WO2020248433A1

WO2020248433A1 - Method for preparing composite nano-material hybrid membrane and hybrid membrane prepared thereby

Info

Publication number: WO2020248433A1
Application number: PCT/CN2019/107683
Authority: WO
Inventors: 王祝愿; 梁松苗; 康燕; 彭伟; 金焱; 吴宗策; 胡利杰
Original assignee: 时代沃顿科技有限公司
Priority date: 2019-06-12
Filing date: 2019-09-25
Publication date: 2020-12-17
Also published as: CN110292864B; CN110292864A

Abstract

A method for preparing a composite nano-material hybrid membrane and a hybrid membrane prepared thereby. The preparation method comprises the steps of: (1) dispersing a nano cellulose crystal in water to obtain a dispersed nano cellulose crystal liquid; (2) dispersing graphene oxide in water to obtain a dispersed graphene oxide liquid; (3) mixing the dispersed nano cellulose crystal liquid and the dispersed graphene oxide liquid into a mixed liquid; (4) treating a base membrane with a hydrophilic treatment liquid; (5) coating the mixed liquid onto the treated base membrane to form a functional layer; and (6) performing post-treatment and drying to obtain a composite nano-material hybrid membrane.

Description

Preparation method of composite nano material hybrid membrane and hybrid membrane prepared thereby

Technical field

The present disclosure relates to the technical field of filtration membranes, in particular to a method for preparing a composite nanomaterial hybrid membrane and a hybrid membrane prepared therefrom. The method realizes regulation and control of the pore size of the hybrid membrane, enhances the mechanical properties of the hybrid membrane, and improves the stability of the hybrid membrane under strong cross-flow and long-term operation.

Background technique

With the process of industrialization and urbanization, the lack of safe and reliable water resources has become one of the biggest challenges facing mankind. However, the domestic and industrial wastes brought by human activities have caused serious pollution to water resources and exacerbated this problem. In order to solve the problems of water pollution and water scarcity, efficient, energy-saving, and reliable water treatment solutions have become one of the most urgent needs of mankind. These programs include seawater desalination, wastewater reuse, surface water purification, and more. Among these treatment schemes, membrane treatment is one of the most efficient methods.

Traditional high molecular polymers are currently the most widely used membrane materials and are mostly prepared by interfacial polymerization. However, polymer membrane materials have some difficult to overcome shortcomings, such as oxidation resistance, pollution resistance, and poor chlorine resistance. In addition, there is a trade-off effect between the selectivity and permeability of traditional polymer membranes, that is, there is an upper-bound curve restriction relationship between selectivity and permeability. These problems limit the Application and development. The composite separation membrane with nanomaterials as the functional layer is expected to solve these problems and become a major member of the next generation of separation membranes.

Jijo Abraham and Rahul R.Nair ^[1] used vacuum filtration to deposit graphene oxide (GO) into a thin film (micron level), then swelled under different humidity to obtain separation membranes with different interlayer spacings, and maintained them by physical fixation. The dimensional stability of the interlayer spacing, the obtained film shows excellent selectivity to salt ions and dye molecules (the rejection rate of sodium chloride is more than 97%). However, the efficiency of this method is very low, and it is currently only suitable for small-scale development and application. Moreover, the special water inlet method of the separation membrane makes it also have natural disadvantages in the utilization of effective membrane area.

Q. Yang ^[2] et al. used a multi-stage centrifugal separation method to screen out large-size graphene oxide sheets with a size of about 10-20 μm, and then layered them on alumina or nylon porous ultrafiltration membranes by vacuum filtration. The layer is ultra-thin (less than 10nm) graphene oxide active layer, and the obtained composite membrane has good solvent permeability, and the rejection rate of methyl blue and rose red in methanol reaches 99.9%. However, the preparation process of the raw materials and the membrane of this method takes a long time and is not suitable for industrialized continuous production. Secondly, due to the lack of an effective cross-linking enhancement process, the stability of the membrane under cross-flow is also hidden.

Aaron Morelos-Gomez ^[3] et al. used PVA-treated polysulfone ultrafiltration membrane as a support layer, and used a spray method to simultaneously laminate multilayer graphene and single-layer graphene oxide on the surface of the treated support layer, and then used High temperature treatment at 100°C for 1 hour and immersion in calcium chloride solution for one hour, the resulting hybrid membrane has a retention of over 85% of sodium chloride and maintains good stability under strong cross-flow operation. However, in this method, the pre-treatment of the support layer and the post-treatment of the separation membrane take a long time (total processing time> 3h), which affects production efficiency and increases production costs. In addition, due to the strong hydrophobicity of graphene, the resulting hybrid separation membrane has a low water flux.

Patent US9108158B2 describes a method for preparing graphene oxide (GO) separation membranes by vacuum filtration. The steps include: firstly dispersing GO powder into a uniform aqueous dispersion by means of ultrasound, and then centrifugally separating the multi-layers and removing the remaining The lower single-layer solution is filtered onto the porous support layer, and finally a certain post-treatment is performed to obtain a membrane sample. As mentioned above, this preparation method is not conducive to industrialization, and the performance of the obtained product is not good, and the long-term operation stability is difficult to guarantee. Patent US9902141B2 describes a method in which graphene oxide is used as the main membrane material and then cross-linked with dopamine and trimesoyl chloride to form a film. After chemical cross-linking treatment, the selectivity of the membrane is significantly improved. However, the film forming method does not completely avoid amide bonds, so there are still many problems faced by polymer films, such as poor oxidation resistance and chlorine resistance. Patent US10183259B2 describes the application and preparation method of ultra-thin graphene oxide film for ion removal. It is also prepared by vacuum filtration, and the thickness of the active functional layer of the film is controlled between 2-20 nm.

At present, the existing preparation technology of nanomaterial separation membrane mainly adopts vacuum suction filtration of graphene oxide aqueous dispersion, stacking on an ultrafiltration or microfiltration support layer to form a functional layer, and finally preparing a composite separation membrane. This method requires an external force-driven filtration process, which not only consumes large amounts of energy, but also has low production efficiency, making it difficult to achieve continuous production. Secondly, the control methods for graphene composite separation membranes are relatively limited. A small number of small-molecule monomers are used to assist cross-linking. This will inevitably introduce a large number of amide bonds, ester bonds, etc., resulting in oxidation resistance and solvent resistance of the functional layer. Affected by these chemical bonds, it is impossible to fully highlight the superiority of nanomaterials. Part of the technical path adopts high-temperature post-processing and introduces methods such as multi-layer graphene. These methods also have the problems of low production efficiency or poor membrane performance. Finally, since the functional layer of nanomaterials is only maintained by physical forces, there are many problems with dimensional stability and stability in use, and the existing technical path does not pay attention to the mechanical strength of the material itself.

references

[1]Abraham J, Vasu K S, Williams C D, et al. Tunable sieving of ions using graphene oxide membranes[J].Nature Nanotechnology,2017,12(6):546-550.

[2]Yang Q, Su Y, Chi C, et al. Ultrathin graphene-based membrane with precisemolecular sieving and ultrafast solvent permeation[J]. Nature Materials, 2017, 16(12): 1198-1202.

[3]Morelos-Gomez A, Cruz-Silva R, Muramatsu H, et al. Effective NaCl and dye rejection of hybrid graphene oxide/graphene layered membranes[J]. Nature Nanotechnology, 2017.

Summary of the invention

The problem to be solved by the invention

In order to solve the current ubiquitous preparation and performance problems of nanomaterial separation membranes as much as possible, the present disclosure proposes a method for preparing a composite separation membrane using nano cellulose crystals and graphene oxide hybridization.

Solution to the problem

The present disclosure provides a method for preparing a composite nano-material hybrid film, which includes the following steps:

(1) Disperse nano-cellulose crystals in water to obtain a nano-cellulose crystal dispersion;

(2) Disperse graphene oxide in water to obtain a graphene oxide dispersion;

(3) Mixing the nano cellulose crystal dispersion liquid and the graphene oxide dispersion liquid to form a mixed dispersion liquid;

(4) Treat the base membrane with hydrophilic treatment liquid;

(5) Coating the mixed dispersion liquid on the base film after the above treatment to form a functional layer;

(6) A composite nano-material hybrid film is obtained after post-processing and drying.

The preparation method according to the present disclosure is characterized in that the mass concentration of nano-cellulose crystals in the nano-cellulose crystal dispersion is 0.0001-0.05%, preferably 0.001-0.01%; the mass of the graphene oxide in the graphene oxide dispersion is The concentration is 0.0001-0.05%, preferably 0.001-0.01%; preferably, the dispersion of the above steps (1) and (2) is performed under ultrasonic treatment.

The preparation method according to the present disclosure is characterized in that the mixing ratio of the nano cellulose crystal dispersion liquid and the graphene oxide dispersion liquid in step (3), that is, the nano cellulose crystal dispersion liquid: the graphene oxide dispersion liquid is (1) ～30):(70～99), preferably (1～20):(80～99), more preferably (1～10):(90～99), still more preferably (2～10):(90 ~98), more preferably (5-10):(90-95), based on the mass of nanocellulose crystals and graphene oxide.

The preparation method according to the present disclosure is characterized in that the base membrane in step (4) is selected from polysulfone, polyethersulfone, polyacrylonitrile, nylon, polytetrafluoroethylene, polyvinyl chloride, polyether ether One or more ultrafiltration membranes or microfiltration membranes of ketones and porous alumina sheets, preferably polysulfone or polyethersulfone ultrafiltration membranes; the hydrophilic treatment liquid contains polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl One or more of ethylene glycol.

The preparation method according to the present disclosure is characterized in that the mass concentration of one or more of polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol in the hydrophilic treatment solution is 0.01 to 5%, preferably 0.1～1%.

The preparation method according to the present disclosure is characterized in that the thickness of the functional layer in step (5) is 10-500 nm, preferably 50-100 nm.

The preparation method according to the present disclosure is characterized in that the coating method in step (5) is spraying.

The preparation method according to the present disclosure is characterized in that the post-treatment in step (6) includes ion cross-linking treatment using an ion-crosslinking agent treatment solution.

The preparation method according to the present disclosure is characterized in that the ionic crosslinking agent is one or more of calcium chloride, magnesium chloride, and magnesium sulfate. Preferably, the ionic crosslinking agent in the ionic crosslinking agent treatment solution The mass concentration of is 1 to 10%, preferably 3 to 5%.

The present disclosure also provides a composite nanomaterial hybrid film prepared by the preparation method according to the present disclosure.

Effect of invention

The following technical effects are achieved by adopting the preparation method of the present disclosure:

1. The preparation process is highly efficient, and the process is suitable for industrial scale-up production;

2. Realize the adjustment of the size of the pores to adapt to different application scenarios;

3. The post-treatment process is simple and efficient, which further improves the preparation efficiency;

4. Enhance the mechanical properties of the membrane material itself, and improve the stability of the membrane under strong cross-flow and long-term operation.

Description of the drawings

Fig. 1 is a diagram of the contact angle of the base membrane of Example 1 before and after the hydrophilic treatment.

Figure 2 shows the membrane samples GO-98/CNC-2, GO-95/CNC-5 and GO-90/CNC-10 in Examples 1 to 3 and the membrane samples GO of Comparative Example 1 and Comparative Example 2. , CNC surface electron microscope photos.

Figure 3 shows the membrane samples GO-98/CNC-2, GO-95/CNC-5 and GO-90/CNC-10 in Examples 1 to 3 and the membrane samples GO of Comparative Example 1 and Comparative Example 2. , CNC section view.

Fig. 4 is a graph showing the adhesion performance between the film material and the base film.

Fig. 5 and Fig. 6 are the tensile test results of the diaphragm material and the SEM topography of the fracture surface after breaking.

Fig. 7 is a graph showing the separation performance of the membranes of Comparative Example 1 and Comparative Example 3 for methyl orange aqueous solution.

Figure 8 shows the GO diaphragm of Comparative Example 1, the CNC diaphragm of Comparative Example 2, and the GO-98/CNC-2, GO-95/CNC-5 and GO-90/CNC-10 diaphragms of Examples 1 to 3. Flux data.

9 is a graph showing the separation performance of the membranes of Example 1 to Example 3 and Comparative Example 1 and Comparative Example 2 for the dye methyl orange.

Fig. 10 and Fig. 11 are performance graphs of the diaphragm operation of Comparative Example 1 and Example 2, respectively.

Detailed ways

Throughout this specification, references to "one embodiment" or "embodiment" or "in another embodiment" or "in certain embodiments" or "in some embodiments of this application" mean that At least one embodiment includes specific reference elements, structures, or features related to the embodiment. Therefore, the phrases "in one embodiment" or "in an embodiment" or "in another embodiment" or "in certain embodiments" or "in part of this application" appearing in various places throughout the specification In the embodiments, "not all refer to the same embodiment. In addition, specific elements, structures, or characteristics may be combined in one or more embodiments in any suitable manner.

Unless otherwise required in this application, throughout the specification and subsequent claims, the word "comprise" and its English variants such as "comprises" and "comprising" shall be interpreted as open-ended The inclusive meaning of "including but not limited to".

It should be understood that the singular article "一" (corresponding to English "a", "an" and "the") used in the description of this application and the appended claims includes plural objects unless the context clearly indicates otherwise Local regulations. It should also be understood that the term "or" is usually used in its meaning including "and/or", unless the context clearly specifies otherwise.

Graphene is a two-dimensional material with high mechanical strength and good chemical stability. In particular, porous single-layer graphene is the most ideal separation membrane. However, the preparation and pore formation process of graphene is currently not suitable for large-scale applications. Graphene oxide, as a derivative of graphene, is a two-dimensional material that can be prepared on a large scale. The defects caused by the oxidation process are good water channels. At the same time, the introduction of a large number of hydroxyl and carboxyl groups can also increase its hydrophilicity. Sex. Therefore, the present disclosure selects graphene oxide (preferably, with a thickness of 1-10 nm and a size of 1-20 μm) as the main film material.

Secondly, in order to control the pores while enhancing the mechanical properties of the membrane material, the present disclosure selects nano cellulose crystals, especially rod-shaped nano cellulose crystals (preferably, the diameter is 5-20 nm, the length is 100-300 nm) as the pores. Regulator and mechanical enhancer. On the one hand, the diameter of nano-cellulose crystals is much larger than the thickness and spacing of graphene oxide sheets, and the introduction of crystals can significantly increase the layer spacing. On the other hand, there are a large number of hydroxyl groups on the surface of nanocellulose crystals, which have a strong affinity with the hydroxyl groups on the surface of graphene oxide, and can form strong forces such as hydrogen bonds. At the same time, the size of the nanocellulose crystals is not too large to hinder graphite oxide. The force between the olefin sheets, so the introduction of nano-cellulose crystals can improve the mechanical properties of the membrane material.

Based on the above inventive concept, the present disclosure provides a method for preparing a composite nanomaterial hybrid film, which includes the following steps:

(2) Disperse graphene oxide in water to obtain a graphene oxide dispersion;

(4) Treat the base membrane with hydrophilic treatment liquid;

It should be noted that, in the present disclosure, there is no sequence between steps (1), (2), and (4), and there is no sequence between steps (3) and (4). That is, the sequence of the preparation of the nanocellulose crystal dispersion liquid, the preparation of the graphene oxide dispersion liquid, and the treatment of the base film is optional and not limited. On the other hand, for the preparation of the mixed dispersion and the treatment of the base film, the sequence of these steps is also optional and not limited.

In step (1), disperse nanocellulose crystals (CNC), preferably in powder form, in water, preferably in deionized water. The mass concentration of nanocellulose crystals in the nanocellulose crystal dispersion is 0.0001 to 0.05%. , Preferably 0.001 to 0.01%. The nanocellulose crystals (CNC) are commercially available.

In step (2), graphene oxide (GO), preferably in powder form, is dispersed in water, preferably in deionized water, and the mass concentration of graphene oxide in the graphene oxide dispersion is 0.0001 to 0.05%, preferably 0.001 ~0.01%. Graphene oxide may be a single layer or multiple layers, preferably a single layer. The graphene oxide (GO) is commercially available.

Preferably, the dispersion of the above steps (1) and (2) is performed under ultrasonic treatment. Preferably, the ultrasonic power is between 50-100W.

In step (3), the mixing ratio of nano cellulose crystal dispersion liquid and graphene oxide dispersion liquid, that is, nano cellulose crystal dispersion liquid: graphene oxide dispersion liquid is (1-30): (70-99), preferably (1-20): (80-99), more preferably (1-10): (90-99), still more preferably (2-10): (90-98), still more preferably (5 to 10): (90～95), based on the mass of nano cellulose crystals and graphene oxide.

When the mass ratio of nanocellulose crystals is more than 1%, with the increase in the amount of addition, due to the synergistic effect of enhanced pores and enhanced mechanical properties, the flux and retention performance of the hybrid membrane will increase together, and continue to increase nanocellulose The mass ratio of the crystal reaches 30%, and the flux continues to increase. However, if the mass ratio of nanocellulose crystals is further increased to exceed 30%, the molecular weight cut-off will be large, and the resulting functional layer will be too hydrophilic, which will affect the stability of the membrane in aqueous solution. On the other hand, if the mass ratio of the nano-cellulose crystals is less than 1%, the added amount is too small, so the synergistic effect of channel enhancement and mechanical performance enhancement cannot be achieved.

In step (4), the base membrane is treated with a hydrophilic treatment solution. The base membrane is selected from polysulfone (PSF), polyethersulfone (PES), polyacrylonitrile (PAN), nylon (PA), polytetrafluoroethylene (PVDF), polyvinyl chloride (PVC), polyether ether One or more ultrafiltration membranes or microfiltration membranes of ketone (PEEK) and porous alumina sheets. Preference is given to ultrafiltration membranes of polysulfone or polyethersulfone. Preferably, the hydrophilic treatment liquid contains one or more of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG). Preferably, the mass concentration of one or more of the polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol in the hydrophilic treatment liquid is 0.01 to 5%, preferably 0.1 to 1%.

The hydrophilic treatment liquid may also contain a small amount of aldehyde crosslinking agents, such as glyoxal, glutaraldehyde, and the like. The aldehyde cross-linking agent can undergo an aldol condensation reaction with the hydroxyl groups of the macromolecular substances in the treatment liquid to form a cross-linked network structure, which can effectively prevent the macromolecular substances of the hydrophilic treatment from being lost in the water flow. The adding range of the aldehyde crosslinking agent is 0.0001 to 0.5% by mass concentration, preferably 0.01 to 0.1%.

As an illustrative example, the treatment of the base film may include: immersing the selected base film in the hydrophilic treatment solution for 3-30 minutes, and baking it in an oven at 60-80°C for 5-30 minutes, and repeating 2 if necessary. ~3 times of this step to obtain a hydrophilic treated base film.

In the present disclosure, the main purpose of the hydrophilic treatment of the base membrane is that the improvement of the hydrophilicity of the base membrane is beneficial to the spreading of the film forming solution on the surface of the base membrane, and can effectively improve the uniformity of the film formation.

In step (5), the mixed dispersion is coated on the base film after the above treatment to form a functional layer. The coating method can be brush coating, spray coating, dip coating, or roll coating. In the present disclosure, the preferred coating method is spraying. The spraying method can be different from the traditional filtration film forming method, and the base film in the present disclosure is subjected to hydrophilic treatment, which is beneficial to spreading the mixed dispersion liquid on the surface of the base film after spraying.

The thickness of the functional layer obtained after coating is 10 to 500 nm, preferably 50 to 100 nm. At this time, the obtained membrane has the best comprehensive performance of permeation and separation. When the functional layer is less than 10nm, more defects are likely to occur, which affects its selection performance. When the thickness of the membrane is greater than 500nm, although the separation performance is still ideal at this time, the increase in mass transfer resistance caused by the thickness of the membrane makes the flux greatly decline.

In step (6), the post-treatment includes using an ion cross-linking agent treatment solution to perform ion cross-linking treatment. Preferably, the ionic crosslinking agent is one or more of calcium chloride, magnesium chloride, and magnesium sulfate. Preferably, the mass concentration of the ionic crosslinking agent in the ionic crosslinking agent treatment solution is 1-10%, preferably 3～5%.

The advantage of ionic crosslinking treatment is that there are many hydroxyl groups on graphene oxide, and there are also a large number of hydroxyl groups on nano-cellulose crystal macromolecules. Since metal ions can form ionic bonds with hydroxyl groups, ionic bonds can be effectively introduced by introducing metal ions. A strong force is formed between the nanomaterials to increase its packing density, thereby improving the selectivity and operational stability of the diaphragm.

As an illustrative example, the post-treatment of ionic crosslinking may include: spraying an aqueous solution with ionic crosslinking agent dissolved on the surface of the membrane obtained in step (5), standing for 10 minutes, and placing it in a 100°C oven for heat treatment for 20-40 minutes You can get the final diaphragm product.

Other post-treatments are not limited. For example, the membrane can be treated with hot water and/or soaked in glycerin, and then dried.

The present disclosure also provides a hybrid membrane prepared according to the preparation method. The hybrid membrane can be applied to separation and concentration technologies in the fields of water treatment, dyes, biochemical, food, and environmental protection.

The technical solutions of the present disclosure will be further described in detail below in conjunction with embodiments, but they are not intended to limit the present disclosure.

In the examples, all raw materials used are commercially available.

Example one

Preparation of graphene oxide (GO) dispersion: Disperse 0.025g of single-layer graphene oxide (with a thickness of about 1nm and a size of 2-10μm) in 50g of deionized water under 100W power ultrasound. The ultrasound process lasts for 10min. The concentration of graphene oxide in the liquid is 0.05% by mass.

Preparation of nano cellulose crystal (CNC) dispersion: 0.025 g of nano cellulose crystal powder (10 nm in diameter and 200 nm in length) was dispersed in 50 g of water, and the concentration of nano cellulose crystals in the dispersion was 0.05% by mass.

The GO dispersion and the CNC dispersion are mixed in a mass ratio of 98:2 to obtain a mixed dispersion.

Polyethersulfone (PES) filter membrane was selected as the base membrane, the membrane pore size was 0.45μm, and the membrane diameter was 9mm. The base membrane is soaked in a 0.1% by mass polyvinylpyrrolidone (PVP) aqueous solution for 1 minute and then dried to improve the hydrophilicity of the membrane. The above-mentioned mixed dispersion is coated on the hydrophilic treated base film by spraying, and the thickness of the obtained functional layer is controlled at 100 nm.

After spraying, it is blown dry, and then a layer of 1% by mass magnesium sulfate aqueous solution is sprayed for ion cross-linking treatment for 10 minutes, and then placed in an oven at 100°C for half an hour to obtain a film sample, marked as GO-98/CNC-2.

Example two

The GO dispersion and the CNC dispersion were mixed in a mass ratio of 95:5 to obtain a mixed dispersion.

After spraying, blow dry, spray a layer of 1% by mass magnesium sulfate aqueous solution for ion cross-linking treatment for 10 minutes, and put it in an oven at 100°C for half an hour to obtain a film sample, labelled GO-95/CNC-5.

Example three

The above-mentioned GO dispersion and CNC dispersion are mixed at a mass ratio of 90:10 to obtain a mixed dispersion.

After spraying, blow dry, and spray a layer of 1% by mass magnesium sulfate aqueous solution for ion cross-linking treatment for 10 minutes, and put it in an oven at 100°C for half an hour to obtain a film sample, labeled GO-90/CNC-10.

Comparative example one

Preparation of graphene oxide (GO) dispersion: Disperse 0.025g of single-layer graphene oxide (with a thickness of about 1nm and a size of 2-10μm) in 100g of deionized water under ultrasound of 100W power. The ultrasound process lasts for 10min. The concentration of graphene oxide in the liquid was 0.025% by mass.

Polyethersulfone (PES) filter membrane was selected as the base membrane, the membrane pore size was 0.45μm, and the membrane diameter was 9mm. The base membrane is soaked in a 0.1% by mass polyvinylpyrrolidone (PVP) aqueous solution for 1 minute and then dried to improve the hydrophilicity of the membrane. The GO dispersion is sprayed on the hydrophilic treated base film, and the thickness of the obtained functional layer is controlled at 100 nm.

After spraying, it was blown dry, and a layer of 1% by mass magnesium sulfate aqueous solution was sprayed for ion cross-linking treatment for 10 minutes, and then placed in an oven at 100°C for half an hour to obtain a film sample, labeled as GO.

Comparative example two

Preparation of nano cellulose crystal (CNC) dispersion: 0.025 g of nano cellulose crystal powder (10 nm in diameter and 200 nm in length) is dispersed in 100 g of water, and the concentration of nano cellulose crystals in the dispersion is 0.025% by mass.

Polyethersulfone (PES) filter membrane was selected as the base membrane, the membrane pore size was 0.45μm, and the membrane diameter was 9mm. The base membrane is soaked in a 0.1% by mass polyvinylpyrrolidone (PVP) aqueous solution for 1 minute and then dried to improve the hydrophilicity of the membrane. The above-mentioned CNC dispersion is coated on the hydrophilic treatment base film by spraying, and the thickness of the obtained functional layer is controlled at 100 nm.

After spraying, it is blown dry, and a layer of 1% by mass magnesium sulfate aqueous solution is sprayed for ion cross-linking treatment for 10 minutes, and then placed in an oven at 100° C. for half an hour to obtain a film sample, which is marked as CNC.

Comparative example three

Polyethersulfone (PES) filter membrane was selected as the base membrane, the membrane pore size was 0.45μm, and the membrane diameter was 9mm. The base film was soaked in a 0.1% by mass polyvinylpyrrolidone (PVP) aqueous solution for 1 minute and then dried to improve the hydrophilicity of the film. The GO dispersion is sprayed on the hydrophilic treated base film, and the thickness of the obtained functional layer is controlled at 100 nm.

After spraying, it was blown dry, and it was directly placed in an oven at 100°C for half an hour without ion cross-linking to obtain a membrane sample, labeled nc-GO.

It should be noted that the contact angle of pure water on the surface of the base film and the contact angle of the dispersion on the surface of the base film are tested with a contact angle measuring instrument (DSA 30, Kruss GmbH).

A to D in FIG. 1 are the graphene oxide dispersion in Example 1, and the graphene oxide dispersion is added to the graphene oxide dispersion at 2% by mass, 5% by mass, and 10% by mass based on the mass of the graphene oxide dispersion. A diagram of the contact angle of the mixed dispersion liquid obtained after the nanocellulose crystal dispersion liquid in Example 1 is added to the surface of the base film membrane of Example 1. It can be seen from the figure that as the content of nanocellulose crystals in the mixed dispersion increases, the contact angle of the mixed dispersion on the same base film becomes smaller and smaller, indicating that the addition of nanocellulose crystals is beneficial to the dispersion in the base film. Spread on the film, so the resulting film will be more uniform.

E and F in FIG. 1 are diagrams of the contact angles of the graphene oxide dispersion liquid in the first embodiment on the surface of the base film in the first embodiment before and after the hydrophilic treatment. It can be seen from the figure that, compared with the contact angle before the hydrophilic treatment (E), the contact angle after the hydrophilic treatment (F) is reduced by three times (the contact angle before treatment is 47.6°, and the contact angle after treatment is 17.5°). This shows that through the hydrophilic treatment, the spreadability of the dispersion on the surface of the base film is effectively improved, thereby improving the uniformity of film formation.

2A and 2E are the surface electron micrographs of the sample (GO) of Comparative Example 1 and the sample (CNC) of Comparative Example 2, respectively, and Figures 2B ~ 2D are the samples GO-98/CNC- of Examples 1 to 3, respectively. 2. Surface electron microscope photos of GO-95/CNC-5 and GO-90/CNC-10.

All electron microscopy photos are obtained by field emission scanning electron microscopy (SEM, Hitachi S-4300). The samples need to be sprayed with gold before shooting. It can be seen from Figures 2B to 2D that the surface of the membrane prepared by the method of the present disclosure is relatively uniform, and there is no large-scale aggregation of graphene or cellulose, which proves that the two nanomaterials can achieve uniform dispersion and finally form together Stacked functional layer structure.

Among them, Figures 3B to 3D are cross-sectional views of the membrane samples GO-98/CNC-2, GO-95/CNC-5 and GO-90/CNC-10 in Examples 1 to 3, respectively, Figures 3A and 3E The cross-sectional views of GO and CNC of the diaphragm samples of Comparative Example 1 and Comparative Example 2, respectively, and Fig. 3F is the XRD characterization diagram of these 5 diaphragm samples.

The cross-sectional image is obtained by field emission scanning electron microscope (SEM, Hitachi S-4300) test. The XRD characterization map is obtained by X-ray diffractometer (Thermo Scientific ESCALab 250Xi) test.

In Figure 3F, from top to bottom, the proportion of CNC is getting higher and higher, and it can be seen that the diffraction angle is getting smaller and smaller. According to the Bragg equation, the layer spacing is gradually increasing, which proves that the channel control of the GO functional layer has been successfully achieved by CNC. .

Fig. 4 is a graph showing the adhesion performance between the film material and the base film. The test method is to cut the membrane into 2*5cm splines, fully bond the front side of the membrane (that is, the side with the functional layer) and the tape, gently pull one end to separate the membrane from the tape, and fix them on the Both ends of the tensile testing machine (model SurPassTM 3) are stretched at a speed of 5mm/min, and the changes in the pull-down force are recorded. It can be seen from the figure that the pure GO film is almost completely peeled off after being bonded and stretched with tape, and the interfacial adhesion is between 0.6-0.8N. With the continuous increase of the content of nano cellulose crystals (CNC), the tape is bonded and stretched. After stretching, the part falling off becomes less and less, and the more complete the surface of the diaphragm, indicating that the adhesion is enhanced.

Figures 5 and 6 are the tensile test results of the diaphragm material and the SEM morphology of the fracture surface after breaking. The specific test method is as follows: respectively apply the mixed dispersion in Examples 1 to 3 and the dispersion in Comparative Example 1 directly on a glass plate to dry, and then put it in a 1% by mass magnesium sulfate solution for ion cross-linking treatment for 10 minutes, Treat it in an oven at 100°C for 30 minutes to obtain a film. Cut the membrane into 1cm*5cm splines, and fix them on a tensile testing machine (model SurPassTM 3). The effective spline size is 1cm*3cm, stretch at a speed of 1mm/min, and record the force and displacement data until Pull off.

The SEM morphology map of the fracture surface is obtained by observing the surface morphology of the fracture site by using a field emission scanning electron microscope (SEM, Hitachi S-4300) on the broken spline.

Among them, Figures 6A to 6D are respectively the SEM morphology of the fracture surface of the diaphragm material prepared with GO, GO-98/CNC-2, GO-95/CNC-5, GO-90/CNC-10 dispersions. . Combining Figure 5 and Figure 6, it can be seen that as the content of nano cellulose crystals (CNC) increases, the tensile strength of the diaphragm material gradually increases, and the elongation at break gradually decreases. The electron microscope image of the fracture shows that after the fracture The slip distance gradually decreases.

Figures 4 to 6 illustrate that the addition of CNC not only increases the bonding performance between the diaphragm material and the base film, but also increases the mechanical properties of the material itself. The improvement of these properties is beneficial to the diaphragm under strong cross-flow and long-term operation. The stability.

Fig. 7 is a graph showing the separation performance of the membranes of Comparative Example 1 and Comparative Example 3 for methyl orange aqueous solution. The test pressure is 2MPa, the raw water concentration is 50ppm, and the cross-flow test is performed at room temperature. It can be seen from Figure 7 that the membrane flux decreased slightly before and after the ion crosslinking (about 2.2×10 ^-6 m ³ m ^-2 s ^-1 before crosslinking, and about 2.0×10 ^-6 m ³ after crosslinking. m ^-2 s ^-1 ). However, the rejection rate increased from 72.6% to 95.3%, indicating that the introduction of ion crosslinking has greatly enhanced the integrity and stability of the film.

Figure 8 shows the GO diaphragm of Comparative Example 1, the CNC diaphragm of Comparative Example 2, and the GO-98/CNC-2, GO-95/CNC-5 and GO-90/CNC-10 diaphragms of Examples 1 to 3. The flux data. The test condition is that pure water (conductivity less than 10S/m) is used as raw water, and the operating pressure is 50psi. It can be seen from this figure that with the increase of CNC content, the pure water flux of the membrane continues to increase, indicating that the addition of nanocellulose crystals achieves the enhancement of the pores of the membrane.

9 is a graph showing the separation performance of the membranes of Example 1 to Example 3 and Comparative Example 1 and Comparative Example 2 for the dye methyl orange, respectively. The test pressure is 2MPa, the raw water is 50ppm methyl orange aqueous solution, and the test is carried out under cross-flow conditions. It can be seen from Figure 9 that when the content of nanocellulose crystals is less than 5% by mass, the flux and rejection rate increase at the same time. This may be due to the synergy of pores and mechanical properties. The crystal content and flux continue to rise, but the retention performance continues to decline. The retention rate of the pure CNC membrane for methyl orange is only 23%. Therefore, it is preferable to control the content of nano-cellulose crystals between 2-10% according to actual needs.

Fig. 10 is a performance diagram of the diaphragm operation of Comparative Example 1, and Fig. 11 is a performance diagram of the GO-95/CNC-5 diaphragm of Example 2 in long-term operation. Figures 10 and 11 were obtained according to the following method: the GO membrane of Comparative Example 1 and the GO-95/CNC-5 membrane of Example 2 were simultaneously under a cross-flow of 2MPa, and a rhodamine aqueous solution with a concentration of 50 mass ppm was used as raw water. Run continuously at room temperature for 48 hours. The experimental comparison results show that the removal rate of the blank sample (that is, the GO membrane of Comparative Example 1) drops significantly (to about 80%) after running for 15 hours. However, Example 2 The GO-95/CNC-5 membrane still maintains good stability after 48 hours of operation (the removal rate is maintained above 90%). This shows that the present disclosure can effectively improve the stability of the diaphragm under strong cross-flow and long running time.

Table 1 below shows the selective separation of the GO-95/CNC-5 membrane of Example 2 for small molecular substances.

Table I

The flux and rejection rate are obtained by the following methods: the test condition is 2MPa cross-flow and room temperature, the raw water adopts the corresponding small molecule monomer aqueous solution, the mass concentration is 20ppm, and the concentration of raw water and product water adopts ultraviolet-visible spectrophotometer ( SHIMADZU-UV2550) test.

It can be seen from Table 1 that the membrane obtained by the present disclosure has a better selectivity (>70%) for small molecular substances with a molecular weight between 200 and 400, compared with the prior art (most of the molecular weight cut-off In the range of 500-1000), the diaphragm of the present disclosure has better selectivity and can better adapt to different application requirements.

Claims

A preparation method of composite nano-material hybrid membrane, which is characterized in that it comprises the following steps:

(1) Disperse nano-cellulose crystals in water to obtain a nano-cellulose crystal dispersion;

(2) Disperse graphene oxide in water to obtain a graphene oxide dispersion;

(3) Mixing the nano cellulose crystal dispersion liquid and the graphene oxide dispersion liquid to form a mixed dispersion liquid;

(4) Treat the base membrane with hydrophilic treatment liquid;

(5) Coating the mixed dispersion liquid on the base film after the above treatment to form a functional layer;

(6) A composite nano-material hybrid film is obtained after post-processing and drying.
The preparation method according to claim 1, characterized in that the mass concentration of nano-cellulose crystals in the nano-cellulose crystal dispersion is 0.0001-0.05%, preferably 0.001-0.01%; the graphene oxide in the graphene oxide dispersion is The mass concentration is 0.0001-0.05%, preferably 0.001-0.01%; preferably, the dispersion of the above steps (1) and (2) is performed under ultrasonic treatment.
The preparation method according to claim 1 or 2, characterized in that the mixing ratio of the nano cellulose crystal dispersion liquid and the graphene oxide dispersion liquid in step (3), that is, the nano cellulose crystal dispersion liquid: the graphene oxide dispersion liquid It is (1-30): (70-99), preferably (1-20): (80-99), more preferably (1-10): (90-99), and still more preferably (2-10) : (90-98), more preferably (5-10): (90-95), based on the mass of nanocellulose crystals and graphene oxide.
The preparation method according to any one of claims 1 to 3, wherein the base membrane in step (4) is selected from polysulfone, polyethersulfone, polyacrylonitrile, nylon, polytetrafluoroethylene, Ultrafiltration membranes or microfiltration membranes of one or more of polyvinyl chloride, polyetheretherketone, and porous alumina sheets, preferably polysulfone or polyethersulfone ultrafiltration membranes; the hydrophilic treatment liquid comprises polyethylene One or more of alcohol, polyvinylpyrrolidone, and polyethylene glycol.
The preparation method according to claim 4, wherein the mass concentration of one or more of polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol in the hydrophilic treatment liquid is 0.01 to 5%, Preferably it is 0.1 to 1%.
The preparation method according to any one of claims 1 to 5, wherein the thickness of the functional layer in step (5) is 10 to 500 nm, preferably 50 to 100 nm.
The preparation method according to any one of claims 1 to 6, wherein the coating method in step (5) is spraying.
The preparation method according to any one of claims 1 to 7, characterized in that the post-treatment in step (6) comprises using an ion-crosslinking agent treatment solution for ion cross-linking treatment.
The preparation method according to claim 8, wherein the ionic crosslinking agent is one or more of calcium chloride, magnesium chloride, and magnesium sulfate. Preferably, the ionic crosslinking agent in the treatment solution is ionically crosslinked The mass concentration of the agent is 1 to 10%, preferably 3 to 5%.
A composite nano-material hybrid membrane prepared by the preparation method according to any one of claims 1-9.