A surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane

Abstract

The invention discloses a surface self-assembly modification method for improving the hydrophilicity of a polyvinylidene fluoride hollow fiber membrane. The invention firstly performs alkali treatment and oxidation on the PVDF hollow fiber membrane to form hydroxyl groups and carboxyl groups on the membrane surface, and then alternately deposits positively charged Ag@TiO2 and negatively charged sodium alginate on the membrane surface until the required number of layers is reached, and the outermost layer is Ag@TiO2. The method of the invention is simple and effective, is carried out in water, has a mild reaction process, and saves space. The membrane separation technology is coupled with the photocatalytic technology to significantly improve the hydrophilicity and anti-pollution properties of the membrane.

Description

Technical Field

[0001] The invention relates to the field of membrane technology, and in particular to a surface self-assembly modification method for improving the hydrophilicity of a polyvinylidene fluoride (PVDF) hollow fiber membrane. Background Art

[0002] Membrane separation is a widely used separation technology. Compared with other technologies, this technology has the advantages of low energy consumption, mild operating conditions, no additives, high separation efficiency and easy scale-up, as well as greater safety for production activities. Polyvinylidene fluoride (PVDF) membrane is currently considered to be an ideal separation membrane material due to its excellent properties, such as good thermal stability, good chemical resistance, aging resistance, excellent mechanical strength and film-forming properties, and has been widely used in scientific research and industrial processes. However, the hydrophobicity of PVDF makes it easy to be contaminated when treating aqueous solutions of natural organic matter, absorbed by the membrane surface or blocked by membrane pores, resulting in reduced membrane flux, reduced separation efficiency, increased operating costs, and greatly shortened membrane life.

[0003] Layer-by-layer self-assembly is a method of alternately depositing polyelectrolyte solutions (or nanoparticle suspensions) with opposite charges layer by layer under the action of electrostatic attraction, hydrogen bonding, van der Waals forces, etc., so that the layers spontaneously assemble into a film with a complete and stable structure and certain specific functions. This method is a simple preparation process that does not require complex equipment; the structure is controllable, and the thickness of the composite film can be controlled by controlling parameters such as the number of assembly groups and the concentration of polyelectrolytes; it is a low-cost, environmentally friendly and practical method.

[0004] Photocatalytic technology is widely used in sewage treatment due to its advantages of low cost, environmental protection, no secondary pollution and high efficiency. TiO2 has been widely studied due to its low price, wide source, no secondary pollution, stable chemical and physical properties, and is currently the most widely used photocatalyst. The photocatalytic performance of TiO2 is limited by the large bandgap and the rapid recombination of photoexcited electron-hole pairs. The photocatalytic efficiency can be improved by depositing precious metal Ag.

[0005] In view of this, the present invention provides a layer-by-layer self-assembly surface modification method to achieve the combination of membrane separation technology and photocatalytic technology, and improve the hydrophilicity and anti-fouling properties of PVDF membranes. Summary of the invention

[0006] The purpose of the present invention is to provide a layer-by-layer self-assembly surface modification method, by combining Ag@TiO2, a hydrophilic layer is formed on the membrane surface, and the membrane surface structure and performance are regulated by depositing different numbers of layers, so as to realize the combination of membrane separation technology and photocatalytic technology and improve the hydrophilicity and anti-fouling property of PVDF membrane.

[0007] The technical solution of the present invention is as follows:

[0008] A surface self-assembly modification method for improving the hydrophilicity of a polyvinylidene fluoride hollow fiber membrane comprises the following steps:

[0009] (1) dissolving titanium sulfate in deionized water, adding silver nitrate and PVP (polyvinyl pyrrolidone) and stirring to dissolve, then heating to 170-190° C. for hydrothermal reaction for 5-7 h, cooling naturally to room temperature, collecting the powdered product, centrifuging and washing, and drying to obtain Ag@TiO2;

[0010] The preferred mass ratio of titanium sulfate to silver nitrate to PVP is 48:0.68:1;

[0011] The preferred hydrothermal reaction temperature is 180°C and the time is 6h;

[0012] The specific centrifugal washing method is: ultrasonically dispersing the collected powdered product in water and ethanol, then centrifuging, and repeating the ultrasonic dispersion and centrifugation process three times to thoroughly wash;

[0013] The preferred drying temperature is 80°C;

[0014] (2) placing the PVDF membrane in a mixed aqueous solution of KOH and KMnO4 for alkali treatment and oxidation to form hydroxyl and carboxyl groups on the surface of the PVDF membrane for later use;

[0015] Preferably, in the mixed aqueous solution of KOH and KMnO4, the concentration of KOH is 2 mol / L, and the concentration of KMnO4 is 0.2 mol / L;

[0016] The preferred reaction temperature for the alkali treatment and oxidation is 50°C and the reaction time is 0.5h;

[0017] (3) immersing the PVDF membrane with hydroxyl and carboxyl groups obtained in step (2) in a Ag@TiO2 suspension to fully adsorb Ag@TiO2, then taking it out and rinsing it with water (to remove the Ag@TiO2 that is not firmly adsorbed) for later use;

[0018] The preparation method of the Ag@TiO2 suspension is as follows: add the Ag@TiO2 obtained in step (1) into water, adjust the pH to 2.0-2.2 with HCl, and ultrasonically disperse for 0.5h to obtain the Ag@TiO2 suspension; preferably, the concentration of Ag@TiO2 in the Ag@TiO2 suspension is 2g / L;

[0019] It is preferred that the immersion time of the PVDF membrane with hydroxyl and carboxyl groups in the Ag@TiO2 suspension is 0.5 h;

[0020] (4) immersing the PVDF membrane adsorbed with Ag@TiO2 obtained in step (3) in a sodium alginate solution to fully adsorb the sodium alginate, then taking it out and rinsing it with water (to remove the sodium alginate that is not firmly adsorbed) for later use;

[0021] The preparation method of the sodium alginate solution is as follows: dissolving the sodium alginate in a 0.5 mol / L sodium chloride solution to obtain the sodium alginate solution; preferably, the concentration of the sodium alginate in the sodium alginate solution is 2 g / L;

[0022] The immersion time of the PVDF membrane adsorbed with Ag@TiO2 in the sodium alginate solution is preferably 0.5 h;

[0023] (5) repeating the operations of steps (3) and (4), and making the outermost layer Ag@TiO2, to obtain a surface-modified PVDF membrane;

[0024] The outermost layer of the resulting surface-modified PVDF membrane is Ag@TiO2, and step (3) is repeated up to three times.

[0025] The beneficial effects of the present invention are:

[0026] The method is simple and effective, all carried out in water, the reaction process is mild, and it saves space. The combination of membrane separation technology and photocatalytic technology significantly improves the hydrophilicity and anti-fouling properties of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a comparison chart of pure water flux of modified PVDF membranes with different numbers of deposited layers.

[0028] Figure 2 This is a comparison chart of bovine albumin retention rates of modified PVDF membranes with different numbers of deposited layers.

[0029] Figure 3 This is a comparison chart of the flux recovery rate of modified PVDF membranes with different numbers of deposited layers. DETAILED DESCRIPTION

[0030] The present invention is further described below by means of specific embodiments, but the protection scope of the present invention is not limited thereto.

[0031] The PVDF hollow fiber membrane used in the following examples was purchased from Guangzhou Haike Filter Membrane Technology Co., Ltd., and the membrane pore diameter was 0.1 μm.

[0032] Example 1

[0033] (1) Preparation of Ag@TiO2: First, 4.8 g of titanium sulfate was dissolved in 60 ml of deionized water and fully dissolved. Then, 0.068 g of silver nitrate and 0.1 g of PVP were added and fully dissolved and stirred. Then, the solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and hydrothermally treated at 180 ° C for 6 hours. After natural cooling, the obtained powder was collected. Subsequently, the obtained powder was ultrasonically dispersed and centrifuged, and ultrasonically dispersed and centrifuged in water and ethanol three times to be thoroughly washed. The washed sample was dried at 80 ° C.

[0034] (2) The PVDF hollow fiber membrane was immersed in a mixed aqueous solution of KOH and KMnO4 for alkaline treatment and oxidation, the concentration of KOH was 2 mol / L, the concentration of KMnO4 was 0.2 mol / L, the reaction temperature was 50°C, and the reaction time was 0.5 h.

[0035] (3) Ag@TiO2 was dispersed in water, the pH was adjusted to 2.0-2.2 with HCl, and ultrasonic dispersion was performed for 0.5 h. The Ag@TiO2 concentration was 2 g / L. The PVDF membrane with hydroxyl and carboxyl groups was immersed in the Ag@TiO2 suspension to fully adsorb Ag@TiO2. The membrane was immersed for 0.5 h, and the weakly adsorbed Ag@TiO2 was washed with water to obtain the surface-modified membrane M1.

[0036] The test results show that the pure water flux is 192.43L / (m 2 h), the retention rate of 1 g / L bovine serum albumin solution passing through the membrane was 78.32%. After washing with clean water and irradiating with ultraviolet light for 2 h, the flux recovery rate was 83.69%.

[0037] Example 2

[0038] (1) Preparation of Ag@TiO2: First, 4.8 g of titanium sulfate was dissolved in 60 ml of deionized water and fully dissolved. Then, 0.068 g of silver nitrate and 0.1 g of PVP were added and fully dissolved and stirred. Then, the solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and hydrothermally treated at 180 ° C for 6 hours. After natural cooling, the obtained powder was collected. Subsequently, the obtained powder was ultrasonically dispersed and centrifuged, and ultrasonically dispersed and centrifuged in water and ethanol three times to be thoroughly washed. The washed sample was dried at 80 ° C.

[0039] (2) The PVDF hollow fiber membrane was immersed in a mixed aqueous solution of KOH and KMnO4 for alkaline treatment and oxidation, the concentration of KOH was 2 mol / L, the concentration of KMnO4 was 0.2 mol / L, the reaction temperature was 50°C, and the reaction time was 0.5 h. Ag@TiO2 was dispersed in water, the pH was adjusted to 2.0-2.2 with HCl, and ultrasonically dispersed for 0.5 h, the concentration of Ag@TiO2 was 2 g / L. Sodium alginate was dissolved in 0.5 mol / L sodium chloride solution, and the concentration of sodium alginate was 2 g / L.

[0040] (3) Soak the PVDF membrane with hydroxyl and carboxyl groups in a Ag@TiO2 suspension to fully adsorb Ag@TiO2 for 0.5 h, and then rinse the Ag@TiO2 that is not firmly adsorbed with water.

[0041] (4) The PVDF membrane adsorbed with Ag@TiO2 was immersed in a sodium chloride solution of sodium alginate to fully adsorb the sodium alginate. The solution was immersed for 0.5 h, and the sodium alginate that was not firmly adsorbed was rinsed with water.

[0042] (5) Repeat step (3) to obtain a surface-modified PVDF membrane M2.

[0043] The test results show that the pure water flux is 268.41L / (m 2 h), the retention rate of 1 g / L bovine serum albumin solution passing through the membrane was 83.67%. After washing with clean water and irradiating with ultraviolet light for 2 h, the flux recovery rate was 88.91%.

[0044] Experimental Example 3

[0045] (1) Preparation of Ag@TiO2: First, 4.8 g of titanium sulfate was dissolved in 60 ml of deionized water and fully dissolved. Then, 0.068 g of silver nitrate and 0.1 g of PVP were added and fully dissolved and stirred. Then, the solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and hydrothermally treated at 180 ° C for 6 hours. After natural cooling, the obtained powder was collected. Subsequently, the obtained powder was ultrasonically dispersed and centrifuged, and ultrasonically dispersed and centrifuged in water and ethanol three times to be thoroughly washed. The washed sample was dried at 80 ° C.

[0046] (2) The PVDF hollow fiber membrane was immersed in a mixed aqueous solution of KOH and KMnO4 for alkaline treatment and oxidation, the concentration of KOH was 2 mol / L, the concentration of KMnO4 was 0.2 mol / L, the reaction temperature was 50°C, and the reaction time was 0.5 h. Ag@TiO2 was dispersed in water, the pH was adjusted to 2.0-2.2 with HCl, and ultrasonically dispersed for 0.5 h, the concentration of Ag@TiO2 was 2 g / L. Sodium alginate was dissolved in 0.5 mol / L sodium chloride solution, and the concentration of sodium alginate was 2 g / L.

[0047] (3) Soak the PVDF membrane with hydroxyl and carboxyl groups in a Ag@TiO2 suspension to fully adsorb Ag@TiO2 for 0.5 h, and then rinse the Ag@TiO2 that is not firmly adsorbed with water.

[0048] (4) The PVDF membrane adsorbed with Ag@TiO2 was immersed in a sodium chloride solution of sodium alginate to fully adsorb the sodium alginate. The solution was immersed for 0.5 h, and the sodium alginate that was not firmly adsorbed was rinsed with water.

[0049] (5) Repeat steps (3) and (4) once, and then repeat step (3) to obtain a surface-modified PVDF membrane M3.

[0050] The test results show that the pure water flux is 296.91L / (m 2 h), the retention rate of 1 g / L bovine serum albumin solution passing through the membrane was 89.61%. After washing with clean water and irradiating with ultraviolet light for 2 h, the flux recovery rate was 92.34%.

[0051] Comparative Example 1

[0052] The PVDF hollow fiber membrane was not modified in any way to obtain membrane M0.

[0053] The test results show that the pure water flux is 153.37L / (m 2 h), the retention rate of 1 g / L bovine serum albumin solution passing through the membrane was 62.93%. After washing with clean water and irradiating with ultraviolet light for 2 h, the flux recovery rate was 52.14%.

Claims

1. A surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane, characterized in that: The following steps are involved: (1) dissolving titanium sulfate in deionized water, adding silver nitrate and PVP, stirring and dissolving, then heating to 170-190° C. for hydrothermal reaction for 5-7 h, cooling naturally to room temperature, collecting the powdered product, washing by centrifugation, and drying to obtain Ag@TiO2; (2) placing the PVDF membrane in a mixed aqueous solution of KOH and KMnO4 for alkali treatment and oxidation to form hydroxyl and carboxyl groups on the surface of the PVDF membrane for later use; (3) immersing the PVDF membrane with hydroxyl and carboxyl groups obtained in step (2) in a Ag@TiO2 suspension to fully adsorb Ag@TiO2, then taking it out and rinsing it with water for later use; (4) immersing the PVDF membrane adsorbed with Ag@TiO2 obtained in step (3) in a sodium alginate solution to fully adsorb the sodium alginate, then taking it out and rinsing it with water for later use; (5) Repeat steps (3) and (4) and make the outermost layer Ag@TiO2 to obtain a surface-modified PVDF membrane.

2. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (1), the mass ratio of titanium sulfate to silver nitrate and PVP is 48:0.68:

1.

3. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (2), in the mixed aqueous solution of KOH and KMnO4, the concentration of KOH is 2 mol / L, and the concentration of KMnO4 is 0.2 mol / L.

4. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (2), the reaction temperature of the alkali treatment and oxidation is 50° C., and the reaction time is 0.5 h.

5. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (3), the preparation method of the Ag@TiO2 suspension is: add the Ag@TiO2 obtained in step (1) into water, adjust the pH to 2.0-2.2 with HCl, and ultrasonically disperse for 0.5h to obtain; in the Ag@TiO2 suspension, the concentration of Ag@TiO2 is 2g / L.

6. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (3), the PVDF membrane with hydroxyl and carboxyl groups is immersed in the Ag@TiO2 suspension for 0.5 h.

7. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (4), the sodium alginate solution is prepared by dissolving sodium alginate in a 0.5 mol / L sodium chloride solution; the concentration of sodium alginate in the sodium alginate solution is 2 g / L.

8. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (4), the PVDF membrane adsorbed with Ag@TiO2 is immersed in the sodium alginate solution for 0.5 h.

9. The surface self-assembly modification method for improving the hydrophilicity of polyvinylidene fluoride hollow fiber membrane according to claim 1, characterized in that: In step (5), the outermost layer of the surface-modified PVDF membrane obtained is Ag@TiO2, and step (3) is repeated three times.

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