A graphene composite film for filtration and a preparation method and use thereof

Abstract

This invention discloses a graphene composite film for filtration, its preparation method, and its applications. The graphene composite film consists of a surface layer, an inner layer, and a bottom layer. The surface layer is a filtration layer, the inner layer is an auxiliary support layer, and the bottom layer is a reinforcing support layer. The surface layer is nanoporous graphene, the inner layer is a carbon nanotube network, and the bottom layer is a flexible metal mesh or cellulose acetate. This invention combines graphene film with carbon nanotube film and develops a method for introducing nanopores, thereby obtaining a high-density, uniformly distributed, self-supporting nanoporous graphene composite film. This invention greatly promotes the practical application of graphene films in water purification. The film of this invention can be used for water filtration in the environmental field and material separation in the chemical industry.

Description

Technical Field

[0001] This invention belongs to the field of filtration technology, and relates to a graphene composite film, particularly to a graphene composite film for filtration, its preparation method, and its uses. Background Technology

[0002] Water resources are the cornerstone of global industry, agriculture, energy, and economic growth, and are indispensable for human survival and economic development. However, with the improvement of living standards and rapid economic development, the world is facing a severe challenge of scarce freshwater resources. Water scarcity is also a decisive factor restricting national and military development. In field operations and survival, especially in arid and water-scarce areas or areas polluted by chemicals or organisms, ensuring personnel's water supply and drinking water safety is crucial for maintaining normal survival and life, and plays a decisive role in the completion of field missions.

[0003] Seawater desalination and polluted water purification are effective ways to address the scarcity of freshwater resources. Water purification methods are mainly divided into membrane separation and thermal separation. Membrane separation utilizes membrane materials to separate water and molecules, primarily using reverse osmosis technology, which is currently the main method used for water purification. The core of reverse osmosis technology is the reverse osmosis filtration membrane, and its permeability and selectivity play a crucial and decisive role in water purification efficiency. In reverse osmosis membrane-based water purification methods, water permeability is inversely proportional to membrane thickness. Compared to thicker commercial membrane composite filtration membranes, cellulose acetate filtration membranes, and metal-organic framework materials, atomically thin two-dimensional membranes do not contain bent water molecule or ion-selective channels, which helps reduce the physical and electrostatic interactions between water molecules and the membrane surface, thus improving water permeation efficiency.

[0004] As an atomically thin two-dimensional material, graphene possesses excellent chemical and thermal stability, which can solve the problem that commercial organic polymer films, due to their material composition and structural characteristics, cannot purify water sources contaminated with organic pollutants. Furthermore, graphene exhibits excellent resistance to biofouling and antibacterial properties, preventing issues such as reduced water permeability and selectivity caused by scale buildup during the separation process. These characteristics offer opportunities for constructing high-performance separation membranes.

[0005] Defect-free graphene possesses excellent mechanical properties. However, grain boundaries within large-area graphene significantly reduce these properties, and introducing nanopores further diminishes them. Separation processes rely on the separation of molecules at the molecular scale. Tiny fractures in the separation film, as well as uneven distribution of nanopore size and surface charge, drastically reduce separation efficiency and selectivity. Therefore, effectively controlling the structure and charge of graphene to achieve large-area nanoporous graphene filter membranes while ensuring excellent separation efficiency and performance is crucial for meeting practical application requirements. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a graphene composite film for filtration, its preparation method, and its applications. It combines graphene film with carbon nanotube film and develops a nanopore introduction method, thereby obtaining a high-density, uniformly distributed, self-supporting nanoporous graphene composite film material.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] This graphene composite film for filtration includes a surface layer and an inner layer. The surface layer is a filter layer, and the inner layer is an auxiliary support layer. The surface layer is nanoporous graphene, and the inner layer is a carbon nanotube network. The surface layer is composed of a single layer or multiple layers of nanoporous graphene film, and the inner layer is composed of a carbon nanotube network film.

[0009] Furthermore, a bottom layer is provided below the inner layer, which is a reinforcing support layer; the bottom layer is composed of a flexible metal mesh or a cellulose acetate film.

[0010] Furthermore, the nanoporous graphene constituting the surface layer is supported by a carbon nanotube network in the inner layer, which interacts with the supported nanoporous graphene through chemical bonds; the carbon nanotube network separates the nanoporous graphene into multiple small lattices and acts as a framework supporting the nanoporous graphene. The flexible metal mesh is a stainless steel filter mesh, a titanium alloy filter mesh, or a lightweight alloy mesh.

[0011] A method for preparing the above-mentioned graphene composite film for filtration includes the following steps:

[0012] (1) Synthesis of graphene films by chemical vapor deposition

[0013] A copper foil substrate was placed inside a quartz tube in a tube furnace as a catalyst substrate and then evacuated. The system was then heated under a hydrogen gas flow to anneal the copper foil in a hydrogen atmosphere. After annealing, methane gas was introduced. After growth and maturation, the system was rapidly cooled to room temperature to obtain a graphene film.

[0014] (2) Carbon nanotube thin films were prepared by chemical vapor deposition.

[0015] Ferrocene and sulfur powder were dissolved in xylene as precursor solution A; a hydrogen / argon mixed gas was introduced into a tube furnace after heating, and precursor solution A was injected into a quartz tube. After growth and maturation, carbon nanotube films were obtained.

[0016] (3) Preparation of graphene-carbon nanotube composite films

[0017] The carbon nanotube film was transferred onto a copper foil on which a graphene film was grown, and then heated to enhance the bonding between the graphene film and the carbon nanotube film. Subsequently, the copper foil with the carbon nanotube film was transferred to FeCl3 solution for etching. After etching and cleaning, the graphene carbon nanotube film was obtained.

[0018] (4) Introducing nanopores on graphene carbon nanotube films using the mesoporous silica template method.

[0019] Ethanol, water, hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate were used to prepare a precursor solution B for mesoporous silica. Graphene carbon nanotube films were grown and matured in precursor solution B and then aged overnight in an oven. After aging, the surfactant was removed with hydrochloric acid-ethanol solution, and residual ethanol was washed away with deionized water. After cleaning, oxygen plasma etching was used to control the pore size and porosity of the graphene. Finally, the films were immersed in HF solution until the mesoporous silica template was removed, resulting in nanoporous graphene carbon nanotube films.

[0020] (5) Substrate: Flexible metal mesh or cellulose acetate film

[0021] The nanoporous graphene carbon nanotube film prepared above is immersed in pure aqueous solution, then retrieved and transferred using a flexible metal mesh or cellulose acetate film, and dried to obtain a nanoporous graphene carbon nanotube composite film reinforced and supported by a flexible metal mesh or cellulose acetate film.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) This invention selects carbon nanotube materials that match the structure of graphene as the self-supporting material for monolayer graphene films. Assembly is achieved through physicochemical processes to maintain the structural integrity of the graphene film over a large area, thereby increasing the film's mechanical strength. This invention is superior to similar materials reported to date.

[0024] 2) This invention introduces high-density, uniform and narrow-pore-size nanopores into graphene by selecting a suitable nanopore preparation method. The pore size range is less than or equal to 2 nm, which can improve the mechanical properties and separation selectivity of nanoporous graphene.

[0025] 3) This invention adjusts the surface charge of the film by regulating the pH value of the solution to increase the interaction force and interaction time between smaller molecular ions and nanoporous graphene film, thereby achieving efficient water purification and molecular separation.

[0026] 4) To address the problems of low selectivity, small area, and weak mechanical strength faced by atomically thin two-dimensional materials in practical water purification research, this invention constructs a large-area nanoporous graphene composite film for efficient water purification, improving water purification efficiency and selectivity. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the nanoporous graphene composite film of the material in Example 1;

[0028] Figure 2 This is a transmission electron microscope (TEM) image of the nanoporous graphene composite film of the material in Example 1.

[0029] Figure 3 The images show aberration-corrected electron microscopy (SEM) images and pore size distribution diagrams of the nanoporous graphene composite film of the material in Example 1.

[0030] Figure 4 The image shows the stress-strain curve of the nanoporous graphene composite film of the material in Example 1. Detailed Implementation

[0031] This invention first proposes a graphene composite film for filtration, comprising a surface layer and an inner layer. The surface layer is a filter layer, and the inner layer is an auxiliary support layer. The surface layer is composed of nanoporous graphene, and the inner layer is a carbon nanotube network. The surface layer is composed of a single layer or multiple layers of nanoporous graphene film, and the inner layer is composed of a carbon nanotube network film. In a preferred embodiment of this invention, a bottom layer may also be provided, disposed below the inner layer, serving as a reinforcing support layer; the bottom layer is composed of a flexible metal mesh or a cellulose acetate film.

[0032] In this invention, the surface layer can be composed of a single layer or multiple layers of nanoporous graphene film, the inner layer is composed of a carbon nanotube network film, and the bottom layer is composed of a flexible metal mesh or a cellulose acetate film. The nanoporous graphene constituting the surface layer is supported by the carbon nanotube network in the inner layer, and the carbon nanotube network interacts with the supported nanoporous graphene through chemical bonds; the carbon nanotube network separates the nanoporous graphene into multiple small lattices and acts as a framework supporting the nanoporous graphene. In the preferred embodiment of this invention, the flexible metal mesh is a stainless steel filter mesh, a titanium alloy filter mesh, or a lightweight alloy mesh.

[0033] To prepare a graphene composite film that meets the above requirements, this invention also proposes a method for preparing the graphene composite film, specifically including the following steps:

[0034] (1) Synthesis of graphene films by chemical vapor deposition

[0035] A copper foil substrate was placed inside a quartz tube in a tube furnace as a catalyst substrate and then evacuated. The system was then heated under a hydrogen gas flow to anneal the copper foil in a hydrogen atmosphere. After annealing, methane gas was introduced. After growth and maturation, the system was rapidly cooled to room temperature to obtain a graphene film.

[0036] (2) Carbon nanotube thin films were prepared by chemical vapor deposition.

[0037] Ferrocene and sulfur powder were dissolved in xylene as precursor solution A; a hydrogen / argon mixed gas was introduced into a tube furnace after heating, and precursor solution A was injected into a quartz tube. After growth and maturation, carbon nanotube films were obtained.

[0038] (3) Preparation of graphene-carbon nanotube composite films

[0039] The carbon nanotube film was transferred onto a copper foil on which a graphene film was grown, and then heated to enhance the bonding between the graphene film and the carbon nanotube film. Subsequently, the copper foil with the carbon nanotube film was transferred to FeCl3 solution for etching. After etching and cleaning, the graphene carbon nanotube film was obtained.

[0040] (4) Introducing nanopores on graphene carbon nanotube films using the mesoporous silica template method.

[0041] Ethanol, water, hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate were used to prepare a precursor solution B for mesoporous silica. Graphene carbon nanotube films were grown and matured in precursor solution B and then aged overnight in an oven. After aging, the surfactant was removed with hydrochloric acid-ethanol solution, and residual ethanol was washed away with deionized water. After cleaning, oxygen plasma etching was used to control the pore size and porosity of the graphene. Finally, the films were immersed in HF solution until the mesoporous silica template was removed, resulting in nanoporous graphene carbon nanotube films.

[0042] (5) Substrate: Flexible metal mesh or cellulose acetate film

[0043] The nanoporous graphene carbon nanotube film prepared above is immersed in pure aqueous solution, then retrieved and transferred using a flexible metal mesh or cellulose acetate film, and dried to obtain a nanoporous graphene carbon nanotube composite film reinforced and supported by a flexible metal mesh or cellulose acetate film.

[0044] The above preparation method can obtain a nanoporous graphene-carbon nanotube composite film that meets the requirements of this invention. This invention applies the composite film to water filtration in the environmental field and material separation in the chemical field.

[0045] The present invention will be further illustrated below with reference to examples and accompanying drawings. However, these examples do not limit the scope of protection of the present invention. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0046] Example 1

[0047] 1) Preparation of graphene films

[0048] Single-layer / multi-layer graphene films were synthesized using chemical vapor deposition (CVD). A 25 μm thick copper foil substrate was placed inside a quartz tube in a tube furnace as the catalytic substrate, and the furnace was evacuated to 40 mtorr. The system was then heated to 1040-1100 °C under a hydrogen gas flow of 7 sccm, and the copper foil was annealed in a hydrogen atmosphere for 30 minutes. Next, methane gas was introduced at 10 sccm, and after several tens of minutes of growth, the system was rapidly cooled to room temperature in a hydrogen atmosphere to finally obtain the graphene film.

[0049] 2) Preparation of carbon nanotube thin films

[0050] Carbon nanotube films were prepared by chemical vapor deposition. 45 mg of ferrocene and 1 mg of sulfur powder were dissolved in 1 mL of xylene as a precursor solution. After heating the tubular furnace to 950-1200 °C, a 15-25% hydrogen / argon mixed gas was introduced at a flow rate of 1500 sccm. The precursor solution was then introduced at a rate of 1 mL / h. -1 The carbon nanotube film is obtained by injecting the solution into a quartz tube at a high speed and growing for several tens of minutes. The prepared carbon nanotube film needs to be treated with H2O2 and HNO3 in sequence to remove surface impurities, and finally soaked in ethanol for storage until use.

[0051] 3) Preparation of graphene composite films

[0052] Carbon nanotube films dispersed in an ethanol solution were cut into appropriate sizes and then placed in ultrapure water. Once the carbon nanotube films floated stably on the water surface, they were transferred to a copper foil on which graphene films had been grown. The copper foil was then heated at 100-200°C for several minutes to enhance the bonding between the graphene and carbon nanotube films. The copper foil with the carbon nanotube films was then transferred to a FeCl3 solution and etched for several hours. After multiple washes, a graphene composite film was obtained.

[0053] 4) Preparation of nanoporous graphene composite films

[0054] Nanopores were introduced into graphene using a mesoporous silica template method. The graphene composite film was grown in a mesoporous silica precursor solution at 60-100°C for several hours, followed by overnight aging in a 100°C oven. After aging, the surfactant was removed with a 0.1M hydrochloric acid-ethanol solution, and residual ethanol was washed away with deionized water. Following cleaning, the graphene was etched with oxygen plasma at tens of watts and 10 Pa for several seconds to control the pore size. Finally, the mesoporous silica template was removed by immersion in a 10% HF solution for several hours, yielding the nanoporous graphene composite film.

[0055] Scanning electron microscope image of nanoporous graphene composite film is shown below Figure 1 The transmission electron microscope image of the nanoporous graphene composite film of this material is shown below. Figure 2 The nanoporous graphene in this material is tightly bonded to carbon nanotubes, exhibiting structural integrity. Aberration-corrected electron microscopy images and pore size distribution diagrams of the nanoporous graphene composite film are shown below. Figure 3 ,Depend on Figure 3 It can be seen that this material possesses good porosity and pore size uniformity. The stress-strain curves of the nanoporous graphene composite film are shown below. Figure 4 This material possesses excellent structural integrity and mechanical strength.

Claims

1. A graphene composite film for filtration, characterized in that, It includes a surface layer and an inner layer. The surface layer is a filter layer, and the inner layer is an auxiliary support layer. The surface layer is composed of a single layer or multiple layers of nanoporous graphene film, and the inner layer is composed of carbon nanotube film. The method for preparing the graphene composite film for filtration includes the following steps: (1) Synthesis of graphene films by chemical vapor deposition A copper foil substrate was placed inside a quartz tube in a tube furnace as a catalyst substrate and then evacuated. The system was then heated under a hydrogen gas flow to anneal the copper foil in a hydrogen atmosphere. After annealing, methane gas was introduced. After growth and maturation, the system was rapidly cooled to room temperature to obtain a graphene film. (2) Carbon nanotube thin films were prepared by chemical vapor deposition. Ferrocene and sulfur powder were dissolved in xylene as precursor solution A; a hydrogen / argon mixed gas was introduced into a tube furnace after heating, and precursor solution A was injected into a quartz tube. After growth and maturation, carbon nanotube films were obtained. (3) Preparation of graphene-carbon nanotube composite films The carbon nanotube film was transferred onto a copper foil on which a graphene film was grown, and then heated to enhance the bonding between the graphene film and the carbon nanotube film. Subsequently, the copper foil with the carbon nanotube film was transferred to FeCl3 solution for etching. After etching and cleaning, the graphene carbon nanotube film was obtained. (4) Introducing nanopores on graphene carbon nanotube films using the mesoporous silica template method Ethanol, water, hexadecyltrimethylammonium bromide, ammonia, and tetraethyl orthosilicate were used to prepare a precursor solution B for mesoporous silica. Graphene carbon nanotube films were grown and matured in precursor solution B and then aged overnight in an oven. After aging, the surfactant was removed with hydrochloric acid-ethanol solution, and residual ethanol was washed away with deionized water. After cleaning, oxygen plasma etching was used to control the pore size and porosity of the graphene. Finally, the films were immersed in HF solution until the mesoporous silica template was removed, resulting in nanoporous graphene carbon nanotube films. (5) Substrate: flexible metal mesh or cellulose acetate film The nanoporous graphene carbon nanotube film prepared above is immersed in pure aqueous solution, then retrieved and transferred using a flexible metal mesh or cellulose acetate film, and dried to obtain a nanoporous graphene carbon nanotube composite film reinforced and supported by a flexible metal mesh or cellulose acetate film.

2. The graphene composite film for filtration according to claim 1, characterized in that, Below the inner layer, there is a bottom layer, which is a reinforcing support layer; the bottom layer is composed of a flexible metal mesh or a cellulose acetate film.

3. The graphene composite film for filtration according to claim 2, characterized in that, The nanoporous graphene film constituting the surface layer is supported by a carbon nanotube film in the inner layer. The carbon nanotube film interacts with the nanoporous graphene film it supports through chemical bonds. The carbon nanotube film separates the nanoporous graphene film into multiple small lattices and acts as a framework supporting the nanoporous graphene film. The flexible metal mesh is a stainless steel filter mesh, a titanium alloy filter mesh, or a lightweight alloy mesh.

4. The graphene composite film for filtration according to claim 1, characterized in that, Step (1) is as follows: a 25 µm thick copper foil substrate is placed inside a quartz tube in a tube furnace as a catalyst substrate and then evacuated to 40 mtorr; the system is then heated to 1040-1100 °C under a hydrogen gas flow of 7 sccm and the copper foil is annealed in a hydrogen atmosphere for 30 minutes; then 10 sccm of methane gas is introduced, and after growth, the system is rapidly cooled to room temperature in a hydrogen atmosphere to finally prepare a graphene film.

5. The graphene composite film for filtration according to claim 1, characterized in that, Step (2) is as follows: 45 mg of ferrocene and 1 mg of sulfur powder are dissolved in 1 mL of xylene as a precursor solution. After the tube furnace is heated to 950-1200℃, 15-25% hydrogen / argon mixed gas is introduced at a flow rate of 1500 sccm. The precursor solution is injected into the quartz tube at a rate of 1 mL•h-1. After growth, carbon nanotube films are obtained. The prepared carbon nanotube films need to be treated with H2O2 and HNO3 in sequence to remove surface impurities. Finally, they are soaked in ethanol for storage and later use.

6. The graphene composite film for filtration according to claim 1, characterized in that, Step (3) is as follows: the carbon nanotube film dispersed in the ethanol solution is cut into appropriate sizes, and then the carbon nanotube film is placed in ultrapure water. When the carbon nanotube film floats flat and stable on the water surface, it is transferred to the copper foil on which the graphene film has been grown. Then, it is heated at 100-200℃ for several minutes to enhance the bonding between the graphene and the carbon nanotube film. Then, the copper foil with the carbon nanotube film is transferred to FeCl3 solution, and etching and cleaning operations are performed in sequence to obtain the graphene carbon nanotube film.

7. The graphene composite film for filtration according to claim 1, characterized in that, Step (4) is as follows: Prepare a precursor solution of mesoporous silica by mixing 15 mL of ethanol, 35 mL of water, 0.08 g of cetyltrimethylammonium bromide, 5 µL of ammonia and 40 µL of tetraethyl orthosilicate. Place the graphene carbon nanotube film in the solution and grow it at 60-100 °C. Then age it overnight in an oven at 100 °C. After aging, remove the surfactant with 0.1 M hydrochloric acid ethanol solution and wash away the residual ethanol with deionized water. After cleaning, etch the graphene with oxygen plasma at 10 Pa to control the pore size. Finally, soak it in 10% HF solution until the mesoporous silica template is removed. The nanoporous graphene carbon nanotube film is then prepared.

8. The graphene composite film for filtration according to claim 1, characterized in that, In step (5), the prepared nanoporous graphene carbon nanotube film is immersed in pure aqueous solution for 30 seconds.

9. The use of the graphene composite film for filtration as described in any one of claims 1-3, characterized in that, The graphene composite film is used for water filtration or chemical material separation.

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