METHOD FOR PREPARING SELF-SUPPORTING COMPOSITE NANOFILTRATION MEMBRANE

Abstract

A method for preparing a self-supporting composite nanofiltration membrane is provided. A porous graphene-based two-dimensional sheet material is prepared by taking amino graphene quantum dots as the main body and subjecting them to an interfacial polymerization reaction with polyacyl chloride, and then the porous graphene-based two-dimensional sheet material is encapsulated in-situ with polyamide by an in-situ encapsulating technology to prepare a self-supporting porous graphene/polyamide separation layer with excellent permeability and high selectivity.

Claims

1. A method for preparing a self-supporting composite nanofiltration membrane, comprising the following steps: (1) a preparation of an amino graphene quantum dots: dispersing a predetermined amount of graphene oxide in distilled water by ultrasonic shaking to obtain a graphene oxide dispersion, adding a predetermined amount of ammonia water, mixing uniformly to obtain a mixture and transferring the mixture to a reaction kettle; sealing and placing the reaction kettle in a muffle furnace for a chemical cleavage reaction, and after a completion of the chemical cleavage reaction, cooling, filtering, distilling at a reduced pressure, freeze drying and conducting secondary dissolution, filtering and freeze drying to obtain the amino graphene quantum dots, wherein: a concentration of the graphene oxide dispersion is 0.01-1 w/v %, and a volume ratio of the ammonia water to the graphene oxide dispersion is (1-4):1; and a temperature in the muffle furnace is 100-140 C., and a treatment time is 4-6 h; (2) a preparation of a porous graphene-based two-dimensional sheet material: placing a substrate membrane rinsed with distilled water at a bottom of a sand core funnel; preparing the amino graphene quantum dots obtained in the step (1) into an aqueous solution with a concentration of 0.01-1 w/v % and adjusting a pH of the aqueous solution to 11-13 to obtain a pH-adjusted aqueous solution, sequentially adding the pH-adjusted aqueous solution of the amino graphene quantum dots and a polyacyl chloride organic solution with a concentration of 0.01-1 w/v % into the sand core funnel in turn, carrying out an interfacial polymerization reaction for a predetermined time to obtain the porous graphene-based two-dimensional sheet material; and (3) a preparation of a composite nanofiltration membrane: immediately after the step (2), injecting an aqueous solution of polyamine quantitatively and uniformly into a solution obtained after the interfacial polymerization reaction in the step (2) by an injector to continue the interfacial polymerization reaction, encapsulating the porous graphene-based two-dimensional sheet material in situ by a polyamide to prepare a porous graphene/polyamide separation layer, removing an aqueous phase solution and an organic phase solution, loading the porous graphene/polyamide separation layer onto the substrate membrane, and subjecting to a heat treatment to prepare the self-supporting composite nanofiltration membrane.

2. The method according to claim 1, wherein in the step (1), pore sizes of filter membranes selected for filtering are 0.22 and 0.1 m, and the operation of distilling at the reduced pressure is conducted at a temperature of 70-90 C. for a time of 0.5-2 h.

3. The method according to claim 1, wherein the substrate membrane in the step (2) is selected from the group consisting of a polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, and polytetrafluoroethylene ultra/microfiltration membrane.

4. The method according to claim 1, wherein a volume ratio of the aqueous solution of the amino graphene quantum dots to the organic solution of polyacyl chloride in the step (2) is (1-10):1, and a time of the interfacial polymerization reaction is 10-120 s.

5. The method according to claim 1, wherein in the step (2), the polyacyl chloride is at least one selected from the group consisting of trimesoyl chloride, pyromellitic acid chloride, phthaloyl chloride, isophthaloyl chloride and terephthaloyl chloride; and a solvent of the organic solution is at least one selected from the group consisting of n-hexane, cyclohexane, n-heptane and isoparaffin.

6. The method according to claim 1, wherein in the step (3), the polyamine is at least one selected from the group consisting of ethylenediamine, butanediamine, pentanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, piperazine, o-phenylenediamine, m-phenylenediamine and p-phenylenediamine.

7. The method according to claim 1, wherein a concentration of the aqueous solution of polyamine in the step (3) is 0.01-0.1 w/v, and a time for the continued interfacial polymerization reaction is 10-120 s.

8. The method according to claim 1, wherein the heat treatment in the step (3) is conducted at a temperature of 40-50 C. for a treatment time of 5-15 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a transmission electron microscope diagram of the amino graphene quantum dots prepared in an Example;

[0024] FIG. 2 is a transmission electron microscope diagram of a porous graphene-based two-dimensional sheet material obtained in the step (2) of Examples 1 and 4;

[0025] FIG. 3 is a surface electron microscope diagram of a composite nanofiltration membrane prepared in Example 4; and

[0026] FIG. 4 is a cross-sectional electron microscope diagram of the composite nanofiltration membrane prepared in Example 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solution of the present invention will be described in detail with reference to the accompanying drawings and examples hereafter.

Example 1

[0028] A method for preparing a self-supporting composite nanofiltration membrane included the following steps. [0029] (1) Preparation of the amino graphene quantum dots: 45 mg of graphene oxide was dispersed in 45 mL of distilled water by ultrasonic shaking, added with 15 mL of ammonia water, mixed uniformly and then transferred to a reaction kettle, and the reaction kettle was sealed and placed in a muffle furnace and reacted at a constant temperature of 120 C. for 5 h. After cooling, it was filtered by a sand core filter equipped with a polyethersulfone filter membrane (with a pore size of 0.22 m), then the filtrate was distilled under reduced pressure in a water bath at 80 C. for 1 h, and then freeze-dried to obtain amino graphene quantum dots powder. The amino graphene quantum dots powder was re-dissolved and subjected to secondary filtration with a polyethersulfone filter membrane (with a pore size of 0.1 m), and then freeze-dried again to obtain a light yellow amino graphene quantum dots powder, of which the transmission electron microscope diagram was shown in FIG. 1, where the particle size distribution of the amino graphene quantum dots was in a relatively narrow particle size distribution range of 2-4 nm, and an average particle size was about 3.4 nm. [0030] (2) Preparation of porous graphene-based two-dimensional sheet material: a Polyethersulfone filter membrane (with a pore size of 0.1 m) was used as a base membrane, which was first rinsed with distilled water and then placed at the bottom of a sand core funnel, subsequently the light yellow amino graphene quantum dots powder obtained in the step (1) was prepared into an aqueous solution of the amino graphene quantum dots with a concentration of 0.5 w/v %, and the pH of the solution was adjusted to 12.5. 1.5 mL of this solution and 1.5 ml of a solution of trimesoyl chloride in n-hexane with a concentration of 0.1 w/v % were sequentially added into the sand core funnel, and then subjected to an interfacial polymerization reaction for 60 s to obtain a porous graphene-based two-dimensional sheet material, of which the transmission electron microscope diagram was shown in FIG. 2. For the porous graphene-based two-dimensional sheet material, the diameter was about 2 m, the lamellar thickness was 3.2 nm, and the pore size was concentrated between 2.1-3.9 nm. [0031] (3) Preparation of composite nanofiltration membrane: immediately after the step (2), 1.5 mL of a piperazine aqueous solution with a concentration of 0.04 w/v % was injected into the solution obtained after the interfacial polymerization reaction in the step (2) with an injector at a uniform speed, and the reaction was continued for 60 s to obtain a porous graphene/polyamide separation layer. After the aqueous phase solution and the organic phase solution were removed, the porous graphene/polyamide separation layer was loaded onto the polyethersulfone filter membrane substrate, and the obtained composite membrane was subjected to heat treatment at 45 C. for 10 min to prepare the self-supporting composite nanofiltration membrane.

[0032] The prepared self-supporting composite nanofiltration membrane was tested with a Congo Red solution system of 0.1 g L.sup.1 under a pressure of 0.6 MPa. It had a permeation flux of 2.9 L m.sup.2 h.sup.1 bar.sup.1, and a rejection rate of 99.8% for Congo Red.

Example 2

[0033] A method for preparing a self-supporting composite nanofiltration membrane included the following steps. [0034] (1) it was the same as the step (1) of Example 1; [0035] (2) the other steps and conditions were the same as the step (2) of Example 1 except that the time for the interfacial polymerization reaction was 10 s; and [0036] (3) preparation of a composite nanofiltration membrane: immediately after the step (2), 1.5 mL of a piperazine aqueous solution with a concentration of 0.02 w/v % was injected into the solution obtained after the interfacial polymerization reaction in the step (2) at a uniform speed, and the reaction was continued for 60 s to obtain a porous graphene/polyamide separation layer. After the aqueous phase solution and the organic phase solution were removed, the porous graphene/polyamide separation layer was loaded onto the polyethersulfone filter membrane substrate, and the obtained composite membrane was subjected to heat treatment at 45 C. for 10 min to prepare the self-supporting composite nanofiltration membrane.

[0037] The prepared self-supporting composite nanofiltration membrane was tested with a Congo Red and methyl orange solution system of 0.1 g L.sup.1 and a Na.sub.2SO.sub.4 solution system of 1 g.Math.L.sup.1 under a pressure of 0.2 MPa. It had a permeation flux of 9.1 L.Math.m.sup.2.Math.h.sup.1.Math.bar.sup.1, a rejection rate of 99.8% for Congo Red, a rejection rate of 43.5% for methyl orange, a rejection rate of 33.3% for SO.sub.4.sup.2 ions, and a separation factor of 117.19 for Congo Red/SO.sub.4.sup.2.

Example 3

[0038] A method for preparing a self-supporting composite nanofiltration membrane included the following steps. [0039] (1) it was the same as the step (1) of Example 1; [0040] (2) the other steps and conditions were the same as the step (2) of Example 1 except that the time for the interfacial polymerization reaction was 30 s; and [0041] (3) it was the same as the step (3) of Example 2.

[0042] The prepared self-supporting composite nanofiltration membrane was tested with a Congo Red and methyl orange solution system of 0.1 g.Math.L.sup.1 and a Na.sub.2SO.sub.4 solution system of 1 g.Math.L.sup.1 under a pressure of 0.2 MPa. It had a permeation flux of 13.8 L.Math.m.sup.2.Math.h.sup.1.Math.bar.sup.1, a rejection rate of 99.5% for Congo Red, a rejection rate of 38.6% for methyl orange, a rejection rate of 30.2% for SO.sub.4.sup.2 ions, and a separation factor of 92.13 for Congo Red/SO.sub.4.sup.2.

Example 4

[0043] A method for preparing a self-supporting composite nanofiltration membrane included the following steps. [0044] (1) it was the same as the step (1) of Example 1; [0045] (2) it was the same as the step (2) of Example 1; [0046] (3) it was the same as the step (3) of Example 2.

[0047] The surface electron microscope diagram of the self-supporting composite nanofiltration membrane prepared in this example was shown in FIG. 3. Unlike the traditional spherical, leaf-like or ridge-valley-like polyamide separation layer, the composite nanofiltration membrane prepared in this example had a relatively smooth surface, and the porous graphene-based two-dimensional sheet material maintained the sheet-like morphology during synthesis and was uniformly wrapped by a polyamide layer.

[0048] The cross-sectional electron microscope diagram of the aforementioned self-supporting composite nanofiltration membrane was shown in FIG. 4, and the thickness of the separation layer of the prepared composite nanofiltration membrane was 18.6 nm, showing an ultra-thin structure.

[0049] The aforementioned self-supporting composite nanofiltration membrane was tested with a Congo Red and methyl orange solution system of 0.1 g.Math.L.sup.1 and a Na.sub.2SO.sub.4 solution system of 1 g.Math.L.sup.1 under a pressure of 0.2 MPa. It had a permeation flux of 28.4 L.Math.m.sup.2.Math.h.sup.1.Math.bar.sup.1, a rejection rate of 99.4% for Congo Red, a rejection rate of 26.7% for methyl orange, a rejection rate of 16.7% for SO4.sup.2 ions, and a separation factor of 98.51 for Congo Red/SO.sub.4.sup.2. The self-supporting composite nanofiltration membrane was tested for permeability for 48 h, and it was found that it could maintain a high rejection rate over 99% for Congo Red, while the permeation flux was slightly reduced. In a strong-alkali resistance test, it still could maintain the high rejection rate over 99% for Congo Red, and the permeation flux did not change much.

Example 5

[0050] (1) it was the same as the step (1) of Example 1; [0051] (2) the other steps and conditions were the same as the step (2) of Example 1 except that the time for the interfacial polymerization reaction was 120 s; and [0052] (3) it was the same as the step (3) of Example 2.

[0053] The prepared nanofiltration membrane was tested with a Congo Red solution system of 0.1 g.Math.L.sup.1 under a pressure of 0.2 MPa. It had a permeation flux of 66.8 L.Math.m.sup.2.Math.h.sup.1.Math.bar.sup.1, and a rejection rate of 90.4% for Congo Red.