Inorganic gas separation membrane constructed with carbon quantum dots

Abstract

The application provides a kind of gas separation membrane constructed with cheap carbon quantum dots, which is used for the separation and purification of CO2 in CO2 / CH4, CO2 / N2 and other mixed gases.The preparation method of the carbon-based membrane is simple and has good repeatability. Through solvent dispersion of carbon quantum dots, high-temperature drop coating and inert atmosphere calcination, an inorganic separation membrane capable of selectively separating CO2 is obtained. The inorganic separation membrane can realize gas separation at room temperature, has good thermal stability, and the selectivity and permeation flux of the membrane can be increased under high temperature conditions, which is very beneficial for the capture and utilization of CO2 in high-temperature flue gas. The preparation cost of the separation membrane is low, the method is simple, the repeatability is good, the thermal stability is excellent, and the separation membrane has a broad development prospect.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation, specifically relating to the application of a novel inorganic membrane constructed from carbon quantum dots in gas separation. Background Technology

[0002] Separation is a crucial step in chemical processes, accounting for approximately 40-60% of the total energy consumption in chemical production. Traditional separation methods include absorption, adsorption, distillation, and extraction, but these processes are often energy-intensive. Therefore, the search for novel separation methods has become a research hotspot. In recent years, inorganic membrane separation technology, with its high efficiency and low energy consumption, has been increasingly applied to the separation, purification, recovery, and capture of gases and liquids. The core of membrane separation lies in the development and application of membrane materials. Currently, widely studied membrane materials are mainly classified into four categories: organic polymer membranes, inorganic membranes, organic-inorganic hybrid membranes, and liquid membranes. Among them, inorganic membranes have attracted widespread attention due to their rich variety, diverse pore structures, and selective adsorption of specific molecules.

[0003] Quantum dots are a class of inorganic materials with sizes ranging from 2-10 nm and regular shapes. In recent years, carbon quantum dots have become a research hotspot due to their simple preparation methods, wide and inexpensive raw material sources, and abundant surface functional groups. Carbon quantum dots are typically ellipsoidal nanoparticles with sizes less than 10 nm, composed of hybrid carbon and abundant active functional group sites (-COOH, -OH, -NH2, etc.). Thanks to their small size and abundant surface functional groups, carbon quantum dots easily combine with organic precursors or modify the surface of membrane materials. Therefore, carbon quantum dots also have applications in membrane separation. For example, in wastewater treatment, due to the conversion of the surface functional groups -COOH and -COO-, carbon quantum dots exhibit electronegativity over a wide pH range, which can significantly improve the hydrophilicity of the membrane surface. Modifying the surface of permeate membranes with carbon quantum dots can significantly improve the separation performance of water separation membranes. Furthermore, the combination of carbon quantum dots with polymers to form membranes can significantly improve the mechanical strength and stability of the membranes. Recent reports indicate that the incorporation of a small amount of carbon quantum dots can improve the selectivity of mixed matrix membranes for separating ethylene and ethane by approximately 60%, reaching 99.5%. However, to date, the application of quantum dots in the membrane field has primarily focused on doping modification, and there are no reports of preparing separation membranes using quantum dots as precursors. Summary of the Invention

[0004] The purpose of this invention is to construct a novel inorganic membrane using carbon quantum dots for the separation and purification of various mixed gases. Carbon quantum dots possess a certain rigidity and size, and their abundant surface functional groups provide a foundation for the formation of gas separation membranes with specific porous structures through connections between carbon quantum dots and between carbon quantum dots and other molecules or ions. This novel inorganic membrane has not been previously reported, and its fabrication method is simple, efficient, and reproducible.

[0005] The separation membrane described in this invention is used for gas separation. The separation membrane is a novel inorganic membrane constructed from carbon quantum dots, and its preparation method is as follows:

[0006] (1) Disperse carbon quantum dots in a solvent to form a colloidal dispersion system;

[0007] (2) An initial supported film is obtained by hot-drop coating of an appropriate amount of carbon quantum dot colloid onto the surface of a carrier in an oven;

[0008] (3) Calcination in an inert atmosphere, controlling the post-treatment time, temperature and heating rate to regulate the thickness and properties of the film.

[0009] Based on the above technical solutions, preferably, the carbon quantum dots have a size of 2-10 nanometers and have abundant active functional group sites (-COOH, -OH, -NH2) on their surface.

[0010] Based on the above technical solution, preferably, the solvent is H2O, DMF, etc., with DMF being the most suitable solvent; the concentration of the carbon quantum dot colloid is 0.2-2 g / L. -1 The optimal concentration is 1 g / L. -1 .

[0011] Based on the above technical solutions, preferably, the carrier is Al2O3 or a polymer carrier, the minimum pore size of the carrier is 5nm and the diameter is 18mm, and 0.2mL of carbon quantum dot colloid is hot-drop coated in an oven to obtain an initial support film. The drop coating temperature is 100-200℃ and the heat preservation time is 2-10h.

[0012] Based on the above technical solutions, the preferred post-processing method is as follows: the atmosphere is flowing Ar, the calcination temperature is 300-400℃, and the holding time is 5-20h.

[0013] By adjusting carbon quantum dots and membrane preparation conditions, such as carbon quantum dot size and surface functional group types, solvent, oven temperature, furnace atmosphere, calcination temperature, and holding time, the permeation flux and selectivity of the separation membrane can be controlled.

[0014] The carbon quantum dots described in this invention can be synthesized by various methods, such as hydrothermal synthesis, acid hydrolysis, and electrolysis. For specific synthesis methods, please refer to relevant literature.

[0015] The carbon quantum dots described in this invention are synthesized by freeze-drying the reaction solution and then storing them in the dark as powder.

[0016] The separation membrane described in this invention is applied to gas separation. It achieves efficient separation and purification of multi-component gases by constructing an inorganic membrane with specific pore size and properties using carbon quantum dots.

[0017] The separation membrane described in this invention is used for gas separation. The carbon quantum dots are 2-10 nm in size and have a regular shape. Their surfaces have abundant active functional group sites (-COOH, -OH, -NH2, etc.). Under specific temperature and atmospheric conditions, they can react and connect with other carbon quantum dots or molecules and ions to form a three-dimensional network structure. Gas molecules with specific sizes or characteristics can pass through the pores formed between carbon quantum dots or between carbon quantum dots and other molecules and ions through mechanisms such as adsorption and diffusion, thereby achieving the separation and purification of specific gases.

[0018] The separation membrane described in this invention is applied to gas separation and can selectively separate CO2 from mixed gases. The gas mixtures, such as CO2 / N2 and CO2 / CH4, can be used for the separation and purification of CO2 in various mixed gases such as CO2 / N2 and CO2 / CH4.

[0019] The carbon-based separation membrane described in this invention is constructed from pure carbon quantum dot material. The pore size and physicochemical properties of the constructed separation membrane can be controlled by adjusting the properties of the carbon quantum dots. The prepared carbon quantum dots are dispersed in a solvent (deionized water, ethanol, DMF, etc.) to form a colloidal dispersion system, which needs to be stored in the dark. An appropriate amount of carbon quantum dot colloid is drop-coated onto the surface of an Al2O3 support in a forced-air drying oven, followed immediately by heat treatment. The dried membrane is then calcined in an atmosphere furnace to obtain a supported carbon-based separation membrane capable of selectively separating CO2 gas.

[0020] The gas separation membrane described in this invention has a simple preparation method, low cost, good repeatability, and good thermal stability, and has broad development prospects.

[0021] The separation membrane described in this invention is used for the separation of mixed gases. It can achieve selective separation of CO2 gas in mixed gases at normal temperature and pressure. Increasing the membrane expansion pressure difference (pressurizing the gas supply side or evacuating the permeate side) or raising the test temperature can further improve the membrane permeate flux and gas selectivity, which is very beneficial for capturing and utilizing CO2 in high-temperature flue gas. Detailed Implementation

[0022] The following embodiments will further illustrate the present invention, but are not intended to limit the invention.

[0023] Example 1

[0024] According to the technical solution of this invention, 0.1 g of hydrothermal synthesized carbon quantum dot powder [D.Wang, Z.Wang, Q.Zhan, Y.Pu, J.Wang, N.Foster, L.Dai, Facile and scalable preparation of fluorescent carbon dots for multifunctional applications. Engineering 3 (2017) 402–408.] is dispersed in 50 mL of deionized water and stirred thoroughly or sonicated appropriately to form a carbon quantum dot colloidal dispersion system; the temperature of the forced-air drying oven is set to 100 °C, and 0.2 mL of carbon quantum dot colloid is drop-coated onto the surface of an Al2O3 support with a diameter of 18 mm, a thickness of 1 mm, and a minimum pore size of 5 mm. After being kept at this temperature for 10 h, the mixture is allowed to cool naturally; the dried film is placed in an atmosphere furnace, and flowing Ar gas is introduced at a flow rate of 100 mL / min. -1 1℃ min -1 Heat to 300℃, hold for 10 hours, then reduce temperature by 1℃ per minute. -1 The temperature was lowered to room temperature. Gas separation tests were conducted on the calcined membrane under ambient pressure and room temperature conditions. The CO2 / CH4 separation selectivity was 11.2, the CO2 / N2 selectivity was 10.5, and the CO2 permeability reached 3.58 × 10⁻⁶. -9 mol m -2 s -1 Pa -1 .

[0025] Example 2

[0026] According to the technical solution of this invention, 0.1 g of hydrothermal synthesized carbon quantum dot powder [D.Wang, Z.Wang, Q.Zhan, Y.Pu, J.Wang, N.Foster, L.Dai, Facile and scalable preparation of fluorescent carbon dots for multifunctional applications. Engineering 3 (2017) 402–408.] was dispersed in 50 mL of deionized water, ethanol, and DMF, respectively, and stirred thoroughly or sonicated appropriately. The carbon quantum dots have very low solubility in ethanol, but can form a colloidal dispersion system in the other two solvents. The temperature of the forced-air drying oven was set to 100℃, and 0.2 mL of two carbon quantum dot colloids (solvents: deionized water and DMF, respectively) were drop-coated onto the surface of an Al2O3 support with a diameter of 18 mm, a thickness of 1 mm, and a minimum pore size of 5 mm. After being kept at this temperature for 10 h, the mixture was allowed to cool naturally. The dried film was placed in an atmosphere furnace, and flowing Ar gas was introduced at a flow rate of 100 mL / min. -11℃ min -1 Heat to 300℃, hold for 10 hours, then reduce temperature by 1℃ per minute. -1 The temperature was lowered to room temperature. Gas separation tests were conducted on the calcined membrane under ambient pressure and room temperature conditions. The CO2 / CH4 separation selectivity and CO2 permeability are shown in Table 1.

[0027] Table 1:

[0028]

[0029] Example 3

[0030] According to the technical solution of this invention, 0.01 g, 0.02 g, 0.05 g, and 0.1 g of hydrothermal synthesized carbon quantum dot powder [D.Wang, Z.Wang, Q.Zhan, Y.Pu, J.Wang, N.Foster, L.Dai, Facile and scalable preparation of fluorescent carbon dots for multifunctional applications. Engineering 3 (2017) 402–408.] were dispersed in 50 mL of LDM, and thoroughly stirred or appropriately sonicated to form a carbon quantum dot colloidal dispersion system. The carbon quantum dot content was 0.2 g L, respectively. -1 0.4g L -1 1.0g L -1 2.0g L -1 The oven temperature was set to 100℃. 0.2 mL of carbon quantum dot colloid was drop-coated onto the surface of an Al₂O₃ support with a diameter of 18 mm, a thickness of 1 mm, and a minimum pore size of 5 mm. After holding at this temperature for 10 hours, the film was allowed to cool naturally. The dried film was then placed in an atmosphere furnace, and flowing Ar gas was introduced at a flow rate of 100 mL / min. -1 1℃ min -1 Heat to 300℃, hold for 10 hours, then reduce temperature by 1℃ per minute. -1 The temperature was lowered to room temperature. Gas separation tests were conducted on the calcined membrane under ambient pressure and room temperature conditions. The CO2 / CH4 separation selectivity and CO2 permeability are shown in Table 2.

[0031] Table 2:

[0032]

[0033] Example 4

[0034] According to the technical solution of this invention, 0.05g of hydrothermal synthesized carbon quantum dot powder [D.Wang, Z.Wang, Q.Zhan, Y.Pu, J.Wang, N.Foster, L.Dai, Facile and scalable preparation of fluorescent carbon dots for multifunctional applications. Engineering 3 (2017) 402–408.] is dispersed in 50ml LDMF, and thoroughly stirred or appropriately sonicated to form a carbon quantum dot colloidal dispersion system, wherein the carbon quantum dot content is 1g L -1 The oven was set to temperatures of 100℃, 125℃, 150℃, 175℃, and 200℃. 0.2 mL of carbon quantum dot colloid was drop-coated onto the surface of an Al₂O₃ support with a diameter of 18 mm, a thickness of 1 mm, and a minimum pore size of 5 mm. After holding at these temperatures for 10 hours, the film was allowed to cool naturally. The dried film was then placed in an atmosphere furnace, and flowing Ar gas was introduced at a flow rate of 100 mL / min. -1 1℃ min -1 Heat to 300℃, hold for 10 hours, then reduce temperature by 1℃ per minute. -1 The temperature was lowered to room temperature. Gas separation tests were conducted on the calcined membrane under ambient pressure and room temperature conditions. The CO2 / CH4 separation selectivity and CO2 permeability are shown in Table 3.

[0035] Table 3:

[0036]

[0037] Example 5

[0038] According to the technical solution of this invention, 0.05g of hydrothermal synthesized carbon quantum dot powder [D.Wang, Z.Wang, Q.Zhan, Y.Pu, J.Wang, N.Foster, L.Dai, Facile and scalable preparation of fluorescent carbon dots for multifunctional applications. Engineering 3 (2017) 402–408.] is dispersed in 50ml LDMF, and thoroughly stirred or appropriately sonicated to form a carbon quantum dot colloidal dispersion system, wherein the carbon quantum dot content is 1g L -1 The oven temperature was set to 100℃. 0.2 mL of carbon quantum dot colloid was drop-coated onto the surface of an Al₂O₃ support with a diameter of 18 mm, a thickness of 1 mm, and a minimum pore size of 5 mm. After holding at this temperature for 10 hours, the film was allowed to cool naturally. The dried film was then placed in an atmosphere furnace, and flowing Ar gas was introduced at a flow rate of 100 mL / min.-1 1℃ min -1 The temperature was sequentially increased to 300℃, 325℃, 350℃, 375℃, and 400℃, held for 10 hours, and then increased by 1℃ per minute. -1 The temperature was lowered to room temperature. Gas separation tests were conducted on the calcined membrane under ambient pressure and room temperature conditions. The CO2 / CH4 separation selectivity and CO2 permeability are shown in Table 4.

[0039] Table 4:

[0040]

[0041]

[0042] Example 6

[0043] According to the technical solution of this invention, 0.05g of hydrothermal synthesized carbon quantum dot powder [D.Wang, Z.Wang, Q.Zhan, Y.Pu, J.Wang, N.Foster, L.Dai, Facile and scalable preparation of fluorescent carbon dots for multifunctional applications. Engineering 3 (2017) 402–408.] is dispersed in 50ml LDMF, and thoroughly stirred or appropriately sonicated to form a carbon quantum dot colloidal dispersion system, wherein the carbon quantum dot content is 1g L -1 The oven temperature was set to 100℃. 0.2 mL of carbon quantum dot colloid was drop-coated onto the surface of an Al₂O₃ support with a diameter of 18 mm, a thickness of 1 mm, and a minimum pore size of 5 mm. After holding at this temperature for 10 hours, the film was allowed to cool naturally. The dried film was then placed in an atmosphere furnace, and flowing Ar gas was introduced at a flow rate of 100 mL / min. -1 1℃ min -1 Heat to 350℃, hold for 2 hours, 5 hours, 10 hours, 15 hours, and 20 hours respectively, then reduce the temperature by 1℃ per minute. -1 The temperature was lowered to room temperature. Gas separation tests were conducted on the calcined membrane under ambient pressure and room temperature conditions. The CO2 / CH4 separation selectivity and CO2 permeability are shown in Table 5.

[0044] Table 5:

[0045]

[0046] Example 7

[0047] According to the technical solution of this invention, 0.05g of hydrothermal synthesized carbon quantum dot powder [D.Wang, Z.Wang, Q.Zhan, Y.Pu, J.Wang, N.Foster, L.Dai, Facile and scalable preparation of fluorescent carbon dots for multifunctional applications. Engineering 3 (2017) 402–408.] is dispersed in 50ml LDMF, and thoroughly stirred or appropriately sonicated to form a carbon quantum dot colloidal dispersion system, wherein the carbon quantum dot content is 1g L -1 The oven temperature was set to 100℃. 0.2 mL of carbon quantum dot colloid was drop-coated onto the surface of an Al₂O₃ support with a diameter of 18 mm, a thickness of 1 mm, and a minimum pore size of 5 mm. After holding at this temperature for 10 hours, the film was allowed to cool naturally. The dried film was then placed in an atmosphere furnace, and flowing Ar gas was introduced at a flow rate of 100 mL / min. -1 1℃ min -1 Heat to 350℃, hold for 15 hours, then reduce temperature by 1℃ / min. -1 Cool to room temperature. Increase the test temperature and perform gas separation tests on the calcined membrane. The CO2 / CH4 separation selectivity and CO2 permeability are shown in Table 6.

[0048] Table 6:

[0049]

[0050] Many examples can be listed above. The applicant’s extensive experimental data proves that as long as it is within the scope of the technical solution of this invention, carbon quantum dots can be successfully used to construct separation membranes and selectively separate CO2 from mixed gases.

Claims

1. An inorganic gas separation membrane constructed from carbon quantum dots, characterized in that, The preparation method is as follows: (1) Disperse carbon quantum dots in a solvent to form a colloidal dispersion system; (2) Carbon quantum dot colloids were drop-coated onto the surface of a carrier by a hot drop-coating method and then dried. The carrier is an Al2O3 carrier; (3) The dried film is calcined in an inert atmosphere; The atmosphere is flowing Ar, the calcination temperature is 300-400℃, and the holding time is 5-20h.

2. The separation membrane according to claim 1, characterized in that, The carbon quantum dots have a size of 2-10 nanometers.

3. The separation membrane according to claim 1, characterized in that, The concentration of the carbon quantum dot colloid is 0.2-2 g / L. -1 .

4. The separation membrane according to claim 1, characterized in that, The solvent is water or DMF.

5. The separation membrane according to claim 1, characterized in that, The hot drop coating method involves using a high-temperature oven for hot drop coating.

6. The separation membrane according to claim 1, characterized in that, The drop coating temperature is 100-200℃, and the holding time is 2-10h.

7. The separation membrane according to claim 1, characterized in that, It can selectively separate CO2 from various mixed gases.

8. The separation membrane according to claim 1 or 7, characterized in that, Used for the separation of CO2 in CO2 / N2 or CO2 / CH4 gas mixtures.

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