Preparation method of uranium dioxide-carbon composite porous material

Abstract

The application relates to a preparation method of a uranium dioxide-carbon composite porous material, which comprises the following steps: 1) preparing a resorcinol-formaldehyde sol; 2) storing the resorcinol-formaldehyde sol in a constant-temperature sealed state, and performing air drying to obtain a resorcinol-formaldehyde aerogel; 3) performing high-temperature treatment on the resorcinol-formaldehyde aerogel in an argon atmosphere to obtain a porous carbon material; 4) preparing a uranium oxide precursor solution; 5) immersing the porous carbon material in the uranium oxide precursor solution, and then performing drying in air, and repeating the above steps for multiple times to obtain a porous material blank; and 6) performing high-temperature treatment on the porous material blank in a low-pressure environment to obtain the uranium dioxide-carbon composite porous material. The preparation process is simple, and no expensive equipment is needed. The uranium dioxide-carbon composite porous material has high phase purity, good structural stability, and the density, specific surface area and conductivity of the material can be controlled in a large range according to design requirements, so that the application of the material in the fields of catalysis and thermoelectricity can be met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of porous ceramic material preparation, and particularly relates to a preparation method of uranium dioxide-carbon composite porous material. BACKGROUND

[0002] Uranium dioxide is an important nuclear material and has been widely used as reactor fuel. In recent years, uranium dioxide has attracted much attention as a thermoelectric material. Its Seebeck coefficient at room temperature is significantly higher than that of traditional thermoelectric materials. Uranium dioxide is a p-type intrinsic material, and its band gap is close to the top of the solar energy absorption band gap-efficiency curve, so it is a high-efficiency solar cell material. In addition, uranium dioxide has excellent radiation resistance, and has great application potential as an electronic device in high-energy radiation environment. In addition, the potential application of uranium dioxide in optical materials, catalysis and other fields has also attracted widespread attention.

[0003] However, except as nuclear fuel elements, uranium dioxide has not been widely used in other fields. The reason is that, on the one hand, the performance of uranium dioxide material needs to be further improved. For example, in the field of thermoelectricity, the thermoelectric performance of a material is the result of the combined action of the Seebeck coefficient, thermal conductivity and electrical conductivity of the material. Although uranium dioxide has a high Seebeck coefficient, its extremely low electrical conductivity leads to a non-outstanding thermoelectric figure of merit. In the field of catalysis, a high specific surface area of a catalyst is beneficial to its catalytic activity, and the material also needs to have a certain structural strength to avoid environmental problems caused by the loss of catalyst during use. On the other hand, the preparation means of uranium dioxide material is still limited. At present, the preparation, molding and performance evaluation of uranium dioxide material mainly focus on dense bulk materials and thin film materials, and there are very few reports on the preparation of uranium dioxide porous ceramics. Ran et al. used silica colloidal crystals as templates, casted molten uranyl nitrate into the templates, calcined at high temperature, then reduced in a hydrogen atmosphere, and finally obtained uranium dioxide mesoporous materials by chemical etching to remove the templates. However, the uranium dioxide porous material prepared by this method has low structural strength, and it is difficult to obtain a complete porous ceramic bulk material.

[0004] With the development of technology, the requirements for material performance are constantly improving, and single-component materials and structures are increasingly difficult to meet the use requirements. Traditional materials have made remarkable achievements in the aspects of multi-material compounding and microstructure design, etc. Compared with this, uranium oxide materials have a large gap in material design and preparation technology, which to a great extent limits the application range of uranium oxide materials. SUMMARY

[0005] The present application aims to overcome the above background and existing problems, and provides a preparation method of uranium dioxide-carbon composite porous material. The prepared uranium dioxide-carbon composite porous material has high phase purity, good structural stability, and the material density, specific surface area, and electrical conductivity can be controlled in a large range according to design requirements. The uranium dioxide-carbon composite porous material prepared by the method is particularly suitable for use as a catalyst or a thermoelectric material.

[0006] The present application provides a preparation method of uranium dioxide-carbon composite porous material, which is carried out as follows:

[0007] (1) Resorcinol and formaldehyde solution are used as raw materials, glacial acetic acid is used as a catalyst, and the mixture is dissolved in deionized water, stirred uniformly, and then resorcinol-formaldehyde sol is prepared;

[0008] (2) The resorcinol-formaldehyde sol obtained in step (1) is placed in a thermostat for constant temperature and sealed preservation, the constant temperature is 50-90℃, the preservation time is 1-10 days, and then the resorcinol-formaldehyde aerogel is obtained by drying in air for 1-5 days;

[0009] (3) The resorcinol-formaldehyde aerogel obtained in step (2) is placed in a tube furnace and treated at high temperature under argon atmosphere, the treatment temperature is 600-1200℃, the heating rate is 1-5℃ / min, the holding time is 1-5h, and the porous carbon material is obtained by cooling to room temperature;

[0010] (4) The uranium oxide precursor, structure directing agent, and organic additive are dissolved in a mixed solvent of deionized water and ethanol, stirred uniformly, and then aged for 1-7 days to prepare a uranium oxide precursor solution;

[0011] (5) The porous carbon material obtained in step (3) is placed in the uranium oxide precursor solution prepared in step (4), and the residual gas in the porous carbon material is removed by static treatment under low vacuum environment, and then dried in air. The above steps are repeated for 1-10 times to obtain a porous material blank; wherein, the vacuum treatment time is 1-5min, the vacuum degree is 10-50kPa, and the drying time is 12-96h;

[0012] (6) The porous material blank obtained in step (5) is placed in a tube furnace and treated at high temperature under low pressure environment, the vacuum degree is 100-10000Pa, the treatment temperature is 900-1200℃, the heating rate is 0.5-3℃ / min, the holding time is 1-5h, and the uranium dioxide-carbon composite porous material is obtained by cooling to room temperature.

[0013] Further, the resorcinol is dissolved in deionized water in step (1), and then formaldehyde solution and glacial acetic acid are added; the molar ratio of resorcinol to formaldehyde is 1:2; wherein the mass-volume ratio of resorcinol, deionized water, formaldehyde solution and glacial acetic acid is (1-15) g:(5-100) mL:(1-30) mL:(20-1000) μL.

[0014] Further, the mass fraction of the formaldehyde solution is 37%.

[0015] Further, the molar mass-volume ratio of the uranium oxide precursor, the structure-directing agent / organic additive, deionized water and ethanol in step (4) is (0.01-0.05) mol:(0.5-8.0) g:(1.0-6.0) g:(1.0-10.0) mL:(10-60) mL.

[0016] Further, the uranium oxide precursor in step (4) is uranyl nitrate, uranyl chloride or uranyl acetate.

[0017] Further, the structure-directing agent in step (4) is F127 or P123.

[0018] Further, the organic additive in step (4) is acetylacetone or polyethyleneimine.

[0019] Further, the constant temperature in step (2) is 60-80℃, the preservation time is 1-10 days, and then the resorcinol-formaldehyde aerogel is obtained by drying in air for 1-5 days.

[0020] Further, the treatment temperature in step (3) is 800-1000℃, the heating rate is 2-4℃ / min, and the holding time is 1-5h.

[0021] Further, the vacuum degree in step (6) is 1000-5000 Pa, the treatment temperature is 1000-1100℃, the heating rate is 1-2℃ / min, and the holding time is 1-5h.

[0022] The present application comprises the following beneficial effects:

[0023] First, the uranium dioxide-carbon composite porous material prepared by the present application has high phase purity and good structural stability, and the material density, specific surface area and conductivity can be controlled in a large range according to design requirements.

[0024] Second, the porous carbon in the present application has high strength as a framework, which ensures the stability of the structure of the composite porous material; on the other hand, it provides a carbon source to participate in the carbothermal reduction reaction to obtain UO2 phase, which also avoids the problem of material shrinkage and cracking during high-temperature reduction treatment in a hydrogen atmosphere.

[0025] Third, the prepared uranium dioxide-carbon composite porous material can balance specific surface area and structural strength (390m 2 / g@1.2MPa), and has great application value in the field of uranium dioxide catalysis.

[0026] Fourth, in the prepared uranium dioxide-carbon composite porous material, uranium dioxide has a high Seebeck coefficient, the introduction of carbon compensates for the insufficient conductivity of uranium dioxide, and the porous structure is beneficial to maintaining low thermal conductivity of the material, so that the composite porous material has high thermoelectric performance.

[0027] Fifth, the preparation method of the uranium dioxide-carbon composite porous material is simple in experimental process, convenient in operation control, and does not need expensive experimental equipment. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a sample photo of the uranium dioxide-carbon composite porous material;

[0029] Figure 2 is an XRD spectrum of the uranium dioxide-carbon composite porous material. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear and apparent, the spirit of the disclosed content will be described in detail below, and any person skilled in the art can make changes and modifications to the technology taught by the content of the present application without departing from the spirit and scope of the content of the present application.

[0031] The illustrative embodiments of the present application and their descriptions are used to explain the present application, but are not as a limitation of the present application.

[0032] Embodiment 1:

[0033] The preparation method of the uranium dioxide-carbon composite porous material of the present embodiment is specifically realized by the following steps:

[0034] (1) 2.4g of resorcinol is dissolved in 10mL of deionized water, then 4.3mL of formaldehyde solution and 165μL of glacial acetic acid are added, and the resorcinol-formaldehyde sol is prepared after stirring uniformly;

[0035] (2) The resorcinol-formaldehyde sol obtained in step (1) is sealed and stored in a thermostat at a constant temperature of 80℃ for 3 days, and then dried in air for 2 days to obtain a resorcinol-formaldehyde aerogel;

[0036] Resorcinol and formaldehyde are reacted to generate a resorcinol-formaldehyde aerogel, and a porous carbon material is obtained after carbonization treatment. The porous carbon material is used as a porous template in the present patent, and participates in a carbothermal reduction reaction at high temperature to reduce uranium oxide into UO2.

[0037] (3) The resorcinol-formaldehyde aerogel obtained in step (2) is placed in a tube furnace and treated at high temperature under an argon atmosphere, the treatment temperature is 1000℃, the heating rate is 2℃ / min, the holding time is 2h, and the porous carbon material is obtained after cooling to room temperature;

[0038] (4) 8.5g of uranyl acetate, 2g of F127 and 3g of acetylacetone are dissolved in a mixed solvent of 2mL of deionized water and 30mL of ethanol, and after stirring uniformly, a uranium oxide precursor solution is prepared by standing and aging for 2 days;

[0039] (5) The porous carbon material obtained in step (3) is placed in the uranium oxide precursor solution prepared in step (4), and the residual gas inside the porous carbon material is removed by standing and treating under low vacuum, the vacuum treatment time is 1min, and the vacuum degree is 20kPa; then it is dried in air, the drying time is 24h, the above steps are cycled 2 times, and a porous material blank is obtained;

[0040] (6) The porous material blank obtained in step (5) is placed in a tube furnace and treated at high temperature under low pressure, the vacuum degree is 500Pa, the treatment temperature is 1000℃, the heating rate is 0.5℃ / min, the holding time is 3h, and the uranium dioxide-carbon composite porous material is obtained after cooling to room temperature.

[0041] The macroscopic photograph of the uranium dioxide-carbon composite porous material sample obtained in the present embodiment is shown in Figure 1 , and the sample structure is intact without defects, which can prove that the material has good structural stability. The sample density is 0.6g / cm 3 , and the specific surface area is 470m 2 / g. Analysis by an X-ray diffractometer shows that the sample phase is UO2. The mechanical properties of the uranium dioxide-carbon composite porous material sample are tested, and the compressive strength is 0.45MPa.

[0042] Example 2:

[0043] A preparation method of a uranium dioxide-carbon composite porous material, which is realized according to the following steps:

[0044] (1) 10.0g of resorcinol is dissolved in 40mL of deionized water, 18mL of formaldehyde solution and 520μL of glacial acetic acid are added, and a resorcinol-formaldehyde sol is prepared after stirring uniformly;

[0045] (2) The resorcinol-formaldehyde sol obtained in step (1) is placed in a thermostat for constant temperature sealed storage, the constant temperature is 60℃, the storage time is 7 days, and then dried in air for 4 days to obtain a resorcinol-formaldehyde aerogel;

[0046] (3) The resorcinol-formaldehyde aerogel obtained in step (2) is placed in a tube furnace for high-temperature treatment under an argon atmosphere, the treatment temperature is 800℃, the heating rate is 1℃ / min, the holding time is 1h, and the porous carbon material is obtained after cooling to room temperature;

[0047] (4) 6.8g of uranyl chloride, 3.5g of P123 and 3g of polyethyleneimine are dissolved in a mixed solvent of 4mL of deionized water and 50mL of ethanol, stirred uniformly and then aged for 5 days to prepare a uranium oxide precursor solution;

[0048] (5) The porous carbon material obtained in step (3) is placed in the uranium oxide precursor solution prepared in step (4), and the residual gas inside the porous carbon material is removed by standing treatment under low vacuum, the vacuum treatment time is 3min, and the vacuum degree is 40kPa; then dried in air for 48h, the above steps are cycled 5 times to obtain a porous material blank;

[0049] (6) The porous material blank obtained in step (5) is placed in a tube furnace for high-temperature treatment under low pressure, the vacuum degree is 1000Pa, the treatment temperature is 1200℃, the heating rate is 1℃ / min, the holding time is 2h, and the uranium dioxide-carbon composite porous material is obtained after cooling to room temperature.

[0050] The XRD pattern of the uranium dioxide-carbon composite porous material sample obtained in this example is shown in Figure 2 The results show that the main phase of the uranium dioxide-carbon composite porous material is UO2. The specific surface area of the uranium dioxide-carbon composite porous material sample is 390m 2 / g, the compressive strength is 1.2MPa, the electrical conductivity at 300K is 16.5S / cm, the Seebeck coefficient is-248μV / K, and the power factor is 1.01μW / cm·K 2 .

[0051] Example 3:

[0052] A method for preparing a uranium dioxide-carbon composite porous material, which is realized by the following steps:

[0053] (1) 12.0g of resorcinol is dissolved in 20mL of deionized water, then 21.7mL of formaldehyde solution and 780μL of glacial acetic acid are added, and the mixture is stirred uniformly to prepare a resorcinol-formaldehyde sol;

[0054] (2) The resorcinol-formaldehyde sol obtained in step (1) is placed in a thermostat for constant temperature sealed storage, the constant temperature is 85℃, the storage time is 4 days, and then dried in air for 5 days to obtain a resorcinol-formaldehyde aerogel;

[0055] (3) The resorcinol-formaldehyde aerogel obtained in step (2) is placed in a tube furnace for high-temperature treatment under an argon atmosphere, the treatment temperature is 1200℃, the heating rate is 4℃ / min, the holding time is 3h, and the porous carbon material is obtained after cooling to room temperature;

[0056] (4) 15g of uranyl nitrate, 5g of F127 and 3g of acetylacetone are dissolved in a mixed solvent of 8mL of deionized water and 55mL of ethanol, stirred uniformly, and then aged for 5 days to prepare a uranium oxide precursor solution;

[0057] (5) The porous carbon material obtained in step (3) is placed in the uranium oxide precursor solution prepared in step (4), and the residual gas inside the porous carbon material is removed by standing and treating in a low vacuum environment, the vacuum treatment time is 2min, and the vacuum degree is 25kPa; then dried in air, the drying time is 72h, the above steps are repeated 4 times to obtain a porous material blank;

[0058] (6) The porous material blank obtained in step (5) is placed in a tube furnace for high-temperature treatment under a low-pressure environment, the vacuum degree is 200Pa, the treatment temperature is 1100℃, the heating rate is 2℃ / min, the holding time is 4h, and the uranium dioxide-carbon composite porous material is obtained after cooling to room temperature.

[0059] The density of the uranium dioxide-carbon composite porous material sample obtained in this example is 0.95g / cm 3 , the specific surface area is 320m 2 / g, the conductivity at 300K is 18.3S / cm, the Seebeck coefficient is-275μV / K, and the power factor is 1.38μW / cm·K 2 .

[0060] Example 4:

[0061] A method for preparing a uranium dioxide-carbon composite porous material, which is realized by the following steps:

[0062] (1) 4.0g of resorcinol is dissolved in 5mL of deionized water, then 7.2mL of formaldehyde solution and 138μL of glacial acetic acid are added, and the mixture is stirred uniformly to prepare a resorcinol-formaldehyde sol;

[0063] (2) The resorcinol-formaldehyde sol obtained in step (1) is placed in a thermostat for constant temperature sealed storage, the constant temperature is 70℃, the storage time is 7 days, and then dried in air for 3 days to obtain a resorcinol-formaldehyde aerogel;

[0064] (3) The resorcinol-formaldehyde aerogel obtained in step (2) is placed in a tube furnace and treated at a high temperature under an argon atmosphere, the treatment temperature is 800℃, the heating rate is 2℃ / min, the holding time is 4h, and the porous carbon material is obtained after cooling to room temperature;

[0065] (4) 6.4g of uranyl acetate, 1.5g of P123 and 1.0g of acetylacetone are dissolved in a mixed solvent of 1.0mL of deionized water and 30mL of ethanol, stirred uniformly and then aged for 2 days to prepare a uranium oxide precursor solution;

[0066] (5) The porous carbon material obtained in step (3) is placed in the uranium oxide precursor solution prepared in step (4), and the residual gas inside the porous carbon material is removed by standing and treating under a low vacuum environment, the vacuum treatment time is 1min, and the vacuum degree is 30kPa; then dried in air, the drying time is 48h, the above steps are cycled 5 times to obtain a porous material blank;

[0067] (6) The porous material blank obtained in step (5) is placed in a tube furnace and treated at a high temperature under a low pressure environment, the vacuum degree is 5000Pa, the treatment temperature is 900℃, the heating rate is 1℃ / min, the holding time is 5h, and the uranium dioxide-carbon composite porous material is obtained after cooling to room temperature.

[0068] The density of the uranium dioxide-carbon composite porous material sample obtained in this example is ~1.35g / cm 3 , the specific surface area is 240m 2 / g, the compressive strength is 1.7MPa, and the conductivity at 300K is 22.3S / cm.

Claims

1. A method for preparing a uranium dioxide-carbon composite porous material, characterized in that The preparation method is carried out according to the following contents: (1) resorcinol and formaldehyde solution as raw material, glacial acetic acid as catalyst, dissolved in deionized water, stirred uniformly after preparation of resorcinol-formaldehyde sol; (2) the resorcinol-formaldehyde sol obtained in step (1) is placed in a thermostat for constant temperature sealed preservation, the constant temperature is 50~90℃, the preservation time is 1~10 days, then dried in air for 1~5 days, and the resorcinol-formaldehyde aerogel is obtained; (3) the resorcinol-formaldehyde aerogel obtained in step (2) is placed in a tube furnace, treated at high temperature under argon atmosphere, the treatment temperature is 600~1200℃, the heating rate is 1~5℃ / min, the holding time is 1~5h, and the porous carbon material is obtained after cooling to room temperature; (4) the uranium oxide precursor, structure directing agent and organic additive are dissolved in a mixed solvent of deionized water and ethanol, stirred uniformly, and then aged for 1~7 days to prepare a uranium oxide precursor solution; the molar mass volume ratio of the uranium oxide precursor, structure directing agent, organic additive, deionized water and ethanol is (0.01~0.05) mol:(0.5~8.0) g:(1.0~6.0) g:(1.0~10.0) mL:(10~60) mL; the structure directing agent is F127 or P123; the organic additive is acetylacetone or polyethyleneimine; (5) the porous carbon material obtained in step (3) is placed in the uranium oxide precursor solution prepared in step (4), and the residual gas in the porous carbon material is removed by standing treatment under low vacuum environment, then dried in air, the above steps are repeated for 1~10 times to obtain a porous material blank; wherein the vacuum treatment time is 1~5 min, the vacuum degree is 10~50 kPa, and the drying time is 12~96 h; (6) the porous material blank obtained in step (5) is placed in a tube furnace and treated at high temperature under low pressure environment, the vacuum degree is 100~10000 Pa, the treatment temperature is 900~1200℃, the heating rate is 0.5~3℃ / min, the holding time is 1~5h, and the uranium dioxide-carbon composite porous material is obtained after cooling to room temperature.

2. The method according to claim 1, wherein In step (1), resorcinol is dissolved in deionized water, and then formaldehyde solution and glacial acetic acid are added; the molar ratio of resorcinol and formaldehyde is 1:2; wherein the mass volume ratio of resorcinol, deionized water, formaldehyde solution and glacial acetic acid is (1~15) g:(5~100) mL:(1~30) mL:(20~1000) μL.

3. The method of claim 1, wherein the method further comprises the step of: The mass fraction of the formaldehyde solution is 37%. ​ 4. The method of claim 1, wherein the method further comprises the step of: In step (4), the uranium oxide precursor is uranyl nitrate, uranyl chloride or uranyl acetate. ​ 5. The method of claim 1, wherein the method further comprises the step of: In step (2), the constant temperature is 60~80℃, the preservation time is 1~10 days, then dried in air for 1~5 days to obtain the resorcinol-formaldehyde aerogel. ​ 6. The method of claim 1, wherein the method further comprises the step of: In step (3), the treatment temperature is 800~1000℃, the heating rate is 2~4℃ / min, and the holding time is 1~5h. ​ 7. The method of claim 1, wherein the method further comprises the step of: The vacuum degree in step (6) is 1000-5000 Pa, the treatment temperature is 1000-1100 ℃, the heating rate is 1-2 ℃ / min, and the holding time is 1-5 h. ​

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