Preparation method of molybdenum carbide nanoframe material and prepared material

Abstract

The application discloses a preparation method of a molybdenum carbide nanoframe material, which comprises the following steps: dissolving a first transition metal acetate, dimethyl imidazole and cetyl trimethyl ammonium bromide in water respectively to prepare solutions and prepare a precursor; then, a second transition metal acetate solution, a dimethyl imidazole solution and a cetyl trimethyl ammonium bromide solution are added into the precursor to prepare a precursor composite; then, the precursor composite and a molybdate are dissolved in a dimethyl formamide solution to prepare a molybdate composite; finally, the molybdate composite is high-temperature carbonized in a nitrogen atmosphere at 700-900 DEG C to obtain the molybdenum carbide nanoframe material. The material has a highly dispersed MoC and Mo2C two-phase crystal structure, rich pore structures and good conductivity, and is applied to supercapacitors and capacitive deionization devices as an electrode material, and exhibits excellent electrochemical performance and capacitive desalination efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation of transition metal carbides, in particular to a preparation method of a highly dispersed molybdenum carbide nanoframe material and the prepared material. BACKGROUND

[0002] As a kind of transition metal carbide, molybdenum carbide has the advantages of high electrical conductivity and good structural stability, and is widely used in chemical industry, electronic devices, aerospace, energy conversion and storage, and electrocatalysis. At present, the preparation methods of molybdenum carbide mainly include chemical vapor deposition, programmed temperature method and carbothermal reduction method. However, these methods usually have the problems of complex preparation process, high reaction temperature and high energy consumption, low specific surface area of the prepared molybdenum carbide, large particle size and uneven particle size distribution, and difficult to control the morphology. In recent years, researchers found that using molybdenum-containing metal organic framework materials (MOFs) as precursors, nanometer molybdenum carbide can be prepared through high temperature carbonization process. Although the molybdenum carbide particles prepared by this method are small, the types and structures of molybdenum-containing MOFs are limited, which restricts the improvement of the practical application performance. SUMMARY

[0003] The purpose of the present application is to provide a preparation method of molybdenum carbide nanoframe material. The molybdenum carbide prepared by the method has a highly dispersed MoC and Mo2C two-phase crystal structure, a rich pore structure and good electrical conductivity. When it is applied to supercapacitors and capacitive deionization devices as electrode materials, it exhibits excellent electrochemical performance and capacitive desalination efficiency.

[0004] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0005] A preparation method of molybdenum carbide nanoframe material, comprising the following steps:

[0006] Step S1: Dissolve the first transition metal acetate, dimethyl imidazole and cetyltrimethylammonium bromide in water respectively to form solutions, mix them and then perform hydrothermal reaction at 110-130℃ for 3-5 hours to obtain a precursor, the molar ratio of the first transition metal acetate to dimethyl imidazole and cetyltrimethylammonium bromide is 2:5:0.6 in turn;

[0007] Step S2: Add the second transition metal acetate solution, dimethyl imidazole solution and cetyltrimethylammonium bromide solution into the precursor prepared in step S1 in turn, and perform hydrothermal reaction at 110-130℃ for 2-3 hours to obtain a precursor composite, the mass ratio of the second transition metal acetate to the precursor is 5:4, and the molar ratio of the second transition metal acetate to dimethyl imidazole and cetyltrimethylammonium bromide is 0.5:1.25:0.15 in turn;

[0008] Step S3: Dissolve the precursor complex and molybdate prepared in step S2 in dimethylformamide solution, stir, and then hydrothermally react at 110-130℃ for 5-7 hours to obtain the molybdate complex. The mass ratio of the precursor complex to the molybdate is 1:1-2.

[0009] Step S4: The molybdate composite prepared in step S3 is carbonized at high temperature for 3 hours under a nitrogen atmosphere at 700-900℃ to obtain molybdenum carbide nanoframework material.

[0010] Preferably, the first transition metal acetate is one of zinc acetate dihydrate or cobalt acetate tetrahydrate, and the precursor is one of T-ZIF-8 formed by the reaction of zinc with dimethylimidazole or T-ZIF-67 formed by the reaction of cobalt with dimethylimidazole.

[0011] Preferably, the second transition metal acetate is one of zinc acetate dihydrate and cobalt acetate tetrahydrate, and the complex is one of zinc / cobalt complex T-ZIF-8 / ZIF-67, cobalt / zinc complex T-ZIF-67 / ZIF-8, and zinc / zinc complex T-ZIF-8 / ZIF-8.

[0012] Preferably, the molybdate is one of ammonium molybdate or sodium molybdate dihydrate.

[0013] Another objective of this invention is to provide a molybdenum carbide nanoframework material prepared by the above-described preparation method.

[0014] In this invention, highly dispersed molybdenum carbide nanoframework materials are prepared using MOFs as precursors through ion exchange combined with high-temperature carbonization. This method overcomes the drawbacks of conventional methods, such as large particle size, uneven particle size distribution, and difficulty in controlling morphology of prepared molybdenum carbide particles, and avoids the problem of poor dispersion due to particle agglomeration. The molybdenum carbide nanoframework materials prepared in this invention are used as electrode materials to assemble supercapacitors and capacitive deionization devices, achieving a current density of 0.5 A g. -1 At that time, the electrolyte was 1 mol L. -1 In sodium chloride solution, the material exhibits a capacitance as high as 185.4 F g. -1 500mg L -1 The sodium chloride solution, at a voltage of 1.4V, showed a CDI desalination capacity of 73.6 mg / g. -1 The desalination rate remained at 92.1% after 50 cycles of testing. Attached Figure Description

[0015] Figure 1 Scanning electron microscope (SEM) image (A), transmission electron microscope (TEM) image (B), high-magnification transmission electron microscope (HEM) image (C), and elemental mapping diagram (DF) of carbon / molybdenum for molybdenum nanoframework material;

[0016] Figure 2 X-ray diffraction pattern of the molybdenum carbide nanoframe material;

[0017] Figure 3 Raman spectrum of the molybdenum carbide nanoframe material;

[0018] Figure 4 X-ray photoelectron spectroscopy of the molybdenum carbide nanoframe material: (A) full spectrum, (B) Mo 3d spectrum;

[0019] Figure 5 (A) nitrogen adsorption-desorption isotherm, (B) pore size distribution of the molybdenum carbide nanoframe material;

[0020] Figure 6 Cyclic voltammogram of the molybdenum carbide nanoframe material for supercapacitor (electrolyte: 1 mole per liter sodium chloride solution);

[0021] Figure 7 Charge-discharge curve of the molybdenum carbide nanoframe material for supercapacitor (electrolyte: 1 mole per liter sodium chloride solution);

[0022] Figure 8 Specific capacitance performance of the molybdenum carbide nanoframe material;

[0023] Figure 9 Electrochemical impedance curve of the molybdenum carbide nanoframe material;

[0024] Figure 10 Photos of the device and components based on molybdenum carbide capacitive deionization (CDI);

[0025] Figure 11 (A) desalination amount over time curve, (B) Ragone curve of desalination amount and desalination rate of the molybdenum carbide CDI based on the molybdenum carbide nanoframe material;

[0026] Figure 12 Desalination amount of the molybdenum carbide nanoframe material CDI based on different NaCl concentrations;

[0027] Figure 13 Desalination amount of the molybdenum carbide nanoframe material CDI based on different voltages;

[0028] Figure 14 Stability curve of the molybdenum carbide nanoframe material CDI based on 50 cycles. DETAILED DESCRIPTION

[0029] The application will be further described below through specific examples.

[0030] Example 1 Preparation method 1 of the molybdenum carbide nanoframe material

[0031] First, 0.439 g (2.0 mmol) of zinc acetate dihydrate, 4.105 g (5.0 mmol) of dimethylimidazole, and 0.217 g (0.6 mmol) of hexadecyltrimethylammonium bromide (CTAB) were dissolved in deionized water to prepare solutions. These three solutions were then mixed and stirred for 0.5 hours. The mixture was transferred to an autoclave, heated at 120°C for 4 hours, centrifuged, washed three times with ethanol, and vacuum dried to obtain the precursor (T-ZIF-8).

[0032] Then, 0.125 g (0.5 mmol) of cobalt acetate tetrahydrate was dissolved in 20 mL of aqueous solution, and 100 mg of the precursor T-ZIF-8 was added to the above solution and ultrasonically dispersed for 10 min. 1.03 g (1.25 mmol) of dimethylimidazole and 0.054 g (0.15 mmol) of CTAB were dissolved in 10 mL of deionized water and added to the cobalt / T-ZIF-8 dispersion. The mixture was stirred and reacted in an autoclave at 120 °C for 2 h. After centrifugation to separate the solid, the mixture was washed with ethanol and vacuum dried to obtain the purple complex (T-ZIF-8 / ZIF-67).

[0033] Subsequently, 100 mg of the prepared T-ZIF-8 / ZIF-67 complex was added to 15 mL of DMF solution and ultrasonically dispersed. 200 mg (0.16 mmol) of ammonium molybdate tetrahydrate was added to the dispersion and stirred for 10 minutes. The mixture was then transferred to an autoclave and reacted at 120°C for 6 hours. After cooling to room temperature, a grayish-purple molybdate complex (T-ZIF-8 / ZIF-67 / MoO4) was obtained. The product was centrifuged, washed with ethanol, and dried.

[0034] Finally, the molybdate composite was subjected to high-temperature pyrolysis at 800 degrees Celsius under nitrogen for 3 hours to obtain molybdenum carbide material with a nanoframework structure.

[0035] In this embodiment, the scanning electron microscope (SEM) image, transmission electron microscope (TEM) image, high-magnification TEM image, and carbon / molybdenum elemental mapping diagram of the molybdenum carbide nanoframework material are shown below. Figure 1 As shown in Figure AF, the synthesized molybdenum carbide possesses a nanoframework structure, with MoC / Mo2C two-phase crystals uniformly dispersed in the MOF-derived carbon matrix. The X-ray diffraction pattern is shown below. Figure 2 As shown, the synthesized molybdenum carbide nanoframework material further demonstrates that it possesses a two-phase crystal structure of MoC (JCPDS No. 45-1015) and Mo2C (JCPDS No. 35-0787). Figure 3 The Raman spectra show that the proportion of graphitized carbon (G peak) in the molybdenum carbide nanoframework material is slightly higher than that of amorphous carbon (D peak). Figure 4X-ray photoelectron spectroscopy (XPS) of the molybdenum carbide nanoframework material shows that Mo was successfully embedded in the material. Figure 4 A), High-resolution XPS spectra of the Mo 3d region ( Figure 4 Two pairs of peaks were observed in B). The first pair of peaks: Mo 3d 5 / 2 The peak is at 228.88 eV, Mo 3d 3 / 2 The peaks are at 231.95 eV, and these peaks can be attributed to Mo-Mo or Mo-C bonds; the second pair of peaks are located at higher binding energies (Mo 3d). 5 / 2 At 232.98eV, Mo 3d 3 / 2 At 236.01 eV, the bond is a Mo-O bond. The nitrogen adsorption-desorption isotherm is as follows: Figure 5 As shown in Figure A, a hysteresis loop appears between relative pressures of 0.4 and 0.9, indicating that the molybdenum carbide nanoframework material possesses mesoporous structural characteristics, which is consistent with its mesopore size distribution curve. Figure 5 B).

[0036] Example 2: Preparation method of molybdenum carbide nanoframework material 2

[0037] First, 0.439 g (2.0 mmol) of zinc acetate dihydrate, 4.105 g (5.0 mmol) of dimethylimidazole, and 0.217 g (0.6 mmol) of CTAB were dissolved in deionized water to prepare solutions. These three solutions were then mixed and stirred for 0.5 hours. The mixture was transferred to an autoclave, heated at 110°C for 5 hours, centrifuged, washed with ethanol, and vacuum dried to obtain the precursor (T-ZIF-8).

[0038] Then, 0.125 g (0.5 mmol) of cobalt acetate tetrahydrate was dissolved in 20 mL of aqueous solution, and 100 mg of the precursor T-ZIF-8 was added to the above solution and ultrasonically dispersed for 10 min. Then, 1.03 g (1.25 mmol) of dimethylimidazole and 0.054 g (0.15 mmol) of CTAB were dissolved in 10 mL of deionized water and added to the cobalt / T-ZIF-8 dispersion. The mixture was stirred and reacted in an autoclave at 110 °C for 3 h. The resulting solid was centrifuged, washed with ethanol, and vacuum dried to obtain the purple complex (T-ZIF-8 / ZIF-67).

[0039] Subsequently, 100 mg of the prepared T-ZIF-8 / ZIF-67 complex was added to 15 mL of DMF solution and ultrasonically dispersed. 100 mg (0.08 mmol) of ammonium molybdate tetrahydrate was added to the dispersion and stirred for 10 minutes. The mixture was then transferred to an autoclave and reacted at 130°C for 5 hours. After cooling to room temperature, the resulting molybdate complexes T-ZIF-8 / ZIF-67 / MoO4, ranging from grayish-purple to varying proportions, were obtained. The products were separated by centrifugation, washed with ethanol, and dried.

[0040] Finally, the material is subjected to high-temperature pyrolysis at 700 degrees Celsius under nitrogen for 4 hours to obtain molybdenum carbide material with a nanoframework structure.

[0041] Example 3: Preparation method of molybdenum carbide nanoframework material 3

[0042] First, 0.498 g (2.0 mmol) of cobalt acetate tetrahydrate, 4.105 g (5.0 mmol) of dimethylimidazole, and 0.217 g (0.6 mmol) of CTAB were dissolved in deionized water to prepare solutions. These three solutions were then mixed and stirred for 0.5 hours. The mixture was transferred to an autoclave and reacted at 130°C for 3 hours. The product was collected by centrifugation, washed three times with ethanol, and then vacuum dried to obtain the purple precursor (T-ZIF-67).

[0043] Then, 0.125 g (0.5 mmol) of cobalt acetate tetrahydrate was dissolved in 20 mL of aqueous solution, and 100 mg of the precursor T-ZIF-67 was added to the above solution and ultrasonically dispersed for 10 minutes. Then, 1.03 g (1.25 mmol) of dimethylimidazole and 0.054 g (0.15 mmol) of CTAB were dissolved in 10 mL of deionized water and added to the cobalt / T-ZIF-67 dispersion. The mixture was stirred and reacted in an autoclave at 130 °C for 2 hours. After centrifugation and washing with ethanol, the mixture was vacuum dried to obtain the purple complex (T-ZIF-67 / ZIF-67).

[0044] Subsequently, 100 mg of the prepared T-ZIF-67 / ZIF-67 complex was added to 15 mL of DMF solution and ultrasonically dispersed. 200 mg (0.16 mmol) of ammonium molybdate tetrahydrate was added to the dispersion and stirred for 10 minutes. The mixture was then transferred to an autoclave and reacted at 110°C for 7 hours. After cooling to room temperature, the resulting molybdate complex T-ZIF-67 / ZIF-67 / MoO4 was centrifuged, washed with ethanol, and dried.

[0045] Finally, T-ZIF-67 / ZIF-67 / MoO4 was subjected to high-temperature pyrolysis at 900 degrees Celsius under nitrogen for 2 hours to obtain molybdenum carbide material with a nanoframework structure.

[0046] Example 4: Preparation method of molybdenum carbide nanoframework material 4

[0047] First, 0.439 g (2.0 mmol) of zinc acetate dihydrate, 4.105 g (5.0 mmol) of dimethylimidazole, and 0.217 g (0.6 mmol) of CTAB were dissolved in deionized water to prepare solutions. These three solutions were then mixed and stirred for 0.5 hours. The mixture was transferred to an autoclave and reacted at 120°C for 4 hours. After centrifugation and washing with ethanol, the mixture was vacuum dried to obtain a white precursor (T-ZIF-8).

[0048] Then, 0.110 g (0.5 mmol) of zinc acetate dihydrate was dissolved in 20 mL of aqueous solution, and 100 mg of the precursor T-ZIF-8 was added to the above solution and ultrasonically dispersed for 10 minutes. Then, 1.03 g (1.25 mmol) of dimethylimidazole and 0.054 g (0.15 mmol) of CTAB were dissolved in 10 mL of deionized water and added to the zinc / T-ZIF-8 dispersion. The mixture was stirred and reacted in an autoclave at 120 °C for 2 hours. After centrifugation and washing with ethanol, the mixture was vacuum dried to obtain a white complex (T-ZIF-8 / ZIF-8).

[0049] Subsequently, 100 mg of the T-ZIF-8 / ZIF-8 complex was added to 15 mL of DMF solution and ultrasonically dispersed. 200 mg (0.16 mmol) of ammonium molybdate tetrahydrate was added to the dispersion and stirred for 10 minutes. The mixture was then transferred to an autoclave and reacted at 120°C for 6 hours. After cooling to room temperature, the molybdate complex T-ZIF-8 / ZIF-8 / MoO4 was obtained, centrifuged, washed with ethanol, and dried.

[0050] Finally, T-ZIF-8 / ZIF-8 / MoO4 was subjected to high-temperature pyrolysis at 800 degrees Celsius under nitrogen for 3 hours to obtain molybdenum carbide material.

[0051] Performance testing of molybdenum carbide nanoframework materials

[0052] The 2 mg molybdenum carbide prepared in Example 1 was used as the electrode material and coated onto a 1×2 cm plate. 2 The conductive graphite paper was used as the test electrode, and together with the platinum wire counter electrode and the Ag / AgCl reference electrode, a supercapacitor was assembled and connected to a 1 mol L... -1 The capacitance performance was tested in a sodium chloride solution, and the test results are as follows: Figures 6 to 9 As shown, the molybdenum carbide nanoframework material exhibits a high specific capacity (current density of 0.5 A g). -1 At that time, the capacitance was 185.4 F g. -1 It exhibits rapid charge-discharge characteristics and good conductivity. 16 mg of molybdenum carbide was used as the electrode material and uniformly coated to a depth of 2 × 2 cm. 2A CDI cathode was prepared on conductive graphite paper, and a CDI anode was prepared using the same method. These were then assembled into a symmetrical capacitive deionization CDI device. Figure 10 Performance testing was conducted, and the test results are as follows: Figures 11 to 14 As shown. The material was in 500 mg / L. -1 The sodium chloride solution had a salt adsorption capacity of 73.6 mg / g at a voltage of 1.4 V. -1 ( Figure 11 A). From Figure 11 The Ragone curves of the desalination amount versus desalination rate of B show that the molybdenum carbide nanoframework material has a rapid desalination rate. Figure 12 and Figure 13 Further studies showed that the CDI of the molybdenum carbide nanoframework material increased with increasing sodium chloride solution concentration and applied voltage. Specifically, the CDI increased with increasing sodium chloride solution concentration and applied voltage at a concentration of 500 mg / L. -1 Cyclic desalination experiments conducted in sodium chloride solution showed that the prepared material exhibited good cyclic stability, with the desalination rate remaining at 92.1% after 50 cycles. Figure 14 ).

[0053] The above embodiments are merely illustrative of the concept and implementation of the present invention and are not intended to limit it. Under the concept of the present invention, technical solutions without substantial changes are still within the scope of protection.

Claims

1. A method for preparing a molybdenum carbide nanoframe material as an electrode material for supercapacitors and capacitive deionization devices, characterized by: The molybdenum carbide nanoframe material has two-phase crystal structures of MoC and Mo2C, and the proportion of graphitized carbon in the molybdenum carbide nanoframe material is higher than that of amorphous carbon, and the preparation method comprises the following steps: Step S1: zinc acetate dihydrate, dimethyl imidazole and cetyl trimethyl ammonium bromide are respectively dissolved in water to prepare solutions, and after mixing, a hydrothermal reaction is carried out at 110-130 DEG C for 3-5 hours to obtain a T-ZIF-8 precursor, and the molar ratio of zinc acetate dihydrate, dimethyl imidazole and cetyl trimethyl ammonium bromide is 2:5:0.6 in turn; Step S2: to the T-ZIF-8 precursor prepared in step S1, a cobalt acetate tetrahydrate solution, a dimethyl imidazole solution and a cetyl trimethyl ammonium bromide solution are sequentially added, and a hydrothermal reaction is carried out at 110-130 DEG C for 2-3 hours to obtain a T-ZIF-8 / ZIF-67 precursor composite, and the mass ratio of the cobalt acetate tetrahydrate to the T-ZIF-8 precursor is 5:4, and the molar ratio of the cobalt acetate tetrahydrate to dimethyl imidazole and cetyl trimethyl ammonium bromide is 0.5:1.25:0.15 in turn; Step S3: the T-ZIF-8 / ZIF-67 precursor composite prepared in step S2 and a molybdate are dissolved in a dimethyl formamide solution, stirred and then subjected to a hydrothermal reaction at 110-130 DEG C for 5-7 hours to obtain a T-ZIF-8 / ZIF-67 / MoO4 molybdate composite, and the mass ratio of the T-ZIF-8 / ZIF-67 precursor composite to the molybdate is 1:1-2; Step S4: the T-ZIF-8 / ZIF-67 / MoO4 molybdate composite prepared in step S3 is subjected to high-temperature carbonization in an inert atmosphere at 700-900 DEG C for 2-4 hours to obtain a molybdenum carbide nanoframe material.

2. The method for preparing the molybdenum carbide nanoframework material as described in claim 1, characterized in that, The molybdate is one of ammonium molybdate and sodium molybdate dihydrate.

3. The method of claim 1, wherein the molybdenum carbide nanoframe material is prepared by the steps of: preparing a mixture of molybdenum oxide and a carbon source; and heating the mixture to a temperature of 800-1200 °C in an inert atmosphere. The inert atmosphere is nitrogen or argon.

4. The preparation method of the molybdenum carbide nanoframe material according to claim 1, wherein in step S1, the zinc acetate dihydrate, dimethyl imidazole and cetyl trimethyl ammonium bromide are respectively dissolved in water to prepare solutions, and after mixing, a hydrothermal reaction is carried out at 120 DEG C for 4 hours to obtain a T-ZIF-8 precursor; in step S2, to the T-ZIF-8 precursor prepared in step S1, a cobalt acetate tetrahydrate solution, a dimethyl imidazole solution and a cetyl trimethyl ammonium bromide solution are sequentially added, and a hydrothermal reaction is carried out at 120 DEG C for 2 hours to obtain a T-ZIF-8 / ZIF-67 precursor composite; in step S3, the T-ZIF-8 / ZIF-67 precursor composite prepared in step S2 and a molybdate are dissolved in a dimethyl formamide solution, stirred and then subjected to a hydrothermal reaction at 120 DEG C for 6 hours to obtain a T-ZIF-8 / ZIF-67 / MoO4 molybdate composite, and the mass ratio of the T-ZIF-8 / ZIF-67 precursor composite to the molybdate is 1:1-2; ​ Step S4: the T-ZIF-8 / ZIF-67 / MoO4 molybdate composite prepared in step S3 is carbonized at 800 DEG C under inert atmosphere for 3 hours to obtain a carbonized molybdenum nanoframe material.

5. A molybdenum carbide nanoframe material, characterized by which is prepared by the preparation method according to any one of claims 1 to 4. which is prepared by the preparation method according to any one of claims 1 to 4.

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