Monatomic site catalyst as well as preparation method and application thereof

Abstract

The invention discloses a monatomic site catalyst as well as a preparation method and application thereof. According to the invention, an iodine atom doping induced asymmetric Co-N4 / C-I coordination environment is utilized to adjust a local electronic structure, and in combination with an etching effect of in-situ decomposition and release of ammonia gas, dual synergy of atomic scale activity excitation and mesoscale mass transfer enhancement is successfully realized. According to the method, the intrinsic catalytic activity of the catalyst is remarkably improved, the exposure number and accessibility of active sites are remarkably increased, and the mass transfer coefficient of pollutants is effectively increased by 2.3 times. According to the invention, the capability of the catalyst for activating peroxymonosulfate (PMS) to generate singlet oxygen (1O2) is obviously enhanced, the highest steady-state concentration of 1O2 reaches 0.295 mM, and the normalization rate constant for degrading pollutants such as ciprofloxacin (CIP) is improved by 10.3 times compared with that of an original system. The preparation method disclosed by the invention is high in universality, and the obtained catalyst has excellent anti-interference capability on coexisting zwitterions, organic matters and actual water bodies.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more particularly to a single-atom-site catalyst, its preparation method, and its application. Background Technology

[0002] With the deepening of global industrialization, the concentration of emerging pollutants (ECs) in natural water bodies is constantly rising. Among them, quinolone antibiotics, represented by CIPs, have become one of the major challenges facing modern water treatment due to their broad bioactivity and environmental persistence. These substances not only have long-term toxic effects on aquatic ecosystems, but may also enter the human body through bioaccumulation, inducing the generation of drug resistance genes. Advanced oxidation processes (AOPs) based on PMS are widely used in the deep treatment of recalcitrant organic wastewater due to their advantages such as high oxidation potential, stable properties, and wide applicable pH range. Among various catalysts, carbon-based single-atom catalysts (SACs) have shown great research value due to their advantages such as high metal atom utilization, tunable coordination environment, and low cost. However, traditional cobalt-based single-atom catalysts (Co-NCs) still face three major bottlenecks in practical applications: 1. Limited intrinsic activity: The symmetrical Co-N4 coordination structure has an overly stable electron distribution, resulting in weak adsorption energy for PMS molecules and slow interfacial electron transfer rate, making it difficult to achieve efficient intrinsic catalytic cycling. 2. Poor site accessibility: Carbon supports prepared by traditional pyrolysis methods often have a dense graphitized layer, with a large number of metal active sites buried deep inside the carbon layer, unable to effectively contact the reaction substrate. 3. Low mass transfer efficiency: In complex heterogeneous catalytic reactions, the diffusion rate of the reaction substrate and PMS on the catalyst surface often determines the overall degradation efficiency of the reaction. Especially when treating high-flow-rate wastewater, existing catalysts are insufficient to meet the requirements for rapid purification.

[0003] Patent application CN113351236A discloses a method for constructing porous single-atom catalysts using sodium chloride (NaCl) salt templates. This method primarily utilizes the physical occupancy effect of NaCl, which increases the surface area, but the resulting active sites still exhibit the traditional Co-N4 structure, failing to break electronic symmetry at the atomic scale. Furthermore, the salt template method typically requires cumbersome freeze-drying and washing processes and is difficult to implement directional coordination engineering control. Summary of the Invention

[0004] The present invention aims to provide a single-atom site catalyst, its preparation method and application, which significantly improves the intrinsic activity of the catalyst.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a single-atom-site catalyst includes the following steps: S1. Prepare ZnCo-ZIF precursor powder with zeolite imidazole framework. S2. The zeolite imidazole framework ZnCo-ZIF precursor powder from step S1 is heat-treated under an inert atmosphere and then ground to obtain carbon-supported cobalt single-atom substrate material Co-NC. S3. Using chemical vapor deposition, the carbon-supported cobalt single-atom substrate material Co-NC obtained in step S2 is placed in the center of a tube furnace, and NH4I powder is placed upstream of the tube furnace. Under the influence of an inert atmosphere, NH3 generated from the decomposition of NH4I is used to etch Co-NC in situ, and iodine atoms are simultaneously introduced to form an asymmetric coordination structure with the cobalt active sites to obtain the Co-INC catalyst.

[0006] This invention uses the zeolite imidazole framework ZnCo-ZIF as a precursor and prepares a Co-INC catalyst by ammonium iodide (NH4I)-assisted chemical vapor deposition (CVD). By utilizing the asymmetric Co-N4 / CI coordination environment induced by iodine atom doping to regulate the local electronic structure, and combining it with the etching effect of in-situ decomposition and release of ammonia (NH3), a dual synergistic effect of atomic-scale activity excitation and mesoscale mass transfer enhancement is successfully achieved.

[0007] Single-atom site catalysts are a new type of catalytic material whose core active site is composed of a single metal atom. Their key feature is that the catalytic active component exists in the form of isolated, uniformly dispersed single atoms. These single atoms are anchored to the surface of a support material with a high specific surface area through strong interactions, forming a stable "metal-support" interface structure, without atomic aggregation or clustering.

[0008] According to embodiments of the present invention, the present invention can be further optimized, and the optimized technical solution is as follows: In one preferred embodiment, in step S3, the reaction temperature of the chemical vapor deposition method is 500~1000℃, and the reaction time is 2~4 h.

[0009] In one preferred embodiment, in step S3, the carbon-supported cobalt single-atom substrate material Co-NC obtained in S2 is placed in the high-temperature zone of a tube furnace, the temperature range of the high-temperature zone being 800~900℃, and the NH4I powder is placed in the low-temperature volatilization zone, the temperature range of the low-temperature volatilization zone being 500-600℃.

[0010] Guided by an inert gas stream, within this temperature range, the NH3 released from the thermal decomposition of NH4I and the iodine-containing vapor undergo physicochemical reactions with Co-NC in the high-temperature region. NH3 reacts with unstable components in the carbon framework, producing microporous and mesoporous structures; while iodine atoms are anchored in the carbon network surrounding cobalt atoms through nucleophilic substitution or radical addition reactions. After cooling to room temperature, the product is removed, yielding the target catalyst Co-INC. The inert atmosphere in step S3 is 10~100 sccm of argon.

[0011] In one preferred embodiment, in step S3, the mass ratio of the carbon-supported cobalt single-atom substrate material Co-NC to NH4I powder is 1:(1~20), preferably 1:(5~20).

[0012] The NH3 released from the in-situ decomposition of NH4I at high temperature generates a vapor-phase chemical ablation effect, transforming the dense carbon layer of the catalyst into a porous structure with abundant mesopores. In this invention, the CVD process significantly enhances the exposure of active sites and mass transfer efficiency, resulting in a cobalt site density of up to 0.165 mmol g in the obtained Co-INC. -1 CIP quality transfer factor K f It is 2.3 times better than the original Co-NC system, effectively solving the mass transfer bottleneck in heterogeneous catalysis.

[0013] In step S3, in-situ doping with iodine atoms creates a unique asymmetric Co-N4 / CI coordination environment near the cobalt active site. The introduction of iodine induces a redistribution of the local electronic structure, significantly enhancing the intrinsic catalytic activity of the cobalt site and thus effectively strengthening the adsorption energy for PMS molecules.

[0014] In one preferred embodiment, in step S2, the heat treatment temperature is 850~950 °C, and the heating rate is 5~10 °C / min. -1 The retention time is 2-4 hours.

[0015] Preferably, the heat treatment temperature in S2 is 900~950 ℃, and the holding time is 3~4 h. Utilizing the low boiling point (907 ℃) of Zn atoms, their in-situ evaporation during pyrolysis can effectively isolate metal Co atoms, preventing their aggregation, thereby ensuring that cobalt is highly dispersed on the carbon substrate in single-atom form.

[0016] Preferably, the heating rate in S2 is 5~7 °C min. -1 The inert atmosphere is argon, and the argon flow rate is 80~100 sccm.

[0017] In one preferred embodiment, the catalyst is Co-N4 / Cl, and the density of cobalt active sites is 0.15~0.18 mmol g. -1 The d-band center of Co is -0.6 to -0.4 eV, and the catalyst exhibits a significant mesoporous distribution in the range of 3.5 to 5 nm, showing a richer mesoscale pore structure.

[0018] In one preferred embodiment, the core feature of this catalyst lies in its unique cross-scale structural characteristics: ① Atomic scale: The introduction of CI coordination. According to density functional theory (DFT) calculations, the introduction of iodine shifts the d-band center of Co from approximately -0.85 eV (conventional Co-NC) to -0.54 eV. This modulation of the electronic structure enhances the adsorption energy of PMS molecules at the Co active site to -2.54 eV, significantly superior to the adsorption strength of pristine graphene or pure Co-N4 structures (typically around -1.5 eV); ② Mesoscale: High site accessibility. The Co density is increased from approximately 0.05 mmol g / L in conventional methods. -1 Increased to 0.165 mmol g -1 This indicates that NH3 etching effectively constructed close-range reaction channels.

[0019] The catalyst in this invention can efficiently activate PMS, mainly through a non-radical pathway. 1 O2. In experiments degrading CIP, the Co-INC / PMS system exhibited excellent activity: the normalized rate constant k reached 507 min. -1 M -1 It is a Co-NC system (49 min) -1 M -1 It is 10.3 times that of [previous species]. It can produce concentrations as high as 0.295 mM. 1 It contains O2 and has a universal degradation ability for a variety of typical antibiotic pollutants (such as SMX, 4-CP, Ph, CBZ, etc.).

[0020] This invention also discloses the application of a single-atom-site catalyst in the degradation of organic pollutants. The catalyst is added together with PMS to wastewater containing organic pollutants, and the PMS is catalytically activated to produce… 1 O2 helps degrade pollutants.

[0021] In one preferred embodiment, the organic pollutant is selected from one or more of CIP, sulfamethoxazole, carbamazepine, phenol, tetracycline, and p-chlorophenol; the catalyst dosage is 0.02~0.05 g / L. -1 The concentration of PMS was 0.5~2.0 mM.

[0022] During the degradation of CIP, the rate constant k reached 1.01 min. -1 The typical cations and anions, along with high concentrations of humic acid (HA), have virtually no hindering effect on the CIP removal performance of the Co-INC / PMS system, demonstrating that the catalyst exhibits extremely strong chemoselectivity and anti-interference capabilities along the non-radical-dominated reaction pathway. Furthermore, the modified single-atom center possesses extremely high chemical structural stability. After five cycles of testing, the catalyst maintained a CIP removal rate of over ~95%, with no significant decrease in catalytic activity.

[0023] In one preferred embodiment, the pH value of the wastewater containing organic pollutants is 4.0 to 10.0. The catalyst of the present invention maintains extremely high catalytic activity under both strong acid and strong alkaline environments and exhibits excellent tolerance to solution pH.

[0024] In one preferred embodiment, the application is achieved by constructing a continuous water purification device, in which a catalyst is loaded onto a PVDF membrane substrate to form a catalytic filter membrane, and pollutant-containing wastewater is continuously and deeply purified by passing through the filter membrane under pressure.

[0025] During the activation of PMS, the highest steady-state concentration of generated singlet oxygen reached 0.295 mM, and it exhibited a high degree of selective degradation ability for electron-rich organic pollutants.

[0026] S1 can use commercially available zeolite imidazole framework ZnCo-ZIF, or the following steps can be used to prepare zeolite imidazole framework ZnCo-ZIF precursor powder: 1) Dissolve Co(NO3)2·6H2O and Zn(NO3)2·6H2O in methanol to prepare solution A; dissolve 2-methylimidazole in methanol to prepare solution B. Inject solution A into solution B under ultrasonic conditions and sonicate for 5-15 min to ensure homogeneous mixing, thus obtaining a mixed solution. 2) Stir the mixed solution from step 1) at 20-30°C for 3-5 hours; 3) After stirring, the mixture from step 2) is collected by centrifugation and washed with methanol. The collected solid precipitate is then vacuum dried at 60-80 °C for at least 12 h to obtain the zeolite imidazole framework ZnCo-ZIF. This invention ensures the formation of highly dispersed single-atom sites during subsequent heat treatment by precisely controlling the molar ratio of zinc salt to cobalt salt in solution A to (10-20):1, resulting in a framework material with high porosity and good thermochemical stability. In the above preparation method, in step 1), the mass ratio of Co(NO3)2·6H2O, Zn(NO3)2·6H2O, and 2-methylimidazolium in the mixture is (0.08-0.12):(1.5-1.8):(1.8-2.0), preferably 0.1025:1.674:1.848.

[0027] Compared with the patent application with publication number CN113351236A, the NH4I-mediated CVD method proposed in this invention achieves the integration of "etching" and "coordination", which significantly improves the intrinsic activity and mass transfer efficiency of the catalyst.

[0028] The preparation principle of the catalyst of this invention is as follows: The in-situ decomposition of NH4I at high temperature releases NH3 and iodine-containing species. During pyrolysis, the released NH3 molecules undergo a vigorous gas-solid interface reaction with the carbon matrix, inducing abundant hierarchical mesoporous structures on the dense carbon framework through controlled carbon atom vaporization and stripping. This exposes deeply embedded sites, breaking down the physical barrier of the carbon substrate and bringing Co-N4 sites, previously embedded in the bulk phase, to the surface. This significantly improves the accessibility of active sites and enhances mass transfer efficiency. The mesoporous channels significantly shorten the diffusion path between reactants and products, optimizing the mass transfer kinetics at the three-phase interface. Simultaneously, the active iodine species generated from NH4I decomposition diffuse into the carbon lattice via thermal diffusion. Since the atomic radius of iodine (~1.33 Å) is significantly larger than that of carbon (~0.77 Å) and nitrogen (~0.75 Å), the introduction of iodine induces significant lattice distortion and stress field in the carbon substrate, constructing a unique asymmetric Co-N4 / CI coordination environment, effectively modulating the electronic structure of the cobalt center, optimizing the adsorption energy of PMS, and thus significantly improving the intrinsic activity of the catalyst.

[0029] Compared with the prior art, the beneficial effects of the present invention include: 1. Precise control of electronic structure was achieved: by breaking the symmetry of Co-N4 with iodine atoms, the reaction energy barrier in the PMS activation process was reduced (the rate-limiting step energy barrier was reduced to -0.84 eV), thereby improving intrinsic activity.

[0030] 2. Significantly enhanced mass transfer rate: Abundant mesoporous channels were constructed using a vapor-phase etching strategy, effectively solving the diffusion limitation problem in heterogeneous catalysis and maximizing the utilization efficiency of active sites.

[0031] 3. Exhibits excellent stability and anti-interference ability: because it is based on... 1 The system utilizes an O2-dominated non-radical pathway and is effective against common inorganic anions and cations (such as Cl). -1 SO4 2- Mg 2+ It exhibits strong tolerance to natural organic matter (HA) and remains stable within a pH range of 4.0 to 10.0. 4. It possesses excellent practical application potential: Experiments have demonstrated its efficient operation in actual river water, well water, and even seawater, and it can be applied in continuous flow membrane treatment devices, demonstrating its value for industrial-scale promotion. Attached Figure Description

[0032] Figure 1 The images show the XRD patterns of the catalysts prepared in Example 1 and Comparative Example 1.

[0033] Figure 2 This is a high-angle annular dark-field scanning transmission electron microscope (HADDF-STEM) image of the catalyst prepared in Example 1.

[0034] Figure 3 The image shows the EDS elemental distribution of the catalyst prepared in Example 1.

[0035] Figure 4 The above are BET diagrams of the catalysts prepared in Example 1 and Comparative Example 1.

[0036] Figure 5 The image shows the pore size distribution of the catalysts prepared in Example 1 and Comparative Example 1.

[0037] Figure 6 The adsorption kinetics of CIP on the catalysts prepared in Example 1 and Comparative Example 1 are shown.

[0038] Figure 7 XPS plots of the catalysts prepared in Example 1 and Comparative Example 1.

[0039] Figure 8 The images show the XPS high-resolution spectra of Co 2p in the catalysts prepared in Example 1 and Comparative Example 1.

[0040] Figure 9 The EPR spectra of the catalysts prepared in Example 1 and Comparative Example 1 are shown.

[0041] Figure 10 The catalysts prepared in Example 1 and Comparative Example 1 were used to test their performance in catalytic degradation of CIP.

[0042] Figure 11 The catalysts prepared in Example 1 and Comparative Example 2 were used to test their performance in catalytic degradation of CIP.

[0043] Figure 12 The catalysts prepared in Example 1 and Comparative Example 3 were used to test their performance in catalytic degradation of CIP.

[0044] Figure 13 The catalysts prepared in Example 1 and Comparative Example 1 were used in the PMS system to generate... 1 O2 concentration.

[0045] Figure 14 This is a test of the catalytic degradation performance of different antibiotic pollutants by the catalyst prepared in Example 1.

[0046] Figure 15 The effects of pH, coexisting ions, natural organic matter, and actual water body on the catalytic degradation performance of the catalyst prepared in Example 1 were tested.

[0047] Figure 16 This describes the continuous flow membrane system constructed in Example 1 and the results of its CIP process. Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solution of the present invention, a detailed description is provided below in conjunction with specific implementation examples and experimental data.

[0049] Unless otherwise specified, all raw materials and reagents involved in this invention are purchased through commercial channels.

[0050] Example 1: The entire process of preparing Co-INC catalyst 1) Synthesis of ZnCo-ZIF precursor: 45 mL of methanol was added to beaker 1 to dissolve 1.674 g Zn(NO3)2·6H2O and 0.1025 g Co(NO3)2·6H2O. Magnetic stirring was started, followed by sonication for 10 min to ensure complete dispersion of the metal ions. 30 mL of methanol was added to beaker 2 to dissolve 1.848 g 2-methylimidazole. Under vigorous stirring, the mixture from beaker 1 was rapidly poured into beaker 2 and sonicated for 10 min. The mixture was continuously stirred at 25 °C for 4 h. Subsequently, the suspension was centrifuged at high speed (10000 rpm, 3 min), and the purple precipitate was collected. The precipitate was washed three times with anhydrous methanol to remove unreacted ligands and impurities. Finally, the solid was dried in a vacuum drying oven at 70 °C for 12 h.

[0051] 2) Preparation of Co-NC substrate: The dried ZnCo-ZIF powder was evenly spread in a quartz boat and placed in the central isothermal zone of a horizontal tube furnace. After purging the air by introducing high-purity argon gas (flow rate 100 sccm), the temperature was programmed to increase at 5℃ / min. -1 The pyrolysis rate was increased to 900 °C and maintained at that temperature for 3 hours. During the pyrolysis process, zinc atoms volatilized in large quantities due to their low boiling point (907 °C), leaving highly dispersed cobalt single-atom sites in situ. After the reaction was completed, the furnace was allowed to cool naturally, and the resulting black powder was ground and labeled as Co-NC.

[0052] 3) CVD Modification of Co-INC: 100 mg of Co-NC powder was placed in the downstream high-temperature zone (850 °C) of a tube furnace, and 500 mg of NH4I powder was placed in the upstream low-pressure volatilization zone (temperature controlled at approximately 500-600 °C). Guided by an argon gas flow (80 sccm), the NH3 and iodine-containing vapors released by the thermal decomposition of NH4I reacted with Co-NC in the high-temperature zone. NH3 reacted with unstable parts of the carbon framework, producing microporous and mesoporous structures; while iodine atoms were anchored in the carbon network surrounding cobalt atoms through nucleophilic substitution or radical addition reactions. After cooling to room temperature, the product was removed to obtain the target catalyst Co-INC.

[0053] Comparative Example 1: A catalyst, the preparation method of which differs from that of Example 1, is that the NH4I CVD treatment in step 3) is omitted. That is, the black powder obtained in step 2) is used directly as the catalyst, denoted as Co-NC.

[0054] Comparative Example 2: A catalyst, the preparation method of which differs from that of Example 1, is provided in which the temperature of the downstream high-temperature zone in step 3) is set to 650°C and 750°C, respectively denoted as Co-INC-650 and Co-INC-750.

[0055] Comparative Example 3: A catalyst, the preparation method of which differs from that of Example 1, is that the NH4I used in step 3) is replaced with ammonium chloride and ammonium bromide, which are used as chlorine source and bromine source, respectively, and incorporated into Co-NC, and are denoted as Co-ClNC and Co-BrNC, respectively.

[0056] The XRD patterns of the catalysts prepared in Example 1 and Comparative Example 1 are shown below. Figure 1 As shown. Co-INC retains the graphite structure of the Co-NC matrix, characterized by typical (002) and (100) diffraction peaks at approximately 22 and 44. The absence of characteristic peaks for metallic cobalt indicates that the metal sintering process was suppressed and that cobalt existed in a highly dispersed state.

[0057] Figure 2 , Figure 3 The images shown are high-angle annular dark-field scanning transmission electron microscope (HADDF-STEM) images and EDS elemental distribution maps of the catalyst prepared in Example 1. Figure 2 Dense, bright single points were captured, and no signs of cobalt metal nanoparticles or clusters were found. This indicates that even at high loading levels, iodine doping and the NH3 etching process did not induce the aggregation of metal atoms. Figure 3 This further confirms the uniform distribution of Co, N, C, and I on the carbon substrate in Co-NC@TA.

[0058] Figure 4 , Figure 5 The BET curves and pore size distribution diagrams of the catalysts prepared in Example 1 and Comparative Example 1 are shown, respectively. The Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption isotherms and pore size distribution analysis results further confirm that the specific surface area of ​​Co-INC is significantly increased, and obvious mesoporous distribution peaks appear in the range of 3.5~5 nm, which provides a hardware basis for the mass transfer of macromolecules.

[0059] Figure 6 The adsorption kinetics of CIP by the catalysts prepared in Example 1 and Comparative Example 1 show that the mass transfer coefficient K of Co-INC to CIP is... f 831×10 -4 ms -1 The mass transfer efficiency is 2.3 times that of the Co-NC system, indicating that the CVD process significantly enhances the exposure of active sites and mass transfer efficiency, effectively solving the mass transfer bottleneck in heterogeneous catalysis.

[0060] Figure 7 In the XPS full spectrum of the catalysts prepared in Example 1 and Comparative Example 1, typical I characteristic peaks were observed, indicating that iodine had been successfully doped.

[0061] Figure 8 The Co 2p energy spectrum of the catalyst prepared in Example 1 showed that its binding energy shifted by ~0.3 eV compared to Co-NC. This is attributed to the greater electronegativity difference or coordination asymmetry of iodine atoms compared to nitrogen atoms, which led to the reconstruction of the charge distribution around the cobalt center.

[0062] Figure 9 In the EPR spectra of the catalysts prepared in Example 1 and Comparative Example 1, it can be clearly observed that in TEMP- 1 In the O2 system, the Co-INC activated PMS produced... 1 The O2 signal strength is much higher than that of Co-NC, indicating that it has higher efficiency. 1O2 production efficiency. The hollow structure of Co-INC provides more accessible active sites, enabling it to more efficiently activate PMS and produce high concentrations of O2 through disproportionation reactions. 1 O2, thereby achieving enhanced removal of pollutants such as CIP.

[0063] The application of this method will be tested below, taking into account the above embodiments and comparative examples.

[0064] Application Example 2: The carbon-based cobalt single-atom catalysts prepared in Example 1 (Co-INC) and Comparative Example 1 (Co-NC) were used to activate the PMS degradation performance of CIP. The specific experimental procedures are as follows: 1) All degradation reactions were carried out in 100 mL conical flasks, each containing 50 mL of CIP solution, with the initial concentration of CIP set at 20 mg L⁻¹.

[0065] 2) Weigh 2 mg of the Co-INC catalyst prepared in Example 1 and the Co-NC catalyst prepared in Comparative Example 1 respectively, and introduce them into the above CIP solution.

[0066] 3) Place the reaction system in the dark to eliminate photolysis interference, and add PMS (final concentration of 1 mM) to the solution under continuous mechanical stirring at 400 rpm to start the degradation reaction.

[0067] 4) At predetermined time intervals (i.e., 0 min, 0.5 min, 1 min, 1.5 min, 2 min, 3 min, 4 min, and 5 min after the start of the reaction), use a syringe to draw 0.5 mL of the reaction solution from the reaction system and quickly inject it into a centrifuge tube containing 1 mL of methanol for quenching to terminate the reaction.

[0068] 5) The quenched mixed solution was filtered through a polytetrafluoroethylene (PTFE) needle filter with a pore size of 0.45 μm. The residual concentration of CIP in the filtrate was determined using a high performance liquid chromatograph (HPLC, model LC-20 AT, Shimadzu Corporation) to calculate the degradation rate.

[0069] The experiment was repeated twice for all groups, and the average value was taken. The results are as follows: Figure 10 As shown. Figure 10The results show that the catalyst prepared in Example 1 can achieve approximately 100% degradation of CIP within 300 s. In contrast, Comparative Example 1 (Co-NC) without iodine treatment only achieved about 40% degradation of CIP in the same time period, which is significantly better than the pure PMS system and the Co3O4 nanoparticle system. This demonstrates the decisive role of NH4I modification in enhancing the catalytic activity of carbon-based cobalt single atoms. This indicates that the NH4I treatment in this invention may have optimized the coordination environment of the Co center, generating more abundant and easily accessible active sites, thus enabling the catalyst to activate PMS and produce... 1 O2's capabilities have been greatly enhanced. 1 O2 yield as follows Figure 13 As shown, the concentration is 0.295 mM, which is 2.4 times that of the original Co-NC system, thus macroscopically representing a qualitative change in degradation performance.

[0070] Application Example 3: The catalysts obtained in Example 1 (Co-INC-850) and Comparative Example 2 (Co-INC-650 and Co-INC-750) were used to activate the PMS degradation performance of CIP. The specific experimental process is as follows.

[0071] The difference between this application example and application example 2 is that the catalysts prepared in example 1 and comparative example 2 are tested. The results are as follows... Figure 11 As shown. Figure 11 The results show that 850 °C is the optimal temperature for CVD modification in this invention. The Co-INC catalyst prepared at this temperature achieves the best balance between high exposure of active sites and intrinsic activity activation, effectively transforming the smooth, dense carbon layer on the Co-NC surface into a mesoporous structure with high porosity. This maximizes the exposure and accessibility of active sites, exhibiting the best pollutant degradation kinetics. At lower temperatures (e.g., 650 °C and 750 °C), the etching effect of ammonia is weak, failing to generate sufficient pore structures, resulting in limited mass transfer rates. The doping efficiency of iodine atoms and the degree of distortion of the coordination field are also limited, making it difficult to effectively activate the intrinsic catalytic activity of cobalt sites, leading to the activation of PMS and the generation of singlet oxygen (…). 1 The efficiency of O2 decreases.

[0072] Application Example 4: The catalysts obtained in Example 1 (Co-INC) and Comparative Example 3 (Co-ClNC and Co-BrNC) were used to activate the performance of PMS in degrading CIP. The specific experimental process is as follows.

[0073] The difference between this application example and application example 2 is that the catalysts prepared in example 1 and comparative example 3 are tested. The results are as follows... Figure 12 As shown. Figure 12The results show that Co-INC prepared using NH4I as a dopant source exhibits significantly better degradation performance of CIP than Co-BrNC and Co-ClNC, almost completely removing CIP within 300 s; while the residual rates of Co-BrNC and Co-ClNC at 300 s are approximately 18% and 22%, respectively. Experimental results indicate that under the same CVD conditions, the type of dopant source has a decisive influence on the final catalyst activity, with the activity order being: Co-INC > Co-BrNC > Co-ClNC. This is mainly attributed to the differences in the physicochemical properties of halogen atoms: during high-temperature pyrolysis and carbonization, the larger iodine atoms, when escaping from the carbon lattice or intercalating between carbon layers, produce more significant lattice distortion and porosity expansion effects. Simultaneously, iodine has the lowest electronegativity, resulting in a relatively weaker ability to pull electrons from the central metal Co (or it is easier to act as an electron donor), which is more conducive to optimizing the electron density (d-band center) of the Co center, placing it in the optimal energy state for activating PMS molecules. In contrast, the more electronegative Cl and Br may result in an excessively low electron density at the Co center, which is not conducive to electron transfer to PMS and thus reduces the reactivity.

[0074] Application Example 5: The performance test of the catalyst obtained in Example 1 for catalytic degradation of different antibiotic pollutants is shown in the following results. Figure 14 As shown, Co-INC exhibits excellent removal efficiency for electron-rich organic pollutants (such as RhB, TC, CBZ, etc.), achieving almost 100% removal within 5 minutes. However, it shows a lower removal rate for electron-deficient pollutants, indicating that its production... 1 O2 has a high degree of selectivity.

[0075] Application Example 6: Environmental tolerance and stability tests of the catalyst obtained in Example 1 (1) Test of the catalytic degradation performance of the catalyst obtained in Example 1 on CIP under different initial pH values ​​of the reaction solution: The difference between this application example and application example 2 is that only the catalyst prepared in Example 1 was tested; the initial pH value of the reaction solution was adjusted to 4.1, 5.5, 7.0, 8.5, and 10.0 respectively using H2SO4 solution and NaOH solution, and then the catalyst and PMS were added. The results are as follows. Figure 15 The pH effect curve is shown in the figure. Figure 15The results showed that the catalyst exhibited excellent degradation performance of CIP within a wide pH range of 4.1 to 10.0, with a degradation rate reaching approximately 100% within 5 minutes. This indicates that the Co-INC catalytic system maintains extremely high catalytic activity under both strong acid and strong alkaline conditions, demonstrating excellent tolerance to solution pH levels and overcoming the strict pH limitations imposed by traditional Fenton-like technologies.

[0076] (2) Test on the effect of coexisting ions and natural organic matter on the catalytic degradation performance of the catalyst obtained in Example 1 for CIP: The difference between this application example and application example 2 is that only the catalyst prepared in Example 1 is tested; a certain amount of common inorganic anions (such as Cl-) are added to the reaction solution in advance. - NO3 - SO4 2- ), cations (such as K) + Ca 2+ Mg 2+ ) and natural organic matter (HA), to achieve concentrations of 5 mM and 10 mg L, respectively. -1 Then the degradation reaction is restarted. The results are as follows: Figure 15 As shown, typical anions and cations and high concentrations of humic acid (HA) have almost no hindering effect on the CIP removal performance of the Co-INC / PMS system, demonstrating that the catalyst has extremely strong chemoselectivity and anti-interference ability in the non-radical-dominated reaction pathway.

[0077] (3) Testing the performance of the catalyst obtained in Example 1 in natural water bodies for catalytic degradation of CIP: The difference between this application example and application example 2 is that the reaction solution does not use deionized water, but is prepared using seawater, river water, and well water collected from the actual environment, respectively. The results are as follows: Figure 15 As shown, although the degradation rate of this catalyst fluctuates slightly in various natural water bodies with complex compositions, the final degradation performance is good, indicating that this catalyst has broad application potential in treating actual environmental wastewater.

[0078] (4) Cyclic stability and metal leaching test of the catalyst obtained in Example 1: To examine the reusability of the catalyst, the catalyst after reaction was recovered by centrifugation, washed and dried, and then subjected to a cyclic degradation test under the same conditions. The results are as follows: Figure 13 As shown in the cycling curves, after five cycles, the catalyst maintained a CIP removal rate of over 95%, with no significant decrease in catalytic activity. Simultaneously, ICP-OES analysis of the cobalt ion concentration in the post-reaction solution revealed extremely low Co leaching levels, far below national emission standards, demonstrating the exceptionally high chemical structural stability of the single-atom centers modified with NH4I.

[0079] Application Example 7: Application of Continuous Flow Membrane Systems Figure 16 The results of treating CIP using the continuous flow membrane system constructed in Example 1 are shown. During 12 hours of continuous operation, the CIP degradation rate remained consistently at ~100%, and the TOC removal rate remained stable. Simultaneously, the leaching concentration of the active metal Co was extremely low, far below the environmental safety threshold, demonstrating the practical application potential of this catalyst in industrial wastewater treatment.

[0080] Parts not described in detail in this invention can be implemented by referring to existing technologies. The above-described facts are merely illustrative of the invention and are not intended to limit it. Any modifications and alterations made to the above embodiments within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a single-atom-site catalyst, characterized in that, Includes the following steps: S1. Prepare ZnCo-ZIF precursor powder with zeolite imidazole framework. S2. The zeolite imidazole framework ZnCo-ZIF precursor powder from step S1 is heat-treated under an inert atmosphere and then ground to obtain carbon-supported cobalt single-atom substrate material Co-NC. S3. Using chemical vapor deposition, the carbon-supported cobalt single-atom substrate material Co-NC obtained in step S2 is placed in the center of a tube furnace, and NH4I powder is placed upstream of the tube furnace. Under the influence of an inert atmosphere, NH3 generated from the decomposition of NH4I is used to etch Co-NC in situ, and iodine atoms are simultaneously introduced to form an asymmetric coordination structure with the cobalt active sites to obtain the Co-INC catalyst.

2. The preparation method according to claim 1, characterized in that, In step S3, the reaction temperature of the chemical vapor deposition method is 500~1000 ℃, and the reaction time is 2~4 h.

3. The preparation method according to claim 2, characterized in that, In step S3, the carbon-supported cobalt single-atom substrate material Co-NC obtained in S2 is placed in the high-temperature zone of a tube furnace, the temperature range of which is 800~900 ℃, and the NH4I powder is placed in the low-temperature volatilization zone, the temperature range of which is 500-600 ℃.

4. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of carbon-supported cobalt single-atom substrate material Co-NC to NH4I powder is 1:(1~20), preferably 1:(5~20).

5. The preparation method according to claim 1, characterized in that, In step S2, the heat treatment temperature is 850~950 ℃, and the heating rate is 5~10 ℃ min. -1 The retention time is 2-4 hours.

6. A single-atom-site catalyst, characterized in that, The catalyst is Co-N4 / Cl, with a cobalt active site density of 0.15–0.18 mmol g. -1 The d-band center of Co is -0.6 to -0.4 eV, and the catalyst exhibits a significant mesoporous distribution in the range of 3.5 to 5 nm.

7. The application of a single-atom-site catalyst prepared by the method according to claim 6 or any one of claims 1-5 in the degradation of organic pollutants, characterized in that: The catalyst and PMS are added together to wastewater containing organic pollutants, and the PMS is catalytically activated to produce... 1 O2 helps degrade pollutants.

8. The application according to claim 7, characterized in that: The organic pollutant is selected from one or more of CIP, sulfamethoxazole, carbamazepine, phenol, tetracycline, and p-chlorophenol; the catalyst dosage is 0.02~0.05 g / L. -1 The concentration of PMS was 0.5~2.0 mM.

9. The application according to claim 7, characterized in that: The pH value of the wastewater containing organic pollutants is 4.0~10.

0.

10. The application according to claim 7, characterized in that: The application is achieved by constructing a continuous water purification device, in which a catalyst is loaded onto a PVDF membrane substrate to form a catalytic filter membrane, and pollutant-containing wastewater is continuously and deeply purified by passing through the filter membrane under pressure.

Images