Method for increasing lignocarbon micro-mesopores based on solvent penetration and use of lignocarbon prepared thereby

Abstract

A method for increasing lignocellulosic carbon microporous and mesoporous based on solvent permeation, characterized by comprising the following steps: cutting wood into thin slices of a predetermined size, and performing thermal modification; soaking the wood slices pre-carbonized in step 1) in a polar solvent for 6-10 hours, and ultrasonic oscillation; the polar solvent includes acetone, ethanol, petroleum ether, ethyl acetate, methanol and water; soaking the slices treated in step 2) in a polar solvent for 8-20 hours; drying; calcining the dried wood slices in a protective atmosphere to form lignocellulosic carbon. In the present application, the cellulose / hemicellulose in the cell wall is initially pyrolyzed by thermal modification to form a cutin layer, and then the porosity of the thermal modified wood cell wall is improved by the similar phase solubility and permeation of the polar small molecule solvent, and finally the microporous / mesoporous volume of the wood-derived carbon cell wall is simply and efficiently improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a lignocellulosic carbon, in particular to a method for increasing the microporous and mesoporous structure of lignocellulosic carbon based on solvent infiltration, lignocellulosic carbon and its use. BACKGROUND

[0002] Nature's ecosystems contain countless fascinating operating rules. The discovery of Murray's law explains the relationship between the hierarchical porous structure of animals and plants (such as animal blood vessels, plant stems and leaves, and respiratory systems) and material transport. Natural selection has endowed animals and plants with material transport exchange pathways that have low resistance, high efficiency, and low energy consumption in limited space. Multiscale hierarchical porous materials have been widely used in the fields of electrochemical catalysis, ion batteries, and supercapacitors. It can be predicted that exploring the multiscale hierarchical porous structure of nature has important value in enhancing the added value of materials.

[0003] Wood, as a renewable natural polymer material, has unique physicochemical properties and macroscopic and microscopic structures, making wood and its derived materials widely used in flexible sensing, ion batteries, supercapacitors, and other fields. Importantly, wood structures have hierarchical porous array structures such as conduits, rays, pits, and cell cavities, which provide efficient material transport paths and low material migration resistance for wood and its derived materials as energy storage thick electrodes. Wood-derived carbon can well inherit and retain the wood conduit, ray, pit, and cell cavity structures. These structures provide wood-derived carbon thick electrodes with 80% of the micrometer-sized large cavity volume and good mechanical properties, and also provide good substrate conditions for the loading of active materials (metal oxides, conductive polymers, metal hydroxides, and carbon nanotubes / graphene oxide, etc.), thereby enhancing the energy storage capacity of wood-derived carbon composite electrodes. At the same time, research on the microporous / mesoporous structure of wood-derived carbon mainly adopts strong acid and strong base etching of wood-derived carbon or removes part of the wood composition (lignin and hemicellulose) through chemical methods to enrich the pore structure and specific surface area of wood-derived carbon. However, it is clear that such microporous / mesoporous regulation strategies have the problems of etching area limited to the surface of wood tracheids, serious damage to the integrity of wood-derived carbon, uncontrollable pore size, and high pollution in the acid and base chemical treatment process.

[0004] Inspired by Murray's law, we noticed that there are abundant micro-mesopores in the cell wall of wood. About 40% of the cellulose component and the hierarchical structure of lignin and hemicellulose make the cell wall of wood have a large number of micro-mesopores below 20 nm. At the same time, the functional groups such as hydroxyl groups of cellulose, hemicellulose and lignin help the penetration of small polar molecules in the cell wall, thereby changing the degree of crosslinking between wood polymers to produce more dynamic nanopores to make the wood expand. Unfortunately, the crosslinking degree between the components of the wood cell wall is changed during the pyrolysis at high temperature, and a large amount of oil substances are decomposed, resulting in the closure and loss of a large number of micro-mesoporous structures, so that the specific surface area and porosity of the wood-derived carbon are low. Therefore, it is the key to develop high-performance multi-scale hierarchical porous wood-derived materials to simply and efficiently keep the micro-mesoporous structure of wood-derived carbon. SUMMARY

[0005] The technical problem solved by the present application is to overcome the shortcomings of the prior art and provide a method for increasing the micro-mesopores of wood carbon based on solvent penetration, wood carbon and its application.

[0006] To solve the above technical problems, the technical solution provided by the present application is as follows: a method for increasing the micro-mesopores of wood carbon based on solvent penetration, comprising the following steps:

[0007] 1) cutting wood into thin slices of a predetermined size and performing thermal modification;

[0008] 2) soaking the wood slices pre-carbonized in step 1) in a polar solvent for 6-10 hours and ultrasonic oscillation; the polar solvent includes acetone, ethanol, petroleum ether, ethyl acetate, methanol and water;

[0009] 3) soaking the slices treated in step 2) in a polar solvent for 8-20 hours;

[0010] 4) drying;

[0011] 5) calcining the dried wood slices in a protective atmosphere to form wood carbon.

[0012] The above-mentioned method for increasing the micro-mesopores of wood carbon based on solvent penetration is preferably repeated steps 3) and 4) 2-3 times.

[0013] The above-mentioned method for increasing the micro-mesopores of wood carbon based on solvent penetration is preferably that the temperature of thermal modification in step 1) is 150-250℃ and the time is 4-7 hours.

[0014] The above-mentioned method for increasing the micro-mesopores of wood carbon based on solvent penetration is preferably that the thickness of the slices is not more than 5mm.

[0015] Preferably, the temperature of the calcination in step 5) is 500-900℃, and the time is 7-9 hours.

[0016] Preferably, the calcination in step 5) is calcination at 250-320℃ and 780-880℃ for 3-4 h and 4-5 h, respectively.

[0017] The use of the lignocarbon prepared by the above method for increasing the micropore / mesopore volume of wood-derived carbon in an electrode.

[0018] The use of the lignocarbon prepared by the above method for increasing the micropore / mesopore volume of wood-derived carbon in a sewage catalyst and a sewage adsorbent.

[0019] The use of the lignocarbon prepared by the above method for increasing the micropore / mesopore volume of wood-derived carbon in an electrocatalyst.

[0020] Compared with the prior art, the present application has the advantages that: in the present application, the cellulose / hemicellulose in the cell wall is preliminarily pyrolyzed by heat modification to form a cuticle layer, and then the porosity of the heat-modified wood cell wall is improved by the similar phase solubility and penetration of a polar small molecule solvent, so that the micropore / mesopore volume of the wood-derived carbon cell wall is finally simply and efficiently increased.

[0021] The micropore / mesopore distribution of the charcoal tube cell wall is uniform, and the pore volume of the tube cell wall is significantly increased. The solvent penetration strategy significantly reduces the strict preparation conditions required for acid-base activation of the wood-derived carbon thick electrode, conforms to the development trend of green environmental protection, and provides a new solution for the sustainable development of wood resources. The lignocarbon of the present application has excellent pore structure, easy processing and excellent mechanical properties, and shows great application potential in the fields of supercapacitors and electrocatalytic oxygen evolution. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Nitrogen adsorption-desorption curves of WC, WC-H2O, WC-EtOH and WC-AC.

[0023] Figure 2 Pore size distribution histogram of WC.

[0024] Figure 3 Pore size distribution histogram of WC-H2O.

[0025] Figure 4 Pore size distribution histogram of WC-EtOH.

[0026] Figure 5 Pore size distribution histogram of WC-AC.

[0027] Figure 6 Comparative chart of micropore, mesopore and macropore content for WC, WC-H20, WC-EtOH and WC-AC.

[0028] Figure 7 CV curves of WC, WC-H20, WC-EtOH and WC-AC electrodes at 20 mV s -1

[0029] Figure 8 GCD curves of WC, WC-H20, WC-EtOH and WC-AC electrodes at 5 mA cm -2

[0030] Figure 9 GCD curves of WC-AC electrode at 2, 5, 10, 15 and 20 mA cm -2

[0031] Figure 10 Rate capability chart of WC, WC-H20, WC-EtOH and WC-AC electrodes. Embodiments

[0032] In order to facilitate the understanding of the present application, the following will be a more comprehensive and detailed description of the present application in conjunction with the preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0033] It should be particularly noted that when an element is described as being "fixed, attached, connected or communicated to" another element, it can be directly fixed, attached, connected or communicated to the other element, or indirectly fixed, attached, connected or communicated to the other element through other intermediate connecting elements.

[0034] Unless otherwise defined, all the professional terms used in the following are the same as the meanings commonly understood by the skilled in the art. The professional terms used in the present text are only for the purpose of describing the specific embodiments and are not intended to limit the protection scope of the present application. Embodiments

[0035] A method for increasing the microporous and mesoporous of lignocellulosic carbon based on solvent infiltration, comprising the following steps:

[0036] 1) Cut the wood into thin slices of a predetermined size and perform thermal modification; the thickness of the slices is 2-5 mm. The temperature of the thermal modification is 150-250°C, and the time is 4-7 hours.

[0037] 2) Soak the wood slices pre-carbonized in step 1) in a polar solvent for 6-10 hours and ultrasonically agitate; the polar solvent includes acetone, ethanol, petroleum ether, ethyl acetate, methanol and water; ​​​

[0038] 3) Soak the wood chips treated in step 2) in a polar solvent for 8-20 hours;

[0039] 4) Dry; repeat the step 3) and step 4) for 2-3 times.

[0040] 5) Calcine the dried wood chips in a protective atmosphere to form the wood-based carbon.

[0041] In this embodiment, the calcination in step 5) is at 250-320℃ and 780-880℃ for 3-4 h and 4-5 h, respectively.

[0042] In other embodiments, the calcination in step 5) can be at 500-900℃ for 7-9 hours.

[0043] The wood-based carbon prepared by the method of increasing the micro-mesopore of the wood-based carbon in this embodiment has a significantly increased content of micro-mesopore of 0.4-10 nm.

[0044] The cellulose, hemicellulose and lignin in the cell wall of wood are tightly combined through a large number of hydrogen bonds. In this embodiment, the original structure of part of the cellulose, hemicellulose and lignin can be destroyed by the thermal modification process at 150-250℃ to generate a large number of structural defects and micro-mesopore structures. However, the thermal modification of wood will also decompose a large amount of ester substances, which will seriously block the micro-nanopore channels on the pit canal and pit wall. In this embodiment, we take advantage of the accessibility of free hydroxyl groups on wood fibers to perform solvent infiltration treatment on the thermal modified wood by solvent infiltration of the cell wall of wood. There are two key effects in this process. First, the similar solubility of solvent molecules can remove the oil and fat decomposed from wood, exposing the rich multi-level pore structure generated by the thermal modification of wood. Second, according to the multi-molecular layer adsorption theory and intermolecular cluster theory of wood fibers, the combination and cluster states between solvent molecules and wood fibers are formed to increase the gap between fiber bundles, resulting in a higher micro-mesopore porosity of the cell wall of wood. Finally, the wood-based carbon with rich micro-mesopore structure is obtained by high-temperature carbonization. The wood-based carbon with rich micro-mesopore structure prepared in this invention can be used as a wood-derived carbon electrode for supercapacitors. The wood-based carbon with rich micro-mesopore structure prepared in this invention can also be used in sewage catalysts, sewage adsorbents and electrochemical catalysts.

[0045] To compare the performance of the wood-based carbon in this embodiment, water and ethanol were used as polar solvents to prepare wood-based carbon. The wood-based carbon using water and ethanol as polar solvents is marked as WC-H2O and WC-EtOH, respectively. In this embodiment, the wood-based carbon using acetone as polar solvent is marked as WC-AC, and the wood-based carbon without polar solvent treatment is marked as WC. In other embodiments, the polar solvent can also be petroleum ether, ethyl acetate or methanol.

[0046] Detection revealed that WC, WC-H2O, WC-EtOH, and WC-AC had specific surface areas of 534.1, 648.0, 650.1, and 677.7 m², respectively. 2 g -1 Nitrogen adsorption and desorption isotherms at such times, as shown Figure 1 As shown, the modified samples exhibit a significant enhancement in specific surface area compared to WC. Type I nitrogen adsorption-desorption isotherms indicate that both WC and water-modified WC-H2O are predominantly microporous, while Type IV nitrogen adsorption-desorption isotherms show abundant mesoporous structures in ethanol-modified WC-EtOH and acetone-modified WC-AC. The pore size distribution of the WC, WC-H2O, WC-EtOH, and WC-AC electrodes was obtained through N2-DFT model analysis. Figures 2-5 It is clearly shown that the micropore and mesopore volumes of the WC-H2O, WC-EtOH, and WC-AC electrodes increase after solvent permeation treatment. Furthermore, experimental analysis ( Figure 6 The results showed that the average pore size of WC increased significantly from 1.58 nm to 2.49 nm in WC-AC. The micropore content of WC was 0.1713 cm⁻¹. 3 / g, while the mesoporous content is only 0.0033 cm. 3 / g. The WC-AC micropore content increased to 0.2540 cm. 3 / g, mesoporous content increased to 0.030 cm 3 / g. Ultimately, the solvent infiltration method effectively increased the micropore / mesopore content of the wood-derived carbon electrode by one and ten times, respectively.

[0047] In this embodiment, WC, WC-H2O, WC-EtOH, and WC-AC were used as electrodes, and their electrical properties were tested respectively. The WC, WC-H2O, WC-EtOH, and WC-AC electrodes were subjected to a 20 mV s test in a three-electrode system. −1 Cyclic voltammetry at scan rate ( Figure 7 ) and different current densities (2, 5, 10, 15, 20 and 30 mA cm⁻¹) -2 Constant current charge-discharge test () Figures 8-9 ). Figure 7 For WC, WC-H2O, WC-EtOH and WC-AC electrodes at 20 mV s -1 The CV curves at high scan rates, thanks to the abundant micro-mesoporous structure of WC-AC, show a rectangular voltammetric curve at high scan rates, exhibiting excellent ion diffusion rates. Meanwhile, the WC, WC-H2O, WC-EtOH, and WC-AC electrodes also show excellent ion diffusion rates at 5 mA cm⁻¹. -2The area specific capacitances at current densities of 1, 2, 5, 10, 15 and 20 mA cm -2 ( Figure 8 ) respectively. It is worth noting that the energy storage capacity of WC-AC is twice that of WC electrode due to the solvent permeation pore-forming effect. The WC-AC electrode exhibits good rate capability at current densities of 2, 5, 10, 15 and 20 mA cm -2 −2 ( Figure 9 ) respectively. It can be seen that WC, WC-H2O, WC-EtOH and WC-AC electrodes all exhibit good rate capability due to the excellent carbon skeleton structure. Figure 10

[0048] In this embodiment, polar solvents are used to impregnate and permeate the thermally modified wood, thereby generating dynamic nanopores in the tracheid wall. The polar solvents disturb the hydrogen bonds between the recombined fibers, thereby increasing the porosity. The present application shows that polar solvents, especially acetone, have significant solubility and permeability to ester compounds generated by the decomposition of thermally modified wood, thereby enhancing the mesoporous structure of wood-derived carbon at the micro and pore levels. At the same time, the method of the present application effectively maintains the mechanical strength and surface physicochemical properties of the material. When used as an electrode, the WC-AC wood carbon has a rich pore structure and greater specific surface area, and its surface capacitance is twice that of the WC electrode at a current density of 5 mA cm -2 , while also exhibiting excellent rate capability. This direct, effective and environmentally friendly modification strategy significantly improves the microporous / mesoporous content of wood-derived carbon materials. The polar solvent permeation strategy greatly retains the mechanical strength of the wood-derived carbon structure, increases the richness of the pore structure and specific surface area, thereby providing a new research idea for the study of wood in the field of electrochemical energy storage.​​

Claims

1. A method for increasing the micropores of lignocarbon based on solvent infiltration, characterized in that: Includes the following steps; 1) Cut the wood into thin slices of a predetermined size and perform heat modification; the heat modification temperature in step 1) is 150-250℃, and the time is 4-7 hours; 2) The wood veneers that have undergone the heat modification in step 1) are immersed in a polar solvent for 6-10 hours and subjected to ultrasonic vibration; the polar solvent includes acetone, ethanol, petroleum ether, ethyl acetate, methanol or water; 3) Immerse the slices treated in step 2) in a polar solvent for 8-20 hours; 4) Drying; 5) The dried wood chips are calcined under a protective atmosphere to form wood charcoal.

2. The method for increasing the micropores of lignocarbon based on solvent infiltration according to claim 1, characterized in that: Repeat steps 3) and 4) 2-3 times.

3. The method for increasing lignocarbon micropores based on solvent infiltration according to claim 1, characterized in that: The thickness of the sheet does not exceed 5 mm.

4. The method for increasing the micropores of lignocarbon based on solvent infiltration according to claim 1, characterized in that: The calcination temperature in step 5) is 500-900℃, and the time is 7-9 hours.

5. The method for increasing the micropores of lignocarbon based on solvent infiltration according to claim 1, characterized in that: The calcination in step 5) is carried out at 250-320℃ and 780-880℃ for 3-4 h and 4-5 h, respectively.

6. The use of lignocarbon prepared by the method of increasing lignocarbon micropores based on solvent permeation as described in any one of claims 1-5 in an electrode.

7. The use of lignin-based carbon prepared by the method of increasing lignin-based carbon micropores by solvent permeation as described in any one of claims 1-5 in wastewater catalysts and wastewater adsorbents.

8. The use of lignocarbon prepared by the method of increasing lignocarbon micropores by solvent permeation as described in any one of claims 1-5 in electrocatalysts.

Images