CN108499370A - A kind of preparation method of ion blotting blend film - Google Patents

Abstract

The present invention relates to a kind of preparation methods of ion blotting blend film, include the following steps：(1) synthesis of Macromolecular chain transfer agent：It is synthesized in scheduled ratio in thermal initiator using methyl methacrylate and RAFT reagents；(2) synthesis of amphipathic block functional polymer：The Macromolecular chain transfer agent synthesis that will be synthesized in 4 vinylpyridines, thermal initiator and step (1)；(3) synthesis of template ion polymer complex；(4) casting film：By in step (3) template ion polymer complex and film matrix in scheduled ratio dissolve in a solvent stirring the predetermined time to be uniformly mixed obtain casting solution, by casting solution remove bubble after casting film；(5) it elutes.Present invention hydrophilic block in film forming procedure can move quickly into the surface of film, will not be embedded by PVDF because of template ion too deep without easily eluting, and generate more binding sites on the surface of film, increase ion blotting blend film adsorptive selectivity and adsorption capacity.

Description

A kind of preparation method of ion imprinted blend film

technical field

The invention belongs to the technical field of ion imprinting, and in particular relates to a preparation method of an ion imprinting blend membrane.

Background technique

Molecular (ion) imprinted membrane refers to a type of membrane that contains or is composed of molecularly imprinted polymers. The purpose of molecular recognition is achieved through the memory recognition performance of polymers on template molecules. Its molecular space recognition ability is strong and high-selectivity separation can be achieved. The basic idea is to add imprinted molecules into the polymerization medium, remove the imprinted molecules after film formation, and leave holes matching the size of the imprinted molecules in the network structure of the imprinted polymer layer, and the gap between the imprinted film and the imprinted molecules When it is used to separate the mixture composed of imprinted molecules and other substances, the imprinted membrane can recognize the imprinted molecules, thereby effectively separating the target from the mixture.

At present, the molecular imprinted blend membrane produced by combining molecular imprinting technology and membrane preparation technology is one of the most attractive researches. In the prior art, the molecular imprinting process generally needs to be cross-linked with a cross-linking agent to form a molecular size that is consistent with the size of the imprinted molecule. Matching cavities in turn recognize the target imprinted molecule. Moreover, the prepared imprinted blend membrane usually has the phenomenon that template molecules (ions) are embedded too deeply by the membrane matrix and are not easy to elute, which will greatly reduce the adsorption capacity and adsorption rate of the imprinted blend membrane.

In summary, there is an urgent need to provide a preparation method for ion-imprinted blend membranes with stable structure and performance, not easy to peel off, high adsorption capacity and fast adsorption rate.

Contents of the invention

The purpose of the present invention is to provide a preparation method of an ion imprinted blend membrane with stable structure and performance, not easy to peel off, high adsorption capacity and fast adsorption rate.

The above-mentioned purpose is achieved through the following technical scheme: a preparation method of an ion-imprinted blend membrane, comprising the following steps:

(1) Synthesis of macromolecular chain transfer agent: add methyl methacrylate, RAFT reagent and thermal initiator into the reactor according to a predetermined ratio, add the solvent and seal it under a protective gas for reaction, and precipitate after the reaction is completed Filter, and dry the obtained solid product to constant weight;

(2) Synthesis of amphiphilic block functional polymers: add the macromolecular chain transfer agent synthesized in 4-vinylpyridine, thermal initiator and step (1) to the reactor in a predetermined ratio, after adding the solvent Sealing for reaction, after the reaction is completed, precipitate and filter, and dry the obtained solid product to constant weight;

(3) Synthesis of template ion-polymer complex: the amphiphilic block functional polymer synthesized in step (2) is dispersed in the container that template ion aqueous solution is housed, seals reaction, and then it is filtered after reaction is sufficient , washed with deionized water and freeze-dried;

(4) Membrane casting: Dissolve the template ion-polymer complex and the membrane matrix in the step (3) in a predetermined ratio in a solvent and stir for a predetermined time until mixed uniformly to obtain a casting solution, and leave the casting solution for a predetermined time Remove the air bubbles, then pour the casting solution into the film forming plate, and spread the casting solution into a uniform film, quickly immerse the film in a deionized water bath at a predetermined temperature for film solidification, and wash the film to remove residual solvent ;

(5) Elution: using an eluent to wash the membrane prepared in step (4) to elute template ions to obtain the ion-imprinted blend membrane.

The amphiphilic block functional polymer prepared by the present invention includes A block and B block, wherein the A block is a hydrophobic segment, and has good compatibility with the membrane matrix and a polymer containing unsaturated bonds , used to entangle and fix with the membrane matrix material; the B block is a hydrophilic segment, a hydrophilic polymer with the ability to combine with metal ions and contain unsaturated bonds. In the present invention, the monomer of the A block is methyl methacrylate (MMA), and the monomer of the B block is 4-vinylpyridine (4VP).

In the preparation process, first use MMA and RAFT reagents to polymerize, and then use the obtained macromolecular chain transfer agent PMMA-RAFT as a macromolecular chain transfer agent to polymerize with 4VP, and finally obtain an amphiphilic block copolymer polymethyl methacrylate -Poly(4-vinylpyridine) is abbreviated as PMMA-b-P4VP, using PMMA-b-P4VP functional polymer to combine with template ions to form a metal-organic complex, and then using a solvent, such as dimethylacetamide (DMAc) for the The compound was blended with polyvinylidene fluoride (PVDF), and finally ion-imprinted blend membrane was prepared by non-solvent-induced phase separation (NIPS) with ionized water as coagulation bath.

During the curing process of the membrane matrix, the amphiphilic block functional polymer migrates to the surface of the membrane (also known as surface segregation), so that the metal template moves to the surface of the membrane, and after elution, a 3D complementary metal template is formed on the surface of the cured membrane. hole. During the film formation process, the hydrophilic block of the functional polymer can quickly move to the surface of the membrane through surface segregation, and will not be easily eluted because the template ions are embedded too deeply by PVDF. At the same time, there are more on the surface of the membrane. The hydrophilic block can generate more binding sites, which can quickly combine the target ions with the binding sites on the membrane surface, and finally lead to the increase of the selective adsorption capacity of the ion imprinted blend membrane. The performance is enhanced, the adsorption speed is fast, and the service life enhanced. Thirdly, with the membrane structure formed in this way, the hydrophobic chains in the functional polymer can fully and tightly intertwine with the membrane matrix, making it difficult to fall off from the surface of the imprinted membrane. Ion-imprinted blend membranes get rid of the limitation of using cross-linking agents in the traditional imprinting process. In addition, the synthesis of amphiphilic block functional polymers can control the length of the B block by controlling the reaction time, and improve the adsorption capacity of ion-imprinted blend membranes and Adsorption rate.

As a preference, the further technical scheme is: in the step (1) and step (2), the RAFT reagent, the thermal initiator and the solvent are respectively trithioester, azobisisobutyronitrile and N,N-diisobutyronitrile Methylformamide.

A further technical solution is: the film substrate and the solvent in the step (4) are respectively polyvinylidene fluoride and N,N-dimethylacetamide.

Polyvinylidene fluoride (PVDF) is a semi-crystalline strong hydrophobic polymer, which can quickly solidify in water and has a good film-forming effect. At the same time, PVDF and PMMA can be well entangled and fixed, and the ion-imprinted blend film structure Stable, imprinted material is not easy to fall off.

Further, the template ion is Pt(IV), and the template ion solution is a chloroplatinic acid solution.

A further technical solution is: the eluent in the step (5) is a mixed solution of thiourea and hydrochloric acid. Experiments have proved that the mixed solution of thiourea and hydrochloric acid with appropriate concentration has a good effect on the elution of template Pt(IV) ions.

A further technical solution is: before use of the methyl methacrylate, the polymerization inhibitor is removed through a flash chromatography column filled with basic alumina, and sealed and stored at 2°C in the dark; the azobisiso Nitrile was recrystallized three times in absolute ethanol before use, sealed and stored at 2°C and protected from light; the polyvinylidene fluoride was vacuum-dried at 90°C for 24 hours to remove water before use.

The further technical scheme is: the specific process in the step (1) is: 15.0g methyl methacrylate, 0.1g trithioester reagent and 0.2g azobisisobutyronitrile are dissolved in 36.9mL N,N-dimethyl In base formamide, add the above mixed solution into the reactor, then seal, degas and fill the reactor with nitrogen, put it in a preheated oil bath at 70°C and keep stirring continuously for 6 hours, cool down after the reaction is completed After reaching room temperature, the reacted mixture was diluted with tetrahydrofuran and precipitated three times in excess low-temperature methanol. Finally, the obtained macromolecular chain transfer agent was vacuum-dried at 40° C. for 24 hours.

The further technical scheme is: the specific process in the step (2) is: get the macromolecular chain transfer agent synthesized in the 2.0g step (1), and dissolve 3.0g 4-vinylpyridine and 1mg azobisisobutyronitrile in 12.3mL of dimethylformamide; add the above mixed solution into the reactor, then seal, degas and fill the reactor with nitrogen, in a preheated oil bath at 70°C and keep stirring continuously for 6 hours, After the reaction was completed, it was cooled to room temperature, and the reacted mixture was diluted with dichloromethane, and precipitated three times in excess low-temperature methanol; finally, the obtained amphiphilic block-functional polymer was vacuum-dried at 40° C. for 24 hours.

The further technical scheme is: the specific process in the step (3) is: take 4.00 g of the amphiphilic block functional polymer and disperse it in 100 mL of a solution containing 50 mg of template platinum (IV) ions, pH=0.5±0.1, It was then sealed and kept under constant stirring at 25 °C for 24 h, after which the resulting mixture was filtered, washed with deionized water and lyophilized.

The further technical scheme is: the specific process in the step (4) and step (5) is: dissolving the template ion-polymer complex prepared in the step (3) with polyvinylidene fluoride in a ratio of 3:10 Dissolve in N,N-dimethylacetamide, and prepare the casting solution by mechanical stirring at 60°C for 8 hours. The template ion-polymer complex and polyvinylidene fluoride account for 15% of the weight of the casting solution. %, the casting solution was allowed to stand for at least 3 hours to completely release the air bubbles, and then the obtained casting solution was poured on a clean glass plate and spread into a uniform film at room temperature using a spatula fixed to a gap of 250 μm. The film is then rapidly immersed in a deionized water bath at 25°C for film coagulation, followed by rinsing the formed film to remove residual solvent; the elution of the template ions is carried out by rinsing the film with a 1mol/L HCl solution containing 1% by weight of thiourea, And obtain Pt (Ⅳ) ion imprinted blend membrane.

The further technical scheme is: the synthesis process route of the trithioester is as follows: mix n-dodecyl mercaptan, acetone and methyl trioctyl ammonium chloride in a mixing container, cool and slowly drop them under the protection of nitrogen Predetermined amount of NaOH solution, continue stirring for a predetermined time, then add acetone solution dissolved in CS ₂ , the solution turns red and then stand for a predetermined time, add a predetermined amount of CHCl ₃ , then add a predetermined amount of NaOH solution, and react for a predetermined time, Add a predetermined amount of concentrated hydrochloric acid in water; inflate to remove excess acetone, filter with suction, collect the solid, add isopropanol to filter out the insoluble solid, spin the isopropanol solution, and recrystallize the obtained solid in n-hexane several times to obtain Yellow solid trithioester.

Further technical scheme is: the synthetic specific technique of trithioester is: with RSH (n-dodecanethiol) (48mL, 40.38g, 0.2mol), acetone (160mL) and methyl trioctyl ammonium chloride (phase transfer agent) (3.6mL, 3.2g, 0.008mol) was mixed into a 1L three-necked flask, cooled to 10°C and protected with nitrogen. After slowly adding 50% NaOH solution (16.7g, over 20min) dropwise, continue to stir for 15min, then add a solution of acetone (25mL, 20g, 0.3mol) dissolved with CS2 (12mL, 15.2g, 0.2mol) over a period of over 20min. 20min, after the solution turned red for 10min, CHCl3 (24mL, 35.6g, 0.3mol) was added once, and then 80g of 50% NaOH solution was added, and the reaction time was more than 30min. After one day of reaction, 300mL of water and 50mL of concentrated hydrochloric acid were added. (The sequence of water and hydrochloric acid does not matter, it does not affect) (It is better to add hydrochloric acid first) Post-treatment: Inflate (4-6h) to remove excess acetone, filter with suction, collect solids, add 500mL isopropanol to filter out insoluble solids, spin The isopropanol solution was dried, and the obtained solid was recrystallized in n-hexane (80-100 mL) several times to obtain a yellow solid. (Concentrated recrystallization after the filtrate is collected) (the color of the product should match, if not, continue recrystallization).

The present invention selects suitable functional monomers according to different target ions, and adopts the reversible addition-fragmentation chain transfer polymerization (RAFT) method to synthesize amphiphilic block copolymers, wherein the hydrophobic segment will effectively interact with the film-forming matrix. The molecular chains are entangled and can be effectively anchored in the membrane matrix after film formation, while the hydrophilic chain segments are enriched on the surface of the membrane due to surface segregation, and finally form a complex with hydrophilic and ion recognition and binding capabilities. Multifunctional membrane surface.

The ion imprinted membrane prepared by the present invention does not require additional cross-linking steps. After the membrane is cured and formed, metal ions are directly fixed on the membrane material, and effective recognition sites can be generated after elution. Compared with the complex cross-linking process required in the preparation of traditional ion imprinted materials, this method has certain convenience.

Experiments have proved that the ion imprinted membrane prepared by the present invention can show higher affinity to target ions, not only has a large saturated adsorption capacity, but also has a fast adsorption rate, and has high reusability at the same time, and after five cycles, only about 5% loss of initial adsorption capacity.

Description of drawings

The drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Fig. 1 is the proton nuclear magnetic resonance spectrum figure of PMMA prepared by the present invention and multiple PMMA-b-P4VP;

Fig. 2 is the infrared spectrogram of PMMA prepared by the present invention and multiple PMMA-b-P4VP;

Fig. 3 is the SEM picture of the multiple molds prepared by the present invention;

Fig. 4 is the ATR-FTIR spectrogram of the multiple mode that the present invention prepares;

Fig. 5 is the static contact angle data figure of the film of the various molds prepared by the present invention;

Fig. 6 is the dynamic contact angle data figure of the film of the various molds prepared by the present invention;

Fig. 7 is the pure water flux data figure of the film of the various molds prepared by the present invention;

Figure 8 is a graph showing the pH effect of the ion imprinted blend membrane prepared in one embodiment of the present invention;

Figure 9 is a schematic diagram of the selective adsorption results of the ion imprinted blend membrane prepared in one embodiment of the present invention;

Figure 10 is a schematic diagram of the dynamic separation curve results of the ion imprinted blend membrane prepared in one embodiment of the present invention;

Fig. 11 is a graph showing the adsorption research results of ion-imprinted blend membranes prepared in an embodiment of the present invention in a filtration circulation system;

Fig. 12 is a process route diagram for preparing an amphiphilic block functional polymer according to an embodiment of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings. The description in this part is only exemplary and explanatory, and should not have any limiting effect on the protection scope of the present invention. In addition, those skilled in the art can make corresponding combinations of features in the embodiments in this document and in different embodiments according to the descriptions in this document.

Experimental material

The main raw materials are shown in Table 1

Table 1 The list of main reagents in the experiment

Example

Methyl methacrylate was removed from the polymerization inhibitor through a flash chromatography column filled with basic alumina before use, and sealed and stored at 2°C in the dark; azobisisobutyronitrile was reconstituted in absolute ethanol before use. Crystallized three times, sealed and stored at 2°C, protected from light; polyvinylidene fluoride was vacuum-dried at 90°C for 24 hours to remove water before use.

Synthesis of trithioesters: RSH (n-dodecanethiol) (48mL, 40.38g, 0.2mol), acetone (160mL) and methyl trioctyl ammonium chloride (phase transfer agent) (3.6mL, 3.2g, 0.008mol) into a 1L three-necked flask, cooled to 10°C and protected with nitrogen. After slowly adding 50% NaOH solution (16.7g, over 20min) dropwise, continue to stir for 15min, then add a solution of acetone (25mL, 20g, 0.3mol) dissolved with CS2 (12mL, 15.2g, 0.2mol) over a period of over 20min. 20min, after the solution turned red for 10min, CHCl3 (24mL, 35.6g, 0.3mol) was added once, and then 80g of 50% NaOH solution was added, and the reaction time was more than 30min. After one day of reaction, 300mL of water and 50mL of concentrated hydrochloric acid were added. (The sequence of water and hydrochloric acid does not matter, it does not affect) (It is better to add hydrochloric acid first) Post-treatment: Inflate (4-6h) to remove excess acetone, filter with suction, collect solids, add 500mL isopropanol to filter out insoluble solids, spin The isopropanol solution was dried, and the obtained solid was recrystallized in n-hexane (80-100 mL) several times to obtain a yellow solid. (Concentrated recrystallization after the filtrate is collected) (the color of the product should match, if not, continue recrystallization).

1. Preparation of Pt(IV) ion imprinted blend membrane

(1) Synthesis of macromolecular chain transfer agent: 15.0g methyl methacrylate, 0.1g trithioester reagent and 0.2g azobisisobutyronitrile were dissolved in 36.9mL N,N-dimethylformamide, and the above The mixed solution was added to the reactor, then sealed, degassed and filled with nitrogen in the reactor, placed in a preheated oil bath at 70°C and kept stirring continuously for 6 hours, cooled to room temperature after the reaction was completed, and the reacted The mixture was diluted with tetrahydrofuran and precipitated three times in excess low-temperature methanol. Finally, the obtained macromolecular chain transfer agent was vacuum-dried at 40°C for 24 hours; the product was designated as PMMA-RAFT.

(2) Synthesis of amphiphilic block functional polymer: take 2.0g of the macromolecular chain transfer agent synthesized in step (1), and dissolve 3.0g of 4-vinylpyridine and 1mg of azobisisobutyronitrile in 12.3mL of dimethyl In base formamide; add the above mixed solution into the reactor, then seal, degas and fill the reactor with nitrogen, put it in a preheated oil bath at 70°C and keep stirring continuously for 6 hours, cool down after the reaction is completed to room temperature, the reacted mixture was diluted with dichloromethane, and precipitated three times in excess low-temperature methanol; finally, the obtained amphiphilic block functional polymer was vacuum-dried at 40°C for 24 hours; the product was marked as PMMA -b-P4VP.

(3) Synthesis of template ion-polymer complexes: get 4.00 g of amphiphilic block functional polymers and disperse them in 100 mL of a solution containing 50 mg of template platinum (IV) ions, pH = 0.5 ± 0.1, then seal and dry at 25 was kept under constant stirring for 24 hours at °C, then the resulting mixture was filtered, washed with deionized water and lyophilized;

(4) Film casting: Dissolve the template ion-polymer complex and polyvinylidene fluoride prepared in step (3) in N,N-dimethylacetamide at a ratio of 3:10, and The casting solution was prepared by mechanical stirring for 8 hours, and the template ion-polymer complex and polyvinylidene fluoride accounted for 15% of the weight of the casting solution, and the casting solution was left to stand for at least 3 hours to completely release the bubbles, and then the The obtained casting solution was poured on a clean glass plate, and spread into a uniform film at room temperature using a scraper fixed to a gap of 250 μm; then the film was quickly immersed in a deionized water bath at 25°C for film solidification, and then rinsed to form film to remove residual solvent.

(5) Elution: the template ions were eluted by washing the membrane with a 1 mol/L HCl solution containing 1% by weight thiourea, and a Pt(IV) ion-imprinted blend membrane was obtained. It is denoted as Pt(IV)-IIM.

2. Preparation of non-imprinted blend membrane

Non-imprinted blend membranes were prepared in the same manner as above, except that no template ions were added.

3. Structure and performance characterization of amphiphilic block functional polymer PMMA-b-P4VP

(1) Proton Nuclear Magnetic Resonance Spectrum ( ¹ H NMR)

The H NMR spectra of PMMA and three kinds of amphiphilic block functional polymers PMMA-b-P4VP are shown in Figure 1, where PP1, PP2 and PP3 are the amphiphilic blocks of three B block lengths respectively Functional polymer (block length PP1<PP2<PP3). The chemical shift at 3.60 ppm can be assigned to methoxy-CO- _CH3 (MMA peak at a). In addition, the chemical shift at 1.25 ppm is related to the RAFT terminal hydroxyl group. As shown in the ¹ HNMR spectra of the three PMMA-b-P4VP copolymers, the most notable change in the spectra is the appearance of new chemical shifts at both 8.33 ppm and 6.38 ppm, which are both assigned to the CH groups of the pyridine rings (4VP peak at cd). Other chemical shifts are also marked on the ¹ H NMR spectrum. It can be seen from the figure that the chemical shift areas of 8.33ppm and 6.38ppm also increase with the increase of polymerization time (from 2h to 10h). These results indicated that the PMMA-b-P4VP copolymers had the same composition and that the length of the hydrophilic chain P4VP was different in different PMMA-b-P4VP amphiphilic block copolymers.

(2) Infrared spectroscopy (FTIR)

The infrared spectra of PMMA and three amphiphilic block functional polymers PMMA-b-P4VP are shown in Figure 2, and the main absorption peaks are marked in the figure. The peak at 1730cm ^-1 is attributed to the stretching vibration of the carbonyl group (C=O group exists in the PMMA segment). Compared with the PMMA spectrum, the polymer structure changed significantly after RAFT polymerization of 4VP and PMMA. As shown in the figure, there are two new absorption bands at 1599cm ^-1 and 1556cm ^-1 , corresponding to the C=N and CC stretching vibrations on the aromatic pyridine ring in the P4VP chain segment, respectively. This demonstrates the successful synthesis of the block-functional polymer PMMA-b-P4VP after RAFT polymerization of 4VP and PMMA. With the increase of reaction time, the ratio of peak intensity of B block to that of A block increases. This also indicated that PMMA-b-P4VP block functional polymers with different B block lengths were synthesized.

The results of ¹ H NMR and FTIR proved that the synthesized amphiphilic functional polymer was the desired product. In addition, because of the entanglement between PMMA and PVDF molecular chains, when the amphiphilic functional polymer has a high molecular weight hydrophobic PMMA segment, it can not only ensure that the amphiphilic functional polymer is firmly anchored in the membrane matrix At the same time, it can also ensure that the loss of the hydrophilic P4VP segment is minimized during the membrane making process.

(3) Gel Permeation Chromatography (GPC)

The GPC analysis data of PMMA, PP1, PP2 and PP3 are as shown in table 2, and number average molecular weight (Mn) is listed in table 2, weight average molecular weight (Mw), Z average molecular weight (Mz), peak molecular weight (Mp) and Copolymer dispersion. From the GPC test results, it can be concluded that the number average molecular weights of PP1, PP2 and PP3 are 7.05×10 ⁴ , 7.57×10 ⁴ and 7.86×10 ⁴ g/mol, respectively. The number average molecular weight of PMMA is 6.45×10 ⁴ . It can be seen that the molecular weight of the diblock copolymer is much larger than that of PMMA. These results indicated the successful preparation of PMMA-b-P4VP block functional polymers with different B block molecular weights. In conclusion, the amphiphilic block functional polymer PMMA-b-P4VP was successfully synthesized.

Table 2 GPC analysis data

^a Detection from GPC

3. Structure and performance characterization of Pt(Ⅳ) ion-imprinted blend membrane

The casting solution is composed of PVDF, additives and different kinds of solvents. The additives are PP1-PP3 mentioned above. The mixed composition of solvents such as DMAc, DMF or DMF and THF is listed in Table 3.

Table 3 Casting solution composition

(1) Scanning Electron Microscope (SEM)

In the present invention, eight kinds of membranes from M0 to M7 were prepared, and the morphology of the surface and cross section of the PVDF/PMMA-b-P4VP membrane was analyzed by SEM and shown in FIG. 3 . It can be seen from the figure that the PVDF/PMMA-b-P4VP membranes (M1 to M7) have basically the same structural features as the pure PVDF membrane (M0). It consists of a dense surface and a porous substratum with a finger-like structure. However, the PVDF/PMMA-b-P4VP membranes (M1 to M7) exhibited a larger finger-like porous structure than the pure PVDF membrane (M0). The formation of larger finger-like structures on the porous bottom layer of PVDF/PMMA-b-P4VP membranes (M1 to M7) is due to the presence of the P4VP segment of the amphiphilic copolymer PMMA-b-P4VP in the casting solution, resulting in Instantaneous stratification of the casting solution, resulting in the formation of larger finger-like structures. However, for M1, M2 and M3 analysis, it can be found that the film thickness follows the trend of M1<M2<M3. For this case, it may be because the amphiphilic copolymer PP3 containing the longest P4VP chain in the M3 casting solution, When the film casting solution is immersed in the water coagulation bath, PP3 can move to the surface of the film the fastest (the faster is PP2, the slower is PP1), and then the surface layer of the film can be formed quickly. The film shrinkage is minimal as further solvent outflow from the casting solution is blocked by the skin layer. Therefore, M3 with a thickness of about 125 μm is the thickest of the three. Compared with M3, M4 prepared using DMF as solvent has a smaller thickness. This may be due to the stronger solvent capacity of DMAc for PVDF compared to DMF. In other words, the mutual affinity between PVDF and DMAc was stronger compared with DMF, leading to some entanglement of solvent in the membrane system. But this has not been confirmed. Furthermore, M5 with a thickness of about 29.47 μm is the thinnest among all the films (M0 to M7). This phenomenon may be due to the formation of a porous (pore diameter from 200 to 300 nm) network structure on the membrane surface at the initial stage of membrane formation. During the phase inversion, the solvent bleeds out and the film shrinkage is the highest. Another possible reason may be that THF in the mixed solvent evaporates more, resulting in a thinner film made by phase inversion. Therefore, M5 is the thinnest. A similar phenomenon was also observed by Yang et al. Additionally, the presence of spongy sublayers can be observed between the cortex and the interdigital macrospaces. This can be explained by the local evaporation of THF in the solvent mixture. The polymer concentration increases at the membrane surface, resulting in slower delamination and delayed macrovoid formation. According to the analysis of M3 and M6, when adding a small amount of copolymer, it can be found that the film thickness M6<M3. This result can be explained by thermodynamic factors. When a small amount of copolymer is used as an additive in the casting solution, it can cause instantaneous liquid-liquid delamination, and the total thickness of the film increases with the increase of the copolymer concentration. However, a further increase in the copolymer concentration may retard the phase inversion rate and result in thinner films. Therefore, the film thickness M7<M3.

(2) Porosity of the membrane

Eight kinds of membranes M0-M7 were prepared in the present invention. The porosity of different membranes is shown in Table 4, and the porosity of M1-M3 increases gradually, which can be confirmed from the previous SEM analysis. As the polymerization time increases, the hydrophilic chain P4VP lengthens, and the size of the cross-sectional membrane pores increases after the film is formed, thereby increasing the pore volume and porosity. For M6, M3, and M7, as the ratio of functional polymer to PVDF increased from 20% to 40%, the porosity of the membrane also increased, which was the result of the strengthening of the porogenic effect of the hydrophilic chain P4VP. In addition, because the size of the skin pores of M5 is much larger than that of other membrane skin pores, and according to the principle that the smaller the membrane volume, the greater the porosity, the comprehensive analysis of its porosity is also larger.

Table 4 Porosity analysis data

a The porosity of the membrane matrix was determined by soaking in ethanol.

b Determination of film thickness from SEM images

(3) ATR-FTIR spectrum of the film

The attenuated total reflection infrared spectra of M0～M7 are shown in Figure 4. The film M0 corresponds to the stretching vibration peaks of -CF ₂ and CF at wave numbers 1181 cm ^-1 and 1072 cm ^-1 respectively, and the vibration peaks in the range of 900-800 cm ^-1 belong to Based on the crystallization vibration peak of PVDF; according to the analysis results of the amphiphilic block functional polymer PMMA-b-P4VP above, the corresponding stretching vibration peaks at 1730cm ^-1 , 1599cm ^-1 , and 1556cm ^-1 are respectively assigned to the carbonyl C=O , the C=N and CC stretching vibrations that exist in the aromatic pyridine ring; for the PMMA-b-P4VP/PVDF film as shown in Figure 4 (M1-M7), there are respectively attributed to PMMA-b-P4VP on this spectral line and the characteristic stretching vibration peaks of PVDF. In addition, the peak at 1730cm ^-1 shifted to 1728cm ^-1 after film formation, which is the result of the interaction between PMMA segments and PVDF. The above analysis shows that the amphiphilic functional polymer PMMA-b-P4VP has a good compatibility behavior with PVDF, which is what is needed.

(4) Film surface contact angle

Figure 5 and Figure 6 show the static contact angle and dynamic contact angle of the membrane. As shown in the figure, the static contact angle of the PVDF membrane is 74.5°, reflecting its strong hydrophobicity. After blending with PMMA-b-P4VP, the contact angles of the prepared PMMA-b-P4VP/PVDF blend films decreased, which means that their hydrophilicity was enhanced; During the membrane process, the hydrophilic chain segment can effectively migrate to the surface of the membrane, so the hydrophilicity of the imprinted blend membrane can be enhanced by these effectively enriched hydrophilic groups. For M6, M3, M7, when the ratio of amphiphilic block polymer to PVDF increases from 20% to 40%, the contact angle tends to decrease. The explanation for this phenomenon is that in the NIPS process, the hydrophilic segment P4VP in the amphiphilic block polymer will migrate to the surface of the membrane due to surface segregation, thereby improving the hydrophilicity of the membrane surface. strengthen. In addition, the initial contact angle of M5 is large because the surface of the membrane is very rough, while the dynamic contact angle of M3 shows a rapidly decaying dynamic contact angle, which shows that its membrane pores have strong hydrophilicity. The M0 film still exhibits strong hydrophobicity, so its dynamic contact angle does not experience a large attenuation during the test time. Compared to M0, M1 exhibits enhanced hydrophilicity. During the NIPS process, the hydrophilic segments migrate to the upper surface of the membrane and the surface of the membrane pores, and these enriched P4VP segments increase with the increase of the amphiphilic copolymer content, resulting in the hydrophilicity of the membrane. be further strengthened. On the other hand, the existence of macroporous structure will also cause the dynamic contact angle to decrease sharply in a short time.

(4) Pure water flux

Figure 7 lists the effects of the different membranes mentioned above on the pure water flux. Pure PVDF membrane (M0) did not detect effective pure water flux at an operating pressure of 0.1 MPa due to its strong hydrophobicity. For M1-M3, due to the introduction of amphiphilic block polymers, their pure water flux has been significantly increased. In addition, when the functional polymer synthesis time increased, the PMMA-b-P4VP/PVDF blend membrane The pure water flux increased from 61.77 to 80.44L m ^-2 h ^-1 . This is because the lengthening of the hydrophilic chain P4VP increases the size of the cross-sectional membrane pores, that is, the size of the membrane pores increases and the passage of pure water is strengthened, so it has a larger flux of pure water. When the solvent is DMF+THF, the pure water flux of the PMMA-b-P4VP/PVDF blend membrane is much larger than that of other solvent blend membranes. decreases, the pure water flux increases.

4. Properties of Pt(Ⅳ) ion-imprinted blend membranes

(1) Influence of PH

As shown in Fig. 8, the imprinted blend membrane exhibited high affinity for Pt(IV) ions in the pH range from 0.5 to 3, but the adsorption capacity decreased rapidly as the pH of the solution increased from 3 to 4.5. These results may be attributed to the following reasons: at lower pH, on the one hand, the metal ion platinum exists in the form of [PtCl ₆ ] ^2- under acidic conditions; on the other hand, the ligand groups of the functional polymer It can be protonated in an acidic solution, and then [PtCl ₆ ] ^2- is attracted to the functional polymer through electrostatic interaction and acts on it. When the pH is 3 to 4.5, since the protonation of the ligand groups of the functional polymer is weakened, the electrostatic interaction between the functional polymer and [PtCl ₆ ] ^2- decreases, thereby reducing the adsorption capacity. In addition, when the pH value is higher than 4.5, further adsorption tests are difficult to perform due to the presence of platinum ions in the form of Pt(OH) ₄ precipitates. Therefore, in order to obtain the maximum adsorption capacity of IIM for Pt(IV), the pH of the solution should be adjusted to 0.5.

(2) Selective adsorption

To evaluate the selective separation properties of Pt(IV)-IIM, the competitive adsorption of multiple ions was investigated in a ternary mixture solution containing Pt(IV), Cu(II) and Ni(II). The uptake of Pt(IV)-IIM and NIM to Pt(IV), Cu(II) and Ni(II) are shown in Fig. 9, respectively. It can be seen that Pt(IV)-IIM has high selectivity to Pt(IV), and the presence of Cu(II) and Ni(II) ions in the solution at pH 0.5±0.1 can adsorb Pt(IV) The amount of Pt(IV)-IIM has no significant effect, which indicates that Pt(IV)-IIM can maintain a good adsorption selectivity for platinum ions in the presence of competing ions. This is because of the imprinting effect produced by the imprinting process, which makes Pt(IV)-IIM have specific recognition for platinum ions. Pt(IV)-IIM preferentially recognizes Pt(IV), which demonstrates the successful formation of imprinted holes and the excellent shape memory effect of Pt(IV)-IIM. The K _d value of Pt( _IV ) is significantly larger than that of other metal ions. Therefore, the selectivity coefficients of Pt(IV)-IIM for Pt(IV)/Cu(II) and Pt(IV)/Ni(II) are 13.689 and 23.228, respectively. It is obvious that Pt(IV)-IIM has strong selective adsorption for Pt(IV) in the acidic aqueous solution where the three metal ions coexist.

(3) Pt(IV) separation during membrane filtration

Using 5mg/L Pt(IV) aqueous solution as the raw feed solution, the effective filtration area of the membrane is 38.5cm ² , and the filtration experiment of Pt(IV)-IIM is carried out at a pH of 0.5±0.1, and the breakthrough curve is shown in Figure 10 Show. Since there are many ion-binding sites on the surface and pore walls of the initial membrane, the Pt(IV) ions in the raw feed solution were effectively adsorbed in the first 40 min. As the effective binding sites are occupied, some of the Pt(IV) ions in the feed solution cannot be adsorbed and start to leak. When the available binding sites are fully occupied, the concentration of the permeate solution reaches a maximum value which is the concentration of the feed solution. Thus, a membrane with an area of ^38.5 cm can process 120 mL of feed stock solution up to the breakthrough time (40 min). In addition, the content of P4VP chains in this study was relatively low. In practical applications, the Pt(IV) adsorption capacity can also be enhanced by introducing more P4VP chains into the membrane.

(4) regeneration

To investigate the reusability of Pt(IV)-IIM, five adsorption-elution cycles were repeated with the same Pt(IV)-IIM under optimal conditions. The saturated Pt(IV)-IIM was regenerated with 1mol/L HCl solution containing 1wt% thiourea. The maximum adsorption capacity per cycle is shown in Fig. 11. It can be seen that Pt(IV)-IIM still maintains a high level of adsorption capacity after 5 cycles. The initial adsorption capacity loss is only about 5.1%, indicating that Pt(IV)-IIM is chemically stable and can be used for multiple cycles with effective platinum uptake ensured.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (10)

1. A preparation method for ion imprinted blend membrane, is characterized in that, comprises the steps: (1) Synthesis of macromolecular chain transfer agent: add methyl methacrylate, RAFT reagent and thermal initiator into the reactor according to a predetermined ratio, add the solvent and seal it under a protective gas for reaction, and precipitate after the reaction is completed Filter, and dry the obtained solid product to constant weight; (2) Synthesis of amphiphilic block functional polymers: add the macromolecular chain transfer agent synthesized in 4-vinylpyridine, thermal initiator and step (1) to the reactor in a predetermined ratio, after adding the solvent Sealing for reaction, after the reaction is completed, precipitate and filter, and dry the obtained solid product to constant weight; (3) Synthesis of template ion-polymer complex: the amphiphilic block functional polymer synthesized in step (2) is dispersed in the container that template ion aqueous solution is housed, seals reaction, and then it is filtered after reaction is sufficient , washed with deionized water and freeze-dried; (4) Membrane casting: Dissolve the template ion-polymer complex and the membrane matrix in the step (3) in a predetermined ratio in a solvent and stir for a predetermined time until mixed uniformly to obtain a casting solution, and leave the casting solution for a predetermined time Remove the air bubbles, then pour the casting solution into the film forming plate, and spread the casting solution into a uniform film, quickly immerse the film in a deionized water bath at a predetermined temperature for film solidification, and wash the film to remove residual solvent ; (5) Elution: using an eluent to wash the membrane prepared in step (4) to elute template ions to obtain the ion-imprinted blend membrane. 2. the preparation method of ion imprinted blend membrane according to claim 1 is characterized in that, in described step (1) and step (2), described RAFT reagent, thermal initiator and solvent are respectively trithioester , azobisisobutyronitrile and N,N-dimethylformamide. 3. The preparation method of ion imprinted blend membrane according to claim 2, is characterized in that, the membrane substrate and solvent in described step (4) are respectively polyvinylidene fluoride and N,N-dimethylacetamide . 4. The preparation method of the ion imprinted blend membrane according to claim 3, characterized in that, the eluent in the step (5) is a mixed solution of thiourea and hydrochloric acid. 5. The method for preparing the ion-imprinted blend membrane according to any one of claims 2 to 4, wherein the methyl methacrylate is subjected to flash chromatography filled with basic alumina before use. The polymerization inhibitor was removed from the column, and it was sealed and stored in the dark at 2°C; the azobisisobutyronitrile was recrystallized three times in absolute ethanol before use, and sealed in the dark at 2°C; the polyvinylidene fluoride Vacuum dry at 90°C for 24 h to remove water before use. 6. the preparation method of ion imprinted blend membrane according to claim 5 is characterized in that, the specific process in described step (1) is: with 15.0g methyl methacrylate, 0.1g trithioester reagent and Dissolve 0.2g of azobisisobutyronitrile in 36.9mL of N,N-dimethylformamide, add the above mixed solution into the reactor, then seal, degas and fill the reactor with nitrogen, preheat oil at 70°C bath and kept stirring continuously for 6 hours, cooled to room temperature after the reaction was completed, diluted the reacted mixture with tetrahydrofuran, and precipitated three times in excess low-temperature methanol, and finally, the obtained macromolecular chain transfer agent was heated at 40°C Dry under vacuum for 24 hours. 7. The preparation method of the ion-imprinted blend membrane according to claim 6, characterized in that, the specific process in the step (2) is: get the macromolecular chain transfer agent synthesized in the 2.0g step (1), And 3.0g of 4-vinylpyridine and 1mg of azobisisobutyronitrile were dissolved in 12.3mL of dimethylformamide; the above mixed solution was added to the reactor, then sealed, degassed and filled with nitrogen in the reactor, 70 ℃ in a preheated oil bath and kept stirring continuously for 6 hours. After the reaction was completed, it was cooled to room temperature, and the reacted mixture was diluted with dichloromethane, and precipitated three times in excess low-temperature methanol; finally, the obtained two The hydrophilic block functional polymer was vacuum dried at 40°C for 24 hours. 8. The preparation method of the ion-imprinted blend membrane according to claim 7, characterized in that, the specific process in the step (3) is: take 4.00 g of the amphiphilic block functional polymer and disperse it in 100 mL containing 50 mg Template platinum (IV) ion, pH = 0.5 ± 0.1 solution, then sealed and kept under constant stirring at 25 °C for 24 hours, then the resulting mixture was filtered, washed with deionized water and freeze-dried. 9. The preparation method of ion imprinted blend membrane according to claim 8, is characterized in that, the specific technique in described step (4) and step (5) is: the template ion prepared in step (3)- The polymer complex and polyvinylidene fluoride were dissolved in N,N-dimethylacetamide at a ratio of 3:10, and the casting solution was prepared by mechanical stirring at 60°C for 8 hours. The template ion-high Molecular complexes and polyvinylidene fluoride together account for 15% of the weight of the casting solution. The casting solution is allowed to stand for at least 3 hours to completely release the bubbles. Use a spatula fixed to a gap of 250 μm to form a uniform film; then quickly immerse the film in a deionized water bath at 25°C for film coagulation, and then rinse the formed film to remove residual solvent; /L HCl solution to wash the membrane to elute the template ions, and obtain the Pt(Ⅳ) ion-imprinted blend membrane. 10. the preparation method of ion-imprinted blend membrane according to claim 6 is characterized in that, the synthesis process route of described trithioester is as follows: with n-dodecanethiol, acetone and methyl trioctyl ammonium chloride Mix in a mixing container, cool and slowly add a predetermined amount of NaOH solution dropwise under nitrogen protection, continue to stir for a predetermined time, then add acetone solution dissolved in CS ₂ , let the solution turn red and let it stand for a predetermined time, add a predetermined amount of NaOH solution CHCl ₃ , then add a predetermined amount of NaOH solution, after a predetermined reaction time, add a predetermined amount of concentrated hydrochloric acid in water; inflate to remove excess acetone, filter with suction, collect solids, add isopropanol to filter out insoluble solids, spin dry isopropanol solution, and the obtained solid was recrystallized in n-hexane several times to obtain a yellow solid trithioester.