CN114316318A

CN114316318A - Preparation method of polyurea/two-dimensional material/alumina super-assembled functional film

Info

Publication number: CN114316318A
Application number: CN202111635728.8A
Authority: CN
Inventors: 孔彪; 周姗; 谢磊; 何彦君; 曾洁
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-04-12
Anticipated expiration: 2041-12-29
Also published as: CN114316318B

Abstract

The invention discloses a preparation method of a polyurea/two-dimensional material/alumina super-assembly functional film, which is characterized in that carboxylated graphene oxide is deposited on the surface of AAO under the action of vacuum filtration assistance, and the surface of a GO nano sheet has rich hydroxyl and carboxyl functional groups, so that the GO and the hydroxyl on the surface of the AAO form hydrogen bond assisted interface super-assembly interaction, and the GO grows on the surface of the AAO closely. In addition, in order to relieve the phenomenon that GO is easy to strip in water, a layer of compact polyurea film is grown on the surface of GO by an interfacial polymerization method. The finally obtained PGA composite membrane has a relatively hydrophobic surface, and the PU layer plays a role of a protective layer, so that the PGA is very stable in water, and the potential practical application value is endowed. The PGA composite membrane with potential practical application value is prepared by the interface super-assembly and interface polymerization method.

Description

Preparation method of polyurea/two-dimensional material/alumina super-assembled functional film

Technical Field

The invention belongs to the field of membrane science, and particularly relates to a preparation method of a polyurea/two-dimensional material/alumina super-assembled functional membrane.

Background

Two-dimensional materials refer to nano-sized sheet materials, which can be stacked to form nano-or sub-nano-sized films under vacuum-assisted conditions, and have recently gained wide attention in the field of film science. The two-dimensional film material has the following advantages: 1) can be prepared in large scale. The two-dimensional film material is usually formed by self-stacking of two-dimensional materials, and the simple film forming mode is unlimited in film forming thickness and area; 2) the pore channels are regular. The pore channel of the prepared two-dimensional membrane is formed by stacking nano sheets, and most of the pore channels have regular pore diameters and sizes, so that the membrane is endowed with certain selectivity; 3) the controllability is good. Other functional groups can be modified on the surface of the nano sheet layer to endow the nano sheet layer with certain functions, in addition, the size is controllable, and the size of a nano channel can be increased or reduced by utilizing an intercalation technology. Based on the above advantages, various two-dimensional materials such as graphene oxide, reduced graphene oxide, Mxenes materials, transition metal disulfides, and the like are widely used for constructing nanochannel membrane materials.

However, the current two-dimensional materials still have some challenges, such as stability in water, anti-fouling properties, etc. The two-dimensional nanosheets typically have oxygen-containing functional groups thereon that can bind to water molecules, causing the two-dimensional nanochannel film to swell, thereby degrading the performance of the film.

Disclosure of Invention

The present invention aims to solve the above problems and provide a method for preparing a polyurea/two-dimensional material/alumina super-assembled functional membrane, which can exist stably in water and solve the problem of stability of a two-dimensional nanochannel membrane in water, wherein a PU layer is used as a protective layer to prevent a GO membrane from peeling off in water and to provide PGA with excellent mechanical stability.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a polyurea/two-dimensional material/alumina super-assembled functional film comprises the following steps:

(1) preparing a dispersion liquid of carboxylated Graphene Oxide (GO);

(2) adopting a vacuum filtration method to grow GO on the AAO substrate with the assistance of interface super-assembly;

(3) drying the filtered GO/AAO composite membrane;

(4) preparing water-oil phase solution of synthetic polyurea monomer;

(5) dropwise adding Polyethyleneimine (PEI) onto the surface of the GO/AAO membrane, and volatilizing water to be dry;

(6) dropwise adding a 2, 4-Toluene Diisocyanate (TDI) solution to the surface of GO/AAO containing a PEI polymer chain, and carrying out interfacial polymerization reaction on amino groups between two phases and isocyanate in an oven to generate a compact polyurea film so as to obtain the PGA composite film with high mechanical property.

A polyurea protective layer grows on the surface of graphene oxide, so that PGA is very stable in water, and the PGA membrane prepared by the strategy of the invention adopts Anodic Aluminum Oxide (AAO) containing regular nano-channels as a substrate, so that the PGA membrane not only can be tightly combined with GO, but also can provide rich channels for ion or molecular transmission, and lays a foundation for the practical application of the PGA membrane.

Further, the specific method in the step (1) is as follows: weighing carboxylated graphene oxide, dispersing the carboxylated graphene oxide into deionized water, and performing ultrasonic dispersion, wherein the size of a nanosheet layer of the carboxylated graphene oxide is 3-5 microns.

Further, the concentration of the dispersion of carboxylated graphene oxide was 1 mg/ml.

The carboxylated graphene oxide is adopted, and has two main functions: on one hand, rich oxygen-containing functional groups on the GO nano sheet layer can generate super-assembly interaction with the AAO substrate, so that the GO nano sheet layer and the AAO substrate are tightly combined together; in addition, it can react with the amino groups on the PEI chains, riveting the PEI polymer chains on the surface of the GO membrane.

Further, vacuum filtration is adopted in the step (2), the filtration time is 6-7h, GO grows on the surface of the AAO by adopting a vacuum filtration method, and the membrane with a highly ordered layered structure can be obtained.

Further, the GO/AAO composite membrane obtained by suction filtration in the step (3) is placed in an oven at 80 ℃ and dried for 2-3 h.

Further, the specific method in the step (4) is as follows: firstly, preparing 1-2 w/v% of Polyethyleneimine (PEI) aqueous solution, and dissolving 96-240mg of 50 wt% PEI solution in 58-60ml of deionized water; then 0.4-0.6 w/v% of 2, 4-Toluene Diisocyanate (TDI) is prepared, 0.02-0.04g of TDI is weighed and dissolved in 60ml of n-hexane, and the prepared two solutions are placed in an oven at 60 ℃. Preferably, 1.5 w/v% PEI and 0.5 w/v% TDI monomer are used to prepare the polyurea. Because PEI polymer chains contain abundant amino groups, better polyurea film formation can be ensured, and a more compact polyurea film with a high degree of crosslinking can be obtained under the condition of the concentration.

Further, step (5) add 80-100 μ L of PEI drop-wise to GO/AAO membrane surface, until it volatilizes water to dryness at 60 ℃.

Further, 80-100 mu L of TDI solution is dripped on the surface of GO/AAO containing a PEI polymer chain in the step (6), amino groups between two phases and isocyanate are subjected to interfacial polymerization reaction in a drying oven at 60 ℃, the reaction time is 5min, the whole reaction is carried out at 60 ℃, relatively fast reaction rate of PEI and TDI is ensured, the interfacial polymerization reaction time is 5min, certain permeability of the membrane is maintained under the condition of keeping the membrane compact, and the potential application value of the membrane is ensured.

Polyurea as a waterproof material has excellent stability in water, and can relieve the expansion of the two-dimensional nano-channel membrane in water. The invention adopts polyurea as a waterproof protective layer of GO, and adopts interface super-assembly and interface polymerization dual strategies to prepare the PGA composite membrane, compared with GO/AAO, the PGA composite membrane has a hydrophobic outer surface, has very good stability in water, and has potential practical application value.

According to the invention, an interface super-assembly method is adopted, layer-by-layer assembly is carried out, firstly GO is assembled on an AAO substrate rich in nano-channels, then PEI is deposited on the surface of GO, a layer of polyurea film is grown on the surface of GO after interface polymerization reaction, and finally the PGA film is obtained. Due to the hydrophobicity of the PU film, the prepared film has excellent stability in water and has potential practical application value.

According to the invention, the PGA composite membrane is prepared by adopting carboxylated graphene oxide, and rich carboxyl on a nanosheet layer can form hydrogen bond super-assembly interaction with hydroxyl on AAO, so that the PGA composite membrane can be stably attached to an AAO substrate; in addition, carboxyl functional groups on the nanosheet layer can react with amino groups on a PEI chain, so that interfacial polymerization is promoted, and a PU film grows on the surface of GO. The invention adopts AAO as the substrate of the composite membrane, and the AAO contains rich nano-channels, thereby providing rich approaches for ion molecule transmission and having potential practical application value. The invention adopts PEI and TDI as monomers for synthesizing polyurea, mainly by means of rich amino groups on a PEI polymer chain, and the PEI and TDI can be fully connected and polymerized with isocyanate functional groups on TDI molecules to grow and form a PU film. The invention adopts an interfacial polymerization method to prepare the polyurea film, mainly because the method is simple and has low by-products. The two monomer concentrations adopted by the invention can cause the formation of a relatively compact PU layer, and simultaneously ensure that the PU layer contains rich nano-pores, thereby laying a foundation for the practical application of the PU layer. The PGA composite membrane is prepared by the interface super-assembly and interface polymerization strategies, PU exists, the permeation of water molecules is reduced, the stability of the membrane in water can be improved, and the PGA composite membrane has potential practical application value.

Drawings

FIG. 1 is a flow chart of the present invention for preparing a PGA composite membrane;

FIG. 2 is an optical picture of a PGA composite film prepared according to the present invention;

FIG. 3 is a scanning electron microscope contrast view of the surface of GO/AAO membrane and PGA composite membrane prepared by the present invention;

FIG. 4 is a cross-sectional view of a PU modified GO membrane made in accordance with the present invention;

FIG. 5 is a dot elemental analysis chart of the surface of the PGA composite film prepared by the present invention;

FIG. 6 is a surface element distribution diagram of a PGA composite membrane prepared in accordance with the present invention;

FIG. 7 is a comparison of zeta potential of GO membranes made in accordance with the present invention versus polyurea modified GO membranes;

FIG. 8 is a Fourier transform infrared contrast plot before and after GO modification of polyurea;

FIG. 9 is a graph comparing contact angles of different numbers of layers of modified polyurea;

FIG. 10 is a graph comparing the stability of PGA composite membranes to GO/AAO composite membranes in water.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

Example 1

The preparation method of the PGA composite membrane specifically comprises the following steps:

step 1: firstly, preparing a 1mg/ml dispersion liquid of carboxylated graphene oxide: weighing 3mg of carboxylated graphene oxide, dispersing the carboxylated graphene oxide into 3ml of deionized water, and performing ultrasonic dispersion for 3 hours, wherein the size of a nanosheet layer of the carboxylated graphene oxide is 3 microns;

step 2: growing GO on an AAO substrate by adopting a vacuum filtration method with the assistance of interface super-assembly, wherein the filtration time is about 6-7 h;

and step 3: then placing the filtered GO/AAO composite membrane in an oven at 80 ℃ and drying for 2-3 h;

and 4, step 4: preparing a water-oil phase solution of a synthetic polyurea monomer: firstly, preparing 1.5 w/v% (mg/ml) of Polyethyleneimine (PEI) aqueous solution, and dissolving 180mg of 50 wt% PEI solution into deionized water to 60 ml; then 0.5 w/v% (mg/ml) of 2, 4-Toluene Diisocyanate (TDI) is prepared, about 0.03g of TDI is weighed and dissolved in 60ml of n-hexane, and the prepared two solutions are placed in an oven at 60 ℃;

and 5: after that, first 100 μ L of PEI was dropped on the GO/AAO membrane surface, until it evaporated the water to dryness at 60 ℃;

step 6: then, 100 mu L of TDI solution is dripped on the GO/AAO surface containing a PEI polymer chain, the amino group between the two phases and isocyanate generate an interfacial polymerization reaction in a drying oven at 60 ℃, the reaction time is 5min, and a compact polyurea film is generated;

and 7: the final PGA composite film having high mechanical properties was obtained.

FIG. 1 is a flow chart of the preparation of PGA composite membranes by vacuum filtration interfacial super-assembly and interfacial polymerization in example 1. Firstly, a layer of GO membrane grows on an AAO substrate by adopting a vacuum filtration method, and then a layer of polyurea thin protective membrane grows on the surface of GO by an interface polymerization method, so that the final PGA membrane can be obtained.

Fig. 2 is an optical image of the PGA composite film prepared in example 1, and fig. 2a is a schematic representation of the PGA composite film. FIGS. 2(b-f) are polyurea films grown with one to five layers on the GO/AAO surface, respectively.

Example 2

step 1: firstly, preparing a 1mg/ml dispersion liquid of carboxylated graphene oxide: weighing 5mg of carboxylated graphene oxide, dispersing the carboxylated graphene oxide into 5ml of deionized water, and performing ultrasonic dispersion for 3 hours, wherein the size of a nanosheet layer of the carboxylated graphene oxide is 5 microns;

and 4, step 4: preparing a water-oil phase solution of a synthetic polyurea monomer: firstly, preparing 1 w/v% (mg/ml) of Polyethyleneimine (PEI) aqueous solution, and dissolving 96mg of 50 wt% PEI solution in deionized water to 58 ml; then 0.4 w/v% (mg/ml) of 2, 4-Toluene Diisocyanate (TDI) is prepared, about 0.024g of TDI is weighed and dissolved in 60ml of n-hexane, and the prepared two solutions are placed in an oven at 60 ℃;

and 5: after that, 80 μ L of PEI was first added dropwise to the GO/AAO membrane surface, until it evaporated the water to dryness at 60 ℃;

step 6: then, 80 mu L of TDI solution is dripped on the GO/AAO surface containing a PEI polymer chain, the amino group between the two phases and isocyanate generate an interfacial polymerization reaction in a drying oven at 60 ℃, the reaction time is 5min, and a compact polyurea film is generated;

Example 3

step 1: firstly, preparing a 1mg/ml dispersion liquid of carboxylated graphene oxide: weighing 7mg of carboxylated graphene oxide, dispersing the carboxylated graphene oxide into 7ml of deionized water, and performing ultrasonic dispersion for 3 hours, wherein the size of a nanosheet layer of the carboxylated graphene oxide is 5 microns;

and 4, step 4: preparing a water-oil phase solution of a synthetic polyurea monomer: firstly, preparing 2 w/v% (mg/ml) of Polyethyleneimine (PEI) aqueous solution, and dissolving 240mg of 50 wt% PEI solution in deionized water to 60 ml; then 0.6 w/v% of 2, 4-Toluene Diisocyanate (TDI) is prepared, about 0.036g of TDI is weighed and dissolved in 60ml of n-hexane, and the prepared two solutions are placed in a drying oven at 60 ℃;

and 5: then, 90 μ L of PEI is firstly dripped on the GO/AAO membrane surface, and the PEI is evaporated to be dry at 60 ℃;

step 6: then, 90 mu L of TDI solution is dripped on the GO/AAO surface containing a PEI polymer chain, the amino group between the two phases and isocyanate generate an interfacial polymerization reaction in a drying oven at 60 ℃, the reaction time is 5min, and a compact polyurea film is generated;

The PGA composite films obtained in example 1 were tested

1. Appearance characterization diagram of PGA composite membrane

GO or GO decorated by PU is carefully peeled off from the AAO substrate, and is carefully cut into small pieces by a pair of small scissors, and the small pieces are observed by a scanning electron microscope. Figure 3 compares the surface topography of GO with GO films grown with PU layers. Where fig. 3a, b are surfaces without a grown GO film, significant wrinkles can be seen; fig. 3c, d is a GO film with a PU layer grown on the surface, which can be seen to become rougher compared to the GO film surface.

Fig. 4 is a cross section of a PU-modified GO membrane layer, and it can be seen that GO still exhibits a layered stacked structure, which contains abundant interlayer nanochannels.

FIG. 5 is a point scan of the GO surface modified with PU, and two points are respectively selected on the GO surface, both of which can be found to contain abundant nitrogen elements, which indicates that the GO surface is successfully modified with polyurea.

Fig. 6 is a scan of the PU modified GO surface, and it can be seen that nitrogen is uniformly distributed on the selected GO surface, which indicates that polyurea is uniformly grown on the surface of the GO layer.

2. Performance characterization of PGA composite films

GO or polyurea modified GO film carefully layered AAO substrate was peeled off, after which it was ground to pieces with a mortar and tested for fourier transform infrared and surface charge changes, respectively. FIG. 7 is a comparison graph before and after modification, FIGS. 7a, b are zeta potential distribution plots of GO membrane and polyurea modified GO membrane, respectively, FIG. 7 compares zeta potentials of the two membranes, the zeta potential of a pure GO membrane is-25.8 mV, and the zeta potential of the GO membrane after modification of polyurea is around +55.1mV, which also supports successful modification of polyurea. FIG. 8 is a Fourier transform infrared contrast graph before and after modification, and it can be seen that the peak appears at 2800-2900cm-1 after modification of polyurea, which is the peak from saturated hydrocarbon on PEI chain, and 1500-1600cm-1 appears the fine structure peak of benzene ring, most importantly, C-N vibration peak of polyurea appears at 1302cm-1, which indicates that polyurea is successfully modified on GO.

3. Hydrophilic and hydrophobic property test of PGA composite membrane

Fig. 9 is a test of the hydrophilicity and hydrophobicity of the PGA composite membrane prepared by the interfacial super-assembly and interfacial polymerization strategies. A0.2. mu.L drop of water was dropped onto the surface of the film, and the contact angle after stabilization was measured and photographed. Fig. 9a is a contact angle test of GO/AAO composite membrane, which can be seen to exhibit excellent hydrophilicity due to the rich oxygen-containing functional groups on the GO surface. Fig. 9b-f show the hydrophilicity and hydrophobicity of the PGA composite membrane modified with different numbers of polyurea layers (1-5 times), and it can be seen that the surface of the GO membrane modified with polyurea has very good water repellency, indicating that polyurea functions as a protective layer.

4. Stability testing of PGA composite films

To test the stability of the PGA composite membrane, a GO/AAO composite membrane without a modified polyurea was prepared, and then soaked in a 1M KCl solution to test the stability thereof. Fig. 10a and b are pictures of the GO/AAO and PGA composite membranes just after soaking, respectively, and after soaking for 24h, it can be seen that the GO/AAO composite membrane has obvious cracks, and PGA still exists in the electrolyte solution stably, which indicates that PGA has very good stability and potential practical application value.

The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.

Claims

1. A preparation method of a polyurea/two-dimensional material/alumina super-assembled functional film is characterized by comprising the following steps:

(1) preparing a dispersion liquid of carboxylated graphene oxide;

(3) drying the filtered GO/AAO composite membrane;

(4) preparing water-oil phase solution of synthetic polyurea monomer;

2. The preparation method of the polyurea/two-dimensional material/alumina super-assembled functional film according to claim 1, wherein the specific method in the step (1) is as follows: weighing carboxylated graphene oxide, dispersing the carboxylated graphene oxide into deionized water, and performing ultrasonic dispersion, wherein the size of a nanosheet layer of the carboxylated graphene oxide is 3-5 microns.

3. The method for preparing the polyurea/two-dimensional material/alumina super-assembled functional film according to claim 2, wherein the concentration of the dispersion liquid of the carboxylated graphene oxide is 1 mg/ml.

4. The preparation method of the polyurea/two-dimensional material/alumina super-assembled functional film according to claim 1, wherein the step (2) adopts vacuum filtration, and the filtration time is 6-7 h.

5. The preparation method of the polyurea/two-dimensional material/alumina super-assembled functional film according to claim 1, wherein the GO/AAO composite film obtained by suction filtration in the step (3) is dried in an oven at 80 ℃ for 2-3 h.

6. The preparation method of the polyurea/two-dimensional material/alumina super-assembled functional film according to claim 1, wherein the specific method in the step (4) is as follows: firstly, preparing 1-2 w/v% of Polyethyleneimine (PEI) aqueous solution, and dissolving 96-240mg of 50 wt% PEI solution in 58-60ml of deionized water; then 0.4-0.6 w/v% of 2, 4-Toluene Diisocyanate (TDI) is prepared, 0.02-0.04g of TDI is weighed and dissolved in 60ml of n-hexane, and the prepared two solutions are placed in an oven at 60 ℃.

7. The method for preparing the polyurea/two-dimensional material/alumina super-assembled functional membrane as claimed in claim 1, wherein in the step (5), 80-100 μ L of PEI is dripped on the surface of the GO/AAO membrane, and the PEI is used for volatilizing water to be dry at 60 ℃.

8. The method for preparing the polyurea/two-dimensional material/alumina super-assembled functional film according to claim 1, wherein in the step (6), 80 to 100 μ L of TDI solution is dripped on the GO/AAO surface containing PEI polymer chains, and the amino group and isocyanate between the two phases are subjected to interfacial polymerization reaction in an oven at 60 ℃ for 5 min.