Method for preparing graphene oxide composite forward osmosis membrane

Abstract

This invention relates to a method for preparing a graphene oxide composite forward osmosis membrane. The method comprises: preparing a mixed solution, wherein the mixed solution is an aqueous dispersion comprising graphene oxide and acidified carbon nanotubes, and the mass ratio of graphene oxide to acidified carbon nanotubes is 2-18; performing vacuum filtration on the mixed solution to form a membrane; and drying the membrane to obtain the graphene oxide composite forward osmosis membrane. The preparation method of this invention is simple and efficient, and can prepare forward osmosis water treatment membranes that maintain good retention performance while exhibiting high water flux, good bactericidal performance, and large-scale application.

Description

Technical Field

[0001] This invention relates to a method for preparing a forward osmosis membrane, and particularly to a method for preparing a graphene oxide composite forward osmosis membrane. Background Technology

[0002] To address the current water resource situation, various approaches and methods are being adopted. Among these, membrane separation technology has become a trend in water treatment. Microfiltration, nanofiltration, ultrafiltration, and reverse osmosis are fully mature and industrially applied. Forward osmosis, a membrane separation technology developed in recent years, relies primarily on the concentration difference across the membrane to spontaneously achieve water transfer. Because this process does not require external pressure, the equipment is simple, does not require high pressure resistance, consumes less energy, and is more economical, making it one of the current research hotspots in the field of membrane separation.

[0003] In the field of membrane materials, two-dimensional nanosheet membranes have attracted widespread attention due to their excellent mechanical properties and tunable molecular / ion sieving performance. In recent years, two-dimensional membranes have been extensively studied for the sieving of gases, metal ions, solvents, dyes, etc. As an important two-dimensional nanomaterial, graphene oxide (GO) has enormous 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 for water purification.

[0004] GO membranes are mainly divided into GO-based hybrid membranes and GO layered membranes. Among them, GO layered membranes are constructed by stacking GO sheets layer by layer using a physical deposition method. Because layered membranes have good permeability to water molecules and can selectively separate solutes by relying on the volume exclusion effect of nanoscale interlayer spacing, and because the interlayer spacing of GO layered membranes can be adjusted to achieve the separation of solutes of different sizes, GO layered membranes have great potential for modification and have important application prospects in the field of water treatment.

[0005] GO layered membranes are simple to prepare, offer good separation performance, and possess excellent hydrophilicity, making them highly promising for water treatment. However, two problems remain. First, the large tortuosity of GO membranes significantly limits their water flux, hindering large-scale application. Second, GO membranes have weak bactericidal properties; in practical applications, microorganisms in the water easily aggregate and multiply on the membrane, leading to decreased membrane lifespan and performance. Improving the water flux and bactericidal performance of GO membranes while maintaining good retention capacity is key to preparing forward osmosis water treatment membranes suitable for large-scale application. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing a graphene oxide composite forward osmosis membrane. The graphene oxide composite forward osmosis membrane is prepared by physically incorporating a specific proportion of carbon nanotubes (CNTs) or carbon nanotubes and graphene oxide quantum dots (GO quantum dots) into graphene oxide. This preparation method is simple and efficient, enabling the fabrication of forward osmosis water treatment membranes that maintain good retention performance while exhibiting high water flux, excellent bactericidal properties, and large-scale applicability.

[0007] One object of the present invention is to provide a method for preparing a graphene oxide composite forward osmosis membrane, comprising the following steps: preparing a mixed solution, wherein the mixed solution is an aqueous dispersion comprising graphene oxide and acidified carbon nanotubes, and the mass ratio of graphene oxide to acidified carbon nanotubes is 2 to 18; performing vacuum filtration on the mixed solution to form a membrane; and drying the membrane to obtain a graphene oxide composite forward osmosis membrane.

[0008] This preparation method enables the production of forward osmosis water treatment membranes that maintain good retention performance, have high water flux, good bactericidal properties, and can be applied on a large scale.

[0009] Furthermore, in the above mixture, the mass ratio of graphene oxide to acidified carbon nanotubes is 4–9. The resulting membrane can better increase water flux while maintaining the desired retention performance.

[0010] Furthermore, the above mixture also includes graphene oxide quantum dots, and the mass ratio of the acidified carbon nanotubes to the graphene oxide quantum dots in the mixture is 0.5–4. The resulting membrane exhibits both increased water flux and superior antibacterial properties.

[0011] Furthermore, in the above mixture, the mass ratio of the acidified carbon nanotubes to the graphene oxide quantum dots is 1 to 2. The resulting membrane exhibits a better balance between water flux and antibacterial properties.

[0012] Furthermore, in the above mixture, the concentrations of graphene oxide, acidified carbon nanotubes, and graphene oxide quantum dots are all 0.01–0.1 mg / L. This improves preparation efficiency and facilitates the preparation of accurately concentrated aqueous dispersions.

[0013] Furthermore, the aforementioned acidified carbon nanotubes are obtained by acidifying carbon nanotubes with a strong acid. This increases the dispersibility of the carbon nanotubes.

[0014] Furthermore, the aforementioned strong acid is a mixture of concentrated sulfuric acid and concentrated nitric acid, or concentrated nitric acid. This reduces the inter-tube entanglement of carbon nanotubes, thereby increasing the dispersibility of carbon nanotubes.

[0015] Furthermore, the above drying process involves vacuum drying for more than 12 hours. This results in better membrane compactness.

[0016] Another object of the present invention is to provide a graphene oxide composite forward osmosis membrane comprising graphene oxide and acidified carbon nanotubes, wherein the mass ratio of the graphene oxide to the acidified carbon nanotubes is 2 to 18. With this structure, the forward osmosis membrane can maintain good retention performance and has the advantages of high water flux, good bactericidal performance, and large-scale application.

[0017] Furthermore, the aforementioned graphene oxide composite forward osmosis membrane also contains graphene oxide quantum dots, and the mass ratio of the acidified carbon nanotubes to the graphene oxide quantum dots is 0.5–4. This structure enhances the bactericidal performance of the forward osmosis membrane.

[0018] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0019] Figure 1 The images show SEM images of graphene oxide, carbon nanotubes before and after acidification, and graphene oxide quantum dots involved in this invention.

[0020] Figure 2 The images show the AFM diagrams of graphene oxide, acidified carbon nanotubes, and graphene oxide quantum dots involved in this invention.

[0021] Figure 3 XPS images of graphene oxide, carbon nanotubes before and after acidification, and graphene oxide quantum dots involved in this invention.

[0022] Figure 4 SEM surface and cross-sectional views of the membranes prepared in the comparative example, Example 1, and Example 3 are shown.

[0023] Figure 5 Morphology and roughness of the films prepared in Comparative Examples, Example 1, and Example 3 are shown.

[0024] Figure 6 The XRD patterns and partial patterns of the membranes prepared in the comparative example, Example 1, and Example 3 are shown.

[0025] Figure 7 The graph shows the improvement in bactericidal performance of the films prepared in Comparative Examples, Example 1, and Example 3 compared to Nylon 66. Detailed Implementation

[0026] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0027] First Implementation Method

[0028] According to a first embodiment of the present invention, a GO-CNT composite graphene oxide composite forward osmosis membrane (i.e., a GO-CNT composite forward osmosis membrane) can be obtained, and its preparation method includes the following steps:

[0029] S1: Prepare a mixture, wherein the mixture is an aqueous dispersion comprising graphene oxide and acidified carbon nanotubes, and the mass ratio of graphene oxide to acidified carbon nanotubes is 2 to 18.

[0030] S2: Vacuum filter the above mixture to form a film;

[0031] S3: The above membrane is dried to obtain a graphene oxide composite forward osmosis membrane.

[0032] Each step will be described in detail below.

[0033] For step S1, the mixture can be prepared by mixing graphene oxide (i.e., GO nanosheets) and acidified carbon nanotubes and then dispersing them in water; or by preparing graphene oxide aqueous dispersion and acidified carbon nanotube aqueous dispersion separately and then mixing the two.

[0034] Graphene oxide can be obtained through preparation or by purchasing commercially available materials. It should be noted that graphene oxide generally refers to graphene oxide materials with a sheet diameter of several hundred nanometers or larger. However, since there is no clear standard specifying its sheet diameter range, for the sake of clarity in this invention, it is hereby specified that "graphene oxide" involved / used in this invention refers to graphene oxide materials with a sheet diameter of 500 nm or larger. For example, it can be graphene oxide materials with a sheet diameter of 500 nm to 100 μm.

[0035] Acidified carbon nanotubes refer to carbon nanotubes that have undergone acid treatment, which can be obtained by acidifying carbon nanotubes with a strong acid. Carbon nanotubes can be prepared or purchased commercially, and can be single-walled or multi-walled carbon nanotubes. Considering cost, multi-walled carbon nanotubes are preferred.

[0036] It should be noted that acidified carbon nanotubes must be used in step S1. This is because carbon nanotubes are very long and severely entangled, resulting in uneven dispersion in the matrix. Acidification significantly reduces the entanglement between the tubes, improving their dispersibility in the matrix. This, in turn, allows for better dispersion of CNTs in GO, providing more water flow paths and further increasing the water flux of the GO-CNT composite forward osmosis membrane. Unacidified CNTs, on the other hand, cannot disperse at all in water and cannot form a membrane.

[0037] Furthermore, the aforementioned strong acid can be a mixture of concentrated sulfuric acid and concentrated nitric acid, or concentrated nitric acid. When using a mixture of concentrated sulfuric acid and concentrated nitric acid, the length of the carbon nanotubes can be further shortened, which is therefore preferred. In this mixture, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is preferably 3:1.

[0038] In the above mixture, the preferred concentrations of graphene oxide and acidified carbon nanotubes are 0.01–0.1 mg / mL. When the concentration is below 0.01 mg / mL, the volume of aqueous dispersion required for film formation is too large, the filtration time is too long, and the preparation efficiency is low; when the concentration is above 0.1 mg / mL, the formed aqueous dispersion is uneven, precipitation is easy to occur, and the concentration of the obtained solution is inaccurate.

[0039] In step S1, the mass ratio of GO to acidified CNTs in the mixture is 2–18, i.e., the mass ratio of GO to acidified CNTs is 2:1–18:1. If this mass ratio is less than 2, the proportion of CNTs is too large, resulting in a large water flux of the composite membrane, but a significant reduction in retention performance. If this mass ratio is greater than 18, the proportion of CNTs is too small, insufficient to increase the interlayer spacing of GO, and its contribution to increasing water flux is too small. From the same perspective, a more preferable mass ratio of GO to acidified CNTs is 4–9. Within this range, it is possible to better increase water flux while maintaining the required retention performance.

[0040] For step S2, this embodiment uses vacuum filtration to form the membrane. This allows for improved membrane formation efficiency through vacuum assistance and ensures a relatively dense membrane. Step S2 can be performed using a general vacuum filtration method, for example, by using a filtration apparatus as follows: The filter membrane is fixed between the filter head and the filter cup, and the filter head and filter cup are secured with clamps. The apparatus is then placed on a filtration flask. A mixture including GO and acidified CNTs is then injected into the filter cup, followed by appropriate rinsing and dilution with a certain volume of deionized water. Then, the vacuum pump connected to the filtration flask is turned on for filtration until the solution in the filter cup is completely drained and the membrane surface on the filter membrane turns black.

[0041] In the aforementioned vacuum filtration, the filter membrane can be made of commonly used materials such as nylon or polyvinylidene fluoride. Considering mechanical properties, nylon membranes, such as nylon 66, are preferred. Furthermore, appropriate membrane size and pore size can be selected based on material requirements and film formation criteria. For example, the pore size can be chosen to retain the dispersed phase while filtering out the liquid phase. Additionally, appropriate amounts of deionized water can be added during filtration to ensure that all the mixture is used for film formation.

[0042] For step S3, the membrane can be dried using conventional drying methods. Considering the membrane's density, vacuum drying is preferred, and the drying time is at least 12 hours.

[0043] The graphene oxide composite forward osmosis membrane (GO-CNT composite forward osmosis membrane) prepared by the preparation method described in the first embodiment above exhibits improved water flux by inserting CNTs between the GO sheets. This insertion creates protrusions and cracks between the originally tightly packed GO sheets, expanding the interlayer structure between the GO sheets. The CNT channels provide a frictionless and ultra-fast flow path for water. Furthermore, the insertion of CNTs between the GO sheets imparts bactericidal properties. When E. coli comes into direct contact with CNTs, it increases the pressure on the bacterial membrane, inducing further rupture and thus enhancing the bactericidal performance of the forward osmosis membrane.

[0044] Second Implementation Method

[0045] This second embodiment further introduces GO quantum dots based on the first embodiment. Using the preparation method described in this second embodiment, a CO-CNT-GO quantum dot composite graphene oxide composite forward osmosis membrane (i.e., a GO-CNT-GO quantum dot composite forward osmosis membrane) can be obtained.

[0046] The preparation method involved in this second embodiment may include the following steps:

[0047] S1': Prepare a mixture, wherein the mixture is an aqueous dispersion comprising graphene oxide, acidified carbon nanotubes and graphene oxide quantum dots, and the mass ratio of graphene oxide to acidified carbon nanotubes is 2 to 18, and the mass ratio of acidified carbon nanotubes to graphene oxide quantum dots is 0.5 to 4.

[0048] S2': Vacuum filtration of the above mixture to form a film;

[0049] S3': The above membrane is dried to obtain a graphene oxide composite forward osmosis membrane.

[0050] In this second embodiment, steps S2' and S3' are the same as S2 and S3 in the first embodiment described above, and will not be repeated here.

[0051] For step S1', the mixture can be prepared by dispersing graphene oxide, acidified carbon nanotubes, and graphene oxide quantum dots in water; or by preparing graphene oxide aqueous dispersion, acidified carbon nanotube aqueous dispersion, and graphene oxide quantum dot aqueous dispersion separately and then mixing the three.

[0052] Graphene oxide quantum dots can be obtained by preparation or by purchasing commercially available materials. It should be noted that, for clarity and to distinguish this invention from the "graphene oxide" referred to herein, "graphene oxide quantum dots or GO quantum dots" as used in this invention refer to graphene oxide materials with a sheet diameter of less than 100 nm.

[0053] Similarly, in the above mixture, the preferred concentrations of graphene oxide, acidified carbon nanotubes, and graphene oxide quantum dots are 0.01–0.1 mg / mL. When the concentration is below 0.01 mg / mL, the volume of aqueous dispersion required for film formation is too large, the filtration time is too long, and the preparation efficiency is low; when the concentration is above 0.1 mg / mL, the formed aqueous dispersion is uneven, precipitation is easy to occur, and the concentration of the obtained solution is inaccurate.

[0054] Furthermore, as mentioned above, the mass ratio of acidified CNTs to GO quantum dots is 0.5–4. If this mass ratio is less than 0.5, the excessive GO quantum dot content will block the water channels generated by CNTs, which is not conducive to increasing water flux; if this mass ratio is greater than 4, the GO quantum dot content is too low, and its contribution to antibacterial properties is insufficient. From the same point of view, a more preferable mass ratio of CNTs to GO quantum dots is 1–2, and the most preferred is 1.

[0055] According to the preparation method of this second embodiment, by inserting CNTs and GO quantum dots between GO sheets, the small size of GO quantum dots results in a large number of cutting edges, which greatly enhances the bactericidal performance due to the edge cutting effect. In addition, GO quantum dots can generate reactive oxygen free radicals, which have extremely strong oxidizing properties. These free radicals can decompose lipids on the cell membrane of E. coli, disrupt some physiological processes during cell growth, thereby inhibiting bacterial growth and reproduction, leading to bacterial death, and thus greatly enhancing the bactericidal performance of the forward osmosis membrane.

[0056] Example

[0057] The present invention will now be described in detail through embodiments. These embodiments are intended to further explain the present invention, and their scope is not limited thereto.

[0058] Examples 1-4 and the comparative examples were implemented according to the following steps:

[0059] (1) Acidification treatment of CNTs

[0060] Take 0.800g of multi-walled carbon nanotubes and place them in 100mL of a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. Disperse the solution by ultrasonication for 6h, cool it to room temperature, wash it with a large amount of deionized water, filter it through polytetrafluoroethylene filter paper and wash it with water until neutral. Dry it under vacuum at 75℃ for 24h before use.

[0061] (2) Preparation of aqueous dispersion mixture

[0062] According to the composition shown in Table 1 below, each component was prepared into an aqueous dispersion of 1 mg / mL using deionized water. The dispersions were stirred at 600 rpm for 30 min to ensure uniformity. Next, a mixture was prepared according to the composition and volume shown in Table 1 below to obtain the mixture with the mass ratios shown in Table 1.

[0063] (3) Vacuum filtration

[0064] A 50mm diameter nylon 66 substrate membrane is fixed between the filter head and the filter cup, and secured with metal clips to ensure a tight seal. The mixture is poured in, followed by a certain amount of deionized water for rinsing and dilution. The vacuum pump is then turned on to extract the membrane. Once the solution has been completely extracted and the membrane surface turns black, the membrane is carefully removed from the apparatus.

[0065] (4) Drying

[0066] Transfer the membrane to a vacuum drying chamber and dry for at least 12 hours.

[0067] Thus, Examples 1 and 2 yielded a GO-CNT composite graphene oxide composite forward osmosis membrane (GO-CNT composite forward osmosis membrane), Examples 3 and 4 yielded a GO-CNT-GO quantum dot composite graphene oxide composite forward osmosis membrane (GO-CNT-GO quantum dot composite forward osmosis membrane), and the comparative example yielded a GO forward osmosis membrane.

[0068] Table 1. Composition, amount of aqueous dispersion, and mass ratio of Examples 1-4 and Comparative Examples.

[0069]

[0070]

[0071] [Structural Analysis]

[0072] The structures of the forward osmosis membranes prepared in Comparative Example 1, Example 1, and Example 3 were determined and analyzed.

[0073] (1) SEM analysis

[0074] The microstructure of the membrane was observed using a scanning electron microscope (SEM). A Hitachi SU8100 microscope (Japan) was used, and the detection conditions were: ambient temperature: 23±2℃, relative humidity: ≤50%. The operating voltage for the Ac image was 5KV, and the accelerating voltage for the d image was 25KV. SEM surface and cross-sectional images of the membrane were obtained.

[0075] SEM surface and cross-sectional images of the membranes involved in Comparative Example 1, Example 1, and Example 3 are shown in the figure. Figure 4 .exist Figure 4In the diagram, (a, b) are SEM surface and cross-sectional images of the GO forward osmosis membrane prepared in the comparative example; (c, d) are SEM surface and cross-sectional images of the GO-CNT composite forward osmosis membrane prepared in Example 1; and (e, f) are SEM surface and cross-sectional images of the GO-CNT-GO quantum dot composite forward osmosis membrane prepared in Example 3.

[0076] It can be seen that the GO forward osmosis membrane prepared in the comparative example has a relatively smooth surface with a few protrusions between GO nanoparticles, and the GO nanosheets are arranged in regular layers on the membrane cross-section. After adding a certain amount of CNTs (Fig. (4c,d)), some cracks appeared on the membrane surface, which is beneficial to increasing the water flux of the membrane; on the membrane cross-section, due to the presence of CNTs, the arrangement of GO nanosheets became irregular. After adding a certain amount of GO quantum dots ( Figure 4 (e,f)) Due to the small size of GO quantum dots, they were not clearly observed in the image and did not have a significant impact on the morphology of the film.

[0077] (2) AFM analysis

[0078] The morphology and roughness of the film were observed using atomic force microscopy (AFM). An AFM (Bruker Dimension Icon, Germany) was used, and the following conditions were observed: ambient temperature: 23±2℃, relative humidity: ≤50%, imaging mode: peak force tapping; microcantilever force constant: 0.4 N / m; scan rate: 1 Hz.

[0079] SEM surface and cross-sectional images of the membranes involved in Comparative Example 1, Example 1, and Example 3 are shown in the figure. Figure 5 .exist Figure 5 In the figure, (a) shows the morphology and roughness of the GO forward osmosis membrane; (b) shows the morphology and roughness of the GO-CNT composite forward osmosis membrane; and (c) shows the morphology and roughness of the GO-CNT-GO quantum dot composite forward osmosis membrane.

[0080] It can be seen that the surface of the GO forward osmosis membrane has some undulations, but the overall roughness is relatively small, with a root mean square roughness Rq and an arithmetic mean roughness Ra of 1.38 nm and 1.10 nm, respectively. After incorporating a certain amount of CNTs ( Figure 5 (b) The outline of CNTs can be clearly observed on the film surface. CNTs and GO are well fused together. Because CNTs are well inserted between the GO layers, the originally flat GO layers become convex, and the roughness increases significantly. The root mean square roughness Rq and the arithmetic mean roughness Ra increase to 5.35 nm and 4.44 nm, respectively. After a certain amount of GO quantum dots are doped ( Figure 5(c) Due to the small size of GO quantum dots, the outline of GO quantum dots was not clearly observed on the membrane surface. However, compared with the GO-CNT composite forward osmosis membrane, the roughness of the GO-CNT-GO quantum dot composite forward osmosis membrane was slightly increased, with the root mean square roughness Rq and the arithmetic mean roughness Ra increasing to 6.00 nm and 4.63 nm, respectively.

[0081] (3) XRD analysis

[0082] The structure of the membrane was determined by X-ray diffraction (XRD). An X-ray diffractometer (Rigaku SmartLab, Japan) was used, with the following detection conditions: ambient temperature: 23±2℃, relative humidity: ≤50% (Cu-kλ, 40KV, 40mA, λ=0.154nm). The XRD pattern of the membrane was obtained.

[0083] The XRD patterns and partial illustrations of the membranes involved in the comparative examples, Example 1, and Example 3 are shown in the figure. Figure 6 .exist Figure 6 In the image, (a) shows the XRD patterns of the GO forward osmosis membrane, the GO-CNT composite forward osmosis membrane, the GO-CNT-GO quantum dot composite forward osmosis membrane, and CNT and GO quantum dots; (b) shows the partial XRD patterns of the GO forward osmosis membrane, the GO-CNT composite forward osmosis membrane, and the GO-CNT-GO quantum dot composite forward osmosis membrane.

[0084] As can be seen, due to the low content of CNTs and GO quantum dots in GO, no obvious peaks of CNTs and GO quantum dots appeared in the XRD patterns of the GO forward osmosis membrane, the GO-CNT composite forward osmosis membrane, and the GO-CNT-GO quantum dot composite forward osmosis membrane. Therefore, the peak of GO was selected as the research object. Figure 6 (b) It can be seen that, compared with the GO forward osmosis membrane, the peaks of the GO-CNT composite forward osmosis membrane and the GO-CNT-GO quantum dot composite forward osmosis membrane shift significantly to lower angles. According to the Bragg equation (λ=2dsinθ), the interlayer spacing of GO increases significantly after the incorporation of CNTs. This is because the incorporation of CNTs creates protrusions between the originally tightly packed GO sheets on the membrane surface, increasing the interlayer spacing. This provides more water channels for the forward osmosis membrane, which is beneficial to improving the water flux of the forward osmosis membrane. In addition, compared with the GO-CNT composite forward osmosis membrane, the GO peak of the GO-CNT-GO quantum dot composite forward osmosis membrane did not shift significantly. This is because the size of GO quantum dots is small and insufficient to increase the interlayer spacing between GO sheets.

[0085] In addition, the structures of GO as a film-forming material, CNTs before and after acidification, and GO quantum dots were also determined.

[0086] Figure 1 (a) Figure 2(a,b) Figure 3 (a) shows the SEM, AFM and XPS results for GO. Figure 1 (d) Figure 2 (e,f) Figure 3 (d) shows the SEM, AFM and XPS results of GO quantum dots. Figure 1 (b,c) show the SEM images of CNTs before and after acidification treatment. Figure 2 (c,d) show AFM images of acidified CNTs. Figure 3 (b, c) show the XPS images before and after CNT acidification. The measurement conditions for SEM, AFM, and XPS were the same as above.

[0087] In particular, for CNT acidification treatment, by Figure 1 The SEM images (b, c) show that untreated CNTs are elongated tubular structures with long tube lengths, and the tubes are intertwined in a "ball of yarn" structure. After acid treatment, most CNTs are reduced to tube lengths of only a few hundred or even tens of nanometers. Acid treatment significantly increases the number of CNT ports, effectively increasing the specific surface area, and the intertwining between tubes completely disappears. Figure 2 The AFM images (c, d) show that the outer diameter of the acidified CNTs is approximately tens of nanometers, and the tube length ranges from tens to hundreds of nanometers. Due to the acidification process, numerous defects exist on the tube walls of the CNTs. Unacidified CNTs are difficult to disperse in solvents; therefore, atomic force microscopy analysis was not performed on unacidified CNTs. Figure 3 XPS plots (b, c) show that unacidified CNTs are composed of carbon and oxygen elements, with a relatively low oxygen content and few oxygen-containing functional groups. Therefore, they cannot disperse well in water and cannot form films directly. After acidification, the relative oxygen content increases, and the number of oxygen-containing functional groups increases, allowing for uniform dispersion in water. Furthermore, nitric acid was used during the acidification process, introducing a small amount of nitrogen. The above structural information of CNTs before and after acidification indicates that acidification improves the dispersibility of CNTs in the matrix.

[0088] [Membrane Performance Measurement]

[0089] To evaluate the performance of the prepared forward osmosis membranes, the membranes obtained in Examples 1-4 and the comparative examples were tested for three aspects: bactericidal performance, water flux, and retention performance.

[0090] (1) Sterilization performance

[0091] The bactericidal performance was determined as follows: *E. coli* was added to sterile LB broth and incubated overnight in a 37°C shaking incubator. The bacterial suspension was obtained by centrifugation for 5 minutes using a high-speed centrifuge. This step was repeated three times. The bacterial concentration was then diluted to 1×10⁻⁶ with sterile physiological saline. 6 CFU / mL. The membrane was cut into 2cm × 2cm squares and irradiated under UV light for 0.5h. Using sterile forceps, the membrane was inserted into the diluted bacterial suspension and incubated at 37℃ with shaking for 2h. After incubation, the membrane surface was rinsed with 5mL of sterile physiological saline and sonicated for 15min to completely detach the E. coli from the membrane surface. 0.1mL of the collected rinsing solution was spread onto LB agar plates and then incubated at 37℃ for 20h. Finally, the bactericidal activity (Rb) of the composite membrane was calculated based on the number of E. coli colonies on the plates. s The specific calculation formula is as follows:

[0092]

[0093] In the formula, N N It is the total number of bacterial colonies after contact with Nylon 66, N G It is the total number of bacterial colonies after contact with each type of forward osmosis membrane.

[0094] The calculation method for increasing the ratio is as follows: First, calculate the bactericidal property of nylon 66. Then, subtract the bactericidal property of nylon 66 from the bactericidal property of other membranes and divide by the bactericidal property of nylon 66 to get the ratio of the bactericidal property of the membrane.

[0095] The bactericidal performance results of the membranes prepared in Examples 1-4 and Comparative Examples are shown in Table 2 and 3. Figure 7 .

[0096] The results show that the bactericidal performance improvement ratio of both the GO-CNT composite forward osmosis membrane and the GO-CNT-GO quantum dot composite forward osmosis membrane is higher than that of the GO forward osmosis membrane, indicating that the bactericidal performance of both membranes is superior to that of the GO forward osmosis membrane. Compared with the GO forward osmosis membrane, the bactericidal performance of the GO-CNT composite forward osmosis membrane with a specific proportion of CNT is slightly improved by 4-7%, while the bactericidal performance of the GO-CNT-GO quantum dot composite forward osmosis membrane with a specific proportion of CNT and GO quantum dots is significantly improved by 20-32%.

[0097] (2) Water flux

[0098] The method for determining water flux is as follows: The prepared membrane is fixed between the filter head and filter cup of the membrane fabrication device, and both are secured with metal clamps to ensure a tight seal. A certain amount of ultrapure water is then injected into the filter cup. After standing for 2 hours, the mass m (g) of the ultrapure water in the filtration flask is weighed and converted into the volume V (L) of ultrapure water. Water flux is expressed as Jw (L h). - 1 m -2 The effective area of ​​the membrane is denoted by A(m²), the time interval is denoted by t(h), and the membrane's effective area is denoted by A(m²). 2 This indicates that in this experiment, t = 2h, A = 1.26 × 10⁻⁶. -3 m 2 ( Figure 2-2 b), The calculation formula is as follows:

[0099]

[0100] The water flux measurement results of the membranes obtained in Examples 1-4 and the comparative examples are also shown in Table 2.

[0101] The measurement results show that, compared with the GO forward osmosis membrane obtained in the comparative example, the water flux of the GO-CNT composite forward osmosis membranes prepared in Examples 1 and 2 is significantly increased. This is because the incorporation of CNTs causes protrusions and cracks to form between the originally tightly packed GO sheets on the membrane surface, thereby expanding the interlayer structure between the GO sheets. The channels of CNTs provide a frictionless and ultra-fast path for water flow. When a certain amount of GO quantum dots are incorporated, the water flux of the GO-CNT-GO quantum dot composite forward osmosis membranes prepared in Examples 3 and 4 is slightly reduced. This is because the GO quantum dots are small in size and insufficient to expand the interlayer structure between the GO sheets, nor can they provide more water channels. At the same time, they hinder some water flow through the internal channels of CNTs, thus slightly reducing the water flux.

[0102] (3) Retention performance

[0103] The method for determining the retention performance is as follows: First, the prepared membrane is compacted into a self-made U-shaped trough using a leak-proof gasket, and both ends are clamped to prevent leakage. Then, deionized water is added to one side of the U-shaped trough, and a salt solution is added to the other side. A stir bar is then placed in to prevent concentration polarization within the trough during the test. Finally, the probe of the conductivity meter is inserted into the deionized water side, the program is set, and the test can begin. The obtained ionic conductivity can be used to determine the ion concentration through the linear relationship between ionic conductivity and concentration. The ion permeation rate is obtained based on the relationship between ion concentration and time at different times. The ion concentration on the permeation side is C. d (mol L -1 The ionic conductivity on the osmotic side is λ (S cm⁻¹). -1 The conversion coefficient between ionic conductivity and concentration is Λ.m (S cm⁻¹ / mol L) -1 This coefficient is a constant for a given ionic solution. The linear equation is shown below:

[0104]

[0105] Ion rejection rate R is determined by the ion concentration C on the permeation side. d and the ion concentration C of the feed solution f The calculation is as follows:

[0106]

[0107] The molar conductivities Λm of potassium, sodium, and lithium ions are 0.1285, 0.0939, and 0.0915 S / cm, respectively. -1 / molL -1 .

[0108] The retention performance results obtained from Examples 1-4 and the comparative examples are also shown in Table 2.

[0109] The test results show that, compared with the GO forward osmosis membrane prepared in the comparative example, the ion rejection rate of the membranes prepared in Examples 1 to 4 is slightly lower. This is because the rejection rate is sacrificed due to the increase in other membrane properties, but the sacrifice is not significant. The membranes prepared in Examples 1 to 4 still have good rejection rates and meet the rejection requirements.

[0110] Table 2 shows the performance test results of the membranes obtained in Examples 1-4 and Comparative Examples.

[0111]

[0112] Based on the above results, it can be seen that, compared with the GO forward osmosis membrane prepared in the comparative example, the GO-CNT composite forward osmosis membranes prepared in Examples 1 and 2, as well as the GO-CNT-GO quantum dot composite forward osmosis membranes prepared in Examples 3 and 4, all maintain good retention performance while having greater water flux and better bactericidal performance; furthermore, the GO-CNT-GO quantum dot composite forward osmosis membrane has even better bactericidal performance than the GO-CNT composite forward osmosis membrane.

[0113] The preparation method involved in this invention can prepare graphene oxide composite forward osmosis membranes that improve water flux and sterilization performance while maintaining good retention performance. This preparation method is simple and efficient and can be applied on a large scale to the preparation of forward osmosis water treatment membranes.

[0114] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene oxide composite forward osmosis membrane, characterized in that, Includes the following steps: A mixture is prepared, wherein the mixture is an aqueous dispersion comprising graphene oxide and acidified carbon nanotubes, and the mass ratio of graphene oxide to acidified carbon nanotubes is 2 to 18, wherein the acidified carbon nanotubes are prepared by ultrasonically dispersing carbon nanotubes in a mixed acid solution composed of concentrated sulfuric acid and concentrated nitric acid for 6 hours. The mixture is vacuum filtered to form a film; The membrane was subjected to vacuum drying for more than 12 hours to obtain a graphene oxide composite forward osmosis membrane.

2. The method for preparing the graphene oxide composite forward osmosis membrane according to claim 1, characterized in that, In the mixture, the mass ratio of graphene oxide to acidified carbon nanotubes is 4 to 9.

3. The method for preparing the graphene oxide composite forward osmosis membrane according to claim 1 or 2, characterized in that, The mixture also includes graphene oxide quantum dots, and the mass ratio of the acidified carbon nanotubes to the graphene oxide quantum dots in the mixture is 0.5 to 4.

4. The method for preparing the graphene oxide composite forward osmosis membrane according to claim 3, characterized in that, In the mixture, the mass ratio of the acidified carbon nanotubes to the graphene oxide quantum dots is 1 to 2.

5. The method for preparing the graphene oxide composite forward osmosis membrane according to claim 3, characterized in that, In the mixture, the concentrations of graphene oxide, acidified carbon nanotubes, and graphene oxide quantum dots are all 0.01~0.1 mg / L.

6. A graphene oxide composite forward osmosis membrane prepared by the preparation method according to any one of claims 1-5, characterized in that, It comprises graphene oxide and acidified carbon nanotubes, wherein the mass ratio of graphene oxide to acidified carbon nanotubes is 2 to 18.

7. The graphene oxide composite forward osmosis membrane according to claim 6, characterized in that, It also contains graphene oxide quantum dots, and the mass ratio of the acidified carbon nanotubes to the graphene oxide quantum dots is 0.5 to 4.

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