阅读说明：本技术 一种原位氮掺杂多孔碳材料及其制备方法 (In-situ nitrogen-doped porous carbon material and preparation method thereof ) 是由 庞思平 李佳哲 孙成辉 严致远 宋建伟 于 2020-06-17 设计创作，主要内容包括：本发明涉及一种原位氮掺杂多孔碳材料的制备方法,属于材料科学技术领域。以原位合成的镁铝水滑石为辅助造孔剂,采用酚类或甲基取代酚、甲醛同含氮单体共聚,一锅法水热生成氮掺杂碳前驱体,然后经高温焙烧和酸处理得到多孔碳材料。通过控制酚醛的摩尔比、含氮聚合单体的用量、镁铝和酚聚合单体的比例、水热反应条件,实现了氮掺杂多孔碳的比表面积、孔径分布和掺氮量的调控；制备得到的材料残炭率高、孔径分布范围窄。所述方法可避免使用氢氟酸,可操作性强,相对环境友好。(The invention relates to a preparation method of an in-situ nitrogen-doped porous carbon material, belonging to the technical field of material science. The method comprises the steps of taking in-situ synthesized magnesium-aluminum hydrotalcite as an auxiliary pore-forming agent, copolymerizing phenols or methyl substituted phenols, formaldehyde and nitrogen-containing monomers, hydrothermally generating a nitrogen-doped carbon precursor by a one-pot method, and then roasting at high temperature and carrying out acid treatment to obtain the porous carbon material. The regulation and control of the specific surface area, the pore size distribution and the nitrogen doping amount of the nitrogen-doped porous carbon are realized by controlling the molar ratio of the phenolic aldehyde, the dosage of the nitrogen-containing polymeric monomer, the proportion of the magnesium-aluminum and the phenol polymeric monomer and the hydrothermal reaction condition; the prepared material has high carbon residue rate and narrow pore size distribution range. The method can avoid using hydrofluoric acid, has strong operability and is relatively environment-friendly.)

1. An in-situ nitrogen-doped porous carbon material, characterized in that: the specific surface area of the in-situ nitrogen-doped porous carbon material is more than 800m²The nitrogen exists in the form of graphite nitrogen, pyridine nitrogen and pyrrole nitrogen, wherein the average pore diameter is 15-35 nm, the nitrogen content is 1-10 wt%.

2. A method of preparing the in-situ nitrogen-doped porous carbon material of claim 1, wherein: the method comprises the following steps:

(1) preparing a precursor: preparing a mixed salt solution from soluble magnesium salt and soluble aluminum salt according to the molar ratio of magnesium element to aluminum element of 3:2, preparing a mixed alkali solution from sodium carbonate and sodium hydroxide, dropwise adding the mixed alkali solution into the mixed salt solution, then adding a formaldehyde aqueous solution and a compound I, stirring for 1-3 h, adjusting the pH to 7.5-11 with the sodium hydroxide solution, and heating to 30-50 ℃ for reaction for 1-3 h; after the reaction is finished, adding a nitrogen-containing polymerization monomer, heating to 70-100 ℃, carrying out a hydrothermal reaction for 12-48 h, drying at 110-150 ℃ for 8-24 h after the reaction is finished, and grinding to obtain a precursor;

wherein the addition amount of the mixed alkali solution enables magnesium and aluminum in the mixed salt solution to be completely precipitated, and the ratio of the total mole number of magnesium salt and aluminum salt to the mole number of the compound I is 1: 0.5-1: 2; the molar ratio of the compound I to formaldehyde is 1: 1-1: 3; the molar ratio of the nitrogen-containing polymeric monomer to the compound I is 0.1-0.4: 1; the nitrogenous polymeric monomer is dicyandiamide, hexamethylenetetramine or melamine; the structural formula of the compound I is as follows:

(2) and (3) high-temperature roasting: roasting the precursor under the protection of protective gas, firstly heating to 150-200 ℃ at a heating rate of less than or equal to 2 ℃/min, and preserving heat for 1-3 h, and then heating to 600-1400 ℃ at a heating rate of 5-10 ℃/min, and preserving heat for 1-6 h; cooling to room temperature to obtain a nitrogen-doped carbon material containing metal oxide;

(3) acid treatment: grinding the roasted nitrogen-doped material containing the metal oxide into powder, adding hydrochloric acid, sulfuric acid or nitric acid into the powder at room temperature, stirring and dispersing for 2-10 h, and washing and drying a filter cake obtained by filtering to obtain the in-situ nitrogen-doped porous carbon material.

3. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: the molar ratio of the compound I to formaldehyde in the step (1) is 1: 1.5-1: 2.

4. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: in the step (1), the hydrothermal reaction temperature is 80-90 ℃, and the reaction time is 18-24 h.

5. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: the molar ratio of the nitrogen-containing polymeric monomer to the compound I in the step (1) is 0.2-0.3: 1.

6. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: in the step (1), the drying temperature is 110-120 ℃, and the drying time is 10-16 h.

7. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: in the step (1), the soluble magnesium salt is more than one of magnesium chloride, magnesium nitrate and magnesium sulfate; the soluble aluminum salt is more than one of aluminum chloride, aluminum nitrate and aluminum sulfate.

8. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: in the step (2), the temperature is increased to 160-180 ℃ at a temperature increase rate of less than or equal to 2 ℃/min.

9. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: in the step (2), the temperature is increased to 800-1000 ℃ at the temperature increase rate of 6-8 ℃/min.

10. The method of claim 2, wherein the in-situ nitrogen-doped porous carbon material comprises: in the step (3), the drying temperature is 80-120 ℃, and the drying time is 2-8 h.

Technical Field

The invention relates to an in-situ nitrogen-doped porous carbon material and a preparation method thereof, belonging to the technical field of material science.

Background

The porous carbon material has the characteristics of low cost, light weight, no toxicity, surface chemical inertia, high temperature resistance, acid and alkali resistance, high mechanical stability, good conductivity, adsorptivity, large specific surface area, pore volume and the like, and shows huge application potential in the fields of gas adsorption, hydrogen storage, catalysis, fuel cells, electrochemical double-layer capacitors and the like, thereby being attracted by much attention.

The porous carbon material prepared by taking phenolic resin as a carbon source and not adopting an auxiliary pore-forming technology is mainly microporous, has small specific surface area which is generally lower than 100m²G, pore volume less than 0.1cm³The catalyst has no practical application value in the fields of fuel cells and catalysis. In order to improve the specific surface area, conductivity and pore size distribution of the porous carbon, an auxiliary pore-forming method is often adopted to improve the pore size of the porous carbon, and nitrogen atoms are introduced into the porous carbon to improve the wettability, biocompatibility and conductivity of the material, so that the performance of the porous carbon in the fields of super-capacitance, catalysis and the like is improved.

The preparation method of the nitrogen-doped porous carbon generally comprises two methods: one method is to prepare porous carbon and then introduce nitrogen atoms by a method such as dip firing or chemical deposition, but this method is generally low in nitrogen doping content and the doping amount is difficult to control. The other method is the template method, which is the most mature and efficient method for preparing porous carbon. The template method is further classified into a hard template method and a soft template method. The corresponding porous carbon materials can be obtained by taking silicon oxides with various structures as templates, such as ordered porous carbon synthesized by taking MCM-48, hexagonal aluminosilicate and the like as templates and phenolic resin as a carbon source, wherein the aperture is 0.6-2 nm; porous molecular sieves such as SBA-15, CMK-5 and the like are used as hard templates, and porous carbon materials with ordered pore canals can be synthesized. However, no matter the silicon oxide is used as a soft template or a hard template, the working procedure is long in the post-treatment, and hydrofluoric acid is required to etch and remove template agents such as silicon dioxide, so that the toxicity is high.

Disclosure of Invention

In view of the above, the present invention provides an in-situ nitrogen-doped porous carbon material and a preparation method thereof. The method comprises the steps of taking magnesium-aluminum hydrotalcite synthesized in situ as an auxiliary pore-forming agent, copolymerizing phenols or methyl substituted phenols and formaldehyde with nitrogen-containing monomers, hydrothermally generating a nitrogen-doped carbon precursor by a one-pot method, and then roasting at high temperature and carrying out acid treatment to obtain the porous carbon material. The regulation and control of the specific surface area, the pore size distribution and the nitrogen doping amount of the nitrogen-doped porous carbon can be realized by controlling the molar ratio of the phenolic aldehyde, the dosage of the nitrogen-containing polymeric monomer, the proportion of the magnesium-aluminum and the phenol polymeric monomer and the hydrothermal reaction condition; the prepared material has high carbon residue rate and narrow pore size distribution range. The preparation method can avoid using hydrofluoric acid, has strong operability and is relatively environment-friendly. The material can be used as a catalyst carrier and can also be applied to the preparation of electrode materials.

In order to achieve the above object, the technical solution of the present invention is as follows.

An in-situ nitrogen-doped porous carbon material, the specific surface area of which is more than 800m²The nitrogen exists in the form of graphite nitrogen, pyridine nitrogen and pyrrole nitrogen, wherein the average pore diameter is 15-35 nm, the nitrogen content is 1-10 wt%.

The invention discloses a preparation method of an in-situ nitrogen-doped porous carbon material, which comprises the following steps:

(1) preparing a precursor: preparing a mixed salt solution from soluble magnesium salt and soluble aluminum salt according to the molar ratio of magnesium element to aluminum element of 3:2, preparing a mixed alkali solution from sodium carbonate and sodium hydroxide, slowly dropwise adding the mixed alkali solution into the mixed salt solution, then adding a formaldehyde aqueous solution and a compound I, stirring for 1-3 h, adjusting the pH to 7.5-11 with the sodium hydroxide solution, and heating to 30-50 ℃ for reaction for 1-3 h; after the reaction is finished, adding a nitrogen-containing polymerization monomer, heating to 70-100 ℃, carrying out a hydrothermal reaction for 12-48 h, drying at 110-150 ℃ for 8-24 h after the reaction is finished, and grinding to obtain a precursor;

wherein the addition amount of the mixed alkali solution enables magnesium and aluminum in the mixed salt solution to be completely precipitated, and the ratio of the total mole number of magnesium salt and aluminum salt to the mole number of the compound I is 1: 0.5-1: 2; the molar ratio of the compound I to formaldehyde is 1: 1-1: 3; the molar ratio of the nitrogen-containing polymeric monomer to the compound I is 0.1-0.4: 1; the nitrogenous polymeric monomer is dicyandiamide, hexamethylenetetramine or melamine; the structural formula of the compound I is as follows:

(2) and (3) high-temperature roasting: roasting the precursor under the protection of protective gas, firstly heating to 150-200 ℃ at a heating rate of less than or equal to 2 ℃/min, and preserving heat for 1-3 h, and then heating to 600-1400 ℃ at a heating rate of 5-10 ℃/min, and preserving heat for 1-6 h; cooling to room temperature to obtain a nitrogen-doped carbon material containing metal oxide;

(3) acid treatment: grinding the roasted nitrogen-doped material containing the metal oxide into powder, adding hydrochloric acid, sulfuric acid or nitric acid into the powder at room temperature, stirring and dispersing for 2-10 h, and washing and drying a filter cake obtained by filtering to obtain the in-situ nitrogen-doped porous carbon material.

Preferably, the molar ratio of the compound I to formaldehyde in the step (1) is 1: 1.5-1: 2.

Preferably, the hydrothermal reaction temperature in the step (1) is 80-90 ℃, and the reaction time is 18-24 h.

Preferably, the molar ratio of the nitrogen-containing polymeric monomer to the compound I in the step (1) is 0.2-0.3: 1.

Preferably, in the step (1), the drying temperature is 110-120 ℃, and the drying time is 10-16 h.

Preferably, the soluble magnesium salt in the step (1) is more than one of magnesium chloride, magnesium nitrate and magnesium sulfate; the soluble aluminum salt is more than one of aluminum chloride, aluminum nitrate and aluminum sulfate.

Preferably, in the step (2), the temperature is increased to 160-180 ℃ at a temperature increase rate of less than or equal to 2 ℃/min.

Preferably, in the step (2), the temperature is increased to 800-1000 ℃ at a temperature increase rate of 6-8 ℃/min.

Preferably, in the step (3), the drying temperature is 80-120 ℃, and the drying time is 2-8 h.

Advantageous effects

In the method, in the precursor process, the soluble magnesium salt and the soluble aluminum salt can generate a hydrotalcite structure through hydrothermal crystallization. The hydrotalcite structure has rich hydroxyl groups on the surface, has a regular layered structure, is a sheet-like stacked mesoporous structure, has relatively open pore channels, and has a nano-scale (generally 1nm) interlayer spacing, wherein a polymerized monomer diffuses into the interlayer structure of the hydrotalcite and undergoes a polymerization reaction at subsequent temperature rise. Meanwhile, the sheet structure of the hydrotalcite can be uniformly dispersed in a reaction system, and a good pore-forming effect is achieved. In the high-temperature roasting process, the hydrotalcite is decomposed to generate corresponding oxides, and releases micromolecular substances to play a role in assisting pore formation. The generated oxide is removed by acid cleaning, and the aim of pore forming is further achieved.

Specifically, the method comprises the following steps: in the step (1), the polymerization reaction speed of the phenolic aldehyde is very low under the room temperature condition, and in the process of preparing the precursor, the precipitate is uniformly distributed in the aqueous solution of the phenolic aldehyde, and meanwhile, phenolic aldehyde molecules can also diffuse into hydrotalcite layers. When the pH value is adjusted to 7.5-11 and the temperature is increased to 30-50 ℃, the phenolic aldehyde starts to react, and the compound I and the aldehyde do not react with the hydrotalcite at the stage. The hydrotalcite is dispersed in an aqueous solution of the compound i and the aldehyde, and the compound i and the aldehyde are diffused into the hydrotalcite layers. If phenolic resin is used as a carbon source at this stage, the pore-forming agent cannot be dispersed in the resin, and the carbon obtained after roasting has a small specific surface area and is mainly microporous. The compound I and aldehyde generate hydroxyl ortho-position or para-position substituted methylol under the base catalysis, and the reaction can be carried out at a lower reaction temperature, so that the initial reaction temperature is controlled to be 30-50 ℃, the reaction time is 1-3 h, the preferable reaction time is 2h, and the molar ratio of the compound I to the aldehyde is generally 1: 1-1: 3, and is preferably 1: 1.5-1: 2. After the prepolymerization is finished, adding a nitrogen-containing polymeric monomer, wherein the nitrogen content of the finally prepared porous carbon can be changed by changing the dosage of the nitrogen-containing polymeric monomer, but when the molar ratio of the nitrogen-containing polymeric monomer to the compound I is more than 0.4:1, excessive nitrogen-containing monomer is dissociated in the polymerization stage and cannot play a role in nitrogen doping. The temperature is raised to 70-100 ℃, the color of the solution gradually becomes dark, and gel formed by copolymerization of the compound I, aldehyde and the nitrogen-containing polymeric monomer is formed, the gel time is related to the pH value of the system and the reaction temperature, the alkalinity is strong, the reaction temperature is high, and the gel time is short. Typically, as the temperature rises to 80 ℃, the gel is completed within a few minutes. The second stage of polymerization is dehydration and formaldehyde removal among hydroxymethyl phenol molecules, the molecular weight of the polymer is continuously increased in the second stage, in order to control the molecular weight and avoid the generation of thermosetting resin, the hydrothermal reaction temperature is 70-100 ℃, and the optimal temperature is 80-90 ℃; the hydrothermal reaction time is 12-48 h, and formaldehyde is generated in the hydrothermal reaction process. After the hydrothermal reaction is finished, the temperature is raised, and the water is evaporated until the water is dried to obtain dark red xerogel.

In the step (2), the carbon precursor shrinks during the roasting process, and releases residual moisture inside, so that the temperature rise rate is not too high when the temperature is required to be below 200 ℃ in order to maintain the shape of the precursor, and the carbon precursor is kept for a period of time, raised to the target temperature and kept for several hours. In the roasting process, the removal of small molecules and the decomposition of hydrotalcite play a role of pore formation, and the pores are mainly micropores and mesopores. And after roasting, cooling to room temperature to obtain the nitrogen-doped carbon material containing the metal oxide.

In the step (3), the roasted product is treated with an acid to fully decompose residual carbonate, metal oxides generated by decomposition and the like, and simultaneously, the function of activating the carbon surface is achieved, and the wettability and the coordination performance of the carbon are improved. Nitric acid is generally preferred.

Drawings

FIG. 1 is a schematic pore-forming diagram of the method of the present invention.

FIG. 2 is a graph showing the physical adsorption curve and the pore size distribution of the final product in example 1.

FIG. 3 shows the X-ray photoelectron spectroscopy (XPS) characterization of the final product of example 1.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

(1) In order to characterize the specific surface area, pore volume, pore diameter and pore diameter distribution of the final product, N of the samples was carried out in an Autosorb-type gas adsorber produced by Quantachrome, USA₂Adsorption-desorption analysis. Before measurement, the sample needs to be degassed at 180 ℃ for 180min, and the test conditions are as follows: n is a radical of₂As adsorbate, He is a carrier gas.

(2) To examine the chemical composition of the surface of the final product and the chemical state of each element, XPS analysis of samples was performed on an AXIS ULTRA DLD spectrometer manufactured by Kratos. The excitation light source is Al target K α radiation source (h ν 1486.6eV), and the binding energy is corrected based on the C1s peak (284.6 eV).

(3) As shown in FIG. 1, hydrotalcite-assisted pore formation is adopted in the method described in the following examples, wherein a black layer is a hydrotalcite structure, an oxide is generated after calcination, and a porous structure is generated after acid treatment of a black irregular particle part in the figure.