Hydrogel film as well as preparation method and application thereof
By doping porous hydrogel membranes with hydrophilic molecularly imprinted polymers, the problems of poor swelling mechanical properties of hydrogels in water and loss of traditional MIPs were solved, achieving high adsorption capacity and selective adsorption of BPA.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-04-10
AI Technical Summary
Existing hydrogels exhibit significantly reduced mechanical properties when swollen in water, limiting their application in pollutant adsorption. Furthermore, traditional molecularly imprinted polymer particle adsorption suffers from issues such as loss, high mass transfer resistance, and low regeneration efficiency.
Using a porous semi-interpenetrating hydrogel as the matrix, hydrophilic molecularly imprinted polymers (MIPs) are doped and prepared via free radical polymerization. These MIPs are then combined with N-isopropylacrylamide and carboxymethyl chitosan to form a composite hydrogel film, which enhances mechanical strength and selectivity through interactions such as hydrogen bonding.
The prepared hydrogel membrane has an adsorption capacity of up to 113.22 mg/g, exhibits excellent selectivity and regeneration performance, and maintains an adsorption efficiency of 99% after six cycles, significantly improving the removal effect of BPA in water.
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Figure CN121819785A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a hydrogel membrane, in particular a hydrogel membrane and a preparation method and application thereof. BACKGROUND
[0002] Bisphenol A (BPA) is a typical endocrine disruptor (EDCs) and is widely used in the production of polycarbonate, epoxy resin and other plastic products. The limit value of BPA in the "Drinking Water Health Standards" (GB 5749-2022) is 10000 ng / L, but actual research shows that if exposed to BPA for a long time at a low dose, even if the concentration is much lower than the limit value, it may still cause toxicological effects, and endocrine and metabolic activities, reproductive development will be affected. BPA is widely used, and its exposure in environmental water bodies is very common, therefore, it is urgent to develop a high-efficiency and selective BPA removal technology in water bodies.
[0003] Adsorption is a common method for removing BPA because of its simple operation and fast removal rate. Molecularly imprinted polymers (MIPs) have important application prospects in the fields of pollutant separation, sensors, protein enrichment, etc. due to their conformational predetermination, specific recognition and long-term stability.
[0004] Traditional MIPs have poor accessibility of recognition sites due to the easy aggregation of hydrophobic functional monomers (such as methacrylic acid) in aqueous phase. The introduction of hydrophilic functional monomers (such as acrylamide derivatives) or water-compatible cross-linking agents (such as polyvinyl alcohol) into molecularly imprinted polymers can improve the water dispersibility of MIPs while maintaining the specific cavity structure, and improve the adsorption performance of MIPs. Although directly using MIP particles for adsorption of pollutants has the characteristics of lower material cost and larger static adsorption capacity, the separation thereof needs to rely on additional steps such as filtration and centrifugation, which is easy to cause particle loss and secondary pollution, and the mass transfer resistance between particles is large, the adsorption-desorption rate is slow, and the regeneration efficiency is low. The adsorption technology based on membrane can realize the integration of adsorption and separation, the porous structure of the membrane shortens the mass transfer path, and no additional separation process is needed, so that the adsorption and regeneration can be completed in situ, which significantly reduces the energy consumption; at the same time, the continuous phase structure of the membrane avoids the problem of particle loss, improves the reuse efficiency of MIPs, and is more easily modularized for large-scale application. Compared with this, the adsorption-based pollutant separation and removal technology based on membrane materials has high stability and mechanical strength, and is simple to operate, has high solid-liquid separation efficiency, and can be recycled. For example, by loading nano-adsorbents (such as MOFs, carbon materials) onto a porous membrane substrate, high adsorption capacity and fast mass transfer can be achieved at the same time, and separation can be completed by simply filtering after adsorption, avoiding the cumbersome steps of centrifugation or sedimentation of traditional adsorbents. In addition, the membrane material can be regenerated efficiently by reverse flushing or chemical desorption, and the loss rate is much lower than that of the particle adsorbent, which has a wide application in the removal of environmental pollutants in water bodies.
[0005] Hydrogel-based membrane adsorption has become a research hotspot in recent years, effectively combining the high hydrophilicity, three-dimensional network structure, and continuity and operability of membrane materials, exhibiting unique advantages. The swelling properties of hydrogels give them good permeability in aqueous solutions, significantly reducing mass transfer resistance. Ícaro crosslinked β-cyclodextrin (β-CD) and hydroxypropyl methylcellulose (HPMC) with citric acid via esterification, binding the hydrophobic cavities of β-CD to the gel polymer for the adsorption of BPA. The adsorption capacity was 14.6 mg / g (DE SOUZA Í FT, PETRI DF S. β-Cyclodextrin hydroxypropyl methylcellulose hydrogels for bisphenol A adsorption [J]. Journal of Molecular Liquids, 2018, 266: 640-8.). Hou designed and prepared a novel self-assembled hydrogel constructed from cyclodextrin polymer (β-CD) / ferrocene-modified polyacrylic acid (PAA-Fc) for the removal of BPA from water by means of host-guest interaction. The maximum adsorption capacity for BPA was 23.61 mg / g (HOU N, WANGR, WANG F, et al. Self-assembled hydrogels constructed via host-guest polymers with highly efficient dye removal capability for wastewater treatment [J]. Colloid Surf A-Physicochem Eng Asp, 2019, 579.).
[0006] However, when hydrogels swell significantly in water, their mechanical properties decrease considerably, exhibiting characteristics such as low stress strength and poor toughness. This severely limits the application of hydrogels in the adsorption of pollutants in water. Summary of the Invention
[0007] Objectives of the invention: The objective of this invention is to provide a hydrogel membrane with high adsorption capacity, excellent selectivity, and good regeneration performance; another objective of this invention is to provide a method for preparing the above-mentioned hydrogel membrane; a third objective of this invention is to provide an application of the above-mentioned hydrogel membrane in the adsorption of bisphenol A.
[0008] Technical solution: The hydrogel membrane of the present invention has a porous structure and uses a semi-interpenetrating hydrogel made of N-isopropylacrylamide and carboxymethyl chitosan as the matrix. The matrix is doped with a hydrophilic molecularly imprinted polymer. The raw materials for preparing the molecularly imprinted polymer include 2-acrylamide-2-methylpropanesulfonic acid and styrene.
[0009] Preferably, the concentration of the hydrophilic molecularly imprinted polymer in the matrix is 0.04-0.075 g / mL, and the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to styrene is 1:0.5-4.
[0010] The method for preparing the hydrogel membrane according to the present invention includes the following steps: (1) Synthesis of hydrophilic molecularly imprinted polymers: using 2-acrylamide-2-methylpropanesulfonic acid and styrene as monomers and bisphenol A as template molecule, hydrophilic molecularly imprinted polymers were synthesized by free radical polymerization. (2) Preparation of semi-interpenetrating hydrogel precursor: Using the semi-interpenetrating hydrogel prepared from N-isopropylacrylamide and carboxymethyl chitosan as raw material, a precursor solution was prepared; (3) Preparation of semi-interpenetrating network gel molecularly imprinted hydrogel membrane: The hydrophilic molecularly imprinted polymer is mixed with the precursor solution and an initiator is added to obtain the hydrogel membrane.
[0011] In step (1), a crosslinking agent and an initiator are added. The crosslinking agent is ethylene glycol dimethacrylate, and the initiator is azobisisobutyronitrile. The template molecule needs to be removed later. When removing the template molecule, a mixture of ethanol and acetic acid is used for elution.
[0012] In step (2), a crosslinking agent and an accelerator also need to be added. The crosslinking agent is methylenebisacrylamide and the accelerator is tetramethylethylenediamine.
[0013] The initiator mentioned in step (3) is an ammonium persulfate solution.
[0014] The application of the hydrogel membrane described in this invention in the adsorption of bisphenol A includes the following steps: heating and evaporating pure water and plastic together to concentrate the water, and then adding the hydrogel membrane for adsorption.
[0015] Invention Principle: This method is based on the organic combination of hydrophilic molecularly imprinted polymers and semi-interpenetrating network hydrogels to prepare a hydrogel membrane for removing BPA from water. First, using BPA as a template molecule and hydrophilic 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and styrene (St) as functional monomers, water-soluble molecularly imprinted polymers (MIPs) are synthesized through free radical polymerization. After elution, imprinted cavities with specific recognition capabilities for BPA are formed. Subsequently, the MIPs are uniformly dispersed as functional additives in a semi-interpenetrating network hydrogel precursor composed of N-isopropylacrylamide (NIPAM) and carboxymethyl chitosan (CMCS), and cross-linked and cured to form a composite hydrogel membrane. In this structure, MIPs provide highly selective adsorption sites, while the semi-interpenetrating network formed by CMCS and NIPAM not only regulates the gel pore size to promote BPA mass transfer, but also binds tightly to MIPs through interactions such as hydrogen bonds, significantly enhancing the mechanical strength and structural stability of the material, ultimately obtaining a composite adsorbent material with high adsorption capacity, excellent selectivity and easy regeneration performance.
[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The hydrogel membrane prepared by this method has a high adsorption capacity, up to 113.22 mg / g; (2) The hydrogel membrane prepared by this method has excellent regeneration performance. After six cycles of use, the adsorption efficiency of BPA can still reach 99%, which has excellent reusability; (3) The hydrogel membrane prepared by this method has high selectivity for the removal of BPA in water. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the hydrogel membrane preparation process; Figure 2 A comparison chart showing the hydrophilicity test results of MIPs prepared in Example 1 and Example 2; Figure 3 Images show the microstructures of different hydrogel films, where 3a is Example 1 and 3b is Comparative Example 3. Figure 4 The infrared spectra of MIPs, MIP@BPA, and BPA prepared in Example 1 are shown. Figure 5 Infrared spectra of MIPs, NIPAM / CMCS and MIP@N / C prepared in Example 1; Figure 6 The images show a comparison of the appearance of MIP@N / C and N / C obtained in Example 1 before (a) and after immersion in water (b). Figure 7 Langmuir model (a) and Freundlich model (b) of MIP@N / C prepared in Example 1 at different temperatures. Figure 8 The adsorption kinetics fitting data for MIP@N / C prepared in Example 1 were obtained using pseudo-first-order and pseudo-second-order models; Figure 9 The data are the reproducibility analysis data of MIP@N / C obtained in Example 1; Figure 10 The selective adsorption data of MIP@N / C prepared in Example 1 for BPA, BPF and PTBP are shown. Figure 11 Data on the selective adsorption of BPA, BPF, and PTBP by the hydrogel membrane prepared in Comparative Example 4. Figure 12 The images show the HPLC chromatograms of the concentrated sample before and after adsorption and the eluted enriched sample in Example 1. In the images, A is a takeout box, B is a mineral water bottle, and C is a PC plastic bucket. Detailed Implementation
[0018] The technical solution of the present invention will be further described below with reference to the embodiments.
[0019] Example 1
[0020] The hydrogel membrane of the present invention uses a semi-interpenetrating hydrogel prepared from N-isopropylacrylamide and carboxymethyl chitosan as a matrix. The matrix is doped with a molecularly imprinted polymer, the concentration of which is 0.06 g / mL. The raw materials for preparing the molecularly imprinted polymer include 2-acrylamide-2-methylpropanesulfonic acid and styrene in a molar ratio of 1:1.
[0021] like Figure 1 The method for preparing the hydrogel membrane of the present invention includes the following steps: (1) Synthesis of hydrophilic MIPs 1 mmol BPA, 2.5 mmol AMPS, and 2.5 mmol St were dissolved sequentially in 20 mL of DMF solution and stirred to generate a prepolymer solution. The prepolymer solution was purged with inert nitrogen gas for 20 min, followed by the addition of 1.88 mL of ethylene glycol dimethacrylate (EGDMA) crosslinking agent and 35 mg of azobisisobutyronitrile (AIBN) initiator. The mixture was sonicated for 15 min, allowed to stand at room temperature for 6 h, and then subjected to polymerization in a water bath at 50 °C for 24 h. Finally, the resulting MIPs were collected and eluted with a 9:1 (v / v) ethanol / acetic acid eluent to remove the template molecule BPA. The cleanliness of the template was assessed using a UV spectrophotometer until no BPA peak was detected at 278 nm. Residual acetic acid was then washed away with ethanol. The MIPs were vacuum dried at 60 °C, then removed and ground to obtain MIPs powder, which was then sealed and stored at room temperature.
[0022] (2) Preparation of semi-interpenetrating hydrogel NIPAM / CMCS precursor Dissolve 1.55 g NIPAM and 0.51 g CMCS in 17 ml of deionized water, mix thoroughly, and then add 25.344 mg of crosslinking agent NN-methylenebisacrylamide (MBA) and 50 µL of accelerator tetramethylethylenediamine (TEMED) to obtain a NIPAM / CMCS precursor solution. After sonication for 15 min, store in a cool place. The precursor obtained in this invention is abbreviated as N / C.
[0023] (3) Preparation of semi-interpenetrating network gel molecularly imprinted hydrogel membrane Mix 2 ml of precursor solution with 0.12 g of MIPs powder, stir well, then add 200 μL of 0.08 g / ml initiator ammonium persulfate solution and stir. Pour the mixture into a mold, scrape off any protruding parts to make the gel film 1 mm thick, and let it stand at room temperature for 24 h to obtain a semi-interpenetrating network gel molecularly imprinted membrane. Remove it from the mold and immerse it in deionized water for 24 h, changing the water every 8 h to wash away unreacted monomers in the network. After washing, freeze-dry for later use to obtain a hydrogel membrane. In this embodiment, the concentration of MIPs in the precursor solution is 0.06 g / mL. The hydrogel membrane prepared by this invention is abbreviated as MIP@N / C.
[0024] Example 2
[0025] The similarities between this embodiment and embodiment 1 will not be repeated here. The difference is that in step (1), the amounts of AMPS and St added are 1 mmol and 4 mmol, respectively.
[0026] Example 3
[0027] The similarities between this embodiment and Embodiment 1 will not be repeated here. The difference is that in step (1), the amounts of AMPS and St added are 2 mmol and 3 mmol, respectively.
[0028] Example 4
[0029] The similarities between this embodiment and Embodiment 1 will not be repeated here. The difference is that in step (1), the amounts of AMPS and St added are 3 mmol and 2 mmol, respectively.
[0030] Example 5
[0031] The similarities between this embodiment and Example 1 will not be repeated here. The difference is that the amount of MIPs added in step (3) is 0.10g. In this embodiment, the concentration of MIPs in the precursor solution is 0.05g / mL.
[0032] Example 6 The similarities between this embodiment and Example 1 will not be repeated here. The difference is that the amount of MIPs added in step (3) is 0.08g. In this embodiment, the concentration of MIPs in the precursor solution is 0.04g / mL.
[0033] Example 7
[0034] The similarities between this embodiment and Example 1 will not be repeated here. The difference is that the amount of MIPs added in step (3) is 0.15g. In this embodiment, the concentration of MIPs in the precursor solution is 0.075g / mL.
[0035] Comparative Example 1 This comparative example uses methacrylic acid (MAA) and St to prepare a bifunctional monomer molecularly imprinted polymer. The difference from Example 1 is that AMPS is replaced with the same number of moles of MAA.
[0036] Comparative Example 2 The similarities between this comparative example and Example 1 will not be repeated here. The difference is that in step (1), the amounts of AMPS and St added are 4 mmol and 1 mmol, respectively.
[0037] Comparative Example 3 The similarities between this comparative example and Example 1 will not be repeated here. The difference is that the amount of MIPs added in step (3) is 0.2g. In this example, the concentration of MIPs in the precursor solution is 0.1g / mL.
[0038] Comparative Example 4 The similarities between this comparative example and Example 1 will not be repeated here. The difference is that step (1) is deleted and the amount of MIPs added in step (3) is 0.
[0039] The adsorption capacity of the MIPs obtained in Examples 1-4 and Comparative Example 2 was tested, and the data are shown in Table 1.
[0040] Table 1. Adsorption capacity data of MIPs obtained from each experiment As shown in Table 1, when the ratio of AMPS to St is within a certain range, the adsorption capacity of MIPs prepared by this method is not less than 69 mg / g, and can reach up to 77.43 mg / g. Since the adsorption capacity of MIPs directly affects the adsorption capacity of the final hydrogel membrane, and the two are positively correlated, it can be concluded without doubt that the hydrogel membrane prepared by this method also has a high adsorption capacity for BPA.
[0041] The BPA adsorption performance of the hydrogel membranes prepared in Examples 1, 5-6 and Comparative Example 3 was tested, and the data are shown in Table 2.
[0042] Table 2. Adsorption capacity of hydrogel membranes for BPA obtained in each experiment. Experiment Adsorption capacity Q of the hydrogel film e (mg / g) Standard error Example 1 113.22 2.661 Example 5 86.16 4.308 Example 6 65.95 3.297 Example 7 55.54 2.782 Comparative Example 3 26.31 1.3155 MIPs possess cavities that can specifically adsorb BPA, and their content directly affects the adsorption effect of MIP@N / C. Table 2 shows that when the added MIPs are in the range of 0.04-0.075 g / mL, the hydrogel membrane prepared by this method exhibits high adsorption performance for BPA. The adsorption effect of MIP@N / C is closely related to the doping amount of MIPs. The best adsorption effect, reaching 113.22 mg / g, is achieved when the concentration of MIPs in the hydrogel precursor solution is 0.06 g / mL (Example 1). As the MIPs concentration increases, the adsorption effect gradually decreases. This is because in the nanoparticle composite hydrogel system, multiple polymer chains are cross-linked and fixed on the particle surface through hydrogen bonds and coordination bonds. When the content of nanoparticles is too high, nanoparticle aggregation occurs, affecting the uniformity of the hydrogel membrane. Therefore, the presence of excessive MIPs nanoparticles will lead to aggregation, affecting the uniformity of the hydrogel membrane and thus its adsorption performance.
[0043] The MIP@N / C prepared in this invention was subjected to isothermal adsorption, adsorption kinetics, selective adsorption, and regeneration experiments. The test methods are as follows.
[0044] (1) Isothermal adsorption and adsorption kinetics experiments Kinetic adsorption experiments of MIP@N / C were conducted at 298 K, and the adsorption behavior of MIP@N / C was analyzed using pseudo-first-order and pseudo-second-order kinetic formulas (1) and (2), and the adsorption parameters were calculated. A mixed solution of water / methanol with a volume ratio of 9:1 was used in the adsorption experiment. MIP@N / C was immersed in 3 ml of BPA solution with an initial concentration of 0.15 g / L and allowed to stand for different times. The equilibrium concentration of the supernatant of the adsorption solution after different adsorption times was detected using a UV-Vis spectrophotometer.
[0045]
[0046] Where t represents the adsorption time (min). Q e and Q t (mg / g) represent the adsorption amount at equilibrium and the adsorption amount at time t, respectively. k 1 and k 2 These are the pseudo-first-order rate constant (1 / min) and the pseudo-second-order rate constant (g / mg / min), respectively.
[0047] Isothermal adsorption experiments were conducted on MIP@N / C. The adsorption behavior of 3 ml adsorption solution with BPA concentration range of 0.025~0.23 g / L at temperatures of 288 K, 298 K, and 308 K was studied using the formulas of Langmuir (3) and Friedrich (4).
[0048]
[0049] in, C e (mg / L) represents the equilibrium concentration of BPA. Q e and Q m (mg / g) represent the adsorption amount at equilibrium and the maximum adsorption capacity, respectively. K L and K f These are Langmuir constant (L / mg) and Friedrich affinity coefficient (mg / g), respectively.
[0050] (2) Selective adsorption performance and regeneration efficiency The selective adsorption capacity of MIP@N / C for 50 mg / L BPA, BPF, and PTBP was investigated. The concentrations of BPA, BPF, and PTBP were determined using a UV-Vis spectrophotometer by measuring the absorbance at 278 nm, 276 nm, and 280 nm. The selectivity of MIP@N / C was evaluated using a selectivity factor (α), calculated as follows: α = RE template / RE analogue ,in, RE template Template molecule removal efficiency, RE analogue The removal efficiency of analog molecules.
[0051] The formula for calculating removal efficiency (RE) is: RE = ( C initial -C equilibrium ) / C initial ×100%， in, C initial This represents the initial concentration of molecules in the solution. C equilibrium This represents the concentration of molecules in the solution at equilibrium.
[0052] After the rebinding test, MIP@N / C was regenerated using an ethanol / water eluent with a volume ratio of 9:1 until BPA was no longer detected in the eluent. The regenerated membrane was subjected to six cycles of adsorption testing, and the binding capacity of MIP@N / C to BPA was recalculated after each cycle.
[0053] The hydrophilicity of the MIPs prepared in Example 1 and Comparative Example 1 was tested, and the results of the water contact angle are as follows: Figure 2 As shown in the figure, within 0.5s, water droplets on the MIPs with added AMPS (Example 1) rapidly spread on the MIPs surface; while the water contact angle of the MIPs prepared using MAA functional monomers (Comparative Example 1) was significantly larger. Although its water contact angle was less than 90°, water droplets could not spread on its surface after 5s. This shows that AMPS has a significant effect on improving the hydrophilicity of MIPs, proving that step (1) of Example 1 successfully synthesized hydrophilic MIPs.
[0054] The porous structure of the adsorption membrane surface and interior not only determines the mass transfer process during adsorption but also affects the distribution of binding sites and the adsorption effect. For example... Figure 3 The hydrogel membrane exhibits a porous structure. The MIPs distributed within the hydrogel membrane provide numerous adsorption sites for BPA and also positively influence the membrane's structural stability, enhancing its stability in water, reducing swelling, and preventing rupture due to excessive water absorption. As the concentration of MIPs in the hydrogel membrane increases, the pore size inside the membrane enlarges, indicating that the amount of MIPs affects the membrane's microstructure. However, excessive MIP powder (…) Figure 3 b) Aggregation on the surface and in the pores of the hydrogel membrane may lead to micropore blockage, reduce the mass transfer rate of BPA, reduce the accessibility of adsorption sites, and thus reduce its adsorption capacity.
[0055] The structures of MIPs, NIPAM / CMCS, and MIP@N / C were characterized using FT-IR. Figure 4 It can be seen that, compared with MIPs, the most significant difference in the infrared spectra of MIP@BPA (representing MIPs that have just been synthesized and have not yet eluted BPA, at which point the cavity of the MIPs contains a large amount of BPA, hence the name MIP@BPA) and BPA lies in the presence of BPA, specifically in the 3500-3200 cm⁻¹ region. -1 A broad and strong OH stretching vibration peak (characteristic peak of phenolic hydroxyl group) appears at [a specific location], while this peak is very weak in MIPs spectra, indicating that the BPA template molecule has been successfully eluted from the polymer matrix, leaving a cavity that can specifically recognize BPA. Figure 5 It can be seen that after adding MIPs to the NIPAM / CMCS hydrogel, the growth rate at 1732 cm⁻¹ is significantly higher. -1An absorption peak was observed originating from the C=O stretching vibration of the ester group (-COOR-) in the MIPs, while the hydrogel itself exhibited an absorption peak at 1592 cm⁻¹. -1 carboxylates (COO) - absorption peak and 1632 cm⁻¹ -1 The characteristic peak of the secondary amide group (-NH-CO-) was still retained, proving the successful introduction of MIPs into the hydrogel membrane. After the introduction of MIPs, the peak at 10¹⁰ cm⁻¹ was observed. -1 ~1300cm -1 A broad and distinct absorption band appeared at the interface. The reason for this broad peak is likely that at the interface between MIPs and the hydrogel network, the functional groups of the two are close to each other. The sulfonic acid group (-SO3H) on the surface of MIPs can act as a strong hydrogen bond donor, reacting with the carbonyl oxygen (C=O) of poly(N-isopropylacrylamide) (PNIPAM) or the carboxylate oxygen (-COO) of CMCS in the hydrogel. - The hydroxyl group (-OH) forms strong hydrogen bonds with the poly(N-isopropylacrylamide) group, while the hydrophobic portion (benzene ring of styrene) in the MIPs may interact hydrophobically with the hydrophobic isopropyl group of poly(N-isopropylacrylamide) (PNIAM), altering the hydrogen bond structure. These multiple interactions result in a broad absorption peak in this range. This indicates that the MIPs and hydrogel are not simply physically mixed, but rather form a new hydrogen bond network. Figure 6 It can be seen that the swelling capacity of MIP@N / C is reduced compared to NIPAM / CMCS (i.e. N / C), indicating that the newly formed hydrogen bonds act as additional physical cross-linking points, making the entire polymer network more compact and restricting the entry of water molecules and the expansion of the network. This proves that the introduction of MIPs significantly modulates the structure of the hydrogel and improves the stability of MIP@N / C in water.
[0056] Isothermal adsorption experiments were conducted on the MIP@N / C substrate prepared in Example 1 at three different temperatures: 288 K, 298 K, and 308 K to detect the adsorption of the target molecule BPA. The adsorption results were fitted using two commonly used isothermal adsorption models, Langmuir and Freundlich, respectively. The fitting curves are shown below. Figure 7 As shown in (a) and 7(b), the relevant isothermal adsorption model parameters calculated by the formula are shown in Table 3. Although the R of the Langmuir model is... 2 Slightly larger than the Freundlich model, but at 308K the Langmuir model fits poorly, while the Freundlich model has a lower R value. 2 It is more stable. It can be inferred that the Freundlich model is the most suitable choice for BPA adsorption, with multilayer adsorption on the surface.
[0057] Table 3. Parameters of the MIP@N / C isothermal adsorption model obtained in Example 1
[0058] To investigate and verify the time-dependent adsorption behavior of MIP@N / C prepared in Example 1, adsorption kinetics experiments were conducted at a BPA concentration of 150 mg / L. Two kinetic models, pseudo-first-order and pseudo-second-order, were used for data fitting, and the fitting curves are shown below. Figure 8 As shown in Table 4, the calculated kinetic parameters are as follows. It can be seen that the adsorption of BPA by MIP@N / C rapidly increases within the first 60 minutes and approaches equilibrium around 4 hours. A possible explanation for this phenomenon is that the presence of an imprinted cavity in MIP@N / C enhances its ability to accurately identify BPA.
[0059] Table 4. Kinetic fitting data of MIP@N / C combined with BPA obtained in Example 1
[0060] Based on the study of isothermal adsorption, the data were processed and fitted, and the thermodynamic parameters were calculated using the following formulas. The calculated thermodynamic parameters are shown in Table 5.
[0061]
[0062] Table 5. Thermodynamic parameters of BPA adsorption on MIP@N / C prepared in Example 1
[0063] Table 5 shows that the ΔG value is relatively small throughout the adsorption process, indicating that the adsorption reaction is reversible. As the temperature increases, the absolute value of ΔG gradually increases. This is because, with increasing temperature, the hydrogen bonds formed between the amide groups and water gradually transform into interactions between amide groups, enhancing the association between hydrophobic isopropyl groups, increasing the hydrophobicity of the hydrogel, and thus improving the affinity for BPA. The positive value of ΔH indicates that the adsorption process is accompanied by an endothermic reaction; increasing the temperature is beneficial for improving the adsorption effect. As shown in Table 6, the adsorption capacity at 298 K (113.66 mg / g) is higher than that at 288 K (66.21 mg / g). However, when the temperature continues to rise to 308 K, the adsorption capacity decreases. This is because 308 K is higher than the phase transition temperature (LCST) of the NIPAM gel, causing changes in the long-chain structure of the gel polymer. The spatial contraction makes it difficult for the adsorption sites to bind BPA, thus reducing the adsorption capacity at 308 K. The adsorption capacity is highest at 298 K.
[0064] Table 6. Maximum adsorption capacity of MIP@N / C prepared in Example 1 at different temperatures. Q m (mg / g) 288K 298K 308K MIP@N / C 66.21 113.66 72.14 Adsorption-desorption experiments were conducted on MIP@N / C to verify its regeneration performance. The desorption solution was a 9:1 volume ratio of ethanol / water mixture. Although both water and ethanol are good solvents for NIPAM, when ethanol and water coexist, the solvent molecules disrupt the hydrogen bonds between the amide groups and the solvent. The affinity between ethanol and water molecules is greater than the affinity between the chain segments and water molecules, and between the chain segments and ethanol molecules in the gel. This leads to a "co-insoluble" phenomenon in the NIPAM in the hydrogel membrane in the ethanol / water mixture, causing the polymer network to collapse and rapidly elute the bound BPA. Figure 9 As shown, after six cycles, the same MIP@N / C still achieves an adsorption efficiency of 99% for BPA, demonstrating that the MIP@N / C prepared in this invention has excellent reusability.
[0065] The adsorption selectivity of MIP@N / C for BPA structural analogs on tert-butylphenol and bisphenol F was investigated. The concentrations of BPA and its structural analogs were both 50 mg / L. The experimental results are as follows: Figure 10 As shown, the removal efficiencies of MIP@N / C for BPA, BPF, and p-tert-butylphenol were 86.86%, 76.53%, and 9.57%, respectively, with corresponding selectivity factors α of 1.13 and 9.07 for BPF and p-tert-butylphenol, respectively. BPF has a structure similar to BPA but a smaller molecule, therefore MIP@N / C exhibits similar adsorption effects for BPF. However, due to the presence of specific binding sites, MIP@N / C has a higher adsorption capacity for BPA. p-tert-butylphenol has a more significant structural difference from BPA, resulting in a lower adsorption capacity. This indicates that the unique recognition sites in MIP@N / C exhibit selective adsorption characteristics for BPA and its analogues.
[0066] The NIPAM / CMCS hydrogel membrane without added hydrophilic MIPs (Comparative Example 4) was added to 3 mL of BPA, BPF, and PTBP solutions at a concentration of 50 mg / L, respectively. After adsorption for 24 h, the concentrations of BPA, BPF, and PTBP were determined using a UV-Vis spectrophotometer by measuring the absorbance at 278 nm, 276 nm, and 280 nm, and the adsorption efficiency was calculated. The results are as follows: Figure 11 As shown in the figure, the removal efficiency of the hydrogel membrane for the three structural analogs is all below 7%, and the difference in removal efficiency is not significant, indicating that the NIPAM / CMCS hydrogel membrane without added hydrophilic MIPs has no selective adsorption effect on BPA. The trace adsorption of the three bisphenol structural analogs by the NIPAM / CMCS hydrogel membrane without added hydrophilic MIPs comes from the formation of hydrogen bonds between some free carboxyl / hydroxyl groups in the hydrogel polymer network and the target substances, which adsorb a small amount of the target substances into the pores of the hydrogel.
[0067] Application Example 1 The application of the hydrogel membrane described in this invention for adsorbing bisphenol A includes the following steps: 1100 mL of purified water is heated and concentrated to 10 mL along with a takeout box, a mineral water bottle, and a PC plastic bucket, respectively, to obtain a concentrated enriched water sample containing BPA for testing. One MIP@N / C membrane obtained in Example 1 is adsorbed into 3 mL of the enriched water sample and eluted in 1 mL of methanol. The eluted enriched sample and the concentrated samples before and after adsorption are subjected to HPLC analysis to verify the feasibility of the prepared MIP@N / C as an adsorbent.
[0068] Considering the low concentration of bisphenol A (BPA) in everyday water samples, it is presumed that the water samples themselves may not contain BPA. However, the plastic packaging material containing the water may release BPA into the water at high temperatures. Therefore, to simulate the process of BPA release from packaging plastic into water, an experiment was conducted for this application example. The test results are as follows: Figure 12 As shown.
[0069] like Figure 12 As shown, the BPA peak in the concentrated samples from takeout boxes, mineral water bottles, and PC plastic containers appeared at 6.12 min before and after adsorption. BPA was detected in all three types of actual water samples obtained using the concentration and enrichment method, with the largest BPA peak observed in the PC plastic container. After adsorption by MIP@N / C, the BPA peak at 6.12 min significantly decreased in all three concentrated water samples, and a distinct BPA peak was also detected in the eluent. This indicates that MIP@N / C maintains a certain capacity to adsorb BPA even in actual water environments with low BPA content.
Claims
1. A hydrogel membrane, characterized in that, The hydrogel membrane has a porous structure and uses a semi-interpenetrating hydrogel made of N-isopropylacrylamide and carboxymethyl chitosan as the matrix. The matrix is doped with a hydrophilic molecularly imprinted polymer. The raw materials for preparing the molecularly imprinted polymer include 2-acrylamide-2-methylpropanesulfonic acid and styrene.
2. The hydrogel membrane according to claim 1, characterized in that, The concentration of the hydrophilic molecularly imprinted polymer in the matrix is 0.04-0.075 g / mL.
3. The hydrogel membrane according to claim 1, characterized in that, The molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to styrene is 1:0.5-4.
4. A method for preparing the hydrogel membrane according to claim 1, characterized in that, Includes the following steps: (1) Synthesis of hydrophilic molecularly imprinted polymers: using 2-acrylamide-2-methylpropanesulfonic acid and styrene as monomers and bisphenol A as template molecule, hydrophilic molecularly imprinted polymers were synthesized by free radical polymerization. (2) Preparation of semi-interpenetrating hydrogel precursor: Using the semi-interpenetrating hydrogel prepared from N-isopropylacrylamide and carboxymethyl chitosan as raw material, a precursor solution was prepared; (3) Preparation of semi-interpenetrating network gel molecularly imprinted hydrogel membrane: The hydrophilic molecularly imprinted polymer is mixed with the precursor solution and an initiator is added to obtain the hydrogel membrane.
5. The preparation method according to claim 4, characterized in that, In step (1), a crosslinking agent and an initiator are also required. The crosslinking agent is ethylene glycol dimethacrylate, and the initiator is azobisisobutyronitrile.
6. The preparation method according to claim 4, characterized in that, The template molecules mentioned in step (1) need to be removed later. When removing the template molecules, a mixture of ethanol and acetic acid is used for elution.
7. The preparation method according to claim 4, characterized in that, In step (2), a crosslinking agent and an accelerator also need to be added. The crosslinking agent is methylenebisacrylamide and the accelerator is tetramethylethylenediamine.
8. The preparation method according to claim 4, characterized in that, The initiator mentioned in step (3) is an ammonium persulfate solution.
9. The application of the hydrogel membrane according to claim 1 in the adsorption of bisphenol A.
10. The application according to claim 9, characterized in that, Includes the following steps: Pure water and plastic are heated together to evaporate and concentrate the water, and then the hydrogel membrane is added for adsorption.