CN106006634A - Method for one-step synthesis of nitrogen-doped microporous carbon from amino acid-zinc complex - Google Patents

Abstract

The invention discloses a method for one-step synthesis of nitrogen-doped microporous carbon from an amino acid zinc complex. In this method, the zinc complex formed by the coordination of amino acids and zinc salts is used as the carbon precursor. After high-temperature heat treatment at 910°C and above, highly dispersed zinc species at the molecular level are in situ carbon thermally reduced to form simple zinc, which volatilizes from the inside out to form A microporous carbon material containing through-channels. This method not only realizes the doping of nitrogen element, but also the prepared carbon material has a large specific surface area and concentrated micropore distribution. In addition, the preparation method is simple to operate, easy to be implemented in industry and produced in large quantities.

Description

A One-step Synthesis of Nitrogen-doped Microporous Carbons from Amino Acid Zinc Complexes

technical field

The invention belongs to the technical field of porous carbon preparation, and relates to a method for one-step synthesis of nitrogen-doped microporous carbon from amino acid zinc complexes.

Background technique

Carbon materials are widely used as supercapacitor electrode materials due to their high electrochemical conductivity, high thermal stability, controllable pore structure, tunable surface chemical properties, compatibility of composite materials and easy processing. Supercapacitors of carbon-based materials mainly rely on the micropores on the surface of the material as active sites for adsorbing electrolyte ions to form an electric double layer to store energy, especially micropores with a pore size of less than 1 nm play a more important role in the formation of the electric double layer. effect. However, the diffusion performance of electrolyte ions inside the micropores is easily limited, which reduces the utilization of the micropores inside the material, so this type of capacitor generally has the problem of poor rate performance. One of the effective ways to solve such problems is to introduce heteroatoms into the microporous carbon materials, modify the surface chemistry of the carbon materials in a directional manner, adjust the electrical conductivity of the materials, improve the wettability of the materials, and increase the utilization of micropores. Another method is to regulate the pore permeability of micropores to reduce the diffusion resistance of electrolyte ions in them.

At present, the methods for preparing microporous carbon mainly include activation method and template method, and the activation method is divided into physical activation method (using water vapor, CO ₂ and other gases as activators) and chemical activation method (using H ₃ PO ₄ , ZnCl ₂ , KOH, NaOH, etc. are activators). Among them, the zinc chloride activation method is one of the commonly used methods for the preparation of activated carbon. During the activation process, the dehydrogenation of zinc chloride limits the formation of tar and leads to the aromatization of carbon precursors. As the temperature rises to 450-600°C, zinc chloride vaporizes and deposits inside the carbon precursor, and after pickling and water washing to remove zinc chloride, a porous structure activated carbon with a large specific surface area is formed. In the activation method, the activator is randomly distributed in the carbon precursor, and the activation process mainly relies on the interaction between the activator and the carbon precursor to form pores from the outside to the inside, so the resulting pore structure is irregular and the pore penetration is poor. When such materials are used as supercapacitor electrode materials, electrolyte ions are not easy to enter these irregular micropores, resulting in a decrease in the effective utilization of the surface of the electrode material.

The template method is also a commonly used method for preparing microporous carbon materials, but due to the limitation of the pore structure of the template material itself, the prepared carbon materials often have large pore diameters. In addition, it is necessary to use hydrofluoric acid or sodium hydroxide and other environmentally polluting chemical reagents to remove the template, which will undoubtedly increase the preparation cost of carbon materials. On the other hand, in recent years, some researchers have reported the method of using metal-organic frameworks (MOFs) to prepare microporous carbon materials with microporous structure. Although the compound has the advantages of adjustable pore size, large specific surface area and various structures, the product yield of this method is low and it is not easy to prepare on a large scale. In addition, the pore permeability of carbon materials synthesized by this method needs to be improved, which is not conducive to the transmission of electrolyte ions when used as electrode materials.

Based on this, the present invention proposes a method for one-step synthesis of nitrogen-doped microporous carbon from amino acid zinc complexes, relying on the stabilization of functional groups, using the zinc complexes formed by the coordination of amino acids and zinc salts as carbon precursors, and zinc species in The molecular level is highly dispersed in the complex. After high-temperature heat treatment at 910°C and above, the zinc species is in-situ carbon thermally reduced to form zinc element and converted into zinc vapor, and due to the internal pressure, it is dynamically volatilized from the inside to the outside, thus forming a A microporous carbon material with a concentrated pore size distribution through the channels. In addition, amino acids contain abundant amino functional groups, and at the same time realize the doping of nitrogen elements.

Contents of the invention

The purpose of the present invention is to provide a method for one-step synthesis of nitrogen-doped microporous carbon from amino acid zinc complex. In this method, zinc complexes formed by the coordination of amino acids rich in amino groups and carboxyl groups and zinc salts are used as carbon precursors. Under high-temperature inert atmosphere conditions, highly dispersed zinc species generate elemental zinc in situ and volatilize from the inside to the outside to obtain a porous Nitrogen-doped carbon materials with microporous structure. The prepared microporous carbon material is used as an electrode material for a supercapacitor, and has a high specific capacitance value and good cycle stability.

The preparation method of this nitrogen-doped microporous carbon comprises the following steps:

(1) Mix amino acids, zinc salts and water, and dry to obtain a carbon precursor. The carbon precursor is heat-treated at a high temperature of 910°C or higher under an inert atmosphere to form nitrogen-doped micropores with high specific surface area and through-hole channels. carbon.

In order to obtain a carbon material with higher specific surface area, more concentrated pore size distribution and better electrochemical performance, the molar ratio of the amino acid to the zinc salt is 0.2-10:1.

The amino acids include all amino acids, preferably the amino acids are glutamic acid, aspartic acid, histidine, lysine, glycine, alanine, leucine, isoleucine, cysteine, tryptophan , one or more of threonine and arginine. The zinc salt is at least one of zinc chloride, zinc acetate, zinc sulfate, and zinc nitrate.

The inert atmosphere refers to nitrogen or argon atmosphere.

The carbon material obtained by the invention contains nitrogen element, has high specific surface area, and the micropore size distribution is concentrated at 0.5-1.2nm.

The inventiveness of the present invention is embodied in that the present invention uses the zinc complex formed by the coordination of amino acids and carboxyl-rich amino acids and zinc salts as the carbon precursor, wherein the zinc ions are highly dispersed in the carbon precursor due to the coordination. In the process of heat treatment, when the zinc species formed by carbon thermal reduction reaches the boiling point (≥910°C), zinc vapor is formed. Due to the internal pressure, it volatilizes from the inside to the outside and dynamically creates pores, so that it can be synthesized in one step. Atom-doped microporous carbon materials. This method is completely different from the principle of traditional zinc chloride chemical activation. The method proposed by the present invention belongs to physical activation and the temperature is higher (≥910° C.), while the traditional zinc chloride activation belongs to chemical activation and the temperature is between 450-600° C.

The beneficial effect of the present invention is that the present invention uses the zinc complexes formed by the coordination of amino acids rich in amino and carboxyl groups and zinc salts as carbon precursors to form a carbon precursor with a through-hole structure, concentrated micropore pore size distribution, and nitrogen atom doping. Microporous carbon materials. In addition, the method is simple and feasible, and suitable for large-scale production.

Description of drawings

Figure 1 is a transmission electron microscope image (TEM) of the microporous carbon material prepared in Example 1 of the present invention, wherein the molar ratio of L-glutamic acid to zinc chloride is 0.5:1.

Fig. 2 is the nitrogen adsorption curve of the microporous carbon material prepared in Example 1 of the present invention.

Fig. 3 is the pore size distribution curve of the microporous carbon material prepared in Example 1 of the present invention.

Figure 4(a)(b) are the cyclic voltammetry curves and galvanostatic charge-discharge curves of the microporous carbon material prepared in Example 1 of the present invention in a three-electrode system in 6molL ^-1 KOH electrolyte, respectively.

Fig. 5 shows the change of specific capacitance of the microporous carbon material prepared in Example 1 of the present invention in 6mol L ^-1 KOH electrolyte under different current densities.

Fig. 6 is a graph of the long-term cycle performance of the microporous carbon material prepared in Example 1 of the present invention as a supercapacitor electrode material.

Fig. 7 is the leakage current curve of the microporous carbon material prepared in Example 1 of the present invention as the supercapacitor electrode material under the two-electrode system.

Fig. 8 is the self-discharge curve of the microporous carbon material prepared in Example 1 of the present invention as the supercapacitor electrode material under the two-electrode system.

detailed description

The following examples are further illustrations of the present invention, but do not limit the scope of the present invention.

Example 1

This example provides a method for synthesizing nitrogen-doped microporous carbon in one step from an amino acid zinc complex. The complex formed by the coordination of L-glutamic acid rich in amino and carboxyl functional groups and zinc chloride is used as the carbon precursor. Nitrogen-doped microporous carbons with through-channels were obtained by in-situ carbon thermal reduction of highly dispersed zinc species under high-temperature carbonization conditions to simple zinc volatilization from the inside to the outside. The specific operation steps are as follows:

L-glutamic acid and ZnCl ₂ with a molar ratio of 0.5:1 were dissolved in deionized water respectively, and then the two solutions were stirred and mixed evenly, and dried to obtain a carbon precursor.

The dried carbon precursor was placed in a high-temperature furnace with an argon atmosphere, and the temperature was raised to 910°C at a rate of 5°C/min and kept at this temperature for 2 hours to obtain a nitrogen-doped microporous carbon material. Figure 1 is a transmission electron microscope photo of the material, from which it can be seen that it has a rich microporous structure, and the pore size distribution is relatively uniform. Fig. 2 is the nitrogen adsorption isotherm of this material, and this curve is type I distribution, shows that this material contains a large amount of micropores. Its specific surface area is as high as 1203m ² g ^-1 . Figure 3 is the pore size distribution curve of the material, which shows that the pore size distribution of the material is relatively concentrated, mainly in the range of 0.5-1.2nm. Its nitrogen element content is 4.62% through elemental analysis.

This example also analyzed the electrochemical performance of the obtained microporous carbon material as an electrode material for a supercapacitor. Figure 4 is the cyclic voltammetry curve and constant current charge-discharge curve of the microporous carbon material in the three-electrode system in 6mol L ^-1 KOH electrolyte. Figure 4(a) presents a rectangular-like shape, indicating that this material is an ideal electric double layer electrode material. Figure 4(b) The constant current charge and discharge curve is a triangular symmetrical structure, indicating that the material exhibits good capacitive performance. It can be seen from Figure 5 that the material has good rate performance. The specific capacitance is 217F g ^-1 when the current density is 0.5A g ^-1 and 160F g ^{-1 when the current density is 20A g -1 ,} and the capacity retention rate is 74%. And in a two-electrode system with a current density of 1A g ^-1 for 30,000 cycles, the capacity only decays by 9% (Fig. 6). Figure 7 is the leakage current curve of the material measured under the superelectric two-electrode system, and the leakage current is as low as 2.3μA mg ^-1 . Figure 8 shows the self-discharge curve of the material measured under the superelectric two-electrode system. The self-discharge is relatively light, and the voltage drops from 1V to 0.63V after 24 hours, indicating that the supercapacitor assembled with this material has good stability.

Example 2

This example provides a method for synthesizing nitrogen-doped microporous carbon in one step from an amino acid zinc complex. The complex formed by the coordination of L-glutamic acid rich in amino and carboxyl functional groups and zinc chloride is used as the carbon precursor. Nitrogen-doped microporous carbons with through-channels were obtained by in-situ carbon thermal reduction of highly dispersed zinc species under high-temperature carbonization conditions to simple zinc volatilization from the inside to the outside. The specific operation steps are as follows:

L-glutamic acid and ZnCl ₂ with a molar ratio of 2:1 were dissolved in deionized water respectively, and then the two solutions were stirred and mixed evenly, and dried to obtain a carbon precursor.

The dried carbon precursor was placed in a high-temperature furnace with an argon atmosphere, and the temperature was raised to 910°C at a rate of 5°C/min and kept at this temperature for 2 hours to obtain a nitrogen-doped microporous carbon material. The material has a rich microporous structure, its specific surface area is 761m ² g ^-1 , and the pore size distribution is concentrated at 0.5-1.2nm.

Example 3

This example provides a method for synthesizing nitrogen-doped microporous carbon in one step from an amino acid zinc complex. The complex formed by the coordination of L-glutamic acid rich in amino and carboxyl functional groups and zinc acetate is used as the carbon precursor. Nitrogen-doped microporous carbons with through-channels were obtained by in-situ carbon thermal reduction of highly dispersed zinc species under high-temperature carbonization conditions to simple zinc volatilization from the inside to the outside. The specific operation steps are as follows:

L-glutamic acid and Zn(AC) ₂ with a molar ratio of 0.5:1 were dissolved in deionized water respectively, and then the two solutions were stirred and mixed evenly, and dried.

The dried carbon precursor was placed in a high-temperature furnace with an argon atmosphere, and the temperature was raised to 910°C at a rate of 5°C/min and kept at this temperature for 2 hours to obtain a nitrogen-doped microporous carbon material. Its specific surface area is 770 m ² g ^-1 .

Example 4

This example provides a method for synthesizing nitrogen-doped microporous carbon in one step from an amino acid zinc complex. The complex formed by the coordination of L-lysine rich in amino and carboxyl functional groups and zinc chloride is used as the carbon precursor. Nitrogen-doped microporous carbons with through-channels were obtained by in-situ carbon thermal reduction of highly dispersed zinc species under high-temperature carbonization conditions to simple zinc volatilization from the inside to the outside. The specific operation steps are as follows:

Weigh the corresponding mass of L-lysine and ZnCl ₂ with a molar ratio of 1:1 and dissolve them in deionized water respectively, then stir and mix the two solutions evenly, and dry them.

The dried carbon precursor was placed in a high-temperature furnace with an argon atmosphere, and the temperature was raised to 910°C at a rate of 5°C/min and kept at this temperature for 2 hours to obtain a nitrogen-doped microporous carbon material. Its specific surface area is 615 m ² g ^-1 .

Example 5

This example provides a method for synthesizing nitrogen-doped microporous carbon in one step from an amino acid zinc complex. The complex formed by the coordination of L-arginine rich in amino and carboxyl functional groups and zinc chloride is used as the carbon precursor. Nitrogen-doped microporous carbons with through-channels were obtained by in-situ carbon thermal reduction of highly dispersed zinc species under high-temperature carbonization conditions to simple zinc volatilization from the inside to the outside. The specific operation steps are as follows:

Weigh the corresponding mass of L-arginine and ZnCl ₂ with a molar ratio of 1:1 and dissolve them in deionized water respectively, then stir and mix the two solutions evenly, and dry them.

The dried carbon precursor was placed in a high-temperature furnace with an argon atmosphere, and the temperature was raised to 910°C at a rate of 5°C/min and kept at this temperature for 2 hours to obtain a nitrogen-doped microporous carbon material. Its specific surface area is 1117m ² g ^-1 .

Example 6

This example provides a method for synthesizing nitrogen-doped microporous carbon in one step from an amino acid zinc complex. The complex formed by the coordination of L-aspartic acid rich in amino and carboxyl functional groups and zinc chloride is used as the carbon precursor. Nitrogen-doped microporous carbons with through-channels were obtained by in-situ carbon thermal reduction of highly dispersed zinc species under high-temperature carbonization conditions to simple zinc volatilization from the inside to the outside. The specific operation steps are as follows:

The corresponding mass of L-aspartic acid and ZnCl ₂ were weighed and dissolved in deionized water at a molar ratio of 0.5:1, and then the two solutions were stirred and mixed evenly, and dried.

The dried carbon precursor was placed in a high-temperature furnace with an argon atmosphere, and the temperature was raised to 910°C at a rate of 5°C/min and kept at this temperature for 2 hours to obtain a nitrogen-doped microporous carbon material. Its specific surface area is 1196m ² g ^-1 .

Comparative Example 1

In this example, glutamic acid was used as a carbon source, and it was heat-treated by the same method as in the above example to obtain a nitrogen-doped carbon material. Nitrogen adsorption results show that its specific surface area is only 39m ² g ^-1 .

Claims (5)

1. A method for synthesizing nitrogen-doped microporous carbons from amino acid zinc complexes in one step, characterized in that amino acids, zinc salts are mixed with water, and dried to obtain amino acid zinc complexes, which are used as carbon precursors in an inert atmosphere , after heat treatment at a high temperature of 910°C or higher, a nitrogen-doped microporous carbon with a concentrated pore size distribution containing through channels is formed. 2. A method for one-step synthesis of nitrogen-doped microporous carbon from amino acid zinc complexes according to claim 1, characterized in that the molar ratio of amino acid to zinc salt is 0.2-10:1. 3. a kind of method for synthesizing nitrogen-doped microporous carbon from amino acid zinc complex one-step according to claim 1, it is characterized in that, described amino acid is glutamic acid, aspartic acid, histidine, lysine One or more of acid, glycine, alanine, leucine, isoleucine, cysteine, tryptophan, threonine and arginine. 4. a kind of method from amino acid zinc complex one-step synthetic nitrogen-doped microporous carbon according to claim 1, is characterized in that, described zinc salt is zinc chloride, zinc acetate, zinc sulfate, zinc nitrate in one or several. 5. A method for one-step synthesis of nitrogen-doped microporous carbon from amino acid zinc complexes according to claim 1, wherein the inert atmosphere refers to nitrogen or argon atmosphere.