Method for directly growing ultrathin porous graphene separation membrane

Abstract

The invention, belonging to the field of membrane technology, presents a method for the direct growth of ultrathin porous graphene separation membranes. Etching agent, organic solvent and polymer are coated on metal foil, and then they are calcined at high temperature in absence of oxygen; after removal of metal substrate and reaction products, single-layered or multi-layered porous graphene membranes are obtained. Alternatively, the dispersion or solution of etching agent is coated on metal foil, on which a polymer film is then overlaid. The obtained sample is subsequently calcined at high temperature in absence of oxygen; after removal of metal substrate and reaction products, single-layered or multi-layered porous graphene membranes are obtained. The method involved in this invention is simple and highly efficient, and allows direct growth of ultrathin porous graphene separation membranes, without needing expensive apparatuses, chemicals and graphene raw material. Additionally, the graphene membranes prepared with this method have controlled pore size, ultrahigh water flux and strong resistance to irreversible fouling.

Claims

1. A method for direct growth of porous graphene separation membrane on a metal foil, comprising: (1) directly coating mixture of an etching agent, an organic solvent A and a polymer on a metal foil, and calcining the mixture and the metal foil at high temperature in absence of oxygen; wherein a mass ratio of the etching agent to the polymer to the organic solvent A is 1:0.5-50:100-1000, alternatively, coating a dispersion or solution of the etching agent on a metal foil, on which a polymer film is overlaid; calcining the obtained metal foil at high temperature in absence of oxygen; wherein a mass ratio of the etching agent to the polymer to a solvent B or a dispersion B is 1:0.5-50:100-1000; the calcination is performed at 400-1200° C. for 0.17-4 hours; wherein the solvent B or the dispersion B is used for dissolution or dispersion of the etching agent, wherein the etching agent is polyoxometalate, metal nitrates, metal oxide, or a mixture of thereof, and a mass concentration of the etching agent solution or dispersion is 0.1%-20%, wherein the polymer is polyvinyl butyral or/and polymethylmethacrylate, wherein the organic solvent A is methanol, ethanol, isopropyl alcohol, acetone, chloroform, or a mixture thereof, the solvent B or the dispersion B is ethanol or/and water, wherein the metal foil is copper foil or nickel foil, and wherein the oxygen-free condition is inert gas protection or vacuum, (2) removing the metal foil and reaction products to obtain the porous graphene separation membranes; wherein the porous graphene separation membranes consist of single-layered, double-layered or multi-layered graphene.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1: The Raman spectrum of graphene membrane obtained from Example 1.

(2) FIG. 2: The SEM image of graphene membrane obtained from Example 1.

(3) FIG. 3: The SEM image of graphene membrane obtained from Example 2.

(4) FIG. 4: The SEM image of graphene membrane obtained from Example 5.

DETAILED DESCRIPTION

(5) Some examples are given to further illustrate the detail preparation process of porous graphene membranes, and it should be emphasized that this invention is not confined to these examples as follows.

Example 1

(6) Typically, PMMA and corresponding amount of Cu(NO.sub.3).sub.2.3H.sub.2O are successively dissolved into acetone to obtain a solution in which the mass ratio of Cu(NO.sub.3).sub.2 to PMMA to acetone is 1:5:200. Subsequently, 10 μL of the solution is spin-coated at 1500 r/min on a 1 cm×1 cm Cu foil, followed by natural drying to allow the evaporation of acetone. The Cu foil with a Cu(NO.sub.3).sub.2/PMMA layer is then calcined at 800° C. for 1 h in a 400 sccm Ar flow at a total pressure of 100 Pa, followed by a another calcination at 1000° C. for 30 min in a 400 sccm Ar/10 sccm H.sub.2 flow at the same total pressure of 100 Pa. After its cooling down to room temperature, the obtained sample is floated on the surface of 2.5 M FeCl.sub.3/0.5 M HCl solution to remove Cu foil and reaction products. At last, the sample left on water surface is transferred on other substrates for filtration.

(7) As shown in FIG. 1 revealing the Raman spectrum of the sample, two strong peaks centered at 1590 cm.sup.−1 (G band) and 2684 cm.sup.−1 (2D band), the typical characteristic peaks of graphene, can be obviously observed, which suggests that porous graphene is successfully obtained by thermal conversion of PMMA on Cu foil.

(8) In SEM image (FIG. 2), an abundance of pores can be clearly observed as black circular dots with an average size of 20 nm. Its water flux is measured to be 48000 L m.sup.−2 h.sup.−1 bar.sup.−1.

Example 2

(9) Based on the method shown in Example 1, a solution in which the mass ratio of Cu(NO.sub.3).sub.2 to PMMA to acetone is 1:2.5:100 is prepared. Subsequently, 10 μL of the solution is spin-coated at 1500 r/min on a 1 cm×1 cm Cu foil, followed by natural drying to allow the evaporation of acetone. The Cu foil with a Cu(NO.sub.3).sub.2/PMMA layer is then calcined at 800° C. for 1 h in a 400 sccm Ar flow at ambient pressure. After its cooling down to room temperature, the obtained sample is floated on the surface of 2.5 M FeCl.sub.3/0.5 M HCl solution to remove Cu foil and reaction products. At last, the sample left on water surface is transferred on other substrate for filtration.

(10) A shown in FIG. 3, porous graphene membrane is successfully obtained with an average size of 35 nm. Its water flux is measured to be 105000 L m.sup.−2 h.sup.−1 bar.sup.−1.

Example 3

(11) Typically, 0.1 g Fe(NO.sub.3).sub.3.9H.sub.2O and 2.5 g PVB are dissolved in 100 g ethanol to obtain a homogeneous solution. Subsequently, 20 μL of the solution is spin-coated at 1000 r/min on a 2 cm×2 cm Ni foil, followed by natural drying to allow the evaporation of ethanol. The Ni foil with a Fe(NO.sub.3).sub.3/PVB layer is then calcined at 800° C. for 1 h in a 400 sccm Ar flow at a total pressure of 50 Pa, followed by a another calcination at 800° C. for 30 min in a 400 sccm Ar/10 sccm H.sub.2 flow at the same total pressure of 50 Pa. After its cooling down to room temperature, the obtained sample is floated on the surface of 2 wt % (NH.sub.4).sub.2S.sub.2O.sub.8 solution to remove Cu foil and reaction products. At last, the sample left on water surface is transferred on other substrates for filtration.

Example 4

(12) Based on the method shown in Example 1, a solution in which the mass ratio of Cu(NO.sub.3).sub.2 to PMMA to acetone is 1:2.5:100 is prepared. Then, a 10 cm×5 cm Cu foil is immersed in the solution for 1 min, and subsequently pulled out at 1 mm/min. The Cu foil with a Cu(NO.sub.3).sub.2/PMMA layer is then calcined at 1000° C. for 10 min in a 400 sccm Ar flow at ambient pressure, followed by a another calcination at 1000° C. for 30 min in a 400 sccm Ar/10 sccm H.sub.2 flow at ambient pressure. After its cooling down to room temperature, the obtained sample is then covered with a layer of 15 wt % polyethersulfone (PES)/N,N-Dimethylformamide solution using a scraper. The sample obtained is rapidly immersed in water. After removal of Cu foil and reaction products with 2.5 M FeCl.sub.3/0.5 M HCl solution, the porous graphene/PES composite membrane is obtained.

Example 5

(13) Typically, 1 g Fe(NO.sub.3).sub.3.9H.sub.2O is dissolved in 50 g ethanol to obtain a homogeneous solution. The solution is dropped on a 20 cm×10 cm Cu foil to form a liquid film, on which domestic preservative film is then overlaid. They are subsequently hot-pressed into a three-layered structure. The sample obtained is then calcined at 900° C. for 30 min in a 800 sccm Ar flow at ambient pressure. After its cooling down to room temperature, the obtained sample is then covered with a layer of 15 wt % polyvinylidene fluoride (PVDF)/polyvinyl pyrrolidone/N,N-Dimethylformamide solution using a scraper. The sample obtained is rapidly immersed in water. After removal of Cu foil and reaction products with 2.5 M FeCl.sub.3/0.5 M HCl solution, the porous graphene/PVDF composite membrane is obtained.

(14) A shown in FIG. 4, porous graphene/PVDF composite membrane is successfully obtained with an average pore size of approximately 50 nm.