ultrasonic, centrifugal washing is carried out twice, and the clean accumulation body is obtained; the clean accumulation body is placed in a methanol solution, ultrasonic, centrifugal nanosheet peeling is carried out, and the metal organic framework nanosheet is obtained. The power of ultrasonic is 15000 Hz-24000 Hz; the time of ultrasonic is 45 min-60 min. When the first washing is carried out, the rotation speed of centrifugal is 3500 r / min-8000 r / min; when the second washing is carried out, the rotation speed of centrifugal is 3500 r / min-8000 r / min; when the nanosheet peeling is carried out, the rotation speed of centrifugal is 3500 r / min-8000 r / min; the time of high-speed centrifugal machine can be 3 min-10 min. Illustratively, the metal organic framework nanosheet in step 3 is peeled from the accumulation body in step two, and the method is to use a specific ultrasonic frequency and time and high-speed centrifugal rotation speed; the accumulation body of the metal organic framework nanosheet is ultrasonic and centrifugal multiple times, and the unreacted benzoic acid and dimethylformamide can be removed before dispersing the sheet-shaped material. Illustratively, the washing can be carried out on a 0.22 um membrane. The product can be referred to Figure 2 .

[0073] The metal organic framework nanosheet prepared in the application has a high aspect ratio; the extremely low longitudinal size of the nanomaterial is ensured, the thickness is only 2-5 nm in the measurement of an atomic force microscope, and the maximum transverse size can reach 10 um. The large-size metal organic framework nanosheet ensures that the material has a larger contact area with the support layer under the condition of a small amount of material addition, avoids the problem of defects of the forward osmosis membrane caused by the collapse of the separation layer, can control the process of interfacial polymerization by using the stability and specific functional groups of the metal organic framework nanosheet, greatly reduces the thickness of the separation layer under the premise of ensuring the integrity of the separation layer, increases the effective contact area of the larger separation layer and support layer, and compared with the three-dimensional sandwich material which is easy to agglomerate and causes a large thickness change and a large spacing between the separation layer and the support layer, the forward osmosis membrane prepared by the method greatly improves the interlayer stability.

[0074] The metal organic framework nanosheet takes zirconium metal clusters as the center and 1,3,5-tri(carboxyphenyl) benzoic acid (H3BTB) as the ligand, forms a uniform pore structure, and the metal organic framework nanosheet has super-small pores The super-small pore structure ensures that the prepared metal organic framework nanosheet sandwich composite membrane has a suitable and uniform pore size, which can not only ensure that water molecules and lithium ions can smoothly pass through the membrane pores, but also can intercept other impurity ions, so that the water flux is larger under the condition of ensuring the function of more efficient lithium ion concentration.

[0075] The separation layer of the conventional forward osmosis membrane is formed on the surface of the support layer with a large pore size, and the separation layer has the disadvantages of high thickness and many non-selective pores; the metal organic framework nanosheet is pre-deposited on the surface of the support layer to form a sandwich layer of nanosheet-shaped material on the surface of the support layer with a large pore size, so that the disadvantages of many non-selective pores of the forward osmosis membrane are reduced; similarly, the interlayer spacing between the nanosheet-shaped material can better store amine monomers, and the super-small porosity can better control the release rate of the amine monomers, so as to control the thickness of the separation layer.

[0076] The embodiment of the present application specifically provides a preparation method of Zr-BTB metal organic framework nanosheet for ion concentration, comprising the following steps:

[0077] At room temperature, 6.6g of benzoic acid is dissolved in 30ml of dimethylformamide (DMF) and ultrasonicated (1h-2h), then 0.11g of zirconium chloride and 0.11g of 1,3,5-tris (carboxyphenyl) benzoic acid (H3BTB) are added and ultrasonicated (15min-45min), 3mL-10mL of pure water is added to improve the crystallinity of the product and better control the growth trend, the mixed solution is placed in a 100ml reaction kettle and placed in a 120℃ oven for reaction for 36h, then naturally cooled to room temperature, and the unreacted benzoic acid and dimethylformamide are filtered off; and repeatedly washed with dimethylformamide (DMF) and methanol; the washed solid is distributed in methanol and DMF and washed and peeled off under a specific ultrasonic frequency. The accumulated body and the metal organic framework sheet are separated by using a high-speed centrifuge. Finally, the metal organic framework sheet is dispersed in methanol and sealed for storage.

[0078] The test conditions of the prepared membrane include: using deionized water as the raw liquid, 1mol / L NaCl as the draw liquid, and testing the performance of the prepared forward osmosis membrane under the condition that the membrane surface flow rate is 12.5cm / s at room temperature, the water flux J V And the reverse salt flux J S are calculated according to the following formula respectively:

[0079]

[0080] In the formula, △V represents the permeation volume (L), A eff represents the effective area of the membrane (m2), C t represents the salt concentration on the raw water side t time (g / L), V tVolume (L) of t time on the raw water side, and △t represents the permeation time (h).

[0081] The lithium ion rejection rate (R) and lithium ion concentration factor (fc) of different membranes were calculated using 2 mol / L sodium chloride as the draw solution and a lithium chloride solution with a lithium ion concentration of 2000 mg / L as the raw material solution.

[0082]

[0083] In the formula, C d is the final Li + concentration (mg / L) of the draw solution, V d is the final volume (L) of the draw solution, C0 is the Li + treatment concentration (mg / L) of the raw material solution, V p is the permeation volume (L), and C t is the final lithium ion concentration (mg / L) of the raw material solution. + The lithium ion concentration was tested by inductively coupled plasma emission spectrometry (ICP).

[0084] In the preparation process of the embodiment of the application, metal organic framework nanosheets are added, the preparation process is simple, the cost is low, the prepared forward osmosis membrane significantly improves the water flux, reduces the reverse salt flux, and increases the pollutant removal performance.

[0085] In the preparation method of the metal organic framework nanosheet sandwiched forward osmosis membrane for ion concentration provided in the embodiment of the application, the metal organic framework nanosheets are peeled from the top to the bottom of a metal organic framework nanosheet accumulation body; compared with 3D materials, the metal organic framework nanosheets can be better distributed on the surface of the membrane to effectively avoid material agglomeration. In addition, the metal organic framework nanosheet Zr-BTB with super-small pores is formed by the coordination between zirconium ions and 1,3,5-tris(carboxyphenyl) benzoic acid (H3BTB). The metal organic framework nanosheet Zr-BTB is uniformly distributed and fixed in the separation layer of the forward osmosis membrane through the action of interfacial polymerization, and a metal organic framework nanosheet sandwiched forward osmosis membrane for ion concentration is prepared.

[0086] Comparative Example 1

[0087] Please refer to Figure 3 The base membrane is a flat plate type ultrafiltration membrane made of nylon material, the base membrane is immersed in a 2.3% m / m m-phenylenediamine aqueous phase solution for 4 min, dried, then 0.2% m / m trimesoyl chloride organic phase solution is poured on the surface of the base membrane, the excess organic phase solution is poured off after 60 s, and finally heat treatment is carried out at 60 DEG C for 2 min.

[0088] The prepared forward osmosis membrane is evaluated, the flow rate of both sides of the membrane surface is 12.5 cm / s, the feed liquid is deionized water, the draw liquid is 1 mol / L sodium chloride solution, and the test is carried out at room temperature for 30 min; the water flux of the prepared forward osmosis membrane is 13.7 L / (m 2 .h), and the reverse salt flux is 1.5793 g / (m 2 .h). The ion concentration experiment is carried out, and 2000 mg / L Li + solution is used as the raw material liquid, and 1 mol / L sodium chloride solution is used as the draw liquid.

[0089] Example 1

[0090] Based on the preparation method of the forward osmosis membrane in Comparative Example 1, the difference is that the metal organic framework nanosheet is dispersed into the organic phase solution by ultrasonic for 30 min, and the content of the metal organic framework nanosheet is (0.05 mg); the average water flux of the forward osmosis membrane is 19.58 LMH, and the reverse salt flux is 1.104 g MH; the ion concentration experiment is carried out, and 2000 mg / L Li + solution is used as the raw material liquid, and 1 mol / L sodium chloride solution is used as the draw liquid.

[0091] Example 2

[0092] Please refer to Figure 4 , based on the preparation method of the forward osmosis in Example 1 of the application, the content of the metal organic framework nanosheet is 0.1 mg. The average water flux of the forward osmosis membrane is 23.62 LMH, and the reverse salt flux is 0.736 g MH; the ion concentration experiment is carried out, and 2000 mg / L Li + solution is used as the raw material liquid, and 1 mol / L sodium chloride solution is used as the draw liquid.

[0093] Example 3

[0094] Based on the preparation method of the forward osmosis in Example 1 of the application, the content of the metal organic framework nanosheet is (0.15 mg). The average water flux of the forward osmosis membrane is 20.34 LMH, and the reverse salt flux is 0.961 g MH; the ion concentration experiment is carried out, and 2000 mg / L Li + solution is used as the raw material liquid, and 1 mol / L sodium chloride solution is used as the draw liquid.

[0095] Based on the above Comparative Example 1, Example 1 to Example 3, the test data of the forward osmosis membrane are compared in detail as shown in Table 1.

[0096] Table 1. Comparison of various test data of the forward osmosis membrane

[0097]

[0098] As can be seen from Table 1, the water flux of the forward osmosis membrane added with the metal organic framework nanosheet material is increased, the reverse salt flux is reduced, and the lithium ion recovery rate is improved. In the embodiment of the present application, the metal organic framework nanosheet material is applied to the membrane process of forward osmosis, the performance of the membrane is improved, and significant technical effects are achieved.

[0099] Example 4

[0100] The preparation method of the metal organic framework nanosheet sandwiched forward osmosis membrane in the embodiment of the present application comprises the following steps:

[0101] obtain a water phase solution of a small molecule diamine monomer, an organic phase solution of a polyacyl chloride, and a base film with Zr-BTB metal organic framework nanosheets deposited on the surface; after the base film with Zr-BTB metal organic framework nanosheets deposited on the surface is soaked in the water phase solution of the small molecule diamine monomer for a first preset time, the excess liquid is removed and dried to obtain a dried base film; the dried base film is soaked in the organic phase solution of the polyacyl chloride for a second preset time to form a polyamide layer through an interfacial polymerization reaction, and a metal organic framework nanosheet sandwiched forward osmosis membrane is obtained; the metal organic framework nanosheet sandwiched forward osmosis membrane is heat treated at 45℃ for 1min to obtain a final metal organic framework nanosheet sandwiched forward osmosis membrane;

[0102] In the water phase solution, the small molecule diamine monomer is m-phenylenediamine, and the mass percentage concentration of the small molecule diamine monomer is 1.5%; in the organic phase solution, the polyacyl chloride is trimesoyl chloride, the organic solvent is n-hexane, and the mass percentage concentration of the polyacyl chloride is 0.15%; the material of the base film is nylon; in the base film with Zr-BTB metal organic framework nanosheets deposited on the surface, the content of the Zr-BTB metal organic framework nanosheets is 0.003980mg / cm 2 ; the first preset time is 3min; and the second preset time is 45s.

[0103] In the embodiment of the present application, the obtaining step of the base film with Zr-BTB metal organic framework nanosheets deposited on the surface comprises: obtaining Zr-BTB metal organic framework nanosheets; based on the aqueous solution of the Zr-BTB metal organic framework nanosheets, the Zr-BTB metal organic framework nanosheets are deposited on the surface of the base film by vacuum filtration to obtain a base film with Zr-BTB metal organic framework nanosheets deposited on the surface; wherein the pressure of the vacuum filtration is 0.01Mpa.

[0104] The step of obtaining the Zr-BTB metal organic framework nanosheet includes: step 1, dissolving benzoic acid in dimethylformamide at room temperature, after one-time ultrasonic, adding zirconium tetrachloride and 1, 3, 5-tri (carboxyphenyl) benzoic acid and ultrapure water, and obtaining a mixed solution after two-time ultrasonic; step 2, placing the obtained mixed solution at a temperature of 85 DEG C for 14 hours to obtain an initial metal organic framework nanosheet accumulation body; and step 3, washing and peeling the initial metal organic framework nanosheet accumulation body by ultrasonic and centrifugal to obtain the Zr-BTB metal organic framework nanosheet; wherein the mass ratio of zirconium tetrachloride to benzoic acid is 1:35; the volume ratio of ultrapure water to dimethylformamide is 0.05; the mass ratio of zirconium tetrachloride to 1, 3, 5-tri (carboxyphenyl) benzoic acid (H3BTB) is 1:1; the one-time ultrasonic time is 1 hour; and the two-time ultrasonic time is 15 minutes.

[0105] In step 3 of the embodiment of the present application, the first stage washing includes: dispersing the initial metal organic framework nanosheet accumulation body into dimethylformamide, washing by ultrasonic and centrifugal to obtain a washed accumulation body; the second stage washing includes: placing the washed accumulation body into a methanol solution, washing by ultrasonic and centrifugal to obtain a clean accumulation body; and the peeling includes: placing the clean accumulation body into a methanol solution, peeling the nanosheet by ultrasonic and centrifugal to obtain a metal organic framework nanosheet; wherein the first stage washing is repeated for multiple times by changing the form of dimethylformamide dispersion liquid; in the steps of the first stage washing, the second stage washing and the peeling, the ultrasonic time is 45 minutes, the ultrasonic power is 15000 Hz, the centrifugal speed is 3500 r / min, and the centrifugal time is 3 minutes.

[0106] Embodiment 5

[0107] The preparation method of the metal organic framework nanosheet sandwiched forward osmosis membrane provided by the embodiment of the present application is different from the embodiment 4 only in that,

[0108] The metal organic framework nanosheet sandwiched forward osmosis membrane is heat treated at 65 DEG C for 3 minutes to obtain a final metal organic framework nanosheet sandwiched forward osmosis membrane;

[0109] In the aqueous solution, the small molecule diamine monomer is piperazine, and the mass percentage concentration of the small molecule diamine monomer is 2%; in the organic phase solution, the mass percentage concentration of the polyacyl chloride is 0.2%; the material of the base film is polyvinylidene fluoride; and in the base film in which the Zr-BTB metal organic framework nanosheet is deposited on the surface, the content of the Zr-BTB metal organic framework nanosheet is 0.01 mg / cm 2 ; the first preset time length is 5 minutes; and the second preset time length is 450 seconds;

[0110] The pressure of vacuum filtration is 0.04 Mpa;

[0111] In the step of obtaining the Zr-BTB metal organic framework nanosheet, the obtained mixed solution is placed at a temperature of 125 DEG C for 30 hours to obtain an initial metal organic framework nanosheet accumulation body; the initial metal organic framework nanosheet accumulation body is washed and peeled off in sequence by using ultrasonic and centrifugal methods to obtain the Zr-BTB metal organic framework nanosheet.

[0112] The mass ratio of zirconium tetrachloride to benzoic acid is 1:50; the volume ratio of ultrapure water to dimethylformamide is 0.1; the mass ratio of zirconium tetrachloride to 1,3,5-tris(carboxyphenyl) benzoic acid (H3BTB) is 1:1.2; the first ultrasonic time is 1.5 hours, and the second ultrasonic time is 30 minutes.

[0113] In the steps of the first stage washing, the second stage washing and the peeling, the ultrasonic time is 50 minutes, the ultrasonic power is 20000 Hz; the centrifugal speed is 5000 r / min, and the centrifugal time is 5 minutes.

[0114] Example 6

[0115] The preparation method of the metal organic framework nanosheet sandwiched forward osmosis membrane provided by the embodiment of the application comprises the following steps:

[0116] The water phase solution of the small molecule diamine monomer, the organic phase solution of the polyacyl chloride and the base film with the Zr-BTB metal organic framework nanosheet deposited on the surface are obtained; the base film with the Zr-BTB metal organic framework nanosheet deposited on the surface is soaked in the water phase solution of the small molecule diamine monomer for a first preset time, then the excess liquid is removed and dried to obtain a dried base film; the dried base film is soaked in the organic phase solution of the polyacyl chloride for a second preset time to form a polyamide layer through an interfacial polymerization reaction, thereby obtaining a metal organic framework nanosheet sandwiched forward osmosis membrane; the metal organic framework nanosheet sandwiched forward osmosis membrane is heat treated at 85 DEG C for 6 minutes to obtain a final metal organic framework nanosheet sandwiched forward osmosis membrane.

[0117] In the water phase solution, the small molecule diamine monomer is dopamine, and the mass percentage concentration of the small molecule diamine monomer is 3%; in the organic phase solution, the polyacyl chloride is trimesoyl chloride, the organic solvent is n-hexane, and the mass percentage concentration of the polyacyl chloride is 0.3%; the material of the base film is polyether sulfone; in the base film with the Zr-BTB metal organic framework nanosheet deposited on the surface, the content of the Zr-BTB metal organic framework nanosheet is 0.015923 mg / cm 2 The first preset time is 10 minutes, and the second preset time is 60 seconds.

[0118] In the embodiment of the present application, the obtaining step of the base film with the surface deposited with Zr-BTB metal organic framework nanosheets comprises: obtaining Zr-BTB metal organic framework nanosheets; based on an aqueous solution of the Zr-BTB metal organic framework nanosheets, depositing the Zr-BTB metal organic framework nanosheets on the surface of the base film by vacuum suction filtration to obtain the base film with the surface deposited with Zr-BTB metal organic framework nanosheets; the pressure of the vacuum suction filtration is 0.06 Mpa.

[0119] The step of obtaining the Zr-BTB metal organic framework nanosheets comprises: step 1, dissolving benzoic acid in dimethylformamide at room temperature, after one-time ultrasonic, adding zirconium tetrachloride, 1,3,5-tris(carboxyphenyl) benzoic acid and ultrapure water, and obtaining a mixed solution after two-time ultrasonic; step 2, placing the obtained mixed solution at a temperature of 175 ℃ for 52 h to obtain an initial metal organic framework nanosheet accumulation body; step 3, washing and peeling the initial metal organic framework nanosheet accumulation body by ultrasonic and centrifugal to obtain Zr-BTB metal organic framework nanosheets.

[0120] In step 1, the mass ratio of zirconium tetrachloride to benzoic acid is 1:75; the volume ratio of ultrapure water to dimethylformamide is 0.19; the mass ratio of zirconium tetrachloride to 1,3,5-tris(carboxyphenyl) benzoic acid (H3BTB) is 1:1.5; the one-time ultrasonic time is 2 h; and the two-time ultrasonic time is 45 min.

[0121] In step 3, the first stage of washing comprises: dispersing the initial metal organic framework nanosheet accumulation body into dimethylformamide, washing by ultrasonic and centrifugal to obtain a washed accumulation body; the second stage of washing comprises: placing the washed accumulation body into a methanol solution, washing by ultrasonic and centrifugal to obtain a clean accumulation body; and the peeling comprises: placing the clean accumulation body into a methanol solution, peeling the nanosheets by ultrasonic and centrifugal to obtain metal organic framework nanosheets; wherein, the first stage of washing is repeated multiple times by changing the form of dimethylformamide dispersion liquid; in the steps of the first stage of washing, the second stage of washing and the peeling, the ultrasonic time is 60 min, the ultrasonic power is 24000 Hz; the centrifugal speed is 8000 r / min, and the centrifugal time is 10 min.

[0122] In summary, the embodiment of the present application discloses a kind of metal organic framework nanosheet sandwich positive osmosis membrane for ion concentration and preparation method thereof, the preparation method includes that m-phenylenediamine is dissolved in deionized water, and aqueous monomer solution is prepared;Homotriacyl chloride is dissolved in n-hexane, and organic phase solution is prepared, metal organic framework nanosheet material prepared by the present application is uniformly dispersed in ultrapure water, metal organic framework nanosheet material is pre-deposited on base film, and the base film of pre-deposited metal organic framework nanosheet is poured with a proper amount of aqueous monomer solution and soaked, and air-dried, to obtain the film after air-drying;Organic phase solution is added to the surface of the film after air-drying, for interfacial polymerization reaction and forming separation layer, to obtain a kind of metal organic framework nanosheet sandwich positive osmosis membrane for ion concentration.The technical scheme of the embodiment of the present application can solve the problems of traditional positive osmosis membrane preparation process, high thickness of separation layer, low membrane water flux caused by non-selective collapse, poor salt rejection performance, low lithium resource recovery efficiency and the like.Further specific explanation, the present application is stripped into metal organic framework nanosheet by three-dimensional nanomaterial, and is added to the separation layer of positive osmosis by vacuum filtration and interfacial polymerization mechanism analysis shows that metal organic framework nanosheet can introduce additional water channel in separation layer;In the present application, the doping of metal organic framework nanosheet material improves the water permeability of positive osmosis membrane, and the pore formed by coordination of zirconium ion and 1,3,5-tri (carboxyphenyl) benzoic acid (H3BTB) effectively improves the salt rejection performance.

[0123] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it, although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that: the specific embodiments of the present application can be modified or replaced, without departing from the spirit and scope of the present application, any modification or equivalent replacement, which should be covered in the protection scope of the claims of the present application.

Claims

1. A metal-organic framework nanosheet sandwich forward osmosis membrane, characterized in that, The metal-organic framework nanosheet sandwich forward osmosis membrane is a sandwich structure consisting of a base membrane, Zr-BTB metal-organic framework nanosheets, and a polyamide layer. The base film surface is loaded with the Zr-BTB metal-organic framework nanosheets, and the polyamide layer is polymerized on the surface of the Zr-BTB metal-organic framework nanosheets; The steps for obtaining Zr-BTB metal-organic framework nanosheets include: dissolving benzoic acid in dimethylformamide at room temperature, sonicating once, then adding zirconium tetrachloride, 1,3,5-tris(carboxyphenyl)benzoic acid, and ultrapure water, and sonicating a second time to obtain a mixture; placing the obtained mixture at 85℃~175℃ for 14h~52h to obtain an initial metal-organic framework nanosheet stack; and washing and exfoliating the initial metal-organic framework nanosheet stack by sonication and centrifugation to obtain Zr-BTB metal-organic framework nanosheets. In the step of dissolving benzoic acid in dimethylformamide at room temperature, sonicating once, then adding zirconium tetrachloride, 1,3,5-tris(carboxyphenyl)benzoic acid, and ultrapure water, and sonicating a second time to obtain a mixed solution, the mass ratio of zirconium tetrachloride to benzoic acid is 1:(35-75); the volume ratio of ultrapure water to dimethylformamide is greater than 0 and less than or equal to 0.19; the mass ratio of zirconium tetrachloride to 1,3,5-tris(carboxyphenyl)benzoic acid (H3BTB) is 1:(1-1.5); the first sonication time is 1h-2h; and the second sonication time is 15min-45min.

2. A method for preparing the metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 1, characterized in that, Includes the following steps: Aqueous solutions of small molecule diamine monomers, organic solutions of polyacrylamide chlorides, and base films with Zr-BTB metal-organic framework nanosheets deposited on their surfaces were obtained. The substrate film with Zr-BTB metal-organic framework nanosheets deposited on its surface is immersed in an aqueous solution of the small molecule diamine monomer and kept for a first preset time. Then, excess liquid is removed and the substrate film is dried to obtain the dried substrate film. The dried base membrane is immersed in the organic phase solution of the polyacrylamide chloride and kept for a second preset time to allow an interfacial polymerization reaction to occur to form a polyamide layer, thereby obtaining a metal-organic framework nanosheet sandwich forward osmosis membrane.

3. The method for preparing a metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 2, characterized in that, In the aqueous solution, the small molecule diamine monomer is m-phenylenediamine, piperazine, or dopamine; In the organic phase solution, the polyacrylamide chloride is pyromellitic acid chloride, and the organic solvent is n-hexane; The base film is made of nylon, polyethersulfone, or polyvinylidene fluoride.

4. The method for preparing a metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 3, characterized in that, In the aqueous solution, the mass percentage concentration of the small molecule diamine monomer is 1.5% to 3%. In the organic phase solution, the mass percentage concentration of polyacrylamide chloride is 0.15% to 0.3%. The Zr-BTB metal-organic framework nanosheets deposited on the surface of the substrate film contain 0.003980 mg / cm³ of Zr-BTB metal-organic framework nanosheets. 2 ~0.015923mg / cm 2 ; The first preset duration is 3 min to 10 min; The second preset duration is 45s to 60s.

5. The method for preparing a metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 2, characterized in that, After immersing the dried base membrane in the organic phase solution of the polyacrylamide chloride for a second preset time to allow interfacial polymerization to form a polyamide layer and obtain a metal-organic framework nanosheet sandwich forward osmosis membrane, the process further includes: The metal-organic framework nanosheet sandwiched forward osmosis membrane was heat-treated at 45℃~85℃ for 1min~6min to obtain the final metal-organic framework nanosheet sandwiched forward osmosis membrane.

6. The method for preparing a metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 2, characterized in that, The steps for obtaining the substrate film with Zr-BTB metal-organic framework nanosheets deposited on its surface include: Obtain Zr-BTB metal-organic framework nanosheets; A base film with Zr-BTB metal-organic framework nanosheets deposited on its surface was obtained by vacuum filtration of an aqueous solution of Zr-BTB metal-organic framework nanosheets.

7. The method for preparing a metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 6, characterized in that, In the step of depositing Zr-BTB metal-organic framework nanosheets onto the surface of a base film by vacuum filtration to obtain a base film with Zr-BTB metal-organic framework nanosheets deposited on its surface, the vacuum filtration pressure is 0.01 MPa to 0.06 MPa.

8. The method for preparing a metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 6, characterized in that, The step of washing and exfoliating the initial metal-organic framework nanosheet stack using ultrasonication and centrifugation to obtain Zr-BTB metal-organic framework nanosheets includes: The first stage of washing includes: dispersing the initial metal-organic framework nanosheet stack in dimethylformamide, washing it by ultrasonication and centrifugation to obtain the washed stack. The second stage of washing includes: placing the washed aggregate in a methanol solution and washing it by sonication and centrifugation to obtain a clean aggregate; The process includes: placing the cleaned stack in a methanol solution and performing ultrasonic and centrifugal exfoliation to obtain metal-organic framework nanosheets; The first stage of washing was repeated multiple times by changing the dimethylformamide dispersion.

9. The method for preparing a metal-organic framework nanosheet sandwich forward osmosis membrane according to claim 8, characterized in that, In the first stage of washing, the second stage of washing, and the stripping process, the ultrasonic time is 45 min to 60 min, the ultrasonic power is 15000 Hz to 24000 Hz, the centrifugation speed is 3500 r / min to 8000 r / min, and the centrifugation time is 3 min to 10 min.

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