A palladium-based catalyst, its preparation method and use, a palladium-based modified electrode and its use, a method for the electrocatalytic reduction of perfluoro- and / or polyfluoroalkyl substances

Abstract

The application provides a palladium-based catalyst and a preparation method and application thereof, a palladium-based modified electrode and application thereof, and a method for electrocatalytic reduction of perfluoro and / or polyfluoro alkyl substances, and relates to the technical field of electrocatalysis. The application is characterized in that a nitrogen-doped carbon material with a microporous structure and a doped form of nitrogen including pyrrole nitrogen is loaded in a palladium salt aqueous solution. During the loading process, pyrrole nitrogen is preferentially coordinated with palladium ions to form palladium-nitrogen bonds, so that the palladium ions are anchored and adsorbed on the nitrogen-doped carbon material, and then reduced, and the palladium remains in the anchored position to form palladium monomers, thereby reducing the agglomeration of palladium monomers and improving the catalytic efficiency of the palladium-based catalyst in electrocatalytic reduction of perfluoro and / or polyfluoro alkyl substances into fluorine ions. Moreover, pyrrole nitrogen is beneficial to the adsorption and desorption of active hydrogen, and the mesoporous structure is beneficial to the contact between the perfluoro and / or polyfluoro alkyl substances and the active hydrogen, so that the active hydrogen is accurately defluorinated to promote the electrocatalytic reaction and further improve the catalytic efficiency of the palladium-based catalyst.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a palladium-based catalyst and its preparation method and application, a palladium-modified electrode and its application, and a method for the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances. Background Technology

[0002] Perfluorinated and / or polyfluoroalkyl substances (PFAS) are fluorine-containing substances containing at least one perfluorinated methyl (-CF3) or methylene carbon atom (-CF2-), and these carbon atoms are not bonded to hydrogen (H), chlorine (Cl), bromine (Br), or iodine (I) atoms. PFAS are a class of synthetic organic compounds that are widely used in industrial and consumer products due to their extremely high chemical stability, thermal stability, and hydrophobicity. PFAS can persist in the environment for a long time and are figuratively called "permanent chemicals." They also exhibit bioaccumulation and toxicity; therefore, a green and efficient degradation method is urgently needed to completely break their stable CF bonds.

[0003] Currently, degradation technologies for PFAS mainly include oxidation and biological methods. However, traditional advanced oxidation processes rely on free radical attack, which has limited efficiency in degrading structurally resilient long-chain PFAS and may generate unknown intermediate products. Biological methods suffer from bottlenecks such as long processing cycles and poor adaptability to long-chain PFAS. Electrochemical reduction defluorination technology offers a new approach, the core of which lies in the in-situ generation of highly active reducing species on the cathode, which directly attack and break the CF bonds.

[0004] Palladium was loaded onto a nitrogen-doped carbon substrate as the key active component to construct a palladium-based catalyst-centric catalytic system, demonstrating excellent potential in the electrochemical catalytic degradation of PFAS. This system typically utilizes the excellent adsorption and conductivity of nitrogen-doped carbon for PFAS, combined with palladium's catalytic defluorination capability. Under an electric field, PFAS molecules are enriched on the electrode surface, and the CF bond is broken via palladium catalysis, thus achieving efficient degradation and partial defluorination. However, palladium has poor dispersibility and is prone to aggregation, resulting in low catalytic efficiency of palladium-based catalysts in the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a palladium-based catalyst, its preparation method and application, a palladium-modified electrode and its application, and a method for the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances. The palladium-based catalyst prepared by the method provided by this invention exhibits high catalytic efficiency in the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a palladium-based catalyst, comprising the following steps: A palladium-based catalyst is obtained by loading nitrogen-doped carbon materials into an aqueous solution of palladium salt, which reduces the palladium salt to palladium single atoms. The nitrogen element in the nitrogen-doped carbon material is doped on the surface of the carbon material or in the carbon skeleton of the carbon material. The nitrogen doping form in the nitrogen-doped carbon material includes pyrrole nitrogen; The nitrogen-doped carbon material has both mesoporous and microporous structures.

[0007] Preferably, the method for preparing the nitrogen-doped carbon material includes the following steps: Chitosan, proton-type acid, thermally decomposable potassium salt activator and water were mixed and freeze-dried to obtain carbon-nitrogen precursor; The carbon-nitrogen precursor is pyrolyzed and carbonized under a protective atmosphere to obtain a nitrogen-doped carbon material.

[0008] Preferably, the protic acid includes acetic acid and / or hydrogen chloride; The thermally decomposable potassium salt activator includes potassium carbonate; The mass ratio of chitosan to protonic acid is 1:0.5~2; The mass ratio of chitosan to thermally decomposable potassium salt activator is 1:1~2.

[0009] Preferably, the palladium salt comprises palladium chloride and / or palladium nitrate; The mass ratio of the palladium salt to the nitrogen-doped carbon material is 0.4~2:50.

[0010] The present invention provides a palladium-based catalyst prepared by the preparation method described above, comprising a nitrogen-doped carbon material and palladium single atoms supported on the nitrogen-doped carbon material.

[0011] Preferably, the loading of palladium single atoms is 0.5~2wt%.

[0012] The present invention also provides a palladium-based modified electrode, comprising a carbon electrode and a modification layer loaded on the surface of the carbon electrode; The modified layer includes a catalyst, a binder, and a conductive agent; The catalyst is the palladium-based catalyst described in the above technical solution.

[0013] The present invention also provides the application of the palladium-based catalyst or the palladium-based modified electrode described in the above technical solutions in the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances.

[0014] The present invention also provides a method for the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances, comprising the following steps: A three-electrode system is used to electrocatalytically reduce perfluorinated and / or polyfluoroalkyl substances in an electrolyte. The working electrode in the three-electrode system is a modified electrode, which is the palladium-based modified electrode described in the above technical solution. Alternatively, the modification layer of the modified electrode may contain a palladium-based catalyst, wherein the palladium-based catalyst is the palladium-based catalyst described in the above technical solution.

[0015] Preferably, the electrocatalytic reduction potential is -1 to -0.5V; The electrocatalytic reduction is carried out in an electrolysis system, which includes a cathode chamber and an anode chamber. The cathode chamber and the anode chamber are separated by an ion exchange membrane; The cathode chamber is used to hold the cathode electrolyte; the anode chamber is used to hold the anode electrolyte. The ion exchange membrane includes a Nafion-117 proton exchange membrane or a sulfonated polyether ether ketone membrane.

[0016] This invention provides a method for preparing a palladium-based catalyst, comprising the following steps: loading a nitrogen-doped carbon material in an aqueous solution of a palladium salt under a nitrogen atmosphere, thereby reducing the palladium salt to palladium single atoms to obtain a palladium-based catalyst; wherein the nitrogen element in the nitrogen-doped carbon material is doped on the surface of the carbon material or in the carbon framework of the carbon material; wherein the nitrogen doping form in the nitrogen-doped carbon material includes pyrrole nitrogen; and wherein the nitrogen-doped carbon material has a mesoporous structure and a microporous structure. This invention involves loading nitrogen-doped carbon materials with microporous and mesoporous structures, including pyrrolidine nitrogen, into an aqueous palladium salt solution. During loading, pyrrolidine nitrogen preferentially coordinates with palladium ions to form Pd-N bonds, anchoring the palladium ions to the nitrogen-doped carbon material. Upon reduction, the palladium remains at the anchored position, forming palladium single atoms, thus reducing palladium single-atom aggregation and improving the catalytic efficiency of the prepared palladium-based catalyst in the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions. Furthermore, pyrrolidine nitrogen facilitates the adsorption and desorption of active hydrogen (H). The mesoporous structure, as a rapid transport channel for macromolecules, effectively breaks the kinetic limitation of PFAS diffusion to the active center, significantly improving the accessibility and mass transfer flux of reactants, and facilitating the contact between perfluorinated and / or polyfluoroalkyl substances and active hydrogen. Simultaneously, the mesoporous space extends the lifetime of active hydrogen through physical confinement, suppressing the occurrence of hydrogen evolution side reactions, thereby improving the effective collision efficiency between H and PFAS molecules. Mesoporous structures and nitrogen-anchored palladium single-atom sites synergistically construct an efficient micro-reaction interface that integrates enrichment and reaction, achieving spatial coupling of substrate enrichment, active site exposure, and reaction process, thereby enhancing interfacial reaction efficiency and resulting in a palladium-based catalyst with high catalytic efficiency.

[0017] Furthermore, traditional nitrogen-doped carbon materials often use nitrogen-containing carbon precursors such as ammonia and melamine, which have problems such as high cost, high toxicity, and high risk. In contrast, this invention uses chitosan as a nitrogen-doped carbon precursor, which itself contains about 7 wt% nitrogen. Nitrogen-doped carbon materials with a hierarchical porous structure can be prepared without the need for an additional nitrogen source. The preparation method is simple to operate, has low environmental pollution, and is suitable for industrial production. Attached Figure Description

[0018] Figure 1 XPS image of nitrogen-doped carbon material prepared in Example 1; Figure 2 The results are the BET test results of the nitrogen-doped carbon material prepared in Example 1; Figure 3 XPS image of the palladium-based catalyst prepared in Example 1; Figure 4 The diagram shows the catalytic efficiency of the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions in Example 1. Figure 5 This is a graph showing the catalytic efficiency of the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions in Example 2; Figure 6 XPS image of the nitrogen-doped carbon material prepared in Example 3; Figure 7 The results are the BET test results of the nitrogen-doped carbon material prepared in Example 3; Figure 8 The graph shows the catalytic efficiency of electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions in Example 2 and Comparative Example 1. Detailed Implementation

[0019] This invention provides a method for preparing the palladium-based catalyst described above, comprising the following steps: Nitrogen-doped carbon material is loaded into an aqueous palladium salt solution and then reduced to reduce the palladium salt in the aqueous palladium salt solution to palladium single atoms, thus obtaining a palladium-based catalyst. The nitrogen element in the nitrogen-doped carbon material is doped on the surface of the carbon material or in the carbon skeleton of the carbon material. The nitrogen doping form in the nitrogen-doped carbon material includes pyrrole nitrogen; The nitrogen-doped carbon material has both mesoporous and microporous structures.

[0020] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0021] In this invention, the method for preparing the nitrogen-doped carbon material may include the following steps: Chitosan, proton-type acid, thermally decomposable potassium salt activator and water were mixed and freeze-dried to obtain carbon-nitrogen precursor; The carbon-nitrogen precursor is pyrolyzed and carbonized under a protective atmosphere to obtain a nitrogen-doped carbon material.

[0022] This invention involves mixing chitosan, a proton-type acid, a thermally decomposable potassium salt activator, and water, followed by freeze-drying to obtain a carbon-nitrogen precursor.

[0023] In this invention, the chitosan can be used in the form of chitosan powder; the degree of deacetylation of the chitosan can be ≥90%. In this invention, the protic acid can include acetic acid and / or hydrogen chloride; the protic acid and water can be used in the form of an aqueous solution of the protic acid, specifically an aqueous solution of acetic acid and / or hydrochloric acid; the concentration of the aqueous acetic acid solution can be 0.5~2wt%, specifically 0.5wt%, 0.8wt%, 1wt%, 1.5wt%, or 2wt%; the concentration of the hydrochloric acid can be 1~3wt%, specifically 1wt%, 1.5wt%, 2wt%, 2.5wt%, or 3wt%. In this invention, the mass ratio of chitosan to proton acid can be 1:0.5~2, specifically 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5 or 1:2; in this invention, the thermally decomposable potassium salt activator can include potassium carbonate; the mass ratio of chitosan to thermally decomposable potassium salt activator can be 1:1~2, specifically 1:1, 1:1.2, 1:1.5, 1:1.8 or 1:2.

[0024] In this invention, mixing chitosan, a proton-type acid, a thermally decomposable potassium salt activator, and water can specifically involve first mixing an aqueous solution of chitosan and a proton-type acid to obtain a colloid; then second mixing the colloid with the thermally decomposable potassium salt activator. This invention utilizes the H+ in the proton-type acid... + It binds to the free amino groups (-NH2) in chitosan, protonating them to form positively charged -NH3. + This process disrupts the hydrogen bonds between the molecular chains, allowing the chitosan molecular chains to expand and disperse in the water, forming a uniform colloid.

[0025] In this invention, the freeze-drying process may include sequential pre-freezing and drying sublimation. The pre-freezing temperature can be -80 to -60°C, specifically -75°C, -70°C, or -65°C. The pre-freezing time can be 8 to 12 hours, specifically 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. The pre-freezing can be performed in an ultra-low temperature freezer. The drying sublimation temperature can be -35 to -20°C, specifically -35°C, -30°C, -25°C, or -20°C. The drying sublimation time can be 24 to 48 hours, specifically 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours. The drying sublimation can be performed in a freeze dryer. Through freeze-drying, in the pre-freezing stage, the mixed solution forms ice crystals. In the sublimation drying stage, the ice crystals directly sublimate, forming a porous structure, resulting in nitrogen-doped carbon materials with both mesoporous and microporous structures.

[0026] After obtaining the carbon-nitrogen precursor, the present invention pyrolyzes and carbonizes the carbon-nitrogen precursor under a protective atmosphere to obtain a nitrogen-doped carbon material.

[0027] In this invention, the protective atmosphere can be an inert atmosphere and / or nitrogen, and the inert atmosphere can specifically be argon; the flow rate of the protective atmosphere can be 80~120 mL / min, specifically 80 mL / min, 90 mL / min, 100 mL / min, 110 mL / min or 120 mL / min.

[0028] In this invention, the pyrolysis carbonization may include sequentially performing a first pyrolysis carbonization and a second pyrolysis carbonization; the temperature of the first pyrolysis carbonization may be 350~400℃, specifically 350℃, 370℃, 390℃ or 400℃; the holding time of the first pyrolysis carbonization may be 0.5~1h, specifically 0.5h, 0.6h, 0.8h or 1h; the heating rate to the holding temperature of the first pyrolysis carbonization may be 2~4℃ / min, specifically 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min or 4℃ / min. In this invention, the temperature of the second pyrolysis carbonization can be 650~800℃, specifically 650℃, 700℃, 750℃, 780℃ or 800℃; the holding time of the second pyrolysis carbonization can be 1~1.5h, specifically 1h, 1.1h, 1.3h or 1.5h; the heating rate to the holding temperature of the second pyrolysis carbonization can be 4~6℃ / min, specifically 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min or 6℃ / min. During pyrolysis, chitosan undergoes a molten state. If the temperature rises too quickly, the material surface will solidify rapidly, sealing in the tar produced internally. This invention employs a slow heating rate of 3°C / min in the first pyrolysis carbonization stage, allowing sufficient time for the chitosan to decompose gently. In this stage, the internal tar can diffuse out through the initially formed micropores and mesopores before the material skeleton is fully solidified, cross-linking to form a robust carbon skeleton. This prevents the subsequent second pyrolysis carbonization stage from causing structural collapse due to violent shrinkage, ensuring the resulting carbon skeleton retains its mesoporous and microporous structures. Simultaneously, the relatively low temperature in the first stage helps retain the original high nitrogen content in chitosan. In this stage, nitrogen mainly exists in active forms such as pyrrole-N and pyridine-N at the edges or defects of the carbon skeleton. Low-temperature pretreatment "anchors" these nitrogen atoms, forming stable nitrogen doping.

[0029] After completing the pyrolysis carbonization, the present invention may further include cooling the reactants obtained from the pyrolysis carbonization to room temperature, and then sequentially performing acid leaching, water washing, drying, and pulverization to obtain the nitrogen-doped carbon material. In this invention, the acid used for acid leaching may include hydrochloric acid; the concentration of the hydrochloric acid may be 0.5~2 mol / L, specifically 0.8 mol / L, 1 mol / L, 1.2 mol / L, or 1.5 mol / L; the mass ratio of the reactants to the volume of hydrochloric acid may be 0.05~1 g: 25~50 mL, specifically 1 g: 25 mL, 1 g: 35 mL, 1 g: 45 mL, 1 g: 50 mL, 0.8 g: 50 mL, or 0.5 g: 50 mL. This invention, through acid leaching, removes residual potassium salts and other inorganic impurities from the nitrogen-doped carbon material, which is beneficial for the unobstructed flow of pores.

[0030] This invention does not specifically limit the amount of water used for washing or the number of washing cycles, as long as the acid-leached product is washed until neutral. In this invention, the drying temperature can be 100~120℃, specifically 100℃, 105℃, 110℃, 115℃, or 120℃; the drying time can be 4~6 hours, specifically 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours. In this invention, the pulverization can include grinding; the particle size of the nitrogen-doped carbon material can be 30~150 μm, specifically 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, or 150 μm.

[0031] In this invention, the palladium salt may include palladium chloride and / or palladium nitrate; the mass ratio of the palladium salt to the nitrogen-doped carbon material may be 0.4 to 2:50, specifically 0.5:50, 0.8:50, 1:50, 1.2:50, or 1.5:50. In this invention, the palladium salt aqueous solution may also contain hydrochloric acid; the concentration of the hydrochloric acid may be 0.5 to 2 mol / L, specifically 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L; the concentration of the palladium salt in the hydrochloric acid solution may be 400 to 600 mg / L, specifically 400 mg / L, 450 mg / L, 500 mg / L, 550 mg / L, or 600 mg / L.

[0032] In this invention, the load may include a stirring and mixing load and a static load; the stirring and mixing time may be 6 to 12 hours, specifically 6 hours, 8 hours, 10 hours, 11 hours, or 12 hours. In this invention, the temperature of the load may be room temperature, or 15 to 30°C, specifically 15°C, 20°C, 25°C, or 30°C; the loading time may be 10 to 12 hours, specifically 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours.

[0033] After the loading is completed, the present invention further includes washing and drying the solid obtained by the loading. In the present invention, the washing may include water washing; the drying temperature may be 60~80℃, specifically 60℃, 65℃, 70℃, 75℃ or 80℃; the drying time may be 12~24h, specifically 12h, 16h, 20h, 22h or 24h.

[0034] In this invention, the reduction can be carried out under a protective atmosphere; the protective atmosphere can be an inert atmosphere and / or nitrogen; the inert atmosphere can specifically be argon; the reduction temperature can be 300~500℃, specifically 300℃, 350℃, 400℃, 450℃ or 500℃; the reduction time can be 1~2h, specifically 1h, 1.2h, 1.5h, 1.8h or 2h. This invention uses a nitrogen atmosphere for reduction to prevent oxidation of the nitrogen-doped carbon material and to reduce the palladium salt to palladium single atoms.

[0035] This invention provides a palladium-based catalyst comprising a nitrogen-doped carbon material and palladium single atoms supported on the nitrogen-doped carbon material; In this invention, the loading of palladium single atoms can be 0.5~2wt%, specifically 0.5wt%, 1wt%, 1.5wt%, or 2wt%. In this invention, the pore size of the mesoporous structure is 2~50nm; the pore size of the microporous structure is <2nm. In this invention, the porosity of the mesoporous structure can be 20~50%, specifically 30%, 35%, or 40%; the porosity of the microporous structure can be 30~60%, specifically 35%, 45%, or 55%. In this invention, the nitrogen doping form in the nitrogen-doped carbon material can also include graphitic nitrogen and / or pyridine nitrogen.

[0036] In this invention, the amount of nitrogen doping in the nitrogen-doped carbon material can be 0.5 to 2 wt%, specifically 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, or 1.8 wt%.

[0037] The present invention also provides a palladium-based modified electrode, comprising a carbon electrode and a modification layer loaded on the surface of the carbon electrode; The modified layer includes a catalyst, a binder, and a conductive agent; The catalyst is the palladium-based catalyst described in the above technical solution.

[0038] In this invention, the carbon electrode may specifically be a carbon cloth electrode; the binder includes sodium alginate and / or polydopamine; the molecular weight of the sodium alginate may be 10,000~200,000 Da, specifically 10,000 Da, 50,000 Da, 100,000 Da, 150,000 Da or 200,000 Da; the molecular weight of the polydopamine may be 10,000~100,000 Da, specifically 10,000 Da, 30,000 Da, 50,000 Da, 80,000 Da or 100,000 Da; the conductive agent may include acetylene black. In this invention, the mass ratio of the catalyst to the binder can be 5 to 15:1, specifically 5:1, 6:1, 8:1, 10:1, 12:1 or 15:1; the mass ratio of the catalyst to the conductive agent is 5 to 9:1, specifically 5:1, 6:1, 7:1, 8.5:1 or 9:1.

[0039] In this invention, the preparation method of the palladium-modified electrode may include the following steps: dispersing a catalyst, a binder, and a conductive agent in water to obtain a slurry; The slurry is coated onto the surface of a carbon electrode, dried, and then immersed in an aqueous calcium chloride solution for crosslinking to obtain the palladium-modified electrode. This invention utilizes a crosslinking reaction between an aqueous calcium chloride solution and sodium alginate to firmly adhere the catalyst to the carbon electrode surface.

[0040] In this invention, the mass ratio of the catalyst to water can be 85:0.5~2, specifically 85:0.5, 85:1, 85:1.5, or 85:2; the dispersion includes sequential grinding dispersion and ultrasonic dispersion; the ultrasonic dispersion time can be 30~60 min, specifically 30 min, 40 min, 50 min, or 60 min. In this invention, the coating can include blade coating or drop coating, specifically drop coating using a pipette or blade coating using a scraper. In this invention, the carbon electrode further includes pretreatment before use; the pretreatment step can include: performing cyclic voltammetry on the carbon electrode until the scanned curves coincide. In this invention, the scanning conditions can include: scanning potential of -1.0V to +0.6V; scanning rate of 100mV / s; and 60~100 scan cycles. In this invention, the drying temperature can be 60-70°C, specifically 60°C, 62°C, 65°C, or 70°C; the drying time can be 10-20 hours, specifically 10 hours, 13 hours, 15 hours, 18 hours, or 20 hours. In this invention, the concentration of the calcium chloride aqueous solution can be 2-5 wt%, specifically 2 wt%, 3 wt%, 4 wt%, or 5 wt%. After completing the crosslinking, this invention further includes washing the crosslinked product with water and then drying it.

[0041] The present invention also provides the application of the palladium-based catalyst or the palladium-based modified electrode described in the above technical solutions in the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances.

[0042] The present invention also provides a method for the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances, comprising the following steps: A three-electrode system is used to electrocatalytically reduce perfluorinated and / or polyfluoroalkyl substances in an electrolyte. The working electrode in the three-electrode system is a modified electrode, which is the palladium-based modified electrode described in the above technical solution. Alternatively, the modification layer of the modified electrode may contain a palladium-based catalyst, wherein the palladium-based catalyst is the palladium-based catalyst described in the above technical solution.

[0043] In this invention, the electrocatalytic reduction can be carried out in an electrolysis system, which may include a cathode chamber and an anode chamber. The electrolysis system used for the electrocatalytic reduction may specifically be a three-port H-type sand core electrolyzer. The cathode chamber and the anode chamber may be separated by an ion exchange membrane. The cathode chamber is used to hold the cathode electrolyte. The anode chamber is used to hold the anode electrolyte. The ion exchange membrane may include a Nafion-117 proton exchange membrane or a sulfonated polyether ether ketone membrane (SPEEK membrane).

[0044] In this invention, the cathode electrolyte may include perfluorinated and / or polyfluoroalkyl substances, sodium sulfate, and water; the concentration of the perfluorinated and / or polyfluoroalkyl substances in the cathode electrolyte may be 0.1~50 μmol / L, specifically 0.5 μmol / L, 1 μmol / L, 5 μmol / L, 10 μmol / L, 25 μmol / L, or 40 μmol / L; the concentration of sodium sulfate may be 0.04~0.06 mol / L, specifically 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, 0.055 mol / L, or 0.06 mol / L; the anode electrolyte may include sodium sulfate and water; the concentration of sodium sulfate in the anode electrolyte may be 0.04~0.06 mol / L, specifically 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, 0.055 mol / L, or 0.06 mol / L.

[0045] In this invention, the auxiliary electrode in the three-electrode system can be a platinum electrode, specifically a platinum sheet electrode; the reference electrode in the three-electrode system can be a silver / silver chloride electrode. In this invention, the auxiliary electrode can be located in the anode chamber; the reference electrode and the working electrode can be located in the cathode chamber. In this invention, the electrocatalytic reduction potential can be -1 to -0.5V, specifically -0.9V, -0.8V, -0.7V, or -0.6V. This invention performs electrocatalytic reduction by mixing sodium sulfate and perfluorinated and / or polyfluoroalkyl substances in the cathode electrolyte, separated by a proton exchange membrane. This prevents oxygen generated at the anode from entering the cathode and interfering with the generation of active hydrogen at the cathode, thus reducing the occurrence of side reactions; simultaneously, it avoids perfluorinated and / or polyfluoroalkyl substances entering the anode chamber, preventing the generation of byproducts.

[0046] To further illustrate the present invention, the solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0047] In all embodiments of the present invention, all reagents used were purchased from Maclean's reagents, and the parameters of the reagents and materials are shown in Table 1.

[0048] Table 1. Reagent and material parameters used in the examples.

[0049] Example 1 Chitosan powder was dissolved in a 1 wt% aqueous acetic acid solution and magnetically stirred until completely dissolved to form a colloid. K2CO3 was added to the colloid and stirred until homogeneous. The mixture was then pre-frozen overnight in an ultra-low temperature freezer at -80°C and then sublimated in a freeze dryer at -80°C for 24 hours to obtain a fluffy and porous carbon-nitrogen precursor. The mass ratio of chitosan powder to acetic acid was 1:1, and the mass ratio of chitosan to K2CO3 was 1:1.

[0050] The obtained carbon-nitrogen precursor was placed in the center of a tube furnace and heated by a programmed temperature control. The furnace was heated to 400°C at a rate of 3°C / min under an argon flow of 100 mL / min for pyrolysis and carbonization for 0.5 h. Then, the furnace was heated to 800°C at a rate of 5°C / min under an argon flow of 100 mL / min for pyrolysis and carbonization for 1 h. After the reaction, the furnace was allowed to cool naturally to room temperature. The resulting black solid was soaked in 30 mL of 1 mol / L hydrochloric acid to remove residual potassium salts and other inorganic impurities. The solid was repeatedly washed with deionized water until the filtrate was neutral. The solid was dried in a vacuum oven at 120°C for 5 h to obtain nitrogen-doped carbon material.

[0051] Figure 1 The image shows the XPS plot of the nitrogen-doped carbon material prepared in Example 1. Figure 1 It can be seen that the nitrogen doping forms in the nitrogen-doped carbon material prepared in Example 1 include pyrrole nitrogen, pyridine nitrogen and nitrogen oxide, and the doping amount of pyrrole nitrogen is high.

[0052] The nitrogen-doped carbon material prepared in Example 1 was subjected to BET testing. Figure 2 The BET test results for the nitrogen-doped carbon material prepared in Example 1 are shown in the inset, which is the N2 adsorption-desorption isotherm. Figure 2 It can be seen that the specific surface area of ​​the nitrogen-doped carbon material prepared in Example 1 is 3830 m². 2 ·g -1 The average pore size is 0.9588 nm; the total pore volume is 1.8362 cm³. 3 ·g -1 This indicates that the nitrogen-doped carbon material prepared in Example 1 has a high specific surface area and total pore volume, with an average pore size in the micrometer range.

[0053] Palladium chloride was dissolved in 1 mol / L hydrochloric acid to obtain a 500 mg / L palladium chloride hydrochloric acid solution. Nitrogen-doped carbon material was dispersed in water to obtain a 500 mg / L nitrogen-doped carbon material hydrochloric acid dispersion. The nitrogen-doped carbon material hydrochloric acid dispersion and the palladium chloride hydrochloric acid solution were mixed at a volume ratio of 100:1, stirred for 12 h, sealed, and allowed to stand at room temperature for 12 h. The solid product obtained was washed with deionized water and dried at 60 °C for 12 h until all water was evaporated, yielding a solid powder. The dried powder was placed in a ceramic boat and placed in a tube furnace. Under nitrogen protection, the temperature was increased to 450 °C at a rate of 3 °C / min and maintained at this temperature for 2 h to reduce palladium ions to palladium single atoms, forming a palladium single atom-pyrrole nitrogen coordination. After the reduction reaction was completed, the reaction product was cooled to room temperature to obtain a palladium-based catalyst.

[0054] The obtained palladium-based catalyst was characterized by XPS. Figure 3 The image shows the XPS plot of the palladium-based catalyst prepared in Example 1. Figure 3 It can be seen that the palladium single atom successfully coordinated with the pyrrole nitrogen, and that... Figure 3 It can be seen that in the obtained palladium-based catalyst, palladium exists in the form of palladium single atoms, rather than in the form of palladium nanoparticles.

[0055] Sodium alginate, acetylene black, and the obtained palladium-based catalyst were mixed uniformly at a mass ratio of 15:10:85. Deionized water (mass ratio of palladium-based catalyst to deionized water was 85:1) was added while grinding, and the mixture was ultrasonically treated for 30 min to further disperse the slurry. The resulting slurry was drop-coated onto the surface of pretreated carbon cloth (1.5 cm × 2 cm) using a pipette and dried at 60 °C. The dried product was immersed in a 3 wt% calcium chloride aqueous solution to crosslink the surface, then rinsed with deionized water and dried to obtain the palladium-modified electrode. The catalyst loading in the palladium-modified electrode was calculated as 5 mg / cm³ based on the mass difference between the carbon cloth and the palladium-modified electrode. 2 .

[0056] A three-electrode electrolysis system was constructed using the obtained palladium-modified electrode as the working electrode, a platinum electrode as the auxiliary electrode, and a silver / silver chloride electrode as the reference electrode. The electrolysis chamber was a three-port H-type sand-core electrolytic cell, with a Nafion-117 proton exchange membrane used as the isolation barrier between the cathode and anode chambers. The cathode electrolyte consisted of a 0.05 mol / L Na₂SO₄ aqueous solution and a 10 μmol / L perfluorooctanoic acid (PFOA) aqueous solution; the anode electrolyte was a 0.05 mol / L Na₂SO₄ aqueous solution. Electrocatalytic reduction was performed by applying a working potential of -1.2 V (Ag / AgCl) to the working electrode using a Chenhua electrochemical workstation. Samples were taken every 5 minutes to detect the concentrations of fluoride ions and PFOA.

[0057] Figure 4 This is a graph showing the catalytic efficiency of the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions in Example 1. Figure 4 It can be seen that the palladium-modified electrode has a good effect on the degradation of PFOA, achieving 90% removal of PFOA in 2 hours. PFOA is transformed into short-chain polyfluorinated compounds, the fluoride ion concentration continues to rise, and finally most of PFOA is degraded within 6 hours.

[0058] Example 2 The palladium-modified electrode provided in Example 1 was used to degrade a 50 μmol / L aqueous solution of perfluorooctanoic acid. The three-electrode electrolysis system was constructed in the same way as in Example 1, and samples were taken every 60 min.

[0059] Figure 5 This is a catalytic efficiency graph showing the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions in Example 2. Figure 5 It can be seen that for high-concentration perfluorooctanoic acid aqueous solutions, palladium-modified electrodes still have a better effect on PFOA degradation, and most of the PFOA is degraded within 30 hours.

[0060] Example 3 Nitrogen-doped carbon materials were prepared using the preparation method provided in Example 1. The only difference from Example 1 is that the mass ratio of chitosan to K2CO3 is 1:2.

[0061] Figure 6 The XPS image of the nitrogen-doped carbon material prepared in Example 3 is shown below. Figure 6 It can be seen that the nitrogen doping forms in the nitrogen-doped carbon material prepared in Example 3 include pyrrole nitrogen, pyridine nitrogen and nitrogen oxide, but the doping amount of pyrrole nitrogen is slightly lower than that in the nitrogen-doped carbon material in Example 1.

[0062] Figure 7 The inset shows the BET test results of the nitrogen-doped carbon material prepared in Example 3. The inset is the N2 adsorption-desorption isotherm. Figure 7 It can be seen that the specific surface area of ​​the nitrogen-doped carbon material prepared in Example 3 is 1848.7 m². 2 ·g -1 The average pore size is 0.9501 nm; the total pore volume is 0.8782 cm³. 3 ·g -1 Although the performance of the nitrogen-doped carbon material prepared in Example 3 is slightly lower than that in Example 1, its specific surface area, average pore size, and total pore volume are still higher.

[0063] Comparative Example 1 A palladium-modified electrode was prepared using the method provided in Example 1, and a three-electrode electrolysis system was constructed to degrade a 50 μmol / L aqueous solution of perfluorooctanoic acid. The three-electrode electrolysis system was constructed using the same method as in Example 1, with samples taken every 60 minutes. The only difference from Example 1 was that the palladium-based catalyst prepared in Example 1 was replaced with a commercially available Pd nanoparticle catalyst (i.e., the palladium element in the palladium-based catalyst in Example 1 exists in the form of palladium single atoms, while the palladium element in the commercially available Pd nanoparticle catalyst in Comparative Example 1 exists as palladium nanoparticles formed by the aggregation of several palladium single atoms).

[0064] Figure 8 This is a graph showing the catalytic efficiency of the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions in Example 2 and Comparative Example 1. Figure 8 It is evident that the palladium-based catalyst provided by this invention has a much higher catalytic efficiency in the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances to fluoride ions than commercially available Pd nanoparticle catalysts.

[0065] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a palladium-based catalyst, characterized in that, Includes the following steps: Nitrogen-doped carbon material is loaded into an aqueous palladium salt solution and then reduced to reduce the palladium salt in the aqueous palladium salt solution to palladium single atoms, thus obtaining a palladium-based catalyst. The nitrogen element in the nitrogen-doped carbon material is doped on the surface of the carbon material or in the carbon skeleton of the carbon material. The nitrogen doping form in the nitrogen-doped carbon material includes pyrrole nitrogen; The nitrogen-doped carbon material has both mesoporous and microporous structures.

2. The preparation method according to claim 1, characterized in that, The method for preparing the nitrogen-doped carbon material includes the following steps: Chitosan, proton-type acid, thermally decomposable potassium salt activator and water were mixed and freeze-dried to obtain carbon-nitrogen precursor; The carbon-nitrogen precursor is pyrolyzed and carbonized under a protective atmosphere to obtain a nitrogen-doped carbon material.

3. The preparation method according to claim 2, characterized in that, The protic acid includes acetic acid and / or hydrogen chloride; The thermally decomposable potassium salt activator includes potassium carbonate; The mass ratio of chitosan to protonic acid is 1:0.5~2; The mass ratio of chitosan to thermally decomposable potassium salt activator is 1:1~2.

4. The preparation method according to claim 1, characterized in that, The palladium salt includes palladium chloride and / or palladium nitrate; The mass ratio of the palladium salt to the nitrogen-doped carbon material is 0.4~2:50; The reduction is carried out in a protective atmosphere; The reduction temperature is 300~500℃, and the time is 1~2h.

5. The palladium-based catalyst prepared by the method according to any one of claims 1 to 4, characterized in that, It includes nitrogen-doped carbon material and palladium single atoms loaded on the nitrogen-doped carbon material.

6. The palladium-based catalyst according to claim 5, characterized in that, The loading of palladium single atoms is 0.5~2wt%.

7. A palladium-modified electrode, characterized in that, Includes a carbon electrode and a modification layer loaded on the surface of the carbon electrode; The modified layer includes a catalyst, a binder, and a conductive agent; The catalyst is the palladium-based catalyst according to any one of claims 5 to 6.

8. The use of the palladium-based catalyst according to any one of claims 5 to 6 or the palladium-based modified electrode according to claim 7 in the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances.

9. A method for the electrocatalytic reduction of perfluorinated and / or polyfluoroalkyl substances, characterized in that, Includes the following steps: A three-electrode system is used to electrocatalytically reduce perfluorinated and / or polyfluoroalkyl substances in an electrolyte, wherein the working electrode in the three-electrode system is a modified electrode, and the modified electrode is the palladium-based modified electrode as described in claim 7; Alternatively, the modification layer of the modified electrode comprises a palladium-based catalyst, wherein the palladium-based catalyst is the palladium-based catalyst according to any one of claims 5 to 6.

10. The method according to claim 9, characterized in that, The potential for the electrocatalytic reduction is -1 to -0.5V; The electrocatalytic reduction is carried out in an electrolysis system, which includes a cathode chamber and an anode chamber. The cathode chamber and the anode chamber are separated by an ion exchange membrane; The cathode chamber is used to hold the cathode electrolyte; the anode chamber is used to hold the anode electrolyte. The ion exchange membrane includes a Nafion-117 proton exchange membrane or a sulfonated polyether ether ketone membrane.

Images