CN113941259A

CN113941259A - Preparation method of high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification functions

Info

Publication number: CN113941259A
Application number: CN202111246133.3A
Authority: CN
Inventors: 陈英波; 赵冰磊; 王传风
Original assignee: Tianjin Polytechnic University
Current assignee: Tianjin Polytechnic University
Priority date: 2021-10-26
Filing date: 2021-10-26
Publication date: 2022-01-18

Abstract

The invention provides a high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and surface grafting hydrophilic modificationThe preparation method comprises the steps of blending polyacrylonitrile and other high molecular polymers, then carrying out phase inversion, further hydrolyzing and chemically grafting to prepare the anti-fouling ultrafiltration membrane, wherein the hydrolysis and chemical grafting method can be used for preparing the functionalized TiO₂The nano particles are fixed on the surface of the membrane, the phenomenon of excessive swelling of polyacrylonitrile in the hydrolysis process can be solved by the blending membrane, and the prepared composite ultrafiltration membrane has high pure water flux, good membrane surface hydrophilicity, strong anti-fouling performance, stable surface structure and long-term stable operation.

Description

Preparation method of high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification functions

Technical Field

The invention belongs to the technical field of ultrafiltration membrane preparation, and particularly relates to a preparation method of a high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and surface grafting hydrophilic modification.

Background

Ultrafiltration is a membrane separation technology between microfiltration and nanofiltration, has the aperture range of 2nm-50nm, can effectively remove microorganisms and macromolecular substances in water, has the advantages of small floor area, high efficiency, low energy consumption, environmental protection and the like, and has wide application in the actual water treatment production process.

The membrane pollution is one of the main problems faced by ultrafiltration membranes, and in the water treatment process, microorganisms or organic macromolecules in a water body are adsorbed on the surfaces of the ultrafiltration membranes to form compact pollution layers, so that the water flux is reduced, the treatment efficiency is reduced, the service life of the ultrafiltration membranes is shortened, and the energy consumption and the maintenance cost are increased. In order to overcome the problem of ultrafiltration membrane pollution, common methods include selecting a novel hydrophilic polymer material, doping an inorganic nano material or surface modification and the like.

At present, materials for preparing the ultrafiltration membrane mainly comprise polyvinylidene fluoride, polysulfone, polyether sulfone and other hydrophobic materials, and the materials have good mechanical property, thermal stability and film forming property, but the membrane has poor dirt resistance. Polyacrylonitrile contains a large amount of cyano groups, and is easy to hydrolyze in strong alkali to generate carboxyl, so that the surface of the membrane is more hydrophilic. But has the disadvantages that the polyacrylonitrile membrane is hydrolyzed to generate swelling phenomenon, so that the aperture and the water flux of the polyacrylonitrile membrane are both reduced, and the mechanical property and the stability are reduced. Therefore, the polyacrylonitrile and other high molecular polymers with stable frameworks are blended, the membrane structure is regulated and controlled through compatibility among different polymers, the flux of the membrane is improved, meanwhile, the polyacrylonitrile with better hydrophilicity can be segregated to the surface of the membrane at the moment of phase inversion, a large amount of cyano groups appear on the surface of the membrane, the hydrophilicity and the dirt resistance of the surface of the membrane are improved, and more reaction sites are provided for further reaction. Different polymer molecular chains are mutually wound to form a stable interpenetrating structure, and the structure effectively prevents polyacrylonitrile from swelling in the hydrolysis process, so that the mechanical property of the composite membrane can be improved while the pollution resistance is not lost.

To further improve the hydrophilicity and anti-fouling properties of ultrafiltration membranes, inorganic nanomaterials are also commonly incorporated into ultrafiltration membranes. The hydrophilic inorganic material is easy to form hydrogen bond with water molecule to form hydration layer on the membrane surface for blocking microbe and waterMacromolecular substances are adsorbed on the surface of the membrane, so that the anti-fouling performance of the membrane is improved. Titanium dioxide (TiO)₂) The titanium dioxide is an inorganic nano particle with particularly good hydrophilicity, contains a plurality of hydroxyl groups on the surface, is easy to form hydrogen bond action with water molecules, has good dispersibility in water, has the characteristics of low price, environmental protection and the like compared with hydrophilic inorganic materials such as graphene oxide, molybdenum disulfide and the like, and is widely applied to hydrophilic modification of a polymeric membrane. Much research has been conducted on TiO₂Blending with polymer to improve the permeation flux and anti-fouling performance of the membrane, but TiO₂The compatibility with organic matters is poor, and the agglomeration phenomenon is easy to occur, so that the membrane performance is reduced. To TiO 2₂The nano particles are subjected to surface treatment and then blended, so that the agglomeration phenomenon of the nano particles in a polymer can be improved, the flux and the stain resistance of an ultrafiltration membrane are improved, but the agglomeration phenomenon of the nano particles still occurs when the content of the nano particles is increased. Surface coating is also often carried out with TiO₂The nanometer particle improves the performance of the ultrafiltration membrane, Davari and the like coat a poly-dopamine layer on a polyether sulfone support membrane, and then TiO is deposited₂Nanoparticles of TiO by adhesion₂The nanoparticles are firmly fixed on the membrane surface, and the adhered TiO₂The nano particles are unevenly distributed and laminated, the anti-fouling performance of the composite membrane prepared by the method is greatly improved, but the polydopamine coating is compact, so that the flux of the membrane is relatively small. Therefore, the method has great significance for the water treatment industry by improving the flux and the dirt resistance of the ultrafiltration membrane at the same time. The surface grafting can fix the nano particles on the surface of the membrane, and can also effectively solve the phenomena of agglomeration and performance reduction, including plasma treatment grafting, chemical grafting and the like. Chi et al plasma treated a Polytetrafluoroethylene (PTFE) membrane with polyacrylic acid as a bridging and finally grafted TiO functional₂The preparation conditions of the particles are harsh, and free radicals generated on the surface of the membrane subjected to plasma treatment are easy to reduce and disappear, so that the polyacrylic acid grafting content is low, and the anti-fouling performance of the membrane is further reduced. The research shows that the surface chemical grafting has the advantages of strong covalent bond between the functional groups on the surfaces of the nano particles and the membrane, stable structure, difficult agglomeration and the likeThe method can be used for modifying an antifouling ultrafiltration membrane, but most ultrafiltration membranes lack reaction sites on the surface, so the research on the aspect is less.

Disclosure of Invention

In order to solve the technical problems, the invention provides a preparation method of a high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and surface grafting hydrophilic modification. The invention blends polymers with different proportions to regulate the membrane pore structure, prepares a high-flux ultrafiltration membrane, solves the phenomenon of excessive swelling of polyacrylonitrile in the hydrolysis process due to an interpenetrating structure formed by different polymer molecular chains, and keeps the membrane pore structure and the performance stable. Firstly adopts the hydrolysis and chemical grafting method to carry out the functionalization of TiO₂The nano particles are fixed on the surface of the membrane, so that one-to-one grafting reaction on the surface of the membrane is realized, and the surface agglomeration phenomenon is solved. During the film forming process, cyano groups are segregated to the surface of the film, hydrolyzed, chemically grafted and modified, and multiple hydrophilic effects are superposed. The prepared composite ultrafiltration membrane has excellent mechanical property, high pure water flux, good membrane surface hydrophilicity, strong anti-fouling performance and stable surface structure, graft particles are not easy to fall off, and the composite ultrafiltration membrane can stably run for a long time.

Therefore, the technical scheme of the invention is as follows:

1) functionalized TiO₂The preparation of (1): mixing certain amount of silane coupling agent and TiO₂Adding nano particles into ultrapure water, quickly adding 1-5 mL of triethylamine, magnetically stirring in a dark place, heating in a water bath for 6h, wherein the heating temperature is 45-90 ℃, centrifuging after the reaction is finished, washing with deionized water for several times until the eluate is neutral, and drying in vacuum to obtain the functionalized TiO₂Nanoparticles.

2) Preparing an ultrafiltration membrane: adding 1-4 wt% of pore-forming agent into 74-86 wt% of solvent, performing ultrasonic dispersion to obtain uniformly dispersed solution, then adding Polyacrylonitrile (PAN) and another polymer for blending, heating in a water bath, and performing mechanical stirring reaction for 4-12 hours, wherein the water bath temperature is 45-90 ℃, the mechanical stirring speed is 100-400 r/min, performing vacuum defoaming after the reaction is completed, coating a flat membrane by using an automatic membrane coating machine, and then soaking in deionized water.

3) And (3) hydrolysis of the ultrafiltration membrane: soaking the prepared membrane in strong base with different concentrations for different time, and washing the hydrolysis membrane with deionized water until the eluate is neutral.

4) Preparation of a grafted ultrafiltration membrane: soaking the hydrolysis membrane in ultrapure water, adding a certain amount of 1- (3-dimethylaminopropyl) -3-hexylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), reacting for 10-60 min, and then, reacting the functionalized TiO₂And adding the nanoparticles into the solution, magnetically stirring, reacting for 12-24 hours in a dark place, and washing the surface with deionized water.

Further, the silane coupling agent in the step 1) is one of 3-aminopropyl-triethoxysilane, 3-aminopropyl-trimethoxysilane and N-beta- (aminoethyl) -gamma-aminopropyltrimethoxysilane.

Further, the silane coupling agent and TiO described in step 1)₂The mass ratio is 1: 1-5.

Further, in the step 2), the pore-forming agent is one or a mixture of several of polyvinylpyrrolidone (PVP), lithium chloride (LiCl) and polyvinyl alcohol (PEG), and the solvent is one of N, N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP).

Further, the other polymer in the step 2) is one of Polysulfone (PS), Polyethersulfone (PES) and polyvinylidene fluoride (PVDF).

Further, the blending proportion of the other polymer in the step 2) is 0-100%.

Further, in the step 3), the strong base is one of sodium hydroxide (NaOH) and potassium hydroxide (KOH).

Further, the concentration of the strong alkali in the step 3) is 0.5-3.5 mol/L, and the soaking time is 0.5-8 h.

Further, the mass ratio of the EDC to the NHS in the step 4) is 1-5: 1.

Further, the content of the functionalized titanium dioxide in the solution in the step 4) is 0.1-2.5 g/L.

Compared with the prior art, the invention has the following advantages:

1) the membrane structure is regulated and controlled by a method of blending polyacrylonitrile and another polymer, so that the phenomenon of excessive swelling of polyacrylonitrile in the hydrolysis process is solved, the pore structure and the performance of the membrane are kept stable, and the flux of the ultrafiltration membrane is improved.

2) Firstly adopts the hydrolysis and chemical grafting method to carry out the functionalization of TiO₂The nano particles are fixed on the surface of the membrane, so that the problems of hydrophilic inorganic nano particles agglomeration and easy falling are solved.

3) The ultrafiltration membrane prepared by the method has high flux, good hydrophilicity, strong anti-fouling performance and stable surface structure, can stably run for a long time, and the used TiO₂The particles are green and environment-friendly, have low price and good market prospect.

Drawings

FIG. 1 shows TiO obtained in example 1₂And functionalized TiO₂A fourier infrared map of the nanoparticles;

FIG. 2 shows the surface-grafted functionalized TiO obtained in example 1₂Scanning electron microscope images of the surface of the ultrafiltration membrane;

Detailed Description

The invention is further described below with reference to the accompanying drawings and examples.

Examples 1 to 5

The preparation process is basically the same, and the difference is only that: changing the soaking time in the step 3).

1) Functionalized TiO₂The preparation of (1): 5g of 3-aminopropyl-triethoxysilane and 5g of TiO₂Adding nano particles into 500mL of ultrapure water, rapidly adding 2mL of triethylamine, magnetically stirring in a dark place, heating in a water bath for 6h, wherein the heating temperature is 80 ℃, centrifuging after the reaction is finished, washing for 3 times by using deionized water until the eluate is neutral, and drying in vacuum to obtain the functionalized TiO₂Nanoparticles.

2) Preparing an ultrafiltration membrane: adding 1 wt% of PVP into 79 wt% of DMAc solvent, performing ultrasonic dispersion for 2h to obtain a uniformly dispersed solution, then adding PAN and PES to perform blending, wherein the blending ratio of the PAN and the PES is 2: 8, the total content is 20 wt%, the water bath temperature is 60 ℃, the mechanical stirring speed is 250r/min, performing vacuum defoaming after the reaction is finished, coating a flat membrane by using an automatic membrane coating machine, and then soaking the flat membrane in deionized water.

3) And (3) hydrolysis of the ultrafiltration membrane: the prepared membrane was soaked in 2mol/L NaOH solution for the time shown in Table 1, and the hydrolyzed membrane was rinsed with deionized water until the eluate was neutral.

4) Preparation of a grafted ultrafiltration membrane: the hydrolyzed membrane was soaked in 500mL of ultrapure water, 1g EDC and 0.5g NHS were added, the reaction was carried out for 30min, and then 0.5g functionalized TiO was added₂Adding the nano particles into the solution, magnetically stirring, reacting for 24 hours in a dark place, and washing the surface with deionized water.

Functionalized TiO prepared in example 1₂The nano particles are subjected to infrared characterization, and an absorption peak of-NH 2 at 3250cm-1, an absorption peak of C-N at 1100cm-1 and a characteristic absorption peak of Si-O-Ti at 1020cm-1 can be obtained from the graph shown in figure 1. FIG. 2 is an SEM electron micrograph of the surface of the ultrafiltration membrane, and it can be seen from FIG. 2 that a large amount of functionalized TiO exists on the surface of the ultrafiltration membrane₂Nanoparticles, indicating successful preparation of grafted ultrafiltration membranes.

TABLE 1 EXAMPLES 1 to 5 specific embodiments

From examples 1 to 5, it is known that when the membrane is soaked in NaOH for 3 hours, the water contact angle of the membrane surface is 39 degrees at the minimum, the hydrophilicity is the best, and the difference between the water flux and the retention of the BSA solution is not large.

Examples 6 to 8

The preparation process is basically the same, and the difference is only that: varying the concentration of NaOH in step 3).

1) Functionalized TiO₂The preparation of (1): 5g of 3-aminopropyl-triethoxysilane and 5g of TiO₂Adding the nanoparticles into 500mL of ultrapure water, rapidly adding 2mL of triethylamine, magnetically stirring in a dark place, heating in a water bath for 6h at 80 ℃, centrifuging after the reaction is finished, and washing with deionized water3 times until the eluate is neutral, and vacuum drying to obtain the functionalized TiO₂Nanoparticles.

3) And (3) hydrolysis of the ultrafiltration membrane: the prepared membrane was soaked in NaOH solution of the concentration shown in table 2 for 3h, and the hydrolyzed membrane was washed with deionized water until the eluate was neutral.

TABLE 2 examples 6 to 8 specific embodiments

As can be seen from examples 6 to 8, when the concentration of NaOH was 2mol/L, the water contact angle of the membrane surface was 40 ℃ or less, the hydrophilicity was the best, and the flux was reduced to 381L/m²H.bar, the retention of BSA solution reaches a maximum of 96.1%.

Example 9

1) Preparing an ultrafiltration membrane: adding 1 wt% of PVP into 79 wt% of DMAc solvent, performing ultrasonic dispersion for 2h to obtain a uniformly dispersed solution, then adding 20 wt% of PES, heating in a water bath, mechanically stirring for reaction for 12h, wherein the water bath temperature is 60 ℃, the mechanical stirring speed is 250r/min, performing vacuum defoaming after the reaction is finished, coating a flat membrane by using an automatic coating machine, and then soaking in deionized water.

Example 10

1) Preparing an ultrafiltration membrane: adding 1 wt% of PVP into 79 wt% of DMAc solvent, performing ultrasonic dispersion for 2h to obtain a uniformly dispersed solution, then adding PAN and PES to perform blending, wherein the blending ratio of the PAN and the PES is 2: 8, the total content is 20 wt%, heating in a water bath, performing mechanical stirring reaction for 12h, wherein the water bath temperature is 60 ℃, the mechanical stirring speed is 250r/min, performing vacuum defoaming after the reaction is finished, coating a flat membrane by using an automatic membrane coating machine, and then soaking in deionized water.

The water contact angle, pure water flux, BSA rejection, and flux recovery rate were measured for examples 7, 9, and 10, and the data are shown in table 3, and the membrane prepared in example 10 was subjected to a long-term stability test to observe the change in flux.

Table 3 examples 7, 9, 10 specific embodiments

By comparison, example 7 gave the best overall performance, and in long-term testing the initial flux was 468L/m²H.bar, reduced by 14%, tested 24h flux stabilized at 402L/m²H.bar is essentially unchanged.

Although the present invention has been described in connection with the accompanying drawings and the accompanying tables, the present invention is not limited thereto, and various modifications made by the method concept and technical solution of the present invention are within the scope of the present invention.

Claims

1. A preparation method of a high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification is characterized by comprising the following steps:

2) Preparing an ultrafiltration membrane: adding 1-4 wt% of pore-forming agent into 74-86 wt% of solvent, performing ultrasonic dispersion to obtain uniformly dispersed solution, then adding Polyacrylonitrile (PAN) and another high polymer for blending, heating in a water bath, and performing mechanical stirring reaction for 4-12 hours, wherein the water bath temperature is 45-90 ℃, the mechanical stirring speed is 100-400 r/min, performing vacuum defoaming after the reaction is completed, coating a flat membrane by using an automatic membrane coating machine, and then soaking in deionized water.

3) And (3) hydrolysis of the ultrafiltration membrane: soaking the prepared membrane in strong alkali with different concentrations for different time, and washing the hydrolysis membrane with deionized water until the eluate is neutral.

2. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: the silane coupling agent in the step 1) is one of 3-aminopropyl-triethoxysilane, 3-aminopropyl-trimethoxysilane and N-beta- (aminoethyl) -gamma-aminopropyltrimethoxysilane.

3. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: silane coupling agent and TiO described in step 1)₂The mass ratio is 1: 1-5.

4. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: in the step 2), the pore-foaming agent is one or a mixture of several of polyvinylpyrrolidone (PVP), lithium chloride (LiCl) and polyvinyl alcohol (PEG), and the solvent is one of N, N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP).

5. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: the other polymer in the step 2) is one of Polysulfone (PS), Polyethersulfone (PES) and polyvinylidene fluoride (PVDF).

6. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: the blending proportion of the other polymer in the step 2) is 0-100%.

7. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: in the step 3), the strong base is one of sodium hydroxide (NaOH) and potassium hydroxide (KOH).

8. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: the concentration of the strong alkali in the step 3) is 0.5-3.5 mol/L, and the soaking time is 0.5-8 h.

9. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: the mass ratio of the EDC to the NHS in the step 4) is 1-5: 1.

10. The preparation method of the high-flux anti-fouling ultrafiltration membrane with membrane structure regulation and hydrophilic modification as claimed in claim 1, is characterized in that: the content of the functionalized titanium dioxide in the solution in the step 4) is 0.1 g/L-2.5 g/L.