Preparation method of PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane

Abstract

A preparation method for a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane relates to a preparation method for a lithium ion imprinted membrane. The present invention uses PPy to coat rGO, relying on the functional groups of PPy to cross-link with the substances on the base membrane. The ion imprinted material is loaded on the outermost layer to obtain an electrically controlled ion imprinted membrane with excellent ion adsorption performance, overcome the shortcomings of traditional ion imprinted membrane materials, broaden the scope of use of PPy, and improve the overall conductivity and its reduction potential. Method: 1. Prepare SP-PDA@PVDF membrane; 2. Prepare PPy / rGO conductive polymer; 3. Prepare PPy / rGO@PDA@PVDF membrane; 4. Prepare IIP@PVDF membrane. The present invention relies on the electric field force of an external electric field to accelerate the diffusion of target ions to the membrane surface, greatly improves the adsorption rate of ions by the ion imprinted membrane, and greatly improves the adsorption performance of the membrane in an acidic environment.

Description

Technical Field

[0001] The invention relates to a preparation method of a lithium ion imprinted membrane. Background Art

[0002] Lithium is primarily found in ores, salt lake brine, and seawater. Salt lake brine accounts for two-thirds of the lithium content. Therefore, mining lithium from salt lake brine and seawater is a promising alternative to address lithium shortages.

[0003] Ion imprinting technology, one of the most common methods for extracting lithium from salt lake brine, has the advantages of large adsorption capacity and high selectivity. This is mainly because ion imprinting technology is developed based on molecular imprinting technology. In actual salt lake brine, in addition to lithium ions, there are also large amounts of other ions such as magnesium ions. Therefore, the selective ion imprinting technology is very suitable for lithium extraction. However, traditional ion imprinting membranes have obvious disadvantages. The slow adsorption rate and decreased cyclic adsorption capacity have significantly limited their development. Therefore, a method combining electrochemical switching ion exchange technology with ion imprinting technology has been developed to improve the shortcomings of ion imprinting technology. However, in the process of combining electrochemical switching ion exchange technology, improving the conductivity of the material to obtain a higher applied voltage becomes an inevitable problem. Therefore, it is very important to explore a preparation process for materials that can operate stably under high voltage. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above technical shortcomings of traditional ion-imprinted membrane materials and to provide a preparation method for PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane.

[0005] This method uses polypropylene (PPy) to coat rGO, relying on the functional groups of PPy to crosslink with the substrate. An ion-imprinted material is loaded on the outermost layer to create an electrically controlled ion-imprinted membrane with excellent ion adsorption properties. This overcomes the shortcomings of traditional ion-imprinted membrane materials, broadens the application range of PPy, and improves its overall conductivity and reduction potential.

[0006] A method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane is specifically completed by the following steps:

[0007] 1. Preparation of SP-PDA@PVDF membrane:

[0008] ①, mixing sodium periodate solution and sodium acetate buffer solution to obtain a mixed solution; dissolving dopamine hydrochloride in the mixed solution to obtain a modified solution;

[0009] ② Place a piece of PVDF membrane on the surface of the modified solution, so that one side of the PVDF membrane contacts the modified solution and the other side contacts the air to obtain a reaction system; at room temperature, the reaction system is heated at 120-150 r·min.-1 The PVDF membrane was oscillated at an oscillation speed of 100 nm for 6 to 7 hours, with one side of the PVDF membrane in contact with the modification solution and the other side in contact with the air. After the oscillation was completed, a PVDF membrane with one side modified was obtained.

[0010] ③. Place the modified PVDF membrane on the surface of the modified solution again, so that the unmodified side of the PVDF membrane contacts the modified solution and the modified side contacts the air to obtain a reaction system; at room temperature, the reaction system is heated at 120-150 r·min. -1 The membrane was oscillated at an oscillation speed of 6 to 7 h, then washed with water and dried to obtain the SP-PDA@PVDF membrane;

[0011] 2. Preparation of PPy / rGO conductive polymer:

[0012] The reduced graphene oxide was added to anhydrous ethanol and stirred, and then pyrrole was added, ultrasonicated, and then FeCl3 solution was added. The mixture was reacted in an ice bath for 8 to 12 hours, and finally washed with hydrochloric acid and dried to obtain a PPy / rGO conductive polymer.

[0013] 3. Preparation of PPy / rGO@PDA@PVDF membrane:

[0014] The PPy / rGO conductive polymer and anhydrous methanol were mixed, sonicated, and then ethylene glycol dimethacrylate was added to obtain a mixed solution; the SP-PDA@PVDF membrane was immersed in the mixed solution, and then the temperature was raised to 60°C to 70°C, and stirred at 60°C to 70°C for a period of time. The PVDF membrane was then removed, rinsed with deionized water, and dried to obtain the PPy / rGO@PDA@PVDF membrane;

[0015] 4. Preparation of IIP@PVDF membrane:

[0016] ①, add methacrylic acid to methanol, heat and stir for a period of time, then add lithium chloride and benzo-12-crown-4-ether, stir at room temperature for a period of time to obtain a mixed solution;

[0017] ②. Immerse the PPy / rGO@PDA@PVDF membrane in the mixed solution prepared in step 4①, then add ethylene glycol dimethacrylate and azobisisobutyronitrile, introduce nitrogen into the system, and then condense and reflux for a period of time under nitrogen atmosphere protection and a temperature of 70℃~75℃. After taking out the membrane, rinse it with deionized water, then pickle it with hydrochloric acid, and dry it to obtain a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane.

[0018] The main principles of the present invention:

[0019] PPy is a heterocyclic conjugated conductive polymer with high conductivity, reversible electrochemical redox properties, and strong charge transfer capabilities. PPy can capture and release these dopant ions during electrochemical redox reactions, balancing the charge within the film. However, charge accumulation during the redox process and the delocalized electrons generated within PPy hinder its cation exchange capacity, necessitating modification with large electronegative species. rGO, a carbon-based material with excellent conductivity, possesses electronegativity upon ionization of its edge carboxyl groups. This electronegativity counteracts the positive potential of the delocalized electrons in PPy, immobilizing it within the polymer matrix and thus enhancing its cation exchange capacity. Furthermore, the conductive polymer formed by PPy coating rGO addresses the problem of rGO's lack of functional groups and difficulty in cross-linking. The π-π interaction between the two enhances overall conductivity. Composite membranes combining electroactive lithium ion exchange materials with ion-imprinted materials, which exhibit similar "synergistic effects," exhibit excellent cycling stability, adsorption capacity, and protonation resistance.

[0020] Beneficial effects of the present invention:

[0021] 1. Compared with traditional lithium ion imprinting, the present invention only needs to adjust the applied potential during the adsorption and desorption process, while traditional ion imprinting needs to rely on acid washing during the adsorption and desorption process. Therefore, the present invention is more environmentally friendly and has good cyclic adsorption capacity.

[0022] 2. The present invention relies on the electric field force of an external electric field to accelerate the diffusion of target ions to the membrane surface, greatly improving the adsorption rate of ions by the ion-imprinted membrane and significantly improving the adsorption performance of the membrane in an acidic environment.

[0023] 3. The present invention coats reduced graphene oxide with polypyrrole and utilizes the functional groups of polypyrrole to modify the surface defects of reduced graphene oxide, thereby directly loading the reduced graphene oxide on the membrane, thereby avoiding the defect of insufficient reduction degree in the process of first loading graphene oxide and then reducing it to reduced graphene oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the FI-TR spectrum of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0025] Figure 2 This is the XPS spectrum of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0026] Figure 3 is the adsorption capacity of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0027] Figure 4 The selective adsorption performance of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0028] Figure 5 This is a graph showing the cycling stability of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0029] Figure 6 This is a graph showing the protonation resistance of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1. DETAILED DESCRIPTION

[0030] Specific embodiment 1: This embodiment is a method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane, which is specifically completed by the following steps:

[0031] 1. Preparation of SP-PDA@PVDF membrane:

[0032] ①, mixing sodium periodate solution and sodium acetate buffer solution to obtain a mixed solution; dissolving dopamine hydrochloride in the mixed solution to obtain a modified solution;

[0033] ② Place a piece of PVDF membrane on the surface of the modified solution, so that one side of the PVDF membrane contacts the modified solution and the other side contacts the air to obtain a reaction system; at room temperature, the reaction system is heated at 120-150 r·min. -1 The PVDF membrane was oscillated at an oscillation speed of 100 nm for 6 to 7 hours, with one side of the PVDF membrane in contact with the modification solution and the other side in contact with the air. After the oscillation was completed, a PVDF membrane with one side modified was obtained.

[0034] ③. Place the modified PVDF membrane on the surface of the modified solution again, so that the unmodified side of the PVDF membrane contacts the modified solution and the modified side contacts the air to obtain a reaction system; at room temperature, the reaction system is heated at 120-150 r·min. -1 The membrane was oscillated at an oscillation speed of 6 to 7 h, then washed with water and dried to obtain the SP-PDA@PVDF membrane;

[0035] 2. Preparation of PPy / rGO conductive polymer:

[0036] The reduced graphene oxide was added to anhydrous ethanol and stirred, and then pyrrole was added, ultrasonicated, and then FeCl3 solution was added. The mixture was reacted in an ice bath for 8 to 12 hours, and finally washed with hydrochloric acid and dried to obtain a PPy / rGO conductive polymer.

[0037] 3. Preparation of PPy / rGO@PDA@PVDF membrane:

[0038] The PPy / rGO conductive polymer and anhydrous methanol were mixed, sonicated, and then ethylene glycol dimethacrylate was added to obtain a mixed solution; the SP-PDA@PVDF membrane was immersed in the mixed solution, and then the temperature was raised to 60°C to 70°C, and stirred at 60°C to 70°C for a period of time. The PVDF membrane was then removed, rinsed with deionized water, and dried to obtain the PPy / rGO@PDA@PVDF membrane;

[0039] 4. Preparation of IIP@PVDF membrane:

[0040] ① Add methacrylic acid to methanol, heat and stir for a period of time, then add lithium chloride and benzo-12-crown-4-ether, stir at room temperature for a period of time to obtain a mixed solution;

[0041] ②. Immerse the PPy / rGO@PDA@PVDF membrane in the mixed solution prepared in step 4①, then add ethylene glycol dimethacrylate and azobisisobutyronitrile, introduce nitrogen into the system, and then condense and reflux for a period of time under nitrogen atmosphere protection and a temperature of 65℃~75℃. After taking out the membrane, rinse it with deionized water, then pickle it with hydrochloric acid, and dry it to obtain a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane.

[0042] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that: the concentration of the sodium periodate solution described in step 1 ① is 20 mmol / L; the concentration of the sodium acetate buffer solution described in step 1 ① is 50 mmol / L; the volume ratio of the sodium periodate solution to the sodium acetate buffer solution described in step 1 ① is 20:80; the mass ratio of dopamine hydrochloride described in step 1 ① to the volume ratio of the mixed solution is 0.2 g:100 mL.

[0043] The other steps are the same as those in the first embodiment.

[0044] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the PVDF membrane described in step 1② has a pore size of 0.45 μm and a diameter of 47 mm. The other steps are the same as those of specific embodiment 1 or 2.

[0045] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that: in step 2, the volume ratio of the reduced graphene oxide to anhydrous ethanol is (0.2 g to 0.5 g): (25 mL to 50 mL); the volume ratio of the reduced graphene oxide to pyrrole is (0.2 g to 0.5 g): (0.6 mL to 1 mL); and the volume ratio of the reduced graphene oxide to FeCl3 solution is (0.2 g to 0.5 g): (15 mL to 25 mL). The other steps are the same as specific embodiments 1 to 3.

[0046] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the concentration of the FeCl3 solution in step 2 is 1 mol / L; the stirring time in step 2 is 20 to 40 minutes; the ultrasonic treatment time in step 2 is 5 to 10 minutes; and the concentration of hydrochloric acid in step 2 is 1 mol / L. The other steps are the same as those in specific embodiments 1 to 4.

[0047] Specific embodiment six: This embodiment differs from specific embodiments one to five in that: the volume ratio of the mass of the PPy / rGO conductive polymer described in step three to anhydrous methanol is 0.2 g: (80 mL to 100 mL); the volume ratio of the mass of the PPy / rGO conductive polymer described in step three to ethylene glycol dimethacrylate is 0.2 g: (0.1 mL to 0.15 mL); in step three, the reaction is stirred at 60°C to 70°C for 6h to 8h, and the stirring speed is 30 to 50 r·min -1 The ultrasonic treatment time in step 3 is 5 to 10 minutes. The other steps are the same as those in specific embodiments 1 to 5.

[0048] Specific Embodiment 7: This embodiment differs from Specific Embodiments 1 to 6 in that the volume ratio of methacrylic acid to methanol in step 4 (1) is 0.1:90; the volume ratio of lithium chloride to methanol in step 4 (1) is 0.1 g:90 mL; and the volume ratio of benzo-12-crown-4-ether to methanol in step 4 (1) is 0.05:90. Other steps are the same as Specific Embodiments 1 to 6.

[0049] Specific embodiment eight: The difference between this embodiment and specific embodiments one to seven is that the heating and stirring in step four ① is at 40°C and the stirring speed is 30r·min -1 ~60r·min -1 The stirring time at room temperature in step 4① is 20min to 30min. The other steps are the same as those in specific embodiments 1 to 7.

[0050] Specific Embodiment 9: This embodiment differs from Specific Embodiments 1 to 8 in that the volume ratio of ethylene glycol dimethacrylate in step 4 (2) to methanol in step 4 (1) is 0.1:90; and the volume ratio of azobisisobutyronitrile in step 4 (2) to methanol in step 4 (1) is 0.02 g:90 mL. Other steps are the same as Specific Embodiments 1 to 8.

[0051] Specific Embodiment 10: This embodiment differs from Specific Embodiments 1 to 9 in that in step 4 (2), the membrane is refluxed under nitrogen at 75°C for 24 hours or at 65°C for 20 hours. After removal, the membrane is rinsed 3 to 5 times with deionized water and then pickled once or twice with hydrochloric acid, each pickling time lasting 12 to 16 hours. The concentration of the hydrochloric acid is 1 mol / L. The other steps are the same as Specific Embodiments 1 to 9.

[0052] The following examples are used to verify the beneficial effects of the present invention:

[0053] Example 1: A method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane is specifically completed by the following steps:

[0054] 1. Preparation of SP-PDA@PVDF membrane:

[0055] ①, mix 20 mL of sodium periodate solution and 80 mL of sodium acetate buffer solution to obtain a mixed solution; dissolve 0.2 g of dopamine hydrochloride in the mixed solution to obtain a modified solution;

[0056] The concentration of the sodium periodate solution described in step 1① is 20mmol / L;

[0057] The concentration of the sodium acetate buffer solution described in step 1① is 50mmol / L;

[0058] ② Place a piece of PVDF membrane on the surface of the modified solution, so that one side of the PVDF membrane contacts the modified solution and the other side contacts the air to obtain a reaction system; at 25°C, the reaction system is rotated at 120 r·min. -1 The membrane was oscillated at an oscillation speed of 100 nm for 6 h, with one side of the PVDF membrane in contact with the modification solution and the other side in contact with air. After the oscillation was completed, a one-side modified PVDF membrane was obtained.

[0059] The PVDF membrane described in step 1② has a pore size of 0.45 μm and a diameter of 47 mm;

[0060] ③. Mix 20 mL of sodium periodate solution (20 mmol / L) and 80 mL of sodium acetate buffer solution (50 mmol / L) to obtain a mixed solution; dissolve 0.2 g of dopamine hydrochloride in the mixed solution to obtain a modified solution; place the modified PVDF membrane on the surface of the modified solution again, so that the unmodified side of the PVDF membrane contacts the modified solution and the modified side contacts the air, to obtain a reaction system; and rotate the reaction system at room temperature at 120 r·min. -1 The membrane was oscillated at an oscillation speed of 6 h, washed with water three times, and dried to obtain the SP-PDA@PVDF membrane;

[0061] 2. Preparation of PPy / rGO conductive polymer:

[0062] 0.5 g of reduced graphene oxide was added to 25 mL of anhydrous ethanol and stirred for 30 min. Then, 0.6 mL of pyrrole was added and ultrasonicated for 5 min. Then, 15.15 mL of FeCl3 solution was added and reacted in an ice bath for 12 h. Finally, the mixture was washed three times with 1 mol / L hydrochloric acid and dried to obtain PPy / rGO conductive polymer.

[0063] The concentration of the FeCl3 solution described in step 2 is 1 mol / L;

[0064] 3. Preparation of PPy / rGO@PDA@PVDF membrane:

[0065] 0.2 g of PPy / rGO conductive polymer was mixed with 100 mL of anhydrous methanol and ultrasonicated for 5 min. Then 0.1 mL of ethylene glycol dimethacrylate (EGDMA) was added to obtain a mixed solution. The SP-PDA@PVDF membrane was immersed in the mixed solution and then heated to 65 °C. The mixture was stirred at 65 °C and 30 r·min. -1 The reaction was carried out under the conditions of 8h, and then the PVDF membrane was taken out, rinsed with deionized water, and dried to obtain the PPy / rGO@PDA@PVDF membrane;

[0066] 4. Preparation of IIP@PVDF membrane:

[0067] ①, add 0.1mL methacrylic acid (MAA) to 90mL methanol, and stir at 30r·min -1 and 40°C for 30 min under magnetic stirring, then 0.1 g of lithium chloride (LiCl) and 0.05 mL of benzo-12-crown 4-ether (B12C4) were added, and stirred at room temperature for 30 min to obtain a mixed solution;

[0068] ②, immerse the PPy / rGO@PVDF membrane in the mixed solution prepared in step 4①, then add 0.1mL ethylene glycol dimethacrylate (EGDMA) and 0.02g azobisisobutyronitrile (AIBN), introduce nitrogen into the system, and then condense and reflux under nitrogen atmosphere protection at 75°C for 24h. After taking out the membrane, rinse it with deionized water, then pickle it with hydrochloric acid, and dry it to obtain PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane (IIP@PVDF);

[0069] In step 4②, the membrane was taken out and rinsed with deionized water 5 times, and then pickled with hydrochloric acid 2 times, each pickling time was 12 hours; the concentration of the hydrochloric acid was 1 mol / L.

[0070] Comparative Example 1: This example differs from Example 1 in that lithium chloride is omitted in step 4, and the final product is named NIP@PVDF. The other steps and parameters are the same as in Example 1.

[0071] Comparative Example 2: This example differs from Example 1 in that reduced graphene oxide (rGO) is omitted in step 2, and the final product is named Li-PPy@PVDF. Other steps and parameters are the same as in Example 1.

[0072] Figure 1 This is the FI-TR spectrum of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0073] from Figure 1 It can be seen that the groups present in PVDF, SP-PDA@PVDF, PPy / rGO@PDA@PVDF and IIP@PVDF were characterized by FT-IR, as shown in the figure. SP-PDA@PVDF membrane has a peak at 1513 cm -1 3000-3700cm -1 and 1640cm -1 A new characteristic absorption band appears at 1716cm, which corresponds to the bending vibration of the NH bond of PDA, the stretching vibration of OH and -NH2 groups and the resonance vibration of the CC bond in the aromatic ring. -1 The absorption bands at 1728 cm-1 correspond to the CO bonds in the -COOH groups in SP-PDA. The presence of these absorption bands indicates that the SP-PDA@PVDF membrane has been successfully prepared. In addition, the absorption bands at 1728 cm-1 caused by the -COOH groups on the rGO sheet -1 The stretching vibration band at also appears on IIP@PVDF and PPy / rGO@PVDF. Therefore, it can be concluded that graphene oxide is doped with IIP@PVDF and PPy / rGO@PVDF.

[0074] Since polypyrrole also contains imine groups, the 3000-3700 cm -1 The broad peak at 2923 cm -1 and 2854cm -1 The peak at 1166 cm is also due to the CH bond in polypyrrole. -1 However, due to the π-π effect between PPy and rGO, the appearance of other infrared peaks of PPy is obscured, so the characteristic peaks of PPy, such as 1540, 1030 and 1290 cm-1, are not found in IIP@PVDF and PPy / rGO@PVDF. -1 Corresponding to the symmetric stretching vibration of the pyrrole ring, the bending vibration of the NH bond and the in-plane vibration of the CH.

[0075] Figure 2 This is the XPS spectrum of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0076] from Figure 2 It can be seen that the composition of the surface of the prepared IIP@PVDF membrane before and after adsorption was further analyzed by XPS. Figure 2 The full spectrum scan in a shows obvious O elements, indicating that Li + A "macrocyclic effect" is formed between B12C4, which enhances the adsorption capacity of Li+. Figure 2 As can be seen in b, lithium elements can be scanned only in the film after adsorption, indicating that lithium elements are successfully adsorbed onto the film after applying a negative potential, while lithium elements are expelled after applying a positive potential.

[0077] Figure 3 is the adsorption capacity of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0078] like Figure 3 As shown in a, the adsorption capacity of the IIP@PVDF composite membrane increases with the increase of applied voltage. The adsorption capacity of Li on the IIP@PVDF electrode reaches its maximum value (181 mg·g -1 ). After the voltage exceeded 1.2 V, it was found that the adsorption capacity remained at a stable value. Therefore, it can be inferred that the voltage can greatly accelerate the adsorption rate after the voltage is applied. This is mainly because the diffusion rate of Li to the membrane surface increases with the increase of voltage. Figure 3 As shown in Figure 2 (b), the high adsorption capacity of IIP@PVDF is the result of multiple factors. When voltage is applied, Li can bind to some adsorption sites that are not fully exposed, resulting in a much higher adsorption capacity than when no voltage is applied. Compared to Li-PPy@PVDF without rGO, the adsorption capacity is also significantly improved. This is due to the larger surface area of ​​rGO. The amount of PPy loaded on rGO is much greater than when loaded directly on the PVDF membrane. Therefore, when B12C4 is grafted onto the PPy layer, IIP@PVDF can obtain more adsorption sites.

[0079] Figure 4 The selective adsorption performance of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0080] Selective adsorption capacity Figure 4 As shown in the figure, the IIP@PVDF prepared in Example 1 has a strong affinity for Na + , K + and Mg 2+The selectivity coefficients are 4.71, 7.07 and 3.53 respectively. This is mainly due to the interaction between crown ether (0.1273nm) and Li + (0.120nm) is close in radius, so it can be adsorbed into the ring of crown ether. + (0.120nm) and Mg 2+ The radius of the ions is also similar (0.198 nm), so the separation and adsorption of Li / Mg are lower than those of other ions.

[0081] Figure 5 This is a graph showing the cycling stability of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0082] The cyclic adsorption performance of the present invention is as follows Figure 5 As shown in the figure, after 10 cycles of adsorption, the adsorption amount did not show a significant decrease compared with the first time, and the adsorption amount could still reach 174 mg.g after the tenth desorption. -1 This is due to the fact that in the ESIX process, the adsorption and desorption of ions are achieved by adjusting the reduction and oxidation potential of the membrane. + The removal process will not damage the membrane structure, while traditional ion imprinted membranes rely on acid washing, which will damage the membrane.

[0083] Figure 6 This is a graph showing the protonation resistance of the PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane prepared in Example 1;

[0084] The anti-protonation properties of the present invention are as follows Figure 6 As shown in Figure 2, when the pH value does not reach a very low value, the material can still be observed to have good adsorption capacity, which is caused by the weakening of protonation under electrical driving. As the pH decreases, the generation of protons also reduces the adsorption capacity, but compared with traditional ion-imprinted materials, the adsorption capacity at pH = 1 is still 83 mg.g -1 .

Claims

1. A method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of SP-PDA@PVDF membrane: ①, mixing sodium periodate solution and sodium acetate buffer solution to obtain a mixed solution; dissolving dopamine hydrochloride in the mixed solution to obtain a modified solution; ② Place a piece of PVDF membrane on the surface of the modified solution, so that one side of the PVDF membrane contacts the modified solution and the other side contacts the air to obtain a reaction system; at room temperature, the reaction system is heated at 120-150 r·min. -1 The PVDF membrane was oscillated at an oscillation speed of 100 nm for 6 to 7 hours, with one side of the PVDF membrane in contact with the modification solution and the other side in contact with the air. After the oscillation was completed, a PVDF membrane with one side modified was obtained. ③. Place the modified PVDF membrane on the surface of the modified solution again, so that the unmodified side of the PVDF membrane contacts the modified solution and the modified side contacts the air to obtain a reaction system; at room temperature, the reaction system is heated at 120-150 r·min. -1 The membrane was oscillated at an oscillation speed of 6 to 7 h, then washed with water and dried to obtain the SP-PDA@PVDF membrane; 2. Preparation of PPy / rGO conductive polymer: The reduced graphene oxide was added to anhydrous ethanol and stirred, and then pyrrole was added, ultrasonicated, and then FeCl3 solution was added. The mixture was reacted in an ice bath for 8 to 12 hours, and finally washed with hydrochloric acid and dried to obtain a PPy / rGO conductive polymer.

3. Preparation of PPy / rGO@PDA@PVDF membrane: The PPy / rGO conductive polymer and anhydrous methanol were mixed, sonicated, and then ethylene glycol dimethacrylate was added to obtain a mixed solution; the SP-PDA@PVDF membrane was immersed in the mixed solution, and then the temperature was raised to 60°C to 70°C, and stirred at 60°C to 70°C for a period of time. The PVDF membrane was then removed, rinsed with deionized water, and dried to obtain the PPy / rGO@PDA@PVDF membrane; 4. Preparation of IIP@PVDF membrane: ① Add methacrylic acid to methanol, heat and stir for a period of time, then add lithium chloride and benzo-12-crown-4-ether, stir at room temperature for a period of time to obtain a mixed solution; ②. Immerse the PPy / rGO@PDA@PVDF membrane in the mixed solution prepared in step 4①, then add ethylene glycol dimethacrylate and azobisisobutyronitrile, introduce nitrogen into the system, and then condense and reflux for a period of time under nitrogen atmosphere protection and a temperature of 65℃~75℃. After taking out the membrane, rinse it with deionized water, then pickle it with hydrochloric acid, and dry it to obtain a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane.

2. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The concentration of the sodium periodate solution described in step 1① is 20mmol / L; the concentration of the sodium acetate buffer solution described in step 1① is 50mmol / L; the volume ratio of the sodium periodate solution described in step 1① to the sodium acetate buffer solution is 20:80; the mass ratio of dopamine hydrochloride described in step 1① to the volume ratio of the mixed solution is 0.2g:100mL.

3. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The PVDF membrane described in step 1② has a pore size of 0.45 μm and a diameter of 47 mm.

4. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The volume ratio of the mass of the reduced graphene oxide described in step 2 to anhydrous ethanol is (0.2g~0.5g):(25mL~50mL); the volume ratio of the mass of the reduced graphene oxide described in step 2 to pyrrole is (0.2g~0.5g):(0.6mL~1mL); the volume ratio of the mass of the reduced graphene oxide described in step 2 to the FeCl3 solution is (0.2g~0.5g):(15mL~25mL).

5. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The concentration of the FeCl3 solution in step 2 is 1 mol / L; the stirring time in step 2 is 20 min to 40 min; the ultrasonic treatment time in step 2 is 5 min to 10 min; the concentration of the hydrochloric acid in step 2 is 1 mol / L.

6. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The volume ratio of the PPy / rGO conductive polymer described in step 3 to anhydrous methanol is 0.2 g: (80 mL to 100 mL); the volume ratio of the PPy / rGO conductive polymer described in step 3 to ethylene glycol dimethacrylate is 0.2 g: (0.1 mL to 0.15 mL); in step 3, the reaction is stirred at 60°C to 70°C for 6h to 8h, and the stirring speed is 30 to 50 r·min -1 ; The ultrasonic time described in step three is 5min to 10min.

7. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The volume ratio of methacrylic acid to methanol in step 4 ① is 0.1:90; the volume ratio of lithium chloride to methanol in step 4 ① is 0.1 g:90 mL; the volume ratio of benzo-12-crown 4-ether to methanol in step 4 ① is 0.05:

90.

8. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The heating and stirring in step 4① is carried out at 40℃ and a stirring speed of 30r·min -1 ~60r·min -1 Stir for 20 min to 40 min under the conditions; the stirring time in step 4 ① at room temperature is 20 min to 30 min.

9. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that The volume ratio of ethylene glycol dimethacrylate described in step 4 ② to methanol described in step 4 ① is 0.1:90; the volume ratio of azobisisobutyronitrile described in step 4 ② to methanol described in step 4 ① is 0.02g:90mL.

10. The method for preparing a PPy-coated rGO directly loaded electrically controlled lithium ion imprinted membrane according to claim 1, characterized in that In step 4②, the membrane is refluxed under nitrogen atmosphere at 75°C for 24 hours or refluxed at 65°C for 20 hours. After the membrane is taken out, it is rinsed with deionized water 3 to 5 times, and then pickled with hydrochloric acid 1 to 2 times, each pickling time is 12 to 16 hours; the concentration of the hydrochloric acid is 1 mol / L.

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