Preparation and application of antimony-nitrogen co-doped turbostratic layered carbon material for treating fluorine wastewater

Abstract

The application belongs to the technical field of water treatment and resource, and discloses a kind of antimony-nitrogen co-doped turbo layered carbon-based material for treating fluorine wastewater, preparation and application of capacitive deionization electrode, with supramolecule as precursor, carbon skeleton is formed by pyrolysis and then element doping to prepare antimony-nitrogen co-doped turbo layered carbon-based material as anode material, with carboxyl activated carbon as cathode material, cathode and anode jointly constitute capacitive deionization system.Antimony-nitrogen co-doped turbo layered carbon-based material has layered loose controllable mesoporous structure, rich active sites and excellent specific capacitance caused by typical faradic pseudocapacitance.Antimony-nitrogen co-doped turbo layered carbon-based material capacitive deionization electrode shows excellent fluorine ion adsorption capacity in fluorine-containing wastewater, specifically, fast adsorption rate and large adsorption capacity.The capacitive deionization electrode has good engineering application prospect in actual wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of water treatment and resource utilization technology, and in particular to the preparation and application of an antimony-nitrogen co-doped turbine layered carbon-based material and a capacitor deionization electrode for treating fluoride wastewater. Background Technology

[0002] The Earth's freshwater reserves are scarce, and the global water resources situation has long been precarious. Simultaneously, with societal development, human activities have increasingly damaged and polluted water resources, while water pollution control technologies have lagged behind. Among numerous water pollutants, fluoride is extremely harmful and difficult to remove. Furthermore, due to continuous global industrial development and progress, the volume of fluoride-containing wastewater has further expanded, polluting more and more water bodies and posing a greater threat to usable water resources. Excessive fluoride intake can cause various diseases, affecting human survival and health. Therefore, establishing effective fluoride removal technologies is crucial. Currently, ion exchange, electrolysis, adsorption, and precipitation methods have been developed and are widely used to remove fluoride ions from wastewater. Adsorption is a commonly used water treatment method that has attracted considerable attention from scholars; it is also one of the most effective and reliable methods for fluoride removal, with high-performance adsorption materials being a key factor in efficient fluoride removal. The adsorption process of F- by an adsorbent typically involves three basic steps: (1) F- diffuses from the solution through the boundary layer surrounding the adsorbent particles or is transported to the outer surface of the adsorbent particles, a process known as molecular diffusion; (2) F- is adsorbed on the surface of the adsorbent particles; (3) F- adsorbs onto the surface of the adsorbent. - Intraparticle diffusion refers to the exchange of substances within adsorbed particles or their transfer to the inner surface of the adsorbed particles. The excellent adsorption properties of adsorbents are mainly due to their dense microporous structure, large specific surface area, or the presence of groups that can form chemical bonds with the adsorbate. Chemical precipitation involves adding soluble chemical agents to fluoride-containing wastewater, causing them to react with ionic inorganic pollutants to form fluoride precipitates that are insoluble or sparingly soluble in water, thus reducing the fluoride content in the water. Coagulation sedimentation and chemical precipitation are two commonly used precipitation methods and are also frequently used methods for fluoride removal. Ion exchange utilizes ion exchange resins to selectively remove pollutants from wastewater. While removing target ions, it also releases equivalent ions into the solution to maintain electroneutrality. Ion exchange for fluoride removal involves exchanging anions in the ion exchange resin with F- in the water, thereby reducing the F- concentration. Membrane treatment for fluoride removal utilizes numerous tiny pores on a special membrane, allowing F- in the liquid to selectively permeate based on the particle size of the mixture. -Membrane treatment methods, including reverse osmosis, electrodialysis, ultrafiltration, and nanofiltration, are relatively user-friendly separation technologies. However, these methods invariably suffer from problems such as inconvenient operation, large footprint, high cost, and susceptibility to secondary pollution, which means they have significant drawbacks and obstacles in practical applications.

[0003] Capacitive deionization (CDI) is a technology that removes ionic contaminants through an electroadsorption process by applying a low potential voltage between paired electrodes. During adsorption, this voltage causes ions in the solution to migrate directionally to the electrodes and be stored in the electric double layer. During desorption, applying zero or reverse voltage to the electrodes releases the accumulated ions back into the solution, thus regenerating the system. CDI technology has advantages such as low energy consumption, strong regeneration capacity, no secondary pollution, and flexible scale. However, traditional CDI technology also has some drawbacks, with low adsorption capacity and slow adsorption rate being the main problems. For example, commercially available activated carbon with low capacitance has poor electroadsorption capacity for fluoride ions. Similarly, the fluoride ion electroadsorption capacity of carbon-based materials such as carbonized aerogels and biochar is difficult to exceed 0.5 mmol / g. Overall, research and development of CDI electrodes for fluoride removal are limited; therefore, developing novel carbon-based fluoride removal materials that can improve electroadsorption performance remains a major challenge in the field of CDI. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing and applying an antimony-nitrogen co-doped turbine layered carbon-based material and a capacitive deionization electrode for treating fluoride wastewater. By applying the antimony-nitrogen co-doped turbine layered carbon-based material to the capacitive deionization electrode, it exhibits a large capacity and fast rate of fluoride ion adsorption in fluoride-containing wastewater.

[0005] The technical solution adopted by this invention to solve the technical problem is:

[0006] The first aspect of this invention provides an antimony-nitrogen co-doped turbine layered carbon-based material for treating fluoride wastewater. The antimony-nitrogen co-doped turbine layered carbon-based material has a layered, loose, and controllable mesoporous structure, abundant active sites, and excellent specific capacitance due to the typical Faraday pseudocapacitive effect. It has uniform particle size and regular geometric micro-rolled shape. The antimony-nitrogen co-doped turbine layered carbon-based material electrode exhibits excellent fluoride ion adsorption capacity in fluoride-containing wastewater, specifically manifested in fast adsorption rate and large adsorption capacity.

[0007] A second aspect of the present invention provides a method for preparing the antimony-nitrogen co-doped turbine layered carbon-based material, comprising:

[0008] (1) At 25°C, pyromellitic acid and melamine are dissolved in distilled water and stirred for 8-12 hours. The resulting solution is then semi-sealed in a drying oven at 100-120°C for 20-25 hours. The temperature of the drying oven is then increased by 8-12°C for 6-10 hours. Finally, the semi-solid is completely dried to obtain the precursor.

[0009] (2) The precursor is fed into a tube furnace and heated to 800-1000℃ for 1-3 hours in a nitrogen atmosphere at a heating rate of 2-5℃ / min. After washing and drying with deionized water, a carbon-based framework is obtained. The carbon-based framework is dispersed in ethanol, and then antimony nitrate is added. The mixture is then stirred immediately for 1-2 hours to obtain a mixture.

[0010] (3) The resulting mixture was transferred to a Teflon high-pressure reactor and reacted at 130-150℃ for 10-14 hours. The mixture was then washed with distilled water and ethanol, and dried to obtain antimony-nitrogen co-doped turbine layered carbon-based material.

[0011] Furthermore, the mass ratio of pyromellitic acid to melamine is 1.2–1.8:0.8–1.2.

[0012] Furthermore, the mass ratio of melamine to distilled water is 1.2-1.8g:90-110mL.

[0013] Furthermore, the mass of the carbon-based skeleton and the volume of ethanol used are 0.8-1.2g:150-250mL.

[0014] Furthermore, the mass ratio of antimony nitrate to carbon-based skeleton is 0.8–1.2:0.1–0.3.

[0015] The third aspect of the present invention provides a capacitive deionization electrode prepared from the antimony-nitrogen co-doped turbine layered carbon-based material, the preparation method comprising: grinding and mixing the antimony-nitrogen co-doped turbine layered carbon-based material, conductive carbon black and polytetrafluoroethylene at contents of 80%, 10% and 10% respectively, and ultrasonically sonicating for 8-12 minutes to obtain a slurry, uniformly dripping the slurry onto graphite paper, and then drying it at 75-85°C for 3-5 hours to finally form a capacitive deionization electrode.

[0016] The fourth aspect of the present invention provides a method for preparing a capacitive deionization device using the aforementioned capacitive deionization electrode. The capacitive deionization electrode is used as the anode to capture fluoride ions. Carboxyl activated carbon, conductive carbon black and polytetrafluoroethylene are ground and mixed at contents of 80%, 10% and 10%, respectively. The mixture is then ultrasonically sonicated for 8-12 minutes to obtain a slurry. The slurry is uniformly dripped and coated onto graphite paper, and then dried at 75-85°C for 3-5 hours to finally form a cathode. The anode and cathode together constitute the capacitive deionization device.

[0017] The fifth aspect of this invention provides an application of the capacitor deionization device in the treatment of fluoride wastewater. Fluoride wastewater is added to a CDI reactor, and the capacitor deionization device applies a voltage of 1.0-1.4V for electroadsorption, with an adsorption time of 55-70 minutes. After adsorption is completed, the applied voltage is changed to -1.0-1.4V, the desorption time is 55-70 minutes, and the desorbed electrode is immersed in deionized water for later use.

[0018] Furthermore, the fluoride wastewater is a sodium fluoride solution.

[0019] Furthermore, in the adsorption experiment, samples were collected every 15 minutes, with 0.5 mL of solution taken each time.

[0020] This invention uses a self-assembly method to synthesize a structurally ordered turbine-like layered carbon-based material, and incorporates antimony-nitrogen dual-element doping into the carbon-based material to prepare a loose, porous mesoporous channel that facilitates rapid ion diffusion.

[0021] Using supramolecular materials synthesized from pyromellitic acid and melamine as precursors, the precursors were pyrolyzed to obtain turbine-like layered carbon-based materials. Antimony-nitrogen co-doping was then incorporated into the material to prepare antimony-nitrogen co-doped turbine-like layered carbon-based materials. The prepared antimony-nitrogen co-doped turbine-like layered carbon-based materials exhibit uniform particle size, regular geometric micro-rolled shapes, and good diffusivity and dispersibility. Antimony-nitrogen co-doping enhances the overall stability of the material and accelerates the electron transport rate within the carbon-based material. Furthermore, when used as the anode of a CDI electrode, this invention exhibits a significant Faraday pseudocapacitive effect, causing the CDI electrode to form a supercapacitor, increasing its specific capacitance, and enhancing its electroadsorption performance.

[0022] In a 50 mg / L sodium fluoride solution, at a voltage of 1.2 V, the CDI system using antimony-nitrogen co-doped turbine layered carbon-based material as the electrode anode exhibited an excellent fluoride ion adsorption capacity of 1.82 mmol / g.

[0023] To verify the unique structural engineering design described above, the electrode material of this invention was characterized by SEM, which demonstrated the feasibility of the structure, the effectiveness of the synthesis, and the actual presence of the chemical components at the microstructural level. Furthermore, in control experiments under different reaction conditions, the electroadsorption behavior was affected by factors such as pH and interfering ions. These conditional experiments provided a wealth of data for analyzing the electrode's ability to remove fluoride ions, and fluid dynamics simulations provided a theoretical basis for analyzing solute distribution and mass transfer processes, thus allowing for further investigation into the electroadsorption mechanism of turbine-like layered carbon-based materials. In addition, the cycling stability of the invented electrode material was also studied and demonstrated to possess excellent cycling stability.

[0024] The advantages and positive effects of this invention are:

[0025] (1) The antimony-nitrogen co-doped turbine layered carbon-based material prepared by the present invention has a layered, loose and controllable mesoporous structure, abundant active sites and excellent specific capacitance brought about by the typical Faraday pseudocapacitive effect.

[0026] (2) The capacitive deionization electrode based on antimony-nitrogen co-doped turbine layered carbon material prepared in this invention is applied to the efficient adsorption of fluoride ions in wastewater. This capacitive deionization electrode exhibits a significant Faraday pseudocapacitive effect, demonstrating a large capacity and rapid adsorption rate of fluoride ions in fluoride-containing wastewater, and achieving good fluoride ion selectivity. Attached Figure Description

[0027] Figure 1 Scanning electron microscope image of antimony-nitrogen co-doped turbine-like carbon-based material;

[0028] Figure 2 This is a schematic diagram of the material synthesis and electrode device operation.

[0029] Figure 3 Cyclic voltammetry curves showing redox peaks representing pseudocapacitive properties of the material;

[0030] Figure 4 This is a diagram showing the phase composition analysis of the material obtained by X-ray powder diffraction.

[0031] Figure 5 The adsorption capacity diagrams of the antimony-nitrogen co-doped turbine layered carbon-based material for different interfering ions, different initial pH, different initial voltage, and different test concentrations are shown. Among them, a is the adsorption capacity diagram for different initial voltages, b is the adsorption capacity diagram for different test concentrations, c is the adsorption capacity diagram for different initial pH, and d is the adsorption capacity diagram for different interfering ions.

[0032] Figure 6 The graph shows the cycling stability after 20 cycles, where the adsorption capacity remains at 90% of the initial value. Detailed Implementation

[0033] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0034] Example 1

[0035] A method for preparing an antimony-nitrogen co-doped turbine layered carbon-based material includes:

[0036] At 25°C, 2.287 g of 1,2,4,5-benzenetetracarboxylic acid and 1.513 g of melamine were dissolved in 100 mL of distilled water and stirred for 10 hours. The resulting solution was then semi-sealed in a 110°C drying oven for 24 hours. The oven temperature was then increased by 10°C for 8 hours, and the resulting semi-solid was completely dried to obtain the precursor. The precursor was placed in a tube furnace and heated to 900°C for 2 hours in a nitrogen atmosphere at a heating rate of 5°C / min. After washing with deionized water and drying, a carbon-based framework was obtained. The carbon-based framework (0.2 g) was dispersed in ethanol (40 mL), and then antimony nitrate (1.0 g) was added, followed by immediate stirring for 1 hour. The resulting mixture was transferred to a Teflon high-pressure reactor and reacted at 140°C for 12 hours. The sample was then washed three times each with distilled water and ethanol and dried. The resulting product is an antimony-nitrogen co-doped turbine layered carbon-based material.

[0037] Figure 1 This is a scanning electron microscope image of an antimony-nitrogen co-doped turbine layered carbon-based material.

[0038] Figure 4 This is a diagram showing the phase composition analysis of the material obtained by X-ray powder diffraction.

[0039] Example 2

[0040] The fabrication of capacitive deionization electrodes and the construction of capacitive deionization devices, such as... Figure 2 As shown.

[0041] For the anode, antimony-nitrogen co-doped turbine layered carbon-based material, conductive carbon black, and polytetrafluoroethylene were ground and mixed at contents of 80%, 10%, and 10%, respectively, and ultrasonically mixed for 10 minutes to obtain a slurry. The obtained slurry was rolled onto graphite paper by a rolling method, and then dried at 80°C for 4 hours to finally prepare a capacitive deionization electrode.

[0042] Our CDI system employs an asymmetric electrode, using a capacitive deionization electrode as the anode to capture fluoride ions. Carboxyl-activated carbon is selected as the cathode material. Carboxyl-activated carbon, conductive carbon black, and polytetrafluoroethylene are ground and mixed at contents of 80%, 10%, and 10%, respectively, and ultrasonically sonicated for 10 minutes to obtain a slurry. The slurry is then evenly dripped and coated onto graphite paper, and dried at 80°C for 4 hours to finally form the cathode. The anode and cathode together constitute the capacitive deionization device.

[0043] Sodium fluoride solution was added to the CDI reactor for electroadsorption experiments. A voltage of 1.2V was applied across the electrodes of the capacitive deionization device. The adsorption time for each experiment was 60 min, and samples were collected every 15 minutes, with 0.5 mL of solution taken each time. After adsorption was complete, the applied voltage was changed to -1.2V, and the desorption time was approximately 60 min. The desorbed electrodes were then immersed in deionized water for later use.

[0044] Example 3

[0045] Applications and Testing:

[0046] Electroadsorption experiments were conducted in a 50 mg / L sodium fluoride solution. All experiments used a capacitive deionization electrode made of antimony-nitrogen co-doped turbine-layered carbon-based material as the anode and carboxyl-based activated carbon as the cathode. 0.5 mL of solution was taken for each sample, and the fluoride ion content was determined by ion chromatography.

[0047] To analyze the effect of common interfering ions in water on the adsorption of fluoride ions by antimony-nitrogen co-doped turbine layered carbon materials, chloride ions, nitrate ions, sulfate ions, and bicarbonate ions of the same concentration were added to a 50 mg / L sodium nitrate solution, respectively, to further understand the selectivity of the antimony-nitrogen co-doped turbine layered carbon materials for fluoride ions. The results are as follows: Figure 5 As shown in Figure d, the results indicate that chloride, bicarbonate, and nitrate ions have only a minor effect on the defluorination performance of the antimony-nitrogen co-doped turbine layered carbon-based material. The largest effect can be attributed to the presence of sulfate ions, likely due to their high charge density. Nevertheless, the material still exhibits a strong fluoride ion adsorption capacity. This demonstrates the unique resistance to interference and selectivity for fluoride ions in the antimony-nitrogen co-doped turbine layered carbon-based material.

[0048] The adsorption capacities at different initial pH values ​​(3, 5, 7, 9, and 11) indicate that the electrode performs well over a wide pH range. The adsorption capacity is highest at pH 5, and decreases under alkaline conditions but still remains at a relatively high level.

[0049] The adsorption capacities at different initial voltages (0.8V, 1.0V, 1.2V, and 1.4V) show that the antimony-nitrogen co-doped turbine-layered carbon-based material's ability to remove fluoride ions increases with increasing voltage. This is because a higher potential difference leads to a denser double-layer capacitance around the electrode interface. Under the influence of an applied electric field, the material's electroadsorption process exhibits fluoride removal performance that more closely resembles pseudo-second-order kinetics.

[0050] The adsorption capacities at different test concentrations (10 mg / L, 20 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, and 500 mg / L) showed that the antimony-nitrogen co-doped turbine layered carbon-based material's ability to remove fluoride ions increased with increasing initial solution concentration. As the concentration increased, the concentration gradient between the solution and the electrode surface increased, reducing the diffusion resistance in the solution and enhancing the driving force for ion migration.

[0051] The fluoride ion electroadsorption capacity of the manufactured electrode is calculated as follows:

[0052]

[0053] Where Qe (mg / g) refers to the electro-adsorption capacity of fluoride ions over a certain period of time, C0 (mg / L) and Ce (mg / L) represent the fluoride ion concentrations at the initial time and time t, respectively, m (g) is the weight of the electrode material, and V (mL) represents the volume of the solution at that time.

[0054] The method for calculating the fluoride ion electro-adsorption rate is as follows:

[0055]

[0056] Where Vt (mg / g / min) refers to the nitrate electroadsorption rate, Qe (mg / g) refers to the fluoride ion electroadsorption capacity within a certain time, and t (min) is the reaction time.

[0057] Figure 3 The material shows the cyclic voltammetry test curve of the redox peak representing the pseudocapacitive performance. Cyclic voltammetry tests were performed using a three-electrode electrochemical workstation. The test solution was 20-100 ml of 0.2-0.8 mol / L sodium fluoride solution. The number of cycles per test was set to 3, the scan rate was set to 5-100 mV / s, and the voltage range was set to -1.2V-0.5V.

[0058] To ensure cyclic stability, maintaining 90% of the initial adsorption capacity after 20 cycles, sodium fluoride solution was added to the CDI reactor for electroadsorption experiments. A voltage of 1.2V was applied across the capacitor deionization device, with an adsorption time of 60 min for each experiment. After adsorption, the applied voltage was changed to -1.2V, with a desorption time of approximately 60 min, and this cycle was repeated 20 times. After each cycle, 0.5 mL of solution was collected, and the fluoride ion content was determined by ion chromatography. The results are as follows: Figure 6 As shown.

[0059] Comparative Example 1

[0060] The only difference from Example 1 is that the mass ratio of the antimony nitrate to the carbon-based skeleton is set to 0.4:0.1.

[0061] Comparative Example 2

[0062] The only difference from Example 1 is that the mass ratio of the antimony nitrate to the carbon-based skeleton is set to 1.6:0.1.

[0063] Electroadsorption performance tests were conducted on the materials prepared in Comparative Examples 1 and 2, and it was found that the fluoride ion removal capacity of Comparative Examples 1 and 2 was far inferior to that of the antimony-nitrogen co-doped turbine layered carbon-based material prepared in Example 1.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. An antimony-nitrogen co-doped turbine-like layered carbon-based material for treating fluoride ion wastewater, characterized in that, The antimony-nitrogen co-doped turbine-like layered carbon-based material has a layered, loose, and controllable mesoporous structure, abundant active sites, uniform particle size, and regular geometric micro-rolled shape; the preparation method of the antimony-nitrogen co-doped turbine-like layered carbon-based material includes: (1) At 25°C, pyromellitic acid and melamine are dissolved in distilled water and stirred for 8-12 hours. The resulting solution is then semi-sealed in a drying oven at 100-120°C for 20-25 hours. The temperature of the drying oven is then increased by 8-12°C for 6-10 hours. Finally, the semi-solid is completely dried to obtain the precursor. (2) The precursor is fed into a tube furnace and heated to 800-1000℃ for 1-3 hours in a nitrogen atmosphere at a heating rate of 2-5℃ / min. After washing and drying with deionized water, a carbon-based framework is obtained. The carbon-based framework is dispersed in ethanol, and then antimony nitrate is added. The mixture is stirred immediately for 1-2 hours to obtain a mixture. The mass ratio of antimony nitrate to carbon-based framework is 0.8~1.2:0.1~0.

3. (3) The obtained mixture was transferred to a Teflon high-pressure reactor and reacted at 130-150℃ for 10-14 hours. Then the sample was washed with distilled water and ethanol respectively and dried to obtain antimony-nitrogen co-doped turbine layered carbon-based material. Based on the capacitive deionization electrode of the antimony-nitrogen co-doped turbine layered carbon-based material, it exhibited obvious Faraday pseudocapacitance effect and showed large capacity and fast rate adsorption of fluoride ions in fluoride-containing wastewater.

2. The antimony-nitrogen co-doped turbine layered carbon-based material according to claim 1, characterized in that, The mass ratio of pyromellitic acid to melamine is 1.2~1.8:0.8~1.

2.

3. The antimony-nitrogen co-doped turbine-like layered carbon-based material according to claim 1, characterized in that, The mass of melamine and the volume of distilled water used are 1.2-1.8g:90-110mL.

4. The antimony-nitrogen co-doped turbine-like layered carbon-based material according to claim 1, characterized in that, The mass of the carbon-based skeleton and the volume of ethanol used are 0.8-1.2g:150-250mL.

5. The capacitive deionization electrode of the antimony-nitrogen co-doped turbine layered carbon-based material according to any one of claims 1-4, characterized in that, The preparation method is as follows: Antimony-nitrogen co-doped turbine layered carbon-based material, conductive carbon black, and polytetrafluoroethylene were ground and mixed at contents of 80%, 10%, and 10%, respectively. The mixture was then ultrasonicated for 8-12 minutes to obtain a slurry. The slurry was then uniformly dripped and coated onto graphite paper, and then dried at 75-85℃ for 3-5 hours to finally produce a capacitive deionization electrode.

6. A method for preparing a capacitive deionization device using the capacitive deionization electrode of claim 5, characterized in that, include: An asymmetric electrode is used, with a capacitive deionization electrode as the anode to capture fluoride ions. Carboxyl activated carbon, conductive carbon black, and polytetrafluoroethylene are ground and mixed at contents of 80%, 10%, and 10%, respectively, and ultrasonically mixed for 8-12 minutes to obtain a slurry. The slurry is then uniformly dripped and coated onto graphite paper, and then dried at 75-85℃ for 3-5 hours to prepare the cathode. The anode and cathode together constitute the capacitive deionization device.

7. The application of the capacitor deionization device obtained according to claim 6 in the treatment of fluoride wastewater, characterized in that, Fluorine wastewater is added to a capacitor deionization device, which applies a voltage of 1.0-1.4V for electroadsorption for 55-70 minutes. After adsorption is complete, the applied voltage is changed to -1.0-1.4V, and the desorption time is 55-70 minutes. The desorbed electrode is then soaked in deionized water for later use.

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