Preparation method and application of rice husk-based multi-heteroatom doped carbon nanosheets

Abstract

The present invention discloses a preparation method and application of rice husk-based multi-heteroatom doped carbon nanosheets, belonging to the technical fields of carbon material preparation and energy storage technology. The preparation method of the rice husk-based multi-heteroatom doped carbon nanosheets of the present invention comprises the following steps: carbonizing rice husks, and then putting them into a KOH solution and stirring to obtain pre-carbonized rice husks; mixing the pre-carbonized rice husks with ammonium dihydrogen phosphate, thiosalicylic acid and an activator in water to obtain a nitrogen, phosphorus and sulfur doped nanosheet precursor; calcining the nitrogen, phosphorus and sulfur doped nanosheet precursor to obtain the rice husk-based multi-heteroatom doped carbon nanosheets. The present invention uses the carbon after de-siliconization of rice husks as the raw material, ammonium dihydrogen phosphate as the phosphorus source and nitrogen source, and thiosalicylic acid as the sulfur source, and synthesizes nitrogen, phosphorus and sulfur doped flocculent carbon nanosheets by a one-step in-situ method, and applies them to zinc ion hybrid capacitors. The introduction of nitrogen, phosphorus and sulfur heteroatoms improves the electron conduction performance of the material and increases the defect sites for ion adsorption.

Description

Technical Field

[0001] The present invention relates to the technical fields of carbon material preparation and energy storage technology, and particularly relates to a preparation method and application of rice husk-based multi-heteroatom doped carbon nanosheets. Background Art

[0002] With the large-scale cultivation of rice, a large amount of by-product rice husks are generated worldwide every year. Currently, rice husks are mainly used as livestock feed, but such utilization methods have low added value and cause certain resource waste. Converting rice husks into high-performance carbon electrode materials and applying them to energy storage devices is one of the research directions. At present, Ye Lanlan et al. used the solution method, with rice husks as the carbon precursor and zinc chloride as the activator, and obtained a three-dimensional porous graphene-like carbon material through pickling and alkali washing processes (CN201910522642.0); in addition, Guo Qianqian et al. adopted a hydrothermal carbonization and high-temperature activation process, and prepared a hierarchical porous carbon material using a KOH activation strategy (CN202211611869.0). However, the post-treatment processes in the above patents all involve the treatment with strong acid solutions, which will cause certain pollution. Therefore, there is an urgent need to design a method for preparing carbon materials simply without acid. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method and application of rice husk-based multi-heteroatom doped carbon nanosheets. The present invention uses the carbon after de-siliconization of rice husks as the raw material, ammonium dihydrogen phosphate as the phosphorus source and nitrogen source, and thiosalicylic acid as the sulfur source, and synthesizes nitrogen, phosphorus, and sulfur doped flocculent carbon nanosheets by a one-step in-situ method, and applies them to zinc-ion hybrid capacitors. The introduction of nitrogen, phosphorus, and sulfur heteroatoms improves the electron conduction performance of the material and increases the defect sites for ion adsorption. The preparation process of the present invention is simple and easy to scale up production, which not only reduces environmental pollution but also realizes the high-value utilization of biomass resources.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] One of the technical solutions of the present invention: provides a preparation method of rice husk-based multi-heteroatom doped carbon nanosheets, including the following steps:

[0006] Carbonize the rice husks, and then put them into a KOH solution and stir to obtain pre-carbonized rice husks;

[0007] Mix the pre-carbonized rice husks with ammonium dihydrogen phosphate, thiosalicylic acid, and an activator in water to obtain a nitrogen, phosphorus, and sulfur doped nanosheet precursor;

[0008] Calcine the nitrogen, phosphorus, and sulfur doped nanosheet precursor to obtain the rice husk-based multi-heteroatom doped carbon nanosheets.

[0009] Preferably, the temperature of the carbonization treatment is 500 °C and the time is 2 h.

[0010] Preferably, the stirring time is 6 - 12 h; the concentration of the KOH solution is 2 mol / L.

[0011] Preferably, the activator is potassium bicarbonate; the mass ratio of the pre-carbonized rice husk, ammonium dihydrogen phosphate, thiosalicylic acid and potassium bicarbonate is 1:0.5:1:5 - 7, and the mass ratio of the pre-carbonized rice husk to the water is 1:15 - 25.

[0012] In the present invention, potassium bicarbonate is used as the activator and template, replacing the expensive metal oxide template, reducing the preparation cost and reducing the use of acid in the post-treatment process.

[0013] Preferably, the temperature of the mixing is 60 °C and the time is 2 - 6 h.

[0014] Preferably, the calcination is carried out by heating to 900 °C at a rate of 5 °C / min and then holding for 60 min; the calcination is carried out under a protective atmosphere.

[0015] The second technical solution of the present invention: Provide a rice husk-based multi-heteroatom-doped carbon nanosheet obtained according to the above preparation method.

[0016] The third technical solution of the present invention: Provide an application of the above rice husk-based multi-heteroatom-doped carbon nanosheet in the preparation of a zinc ion hybrid capacitor.

[0017] The fourth technical solution of the present invention: Provide a preparation method of a zinc ion hybrid capacitor, comprising the following steps:

[0018] Mix the above-mentioned rice husk-based multi-heteroatom-doped carbon nanosheet with a PTFE binder, press into a film, slice and dry to obtain a positive electrode material; use a zinc foil as the negative electrode and a Zn(CF3SO3)2 solution as the electrolyte to assemble a button-type zinc ion hybrid capacitor.

[0019] Preferably, the solid content of the PTFE binder is 60%, the mass ratio of the rice husk-based multi-heteroatom-doped carbon nanosheet to the PTFE binder is 1:9; the concentration of the Zn(CF3SO3)2 solution is 1 mol / L.

[0020] The fourth technical solution of the present invention: Provide a zinc ion hybrid capacitor obtained according to the above preparation method.

[0021] The technical principle of the present invention is as follows:

[0022] The rice husk-based multi-heteroatom doped foamy carbon nanosheets of the present invention are prepared by in-situ activation and tailoring of rice husk carbon after carbonization and desiliconization under the strategy of potassium bicarbonate. Ammonium dihydrogen phosphate is used as the nitrogen and phosphorus source, and thiosalicylic acid is used as the sulfur source. During the reaction process, the potassium salt generated by the decomposition of potassium bicarbonate reacts with the carbon matrix, and the generated gas physically activates the carbon matrix. The specific mechanism is as follows: First, pre-carbonized rice husk, ammonium dihydrogen phosphate, thiosalicylic acid, and potassium bicarbonate are uniformly mixed in a solution. As the temperature rises, the rice husk carbon reacts with potassium bicarbonate to generate a hierarchical pore structure. At the same time, potassium bicarbonate decomposes to generate potassium salts, which react with the carbon matrix to produce potassium carbonate and decompose to generate carbon dioxide; the generated carbon dioxide reacts with the carbon matrix to generate carbon monoxide. Ammonium dihydrogen phosphate generates nitrogen and phosphorus-containing compounds during the reaction process. These gases physically activate the carbon matrix and assist the chemical activation of potassium salts, thereby generating hierarchical pores, providing a large number of adsorption sites and channels for the adsorption and transmission of electrolyte ions. In addition, through in-situ doping, the compound reacts with the carbon matrix, replaces some carbon atoms, introduces nitrogen, phosphorus, and sulfur heteroatoms, and generates defect sites, providing a high-speed path for the rapid transmission of electrons and generating additional capacity. Finally, the rice husk-based multi-heteroatom doped foamy carbon nanosheets are obtained through steps such as washing with water and drying.

[0023] The beneficial technical effects of the present invention are as follows:

[0024] The present invention uses the carbon after desiliconization of rice husk as the raw material, ammonium dihydrogen phosphate as the phosphorus and nitrogen source, and thiosalicylic acid as the sulfur source, and synthesizes nitrogen, phosphorus, and sulfur-doped flocculent carbon nanosheets by a one-step in-situ method, and applies them to zinc-ion hybrid capacitors. The introduction of nitrogen, phosphorus, and sulfur heteroatoms improves the electron conduction performance of the material and increases the defect sites for ion adsorption.

[0025] The prepared multi-heteroatom doped foamy carbon nanosheets have a high specific surface area. When used as the positive electrode material of a zinc-ion hybrid capacitor in an aqueous electrolyte of Zn(CF3SO3)2, at a current density of 0.1 A / g, its capacity is 198.56 mAh / g and the energy density is 167.69 Wh / kg; at a current density of 20 A / g, its capacity reaches 119.22 mAh / g and the energy density is 80.92 Wh / kg; at a current density of 5 A / g, after 23,000 cycles, the capacity retention rate is 99.98%. It can be seen that it has a high energy density, good rate performance and cycle life, and exhibits excellent electrochemical performance.

[0026] The preparation process of the present invention is simple and easy to scale up production, which not only reduces environmental pollution but also realizes the high-value utilization of biomass resources. Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0028] Figure 1 It is the nitrogen adsorption - desorption isotherm of the product of Example 2.

[0029] Figure 2 It is the field - emission scanning electron microscope image of the product of Example 2.

[0030] Figure 3 It is the capacitance change curve of the zinc - ion hybrid capacitor assembled with the product of Example 2.

[0031] Figure 4 It is the cyclic stability test of the zinc - ion hybrid capacitor assembled with the product of Example 2. Detailed Embodiments

[0032] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0033] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0035] Regarding the use of "comprising", "including", "having", "containing", etc. in the present invention, they are all open - ended terms, meaning including but not limited to.

[0036] "Room temperature" in the present invention, unless otherwise specified, is calculated as 20 - 30 °C.

[0037] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0038] Example 1

[0039] Preparation of carbon nanosheets:

[0040] (1) Pretreatment of reactants: Wash the rice husks, carbonize them at 500 °C for 2 h, then grind them to an average particle size of 5 μm, and then mix them with 2 mol / L KOH solution, stir for 6 h, filter and dry to obtain pre-carbonized rice husks;

[0041] Then add 1 g of pre-carbonized rice husks, 0.5 g of ammonium dihydrogen phosphate, 1 g of thiosalicylic acid, and 5 g of potassium bicarbonate to 15 mL of water, and heat at 60 °C for 3 h to obtain a nitrogen, phosphorus, and sulfur-doped nanosheet precursor;

[0042] (2) Preparation of multi-heteroatom-doped foamy carbon nanosheets: Put the nitrogen, phosphorus, and sulfur-doped nanosheet precursor obtained in step (1) into a magnetic boat in a tube furnace, heat it to 900 °C at a heating rate of 5 °C / min, keep it at a constant temperature for 60 min, then naturally cool to room temperature, take out the product, wash it with water to remove impurities, dry it, and grind it to an average particle size of 2 μm to obtain multi-heteroatom-doped foamy carbon nanosheets (denoted as NPS-FC5). After measurement, the specific surface area of this carbon nanosheet is 1389.3 m 2 / g, and the contents of nitrogen, phosphorus, and sulfur are 0.78 at.%, 0.33 at.%, and 1.25 at.%, respectively.

[0043] Example 2

[0044] Preparation of carbon nanosheets:

[0045] (1) Pretreatment of reactants: Wash the rice husks, carbonize them at 500 °C for 2 h, then grind them to an average particle size of 5 μm, and then mix them with 2 mol / L KOH solution, stir for 9 h, filter and dry to obtain pre-carbonized rice husks;

[0046] Then add 1 g of pre-carbonized rice husks, 0.5 g of ammonium dihydrogen phosphate, 1 g of thiosalicylic acid, and 6 g of potassium bicarbonate to 20 mL of water, and heat at 60 °C for 4 h to obtain a nitrogen, phosphorus, and sulfur-doped nanosheet precursor;

[0047] (2) Preparation of multi-heteroatom-doped foamy carbon nanosheets: Put the nitrogen, phosphorus, and sulfur-doped nanosheet precursor obtained in step (1) into a magnetic boat in a tube furnace, heat it to 900 °C at a heating rate of 5 °C / min, keep it at a constant temperature for 60 min, then naturally cool to room temperature, take out the product, wash it with water to remove impurities, dry it, and grind it to an average particle size of 2 μm to obtain multi-heteroatom-doped foamy carbon nanosheets (denoted as NPS-FC6). After measurement, the specific surface area of this carbon nanosheet is 1976.8 m 2 / g, the contents of nitrogen, phosphorus, and sulfur are 2.21 at.%, 0.43 at.%, and 1.41 at.%, respectively.

[0048] Figure 1 is the nitrogen adsorption - desorption isotherm of the product of Example 2. From Figure 1 it can be seen that the specific surface area of the nitrogen, phosphorus, and sulfur - doped foamed carbon prepared by the present invention ranges from 1524.6 to 1976.8 m 2 / g, having a high specific surface area, up to 1976.8 m 2 / g.

[0049] Figure 2 is the field - emission scanning electron micrograph of the product of Example 2. From Figure 2 it can be seen that the present invention uses de - siliconized rice husk as the carbon precursor, potassium bicarbonate as the tailor - made agent and template, ammonium dihydrogen phosphate as the nitrogen - and phosphorus - doping agent, and thiosalicylic acid as the sulfur - doping agent. Through the processes of tailoring and in - situ doping, multi - heteroatom - doped foamed carbon nanosheets are obtained. Under the physical activation of the gases generated by the decomposition of ammonium dihydrogen phosphate and potassium bicarbonate, a bubble - like structure is formed, and under the tailoring action of potassium bicarbonate, an interconnected foamed structure with hierarchical pores is obtained, having a large number of micropores, mesopores, and macropores.

[0050] Example 3

[0051] Preparation of carbon nanosheets:

[0052] (1) Pretreatment of reactants: Wash the rice husk, carbonize it at 500 °C for 2 h, then grind it to an average particle size of 5 μm, and then mix it with a 2 mol / L KOH solution, stir for 12 h, filter and dry to obtain pre - carbonized rice husk;

[0053] Then add 1 g of pre - carbonized rice husk, 0.5 g of ammonium dihydrogen phosphate, 1 g of thiosalicylic acid, and 7 g of potassium bicarbonate to 25 mL of water, and after heating at 60 °C for 5 h, obtain a nitrogen, phosphorus, and sulfur - doped nanosheet precursor;

[0054] (2) Preparation of multi - heteroatom - doped foamed carbon nanosheets: Put the nitrogen, phosphorus, and sulfur - doped nanosheet precursor obtained in step (1) into a magnetic boat in a tubular furnace, heat it to 900 °C at a heating rate of 5 °C / min, keep it at a constant temperature for 60 min, then naturally cool to room temperature, take out the product, wash it with water to remove impurities, dry it, and grind it to an average particle size of 2 μm to obtain multi - heteroatom - doped foamed carbon nanosheets (denoted as NPS - FC7). After measurement, the specific surface area of this carbon nanosheet is 1736.7 m 2 / g, and the contents of nitrogen, phosphorus, and sulfur are 1.08 at.%, 0.36 at.%, and 1.33 at.%, respectively.

[0055] Comparative Example 1

[0056] The difference from Example 2 is only that the addition of ammonium dihydrogen phosphate is omitted, and sulfur-doped foamy carbon nanosheets are obtained. It is measured that the specific surface area of this carbon nanosheet is 1637.3 m 2 / g, and the sulfur content is 0.93 at.%.

[0057] Comparative Example 2

[0058] The difference from Example 2 is only that the addition of thiosalicylic acid is omitted, and nitrogen and phosphorus-doped foamy carbon nanosheets are obtained. It is measured that the specific surface area of this carbon nanosheet is 1609.1 m 2 / g, and the nitrogen and phosphorus contents are 1.18 at.% and 0.96 at.%, respectively.

[0059] Comparative Example 3

[0060] The difference from Example 2 is only that the addition of ammonium dihydrogen phosphate and thiosalicylic acid is omitted, and foamy carbon nanosheets are obtained. It is measured that the specific surface area of this carbon nanosheet is 1500.4 m 2 / g.

[0061] Effect verification

[0062] The carbon nanosheets prepared in Examples 1-3 and Comparative Examples 1-3 are mixed with a PTFE binder with a solid content of 60% according to a mass ratio of 1:9, and a positive electrode material is obtained through processes of pressing into a film, slicing, and drying; using a zinc foil as the negative electrode, a 1 mol / L Zn(CF3SO3)2 solution as the electrolyte, and paper fiber as the separator, a button-type zinc-ion hybrid capacitor is assembled for electrochemical performance testing.

[0063] It is measured that in the zinc-ion hybrid capacitor assembled with the carbon nanosheets of Example 1, when the current density is 0.1 A / g, the capacity of NPS-FC5 is 115.12 mAh / g, and the energy density is 98.35 Wh / kg; when the current density is 20 A / g, the capacity of NPS-FC5 is 56.51 mAh / g, and the energy density is 31.27 Wh / kg.

[0064] Figure 3 is the capacitance change curve of the zinc-ion hybrid capacitor assembled with the product of Example 2.

[0065] Figure 4 is the cycle stability test of the zinc-ion hybrid capacitor assembled with the product of Example 2.

[0066] From Figure 3 and Figure 4As shown, in the zinc-ion hybrid capacitor assembled with the carbon nanosheets of Example 2, when the current density is 0.1 A / g, the capacity of NPS-FC6 is 198.56 mAh / g and the energy density is 167.69 Wh / kg; when the current density is 0.5 A / g, the capacity of NPS-FC6 is 172.14 mAh / g and the energy density is 143.91 Wh / kg; when the current density is 1 A / g, the capacity of NPS-FC6 is 160.77 mAh / g and the energy density is 133.45 Wh / k; when the current density is 5 A / g, the capacity of NPS-FC6 is 136.03 mAh / g and the energy density is 104.90 Wh / kg; when the current density is 20 A / g, the capacity of NPS-FC6 is 119.22 mAh / g and the energy density is 80.92 Wh / kg; at a current density of 5 A / g, after 23,000 cycles, the capacity retention rate is 99.98% and the Coulombic efficiency is 99.98%.

[0067] In the zinc-ion hybrid capacitor assembled with the carbon nanosheets of Example 3, when the current density is 0.1 A / g, the capacity of NPS-FC7 is 162.35 mAh / g and the energy density is 133.27 Wh / kg; when the current density is 20 A / g, the capacity of NPS-FC7 is 86.3 mAh / g and the energy density is 64.26 Wh / kg.

[0068] In the zinc-ion hybrid capacitor assembled with the carbon nanosheets of Comparative Example 1, when the current density is 0.1 A / g, the capacity is 154.97 mAh / g and the energy density is 130.76 Wh / kg; when the current density is 20 A / g, the capacity reaches 48.22 mAh / g and the energy density is 30.84 Wh / kg.

[0069] In the zinc-ion hybrid capacitor assembled with the carbon nanosheets of Comparative Example 2, when the current density is 0.1 A / g, the capacity is 129.45 mAh / g and the energy density is 109.02 Wh / kg; when the current density is 20 A / g, the capacity reaches 34.22 mAh / g and the energy density is 20.19 Wh / kg.

[0070] In the zinc-ion hybrid capacitor assembled with the carbon nanosheets of Comparative Example 3, when the current density is 0.1 A / g, the capacity is 116.44 mAh / g and the energy density is 97.54 Wh / kg; when the current density is 20 A / g, the capacity reaches 26.78 mAh / g and the energy density is 15.82 Wh / kg.

[0071] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the spirit of the design of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing rice husk-based multi-heteroatom doped carbon nanosheets, characterized in that: Here are the steps: The rice husk was washed, carbonized at 500°C for 2 h, then ground to an average particle size of 5 μm, mixed with a 2 mol / L KOH solution, stirred for 9 h, filtered, and dried to obtain pre-carbonized rice husk; Then, 1 g of the pre-carbonized rice husk, 0.5 g of diammonium phosphate, 1 g of thiosalicylic acid, and 6 g of potassium bicarbonate were added to 20 mL of water, and heated at 60° C. for 4 h to obtain a nitrogen-phosphorus-sulfur doped nanosheet precursor; The nitrogen, phosphorus and sulfur doped nanosheet precursor is placed in a magnetic boat in a tubular furnace, heated to 900°C at a heating rate of 5°C / min, kept at a constant temperature for 60 minutes, and then naturally cooled to 20-30°C. The product is taken out, washed with water to remove impurities, dried, and ground to an average particle size of 2μm to obtain the rice husk-based multi-heteroatom doped carbon nanosheet.

2. A rice husk-based multi-heteroatom doped carbon nanosheet obtained according to the preparation method of claim 1.

3. Use of the rice husk-based multi-heteroatom doped carbon nanosheets according to claim 2 in the preparation of zinc ion hybrid capacitors.

4. A method for preparing a zinc ion hybrid capacitor, characterized in that: The following steps are involved: The rice husk-based multi-heteroatom doped carbon nanosheets described in claim 2 are mixed with a PTFE binder, pressed into a film, sliced, and dried to obtain a positive electrode material; zinc foil is used as a negative electrode and a Zn(CF3SO3)2 solution is used as an electrolyte to assemble a button-type zinc ion hybrid capacitor.

5. A zinc ion hybrid capacitor obtained according to the preparation method of claim 4.

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