Preparation method and application of a porous carbon containing benzoxazine-based graphenoid nanosheets

Abstract

The present application relates to the preparation of 2D nanosheet, in particular to a kind of preparation method and application of benzoxazine-based graphene-like nanosheet porous carbon;By controlling the proportion of activator CH3COOK, it leads to the successful preparation of benzoxazine-based graphene-like nanosheet;By adjusting the ratio of crude carbon and activator CH3COOK, successfully prepared graphene-like nanosheet with large aspect ratio, flat and transparent, containing wrinkle, thin (5 nm). The specific capacitance of the related material in the three-electrode system reaches 151 Fg ‑1 , with excellent capacitance retention rate (78.1%). Assembled into symmetric supercapacitor device, with excellent cycle stability, and when the power density is 250 W kg ‑1 , the energy density of the capacitor reaches 3.37 Wh kg ‑1 . Compared with toxic reagents and complex preparation process, the method has the advantages of green environmental protection and simple operation.

Description

Technical Field

[0001] This invention relates to the preparation of 2D nanosheets, specifically to a method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets and its application. Background Technology

[0002] 2D porous carbon nanosheets, also known as graphene-like porous carbon nanosheets, possess immense potential as electrode materials for supercapacitors due to their large aspect ratio and specific surface area. They not only provide a large active surface area for energy storage but also shorten the ion diffusion distance during charge and discharge. Typically, there are two methods for preparing 2D porous carbon nanosheets: top-down and bottom-up approaches. Common bottom-up methods, such as chemical vapor deposition (CVD), can prepare high-quality nanosheets with few or even single layers, but this synthesis method is costly and has low yields. However, many top-down methods have also been used to prepare 2D porous nanosheets, such as the expansion exfoliation of graphite under harsh conditions, chemical etching of bulk carbon, or molten salt-based methods. Among these methods, molten salt-based methods serve two functions: acting as a chemical activator for pore formation and providing a liquid reaction environment for nanosheet formation at high temperatures. However, most activators are used as pore-forming agents in the preparation of activated carbon. Only a few studies have used activators to produce graphene-like porous carbon nanosheets. Currently, only two activators, KOH and HCOOK, have been used to prepare 2D nanosheet structures. However, KOH is highly corrosive, and these carbon precursors are mainly concentrated in natural biomass, resulting in a loose carbon structure that is prone to collapse. Summary of the Invention

[0003] This invention overcomes the shortcomings of existing technologies and provides a method for preparing benzoxazine-based porous carbon containing graphene-like nanosheets. Using three-dimensionally cross-linked polybenzoxazine as a precursor and low-toxicity potassium acetate as an activator, porous carbon containing 2D nanosheets was prepared for the first time using these two raw materials by adjusting the carbon / alkali ratio. The morphology, size, and thickness of the 2D nanosheets were further characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The two-dimensional porous carbon nanosheets prepared by this invention have a high aspect ratio, a sheet diameter greater than 10 µm, and an ultrathin thickness (5 nm). The 2D structure not only shortens the ion diffusion distance and accelerates electron transfer but also provides a larger contact area for electrolyte ions, thus showing great application potential in the field of supercapacitors.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets, comprising the following steps: (1) Synthesis of thiobisphenol thiopheneamine type benzoxazine monomer: 4,4'-dihydroxydiphenyl sulfide, 2-thiophene methylamine and paraformaldehyde were reacted at a certain temperature for several hours, the solvent was removed by rotary evaporation, and the product was washed with alkali and water to obtain a white powder benzoxazine monomer. (2) Preparation of crude carbon; benzoxazine monomer was blended with F127 and gradient cured to obtain polybenzoxazine; the polybenzoxazine was pre-carbonized to obtain crude carbon; (3) Preparation of porous carbon containing graphene-like nanosheets: Crude carbon and activator CH3COOK were calcined at high temperature under an inert atmosphere, and finally acid washed, water washed and dried to obtain benzoxazine-based porous carbon containing graphene-like nanosheets.

[0005] Furthermore, the reaction temperature in step (1) is 75~90 ℃, the reaction time is 1~3 h, and the alkaline solution mentioned in step (1) is a 1M sodium hydroxide solution.

[0006] Furthermore, in step (1), the molar ratio of 4,4'-dihydroxydiphenyl sulfide, 2-thiophene methylamine and paraformaldehyde is 1:2:4.

[0007] Furthermore, in step (2), the mass ratio of the benzoxazine monomer to F127 is 1:0.5~1:3, and the pre-carbonization temperature is 500~700 ℃.

[0008] Furthermore, the solvent used in step (2) is toluene, chloroform, N,N-dimethylformamide (DMF), or dioxane.

[0009] Furthermore, the gradient curing steps in step (2) are as follows: maintain 120 ℃ for 1~3 h, maintain 140 ℃ for 1~3 h, maintain 160 ℃ for 1~3 h, maintain 180 ℃ for 1~3 h, and maintain 200 ℃ for 1~3 h.

[0010] Furthermore, in step (3), the mass ratio of crude carbon to activator CH3COOK is 1:0.25~1:5, the calcination temperature range is 700~1000 ℃, the calcination time is 0.5~3 h, and the inert atmosphere is N2 or Ar atmosphere.

[0011] Furthermore, in step (3), the acid solution is a 3M hydrochloric acid solution.

[0012] In addition, the present invention also provides the application of porous carbon containing benzoxazine-based graphene-like nanosheets obtained by the above preparation method in the preparation of supercapacitors.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a simple and rapid method for preparing graphene-like porous nanosheets. By using potassium acetate as an activator, this method has the advantages of being green, environmentally friendly, and simple to operate compared to toxic reagents and complex preparation processes.

[0014] Compared with existing technologies, this invention produces graphene-like nanosheets with a large aspect ratio and ultrathin thickness by changing the alkali / carbon ratio. This method is expected to achieve industrial production. Attached Figure Description

[0015] Figure 1 The benzoxazine monomer prepared in Example 1 of this invention 1 H NMR spectrum.

[0016] Figure 2 The image shows the FTIR spectrum of the benzoxazine monomer prepared in Example 1 of this invention.

[0017] Figure 3 This is a SEM image of the porous carbon containing graphene-like nanosheets prepared in Example 1 of the present invention.

[0018] Figure 4 This is a TEM image of the graphene-like nanosheets prepared in Example 1 of the present invention.

[0019] Figure 5 The image shows the AFM pattern of the graphene-like nanosheets prepared in Example 1 of this invention.

[0020] Figure 6 This is a SEM image of the porous carbon prepared in the comparative example of this invention.

[0021] Figure 7 This is a comparison of the electrochemical performance of three carbon materials prepared in Example 1 and the comparative example of the present invention.

[0022] Figure 8 A performance comparison of PCs-1:1 and PCCGNs-1:4 prepared in this invention assembled into a symmetrical supercapacitor. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments. Example

[0024] A method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets includes the following steps: (1) Synthesis of bisphenol S-thiopheneamine type benzoxazine monomer: 4,4'-dihydroxydiphenyl sulfide (0.02 mol, 4.36 g), 2-thiophene methylamine (0.04 mol, 4.52 g), and paraformaldehyde (0.08 mol, 2.52 g) were added to a three-necked flask and reacted at 85 °C for 2 h. The mixture was washed with 1M NaOH solution and then with distilled water until neutral to obtain the target product (bisphenol S-thiopheneamine type benzoxazine monomer). The characterization of the benzoxazine monomer is shown in the attached figure. Figure 1 and 2 As shown.

[0025] from Figure 1 It can be seen that the two peaks at 4.89 ppm and 4.10 ppm are the proton peaks of the methylene groups at O-CH2-N and Ar-CH2-N, respectively. The peak at 3.97 ppm is the proton peak of the methylene groups connected to the oxazine and thiophene rings. This indicates that the benzoxazine monomer was successfully synthesized. Figure 2 It can be seen that 1595 cm -1 The absorption peak at 1014 cm⁻¹ corresponds to the skeletal vibration of the benzene ring. -1 and 1220 cm -1 The two characteristic peaks at 1372 cm⁻¹ correspond to the symmetric and asymmetric stretching vibrations of the COC on the oxazine ring, respectively. Furthermore, 1372 cm⁻¹ -1 The peak value at 929 cm corresponds to the antisymmetric stretching vibration of the CNC. -1 The characteristic vibrational peaks of the oxazine ring further confirm the successful synthesis of the bisphenol S thiopheneamine type benzoxazine monomer.

[0026] (2) Preparation of crude carbon: Benzoxazine monomer and F127 (polyoxyethylene polyoxypropylene ether) were dissolved in DMF at a mass ratio of 1:1 to form a yellow transparent solution. The solvent was then removed by a water pump or oil pump. Curing was then carried out under specific curing conditions (140 ℃ / 2 h, 160 ℃ / 2 h, 180 ℃ / 2 h, 200 ℃ / 2 h) to obtain three-dimensionally cross-linked polybenzoxazine. The polybenzoxazine was pre-carbonized at 600 ℃ for 3 h under an inert atmosphere to obtain crude carbon.

[0027] (3) Preparation of porous carbon containing graphene-like nanosheets: Crude carbon and potassium acetate were mixed in a certain proportion (mass ratio of 1:4) and calcined at 800 °C for 1.5 h under an inert atmosphere to obtain porous carbon containing graphene-like nanosheets, denoted as PCCGNs-1:4.

[0028] SEM images of the porous carbon containing graphene-like nanosheets prepared in this example are attached. Figure 3As shown, the graphene-like nanosheets possess a large aspect ratio and a wrinkled nanosheet structure, with the lateral dimensions of the nanosheets reaching several micrometers. TEM images of the graphene-like nanosheets prepared in this embodiment are attached. Figure 4 As shown, this further demonstrates the preparation of transparent graphene-like nanosheets with a folded structure, and the uniform distribution of numerous micropores on the surface of the carbon nanosheets. The AFM image of the graphene-like nanosheets prepared in this embodiment is attached. Figure 5 As shown, the thickness and size of the graphene-like nanosheets were further characterized. The figures reveal that the surfaces of these nanosheets are very flat with some wavy wrinkles. Furthermore, the thickness of these nanosheets is approximately 5 nm. Based on the literature report that the theoretical thickness of a single-layer graphene is 0.34 nm, it can be calculated that these graphene nanosheets contain 14 single-layer graphene layers. In a three-electrode system, when the current density is 0.5 Ag... -1 At that time, the specific capacitance was 151 Fg. -1 Continue increasing the current density to 20 Ag. -1 At that time, the specific capacitance was 118 Fg. -1 The capacitance retention rate reached 78.1%. When assembled into a symmetrical dual-electrode configuration, the power density was 250 W / kg. -1 The energy density reaches 3.37 Wh / kg. -1 .

[0029] Comparative Example The difference from the above embodiments is that: The crude carbon prepared above was mixed with potassium acetate in other proportions, with the mass ratio of crude carbon to potassium acetate being 1:0.25 or 1:1. The mixture was then calcined at 800 °C for 1.5 h under an inert atmosphere to obtain microporous carbon, namely PCs-1:0.25 and PCs-1:1.

[0030] SEM images of the porous carbon prepared in this comparative example are attached. Figure 6 As shown, when the ratio of crude carbon to activator is 1:0.25, the activation effect is weak, and the carbon material mainly exists in a blocky form. When the mass ratio of crude carbon to activator is 1:1, it can be seen that the surface of the carbon material is significantly etched, existing as interconnected macropores, without forming a nanosheet structure. In the three-electrode system, the specific capacitance of PCs-1:1 and PCs-1:0.25 are 156 Fg, respectively. -1 and 102.0 Fg -1 ;Continuing to increase the current density to 20 Ag⁻¹, the specific capacitance is 115.3 Fg. -1 and 47.3 Fg -1 The capacitance retention rates were 73.9% and 46.4%, respectively. PCs were assembled into a symmetrical supercapacitor at a 1:1 ratio, achieving a power density of 250 W / kg.-1 At that time, the energy density was 2.98 Wh / kg. -1 .

[0031] Figure 7 Comparison of the electrochemical performance of different samples prepared in Example 1 and the comparative example in a three-electrode system. (a) Scan rate of 5 mV / s -1 (b, c) CV curves of PCs-1:1 and PCCGNs-1:4 at different scan rates; (d) CV curves of a current density of 0.5 Ag. -1 (e) GCD curve at different current densities; (f) Nyquist plot.

[0032] Figure 8 Electrochemical performance of different samples prepared for Example 1 and the comparative example in a two-electrode system; (a, d) CV curves of PCs-1:1 / / PCs-1:1 and PCCGNs-1:4 / / PCCGNs-1:4 at different potential windows; (b, e) CV curves of PCs-1:1 / / PCs-1:1 and PCCGNs-1:4 / / PCCGNs-1:4 at different scan rates; (c) CV curves of PCs-1:1 / / PCs-1:1 and PCCGNs-1:4 / / PCCGNs-1:4 at a scan rate of 5 mV / s. -1 Comparison of CV curves; (f) PCs-1:1 / / PCs-1:1 and PCCGNs-1:4 / / PCCGNs-1:4 at a current density of 0.5 Ag -1 Comparison of GCD; (gi) Comparison of specific capacitance, EIS, energy density and power density of two symmetrical supercapacitors.

Claims

1. A method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets, characterized in that, Includes the following steps: (1) Synthesis of thiobisphenol thiopheneamine type benzoxazine monomer: 4,4'-dihydroxydiphenyl sulfide, 2-thiophene methylamine and paraformaldehyde were reacted at a certain temperature for several hours, the solvent was removed by rotary evaporation, and the product was washed with alkali and water to obtain a white powder benzoxazine monomer. (2) Preparation of crude carbon; benzoxazine monomer was blended with F127 and gradient cured to obtain polybenzoxazine; the polybenzoxazine was pre-carbonized to obtain crude carbon; (3) Preparation of porous carbon containing graphene-like nanosheets: Crude carbon and activator CH3COOK were calcined at a mass ratio of 1:4 under a high temperature and inert atmosphere, and finally acid washed, water washed and dried to obtain benzoxazine-based porous carbon containing graphene-like nanosheets.

2. The method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets according to claim 1, characterized in that, The reaction temperature in step (1) is 75~90 ℃ and the reaction time is 1~3 h. The alkali mentioned in step (1) is a 1M sodium hydroxide solution.

3. The method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets according to claim 1, characterized in that, In step (1), the molar ratio of 4,4'-dihydroxydiphenyl sulfide, 2-thiophene methylamine and paraformaldehyde is 1:2:

4.

4. The method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets according to claim 1, characterized in that, In step (2), the mass ratio of benzoxazine monomer to F127 is 1:0.5~1:3, and the pre-carbonization temperature is 500~700 ℃.

5. The method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets according to claim 1, characterized in that, The solvent used in step (2) is toluene, chloroform, N,N-dimethylformamide or dioxane.

6. The method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets according to claim 1, characterized in that, The gradient curing steps in step (2) are as follows: 120 ℃ for 1~3 h, 140 ℃ for 1~3 h, 160 ℃ for 1~3 h, 180 ℃ for 1~3 h, and 200 ℃ for 1~3 h.

7. The method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets according to claim 1, characterized in that, In step (3), the calcination temperature range is 700~1000 ℃, the calcination time is 0.5~3 h, and the inert atmosphere is N2 or Ar atmosphere.

8. The method for preparing porous carbon containing benzoxazine-based graphene-like nanosheets according to claim 1, characterized in that, Step (3) The acid solution is a 3M hydrochloric acid solution.

9. The application of porous carbon containing benzoxazine-based graphene-like nanosheets obtained by the preparation method according to any one of claims 1-8 in the preparation of supercapacitors.

Images