A cobalt-oxygen co-doped modified graphite phase carbon nitride catalyst, a preparation method and application thereof

Abstract

The application discloses a cobalt-oxygen co-doped modified graphite phase carbon nitride catalyst, a preparation method and application thereof, and relates to the technical field of catalysts. The preparation method is as follows: polyvinylpyrrolidone, 2-methylimidazole and cobalt nitrate hexahydrate are mixed and wet ball-milled to obtain a Co imidazole coordination compound; the Co imidazole coordination compound is mixed with melamine and then ground, the mixture is mixed with oxalic acid dihydrate and then ground and dissolved, and after dispersion treatment, centrifugal separation, washing, drying, grinding, sieving and anaerobic calcination, the product is cooled, washed, dried, ground and sieved. The O atom doping in the obtained catalyst destroys the ordered stacking layered structure of g-C3N4, so that the carbon nitride has a larger specific surface area, more active sites can be exposed, the catalytic activity of the peroxymonosulfate is enhanced, and the degradation efficiency of organic pollutants in water is improved. The preparation method is simple in operation, low in cost and suitable for popularization and application in industry.

Description

Technical Field

[0001] This invention relates to a cobalt-oxygen co-doped modified graphite-phase carbon nitride catalyst, its preparation method, and its application, belonging to the field of water pollution control technology. Background Technology

[0002] Atrazine (ATZ) is a triazine selective herbicide widely used for weed control in fields of crops such as corn and sorghum. Due to the stable chlorotriazine heterocycle in its molecular structure, ATZ exhibits high chemical stability and resistance to biodegradation in natural water bodies, but also has a long half-life, easily persisting in the environment through surface runoff and groundwater infiltration. Studies have shown that ATZ and its main metabolites possess endocrine-disrupting activity and potential ecotoxicity, posing a serious threat to human health and the ecological environment. The European Union has included ATZ in its list of restricted substances for drinking water quality. Therefore, developing efficient and economical ATZ removal technologies from water bodies is of significant practical importance.

[0003] Advanced oxidation processes (AOPs) are currently one of the mainstream technologies for treating recalcitrant organic pollutants. They rapidly oxidize, degrade, and even mineralize organic pollutants by generating reactive oxygen species with high redox potentials, offering advantages such as fast reaction rates and thorough degradation. Persulfate-activated advanced oxidation technology (PMS) has become a research hotspot in water pollution control due to its high oxidation efficiency, wide pH adaptability, and ease of operation. PMS requires catalyst activation to generate reactive species such as sulfate radicals and hydroxyl radicals; therefore, designing efficient and stable PMS activation catalysts is crucial for the practical application of PMS-AOP technology.

[0004] Graphitic carbon nitride (g-C3N4) is a non-metallic polymer semiconductor material with advantages such as simple preparation process, wide availability of raw materials, good thermochemical stability, and abundant nitrogen coordination sites, avoiding the risk of secondary metal pollution that may be caused by traditional metal-based catalysts. However, pure g-C3N4 has inherent defects such as small specific surface area, low active site density, and poor electron transport capability, resulting in low activation efficiency of PMS when used alone, which is difficult to meet the needs of practical water treatment.

[0005] To improve the catalytic performance of g-C3N4, existing technologies have explored various modification strategies, including heteroatom doping, morphology control, defect engineering, and single-atom loading. For example, Chinese patent document CN113101963A discloses a method for preparing ultrathin phosphorus-doped carbon nitride nanosheets, which enhances the photocatalytic activity of carbon nitride by introducing phosphorus heteroatoms. However, this technology is mainly aimed at photocatalytic systems and has limited applicability to PMS-activated degradation of pesticide pollutants. Single-atom catalysis technology can maximize the exposure and utilization of active sites at the atomic scale. Due to its high affinity for PMS and moderate redox potential, the transition metal cobalt (Co) is considered one of the most promising active elements in PMS activation. Anchoring Co in single-atom form within the g-C3N4 framework can effectively inhibit metal aggregation and leaching while maintaining high catalytic activity. However, the catalytic activity of Co-doped graphitic carbon nitride catalysts in activating PMS to degrade ATZ in water remains limited. Summary of the Invention

[0006] The purpose of this invention is to provide a cobalt-oxygen co-doped modified graphitic carbon nitride catalyst, its preparation method and its application. This catalyst has high degradation efficiency for organic pollutants in water, providing a new approach for its practical application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a cobalt-oxygen co-doped modified graphite-phase carbon nitride catalyst includes the following steps:

[0009] S1. Polyvinylpyrrolidone, 2-methylimidazole and cobalt nitrate hexahydrate were mixed and wet-milled, then centrifuged, washed, dried and ground and sieved to obtain Co-imidazole coordination compound;

[0010] S2. Mix the Co-imidazolium coordination compound with melamine and grind them. Then mix the mixture with oxalic acid dihydrate, grind and dissolve it. After dispersion treatment, centrifuge, wash, dry, grind and sieve, and calcine in an oxygen-free environment. The calcined product is then cooled, washed, dried, ground and sieved.

[0011] Preferably, in step S1, the mass ratio of polyvinylpyrrolidone, 2-methylimidazolium, and cobalt nitrate hexahydrate is (3-5):(3-5):(2-4).

[0012] Preferably, in step S1, the rotation speed of the wet ball mill is 300-500 rpm, and the ball milling time is 1-3 hours.

[0013] Preferably, in step S1, the drying conditions are: under vacuum, 60-80°C, for 20-30 hours.

[0014] Preferably, the mass content of the Co-imidazolium coordination compound in the mixture of step S2 is 50-70%.

[0015] Preferably, in step S2, the mass ratio of the mixture to oxalic acid dihydrate is 1:(0.6-0.9).

[0016] Preferably, in step S2, the conditions for anaerobic calcination are: 450-550℃, 5-8h.

[0017] A cobalt-oxygen co-doped modified graphitic carbon nitride catalyst is prepared by any of the methods described above.

[0018] Application of catalysts prepared by any of the above methods in the degradation of organic pollutants in water by activated PMS.

[0019] Preferably, the organic pollutant is ATZ at a concentration of 3-8 ppm; the catalyst dosage is 0.4-0.8 g / L, the PMS dosage is 0.2-0.4 g / L, and the water pH is 7-8; and NO3 is added to the water. - and SO4 2- Afterwards, the degradation efficiency is improved.

[0020] The beneficial effects of this invention are as follows:

[0021] Doping and modification with single Co atoms does not alter the framework structure of carbon nitride, but doping with O atoms disrupts the ordered stacked layered structure of g-C3N4, resulting in a larger specific surface area for carbon nitride. This exposes more active sites, enhancing its catalytic activity against persulfate and thus improving the degradation efficiency of organic pollutants in water. Furthermore, the preparation method is simple, low-cost, and suitable for industrial-scale promotion and application. Attached Figure Description

[0022] Figure 1 Aberration-corrected electron micrograph of 1:0.7 Co-Og-C3N4;

[0023] Figure 2 XRD diffraction patterns of original graphitic carbon nitride, cobalt-doped graphitic carbon nitride, and cobalt and oxygen co-doped graphitic carbon nitride.

[0024] Figure 3 Infrared spectra of original graphitic carbon nitride, cobalt-doped graphitic carbon nitride, and cobalt and oxygen co-doped graphitic carbon nitride.

[0025] Figure 4 XPS spectra of 1:0.7 Co-Og-C3N4: (a) overall spectrum; (b) Co2p spectrum; (c) C1s spectrum; (d) N1s spectrum; (e) O1s spectrum;

[0026] Figure 5 The degradation rate curves of ATZ catalytic degradation were shown for original graphitic carbon nitride and cobalt-oxygen co-doped graphitic carbon nitride with different cobalt and oxygen atom ratios.

[0027] Figure 6 The degradation rate curves of ATZ catalytic degradation by 1:0.7 Co-Og-C3N4 under different catalyst dosages are shown.

[0028] Figure 7 The degradation rate curves of ATZ catalytically degraded by 1:0.7 Co-Og-C3N4 at different PMS concentrations are shown.

[0029] Figure 8 The degradation rate curves of ATZ catalyzed by 1:0.7 Co-Og-C3N4 at different pH values ​​are shown.

[0030] Figure 9 The graph shows the degradation rate curve of ATZ catalytically degraded by 1:0.7 Co-Og-C3N4 under optimal conditions.

[0031] Figure 10 The effect of 1:0.7 Co-Og-C3N4 activating persulfate to degrade ATZ under the interference of coexisting anions is shown in the figure.

[0032] Figure 11 Degradation diagram of 1:0.7 Co-Og-C3N4 under different pollutants;

[0033] Figure 12 The figure shows a 6-cycle experiment of ATZ degradation by 1:0.7 Co-Og-C3N4;

[0034] Figure 13 The figure shows a continuous flow experiment of ATZ degradation by 1:0.7 Co-Og-C3N4. Detailed Implementation

[0035] To better understand the present invention, preferred embodiments are described below with reference to specific examples. It should be understood that these descriptions are only for further illustrating the features and advantages of the present invention and are not intended to limit the scope of the claims.

[0036] The sources of the raw materials used in this invention are not particularly limited and can all be obtained commercially or prepared according to conventional methods in the field.

[0037] There are no particular limitations on the purity of the raw materials used in this invention, but it is preferred to use analytical grade or purity grades commonly used in the field of catalyst preparation.

[0038] Example 1

[0039] The preparation of pristine graphitic carbon nitride follows these steps:

[0040] 10g of melamine was weighed and placed in a tube furnace, heated to 600℃ at a heating rate of 3℃ / min, and calcined at this temperature in an oxygen-free environment for 3 hours. During calcination, the nitrogen flow rate was controlled at 25mL / min to maintain a stable oxygen-free environment. After calcination, the tube furnace was allowed to cool naturally to room temperature. The product was then removed, ground, and sieved to obtain g-C3N4 solid powder.

[0041] The preparation of cobalt single-atom carbon nitride follows these steps:

[0042] Weigh 4.3200g of polyvinylpyrrolidone K30, 4.7200g of 2-methylimidazole, and 3.4911g of cobalt nitrate hexahydrate. Add the above-mentioned medicine bottle to an agate jar, then add 12ml of methanol and a certain amount of zirconium oxide, mix, and ball mill at 480rpm for 2h. Then centrifuge at 8000r for 5min, wash 2-3 times with ethanol, dry under vacuum at 70℃ for 24h, and grind through a 60-mesh sieve to obtain the imidazole coordination compound of Co, denoted as Co-ICC. Grind and mix Co-ICC with melamine at proportions of 20%, 40%, 60%, and 80% of the total mass (quantitative), respectively, calcine at 500°C in an oxygen-free environment for 6h, cool to room temperature, dry, grind, and pass through a 60-mesh sieve to obtain Co-g-C3N4 with different cobalt contents.

[0043] The preparation steps of oxygen-doped cobalt single-atom carbon nitride are as follows:

[0044] Co-ICC and melamine were thoroughly ground and mixed at a mass ratio of 3:2. This mixture was then further ground and mixed with oxalic acid dihydrate at mass ratios of 1:1, 1:0.7, 1:0.5, 1:0.3, and 1:0.1, respectively. The mixed powder was dissolved in n-hexane, sonicated for 1 hour and stirred continuously for 2 hours. The mixed solution was then centrifuged at 8000 rpm for 5 minutes and washed 2-3 times with ethanol. It was then placed in a vacuum drying oven at 70°C and dried for more than 8 hours. The mixture was then ground through a 60-mesh sieve and calcined at 500°C in an oxygen-free environment for 6 hours. After cooling to room temperature, it was washed, dried, ground, and sieved to obtain a series of Co-Og-C3N4 with different O doping amounts.

[0045] The prepared 1:0.7 Co-Og-C3N4 was subjected to spherical aberration electron microscopy analysis, see [reference needed]. Figure 1In low-magnification HAADF-STEM images (20 nm and 5 nm scale bars), the catalyst exhibits a typical two-dimensional lamellar structure with no obvious large particles or clusters on the surface. Further magnification to a high-magnification 2 nm scale bar in the HAADF-STEM image clearly reveals numerous highly dispersed bright spots, corresponding to Co single atoms with higher atomic numbers. This indicates that Co is uniformly dispersed in single-atom form on the g-C3N4 substrate without agglomeration. The elemental distribution of the catalyst was analyzed using energy dispersive spectroscopy (EDS-mapping). Figure 1 As shown, the four elements C, N, O, and Co are uniformly distributed throughout the scanning area. C and N constitute the basic framework of g-C3N4, O is uniformly doped into the substrate, and Co is atomically dispersed, further confirming the successful loading of Co single atoms and the uniform doping of O. In summary, the aberration-corrected electron microscopy and elemental surface scanning results indicate that in the Co-Og-C3N4 catalyst prepared in this invention, Co is anchored in the g-C3N4 framework in the form of single atoms, and O is uniformly doped, with no significant agglomeration or segregation observed in either element.

[0046] Figure 2 The images show the XRD diffraction patterns of the prepared original graphitic carbon nitride, cobalt single-atom-doped graphitic carbon nitride, and oxygen-doped cobalt single-atom-doped graphitic carbon nitride. From... Figure 2 It can be seen that the characteristic diffraction peaks of g-C3N4 at 2θ of 12.9° and 27.6° match the macrocyclic structure and the characteristic peaks of aromatic interlayer stacking in the 3S-triazine structure, respectively. The formation of the characteristic diffraction peaks of g-C3N4 at 2θ of 12.9° and 27.6° indicates that g-C3N4 has a graphite-like layered stacking with π-conjugated planes. With the addition of Co, the diffraction peak intensity of the Co-g-C3N4 sample at 27.6° is significantly lower than that of g-C3N4. Furthermore, with the addition of O, the diffraction peak intensity of the Co-Og-C3N4 sample at 27.6° is further weakened, and the peak shape shows a significant broadening. This is because oxalic acid dihydrate, as an O single atom, is added to the ball mill jar to prepare the precursor, and then undergoes a pyrolysis reaction with melamine as a catalyst, which destroys the ordered stacked layered structure of g-C3N4. No new diffraction peaks related to Co were found in Co-g-C3N4 and Co-Og-C3N4 materials, indicating that the addition of Co did not form cobalt oxide or other configurations, nor did it change the crystal characteristics of the original g-C3N4.

[0047] Infrared spectroscopy was performed on the prepared pristine graphitic carbon nitride, doped graphitic carbon nitride, and cobalt-oxygen co-doped graphitic carbon nitride. (See also...) Figure 3 As shown, the FT-IR absorption peak of g-C3N4 is mainly concentrated at 800 cm⁻¹. -11200-1650 cm -1 and 3100-3500 cm -1 Location. Among them, located at 800 cm -1 The nearby absorption peaks correspond to the characteristic bending vibrations of the triazine ring; 1200-1650 cm⁻¹ -1 The absorption peaks within the range correspond to the stretching vibrations of the CN heterocycle; 3100-3500 cm⁻¹ -1 The broad absorption peaks within the range correspond to the stretching vibrations of NH2 or NH groups and the OH stretching vibrations of physically adsorbed water. Compared with g-C3N4, the characteristic absorption peak positions of Co-g-C3N4 and Co-Og-C3N4 samples did not shift significantly, indicating that the doping of Co single atoms and the co-doping of O atoms did not disrupt the basic chemical framework structure of g-C3N4. However, in the Co-Og-C3N4 sample, the 1200-1650 cm⁻¹ peaks... -1 The absorption peak intensities within the range showed some variation, and some peak shapes broadened slightly. This may be due to the introduction of O atoms forming CO bonds in the g-C3N4 framework, while also perturbing the CN heterocyclic structure. Furthermore, the absorption peak intensities of the three samples at 800 cm⁻¹... -1 The characteristic peaks of the triazine ring at the xylene ring were well preserved, indicating that the basic triazine ring structure of g-C3N4 was retained during the doping process. FT-IR characterization results showed that the successful introduction of Co single atoms and O atoms did not change the basic framework structure of g-C3N4, but the doping of O atoms caused some perturbation to the CN heterocyclic structure, which is consistent with the result of reduced layered order observed in XRD characterization.

[0048] The prepared Co-Og-C3N4 catalyst was characterized by X-ray photoelectron spectroscopy. Full spectrum scan results. Figure 4 As shown in region a, the sample mainly contains four elements: C, N, O, and Co, which is consistent with the results of energy dispersive spectroscopy (EDS). Figure 4 The middle b region shows the high-resolution XPS spectrum of Co 2p, with two characteristic peaks at binding energies of approximately 780.0 eV and 795.0 eV, corresponding to the spin-orbit splitting peaks of Co 2p3 / 2 and Co 2p1 / 2, respectively. The Co 2p3 / 2 peak can be fitted to two sub-peaks at 780.0 eV and 781.5 eV, belonging to Co(III) and Co(II) species, respectively. Furthermore, a distinct satellite peak was observed at 786.0 eV, further confirming the presence of Co. Notably, the characteristic peak of metallic Co at a binding energy of approximately 778.0 eV was not detected, indicating that Co exists in its oxidized form. Combined with XRD and aberration-corrected electron microscopy results, Co is dispersed as single atoms within the g-C3N4 framework. Figure 4The middle c region shows the high-resolution XPS spectrum of the catalyst's C1s phase. As shown in the figure, the C1s spectrum can be fitted with three characteristic peaks. The characteristic peak at 284.8 eV belongs to the CC / C=C bond, corresponding to the sp2 hybrid carbon in the graphitized carbon framework; the characteristic peak at 286.4 eV belongs to the CO bond, indicating that oxygen atoms have been successfully doped into the g-C3N4 structure, forming a carbon-oxygen bond; the characteristic peak at 288.5 eV belongs to the NC=N structure, which is the characteristic carbon species of the triazine ring in g-C3N4, originating from the polymerization of melamine during calcination. No characteristic peaks belonging to cobalt carbide (Co-C) were observed in the C1s spectrum, further confirming that Co coordinates with N in a single-atom form rather than forming a carbide. Figure 4 The middle d region shows the high-resolution XPS spectrum of N1s. The N1s spectrum can be fitted to three sub-peaks at approximately 398.5 eV, 399.5 eV, and 401.0 eV, corresponding to pyridine N, Co-N coordination bonds, and graphitic N, respectively. The presence of the Co-N characteristic peak indicates that the Co atom has formed a coordination bond with the N atom in the g-C3N4 framework, achieving stable anchoring of the Co single atom. Figure 4 The middle e region shows the high-resolution XPS spectrum of O1s. The O1s spectrum can be fitted to two characteristic peaks at approximately 531.5 eV and 533.0 eV, which are attributed to the Co-O bond and the CO / C=O bond, respectively, indicating that O atoms have been successfully doped into the g-C3N4 structure. XPS characterization results show that Co is anchored in the g-C3N4 framework in single-atom form through Co-N coordination bonds, and O atoms have been successfully doped into the g-C3N4 structure, thus successfully preparing the Co-Og-C3N4 catalyst.

[0049] Example 2

[0050] The original graphitic carbon nitride, cobalt-doped graphitic carbon nitride, cobalt and oxygen co-doped graphitic carbon nitride, and cobalt and oxygen co-doped graphitic carbon nitride prepared in Example 1 were applied to activate persulfate degradation of ATZ in water.

[0051] First, prepare an ATZ aqueous solution with a concentration of 5 ppm. Add 40 mg of the catalyst prepared in Example 1 to 100 mL of ATZ aqueous solution and stir magnetically for 30 min to reach adsorption / desorption equilibrium.

[0052] After reaching adsorption-desorption equilibrium, 1 mL of the solution was taken and marked as point 0. After the timing started, 30 mg of PMS was added to the ATZ aqueous solution to carry out the reaction. With continuous stirring, 1 mL samples were taken at times of 0, 0.5, 1, 1.5, 2, 2.5, 3, and 5 min. After stopping the reaction in the sample by adding 0.5 mL of methanol solution, the sample was filtered through a 0.22 μm aqueous filter membrane. The concentration of the target pollutant ATZ in the sample was determined by Agilent high-performance liquid chromatography, and the degradation rate was calculated.

[0053] Figure 5 This is a graph showing the degradation rate of ATZ by catalytic degradation of the original graphitic carbon nitride, cobalt-doped graphitic carbon nitride, and cobalt and oxygen co-doped graphitic carbon nitride prepared in Example 1. Figure 5 The experimental data shows that cobalt-doped graphitic carbon nitride with 60% cobalt doping exhibits better degradation performance, reaching 88.47% within 5 minutes. Furthermore, cobalt-oxygen co-doped graphitic carbon nitride with a 1:0.7 oxygen doping ratio demonstrates even better performance, achieving a degradation rate of 96.20% within 3 minutes. This is because oxygen doping disrupts the ordered layered stacking structure of g-C3N4, increasing the specific surface area of ​​the catalyst and exposing more active sites, which is beneficial for the adsorption and activation of PMS molecules on the catalyst surface. Simultaneously, the introduction of oxygen atoms can regulate the electronic structure around Co single atoms, enhancing the stability of the Co-N coordination bond and promoting electron transfer between Co active sites and PMS, thereby accelerating the generation of active free radicals and improving the degradation rate and efficiency of ATZ. However, excessive O (1:1 oxygen doping ratio) doping can lead to excessive disruption of the layered stacking structure of g-C3N4, affecting the overall stability and electron transport performance of the material. Furthermore, excessive structural defects result in an overly loose catalyst surface, which in turn hinders the adsorption and diffusion of PMS and ATZ on the catalyst surface. Meanwhile, excessive O will excessively interfere with the coordination environment of Co, forming too many Co-O coordination bonds, weakening the key Co-N active centers, and thus reducing the activation efficiency of PMS. Therefore, cobalt and oxygen co-doped graphitic carbon nitride with a doping ratio of 1:0.7 has the best effect on the degradation of ATZ.

[0054] Example 3

[0055] To determine the effect of catalyst dosage on catalyst performance and to determine the optimal catalyst concentration, only the catalyst concentration was changed, while other reaction conditions remained the same as in Example 2.

[0056] The catalyst concentrations were set to 0 g / L, 0.3 g / L, 0.5 g / L, 1 g / L, and 2 g / L. Adsorption and degradation experiments were conducted in the manner of catalyst performance experiments, and then the peak area was measured.

[0057] Figure 6The degradation rate curves of ATZ by 1:0.7 Co-Og-C3N4 prepared in Example 1 under different catalyst dosages are shown in the figure. As can be seen from the figure, the degradation efficiency of ATZ gradually increases with the catalyst dosage increasing from 0.3 g / L to 0.5 g / L, reaching a high degradation rate of 99.34% at a concentration of 0.5 g / L. When the catalyst dosage is 1 g / L, the degradation rate of ATZ decreases to approximately 93.50% within 5 minutes of reaction; when the dosage increases to 2 g / L, the degradation rate decreases to approximately 29.73%. This is because when the catalyst dosage increases from 0.3 g / L to 0.5 g / L, the number of active sites in the system increases, leading to an increase in the generation of active free radicals, thus increasing the degradation efficiency to 99.34%. However, when the dosage was increased to 1 g / L and 2 g / L, the excess catalyst caused particle agglomeration and reduced the effective active sites. At the same time, the excess free radicals underwent self-quenching reactions, resulting in a decrease in utilization. In addition, PMS was relatively insufficient and could not be fully utilized, so the degradation rate actually decreased to 93.50% and 29.73%.

[0058] Example 4

[0059] To determine the effect of oxidant (PMS) dosage on catalyst performance and to determine the optimal oxidant concentration, only the oxidant concentration was changed, while other reaction conditions remained the same as in Example 2.

[0060] The oxidant concentrations were set to 0 g / L, 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.5 g / L, and 1 g / L. Adsorption degradation experiments were conducted using the catalyst performance experiment method, and then the peak area was measured.

[0061] Figure 7 The graph shows the degradation rate curves of ATZ catalytically degraded by 1:0.7 Co-Og-C3N4 prepared in Example 1 under different oxidant dosages. As can be seen from the graph, the degradation rate is positively correlated with the concentration of PMS; the higher the PMS concentration, the more active free radicals are generated by the catalyst activating PMS, resulting in a faster generation rate and thus a faster degradation rate. At a PMS concentration of 1 g / L, the degradation rate reached 99.92% in 0.5 min. However, considering economic efficiency and practical operation, a PMS concentration of 0.3 g / L was selected.

[0062] Example 5

[0063] To determine the effect of the initial pH of the solution on the catalyst performance and to provide the optimal pH conditions, only the initial pH of the solution was changed, while other reaction conditions remained the same as in Example 2.

[0064] The pH values ​​were set to 5, 7, and 9, and the adsorption degradation experiment was conducted in the manner of a catalyst performance experiment. Then, the peak area was measured.

[0065] Figure 8 The graph shows the degradation rate curves of ATZ catalytically degraded by 1:0.7 Co-Og-C3N4 prepared in Example 1 at different pH values. As can be seen from the graph, when pH=5, the degradation rate of ATZ reaches 50.52% within 7 min; when pH=7, the degradation rate is approximately 97.11%; and when pH=9, the degradation rate is only 90.56%. This is because, under near-neutral conditions (pH=7), the electrostatic adsorption between the catalyst surface charge and PMS is optimal, allowing the catalytic activity of the Co single-atom active sites to be fully utilized, which is beneficial for the efficient generation of active free radicals such as SO4-· and ·OH. When pH=5, the excessive acidity leads to excessive protonation of the catalyst surface, inhibiting the adsorption and activation of PMS. Simultaneously, some Co active sites may dissolve under strong acid conditions, reducing catalytic efficiency. When pH=9, under alkaline conditions, SO4-· readily reacts with OH- to generate ·OH with a lower oxidation potential, and quenching occurs between free radicals, resulting in a slight decrease in degradation efficiency. Therefore, pH=7 is preferred as the optimal reaction condition.

[0066] Example 6

[0067] Based on the optimal catalyst and optimal reaction conditions determined in Examples 2, 3, 4, and 5, experiments were conducted under the conditions of a 1:0.7 cobalt-oxygen catalyst, an oxidant concentration of 0.3 g / L, a catalyst concentration of 0.5 g / L, and a neutral environment with pH=7, and then tests were performed.

[0068] Figure 9 The degradation rate curve of ATZ catalytically degraded by 1:0.7 Co-Og-C3N4 prepared in Example 1 under optimal conditions is shown. Figure 9 It can be seen that under optimal conditions, the degradation efficiency of ATZ by 1:0.7 Co-Og-C3N4 is as high as 99.99%.

[0069] Example 7

[0070] To verify the effect of different anions on the degree of inhibition of ATZ degradation efficiency, an experiment was conducted under the conditions of Example 6, followed by testing.

[0071] Figure 10 The graph shows the degradation effect of ATZ by 1:0.7 Co-Og-C3N4 prepared in Example 1 on activated persulfate under the interference of coexisting anions. As can be seen from the graph, the catalyst exhibits the best degradation performance when no interfering anions are present in the reaction system (Blank group). The addition of HCO3... - Afterwards, the degradation efficiency was significantly inhibited; with the addition of Cl - Post-degradation efficiency was slightly inhibited; the addition of NO3- Afterwards, the degradation efficiency was slightly promoted; the addition of SO4 2- Subsequently, the degradation efficiency was moderately improved.

[0072] Example 8

[0073] To investigate the degradation ability of the prepared Co-Og-C3N4 catalyst for different organic pollutants, under the experimental conditions of Example 6, eight typical organic pollutants, namely bisphenol A (BPA), tetracycline (TC), rhodamine B (RhB), acetaminophen (IP), sulfamethoxazole (SMX), p-nitrophenol (PN), atrazine (ATZ), and indole, were selected as target substrates for catalytic activation PMS degradation experiments.

[0074] See Figure 11 As shown in the figure, the catalyst exhibits good degradation performance for all tested organic pollutants. It shows the best degradation effect on ATZ and indole, achieving rapid removal even in the initial stage of the reaction. It also demonstrates high degradation efficiency for BPA, TC, RhB (represented as RB in the figure), IP, SMX, and PN, all achieving ideal removal rates in a short time.

[0075] Example 9

[0076] To evaluate the reusability and long-term stability of the Co-Og-C3N4 catalyst, six cycles of degradation experiments were conducted under the experimental conditions of Example 6.

[0077] See Figure 12 As shown in the figure, the catalyst exhibited the best degradation performance in the first cycle, with the degradation rate of ATZ approaching 100% within a short reaction time. The degradation efficiency decreased slightly in the second cycle. From the third to the sixth cycle, the degradation efficiency further decreased, but in the sixth cycle, the degradation rate of ATZ remained as high as 96.98%.

[0078] Example 10

[0079] To investigate the long-term operational stability and practical application potential of the Co-Og-C3N4 catalyst in a continuous flow reaction system, the catalyst was filled into a continuous flow reactor under the optimal experimental conditions of Example 6, and its degradation performance on ATZ during long-term operation was examined.

[0080] Figure 13The graph shows the ATZ degradation rate curve of the 1:0.7 Co-Og-C3N4 catalyst prepared in Example 1 after 12 h of operation in a continuous flow reactor. As can be seen from the graph, the Blank group (PMS alone, without catalyst) showed an ATZ degradation rate of only about 10% during the reaction, indicating that PMS alone cannot effectively degrade ATZ. After adding the Co-Og-C3N4 catalyst, the ATZ degradation rate remained stable at around 98% throughout 12 h of continuous operation, without significant decrease. This indicates that the catalyst has good mechanical strength and erosion resistance, making it suitable for continuous flow processes in practical water treatment.

Claims

1. A method for preparing a cobalt-oxygen co-doped modified graphite-phase carbon nitride catalyst, characterized in that, Includes the following steps: S1. Polyvinylpyrrolidone, 2-methylimidazole and cobalt nitrate hexahydrate were mixed and wet-milled, then centrifuged, washed, dried and ground and sieved to obtain Co-imidazole coordination compound; S2. The Co-imidazolium coordination compound was mixed with melamine and ground. The mixture was then mixed with oxalic acid dihydrate, ground and dissolved. After dispersion treatment, it was centrifuged, washed, dried, ground and sieved, and then calcined in an oxygen-free environment. The product from anaerobic calcination is then cooled, washed, dried, ground, and sieved.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of polyvinylpyrrolidone, 2-methylimidazolium, and cobalt nitrate hexahydrate is (3-5):(3-5):(2-4).

3. The preparation method according to claim 1, characterized in that, In step S1, the wet ball milling speed is 300-500 rpm, and the milling time is 1-3 hours.

4. The preparation method according to claim 1, characterized in that, In step S1, the drying conditions are: under vacuum, 60-80℃, for 20-30 hours.

5. The preparation method according to claim 1, characterized in that, In the mixture of step S2, the mass content of the Co-imidazolium coordination compound is 50-70%.

6. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of the mixture to oxalic acid dihydrate is 1:(0.6-0.9).

7. The preparation method according to claim 1, characterized in that, In step S2, the conditions for anaerobic calcination are: 450-550℃, 5-8h.

8. A cobalt-oxygen co-doped modified graphitic carbon nitride catalyst, characterized in that, Prepared by the method described in any one of claims 1-7.

9. The application of the catalyst prepared by the method according to any one of claims 1-7 in the degradation of organic pollutants in water by activated PMS.

10. The application according to claim 9, characterized in that, The organic pollutant is ATZ, with a concentration of 3-8 ppm; the catalyst dosage is 0.4-0.8 g / L, the PMS dosage is 0.2-0.4 g / L, and the water pH is 7-8; NO3 is added to the water. - and SO4 2- Afterwards, the degradation efficiency is improved.

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