AU2020101074A4

AU2020101074A4 - Licorice root residue-based hierarchical porous carbon, preparation method and application thereof

Info

Publication number: AU2020101074A4
Application number: AU2020101074A
Authority: AU
Inventors: Liwei Chen; Yanyan DANG; Genlin ZHANG; Qianyun ZHOU
Original assignee: Shihezi University
Current assignee: Shihezi University
Priority date: 2019-08-15
Filing date: 2020-06-22
Publication date: 2020-08-06
Anticipated expiration: 2028-06-22
Also published as: CN110467181A

Abstract

LICORICE ROOT RESIDUE-BASED HIERARCHICAL POROUS CARBON, PREPARATION METHOD AND APPLICATION THEREOF ABSTRACT The present invention relates to the technical field of carbon material, and in particular to a licorice root residue-based hierarchical porous carbon, and a preparation method and application thereof. The preparation method provided by the present invention has simple steps and is suitable for industrial production; recycling of resource is achieved with licorice root residue as a precursor; meanwhile, the licorice root residue-based hierarchical porous carbon prepared by the preparation method features high specific surface area and rational pore size distribution, resulting in high energy density when serving as an electrode material. 3/3 00 C4-700 200O 100 0 0.0 0.1 0.2 0.3 04 0.5 0.8 07 0.8 0.9 1.0 Relative pressure (P/PO) FIG. 5 0.04 0.03 0.02 S0.01 0.00 ++++ 02 4 810 Pore size (nm) FIG. 6

Description

3/3

00 C4-700

200O

100

0

0.0 0.1 0.2 0.3 04 0.5 0.8 07 0.8 0.9 1.0 Relative pressure (P/PO)

FIG. 5

0.04

0.03

0.02

S0.01

0.00 ++++

02 4 810 Pore size (nm)

FIG. 6

LICORICE ROOT RESIDUE-BASED HIERARCHICAL POROUS CARBON, PREPARATION METHOD AND APPLICATION THEREOF

TECHNICAL FIELD The present invention relates to the technical field of carbon material, and in particular to a licorice root residue-based hierarchical porous carbon, and a preparation method and application thereof. BACKGROUND With the rapid growth of the global population and the over-dependence on fossil energy, people are facing an increasingly serious energy crisis and environmental problems. Therefore, it is necessary to develop clean, efficient, renewable new energy resources and to explore storage and conversion technologies. A super capacitor, principally composed of an electrode, a diaphragm, electrolytes, and a current collector, is a brand-new capacitor established on the basis of a theory of the electric double layer. Particularly, an electrode material for supercapacitors, as a main component of an energy storage device, plays a decisive role in electrochemical properties of the energy storage device. Biomass, as an abundant renewable resource, will be an important resource for human's future survival and development. Dehydrogenation and deoxidation of biomass at high temperatures to prepare carbon materials is an effective approach to biomass utilization. In the prior art, more and more attention has been paid to preparing carbon materials with biomass as a carbon source, related researchers have prepared carbon materials in various ways, e.g., chemical activation, template method, or C02 activation. However, the foregoing solutions have the following drawbacks: precursor pretreatment is too tedious to adapt to industrial production; carbon materials prepared feature low specific surface area and irrational pore size distribution, resulting in low energy density when serving as electrode materials. So far, problems with large output of solid waste, low use efficiency, and failure to recycle effectively still exist in traditional Chinese herbs processing industry, further leading to a waste of a mass of herb residues. Particularly, approximately 70% of solid waste is discharged after extraction of such active substances as glycyrrhizic acid from licorice roots. Such waste is partly used in the feed industry but is mostly subjected to landfill or incineration as solid waste. Not only does this lead to a waste of resources, but also brings enormous pressure to the environment. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

OBJECT OF THE INVENTION It is the object of the present invention to substantially overcome or at least ameliorate one or more of the disadvantages of the prior art or to provide a useful alternative. SUMMARY In one embodiment, the present invention provides a licorice root residue-based hierarchical porous carbon, and a preparation method and application thereof. The preparation method has simple steps and is suitable for industrial production; recycling of resource is achieved with licorice root residue as a precursor; meanwhile, the licorice root residue-based hierarchical porous carbon prepared by the preparation method features high specific surface area and rational pore size distribution, resulting in high energy density when serving as an electrode material. In one aspect, the present invention provides a preparation method of a licorice root residue based hierarchical porous carbon, including the following steps: conducting primary heat treatment on licorice root residues to obtain a precarbonized product; mixing the precarbonized product with alkali liquor, drying, and conducting secondary heat treatment, to obtain the licorice root residue-based hierarchical porous carbon. Preferably, pretreatment is conducted on the licorice root residues before the primary heat treatment. The pretreatment includes washing and drying. Preferably, the primary heat treatment is conducted in a nitrogen (N2) atmosphere. A temperature of the primary heat treatment is 300 to 400°C, and a holding time of the primary heat treatment is 50 to 70 min. Preferably, a rate of heating to the temperature of the primary heat treatment is 4 to 6°C/min. Preferably, the alkali liquor is an aqueous potassium hydroxide solution. A concentration of the alkali liquor is 0.7 to 2 mol/L. Preferably, a mass ratio of alkali in the alkali liquor to the precarbonized product is (1-3):1. Preferably, the secondary heat treatment is conducted in a nitrogen (N2) atmosphere. A temperature of the secondary heat treatment is 700 to 800°C, and a holding time of the secondary heat treatment is 100 to 150 min. Preferably, a rate of heating to the temperature of the secondary heat treatment is 4 to 6°C/min. In a further aspect, the present invention provides a licorice root residue-based hierarchical porous carbon prepared by the preparation method according to the above technical solutions. The licorice root residue-based hierarchical porous carbon has a specific surface area of 1,100 to 1,928 m2/g, a total pore volume of 0.53 to 0.87 cm 3/g, a microporosity of 65% to 75%, and a sum of mesoporosity and macroporosity of 22% to 35%.

In a further aspect the present invention provides use of the licorice root residue-based hierarchical porous carbon according to the above technical solutions in electrochemistry. In a further aspect, the present invention provides a preparation method of a licorice root residue-based hierarchical porous carbon, including the following steps: conducting primary heat treatment on licorice root residues to obtain a precarbonized product; mixing the precarbonized product with alkali liquor, drying, and conducting secondary heat treatment, to obtain the licorice root residue-based hierarchical porous carbon. Using licorice root residue as a precursor to prepare the licorice root residue-based hierarchical porous carbon, the present disclosure results in recycling and higher value application of licorice root residues; meanwhile, the present disclosure further solves current environment pollution problems brought by incineration and landfill of licorice root residues; further, a specific biomass structure of the licorice root residue ensures that the licorice root residue-based hierarchical porous carbon prepared with licorice root residue as a precursor has a higher specific surface area and a good porous structure; based on the above, the present application uses alkali as an activator, and the more efficient activation way further improves the rational degree of pore size distribution of the licorice root residue-based hierarchical porous carbon, leading to higher specific capacitance and good cycle stability when serving as an electrode material. According to examples, the licorice root residue-based hierarchical porous carbon prepared by the preparation method of the present disclosure has a specific surface area of 1,100 to 1,928 m2 /g and a total pore volume of 0.53 to 0.87 cm 3/g. When the licorice root residue-based hierarchical porous carbon serves as an electrode material for super capacitor, the specific capacitance is as high as 260.8 and 185.54 F/g at current densities of 0.5 and1 A/g, respectively, exhibiting excellent capacitance performance. Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". BRIEF DESCRIPTION OF DRAWINGS A preferred embodiment of the present invention will now be described by way of specific embodiments with reference to the examples and accompanying drawings in which: FIG. 1 shows an SEM micrograph of a licorice root residue-based hierarchical porous carbon prepared in Example 1; FIG. 2 shows an SEM micrograph of a licorice root residue-based hierarchical porous carbon prepared in Example 3; FIG. 3 shows an SEM micrograph of a licorice root residue-based hierarchical porous carbon prepared in Example 4;

FIG. 4 shows an SEM micrograph of a licorice root residue-based hierarchical porous carbon prepared in Example 5; FIG. 5 illustrates a nitrogen adsorption-desorption isotherm of the licorice root residue-based hierarchical porous carbon prepared in Example 5; FIG. 6 illustrates pore size distribution of the licorice root residue-based hierarchical porous carbon prepared in Example 5. DETAILED DESCRIPTION The present disclosure relates to a preparation method of a licorice root residue-based hierarchical porous carbon, including the following steps: conducting primary heat treatment on licorice root residues to obtain a precarbonized product; mixing the precarbonized product with alkali liquor, drying, and conducting secondary heat treatment, to obtain the licorice root residue-based hierarchical porous carbon. In the present disclosure, all raw material components are commercially available products well known to those skilled in the art unless otherwise specified. The present disclosure conducts primary heat treatment on licorice root residues to obtain a precarbonized product; in the present disclosure, pretreatment is preferably conducted on the licorice root residues before the primary heat treatment, and the pretreatment preferably includes washing and drying; neither washing nor drying is particularly limited in the present disclosure as long as washing and drying processes used are well known to those skilled in the art. After drying, the pretreated licorice root residues may preferably be cut up into a particle size range from 100 to 140 mesh in case of a large size. In the present disclosure, the primary heat treatment is preferably conducted in a nitrogen (N2) atmosphere; a temperature of the primary heat treatment is preferably 300 to 400°C, more preferably 320 to 380°C, and most preferably 350°C; a holding time of the primary heat treatment is preferably 50 to 70 min, more preferably 55 to 65 min, and most preferably 60 min. In the present disclosure, a rate of heating to the temperature of the primary heat treatment is preferably 4 to 6°C/min, more preferably 4.5 to 5.5°C/min, and most preferably 5°C/min. In the present disclosure, the primary heat treatment is preferably conducted in a tube furnace; preferably, the detailed operating process of the primary heat treatment is as follows: filling the pretreated licorice root residues in a combustion boat, placing the combustion boat in the tube furnace, pumping in N2 to empty the air from the tube furnace (and maintaining such a nitrogen environment), heating to 300 to 400°C at a rate of 4 to 6°C/min, and holding the temperature for 50 to 70 min. In the present disclosure, preferably, the primary heat treatment is followed by cooling treatment, to obtain the precarbonized product; the cooling treatment is preferably furnace cooling.

In the present disclosure, the primary heat treatment has the following functions: first, preservation of an original plant structure of the licorice root residue; second, formation of a firm scaffold, for fear that etching of the precarbonized product in the alkali liquor causes such unfavorable effects as porous collapse. After the precarbonized product is obtained, the precarbonized product and the alkali liquor are mixed and dried in the present disclosure, followed by secondary heat treatment, to obtain the licorice root residue-based hierarchical porous carbon. In the present disclosure, the alkali liquor is preferably an aqueous potassium hydroxide solution; a concentration of the alkali liquor is preferably 0.7 to 2 mol/L, more preferably 1.42 to 2 mol/L, and most preferably 2 mol/L; in the present disclosure, a mass ratio of alkali in the alkali liquor to the precarbonized product is preferably (1-3):1. In the present disclosure, the mixing is preferably conducted under stirring conditions. The stirring is not particularly limited in the present disclosure as long as stirring process is well known to those skilled in the art. In the present disclosure, the drying temperature is preferably 60 to 80°C, and more preferably to 70°C; the drying time is preferably 5 to 15 h, more preferably 8 to 12 h, and most preferably h; in the present disclosure, the drying is preferably conducted in an air dry oven. After drying, products obtained after drying are ground in the present disclosure. The grinding is not particularly limited in the present disclosure as long as grinding process is well known to those skilled in the art. In the present disclosure, the secondary heat treatment is preferably conducted in a nitrogen (N2) atmosphere; a temperature of the secondary heat treatment is preferably 700 to 800°C, more preferably 720 to 780°C, and most preferably 750°C; a holding time of the secondary heat treatment is preferably 100 to 150 min, more preferably 110 to 140 min, and most preferably 120 to 130 min. In the present disclosure, a rate of heating to the temperature of the secondary heat treatment is preferably 4 to 6°C/min, more preferably 4.5 to 5.5°C/min, and most preferably 5°C/min. In the present disclosure, the secondary heat treatment is preferably conducted in a tube furnace; preferably, the detailed operating process of the secondary heat treatment is as follows: filling the ground products in a combustion boat, placing the combustion boat in the tube furnace, pumping in N2 to empty the air from the tube furnace (and maintaining such a nitrogen environment), heating to 700 to 800°C at a rate of 4 to 6°C/min, and holding the temperature for 100 to 150 min. In the present disclosure, the function of the secondary heat treatment is to thermally decompose organic compounds in licorice root residues and increase the graphitization degree of a carbon material.

In the present disclosure, after the secondary heat treatment process is completed, the resulting products are preferably post-processed to obtain the licorice root residue-based hierarchical porous carbon; in the present disclosure, the post-processing preferably includes cooling, pickling, water washing and drying successively; the cooling is preferably furnace cooling; the pickling preferably refers to washing with 1 mol/L dilute hydrochloric acid to remove residual alkali; the water washing is not particularly limited in the present disclosure as long as water washing process is well known to those skilled in the art and products are washed until neutral. In the present disclosure, the drying is preferably conducted in an air dry oven; the drying time is preferably 12 h; the drying temperature is not particularly limited in the present disclosure as long as the drying is conducted at drying temperatures well known to those skilled in the art. The present disclosure further provides a licorice root residue-based hierarchical porous carbon prepared by the preparation method according to the above technical solutions. The licorice root residue-based hierarchical porous carbon has a specific surface area of 1,100 to 1,928 m2 /g, a total pore volume of 0.53 to 0.87 cm 3/g, a microporosity of 65% to 75%, and a sum of mesoporosity and macroporosity of 25% to 35%. The present disclosure further provides use of the licorice root residue-based hierarchical porous carbon according to the above technical solutions in electrochemistry. Preferably, the use is that the licorice root residue-based hierarchical porous carbon serves as an electrode material for super capacitor. The licorice root residue-based hierarchical porous carbon, the preparation method and the application thereof as provided by the present disclosure will be described in detail in connection with the following examples, but they should not be construed as limiting the claimed scope of the present disclosure. Example 1 After licorice root residues are washed and dried, 2 g of licorice root residues were cut up into a combustion boat; the combustion boat was placed in a tube furnace, N2 was pumped in to empty the air from the tube furnace (and such a nitrogen environment was maintained), followed by heating to 350°C at a rate of 5°C/min, and holding the temperature for 60 min. After stopping heating, the combustion boat was cooled down to room temperature in the furnace to obtain a precarbonized product. One gram of the precarbonized product was added in 50 mL of 0.7 mol/L aqueous KOH solution (a mass ratio of the precarbonized product to KOH was 1:1), stirred well, and dried in an air dry oven for 10 h at 80°C. The above dried product was ground; the ground product was then filled in a combustion boat; the combustion boat was placed in the tube furnace, N2 was pumped in to empty the air from the tube furnace (and such a nitrogen environment was maintained), followed by heating to 750°C at a rate of 5°C/min, and holding the temperature for 120 min. After stopping heating, the combustion boat was cooled down to room temperature in the furnace; the resulting product was successively pickled (with 1 mol/L dilute hydrochloric acid) and washed with water until neutral, followed by drying in the air dry oven for 12 h, to obtain a licorice root residue-based hierarchical porous carbon (labeled as C-1-750). Example 2 For the preparation method of the licorice root residue-based hierarchical porous carbon, refer to Example 1. The only difference was that a mass ratio of the precarbonized product to KOH was 1:2; the licorice root residue-based hierarchical porous carbon was labeled as C-2-750. Example 3 For the preparation method of the licorice root residue-based hierarchical porous carbon, refer to Example 1. The only difference was that a mass ratio of the precarbonized product to KOH was 1:3; the licorice root residue-based hierarchical porous carbon was labeled as C-3-750. Example 4 For the preparation method of the licorice root residue-based hierarchical porous carbon, refer to Example 1. The only difference was that a mass ratio of the precarbonized product to KOH was 1:3 and a temperature of the secondary heat treatment was 700°C; the licorice root residue-based hierarchical porous carbon was labeled as C-3-700. Example 5 For the preparation method of the licorice root residue-based hierarchical porous carbon, refer to Example 1. The only difference was that a mass ratio of the precarbonized product to KOH was 1:3 and a temperature of the secondary heat treatment was 800°C; the licorice root residue-based hierarchical porous carbon was labeled as C-3-800. Comparative Example 1: For the preparation method of the porous carbon, refer to Example 1. The only difference was that a process of mixing with KOH was not included during the secondary heat treatment. Comparative Example 2: For the preparation method of the porous carbon, refer to Example 1. The only difference was that the secondary heat treatment was conducted directly after mixing licorice root residues with KOH, without primary heat treatment. Test Example 1 SEM was conducted on licorice root residue-based hierarchical porous carbons prepared in Examples 1, 3, 4, and 5. Results are illustrated in FIGS. 1 to 4. As illustrated in FIGS. 1 and 2, as a ratio of activated KOH increases, pores on the surface of the prepared carbon material appears open or closed; this helps increase a contact area of electrolytes with the carbon material and provide a good ion transport channel; as illustrated in FIGS. 2 to 4, high temperature carbonization further helps form a good pore structure by removing organic compounds, but overtemperature may also cause material surface defects and porous collapses. The licorice root residue-based hierarchical porous carbon prepared in Example 4 was subjected to a nitrogen adsorption-desorption isotherm test (test result is illustrated in FIG. 5), and a map of pore size distribution of the corresponding licorice root residue-based hierarchical porous carbon was obtained (as illustrated in FIG. 6). From FIG. 5, the nitrogen adsorption-desorption isotherm of the licorice root residue-based hierarchical porous carbon is typically type I, and paths of adsorption and desorption curves are essentially coincident. The trend of the isotherm increases remarkably when P/PO ranges from 0 to 0.2, which indicates that there are a huge number of micropores in the sample; the isotherm rises slowly when P/P0 is 0.2, and the sample has a type H4 hysteresis loop when P/PO ranges from 0.1 to 1.0, indicating that there are some meso-pores in the sample; from FIG. 6, pore sizes of the sample mainly represent 0-2 nm micropores, as well as a certain amount of meso-pores and macropores. A huge number of micropores provide an abundant specific surface area and pore volume, and such a hierarchical porous structure plays a promoting role in ion diffusion and transport of electrolytes, which is consistent with the result of the nitrogen adsorption-desorption isotherm. Test Example 2 Licorice root residue-based hierarchical porous carbons prepared in Examples 1 to 5 and the porous carbon prepared in Comparative Example 1 served as electrode materials for super capacitor, respectively, and they were subjected to electrochemical performance test with 6 M KOH solution as an electrolyte solution at a current density of 1 A/g. Test results are shown in Table 1:

Table 1 Specific capacitance of licorice root residue-based hierarchical porous carbons prepared in Examples 1 to 5 as electrode materials for super capacitor

Example 3 Example 4 Example5 Comparative Comparative Example 1 Example 2 Example Example2 Specific capacitance 92.69 102.48 123.38 185.54 155.50 20.02 41.24 (F/g)

From the above examples, licorice root residue-based hierarchical porous carbons prepared by the preparation method of the present invention feature high specific surface area and specific capacitance.

The above descriptions are merely preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications shall also be deemed as falling within the protection scope of the present disclosure.

Claims

What is claimed is:

1. A preparation method of a licorice root residue-based hierarchical porous carbon, comprising the following steps: conducting primary heat treatment on licorice root residues to obtain a precarbonized product; mixing the precarbonized product with alkali liquor, drying, and conducting secondary heat treatment, to obtain the licorice root residue-based hierarchical porous carbon.

2. The preparation method according to claim 1, wherein pretreatment is conducted on the licorice root residues before the primary heat treatment; the pretreatment comprises washing and drying; wherein the primary heat treatment is conducted in a nitrogen (N2) atmosphere; a temperature of the primary heat treatment is 300 to 400°C, and a holding time of the primary heat treatment is 50 to 70 min, preferably, wherein a rate of heating to the temperature of the primary heat treatment is 4 to 6°C/min;

wherein the secondary heat treatment is conducted in a nitrogen (N2) atmosphere; a temperature of the secondary heat treatment is 700 to 800°C, and a holding time of the secondary heat treatment is 100 to 150 min; preferably, wherein a rate of heating to the temperature of the secondary heat treatment is 4 to 6°C/min.

3. The preparation method according to claim 1, wherein the alkali liquor is an aqueous potassium hydroxide solution; a concentration of the alkali liquor is 0.7 to 2 mol/L, preferably, wherein a mass ratio of alkali in the alkali liquor to the precarbonized product is (1-3):1.

4. A licorice root residue-based hierarchical porous carbon prepared by the preparation method according to any one of claims 1 to 3, wherein the licorice root residue-based hierarchical porous carbon has a specific surface area of 1,100 to 1,928 m 2/g, a total pore volume of 0.53 to 0.87 cm/g, a microporosity of 65% to 75%, and a sum of mesoporosity and macroporosity of 22% to 35%.

5. An application of the licorice root residue-based hierarchical porous carbon according to claim 4 in electrochemistry.