Activated composite biochar electrode and preparation method and application thereof

Abstract

The application discloses an activated composite biochar electrode and a preparation method and application thereof, and belongs to the technical field of activated composite biochar electrode. The activated composite biochar electrode is obtained by coating an electrode slurry containing activated composite biochar, a conductive agent and a binder on a current collector and drying; the activated composite biochar is obtained by activating original biochar by an alkaline activator, then performing heat preservation treatment at 150-250 DEG C, and then performing high-temperature activation treatment at 500-700 DEG C; the original biochar is obtained by performing pre-carbonization treatment on biomass raw materials at 350-450 DEG C; and the biomass raw materials are obtained by mixing shrimp shells and tobacco stalks according to a mass ratio of 1:1-1:3. The application uses shrimp shells and tobacco stalks as raw materials to prepare activated composite biochar, and the prepared activated composite biochar has the advantages of stable structure, large specific surface area and rich pore structure; and the activated composite biochar electrode prepared from the activated composite biochar can be used for electric adsorption desalination in capacitive deionization.

Description

Technical Field

[0001] The invention relates to an activated composite biochar electrode and a preparation method and application thereof, and belongs to the technical field of environmental protection. Background Art

[0002] Water pollution and water shortages have become major challenges to global sustainable development. Rapid population growth, industrialization, and the impact of climate change are driving an ever-increasing demand for clean water. Therefore, the development and research of water treatment and desalination technologies are crucial to addressing these water resource challenges. Developing low-energy, high-efficiency, and environmentally friendly desalination technologies is crucial, as it will promote green development and boost economic growth.

[0003] Capacitive deionization (CDI) technology is a water desalination and purification technology based on the theory of double-layer capacitance. It offers advantages such as low energy consumption and environmental friendliness. It is used in wastewater treatment to meet standards for trace heavy metals, hard water softening, brackish water treatment, and seawater desalination. Electrode materials are the core component of CDI technology, and carbon materials are currently the most common. Carbon materials primarily include activated carbon, carbon nanotubes, carbon nanofibers, carbon aerogels, graphene, and their modified materials. Activated carbon is a black, porous solid carbon produced from coal by pulverizing and forming it, or by carbonizing and activating uniform coal particles. However, its production requires large quantities of non-renewable coal, resulting in a waste of resources and resulting in low electrical adsorption performance for the resulting electrode materials. While carbon nanotubes, carbon nanofibers, carbon aerogels, and graphene exhibit excellent electrical adsorption properties, their complex synthesis and higher costs limit their large-scale production.

[0004] Biomass material is a sustainable renewable resource that is inexpensive, widely present in nature, and easy to obtain and prepare. If it is used in the preparation of electrodes, it can not only solve the environmental and land problems caused by the random accumulation of biomass, but also enable its resource utilization, maximizing the economic value and application potential of biomass.

[0005] At present, the application of biomass materials mainly involves carbonizing, activating and modifying a single type of biomass material to obtain composite biochar. The obtained composite biochar is mainly used in supercapacitors. For example: Chinese patent CN202010840785.9 discloses a high-nitrogen biochar composite material, its preparation method and use, and the preparation method comprises the following steps: 1) acid-washing the high-nitrogen biomass raw material and then washing it to neutrality; 2) pyrolyzing the high-nitrogen biomass raw material and an alkali metal salt blend in a carbon-rich atmosphere to obtain nitrogen self-doped activated biochar; 3) coating the nitrogen self-doped activated biochar with metal oxides and hydrothermally carbonizing it to obtain a high-nitrogen biochar composite material, which is used as an electrode for supercapacitors or ion batteries; Chinese patent CN202110030283.4 discloses a composite biochar-based material, its preparation method and use, and the preparation method comprises the following steps: 1) pyrolyzing the biomass in a nitrogen atmosphere, cooling it to room temperature, and then cleaning it. The method comprises the following steps: 1) immersing the carbonized material in a KOH solution, mixing the mixture, drying the mixture, heating the mixture to 700° C. at 2 to 3° C. / min under a nitrogen atmosphere for activation, cooling the mixture to room temperature, washing and drying the mixture to obtain an activated material; 2) dispersing the carbonized material in a KOH solution, mixing the mixture, drying the mixture, heating the mixture to 700° C. at 2 to 3° C. / min under a nitrogen atmosphere for activation, cooling the mixture to room temperature, washing and drying the mixture to obtain an activated material; 3) dispersing graphene oxide in water, adjusting the pH to 8 to 9, and then adding a mixed solution of ethylenediamine and ethanol to the above-mentioned graphene aqueous solution, stirring the mixture at room temperature, and obtaining a modified graphene oxide; 4) dispersing the modified graphene oxide in an acetic acid solution, adding substituted aniline and water, stirring the mixture continuously, adding an aqueous ammonium sulfate solution dropwise, and continuing to stir the mixture. After the reaction, the mixture is neutralized with NaOH, precipitated in anhydrous ethanol, and dried to obtain a modified graphene oxide / polyaniline composite material; 5) then immersing the modified graphene oxide / polyaniline composite material and the activated material in a KOH solution, mixing the mixture, drying the mixture, heating the mixture to 700° C. at 2 to 3° C. / min under a nitrogen atmosphere for activation, cooling the mixture to room temperature, washing and drying the mixture to obtain a composite biochar-based material for use in supercapacitors. However, the above preparation process is complicated and costly, which limits the large-scale production and application of composite biochar.

[0006] At present, there are no reports on the preparation of activated composite biochar electrodes from shrimp shells and tobacco stalks as composite biomass raw materials, and there are no reports on the use of activated composite biochar electrodes made from shrimp shells and tobacco stalks for water desalination in capacitive deionization. Summary of the Invention

[0007] In view of the above problems existing in the prior art, the purpose of the present invention is to provide an activated composite biochar electrode and a preparation method and application thereof.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] An activated composite biochar electrode is obtained by coating an electrode slurry containing activated composite biochar, a conductive agent, and a binder on a current collector and drying it; the activated composite biochar is obtained by activating raw biochar with an alkaline activator, first heat-insulating it at 150-250°C, and then high-temperature activation treatment at 500-700°C; the raw biochar is obtained by pre-carbonizing biomass raw materials at 350-450°C; the biomass raw materials are obtained by mixing shrimp shells and tobacco stalks in a mass ratio of 1:1 to 1:3.

[0010] In one embodiment, the electrode slurry is obtained by mixing activated composite biochar, a conductive agent, a binder and a solvent.

[0011] The preparation of an activated composite biochar electrode comprises the following steps:

[0012] a) crushing and sieving shrimp shells and tobacco stalks, respectively, and then uniformly mixing the obtained shrimp shell and tobacco stalk powders in a mass ratio of 1:1 to 1:3 to obtain a biomass raw material; then placing the biomass raw material in a muffle furnace, heating it to 350 to 450° C. under oxygen-limited conditions, and pre-carbonizing it for 1 to 2 hours to obtain raw biochar;

[0013] b) dispersing the raw biochar prepared in step a) in an alkaline activator aqueous solution and stirring for 2 to 8 hours, filtering, drying, and then placing the dried sample in a tube furnace; under inert gas protection, first heating to 150 to 250° C. and holding for 15 to 45 minutes, then heating to 500 to 700° C. and high-temperature activation for 1 to 2 hours to obtain activated composite biochar;

[0014] c) mixing the activated composite biochar prepared in step b) with a conductive agent and a binder, then adding the obtained mixture into a solvent and stirring and mixing uniformly to form an electrode slurry, then evenly coating the electrode slurry on a current collector, and drying at 60-80° C. for 10-15 hours to obtain an activated composite biochar electrode.

[0015] In one embodiment, in step a), the shrimp shells and tobacco stalks are crushed and sieved with a mesh size of 120 meshes.

[0016] In one embodiment, in step a), the heating rate is 2-5°C / min.

[0017] In a preferred embodiment, in step a), the temperature is raised to 400° C. at a heating rate of 5° C. / min under oxygen-limited conditions for pre-carbonization for 1 hour, and then cooled to room temperature to obtain raw biochar.

[0018] In one embodiment, in step b), the alkaline activator aqueous solution is a 0.05-0.3 mol / L KOH solution.

[0019] In one embodiment, in step b), the heating rate is 2-5°C / min.

[0020] In one embodiment, in step b), the inert gas is nitrogen.

[0021] In a preferred embodiment, in step b), the temperature is first raised to 200°C at a heating rate of 5°C / min and kept at this temperature for 30 minutes, and then raised to 700°C at a heating rate of 5°C / min for high-temperature activation for 2 hours.

[0022] In one embodiment, in step b), high-temperature activation is performed for 1 to 2 hours, and after cooling to room temperature, the activated sample is taken out, acid-washed, water-washed, and dried to obtain activated composite biochar.

[0023] In a preferred embodiment, in step b), the surface of the substrate is first washed with dilute hydrochloric acid (preferably 10 wt % hydrochloric acid) for 5 to 10 minutes, and then rinsed with water until the pH value is 6.5 to 7.0.

[0024] In one embodiment, in step c), the conductive agent is Super P or superconducting carbon black, and the binder is polytetrafluoroethylene or polyvinylidene fluoride.

[0025] In one embodiment, in step c), the activated composite biochar, the conductive agent, and the binder are mixed in a mass ratio of 8:1:1.

[0026] In one embodiment, in step c), the solvent is ethanol.

[0027] In one embodiment, in step c), 20 to 60 mg of a mixture consisting of activated composite biochar, a conductive agent, and a binder is added to 1 mL of a solvent and stirred and mixed uniformly to form an electrode slurry.

[0028] In one embodiment, in step c), the current collector is graphite paper.

[0029] The invention discloses an application of an activated composite biochar electrode for electrosorption desalination in capacitive deionization.

[0030] In one embodiment, when performing desalination treatment, the voltage is 0.6 to 1.0 V, the electrode spacing is 1 to 5 mm, the flow rate is 10 to 30 ml / min, and the treatment time is 1 to 5 hours.

[0031] Compared with the prior art, the beneficial technical effects of the present invention are:

[0032] The present invention uses shrimp shells and tobacco stalks as raw materials to prepare activated composite biochar. The prepared activated composite biochar has a stable structure, a large specific surface area and a rich pore structure (the specific surface area can reach about 1753m 2 / g or more, with a total pore volume of 1.17 cm 3 / g or more), the activated composite biochar electrode prepared from the activated composite biochar has a maximum desalination capacity of up to 84.50 mg / g in a 500 mg / L NaCl solution, and can be used for electrosorption desalination in capacitive deionization; the present invention can not only make full use of biomass resources and have good economic, social and ecological benefits, but also has a simple preparation process, easy-to-control reaction conditions, low cost, and great application potential in industrial production; therefore, compared with the prior art, the present invention has significant advancement and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The SEM images of activated composite biochar and composite biochar-1.3 prepared with different KOH concentrations in the present invention are shown;

[0034] Figure 2 The activated composite biochar prepared by the present invention 0.05 and N2 adsorption-desorption isotherms (a) and pore size distribution diagram (b) of composite biochar-1.3;

[0035] Figure 3 The activated composite biochar prepared by the present invention 0.05 Cyclic voltammetry curve of the electrode;

[0036] Figure 4 The activated composite biochar electrode prepared by the present invention 0.05 Electrochemical impedance spectroscopy (EIS)

[0037] Figure 5 The activated composite biochar prepared by the present invention 0.05 Desalination capacity at different voltages. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described in detail below with reference to specific embodiments and comparative examples.

[0039] Example 1

[0040] a) crushing shrimp shells and tobacco stalks separately and passing them through a 120-mesh sieve; then mixing the resulting shrimp shell and tobacco stalk powders in a mortar at a mass ratio of 1:1.3; and then pre-carbonizing the mixture in a muffle furnace at a heating rate of 5°C / min to 400°C under oxygen-limited conditions for 1 hour to obtain raw biochar;

[0041] b) The original biochar was dispersed in a 0.05 mol / L KOH solution and stirred for 6 hours, filtered, dried, and then the dried sample was placed in a tube furnace; under the protection of inert gas, the temperature was first increased to 200°C at a heating rate of 5°C / min and kept warm for 30 minutes, and then the temperature was increased to 700°C at a heating rate of 5°C / min and activated for 2 hours. After naturally cooling to room temperature, the sample was taken out, first washed with 10 wt% hydrochloric acid for 10 minutes, then rinsed with water to a pH of 6.5-7.0, and then dried at 80°C for 12 hours to obtain activated composite biochar, which was recorded as: activated composite biochar 0.05 .

[0042] The activated composite biochar prepared in this example 0.05 The SEM images are as follows Figure 1 shown.

[0043] The activated composite biochar prepared in this example 0.05 The N2 adsorption-desorption isotherm (a) and pore size distribution diagram (b) are shown in Figure 2 shown.

[0044] The specific surface area of ​​the activated composite biochar prepared in this embodiment is about 1753.11m 2 / g, and the total pore volume is about 1.17 cm 3 / g.

[0045] c) The activated composite biochar, Super P and polytetrafluoroethylene were mixed in a mass ratio of 8:1:1, and then the obtained mixture was added to ethanol and stirred and mixed uniformly to prepare an electrode slurry (in this embodiment: 16 mg of activated composite biochar, 2 mg of Super P and 3.5 mg of 60 wt% polytetrafluoroethylene concentrate were added to 0.5 mL of ethanol as a basis to prepare the electrode slurry), and then the electrode slurry mixture was evenly coated on graphite paper and dried at 80° C. for 12 hours to prepare an activated composite biochar electrode.

[0046] The prepared activated composite biochar electrodes were cut into two sizes: 1 cm × 1 cm and 4 cm × 4 cm. The former was used for electrochemical characterization tests in a three-electrode system, and the latter was used for water desalination in capacitive deionization, as follows:

[0047] In the three-electrode system, the working electrode is a composite biochar electrode, the counter electrode is a platinum wire electrode, the reference electrode is an Ag / AgCl electrode, and the electrolyte is a 1 mol / L NaCl solution. The cyclic voltammetry and electrochemical impedance spectroscopy curves were tested by an electrochemical workstation. The results are as follows: Figure 3 and Figure 4 As shown, the contact angle (θ) of the electrode is 27.00 and the specific capacitance is 186.40 F / g;

[0048] In capacitive deionization, the initial concentration of NaCl solution is 500 mg / L, the voltage is 0.6-1.0 V, the electrode spacing is 5 mm, the flow rate is 15 mL / min, and the treatment time is 5 hours. Figure 5 The figure shows the desalination capacity of the activated composite biochar electrode at different voltages. When the voltage is 0.8V, the maximum desalination capacity is 84.50mg / g.

[0049] Example 2

[0050] The difference between this embodiment and embodiment 1 is that the concentrations of the KOH solution in step b) are 0.01, 0.05, 0.1, 0.2, and 0.3 mol / L, respectively. The activated composite biochars prepared are respectively recorded as: activated composite biochars 0.01 , activated composite biochar 0.05 , activated composite biochar 0.1 , activated composite biochar 0.2 , activated composite biochar 0.3 .

[0051] The SEM image of the activated composite biochar prepared in this example is also shown in FIG. Figure 1 As shown. Figure 1 It can be seen that the activated composite biochar obtained by KOH solution activation has a larger pore structure than the composite biochar obtained without KOH solution activation, indicating that KOH can effectively increase the pore structure of biochar.

[0052] The contact angle and specific capacitance of the activated composite biochar electrode prepared in this example are shown in Table 1.

[0053] Table 1

[0054] KOH concentration (mol / L) 0.01 0.05 0.1 0.2 0.3 Contact angle (θ) 75.80 27.00 27.47 39.52 36.28 Specific capacitance (F / g) 134.27 186.40 178.57 166.10 160.11

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that the original biochar in step b) is not activated with KOH solution; and the conductive agents in step c) are Super P and superconducting carbon black, respectively.

[0057] The specific capacitance of the activated composite biochar electrode prepared in this comparative example is shown in Table 2.

[0058] Table 2

[0059] Conductive agent Super P Superconducting carbon black Specific capacitance (F / g) 99.78 88.82

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 1 is that the original biochar in step b) is not activated with KOH solution; and the binders in step c) are polytetrafluoroethylene and polyvinylidene fluoride, respectively.

[0062] The specific capacitance of the activated composite biochar electrode prepared in this comparative example is shown in Table 3.

[0063] Table 3

[0064] adhesive polytetrafluoroethylene polyvinylidene fluoride Specific capacitance (F / g) 99.78 67.44

[0065] Comparative Example 3

[0066] The difference between this comparative example and Example 1 is that the mass ratios of shrimp shells and tobacco stems in step a) are 1:1, 1:1.3, 1:1.5, 1:2, and 1:3, respectively; the original biochar in step b) is not activated with a KOH solution; and the composite biochars obtained are respectively designated as composite biochar-1, composite biochar-1.3, composite biochar-1.5, composite biochar-2, and composite biochar-3;

[0067] The specific surface area of ​​the composite biochar-1.3 prepared in this comparative example is about 1627.30 m 2 / g, and the total pore volume is about 0.98cm 3 / g.

[0068] The SEM image of the composite biochar-1.3 prepared in this comparative example is as follows Figure 1 shown.

[0069] The N2 adsorption-desorption isotherm (a) and pore size distribution diagram (b) of the composite biochar-1.3 prepared in this comparative example are shown in FIG. Figure 2 shown.

[0070] The desalination capacity of the composite biochar-1.3 prepared in this comparative example is 31.88 mg / g.

[0071] The contact angle and specific capacitance of the composite biochar electrode prepared in this comparative example are shown in Table 4.

[0072] Table 4

[0073] Mass ratio 1:1 1:1.3 1:1.5 1:2 1:3 Contact angle (θ) 126.64 68.03 75.27 74.15 133.34 Specific capacitance (F / g) 71.72 99.78 89.64 91.40 73.82

[0074] Combining Example 1 and Comparative Examples 1-3, it can be seen that under the same conditions, the activated composite biochar prepared by activation with the activator KOH solution has a larger specific surface area, richer pore structure and higher specific capacitance than the composite biochar prepared without activation with the activator KOH solution, and the desalination capacity of the water body is also higher.

[0075] Comparative Example 4

[0076] The difference between this comparative example and Example 1 is that the biomass raw material used in step a) is shrimp shell; and the original biochar in step b) is not activated by KOH solution.

[0077] The specific capacitance of the shrimp shell biochar electrode obtained in this comparative example is 23.10 F / g.

[0078] Comparative Example 5

[0079] The difference between this comparative example and Example 1 is that the biomass raw material used in step a) is tobacco stalks; and the original biochar in step b) is not activated by KOH solution.

[0080] The specific capacitance of the tobacco stem biochar electrode obtained in this comparative example is 54.98 F / g.

[0081] Combining Example 1 and Comparative Examples 4-5, it can be seen that under the same conditions, the composite biochar electrode prepared from shrimp shells and tobacco stalks has better electrochemical performance than the biomass electrode prepared from shrimp shells or tobacco stalks alone.

[0082] Comparative Example 6

[0083] The difference between this comparative example and Example 1 is that the biomass raw material used in step a) is fir; the carbon material used to prepare the electrode in the corresponding step c) is wood activated carbon made from fir; and the prepared electrode is a wood activated carbon electrode.

[0084] The specific capacitance of the wood activated carbon electrode obtained in this comparative example is 46.52 F / g, and the water desalination capacity is 18.81 mg / g.

[0085] Combining Example 1 and Comparative Example 6, it can be seen that under the same conditions, the composite biochar electrode prepared from shrimp shells and tobacco stalks has better electrochemical performance than the electrode prepared from a single other type of biomass, and the desalination capacity of the water body is also higher.

[0086] Comparative Example 7

[0087] The difference between this comparative example and Example 1 is that the biomass raw material used in step a) is a mixture of shrimp shells and water hyacinths in a mass ratio of 1:1.3; and the concentrations of the KOH solution in step b) are 0.05, 0.1, 0.2, and 0.3 mol / L, respectively.

[0088] In this comparative example, the desalination capacity of the activated composite biochar electrode obtained by activation with 0.05 mol / L KOH solution was 25.76 mg / g.

[0089] The specific capacitance of the comparative activated composite biochar electrode obtained in this comparative example is shown in Table 5.

[0090] Table 5

[0091] KOH concentration (mol / L) 0.05 0.1 0.2 0.3 Specific capacitance (F / g) 72.86 75.68 50.05 40.96

[0092] Combining Example 1 and Comparative Example 7, it can be seen that under the same conditions, the activated composite biochar electrode prepared from shrimp shells and tobacco stalks has better electrochemical properties than the comparative activated composite biochar electrode prepared from shrimp shells and water hyacinth biomass, and the desalination capacity of the water body is also higher, indicating that the combination of shrimp shells and tobacco stalks used in the present invention is non-obvious and irreplaceable.

[0093] Finally, it is necessary to point out here that the above is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered within the scope of protection of the present invention.

Claims

1. An activated composite biochar electrode for electrosorption desalination in capacitive deionization, characterized by: The method is obtained by coating an electrode slurry containing activated composite biochar, a conductive agent and a binder on a current collector and drying the resulting mixture; the activated composite biochar is obtained by activating the original biochar with an alkaline activator, firstly heat-insulating it at 150-250°C, and then performing high-temperature activation at 500-700°C; the original biochar is obtained by pre-carbonizing biomass raw materials at 350-450°C; the biomass raw materials are obtained by mixing shrimp shells and tobacco stalks in a mass ratio of 1:1 to 1:

3.

2. A method for preparing the activated composite biochar electrode according to claim 1, characterized in that: The steps include: a) crushing and sieving shrimp shells and tobacco stalks, respectively, and then uniformly mixing the obtained shrimp shell and tobacco stalk powders in a mass ratio of 1:1 to 1:3 to obtain a biomass raw material; then placing the biomass raw material in a muffle furnace, heating it to 350 to 450° C. under oxygen-limited conditions, and pre-carbonizing it for 1 to 2 hours to obtain raw biochar; b) dispersing the raw biochar prepared in step a) in an alkaline activator aqueous solution and stirring for 2 to 8 hours, filtering, and drying, then placing the dried sample in a tube furnace, under inert gas protection, first heating to 150 to 250° C. and holding for 15 to 45 minutes, then heating to 500 to 700° C. and high-temperature activation for 1 to 2 hours to obtain activated composite biochar; c) mixing the activated composite biochar prepared in step b) with a conductive agent and a binder, then adding the obtained mixture into a solvent and stirring and mixing uniformly to form an electrode slurry, then evenly coating the electrode slurry on a current collector, and drying at 60-80° C. for 10-15 hours to obtain an activated composite biochar electrode.

3. The preparation method according to claim 2, wherein: In step b), the alkaline activator aqueous solution is a 0.05-0.3 mol / L KOH solution.

4. The preparation method according to claim 2, wherein: In step b), high-temperature activation is performed for 1 to 2 hours, and after cooling to room temperature, the activated sample is taken out, acid-washed, water-washed, and dried to obtain activated composite biochar.

5. The preparation method according to claim 4, characterized in that: In step b), the surface of the substrate is first washed with dilute hydrochloric acid for 5 to 10 minutes and then rinsed with water until the pH value is 6.5 to 7.

0.

6. The preparation method according to claim 2, wherein: In step c), the conductive agent is Super P or superconducting carbon black, and the binder is polytetrafluoroethylene or polyvinylidene fluoride.

7. The preparation method according to claim 2, characterized in that: In step c), the activated composite biochar, the conductive agent, and the binder are mixed in a mass ratio of 8:1:

1.

8. The preparation method according to claim 2, wherein: In step c), the current collector is graphite paper.

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