Lignin-based ultrathin porous carbon material loaded with metal-sulfur coordination structure and preparation method and application thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF CHEM IND OF FOREST PROD CHINESE ACAD OF FORESTRY
- Filing Date
- 2026-04-02
- Publication Date
- 2026-06-19
Smart Images
Figure CN122233355A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalytic functional materials technology, specifically to a lignin-based ultrathin porous carbon material with a metal-sulfur coordination structure and its preparation method, and to the application of this material in electrochemical energy conversion, catalytic synthesis and organic electrosynthesis. Background Technology
[0002] Functional carbon materials possess excellent electrical conductivity, chemical stability, and structural tunability, and are relatively inexpensive, thus showing promising applications in electrochemical energy conversion and organic electrosynthesis. To enhance electrochemical reactivity and selectivity, current techniques typically introduce metallic active components into carbon supports, particularly through coordination interactions between metals and heteroatoms to construct atomically or highly dispersed active structures. Among these, metal-sulfur coordination structures have attracted significant attention due to their ability to influence the electronic structure of the metal center and the adsorption behavior of reaction intermediates.
[0003] Biomass-derived carbon materials, especially lignin-derived carbon materials, are widely available, renewable, and rich in oxygen-containing functional groups, making them important precursors for constructing functional carbon materials. However, lignin molecules have complex structures, and their dissolution and aggregation behaviors are easily affected by pH and ionic environments. Achieving three-dimensional network construction of lignin precursors under relatively simple process conditions, and further obtaining ultrathin, porous, and three-dimensionally interconnected carbon framework structures, remains challenging. Existing construction methods typically rely on external hard templates or multi-step pore-forming processes, which are cumbersome, costly, and involve complex post-processing. Furthermore, during pyrolysis and carbonization, carbon layers are prone to stacking and densification, leading to damaged pore structures and insufficient exposure of active sites, thus affecting mass transfer processes and site utilization efficiency. Simultaneously, metal species are prone to migration and aggregation, potentially forming crystalline metal or crystalline metal sulfide particles, resulting in disruption of the metal-sulfur coordination structure, decreased active site density, and reduced stability. Therefore, there is still a lack of effective technical solutions that are simple, scalable, and reproducible in order to construct a porous carbon framework while suppressing metal crystallization and agglomeration, and to form a stable, highly dispersed metal-sulfur coordination structure. Summary of the Invention
[0004] The purpose of this invention is to provide a lignin-based ultrathin porous carbon material with a metal-sulfur coordination structure, its preparation method, and its applications. This addresses the problems in existing lignin-based carbon materials, such as reliance on additional templates or multi-step pore-forming processes, complex preparation procedures, and the tendency for metal species to migrate and aggregate during pyrolysis and carbonization, making it difficult to simultaneously achieve porous framework construction and stable metal-sulfur coordination structure formation. This method is simple, suitable for large-scale preparation, and the resulting material can be used in electrochemical energy conversion, catalytic synthesis, and organic electrosynthesis.
[0005] The technical solution adopted in this invention is as follows: A method for preparing a lignin-based ultrathin porous carbon material with a metal-sulfur coordination structure, comprising the following steps: dissolving or dispersing lignin or its modified lignin under alkaline conditions and then acidifying it to form a three-dimensional network, and generating inorganic salt components in situ through acid-base neutralization; adding a metal source and a sulfur-containing precursor to the resulting system, loading it into the three-dimensional network; freeze-drying the obtained precursor to form a leached salt microcrystalline structure within the three-dimensional network; subsequently pyrolyzing and carbonizing the freeze-dried precursor; and leaching and / or washing the pyrolysis product to remove the salt microcrystalline structure, thereby obtaining the lignin-based ultrathin porous carbon material with a metal-sulfur coordination structure.
[0006] Furthermore, the lignin is one or more of alkali lignin, enzymatically hydrolyzed lignin, and sulfate lignin; the modified lignin is one or more of carboxylated lignin, sulfonated lignin, oxidized lignin, hydroxymethylated lignin, etherified lignin, or esterified lignin.
[0007] Furthermore, the acidification adjustment brings the pH of the system to 3-6, preferably 4-5.
[0008] Furthermore, the in-situ generated inorganic salt component comprises one or more of sulfates, chlorides, and / or nitrates, and forms a salt microcrystalline structure that can be subsequently leached or washed away during freeze-drying.
[0009] Furthermore, the leaching and / or washing treatment includes water washing, acid washing, or a combination thereof, to remove the salt microcrystalline structure.
[0010] Furthermore, the metal source is selected from one or more of the chloride, nitrate, sulfate, and acetate salts of Cu, Fe, Co, Ni, Mn, Zn, Mo, W, Ag, Pd, Pt, Au, or Sn.
[0011] Furthermore, the sulfur-containing precursor is selected from one or more of thiophenes, thiazoles, thioethers, thiols, or thioureas.
[0012] Furthermore, the pyrolysis carbonization is carried out under an inert atmosphere and / or a reducing atmosphere, and the pyrolysis temperature is 700–900 °C.
[0013] Furthermore, the lignin-based ultrathin porous carbon material obtained by the above preparation method consists of a porous carbon framework composed of three-dimensionally interconnected ultrathin pleated carbon nanosheets, with metal dispersed in the porous carbon framework in the form of a metal-sulfur coordination structure.
[0014] Furthermore, the lignin-based ultrathin porous carbon material with a supported metal-sulfur coordination structure is applied in electrochemical energy conversion, catalytic synthesis, electro-oxidation of small organic molecules, electro-reduction of nitrates, and electrocatalytic CN coupling synthesis.
[0015] Compared with the prior art, the advantages of the present invention are as follows:
[0016] (1) The process is simple and suitable for large-scale preparation. The present invention uses lignin or modified lignin as carbon source and achieves the construction of lignin-based porous carbon skeleton and the formation of metal-sulfur coordination structure through the process of "alkaline dissolution or dispersion - acidification regulation - freeze drying - pyrolysis carbonization - leaching and / or washing treatment". No additional complex external templates are required. The process is relatively simple and suitable for large-scale preparation.
[0017] (2) Three-dimensional interconnected ultrathin porous framework, which facilitates mass transfer and site exposure. In this invention, inorganic salt components are freeze-dried to form leached salt microcrystal structures within a three-dimensional network, and are removed during subsequent leaching and / or washing processes. This facilitates the formation of a three-dimensionally interconnected ultrathin pleated porous carbon framework, which is beneficial for the exposure of active sites and mass transfer during the reaction process.
[0018] (3) The metal-sulfur coordination structure provides stable anchoring and inhibits metal aggregation and crystallization. The present invention introduces a sulfur-containing precursor during the preparation process, so that the metal and sulfur form a metal-sulfur coordination structure, which is beneficial to inhibiting the migration, agglomeration and crystallization of metal species during pyrolysis, thereby promoting the dispersion of metal species and the stability of the material structure.
[0019] (4) The application direction is clear and it is suitable for a variety of electrocatalytic processes. The lignin-based ultrathin porous carbon material obtained by this invention can be applied to processes such as electrochemical energy conversion, catalytic synthesis, electro-oxidation of small organic molecules, electro-reduction of nitrates, and electrocatalytic CN coupling synthesis. Attached Figure Description
[0020] Figure 1 The image shows a scanning electron microscope (SEM) image of the material obtained in Example 1. Figure 2 The image shows a transmission electron microscope (TEM) image of the material obtained in Example 1. Figure 3 High-angle annular dark-field scanning transmission electron microscope (HAADF–STEM) image of the material obtained in Example 1; Figure 4 The X-ray diffraction (XRD) patterns of the material obtained in Example 1 before and after washing are shown. Detailed Implementation
[0022] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples and application examples.
[0023] Example 1: Preparation of lignin-based ultrathin porous carbon material (Cu–S@LC) supported on Cu–S coordination structure
[0024] First, carboxylated lignin (KL–COOH, 1.0 g) was dispersed in deionized water (20 mL), followed by the addition of NaOH (0.15 g). The mixture was magnetically stirred at room temperature until the lignin was completely dissolved, resulting in a homogeneous solution. Under continuous stirring, the pH of the solution was adjusted to 4–5 by slow dropwise addition of 2.0 M H₂SO₄ to form a three-dimensional network precursor of lignin. A copper salt solution was prepared by dissolving CuCl₂·2H₂O (26.8 mg, 0.157 mmol) in deionized water (1.0 mL), and this solution was slowly added dropwise to the lignin dispersion system under stirring. The mixture was then stirred at room temperature for 3 h to ensure sufficient dispersion of copper ions. Thiophene (400 μL) was then added as a sulfur source, and the reaction was continued with stirring at room temperature for another 3 h. After the reaction, the resulting suspension was lyophilized to obtain a solid precursor. The precursor was placed in a tube furnace and incubated at 5 °C·min⁻¹ under a N₂ atmosphere. 1 The temperature was increased to 800 °C at a rising rate and held for 3 h. After natural cooling to room temperature, the resulting black solid was collected. The solid was thoroughly washed with deionized water to remove residual soluble inorganic salts from the pyrolysis process until the pH of the filtrate was close to neutral. Finally, it was dried to obtain the target material Cu–S@LC.
[0025] Scanning electron microscopy (SEM) results show that Cu–S@LC exhibits a three-dimensional interconnected, wrinkled, ultrathin nanosheet network structure with open pores. Figure 1 Transmission electron microscopy (TEM) further revealed that the sample consisted of ultrathin sheets, and no obvious large-particle crystalline metal / metal sulfide nanoparticles were observed. Figure 2 High-angle annular dark-field scanning transmission electron microscopy (HAADF–STEM) reveals dispersed, isolated bright spots uniformly distributed on a carbon substrate, indicating that the metal species are in a highly dispersed state. Figure 3 Before washing, X-ray diffraction (XRD) revealed crystalline diffraction peaks caused by soluble salt / salt template. After washing, these peaks significantly weakened or disappeared, with amorphous carbon dispersion peaks dominating. This indicates that the salt microcrystalline components were removed after washing, and no significant strong crystalline peaks of metal sulfides were observed in the sample.
[0026] Example 2: Preparation of Cu–S@LC materials with different types of lignin
[0027] Hydroxymethylated lignin (1.0 g) was dispersed in deionized water (20 mL), and NaOH (0.15 g) was added and magnetically stirred at room temperature until completely dissolved. Then, 2.0 M H₂SO₄ was added dropwise under continuous stirring to slowly adjust the pH to 4–5, forming a stable lignin dispersion system. CuCl₂·2H₂O (26.8 mg, 0.157 mmol) was dissolved in deionized water (1.0 mL) and added dropwise to the above system, stirred at room temperature for 3 h. Thiophene (400 μL) was then added and stirring continued for 3 h. After the reaction was complete, the solid precursor was lyophilized and then subjected to a reaction at 5 °C·min⁻¹ under a N₂ atmosphere. 1 The sample was heated to 800 °C and held for 3 h. After cooling, it was thoroughly washed with deionized water until the pH of the filtrate was close to neutral and then dried to obtain the sample. Morphological and structural characterization showed that the obtained sample still exhibited a three-dimensional interconnected ultrathin folded lamellar structure, and no obvious large crystalline metal or metal sulfide particles were observed.
[0028] Example 3: Preparation of Cu–S@LC materials at different pyrolysis temperatures
[0029] The precursor preparation and freeze-drying steps were completed according to the method in Example 1 to obtain a solid precursor. The precursor was placed in a tube furnace and freeze-dried at 5 °C / min under a N2 atmosphere. 1 The samples were heated to 700 °C or 900 °C and held for 3 h, respectively. After cooling, they were thoroughly washed with deionized water until the pH of the filtrate was close to neutral and then dried to obtain the corresponding samples. Morphological and structural characterization showed that the obtained samples still exhibited a three-dimensional interconnected ultrathin folded lamellar structure, and no obvious large crystalline metal or metal sulfide particles were observed, indicating that high dispersion loading of metal species can still be achieved in the 700–900 °C range.
[0030] Example 4: Preparation of M–S@LC materials with different metal types
[0031] Carboxylated lignin (KL–COOH, 1.0 g) was dispersed in deionized water (20 mL), and NaOH (0.15 g) was added and stirred at room temperature until completely dissolved. Then, 2.0 M H₂SO₄ was added dropwise to adjust the pH to 4–5 to form a stable dispersion. NiCl₂·6H₂O was dissolved in deionized water (1.0 mL) at a metal ion molar ratio of 0.157 mmol and added dropwise to the above system, and stirred at room temperature for 3 h. Thiophene (400 μL) was added and stirring continued for 3 h. The mixture was then lyophilized to obtain a solid precursor, which was then subjected to a reaction at 5 °C·min⁻¹ under a N₂ atmosphere. 1The temperature was raised to 800 °C and held for 3 h. After cooling, the sample was washed with deionized water until the pH of the filtrate was close to neutral and then dried to obtain the sample. Morphological and structural characterization showed that the obtained sample still exhibited a three-dimensional interconnected ultrathin folded lamellar structure, and no obvious large crystalline metal or metal sulfide particles were observed. This indicates that the method of the present invention is applicable to the construction of lignin-based ultrathin porous carbon materials with metal-sulfur coordination structures using different metal sources.
[0032] Example 5: Preparation of Cu–S@LC materials with different Cu salt types
[0033] Carboxylated lignin (KL–COOH, 1.0 g) was dispersed in deionized water (20 mL), and NaOH (0.15 g) was added and stirred at room temperature until completely dissolved. 2.0 M H₂SO₄ was added dropwise to adjust the pH to 4–5 to form a stable dispersion. Cu(NO₃)₂·3H₂O was then dissolved in Cu… 2 0.157 mmol of thiophene was dissolved in 1.0 mL of deionized water and added dropwise to the above system. The mixture was stirred at room temperature for 3 h. Then, 400 μL of thiophene was added and stirring continued for another 3 h. After the reaction was complete, the mixture was lyophilized and dried at 5 °C·min⁻ under a N₂ atmosphere. 1 The sample was heated to 800℃ and held for 3 h. After cooling, it was washed with water until the pH of the filtrate was close to neutral and then dried to obtain the sample. Morphological and structural characterization showed that the obtained sample still exhibited a three-dimensional interconnected ultrathin folded lamellar structure. No obvious large crystalline metal or metal sulfide particles were observed, indicating that different copper salt precursors can be used to construct stable Cu–S coordination structure loading structures.
[0034] Example 6: Preparation of Cu–S@LC materials with different sulfur source types
[0035] Carboxylated lignin (KL–COOH, 1.0 g) was dispersed in deionized water (20 mL), and NaOH (0.15 g) was added and stirred at room temperature until completely dissolved. 2.0 M H₂SO₄ was added dropwise to adjust the pH to 4–5 to form a stable dispersion. CuCl₂·2H₂O (26.8 mg, 0.157 mmol) was dissolved in deionized water (1.0 mL) and added dropwise to the above system, and stirred at room temperature for 3 h. Thiazole (355 μL, approximately 426 mg, 5.00 mmol) was then added as a sulfur source, and stirring continued for 3 h. After the reaction was complete, the mixture was lyophilized and dried under N₂ atmosphere at 5 °C·min⁻¹. 1 The sample was heated to 800 °C and held for 3 h. After cooling, it was washed with water until the pH of the filtrate was close to neutral and then dried to obtain the sample. Morphological and structural characterization showed that the obtained sample still exhibited a three-dimensional interconnected ultrathin folded lamellar structure. No obvious large crystalline metal or metal sulfide particles were observed, indicating that this method is applicable to the construction of metal-sulfur coordination structures using different types of sulfur-containing precursors.
[0036] Application Example 1: Electrocatalytic application of Cu–S@LC in the reduction of nitrite to prepare cyclohexanone oxime
[0037] The Cu–S@LC material prepared in Example 1 was dispersed in an ethanol / deionized water mixed solvent, and Nafion solution was added as a binder. The dispersion was ultrasonically performed to form a catalyst ink, which was then drop-coated onto a conductive substrate (such as carbon paper or carbon cloth) and dried to serve as the working electrode. An electrochemical reaction was carried out using a diaphragm-supported two-chamber electrolytic cell, with a pretreated Nafion 117 membrane separating the anode and cathode chambers. In a standard three-electrode system, the electrode loaded with Cu–S@LC was used as the working electrode, a platinum sheet or graphite rod as the counter electrode, and Hg / HgO as the reference electrode. The potential was converted to a reversible hydrogen electrode (RHE). 0.1 M KHCO3 electrolyte was added to the cathode chamber, along with nitrite (NO2⁻, 0.1 mM) and cyclohexanone (CYC, 50 mM). Electrolysis was performed at room temperature within a potential range of −0.6 to −1.2 V vs. RHE for 0.5 h. After the reaction, the electrolyte in the cathode chamber was collected, and the cyclohexanone oxime was qualitatively and quantitatively analyzed by high-performance liquid chromatography (HPLC). The yield and Faradaic efficiency were calculated accordingly. The test results showed that the cyclohexanone oxime product could be detected and quantified under the above conditions, indicating that Cu–S@LC can drive the electroreduction of nitrite and C–N coupling with cyclohexanone, thereby realizing the electrosynthesis of cyclohexanone oxime (Table 1).
[0038] Table 1. Results of electrosynthesis performance tests of cyclohexanone oxime Reaction potential (V vs. RHE) <![CDATA[Cyclohexanone oxime yield (mmol·h⁻ 1 ·cm⁻ 2 )]]> Faraday efficiency (%) −0.6 0.032 37.1 −0.7 0.066 40.5 −0.8 0.106 47.2 −0.9 0.171 66.6 −1.0 0.131 46.0 −1.1 0.087 24.1 −1.2 0.085 20.7
[0039] Application Example 2: Electrocatalytic application of Cu–S@LC in the electrooxidation of methanol to formamide
[0040] The Cu–S@LC material prepared in Example 1 was formulated into a catalyst ink (e.g., using ethanol / deionized water as a dispersant, adding a small amount of binder such as Nafion solution, and ultrasonically dispersed until homogeneous), drop-coated onto a conductive substrate (such as carbon paper or carbon cloth), and dried to serve as the working electrode. Electrochemical reaction tests were conducted using a standard three-electrode system, with a platinum sheet or graphite rod as the counter electrode and Ag / AgCl as the reference electrode, and the potential was converted to a reversible hydrogen electrode (RHE). 0.5 M NaHCO3 was added to the electrolytic cell as the supporting electrolyte, along with methanol (1.0 M) as the carbon source substrate and ammonia (0.8 M) as the nitrogen source. Constant potential electrolysis was performed at room temperature within the potential range of 1.9–2.6 V vs. RHE for 0.5 h. After the reaction, the electrolyte was collected, and the formamide product was qualitatively and quantitatively analyzed by high-performance liquid chromatography (HPLC), and the formamide yield and Faraday efficiency were calculated accordingly. Test results show that, within the above electrolyte system and potential window, Cu–S@LC can drive the electro-oxidation of methanol and react with an ammonia source via a C–N coupling reaction to generate formamide. This indicates that the material is suitable for applications related to the electro-oxidation of alcohol substrates coupled with the electro-synthesis of amide products from nitrogen-containing species (Table 2).
[0041] Table 2. Test results of electrosynthesis performance of formamide Reaction potential (V vs. RHE) <![CDATA[Formamide yield (mmol·h⁻ 1 ·cm⁻ 2 )]]> Faraday efficiency (%) 1.9 0.026 35.9 2.0 0.048 25.1 2.1 0.062 18.8 2.2 0.096 18.7 2.3 0.106 15.8 2.4 0.120 13.8 2.5 0.124 13.1 2.6 0.124 11.2
[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a lignin-based ultrathin porous carbon material with a supported metal-sulfur coordination structure, characterized in that, Includes the following steps: (1) After dissolving or dispersing lignin or modified lignin under alkaline conditions, acidification is carried out to regulate the formation of a three-dimensional network of lignin, and inorganic salt components are generated in situ through acid-base neutralization. (2) Add a metal source and a sulfur-containing precursor to the system obtained in step (1) and load it into the three-dimensional network; (3) The precursor obtained in step (2) is freeze-dried to form a salt microcrystalline structure in the three-dimensional network of the inorganic salt components; (4) The freeze-dried precursor obtained in step (3) is subjected to pyrolysis and carbonization; (5) The pyrolysis products are leached and / or washed to remove the salt microcrystalline structure and obtain the lignin-based ultrathin porous carbon material with the metal-sulfur coordination structure.
2. The preparation method according to claim 1, characterized in that: The lignin is one or more of alkali lignin, enzymatically hydrolyzed lignin, and sulfate lignin; the modified lignin is one or more of carboxylated lignin, sulfonated lignin, oxidized lignin, hydroxymethylated lignin, etherified lignin, or esterified lignin.
3. The preparation method according to claim 1, characterized in that: The acidification adjustment brings the pH of the system to 3-6, preferably 4-5.
4. The preparation method according to claim 1, characterized in that: The in-situ generated inorganic salt component includes one or more of sulfates, chlorides and / or nitrates, and forms a salt microcrystalline structure that can be removed by subsequent leaching and / or washing during freeze-drying.
5. The preparation method according to claim 1, characterized in that: The leaching and / or washing treatment includes water washing, acid washing, or a combination thereof, to remove the salt microcrystalline structure.
6. The preparation method according to claim 1, characterized in that: The metal source is selected from one or more of the chloride, nitrate, sulfate, and acetate salts of Cu, Fe, Co, Ni, Mn, Zn, Mo, W, Ag, Pd, Pt, Au, or Sn.
7. The preparation method according to claim 1, characterized in that: The sulfur-containing precursor is selected from one or more of thiophenes, thiazoles, thioethers, thiols, or thioureas; the pyrolysis carbonization is carried out under an inert atmosphere and / or a reducing atmosphere, and the pyrolysis temperature is 700–900 °C.
8. A lignin-based ultrathin porous carbon material with a supported metal-sulfur coordination structure, characterized in that, The material is composed of a porous carbon framework consisting of three-dimensionally interconnected ultrathin pleated carbon nanosheets, with metal dispersed in the porous carbon framework in the form of a metal-sulfur coordination structure, and the material is prepared by the preparation method according to any one of claims 1 to 7.
9. The application of the lignin-based ultrathin porous carbon material according to claim 8 in electrochemical energy conversion, catalytic synthesis, electro-oxidation of small organic molecules, electro-reduction of nitrates and electrocatalytic CN coupling synthesis.