WO2021068292A1 - 一种具有帐篷状结构的氧化石墨烯膜及其制备方法与应用 - Google Patents

一种具有帐篷状结构的氧化石墨烯膜及其制备方法与应用 Download PDF

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WO2021068292A1
WO2021068292A1 PCT/CN2019/112991 CN2019112991W WO2021068292A1 WO 2021068292 A1 WO2021068292 A1 WO 2021068292A1 CN 2019112991 W CN2019112991 W CN 2019112991W WO 2021068292 A1 WO2021068292 A1 WO 2021068292A1
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graphene oxide
oxide film
film
tent
membrane
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PCT/CN2019/112991
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French (fr)
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陈宝梁
杨凯杰
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浙江大学
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis

Definitions

  • the invention belongs to the field of environmental protection material preparation, and specifically relates to an ultra-thin graphene oxide with a tent-like structure, and a preparation method and application thereof.
  • Membrane separation technology is a technology that uses pore sieving to achieve selective separation of nanoparticles, molecules and ions.
  • the membrane separation process plays an irreplaceable role in the fields of chemical purification, resource recovery and environmental pollution control.
  • the graphene oxide film has attracted widespread attention from the scientific and industrial circles due to its special interlayer structure.
  • the sieving pores of graphene oxide membranes are two-dimensional interlayer spaces.
  • Research by Joshi et al. found that in aqueous solution, the interlayer distance of graphene oxide film is about 0.9nm, and its sieving channel can accurately block molecules or ions with a hydration radius greater than 0.45nm, while allowing the hydration radius to be less than 0.45.
  • a sandwich-like sandwich structure can be constructed, thereby achieving an overall increase in the distance between graphene oxide membrane layers and an increase in water flux (Burress, JWet al. Graphene Oxide Framework Materials) :Theoretical Predictions and Experimental Results.Angew.Chem.Int.Ed.Engl.49,8902-4,(2010).Hung,W.etal.Cross-Linking with Diamine Monomers to Prepare Composite Graphene Oxide-FrameworkMembranes with Varying D-Spacing.Chem.Mater.26,2983-2990,(2014).Yang,J.et al.Self-Assembly of Thiourea-Crosslinked Graphene Oxide FrameworkMembranesTowardSeparationofSmallMolecules.Adv.Mater.30,1705775, (2016).Huang,H.et al.Ul
  • the sandwich structure constructed by ordinary nano-material intercalation can increase the water flux of the membrane, the increase in water flux is often at the expense of the selectivity of the membrane itself, and the intercalation of simple nano-materials is difficult
  • the molecular cross-linking method may theoretically realize the adjustment of the distance between graphene oxide film layers on the molecular scale, it is due to the hydration of the molecules in water, the easy deformation, and the force of molecules of different chain lengths on the graphene sheets.
  • An invention patent with application number CN201710964971.1 discloses a nanoparticle intercalated graphene oxide film and its preparation method and application. It sprays the graphene oxide and nano-particle mixture directly onto the microporous filter membrane substrate by electrostatic spraying method, thereby obtaining the nano-particle intercalated graphene oxide film.
  • the nanoparticle intercalation graphene oxide film can effectively increase the graphene oxide sheet layer spacing, increase the water flux, and maintain a relatively high rejection rate for organic dyes.
  • this electrostatic spraying method can realize the intercalation of nanoparticles between graphene film layers, it cannot achieve precise control of the distance between graphene film layers at the molecular level.
  • the ideal membrane structure must meet the following conditions: (1) It has an ultra-thin structure to ensure efficient water flux, and (2) It has good mechanical stability to ensure The stability of the structure during the application process, (3) has an adjustable sieving channel, and has a narrow sieving size distribution.
  • the purpose of the present invention is to solve the problems existing in the prior art and provide an improved filtration assembly method that can reliably prepare ultra-thin graphene oxide films. Based on this assembly method, we propose a new tent-like nanostructure construction strategy to control the structure, surface properties, water flux and screening performance of ultra-thin graphene.
  • the inventive concept of the present invention is to design an ultra-thin graphene oxide film with a tent-like structure. It uses graphene oxide as the basic building unit, and uses nanoparticle intercalation as the construction method. By covering the flexible graphene oxide on the hard The surface of the nanoparticles forms a tent-like structure to realize the construction of the tent-like structure.
  • the tent-like nanostructure constructed between the ultra-thin graphene oxide membrane layers can effectively increase the water flux of the membrane itself while retaining its retention performance.
  • the sieving performance of the membrane can be adjusted in molecular precision, and the selective separation of small molecules with angstrom size differences in water can be achieved.
  • the water flux of the graphene oxide composite membrane with tent-like nanostructure is 1.3-60 times higher than that of the original ultra-thin graphene oxide membrane.
  • this ultra-thin graphene oxide film with tent-like nanostructures can also achieve surface roughness, surface hydrophilicity and hydrophobicity, and surface electrical properties. Due to its adjustable screening performance, precise selectivity, high water flux and controllable surface properties, the membrane has huge application prospects in the field of water purification and membrane separation.
  • the present invention provides a graphene oxide membrane with a tent-like structure in order to solve the problems of low water flux and the inaccurate adjustment of the screening channel existing in the existing graphene oxide membrane.
  • the surface is intercalated with nanoparticles to form a distributed tent-like nanostructure; in the tent-like nanostructure, the graphene oxide sheet layer covers the nanoparticles and forms tent-like protrusions under the support of the nanoparticles.
  • the tent-like nano structure is formed with rigid nano particles as a support, and the position of the nano particles has a relatively high spatial height, and then gradually decreases in height to both sides, in the form of a tent. Due to the limitation of the formation mechanism of the tent-like nanostructure, the thickness of the graphene oxide film should not be too thick, and should be in the form of a thin layer.
  • the graphene oxide film is assembled on a flexible support film.
  • the flexible support membrane can also be replaced by other substrates.
  • the graphene oxide membrane can be directly assembled on the surface of the AAO membrane, the surface of the hollow fiber membrane and other application components.
  • the graphene oxide membrane is assembled by means of negative pressure suction filtration.
  • the negative pressure suction filtration method is beneficial to accurately control the added amount of the assembly unit, and is beneficial to control the thickness of the film and the uniformity of the formed structure.
  • the graphene oxide film after the graphene oxide film is assembled into a film, the graphene oxide can be completely reduced or partially reduced.
  • the nanoparticle is a material that can interact and bond with the oxygen-containing functional group of graphene oxide by hydrogen bonding or chemical bonding.
  • the selected nanoparticles can have hydrogen bonds or other chemical bonds with the oxygen-containing functional groups on the surface of the graphene oxide to enhance the stability of the membrane structure.
  • the nanoparticles are silica nanoparticles or silver nanoparticles. It is further preferred to be silica nanoparticles, because the silica nanoparticles are an inexpensive material, and the hydrogen bonds on the surface thereof can be connected to the carboxyl groups on the surface of the graphene oxide through hydrogen bonds.
  • the size of the nanoparticles is preferably 10-1000 nm.
  • the purpose is to make the graphene oxide better cover the nanoparticles during the assembly process to build a tent-like structure.
  • the thickness of the graphene oxide film is less than 50 ⁇ m, and the thickness is preferably nanometer level, so as to ensure the water flux of the film. .
  • the flexible supporting film is a polycarbonate film.
  • the present invention provides a method for preparing a graphene oxide membrane with a tent-like structure according to any one of the technical solutions of the first aspect, the specific steps of which are: covering the filter surface of the suction filter device with a layer A buffer layer with uniform pores, and then a flexible support film is placed on the buffer layer; the dispersion liquid containing nanoparticles and graphene oxide is placed in a suction filtration device, and vacuum filtration is used to assemble it on the flexible support film to form the Graphene oxide film with nanoparticle intercalation.
  • the suction filter device is a glass suction filter funnel.
  • the pore size of the buffer layer is less than or equal to the pore size of the support layer, and the pore structure needs to be uniform, so as to uniformly disperse the vacuum pressure.
  • the buffer layer is a mixed cellulose ester film.
  • the pore size of the buffer layer is preferably 5 to 5000 nm.
  • the buffer layer is wetted with water and attached to the filter surface, and the flexible support film is wetted with water and attached to the buffer layer .
  • the mass ratio of nanoparticles:graphene oxide is 0.01-10.
  • the intercalation ratio of the nanoparticles can control the size and quantity of the tent-like structure, thereby realizing the adjustment of the screening channel and the adjustment of the surface properties of the membrane. Controlling the mass ratio between 0.01-10 can enable the membrane to selectively separate small molecular substances, and an excessively high intercalation ratio will reduce the membrane's retention performance.
  • the graphene oxide film obtained after vacuum filtration needs to be dried.
  • the present invention provides a graphene oxide film prepared by the preparation method described in any one of the technical solutions of the foregoing second aspect.
  • the present invention provides a method for adjusting the sieving channel of a graphene oxide film, which is done in the process of preparing the graphene oxide film by using the preparation method described in any of the technical solutions in the second aspect described above, By adjusting the intercalation ratio of nanoparticles in the graphene oxide film, the sieve channel adjustment on the angstrom scale is achieved.
  • the present invention provides a method for adjusting the surface roughness of a graphene oxide film.
  • the method is to prepare the graphene oxide film by using the preparation method described in any of the technical solutions in the second aspect.
  • the surface roughness of the film can be adjusted by adjusting the intercalation ratio of the nanoparticles in the graphene oxide film.
  • the present invention provides a method for adjusting the surface hydrophilicity and hydrophobicity of a graphene oxide film.
  • the method is that in the process of preparing the graphene oxide film by using the preparation method described in any one of the technical solutions in the second aspect described above, By adjusting the intercalation ratio of the nanoparticles in the graphene oxide film, the hydrophilic and hydrophobicity of the film surface can be adjusted.
  • the present invention provides a method for adjusting the surface electrical properties of a graphene oxide film.
  • the method is to prepare the graphene oxide film by using the preparation method described in any of the technical solutions in the second aspect.
  • the electrical properties of the film surface can be adjusted.
  • the present invention provides a membrane separation device or a water purification device made of the graphene oxide film according to any one of the technical solutions of the first aspect or the third aspect.
  • the beneficial effects of the present invention are as follows: 1) The present invention further realizes the construction of tent-shaped nanostructures by intercalating nanoparticles into the ultra-thin structure. Utilizing the ⁇ - ⁇ interaction between the graphene oxide sheets and the hydrogen bonding between the particles and the graphene oxide, the obtained composite film can maintain a stable structure in different pH aqueous solutions. Its special nano-tent-like structure uses the raised space to increase the water flux, while retaining the surrounding stacked structure to achieve molecular sieving. Therefore, this structure can maximize the water flux while retaining the retention performance. Compared with the original ultra-thin graphene oxide membrane, the composite membrane has 1.3-60 times higher water flux than the original ultra-thin graphene oxide membrane under the premise of the same retention performance.
  • the present invention establishes an improved filtration assembly method for ultra-thin graphene oxide membranes with tent-like nanostructures, and realizes the reliable preparation of ultra-thin graphene oxide membranes on flexible substrates, and by intercalating nanoparticles into Inside the ultra-thin structure, the construction of a tent-like nanostructure on a flexible substrate is further realized.
  • it is difficult to achieve uniform pores in general commercial glass funnels.
  • the uneven water flow during the filtration process will cause the uneven assembly of graphene oxide sheets during the preparation of ultra-thin graphene oxide membranes, resulting in The ultra-thin structure has more cracks that are hard to find with the naked eye.
  • the present invention can adjust the intercalation ratio of nanoparticles, so that the screening channel of the membrane can be adjusted on the angstrom scale, and the selective separation of small molecules of similar size can be achieved.
  • the intercalation ratio of nanoparticles by adjusting the intercalation ratio of nanoparticles, the surface roughness, wettability and surface electrical properties of the film can be controlled in an orderly manner.
  • the water flux of the ultra-thin graphene oxide film with a tent-like structure prepared by the present invention is 1.3-60 times that of the original ultra-thin graphene oxide film.
  • the membrane can exist stably in different pH aqueous solutions, and its screening channel can be adjusted on the molecular scale by adjusting the intercalation ratio of nanoparticles, and can selectively screen small molecules with similar sizes (molecular weight gap>100Da).
  • the composite membrane has broad application prospects in the field of environmental pollution control and membrane separation technology.
  • FIG. 1 Ultra-thin graphene oxide film prepared by traditional filtration assembly method.
  • A Photograph of ultra-thin graphene oxide film
  • B Scanning electron microscope image of ultra-thin graphene oxide film.
  • FIG. 2 The ultra-thin graphene oxide film prepared by the improved filtration assembly method of the present invention.
  • A Photograph of ultra-thin graphene oxide film
  • B Scanning electron microscope image of ultra-thin graphene oxide film.
  • FIG. 3 The filter assembly process of the membrane structure.
  • A Schematic diagram of improved filtration assembly process
  • B Schematic diagram of glass funnel
  • C Schematic diagram of buffer layer
  • D Schematic diagram of support layer
  • E Schematic diagram of tent-shaped ultra-thin graphene oxide film
  • b Peeling funnel SEM image of (c) SEM image of buffer layer, (d) SEM image of support layer, (e) SEM image of ultra-thin graphene oxide film with tent-like structure.
  • Fig. 7 Tyndall phenomenon after the dispersion liquid was allowed to stand for one week.
  • A Tyndall phenomenon of graphene oxide dispersion
  • B Tyndall phenomenon of nano-silica dispersion
  • C Tyndall phenomenon of graphene oxide + nano-silica dispersion.
  • Fig. 8 is an appearance photograph of an ultra-thin graphene oxide film with a tent-like structure.
  • Figure 9 The structural stability of the membrane material prepared in the present invention in pure water, acidic hydrochloric acid solution and alkaline ammonia solution.
  • Figure 10 The stability in water of a micron-thick graphene oxide film prepared by a traditional filtration assembly method.
  • Figure 11 Bonding between nano-silica and graphene oxide sheets.
  • A The infrared characterization spectra of Examples 2-5,
  • B the schematic diagram of the bonding between graphene oxide and silica.
  • Figure 12 The surface microstructure of the ultra-thin graphene oxide film with a tent-like structure prepared by the present invention.
  • A the surface microstructure of Example 2
  • B the surface microstructure of Example 3
  • C the surface microstructure of Example 4
  • D the surface microstructure of Example 5.
  • FIG. 13 Atomic force microscope image of an ultra-thin graphene oxide film with a tent-like structure prepared by the present invention.
  • A the surface microstructure of Example 2
  • B the surface microstructure of Example 3
  • C the surface microstructure of Example 4
  • D the surface microstructure of Example 5.
  • Fig. 14 The cross-sectional microstructure of the ultra-thin graphene oxide film with a tent-like structure prepared by the present invention.
  • A the cross-sectional microstructure of Example 2
  • B the cross-sectional microstructure of Example 3
  • C the cross-sectional microstructure of Example 4
  • D the cross-sectional microstructure of Example 5.
  • FIG. 18 Water flux evaluation of membrane.
  • A The water flux of different embodiments
  • B The change of water flux under different applied pressures.
  • Figure 19 retains size information of nanoparticles or molecules.
  • Figure 20 Evaluation of the retention performance of ultra-thin graphene oxide film with tent-like structure for nano-silver and different molecules.
  • A Example 1-5 for the retention performance and flux evaluation of nano-silver
  • B Example 1-5 for the retention performance and flux evaluation of Eosin Y
  • C Example 1-5 for methyl Evaluation of retention performance and flux of orange
  • D Evaluation of retention performance and flux of p-hydroxybenzoic acid in Examples 1-5.
  • FIG. 21 Selective separation of different mixed molecules by ultra-thin graphene oxide membrane with a tent-like structure.
  • A Schematic diagram of selective separation mechanism
  • B the selective separation of Eosin Y and p-hydroxybenzoic acid in Example 4
  • C The selective separation of Eosin Y and methyl orange in Example 3
  • D Example 2 for the selective separation of methyl orange and p-hydroxybenzoic acid.
  • Fig. 22 Surface structure of ultra-thin graphene oxide film with tent-like structure with nano-silver intercalation.
  • A The surface microstructure of the film material obtained by 1 ⁇ m nano silver intercalation
  • B the surface microstructure of the film material obtained by 10 nm nano silver intercalation.
  • Figure 23 is a scanning electron micrograph of a film prepared with an AAO film as a supporting substrate.
  • Figure 24 Scanning electron microscope image of ultra-thin graphene oxide prepared with nylon membrane as a buffer layer
  • buffer layer mixed cellulose ester film
  • Comparative Example 1 which uses the traditional filter assembly method to prepare an ultra-thin graphene oxide film.
  • the specific process is as follows:
  • Figure 1A shows the appearance of the ultra-thin graphene oxide film prepared by the traditional filtration assembly method.
  • Fig. 1B when viewed from a microscopic point of view, the obtained film has many cracks. These defects are difficult to visually detect with the naked eye, but the existence of these defects will seriously affect the performance of the membrane.
  • Figure 2 shows the ultra-thin graphene oxide film prepared by the improved filtration assembly method of the present invention. The amount of graphene oxide used in Example 1 and Comparative Example 1 is the same. Comparing the microstructures, it can be found that the ultra-thin graphene oxide film prepared by the improved method of the present invention has a complete structure, and no damaged parts are found under scanning electron microscope observation.
  • the improved filter assembly method of the present invention is shown in Figure 3A. Since ordinary commercial glass funnels cannot achieve a uniform, micron-level pore structure (Figure 3B, b), when vacuum pressure is applied, most of the vacuum force will act on the supporting membrane above the pores. The part closely adhering to the glass particles exerts a weak force. Induced by the uneven force, the graphene oxide layer tends to be loaded on the part with greater force, and the other parts that cannot be covered by the graphene oxide become defective structures. As shown in Figure 3, based on the traditional filter assembly, we designed a buffer layer between the glass funnel and the supporting membrane (Figure 3C, c). The buffer layer is required to have a uniform pore structure.
  • the pore size is less than or equal to the pore size of the support layer.
  • the vacuum pressure from the glass funnel will be evenly dispersed by the buffer layer and gently act on the support layer.
  • graphene oxide sheets can be uniformly assembled on the supporting film.
  • Comparative Example 1 Although some studies have used traditional filtration and assembly methods to prepare ultra-thin graphene oxide membranes, most of the preparation of ultra-thin structures is based on rigid support membranes, such as AAO (Anodic Aluminum Oxide) membranes. As shown in Comparative Example 1, the ultra-thin graphene oxide film structure prepared by using a flexible support film will inevitably have minor defects. In order to prove the advantages of the ultra-thin graphene oxide film supported by a flexible substrate, Comparative Example 2 prepared an ultra-thin graphene oxide film with the AAO film as the supporting film according to the traditional filtration assembly method, and carried out the flexible characteristics of the two Contrast. The specific preparation process is as follows:
  • the comparison between the two shows that the ultra-thin graphene oxide film based on the flexible support film has better flexibility and can better meet the needs of practical applications.
  • the improved filtration assembly method of the present invention solves the problem of defects in the preparation of ultra-thin graphene oxide on a flexible support film, and provides a reliable and stable preparation method for the assembly of the ultra-thin graphene oxide film on a flexible substrate.
  • buffer layer mixed cellulose ester film
  • Example 3 Example 4 and Example 5.
  • the mixed dispersion after configuration is sonicated for 10 minutes at an ultrasonic frequency of 53KHZ and a power output of 60% to make it fully dispersed.
  • FIG. 8 The appearance of the ultra-thin graphene oxide film with a tent-like structure prepared by the improved filtering assembly method of the present invention is shown in FIG. 8. Due to the ultra-thin structure, the resulting film has good light transmittance.
  • the membrane material prepared by the present invention in an aqueous solution of different pH, and subjected it to shaking for 24 hours to observe its final structural integrity.
  • the membrane material prepared in the present invention can maintain a stable structure in water, acidic hydrochloric acid solution and alkaline ammonia solution.
  • Figure 10 shows the micron-thickness pure graphene oxide film prepared by the traditional filtration assembly process. As shown in the figure, it is very unstable in water without adding nano-silica, and its structure is slightly shaken. It will disintegrate and is not suitable for application in actual water purification.
  • Fig. 12 shows the surface microstructure of the film prepared by the present invention.
  • Fig. 12A when a flexible graphene oxide film covers the silica surface, the surface will form a tent-like structure. With the gradual increase in the proportion of silica intercalation, this tent-like structure will gradually increase, and eventually cover the entire membrane surface.
  • the three-dimensional image of the atomic force microscope can more intuitively reflect this raised tent-like structure.
  • a mountain-like structure appeared on the surface of the film.
  • this raised structure gradually increases, and finally inter-connects with each other, forming undulating layers.
  • the surface structure of the tent, the atomic force microscope characterization and the scanning electron microscope characterization results are completely consistent, and jointly confirmed the construction of this tent-like nanostructure.
  • the cross-sectional structure of the film is shown in Figure 14.
  • the thickness of the film prepared in Example 2 is only about 20 nm, and the thickness of the film prepared in Example 3 is basically the same as that in Example 2, which shows that at a low silicon dioxide intercalation ratio, The thickness can be basically kept consistent, and most of the stacked structure can be retained. As the proportion of silica intercalation increases, the thickness of the film gradually increases, and the interlayer structure gradually becomes looser.
  • the thickness of Example 4 is about 200 nm, and the thickness of Example 5 is about 400 nm.
  • the thickness of the film can be controlled by the amount of graphene oxide added or the intercalation ratio of silicon dioxide. On the whole, the prepared films have ultra-thin thickness at the local nanometer level.
  • Figure 15 shows the changes in the surface roughness of the membrane. As shown in the figure, as the proportion of silica intercalation increases, more tent-like structures are constructed, and the resulting membrane surface becomes more rugged on the microscopic scale. The roughness of the film surface increases. The characterization of the surface roughness shows that the adjustment of the silicon dioxide intercalation ratio can realize the adjustment of the film surface roughness.
  • Figure 16 shows the changes in the hydrophilicity and hydrophobicity of the membrane surface.
  • the contact angle of water droplets on the film surface gradually increases, indicating that its hydrophobicity gradually increases.
  • the evaluation of surface hydrophilicity and hydrophobicity indicates that the intercalation of silica will increase the hydrophobicity of the membrane surface.
  • Figure 17 shows the changes in the electrical properties of the film surface. As shown in the figure, as the proportion of silicon dioxide intercalation increases, the negative charge of the film surface gradually weakens. The measurement of the zeta potential of the film surface shows that the intercalation of silicon dioxide can adjust the electrical changes of the film surface.
  • the application field and performance of the membrane are closely related to the surface roughness, hydrophobicity and surface electrical properties of the membrane. These adjustable surface properties can give this ultra-thin film a wider range of applications and better performance.
  • Figure 18A shows the change in water flux of the membrane structure.
  • the water flux of the original ultra-thin graphene (Example 1) is 23.8 L/m 2 /h/bar.
  • the water flux of Example 2 is 23.8 L/m 2 /h/bar.
  • the water fluxes of Example 2, Example 3, Example 4, and Example 5 are 39.73, 44.25, 166.18, 1508.78 L/m 2 /h/ respectively. bar.
  • the water flux of Example 5 is increased by about 65 times.
  • the reason for the increase in water flux is that the tent-like structure creates a larger interlayer passage, which is conducive to the rapid passage of water.
  • the mechanism is shown in the inset diagram in Figure 18A.
  • Figure 18B shows the relationship between the water flux and the applied pressure represented by Example 3. As shown in Fig. 18B, as the applied pressure increases, the water flux of the membrane increases linearly with the increase of applied pressure. This result shows that the constructed tent-like structure has strong mechanical stability and can remain stable under increased pressure, because if the tent-like structure is deformed under pressure, the change curve of water flux will be curvilinear. , Rather than linear correlation.
  • Example 5 has the same retention performance as Example 1, but its flux is 29 times higher than Example 1.
  • Example 4 has more silica intercalation.
  • Example 3 the shear molecular weight of Example 3 is about 330 Da.
  • Example 1 and Example 2 both have the same rejection rate for p-hydroxybenzoic acid, but the water flux of Example 2 with a tent-like structure is higher than that of the original ultra-thin graphene oxide film of Example 1. 1.3 times, indicating that the tent-like structure can effectively enhance its water flux under the premise of ensuring the interception efficiency.
  • Example 5 (>700Da)>Example 4 ( ⁇ 700Da)>Example 3 ( ⁇ 330Da)>Example 2 ( ⁇ 140Da) ⁇ Example 1 ( ⁇ 140Da). This result shows that the intercalation of silica nanoparticles can effectively regulate the sieving channel of the membrane on the molecular scale.
  • Figure 21A shows the mechanism of selective separation of molecules of similar size.
  • the separation process is based on size sieving. Molecules smaller than the intercepted pores can penetrate the membrane structure, and molecules larger than the intercepted pores will be intercepted, thereby achieving mixed molecules. Separate.
  • the specific operation process is to mix the two molecules uniformly according to the mass ratio of 1:1, take 10ml as the use liquid, add it to the filter, and filter under pressure. After half the volume is filtered, the filtrate is taken to determine the amount of the membrane-passing molecules. purity.
  • the method for measuring the purity of the trapped molecules is as follows.
  • Example 4 After all the solution is filtered, the molecules trapped on the membrane surface are re-dissolved with 5ml and their purity is determined.
  • Example 4 we evaluated the selective separation of Example 4 for Eosin Y+p-hydroxybenzoic acid. As shown in Figure 21B, after one pass through the membrane, the purity of p-hydroxybenzoic acid in the filtrate reached 99.87%, and the purity of the retained Eosin Y reached 97%. It shows that Example 4 can be used for the precise separation of Eosin Y and p-hydroxybenzoic acid.
  • Example 3 we evaluated the selective separation performance of Example 3 for Eosin Y and Methyl Orange ( Figure 21C). Since Eosin Y and methyl orange have very similar sizes, the concentration of methyl orange in the filtrate can reach 95% after three passes through the membrane, and the purity of the retained Eosin Y can reach 98% after two passes through the membrane. . Finally, we further evaluated the separation performance of Example 3 for methyl orange and p-hydroxybenzoic acid. As shown in Figure 21D, the purity of the retained methyl orange can reach 99% through one pass through the membrane, and the concentration of p-hydroxybenzoic acid in the filtrate can reach 97% through two passes through the membrane.
  • Example 6 has a tent-like structure similar to Example 3, except that the size of the constructed tent-like structure is different due to the difference in the size of the nanoparticles. Since the sieving performance and part of the surface properties of the membrane are determined by its microstructure, the sieving performance and surface properties of the membrane can also be adjusted by adjusting the ratio of nano-silver intercalation.
  • Example 6 illustrates that, according to the method of the present invention, nanoparticles of different sizes and different materials can also realize the construction of a nano-tent-like structure between the ultra-thin graphene oxide film layers.
  • buffer layer mixed cellulose ester film
  • the mixed dispersion after configuration is sonicated for 10 minutes at an ultrasonic frequency of 53KHZ and a power output of 60% to make it fully dispersed.
  • the film structure prepared by using the AAO film as the substrate is shown in Figure 23. Comparing FIG. 12B, we can find that the method of the present invention can still produce an ultra-thin graphene oxide film with a tent-like structure by changing the substrate, indicating that the method described in the present invention is not limited to flexible substrates.
  • the uniform distribution of the vacuum negative pressure can be satisfied, so as to realize the preparation of ultra-thin and uniform graphene oxide film.
  • a nylon membrane with a cut-off pore of 0.22 ⁇ m as the buffer layer to verify it.
  • the specific process of film formation is the same as in Example 1, except that the buffer layer is replaced with a nylon microporous filter membrane.
  • Figure 24 shows the ultra-thin graphene oxide membrane prepared with nylon microporous filter membrane as the buffer layer.
  • the obtained membrane has a complete ultra-thin structure.
  • the structure characterized by scanning electron microscopy is similar to that of mixed cellulose.
  • the ultra-thin structure prepared by ester as a buffer layer is basically the same. It is explained that as long as the pore structure of the buffer layer meets the requirements, a uniform and non-broken ultra-thin graphene oxide membrane can be obtained.
  • the mixed cellulose ester or nylon microporous filter membrane used in the present invention is only preferred in the present invention.

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  • Separation Using Semi-Permeable Membranes (AREA)
  • Carbon And Carbon Compounds (AREA)

Abstract

一种具有帐篷状纳米结构的氧化石墨烯膜及其制备方法与应用。建立了改进的过滤组装法，实现了超薄氧化石墨烯膜在柔性基底上的可靠制备。通过将纳米颗粒插层到超薄结构内部，实现了超薄结构中帐篷状纳米结构的构建。特殊的纳米帐篷状结构能在保留截留性能的前提下，实现水通量的最大化。通过纳米颗粒插层比例的调节，该膜的筛分通道可实现分子尺度上的调控，并能选择性分离相似尺寸的小分子。该膜在不同pH水溶液中结构稳定，且膜的表面粗糙度、可润湿性及表面电性可调。该膜优异的分离性能，以及可调的结构与性质，使其在环境污染治理领域及膜分离技术领域有很广泛的应用前景。

Description

一种具有帐篷状结构的氧化石墨烯膜及其制备方法与应用 技术领域
本发明属于环保材料制备领域，具体涉及一种具有帐篷状结构的超薄氧化石墨烯及其制备方法与应用。
背景技术
膜分离技术是一种利用孔筛分作用实现对纳米颗粒、分子以及离子选择性分离的技术。膜分离过程在化学纯化、资源回收以及环境污染治理领域有着不可替代的作用。近期，氧化石墨烯膜由于其特殊的层间结构引起了科研界及工业界的广泛关注。与传统的膜材料不同，氧化石墨烯膜的筛分孔隙是二维的层间的空间。Joshi等人研究发现，在水溶液中，氧化石墨烯膜的层间距离为0.9nm左右，其筛分通道可以精确地阻隔水化半径大于0.45nm的分子或离子，而让水化半径小于0.45的分子或离子通过(Joshi,R.K.et al.Precise and Ultrafast Molecular Sieving through Graphene Oxide Membranes.Science 343,752-754,(2014).)。如此狭窄的筛分通道在选择性膜分离领域引起了广泛兴趣与关注。
为了扩大氧化石墨烯膜的应用领域，不少研究致力于氧化石墨烯膜层间距离的有序调控。例如，通过水化程度的控制、或者阳离子的交联作用，可以缩小氧化石墨烯膜的层间距离，使其能够选择性得分离离子(Abraham,J.et al.Tunable Sieving of Ions Using Graphene Oxide Membranes.Nat.Nanotechnol.12,546-550,(2017).Chen,L.et al.Ion Sieving in Graphene Oxide Membranes Via Cationic Control of Interlayer Spacing.Nature 550,380-383,(2017).)。通过分子的交联，碳纳米管的插层，可以构建类三明治的夹层结构，从而实现氧化石墨烯膜层间距离的整体增加以及水通量的提升(Burress,J.W.et al.Graphene Oxide Framework Materials:Theoretical Predictions and Experimental Results.Angew.Chem.Int.Ed.Engl.49,8902-4,(2010).Hung,W.et al.Cross-Linking with Diamine Monomers to Prepare Composite Graphene Oxide-Framework Membranes with Varying D-Spacing.Chem.Mater.26,2983-2990,(2014).Yang,J.et al.Self-Assembly of Thiourea-Crosslinked Graphene Oxide Framework Membranes Toward Separation of Small Molecules.Adv.Mater.30,1705775,(2018).Huang,H.et al.Ultrafast Viscous Water Flow through Nanostrand-Channelled Graphene Oxide Membranes.Nat.Commun.4,2979,(2013).Han,Y.,Jiang,Y.&Gao,C.High-Flux Graphene Oxide  Nanofiltration Membrane Intercalated by Carbon Nanotubes.ACS Appl.Mater.Inter.7,8147-8155,(2015).)。普通纳米材料插层所构建的三明治结构，虽然可以提升膜的水通量，但是，其水通量的增加往往是以牺牲膜本身的选择性为代价的，且简单纳米材料的插层很难实现氧化石墨烯膜的筛分通道的精细调节，也不能实现氧化石墨烯膜对于小分子的选择性分离。分子交联的方法虽然理论上可能实现氧化石墨烯膜层间距离在分子尺度上的调节，但是，由于分子在水中水化作用、易变形性、以及不同链长分子对石墨烯片层作用力的不同，分子交联的氧化石墨烯膜很难在水环境中实现层间距离的精细调节，同时也不能实现对水中混合分子的选择性分离。此外，在膜分离过程中，膜的截留孔隙、水通量是两个难以调和的矛盾体，例如：更大的筛分通道能获得更高的水通量，但是大的筛分通道却难以截留小的过滤物(Park,H.B.,Kamcev,J.,Robeson,L.M.,Elimelech,M.&Freeman,B.D.Maximizing the Right Stuff:The Trade-Off Between Membrane Permeability and Selectivity.Science 356,1137,(2017).)。
在申请号为CN201710964971.1的发明专利中公开了一种纳米粒子插层氧化石墨烯薄膜及制备方法与应用。其通过静电喷涂的方法将氧化石墨烯与纳米粒子混合液直接喷涂至微孔滤膜基底上，从而得到纳米粒子插层氧化石墨烯膜。该方法中纳米粒子插层氧化石墨烯薄膜能有效增加氧化石墨烯片层间距，提高水通量，同时对有机染料保持较高截留率。这种静电喷涂的方法虽然能实现纳米粒子在石墨烯膜层间的插层，但是其无法在分子级别上，实现石墨烯膜层间距离的精确调控。单方面增加距离虽然能增大水通量，但是其势必会削弱膜本身的选择性。同时，静电喷涂的方法难以精确调控氧化石墨烯膜的添加量，不能保证膜结构的均匀程度，也很难实现超薄结构膜的制备。
综上所述，虽然不少研究提出了氧化石墨烯膜内部结构的调节方法，但是根据现有技术，氧化石墨烯的筛分通道还是很难在水环境中实现分子级别的调节，并实现对水中混合小分子的选择性分离。超薄的氧化石墨烯膜结构已经被报道，但是传统的过滤组装方法并不可靠，制备得到的超薄结构往往带有微小的破缺。此外，现有的结构调控策略很难调节氧化石墨烯膜水通量与选择性之间的矛盾，通过增加筛分通道来获得更高的水通量往往都是以牺牲膜本身的选择性为代价。综合考虑膜的筛分性能与实际应用，理想的膜结构必须具备以下几个条件：(1)具有超薄的结构来保证高效的水通量，(2)具有较好的机械稳定性来保证应用过程中结构的稳定性，(3)具有可调节的筛分通道，且具有窄的筛分尺寸分布。
发明内容
本发明的目的在于解决现有技术中存在的问题，提供一种改进的过滤组装方 法，能可靠得制备超薄氧化石墨烯膜。基于此组装方法，我们提出了一种新型的帐篷状纳米结构的构建策略，用于调控超薄石墨烯的结构、表面性质、水通量和筛分性能。
本发明的发明构思是设计一种具有帐篷状结构的超薄氧化石墨烯膜，它以氧化石墨烯为基本构建单位，以纳米颗粒插层为构建手段，通过将柔性的氧化石墨烯覆盖在坚硬的纳米颗粒表面形成帐篷状结构从而来实现帐篷状结构的构建。这种在超薄氧化石墨烯膜层间构建的帐篷状纳米结构能在保留其截留性能的前提下，有效提高膜本身的水通量。通过控制纳米颗粒的插层比例，膜的筛分性能可以实现分子精度上的调节，并能实现对水中埃级尺寸差异的小分子实现选择性分离。在保证相同截留性能的前提下，具有帐篷状纳米结构的氧化石墨烯复合膜的水通量比原始的超薄氧化石墨烯膜高1.3–60倍。同时，通过调控插层的纳米颗粒比例，这种具有帐篷状纳米结构的超薄氧化石墨烯膜还能实现表面粗糙度、表面亲疏水性、及表面电性的调节。由于其可调的筛分性能、精确的选择性、高的水通量以及可控的表面性质，该膜在水体净化及膜分离领域有巨大的应用前景。
本发明具体通过以下技术方案实现：
第一方面，本发明为了解决现有的氧化石墨烯膜存在的水通量低、筛分通道无法准确调节的问题，提供了一种具有帐篷状结构的氧化石墨烯膜，该氧化石墨烯膜表面通过纳米颗粒插层形成分布式的帐篷状纳米结构；所述帐篷状纳米结构中，氧化石墨烯片层覆盖于纳米颗粒上方并在纳米颗粒的支撑下形成帐篷状凸起。
在本发明中，帐篷状纳米结构是以刚性的纳米颗粒为支撑形成的，纳米颗粒所在位置具有较高的空间高度，然后向两侧逐渐高度降低，呈帐篷形式。由于帐篷状纳米结构的形成机理所限，氧化石墨烯膜的厚度不能过厚，应当呈薄层状。
作为第一方面中技术方案的优选，所述氧化石墨烯膜组装于柔性支撑膜上。当然，柔性支撑膜也可以由其他的基底代替，例如该氧化石墨烯膜可以直接组装在AAO膜表面，中空纤维膜等应用组件的表面。
作为第一方面中技术方案的优选，所述的氧化石墨烯膜通过负压抽滤方式组装。负压抽滤方式的方式相对于其他的成膜形式，有利于精确控制组装单元的添加量，有利于调控膜的厚度以及形成结构的均匀性。
作为第一方面中技术方案的优选，所述氧化石墨烯膜组装成膜后，氧化石墨烯可以进行完全还原，或部分还原。
作为第一方面中技术方案的优选，所述的纳米颗粒为能与氧化石墨烯的含氧官能团进行氢键或化学键相互作用结合的材质。所选择的纳米颗粒能与氧化石墨烯表面的含氧官能团能发生氢键或者其他化学键作用，以此来增强膜结构的稳定 性。
作为第一方面中技术方案的优选，所述的纳米颗粒为二氧化硅纳米颗粒或银纳米颗粒。进一步优选为二氧化硅纳米颗，原因是二氧化硅纳米颗粒是一种廉价的材料，且其表面的氢键能与氧化石墨烯表面的羧基通过氢键连接。
作为第一方面中技术方案的优选，所述的纳米颗粒尺寸优选10～1000nm。目的是使氧化石墨烯在组装过程中可以更好地覆盖纳米颗粒，以此来构建帐篷状结构。
作为第一方面中技术方案的优选，所述氧化石墨烯膜的厚度<50μm，优选厚度为纳米级，以此来保证膜的水通量。。
作为第一方面中技术方案的优选，所述的柔性支撑膜为聚碳酸酯膜。
第二方面，本发明提供了一种前述的第一方面中任一技术方案所述具有帐篷状结构的氧化石墨烯膜制备方法，其具体步骤为：在抽滤装置的过滤面上覆盖一层孔隙均匀的缓冲层，然后将柔性支撑膜置于缓冲层上；将含有纳米颗粒和氧化石墨烯的分散液置于抽滤装置中，通过真空抽滤使其在柔性支撑膜上组装形成所述具有纳米颗粒插层的氧化石墨烯膜。
作为第二方面中技术方案的优选，所述的抽滤装置为玻璃抽滤漏斗。
作为第二方面中技术方案的优选，所述的缓冲层孔隙尺寸小于或等于所述支撑层的孔隙尺寸，孔隙结构需均匀，以此来均匀分散真空压力。
作为第二方面中技术方案的优选，所述的缓冲层为混合纤维素酯膜。
作为第二方面中技术方案的优选，所述的缓冲层的孔隙尺寸优选5～5000nm。
作为第二方面中技术方案的优选，在真空抽滤前，所述的缓冲层用水湿润后贴合于所述过滤面上，所述的柔性支撑膜用水湿润后贴合于所述缓冲层上。
作为第二方面中技术方案的优选，所述的分散液中，纳米颗粒：氧化石墨烯的质量比为0.01～10。纳米颗粒的插层比例可以调控帐篷状结构的大小与数量，进而实现筛分通道的调节，及膜表面性质的调节。质量比例控制在0.01–10之间可以使膜能选择性分离小分子物质，过高的插层比例会造成膜截留性能的降低。
作为第二方面中技术方案的优选，真空抽滤后得到的氧化石墨烯膜需经过干燥。
第三方面，本发明提供了一种前述的第二方面中任一技术方案所述制备方法制备得到的氧化石墨烯膜。
第四方面，本发明提供了一种调节氧化石墨烯膜的筛分通道的方法，其做法是在利用前述的第二方面中任一技术方案所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现埃级尺度上的筛分通 道调节。
第五方面，本发明提供了一种调节氧化石墨烯膜的表面粗糙度的方法，其做法是在利用前述的第二方面中任一技术方案所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现膜表面粗糙度调节。
第六方面，本发明提供了一种调节氧化石墨烯膜的表面亲疏水性的方法，其做法是在利用前述的第二方面中任一技术方案所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现膜表面亲疏水性调节。
第七方面，本发明提供了一种调节氧化石墨烯膜的表面电性的方法，其做法是在利用前述的第二方面中任一技术方案所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现膜表面电性调节。
第八方面，本发明提供了一种由前述的第一方面或者第三方面中任一技术方案所述氧化石墨烯膜制成的膜分离器件或水体净化设备。
本发明的有益效果如下：1)本发明通过将纳米颗粒插层到超薄结构内部，进一步实现了帐篷状纳米结构的构建。利用氧化石墨烯片层之间的π-π相互作用，以及颗粒和氧化石墨烯之间的氢键作用，得到的复合膜在不同pH水溶液中都能保持结构稳定。其特殊的纳米帐篷状结构利用凸起的空间来增大水通量，又能保留周围的堆叠结构来实现对分子的筛分。因此，这种结构能在保留截留性能的前提下，实现水通量的最大化。与原始超薄氧化石墨烯膜相比，在相同截留性能的前提下，该复合膜比原始超薄氧化石墨烯膜的水通量高1.3–60倍。
2)本发明针对具有帐篷状纳米结构的超薄氧化石墨烯膜，建立了改进的过滤组装方法，实现了超薄氧化石墨烯膜在柔性基底上的可靠制备，且通过将纳米颗粒插层到超薄结构内部，进一步实现了柔性基底上帐篷状纳米结构的构建。常规的过滤组装过程，由于一般商业玻璃漏斗难以做到孔隙均匀，在过滤过程中不均匀的水流会导致在超薄氧化石墨烯膜制备过程中氧化石墨烯片层组装的不均匀，从而导致得到的超薄结构具有较多的、肉眼难以发现的破缺。当使用柔性的膜材料为支撑层的时候，这种破缺结构的存在更为明显。为解决超薄氧化石墨烯膜制备过程的不均匀性，我们在抽滤装置(如玻璃漏斗)与支撑膜之间设计了一层多孔的缓冲层。缓冲层的孔隙均匀，在缓冲层均匀孔隙的诱导下，真空压力可以均匀地分散，并作用于支撑层上，诱导产生的均匀剪切力可以驱动GO片层进行均匀组装，实现超薄氧化石墨烯膜的可靠制备。
3)基于上述改进的过滤组装方法，本发明可以通过调节纳米颗粒的插层比例，使得该膜的筛分通道可以实现埃级尺度上的调节，并能实现相似尺寸小分子 的选择性分离。此外，通过调节纳米颗粒的插层比例，该膜的表面粗糙度、可润湿性及表面电性都可实现有序调控。
4)本发明制备的具有帐篷状结构的超薄氧化石墨烯膜，与原始超薄氧化石墨烯膜相比，其水通量是原始超薄氧化石墨烯的1.3–60倍。而且，膜能在不同pH水溶液中稳定存在，其筛分通道可以通过调控纳米颗粒的插层比例实现分子尺度上的调节，能选择性筛分具有相似尺寸的小分子(分子量差距>100Da)。该复合膜在环境污染治理领域及膜分离技术领域有很广泛的应用前景。
附图说明
图1传统过滤组装法制备得到的超薄氧化石墨烯膜。(A)超薄氧化石墨烯膜照片，(B)超薄氧化石墨烯膜扫描电镜图。
图2本发明改进过滤组装法制备得到的超薄氧化石墨烯膜。(A)超薄氧化石墨烯膜照片，(B)超薄氧化石墨烯膜扫描电镜图。
图3膜结构的过滤组装过程。(A)改进过滤组装过程的示意图，(B)玻璃漏斗示意图，(C)缓冲层示意图，(D)支撑层示意图，(E)具有帐篷状超薄氧化石墨烯膜示意图，(b)剥离漏斗的扫描电镜图，(c)缓冲层的扫描电镜图，(d)支撑层的扫描电镜图，(e)具有帐篷状结构超薄氧化石墨烯膜的扫描电镜图。
图4以不同材质膜材料为支撑膜的超薄氧化石墨烯膜的柔韧性评价。(A)以AAO膜为支撑膜的超薄氧化石墨烯膜柔折180°后的状态，(B)以混合纤维素酯膜为支撑膜的超薄氧化石墨烯膜柔折180°后的状态。
图5氧化石墨烯与二氧化硅的红外图谱。
图6氧化石墨烯与二氧化硅的表面Zeta电位。
图7分散液静置一周后的丁达尔现象。(A)氧化石墨烯分散液的丁达尔现象，(B)纳米二氧化硅分散液的丁达尔现象，(C)氧化石墨烯+纳米二氧化硅分散液的丁达尔现象。
图8具有帐篷状结构超薄氧化石墨烯膜的外观照片。
图9本发明中制备的膜材料在纯水、酸性盐酸溶液及碱性氨水溶液中的结构稳定性。
图10传统过滤组装法制备的微米级厚的氧化石墨烯膜在水中的稳定性。
图11纳米二氧化硅与氧化石墨烯片层之间的结合。(A)实施例2-5的红外表征图谱，(B)氧化石墨烯与二氧化硅之间结合的示意图。
图12本发明制备的具有帐篷状结构的超薄氧化石墨烯膜的表面微观结构。(A)实施例2的表面微观结构，(B)实施例3的表面微观结构，(C)实施例4的表面微观结构，(D)实施例5的表面微观结构。
图13本发明制备的具有帐篷状结构的超薄氧化石墨烯膜的原子力显微镜图。(A)实施例2的表面微观结构，(B)实施例3的表面微观结构，(C)实施例4的表面微观结构，(D)实施例5的表面微观结构。
图14本发明制备的具有帐篷状结构的超薄氧化石墨烯膜的截面微观结构。(A)实施例2的截面微观结构，(B)实施例3的截面微观结构，(C)实施例4的截面微观结构，(D)实施例5的截面微观结构。
图15膜结构的表面粗糙度评价。
图16膜结构的表面亲疏水性评价。
图17膜结构的表面电性评价。
图18膜的水通量评价。(A)不同实施例的水通量，(B)不同施加压力下水通量的变化。
图19截留纳米颗粒或分子的尺寸信息。
图20具有帐篷状结构超薄氧化石墨烯膜对于纳米银及不同分子的截留性能评价。(A)实施例1-5对于纳米银的截留性能及通量评价，(B)实施例1-5对于曙红Y的截留性能及通量评价，(C)实施例1-5对于甲基橙的截留性能及通量评价，(D)实施例1-5对于对羟基苯甲酸的截留性能及通量评价。
图21具有帐篷状结构超薄氧化石墨烯膜对于不同混合分子的选择性分离。(A)选择性分离机理示意图，(B)实施例4对于曙红Y和对羟基苯甲酸的选择性分离，(C)实施例3对曙红Y和甲基橙的选择性分离，(D)实施例2对于甲基橙和对羟基苯甲酸的选择性分离。
图22纳米银插层的具有帐篷状结构的超薄氧化石墨烯膜表面结构。(A)1μm纳米银插层得到的膜材料表面微观结构，(B)10nm纳米银插层得到的膜材料表面微观结构。
图23以AAO膜为支撑基底制备得到的膜的扫描电镜图。
图24以尼龙膜为缓冲层制备得到的超薄氧化石墨烯的扫描电镜图
具体实施方式
下面结合附图和实施例对本发明做进一步阐述，以便本领域技术人员更好地理解本发明的实质。本发明中试剂或材料，若无特殊说明，均为市售产品。
为体现改进方法的优势，我们采用两种制备方法：1.传统过滤组装方法，2.本发明中改进的过滤组装方法，制备了两张超薄氧化石墨烯膜。通过观察、对比了两种方法制备所得的超薄氧化石墨烯膜的微观结构，来体现本发明中改进方法的优势。
实施例1.
利用本发明中改进的过滤组装法制备超薄氧化石墨烯膜的具体过程如下：
(1)将缓冲层(混合纤维素酯膜)置于剥离漏斗上，用水润湿，使两者充分贴合。
(2)将支撑膜(聚碳酸酯膜)置于缓冲层上，用水润湿，使两者充分贴合。
(3)配置浓度为1.5mg/L氧化石墨烯分散液，并超声10min使其充分分散。
(4)取10ml配置的氧化石墨烯分散液，在0.9bar的真空压下过滤组装，得到膜结构。
(5)取得的膜结构在60℃条件下干燥。
对比例1.
为对比本发明中改进方法与传统过滤组装方法的区别，我们设计了对比例1，利用传统过滤组装法制备超薄氧化石墨烯膜，具体过程如下：
(1)将支撑膜(聚碳酸酯膜)置于玻璃基底上，用水润湿，使两者充分贴合。
(2)配置浓度为1.5mg/L氧化石墨烯分散液，并超声10min使其充分分散。
(3)取10ml配置的氧化石墨烯分散液，在0.9bar的真空压下过滤组装，得到膜结构。
(4)取得的膜结构在60℃条件下干燥。
图1A展示了利用传统过滤组装法制备得到的超薄氧化石墨烯膜的外观。如图1B所示，在微观的角度观察，得到的膜具有很多的破缺。这些缺陷很难用肉眼直观地发现，但是这些破缺的存在会严重影响膜的性能。图2展示了利用本发明改进的过滤组装法制备得到的超薄氧化石墨烯膜。实施例1与对比例1使用的氧化石墨烯量一致，对比微观结构可发现，利用本发明改进法制备的超薄氧化石墨烯膜具有完整的结构，扫描电镜下观察没有发现破损部分。
本发明改进的过滤组装方法如图3A所示。由于一般的商业玻璃漏斗无法做到均匀的、微米级的孔隙结构(图3B，b)，所以，当施加真空压的时候，大部分的真空力将作用于处于孔隙上部的支撑膜，而对于与玻璃颗粒紧密贴合的部分施以较弱的作用力。在不均匀的作用力的诱导下，氧化石墨烯片层会倾向于负载在作用力较大的部分，而使其他氧化石墨烯不能覆盖的部分成为缺陷结构。如图3所示，在传统过滤组装的基础上，我们在玻璃漏斗与支撑膜之间设计了一层缓冲层(图3C，c)，这层缓冲层的要求是得具有均匀的孔隙结构，且孔隙尺寸小于或等于支撑层的孔隙尺寸。在这层缓冲层的作用下，来自于玻璃漏斗的真空压会被缓冲层均匀分散，并柔和地作用于支撑层上。在均匀、柔和的水力剪切力作 用下，氧化石墨烯片层能均匀组装在支撑膜上，通过控制氧化石墨烯添加的量，我们可以获得超薄的、结构完整的氧化石墨烯膜。相比与传统的直接过滤组装法，本发明中改进的过滤组装法更为可靠，高效。
对比例2.
虽然已有部分研究利用传统的过滤组装方法制备了超薄的氧化石墨烯膜，但是大多数超薄结构的制备是基于硬质的支撑膜实现的，如AAO(Anodic Aluminum Oxide)膜。正如对比例1所示，利用柔性的支撑膜制备的超薄氧化石墨烯膜结构不可避免会出现微小的缺陷。为证明以柔性基底为支撑的超薄氧化石墨烯膜的优势，对比例2根据传统的过滤组装法制备了以AAO膜为支撑膜的超薄氧化石墨烯膜，并对两者的柔性特征进行了对比。具体制备过程如下：
(1)将AAO膜置于玻璃基底上，用水润湿，使两者充分贴合。
(2)配置浓度为1.5mg/L氧化石墨烯分散液，并超声10min使其充分分散。
(3)取10ml配置的氧化石墨烯分散液，在0.9bar的真空压下过滤组装，得到膜结构。
(4)取得的膜结构在60℃条件下干燥。
在硬质支撑膜上容易实现超薄氧化石墨烯膜的制备，原始是因为当硬质的支撑膜置于玻璃漏斗上时，它不会像柔性的支撑膜一样与玻璃基底充分接触，从而真空压可以相对均匀地作用于硬质支撑膜上。但是以硬质支撑膜为基底的超薄氧化石墨烯很难应用于实际过滤过程，原因是其结构较为脆弱，易破碎。图4展示了两者的柔韧性，将以AAO膜为支撑膜的超薄氧化石墨烯柔折90°，该膜结构立即破碎。而以本发明改进法制备的以柔性支撑膜为基底的超薄氧化石墨烯膜再柔折180°之后膜结构还是保持完整。两者对比，说明以柔性支撑膜为基底的超薄氧化石墨烯膜具有更好的柔韧性，更加能满足实际应用的需要。而本发明改进的过滤组装方法，解决了在柔性支撑膜上制备超薄氧化石墨烯存在的缺陷问题，为超薄氧化石墨烯膜在柔性基底上的组装提供了可靠、稳定的制备途径。
实施例2-5
为了让本领域的研发人员更好地理解超薄氧化石墨烯膜中帐篷状纳米结构的构建，下面我们通过具体实施例与附图对本发明做进一步阐述。拥有帐篷状结构的超薄氧化石墨烯膜的具体步骤如下：
(1)将缓冲层(混合纤维素酯膜)置于剥离漏斗上，用水润湿，使两者充分贴合。
(2)将支撑膜(聚碳酸酯膜)置于缓冲层上，用水润湿，使两者充分贴合。
(3)配置氧化石墨烯分散液，并将二氧化硅(30nm)分散液加入到氧化石 墨烯分散液中，其中氧化石墨烯的浓度控制在1.5mg/L，添加的二氧化硅的量与氧化石墨烯的质量比例分别为0.01:1，0.1:1，1：1和10:1，并且分别记为实施2，
实施例3，实施例4和实施例5。
(4)配置完成后的混合分散液在在超声频率53KHZ，功率输出60％条件下超声10min，使其充分分散。
(5)取10ml分散液，添加到过滤器中，在1bar的真空压下抽滤，形成膜结构。
(6)得到的膜结构在60℃条件下进行干燥。
(上述实施例只是本发明的优选方式，且各参数可以根据实际需要进行调整。)
通过红外图谱表征，使用的氧化石墨烯与二氧化硅纳米颗粒表面都带有丰富的官能团结构(图5)。含氧官能团能在水中解离，并赋予纳米颗粒强的负电表面(图6)。如图7所示，氧化石墨烯分散液、纳米二氧化硅分散液和他们的混合溶液在静置一周后仍表现出明显的丁达尔效应，说明在表面负电的排斥力下，这些纳米材料可以在分散剂的条件下在水中充分分散。组装单元良好的分散性为结构的均匀组装提供了前提条件。
通过本发明改进的过滤组装方法，制备得到的具有帐篷状结构的超薄氧化石墨烯膜外观如图8所示。由于超薄的结构，得到的膜具有很好的透光性。为评价膜在水溶液中的稳定性，我们将本发明制得的膜材料置于不同pH的水溶液中，并施以震荡24h，观察其最终的结构完整性。如图9所示，本发明中制备的膜材料在水中、酸性盐酸溶液中及碱性氨水溶液中都能保持结构稳定。图10展示了用传统过滤组装过程制备的微米级厚度的纯氧化石墨烯膜，如图所示，在不添加纳米二氧化硅的条件下，其在水中很不稳定，施以轻微震荡其结构就会解体，不适合在实际水体净化中应用。
通过红外图谱表征(图11A)，我们可以发现，二氧化硅插层之后，源自氧化石墨烯表面的C＝O官能团与源于二氧化硅表面的-OH官能团同时削弱，随着二氧化硅插层比例的增加，削弱的程度逐渐加强，说明二氧化硅表面的-OH与氧化石墨烯表面的C＝O相互结合，形成了氢键作用。由于二氧化硅会倾向于同氧化石墨烯表面的含氧官能团结合，其会优先占据氧化石墨烯表面的亲水部位，并使氧化石墨烯疏水部分之间通过π-π相互作用结合，形成水中稳定的结构。二氧化硅与氧化石墨烯相互作用形成的结构如图11B所示。
图12展示了本发明制备的膜的表面微观结构，如图12A所示，当柔性的氧化石墨烯膜覆盖到二氧化硅表面时，其表面会形成帐篷状的结构。随着二氧化硅插层比例的逐渐增加，这种帐篷状的结构会逐渐多，最终覆盖整个膜表面。
原子力显微镜的三维成像图能更加直观地体现这种凸起的帐篷状结构。如图13所示，插层二氧化硅之后，膜表面出现了山峰状的结构，随着二氧化硅插层比例的增加，这种凸起的结构逐渐增加，最终相互交连，形成层峦起伏的表面结构，原子力显微镜的表征与扫描电镜的表征结果完全一致，共同证实了这种帐篷状纳米结构的构建。
膜的截面结构如图14所示，实施例2制备得到膜的厚度仅为20nm左右，实施例3制备得到的膜厚度基本与实施例2一致，说明在低的二氧化硅插层比例下，其厚度基本可以保持一致，大部分的堆叠结构能被保留下来。随着二氧化硅插层比例的增加，膜的厚度逐渐增加，同时其层间结构也逐渐变得酥松。实施例4的厚度为200nm左右，而实施例5的厚度为400nm左右。膜的厚度可以通过氧化石墨烯添加量或者二氧化硅的插层比例实现调控。综合来看，制备得到的膜都局域纳米级的超薄厚度。
图15展现了膜表面粗糙度的变化，如图所示，随着二氧化硅插层比例的增加，更多的帐篷状结构被构建，得到的膜表面在微观尺度上变得更为崎岖，膜表面的粗糙度增加。表面粗糙度的表征说明，二氧化硅插层比例的调控可以实现膜表面粗糙程度的调节。
图16展现了膜表面亲疏水性的变化。如图所示，随着二氧化硅插层比例的增加，膜表面水滴接触角逐渐增大，说明其疏水性逐渐增强。表面亲疏水性的评价，说明二氧化硅的插层会增加膜表面的疏水性，通过调控二氧化硅的插层比例，可以实现对膜表面亲疏水性的调节。
图17展现了膜表面电性的变化。如图所示，随着二氧化硅插层比例的增加，膜表面的负电性逐渐减弱。膜表面Zeta电位的测定说明二氧化硅的插层可调节膜表面的电性变化。
在实际应用中，膜的应用领域与性能与膜的表面粗糙度、亲疏水性和表面电性密切相关。这些可调节的表面性质可以赋予这种超薄膜更加广泛的应用空间与更加优异的性能。
图18A展现了膜结构水通量的变化。如图所示，原始超薄石墨烯(实施例1)的水通量为23.8L/m 2/h/bar。当都构建帐篷状结构之后，其水通量逐渐增加，实施例2，实施例3，实施例4，实施例5的水通量分别为39.73，44.25，166.18，1508.78L/m 2/h/bar。与实施例1相比，实施例5的水通量提升了65倍左右。其水通量增大的原因是帐篷状结构创造了更大的层间通道，有利于水流的快速通过，其机理如图18A内的插入图所示。图18B展示了以实施例3为代表的，水通量与施加压力之间的关系。如图18B所示，随着施加压力的增加膜的水通量随着 施加压力的增加线性上升。这一结果表明，构建的帐篷状结构具有较强的机械稳定性，能在增大的压力下保持稳定，因为如果帐篷状的结构在压力作用下变形，水通量的变化曲线会呈曲线相关，而非直线相关。
为评价实施例1-5的截留性能，我们选取了银纳米颗粒(直径10nm)，以及不同尺寸的小分子作为截留物进行过滤分离实验，其具体的尺寸信息如图19所示。如图20A，所示实施例1-5对纳米都呈现优异的截留性能，截留率都为90％以上，说明膜的孔隙都小于10nm。对比实施例1与实施例5，实施例5具有与实施例1一致的截留性能，但是其通量却比实施例1高29倍。如图20B所示，实施例1-4对于曙红Y(分子量＝692Da)都表现出非常好的截留性能(截留率大于95％)，同样，实施例4因为具有更多的二氧化硅插层，在与实施例1具有相同截留性能的前提下，实施例4的通量是实施例1的4倍。而实施例5由于具备较大的层间通道，所以其不能有效留曙红Y分子。由此可知实施例5的剪切分子量大于700Da。对于甲基橙(分子量＝327Da)，实施例1-3都表现出较好的截留性能(截留率大于90％)，但是实施例4对于其的截留性能只有70％。实施例4对于曙红Y和甲基橙不同的截留性能表示实施例4的截切分子量为700Da左右。如图20D所示，由于对羟基苯甲酸分子尺寸过小，实施例1-5都不能对其产生有效截留。由此可知，实施例3的剪切分子量为330Da左右。此外，实施例1与实施2相比，两者对于对羟基苯甲酸具有相同的截留率，但是具有帐篷状结构的实施例2的水通量却比实施例1原始超薄氧化石墨烯膜高1.3倍，说明帐篷状结构可以在保证截留效率的前提下，有效增强其水通量。通过膜对于不同分子量分子的截留性能评价，我们可以得到，不同膜的剪切分子量为：实施例5(>700Da)>实施例4(～700Da)>实施例3(～330Da)>实施例2(<140Da)≈实施例1(<140Da)。这一结果说明，二氧化硅纳米颗粒的插层可以有效地在分子尺度上调控膜的筛分通道。
鉴于帐篷状结构筛分性能的精密可调性，我们随后也评价了实施例对于混合小分子的选择性分离性能。图21A展示了，对于相似尺寸分子选择性分离的机理，分离过程基于尺寸筛分实现，小于截留孔隙的分子可以透过膜结构，而大于截留孔隙的分子则会被截留，从而实现混合分子的分离。具体操作过程为，将两种分子按照质量比为1:1均匀混合，取10ml作为使用液，添加到过滤器中，加压过滤，至一半体积过滤之后，取过滤液测定其中过膜分子的纯度。被截留分子的纯度的测定方法如下，待所有溶液过滤之后，用5ml重新溶解截留于膜表面的分子，并测定其纯度。鉴于实施例4具有相对较高的通量，且其对于曙红Y和对羟基苯甲酸具有不同的筛分性能，我们评价了实施例4对于曙红Y+对羟基 苯甲酸的选择性分离。如图21B所示，一次过膜之后，过滤液中对羟基苯甲酸的纯度达到了99.87％，而被截留的曙红Y的纯度达到了97％。说明实施例4可用于曙红Y和对羟基苯甲酸的精确分离。同样，我们评价了实施例3对于曙红Y和甲基橙的选择性分离性能(图21C)。由于曙红Y和甲基橙拥非常相近的尺寸，通过3次过膜，过滤液中甲基橙的浓度可达到95％，而通过2次过膜，截留的曙红Y纯度可达到98％。最后，我们进一步评价了实施例3对于甲基橙与对羟基苯甲酸的分离性能。如图21D所示，通过一次过膜，被截留的甲基橙纯度可以达到99％，而通过2次过膜，过滤液中对羟基苯甲酸的浓度可以达到97％。对于相似尺寸分子的选择性分离实验充分证明，二氧化硅纳米颗粒插层可以精确调控超薄氧化石墨烯膜的筛分通道，同时，得到的膜结构可以实现对相似尺寸的选择性分离。
实施例6
为了证实其他纳米颗粒构建帐篷状结构的可能性，我们后期选取了平均直径为1μm以及平均尺寸为10nm的纳米银颗粒进行了实验。材料的制备过程与实施例3一致。如图22所示，实施例6具有与实施例3相似的帐篷状结构，只是由于纳米颗粒尺寸的不同，构建的帐篷状结构的大小不同。由于膜的筛分性能与部分表面性质由其微观结构决定，所以，通过纳米银插层比例的调节，也能实现对膜筛分性能与表面性质的调节。实施例6说明，按照本发明的方法，不同尺寸的、不同材料的纳米颗粒也能在超薄氧化石墨烯膜层间实现纳米帐篷状结构的构建。
实施例7
为了证实利用本发明的方法可以在不同支撑基底表面形成这种具有帐篷状结构的超薄氧化石墨烯膜，我们后期选取了AAO膜作为基底，进行了膜组装实验。具体过程如下：
(1)将缓冲层(混合纤维素酯膜)置于剥离漏斗上，用水润湿，使两者充分贴合。
(2)将支撑膜，微孔AAO膜置于缓冲层上，用水润湿，使两者充分贴合。
(3)配置氧化石墨烯分散液，并将二氧化硅(30nm)分散液加入到氧化石墨烯分散液中，其中氧化石墨烯的浓度控制在1.5mg/L，添加的二氧化硅的量与氧化石墨烯的质量比例分别为0.1:1
(4)配置完成后的混合分散液在在超声频率53KHZ，功率输出60％条件下超声10min，使其充分分散。
(5)取10ml分散液，添加到过滤器中，在1bar的真空压下抽滤，形成膜 结构。
(6)得到的膜结构在60℃条件下进行干燥。
利用AAO膜为基底制备得到的膜结构如图23所示。对比图12B，我们可以发现，改变基底，利用本发明的方法还是可以制备出具有帐篷状结构的超薄氧化石墨烯膜，说明，本发明中所阐述的方法并不仅仅局限于柔性基底。
实施例8
在缓冲层的选择中，我们认为只要缓冲层孔隙均匀，孔径小于或等于支撑层的孔径即可满足对真空负压的均匀分布，从而实现超薄、均匀氧化石墨烯膜的制备。为了证实缓冲层的可替换性，我们选取了截留孔隙为0.22μm的尼龙膜为缓冲层进行了证实。成膜的具体过程与实施例1一致，只是将其中的缓冲层替换为尼龙微孔滤膜。
图24展示了以尼龙微孔滤膜为缓冲层制备得到的超薄氧化石墨烯膜，如图所示，得到的膜具有完整的超薄结构，其扫描电镜下表征的结构与以混合纤维素酯为缓冲层制备得到的超薄结构基本一致。说明，只要缓冲层的孔隙结构满足要求，就可得到均匀、无破缺的超薄氧化石墨烯膜，本发明中使用的混合纤维素酯，或尼龙微孔滤膜只为本发明的优选。
根据以上所述，本领域的普通技术人员，在不脱离本发明的精神和范围的情况下，还可以做出各种变化和变型。因此凡采取等同替换或等效变换的方式所获得的技术方案，均落在本发明的保护范围内。

Claims (21)

  1. 一种具有帐篷状结构的氧化石墨烯膜，其特征在于，氧化石墨烯膜层间通过纳米颗粒插层形成分布式的帐篷状纳米结构；所述帐篷状纳米结构中，氧化石墨烯片层覆盖于纳米颗粒上方并在纳米颗粒的支撑下形成帐篷状凸起。
  2. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述氧化石墨烯膜组装于柔性支撑膜上。
  3. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述的氧化石墨烯膜通过负压抽滤方式组装。
  4. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述氧化石墨烯膜组装成膜后，氧化石墨烯可以进行完全还原，或部分还原。
  5. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述的纳米颗粒优选为能与氧化石墨烯的含氧官能团进行氢键或化学键相互作用结合的材质。
  6. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述的纳米颗粒为二氧化硅纳米颗粒或银纳米颗粒。
  7. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述的纳米颗粒尺寸优选10～1000nm。
  8. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述氧化石墨烯膜的厚度<50μm，优选厚度为纳米级。
  9. 根据权利要求1所述的具有帐篷状结构的氧化石墨烯膜，其特征在于，所述的柔性支撑膜为聚碳酸酯膜。
  10. 一种如权利要求1～9任一所述具有帐篷状结构的氧化石墨烯膜制备方法，其特征在于，在抽滤装置的过滤面上覆盖一层孔隙均匀的缓冲层，然后将柔性支撑膜置于缓冲层上；将含有纳米颗粒和氧化石墨烯的分散液置于抽滤装置中，通过真空抽滤使其在柔性支撑膜上组装形成具有纳米颗粒插层的氧化石墨烯膜。
  11. 如权利要求10所述的制备方法，其特征在于，所述的抽滤装置为玻璃抽滤漏斗。
  12. 如权利要求10所述的制备方法，其特征在于，所述的缓冲层孔隙尺寸小于或等于所述支撑层的孔隙尺寸。
  13. 如权利要求10所述的制备方法，其特征在于，所述的缓冲层为混合纤维素酯膜；所述的缓冲层的孔隙尺寸优选5～5000nm。
  14. 如权利要求10所述的制备方法，其特征在于，在真空抽滤前，所述的缓冲层用水湿润后贴合于所述过滤面上，所述的柔性支撑膜用水湿润后贴合于所述缓冲层上；真空抽滤后得到的氧化石墨烯膜优选需经过干燥。
  15. 如权利要求10所述的制备方法，其特征在于，所述的分散液中，纳米颗粒：氧化石墨烯的质量比为0.01～10。
  16. 一种如权利要求10～15任一所述制备方法制备得到的氧化石墨烯膜。
  17. 一种调节氧化石墨烯膜的筛分通道的方法，其特征在于，在利用如权利要求10～15任一所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现分子尺度上的筛分通道调节。
  18. 一种调节氧化石墨烯膜的表面粗糙度的方法，其特征在于，在利用如权利要求10～15任一所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现膜表面粗糙度调节。
  19. 一种调节氧化石墨烯膜的表面亲疏水性的方法，其特征在于，在利用如权利要求10～15任一所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现膜表面亲疏水性调节。
  20. 一种调节氧化石墨烯膜的表面电性的方法，其特征在于，在利用如权利要求10～15任一所述制备方法制备氧化石墨烯膜的过程中，通过调控纳米颗粒在氧化石墨烯膜中的插层比例实现膜表面电性调节。
  21. 一种由权利要求1～9或者权利要求16任一所述氧化石墨烯膜制成的膜分离器件或水体净化设备。
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