Nitrogen-doped graphene aerogel for H2S removal and preparation method thereof

Abstract

The invention belongs to the technical field of catalytic conversion materials, and particularly relates to nitrogen-doped graphene aerogel for H2S removal and a preparation method of the nitrogen-doped graphene aerogel. The preparation method of the nitrogen-doped graphene aerogel for H2S removal comprises the following steps: (1) uniformly mixing a graphene oxide aqueous solution with a nitrogen source to obtain a mixed solution; (2) carrying out a hydrothermal reaction on the mixed solution, and after the hydrothermal reaction is finished, freeze-drying the obtained hydrogel to obtain aerogel; and (3) carrying out carbonization treatment on the aerogel, so as to obtain the nitrogen-doped graphene aerogel for removing H2S. According to the nitrogen-doped graphene aerogel for H2S removal disclosed by the invention, large-size graphene sheet layers are mutually connected to form a macroporous and mesoporous mass transfer passage inside the nitrogen-doped graphene aerogel, and the surface of the material has a rich microporous structure and a high-content nitrogen doping characteristic, so that efficient adsorption and removal of H2S molecules can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic conversion materials, and particularly relates to a nitrogen-doped graphene aerogel for H2S removal and a preparation method thereof. Background Art

[0002] With growing energy demands and rapid industrialization, large quantities of H2S-containing industrial waste gas are emitted. H2S waste gas is toxic and poses serious risks to both the environment and human health. Removing H2S from the gas phase by catalytically converting it into elemental sulfur is crucial for environmental protection.

[0003] At present, the industry generally adopts a high-temperature dry H2S fine removal process based on metal oxides (above 200°C), which can remove the sulfur content to below 0.5 ppm. However, this method has high energy consumption and is prone to excessive oxidation of H2S during the removal process, generating secondary pollutants such as SO2 (Sep. Purif. Technol. 2022, 286: 120458).

[0004] Carbon materials can catalyze the conversion of H2S to elemental sulfur at room temperature, offering a low-temperature, low-energy, and highly efficient method. Existing materials such as activated carbon, carbon fiber, and graphene oxide (GO) still suffer from poor catalytic conversion of H2S.

[0005] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0006] The object of the present invention is to provide a nitrogen-doped graphene aerogel for H2S removal and a preparation method thereof, so as to help solve or improve the problem that existing carbon materials have poor catalytic conversion effect on H2S.

[0007] In order to achieve the above-mentioned object, the present invention provides the following technical solution: a method for preparing nitrogen-doped graphene aerogel for H2S removal, comprising the following steps: (1) uniformly mixing a graphene oxide aqueous solution and a nitrogen source to obtain a mixed solution; (2) subjecting the mixed solution to a hydrothermal reaction, and after the hydrothermal reaction, freeze-drying the obtained hydrogel to obtain an aerogel; and (3) carbonizing the aerogel to obtain the nitrogen-doped graphene aerogel for H2S removal.

[0008] Preferably, the nitrogen source is dicyandiamide, and the mass ratio of the graphene oxide to the dicyandiamide is 1:(0.5-1).

[0009] Preferably, the concentration of the graphene oxide aqueous solution is 2-5 g / L.

[0010] Preferably, the temperature of the hydrothermal reaction is 160-180° C., and the time of the hydrothermal reaction is 10-12 h.

[0011] Preferably, the carbonization temperature is 700-850° C., the carbonization time is 2-3 hours, and the carbonization is carried out in an inert atmosphere.

[0012] Preferably, the graphene oxide has a thickness of ≤1 μm and a single-layer sheet diameter of 0.2-10 μm.

[0013] Preferably, the freeze-drying temperature is ≤-80°C, and the freeze-drying time is 3-5 days.

[0014] Preferably, before adding the nitrogen source, the step of stirring and ultrasonically dispersing the graphene oxide aqueous solution for 1-2 hours is further included; after adding the nitrogen source, the step of ultrasonically dispersing for 10-15 minutes to mix uniformly is further included.

[0015] The present invention also provides a nitrogen-doped graphene aerogel for H2S removal, which adopts the following technical solution: a nitrogen-doped graphene aerogel for H2S removal, wherein the nitrogen-doped graphene aerogel for H2S removal is prepared by the method described above.

[0016] The present invention also provides an application of the nitrogen-doped graphene aerogel for H2S removal, and an application of the nitrogen-doped graphene aerogel for H2S removal as described above in catalytic conversion of H2S.

[0017] Beneficial effects:

[0018] The nitrogen-doped graphene aerogel for H2S removal of the present invention uses graphene oxide (GO) as a carbon precursor. After a hydrothermal reduction reaction, GO can self-assemble and connect to form a bulk graphene aerogel with a rich pore structure and good mechanical properties. In addition, the two-dimensional structure and abundant oxygen-containing functional groups (such as hydroxyl groups and carboxyl groups) of GO provide sufficient active sites for the doping of nitrogen atoms, which helps to construct a bulk nitrogen-doped graphene aerogel with rich micropores and high nitrogen content.

[0019] The nitrogen-doped graphene aerogel for H2S removal of the present invention uses dicyandiamide as a nitrogen source. During the hydrothermal growth process of GO gel, an appropriate amount of dicyandiamide can be uniformly mixed on the GO sheets to form a gel. After subsequent carbonization treatment, nitrogen atoms are stably embedded in the carbon skeleton, making the GO aerogel surface weakly alkaline and providing the GO aerogel with abundant active sites. At the same time, the embedding of nitrogen atoms promotes the formation of a microporous structure on the GO aerogel surface that matches the size of H2S molecules, which helps to improve the H2S removal effect of the GO aerogel material.

[0020] The nitrogen-doped graphene aerogel for H2S removal of the present invention has a black three-dimensional cylindrical structure, with large-sized graphene sheets interconnected inside to form macroporous and mesoporous mass transfer pathways. The surface of the material has rich microporous structures and high-content nitrogen doping characteristics, which can achieve efficient adsorption and removal of H2S molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0022] Figure 1 (a) A physical photograph and (b) a field emission scanning electron microscope image of the nitrogen-doped graphene aerogel for H2S removal in Example 1.

[0023] Figure 2 1. The nitrogen adsorption-desorption curve (a) and pore size distribution diagram (b) of the nitrogen-doped graphene aerogel for H2S removal in Example 1.

[0024] Figure 3 This is the N1s XPS spectrum of the nitrogen-doped graphene aerogel for H2S removal in Example 1.

[0025] Figure 4 This is the H2S breakthrough curve of the nitrogen-doped graphene aerogel for H2S removal in Example 1.

[0026] Figure 5 This is the H2S breakthrough curve of the nitrogen-doped graphene aerogel for H2S removal in Example 6.

[0027] Figure 6 (a) and (b) the nitrogen adsorption-desorption curve of the nitrogen-doped graphene aerogel for H2S removal in Example 6.

[0028] Figure 7 These are the physical photograph (a) and field emission scanning electron microscope image (b) of the GO aerogel of Comparative Example 1.

[0029] Figure 8 These are a physical photograph (a) and a field emission scanning electron microscope image (b) of the ammonium citrate graphene aerogel of Comparative Example 2.

[0030] Figure 9 (a) is a nitrogen adsorption / desorption curve diagram and (b) is a pore size distribution diagram of the ammonium citrate graphene aerogel of Comparative Example 2.

[0031] Figure 10 This is the N1s XPS spectrum of the ammonium citrate graphene aerogel of Comparative Example 2.

[0032] Figure 11 This is the H2S penetration curve of the ammonium citrate graphene aerogel of Comparative Example 2.

[0033] Figure 12 (a) and (b) the nitrogen adsorption-desorption curve of the uncarbonized nitrogen-doped graphene aerogel of Comparative Example 5.

[0034] Figure 13 3 is a comparison chart of the saturated sulfur capacity of the graphene aerogels of Example 1, Example 6, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0036] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0037] The present invention addresses the problem that current carbon materials have poor catalytic conversion effect on H2S and provides a method for preparing nitrogen-doped graphene aerogel for H2S removal.

[0038] The preparation method of nitrogen-doped graphene aerogel for H2S removal according to an embodiment of the present invention comprises the following steps: (1) uniformly mixing a graphene oxide aqueous solution and a nitrogen source to obtain a mixed solution; (2) subjecting the mixed solution to a hydrothermal reaction, and after the hydrothermal reaction, freeze-drying the obtained hydrogel to obtain an aerogel; and (3) carbonizing the aerogel to obtain nitrogen-doped graphene aerogel for H2S removal.

[0039] The present invention uses graphene oxide (GO) as a carbon precursor, adds a nitrogen source to a GO aqueous solution and mixes them evenly, reduces and self-assembles the GO through a hydrothermal reaction, and then freeze-dries and carbonizes it at high temperature to finally produce a nitrogen-doped graphene aerogel with a three-dimensional macroscopic block structure, abundant micropores and a high nitrogen content.

[0040] First, the nitrogen-doped graphene aerogel for H2S removal of the present invention uses GO as a carbon precursor. After a hydrothermal reduction reaction, GO can self-assemble and connect to form a bulk graphene aerogel with a rich pore structure and good mechanical properties. In addition, the two-dimensional structure of GO and its abundant oxygen-containing functional groups (such as hydroxyl groups and carboxyl groups) provide sufficient active sites for the doping of nitrogen atoms, which helps to construct a bulk nitrogen-doped graphene aerogel with rich micropores and high nitrogen content.

[0041] Secondly, the nitrogen-doped graphene aerogel described in the present invention uses dicyandiamide as a nitrogen source. During the hydrothermal growth process of GO gel, an appropriate amount of dicyandiamide can be uniformly mixed on the GO sheets to form a gel. After subsequent carbonization treatment, the nitrogen atoms are stably embedded in the carbon skeleton, making the GO aerogel surface weakly alkaline and providing the GO aerogel with abundant active sites. At the same time, the embedding of nitrogen atoms promotes the formation of a microporous structure on the surface of the GO aerogel that matches the size of the H2S molecule, which helps to improve the H2S removal effect of the GO aerogel material.

[0042] In a preferred embodiment of the method for preparing nitrogen-doped graphene aerogel for H2S removal of the present invention, the nitrogen source is dicyandiamide, and the mass ratio of graphene oxide to dicyandiamide is 1:(0.5-1) (for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1); wherein, if the usage ratio of dicyandiamide is too small, the nitrogen content of the carbon aerogel will be too low, and the H2S removal performance will be poor; if the usage ratio of dicyandiamide is too large, the carbon skeleton will be damaged, and it will be difficult to form a carbon aerogel structure.

[0043] Preferably, the concentration of the graphene oxide aqueous solution is 2-5 g / L (eg, 2 g / L, 3 g / L, 4 g / L or 5 g / L).

[0044] In a preferred embodiment of the method for preparing nitrogen-doped graphene aerogel for H2S removal of the present invention, the temperature of the hydrothermal reaction is 160-180°C (e.g., 160°C, 165°C, 170°C, 175°C, or 180°C), and the hydrothermal reaction time is 10-12 hours (e.g., 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours). When the hydrothermal reaction temperature is lower than 160°C, the carbon aerogel's three-dimensional network structure has a low degree of crosslinking, the aerogel has poor mechanical strength, and is prone to collapse; when the hydrothermal reaction temperature is higher than 180°C, the over-reduction process can cause excessive stacking and rupture of the graphene sheets. Furthermore, the degree of reduction also needs to take the hydrothermal time into consideration. When the hydrothermal reaction time is less than 10 hours, the degree of reduction is insufficient and the doped nitrogen element is insufficient; when the hydrothermal reaction time exceeds 12 hours, it is easy to cause excessive stacking and rupture of the over-reduced graphene sheets.

[0045] In a preferred embodiment of the method for preparing nitrogen-doped graphene aerogel for H2S removal of the present invention, the carbonization temperature is 700-850°C (e.g., 700°C, 730°C, 750°C, 780°C, 810°C, 830°C, 840°C, or 850°C), and the carbonization time is 2-3 hours (e.g., 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3 hours). When the carbonization temperature is too low, the specific surface area of ​​the sample obtained after carbonization is small, and the H2S gas removal performance is poor; when the carbonization temperature is higher than 850°C, the sample structure is destroyed and the quality loss is severe. When the carbonization time is less than 2 hours, the sample is difficult to be completely carbonized; when the carbonization time exceeds 3 hours, the sample structure is destroyed and the quality loss is severe; the carbonization is carried out in an inert atmosphere (e.g., nitrogen, argon, or other rare gases).

[0046] Preferably, the carbonization temperature is 750-850°C.

[0047] In a preferred embodiment of the present invention's method for preparing nitrogen-doped graphene aerogel for H2S removal, the graphene oxide has a thickness of ≤1 μm and a single-layer flake diameter of 0.2-10 μm. This facilitates the preparation of a high-specific-surface-area graphene aerogel, and the small flake diameter (0.2-10 μm) facilitates uniform dispersion during the gelation process, resulting in a denser distribution of crosslinking sites and the formation of numerous microporous structures.

[0048] In a preferred embodiment of the method for preparing nitrogen-doped graphene aerogel for H2S removal of the present invention, the freeze-drying temperature is ≤ -80°C, and the freeze-drying time is 3-5 days (e.g., 3 days, 4 days, or 5 days). The purpose of freeze-drying is to completely dry the aerogel. Simultaneously, rapid freezing (≤ -80°C) inhibits ice crystal growth, forming a nanoscale ice crystal template, helping to prevent material shrinkage and promoting the formation of abundant micropores and a large specific surface area.

[0049] Specifically, the hydrogel can be placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3-5 days to sublime the solid water in the hydrogel to obtain an aerogel.

[0050] In a preferred embodiment of the method for preparing nitrogen-doped graphene aerogel for H2S removal of the present invention, before adding the nitrogen source, the method further includes stirring and ultrasonically dispersing the graphene oxide aqueous solution for 1-2 hours (for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2 hours); after adding the nitrogen source, the method further includes ultrasonicating for 10-15 minutes (for example, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes) to mix uniformly.

[0051] The present invention also proposes a nitrogen-doped graphene aerogel for H2S removal. The nitrogen-doped graphene aerogel for H2S removal in the embodiments of the present invention is prepared using the method described above. The nitrogen-doped graphene aerogel for H2S removal of the present invention has a black three-dimensional cylindrical structure, with large-scale graphene sheets interconnected to form macroporous and mesoporous mass transfer pathways. The material surface has a rich microporous structure and high nitrogen doping content, enabling efficient adsorption and removal of H2S molecules.

[0052] The nitrogen-doped graphene aerogel for H2S removal and its preparation method of the present invention are described in detail below through specific examples.

[0053] The sources of the main raw materials used in the following examples are: graphene oxide (few layers) was purchased from Shenzhen Suiheng Technology Co., Ltd., dicyandiamide (99.99%) was purchased from Shanghai Maclean Technology Co., Ltd., and ammonium citrate (98.5%) was purchased from Tianjin Guangfu Fine Chemical Research Institute.

[0054] Example 1

[0055] The preparation method of nitrogen-doped graphene aerogel for H2S removal in this embodiment includes the following steps:

[0056] (1) Weigh 0.24 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 30 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water to obtain a mixed solution.

[0057] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven, heated to 175°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel;

[0058] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 800° C. at a rate of 100° C., kept at 800° C. for 180 min, and then cooled to room temperature along with the furnace to obtain the nitrogen-doped graphene aerogel for H 2 S removal of this embodiment.

[0059] Example 2

[0060] The preparation method of nitrogen-doped graphene aerogel for H2S removal in this embodiment includes the following steps:

[0061] (1) Weigh 0.26 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 30 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water to obtain a mixed solution.

[0062] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven, heated to 170°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel;

[0063] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 800° C. at a rate of 100° C., kept at 800° C. for 180 min, and then cooled to room temperature along with the furnace to obtain the nitrogen-doped graphene aerogel for H 2 S removal of this embodiment.

[0064] Example 3

[0065] The preparation method of nitrogen-doped graphene aerogel for H2S removal in this embodiment includes the following steps:

[0066] (1) Weigh 0.16 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 20 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water to obtain a mixed solution.

[0067] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven, heated to 180°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel;

[0068] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 800° C. at a rate of 100° C., kept at 800° C. for 150 min, and then cooled to room temperature along with the furnace to obtain the nitrogen-doped graphene aerogel for H 2 S removal of this embodiment.

[0069] Example 4

[0070] The preparation method of nitrogen-doped graphene aerogel for H2S removal in this embodiment includes the following steps:

[0071] (1) Weigh 0.40 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 80 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water, thereby obtaining a mixed solution.

[0072] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven. The temperature was raised to 160°C for hydrothermal reaction for 12 hours to reduce GO and self-assemble to form a hydrogel. The hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel.

[0073] Then, the aerogel is obtained by freeze-drying the hydrogel in a freeze-drying box at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel.

[0074] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 850° C. at a rate of 1000 ℃, kept at 850° C. for 150 minutes, and then cooled to room temperature along with the furnace to obtain the nitrogen-doped graphene aerogel for H2S removal of this embodiment.

[0075] Example 5

[0076] The preparation method of nitrogen-doped graphene aerogel for H2S removal in this embodiment includes the following steps:

[0077] (1) Weigh 0.32 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. 20 mL of the fully dispersed GO solution was added to a glass reaction bottle, and 20 mg of dicyandiamide powder was weighed and added to the glass reaction bottle. The mixture was ultrasonicated for 15 min at room temperature to uniformly mix the two raw materials in water, thereby obtaining a mixed solution.

[0078] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven. The temperature was raised to 180°C for hydrothermal reaction for 12 hours to reduce GO and self-assemble to form a hydrogel. The hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel. The hydrogel was then freeze-dried in a freeze drying oven at a temperature below -80°C for 5 days to sublime the solid water in the hydrogel to obtain an aerogel.

[0079] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 750° C. at a rate of 100° C., kept at 750° C. for 150 min, and then cooled to room temperature along with the furnace to obtain the nitrogen-doped graphene aerogel for H 2 S removal of this embodiment.

[0080] Example 6

[0081] The preparation method of nitrogen-doped graphene aerogel for H2S removal in this embodiment includes the following steps:

[0082] (1) Weigh 0.24 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 30 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water to obtain a mixed solution.

[0083] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven. The temperature was raised to 175°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel.

[0084] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1The temperature was raised to 700° C. at a rate of 100° C., kept at 700° C. for 180 min, and then cooled to room temperature along with the furnace to obtain the nitrogen-doped graphene aerogel for H 2 S removal of this embodiment.

[0085] Comparative Example 1

[0086] The preparation method of the GO aerogel of this comparative example comprises the following steps:

[0087] (1) Weigh 0.24 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it to obtain a graphene oxide (GO) aqueous solution.

[0088] (2) 20 mL of fully dispersed GO solution was added to a glass reaction bottle, placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven. The temperature was raised to 175°C for hydrothermal reaction for 12 h to reduce GO and self-assemble to form a hydrogel. The hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel. The aerogel was then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel.

[0089] (3) Place the aerogel in a tubular furnace and heat it at 50°C for half an hour under an argon atmosphere. -1 The temperature was raised to 800° C. at a rate of 100° C., kept at 800° C. for 180 min, and then cooled to room temperature along with the furnace to obtain the GO aerogel of this comparative example.

[0090] Comparative Example 2

[0091] The preparation method of the ammonium citrate graphene aerogel of this comparative example comprises the following steps:

[0092] (1) Weigh 0.24 g of GO and put it into a beaker filled with 80 mL of deionized water. At room temperature, sonicate the GO aqueous solution for 1.5 h to uniformly disperse it to obtain a graphene oxide (GO) aqueous solution; weigh 1 g of ammonium citrate and dissolve it in 20 mL of deionized water, sonicate it at room temperature for 10 min to uniformly disperse the ammonium citrate in the aqueous solution; take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle, measure 6 mL of ammonium citrate aqueous solution and add it to the glass reaction bottle at a rate of 3 drops per second (after literature review and preliminary experimental optimization, the mass ratio of ammonium citrate to graphene in the ammonium citrate graphene aerogel with the best product performance is 5:1), and continue to sonicate the mixture at room temperature for 15 min to uniformly mix the two raw materials in water to obtain a mixed solution;

[0093] (2) The mixed solution is placed in a polytetrafluoroethylene-lined reactor, sealed and placed in an oven for hydrothermal reaction at 120°C for 12 hours (after literature review and preliminary experimental optimization, the hydrothermal temperature of ammonium citrate graphene aerogel with the best product performance is 120°C, and the ammonium citrate graphene aerogel obtained thereby is the most stable; too high a hydrothermal temperature will cause the structure of the ammonium citrate graphene aerogel to collapse; too low a hydrothermal temperature will lead to incomplete reaction and the ammonium citrate graphene aerogel product will be too dense), so that GO is reduced and self-assembled to form a hydrogel; the hydrogel is placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying box at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel;

[0094] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 800° C. at a rate of 100° C., kept at 800° C. for 180 min, and then cooled to room temperature along with the furnace to obtain the ammonium citrate graphene aerogel of this comparative example.

[0095] Comparative Example 3

[0096] The preparation method of a small amount of nitrogen-doped graphene aerogel in this comparative example comprises the following steps:

[0097] (1) Weigh 0.24 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 18 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water, thereby obtaining a mixed solution.

[0098] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven, heated to 175°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel;

[0099] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 800° C. at a rate of 100° C., kept at 800° C. for 180 min, and then cooled to room temperature along with the furnace to obtain a small amount of nitrogen-doped graphene aerogel of this comparative example.

[0100] Comparative Example 4

[0101] The preparation method of the excess nitrogen-doped graphene aerogel of this comparative example comprises the following steps:

[0102] (1) Weigh 0.24 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 65 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water to obtain a mixed solution.

[0103] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven, heated to 175°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel;

[0104] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 800° C. at a rate of 100° C., kept at 800° C. for 180 min, and then cooled to room temperature along with the furnace to obtain the excess nitrogen-doped graphene aerogel of this comparative example.

[0105] Comparative Example 5

[0106] The preparation method of the uncarbonized nitrogen-doped graphene aerogel of this comparative example comprises the following steps:

[0107] (1) Weigh 0.24 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 30 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water to obtain a mixed solution.

[0108] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven, heated to 175°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel, thereby obtaining the uncarbonized nitrogen-doped graphene aerogel of this comparative example.

[0109] Comparative Example 6

[0110] The preparation method of the graphene aerogel with a higher carbonization temperature in this comparative example comprises the following steps:

[0111] (1) Weigh 0.24 g of GO and place it in a beaker filled with 80 mL of deionized water. Ultrasonicate the GO aqueous solution for 1.5 h at room temperature to uniformly disperse it, thereby obtaining a graphene oxide (GO) aqueous solution. Take 20 mL of the fully dispersed GO solution and add it to a glass reaction bottle. Weigh 30 mg of dicyandiamide powder and add it to the glass reaction bottle. Ultrasonicate the mixture for 15 min at room temperature to uniformly mix the two raw materials in water to obtain a mixed solution.

[0112] (2) The mixed solution was placed in a polytetrafluoroethylene-lined reactor, sealed, and placed in an oven. The temperature was raised to 175°C for hydrothermal reaction for 12 hours, so that GO was reduced and self-assembled to form a hydrogel; the hydrogel was placed in a freezer below -80°C to freeze and solidify the water in the hydrogel, and then freeze-dried in a freeze drying oven at a temperature below -80°C for 3 days to sublime the solid water in the hydrogel to obtain an aerogel.

[0113] (3) Place the aerogel in a tubular furnace and keep it at 50°C for half an hour under an argon atmosphere. Ensure that the air in the tubular furnace is exhausted before heating. -1 The temperature was raised to 900℃ at a speed of 1000℃, kept at 900℃ for 180min, and then cooled to room temperature with the furnace. It was found that the sample was almost completely lost at this carbonization temperature, and it was difficult to collect the carbonized product.

[0114] Experimental example

[0115] 1. Actual photos and field emission scanning electron microscope test:

[0116] Figure 1 The actual photograph (a) and field emission scanning electron microscope image (b) of the nitrogen-doped graphene aerogel for H2S removal in Example 1.

[0117] Photos of the nitrogen-doped graphene aerogel for H2S removal in Example 1 show that the material is a black, cylindrical, three-dimensional block with a cross-sectional diameter of 1.5 cm and a height of 1 cm. Field emission scanning electron microscopy reveals that the nitrogen-doped graphene aerogel internally comprises a three-dimensional network of GO sheets, providing macroporous and mesoporous mass transfer pathways for H2S removal.

[0118] Figure 7 The physical photo (a) and field emission scanning electron microscope image (b) of the GO aerogel of Comparative Example 1 are shown; Figure 7The GO aerogel in Comparative Example 1 is a black, cylindrical block with a cross-sectional diameter of 1 cm and a height of 1.6 cm. Field emission scanning electron microscopy images show that the GO aerogel has a very dense internal structure and relatively few pores, which is not conducive to the catalytic conversion of H2S.

[0119] Figure 8 The following are a photograph (a) and a field emission scanning electron microscopy image (b) of the ammonium citrate graphene aerogel from Comparative Example 2. As can be seen, the ammonium citrate graphene aerogel is a black, cylindrical block with a cross-sectional diameter of 1.2 cm and a height of 2 cm. The field emission scanning electron microscopy image shows that the internal structure of the ammonium citrate graphene aerogel is looser than that of the GO aerogel from Comparative Example 1, but is denser than that of the nitrogen-doped graphene aerogel for H2S removal from Example 1.

[0120] 2. Nitrogen adsorption-desorption curve and pore size test:

[0121] Figure 2 The nitrogen adsorption-desorption curve (a) and pore size distribution diagram (b) of the nitrogen-doped graphene aerogel for H2S removal in Example 1 are shown. It can be seen from the nitrogen adsorption-desorption curve that when the nitrogen relative pressure is very low, the nitrogen molecules preferentially fill the micropores of the nitrogen-doped graphene aerogel for H2S removal in Example 1, resulting in a sharp increase in the adsorption amount. The adsorption curve has a linear upward trend. As the relative pressure further increases, the adsorption curve and the desorption curve show a hysteresis loop shape. This is due to the capillary condensation phenomenon caused by the presence of mesopores. When the relative pressure is close to 1, the nitrogen molecules undergo multi-layer adsorption on the surface of the macropores, resulting in a sharp increase in the adsorption amount. The specific surface area of ​​the nitrogen-doped graphene aerogel is calculated to be 460m 2 g -1 ;Depend on Figure 2 The pore size distribution diagram in (b) further proves that it is rich in large-medium-small porous structure.

[0122] Figure 6 The nitrogen adsorption-desorption curve (a) and pore size distribution diagram (b) of the nitrogen-doped graphene aerogel for H2S removal of Example 6 can be seen from the nitrogen adsorption-desorption curve. When the nitrogen relative pressure is very low, the nitrogen molecules preferentially fill the micropores of the graphene aerogel with a lower carbonization temperature in Example 6, resulting in a sharp increase in the adsorption amount. The adsorption curve has a linear upward trend. As the relative pressure increases further, the adsorption curve and the desorption curve show a hysteresis loop shape. This is due to the capillary condensation phenomenon caused by the presence of mesopores. When the relative pressure is close to 1, nitrogen molecules undergo multi-layer adsorption on the surface of the macropores, resulting in a sharp increase in the adsorption amount. By observing the shape of the adsorption-desorption curve, it is almost similar to that of Example 1, except that the nitrogen saturation adsorption amount is small, and the specific surface area and pore volume are small. After calculation, the specific surface area of ​​the nitrogen-doped graphene aerogel reaches 180m 2g -1 ;Depend on Figure 6 The pore size distribution diagram of (b) further proves that the pore structure is similar to that of Example 1 and is rich in large-medium-small porous structures.

[0123] Figure 9 It is the nitrogen adsorption-desorption curve (a) and pore size distribution diagram (b) of ammonium citrate graphene aerogel of comparative example 2. It can be seen from the nitrogen adsorption-desorption curve that when the relative pressure of nitrogen is very low, nitrogen molecules preferentially fill the micropores of ammonium citrate graphene aerogel. At this time, the adsorption curve does not change, indicating that there are almost no micropores in the material. As the relative pressure increases further, the adsorption curve and the desorption curve show a hysteresis loop shape. This is due to the capillary condensation phenomenon caused by the presence of mesopores. When the relative pressure is close to 1, nitrogen molecules undergo multi-layer adsorption on the macropore surface, resulting in a sharp increase in the adsorption amount. Due to the lack of microporous structure with a specific surface area, the specific surface area of ​​ammonium citrate graphene aerogel is calculated to be 60m 2 g -1 ,Depend on Figure 9 (b) The pore size distribution diagram of ammonium citrate graphene aerogel shows that the volume of micropores (<2nm) is zero, further indicating that the pore structure of ammonium citrate is composed of macropores and mesopores.

[0124] Figure 12 This is the nitrogen adsorption and desorption curve (a) and pore size distribution diagram (b) of the uncarbonized nitrogen-doped graphene aerogel of Example 5. It can be seen that when the relative pressure of nitrogen is very low, nitrogen molecules preferentially fill the micropores. At this time, the adsorption curve of the uncarbonized dicyandiamide graphene aerogel does not change, indicating that there are almost no micropores without carbonization of the material; as the relative pressure increases further, the adsorption curve and the desorption curve show a hysteresis ring shape, which is due to the capillary condensation phenomenon caused by the presence of mesopores; when the relative pressure reaches the maximum value, the material shows an insignificant linear upward trend, and the uncarbonized nitrogen-doped graphene aerogel is mainly composed of mesopores and a small number of macropores. The specific surface area of ​​the uncarbonized nitrogen-doped graphene aerogel is only 2.7m 2 g -1 ,It can be seen from the pore size distribution diagram that the uncarbonized nitrogen-doped graphene aerogel contains almost no micropores and is mainly composed of mesopores and a small part of macropores.

[0125] 3. Elemental analysis of the nitrogen-doped graphene aerogels for H2S removal of Examples 1-3 and the ammonium citrate graphene aerogel of Comparative Example 2:

[0126] The elemental analysis results are shown in Table 1:

[0127] Table 1 Elemental analysis of graphene aerogel

[0128]

[0129] 4.N1s XPS spectrum test:

[0130] The N1s XPS spectrum of the nitrogen-doped graphene aerogel for H2S removal in Example 1 is shown in FIG. Figure 3 The high-resolution N1s spectrum peak position shows that the nitrogen in the nitrogen-doped graphene aerogel is mainly composed of pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, and nitrogen oxide, with pyridinic nitrogen being the main doping type, accounting for 45%.

[0131] Figure 10 This is the N1s XPS spectrum of the ammonium citrate graphene aerogel of Comparative Example 2. The high-resolution N1s spectrum peak position indicates that the nitrogen in the ammonium citrate graphene aerogel of Comparative Example 2 consists of graphitic nitrogen, pyrrolic nitrogen, and pyridinic nitrogen, with the pyridinic nitrogen content accounting for only 10%.

[0132] 5. Catalytic conversion performance test:

[0133] Test method: Take 20mg of graphene aerogel sample and test its H2S catalytic conversion performance in a continuous flow fixed bed reactor at room temperature and pressure (25℃, 101kPa). -1 The outlet H2S gas concentration is detected every 5 minutes through the reactor using a gas chromatograph equipped with a packed column and a flame photometric detector. When the outlet concentration is consistent with the inlet concentration, the catalytic conversion of the sample reaches saturation.

[0134] Figure 4 This is the H2S breakthrough curve of the nitrogen-doped graphene aerogel for H2S removal in Example 1. This shows that the nitrogen-doped graphene aerogel for H2S removal has excellent catalytic H2S conversion performance, with a breakthrough time of 2000 min, and the catalytic conversion of H2S reaches saturation; its calculated saturated sulfur capacity reaches 3.36 g / L. -1 ( Figure 13 ).

[0135] The H2S catalytic conversion performance of the graphene aerogel with a lower carbonization temperature in Example 6 was measured in the same manner as in Example 1. The results showed that the graphene aerogel with a lower carbonization temperature had a certain H2S catalytic conversion performance. Due to the lower carbonization temperature, the specific surface area and pore volume were smaller, and the penetration time for H2S catalytic conversion and removal was 450 min ( Figure 5 ),Depend on Figure 13 It can be seen that its sulfur capacity is calculated to be 2.217 gg -1 This indicates the necessity of larger specific surface area and pore volume for H2S catalytic conversion and removal performance.

[0136] The H2S catalytic conversion performance of the GO aerogel of Comparative Example 1 was determined in the same manner as in Example 1. The results showed that the GO aerogel of Comparative Example 1 was instantly penetrated when used for H2S catalytic conversion and removal, and the sulfur capacity was 0 ( Figure 13 ). This shows the necessity of nitrogen doping for the catalytic conversion and removal of H2S.

[0137] Figure 11 This is the H2S penetration curve of the ammonium citrate graphene aerogel of comparative example 2. It can be seen that the ammonium citrate graphene aerogel has a certain H2S catalytic conversion performance. The penetration time for H2S catalytic conversion and removal is 60 minutes. Figure 13 It can be seen from the calculation that its sulfur capacity is 0.104gg -1 This indicates the necessity of suitable nitrogen source and nitrogen doping form for catalytic conversion and removal of H2S.

[0138] The H2S catalytic conversion performance of the small amount of nitrogen-doped graphene aerogel of Comparative Example 3 was determined in the same manner as in Example 1. The results showed that the small amount of nitrogen-doped graphene aerogel had a certain H2S catalytic conversion performance. Due to the low nitrogen content, the penetration time for H2S catalytic conversion and removal was 65 minutes. Figure 13 It can be seen from the calculation that its sulfur capacity is 0.063gg -1 This indicates that sufficient nitrogen source input is necessary for the catalytic conversion and removal performance of H2S.

[0139] The H2S catalytic conversion performance of the excess nitrogen-doped graphene aerogel of Comparative Example 4 was measured in the same manner as in Example 1. The results showed that the excess nitrogen source graphene aerogel of Comparative Example 4 was instantly penetrated when used for H2S catalytic conversion and removal, and the sulfur capacity was 0 ( Figure 13 ). This shows that appropriate nitrogen source input is necessary for the catalytic conversion and removal performance of H2S.

[0140] The H2S catalytic conversion performance of the uncarbonized nitrogen-doped graphene aerogel of Comparative Example 5 was measured in the same manner as in Example 1. The results showed that the uncarbonized nitrogen-doped graphene aerogel of Comparative Example 5 was instantly penetrated when used for H2S catalytic conversion and removal, and the sulfur capacity was 0 ( Figure 13 ). This shows that carbonization treatment is necessary for the catalytic conversion and removal performance of H2S.

[0141] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing nitrogen-doped graphene aerogel for H2S removal, characterized in that: The steps include: (1) uniformly mixing the graphene oxide aqueous solution and the nitrogen source to obtain a mixed solution; (2) subjecting the mixed solution to a hydrothermal reaction, and freeze-drying the resulting hydrogel to obtain an aerogel after the hydrothermal reaction is completed; (3) Carbonizing the aerogel to obtain the nitrogen-doped graphene aerogel for H2S removal.

2. The method for preparing nitrogen-doped graphene aerogel for H2S removal according to claim 1, wherein: The nitrogen source is dicyandiamide, and the mass ratio of the graphene oxide to the dicyandiamide is 1:(0.5-1).

3. The method for preparing nitrogen-doped graphene aerogel for H2S removal according to claim 1, wherein: The concentration of the graphene oxide aqueous solution is 2-5 g / L.

4. The method for preparing nitrogen-doped graphene aerogel for H2S removal according to claim 1, wherein: The temperature of the hydrothermal reaction is 160-180° C., and the time of the hydrothermal reaction is 10-12 hours.

5. The method for preparing nitrogen-doped graphene aerogel for H2S removal according to claim 1, wherein: The carbonization temperature is 700-850°C and the carbonization time is 2-3h; The carbonization is carried out in an inert atmosphere.

6. The method for preparing nitrogen-doped graphene aerogel for H2S removal according to claim 1, wherein: The thickness of the graphene oxide is ≤1 μm, and the diameter of a single layer is 0.2-10 μm.

7. The method for preparing nitrogen-doped graphene aerogel for H2S removal according to claim 1, wherein: The freeze-drying temperature is ≤-80°C, and the freeze-drying time is 3-5 days.

8. The method for preparing nitrogen-doped graphene aerogel for H2S removal according to claim 1, wherein: Before adding the nitrogen source, the method further comprises the steps of stirring and ultrasonically dispersing the graphene oxide aqueous solution for 1-2 hours; After adding the nitrogen source, the method further includes performing ultrasonication for 10-15 minutes to mix the mixture uniformly.

9. A nitrogen-doped graphene aerogel for H2S removal, characterized in that: The nitrogen-doped graphene aerogel for H2S removal is prepared by the method according to any one of claims 1 to 8.

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