A method for preparing a GQD film by thermal spraying combined with chemical vapor deposition and application thereof

Abstract

The application discloses a method for preparing a GQD film by a thermal spraying combined chemical vapor deposition method and application, and the method comprises the following steps: preparing graphene quantum dots GQD; dispersing the GQD in a solvent to obtain a GQD colloidal solution; spraying the GQD colloidal solution on the surface of a carrier by a thermal spraying method, and then drying to obtain a sprayed film; and under a flowing inert atmosphere, performing thermal treatment on the sprayed film and a polymer containing an amino group or an imino group, so that small molecules decomposed by the thermal treatment are vapor deposited on the surface of the sprayed film and cross-linking reactions occur between the small molecules and groups on the surface of the film, thereby obtaining a GQD film.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and more specifically, to a method and application for preparing GQD membranes using thermal spraying combined with chemical vapor deposition. Background Technology

[0002] CO2 separation is a crucial process for natural gas purification, flue gas recovery from thermal cracking, and mitigation of the greenhouse effect. Compared to traditional CO2 capture processes, membrane separation technology offers advantages such as high separation efficiency, ease of operation, and low cost, and is considered an important means of CO2 capture. Inorganic porous materials (such as zeolites and metal-organic frameworks) possess uniform pore structures, enabling higher selectivity in separation systems; however, their intrinsic pore size limits the separation systems that can be applied to the same material. For polymer membranes, which are readily applicable to industrial applications, membrane composite membranes have been extensively studied in recent years to improve their permeability. To prevent polymer solutions from penetrating into the porous support, a transition layer is usually modified on the surface of the porous support; however, the permeability of the transition layer itself can affect the overall membrane separation performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a method and application for preparing GQD membranes by thermal spraying combined with chemical vapor deposition. By using graphene quantum dots as building blocks, a GQD-H2O colloidal solution is uniformly sprayed onto the surface of a porous carrier to form a continuous membrane. Subsequently, further heat treatment is performed to deposit small molecule compounds onto the membrane surface and crosslink them with the membrane surface groups to obtain a GQD membrane, which can be applied to the efficient separation of CO2 in CO2 / N2 and CO2 / CH4.

[0004] Furthermore, in the preparation method of the present invention, GQD molecules are stacked and cross-linked to form the main structure of the GQD membrane, thereby improving the gas permeability of the membrane; the vapor deposition of small molecules regulates the pore size and adsorption characteristics of the membrane surface, thereby improving the separation selectivity of the membrane.

[0005] Furthermore, the present invention utilizes a method for preparing GQD membranes by combining thermal spraying with chemical vapor deposition. By adjusting the amount of sprayed membrane liquid, the membrane thickness is controlled, and the calcination temperature, calcination time, and deposition amount of small molecules during the heat treatment process are changed, thereby optimizing the separation performance.

[0006] Furthermore, the method for preparing GQD membranes by thermal spraying combined with chemical vapor deposition provided by the present invention, wherein the vapor deposition of small molecule compounds is mainly used to control the surface pore properties, and substances that are conducive to the permeation of target molecules can be selected for chemical vapor deposition according to the target separation system, so as to realize the customized preparation of membranes.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing GQD films using thermal spraying combined with chemical vapor deposition includes the following steps:

[0009] (1) Citric acid was pyrolyzed to obtain graphene quantum dots (GQDs);

[0010] (2) Disperse the graphene quantum dots GQD in a solvent and sonicate for 5 min to 10 min to obtain a GQD colloidal solution;

[0011] (3) The GQD colloidal solution is sprayed onto the surface of the carrier by thermal spraying and then dried at 80℃~120℃ to obtain the sprayed film.

[0012] (4) Under a flowing inert atmosphere, the sprayed film is heat-treated with a polymer containing amino or imino groups so that the decomposed small molecules are deposited onto the surface of the sprayed film and cross-linked with the groups on the surface of the film to obtain the GQD film.

[0013] Optionally, step (4) specifically includes: placing the sprayed film and the polymer containing amino or imino groups in a tube furnace and performing heat treatment under a flowing inert atmosphere, wherein the sprayed film is placed on the downstream side, so that the decomposed small molecules are deposited on the film surface and further crosslinked with the film surface groups to obtain a GQD film.

[0014] Optionally, in step (4), the amino- or imino-containing polymer includes at least one of polyethyleneimine, diethylenetriamine, ethylenediamine, and hexadecylamine.

[0015] Optionally, in step (4), the heat treatment includes: at 0.5°C for 1 minute. -1 ~5℃min -1 The temperature is increased to 250℃~450℃ at a heating rate and held for 3h~30h; preferably, the heating rate is 1℃min. -1 The temperature was increased to 300℃~400℃ at a heating rate and held at that temperature for 5 hours.

[0016] Optionally, in step (4), the dosage of the vapor-deposited material is 3 mg to 15 mg; the inert atmosphere includes one of nitrogen, helium and argon.

[0017] Optionally, in step (1), the pyrolysis temperature is 180℃~210℃, preferably 190℃~210℃, and the pyrolysis time is 15min~90min, preferably 30min.

[0018] Optionally, the particle size of graphene quantum dots (GQDs) is <10 nm.

[0019] Optionally, in step (2), the solvent includes one of water, ethanol and N,N-dimethylformamide.

[0020] Optionally, the concentration of the GQD colloidal solution is 2 mg / mL to 10 mg / mL, preferably 5 mg / mL.

[0021] Optionally, in step (3), the spraying distance of the thermal spraying is 8cm to 20cm, preferably 15cm, the spraying temperature is 150℃ to 210℃, and the amount of spraying film liquid is 1mL to 4mL.

[0022] Optionally, in step (3), the carrier includes one of porous alumina, porous zirconium oxide, and porous titanium oxide.

[0023] Optionally, the structure of the carrier may be flat or tubular.

[0024] Optionally, the pore size of the carrier is 70 nm.

[0025] The present invention also discloses a GQD membrane prepared by the method described above.

[0026] The present invention also discloses the application of a GQD membrane prepared by the method described above in gas separation.

[0027] Implementing the embodiments of the present invention will have the following beneficial effects:

[0028] (1) The method provided by this invention employs an improved thermal spraying technique, which facilitates rapid evaporation of the solvent when the film solution comes into contact with the heated carrier, preventing small-sized GQD nanoparticles from penetrating into the carrier along with the solvent. This is beneficial for forming a continuous and dense ultrathin film on the carrier surface. Therefore, the film prepared using thermal spraying technology reduces the length of gas diffusion and increases gas permeability.

[0029] (2) The method provided by the present invention uses chemical vapor deposition technology. When the sprayed membrane is heat-treated, the surface pore size is controlled in situ by small molecule substances. That is, during the pore formation period, small molecule amines crosslink with GQD surface groups. By different heat treatment temperatures and molecular deposition amounts, the size of the surface pores and adsorption properties are adjusted to improve the separation performance of the GQD membrane.

[0030] (3) The building blocks used in the method provided by this invention are GQDs, which can be synthesized through simple direct pyrolysis or hydrothermal methods. The raw materials are widely available and inexpensive. The building blocks are small-sized zero-dimensional materials, and their own structure has little impact on the assembled membrane. It is only necessary to improve the abundant surface groups to promote their stacking and cross-linking to form a dense membrane. To improve the selectivity of different separation systems, when adjusting the pore structure afterward, easily decomposable and volatile substances with strong affinity for target molecules are selected for the vapor deposition process. Therefore, the entire membrane preparation process is relatively simple and has the benefit of customized pore structure. Attached Figure Description

[0031] Figure 1 The image shows a cross-sectional SEM image of the GQD membrane prepared under different heating stage temperatures of 150°C, 180°C, and 210°C as described in Example 2 of this invention.

[0032] Figure 2 The images show the SEM surface morphology of the GQD membranes prepared under different membrane liquid spraying volumes of 1 mL, 2 mL, 3 mL, and 4 mL as described in Example 3 of this invention. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0034] Comparative Example 1

[0035] Preparation of pure graphene quantum dot (GQD) membranes: GQD prepared by pyrolysis of citric acid at 210℃ for 30 min was used. 0.025 g of GQD was weighed and dispersed in 5 mL of deionized water, then sonicated for 10 min to obtain a homogeneous membrane solution. The heating stage temperature was set to 180℃. A porous alumina support was placed on the heating stage, and 2 mL of the membrane solution was uniformly sprayed onto the support surface using a laboratory spray gun. After spraying, the membrane was placed in an 80℃ oven for further drying. Then, the membrane was calcined under an Ar atmosphere at 1℃ for 1 min. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ per minute. -1 The membrane was cooled to room temperature to obtain a pure GQD membrane. The prepared membrane was then sealed in a membrane module, and the CO2 permeation rate at room temperature was measured to be 7.09 × 10⁻⁶. -7 mol m -2 s -1 Pa -1 The separation selectivity for CO2 / N2 was 3.85, and the separation selectivity for CO2 / CH4 was 4.06.

[0036] Example 1

[0037] 0.15g of citric acid was weighed and ground into powder, and placed in ovens at 180℃, 190℃, 200℃, and 210℃ respectively for pyrolysis reaction for 30 min. After the reaction was completed, 15mL of deionized water was added to each, and the mixture was magnetically stirred for 10 h. The mixture was then filtered through a 0.22 μm filter membrane, and the filtrate was freeze-dried for 48 h to obtain graphene quantum dot powder. 0.025g of GQD prepared at each of the four pyrolysis temperatures was weighed and dispersed in 5mL of deionized water, and sonicated for 10 min to obtain a uniform membrane solution. The heating stage temperature was set to 180℃, and the porous alumina support was placed on the heating stage. 2mL of membrane solution was uniformly sprayed onto the support surface using a laboratory spray gun. After spraying, the membrane was placed in an 80℃ oven for further drying. Then, the membrane was placed together with polyethyleneimine under an Ar atmosphere and calcined at 1℃ for 1 min. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ per minute. -1 The temperature was lowered to room temperature to obtain the GQD membrane. The prepared GQD membrane was sealed in a membrane module, and the CO2 permeation and the separation selectivity of CO2 / N2 and CO2 / CH4 were measured at room temperature, as shown in Table 1.

[0038] Table 1. Membrane performance results at different citric acid pyrolysis temperatures.

[0039]

[0040] Example 2

[0041] GQD was prepared by pyrolysis of citric acid at 210℃ for 30 min. 0.025 g of GQD was weighed and dispersed in 5 mL of deionized water, then sonicated for 10 min to obtain a homogeneous membrane solution. The heating stage was set to 150℃, 180℃, and 210℃. A porous alumina support was placed on the heating stage, and 2 mL of the membrane solution was uniformly sprayed onto the support surface using a laboratory spray gun. After spraying, the membrane was placed in an 80℃ oven for further drying. Then, the membrane was calcined together with polyethyleneimine under an Ar atmosphere, with the membrane positioned downstream of the polyethyleneimine, at 1℃ for 1 min. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ per minute. -1 Cooling to room temperature, a GQD membrane is obtained, such as... Figure 2 As shown in Table 2, the prepared GQD membrane was sealed in a membrane module, and the CO2 permeation and CO2 / N2 and CO2 / CH4 separation selectivity were measured at room temperature.

[0042] Table 2. Film performance results at different thermal spraying temperatures.

[0043]

[0044]

[0045] Example 3 Citric acid 210 was selected o GQD was prepared by pyrolysis at C for 30 min. 0.025 g of GQD was weighed and dispersed in 5 mL of deionized water, then sonicated for 10 min to obtain a homogeneous membrane solution. The heating stage temperature was set to 180°C. o C. Place the porous alumina support on a heating stage, and use a laboratory spray gun to evenly spray 1 mL, 2 mL, 3 mL, and 4 mL of membrane solution onto the support surface, respectively. After spraying, place the membrane at 80°C. o Further drying in a C oven. Then, the film is placed together with polyethyleneimine and calcined under an Ar atmosphere, with the film positioned downstream of the polyethyleneimine, at 1... o C min -1 Heat up to 350 o C, incubate for 5 hours, then add 1 o C min -1 Cooling to room temperature, a GQD membrane is obtained, such as... Figure 2 As shown in Table 3, the prepared GQD membrane was sealed in a membrane module, and the CO2 permeation and CO2 / N2 and CO2 / CH4 separation selectivity were measured at room temperature.

[0047] Table 3. Film performance results under different spray coating liquid volumes

[0048]

[0049] Example 4

[0050] GQD was prepared by pyrolysis of citric acid at 210℃ for 30 min. 0.025 g of GQD was weighed and dispersed in 5 mL of deionized water, then sonicated for 10 min to obtain a homogeneous membrane solution. The heating stage was set to 180℃, and the porous alumina support was placed on the heating stage. 2 mL of the membrane solution was evenly sprayed onto the support surface using a laboratory spray gun. After spraying, the membrane was placed in an 80℃ oven for further drying. Then, the membrane was calcined separately with polyethyleneimine, diethylenetriamine, ethylenediamine, and hexadecylamine under an Ar atmosphere, with the membrane placed downstream, at 1℃ for 1 min. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ per minute. -1 The mixture was cooled to room temperature to obtain the GQD membrane. The prepared GQD membrane was sealed in a membrane module, and the CO2 permeation and the separation selectivity of CO2 / N2 and CO2 / CH4 were measured at room temperature, as shown in Table 4.

[0051] Table 4. Membrane performance results for polymers containing different amino or imino groups.

[0052]

[0053] Example 5

[0054] GQD was prepared by pyrolysis of citric acid at 210℃ for 30 min. 0.025 g of GQD was weighed and dispersed in 5 mL of deionized water, then sonicated for 10 min to obtain a homogeneous membrane solution. The heating stage was set to 180℃, and the porous alumina support was placed on the heating stage. 2 mL of the membrane solution was evenly sprayed onto the support surface using a laboratory spray gun. After spraying, the membrane was placed in an 80℃ oven for further drying. Then, the membrane was calcined together with polyethyleneimine under an Ar atmosphere, with polyethyleneimine dosages of 3 mg, 9 mg, and 15 mg, respectively. The membrane was placed downstream of the polyethyleneimine and calcined at 1℃ for 1 min. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ per minute. -1 The temperature was lowered to room temperature to obtain the GQD membrane. The prepared GQD membrane was sealed in a membrane module, and the CO2 permeation and the separation selectivity of CO2 / N2 and CO2 / CH4 were measured at room temperature, as shown in Table 5.

[0055] Table 5. Membrane performance results under different polyethyleneimine dosages.

[0056]

[0057] Example 6

[0058] GQD was prepared by pyrolysis of citric acid at 210℃ for 30 min. 0.025 g of GQD was weighed and dispersed in 5 mL of deionized water, then sonicated for 10 min to obtain a homogeneous membrane solution. The heating stage was set to 180℃, and the porous alumina support was placed on the heating stage. 2 mL of the membrane solution was evenly sprayed onto the support surface using a laboratory spray gun. After spraying, the membrane was placed in an 80℃ oven for further drying. Then, the membrane was calcined together with polyethyleneimine under an Ar atmosphere, with the membrane positioned downstream of the polyethyleneimine, at 1℃ for 1 min. -1 The temperatures were raised to 250℃, 300℃, 400℃, and 450℃ respectively, and held for 5 hours before being reduced by 1℃ per minute. -1 The mixture was cooled to room temperature to obtain the GQD membrane. The prepared GQD membrane was sealed in a membrane module, and the CO2 permeation and the separation selectivity of CO2 / N2 and CO2 / CH4 were measured at room temperature, as shown in Table 6.

[0059] Table 6. Membrane performance results at different calcination temperatures.

[0060]

[0061] Based on the above results, this invention has rationally selected the preparation conditions of GQD membranes through multiple experiments. By selecting a small-sized zero-dimensional material, GQD, as the building block and using thermal spraying technology, the main structure of the membrane is constructed on the surface of a porous carrier. Then, chemical vapor deposition is used to control the surface pore size and adsorption characteristics of the membrane using small molecules, thereby custom-preparing GQD membranes for CO2 separation. The applicant's extensive experimental data proves that the preparation method of this invention can successfully prepare GQD membranes using a combination of spraying and chemical vapor deposition and apply them to gas separation.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing GQD films using thermal spraying combined with chemical vapor deposition, characterized in that, Includes the following steps: (1) Citric acid was pyrolyzed to obtain graphene quantum dots (GQDs); (2) Disperse the graphene quantum dots GQD in a solvent and sonicate for 5 min to 10 min to obtain a GQD colloidal solution; (3) The GQD colloidal solution is sprayed onto the surface of the carrier by thermal spraying and then dried at 80℃~120℃ to obtain the sprayed film. (4) Under a flowing inert atmosphere, the sprayed film is heat-treated with a polymer containing amino or imino groups so that the decomposed small molecules are deposited onto the surface of the sprayed film and cross-linked with the groups on the surface of the film to obtain the GQD film.

2. The method for preparing GQD films by thermal spraying combined with chemical vapor deposition according to claim 1, characterized in that, In step (1), the pyrolysis temperature is 180℃~210℃ and the pyrolysis time is 15min~90min; The particle size of the graphene quantum dots (GQDs) is <10 nm.

3. The method for preparing GQD films by thermal spraying combined with chemical vapor deposition according to claim 1, characterized in that, In step (2), the solvent includes one of water, ethanol, and N,N-dimethylformamide; The concentration of the GQD colloidal solution is 2 mg / mL to 10 mg / mL.

4. The method for preparing GQD films by thermal spraying combined with chemical vapor deposition according to claim 1, characterized in that, In step (3), the spraying distance of the thermal spraying is 8cm to 20cm, the spraying temperature is 150℃ to 210℃, and the amount of spraying film liquid is 1mL to 4mL.

5. The method for preparing GQD films by thermal spraying combined with chemical vapor deposition according to claim 1, characterized in that, In step (3), the carrier includes one of porous alumina, porous zirconium oxide, and porous titanium oxide; The carrier can be flat or tubular in structure.

6. The method for preparing GQD films by thermal spraying combined with chemical vapor deposition according to claim 1, characterized in that, In step (4), the amino or imino-containing polymer includes at least one of polyethyleneimine, diethylenetriamine, ethylenediamine, and hexadecylamine.

7. The method for preparing GQD films by thermal spraying combined with chemical vapor deposition according to claim 1, characterized in that, In step (4), the heat treatment includes: at 0.5℃ min -1 ~5℃min -1 The temperature is increased to 250℃~450℃ at a heating rate and held for 3h~30h. The dosage of the vapor-deposited material is 3 mg to 15 mg; Inert atmospheres include one of nitrogen, helium, and argon.

8. A GQD membrane prepared by the method according to any one of claims 1-7.

9. The application of a GQD membrane prepared by the method according to any one of claims 1-7 in gas separation.

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