Preparation method of modified covalent organic framework photocatalyst and application of modified covalent organic framework photocatalyst in field of enteromorpha green tide

Abstract

The invention relates to a modified covalent organic framework (COF) photocatalyst (SNW-1 (at) CuS-D and SNW-1 (at) CuS-S. SNW-1 is loaded on the surface of the CuS photocatalyst through an electrostatic adsorption method, so that the SNW-1 (at) CuS-D photocatalyst is synthesized; sNW-1 is loaded on the surface of the CuS photocatalyst through a hydrothermal method, so that the SNW-1 coated CuS-S photocatalyst is synthesized. Meanwhile, the two composite materials are used for inhibition experiment research on green tide algae-enteromorpha under visible light. When the doping amount of the two composite material photocatalysts is 0.15 g / L, the composite material photocatalysts have an effective inhibition effect on enteromorpha. After 120 hours of experimental treatment, the inactivation rate of the enteromorpha microcosmic propagules reaches 70%; after 144 hours of treatment, the relative growth rate of the three-week-old enteromorpha seedlings is reduced to 0.011. Meanwhile, chlorophyll a is reduced to the minimum and is 257.84 mu g / g FW, the content of MDA is increased to 206.2 nmol / g FW, meanwhile, the content of various antioxidant enzymes is increased firstly and then reduced in the photocatalysis process, and an antioxidant system is damaged. The material provides a reference idea for COF modification and enteromorpha green tide treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photocatalytic technology for inhibiting algae, in particular to a preparation method of two kinds of modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S and application thereof in the field of green tide of Enteromorpha. BACKGROUND

[0002] Marine ecosystems have long been considered one of the most important ecosystems on Earth; however, in recent years, the phenomenon of marine ecological disturbance known as "green tide" has occurred frequently, causing serious impacts on coastal ecological environment, economic activities, and human livelihoods. Since 2007, the Yellow Sea region of China has been subjected to large-scale green tide invasion every summer. Green tide has been identified as a global marine environmental problem, with relevant records in multiple regions around the world. Green tide has multiple negative impacts on marine ecosystems and human activities: research has found that the overgrowth of large green algae Enteromorpha can block sunlight and inhibit the growth of benthic algae; the decomposition of algal biomass consumes dissolved oxygen in seawater; and the chemical substances released by Enteromorpha have toxic effects on other marine organisms. The formation of green tide is mainly influenced by multiple factors such as seawater eutrophication, suitable water temperature, and light conditions. Eutrophication, mainly caused by nitrogen and phosphorus pollutants emitted by human activities, is not only a key factor for red tide occurrence but also an important inducement for green tide spread. Global climate change has led to a continuous rise in seawater temperature, which is also considered a key driver of green tide outbreaks.

[0003] In recent years, photocatalytic technology, as an efficient and environmentally friendly advanced oxidation process, has attracted attention due to its great potential in controlling harmful algal blooms. For the green tide phenomenon caused by large algae (such as Sargassum), traditional control methods (including physical removal and chemical treatment) have been repeatedly frustrated due to low efficiency, high operating costs, and the risk of secondary pollution. In contrast, photocatalytic technology generates active oxygen (such as hydroxyl radicals OH, superoxide anions O2 ⁻ ) under light through semiconductor materials, which can effectively destroy algal cell structure and inhibit photosynthetic activity, ultimately leading to algal cell death, providing a promising solution for controlling harmful algal blooms.

[0004] Among the new organic photocatalysts, covalent organic frameworks (COFs) are defined as a class of porous organic materials formed by covalent bonds, with high specific surface area, ordered pore structure and tunable electronic band structure. In the field of photocatalysis, covalent organic framework materials are widely studied due to their strong visible light absorption ability and high structural tunability. Among them, covalent organic frameworks based on triazine are of great concern due to their high chemical stability and electron-withdrawing properties of triazine motifs, which can promote the separation and migration of photo-generated carriers, and their high porosity makes them have strong adsorption capacity. However, challenges such as rapid recombination of photo-generated carriers and easy structural degradation under photocatalytic conditions have been found, which limit their practical application.

[0005] Copper sulfide is characterized as a narrow-band-gap p-type semiconductor with an energy gap of about 1.85 eV, enabling it to be excited by visible light of about 550 nm. As a photocatalyst, the most prominent advantage of copper sulfide is its unique broad-spectrum solar response and high photo-thermal synergistic effect. It not only can effectively utilize visible light to near-infrared light through localized surface plasmon resonance (LSPR), greatly improving the utilization rate of solar energy, but also can convert light energy into heat energy. Due to its strong visible light collection ability and high carrier mobility, in addition, it also has the advantages of low cost, high charge separation efficiency and environmental friendliness. Therefore, we selected CuS to modify SNW-1. The composite material not only has strong adsorption capacity, but also has strong photocatalytic capacity. SUMMARY

[0006] The purpose of the present application is to provide two kinds of modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S and their preparation methods, and to study the visible light photocatalytic inhibition of Enteromorpha. The two kinds of SNW-1@CuS-D and SNW-1@CuS-S composite photocatalysts are prepared by electrostatic adsorption method and hydrothermal synthesis method. The electrostatic adsorption method and the hydrothermal synthesis method are simple to operate, and the cost used in the synthesis process is relatively low. Various characterization experiments confirm the successful preparation of the expected materials. And the materials are applied to the inhibition experiment of Enteromorpha. SNW-1@CuS-D is irradiated by visible light for 120 h, and SNW-1@CuS-D photocatalyst shows the best photocatalytic performance, which can remove 70% of the microscopic propagule cells. SNW-1@CuS-S is irradiated by visible light for 144 h, and the relative growth rate of three-week-old Enteromorpha seedlings is inhibited to 0.011. The present application uses two kinds of modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S to inactivate Enteromorpha microscopic propagules and inhibit the growth of Enteromorpha seedlings, and to strengthen the application treatment in the Enteromorpha green tide.

[0007] The technical scheme of the present application is: Step one: Synthesis of Cu2O: 1.596 g Cu(CH3COO)2.H2O, 1.53 g glucose and 0.666 g PVP (K-30) were dissolved into 120 mL DMF. The mixture was stirred vigorously for 90 min, then heated to 80 °C for 10 min under continuous stirring. The resulting powder was washed with deionized water and ethanol alternately for several times; Step two: Synthesis of CuS: Cu2O was dissolved in deionized water at a concentration of 2 mg mL -1 , then 54 mL aqueous Na2S solution (0.086 mol L -1 ) was added dropwise into 26 mL of the above solution under magnetic stirring. After the addition was completed, the reaction was continued for 5 min, and the final CuS spheres were collected after washing with deionized water completely; Step three: Synthesis of SNW-1: Melamine (470 mg, 3.73 mmol) and terephthaldehyde (750 mg, 5.59 mmol) were dissolved in DMSO (23 mL) by a typical solvothermal method, and heated at 180 °C for 14 h in a polytetrafluoroethylene-lined laboratory autoclave. Subsequently, the product was thoroughly washed with excess acetone (30 mL x 2) and dichloromethane (30 mL x 2). Finally, dried in an oven at 60 °C for 12 h to obtain white powder SNW-1; Step four: Synthesis of SNW-1@CuS-D: 125.05 mg SNW-1 was dispersed in 100 mL deionized water and ultrasonically treated for 10 min. 20 mg of copper sulfide was added, and the mixture was magnetically stirred for 2 h. After centrifuging the mixture, the supernatant was discarded, and the product was dried at 60 °C for 12 h to obtain SNW-1@CuS-D.

[0008] Alternatively: Synthesis of SNW-1@CuS-S: Melamine (470 mg, 3.73 mmol) and terephthaldehyde (750 mg, 5.59 mmol) were dissolved in DMSO (23 mL) by a typical solvothermal method, and the mixture was ultrasonically treated for 5 min to form a transparent solution. 0.2178 mg of copper sulfide was added to the solution, and the mixture was ultrasonically treated for another 10 min. The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave and heated at 180 °C for 14 h. Subsequently, the product was thoroughly washed with excess acetone (30 mL x 2) and dichloromethane (30 mL x 2). Finally, dried in an oven at 60 °C for 12 h to obtain SNW-1@CuS-S.

[0009] This invention discloses modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S prepared by the above-mentioned method. These two materials exhibit good removal efficiency of microscopic propagules, with an inactivation rate of 70% after 120 h; and good seedling growth inhibition effect, with a relative growth rate decrease to 0.011 after 144 h.

[0010] Compared with existing algae removal technologies, this invention has the following advantages: 1. The modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S prepared in this invention have high visible light photocatalytic activity and excellent adsorption performance. The efficient inhibition effect is the result of the synergistic effect of photocatalysis and adsorption.

[0011] 2. The modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S prepared in this invention have a wider light absorption range and can utilize visible light more effectively.

[0012] 3. The modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S are prepared by electrostatic adsorption and hydrothermal synthesis, respectively. The methods are simple, can be mass-produced, and require readily available materials with low cost. Attached Figure Description

[0013] Figure 1 X-ray diffraction patterns and Fourier transform infrared spectra of SNW-1, CuS, SNW-1@CuS-D, and SNW-1@CuS-S photocatalysts; Figure 2 The removal rates of Ulva prolifera by multiple photocatalysts, including control group, SNW-1, CuS, and SNW-1@CuS-D, were compared. Figure 3 The effects of the control group, SNW-1, CuS treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-D on the chlorophyll a content of Ulva proliferators were investigated. Figure 4 The effects of the control group, SNW-1, CuS-treated group, and modified covalent organic framework photocatalyst SNW-1@CuS-D on the soluble protein content of Ulva prolifera microstructures were investigated. Figure 5 The effects of the control group, SNW-1, CuS-treated group, and modified covalent organic framework photocatalyst SNW-1@CuS-D on the malondialdehyde content of Ulva proliferators were investigated. Figure 6The relative growth inhibition rates of the control group, SNW-1, CuS, SNW-1@CuS-D treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-S on three-week-old Ulva seedlings were measured. Figure 7 The effects of the control group, SNW-1, CuS, SNW-1@CuS-D treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-S on the chlorophyll a content of three-week-old Ulva seedlings were investigated. Figure 8 The effects of the control group, SNW-1, CuS, SNW-1@CuS-D treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-S on the malondialdehyde content of three-week-old Ulva seedlings were investigated. Detailed Implementation

[0014] The present invention will now be described in further detail with reference to specific embodiments.

[0015] Example 1 A method for preparing modified covalent organic framework photocatalysts SNW-1@CuS-D and SNW-1@CuS-S, the specific steps of which are as follows: 1) Synthesis of Cu₂O: 1.596 g Cu(CH₃COO)₂·H₂O, 1.53 g glucose, and 0.666 g PVP (K⁻³⁰) were dissolved in 120 mL DMF. The mixture was stirred vigorously for 90 minutes, and then heated to 80 °C for 10 minutes with continuous stirring. The resulting powder was washed several times alternately with deionized water and ethanol. 2) Synthesis of CuS: Cu2O was prepared at a concentration of 2 mg·mL⁻¹ -1 The concentration of Na₂S was dissolved in deionized water, and then 54 mL of Na₂S aqueous solution (0.086 mol·L⁻¹) was added under magnetic stirring. -1 Add the spores dropwise to 26 mL of the above solution. After the addition is complete, continue the reaction for 5 minutes, then wash thoroughly with deionized water and collect the final CuS spheres. 3) Synthesis of SNW-1: Melamine (470 mg, 3.73 mmol) and terephthalaldehyde (750 mg, 5.59 mmol) were dissolved in DMSO (23 mL) using a typical solvothermal method and heated at 180°C for 14 hours in a PTFE-lined laboratory autoclave. Subsequently, the product was thoroughly washed with excess acetone (30 mL × 2) and dichloromethane (30 mL × 2). Finally, it was dried in an oven at 60°C for 12 hours to obtain a white powder. 4) Synthesis of SNW-1@CuS-D: 125.05 mg of SNW-1 was dispersed in 100 mL of deionized water and sonicated for 10 minutes. 20 mg of copper sulfide was added, and the mixture was magnetically stirred for 2 hours. After centrifugation, the supernatant was discarded, and the product was dried at 60°C for 12 hours to obtain SNW-1@CuS-D.

[0016] 5) Synthesis of SNW-1@CuS-S: Melamine (470 mg, 3.73 mmol) and terephthalaldehyde (750 mg, 5.59 mmol) were dissolved in DMSO (23 mL) using a typical solvothermal method. The mixture was sonicated for 5 minutes to form a clear solution. 0.2178 mg of copper sulfide was added to this solution, and the mixture was sonicated again for 10 minutes. The solution was transferred to a polytetrafluoroethylene-lined autoclave and heated at 180°C for 14 hours. Subsequently, the product was thoroughly washed with excess acetone (30 mL × 2) and dichloromethane (30 mL × 2). Finally, it was dried in an oven at 60°C for 12 hours to obtain SNW-1@CuS-S.

[0017] Test 1: Using *Ulva prolifera* microscopic propagules as the test subject, the removal efficiency of different photocatalysts was investigated using the removal rate as an indicator, and the photocatalyst with better performance was selected for subsequent experiments. Healthy *Ulva prolifera* plants were selected, and the experiment was conducted in a constant temperature incubator at 22±1℃, with a light intensity of 3000 lux and a photoperiod of 12 hours light / 12 hours dark. Microscopic propagules were collected for subsequent experiments. The density of microscopic propagules was set at 14.929 × 10⁻⁶. 5 Cells / mL. Each experimental group was divided into three replicates, and the results were averaged. During the experiment, the number of surviving microscopic reproductive cells was calculated by measuring chlorophyll a content and constructing a standard curve at the required time points, and growth curves were plotted.

[0018] Test 2: Using *Ulva prolifera* micropropagules as the test subject, and comparing the inactivation effects of micropropagules on the control group, SNW-1 treatment group, CuS treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-D treatment group with chlorophyll a content as the indicator. The experimental conditions were the same as in Test 1. Each time, 10 mL of micropropagule mixture was collected and centrifuged at 4℃ and 5000 r / min for 15 min to collect the micropropagule cells. After centrifugation, 96% ethanol solution was added to the centrifuge tube, and extraction was performed at 4℃ in the dark for 24 h, followed by centrifugation at 4℃ and 5000 r / min for 15 min. 200 µL of the supernatant was added to a 96-well plate, and absorbance was measured at 665 nm and 649 nm. The chlorophyll a content was calculated using the following formula: Ca (mg / L) = 13.95 × A 663 nm-6.88×A 646 nm.

[0019] Test 3: Using *Ulva prolifera* microscopic propagules as the test subject, the inactivation effect of microscopic propagules was compared among the control group, SNW-1 treatment group, CuS treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-D treatment group, with the soluble protein content of the microscopic propagule cells as the indicator. The experimental conditions were the same as in Test 1. Each time, 10 mL of the microscopic propagule mixture was taken, centrifuged at 4℃ and 5000 r / min for 15 min, then washed once with PBS solution, and finally, PBS solution was added to a final volume of 4 mL. Cell disruption was performed using an ultrasonic cell disruptor. The disrupted solution was centrifuged again, and the supernatant was used as the test sample. 5 µL of the supernatant was placed in a 96-well plate, 250 µL of G-250 staining solution was added, and the absorbance at 595 nm was measured using a microplate reader. The protein concentration was calculated based on the protein standard curve.

[0020] Test 4: Using *Ulva prolifera* microscopic propagules as the test subject, the inactivation effect of malondialdehyde (MDA) in the microscopic propagule cells was compared with that of the control group, SNW-1 treatment group, CuS treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-D treatment group. The experimental conditions were the same as in Test 1, and the microscopic propagule cells were treated according to the Nanjing Jiancheng MDA assay kit (TBA method). 10 mL of the microscopic propagule mixture was taken each time, centrifuged at 4℃ and 5000 r / min for 15 min, then washed once with PBS solution, and finally, PBS solution was added to a final volume of 4 mL. The cells were then disrupted using an ultrasonic cell disruptor. The disrupted solution was centrifuged again, and the supernatant was the MDA extract. The supernatant was used to add reagents according to the kit instructions, and 200 μL was added to a 96-well plate. The absorbance was measured at 532 nm using a microplate reader, and the MDA content in the sample was subsequently calculated using the formula.

[0021] Test 5: Three-week-old seedlings of *Ulva prolifera* were used as test subjects. The relative growth rate of *Ulva prolifera* seedlings was used as the index to compare the growth inhibition effects of the control group, SNW-1 treatment group, CuS treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-S treatment group. The seedling density was 1.5 g / L. The experiment was conducted in a constant temperature and light incubator, with the temperature set at 25 degrees Celsius and the light intensity at 100 μmol / L. −2 s −1The experiment employed a 12-hour light-dark cycle. Each experimental group was divided into three replicates, and the average results were taken. The fresh weight (FW) of three-week-old seedlings was measured daily during the experiment. Samples were removed from the culture flasks, surface moisture was blotted with dry paper towels, and then weighed. The relative growth rate (RGR) was calculated using the following formula: RGR (% / day) = (lnWt2 – lnWt1) / (t2 – t1) × 100, where Wt1 and Wt2 represent the fresh weight values ​​measured at time points t1 and t2, respectively, and (t2 – t1) represents one day.

[0022] Test 6: Using three-week-old seedlings of *Ulva prolifera* as the test subjects, the growth inhibition effects of the control group, SNW-1 treatment group, CuS treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-S treatment group were compared using chlorophyll a content as an indicator. The experimental conditions were the same as in Test 5. 0.01 g of sample was weighed and extracted with 3 mL of anhydrous methanol. The mixture was stored at 4℃ in the dark for 24 hours, and then centrifuged at 4℃ and 5000 r / min for 15 min. 200 µL of the supernatant was added to a 96-well plate, and the absorbance was measured at wavelengths of 470, 653, and 666 nm.

[0023] Test 7: Using three-week-old *Ulva prolifera* seedlings as the test subjects, the growth inhibition effects of the control group, SNW-1 treatment group, CuS treatment group, and modified covalent organic framework photocatalyst SNW-1@CuS-S treatment group were compared, with MDA content as the indicator. The experimental conditions were the same as in Test 5. *Ulva prolifera* seedlings were treated according to the Nanjing Jiancheng Malondialdehyde MDA Assay Kit (TBA method). 0.01 g of sample was weighed, washed once with PBS, and the volume was adjusted to 4 ml with PBS. The sample was mechanically homogenized under ice bath conditions and then centrifuged at 4℃ and 5000 r / min for 15 min. The supernatant was the MDA extract. The supernatant was used to add reagents according to the kit instructions to prepare the system. Finally, 200 μL was added to a 96-well plate, and the absorbance was measured at 532 nm using a microplate reader. The MDA content in the sample was then calculated using the formula.

[0024] Depend on Figure 2 As can be seen, after 120 hours of photocatalytic treatment, the SNW-1@CuS-D group reduced the concentration of microbezoars to 4.46 times. 5Cells / mL, corresponding to an inactivation efficiency exceeding 70%. Comparative analysis showed that the residual microbiota concentration in the copper sulfide group was slightly higher than that in the SNW-1 group. This observation indicates that although SNW-1 has limited photocatalytic activity, it mainly exerts its algicidal effect through competitive adsorption and aggregation-induced death. In contrast, CuS exhibits a dual function—directly inactivating microbiota and inhibiting their growth and germination. SNW-1@CuS-D achieves superior performance by integrating these mechanisms, realizing a synergistic enhancement of adsorption-driven immobilization and photocatalytic inhibition.

[0025] Depend on Figure 3 It is evident that chlorophyll a, as the main photosynthetic pigment in algal cells, directly regulates light capture efficiency and carbon assimilation capacity. High chlorophyll a content is closely related to vigorous photosynthetic activity and rapid biomass accumulation, while a decrease in content leads to weakened low-light adaptation and reduced ecological competitiveness. Notably, chlorophyll a concentration is positively correlated with micropropagule density, thus serving as a proxy indicator of cell viability. Compared to the control group, the photocatalytic treatment group showed a significant decrease in chlorophyll a content within 120 hours (p<0.01), indicating that photocatalytic activity induces micropropagule death and metabolic inactivation. These findings directly demonstrate that photocatalytic activity is the direct cause of cell death.

[0026] Depend on Figure 4 As can be seen, the initial soluble protein content was 0.0611 mg / mL. Within 0-12 h, the trend of soluble protein content change was similar to that of chlorophyll a content. The decrease in soluble protein content indicates damage to algal cells. Furthermore, the SNW-1@CuS-D treatment group showed the highest degree of algal cell damage (finally 0.08 mg / mL). This indirectly proves that the SNW-1@CuS-D material exhibits the best photocatalytic activity, followed by the SNW-1 material. The SNW-1@CuS-D material demonstrates excellent removal rate of microscopic reproductive somatic cells.

[0027] Depend on Figure 5 As can be seen, the MDA content in the SNW-1@CuS-D treated group was increased and higher than that in the control group. This indicates that the cell membranes of the microscopic proliferating somatic cells in this group were damaged. During the 120-hour photocatalyst exposure, the MDA content gradually increased. At 120 hours, the MDA concentration in the SNW-1@CuS-D group reached 17.72 nmol / mg, significantly higher than other groups (p<0.01). This phenomenon is attributed to the enhanced reactive oxygen species exposure mediated by SNW-1@CuS-D-mediated cell adsorption, which exacerbated the damage to the photocatalytic membrane.

[0028] Depend on Figure 6As can be seen, on day 6, the RGR value of the SNW1@CuS-S group decreased to 0.011, and that of the CuS group decreased to 0.019. No statistically significant difference was observed between the two groups, and both showed a continuous downward trend after two days. The decrease in the SNW-1@CuS-D group was significantly smaller than that of the two groups. The RGR value of the SNW-1@CuS-S group was similar to that of the SNW-1@CuS-D group. The control group showed fluctuations of first increasing and then decreasing in the later stages, which was attributed to limited growth space. The SNW-1 group was highly similar to the control group, but the value was slightly lower. Compared with the CuS and SNW-1@CuS-S groups, the SNW-1@CuS-D group had a weaker inhibitory effect on the growth of *Ulva prolifera* seedlings, but it was more significant than that of the SNW-1 group. The SNW-1@CuS-S material has been shown to combine the strong photocatalytic activity of CuS with the matrix advantages of SNW-1. Depend on Figure 7 As can be seen, the chlorophyll a content in the control group and the SNW-1 group continuously increased, showing a significant difference compared to day 0. The SNW-1@CuS-S group, however, showed a continuous decreasing trend, with the content dropping to 257.35 μg / mg FW after 144 hours, a significant difference compared to day 0, but no significant differences were found between the groups on the same day. Chlorophyll a analysis provides physiological insights into the potential mechanisms underlying the differences in photocatalyst efficiency. The study found that photocatalytic materials (CuS and SNW-1@CuS-S) can significantly degrade chlorophyll a in *Ulva prolifera* seedlings, leading to damage to the core components of the photosynthetic apparatus.

[0029] Depend on Figure 8 As can be seen, all groups showed a gradual upward trend after 2 days of treatment, followed by a significant decrease on day 3, and then a continuous decline. In the SNW-1@CuS-S group, after 144 hours of treatment, the MDA content decreased to 206.02 nmol / g FW. The MDA level initially increased and then decreased over 3 days, suggesting that membrane damage had begun to accumulate. The subsequent decrease was interpreted as the initiation of programmed cell death or large-scale cell lysis, leading to a reduction in MDA metabolite levels. This change reflects a more complex physiological breakdown mechanism, although ultimately irreversible.

[0030] The above description is only a preferred embodiment of the present invention. All changes and modifications made in accordance with the claims of the present invention are within the scope of the present invention.

Claims

1. A method for preparing a modified covalent organic framework photocatalyst, characterized in that, Includes the following steps: Step 1: Synthesis of Cu2O: 1.596g Cu(CH3COO)2·H2O, 1.53g glucose and 0.666g PVP (K-30) were dispersed in 120mL DMF. The mixture was stirred vigorously for 90 minutes, and then heated to 80℃ with continuous stirring and held for 10 minutes. The resulting powder was washed several times with deionized water and ethanol alternately. Step 2: Synthesis of CuS: Cu2O was prepared at a concentration of 2 mg·mL⁻¹ -1 The concentration was dissolved in deionized water, and then 54 mL of 0.086 mol·L⁻¹ solution was added under magnetic stirring. -1 Na2S aqueous solution was added dropwise to 26 mL of the above solution. After the addition was complete, the reaction continued for 5 minutes. After complete washing with deionized water, the final CuS spheres were collected. Step 3: Synthesis of SNW-1: 470 mg, 3.73 mmol melamine and 750 mg, 5.59 mmol terephthalaldehyde were dissolved in 23 mL DMSO and heated at 180°C for 14 hours in a PTFE-lined laboratory autoclave. The product was then thoroughly washed with excess acetone and dichloromethane and dried in an oven at 60°C for 12 hours to obtain a white powder, SNW-1. Synthesis of SNW-1@CuS-D: 125.05 mg SNW-1 was dispersed in 100 mL deionized water and sonicated for 10 minutes. 20 mg copper sulfide was added, and the mixture was magnetically stirred for 2 hours. After centrifugation, the supernatant was discarded, and the product was dried at 60°C for 12 hours to obtain SNW-1@CuS-D. Alternatively, the synthesis of SNW-1@CuS-S: 470 mg, 3.73 mmol melamine and 750 mg, 5.59 mmol terephthalaldehyde were dissolved in 23 mL DMSO. The mixture was sonicated for 5 minutes to form a transparent solution. 0.2178 mg copper sulfide was added to the solution, and the mixture was sonicated for another 10 minutes. The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave and heated at 180°C for 14 hours. The product was then thoroughly washed with excess acetone and dichloromethane; and dried in an oven at 60°C for 12 hours to obtain SNW-1@CuS-S.

2. A modified covalent organic framework photocatalyst SNW-1@CuS-D / SNW-1@CuS-S prepared by the preparation method of claim 1.

3. The application of the modified covalent organic framework photocatalyst SNW-1@CuS-D / SNW-1@CuS-S as described in claim 2 in suppressing green tides.

4. The application according to claim 3, characterized in that, The tested algae was *Ulva prolifera*.

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