Capacitive deionization electrode for treating low-concentration fluoride ion wastewater and preparation and application thereof

Abstract

The application relates to the preparation and application of a capacitive deionization electrode for treating low-concentration fluoride ion wastewater, and belongs to the technical field of capacitive deionization. A cerium-nitrogen co-modified turbo layered carbon material prepared by taking a supramolecule as a precursor, forming a carbon skeleton through pyrolysis and then performing metal modification control is used as an anode, carboxyl activated carbon is used as a cathode, and the cathode and the anode jointly form a capacitive deionization system. The cerium-nitrogen co-modified turbo layered carbon material electrode has a layered loose controllable mesoporous structure, a large number of active sites caused by unsaturated coordination vacancies and excellent electric double-layer capacitive behavior. The cerium-nitrogen co-modified turbo layered carbon material electrode has excellent fluoride ion adsorption capacity in low-concentration fluoride-containing wastewater, specifically, the adsorption rate is fast and the adsorption capacity is large, and the effluent concentration can reach below the relevant standard. The capacitive deionization electrode material has a good engineering application prospect in actual wastewater treatment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water treatment and resource utilization, specifically to the technical field of capacitive deionization, and particularly relates to a capacitive deionization device with a turbine layered carbon material loaded with trivalent cerium with abundant unsaturated sites as an anode for efficient adsorption of fluoride ions in wastewater and a preparation method thereof. BACKGROUND

[0002] Fluoride ions (F - ) are widely present in the natural environment, especially in the global water cycle, posing a potential threat to humans and other organisms. They are beneficial to human health at low levels but can be harmful at high levels. High concentrations of fluoride intake can cause skeletal and dental fluorosis, and in severe cases, even complete loss of bone function, posing a great threat to health. According to the World Health Organization (WHO) guidelines for drinking water quality, the fluoride concentration in drinking water should be strictly controlled below 1.5 mg / L. With the intensification of industrial wastewater and domestic sewage discharge activities, the fluoride content in the global water cycle is becoming increasingly high, and new technologies for removing fluoride from wastewater are gradually gaining attention and development. Currently, ion exchange, electrolysis, adsorption, and precipitation methods have been developed and are commonly used to remove fluoride ions from wastewater. Adsorption is a commonly used water treatment method that has attracted the attention of many scholars, and it is also one of the most effective and reliable methods for removing fluoride. Adsorbents with excellent adsorption performance are key factors for efficient fluoride removal. The adsorption process of F - by adsorbents generally includes three basic steps: (1) F - diffusion or transport from the solution to the outer surface of the adsorbent particle through the boundary layer around the adsorbent particle, referred to as molecular diffusion; (2) adsorption of F - on the surface of the adsorbent particle; and (3) exchange of F - on the surface of the adsorbent with substances inside the adsorbent particle or transfer to the inner surface of the adsorbent particle, referred to as intraparticle diffusion. The good adsorption properties of adsorbents are mainly due to their dense pore structure and large specific surface area or the presence of groups that can form chemical bonds with the adsorbate. Chemical precipitation is a method in which a soluble chemical agent is added to wastewater containing fluoride, causing it to react with ionic inorganic pollutants to form fluoride precipitates that are insoluble or difficult to dissolve in water, thereby reducing the fluoride content in the water. Coagulation and precipitation and chemical precipitation are two commonly used precipitation methods and are also widely used methods for removing fluoride. The principle of ion exchange is to use ion exchange resins to selectively remove pollutants from wastewater, removing target ions while releasing equivalent ions into the solution to maintain the electrical neutrality of the solution. Ion exchange for removing fluoride involves exchanging anions in ion exchange resins with F - in water, thereby reducing the F -The purpose of the membrane treatment method is to remove fluorine by using a large number of micro-holes on a special film, and selectively permeating F in the liquid according to the size of the mixture particle size - The membrane treatment method mainly includes reverse osmosis, electrodialysis, ultrafiltration and nanofiltration, and is a relatively friendly separation technology. However, these methods have the problems of inconvenient operation, large floor area, high cost and easy secondary pollution, which means that these methods have great defects and obstacles in practical application.

[0003] As an electro-adsorption method, capacitive deionization has made excellent progress in ion removal applications due to its low cost and no secondary pollution. In a typical capacitive deionization process, a low-energy voltage is applied to two parallel electrodes in a working system, and charged ions are quickly captured by electrodes with opposite charges and enriched by electrode regeneration for further processing, so as to realize the separation and removal of ions from the solution. At present, the application of capacitive deionization in fluorine removal is less, and it may be a potential and excellent fluorine removal technology. The performance of the capacitive deionization system is closely related to the performance of the electrode material. Carbon-based materials have been long-term concerned, continuously explored and developed due to their rich forms, stable structural performance and excellent conductivity, and the capacitive deionization electrode has achieved remarkable results in seawater desalination. However, the lack of active sites in the structure and the weak double-layer capacitance (EDLC) of the original carbon-based electrode enlarge the limitation of its ion removal capacity, and the physical interaction between carbon and F - In order to overcome the known limitations, metal-doped site-modified electrode materials are created and are considered to be an effective strategy to stimulate the performance of deionization, and various composite electrode technologies are derived, such as Faraday effect metal oxide loading, metal / nitrogen co-doping and bimetallic sensing, which have made groundbreaking achievements in deionization and fluorine removal. There are multiple additional synergistic effects in these mechanisms to improve the target performance. SUMMARY

[0004] In order to solve the above problems, the application provides a preparation and application of a capacitive deionization electrode for treating low-concentration fluorine ion wastewater. The capacitive deionization electrode exhibits a large number of unsaturated coordination vacancies, exhibits a large capacity, a fast rate of adsorption of fluorine ions in low-concentration fluorine wastewater, and realizes good fluorine ion selectivity.

[0005] The application also provides a preparation method of the electrode material and application effects of the electrode material in treating fluorine wastewater.

[0006] The preparation of a capacitive deionization electrode for treating low-concentration fluoride ion wastewater involves using supramolecular precursors, pyrolysis to form a carbon skeleton, and then metal modification to control the preparation of a cerium-nitrogen co-modified turbine layered carbon-based material as the anode, and carboxyl activated carbon as the cathode. The cathode and anode together form a capacitive deionization system.

[0007] The preparation method of the cerium-nitrogen co-modified turbine layered carbon-based material for the capacitor deionization anode is as follows:

[0008] 1) At 25℃, dissolve 2-2.5 g of 1,2,4,5-benzenetetracarboxylic acid and 1-2 g of melamine in 80-120 ml of distilled water and stir for 8-12 hours. Place the resulting solution in a semi-sealed drying oven at 100-120℃ for 22-26 hours. Then, increase the temperature of the drying oven by 8-12℃ for 6-10 hours. Finally, completely dry the resulting semi-solid to obtain the precursor.

[0009] 2) The precursor is fed into a tube furnace and heated in a nitrogen atmosphere at 1-10℃ for min. -1 Heating to 800-1100℃ for 1-3 hours at a rising rate, followed by washing and drying with deionized water, yields a carbon-based framework. The carbon-based framework (0.1-0.3 g) is dispersed in distilled water (10-50 mL), and then cerium nitrate hexahydrate (0.8-1.2 g) is added. The mixture is immediately stirred for 0.5-2 hours, followed by ultrasonic treatment for 10-50 minutes. The pH of the resulting mixture is adjusted to 11-13 with potassium hydroxide, and then stirred for 1-3 hours. The mixture is then washed three times with distilled water and dried. The resulting solid is placed in a muffle furnace and heated at 1-10℃ for [time missing]. -1 Heating to 800-1100℃ for 1-5 hours at a heating rate, then washing and drying with deionized water, yields a cerium-nitrogen co-modified turbine layered carbon-based material.

[0010] The electrode is prepared as follows:

[0011] 1) For the anode, cerium-nitrogen co-modified turbine layered carbon-based material, conductive carbon black, and polytetrafluoroethylene were ground and mixed at mass contents of 80%, 10%, and 10%, respectively, and ultrasonically mixed for 8-12 minutes to obtain a slurry. The slurry was uniformly dripped and coated onto graphite paper, and then dried at 60-100℃ for 2-8 hours to finally form the electrode. Simultaneously, carboxyl activated carbon was selected as the cathode material, and the cathode was prepared using the same steps.

[0012] 2) The obtained slurry is evenly pressed onto graphite paper using a rolling method, and then dried at 60-100℃ for 2-8 hours to finally form an electrode;

[0013] 3) Select carboxyl activated carbon as the cathode material and prepare the cathode using the same steps;

[0014] The method for constructing the capacitor deionization device is as follows:

[0015] 1) Our CDI system uses an asymmetric electrode, employing cerium-nitrogen co-modified turbine layered carbon-based material as the anode to capture fluoride ions, and carboxyl activated carbon as the cathode for adsorption-desorption experiments;

[0016] 2) In the adsorption experiment, sodium fluoride solution was added to the CDI reactor, and a voltage of 1.0-1.4V was applied to the two electrodes of the battery. The adsorption time for each group of experiments was 100-140 min. Samples were collected every 10-20 minutes, and 0.5 mL of solution was taken each time.

[0017] 3) After adsorption is complete, the applied voltage is changed to -1.0-1.4V, the desorption time is about 100-140min, and the desorbed electrode is soaked in deionized water for later use.

[0018] This invention uses a self-assembly method to synthesize a structurally ordered turbine-like layered carbon-based material, and uses a valence state control method to load a large amount of trivalent cerium with abundant unsaturated sites onto the carbon-based material, thus preparing a cerium-nitrogen co-modified turbine-like layered carbon-based material with loose and porous mesoporous channels that facilitate rapid ion diffusion.

[0019] The advantages and effects of this invention are as follows:

[0020] Using supramolecular materials synthesized from pyromellitic acid and melamine as precursors, the precursors were pyrolyzed to obtain turbine-like layered carbon-based materials. By controlling the loading of trivalent cerium on the carbon matrix, cerium-nitrogen co-modified turbine-like layered carbon-based materials were prepared. The prepared cerium-nitrogen co-modified turbine-like layered carbon-based materials are uniform in particle size and exhibit regular laminar flow characteristics, demonstrating good diffusivity and dispersibility. Controlling the valence state of the loaded cerium enhances the overall adsorption potential of the material, and it contains a large number of active oxygen vacancies. Furthermore, when used as the anode of a CDI electrode, this invention exhibits a significant double-layer effect, good specific capacitance, and strong electroadsorption performance, and can effectively adsorb low-concentration fluoride wastewater.

[0021] In a 10 mg / L sodium fluoride solution, at a voltage of 1.2 V, the CDI system using cerium-nitrogen co-modified turbine layered carbon-based material as the electrode anode exhibited an excellent fluoride ion adsorption capacity of 1.23 mmol / g.

[0022] To verify the unique structural engineering design described above, the electrode material of this invention was characterized using XPS and SEM, demonstrating the feasibility of the structure, the effectiveness of the synthesis, and the actual presence of the chemical components at the levels of composition and microstructure. 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 adsorption kinetic 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. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of materials synthesized using the valence state control method.

[0024] Figure 2 This is a scanning electron microscope image of a cerium-nitrogen co-modified turbine layered carbon-based material electrode.

[0025] Figure 3 It is a cyclic voltammetry test curve representing the proportion of capacitance contribution during the operation of the material electrode.

[0026] Figure 4 This is an X-ray photoelectron spectroscopy experiment demonstrating that the material has abundant oxygen vacancies.

[0027] Figure 5 This is an adsorption capacity diagram of cerium-nitrogen co-modified turbine layered carbon-based material for different interfering ions, different initial pH, different initial voltage, and different test concentrations.

[0028] Figure 6 The figure shows the fitting results of the material electrode adsorption experiment using pseudo-first-order and pseudo-second-order adsorption kinetics and adsorption isotherm models.

[0029] Figure 7 This is a cycle stability graph showing that the adsorption capacity remains at 75% after 20 cycles. Detailed Implementation

[0030] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0031] Example 1

[0032] Preparation of cerium-nitrogen co-modified turbine layered carbon-based materials:

[0033] 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. Finally, the semi-solid was completely dried to obtain the precursor. The precursor was then placed in a tube furnace and dried at 5°C for 1 minute under nitrogen atmosphere. -1 After heating to 900℃ for 2 hours at a controlled heating rate, the sample was washed with deionized water and dried to obtain a carbon-based framework. The carbon-based framework (0.2 g) was dispersed in distilled water (30 mL), and then cerium nitrate hexahydrate (1.0 g) was added. The mixture was immediately stirred for 1 hour, followed by sonication for 30 minutes. The pH of the resulting mixture was adjusted to 12 with potassium hydroxide, and then stirred for another 2 hours. The sample was then washed three times with distilled water and dried. The resulting solid was placed in a muffle furnace and heated at 5℃ for 1 minute. -1 After heating to 900℃ for 3 hours at a heating rate, the product is washed with deionized water and dried. The resulting product is a cerium-nitrogen co-modified turbine layered carbon-based material.

[0034] Electrode fabrication and device construction:

[0035] For the anode, cerium-nitrogen co-modified 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 resulting slurry was rolled onto graphite paper using a rolling method, and then dried at 80°C for 4 hours to finally form the electrode. Simultaneously, carboxyl-activated carbon was selected as the cathode material, and the cathode was prepared using the same steps.

[0036] Our CDI system employs an asymmetric electrode, using a cerium-nitrogen co-modified turbine-layered carbon-based material as the anode to capture fluoride ions, and carboxyl-modified activated carbon as the cathode for adsorption-desorption experiments. In the adsorption experiment, sodium fluoride solution was added to the CDI reactor, and a voltage of 1.2V was applied across the electrodes. The adsorption time for each experiment was 120 min, with samples collected every 15 minutes, each time taking 0.5 mL of solution. After adsorption was complete, the applied voltage was changed to -1.2V, and the desorption time was approximately 120 min. The desorbed electrode was then immersed in deionized water for later use.

[0037] Example 2

[0038] Electroadsorption performance test:

[0039] Electroadsorption experiments were conducted in a 10 mg / L sodium fluoride solution. All experiments used cerium-nitrogen co-modified turbine-like layered carbon material as the anode and carboxyl-modified 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.

[0040] To analyze the effect of common interfering ions in water on the adsorption of fluoride ions by cerium-nitrogen co-modified turbine layered carbon materials, chloride ions, nitrate ions, sulfate ions, and bicarbonate ions of the same concentration were added to a 10 mg / L sodium nitrate solution to gain a deeper understanding of the selectivity of cerium-nitrogen co-modified turbine layered carbon materials for fluoride ions.

[0041] The fluoride ion electroadsorption capacity of the manufactured electrode is calculated as follows:

[0042]

[0043] 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.

[0044] The method for calculating the fluoride ion electro-adsorption rate is as follows:

[0045]

[0046] 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.

[0047] Example 3

[0048] Adsorption kinetics simulation

[0049] Numerical fitting of the material electrode adsorption experiments was performed using pseudo-first-order and pseudo-second-order adsorption kinetics and adsorption isotherm models to explore the dominant factors and adsorption modes of the adsorption process, and to analyze the adsorption process in greater depth. The adsorption isotherm models used were the Langmuir adsorption isotherm model and the Friedrich adsorption isotherm model.

[0050] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing a capacitive deionization electrode for treating low-concentration fluoride ion wastewater, wherein a cerium-nitrogen co-modified turbine layered carbon-based material prepared by pyrolysis to form a carbon skeleton and then by metal modification is used as the anode, and carboxyl activated carbon is used as the cathode, and the cathode and anode together constitute a capacitive deionization system. The preparation method of the cerium-nitrogen co-modified turbine layered carbon-based material of the anode of the capacitor deionization electrode is as follows: 1) At 25℃, dissolve 2-2.5 g of 1,2,4,5-benzenetetracarboxylic acid and 1-2 g of melamine in 80-120 ml of distilled water and stir for 8-12 hours. Place the resulting solution in a semi-sealed drying oven at 100-120℃ for 22-26 hours. Then, increase the temperature of the drying oven by 8-12℃ for 6-10 hours. Finally, completely dry the resulting semi-solid to obtain the precursor. 2) The precursor is fed into a tube furnace and heated in a nitrogen atmosphere at 1-10℃ for min. -1 Heating to 800-1100℃ for 1-3 hours at a heating rate, followed by washing and drying with deionized water, yields a carbon-based framework. 0.1-0.3 g of the carbon-based framework is dispersed in 10-50 mL of distilled water, then 0.8-1.2 g of cerium nitrate hexahydrate is added, followed by immediate stirring for 0.5-2 hours, and then ultrasonic treatment for 10-50 minutes. The pH of the resulting mixture is adjusted to 11-13 with potassium hydroxide, and then stirred for 1-3 hours. The sample is then washed three times with distilled water and dried. The resulting solid is placed in a muffle furnace and heated at 1-10℃ for [time missing]. -1 Heating to 800-1100℃ for 1-5 hours at a heating rate, then washing and drying with deionized water, the resulting product is cerium-nitrogen co-modified turbine layered carbon-based material; The electrode is prepared as follows: 1) For the anode, cerium-nitrogen co-modified turbine layered carbon-based material, conductive carbon black and polytetrafluoroethylene were ground and mixed at mass contents of 80%, 10% and 10% respectively, and ultrasonically mixed for 8-12 minutes to obtain a slurry; the slurry was evenly dripped and coated on graphite paper, and then dried at 60-100℃ for 2-8 hours to finally form the electrode; at the same time, carboxyl activated carbon was selected as the cathode material, and the cathode was prepared using the same steps. 2) The obtained slurry is evenly pressed onto graphite paper using a rolling method, and then dried at 60-100℃ for 2-8 hours to finally form an electrode; 3) Select carboxyl activated carbon as the cathode material and prepare the cathode using the same steps.

2. A capacitive deionization electrode for treating low-concentration fluoride ion wastewater, characterized in that, The electrode is prepared by the method described in claim 1.

3. The application of the capacitive deionization electrode for treating low-concentration fluoride ion wastewater prepared by the method of claim 1, characterized in that, A capacitor is used to treat wastewater with low concentrations of fluoride ions. The construction method of the capacitor deionization system is as follows: 1) The CDI system uses an asymmetric electrode, employing cerium-nitrogen co-modified turbine layered carbon-based material as the anode to capture fluoride ions, and carboxyl activated carbon as the cathode for adsorption-desorption experiments; 2) In the adsorption experiment, sodium fluoride solution was added to the CDI reactor, and a voltage of 1.0-1.4V was applied to the two electrodes of the battery. The adsorption time for each group of experiments was 100-140 min. Samples were collected every 10-20 minutes, and 0.5 mL of solution was taken each time. 3) After adsorption is complete, the applied voltage is changed to -1.0-1.4V, the desorption time is 100-140min, and the desorbed electrode is soaked in deionized water for later use.

Images