Algae residue carbon-based photocatalyst and its preparation method and application

Abstract

This invention relates to the field of photocatalytic materials technology, specifically to an algal residue carbon-based photocatalyst, its preparation method, and its application. The catalyst is prepared by treating algal residue with sodium hydroxide to obtain algal residue powder, impregnating and loading it with a metal salt, and then co-sintering it to obtain metal-modified algal residue biochar. After treatment with concentrated nitric acid to introduce carboxyl groups, thiophenepyridine polyhydroxy ligands are grafted onto it, and finally ball-milled with Fe3O4 to form the catalyst. The thiophenepyridine polyhydroxy ligands are prepared by Heck coupling of 4-bromo-2-thiophenecarboxaldehyde and 2-vinylnicotinic acid, followed by Schiff base condensation with 2-aminonicotinic acid and then amidation with tris(hydroxymethyl)aminomethane. This catalyst can efficiently photocatalyze the degradation of tetracycline hydrochloride, providing a more sustainable solution for the efficient purification of tetracycline-contaminated water bodies.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, and in particular to an algal residue carbon-based photocatalyst, its preparation method, and its application. Background Technology

[0002] Tetracycline antibiotics, as broad-spectrum antibacterial drugs, are widely used in the treatment of human diseases, animal husbandry, and the prevention and control of agricultural diseases. However, due to their low metabolic rate in organisms (only about 30% is absorbed), a large amount of unused tetracycline enters the aquatic environment through medical wastewater, aquaculture wastewater, and agricultural runoff, becoming a typical emerging pollutant. Tetracycline in the environment not only has acute toxicity to aquatic organisms (such as inhibiting algal photosynthesis and interfering with fish growth and development), but it can also induce the production of drug-resistant genes in microorganisms, accumulating through the food chain and posing a potential threat to human health. Studies have shown that long-term exposure to low concentrations of tetracycline may lead to an imbalance in the human gut microbiota, increased antibiotic resistance, and even an increased risk of bacterial infections.

[0003] Currently, technologies for treating tetracycline in water mainly include physical adsorption, chemical oxidation, biodegradation, and photocatalytic degradation. Physical adsorption methods (such as activated carbon adsorption), while simple to operate, only transfer the pollutant, easily causing secondary pollution and making adsorbent regeneration difficult. Chemical oxidation methods (such as Fenton's reagent and ozone oxidation), while having high degradation efficiency, require large amounts of chemical reagents, resulting in high costs and the generation of toxic intermediates. Biodegradation relies on microbial metabolism and is affected by the antibacterial properties of tetracycline itself, leading to slow degradation rates and a narrow applicable concentration range. Photocatalytic degradation technology has become a research hotspot due to its advantages of high efficiency and no secondary pollution; however, its core catalysts (such as TiO2 and ZnO) suffer from problems such as narrow light response range, high recombination rate of photogenerated carriers, poor stability, and difficulty in recovery, limiting practical applications.

[0004] In existing photocatalytic systems, to improve the degradation efficiency of tetracycline, it is often necessary to combine it with oxidants such as potassium persulfate to activate and generate free radicals. However, this process depends on specific metal ions (such as Co). 2+ Mn 2+ The catalytic effect of these catalysts can easily lead to the leaching and pollution of metal ions. Furthermore, most catalysts are pH sensitive and tend to aggregate and deactivate under acidic or alkaline conditions, making them unsuitable for complex aquatic environments. In addition, traditional catalysts often use artificially synthesized supports (such as graphene and carbon nanotubes) as substrates, resulting in high costs and environmentally unfriendly preparation processes. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose an algal residue carbon-based photocatalyst, its preparation method and application.

[0006] To achieve the above objectives, the present invention provides a method for preparing an algal residue carbon-based photocatalyst, comprising the following steps:

[0007] S1. After washing and drying, the algal residue is crushed to 80 mesh, immersed in a 20% sodium hydroxide solution, stirred thoroughly, ultrasonically treated for 15 minutes, and then soaked at room temperature for 12 hours to remove oily substances from the algal residue. After discarding the residual liquid, it is dried to obtain algal residue powder.

[0008] S2. Add algal residue powder and metal salt to deionized water, sonicate for 20-30 min, transfer to a shaker, shake at 150 rpm for 24 h, filter, dry to constant weight, pass through a 50 mesh sieve, place in a muffle furnace, heat to 500℃ at a heating rate of 5℃ / min, hold for 3 h, cool to room temperature to obtain metal-modified algal residue biochar. The purpose of this step is to load metal ions onto algal residue and sinter at high temperature to form metal-modified algal residue biochar. The metal species can serve as photocatalytic active centers, while the biochar formed by algal residue carbonization provides a conductive framework to promote the transfer of photogenerated electrons.

[0009] S3. Add metal-modified algal residue biochar to concentrated nitric acid, heat to 100-110℃, react for 3-5 hours. After the reaction is complete, cool to room temperature, filter, and wash the obtained solid with deionized water until the pH of the washing solution is neutral. After drying, carboxylated metal algal residue biochar is obtained. The purpose of this step is to introduce carboxyl groups on the surface of metal-modified algal residue biochar through the strong oxidizing property of concentrated nitric acid, increase the surface active sites, provide reaction groups for the subsequent esterification reaction with thiophenepyridine polyhydroxy ligands, and further remove residual amorphous carbon impurities. The introduction of carboxyl groups can also enhance the hydrophilicity of biochar, which is beneficial to the dispersion of the catalyst in water during subsequent application.

[0010] S4. Carboxylated metal algal residue biocarbon is added to dichloromethane, followed by thiophenepyridine polyhydroxy ligand, p-toluenesulfonic acid, and N,N-dicyclohexylcarbodiimide. The mixture is stirred at room temperature for 8-12 hours, filtered, washed with ethanol, dried, and placed in a high-energy ball mill with Fe3O4 added. The mill is set to a speed of 300 rpm for 2 hours to obtain an algal residue carbon-based photocatalyst. The core function of this step is to graft the thiophenepyridine polyhydroxy ligand onto the surface of the carboxylated biocarbon through esterification, while the composite Fe3O4 imparts magnetic recyclability to the catalyst.

[0011] Preferably, in step S2, the algae residue powder and metal salt are added to the deionized water at a ratio of 0.003-0.007 mol of metal salt per gram of algae residue powder.

[0012] Preferably, in step S2, the weight ratio of algal residue powder to deionized water is 1:8-12.

[0013] Preferably, the metal salt in step S2 refers to one of manganese chloride, magnesium chloride, or cobalt chloride.

[0014] Preferably, in step S3, the metal-modified algal residue biochar and concentrated nitric acid are in a weight ratio of 1:3-5.

[0015] Preferably, in step S3, concentrated nitric acid refers to a nitric acid solution with a mass concentration of 68%.

[0016] Preferably, in step S4, the carboxylated metal algal residue biochar, dichloromethane, thiophenepyridine polyhydroxy ligand, p-toluenesulfonic acid, N,N-dicyclohexylcarbodiimide and Fe3O4 are in a weight ratio of 1:8-12:0.1-0.2:0.01-0.03:0.2-0.4:0.1-0.3.

[0017] Preferably, the catalytic mechanism of the algal residue carbon-based photocatalyst in step S4 is as follows:

[0018] Metals (such as Mn) supported in algal residue carbon-based photocatalysts 2+ Mg 2+ Co 2+ The photocatalytic reaction is mediated by the active center of the metal ions, which generates a photocatalytic effect through the synergistic interaction between the metal ions, ligands, and carbon matrix. The specific mechanism is as follows:

[0019] Metal ions form strong coordination bonds with the bispyridine ring of the thiophene pyridine polyhydroxy ligand, becoming the "transport hub" for photogenerated electrons. Under visible light irradiation, the conjugated π system of the ligand absorbs light energy to generate photogenerated electron-hole pairs. The empty d orbitals of the metal ion can efficiently capture the photogenerated electrons transferred by the ligand, preventing electron-hole recombination. This process significantly improves the carrier separation efficiency, providing sufficient electrons for subsequent reduction reactions. Simultaneously, the redox properties of the metal ion directly participate in the generation of active species. The captured photogenerated electrons are transferred to the carbon matrix surface via the d orbitals of the metal ion, where they undergo a single-electron reduction reaction with oxygen adsorbed on the catalyst surface (O2 + e^(-2-)). - →·O2 - ), generating superoxide radicals (·O2) with strong oxidizing properties. - Furthermore, the presence of metal ions can enhance the catalyst's adsorption capacity for tetracycline by modulating the surface charge distribution, making the substrate more readily adsorbed by •O2. - Contact accelerates the degradation reaction; it is evident that metal ions are not only the "capture-transfer center" of photogenerated electrons, but also the core bridge connecting ligand light absorption and active species generation. Their own electronic properties and coordination environment jointly determine the photocatalytic efficiency and are the main driving force for the photocatalytic effect. Ligands, on the other hand, assist metals in performing their functions by enhancing light absorption, stabilizing metal coordination, and improving hydrophilicity. The two work together to achieve efficient photocatalysis.

[0020] Preferably, the preparation method of the thiophenepyridine polyhydroxy ligand in step S4 includes the following steps:

[0021] (1) Under nitrogen protection, 4-bromo-2-thiophenecarboxaldehyde, 2-vinylnicotinic acid, sodium acetate, palladium acetate and tris(o-methylphenyl)phosphine were added to N,N-dimethylformamide, heated to 120-140℃, reacted for 4-6 h, cooled to room temperature, filtered, added deionized water, extracted three times with ethyl acetate, combined the organic phases, washed with saturated brine, separated and collected the organic phase, dried with anhydrous sodium sulfate, filtered, concentrated under reduced pressure to remove solvent, and the crude product was purified by silica gel column chromatography with petroleum ether:ethyl acetate 3:1 as the eluent to obtain intermediate 1. The chemical reaction equation is as follows:

[0022] ,

[0023] The product was characterized by 1H NMR. This step of the reaction was a palladium-catalyzed Heck coupling reaction. In the reaction, palladium acetate generated an active Pd(0) species under the action of tris(o-methylphenyl)phosphine ligand. It then underwent oxidative addition with the C-Br bond in 4-bromo-2-thiophenecarboxaldehyde to form a Pd(II) complex. Subsequently, the carbon-carbon double bond of 2-vinylnicotinic acid was inserted into the Pd(II)-C bond, and after β-H elimination, intermediate 1 containing a thiophene-pyridine conjugated structure was generated. Sodium acetate was used to neutralize the hydrobromic acid generated in the base reaction and maintain the activity of the palladium catalyst. Finally, the catalytic cycle was completed through the synergistic effect of the ligand and palladium, and the carbon-carbon bond was constructed.

[0024] (2) Under nitrogen protection, intermediate 1 and 2-aminonicotinic acid were added to anhydrous ethanol, heated to 75-85℃, reacted for 3-4 h, cooled to 0℃, and kept at that temperature for 1 h. A large amount of solid was observed to precipitate. The solid was filtered, collected, washed, and dried to obtain intermediate 2. The chemical reaction equation is as follows:

[0025] ,

[0026] The product was characterized by H NMR. This step is a Schiff base condensation reaction between an aldehyde group and an amino group. The aldehyde group in intermediate 1 is electrophilic. The amino group of 2-aminonicotinic acid acts as a nucleophile to attack the carbonyl carbon of the aldehyde group, forming a hydroxyamine intermediate through nucleophilic addition. Under heating conditions, the intermediate undergoes a dehydration elimination reaction to generate a stable imine bond. The imine bond is further conjugated with the thiophene-pyridine conjugated system, which enhances the stability of the product. Low-temperature cooling causes intermediate 2 to precipitate in solid form.

[0027] (3) Add intermediates 2,1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to dichloromethane, stir in the dark for 30-50 min, then add tris(hydroxymethyl)aminomethane, and react at room temperature for 8-12 h. Wash the organic phase once with saturated sodium bicarbonate and once with deionized water, dry with anhydrous sodium sulfate, and concentrate under reduced pressure to remove the organic solvent. The crude product is recrystallized from a mixed solution of ethyl acetate / petroleum ether to obtain thiophene pyridine polyhydroxy ligands. The chemical reaction equation is as follows:

[0028] ,

[0029] The product was characterized by 1H NMR. This step was an amidation reaction of the carboxyl and amino groups. Under the action of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), the carboxyl group of intermediate 2 was activated to generate a highly active NHS ester. The amino group of tris(hydroxymethyl)aminomethane acted as a nucleophile to attack the carbonyl carbon of the active ester, and a nucleophilic substitution reaction was carried out to form an amide bond. After the reaction was completed, the byproducts were removed by washing, and finally, pure thiophenepyridine polyhydroxy ligands were obtained by recrystallization. The formation of amide bonds allowed the ligands to retain both polyhydroxy groups and conjugated coordination sites.

[0030] Preferably, the thiophenepyridine polyhydroxy ligand is the core functional unit of this invention, and its function and mechanism stem from its unique molecular structure and electronic properties, specifically manifested in the following four synergistic effects:

[0031] Visible light capture and photogenerated carrier generation: The thiophene ring and the bispyridine ring in the ligand molecule are connected by a conjugated π system, forming a large π-bonded conjugated structure. This structure can efficiently absorb visible light through the π→π* transition from bonding π orbitals to antibonding π orbitals, thus exciting and generating photogenerated electron-hole pairs. This conjugated structure can also suppress photogenerated carrier recombination through delocalization, providing sufficient active species for photocatalytic reactions.

[0032] Coordination anchoring and activity regulation of metal ions: The bispyridine ring in the ligand molecule contains an electron-rich nitrogen atom. Its lone pair electrons can form strong coordination bonds with the empty d orbitals of the metal ions (such as Co, Mn, Mg) supported in the catalyst. Some can also form d-pπ back-bonding bonds (the d orbitals filled with electrons of the metal ion feed back electrons to the empty p* antibonding orbitals of the ligand nitrogen atom). This coordination effect anchors the metal ions firmly to the carbon matrix surface, preventing them from dissolving during catalysis (maintaining the stability of the active center); on the other hand, it regulates the redox potential of the metal ions through electronic effects, optimizing their ability to capture and transport photogenerated electrons, indirectly improving the generation efficiency of active species (such as superoxide radicals).

[0033] Enhanced hydrophilicity and substrate adsorption: The polyhydroxyl groups in the ligand molecule are linked to tris(hydroxymethyl)aminomethane via amide bonds. These hydroxyl groups can form hydrogen bonds with water molecules, significantly improving the aqueous dispersibility of the catalyst. Simultaneously, intermolecular forces exist between the hydroxyl groups and the amide and phenolic hydroxyl groups in the tetracycline hydrochloride molecule, enhancing the surface adsorption of tetracycline on the catalyst, making it easier for the substrate to contact the active species and accelerating the catalytic reaction process.

[0034] Stable connection with the carbon matrix: The ligand undergoes esterification with the carboxyl groups on the surface of carboxylated metallized algal biochar via its terminal carboxyl groups, ensuring that the ligand does not detach during ball milling and catalysis. This covalent connection enables the conjugated system of the ligand to form a "molecular wire" with the conductive network of the carbon matrix, promoting the transfer of photogenerated electrons from the ligand to the carbon matrix and further improving catalytic efficiency.

[0035] Preferably, in step (1), the molar ratio of 4-bromo-2-thiophenecarboxaldehyde, 2-vinylnicotinic acid, sodium acetate, palladium acetate and tris(o-methylphenyl)phosphine is 1:1-1.2:2-3:0.03-0.07:0.1-0.2.

[0036] Preferably, in step (1), the weight ratio of 4-bromo-2-thiophene formaldehyde, N,N-dimethylformamide and deionized water is 1:8-12:4-8.

[0037] Preferably, in step (2), the molar ratio of intermediate 1 and 2-aminonicotinic acid is 1:1-1.2.

[0038] Preferably, in step (2), intermediate 1 and anhydrous ethanol are in a weight ratio of 1:4-6.

[0039] Preferably, in step (3), the molar ratio of intermediate 2, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and tris(hydroxymethyl)aminomethane is 1:1.2-1.5:1-1.2:1-1.2.

[0040] Preferably, in step (3), intermediate 2 and dichloromethane are in a weight ratio of 1:15-20.

[0041] Preferably, the ethyl acetate / petroleum ether mixed solution in step (3) refers to the mixture of ethyl acetate and petroleum ether in a weight ratio of 2:3.

[0042] Furthermore, the present invention also provides an algal residue carbon-based photocatalyst prepared by the above-described preparation method.

[0043] Furthermore, the present invention also provides the application of the above-mentioned algal residue carbon-based photocatalyst in the photocatalytic decomposition of tetracycline hydrochloride.

[0044] The beneficial effects of this invention are:

[0045] 1. This invention prepares carbon-based photocatalysts using algal residue as raw material, successfully transforming waste algal residue generated from eutrophication into high-performance photocatalytic materials. The bio-carbon formed after carbonization of algal residue possesses abundant pore structure and good electrical conductivity, providing an excellent carrier for photocatalytic reactions. This not only solves the environmental pollution problem caused by algal residue accumulation but also reduces the cost of catalyst preparation. Compared to traditional catalysts based on artificially synthesized carbon materials, this invention uses widely available and inexpensive raw materials, and the preparation process has low energy consumption, resulting in significant environmental and economic benefits.

[0046] 2. This invention significantly enhances the visible light absorption capacity and photogenerated carrier separation efficiency of the catalyst by grafting thiophene-pyridine polyhydroxy ligands. The thiophene-pyridine conjugated structure of the ligand can efficiently capture visible light, generating a large number of photogenerated electron-hole pairs, and the delocalization effect of the conjugated system can effectively suppress carrier recombination; the polyhydroxy groups enhance the catalyst's adsorption capacity for tetracycline, ensuring close contact between the substrate and the active site. Simultaneously, the catalyst maintains stable activity in a wide pH range of water bodies (pH 3-11), efficiently degrading tetracycline regardless of whether the water is acidic, neutral, or alkaline. It is suitable for practical wastewater systems with varying acidity and alkalinity, solving the problems of traditional catalysts' pH sensitivity and narrow applicability.

[0047] 3. This invention effectively inhibits metal ion dissolution and ligand detachment through the coordination of metal ions with ligands and the covalent connection between ligands and the carbon matrix, significantly improving the catalyst's cycle stability and allowing for long-term repeated use while maintaining high activity. Furthermore, the catalyst is magnetically endowed by composite Fe3O4, enabling rapid separation and recovery after the reaction using a simple external magnetic field. This avoids catalyst loss and secondary pollution caused by traditional centrifugation or filtration, reduces separation costs, and significantly improves the feasibility of the catalyst in practical wastewater treatment, laying the foundation for large-scale promotion.

[0048] 4. The catalyst of this invention can directly utilize visible light and oxygen in water to generate superoxide radicals, which dominate the degradation reaction, reducing dependence on exogenous oxidants such as potassium persulfate. This characteristic not only simplifies the reaction process and reduces treatment costs, but also avoids secondary pollution (such as oxidant residues and byproduct generation) that may be caused by exogenous oxidants. Compared with traditional photocatalytic systems that rely on oxidant activation, this invention reduces potential environmental risks and provides a more sustainable solution for the efficient purification of tetracycline-contaminated water. Attached Figure Description

[0049] Figure 1 The H NMR spectrum of intermediate 1 prepared in Example 2 of this invention.

[0050] Figure 2The H NMR spectrum of intermediate 2 prepared in Example 2 of this invention.

[0051] Figure 3 The 1H NMR spectrum of the thiophenepyridine polyhydroxy ligand prepared in Example 2 of this invention.

[0052] Figure 4 The FTIR infrared spectra of the carboxylated metal algal residue biocarbon prepared in Examples 1-3 of this invention are shown.

[0053] Figure 5 This is a SEM image of the algal residue carbon-based photocatalyst prepared in Example 1 of the present invention.

[0054] Figure 6 This is a SEM image of the algal residue carbon-based photocatalyst prepared in Example 2 of the present invention.

[0055] Figure 7 This is a SEM image of the algal residue carbon-based photocatalyst prepared in Example 3 of the present invention. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0057] Preparation Example 1: The specific preparation method of thiophenepyridine polyhydroxy ligand includes the following steps:

[0058] (1) Under nitrogen protection, 10g of 4-bromo-2-thiophene carboxaldehyde, 7.81g of 2-vinylnicotinic acid, 8.59g of sodium acetate, 0.35g of palladium acetate and 1.59g of tris(o-methylphenyl)phosphine were added to 80g of N,N-dimethylformamide, heated to 120℃ and reacted for 4h. After cooling to room temperature, the mixture was filtered, 40g of deionized water was added, and the mixture was extracted three times with ethyl acetate. The organic phases were combined, washed with saturated brine, and the organic phases were separated and collected. The organic phases were dried with anhydrous sodium sulfate, filtered, concentrated under reduced pressure to remove the solvent, and the crude product was purified by silica gel column chromatography with petroleum ether: ethyl acetate 3:1 as the eluent to obtain intermediate 1.

[0059] (2) Under nitrogen protection, 15g of intermediate 1 and 7.99g of 2-aminonicotinic acid were added to 60g of anhydrous ethanol, heated to 75℃, reacted for 3h, cooled to 0℃, and kept warm for 1h. A large amount of solid was observed to precipitate. The solid was filtered, collected, washed, and dried to obtain intermediate 2.

[0060] (3) 20g of intermediate 2, 12.13g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 6.07g of N-hydroxysuccinimide were added to 300g of dichloromethane and stirred in the dark for 30min. Then 6.39g of tris(hydroxymethyl)aminomethane was added and the reaction was carried out at room temperature for 8h. The organic phase was washed once with saturated sodium bicarbonate and once with deionized water. After drying with anhydrous sodium sulfate, the organic solvent was removed by vacuum concentration. The crude product was recrystallized from the ethyl acetate / petroleum ether mixture (ethyl acetate and petroleum ether were mixed in a weight ratio of 2:3) to obtain thiophenepyridine polyhydroxy ligand.

[0061] Preparation Example 2: The specific preparation method of thiophenepyridine polyhydroxy ligand includes the following steps:

[0062] (1) Under nitrogen protection, 10g of 4-bromo-2-thiophene carboxaldehyde, 8.59g of 2-vinylnicotinic acid, 10.73g of sodium acetate, 0.59g of palladium acetate and 2.39g of tris(o-methylphenyl)phosphine were added to 100g of N,N-dimethylformamide, heated to 130℃ and reacted for 5h. After cooling to room temperature, the mixture was filtered, 60g of deionized water was added, and the mixture was extracted three times with ethyl acetate. The organic phases were combined, washed with saturated brine, and the organic phases were separated and collected. The organic phases were dried with anhydrous sodium sulfate, filtered, concentrated under reduced pressure to remove the solvent, and the crude product was purified by silica gel column chromatography with petroleum ether: ethyl acetate 3:1 as the eluent to obtain intermediate 1.

[0063] (2) Under nitrogen protection, 15g of intermediate 1 and 8.79g of 2-aminonicotinic acid were added to 75g of anhydrous ethanol, heated to 80℃, reacted for 3.5h, cooled to 0℃, and kept warm for 1h. A large amount of solid was observed to precipitate. The solid was filtered, collected, washed, and dried to obtain intermediate 2.

[0064] (3) 20g of intermediate 2, 13.64g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 6.67g of N-hydroxysuccinimide were added to 340g of dichloromethane and stirred in the dark for 40min. Then 7.02g of tris(hydroxymethyl)aminomethane was added and reacted at room temperature for 10h. The organic phase was washed once with saturated sodium bicarbonate and once with deionized water. After drying with anhydrous sodium sulfate, the organic solvent was removed by vacuum concentration. The crude product was recrystallized from the ethyl acetate / petroleum ether mixture (ethyl acetate and petroleum ether were mixed in a weight ratio of 2:3) to obtain thiophenepyridine polyhydroxy ligand.

[0065] Preparation Example 3: The specific preparation method of thiophenepyridine polyhydroxy ligand includes the following steps:

[0066] (1) Under nitrogen protection, 10g of 4-bromo-2-thiophene carboxaldehyde, 9.37g of 2-vinylnicotinic acid, 12.88g of sodium acetate, 0.82g of palladium acetate and 3.19g of tris(o-methylphenyl)phosphine were added to 120g of N,N-dimethylformamide, heated to 140℃ and reacted for 6h. After cooling to room temperature, the mixture was filtered, 80g of deionized water was added, and the mixture was extracted three times with ethyl acetate. The organic phases were combined, washed with saturated brine, and the organic phases were separated and collected. The organic phases were dried with anhydrous sodium sulfate, filtered, concentrated under reduced pressure to remove the solvent, and the crude product was purified by silica gel column chromatography with petroleum ether: ethyl acetate 3:1 as the eluent to obtain intermediate 1.

[0067] (2) Under nitrogen protection, 15g of intermediate 1 and 9.59g of 2-aminonicotinic acid were added to 90g of anhydrous ethanol, heated to 85℃, reacted for 4h, cooled to 0℃, and kept warm for 1h. A large amount of solid was observed to precipitate. The solid was filtered, collected, washed, and dried to obtain intermediate 2.

[0068] (3) 20g of intermediate 2, 15.16g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 7.28g of N-hydroxysuccinimide were added to 400g of dichloromethane and stirred in the dark for 50min. Then 7.66g of tris(hydroxymethyl)aminomethane was added and the reaction was carried out at room temperature for 12h. The organic phase was washed once with saturated sodium bicarbonate and once with deionized water. After drying with anhydrous sodium sulfate, the organic solvent was removed by vacuum concentration. The crude product was recrystallized from the ethyl acetate / petroleum ether mixture (ethyl acetate and petroleum ether were mixed in a weight ratio of 2:3) to obtain thiophenepyridine polyhydroxy ligand.

[0069] Comparative preparation example: The difference between the comparative preparation example and preparation example 2 is that 4-bromo-2-thiophenecaraldehyde is replaced with 4-bromobenzaldehyde, while the rest remains unchanged, and phenylpyridine polyhydroxy ligands are finally prepared.

[0070] Example 1: A specific preparation method of an algal residue carbon-based photocatalyst, comprising the following steps:

[0071] S1.100g of algal residue was washed, dried and pulverized to 80 mesh, then immersed in a 20% sodium hydroxide solution, stirred thoroughly and ultrasonically treated for 15 minutes, then soaked at room temperature for 12 hours to remove oily substances from the algal residue. After discarding the residual liquid, it was dried to obtain algal residue powder.

[0072] S2. Add 70g of algal residue powder and 26.43g of manganese chloride to 560g of deionized water, sonicate for 20min, transfer to a shaker, shake at 150rpm for 24h, filter, dry to constant weight, pass through a 50-mesh sieve, put into a muffle furnace, heat to 500℃ at a heating rate of 5℃ / min, hold for 3h, cool to room temperature, and obtain metal-modified algal residue biochar.

[0073] S3. Add 60g of metal-modified algal biochar to 180g of concentrated nitric acid with a mass concentration of 68%, heat to 100℃, react for 3h, after the reaction is completed, cool to room temperature, filter, wash the obtained solid with deionized water until the pH of the washing solution is neutral, and dry to obtain carboxylated metal algal biochar.

[0074] S4. Add 50g of carboxylated metal algal residue biocarbon to 400g of dichloromethane, then add 5g of thiophenepyridine polyhydroxy ligand prepared according to Preparation Example 1, 0.5g of p-toluenesulfonic acid and 10g of N,N-dicyclohexylcarbodiimide, stir at room temperature for 8h, filter, wash with ethanol, dry, put into a high-energy ball mill, add 5g of Fe3O4, set the speed to 300rpm, and the time to 2h to obtain algal residue carbon-based photocatalyst.

[0075] Example 2: A specific preparation method of an algal residue carbon-based photocatalyst, comprising the following steps:

[0076] S1.100g of algal residue was washed, dried and pulverized to 80 mesh, then immersed in a 20% sodium hydroxide solution, stirred thoroughly and ultrasonically treated for 15 minutes, then soaked at room temperature for 12 hours to remove oily substances from the algal residue. After discarding the residual liquid, it was dried to obtain algal residue powder.

[0077] S2. Add 70g of algal residue powder and 33.32g of magnesium chloride to 700g of deionized water, sonicate for 25min, transfer to a shaker, shake at 150rpm for 24h, filter, dry to constant weight, pass through a 50-mesh sieve, place in a muffle furnace, heat to 500℃ at a heating rate of 5℃ / min, hold for 3h, cool to room temperature, and obtain metal-modified algal residue biochar.

[0078] S3. Add 60g of metal-modified algal biochar to 240g of concentrated nitric acid with a mass concentration of 68%, heat to 105℃, react for 4h, after the reaction is completed, cool to room temperature, filter, wash the obtained solid with deionized water until the pH of the washing solution is neutral, and dry to obtain carboxylated metal algal biochar.

[0079] S4. Add 50g of carboxylated metal algal residue biocarbon to 500g of dichloromethane, then add 7.5g of thiophenepyridine polyhydroxy ligand prepared according to Preparation Example 2, 1g of p-toluenesulfonic acid and 15g of N,N-dicyclohexylcarbodiimide, stir at room temperature for 10h, filter, wash with ethanol, dry, put into a high-energy ball mill, add 10g of Fe3O4, set the speed to 300rpm, and the time to 2h to obtain algal residue carbon-based photocatalyst.

[0080] Example 3: A specific preparation method of an algal residue carbon-based photocatalyst, comprising the following steps:

[0081] S1.100g of algal residue was washed, dried and pulverized to 80 mesh, then immersed in a 20% sodium hydroxide solution, stirred thoroughly and ultrasonically treated for 15 minutes, then soaked at room temperature for 12 hours to remove oily substances from the algal residue. After discarding the residual liquid, it was dried to obtain algal residue powder.

[0082] S2. Add 70g of algal residue powder and 46.65g of cobalt chloride to 840g of deionized water, sonicate for 30min, transfer to a shaker, shake at 150rpm for 24h, filter, dry to constant weight, pass through a 50-mesh sieve, place in a muffle furnace, heat to 500℃ at a heating rate of 5℃ / min, hold for 3h, cool to room temperature, and obtain metal-modified algal residue biochar.

[0083] S3. Add 60g of metal-modified algal biochar to 300g of concentrated nitric acid with a mass concentration of 68%, heat to 110℃, react for 5h, after the reaction is completed, cool to room temperature, filter, wash the obtained solid with deionized water until the pH of the washing solution is neutral, and dry to obtain carboxylated metal algal biochar.

[0084] S4. Add 50g of carboxylated metal algal residue biocarbon to 600g of dichloromethane, then add 10g of thiophenepyridine polyhydroxy ligand prepared according to Preparation Example 3, 1.5g of p-toluenesulfonic acid and 20g of N,N-dicyclohexylcarbodiimide, stir at room temperature for 12h, filter, wash with ethanol, dry, put into a high-energy ball mill, add 15g of Fe3O4, set the speed to 300rpm, and the time to 2h to obtain algal residue carbon-based photocatalyst.

[0085] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that: in step S4, thiophenepyridine polyhydroxy ligand is not added. Instead, 50g of carboxylated metal algal residue biocarbon is directly put into a high-energy ball mill and 15g of Fe3O4 is added. The speed is set to 300rpm and the time is 2h to obtain algal residue carbon-based photocatalyst.

[0086] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the thiophenepyridine polyhydroxy ligand prepared in step S4 according to Preparation Example 2 is replaced with 2-pyridinemethanol.

[0087] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the thiophene pyridine polyhydroxy ligand prepared according to Preparation Example 2 in step S4 is replaced with the phenyl pyridine polyhydroxy ligand prepared according to the comparative preparation example.

[0088] Comparative Example 4: The difference between Comparative Example 3 and Example 2 is that step S3 is omitted, and the metal-modified algal residue biocarbon obtained in step S2 is directly prepared into algal residue carbon-based photocatalyst according to the process in step S4.

[0089] Performance testing:

[0090] 1. Degradation rate under different pH conditions: A 50 mg / L tetracycline hydrochloride solution was prepared and the pH was adjusted to 3, 5, 7, 9, and 11 to form five groups, with seven parallel experiments in each group. The algal residue carbon-based photocatalysts prepared in Examples 1-3 and Comparative Examples 1-4 were added to the tetracycline hydrochloride solutions at different pH values ​​at an addition amount of 0.6 g / L, followed by the addition of 0.6 g / L potassium persulfate. The solution was irradiated with a 300W xenon lamp (equipped with a 420 nm filter to simulate visible light). After 2 hours, samples were taken, filtered through a 0.22 μm filter membrane, and the absorbance of the solution at 357 nm (the characteristic absorption peak of tetracycline hydrochloride) was measured using a UV-Vis spectrophotometer. The degradation rate was calculated as (initial concentration - remaining concentration) / initial concentration × 100%. The experimental results are shown in Table 1.

[0091] 2. Cyclic stability: Prepare a 50 mg / L tetracycline hydrochloride solution, adjust the pH to 3, add the algal residue carbon-based photocatalyst prepared in Examples 1-3 and Comparative Examples 1-4 at an addition rate of 0.6 g / L, and then add 0.6 g / L potassium persulfate. Irradiate with a 300W xenon lamp (equipped with a 420 nm filter to simulate visible light). After 2 hours, take a sample, filter it through a 0.22 μm filter membrane, and measure the absorbance of the solution at 357 nm (characteristic absorption peak of tetracycline hydrochloride) using a UV-Vis spectrophotometer. Calculate the degradation rate. After completion, separate the catalyst by applying an external magnetic field (0.5 T). After washing and drying, it is considered as completing one cycle. A total of ten cycles are performed. Calculate the ratio of the degradation efficiency of the tenth cycle to the degradation efficiency of the first cycle, which is the cyclic stability.

[0092] 3. Free radical quenching experiment: Prepare a 50 mg / L tetracycline hydrochloride solution, divided into 7 groups. Use 50 mM isopropanol and 500 mM methanol to quench hydroxyl radicals and sulfate radicals, respectively, and 20 mM... L-Ascorbic acid quenched superoxide radicals. Each group was supplemented with the following free radical quenchers: ① Isopropanol, ② Methanol, ③ L-Ascorbic acid, ④ Isopropanol + Methanol, ⑤ Isopropanol + L-Ascorbic acid, ⑥ Methanol + L-Ascorbic acid, and ⑦ Blank. Three parallel experiments were conducted in each group. The algal residue carbon-based photocatalyst prepared in Examples 1-3 was added at a rate of 0.6 g / L, followed by 0.6 g of potassium persulfate. The pH was adjusted to 3, and the solution was irradiated with a 300W xenon lamp (equipped with a 420 nm filter to simulate visible light). After 2 hours, samples were taken, filtered through a 0.22 μm filter, and the absorbance of the solution at 357 nm (characteristic absorption peak of tetracycline hydrochloride) was measured using a UV-Vis spectrophotometer. The degradation rate of the samples with different quenchers in each group was calculated as (initial concentration - remaining concentration) / initial concentration × 100%. The experimental results are shown in Table 2.

[0093] Table 1. Degradation rate and cycling stability under different pH conditions

[0094] pH=3 Degradation rate / % pH=5 Degradation rate / % pH=7 Degradation rate / % pH=9 Degradation rate / % pH=11 Degradation rate / % Cyclic stability / % Example 1 97.2 95.8 96.1 94.5 94.3 91.8 Example 2 96.5 96.3 95.0 95.7 94.7 92.6 Example 3 97.0 94.9 95.8 95.2 94.1 92.0 Comparative Example 1 68.3 69.0 65.5 60.2 55.8 45.2 Comparative Example 2 84.5 82.1 78.3 80.5 58.4 60.3 Comparative Example 3 89.6 87.2 83.1 85.7 75.1 76.5 Comparative Example 4 75.2 73.8 70.5 72.3 51.3 52.7

[0095] Table 2 Free radical quenching experiments

[0096] ① Degradation rate / % ② Degradation rate / % ③ Degradation rate / % ④ Degradation rate / % ⑤ Degradation rate / % ⑥ Degradation rate / % ⑦ Degradation rate / % Example 1 82.92 81.87 24.33 81.93 22.11 50.82 97.76 Example 2 80.18 81.52 32.22 80.58 32.57 27.49 96.62 Example 3 83.22 81.58 34.04 81.70 55.85 63.74 97.42

[0097] Performance Analysis:

[0098] As can be seen from the experimental data in Table 1, the algal residue carbon-based photocatalysts prepared using this invention in Examples 1-3 maintained excellent degradation performance over a wide pH range (3-11), while the degradation performance of the comparative examples was not only lower overall, but also more affected by pH fluctuations. This difference stems primarily from the unique structural design and functional synergy of the examples.

[0099] From a structural perspective, the thiophenepyridine polyhydroxy ligand in the embodiments is the key functional unit. The polyhydroxy ligands in its molecule interact closely with water molecules through hydrogen bonds, which significantly improves the dispersion stability of the catalyst in the aqueous phase. Regardless of whether the hydroxyl groups are protonated or deprotonated, the surface charge distribution of the catalyst is not significantly changed, avoiding aggregation at extreme pH levels and ensuring effective contact between the active center and the substrate. At the same time, the polyhydroxy ligands form stable intermolecular forces with the amide and phenolic hydroxyl groups in the tetracycline molecule. Even if tetracycline is in different forms such as protonated, amphoteric, or deprotonated at different pH levels, it can still be efficiently adsorbed by the catalyst, reducing the influence of pH on substrate binding.

[0100] More importantly, in the embodiments, the generation and action of the dominant active species are minimally affected by pH. The thiophene ring of the thiophene-pyridine polyhydroxy ligand forms a continuous conjugated π system with the bispyridine ring, which can efficiently generate photogenerated electrons under visible light irradiation, and the delocalization effect of the conjugated structure significantly suppresses carrier recombination. The photogenerated electrons are rapidly transferred to the surface through the ester bond between the ligand and the carbon matrix, preferentially reacting with adsorbed oxygen to generate superoxide radicals (·O2). - Under acidic conditions, ·O2 - With H + They combine to form HO2·, and their oxidizing activities are similar; under alkaline conditions, ·O2 - It exists stably, and both forms can efficiently attack the electron-rich sites of tetracycline. The pH adaptability of this active species allows the examples to maintain high degradation efficiency at different pH levels.

[0101] In contrast, the performance defects of the comparative examples stem directly from structural deficiencies: due to the lack of thiophenepyridine polyhydroxy ligands, the comparative examples lack both efficient photogenerated carrier generation capabilities and the ability to stably adsorb different forms of tetracycline, resulting in significantly lower degradation performance compared to the examples; the comparative examples using simple ligands, lacking a conjugated system or polyhydroxy ligands, have a narrowed light absorption range, decreased hydrophilicity, and intensified aggregation at extreme pH levels, leading to greater fluctuations in degradation performance; the comparative examples omitting carboxylation treatment have low ligand grafting rates, hindered electron transport, and insufficient hydrophilicity, resulting in overall low degradation performance that is significantly affected by pH.

[0102] As can also be seen from Table 1, the cycle stability of the algal residue carbon-based photocatalysts prepared by the present invention in Examples 1-3 is significantly better than that of the comparative examples, which is closely related to the stability design of its structure.

[0103] In this embodiment, the thiophene pyridine polyhydroxy ligand is covalently linked to the carboxylated metal algal residue biochar via ester bonds. This high bond energy prevents breakage during cycling, ensuring the ligand does not detach. Simultaneously, the pyridine ring of the ligand forms strong coordination bonds (including d-pπ back bonds) with the metal ions, resulting in stable coordination and effectively inhibiting the dissolution of metal ions during cycling, reducing the loss of active sites. Furthermore, Fe3O4 is tightly composited with the carbon matrix through high-energy ball milling, exhibiting magnetic stability and allowing for efficient recovery via magnetic separation in each cycle, reducing physical catalyst loss. These structural designs collectively ensure that the embodiment maintains high activity even after multiple cycles.

[0104] The poor cycling stability of the comparative examples stemmed from structural defects: in the comparative example without the addition of thiophenepyridine polyhydroxy ligands, the metal ions lacked coordination anchoring, making them prone to dissolution during cycling and resulting in rapid loss of the active center; in the comparative example with simple ligands as substitutes, the ligands were not firmly connected to the carbon matrix, making them prone to detachment during cycling, leading to a decrease in light absorption and electron transport capabilities; in the comparative example omitting carboxylation treatment, the ligand grafting rate was low, resulting in severe ligand detachment during cycling, and the poor hydrophilicity exacerbated aggregation, further reducing stability.

[0105] As can be seen from the experimental data in Table 2, the superoxide radical plays a dominant role in the process of activating potassium persulfate to catalyze the degradation of tetracycline hydrochloride in the algal residue carbon-based photocatalyst prepared in the examples, while the hydroxyl radical and sulfate radical have a weaker effect. This result is directly related to the photogenerated electron transfer pathway and the generation law of active species in the catalyst.

[0106] The generation of superoxide radicals originates from the highly efficient photoresponsiveness and electron transport properties of thiophene-pyridine polyhydroxy ligands. The thiophene ring and the bispyridine ring in the ligand molecule form a continuous conjugated π system, which can undergo π→π* transitions under visible light irradiation, efficiently generating photogenerated electron-hole pairs. The delocalization effect of the conjugated structure significantly suppresses the recombination of photogenerated carriers, allowing photogenerated electrons to be efficiently retained and rapidly transferred to the carbon matrix surface via ester bonds between the ligand and the carbon matrix. Simultaneously, the polyhydroxy ligands in the ligand can enhance the catalyst's adsorption capacity for oxygen in water through hydrogen bonding, providing sufficient reaction substrates for photogenerated electrons. The photogenerated electrons on the carbon matrix surface have strong reducing properties and can undergo single-electron reduction reactions with adsorbed oxygen to generate superoxide radicals; this process is the main source of superoxide radicals.

[0107] The core mechanism of superoxide radical degradation of tetracycline is nucleophilic oxidative attack: tetracycline molecules contain multiple electron-rich functional groups (such as amide groups, phenolic hydroxyl groups, and C=C double bonds). These groups can be stably adsorbed on the catalyst surface by binding with the polyhydroxyl groups of the ligands through hydrogen bonds. Superoxide radicals (or their conjugate acid HO2· under acidic conditions) are more likely to target these sites with high electron cloud density, destroying the conjugate skeleton structure of tetracycline through addition reactions. Subsequently, superoxide radicals continue to participate in the oxidation reaction, gradually breaking the side chains and functional groups of tetracycline molecules, degrading them into small molecule intermediates, and finally achieving mineralization.

[0108] In summary, the superior performance of the embodiments stems from the synergistic effect of the ligand-metal-carbon matrix: the thiophenepyridine polyhydroxy ligand provides efficient light absorption, stable coordination sites, and hydrophilicity; the metal ion becomes the active center through coordination and regulates electron transfer; carboxylation treatment enhances ligand grafting and hydrophilicity; and magnetic composite improves recovery efficiency. This multi-dimensional synergistic design enables the embodiments to maintain high degradation performance over a wide pH range and long cycles, while the comparative embodiments, lacking key structures or components, cannot achieve the above synergy and exhibit significantly inferior performance. This fully verifies the significant progress made in photocatalyst structural design in this invention.

[0109] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an algal residue carbon-based photocatalyst, characterized in that, Includes the following steps: S1. After washing and drying, the algal residue is crushed to 80 mesh, immersed in a 20% sodium hydroxide solution, stirred thoroughly, ultrasonically treated for 15 minutes, and then soaked at room temperature for 12 hours to remove oily substances from the algal residue. After discarding the residual liquid, it is dried to obtain algal residue powder. S2. Add algal residue powder and metal salt to deionized water, sonicate for 20-30 min, transfer to a shaker, shake at 150 rpm for 24 h, filter, dry to constant weight, pass through a 50 mesh sieve, place in a muffle furnace, heat to 500℃ at a heating rate of 5℃ / min, hold for 3 h, cool to room temperature, and obtain metal-modified algal residue biochar. S3. Add metal-modified algal biochar to concentrated nitric acid, heat to 100-110℃, react for 3-5 hours, cool to room temperature after the reaction is complete, filter, wash the obtained solid with deionized water until the pH of the washing solution is neutral, and dry to obtain carboxylated metal algal biochar. S4. Add carboxylated metal algal residue biocarbon to dichloromethane, then add thiophenepyridine polyhydroxy ligand, p-toluenesulfonic acid and N,N-dicyclohexylcarbodiimide, stir at room temperature for 8-12 hours, filter, wash with ethanol, dry, put into a high-energy ball mill, add Fe3O4, set the speed to 300 rpm, time to 2 hours, to obtain algal residue carbon-based photocatalyst; The preparation method of the thiophenepyridine polyhydroxy ligand includes the following steps: (1) Under nitrogen protection, 4-bromo-2-thiophene carboxaldehyde, 2-vinylnicotinic acid, sodium acetate, palladium acetate and tris(o-methylphenyl)phosphine were added to N,N-dimethylformamide, heated to 120-140℃, reacted for 4-6h, cooled to room temperature, filtered, added deionized water, extracted three times with ethyl acetate, combined the organic phases, washed with saturated brine, separated and collected the organic phase, dried with anhydrous sodium sulfate, filtered, concentrated under reduced pressure to remove solvent, and the crude product was purified by silica gel column chromatography with petroleum ether: ethyl acetate 3:1 as the eluent to obtain intermediate 1; (2) Under nitrogen protection, intermediate 1 and 2-aminonicotinic acid were added to anhydrous ethanol, heated to 75-85℃, reacted for 3-4h, cooled to 0℃, and kept warm for 1h. A large amount of solid was observed to precipitate. The solid was filtered, collected, washed, and dried to obtain intermediate 2. (3) Add intermediates 2, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to dichloromethane, stir in the dark for 30-50 min, then add tris(hydroxymethyl)aminomethane, and react at room temperature for 8-12 h. Wash the organic phase once with saturated sodium bicarbonate and once with deionized water, dry with anhydrous sodium sulfate, and then concentrate under reduced pressure to remove the organic solvent. The crude product is then recrystallized from a mixed solution of ethyl acetate / petroleum ether to obtain thiophene pyridine polyhydroxy ligand.

2. The method for preparing the algal residue carbon-based photocatalyst according to claim 1, characterized in that, In step S2, algae residue powder and metal salt are added to deionized water at a ratio of 0.003-0.007 mol of metal salt per gram of algae residue powder. The weight ratio of algae residue powder to deionized water is 1:8-12. The metal salt refers to one of manganese chloride, magnesium chloride, or cobalt chloride.

3. The method for preparing the algal residue carbon-based photocatalyst according to claim 1, characterized in that, In step S3, the metal-modified algal residue biochar and concentrated nitric acid are in a weight ratio of 1:3-5, where concentrated nitric acid refers to a nitric acid solution with a mass concentration of 68%.

4. The method for preparing the algal residue carbon-based photocatalyst according to claim 1, characterized in that, In step S4, the carboxylated metal algal residue biochar, dichloromethane, thiophenepyridine polyhydroxy ligand, p-toluenesulfonic acid, N,N-dicyclohexylcarbodiimide and Fe3O4 are in a weight ratio of 1:8-12:0.1-0.2:0.01-0.03:0.2-0.4:0.1-0.

3.

5. The method for preparing the algal residue carbon-based photocatalyst according to claim 1, characterized in that, In step (1), the molar ratio of 4-bromo-2-thiophene carboxaldehyde, 2-vinylnicotinic acid, sodium acetate, palladium acetate, and tris(o-methylphenyl)phosphine is 1:1-1.2:2-3:0.03-0.07:0.1-0.2, and the weight ratio of 4-bromo-2-thiophene carboxaldehyde, N,N-dimethylformamide, and deionized water is 1:8-12:4-8.

6. The method for preparing the algal residue carbon-based photocatalyst according to claim 1, characterized in that, In step (2), intermediate 1 and 2-aminonicotinic acid are in a molar ratio of 1:1-1.2, and intermediate 1 and anhydrous ethanol are in a weight ratio of 1:4-6.

7. The method for preparing the algal residue carbon-based photocatalyst according to claim 1, characterized in that, In step (3), intermediate 2, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide and tris(hydroxymethyl)aminomethane are in a molar ratio of 1:1.2-1.5:1-1.2:1-1.2, intermediate 2 and dichloromethane are in a weight ratio of 1:15-20, and the ethyl acetate / petroleum ether mixed solution refers to the mixture of ethyl acetate and petroleum ether in a weight ratio of 2:

3.

8. A carbon-based photocatalyst based on algal residue, prepared by the method described in any one of claims 1-7.

9. The application of the algal residue carbon-based photocatalyst according to claim 8 in the photocatalytic decomposition of tetracycline hydrochloride.

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