A forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer and its preparation method.

Abstract

This invention belongs to the field of membrane separation technology and discloses a forward osmosis (FO) membrane with tannic acid-reduced graphene oxide as the intermediate layer and its preparation method. The method includes the following steps: pretreatment of a polyethersulfone support; synthesis and chemical reduction of graphene oxide; coordination of iron ions; self-assembly of tannic acid-reduced graphene oxide; and interfacial polymerization of m-phenylenediamine and trimesoyl chloride to obtain a TFN-FO membrane. The TFN-FO membrane can be applied to seawater desalination, wastewater concentration treatment, and the concentration of raw materials. The advantages of this invention are: the reduction of graphene oxide by tannic acid improves the stability of the intermediate layer through coordination with iron ions; and the morphology and thickness of the polyamide layer can be adjusted to form an FO membrane separation layer with high flux and high salt rejection performance.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and specifically relates to a reduced graphene oxide interlayer forward osmosis membrane and its preparation method. Background Technology

[0002] Forward osmosis membranes have advantages such as low energy consumption, low production cost, wide separation range, and high separation efficiency. Compared with other membrane separation technologies, they have shown superior performance in seawater desalination and wastewater treatment (E. Yang, C.-M. Kim, J.-h. Song, H. Ki, M.-H. Ham, I.S. Kim, Enhanced desalination performance of forwardosmosis membranes based on reduced graphene oxide laminates coated with hydrophilic polydopamine, Carbon, 117(2017)293-300). Polyamide composite membranes (TFC membranes) are mainly composed of a non-porous and highly cross-linked polyamide active layer (PA layer) and a porous support layer. Due to their stable performance, low preparation cost, and large-scale production capabilities, they dominate the production and application of TFC forward osmosis (FO) membranes. Traditional forward osmosis membranes have a relatively thick PA layer, resulting in a low water flux. Furthermore, the PA layer is generally formed by interfacial polymerization on the support layer, which usually has a large pore size. This can easily cause the polyamide separation layer to collapse at the pores of the support layer, thus forming non-selective defect pores that affect the salt rejection performance of the forward osmosis membrane.

[0003] Currently, to address the aforementioned issues, existing technologies typically improve the forward osmosis membrane structure and enhance separation performance by preparing an intermediate layer forward osmosis membrane; and by embedding nanomaterials between the base membrane and the separation layer, the diffusion rate of aqueous amine monomers is reduced through the interaction of the nanomaterials with the aqueous monomers. As an important two-dimensional nanomaterial, graphene oxide (GO) has great potential in the field of separation. Due to its superior ion selectivity, good mechanical strength, ease of chemical modification, and potential for fouling resistance, GO membranes have broad prospects in water purification (X. Song, Y. Zhang, HMAbdel-Ghafar, E.-SAAbdel-Aal, M. Huang, S. Gul, H. Jiang, Polyamide membrane with an ultrathin GO interlayer on macroporous substrate for minimizing internal concentration polarization in forward osmosis, Chemical Engineering Journal, 412(2021)). However, the oxygen-containing groups in GO make it easily redispersible in water when used for water treatment, and the stability of the intermediate layer formed by GO is poor. In addition, GO has a weak interaction with the aqueous amine monomer, which limits the control of the separation layer structure.

[0004] According to reports, catechol and inorganic crosslinking agent (Fe) in tannic acid (TA) 3+ TA molecules can rapidly coordinate to form a hydrophilic thin layer with a high repulsion to NaCl. Furthermore, TA molecules can influence the morphology of the PA layer by inhibiting the diffusion of reactive monomers during interfacial polymerization, thus resulting in high permeability. Therefore, TA-Fe 3+ Sandwich layers can be used to overcome the trade-off between permeability and selectivity (F. Xiao, H. Ge, Y. Wang, S. Bian, Y. Tong, C. Gao, G. Zhu, Novel thin-film composite membrane with polydopamine-modified polyethylene support and tannic acid-Fe). 3+ interlayer for forward osmosis applications, Journal of Membrane Science, 642(2022)119976). Summary of the Invention

[0005] The purpose of this invention is to provide a forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer and its preparation method, thereby solving one or more of the aforementioned technical problems. The technical solution provided by this invention can improve the poor water permeability and reverse solute rejection of traditional forward osmosis membranes; at the same time, it can avoid the technical problems of poor stability of the GO intermediate layer and weak controllability of the separation layer.

[0006] The technical solution of this invention is as follows:

[0007] A method for preparing a forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer includes the following steps:

[0008] (1) Preparation of graphene oxide TrGO reduced by tannic acid: Ammonia and tannic acid TA were added to the aqueous solution of graphene oxide GO, with a mass ratio of TA to GO of 0-5. The chemical reduction process was completed by stirring at 65-95℃ for 15-60 min.

[0009] (2) Base membrane pretreatment: Using polyethersulfone membrane as support, soak it in dopamine solution for 8-12 hours, and then rinse it with deionized water.

[0010] (3) Preparation of the intermediate layer: The pretreated base film obtained in step (2) is immersed in FeCl3 solution for 3-7 min, taken out and rinsed with deionized water, then immersed in TrGO solution for 3-7 min, and then rinsed with deionized water.

[0011] (4) Preparation of polyamide layer: First, pour the aqueous solution of m-phenylenediamine, triethylamine and sodium dodecyl sulfate onto the membrane surface obtained in step (3), soak it, and remove the excess aqueous solution with a rubber rod; then pour the pyromellitic trichlorohexane solution onto the layer that was soaked with m-phenylenediamine, keep it, and rinse it with hexane; finally, dry the membrane in an oven, and then obtain the tannic acid reduced graphene oxide as the intermediate layer forward osmosis membrane.

[0012] Furthermore, the graphene oxide in step (1) can be self-made or commercially available; the diameter of GO is 500nm to 2μm and the thickness is 1 to 2nm.

[0013] Furthermore, in step (1), the mass ratio of TA and GO is 0-5, and the resulting products are named TrGO 0-5.

[0014] Furthermore, the concentration of the graphene oxide (GO) aqueous solution in step (1) is 15-20 mg / L. -1 .

[0015] Furthermore, in step (1), the mass percentage concentration of ammonia is 25-30%, and the mass ratio of ammonia to GO is 200:3-80:1.

[0016] Furthermore, in step (2), the pore size of the polyethersulfone membrane is 0.2-0.5 μm. If the pore size is too small, the flux will decrease, and the pore size cannot be larger than the size of the GO nanosheets; the concentration of the dopamine solution is 2 g / L. -1 The pH value is 8.5.

[0017] Further, the specific steps of step (4) are as follows: First, pour an aqueous solution of 2 wt.% m-phenylenediamine, 1 wt.% triethylamine and 0.1 wt.% sodium dodecyl sulfate (the proportion of the components in the overall aqueous solution) onto the membrane surface obtained in step (3), soak for 5 min, and remove excess aqueous solution with a rubber rod; then, invert a 0.15 wt.% pyromellitic acid chloride hexane solution onto the layer that was soaked with m-phenylenediamine, keep for 1 min, and then rinse with hexane; finally, dry the membrane in a 70°C oven for 5 min, and then obtain the tannic acid reduced graphene oxide as the intermediate layer forward osmosis membrane.

[0018] The present invention also provides a forward osmosis membrane prepared by the method described above for preparing a forward osmosis membrane with tannic acid reduced graphene oxide as an intermediate layer.

[0019] The aforementioned tannic acid-reduced graphene oxide forward osmosis membrane, using TFN-TrGO 0.2 as the intermediate layer, achieves a water flux of 46.40 L / m³. -2 h -1 The reverse salt flux was only 3.03 gm. -2 h -1 Furthermore, the separation stability was maintained during a long-term test of 70 hours. The TFN-FO membrane was used in separation experiments with deionized water as the feed solution and 1M NaCl solution as the driving fluid. Detailed description of the invention:

[0021] The technical solution of this invention is to use TA to reduce GO and catechol groups with Fe. 3+ The TrGO intermediate layer was prepared by coordination self-assembly, thereby adjusting the thickness and surface structure of the PA layer, ultimately obtaining a stable TFN-FO membrane with high water flux and high salt rejection rate. The specific steps are as follows:

[0022] (1) Obtaining graphene oxide (GO): GO can be obtained by preparation or by purchasing commercially available products.

[0023] (2) Preparation of tannic acid-reduced graphene oxide (TrGO): In 100 mL of GO solution (15 mg / L) -1Add 0.4 mL of ammonia (25%) and a certain amount of tannic acid (TA) to the solution, and stir at 65–95 °C for 15–60 min to complete the chemical reduction process. Products with TA:GO mass ratios of 0, 0.2, 1, and 5 are named TrGO 0, TrGO 0.2, TrGO 1, and TrGO5, respectively. The modified product with TA:GO = 0.2 (excluding ammonia) is named TrGO.

[0024] (3) Base film pretreatment: Using a 0.22 μm polyethersulfone membrane as a support, 2 g L -1 Soak in a dopamine solution with a pH of 8.5 for 10 hours, then rinse with deionized water.

[0025] (4) Preparation of the intermediate layer: The pretreated base film obtained in (3) is immersed in 100 mL of FeCl3 solution with a certain molar concentration ratio of TA for 5 min. After taking it out, it is rinsed with deionized water and then immersed in 100 mL of the corresponding TrGO solution for 5 min, and then rinsed with deionized water.

[0026] (5) Preparation of the polyamide layer: First, an aqueous solution of 2 wt.% m-phenylenediamine, 1 wt.% triethylamine, and 0.1 wt.% sodium dodecyl sulfate was poured onto the membrane surface and soaked for 5 min. Excess aqueous solution was removed with a rubber rod. Then, a 0.15 wt.% trimesoyl chloride hexane solution was inverted onto the layer soaked in m-phenylenediamine and held for 1 min, followed by rinsing with hexane. Finally, the membrane was dried in a 70°C oven for 5 min to obtain the TFN-FO membrane.

[0027] A further improvement of this invention lies in the addition of ammonia in the preparation method of GO reduction by TA. In the preparation method of GO reduction by TA, the ratio of TA to GO is 0.2, 1, and 5, respectively. For the pretreatment of the base film, 2g L... -1 Soak in a dopamine solution with a pH of 8.5 for 10 hours. Utilize catechol and Fe... 3+ The coordination self-assembly of TrGO intermediate layer.

[0028] This invention reduces graphene oxide by adjusting the content of tannic acid, followed by Fe... 3+ The preparation of graphene oxide interlayers by self-assembly through coordination with catechol groups is an improvement over the traditional method of preparing graphene oxide interlayers by vacuum filtration.

[0029] According to the method described herein, the separation layer thickness of the obtained TFN-FO membrane is 240–414 nm. Specifically, the TFN-FO membrane with TrGO0.2 as the intermediate layer achieved a water flux of 46.40 L / m³ in a separation experiment using deionized water as the feed solution and 1 M NaCl solution as the driving force.-2 h -1 The reverse salt flux was only 3.03 gm. -2 h -1 Furthermore, it maintained separation stability during a long-term test of 70 hours.

[0030] In the process of preparing the graphene oxide interlayer by self-assembly in this invention, if the content of graphene oxide assembled on the film cannot be accurately controlled, even small changes will cause large errors in the FO film.

[0031] In this invention, catechol in tannic acid (TA) and inorganic crosslinking agent (Fe) 3+ TA molecules can rapidly coordinate to form a hydrophilic thin layer with a high repulsion to NaCl. Furthermore, TA molecules can influence the morphology of the PA layer by inhibiting the diffusion of reactive monomers during interfacial polymerization, thus resulting in high permeability. Therefore, TA-Fe 3+ The interlayer can be used to overcome the trade-off between permeability and selectivity. Simultaneously, the chemical reduction of GO (named TrGO) is accomplished using an aqueous mixture containing TA and ammonia. TA reduces the oxygen-containing groups of GO, enhancing its water stability; on the other hand, residual phenolic groups that did not participate in the chemical reduction are retained in the sp(s) of the TrGO nanosheets through simultaneous π-π stacking. 2 The region acts as a hydrophilic decoration. Therefore, the one-step chemical reaction between TA and GO can produce the properties required for stable and selective water channels. The addition of ammonia to the solution helps to maximize the charge density of the TrGO nanosheets, thereby improving dispersion stability. More importantly, it plays a key role in effectively promoting the reaction process.

[0032] One of the innovations of this invention is to use tannic acid to reduce graphene oxide and increase the stability of graphene oxide as an intermediate layer by coordinating with Fe3+. At the same time, the structure of the polyamide layer is adjusted by using graphene oxide as an intermediate layer and the tannic acid molecules on it to improve the performance of the FO film.

[0033] The advantage of using the method described in this invention to synthesize a forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer is that TA can reduce GO, improving the stability of TrGO in water. Simultaneously, Fe... 3+As a bridge, the TrGO layer coordinates with the catechol groups on dopamine and TA respectively, which can improve the adhesion between TrGO and the membrane. Furthermore, the TrGO interlayer can slow down the penetration of PA into the macroporous matrix, reducing the thickness of the PA layer. The TA layer on top of TrGO can also facilitate the diffusion of m-phenylenediamine during interfacial polymerization, thereby increasing the density of the PA layer. In summary, the tannic acid-reduced graphene oxide (TAO) intermediate layer of the forward osmosis membrane prepared in this invention can improve the technical problems of poor water permeability and reverse salt rejection of traditional forward osmosis membranes, while avoiding the problems of poor stability of the GO interlayer and weak controllability of the separation layer. Compared with traditional forward osmosis membranes, the separation layer of the forward osmosis membrane prepared in this invention has no obvious defects, and the separation layer is thinner and denser. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the chemical reduction of GO by TA in Examples 2-4;

[0035] Figure 2 (1) and (2) are atomic force microscopy images of the original GO and TrGO 0.2, respectively;

[0036] Figure 3 (1) and (2) are scanning electron microscope images (surface images) of the FO film in Examples 1 and 2, respectively;

[0037] Figure 4 (1) and (2) are scanning electron microscope images (cross-sectional views) of the FO films in Examples 1 and 2, respectively;

[0038] Figure 5 This is a schematic diagram illustrating how TrGO prevents polyamide from getting trapped in the macroporous polyethersulfone matrix in Examples 2-4;

[0039] Figure 6 These are the performance test graphs from Examples 1 to 5;

[0040] Figure 7 This is a graph showing the long-term stability test results in Example 2;

[0041] Figure 8 The diagram shows the apparatus used for FO testing in Examples 1-5. Detailed Implementation

[0042] The specific embodiments of the present invention will be further described in detail below with reference to the examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0043] Methods for testing water flux and salt flux: The mass of the sampled liquid is continuously recorded by an automatic counting balance. The water flux can be obtained by formula (1) based on the change in the mass of the sampled liquid before and after operation. The ion concentration can be calculated by testing the conductivity of the feed liquid before and after operation. The reverse salt flux can be obtained by formula (2) based on the change in the volume of the feed liquid before and after operation.

[0044] Water flux and salt flux are determined by formula (1) and formula (2), respectively.

[0045]

[0046] In the formula, J w The water flux of the membrane (L m) -2 h -1 ), Δm is the decrease in feed mass (g), ρ is the density of water (g / L), A m It is the effective membrane area (m²) 2 ), where Δt is the test time (h).

[0047]

[0048] In the formula, J s Represents the reverse salt flux of the membrane (gm). -2 h -1 ), C0 and C t V0 and Vt represent the initial and time t salt concentrations (g / L) in the feed solution, respectively. t The volumes (L) of the feed solution at the initial stage and at time t are given. The concentration of the solute can be determined by measuring the conductivity. A m It is the effective membrane area (m²) 2 ), where Δt is the test time (in hours).

[0049] Definition or measurement method of thickness and surface morphology: The PA layer of the membrane has a leaf-like protrusion structure. The introduction of the intermediate layer in this invention makes the resulting PA layer have a richer leaf-like structure. The separation layer thickness mentioned in this invention refers to the total thickness of the PA layer containing the leaf-like protrusions and the TrGO intermediate layer, which is determined by scanning electron microscopy.

[0050] Example 1:

[0051] (1) Direct interfacial polymerization on polyethersulfone membrane: First, an aqueous solution of 2 wt.% m-phenylenediamine, 1 wt.% triethylamine, and 0.1 wt.% sodium dodecyl sulfate was poured onto the surface of the PES-based membrane and soaked for 5 min. Excess aqueous solution was removed with a rubber rod. Then, a 0.15 wt.% hexane solution was inverted onto the layer soaked with m-phenylenediamine and held for 1 min, followed by rinsing with hexane. Finally, the membrane was dried in a 70°C oven for 5 min to obtain the TFN-FO membrane.

[0052] (2) Membrane testing: Deionized water was used as the raw material and 1M NaCl solution was used as the driving liquid for separation experiments.

[0053] Example 2:

[0054] (1) Obtaining graphene oxide (GO): GO can be obtained by preparation or by purchasing commercially available products.

[0055] (2) Base film pretreatment: Using a 0.22 μm polyethersulfone membrane as a support, 2 g L -1 Soak in a dopamine solution with a pH of 8.5 for 10 hours, then rinse with deionized water.

[0056] (3) The preparation and testing of the polyamide layer are the same as in Example 1.

[0057] Example 3:

[0058] Step (1) is the same as in Example 2;

[0059] (2) Base film pretreatment: Using a 0.22 μm polyethersulfone membrane as a support, 2 g L -1 Soak in a dopamine solution with a pH of 8.5 for 10 hours, then rinse with deionized water.

[0060] (3) Preparation of the intermediate layer: The pretreated base film obtained in (2) was immersed in 100 mL of GO solution for 5 min, and then rinsed with deionized water.

[0061] (4) The preparation and testing of the polyamide layer are the same as in Example 1.

[0062] Example 4:

[0063] (1) Obtaining graphene oxide (GO): GO can be obtained by preparation or by purchasing commercially available products.

[0064] (2) Preparation of tannic acid-reduced graphene oxide (TrGO): In 100 mL of GO solution (15 mg / L) -1 Add 0.4 mL of ammonia (25%) and 0.3 mg of tannic acid (TA) to the solution, and stir at 95 °C for 30 min to complete the chemical reduction process.

[0065] (3) Base film pretreatment: Using a 0.22 μm polyethersulfone membrane as a support, 2 g L -1 Soak in a dopamine solution with a pH of 8.5 for 10 hours, then rinse with deionized water.

[0066] (4) Preparation of the intermediate layer: The pretreated base film obtained in (3) was immersed in 100 mL of 0.286 mg L -1Immerse in FeCl3 solution for 5 min, remove and rinse with deionized water, then soak in 100 mL TrGO solution obtained from (2) for 5 min, and then rinse with deionized water.

[0067] (5) The preparation and testing of the polyamide layer are the same as in Example 1.

[0068] Example 5:

[0069] Step (1) is the same as in Example 2;

[0070] (2) Preparation of tannic acid-reduced graphene oxide (TrGO): In 100 mL of GO solution (15 mg / L) -1 Add 0.4 mL of ammonia (25%) and 1.5 mg of tannic acid (TA) to the solution, and stir at 95 °C for 30 min to complete the chemical reduction process.

[0071] Step (3) is the same as in Example 2.

[0072] (4) Preparation of the intermediate layer: The pretreated base film obtained in (3) was immersed in 100 mL of 1.43 mg L -1 Immerse in FeCl3 solution for 5 min, remove and rinse with deionized water, then soak in 100 mL TrGO solution obtained from (2) for 5 min, and then rinse with deionized water.

[0073] Step (5) is the same as in Example 1.

[0074] Example 6:

[0075] Step (1) is the same as in Example 2;

[0076] (2) Preparation of tannic acid-reduced graphene oxide (TrGO): In 100 mL of GO solution (15 mg / L) -1 Add 0.4 mL of ammonia (25%) and 7.5 mg of tannic acid (TA) to the mixture, and stir at 95 °C for 30 min to complete the chemical reduction process.

[0077] Step (3) is the same as in Example 2.

[0078] (4) Preparation of the intermediate layer: The pretreated base film obtained in (3) was immersed in 100 mL of 7.15 mg L -1 Immerse it in FeCl3 solution for 5 min, then rinse it with deionized water, then soak it in 100 mL TrGO solution obtained from (2) for 5 min, and then rinse it with deionized water.

[0079] Step (5) is the same as in Example 1.

[0080] Example 7:

[0081] Step (1) is the same as in Example 2;

[0082] (2) Preparation of tannic acid-reduced graphene oxide (TrGO): In 100 mL of GO solution (15 mg / L) -1 Add 0.3 mg of tannic acid (TA) to the mixture and stir at 95°C for 30 min to complete the chemical reduction process.

[0083] (3) Base film pretreatment: Using a 0.22 μm polyethersulfone membrane as a support, 2 g L -1 Soak in a dopamine solution with a pH of 8.5 for 10 hours, then rinse with deionized water.

[0084] (4) Preparation of the intermediate layer: The pretreated base film obtained in (3) was immersed in 100 mL of 0.286 mg L -1 Immerse in FeCl3 solution for 5 min, remove and rinse with deionized water, then soak in 100 mL TrGO solution obtained from (2) for 5 min, and then rinse with deionized water.

[0085] (5) The preparation and testing of the polyamide layer are the same as in Example 1.

[0086] Table 1 shows the results of the forward osmosis experiments of the FO membranes synthesized in Examples 1-7. The experimental temperature was room temperature (25℃).

[0087] Table 1. Results of forward osmosis experiments on the FO membranes synthesized in Examples 1-7.

[0088]

[0089]

[0090] Figure 2 This demonstrates the successful reduction of graphene oxide by tannic acid; Figure 3 4. By comparing with interfacial polymerization directly on polyethersulfone film, it is demonstrated that the reduced graphene oxide interlayer successfully modulates the surface structure and thickness of the polyamide layer; Figure 5 A schematic diagram illustrating the principle of reducing the thickness of polyamide by reducing the graphene oxide interlayer; Figure 6 Figure 7 illustrates the performance and long-term stability of the prepared membrane.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer, characterized in that, Includes the following steps: (1) Preparation of graphene oxide TrGO reduced by tannic acid: Ammonia and tannic acid TA were added to an aqueous solution of graphene oxide GO. The mass ratio of TA to GO was 0.2-5. The chemical reduction process was completed by stirring at 65-95 °C for 15-60 min. The mass percentage concentration of ammonia was 25-30%, and the mass ratio of ammonia to GO was 200:3-80:

1. (2) Base membrane pretreatment: Using a polyethersulfone membrane as a support, the membrane was soaked in dopamine solution for 8-12 h, then rinsed with deionized water; the pore size of the polyethersulfone membrane was 0.2-0.5 μm; the concentration of the dopamine solution was 2 g / L. -1 The pH value is 8.

5. (3) Preparation of the intermediate layer: The pretreated base film obtained in step (2) is immersed in FeCl3 solution for 3-7 min, taken out and rinsed with deionized water, then immersed in TrGO solution for 3-7 min, and then rinsed with deionized water. (4) Preparation of polyamide layer: First, pour the aqueous solution of m-phenylenediamine, triethylamine and sodium dodecyl sulfate onto the membrane surface obtained in step (3) and soak it. Remove the excess aqueous solution with a rubber rod. Then, pour the pyromellitic chlorohexane solution onto the layer that was soaked with m-phenylenediamine, keep it, and rinse it with hexane. Finally, dry the membrane in an oven. Then, the tannic acid reduced graphene oxide as the intermediate layer forward osmosis membrane is obtained.

2. The method for preparing a forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer according to claim 1, characterized in that, In step (1), the graphene oxide can be made in-house or commercially available; the diameter of GO is 500 nm to 2 μm and the thickness is 1 to 2 nm.

3. The method for preparing a forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer as described in claim 1, characterized in that, In step (1), the concentration of the graphene oxide (GO) aqueous solution is 15-20 mg / L. -1 .

4. The method for preparing a forward osmosis membrane with tannic acid-reduced graphene oxide as the intermediate layer as described in claim 1, characterized in that, Step (4) specifically involves: first, pouring an aqueous solution of 2 wt.% m-phenylenediamine, 1 wt.% triethylamine, and 0.1 wt.% sodium dodecyl sulfate onto the membrane surface obtained in step (3), soaking it for 5 min, and removing excess aqueous solution with a rubber rod; then, inverting a 0.15 wt.% pyromellitic acid chloride hexane solution onto the layer that was soaked with m-phenylenediamine, keeping it for 1 min, and then rinsing it with hexane; finally, drying the membrane in a 70 °C oven for 5 min, thereby obtaining the tannic acid-reduced graphene oxide as the intermediate forward osmosis membrane.

5. A forward osmosis membrane prepared by the method of preparing a forward osmosis membrane with tannic acid reduced graphene oxide as an intermediate layer as described in any one of claims 1-4.

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