Preparation of modified PTFE anti-pollution nanofiltration membrane and application of modified PTFE anti-pollution nanofiltration membrane in dye wastewater

Abstract

The invention relates to a preparation method of a modified PTFE anti-pollution nanofiltration membrane and application of the modified PTFE anti-pollution nanofiltration membrane in separation of dye and salt. The method comprises the following steps: pretreating a PTFE base membrane, soaking the PTFE base membrane in absolute ethyl alcohol and deionized water to remove surface impurities and dredge pore channels; part of C-F bonds on the surface of the PTFE membrane are broken by adopting nitrogen plasma treatment, so that the surface activity of the PTFE membrane is enhanced; the preparation method comprises the following steps: dispersing MXene nanosheets in a dopamine solution, ultrasonically mixing uniformly, and loading the MXene nanosheets on the surface of a PTFE membrane through vacuum filtration; and finally, immersing the membrane into a mixed solution of carboxymethyl chitosan and polyethyleneimine, and forming a stable composite separation layer by utilizing a glutaraldehyde cross-linking reaction. The problems of low flux and poor stability in the prior art are solved through the following innovation points: 1) PTFE is selected as a base material, and the excellent chemical stability and mechanical strength of the PTFE provide long-term operation guarantee for the membrane; (2) the layered MXene nanosheets are introduced to construct a unique water transmission channel, so that the membrane flux is remarkably improved; and 3) a compact and hydrophilic separation layer is formed through a cross-linked network of carboxymethyl chitosan and polyethyleneimine, and abundant amino groups on the surface form a hydration layer through hydrogen-bond interaction, so that contact of pollutants is effectively blocked, and excellent anti-pollution performance is realized. The separation efficiency of the composite membrane on dye and salt can reach 99% or above, and meanwhile, the composite membrane has high water flux and long-term stability and is particularly suitable for resourceful treatment of high-salt dye wastewater.

Description

Technical Field

[0001] The present invention relates to a preparation method of a modified PTFE anti-pollution nanofiltration membrane, belonging to the technical field of membrane preparation, and specifically designs a preparation method of a PTFE dye and salt separation composite membrane. The PTFE composite membrane has the advantages of strong anti-pollution ability, high separation efficiency, large mechanical strength of the membrane, high pure water flux, etc., and is suitable for the dye and salt separation system. Background Art

[0002] Synthetic dyes are widely used in industries such as textiles, papermaking, and leather. During their production process, a large amount of dye wastewater containing salts (such as NaCl, Na2SO4) is often generated. Such wastewater has the characteristics of complex composition, high chroma, and high salinity. Traditional treatment methods such as physical methods (precipitation, adsorption), chemical methods (oxidation, reduction), and biological methods (activated sludge) are difficult to effectively separate dyes and salts, seriously restricting wastewater reuse and environmental protection.

[0003] Membrane separation technology separates and filters wastewater through microporous membranes and nanofiltration membranes, and has become a research hotspot for dye-salt separation due to its advantages such as high efficiency and energy conservation. However, the existing nanofiltration membranes still have the following technical bottlenecks: 1) Flux limitation. For example, the nanofiltration membrane prepared by interfacial polymerization using cyclen and isophthaloyl chloride as monomers as described in patent CN202510220221 has a dense honeycomb-like nanoporous structure, but the water flux is only 10.74 L·m -2 ·h -1 ·bar -1 ; 2) Insufficient stability. For example, the nanofiltration membrane prepared by hydrogen bonding of g-C3N4 nanosheets and KANF as described in patent CN202311873789 has a decline in long-term use performance due to weak interaction forces.

[0004] Due to its excellent chemical inertness, thermal stability, and mechanical strength, PTFE material is an ideal high-performance membrane substrate. However, its surface hydrophobicity easily leads to membrane pollution and flux decline. Existing modification technologies mostly focus on improving the hydrophilicity of PTFE, but often sacrifice its inherent advantages or introduce structural instability. Therefore, developing a PTFE-based composite nanofiltration membrane with high flux, strong anti-pollution ability, and long-term stability is of great significance for promoting the progress of dye wastewater treatment technology. Summary of the Invention

[0005] A preparation method of a modified PTFE anti-pollution nanofiltration membrane for dye and salt separation, the specific steps are as follows: The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and hydrophobic pores. The PTFE membrane was modified by plasma treatment using nitrogen as the reactive gas, which caused some C-F bonds on the PTFE membrane surface to break. The MXene nanosheets were added to an aqueous solution of 1 wt% dopamine and ultrasonically mixed evenly, and then vacuum filtered onto the PTFE membrane surface under 0.01 Mpa. After wiping with industrial filter paper, the membrane was completely immersed in a mixed solution of carboxymethyl chitosan and polyethyleneimine with a certain mass fraction for a period of time, and then at a certain temperature, the membrane was crosslinked in an aqueous solution of glutaraldehyde with a certain volume fraction. After reacting for a period of time, it was vacuum dried for 10 min, and finally a modified PTFE composite membrane was formed.

[0006] Among them, the content of MXene nanosheets in the dopamine aqueous solution is 0.01 - 0.1 wt%; Among them, the content of carboxymethyl chitosan in the aqueous solution is 0.1 - 0.5 wt%; Among them, the content of polyethyleneimine in the aqueous solution is 0.5 - 0.8 wt%; Among them, the crosslinking temperature of the membrane in the aqueous solution of glutaraldehyde is 30 - 60 °C; Among them, the volume fraction of the aqueous solution of glutaraldehyde is 5 - 15 vol%; Among them, the crosslinking time of the membrane in the aqueous solution of glutaraldehyde is 20 - 80 min; Beneficial effects

[0007] (1) Excellent long-term stability By treating the PTFE-based membrane with nitrogen plasma, some C-F bonds on its surface are broken to form active sites, enhancing the interfacial binding force; the MXene nanosheets are fixed on the PTFE membrane surface through dopamine chemical bonding. Compared with the traditional hydrogen bond or physical adsorption method, the attachment stability of two-dimensional materials is significantly improved, avoiding the shedding of nanosheets during long-term operation and ensuring the long-term reliability of membrane performance.

[0008] (2) High-flux performance The layered structure of MXene nanosheets constructs an efficient water transport channel in the membrane, greatly improving the permeation efficiency of water molecules and overcoming the problem of low flux of traditional nanofiltration membranes; plasma pretreatment optimizes the pore structure on the PTFE membrane surface, further promoting the rapid passage of water molecules.

[0009] (3) Excellent anti-pollution performance Carboxymethyl chitosan and polyethyleneimine are crosslinked by glutaraldehyde to form a dense and hydrophilic separation layer, which is rich in hydrophilic groups such as amino groups on the surface. A stable hydration layer is formed through hydrogen bonding, effectively blocking the adsorption and deposition of dye molecules and organic pollutants on the membrane surface; the smooth network structure on the membrane surface reduces pollutant attachment, significantly reducing the risk of membrane fouling and extending the service life. Detailed implementation method

[0010] Control example 1: The PTFE commercial membrane was first pretreated by soaking in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and hydrophobic pores. The performance test was carried out with a mixed solution of dye and salt (methyl orange:sodium sulfate = 100 ppm:1000 ppm) at 5 bar. The flux of the PTFE membrane was 1500.48 L·m -2 ·h -1 , the rejection rate of methyl orange was 12.37%, and the rejection rate of Na2SO4 was 4.23%. Example

[0011] The PTFE commercial membrane was first pretreated by soaking in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and hydrophobic pores. The PTFE membrane was modified by plasma treatment using nitrogen as the active gas. After wiping with industrial filter paper, 0.01 wt% MXene nanosheets were ultrasonically dispersed into an aqueous solution of 1 wt% dopamine, and then vacuum filtered onto the PTFE membrane surface at 0.01 Mpa. After wiping with industrial filter paper, the membrane was completely immersed in a mixed solution of 0.1 wt% carboxymethyl chitosan and 0.5 wt% polyethyleneimine for 10 min, and then at 30 °C, the membrane was crosslinked in a 5 vol% aqueous glutaraldehyde solution for 20 min and then vacuum dried for 10 min to finally form a modified PTFE composite membrane. The performance test was carried out with a mixed solution of dye and salt (methyl orange:sodium sulfate = 100 ppm:1000 ppm) at 5 bar. The flux of the PTFE membrane was 55.79 L·m -2 ·h -1 ·bar -1 , the rejection rate of methyl orange was 92.37%, and the rejection rate of Na2SO4 was 13.83%. After 7 days of long-term operation, the rejection rate of methyl orange of the prepared modified PTFE membrane was 91.34%, and the rejection rate of sodium sulfate was 14.63%. Example

[0012] The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and open pores. Air was used as the plasma treatment gas for nitrogen to modify the PTFE membrane. After wiping with industrial filter paper, 0.02 wt% of MXene nanosheets were ultrasonically dispersed into an aqueous solution of 1 wt% dopamine, and then vacuum filtered onto the surface of the PTFE membrane at 0.01 Mpa. After wiping with industrial filter paper, the membrane was completely immersed in a mixed solution of 0.2 wt% carboxymethyl chitosan and 0.6 wt% polyethyleneimine for 10 min, and then at 40 °C, the membrane was crosslinked in a 6 vol% aqueous glutaraldehyde solution for 30 min, followed by vacuum drying for 10 min to finally form a modified PTFE composite membrane. The performance was tested with a mixed solution of dye and salt (methyl orange: sodium sulfate = 100 ppm: 1000 ppm) at 5 bar. The flux of the PTFE membrane was 52.65 L·m -2 ·h -1 ·bar -1 , the rejection rate of methyl orange was 94.64%, and the rejection rate of Na2SO4 was 15.13%. After 7 days of long-term operation, the rejection rate of methyl orange of the prepared modified PTFE membrane was 92.87%, and the rejection rate of sodium sulfate was 15.73%. Example

[0013] The PTFE commercial membrane was first pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and open pores. Air was used as the plasma treatment gas for nitrogen to modify the PTFE membrane. After wiping with industrial filter paper, 0.03 wt% of MXene nanosheets were ultrasonically dispersed into an aqueous solution of 1 wt% dopamine in water, and then vacuum filtered onto the surface of the PTFE membrane at 0.01 Mpa. After wiping with industrial filter paper, the membrane was completely immersed in a mixed solution of 0.3 wt% carboxymethyl chitosan and 0.7 wt% polyethyleneimine for 10 min, and then at 50 °C, the membrane was crosslinked in a 7 vol% aqueous glutaraldehyde solution for 40 min, followed by vacuum drying for 10 min to finally form a modified PTFE composite membrane. The performance was tested with a mixed solution of dye and salt (methyl orange: sodium sulfate = 100 ppm: 1000 ppm) at 5 bar. The flux of the PTFE membrane was 51.33 L·m -2 ·h -1 ·bar -1 , the rejection rate of methyl orange was 99.11%, and the rejection rate of Na2SO4 was 16.26%. After 7 days of long-term operation, the rejection rate of methyl orange of the prepared modified PTFE membrane was 98.65%, and the rejection rate of sodium sulfate was 17.95%. Example

[0014] The commercial PTFE membrane was pretreated by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and open pores. The PTFE membrane was modified by plasma treatment using nitrogen as the reactive gas. After wiping with industrial filter paper, 0.04 wt% MXene nanosheets were ultrasonically dispersed into an aqueous solution of 1 wt% dopamine, and then vacuum filtered onto the surface of the PTFE membrane at 0.01 Mpa. After wiping with industrial filter paper, the membrane was completely immersed in a mixed solution of 0.4 wt% carboxymethyl chitosan and 0.8 wt% polyethyleneimine for 10 min, and then at 60 °C, the membrane was cross-linked in an 8 vol% aqueous glutaraldehyde solution for 50 min and then vacuum dried for 10 min to finally form a modified PTFE composite membrane. The performance was tested with a mixed solution of dye and salt (methyl orange: sodium sulfate = 100 ppm: 1000 ppm) at 5 bar. The flux of the PTFE membrane was 49.27 L·m -2 ·h -1 ·bar -1 , the rejection rate of methyl orange was 99.47%, and the rejection rate of Na2SO4 was 17.83%. After 7 days of long-term operation, the rejection rate of methyl orange of the prepared modified PTFE membrane was 99.26%, and the rejection rate of sodium sulfate was 17.33%.

Claims

1. A preparation method of a modified PTFE anti-pollution nanofiltration membrane for the separation of dyes and salts, and the specific steps are as follows: First, pre-treat the PTFE commercial membrane by soaking it in absolute ethanol and deionized water for 1 h respectively, aiming to remove surface impurities and hydrophobic pores, and use air as the plasma treatment of nitrogen gas to modify the PTFE membrane. Disperse the MXene nanosheets into an aqueous solution of 1 wt% dopamine by ultrasonic treatment, and then vacuum filter it onto the surface of the PTFE membrane under 0.01 Mpa. After wiping with industrial filter paper, immerse the membrane completely into a mixed solution of carboxymethyl chitosan and polyethyleneimine with a certain mass fraction for a period of time, and then at a certain temperature, crosslink the membrane in an aqueous solution of glutaraldehyde with a certain volume fraction. After reacting for a period of time, vacuum dry it for 10 min to finally form a modified PTFE composite membrane.

2. A preparation method of a modified PTFE anti-pollution nanofiltration membrane for separating dyes and salts as described in claim 1, characterized in that: The content of the MXene nanosheets in the dopamine aqueous solution is 0.01 - 0.1 wt%.

3. A preparation method of a modified PTFE anti-pollution nanofiltration membrane for separating dyes and salts as described in claim 1, characterized in that: The content of the carboxymethyl chitosan in the aqueous solution is 0.1 - 0.5 wt%.

4. A preparation method of a modified PTFE anti-pollution nanofiltration membrane for separating dyes and salts as described in claim 1, characterized in that: The content of the polyethyleneimine in the aqueous solution is 0.5 - 0.8 wt%.

5. A preparation method of a modified PTFE anti-pollution nanofiltration membrane for separating dyes and salts as described in claim 1, characterized in that: The crosslinking temperature of the membrane in the aqueous solution of glutaraldehyde is 30 - 60 °C.

6. A preparation method of a modified PTFE anti-pollution nanofiltration membrane for separating dyes and salts as described in claim 1, characterized in that: The volume fraction of the aqueous solution of glutaraldehyde is 5 - 15 vol%.

7. A preparation method of a modified PTFE anti-pollution nanofiltration membrane for separating dyes and salts as described in claim 1, characterized in that: The crosslinking time of the membrane in the aqueous solution of glutaraldehyde is 20 - 80 min.