A near-two-dimensional carbon nano-onion and its hydrothermal synthesis method

Abstract

The present invention belongs to the technical field of near-two-dimensional carbon nanomaterials, and particularly relates to a hydrothermal synthesis method of near-two-dimensional carbon nano-onions, comprising the following steps: calcining hydrotalcite to obtain a calcined product CLDH; adding CLDH into an OⅡ solution to adsorb OⅡ to prepare adsorption products CLDH-OⅡ with different adsorption amounts; subjecting CLDH-OⅡ to a hydrothermal reaction to obtain a precipitate; washing the precipitate with an acid and washing impurities adhering to the surface of the precipitate with water to obtain a solid product, which is the described near-two-dimensional carbon nano-onions. The present invention uses a hydrothermal reaction to prepare near-two-dimensional carbon nano-onions, the reaction conditions are milder, and the required energy is lower; the process flow is simple, easy to operate and control; water is used as a reaction medium, which is an environmentally friendly material.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon nanomaterials, and particularly to a nearly two-dimensional carbon nano-onion and a hydrothermal synthesis method thereof. Background Art

[0002] Carbon nano-onions (CNOs), also known as onion-like nanostructured carbon, are a novel zero-dimensional carbon nanomaterial initially discovered by Japanese scholar Sumio Iijima in 1980. They are carbon allotropes like fullerenes, carbon nanotubes, and graphene. Their morphology is an onion-like or polyhedral particle carbon atom cluster composed of several concentric spherical graphite shell layers, with dimensions in the nanometer range. The structure can be divided into CNOs with only graphite carbon layers, hollow CNOs, and non-hollow CNOs.

[0003] Due to their unique physical and chemical properties, carbon nano-onions have received extensive attention since their discovery. Due to their own spherical mesoscopic scale spatial structure, carbon onions have a very high specific surface area, which makes them potentially applicable in many fields such as drug mass transfer, superconducting materials, lithium-ion batteries, hydrogen storage materials, catalyst carriers, field emission electron sources, and supercapacitors. Therefore, researchers have adopted various synthesis methods to synthesize nano-carbon onions and study their properties. In the past nearly 30 years, their preparation methods have mainly focused on arc discharge, electron beam irradiation, plasma method, vacuum heat treatment of nanodiamonds, pyrolysis of organometallic polymers, laser irradiation method, etc. However, most of these methods require relatively high energy (for example, the heat treatment of nanodiamonds to prepare CNOs usually requires a high temperature condition of over 1400 °C and remains in a vacuum environment) or special catalysts (for example, the CVD method to prepare CNOs usually requires Ni / Al, Cu, etc. as catalysts and a high temperature condition of over 500 °C).

[0004] The methods for synthesizing carbon nano-onions discovered so far are still in the primary stage and are troubled by problems such as yield, quality, purity, and operation difficulties. Therefore, it is necessary to develop some new technologies and methods to easily prepare high-quality CNOs to meet the deficiencies in scientific research and applications. Summary of the Invention

[0005] The purpose of the present invention is to provide a nearly two-dimensional carbon nano-onion and a hydrothermal synthesis method thereof, which solves the problem that the existing synthesis methods require relatively high energy to prepare carbon nano-onions.

[0006] The present invention is realized through the following technical solutions:

[0007] The present invention discloses a hydrothermal synthesis method of a nearly two-dimensional carbon nano-onion, comprising the following steps:

[0008] S1. Calcinate the hydrotalcite to obtain the calcined product CLDH;

[0009] S2. Add the calcined product CLDH to the OII solution to adsorb OⅡ, collect the solid product, and prepare the adsorption product CLDH-OⅡ with different adsorption amounts;

[0010] S3. Perform a hydrothermal reaction on the adsorption product CLDH-OⅡ to obtain a precipitate;

[0011] S4. Wash the precipitate with acid and wash the impurities adhering to the surface of the precipitate with water to obtain the solid product, which is the near-two-dimensional carbon nano-onion described above.

[0012] Further, in S1, the calcination temperature of the hydrotalcite is 300 - 600 °C, and the calcination duration is 3 h.

[0013] Further, in S2, add a certain mass of the calcined product CLDH to OII solutions with different concentrations, centrifuge and separate after adsorption for 12 h, collect the supernatant to measure the OII concentration, calculate the adsorption amount of OII, and obtain the adsorption product CLDH-OⅡ with different adsorption amounts.

[0014] Further, in S3, the hydrothermal reaction duration is 3 - 36 h, and the temperature is 150 - 250 °C.

[0015] Further, in S3, during the hydrothermal reaction, the solid-liquid ratio of the adsorption product to water is 1 g:5 mL - 1 g:30 mL.

[0016] Further, in S3, the hydrothermal reaction is carried out in a reaction kettle.

[0017] Further, in S4, the acid used is hydrochloric acid.

[0018] The present invention also discloses the near-two-dimensional carbon nano-onion prepared by the above hydrothermal synthesis method. The near-two-dimensional carbon nano-onion has a hollow ring structure, the particle size is distributed in 13 - 35 nm, and there are neat and clear concentric lattice fringes.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The present invention discloses a hydrothermal synthesis method of nearly two-dimensional carbon nano-onions. The calcined product of hydrotalcite (i.e., CLDH) can be restored to a two-dimensional layered hydrotalcite and hydrotalcite-like structure in an aqueous solution, and a large amount of anions are adsorbed from the solution into the nano-interlayer domain (usually less than 1 nanometer) and the outer surface between its structural sheets. This is the unique structure memory effect of hydrotalcite and hydrotalcite-like materials. Utilizing this structure memory effect, anionic dye Orange II (OII) can be effectively adsorbed into the nano-interlayer domain and the outer surface, and the adsorption amount of OII can be controlled by regulating the addition amount of OII. Subsequently, a hydrothermal reaction is carried out. During the hydrothermal reaction, organic substances polymerize in the nano-confined two-dimensional space, and finally a nano-carbon material with a nearly two-dimensional structure is formed, thereby realizing the preparation of nearly two-dimensional carbon nano-onions. Compared with traditional methods such as arc discharge, electron beam irradiation, plasma method, and vacuum heat treatment of nanodiamonds, the hydrothermal reaction has milder reaction conditions and lower energy requirements; the hydrothermal synthesis method of nearly two-dimensional carbon nano-onions of the present invention uses water as the reaction medium, which is environmentally friendly. The present invention prepares nearly two-dimensional carbon nano-onions through a hydrothermal reaction, and the process flow is simple, easy to operate and regulate.

[0021] Furthermore, for the hydrothermal synthesis method of nearly two-dimensional carbon nano-onions provided by the present invention, the preparation of carbon nano-onions can be achieved at a temperature of 150 - 250 °C, and the reaction conditions are milder. Description of the Drawings

[0022] Figure 1 is the XRD pattern of the products in Examples 1 - 5 and Comparative Example 1;

[0023] Figure 2 is the XRD pattern of the product of hydrotalcite at different calcination temperatures using the structure memory effect to restore the hydrotalcite structure;

[0024] Figure 3 is the Tyndall effect diagram of the diluted solutions of the products in Examples 1 - 5 and Comparative Example 1;

[0025] Figure 4 is the particle size diagram of the diluted solutions of the products in Examples 1 - 5 and Comparative Example 1;

[0026] Figure 5 is the transmission electron microscope image of the products in Examples 1 - 5 and Comparative Example 1;

[0027] Figure 6 is the atomic force microscope AFM image of the products in Examples 1 - 5 and Comparative Example 1;

[0028] Figure 7 is the transmission electron microscope image of the products in Example 6 at different hydrothermal times;

[0029] Figure 8It is the transmission electron microscopy image of the products at different hydrothermal temperatures in Example 7;

[0030] Figure 9 It is the transmission electron microscopy image of the products at different solid-liquid ratios in Example 8. Detailed implementation manners

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments.

[0032] The components described and illustrated in the accompanying drawings and embodiments of the present invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the present invention claimed, but only represents a selected embodiment of the present invention. Based on the accompanying drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0033] It should be noted that: the term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, so that a process, element, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or device.

[0034] The present invention discloses a hydrothermal synthesis method of near-two-dimensional carbon nano-onions, comprising the following steps:

[0035] S1. Calcine hydrotalcite (LDH) to obtain a calcined product CLDH;

[0036] S2. Add CLDH to an OⅡ solution to adsorb OⅡ, collect the solid product to prepare an adsorption product CLDH-OⅡ with different adsorption amounts, and the obtained product is named CLDH-OⅡ-x, where x represents the adsorption amount of CLDH for OII, and the unit is mg / g;

[0037] S3. Put CLDH-OⅡ into a reaction kettle for hydrothermal reaction to obtain a precipitate;

[0038] S4. Wash the precipitate with hydrochloric acid to dissolve the metal oxides or hydroxides from CLDH, and then wash away the impurities adhering to the solid surface with water to obtain a carbon material, that is, near-two-dimensional carbon nano-onions;

[0039] Further, in S2, the calcination temperature of the hydrotalcite is 300-600 °C, and the calcination duration is 3 h, which is appropriate to not damage the structure memory effect of the hydrotalcite.

[0040] Further, in S3, the solid-liquid mass ratio of the hydrothermal reaction is 1 g:5 mL - 1 g:30 mL.

[0041] In S3, the duration of the hydrothermal reaction is 3-36 h, and the temperature is 150-250 °C.

[0042] The present invention will be further described below in conjunction with specific implementation cases:

[0043] Example 1

[0044] The present invention discloses a hydrothermal synthesis method of nearly two-dimensional carbon nano-onions, which specifically includes the following steps:

[0045] Calcine the hydrotalcite (LDH) to obtain a calcined product CLDH;

[0046] Add a certain amount of CLDH to a certain concentration of OⅡ solution according to the adsorption amount of CLDH for OⅡ being 50 mg / g, and after adsorption for 12 h, centrifuge and separate to collect the solid product to obtain CLDH-OⅡ-50;

[0047] Transfer CLDH-OⅡ-50 and water to a reaction kettle according to the solid-liquid mass ratio of 1:10 for hydrothermal reaction. The reaction duration is 24 h and the temperature is 200 °C to obtain a precipitate;

[0048] After the reaction is completed, wash the precipitate with hydrochloric acid to dissolve the metal oxide or hydroxide from CLDH to obtain a carbon material HTC-50;

[0049] Wash HTC-50 with pure water to remove impurities such as hydrochloric acid adhering to the surface to obtain the target product of nearly two-dimensional carbon nano-onions.

[0050] The calcination temperature is preferably such that the structure memory effect of the hydrotalcite is not damaged, that is, the performance of the hydrotalcite using the structure memory effect to adsorb OII should not be damaged. As Figure 2 shown, through experiments, it can be known that calcination at 300-600 °C will not damage the structure memory effect of the hydrotalcite. In this example, calcination is carried out at 500 °C.

[0051] Example 2

[0052] The present invention discloses a hydrothermal synthesis method of nearly two-dimensional carbon nano-onions, which specifically includes the following steps:

[0053] Calcine the hydrotalcite (LDH) at 500 °C to obtain a calcined product CLDH;

[0054] A certain amount of CLDH was added to a certain concentration of OⅡ solution according to the adsorption amount of CLDH for OⅡ being 100 mg / g. After adsorption for 12 h, centrifugation was carried out to separate, and the solid product was collected to prepare CLDH-OⅡ-100;

[0055] CLDH-OⅡ-100 and water were transferred to a reaction kettle according to the solid-liquid mass ratio of 1:10 for hydrothermal reaction. The reaction duration was 24 h and the temperature was 200 °C to obtain a precipitate;

[0056] After the reaction ended, the precipitate was washed with hydrochloric acid to dissolve the metal oxide or hydroxide from CLDH, and the carbon material HTC-100 was obtained;

[0057] HTC-100 was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface, and the target product, nearly two-dimensional carbon nano-onions, was obtained.

[0058] Example 3

[0059] The present invention discloses a hydrothermal synthesis method of nearly two-dimensional carbon nano-onions, which specifically includes the following steps:

[0060] The hydrotalcite (LDH) was calcined at 500 °C to obtain the calcined product CLDH;

[0061] A certain amount of CLDH was added to a certain concentration of OⅡ solution according to the adsorption amount of CLDH for OⅡ being 200 mg / g. After adsorption for 12 h, centrifugation was carried out to separate, and the solid product was collected to prepare CLDH-OⅡ-200;

[0062] CLDH-OⅡ-200 and water were transferred to a reaction kettle according to the solid-liquid mass ratio of 1:10 for hydrothermal reaction. The reaction duration was 24 h and the temperature was 200 °C to obtain a precipitate;

[0063] After the reaction ended, the precipitate was washed with hydrochloric acid to dissolve the metal oxide or hydroxide from CLDH, and the carbon material HTC-200 was obtained;

[0064] HTC-200 was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface, and the target product, nearly two-dimensional carbon nano-onions, was obtained.

[0065] Example 4

[0066] The present invention discloses a hydrothermal synthesis method of nearly two-dimensional carbon nano-onions, which specifically includes the following steps:

[0067] The hydrotalcite (LDH) was calcined at 500 °C to obtain the calcined product CLDH;

[0068] A certain amount of CLDH was added to a certain concentration of OⅡ solution according to the adsorption amount of CLDH for OⅡ being 400 mg / g. After adsorption for 12 h, centrifugation was carried out to separate, and the solid product was collected to prepare CLDH-OⅡ-400;

[0069] CLDH-OⅡ-400 and water were transferred to a reaction kettle according to the solid-liquid mass ratio of 1:10 for hydrothermal reaction. The reaction duration was 24 h and the temperature was 200 °C to obtain a precipitate;

[0070] After the reaction ended, the precipitate was washed with hydrochloric acid to dissolve the metal oxide or hydroxide from CLDH, and the carbon material HTC-400 was obtained;

[0071] HTC-400 was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface, and the target product near-two-dimensional carbon nano-onions was obtained.

[0072] Example 5

[0073] The present invention discloses a hydrothermal synthesis method of near-two-dimensional carbon nano-onions, which specifically includes the following steps:

[0074] The hydrotalcite (LDH) was calcined at 500 °C to obtain the calcined product CLDH;

[0075] A certain amount of CLDH was added to a certain concentration of OⅡ solution according to the adsorption amount of CLDH for OⅡ being 1000 mg / g. After adsorption for 12 h, centrifugation was carried out to separate, and the solid product was collected to prepare CLDH-OⅡ-1000;

[0076] CLDH-OⅡ-1000 and water were transferred to a reaction kettle according to the solid-liquid mass ratio of 1:10 for hydrothermal reaction. The reaction duration was 24 h and the temperature was 200 °C to obtain a precipitate;

[0077] After the reaction ended, the precipitate was washed with hydrochloric acid to dissolve the metal oxide or hydroxide from CLDH, and the carbon material HTC-1000 was obtained;

[0078] HTC-1000 was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface, and the target product near-two-dimensional carbon nano-onions was obtained.

[0079] Example 6

[0080] The present invention discloses a hydrothermal synthesis method of near-two-dimensional carbon nano-onions, which specifically includes the following steps:

[0081] The hydrotalcite (LDH) was calcined at 500 °C to obtain the calcined product CLDH;

[0082] A certain amount of CLDH was added to a certain concentration of OⅡ solution according to the adsorption capacity of CLDH for OⅡ being 1000 mg / g. After adsorption for 12 h, centrifugation was carried out to separate, and the solid product was collected to prepare CLDH - OⅡ - 1000;

[0083] CLDH - OⅡ - 1000 and water were transferred to a reaction kettle according to the solid - liquid mass ratio of 1:10 for hydrothermal reaction. The reaction duration was adjusted to 3 h, 9 h, 18 h, and 36 h respectively, and the temperature was 200 °C to obtain a precipitate;

[0084] After the reaction ended, the precipitate was washed with hydrochloric acid to dissolve the metal oxides or hydroxides from CLDH to obtain a carbon material;

[0085] The carbon material was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface, and the target product, near - two - dimensional carbon nano - onions, was obtained.

[0086] Example 7

[0087] The present invention discloses a hydrothermal synthesis method of near - two - dimensional carbon nano - onions, which specifically includes the following steps:

[0088] The hydrotalcite (LDH) was calcined to obtain the calcined product CLDH;

[0089] A certain amount of CLDH was added to a certain concentration of OⅡ solution according to the adsorption capacity of CLDH for OⅡ being 1000 mg / g. After adsorption for 12 h, centrifugation was carried out to separate, and the solid product was collected to prepare CLDH - OⅡ - 1000;

[0090] CLDH - OⅡ - 1000 and water were transferred to a reaction kettle according to the solid - liquid mass ratio of 1:5 for hydrothermal reaction. The reaction duration was 24 h, and the temperature was adjusted to 150 °C, 180 °C, 200 °C, and 250 °C respectively to obtain a precipitate;

[0091] After the reaction ended, the precipitate was washed with hydrochloric acid to dissolve the metal oxides or hydroxides from CLDH to obtain a carbon material;

[0092] The carbon material was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface, and the target product, near - two - dimensional carbon nano - onions, was obtained.

[0093] Example 8

[0094] The present invention discloses a hydrothermal synthesis method of near - two - dimensional carbon nano - onions, which specifically includes the following steps:

[0095] The hydrotalcite (LDH) was calcined to obtain the calcined product CLDH;

[0096] A certain amount of CLDH was added to a solution of OⅡ at an adsorption amount of 1000 mg / g of CLDH for OⅡ. After adsorption for 12 h, centrifugation was carried out to collect the solid product to prepare CLDH-OⅡ-1000;

[0097] The solid-liquid ratios of CLDH-OⅡ-1000 and water were adjusted to 1 g:5 mL, 1 g:10 mL, and 1 g:30 mL respectively. After mixing, it was transferred to a reaction kettle for hydrothermal reaction. The reaction duration was 24 h and the temperature was 200 °C to obtain a precipitate;

[0098] After the reaction, the precipitate was washed with hydrochloric acid to dissolve the metal oxides or hydroxides from CLDH to obtain a carbon material;

[0099] The carbon material was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface to obtain the target product, nearly two-dimensional carbon nano-onions.

[0100] Control Example 1

[0101] OII was directly subjected to hydrothermal reaction according to the water addition amount with a solid-liquid mass ratio of 1:10. The hydrothermal reaction duration was 24 h and the temperature was 200 °C. After the reaction, the precipitate was washed with hydrochloric acid to obtain a carbon material HTC-OII. The HTC-OII was washed with pure water to remove impurities such as hydrochloric acid adhering to the surface to obtain the target product.

[0102] X-ray diffraction analysis was carried out on the carbon materials obtained in Examples 1-8 and Control Example 1 to identify the phases of the products. The results are as Figure 1 shown. By comparing and analyzing each product with PDF-41-1487 in the standard card library, it was found that each product showed a graphite (002) diffraction peak, indicating that the products had a graphite carbon sheet layer structure.

[0103] The carbon materials obtained in Examples 1-8 and Control Example 1 were dispersed in water, and the Tyndall effect of the dilution was observed. The results are as Figure 3 shown. It was found that different degrees of Tyndall effect occurred in the carbon material dilutions, indicating that the carbon material dilutions were all nano-dispersions and the sizes of the carbon materials were all less than 100 nm.

[0104] The particle sizes of the carbon material dilutions in Examples 1-8 and Control Example 1 were measured using a laser particle size analyzer. The results are as Figure 4As shown, it was found that the particle size in the HTC-OII diluent was 68 - 91 nm, the particle size in the HTC-50 diluent was 220 - 495 nm, the particle size in the HTC-100 diluent was 220 - 342 nm, the particle size in the HTC-200 diluent was 142 - 220 nm, the particle size in the HTC-400 diluent was 106 - 220 nm, and the particle size in the HTC-1000 diluent was 220 - 396 nm. Combining Figure 3 with the Tyndall effect diagrams of each diluent, it can be inferred that the carbon materials in each diluent have undergone different degrees of agglomeration, resulting in particle sizes greater than 100 nm in all diluents except HTC-OII.

[0105] The carbon materials obtained in Examples 1 - 8 and Comparative Example 1 were observed by transmission electron microscopy. The results are as Figure 5 shown. The carbon materials obtained under these several reaction conditions are all hollow ring structures, with a size distribution between 13 - 35 nm, having neat and very clear concentric circular lattice fringes. The lattice spacing is close to the (002) crystal plane spacing (0.34 nm) and (100) crystal plane spacing (0.21 nm) of graphite, indicating that the carbon material is carbon nano-onion and has a relatively high crystallinity. By comparison, it can be seen that the carbon material directly obtained by hydrothermal carbonization of OII mainly consists of large sheet-like amorphous carbon materials and a small amount of small particle carbon nano-onions, indicating that under hydrothermal conditions without the presence of LDH, the organic matter OII cannot be fully converted into carbon nano-onions.

[0106] The carbon materials obtained in Examples 1 - 8 and Comparative Example 1 were observed by atomic force microscopy. The results are as Figure 6 shown. The height distribution of the carbon nano-onions obtained under these several reaction conditions is between 0 - 7.60 nm, mostly between 0.36 - 3.26 nm, that is, only 1 - 9 layers of carbon atoms thick. From the observation by electron microscopy, the size distribution of the carbon nano-onions is between 13 - 35 nm. Therefore, it can be considered that the carbon nano-onions prepared in the present invention are a kind of near-two-dimensional carbon nano-onions.

[0107] The product obtained in Example 6 was analyzed by transmission electron microscopy. As Figure 7 shown, when the reaction duration was adjusted to 3 h, 9 h, 18 h, and 36 h respectively, the transmission electron micrographs of the obtained products showed that carbon nano-onions could be obtained under different hydrothermal reaction durations, and obvious hollow ring structures and concentric circular lattice fringes could be seen.

[0108] The product obtained in Example 7 was analyzed by transmission electron microscopy. As Figure 8As shown, the reaction temperatures were adjusted to 150 °C, 180 °C, 200 °C, and 250 °C respectively. Transmission electron microscopy images of the obtained products indicate that carbon nano-onions can be obtained at different hydrothermal reaction temperatures, and obvious concentric circular lattice fringes can be seen.

[0109] Perform transmission electron microscopy analysis on the product obtained in Example 8. As Figure 9 shown, the solid-liquid ratios were adjusted to 1 g:5 mL, 1 g:10 mL, and 1 g:30 mL respectively. Transmission electron microscopy images of the obtained products indicate that carbon nano-onions can be obtained by hydrothermal reaction at different solid-liquid ratios, and obvious concentric circular lattice fringes can be seen.

Claims

1. A hydrothermal synthesis method of near-two-dimensional carbon nano-onions, characterized in that, It includes the following steps: S1. Calcinate the hydrotalcite to obtain a calcined product CLDH; S2. Add the calcined product CLDH to the OII solution to adsorb OⅡ, collect the solid product, and prepare adsorption products CLDH-OⅡ with different adsorption amounts; S3. Conduct a hydrothermal reaction on the adsorption product CLDH-OⅡ to obtain a precipitate; S4. Wash the precipitate with acid and wash the impurities adhering to the surface of the precipitate with water to obtain a solid product, which is the near-two-dimensional carbon nano-onion described above.

2. The hydrothermal synthesis method of a nearly two-dimensional carbon nano-onion according to claim 1, characterized in that, In S1, the calcination temperature of the hydrotalcite is 300-600°C, and the calcination duration is 3 h.

3. A hydrothermal synthesis method of nearly two-dimensional carbon nano-onions according to claim 1, characterized in that, In S2, add a certain mass of the calcined product CLDH to OII solutions with different concentrations, centrifuge and separate after adsorption for 12 h, collect the supernatant to measure the OII concentration, calculate the adsorption amount of OII, and obtain adsorption products CLDH-OⅡ with different adsorption amounts.

4. The hydrothermal synthesis method of a near-two-dimensional carbon nano-onion according to claim 1, wherein In S3, the hydrothermal reaction duration is 3-36 h, and the temperature is 150-250°C.

5. A hydrothermal synthesis method of a near-two-dimensional carbon nano-onion according to claim 1, characterized in that, In S3, during the hydrothermal reaction, the solid-liquid ratio of the adsorption product to water is 1 g:5 mL to 1 g:30 mL.

6. The hydrothermal synthesis method of a near-two-dimensional carbon nano-onion according to claim 1, wherein In S3, the hydrothermal reaction is carried out in a reaction kettle.

7. The hydrothermal synthesis method of a near-two-dimensional carbon nano-onion according to claim 1, characterized in that, In S4, the acid used is hydrochloric acid.

8. The nearly two-dimensional carbon nano-onions prepared by the hydrothermal synthesis method according to any one of claims 1-6, characterized in that, The near-two-dimensional carbon nano-onion has a hollow ring structure, the particle size is distributed in 13-35 nm, and there are neat and clear concentric lattice fringes.

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