Interface polymerization preparation method of maleic anhydride functionalized graphene composite nanofiltration membrane

Abstract

The invention discloses an interfacial polymerization preparation method of a maleic anhydride functionalized graphene composite nanofiltration membrane, and belongs to the field of nanofiltration membrane preparation. The invention relates to a preparation method of a nanofiltration membrane with maleic anhydride modified graphene oxide (MG) as an additive. Compared with unmodified graphene oxide (GO), the maleic anhydride modified graphene oxide (MG) has better hydrophilicity, surface activity and anti-pollution capacity, and the modified composite nanofiltration membrane is prepared by adding the maleic anhydride modified graphene oxide (MG) as a nano material into a polypiperazine amide layer. Under the optimal membrane preparation conditions that the addition concentration of MG is 0.006 wt%, the water flux of the functionalized graphene composite nanofiltration membrane is 68.57 L.m <-2 >. H <-1 >, the retention rate is 97.6%, the flux recovery rate is 98.7%, and the functionalized graphene composite nanofiltration membrane shows excellent performance.

Description

Technical Field

[0001] The present invention belongs to the field of nanofiltration membrane preparation, and specifically relates to a method for preparing a nanofiltration membrane by interfacial polymerization using a polysulfone ultrafiltration membrane as the base membrane and maleic anhydride-modified graphene oxide (MG) as an additive. Background Art

[0002] Nanofiltration membranes have a wide range of applications in the fields of water treatment, separation and purification, etc. However, the composite nanofiltration membranes prepared by the interfacial polymerization method still need to improve their hydrophilic properties, resulting in low separation efficiency, increased energy consumption, and the anti-fouling ability of the membranes is also expected to be enhanced. In order to improve the performance of nanofiltration membranes, researchers have tried to modify nanofiltration membranes by adding various nanomaterials.

[0003] Graphene oxide (GO) is a highly oxidized product of graphene, with a layered structure extremely similar to that of graphene, and its surface is rich in a large number of oxygen-containing active groups such as hydroxyl groups, carboxyl groups, and epoxy groups. Due to its unique structure and properties, graphene oxide shows certain potential in the modification of membrane materials. However, ordinary graphene oxide has limitations in terms of hydrophilicity, surface activity, etc., and it is difficult to effectively improve the comprehensive performance of nanofiltration membranes. Therefore, it is of great practical significance to develop a preparation method that can effectively improve the water flux and anti-fouling ability of nanofiltration membranes.

[0004] Maleic anhydride-graphene oxide (MG) also has functional groups such as hydroxyl groups, carboxyl groups, and epoxy groups on its surface, and has a larger interlayer spacing compared with GO, making it have excellent hydrophilicity, surface activity, and anti-fouling ability. Aiming at the problems existing in polyamide composite nanofiltration membranes, graphene oxide modified with maleic anhydride and graphene oxide are added as nanomaterials to the poly(piperazine amide) layer to prepare a composite nanofiltration membrane with excellent performance. Summary of the Invention

[0005] The content of the present invention aims at the problems existing in the prior art, such as the low water flux of traditional nanofiltration membranes, insufficient anti-fouling ability, and the difficulty in effectively improving the comprehensive performance of nanofiltration membranes by ordinary graphene oxide modification. The present invention provides an interfacial polymerization preparation method for a maleic anhydride-functionalized graphene composite nanofiltration membrane. Using a polysulfone ultrafiltration membrane as the base membrane and maleic anhydride-graphene oxide (MG) as an additive, and by using the interfacial polymerization method, the prepared composite nanofiltration membrane has high water flux, high anti-fouling ability, and excellent retention performance.

[0006] To achieve the above invention object, the present invention adopts the following technical solutions.

[0007] An interfacial polymerization preparation method for a maleic anhydride-functionalized graphene composite nanofiltration membrane, comprising the following steps:

[0008] 1) Cut the polysulfone-based membrane into an appropriate size, soak it in deionized water for more than 24 h, and fix the polysulfone-based membrane on the membrane preparation mold;

[0009] 2) Prepare an aqueous solution of MG nanoparticles, mix it with an aqueous solution of piperazine after ultrasonic treatment for 40 min to obtain an aqueous solution;

[0010] 3) Dissolve trimesoyl chloride in n-hexane and stir well to obtain an oil-phase solution;

[0011] 4) Pour the aqueous solution into the mold with the fixed polysulfone-based membrane, soak and react for 2 min, and blow dry with nitrogen;

[0012] 5) Pour the oil-phase solution into the mold, soak and react for 1 min to initiate an interfacial polymerization reaction to form a poly(piperazine amide) layer, and then put the mold into a vacuum drying oven for heat treatment at 60 °C for 8 min to promote the complete polymerization reaction, and a composite nanofiltration membrane with a stable cross-linked structure is prepared.

[0013] In step 1), the appropriate size cut can be cut into a size of 10 cm × 10 cm; the pore size of the polysulfone-based membrane can be 20 - 50 nm, and the molecular weight cut-off range is 10 - 30 kDa.

[0014] In step 2), for the preparation of the aqueous solution of MG nanoparticles, powdered graphene oxide modified with maleic anhydride (MG) can be weighed and added to deionized water at a mass concentration of 0.002 - 0.012 wt%, preferably 0.006 wt%; the aqueous solution of piperazine is prepared by dissolving piperazine in deionized water to prepare an aqueous solution of piperazine with a concentration of 2.0 wt%. When the MG concentration is too high (such as 0.012 wt%), agglomeration will occur, resulting in an increase in the water transfer resistance of the membrane and affecting the water flux. Therefore, the optimal addition amount of MG is 0.006 wt%.

[0015] In step 3), the concentration of trimesoyl chloride can be 0.1 - 0.5 wt%, that is, 0.1 - 0.5 g of trimesoyl chloride is contained in every 100 g of the oil-phase solution.

[0016] The present invention prepares a nanofiltration membrane using graphene oxide modified with maleic anhydride (MG) as an additive. The graphene oxide modified with maleic anhydride has better hydrophilicity, surface activity and anti-pollution ability, and is added as a nanomaterial to the poly(piperazine amide) layer to prepare a modified composite nanofiltration membrane. Under the optimal membrane preparation conditions: the MG addition concentration is 0.006 wt%, the water flux of the prepared functionalized graphene composite nanofiltration membrane is 68.57 L·m -2 ·h -1 , the rejection rate is 97.6%, and the flux recovery rate is 98.7%, showing excellent performance.

[0017] A large number of hydrophilic active groups such as hydroxyl, carboxyl, and epoxy groups are rich on the surface of MG, which enhances the hydrophilicity of the membrane surface, increases the water flux, and the addition of MG can help the reaction on the membrane surface to form a thinner polyamide dense layer, reducing the water penetration resistance.

[0018] When the concentration of MG reaches 0.012 wt%, agglomeration will occur, resulting in an increase in the water transfer resistance of the membrane and affecting the water flux of the membrane. The optimal addition amount of MG is 0.006 wt%.

[0019] The addition of MG has a certain impact on the hydrophilicity and hydrophobicity of the membrane surface. The improvement effect of MG on the hydrophilicity of the membrane is better because the regularity of MG is low, the particle size is small, the lamellar spacing is smaller, and the water transfer resistance is smaller.

[0020] The membrane is prone to pollution during the water treatment process, resulting in a decrease in water flux. MG is negatively charged, and the surface of the MG composite membrane is smoother, which is beneficial to enhancing the anti-pollution ability. When the addition amount of MG is 0.006 wt%, the anti-pollution ability is the best.

[0021] Compared with the existing technology, the present invention introduces MG as an additive into the composite nanofiltration membrane and obtains the optimal membrane preparation conditions. Compared with the composite nanofiltration membrane with GO as an additive, the composite nanofiltration membrane prepared by adding MG significantly improves the water flux while maintaining a high rejection rate, improves the hydrophilicity of the membrane, and enhances the anti-pollution ability of the membrane. Therefore, MG as an additive has a better modification effect than GO. Brief Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the device for testing the membrane separation performance.

[0023] Figure 2 It is the standard curve of the conductivity of Na2SO4 solution (low concentration).

[0024] Figure 3 It is the standard curve of the conductivity of Na2SO4 solution (high concentration).

[0025] Figure 4 It is a schematic diagram of the pure water flux of nanofiltration composite membranes with different concentrations.

[0026] Figure 5 It is a schematic diagram of the Na2SO4 rejection rate of nanofiltration membranes with different concentrations.

[0027] Figure 6 It is the infrared spectrum of composite membranes with different concentrations.

[0028] Figure 7 It is a schematic diagram of the static contact angle on the surface of the composite nanofiltration membrane.

[0029] Figure 8Schematic diagram of the water flux recovery rate of the composite membrane against BSA contamination. Detailed implementation manners

[0030] To facilitate those skilled in the art to better understand the technology of the present invention, some non-limiting embodiments are further disclosed herein to further describe the present invention in detail. All the reagents used in the present invention can be directly purchased from the market or can be prepared by the methods described in the invention.

[0031] The embodiment of the present invention is a preparation method of a nanofiltration membrane using maleic anhydride modified graphene oxide (MG) as an additive. The maleic anhydride modified graphene oxide has better hydrophilicity, surface activity and anti-pollution ability. It is used as a nanomaterial and added to the poly(piperazine amide) layer to prepare a modified composite nanofiltration membrane. Under the optimal membrane preparation conditions: the MG addition concentration is 0.006 wt%, the water flux of the functionalized graphene composite nanofiltration membrane is 68.57 L·m -2 ·h -1 , the rejection rate is 97.6%, and the flux recovery rate is 98.7%, showing excellent performance. It includes:

[0032] (1) Functionalized graphene composite nanofiltration membrane

[0033] (2) Thermally cross-linking MG to form a membrane by interfacial polymerization

[0034] The experimental steps of using MG as an additive to prepare a new composite nanofiltration membrane with better membrane performance by interfacial polymerization on the basis of a polysulfone ultrafiltration membrane as the substrate membrane and characterizing it are as follows:

[0035] 1. Prepare an interfacial polymerization composite membrane:

[0036] Take out the polysulfone substrate membrane from the preservation solution. The polysulfone substrate membrane is a high-performance membrane material with good heat resistance. Cut the polysulfone substrate membrane into an appropriate size, soak it in deionized water for more than 24 h, and fix the substrate membrane on the membrane preparation mold; respectively prepare aqueous solutions of GO and MG nanoparticles with certain concentrations, mix them with an aqueous solution of piperazine with a certain concentration after ultrasonic treatment for 40 min to obtain an aqueous phase solution; weigh a certain amount of trimesoyl chloride and dissolve it in n-hexane, and stir well to obtain an oil phase solution; pour the aqueous phase solution into the mold with the fixed substrate membrane and soak for reaction for 2 min, and blow dry with nitrogen; pour the oil phase solution into it and soak for reaction for 1 min, and place it in a vacuum drying oven for heat treatment at 60 °C for 8 min to obtain a composite nanofiltration membrane with a stable cross-linked structure.

[0037] The water flux and rejection rate of composite nanofiltration membranes with the addition concentrations of MG and GO ranging from 0 to 0.012 wt% were tested, and the preferred addition concentrations of MG and GO were 0.006 and 0.008 wt% respectively. The above steps were repeated to prepare the composite nanofiltration membranes. Among them, 0 represents the blank nanofiltration membrane; the composite membranes with the addition concentrations of MG and GO of 0.006 and 0.008 wt% were denoted as MG-1 and GO-1 respectively; the composite membranes with the highest addition concentration of MG and GO of 0.012 wt% were denoted as MG-2 and GO-2 respectively.

[0038] 2. Membrane separation performance test:

[0039] The main evaluation parameters of the nanofiltration membrane separation performance are water flux and rejection rate. In this experiment, both the water flux and rejection rate were measured by a Flowmem0021-HP high-pressure flat membrane pilot test machine. The schematic diagram of the device is as Figure 1 shown. It includes a feed liquid tank 1, an air pump 2, an inlet pressure gauge 3, a membrane sheet tank 4, an outlet pressure gauge 5, and a permeate outlet 6. Since the operating pressure of this experiment reaches 6 bar, it is necessary to ensure that all components are connected by pressure-resistant pipelines, and the measuring range of the pressure gauge should meet the requirements.

[0040] 2.1 Water flux test:

[0041] The effective membrane area for the test of each membrane sheet is 70 cm 2 , the pure water feed is 3 L, the operating pressure is 6 bar, and the test stability is 25 ± 1 °C. The specific steps are as follows: The prepared membrane sheet was cut into a 7 cm × 10 cm membrane sheet with a template iron sheet; the cut membrane sheet was placed with the active layer facing down in the equipment operation tank and fixed with the tank cover, and about 3 L of pure water was added to the feed liquid tank; the operation frequency was 50 Hz and the pressure was 6 bar, and the membrane sheet was pre-pressed for 10 min; after the pre-pressing was completed, the conditions were kept unchanged, and the volume V of the liquid permeated through the outlet was measured within the time Δt.

[0042] The water flux of the membrane was calculated using the following formula:

[0043]

[0044] Among them, J is the water flux of the membrane (L / m 2 ·h), V is the volume of the permeate within the time Δt (L), Δt is the time (h), and A is the membrane area (m 2 ), and in this experiment, A is 0.008 m 2 .

[0045] The experimental results are as Figure 4As shown in the figure, it can be seen that after adding the functionalized graphene material, the water flux of the membrane has been significantly improved. When the addition concentration of MG is 0.006 wt%, the membrane water flux reaches 68.57 L·m -2 ·h -1 , compared with the blank membrane, the flux is increased by 83.88%. When the addition concentration of GO is 0.008 wt%, the membrane water flux reaches 64.29 L·m -2 ·h -1 , and the flux is increased by 72.40%. This is due to the commonalities of MG and GO. On the one hand, water molecules can pass through the unique nano-interlayer of the functionalized graphene, and because the surfaces of GO and MG are rich in a large number of hydrophilic active groups such as hydroxyl, carboxyl, and epoxy groups, the hydrophilic property of the membrane surface is enhanced, improving the water flux; on the other hand, the addition of MG and GO can contribute to the formation of a thinner polyamide dense layer on the membrane surface, reducing the water penetration resistance. However, as the concentration of nanoparticles continues to increase, the membrane water flux shows a downward trend, which is due to the agglomeration of MG and GO on the membrane surface, increasing the water transfer resistance of the membrane. It can also be seen from this that the hydrophilic property of MG is stronger than that of GO, and the polyamide separation layer on the surface of the prepared composite nanofiltration membrane is thinner and less likely to agglomerate on the membrane surface.

[0046] 2.2 Retention rate test:

[0047] The separation performance of the composite nanofiltration membrane can be evaluated by the retention rate of different valence salts. In this experiment, the retention of the composite membrane for Na2SO4 solution was measured. After measuring the water flux, the pure water was replaced with a 2 g / L Na2SO4 solution, and the test conditions and the operating steps of the device were the same as those of the water flux operation steps. After pre-pressing for 10 min, the salt solution flux was measured, and the conductivities of the permeate and the concentrate were recorded. Through the linear relationship between conductivity and concentration (as shown in Figure 2 、 Figure 3 ), the salt concentration Cp of the permeate and the salt concentration C of the concentrate were obtained. f . And the retention rate was calculated using the following formula:

[0048]

[0049] Where: R is the retention rate (%), Cp is the concentration of the solute in the permeate (mg / L), and Cc is the concentration of the solute in the concentrate (mg / L).

[0050] After testing, the retention of all composite membranes for Na2SO4 solution is as shown in Figure 5As shown in the figure, it can be seen that the rejection rates of all membranes for Na2SO4 are maintained above 96%, indicating that the prepared composite membranes are all negatively charged nanofiltration membranes. With the increase in the concentration of added nanoparticles, the rejection rate decreases slightly, indicating that there is a trade-off effect in both nanofiltration composite membranes. However, due to the addition of GO and MG, the impact of this effect is relatively small.

[0051] 3. Analysis of membrane surface groups:

[0052] The chemical groups on the membrane surface can be measured by a Fourier transform infrared spectrometer (FTIR). In this experiment, a Bruker VERTXE 70 type Fourier transform infrared spectrometer was used to measure the chemical groups on the surface of the composite membrane. The number of scans was 16 times, and the resolution was 4 cm -1 , and the scanning range was 4000 - 400 cm -1 . The infrared spectra of the membrane surface and its corresponding background were recorded using OPUS 6.5 software. The membrane pieces should be dried before measurement.

[0053] The experimental results are as Figure 6 shown. It can be seen from the figure that 1323 cm -1 and 1294 cm -1 are the asymmetric stretching vibration peaks of O=S=O, 1244 cm -1 is the asymmetric stretching vibration peak of C-O-C in Ar-O-Ar, 1168 cm -1 and 1151 cm -1 are the symmetric stretching vibration peaks of O=S=O, 1585 cm -1 , 1504 cm -1 and 1487 cm -1 are the in-plane stretching vibration peaks of the benzene ring. All of the above are the characteristic peaks of the polysulfone support layer. 1618 cm -1 is the N-H deformation vibration peak (amide I characteristic peak) in poly(piperazine amide). In the GO and MG membranes, the asymmetric stretching vibration peak of the carboxyl group is at 1737 cm -1 . With the increase in the amount of added nanoparticles, the peak intensity increases.

[0054] 4. Measurement of membrane hydrophilic and hydrophobic properties:

[0055] The contact angle of the composite membrane surface was measured using a HARKE SPCAX3 type contact angle measuring instrument. The specific steps were as follows: Six membrane pieces with a size of 1 cm × 1 cm were cut from different positions of the prepared composite membrane pieces and freeze-dried for later use; the membrane pieces were fixed on the surface of the cover glass with double-sided tape, the water needle was adjusted to 5 mm above the membrane, and 3 μL of water was dropped onto the membrane surface; after 30 s, the picture was saved through the software, and the contact angle was measured; during the measurement process, the temperature was maintained at 20 ± 1 °C, and the humidity was 40% - 50%. Six contact angles were measured for each sample and the average value was taken.

[0056] The contact angle measurement results of each nanofiltration composite membrane are as follows Figure 7 shown. It can be seen from the figure that the contact angles of all composite membranes added with nanoparticles are much lower than those of the blank membrane, that is, the hydrophilicity is stronger than that of the blank membrane. The enhancement of the hydrophilicity of these membranes benefits from the addition of hydrophilic materials such as MG and GO. And it can be seen from the figure that MG has a better effect on improving the hydrophilicity of the membrane than GO. This is because MG has low regularity, small particle size and smaller interlayer spacing, resulting in less resistance to water transfer.

[0057] 5. Determination of membrane antifouling performance

[0058] In this experiment, bovine serum albumin (BSA) solution was used to detect the antifouling performance of the membrane. First, in the water flux test system, the stable pure water flux J w,1 was recorded, and then the pure water was replaced with a 1 g / L concentration of BSA solution. The change of the permeation flux of BSA with time was recorded until the flux tended to be stable. Then the whole system was thoroughly cleaned with deionized water for a period of time (the time is not included in the chart), and then J w,2 was recorded again with the change of time. Repeat the same steps several times, and calculate the total fouling rate (R t ) and the flux recovery rate after washing with water (FRR).

[0059] The experimental results are as follows Figure 8 shown. It can be seen from the figure that after replacing deionized water with BSA solution, the water fluxes of all membranes decreased slightly. The water flux of the blank membrane decreased the most, and the flux decline rate reached 14.6%. The total fouling rates of the GO membrane and the MG membrane were 12.3% and 8.2% respectively, indicating the influence of BSA on the membrane flux: blank membrane > GO membrane > MG membrane. This is because BSA is a negatively charged protein, and GO and MG also carry negative charges. The electrostatic repulsion effect makes the membrane have a weaker BSA adsorption ability, and the smoother surface of the composite membrane is beneficial to the enhancement of the antifouling ability. Also, because the surface of the MG membrane is smoother than that of the GO membrane, the antifouling ability of the MG membrane is stronger than that of the GO membrane. After BSA fouling, when washed with deionized water, the flux recovery rates of the blank membrane, the GO membrane and the MG membrane were 95.0%, 97.1% and 98.7% respectively.

[0060] The advantage of the present invention is that the composite nanofiltration membrane prepared by adding functionalized graphene materials significantly improves the water flux and antifouling performance while maintaining a high rejection rate, and improves the hydrophilic performance of the membrane. And the following conclusions can be drawn: when the addition concentration of MG is 0.006 wt%, the membrane performance is the best. At this time, the membrane water flux reaches 68.57 L·m -2 ·h -1 , the rejection rate reaches 97.6%, and the flux recovery rate reaches 98.7%.

[0061] The above are only the preferred embodiments of the present invention. For those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane, characterized in that Using a polysulfone ultrafiltration membrane as the base membrane and maleic anhydride-functionalized graphene oxide as an additive, a graphene composite nanofiltration membrane is prepared by interfacial polymerization to improve water flux and rejection performance.

2. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane as described in claim 1, characterized in that The pore size of the polysulfone ultrafiltration membrane is 20 - 50 nm, and the molecular weight cut-off range is 10 - 30 kDa.

3. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane as described in claim 1, characterized in that The addition amount of the maleic anhydride-functionalized graphene oxide is 0.002wt% - 0.012 wt%.

4. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane according to claim 3, characterized in that The addition amount of the maleic anhydride-functionalized graphene oxide is 0.006wt%.

5. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane according to claim 4, characterized in that The water flux of the prepared graphene composite nanofiltration membrane is 68.57 L·m -2 ·h -1 , the rejection rate of Na2SO4 is 97.6%, and the flux recovery rate is 98.7%.

6. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane as described in claim 1, characterized in that The specific steps of the preparation method are as follows: 1) Cut the polysulfone base membrane into an appropriate size, soak it in deionized water for more than 24 h, and fix the polysulfone base membrane on the membrane preparation mold. 2) Prepare an aqueous solution of graphene oxide nanoparticles, mix it with an aqueous piperazine solution after ultrasonic treatment for 40 min to obtain an aqueous phase solution. 3) Dissolve trimesoyl chloride in n-hexane and stir well to obtain an oil phase solution. 4) Pour the aqueous phase solution into the mold with the fixed polysulfone base membrane, soak and react for 2 min, and dry it with nitrogen. 5) Pour the oil phase solution into the mold, soak and react for 1 min to initiate an interfacial polymerization reaction to form a poly(piperazine amide) layer, and then put the mold into a vacuum drying oven for heat treatment at 60 °C for 8 min to promote the complete polymerization reaction, and a graphene composite nanofiltration membrane with a stable cross-linked structure is prepared.

7. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane according to claim 6, characterized in that In step 2), for the preparation of the aqueous solution of graphene oxide nanoparticles, first weigh the maleic anhydride-modified graphene oxide powder and add it to deionized water at a mass concentration of 0.002wt% - 0.012 wt%.

8. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane according to claim 6, characterized in that In step 2), the aqueous piperazine solution used is an aqueous piperazine solution with a concentration of 2.0 wt%.

9. The interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane according to claim 6, characterized in that In step 3), the concentration of the trimesoyl chloride is 0.1wt% - 0.5 wt%.

10. A graphene composite nanofiltration membrane prepared by the interfacial polymerization preparation method of a maleic anhydride-functionalized graphene composite nanofiltration membrane according to any one of claims 1 - 9.

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