An MXene confined bimetallic organic framework derived heterojunction material anode and a preparation method and application thereof

Abstract

The application discloses an MXene confined bimetallic organic framework derived heterojunction material anode and a preparation method and application thereof, and belongs to the technical field of phosphorus adsorption materials. The active material of the anode is an MXene confined bimetallic organic framework derived heterojunction material; the preparation method of the active material comprises the following steps: (1) mixing iron salt, lanthanum salt, MXene, terephthalic acid and an organic solvent, and performing a solvothermal reaction to obtain an MXene confined bimetallic organic framework precursor material; and (2) performing calcination derivation on the MXene confined bimetallic organic framework precursor material in an inert atmosphere. The preparation method is simple and low in cost, and the prepared MXene confined bimetallic organic framework derived heterojunction material anode has the advantages of high adsorption capacity, fast adsorption rate, strong selectivity, wide pH application range and the like for phosphate.

Description

Technical Field

[0001] This invention relates to the field of phosphorus adsorption materials technology, specifically to an MXene-confined bimetallic organic framework-derived heterojunction anode, its preparation method, and its application. Background Technology

[0002] Excessive phosphorus input has become a major contributing factor to global water environment degradation. During agricultural runoff, industrial wastewater, and urban sewage discharge, large amounts of phosphate enter water bodies, easily triggering abnormal algal growth and eutrophication, thereby disrupting the aquatic ecological balance and reducing water quality safety levels. Existing phosphorus removal technologies, such as chemical precipitation, biological methods, and membrane separation processes, generally suffer from high operating costs, limited resource recovery efficiency, or complex treatment processes, making it difficult to meet long-term stable application requirements. Therefore, developing high-performance, low-energy-consumption phosphate removal technologies and functional materials with resource recovery potential has become an urgent research direction in the field of environmental engineering.

[0003] In recent years, metal-organic frameworks (MOFs) have attracted widespread attention in the field of water treatment due to their high specific surface area and tunable structure. Bimetallic MOFs, in particular, exhibit superior adsorption and catalytic performance due to metal synergistic effects. However, MOFs themselves have poor conductivity and low electron transport efficiency, easily leading to charge migration restriction and polarization in electro-driven systems, thus limiting their performance improvement. MXenes, with their excellent conductivity, can construct continuous electron transport channels, reduce charge migration impedance, and promote interfacial electronic coupling and synergistic effects, thereby significantly improving the overall performance of the material in electrochemical systems. Summary of the Invention

[0004] The purpose of this invention is to provide an MXene-confined bimetallic organic framework-derived heterojunction material anode, its preparation method, and its application. This material not only possesses excellent adsorption performance but also exhibits good stability and efficient recycling capability in an electrochemical environment, showing broad application prospects.

[0005] This invention first provides a method for preparing MXene-confined bimetallic organic framework-derived heterojunction materials, comprising the following steps: (1) Iron salt, lanthanum salt, MXene, terephthalic acid and organic solvent are mixed and subjected to a solvothermal reaction to obtain MXene confined bimetallic organic framework precursor material; (2) The MXene confined bimetallic organic framework precursor material is calcined and derivatized in an inert atmosphere to obtain MXene confined bimetallic organic framework derived heterojunction material.

[0006] In the above preparation method, in step (1), the iron salt is at least one of ferric chloride, ferrous chloride and ferric nitrate; The lanthanum salt is lanthanum chloride and / or lanthanum nitrate; The ratio of the total moles of the iron salt and lanthanum salt to the moles of terephthalic acid is 0.25-4:1; specifically, it can be 1:1. The mass ratio of MXene to the total mass of iron salt, lanthanum salt and terephthalic acid is 0.01-0.25:1, specifically 0.025:1; The organic solvent is at least one of N,N dimethylformamide, ethanol, and dimethyl sulfoxide; The ratio of the total molar amount of the organic solvent to the iron salt and lanthanum salt is 15-75 mL:5 mmol, preferably 25 mL:5 mmol.

[0007] In the preparation method described above, in step (1), the molar ratio of lanthanum in the lanthanum salt to iron in the iron salt is 0.25-3:1; preferably 0.75-3:1 or 0.75-2:1; more preferably 0.75:1.

[0008] In the above preparation method, in step (1), the temperature of the solvothermal reaction is 60-300 ℃; specifically, it can be 110 ℃; the time of the solvothermal reaction is 6-72 h; specifically, it can be 12 h. In step (2), the calcination temperature is 400-1000 ℃; preferably 800-1000 ℃; more preferably 900 ℃; The heating program derived from calcination is as follows: heat from room temperature to half of the target temperature, hold for 30-90 minutes, continue heating to the target temperature, and then hold for 0.5-5 hours. Specifically, the heating process derived from calcination is as follows: raise the temperature from room temperature to half of the target temperature, hold for 30 minutes, continue to raise the temperature to the target temperature, and then hold for 2 hours. In the calcination derivation step, the heating rate is 2-30 ℃ / min; specifically, it can be 10 ℃ / min.

[0009] The preparation method further includes the steps of washing the precursor sequentially with N,N dimethylformamide, anhydrous ethanol and water after a solvothermal reaction, and then drying it.

[0010] Specifically, the drying temperature is 50-120 ℃; specifically, it can be 60 ℃.

[0011] The preparation method described above includes the following steps: etching the precursor MAX in an etching solution, followed by freeze-drying to obtain the Mxene material.

[0012] Specifically, the etching solution is 30 mL of HF solution with a mass fraction of 49% or a mixed solution of 1 g LiF and 10 mL of 9 MHCl; When the etching solution is an HF solution, the dosage of the MAX precursor is 1-5 g, preferably 2 g. When the etching solution is a mixed solution of LiF and HCl, the dosage of the MAX precursor is 0.5-5 g, preferably 1 g; the etching method is preferably HF etching.

[0013] In the above preparation method, the etching time is 12-48 h, specifically 24 h; The etching temperature is 25-55 ℃, specifically 35 ℃; The freeze-drying time is 6-36 hours, specifically 24 hours.

[0014] In the above preparation method, in step (2), the inert atmosphere is a nitrogen or argon atmosphere; The inert gas is introduced at a flow rate of 5-300 mL / min; specifically, it can be 100 mL / min.

[0015] Second, the present invention provides MXene confined bimetallic organic framework-derived heterojunction materials prepared by the above preparation method.

[0016] Third, the present invention provides an MXene-confined bimetallic organic framework-derived heterojunction material anode, wherein the active material is the aforementioned MXene-confined bimetallic organic framework-derived heterojunction material.

[0017] Specifically, the MXene confined bimetallic organic framework-derived heterojunction anode is made by coating a conductive substrate with a mixture of the active material, conductive material and binder in a solvent.

[0018] In the aforementioned MXene-confined bimetallic organic framework-derived heterojunction anode, the conductive material is conductive carbon black; The adhesive is polyvinylidene fluoride; The solvent is at least one of N-methylpyrrolidone and anhydrous ethanol; The conductive substrate is any one of titanium plate, titanium mesh, stainless steel plate, stainless steel mesh, nickel plate, nickel foam, graphite paper, graphite plate, and graphite felt. The mass ratio of the active material, conductive material and binder is 1-10:1:1; specifically, it can be 8:1:1. The total mass ratio of the active material, conductive material, and binder to the volume ratio of the solvent is 1 g: 5-30 mL; specifically, it can be 1 g: 10 mL.

[0019] Fourth, the present invention also provides a method for preparing the above-mentioned MXene-confined bimetallic organic framework-derived heterojunction material anode, comprising the following steps: uniformly mixing the active material, conductive material and binder in a solvent to prepare a slurry, then uniformly coating it on a conductive substrate, and drying it to obtain the MXene-confined bimetallic organic framework-derived heterojunction material anode.

[0020] Specifically, the drying process involves drying in a vacuum oven at 60-200 ℃ for 6-48 h; more specifically, drying in a vacuum oven at 80 ℃ for 12 h.

[0021] Finally, this invention provides the application of the above-mentioned MXene confined bimetallic organic framework-derived heterojunction material anode in phosphorus removal from wastewater.

[0022] In the above applications, the MXene-confined bimetallic organic framework-derived heterojunction material is anode-assembled into an electroadsorption system for phosphorus removal; Specifically, the cathode of the electro-adsorption system is made by coating a conductive substrate with a mixture of activated carbon, conductive material and binder in a solvent; The activated carbon can be commercially available powdered activated carbon from any source; The conductive material, binder, and solvent must all be consistent with the anode of the MXene confined bimetallic organic framework-derived heterojunction material. The two electrodes can be of any shape and thickness, but the dimensions of the two pairs of electrodes must be consistent. The distance between the two electrodes is 1-10 mm; specifically, it can be 3 mm. The voltage between the two electrodes is 0.8-3 V; specifically, it can be 1.2 V.

[0023] In the above applications, the wastewater can be phosphorus-containing wastewater from any source, specifically secondary effluent from a wastewater treatment plant; The wastewater may be phosphate-containing wastewater; The phosphate concentration in the wastewater was 1-500 mg P / L; Specifically, the wastewater also contains Cl. - NO3 - HCO3 - SO4 2- and at least one of FA.

[0024] In the above applications, the wastewater treatment process is a circulating flow; The circulation flow rate is 5-100 mL / min; specifically, it can be 20 mL / min.

[0025] In the above applications, the MXene-confined bimetallic organic framework-derived heterojunction material anode is recyclable; In the recycling process, NaOH solution is used for phosphorus desorption; specifically, the concentration of the NaOH solution is 0.05-1 mol / L, preferably 0.5 mol / L.

[0026] The present invention has the following beneficial effects: (1) The anode preparation method of the present invention is simple and does not require high-end or complex equipment, which can reduce the preparation cost; (2) Compared with existing adsorbents, the present invention has the advantages of high actual adsorption capacity, fast adsorption rate, strong selectivity and wide pH range. (3) The MXene confined bimetallic organic framework-derived heterojunction material anode of the present invention is grown by MOF on MXene, which not only increases the electrochemical performance of the material and improves the phosphate adsorption capacity of the material, but also improves the stability and selectivity of the material. (4) By adjusting the MXene content, the adsorption performance of the heterojunction material can be controlled, thereby optimizing the electrochemical performance of the electrode. (5) When the MXene confined bimetallic organic framework-derived heterojunction material anode prepared in this invention is used for the adsorption of phosphate in actual wastewater, it has strong anti-interference ability against coexisting substances and can be regenerated and reused multiple times. (6) The MXene-confined bimetallic organic framework-derived heterojunction material anode prepared in this invention has a higher phosphate adsorption capacity and rate than the La-Fe bimetallic organic framework-derived structure anode without MXene.

[0027] Overall, this invention, through innovative preparation methods, effectively improves the electrochemical performance and phosphate removal efficiency of MXene-confined bimetallic organic framework-derived heterojunction anodes, demonstrating significant environmental protection benefits and practical application value. Attached Figure Description

[0028] Figure 1 This is a diagram showing the adsorption kinetics of phosphate on the anode prepared at different derivation temperatures in Example 1.

[0029] Figure 2 The diagram shows the adsorption kinetics of phosphate on anodes prepared with different MXene contents in Example 2.

[0030] Figure 3 This is a comparison chart of the adsorption rates of phosphates on anodes prepared with different MXene contents in Example 2.

[0031] Figure 4The image shows the X-ray polycrystalline diffraction (XRD) patterns of MXene-confined bimetallic organic framework-derived heterojunction materials prepared with different MXene contents in Example 2.

[0032] Figure 5 The images show transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected electron diffraction (SAED) patterns of the derived heterojunction material prepared with 10% MXene content (10% MXene) in Example 2; among them, Figure 5 In the image, a is a 200 nm TEM image; b is a 100 nm TEM image; c is an HRTEM image; d is a SAED image; and e is an elemental distribution map.

[0033] Figure 6 This is the adsorption isotherm of phosphate by the 10% MXene anode in Example 3.

[0034] Figure 7 The graph shows the adsorption effect of 10% MXene anode on phosphate at different solution temperatures in Example 4.

[0035] Figure 8 This is a graph showing the adsorption effect of 10% MXene anode on phosphate under different coexisting conditions in Example 5.

[0036] Figure 9 The graph shows the adsorption effect of 10% MXene anode on phosphate at different initial pH values ​​in Example 6.

[0037] Figure 10 The graph shows the effect of the number of adsorption-desorption cycles and the concentration of regenerated solution on the adsorption of phosphate in Example 7 with 10% MXene anode.

[0038] Figure 11 This is a diagram showing the adsorption effect of 10% MXene anode on phosphate in the secondary effluent of the wastewater treatment plant in Example 8.

[0039] Figure 12 The cyclic voltammetry (CV) curves of the 10% MXene anode at different scan rates in Example 9 are shown.

[0040] Figure 13 This is a CV curve of anodes with different MXene contents at 100 mV / s in Example 9.

[0041] Figure 14 The electrochemical impedance spectroscopy (EIS) diagrams are shown for anodes with different MXene contents in Example 9.

[0042] Figure 15 The image shows the constant current charge-discharge (GCD) diagrams of anodes with different MXene contents in Example 9. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0044] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0045] Unless otherwise specified, the quantitative experiments in the following examples are all repeated three times, and the results are averaged.

[0046] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0047] The preparation method of MXene used in the following examples is as follows: 2g of MAX (Ti3AlC2) was slowly added to 30 mL of HF solution with a mass fraction of 49%. The mixture was magnetically stirred at 35 °C for 24 h. The mixture was then centrifuged at 3500 rpm and the supernatant was discarded. Ultrapure water was added and the mixture was centrifuged repeatedly until the pH of the supernatant reached about 6-7. After centrifugation, the sample was rapidly frozen in liquid nitrogen and freeze-dried in a refrigerated dryer for 24 h to obtain MXene. The MXene was then stored at low temperature for later use.

[0048] In the following embodiments, the MXene-confined bimetallic organic framework-derived heterojunction anode is named according to the actual mass percentage of MXene in the derived heterojunction material. The yield of MXene in the derived heterojunction material compared to the non-derived material is 100%, and the yield of the bimetallic MOF derivative is 25% of the total mass of all metal salts and ligands, denoted as x%MXene. x% represents the actual percentage of MXene added (by mass) in the bimetallic MOF derivative. Specifically, it can be labeled as: 0%MXene, 5%MXene, 10%MXene, 20%MXene, 30%MXene, and 100%MXene, where 0%MXene and 100%MXene represent the La-Fe MOF derivative without MXene and the pure MXene anode, respectively.

[0049] The graphite paper used in the following examples has a size of 9 cm × 9 cm × 0.5 cm.

[0050] Example 1: Preparation of MXene-confined bimetallic organic framework-derived heterojunction anodes and their phosphate adsorption properties at different temperatures.

[0051] Taking a 10% MXene electrode with a derivation temperature of 900 ℃ as an example, the specific steps are as follows: Step 1: Preparation of the MXene-confined bimetallic organic framework precursor (MXene mass ratio to the total mass of iron salt, lanthanum salt, and terephthalic acid is 0.025:1): Weigh 0.7723 g (2.86 mmol) ferric chloride hexahydrate, 0.7958 g (2.14 mmol) lanthanum chloride heptahydrate, 0.0600 g (10% mass ratio) MXene, and 0.8307 g (5 mmol) terephthalic acid. Dissolve them sequentially in 25 mL of N,N-dimethylformamide, sonicate until homogeneous, place in a polytetrafluoroethylene liner, transfer to a reaction vessel, and heat continuously in an oven at 110 ℃ for 12 h. After the reaction, wash three times sequentially with N,N-dimethylformamide, anhydrous ethanol, and water, and dry at 60 ℃ for later use.

[0052] Step 2: Preparation of MXene-confined bimetallic organic framework-derived heterojunction materials: 3 g of the precursor prepared in Step 1 was calcined and derivatized in a tube furnace under a nitrogen atmosphere of 100 mL / min at a derivation temperature of 900 ℃. The heating program was as follows: heating from room temperature to 450 ℃ at a heating rate of 10 ℃ / min, holding for 30 min, then heating from 450 ℃ to 900 ℃ at a heating rate of 10 ℃ / min, holding for 2 h, and then cooling and storing for later use.

[0053] Step 3: Preparation of MXene-confined bimetallic organic framework-derived heterojunction anode: The MXene-confined bimetallic organic framework-derived heterojunction material prepared above is mixed with carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1 and N-methylpyrrolidone in a ratio of 1g of N-methylpyrrolidone to 10 mL of N-methylpyrrolidone to prepare a uniform slurry. This slurry is then uniformly coated onto cleaned graphite paper and dried in a vacuum oven at 80 ℃ for 12 h to obtain the MXene-confined bimetallic organic framework-derived heterojunction anode.

[0054] Step 4: Preparation of Activated Carbon Electrode: Powdered activated carbon was purchased from Shandong Keyuan Biochemical Co., Ltd., 200-mesh powdered activated carbon (CAS: 7440-44-0, item number: A805338-500g). The powdered activated carbon was boiled in water for 6 hours to remove impurities, and then dried in a vacuum oven at 80 ℃. 30 g of the dried activated carbon was mixed with 800 mL of 5 mol / L nitric acid solution and stirred at 60 ℃ for 3 hours. After stirring, the mixture was filtered, washed, and the filter cake was dried to obtain carboxyl-modified activated carbon. The prepared carboxyl-modified activated carbon was mixed with carbon black, polyvinylidene fluoride, and N-methylpyrrolidone to form a homogeneous slurry, which was then used to prepare the activated carbon electrode for later use. The preparation method of the activated carbon electrode is the same as that of the MXene-confined bimetallic organic framework-derived heterogeneous material anode described above.

[0055] Step 5: Assemble the prepared electrodes into an electroadsorption system (chamber volume 50×50×3 mm), with a distance of 3 mm between the two electrode plates and an effective contact area of ​​5×5 cm². 2 The device was used for an electro-adsorption experiment of phosphate, and the concentration of the phosphate solution (prepared with potassium dihydrogen phosphate) used in the experiment was 50 mg P / L.

[0056] Steps six through eleven: Prepare materials with derivation temperatures of 400, 500, 600, 700, 800, and 900 °C respectively (the derivation temperature program is: raise the temperature from room temperature to half the target temperature, hold for 30 min, continue raising the temperature to the target temperature, and then hold for 2 h; the heating rate is 10 °C / min); then prepare electrodes according to the above method for phosphate adsorption experiments. The phosphate concentration is 50 mg P / L, the total volume of the phosphate solution is 100 mL, the circulation flow rate is 20 mL / min, the voltage is 1.2 V, the electroadsorption time is 6 h, and the adsorption temperature is 25 °C.

[0057] Step 12, Phosphorus Concentration Determination: A sample is taken from the solution after the above reaction using a disposable syringe, and then... (The sentence is incomplete and requires further context to be fully translated.) μ After filtration through an aqueous cellulose membrane, the phosphorus concentration in the filtrate was determined using a Hach spectrophotometer.

[0058] The experiment was set up in three replicates, and the results were averaged.

[0059] The results are as follows Figure 1 As shown, with the increase of derivatization temperature, the electroadsorption capacity of different electrodes increases significantly and the adsorption rate accelerates; when the derivatization temperature is 900 °C, the electroadsorption capacity of the electrode reaches its maximum and the adsorption rate is the fastest.

[0060] Example 2: Preparation of confined bimetallic organic framework-derived heterojunction anodes with different MXene contents and their phosphate adsorption properties.

[0061] Taking the preparation of a 10% MXene electrode as an example, the specific steps are as follows: Steps one through five are the same as steps one through five in Example 1.

[0062] Steps six through twelve: Prepare electrodes containing 0% MXene (0.7723 g, 2.86 mmol ferric chloride hexahydrate, 0.7958 g, 2.14 mmol lanthanum chloride heptahydrate), 5% MXene, 10% MXene, 15% MXene, 20% MXene, 30% MXene, and 100% MXene for phosphate adsorption experiments. The preparation process is the same as steps one through five above, only the proportion of MXene is changed. The phosphate concentration is 50 mg P / L, the total volume of the phosphate solution is 100 mL; the circulation flow rate is 20 mL / min, the voltage is 1.2 V, the electroadsorption time is 6 h, and the adsorption temperature is 25 °C.

[0063] Step 13: Phosphorus concentration determination, same as step 12 in Example 1.

[0064] The experiment was set up in three replicates, and the results were averaged.

[0065] The results are as follows Figure 2 As shown, with the increase of MXene content, the electro-adsorption capacity of the anode of the heterojunction material increases significantly. When the MXene content is 10% (10% MXene), the electro-adsorption capacity of the electrode reaches the maximum. With the continued increase of MXene content, the adsorption capacity shows a slight downward trend. Figure 3 The graph shows the adsorption rates of electrodes with different MXene contents. It can be seen from the graph that 10% MXene exhibits the fastest adsorption rate, reaching as high as 0.6639 mg P. g -1 min -1 .

[0066] Figure 4 The XRD patterns of the derived heterojunction materials with different MXene contents are shown. The XRD patterns reveal that the derived materials mainly consist of MXene, Fe3O4, and La2O3 phases. Furthermore, the higher the MXene content, the more pronounced the MXene phase peak.

[0067] Figure 5 The images show TEM, HRTEM, and SAED images of a derived heterojunction material with 10% MXene content. Figure 5 As can be clearly seen from 'a' and 'b', the derived heterostructure material has a regular layered structure. For example... Figure 5 As shown in c, the lattice spacing corresponding to the (002) crystal plane of La2O3 is 0.32 nm, while the obvious lattice spacings corresponding to the (220) and (400) crystal planes of Fe3O4 are 0.20 nm and 0.28 nm, respectively. Figure 4The d-selective area electron diffraction (SAED) pattern further confirmed that these rings were attributed to the (002) and (200) crystal planes of La2O3 and the (400) and (220) crystal planes of Fe3O4, respectively. Figure 4 As can be seen from the 'e', ​​La and Fe are uniformly distributed on the MXene sheets, indicating the successful construction of the MXene-confined La2O3-Fe3O4 heterojunction structure. This is consistent with the XRD results.

[0068] Example 3: Adsorption isotherm of phosphate by 10% MXene anode.

[0069] Step 1: Prepare phosphate solutions with concentrations of 5, 10, 15, 25, 50, 100, 200, and 350 mg P / L using potassium dihydrogen phosphate (KH2PO4). Assemble the electroadsorption system according to step 5 of Example 1.

[0070] Step 2, Adsorption conditions: phosphate solution volume is 100 mL, circulation flow rate is 20 mL / min, voltage is 1.2 V, electroadsorption time is 6 h, and adsorption temperature is 25℃.

[0071] Step 3: Phosphate concentration determination, same as step 12 in Example 1.

[0072] The experiment was set up in three replicates, and the results were averaged.

[0073] Figure 6 The isotherm for phosphate adsorption on a 10% MXene anode shows that the adsorption of phosphate by this electrode material is consistent with the Langmuir model, and the electro-adsorption capacity fitted by the isotherm is as high as 363.42 mg P / g.

[0074] Example 4: Adsorption performance of phosphate by a 10% MXene anode at different solution temperatures.

[0075] Step 1: Prepare a phosphate solution with a concentration of 50 mg P / L using potassium dihydrogen phosphate (KH2PO4), and assemble it into an electroadsorption system according to step 5 of Example 1.

[0076] Step 2, Adsorption conditions: Adsorption temperature 25℃-55℃, total volume of phosphate solution 100 mL; circulation flow rate 20 mL / min, voltage 1.2 V, electroadsorption time 6 h.

[0077] Step 3: Phosphate concentration determination, same as step 12 in Example 1.

[0078] The experiment was set up in three replicates, and the results were averaged.

[0079] The effect of solution temperature on phosphate adsorption is shown in the figure. Figure 7.from Figure 7 It can be seen that solution temperature has a significant promoting effect on phosphate adsorption performance. As the temperature increases from 25℃ to 55℃, the equilibrium adsorption capacity of phosphate gradually increases, with the maximum adsorption capacity increasing from about 125 mg P / g to nearly 140 mg P / g, and the adsorption rate also significantly increases.

[0080] Example 5: Adsorption performance of phosphate by a 10% MXene anode under different coexisting conditions.

[0081] Step 1: Prepare a phosphate solution with a concentration of 50 mg P / L using potassium dihydrogen phosphate (KH2PO4), which contains the anion Cl-. - NO3 - HCO3 - SO4 2- The organic matter FA, which are prepared from NaCl, NaNO3, NaHCO3, Na2SO4 and FA respectively, are used. The concentrations of the coexisting ions are set at three gradients: 10 mg / L, 50 mg / L and 100 mg / L. The electroadsorption system is assembled according to step five of Example 1.

[0082] Step 2, Adsorption conditions: Total volume of phosphate solution 100 mL; circulation flow rate 20 mL / min; voltage 1.2 V; electroadsorption time 6 h; adsorption temperature 25 °C.

[0083] Step 3: Phosphate concentration determination, same as step 12 in Example 1.

[0084] The experiment was set up in three replicates, and the results were averaged.

[0085] The effect of coexisting substances on phosphate adsorption is shown in Figure 8 As can be seen from the figure, in the presence of coexisting ions, NO3... - and Cl - It has little effect on the electro-adsorption process of phosphates. SO4 2- HCO3 - FA has a slight effect on the electro-adsorption process of phosphate, but the effect is not significant.

[0086] Example 6: Adsorption performance of phosphate by 10% MXene anode at different pH values.

[0087] Step 1: Prepare a series of 50 mg P / L phosphate solutions (prepared with potassium dihydrogen phosphate) with different pH values ​​using 0.1 M hydrochloric acid (HCl) solution and sodium hydroxide (NaOH) solution, with pH values ​​of 2, 4, 6, 7, 8, 10, and 12. Assemble the electroadsorption system according to step 5 of Example 1.

[0088] Step 2, Adsorption conditions: Total volume of phosphate solution 100 mL; circulation flow rate 20 mL / min; voltage 1.2 V; electroadsorption time 6 h; adsorption temperature 25 °C.

[0089] Step 3: Phosphate concentration determination, same as step 12 in Example 1.

[0090] The experiment was set up in three replicates, and the results were averaged.

[0091] The adsorption results of phosphate at different pH values ​​are shown in the figure. Figure 9 It can be seen that the 10% MXene electrode exhibits high phosphorus adsorption capacity across a pH range of 2-8, with a more pronounced adsorption capacity under acidic conditions. This is because protonation enhances the electrostatic adsorption on the surface of positively charged materials under acidic conditions. Therefore, this adsorbent has a wide pH applicability.

[0092] Example 7: Effects of adsorption-desorption cycle and regeneration solution concentration on the phosphate adsorption performance of 10% MXene anode.

[0093] Step 1: Prepare 100 mL of phosphate solution with 50 mg P / L using potassium dihydrogen phosphate (KH2PO4) to conduct an adsorption-desorption cycle experiment. Experimental conditions: total volume of phosphate solution 100 mL; circulation flow rate 20 mL / min; voltage 1.2 V; adsorption time 6 h; adsorption temperature 25℃.

[0094] Assemble the electroadsorption system according to step five of Example 1.

[0095] Step 2: Replace the adsorbed solution with 100 mL of 0.05-1 mol / L NaOH solution for phosphate desorption. The circulation flow rate is 20 mL / min, the voltage is adjusted to -1.2 V, and the desorption time is 1 h. Repeat the above adsorption and desorption steps.

[0096] Step 3: Phosphate concentration determination, same as step 12 in Example 1.

[0097] The experiment was set up in three replicates, and the results were averaged.

[0098] Figure 10 The effect of adsorption-desorption cycle number and NaOH concentration on phosphate adsorption of 10% MXene electrode was investigated. The figure shows that the adsorption performance of the material gradually decreases with the increase of adsorption-desorption cycle number. The highest adsorption capacity of 40.83% can be maintained within five cycles. The electrode regenerated with 0.5 mol / L NaOH solution still maintains an adsorption capacity of 54.45 mgP / g after 5 cycles.

[0099] Example 8: Adsorption performance of 10% MXene anode on phosphate in secondary effluent from wastewater treatment plant.

[0100] Step 1: An adsorption-desorption cycle experiment was conducted on the phosphate solution in the secondary effluent of the wastewater treatment plant using a 10% MXene anode. The experimental conditions were: total volume of phosphate solution in the secondary effluent of the wastewater treatment plant 100 mL; circulation flow rate 20 mL / min; adsorption voltage 1.2 V; adsorption time 1 h; and adsorption temperature 25℃. The various indicators of the secondary effluent from this wastewater treatment plant are shown in Table 1.

[0101] Assemble the electroadsorption system according to step five of Example 1.

[0102] Step 2: Replace the phosphate solution in the secondary effluent of the wastewater treatment plant with 100 mL of 0.5 mol / L NaOH solution for desorption. The circulation flow rate is 20 mL / min, the voltage is adjusted to -1.2 V, and the desorption time is 1 h. Repeat the above adsorption-desorption steps.

[0103] Step 3: Phosphate concentration determination, same as step 12 in Example 1.

[0104] The experiment was set up in three replicates, and the results were averaged.

[0105] Figure 11 The figure shows the adsorption performance of a 10% MXene electrode on phosphate in the secondary effluent of a wastewater treatment plant. As can be seen from the figure, after the first 25 cycles, the effluent phosphate concentration was 0.278 mg P / L, with a removal rate as high as 86.63%, meeting the Class IV requirement of the Surface Water Environmental Quality Standard (GB 3838-2002) (0.3 mg P / L). After 27 cycles, the effluent phosphate concentration was 0.45 mg P / L, with a removal rate of 78.23%, meeting the Class I standard of the Integrated Wastewater Discharge Standard (GB 8978-1996) (0.5 mg P / L), indicating that this electrode has good prospects for practical application.

[0106] Table 1. Secondary effluent quality of wastewater treatment plant

[0107] Example 9: Electrochemical properties of a 10% MXene anode.

[0108] Step 1: Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD) were performed using an electrochemical workstation (CHI660E) in a three-electrode system, where the 10% MXene electrode, platinum mesh electrode, and Ag / AgCl electrode were used as the working electrode, counter electrode, and reference electrode, respectively.

[0109] Step 2: The above tests were performed in a neutral pH phosphate solution (1 M KH₂PO₄). The CV scan potential range was -0.2 to 1.2 V, and the scan rates included 5, 10, 20, 50, and 100 mV s. -1 EIS testing at 10 6 The GCD test was conducted in the frequency range of Hz to 0.01 Hz. The GCD test was performed at 1.0 A g. -1 The experiment was conducted at a current density of [specific value].

[0110] Figure 12 The figure shows the CV curves of the 10% MXene electrode at different scan rates. As can be seen from the figure, the area of ​​the CV curve gradually increases with increasing scan rate, indicating that the 10% MXene electrode has excellent electrochemical performance. Furthermore, the CV curves exhibit an approximately spindle shape with pseudocapacitive characteristics, suggesting that the energy storage process is synergistically contributed by the double-layer capacitance and the surface Faraday reaction. Figure 13 The CV curves for different electrodes at 100 mV / s clearly show that the 10% MXene electrode has the largest area under the curve, indicating that it has the best electrochemical performance and the best charge storage capacity. Furthermore, the CV curve of the 10% MXene electrode is more robust and has weaker polarization, indicating that it possesses faster charge response kinetics and higher reversibility.

[0111] Figure 14 and 15 The EIS and GCD plots for anodes with different MXene contents are shown. The plots reveal that the 10% MXene anode exhibits the smallest semicircle in the high-frequency region, indicating the lowest charge transfer resistance (Rct). The near-vertical trend in the low-frequency region further suggests reduced ion diffusion resistance and more ideal capacitance characteristics. Furthermore, the 10% MXene electrode demonstrates the longest charge-discharge time and the smallest voltage drop. These results indicate that the 10% MXene electrode possesses excellent electrochemical properties. This is consistent with the experimental results of Example 2.

Claims

1. A method for preparing an MXene-confined bimetallic organic framework-derived heterojunction material, comprising the following steps: (1) Iron salt, lanthanum salt, MXene, terephthalic acid and organic solvent are mixed and subjected to a solvothermal reaction to obtain MXene confined bimetallic organic framework precursor material; (2) The MXene confined bimetallic organic framework precursor material is calcined and derivatized in an inert atmosphere to obtain MXene confined bimetallic organic framework derived heterojunction material.

2. The preparation method according to claim 1, characterized in that: In step (1), the iron salt is at least one of ferric chloride, ferrous chloride, and ferric nitrate; The lanthanum salt is lanthanum chloride and / or lanthanum nitrate; The ratio of the total molar number of the iron salt and lanthanum salt to the molar number of terephthalic acid is 0.25-4:1; The mass ratio of MXene to the total mass of iron salt, lanthanum salt, and terephthalic acid is 0.01-0.25:1; The organic solvent is at least one of N,N dimethylformamide, ethanol, and dimethyl sulfoxide; The ratio of the total molar amount of the organic solvent to the iron salt and lanthanum salt is 15-75 mL:5 mmol.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the molar ratio of lanthanum in the lanthanum salt to iron in the iron salt is 0.25-3:1; preferably 0.75:

1.

4. The preparation method according to any one of claims 1-3, characterized in that: In step (1), the temperature of the solvothermal reaction is 60-300 °C; The solvothermal reaction time is 6-72 h; In step (2), the calcination temperature is 400-1000 ℃; preferably 900 ℃. The heating program derived from calcination is as follows: heat from room temperature to half of the target temperature, hold for 30-90 minutes, continue heating to the target temperature, and then hold for 0.5-5 hours. In the calcination derivation step, the heating rate is 2-30 °C / min.

5. The MXene confined bimetallic organic framework-derived heterojunction material prepared by the preparation method according to any one of claims 1-4.

6. An MXene-confined bimetallic organic framework-derived heterojunction anode, characterized in that: The active material of the anode of the MXene-confined bimetallic organic framework-derived heterojunction material is the MXene-confined bimetallic organic framework-derived heterojunction material as described in claim 5.

7. The MXene-confined bimetallic organic framework-derived heterojunction anode according to claim 6, characterized in that: The MXene confined bimetallic organic framework-derived heterojunction anode is made by coating a conductive substrate with a mixture of the active material, conductive material, and binder in a solvent.

8. The MXene-confined bimetallic organic framework-derived heterojunction anode according to claim 7, characterized in that: The conductive material is conductive carbon black; The adhesive is polyvinylidene fluoride; The solvent is at least one of N-methylpyrrolidone and anhydrous ethanol; The conductive substrate is any one of titanium plate, titanium mesh, stainless steel plate, stainless steel mesh, nickel plate, nickel foam, graphite paper, graphite plate, and graphite felt. The mass ratio of the active material, conductive material and binder is 1-10:1:1; The total mass ratio of the active material, conductive material, and binder to the volume ratio of the solvent is 1 g: 5-30 mL.

9. The application of MXene confined bimetallic organic framework-derived heterojunction anodes according to any one of claims 6-8 in wastewater phosphorus removal.

10. The application according to claim 9, characterized in that: In the application described above, the MXene confined bimetallic organic framework-derived heterojunction material is anode-assembled into an electroadsorption system for phosphorus removal. The wastewater is phosphate-containing wastewater; The phosphate concentration in the wastewater was 1-500 mg P / L; Specifically, the wastewater also contains Cl. - NO3 - HCO3 - SO4 2- and at least one of FA.

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