CN114950148A

CN114950148A - Layer-by-layer self-assembly preparation method of graphene oxide nanofiltration membrane

Info

Publication number: CN114950148A
Application number: CN202210562906.7A
Authority: CN
Inventors: 邵文尧; 陈忠岩; 王蕊
Original assignee: Xiamen University
Current assignee: Xiamen University
Priority date: 2022-05-23
Filing date: 2022-05-23
Publication date: 2022-08-30

Abstract

A layer-by-layer self-assembly preparation method of a graphene oxide nanofiltration membrane belongs to the field of nanofiltration membrane preparation. The more firm GO laminar membrane is assembled by utilizing the ionization and negative electricity property of carboxyl on GO in aqueous solution through the electrostatic interaction between the negatively charged GO and polyelectrolyte, and the interlayer spacing and the crosslinking level of the GO membrane are adjusted by a crosslinking agent EDA. In the preparation method, HPEI, EDA or PEI is used to study the influence of different additives on the surface appearance and performance of the nanofiltration membrane. The prepared membrane shows remarkable improvement on the performances such as hydrophilicity, water flux, solute interception and the like. The membrane preparation process based on the layer-by-layer self-assembly technology is efficient and easy to implement, the thickness of the prepared membrane is controllable, the separation requirements of multiple occasions can be met, and the membrane has industrial amplification application potential.

Description

Layer-by-layer self-assembly preparation method of graphene oxide nanofiltration membrane

Technical Field

The invention belongs to the field of nanofiltration membrane preparation, and particularly relates to a layer-by-layer self-assembly preparation method of a graphene oxide nanofiltration membrane by using a polyether sulfone ultrafiltration membrane as a base membrane and using graphene oxide and three different organic additives.

Background

Membranes are widely found in living organisms, are discontinuous regions between two phases, and have selective separability. The membrane separation technology is initially used for seawater desalination, is rapidly developed from the middle of the last century, is an important separation method at present, and is widely applied to the fields of environmental protection, petrifaction, biochemistry, water treatment, food processing, decoloration and the like. The membrane separation realizes the separation, purification, concentration and the like of two or more component fluids (liquid or gaseous) in a molecular range by utilizing driving forces such as concentration difference, pressure difference and potential difference, and has the advantages of no phase change, high efficiency, greenness, energy conservation, mild condition, convenience in recovery and the like.

Membrane separation techniques can be classified into microfiltration, ultrafiltration, nanofiltration and reverse osmosis, depending on the pore size of the membrane. The separation effect of nanofiltration is between ultrafiltration and reverse osmosis, and the membrane aperture is smaller than that of microfiltration and ultrafiltration, so that the separation effect is better than that of ultrafiltration and microfiltration; compared with reverse osmosis with high operation pressure (usually 1.5-10.5 MPa), the nanofiltration has low transmembrane pressure difference and high economical efficiency. The nanofiltration technology has the characteristics of excellent separation performance, high stability, energy conservation and the like, is widely applied to treatment of industrial and domestic wastewater, water softening, recovery or removal of small molecular organic matters and the like, and the research on the properties and industrial application of the nanofiltration membrane becomes a new research hotspot. In the preparation method of the nanofiltration membrane, an interfacial polymerization method, an L-S phase conversion method, a chemical modification method, a Layer-by-Layer self-assembly method, and the like are included at present, wherein a Layer-by-Layer self-assembly (LBL) technology is used as a new technology which is developing rapidly, plays an increasingly important role in the fields of chemistry, physics, biology, materials, nano science, medicine, and the like, and continuously promotes the technological progress and the economic development.

The layer-by-layer assembly (LBL) is a multilayer film construction technology, and the multilayer film is constructed by alternately depositing units by utilizing the non-covalent bond interaction force or covalent bond connection between nano materials/polyelectrolytes. Compared with other film-making methods, the layer-by-layer assembly film-forming method is relatively simple and environment-friendly.

Graphene Oxide (GO) has a unique two-dimensional structure, has strong mechanical properties, and can be stably dispersed in an aqueous solution. The GO nanosheets are efficiently stacked by using non-covalent bond interaction forces such as static electricity, hydrogen bonds, van der Waals force, pi-pi stacking effect and the like, and are potential membrane technical materials. Wansuk Choi et al surface-modified PA-TFC RO membranes by layer-by-layer assembly of negatively charged GO and positively charged Aminated GO (AGO). After 10 times of layer assembly cycles, the surface roughness of the PA-TFC-GO membrane is reduced to 21.5nm from 46.5nm, and the contact angle is reduced to 25.9 +/-3.0 from 70.6 +/-2.4 degrees, and the anti-pollution and chlorine resistance of the membrane are enhanced by improving the hydrophilicity and smoothness of the membrane (ACS appl. Mater. interfaces 2013,5,23, 12510-. Although the application of GO in membrane technology is more fully studied, there are still key problems to be solved such as poor compatibility, low permeation flux, etc.

Disclosure of Invention

The invention aims to provide a Graphene Oxide (GO) composite nanofiltration membrane with wide application range and good nanofiltration performance aiming at the blank of the existing research technology, and provides a layer-by-layer self-assembly preparation method of the graphene oxide nanofiltration membrane.

The invention comprises the following steps:

1) weighing certain mass of flaky GO, grinding, adding pure water to prepare 80mL of GO solution, and performing ultrasonic treatment to obtain GO dispersion liquid;

2) weighing a certain amount of polyelectrolyte additive, adding water, magnetically stirring to prepare 80mL of additive solution, and stirring for 1 h;

3) and mixing the GO dispersion liquid and the additive solution to obtain a filter-pressing solution, uniformly stirring, pouring into an ultrafiltration cup, pressurizing and filtering under 1.6bar, stopping pressurizing when the volume of the permeation solution is 125mL, and drying the membrane.

In the step 1), the optimal concentration condition of the GO solution is 0.1-0.2 mg/mL; the ultrasonic frequency can be 40 +/-2 kHz, and the ultrasonic time is 1 h.

In step 2), the polyelectrolyte additive may be usedUsing Polyethyleneimine (PEI), polyethyleneimine (HPEI) or Ethylenediamine (EDA); the rotation speed of the water adding magnetic stirring can be 600rpm, and the stirring time is 1 h; when the polyelectrolyte additive adopts PEI, the thickness of the self-assembled layer is 524.8-971.4 nm, and the water permeation flux is 150-615 L.m ^-2 ·h ^-1 ·bar ^-1 (ii) a When the polyelectrolyte additive adopts HPEI, the water flux of the membrane is 1350L-m ^-2 ·h ^-1 ·bar ^-1 The retention rate for Evans blue is nearly 100%.

In the step 3), the membrane can be dried for 1h under the conditions of 60 ℃ and vacuum degree of-0.9 bar.

The invention provides a composite nanofiltration membrane, which is prepared by a layer-by-layer self-assembly method by using graphene oxide and different polyelectrolyte additives as membrane preparation materials.

The design idea of the invention is as follows: layer-by-layer self-assembly can be realized among GO sheets through non-covalent bond interaction forces such as hydrogen bonds, van der waals force and the like, but the GO laminated membrane assembled by the non-covalent bond interaction forces has poor stability and durability in the actual separation process. Thus, electrostatic interactions between negatively charged carboxyl groups on GO and polyelectrolytes are exploited to assemble a more robust GO layered membrane. Meanwhile, the introduction of the flexible polyelectrolyte is expected to enhance the compatibility of the self-assembly material and the base membrane.

The composite nanofiltration membrane is prepared by GO and different additives by utilizing a layer-by-layer self-assembly technology. Obtaining the optimal film-making conditions: the GO concentration is below 0.2mg/mL, and when the polyelectrolyte additive uses Polyethyleneimine (PEI), the retention rate of the membrane on Evans blue can reach 95.4%; after the HPEI is used as the polyelectrolyte additive or the cross-linking agent EDA is added, the hydrophilicity and hydrophobicity, the water flux and the evans blue retention rate of the membrane are all obviously different, wherein the water flux of the membrane with the HPEI as the polyelectrolyte additive is 1350 L.m ^-2 ·h ^-1 ·bar ^-1 The retention rate of Evans blue is close to 100%, and various performances are remarkably improved.

According to the invention, a layer-by-layer self-assembly technology is utilized, GO and different additives are assembled on a PES (polyether sulfone) base film to prepare a nanofiltration membrane, the influence of different preparation conditions on the separation performance of a GO laminated membrane is researched, and the appearance is characterized.

The invention comprises the following steps:

1) stacking polyelectrolyte PEI and GO by a layer-by-layer self-assembly technology;

2) stacking polyelectrolytes HPEI and GO by a layer-by-layer self-assembly technology;

3) and stacking the cross-linking agents EDA and GO by a layer-by-layer self-assembly technology.

Compared with the prior art, the invention has the characteristics and beneficial effects that:

according to the invention, by utilizing the ionization negative charge property of carboxyl on GO in an aqueous solution, a firmer GO layered membrane is assembled through electrostatic interaction between the negatively charged GO and polyelectrolyte, and the interlayer spacing and the crosslinking level of the GO membrane are adjusted through a crosslinking agent EDA. In the preparation method, the polyelectrolyte HPEI or the cross-linking agent EDA is used for replacing PEI, and the influence of different additives on the surface appearance and the performance of the nanofiltration membrane is researched. The prepared membrane shows remarkable improvement on the performances such as hydrophilicity, water flux, solute interception and the like. When the PEI is a polyelectrolyte additive, the thickness of the self-assembled layer is 524.8-971.4 nm, and the water permeation flux is 150-615 L.m ^-2 ·h ^-1 ·bar ^-1 The highest retention rate of evans blue reaches 95.4 percent, and the water flux of the membrane is 1350 L.m when HPEI is used as a polyelectrolyte additive ^-2 ·h ^-1 ·bar ^-1 The retention rate of Evans blue is nearly 100%. The membrane preparation process based on the layer-by-layer self-assembly technology is efficient and easy to implement, the thickness of the prepared membrane is controllable, the separation requirements of multiple occasions can be met, and the membrane has application potential.

Drawings

Fig. 1 is a schematic diagram of a device for testing the performance of a GO layered nanofiltration membrane.

Figure 2 is SEM images of membrane surface at different GO concentrations (PEI is polyelectrolyte additive): (a) PES substrate; (b) GO-PEI-1; (c) GO-PEI-2; (d) GO-PEI-3; (e) GO-PEI-4.

Figure 3 is SEM image of membrane cross-section for different GO concentrations (PEI is polyelectrolyte additive): (a) PES substrate; (b) GO-PEI-1; (c) GO-PEI-2; (d) GO-PEI-3; (e) GO-PEI-4.

Figure 4 is a graph of active layer thickness for different GO concentrations (PEI is polyelectrolyte additive).

Figure 5 is a comparison graph of static contact angles of membrane surfaces for different GO concentrations (PEI is polyelectrolyte additive).

Figure 6 is a comparison graph of membrane water flux for different GO concentrations (PEI is polyelectrolyte additive).

FIG. 7 is a comparison graph of Evans blue flux for different GO concentrations (PEI is a polyelectrolyte additive).

Figure 8 is a graph comparing evans blue retention of membranes at different GO concentrations (PEI is polyelectrolyte additive).

FIG. 9 is an SEM image of the surface of a membrane with the polyelectrolyte modified and the crosslinker added: (a) PES; (b) GO-PEI-4; (c) GO-HPEI; (d) GO-EDA.

FIG. 10 is an SEM image of a cross-section of a membrane with a modified polyelectrolyte and added cross-linking agent: (a) PES; (b) GO-PEI-4; (c) GO-HPEI; (d) GO-EDA.

FIG. 11 is a graph comparing contact angles of membranes with varying polyelectrolytes and with the addition of cross-linking agents.

FIG. 12 is a comparison graph of water flux for membranes with varying polyelectrolytes and the addition of cross-linking agents.

FIG. 13 is a graph comparing Evans blue flux with varying polyelectrolyte and addition of cross-linking agent.

FIG. 14 is a graph comparing evans blue retention for varying polyelectrolytes and adding a cross-linking agent.

Detailed Description

In order that those skilled in the art will better understand the technology of the present invention, the following embodiments are further described with reference to the accompanying drawings.

The reagents used in the present invention are either commercially available directly or can be prepared by the methods described in the present invention. The method is characterized in that a novel nanofiltration membrane with better membrane performance is prepared on a polyethersulfone ultrafiltration base membrane by using a GO solution and different additives through a layer-by-layer self-assembly technology, and the detailed experimental steps for characterization and analysis of the nanofiltration membrane are as follows:

1. preparing a GO layered nanofiltration membrane:

1) accurately weighing a certain mass of flaky GO, grinding for about 3min, adding 80mL of pure water, and performing ultrasonic treatment (frequency is 40 +/-2 kHz) for 1h to obtain a GO dispersion liquid with a certain concentration;

2) accurately weighing 0.32g of PEI, adding 80mL of pure water, and magnetically stirring (rotating speed of 600rpm) for 1h to obtain a 0.4% PEI solution;

3) soaking a PES (polyether sulfone) base membrane in pure water for 1 hour, fixing the PES base membrane at the bottom of an ultrafiltration cup, and then filtering 100mL of pure water under 1bar pressure;

4) mixing the GO dispersion liquid and the PEI solution, uniformly stirring, pouring into an ultrafiltration cup, pressurizing and filtering at 1.6bar, and stopping pressurizing when the volume of the permeation liquid is 125 mL;

5) taking down the cup body of the ultrafiltration cup, and drying the membrane for 1h at the temperature of 60 ℃ and the vacuum degree of-0.9 bar.

6) When the polyelectrolyte type is changed or the cross-linking agent is used, the PEI in the above step is replaced by HPEI or EDA with the same content, and the GO dispersion concentration is fixed to be 0.4mg/mL, and the rest conditions are unchanged.

Fig. 1 is a schematic diagram of a device for testing the performance of a GO layered nanofiltration membrane. Mainly comprises a nitrogen steel cylinder connected with an ultrafiltration cup capable of high-pressure operation, and a lifting platform for adjusting the height.

The composition of the filter-pressed solution corresponding to the membrane number of each example is given in Table 1.

TABLE 1

2. And (3) film appearance characterization:

the scanning electron microscope scans the surface of a sample by utilizing extremely narrow electron beams, and amplifies the surface of the sample in a point-by-point imaging mode, so that the qualitative or quantitative analysis is carried out on the microstructure such as the film surface, the section morphology, the pore structure, the thickness of an active layer, the roughness and the like. In the experiment, the morphology and the structure of the surface of a film sample are characterized by using a German ZEISS SIGMA type Scanning Electron Microscope (SEM). Freezing and cutting the dried membrane sample, fixing the membrane sample on a sample table, spraying platinum, and observing under the acceleration voltage of 20kV and the magnification of 10000 or 20000.

3. And (3) determining the hydrophilic and hydrophobic performances of the membrane:

the hydropathic and hydrophobic properties of a membrane are generally measured by contact angle magnitude. The contact angle is also called wetting angle, and refers to the spreading angle of a liquid on a fixed surface when the liquid reaches thermodynamic equilibrium on the surface. The better the hydrophilicity of the surface, the smaller the spreading angle of the liquid and therefore the smaller the contact angle. In the experiment, a HARKE SPCAX3 type contact angle tester is used for measuring the contact angle of the surface of the nanofiltration membrane, and the contact angle tester can be used for characterizing the hydrophilic and hydrophobic properties of the membrane. The water amount is 3 mu L each time, and the contact time of the liquid and the surface of the nanofiltration membrane is 30 s. To improve the accuracy of the measurement data, the contact angle was measured 5 times per film sample and averaged.

4. And (3) measuring the membrane flux and the retention rate:

the flux and rejection of the membrane were measured using an ultrafiltration cup and pressurized using a nitrogen cylinder.

4.1 flux:

the effective area of each membrane is about 40cm ² The steps of measuring flux are as follows:

1) fixing the membrane with the skin layer facing upwards at the bottom of the ultrafiltration cup;

2) pouring 300mL of the solution into the ultrafiltration cup, and pre-pressing about 50mL at 1bar (if the filtration speed is too slow at 1bar, the pressure can be increased properly);

3) starting timing after the pre-pressing is finished, and recording the pressure and the volume of the permeation liquid within a certain time;

4) the flux is calculated as follows:

wherein J is the flux (L.m) of the membrane ^-2 ·h ^-1 ·bar ^-1 ) And V is the volume of the permeate (m) ³ ) A is the effective membrane area (m) of the membrane ² ) P is the filtration pressure (bar) and Δ t is the filtration time (h).

4.2 rejection:

(a) and (3) testing the retention rate of the salt solution:

the salt rejection rate of the nanofiltration membrane is measured by using sodium sulfate (molecular weight: 142.04). The measurement steps are as follows:

1) preparing 300mL of 2g/L sodium sulfate solution, and pouring into an ultrafiltration cup;

2) after pre-pressing for more than ten milliliters, collecting permeate and concentrated solution, and respectively measuring the conductivity;

3) obtaining the concentration C of the permeate according to the conductivity-concentration curve of the sodium sulfate _p And concentrate concentration C _f ；

4) The retention rate is calculated as follows:

wherein R is the retention (%) of the membrane, C _p And C _f The sodium sulfate concentrations (g/L) in the permeate and the concentrate were determined, respectively.

(b) Evans blue retention test:

the invention utilizes Evans blue (molecular weight: 960.81) to measure the dye retention rate of the nanofiltration membrane. The measurement steps are as follows:

1) preparing 300mL of Evans blue solution with the concentration of 50mg/L, and pouring the solution into an ultrafiltration cup;

2) pre-pressing for 10min, collecting the permeate and the concentrated solution, and measuring absorbance (diluting when the concentration is too high) at wavelength 608nm with an ultraviolet spectrophotometer;

3) obtaining the concentration C of the permeate according to the absorbance-concentration curve of Evans blue _p And concentrate concentration C _f ；

4) The retention rate is calculated as follows:

wherein R is the retention rate (%) of the membrane, C _p And C _f The concentration of Evans blue (mg/L) in the permeate and the concentrate, respectively.

Figure 2 gives SEM images of the membrane surface for different GO concentrations (PEI is polyelectrolyte additive): (a) PES substrate; (b) GO-PEI-1; (c) GO-PEI-2; (d) GO-PEI-3; (e) GO-PEI-4.

Figure 3 gives SEM images of membrane sections at different GO concentrations (PEI is polyelectrolyte additive): (a) PES substrate; (b) GO-PEI-1; (c) GO-PEI-2; (d) GO-PEI-3; (e) GO-PEI-4.

Figure 4 gives a thickness map of active layer for different GO concentrations (PEI is polyelectrolyte additive).

Figure 5 gives a comparison graph of static contact angles of the membrane surface for different GO concentrations (PEI is polyelectrolyte additive).

Figure 6 gives a comparison of membrane water flux for different GO concentrations (PEI is polyelectrolyte additive).

Figure 7 gives a comparison of evans blue flux for different GO concentrations (PEI is polyelectrolyte additive).

Figure 8 gives a comparison of evans blue retention of the membrane (PEI is polyelectrolyte additive) for different GO concentrations.

FIG. 9 shows SEM images of the surface of a membrane with the polyelectrolyte modified and the crosslinker added: (a) PES; (b) GO-PEI-4; (c) GO-HPEI; (d) GO-EDA.

FIG. 10 shows SEM images of cross-sections of membranes with the polyelectrolyte changed and the crosslinker added: (a) PES; (b) GO-PEI-4; (c) GO-HPEI; (d) GO-EDA.

FIG. 11 shows a comparison of membrane contact angles for varying polyelectrolytes and adding a cross-linking agent.

FIG. 12 is a graph showing a comparison of water flux for membranes with varying polyelectrolytes and with the addition of a cross-linking agent.

FIG. 13 shows a comparison of Evans blue flux for varying polyelectrolytes and adding a cross-linking agent.

FIG. 14 shows a comparison of evans blue retention for varying polyelectrolytes and the addition of a cross-linking agent.

By comprehensively analyzing the experimental results, the invention obtains the following conclusion:

1. with the increase of GO concentration, the surface and section structure of the membrane has no obvious change, the thickness of the skin layer is gradually increased, the hydrophilicity is increased and then reduced, the water flux is gradually reduced, the flux to Evans blue is gradually reduced, and the interception rate is obviously increased;

2. when the GO concentration in the filter-pressing solution is 0.2mg/mL, the rejection rate of the nanofiltration membrane on Evans blue is the highest and reaches 95.4%, and the rejection rate is the optimal GO concentration under the experimental concentration gradient;

3. when hydrophilicity is tested, GO-PEI has the smallest contact angle, and the hydrophilicity is GO-PEI & gtGO-EDA & gtPES & gtGO-HPEI. It is likely that HPEI densifies the surface structure of the membrane, reducing porosity and hence hydrophilicity of the membrane.

4. The performances of GO-PEI-4 and GO-HPEI are relatively close, and both have low flux and high rejection rate. The GO formed is close in lamellar spacing, probably due to the similar properties of PEI and HPEI.

5. GO-EDA has high flux and low rejection rate, which is probably because the cross-linking agent has larger influence on the size of the interlayer distance, and C-N covalent bonds formed by EDA between GO layers increase the interlayer distance, so that most of sodium sulfate and evans blue can smoothly pass through the membrane.

6. Under the optimal GO concentration, after the polyelectrolyte PEI is changed into HPEI or a cross-linking agent EDA is added, the membrane surface and section structures have no obvious difference, and the hydrophilicity and hydrophobicity, the water flux, the Evans blue flux and the retention rate have obvious difference.

The optimal concentration condition of the GO membrane is 0.2mg/mL, and when the polyelectrolyte additive uses Polyethyleneimine (PEI), the retention rate of the membrane on Evans blue can reach 95.4%; after the additive uses Hyperbranched Polyethyleneimine (HPEI) or crosslinking agent Ethylenediamine (EDA), the hydrophilicity and hydrophobicity, water flux and Evans blue retention rate of the membrane are obviously different. The water flux of the membrane in which the polyelectrolyte additive is HPEI is 1350 L.m ^-2 ·h ^-1 ·bar ^-1 The rejection rate of evans blue is close to 100%, and the GO composite nanofiltration membrane has the optimal performance.

The above description is only a preferred embodiment of the present invention, and it will be apparent to those skilled in the art that several modifications and enhancements can be made without departing from the technical principles of the present invention, and such modifications and enhancements should also be considered as the protection scope of the present invention.

Claims

1. A layer-by-layer self-assembly preparation method of a graphene oxide nanofiltration membrane is characterized by comprising the following steps:

2. The layer-by-layer self-assembly preparation method of a graphene oxide nanofiltration membrane according to claim 1, wherein in step 1), the concentration of the GO solution is 0.1-0.2 mg/mL.

3. The layer-by-layer self-assembly preparation method of the graphene oxide nanofiltration membrane as claimed in claim 1, wherein in the step 1), the ultrasonic frequency is 40 ± 2kHz, and the ultrasonic time is 1 hour.

4. The method for preparing the graphene oxide nanofiltration membrane by layer-by-layer self-assembly according to claim 1, wherein in the step 2), PEI, HPEI or EDA is adopted as the polyelectrolyte additive.

5. The layer-by-layer self-assembly preparation method of the graphene oxide nanofiltration membrane as claimed in claim 1, wherein in the step 2), the rotation speed of the water-adding magnetic stirring is 600rpm, and the stirring time is 1 h.

6. The layer-by-layer self-assembly preparation method of the graphene oxide nanofiltration membrane as claimed in claim 1, wherein in the step 3), the membrane is dried for 1 hour at 60 ℃ and under a vacuum degree of-0.9 bar.

7. The layer-by-layer self-assembly preparation method of the graphene oxide nanofiltration membrane as claimed in claim 4, wherein when PEI is adopted as the polyelectrolyte additive, the thickness of the self-assembly layer is 524.8-971.4 nm, and the water permeation flux is 150-615L-m ^-2 ·h ^-1 ·bar ^-1 (ii) a When the polyelectrolyte additive adopts HPEI, the water flux of the membrane is 1350 L.m ^-2 ·h ^-1 ·bar ^-1 The retention rate for Evans blue is nearly 100%.

8. The graphene oxide nanofiltration membrane prepared by the preparation method of any one of claims 1 to 7.