Multilayer core-shell MgAl-LDH electro-adsorption phosphorus removal positive electrode material

Abstract

The invention discloses a positive electrode material of an upward flow type electrochemical dephosphorization system, and the preparation method comprises the following steps: preparing a polyaniline-coated ZIF-8 derived carbon loaded magnesium-aluminum double-metal hydroxide electrode material, and the preparation process comprises ZIF-8 carbonization in a nitrogen atmosphere, aniline oxidation polymerization, and loading of magnesium-aluminum double-metal hydroxide by a coprecipitation method; the electro-adsorption positive electrode material belongs to a polyaniline magnesium aluminum double-metal hydroxide mesoporous synergistic platform in ZIF-8 derived carbon, and has a nano frame with strong pore accessibility and high electrochemical activity; the synergistic process comprises attraction of polyaniline to phosphate ions and trapping of the magnesium-aluminum double-metal hydroxide. The electrode prepared by the method has a unique mesoporous framework, a large number of phosphorus removal sites are obtained on the surface of the electrode, a rapid ion storage behavior mainly based on a capacitance control process is realized on a solid-liquid interface, phosphate in water can be effectively separated in an electro-adsorption system, and the method is a pollution control process with a clear mechanism.

Description

Technical Field

[0001] The present invention relates to the technical fields of environmental materials and sewage treatment, and particularly relates to a magnesium-aluminum double metal hydroxide electro-adsorption phosphorus removal cathode material coated with polyaniline and derived from ZIF-8 carbon, and a preparation method and application thereof. Background Art

[0002] The eutrophication problem caused by the excessive enrichment of phosphorus in water bodies seriously threatens the sustainable utilization of water resources and human health. Countries have formulated strict standards for sewage phosphorus emissions. For example, China requires that the total phosphorus emission concentration shall not exceed 0.5 mg / L. Traditional phosphorus removal technologies such as chemical precipitation, biodegradation, and physical treatment have many disadvantages in terms of removal efficiency, sludge production, energy consumption, and operation time.

[0003] As a low-energy consumption, high-efficiency, and environmentally friendly ion removal method, the electro-assisted adsorption technology applies a voltage between parallel electrodes to promote the rapid migration and storage of charged ions in the electrodes, thereby achieving the removal of ions from water bodies. This technology has the advantages of fast reaction rate, easy recovery and enrichment of ions, and avoidance of secondary pollution. In the electro-assisted adsorption technology, the performance of the electrode material plays a key role in the phosphorus removal effect. An ideal electrode material should have characteristics such as good stability, electrical conductivity, high specific surface area, and low resistance.

[0004] At present, carbon electrodes are an important part of the electro-assisted adsorption technology. Although activated carbon, biochar, metal-organic frameworks (MOFs) and their derivatives have been applied to the adsorption and removal of phosphates, the removal ability of activated carbon and biochar is poor, and the adsorption and desorption ability of MOF and its derivatives for phosphates is also limited. Layered double hydroxides (LDHs) are widely used in the field of ion adsorption due to their large interlayer spacing, rich chemical composition, strong ion exchange ability, and good chemical stability. Among them, MgAl-LDH is highly stable when exposed to phosphates and is a very promising phosphorus removal material. However, single LDHs are prone to stacking during synthesis, and the functional groups are limited, resulting in unsatisfactory phosphate removal performance. Combining LDHs with functional materials is a feasible strategy to improve their phosphorus removal performance.

[0005] As an organic polymer compound, polyaniline (PANI) has the advantages of good environmental stability, low cost, convenient synthesis, and simple acid-base doping / dedoping process. Its abundant amine and imine groups are conducive to adsorbing phosphate ions through hydrogen bonding and electrostatic interactions. At the same time, as a conductive polymer, it can enhance the conductivity of the composite material and provide additional pseudocapacitance, thereby improving the energy density. ZIF-8-derived carbon has a high specific surface area, hierarchical pore structure, high porosity, high conductivity, and excellent cycle stability. The nitrogen-doped porous carbon material formed after carbonization has enhanced wettability, which is beneficial to the assembly of functional materials. Based on this, it is of great significance to develop an electrode material combining polyaniline, ZIF-8-derived carbon, and MgAl-LDH to improve the electroadsorption phosphorus removal efficiency. Summary of the Invention

[0006] The object of the present invention is to provide a positive electrode material for electroadsorption phosphorus removal, which is magnesium-aluminum double metal hydroxide supported by ZIF-8-derived carbon coated with polyaniline, and its preparation and application.

[0007] The positive electrode material of the present invention 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) double metal hydroxide, and 3 indicates that the magnesium-aluminum ratio is 3:1.

[0008] The positive electrode material for electroadsorption phosphorus removal, which is magnesium-aluminum double metal hydroxide supported by ZIF-8-derived carbon coated with polyaniline of the present invention, is prepared by mixing an adhesive PTFE, conductive carbon black, and an active material. They are added to a beaker according to a mass ratio of 1:1:7-9, and after adding an amount of ethanol covering the bottom of the beaker, ultrasonic treatment is carried out to make them fully dispersed and mixed, so that the mixed product presents a paste-like state, and then the composite material for coating on the positive electrode of the phosphorus removal system is obtained.

[0009] The method for preparing the active material is divided into three steps:

[0010] a) Preparation of ZIF-8-derived carbon, i.e., ZC: Dissolve 0.02 mol of Zn(NO3)2·6H2O in 150 ml of methanol to form a clear solution A; at the same time, dissolve 2-methylimidazole with a molar amount 3-4 times that of Zn(NO3)2·6H2O in another 150 ml of methanol to form a clear solution B; then, pour solution B into solution A under stirring and continuously stir at room temperature for 24 hours. Centrifuge the white precipitate, wash it three times with methanol, and vacuum dry it overnight at 60°C to obtain ZIF-8;

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

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

[0013] c) Preparation of active material: 200 mg of ZC@PANI composite material was dispersed in 100 mL of deionized water and ultrasonically dispersed for 30 min; then, a total of 3 mmol of MgCl2 and AlCl3 was added to the above dispersant and ultrasonically treated for another 10 min; then stirred at room temperature for 1 h, and the pH value was adjusted to 10 with 1 M NaOH aqueous solution; the precipitate was aged at room temperature for 4 h; the obtained product was collected by centrifugation, washed with deionized water and absolute 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 to 2-methylimidazole is preferably 1:3.5.

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

[0016] In the preparation process of step b), the stirring time is 12 h, and the synthesized product is relatively better.

[0017] In the preparation process of step c), the molar ratio of MgCl2 to AlCl3 is preferably 3:1.

[0018] The positive electrode material is applied to environmental remediation, specifically for electro-adsorption capture of low-concentration phosphate ions in water environment, showing a relatively high phosphate ion adsorption capacity.

[0019] The active material in the positive electrode of the electro-adsorption system of the present invention has at least the following beneficial effects:

[0020] The dephosphorization sites with EDL double-layer capacitance adsorption and Faraday reversible conversion

[0021] As an active material with high redox activity and high surface charge density, when combined with an electro-adsorption system, it can be used in fields such as environmental remediation and sewage treatment.

[0022] In the electro-adsorption system of the present invention, the active material of the positive electrode uses ZIF-8-derived carbon as a precursor and is coated with an appropriate amount of polyaniline, optimizing the electrochemical activity and structural stability of the conductive framework. At the same time, the loaded magnesium-aluminum double metal hydroxide significantly enhances the activity of the surface dephosphorization sites. At the solid-liquid interface, this electrode material shows extremely strong affinity for phosphate. The synergistic effect of its surface redox reaction and double-layer capacitance realizes the rapid electro-adsorption of phosphate, thus showing excellent performance in achieving the up-to-standard discharge of pollutants.

[0023] The active material in the positive electrode of the electro-adsorption system of the present invention is characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption-desorption test, X-ray photoelectron spectroscopy, infrared spectroscopy, etc., and tested through a series of phosphorus removal experiments. The results show that this active material has good removal ability, good stability, a multi-layer core-shell structure within nanoconfinement, good application prospects, and low preparation cost.

[0024] The active material in the positive electrode of the electro-adsorption system of the present invention shows practicality in a neutral solution and maintains the regenerative electro-absorption ability during continuous cycling.

[0025] 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.

[0026] The active material in the positive electrode of the electro-adsorption system of the present invention has a multi-layer core-shell structure on the surface, obvious lattice fringes, a mesoporous structure, MgAl-LDH is successfully loaded, has multiple interaction forces, and the interaction forces are strong, and also shows good phosphorus removal performance at low concentrations.

[0027] The active material in the positive electrode of the electro-adsorption system of the present invention, as an effective electro-adsorption electrode, provides a technical basis for the preparation and application of magnesium-aluminum double metal hydroxide loaded on polyaniline-coated ZIF-8-derived carbon.

[0028] According to some embodiments of the present invention, in the positive electrode active material, by utilizing the high specific surface area and conductivity of ZC, the conductivity and active groups of polyaniline, and the high adsorption capacity of MgAl-LDH, a core-shell structure with rich active sites is constructed, realizing the multi-mechanism synergistic adsorption of phosphate.

[0029] The present invention provides an application of the above-mentioned cathode material in separating harmful substances in the environment.

[0030] During the regeneration process of the present invention, phosphate can be effectively desorbed from the adsorbent and enriched in the regeneration solution, achieving efficient recovery of phosphate. This enrichment and recovery ability not only reduces resource waste but also lowers the treatment cost, with significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the N2 adsorption / desorption isotherm curve of the cathode material ZPMA3 prepared in the embodiment of the present invention;

[0032] Figure 2 It is the pore size distribution of the cathode material ZPMA3 prepared in the embodiment of the present invention;

[0033] Figure 3 It is the infrared characterization diagram of the cathode material ZPMA3 prepared in the embodiment of the present invention;

[0034] Figure 4 It is the X-ray diffraction characterization diagram of the cathode material ZPMA3 prepared in the embodiment of the present invention;

[0035] Figure 5 It is the X-ray photoelectron spectroscopy characterization diagram of the cathode material ZPMA3 prepared in the embodiment of the present invention;

[0036] Figure 6 It is the voltammetric cycle curve diagram of the cathode material ZPMA3 prepared in the embodiment of the present invention;

[0037] Figure 7 It is the adsorption situation of the cathode material ZPMA3 prepared in the embodiment of the present invention for low-concentration phosphate;

[0038] Figure 8 It is the adsorption capacity diagram of the cathode material ZPMA3 prepared in the embodiment of the present invention for phosphorus-containing wastewater;

[0039] Figure 9 It is the transmission electron microscope diagram of the cathode material ZPMA3 prepared in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0041] Embodiment 1

[0042] The positive electrode active material prepared in this example is denoted as ZPMA3. Among them, Z refers to ZIF-8-derived carbon (ZC); P refers to polyaniline (PNAI); MA refers to magnesium (Mg) aluminum (Al) double metal hydroxide, and 3 indicates that the magnesium-aluminum ratio is 3:1.

[0043] The preparation method is as follows:

[0044] Preparation of ZIF-8-derived carbon (ZC): Dissolve Zn(NO3)2·6H2O (5.95 g) in 150 mL of methanol to form a clear solution A. At the same time, dissolve 2-methylimidazole (6.16 g) in another 150 mL of methanol to form a clear solution B. Then, pour solution B into solution A under stirring and continuously stir at room temperature for 24 hours. Centrifuge the white precipitate, wash it three times with methanol, and vacuum dry it overnight at 60 °C to obtain ZIF-8. Then, under nitrogen purging, calcine the obtained ZIF-8 at 800 °C (heating rate: 5 °C / min) for 2 h. After cooling to room temperature, grind the prepared sample into powder and ultrasonically wash it with 2M hydrochloric acid for 30 minutes, and then wash it with deionized water until the pH is neutral. Then, vacuum dry the prepared material overnight at 60 °C to obtain ZIF-8-derived carbon.

[0045] Preparation of ZC@PANI composite material by oxidative chemical polymerization reaction of aniline on the surface of ZC material: Disperse 150 mg of ZC in 100 mL of 2M hydrochloric acid aqueous solution. After ultrasonic treatment for 30 min, add 450 μL of aniline to the dispersion under vigorous stirring and continuously stir for 30 min. Then, add the oxidant (50 mL of 0.1M ammonium persulfate) to the above solution at a flow rate of 5 ml / min and continuously stir at room temperature for 12 hours. Finally, centrifuge to collect the dark green sample, wash it with deionized water and absolute ethanol, and vacuum dry it overnight at 60 °C.

[0046] Preparation of the active material: Disperse 200 mg of ZC@PANI in 100 mL of deionized water and perform ultrasonic dispersion for 30 min. Then, add MgCl2 (0.2142 g) and AlCl3 (0.1001 g) to the above dispersant and further ultrasonic for 10 min. Stir the above mixed solution at room temperature for 1 h, and adjust the pH value to 10 with 1M NaOH aqueous solution. The precipitate is aged at room temperature (22 °C) for 4 h. Centrifuge to collect the obtained product, wash it with deionized water and absolute ethanol, and vacuum dry it overnight at 60 °C.

[0047] Preparation of the positive electrode of the electro-adsorption system:

[0048] Take 20 mg of the active material ZPMA3, 2.5 mg of PTFE (diluted 10 times with ethanol for easy pipetting), and 2.5 mg of conductive carbon black and add them to a beaker with a capacity of 50 ml. Add ethanol until it just fills the bottom of the beaker. Perform ultrasonic oscillation treatment on the mixed liquid for 30 minutes. Transfer the mixture to an agate mortar and grind it thoroughly until the ethanol completely evaporates. Then add a few drops of ethanol solution and continue grinding to obtain a black colloidal mixture, which is the positive electrode material used for coating on the electrode sheet.

[0049] The specific surface area and porosity were studied by N2 adsorption - desorption isotherms, as Figure 1 and Figure 2 shown. The specific surface area of the ZPMA3 composite material is about 14.1 m 2 g -1 , and the pore diameters are mostly between 2 - 50 nm.

[0050] Fourier transform infrared spectroscopy was used for the study, as Figure 3 shown. All the prepared ZPMA3 showed strong hydroxyl stretching, C - N and N=Q=N stretching vibrations, and the stretching and bending vibrations of the metal - oxygen bond (M - O) and metal - hydroxide bond (M - OH) of Mg and Al verified the core - shell structure design of the ZPMA3 composite material.

[0051] X - ray diffraction was used to confirm that the prepared positive electrode material has good crystallinity and purity, as Figure 4 . Characteristic peaks appeared at 2θ = 11.44°, 23.02°, 34.56°, 39.18°, 45.68°, 60.64° and 61.91°, which are consistent with the standard card (JCPDS card number 35 - 0965) of Mg6Al2(OH) 18 ·mH2O.

[0052] The chemical composition and electronic state of the composite material ZPMA3 were studied by X - ray photoelectron spectroscopy measurement. As Figure 5 shown, the spectral investigation indicates that the surface of the ZPMA3 sample contains elements such as Mg, Al, C, N, and O, which is in complete agreement with the above results.

[0053] Cyclic voltammetry tests of ZPMA3 were carried out using a three - electrode system in 1 mol L -1 KH2PO4 solution. As Figure 6 shown, as the scanning rate increases, the loop area expands. ZPMA3 maintains obvious redox peaks, which correspond to highly reversible surface redox reactions.

[0054] Using ZPMA3 as the active material, an electro-adsorption positive electrode was prepared and introduced into an up-flow electro-adsorption system. Under the condition of a phosphate concentration of 10 mg / L, the adsorption capacity of the active electrode for phosphate ions was evaluated through an equilibrium adsorption experiment, as Figure 7 shown. The results indicate that its adsorption capacity is as high as 40.18 mg / g, which is inseparable from the unique mesoporous structure and the abundant phosphorus-removing sites on the surface.

[0055] Using ZPMA3 as the active material, an electro-adsorption positive electrode was prepared and introduced into an up-flow electro-adsorption system. Under the condition of a low total phosphorus of 3.4 mg / L, the performance of phosphate removal was studied. The results show that ( Figure 8 ), after 3 hours, the effluent is lower than the limit value of the phosphate concentration in the World Health Organization's discharge standard, indicating the potential for further large-scale utilization.

[0056] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A phosphorus electro-adsorption removal positive electrode material of magnesium-aluminum double metal hydroxide supported on ZIF-8-derived carbon coated with polyaniline, characterized in that, The electrode is prepared by mixing binder PTFE, conductive carbon black and active material, adding them to a beaker according to a mass ratio of 1:1:7 - 9, adding an amount of ethanol covering the bottom of the beaker, and then performing ultrasonic treatment to make them fully dispersed and mixed, so that the mixed product presents a paste, and the composite material for coating on the positive electrode of the phosphorus removal system is obtained.

2. The electro-adsorption dephosphorization positive electrode material of magnesium-aluminum double metal hydroxide supported on ZIF-8-derived carbon coated with polyaniline according to claim 1, characterized in that, The method for preparing the active material is divided into three steps: a) Preparation of ZIF-8-derived carbon, i.e., ZC: Dissolve 0.02 mol of Zn(NO3)2·6H2O in 150 mL of methanol to form a clear solution A; at the same time, dissolve 2-methylimidazole with a molar amount 3 - 4 times that of Zn(NO3)2·6H2O in another 150 mL of methanol to form a clear solution B; then, pour solution B into solution A under stirring and continuously stir at room temperature for 24 hours, centrifuge the white precipitate, wash it three times with methanol, and vacuum dry it overnight at 60 °C to obtain ZIF-8; Then, under nitrogen purge, calcine the obtained ZIF-8 at 800 °C for 2 h; after cooling to room temperature, grind the prepared sample into powder, perform ultrasonic pickling with 2M hydrochloric acid for 30 minutes, and then wash it with deionized water until the pH is neutral; then, vacuum dry the prepared material overnight at 60 °C to obtain ZIF-8-derived carbon ZC; b) Preparation of ZC@PANI composite material by oxidative chemical polymerization reaction of aniline on the surface of ZC material: Disperse 150 mg of ZC in 100 mL of 2M hydrochloric acid aqueous solution, after ultrasonic treatment for 30 min, add 450 μL of aniline to the dispersion under vigorous stirring and continuously stir for 30 min; then, add 50 mL of 0.1M ammonium persulfate as an oxidant to the above solution at a flow rate of 2 - 5 ml / min and continuously stir at room temperature for 12 hours; finally, centrifuge to collect the dark green sample, wash it with deionized water and absolute ethanol, and vacuum dry it overnight at 60 °C to obtain ZC@PANI composite material; c) Preparation of active material: Disperse 200 mg of ZC@PANI composite material in 100 mL of deionized water and perform ultrasonic dispersion for 30 min; then, add a total of 3 mmol of MgCl2 and AlCl3 to the above dispersant and further perform ultrasonic treatment for 10 min; then stir at room temperature for 1 h, adjust the pH value to 10 with 1M NaOH aqueous solution; precipitate and age at room temperature for 4 h; centrifuge to collect the obtained product, wash it with deionized water and absolute ethanol, and vacuum dry it overnight at 60 °C to obtain the active material.

3. The electro-adsorption dephosphorization positive electrode material of magnesium-aluminum double metal hydroxide supported on ZIF-8-derived carbon coated with polyaniline according to claim 2, characterized in that, In the preparation process described in step a), the molar ratio of Zn(NO3)2·6H2O to 2-methylimidazole is preferably 1:3.

5.

4. The electroadsorption phosphorus removal positive electrode material of magnesium-aluminum double metal hydroxide supported on ZIF-8 derived carbon coated with polyaniline according to claim 2, characterized in that, In the preparation process described in step b), the ammonium persulfate solution is preferably added to the dispersion at a flow rate of 3 ml / min.

5. The positively charged electrode material for electro-adsorptive phosphorus removal, which is magnesium-aluminum double metal hydroxide supported on ZIF-8-derived carbon coated with polyaniline according to claim 2, is characterized in that In the preparation process described in step b), the stirring time is 12 hours, and the synthesized product is relatively good.

6. The electro-adsorption dephosphorization positive electrode material of magnesium-aluminum double metal hydroxide supported on ZIF-8-derived carbon coated with polyaniline according to claim 2, characterized in that, In the preparation process described in step c), the molar ratio of MgCl2 to AlCl3 is preferably 3:

1.

7. Application of the electro-adsorption phosphorus-removing positive electrode material of magnesium-aluminum double metal hydroxide supported on ZIF-8-derived carbon coated with polyaniline according to claim 1, characterized in that, The described cathode material is applied to environmental remediation, specifically for the electro-adsorption capture of low-concentration phosphate ions in water environment, showing a relatively high adsorption capacity for phosphate ions.

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