Composite catalyst and cathode material and electrocatalytic system comprising same

Abstract

The application discloses a composite catalyst containing tin dioxide / carbon dot (SnO2 / CDs) composite particles, the particle size of the composite particles is 1-50 mu m, the CDs are uniformly distributed in the composite particles, the average particle size of the CDs is 1-10 nm, and the content of the CDs in the composite particles is 0.01-5 wt%. The application provides the aforementioned composite catalyst and a cathode material and an electrocatalysis system containing the same, and the composite catalyst is particularly suitable for treating water containing refractory new pollutants by using electrochemical advanced oxidation technology (EAOPs), has excellent hydrogen peroxide selectivity, and can realize efficient pollutant degradation.

Description

Background Technology

[0001] In recent years, emerging pollutants (ECs) such as antibiotics and endocrine disruptors have been widely detected in aquatic environments. These pollutants exhibit bioaccumulation, persistence, and ecotoxicity, posing a serious challenge to traditional biological treatment processes. Electrochemical advanced oxidation processes (EAOPs), due to their ability to generate highly oxidizing hydroxyl radicals (·OH) in situ, can achieve complete mineralization of organic pollutants and has become a research hotspot in the field of water treatment. Among these, the two-electron oxygen reduction reaction (2e⁻) is particularly important. - The electro-Fenton system, which synthesizes hydrogen peroxide (H2O2) in situ via ORR and further activates it to generate ·OH through the Fenton reaction, is considered one of the most promising technical routes due to its green, efficient, and non-reactive nature.

[0002] However, to achieve efficient 2e - The key to ORR lies in the design of electrocatalysts. Currently, the following types of catalytic systems are mainly used in this field: (1) Noble metal catalyst systems: such as Pd, Pt, Au and their alloys, which are controlled by... The adsorption energy of OOH intermediates can improve the selectivity of H2O2 to a certain extent. However, such materials have inherent defects such as high cost, scarce resources, easy loss and poisoning during long-term operation, and difficulty in large-scale application. (2) Single-atom catalysts (SACs): By constructing precise MN x Coordination structure regulates the ORR pathway, theoretically achieving high 2e⁻ selectivity. However, its practical application is limited by complex synthesis processes, difficulty in batch preparation, and insufficient stability due to the easy migration and aggregation of metal atoms under electrochemical conditions. (3) Metal oxide catalysts: n-type semiconductor oxides, represented by tin dioxide (SnO2), have advantages such as high chemical stability, low cost, and environmental friendliness, making them ideal non-noble metal catalysts. However, the inherent electronic structure characteristics of SnO2 (low d-band center and strong O2 adsorption) make it more inclined to the four-electron pathway (4e⁻) in the ORR process. - ORR (or direct reduction to H2O instead of H2O2) severely limits the in-situ yield of H2O2 and the subsequent efficiency of ·OH formation.

[0003] To address the aforementioned issues, existing technologies primarily optimize catalyst active sites through strategies such as doping (e.g., heteroatoms like N and S), defect engineering (constructing oxygen vacancies), or morphology manipulation (nano-sizing, crystal facet exposure). However, these methods are essentially still "active site enhancement" strategies, focusing on regulating reaction thermodynamics (adsorption energy) and lacking direct control over electron transport kinetics. In the electrocatalytic ORR process, the rate of electron transfer from the electrode to adsorbed oxygen molecules is a key factor determining the reaction pathway: excessively rapid electron transport can easily lead to the breaking of OO bonds, thereby triggering 4e... - The path; however, existing methods cannot effectively "slow down" this electron transport process, thus making it difficult to fundamentally suppress 4e. - ORR, increase 2e - Selectivity.

[0004] In summary, there is an urgent need in this field to develop a new technical solution that, while maintaining the advantages of SnO2's high stability and low cost, can effectively suppress 4e by precisely controlling electron transport dynamics. - ORR path, significantly improves 2e - ORR selectivity and H2O2 yield, thereby enhancing the ability to degrade new pollutants. Summary of the Invention

[0005] In view of this, the present invention provides a composite catalyst and a cathode material comprising the same, as well as an electrocatalytic system, which is particularly suitable for treating water containing recalcitrant new pollutants using electrochemical advanced oxidation technologies (EAOPs), exhibiting excellent hydrogen peroxide selectivity and enabling efficient pollutant degradation.

[0006] In a first aspect, the present invention provides a composite catalyst containing tin dioxide / carbon dots (SnO2 / CDs) composite particles, wherein the particle size of the composite particles is 1-50 μm, the CDs are uniformly distributed in the composite particles, the average particle size of the CDs is 1-10 nm, and the content of the CDs in the composite particles is 0.01-5 wt%.

[0007] Preferably, in the composite catalyst, the composite particles have a particle size of 2-20 μm and a petal-like surface, the CDs have an average particle size of 3-7 nm, and the CDs in the composite particles have a content of 0.2-0.5 wt%.

[0008] The carbon-dots (CDs) of this invention refer to zero-dimensional carbon particles with an average particle size of no more than 10 nm, which typically have an amorphous carbonized polymer core.

[0009] In this invention, carbon dots are uniformly distributed in the composite particles. "Uniform" means that various elements, such as carbon, oxygen, and tin, are evenly distributed throughout the particles. Whether the distribution is uniform can be observed, for example, through a transmission electron microscopy (TEM) elemental distribution map. The composite particles with uniformly distributed carbon dots can be prepared by using a hydrothermal method with carbon dots and a tin dioxide precursor compound (e.g., tin chloride).

[0010] In some embodiments, the particle size of the composite particles of the present invention is 1-50 μm, 2-20 μm or 5-15 μm, for example, it can be 1 μm, 2 μm, 3 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 40 μm or 50 μm.

[0011] In some embodiments, the average particle size of the carbon dots of the present invention is 1-10 nm or 3-7 nm, for example, it can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm.

[0012] In some embodiments, the CDs in the composite particles are 0.01-5 wt%, 0.1-1 wt%, or 0.2-0.5 wt%, for example, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0013] In some preferred embodiments, the surface of the composite particles in the composite catalyst is petal-shaped.

[0014] The "petal-like" structure of this invention refers to a hierarchical assembly composed of a central core and nanoscale sheets or rod-shaped protrusions extending radially outward from its surface. The central core is spherical with a particle size in the micrometer range (1-50 μm). The nanosheets or rod-shaped protrusions are arranged radially outward from the core surface in a three-dimensional pattern, forming a flower cluster morphology resembling overlapping petals. Open gaps exist between the sheets, and the overall structure constitutes a high specific surface area three-dimensional structure with multi-level pores. This structure differs from smooth solid spheres, core-shell encapsulated bodies, or random aggregates, and is characterized by the radial nanosheets providing abundant surface active sites and material transport channels.

[0015] In a second aspect, the present invention provides a method for preparing the composite catalyst described in any of the foregoing claims, comprising the following steps: S1: Citric acid and ethylenediamine react under hydrothermal conditions to obtain a CDs solution; and, S2: Prepared by mixing tin chloride, hydrated citric acid and the CDs solution, reacting under hydrothermal conditions, and then annealing.

[0016] Preferably, the preparation method includes the following steps: S1: Citric acid and ethylenediamine react in a molar ratio of 2:1 to 1:2 under hydrothermal conditions at 150-200℃ to obtain a CDs solution; and, S2: Mix tin chloride, citric acid dihydrate and the CDs solution, wherein the molar ratio of tin chloride to citric acid dihydrate is 5:1 to 2:1; react the mixture under hydrothermal conditions at 150-200℃ for 6-24h, and then anneal it at 300-700℃ for 1-5h to obtain the solution.

[0017] In some embodiments, the concentration of the CDs solution obtained in step S1 is 10-800 mg / mL, 50-500 mg / mL, or 100-300 mg / mL, for example, it can be 10 mg / mL, 20 mg / mL, 50 mg / mL, 80 mg / mL, 100 mg / mL, 150 mg / mL, 200 mg / mL, 250 mg / mL, 300 mg / mL, 400 mg / mL, 500 mg / mL, 600 mg / mL, 700 mg / mL, or 800 mg / mL.

[0018] In some embodiments, the molar ratio of citric acid to ethylenediamine in step S1 is approximately 1:1.

[0019] In some embodiments, the molar ratio of tin chloride and citric acid dihydrate in step S2 is approximately 3:1.

[0020] In some embodiments, in the reaction system of step S2, the mass ratio of tin element to CDs solution is 100:1 to 5:1 or 50:1 to 10:1, for example, it can be 100:1, 80:1, 60:1, 50:1, 40:1, 30:1, 20:1, 15:1, 10:1, 8:1, 6:1 or 5:1.

[0021] In some embodiments, the temperature of the hydrothermal reaction in steps S1 and / or S2 may be, for example, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, or 200°C.

[0022] In some embodiments, the hydrothermal reaction time in step S1 is 2-12h or 3-7h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0023] In some embodiments, the hydrothermal reaction time in step S2 is 6-24h or 10-15h, for example, it can be 6h, 8h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 18h, 20h, 22h or 24h.

[0024] In some embodiments, the annealing temperature in step S2 is 300-700℃ or 400-600℃, for example, it can be 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃ or 700℃.

[0025] In some embodiments, the annealing time in step S2 is 1-5h or 2-4h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h.

[0026] Thirdly, the present invention provides a cathode material comprising a substrate and a composite catalyst as described in any of the preceding claims covering the surface of the substrate.

[0027] Preferably, the substrate is selected from at least one of conductive carbon materials, metal foils, metal meshes, or conductive oxide substrates.

[0028] Preferably, the conductive carbon material includes at least one of graphite felt, carbon felt, graphite plate, carbon cloth, carbon paper, graphene film, or carbon nanotube array.

[0029] Preferably, the substrate is graphite felt.

[0030] In some embodiments, the method for preparing the cathode material includes coating a dispersion of the composite catalyst onto the surface of a substrate and then drying it.

[0031] Preferably, the dispersion of the composite catalyst is a Nafion-ethanol solution.

[0032] Preferably, the concentration of the composite catalyst in the dispersion of the composite catalyst is 0.1-20 wt% or 1-10 wt%, for example, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%.

[0033] In some embodiments, the loading of the composite catalyst in the cathode material is 0.1-10 mg / cm², 0.5-5 mg / cm², or 1-3 mg / cm², for example, it can be 0.1 mg / cm², 0.2 mg / cm², 0.5 mg / cm², 0.8 mg / cm², 1 mg / cm², 1.2 mg / cm², 1.5 mg / cm², 1.67 mg / cm², 2 mg / cm², 2.5 mg / cm², 3 mg / cm², 4 mg / cm², 5 mg / cm², 6 mg / cm², 8 mg / cm², or 10 mg / cm².

[0034] Fourthly, the present invention provides an electrocatalytic system comprising an anode, a cathode, and an electrolyte. The anode is a platinum sheet; the cathode is any of the cathode materials described above. The electrolyte comprises at least one of sodium sulfate or sodium nitrate, preferably sodium sulfate.

[0035] In some embodiments, the pH of the electrolyte is 1 to 7, preferably 3-7, and more preferably 3-5.

[0036] In some embodiments, the concentration of the electrolyte is 0.01-2 mol / L.

[0037] Fifthly, the present invention provides the application of the composite catalyst, the cathode material, and the electrocatalytic system described in any of the foregoing claims in water treatment.

[0038] Preferably, the water to be treated includes recalcitrant new pollutants (ECs).

[0039] In some embodiments, the recalcitrant new pollutant is an antibiotic or endocrine disruptor, such as one or more of carbamazepine (CBZ), enrofloxacin (ENR), sulfamethoxazole (SMX), or bisphenol A (BPA).

[0040] Sixthly, the present invention provides the application of the composite catalyst, cathode material, and electrocatalytic system described in any of the foregoing claims in the field of electrochemical advanced oxidation technologies (EAOPs).

[0041] In some embodiments, the composite catalyst of the present invention enables the electrocatalytic system to achieve a selectivity of 60% or more, or 70% or more, for hydrogen peroxide in the field of electrochemical advanced oxidation technologies (EAOPs) or in water treatment applications. The selectivity of hydrogen peroxide refers to the degree of hydrogen peroxide produced during the oxygen reduction reaction (ORR) via a two-electron pathway (2e...). - ORR: O2 + 2H+ + 2e -→ The selectivity of H2O2 in reducing oxygen is the percentage of electrons consumed out of the total number of electrons involved in the oxygen reduction reaction. It can be obtained through a rotating ring-disk electrode (RRDE) test, calculated as: H2O2 selectivity (%) = 200 × (I_ring / N) / (I_disk + I_ring / N), where I_disk is the disk electrode current, I_ring is the ring electrode current, and N is the ring electrode's efficiency in collecting H2O2. Alternatively, it can be calculated based on the number of transferred electrons, determined by chemical titration / spectrophotometry to measure the actual molar amount of H2O2 generated, i.e., selectivity (%) = (2 × n_H2O2) / n_total_e - × 100%, where n_H2O2 is the actual number of moles of H2O2 generated, and n_total_e - This represents the total number of moles of electrons transferred through the ORR. Attached Figure Description

[0042] Figure 1 (a) Schematic diagram of the synthesis of SnO2 / CDs composite material of the present invention; (b) SEM images of SnO2 of Synthesis Example 6 and (c) SnO2 / CDs-2 of Synthesis Example 3; (d) TEM image of CDs of Synthesis Example 1 (inset: HRTEM image); (e) HRTEM image of SnO2 / CDs-2 and (f) corresponding SAED spectrum; (g) HAADF image of SnO2 / CDs-2 and (hj) corresponding elemental distribution map: (h) C, (i) O, (j) Sn.

[0043] Figure 2 SEM images of (a) SnO2 / CDs-1, (b) SnO2 / CDs-3 and (c) SnO2 / CDs-4. Figure 3 (a) LSV curves of SnO2, SnO2 / CDs-1, SnO2 / CDs-2, SnO2 / CDs-3, and SnO2 / CDs-4, where the lower half represents the disk current and the upper half represents the ring current; (b) H2O2 selectivity for the five samples; (c) Electron transfer number for the five samples. Figure 4 (a) LSV curves of CDs, where the lower half represents the disk current density and the upper half represents the ring current; (b) Calculation results of H2O2 selectivity and electron transfer number.

[0044] Figure 5(a) Degradation performance of SMX by different electrodes; (b) Corresponding degradation kinetic constants; (c) Effect of different current densities on SMX degradation by the SnO2 / CDs-2 / GF electrode; (d) Corresponding degradation kinetic constants. 0.1 M Na2SO4 electrolyte was used throughout the experiment, and the initial pH was set to 7; the constant current applied in (a) was 11 mA cm⁻¹. -2 .

[0045] Figure 6 (a) Effect of initial pH on the degradation of SMX by the SnO2 / CDs-2 / GF electrode; (b) Corresponding degradation kinetic constants; (c) Degradation performance of the SnO2 / CDs-2 / GF electrode for different pollutants; (d) Corresponding kinetic constants. 0.1 M Na2SO4 electrolyte was used throughout the experiment, and a 13 mA cm⁻¹ pH was applied. -2 A constant current; in (c), the initial pH is set to 7.

[0046] Figure 7 Transient photovoltage first-order kinetic simulation curves of SnO2, SnO2 / CDs-1, SnO2 / CDs-2, SnO2 / CDs-3 and SnO2 / CDs-4 catalysts.

[0047] Figure 8 : Schematic diagram of the working principle of the electrocatalytic system of this invention. Detailed Implementation

[0048] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0049] The present invention will be further described in detail below through specific embodiments.

[0050] Unless otherwise specified, "%" in this invention refers to the mass percentage (wt%).

[0051] Example raw material The chemical reagents were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and were used directly without purification.

[0052] Graphite felt: Purchased from Hunan Jinbo Carbon, model KBC-RSG-50.

[0053] instrument Scanning electron microscope (SEM): Zeiss Sigma 500, Germany.

[0054] Transmission electron microscope (TEM): Thermo Scientific Talos F200X G2, USA.

[0055] Elemental analyzer: Elementar vario EL cube, Germany.

[0056] Electrochemical workstation: Gamry Reference 3000, USA.

[0057] Transient surface photovoltameter: Fluxim Paios, Switzerland Synthesis example 1 Preparation of carbon dot CDs Citric acid (1.05 g) and ethylenediamine (335 μL) were simultaneously added to ultrapure water (10 mL) and stirred until completely dissolved. The resulting solution was then transferred to a 20 mL polytetrafluoroethylene-lined high-pressure reactor. The reactor was placed in an oven and heated at 180°C for 5 hours. After the reaction was complete, the reactor was cooled to room temperature by water cooling or natural cooling. The resulting product was a transparent brownish-black solution, which was dialyzed to obtain a CDs solution. The sample was then concentrated to 1 mL for subsequent use.

[0058] Synthesis Example 2-5: Preparation of SnO2 / CDs Composite Catalyst Weigh out 0.004 mol SnCl₂·2H₂O, 0.001 mol sodium citrate dihydrate, and 0.004 mol NaOH. Transfer these reagents to a beaker containing a mixture of 12 mL anhydrous ethanol and 18 mL deionized water, and add 10 mg, 20 mg, 30 mg, and 40 mg of pre-prepared CDs solutions. Stir with a glass rod until completely dissolved. Then transfer the resulting solution to a 40 mL hydrothermal synthesis reactor, seal it, and heat at 180 °C for 12 hours. After heating, allow the reactor to cool naturally to room temperature. Separate by centrifugation and wash the precipitate several times with ultrapure water and anhydrous ethanol. After washing, dry the precipitate in an oven at 80 °C for 12 hours. Grind the dried solid sample into powder, and then calcine it in a muffle furnace at 500 °C for 2 hours to obtain the composite material. The obtained samples were designated as SnO2 / CDs-1, SnO2 / CDs-2, SnO2 / CDs-3, and SnO2 / CDs-4, respectively.

[0059] Synthesis Example 6: Preparation of SnO2 Weigh out 0.004 mol SnCl₂·2H₂O, 0.001 mol sodium citrate dihydrate, and 0.004 mol NaOH. Transfer these reagents to a beaker containing a mixture of 12 mL anhydrous ethanol and 18 mL deionized water, and stir with a glass rod until completely dissolved. Then transfer the resulting solution to a 40 mL hydrothermal synthesis reactor, seal it, and heat at 180°C for 12 hours. After heating, allow the reactor to cool naturally to room temperature. Separate by centrifugation, and wash the precipitate several times with ultrapure water and anhydrous ethanol. After washing, dry the precipitate in an oven at 80°C for 12 hours. Grind the dried solid sample into powder, and then calcine it in a muffle furnace at 500°C for 2 hours to obtain the synthesized SnO₂ powder.

[0060] The content of different elements in each sample was analyzed using an elemental analyzer. The carbon point content in the catalyst of each synthesis example is shown in the table below: Table 1. Carbon point content in the synthesis catalyst <![CDATA[SnO2]]> 100 0 <![CDATA[SnO2 / CDs-1]]> 99.79 0.21 <![CDATA[SnO2 / CDs-2]]> 99.72 0.28 <![CDATA[SnO2 / CDs-3]]> 99.65 0.35 <![CDATA[SnO2 / CDs-4]]> 99.58 0.42 Examples 1-4 Preparation of Electrocatalytic Systems The electrocatalytic system of the present invention includes: Cathode: SnO2 / CDs electrode; Anode: Pt electrode; Electrolyte: Na2SO4 electrolyte, concentration 0.1mol / L.

[0061] The cathode was prepared as follows: 10 mg of the product from Synthesis Examples 2-5 was added to 1 mL of Nafion-ethanol solution (5%) and ultrasonically dispersed. The resulting dispersion was then drop-coated onto a 2×3 cm plate. 2 The graphite felt surface is dried to obtain the cathode. The cathodes are respectively designated as SnO2 / CDs-1 / GF, SnO2 / CDs-2 / GF, SnO2 / CDs-3 / GF and SnO2 / CDs-4 / GF.

[0062] Comparative Example 1: SnO2 Electrocatalytic System Except for replacing SnO2 / CDs with SnO2 from Synthesis Example 6, the cathode was identical to that of Example 1. Comparative Example 2: CDs Electrocatalytic System Except for replacing SnO2 / CDs with CDs from Synthesis Example 1 at the cathode, everything else is the same as in Example 1.

[0063] Test Example 1 Characterization The morphology and microstructure of the catalysts in the embodiments and comparative examples of this invention were systematically characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 1 bc and Figure 2 As shown in Figure ac, the samples exhibit a significant morphological evolution with increasing carbon dot (CD) loading. The original SnO2 shows a smooth spherical morphology. Figure 1 b). When 10 mg of CDs were introduced, its surface became rough ( Figure 2 a). When the CDs content increased to 20 mg, a well-defined nanoflower-like structure was formed ( Figure 1 c). However, further increasing the CDs loading (30-40 mg) leads to the gradual collapse of this hierarchical structure. Figure 2 bc). The unique nanoflower morphology of SnO2 / CDs-2 is expected to significantly increase the specific surface area, thereby enhancing its catalytic performance, and is therefore the optimal choice.

[0064] To gain a deeper understanding of its structural characteristics, TEM analysis was performed. For example... Figure 1 As shown in d, the CDs are uniformly dispersed with an average particle size of approximately 5 nm. The corresponding high-resolution transmission electron microscopy (HRTEM) image ( Figure 1 The inset (d) shows a lattice spacing of 0.21 nm, which can be attributed to the (002) crystal plane of graphitized carbon. For the SnO2 / CDs-2 composite material ( Figure 1 e), a lattice spacing of 0.34 nm was observed, corresponding to the (110) crystal plane of SnO2. Notably, lattice fringes of CDs were observed near the SnO2 lattice fringes, indicating a strong interfacial coupling between the two. Selected area electron diffraction (SAED) pattern ( Figure 1 f) The (110), (101), (200), (211), and (112) crystal planes, which can be attributed to rutile SnO2, confirm its high crystallinity. Furthermore, the elemental distribution diagram ( Figure 1 gj) indicates that C, O and Sn are uniformly distributed throughout the composite material.

[0065] Test Example 2: Evaluation of Oxygen Reduction Performance Oxygen reduction performance was evaluated using a rotating ring-disk electrode (RRDE) test (electrochemical workstation) to quantitatively analyze H₂O₂ selectivity and electron transfer number. All experiments were conducted in O₂-saturated 0.1 M Na₂O₂ solution. S The process takes place in O4 electrolyte. According to existing research, the active sites of metal oxides are generally associated with metal centers that favor O2 adsorption. Therefore, on SnO2, Sn sites are considered the main active sites for H2O2 formation. Figure 3As shown in Figure a, the linear sweep voltammetry (LSV) curves simultaneously display the disk current and ring current, corresponding to ORR activity and H2O2 detection, respectively. Among all samples, SnO2 / CDs-2 exhibited the highest ring current, indicating its highest H2O2 generation efficiency. Quantitative analysis results ( Figure 3 (bc) indicates that SnO2 / CDs-2 exhibits the highest H2O2 selectivity (approximately 75%) in the potential range of -0.65 to -0.45 V (relative to Ag / AgCl), suggesting that it primarily follows the two-electron ORR pathway. In contrast, the selectivities of SnO2 / CDs-3, SnO2 / CDs-4, and SnO2 / CDs-1 are approximately 68%, 65%, and 61%, respectively, while pristine SnO2 has the lowest selectivity (approximately 55%). The electron transfer number corresponding to SnO2 / CDs-2 is approximately 2.5 ( Figure 3 c), further confirming its preference for 2e - ORR pathway. In contrast, SnO2 has a higher electron transfer number (approximately 2.85), indicating that 4e... - The pathways contribute more. SnO2 / CDs-1 (approximately 2.78), SnO2 / CDs-3 (approximately 2.65), and SnO2 / CDs-4 (approximately 2.70) show values ​​in between, consistent with their respective selective variation trends.

[0066] Control experiment ( Figure 4 This indicates that individual CDs exhibit poor ORR activity, with low H2O2 selectivity (approximately 30%) and high electron transfer number (approximately 3.5), suggesting that they primarily follow the 4e-glucose transition law. - These results indicate that SnO2 provides the main active sites, while CDs act as co-catalysts to regulate electron transfer behavior, rather than directly participating in the reaction as active centers.

[0067] Test Example 3: Evaluation of Electrocatalytic Performance To evaluate the electrocatalytic degradation performance of the prepared catalyst, sulfamethoxazole (SMX) was selected as the model pollutant. Degradation experiments were conducted in a single-chamber electrolyzer using a two-electrode system, with a Pt sheet as the anode and the prepared electrode as the cathode. All experiments were performed under constant current conditions, with continuous air circulation to ensure oxygen saturation. The initial concentration of pollutants (ECs) in the electrolyte was fixed at 0.2 mg / L. -1 The effects of key operating parameters such as electrode type, current density, solution pH, and contaminant type were systematically investigated. The experiment was conducted using 0.1 M Na₂SO₄ at a current density of 11 mA cm⁻¹. -2 Furthermore, under the condition of an initial pH of 7, the degradation performance of different electrodes on SMX was as follows: Figure 5 As shown in figure a, the corresponding pseudo-first-order dynamic constants are shown in figure a. Figure 5b. Among all samples, the SnO2 / CDs-2 / GF electrode exhibited the highest degradation rate constant (0.186 min). -1 This superior performance can be attributed to the optimized electron transport kinetics induced by appropriate CDs loading. Therefore, an optimal balance between electron transport rate and active site accessibility is achieved in SnO2 / CDs-2, resulting in maximum degradation efficiency. The effects of different current densities on the electrode degradation of SMX and the corresponding degradation kinetic constants are shown in the figure. Figure 6 The result is shown in Figure cd. The current density is 13 mA cm⁻¹. -2 At this time, the electrode degradation kinetic constant is at its maximum.

[0068] At a current density of 13 mA cm⁻¹ -2 The effect of solution pH on SMX degradation was further investigated under certain conditions. Figure 6 ab). The highest degradation rate constant (0.37 min) was obtained at pH 3. -1 Under strongly acidic conditions, the formation and activation of H₂O₂ are more favorable. To assess the universality of this system, under the same conditions (pH 7, 13 mA cm⁻¹), -2 The degradation of various ECs (including carbamazepine CBZ, enrofloxacin ENR, sulfamethoxazole SMX, and bisphenol A (BPA)) was studied. Figure 6 As shown in cd, the SnO2 / CDs-2 / GF electrode exhibits high degradation efficiency for all tested pollutants, and their kinetic constants are relatively similar, indicating that it has broad applicability.

[0069] Test Example 4: Mechanism Verification To reveal the underlying reasons for the enhanced 2e-ORR selectivity, this study employed transient photovoltage (TPV) measurements to probe the interfacial electron transfer dynamics. Figure 7 Figures a and 7b show the pseudo-first-order kinetic fits of the TPV curves for different samples. All samples exhibit typical decay behavior, and the fitted decay rate constant increases with increasing carbon dot (CD) loading from SnO2 (22.32 ms) to SnO2 (22.32 ms). -1 Monotonically decreased to SnO2 / CDs-4 (1.98 ms) -1 This trend confirms that the introduction of CDs gradually slows down electron transfer at the catalyst / electrolyte interface. Importantly, moderate electron transfer kinetics are crucial for achieving high 2e2electrolyte levels. - ORR selectivity is crucial. For pristine SnO2, rapid electron transfer promotes an excess electron supply, which favors OO bond breaking and 4e bond cleavage. -The ORR pathway. In contrast, the introduction of CDs inhibits electron transfer, limiting the number of electrons available to adsorbed O2, thereby promoting the formation and stabilization of the *OOH intermediate, and consequently driving the 2e- ... - ORR path.

[0070] All technical solutions described above that fall within the scope of this invention's conceptual framework are protected by this invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of this invention should also be considered within the scope of protection of this invention.

Claims

1. A composite catalyst comprising tin dioxide / carbon dots (SnO2 / CDs) composite particles, wherein the particle size of the composite particles is 1-50 μm, the CDs are uniformly distributed in the composite particles, the average particle size of the CDs is 1-10 nm, and the content of the CDs in the composite particles is 0.01-5 wt%.

2. The composite catalyst according to claim 1, wherein the composite particles have a particle size of 2-20 μm and a petal-like surface, the CDs have an average particle size of 3-7 nm, and the CDs have a content of 0.2-0.5 wt% in the composite particles.

3. A method for preparing the composite catalyst according to any one of claims 1-2, comprising the following steps: S1: Citric acid and ethylenediamine react under hydrothermal conditions to obtain a CDs solution; and, S2: Prepared by mixing tin chloride, hydrated citric acid and the CDs solution, reacting under hydrothermal conditions, and then annealing.

4. The method according to claim 3, wherein the preparation method comprises the following steps: S1: Citric acid and ethylenediamine react in a molar ratio of 2:1 to 1:2 under hydrothermal conditions at 150-200℃ to obtain a CDs solution; and, S2: Mix tin chloride, citric acid dihydrate and the CDs solution, wherein the molar ratio of tin chloride to citric acid dihydrate is 5:1 to 2:1; react the mixture under hydrothermal conditions at 150-200℃ for 6-24h, and then anneal it at 300-700℃ for 1-5h to obtain the solution.

5. A cathode material comprising a substrate and a composite catalyst as described in any one of claims 1-2, coated on the surface of the substrate.

6. The cathode material according to claim 5, wherein the loading of the composite catalyst in the cathode material is 0.1-10 mg / cm³. 2 .

7. An electrocatalytic system comprising an anode, a cathode, and an electrolyte; wherein the anode is a platinum sheet; the cathode is the cathode material according to any one of claims 5-6; and the electrolyte contains sodium sulfate.

8. The application of the composite catalyst according to any one of claims 1-2, the cathode material according to any one of claims 5-6, and the electrocatalytic system according to claim 7 in water treatment.

9. In the application of claim 8, the water to be treated includes one or more of the following: recalcitrant new pollutants (ECs): carbamazepine CBZ, enrofloxacin ENR, sulfamethoxazole SMX, or bisphenol A (BPA).

10. The application of the composite catalyst according to any one of claims 1-2, the cathode material according to any one of claims 5-6, and the electrocatalytic system according to claim 7 in the field of electrochemical advanced oxidation technologies (EAOPs).

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