Preparation method and application of non-expansive graphene oxide ribbon membrane

Abstract

The invention relates to a preparation method and application of a non-expansive graphene oxide ribbon membrane, and belongs to the technical field of separation of strontium and cesium in radioactive wastewater. The preparation method comprises the following steps: mixing carbon nanotubes, concentrated sulfuric acid and potassium permanganate, performing strong ultrasonic exfoliation, then mixing with an ice-water mixture containing H2O2, and performing post-treatment to obtain a graphene oxide ribbon suspension; the suspension liquid is subjected to dilution with water, ultrasonic treatment and membrane preparation in sequence, and the non-expansive graphene oxide ribbon membrane is obtained. According to the preparation method, the graphene oxide ribbon membrane is prepared by taking the carbon nano tube as a raw material, the carbon nano tube is effectively cut by virtue of strong ultrasonic stripping, and the non-expansive graphene oxide ribbon membrane is prepared by virtue of a series of treatment on the obtained graphene oxide ribbon suspension.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a non-expandable graphene oxide strip membrane, belonging to the technical field of separating strontium and cesium in radioactive waste water. Background Art

[0002] Radioactive wastewater generally refers to waste liquid containing radionuclides and other harmful chemicals generated during the operation of nuclear power plants or the processing of nuclear fuel and nuclear facilities. These waste liquids are characterized by a wide variety, high concentration, strong radioactivity, and great harm to humans and animals. Radioactive wastewater contains radioactive elements with long half-lives such as cesium-137, strontium-90, deuterium, iodine-129, and a variety of fission products and activation products. Since its radioactive substances cannot be completely removed by conventional means, special treatment is required to reduce its potential hazards. Strontium and cesium in radioactive wastewater have attracted much attention due to their high yield, long half-life, and high radiation dose. Moreover, strontium and cesium have physical and chemical properties similar to potassium and calcium, which enable them to migrate rapidly in the environment and be easily absorbed by organisms, thereby showing more significant biological toxicity and environmental risks. Therefore, it is of great significance to effectively separate strontium and cesium from radioactive wastewater.

[0003] Treatment methods for radioactive wastewater include chemical precipitation, ion exchange, adsorption, evaporation concentration, membrane separation technology and biological treatment. Among them, membrane separation technology is to filter or reverse osmosis wastewater through membrane materials to remove suspended matter, colloids and dissolved matter, including radioactive elements. However, selecting appropriate membrane materials and preventing membrane contamination and membrane aging are the key to this method.

[0004] Graphene oxide membranes and their analogs have unique advantages in the separation of radioactive strontium and cesium. First, the forward osmosis separation membrane uses osmotic pressure difference as the driving force and does not require additional energy, which is very suitable for the continuous separation of strontium and cesium in radioactive waste liquid. Secondly, strontium and cesium have weak surface binding ability with graphene oxide and can quickly penetrate through the graphene oxide membrane, while other radioactive nuclides will be effectively blocked by the graphene oxide membrane, thereby achieving efficient separation of strontium and cesium. Furthermore, in the harsh environment of radioactive waste liquid (strong acid, high radiation), the conjugated aromatic skeleton of graphene oxide can effectively resist strong acid, radiation damage and free radical erosion caused by gamma rays.

[0005] However, graphene oxide membranes have a large number of oxygen-containing groups, which are easy to bind water molecules, resulting in interlayer expansion of graphene oxide membranes, which greatly limits the selectivity and separation efficiency of the membranes. In order to inhibit the expansion behavior of graphene oxide membranes, many attempts have been made, such as GOM coating, reduction of graphene oxide, particle (ions, molecules and nanoparticles) intercalation, etc. However, the above preparation methods are still difficult to effectively solve the inherent defects of membrane expansion, and the preparation methods are complicated. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a non-expandable graphene oxide ribbon membrane, so as to solve the problem in the prior art that the graphene oxide membrane has high expansion, which limits the selectivity and separation efficiency of the membrane.

[0007] The second object of the present invention is to provide a non-expandable graphene oxide ribbon membrane for use in separating cesium and strontium ions from radioactive wastewater, so as to solve the problem of low efficiency in separating strontium and cesium from radioactive wastewater in the prior art.

[0008] In order to achieve the above purpose, the technical solution of the present invention is:

[0009] A method for preparing a non-expandable graphene oxide ribbon film comprises the following steps: mixing carbon nanotubes, concentrated sulfuric acid and potassium permanganate, exfoliating by strong ultrasonication, then mixing with an ice-water mixture containing H2O2, and post-treating to obtain a graphene oxide ribbon suspension; and diluting the suspension with water, ultrasonically treating and forming a film to obtain a non-expandable graphene oxide ribbon film.

[0010] The preparation method of the non-expandable graphene oxide ribbon membrane of the present invention is a pioneering invention. The present invention uses carbon nanotubes as raw materials to prepare the graphene oxide ribbon membrane, effectively cuts the carbon nanotubes by strong ultrasonic stripping, and obtains the non-expandable graphene oxide ribbon membrane by a series of treatments on the obtained graphene oxide ribbon suspension. The non-expandability of the membrane improves the selective permeability and separation efficiency of ions.

[0011] Preferably, the frequency of the strong ultrasonic stripping is 40 to 100 kHz. More preferably, it is 80 kHz. Strong ultrasonic stripping can produce concentrated high-energy cavitation and vibration, which breaks the CC bonds, epoxy, ketone groups and other groups of carbon nanotubes, effectively crushes the carbon nanotubes, reduces their sheet diameter, and thus increases the content of graphene oxide nanosheets and improves dispersibility. The hydroxyl radicals and hydrogen radicals formed by water molecules under the induction of strong ultrasound combine with the carbon radicals formed by the break on the sheet to generate hydroxyl or ether oxygen groups, and the carbon radicals that have not been hydrolyzed form new CC bonds, which break the hydroxyl groups and convert them into ketone groups.

[0012] Preferably, the temperature of the strong ultrasonic stripping is 40-60°C, and the time is 3-8h. When the temperature of the strong ultrasonic stripping is lower than 40°C or higher than 60°C, the carbon nanotubes cannot be cut efficiently, and the prepared graphene oxide ribbon film has poor film-forming properties. At 40-60°C, the comprehensive performance of the prepared graphene oxide ribbon film is better, that is, the film can still maintain good dimensional stability during water absorption. The time is controlled at 3-8h, which can control the reaction rate to a certain extent so that the cutting reaction reaches an appropriate degree, and at the same time, it can also ensure the purity of the product to a certain extent and avoid the generation of by-products.

[0013] In order to improve the preparation efficiency of graphene oxide ribbons, preferably, the usage ratio of the carbon nanotubes, concentrated sulfuric acid and potassium permanganate is 1 g: (125-135) mL: (5-6) g.

[0014] Preferably, the volume ratio of the ice-water mixture to concentrated sulfuric acid is 1:(1-1.1), and the volume fraction of the 30 wt% H2O2 solution in the ice-water mixture containing H2O2 is 0.75%-1.5%.

[0015] Preferably, the membrane is formed by filtration through a polyethersulfone membrane. The polyethersulfone membrane of the present invention has a wide range of chemical compatibility and temperature resistance, can effectively remove impurities and particles after filtration, and has stable properties.

[0016] Preferably, the post-treatment is to centrifuge the mixed solution to obtain a solid, and then dialyze the solid to obtain a graphene oxide ribbon suspension.

[0017] In order to further improve the success rate of film formation, preferably, the dispersion degree of the suspension after dilution with water is 3.0 to 5.0×10 -2 g / L.

[0018] Preferably, the ultrasonic treatment time is 20 to 30 minutes.

[0019] More preferably, the pore size of the polyethersulfone filter membrane is 0.1-0.2 μm.

[0020] The second technical solution of the present invention is:

[0021] Application of a non-expandable graphene oxide ribbon membrane in separation of cesium and strontium ions in radioactive wastewater.

[0022] The non-expandable graphene oxide ribbon film of the present invention has a two-stage unique structure, that is, a two-layer superimposed interwoven structure, and the nanopores are fixed by the two-stage unique structure, the interlayer insertion of water molecules is suppressed, and the non-expandable membrane pore construction is realized. The non-expandability of the graphene oxide ribbon film prevents the further embedding of water molecules at the edge of the nanoribbon, locks the entire sheet structure, and enables the film to maintain a constant interlayer spacing in both dry and wet states, thereby suppressing the peripheral expansion of the graphene oxide ribbon film. By controlling the strong π-π interaction of the low-defect aromatic face in the central axis area, the stability and durability of the film are improved.

[0023] The non-expandable graphene oxide ribbon membrane of the present invention has constant nanochannels and low mass transfer resistance, which enables efficient separation of cesium and strontium ions, while maintaining good inhibition of other ions. The separation coefficient for cesium ions in radioactive wastewater is f Cs / UO2 ≥6309, the separation factor of strontium ion is f Sr / UO2 ≥2699. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of a device for a permeation experiment of the present invention;

[0025] Figure 2 The stacking model and the scanning electron microscope (SEM) images of the surface and cross section of Experimental Example 1 of the present invention; wherein a and d are the stacking models of GOM and OGRM, respectively; b and e are the surface SEM images of GOM and OGRM, respectively (the inset is the filtered image); c and f are the SEM images of the cross section of GOM and OGRM, respectively (the inset of f is the smooth cross section of OGRM);

[0026] Figure 3 TEM spectra of Experimental Example 1 of the present invention; wherein a and c are TEM spectra of GO at different magnifications; a and c are TEM spectra of OGR at different magnifications;

[0027] Figure 4 Graphs showing the experimental results of Experimental Example 2 of the present invention; wherein, a is the X-ray diffraction (XRD) spectra of GOM and OGRM before and after being wetted by water (corresponding to the solid line and the dotted line, respectively); b and c are transmission electron microscope (TEM) images of OGR multilayer nanobelts at different magnifications; d is the Raman spectra of GOM and OGRM; e is the analytical graph of the C1s X-ray photoelectron spectrum (XPS) of GOM and OGRM; f is the Fourier transform infrared spectrum (FTIR) of v(CC) in the original GOM and OGRM;

[0028] Figure 5 The permeation test result diagram of Experimental Example 3 of the present invention; wherein ag is Na + , K+ , Cs + Mg 2+ , Ca 2+ , Sr 2+ 、UO2 2+ The permeation process through GOM and OGRM; h is the comparison diagram of different ion rejection rates in GOM and OGRM; i is the relative permeability of water and different ions;

[0029] Figure 6 The permeation test result diagram of Experimental Example 3 of the present invention; wherein a is Fe 3+ The permeation process, b is the test ion relative to UO2 2+ The separation factor. DETAILED DESCRIPTION

[0030] As a typical graphene analog, graphene oxide ribbons (derived from carbon nanotubes) retain the significant structural features similar to graphene oxide, including honeycomb structural units, huge aromatic faces, and abundant oxygen-containing groups. However, compared with two-dimensional graphene oxide, the quasi-one-dimensional topological structure of graphene oxide ribbons gives it a huge aspect ratio, which in turn produces a large number of carbonyl and carboxyl groups on its edges, and fewer hydroxyl and ether groups on the basal plane. In addition, the ribbon morphology leads to a unique woven structure in the graphene oxide ribbons.

[0031] The graphene oxide membrane prepared in the prior art is easy to combine with water molecules, resulting in interlayer expansion, which limits the selectivity and separation efficiency of the membrane. The graphene oxide ribbon membrane prepared by the present invention has a unique weaving structure, which prevents water molecules from further embedding at the edge of the nanoribbon, so that the membrane maintains a constant interlayer spacing in both dry and wet states, avoiding interlayer expansion. At the same time, the strong π-π interaction of the low-defect aromatic face in the central axis area further improves the stability and durability of the membrane. And the nanochannels formed by the unique weaving structure realize the separation of Cs + and Sr 2+ Efficient separation.

[0032] The present invention mixes carbon nanotubes, concentrated sulfuric acid and potassium permanganate and then performs strong ultrasonic stripping. Under the environment of concentrated sulfuric acid, potassium permanganate, as a strong oxidant, can oxidize the carbon atoms in the carbon nanotubes to form oxygen-containing functional groups (such as carboxyl, hydroxyl, etc.), and at the same time increase their spacing, creating conditions for the subsequent stripping process. Sulfuric acid molecules can be inserted into the carbon nanotube interlayer to form sulfuric acid-carbon nanotube interlayer compounds, thereby increasing the carbon nanotube interlayer spacing, providing space for subsequent oxidation reactions, and also synergizing with potassium permanganate to enhance the oxidation effect, making the edges and defective parts of the carbon nanotubes more easily oxidized. After ultrasonic stripping, the mixture is mixed with an ice-water mixture containing H2O2, and the ice-water mixture containing hydrogen peroxide can be used to reduce the excess potassium permanganate in the reaction system, thereby terminating the oxidation reaction, and the ice-water mixture also controls the reaction temperature to prevent the reaction from being too violent.

[0033] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0034] 1. The specific embodiment of the method for preparing the non-expandable graphene oxide ribbon film of the present invention is as follows:

[0035] Example 1

[0036] The method for preparing the non-expandable graphene oxide ribbon film of this embodiment adopts the following steps:

[0037] 400mL of concentrated sulfuric acid was slowly added to 3g of carbon nanotubes, and stirred evenly to obtain a first mixed solution; 18.0g of potassium permanganate was added to the first mixed solution in batches to obtain a second mixed solution, and then strong ultrasonic stripping was performed at 50°C for 5h, and the frequency of the strong ultrasonic stripping was 80kHz. After the reactants were cooled to room temperature, they were poured into 400mL of an ice-water mixture containing 30% H2O2 (3.0mL) to obtain a third mixed solution. Then, the third mixed solution was centrifuged, and the solid was dialyzed until no manganese ions and sulfate anions were detected, and the final graphene oxide belt suspension was obtained; wherein the scale of the dialysis bag used for dialysis was 40mm×80mm, the volume was 10 ml, the molecular weight cutoff was 14000Da, and the solutions on both sides of the dialysis were ultrapure water, and the solid after centrifugation + 5 ml of ultrapure water formed a graphene oxide mixed solution.

[0038] Accurately weigh 0.595 g of the graphene oxide ribbon suspension and dilute it into 100 mL of deionized water to obtain 3.36 × 10 -2 After ultrasonic treatment at 80 kHz for 20 min, the suspension was vacuum filtered through a 0.2 μm polyethersulfone membrane to obtain a non-expanded graphene oxide ribbon membrane (OGRM).

[0039] Example 2

[0040] The method for preparing the non-expandable graphene oxide ribbon film of this embodiment adopts the following steps:

[0041] 200 mL of concentrated sulfuric acid was slowly added to 1.6 g of carbon nanotubes and stirred to obtain a first mixed solution; 8.0 g of potassium permanganate was added to the first mixed solution in batches to obtain a second mixed solution, and then strong ultrasonic stripping was performed at 40 ° C for 8 hours, and the frequency of the strong ultrasonic stripping was 40 kHz. After the reactants were cooled to room temperature, they were poured into 200 mL of an ice-water mixture containing 30% H2O2 (3.0 mL) to obtain a third mixed solution. Then, the third mixed solution was centrifuged and the solid was dialyzed until no manganese ions and sulfate anions were detected to obtain a final graphene oxide ribbon suspension.

[0042] Accurately weigh 0.826 g of the graphene oxide ribbon suspension and dilute it into 100 mL of deionized water to obtain 5×10 -2 After ultrasonic treatment at 40 kHz for 30 min, the suspension was vacuum filtered through a 0.2 μm polyethersulfone membrane to obtain a non-expanded graphene oxide ribbon membrane (OGRM-1).

[0043] Example 3

[0044] The method for preparing the non-expandable graphene oxide ribbon film of this embodiment adopts the following steps:

[0045] Slowly add 400mL of concentrated sulfuric acid to 3.0g of carbon nanotubes and stir to obtain a first mixed solution; add 18.0g of potassium permanganate to the first mixed solution in batches to obtain a second mixed solution, and perform strong ultrasonic stripping for 3h at a temperature of 60°C, and the frequency of the strong ultrasonic stripping is 100kHz. After the reactant is cooled to room temperature, pour it into 400mL of an ice-water mixture containing 30% H2O2 (3.0mL) to obtain a third mixed solution. Then, the third mixed solution is centrifuged and the solid is dialyzed until no manganese ions and sulfate anions are detected to obtain a final graphene oxide ribbon suspension.

[0046] Weigh 0.595 g of the above graphene oxide ribbon suspension accurately and dilute it into 100 mL of deionized water to obtain 3.36 × 10 -2 After ultrasonic treatment at 100 kHz for 30 min, the suspension was vacuum filtered through a 0.2 μm polyethersulfone membrane to obtain a non-expanded graphene oxide ribbon membrane (OGRM-2).

[0047] 2. Examples of the application of the non-expandable graphene oxide ribbon membrane of the present invention in separating cesium and strontium ions from radioactive wastewater The schematic diagram of the device for the permeation experiment involved in the following examples is as follows: Figure 1 As shown, the specific operations are as follows:

[0048] The permeation test apparatus consists of two identical chambers, the feed side and the suction side, both of which have an effective area of ​​2.01 cm 2 The feed side is filled with 170 mL of multi-component solution, which consists of 0.01 mol / L NaNO3, KNO3, CsNO3, Mg(NO3) 2 、Ca(NO3) 2 、Sr(NO3) 2 、Fe(NO3) 3 and 0.001mol / L UO2(NO3) 2 The feed side also contains a certain amount of 1.0 mol / L sucrose, and the hydration diameter of sucrose is As an impermeable solute, it plays a driving role in providing a concentration gradient. + As a typical example of actinides and lanthanides, uranium was selected for comparison because it has similar hydrate diameters and chemical properties to cesium and strontium. The experiment was carried out at room temperature. During the experiment, both sides were gently stirred at 200 rpm, and the pH value on both sides of the membrane was kept at 2.3 by adding HCl / NaOH solution. At regular intervals, 2.0 mL of samples were extracted, and the salt concentration was determined by ion chromatography, and the entire permeation process of the test ions was recorded.

[0049] The ion permeability R can be calculated by formula (1):

[0050]

[0051] In the formula, C t is the ion concentration detected on the extraction side at a specific permeation time t; V is the volume of the extraction solution, 170 mL; A is the effective membrane area, 2.01 cm 2 .

[0052] According to formula (2), the relative separation coefficient (f) of different ions is obtained, which represents the selectivity of ions:

[0053]

[0054] In the formula, R a and R b are the ion permeabilities of component a and component b, respectively.

[0055] Example 4

[0056] In this example, the non-expanded graphene oxide ribbon membrane (OGRM) prepared in Example 1 was used to separate cesium and strontium ions in radioactive wastewater through a permeation experiment. The separation coefficient results are shown in Table 1.

[0057] Table 1 Separation coefficient of OGRM for cesium and strontium ions

[0058]

[0059] Example 5

[0060] In this example, the non-expanded graphene oxide strip membrane (OGRM-1) prepared in Example 2 was used to separate cesium and strontium ions in radioactive wastewater through a permeation experiment. The separation coefficient results are shown in Table 2.

[0061] Table 2 Separation coefficient of OGRM-1 for cesium and strontium ions

[0062]

[0063]

[0064] Example 6

[0065] In this example, the non-expanded graphene oxide strip membrane (OGRM-2) prepared in Example 3 was used to separate cesium and strontium ions in radioactive wastewater through a permeation experiment. The separation coefficient results are shown in Table 3.

[0066] Table 3 Separation coefficient of OGRM-2 for cesium and strontium ions

[0067]

[0068] 3. Comparison

[0069] The preparation method of the graphene oxide film of this comparative example adopts the following steps:

[0070] A mixed acid of 360 mL of sulfuric acid and 40 mL of phosphoric acid is slowly added to a mixture of 3.0 g of graphite powder and 18.0 g of KMnO4. The mixed solution is heated to 50°C, stirred for 12 hours, and cooled to room temperature; 400 mL of an ice-water mixture containing 3.0 mL of 30% hydrogen peroxide is added. Then, the mixed solution is centrifuged at 4000 rpm to remove the diluted acid, and the residual solid is dialyzed several times until no metal ions and sulfate anions are detected by an inductively coupled plasma mass spectrometer, thereby obtaining a graphene oxide suspension.

[0071] Weigh 0.595 g of graphene oxide suspension accurately and dilute it into 100 mL of deionized water to obtain 3.36 × 10 -2 After ultrasonic treatment for 20 min, the suspension was filtered through a 0.2 μm polyethersulfone membrane to obtain a graphene oxide membrane (GOM).

[0072] In this comparative example, the obtained graphene oxide membrane (GOM) is used to separate cesium and strontium ions in radioactive wastewater through a permeation experiment, and the separation coefficient results are shown in Table 4.

[0073] By comparing the separation coefficients of cesium and strontium ions in Table 4 and Table 1, it is found that the non-expandable graphene oxide ribbon membrane prepared by the present invention can significantly improve the separation effect of cesium and strontium ions in radioactive wastewater.

[0074] Table 4 Separation coefficient of GOM for cesium and strontium ions

[0075]

[0076] IV. Experimental Examples

[0077] Experimental Example 1

[0078] In this experimental example, the spatial structure, morphology and crystal structure of the GOM prepared in the comparative example and the OGRM prepared in Example 1 were studied. The results are as follows: Figure 2 , 3 As shown in Figure 2. The stacking model is as follows: Figure 2 As shown in a and d, the SEM images of the surface are Figure 2 As shown in b and e (the inset is the filtered image), the SEM images of the cross section are as follows Figure 2 As shown in c and f (the inset is a smooth cross section), the TEM images are Figure 3 shown.

[0079] SEM images show that the average thickness of GOM is 2.5 μm and the average thickness of OGRM is 2.7 μm ( Figure 2 As shown in c and f in the figure). Since the lateral size of graphene oxide is several micrometers, many wrinkles and curls are spontaneously generated, which also leads to a large number of wrinkles and grooves on the surface and cross section of the layered GOM ( Figure 2 In contrast, the narrow width of 400 nm in OGR makes its stacking more like a compact textile, which makes the final OGRM surface smooth ( Figure 2 The cross section of OGRM shows a fuzzy horizontal texture ( Figure 2 It is also worth noting that some ribbon-like fragments appeared at the bottom of the torn OGRM, which looked like damaged fabrics, indicating that there may be a woven structure in the OGRM. Figure 3 ) further verified Figure 2 the correctness of the results.

[0080] Experimental Example 2

[0081] In this experimental example, the lamellar structure and internal mechanism of the GOM prepared in the comparative example and the OGRM prepared in Example 1 are studied. The XRD patterns are as follows: Figure 4 As shown in a, the TEM image is Figure 4 As shown in b and c, the Raman spectrum is as follows Figure 4 As shown in (d), the XPS analysis diagram is as follows Figure 4 As shown in Figure e, the FTIR image of v(CC) is as follows Figure 4 As shown in figure f.

[0082] In this experiment, XRD patterns were used to study the lamellar structures of GOM and OGRM. Figure 4 As shown in a). Among them, the nanochannel size of GOM is After wetting with water, the channel size increases to This shows that the graphene oxide film (GOM) of the comparative example has expansion. In contrast, the diffraction of OGRM at 11.31° is almost unchanged whether it is dry or wet, and its interlayer spacing is The graphene oxide ribbon membrane of the present invention is proved to be non-swelling. Since there is a strong dependence between ion selectivity and precise nanofiltration channels, this finding has inspiring significance for membrane separation based on graphene oxide and its analogs.

[0083] Subsequently, a series of spectroscopic and transmission electron microscopic analyses were performed to investigate the unexpanded interlayer spacing in OGRM. Significant differences were observed in the XRD spectra of OGRM and GOM ( Figure 4 As shown in a), in addition to the diffraction at 11.31°, OGRM also has a second broad peak at 20.48°, while GOM does not. Based on previous studies, this experiment assigns it to the OGRM peak here, which is related to graphite-like stacks. According to the Bragg equation, the compacted layer spacing d is calculated to be That is, the OGR (graphene oxide ribbon) maintains a tight graphite-like stacking in the aromatic groups between adjacent nanoribbons. Here, the fact that the longitudinal decompression of MWCNTs (multi-walled carbon nanotubes) is produced should be taken into account. There are abundant oxygen-containing groups at the edges of the OGR, but a relatively complete aromatic skeleton is maintained along its axis. Therefore, a hypothesis is proposed that the strong π-π interaction in the central region of the OGR locks the entire membrane fabrication process and prevents the expansion of the oxidized edge in water. This hypothesis can be further confirmed by TEM testing. After long-term ultrasonic peeling, a large number of multilayer nanoribbons were still observed in the TEM image of the OGRM, while no single-layer nanoribbons were observed, indicating that there is a tight stacking between adjacent OGRMs. This result also further proves the non-expansion property of the graphene oxide ribbon membrane of the present invention ( Figure 4 (as shown in b and c).

[0084] like Figure 4 As shown in Figure d, five bands were observed in the first-order Raman spectrum, which were labeled D′, G, D″, D, and D*. The relative intensities of the D and G bands were used to evaluate the symmetry and crystallinity of the honeycomb lattices in GOM and OGRM. D / I G =1.26 than GOM's I D / I G =1.40, which indicates that OGR has fewer structural defects and a more regular aromatic profile.

[0085] Different profiles are observed in the C1s spectra of GOM and OGRM ( Figure 4 (e). It is worth mentioning that at 286.7 eV, the band in OGRM is significantly weaker than that in GOM. This indicates that OGRM has a lower oxidation level but a more regular aromatic face. In addition, after careful calibration of metallic gold powder, the binding energy of the first low-energy band of OGRM is 284.2 eV, which is lower than 284.5 eV of GOM. This indicates that the ratio of CC and C=C groups is different. This result once again illustrates that OGR has a relatively complete aromatic lattice and stable π stacking.

[0086] The vibration frequency of the group depends on the conjugation level of the main chain of the molecule. As the aromaticity of the conjugated system increases, the excitation force constant of the conjugated group becomes smaller, causing the vibration to shift to a lower wave number. Figure 4 As shown in Figure 5, compared with graphene oxide GO, the v(C=C) in the graphene oxide ribbon OGR surprisingly shifts to the low energy direction by 33 cm -1 , indicating that the aromaticity of OGR is significantly improved. In summary, the longitudinally decompressed MWCNTs lead to the retention of complete aromatic faces in the central region of OGR, thereby inducing strong π-π interactions between adjacent nanoribbons and preventing the peripheral expansion of OGR.

[0087] Experimental Example 3

[0088] This experimental example studies the separation of various ions in the permeation experiment of the comparative example GOM and the OGRM of Example 1 to verify the selectivity of different membranes for ions. The experimental method is consistent with the permeation experiment in the example. The results are as follows: Figure 5 , 6 shown.

[0089] according to Figure 5 AF and Figure 6 It can be seen that the permeability of monovalent ions is about 2.4 times that of divalent ions and higher than that of trivalent Fe 3+ 2 orders of magnitude higher ( Figure 6 As shown in a), compared with UO2 2+ 3-4 orders of magnitude higher ( Figure 6 This makes Cs in GOM and OGRM + and Sr 2+ Relative to Fe 3+ and UO2 2+ The separation of OGRM is more ideal. Among them, the separation coefficients of OGRM are f Cs / Fe =222.77, f Sr / Fe =95.38, It is worth noting that Cs + and Sr 2+ The ion penetration rate in OGRM is faster, which is 1.23 times and 1.72 times that of GOM, respectively ( Figure 5 However, in OGRM, Fe 3+ and UO2 2+ Almost 100% rejection was maintained within 12 h, indicating that transition metal nuclides, actinides, and lanthanides may be completely rejected. These advantages enable OGRM to separate Cs from complex radioactive waste under harsh conditions. + and Sr 2+ .

[0090] Generally speaking, there are many factors that affect ion permeation, such as membrane d-spacing size exclusion, Gibbs-Donan effect, surface adsorption (including electrostatics, hydrogen bonding, coordination, ion-π interaction), permeation pathway, etc. Among them, the permeation pathway including length and site is crucial to regulating the selectivity and separation efficiency of the membrane. In the present study, the average interlayer spacing of wet GOM is This is sufficient to allow ions to diffuse across the membrane. 3+ and UO2 2+ The extremely low permeability may be due to the synergistic effect of size exclusion and surface adsorption. For OGRM, due to its unique two-stage structure, i.e., two layers of superimposed and interwoven woven structure, the permeation pathway is significantly different. The average spacing caused by strong π-π interaction is It is so narrow that nothing can get in, not even water molecules. Due to the abundance of oxygen-containing groups, the edges of the nanoribbons form The extended spacing of the OGRMs enables the rapid diffusion of hydrated ions. However, these edge nanochannels are strictly confined by the π stacking in the central region and exhibit non-expanding properties. It is worth noting that the non-uniform surface and random stacking in OGRMs still provide some suitable channels to accommodate and transport large hydrated ions, although the average diameter of these nanochannels is small.

[0091] according to Figure 5As shown in Fig. i, it can be observed that all monovalent and divalent ions permeate faster in OGRM than in GOM. It is noteworthy that their relative permeabilities in the two membranes are inconsistent with the relative water flux, but are higher than the relative water flux. Assuming that the ion diffusion is completely controlled by the permeation pathway, their relative permeabilities in the two membranes should be the same as the relative water flux. This anomaly indicates that the diffusion of ions is affected by the surface properties of the membrane in addition to the permeation pathway. In contrast, the graphene oxide membrane has a stronger barrier effect on these ions than the graphene oxide ribbon membrane. And the ion rejection is very consistent with their hydrate diameter, that is, Cs + <K + <Na + <Sr 2+ <Ca 2+ <Mg 2+ .

Claims

1. A method for preparing a non-expandable graphene oxide ribbon film, characterized in that: The following steps are involved: The carbon nanotubes, concentrated sulfuric acid and potassium permanganate are mixed, strongly ultrasonically exfoliated, and then mixed with an ice-water mixture containing H2O2 and post-treated to obtain a graphene oxide ribbon suspension; the suspension is successively diluted with water, ultrasonically treated and film-formed to obtain a non-expandable graphene oxide ribbon film.

2. The method for preparing the non-expandable graphene oxide ribbon film according to claim 1, characterized in that: The frequency of the strong ultrasonic peeling is 40 to 100 kHz.

3. The method for preparing the non-expandable graphene oxide ribbon film according to claim 2, characterized in that: The temperature of the strong ultrasonic peeling is 40-60° C. and the time is 3-8 hours.

4. The method for preparing the non-expandable graphene oxide ribbon film according to claim 1, characterized in that: The usage ratio of the carbon nanotubes, concentrated sulfuric acid and potassium permanganate is 1 g: (125-135) mL: (5-6) g.

5. The method for preparing the non-expandable graphene oxide ribbon film according to claim 4, characterized in that: The volume ratio of the ice-water mixture to concentrated sulfuric acid is 1:(1-1.1), and the volume fraction of the 30wt% H2O2 solution in the ice-water mixture containing H2O2 is 0.75%-1.5%.

6. The method for preparing the non-expandable graphene oxide ribbon film according to any one of claims 1 to 5, characterized in that: The membrane formation is carried out by filtration through a polyethersulfone membrane.

7. The method for preparing the non-expandable graphene oxide ribbon film according to any one of claims 1 to 5, characterized in that: The post-treatment is to centrifuge the mixed solution to obtain a solid, and then dialyze the solid to obtain a graphene oxide ribbon suspension.

8. The method for preparing the non-expandable graphene oxide ribbon film according to any one of claims 1 to 5, characterized in that: The dispersion degree of the suspension after dilution with water is 3.0 to 5.0×10 -2 g / L.

9. The method for preparing the non-expandable graphene oxide ribbon film according to claim 8, characterized in that: The ultrasonic treatment time is 20 to 30 minutes.

10. Application of a non-expandable graphene oxide ribbon membrane in separating cesium and strontium ions from radioactive wastewater, characterized in that: The non-expandable graphene oxide ribbon film is prepared according to the preparation method according to any one of claims 1-9.

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