A modified g-C3N4, its preparation method and water treatment application

Abstract

The application relates to a modified g-C3N4, a preparation method thereof and water treatment application, and particularly discloses application of the modified g-C3N4 in activating sodium percarbonate to degrade organic pollutants in water, which comprises the following steps: adding the modified g-C3N4 into wastewater containing organic pollutants, adding sodium percarbonate to obtain a reaction system after adsorption balance is reached, and performing catalytic degradation by using the reaction system. The application provides the application of the modified g-C3N4 in activating sodium percarbonate to degrade organic pollutants in water, and the sodium percarbonate has high activation effect, has extremely high degradation effect on various organic pollutants in a wide pH value range and different complex water qualities. In the presence of high-concentration inorganic salts, the sodium percarbonate still has extremely strong organic pollutant degradation effect, and the degradation effect does not obviously decrease in multiple recycling.

Description

Technical Field

[0001] This invention relates to the field of water pollution treatment technology, specifically to a modified g-C3N4, its preparation method, and its water treatment applications. Background Technology

[0002] Marine aquaculture systems discharge large amounts of wastewater during water exchange. Besides nitrogen compounds and organic carbon, this wastewater contains high concentrations of salt and various antibiotics. Advanced oxidation processes (AOPs) are considered a promising remediation technology for removing antibiotics from water, generating hydroxyl radicals (…). • OH), sulfate radicals (SO4) •- ), superoxide anion radical (O2) •- Singlet oxygen () 1 O2) and carbonate free radicals (CO3) •- Reactive oxygen species (ROS) such as sodium percarbonate (SPC) can efficiently degrade antibiotics. Sodium percarbonate can be used as an oxidant in advanced oxidation technologies to degrade pollutants in water.

[0003] Traditional sodium percarbonate activation techniques typically employ ultraviolet light and ultrasound, but these methods are not suitable for practical applications. Graphite carbon nitride (g-C3N4), as a non-metallic photocatalytic material, is considered a promising visible light photocatalytic material due to its two-dimensional conjugated structure, high stability, non-toxicity, and low cost. However, traditional g-C3N4-based catalysts suffer from poor catalytic performance during sodium percarbonate activation, and their degradation efficiency for pollutants in water is often affected by high concentrations of inorganic salts in the water. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems of poor catalytic effect and low degradation efficiency of pollutants in water containing highly difficult inorganic salt water in the process of activating sodium percarbonate in the prior art, and to provide an application of modified g-C3N4 in the degradation of organic pollutants in water by activating sodium percarbonate.

[0005] According to an experimental example of the present invention, in a first aspect, an application of modified g-C3N4 in the degradation of organic pollutants in water by activated sodium percarbonate is provided, comprising the following steps: adding modified g-C3N4 to wastewater containing organic pollutants, adding sodium percarbonate after reaching adsorption equilibrium to obtain a reaction system, and using the reaction system for catalytic degradation.

[0006] In some experimental examples of the present invention, the modified g-C3N4 reached adsorption equilibrium under light-protected conditions and was catalytically degraded by adding sodium percarbonate under light irradiation.

[0007] In some experimental examples of the present invention, the concentration of the modified g-C3N4 in the organic wastewater is 0.2 g / L-0.6 g / L; The concentration of sodium percarbonate in the organic wastewater is 0.5 mM-4 mM.

[0008] According to some embodiments of the present invention, in a second aspect, a method for preparing modified g-C3N4 is provided, comprising the following steps: calcining a carbon-nitrogen source once and grinding and mixing it with molten salt, then calcining it a second time to obtain an intermediate, and washing and drying the intermediate to obtain modified g-C3N4.

[0009] In some embodiments of the present invention, the carbon and nitrogen source is melamine, and the molten salt includes one or more of lithium salt and potassium salt.

[0010] In some embodiments of the present invention, the calcination temperature for the first calcination is 500-600℃, and the calcination time is 3-5h.

[0011] In some embodiments of the present invention, the mass ratio of the carbon-nitrogen source powder to the lithium source powder is 1:4-5, and the mass ratio of the carbon-nitrogen source powder to the potassium source powder is 1:5-6.

[0012] In some embodiments of the present invention, the calcination temperature of the secondary calcination is 550℃-600℃, and the calcination time is 3-5h.

[0013] In some embodiments of the present invention, the washing method is to wash once or more using deionized water with a water temperature of ≥80°C; The drying method involves drying under vacuum for 10-12 hours at a temperature of 50-60°C.

[0014] According to some embodiments of the present invention, in a third aspect, a modified g-C3N4 is provided, which is prepared by the preparation method described above.

[0015] The technical solution of this invention has the following advantages: 1. The present invention provides an application of modified g-C3N4 in the degradation of organic pollutants in water by activated sodium percarbonate, comprising the following steps: adding modified g-C3N4 to wastewater containing organic pollutants, adding sodium percarbonate after reaching adsorption equilibrium to obtain a reaction system, and using the reaction system for catalytic degradation.

[0016] This invention provides the application of modified g-C3N4 in the degradation of organic pollutants in water using activated sodium percarbonate. It exhibits high sodium percarbonate activation efficiency and demonstrates extremely high degradation effects on various pollutants across a wide pH range and in complex water qualities. Even in the presence of high concentrations of inorganic salts, it maintains a strong degradation effect on pollutants, and its degradation efficiency does not significantly decrease after repeated use. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 These are the XRD patterns of the materials prepared in Example 1 and Comparative Example 1 of the present invention; Figure 2 These are the FTIR spectra of the materials prepared in Example 1 and Comparative Example 1 of this invention; Figure 3 These are the XPS spectra of the materials prepared in Example 1 and Comparative Example 1 of this invention; Figure 4 These are the C1s XPS spectra (a), N1s XPS spectra (b), and K2p XPS spectra (c) of the materials prepared in Example 1 and Comparative Example 1 of the present invention. Figure 5 These are Cl2p XPS spectra (a) and Li1s XPS spectra (b) of the materials prepared in Example 1 and Comparative Example 1 of the present invention. Figure 6 These are SEM images of the materials prepared in Example 1(a) and Comparative Example 1(b) of the present invention; Figure 7 These are TEM images of the materials prepared in Example 1(a) and Comparative Example 1(b) of the present invention; Figure 8 These are the ultraviolet-visible diffuse reflectance diagrams (a), Kubellka-Munk function versus photon energy diagram (b), and band structure diagram (c) of the materials prepared in Example 1 and Comparative Example 1 of this invention. Figure 9 These are the VB-XPS spectra of the materials prepared in Example 1 and Comparative Example 1 of this invention; Figure 10 These are the PL spectra of the materials prepared in Example 1 and Comparative Example 1 of the present invention; Figure 11 These are PL lifetime diagrams of the materials prepared in Example 1 and Comparative Example 1 of the present invention; Figure 12 These are the EIS diagrams of the materials prepared in Example 1 and Comparative Example 1 of this invention; Figure 13 These are transient photocurrent response diagrams of the materials prepared in Example 1 and Comparative Example 1 of the present invention; Figure 14This describes the effect of the material prepared in Example 1 of the present invention on the removal of SMX under different quenchers; Figure 15 This is a degradation diagram of SMX in different catalytic systems; Figure 16 This is a graph showing the effect of different dosages of the material prepared in Example 1 of the present invention on the removal of SMX. Figure 17 This is a graph showing the effect of different SPC concentrations on SMX removal according to the present invention; Figure 18 This is a degradation diagram of SMX by the material prepared in Example 1 of the present invention in different water bodies; Figure 19 These are graphs showing the removal effect of the material prepared in Example 1 of this invention on SMX at different pH values; Figure 20 This is a graph showing the removal effect of the material prepared in Example 1 of the present invention on different concentrations of SMX; Figure 21 This is a diagram showing the removal effect of the material prepared in Example 1 of the present invention on different pollutants in seawater; Figure 22 This describes the effect of the material prepared in Example 1 of the present invention on the removal effect of SMX in high concentrations of different salt ions; Figure 23 This is a test of the stability and reusability of the catalytic degradation system of this invention; Figure 24 This is a comparison of the XRD patterns of the material prepared in Example 1 of the present invention before and after use. Detailed Implementation

[0019] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0020] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0021] Example 1 (1) 5g of melamine was calcined in a crucible under air atmosphere at a temperature of 550℃ for 4h to obtain raw g-C3N4.

[0022] (2) Take 1.2g of raw g-C3N4, 5.4g of lithium chloride as lithium source, and 6.6g of potassium chloride as potassium source. Grind them thoroughly until there is no obvious particle feel. Then calcine them in air atmosphere at a temperature of 550℃ for 4h to obtain an intermediate.

[0023] (3) After the intermediate is naturally cooled to room temperature, the intermediate is washed multiple times with deionized water at a temperature ≥80℃ and dried under vacuum at 60℃ for 12h to obtain modified g-C3N4 (PHI).

[0024] Example 2 (1) 5g of melamine was calcined in a crucible under air atmosphere at a temperature of 500℃ for 5h to obtain raw g-C3N4.

[0025] (2) Take 1.2g of raw g-C3N4, 4.8g of lithium chloride as lithium source, and 7.2g of potassium chloride as potassium source. Grind them thoroughly until there is no obvious particle feel. Then calcine them in air atmosphere at a temperature of 600℃ for 3h to obtain an intermediate.

[0026] (3) After the intermediate is naturally cooled to room temperature, the intermediate is washed multiple times with deionized water at a temperature ≥80℃ and dried under vacuum at 60℃ for 12h to obtain modified g-C3N4 (PHI).

[0027] Example 3 (1) 5g of melamine was calcined in a crucible under air atmosphere at a temperature of 600℃ for 3h to obtain raw g-C3N4.

[0028] (2) Take 1.2g of raw g-C3N4, 6.0g of lithium chloride as lithium source, and 6.0g of potassium chloride as potassium source. Grind them thoroughly until there is no obvious particle feel. Then calcine them in air atmosphere at a temperature of 550℃ for 3h to obtain an intermediate.

[0029] (3) After the intermediate is naturally cooled to room temperature, the intermediate is washed multiple times with deionized water at a temperature ≥80℃ and dried under vacuum at 60℃ for 12h to obtain modified g-C3N4 (PHI).

[0030] Comparative Example 1 (1) 5g of melamine was calcined in a crucible under air atmosphere at a temperature of 600℃ for 3h to obtain raw g-C3N4 (PCN).

[0031] Test case In the following test and experimental examples, the modified g-C3N4 prepared in Examples 1-3 is referred to as PHI, and the original g-C3N4 prepared in Comparative Example 1 is referred to as PCN.

[0032] 1. X-ray diffraction (XRD) test X-ray diffraction (XRD) tests were performed on the modified g-C3N4 (PHI) prepared in Example 1 of this invention and the g-C3N4 (PCN) prepared in Comparative Example 1. Figure 1 As shown, PCN exhibits two characteristic diffraction peaks at 13.0° and 27.5°, corresponding to the (100) and (002) crystal planes of PCN, respectively attributable to the in-plane repeating stacking of tri-s-triazine units in the conjugated aromatic units and the interlayer stacking of the conjugated aromatic system. Notably, the (100) diffraction peak of PHI shifts from 13.0° to 7.94°, mainly due to the rearrangement of heptaazine units. Compared to PCN, the (002) characteristic peak of PHI shifts slightly to a higher angle from 27.5° to 28.1°, due to the strong interlayer interactions of PHI, exhibiting a narrower interlayer distance.

[0033] 2. Fourier Transform Infrared Spectroscopy (FTIR) Test Fourier transform infrared spectroscopy was performed on the modified g-C3N4 (PHI) prepared in Example 1 of this invention and the g-C3N4 (PCN) prepared in Comparative Example 1 to investigate the chemical structure of the prepared materials, such as... Figure 2 As shown, in both samples, 805 cm -1 The sharp characteristic peak at 1100–1700 cm⁻¹ is attributed to the bending vibration mode of the heptaazine ring, indicating the formation of the g-C₃N₄ structure. -1 The characteristic peak at 3000–3500 cm⁻¹ is due to the skeletal stretching vibration of the CN heterocycle. -1 The absorption band at 2165 cm⁻¹ is characteristic of the stretching vibration of the NH group. In contrast, the absorption band of PHI is significantly sharper and stronger than that of PCN, possibly due to the more ordered stacking of the heptaazine units, further confirming the increased crystallinity of PHI. At 2165 cm⁻¹... -1 A new peak was observed at K, which is attributed to the asymmetric stretching mode of the cyano group (-C≡N) derived from the terminal -C-NH2. + Possibly in the form of (-C≡N)-K + The form was introduced into the g-C3N4 framework.

[0034] 3. X-ray photoelectron spectroscopy (XPS) test X-ray photoelectron spectroscopy (XPS) was performed on the modified g-C3N4 (PHI) prepared in Example 1 of this invention and the g-C3N4 (PCN) prepared in Comparative Example 1. Figure 3 As shown, C, N, and O elements were observed in both PCN and PHI, while K was also observed in PHI. The C 1s spectra of PCN and PHI (…) Figure 4 a) consists of three characteristic peaks. Specifically, the PHI spectrum shows main peaks at 288.18, 286.7 eV, and 284.8 eV, which are attributed to NC=N and C-NH, respectively. x And uncertain carbon (CC / C=C). The N 1s XPS spectra of PCN and PHI are shown in [reference needed]. Figure 4 In the middle b, PHI has four peaks similar to PCN. The strongest peak (i.e., 398.6 eV) is the sp involved in the tri-S-triazine ring. 2 The hybrid nitrogen (N=CC) peaks at 400.51 eV and 401.3 eV are attributed to the N-(C)3 and CNH groups. The CN=C, N-(C)3, and NC=N groups form the heptaazine ring unit, constituting the basic substructural unit of PCN, further indicating that the fundamental characteristic structure of PHI remains unchanged, consistent with the conclusions drawn from Fourier transform infrared spectroscopy. The peak at 403.93 eV is attributed to the charging effect or positive charge localization within the heterocycle. Furthermore, the XPS spectrum of K 2p in PHI can be observed (…). Figure 4 c) Two binding energy peaks appear at 293 eV and 295.8 eV, which are different from the binding energy peak of metal K (294.7 eV). The doublet spacing of the K 2p photoelectron line is 2.8 eV, thus proving that K in PHI is K2p. + It exists in ionic form. For example... Figure 5 As shown, no signals corresponding to Cl 2p and Li 1s were observed after washing with deionized water, indicating that PHI does not contain Cl and Li.

[0035] 4. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) testing The modified g-C3N4 (PHI) prepared in Example 1 of this invention and the g-C3N4 (PCN) prepared in Comparative Example 1 were subjected to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) tests to characterize the morphology and microstructure of the prepared materials. Figure 6 As shown, PHI exhibits a cluster-like nanorod structure with a width of 50–100 nm. Figure 6 (a) PCN exhibits a typical micron-scale bulk amorphous structure. Figure 6 (b) The reason why the PHI sample exhibits a clustered nanorod structure may be that during the molten salt process, the precursor's stacked structure cannot adhere to the salt, thus forming nanorod structures only in the interstices of the salt. This clustered nanorod structure can provide a longer optical path for light absorption, offering more exposed active sites for the photocatalytic reaction. TEM images further confirm the crystallinity of the PHI sample. Figure 7 As shown, TEM images of PHI ( Figure 7(a) further verified its clustered nanorod structure, and the microstructure of PCN exhibited a typical aggregated amorphous state. Figure 7 (b) Meanwhile, no clear lattice fringes were identified in the high-resolution TEM image of PCN, indicating its disordered structure and low crystallinity. In contrast, the high-resolution TEM image of PHI in the figure shows clear, regular lattice fringes with a crystal plane spacing of 0.269 nm, which may be designated as the interlayer distance, corresponding to the (002) crystal plane of PCN, consistent with the XRD results. The ordered structure of PHI may be conducive to the migration of photogenerated charges.

[0036] 5. Ultraviolet-Vis-NearInfrared Diffuse Reflectance (UV-Vis-DRS) and X-ray Photoelectron Spectroscopy (XPS) Valence Band Spectroscopy Analysis The modified g-C3N4 (PHI) prepared in Example 1 of this invention and the g-C3N4 (PCN) prepared in Comparative Example 1 were subjected to UV-Vis diffuse reflectance testing, as shown below. Figure 8 As shown in Figure a, in the visible light region, PCN's light absorption is weaker than PHI's. This may be due to PCN's lower crystallinity, leading to reduced absorption in the conjugated system. Furthermore, PHI, with its stronger visible light absorption, may generate more photogenerated charge carriers, thereby accelerating the photocatalytic oxidation and degradation of pollutants. Based on the converted Kubelka-Munk function (… Figure 8 (b) Estimate the band gaps of PCN and PHI. E g The values ​​are 2.48 and 2.59 eV, respectively. Figure 8 (c) PHI has a wider band gap. Therefore, the change in band gap is not the factor leading to the excellent catalytic activity of PHI. Furthermore, the valence band potential of the prepared sample was estimated using VB-XPS spectroscopy (c). E VB,XPS The corresponding values ​​of PCN and PHI were measured. E VB,XPS The values ​​are 2.08 and 2.15 eV respectively. Figure 9 ). Calculate the corresponding standard hydrogen electrode (pH=7) using the following formula. E VB,NHE : E VB,NHE = φ + E VB,XPS – 4.44 ,in φ Represents the instrument's work function ( φ = 4.2 eV). From this, the values ​​of PCN and PHI can be calculated. E VB,NHE The values ​​are 1.84 and 1.91 V, respectively. Using the formula... E CB = E VB -E g The equations were used to calculate the conduction bands of PCN and PHI. E CB The values ​​are -0.64 and -0.68 V, respectively (relative to the standard hydrogen electrode (pH=7)). Based on the above results, the band structure of the photomaterial is as follows: Figure 8 As shown in c. Photogenerated electrons / holes (e - / h + The oxidation / reduction capability of PHI is determined by the VB / CB positions of the semiconductor. CB (-0.68 V vs. NHE) ratio of O2 / O2 •- The standard reduction potential (-0.33V vs. NHE) is more negative, indicating that the e in CB is more negative. - It can react with O2 to produce O2. •- PHI's E VB (1.91 V vs. NHE) is a better correction than PCN (1.84 V vs. NHE), indicating that its h + Its oxidizing power is enhanced. Its potential is less than • OH / H₂O (2.27 V vs. NHE), therefore h + Cannot oxidize H2O to produce • OH.

[0037] 6. Fluorescence spectroscopy (PL) curve testing Steady-state photoluminescence (PL) emission spectroscopy was performed on the modified g-C3N4 (PHI) prepared in Example 1 of this invention and the g-C3N4 (PCN) prepared in Comparative Example 1 to analyze electron-hole separation and charge transfer efficiency. Figure 10 As shown, PCN exhibits a strong and broad PL emission peak, while PHI produces a significantly weaker signal. This indicates that PHI has a lower recombination rate of photogenerated carriers, allowing for more efficient utilization of photogenerated electrons, which is more conducive to photocatalytic removal of pollutants. This may be a combined result of increased crystallinity of the extended conjugated system, increased BET specific surface area, and increased active sites. Time-resolved fluorescence (TRF) spectroscopy... Figure 11 The transfer dynamics of photogenerated carriers were evaluated. The decay curve was fitted to a triple exponential function (Equation 1), and the average radiative lifetime of the photogenerated charge (τ) was calculated. ave The calculation is performed using Equation 2. Based on the calculation, τ for PCN and PHI... ave The lifetimes are 1.073 ns and 0.443 ns, respectively. The shortened lifetime of PHI is due to the increased in-plane crystallinity and reduced interlayer distance, which accelerates charge transfer without recombination, further demonstrating that the separation and transfer of photogenerated carriers in PHI are very rapid.

[0038] (Equation 1) (Equation 2) In the formula, A1, A2, and A3 are constants; τ1, τ2, and τ3 are the fitted lifetimes.

[0039] 7. Electrochemical Impedance Spectroscopy (EIS) Measurement Electrochemical impedance spectroscopy (EIS) tests were performed on the modified g-C3N4 (PHI) prepared in Example 1 of this invention and the g-C3N4 (PCN) prepared in Comparative Example 1. Figure 12 As shown, the arc of the PHI Nyquist curve decreases compared to PCN with increasing crystallinity, indicating a faster charge transfer rate in PHI. This is attributed to the construction of long-range ordered structures and the introduction of K+ in PHI. + It serves as a transport channel for interlayer electron transfer. Furthermore, such as Figure 13 As shown, under visible light (λ>420 nm) irradiation, PHI has a higher photocurrent density than PCN, indicating that the optimized crystal structure further accelerates the movement and diffusion of photogenerated carriers.

[0040] 8. Identification of active species and investigation of their mechanisms Using the PHI prepared in Example 1 as a representative catalyst, a series of controlled experiments were conducted to analyze the main active species in the PHI / SPC / visible light system. Isopropanol (TBA), phenol (PhOH), histidine (L-His), chloroform (CF), and disodium ethylenediaminetetraacetate (EDTA-2Na) were used as hydroxyl radicals, respectively. • OH), hydroxyl radicals ( • OH) / carbonate radical (CO3) •- Singlet oxygen () 1 O2), superoxide anion radicals (O2) •- ), photogenerated holes (h) + The quencher. The results were as follows: Figure 14 As shown, add • The degradation efficiency of SMX decreased slightly after 100 mM TBA was applied as an OH quencher. This result indicates that... • OH is not the major active species for SMX degradation. Furthermore, the addition of 5 mg / L PhOH almost completely inhibited SMX degradation, indicating that CO32-... •- It is the main active species for the degradation of SMX in the PHI / SPC / Vis system. In 5 mM L-His ( 1 In the presence of an O2 quencher, the removal rate of SMX decreased significantly to 30%. This indicates that... 1 O2 plays an indispensable role in the degradation of SMX. The addition of 5 mM CF (O2) •-After the quencher was applied, the removal rate of SMX remained almost unchanged. This indicates that O2 removal efficiency remained almost unchanged. •- This is not the direct cause of SMX degradation. The degradation efficiency of SMX decreased sharply upon the addition of 5 mM EDTA-2Na, indicating that h... + It is the main active species for the degradation of SMX in the PHI / SPC / visible light system.

[0041] Application Example 1 1. Pollutant Degradation Experiment Unless otherwise specified, all degradation experiments were conducted in quartz reaction tubes containing a 30 mL suspension of 0.6 g / L material, 4 mM SPC, and 5 mg / L SMX at an ambient temperature of 25 ± 1 °C. In short, 18 mg of the prepared material was first added to a quartz reaction tube containing 30 mL of SMX solution. The reaction tube was then placed in a photocatalytic reactor (Beijing Technology Co., Ltd., PL-05, China), and the mixture was stirred in the dark for 40 min to establish adsorption-desorption equilibrium. Catalytic degradation experiments were then conducted using a xenon lamp as the visible light source (10 W, 400 nm < λ < 800 nm). At the moment the lamp was turned on, SPC was added to the reaction solution to achieve a concentration of 4 mM. After initiating the catalytic reaction, 1 mL of the resulting solution was taken at regular intervals, filtered through a 0.22 µm polyethersulfone needle filter to remove the photocatalytic material, and then quenched by mixing with an equal volume of methanol.

[0042] The pollutant concentration was determined using high-performance liquid chromatography (HPLC, Waters Alliancee 2695, USA) to measure the SMX concentration in the sample. The HPLC system was equipped with a Zorbax Eclipse XDB-C18 column (4.6 mm × 250 mm, 5 μm). The chromatographic conditions for SMX were as follows: mobile phase was methanol / formic acid buffer (50:50 v / v, containing 0.1% formic acid), and the flow rate was 0.5 mL / min. -1 The injection volume was 10 μL, the temperature was 35 ℃, and the detection wavelength was 273 nm. The methods for determining other pollutants are shown in Table 1.

[0043] Table 1. Methods for determining organic pollutants

[0044] Mobile phase A: 0.1% formic acid in water; Mobile phase B: methanol Based on the experimental methods described above, SMX was selected as the target pollutant to evaluate the degradation performance of the PHI / SPC / visible light system. Figure 15As shown, SMX could not be degraded within 15 min in the PHI, SPC, visible light, SPC / visible light, PCN / SPC, and PHI / SPC systems. These results indicate that SPC, the materials (PCN and PHI), or visible light itself cannot oxidize SMX, and PCN and PHI cannot activate SPC to degrade SMX under light-free conditions. Under visible light irradiation, the degradation efficiencies of PCN and PHI on SMX were 12% and 53%, respectively. The improved photocatalytic performance may be due to the higher in-plane crystallinity of PHI, which dominates overall charge separation and photocatalytic activity. Meanwhile, the degradation efficiency (53%) in the PCN / SPC / visible light system was unsatisfactory, possibly because SPC was not fully activated, resulting in only trace amounts of active material. Notably, the PHI / SPC / visible light system could degrade SMX 100% within 15 min. These results demonstrate a strong synergistic effect between PHI, SPC, and visible light on SMX degradation, significantly enhancing the catalytic activity of the system. This demonstrates that PHI has a stronger and more efficient activation ability for SPC compared to PCN.

[0045] 2. Effects of different catalyst dosages and oxide SPC concentrations on pollutant degradation Following the experimental method described in Example 1, the effects of PHI dosage and SPC concentration on SMX degradation were investigated. Under visible light irradiation, with an initial SMX concentration of 5 mg / L, pH 5.4, SPC concentration of 4 mM, and a temperature of 25 ± 1 °C, the reaction was carried out for 15 min. Figure 16 As shown, the degradation efficiency of SMX increased from 94% to 100% as the PHI loading increased from 0.2 g / L to 0.6 g / L. This is because more PHI provides more catalytic active sites for SPC activation. However, no significant increase in degradation rate was observed after further increasing the PHI loading. Therefore, a material loading of 0.6 g / L was chosen for the remaining experiments.

[0046] Under visible light irradiation, with an initial SMX concentration of 5 mg / L, pH 5.4, PHI concentration of 0.6 g / L, and a temperature of 25 ± 1 °C for 15 min, increasing the SPC concentration from 0.5 mM to 4 mM also significantly promoted the degradation of SMX. Figure 17 As shown, the removal rate increased from 76% to 100%, indicating that the higher the SPC concentration, the better the SMX removal effect, which may be due to the generation of more reactive oxygen species (ROS). However, when the added SPC dosage exceeded 4 mM, the increase in degradation efficiency was not significant (100% degradation of SMX was achieved within 15 min in all cases). Therefore, a dosage of 4 mM SPC was selected for other experiments.

[0047] 3. The impact of environmental factors on pollutant degradation Based on the experimental methods described in the pollutant degradation experiment, the effects of different pH values ​​and aquatic environments on pollutant degradation were investigated. Figure 18 As shown, the PHI / SPC / Vis system developed in this application exhibits better degradation performance in real water bodies containing a large number of inorganic ions and other competing pollutants than in laboratory ultrapure water (control). The PHI / SPC / Vis system demonstrates excellent performance in tap water, natural river water, wastewater treatment plant effluent, and seawater. The promoting effect in seawater is the most significant, indicating that this system has excellent prospects for practical application in the treatment of marine aquaculture wastewater.

[0048] like Figure 19 As shown, Figure 19 The degradation of SMX by the PHI / SPC / visible light system in solutions with different pH values ​​is presented. The degradation efficiency showed no significant change between pH 4 and 12, but decreased slightly to 96.5% at pH 2. This is because the decomposition of H₂O₂ during SPC activation is the primary source of ROS generation. The peroxides in percarbonate decompose less under acidic conditions, leading to increased CO₃²⁻ production. •- , 1 O2 and O2 •- The reduction was observed. However, the degradation efficiency of SMX increased at pH=12. This is because the h in the system decreased under alkaline conditions. + It can oxidize OH - Generate a large number of • OH, which in turn produces CO3. •- , 1 O2 and O2 •- Therefore, the PHI / SPC / visible light system exhibits excellent degradation ability for SMX over a wide pH range, further demonstrating its potential in practical applications. Furthermore, the catalytic activity of the PHI / SPC / visible light system at different SMX concentrations was investigated. Figure 20 As shown, the PHI / SPC visible light system can achieve efficient degradation of SMX in the concentration range of 1 mg / L-15 mg / L.

[0049] 4. Degradation experiments on different pollutants Figure 21The study demonstrated the ability of the PHI / SPC / visible light system to degrade various common pollutants in marine aquaculture wastewater, including sulfonamides (SMX and SDZ), quinolones (CIP and NOR), and tetracyclines (TC). The results showed that the system achieved 100% removal rates of sulfamethoxazole (SMX), sulfadiazine (SDZ), ciprofloxacin (CIP), norfloxacin (NOR), and tetracycline hydrochloride (TC) from actual seawater within 10 minutes, showcasing the potential of the PHI / SPC / visible light system for degrading various residual antibiotics.

[0050] 5. Degradation experiment of SMX under high salt conditions Five common anions (NO3) at different concentrations were compared. - HCO3 - CO3 2- SO4 2- and Cl - The PHI / SPC / visible light system developed in this application was introduced to evaluate its catalytic performance under different salinity conditions. Figure 22 As shown, in the introduced Cl - Subsequently, it significantly enhanced the catalytic activity of the PHI / SPC visible light system, and with the increase of Cl... - The increased concentration of Cl further enhanced the promoting effect on SMX degradation. - SMX can be completely removed within 5 minutes. Furthermore, other types of salinity also have a positive impact on SMX degradation. Generally, coexisting inorganic anions, especially CO3 in radical-dominated AOPs, are also affected. 2- HCO3 - and Cl - It can convert highly oxidizing free radicals into a state with lower oxidizing capacity or even scavenge free radicals. However, even in the presence of high concentrations of anions, the PHI / SPC / visible light system did not show any inhibitory effect from anions; on the contrary, it promoted the reaction, indicating that it has excellent removal effect on organic pollutants in high-salinity wastewater.

[0051] The PHI material prepared in the embodiments of the present invention was continuously run five times under the same conditions to evaluate the stability of the PHI / SPC / visible light system in the degradation of SMX. After each run, the used material was filtered and washed multiple times with deionized water and anhydrous ethanol, and then recycled. Figure 23 This indicates that PHI maintained a high degradation efficiency of 92% for SMX after 5 cycles, demonstrating its good stability in the PHI / SPC / visible light system. Furthermore, the XRD pattern of the cycled PHI retained the same characteristic peaks as the original PHI. Figure 24These results indicate that PHI exhibits a highly stable crystal structure and strong resistance to photocorrosion during SPC activation. Therefore, PHI has the potential to activate SPC in real-world water bodies for efficient SMX degradation.

[0052] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. The application of modified g-C3N4 in the degradation of organic pollutants in high-salt water by activated sodium percarbonate, characterized in that, The process includes the following steps: adding modified g-C3N4 to wastewater containing organic pollutants, wherein the modified g-C3N4 reaches adsorption equilibrium under light-protected conditions, and sodium percarbonate is added under light conditions for catalytic degradation; The modified g-C3N4 was prepared by the following method: carbon and nitrogen source was calcined once and then ground and mixed with molten salt, followed by a second calcination to obtain an intermediate. The intermediate was then washed and dried to obtain the modified g-C3N4. The carbon and nitrogen source is melamine, and the molten salt includes one or more of lithium salt and potassium salt. The organic pollutants in the high saline water include any one of sulfonamides, quinolones, and tetracyclines; The high-salt water contains inorganic anions NO3-. HCO3 CO3 2 SO4 2 and Cl Any one of them; The concentration of the inorganic anion is 200 mM.

2. The application according to claim 1, characterized in that, The concentration of the modified g-C3N4 in the organic wastewater is 0.2 g / L-0.6 g / L; and / or, The concentration of sodium percarbonate in the organic wastewater is 0.5 mM-4 mM.

3. The application according to claim 1, characterized in that, The calcination temperature for the first calcination is 500-600℃, and the calcination time is 3-5 hours.

4. The application according to claim 1, characterized in that, The mass ratio of the carbon-nitrogen source powder to the lithium source powder is 1:4-5, and the mass ratio of the carbon-nitrogen source powder to the potassium source powder is 1:5-6.

5. The application according to claim 1, characterized in that, The secondary calcination temperature is 550℃-600℃, and the calcination time is 3-5h.

6. The application according to claim 1, characterized in that, The washing method involves washing once or more with deionized water at a temperature ≥80℃; and / or, The drying method involves drying under vacuum for 10-12 hours at a temperature of 50-60°C.

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