Coconut shell charcoal-based composite electrode material, preparation method thereof and application of the composite electrode material in electric adsorption removal of phosphate ions in water

Abstract

The application discloses a coconut shell charcoal-based composite electrode material and a preparation method and application thereof, and the composite electrode material comprises coconut shell charcoal and graphene loaded on the surface of the coconut shell charcoal; the coconut shell charcoal has a three-dimensional porous structure; and the graphene is loaded on the surface of the coconut shell charcoal to form a high-efficiency conductive network structure. By introducing the graphene into the coconut shell charcoal, the three-dimensional skeleton structure of the coconut shell charcoal provides a uniform dispersion carrier for the graphene, and more active sites are exposed; the high conductivity of the graphene improves the charge transmission efficiency of the electrode, and the plugging of the pores of the coconut shell charcoal is inhibited; the composite material has higher conductivity and more active sites, and the removal efficiency of the material on the phosphate is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of water treatment functional material preparation and water environment management technology, and specifically relates to a coconut shell carbon-based composite electrode material, its preparation method and its application in electro-adsorption removal of phosphate ions in water. Background Technology

[0002] Phosphate is a key factor contributing to eutrophication in water bodies. Excessive phosphate levels can trigger algal blooms, red tides, and damage aquatic ecosystems. Total phosphorus has become a major pollutant exceeding standards in my country's surface water, making efficient phosphorus removal an urgent need for aquatic ecological environment protection. Existing phosphorus removal technologies each have their drawbacks: biological phosphorus removal is easily affected by environmental factors such as temperature and carbon sources, resulting in unstable efficiency; chemical precipitation methods consume large amounts of reagents, produce high levels of sludge, easily cause secondary pollution, and are ineffective at removing hypophosphite and special forms of organic phosphorus; traditional adsorption methods have low adsorption saturation and are highly pH sensitive; crystallization methods have stringent requirements on influent water quality parameters, limiting their applicability.

[0003] Electroadsorption (CDI) technology achieves ion adsorption and separation based on the double-layer theory, offering advantages such as low energy consumption, regenerable electrodes, and no secondary pollution. Electrode materials are the core of its performance. Carbon-based materials are the mainstream choice for CDI electrodes. Among them, coconut shell carbon, as a high-quality biomass-derived carbon, possesses advantages such as a naturally hierarchical porous structure, high specific surface area, high graphitization degree, stable physicochemical properties, and readily available, green, and economical raw materials, making it an ideal substrate for preparing phosphorus removal electrodes. However, single coconut shell carbon electrodes suffer from micropore agglomeration, insufficient charge transport efficiency, and low phosphate ion removal efficiency. Summary of the Invention

[0004] Objectives of the Invention: The first objective of this invention is to provide a coconut shell carbon-based composite electrode material that improves the removal efficiency of phosphates; the second objective of this invention is to provide a method for preparing the coconut shell carbon-based composite electrode material; and the third objective of this invention is to provide applications of the coconut shell carbon-based composite electrode material.

[0005] Technical solution: The coconut shell carbon-based composite electrode material of the present invention includes coconut shell carbon and graphene loaded on the surface of coconut shell carbon. The coconut shell carbon has a three-dimensional porous structure, and the graphene loaded on the surface of the coconut shell carbon forms a highly efficient conductive network structure.

[0006] The composite of graphene and coconut shell carbon utilizes the three-dimensional porous structure of coconut shell carbon and the high conductivity of graphene. The synergistic effect of these two materials improves the charge transport efficiency of the electrode, prevents graphene agglomeration, and inhibits the clogging of the pores in the coconut shell carbon. Preferably, the graphene powder accounts for 5-10% of the total mass of the coconut shell carbon and graphene in the composite electrode material.

[0007] More preferably, the graphene powder in the composite electrode material accounts for 5 to 7.5% of the total mass of coconut shell carbon and graphene.

[0008] The preparation method of the coconut shell carbon-based composite electrode material of the present invention includes the following steps:

[0009] (1) The coconut shell charcoal is acid-washed to remove impurities, washed and dried to obtain pretreated coconut shell charcoal;

[0010] (2) Add the pretreated coconut shell biochar powder and graphene powder to a solvent and mix them evenly by ultrasonication so that the graphene is loaded on the surface of the coconut shell biochar to obtain the graphene / coconut shell biochar composite electrode material.

[0011] Preferably, in step (1), the pickling is performed using 0.05~0.15 M hydrochloric acid, and the washing is performed by repeatedly washing with deionized water until neutral.

[0012] Preferably, in step (2), the solvent is ethanol.

[0013] The biomass electrode of the present invention contains the coconut shell carbon-based composite electrode material.

[0014] Preferably, the electrode is prepared by mixing the composite electrode material with an adhesive and a solvent to obtain a slurry, which is then uniformly coated onto a current collector to obtain a biomass electrode.

[0015] Preferably, the adhesive is polytetrafluoroethylene (PTFE). More preferably, the mass ratio of the composite electrode material to the adhesive is 1:1 to 1:2.

[0016] The application of the coconut shell carbon-based composite electrode material or electrode described in this invention in the electroadsorption removal of phosphate.

[0017] Preferably, during desalination, a voltage of 0~1.6 V is applied across the electrode plates, and the flow rate of the solution is 10~18 mL / min.

[0018] Mechanism of Invention: Coconut shell charcoal, as a biomass carbon material, possesses abundant pore structure and high specific surface area, providing numerous active sites for the electroadsorption of phosphates. Graphene exhibits excellent conductivity and mechanical strength, but its layers are prone to stacking. By combining graphene with coconut shell charcoal, utilizing the three-dimensional framework structure of coconut shell charcoal as a support, the stacking of graphene layers is effectively suppressed. Simultaneously, graphene constructs a three-dimensional conductive network on the surface of coconut shell charcoal, significantly improving the overall conductivity of the composite material. The three-dimensional framework structure of coconut shell charcoal provides a uniformly dispersed carrier for graphene, exposing more active sites; the high conductivity of graphene enhances the charge transport efficiency of the electrode and inhibits the clogging of the pores in coconut shell charcoal. Through the synergistic effect of both, the composite electrode material exhibits high capacity, high efficiency, and good stability in the electroadsorption removal of phosphates.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By introducing graphene into coconut shell carbon, the two work synergistically, and the composite material has higher conductivity and more active sites, which significantly improves the removal efficiency of the material for phosphate; (2) The composite electrode material with a graphene content of 5% has a specific capacitance of 48.45 F / g, which is about 2.3 times higher than that of pure coconut shell carbon electrode material; (3) The composite electrode material of the present invention has a simple preparation process, low cost, and is suitable for large-scale production, and has good economic benefits; (4) The composite electrode material of the present invention exhibits high capacity, high efficiency and good stability in the application of electro-adsorption removal of phosphate, and is suitable for the treatment of phosphorus pollution in eutrophic waters, and also has the potential for phosphorus resource recovery. Attached Figure Description

[0020] Figure 1 Cyclic voltammetry curves of electrodes prepared from the coconut shell carbon composite electrode materials obtained in Examples 1-3 and Comparative Examples 1-2 are shown.

[0021] Figure 2 Cyclic voltammetry curves of electrodes prepared from the composite electrode materials obtained in Example 1, Comparative Example 1, and Comparative Example 3.

[0022] Figure 3 A comparison graph showing the change of phosphate ion concentration over time in the electroadsorption experiment between the coconut shell carbon electrode prepared in Comparative Example 1 and the electrode prepared from the composite electrode material prepared in Example 1.

[0023] Figure 4 A comparison of the adsorption capacity of the coconut shell carbon electrode prepared in Comparative Example 1 and the electrode prepared from the composite electrode material prepared in Example 1 over time in an electroadsorption experiment.

[0024] Figure 5 A comparison of the phosphate ion concentration over time at different voltages for electrodes prepared from the composite electrode material obtained in Example 1.

[0025] Figure 6 A bar chart showing the phosphate removal amount of the electrode prepared from the composite electrode material obtained in Example 1 at different voltages;

[0026] Figure 7 The bar chart shows the phosphate removal of electrodes prepared from the composite electrode material obtained in Example 1 at different initial concentrations. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the embodiments.

[0028] Example 1

[0029] The coconut shell carbon-based composite electrode material of the present invention is prepared by the following steps:

[0030] (1) Pretreatment of coconut shell charcoal

[0031] ① Acid washing: Clean the purchased coconut shell charcoal with 0.1 mol hydrochloric acid.

[0032] ② Washing and drying: Wash the above coconut shell charcoal repeatedly with deionized water until it is neutral (pH≈7); place the washed commercial coconut shell charcoal in a vacuum oven and dry it at 60℃ for later use.

[0033] (2) Composite of coconut shell carbon and graphene

[0034] 47.5 mg of pretreated coconut shell carbon powder and 2.5 mg of graphene powder were placed in a beaker, and ethanol was added until the powder was submerged. The mixture was sonicated at 100 Hz for 20 minutes to obtain a 5% graphene / coconut shell carbon composite electrode material.

[0035] Example 2

[0036] Based on Example 1, in step (2), the mass of coconut shell carbon powder was changed to 46.25 mg and the mass of graphene powder was changed to 3.75 mg. Under the same conditions, a 7.5% graphene / coconut shell carbon composite electrode material was obtained.

[0037] Example 3

[0038] Based on Example 1, in step (2), the mass of coconut shell carbon powder was changed to 45 mg, the mass of graphene powder was changed to 5 mg, and the rest of the conditions remained unchanged, to obtain a 10% graphene / coconut shell carbon composite electrode material.

[0039] Comparative Example 1

[0040] Based on Example 1, only step (1) is performed to obtain the coconut shell carbon electrode material.

[0041] Comparative Example 2

[0042] Based on Example 1, in step (2), the mass of coconut shell carbon powder was changed to 48.75 mg and the mass of graphene powder was changed to 1.25 mg. Under the same conditions, a 2.5% graphene / coconut shell carbon composite electrode material was obtained.

[0043] Comparative Example 3

[0044] Based on Example 1, in step (2), the graphene powder was replaced with amino graphene powder (about 12 wt%), hydroxyl graphene powder (about 15 wt%), and carboxyl graphene powder (about 12 wt%), while the other conditions remained unchanged.

[0045] Electrochemical characterization

[0046] Cyclic voltammetry was performed on an electrochemical workstation. The electrolyte was 40 mL of 0.5 mol / L sodium chloride solution. The reference electrode was a saturated calomel electrode, the counter electrode was a platinum electrode, and the working electrode was an electrode made of coconut shell carbon-based composite material. The scanning voltage was -0.4 ~ 0.6 V, and the scan rate was 10 mV / s.

[0047] Working electrode preparation method:

[0048] The graphite paper was cut into rectangular electrode sheets of 2.0 cm × 1.2 cm. The sheets were then cleaned with deionized water and anhydrous ethanol to ensure that there were no impurities on the surface of the graphite paper. Finally, the sheets were placed in an oven and dried at 60°C for 6 hours. After drying, the sheets were removed and cooled to room temperature.

[0049] Weigh 0.05 g of electrode material (the electrode materials prepared in Examples 1-3 and Comparative Examples 1-3) and 0.0833 g of polytetrafluoroethylene dispersion (mass fraction of 60%) into a beaker (this is the mass of the three working electrode sheets to be coated). Add a small amount of ethanol to the mixture to make it into a slurry state. Then, stir it thoroughly to achieve uniform mixing. Place the beaker in an ultrasonic device for ultrasonic treatment for 30 min. After the material has solidified, divide it into three equal parts and coat them evenly onto graphite sheets with a size of 2 cm × 1.2 cm. Then, place the coated electrode sheets in an oven and dry them at a constant temperature of 60°C for 12 h to obtain the working electrodes.

[0050]

[0051] In the formula, I is the response current, A; m is the mass of the electrode material, g; v is the voltage scan rate, mV / s; ∆V is the voltage window, V; C CV ρ is the specific capacitance of the electrode material, F / g.

[0052] Test results are as follows Figures 1-2 As shown.

[0053] Depend on Figure 1It can be seen that the composite electrode material doped with 5% graphene has the largest curve area; the composite electrode materials doped with more than 5% graphene have similar curve areas, which decrease with increasing graphene content, and are all smaller than the composite electrode material doped with 5% graphene; the composite electrode materials doped with less than 5% graphene have the second largest curve area, which is less than that of the composite electrode material doped with 5% graphene. Using the specific capacitance formula above, the specific capacitance of the composite electrode material doped with 5% graphene is 48.45 F / g, the specific capacitance of the composite electrode material doped with 7.5% graphene is 23.84 F / g, the specific capacitance of the composite electrode material doped with 10% graphene is 21.56 F / g, the specific capacitance of the composite electrode material doped with 2.5% graphene is 19.54 F / g, and the specific capacitance of the pure coconut shell carbon electrode material is 21.25 F / g. The composite electrode material doped with 5% graphene exhibited a highly closed test curve, weakened redox peaks, and a shape closest to an ideal rectangle. The test curves of composite electrode materials doped with more than 5% graphene all showed slight distortion and a drop in current, possibly due to excessive graphene blocking the pores and hindering ion transport. Compared to the pure coconut shell carbon electrode prepared in Comparative Example 1, the composite electrode material doped with 5% graphene showed nearly double the current, a stable potential window, and a specific capacitance approximately 2.3 times that of the pure coconut shell carbon material.

[0054] Depend on Figure 2 It can be seen that the area of ​​the composite electrode material doped with 5% amino graphene and 5% carboxyl graphene is smaller than that of the composite electrode material doped with 5% graphene. Calculated using the specific capacitance formula, their specific capacitances are 23.93 F / g and 15.33 F / g, respectively, indicating that the charge storage capacity of both composite electrode materials needs to be improved. Although the area of ​​the composite electrode material doped with 5% hydroxyl graphene is larger, its specific capacitance is 21.98 F / g, indicating that this type of composite electrode material actually stores less charge and may introduce irreversible Faraday side reactions.

[0055] Adsorption performance test

[0056] 1. The phosphate ion removal performance of materials with different graphene contents

[0057] (1) Electrode preparation

[0058] The graphite paper was cut into 6 cm × 6 cm sizes and cleaned with deionized water and anhydrous ethanol in sequence to ensure that there were no impurities on the surface of the graphite paper. Finally, it was placed in an oven and dried at 60°C for 6 hours. After that, it was taken out and cooled to room temperature.

[0059] Weigh 0.05 g of electrode material (prepared in Example 1 and Comparative Example 1) and 0.0833 g of polytetrafluoroethylene dispersion (60% by mass) into a beaker, add a small amount of ethanol to make it into a slurry, and then stir it thoroughly to achieve uniform mixing. Then place the beaker in an ultrasonic device for ultrasonic treatment for 30 min. After the material is formed, coat it evenly on a graphite sheet with a size of 6 cm × 6 cm (the effective coating area is 3 cm × 3 cm). Prepare two electrodes using the same operation method. Then place the coated electrode sheets in an oven and dry them at a constant temperature of 80°C for 12 h to obtain a pair of electrode sheets suitable for one device.

[0060] (2) Capacitor deionization desalination device

[0061] The capacitive deionization (CDI) device consists of a CDI unit [using the electrode sheet prepared in step (1)], a DC power supply, a peristaltic pump, a storage tank, a magnetic stirrer, and a conductivity meter. First, a potassium dihydrogen phosphate solution of a certain concentration is prepared as the initial solution and pumped into the CDI module using the peristaltic pump. Then, the power is turned on, and the conductivity of the solution is read and recorded. The conductivity change of the solution is monitored in real time using the conductivity meter, and the concentration of the solution is calculated from the conductivity. The phosphate ion concentration is determined using the ammonium molybdate spectrophotometric method. 1 mL of ascorbic acid and 2 mL of ammonium molybdate are added sequentially to water samples with different adsorption times, and color development is performed for 13 min.

[0062] The removal amount and rate of phosphate ions from the materials prepared in Example 1 and Comparative Example 1 were tested in a 100 mL volume of 20 mg / L potassium dihydrogen phosphate solution under an applied directional voltage of 1.6 V, a flow rate of 25 r / min, and the results are as follows: Figure 3 and Figure 4 As shown.

[0063] Figure 3 The graph shows the change in the concentration of the adsorption solution for the two electrodes over time. As can be seen from the graph, the pure coconut shell carbon electrode reaches adsorption equilibrium at around 70 minutes (the adsorption capacity at different times is similar and there is no significant change), reaching the upper limit of the adsorption capacity. The 5% graphene / coconut shell carbon electrode has a greater adsorption capacity than the pure coconut shell carbon electrode at 80 minutes, and the adsorption rate is still greater than that of the pure coconut shell carbon electrode, indicating that there is still some adsorption space.

[0064] Figure 4The graph shows the change in adsorption capacity (difference in solution concentration before and after adsorption) of the two electrodes over time. As can be seen from the graph, at 80 min, the adsorption capacity of the pure coconut shell carbon electrode was 9.67 mg / g; the adsorption capacity of the 5% graphene / coconut shell carbon electrode reached 12.67 mg / g. The phosphorus removal capacity of the material after combining coconut shell carbon and graphene was further improved, indicating that the addition of graphene significantly improved the adsorption performance of the electrode. Graphene may have provided more active sites or improved the conductivity of the electrode.

[0065] 2. Performance testing of phosphate ion removal under different voltage conditions

[0066] Test method: The electrode prepared using the electrode material prepared in Example 2 was tested for phosphate removal performance in a 20 mg / L potassium dihydrogen phosphate solution at a flow rate of 25 r / min under different voltages (0V, 0.8V, 1.2V, 1.6V, 2.0V). The results are as follows: Figure 5 , 6 As shown.

[0067] Depend on Figure 5 The data shows that the initial concentration for all voltage groups was 20.0 mg / L. Under 0 V voltage, the solution concentration was consistently higher than that of other voltage groups at each time point, indicating that voltage application promoted the electroadsorption of phosphate ions. Under 1.6 V voltage, the initial concentration was 20.0 mg / L, but after 80 min of adsorption, the residual concentration decreased to 13.7 mg / L, a decrease of 6.3 mg / L, which was greater than the decrease in other voltage groups, demonstrating higher removal efficiency.

[0068] Depend on Figure 6 It was found that under voltage conditions of 0V, 0.8V, 1.2V, 1.6V, and 2.0V, the phosphate removal amounts after 80 min were 6.65 mg / g, 7.38 mg / g, 9.39 mg / g, 12.67 mg / g, and 7.38 mg / g, respectively. The phosphate removal amount gradually increased with increasing voltage. This is because higher voltage results in a stronger electric field, which promotes the Coulombic interaction between ions and the electrode, enhances ion transport and penetration, and facilitates the formation of a stronger electric double layer. However, when the voltage exceeds 1.6V, the stability limit of water is exceeded, and water electrolysis side reactions occur on the electrode surface, generating H2 and O2 bubbles. These bubbles clog the electrode pores, hindering the migration of phosphate ions to the active sites. Simultaneously, the electrolysis side reactions consume a large amount of electrical energy, reducing the energy efficiency of electroadsorption. Furthermore, excessively high electric fields can cause some adsorbed phosphate ions to desorb, reducing their adsorption capacity.

[0069] 3. Phosphate ion removal performance under different initial concentration conditions

[0070] Test method: Electrodes prepared using the composite electrode material prepared in Example 2 were tested for phosphate ion removal performance in potassium dihydrogen phosphate solutions with initial concentrations of 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, and 25 mg / L, under conditions of 1.6 V voltage and 25 r / min flow rate. The results are as follows: Figure 7 As shown.

[0071] Depend on Figure 7 The results showed that when the initial solution concentrations for phosphorus removal were 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, and 25 mg / L, the phosphorus removal amounts were 4.94 mg / g, 6.39 mg / g, 11.10 mg / g, 12.67 mg / g, and 16.99 mg / g, respectively. The phosphorus removal capacity of the composite electrode material gradually increased with increasing initial concentration. This is mainly because a high concentration of electrolyte reduces the diffusion barrier of the solute in the solution, thereby reducing mass transfer resistance and accelerating ion transfer and adsorption.

Claims

1. A coconut shell carbon-based composite electrode material, characterized in that, The composite electrode material includes coconut shell carbon and graphene loaded on the surface of coconut shell carbon. The coconut shell carbon has a three-dimensional porous structure, and the graphene loaded on the surface of the coconut shell carbon forms a highly efficient conductive network structure.

2. The coconut shell carbon-based composite electrode material according to claim 1, characterized in that, In the composite electrode material, graphene powder accounts for 5-10% of the total mass of coconut shell carbon and graphene.

3. The coconut shell carbon-based composite electrode material according to claim 2, characterized in that, In the composite electrode material, graphene powder accounts for 5-7.5% of the total mass of coconut shell carbon and graphene.

4. A method for preparing the coconut shell carbon-based composite electrode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) The coconut shell charcoal is acid-washed to remove impurities, washed and dried to obtain pretreated coconut shell charcoal; (2) Add the pretreated coconut shell biochar powder and graphene powder to a solvent and mix them evenly by ultrasonication so that the graphene is loaded on the surface of the coconut shell biochar to obtain the graphene / coconut shell biochar composite electrode material.

5. The method for preparing the coconut shell carbon-based composite electrode material according to claim 4, characterized in that, In step (1), the pickling is performed using 0.05~0.15 M hydrochloric acid, and the washing is performed by repeatedly washing with deionized water until neutral.

6. A biomass electrode containing the coconut shell carbon-based composite electrode material according to any one of claims 1 to 3.

7. The electrode according to claim 6, characterized in that, The electrode is prepared by mixing the composite electrode material with an adhesive and a solvent to obtain a slurry, which is then uniformly coated onto a current collector to obtain a biomass electrode.

8. The electrode according to claim 7, characterized in that, The adhesive is polytetrafluoroethylene.

9. The electrode according to claim 8, characterized in that, The mass ratio of the composite electrode material to the binder is 1:1 to 1:

2.

10. The application of a coconut shell carbon-based composite electrode material according to any one of claims 1 to 3 or an electrode according to claims 6 to 9 in the electro-adsorption removal of phosphate.

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