NANOFILTRATION COMPOSITE MEMBRANE, AND PREPARATION METHOD AND APPLICATION THEREOF

Abstract

The present invention discloses a nanofiltration composite membrane, a preparation method and application thereof. The preparation method comprises: A) preparing 2D nano-material dispersion; B) first preparing a solution of a polymer material with a certain concentration, continuously adding a poor solvent under stirring conditions to subject the polymer material to chemical reaction to obtain a dispersion containing negatively charged polymer gel particles; C) subjecting the nano-material dispersion in step A) and the dispersion prepared in step B) to blending, membrane preparation and drying, and then placing the membrane into an alkaline solution with a certain concentration and pure water for soaking to obtain a nanofiltration composite membrane. The nanofiltration composite membrane can efficiently remove heavy metal complex ions through the synergistic effect of pore size screening and charge repulsion. Moreover, the rejection rate and flux of the nanofiltration composite membrane have not changed obviously after use for a long time.

Claims

1. A nanofiltration composite membrane, wherein a preparation method of the nanofiltration composite membrane comprises the following steps: A) preparing a 2D nano-material dispersion; B) first preparing a solution of a polymer material with a certain concentration, continuously adding a poor solvent under stirring conditions to subject the polymer material to chemical reaction to obtain a dispersion containing negatively charged polymer gel particles; and C) subjecting the nano-material dispersion in step A) and the dispersion prepared in step B) to blending, membrane preparation and drying, and then placing the membrane into an alkaline solution with a certain concentration and pure water for soaking to obtain a nanofiltration composite membrane.

2. The nanofiltration composite membrane according to claim 1, wherein the polymer material comprises any one of polymethacrylic acid, sodium polyethylene sulfonate, polyacrylonitrile and polymethyl acrylate.

3. The nanofiltration composite membrane according to claim 1, wherein the 2D nano-material comprises any one of graphene oxide, MoS2, LDH, or Mxene.

4. The nanofiltration composite membrane according to claim 3, wherein the polymer gel particles in step B) have a particle size of 0.5-10 nm.

5. The nanofiltration composite membrane according to claim 1, wherein the 2D nano-material dispersion prepared in step A) has a concentration of 0.001-10 mg/mL.

6. The nanofiltration composite membrane according to claim 1, wherein the poor solvent in step B) comprises, but is not limited to, ethanol, water, hexane, acetonitrile and petroleum ether, and an added volume of the poor solvent accounts for 5%-85% of a total volume of the solution.

7. The nanofiltration composite membrane according to claim 1, wherein the membrane thickness is controlled to be 5 nm to 50 μm when the membrane is made in step C).

8. The nanofiltration composite membrane according to claim 7, wherein a method for membrane preparation in step C) comprises, but is not limited to, any one of vacuum filtration, heating stage tape casting, and a method for membrane preparation by a spin coater.

9. The nanofiltration composite membrane according to claim 1, wherein when the nano-material dispersion in step A) is blended with the solution prepared in step B), the mass ratio of the 2D nano-material to the polymer material is 1:(0.001-10).

10. Application of the nanofiltration composite membrane according to claim 1, wherein the nanofiltration composite membrane is used for removing heavy metal complex ions from water.

11. The nanofiltration composite membrane according to claim 2, wherein the 2D nano-material comprises any one of grapheme oxide, MoS2, LDH, or Mxene.

12. The nanofiltration composite membrane according to claim 11, wherein the polymer gel particles in step B) have a particle size of 0.5-10 nm.

13. The nanofiltration composite membrane according to claim 2, wherein the poor solvent in step B) comprises, but is not limited to, ethanol, water, hexane, acetonitrile and petroleum ether, and an added volume of the poor solvent accounts for 5%-85% of a total volume of the solution.

14. The nanofiltration composite membrane according to claim 2, wherein the membrane thickness is controlled to be 5 nm to 50 μm when the membrane is made in step C).

15. The nanofiltration composite membrane according to claim 14, wherein a method for membrane preparation in step C) comprises, but is not limited to, any one of vacuum filtration, heating stage tape casting, and a method for membrane preparation by a spin coater.

16. The nanofiltration composite membrane according to claim 2, wherein when the nano-material dispersion in step A) is blended with the solution prepared in step B), the mass ratio of the 2D nano-material to the polymer material is 1:(0.001-10).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a schematic diagram of a nanofiltration composite membrane;

[0027] FIG. 2 is a preparation flowchart of a nanofiltration composite membrane;

[0028] FIG. 3 is an optical photograph of a nanofiltration composite membrane prepared in Example 1;

[0029] FIG. 4 is a transmission electron microscope (TEM) photograph of a nanofiltration composite membrane prepared in Example 1;

[0030] FIG. 5 is a diagram showing the removal of different heavy metal complex ions by the nanofiltration composite membrane prepared in Example 1;

[0031] FIG. 6 is a diagram showing the removal of complex ions of different coordination heavy metals by the nanofiltration composite membrane prepared in Example 1;

[0032] FIG. 7 is a diagram showing a long-time test of removal of Cu-EDTA by the nanofiltration composite membrane prepared in Example 1; and

[0033] FIG. 8 is a comparison of Cu-EDTA rejection rates of a pure Graphene Oxide (GO) membrane in Comparative Example 1 and a nanofiltration composite membrane (GO/PMAA) of the present invention.

DETAILED DESCRIPTION

[0034] The present invention is further described below with reference to specific embodiments.

EXAMPLE 1

[0035] A method for preparing a nanofiltration membrane for removing heavy metal complex ions in this example comprises the following steps:

[0036] 1) Using water as a solvent, preparing a GO dispersion with a concentration of 10 mg/mL;

[0037] 2) Dissolving polymethacrylic acid (PMAA) in dimethylacetamide (DMAc) to obtain a solution (PMAA/DMAc) with a concentration of 100 mg/ml, continuously adding petroleum ether with stirring to induce the generation of polymer gel particles, and further subjecting the polymer material to nucleophilic reaction to obtain a dispersion containing negatively charged polymer gel particles; wherein an added volume of the petroleum ether accounts for 5% of a total volume of the solution; and the polymer gel particles have a particle size of 0.5-10 nm, which is confirmed by TEM characterization;

[0038] 3) Blending the GO dispersion in step 1) with the solution obtained in step 2), wherein the mass ratio of the GO to the PMAA in the blended solution is 1:1.

[0039] Prepare a membrane by vacuum filtration, wherein the thickness of the membrane is controlled at 1 μm; after the membrane is dried, first place the membrane in a 10% wt disodium hydrogen phosphate solution for soaking for 2 h, and then soak the membrane in pure water, and take out the membrane to obtain the GO nanofiltration composite membrane. FIG. 1 is a schematic structural diagram of a nanofiltration composite membrane.

[0040] FIG. 2 is a preparation flowchart of a nanofiltration composite membrane, illustrating preparation steps of the nanofiltration composite membrane. FIG. 3 is an optical photograph of a (GO/PMAA) nanofiltration composite membrane prepared in Example 1.

[0041] FIG. 4 is a TEM photograph of the nanofiltration composite membrane prepared according to the method in Example 1. As can be seen from FIG. 4, the size of the polymer gel particles is 2-3 nm, and the polymer gel particles are uniformly dispersed in the GO membrane without obvious agglomeration.

EXAMPLE 2

[0042] A method for preparing a nanofiltration composite membrane for removing heavy metal complex ions in this example comprises the following steps:

[0043] 1) Using water as a solvent, preparing a molybdenum disulfide (MoS2) dispersion with a concentration of 0.02 mg/mL;

[0044] 2) Dissolving polyacrylonitrile (PAN) in N-methyl pyrrolidone (NMP) to obtain a (PAN/NMP) solution with a concentration of 1 mg/ml, continuously adding water with stirring, wherein an added volume of the water accounts for 15% of a total volume of the solution; subjecting the polymer material to nucleophilic reaction to obtain a dispersion containing negatively charged polymer gel particles; the polymer gel particles have a particle size of 0.5-10 nm which is confirmed by TEM characterization;

[0045] 3) Blending the MoS2 dispersion in step 1) with the solution obtained in step 2), wherein the mass ratio of the MoS.sub.2 to the PAN in the blended solution is 1:0.001, and preparing a membrane by using heating stage tape casting, wherein the membrane thickness is controlled at 50 μm; after the membrane is dried, place the membrane in a 1% wt KHCO.sub.3 solution for soaking for 24 h, followed by pure water, and take out the membrane to obtain the MoS.sub.2 nanofiltration composite membrane.

EXAMPLE 3

[0046] A method for preparing a nanofiltration composite membrane for removing heavy metal complex ions in this example comprises the following steps:

[0047] 1) Using water as a solvent, preparing a GO dispersion with a concentration of 0.001 mg/mL.

[0048] 2) Preparing a polymethyl acrylate (PAN/NMP) solution (0.1 mg/ml), and continuously adding anhydrous ethanol with stirring, wherein an added volume of the anhydrous ethanol accounts for 85% of a total volume of the solution; subjecting the polymer material to nucleophilic reaction to obtain a dispersion containing negatively charged polymer gel particles; the polymer gel particles have a particle size of 0.5-10 nm which is confirmed by TEM characterization;

[0049] 3) Blending the GO dispersion in step 1) with the solution obtained in step 2), wherein the mass ratio of the GO to the PMA in the blended solution is 1:10, and preparing a membrane by using a spin coater, wherein the membrane thickness is controlled at 5 nm; after the membrane is dried, first place the membrane in a 0.05% wt NaOH solution for soaking for 24 h, then soak the membrane in pure water, and take out the membrane to obtain a (GO/PMA) nanofiltration composite membrane.

Comparative Example

[0050] This comparative example is a method for preparing a GO membrane, which comprises the following steps:

[0051] Using water as a solvent, preparing a GO dispersion with a concentration of 10 mg/mL; preparing a membrane by vacuum filtration, wherein the membrane thickness is controlled at 1 μm, and drying the membrane to obtain the GO membrane.

EXAMPLE b 4

[0052] In this example, the performance test of the membranes prepared in Example 1 and comparative example is as follows:

[0053] The nanofiltration composite membrane prepared by the present invention is used for performing removal testing on complex ions of different complexing agents (metal complex ions) and coordination heavy metals, and specific experimental conditions are as follows: Cu-EDTA, Ni-EDTA and Cr-EDTA solutions with concentrations of 10 mg/L (calculated by heavy metal ions) respectively are adopted to simulate wastewater, and the nanofiltration composite membrane prepared in Example 1 is adopted for filtration test.

[0054] The test is conducted by dead end filtration, and the filtration pressure is controlled at 1 bar by a vacuum water pump. The concentrations of heavy metals in a stock solution and a filtrate are determined by inductively coupled plasma (ICP). The rejection rate (R%) and a calculation method are calculated according to Formula 1:

[00001]$\begin{array}{cc}R\%=\frac{c_0-c_t}{c_0}\times 100\%& \mathrm{Formula}1\end{array}$

where c.sub.0 and c.sub.t are the concentrations of heavy metals in the stock solution and the filtrate respectively.

[0055] A method for calculating a flux is implemented according to Formula 2

[00002]$\begin{array}{cc}\mathrm{Flux}=\frac{V}{A.Math.t.Math.\Delta P}& \mathrm{Formula}2\end{array}$

where v, A, t, and Δp are the volume of the filtrate, the area of a tested membrane, test time and transmembrane pressure respectively.

[0056] FIG. 5 is a diagram showing the removal of different heavy metal complex ions by the nanofiltration composite membrane prepared in Example 1. In the figure, for each heavy metal complex ion, a left histogram represents flux and a right histogram represents rejection rate. The results show that the nanofiltration composite membrane of the present invention has rejection rates more than 96% for Cu-NTA, Cu-CA and Cu-EDTA and flux more than 12 L/m.sup.2h.

[0057] FIG. 6 is a diagram showing the removal of complex ions of different coordination heavy metals by the nanofiltration composite membrane prepared in Example 1. In the figure, for complex ions of each coordination heavy metal, a left histogram represents flux and a right histogram represents rejection rate. The results show that the nanofiltration composite membrane of the present invention has rejection rates more than 97% for Cu-EDTA, Ni-EDTA and Cr-EDTA and flux more than 12 L/m.sup.2h.

EXAMPLE 5

[0058] In this example, the long-term performance test of the membrane prepared in Example 1 is carried out, a test method is basically the same as that of Example 4, except that the test conditions are: the concentration of Cu-EDTA in a simulated solution is 10 ppm, the test is conducted by dead end filtration, and the filtration pressure is controlled at 1 bar by a vacuum water pump.

[0059] FIG. 7 shows a long-time test of removal of Cu-EDTA by the nanofiltration composite membrane prepared in Example 1. In the figure, an upper curve represents the change of rejection rate, and a lower curve represents the change of flux. The results show that there is no obvious change in the flux and rejection rate during the continuous 120h test, which indicates that the nanofiltration membrane of the present invention still maintains good removal performance after operating for 120 h.

EXAMPLE 6

[0060] This example compares the Cu-EDTA rejection rates of the pure GO membrane and the nanofiltration composite membrane (GO/PMAA membrane) of the present invention. The test method is basically the same as that of Example 4, except that the concentration of Cu-EDTA in a simulated solution is 10 ppm.

[0061] FIG. 8 is a comparison of Cu-EDTA rejection rates of a pure graphene oxide (GO) membrane in Comparative Example 1 and the nanofiltration composite membrane (GO/PMAA) of the present invention. The rejection rate of the pure GO membrane is 41%, and the rejection rate of the GO membrane of the present invention is 97%.

[0062] According to the results, compared with the GO membrane, the (GO/PMAA) nanofiltration composite membrane of the present invention has higher negative electricity performance; and the removal performance of the nanofiltration composite membrane on the heavy metal complex ions with negative charge can be effectively improved through the electrostatic repulsion performance. In addition, the doping of the polymer particles can significantly improve the size screening performance of the membrane. Through the synergy of the two effects, the composite membrane of the present invention can obviously improve the rejection performance on heavy metal complex ions.

[0063] The present invention has been described in detail above in combination with the specific exemplary examples. However, it should be understood that various modifications and variations can be made without departing from the scope of the present invention as defined by the appended claims. The detailed description and accompanying drawings should be considered as illustrative only and not restrictive, and if there are any such modifications and variations, they will fall within the scope of the present invention described herein. In addition, the background is intended to illustrate the research and development status and significance of the technology, and is not intended to limit the present invention or the present application and application fields of the present invention.