CN110538584B

CN110538584B - Preparation method of palladium ion imprinted copolymer membrane and application of palladium ion imprinted copolymer membrane

Info

Publication number: CN110538584B
Application number: CN201910684733.4A
Authority: CN
Inventors: 曾坚贤; 马溢昌; 周虎; 刘国清; 蹇建; 袁正求; 刘源
Original assignee: Hunan University of Science and Technology
Current assignee: Hunan University of Science and Technology
Priority date: 2019-07-26
Filing date: 2019-07-26
Publication date: 2021-07-20
Anticipated expiration: 2039-07-26
Also published as: CN110538584A

Abstract

The invention belongs to the field of preparation, and particularly relates to a preparation method of a palladium ion imprinted copolymer membrane and application of the palladium ion imprinted copolymer membrane, wherein the preparation method of the palladium ion imprinted copolymer membrane comprises the following steps: (1) preparation of dihydroxy-terminated polysulfone: carrying out nucleophilic polycondensation reaction on 4, 4-dichlorodiphenyl sulfone and bisphenol A to prepare dihydroxy-terminated polysulfone; (2) synthesizing a macromolecular chain transfer agent; (3) preparing a triblock copolymer; (4) preparing a metal-organic compound; (5) and (4) film forming. The palladium ion imprinted copolymer membrane prepared by the invention has the advantages of large selective adsorption capacity, high adsorption speed, long service life, good membrane separation capacity and extremely high flux, and can greatly improve the separation efficiency of palladium ions. The non-imprinted copolymer membrane prepared by the method has good specific selection on palladium ions under the condition of an acid solution, the specific selection on the palladium ion imprinted copolymer membrane is higher, and palladium (II) can be effectively separated from electroplating rinsing wastewater.

Description

Preparation method of palladium ion imprinted copolymer membrane and application of palladium ion imprinted copolymer membrane

Technical Field

The invention belongs to the technical field of membrane separation, and particularly relates to a preparation method of a palladium ion imprinted copolymer membrane and application of the palladium ion imprinted copolymer membrane.

Background

Palladium ions are an important precious metal element and are basic raw materials with high application value in industry, and the serious environmental pollution is caused by the random discharge. Therefore, it is important to develop a technology for separating and recovering metallic palladium from a waste aqueous solution. In the last decades, many methods for separating metal ions from aqueous solutions have been reported, wherein the membrane separation technology has the characteristics of easy operation, low energy consumption and easy production planning, so that the membrane separation technology has great potential in the application of the future separation field. In recent years, the recycling of valuable articles has received increasing attention from metals, in particular from secondary sources (waste). Many processes include solvent extraction, solid phase extraction or ion exchange, co-precipitation, reverse osmosis, membrane filtration and adsorption, and are widely used to extract or separate metal ion wastewater from waste. Therefore, there is increasing research into how to effectively remove and recover palladium from secondary resources (wastewater). The development direction is also towards the separation and enrichment technology of trace and ultra-trace.

In the prior art, methods for preparing carbon nanosheets by using biomass carbon mainly comprise a plasma enhanced chemical vapor deposition method, an arc discharge method, a template method and the like, and the methods have high equipment requirements and low product yield. In addition, the cost of the material is also a factor to be considered.

Although membrane separation technology has many advantages, it lacks the selective separation ability for a specific metal ion, and ion imprinted membrane combines the membrane separation technology with the ion imprinted technology, thus solving the problem. The ion imprinting blend membrane is prepared by adsorbing target metal ions by using a functional polymer to form a metal-organic complex, preparing the metal-organic complex and a membrane substrate material into a membrane casting solution, forming a membrane by a non-solvent induced phase separation method, and finally eluting template ions while leaving three-dimensional cavities (also called imprinting sites) with the size of the template ions at corresponding sites. Meanwhile, the research on the ion imprinted membrane is reported, and the prepared imprinted membrane has the problems of small adsorption capacity, low membrane flux, poor retention capacity and the like.

In conclusion, a method for preparing a palladium ion imprinted copolymer membrane is continuously developed, and the ion imprinting has the characteristics of increased adsorption capacity, high adsorption speed, long service life, good membrane separation capacity and high membrane flux, and can greatly improve the palladium ion separation efficiency.

Disclosure of Invention

The invention aims to provide a method for preparing a palladium ion imprinted copolymer membrane, and the ion imprinting has the characteristics of increased adsorption capacity, high adsorption speed, long service life, better membrane separation capacity and high membrane flux and can greatly improve the palladium ion separation efficiency.

The above purpose is realized by the following technical scheme: a preparation method of a palladium ion imprinted copolymer membrane comprises the following steps:

(1) preparation of dihydroxy-terminated polysulfone: carrying out nucleophilic polycondensation reaction on 4, 4-dichlorodiphenyl sulfone and bisphenol A to prepare dihydroxy-terminated polysulfone;

(2) synthesis of macromolecular chain transfer agent: adding dihydroxy-terminated polysulfone, trithiocarbonate, 4-dimethylaminopyridine and anhydrous dichloromethane into a reaction vessel, then introducing nitrogen to purge for a predetermined time, dropwise adding dicyclohexylcarbodiimide in dispersed dichloromethane into the reaction vessel to react for a predetermined time, and purifying the reacted mixture to obtain a macromolecular chain transfer agent;

(3) preparation of triblock copolymer: carrying out sealing reaction on azobisisobutyronitrile, 4-vinylpyridine, N-dimethylacetamide and the macromolecular chain transfer agent in the step (2) in a nitrogen atmosphere for a preset time to obtain a product, and finely purifying the product to obtain a triblock copolymer;

(4) preparation of metal-organic complex: fully combining palladium (II) ions with the triblock copolymer in the step (3) to obtain a required metal-organic composite;

(5) film forming: independently preparing a metal-organic compound into a membrane casting solution, or dissolving the metal-organic compound and polysulfone in a predetermined ratio into N, N-dimethylacetamide to prepare the membrane casting solution; and standing the casting solution for a preset time to release bubbles, pouring the casting solution on a forming plate and flatly paving the casting solution to form a uniform film, quickly immersing the film in a deionized water bath for film solidification, and eluting palladium (II) ions after removing the residual solvent to obtain the palladium ion imprinted copolymer film.

The ABA type triblock amphiphilic copolymer P4VP-PSF-P4VP is prepared, in the invention, an A block chain is poly 4-vinylpyridine (4VP), a B block chain is Polysulfone (PSF), hydroxyl terminated polysulfone is firstly synthesized, then RAFT chain transfer agent is connected to two ends of polysulfone by esterification reaction to synthesize macromolecular chain transfer agent, finally, a functional polymer is prepared by a reversible addition fragmentation chain transfer polymerization method, and the functional polymer and the polysulfone are formed into a film by a non-solvent induced phase separation method (NIPS) according to a certain proportion. Then, combining a P4VP-PSF-P4VP functional polymer with template metal ions to form a metal-organic compound, blending the compound and polysulfone by using dimethylacetamide (DMAc) as a solvent, and finally washing the metal ions to obtain the palladium ion imprinted copolymer membrane.

The hydrophilic block of the amphiphilic functional polymer of the palladium ion imprinted copolymer membrane prepared by the invention can rapidly move to the surface of the membrane through surface segregation in the non-solvent induced phase separation process, and a compact surface membrane structure can be formed due to the self-assembly behavior of the block copolymer, thereby being beneficial to metal ion separation. Meanwhile, more hydrophilic blocks are arranged on the surface of the membrane to generate more binding sites, so that target ions can be quickly combined with the binding sites on the surface of the membrane, the selective adsorption capacity of the palladium ion imprinted copolymer membrane is increased, the performance is enhanced, the adsorption speed is high, the service life is prolonged, and good membrane separation capacity can be provided by combining a spongy membrane structure and a compact surface layer structure.

Dissolving 4, 4-dichlorodiphenyl sulfone, bisphenol A and potassium carbonate in a mixed solution of N-methyl-2-pyrrolidone and toluene according to a predetermined ratio in the step (1), reacting the mixed solution in a three-neck round-bottom flask provided with a Dean-Stark device, introducing nitrogen into the three-neck round-bottom flask for a predetermined time before reaction, fully stirring, heating and refluxing at 150-155 ℃ for a predetermined time until water generated by the reaction is removed, and slowly raising the temperature to 175 ℃ to remove the toluene; dissolving the obtained product in tetrahydrofuran, then precipitating into a mixed solution of hydrochloric acid aqueous solution and methanol, filtering, repeating the dissolving, precipitating and filtering at least twice according to the steps, taking a filter cake, cleaning the filter cake with deionized water at 80 ℃, and then drying in vacuum to obtain the dihydroxy-terminated polysulfone.

The further technical scheme is that in the step (1), the molar ratio of 4, 4-dichlorodiphenyl sulfone to bisphenol A to potassium carbonate is 4:4:1, and the volume ratio of the mixed solution of N-methyl-2-pyrrolidone and toluene is 3: 1.

The further technical scheme is that the mixture reacted in the step (2) is filtered to remove 4-dimethylamino pyridine, filtrate is precipitated in methanol after being subjected to rotary evaporation and concentration, the obtained precipitate is dissolved in dichloromethane after being filtered, then the dissolved solution is precipitated in methanol, then the precipitate is filtered, the steps are repeated until the precipitate is cleaned, and finally the purified precipitate is filtered and then is dried in vacuum to obtain the macromolecular chain transfer agent.

The further technical scheme is that in the step (3), a reactor with reactants is vacuumized at 0 ℃, nitrogen is introduced, the reactor is sealed in the nitrogen atmosphere after three times of circulation, polymerization is carried out for a preset time, the prepared polymer is cooled to room temperature and then precipitated in deionized water, the filtered product is dissolved in N, N-dimethylacetamide, then precipitated in deionized water and filtered, the precipitate is filtered, the steps are repeated until the polymer is cleaned, and finally the polymer is cleaned with methanol and then dried in vacuum to obtain the triblock copolymer.

The further technical scheme is that the reaction temperature in the step (3) is 80 ℃, the reaction time is 24 hours, and the mass ratio of the macromolecular chain transfer agent to the azodiisobutyronitrile to the 4-vinylpyridine is 1:5: 2000.

The further technical scheme is that in the step (4), the mass ratio of palladium (II) ions to the triblock copolymer is 1:200, the reaction time is more than 24 hours, the obtained mixture is subjected to suction filtration after the reaction is finished, and the metal-organic compound is obtained after the mixture is washed by deionized water.

The further technical scheme is that in the step (5), the metal-organic compound is independently prepared into a casting solution, and a non-woven fabric is used for supporting during membrane preparation.

The further technical scheme is that the specific steps of the membrane casting solution in the step (5) are as follows: and pouring the casting solution onto a clean glass plate after standing to release bubbles, flatly paving the casting solution into a uniform film at room temperature by using a scraper fixed to a gap of 250 mu M, quickly immersing the film into a deionized water bath at 25 ℃ to perform film solidification, then transferring the film into clean deionized water, standing for 24 hours to remove residual solvent, and eluting palladium (II) ions by using a mixed solution containing 0.5M hydrochloric acid and 0.5M thiourea to obtain the palladium ion imprinted copolymer film.

Preferably, the mass ratio of the metal-organic composite to the polysulfone is 7: 3.

The triblock copolymer has good film forming property, can form a film independently, or can be mixed with polysulfone homopolymer in any proportion, so that the palladium ion imprinted copolymer film has more polymer amount and larger adsorption amount; in addition, the structure of the membrane can be adjusted by adjusting the proportion of the triblock copolymer in the membrane forming process, experiments prove that the palladium ion imprinted copolymer membrane which is integrally in a sponge structure can be obtained under the condition of seventy percent of triblock polymerization and thirty percent of polysulfone adopted, the membrane structure can provide a good interception effect, and meanwhile, the triblock copolymer membranes and polysulfone formed membranes in different proportions have high flux and can effectively improve the separation efficiency; in addition, experiments prove that even the non-ionic imprinted membrane prepared by the method has high adsorption capacity to palladium ions, so the palladium ion imprinted copolymer membrane prepared by the method has high adsorption capacity and high selectivity interception to the palladium ions.

In order to achieve the above object, the present invention further provides an application of the palladium ion imprinted copolymer membrane, wherein the palladium ion imprinted copolymer membrane is prepared by any one of the above preparation methods of the palladium ion imprinted copolymer membrane, and the specific application method is as follows: adjusting the pH value of the palladium-nickel alloy electroplating wastewater to 2.0, and then enriching and recovering palladium (II) ions by using the palladium ion imprinted copolymer membrane through the palladium ion imprinted copolymer membrane.

Experiments prove that the non-imprinted copolymer membrane prepared by the invention has good specificity selection on palladium ions under the condition of acid solution,the specificity of the palladium ion imprinted copolymer membrane is higher; a non-imprinted co-polymer membrane was obtained using seventy percent triblock polymerization and thirty percent polysulfone, and when the filtration time reached 50 minutes, 96.75. + -. 2.71% of the palladium ions were retained and most of the metal cations, such as nickel (II), sodium (I), potassium (I), magnesium (II) and calcium (II), passed through the membrane with negligible retention. However, anions, such as chloride, sulfate and nitrate, have relatively higher rejection rates than cations, with 27.47 ± 1.12% total chloride rejection due to PdCl₄ ^2-(chloropalladate ion) was formed and then trapped by a membrane. And when the palladium ion imprinted copolymer membrane was used, the effective area was 38.5cm²The palladium ion imprinted copolymer membrane can treat about 150mL of rinsing wastewater for 50min, the palladium ion retention rate is 99.53 +/-2.79, and the adsorption capacity of palladium ions is 739.48 +/-20.71 mg/m²The average membrane flux is 46.75 +/-1.42L/m²H. The results show that the membrane has the potential for separating pd (ii) from the actual electroplating rinse wastewater.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a schematic diagram showing the mechanism of P4VP-PSF-P4VP synthesis in an embodiment;

FIG. 2 is a diagram showing the adsorption mechanism of Pd (II) by the P4VP-PSF-P4VP/PSF film in the example;

FIG. 3 is a graph of HO-PSF-OH, CTA-PSF-CTA and P4VP-PSF-P4VP¹A HNMR map;

FIG. 4 is an infrared spectrum of OH-PSF-OH and P4VP-PSF-P4 VP;

FIG. 5 is a thermogravimetric plot of OH-PSF-OH, P4VP-PSF-P4VP, and DDMAT-PSF-DDMAT;

FIG. 6 is a scanning electron microscope image of the upper surface of a triblock polymer non-imprinted blend membrane in different proportions: (a) m0, (b) M1, (c) M2, (d) M3, (e) M4, (f) M5, (g) M6, (h) M7;

FIG. 7 is a scanning electron microscope image of the cross section of the triblock polymer non-imprinted blend membrane in different proportions: (a) m0, (b) M1, (c) M2, (d) M3, (e) M4, (f) M5, (g) M6, (h) M7;

FIG. 8 is a surface topography map of AFM characterized M0-M7;

FIG. 9 is a schematic diagram of the static water contact angle tests of M1-M8;

FIG. 10 is a schematic diagram showing pure water fluxes of M1 to M7;

fig. 11 is a graph showing the adsorption capacities of M1 to M7 for Pd (ii) ions (initial concentration of feed solution was 60mg/L, H ═ 2);

FIG. 12 is a graph showing the results of selective adsorption amount measurement of Pd (II) and Cu (II) on a palladium ion imprinted copolymer membrane (Pd (II) -IIM) in the presence of Ni (II), Cu (II) as interfering ions (initial concentration of each metal ion 60 mg/L; Ru (III) -IIM, NIM mass, 0.05 g; pH 2.0; experiment temperature, 25 ℃).

Detailed Description

The present invention will now be described in detail with reference to the drawings, which are given by way of illustration and explanation only and should not be construed to limit the scope of the present invention in any way. Furthermore, features from embodiments in this document and from different embodiments may be combined accordingly by a person skilled in the art from the description in this document.

The reagents and instruments used in the examples are shown in tables 1 and 2

TABLE 1 Main reagents

TABLE 2 Experimental instruments

Pretreatment of reagents

In order to ensure the smooth operation of the experiment and ensure that the experimental result is not interfered by impurities, the main reagent needs to be purified before the experiment.

Activating the molecular sieve: the molecular sieve is put into a muffle furnace to be heated for 4 hours at 500 ℃, cooled to 100 ℃ along with the furnace, and then respectively added into a round-bottom flask containing DMAc, DMF and dichloromethane, and the molecular sieve absorbs the water in the DMAc, DMF and dichloromethane to purify the DMAc, DMF and dichloromethane.

4, 4-dichlorodiphenyl sulfone (DCDPS): two recrystallizations (DCDPS: TOL ═ 1: 1.1) were performed from hot toluene to remove impurities.

Bisphenol a (bpa): it was recrystallized twice from hot toluene (BPA: TOL ═ 1: 5.3) and dried at 125 ℃ for 24 hours.

Azobisisobutyronitrile (AIBN): recrystallization twice from hot methanol to remove impurities. And (5) putting the mixture into a refrigerator for storage.

4-vinylpyridine (4-VP): and (3) removing the polymerization inhibitor by column chromatography or reduced pressure distillation in alkaline aluminum oxide.

Styrene (St): and (3) removing the polymerization inhibitor by column chromatography or reduced pressure distillation in alkaline aluminum oxide.

Potassium carbonate: drying to remove water for 24 hours.

Synthesis of dihydroxyl-terminated polysulfone (HO-PSF-OH)

DCDPS (43.8mmol), BPA (42.5mmol) and K₂CO₃(13.2mmol) was dissolved in 60ml of a mixed solution of NMP and toluene (v/v. 3/1) in a three-necked round-bottomed flask equipped with a Dean-stark trap. The reaction apparatus was purged with nitrogen for at least 30 minutes, and then sufficiently stirred at room temperature for 2 hours. Subsequently, the reaction mixture was heated under reflux at 152 ℃ for 8 hours, the water produced by the reaction was completely removed by azeotropic distillation with toluene, and the temperature was slowly raised to 175 ℃ to remove toluene. After the reaction was polymerized for 8 hours, it was exposed to air to stop the reaction and cooled to room temperature, precipitated into an aqueous hydrochloric acid/methanol mixed solution, and then filtered. The resulting polymer was dissolved in THF, then precipitated into an aqueous hydrochloric acid/methanol mixed solution, and filtered. Dissolution, precipitation and filtration were repeated three times. After filtration, the polymer was washed with deionized water at 80 ℃ for 4 hours. Finally, the polymer was dried in a vacuum oven at 90 ℃ for 24 hours to give double endsHydroxy polysulfone (HO-PSF-OH).

Synthesis of macromolecular chain transfer agent (DDMAT-PSF-DDMAT)

HO-PSF-OH (10g,0.625mmol), DDMAT (1.92mmol), DMAP (0.18mmol) and dry dichloromethane (75mL) were added to a 150mL round bottom flask equipped with a condenser, magnetic stirrer and gas access. After purging with nitrogen at 0 ℃ for 3 hours, DCC dispersed in a small amount of dichloromethane was added dropwise to the reaction mixture, warmed to room temperature, and stirred for reaction for 72 hours. The reaction mixture was filtered to remove the catalyst DMAP, concentrated by rotary evaporation and precipitated into methanol. The resulting precipitate was filtered, redissolved in dichloromethane and reprecipitated in methanol, and this process was repeated three times. And (3) after filtration, putting the mixture into a vacuum drying oven at 60 ℃ for drying for 24 hours to obtain the macromolecular chain transfer agent (DDMAT-PSF-DDMAT).

Functional polymer (P4VP-PSF-P4VP)

A Schlenk flask equipped with a magnetic stirrer was charged with AIBN (0.02mmol), DDMAT-PSF-DDMAT (0.1mmol), 4-VP (40mmol) and DMAc (10 mL). The schlenk flask was evacuated at 0 ℃, then nitrogen was introduced, and the flask was sealed under nitrogen after three cycles. The resulting mixture was subjected to RAFT polymerization in an oil bath at 80 ℃ for 24 hours. The polymer prepared was cooled to room temperature and precipitated into deionized water. The filtered product was dissolved in DMAc and reprecipitated in deionized water and repeated twice. Finally, the polymer was washed with methanol, and the resulting fine polymer was dried in a vacuum oven at 90 ℃ for 24 hours. Finally obtaining the P4VP-PSF-P4VP triblock product. The molar ratio thereof is [ AIBN ]: [ DDMAT-PSF-DDMAT ]: [4-VP ] ═ 1:5: 2000. Polymers according to the other two ratios ([ AIBN ]: [ DDMAT-PSF-DDMAT ]: [4-VP ] ═ 1:5:500/1000) were also synthesized in the same step. With [ AIBN ]: [ DDMAT-PSF-DDMAT ]: p4VP-PSF-P4VP synthesized at [4-VP ] ═ 1:5:500/1000/2000 were named BCP1, BCP2 and BCP3, respectively, and their synthesis conditions and characteristics are shown in table 3.

TABLE 3 Synthesis conditions and Properties of amphiphilic triblock copolymers

Synthesis of metal-polymer complex (P4VP-PSF-P4VP) -Pd (II)

Placing 100mL of solution with Pd (II) content of 500mg/L and 4g of functional polymer P4VP-PSF-P4VP in a beaker for sealing, placing the beaker in a constant-temperature oscillation water bath kettle at 25 ℃, and carrying out oscillation adsorption for 24 hours to ensure that the metal ions and the functional polymer are fully combined; the mixture was then filtered with suction, the solid polymer was filtered off and unbound Pd (ii) was washed off with deionized water and finally in a vacuum oven at 90 ℃.

Preparation of non-imprinted blend membranes

It will be studied that the adsorption amount obtained was the largest under the conditions of a polymer concentration of 22 wt%, a ratio of polymer synthesis components of 1:5:2000, and a blending ratio of polymer and PSF of 70:30, where the blotting membrane was prepared under the preparation condition of M6. The compositions of the respective films and film forming conditions are shown in table 4.

TABLE 4 composition of film and conditions for film formation

The temperature of the coagulation bath is 25 ℃, the temperature of the film making is 25 ℃, and the relative humidity of the environment is 70%.

Preparation of ion imprinted copolymer membrane of palladium ion

Dissolving the P4VP-PSF-P4VP-Pd (II) complex and polysulfone in a certain ratio (PSF 30%, P4VP-PSF-P4VP 70%) in N, N' -dimethylacetamide (DMAc), filling into a casting bottle (containing a magnetic rotor), and stirring for 24 hours on a constant-temperature magnetic stirrer at room temperature to obtain a clear homogeneous casting solution. The casting solution is left to stand for more than 24 hours to release bubbles. The polymer solution was poured onto a clean, dust-free glass plate and a 250 μm thick film was quickly drawn off with an adjustable applicator. Immediately thereafter, the mixture was placed in a coagulation bath (deionized water) at room temperature. After the film was peeled off the glass plate, it was placed in deionized water with a clean volume. Ensuring the complete phase separation process and removing the residual solvent. The elution process is usually carried out from hydrochloric acid/thiourea(0.5mol L^-1/0.5mol L^-1) The metal ions are removed from the mixed solution. After elution, a palladium ion imprinted membrane is obtained.

The polymer concentration in the casting solution, the ratio of polymer synthesis components, and the blending ratio of polymer and PSF as three important phase inversion parameters can affect the microstructure of the final film and the performance of the film. The polymer concentration was set to 22 wt% in this example.

In another embodiment, the metal-organic composite is separately prepared into a membrane casting solution, and a non-woven fabric is used as a support, and then the membrane is formed by the above method.

Characterization of the Polymer

Nuclear magnetic resonance hydrogen spectrogram analysis

Three portions A, B, C of FIG. 3 show 1HNMR maps of HO-PSF-OH, CTA-PSF-CTA and P4VP-PSF-P4VP, respectively, from which their chemical composition and chemical structure can be determined.

Chemical shifts representing aromatic hydrogens on the PSF backbone appear at δ -6.74-7.85 ppm in fig. 3A, with chemical shifts labeled a, b at 6.75ppm and 7.09ppm, respectively, representing hydrogens on the terminal phenyl ring ortho and meta to the hydroxyl group, respectively. At the same time, at δ of 1.74ppm, i.e., the position marked with h in the figure, the chemical shift corresponding to the aliphatic hydrogen in isopropylidene appears. This indicates that our 4, 4-dichlorodiphenyl sulfone and bisphenol A have been successfully reaction polycondensed.

As can be seen from the spectrum in FIG. 3B, the position marked by a at 3.27ppm is a methylene group (-S-CH)_2-C₁₀H₂₀-) chemical shifts, b is marked with (-S-CH) at 0.86ppm₂-C₁₀H₂₀-CH₃) This demonstrates our success in grafting trithiolates onto hydroxyl terminated polysulfones.

The nuclear magnetic structure diagram of P4VP-PSF-P4VP is depicted in FIG. 3C, which shows the spectra of the macromolecular chain transfer agent (CTA-PSF-CTA) with three more chemical shifts, mainly the chemical shifts of the aromatic hydrogens on the pyridine ring, labeled a, b (8.35ppm and 6.40ppm) and the chemical shifts of the hydrogens on the vinyl chain of P4VP, labeled C, d (1.488ppm), thus demonstrating the successful synthesis of amphiphilic functional polymers.

Infrared spectroscopic analysis

The IR spectra of HO-PSF-OH (a) and P4VP-PSF-P4VP (b) are shown in FIG. 4. In line (a), 3448cm^-1The broad adsorption peak at (A) belongs to terminal hydroxyl, 1295cm^-1,1150cm^-1And 1078cm^-1The stretching vibration peak is derived from the stretching vibration peak of sulfone group (-S ═ O) on the main stem of the block copolymer, 1585 and 1488cm^-1The peak at (a) is due to the aromatic C-C stretch. In line (b), the IR spectrum of P4VP-PSF-P4VP shows some new stretching vibration peaks, e.g. 1735cm^-1The peak at position (A) is derived from C ═ O of the ester group, and the peak at position (C13) is 1413cm^-1、1487cm^-1。1592cm^-1The peak at (a) belongs to the stretching vibration peak of the C ═ N bond on the pyridine ring. These stretching vibration peaks confirmed the successful synthesis of P4VP-PSF-P4 VP.

Thermogravimetric analysis

Thermogravimetric analysis was performed by a thermobalance. From FIG. 5, we can find that the thermogravimetric curves of the dihydroxyl-terminated polysulfone (HO-PSF-OH) and the macromolecular chain transfer agent (CTA-PSF-CTA) are very close, and the weight loss speed is obviously accelerated at 550 ℃. The macromolecule chain transfer agent has slight weight loss phenomenon between 200 ℃ and 350 ℃, which can be attributed to the breakage of carbon-sulfur single bond in trithiocarbonate.

Unlike the two, the functional polymer (P4VP-PSF-P4VP) has a distinct three-step thermal decomposition process. The first small weight loss started at about 180 ℃ corresponding to the cleavage of the 4-VP side chain in P4VP-PSF-P4 VP. The second major weight loss occurred around 400 ℃ due to thermal decomposition of P4 VP. While the third major loss occurs at 500 c, which is consistent with the thermal decomposition temperature of the PSF framework.

Analysis by scanning electron microscope

The morphology of the upper surface and the cross section of the pure polysulfone membranes and the other 7 non-imprinted co-mixed membranes was observed by Scanning Electron Microscopy (SEM). As shown in fig. 6 and 7 as M0, M1, M2, M3, M4, M5, M6, and M7. The blending degree of the 7 membranes is different, and the proportion of the added functional monomer is also different.

From the picture scanned by an electron microscope, under the conditions that deionized water is taken as a coagulating bath and the temperature is 25 ℃, the polysulfone membrane made of pure polysulfone has fewer surface pores and small pore diameter, and only a few macropores are seen from the section, and the part supporting the membrane structure is mainly of a honeycomb structure. This structure is formed because the polysulfone dope solution, when immersed in water, immediately presents a denser skin layer on the surface at a rapid rate. The solvent in the surface layer of the liquid film can only form finger-shaped holes through a very small number of small holes and exchange with non-solvent, and the liquid film in a slightly deeper layer can only form a film according to a delayed phase separation mechanism, namely, non-through honeycomb-shaped holes are formed. Compared with the non-imprinted co-mixed membrane, the hydrophilicity of the non-imprinted co-mixed membrane is remarkably improved due to the addition of the functional monomer 4-VP, when the membrane casting solution is immersed in water, a plurality of holes are rapidly formed on the surface, the solvent and the non-solvent in the liquid membrane are rapidly exchanged, and the instantaneous phase separation is performed to form a macroporous structure.

All films use P4VP-PSF-P4VP as bulk material and PSF as modifier. Various casting solutions consisting of different block copolymers and PSF additives were prepared according to table 3, all films being formed by the NIPS process in deionized water. Fig. 6 and 7 show the top surface and cross-sectional sem images of the film, respectively. As is clear from fig. 6, all the films had a smooth surface, with no cracks and large pores on the film surface. FIG. 7 shows the cross-sectional morphology of the membrane, showing the effect of different compositions of the casting solution on the morphology of the membrane. The cross-sectional structure of the original PSF film (M0) consisted of a top dense skin layer, fingers, and a bottom cellular structure. As can be seen from fig. 7(b-f), the cross-sectional structure of M1-M5 is mainly composed of four parts: a dense skin structure at the top, followed by a finger-like pore structure, a middle macroporous structure, and a thin sponge structure at the bottom. In addition, it can be seen by observing the microstructure of the M1-M5 film that as the content of P4VP-PSF-P4VP increases, the thickness of the skin layer increases and the size of the finger-like pores increases. The reasons for these phenomena are: the cross-section of the membrane is mainly occupied by the finger-like pore structure, indicating that transient delamination is still a major part of the phase separation process. However, the rate of phase separation was reduced for the M1-M5 membrane solutions compared to that of the M0 membrane solutions. The rate of phase separation decreased with increasing percentages of P4VP-PSF-P4VP in the M1-M5 casting solution, indicating that transient delamination shifted to delayed delamination with increasing levels of P4VP-PSF-P4 VP. Thus, a higher concentration of P4VP-PSF-P4VP retards delamination to a greater extent, resulting in a thicker skin layer. The diffusion rate of the coagulation medium and solvent is limited due to the presence of the thicker skin layer, which allows the polymer dilute phase to grow and coalesce for a longer duration, resulting in larger finger-like pores. Thus, the reason for the larger finger-like pores of a typical asymmetric membrane structure with a higher percentage of P4VP-PSF-P4VP is explained.

M1-M5 show typical asymmetric structures, but M6 and M7 (g, h of FIG. 7) show completely different cross-sectional morphologies. This is due to the different film forming behavior, with delayed delamination being a major component of the phase separation process. Due to the preparation conditions of P4VP-PSF-P4VP of M6 and M7 ([ AIBN ]: DDMAT-PSF-DDMAT ]: 4VP ]: 1:5:2000), BCP3 has longer hydrophilic sections, and the thermodynamic stability of the casting solution is enhanced. The hydrophilic segment has good water resistance, allowing the hydrophilic polymer to slowly precipitate in the coagulation bath, resulting in delayed delamination. It is well known that transient phase separation tends to produce a finger-like porous structure, but delayed stratification tends to form a sponge-like structure. M7 has a BCP3 percentage of 50%, and M7 has a cross-sectional structure including a lace structure in the top layer and a macroporous structure in the bottom layer of the film. When BCP3 increased to 70% in M6, the film consisted entirely of a sponge structure. M7 has a lower BCP3 content than M6, resulting in faster phase conversion. Thus, as described above, the thick skin layer of M7 allows for polymer lean phase growth and coalescence.

Atomic force microscopy analysis

The surface morphology of each film was further characterized by atomic force microscopy AFM. The three-dimensional AFM image is shown in FIG. 8, with a scan area of 5. mu. m.times.5. mu.m, and the roughness parameters of all films obtained by AFM analysis software are shown in Table 5. As shown in fig. 8, the original PSF film (M0) had a relatively dense top surface and small pores, whereas the surface of the P4VP-PSF-P4VP/PSF hybrid film (M1-M7) was rougher, including convex and wavy. It can also be seen from these images that as the percentage of P4VP-PSF-P4VP increases, the film surface becomes rough. As the amphiphilic block copolymer content of the casting solution increases, it is expected that more hydrophilic segments of P4VP will self-assemble at the surface of the membrane, thereby promoting higher surface roughness. This explains the reason why the membrane surface is rough, which has a high content of amphiphilic block copolymer. Table 5 summarizes the root mean square roughness (rq) and average roughness (ra) of the films, which further supports the above conclusions.

TABLE 5 root mean square roughness (rq) and average roughness (ra) of the films

Scan area 5 μm × 5 μm

Hydrophilicity of the membrane

The static water contact angle of each film is shown in fig. 9. It can be seen that the static water contact angle of the pure polysulfone membrane is relatively high compared to other membranes, indicating that polysulfone is less hydrophilic. With different BCPs (BCP 1, BCP2 and BCP3, respectively, M1, M3 and M6), when the percentage of P4VP-PSF-P4VP in the casting solution reaches 70%, the hydrostatic contact angle of the membrane between M1, M3 and M6 decreases significantly (M1 ═ 66.50 ± 2.66> M3 ═ 51.13 ± 2.05> M6 ═ 38.87 ± 1.55), and the decrease in M6 is particularly significant. This well illustrates the hydrophilicity of the P4VP segment of the amphiphilic block copolymer (P4VP-PSF-P4VP), which self-assembles on the membrane surface and pore walls during phase inversion, thereby significantly increasing the hydrophilicity of the membrane. The trend of the progressive decrease in the hydrostatic contact angle between M1, M3, and M6 was due to the change in P4VP content in P4VP-PSF-P4VP (see Table 3). Furthermore, as shown in fig. 9, as the percentage of BCP in the casting solution increases, the static water contact angle of the film becomes smaller using the same BCP, i.e., M2> M1 at BCP1, M5> M4> M3 at BCP2, and M7> M6 at BCP 3. At higher BCP percentages, an increase in migration of the hydrophilic P4VP segment to the membrane surface may result due to slower delamination rates, resulting in a decrease in static water contact angle.

Pure water flux of the membrane

The pure water flux for all the prepared membranes is shown in fig. 10, which is one of the important characteristics for measuring the performance of the separation membrane. (Driving force for Water filtration 0.1 MPa; temperature 25 ℃ C.; repeat of each experiment)Three times to reduce errors) the original polysulfone membrane (M0) has a very low water flux at a pressure of 0.1MPa due to its strong hydrophobicity. The addition of the amphiphilic block copolymer P4VP-PSF-P4VP greatly improved the water flux of the mixed membrane (M1-M7). These results are in good agreement with the compositional and structural characteristics of the blended films discussed in the previous section. From the characteristics of the scanning electron microscope, the finger pore structure and the macroporous structure are the main components of the membrane structure. The maximum water flux of M1 was 974.12l/M²H, the porosity is 77.68%, and the film thickness is only 68.23 μm, so the larger the volume porosity, the thinner the film thickness (as shown in Table 1), the smaller the diffusion resistance of water, and the higher the pure water flux. When the BCP percentage of BCP1 increased from 50% to 70%, the pure water flux of the membrane was from 103.16 l/M of M2²H sharply increases to 974.12l/M of M1²H. A similar phenomenon occurs with BCP2, with pure water flow rates from 427.53l/M of M5 (50% BCP2)²H rapidly increased to 972.23l/M of M3 (70% BCP2)²H. This may be due to the following reasons: as the content of amphiphilic block copolymer in the casting solution increases, the hydrophilicity of the membrane increases and more water permeable P4VP micro-domains are formed in the mixed membrane. Further, as the percentage of BCP increases, both the bottom sponge layer and the film thickness become thinner, thereby reducing the diffusion resistance of water. Although the same BCP percentage was 70%, the water flux of M6 (796.13 l/M)²H) is lower than M1 or M3. This phenomenon may be caused by two factors: on the one hand, the trend of hydrophilicity between M1, M3, and M6 gradually increases (see fig. 9), resulting in a possible increase in water flux; on the other hand, as can be seen from fig. 3.8, M6 consists entirely of a dense sponge-like structure, providing greater transmission resistance than a finger-like structure and thus leading to a reduction in water flux. Higher transfer resistance may be a dominant factor compared to hydrophilicity. Therefore, the water flux of M6 was lower. In addition, the pure water flux of M7 was also higher than that of M6. From a cross-sectional scanning electron microscope (see fig. 7), the cross-sectional structure of the M7, including the flower edge structure of the top layer and the large pore structure of the bottom layer of the membrane, significantly improves the water permeability of the M7. In conclusion, the structure of the membrane, the thickness of the membrane and the hydrophilicity have a great influence on the pure water flux of the membrane.

The adsorption capacity of all membrane samples for pd (ii) ions was studied, and the membranes were shaken in pd (ii) solution (60mg/L) at pH 2 for 24 hours to reach adsorption saturation. As can be seen from FIG. 11, all the P4VP-PSF-P4VP/PSF mixed films have good adsorption capacity for palladium (II) ions, while the highest adsorption capacity of M6 can reach 103.1mg/g, and can be chelated with metal ions due to the lone pair of electrons of N atom in the 4-VP structure. In addition, as shown in FIG. 2, PdCl₂Ionised to PCl₄ ^2-The N atom on the pyridine is protonated in the low pH acid solution, causing an electrostatic interaction between them. Therefore, the P4VP-PSF-P4VP/PSF blended film has good adsorption capacity. The adsorption amounts of M1, M3 and M6 were 9.03mg/g, 51.21mg/g and 103.10mg/g, respectively. This phenomenon of adsorption capacity may be attributed to the change in the length of the P4VP segment in the amphiphilic block copolymer P4VP-PSF-P4 VP. As BCP3 has longer P4VP fragment, more binding sites are provided for Pd (II), and the adsorption capacity is improved. With the decrease of the content of the amphiphilic triblock copolymer in the membrane casting solution, the adsorption capacity of the membrane is reduced, the adsorption capacity of M2 is reduced by 7.2 mg/g compared with M1, the adsorption capacity of M5 is reduced by 21.4mg/g compared with M3, and the adsorption capacity of M7 is reduced by 23.7mg/g compared with M6. The results show that the content of the amphiphilic block copolymer P4VP-PSF-P4VP is an important factor influencing the adsorption capacity. In consideration of water flux and palladium (II) ion adsorption performance, M1, M3 and M6 were selected for palladium ion separation studies.

Selective adsorption of Pd (II) by palladium ion imprinted copolymer membrane in multi-component mixed solution

A simulated real aqueous solution environment is adopted, namely, a plurality of anions and cations coexist at the same time, and Ni (II) and Cu (II) are selected as interfering ions. The solution comprised sodium chloride, magnesium chloride, calcium chloride, copper sulfate, nickel nitrate and palladium chloride, and was operated at a pH of 2.0, a temperature of 25 deg.C and an initial concentration of each ion of 60 mg/L. After 10h of adsorption process, the concentration of the residual metal ions is detected to calculate the adsorption quantity. As shown in Table 6, the adsorption amounts of sodium ions, magnesium ions and calcium ions were negligible for both the palladium ion imprinted copolymer membrane (Pd (II) -IIM) and the non-ionic imprinted copolymer membrane (NIM) [48 ]. While the adsorption capacity to copper ions and nickel ions is kept at a very low level. Pd (ii) -IIM exhibited higher selectivity for palladium ions relative to NIM. The above results demonstrate that the Pd (II) -IIM prepared in the present study has potential application in selective separation of palladium ions in real aqueous environment.

TABLE 6 Selective adsorption of Pd (II) in the multicomponent System by blotting and non-blotting membranes (initial concentration of each metal ion 60 mg. multidot.L)^-1(ii) a Pd (II) -IIM, NIM mass, 0.05 g; the pH value is 2.0; experiment temperature, 25 ℃)

Application examples

The washing wastewater comes from a palladium-nickel alloy electroplating plant located in Taoism City of Hunan province of China. The electroplating process mainly comprises degreasing, acid washing, bright nickel electroplating, nickel activation, palladium-nickel alloy electroplating, hard gold washing, electroplating and the like. The main conditions of palladium-nickel alloy electroplating are as follows: pd 13g/L, Ni 10g/L, brightener 6mL/L, temperature 60 ℃, pH4.0, cathode current density 60A/dm². The wastewater used was from a rinse plant after the palladium-nickel alloy plating plant and its pH was adjusted to 2.0 prior to this experiment. The filtration time was controlled at 50 minutes. The concentrations of the respective compositions in the rinse waste water before and after filtration were compared using M6, and the total rejection rate of the respective compositions was calculated, and 96.75 ± 2.71% of palladium ions were retained when the filtration time reached 50 minutes. Most metal cations, such as nickel (II), sodium (I), potassium (I), magnesium (II) and calcium (II), pass through the membrane with negligible retention. However, anions, such as chloride, sulfate and nitrate, have relatively higher rejection rates than cations. 27.47. + -. 1.12% total chloride rejection due to PdCl₄ ^2-(chloropalladate ion) was formed and then trapped by a membrane. The results show that M6 can effectively separate palladium (II) from the actual electroplating rinse wastewater. Typically, the discharge of wastewater is about 17 cubic meters per hour from the flushing car of the plant. In view of the production fluctuations we use 20m³Measured in terms of the discharge amount per hourAnd (4) calculating the area of the membrane. According to the above results, the effective area was 38.5cm²The M6 can treat about 150mL of rinsing wastewater for 50min, the palladium ion retention rate is 96.75 +/-2.71 percent, and the adsorption capacity of palladium ions is 718.83 +/-20.13 mg/M²The average membrane flux is 46.75 +/-1.42L/m²H. Thus, a membrane of about 530 square meters area can meet the wastewater treatment requirements with a discharge of 20 cubic meters per hour. If a hollow fiber membrane module of M6 (phi 225X 1757mm, membrane area/each of about 55M) is used²) Only ten modules are needed. After saturation of the adsorption, the palladium can be easily eluted from the filter and further recovered. Thus, the membrane has the potential for separating pd (ii) from the actual electroplating rinse wastewater.

Generally, the discharge of waste water from the flushing car of a plant is about 17 cubic meters per hour, and in view of the fluctuations in production, we use 20m³The membrane area was calculated as the discharge per hour. Through experimental research, the effective area is 38.5cm²The M8 can treat about 150mL of rinsing wastewater for 50min, the palladium ion retention rate is 99.53 +/-2.79, and the adsorption capacity of palladium ions is 739.48 +/-20.71 mg/M²The average membrane flux is 46.75 +/-1.42L/m²H. Thus, a membrane of about 530 square meters area can meet the wastewater treatment requirements with a discharge of 20 cubic meters per hour. If a hollow fiber membrane module of M8 (phi 225X 1757mm, membrane area/each of about 55M) is used²) Only ten modules are needed. After saturation of the adsorption, the palladium can be easily eluted from the filter and further recovered. Therefore, the blotting membrane has the potential for separating pd (ii) from the actual electroplating rinse wastewater.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a palladium ion imprinted copolymer membrane is characterized by comprising the following steps:

(2) synthesis of macromolecular chain transfer agent: adding dihydroxy-terminated polysulfone, trithioester, 4-dimethylaminopyridine and anhydrous dichloromethane into a reaction vessel, then introducing nitrogen to purge for a predetermined time, dropwise adding dicyclohexylcarbodiimide in dispersed dichloromethane into the reaction vessel to react for a predetermined time, and purifying the reacted mixture to obtain a macromolecular chain transfer agent;

2. The method for preparing a palladium ion imprinted copolymer membrane according to claim 1, wherein in the step (1), 4-dichlorodiphenyl sulfone, bisphenol a and potassium carbonate are dissolved in a mixed solution of N-methyl-2-pyrrolidone and toluene according to a predetermined ratio, the mixed solution is reacted in a three-neck round-bottom flask provided with a Dean-Stark device, nitrogen is introduced into the three-neck round-bottom flask for a predetermined time before the reaction, then the reaction is stirred sufficiently, heated and refluxed at 150 to 155 ℃ for a predetermined time until water generated by the reaction is removed, and then the temperature is slowly raised to 175 ℃ to remove toluene; dissolving the obtained product in tetrahydrofuran, then precipitating into a mixed solution of hydrochloric acid aqueous solution and methanol, filtering, repeating the dissolving, precipitating and filtering at least twice according to the steps, taking a filter cake, cleaning the filter cake with deionized water at 80 ℃, and then drying in vacuum to obtain the dihydroxy-terminated polysulfone.

3. The method for preparing the palladium ion imprinted copolymer membrane according to claim 2, wherein the molar ratio of 4, 4-dichlorodiphenyl sulfone to bisphenol a to potassium carbonate in the step (1) is 4:4:1, and the volume ratio of the mixed solution of N-methyl-2-pyrrolidone and toluene is 3: 1.

4. The method for preparing a palladium ion imprinted copolymer membrane according to claim 2, wherein the mixture after the reaction in step (2) is filtered to remove 4-dimethylaminopyridine, the filtrate is concentrated by rotary evaporation and then precipitated in methanol, the obtained precipitate is filtered and then dissolved in dichloromethane, the dissolved solution is precipitated in methanol, the precipitate is filtered, the above steps are repeated until the precipitate is washed, and finally the purified precipitate is filtered and then dried in vacuum to obtain the macromolecular chain transfer agent.

5. The method for preparing a palladium ion imprinted copolymer membrane according to claim 4, wherein in the step (3), the reactor to which the reactant is added is evacuated at 0 ℃, then nitrogen is introduced, the cycle is performed three times, then the reactor is sealed under nitrogen atmosphere, then polymerization is performed for a predetermined time, the prepared polymer is cooled to room temperature and then precipitated in deionized water, the filtered product is dissolved in N, N-dimethylacetamide, then the product is precipitated in deionized water and then filtered, the precipitate is filtered, the above steps are repeated until the polymer is washed, finally the polymer is washed with methanol and then vacuum-dried to obtain the triblock copolymer.

6. The method for preparing a palladium ion imprinted copolymer membrane according to claim 5, wherein the reaction temperature in the step (3) is 80 ℃, the reaction time is 24 hours, and the ratio of the amounts of the macromolecular chain transfer agent, azobisisobutyronitrile, and 4-vinylpyridine is 1:5: 2000.

7. The preparation method of the palladium ion imprinted copolymer membrane according to claim 6, wherein the mass ratio of the palladium (II) ions to the triblock copolymer in the step (4) is 1:200, the reaction time is more than 24 hours, and after the reaction is completed, the obtained mixture is filtered by suction and washed with deionized water to obtain the metal-organic composite.

8. The method for preparing a palladium ion imprinted copolymer membrane according to any one of claims 1 to 7, wherein in the step (5), the metal-organic composite is separately prepared as a membrane casting solution, and a non-woven fabric is used as a support during membrane formation.

9. The method for preparing the palladium ion imprinted copolymer membrane according to any one of claims 1 to 7, wherein the step (5) of casting the membrane with the membrane casting solution comprises the following specific steps: and pouring the casting solution onto a clean glass plate after standing to release bubbles, flatly paving the casting solution into a uniform film at room temperature by using a scraper fixed to a gap of 250 mu M, quickly immersing the film into a deionized water bath at 25 ℃ to perform film solidification, then transferring the film into clean deionized water, standing for 24 hours to remove residual solvent, and eluting palladium (II) ions by using a mixed solution containing 0.5M hydrochloric acid and 0.5M thiourea to obtain the palladium ion imprinted copolymer film.

10. The application of the palladium ion imprinted copolymer membrane is characterized in that the palladium ion imprinted copolymer membrane is prepared by the preparation method of the palladium ion imprinted copolymer membrane as claimed in any one of claims 1 to 9, and the specific application method is as follows: adjusting the pH value of the palladium-nickel alloy electroplating wastewater to 2.0, and then enriching and recovering palladium (II) ions by using the palladium ion imprinted copolymer membrane through the palladium ion imprinted copolymer membrane.