Graphene aerogel and preparation method and application thereof

Abstract

The present application relates to a kind of graphene aerogel and its preparation method and application, first, in strong oxidizing acidic system, expandable graphite is prepared epoxy type graphite oxide by controllable oxidation;The prepared epoxy type graphite oxide is sol-gel treatment with L-cysteine and 2,5-diaminobenzonitrile organic functional monomer, it is converted into graphene hydrogel material with three-dimensional structure by heat treatment;Using hydroxylamine hydrochloride, the prepared three-dimensional graphene hydrogel is oxidized, and nitrile group is converted into amidoxime group;Graphene hydrogel material with amidoxime group and amino group is dried, and graphene aerogel for adsorbing uranyl ion in radioactive wastewater is obtained.The preparation method of the present application is simple and feasible, the obtained graphene aerogel has high adsorption performance and selectivity, and can efficiently adsorb and remove uranyl ion from radioactive wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of functionalized graphite mineral material preparation, in particular, to a graphene aerogel and its preparation method and application. BACKGROUND

[0002] Currently, nuclear energy as a highly efficient, clean and sustainable energy form, has received extensive attention worldwide. However, the management of nuclear waste generated during the production, processing and disposal of nuclear fuel has been a major challenge. Uranyl ion (UO2 2+ ) is one of the important transport substances in the nuclear fuel cycle, and its radioactivity and chemical toxicity pose a potential threat to the environment and human health.

[0003] Currently, a variety of materials for adsorption and recovery of uranyl ions have been developed, including adsorbents, resins and various nanomaterials. Among them, graphene as a two-dimensional carbon material, due to its excellent electrical conductivity, high specific surface area and chemical stability, is widely studied for adsorption of environmental pollutants and catalytic applications. However, traditional two-dimensional graphene materials have some limitations in large-scale applications, such as dispersion in solution, availability and process scalability.

[0004] Therefore, it is necessary to develop a new type of adsorbent material that can efficiently adsorb uranyl ions while having good operability and process scalability. SUMMARY

[0005] The present application aims to provide a method for preparing a three-dimensional graphene aerogel with high adsorption of uranyl ions. The method prepares a three-dimensional graphene aerogel with high specific surface area and excellent adsorption performance through specific process steps. The aerogel shows excellent adsorption capacity and selectivity in adsorbing uranyl ions, and has the potential to be widely used in nuclear waste management and nuclear fuel cycle.

[0006] In view of the deficiencies in the prior art, the present application aims to solve one or more problems in the prior art. For example, one of the purposes of the present application is to provide a method for preparing a three-dimensional graphene aerogel with high adsorption of uranyl ions, which has a short process flow and low energy consumption.

[0007] The present application provides a method for preparing a graphene aerogel. The method comprises the following steps:

[0008] 1) Slowly add an epoxy functional group regulator to an acidic mixed solution of expandable graphite and a strong oxidizing agent, and stir, wash and dry to obtain an epoxy-type graphite oxide.

[0009] The epoxy functional group regulator in step 1) is pure water or deionized water with a resistivity of no less than 18 MΩ·cm, and the acidic solution is high-purity H2SO4 of 98% or more. The relative content of the epoxy group in the epoxy-type graphite oxide is no less than 10%.

[0010] The specific process of step 1) is as follows: after the expandable graphite and the acidic system of the strong oxidant are uniformly stirred for 15 min, the reaction temperature is controlled to be no more than 10℃, the volume ratio of the functional group regulator to the acid in the system is 1:4-6, the functional group regulator is automatically added dropwise into the mixed system through a peristaltic pump, and the system is uniformly stirred.

[0011] 2) The epoxy-type graphite oxide in step 1) is mixed with a grafting modifier solution, and after heat treatment in an open system at normal pressure, a three-dimensional graphene hydrogel is obtained.

[0012] The grafting modifier in step 2) is a mixture of L-cysteine and 2,5-diaminobenzonitrile, and the molar ratio of L-cysteine to 2,5-diaminobenzonitrile is 1:0.5-3; the three-dimensional graphene hydrogel structure contains amino groups and nitrile groups.

[0013] The specific process of step 2) is as follows: the epoxy-type graphite oxide and the grafting modifier are mixed in a mass ratio of 1:0.2-5, then ultrapure water is added in a ratio of 1:1.5-6 g / L, and the mixture is continuously dispersed under the combined action of ultrasonic and magnetic stirring for 2-8 h, then the mixture is left to stand in an open system at normal pressure at 60-100℃ for 3-24 h, and a three-dimensional graphene hydrogel is obtained.

[0014] 3) The graphene hydrogel in step 2) is immersed in a liquid oxidant, washed and dried to obtain a graphene aerogel.

[0015] The liquid oxidant in step 3) is NH2OH·HCl; the graphene aerogel structure contains amidoxime groups and amino groups.

[0016] The specific process of step 3) is as follows: the three-dimensional graphene hydrogel in step 2) is immersed in an NH2OH·HCl solution in a mass ratio of 1:0.5-4, and left to stand in an open system at normal pressure at 50-80℃ for 2-10 h, then filtered, washed, and cold-dried, and then treated in a low-temperature plasma surface treatment instrument in a CF4 plasma atmosphere at a power of 60-70 W for 5 min to obtain a three-dimensional graphene aerogel.

[0017] The grafting functionalization method provided by the application is that the good chemical reactivity of the epoxy group in the graphite oxide and the sulfhydryl in the L-cysteine can cause a nucleophilic substitution reaction to graft the L-cysteine on the structure layer of the epoxy type graphite oxide under the condition of normal pressure water bath heating, and the good amide reactivity of the carboxyl in the L-cysteine structure and the amino in the 2,5-diaminobenzonitrile can further functionalize the grafted 2,5-diaminobenzonitrile under the condition of normal pressure water bath heating. The grafted L-cysteine and 2,5-diaminobenzonitrile reduce the stacking of the graphite oxide sheet layer, enhance the three-dimensional porous structure in the aerogel, and greatly improve the specific surface area of the aerogel.

[0018] In addition, the grafting functionalization of the L-cysteine and the 2,5-diaminobenzonitrile effectively increases the types and quantity of functional groups in the graphene aerogel structure, thereby helping the adsorption and separation of the uranyl ion of the radionuclide.

[0019] The advantage of the application is that the three-dimensional graphene aerogel prepared according to the method has the excellent electrical conductivity of the general aerogel, the large specific surface area of the graphene, the low energy consumption and no pollution, the controllable shape, the good mechanical property, the micro-porous structure, and the functional groups of the hydroxyl, the carboxyl, the amino, the sulfonic acid group and the amidoxime group on the surface, which have good adsorption and selectivity to the uranyl ion, and the three-dimensional graphene aerogel has great application prospect in the selective adsorption and separation of the uranyl ion in the radioactive wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and other objects and features of the application will become more apparent from the following description made with reference to the accompanying drawings, in which:

[0021] Figure 1 Fig. 1 shows the C1s graph of the epoxy type graphite oxide prepared in Example 1;

[0022] Figure 2 Fig. 2 shows the organic dispersion suspension graph of the epoxy type graphite oxide prepared in Example 2;

[0023] Figure 3 Fig. 3 shows the morphology graph of the three-dimensional graphene hydrogel prepared in Example 3;

[0024] Figure 4 Fig. 4 shows the scanning electron microscope graph of the three-dimensional graphene hydrogel prepared in Example 3;

[0025] Figure 5 Fig. 5 shows the morphology graph of the three-dimensional graphene aerogel prepared in Example 4;

[0026] Figure 6 Fig. 6 shows the infrared spectrum graph of the three-dimensional graphene aerogel prepared in Example 4. DETAILED DESCRIPTION

[0027] The following examples are merely representative of the more optimal embodiments of the application and are not to be construed as limiting the scope of the application. Those skilled in the art will be able to make modifications and variations in the embodiments described herein without departing from the scope of the application. The application is to be limited only by the claims that follow.

[0028] Example 1

[0029] Preparation of epoxy-type graphite oxide. 1 g of fine expandable graphite was used as raw material, 30 mL of 98% mass concentration concentrated sulfuric acid was added, 3 g of potassium permanganate was slowly added, after 20 min of ice water bath at 5 ℃, 1 mL of ultrapure water was added dropwise to the system by peristaltic pump, and stirring was continued for 2 h. The solution after reaction was poured into a 1000 mL ice water mixture prepared by ultrapure water, 2 mL of hydrogen peroxide was added after magnetic stirring for 30 min in this process, and then washed with ultrapure water until neutral, dried to obtain epoxy-type graphite oxide.

[0030] Figure 1 Epoxy-type graphite oxide C1s graph prepared for this example. From Figure 1 It can be seen that the epoxy group content in the epoxy-type graphite oxide is 16%.

[0031] Example 2

[0032] Preparation of epoxy-type graphite oxide organic dispersion suspension. 1 g of epoxy-type graphite oxide, 0.5 g of L-cysteine and 0.5 g of 2,5-diaminobenzonitrile were added to 500 mL of ultrapure water, ultrasonic dispersion was carried out under the action of ultrasonic and magnetic stirring for 4 h, and 2 mg·mL -1 Epoxy-type graphite oxide organic dispersion suspension.

[0033] Figure 2 Dispersion graph of epoxy-type graphite oxide organic dispersion suspension prepared for this example. From Figure 2 It can be seen that the epoxy-type graphite oxide and the modifier are well dispersed.

[0034] Example 3

[0035] Preparation of three-dimensional graphene hydrogel. 30 mL of 2 mg·mL -1 Epoxy-type graphite oxide organic dispersion suspension was placed in a constant temperature heater at 80 ℃, and three-dimensional graphene oxide hydrogel was prepared after standing for 3 h.

[0036] Figure 3 and Figure 4The macro and micro morphology of the three-dimensional graphene hydrogel prepared in this example are shown in the figures. As can be seen from the figures, the three-dimensional graphene hydrogel has formed a three-dimensional macroscopic aggregate, and the interior presents a porous structure.

[0037] Example 4

[0038] The three-dimensional graphene aerogel was prepared. In a system with a pH value of 8, the three-dimensional graphene hydrogel was added to a hydroxylamine hydrochloride solution in a mass ratio of 1:1, and was left to react at 60°C for 4h. After washing, it was placed in a vacuum freeze dryer for freeze drying for 36h, and then was treated by a low-temperature plasma surface treatment instrument for 5min to obtain the three-dimensional graphene aerogel.

[0039] Figure 5 and Figure 6 The morphology and infrared spectrum of the three-dimensional graphene aerogel prepared in this example are shown in the figures. As can be seen from the figures, the three-dimensional graphene aerogel also has a good three-dimensional structure, and contains a large number of functional groups in the structure, which provides many active adsorption sites for the adsorption of uranyl ions.

[0040] Example 5

[0041] Adsorption of three-dimensional graphene aerogel to uranyl. 40mL of a uranium solution with a concentration of 100mg·mL-1 was accurately measured in a 100mL conical flask, and the pH was adjusted to 4 by dropwise addition of 0.10mg·mL-1 HNO3 and Na2CO3 solution. Then 10mg of three-dimensional graphene aerogel material was added to each conical flask, which was sealed and placed in a constant-temperature water bath shaker, with a temperature of 25°C and a time of 24h. After reaching adsorption equilibrium, the mixture was centrifuged to take the supernatant, and the remaining uranium concentration was determined using ICP-AES. According to the adsorption amount formula, the adsorption capacity of the three-dimensional graphene aerogel to uranyl ions was calculated to be 289.6mg·g-1. -1 -1 -1 ​​​

Claims

1. A method for preparing a graphene aerogel, characterized by, The method comprises the following steps: 1) slowly adding an epoxy functional group regulator to an acid mixed solution of expandable graphite and a strong oxidizing agent, and stirring, washing, and drying to obtain an epoxy type graphite oxide; The epoxy functional group regulator is pure water with an electrical resistivity of no less than 18 MΩ·cm, and the acid solution is H2SO4 with a purity of no less than 98%; the relative content of epoxy groups in the epoxy type graphite oxide is no less than 10%; The specific process of step 1) is as follows: after the acid system of expandable graphite and a strong oxidizing agent is stirred uniformly for 15 min, the volume ratio of the functional group regulator to the acid in the system is controlled to be 1:4-6, the functional group regulator is automatically added dropwise into the mixed system through a peristaltic pump, and stirring is uniformly performed; 2) mixing the epoxy type graphite oxide in step 1) with a grafting modifier solution uniformly, and obtaining a three-dimensional graphene hydrogel through heat treatment in an open system under normal pressure; The grafting modifier is a mixture of L-cysteine and 2,5-diaminobenzonitrile, and the molar ratio of L-cysteine to 2,5-diaminobenzonitrile is 1:0.5-3; the three-dimensional graphene hydrogel structure contains amino groups and nitrile groups; The specific process of step 2) is as follows: the epoxy type graphite oxide and the grafting modifier are mixed according to a mass ratio of 1:0.2-5, then super-pure water is added according to a ratio of 1:1.5-6 g / L, and the mixture is continuously dispersed under the joint action of ultrasonic and magnetic stirring for 2-8 h, and then the three-dimensional graphene hydrogel is obtained by standing in an open system under normal pressure at 60-100°C for 3-24 h; 3) immersing the graphene hydrogel in step 2) in a liquid oxidizing agent, and washing and drying to obtain a graphene aerogel; The liquid oxidizing agent is NH2OH·HCl; the graphene aerogel structure contains amidoxime groups and amino groups; The specific process of step 3) is as follows: the three-dimensional graphene hydrogel in step 2) is immersed in an NH2OH·HCl solution according to a mass ratio of 1:0.5-4, and then the mixture is left to stand in an open system under normal pressure at 50-80°C for 2-10 h, and then the three-dimensional graphene aerogel is obtained by filtering, washing, supercritical drying, and treating with a low-temperature plasma surface treatment instrument in a CF4 plasma atmosphere at a power of 60-70 W for 5 min.

2. Graphene aerogel, characterized in that, The graphene aerogel is prepared by the preparation method in claim 1.

3. Use of graphene aerogel according to claim 1, characterized in that, Material for adsorbing uranyl ions in radioactive wastewater.

Images