Porous carbon material derived from shaddock peel as well as preparation method and application of porous carbon material

Abstract

The invention discloses a pomelo peel-derived porous carbon material and a preparation method and application thereof, and relates to the field of water treatment.The pomelo peel-derived porous carbon material is prepared by using waste pomelo peel as a carbon source, performing pre-carbonization treatment, then using potassium chloride as a reinforcing agent and potassium hydroxide as an activating agent, and forming pomelo peel-derived porous carbon with a porous structure through a one-step activation method; the rich pore diameter can increase active sites capable of accommodating sodium ions, so that the desalination amount is increased. The comprehensive desalination amount can reach 24.6 mg / g under the applied voltage of 1.2 V. The material is simple in preparation process, raw materials are easy to obtain, and a new thought is provided for constructing biomass-derived porous carbon when heteroatom doping is not carried out.

Description

Technical Field

[0001] The present invention relates to the field of water treatment, and particularly to a porous carbon material derived from pomelo peel, a preparation method thereof, and an application thereof. Background Art

[0002] Capacitive deionization technology (CDI) is an emerging seawater desalination technology, which has been favored by researchers due to its operability, environmental friendliness, and low-cost benefits. CDI forms an electric field by applying a voltage on both sides of the electrode. Under the action of the electric field, ions are adsorbed onto the electrode surface or inside the electrode. After removing the voltage or applying a reverse voltage, the ions are released, realizing the regeneration of the electrode. CDI highly depends on the properties of the electrode material itself. Based on the ionic radius of sodium ions, if the material itself contains a large number of pores that can accommodate sodium ions, it can provide suitable active sites for sodium ions, thereby achieving high-performance adsorption of sodium ions. Biomass-derived carbon materials are widely used in the electrodes of CDI due to their advantages such as easily available raw materials, low price, and controllable morphology. For example, Li et al. prepared a porous carbon material derived from fruits. By applying a voltage of 1.2V, in a 100mg / L sodium chloride solution, the comprehensive desalination amount can reach 18.02mg / g; Zheng et al. prepared nitrogen-doped porous carbon from silkworm cocoon waste. At a voltage of 1.2V, in a 100mg / L sodium chloride solution, the salt adsorption amount can reach 22mg / g, and the capacity retention rate after 50 adsorption and desorption cycles is as high as 97%. Therefore, biomass-derived porous carbon as a CDI electrode material is a promising solution. Summary of the Invention

[0003] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a porous carbon material derived from pomelo peel, a preparation method thereof, and an application thereof.

[0004] The technical solution of the present invention is as follows:

[0005] A preparation method of a porous carbon material derived from pomelo peel, comprising the following steps:

[0006] S1: Take the spongy part of pomelo peel as a carbon source, wash and dry it, and then perform freeze-drying until the moisture is completely removed to obtain dry pomelo white peel;

[0007] S2: Crush the pomelo white peel with a pulverizer, sieve to obtain powder, and then pre-calcine the powder in an argon atmosphere to obtain a pre-carbonized sample;

[0008] S3: Mix the pre-carbonized sample with potassium hydroxide and potassium chloride, add deionized water and stir evenly, and dry to obtain a precursor;

[0009] S4: Calcinate the precursor at 600 - 1000 °C under an argon atmosphere to obtain a porous carbon material derived from pomelo peel.

[0010] As a preferred embodiment of the present invention, in step S3, the mass ratio of the pre-carbonized sample, potassium hydroxide, and potassium chloride is 1 - 3:1 - 3:6 - 9.

[0011] As a preferred embodiment of the present invention, in step S2, the pre-calcination temperature is 300 - 500 °C, and the pre-calcination time is 40 - 60 min.

[0012] As a preferred embodiment of the present invention, in step S4, the calcination time is 100 - 120 min.

[0013] As a preferred embodiment of the present invention, in steps S2 and S4, the gas flow rate in the argon atmosphere is 80 - 120 mL / min.

[0014] As a preferred embodiment of the present invention, in step S3, the drying is specifically: drying at 70 - 90 °C for 700 - 800 min.

[0015] The present invention also discloses a porous carbon material derived from pomelo peel, which is prepared by using the preparation method described in any one of the above.

[0016] The present invention also discloses an application of the porous carbon material derived from pomelo peel as described above in the preparation of a negative electrode material for capacitive deionization. Mix the porous carbon material derived from pomelo peel, a conductive agent, and a binder, then add 1-methyl-2-pyrrolidone to obtain a uniform slurry. Using a graphite sheet as a current collector, coat the slurry on the surface of the current collector, and obtain a negative electrode plate after drying.

[0017] As a preferred embodiment of the present invention, the conductive agent is at least one of activated carbon, conductive acetylene black, and carbon nanotubes.

[0018] As a preferred embodiment of the present invention, the binder is polyvinylidene fluoride or carboxymethyl cellulose.

[0019] The beneficial effects of the present invention are as follows: The process for preparing the porous carbon of the present invention is simple, and the material obtained under the simple preparation process has a high yield. The microstructure has well-developed pores and a large specific surface area, providing abundant active sites for the adsorption of sodium ions. Under the action of the porous structure, the sodium ion adsorption capacity is improved, and during 30 long-cycle adsorption and desorption processes, the capacity retention rate can reach more than 90%. Description of the Drawings

[0020] Figure 1 It is a morphology structure diagram of the porous carbon material prepared in Example 1 of the present invention;

[0021] Figure 2Morphology structure diagram of the porous carbon material prepared in Example 2 of the present invention;

[0022] Figure 3 Morphology structure diagram of the porous carbon material prepared in Example 3 of the present invention;

[0023] Figure 4 Morphology structure and element distribution diagram of the porous carbon material prepared in Example 2 of the present invention;

[0024] Figure 5 XRD of the porous carbon materials prepared in Examples 1, 2, and 3 of the present invention;

[0025] Figure 6 CV curves of the porous carbon materials prepared in Examples 1, 2, and 3 of the present invention at 2 mV / s;

[0026] Figure 7 CV curves of the porous carbon material prepared in Example 2 of the present invention at different scan rates;

[0027] Figure 8 Specific capacitance comparison of the porous carbon materials prepared in Examples 1, 2, and 3 of the present invention at different scan rates;

[0028] Figure 9 CV curves of the porous carbons prepared in Examples 2, 4, and 5 of the present invention at a scan rate of 2 mV / s;

[0029] Figure 10 Desalination performance diagram of the porous carbon with a porous structure prepared in Example 2 of the present invention after 30 adsorption / desorption cycles. Detailed implementation manners

[0030] Regarding the electrode material mainly composed of porous carbon in CDI mentioned in the background art, this material realizes the removal of ions in brackish water in CDI due to advantages such as easy availability of raw materials, low price, and large specific capacity. However, porous carbon also has defects such as low charge efficiency and poor cycle stability. The reason for these defects may be that the ion transport efficiency is poor due to uneven pore size distribution or sparse pore volume, thus hindering the full play of porous carbon materials in the field of CDI. Based on the above existing problems, the present invention provides a preparation method of porous carbon rich in pores derived from pomelo peel. Specifically, the natural porous structure on the surface of pomelo peel can still be retained to form a carbon skeleton after recarbonization, and then it is etched and activated by potassium hydroxide at high temperature to form porous carbon. During the etching process, the carbon skeleton reacts with potassium hydroxide initially to generate elemental potassium and potassium carbonate, and potassium carbonate further reacts with the carbon skeleton at high temperature to generate elemental potassium. In this process, the carbon skeleton is etched to construct micropores; subsequently, the elemental potassium at high temperature will exist in the form of steam, and the intercalation effect of potassium steam will cause the carbon layer to expand and peel off to form mesopores; at a higher temperature, the carbon skeleton is severely etched and collapses to form macropores. Based on the above principle, considering that the melting point of potassium chloride is 770 °C, then it will be in a molten state at a temperature higher than this, and the additional free potassium ions can further react with the carbon skeleton in an alkaline environment, thereby realizing the synergistic activation of carbon.

[0031] A preparation method of a porous carbon material rich in pores derived from pomelo peel, comprising the following steps:

[0032] S1: Take the spongy part of pomelo peel as a carbon source, wash it and dry it in the air. In the following examples, specifically, use 0.1M sodium hydroxide to degrease and then let it stand for washing for one day, then wash it with deionized water, and then place it in a freeze dryer for freeze drying until the water is completely removed to obtain dry pomelo white peel;

[0033] S2: Crush the obtained pomelo white peel with a pulverizer, sieve to obtain powder, and then pre-calcine the powder in an argon atmosphere to obtain a pre-carbonized sample, and name it PC;

[0034] S3: Mix the pre-carbonized sample with potassium hydroxide and potassium chloride, add deionized water and stir evenly, and then dry it to obtain a precursor;

[0035] S4: Calcinate the precursor at 600 - 1000 °C in an argon atmosphere to obtain a porous carbon material rich in pores derived from pomelo peel, and name the material KPC-n, where n represents the calcination temperature, specifically, the calcination temperature is 600, 700, 800, 900 or 1000 °C.

[0036] Preferably, in step S3, the mass ratio of the pre-carbonized sample to potassium hydroxide and potassium chloride is 1 - 3:1 - 3:6 - 9.

[0037] Preferably, in step S2, the temperature of the pre-calcination is 300-500°C, and the pre-calcination time is 40-60 min.

[0038] As a preferred embodiment of the present invention, in step S4, the calcination time is 100-120 min.

[0039] As a preferred embodiment of the present invention, in steps S2 and S4, the gas flow rate in the argon atmosphere is 80-120 mL / min.

[0040] As a preferred embodiment of the present invention, in step S3, the drying is specifically: drying treatment at 70-90°C for 720 min.

[0041] The present invention also discloses a porous carbon material derived from pomelo peel, which is prepared by using any one of the above preparation methods.

[0042] The present invention also discloses an application of the porous carbon material derived from pomelo peel as described above in the preparation of a negative electrode material for capacitive deionization. The porous carbon material, a conductive agent, and a binder are mixed, and then 1-methyl-2-pyrrolidone is added to obtain a uniform slurry. Using a graphite sheet as a current collector, the slurry is coated on the surface of the current collector, and a negative electrode plate is obtained after drying.

[0043] Preferably, the conductive agent is at least one of activated carbon, conductive acetylene black, and carbon nanotubes.

[0044] Further, the binder is polyvinylidene fluoride or carboxymethyl cellulose.

[0045] The carbon material prepared by the one-step activation method of the present invention has a high porosity, a large specific surface area, and a stable desalination capacity.

[0046] The embodiments of the present invention are described in detail below. The following described embodiments are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0047] Example 1

[0048] A preparation method of a porous carbon material derived from pomelo peel includes the following steps:

[0049] S1: Take out the white part of the pomelo peel, wash it, and freeze-dry it to remove moisture, and then use a pulverizer to break it into pomelo peel raw powder with a 200-mesh sieve.

[0050] S2: Pre-calcine the pomelo peel raw powder in an argon environment, keep it at 400°C for 60 min to obtain pre-carbonized pomelo peel-derived carbon.

[0051] S3. Mix the pomelo peel-derived carbon, potassium chloride, and potassium hydroxide in a ratio of 2.5:2.5:3.5 in 50 ml of aqueous solution to form a homogeneous mixture, and obtain a precursor after drying and grinding.

[0052] Calcine the precursor in an argon atmosphere, heat it to 600 °C and hold for 120 min to obtain the porous carbon KPC-600 with a pore-rich structure derived from pomelo peel.

[0053] Example 2

[0054] A preparation method of a pore-rich carbon material derived from pomelo peel, comprising the following steps:

[0055] S1: Take out the white part of the pomelo peel, wash it, freeze-dry it to remove moisture, and then use a crusher to break it into pomelo peel raw powder passing through a 200-mesh sieve.

[0056] S2: Pre-calcine the pomelo peel raw powder in an argon atmosphere, hold at 400 °C for 60 min to obtain pre-carbonized pomelo peel-derived carbon.

[0057] S3: Mix the pomelo peel-derived carbon, potassium chloride, and potassium hydroxide in a ratio of 2.5:2.5:3.5 in 50 mL of aqueous solution to form a homogeneous mixture, and obtain a precursor after drying and grinding.

[0058] S4: Calcine the precursor in an argon atmosphere, heat it to 800 °C and hold for 120 min to obtain the porous carbon KPC-800 with a pore-rich structure derived from pomelo peel.

[0059] Example 3

[0060] A preparation method of a porous carbon with a pore-rich structure derived from pomelo peel, comprising the following steps:

[0061] S1: Take out the white part of the pomelo peel, wash it, freeze-dry it to remove moisture, and then use a crusher to break it into pomelo peel raw powder passing through a 200-mesh sieve.

[0062] S2: Pre-calcine the pomelo peel raw powder in an argon atmosphere, hold at 400 °C for 60 min to obtain pre-carbonized pomelo peel-derived carbon.

[0063] S3: Mix the pomelo peel-derived carbon with potassium hydroxide and potassium chloride in a ratio of 2.5:2.5:3.5 in 50 ml of aqueous solution to form a homogeneous mixture, and obtain a precursor after drying and grinding.

[0064] Calcine the precursor in an argon atmosphere, heat it to 1000 °C and hold for 120 min to obtain the porous carbon KPC-1000 with a pore-rich structure derived from pomelo peel.

[0065] Example 4

[0066] A preparation method of porous carbon with a rich pore structure derived from pomelo peel, comprising the following steps:

[0067] S1: Take out the white part of the pomelo peel, wash it, freeze-dry it to remove moisture, and then use a pulverizer to break it into pomelo peel raw powder with a 200-mesh sieve.

[0068] S2: Pre-calcine the pomelo peel raw powder in an argon environment, keep it at 400 °C for 60 min to obtain pre-carbonized pomelo peel-derived carbon.

[0069] S3: Mix the pomelo peel-derived carbon with potassium hydroxide in a ratio of 2.5:3.5 in 50 mL of aqueous solution to form a homogeneous mixture, dry and grind it to obtain a precursor.

[0070] Calcine the precursor in an argon environment, heat it to 800 °C and keep it for 120 min to obtain porous carbon KPC-KOH with a rich pore structure derived from pomelo peel.

[0071] Example 5

[0072] A preparation method of porous carbon with a rich pore structure derived from pomelo peel, comprising the following steps:

[0073] S1: Take out the white part of the pomelo peel, freeze-dry it to remove moisture, and then use a pulverizer to break it into pomelo peel raw powder.

[0074] S2: Pre-calcine the pomelo peel raw powder in an argon environment, keep it at 400 °C for 60 min to obtain pre-carbonized pomelo peel-derived carbon.

[0075] S3: Mix the pomelo peel-derived carbon with potassium chloride in a ratio of 2.5:2.5 in 50 ml of aqueous solution to form a homogeneous mixture, dry and grind it to obtain a precursor.

[0076] Calcine the precursor in an argon environment, heat it to 800 °C and keep it for 120 min to obtain porous carbon KPC-KCl with a rich pore structure derived from pomelo peel.

[0077] Example 6

[0078] To explore the electrochemical properties of the materials in Examples 1-5, the three-electrode form was used to preliminarily judge their sodium ion adsorption ability, including the following steps:

[0079] Cut a 2 cm × 4 cm graphite paper as the substrate, take a 2 cm × 2 cm part as the usage area, after drying and degreasing treatment, place it in a drying oven and dry for 24 h to make its surface dry and smooth. Mix the material of Example 1 with commercial activated carbon (AC) and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:1:1, then add 2 mL of 1-methyl-2-pyrrolidone and grind to form a uniform slurry, and then slowly drop it onto the graphite paper. Pre-dry it on a heating stage at 35 °C until there is no obvious moisture on the surface, and then transfer it to a forced-air drying oven and dry at 80 °C for 24 h to obtain a three-electrode polar plate.

[0080] Use an Ag / AgCl electrode as the reference electrode and a platinum mesh as the auxiliary electrode, and conduct a three-electrode test in a 1 M sodium chloride solution. Evaluate its reversibility by cyclic voltammetry (CV) and calculate its specific capacitance value.

[0081] Example 7

[0082] A method for preparing an electrode of CDI includes the following steps:

[0083] Cut a graphite paper with a size of 10 cm × 6 cm and a 2 cm × 2 cm hole dug in the middle as the substrate, after drying and degreasing treatment, place it in a drying oven and dry for 24 h to make its surface dry and smooth. Mix the prepared material of Example 1 with commercial activated carbon (AC) and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:1:1, then add 4 mL of 1-methyl-2-pyrrolidone and grind to form a uniform slurry, and then slowly drop it onto the graphite paper. Pre-dry it on a heating stage at 35 °C until there is no obvious moisture on the surface, and then transfer it to a forced-air drying oven and dry at 80 °C for 24 h to obtain a CDI negative electrode plate. In the same way, use AC coated on the graphite paper as the CDI positive electrode.

[0084] Example 8

[0085] An assembly method for a CDI desalination battery includes the following steps:

[0086] Use two acrylic plates as the overall structure of the CDI, divided into an upper plate and a lower plate. The upper plate is provided with a water outlet and a water inlet to ensure that water can enter the CDI; the lower plate is dug with a groove to ensure the accommodation of water flow and the placement of the electrode plate. The basic assembly process is as follows: in the groove of the lower plate, after placing the negative electrode plate, cover the part without coated active material with a titanium sheet to ensure the passage of current, and then fix it with a titanium alloy screw. Assemble the positive electrode in the same way. To prevent short circuit between the two electrodes, a filter cotton or nylon mesh is padded between the electrode plates. After covering the upper plate, tighten it with screws. There is a silica gel pad between the upper plate and the lower plate, which can control the distance between the two electrodes and prevent water overflow at the same time. Thus, the CDI desalination battery is assembled.

[0087] Example 9

[0088] A testing method for a CDI desalination system, comprising the following steps:

[0089] Use a peristaltic pump to introduce water into the CDI desalination cell described in Example 8 to form a dynamic balance between the inlet water and the outlet water. Circulate in this way for 6 hours to release the impurities within the device, and then drain the water. Prepare a sodium chloride solution with a certain concentration and introduce it into the device to form a stable circulation system again. Control the water flow rate to be 100 mL / min when entering and leaving the solution. Monitor the change in conductivity through a conductivity meter to reflect the change in concentration. When the conductivity does not change, use an electrochemical workstation as an external power supply to connect to the CDI, and conduct desalination evaluation after applying voltages of 0.8V, 1.0V, and 1.2V.

[0090] Perform electron microscopy scanning on the specimens of Examples 1-3, and the results are shown in Figure 1-4 , it can be seen from the figure that under the synergistic etching of potassium chloride and potassium hydroxide, the pre-carbonized pomelo peel-derived carbon forms a porous structure. Figure 2 The pore structure of Figure 1 and Figure 3 is significantly more regular than that of

[0091] Perform X-ray diffraction on the specimens of Examples 1-3, and the results are shown in Figure 5 , from Figure 5 it can be seen that obvious characteristic peaks appear at around 26° and near 43° for all three samples, corresponding to the (002) crystal plane and (100) crystal plane of graphite carbon respectively, indicating that the samples are successfully graphitized.

[0092] Figure 6 is the CV curve of the samples KPC-n prepared in Examples 1-3 in a 1M sodium chloride solution with a potential application rate of 2 mv / s. The CV shows that the porous carbon has the largest area at 800°C, indicating that the formation of the pore structure is favorable at this temperature and the specific capacitance is the largest.

[0093] Figures 7-8 is the comparison of the CV curve and specific capacitance of the sample KPC-800 prepared in Example 2 at different scan rates. The curve shows a quasi-rectangular shape, and no obvious distortion occurs even at a scan rate of 100 mv / s, indicating that the material has a double-layer capacitance characteristic. And KPC-800 has the highest specific capacitance value of 272.6 F / g at a scan rate of 2 mv / s, verifying that KPC has the best performance at a calcination temperature of 800°C.

[0094] Figure 9CV curves of Examples 2, 4, and 5 at an applied potential rate of 2 mV / s. When potassium chloride and potassium hydroxide are added simultaneously to biomass carbon at the same calcination temperature, the CV area shown is the largest, indicating that when potassium chloride is added, the potassium ions provided by molten potassium chloride participate in the reaction and are involved in activation together with potassium hydroxide.

[0095] Figure 10 For the material described in Example 2 after assembling the CDI device, 30 adsorption / desorption cycles were carried out in a 500 mg / L sodium chloride solution. It can be seen that the comprehensive desalination capacity in 30 cycles is 24.6 mg / g, indicating that KPC-800 has a large desalination capacity. And the capacity retention rate after 30 cycles is 94.2%, indicating that this material has good cycle stability.

[0096] The above-described embodiments only represent the preferred embodiments of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, according to the technical solutions and concepts described above, various other corresponding changes and deformations can also be made, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a porous carbon material derived from grapefruit peel, characterized in that: The following steps are involved: S1: taking the spongy part of grapefruit peel as a carbon source, washing it and drying it, and then freeze-drying it until the water is completely removed to obtain dried grapefruit white peel; S2: crushing the grapefruit peel with a grinder, sieving to obtain powder, and then pre-calcining the powder in an argon atmosphere to obtain a pre-carbonized sample; S3: mixing the pre-carbonized sample with potassium hydroxide and potassium chloride, adding deionized water, stirring evenly, and drying to obtain a precursor; S4: calcining the precursor at 600-1000° C. in an argon atmosphere to obtain a grapefruit peel-derived porous carbon material.

2. The method for preparing a porous carbon material derived from grapefruit peel according to claim 1, characterized in that: In step S3, the mass ratio of the pre-carbonized sample to potassium hydroxide and potassium chloride is 1-3:1-3:6-9.

3. The method for preparing a porous carbon material derived from grapefruit peel according to claim 1, characterized in that: In step S2, the pre-calcination temperature is 300-500°C, and the pre-calcination time is 40-60 minutes.

4. The method for preparing a porous carbon material derived from grapefruit peel according to claim 1, characterized in that: In step S4, the calcination time is 100-120 min.

5. The method for preparing a porous carbon material derived from grapefruit peel according to claim 1, characterized in that: In steps S2 and S4, the gas flow rate in the argon atmosphere is 80-120 mL / min.

6. The method for preparing a porous carbon material derived from grapefruit peel according to claim 1, characterized in that: In step S3, the drying is specifically: drying at 70-90° C. for 700-800 min.

7. A porous carbon material derived from grapefruit peel, characterized in that: The method is prepared by any one of claims 1 to 6.

8. A use of the grapefruit peel-derived porous carbon material as claimed in claim 7 in the preparation of a capacitor deionization negative electrode material, characterized in that: The porous carbon material derived from grapefruit peel, a conductive agent and a binder are mixed, and 1-methyl-2-pyrrolidone is added to obtain a uniform slurry. A graphite sheet is used as a current collector, and the slurry is coated on the surface of the current collector. After drying, a negative electrode sheet is obtained.

9. The use according to claim 8, characterized in that: The conductive agent is at least one of activated carbon, conductive acetylene black and carbon nanotubes.

10. The use according to claim 8, characterized in that: The binder is polyvinylidene fluoride or carboxymethyl cellulose.

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