Electrochemical selective adsorption electrode material, preparation method and application thereof in thorium adsorption

Abstract

The application discloses an electrochemical selective adsorption electrode material, a preparation method and application of the electrochemical selective adsorption electrode material in thorium adsorption, and utilizes a hydrothermal method to synthesize molybdenum disulfide modified reduced graphene aerogel MoS2@GA electrode material, which is used for selective adsorption and recovery of Th in rare earth, and comprises the following steps: S1, synthesizing nanoflower MoS2 by the hydrothermal method; S2, dissolving the nanoflower MoS2 powder in a graphene oxide aqueous solution and dispersing, adding a reducing agent, heating a hydrothermal reaction kettle, cooling to room temperature, forming a hydrogel, dialysis, freezing, drying, and obtaining molybdenum disulfide doped modified graphene aerogel MoS2@GA electrode material. The molybdenum disulfide modified graphene electrode material prepared by the application has a high thorium adsorption capacity, good cycle performance, selectivity and fast adsorption kinetics, can selectively recover thorium from waste residue leaching solution, and indicates that the electrochemical adsorption method can effectively realize selective recovery of thorium from rare earth.

Description

Technical Field

[0001] This invention relates to the field of adsorption electrode technology, specifically to an electrochemical selective adsorption electrode material, its preparation method, and its application in thorium adsorption. More particularly, it relates to a molybdenum disulfide-modified reduced graphene aerogel MoS2@GA electrode material prepared by hydrothermal synthesis. Background Technology

[0002] Rare earth elements are widely used in many high-tech fields. However, rare earth minerals such as monazite and bastnaesite are often associated with elements like thorium, and the leachates of these minerals contain high concentrations of thorium and rare earth elements. Furthermore, the rare earth mining industry generates large amounts of waste residue containing high concentrations of thorium. Improper disposal of this waste residue can cause serious environmental problems. The thorium contained in the waste residue can also migrate into the environment with rainfall, causing widespread pollution and endangering human health.

[0003] Furthermore, thorium is an excellent nuclear fission material with numerous advantages. Its abundant reserves can meet the ever-increasing energy demands of modern times, leading to widespread interest in thorium-based nuclear reactors. Thorium-based nuclear reactors are an option for fourth-generation nuclear power plants, and with the maturation of thorium-based molten salt nuclear reactor technology, there is a significant demand for thorium-based nuclear fuel. Rare earth minerals such as monazite and bastnaesite, as well as rare earth waste, contain substantial amounts of rare earth elements and thorium. Separating and recovering thorium and rare earth elements from the leachate of this waste is essential. Efficient and clean separation and recovery of thorium from rare earth elements can effectively address the environmental pollution caused by thorium migration and achieve the resource utilization of thorium.

[0004] Currently, the mainstream method for recovering thorium from rare earth elements is solvent extraction. Commercial extractants such as N1923, TBP, ionic liquids, and deep eutectic solvents (DESs) can effectively separate and recover thorium from rare earth elements. However, solvent extraction for thorium recovery requires the use of large amounts of inorganic acids and volatile organic solvents, which may generate secondary low-level radioactive waste and cause wider environmental pollution.

[0005] Therefore, to overcome the aforementioned drawbacks of solvent extraction, research began on adsorption methods using highly selective and low-cost solid adsorbents for separation and recovery. Adsorption methods are suitable for separating and recovering radionuclides from low-concentration wastewater. In recent years, various thorium adsorbents have been rapidly developed, such as metal sulfides, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), graphene, and dry gels, all of which have shown good adsorption effects on thorium.

[0006] However, when using conventional physicochemical adsorption methods, the diffusion and adsorption rates of ions to the adsorbent surface are relatively slow. In addition, the ions adsorbed on the material surface are positively charged, and the Coulomb repulsion hinders the adsorption of subsequent ions on the adsorbent surface, resulting in most of the active sites on the adsorbent surface being unable to adsorb ions, leading to a low adsorption capacity.

[0007] In recent years, electroadsorption has attracted much attention due to its advantages such as low energy consumption, low cost, easy regeneration, and green process. Under the impetus of an electric field, ions in the solution form an electric double layer on the electrode and are adsorbed and eliminated. Compared with physicochemical adsorption, electroadsorption has a higher adsorption efficiency. Electrochemical adsorption is widely used in seawater uranium extraction and radionuclide removal. Electrochemical adsorption can effectively increase the adsorption capacity. Compared with conventional physicochemical adsorption, the electric field between the electrodes can accelerate the migration of ions to the electrode, increase the contact between ions on the electrode, and improve the adsorption capacity. In addition, water splitting on the electrode can neutralize the charge of ions adsorbed on the electrode surface, preventing charged ions from repelling subsequent ions. Electrode materials with good hydrogen evolution (HER) catalytic capabilities help to improve the adsorption capacity, and the development of high-performance HER catalytic electrodes helps to rapidly recover metal ions.

[0008] However, current electrochemical adsorption generally suffers from poor selectivity and cannot selectively adsorb and separate specific elements. Therefore, there is an urgent need for an electrode adsorption material with better selectivity for thorium. Summary of the Invention

[0009] This invention aims to provide an electrochemically selective adsorption electrode material, its preparation method, and its application in thorium adsorption. The reduced graphene aerogel MoS2@GA electrode material modified with molybdenum disulfide synthesized by hydrothermal method has good electrochemical adsorption properties and can selectively remove thorium from rare earth elements.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for preparing an electrochemically selective adsorption electrode material, comprising the hydrothermal synthesis of molybdenum disulfide-modified reduced graphene aerogel MoS2@GA electrode material for the selective adsorption and recovery of Th from rare earth elements, including the following steps:

[0012] S1, Hydrothermal synthesis of nanoflower MoS2;

[0013] S2, the synthesized nanoflower MoS2 powder is dissolved and dispersed in an aqueous solution of graphene oxide, a reducing agent is added, the mixture is heated in a hydrothermal reactor, cooled to room temperature to form a hydrogel, dialyzed, frozen, and dried to obtain a molybdenum disulfide-doped modified graphene aerogel MoS2@GA electrode material.

[0014] According to an embodiment of the present invention, the steps of the hydrothermal synthesis of nanoflower MoS2 include:

[0015] S11, the raw material (NH4)6Mo7O 24 • Dissolve 4H2O and CH4N2S in water, stir until completely dissolved, and transfer to a hydrothermal reactor;

[0016] S12 was heated to a certain temperature and then cooled to room temperature. It was then filtered, washed, and dried to obtain nanoflower MoS2.

[0017] According to an embodiment of the present invention, the mass ratio of the raw materials is 1.14:1 to 1.21:1.

[0018] In step S2 according to an embodiment of the present invention, the mass ratio of MoS2 powder to graphene oxide is 1:2 to 8:1; preferably 1:2 to 4:1.

[0019] For example, 1:1, 1:1.5, 1:2, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, or any point between any two of the above ranges.

[0020] Preferably, the concentration of the graphene oxide aqueous solution is 5 mg / ml to 10 mg / ml.

[0021] For example, 5mg / ml, 6mg / ml, 7mg / ml, 8mg / ml, 9mg / ml, 10mg / ml.

[0022] According to an embodiment of the present invention, the reducing agent includes one or more of ethylenediamine, hydrazine hydrate, and propylenediamine.

[0023] According to an embodiment of the present invention, the amount of ethylenediamine added as a reducing agent is 100ul / ml to 150ul / ml.

[0024] According to an embodiment of the present invention, in step S12, the heating rate is 2-4℃ / min, the temperature is raised to 200-230℃, and maintained for 20-26 hours; the hydrothermal reactor is cooled at a rate of 0.4-1.6℃ / min.

[0025] For example, the temperature is increased from room temperature to 210°C at a rate of 3°C / min and maintained for 24 hours.

[0026] According to an embodiment of the present invention, the hydrothermal reactor was cooled at a rate of 1 °C / min until the sample was cooled to room temperature. The sample was then filtered through a 0.22 μm filter membrane in a vacuum pump, the product was washed, washed 5 times with deionized water and 3 times with anhydrous ethanol, and then dried in an oven at 70 °C to synthesize nanoflower MoS2.

[0027] The present invention also provides an electrochemically selectively adsorbed MoS2@GA electrode material, which is synthesized using the above-mentioned method for preparing electrochemically selectively adsorbed electrode materials.

[0028] According to embodiments of the present invention, the MoS2@GA electrode material can selectively adsorb thorium in rare earth elements during electrochemical adsorption, with an adsorption capacity of up to 4154 mg / g; it has fast adsorption kinetics, with an adsorption capacity of up to 960.45 mg / g within 15 minutes and an adsorption capacity of 1959.62 mg / g for thorium within the first hour.

[0029] According to an embodiment of the present invention, the MoS2@GA electrode material has good cycling performance, and its performance does not significantly decay after 10 cycles, showing great application potential in thorium recovery.

[0030] According to an embodiment of the present invention, the MoS2@GA electrode material has a good removal rate for low concentrations of thorium, achieving a thorium removal rate of 99% within 8 hours, and also exhibits good cycle performance.

[0031] This invention also provides an application of the above-mentioned electrochemically selectively adsorbing MoS2@GA electrode material in the adsorption of thorium, comprising:

[0032] The above-mentioned electrochemically selectively adsorbed MoS2@GA electrode material was used to prepare an adsorption electrode;

[0033] The adsorption electrode was immersed in a Th(NO3)4 solution, and a constant DC voltage of -5V to 0V was applied to the working electrode. Static adsorption was performed without applying voltage to the electrode, and other factors remained the same as for electrochemical adsorption.

[0034] According to an embodiment of the present invention, the pH of the Th(NO3)4 solution is 1 to 3, preferably 1 to 1.5.

[0035] According to an embodiment of the present invention, the concentration of the Th(NO3)4 solution is 10-1000 mg / L, preferably 10-500 mg / L.

[0036] According to an embodiment of the present invention, a constant voltage DC current of -5V to 0V is applied to the working electrode, and the frequency is set to 100 to 1000 Hz.

[0037] For example, apply a voltage of -3V and a frequency of 100Hz.

[0038] According to an embodiment of the present invention, under a 100Hz electrical pulse, the duty cycle is set in the range of 0.2 to 1; preferably 0.2 to 0.4.

[0039] For example, the duty cycles of the electrical pulses are 0.2, 0.4, 0.6, 0.8, and 1.0.

[0040] According to an embodiment of the present invention, the ratio of electrode mass to solution volume is 0.6 g / L to 1.0 g / L.

[0041] According to an embodiment of the present invention, at a voltage of -1V, the adsorption capacity of thorium is 490mg / g, which is much higher than the adsorption capacity of 220mg / g obtained by static adsorption of MoS2@GA material without voltage application; when the voltage drops to -3V, the adsorption capacity increases significantly to 2800mg / g. As the voltage increases, the electric field force drives the formation of a thicker double-layer capacitance on the electrode surface, which promotes the adsorption of thorium on the electrode.

[0042] The beneficial effects of this invention are:

[0043] 1) This invention synthesizes a molybdenum disulfide-modified reduced graphene aerogel (MoS2@GA) electrode material using a hydrothermal method. The MoS2@GA electrode material exhibits high selectivity in electrochemical adsorption, selectively adsorbing thorium from rare earth elements. It also demonstrates an extremely high adsorption capacity, reaching up to 4154 mg / g under optimal conditions. Furthermore, it exhibits rapid adsorption kinetics, with an adsorption capacity of up to 960.45 mg / g within 15 minutes and 1959.62 mg / g within the initial hour. In simulated feed solutions and actual waste leachates, half-wave rectified alternating current electrochemistry (HW-ACE) was used to achieve green separation of thorium and rare earth elements in a mixed feed solution. The electrode shows good selectivity for thorium and can be used to properly treat radioactive waste generated in the rare earth separation industry, reducing environmental hazards.

[0044] 2) In the reduced graphene aerogel MoS2@GA electrode material prepared in this invention, molybdenum disulfide exhibits good selective adsorption of thorium and also possesses excellent HER catalytic performance. However, the weak conductivity of molybdenum disulfide hinders its practical application. Reduced graphene, as the framework of the composite material, has a large specific surface area, excellent conductivity, and high charge mobility. The combination of molybdenum disulfide and reduced graphene oxide framework can enhance the charge transfer between the two, improve the conductivity of molybdenum disulfide, improve its HER ability, and enhance the adsorption capacity of molybdenum disulfide.

[0045] 3) This invention utilizes aerogel prepared by the reduction of molybdenum disulfide-doped graphene oxide as an electrode to achieve efficient recovery of thorium ions from solution. Compared to physicochemical adsorption, electrochemical adsorption has received increasing attention in ion adsorption recovery due to its green process and low energy consumption. Electroadsorption can effectively recover thorium from solution. Compared to conventional physicochemical adsorption, electrochemical adsorption can significantly increase the adsorption capacity of the material under the impetus of an electric field. Half-wave rectified alternating current electrochemistry (HW-ACE) was used to achieve green separation of thorium and rare earth elements in a rare earth and thorium mixture. The use of electrical pulses can prevent the adsorption of other ions on the electrode.

[0046] 4) The MoS2@GA electrode material prepared by this invention also exhibits excellent cycling performance, showing no significant performance degradation after 10 cycles. This material has great application potential in thorium recovery. In particular, the MoS2@GA electrode material also demonstrates good removal rates for low-concentration thorium, achieving a thorium removal rate of 99% within 8 hours. Furthermore, it exhibits excellent cycling performance.

[0047] 5) The graphene electrode modified with molybdenum disulfide prepared in this invention has high thorium adsorption capacity, good cycling performance, fast adsorption kinetics and good selectivity, and can selectively recover thorium from waste leachate. These results indicate that electrochemical adsorption can effectively achieve selective recovery of thorium from rare earth elements. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the device structure used in this invention.

[0049] Figure 2 The graph shows the test performance of the prepared adsorption electrode; Figure 2 a represents the specific capacitance of the electrode prepared when the mass ratio of molybdenum disulfide to graphene is 1:2, at different scan rates in 1 mol / L Na2SO4 solution; Figure 2 b represents the specific capacitance of electrodes with different mass ratios in a 1 mol / L Na2SO4 solution; Figure 2 c represents the BET results for electrodes with different mass ratios; Figure 2 d represents the change in solution pH during electroadsorption; Figure 2 e represents the FTIR-ATR spectrum.

[0050] Figure 3 These are SEM images of electrode materials with different component ratios and SEM images of the electrode after adsorption.

[0051] Figure 4 This is the elemental spectrum of EDS after electrode adsorption;

[0052] Figure 5 XPS spectra after electrode adsorption: (a) C 1s; (b) N 1s; (c) O 1s; (d) Mo 3d; (e) s2p; (f) Th 4f; (g) XPS spectra before and after adsorption;

[0053] Figure 6 This is a graph showing the adsorption performance under direct current.

[0054] Figure 6 a represents the adsorption amount and recovery rate under different voltages; Figure 6 b represents the adsorption capacity and recovery rate at different mass ratios of MoS2 to graphene oxide; Figure 6 c represents the adsorption amount and recovery rate at different pH values; Figure 6d represents the adsorption capacity and recovery rate at different concentrations;

[0055] Figure 7 The graph shows the cycle performance and adsorption kinetics of the adsorption electrode using the electrode material prepared in Example 1. Figure 7 a represents the effect of the ratio of electrode mass to solution volume on the thorium removal rate and adsorption amount; Figure 7 b shows the effect of applying electrical pulses with a voltage of -3V and a frequency of 100Hz with different duty cycles (0.2, 0.4, 0.6, 0.8, 1.0) to the working electrode on the thorium removal rate and adsorption amount in a thorium nitrate solution with an initial thorium ion concentration of 1000ppm. Figure 7 c is a schematic diagram showing the adsorption amount and removal rate of thorium by the electrode after 10 cycles, indicating that the regeneration cycle performance of the adsorption material is good and stable. Figure 7 d is a schematic diagram of the curve of adsorption electrode versus adsorption amount and pseudo-second-order kinetics fitting, with a fitting degree of 99.067%.

[0056] Figure 8 This is a graph showing the adsorption and separation performance of the adsorption electrode of the electrode material prepared in Example 1 in a mixed solution of thorium and rare earth elements, both at a concentration of 1 mmol / L. Figure 8 a is within the duty cycle range of 0.2 to 1 under a 100Hz electrical pulse; Figure 8 b is within the pH range of 1 to 3 under a 100Hz electrical pulse; Figure 8 c is an electrical pulse with a duty cycle of 0.3, where the pulse frequency is adjustable within the range of 100 to 1000.

[0057] Figure 9 This is a graph showing the performance of the adsorption electrode of the electrode material prepared in Example 1 for separating thorium-containing rare earth waste residue; Figure 9 a is the separation coefficient between thorium and rare earth elements in the electrode pair; Figure 9 b represents the removal rate of thorium and rare earth elements by the electrode;

[0058] Figure 10 It is a diagram of the material's microstructure;

[0059] Figure 11 This is a schematic diagram of the electrochemical adsorption mechanism of thorium.

[0060] Figure 12 These are graphs showing the thorium adsorption effect of electrodes with different ratios. Detailed Implementation

[0061] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0062] (NH4)6Mo7O 24 • 4H₂O and CH₄N₂S were analytical grade and purchased from Shanghai Adamas Reagent Co., Ltd.; graphene oxide (95% purity) was from Shanghai Huifeng Carbon, ethylenediamine (99% purity) was purchased from West Asia Chemical, ethanol (99% purity) was purchased from Xilong Scientific, Th(NO₃)₄ (99% purity) was obtained, rare earth nitrate solutions were obtained by dissolving the corresponding rare earth oxides (REO) (99.99% purity) in nitric acid, and sodium sulfate (99.9% purity) was purchased from Sinopharm Chemical Reagent Co., Ltd. All reagents were analytical grade and required no further purification before use.

[0063] Effect of electrode raw material ratio on adsorption

[0064] This invention has discovered that the mass ratio of MoS2 to graphene oxide in the MoS2@GA electrode is one of the important factors affecting the adsorption capacity. The following study investigates the effect of the electrode ratio on the adsorption capacity by synthesizing a series of electrode materials with different mass ratios of MoS2 to graphene oxide ranging from 0 to 8, in order to illustrate the beneficial effects of this invention.

[0065] Example 1

[0066] 1) Hydrothermal synthesis of nanoflower MoS2

[0067] 2.48g (NH4)6Mo7O 24 • 4H₂O and 2.14 g CH₄N₂S were dissolved in 60 mL of deionized water and stirred until completely dissolved. The solution was then transferred to a 100 mL PPL-lined hydrothermal reactor and heated from room temperature to 210 °C at a rate of 3 °C / min, maintaining this temperature for 24 hours. The hydrothermal reactor was then cooled at a rate of 1 °C / min until the sample reached room temperature. The sample was then filtered through a 0.22 μm filter using a vacuum pump. The product was washed five times with deionized water and three times with anhydrous ethanol, and then dried in an oven at 70 °C to synthesize nanoflower MoS₂.

[0068] 2) Preparation of MoS2@GA electrode material:

[0069] MoS2:Go = 1:2 graphene aerogel MoS2@GA electrode material

[0070] 100 mg of MoS2 powder prepared by the hydrothermal method in step 1) was added to 40 ml of a 5 mg / ml graphene oxide aqueous solution. The mixture was then sonicated for 30 minutes to ensure that molybdenum disulfide was fully dispersed in the solution. 2 ml of the mixture was transferred to a 25 ml hydrothermal reactor, and 100 μl of ethylenediamine was added as a reducing agent. The solution in the reactor liner was sonicated for 5 minutes to mix thoroughly. The hydrothermal reactor was placed in an oven and heated to 120°C at a rate of 1.5°C / min and maintained at that temperature for 14 hours.

[0071] After the sample cooled to room temperature, the formed hydrogel was poured out and dialyzed with 200 ml of 5% ethanol aqueous solution for 6 hours, repeated 3 times. After the sample was removed from the ethanol aqueous solution, it was placed in a refrigerator and completely frozen at (-18°C) for 12 hours, and then dried in an oven at 70°C to obtain molybdenum disulfide-doped modified graphene aerogel MoS2@GA electrode material.

[0072] Example 2

[0073] MoS2:Go = 1:1 graphene aerogel MoS2@GA electrode material

[0074] The preparation method for step 1) is the same as in Example 1.

[0075] 10 mg of MoS2 powder prepared by the hydrothermal method in step 1) was added to 2 ml of a 5 mg / ml aqueous solution of graphene oxide. The mixture was then sonicated for 30 minutes to ensure that molybdenum disulfide was fully dispersed in the solution. The mixture was transferred to a 25 ml hydrothermal reactor, and 100 μl of ethylenediamine was added as a reducing agent. The solution in the reactor liner was sonicated for 5 minutes to mix evenly. The hydrothermal reactor was placed in an oven and heated to 120 °C at a rate of 1.5 °C / min and maintained for 14 hours. After the sample cooled to room temperature, the formed hydrogel was poured out and dialyzed with 200 ml of 5% ethanol aqueous solution for 6 hours, repeated 3 times. After the sample was removed from the ethanol aqueous solution, it was placed in a refrigerator and completely frozen at (-18 °C) for 12 hours, and then dried in an oven at 70 °C to obtain the molybdenum disulfide-doped modified graphene aerogel MoS2@GA electrode material.

[0076] Example 3

[0077] MoS2:Go = 8:1 graphene aerogel MoS2@GA electrode material

[0078] The preparation method for step 1) is the same as in Example 1.

[0079] 80 mg of MoS2 powder prepared by the hydrothermal method in step 1) was added to 2 ml of a 5 mg / ml aqueous solution of graphene oxide. The mixture was then sonicated for 30 minutes to ensure that molybdenum disulfide was fully dispersed in the solution. The mixture was transferred to a 25 ml hydrothermal reactor, and 100 μl of ethylenediamine was added as a reducing agent. The solution in the reactor liner was sonicated for 5 minutes to mix evenly. The hydrothermal reactor was placed in an oven and heated to 120 °C at a rate of 1.5 °C / min and maintained for 14 hours. After the sample cooled to room temperature, the formed hydrogel was poured out and dialyzed with 200 ml of 5% ethanol aqueous solution for 6 hours, repeated 3 times. After the sample was removed from the ethanol aqueous solution, it was placed in a refrigerator and completely frozen at (-18 °C) for 12 hours, and then dried in an oven at 70 °C to obtain the molybdenum disulfide-doped modified graphene aerogel MoS2@GA electrode material.

[0080] Examples 4-8

[0081] The mass ratio of MoS2 to graphene oxide was 0.5, 0.6, 0.7, 0.8, and 1.0, and other operating steps were the same as in Example 1.

[0082] from Figure 3 The SEM images show that the density of molybdenum disulfide nanoflowers on the graphene aerogel surface increases with increasing molybdenum disulfide content, eventually completely covering the graphene. Nitrogen adsorption-desorption analysis indicates that increasing molybdenum disulfide content reduces the specific surface area of ​​the material, which is detrimental to thorium adsorption. When the mass ratio of molybdenum disulfide to graphene is 2:1, the specific surface area of ​​the aerogel is 20.2 m². 2 / g, when the amount of molybdenum disulfide added increases, the specific surface area of ​​the aerogel with a molybdenum disulfide to graphene mass ratio of 4:1 is 12.5m². 2 / g. When the amount of molybdenum disulfide added continues to increase, the specific surface area of ​​the aerogel with a molybdenum disulfide to graphene mass ratio of 8:1 is 7.6 m². 2 The adsorption capacity of the electrode was further reduced to 300 mg / g, and the adsorption capacity decreased as the specific surface area of ​​the material decreased. Cyclic voltammetry also clearly demonstrated the effect of electrode material ratio on electrode specific capacitance. Adding a small amount of molybdenum disulfide to the reduced graphene aerogel was beneficial to increasing the electrode specific capacitance, but the specific capacitance decreased with increasing molybdenum disulfide content. A higher specific capacitance is conducive to the formation of an electric double layer of ions on the electrode surface, increasing the probability of thorium contact on the electrode and thus promoting adsorption.

[0083] Similarly from Figure 6 As can be seen from b, as the mass ratio of MoS2 to graphene oxide increases, the adhesion of thorium to the electrode surface is enhanced, but the adsorption effect of the electrode material on thorium weakens and the adsorption amount decreases.

[0084] Figure 12 The graphs show the adsorption effects of electrodes prepared using MoS2:Go electrode materials with different mass ratios. The adsorption effects of graphene aerogels with different ratios are evident, clearly demonstrating that thorium is well adsorbed on the electrode surface. The thorium hydroxide formed near the electrode covers the electrode surface, indicating that molybdenum disulfide modification of graphene is effective and can significantly improve the adsorption capacity of graphene aerogels for thorium. When the amount of molybdenum disulfide added to the graphene is low, the white thorium hydroxide cannot adhere to the electrode surface, and most of the adsorbed thorium hydroxide remains in the bulk solution.

[0085] Comparative Example 1

[0086] Preparation of reduced graphene aerogels without MoS2 modification:

[0087] Take 2 ml of a 5 mg / ml graphene oxide aqueous solution and transfer it to a 25 ml hydrothermal reactor. Add 100 μl of ethylenediamine as a reducing agent. Sonicate the solution in the reactor lining for 5 minutes to mix thoroughly. Place the hydrothermal reactor in an oven and raise the temperature to 120 degrees Celsius at a rate of 1.5 degrees Celsius / min, and maintain the temperature for 14 hours.

[0088] After the sample cooled to room temperature, the formed hydrogel was poured out and dialyzed with 200 ml of 5% ethanol aqueous solution for 6 hours, repeated 3 times. After the sample was removed from the ethanol aqueous solution, it was placed in a refrigerator and completely frozen at (-18°C) for 12 hours, and then dried in an oven at 70°C to obtain the reduced graphene aerogel electrode material.

[0089] An adsorption electrode was prepared using the reduced graphene aerogel electrode material in Comparative Example 1. When a voltage of -3V was applied to the working electrode and the electrode was pure reduced graphene aerogel, the adsorption capacity of thorium on the electrode surface was poor due to the limited number of adsorption active sites on the electrode and the low HER catalytic ability. As water decomposed on the electrode, the local pH near the electrode increased, and thorium hydrolyzed near the electrode to form flocculent hydroxides that floated in the solution.

[0090] from Figure 12 As can be seen from the data, in Comparative Example 1, without the modification of MoS2, the reduced graphene aerogel does not adsorb thorium, indicating that the modification of graphene aerogel by molybdenum disulfide is effective. The molybdenum disulfide on the graphene surface plays a role, and the adsorption effect is enhanced with the increase of the amount of molybdenum disulfide, and thorium is adsorbed on the electrode surface.

[0091] Comparative Example 2

[0092] The mass ratio of MoS2 to graphene oxide is 1:4.

[0093] 1) The operation steps are the same as in Example 1.

[0094] 2) Add 5 mg of MoS2 powder prepared by the hydrothermal method in step 1) to 4 ml of a 5 mg / ml graphene oxide aqueous solution. Then, sonicate the mixture for 30 minutes to ensure sufficient dispersion of molybdenum disulfide in the solution. Transfer the mixture to a 25 ml hydrothermal reactor, add 100 μl of ethylenediamine as a reducing agent, and sonicate the solution in the reactor liner for 5 minutes to mix thoroughly. Place the hydrothermal reactor in an oven and heat to 120°C at a rate of 1.5°C / min, maintaining the temperature for 14 hours. After cooling the sample to room temperature, pour out the formed hydrogel and dialyze it with 200 ml of a 5% (v / v) ethanol aqueous solution for 6 hours, repeating this process three times. After removing the sample from the ethanol aqueous solution, freeze it completely at -18°C for 12 hours, and then dry it in an oven at 70°C to obtain the molybdenum disulfide-doped modified graphene aerogel MoS2@GA electrode material.

[0095] MoS2@GA electrode material was immersed in a thorium nitrate solution as the working electrode, and a constant voltage DC current was applied to the working electrode to accelerate the migration of thorium to the electrode material. However, due to the limited number of adsorption active sites on the adsorbent material with a MoS2 to graphene oxide mass ratio of 0.4, the adsorption effect was not ideal.

[0096] The results showed that the adsorption effect of thorium in the solution on the electrode was poor, with only a portion being adsorbed onto the electrode surface, and most of the thorium forming flocculent hydroxides in the solution near the electrode.

[0097] from Figure 12 Comparing the top three images with the bottom image showing an increased molybdenum disulfide ratio, it can be seen that the white thorium hydroxide does not adhere to the electrode. Therefore, the adsorption effect of the electrode is poor when the mass ratio of MoS2 to graphene oxide is 1:4.

[0098] Adsorption performance experiment

[0099] Electrodes were prepared using the graphene aerogel MoS2@GA electrode material prepared in Example 1, and their adsorption performance was tested.

[0100] All adsorption experiments were conducted in a 50 ml electrolytic cell using a three-electrode system. The working electrode and the auxiliary electrode were placed in the electrolytic cell 1 cm apart. Thorium of different concentrations (10-1000 mg / L) and pH ranges (1-3) were placed in the electrolytic cell.

[0101] The power supply uses the Princeton V200 constant voltage and fast pulse mode to provide power, with the voltage set from -1 to -5V, the frequency set from 100 to 1000Hz, and the pulse duty cycle set from 0.2 to 1.

[0102] The changes in the concentrations of RES, Th, Al, Ca, and Mg ions in the solution before and after electrochemical adsorption were determined using ICP-OES (Horiba Jobin Yvon SAS). Adsorption in liquid nitrogen at 77 K and desorption at 373 K were performed using Brunol-Emmett-Tyler BET (Autosorb-iQ). The specific surface area and porosity of the MoS2@GA electrode material were tested. The specific surface area and porosity of the MoS2@GA electrode material prepared in Example 1 are as follows: Figure 2 As shown in Figure c, it can be seen that the addition of graphene increases the specific surface area of ​​molybdenum disulfide, increasing it from 7.6 m² / s² to... 2 / g increased to 20.31m 2 / g.

[0103] The adsorption capacity and removal rate of thorium were calculated by formulas (1) and (2), respectively, and the partition coefficient (Kd, mL / g) and adsorption separation factor (SF) were determined by formulas (3) and (4).

[0104]

[0105] In the formula, C0 and C t (mg / L) represents the initial concentration of ions in the solution and the concentration of ions in the solution after adsorption, V represents the volume of the solution (ml), and m represents the mass of the adsorption electrode (mg).

[0106] The dynamic parameters are calculated using the pseudo-first-order dynamic model formula (5) and the pseudo-second-order dynamic model formula (6). The closest dynamic model is the one with a correlation coefficient R2 close to 1.

[0107] In(q e -q t ) = lnq t -k 1t (5)

[0108]

[0109] q e (mg / g) represents the amount of adsorption at equilibrium, q t (mg / g) represents the adsorption amount at time t, t(h) is the adsorption time, formula (5), k 1(h-1) k2(g / (mg.h)) is the first-order rate constant, and k2(g / (mg.h)) is the second-order rate constant, as shown in formula (6).

[0110]

[0111] Cp(F g -1) represents the specific capacitance of the MoS2@rGA electrode, Vf(V) and Vi(V) are the initial and final voltages of the cyclic voltammetry, i(A) is the instantaneous current at potential V, m(g) is the mass of the electrode, and V(Vs-1) is the scan rate.

[0112] Figure 6 When a is MoS2:Go electrode material with a ratio of 1:2, the adsorption capacity and recovery rate of the adsorption electrode under different voltages show that the applied voltage has a significant impact on the adsorption capacity. As the voltage increases, the adsorption capacity increases rapidly, but it does not increase indefinitely. When the applied voltage is too high, the adsorption capacity decreases instead, reaching its maximum at -3V.

[0113] Using the same method as in Example 1, MoS2 with different mass ratios was prepared. 2: The electrode materials of Go, with mass ratios of 1:2 (Example 1), 1:1 (Example 2), 2:1, 4:1, 6:1, and 8:1 (Example 3), were obtained from... Figure 6 As can be seen from b, the adsorption capacity is relatively high when the mass ratio is 1:2, and the adsorption effect is poor when the mass ratio is 8:1, which is the lowest. The adsorption and recovery effects are better in the range of 1:2 to 4:1.

[0114] from Figure 6 As can be seen from c, pH value has a significant impact on the adsorption capacity. The adsorption capacity is lower at low pH values, and increases with increasing pH. The adsorption effect is better at pH = 1.5-3, and pH = 2-3 is preferred.

[0115] from Figure 6 As can be seen from d, the electrode exhibits good adsorption performance in thorium solutions with concentrations ranging from 10 to 1000 mg / L. The amount of thorium adsorbed by the electrode increases with increasing solution concentration, while the removal rate decreases with increasing solution concentration. However, outside this range, there is no consistent pattern of increasing or decreasing.

[0116] Electrode material performance testing:

[0117] The adsorption electrode prepared using the electrode material of Example 1 (mass ratio of molybdenum disulfide to graphene = 1:2) was tested using a Princeton V-200 electrochemical workstation. A 1 mol / L sodium sulfate solution was used as the electrolyte within an electrochemical window of 0 to -1 V. The specific capacitance of the electrode was tested at a scan rate of 0.1 V / s. The cyclic voltammetry curve in the sodium sulfate solution was a quasi-rectangular curve without redox peaks, indicating that the graphene-molybdenum disulfide aerogel exhibited high specific capacitance.

[0118] from Figure 2(a) shows the specific capacitance of the electrode in 1 mol / L Na2SO4 solution at different scan rates. The specific capacitance of the aerogel prepared with a mass ratio of molybdenum disulfide to graphene of 1:2 was tested at different scan rates. The test results show that the electrode material has a high specific capacitance.

[0119] The specific capacitance of the electrode was 57.44 F / g at a scan rate of 50 mV / s, 201.6 F / g at 10 mV / s, and 318.9 F / g at 1 mV / s. The cyclic voltammetry curves of the electrode material at different scan rates within the electrochemical window of -1 to 1 V showed a quasi-rectangular shape with no obvious redox peaks, indicating that the electrode material possesses certain pseudocapacitive characteristics. Cyclic voltammetry tests showed that the electrode exhibited mixed capacitive behavior of both electric double-layer capacitance and pseudocapacitance. In electrochemical adsorption, a large capacitance value contributes significantly to the increase in adsorption capacity.

[0120] The specific capacitance of the reduced graphene aerogel is 6.9 F / g. Adding a small amount of molybdenum disulfide nanoflowers to the graphene aerogel can effectively increase the electrode's specific capacitance. When the mass ratio of molybdenum disulfide to graphene is 1:2, the specific capacitance of the aerogel increases significantly to 30.05 F / g. However, when the amount of molybdenum disulfide added is excessive, the electrode specific capacitance decreases with increasing molybdenum disulfide content. The electrode specific capacitance is 9.13 F / g when the mass ratio of molybdenum disulfide to graphene is 1:1, 4.76 F / g when the mass ratio is 1:2, and 3.63 F / g when the mass ratio is 1:4. (See details...) Figure 2 b.

[0121] When the mass ratio of molybdenum disulfide to graphene is 1:2, the electrode has a larger pore volume. Figure 2 c represents the BET results for electrode materials with different molybdenum disulfide to graphene mass ratios; BET tests show that with increasing MoS2 addition, the pore volume and specific surface area decrease, from 20.311 m³ / s. 2 / g decreased to 7.765m 2 / g.

[0122] The pH change of the solution during the electrochemical adsorption process was measured using a Leici pH meter. Figure 2 (d) shows the change in pH value of the solution during the electro-adsorption process. It can be seen that hydroxide ions in the solution are consumed on the electrode during the adsorption process, and the accumulation of hydrogen ions in the solution during the electro-adsorption process causes the pH value of the solution to decrease.

[0123] The synthetic materials Go, TOH, RGA, and the electrode material GA-absorb prepared in Example 1 were studied using an FTIR spectrometer (Nicolet iS 50) in the range of 500-4000 cm⁻¹. -1Infrared spectrum within the range, such as Figure 2 As shown in figure e, the white deposit on the electrode is at 3610 cm⁻¹. -1 With 1637cm -1 The distinct infrared peak at 1070 cm⁻¹ is due to the stretching vibration of thorium hydroxide -OH. -1 This is a Th-O stretching vibration, 1384 cm. -1 1049cm -1 NO 3- The typical infrared peak. Compared to the carboxyl peak at 1710 cm⁻¹ on graphene oxide before and after reduction. -1 Disappeared, and at 2860cm -1 A distinct infrared peak appears at the point where the stretching vibration of -CH2 is observed, indicating that graphene oxide has been reduced.

[0124] Electrode chemical composition and structural characterization

[0125] The morphology of the electrode material prepared in Example 1 before and after adsorption was observed and elemental analysis was performed using field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) (Thermo Fisher Scientific ApreoSLoVac). The scanning voltage was 10.0 kV. The electron microscope clearly showed the distribution of molybdenum disulfide and graphene on the electrode surface with different ratios. Molybdenum disulfide was uniformly distributed on the surface of the graphene nanosheets. With the increase of the molybdenum disulfide addition ratio, the molybdenum disulfide distribution density on the reduced graphene surface increased. Figure 3 As shown in the optical photograph, a large amount of white solid appeared on the electrode after adsorption. Electron microscopy also clearly shows the change in electrode surface morphology before and after adsorption; the electrode surface is covered by the generated hydroxide.

[0126] The adsorbed electrode was characterized using energy dispersive spectroscopy (EDS), and the elemental distribution on the electrode surface was as follows: Figure 4 As shown, the distribution of thorium is clearly displayed, indicating successful adsorption of thorium on the electrode. Notably, molybdenum (Mo) and sulfur (S) are uniformly distributed on the graphene substrate, with an atomic ratio of Mo to S close to 1:2, consistent with the atomic ratio in MoS2. This suggests that the chemical state of MoS2 remains unchanged during the hydrothermal synthesis process.

[0127] The surface composition and elemental chemical valence states of the samples were analyzed using Axis Supra X-ray photoelectron spectroscopy (XPS). Figure 5 XPS spectra after electrode adsorption: (a) C 1s; (b) N 1s; (c) O 1s; (d) Mo 3d; (e) s 2p; (f) Th 4f; (g) XPS spectra before and after adsorption. Monochromatic Al / K was used with an energy of 1486.68 eV and a spot size of 30–400 μm.

[0128] XPS elemental spectrum before electrode adsorption detected electrode C 1s N 1s O 1s Mo 3d ,S 2p The peaks were observed, and a distinct Th4f peak appeared in the overall spectrum after adsorption. It can be observed that the electrode material exhibited distinct Th4f orbital peaks before and after adsorption. C1s XPS spectra showed values ​​of 284.6 eV (CC / C=C), 285.51 eV (C=N), 287.7 eV (C=O), and 291 eV (OC=O), indicating that ethylenediamine successfully reduced graphene oxide and incorporated nitrogen into the graphene.

[0129] In the XPS spectrum of N1s, overlap between N1s and Mo 3p occurs due to the strong X-ray signal of Mo 3p. The Mo 3p peak appears at 394.9 eV, and the N1s peak appears at 398.8 eV. The binding energies of the oxygen spectrum are 531.1 eV and 532 eV, corresponding to Th-O and OH bonds, respectively.

[0130] In the selective adsorption of thorium in this invention, the various influencing factors do not exist in isolation, but rather influence each other, as detailed below:

[0131] Effect of voltage on adsorption

[0132] The applied voltage plays a crucial role in the adsorption performance of the electrode.

[0133] In a 50 ml electrolytic cell, an adsorption electrode prepared with a MoS2 to Go mass ratio of 2:1 was immersed in a 1000 ppm Th(NO3)4 solution at pH 2. A constant DC voltage ranging from -5 V to 0 V (relative to a saturated silver chloride reference electrode) was applied to the working electrode. For static adsorption, with no voltage applied and other factors kept the same as for electrochemical adsorption, at -1 V, the thorium adsorption capacity was 490 mg / g, significantly higher than the 220 mg / g obtained by static adsorption of MoS2@GA material without voltage application. This is because the electric field significantly promoted ion migration and adsorption. When the voltage was reduced to -3 V, the adsorption capacity increased significantly to 2800 mg / g. As the voltage increased, the electric field drove the formation of a thicker electric double layer (EDL) on the electrode surface, promoting thorium adsorption on the electrode.

[0134] The increased electric field force between electrodes accelerates the migration rate of ions between electrodes and the accumulation rate of thorium ions on the electrode surface. The enhanced HER on the co-working electrode causes a sharp increase in local pH value, resulting in an increase in adsorption capacity with voltage.

[0135] The results show that the adsorption capacity increases as the applied voltage increases from 0V to a more negative value, down to -3V. However, when the voltage is further increased, the adsorption capacity of thorium decreases. This is because the current density at the electrode increases with the voltage, leading to an increase in hydrogen evolution at the electrode surface. As a large number of bubbles are released from the electrode surface, they strip the thorium adsorbed on the electrode, causing it to redissolve in the solution and reducing the adsorption capacity. Therefore, -3V is the optimal voltage for adsorption.

[0136] Effect of concentration on adsorption

[0137] like Figure 6 As shown, thorium (CO) with different initial concentrations at pH=2 (10, 50, 100, 200, 300, 400, 500, and 1000 ppm) was electrochemically adsorbed at the working electrode for 8 hours under a -3V voltage. The adsorption capacity of thorium increased with increasing CO, reaching 3800 mg / g in a 1000 ppm thorium solution. MoS2@GA exhibited a high removal rate for low concentrations of thorium. For a 10 ppm thorium solution, the electrochemical adsorption for 8 hours achieved a thorium removal rate as high as 98.37%, with a residual thorium concentration of 0.175 ppm. In a 100 ppm thorium solution, the adsorption capacity reached 523 mg / g, achieving a thorium removal rate of up to 98%. The electrode showed good removal efficiency for low concentrations of thorium in solution. The adsorption capacity of the electrode increased with increasing initial solution concentration, while the thorium ion removal rate decreased with increasing initial concentration.

[0138] Effect of solid-liquid ratio m / v

[0139] The electrode mass to solution volume ratio is a crucial factor affecting thorium ion removal efficiency. As shown in Figure 7(a), in a thorium solution with an initial concentration of 500 ppm and pH = 2, different electrode mass to solution volume ratios (0.2, 0.4, 0.6, 0.8, and 1.0 g / L) were applied to the working electrode with a constant voltage DC current of -3V for 4 hours. Under low solid-liquid ratio conditions, the electrode exhibited a high adsorption capacity for thorium ions, but the removal rate was low. To improve the thorium ion removal rate, the electrode mass to solution volume ratio was increased. With increasing solid-liquid ratio, the adsorption capacity of thorium decreased, but the removal rate increased. At a solid-liquid ratio of 1.0 g / L, a removal rate of 95% was achieved for an initial thorium concentration of 500 ppm.

[0140] The effect of duty cycle

[0141] Duty cycle is an important factor affecting electrochemical adsorption; it is the proportion of the energized time within one electrical pulse cycle to the total pulse cycle time. For example... Figure 7As shown in (b), the effects of applying electrical pulses with a voltage of -3V and a frequency of 100Hz with different duty cycles (0.2, 0.4, 0.6, 0.8, 1.0) to the working electrode on the thorium removal rate and adsorption amount in a thorium nitrate solution with an initial thorium ion concentration of 1000ppm were investigated.

[0142] Electrochemical adsorption experiments were conducted with the same energizing time of 4 hours at different duty cycles. At lower duty cycles, the adsorption capacity of thorium was low because the thorium adsorbed on the electrode surface underwent a prolonged diffusion-dissolution process in the solution. At a duty cycle of 0.2, the thorium adsorbed on the electrode underwent this prolonged diffusion-dissolution process, resulting in a low thorium adsorption capacity of only 495 mg / g. As the duty cycle increased, the diffusion time of thorium adsorbed on the electrode surface decreased, and the adsorption capacity increased significantly. When the duty cycle increased above 0.6, the diffusion-dissolution time was too short within the entire pulse cycle, and the ions adsorbed on the electrode did not have enough time to redissolve into the solution before being adsorbed in the next pulse cycle. At duty cycles above 0.8, the adsorption capacity on the electrode approached that under direct current, achieving an adsorption capacity of 1900 mg / g under direct current.

[0143] Cyclic performance

[0144] The regeneration cycle performance of adsorbent materials is an important factor in evaluating their quality. The electrode was immersed in a thorium solution with an initial concentration of 100 ppm and subjected to a constant voltage DC current of -3V for 8 hours for adsorption. After adsorption, the electrode was desorbed and regenerated by soaking in a 0.1 mol / L nitric acid solution for 30 minutes. For example... Figure 7 As shown in (c), the removal rate of thorium reached 99% after 8 hours of electrochemical adsorption, with an adsorption capacity of up to 522 mg / g. The adsorption capacity and removal rate of thorium remained stable after 10 cycles without significant decrease, and a high removal rate was still maintained in the tenth cycle, indicating that the electrode has good cycle stability.

[0145] Adsorption kinetics and adsorption time

[0146] like Figure 7 As shown in Figure d, the electrode material exhibits rapid adsorption kinetics. In a solution with a thorium ion concentration of 1000 ppm and pH = 3, the adsorption capacity of the electrode reaches as high as 950.45 mg / g within the first 15 minutes, 1959.6 mg / g within the first hour, and a final adsorption capacity of 4154 mg / g after 8 hours of electrochemical adsorption. Nonlinear fitting of the adsorption curve shows that the time versus adsorption curve of the electrode fits the pseudo-second-order kinetics better, with a goodness of fit of 99.067%.

[0147] The effect of pH on adsorption

[0148] This invention has found that solution pH is an important factor affecting the selective adsorption of thorium by electrode materials. The following data show the effect of pH value on the electrochemical adsorption of thorium ions in the range of 1-3 with CO = 1000 ppm.

[0149] To avoid the formation of thorium hydroxide in the solution at higher pH, this invention controls the pH of the solution to below 3. This invention uses equimolar amounts of thorium, all rare earth elements, aluminum, iron, calcium, and magnesium with pH in the range of 1-3, and the concentration of all elements is 1 millimole.

[0150] like Figure 8 As shown, the effect of pH on the adsorption capacity of the MoS2@GA electrode is observed when the voltage applied to the working electrode, where the mass ratio of MoS2 to Go is 1:2, is -3V.

[0151] like Figure 8 As shown in b, when an electrical pulse with a voltage of -3V, a frequency of 100Hz, and a duty cycle of 0.3 is applied to the working electrode, at lower pH values, due to the presence of H+ in the solution... + At higher concentrations, thorium adsorbed on the electrode redissolves into the solution, resulting in low thorium adsorption capacity. As the solution pH increases, the thorium adsorption capacity gradually increases, demonstrating good selective adsorption. With further increases in solution pH, impurity ions adsorbed on the electrode become increasingly difficult to redissolve into the solution, leading to an increase in both rare earth element and rare earth ion adsorption on the MoS2@GA electrode, but a decrease in selectivity for thorium.

[0152] At a pH as low as 1, the adsorption capacity was 168 mg / g. Under low pH conditions, the H+ in the solution... + At higher concentrations, thorium competes with the electrode for adsorption. In solutions with lower pH, the local pH rise caused by water electrolysis near the electrode is smaller. In solutions with higher pH, the larger local pH rise caused by water electrolysis near the electrode is more favorable for the neutralization of thorium ions adsorbed on the electrode to form neutral hydroxides. Furthermore, due to the lower solution pH, the thorium adsorbed on the material redissolves in the solution under high acidity. Within the pH range of 1.5-3, the adsorption capacity of thorium increases significantly with increasing solution pH. This is because at higher pH, the pH increase near the electrode is larger, and the thorium ions adsorbed near the electrode are neutralized to form thorium hydroxide. Also, at higher solution pH, the thorium adsorbed on the electrode cannot dissolve and re-enter the solution. At pH=3, the adsorption capacity reaches as high as 4154 mg / g.

[0153] The effect of duty cycle

[0154] Duty cycle is an important factor affecting the separation performance of electrode materials. In the experiment, an electrical pulse with a voltage of -3V and a frequency of 100Hz was applied to a 1mM simulated solution with pH=2, and the duty cycle of the pulse was between 0.2 and 1. Figure 8 As shown in Figure a, when the pulse duty cycle is 0.2, the thorium adsorbed on the electrode redissolves into the solution due to the longer diffusion time of ions in the solution, resulting in lower adsorption capacity for thorium and rare earth elements. With increasing duty cycle, the adsorption capacity of thorium increases, exhibiting higher selectivity for thorium. When the pulse duty cycle is higher than 0.6, the diffusion time of ions adsorbed on the electrode within one pulse cycle is relatively short. Ions adsorbed on the electrode do not have enough time to diffuse into the solution before being adsorbed in the next pulse cycle, leading to poor adsorption selectivity under high duty cycle pulses. A constant voltage DC current with a duty cycle of 1 adsorbs all ions equally. This is because at a high duty cycle, the diffusion time within one pulse cycle is reduced, and other metal ions adsorbed on the electrode do not have enough time to diffuse into the solution, continuing to be adsorbed in the next pulse cycle. When the pulse duty cycle is 0.3, the electrode material exhibits better selectivity.

[0155] Frequency effect

[0156] The effect of pulse frequency on adsorption performance was investigated in a simulated feed solution with rare earth elements and aluminum, iron, calcium, magnesium, and thorium ions at pH 1.25, each at a concentration of 1 mM. A square wave electrical pulse with a voltage of -3V and a duty cycle of 0.3 was used to power the electrodes for 6 hours. The effect of adjusting the pulse frequency within the range of 100-1000 Hz on the separation performance was studied. Figure 8 As shown in Figure c, the separation factor of thorium ions from other metal ions decreases with increasing pulse frequency. The separation factor of Th and La decreases from 395 at 100 Hz to 90 at 1000 Hz. With increasing pulse frequency and decreasing cycle time, impurity ions adsorbed on the electrode do not have enough time to diffuse before migrating to the electrode in the next cycle's pulse drive and being adsorbed. Th is adsorbed onto the electrode along with impurity ions, reducing the electrode's selectivity. In terms of ion removal rate, the removal rate of rare earth ions increases with increasing frequency. Higher pulse frequencies result in the electrode adsorbing more rare earth elements. The removal rate of Sm in the solution increases from 6.28% at 100 Hz to 21.74% at 200 Hz, and reaches 56.74% at 400 Hz. The electrode exhibits better selectivity for light rare earth elements but weaker selectivity for heavy rare earth elements, with the electrode adsorbing more heavy rare earth elements during the adsorption process. Under optimal conditions, the thorium in the mold solution was removed at a rate of 94%, and aluminum was also effectively removed at a rate of 73.81%. The electrode material exhibited good selective adsorption of thorium in the simulated solution.

[0157] The adsorption mechanism of this invention is as follows:

[0158] Electrochemical adsorption significantly improves the adsorption capacity compared to traditional physicochemical adsorption. In physicochemical adsorption, the ions adsorbed on the material occupy the active sites and carry a positive charge, which hinders the entry of subsequent ions due to Coulomb repulsion, preventing most active sites from adsorbing ions. For example... Figure 10 As shown, this invention employs electrochemical adsorption, overcoming the shortcomings of traditional physicochemical adsorption. By utilizing the electric field between electrodes to drive thorium ions to migrate to the working electrode, the probability of thorium ions contacting the adsorption electrode is increased, making it easier for thorium to be adsorbed on the electrode surface. Thorium ions exist in the form of hydrates [Th(H₂O)ₓ]. 4+ The sulfide-modified electrode surface is captured and fixed to the sulfide surface through Th-S bonds. Molybdenum disulfide modified on the reduced graphene aerogel forming the conductive network framework is an excellent electrochemical hydrogen evolution (HER) catalyst with a low HER overpotential. Hydrated hydrogen ions decompose to generate hydrogen under the catalysis of molybdenum disulfide on the electrode, increasing the hydroxyl concentration on the electrode surface. Positively charged thorium ions adsorbed on the electrode surface are neutralized by the generated hydroxyl groups, avoiding Coulomb repulsion that hinders the adsorption of subsequent ions. Under optimal conditions, an adsorption capacity of 4120 mg / g was obtained. Platinum is an excellent electrochemical oxygen evolution catalyst. Water molecules decompose to form oxygen on the platinum electrode, generating a large amount of H+. Since the OH- at the negative electrode is largely consumed by the ions adsorbed on the electrode during electroadsorption, the H+ concentration in the solution increases, and the pH decreases with increasing electroadsorption time.

[0159] Actual liquid-material separation effect

[0160] The actual feed solution was leached from a mixture of neutralization residue, impurity removal residue, and acid dissolution residue from the rare earth production process. The leaching conditions were 80℃, 1 mol / L nitric acid, a solid-liquid ratio of 1:10 for the waste residue to nitric acid, and a stirring leaching time of 8 hours. Excess acid was neutralized with sodium hydroxide to adjust the solution to pH 3, yielding the actual feed solution. The composition of the actual feed solution is shown in the support information. To improve the electrode's thorium removal rate, the electrode mass to actual feed solution volume ratio was 1 g / L. Optimal separation was achieved when the pH of the actual solution was adjusted to 1.5 during a 100 Hz pulse with a voltage of -3 V and a duty cycle of 0.3. After 4 hours of energizing, the thorium recovery rate reached 74%, and the thorium concentration in the actual feed solution was significantly reduced. Figure 9 As shown, the MoS2@GA electrode material prepared by the method of this invention has a good removal effect on thorium in rare earth elements in actual feed solutions.

[0161] In the separation process, the electrochemical adsorption of thorium generally involves five steps, such as... Figure 11As shown, in step b, all ions in the mixed solution are randomly distributed. In step c, when a voltage is applied to the working electrode, cations and anions migrate to the surface of the working electrode under the drive of the electric field to form an electric double layer (EDL). Thorium ions in the EDL adsorb and bind to sulfides. In step d, the metal ions adsorbed on the electrode surface combine with hydroxide ions near the electrode surface to generate neutral metal hydroxides on the electrode. In step e, after the voltage applied between the electrodes is removed, only thorium ions and thorium hydroxide attached to the electrode surface remain. Other ions with weak binding to the electrode surface diffuse back into the solution and release the active sites on the electrode surface. After a period of electroadsorption; in step f, thorium ions with strong binding ability to molybdenum disulfide continuously neutralize at the active sites to form neutral thorium hydroxide, which accumulates. The thorium hydroxide adsorbed on the electrode surface continuously grows to form particles. Thorium in the solution is adsorbed and enriched on the electrode.

[0162] Therefore, the molybdenum disulfide-modified graphene electrode prepared in this invention has a high thorium adsorption capacity, good cycling performance, fast adsorption kinetics, and good selectivity, and can selectively recover thorium from waste leachate. The above results indicate that electrochemical adsorption can effectively achieve selective recovery of thorium from rare earth elements.

[0163] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an electrochemically selective adsorption electrode material, characterized in that, A molybdenum disulfide-modified reduced graphene aerogel (MoS2@GA) electrode material was synthesized via a hydrothermal method for the selective adsorption and recovery of Th from rare earth elements. The process includes the following steps: S1, Hydrothermal synthesis of nanoflower MoS2; S2, the synthesized nanoflower MoS2 powder is dissolved and dispersed in an aqueous solution of graphene oxide, a reducing agent is added, the mixture is heated in a hydrothermal reactor, cooled to room temperature to form a hydrogel, dialyzed, frozen, and dried to obtain a molybdenum disulfide-doped modified graphene aerogel MoS2@GA electrode material.

2. The preparation method according to claim 1, characterized in that, The steps for synthesizing MoS2 nanoflowers via hydrothermal method include: S11, the raw material (NH4)6Mo7O 24 • Dissolve 4H2O and CH4N2S in water, stir until completely dissolved, and transfer to a hydrothermal reactor; S12 was heated to a certain temperature and then cooled to room temperature. It was then filtered, washed, and dried to obtain nanoflower MoS2. Preferably, the mass ratio of the raw materials is 1.14:1 to 1.21:

1.

3. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of MoS2 powder to graphene oxide is 1:2 to 8:1; preferably 1:2 to 4:

1. For example, 1:1, 1:1.5, 1:2, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, or any point between any two of the above ranges; Preferably, the concentration of the graphene oxide aqueous solution is 5 mg / ml to 10 mg / ml; For example, 5 mg / ml, 6 mg / ml, 7 mg / ml, 8 mg / ml, 9 mg / ml, 10 mg / ml, or any value between any two of the above ranges; Preferably, the reducing agent includes one or more of ethylenediamine, hydrazine hydrate, and propylenediamine; Preferably, the amount of ethylenediamine added as a reducing agent is 100ul / ml to 150ul / ml.

4. The preparation method according to claim 2, characterized in that, In step S12, the heating rate is 2-4℃ / min, the temperature is raised to 200-230℃, and maintained for 20-26 hours; the hydrothermal reactor is cooled at a rate of 0.4-1.6℃ / min. For example, the temperature is increased from room temperature to 210°C at a rate of 3°C / min and maintained for 24 hours; The hydrothermal reactor was cooled at a rate of 1℃ / min until the sample cooled to room temperature. The sample was then filtered through a 0.22μm filter membrane in a vacuum pump. The product was washed with deionized water five times and anhydrous ethanol three times. Finally, it was dried in an oven at 70℃ to synthesize nanoflower MoS2.

5. An electrochemically selective adsorption electrode material, characterized in that, It is synthesized using the preparation method of the electrochemical selective adsorption electrode material according to any one of claims 1 to 4.

6. The electrochemically selective adsorption electrode material according to claim 5, characterized in that, The MoS2@GA electrode material can selectively adsorb thorium in rare earth elements during electrochemical adsorption, with an adsorption capacity of up to 4154 mg / g. It has fast adsorption kinetics, with an adsorption capacity of up to 960.45 mg / g within 15 minutes and an adsorption capacity of 1959.62 mg / g within the first hour. The MoS2@GA electrode material has good cycling performance, and its performance does not significantly decrease after 10 cycles, showing great potential for application in thorium recovery. The MoS2@GA electrode material exhibits excellent removal rates for low-concentration thorium, achieving a thorium removal rate of 99% within 8 hours, and also demonstrates good cycle performance.

7. An application of an electrochemically selectively adsorbing MoS2@GA electrode material in thorium adsorption, characterized in that, include: The electrochemically selectively adsorbing MoS2@GA electrode material as described in claim 5 or 6 is used to prepare an adsorption electrode; The adsorption electrode is immersed in a Th(NO3)4 solution, and a constant DC voltage of -5V to 0V is applied to the working electrode. Static adsorption occurs when no voltage is applied to the electrode, and other factors remain the same as for electrochemical adsorption.

8. The application according to claim 7, characterized in that, The pH of the Th(NO3)4 solution is 1 to 3; preferably 1 to 1.

5.

9. The application according to claim 7, characterized in that, The concentration of the Th(NO3)4 solution is 10–1000 mg / L, preferably 10–500 mg / L. Preferably, a constant voltage DC current of -5V to 0V is applied to the working electrode, with the frequency set between 100 and 1000 Hz. Preferably, the duty cycle of the pulse is set in the range of 0.2 to 1; For example, applying electrical pulses with a voltage of -3V, a frequency of 100Hz, and different duty cycles of 0.2, 0.4, 0.6, 0.8, and 1.0; Preferably, the ratio of electrode mass to solution volume is 0.6 g / L to 1.0 g / L.

10. The application according to claim 7, characterized in that, At a voltage of -1V, the adsorption capacity of thorium is 490mg / g, which is much higher than the adsorption capacity of 220mg / g obtained by static adsorption of MoS2@GA material without applied voltage. When the voltage drops to -3V, the adsorption amount increases significantly to 2800mg / g. As the voltage increases, the electric field force drives the formation of a thicker double-layer capacitance on the electrode surface, which promotes the adsorption of thorium on the electrode.

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