Preparation method and application of conjugated polymer PEDOT: PSS structure regulation membrane

Abstract

The invention discloses a preparation method and application of a conjugated polymer PEDOT: PSS structure regulation membrane, and relates to a preparation method and application of an ultrafiltration membrane. The technical problem that an existing conductive polymer film is low in Pb < 2 + > rejection rate under the acidic condition is solved. The conjugated polymer PEDOT: PSS structure regulation membrane prepared by the invention is applied to interception of divalent lead ions in acidic wastewater. Acid treatment is used in the process of preparing the PEDOT: PSS film, so that PSS components are selectively removed, PEDOT is fiberized, the microstructure is looser, more wrinkled structures are presented on the whole, adsorption of Pb < 2 + > ions is more facilitated, meanwhile, after acid treatment, conjugate pi electrons are highly delocalized on a PEDOT chain which mainly plays a role in adsorption reduction, the electron transmission capacity is enhanced, and the Pb < 2 + > ion absorption efficiency is improved. More Pb < 2 + > is reduced, and finally, permeation of the membrane on water in acid wastewater and adsorption of metal ions are improved.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of an ultrafiltration membrane. Background Art

[0002] With the rapid development of industrialization, the threat of heavy metal ion-containing wastewater to the ecological environment and human health has become increasingly severe. Among them, divalent lead ions Pb 2+ As typical persistent toxic pollutants, they widely exist in the acidic wastewater discharges of industries such as battery manufacturing, electroplating, and mining. Traditional treatment technologies such as chemical precipitation, ion exchange, and activated carbon adsorption generally have problems such as low treatment efficiency, high risk of secondary pollution, and difficulty in adapting to acidic environments during application. Especially under strong acidic conditions with pH < 3, traditional adsorption materials are prone to structural disintegration, resulting in a sharp decline in adsorption capacity.

[0003] In recent years, membrane separation technology has received extensive attention in the field of water treatment due to its advantages such as high efficiency, low energy consumption, and no phase change. Ultrafiltration membranes achieve solute separation through pore size sieving and surface charge effects, but the interception efficiency of heavy metal ions with a hydrated diameter smaller than that of the ultrafiltration membrane is generally lower than 60%. To improve the interception performance, researchers have tried to composite functional materials with the membrane matrix, and conductive polymers have shown special advantages due to their unique charge transport characteristics. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate PEDOT:PSS, as a p-type conjugated polymer, has excellent chemical stability, high conductivity (up to 1000 S / cm), and adjustable surface charge characteristics. The sulfonic acid groups in its molecular chain can coordinate with metal ions. Existing research has shown that the conductivity and mechanical strength of PEDOT:PSS can be significantly improved through acid treatment, which provides the possibility for constructing new functional membrane materials. In the prior art, there are experiments demonstrating the method of using PEDOT:PSS composite membranes to treat copper-containing wastewater, but it does not involve heavy metal removal in acidic environments and does not conduct directional design of the membrane structure. Currently, there is a proposal to coat conductive polymers on the surface of ceramic membranes for heavy metal adsorption, but there are problems such as easy coating shedding and poor long-term stability. In addition, traditional dopants such as dimethyl sulfoxide DMSO can improve the conductivity of PEDOT:PSS, but are prone to decomposition in acidic systems, resulting in the decline of material properties.

[0004] The current technical bottlenecks are mainly reflected in the following three aspects: 1) Conventional ultrafiltration membranes rely on physical interception mechanisms and have low interception efficiency for small-sized ions such as Pb 2+ ; 2) Existing conductive polymer composites are prone to protonation reactions under strong acidic conditions, resulting in the destruction of the conductive network and the inactivation of adsorption sites; 3) Most functionalized membrane materials have problems such as complex preparation processes, rapid flux decline, and poor regeneration performance. It is particularly noteworthy that H + in acidic wastewater will react with Pb 2+Form competitive adsorption, significantly reducing the selectivity of traditional adsorption materials.

[0005] In view of the above problems, there is an urgent need in the art to develop a new type of membrane material with high-efficiency retention performance, excellent chemical stability and reusability. Summary of the Invention

[0006] The present invention aims to solve the technical problem of low rejection rate of existing conductive polymer membranes for Pb 2+ under acidic conditions, and provides a preparation method and application of a conjugated polymer PEDOT:PSS structure-regulated membrane.

[0007] The preparation method of the conjugated polymer PEDOT:PSS structure-regulated membrane of the present invention is carried out according to the following steps:

[0008] 1. Disperse PEDOT:PSS in absolute ethanol, and then mix it with an acid solution to obtain a mixed solution;

[0009] The molar amount of pure acid in the acid solution and the volume ratio of absolute ethanol are (1 mmol to 1.05 mmol): 10 mL;

[0010] The volume ratio of PEDOT:PSS to absolute ethanol is (0.5 to 0.8): 10;

[0011] 2. Spin-drop the mixed solution obtained in step 1 into a suction flask for vacuum filtration, and wash the residual acid with methanol and absolute ethanol in turn, and repeat the washing three times to obtain an acid-modified PEDOT:PSS membrane;

[0012] 3. Dry the modified membrane prepared in step 2 in an oven for 1 min to 2 min, and the drying temperature is 50 °C to 70 °C to obtain a conjugated polymer PEDOT:PSS structure-regulated membrane.

[0013] The conjugated polymer PEDOT:PSS structure-regulated membrane prepared by the present invention is applied to retain divalent lead ions in acidic wastewater. The specific method is: adjust the pH of the acidic wastewater to 2 to 5, and then filter it through the conjugated polymer PEDOT:PSS structure-regulated membrane to separate divalent lead ions.

[0014] The design principle of the present invention: Due to its strong polarity and strong molecular force, acid can break the connection bond between PEDOT and PSS. The acidity promotes the combination of PSS- and H+ to form neutral PSSH, resulting in phase separation of PEDOT and PSS. The PEDOT chain will be untangled from the original entangled state, and the PEDOT chain will change from a coiled benzene-like structure to a linear quinone-like structure, and the π-π stacking is more compact, resulting in enhanced delocalized π electrons, so a large electron cloud density can adsorb more metal ions. Pb in the solution2+ It is mainly adsorbed by the thiophene S on the PEDOT chain. Due to the strong electron transport ability of the PEDOT chain, Pb 2+ is partially reduced to elemental Pb. However, since elemental Pb is extremely easy to oxidize in the air, the oxidized state Pb3O4 of Pb and elemental Pb are mainly observed.

[0015] Based on the unique properties of PEDOT:PSS, the present invention constructs a three-dimensional conductive network through acid doping modification, and utilizes the electron transfer ability of the π-π conjugate skeleton to enhance the chemical adsorption of Pb 2+ Combined with the conductivity of the conductive polymer, metal ions are adsorbed and separated, and at the same time, the sieving effect of the ultrafiltration membrane is used to achieve a dual separation mechanism, which provides an innovative idea for solving the heavy metal pollution of acidic wastewater.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] In the process of preparing the PEDOT:PSS membrane, the present invention uses acid treatment to modify the PEDOT:PSS membrane with acid, so that the PSS component in PEDOT:PSS is selectively removed, and then PEDOT is fibrillated, the microstructure is more porous, and more wrinkled structures are presented as a whole, which is more conducive to the adsorption of Pb 2+ ions, and the change in the morphology structure does not reduce the hydrophilicity of the membrane, but even slightly improves it; at the same time, after acid treatment, the conjugated π electrons are highly delocalized on the PEDOT chain that mainly plays the role of adsorption and reduction, strengthening the electron transport ability, so more Pb 2+ is reduced, which ultimately affects the water permeation of the membrane in acidic wastewater and the adsorption of metal ions.

[0018] The three-dimensional conductive network formed by the PEDOT chains in the membrane of the present invention can undergo strong chemical adsorption with Pb through the π-π conjugate electron transfer mechanism; after acid modification, the benzoic acid structure of PEDOT is converted into a quinone structure, and the quinone structure enhances the adsorption effect of thiophene S on the PEDOT chain. Compared with traditional physical adsorption materials, the saturated adsorption capacity of Pb 2+ is significantly improved, and the ion interception rate can still be maintained at 98.53% in wastewater with pH = 2, breaking through the failure bottleneck of traditional materials in a strong acid environment; acid modification is used, and the membrane conductivity is still stable in the range of 800-1000 S / cm when the pH is less than 3; combined with the dual effects of the pore size sieving of the ultrafiltration membrane and the chemical adsorption of the conductive network, the interception rate of Pb with a concentration of 20 mg / L 2+ is increased to 98.53%, and the water stability of the modified membrane is enhanced. After multiple cycles, more Pb 2+ can still be adsorbed and separated than the unmodified membrane, achieving a technological leap compared with traditional ultrafiltration membranes. 2+ ​Brief Description of the Drawings

[0019] Figure 1 is the process flow chart of the synthesis of the present invention;

[0020] Figure 2 is the data graph of Table 1;

[0021] Figure 3 is the data graph of Table 2;

[0022] Figure 4 is the data graph of Table 3. Detailed Description of the Invention

[0023] Detailed Description of the Invention 1: This embodiment is a preparation method of a conjugated polymer PEDOT:PSS structure regulation film, which is specifically carried out according to the following steps:

[0024] 1. Disperse PEDOT:PSS in absolute ethanol, and then mix it with an acid solution to obtain a mixed solution;

[0025] The molar amount of pure acid in the acid solution and the volume ratio of absolute ethanol are (1 mmol - 1.05 mmol):10 mL;

[0026] The volume ratio of PEDOT:PSS to absolute ethanol is (0.5 - 0.8):10;

[0027] 2. Spin - drip the mixed solution obtained in step 1 into a suction flask for vacuum filtration, and wash the residual acid with methanol and absolute ethanol in turn, repeating the washing three times to obtain an acid - modified PEDOT:PSS film;

[0028] 3. Place the modified film prepared in step 2 in an oven and dry it for 1 min - 2 min, and the drying temperature is 50 °C - 70 °C to obtain a conjugated polymer PEDOT:PSS structure regulation film.

[0029] Detailed Description of the Invention 2: The difference between this embodiment and Detailed Description of the Invention 1 is that: the solute of the acid solution in step 1 is glacial acetic acid, citric acid, phosphoric acid, oxalic acid, nitric acid or sulfuric acid. Others are the same as Detailed Description of the Invention 1.

[0030] Detailed Description of the Invention 3: The difference between this embodiment and Detailed Description of the Invention 1 or 2 is that: the acid solution in step 1 is a sulfuric acid solution with a mass fraction of 98%. Others are the same as Detailed Description of the Invention 1 or 2.

[0031] Detailed Description of the Invention 4: The difference between this embodiment and Detailed Description of the Invention 3 is that: the conductivity of PEDOT:PSS in step 1 is 1000 S / cm. Others are the same as Detailed Description of the Invention 3.

[0032] Embodiment 5: The difference between this embodiment and Embodiment 4 is that the volume ratio of PEDOT:PSS to absolute ethanol in Step 1 is 0.5:10. Others are the same as Embodiment 4.

[0033] Embodiment 6: This embodiment is an application of the conjugated polymer PEDOT:PSS structure regulation membrane in Embodiment 1, specifically applying the conjugated polymer PEDOT:PSS structure regulation membrane to intercept divalent lead ions in acidic wastewater.

[0034] Embodiment 7: The difference between this embodiment and Embodiment 6 is that the specific method of applying the conjugated polymer PEDOT:PSS structure regulation membrane to intercept divalent lead ions in acidic wastewater is: adjusting the pH of the acidic wastewater to 2 - 5, and then filtering through the conjugated polymer PEDOT:PSS structure regulation membrane to separate divalent lead ions. Others are the same as Embodiment 6.

[0035] Embodiment 8: The difference between this embodiment and Embodiment 7 is that the acidic wastewater contains Pb 2+ , and the concentration of Pb 2+ is 5mg / L - 30mg / L. Others are the same as Embodiment 7.

[0036] The present invention is verified by the following experiments:

[0037] Experiment 1: This experiment is a preparation method of a conjugated polymer PEDOT:PSS structure regulation membrane, which is specifically carried out according to the following steps:

[0038] I. Dissolve 0.5 mL of PEDOT:PSS in 10 mL of absolute ethanol, and then mix it with a sulfuric acid solution to obtain a mixed solution;

[0039] The sulfuric acid solution is a sulfuric acid solution with a mass fraction of 98%, and the molar amount of pure sulfuric acid is 1.02 mmol. After conversion, the mass fraction of pure sulfuric acid in the mixed solution is 20%;

[0040] The PEDOT:PSS is purchased from Bayer AG, Germany, and its conductivity is 1000 S / cm;

[0041] II. Spin - drip the mixed solution obtained in Step I into a suction flask for vacuum filtration, slowly add 50 mL of methanol to wash the residual acid, and then add 50 mL of absolute ethanol to continue washing the residual acid after all the methanol has passed through the membrane. Repeat the (methanol + absolute ethanol) washing three times to obtain an acid - modified PEDOT:PSS membrane;

[0042] III. Place the modified membrane prepared in Step 2 in an oven and dry it for 1 min at a drying temperature of 60 °C to obtain a conjugated polymer PEDOT:PSS structure-regulated ultrafiltration membrane, denoted as M-1.

[0043] Experiment 2: The difference between this experiment and Experiment 1 is that the mass fraction of pure sulfuric acid in the blend solution described in Step 1 is 5%. Others are the same as in Experiment 1. The finally obtained ultrafiltration membrane is denoted as M-2.

[0044] Experiment 3: The difference between this experiment and Experiment 1 is that the mass fraction of pure sulfuric acid in the blend solution described in Step 1 is 10%. Others are the same as in Experiment 1. The finally obtained ultrafiltration membrane is denoted as M-3.

[0045] Experiment 4: The difference between this experiment and Experiment 1 is that the mass fraction of pure sulfuric acid in the blend solution described in Step 1 is 15%. Others are the same as in Experiment 1. The finally obtained ultrafiltration membrane is denoted as M-4.

[0046] Experiment 5: The difference between this experiment and Experiment 1 is that the mass fraction of pure sulfuric acid in the blend solution described in Step 1 is 25%. Others are the same as in Experiment 1. The finally obtained ultrafiltration membrane is denoted as M-5.

[0047] Experiment 6: The difference between this experiment and Experiment 1 is that the mass fraction of pure sulfuric acid in the blend solution described in Step 1 is 30%. Others are the same as in Experiment 1. The finally obtained ultrafiltration membrane is denoted as M-6.

[0048] Comparative Example 1: The difference between this experiment and Experiment 1 is that no acid is added in Step 1. Others are the same as in Experiment 1. The finally obtained ultrafiltration membrane is denoted as M-0.

[0049] Application Example 1:

[0050] Respectively fix the ultrafiltration membranes prepared in Experiments 1 to Comparative Example 1 above in an ultrafiltration cup. Add 50 mL of deionized water to the ultrafiltration cup, seal it and connect an air compressor and the ultrafiltration cup. First pre-press the membrane at a pressure of 3 bar. After pre-pressing the membrane, use a stopwatch and a measuring cylinder to measure the volume of the liquid passing through the membrane per unit time, and calculate the water flux according to the following formula:

[0051]

[0052] In the above formula: J is the water flux L / (m 2 ·h·bar), T is the test time (h), V is the volume of the aqueous solution passing through the membrane within time T (L), and A is the effective membrane area (m 2 ).

[0053] According to the above formula, the pure water flux of each ultrafiltration membrane at a pressure of 1 bar can be calculated, and the specific results are shown in Table 1.

[0054] Application Example 2: Preparation of an aqueous Pb 2+ solution, where the concentration of Pb 2+ is 20 mg / L, and the pH is adjusted to 2 with hydrochloric acid; then 25 mL of the above solution is added to an ultrafiltration cup, which is sealed and connected to an air compressor and the ultrafiltration cup. The mixed solution is filtered through the ultrafiltration membranes prepared in Test 1 to Comparative Example 1 under a pressure of 1 bar. The feed liquid and the permeate are taken, filtered through a 0.22 μm filter head, and 1 portion each of the filtered feed liquid and permeate is taken, 1% concentrated nitric acid is added, and the concentration of Pb 2+ in them is detected using a flame atomic absorption spectrophotometer. The rejection rate is an important parameter for evaluating the separation performance of the ultrafiltration membrane.

[0055]

[0056] In the above formula: R is the rejection rate (%), C p is the concentration of ions in the feed liquid (mg / L), and C f is the concentration of ions in the permeate (mg / L).

[0057] According to the above formula, when the concentration of Pb 2+ in the feed liquid is 20 mg / L, the rejection performance of each ultrafiltration membrane for Pb 2+ under a pressure of 1 bar can be calculated. The specific results are shown in Table 1 and Figure 2 .

[0058] Table 1 Ultrafiltration Membrane Performance

[0059]

[0060] As can be seen from Table 1, the addition of acid promotes the rejection performance of the ultrafiltration membrane. The overall effect of adding 20 wt% sulfuric acid (M-1) is the best. The rejection rate of this membrane for Pb 2+ is as high as 98.19%, achieving the maximum rejection of lead elements and being able to fully retain Pb 2+ in the wastewater, and the water flux of this membrane can also reach 72.94%.

[0061] Application Example 3: Conduct simulated actual wastewater multiple-cycle tests for water stability. The wastewater is taken from a lead-acid battery factory in Henan, and the membranes using M-1 and M-0 added are used for comparative tests. First, the membranes are pretreated: the membranes are immersed in pure water for 24 h to remove residual protective agents and air bubbles, then the membranes are installed in the test cell. After sealing the test cell, pure water is introduced, nitrogen is introduced, and it is run at a low pressure of 1 bar for 10 min to check whether the system leaks and to discharge internal air bubbles. First, the initial performance test is carried out, and then the cycle test is carried out. Wastewater (the same as that in Application Example 2) is injected into the test cell, nitrogen is introduced, and it is run at a low pressure of 1 bar for 1 h. Data is recorded every 10 min until it is stable. After completion, the permeate is collected and the determination is made for Pb2+ The rejection rate. After that, the ultrafiltration membrane was chemically cleaned (pickling), and the rejection rate for Pb was re-measured after each cleaning. 2+ The rejection rate, and the pollution-cleaning cycle was repeated 6 times. The specific results are shown in Table 2 and Figure 3 . After 6 actual wastewater cycle tests on the membrane modified with sulfuric acid, the obtained rejection rates were better than those before modification.

[0062] Table 2 Rejection rate test for Pb in 6 simulated actual wastewater cycles 2+

[0063]

[0064] Application Example 4: In order to explore how adding different types of acids in Step 1 affects the separation performance of the membrane, a comparative test was carried out. Another five acids with the same molar amount as in Experiment 1 were added, and their effects on the performance were tested. The five acids were glacial acetic acid, citric acid, phosphoric acid, oxalic acid, and nitric acid. The specific measurement method was the same as in Application Examples 1 and 2, and the specific results are shown in Table 3 below and Figure 4 As shown, sulfuric acid has the strongest polarity among the 6 acids. When the polarity of the acid increases, its degree of self-ionization also increases accordingly, making the conversion degree of the PEDOT chain in PEDOT:PSS from the benzoic acid structure to the quinone structure higher, with more delocalized conjugated π electrons, and thus stronger electron transport ability, further enhancing the adsorption and reduction ability of the PEDOT:PSS@PVDF membrane.

[0065] Table 3 Performance of ultrafiltration membranes with different acids added

[0066]

Claims

1. A method for preparing a conjugated polymer PEDOT:PSS structure-regulating film, characterized in that The preparation method of the conjugated polymer PEDOT:PSS structure-regulated membrane is carried out according to the following steps:

1. Dispersing PEDOT:PSS in anhydrous ethanol and then blending with an acid solution to obtain a blended solution; The volume ratio of the molar amount of pure acid in the acid solution to anhydrous ethanol is (1mmol-1.05mmol):10mL; The volume ratio of PEDOT:PSS to anhydrous ethanol is (0.5-0.8):10; 2. The blended solution obtained in step 1 was dropped into a suction filtration bottle for vacuum filtration, and the residual acid was washed with methanol and anhydrous ethanol in turn, and the washing was repeated three times to obtain an acid-modified PEDOT:PSS membrane; 3. Dry the modified film prepared in step 2 in an oven for 1 min to 2 min at a drying temperature of 50° C. to 70° C. to obtain a conjugated polymer PEDOT:PSS structure-regulated film.

2. The method for preparing a conjugated polymer PEDOT:PSS structure regulating film according to claim 1, characterized in that The solute of the acid solution in step 1 is glacial acetic acid, citric acid, phosphoric acid, oxalic acid, nitric acid or sulfuric acid.

3. The method for preparing a conjugated polymer PEDOT:PSS structure regulating film according to claim 1, characterized in that The acid solution described in step 1 is a sulfuric acid solution with a mass fraction of 98%.

4. The method for preparing a conjugated polymer PEDOT:PSS structure regulating film according to claim 1, characterized in that The conductivity of PEDOT:PSS described in step 1 is 1000 S / cm.

5. The method for preparing a conjugated polymer PEDOT:PSS structure regulating film according to claim 1, characterized in that The volume ratio of PEDOT:PSS to anhydrous ethanol described in step 1 is 0.5:

10.

6. The use of a conjugated polymer PEDOT:PSS structure regulating film as claimed in claim 1, characterized in that Conjugated polymer PEDOT:PSS structure-regulated membrane is used to intercept divalent lead ions in acidic wastewater.

7. The use of a conjugated polymer PEDOT:PSS structure regulating film according to claim 6, characterized in that The specific method of applying the conjugated polymer PEDOT:PSS structure regulating membrane to intercept divalent lead ions in acidic wastewater is: adjusting the pH of the acidic wastewater to 2-5, and then filtering through the conjugated polymer PEDOT:PSS structure regulating membrane to separate the divalent lead ions.

8. The use of a conjugated polymer PEDOT:PSS structure regulating film according to claim 6, characterized in that The acidic wastewater contains Pb 2+ , and Pb 2+ The concentration is 5mg / L~30mg / L.

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