A method for marking nanofiltration membrane channels using host-guest inclusion

Abstract

The application discloses a method for marking nanofiltration membrane channels by using host-guest inclusion, and the method is characterized in that the cavity of beta-cyclodextrin on the nanofiltration membrane is marked by using the inclusion of fluorescent dye curcumin and beta-cyclodextrin, and the curcumin is dissociated from the cavities of beta-cyclodextrin with the big opening upward and the small opening upward by water pressure, the ratio of the big opening upward to the small opening upward of the cavity of beta-cyclodextrin on the nanofiltration membrane is calculated according to the fluorescence change before and after the dissociation, the influence of the ratio of the big opening upward to the small opening upward of the cyclodextrin channel on the retention performance and the permeation flux of the cyclodextrin hydrophilic modified nanofiltration membrane is explored, and the application lays a foundation for performance adjustment of the nanofiltration membrane based on cyclodextrin hydrophilic modification.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane separation technology, specifically relating to a method for marking nanofiltration membrane pores using host-guest inclusion. Background Technology

[0002] The textile and dyeing industry generates large amounts of wastewater with high salinity and color. This wastewater contains dyes, inorganic salts, various types of surfactants, suspended solids, acids, alkalis, and other auxiliary chemicals, causing serious environmental pollution. Moreover, due to the lack of freshwater, continuous environmental degradation, and a growing population, water scarcity is considered a current and future risk to human activities. Therefore, to address the severe freshwater shortage, wastewater or seawater treatment and recycling can be used to meet the growing demand. Membrane separation technology has gradually become a key technology under today's innovation-driven sustainable development strategy. Pressure-driven separation processes, such as reverse osmosis, nanofiltration, and ultrafiltration, have been widely adopted for wastewater treatment due to their high energy efficiency and selectivity, low cost, and ease of operation.

[0003] Studies have shown that the structure and surface morphology of membranes (roughness, pore size distribution, electrokinetic properties, structural and chemical properties) affect membrane performance. The key feature of most separation membranes is their pore structure, among which the most important is the precise control and uniform distribution of pore size. However, since most methods for characterizing the pores on the surface of separation membranes are scanning electron microscopy (SEM), the shape, size and small-scale pore distribution of the membrane pores can be clearly observed at appropriate magnification, but the distribution range of the pores on a large scale cannot be characterized. Therefore, using other novel characterization methods to observe the distribution of membrane pores can help improve membrane performance.

[0004] The fluorescent dye curcumin was introduced into a novel hydrophilic composite nanofiltration membrane prepared by interfacial polymerization of β-cyclodextrin and triformyl chloride on a polyethersulfone-based membrane. This resulted in a separation membrane with fluorescently labeled pores. The hydroxyl groups in the outer space of the β-cyclodextrin improve the hydrophilicity of the nanofiltration membrane, while the hydrophobic interior helps the membrane build rapid transport channels for water molecules, increasing water flux. β-cyclodextrin exhibits excellent shape and size recognition capabilities for certain molecules and ions, enhancing membrane selectivity and thus improving separation performance. Furthermore, the β-cyclodextrin can form inclusion complexes with the fluorescent dye curcumin through host-guest interactions, marking the pores of the nanofiltration membrane and characterizing its pore distribution. This approach not only prepares hydrophilic composite nanofiltration membranes with high permeate flux and high selectivity but also allows for the simultaneous observation of the impact of pore distribution on membrane performance. This provides a new approach for dye separation in nanofiltration membranes and for magnesium-lithium separation, and holds great promise for membrane pore characterization techniques. Summary of the Invention

[0005] The purpose of this invention is to provide a method for labeling nanofiltration membrane pores using host-guest inclusion, addressing the aforementioned technical analysis. The host-guest inclusion involves curcumin and cyclodextrin. The nanofiltration membrane is a hydrophilically modified nanofiltration membrane formed by the polymerization of cyclodextrin and trimesoyl chloride on the surface of a polyethersulfone ultrafiltration membrane. Curcumin, as a guest molecule, emits yellow-green fluorescence under 425nm excitation light. After entering the cyclodextrin cavity and forming a cyclodextrin / curcumin inclusion complex, it is used to label the cyclodextrin pores. Subsequently, the cyclodextrin / curcumin inclusion complex and trimesoyl chloride are polymerized on the surface of the polyethersulfone ultrafiltration membrane to form the nanofiltration membrane. The curcumin-cyclodextrin pores are dissociated by water pressure impacting both sides of the nanofiltration membrane, and the change in fluorescence intensity determines the ratio of the larger opening to the smaller opening on the nanofiltration membrane.

[0006] This invention proposes a method for labeling nanofiltration membrane pores using host-guest inclusion, comprising the following steps: 1) Preparation of host-guest inclusion complex: Curcumin and cyclodextrin were fully dissolved in organic solvent and ultrapure water, respectively. Then, curcumin was added to the cyclodextrin aqueous solution. The mixture was stirred at room temperature for 8-24 hours. After the mixed solution was allowed to stand for 12 hours, it was centrifuged. The precipitate was transferred to a petri dish and freeze-dried to obtain the cyclodextrin / curcumin inclusion complex. 2) Preparation of polyethersulfone ultrafiltration membrane: The polyethersulfone ultrafiltration membrane is prepared by solvent-inducing phase separation technology. Polyethersulfone and polyethylene glycol are dissolved in N,N-dimethylformamide solvent. The mixed solution is stirred continuously at a certain temperature for 12-48 hours, and then allowed to stand for a period of time to remove entrained air bubbles. Subsequently, the casting solution is evenly coated on a flat support and immersed in a solvent-free gel bath for 15-20 seconds to start the phase separation process to prepare the polyethersulfone ultrafiltration membrane. 3) Preparation of nanofiltration membrane: The polyethersulfone ultrafiltration membrane is immersed in an aqueous solution of cyclodextrin / curcumin inclusion complex of different concentrations for 5-15 minutes, and then the membrane is immersed in a pyromellitic trimethylol chloride organic phase for 5-15 minutes. Then, the prepared nanofiltration membrane is heated in a ventilated oven for 10-15 minutes to induce a crosslinking reaction. 4) Marking of nanofiltration membrane pores and testing the fluorescence intensity of nanofiltration membranes with different concentrations of cyclodextrin / curcumin inclusion complexes prepared in 3) under 425 nm excitation light. Subsequently, the front side was back-washed with a flat-panel membrane flux for 6-12 hours until the fluorescence of the nanofiltration membrane did not change. Then, the back side was back-washed with a flat-panel membrane flux for 6-12 hours until the fluorescence of the nanofiltration membrane did not change. The ratio of cyclodextrin with the larger opening facing upward and the smaller opening facing upward was calculated based on the degree of fluorescence reduction.

[0007] A method for labeling nanofiltration membrane pores using host-guest inclusion, characterized in that in step 1), the cyclodextrin is one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, preferably β-cyclodextrin.

[0008] A method for labeling nanofiltration membrane pores using host-guest inclusion, characterized in that in step 1), curcumin is 0.2 g, cyclodextrin is 0.613 g, the organic solvent is one of ethanol, acetone, and toluene, with a volume of 4-5 mL, ultrapure water is 40 mL, and after standing, the centrifugation speed is 5000-10000 rpm, preferably 6000-8000 rpm, the inclusion ratio of cyclodextrin to curcumin is 1:1, and the inclusion constant is 2.433 × 10⁻⁶. 3 M -1 .

[0009] A method for labeling nanofiltration membrane pores using host-guest encapsulation, characterized in that in step 2), the mass fraction of polyethersulfone is 16 wt%, the mass fraction of polyethylene glycol is 14 wt%, the mass fraction of N,N-dimethylformamide is 70 wt%, and the stirring temperature of the mixed solution is 60-80℃, preferably 70℃.

[0010] A method for labeling nanofiltration membrane pores using host-guest encapsulation, characterized in that in step 2), the molecular weight of polyethylene glycol is 400-10000, preferably 4000, and the thickness of the polyethersulfone ultrafiltration membrane is 150-200 μm, preferably 200 μm.

[0011] A method for labeling nanofiltration membrane pores using host-guest inclusion complex, characterized in that in step 3), the concentration of the cyclodextrin / curcumin inclusion complex is 0.2 wt.%, 0.6 wt.%, 0.8 wt.%, 1.2 wt.%, or 1.6 wt.%, and the heating temperature is 50-60°C, preferably 55°C.

[0012] A method for labeling nanofiltration membrane pores using host-guest encapsulation, characterized in that in step 4), the solvent of the organic phase is one of n-hexane, dimethyl sulfide, dimethylformamide, N-methylpyrrolidone, cyclohexane, and n-heptane, preferably n-hexane.

[0013] A method for marking nanofiltration membrane pores using host-guest encapsulation, characterized in that, in step 4), the water pressure is 0.1-0.5 MPa, preferably 0.2-0.3 MPa. Attached Figure Description

[0014] Figure 1 Electron microscope images of the surface of nanofiltration membranes with different concentrations of cyclodextrin.

[0015] Figure 2 Atomic force microscopy images of nanofiltration membranes with different concentrations of cyclodextrin.

[0016] Figure 3 Contact angle diagrams of nanofiltration membranes with different concentrations of cyclodextrin.

[0017] Figure 4Fluorescence images of nanofiltration membranes with different concentrations of cyclodextrin / curcumin.

[0018] Figure 5 Fluorescence patterns of wide and narrow apertures of nanofiltration membranes with different concentrations of cyclodextrin / curcumin. Specific implementation methods

[0019] The present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Example 1: 1) Dissolve 0.2 g curcumin and 0.613 g β-cyclodextrin in 5 mL ethanol and 40 mL ultrapure water respectively. Then add curcumin to the β-cyclodextrin aqueous solution. Stir the mixture at room temperature for 8 h. After the mixture has been allowed to stand for a period of time, centrifuge at 8000 rpm for 10 min. Transfer the precipitate to a petri dish and freeze dry to obtain a β-cyclodextrin / curcumin inclusion complex with an inclusion ratio of 1:1. 2) Dissolve 9.6 g of polyethersulfone and 9.6 g of polyethylene glycol in 40.8 g of N,N-dimethylformamide solvent. Stir the mixture continuously at 60 °C for 24 hours, and then allow it to stand to remove entrained air bubbles. Subsequently, the casting solution is evenly coated on a flat support and immersed in a solvent-free gel bath to start the phase separation process to prepare a polyethersulfone ultrafiltration membrane with a thickness of 200 μm. 3) The polyethersulfone ultrafiltration membrane prepared in 2) was immersed in the aqueous phase solution of 0.2 wt% β-cyclodextrin / curcumin inclusion complex prepared in 1) for 30 minutes, and then the membrane was immersed in the organic phase of 0.2 wt% trimesoyl chloride for 5 minutes. Then, the prepared nanofiltration membrane was heated in a ventilated oven at 55°C for 15 minutes to induce a crosslinking reaction. 4) Marking the nanofiltration membrane pores: Rinse the front and back sides of the nanofiltration membrane prepared in step 3) with 0.4 MPa water pressure, test the fluorescence change before and after rinsing, and calculate the ratio of the wide opening and narrow opening of the cyclodextrin on the nanofiltration membrane surface.

[0021] Example 2: 1) Dissolve 0.2 g curcumin and 0.613 g β-cyclodextrin in 5 mL ethanol and 40 mL ultrapure water respectively. Then add curcumin to the β-cyclodextrin aqueous solution. Stir the mixture at room temperature for 24 h. After the mixture has been allowed to stand for a period of time, centrifuge at 8000 rpm for 10 minutes. Transfer the precipitate to a petri dish and freeze dry to obtain a β-cyclodextrin / curcumin inclusion complex with an inclusion ratio of 1:1. 2) Dissolve 9.6 g of polyethersulfone and 9.6 g of polyethylene glycol in 40.8 g of N,N-dimethylformamide solvent. Stir the mixture continuously at 80 °C for 24 hours, and then allow it to stand to remove entrained air bubbles. Subsequently, the casting solution is evenly coated on a flat support and immersed in a solvent-free gel bath to start the phase separation process to prepare a polyethersulfone ultrafiltration membrane with a thickness of 200 μm. 3) The polyethersulfone ultrafiltration membrane prepared in 2) was immersed in the aqueous phase solution of 0.2 wt% β-cyclodextrin / curcumin inclusion complex prepared in 1) for 30 minutes, and then the membrane was immersed in the organic phase of 0.6 wt% trimesoyl chloride for 5 minutes. Then, the prepared nanofiltration membrane was heated in a ventilated oven at 55°C for 15 minutes to induce a crosslinking reaction. 4) Marking the nanofiltration membrane pores: Rinse the front and back sides of the nanofiltration membrane prepared in step 3) with 0.4 MPa water pressure, test the fluorescence change before and after rinsing, and calculate the ratio of the wide opening and narrow opening of the cyclodextrin on the nanofiltration membrane surface.

[0022] Example 3: 1) Dissolve 0.2 g curcumin and 0.613 g β-cyclodextrin in 5 mL ethanol and 40 mL ultrapure water respectively. Then add curcumin to the β-cyclodextrin aqueous solution. Stir the mixture at room temperature for 24 h. After the mixture has been allowed to stand for a period of time, centrifuge at 8000 rpm for 10 minutes. Transfer the precipitate to a petri dish and freeze dry to obtain a β-cyclodextrin / curcumin inclusion complex with an inclusion ratio of 1:1. 2) Dissolve 9.6 g of polyethersulfone and 9.6 g of polyethylene glycol in 40.8 g of N,N-dimethylformamide solvent. Stir the mixture continuously at 80 °C for 24 hours, and then allow it to stand to remove entrained air bubbles. Subsequently, the casting solution is evenly coated on a flat support and immersed in a solvent-free gel bath to start the phase separation process to prepare a polyethersulfone ultrafiltration membrane with a thickness of 200 μm. 3) The polyethersulfone ultrafiltration membrane prepared in 2) was immersed in the aqueous phase solution of 0.2 wt% β-cyclodextrin / curcumin inclusion complex prepared in 1) for 30 minutes, and then the membrane was immersed in the organic phase of 0.8 wt% trimesoyl chloride for 5 minutes. Then, the prepared nanofiltration membrane was heated in a ventilated oven at 50°C for 15 minutes to induce a crosslinking reaction. 4) Marking the nanofiltration membrane pores: Rinse the front and back sides of the nanofiltration membrane prepared in step 3) with 0.2 MPa water pressure, test the fluorescence change before and after rinsing, and calculate the ratio of the wide opening and narrow opening of the cyclodextrin on the nanofiltration membrane surface.

[0023] Example 4: 1) Dissolve 0.2 g curcumin and 0.613 g β-cyclodextrin in 5 mL ethanol and 40 mL ultrapure water respectively. Then add curcumin to the β-cyclodextrin aqueous solution. Stir the mixture at room temperature for 24 h. After the mixture has been allowed to stand for a period of time, centrifuge at 8000 rpm for 10 minutes. Transfer the precipitate to a petri dish and freeze dry to obtain a β-cyclodextrin / curcumin inclusion complex with an inclusion ratio of 1:1. 2) Dissolve 9.6 g of polyethersulfone and 9.6 g of polyethylene glycol in 40.8 g of N,N-dimethylformamide solvent. Stir the mixture continuously at 80 °C for 24 hours, and then allow it to stand to remove entrained air bubbles. Subsequently, the casting solution is evenly coated on a flat support and immersed in a solvent-free gel bath to start the phase separation process to prepare a polyethersulfone ultrafiltration membrane with a thickness of 200 μm. 3) The polyethersulfone ultrafiltration membrane prepared in 2) was immersed in the aqueous phase solution of 0.2 wt% β-cyclodextrin / curcumin inclusion complex prepared in 1) for 30 minutes, and then the membrane was immersed in the organic phase of 1.2 wt% trimesoyl chloride for 5 minutes. Then, the prepared nanofiltration membrane was heated in a ventilated oven at 55±0.5℃ for 15 minutes to induce a crosslinking reaction. 4) Marking the nanofiltration membrane pores: Rinse the front and back sides of the nanofiltration membrane prepared in step 3) with 0.4 MPa water pressure, test the fluorescence change before and after rinsing, and calculate the ratio of the wide opening and narrow opening of the cyclodextrin on the nanofiltration membrane surface.

[0024] Example 5: 1) Dissolve 0.2 g curcumin and 0.613 g β-cyclodextrin in 5 mL ethanol and 40 mL ultrapure water respectively. Then add curcumin to the β-cyclodextrin aqueous solution. Stir the mixture at room temperature for 24 h. After the mixture has been allowed to stand for a period of time, centrifuge at 8000 rpm for 10 minutes. Transfer the precipitate to a petri dish and freeze dry to obtain a β-cyclodextrin / curcumin inclusion complex with an inclusion ratio of 1:1. 2) Dissolve 9.6 g of polyethersulfone and 9.6 g of polyethylene glycol in 40.8 g of N,N-dimethylformamide solvent. Stir the mixture continuously at 80 °C for 24 hours, and then allow it to stand to remove entrained air bubbles. Subsequently, the casting solution is evenly coated on a flat support and immersed in a solvent-free gel bath to start the phase separation process to prepare a polyethersulfone ultrafiltration membrane with a thickness of 200 μm. 3) The polyethersulfone ultrafiltration membrane prepared in 2) was immersed in the aqueous phase solution of 0.2 wt% β-cyclodextrin / curcumin inclusion complex prepared in 1) for 30 minutes, and then the membrane was immersed in the organic phase of 1.6 wt% trimesoyl chloride for 5 minutes. Then, the prepared nanofiltration membrane was heated in a ventilated oven at 60°C for 15 minutes to induce a crosslinking reaction. 4) Marking the nanofiltration membrane pores: Rinse the front and back sides of the nanofiltration membrane prepared in step 3) with 0.3 MPa water pressure, test the fluorescence change before and after rinsing, and calculate the ratio of the wide opening and narrow opening of the cyclodextrin on the nanofiltration membrane surface.

Claims

1. A method for marking nanofiltration membrane pores using host-guest inclusion, characterized in that, Nanofiltration membranes are formed by polymerization of a host-guest inclusion complex as an aqueous monomer and pyromellitic acid chloride as an oil monomer on the surface of a polyethersulfone ultrafiltration membrane. The host molecule is a cyclodextrin, and the guest molecule is a fluorescent dye. Subsequently, backpressure rinsing is used to dissociate the guest molecule from the host molecule cavity. The ratio of the host molecule with its wide opening facing upwards to its narrow opening facing upwards on the nanofiltration membrane is determined by the degree of fluorescence attenuation. This invention proposes a method for labeling nanofiltration membrane pores using host-guest inclusion complexes, comprising the following steps: 1) Preparation of host-guest inclusion complex, wherein the host-guest inclusion complex is an inclusion complex of cyclodextrin and curcumin. The specific preparation method is as follows: curcumin and cyclodextrin are fully dissolved in organic solvent and ultrapure water, respectively. Then, curcumin is added to the cyclodextrin aqueous solution. The mixture is stirred at room temperature for 8-24 hours. After the mixed solution is allowed to stand for 12 hours, it is centrifuged. The precipitate is transferred to a petri dish and freeze-dried to obtain the cyclodextrin / curcumin inclusion complex. 2) Preparation of polyethersulfone ultrafiltration membrane: Polyethersulfone and polyethylene glycol are dissolved in N,N-dimethylformamide solvent and stirred continuously at a certain temperature for 12-48 hours, and then allowed to stand to remove entrained air bubbles; then, the casting solution is evenly coated on a flat support and immersed in a solvent-free gel bath for 15-20 seconds to prepare polyethersulfone ultrafiltration membrane. 3) Preparation of nanofiltration membrane: Using the host-guest inclusion complex cyclodextrin / curcumin as the aqueous phase monomer and pyromellitic acid chloride as the oil phase monomer, the polyethersulfone ultrafiltration membrane was immersed in aqueous solutions of cyclodextrin / curcumin inclusion complex of different concentrations for 3-30 minutes, and then immersed in the organic phase of pyromellitic acid chloride for 3-5 minutes. Subsequently, the prepared nanofiltration membrane was heated in a ventilated oven for 10-15 minutes to form ester bonds that polymerize on the surface of the polyethersulfone ultrafiltration membrane. 4) Marking of nanofiltration membrane pores and testing the fluorescence intensity of nanofiltration membranes with different concentrations of cyclodextrin / curcumin inclusion complexes prepared in 3) under 425 nm excitation light. Subsequently, the front side was back-washed with a flat-panel membrane flux for 6-12 hours until the fluorescence of the nanofiltration membrane did not change. Then, the back side was back-washed with a flat-panel membrane flux for 6-12 hours until the fluorescence of the nanofiltration membrane did not change. The ratio of cyclodextrin with the larger opening facing upward and the smaller opening facing upward was calculated based on the degree of fluorescence reduction.

2. A method for marking nanofiltration membrane pores using host-guest encapsulation as described in claim 1, characterized in that... In 1), the cyclodextrin is one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

3. A method for marking nanofiltration membrane pores using host-guest encapsulation as described in claim 1, characterized in that... In step 1), the organic solvent is one of ethanol, acetone, or toluene. After standing, the centrifugation speed is 5000-10000 rpm. The inclusion ratio of cyclodextrin to curcumin is 1:1, and the inclusion constant is 2.433 × 10⁻⁶. 3 M -1 .

4. A method for marking nanofiltration membrane pores using host-guest encapsulation as described in claim 1, characterized in that... In step 2), the mass fraction of polyethersulfone is 16 wt%, the mass fraction of polyethylene glycol is 14 wt%, the mass fraction of N,N-dimethylformamide is 70 wt%, and the stirring temperature of the mixed solution is 60-80℃.

5. A method for marking nanofiltration membrane pores using host-guest encapsulation as described in claim 1, characterized in that... In step 2), the molecular weight of polyethylene glycol is 400-10000, and the thickness of the polyethersulfone ultrafiltration membrane is 150-200 μm.

6. A method for marking nanofiltration membrane pores using host-guest encapsulation as described in claim 1, characterized in that... In step 3), the concentrations of the cyclodextrin / curcumin inclusion complex are 0.2 wt.%, 0.6 wt.%, 0.8 wt.%, 1.2 wt.%, and 1.6 wt.%, and the heating temperature is 50-60℃.

7. A method for marking nanofiltration membrane pores using host-guest encapsulation as described in claim 1, characterized in that... In step 4), the solvent for the organic phase is one of n-hexane, dimethyl sulfide, dimethylformamide, N-methylpyrrolidone, cyclohexane, and n-heptane.

8. A method for marking nanofiltration membrane pores using host-guest encapsulation as described in claim 1, characterized in that... In step 4), the water pressure is 0.1-0.5 MPa.

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