Haematococcus pluvialis / cd s composite material, and preparation method and application thereof

Abstract

This invention relates to the field of photocatalysis technology, and more particularly to a Haematococcus pluvialis / CdS composite material, its preparation method, and its applications. The Haematococcus pluvialis / CdS composite material provided by this invention comprises Haematococcus pluvialis and nano-CdS coated on the surface of the Haematococcus pluvialis; the mass content of astaxanthin in the Haematococcus pluvialis is 1-10%. Haematococcus pluvialis contains astaxanthin, which can enhance the ability of CdS to capture photons within the visible light wavelength range, thus acting as a dye sensitizer, while simultaneously inhibiting the recombination of photogenerated electrons / holes and improving the transport and transfer efficiency of photogenerated electrons. Therefore, compared with CdS alone, the Haematococcus pluvialis / CdS composite material exhibits better visible light photocatalytic activity. Results show that the Haematococcus pluvialis / CdS composite material has good visible light photocatalytic performance, achieving a removal rate of 84.5% for the recalcitrant norfloxacin within 60 min, and exhibits good cycling stability.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, and in particular to a Haematococcus pluvialis / CdS composite material, its preparation method, and its application. Background Technology

[0002] With urbanization and industrialization, the overexploitation and overuse of pharmaceuticals have led to drug pollution in the aquatic environment, causing significant ecological and environmental pollution. Quinolones, one of the five most commonly used antibiotics in China, have been widely used in humans and animals. However, due to their poor biodegradability, their residues continuously accumulate in the ecosystem, posing health risks to both the natural environment and human safety.

[0003] Photocatalytic degradation is considered an effective way to remove organic pollutants. Among them, CdS has great application potential in the field of photocatalytic degradation due to its narrow band gap (2.4 eV), strong light absorption, and simple preparation. However, its tendency to aggregate and short photogenerated carrier lifetime result in low photocatalytic activity, which limits its practical application. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a Haematococcus pluvialis / CdS composite material, its preparation method, and its applications. The Haematococcus pluvialis / CdS composite material provided by this invention has excellent visible light photocatalytic performance and can efficiently degrade organic pollutants in water, especially suitable for the degradation of quinolone organic pollutants.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a Haematococcus pluvialis / CdS composite material, comprising Haematococcus pluvialis and nano-CdS coated on the surface of Haematococcus pluvialis; the mass content of astaxanthin in Haematococcus pluvialis is 1~10%.

[0006] Preferably, the mass ratio of Haematococcus pluvialis to nano-CdS is 1:4 to 1:10.

[0007] Preferably, the mass content of astaxanthin in the Haematococcus pluvialis is 5-10%.

[0008] This invention provides a method for preparing the Haematococcus pluvialis / CdS composite material described above, comprising the following steps: Haematococcus pluvialis powder was dispersed in water to obtain a Haematococcus pluvialis dispersion; A complexing agent and a water-soluble cadmium source were sequentially added to the *Hylocereus pluvialis* dispersion to obtain a complexing system; the complexing agent was sodium citrate and / or citric acid. An inorganic weak base and a water-soluble sulfur source were added to the complexation system to make the pH of the system 8-9, and a CdS growth reaction was carried out. After solid-liquid separation, the Haematococcus pluvialis / CdS composite material was obtained.

[0009] Preferably, the CdS growth reaction is carried out at a temperature of 70-90°C for 2-4 hours.

[0010] Preferably, the water-soluble cadmium source includes one or more of cadmium chloride, cadmium nitrate, and cadmium sulfate.

[0011] Preferably, the complexing agent reacts with the Cd in the water-soluble cadmium source. 2+ The molar ratio is 1:1 to 1:4.

[0012] Preferably, the water-soluble sulfur source includes thiourea and / or thioacetamide; the water-soluble cadmium source contains Cd. 2+ With the water-soluble sulfur source S 2- The molar ratio is 1:1 to 1:4.

[0013] This invention provides the application of the Haematococcus pluvialis / CdS composite material described in the above scheme or the Haematococcus pluvialis / CdS composite material prepared by the above scheme as a photocatalyst in the degradation of organic pollutants in water.

[0014] Preferably, the organic pollutants include quinolone organic pollutants; the degradation of organic pollutants in the water body is carried out under conditions with a pH of 5 to 7.

[0015] This invention provides a Haematococcus pluvialis / CdS composite material, comprising Haematococcus pluvialis and nano-CdS coated on the surface of the Haematococcus pluvialis; the mass content of astaxanthin in the Haematococcus pluvialis is 1-10%. Haematococcus pluvialis contains astaxanthin, which can enhance the photon capture ability of CdS within the visible light wavelength range, thus acting as a dye sensitizer, while simultaneously inhibiting the recombination of photogenerated electrons / holes and improving the transport and transfer efficiency of photogenerated electrons. Therefore, compared with CdS alone, the Haematococcus pluvialis / CdS composite material exhibits better visible light photocatalytic activity. Furthermore, combining CdS with Haematococcus pluvialis also improves the dispersibility of CdS, which is beneficial for further enhancing its photocatalytic performance.

[0016] The results of the examples show that the Haematococcus pluvialis / CdS composite material provided by the present invention has good visible light catalytic performance as a photocatalyst. Within 60 min (30 min of dark adsorption + 30 min of light irradiation), the removal rate of norfloxacin (NOR) can reach 84.5%, and it has good cycle stability. After 3 cycles, the degradation efficiency is still maintained at more than 75%. Attached Figure Description

[0017] Figure 1Cell optical density of Haematococcus pluvialis cultured for different number of days and microscopic images of Haematococcus pluvialis cultured for different number of days. 400 images, including (a) the optical density of Haematococcus pluvialis cells after different culture days, (b) 6 days, (c) 10 days, and (d) 14 days; Figure 2 SEM images of Haematococcus pluvialis before and after CdS composite, where (ab) is Haematococcus pluvialis in the later stage, (c) Hp-Q / CdS, (de) Hp-Z / CdS, (fg) Hp-H / CdS, and (h) nano CdS particles; Figure 3 The following are the EDS analysis results of Hp-H / CdS composite materials, including (a) the EDS energy spectrum of Hp-H / CdS and (b) the mapping image of Hp-H / CdS. Figure 4 The XPS spectra of the Hp-H / CdS composite material are shown in the figures: (a) total XPS spectrum, (b) high-resolution XPS spectrum of C 1s, (c) high-resolution XPS spectrum of Cd 3d, and (d) high-resolution XPS spectrum of S 2p. Figure 5 XRD patterns of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS; Figure 6 FT-IR spectra of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS; Figure 7 DRS plots and KM equation curves for Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS and CdS, where (a) is the DRS plot and (b) is the KM equation curve. Figure 8 Thermogravimetric analysis diagrams of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS; Figure 9 The results of the photodegradation experiments are as follows: (ab) are the photodegradation curves of NOR by Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS and CdS under visible light and their pseudo-first-order kinetics, respectively; (c) the photodegradation curve of NOR by pH under visible light; (d) the photodegradation curve of NOR by different catalyst dosages; (e) the three-cycle degradation curve of Hp-H / CdS catalyst; and (f) the degradation efficiency of different organic pollutants. Figure 10 The surface photocurrent and electrochemical impedance spectra of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS and CdS are shown, where (a) is the photocurrent spectrum and (b) is the electrochemical impedance spectrum. Figure 11Mott-Schottky plots of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS are shown, where (a) Hp-Q / CdS, (b) Hp-Z / CdS, (c) Hp-H / CdS, and (d) CdS. Figure 12 The band gap diagrams for Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS, and the photocatalytic mechanism diagram for HpH / CdS are shown, where (a) is the band gap diagram and (b) is the photocatalytic mechanism diagram. Detailed Implementation

[0018] The present invention provides a Haematococcus pluvialis / CdS composite material, comprising Haematococcus pluvialis and nano-CdS coated on the surface of Haematococcus pluvialis; the mass content of astaxanthin in Haematococcus pluvialis is 1~10%.

[0019] In this invention, the mass ratio of Haematococcus pluvialis to nano-CdS is preferably 1:4 to 1:10, and in specific embodiments it can be 1:4, 1:5, 1:6, 1:7, 1:7.2, 1:7.5, 1:8, 1:9 or 1:10.

[0020] In specific embodiments, the mass content of astaxanthin in the Haematococcus pluvialis can be 1%, 1.2%, 2%, 3%, 4%, 4.8%, 5%, 6%, 6.4%, 7%, 8%, 9%, or 10%. Within the above range, the higher the astaxanthin content in the Haematococcus pluvialis, the better the visible light photocatalytic activity of the Haematococcus pluvialis / CdS composite material. This is because astaxanthin has dye sensitization properties, improving the utilization rate of visible light and the transfer and separation of photogenerated electron-hole pairs.

[0021] This invention provides a method for preparing the Haematococcus pluvialis / CdS composite material described above, comprising the following steps: Haematococcus pluvialis powder was dispersed in water to obtain a Haematococcus pluvialis dispersion; A complexing agent and a water-soluble cadmium source were sequentially added to the *Hylocereus pluvialis* dispersion to obtain a complexing system; the complexing agent was sodium citrate and / or citric acid. An inorganic weak base and a water-soluble sulfur source were added to the complexation system to make the pH of the system 8-9, and a CdS growth reaction was carried out. After solid-liquid separation, the Haematococcus pluvialis / CdS composite material was obtained.

[0022] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0023] This invention disperses Haematococcus pluvialis powder in water to obtain a Haematococcus pluvialis dispersion.

[0024] In this invention, the Haematococcus pluvialis powder is preferably obtained by freeze-drying Haematococcus pluvialis; this invention does not have special requirements for the source of the Haematococcus pluvialis, and it can be obtained by methods well known in the art or by commercially available products.

[0025] In this invention, the water is preferably ultrapure water; the amount of water used is not particularly important, as long as it is sufficient to evenly disperse the Haematococcus pluvialis powder. The dispersion method is not particularly important, and any method well-known in the art, such as ultrasonic dispersion, can be used.

[0026] Haematococcus pluvialis ( Haematococcus pluvialis ) is a single-celled freshwater green algae with a life cycle that exhibits typical environmental responsiveness and morphological plasticity, mainly divided into the following two stages: (1) Green swimming stage (Vegetative Growth Phase): The cells are oval or pear-shaped, with a diameter of 15~40 μm, and have two flagella of equal length, allowing them to swim autonomously; the chloroplasts are cup-shaped, rich in chlorophyll, and appear bright green. During this stage, the cells efficiently fix CO2 through photosystem II (PSII), and use nitrates and phosphates to synthesize proteins and lipids, forming a high-density algal community. (2) Red thick-walled spore stage (Aplanospore / Cyst Phase): When environmental pressures such as strong light, nitrogen / phosphorus starvation, high salinity, and oxidative stress persist for more than 48 hours, the cells initiate a stress response program, stop dividing, and enter a dormant state. At the same time, carotenoids, mainly astaxanthin, accumulate in large quantities in lipid droplets, accounting for 1~5% of the dry weight, and can reach more than 10% under extreme conditions. During this stage, photosynthetic efficiency decreases, and cells rely on stored starch and lipids for energy, while resisting photo-oxidative damage through antioxidant defense systems such as superoxide dismutase (SOD) and astaxanthin.

[0027] In the three embodiments of the present invention, the Haematococcus pluvialis used are respectively the green swimming stage (Haematococcus pluvialis - early stage), the green swimming stage transitioning to the red thick-walled spore stage (Haematococcus pluvialis - middle stage), and the red thick-walled spore stage (Haematococcus pluvialis - late stage).

[0028] After obtaining the *Plasmodium globulus* dispersion, the present invention sequentially adds a complexing agent and a water-soluble cadmium source to the *Plasmodium globulus* dispersion to obtain a complexing system.

[0029] In this invention, the complexing agent is sodium citrate and / or citric acid, preferably sodium citrate. In this invention, the function of the complexing agent is to react with Cd... 2+ It complexes, controls the nucleation and growth of CdS, and indirectly protects the sensitized pigments of Haematococcus pluvialis. Taking sodium citrate as an example, its molecule contains three carboxyl groups (-COO... - In aqueous solution, it dissociates to release negatively charged oxygen atoms, which can act as coordinating atoms with Cd. 2+The central metal ion undergoes a coordination complexation reaction to form a water-soluble cadmium-sodium citrate complex.

[0030] In this invention, the water-soluble cadmium source preferably includes one or more of cadmium chloride, cadmium nitrate, and cadmium sulfate, more preferably cadmium chloride, and the cadmium chloride is further preferably CdCl2·2.5H2O. In this invention, the water-soluble cadmium source is preferably used in the form of an aqueous solution. This invention does not specifically limit the concentration of the cadmium source aqueous solution; in the embodiments of this invention, it is specifically 0.5 mol·L⁻¹. -1 CdCl2·2.5H2O solution.

[0031] In this invention, the amounts of Haematococcus pluvialis powder and water-soluble cadmium source are determined based on their respective contents in the Haematococcus pluvialis / CdS composite material. In this invention, the Cd content in the complexing agent and water-soluble cadmium source is... 2+ The preferred molar ratio is 1:1 to 1:4, and in specific embodiments it can be 1:1, 1:2, 1:3, or 1:4. This invention controls the Cd content in the complexing agent and the water-soluble cadmium source. 2+ When the molar ratio is within the above range, it can guarantee that Cd 2+ The complexation is sufficient.

[0032] In this invention, the *Haemaphysalis* dispersion is preferably heated to the temperature required for the CdS growth reaction (70-90°C), and then the complexing agent and water-soluble cadmium source are added sequentially, with stirring for 5-20 min and 15-30 min respectively. This invention, by adding the complexing agent first and then the cadmium source, enables the CdS growth reaction to proceed smoothly. 2+ The uniform and controllable complexation is achieved, thereby realizing the stable and uniform dispersion of subsequent complexes, and finally obtaining CdS with uniform morphology, particle size and good dispersibility.

[0033] After obtaining the complexed system, the present invention adds an inorganic weak base and a water-soluble sulfur source to the complexed system to make the pH value of the system 8-9, performs CdS growth reaction, and separates the solid and liquid to obtain the Haematococcus pluvialis / CdS composite material.

[0034] In this invention, the weak base is preferably one or more of ammonia, ammonium bicarbonate, and ammonium carbonate, more preferably ammonia, and the concentration of the ammonia is preferably 25-28%; the water-soluble sulfur source preferably includes thiourea and / or thioacetamide, more preferably thiourea; the water-soluble cadmium source contains Cd 2+ With the water-soluble sulfur source S 2- The preferred molar ratio is 1:1 to 1:4, and in specific embodiments it can be 1:1, 1:1.2, 1:2, 1:3, or 1:4. In this invention, the water-soluble sulfur source is preferably used in the form of an aqueous solution. This invention does not have special requirements for the concentration of the sulfur source aqueous solution; in the embodiments of this invention, it is specifically 0.5 mol·L⁻¹. -1Thiourea solution.

[0035] In this invention, the preferred temperature for the CdS growth reaction is 70-90°C, and the preferred time is 2-4 hours. In specific embodiments, the temperature for the CdS growth reaction can be 70, 75, 80, 85, or 90°C; and the preferred time can be 2, 2.5, 3, 3.5, or 4 hours. In this invention, the CdS growth reaction is preferably carried out under stirring conditions. During the CdS growth reaction, this invention controls the pH of the reaction system to 8-9 to achieve CdS growth. 2+ Slow-release and sulfur source hydrolysis are performed at matching rates, resulting in CdS with uniform nanocrystal size and good dispersibility.

[0036] In this invention, the CdS growth reaction is preferably carried out under oil bath conditions.

[0037] The present invention does not have any special requirements for the solid-liquid separation method; any solid-liquid separation method well known in the art can be used, such as filtration. After solid-liquid separation, the present invention preferably further includes washing and drying the obtained wet solid with water to obtain the Haematococcus pluvialis / CdS composite material.

[0038] This invention provides the application of the Haematococcus pluvialis / CdS composite material described in the above scheme or the Haematococcus pluvialis / CdS composite material prepared by the above scheme as a photocatalyst in the degradation of organic pollutants in water.

[0039] In this invention, the organic pollutants preferably include quinolone organic pollutants. Norfloxacin is a quinolone antibiotic widely used in the pharmaceutical and aquaculture fields, and is one of the most widely used antibiotics in the world. In the embodiments of this invention, norfloxacin is specifically used as the treatment target.

[0040] In this invention, the degradation of organic pollutants in the water is preferably carried out under conditions with a pH value of 5 to 7.

[0041] This invention does not impose a specific limit on the concentration of organic pollutants in the water body; in the embodiments of this invention, it is specifically 20 mg / L. In this invention, the degradation of organic pollutants in the water body is preferably carried out under visible light irradiation; in the embodiments of this invention, a xenon lamp is used to simulate visible light.

[0042] In this invention, the dosage of the Haematococcus pluvialis / CdS composite material is preferably 0.2~0.6 mg / mL, more preferably 0.4~0.6 mg / mL.

[0043] The following detailed description, in conjunction with embodiments, illustrates the Haematococcus pluvialis / CdS composite material, its preparation method, and its applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0044] The following examples illustrate the preparation process of Haematococcus pluvialis: (1) Preparation of microalgae seed culture BG-11 medium was prepared using distilled water. 100 mL of medium was added to each 250 mL Erlenmeyer flask, and the flasks were autoclaved (121 °C) for 20 minutes. Single colonies of *Haematococcus pluvialis* were picked from the solid medium and inoculated into the liquid medium. After inoculation, the flasks were placed in a constant-temperature shaker at 25 °C and 108 μmol·m⁻¹. 2 ·s) -1 Cultivate under these conditions for 10-15 days to obtain the seed culture for experiments.

[0045] (2) Cultivation of Haematococcus pluvialis using a nutritional model BG-11 medium was prepared using distilled water. 90 mL of medium was added to each 250 mL Erlenmeyer flask, and the flasks were autoclaved (121°C) for 20 minutes. After sterilization, the medium was allowed to cool to room temperature before inoculation. In a laminar flow hood, 10 mL of concentrated seed culture was pipetted into the fresh medium. The final initial cell optical density (OD) was measured. 680 The concentration was 0.1. After inoculation, the culture medium was placed in a shaker and incubated at 25℃ with a light intensity of 108 μmol·(m²·m³). 2 ·s) -1 The light source is a fluorescent lamp, and the light-to-dark ratio is set to 12 L:12 D. For example... Figure 1 As shown, the number of Haematococcus pluvialis cells gradually increases with the increase of culture days until it reaches its maximum biomass. Microscopic observation reveals that Haematococcus pluvialis begins to transform from a green, motile stage to a red, thick-walled spore stage with increasing culture days, as... Figure 1 As shown, (bd) represent Haematococcus pluvialis cultured for 6, 10, and 14 days, respectively. The Haematococcus pluvialis culture solutions after 6, 10, and 14 days were then collected and diluted at 4000 r·min⁻¹. -1 Centrifuge for 10 min, discard the supernatant, wash three times with distilled water, and freeze to dry weight in a freeze dryer to obtain Haematococcus pluvialis powder at different stages. Store the powder in a 4°C freezer for subsequent experiments. The astaxanthin content of Haematococcus pluvialis after 6, 10, and 14 days of culture was 1.2%, 4.8%, and 6.4%, respectively.

[0046] Examples 1-3 Preparation of Haematococcus pluvialis / CdS composite material (Hp / CdS) Haematococcus pluvialis cultured for 6, 10, and 14 days were named Haematococcus pluvialis-early stage (Hp-Q), Haematococcus pluvialis-mid stage (Hp-Z), and Haematococcus pluvialis-late stage (Hp-H). 0.050 g of each of these solutions were ultrasonically dispersed in 150 mL of ultrapure water. The solution was then transferred to a round-bottom flask and heated to 85 °C. Next, 3 mL of 0.4 mol·L⁻¹ water was added sequentially. -1 Sodium citrate solution and 5 mL of 0.5 mol·L⁻¹ -1 The CdCl₂·2.5H₂O solution was stirred for 10 min and 20 min respectively. Then, 2.8 mL of NH₃·H₂O (concentration 25%~28%) and 6 mL of 0.5 mol·L⁻¹ were added to the solution. -1 Thiourea solution. At this point, the solution color will slowly turn yellow, and the reaction will continue at 85°C for 3 h. After the reaction is complete, the product is obtained by filtration and washing, and then Hp-Q / CdS composite material (as Example 1), Hp-Z / CdS composite material (as Example 2), and Hp-H / CdS composite material (as Example 3) are obtained by vacuum drying at 70°C.

[0047] Comparative Example 1 Preparation of CdS: Add 3 mL of 0.4 mol·L⁻¹ sequentially. -1 Sodium citrate solution and 5 mL of 0.5 mol·L⁻¹ -1 A CdCl₂·2.5H₂O solution was added to a round-bottom flask and stirred for 10 min and 20 min, respectively. Then, 2.8 mL of NH₃·H₂O (concentration 25%~28%) and 6 mL of 0.5 mol·L⁻¹ were added to the solution. -1 Thiourea solution. At this point, the solution color slowly turns yellow, and the reaction continues at 85℃ for 3 h. After the reaction is complete, the product is obtained by filtration and washing, and then CdS material is obtained by vacuum drying at 70℃.

[0048] Structural characterization (1) SEM and EDS analysis Figure 2 SEM images of Haematococcus pluvialis before and after CdS composite formation are shown. (ab) Haematococcus pluvialis in the later stage, (c) Hp-Q / CdS, (de) Hp-Z / CdS, (fg) Hp-H / CdS, and (h) nano-CdS particles. Figure 2 In the middle (ab), the microalgae can be observed to have smooth, rounded surfaces and uniform size; from Figure 2As shown in (c), an uneven spherical shell grew on the surface of Haematococcus pluvialis in the early stage, successfully achieving the growth of CdS material on the microalgae surface. The large particle size and tendency to aggregate of the cadmium sulfide material may be related to the cell wall of the microalgae. Figure 2 As can be seen from the image, by coating Haematococcus pluvialis mid-stage with cadmium sulfide, the Haematococcus pluvialis morphology becomes more rounded and the particle size decreases after coating. This is because the cell wall of Haematococcus pluvialis mid-stage begins to thicken, preventing the microalgae from deforming or collapsing, thus providing a morphological advantage for subsequent photocatalytic experiments. Figure 2 The mid-stage (fg) model shows that the morphology of the Haematococcus pluvialis-late-stage / CdS composite material is similar to that of the mid-stage and shows no collapse. From... Figure 2 In the middle (h) it can be clearly observed that cadmium sulfide nanoparticles are uniformly loaded on the surface of microalgae. The particles are small in size and well dispersed, forming a tight interface with the algal matrix, which provides a favorable structural basis for the separation of photogenerated carriers and the adsorption and degradation of pollutants.

[0049] EDS analysis was performed on the Hp-H / CdS composite material, and the results are shown in the figure. Figure 3 . Figure 3 In the image, (a) is the EDS energy spectrum of Hp-H / CdS; (b) is the mapping image of Hp-H / CdS. Figure 3 It can be seen that Cd is evenly distributed on the surface of Haematococcus pluvialis, indicating that CdS successfully coated Haematococcus pluvialis.

[0050] (2) X-ray photoelectron spectroscopy (XPS) Figure 4 XPS results for Hp-H / CdS are shown, including (a) the total XPS spectrum, (b) the high-resolution XPS spectrum of C 1s, (c) the high-resolution XPS spectrum of Cd 3d, and (d) the high-resolution XPS spectrum of S 2p. The total XPS spectrum shows the presence of C 1s, O 1s, Cd 3d, and S 2p signals. The high-resolution XPS spectra are shown in Figures (b) to (d). Due to the incorporation of Haematococcus pluvialis, the Hp-H / CdS composite material exhibits more carbon species. Figure 4 As shown in (b), the C 1s spectrum exhibits three peaks at 284.8 eV, 286.5 eV, and 288.2 eV. The peak at 284.8 eV corresponds to the C-C bond in the Haematococcus pluvialis framework, the peak at 286.45 eV corresponds to the CO bond in the surface hydroxyl group, and the peak at 288.2 eV is attributed to the C=O bond in the carbonyl and carboxyl groups. Figure 4 As shown in (c), the Cd 3d spectrum of CdS exhibits two typical peaks at 404.4 and 411.2 eV, which can be designated as Cd 3d5 / 2 and 3d3 / 2, respectively. Figure 4As shown in (d), S2p exhibits two typical peaks at 160.9 eV and 162.2 eV, which can be designated as S2p3 / 2 and S2p1 / 2, respectively, further verifying the successful synthesis of CdS.

[0051] (3) X-ray powder diffraction analysis (XRD) To investigate the phase structures of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS photocatalysts, XRD analysis was performed, as follows: Figure 5 As shown in the figure, the diffraction peaks of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS composites, and CdS are basically consistent with the standard card of CdS (JCPDS card no. 75-1546), belonging to the cubic zincblende configuration. The results indicate that these two materials were successfully synthesized.

[0052] (4) Fourier transform infrared spectroscopy (FT-IR) The FT-IR spectra of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS are as follows: Figure 6 As shown. These two materials at 458cm -1 and 1056 cm -1 The infrared absorption peaks, corresponding to the asymmetric stretching vibrations of Cd-S, confirmed the successful synthesis of CdS. The Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS complexes showed absorption peaks at 2850 cm⁻¹. -1 An additional peak was observed at 1632 cm⁻¹, attributed to the CH asymmetric stretching vibration in Haematococcus pluvialis. Furthermore, the Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS composites showed peak values ​​at 1632 cm⁻¹. -1 and 1545cm -1 The peak values ​​can be attributed to C=O / CN and NH, indicating that CdS was successfully coated on Haematococcus pluvialis. Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS showed peak values ​​at 3450 cm⁻¹. -1 The relatively broad stretching vibration peak that appears is the OH stretching vibration, which may be due to the adsorption of water from the air on the material surface, resulting in the appearance of the hydroxyl peak.

[0053] (6) Solid UV-Vis Diffuse Reflectance Analysis (DRS) Figure 7Figure (a) shows the DRS results for Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS. Pure CdS exhibits significant absorption in both the ultraviolet and visible light regions due to the excitation of valence electrons, but this absorption decreases rapidly due to fast electron recombination. Compared to pure CdS, the Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS composites show increased visible light absorption intensity. This is because astaxanthin from Haematococcus pluvialis has maximum absorption at 480 nm, acting as a dye sensitizer and enhancing the visible light absorption of Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS. The band gaps of different materials were obtained using the Kubelka-Munk method. According to the Kubelka–Munk (KM) equation: (ahv) 2 = B(hv-Eg) calculates the bandgap energies of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS. For example... Figure 7 As shown in Figure (b), the bandgap energies of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS are 2.22 eV, 2.17 eV, 1.86 eV, and 2.32 eV, respectively.

[0054] (7) Thermogravimetric analysis (TGA) Figure 8 Thermogravimetric analysis of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS is shown. Between 50 and 255 °C, the weight fraction of Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS all decreased by 7.91% due to the evaporation of adsorbed water. Between 255 and 465 °C, Hp-Q / CdS lost 30.61%, while Hp-Z / CdS and Hp-H / CdS both lost 37.91%, with the weight loss attributed to the decomposition of organic matter in the microalgae. Between 265 and 700 °C, Hp-Q / CdS lost 3.72%, while Hp-Z / CdS and Hp-H / CdS both lost 3.84%, due to incomplete decomposition and continued volatilization.

[0055] Photocatalytic performance test The photocatalytic activity of the prepared samples was evaluated by an experiment on the degradation of norfloxacin (NOR) under visible light. The photodegradation experiment was conducted in a PLS-SXE300+ / UV photochemical reactor equipped with a 300W xenon lamp. The entire experiment was carried out at room temperature as follows: 20 mg of the prepared photocatalyst was added to 50 mL of a 20 mg / L norfloxacin solution. Before illumination, the suspension was stirred in the dark for 30 min to reach adsorption-desorption equilibrium. The suspension was then placed under visible light (λ ≥ 420 nm) for 30 min. During the reaction, 4 mL of the suspension was removed from the reaction solution every 5 minutes, and the removed suspension was centrifuged to remove the catalyst. The resulting filtrate was analyzed at 277 nm using a UV-Vis spectrometer. The degradation efficiency was calculated using the following Equation 1: Formula 1; In Equation 1, X represents the degradation efficiency, C0 represents the concentration of norfloxacin solution after adsorption-desorption, and C represents the residual concentration of norfloxacin in the extract.

[0056] like Figure 9 As shown in (a), under dark conditions, after continuous stirring of the photocatalyst and dye for 30 min, all samples exhibited certain adsorption performance in the dark reaction. Under both light and no catalyst conditions, the NOR concentration remained almost unchanged, indicating a strong stable structure and negligible influence of photolysis on the reaction. However, the addition of the catalyst to Hp-Q / CdS had little effect on NOR dye degradation, attributed to the low astaxanthin content in the early-stage Haematococcus pluvialis, resulting in weak dye sensitization. Under 60 min of light irradiation (actually 30 min of visible light reaction), the NOR degradation rates of Hp-Z / CdS and Hp-H / CdS reached 73.2% and 84.5%, respectively. This indicates that the increased astaxanthin content improved the photocatalytic performance of the composite material, due to the dye sensitization effect of astaxanthin, which enhanced the utilization of visible light and the transfer and separation of photogenerated electron-hole pairs.

[0057] The data were fitted using pseudo-first-order reaction kinetics, such as... Figure 9 As shown in (b), the degradation rate constant of Hp-Q / CdS is 0.022 min. –1 Hp-Z / CdS was 0.043 min. –1 The Hp-H / CdS ratio is 0.557 min. –1 The values ​​were CdS (0.018 min) and CdS (0.018 min). –1 The concentrations of astaxanthin were 1.22, 2.38, and 3.17 times higher than those of other dyes, further demonstrating that the higher the astaxanthin content, the stronger the dye sensitization effect and the better the photodegradation performance.

[0058] pH is a crucial factor affecting catalytic reactions. Therefore, the photocatalytic degradation efficiency of NOR by Hp-H / CdS was investigated at different pH values ​​(3, 5, 7, and 9). The pH value was adjusted using nitric acid and sodium hydroxide. Figure 9 As shown in (c), when the pH increases from 3 to 7, C t A decrease in the CO / N ratio leads to an increase in the degradation rate of NOR. This indicates that the photocatalytic degradation of NOR is more efficient under weakly acidic conditions than under strongly acidic conditions. Furthermore, the photocatalytic degradation efficiency of NOR decreases as the pH increases from 7 to 9. This suggests that photocatalytic degradation of NOR is also unfavorable under conditions greater than pH 7. Finally, given the relatively low photocatalytic degradation efficiency of NOR at other pH values, choosing pH = 7 is reasonable.

[0059] The NOR degradation efficiency of the composite material Hp-H / CdS under different catalyst dosages (10 mg, 20 mg, 30 mg) was evaluated. Figure 9 As shown in Figure (d), the degradation efficiency was significantly improved when the dosage increased from 10 mg to 20 mg. This is because the increased catalyst dosage provided more active sites for the reaction and adsorbed more NOR molecules, thereby improving the photodegradation efficiency. When the dosage was increased to 30 mg, the photocatalytic efficiency remained at 79.7%, but the overall photocatalytic efficiency showed a downward trend in the early stage. This was mainly because the increased photocatalyst content led to increased solution turbidity, which in turn caused enhanced light scattering and reduced visible light transmittance.

[0060] The recyclability and photochemical stability of catalysts are important evaluation indicators for practical industrial applications. To evaluate the stability of Hp-H / CdS, three NOR photodegradation cycles were conducted. The procedure was as follows: After the Hp-H / CdS sample underwent photocatalytic degradation, the photocatalyst was separated by vacuum filtration, washed with deionized water and anhydrous ethanol, centrifuged, and dried in an oven at 80℃ for 12 h before being used in the next cycle. Figure 9 Figure (e) shows that the degradation efficiencies of the catalysts in the 1st, 2nd, and 3rd cycles were 84.5%, 80.6%, and 75.1%, respectively. This result indicates that although the degradation efficiency decreased in the three cycles, it could still reach over 75%, demonstrating that Hp-H / CdS has good stability and recyclability.

[0061] To investigate the main active groups in the photocatalytic process, a free radical capture experiment was conducted. The experimental procedure was largely the same as that for the photocatalytic degradation of NOR dyes, except that ammonium oxalate (AO), ascorbic acid (AA), and isopropanol (IPA) were added before degradation as holes (h). + ), superoxide radicals (·O2)– It is a scavenger of hydroxyl radicals (·OH). For example... Figure 9 As shown in (f), the addition of IPA and AO had minimal impact on photocatalytic activity, decreasing by only 4.9% and 13.3% respectively. However, the introduction of BQ significantly reduced photocatalytic performance; specifically, after 30 min of light irradiation, the NOR degradation rate decreased from 84.5% to 21%, indicating a strong inhibition of the photocatalytic process and confirming the effect of O2. – It is the main active species, while ·OH and h + It plays almost no role in the photocatalytic degradation process.

[0062] Surface photocurrent and impedance testing (SPC / EIS) Photocurrent and impedance measurements were performed on Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS. The results are shown in [Figure number missing]. Figure 10 .Depend on Figure 10 As shown in (a), under xenon lamp irradiation, Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS all generate stable and rapid photocurrents. Compared with pure CdS, the composite materials of Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS exhibit stronger photocurrent densities. This can be attributed to the presence of astaxanthin in Haematococcus pluvialis enhancing the capture ability of photons within the visible light wavelength range, acting as a dye sensitizer, inhibiting the recombination of photogenerated electrons / holes, and improving the transmission and transfer efficiency of photogenerated electrons. Hp-H / CdS exhibits the highest photocurrent density compared to Hp-Q / CdS, which has the lowest astaxanthin content. Figure 10 As shown in (b), compared to pure CdS, the charge transfer radii of the Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS composites are reduced in the electrochemical impedance spectroscopy. This indicates a decrease in the solid interfacial layer resistance and surface charge transfer resistance of the Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS composites. Compared to pure CdS, the Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS composites achieve more effective separation of photogenerated electron / hole pairs and faster transfer of interfacial charges. This reasonably explains why Hp-Q / CdS, Hp-Z / CdS, and Hp-H / CdS have higher photoelectrocatalytic activity than pure CdS.

[0063] Mott-Schottky Test Flat-band potentials of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS at different frequencies were measured using the Mott-Schottky method. The results are as follows: Figure 11As shown, (ad) represents the Mott-Schottky plots of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS, respectively. The Mott-Schottky curves show that the slopes are all positive, proving that Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS are all n-type semiconductors. The conduction band potential of n-type semiconductors is close to their flat band potential. The measured flat band potentials of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS are -1.13 V, -1.12 V, -1.08 V, and -1.41 V, respectively. Therefore, the conduction band potentials of Hp-Q / CdS, Hp-Z / CdS, Hp-H / CdS, and CdS can be approximated as -1.13 V, -1.12 V, -1.08 V, and -1.41 V. Combining the band gap widths obtained above, the band structure information (Eband) of all materials can be obtained. VB =E CB + E g The band structure diagrams of different photocatalysts are shown in Figure 12(a). The energy level difference between the conduction band potential of pQ / CdS, Hp-Z / CdS, and Hp-H / CdS composite materials and the conduction band potential of the target product is most suitable for the transfer of photogenerated electrons. Therefore, Hp-H / CdS will have better photocatalytic performance.

[0064] Figure 12 (b) shows the mechanism of photocatalytic degradation of NOR by Hp-H / CdS. Under visible light irradiation, adsorbed NOR is excited, and the generated electrons are injected into the conduction band (CB) of CdS, while holes are formed in the valence band. The photogenerated electrons migrate to the surface of Hp-H / CdS and react with oxygen (O2) to generate ·O2. - These superoxide radicals play a crucial role in converting adsorbed norfloxacin into stable products. Meanwhile, photogenerated holes have two reaction pathways. They can directly oxidize adsorbed norfloxacin or react with adsorbed water molecules (or hydroxyl ions (·OH)) to generate highly reactive ·OH radicals. These hydroxyl radicals are strong oxidants capable of degrading NOR into stable products. Notably, ·OH is not the dominant active species in the Hp-H / CdS photocatalytic degradation of norfloxacin. Superoxide radicals dominate the entire photocatalytic process; therefore, their contribution is greater than that of hydroxyl radicals and holes.

[0065] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Haematococcus pluvialis / CdS composite material, characterized in that, It includes Haematococcus pluvialis and nano-CdS coated on the surface of Haematococcus pluvialis; the mass content of astaxanthin in Haematococcus pluvialis is 1~10%.

2. The Haematococcus pluvialis / CdS composite material according to claim 1, characterized in that, The mass ratio of Haematococcus pluvialis to nano-CdS is 1:4 to 1:

10.

3. The Haematococcus pluvialis / CdS composite material according to claim 1 or 2, characterized in that, The mass content of astaxanthin in the Haematococcus pluvialis is 5-10%.

4. The method for preparing the Haematococcus pluvialis / CdS composite material according to any one of claims 1 to 3, characterized in that, Includes the following steps: Haematococcus pluvialis powder was dispersed in water to obtain a Haematococcus pluvialis dispersion; A complexing agent and a water-soluble cadmium source were sequentially added to the *Hylocereus pluvialis* dispersion to obtain a complexing system; the complexing agent was sodium citrate and / or citric acid. An inorganic weak base and a water-soluble sulfur source were added to the complexation system to make the pH of the system 8-9, and a CdS growth reaction was carried out. After solid-liquid separation, the Haematococcus pluvialis / CdS composite material was obtained.

5. The preparation method according to claim 4, characterized in that, The CdS growth reaction is carried out at a temperature of 70-90℃ for 2-4 hours.

6. The preparation method according to claim 4, characterized in that, The water-soluble cadmium source includes one or more of cadmium chloride, cadmium nitrate, and cadmium sulfate.

7. The preparation method according to claim 4 or 6, characterized in that, The complexing agent reacts with Cd in the water-soluble cadmium source. 2+ The molar ratio is 1:1 to 1:

4.

8. The preparation method according to claim 4, characterized in that, The water-soluble sulfur source includes thiourea and / or thioacetamide; the water-soluble cadmium source contains Cd. 2+ With the water-soluble sulfur source S 2- The molar ratio is 1:1 to 1:

4.

9. The application of the Haematococcus pluvialis / CdS composite material according to any one of claims 1 to 3 or the Haematococcus pluvialis / CdS composite material prepared by the preparation method according to any one of claims 4 to 8 as a photocatalyst in the degradation of organic pollutants in water.

10. The application according to claim 9, characterized in that, The organic pollutants include quinolone organic pollutants; the degradation of organic pollutants in the water body is carried out under conditions of pH 5 to 7.

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