Folded graphene nanofiltration membrane
Technical Field
The invention belongs to the technical field of membranes, and particularly relates to a folded graphene nanofiltration membrane.
Background
The nanofiltration membrane is a pressure-driven separation membrane with the molecular weight cut-off of 200-1000 Da. The nanofiltration technology has the characteristics of low energy consumption, low investment, low maintenance cost, easy operation, high reliability and high flux, and can replace reverse osmosis in many occasions, so the nanofiltration membrane and the nanofiltration technology are widely applied in the fields of food chemical industry, medicine industry, sewage treatment, desalination industry and the like.
Most of the existing nanofiltration membranes are composite structure membranes, namely a polymer skin layer with a selective separation effect is formed on a porous supporting layer. And the skin layer is mostly obtained by an interfacial polymerization method. In the preparation method of the nanofiltration membrane, two monomers with high reaction activity are required to react with an organic phase and a water phase, so that certain environmental pollution is generated in the production process, and the obtained nanofiltration membrane has the defects of poor anti-pollution and anti-chlorine performance and the like.
The graphene film can be obtained on the porous supporting layer by a simple vacuum filtration method by utilizing the very large width-thickness ratio of graphene and the good dispersibility of graphene oxide in water. The discoverer Geim task group of graphene reports that the graphene film has very attractive application prospect in the separation field for the first time, and the application of the graphene film in the separation film field draws global wide attention.
The graphene nanofiltration membrane reported by adv, funct, mater, 2013,23, 3693-3700 can have a retention rate of more than 99% on organic dyes and a retention rate of 60% on Na2SO2 solution, which is due to the precise interlayer nanopores between graphene layers and the abundant negative charges on the surface of graphene oxide. However, the water flux of the graphene nanofiltration membrane reported at present is low due to the restriction relationship between permeability and selectivity. The nanofiltration membrane is a pressure-driven separation membrane with the molecular weight cut-off of 200-1000 Da. The nanofiltration technology has the characteristics of low energy consumption, low investment, low maintenance cost, easy operation, high reliability and high flux, and can replace reverse osmosis in many occasions, so the nanofiltration membrane and the nanofiltration technology are widely applied in the fields of food chemical industry, medicine industry, sewage treatment, desalination industry and the like.
Most of the existing nanofiltration membranes are composite structure membranes, namely a polymer skin layer with a selective separation effect is formed on a porous supporting layer. And the skin layer is mostly obtained by an interfacial polymerization method. In the preparation method of the nanofiltration membrane, two monomers with high reaction activity are required to react with an organic phase and a water phase, so that certain environmental pollution is generated in the production process, and the obtained nanofiltration membrane has the defects of poor anti-pollution and anti-chlorine performance and the like.
The graphene film can be obtained on the porous supporting layer by a simple vacuum filtration method by utilizing the very large width-thickness ratio of graphene and the good dispersibility of graphene oxide in water. The discoverer Geim task group of graphene reports that the graphene film has very attractive application prospect in the separation field for the first time, and the application of the graphene film in the separation film field draws global wide attention.
Disclosure of Invention
The invention aims to provide a high-flux folded graphene nanofiltration membrane which can keep high flux especially under high operating pressure and high salt concentration, aiming at the problems that the graphene nanofiltration membrane is low in water flux, especially under high salt and high operating pressure and the like.
The purpose of the invention is realized by the following technical scheme: a corrugated graphene nanofiltration membrane, the nanofiltration membrane is positioned on a porous support membrane, and the corrugated graphene nanofiltration membrane is obtained by the following steps:
(1) carrying out suction filtration on the AAO base film to obtain a graphene oxide film with the thickness of not more than 100 nm;
(2) placing the AAO base film with the graphene film attached to the surface on the water surface with the surface of the graphene film facing upwards; pressing the AAO basement membrane to make the AAO basement membrane sink, the graphene membrane floats on the water surface.
(3) And (4) fishing up the graphene film floating on the water surface from bottom to top by using the porous support film, so that the graphene film is paved on the surface of the porous support film and is naturally dried.
Further, in the step 2, the pressing position is an edge of the AAO base film.
Further, the thickness of the graphene in the step 1 is 4 nm.
Further, the porosity of the surface of the AAO base film is not less than 40%.
Further, the porous support membrane is selected from one of an MCE membrane, a glass fiber filter membrane (GF), a quartz fiber filter membrane (QZ), a polycarbonate filter membrane (PC), a nylon fiber filter membrane (NL), a polytetrafluoroethylene filter membrane (PTFE), polypropylene (PP), polyvinylidene fluoride (PVDF), a mixed cellulose filter Membrane (MCE), an acetic acid/acetic acid filter membrane (CA), a nitric acid filter membrane (CN), a regenerated cellulose filter membrane (RC), Polyethersulfone (PES), and a ceramic filter membrane.
Further, the porous support membrane is an MCE membrane.
Compared with the prior art, the invention has the following advantages:
1. the method has the advantages of green preparation process, simple and convenient operation and low cost, the whole process is carried out in a water phase, and no organic solvent or highly toxic chemical hazardous substances are involved;
2. the prepared graphene nanofiltration membrane has good thickness controllability, can span 4nm-100nm, and has wide-range regulation and control on flux and rejection rate;
3. the surface wrinkles of the thin film layer exist on the surface of the prepared graphene nanofiltration membrane, so that the permeation area of the graphene nanofiltration membrane is greatly increased, and further the flux is increased;
4. the graphene oxide used by the prepared graphene film is placed at room temperature for more than 3 months, and has good structure and chemical stability.
Drawings
Fig. 1 is a schematic flow chart of peeling a graphene film from an AAO base film.
Fig. 2 is a graph showing an experimental process of peeling a graphene film from an AAO base film of example 1.
Fig. 3 is a graph showing an experimental process of peeling a graphene film from an MCE base film of comparative example 1.
Fig. 4 is an atomic force microscope image of the graphene film obtained in example 1.
Fig. 5 is an atomic force microscope image of the graphene film obtained in example 2.
Fig. 6 is an atomic force microscope image of the graphene film obtained in example 3.
Fig. 7 is a scanned graph of the graphene film prepared in example 1.
Detailed Description
The present invention is described in detail by the following embodiments, which are only used for further illustration of the present invention and should not be construed as limiting the scope of the present invention, and the non-essential changes and modifications made by the person skilled in the art according to the above disclosure are within the scope of the present invention.
Example 1:
as shown in fig. 1, by controlling the concentration of the graphene solution, an ultra-thin graphene oxide film is obtained by suction filtration on an AAO base film by a suction filtration method; placing an AAO base film (with a porosity of 40%) with a graphene oxide film attached to the surface on a water surface with the graphene film facing upward, as shown in fig. 1a and 2 a; pressing the AAO base membrane as in fig. 2b, the AAO base membrane starts to sink as in fig. 2c, and finally, the AAO base membrane sinks to the bottom of the cup, and the graphene membrane (inside the dashed circle) floats on the water surface as in fig. 1b and 2 d.
The graphene film floating on the water surface is fished up from bottom to top by the MCE film, so that the graphene film is laid on the surface of the MCE film, and after the graphene film is naturally dried, as shown in figure 7, a large number of folds are formed on the surface; the thickness was 4nm as measured by atomic force microscopy, as shown in FIG. 4.
Through the steps, the pure water flux of the membrane can reach 32L/m2h bar for 0.01mol/L Na2SO4The retention rate of the solution can reach more than 84 percent, and the retention rate of the direct yellow dye can reach more than 92 percent.
The pure water flux and rejection rate of the membrane were substantially unchanged after the membrane was left in an air environment for 3 months.
Example 2:
by controlling the concentration of the graphene solution, carrying out suction filtration on an AAO (anodic aluminum oxide) base film by a suction filtration method to obtain an ultrathin reduced graphene oxide film; placing the AAO base film (with the porosity of 60%) with the graphene oxide film attached to the surface on the water surface with the surface of the graphene film facing upwards, pressing the edge of the AAO base film to enable the AAO base film to start sinking, finally enabling the AAO base film to sink to the cup bottom, enabling the graphene film to float on the water surface, and successfully stripping the graphene film.
And (3) fishing up the graphene film floating on the water surface from bottom to top by using a regenerated cellulose filter membrane (RC), flatly paving the graphene film on the surface of the substrate, naturally airing to obtain the graphene film with surface wrinkles, and testing the thickness of the graphene film to be 14nm by using an atomic force microscope, as shown in figure 5.
Through the steps, the pure water flux of the membrane can reach 28L/m2h bar for 0.01mol/L Na2SO4The retention rate of the solution can reach more than 92 percent, and the retention rate of the direct yellow dye can reach more than 95 percent.
The pure water flux and rejection rate of the membrane were substantially unchanged after the membrane was left in an air environment for 3 months.
Example 3:
by controlling the concentration of the graphene solution, carrying out suction filtration on an AAO (anodic aluminum oxide) base film by a suction filtration method to obtain an ultrathin reduced graphene oxide film; placing the AAO base film (with the porosity of 60%) with the graphene oxide film attached to the surface on the water surface with the surface of the graphene film facing upwards, pressing the edge of the AAO base film to enable the AAO base film to start sinking, finally enabling the AAO base film to sink to the cup bottom, enabling the graphene film to float on the water surface, and successfully stripping the graphene film.
And (3) fishing up the graphene film floating on the water surface from bottom to top by using an acetic acid/acetic acid filter membrane (CA), flatly paving the graphene film on the surface of the substrate, naturally airing to obtain the graphene film with surface wrinkles, and testing the thickness of the graphene film to be 100nm by using an atomic force microscope, as shown in figure 6.
Through the steps, the pure water flux of the membrane can reach 21L/m2h bar for 0.01mol/L Na2SO4The retention rate of the solution can reach more than 95 percent, and the retention rate of the direct yellow dye can reach more than 99 percent.
The pure water flux and rejection rate of the membrane were substantially unchanged after the membrane was left in an air environment for 3 months.
Comparative example 1
According to the suction filtration method as in example 2, a reduced graphene oxide film with a thickness of 14nm is obtained by suction filtration on an MCE base film, and then the MCE base film (porosity: 60%) with the reduced graphene oxide film attached to the surface is placed on a water surface with the surface on which the graphene film is placed facing upward, as shown in fig. 3a, the MCE base film is pressed against the edge of the MCE base film, and the MCE base film does not sink, as shown in fig. 3b, the graphene film fails to be peeled.
The filtration method is the most uniform method for preparing graphene films, and can control the thickness of a graphene film by regulating and controlling the concentration under a certain amount of filtration liquid, the thickness can be the lowest graphene, the newly added graphene gradually fills the gap of the first graphene layer under the action of pressure along with the increase of the concentration of the graphene, so that the first graphene layer is gradually and completely filled, and then the first graphene layer is developed into a second graphene layer, and the steps are continuously repeated, so that the graphene nano film with the thickness of 2 to ten thousand graphene layers can be prepared. Therefore, the graphene film with the thickness of 4nm can be obtained by simple experimental parameter adjustment by the skilled person.