Two-dimensional nanofilms with high CO2 capture rate and high separation selectivity and their preparation method

Abstract

The application discloses a two-dimensional nanometer membrane with high CO2 capture rate and high separation selectivity, which is graphene, and the graphene has graphene ring oxygen holes with an area of 0.98 nm. The graphene prepared by the method has graphene ring oxygen holes with a size of 0.98 nm, the graphene with the ring oxygen holes with the size has high CO2 capture rate, and the CO2 capture rate reaches 13.8% within 80 ns, and meanwhile, the graphene has high CO2 / N2 separation selectivity, and the N2 capture rate is only 0.39% within 80 ns.

Description

Technical Field

[0001] This invention relates to a two-dimensional nanofilm with high CO2 capture rate and high separation selectivity, and also to a method for preparing the above-mentioned two-dimensional nanofilm. Background Technology

[0002] Traditional amine absorption methods suffer from drawbacks such as high energy consumption and difficult regeneration, while the corrosive effects of alkaline liquids on equipment increase costs. Physical separation technology, on the other hand, offers advantages such as mild operating conditions and low energy consumption, making it a promising CO2 capture technology.

[0003] Currently, industrial separation membranes for capturing CO2 have certain limitations. For example, polymers with high CO2 capture rates often also have high free volumes, resulting in low CO2 / N2 selectivity. Most polymer membranes also lose their sieving ability at high temperatures, exhibiting low selectivity. In recent years, two-dimensional (2D) nanomaterial membranes have attracted widespread attention in the field of CO2 separation due to their excellent and unique physicochemical properties. For example, metal-organic frameworks (MOFs) consist of secondary building units (SBUs) and organic ligands linked by coordination bonds. Previous studies have shown that they have excellent separation performance for CO2. Madaeni et al. prepared polydimethylsiloxane (PDMS) coated polyethersulfone (PES) composite membranes for CO2 capture. Li et al. prepared PDMS / polyacrylonitrile (PAN) composite hollow fiber membranes using a dip-coating method for CO2 / N2 separation. They found that pre-wetting of the PAN substrate can inhibit PDMS intrusion, thereby forming a defect-free selective layer. Chen et al. prepared a polyether block amide (Pebax) / PDMS / PAN composite hollow fiber membrane by dip-coating and demonstrated that the prepared membrane can be used for flue gas treatment and hydrogen purification. Existing two-dimensional (2D) nanomaterial membranes still face the challenge of simultaneously achieving high CO2 capture rate and high separation selectivity. Summary of the Invention

[0004] Objective of the invention: The present invention aims to provide a two-dimensional nanofilm with high CO2 capture rate and high separation selectivity; another objective of the present invention is to provide a method for preparing the above-mentioned two-dimensional nanofilm.

[0005] Technical solution: The two-dimensional nanofilm with high CO2 capture rate and high separation selectivity of the present invention is graphene, and the graphene has graphene epoxy pores with a size of 0.98 nm.

[0006] The porosity of the graphene epoxy pores on the two-dimensional nanofilm is 10. 16 pcs / m 2 .

[0007] The preparation method of the above-mentioned two-dimensional nanofilm with high CO2 capture rate and high separation selectivity includes the following steps:

[0008] (1) First, graphene oxide was prepared using the modified Hummers method:

[0009] (1.1) First, the graphite powder is preliminarily oxidized in an acidic medium (H2SO4) using K2S2O8 and P2O5;

[0010] (1.2) Then, a strong oxidizing mixture (H2SO4 and KMnO4) is used for full oxidation, during which the structure of graphene is damaged;

[0011] (2) The obtained graphene oxide is separated and reduced with hydrazine hydrate to restore the structure of graphene:

[0012] (2.1) Add 10g of graphene oxide to 500mL of deionized water and sonicate.

[0013] (2.2) Add 10 mL of hydrazine hydrate to it, and place the reactants in an oil bath at 100 °C for 22–24 h;

[0014] (3) The black solid product was separated, washed with a large amount of deionized water, and dried at 110-115℃ to obtain a large amount of single-layer and multi-layer graphene.

[0015] (4) Graphene is laid on a silicon nitride substrate and etched with a focused electron beam. Typically, the current density during drilling is 1×10 at 300kV. 5 ~5×10 5 A / m 2 The drilling time for each pore on a single layer of graphene is 25 ns, and nanopores with a diameter of 0.98 nm are etched on the graphene.

[0016] (5) Graphene was placed in an electron beam irradiation chamber at room temperature, with an electron beam accelerating voltage of 50 keV to 5 MeV, a beam current of 20 μA to 2 mA, and an irradiation dose of 1 × 10⁻⁶. 5 Gy~6×10 6 When subjected to electron beam irradiation at Gy, the nanopores on graphene are transformed into epoxy pores.

[0017] The graphene of this invention is prepared by a combination of graphite oxidation exfoliation and liquid-phase reduction.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The graphene prepared by the method of the present invention has epoxy pores with a size of 0.98 nm. Graphene with epoxy pores of this size has a high CO2 capture rate, reaching 13.8% within 80 ns. At the same time, it also has high CO2 / N2 separation selectivity, with an N2 capture rate of only 0.39% within 80 ns. Attached Figure Description

[0019] Figure 1 a is a magnified view of the epoxy pores on the graphene. Figure 1 b represents CO2 and N2 molecules respectively, where N atoms are represented by blue spheres, C atoms by green spheres, and O atoms by red spheres; Figure 1 c represents the constructed verification system model. The left and right sides of the system are a 2D nanomaterial membrane-graphene with epoxy pores (filter) and a piston, respectively. A mixed gas (N2:CO2 molecular ratio of 85:15) is added to the system, and the pressure applied to the piston is 1MPa.

[0020] Figure 2 The graphs show the relationship between gas transport number and time in nanopores pore-1, pore-2, and pore-3, respectively.

[0021] Figure 3 a represents the permeation rate of CO2 and N2 under different nanopore sizes; Figure 3 b represents the selectivity of different sized nanopores for CO2. Detailed Implementation

[0022] Example 1

[0023] The preparation method of the above-mentioned two-dimensional nanofilm with high CO2 capture rate and high separation selectivity includes the following steps:

[0024] (1) First, graphene oxide was prepared using the modified Hummers method:

[0025] (1.1) First, the graphite powder is preliminarily oxidized in an acidic medium using K2S2O8 and P2O5; the acidic medium is a 30% H2SO4 solution.

[0026] (1.2) The graphene structure is damaged during the preparation process by using a strong oxidizing mixture for full oxidation. The strong oxidizing mixture is a mixture of H2SO4 solution and KMnO4 aqueous solution in a volume ratio of 1:1, with the mass fraction of H2SO4 solution being 30% and the mass concentration of KMnO4 aqueous solution being 10%.

[0027] (2) The obtained graphene oxide is separated and reduced with hydrazine hydrate to restore the structure of graphene:

[0028] (2.1) Add 10g of graphene oxide to 500mL of deionized water and sonicate.

[0029] (2.2) Add 10 mL of hydrazine hydrate to it, and place the reactants in an oil bath at 100 °C for 24 h;

[0030] (3) The black solid product was separated, washed with a large amount of deionized water, and dried at 110°C to obtain a large amount of single-layer and multi-layer graphene.

[0031] (4) Graphene is laid on a silicon nitride substrate and etched with a focused electron beam. Typically, the current density during drilling is 2×10 at 300kV. 5 A / m 2 The drilling time for each pore on a single layer of graphene is 25 ns, and nanopores with a diameter of 0.98 nm are etched on the graphene.

[0032] (5) Graphene was placed in an electron beam irradiation chamber at room temperature, with an electron beam accelerating voltage of 100 keV, a beam current of 50 μA, and an irradiation dose of 1 × 10⁻⁶. 5 When subjected to electron beam irradiation at Gy, the nanopores on graphene are transformed into epoxy pores.

[0033] The graphene epoxy pore size obtained in Example 1 was 0.98 nm.

[0034] Example 2

[0035] The preparation method of Example 2 is basically the same as that of Example 1. The only difference is that the etching parameters of step (4) are changed. The drilling time of each hole on the monolayer graphene is 22 ns, and nanopores with a diameter of 0.78 nm are etched on the graphene.

[0036] Example 3

[0037] The preparation method of Example 3 is basically the same as that of Example 1. The only difference is that the etching parameters of step (4) are changed. The drilling time of each hole on the monolayer graphene is 28 ns, and nanopores with a diameter of 1.02 nm are etched on the graphene.

[0038] Figure 1 a represents three graphene nanofilms with corresponding nanopores (epoxy rings) of different sizes obtained in Examples 1-3. The three nanopores of different sizes are named pore-1, pore-2 and pore-3, respectively. The diameters of the nanopores pore-1, pore-2 and pore-3 are pore-1: 0.78 nm, pore-2: 0.98 nm and pore-3: 1.02 nm, respectively.

[0039] like Figure 1As shown in Figure c, the system was constructed for verification. Graphene with graphene-epoxy pores was used as the reverse osmosis nanomembrane, and the piston was a pure graphene plate. The dimensions of the piston and nanomembrane were 12.03 nm * 12.33 nm; the porosity of the nanomembrane was 10. 16 pcs / m 2 .

[0040] The graphene nanofilms with three nanopores (epoxy rings) of different sizes obtained in Examples 1-3 were subjected to CO2 treatment. 2 Capture rate experiment.

[0041] The gas molecules added to the system are N2 and CO2, with N2 having 2550 molecules and CO2 having 450 molecules.

[0042] A box with a volume of 12.03nm*12.33nm*70.59nm was constructed using VMD software. The length, width, and height of the box were 70.59nm, 12.33nm, and 12.03nm, respectively. 2250 N2 molecules and 450 CO2 molecules were added to the box. The two ends of the box were respectively a nanofilm and a graphene piston. Then, a larger box was inserted into the system. The volume of the larger box was 12.03nm*12.33nm*120.00nm.

[0043] The specific verification process is as follows: All molecular models, including the two-dimensional nanofilm, graphene plate, CO2, and N2 molecules, are individually built in simulation software (VMD or Material Studio). The established molecular models are structurally optimized, and corresponding field parameters are generated. A appropriately sized cuboid box is built in the simulation software (VMD), with the two-dimensional nanofilm and the piston (graphene plate) at each end. CO2 and N2 are placed in the middle of the box. Periodic conditions are applied to the built box to eliminate the influence of periodicity. Specifically, in the molecular dynamics simulation program Gromacs, periodic conditions are applied to the built box to ensure that the number of gas molecules in the box remains constant. At a temperature of 273.25 K, the system energy is minimized through 50,000 simulation steps. Equilibrium is maintained for 1 ns in the NVT system, and further equilibrium is maintained in the NPT system under isobaric and isothermal conditions for 100 ns. Specific analysis is performed using the molecular visualization software Visual Molecular Dynamics to observe snapshots of the system at each frame, visually demonstrating the selectivity of the two-dimensional nanofilm for different gases. Further analysis of the simulation data is then conducted. The calculations show that as the simulation time increases, the cumulative number of gas molecules passing through the two-dimensional nanomembrane and the gas permeation rate through different nanopores (the permeation rate is based on...) Figure 3 (The slope is calculated from the slope).

[0044] In the simulated curves of simulation time versus the number of gas molecules passing through the nanopores, the rate of increase in CO2 quantity in the system is higher than that of N2. This indicates that both N2 and CO2 can pass through the graphene epoxy pores. However, as the simulation time increases, the cumulative amount of CO2 passing through the graphene epoxy pores is greater than that of N2, suggesting that the graphene epoxy pores have a good separation ability for CO2 and N2. Figure 2 As can be seen, in the 0.78 nm pore-1 nanopore, only a very small amount of N2 and a relatively small amount of CO2 can pass through. With increasing pore size, the amounts of CO2 and N2 passing through increase significantly. The capture rates of CO2 and N2 in the pore-1 nanopore are 2.67% and 0.12%, respectively; in the pore-2 nanopore, they are 13.8% and 0.39%; and in the pore-3 nanopore, they are 16.2% and 1.28%. Figure 3 a represents the permeation rates of N2 and CO2, respectively. The permeation rate of N2 through pore-1 nanopores is 0, and the permeation rate of CO2 through pore-1 nanopores is 0.10982; the permeation rate of N2 through pore-2 nanopores is 0.33705, and the permeation rate of CO2 through pore-2 nanopores is 2.01387; the permeation rate of N2 through pore-3 nanopores is 1.16336, and the permeation rate of CO2 through pore-3 nanopores is 3.64932. As the pore size increases, the permeation rates of N2 and CO2 per unit time and unit pressure also gradually increase. Although Pore-1 nanopores can achieve almost 100% N2 retention, the CO2 permeation rate under Pore-1 nanopores is also extremely low, which cannot well meet the needs of industrial CO2 separation. Pore-3 nanopores have the highest CO2 permeation rate, but due to the large pore size, a large amount of N2 can also pass through the nanopores. The performance of gas separation of nanopores is judged by the permeation rate of gas molecules through nanopores per unit time. The higher the permeation rate, the better the performance of the nanopores. Figure 3 b) shows the selectivity analysis of nanopores with different pore sizes. Specific data are as follows: the selectivity of pore-1 nanopores for CO2 is 28.41, pore-2 nanopores are 49.51, and pore-3 nanopores are 15.3. The data shows that pore-2 nanopores exhibit high selectivity, indicating that they are more advantageous for separating the target gas CO2 from a mixed gas. The selectivity of the three different pore sizes for CO2 was calculated using the following formula: Selectivity In the formula, C1 is the total amount of CO2 passing through the nanopores, N1 is the total amount of N2 passing through the nanopores, C2 is the total amount of CO2 added to the system, and N2 is the total amount of N2 added to the system.

Claims

1. A method for preparing a two-dimensional nanomembrane with high CO2 capture rate and high separation selectivity, characterized in that, Comprising the following steps: (1) First, using the improved Hummers method to prepare graphene oxide: (1.1) First, using K2S2O8 and P2O5 in an acidic medium to carry out preliminary oxidation of graphite powder; the acidic medium is a 30% H2SO4 solution by mass fraction; (1.2) Then, using a strong oxidizing mixture to carry out full oxidation, and the structure of graphene is damaged in the preparation process; the strong oxidizing mixture is a mixture of H2SO4 solution and KMnO4 aqueous solution in a volume ratio of 1:1, the mass fraction of H2SO4 solution is 30%, and the mass concentration of KMnO4 aqueous solution is 10%; (2) Using hydrazine hydrate to separate and reduce the prepared graphene oxide to restore the structure of graphene: (2.1) Adding 10 g of graphene oxide to 500 mL of deionized water and ultrasonic treatment; (2.2) Adding 10 mL of hydrazine hydrate to it, and placing the reaction material in an oil bath at 100°C for 24 h; (3) Separating out the black solid product, washing with a large amount of deionized water, and drying at 110°C to obtain a large amount of single-layer and multi-layer graphene; (4) The graphene is laid on a silicon nitride substrate, and the graphene is etched by a focused electron beam, usually at 300 kV, and the current density is 2×10 5 A / m 2 when the hole is punched, and the punching time of each hole on the single-layer graphene is 25 ns, and a nanometer hole with a diameter of 0.98 nm is etched on the graphene; (5) The graphene is put into an electron beam irradiation chamber at room temperature, and electron beam irradiation is performed at an electron beam acceleration voltage of 100 KeV, a beam current of 50 μA, and an irradiation dose of 1 x 10 5 Gy, and the nanopore on the graphene becomes an epoxide pore.

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