WO2024016671A1 - Polymeric nanofiltration membrane, and preparation therefor and use thereof - Google Patents

Abstract

A polymeric nanofiltration membrane, and the preparation therefor and a use thereof. The polymeric nanofiltration membrane contains hydrophilic nano composite material nitrogen-doped hollow porous carbon spheres. A preparation process for the polymeric nanofiltration membrane is: adding polyether sulfone, polyvinylpyrrolidone, and the nitrogen-doped hollow porous carbon spheres into a solvent, carrying out ultrasonic stirring to obtain a homogenous suspension, then sequentially carrying out baking and ultrasonic treatment to obtain a homogenous and bubble-free suspension, pouring the homogenous and bubble-free suspension on a glass plate for casting in a thin membrane, immediately soaking the thin membrane in distilled water for coagulating bath, separating the thin membrane from the glass plate after the thin membrane is solidified, drying and storing the thin membrane between sheets.

Description

A polymeric nanofiltration membrane and its preparation and application Technical field

The present invention relates to the technical fields of industrial wastewater treatment and membrane technology, and in particular to a polymeric nanofiltration membrane and its preparation and application.

Background technique

In today's world, water shortage and water pollution are serious environmental problems faced by many countries and governments. Industrial wastewater is one of the known sources of huge water pollution because industrial wastewater discharges include complex pollutant compositions and persistent toxic substances (such as heavy metals and organic dyes). Textile manufacturers are among the industries that generate large amounts of high-salt dye wastewater, which contains toxic heavy metals such as cadmium and lead. A large amount of salt is used in the textile industry, mainly Glauber's salt (Na ₂ SO ₄ ) or sodium chloride (NaCl), to resolve the negative zeta potential of cotton, promote and increase the absorption of dyes, and accelerate the interaction between dyes and cotton. However, the use of traditional adsorption, chemical degradation, biological treatment and other methods to treat complex wastewater is not always effective.

In recent years, membrane technology has shown good results and feedback in industrial wastewater treatment. Among membrane-based water purification technologies, nanofiltration (NF) membranes not only have a high rejection rate for dye molecules and divalent salts, but also have the advantages of low energy consumption, compact design, no need for phase changes, and simple operation. . However, the main problem in the application of nanofiltration membranes is membrane fouling, which will cause higher operating costs and thus hinder the commercialization of nanofiltration membranes.

Contents of the invention

In view of the above shortcomings of the prior art, the purpose of the present invention is to provide a polymeric nanofiltration membrane and its preparation and application. By mixing hydrophilic nanomaterials in the polymeric nanofiltration membrane, the hydrophilicity and negative impact of the membrane surface can be increased. charge density, thereby solving the membrane fouling problem that exists in the application of existing nanofiltration membranes.

In order to achieve the above objects and other related objects, the first aspect of the present invention provides a polymeric nanofiltration membrane, the polymeric nanofiltration membrane contains a hydrophilic nanocomposite material, and the hydrophilic nanocomposite material is a nitrogen-doped hollow porous membrane. carbon balls.

Further, the polymeric nanofiltration membrane contains 0 to 0.5 wt% nitrogen-doped hollow porous carbon spheres, excluding 0; preferably, the polymeric nanofiltration membrane contains 0.20 to 0.30 wt% nitrogen-doped hollow porous carbon spheres. ; More preferably, the polymeric nanofiltration membrane contains 0.25wt% nitrogen-doped hollow porous carbon spheres.

Further, the preparation method of the nitrogen-doped hollow porous carbon spheres includes the following steps:

(1) Mix the ammonium salt solution or ammonia water with ethanol and water and stir evenly, then add ethyl orthosilicate, stir and react under a protective gas atmosphere until white colloidal silica balls appear;

(2) Centrifuge the reaction solution obtained in step (1), collect the silica spheres, clean the silica spheres and then vacuum-dry them to obtain a silica template;

(3) Add the silica template obtained in step (2) to the ethanol/water solution, and disperse and mix evenly by ultrasonic;

(4) Add resorcinol, methanol solution, ethyl orthosilicate, and ethylenediamine to the mixture obtained in step (3), mix evenly, and stir the reaction under a protective gas atmosphere to completely cover the negatively charged mixture. Oxidize the surface of the silica sphere to obtain SiO ₂ @N-RF, which is then washed, centrifuged, and dried;

(5) Heat and carbonize the SiO ₂ @N-RF dried in step (4) under a protective gas atmosphere, and then gradually cool to room temperature;

(6) Etch the product obtained in step (5) with HF aqueous solution to remove the silicon dioxide template to obtain the nitrogen-doped hollow porous carbon spheres.

Further, in the step (1), the volume ratio of ammonium salt solution/ammonia water, ethanol, water and ethyl orthosilicate is 2.5~5:35~40:4~6:4~6, preferably 3.1~4.1 :37.1～38.1:4.6～5.4: 4.6～5.4. The above "/" means "or".

Further, in the step (1), the concentration of the ammonium salt solution or ammonia water is 15 to 25%.

Further, in the step (1), the ammonium salt is selected from any one of ammonium chloride, ammonium sulfate and ammonium carbonate.

Further, in the step (1), after adding ethyl orthosilicate, the reaction is stirred for 1 to 2 hours under a protective gas atmosphere until white colloidal silica balls appear.

Further, the step (1) is performed at normal temperature.

Further, in the steps (3) and (4), the protective gas is selected from nitrogen or argon.

Further, in the step (2), absolute ethanol is used to clean the silica balls, and the number of cleaning times is no less than three times.

Further, in the step (2), the vacuum drying temperature is 65-75°C, preferably 68-72°C.

Furthermore, in the step (2), the vacuum drying time is 20 to 28 hours, preferably 22 to 26 hours.

Further, in the step (3), the volume ratio of ethanol and water in the ethanol/water solution is 6.5-7.5:2.5-3.5, preferably 6.8-7.2:2.8-3.2.

Further, in the step (3), the ultrasonic dispersion time is 25 to 35 minutes.

Further, in the steps (3) and (4), the mass ratio of silica template and resorcinol is 1:0.25~0.35, and the volume ratio of methanol solution, ethyl orthosilicate, and ethylenediamine is 0.35. ~0.60:0.2~0.5:0.5~0.7.

Further, in the step (4), the methanol solution adopts 35% to 40% methanol aqueous solution, preferably 37% methanol aqueous solution.

Further, in the step (4), the stirring reaction temperature is 25-35°C.

Further, in the step (4), the stirring reaction time is 0.5 to 1 h.

Further, in the step (4), water and ethanol are used for washing and centrifugation in sequence, and the washing and centrifugation are performed at least three times.

Further, in the step (4), the drying temperature is 75-85°C, preferably 78-82°C.

Further, in the step (4), the drying time is 10 to 15 hours, preferably 11 to 14 hours.

Further, in the step (5), the heating carbonization temperature is 780-820°C, preferably 790-810°C.

Furthermore, in the step (5), heating is performed using programmed temperature rise, and the heating rate is 2.5-3.5°C/min, preferably 2.8-3.2°C/min.

Further, in the step (5), the heating and carbonization time is 7 to 9 hours, preferably 7.5 to 8.5 hours.

Further, in the step (6), the concentration of the HF aqueous solution is 9-11%, preferably 10%.

It should be noted that the water in the present invention is deionized water.

A second aspect of the present invention provides a preparation process for the polymeric nanofiltration membrane according to the first aspect, which includes the following steps:

Polyethersulfone, polyvinylpyrrolidone, and the nitrogen-doped hollow porous carbon spheres are added to the solvent and stirred ultrasonically to obtain a uniform suspension; the suspension is sequentially baked and ultrasonic treated to obtain a uniform and bubble-free suspension. Suspension; pour the uniform and bubble-free suspension onto a glass plate, cast it into a film, and then immediately soak the film in a coagulation bath in distilled water. After the film solidifies, separate the film from the glass plate, dry and store on paper Between pages, the preparation of the polymeric nanofiltration membrane is completed.

In the preparation process of the present invention, the purpose of baking the suspension is to remove bubbles in the suspension; the main purpose of subjecting the baked suspension to ultrasonic treatment is to help the nitrogen in the water phase to dope the hollow porous The carbon ball particles maintain a stable dispersion state, and at the same time, the bubbles in the suspension are completely removed; after casting into a film, the film needs to be immediately immersed in distilled water for a coagulation bath to start the phase transformation process.

Further, the solvent is selected from any one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

Further, the mass percentage concentrations of the polyethersulfone, polyvinylpyrrolidone, and nitrogen-doped hollow porous carbon spheres in the suspension are 18 to 25 wt%, 0.5 to 2 wt%, and 0 to 0.5 wt%, wherein nitrogen doped The mass percent concentration of the hollow porous carbon spheres is not 0; preferably, the mass percent concentration of the polyethersulfone, polyvinylpyrrolidone, and nitrogen-doped hollow porous carbon spheres in the suspension is 20 to 22 wt%, 0.8 to 1.2wt%, 0.2~0.3wt%.

Further, when the suspension is obtained by ultrasonic stirring, the ultrasonic intensity is 12-24W/m ² , the ultrasonic time is 30-40min, and the stirring speed is 125-175rad/min.

Further, before baking the suspension, it needs to be placed at room temperature for 22 to 26 hours.

Furthermore, the baking temperature is 45-55°C, and the baking time is 1.5-2.5 hours.

Furthermore, after baking, the ultrasonic intensity is 20-25W/m ² and the ultrasonic time is 15-20 minutes.

Further, the uniform and bubble-free suspension was poured onto a glass plate and cast into a thin film.

Furthermore, the thickness of the film is 140-160 μm, preferably 146-151 μm.

A third aspect of the present invention provides the application of the polymeric nanofiltration membrane according to the first aspect and/or the polymeric nanofiltration membrane prepared according to the method according to the second aspect in industrial wastewater treatment.

As mentioned above, the polymeric nanofiltration membrane of the present invention and its preparation and application have the following beneficial effects:

The present invention mixes hydrophilic nanomaterials in the polymeric nanofiltration membrane to increase the hydrophilicity and negative charge density of the membrane surface, thereby effectively and simply solving the membrane fouling problem that exists when traditional nanofiltration membranes are used. At the same time, it can also improve The water flux, solute interception and mechanical strength of the nanofiltration membrane; the present invention uses nitrogen-doped hollow porous carbon spheres (N-HPCS) as the hydrophilic nanomaterial. N-HPCS can use its special hollow porous structure and high affinity Water-based, effectively improves the anti-pollution ability and water flux of nanofiltration membranes.

Description of drawings

Figure 1 shows a graph showing the treated wastewater quality index and membrane flux in Example 7 of the present invention.

Detailed ways

The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

The main factors affecting membrane fouling phenomena are related to membrane surface properties, such as hydrophilicity, charge and roughness. The main way to mitigate membrane fouling is to increase surface hydrophilicity and negative charge density, while reducing surface roughness can improve fouling resistance because most fouling is naturally hydrophobic and negatively charged. Therefore, the present invention proposes a technical solution of mixing hydrophilic nanomaterials in polymeric nanofiltration membranes, which can effectively and simply alleviate the problem of membrane fouling, while also improving the water flux, solute retention and mechanical strength of the nanofiltration membrane. .

Nitrogen-doped hollow porous carbon spheres (N-HPCS) are hollow porous carbon spheres (HPCS) that integrate macropores (central cavity) and mesopores (a large number of nanometer short channels in the shell) into one unit. They have low density. , surface functions, fully exposed active sites, high surface to volume ratio, especially high permeability and high mass transfer and other outstanding features. Based on the structural characteristics of HPCS, the present invention prepares N-HPCS nanocomposite materials by doping electronegative heteroatoms such as nitrogen (N) into it, thereby increasing the negative charge density on the surface of HPCS, thereby improving its hydrophilicity. Based on this, the present invention incorporates N-HPCS into the nanofiltration membrane to improve the anti-pollution ability and water flux of the nanofiltration membrane with its special hollow porous structure and high hydrophilicity.

The present invention adopts a phase conversion method to prepare polymeric nanofiltration membranes containing N-HPCS nanocomposite materials.

The film making process of the present invention is as follows:

Polyethersulfone, polyvinylpyrrolidone, and the nitrogen-doped hollow porous carbon spheres are added to the solvent and stirred ultrasonically to obtain a uniform suspension; the suspension is sequentially baked and ultrasonic treated to obtain a uniform and bubble-free suspension. Suspension; pour the uniform and bubble-free suspension onto a glass plate, cast it into a film, and then immediately soak the film in a coagulation bath in distilled water. After the film solidifies, separate the film from the glass plate, dry and store on paper Between pages, the preparation of the polymeric nanofiltration membrane is completed.

In the preparation process of the present invention, the purpose of baking the suspension is to remove bubbles in the suspension; the main purpose of subjecting the baked suspension to ultrasonic treatment is to help the nitrogen in the water phase to dope the hollow porous The carbon ball particles maintain a stable dispersion state, and at the same time, the bubbles in the suspension are completely removed; after casting into a film, the film needs to be immediately immersed in distilled water for a coagulation bath to start the phase transformation process.

Wherein, the solvent is selected from any one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

Wherein, the mass percentage concentration of polyethersulfone, polyvinylpyrrolidone and nitrogen-doped hollow porous carbon spheres in the suspension is 18-25wt%, 0.5-2wt%, 0-0.5wt%, wherein nitrogen-doped hollow porous carbon spheres are The mass percent concentration of the hollow porous carbon spheres is not 0; preferably, the mass percent concentration of the polyethersulfone, polyvinylpyrrolidone, and nitrogen-doped hollow porous carbon spheres in the suspension is 20 to 22 wt%, 0.8 to 1.2wt%, 0.2~0.3wt%.

Wherein, when the suspension is obtained by ultrasonic stirring, the ultrasonic intensity is 12-24W/m ² , the ultrasonic time is 30-40min, and the stirring speed is 125-175rad/min.

Before baking the suspension, it needs to be placed at room temperature for 22 to 26 hours.

Among them, the baking temperature is 45~55℃, and the baking time is 1.5~2.5h.

Among them, after baking, the ultrasonic intensity is 20-25W/m ² and the ultrasonic time is 15-20 minutes.

In it, a homogeneous and bubble-free suspension is poured onto a glass plate and cast into a thin film.

Wherein, the thickness of the film is 140-160 μm, preferably 146-151 μm.

The N-HPCS nanocomposite material in the present invention is nitrogen-doped hollow porous carbon spheres (N-HPCS). The preparation method includes the following steps:

(1) Mix the ammonium salt solution or ammonia water with ethanol and water and stir evenly, then add ethyl orthosilicate, stir and react under a protective gas atmosphere until white colloidal silica balls appear;

(2) Centrifuge the reaction solution obtained in step (1), collect the silica spheres, clean the silica spheres and then vacuum-dry them to obtain a silica template;

(3) Add the silica template obtained in step (2) to the ethanol/water solution, and disperse and mix evenly by ultrasonic;

(4) Add resorcinol, methanol, ethyl orthosilicate, and ethylenediamine to the mixture obtained in step (3), mix evenly, and then stir the reaction under a protective gas atmosphere so that the negatively charged mixture is completely covered with carbon dioxide. On the surface of the silicon sphere, SiO ₂ @N- RF, then washed, centrifuged, and dried;

(5) Heat and carbonize the SiO ₂ @N-RF dried in step (4) under a protective gas atmosphere, and then gradually cool to room temperature;

(6) Etch the product obtained in step (5) with HF aqueous solution to remove the silicon dioxide template to obtain the nitrogen-doped hollow porous carbon spheres.

Wherein, in the step (1), the volume ratio of ammonium salt solution/ammonia water, ethanol, water and ethyl orthosilicate is 2.5~5:35~40:4~6:4~6, preferably 3.1~4.1 :37.1～38.1:4.6～5.4: 4.6～5.4. The above "/" means "or".

Wherein, in the step (1), the concentration of the ammonium salt solution or ammonia water is 15 to 25%.

Wherein, in the step (1), the ammonium salt is selected from any one of ammonium chloride, ammonium sulfate and ammonium carbonate.

Wherein, in the step (1), after adding ethyl orthosilicate, the reaction is stirred for 1 to 2 hours under a protective gas atmosphere until white colloidal silica balls appear.

Wherein, the step (1) is carried out at normal temperature.

Wherein, in the steps (3) and (4), the protective gas is selected from nitrogen or argon.

Wherein, in the step (2), absolute ethanol is used to clean the silica balls, and the number of cleaning times is no less than three times.

Wherein, in the step (2), the vacuum drying temperature is 65-75°C, and the vacuum drying time is 20-28h, preferably 68-72°C, 22-26h.

Wherein, in the step (3), the volume ratio of ethanol and water in the ethanol/water solution is 6.5-7.5:2.5-3.5, preferably 6.8-7.2:2.8-3.2.

Wherein, in the step (3), the ultrasonic dispersion time is 25 to 35 minutes.

Wherein, in the steps (3) and (4), the mass ratio of silica template and resorcinol is 1:0.25~0.35, and the volume ratio of methanol solution, ethyl orthosilicate and ethylenediamine is 0.35 ~0.60:0.2~0.5:0.5~0.7.

Wherein, in the step (4), the methanol solution adopts 35% to 40% methanol aqueous solution, preferably 37% methanol aqueous solution.

Wherein, in the step (4), the stirring reaction temperature is 25-35°C, and the stirring reaction time is 0.5-1 h.

Wherein, in the step (4), water and ethanol are used to wash and centrifuge in sequence, washing and centrifuging at least three times.

Wherein, in the step (4), the drying temperature is 75-85°C, and the drying time is 10-15h, preferably 78-82°C, 11-14h.

Wherein, in the step (5), the heating carbonization temperature is 780-820°C, and the heating carbonization time is 7-9h, preferably 790-810°C, 7.5-8.5h.

Wherein, in the step (5), programmed temperature rise is used for heating, and the heating rate is 2.5-3.5°C/min, preferably 2.8-3.2°C/min.

Wherein, in the step (6), the concentration of the HF aqueous solution is 9-11%, preferably 10%.

It should be noted that the water in the present invention is deionized water.

The following specific examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to specifically illustrate the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all belong to this invention. protection scope of the invention. The specific process parameters in the following examples are only an example of the appropriate range, that is, those skilled in the art can make selections within the appropriate range through the description herein, and are not limited to the specific values exemplified below.

Example 1

In this example, a nitrogen-doped hollow porous carbon sphere (N-HPCS) was prepared. The specific steps are as follows:

(1) Evenly mix 37.5 mL of ethanol, 3.5 mL of ammonium salt solution and 5 mL of deionized water and stir for 15 minutes;

(2), quickly add 5 mL of tetraethyl orthosilicate (TEOS) to the mixture prepared in (1);

(3) Fill the Erlenmeyer flask with N ₂ at room temperature and stir for 1.5 hours until white colloidal silica balls appear in the Erlenmeyer flask;

(4) Collect the silica balls by centrifugation, wash them three times with absolute ethanol, and then dry them in a vacuum oven at 70°C for 24 hours;

(5). Take 1 g of the SiO ₂ template prepared in (4), add it to a mixture consisting of 140 mL deionized water and 60 mL ethanol solution, and disperse with ultrasonic for 30 minutes and mix;

(6) Add 0.32g resorcinol, 0.48mL 37% methanol solution, 0.3mL tetraethyl orthosilicate (TEOS) and 0.64mL ethylenediamine (as nitrogen source) to the solution obtained in (5), Stir to mix evenly;

(7) Stir the mixture obtained in (6) at 30°C for 45 minutes under N ₂ atmosphere, so that the negatively charged mixture completely covers the surface of the silica sphere to obtain SiO ₂ @N-RF; then wash it with water/ethanol in sequence /Centrifuge three times and dry at 80°C for 12 hours;

(8) Carbonize the dried SiO ₂ @N-RF at 800°C for 8 h at a heating rate of 3°C in an N ₂ atmosphere (20 mL/min), and then gradually cool to room temperature;

(9). Use 10% HF aqueous solution to etch the product obtained in (8) to remove the SiO ₂ template to obtain nitrogen-doped hollow porous carbon spheres (N-HPCS).

Example 2

In this example, a nitrogen-doped hollow porous carbon sphere (N-HPCS) was prepared. The specific steps are as follows:

(1) Evenly mix 35 mL of ethanol, 2.5 mL of ammonium salt solution and 4 mL of deionized water and stir for 15 minutes;

(2), quickly add 4 mL of ethyl orthosilicate (TEOS) to the mixture prepared in (1);

(3) Fill the Erlenmeyer flask with N ₂ at room temperature and stir for 1 to 2 hours until white colloidal silica balls appear in the Erlenmeyer flask;

(4) Collect the silica balls by centrifugation, wash them three times with absolute ethanol, and then dry them in a vacuum oven at 65°C for 26 hours;

(5). Take 1 g of the SiO ₂ template prepared in (4), add it to a mixture consisting of 140 mL deionized water and 60 mL ethanol solution, and disperse with ultrasonic for 25 minutes and mix well;

(6) Add 0.25g resorcinol, 0.35mL 37% methanol solution, 0.25mL tetraethyl orthosilicate (TEOS) and 0.55mL ethylenediamine (as nitrogen source) to the solution obtained in (5), Stir to mix evenly;

(7) Stir the mixture obtained in (6) at 25°C for 1 hour under N ₂ atmosphere, so that the negatively charged mixture completely covers the surface of the silica sphere to obtain SiO ₂ @N-RF; then wash it with water/ethanol in sequence /Centrifuge three times and dry at 75°C for 15h;

(8) Carbonize the dried SiO ₂ @N-RF at 790°C for 8.5h at a heating rate of 2.8°C in an N ₂ atmosphere (20mL/min), and then gradually cool to room temperature;

(9). Use 10% HF aqueous solution to etch the product obtained in (8) to remove the SiO ₂ template to obtain nitrogen-doped hollow porous carbon spheres (N-HPCS).

Example 3

In this example, a nitrogen-doped hollow porous carbon sphere (N-HPCS) was prepared. The specific steps are as follows:

(1) Evenly mix 40 mL of ethanol, 5 mL of ammonium salt solution and 6 mL of deionized water and stir for 20 minutes;

(2), quickly add 6 mL of ethyl orthosilicate (TEOS) to the mixture prepared in (1);

(3) Fill the Erlenmeyer flask with N ₂ at room temperature and stir for 1 hour until white colloidal silica balls appear in the Erlenmeyer flask;

(4) Collect the silica balls by centrifugation, wash them three times with absolute ethanol, and then dry them in a vacuum oven at 75°C for 20 hours;

(5). Take 1 g of the SiO ₂ template prepared in (4), add it to a mixture consisting of 140 mL deionized water and 60 mL ethanol solution, and disperse with ultrasonic for 35 minutes and mix well;

(6) Add 0.35g resorcinol, 0.60mL 37% methanol, 0.5mL tetraethyl orthosilicate (TEOS) and 0.70mL ethylenediamine (as nitrogen source) to the solution obtained in (5), and stir well mixed;

(7) Stir the mixture obtained in (6) at 35°C for 1 hour under N ₂ atmosphere, so that the negatively charged mixture completely covers the surface of the silica sphere to obtain SiO ₂ @N-RF; then wash it with water/ethanol in sequence /Centrifuge three times and dry at 85°C for 10h;

(8) Carbonize the dried SiO ₂ @N-RF at 820°C for 7 h at a heating rate of 3.5°C in an N ₂ atmosphere (20 mL/min), and then gradually cool to room temperature;

(9). Use 10% HF aqueous solution to etch the product obtained in (8) to remove the SiO ₂ template to obtain nitrogen-doped hollow porous carbon spheres (N-HPCS).

Example 4

In this example, a phase conversion method is used to prepare a polymeric nanofiltration membrane containing 0.25wt% nitrogen-doped hollow porous carbon spheres (N-HPCS) nanocomposite. The specific process is as follows:

S1, add 21wt% polyethersulfone (PES), 1wt% polyvinylpyrrolidone (PVP) and 0.25wt% nitrogen-doped hollow porous carbon spheres (using N-HPCS prepared in Example 1) to N,N-dimethyl into acetamide (DMAc) solvent, placed in an ultrasonic generator, and stirred for 35 minutes at an ultrasonic intensity of 20W/ ^m2 and a rotation speed of 150rad/min to obtain a uniform suspension.

S2, place the uniform suspension prepared in step S1 at room temperature for 24 hours and set aside.

S3: Place the suspension in step S2 in an oven at 50°C for 2 hours to remove bubbles in the suspension.

S4. Place the suspension treated in step S3 in a tank ultrasonic wave and treat it for 18 minutes at an ultrasonic intensity of 22W/ ^m2 to help the N-HPCS particles in the water phase maintain a stable dispersion state and at the same time remove the bubbles in the suspension. Completely eliminated.

S5, pour the uniform and bubble-free suspension obtained in step S4 onto the glass plate, and cast the suspension into a 150 μm thick film through an adjustable casting knife.

S6, in order to start the phase conversion process, immediately immerse the film obtained in step S5 in the distilled water coagulation bath. After the film solidifies, the film is separated from the glass plate, dried and stored between paper sheets to complete the preparation of the polymeric nanofiltration membrane.

Example 5

In this example, a phase conversion method is used to prepare a polymeric nanofiltration membrane containing 0.10wt% nitrogen-doped hollow porous carbon spheres (N-HPCS) nanocomposite. The specific process is as follows:

S1, add 20wt% polyethersulfone (PES), 0.8wt% polyvinylpyrrolidone (PVP) and 0.10wt% nitrogen-doped hollow porous carbon spheres (using N-HPCS prepared in Example 1) to N,N-di In methylacetamide (DMAc) solvent, place it in an ultrasonic generator, stir for 40 minutes at an ultrasonic intensity of 12W/ ^m2 and a rotation speed of 175rad/min to obtain a uniform suspension.

S2, place the uniform suspension prepared in step S1 at room temperature for 22 hours and set aside.

S3: Place the suspension in step S2 in an oven at 45°C for 2.5 hours to remove bubbles in the suspension.

S4. Place the suspension treated in step S3 in a tank ultrasonic wave and treat it for 20 minutes at an ultrasonic intensity of 20W/ ^m2 to help the N-HPCS particles in the water phase maintain a stable dispersion state and at the same time remove the bubbles in the suspension. Completely eliminated.

S5, pour the uniform and bubble-free suspension obtained in step S4 onto the glass plate, and cast the suspension into a 140 μm thick film through an adjustable casting knife.

S6, in order to start the phase conversion process, immediately soak the film obtained in step S5 in the distilled water coagulation bath. After the film solidifies, the film is separated from the glass plate, dried and stored between paper sheets to complete the preparation of the polymeric nanofiltration membrane.

Example 6

In this example, a phase conversion method is used to prepare a polymeric nanofiltration membrane containing 0.30wt% nitrogen-doped hollow porous carbon spheres (N-HPCS) nanocomposite. The specific process is as follows:

S1, add 22wt% polyethersulfone (PES), 1.2wt% polyvinylpyrrolidone (PVP) and 0.30wt% nitrogen-doped hollow porous carbon spheres (using N-HPCS prepared in Example 1) to N,N-di into methylacetamide (DMAc) solvent, placed in an ultrasonic generator, and stirred for 30 minutes at an ultrasonic intensity of 24W/ ^m2 and a rotation speed of 130rad/min to obtain a uniform suspension.

S2, place the uniform suspension prepared in step S1 at room temperature for 26 hours and set aside.

S3: Place the suspension in step S2 in an oven at 55°C for 2.5 hours to remove bubbles in the suspension.

S4. Place the suspension treated in step S3 in a tank ultrasonic wave and treat it for 15 minutes at an ultrasonic intensity of 25W/ ^m2 to help the N-HPCS particles in the water phase maintain a stable dispersion state and at the same time remove the bubbles in the suspension. Completely eliminated.

S5, pour the uniform and bubble-free suspension obtained in step S4 onto the glass plate, and cast the suspension into a 160 μm thick film through an adjustable casting knife.

S6, in order to start the phase conversion process, immediately immerse the film obtained in step S5 in the distilled water coagulation bath. After the film solidifies, the film is separated from the glass plate, dried and stored between paper sheets to complete the preparation of the polymeric nanofiltration membrane.

Example 7

This example uses the polymeric nanofiltration membrane prepared in Example 4 to treat wastewater. The treated wastewater quality indicators and membrane flux are as shown in Table 1, Table 2 and Figure 1:

Table 1 Pollutant removal effect

Note: In Table 1, DASA wastewater contains a single organic compound, diaminobenzenesulfonanilide.

Table 2 Membrane flux changes

It can be seen from the above that the polymeric nanofiltration membrane prepared in Example 4 shows a stable rejection rate for salt, DASA organic matter and heavy metal ions; at the same time, during long-term operation, the membrane flux of the polymeric nanofiltration membrane is within 24 hours. There is no obvious decrease, indicating that the modification method of the present invention has a significant positive effect on the stability of the membrane flux and has good application prospects.

The above embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present invention shall still be covered by the claims of the present invention.

Claims (10)

1. A polymeric nanofiltration membrane, characterized in that the polymeric nanofiltration membrane contains hydrophilic nanocomposite material, and the hydrophilic nanocomposite material is nitrogen-doped hollow porous carbon spheres.
2. The polymeric nanofiltration membrane according to claim 1, characterized in that: the polymeric nanofiltration membrane contains 0 to 0.5 wt% nitrogen-doped hollow porous carbon spheres.
3. The polymeric nanofiltration membrane according to claim 1, characterized in that: the preparation method of the nitrogen-doped hollow porous carbon spheres includes the following steps:

   (1) Mix the ammonium salt solution or ammonia water with ethanol and water and stir evenly, add ethyl orthosilicate, and stir and react under a protective gas atmosphere until white colloidal silica balls appear;

   (2) Centrifuge the reaction solution obtained in step (1), collect the silica spheres, clean the silica spheres and then vacuum-dry them to obtain a silica template;

   (3) Add the silica template obtained in step (2) to the ethanol/water solution, and disperse and mix evenly by ultrasonic;

   (4) Add resorcinol, methanol solution, ethyl orthosilicate, and ethylenediamine to the mixture obtained in step (3), mix evenly, and stir the reaction under a protective gas atmosphere to completely cover the negatively charged mixture. Oxidize the surface of the silica sphere to obtain SiO ₂ @N-RF, which is then washed, centrifuged, and dried;

   (5) Heat and carbonize the SiO ₂ @N-RF dried in step (4) under a protective gas atmosphere, and then gradually cool to room temperature;

   (6) Etch the product obtained in step (5) with HF aqueous solution to remove the silicon dioxide template to obtain the nitrogen-doped hollow porous carbon spheres.
4. The polymeric nanofiltration membrane according to claim 3, characterized in that: in the step (1), the volume ratio of ammonium salt solution/ammonia water, ethanol, water and ethyl orthosilicate is 2.5~5:35~40 :4～6:4～6;

   And/or, in the step (1), the concentration of the ammonium salt solution or ammonia water is 15 to 25%;

   And/or, in the step (1), the ammonium salt is selected from any one of ammonium chloride, ammonium sulfate, and ammonium carbonate;

   And/or, in the step (1), after adding ethyl orthosilicate, the reaction is stirred for 1 to 2 hours under a protective gas atmosphere until white colloidal silica balls appear;

   And/or, the step (1) is performed at normal temperature.
5. The polymeric nanofiltration membrane according to claim 3, characterized in that: in the step (2), absolute ethanol is used to clean the silica balls, and the number of cleaning times is no less than three times;

   And/or, in the step (2), the vacuum drying temperature is 65-75°C;

   And/or, in the step (2), the vacuum drying time is 20 to 28 hours;

   And/or, in the step (3), the volume ratio of ethanol and water in the ethanol/water solution is 6.5~7.5:2.5~3.5;

   And/or, in the step (3), the ultrasonic dispersion time is 25 to 35 minutes;

   And/or, in the steps (3) and (4), the mass ratio of silica template and resorcinol is 1:0.25~0.35, and the volume ratio of methanol solution, ethyl orthosilicate and ethylenediamine It is 0.35～0.60:0.2～0.5:0.5～0.7;

   And/or, in the step (4), the stirring reaction temperature is 25-35°C;

   And/or, in the step (4), the stirring reaction time is 0.5 to 1 h;

   And/or, in the step (4), use water and ethanol to wash and centrifuge in sequence, wash and centrifuge at least three times;

   And/or, in the step (4), the drying temperature is 75-85°C;

   And/or, in the step (4), the drying time is 10 to 15 hours.
6. The polymeric nanofiltration membrane according to claim 3, characterized in that: in the step (5), the heating and carbonization temperature is 780～820℃;

   And/or, in the step (5), heating is performed using programmed temperature rise, and the heating rate is 2.5-3.5°C/min;

   And/or, in the step (5), the heating and carbonization time is 7 to 9 hours;

   And/or, in the step (6), the concentration of the HF aqueous solution is 9-11%.
7. A preparation process for the polymeric nanofiltration membrane according to any one of claims 1 to 6, characterized in that it includes the following steps:

   Polyethersulfone, polyvinylpyrrolidone, and the nitrogen-doped hollow porous carbon spheres are added to the solvent and stirred ultrasonically to obtain a uniform suspension; the suspension is sequentially baked and ultrasonic treated to obtain a uniform and bubble-free suspension. suspension;

   The uniform and bubble-free suspension is poured onto a glass plate and cast into a film. The film is then immediately immersed in a coagulation bath of distilled water. After the film solidifies, the film is separated from the glass plate, dried and stored between sheets of paper. , complete the preparation of the polymeric nanofiltration membrane.
8. The preparation process according to claim 7, characterized in that: the solvent is selected from the group consisting of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide any of;

   And/or, the mass percentage concentration of the polyethersulfone, polyvinylpyrrolidone, and nitrogen-doped hollow porous carbon spheres in the suspension is 18 to 25 wt%, 0.5 to 2 wt%, or 0 to 0.5 wt%;

   And/or, when the suspension is obtained by ultrasonic stirring, the ultrasonic intensity is 12-24W/m ² , the ultrasonic time is 30-40min, and the stirring speed is 125-175rad/min;

   And/or, the baking temperature is 45~55℃, and the baking time is 1.5~2.5h;

   And/or, after baking, the ultrasonic intensity is 20-25W/m ² and the ultrasonic time is 15-20 minutes.
9. The preparation process according to claim 7, characterized in that: the thickness of the film is 140-160 μm.
10. Application of the polymeric nanofiltration membrane according to any one of claims 1 to 6 and/or the polymeric nanofiltration membrane prepared according to the method according to any one of claims 7 to 9 in industrial wastewater treatment.