Multilayer core-shell magnesium-aluminum-lDH electrosorption phosphorus removal positive electrode material

Abstract

This invention discloses a positive electrode material for an upward-flowing electrochemical phosphorus removal system. The preparation process includes: preparing a ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electrode material coated with polyaniline. The preparation process includes ZIF-8 carbonization under a nitrogen atmosphere, aniline oxidative polymerization, and co-precipitation loading of magnesium-aluminum bimetallic hydroxide. The electroadsorption positive electrode material belongs to a polyaniline-magnesium-aluminum bimetallic hydroxide mesoporous synergistic platform in ZIF-8 derived carbon, possessing a nanoframework with strong pore accessibility and high electrochemical activity. The synergistic process includes the attraction of phosphate ions by polyaniline and the capture of phosphate ions by magnesium-aluminum bimetallic hydroxide. The electrode prepared by this invention possesses a unique mesoporous framework that obtains a large number of phosphorus removal sites on the electrode surface and achieves rapid ion storage behavior at the solid-liquid interface, mainly through a capacitance-controlled process. In the electroadsorption system, it can effectively separate phosphates from water, representing a pollution control process with a well-defined mechanism.

Description

Technical Field

[0001] This invention relates to the fields of environmental materials and wastewater treatment technology, specifically to a ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline, its preparation method, and its application. Background Technology

[0002] Eutrophication, caused by the excessive accumulation of phosphorus in water bodies, seriously threatens the sustainable use of water resources and human health. Various countries have established strict standards for phosphorus discharge into wastewater; for example, China requires that the total phosphorus discharge concentration not exceed 0.5 mg / L. Traditional phosphorus removal technologies such as chemical precipitation, biodegradation, and physical treatment have many drawbacks in terms of removal efficiency, sludge production, energy consumption, and operating time.

[0003] Electro-assisted adsorption (EAGI) technology, as a low-energy, high-efficiency, and environmentally friendly ion removal method, removes ions from water by applying a voltage between parallel electrodes, causing charged ions to migrate rapidly and be stored on the electrodes. This technology offers advantages such as fast reaction rates, easy ion recovery and enrichment, and avoidance of secondary pollution. In EAGI, the performance of the electrode material plays a crucial role in phosphorus removal efficiency; ideal electrode materials should possess good stability, conductivity, high specific surface area, and low resistivity.

[0004] Currently, carbon electrodes are an important component of electro-assisted adsorption technology. While activated carbon, biochar, metal-organic frameworks (MOFs), and their derivatives have been applied to phosphate adsorption and removal, activated carbon and biochar have relatively poor removal capabilities, and MOFs and their derivatives also have limited adsorption and desorption capacity for phosphate. Layered double hydroxides (LDHs) are widely used in ion adsorption due to their large interlayer spacing, rich chemical composition, strong ion exchange capacity, and good chemical stability. Among them, MgAl-LDH is highly stable when exposed to phosphate and is a highly promising phosphorus removal material. However, standalone LDHs tend to accumulate during synthesis and have limited functional groups, resulting in unsatisfactory phosphate removal performance. Combining LDHs with functional materials is a feasible strategy to improve their phosphorus removal performance.

[0005] Polyaniline (PANI), as an organic polymer compound, possesses advantages such as good environmental stability, low cost, convenient synthesis, and simple acid-base doping / dedoping processes. Its abundant amine and imine groups facilitate the adsorption of phosphate ions through hydrogen bonding and electrostatic interactions. Simultaneously, as a conductive polymer, it can enhance the conductivity of composite materials and provide additional pseudocapacitance, thereby increasing energy density. ZIF-8 derived carbon exhibits high specific surface area, hierarchical porous structure, high porosity, high conductivity, and excellent cycling stability. Furthermore, the nitrogen-doped porous carbon material formed after carbonization possesses enhanced wettability, which is beneficial for the assembly of functional materials. Based on this, developing an electrode material combining polyaniline, ZIF-8 derived carbon, and MgAl-LDH is of great significance for improving the efficiency of electroadsorption phosphorus removal. Summary of the Invention

[0006] The purpose of this invention is to provide a ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline, and its preparation and application.

[0007] The cathode material of this invention is designated ZPMA3, where Z refers to ZIF-8 derived carbon (ZC); P refers to polyaniline (PNAI); MA refers to magnesium (Mg) aluminum (Al) bimetallic hydroxide; and 3 indicates that the magnesium-aluminum ratio is 3:1.

[0008] This invention relates to a ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline. This cathode material is prepared by mixing a binder PTFE, conductive carbon black, and active materials, adding them to a beaker at a mass ratio of 1:1:7-9, adding enough ethanol to cover the bottom of the beaker, and then ultrasonically treating it to fully disperse and mix it, so that the mixture becomes a paste, thus obtaining a composite material for coating the cathode of a phosphorus removal system.

[0009] The method for preparing the active material consists of three steps:

[0010] a) Preparation of ZIF-8 derived carbon, ZC: 0.02 mol Zn(NO3)2·6H2O was dissolved in 150 mL of methanol to form a clear solution A; simultaneously, 3-4 times the amount of 2-methylimidazole (Zn(NO3)2·6H2O) was dissolved in another 150 mL of methanol to form a clear solution B; then, solution B was poured into solution A with stirring, and the mixture was stirred continuously at room temperature for 24 hours. The white precipitate was centrifuged, washed three times with methanol, and dried under vacuum at 60 °C overnight to obtain ZIF-8;

[0011] Then, under nitrogen purging, the obtained ZIF-8 was calcined at 800℃ (heating rate of 5℃ / min) for 2h; after cooling to room temperature, the prepared sample was ground into powder and ultrasonically washed with 2M hydrochloric acid for 30 minutes, followed by washing with deionized water until neutral pH; then, the prepared material was vacuum dried at 60℃ overnight to obtain ZIF-8 derived carbon ZC.

[0012] b) ZC@PANI composite material was prepared by oxidative chemical polymerization of aniline on the surface of ZC material: 150 mg ZC was dispersed in 100 mL of 2 M hydrochloric acid aqueous solution and sonicated for 30 min. Then, 450 μL of aniline was added to the dispersion under vigorous stirring and stirring was continued for 30 min. Then, 50 mL of 0.1 M ammonium persulfate was added to the above solution as an oxidant at a flow rate of 2-5 mL / min and stirring was continued at room temperature for 12 hours. Finally, the dark green sample was collected by centrifugation, washed with deionized water and anhydrous ethanol, and vacuum dried at 60 °C overnight to obtain ZC@PANI composite material.

[0013] c) Preparation of active material: 200 mg ZC@PANI composite material was dispersed in 100 mL of deionized water and ultrasonically dispersed for 30 min; then, 3 mmol of MgCl2 and AlCl3 were added to the above solution and ultrasonically dispersed for another 10 min; then stirred at room temperature for 1 h, and the pH was adjusted to 10 with 1 M NaOH aqueous solution; the precipitate was aged at room temperature for 4 h; the product was collected by centrifugation, washed with deionized water and anhydrous ethanol, and vacuum dried at 60 °C overnight to obtain the active material.

[0014] In the preparation process of step a), the molar ratio of Zn(NO3)2·6H2O and 2-methylimidazole is 1:3.5.

[0015] In step b), the ammonium persulfate solution is added to the dispersion at a flow rate of 3 ml / min.

[0016] In step c), the molar ratio of MgCl2 to AlCl3 is 3:1.

[0017] The aforementioned cathode material is used in environmental remediation, specifically for the electro-adsorption and capture of low-concentration phosphate ions in aquatic environments, exhibiting a high phosphate ion adsorption capacity.

[0018] The active material in the positive electrode of the electroadsorption system of the present invention has at least the following beneficial effects:

[0019] It possesses EDL double-layer capacitive adsorption and Faraday-reversible dephosphorization sites.

[0020] As an active material with high redox activity and high surface charge density, it can be used in environmental remediation and wastewater treatment by combining it with an electroadsorption system.

[0021] In the electroadsorption system of this invention, the active material of the positive electrode uses ZIF-8 derived carbon as a precursor, and the electrochemical activity and structural stability of the conductive framework are optimized by coating with an appropriate amount of polyaniline. Simultaneously, the supported magnesium-aluminum bimetallic hydroxide significantly enhances the activity of the surface dephosphorization sites. At the solid-liquid interface, this electrode material exhibits a very strong affinity for phosphates. The synergistic effect of its surface redox reaction and double-layer capacitance enables rapid electroadsorption of phosphates, thus demonstrating excellent performance in achieving pollutant emission standards.

[0022] The active material in the positive electrode of the electroadsorption system of this invention was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption-desorption testing, X-ray photoelectron spectroscopy, and infrared spectroscopy. A series of phosphorus removal experiments were conducted. The results show that the active material possesses good removal capacity, good stability, a multi-layered core-shell structure within a nanoscale confinement, promising application prospects, and low preparation cost.

[0023] The active material in the positive electrode of the electroadsorption system of the present invention exhibits practicality in neutral solution and maintains regenerative electroabsorption capacity in continuous cycling.

[0024] The active material in the positive electrode of the electro-adsorption system of the present invention, as an electroactive material, has high adsorption capacity, fast adsorption kinetics, excellent electrochemical performance, good selectivity and anti-interference ability, excellent stability and regeneration performance, and has broad application prospects in the field of phosphate removal and recovery.

[0025] The active material in the positive electrode of the electro-adsorption system of the present invention has a multi-layer core-shell structure on its surface, obvious lattice stripes, mesoporous structure, successful loading of MgAl-LDH, and possesses multiple and strong interactions, exhibiting good phosphorus removal performance even at low concentrations.

[0026] The active material in the positive electrode of the electroadsorption system of the present invention serves as an effective electroadsorption electrode, providing a technical basis for the preparation and application of ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxides coated with polyaniline.

[0027] According to some embodiments of the present invention, the positive electrode active material utilizes the high specific surface area and conductivity of ZC, the conductivity and active groups of polyaniline, and the high adsorption capacity of MgAl-LDH to construct a core-shell structure with abundant active sites, thereby achieving multi-mechanism synergistic adsorption of phosphate.

[0028] This invention provides the application of the above-mentioned cathode material in separating harmful substances in the environment.

[0029] This invention enables the effective desorption and enrichment of phosphate ions from the adsorbent into the regeneration solution during the regeneration process, achieving highly efficient phosphate ion recovery. This enrichment and recovery capability not only reduces resource waste but also lowers processing costs, resulting in significant economic and environmental benefits. Attached Figure Description

[0030] Figure 1 The N2 adsorption / desorption isotherm of the cathode material ZPMA3 prepared in the embodiments of the present invention;

[0031] Figure 2 The pore size distribution of the cathode material ZPMA3 prepared in the embodiments of the present invention;

[0032] Figure 3 Infrared characterization image of ZPMA3, the cathode material prepared in an embodiment of the present invention;

[0033] Figure 4 X-ray diffraction characterization pattern of ZPMA3, the cathode material prepared in the embodiments of the present invention;

[0034] Figure 5 X-ray photoelectron spectroscopy characterization of the cathode material ZPMA3 prepared in an embodiment of the present invention;

[0035] Figure 6 The current-voltage cycle curve of the cathode material ZPMA3 prepared in the embodiments of the present invention;

[0036] Figure 7 The adsorption of low-concentration phosphate by the positive electrode material ZPMA3 prepared in the embodiments of the present invention is shown.

[0037] Figure 8 This is a graph showing the adsorption capacity of the positive electrode material ZPMA3 prepared in an embodiment of the present invention for phosphorus-containing wastewater.

[0038] Figure 9 Transmission electron microscope image of ZPMA3, the cathode material prepared in an embodiment of the present invention. Detailed Implementation

[0039] 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.

[0040] Example 1

[0041] The positive electrode active material prepared in this embodiment is denoted as ZPMA3, where Z refers to ZIF-8 derived carbon (ZC); P refers to polyaniline (PNAI); MA refers to magnesium (Mg) aluminum (Al) bimetallic hydroxide; and 3 indicates that the magnesium-aluminum ratio is 3:1.

[0042] The preparation method is as follows:

[0043] Preparation of ZIF-8 derived carbon (ZC): Zn(NO3)2·6H2O (5.95 g) was dissolved in 150 mL of methanol to form a clear solution A. Simultaneously, 2-methylimidazole (6.16 g) was dissolved in another 150 mL of methanol to form a clear solution B. Solution B was then poured into solution A with stirring, and the mixture was stirred continuously at room temperature for 24 hours. The white precipitate was centrifuged, washed three times with methanol, and vacuum dried overnight at 60 °C to obtain ZIF-8. The obtained ZIF-8 was then calcined at 800 °C (heating rate 5 °C / min) for 2 h under nitrogen purging. After cooling to room temperature, the prepared sample was ground into powder and ultrasonically washed with 2 M hydrochloric acid for 30 min, followed by washing with deionized water until neutral pH. The prepared material was then vacuum dried overnight at 60 °C to obtain ZIF-8 derived carbon.

[0044] ZC@PANI composite material was prepared by oxidative chemical polymerization of aniline on the surface of ZC material: 150 mg ZC was dispersed in 100 mL of 2 M hydrochloric acid aqueous solution, and sonicated for 30 min. Then, 450 μL of aniline was added to the dispersion under vigorous stirring, and stirring was continued for 30 min. Next, an oxidant (50 mL of 0.1 M ammonium persulfate) was added to the above solution at a flow rate of 5 mL / min, and stirring was continued at room temperature for 12 hours. Finally, the dark green sample was collected by centrifugation, washed with deionized water and anhydrous ethanol, and vacuum dried overnight at 60 °C.

[0045] Preparation of active material: 200 mg ZC@PANI was dispersed in 100 mL of deionized water and ultrasonically dispersed for 30 min. Then, MgCl2 (0.2142 g) and AlCl3 (0.1001 g) were added to the above dispersant, and ultrasonication was further performed for 10 min. The above mixed solution was stirred at room temperature for 1 h, and the pH was adjusted to 10 with 1 M NaOH aqueous solution. The precipitate was aged at room temperature (22 °C) for 4 h. The obtained product was collected by centrifugation, washed with deionized water and anhydrous ethanol, and vacuum dried overnight at 60 °C.

[0046] Preparation of the positive electrode of the electroadsorption system:

[0047] Take 20 mg of active material ZPMA3, 2.5 mg of PTFE (diluted 10 times with ethanol for easy transfer), and 2.5 mg of conductive carbon black and add them to a 50 ml beaker. Add ethanol until it just fills the bottom of the beaker. Sonicate the mixture for 30 minutes. Transfer the mixture to an agate mortar and grind it thoroughly until the ethanol has completely evaporated. Add a few drops of ethanol solution and continue grinding to obtain a black gel-like mixture, which is the positive electrode material used to coat the electrode sheet.

[0048] The specific surface area and porosity were studied using N2 adsorption-desorption isotherms, such as Figure 1 and Figure 2 As shown, the specific surface area of ​​the ZPMA3 composite material is approximately 14.1 m². 2 g -1 The pore size is mostly between 2-50 nm.

[0049] The study was conducted using Fourier transform infrared spectroscopy, such as... Figure 3 All prepared ZPMA3s exhibited strong hydroxyl stretching, CN and N=Q=N stretching vibrations, and stretching and bending vibrations of Mg and Al metal-oxygen bonds (MO) and metal-hydroxyl bonds (M-OH), which validated the core-shell structure design of the ZPMA3 composites.

[0050] X-ray diffraction confirmed that the prepared cathode material has good crystallinity and purity, such as... Figure 4 Characteristic peaks appear at 2θ = 11.44°, 23.02°, 34.56°, 39.18°, 45.68°, 60.64°, and 61.91°, which are related to Mg6Al2(OH). 18 The mH2O standard card (JCPDS card number 35-0965) is consistent.

[0051] The chemical composition and electronic states of the composite material ZPMA3 were studied using X-ray photoelectron spectroscopy. Figure 5 As shown, the spectral investigation indicates that the ZPMA3 sample surface contains elements such as Mg, Al, C, N, and O, which is completely consistent with the above results.

[0052] In 1 mol L -1 ZPMA3 was subjected to voltammetric cyclic testing using a three-electrode system in KH2PO4 solution. Figure 6 As shown, the ring area increases with increasing scan rate. ZPMA3 maintains a distinct redox peak, which corresponds to the highly reversible surface redox reaction.

[0053] ZPMA3 was used as the active material to prepare an electroadsorption positive electrode, which was then introduced into an upflow electroadsorption system. Under a phosphate concentration of 10 mg / L, the adsorption capacity of the active electrode for phosphate ions was evaluated through equilibrium adsorption experiments. Figure 7 As shown, the results indicate that its adsorption capacity is as high as 40.18 mg / g, which is inseparable from its unique mesoporous structure and abundant phosphorus removal sites on the surface.

[0054] ZPMA3 was used as the active material to prepare the electroadsorption positive electrode, which was then introduced into an upward flow electroadsorption system. Under low total phosphorus conditions of 3.4 mg / L, the removal performance of phosphate was studied. The results showed that ( Figure 8 After 3 hours, the effluent concentration was below the limit for phosphate concentration in the World Health Organization's discharge standards, indicating the potential for further expanded utilization.

[0055] 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. A ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline, characterized in that, The positive electrode material is prepared by mixing PTFE binder, conductive carbon black, and active material in a mass ratio of 1:1:7-9 into a beaker. Ethanol is added to cover the bottom of the beaker, and the mixture is then ultrasonically treated to ensure thorough dispersion and mixing, resulting in a paste-like product. This yields a composite material for coating the positive electrode of a phosphorus removal system. The method for preparing the active material involves three steps: a) Preparation of ZIF-8 derived carbon, ZC: 0.02 mol Zn(NO3)2·6H2O was dissolved in 150 mL of methanol to form a clear solution A; simultaneously, 3-4 times the amount of 2-methylimidazole (Zn(NO3)2·6H2O) was dissolved in another 150 mL of methanol to form a clear solution B; then, solution B was poured into solution A with stirring, and the mixture was stirred continuously at room temperature for 24 hours. The white precipitate was centrifuged, washed three times with methanol, and dried under vacuum at 60 °C overnight to obtain ZIF-8; Then, under nitrogen purging, the obtained ZIF-8 was calcined at 800℃ for 2 hours; after cooling to room temperature, the prepared sample was ground into powder and ultrasonically washed with 2M hydrochloric acid for 30 minutes, and then washed with deionized water until neutral pH; then, the prepared material was vacuum dried at 60℃ overnight to obtain ZIF-8 derived carbon ZC. b) ZC@PANI composite material was prepared by oxidative chemical polymerization of aniline on the surface of ZC material: 150 mg ZC was dispersed in 100 mL of 2 M hydrochloric acid aqueous solution and sonicated for 30 min. Then, 450 μL of aniline was added to the dispersion under vigorous stirring and stirring was continued for 30 min. Then, 50 mL of 0.1 M ammonium persulfate was added to the above solution as an oxidant at a flow rate of 2-5 mL / min and stirring was continued at room temperature for 12 hours. Finally, the dark green sample was collected by centrifugation, washed with deionized water and anhydrous ethanol, and vacuum dried at 60 °C overnight to obtain ZC@PANI composite material. c) Preparation of active material: 200 mg ZC@PANI composite material was dispersed in 100 mL of deionized water and ultrasonically dispersed for 30 min; then, 3 mmol of MgCl2 and AlCl3 were added to the above solution and ultrasonically dispersed for another 10 min; then stirred at room temperature for 1 h, and the pH was adjusted to 10 with 1 M NaOH aqueous solution; the precipitate was aged at room temperature for 4 h; the product was collected by centrifugation, washed with deionized water and anhydrous ethanol, and vacuum dried at 60 °C overnight to obtain the active material.

2. The ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline according to claim 1, characterized in that, In the preparation process described in step a), the molar ratio of Zn(NO3)2·6H2O to 2-methylimidazole is 1:3.

5.

3. The ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline according to claim 1, characterized in that, In step b), the ammonium persulfate solution is added to the dispersion at a flow rate of 3 ml / min.

4. The ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline according to claim 1, characterized in that, In the preparation process described in step c), the molar ratio of MgCl2 to AlCl3 is 3:

1.

5. The application of the ZIF-8 derived carbon-supported magnesium-aluminum bimetallic hydroxide electroadsorption phosphorus removal cathode material coated with polyaniline as described in claim 1, characterized in that, The aforementioned cathode material is used in environmental remediation, specifically for the electro-adsorption and capture of low-concentration phosphate ions in aquatic environments, exhibiting a high phosphate ion adsorption capacity.

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